1 @c Copyright (C) 1988-2018 Free Software Foundation, Inc.
2 @c This is part of the GCC manual.
3 @c For copying conditions, see the file gcc.texi.
10 @c man begin COPYRIGHT
11 Copyright @copyright{} 1988-2018 Free Software Foundation, Inc.
13 Permission is granted to copy, distribute and/or modify this document
14 under the terms of the GNU Free Documentation License, Version 1.3 or
15 any later version published by the Free Software Foundation; with the
16 Invariant Sections being ``GNU General Public License'' and ``Funding
17 Free Software'', the Front-Cover texts being (a) (see below), and with
18 the Back-Cover Texts being (b) (see below). A copy of the license is
19 included in the gfdl(7) man page.
21 (a) The FSF's Front-Cover Text is:
25 (b) The FSF's Back-Cover Text is:
27 You have freedom to copy and modify this GNU Manual, like GNU
28 software. Copies published by the Free Software Foundation raise
29 funds for GNU development.
31 @c Set file name and title for the man page.
33 @settitle GNU project C and C++ compiler
35 gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
36 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
37 [@option{-W}@var{warn}@dots{}] [@option{-Wpedantic}]
38 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
39 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
40 [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
41 [@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{}
43 Only the most useful options are listed here; see below for the
44 remainder. @command{g++} accepts mostly the same options as @command{gcc}.
47 gpl(7), gfdl(7), fsf-funding(7),
48 cpp(1), gcov(1), as(1), ld(1), gdb(1), dbx(1)
49 and the Info entries for @file{gcc}, @file{cpp}, @file{as},
50 @file{ld}, @file{binutils} and @file{gdb}.
53 For instructions on reporting bugs, see
57 See the Info entry for @command{gcc}, or
58 @w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}},
59 for contributors to GCC@.
64 @chapter GCC Command Options
65 @cindex GCC command options
66 @cindex command options
67 @cindex options, GCC command
69 @c man begin DESCRIPTION
70 When you invoke GCC, it normally does preprocessing, compilation,
71 assembly and linking. The ``overall options'' allow you to stop this
72 process at an intermediate stage. For example, the @option{-c} option
73 says not to run the linker. Then the output consists of object files
74 output by the assembler.
75 @xref{Overall Options,,Options Controlling the Kind of Output}.
77 Other options are passed on to one or more stages of processing. Some options
78 control the preprocessor and others the compiler itself. Yet other
79 options control the assembler and linker; most of these are not
80 documented here, since you rarely need to use any of them.
82 @cindex C compilation options
83 Most of the command-line options that you can use with GCC are useful
84 for C programs; when an option is only useful with another language
85 (usually C++), the explanation says so explicitly. If the description
86 for a particular option does not mention a source language, you can use
87 that option with all supported languages.
89 @cindex cross compiling
90 @cindex specifying machine version
91 @cindex specifying compiler version and target machine
92 @cindex compiler version, specifying
93 @cindex target machine, specifying
94 The usual way to run GCC is to run the executable called @command{gcc}, or
95 @command{@var{machine}-gcc} when cross-compiling, or
96 @command{@var{machine}-gcc-@var{version}} to run a specific version of GCC.
97 When you compile C++ programs, you should invoke GCC as @command{g++}
98 instead. @xref{Invoking G++,,Compiling C++ Programs},
99 for information about the differences in behavior between @command{gcc}
100 and @code{g++} when compiling C++ programs.
102 @cindex grouping options
103 @cindex options, grouping
104 The @command{gcc} program accepts options and file names as operands. Many
105 options have multi-letter names; therefore multiple single-letter options
106 may @emph{not} be grouped: @option{-dv} is very different from @w{@samp{-d
109 @cindex order of options
110 @cindex options, order
111 You can mix options and other arguments. For the most part, the order
112 you use doesn't matter. Order does matter when you use several
113 options of the same kind; for example, if you specify @option{-L} more
114 than once, the directories are searched in the order specified. Also,
115 the placement of the @option{-l} option is significant.
117 Many options have long names starting with @samp{-f} or with
118 @samp{-W}---for example,
119 @option{-fmove-loop-invariants}, @option{-Wformat} and so on. Most of
120 these have both positive and negative forms; the negative form of
121 @option{-ffoo} is @option{-fno-foo}. This manual documents
122 only one of these two forms, whichever one is not the default.
126 @xref{Option Index}, for an index to GCC's options.
129 * Option Summary:: Brief list of all options, without explanations.
130 * Overall Options:: Controlling the kind of output:
131 an executable, object files, assembler files,
132 or preprocessed source.
133 * Invoking G++:: Compiling C++ programs.
134 * C Dialect Options:: Controlling the variant of C language compiled.
135 * C++ Dialect Options:: Variations on C++.
136 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
138 * Diagnostic Message Formatting Options:: Controlling how diagnostics should
140 * Warning Options:: How picky should the compiler be?
141 * Debugging Options:: Producing debuggable code.
142 * Optimize Options:: How much optimization?
143 * Instrumentation Options:: Enabling profiling and extra run-time error checking.
144 * Preprocessor Options:: Controlling header files and macro definitions.
145 Also, getting dependency information for Make.
146 * Assembler Options:: Passing options to the assembler.
147 * Link Options:: Specifying libraries and so on.
148 * Directory Options:: Where to find header files and libraries.
149 Where to find the compiler executable files.
150 * Code Gen Options:: Specifying conventions for function calls, data layout
152 * Developer Options:: Printing GCC configuration info, statistics, and
154 * Submodel Options:: Target-specific options, such as compiling for a
155 specific processor variant.
156 * Spec Files:: How to pass switches to sub-processes.
157 * Environment Variables:: Env vars that affect GCC.
158 * Precompiled Headers:: Compiling a header once, and using it many times.
164 @section Option Summary
166 Here is a summary of all the options, grouped by type. Explanations are
167 in the following sections.
170 @item Overall Options
171 @xref{Overall Options,,Options Controlling the Kind of Output}.
172 @gccoptlist{-c -S -E -o @var{file} -x @var{language} @gol
173 -v -### --help@r{[}=@var{class}@r{[},@dots{}@r{]]} --target-help --version @gol
174 -pass-exit-codes -pipe -specs=@var{file} -wrapper @gol
175 @@@var{file} -ffile-prefix-map=@var{old}=@var{new} @gol
176 -fplugin=@var{file} -fplugin-arg-@var{name}=@var{arg} @gol
177 -fdump-ada-spec@r{[}-slim@r{]} -fada-spec-parent=@var{unit} -fdump-go-spec=@var{file}}
179 @item C Language Options
180 @xref{C Dialect Options,,Options Controlling C Dialect}.
181 @gccoptlist{-ansi -std=@var{standard} -fgnu89-inline @gol
182 -fpermitted-flt-eval-methods=@var{standard} @gol
183 -aux-info @var{filename} -fallow-parameterless-variadic-functions @gol
184 -fno-asm -fno-builtin -fno-builtin-@var{function} -fgimple@gol
185 -fhosted -ffreestanding -fopenacc -fopenmp -fopenmp-simd @gol
186 -fms-extensions -fplan9-extensions -fsso-struct=@var{endianness} @gol
187 -fallow-single-precision -fcond-mismatch -flax-vector-conversions @gol
188 -fsigned-bitfields -fsigned-char @gol
189 -funsigned-bitfields -funsigned-char}
191 @item C++ Language Options
192 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
193 @gccoptlist{-fabi-version=@var{n} -fno-access-control @gol
194 -faligned-new=@var{n} -fargs-in-order=@var{n} -fcheck-new @gol
195 -fconstexpr-depth=@var{n} -fconstexpr-loop-limit=@var{n} @gol
196 -ffriend-injection @gol
197 -fno-elide-constructors @gol
198 -fno-enforce-eh-specs @gol
199 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
200 -fno-implicit-templates @gol
201 -fno-implicit-inline-templates @gol
202 -fno-implement-inlines -fms-extensions @gol
203 -fnew-inheriting-ctors @gol
204 -fnew-ttp-matching @gol
205 -fno-nonansi-builtins -fnothrow-opt -fno-operator-names @gol
206 -fno-optional-diags -fpermissive @gol
207 -fno-pretty-templates @gol
208 -frepo -fno-rtti -fsized-deallocation @gol
209 -ftemplate-backtrace-limit=@var{n} @gol
210 -ftemplate-depth=@var{n} @gol
211 -fno-threadsafe-statics -fuse-cxa-atexit @gol
212 -fno-weak -nostdinc++ @gol
213 -fvisibility-inlines-hidden @gol
214 -fvisibility-ms-compat @gol
215 -fext-numeric-literals @gol
216 -Wabi=@var{n} -Wabi-tag -Wconversion-null -Wctor-dtor-privacy @gol
217 -Wdelete-non-virtual-dtor -Wliteral-suffix -Wmultiple-inheritance @gol
218 -Wnamespaces -Wnarrowing @gol
219 -Wnoexcept -Wnoexcept-type -Wclass-memaccess @gol
220 -Wnon-virtual-dtor -Wreorder -Wregister @gol
221 -Weffc++ -Wstrict-null-sentinel -Wtemplates @gol
222 -Wno-non-template-friend -Wold-style-cast @gol
223 -Woverloaded-virtual -Wno-pmf-conversions @gol
224 -Wsign-promo -Wvirtual-inheritance}
226 @item Objective-C and Objective-C++ Language Options
227 @xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling
228 Objective-C and Objective-C++ Dialects}.
229 @gccoptlist{-fconstant-string-class=@var{class-name} @gol
230 -fgnu-runtime -fnext-runtime @gol
231 -fno-nil-receivers @gol
232 -fobjc-abi-version=@var{n} @gol
233 -fobjc-call-cxx-cdtors @gol
234 -fobjc-direct-dispatch @gol
235 -fobjc-exceptions @gol
238 -fobjc-std=objc1 @gol
239 -fno-local-ivars @gol
240 -fivar-visibility=@r{[}public@r{|}protected@r{|}private@r{|}package@r{]} @gol
241 -freplace-objc-classes @gol
244 -Wassign-intercept @gol
245 -Wno-protocol -Wselector @gol
246 -Wstrict-selector-match @gol
247 -Wundeclared-selector}
249 @item Diagnostic Message Formatting Options
250 @xref{Diagnostic Message Formatting Options,,Options to Control Diagnostic Messages Formatting}.
251 @gccoptlist{-fmessage-length=@var{n} @gol
252 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]} @gol
253 -fdiagnostics-color=@r{[}auto@r{|}never@r{|}always@r{]} @gol
254 -fno-diagnostics-show-option -fno-diagnostics-show-caret @gol
255 -fdiagnostics-parseable-fixits -fdiagnostics-generate-patch @gol
256 -fdiagnostics-show-template-tree -fno-elide-type @gol
259 @item Warning Options
260 @xref{Warning Options,,Options to Request or Suppress Warnings}.
261 @gccoptlist{-fsyntax-only -fmax-errors=@var{n} -Wpedantic @gol
262 -pedantic-errors @gol
263 -w -Wextra -Wall -Waddress -Waggregate-return @gol
264 -Walloc-zero -Walloc-size-larger-than=@var{n}
265 -Walloca -Walloca-larger-than=@var{n} @gol
266 -Wno-aggressive-loop-optimizations -Warray-bounds -Warray-bounds=@var{n} @gol
267 -Wno-attributes -Wbool-compare -Wbool-operation @gol
268 -Wno-builtin-declaration-mismatch @gol
269 -Wno-builtin-macro-redefined -Wc90-c99-compat -Wc99-c11-compat @gol
270 -Wc++-compat -Wc++11-compat -Wc++14-compat @gol
271 -Wcast-align -Wcast-align=strict -Wcast-function-type -Wcast-qual @gol
272 -Wchar-subscripts -Wchkp -Wcatch-value -Wcatch-value=@var{n} @gol
273 -Wclobbered -Wcomment -Wconditionally-supported @gol
274 -Wconversion -Wcoverage-mismatch -Wno-cpp -Wdangling-else -Wdate-time @gol
275 -Wdelete-incomplete @gol
276 -Wno-deprecated -Wno-deprecated-declarations -Wno-designated-init @gol
277 -Wdisabled-optimization @gol
278 -Wno-discarded-qualifiers -Wno-discarded-array-qualifiers @gol
279 -Wno-div-by-zero -Wdouble-promotion @gol
280 -Wduplicated-branches -Wduplicated-cond @gol
281 -Wempty-body -Wenum-compare -Wno-endif-labels -Wexpansion-to-defined @gol
282 -Werror -Werror=* -Wextra-semi -Wfatal-errors @gol
283 -Wfloat-equal -Wformat -Wformat=2 @gol
284 -Wno-format-contains-nul -Wno-format-extra-args @gol
285 -Wformat-nonliteral -Wformat-overflow=@var{n} @gol
286 -Wformat-security -Wformat-signedness -Wformat-truncation=@var{n} @gol
287 -Wformat-y2k -Wframe-address @gol
288 -Wframe-larger-than=@var{len} -Wno-free-nonheap-object -Wjump-misses-init @gol
289 -Wif-not-aligned @gol
290 -Wignored-qualifiers -Wignored-attributes -Wincompatible-pointer-types @gol
291 -Wimplicit -Wimplicit-fallthrough -Wimplicit-fallthrough=@var{n} @gol
292 -Wimplicit-function-declaration -Wimplicit-int @gol
293 -Winit-self -Winline -Wno-int-conversion -Wint-in-bool-context @gol
294 -Wno-int-to-pointer-cast -Winvalid-memory-model -Wno-invalid-offsetof @gol
295 -Winvalid-pch -Wlarger-than=@var{len} @gol
296 -Wlogical-op -Wlogical-not-parentheses -Wlong-long @gol
297 -Wmain -Wmaybe-uninitialized -Wmemset-elt-size -Wmemset-transposed-args @gol
298 -Wmisleading-indentation -Wmissing-attributes -Wmissing-braces @gol
299 -Wmissing-field-initializers -Wmissing-include-dirs @gol
300 -Wno-multichar -Wmultistatement-macros -Wnonnull -Wnonnull-compare @gol
301 -Wnormalized=@r{[}none@r{|}id@r{|}nfc@r{|}nfkc@r{]} @gol
302 -Wnull-dereference -Wodr -Wno-overflow -Wopenmp-simd @gol
303 -Woverride-init-side-effects -Woverlength-strings @gol
304 -Wpacked -Wpacked-bitfield-compat -Wpacked-not-aligned -Wpadded @gol
305 -Wparentheses -Wno-pedantic-ms-format @gol
306 -Wplacement-new -Wplacement-new=@var{n} @gol
307 -Wpointer-arith -Wpointer-compare -Wno-pointer-to-int-cast @gol
308 -Wno-pragmas -Wredundant-decls -Wrestrict -Wno-return-local-addr @gol
309 -Wreturn-type -Wsequence-point -Wshadow -Wno-shadow-ivar @gol
310 -Wshadow=global, -Wshadow=local, -Wshadow=compatible-local @gol
311 -Wshift-overflow -Wshift-overflow=@var{n} @gol
312 -Wshift-count-negative -Wshift-count-overflow -Wshift-negative-value @gol
313 -Wsign-compare -Wsign-conversion -Wfloat-conversion @gol
314 -Wno-scalar-storage-order -Wsizeof-pointer-div @gol
315 -Wsizeof-pointer-memaccess -Wsizeof-array-argument @gol
316 -Wstack-protector -Wstack-usage=@var{len} -Wstrict-aliasing @gol
317 -Wstrict-aliasing=n -Wstrict-overflow -Wstrict-overflow=@var{n} @gol
318 -Wstringop-overflow=@var{n} -Wstringop-truncation @gol
319 -Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{|}malloc@r{]} @gol
320 -Wsuggest-final-types @gol -Wsuggest-final-methods -Wsuggest-override @gol
321 -Wmissing-format-attribute -Wsubobject-linkage @gol
322 -Wswitch -Wswitch-bool -Wswitch-default -Wswitch-enum @gol
323 -Wswitch-unreachable -Wsync-nand @gol
324 -Wsystem-headers -Wtautological-compare -Wtrampolines -Wtrigraphs @gol
325 -Wtype-limits -Wundef @gol
326 -Wuninitialized -Wunknown-pragmas -Wunsafe-loop-optimizations @gol
327 -Wunsuffixed-float-constants -Wunused -Wunused-function @gol
328 -Wunused-label -Wunused-local-typedefs -Wunused-macros @gol
329 -Wunused-parameter -Wno-unused-result @gol
330 -Wunused-value -Wunused-variable @gol
331 -Wunused-const-variable -Wunused-const-variable=@var{n} @gol
332 -Wunused-but-set-parameter -Wunused-but-set-variable @gol
333 -Wuseless-cast -Wvariadic-macros -Wvector-operation-performance @gol
334 -Wvla -Wvla-larger-than=@var{n} -Wvolatile-register-var -Wwrite-strings @gol
335 -Wzero-as-null-pointer-constant -Whsa}
337 @item C and Objective-C-only Warning Options
338 @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
339 -Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs @gol
340 -Wold-style-declaration -Wold-style-definition @gol
341 -Wstrict-prototypes -Wtraditional -Wtraditional-conversion @gol
342 -Wdeclaration-after-statement -Wpointer-sign}
344 @item Debugging Options
345 @xref{Debugging Options,,Options for Debugging Your Program}.
346 @gccoptlist{-g -g@var{level} -gdwarf -gdwarf-@var{version} @gol
347 -ggdb -grecord-gcc-switches -gno-record-gcc-switches @gol
348 -gstabs -gstabs+ -gstrict-dwarf -gno-strict-dwarf @gol
349 -gas-loc-support -gno-as-loc-support @gol
350 -gas-locview-support -gno-as-locview-support @gol
351 -gcolumn-info -gno-column-info @gol
352 -gstatement-frontiers -gno-statement-frontiers @gol
353 -gvariable-location-views -gno-variable-location-views @gol
354 -ginternal-reset-location-views -gno-internal-reset-location-views @gol
355 -ginline-points -gno-inline-points @gol
356 -gvms -gxcoff -gxcoff+ -gz@r{[}=@var{type}@r{]} @gol
357 -fdebug-prefix-map=@var{old}=@var{new} -fdebug-types-section @gol
358 -fno-eliminate-unused-debug-types @gol
359 -femit-struct-debug-baseonly -femit-struct-debug-reduced @gol
360 -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} @gol
361 -feliminate-unused-debug-symbols -femit-class-debug-always @gol
362 -fno-merge-debug-strings -fno-dwarf2-cfi-asm @gol
363 -fvar-tracking -fvar-tracking-assignments}
365 @item Optimization Options
366 @xref{Optimize Options,,Options that Control Optimization}.
367 @gccoptlist{-faggressive-loop-optimizations -falign-functions[=@var{n}] @gol
368 -falign-jumps[=@var{n}] @gol
369 -falign-labels[=@var{n}] -falign-loops[=@var{n}] @gol
370 -fassociative-math -fauto-profile -fauto-profile[=@var{path}] @gol
371 -fauto-inc-dec -fbranch-probabilities @gol
372 -fbranch-target-load-optimize -fbranch-target-load-optimize2 @gol
373 -fbtr-bb-exclusive -fcaller-saves @gol
374 -fcombine-stack-adjustments -fconserve-stack @gol
375 -fcompare-elim -fcprop-registers -fcrossjumping @gol
376 -fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules @gol
377 -fcx-limited-range @gol
378 -fdata-sections -fdce -fdelayed-branch @gol
379 -fdelete-null-pointer-checks -fdevirtualize -fdevirtualize-speculatively @gol
380 -fdevirtualize-at-ltrans -fdse @gol
381 -fearly-inlining -fipa-sra -fexpensive-optimizations -ffat-lto-objects @gol
382 -ffast-math -ffinite-math-only -ffloat-store -fexcess-precision=@var{style} @gol
383 -fforward-propagate -ffp-contract=@var{style} -ffunction-sections @gol
384 -fgcse -fgcse-after-reload -fgcse-las -fgcse-lm -fgraphite-identity @gol
385 -fgcse-sm -fhoist-adjacent-loads -fif-conversion @gol
386 -fif-conversion2 -findirect-inlining @gol
387 -finline-functions -finline-functions-called-once -finline-limit=@var{n} @gol
388 -finline-small-functions -fipa-cp -fipa-cp-clone @gol
389 -fipa-bit-cp -fipa-vrp @gol
390 -fipa-pta -fipa-profile -fipa-pure-const -fipa-reference -fipa-icf @gol
391 -fira-algorithm=@var{algorithm} @gol
392 -fira-region=@var{region} -fira-hoist-pressure @gol
393 -fira-loop-pressure -fno-ira-share-save-slots @gol
394 -fno-ira-share-spill-slots @gol
395 -fisolate-erroneous-paths-dereference -fisolate-erroneous-paths-attribute @gol
396 -fivopts -fkeep-inline-functions -fkeep-static-functions @gol
397 -fkeep-static-consts -flimit-function-alignment -flive-range-shrinkage @gol
398 -floop-block -floop-interchange -floop-strip-mine @gol
399 -floop-unroll-and-jam -floop-nest-optimize @gol
400 -floop-parallelize-all -flra-remat -flto -flto-compression-level @gol
401 -flto-partition=@var{alg} -fmerge-all-constants @gol
402 -fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves @gol
403 -fmove-loop-invariants -fno-branch-count-reg @gol
404 -fno-defer-pop -fno-fp-int-builtin-inexact -fno-function-cse @gol
405 -fno-guess-branch-probability -fno-inline -fno-math-errno -fno-peephole @gol
406 -fno-peephole2 -fno-printf-return-value -fno-sched-interblock @gol
407 -fno-sched-spec -fno-signed-zeros @gol
408 -fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol
409 -fomit-frame-pointer -foptimize-sibling-calls @gol
410 -fpartial-inlining -fpeel-loops -fpredictive-commoning @gol
411 -fprefetch-loop-arrays @gol
412 -fprofile-correction @gol
413 -fprofile-use -fprofile-use=@var{path} -fprofile-values @gol
414 -fprofile-reorder-functions @gol
415 -freciprocal-math -free -frename-registers -freorder-blocks @gol
416 -freorder-blocks-algorithm=@var{algorithm} @gol
417 -freorder-blocks-and-partition -freorder-functions @gol
418 -frerun-cse-after-loop -freschedule-modulo-scheduled-loops @gol
419 -frounding-math -fsched2-use-superblocks -fsched-pressure @gol
420 -fsched-spec-load -fsched-spec-load-dangerous @gol
421 -fsched-stalled-insns-dep[=@var{n}] -fsched-stalled-insns[=@var{n}] @gol
422 -fsched-group-heuristic -fsched-critical-path-heuristic @gol
423 -fsched-spec-insn-heuristic -fsched-rank-heuristic @gol
424 -fsched-last-insn-heuristic -fsched-dep-count-heuristic @gol
425 -fschedule-fusion @gol
426 -fschedule-insns -fschedule-insns2 -fsection-anchors @gol
427 -fselective-scheduling -fselective-scheduling2 @gol
428 -fsel-sched-pipelining -fsel-sched-pipelining-outer-loops @gol
429 -fsemantic-interposition -fshrink-wrap -fshrink-wrap-separate @gol
430 -fsignaling-nans @gol
431 -fsingle-precision-constant -fsplit-ivs-in-unroller -fsplit-loops@gol
433 -fsplit-wide-types -fssa-backprop -fssa-phiopt @gol
434 -fstdarg-opt -fstore-merging -fstrict-aliasing @gol
435 -fthread-jumps -ftracer -ftree-bit-ccp @gol
436 -ftree-builtin-call-dce -ftree-ccp -ftree-ch @gol
437 -ftree-coalesce-vars -ftree-copy-prop -ftree-dce -ftree-dominator-opts @gol
438 -ftree-dse -ftree-forwprop -ftree-fre -fcode-hoisting @gol
439 -ftree-loop-if-convert -ftree-loop-im @gol
440 -ftree-phiprop -ftree-loop-distribution -ftree-loop-distribute-patterns @gol
441 -ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize @gol
442 -ftree-loop-vectorize @gol
443 -ftree-parallelize-loops=@var{n} -ftree-pre -ftree-partial-pre -ftree-pta @gol
444 -ftree-reassoc -ftree-sink -ftree-slsr -ftree-sra @gol
445 -ftree-switch-conversion -ftree-tail-merge @gol
446 -ftree-ter -ftree-vectorize -ftree-vrp -funconstrained-commons @gol
447 -funit-at-a-time -funroll-all-loops -funroll-loops @gol
448 -funsafe-math-optimizations -funswitch-loops @gol
449 -fipa-ra -fvariable-expansion-in-unroller -fvect-cost-model -fvpt @gol
450 -fweb -fwhole-program -fwpa -fuse-linker-plugin @gol
451 --param @var{name}=@var{value}
452 -O -O0 -O1 -O2 -O3 -Os -Ofast -Og}
454 @item Program Instrumentation Options
455 @xref{Instrumentation Options,,Program Instrumentation Options}.
456 @gccoptlist{-p -pg -fprofile-arcs --coverage -ftest-coverage @gol
457 -fprofile-abs-path @gol
458 -fprofile-dir=@var{path} -fprofile-generate -fprofile-generate=@var{path} @gol
459 -fsanitize=@var{style} -fsanitize-recover -fsanitize-recover=@var{style} @gol
460 -fasan-shadow-offset=@var{number} -fsanitize-sections=@var{s1},@var{s2},... @gol
461 -fsanitize-undefined-trap-on-error -fbounds-check @gol
462 -fcheck-pointer-bounds -fchkp-check-incomplete-type @gol
463 -fchkp-first-field-has-own-bounds -fchkp-narrow-bounds @gol
464 -fchkp-narrow-to-innermost-array -fchkp-optimize @gol
465 -fchkp-use-fast-string-functions -fchkp-use-nochk-string-functions @gol
466 -fchkp-use-static-bounds -fchkp-use-static-const-bounds @gol
467 -fchkp-treat-zero-dynamic-size-as-infinite -fchkp-check-read @gol
468 -fchkp-check-read -fchkp-check-write -fchkp-store-bounds @gol
469 -fchkp-instrument-calls -fchkp-instrument-marked-only @gol
470 -fchkp-use-wrappers -fchkp-flexible-struct-trailing-arrays@gol
471 -fcf-protection=@r{[}full@r{|}branch@r{|}return@r{|}none@r{]} @gol
472 -fstack-protector -fstack-protector-all -fstack-protector-strong @gol
473 -fstack-protector-explicit -fstack-check @gol
474 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
475 -fno-stack-limit -fsplit-stack @gol
476 -fvtable-verify=@r{[}std@r{|}preinit@r{|}none@r{]} @gol
477 -fvtv-counts -fvtv-debug @gol
478 -finstrument-functions @gol
479 -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} @gol
480 -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{}}
482 @item Preprocessor Options
483 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
484 @gccoptlist{-A@var{question}=@var{answer} @gol
485 -A-@var{question}@r{[}=@var{answer}@r{]} @gol
486 -C -CC -D@var{macro}@r{[}=@var{defn}@r{]} @gol
487 -dD -dI -dM -dN -dU @gol
488 -fdebug-cpp -fdirectives-only -fdollars-in-identifiers @gol
489 -fexec-charset=@var{charset} -fextended-identifiers @gol
490 -finput-charset=@var{charset} -fmacro-prefix-map=@var{old}=@var{new} @gol
491 -fno-canonical-system-headers @gol -fpch-deps -fpch-preprocess @gol
492 -fpreprocessed -ftabstop=@var{width} -ftrack-macro-expansion @gol
493 -fwide-exec-charset=@var{charset} -fworking-directory @gol
494 -H -imacros @var{file} -include @var{file} @gol
495 -M -MD -MF -MG -MM -MMD -MP -MQ -MT @gol
496 -no-integrated-cpp -P -pthread -remap @gol
497 -traditional -traditional-cpp -trigraphs @gol
498 -U@var{macro} -undef @gol
499 -Wp,@var{option} -Xpreprocessor @var{option}}
501 @item Assembler Options
502 @xref{Assembler Options,,Passing Options to the Assembler}.
503 @gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
506 @xref{Link Options,,Options for Linking}.
507 @gccoptlist{@var{object-file-name} -fuse-ld=@var{linker} -l@var{library} @gol
508 -nostartfiles -nodefaultlibs -nostdlib -pie -pthread -rdynamic @gol
509 -s -static -static-pie -static-libgcc -static-libstdc++ @gol
510 -static-libasan -static-libtsan -static-liblsan -static-libubsan @gol
511 -static-libmpx -static-libmpxwrappers @gol
512 -shared -shared-libgcc -symbolic @gol
513 -T @var{script} -Wl,@var{option} -Xlinker @var{option} @gol
514 -u @var{symbol} -z @var{keyword}}
516 @item Directory Options
517 @xref{Directory Options,,Options for Directory Search}.
518 @gccoptlist{-B@var{prefix} -I@var{dir} -I- @gol
519 -idirafter @var{dir} @gol
520 -imacros @var{file} -imultilib @var{dir} @gol
521 -iplugindir=@var{dir} -iprefix @var{file} @gol
522 -iquote @var{dir} -isysroot @var{dir} -isystem @var{dir} @gol
523 -iwithprefix @var{dir} -iwithprefixbefore @var{dir} @gol
524 -L@var{dir} -no-canonical-prefixes --no-sysroot-suffix @gol
525 -nostdinc -nostdinc++ --sysroot=@var{dir}}
527 @item Code Generation Options
528 @xref{Code Gen Options,,Options for Code Generation Conventions}.
529 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
530 -ffixed-@var{reg} -fexceptions @gol
531 -fnon-call-exceptions -fdelete-dead-exceptions -funwind-tables @gol
532 -fasynchronous-unwind-tables @gol
534 -finhibit-size-directive -fno-common -fno-ident @gol
535 -fpcc-struct-return -fpic -fPIC -fpie -fPIE -fno-plt @gol
536 -fno-jump-tables @gol
537 -frecord-gcc-switches @gol
538 -freg-struct-return -fshort-enums -fshort-wchar @gol
539 -fverbose-asm -fpack-struct[=@var{n}] @gol
540 -fleading-underscore -ftls-model=@var{model} @gol
541 -fstack-reuse=@var{reuse_level} @gol
542 -ftrampolines -ftrapv -fwrapv @gol
543 -fvisibility=@r{[}default@r{|}internal@r{|}hidden@r{|}protected@r{]} @gol
544 -fstrict-volatile-bitfields -fsync-libcalls}
546 @item Developer Options
547 @xref{Developer Options,,GCC Developer Options}.
548 @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
549 -dumpfullversion -fchecking -fchecking=@var{n} -fdbg-cnt-list @gol
550 -fdbg-cnt=@var{counter-value-list} @gol
551 -fdisable-ipa-@var{pass_name} @gol
552 -fdisable-rtl-@var{pass_name} @gol
553 -fdisable-rtl-@var{pass-name}=@var{range-list} @gol
554 -fdisable-tree-@var{pass_name} @gol
555 -fdisable-tree-@var{pass-name}=@var{range-list} @gol
556 -fdump-noaddr -fdump-unnumbered -fdump-unnumbered-links @gol
557 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
558 -fdump-final-insns@r{[}=@var{file}@r{]} @gol
559 -fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline @gol
561 -fdump-lang-@var{switch} @gol
562 -fdump-lang-@var{switch}-@var{options} @gol
563 -fdump-lang-@var{switch}-@var{options}=@var{filename} @gol
565 -fdump-rtl-@var{pass} -fdump-rtl-@var{pass}=@var{filename} @gol
566 -fdump-statistics @gol
568 -fdump-tree-@var{switch} @gol
569 -fdump-tree-@var{switch}-@var{options} @gol
570 -fdump-tree-@var{switch}-@var{options}=@var{filename} @gol
571 -fcompare-debug@r{[}=@var{opts}@r{]} -fcompare-debug-second @gol
572 -fenable-@var{kind}-@var{pass} @gol
573 -fenable-@var{kind}-@var{pass}=@var{range-list} @gol
574 -fira-verbose=@var{n} @gol
575 -flto-report -flto-report-wpa -fmem-report-wpa @gol
576 -fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report @gol
577 -fopt-info -fopt-info-@var{options}@r{[}=@var{file}@r{]} @gol
578 -fprofile-report @gol
579 -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
580 -fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose @gol
581 -fstats -fstack-usage -ftime-report -ftime-report-details @gol
582 -fvar-tracking-assignments-toggle -gtoggle @gol
583 -print-file-name=@var{library} -print-libgcc-file-name @gol
584 -print-multi-directory -print-multi-lib -print-multi-os-directory @gol
585 -print-prog-name=@var{program} -print-search-dirs -Q @gol
586 -print-sysroot -print-sysroot-headers-suffix @gol
587 -save-temps -save-temps=cwd -save-temps=obj -time@r{[}=@var{file}@r{]}}
589 @item Machine-Dependent Options
590 @xref{Submodel Options,,Machine-Dependent Options}.
591 @c This list is ordered alphanumerically by subsection name.
592 @c Try and put the significant identifier (CPU or system) first,
593 @c so users have a clue at guessing where the ones they want will be.
595 @emph{AArch64 Options}
596 @gccoptlist{-mabi=@var{name} -mbig-endian -mlittle-endian @gol
597 -mgeneral-regs-only @gol
598 -mcmodel=tiny -mcmodel=small -mcmodel=large @gol
600 -momit-leaf-frame-pointer @gol
601 -mtls-dialect=desc -mtls-dialect=traditional @gol
602 -mtls-size=@var{size} @gol
603 -mfix-cortex-a53-835769 -mfix-cortex-a53-843419 @gol
604 -mlow-precision-recip-sqrt -mlow-precision-sqrt -mlow-precision-div @gol
605 -mpc-relative-literal-loads @gol
606 -msign-return-address=@var{scope} @gol
607 -march=@var{name} -mcpu=@var{name} -mtune=@var{name} @gol
608 -moverride=@var{string} -mverbose-cost-dump}
610 @emph{Adapteva Epiphany Options}
611 @gccoptlist{-mhalf-reg-file -mprefer-short-insn-regs @gol
612 -mbranch-cost=@var{num} -mcmove -mnops=@var{num} -msoft-cmpsf @gol
613 -msplit-lohi -mpost-inc -mpost-modify -mstack-offset=@var{num} @gol
614 -mround-nearest -mlong-calls -mshort-calls -msmall16 @gol
615 -mfp-mode=@var{mode} -mvect-double -max-vect-align=@var{num} @gol
616 -msplit-vecmove-early -m1reg-@var{reg}}
619 @gccoptlist{-mbarrel-shifter -mjli-always @gol
620 -mcpu=@var{cpu} -mA6 -mARC600 -mA7 -mARC700 @gol
621 -mdpfp -mdpfp-compact -mdpfp-fast -mno-dpfp-lrsr @gol
622 -mea -mno-mpy -mmul32x16 -mmul64 -matomic @gol
623 -mnorm -mspfp -mspfp-compact -mspfp-fast -msimd -msoft-float -mswap @gol
624 -mcrc -mdsp-packa -mdvbf -mlock -mmac-d16 -mmac-24 -mrtsc -mswape @gol
625 -mtelephony -mxy -misize -mannotate-align -marclinux -marclinux_prof @gol
626 -mlong-calls -mmedium-calls -msdata -mirq-ctrl-saved @gol
627 -mrgf-banked-regs -mlpc-width=@var{width} -G @var{num} @gol
628 -mvolatile-cache -mtp-regno=@var{regno} @gol
629 -malign-call -mauto-modify-reg -mbbit-peephole -mno-brcc @gol
630 -mcase-vector-pcrel -mcompact-casesi -mno-cond-exec -mearly-cbranchsi @gol
631 -mexpand-adddi -mindexed-loads -mlra -mlra-priority-none @gol
632 -mlra-priority-compact mlra-priority-noncompact -mno-millicode @gol
633 -mmixed-code -mq-class -mRcq -mRcw -msize-level=@var{level} @gol
634 -mtune=@var{cpu} -mmultcost=@var{num} @gol
635 -munalign-prob-threshold=@var{probability} -mmpy-option=@var{multo} @gol
636 -mdiv-rem -mcode-density -mll64 -mfpu=@var{fpu} -mrf16}
639 @gccoptlist{-mapcs-frame -mno-apcs-frame @gol
640 -mabi=@var{name} @gol
641 -mapcs-stack-check -mno-apcs-stack-check @gol
642 -mapcs-reentrant -mno-apcs-reentrant @gol
643 -msched-prolog -mno-sched-prolog @gol
644 -mlittle-endian -mbig-endian @gol
646 -mfloat-abi=@var{name} @gol
647 -mfp16-format=@var{name}
648 -mthumb-interwork -mno-thumb-interwork @gol
649 -mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol
650 -mtune=@var{name} -mprint-tune-info @gol
651 -mstructure-size-boundary=@var{n} @gol
652 -mabort-on-noreturn @gol
653 -mlong-calls -mno-long-calls @gol
654 -msingle-pic-base -mno-single-pic-base @gol
655 -mpic-register=@var{reg} @gol
656 -mnop-fun-dllimport @gol
657 -mpoke-function-name @gol
658 -mthumb -marm -mflip-thumb @gol
659 -mtpcs-frame -mtpcs-leaf-frame @gol
660 -mcaller-super-interworking -mcallee-super-interworking @gol
661 -mtp=@var{name} -mtls-dialect=@var{dialect} @gol
662 -mword-relocations @gol
663 -mfix-cortex-m3-ldrd @gol
664 -munaligned-access @gol
665 -mneon-for-64bits @gol
666 -mslow-flash-data @gol
667 -masm-syntax-unified @gol
669 -mverbose-cost-dump @gol
674 @gccoptlist{-mmcu=@var{mcu} -mabsdata -maccumulate-args @gol
675 -mbranch-cost=@var{cost} @gol
676 -mcall-prologues -mgas-isr-prologues -mint8 @gol
677 -mn_flash=@var{size} -mno-interrupts @gol
678 -mmain-is-OS_task -mrelax -mrmw -mstrict-X -mtiny-stack @gol
679 -mfract-convert-truncate @gol
680 -mshort-calls -nodevicelib @gol
681 -Waddr-space-convert -Wmisspelled-isr}
683 @emph{Blackfin Options}
684 @gccoptlist{-mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} @gol
685 -msim -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol
686 -mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol
687 -mlow-64k -mno-low64k -mstack-check-l1 -mid-shared-library @gol
688 -mno-id-shared-library -mshared-library-id=@var{n} @gol
689 -mleaf-id-shared-library -mno-leaf-id-shared-library @gol
690 -msep-data -mno-sep-data -mlong-calls -mno-long-calls @gol
691 -mfast-fp -minline-plt -mmulticore -mcorea -mcoreb -msdram @gol
695 @gccoptlist{-mbig-endian -mlittle-endian -march=@var{cpu} @gol
696 -msim -msdata=@var{sdata-type}}
699 @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
700 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
701 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
702 -mstack-align -mdata-align -mconst-align @gol
703 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
704 -melf -maout -melinux -mlinux -sim -sim2 @gol
705 -mmul-bug-workaround -mno-mul-bug-workaround}
708 @gccoptlist{-mmac @gol
709 -mcr16cplus -mcr16c @gol
710 -msim -mint32 -mbit-ops
711 -mdata-model=@var{model}}
713 @emph{Darwin Options}
714 @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
715 -arch_only -bind_at_load -bundle -bundle_loader @gol
716 -client_name -compatibility_version -current_version @gol
718 -dependency-file -dylib_file -dylinker_install_name @gol
719 -dynamic -dynamiclib -exported_symbols_list @gol
720 -filelist -flat_namespace -force_cpusubtype_ALL @gol
721 -force_flat_namespace -headerpad_max_install_names @gol
723 -image_base -init -install_name -keep_private_externs @gol
724 -multi_module -multiply_defined -multiply_defined_unused @gol
725 -noall_load -no_dead_strip_inits_and_terms @gol
726 -nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol
727 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
728 -private_bundle -read_only_relocs -sectalign @gol
729 -sectobjectsymbols -whyload -seg1addr @gol
730 -sectcreate -sectobjectsymbols -sectorder @gol
731 -segaddr -segs_read_only_addr -segs_read_write_addr @gol
732 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
733 -segprot -segs_read_only_addr -segs_read_write_addr @gol
734 -single_module -static -sub_library -sub_umbrella @gol
735 -twolevel_namespace -umbrella -undefined @gol
736 -unexported_symbols_list -weak_reference_mismatches @gol
737 -whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol
738 -mkernel -mone-byte-bool}
740 @emph{DEC Alpha Options}
741 @gccoptlist{-mno-fp-regs -msoft-float @gol
742 -mieee -mieee-with-inexact -mieee-conformant @gol
743 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
744 -mtrap-precision=@var{mode} -mbuild-constants @gol
745 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
746 -mbwx -mmax -mfix -mcix @gol
747 -mfloat-vax -mfloat-ieee @gol
748 -mexplicit-relocs -msmall-data -mlarge-data @gol
749 -msmall-text -mlarge-text @gol
750 -mmemory-latency=@var{time}}
753 @gccoptlist{-msmall-model -mno-lsim}
756 @gccoptlist{-msim -mlra -mnodiv -mft32b -mcompress -mnopm}
759 @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
760 -mhard-float -msoft-float @gol
761 -malloc-cc -mfixed-cc -mdword -mno-dword @gol
762 -mdouble -mno-double @gol
763 -mmedia -mno-media -mmuladd -mno-muladd @gol
764 -mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol
765 -mlinked-fp -mlong-calls -malign-labels @gol
766 -mlibrary-pic -macc-4 -macc-8 @gol
767 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
768 -moptimize-membar -mno-optimize-membar @gol
769 -mscc -mno-scc -mcond-exec -mno-cond-exec @gol
770 -mvliw-branch -mno-vliw-branch @gol
771 -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
772 -mno-nested-cond-exec -mtomcat-stats @gol
776 @emph{GNU/Linux Options}
777 @gccoptlist{-mglibc -muclibc -mmusl -mbionic -mandroid @gol
778 -tno-android-cc -tno-android-ld}
780 @emph{H8/300 Options}
781 @gccoptlist{-mrelax -mh -ms -mn -mexr -mno-exr -mint32 -malign-300}
784 @gccoptlist{-march=@var{architecture-type} @gol
785 -mcaller-copies -mdisable-fpregs -mdisable-indexing @gol
786 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
787 -mfixed-range=@var{register-range} @gol
788 -mjump-in-delay -mlinker-opt -mlong-calls @gol
789 -mlong-load-store -mno-disable-fpregs @gol
790 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
791 -mno-jump-in-delay -mno-long-load-store @gol
792 -mno-portable-runtime -mno-soft-float @gol
793 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
794 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
795 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
796 -munix=@var{unix-std} -nolibdld -static -threads}
799 @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
800 -mvolatile-asm-stop -mregister-names -msdata -mno-sdata @gol
801 -mconstant-gp -mauto-pic -mfused-madd @gol
802 -minline-float-divide-min-latency @gol
803 -minline-float-divide-max-throughput @gol
804 -mno-inline-float-divide @gol
805 -minline-int-divide-min-latency @gol
806 -minline-int-divide-max-throughput @gol
807 -mno-inline-int-divide @gol
808 -minline-sqrt-min-latency -minline-sqrt-max-throughput @gol
809 -mno-inline-sqrt @gol
810 -mdwarf2-asm -mearly-stop-bits @gol
811 -mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol
812 -mtune=@var{cpu-type} -milp32 -mlp64 @gol
813 -msched-br-data-spec -msched-ar-data-spec -msched-control-spec @gol
814 -msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec @gol
815 -msched-spec-ldc -msched-spec-control-ldc @gol
816 -msched-prefer-non-data-spec-insns -msched-prefer-non-control-spec-insns @gol
817 -msched-stop-bits-after-every-cycle -msched-count-spec-in-critical-path @gol
818 -msel-sched-dont-check-control-spec -msched-fp-mem-deps-zero-cost @gol
819 -msched-max-memory-insns-hard-limit -msched-max-memory-insns=@var{max-insns}}
822 @gccoptlist{-mbarrel-shift-enabled -mdivide-enabled -mmultiply-enabled @gol
823 -msign-extend-enabled -muser-enabled}
825 @emph{M32R/D Options}
826 @gccoptlist{-m32r2 -m32rx -m32r @gol
828 -malign-loops -mno-align-loops @gol
829 -missue-rate=@var{number} @gol
830 -mbranch-cost=@var{number} @gol
831 -mmodel=@var{code-size-model-type} @gol
832 -msdata=@var{sdata-type} @gol
833 -mno-flush-func -mflush-func=@var{name} @gol
834 -mno-flush-trap -mflush-trap=@var{number} @gol
838 @gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}}
840 @emph{M680x0 Options}
841 @gccoptlist{-march=@var{arch} -mcpu=@var{cpu} -mtune=@var{tune} @gol
842 -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
843 -m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407 @gol
844 -mcfv4e -mbitfield -mno-bitfield -mc68000 -mc68020 @gol
845 -mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort @gol
846 -mno-short -mhard-float -m68881 -msoft-float -mpcrel @gol
847 -malign-int -mstrict-align -msep-data -mno-sep-data @gol
848 -mshared-library-id=n -mid-shared-library -mno-id-shared-library @gol
849 -mxgot -mno-xgot -mlong-jump-table-offsets}
852 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
853 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
854 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
855 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
856 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
859 @gccoptlist{-mabsdiff -mall-opts -maverage -mbased=@var{n} -mbitops @gol
860 -mc=@var{n} -mclip -mconfig=@var{name} -mcop -mcop32 -mcop64 -mivc2 @gol
861 -mdc -mdiv -meb -mel -mio-volatile -ml -mleadz -mm -mminmax @gol
862 -mmult -mno-opts -mrepeat -ms -msatur -msdram -msim -msimnovec -mtf @gol
865 @emph{MicroBlaze Options}
866 @gccoptlist{-msoft-float -mhard-float -msmall-divides -mcpu=@var{cpu} @gol
867 -mmemcpy -mxl-soft-mul -mxl-soft-div -mxl-barrel-shift @gol
868 -mxl-pattern-compare -mxl-stack-check -mxl-gp-opt -mno-clearbss @gol
869 -mxl-multiply-high -mxl-float-convert -mxl-float-sqrt @gol
870 -mbig-endian -mlittle-endian -mxl-reorder -mxl-mode-@var{app-model}}
873 @gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol
874 -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips32r3 -mips32r5 @gol
875 -mips32r6 -mips64 -mips64r2 -mips64r3 -mips64r5 -mips64r6 @gol
876 -mips16 -mno-mips16 -mflip-mips16 @gol
877 -minterlink-compressed -mno-interlink-compressed @gol
878 -minterlink-mips16 -mno-interlink-mips16 @gol
879 -mabi=@var{abi} -mabicalls -mno-abicalls @gol
880 -mshared -mno-shared -mplt -mno-plt -mxgot -mno-xgot @gol
881 -mgp32 -mgp64 -mfp32 -mfpxx -mfp64 -mhard-float -msoft-float @gol
882 -mno-float -msingle-float -mdouble-float @gol
883 -modd-spreg -mno-odd-spreg @gol
884 -mabs=@var{mode} -mnan=@var{encoding} @gol
885 -mdsp -mno-dsp -mdspr2 -mno-dspr2 @gol
888 -mvirt -mno-virt @gol
890 -mmicromips -mno-micromips @gol
892 -mfpu=@var{fpu-type} @gol
893 -msmartmips -mno-smartmips @gol
894 -mpaired-single -mno-paired-single -mdmx -mno-mdmx @gol
895 -mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc @gol
896 -mlong64 -mlong32 -msym32 -mno-sym32 @gol
897 -G@var{num} -mlocal-sdata -mno-local-sdata @gol
898 -mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt @gol
899 -membedded-data -mno-embedded-data @gol
900 -muninit-const-in-rodata -mno-uninit-const-in-rodata @gol
901 -mcode-readable=@var{setting} @gol
902 -msplit-addresses -mno-split-addresses @gol
903 -mexplicit-relocs -mno-explicit-relocs @gol
904 -mcheck-zero-division -mno-check-zero-division @gol
905 -mdivide-traps -mdivide-breaks @gol
906 -mload-store-pairs -mno-load-store-pairs @gol
907 -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol
908 -mmad -mno-mad -mimadd -mno-imadd -mfused-madd -mno-fused-madd -nocpp @gol
909 -mfix-24k -mno-fix-24k @gol
910 -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol
911 -mfix-r10000 -mno-fix-r10000 -mfix-rm7000 -mno-fix-rm7000 @gol
912 -mfix-vr4120 -mno-fix-vr4120 @gol
913 -mfix-vr4130 -mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1 @gol
914 -mflush-func=@var{func} -mno-flush-func @gol
915 -mbranch-cost=@var{num} -mbranch-likely -mno-branch-likely @gol
916 -mcompact-branches=@var{policy} @gol
917 -mfp-exceptions -mno-fp-exceptions @gol
918 -mvr4130-align -mno-vr4130-align -msynci -mno-synci @gol
919 -mlxc1-sxc1 -mno-lxc1-sxc1 -mmadd4 -mno-madd4 @gol
920 -mrelax-pic-calls -mno-relax-pic-calls -mmcount-ra-address @gol
921 -mframe-header-opt -mno-frame-header-opt}
924 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
925 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
926 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
927 -mno-base-addresses -msingle-exit -mno-single-exit}
929 @emph{MN10300 Options}
930 @gccoptlist{-mmult-bug -mno-mult-bug @gol
931 -mno-am33 -mam33 -mam33-2 -mam34 @gol
932 -mtune=@var{cpu-type} @gol
933 -mreturn-pointer-on-d0 @gol
934 -mno-crt0 -mrelax -mliw -msetlb}
937 @gccoptlist{-meb -mel -mmul.x -mno-crt0}
939 @emph{MSP430 Options}
940 @gccoptlist{-msim -masm-hex -mmcu= -mcpu= -mlarge -msmall -mrelax @gol
942 -mcode-region= -mdata-region= @gol
943 -msilicon-errata= -msilicon-errata-warn= @gol
947 @gccoptlist{-mbig-endian -mlittle-endian @gol
948 -mreduced-regs -mfull-regs @gol
949 -mcmov -mno-cmov @gol
950 -mext-perf -mno-ext-perf @gol
951 -mext-perf2 -mno-ext-perf2 @gol
952 -mext-string -mno-ext-string @gol
953 -mv3push -mno-v3push @gol
954 -m16bit -mno-16bit @gol
955 -misr-vector-size=@var{num} @gol
956 -mcache-block-size=@var{num} @gol
957 -march=@var{arch} @gol
958 -mcmodel=@var{code-model} @gol
961 @emph{Nios II Options}
962 @gccoptlist{-G @var{num} -mgpopt=@var{option} -mgpopt -mno-gpopt @gol
963 -mgprel-sec=@var{regexp} -mr0rel-sec=@var{regexp} @gol
965 -mno-bypass-cache -mbypass-cache @gol
966 -mno-cache-volatile -mcache-volatile @gol
967 -mno-fast-sw-div -mfast-sw-div @gol
968 -mhw-mul -mno-hw-mul -mhw-mulx -mno-hw-mulx -mno-hw-div -mhw-div @gol
969 -mcustom-@var{insn}=@var{N} -mno-custom-@var{insn} @gol
970 -mcustom-fpu-cfg=@var{name} @gol
971 -mhal -msmallc -msys-crt0=@var{name} -msys-lib=@var{name} @gol
972 -march=@var{arch} -mbmx -mno-bmx -mcdx -mno-cdx}
974 @emph{Nvidia PTX Options}
975 @gccoptlist{-m32 -m64 -mmainkernel -moptimize}
977 @emph{PDP-11 Options}
978 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
979 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
980 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
981 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
982 -mbranch-expensive -mbranch-cheap @gol
983 -munix-asm -mdec-asm}
985 @emph{picoChip Options}
986 @gccoptlist{-mae=@var{ae_type} -mvliw-lookahead=@var{N} @gol
987 -msymbol-as-address -mno-inefficient-warnings}
989 @emph{PowerPC Options}
990 See RS/6000 and PowerPC Options.
992 @emph{PowerPC SPE Options}
993 @gccoptlist{-mcpu=@var{cpu-type} @gol
994 -mtune=@var{cpu-type} @gol
995 -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb @gol
996 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
997 -m32 -mxl-compat -mno-xl-compat @gol
998 -malign-power -malign-natural @gol
999 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
1000 -msingle-float -mdouble-float @gol
1001 -mupdate -mno-update @gol
1002 -mavoid-indexed-addresses -mno-avoid-indexed-addresses @gol
1003 -mstrict-align -mno-strict-align -mrelocatable @gol
1004 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
1005 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
1006 -msingle-pic-base @gol
1007 -mprioritize-restricted-insns=@var{priority} @gol
1008 -msched-costly-dep=@var{dependence_type} @gol
1009 -minsert-sched-nops=@var{scheme} @gol
1010 -mcall-sysv -mcall-netbsd @gol
1011 -maix-struct-return -msvr4-struct-return @gol
1012 -mabi=@var{abi-type} -msecure-plt -mbss-plt @gol
1013 -mblock-move-inline-limit=@var{num} @gol
1014 -misel -mno-isel @gol
1015 -misel=yes -misel=no @gol
1017 -mspe=yes -mspe=no @gol
1018 -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol
1019 -mprototype -mno-prototype @gol
1020 -msim -mmvme -mads -myellowknife -memb -msdata @gol
1021 -msdata=@var{opt} -mvxworks -G @var{num} @gol
1022 -mrecip -mrecip=@var{opt} -mno-recip -mrecip-precision @gol
1023 -mno-recip-precision @gol
1024 -mpointers-to-nested-functions -mno-pointers-to-nested-functions @gol
1025 -msave-toc-indirect -mno-save-toc-indirect @gol
1026 -mcompat-align-parm -mno-compat-align-parm @gol
1027 -mfloat128 -mno-float128 @gol
1028 -mgnu-attribute -mno-gnu-attribute @gol
1029 -mstack-protector-guard=@var{guard} -mstack-protector-guard-reg=@var{reg} @gol
1030 -mstack-protector-guard-offset=@var{offset}}
1032 @emph{RISC-V Options}
1033 @gccoptlist{-mbranch-cost=@var{N-instruction} @gol
1035 -mabi=@var{ABI-string} @gol
1036 -mfdiv -mno-fdiv @gol
1038 -march=@var{ISA-string} @gol
1039 -mtune=@var{processor-string} @gol
1040 -mpreferred-stack-boundary=@var{num} @gol
1041 -msmall-data-limit=@var{N-bytes} @gol
1042 -msave-restore -mno-save-restore @gol
1043 -mstrict-align -mno-strict-align @gol
1044 -mcmodel=medlow -mcmodel=medany @gol
1045 -mexplicit-relocs -mno-explicit-relocs @gol
1046 -mrelax -mno-relax @gol}
1049 @gccoptlist{-msim -mmul=none -mmul=g13 -mmul=g14 -mallregs @gol
1050 -mcpu=g10 -mcpu=g13 -mcpu=g14 -mg10 -mg13 -mg14 @gol
1051 -m64bit-doubles -m32bit-doubles -msave-mduc-in-interrupts}
1053 @emph{RS/6000 and PowerPC Options}
1054 @gccoptlist{-mcpu=@var{cpu-type} @gol
1055 -mtune=@var{cpu-type} @gol
1056 -mcmodel=@var{code-model} @gol
1058 -maltivec -mno-altivec @gol
1059 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
1060 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
1061 -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mpopcntd -mno-popcntd @gol
1062 -mfprnd -mno-fprnd @gol
1063 -mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mhard-dfp -mno-hard-dfp @gol
1064 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
1065 -m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol
1066 -malign-power -malign-natural @gol
1067 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
1068 -msingle-float -mdouble-float -msimple-fpu @gol
1069 -mupdate -mno-update @gol
1070 -mavoid-indexed-addresses -mno-avoid-indexed-addresses @gol
1071 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
1072 -mstrict-align -mno-strict-align -mrelocatable @gol
1073 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
1074 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
1075 -mdynamic-no-pic -maltivec -mswdiv -msingle-pic-base @gol
1076 -mprioritize-restricted-insns=@var{priority} @gol
1077 -msched-costly-dep=@var{dependence_type} @gol
1078 -minsert-sched-nops=@var{scheme} @gol
1079 -mcall-aixdesc -mcall-eabi -mcall-freebsd @gol
1080 -mcall-linux -mcall-netbsd -mcall-openbsd @gol
1081 -mcall-sysv -mcall-sysv-eabi -mcall-sysv-noeabi @gol
1082 -mtraceback=@var{traceback_type} @gol
1083 -maix-struct-return -msvr4-struct-return @gol
1084 -mabi=@var{abi-type} -msecure-plt -mbss-plt @gol
1085 -mblock-move-inline-limit=@var{num} @gol
1086 -mblock-compare-inline-limit=@var{num} @gol
1087 -mblock-compare-inline-loop-limit=@var{num} @gol
1088 -mstring-compare-inline-limit=@var{num} @gol
1089 -misel -mno-isel @gol
1090 -misel=yes -misel=no @gol
1092 -mvrsave -mno-vrsave @gol
1093 -mmulhw -mno-mulhw @gol
1094 -mdlmzb -mno-dlmzb @gol
1095 -mprototype -mno-prototype @gol
1096 -msim -mmvme -mads -myellowknife -memb -msdata @gol
1097 -msdata=@var{opt} -mreadonly-in-sdata -mvxworks -G @var{num} @gol
1098 -mrecip -mrecip=@var{opt} -mno-recip -mrecip-precision @gol
1099 -mno-recip-precision @gol
1100 -mveclibabi=@var{type} -mfriz -mno-friz @gol
1101 -mpointers-to-nested-functions -mno-pointers-to-nested-functions @gol
1102 -msave-toc-indirect -mno-save-toc-indirect @gol
1103 -mpower8-fusion -mno-mpower8-fusion -mpower8-vector -mno-power8-vector @gol
1104 -mcrypto -mno-crypto -mhtm -mno-htm @gol
1105 -mquad-memory -mno-quad-memory @gol
1106 -mquad-memory-atomic -mno-quad-memory-atomic @gol
1107 -mcompat-align-parm -mno-compat-align-parm @gol
1108 -mfloat128 -mno-float128 -mfloat128-hardware -mno-float128-hardware @gol
1109 -mgnu-attribute -mno-gnu-attribute @gol
1110 -mstack-protector-guard=@var{guard} -mstack-protector-guard-reg=@var{reg} @gol
1111 -mstack-protector-guard-offset=@var{offset}}
1114 @gccoptlist{-m64bit-doubles -m32bit-doubles -fpu -nofpu@gol
1116 -mbig-endian-data -mlittle-endian-data @gol
1119 -mas100-syntax -mno-as100-syntax@gol
1121 -mmax-constant-size=@gol
1124 -mallow-string-insns -mno-allow-string-insns@gol
1126 -mno-warn-multiple-fast-interrupts@gol
1127 -msave-acc-in-interrupts}
1129 @emph{S/390 and zSeries Options}
1130 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
1131 -mhard-float -msoft-float -mhard-dfp -mno-hard-dfp @gol
1132 -mlong-double-64 -mlong-double-128 @gol
1133 -mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol
1134 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
1135 -m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol
1136 -mhtm -mvx -mzvector @gol
1137 -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol
1138 -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard @gol
1139 -mhotpatch=@var{halfwords},@var{halfwords}}
1141 @emph{Score Options}
1142 @gccoptlist{-meb -mel @gol
1146 -mscore5 -mscore5u -mscore7 -mscore7d}
1149 @gccoptlist{-m1 -m2 -m2e @gol
1150 -m2a-nofpu -m2a-single-only -m2a-single -m2a @gol
1152 -m4-nofpu -m4-single-only -m4-single -m4 @gol
1153 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol
1154 -mb -ml -mdalign -mrelax @gol
1155 -mbigtable -mfmovd -mrenesas -mno-renesas -mnomacsave @gol
1156 -mieee -mno-ieee -mbitops -misize -minline-ic_invalidate -mpadstruct @gol
1157 -mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol
1158 -mdivsi3_libfunc=@var{name} -mfixed-range=@var{register-range} @gol
1159 -maccumulate-outgoing-args @gol
1160 -matomic-model=@var{atomic-model} @gol
1161 -mbranch-cost=@var{num} -mzdcbranch -mno-zdcbranch @gol
1162 -mcbranch-force-delay-slot @gol
1163 -mfused-madd -mno-fused-madd -mfsca -mno-fsca -mfsrra -mno-fsrra @gol
1164 -mpretend-cmove -mtas}
1166 @emph{Solaris 2 Options}
1167 @gccoptlist{-mclear-hwcap -mno-clear-hwcap -mimpure-text -mno-impure-text @gol
1170 @emph{SPARC Options}
1171 @gccoptlist{-mcpu=@var{cpu-type} @gol
1172 -mtune=@var{cpu-type} @gol
1173 -mcmodel=@var{code-model} @gol
1174 -mmemory-model=@var{mem-model} @gol
1175 -m32 -m64 -mapp-regs -mno-app-regs @gol
1176 -mfaster-structs -mno-faster-structs -mflat -mno-flat @gol
1177 -mfpu -mno-fpu -mhard-float -msoft-float @gol
1178 -mhard-quad-float -msoft-quad-float @gol
1179 -mstack-bias -mno-stack-bias @gol
1180 -mstd-struct-return -mno-std-struct-return @gol
1181 -munaligned-doubles -mno-unaligned-doubles @gol
1182 -muser-mode -mno-user-mode @gol
1183 -mv8plus -mno-v8plus -mvis -mno-vis @gol
1184 -mvis2 -mno-vis2 -mvis3 -mno-vis3 @gol
1185 -mvis4 -mno-vis4 -mvis4b -mno-vis4b @gol
1186 -mcbcond -mno-cbcond -mfmaf -mno-fmaf -mfsmuld -mno-fsmuld @gol
1187 -mpopc -mno-popc -msubxc -mno-subxc @gol
1188 -mfix-at697f -mfix-ut699 -mfix-ut700 -mfix-gr712rc @gol
1192 @gccoptlist{-mwarn-reloc -merror-reloc @gol
1193 -msafe-dma -munsafe-dma @gol
1195 -msmall-mem -mlarge-mem -mstdmain @gol
1196 -mfixed-range=@var{register-range} @gol
1198 -maddress-space-conversion -mno-address-space-conversion @gol
1199 -mcache-size=@var{cache-size} @gol
1200 -matomic-updates -mno-atomic-updates}
1202 @emph{System V Options}
1203 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
1205 @emph{TILE-Gx Options}
1206 @gccoptlist{-mcpu=CPU -m32 -m64 -mbig-endian -mlittle-endian @gol
1207 -mcmodel=@var{code-model}}
1209 @emph{TILEPro Options}
1210 @gccoptlist{-mcpu=@var{cpu} -m32}
1213 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
1214 -mprolog-function -mno-prolog-function -mspace @gol
1215 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
1216 -mapp-regs -mno-app-regs @gol
1217 -mdisable-callt -mno-disable-callt @gol
1218 -mv850e2v3 -mv850e2 -mv850e1 -mv850es @gol
1219 -mv850e -mv850 -mv850e3v5 @gol
1230 @gccoptlist{-mg -mgnu -munix}
1232 @emph{Visium Options}
1233 @gccoptlist{-mdebug -msim -mfpu -mno-fpu -mhard-float -msoft-float @gol
1234 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} -msv-mode -muser-mode}
1237 @gccoptlist{-mvms-return-codes -mdebug-main=@var{prefix} -mmalloc64 @gol
1238 -mpointer-size=@var{size}}
1240 @emph{VxWorks Options}
1241 @gccoptlist{-mrtp -non-static -Bstatic -Bdynamic @gol
1242 -Xbind-lazy -Xbind-now}
1245 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
1246 -mtune-ctrl=@var{feature-list} -mdump-tune-features -mno-default @gol
1247 -mfpmath=@var{unit} @gol
1248 -masm=@var{dialect} -mno-fancy-math-387 @gol
1249 -mno-fp-ret-in-387 -m80387 -mhard-float -msoft-float @gol
1250 -mno-wide-multiply -mrtd -malign-double @gol
1251 -mpreferred-stack-boundary=@var{num} @gol
1252 -mincoming-stack-boundary=@var{num} @gol
1253 -mcld -mcx16 -msahf -mmovbe -mcrc32 @gol
1254 -mrecip -mrecip=@var{opt} @gol
1255 -mvzeroupper -mprefer-avx128 -mprefer-vector-width=@var{opt} @gol
1256 -mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx @gol
1257 -mavx2 -mavx512f -mavx512pf -mavx512er -mavx512cd -mavx512vl @gol
1258 -mavx512bw -mavx512dq -mavx512ifma -mavx512vbmi -msha -maes @gol
1259 -mpclmul -mfsgsbase -mrdrnd -mf16c -mfma -mpconfig -mwbnoinvd @gol
1260 -mprefetchwt1 -mclflushopt -mxsavec -mxsaves @gol
1261 -msse4a -m3dnow -m3dnowa -mpopcnt -mabm -mbmi -mtbm -mfma4 -mxop @gol
1262 -mlzcnt -mbmi2 -mfxsr -mxsave -mxsaveopt -mrtm -mlwp -mmpx @gol
1263 -mmwaitx -mclzero -mpku -mthreads -mgfni -mvaes @gol
1264 -mshstk -mforce-indirect-call -mavx512vbmi2 @gol
1265 -mvpclmulqdq -mavx512bitalg -mmovdiri -mmovdir64b -mavx512vpopcntdq @gol
1266 -mms-bitfields -mno-align-stringops -minline-all-stringops @gol
1267 -minline-stringops-dynamically -mstringop-strategy=@var{alg} @gol
1268 -mmemcpy-strategy=@var{strategy} -mmemset-strategy=@var{strategy} @gol
1269 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
1270 -m96bit-long-double -mlong-double-64 -mlong-double-80 -mlong-double-128 @gol
1271 -mregparm=@var{num} -msseregparm @gol
1272 -mveclibabi=@var{type} -mvect8-ret-in-mem @gol
1273 -mpc32 -mpc64 -mpc80 -mstackrealign @gol
1274 -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol
1275 -mcmodel=@var{code-model} -mabi=@var{name} -maddress-mode=@var{mode} @gol
1276 -m32 -m64 -mx32 -m16 -miamcu -mlarge-data-threshold=@var{num} @gol
1277 -msse2avx -mfentry -mrecord-mcount -mnop-mcount -m8bit-idiv @gol
1278 -mavx256-split-unaligned-load -mavx256-split-unaligned-store @gol
1279 -malign-data=@var{type} -mstack-protector-guard=@var{guard} @gol
1280 -mstack-protector-guard-reg=@var{reg} @gol
1281 -mstack-protector-guard-offset=@var{offset} @gol
1282 -mstack-protector-guard-symbol=@var{symbol} -mmitigate-rop @gol
1283 -mgeneral-regs-only -mcall-ms2sysv-xlogues @gol
1284 -mindirect-branch=@var{choice} -mfunction-return=@var{choice} @gol
1285 -mindirect-branch-register}
1287 @emph{x86 Windows Options}
1288 @gccoptlist{-mconsole -mcygwin -mno-cygwin -mdll @gol
1289 -mnop-fun-dllimport -mthread @gol
1290 -municode -mwin32 -mwindows -fno-set-stack-executable}
1292 @emph{Xstormy16 Options}
1295 @emph{Xtensa Options}
1296 @gccoptlist{-mconst16 -mno-const16 @gol
1297 -mfused-madd -mno-fused-madd @gol
1299 -mserialize-volatile -mno-serialize-volatile @gol
1300 -mtext-section-literals -mno-text-section-literals @gol
1301 -mauto-litpools -mno-auto-litpools @gol
1302 -mtarget-align -mno-target-align @gol
1303 -mlongcalls -mno-longcalls}
1305 @emph{zSeries Options}
1306 See S/390 and zSeries Options.
1310 @node Overall Options
1311 @section Options Controlling the Kind of Output
1313 Compilation can involve up to four stages: preprocessing, compilation
1314 proper, assembly and linking, always in that order. GCC is capable of
1315 preprocessing and compiling several files either into several
1316 assembler input files, or into one assembler input file; then each
1317 assembler input file produces an object file, and linking combines all
1318 the object files (those newly compiled, and those specified as input)
1319 into an executable file.
1321 @cindex file name suffix
1322 For any given input file, the file name suffix determines what kind of
1323 compilation is done:
1327 C source code that must be preprocessed.
1330 C source code that should not be preprocessed.
1333 C++ source code that should not be preprocessed.
1336 Objective-C source code. Note that you must link with the @file{libobjc}
1337 library to make an Objective-C program work.
1340 Objective-C source code that should not be preprocessed.
1344 Objective-C++ source code. Note that you must link with the @file{libobjc}
1345 library to make an Objective-C++ program work. Note that @samp{.M} refers
1346 to a literal capital M@.
1348 @item @var{file}.mii
1349 Objective-C++ source code that should not be preprocessed.
1352 C, C++, Objective-C or Objective-C++ header file to be turned into a
1353 precompiled header (default), or C, C++ header file to be turned into an
1354 Ada spec (via the @option{-fdump-ada-spec} switch).
1357 @itemx @var{file}.cp
1358 @itemx @var{file}.cxx
1359 @itemx @var{file}.cpp
1360 @itemx @var{file}.CPP
1361 @itemx @var{file}.c++
1363 C++ source code that must be preprocessed. Note that in @samp{.cxx},
1364 the last two letters must both be literally @samp{x}. Likewise,
1365 @samp{.C} refers to a literal capital C@.
1369 Objective-C++ source code that must be preprocessed.
1371 @item @var{file}.mii
1372 Objective-C++ source code that should not be preprocessed.
1376 @itemx @var{file}.hp
1377 @itemx @var{file}.hxx
1378 @itemx @var{file}.hpp
1379 @itemx @var{file}.HPP
1380 @itemx @var{file}.h++
1381 @itemx @var{file}.tcc
1382 C++ header file to be turned into a precompiled header or Ada spec.
1385 @itemx @var{file}.for
1386 @itemx @var{file}.ftn
1387 Fixed form Fortran source code that should not be preprocessed.
1390 @itemx @var{file}.FOR
1391 @itemx @var{file}.fpp
1392 @itemx @var{file}.FPP
1393 @itemx @var{file}.FTN
1394 Fixed form Fortran source code that must be preprocessed (with the traditional
1397 @item @var{file}.f90
1398 @itemx @var{file}.f95
1399 @itemx @var{file}.f03
1400 @itemx @var{file}.f08
1401 Free form Fortran source code that should not be preprocessed.
1403 @item @var{file}.F90
1404 @itemx @var{file}.F95
1405 @itemx @var{file}.F03
1406 @itemx @var{file}.F08
1407 Free form Fortran source code that must be preprocessed (with the
1408 traditional preprocessor).
1413 @item @var{file}.brig
1414 BRIG files (binary representation of HSAIL).
1416 @item @var{file}.ads
1417 Ada source code file that contains a library unit declaration (a
1418 declaration of a package, subprogram, or generic, or a generic
1419 instantiation), or a library unit renaming declaration (a package,
1420 generic, or subprogram renaming declaration). Such files are also
1423 @item @var{file}.adb
1424 Ada source code file containing a library unit body (a subprogram or
1425 package body). Such files are also called @dfn{bodies}.
1427 @c GCC also knows about some suffixes for languages not yet included:
1438 @itemx @var{file}.sx
1439 Assembler code that must be preprocessed.
1442 An object file to be fed straight into linking.
1443 Any file name with no recognized suffix is treated this way.
1447 You can specify the input language explicitly with the @option{-x} option:
1450 @item -x @var{language}
1451 Specify explicitly the @var{language} for the following input files
1452 (rather than letting the compiler choose a default based on the file
1453 name suffix). This option applies to all following input files until
1454 the next @option{-x} option. Possible values for @var{language} are:
1456 c c-header cpp-output
1457 c++ c++-header c++-cpp-output
1458 objective-c objective-c-header objective-c-cpp-output
1459 objective-c++ objective-c++-header objective-c++-cpp-output
1460 assembler assembler-with-cpp
1462 f77 f77-cpp-input f95 f95-cpp-input
1468 Turn off any specification of a language, so that subsequent files are
1469 handled according to their file name suffixes (as they are if @option{-x}
1470 has not been used at all).
1473 If you only want some of the stages of compilation, you can use
1474 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
1475 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
1476 @command{gcc} is to stop. Note that some combinations (for example,
1477 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
1482 Compile or assemble the source files, but do not link. The linking
1483 stage simply is not done. The ultimate output is in the form of an
1484 object file for each source file.
1486 By default, the object file name for a source file is made by replacing
1487 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
1489 Unrecognized input files, not requiring compilation or assembly, are
1494 Stop after the stage of compilation proper; do not assemble. The output
1495 is in the form of an assembler code file for each non-assembler input
1498 By default, the assembler file name for a source file is made by
1499 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
1501 Input files that don't require compilation are ignored.
1505 Stop after the preprocessing stage; do not run the compiler proper. The
1506 output is in the form of preprocessed source code, which is sent to the
1509 Input files that don't require preprocessing are ignored.
1511 @cindex output file option
1514 Place output in file @var{file}. This applies to whatever
1515 sort of output is being produced, whether it be an executable file,
1516 an object file, an assembler file or preprocessed C code.
1518 If @option{-o} is not specified, the default is to put an executable
1519 file in @file{a.out}, the object file for
1520 @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its
1521 assembler file in @file{@var{source}.s}, a precompiled header file in
1522 @file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on
1527 Print (on standard error output) the commands executed to run the stages
1528 of compilation. Also print the version number of the compiler driver
1529 program and of the preprocessor and the compiler proper.
1533 Like @option{-v} except the commands are not executed and arguments
1534 are quoted unless they contain only alphanumeric characters or @code{./-_}.
1535 This is useful for shell scripts to capture the driver-generated command lines.
1539 Print (on the standard output) a description of the command-line options
1540 understood by @command{gcc}. If the @option{-v} option is also specified
1541 then @option{--help} is also passed on to the various processes
1542 invoked by @command{gcc}, so that they can display the command-line options
1543 they accept. If the @option{-Wextra} option has also been specified
1544 (prior to the @option{--help} option), then command-line options that
1545 have no documentation associated with them are also displayed.
1548 @opindex target-help
1549 Print (on the standard output) a description of target-specific command-line
1550 options for each tool. For some targets extra target-specific
1551 information may also be printed.
1553 @item --help=@{@var{class}@r{|[}^@r{]}@var{qualifier}@}@r{[},@dots{}@r{]}
1554 Print (on the standard output) a description of the command-line
1555 options understood by the compiler that fit into all specified classes
1556 and qualifiers. These are the supported classes:
1559 @item @samp{optimizers}
1560 Display all of the optimization options supported by the
1563 @item @samp{warnings}
1564 Display all of the options controlling warning messages
1565 produced by the compiler.
1568 Display target-specific options. Unlike the
1569 @option{--target-help} option however, target-specific options of the
1570 linker and assembler are not displayed. This is because those
1571 tools do not currently support the extended @option{--help=} syntax.
1574 Display the values recognized by the @option{--param}
1577 @item @var{language}
1578 Display the options supported for @var{language}, where
1579 @var{language} is the name of one of the languages supported in this
1583 Display the options that are common to all languages.
1586 These are the supported qualifiers:
1589 @item @samp{undocumented}
1590 Display only those options that are undocumented.
1593 Display options taking an argument that appears after an equal
1594 sign in the same continuous piece of text, such as:
1595 @samp{--help=target}.
1597 @item @samp{separate}
1598 Display options taking an argument that appears as a separate word
1599 following the original option, such as: @samp{-o output-file}.
1602 Thus for example to display all the undocumented target-specific
1603 switches supported by the compiler, use:
1606 --help=target,undocumented
1609 The sense of a qualifier can be inverted by prefixing it with the
1610 @samp{^} character, so for example to display all binary warning
1611 options (i.e., ones that are either on or off and that do not take an
1612 argument) that have a description, use:
1615 --help=warnings,^joined,^undocumented
1618 The argument to @option{--help=} should not consist solely of inverted
1621 Combining several classes is possible, although this usually
1622 restricts the output so much that there is nothing to display. One
1623 case where it does work, however, is when one of the classes is
1624 @var{target}. For example, to display all the target-specific
1625 optimization options, use:
1628 --help=target,optimizers
1631 The @option{--help=} option can be repeated on the command line. Each
1632 successive use displays its requested class of options, skipping
1633 those that have already been displayed.
1635 If the @option{-Q} option appears on the command line before the
1636 @option{--help=} option, then the descriptive text displayed by
1637 @option{--help=} is changed. Instead of describing the displayed
1638 options, an indication is given as to whether the option is enabled,
1639 disabled or set to a specific value (assuming that the compiler
1640 knows this at the point where the @option{--help=} option is used).
1642 Here is a truncated example from the ARM port of @command{gcc}:
1645 % gcc -Q -mabi=2 --help=target -c
1646 The following options are target specific:
1648 -mabort-on-noreturn [disabled]
1652 The output is sensitive to the effects of previous command-line
1653 options, so for example it is possible to find out which optimizations
1654 are enabled at @option{-O2} by using:
1657 -Q -O2 --help=optimizers
1660 Alternatively you can discover which binary optimizations are enabled
1661 by @option{-O3} by using:
1664 gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
1665 gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
1666 diff /tmp/O2-opts /tmp/O3-opts | grep enabled
1671 Display the version number and copyrights of the invoked GCC@.
1673 @item -pass-exit-codes
1674 @opindex pass-exit-codes
1675 Normally the @command{gcc} program exits with the code of 1 if any
1676 phase of the compiler returns a non-success return code. If you specify
1677 @option{-pass-exit-codes}, the @command{gcc} program instead returns with
1678 the numerically highest error produced by any phase returning an error
1679 indication. The C, C++, and Fortran front ends return 4 if an internal
1680 compiler error is encountered.
1684 Use pipes rather than temporary files for communication between the
1685 various stages of compilation. This fails to work on some systems where
1686 the assembler is unable to read from a pipe; but the GNU assembler has
1689 @item -specs=@var{file}
1691 Process @var{file} after the compiler reads in the standard @file{specs}
1692 file, in order to override the defaults which the @command{gcc} driver
1693 program uses when determining what switches to pass to @command{cc1},
1694 @command{cc1plus}, @command{as}, @command{ld}, etc. More than one
1695 @option{-specs=@var{file}} can be specified on the command line, and they
1696 are processed in order, from left to right. @xref{Spec Files}, for
1697 information about the format of the @var{file}.
1701 Invoke all subcommands under a wrapper program. The name of the
1702 wrapper program and its parameters are passed as a comma separated
1706 gcc -c t.c -wrapper gdb,--args
1710 This invokes all subprograms of @command{gcc} under
1711 @samp{gdb --args}, thus the invocation of @command{cc1} is
1712 @samp{gdb --args cc1 @dots{}}.
1714 @item -ffile-prefix-map=@var{old}=@var{new}
1715 @opindex ffile-prefix-map
1716 When compiling files residing in directory @file{@var{old}}, record
1717 any references to them in the result of the compilation as if the
1718 files resided in directory @file{@var{new}} instead. Specifying this
1719 option is equivalent to specifying all the individual
1720 @option{-f*-prefix-map} options. This can be used to make reproducible
1721 builds that are location independent. See also
1722 @option{-fmacro-prefix-map} and @option{-fdebug-prefix-map}.
1724 @item -fplugin=@var{name}.so
1726 Load the plugin code in file @var{name}.so, assumed to be a
1727 shared object to be dlopen'd by the compiler. The base name of
1728 the shared object file is used to identify the plugin for the
1729 purposes of argument parsing (See
1730 @option{-fplugin-arg-@var{name}-@var{key}=@var{value}} below).
1731 Each plugin should define the callback functions specified in the
1734 @item -fplugin-arg-@var{name}-@var{key}=@var{value}
1735 @opindex fplugin-arg
1736 Define an argument called @var{key} with a value of @var{value}
1737 for the plugin called @var{name}.
1739 @item -fdump-ada-spec@r{[}-slim@r{]}
1740 @opindex fdump-ada-spec
1741 For C and C++ source and include files, generate corresponding Ada specs.
1742 @xref{Generating Ada Bindings for C and C++ headers,,, gnat_ugn,
1743 GNAT User's Guide}, which provides detailed documentation on this feature.
1745 @item -fada-spec-parent=@var{unit}
1746 @opindex fada-spec-parent
1747 In conjunction with @option{-fdump-ada-spec@r{[}-slim@r{]}} above, generate
1748 Ada specs as child units of parent @var{unit}.
1750 @item -fdump-go-spec=@var{file}
1751 @opindex fdump-go-spec
1752 For input files in any language, generate corresponding Go
1753 declarations in @var{file}. This generates Go @code{const},
1754 @code{type}, @code{var}, and @code{func} declarations which may be a
1755 useful way to start writing a Go interface to code written in some
1758 @include @value{srcdir}/../libiberty/at-file.texi
1762 @section Compiling C++ Programs
1764 @cindex suffixes for C++ source
1765 @cindex C++ source file suffixes
1766 C++ source files conventionally use one of the suffixes @samp{.C},
1767 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
1768 @samp{.cxx}; C++ header files often use @samp{.hh}, @samp{.hpp},
1769 @samp{.H}, or (for shared template code) @samp{.tcc}; and
1770 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
1771 files with these names and compiles them as C++ programs even if you
1772 call the compiler the same way as for compiling C programs (usually
1773 with the name @command{gcc}).
1777 However, the use of @command{gcc} does not add the C++ library.
1778 @command{g++} is a program that calls GCC and automatically specifies linking
1779 against the C++ library. It treats @samp{.c},
1780 @samp{.h} and @samp{.i} files as C++ source files instead of C source
1781 files unless @option{-x} is used. This program is also useful when
1782 precompiling a C header file with a @samp{.h} extension for use in C++
1783 compilations. On many systems, @command{g++} is also installed with
1784 the name @command{c++}.
1786 @cindex invoking @command{g++}
1787 When you compile C++ programs, you may specify many of the same
1788 command-line options that you use for compiling programs in any
1789 language; or command-line options meaningful for C and related
1790 languages; or options that are meaningful only for C++ programs.
1791 @xref{C Dialect Options,,Options Controlling C Dialect}, for
1792 explanations of options for languages related to C@.
1793 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
1794 explanations of options that are meaningful only for C++ programs.
1796 @node C Dialect Options
1797 @section Options Controlling C Dialect
1798 @cindex dialect options
1799 @cindex language dialect options
1800 @cindex options, dialect
1802 The following options control the dialect of C (or languages derived
1803 from C, such as C++, Objective-C and Objective-C++) that the compiler
1807 @cindex ANSI support
1811 In C mode, this is equivalent to @option{-std=c90}. In C++ mode, it is
1812 equivalent to @option{-std=c++98}.
1814 This turns off certain features of GCC that are incompatible with ISO
1815 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
1816 such as the @code{asm} and @code{typeof} keywords, and
1817 predefined macros such as @code{unix} and @code{vax} that identify the
1818 type of system you are using. It also enables the undesirable and
1819 rarely used ISO trigraph feature. For the C compiler,
1820 it disables recognition of C++ style @samp{//} comments as well as
1821 the @code{inline} keyword.
1823 The alternate keywords @code{__asm__}, @code{__extension__},
1824 @code{__inline__} and @code{__typeof__} continue to work despite
1825 @option{-ansi}. You would not want to use them in an ISO C program, of
1826 course, but it is useful to put them in header files that might be included
1827 in compilations done with @option{-ansi}. Alternate predefined macros
1828 such as @code{__unix__} and @code{__vax__} are also available, with or
1829 without @option{-ansi}.
1831 The @option{-ansi} option does not cause non-ISO programs to be
1832 rejected gratuitously. For that, @option{-Wpedantic} is required in
1833 addition to @option{-ansi}. @xref{Warning Options}.
1835 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1836 option is used. Some header files may notice this macro and refrain
1837 from declaring certain functions or defining certain macros that the
1838 ISO standard doesn't call for; this is to avoid interfering with any
1839 programs that might use these names for other things.
1841 Functions that are normally built in but do not have semantics
1842 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1843 functions when @option{-ansi} is used. @xref{Other Builtins,,Other
1844 built-in functions provided by GCC}, for details of the functions
1849 Determine the language standard. @xref{Standards,,Language Standards
1850 Supported by GCC}, for details of these standard versions. This option
1851 is currently only supported when compiling C or C++.
1853 The compiler can accept several base standards, such as @samp{c90} or
1854 @samp{c++98}, and GNU dialects of those standards, such as
1855 @samp{gnu90} or @samp{gnu++98}. When a base standard is specified, the
1856 compiler accepts all programs following that standard plus those
1857 using GNU extensions that do not contradict it. For example,
1858 @option{-std=c90} turns off certain features of GCC that are
1859 incompatible with ISO C90, such as the @code{asm} and @code{typeof}
1860 keywords, but not other GNU extensions that do not have a meaning in
1861 ISO C90, such as omitting the middle term of a @code{?:}
1862 expression. On the other hand, when a GNU dialect of a standard is
1863 specified, all features supported by the compiler are enabled, even when
1864 those features change the meaning of the base standard. As a result, some
1865 strict-conforming programs may be rejected. The particular standard
1866 is used by @option{-Wpedantic} to identify which features are GNU
1867 extensions given that version of the standard. For example
1868 @option{-std=gnu90 -Wpedantic} warns about C++ style @samp{//}
1869 comments, while @option{-std=gnu99 -Wpedantic} does not.
1871 A value for this option must be provided; possible values are
1877 Support all ISO C90 programs (certain GNU extensions that conflict
1878 with ISO C90 are disabled). Same as @option{-ansi} for C code.
1880 @item iso9899:199409
1881 ISO C90 as modified in amendment 1.
1887 ISO C99. This standard is substantially completely supported, modulo
1888 bugs and floating-point issues
1889 (mainly but not entirely relating to optional C99 features from
1890 Annexes F and G). See
1891 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1892 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1897 ISO C11, the 2011 revision of the ISO C standard. This standard is
1898 substantially completely supported, modulo bugs, floating-point issues
1899 (mainly but not entirely relating to optional C11 features from
1900 Annexes F and G) and the optional Annexes K (Bounds-checking
1901 interfaces) and L (Analyzability). The name @samp{c1x} is deprecated.
1907 ISO C17, the 2017 revision of the ISO C standard (expected to be
1908 published in 2018). This standard is
1909 same as C11 except for corrections of defects (all of which are also
1910 applied with @option{-std=c11}) and a new value of
1911 @code{__STDC_VERSION__}, and so is supported to the same extent as C11.
1915 GNU dialect of ISO C90 (including some C99 features).
1919 GNU dialect of ISO C99. The name @samp{gnu9x} is deprecated.
1923 GNU dialect of ISO C11.
1924 The name @samp{gnu1x} is deprecated.
1928 GNU dialect of ISO C17. This is the default for C code.
1932 The 1998 ISO C++ standard plus the 2003 technical corrigendum and some
1933 additional defect reports. Same as @option{-ansi} for C++ code.
1937 GNU dialect of @option{-std=c++98}.
1941 The 2011 ISO C++ standard plus amendments.
1942 The name @samp{c++0x} is deprecated.
1946 GNU dialect of @option{-std=c++11}.
1947 The name @samp{gnu++0x} is deprecated.
1951 The 2014 ISO C++ standard plus amendments.
1952 The name @samp{c++1y} is deprecated.
1956 GNU dialect of @option{-std=c++14}.
1957 This is the default for C++ code.
1958 The name @samp{gnu++1y} is deprecated.
1962 The 2017 ISO C++ standard plus amendments.
1963 The name @samp{c++1z} is deprecated.
1967 GNU dialect of @option{-std=c++17}.
1968 The name @samp{gnu++1z} is deprecated.
1971 The next revision of the ISO C++ standard, tentatively planned for
1972 2020. Support is highly experimental, and will almost certainly
1973 change in incompatible ways in future releases.
1976 GNU dialect of @option{-std=c++2a}. Support is highly experimental,
1977 and will almost certainly change in incompatible ways in future
1981 @item -fgnu89-inline
1982 @opindex fgnu89-inline
1983 The option @option{-fgnu89-inline} tells GCC to use the traditional
1984 GNU semantics for @code{inline} functions when in C99 mode.
1985 @xref{Inline,,An Inline Function is As Fast As a Macro}.
1986 Using this option is roughly equivalent to adding the
1987 @code{gnu_inline} function attribute to all inline functions
1988 (@pxref{Function Attributes}).
1990 The option @option{-fno-gnu89-inline} explicitly tells GCC to use the
1991 C99 semantics for @code{inline} when in C99 or gnu99 mode (i.e., it
1992 specifies the default behavior).
1993 This option is not supported in @option{-std=c90} or
1994 @option{-std=gnu90} mode.
1996 The preprocessor macros @code{__GNUC_GNU_INLINE__} and
1997 @code{__GNUC_STDC_INLINE__} may be used to check which semantics are
1998 in effect for @code{inline} functions. @xref{Common Predefined
1999 Macros,,,cpp,The C Preprocessor}.
2001 @item -fpermitted-flt-eval-methods=@var{style}
2002 @opindex fpermitted-flt-eval-methods
2003 @opindex fpermitted-flt-eval-methods=c11
2004 @opindex fpermitted-flt-eval-methods=ts-18661-3
2005 ISO/IEC TS 18661-3 defines new permissible values for
2006 @code{FLT_EVAL_METHOD} that indicate that operations and constants with
2007 a semantic type that is an interchange or extended format should be
2008 evaluated to the precision and range of that type. These new values are
2009 a superset of those permitted under C99/C11, which does not specify the
2010 meaning of other positive values of @code{FLT_EVAL_METHOD}. As such, code
2011 conforming to C11 may not have been written expecting the possibility of
2014 @option{-fpermitted-flt-eval-methods} specifies whether the compiler
2015 should allow only the values of @code{FLT_EVAL_METHOD} specified in C99/C11,
2016 or the extended set of values specified in ISO/IEC TS 18661-3.
2018 @var{style} is either @code{c11} or @code{ts-18661-3} as appropriate.
2020 The default when in a standards compliant mode (@option{-std=c11} or similar)
2021 is @option{-fpermitted-flt-eval-methods=c11}. The default when in a GNU
2022 dialect (@option{-std=gnu11} or similar) is
2023 @option{-fpermitted-flt-eval-methods=ts-18661-3}.
2025 @item -aux-info @var{filename}
2027 Output to the given filename prototyped declarations for all functions
2028 declared and/or defined in a translation unit, including those in header
2029 files. This option is silently ignored in any language other than C@.
2031 Besides declarations, the file indicates, in comments, the origin of
2032 each declaration (source file and line), whether the declaration was
2033 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
2034 @samp{O} for old, respectively, in the first character after the line
2035 number and the colon), and whether it came from a declaration or a
2036 definition (@samp{C} or @samp{F}, respectively, in the following
2037 character). In the case of function definitions, a K&R-style list of
2038 arguments followed by their declarations is also provided, inside
2039 comments, after the declaration.
2041 @item -fallow-parameterless-variadic-functions
2042 @opindex fallow-parameterless-variadic-functions
2043 Accept variadic functions without named parameters.
2045 Although it is possible to define such a function, this is not very
2046 useful as it is not possible to read the arguments. This is only
2047 supported for C as this construct is allowed by C++.
2051 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
2052 keyword, so that code can use these words as identifiers. You can use
2053 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
2054 instead. @option{-ansi} implies @option{-fno-asm}.
2056 In C++, this switch only affects the @code{typeof} keyword, since
2057 @code{asm} and @code{inline} are standard keywords. You may want to
2058 use the @option{-fno-gnu-keywords} flag instead, which has the same
2059 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
2060 switch only affects the @code{asm} and @code{typeof} keywords, since
2061 @code{inline} is a standard keyword in ISO C99.
2064 @itemx -fno-builtin-@var{function}
2065 @opindex fno-builtin
2066 @cindex built-in functions
2067 Don't recognize built-in functions that do not begin with
2068 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
2069 functions provided by GCC}, for details of the functions affected,
2070 including those which are not built-in functions when @option{-ansi} or
2071 @option{-std} options for strict ISO C conformance are used because they
2072 do not have an ISO standard meaning.
2074 GCC normally generates special code to handle certain built-in functions
2075 more efficiently; for instance, calls to @code{alloca} may become single
2076 instructions which adjust the stack directly, and calls to @code{memcpy}
2077 may become inline copy loops. The resulting code is often both smaller
2078 and faster, but since the function calls no longer appear as such, you
2079 cannot set a breakpoint on those calls, nor can you change the behavior
2080 of the functions by linking with a different library. In addition,
2081 when a function is recognized as a built-in function, GCC may use
2082 information about that function to warn about problems with calls to
2083 that function, or to generate more efficient code, even if the
2084 resulting code still contains calls to that function. For example,
2085 warnings are given with @option{-Wformat} for bad calls to
2086 @code{printf} when @code{printf} is built in and @code{strlen} is
2087 known not to modify global memory.
2089 With the @option{-fno-builtin-@var{function}} option
2090 only the built-in function @var{function} is
2091 disabled. @var{function} must not begin with @samp{__builtin_}. If a
2092 function is named that is not built-in in this version of GCC, this
2093 option is ignored. There is no corresponding
2094 @option{-fbuiltin-@var{function}} option; if you wish to enable
2095 built-in functions selectively when using @option{-fno-builtin} or
2096 @option{-ffreestanding}, you may define macros such as:
2099 #define abs(n) __builtin_abs ((n))
2100 #define strcpy(d, s) __builtin_strcpy ((d), (s))
2106 Enable parsing of function definitions marked with @code{__GIMPLE}.
2107 This is an experimental feature that allows unit testing of GIMPLE
2112 @cindex hosted environment
2114 Assert that compilation targets a hosted environment. This implies
2115 @option{-fbuiltin}. A hosted environment is one in which the
2116 entire standard library is available, and in which @code{main} has a return
2117 type of @code{int}. Examples are nearly everything except a kernel.
2118 This is equivalent to @option{-fno-freestanding}.
2120 @item -ffreestanding
2121 @opindex ffreestanding
2122 @cindex hosted environment
2124 Assert that compilation targets a freestanding environment. This
2125 implies @option{-fno-builtin}. A freestanding environment
2126 is one in which the standard library may not exist, and program startup may
2127 not necessarily be at @code{main}. The most obvious example is an OS kernel.
2128 This is equivalent to @option{-fno-hosted}.
2130 @xref{Standards,,Language Standards Supported by GCC}, for details of
2131 freestanding and hosted environments.
2135 @cindex OpenACC accelerator programming
2136 Enable handling of OpenACC directives @code{#pragma acc} in C/C++ and
2137 @code{!$acc} in Fortran. When @option{-fopenacc} is specified, the
2138 compiler generates accelerated code according to the OpenACC Application
2139 Programming Interface v2.0 @w{@uref{https://www.openacc.org}}. This option
2140 implies @option{-pthread}, and thus is only supported on targets that
2141 have support for @option{-pthread}.
2143 @item -fopenacc-dim=@var{geom}
2144 @opindex fopenacc-dim
2145 @cindex OpenACC accelerator programming
2146 Specify default compute dimensions for parallel offload regions that do
2147 not explicitly specify. The @var{geom} value is a triple of
2148 ':'-separated sizes, in order 'gang', 'worker' and, 'vector'. A size
2149 can be omitted, to use a target-specific default value.
2153 @cindex OpenMP parallel
2154 Enable handling of OpenMP directives @code{#pragma omp} in C/C++ and
2155 @code{!$omp} in Fortran. When @option{-fopenmp} is specified, the
2156 compiler generates parallel code according to the OpenMP Application
2157 Program Interface v4.5 @w{@uref{http://www.openmp.org/}}. This option
2158 implies @option{-pthread}, and thus is only supported on targets that
2159 have support for @option{-pthread}. @option{-fopenmp} implies
2160 @option{-fopenmp-simd}.
2163 @opindex fopenmp-simd
2166 Enable handling of OpenMP's SIMD directives with @code{#pragma omp}
2167 in C/C++ and @code{!$omp} in Fortran. Other OpenMP directives
2172 When the option @option{-fgnu-tm} is specified, the compiler
2173 generates code for the Linux variant of Intel's current Transactional
2174 Memory ABI specification document (Revision 1.1, May 6 2009). This is
2175 an experimental feature whose interface may change in future versions
2176 of GCC, as the official specification changes. Please note that not
2177 all architectures are supported for this feature.
2179 For more information on GCC's support for transactional memory,
2180 @xref{Enabling libitm,,The GNU Transactional Memory Library,libitm,GNU
2181 Transactional Memory Library}.
2183 Note that the transactional memory feature is not supported with
2184 non-call exceptions (@option{-fnon-call-exceptions}).
2186 @item -fms-extensions
2187 @opindex fms-extensions
2188 Accept some non-standard constructs used in Microsoft header files.
2190 In C++ code, this allows member names in structures to be similar
2191 to previous types declarations.
2200 Some cases of unnamed fields in structures and unions are only
2201 accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union
2202 fields within structs/unions}, for details.
2204 Note that this option is off for all targets but x86
2205 targets using ms-abi.
2207 @item -fplan9-extensions
2208 @opindex fplan9-extensions
2209 Accept some non-standard constructs used in Plan 9 code.
2211 This enables @option{-fms-extensions}, permits passing pointers to
2212 structures with anonymous fields to functions that expect pointers to
2213 elements of the type of the field, and permits referring to anonymous
2214 fields declared using a typedef. @xref{Unnamed Fields,,Unnamed
2215 struct/union fields within structs/unions}, for details. This is only
2216 supported for C, not C++.
2218 @item -fcond-mismatch
2219 @opindex fcond-mismatch
2220 Allow conditional expressions with mismatched types in the second and
2221 third arguments. The value of such an expression is void. This option
2222 is not supported for C++.
2224 @item -flax-vector-conversions
2225 @opindex flax-vector-conversions
2226 Allow implicit conversions between vectors with differing numbers of
2227 elements and/or incompatible element types. This option should not be
2230 @item -funsigned-char
2231 @opindex funsigned-char
2232 Let the type @code{char} be unsigned, like @code{unsigned char}.
2234 Each kind of machine has a default for what @code{char} should
2235 be. It is either like @code{unsigned char} by default or like
2236 @code{signed char} by default.
2238 Ideally, a portable program should always use @code{signed char} or
2239 @code{unsigned char} when it depends on the signedness of an object.
2240 But many programs have been written to use plain @code{char} and
2241 expect it to be signed, or expect it to be unsigned, depending on the
2242 machines they were written for. This option, and its inverse, let you
2243 make such a program work with the opposite default.
2245 The type @code{char} is always a distinct type from each of
2246 @code{signed char} or @code{unsigned char}, even though its behavior
2247 is always just like one of those two.
2250 @opindex fsigned-char
2251 Let the type @code{char} be signed, like @code{signed char}.
2253 Note that this is equivalent to @option{-fno-unsigned-char}, which is
2254 the negative form of @option{-funsigned-char}. Likewise, the option
2255 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
2257 @item -fsigned-bitfields
2258 @itemx -funsigned-bitfields
2259 @itemx -fno-signed-bitfields
2260 @itemx -fno-unsigned-bitfields
2261 @opindex fsigned-bitfields
2262 @opindex funsigned-bitfields
2263 @opindex fno-signed-bitfields
2264 @opindex fno-unsigned-bitfields
2265 These options control whether a bit-field is signed or unsigned, when the
2266 declaration does not use either @code{signed} or @code{unsigned}. By
2267 default, such a bit-field is signed, because this is consistent: the
2268 basic integer types such as @code{int} are signed types.
2270 @item -fsso-struct=@var{endianness}
2271 @opindex fsso-struct
2272 Set the default scalar storage order of structures and unions to the
2273 specified endianness. The accepted values are @samp{big-endian},
2274 @samp{little-endian} and @samp{native} for the native endianness of
2275 the target (the default). This option is not supported for C++.
2277 @strong{Warning:} the @option{-fsso-struct} switch causes GCC to generate
2278 code that is not binary compatible with code generated without it if the
2279 specified endianness is not the native endianness of the target.
2282 @node C++ Dialect Options
2283 @section Options Controlling C++ Dialect
2285 @cindex compiler options, C++
2286 @cindex C++ options, command-line
2287 @cindex options, C++
2288 This section describes the command-line options that are only meaningful
2289 for C++ programs. You can also use most of the GNU compiler options
2290 regardless of what language your program is in. For example, you
2291 might compile a file @file{firstClass.C} like this:
2294 g++ -g -fstrict-enums -O -c firstClass.C
2298 In this example, only @option{-fstrict-enums} is an option meant
2299 only for C++ programs; you can use the other options with any
2300 language supported by GCC@.
2302 Some options for compiling C programs, such as @option{-std}, are also
2303 relevant for C++ programs.
2304 @xref{C Dialect Options,,Options Controlling C Dialect}.
2306 Here is a list of options that are @emph{only} for compiling C++ programs:
2310 @item -fabi-version=@var{n}
2311 @opindex fabi-version
2312 Use version @var{n} of the C++ ABI@. The default is version 0.
2314 Version 0 refers to the version conforming most closely to
2315 the C++ ABI specification. Therefore, the ABI obtained using version 0
2316 will change in different versions of G++ as ABI bugs are fixed.
2318 Version 1 is the version of the C++ ABI that first appeared in G++ 3.2.
2320 Version 2 is the version of the C++ ABI that first appeared in G++
2321 3.4, and was the default through G++ 4.9.
2323 Version 3 corrects an error in mangling a constant address as a
2326 Version 4, which first appeared in G++ 4.5, implements a standard
2327 mangling for vector types.
2329 Version 5, which first appeared in G++ 4.6, corrects the mangling of
2330 attribute const/volatile on function pointer types, decltype of a
2331 plain decl, and use of a function parameter in the declaration of
2334 Version 6, which first appeared in G++ 4.7, corrects the promotion
2335 behavior of C++11 scoped enums and the mangling of template argument
2336 packs, const/static_cast, prefix ++ and --, and a class scope function
2337 used as a template argument.
2339 Version 7, which first appeared in G++ 4.8, that treats nullptr_t as a
2340 builtin type and corrects the mangling of lambdas in default argument
2343 Version 8, which first appeared in G++ 4.9, corrects the substitution
2344 behavior of function types with function-cv-qualifiers.
2346 Version 9, which first appeared in G++ 5.2, corrects the alignment of
2349 Version 10, which first appeared in G++ 6.1, adds mangling of
2350 attributes that affect type identity, such as ia32 calling convention
2351 attributes (e.g. @samp{stdcall}).
2353 Version 11, which first appeared in G++ 7, corrects the mangling of
2354 sizeof... expressions and operator names. For multiple entities with
2355 the same name within a function, that are declared in different scopes,
2356 the mangling now changes starting with the twelfth occurrence. It also
2357 implies @option{-fnew-inheriting-ctors}.
2359 See also @option{-Wabi}.
2361 @item -fabi-compat-version=@var{n}
2362 @opindex fabi-compat-version
2363 On targets that support strong aliases, G++
2364 works around mangling changes by creating an alias with the correct
2365 mangled name when defining a symbol with an incorrect mangled name.
2366 This switch specifies which ABI version to use for the alias.
2368 With @option{-fabi-version=0} (the default), this defaults to 8 (GCC 5
2369 compatibility). If another ABI version is explicitly selected, this
2370 defaults to 0. For compatibility with GCC versions 3.2 through 4.9,
2371 use @option{-fabi-compat-version=2}.
2373 If this option is not provided but @option{-Wabi=@var{n}} is, that
2374 version is used for compatibility aliases. If this option is provided
2375 along with @option{-Wabi} (without the version), the version from this
2376 option is used for the warning.
2378 @item -fno-access-control
2379 @opindex fno-access-control
2380 Turn off all access checking. This switch is mainly useful for working
2381 around bugs in the access control code.
2384 @opindex faligned-new
2385 Enable support for C++17 @code{new} of types that require more
2386 alignment than @code{void* ::operator new(std::size_t)} provides. A
2387 numeric argument such as @code{-faligned-new=32} can be used to
2388 specify how much alignment (in bytes) is provided by that function,
2389 but few users will need to override the default of
2390 @code{alignof(std::max_align_t)}.
2392 This flag is enabled by default for @option{-std=c++17}.
2396 Check that the pointer returned by @code{operator new} is non-null
2397 before attempting to modify the storage allocated. This check is
2398 normally unnecessary because the C++ standard specifies that
2399 @code{operator new} only returns @code{0} if it is declared
2400 @code{throw()}, in which case the compiler always checks the
2401 return value even without this option. In all other cases, when
2402 @code{operator new} has a non-empty exception specification, memory
2403 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
2404 @samp{new (nothrow)}.
2408 Enable support for the C++ Extensions for Concepts Technical
2409 Specification, ISO 19217 (2015), which allows code like
2412 template <class T> concept bool Addable = requires (T t) @{ t + t; @};
2413 template <Addable T> T add (T a, T b) @{ return a + b; @}
2416 @item -fconstexpr-depth=@var{n}
2417 @opindex fconstexpr-depth
2418 Set the maximum nested evaluation depth for C++11 constexpr functions
2419 to @var{n}. A limit is needed to detect endless recursion during
2420 constant expression evaluation. The minimum specified by the standard
2423 @item -fconstexpr-loop-limit=@var{n}
2424 @opindex fconstexpr-loop-limit
2425 Set the maximum number of iterations for a loop in C++14 constexpr functions
2426 to @var{n}. A limit is needed to detect infinite loops during
2427 constant expression evaluation. The default is 262144 (1<<18).
2429 @item -fdeduce-init-list
2430 @opindex fdeduce-init-list
2431 Enable deduction of a template type parameter as
2432 @code{std::initializer_list} from a brace-enclosed initializer list, i.e.@:
2435 template <class T> auto forward(T t) -> decltype (realfn (t))
2442 forward(@{1,2@}); // call forward<std::initializer_list<int>>
2446 This deduction was implemented as a possible extension to the
2447 originally proposed semantics for the C++11 standard, but was not part
2448 of the final standard, so it is disabled by default. This option is
2449 deprecated, and may be removed in a future version of G++.
2451 @item -ffriend-injection
2452 @opindex ffriend-injection
2453 Inject friend functions into the enclosing namespace, so that they are
2454 visible outside the scope of the class in which they are declared.
2455 Friend functions were documented to work this way in the old Annotated
2456 C++ Reference Manual.
2457 However, in ISO C++ a friend function that is not declared
2458 in an enclosing scope can only be found using argument dependent
2459 lookup. GCC defaults to the standard behavior.
2461 This option is deprecated and will be removed.
2463 @item -fno-elide-constructors
2464 @opindex fno-elide-constructors
2465 The C++ standard allows an implementation to omit creating a temporary
2466 that is only used to initialize another object of the same type.
2467 Specifying this option disables that optimization, and forces G++ to
2468 call the copy constructor in all cases. This option also causes G++
2469 to call trivial member functions which otherwise would be expanded inline.
2471 In C++17, the compiler is required to omit these temporaries, but this
2472 option still affects trivial member functions.
2474 @item -fno-enforce-eh-specs
2475 @opindex fno-enforce-eh-specs
2476 Don't generate code to check for violation of exception specifications
2477 at run time. This option violates the C++ standard, but may be useful
2478 for reducing code size in production builds, much like defining
2479 @code{NDEBUG}. This does not give user code permission to throw
2480 exceptions in violation of the exception specifications; the compiler
2481 still optimizes based on the specifications, so throwing an
2482 unexpected exception results in undefined behavior at run time.
2484 @item -fextern-tls-init
2485 @itemx -fno-extern-tls-init
2486 @opindex fextern-tls-init
2487 @opindex fno-extern-tls-init
2488 The C++11 and OpenMP standards allow @code{thread_local} and
2489 @code{threadprivate} variables to have dynamic (runtime)
2490 initialization. To support this, any use of such a variable goes
2491 through a wrapper function that performs any necessary initialization.
2492 When the use and definition of the variable are in the same
2493 translation unit, this overhead can be optimized away, but when the
2494 use is in a different translation unit there is significant overhead
2495 even if the variable doesn't actually need dynamic initialization. If
2496 the programmer can be sure that no use of the variable in a
2497 non-defining TU needs to trigger dynamic initialization (either
2498 because the variable is statically initialized, or a use of the
2499 variable in the defining TU will be executed before any uses in
2500 another TU), they can avoid this overhead with the
2501 @option{-fno-extern-tls-init} option.
2503 On targets that support symbol aliases, the default is
2504 @option{-fextern-tls-init}. On targets that do not support symbol
2505 aliases, the default is @option{-fno-extern-tls-init}.
2508 @itemx -fno-for-scope
2510 @opindex fno-for-scope
2511 If @option{-ffor-scope} is specified, the scope of variables declared in
2512 a @i{for-init-statement} is limited to the @code{for} loop itself,
2513 as specified by the C++ standard.
2514 If @option{-fno-for-scope} is specified, the scope of variables declared in
2515 a @i{for-init-statement} extends to the end of the enclosing scope,
2516 as was the case in old versions of G++, and other (traditional)
2517 implementations of C++.
2519 This option is deprecated and the associated non-standard
2520 functionality will be removed.
2522 @item -fno-gnu-keywords
2523 @opindex fno-gnu-keywords
2524 Do not recognize @code{typeof} as a keyword, so that code can use this
2525 word as an identifier. You can use the keyword @code{__typeof__} instead.
2526 This option is implied by the strict ISO C++ dialects: @option{-ansi},
2527 @option{-std=c++98}, @option{-std=c++11}, etc.
2529 @item -fno-implicit-templates
2530 @opindex fno-implicit-templates
2531 Never emit code for non-inline templates that are instantiated
2532 implicitly (i.e.@: by use); only emit code for explicit instantiations.
2533 @xref{Template Instantiation}, for more information.
2535 @item -fno-implicit-inline-templates
2536 @opindex fno-implicit-inline-templates
2537 Don't emit code for implicit instantiations of inline templates, either.
2538 The default is to handle inlines differently so that compiles with and
2539 without optimization need the same set of explicit instantiations.
2541 @item -fno-implement-inlines
2542 @opindex fno-implement-inlines
2543 To save space, do not emit out-of-line copies of inline functions
2544 controlled by @code{#pragma implementation}. This causes linker
2545 errors if these functions are not inlined everywhere they are called.
2547 @item -fms-extensions
2548 @opindex fms-extensions
2549 Disable Wpedantic warnings about constructs used in MFC, such as implicit
2550 int and getting a pointer to member function via non-standard syntax.
2552 @item -fnew-inheriting-ctors
2553 @opindex fnew-inheriting-ctors
2554 Enable the P0136 adjustment to the semantics of C++11 constructor
2555 inheritance. This is part of C++17 but also considered to be a Defect
2556 Report against C++11 and C++14. This flag is enabled by default
2557 unless @option{-fabi-version=10} or lower is specified.
2559 @item -fnew-ttp-matching
2560 @opindex fnew-ttp-matching
2561 Enable the P0522 resolution to Core issue 150, template template
2562 parameters and default arguments: this allows a template with default
2563 template arguments as an argument for a template template parameter
2564 with fewer template parameters. This flag is enabled by default for
2565 @option{-std=c++17}.
2567 @item -fno-nonansi-builtins
2568 @opindex fno-nonansi-builtins
2569 Disable built-in declarations of functions that are not mandated by
2570 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
2571 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
2574 @opindex fnothrow-opt
2575 Treat a @code{throw()} exception specification as if it were a
2576 @code{noexcept} specification to reduce or eliminate the text size
2577 overhead relative to a function with no exception specification. If
2578 the function has local variables of types with non-trivial
2579 destructors, the exception specification actually makes the
2580 function smaller because the EH cleanups for those variables can be
2581 optimized away. The semantic effect is that an exception thrown out of
2582 a function with such an exception specification results in a call
2583 to @code{terminate} rather than @code{unexpected}.
2585 @item -fno-operator-names
2586 @opindex fno-operator-names
2587 Do not treat the operator name keywords @code{and}, @code{bitand},
2588 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
2589 synonyms as keywords.
2591 @item -fno-optional-diags
2592 @opindex fno-optional-diags
2593 Disable diagnostics that the standard says a compiler does not need to
2594 issue. Currently, the only such diagnostic issued by G++ is the one for
2595 a name having multiple meanings within a class.
2598 @opindex fpermissive
2599 Downgrade some diagnostics about nonconformant code from errors to
2600 warnings. Thus, using @option{-fpermissive} allows some
2601 nonconforming code to compile.
2603 @item -fno-pretty-templates
2604 @opindex fno-pretty-templates
2605 When an error message refers to a specialization of a function
2606 template, the compiler normally prints the signature of the
2607 template followed by the template arguments and any typedefs or
2608 typenames in the signature (e.g. @code{void f(T) [with T = int]}
2609 rather than @code{void f(int)}) so that it's clear which template is
2610 involved. When an error message refers to a specialization of a class
2611 template, the compiler omits any template arguments that match
2612 the default template arguments for that template. If either of these
2613 behaviors make it harder to understand the error message rather than
2614 easier, you can use @option{-fno-pretty-templates} to disable them.
2618 Enable automatic template instantiation at link time. This option also
2619 implies @option{-fno-implicit-templates}. @xref{Template
2620 Instantiation}, for more information.
2624 Disable generation of information about every class with virtual
2625 functions for use by the C++ run-time type identification features
2626 (@code{dynamic_cast} and @code{typeid}). If you don't use those parts
2627 of the language, you can save some space by using this flag. Note that
2628 exception handling uses the same information, but G++ generates it as
2629 needed. The @code{dynamic_cast} operator can still be used for casts that
2630 do not require run-time type information, i.e.@: casts to @code{void *} or to
2631 unambiguous base classes.
2633 @item -fsized-deallocation
2634 @opindex fsized-deallocation
2635 Enable the built-in global declarations
2637 void operator delete (void *, std::size_t) noexcept;
2638 void operator delete[] (void *, std::size_t) noexcept;
2640 as introduced in C++14. This is useful for user-defined replacement
2641 deallocation functions that, for example, use the size of the object
2642 to make deallocation faster. Enabled by default under
2643 @option{-std=c++14} and above. The flag @option{-Wsized-deallocation}
2644 warns about places that might want to add a definition.
2646 @item -fstrict-enums
2647 @opindex fstrict-enums
2648 Allow the compiler to optimize using the assumption that a value of
2649 enumerated type can only be one of the values of the enumeration (as
2650 defined in the C++ standard; basically, a value that can be
2651 represented in the minimum number of bits needed to represent all the
2652 enumerators). This assumption may not be valid if the program uses a
2653 cast to convert an arbitrary integer value to the enumerated type.
2655 @item -fstrong-eval-order
2656 @opindex fstrong-eval-order
2657 Evaluate member access, array subscripting, and shift expressions in
2658 left-to-right order, and evaluate assignment in right-to-left order,
2659 as adopted for C++17. Enabled by default with @option{-std=c++17}.
2660 @option{-fstrong-eval-order=some} enables just the ordering of member
2661 access and shift expressions, and is the default without
2662 @option{-std=c++17}.
2664 @item -ftemplate-backtrace-limit=@var{n}
2665 @opindex ftemplate-backtrace-limit
2666 Set the maximum number of template instantiation notes for a single
2667 warning or error to @var{n}. The default value is 10.
2669 @item -ftemplate-depth=@var{n}
2670 @opindex ftemplate-depth
2671 Set the maximum instantiation depth for template classes to @var{n}.
2672 A limit on the template instantiation depth is needed to detect
2673 endless recursions during template class instantiation. ANSI/ISO C++
2674 conforming programs must not rely on a maximum depth greater than 17
2675 (changed to 1024 in C++11). The default value is 900, as the compiler
2676 can run out of stack space before hitting 1024 in some situations.
2678 @item -fno-threadsafe-statics
2679 @opindex fno-threadsafe-statics
2680 Do not emit the extra code to use the routines specified in the C++
2681 ABI for thread-safe initialization of local statics. You can use this
2682 option to reduce code size slightly in code that doesn't need to be
2685 @item -fuse-cxa-atexit
2686 @opindex fuse-cxa-atexit
2687 Register destructors for objects with static storage duration with the
2688 @code{__cxa_atexit} function rather than the @code{atexit} function.
2689 This option is required for fully standards-compliant handling of static
2690 destructors, but only works if your C library supports
2691 @code{__cxa_atexit}.
2693 @item -fno-use-cxa-get-exception-ptr
2694 @opindex fno-use-cxa-get-exception-ptr
2695 Don't use the @code{__cxa_get_exception_ptr} runtime routine. This
2696 causes @code{std::uncaught_exception} to be incorrect, but is necessary
2697 if the runtime routine is not available.
2699 @item -fvisibility-inlines-hidden
2700 @opindex fvisibility-inlines-hidden
2701 This switch declares that the user does not attempt to compare
2702 pointers to inline functions or methods where the addresses of the two functions
2703 are taken in different shared objects.
2705 The effect of this is that GCC may, effectively, mark inline methods with
2706 @code{__attribute__ ((visibility ("hidden")))} so that they do not
2707 appear in the export table of a DSO and do not require a PLT indirection
2708 when used within the DSO@. Enabling this option can have a dramatic effect
2709 on load and link times of a DSO as it massively reduces the size of the
2710 dynamic export table when the library makes heavy use of templates.
2712 The behavior of this switch is not quite the same as marking the
2713 methods as hidden directly, because it does not affect static variables
2714 local to the function or cause the compiler to deduce that
2715 the function is defined in only one shared object.
2717 You may mark a method as having a visibility explicitly to negate the
2718 effect of the switch for that method. For example, if you do want to
2719 compare pointers to a particular inline method, you might mark it as
2720 having default visibility. Marking the enclosing class with explicit
2721 visibility has no effect.
2723 Explicitly instantiated inline methods are unaffected by this option
2724 as their linkage might otherwise cross a shared library boundary.
2725 @xref{Template Instantiation}.
2727 @item -fvisibility-ms-compat
2728 @opindex fvisibility-ms-compat
2729 This flag attempts to use visibility settings to make GCC's C++
2730 linkage model compatible with that of Microsoft Visual Studio.
2732 The flag makes these changes to GCC's linkage model:
2736 It sets the default visibility to @code{hidden}, like
2737 @option{-fvisibility=hidden}.
2740 Types, but not their members, are not hidden by default.
2743 The One Definition Rule is relaxed for types without explicit
2744 visibility specifications that are defined in more than one
2745 shared object: those declarations are permitted if they are
2746 permitted when this option is not used.
2749 In new code it is better to use @option{-fvisibility=hidden} and
2750 export those classes that are intended to be externally visible.
2751 Unfortunately it is possible for code to rely, perhaps accidentally,
2752 on the Visual Studio behavior.
2754 Among the consequences of these changes are that static data members
2755 of the same type with the same name but defined in different shared
2756 objects are different, so changing one does not change the other;
2757 and that pointers to function members defined in different shared
2758 objects may not compare equal. When this flag is given, it is a
2759 violation of the ODR to define types with the same name differently.
2763 Do not use weak symbol support, even if it is provided by the linker.
2764 By default, G++ uses weak symbols if they are available. This
2765 option exists only for testing, and should not be used by end-users;
2766 it results in inferior code and has no benefits. This option may
2767 be removed in a future release of G++.
2771 Do not search for header files in the standard directories specific to
2772 C++, but do still search the other standard directories. (This option
2773 is used when building the C++ library.)
2776 In addition, these optimization, warning, and code generation options
2777 have meanings only for C++ programs:
2780 @item -Wabi @r{(C, Objective-C, C++ and Objective-C++ only)}
2783 Warn when G++ it generates code that is probably not compatible with
2784 the vendor-neutral C++ ABI@. Since G++ now defaults to updating the
2785 ABI with each major release, normally @option{-Wabi} will warn only if
2786 there is a check added later in a release series for an ABI issue
2787 discovered since the initial release. @option{-Wabi} will warn about
2788 more things if an older ABI version is selected (with
2789 @option{-fabi-version=@var{n}}).
2791 @option{-Wabi} can also be used with an explicit version number to
2792 warn about compatibility with a particular @option{-fabi-version}
2793 level, e.g. @option{-Wabi=2} to warn about changes relative to
2794 @option{-fabi-version=2}.
2796 If an explicit version number is provided and
2797 @option{-fabi-compat-version} is not specified, the version number
2798 from this option is used for compatibility aliases. If no explicit
2799 version number is provided with this option, but
2800 @option{-fabi-compat-version} is specified, that version number is
2801 used for ABI warnings.
2803 Although an effort has been made to warn about
2804 all such cases, there are probably some cases that are not warned about,
2805 even though G++ is generating incompatible code. There may also be
2806 cases where warnings are emitted even though the code that is generated
2809 You should rewrite your code to avoid these warnings if you are
2810 concerned about the fact that code generated by G++ may not be binary
2811 compatible with code generated by other compilers.
2813 Known incompatibilities in @option{-fabi-version=2} (which was the
2814 default from GCC 3.4 to 4.9) include:
2819 A template with a non-type template parameter of reference type was
2820 mangled incorrectly:
2823 template <int &> struct S @{@};
2827 This was fixed in @option{-fabi-version=3}.
2830 SIMD vector types declared using @code{__attribute ((vector_size))} were
2831 mangled in a non-standard way that does not allow for overloading of
2832 functions taking vectors of different sizes.
2834 The mangling was changed in @option{-fabi-version=4}.
2837 @code{__attribute ((const))} and @code{noreturn} were mangled as type
2838 qualifiers, and @code{decltype} of a plain declaration was folded away.
2840 These mangling issues were fixed in @option{-fabi-version=5}.
2843 Scoped enumerators passed as arguments to a variadic function are
2844 promoted like unscoped enumerators, causing @code{va_arg} to complain.
2845 On most targets this does not actually affect the parameter passing
2846 ABI, as there is no way to pass an argument smaller than @code{int}.
2848 Also, the ABI changed the mangling of template argument packs,
2849 @code{const_cast}, @code{static_cast}, prefix increment/decrement, and
2850 a class scope function used as a template argument.
2852 These issues were corrected in @option{-fabi-version=6}.
2855 Lambdas in default argument scope were mangled incorrectly, and the
2856 ABI changed the mangling of @code{nullptr_t}.
2858 These issues were corrected in @option{-fabi-version=7}.
2861 When mangling a function type with function-cv-qualifiers, the
2862 un-qualified function type was incorrectly treated as a substitution
2865 This was fixed in @option{-fabi-version=8}, the default for GCC 5.1.
2868 @code{decltype(nullptr)} incorrectly had an alignment of 1, leading to
2869 unaligned accesses. Note that this did not affect the ABI of a
2870 function with a @code{nullptr_t} parameter, as parameters have a
2873 This was fixed in @option{-fabi-version=9}, the default for GCC 5.2.
2876 Target-specific attributes that affect the identity of a type, such as
2877 ia32 calling conventions on a function type (stdcall, regparm, etc.),
2878 did not affect the mangled name, leading to name collisions when
2879 function pointers were used as template arguments.
2881 This was fixed in @option{-fabi-version=10}, the default for GCC 6.1.
2885 It also warns about psABI-related changes. The known psABI changes at this
2891 For SysV/x86-64, unions with @code{long double} members are
2892 passed in memory as specified in psABI. For example:
2902 @code{union U} is always passed in memory.
2906 @item -Wabi-tag @r{(C++ and Objective-C++ only)}
2909 Warn when a type with an ABI tag is used in a context that does not
2910 have that ABI tag. See @ref{C++ Attributes} for more information
2913 @item -Wctor-dtor-privacy @r{(C++ and Objective-C++ only)}
2914 @opindex Wctor-dtor-privacy
2915 @opindex Wno-ctor-dtor-privacy
2916 Warn when a class seems unusable because all the constructors or
2917 destructors in that class are private, and it has neither friends nor
2918 public static member functions. Also warn if there are no non-private
2919 methods, and there's at least one private member function that isn't
2920 a constructor or destructor.
2922 @item -Wdelete-non-virtual-dtor @r{(C++ and Objective-C++ only)}
2923 @opindex Wdelete-non-virtual-dtor
2924 @opindex Wno-delete-non-virtual-dtor
2925 Warn when @code{delete} is used to destroy an instance of a class that
2926 has virtual functions and non-virtual destructor. It is unsafe to delete
2927 an instance of a derived class through a pointer to a base class if the
2928 base class does not have a virtual destructor. This warning is enabled
2931 @item -Wliteral-suffix @r{(C++ and Objective-C++ only)}
2932 @opindex Wliteral-suffix
2933 @opindex Wno-literal-suffix
2934 Warn when a string or character literal is followed by a ud-suffix which does
2935 not begin with an underscore. As a conforming extension, GCC treats such
2936 suffixes as separate preprocessing tokens in order to maintain backwards
2937 compatibility with code that uses formatting macros from @code{<inttypes.h>}.
2941 #define __STDC_FORMAT_MACROS
2942 #include <inttypes.h>
2947 printf("My int64: %" PRId64"\n", i64);
2951 In this case, @code{PRId64} is treated as a separate preprocessing token.
2953 Additionally, warn when a user-defined literal operator is declared with
2954 a literal suffix identifier that doesn't begin with an underscore. Literal
2955 suffix identifiers that don't begin with an underscore are reserved for
2956 future standardization.
2958 This warning is enabled by default.
2960 @item -Wlto-type-mismatch
2961 @opindex Wlto-type-mismatch
2962 @opindex Wno-lto-type-mismatch
2964 During the link-time optimization warn about type mismatches in
2965 global declarations from different compilation units.
2966 Requires @option{-flto} to be enabled. Enabled by default.
2968 @item -Wno-narrowing @r{(C++ and Objective-C++ only)}
2970 @opindex Wno-narrowing
2971 For C++11 and later standards, narrowing conversions are diagnosed by default,
2972 as required by the standard. A narrowing conversion from a constant produces
2973 an error, and a narrowing conversion from a non-constant produces a warning,
2974 but @option{-Wno-narrowing} suppresses the diagnostic.
2975 Note that this does not affect the meaning of well-formed code;
2976 narrowing conversions are still considered ill-formed in SFINAE contexts.
2978 With @option{-Wnarrowing} in C++98, warn when a narrowing
2979 conversion prohibited by C++11 occurs within
2983 int i = @{ 2.2 @}; // error: narrowing from double to int
2986 This flag is included in @option{-Wall} and @option{-Wc++11-compat}.
2988 @item -Wnoexcept @r{(C++ and Objective-C++ only)}
2990 @opindex Wno-noexcept
2991 Warn when a noexcept-expression evaluates to false because of a call
2992 to a function that does not have a non-throwing exception
2993 specification (i.e. @code{throw()} or @code{noexcept}) but is known by
2994 the compiler to never throw an exception.
2996 @item -Wnoexcept-type @r{(C++ and Objective-C++ only)}
2997 @opindex Wnoexcept-type
2998 @opindex Wno-noexcept-type
2999 Warn if the C++17 feature making @code{noexcept} part of a function
3000 type changes the mangled name of a symbol relative to C++14. Enabled
3001 by @option{-Wabi} and @option{-Wc++17-compat}.
3006 template <class T> void f(T t) @{ t(); @};
3008 void h() @{ f(g); @}
3012 In C++14, @code{f} calls calls @code{f<void(*)()>}, but in
3013 C++17 it calls @code{f<void(*)()noexcept>}.
3015 @item -Wclass-memaccess @r{(C++ and Objective-C++ only)}
3016 @opindex Wclass-memaccess
3017 Warn when the destination of a call to a raw memory function such as
3018 @code{memset} or @code{memcpy} is an object of class type, and when writing
3019 into such an object might bypass the class non-trivial or deleted constructor
3020 or copy assignment, violate const-correctness or encapsulation, or corrupt
3021 virtual table pointers. Modifying the representation of such objects may
3022 violate invariants maintained by member functions of the class. For example,
3023 the call to @code{memset} below is undefined because it modifies a non-trivial
3024 class object and is, therefore, diagnosed. The safe way to either initialize
3025 or clear the storage of objects of such types is by using the appropriate
3026 constructor or assignment operator, if one is available.
3028 std::string str = "abc";
3029 memset (&str, 0, sizeof str);
3031 The @option{-Wclass-memaccess} option is enabled by @option{-Wall}.
3032 Explicitly casting the pointer to the class object to @code{void *} or
3033 to a type that can be safely accessed by the raw memory function suppresses
3036 @item -Wnon-virtual-dtor @r{(C++ and Objective-C++ only)}
3037 @opindex Wnon-virtual-dtor
3038 @opindex Wno-non-virtual-dtor
3039 Warn when a class has virtual functions and an accessible non-virtual
3040 destructor itself or in an accessible polymorphic base class, in which
3041 case it is possible but unsafe to delete an instance of a derived
3042 class through a pointer to the class itself or base class. This
3043 warning is automatically enabled if @option{-Weffc++} is specified.
3045 @item -Wregister @r{(C++ and Objective-C++ only)}
3047 @opindex Wno-register
3048 Warn on uses of the @code{register} storage class specifier, except
3049 when it is part of the GNU @ref{Explicit Register Variables} extension.
3050 The use of the @code{register} keyword as storage class specifier has
3051 been deprecated in C++11 and removed in C++17.
3052 Enabled by default with @option{-std=c++17}.
3054 @item -Wreorder @r{(C++ and Objective-C++ only)}
3056 @opindex Wno-reorder
3057 @cindex reordering, warning
3058 @cindex warning for reordering of member initializers
3059 Warn when the order of member initializers given in the code does not
3060 match the order in which they must be executed. For instance:
3066 A(): j (0), i (1) @{ @}
3071 The compiler rearranges the member initializers for @code{i}
3072 and @code{j} to match the declaration order of the members, emitting
3073 a warning to that effect. This warning is enabled by @option{-Wall}.
3075 @item -fext-numeric-literals @r{(C++ and Objective-C++ only)}
3076 @opindex fext-numeric-literals
3077 @opindex fno-ext-numeric-literals
3078 Accept imaginary, fixed-point, or machine-defined
3079 literal number suffixes as GNU extensions.
3080 When this option is turned off these suffixes are treated
3081 as C++11 user-defined literal numeric suffixes.
3082 This is on by default for all pre-C++11 dialects and all GNU dialects:
3083 @option{-std=c++98}, @option{-std=gnu++98}, @option{-std=gnu++11},
3084 @option{-std=gnu++14}.
3085 This option is off by default
3086 for ISO C++11 onwards (@option{-std=c++11}, ...).
3089 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
3092 @item -Weffc++ @r{(C++ and Objective-C++ only)}
3095 Warn about violations of the following style guidelines from Scott Meyers'
3096 @cite{Effective C++} series of books:
3100 Define a copy constructor and an assignment operator for classes
3101 with dynamically-allocated memory.
3104 Prefer initialization to assignment in constructors.
3107 Have @code{operator=} return a reference to @code{*this}.
3110 Don't try to return a reference when you must return an object.
3113 Distinguish between prefix and postfix forms of increment and
3114 decrement operators.
3117 Never overload @code{&&}, @code{||}, or @code{,}.
3121 This option also enables @option{-Wnon-virtual-dtor}, which is also
3122 one of the effective C++ recommendations. However, the check is
3123 extended to warn about the lack of virtual destructor in accessible
3124 non-polymorphic bases classes too.
3126 When selecting this option, be aware that the standard library
3127 headers do not obey all of these guidelines; use @samp{grep -v}
3128 to filter out those warnings.
3130 @item -Wstrict-null-sentinel @r{(C++ and Objective-C++ only)}
3131 @opindex Wstrict-null-sentinel
3132 @opindex Wno-strict-null-sentinel
3133 Warn about the use of an uncasted @code{NULL} as sentinel. When
3134 compiling only with GCC this is a valid sentinel, as @code{NULL} is defined
3135 to @code{__null}. Although it is a null pointer constant rather than a
3136 null pointer, it is guaranteed to be of the same size as a pointer.
3137 But this use is not portable across different compilers.
3139 @item -Wno-non-template-friend @r{(C++ and Objective-C++ only)}
3140 @opindex Wno-non-template-friend
3141 @opindex Wnon-template-friend
3142 Disable warnings when non-template friend functions are declared
3143 within a template. In very old versions of GCC that predate implementation
3144 of the ISO standard, declarations such as
3145 @samp{friend int foo(int)}, where the name of the friend is an unqualified-id,
3146 could be interpreted as a particular specialization of a template
3147 function; the warning exists to diagnose compatibility problems,
3148 and is enabled by default.
3150 @item -Wold-style-cast @r{(C++ and Objective-C++ only)}
3151 @opindex Wold-style-cast
3152 @opindex Wno-old-style-cast
3153 Warn if an old-style (C-style) cast to a non-void type is used within
3154 a C++ program. The new-style casts (@code{dynamic_cast},
3155 @code{static_cast}, @code{reinterpret_cast}, and @code{const_cast}) are
3156 less vulnerable to unintended effects and much easier to search for.
3158 @item -Woverloaded-virtual @r{(C++ and Objective-C++ only)}
3159 @opindex Woverloaded-virtual
3160 @opindex Wno-overloaded-virtual
3161 @cindex overloaded virtual function, warning
3162 @cindex warning for overloaded virtual function
3163 Warn when a function declaration hides virtual functions from a
3164 base class. For example, in:
3171 struct B: public A @{
3176 the @code{A} class version of @code{f} is hidden in @code{B}, and code
3187 @item -Wno-pmf-conversions @r{(C++ and Objective-C++ only)}
3188 @opindex Wno-pmf-conversions
3189 @opindex Wpmf-conversions
3190 Disable the diagnostic for converting a bound pointer to member function
3193 @item -Wsign-promo @r{(C++ and Objective-C++ only)}
3194 @opindex Wsign-promo
3195 @opindex Wno-sign-promo
3196 Warn when overload resolution chooses a promotion from unsigned or
3197 enumerated type to a signed type, over a conversion to an unsigned type of
3198 the same size. Previous versions of G++ tried to preserve
3199 unsignedness, but the standard mandates the current behavior.
3201 @item -Wtemplates @r{(C++ and Objective-C++ only)}
3203 Warn when a primary template declaration is encountered. Some coding
3204 rules disallow templates, and this may be used to enforce that rule.
3205 The warning is inactive inside a system header file, such as the STL, so
3206 one can still use the STL. One may also instantiate or specialize
3209 @item -Wmultiple-inheritance @r{(C++ and Objective-C++ only)}
3210 @opindex Wmultiple-inheritance
3211 Warn when a class is defined with multiple direct base classes. Some
3212 coding rules disallow multiple inheritance, and this may be used to
3213 enforce that rule. The warning is inactive inside a system header file,
3214 such as the STL, so one can still use the STL. One may also define
3215 classes that indirectly use multiple inheritance.
3217 @item -Wvirtual-inheritance
3218 @opindex Wvirtual-inheritance
3219 Warn when a class is defined with a virtual direct base class. Some
3220 coding rules disallow multiple inheritance, and this may be used to
3221 enforce that rule. The warning is inactive inside a system header file,
3222 such as the STL, so one can still use the STL. One may also define
3223 classes that indirectly use virtual inheritance.
3226 @opindex Wnamespaces
3227 Warn when a namespace definition is opened. Some coding rules disallow
3228 namespaces, and this may be used to enforce that rule. The warning is
3229 inactive inside a system header file, such as the STL, so one can still
3230 use the STL. One may also use using directives and qualified names.
3232 @item -Wno-terminate @r{(C++ and Objective-C++ only)}
3234 @opindex Wno-terminate
3235 Disable the warning about a throw-expression that will immediately
3236 result in a call to @code{terminate}.
3239 @node Objective-C and Objective-C++ Dialect Options
3240 @section Options Controlling Objective-C and Objective-C++ Dialects
3242 @cindex compiler options, Objective-C and Objective-C++
3243 @cindex Objective-C and Objective-C++ options, command-line
3244 @cindex options, Objective-C and Objective-C++
3245 (NOTE: This manual does not describe the Objective-C and Objective-C++
3246 languages themselves. @xref{Standards,,Language Standards
3247 Supported by GCC}, for references.)
3249 This section describes the command-line options that are only meaningful
3250 for Objective-C and Objective-C++ programs. You can also use most of
3251 the language-independent GNU compiler options.
3252 For example, you might compile a file @file{some_class.m} like this:
3255 gcc -g -fgnu-runtime -O -c some_class.m
3259 In this example, @option{-fgnu-runtime} is an option meant only for
3260 Objective-C and Objective-C++ programs; you can use the other options with
3261 any language supported by GCC@.
3263 Note that since Objective-C is an extension of the C language, Objective-C
3264 compilations may also use options specific to the C front-end (e.g.,
3265 @option{-Wtraditional}). Similarly, Objective-C++ compilations may use
3266 C++-specific options (e.g., @option{-Wabi}).
3268 Here is a list of options that are @emph{only} for compiling Objective-C
3269 and Objective-C++ programs:
3272 @item -fconstant-string-class=@var{class-name}
3273 @opindex fconstant-string-class
3274 Use @var{class-name} as the name of the class to instantiate for each
3275 literal string specified with the syntax @code{@@"@dots{}"}. The default
3276 class name is @code{NXConstantString} if the GNU runtime is being used, and
3277 @code{NSConstantString} if the NeXT runtime is being used (see below). The
3278 @option{-fconstant-cfstrings} option, if also present, overrides the
3279 @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
3280 to be laid out as constant CoreFoundation strings.
3283 @opindex fgnu-runtime
3284 Generate object code compatible with the standard GNU Objective-C
3285 runtime. This is the default for most types of systems.
3287 @item -fnext-runtime
3288 @opindex fnext-runtime
3289 Generate output compatible with the NeXT runtime. This is the default
3290 for NeXT-based systems, including Darwin and Mac OS X@. The macro
3291 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
3294 @item -fno-nil-receivers
3295 @opindex fno-nil-receivers
3296 Assume that all Objective-C message dispatches (@code{[receiver
3297 message:arg]}) in this translation unit ensure that the receiver is
3298 not @code{nil}. This allows for more efficient entry points in the
3299 runtime to be used. This option is only available in conjunction with
3300 the NeXT runtime and ABI version 0 or 1.
3302 @item -fobjc-abi-version=@var{n}
3303 @opindex fobjc-abi-version
3304 Use version @var{n} of the Objective-C ABI for the selected runtime.
3305 This option is currently supported only for the NeXT runtime. In that
3306 case, Version 0 is the traditional (32-bit) ABI without support for
3307 properties and other Objective-C 2.0 additions. Version 1 is the
3308 traditional (32-bit) ABI with support for properties and other
3309 Objective-C 2.0 additions. Version 2 is the modern (64-bit) ABI. If
3310 nothing is specified, the default is Version 0 on 32-bit target
3311 machines, and Version 2 on 64-bit target machines.
3313 @item -fobjc-call-cxx-cdtors
3314 @opindex fobjc-call-cxx-cdtors
3315 For each Objective-C class, check if any of its instance variables is a
3316 C++ object with a non-trivial default constructor. If so, synthesize a
3317 special @code{- (id) .cxx_construct} instance method which runs
3318 non-trivial default constructors on any such instance variables, in order,
3319 and then return @code{self}. Similarly, check if any instance variable
3320 is a C++ object with a non-trivial destructor, and if so, synthesize a
3321 special @code{- (void) .cxx_destruct} method which runs
3322 all such default destructors, in reverse order.
3324 The @code{- (id) .cxx_construct} and @code{- (void) .cxx_destruct}
3325 methods thusly generated only operate on instance variables
3326 declared in the current Objective-C class, and not those inherited
3327 from superclasses. It is the responsibility of the Objective-C
3328 runtime to invoke all such methods in an object's inheritance
3329 hierarchy. The @code{- (id) .cxx_construct} methods are invoked
3330 by the runtime immediately after a new object instance is allocated;
3331 the @code{- (void) .cxx_destruct} methods are invoked immediately
3332 before the runtime deallocates an object instance.
3334 As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has
3335 support for invoking the @code{- (id) .cxx_construct} and
3336 @code{- (void) .cxx_destruct} methods.
3338 @item -fobjc-direct-dispatch
3339 @opindex fobjc-direct-dispatch
3340 Allow fast jumps to the message dispatcher. On Darwin this is
3341 accomplished via the comm page.
3343 @item -fobjc-exceptions
3344 @opindex fobjc-exceptions
3345 Enable syntactic support for structured exception handling in
3346 Objective-C, similar to what is offered by C++. This option
3347 is required to use the Objective-C keywords @code{@@try},
3348 @code{@@throw}, @code{@@catch}, @code{@@finally} and
3349 @code{@@synchronized}. This option is available with both the GNU
3350 runtime and the NeXT runtime (but not available in conjunction with
3351 the NeXT runtime on Mac OS X 10.2 and earlier).
3355 Enable garbage collection (GC) in Objective-C and Objective-C++
3356 programs. This option is only available with the NeXT runtime; the
3357 GNU runtime has a different garbage collection implementation that
3358 does not require special compiler flags.
3360 @item -fobjc-nilcheck
3361 @opindex fobjc-nilcheck
3362 For the NeXT runtime with version 2 of the ABI, check for a nil
3363 receiver in method invocations before doing the actual method call.
3364 This is the default and can be disabled using
3365 @option{-fno-objc-nilcheck}. Class methods and super calls are never
3366 checked for nil in this way no matter what this flag is set to.
3367 Currently this flag does nothing when the GNU runtime, or an older
3368 version of the NeXT runtime ABI, is used.
3370 @item -fobjc-std=objc1
3372 Conform to the language syntax of Objective-C 1.0, the language
3373 recognized by GCC 4.0. This only affects the Objective-C additions to
3374 the C/C++ language; it does not affect conformance to C/C++ standards,
3375 which is controlled by the separate C/C++ dialect option flags. When
3376 this option is used with the Objective-C or Objective-C++ compiler,
3377 any Objective-C syntax that is not recognized by GCC 4.0 is rejected.
3378 This is useful if you need to make sure that your Objective-C code can
3379 be compiled with older versions of GCC@.
3381 @item -freplace-objc-classes
3382 @opindex freplace-objc-classes
3383 Emit a special marker instructing @command{ld(1)} not to statically link in
3384 the resulting object file, and allow @command{dyld(1)} to load it in at
3385 run time instead. This is used in conjunction with the Fix-and-Continue
3386 debugging mode, where the object file in question may be recompiled and
3387 dynamically reloaded in the course of program execution, without the need
3388 to restart the program itself. Currently, Fix-and-Continue functionality
3389 is only available in conjunction with the NeXT runtime on Mac OS X 10.3
3394 When compiling for the NeXT runtime, the compiler ordinarily replaces calls
3395 to @code{objc_getClass("@dots{}")} (when the name of the class is known at
3396 compile time) with static class references that get initialized at load time,
3397 which improves run-time performance. Specifying the @option{-fzero-link} flag
3398 suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
3399 to be retained. This is useful in Zero-Link debugging mode, since it allows
3400 for individual class implementations to be modified during program execution.
3401 The GNU runtime currently always retains calls to @code{objc_get_class("@dots{}")}
3402 regardless of command-line options.
3404 @item -fno-local-ivars
3405 @opindex fno-local-ivars
3406 @opindex flocal-ivars
3407 By default instance variables in Objective-C can be accessed as if
3408 they were local variables from within the methods of the class they're
3409 declared in. This can lead to shadowing between instance variables
3410 and other variables declared either locally inside a class method or
3411 globally with the same name. Specifying the @option{-fno-local-ivars}
3412 flag disables this behavior thus avoiding variable shadowing issues.
3414 @item -fivar-visibility=@r{[}public@r{|}protected@r{|}private@r{|}package@r{]}
3415 @opindex fivar-visibility
3416 Set the default instance variable visibility to the specified option
3417 so that instance variables declared outside the scope of any access
3418 modifier directives default to the specified visibility.
3422 Dump interface declarations for all classes seen in the source file to a
3423 file named @file{@var{sourcename}.decl}.
3425 @item -Wassign-intercept @r{(Objective-C and Objective-C++ only)}
3426 @opindex Wassign-intercept
3427 @opindex Wno-assign-intercept
3428 Warn whenever an Objective-C assignment is being intercepted by the
3431 @item -Wno-protocol @r{(Objective-C and Objective-C++ only)}
3432 @opindex Wno-protocol
3434 If a class is declared to implement a protocol, a warning is issued for
3435 every method in the protocol that is not implemented by the class. The
3436 default behavior is to issue a warning for every method not explicitly
3437 implemented in the class, even if a method implementation is inherited
3438 from the superclass. If you use the @option{-Wno-protocol} option, then
3439 methods inherited from the superclass are considered to be implemented,
3440 and no warning is issued for them.
3442 @item -Wselector @r{(Objective-C and Objective-C++ only)}
3444 @opindex Wno-selector
3445 Warn if multiple methods of different types for the same selector are
3446 found during compilation. The check is performed on the list of methods
3447 in the final stage of compilation. Additionally, a check is performed
3448 for each selector appearing in a @code{@@selector(@dots{})}
3449 expression, and a corresponding method for that selector has been found
3450 during compilation. Because these checks scan the method table only at
3451 the end of compilation, these warnings are not produced if the final
3452 stage of compilation is not reached, for example because an error is
3453 found during compilation, or because the @option{-fsyntax-only} option is
3456 @item -Wstrict-selector-match @r{(Objective-C and Objective-C++ only)}
3457 @opindex Wstrict-selector-match
3458 @opindex Wno-strict-selector-match
3459 Warn if multiple methods with differing argument and/or return types are
3460 found for a given selector when attempting to send a message using this
3461 selector to a receiver of type @code{id} or @code{Class}. When this flag
3462 is off (which is the default behavior), the compiler omits such warnings
3463 if any differences found are confined to types that share the same size
3466 @item -Wundeclared-selector @r{(Objective-C and Objective-C++ only)}
3467 @opindex Wundeclared-selector
3468 @opindex Wno-undeclared-selector
3469 Warn if a @code{@@selector(@dots{})} expression referring to an
3470 undeclared selector is found. A selector is considered undeclared if no
3471 method with that name has been declared before the
3472 @code{@@selector(@dots{})} expression, either explicitly in an
3473 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
3474 an @code{@@implementation} section. This option always performs its
3475 checks as soon as a @code{@@selector(@dots{})} expression is found,
3476 while @option{-Wselector} only performs its checks in the final stage of
3477 compilation. This also enforces the coding style convention
3478 that methods and selectors must be declared before being used.
3480 @item -print-objc-runtime-info
3481 @opindex print-objc-runtime-info
3482 Generate C header describing the largest structure that is passed by
3487 @node Diagnostic Message Formatting Options
3488 @section Options to Control Diagnostic Messages Formatting
3489 @cindex options to control diagnostics formatting
3490 @cindex diagnostic messages
3491 @cindex message formatting
3493 Traditionally, diagnostic messages have been formatted irrespective of
3494 the output device's aspect (e.g.@: its width, @dots{}). You can use the
3495 options described below
3496 to control the formatting algorithm for diagnostic messages,
3497 e.g.@: how many characters per line, how often source location
3498 information should be reported. Note that some language front ends may not
3499 honor these options.
3502 @item -fmessage-length=@var{n}
3503 @opindex fmessage-length
3504 Try to format error messages so that they fit on lines of about
3505 @var{n} characters. If @var{n} is zero, then no line-wrapping is
3506 done; each error message appears on a single line. This is the
3507 default for all front ends.
3509 @item -fdiagnostics-show-location=once
3510 @opindex fdiagnostics-show-location
3511 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
3512 reporter to emit source location information @emph{once}; that is, in
3513 case the message is too long to fit on a single physical line and has to
3514 be wrapped, the source location won't be emitted (as prefix) again,
3515 over and over, in subsequent continuation lines. This is the default
3518 @item -fdiagnostics-show-location=every-line
3519 Only meaningful in line-wrapping mode. Instructs the diagnostic
3520 messages reporter to emit the same source location information (as
3521 prefix) for physical lines that result from the process of breaking
3522 a message which is too long to fit on a single line.
3524 @item -fdiagnostics-color[=@var{WHEN}]
3525 @itemx -fno-diagnostics-color
3526 @opindex fdiagnostics-color
3527 @cindex highlight, color
3528 @vindex GCC_COLORS @r{environment variable}
3529 Use color in diagnostics. @var{WHEN} is @samp{never}, @samp{always},
3530 or @samp{auto}. The default depends on how the compiler has been configured,
3531 it can be any of the above @var{WHEN} options or also @samp{never}
3532 if @env{GCC_COLORS} environment variable isn't present in the environment,
3533 and @samp{auto} otherwise.
3534 @samp{auto} means to use color only when the standard error is a terminal.
3535 The forms @option{-fdiagnostics-color} and @option{-fno-diagnostics-color} are
3536 aliases for @option{-fdiagnostics-color=always} and
3537 @option{-fdiagnostics-color=never}, respectively.
3539 The colors are defined by the environment variable @env{GCC_COLORS}.
3540 Its value is a colon-separated list of capabilities and Select Graphic
3541 Rendition (SGR) substrings. SGR commands are interpreted by the
3542 terminal or terminal emulator. (See the section in the documentation
3543 of your text terminal for permitted values and their meanings as
3544 character attributes.) These substring values are integers in decimal
3545 representation and can be concatenated with semicolons.
3546 Common values to concatenate include
3548 @samp{4} for underline,
3550 @samp{7} for inverse,
3551 @samp{39} for default foreground color,
3552 @samp{30} to @samp{37} for foreground colors,
3553 @samp{90} to @samp{97} for 16-color mode foreground colors,
3554 @samp{38;5;0} to @samp{38;5;255}
3555 for 88-color and 256-color modes foreground colors,
3556 @samp{49} for default background color,
3557 @samp{40} to @samp{47} for background colors,
3558 @samp{100} to @samp{107} for 16-color mode background colors,
3559 and @samp{48;5;0} to @samp{48;5;255}
3560 for 88-color and 256-color modes background colors.
3562 The default @env{GCC_COLORS} is
3564 error=01;31:warning=01;35:note=01;36:range1=32:range2=34:locus=01:\
3565 quote=01:fixit-insert=32:fixit-delete=31:\
3566 diff-filename=01:diff-hunk=32:diff-delete=31:diff-insert=32:\
3570 where @samp{01;31} is bold red, @samp{01;35} is bold magenta,
3571 @samp{01;36} is bold cyan, @samp{32} is green, @samp{34} is blue,
3572 @samp{01} is bold, and @samp{31} is red.
3573 Setting @env{GCC_COLORS} to the empty string disables colors.
3574 Supported capabilities are as follows.
3578 @vindex error GCC_COLORS @r{capability}
3579 SGR substring for error: markers.
3582 @vindex warning GCC_COLORS @r{capability}
3583 SGR substring for warning: markers.
3586 @vindex note GCC_COLORS @r{capability}
3587 SGR substring for note: markers.
3590 @vindex range1 GCC_COLORS @r{capability}
3591 SGR substring for first additional range.
3594 @vindex range2 GCC_COLORS @r{capability}
3595 SGR substring for second additional range.
3598 @vindex locus GCC_COLORS @r{capability}
3599 SGR substring for location information, @samp{file:line} or
3600 @samp{file:line:column} etc.
3603 @vindex quote GCC_COLORS @r{capability}
3604 SGR substring for information printed within quotes.
3607 @vindex fixit-insert GCC_COLORS @r{capability}
3608 SGR substring for fix-it hints suggesting text to
3609 be inserted or replaced.
3612 @vindex fixit-delete GCC_COLORS @r{capability}
3613 SGR substring for fix-it hints suggesting text to
3616 @item diff-filename=
3617 @vindex diff-filename GCC_COLORS @r{capability}
3618 SGR substring for filename headers within generated patches.
3621 @vindex diff-hunk GCC_COLORS @r{capability}
3622 SGR substring for the starts of hunks within generated patches.
3625 @vindex diff-delete GCC_COLORS @r{capability}
3626 SGR substring for deleted lines within generated patches.
3629 @vindex diff-insert GCC_COLORS @r{capability}
3630 SGR substring for inserted lines within generated patches.
3633 @vindex type-diff GCC_COLORS @r{capability}
3634 SGR substring for highlighting mismatching types within template
3635 arguments in the C++ frontend.
3638 @item -fno-diagnostics-show-option
3639 @opindex fno-diagnostics-show-option
3640 @opindex fdiagnostics-show-option
3641 By default, each diagnostic emitted includes text indicating the
3642 command-line option that directly controls the diagnostic (if such an
3643 option is known to the diagnostic machinery). Specifying the
3644 @option{-fno-diagnostics-show-option} flag suppresses that behavior.
3646 @item -fno-diagnostics-show-caret
3647 @opindex fno-diagnostics-show-caret
3648 @opindex fdiagnostics-show-caret
3649 By default, each diagnostic emitted includes the original source line
3650 and a caret @samp{^} indicating the column. This option suppresses this
3651 information. The source line is truncated to @var{n} characters, if
3652 the @option{-fmessage-length=n} option is given. When the output is done
3653 to the terminal, the width is limited to the width given by the
3654 @env{COLUMNS} environment variable or, if not set, to the terminal width.
3656 @item -fdiagnostics-parseable-fixits
3657 @opindex fdiagnostics-parseable-fixits
3658 Emit fix-it hints in a machine-parseable format, suitable for consumption
3659 by IDEs. For each fix-it, a line will be printed after the relevant
3660 diagnostic, starting with the string ``fix-it:''. For example:
3663 fix-it:"test.c":@{45:3-45:21@}:"gtk_widget_show_all"
3666 The location is expressed as a half-open range, expressed as a count of
3667 bytes, starting at byte 1 for the initial column. In the above example,
3668 bytes 3 through 20 of line 45 of ``test.c'' are to be replaced with the
3672 00000000011111111112222222222
3673 12345678901234567890123456789
3674 gtk_widget_showall (dlg);
3679 The filename and replacement string escape backslash as ``\\", tab as ``\t'',
3680 newline as ``\n'', double quotes as ``\"'', non-printable characters as octal
3681 (e.g. vertical tab as ``\013'').
3683 An empty replacement string indicates that the given range is to be removed.
3684 An empty range (e.g. ``45:3-45:3'') indicates that the string is to
3685 be inserted at the given position.
3687 @item -fdiagnostics-generate-patch
3688 @opindex fdiagnostics-generate-patch
3689 Print fix-it hints to stderr in unified diff format, after any diagnostics
3690 are printed. For example:
3697 void show_cb(GtkDialog *dlg)
3699 - gtk_widget_showall(dlg);
3700 + gtk_widget_show_all(dlg);
3705 The diff may or may not be colorized, following the same rules
3706 as for diagnostics (see @option{-fdiagnostics-color}).
3708 @item -fdiagnostics-show-template-tree
3709 @opindex fdiagnostics-show-template-tree
3711 In the C++ frontend, when printing diagnostics showing mismatching
3712 template types, such as:
3715 could not convert 'std::map<int, std::vector<double> >()'
3716 from 'map<[...],vector<double>>' to 'map<[...],vector<float>>
3719 the @option{-fdiagnostics-show-template-tree} flag enables printing a
3720 tree-like structure showing the common and differing parts of the types,
3730 The parts that differ are highlighted with color (``double'' and
3731 ``float'' in this case).
3733 @item -fno-elide-type
3734 @opindex fno-elide-type
3735 @opindex felide-type
3736 By default when the C++ frontend prints diagnostics showing mismatching
3737 template types, common parts of the types are printed as ``[...]'' to
3738 simplify the error message. For example:
3741 could not convert 'std::map<int, std::vector<double> >()'
3742 from 'map<[...],vector<double>>' to 'map<[...],vector<float>>
3745 Specifying the @option{-fno-elide-type} flag suppresses that behavior.
3746 This flag also affects the output of the
3747 @option{-fdiagnostics-show-template-tree} flag.
3749 @item -fno-show-column
3750 @opindex fno-show-column
3751 Do not print column numbers in diagnostics. This may be necessary if
3752 diagnostics are being scanned by a program that does not understand the
3753 column numbers, such as @command{dejagnu}.
3757 @node Warning Options
3758 @section Options to Request or Suppress Warnings
3759 @cindex options to control warnings
3760 @cindex warning messages
3761 @cindex messages, warning
3762 @cindex suppressing warnings
3764 Warnings are diagnostic messages that report constructions that
3765 are not inherently erroneous but that are risky or suggest there
3766 may have been an error.
3768 The following language-independent options do not enable specific
3769 warnings but control the kinds of diagnostics produced by GCC@.
3772 @cindex syntax checking
3774 @opindex fsyntax-only
3775 Check the code for syntax errors, but don't do anything beyond that.
3777 @item -fmax-errors=@var{n}
3778 @opindex fmax-errors
3779 Limits the maximum number of error messages to @var{n}, at which point
3780 GCC bails out rather than attempting to continue processing the source
3781 code. If @var{n} is 0 (the default), there is no limit on the number
3782 of error messages produced. If @option{-Wfatal-errors} is also
3783 specified, then @option{-Wfatal-errors} takes precedence over this
3788 Inhibit all warning messages.
3793 Make all warnings into errors.
3798 Make the specified warning into an error. The specifier for a warning
3799 is appended; for example @option{-Werror=switch} turns the warnings
3800 controlled by @option{-Wswitch} into errors. This switch takes a
3801 negative form, to be used to negate @option{-Werror} for specific
3802 warnings; for example @option{-Wno-error=switch} makes
3803 @option{-Wswitch} warnings not be errors, even when @option{-Werror}
3806 The warning message for each controllable warning includes the
3807 option that controls the warning. That option can then be used with
3808 @option{-Werror=} and @option{-Wno-error=} as described above.
3809 (Printing of the option in the warning message can be disabled using the
3810 @option{-fno-diagnostics-show-option} flag.)
3812 Note that specifying @option{-Werror=}@var{foo} automatically implies
3813 @option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not
3816 @item -Wfatal-errors
3817 @opindex Wfatal-errors
3818 @opindex Wno-fatal-errors
3819 This option causes the compiler to abort compilation on the first error
3820 occurred rather than trying to keep going and printing further error
3825 You can request many specific warnings with options beginning with
3826 @samp{-W}, for example @option{-Wimplicit} to request warnings on
3827 implicit declarations. Each of these specific warning options also
3828 has a negative form beginning @samp{-Wno-} to turn off warnings; for
3829 example, @option{-Wno-implicit}. This manual lists only one of the
3830 two forms, whichever is not the default. For further
3831 language-specific options also refer to @ref{C++ Dialect Options} and
3832 @ref{Objective-C and Objective-C++ Dialect Options}.
3834 Some options, such as @option{-Wall} and @option{-Wextra}, turn on other
3835 options, such as @option{-Wunused}, which may turn on further options,
3836 such as @option{-Wunused-value}. The combined effect of positive and
3837 negative forms is that more specific options have priority over less
3838 specific ones, independently of their position in the command-line. For
3839 options of the same specificity, the last one takes effect. Options
3840 enabled or disabled via pragmas (@pxref{Diagnostic Pragmas}) take effect
3841 as if they appeared at the end of the command-line.
3843 When an unrecognized warning option is requested (e.g.,
3844 @option{-Wunknown-warning}), GCC emits a diagnostic stating
3845 that the option is not recognized. However, if the @option{-Wno-} form
3846 is used, the behavior is slightly different: no diagnostic is
3847 produced for @option{-Wno-unknown-warning} unless other diagnostics
3848 are being produced. This allows the use of new @option{-Wno-} options
3849 with old compilers, but if something goes wrong, the compiler
3850 warns that an unrecognized option is present.
3857 Issue all the warnings demanded by strict ISO C and ISO C++;
3858 reject all programs that use forbidden extensions, and some other
3859 programs that do not follow ISO C and ISO C++. For ISO C, follows the
3860 version of the ISO C standard specified by any @option{-std} option used.
3862 Valid ISO C and ISO C++ programs should compile properly with or without
3863 this option (though a rare few require @option{-ansi} or a
3864 @option{-std} option specifying the required version of ISO C)@. However,
3865 without this option, certain GNU extensions and traditional C and C++
3866 features are supported as well. With this option, they are rejected.
3868 @option{-Wpedantic} does not cause warning messages for use of the
3869 alternate keywords whose names begin and end with @samp{__}. Pedantic
3870 warnings are also disabled in the expression that follows
3871 @code{__extension__}. However, only system header files should use
3872 these escape routes; application programs should avoid them.
3873 @xref{Alternate Keywords}.
3875 Some users try to use @option{-Wpedantic} to check programs for strict ISO
3876 C conformance. They soon find that it does not do quite what they want:
3877 it finds some non-ISO practices, but not all---only those for which
3878 ISO C @emph{requires} a diagnostic, and some others for which
3879 diagnostics have been added.
3881 A feature to report any failure to conform to ISO C might be useful in
3882 some instances, but would require considerable additional work and would
3883 be quite different from @option{-Wpedantic}. We don't have plans to
3884 support such a feature in the near future.
3886 Where the standard specified with @option{-std} represents a GNU
3887 extended dialect of C, such as @samp{gnu90} or @samp{gnu99}, there is a
3888 corresponding @dfn{base standard}, the version of ISO C on which the GNU
3889 extended dialect is based. Warnings from @option{-Wpedantic} are given
3890 where they are required by the base standard. (It does not make sense
3891 for such warnings to be given only for features not in the specified GNU
3892 C dialect, since by definition the GNU dialects of C include all
3893 features the compiler supports with the given option, and there would be
3894 nothing to warn about.)
3896 @item -pedantic-errors
3897 @opindex pedantic-errors
3898 Give an error whenever the @dfn{base standard} (see @option{-Wpedantic})
3899 requires a diagnostic, in some cases where there is undefined behavior
3900 at compile-time and in some other cases that do not prevent compilation
3901 of programs that are valid according to the standard. This is not
3902 equivalent to @option{-Werror=pedantic}, since there are errors enabled
3903 by this option and not enabled by the latter and vice versa.
3908 This enables all the warnings about constructions that some users
3909 consider questionable, and that are easy to avoid (or modify to
3910 prevent the warning), even in conjunction with macros. This also
3911 enables some language-specific warnings described in @ref{C++ Dialect
3912 Options} and @ref{Objective-C and Objective-C++ Dialect Options}.
3914 @option{-Wall} turns on the following warning flags:
3916 @gccoptlist{-Waddress @gol
3917 -Warray-bounds=1 @r{(only with} @option{-O2}@r{)} @gol
3919 -Wbool-operation @gol
3920 -Wc++11-compat -Wc++14-compat @gol
3921 -Wcatch-value @r{(C++ and Objective-C++ only)} @gol
3922 -Wchar-subscripts @gol
3924 -Wduplicate-decl-specifier @r{(C and Objective-C only)} @gol
3925 -Wenum-compare @r{(in C/ObjC; this is on by default in C++)} @gol
3927 -Wint-in-bool-context @gol
3928 -Wimplicit @r{(C and Objective-C only)} @gol
3929 -Wimplicit-int @r{(C and Objective-C only)} @gol
3930 -Wimplicit-function-declaration @r{(C and Objective-C only)} @gol
3931 -Winit-self @r{(only for C++)} @gol
3932 -Wlogical-not-parentheses @gol
3933 -Wmain @r{(only for C/ObjC and unless} @option{-ffreestanding}@r{)} @gol
3934 -Wmaybe-uninitialized @gol
3935 -Wmemset-elt-size @gol
3936 -Wmemset-transposed-args @gol
3937 -Wmisleading-indentation @r{(only for C/C++)} @gol
3938 -Wmissing-attributes @gol
3939 -Wmissing-braces @r{(only for C/ObjC)} @gol
3940 -Wmultistatement-macros @gol
3941 -Wnarrowing @r{(only for C++)} @gol
3943 -Wnonnull-compare @gol
3950 -Wsequence-point @gol
3951 -Wsign-compare @r{(only in C++)} @gol
3952 -Wsizeof-pointer-div @gol
3953 -Wsizeof-pointer-memaccess @gol
3954 -Wstrict-aliasing @gol
3955 -Wstrict-overflow=1 @gol
3957 -Wtautological-compare @gol
3959 -Wuninitialized @gol
3960 -Wunknown-pragmas @gol
3961 -Wunused-function @gol
3964 -Wunused-variable @gol
3965 -Wvolatile-register-var @gol
3968 Note that some warning flags are not implied by @option{-Wall}. Some of
3969 them warn about constructions that users generally do not consider
3970 questionable, but which occasionally you might wish to check for;
3971 others warn about constructions that are necessary or hard to avoid in
3972 some cases, and there is no simple way to modify the code to suppress
3973 the warning. Some of them are enabled by @option{-Wextra} but many of
3974 them must be enabled individually.
3980 This enables some extra warning flags that are not enabled by
3981 @option{-Wall}. (This option used to be called @option{-W}. The older
3982 name is still supported, but the newer name is more descriptive.)
3984 @gccoptlist{-Wclobbered @gol
3985 -Wcast-function-type @gol
3987 -Wignored-qualifiers @gol
3988 -Wimplicit-fallthrough=3 @gol
3989 -Wmissing-field-initializers @gol
3990 -Wmissing-parameter-type @r{(C only)} @gol
3991 -Wold-style-declaration @r{(C only)} @gol
3992 -Woverride-init @gol
3993 -Wsign-compare @r{(C only)} @gol
3995 -Wuninitialized @gol
3996 -Wshift-negative-value @r{(in C++03 and in C99 and newer)} @gol
3997 -Wunused-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol
3998 -Wunused-but-set-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol
4001 The option @option{-Wextra} also prints warning messages for the
4007 A pointer is compared against integer zero with @code{<}, @code{<=},
4008 @code{>}, or @code{>=}.
4011 (C++ only) An enumerator and a non-enumerator both appear in a
4012 conditional expression.
4015 (C++ only) Ambiguous virtual bases.
4018 (C++ only) Subscripting an array that has been declared @code{register}.
4021 (C++ only) Taking the address of a variable that has been declared
4025 (C++ only) A base class is not initialized in the copy constructor
4030 @item -Wchar-subscripts
4031 @opindex Wchar-subscripts
4032 @opindex Wno-char-subscripts
4033 Warn if an array subscript has type @code{char}. This is a common cause
4034 of error, as programmers often forget that this type is signed on some
4036 This warning is enabled by @option{-Wall}.
4040 Warn about an invalid memory access that is found by Pointer Bounds Checker
4041 (@option{-fcheck-pointer-bounds}).
4043 @item -Wno-coverage-mismatch
4044 @opindex Wno-coverage-mismatch
4045 Warn if feedback profiles do not match when using the
4046 @option{-fprofile-use} option.
4047 If a source file is changed between compiling with @option{-fprofile-gen} and
4048 with @option{-fprofile-use}, the files with the profile feedback can fail
4049 to match the source file and GCC cannot use the profile feedback
4050 information. By default, this warning is enabled and is treated as an
4051 error. @option{-Wno-coverage-mismatch} can be used to disable the
4052 warning or @option{-Wno-error=coverage-mismatch} can be used to
4053 disable the error. Disabling the error for this warning can result in
4054 poorly optimized code and is useful only in the
4055 case of very minor changes such as bug fixes to an existing code-base.
4056 Completely disabling the warning is not recommended.
4059 @r{(C, Objective-C, C++, Objective-C++ and Fortran only)}
4061 Suppress warning messages emitted by @code{#warning} directives.
4063 @item -Wdouble-promotion @r{(C, C++, Objective-C and Objective-C++ only)}
4064 @opindex Wdouble-promotion
4065 @opindex Wno-double-promotion
4066 Give a warning when a value of type @code{float} is implicitly
4067 promoted to @code{double}. CPUs with a 32-bit ``single-precision''
4068 floating-point unit implement @code{float} in hardware, but emulate
4069 @code{double} in software. On such a machine, doing computations
4070 using @code{double} values is much more expensive because of the
4071 overhead required for software emulation.
4073 It is easy to accidentally do computations with @code{double} because
4074 floating-point literals are implicitly of type @code{double}. For
4078 float area(float radius)
4080 return 3.14159 * radius * radius;
4084 the compiler performs the entire computation with @code{double}
4085 because the floating-point literal is a @code{double}.
4087 @item -Wduplicate-decl-specifier @r{(C and Objective-C only)}
4088 @opindex Wduplicate-decl-specifier
4089 @opindex Wno-duplicate-decl-specifier
4090 Warn if a declaration has duplicate @code{const}, @code{volatile},
4091 @code{restrict} or @code{_Atomic} specifier. This warning is enabled by
4095 @itemx -Wformat=@var{n}
4098 @opindex ffreestanding
4099 @opindex fno-builtin
4101 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
4102 the arguments supplied have types appropriate to the format string
4103 specified, and that the conversions specified in the format string make
4104 sense. This includes standard functions, and others specified by format
4105 attributes (@pxref{Function Attributes}), in the @code{printf},
4106 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
4107 not in the C standard) families (or other target-specific families).
4108 Which functions are checked without format attributes having been
4109 specified depends on the standard version selected, and such checks of
4110 functions without the attribute specified are disabled by
4111 @option{-ffreestanding} or @option{-fno-builtin}.
4113 The formats are checked against the format features supported by GNU
4114 libc version 2.2. These include all ISO C90 and C99 features, as well
4115 as features from the Single Unix Specification and some BSD and GNU
4116 extensions. Other library implementations may not support all these
4117 features; GCC does not support warning about features that go beyond a
4118 particular library's limitations. However, if @option{-Wpedantic} is used
4119 with @option{-Wformat}, warnings are given about format features not
4120 in the selected standard version (but not for @code{strfmon} formats,
4121 since those are not in any version of the C standard). @xref{C Dialect
4122 Options,,Options Controlling C Dialect}.
4129 Option @option{-Wformat} is equivalent to @option{-Wformat=1}, and
4130 @option{-Wno-format} is equivalent to @option{-Wformat=0}. Since
4131 @option{-Wformat} also checks for null format arguments for several
4132 functions, @option{-Wformat} also implies @option{-Wnonnull}. Some
4133 aspects of this level of format checking can be disabled by the
4134 options: @option{-Wno-format-contains-nul},
4135 @option{-Wno-format-extra-args}, and @option{-Wno-format-zero-length}.
4136 @option{-Wformat} is enabled by @option{-Wall}.
4138 @item -Wno-format-contains-nul
4139 @opindex Wno-format-contains-nul
4140 @opindex Wformat-contains-nul
4141 If @option{-Wformat} is specified, do not warn about format strings that
4144 @item -Wno-format-extra-args
4145 @opindex Wno-format-extra-args
4146 @opindex Wformat-extra-args
4147 If @option{-Wformat} is specified, do not warn about excess arguments to a
4148 @code{printf} or @code{scanf} format function. The C standard specifies
4149 that such arguments are ignored.
4151 Where the unused arguments lie between used arguments that are
4152 specified with @samp{$} operand number specifications, normally
4153 warnings are still given, since the implementation could not know what
4154 type to pass to @code{va_arg} to skip the unused arguments. However,
4155 in the case of @code{scanf} formats, this option suppresses the
4156 warning if the unused arguments are all pointers, since the Single
4157 Unix Specification says that such unused arguments are allowed.
4159 @item -Wformat-overflow
4160 @itemx -Wformat-overflow=@var{level}
4161 @opindex Wformat-overflow
4162 @opindex Wno-format-overflow
4163 Warn about calls to formatted input/output functions such as @code{sprintf}
4164 and @code{vsprintf} that might overflow the destination buffer. When the
4165 exact number of bytes written by a format directive cannot be determined
4166 at compile-time it is estimated based on heuristics that depend on the
4167 @var{level} argument and on optimization. While enabling optimization
4168 will in most cases improve the accuracy of the warning, it may also
4169 result in false positives.
4172 @item -Wformat-overflow
4173 @itemx -Wformat-overflow=1
4174 @opindex Wformat-overflow
4175 @opindex Wno-format-overflow
4176 Level @var{1} of @option{-Wformat-overflow} enabled by @option{-Wformat}
4177 employs a conservative approach that warns only about calls that most
4178 likely overflow the buffer. At this level, numeric arguments to format
4179 directives with unknown values are assumed to have the value of one, and
4180 strings of unknown length to be empty. Numeric arguments that are known
4181 to be bounded to a subrange of their type, or string arguments whose output
4182 is bounded either by their directive's precision or by a finite set of
4183 string literals, are assumed to take on the value within the range that
4184 results in the most bytes on output. For example, the call to @code{sprintf}
4185 below is diagnosed because even with both @var{a} and @var{b} equal to zero,
4186 the terminating NUL character (@code{'\0'}) appended by the function
4187 to the destination buffer will be written past its end. Increasing
4188 the size of the buffer by a single byte is sufficient to avoid the
4189 warning, though it may not be sufficient to avoid the overflow.
4192 void f (int a, int b)
4195 sprintf (buf, "a = %i, b = %i\n", a, b);
4199 @item -Wformat-overflow=2
4200 Level @var{2} warns also about calls that might overflow the destination
4201 buffer given an argument of sufficient length or magnitude. At level
4202 @var{2}, unknown numeric arguments are assumed to have the minimum
4203 representable value for signed types with a precision greater than 1, and
4204 the maximum representable value otherwise. Unknown string arguments whose
4205 length cannot be assumed to be bounded either by the directive's precision,
4206 or by a finite set of string literals they may evaluate to, or the character
4207 array they may point to, are assumed to be 1 character long.
4209 At level @var{2}, the call in the example above is again diagnosed, but
4210 this time because with @var{a} equal to a 32-bit @code{INT_MIN} the first
4211 @code{%i} directive will write some of its digits beyond the end of
4212 the destination buffer. To make the call safe regardless of the values
4213 of the two variables, the size of the destination buffer must be increased
4214 to at least 34 bytes. GCC includes the minimum size of the buffer in
4215 an informational note following the warning.
4217 An alternative to increasing the size of the destination buffer is to
4218 constrain the range of formatted values. The maximum length of string
4219 arguments can be bounded by specifying the precision in the format
4220 directive. When numeric arguments of format directives can be assumed
4221 to be bounded by less than the precision of their type, choosing
4222 an appropriate length modifier to the format specifier will reduce
4223 the required buffer size. For example, if @var{a} and @var{b} in the
4224 example above can be assumed to be within the precision of
4225 the @code{short int} type then using either the @code{%hi} format
4226 directive or casting the argument to @code{short} reduces the maximum
4227 required size of the buffer to 24 bytes.
4230 void f (int a, int b)
4233 sprintf (buf, "a = %hi, b = %i\n", a, (short)b);
4238 @item -Wno-format-zero-length
4239 @opindex Wno-format-zero-length
4240 @opindex Wformat-zero-length
4241 If @option{-Wformat} is specified, do not warn about zero-length formats.
4242 The C standard specifies that zero-length formats are allowed.
4247 Enable @option{-Wformat} plus additional format checks. Currently
4248 equivalent to @option{-Wformat -Wformat-nonliteral -Wformat-security
4251 @item -Wformat-nonliteral
4252 @opindex Wformat-nonliteral
4253 @opindex Wno-format-nonliteral
4254 If @option{-Wformat} is specified, also warn if the format string is not a
4255 string literal and so cannot be checked, unless the format function
4256 takes its format arguments as a @code{va_list}.
4258 @item -Wformat-security
4259 @opindex Wformat-security
4260 @opindex Wno-format-security
4261 If @option{-Wformat} is specified, also warn about uses of format
4262 functions that represent possible security problems. At present, this
4263 warns about calls to @code{printf} and @code{scanf} functions where the
4264 format string is not a string literal and there are no format arguments,
4265 as in @code{printf (foo);}. This may be a security hole if the format
4266 string came from untrusted input and contains @samp{%n}. (This is
4267 currently a subset of what @option{-Wformat-nonliteral} warns about, but
4268 in future warnings may be added to @option{-Wformat-security} that are not
4269 included in @option{-Wformat-nonliteral}.)
4271 @item -Wformat-signedness
4272 @opindex Wformat-signedness
4273 @opindex Wno-format-signedness
4274 If @option{-Wformat} is specified, also warn if the format string
4275 requires an unsigned argument and the argument is signed and vice versa.
4277 @item -Wformat-truncation
4278 @itemx -Wformat-truncation=@var{level}
4279 @opindex Wformat-truncation
4280 @opindex Wno-format-truncation
4281 Warn about calls to formatted input/output functions such as @code{snprintf}
4282 and @code{vsnprintf} that might result in output truncation. When the exact
4283 number of bytes written by a format directive cannot be determined at
4284 compile-time it is estimated based on heuristics that depend on
4285 the @var{level} argument and on optimization. While enabling optimization
4286 will in most cases improve the accuracy of the warning, it may also result
4287 in false positives. Except as noted otherwise, the option uses the same
4288 logic @option{-Wformat-overflow}.
4291 @item -Wformat-truncation
4292 @itemx -Wformat-truncation=1
4293 @opindex Wformat-truncation
4294 @opindex Wno-format-overflow
4295 Level @var{1} of @option{-Wformat-truncation} enabled by @option{-Wformat}
4296 employs a conservative approach that warns only about calls to bounded
4297 functions whose return value is unused and that will most likely result
4298 in output truncation.
4300 @item -Wformat-truncation=2
4301 Level @var{2} warns also about calls to bounded functions whose return
4302 value is used and that might result in truncation given an argument of
4303 sufficient length or magnitude.
4307 @opindex Wformat-y2k
4308 @opindex Wno-format-y2k
4309 If @option{-Wformat} is specified, also warn about @code{strftime}
4310 formats that may yield only a two-digit year.
4315 @opindex Wno-nonnull
4316 Warn about passing a null pointer for arguments marked as
4317 requiring a non-null value by the @code{nonnull} function attribute.
4319 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
4320 can be disabled with the @option{-Wno-nonnull} option.
4322 @item -Wnonnull-compare
4323 @opindex Wnonnull-compare
4324 @opindex Wno-nonnull-compare
4325 Warn when comparing an argument marked with the @code{nonnull}
4326 function attribute against null inside the function.
4328 @option{-Wnonnull-compare} is included in @option{-Wall}. It
4329 can be disabled with the @option{-Wno-nonnull-compare} option.
4331 @item -Wnull-dereference
4332 @opindex Wnull-dereference
4333 @opindex Wno-null-dereference
4334 Warn if the compiler detects paths that trigger erroneous or
4335 undefined behavior due to dereferencing a null pointer. This option
4336 is only active when @option{-fdelete-null-pointer-checks} is active,
4337 which is enabled by optimizations in most targets. The precision of
4338 the warnings depends on the optimization options used.
4340 @item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
4342 @opindex Wno-init-self
4343 Warn about uninitialized variables that are initialized with themselves.
4344 Note this option can only be used with the @option{-Wuninitialized} option.
4346 For example, GCC warns about @code{i} being uninitialized in the
4347 following snippet only when @option{-Winit-self} has been specified:
4358 This warning is enabled by @option{-Wall} in C++.
4360 @item -Wimplicit-int @r{(C and Objective-C only)}
4361 @opindex Wimplicit-int
4362 @opindex Wno-implicit-int
4363 Warn when a declaration does not specify a type.
4364 This warning is enabled by @option{-Wall}.
4366 @item -Wimplicit-function-declaration @r{(C and Objective-C only)}
4367 @opindex Wimplicit-function-declaration
4368 @opindex Wno-implicit-function-declaration
4369 Give a warning whenever a function is used before being declared. In
4370 C99 mode (@option{-std=c99} or @option{-std=gnu99}), this warning is
4371 enabled by default and it is made into an error by
4372 @option{-pedantic-errors}. This warning is also enabled by
4375 @item -Wimplicit @r{(C and Objective-C only)}
4377 @opindex Wno-implicit
4378 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
4379 This warning is enabled by @option{-Wall}.
4381 @item -Wimplicit-fallthrough
4382 @opindex Wimplicit-fallthrough
4383 @opindex Wno-implicit-fallthrough
4384 @option{-Wimplicit-fallthrough} is the same as @option{-Wimplicit-fallthrough=3}
4385 and @option{-Wno-implicit-fallthrough} is the same as
4386 @option{-Wimplicit-fallthrough=0}.
4388 @item -Wimplicit-fallthrough=@var{n}
4389 @opindex Wimplicit-fallthrough=
4390 Warn when a switch case falls through. For example:
4408 This warning does not warn when the last statement of a case cannot
4409 fall through, e.g. when there is a return statement or a call to function
4410 declared with the noreturn attribute. @option{-Wimplicit-fallthrough=}
4411 also takes into account control flow statements, such as ifs, and only
4412 warns when appropriate. E.g.@:
4422 @} else if (i < 1) @{
4432 Since there are occasions where a switch case fall through is desirable,
4433 GCC provides an attribute, @code{__attribute__ ((fallthrough))}, that is
4434 to be used along with a null statement to suppress this warning that
4435 would normally occur:
4443 __attribute__ ((fallthrough));
4450 C++17 provides a standard way to suppress the @option{-Wimplicit-fallthrough}
4451 warning using @code{[[fallthrough]];} instead of the GNU attribute. In C++11
4452 or C++14 users can use @code{[[gnu::fallthrough]];}, which is a GNU extension.
4453 Instead of these attributes, it is also possible to add a fallthrough comment
4454 to silence the warning. The whole body of the C or C++ style comment should
4455 match the given regular expressions listed below. The option argument @var{n}
4456 specifies what kind of comments are accepted:
4460 @item @option{-Wimplicit-fallthrough=0} disables the warning altogether.
4462 @item @option{-Wimplicit-fallthrough=1} matches @code{.*} regular
4463 expression, any comment is used as fallthrough comment.
4465 @item @option{-Wimplicit-fallthrough=2} case insensitively matches
4466 @code{.*falls?[ \t-]*thr(ough|u).*} regular expression.
4468 @item @option{-Wimplicit-fallthrough=3} case sensitively matches one of the
4469 following regular expressions:
4473 @item @code{-fallthrough}
4475 @item @code{@@fallthrough@@}
4477 @item @code{lint -fallthrough[ \t]*}
4479 @item @code{[ \t.!]*(ELSE,? |INTENTIONAL(LY)? )?@*FALL(S | |-)?THR(OUGH|U)[ \t.!]*(-[^\n\r]*)?}
4481 @item @code{[ \t.!]*(Else,? |Intentional(ly)? )?@*Fall((s | |-)[Tt]|t)hr(ough|u)[ \t.!]*(-[^\n\r]*)?}
4483 @item @code{[ \t.!]*([Ee]lse,? |[Ii]ntentional(ly)? )?@*fall(s | |-)?thr(ough|u)[ \t.!]*(-[^\n\r]*)?}
4487 @item @option{-Wimplicit-fallthrough=4} case sensitively matches one of the
4488 following regular expressions:
4492 @item @code{-fallthrough}
4494 @item @code{@@fallthrough@@}
4496 @item @code{lint -fallthrough[ \t]*}
4498 @item @code{[ \t]*FALLTHR(OUGH|U)[ \t]*}
4502 @item @option{-Wimplicit-fallthrough=5} doesn't recognize any comments as
4503 fallthrough comments, only attributes disable the warning.
4507 The comment needs to be followed after optional whitespace and other comments
4508 by @code{case} or @code{default} keywords or by a user label that precedes some
4509 @code{case} or @code{default} label.
4524 The @option{-Wimplicit-fallthrough=3} warning is enabled by @option{-Wextra}.
4526 @item -Wif-not-aligned @r{(C, C++, Objective-C and Objective-C++ only)}
4527 @opindex Wif-not-aligned
4528 @opindex Wno-if-not-aligned
4529 Control if warning triggered by the @code{warn_if_not_aligned} attribute
4530 should be issued. This is is enabled by default.
4531 Use @option{-Wno-if-not-aligned} to disable it.
4533 @item -Wignored-qualifiers @r{(C and C++ only)}
4534 @opindex Wignored-qualifiers
4535 @opindex Wno-ignored-qualifiers
4536 Warn if the return type of a function has a type qualifier
4537 such as @code{const}. For ISO C such a type qualifier has no effect,
4538 since the value returned by a function is not an lvalue.
4539 For C++, the warning is only emitted for scalar types or @code{void}.
4540 ISO C prohibits qualified @code{void} return types on function
4541 definitions, so such return types always receive a warning
4542 even without this option.
4544 This warning is also enabled by @option{-Wextra}.
4546 @item -Wignored-attributes @r{(C and C++ only)}
4547 @opindex Wignored-attributes
4548 @opindex Wno-ignored-attributes
4549 Warn when an attribute is ignored. This is different from the
4550 @option{-Wattributes} option in that it warns whenever the compiler decides
4551 to drop an attribute, not that the attribute is either unknown, used in a
4552 wrong place, etc. This warning is enabled by default.
4557 Warn if the type of @code{main} is suspicious. @code{main} should be
4558 a function with external linkage, returning int, taking either zero
4559 arguments, two, or three arguments of appropriate types. This warning
4560 is enabled by default in C++ and is enabled by either @option{-Wall}
4561 or @option{-Wpedantic}.
4563 @item -Wmisleading-indentation @r{(C and C++ only)}
4564 @opindex Wmisleading-indentation
4565 @opindex Wno-misleading-indentation
4566 Warn when the indentation of the code does not reflect the block structure.
4567 Specifically, a warning is issued for @code{if}, @code{else}, @code{while}, and
4568 @code{for} clauses with a guarded statement that does not use braces,
4569 followed by an unguarded statement with the same indentation.
4571 In the following example, the call to ``bar'' is misleadingly indented as
4572 if it were guarded by the ``if'' conditional.
4575 if (some_condition ())
4577 bar (); /* Gotcha: this is not guarded by the "if". */
4580 In the case of mixed tabs and spaces, the warning uses the
4581 @option{-ftabstop=} option to determine if the statements line up
4584 The warning is not issued for code involving multiline preprocessor logic
4585 such as the following example.
4590 #if SOME_CONDITION_THAT_DOES_NOT_HOLD
4596 The warning is not issued after a @code{#line} directive, since this
4597 typically indicates autogenerated code, and no assumptions can be made
4598 about the layout of the file that the directive references.
4600 This warning is enabled by @option{-Wall} in C and C++.
4602 @item -Wmissing-attributes
4603 @opindex Wmissing-attributes
4604 @opindex Wno-missing-attributes
4605 Warn when a declaration of a function is missing one or more attributes
4606 that a related function is declared with and whose absence may adversely
4607 affect the correctness or efficiency of generated code. For example, in
4608 C++, the warning is issued when an explicit specialization of a primary
4609 template declared with attribute @code{alloc_align}, @code{alloc_size},
4610 @code{assume_aligned}, @code{format}, @code{format_arg}, @code{malloc},
4611 or @code{nonnull} is declared without it. Attributes @code{deprecated},
4612 @code{error}, and @code{warning} suppress the warning.
4613 (@pxref{Function Attributes}).
4615 @option{-Wmissing-attributes} is enabled by @option{-Wall}.
4617 For example, since the declaration of the primary function template
4618 below makes use of both attribute @code{malloc} and @code{alloc_size}
4619 the declaration of the explicit specialization of the template is
4620 diagnosed because it is missing one of the attributes.
4624 T* __attribute__ ((malloc, alloc_size (1)))
4628 void* __attribute__ ((malloc)) // missing alloc_size
4629 allocate<void> (size_t);
4632 @item -Wmissing-braces
4633 @opindex Wmissing-braces
4634 @opindex Wno-missing-braces
4635 Warn if an aggregate or union initializer is not fully bracketed. In
4636 the following example, the initializer for @code{a} is not fully
4637 bracketed, but that for @code{b} is fully bracketed. This warning is
4638 enabled by @option{-Wall} in C.
4641 int a[2][2] = @{ 0, 1, 2, 3 @};
4642 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
4645 This warning is enabled by @option{-Wall}.
4647 @item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)}
4648 @opindex Wmissing-include-dirs
4649 @opindex Wno-missing-include-dirs
4650 Warn if a user-supplied include directory does not exist.
4652 @item -Wmultistatement-macros
4653 @opindex Wmultistatement-macros
4654 @opindex Wno-multistatement-macros
4655 Warn about unsafe multiple statement macros that appear to be guarded
4656 by a clause such as @code{if}, @code{else}, @code{for}, @code{switch}, or
4657 @code{while}, in which only the first statement is actually guarded after
4658 the macro is expanded.
4663 #define DOIT x++; y++
4668 will increment @code{y} unconditionally, not just when @code{c} holds.
4669 The can usually be fixed by wrapping the macro in a do-while loop:
4671 #define DOIT do @{ x++; y++; @} while (0)
4676 This warning is enabled by @option{-Wall} in C and C++.
4679 @opindex Wparentheses
4680 @opindex Wno-parentheses
4681 Warn if parentheses are omitted in certain contexts, such
4682 as when there is an assignment in a context where a truth value
4683 is expected, or when operators are nested whose precedence people
4684 often get confused about.
4686 Also warn if a comparison like @code{x<=y<=z} appears; this is
4687 equivalent to @code{(x<=y ? 1 : 0) <= z}, which is a different
4688 interpretation from that of ordinary mathematical notation.
4690 Also warn for dangerous uses of the GNU extension to
4691 @code{?:} with omitted middle operand. When the condition
4692 in the @code{?}: operator is a boolean expression, the omitted value is
4693 always 1. Often programmers expect it to be a value computed
4694 inside the conditional expression instead.
4696 For C++ this also warns for some cases of unnecessary parentheses in
4697 declarations, which can indicate an attempt at a function call instead
4701 // Declares a local variable called mymutex.
4702 std::unique_lock<std::mutex> (mymutex);
4703 // User meant std::unique_lock<std::mutex> lock (mymutex);
4707 This warning is enabled by @option{-Wall}.
4709 @item -Wsequence-point
4710 @opindex Wsequence-point
4711 @opindex Wno-sequence-point
4712 Warn about code that may have undefined semantics because of violations
4713 of sequence point rules in the C and C++ standards.
4715 The C and C++ standards define the order in which expressions in a C/C++
4716 program are evaluated in terms of @dfn{sequence points}, which represent
4717 a partial ordering between the execution of parts of the program: those
4718 executed before the sequence point, and those executed after it. These
4719 occur after the evaluation of a full expression (one which is not part
4720 of a larger expression), after the evaluation of the first operand of a
4721 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
4722 function is called (but after the evaluation of its arguments and the
4723 expression denoting the called function), and in certain other places.
4724 Other than as expressed by the sequence point rules, the order of
4725 evaluation of subexpressions of an expression is not specified. All
4726 these rules describe only a partial order rather than a total order,
4727 since, for example, if two functions are called within one expression
4728 with no sequence point between them, the order in which the functions
4729 are called is not specified. However, the standards committee have
4730 ruled that function calls do not overlap.
4732 It is not specified when between sequence points modifications to the
4733 values of objects take effect. Programs whose behavior depends on this
4734 have undefined behavior; the C and C++ standards specify that ``Between
4735 the previous and next sequence point an object shall have its stored
4736 value modified at most once by the evaluation of an expression.
4737 Furthermore, the prior value shall be read only to determine the value
4738 to be stored.''. If a program breaks these rules, the results on any
4739 particular implementation are entirely unpredictable.
4741 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
4742 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
4743 diagnosed by this option, and it may give an occasional false positive
4744 result, but in general it has been found fairly effective at detecting
4745 this sort of problem in programs.
4747 The C++17 standard will define the order of evaluation of operands in
4748 more cases: in particular it requires that the right-hand side of an
4749 assignment be evaluated before the left-hand side, so the above
4750 examples are no longer undefined. But this warning will still warn
4751 about them, to help people avoid writing code that is undefined in C
4752 and earlier revisions of C++.
4754 The standard is worded confusingly, therefore there is some debate
4755 over the precise meaning of the sequence point rules in subtle cases.
4756 Links to discussions of the problem, including proposed formal
4757 definitions, may be found on the GCC readings page, at
4758 @uref{http://gcc.gnu.org/@/readings.html}.
4760 This warning is enabled by @option{-Wall} for C and C++.
4762 @item -Wno-return-local-addr
4763 @opindex Wno-return-local-addr
4764 @opindex Wreturn-local-addr
4765 Do not warn about returning a pointer (or in C++, a reference) to a
4766 variable that goes out of scope after the function returns.
4769 @opindex Wreturn-type
4770 @opindex Wno-return-type
4771 Warn whenever a function is defined with a return type that defaults
4772 to @code{int}. Also warn about any @code{return} statement with no
4773 return value in a function whose return type is not @code{void}
4774 (falling off the end of the function body is considered returning
4777 For C only, warn about a @code{return} statement with an expression in a
4778 function whose return type is @code{void}, unless the expression type is
4779 also @code{void}. As a GNU extension, the latter case is accepted
4780 without a warning unless @option{-Wpedantic} is used.
4782 For C++, a function without return type always produces a diagnostic
4783 message, even when @option{-Wno-return-type} is specified. The only
4784 exceptions are @code{main} and functions defined in system headers.
4786 This warning is enabled by default for C++ and is enabled by @option{-Wall}.
4788 @item -Wshift-count-negative
4789 @opindex Wshift-count-negative
4790 @opindex Wno-shift-count-negative
4791 Warn if shift count is negative. This warning is enabled by default.
4793 @item -Wshift-count-overflow
4794 @opindex Wshift-count-overflow
4795 @opindex Wno-shift-count-overflow
4796 Warn if shift count >= width of type. This warning is enabled by default.
4798 @item -Wshift-negative-value
4799 @opindex Wshift-negative-value
4800 @opindex Wno-shift-negative-value
4801 Warn if left shifting a negative value. This warning is enabled by
4802 @option{-Wextra} in C99 and C++11 modes (and newer).
4804 @item -Wshift-overflow
4805 @itemx -Wshift-overflow=@var{n}
4806 @opindex Wshift-overflow
4807 @opindex Wno-shift-overflow
4808 Warn about left shift overflows. This warning is enabled by
4809 default in C99 and C++11 modes (and newer).
4812 @item -Wshift-overflow=1
4813 This is the warning level of @option{-Wshift-overflow} and is enabled
4814 by default in C99 and C++11 modes (and newer). This warning level does
4815 not warn about left-shifting 1 into the sign bit. (However, in C, such
4816 an overflow is still rejected in contexts where an integer constant expression
4819 @item -Wshift-overflow=2
4820 This warning level also warns about left-shifting 1 into the sign bit,
4821 unless C++14 mode is active.
4827 Warn whenever a @code{switch} statement has an index of enumerated type
4828 and lacks a @code{case} for one or more of the named codes of that
4829 enumeration. (The presence of a @code{default} label prevents this
4830 warning.) @code{case} labels outside the enumeration range also
4831 provoke warnings when this option is used (even if there is a
4832 @code{default} label).
4833 This warning is enabled by @option{-Wall}.
4835 @item -Wswitch-default
4836 @opindex Wswitch-default
4837 @opindex Wno-switch-default
4838 Warn whenever a @code{switch} statement does not have a @code{default}
4842 @opindex Wswitch-enum
4843 @opindex Wno-switch-enum
4844 Warn whenever a @code{switch} statement has an index of enumerated type
4845 and lacks a @code{case} for one or more of the named codes of that
4846 enumeration. @code{case} labels outside the enumeration range also
4847 provoke warnings when this option is used. The only difference
4848 between @option{-Wswitch} and this option is that this option gives a
4849 warning about an omitted enumeration code even if there is a
4850 @code{default} label.
4853 @opindex Wswitch-bool
4854 @opindex Wno-switch-bool
4855 Warn whenever a @code{switch} statement has an index of boolean type
4856 and the case values are outside the range of a boolean type.
4857 It is possible to suppress this warning by casting the controlling
4858 expression to a type other than @code{bool}. For example:
4861 switch ((int) (a == 4))
4867 This warning is enabled by default for C and C++ programs.
4869 @item -Wswitch-unreachable
4870 @opindex Wswitch-unreachable
4871 @opindex Wno-switch-unreachable
4872 Warn whenever a @code{switch} statement contains statements between the
4873 controlling expression and the first case label, which will never be
4874 executed. For example:
4886 @option{-Wswitch-unreachable} does not warn if the statement between the
4887 controlling expression and the first case label is just a declaration:
4900 This warning is enabled by default for C and C++ programs.
4902 @item -Wsync-nand @r{(C and C++ only)}
4904 @opindex Wno-sync-nand
4905 Warn when @code{__sync_fetch_and_nand} and @code{__sync_nand_and_fetch}
4906 built-in functions are used. These functions changed semantics in GCC 4.4.
4908 @item -Wunused-but-set-parameter
4909 @opindex Wunused-but-set-parameter
4910 @opindex Wno-unused-but-set-parameter
4911 Warn whenever a function parameter is assigned to, but otherwise unused
4912 (aside from its declaration).
4914 To suppress this warning use the @code{unused} attribute
4915 (@pxref{Variable Attributes}).
4917 This warning is also enabled by @option{-Wunused} together with
4920 @item -Wunused-but-set-variable
4921 @opindex Wunused-but-set-variable
4922 @opindex Wno-unused-but-set-variable
4923 Warn whenever a local variable is assigned to, but otherwise unused
4924 (aside from its declaration).
4925 This warning is enabled by @option{-Wall}.
4927 To suppress this warning use the @code{unused} attribute
4928 (@pxref{Variable Attributes}).
4930 This warning is also enabled by @option{-Wunused}, which is enabled
4933 @item -Wunused-function
4934 @opindex Wunused-function
4935 @opindex Wno-unused-function
4936 Warn whenever a static function is declared but not defined or a
4937 non-inline static function is unused.
4938 This warning is enabled by @option{-Wall}.
4940 @item -Wunused-label
4941 @opindex Wunused-label
4942 @opindex Wno-unused-label
4943 Warn whenever a label is declared but not used.
4944 This warning is enabled by @option{-Wall}.
4946 To suppress this warning use the @code{unused} attribute
4947 (@pxref{Variable Attributes}).
4949 @item -Wunused-local-typedefs @r{(C, Objective-C, C++ and Objective-C++ only)}
4950 @opindex Wunused-local-typedefs
4951 Warn when a typedef locally defined in a function is not used.
4952 This warning is enabled by @option{-Wall}.
4954 @item -Wunused-parameter
4955 @opindex Wunused-parameter
4956 @opindex Wno-unused-parameter
4957 Warn whenever a function parameter is unused aside from its declaration.
4959 To suppress this warning use the @code{unused} attribute
4960 (@pxref{Variable Attributes}).
4962 @item -Wno-unused-result
4963 @opindex Wunused-result
4964 @opindex Wno-unused-result
4965 Do not warn if a caller of a function marked with attribute
4966 @code{warn_unused_result} (@pxref{Function Attributes}) does not use
4967 its return value. The default is @option{-Wunused-result}.
4969 @item -Wunused-variable
4970 @opindex Wunused-variable
4971 @opindex Wno-unused-variable
4972 Warn whenever a local or static variable is unused aside from its
4973 declaration. This option implies @option{-Wunused-const-variable=1} for C,
4974 but not for C++. This warning is enabled by @option{-Wall}.
4976 To suppress this warning use the @code{unused} attribute
4977 (@pxref{Variable Attributes}).
4979 @item -Wunused-const-variable
4980 @itemx -Wunused-const-variable=@var{n}
4981 @opindex Wunused-const-variable
4982 @opindex Wno-unused-const-variable
4983 Warn whenever a constant static variable is unused aside from its declaration.
4984 @option{-Wunused-const-variable=1} is enabled by @option{-Wunused-variable}
4985 for C, but not for C++. In C this declares variable storage, but in C++ this
4986 is not an error since const variables take the place of @code{#define}s.
4988 To suppress this warning use the @code{unused} attribute
4989 (@pxref{Variable Attributes}).
4992 @item -Wunused-const-variable=1
4993 This is the warning level that is enabled by @option{-Wunused-variable} for
4994 C. It warns only about unused static const variables defined in the main
4995 compilation unit, but not about static const variables declared in any
4998 @item -Wunused-const-variable=2
4999 This warning level also warns for unused constant static variables in
5000 headers (excluding system headers). This is the warning level of
5001 @option{-Wunused-const-variable} and must be explicitly requested since
5002 in C++ this isn't an error and in C it might be harder to clean up all
5006 @item -Wunused-value
5007 @opindex Wunused-value
5008 @opindex Wno-unused-value
5009 Warn whenever a statement computes a result that is explicitly not
5010 used. To suppress this warning cast the unused expression to
5011 @code{void}. This includes an expression-statement or the left-hand
5012 side of a comma expression that contains no side effects. For example,
5013 an expression such as @code{x[i,j]} causes a warning, while
5014 @code{x[(void)i,j]} does not.
5016 This warning is enabled by @option{-Wall}.
5021 All the above @option{-Wunused} options combined.
5023 In order to get a warning about an unused function parameter, you must
5024 either specify @option{-Wextra -Wunused} (note that @option{-Wall} implies
5025 @option{-Wunused}), or separately specify @option{-Wunused-parameter}.
5027 @item -Wuninitialized
5028 @opindex Wuninitialized
5029 @opindex Wno-uninitialized
5030 Warn if an automatic variable is used without first being initialized
5031 or if a variable may be clobbered by a @code{setjmp} call. In C++,
5032 warn if a non-static reference or non-static @code{const} member
5033 appears in a class without constructors.
5035 If you want to warn about code that uses the uninitialized value of the
5036 variable in its own initializer, use the @option{-Winit-self} option.
5038 These warnings occur for individual uninitialized or clobbered
5039 elements of structure, union or array variables as well as for
5040 variables that are uninitialized or clobbered as a whole. They do
5041 not occur for variables or elements declared @code{volatile}. Because
5042 these warnings depend on optimization, the exact variables or elements
5043 for which there are warnings depends on the precise optimization
5044 options and version of GCC used.
5046 Note that there may be no warning about a variable that is used only
5047 to compute a value that itself is never used, because such
5048 computations may be deleted by data flow analysis before the warnings
5051 @item -Winvalid-memory-model
5052 @opindex Winvalid-memory-model
5053 @opindex Wno-invalid-memory-model
5054 Warn for invocations of @ref{__atomic Builtins}, @ref{__sync Builtins},
5055 and the C11 atomic generic functions with a memory consistency argument
5056 that is either invalid for the operation or outside the range of values
5057 of the @code{memory_order} enumeration. For example, since the
5058 @code{__atomic_store} and @code{__atomic_store_n} built-ins are only
5059 defined for the relaxed, release, and sequentially consistent memory
5060 orders the following code is diagnosed:
5065 __atomic_store_n (i, 0, memory_order_consume);
5069 @option{-Winvalid-memory-model} is enabled by default.
5071 @item -Wmaybe-uninitialized
5072 @opindex Wmaybe-uninitialized
5073 @opindex Wno-maybe-uninitialized
5074 For an automatic (i.e.@ local) variable, if there exists a path from the
5075 function entry to a use of the variable that is initialized, but there exist
5076 some other paths for which the variable is not initialized, the compiler
5077 emits a warning if it cannot prove the uninitialized paths are not
5078 executed at run time.
5080 These warnings are only possible in optimizing compilation, because otherwise
5081 GCC does not keep track of the state of variables.
5083 These warnings are made optional because GCC may not be able to determine when
5084 the code is correct in spite of appearing to have an error. Here is one
5085 example of how this can happen:
5105 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
5106 always initialized, but GCC doesn't know this. To suppress the
5107 warning, you need to provide a default case with assert(0) or
5110 @cindex @code{longjmp} warnings
5111 This option also warns when a non-volatile automatic variable might be
5112 changed by a call to @code{longjmp}.
5113 The compiler sees only the calls to @code{setjmp}. It cannot know
5114 where @code{longjmp} will be called; in fact, a signal handler could
5115 call it at any point in the code. As a result, you may get a warning
5116 even when there is in fact no problem because @code{longjmp} cannot
5117 in fact be called at the place that would cause a problem.
5119 Some spurious warnings can be avoided if you declare all the functions
5120 you use that never return as @code{noreturn}. @xref{Function
5123 This warning is enabled by @option{-Wall} or @option{-Wextra}.
5125 @item -Wunknown-pragmas
5126 @opindex Wunknown-pragmas
5127 @opindex Wno-unknown-pragmas
5128 @cindex warning for unknown pragmas
5129 @cindex unknown pragmas, warning
5130 @cindex pragmas, warning of unknown
5131 Warn when a @code{#pragma} directive is encountered that is not understood by
5132 GCC@. If this command-line option is used, warnings are even issued
5133 for unknown pragmas in system header files. This is not the case if
5134 the warnings are only enabled by the @option{-Wall} command-line option.
5137 @opindex Wno-pragmas
5139 Do not warn about misuses of pragmas, such as incorrect parameters,
5140 invalid syntax, or conflicts between pragmas. See also
5141 @option{-Wunknown-pragmas}.
5143 @item -Wstrict-aliasing
5144 @opindex Wstrict-aliasing
5145 @opindex Wno-strict-aliasing
5146 This option is only active when @option{-fstrict-aliasing} is active.
5147 It warns about code that might break the strict aliasing rules that the
5148 compiler is using for optimization. The warning does not catch all
5149 cases, but does attempt to catch the more common pitfalls. It is
5150 included in @option{-Wall}.
5151 It is equivalent to @option{-Wstrict-aliasing=3}
5153 @item -Wstrict-aliasing=n
5154 @opindex Wstrict-aliasing=n
5155 This option is only active when @option{-fstrict-aliasing} is active.
5156 It warns about code that might break the strict aliasing rules that the
5157 compiler is using for optimization.
5158 Higher levels correspond to higher accuracy (fewer false positives).
5159 Higher levels also correspond to more effort, similar to the way @option{-O}
5161 @option{-Wstrict-aliasing} is equivalent to @option{-Wstrict-aliasing=3}.
5163 Level 1: Most aggressive, quick, least accurate.
5164 Possibly useful when higher levels
5165 do not warn but @option{-fstrict-aliasing} still breaks the code, as it has very few
5166 false negatives. However, it has many false positives.
5167 Warns for all pointer conversions between possibly incompatible types,
5168 even if never dereferenced. Runs in the front end only.
5170 Level 2: Aggressive, quick, not too precise.
5171 May still have many false positives (not as many as level 1 though),
5172 and few false negatives (but possibly more than level 1).
5173 Unlike level 1, it only warns when an address is taken. Warns about
5174 incomplete types. Runs in the front end only.
5176 Level 3 (default for @option{-Wstrict-aliasing}):
5177 Should have very few false positives and few false
5178 negatives. Slightly slower than levels 1 or 2 when optimization is enabled.
5179 Takes care of the common pun+dereference pattern in the front end:
5180 @code{*(int*)&some_float}.
5181 If optimization is enabled, it also runs in the back end, where it deals
5182 with multiple statement cases using flow-sensitive points-to information.
5183 Only warns when the converted pointer is dereferenced.
5184 Does not warn about incomplete types.
5186 @item -Wstrict-overflow
5187 @itemx -Wstrict-overflow=@var{n}
5188 @opindex Wstrict-overflow
5189 @opindex Wno-strict-overflow
5190 This option is only active when signed overflow is undefined.
5191 It warns about cases where the compiler optimizes based on the
5192 assumption that signed overflow does not occur. Note that it does not
5193 warn about all cases where the code might overflow: it only warns
5194 about cases where the compiler implements some optimization. Thus
5195 this warning depends on the optimization level.
5197 An optimization that assumes that signed overflow does not occur is
5198 perfectly safe if the values of the variables involved are such that
5199 overflow never does, in fact, occur. Therefore this warning can
5200 easily give a false positive: a warning about code that is not
5201 actually a problem. To help focus on important issues, several
5202 warning levels are defined. No warnings are issued for the use of
5203 undefined signed overflow when estimating how many iterations a loop
5204 requires, in particular when determining whether a loop will be
5208 @item -Wstrict-overflow=1
5209 Warn about cases that are both questionable and easy to avoid. For
5210 example the compiler simplifies
5211 @code{x + 1 > x} to @code{1}. This level of
5212 @option{-Wstrict-overflow} is enabled by @option{-Wall}; higher levels
5213 are not, and must be explicitly requested.
5215 @item -Wstrict-overflow=2
5216 Also warn about other cases where a comparison is simplified to a
5217 constant. For example: @code{abs (x) >= 0}. This can only be
5218 simplified when signed integer overflow is undefined, because
5219 @code{abs (INT_MIN)} overflows to @code{INT_MIN}, which is less than
5220 zero. @option{-Wstrict-overflow} (with no level) is the same as
5221 @option{-Wstrict-overflow=2}.
5223 @item -Wstrict-overflow=3
5224 Also warn about other cases where a comparison is simplified. For
5225 example: @code{x + 1 > 1} is simplified to @code{x > 0}.
5227 @item -Wstrict-overflow=4
5228 Also warn about other simplifications not covered by the above cases.
5229 For example: @code{(x * 10) / 5} is simplified to @code{x * 2}.
5231 @item -Wstrict-overflow=5
5232 Also warn about cases where the compiler reduces the magnitude of a
5233 constant involved in a comparison. For example: @code{x + 2 > y} is
5234 simplified to @code{x + 1 >= y}. This is reported only at the
5235 highest warning level because this simplification applies to many
5236 comparisons, so this warning level gives a very large number of
5240 @item -Wstringop-overflow
5241 @itemx -Wstringop-overflow=@var{type}
5242 @opindex Wstringop-overflow
5243 @opindex Wno-stringop-overflow
5244 Warn for calls to string manipulation functions such as @code{memcpy} and
5245 @code{strcpy} that are determined to overflow the destination buffer. The
5246 optional argument is one greater than the type of Object Size Checking to
5247 perform to determine the size of the destination. @xref{Object Size Checking}.
5248 The argument is meaningful only for functions that operate on character arrays
5249 but not for raw memory functions like @code{memcpy} which always make use
5250 of Object Size type-0. The option also warns for calls that specify a size
5251 in excess of the largest possible object or at most @code{SIZE_MAX / 2} bytes.
5252 The option produces the best results with optimization enabled but can detect
5253 a small subset of simple buffer overflows even without optimization in
5254 calls to the GCC built-in functions like @code{__builtin_memcpy} that
5255 correspond to the standard functions. In any case, the option warns about
5256 just a subset of buffer overflows detected by the corresponding overflow
5257 checking built-ins. For example, the option will issue a warning for
5258 the @code{strcpy} call below because it copies at least 5 characters
5259 (the string @code{"blue"} including the terminating NUL) into the buffer
5263 enum Color @{ blue, purple, yellow @};
5264 const char* f (enum Color clr)
5266 static char buf [4];
5270 case blue: str = "blue"; break;
5271 case purple: str = "purple"; break;
5272 case yellow: str = "yellow"; break;
5275 return strcpy (buf, str); // warning here
5279 Option @option{-Wstringop-overflow=2} is enabled by default.
5282 @item -Wstringop-overflow
5283 @itemx -Wstringop-overflow=1
5284 @opindex Wstringop-overflow
5285 @opindex Wno-stringop-overflow
5286 The @option{-Wstringop-overflow=1} option uses type-zero Object Size Checking
5287 to determine the sizes of destination objects. This is the default setting
5288 of the option. At this setting the option will not warn for writes past
5289 the end of subobjects of larger objects accessed by pointers unless the
5290 size of the largest surrounding object is known. When the destination may
5291 be one of several objects it is assumed to be the largest one of them. On
5292 Linux systems, when optimization is enabled at this setting the option warns
5293 for the same code as when the @code{_FORTIFY_SOURCE} macro is defined to
5296 @item -Wstringop-overflow=2
5297 The @option{-Wstringop-overflow=2} option uses type-one Object Size Checking
5298 to determine the sizes of destination objects. At this setting the option
5299 will warn about overflows when writing to members of the largest complete
5300 objects whose exact size is known. It will, however, not warn for excessive
5301 writes to the same members of unknown objects referenced by pointers since
5302 they may point to arrays containing unknown numbers of elements.
5304 @item -Wstringop-overflow=3
5305 The @option{-Wstringop-overflow=3} option uses type-two Object Size Checking
5306 to determine the sizes of destination objects. At this setting the option
5307 warns about overflowing the smallest object or data member. This is the
5308 most restrictive setting of the option that may result in warnings for safe
5311 @item -Wstringop-overflow=4
5312 The @option{-Wstringop-overflow=4} option uses type-three Object Size Checking
5313 to determine the sizes of destination objects. At this setting the option
5314 will warn about overflowing any data members, and when the destination is
5315 one of several objects it uses the size of the largest of them to decide
5316 whether to issue a warning. Similarly to @option{-Wstringop-overflow=3} this
5317 setting of the option may result in warnings for benign code.
5320 @item -Wstringop-truncation
5321 @opindex Wstringop-truncation
5322 @opindex Wno-stringop-truncation
5323 Warn for calls to bounded string manipulation functions such as @code{strncat},
5324 @code{strncpy}, and @code{stpncpy} that may either truncate the copied string
5325 or leave the destination unchanged.
5327 In the following example, the call to @code{strncat} specifies a bound that
5328 is less than the length of the source string. As a result, the copy of
5329 the source will be truncated and so the call is diagnosed. To avoid the
5330 warning use @code{bufsize - strlen (buf) - 1)} as the bound.
5333 void append (char *buf, size_t bufsize)
5335 strncat (buf, ".txt", 3);
5339 As another example, the following call to @code{strncpy} results in copying
5340 to @code{d} just the characters preceding the terminating NUL, without
5341 appending the NUL to the end. Assuming the result of @code{strncpy} is
5342 necessarily a NUL-terminated string is a common mistake, and so the call
5343 is diagnosed. To avoid the warning when the result is not expected to be
5344 NUL-terminated, call @code{memcpy} instead.
5347 void copy (char *d, const char *s)
5349 strncpy (d, s, strlen (s));
5353 In the following example, the call to @code{strncpy} specifies the size
5354 of the destination buffer as the bound. If the length of the source
5355 string is equal to or greater than this size the result of the copy will
5356 not be NUL-terminated. Therefore, the call is also diagnosed. To avoid
5357 the warning, specify @code{sizeof buf - 1} as the bound and set the last
5358 element of the buffer to @code{NUL}.
5361 void copy (const char *s)
5364 strncpy (buf, s, sizeof buf);
5369 In situations where a character array is intended to store a sequence
5370 of bytes with no terminating @code{NUL} such an array may be annotated
5371 with attribute @code{nonstring} to avoid this warning. Such arrays,
5372 however, are not suitable arguments to functions that expect
5373 @code{NUL}-terminated strings. To help detect accidental misuses of
5374 such arrays GCC issues warnings unless it can prove that the use is
5375 safe. @xref{Common Variable Attributes}.
5377 @item -Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{|}cold@r{|}malloc@r{]}
5378 @opindex Wsuggest-attribute=
5379 @opindex Wno-suggest-attribute=
5380 Warn for cases where adding an attribute may be beneficial. The
5381 attributes currently supported are listed below.
5384 @item -Wsuggest-attribute=pure
5385 @itemx -Wsuggest-attribute=const
5386 @itemx -Wsuggest-attribute=noreturn
5387 @itemx -Wsuggest-attribute=malloc
5388 @opindex Wsuggest-attribute=pure
5389 @opindex Wno-suggest-attribute=pure
5390 @opindex Wsuggest-attribute=const
5391 @opindex Wno-suggest-attribute=const
5392 @opindex Wsuggest-attribute=noreturn
5393 @opindex Wno-suggest-attribute=noreturn
5394 @opindex Wsuggest-attribute=malloc
5395 @opindex Wno-suggest-attribute=malloc
5397 Warn about functions that might be candidates for attributes
5398 @code{pure}, @code{const} or @code{noreturn} or @code{malloc}. The compiler
5399 only warns for functions visible in other compilation units or (in the case of
5400 @code{pure} and @code{const}) if it cannot prove that the function returns
5401 normally. A function returns normally if it doesn't contain an infinite loop or
5402 return abnormally by throwing, calling @code{abort} or trapping. This analysis
5403 requires option @option{-fipa-pure-const}, which is enabled by default at
5404 @option{-O} and higher. Higher optimization levels improve the accuracy
5407 @item -Wsuggest-attribute=format
5408 @itemx -Wmissing-format-attribute
5409 @opindex Wsuggest-attribute=format
5410 @opindex Wmissing-format-attribute
5411 @opindex Wno-suggest-attribute=format
5412 @opindex Wno-missing-format-attribute
5416 Warn about function pointers that might be candidates for @code{format}
5417 attributes. Note these are only possible candidates, not absolute ones.
5418 GCC guesses that function pointers with @code{format} attributes that
5419 are used in assignment, initialization, parameter passing or return
5420 statements should have a corresponding @code{format} attribute in the
5421 resulting type. I.e.@: the left-hand side of the assignment or
5422 initialization, the type of the parameter variable, or the return type
5423 of the containing function respectively should also have a @code{format}
5424 attribute to avoid the warning.
5426 GCC also warns about function definitions that might be
5427 candidates for @code{format} attributes. Again, these are only
5428 possible candidates. GCC guesses that @code{format} attributes
5429 might be appropriate for any function that calls a function like
5430 @code{vprintf} or @code{vscanf}, but this might not always be the
5431 case, and some functions for which @code{format} attributes are
5432 appropriate may not be detected.
5434 @item -Wsuggest-attribute=cold
5435 @opindex Wsuggest-attribute=cold
5436 @opindex Wno-suggest-attribute=cold
5438 Warn about functions that might be candidates for @code{cold} attribute. This
5439 is based on static detection and generally will only warn about functions which
5440 always leads to a call to another @code{cold} function such as wrappers of
5441 C++ @code{throw} or fatal error reporting functions leading to @code{abort}.
5444 @item -Wsuggest-final-types
5445 @opindex Wno-suggest-final-types
5446 @opindex Wsuggest-final-types
5447 Warn about types with virtual methods where code quality would be improved
5448 if the type were declared with the C++11 @code{final} specifier,
5450 declared in an anonymous namespace. This allows GCC to more aggressively
5451 devirtualize the polymorphic calls. This warning is more effective with link
5452 time optimization, where the information about the class hierarchy graph is
5455 @item -Wsuggest-final-methods
5456 @opindex Wno-suggest-final-methods
5457 @opindex Wsuggest-final-methods
5458 Warn about virtual methods where code quality would be improved if the method
5459 were declared with the C++11 @code{final} specifier,
5460 or, if possible, its type were
5461 declared in an anonymous namespace or with the @code{final} specifier.
5463 more effective with link-time optimization, where the information about the
5464 class hierarchy graph is more complete. It is recommended to first consider
5465 suggestions of @option{-Wsuggest-final-types} and then rebuild with new
5468 @item -Wsuggest-override
5469 Warn about overriding virtual functions that are not marked with the override
5473 @opindex Wno-alloc-zero
5474 @opindex Walloc-zero
5475 Warn about calls to allocation functions decorated with attribute
5476 @code{alloc_size} that specify zero bytes, including those to the built-in
5477 forms of the functions @code{aligned_alloc}, @code{alloca}, @code{calloc},
5478 @code{malloc}, and @code{realloc}. Because the behavior of these functions
5479 when called with a zero size differs among implementations (and in the case
5480 of @code{realloc} has been deprecated) relying on it may result in subtle
5481 portability bugs and should be avoided.
5483 @item -Walloc-size-larger-than=@var{n}
5484 Warn about calls to functions decorated with attribute @code{alloc_size}
5485 that attempt to allocate objects larger than the specified number of bytes,
5486 or where the result of the size computation in an integer type with infinite
5487 precision would exceed @code{SIZE_MAX / 2}. The option argument @var{n}
5488 may end in one of the standard suffixes designating a multiple of bytes
5489 such as @code{kB} and @code{KiB} for kilobyte and kibibyte, respectively,
5490 @code{MB} and @code{MiB} for megabyte and mebibyte, and so on.
5491 @xref{Function Attributes}.
5496 This option warns on all uses of @code{alloca} in the source.
5498 @item -Walloca-larger-than=@var{n}
5499 This option warns on calls to @code{alloca} that are not bounded by a
5500 controlling predicate limiting its argument of integer type to at most
5501 @var{n} bytes, or calls to @code{alloca} where the bound is unknown.
5502 Arguments of non-integer types are considered unbounded even if they
5503 appear to be constrained to the expected range.
5505 For example, a bounded case of @code{alloca} could be:
5508 void func (size_t n)
5519 In the above example, passing @code{-Walloca-larger-than=1000} would not
5520 issue a warning because the call to @code{alloca} is known to be at most
5521 1000 bytes. However, if @code{-Walloca-larger-than=500} were passed,
5522 the compiler would emit a warning.
5524 Unbounded uses, on the other hand, are uses of @code{alloca} with no
5525 controlling predicate constraining its integer argument. For example:
5530 void *p = alloca (n);
5535 If @code{-Walloca-larger-than=500} were passed, the above would trigger
5536 a warning, but this time because of the lack of bounds checking.
5538 Note, that even seemingly correct code involving signed integers could
5542 void func (signed int n)
5552 In the above example, @var{n} could be negative, causing a larger than
5553 expected argument to be implicitly cast into the @code{alloca} call.
5555 This option also warns when @code{alloca} is used in a loop.
5557 This warning is not enabled by @option{-Wall}, and is only active when
5558 @option{-ftree-vrp} is active (default for @option{-O2} and above).
5560 See also @option{-Wvla-larger-than=@var{n}}.
5562 @item -Warray-bounds
5563 @itemx -Warray-bounds=@var{n}
5564 @opindex Wno-array-bounds
5565 @opindex Warray-bounds
5566 This option is only active when @option{-ftree-vrp} is active
5567 (default for @option{-O2} and above). It warns about subscripts to arrays
5568 that are always out of bounds. This warning is enabled by @option{-Wall}.
5571 @item -Warray-bounds=1
5572 This is the warning level of @option{-Warray-bounds} and is enabled
5573 by @option{-Wall}; higher levels are not, and must be explicitly requested.
5575 @item -Warray-bounds=2
5576 This warning level also warns about out of bounds access for
5577 arrays at the end of a struct and for arrays accessed through
5578 pointers. This warning level may give a larger number of
5579 false positives and is deactivated by default.
5582 @item -Wattribute-alias
5583 Warn about declarations using the @code{alias} and similar attributes whose
5584 target is incompatible with the type of the alias. @xref{Function Attributes,
5585 ,Declaring Attributes of Functions}.
5587 @item -Wbool-compare
5588 @opindex Wno-bool-compare
5589 @opindex Wbool-compare
5590 Warn about boolean expression compared with an integer value different from
5591 @code{true}/@code{false}. For instance, the following comparison is
5596 if ((n > 1) == 2) @{ @dots{} @}
5598 This warning is enabled by @option{-Wall}.
5600 @item -Wbool-operation
5601 @opindex Wno-bool-operation
5602 @opindex Wbool-operation
5603 Warn about suspicious operations on expressions of a boolean type. For
5604 instance, bitwise negation of a boolean is very likely a bug in the program.
5605 For C, this warning also warns about incrementing or decrementing a boolean,
5606 which rarely makes sense. (In C++, decrementing a boolean is always invalid.
5607 Incrementing a boolean is invalid in C++17, and deprecated otherwise.)
5609 This warning is enabled by @option{-Wall}.
5611 @item -Wduplicated-branches
5612 @opindex Wno-duplicated-branches
5613 @opindex Wduplicated-branches
5614 Warn when an if-else has identical branches. This warning detects cases like
5621 It doesn't warn when both branches contain just a null statement. This warning
5622 also warn for conditional operators:
5624 int i = x ? *p : *p;
5627 @item -Wduplicated-cond
5628 @opindex Wno-duplicated-cond
5629 @opindex Wduplicated-cond
5630 Warn about duplicated conditions in an if-else-if chain. For instance,
5631 warn for the following code:
5633 if (p->q != NULL) @{ @dots{} @}
5634 else if (p->q != NULL) @{ @dots{} @}
5637 @item -Wframe-address
5638 @opindex Wno-frame-address
5639 @opindex Wframe-address
5640 Warn when the @samp{__builtin_frame_address} or @samp{__builtin_return_address}
5641 is called with an argument greater than 0. Such calls may return indeterminate
5642 values or crash the program. The warning is included in @option{-Wall}.
5644 @item -Wno-discarded-qualifiers @r{(C and Objective-C only)}
5645 @opindex Wno-discarded-qualifiers
5646 @opindex Wdiscarded-qualifiers
5647 Do not warn if type qualifiers on pointers are being discarded.
5648 Typically, the compiler warns if a @code{const char *} variable is
5649 passed to a function that takes a @code{char *} parameter. This option
5650 can be used to suppress such a warning.
5652 @item -Wno-discarded-array-qualifiers @r{(C and Objective-C only)}
5653 @opindex Wno-discarded-array-qualifiers
5654 @opindex Wdiscarded-array-qualifiers
5655 Do not warn if type qualifiers on arrays which are pointer targets
5656 are being discarded. Typically, the compiler warns if a
5657 @code{const int (*)[]} variable is passed to a function that
5658 takes a @code{int (*)[]} parameter. This option can be used to
5659 suppress such a warning.
5661 @item -Wno-incompatible-pointer-types @r{(C and Objective-C only)}
5662 @opindex Wno-incompatible-pointer-types
5663 @opindex Wincompatible-pointer-types
5664 Do not warn when there is a conversion between pointers that have incompatible
5665 types. This warning is for cases not covered by @option{-Wno-pointer-sign},
5666 which warns for pointer argument passing or assignment with different
5669 @item -Wno-int-conversion @r{(C and Objective-C only)}
5670 @opindex Wno-int-conversion
5671 @opindex Wint-conversion
5672 Do not warn about incompatible integer to pointer and pointer to integer
5673 conversions. This warning is about implicit conversions; for explicit
5674 conversions the warnings @option{-Wno-int-to-pointer-cast} and
5675 @option{-Wno-pointer-to-int-cast} may be used.
5677 @item -Wno-div-by-zero
5678 @opindex Wno-div-by-zero
5679 @opindex Wdiv-by-zero
5680 Do not warn about compile-time integer division by zero. Floating-point
5681 division by zero is not warned about, as it can be a legitimate way of
5682 obtaining infinities and NaNs.
5684 @item -Wsystem-headers
5685 @opindex Wsystem-headers
5686 @opindex Wno-system-headers
5687 @cindex warnings from system headers
5688 @cindex system headers, warnings from
5689 Print warning messages for constructs found in system header files.
5690 Warnings from system headers are normally suppressed, on the assumption
5691 that they usually do not indicate real problems and would only make the
5692 compiler output harder to read. Using this command-line option tells
5693 GCC to emit warnings from system headers as if they occurred in user
5694 code. However, note that using @option{-Wall} in conjunction with this
5695 option does @emph{not} warn about unknown pragmas in system
5696 headers---for that, @option{-Wunknown-pragmas} must also be used.
5698 @item -Wtautological-compare
5699 @opindex Wtautological-compare
5700 @opindex Wno-tautological-compare
5701 Warn if a self-comparison always evaluates to true or false. This
5702 warning detects various mistakes such as:
5706 if (i > i) @{ @dots{} @}
5709 This warning also warns about bitwise comparisons that always evaluate
5710 to true or false, for instance:
5712 if ((a & 16) == 10) @{ @dots{} @}
5714 will always be false.
5716 This warning is enabled by @option{-Wall}.
5719 @opindex Wtrampolines
5720 @opindex Wno-trampolines
5721 Warn about trampolines generated for pointers to nested functions.
5722 A trampoline is a small piece of data or code that is created at run
5723 time on the stack when the address of a nested function is taken, and is
5724 used to call the nested function indirectly. For some targets, it is
5725 made up of data only and thus requires no special treatment. But, for
5726 most targets, it is made up of code and thus requires the stack to be
5727 made executable in order for the program to work properly.
5730 @opindex Wfloat-equal
5731 @opindex Wno-float-equal
5732 Warn if floating-point values are used in equality comparisons.
5734 The idea behind this is that sometimes it is convenient (for the
5735 programmer) to consider floating-point values as approximations to
5736 infinitely precise real numbers. If you are doing this, then you need
5737 to compute (by analyzing the code, or in some other way) the maximum or
5738 likely maximum error that the computation introduces, and allow for it
5739 when performing comparisons (and when producing output, but that's a
5740 different problem). In particular, instead of testing for equality, you
5741 should check to see whether the two values have ranges that overlap; and
5742 this is done with the relational operators, so equality comparisons are
5745 @item -Wtraditional @r{(C and Objective-C only)}
5746 @opindex Wtraditional
5747 @opindex Wno-traditional
5748 Warn about certain constructs that behave differently in traditional and
5749 ISO C@. Also warn about ISO C constructs that have no traditional C
5750 equivalent, and/or problematic constructs that should be avoided.
5754 Macro parameters that appear within string literals in the macro body.
5755 In traditional C macro replacement takes place within string literals,
5756 but in ISO C it does not.
5759 In traditional C, some preprocessor directives did not exist.
5760 Traditional preprocessors only considered a line to be a directive
5761 if the @samp{#} appeared in column 1 on the line. Therefore
5762 @option{-Wtraditional} warns about directives that traditional C
5763 understands but ignores because the @samp{#} does not appear as the
5764 first character on the line. It also suggests you hide directives like
5765 @code{#pragma} not understood by traditional C by indenting them. Some
5766 traditional implementations do not recognize @code{#elif}, so this option
5767 suggests avoiding it altogether.
5770 A function-like macro that appears without arguments.
5773 The unary plus operator.
5776 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating-point
5777 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
5778 constants.) Note, these suffixes appear in macros defined in the system
5779 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
5780 Use of these macros in user code might normally lead to spurious
5781 warnings, however GCC's integrated preprocessor has enough context to
5782 avoid warning in these cases.
5785 A function declared external in one block and then used after the end of
5789 A @code{switch} statement has an operand of type @code{long}.
5792 A non-@code{static} function declaration follows a @code{static} one.
5793 This construct is not accepted by some traditional C compilers.
5796 The ISO type of an integer constant has a different width or
5797 signedness from its traditional type. This warning is only issued if
5798 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
5799 typically represent bit patterns, are not warned about.
5802 Usage of ISO string concatenation is detected.
5805 Initialization of automatic aggregates.
5808 Identifier conflicts with labels. Traditional C lacks a separate
5809 namespace for labels.
5812 Initialization of unions. If the initializer is zero, the warning is
5813 omitted. This is done under the assumption that the zero initializer in
5814 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
5815 initializer warnings and relies on default initialization to zero in the
5819 Conversions by prototypes between fixed/floating-point values and vice
5820 versa. The absence of these prototypes when compiling with traditional
5821 C causes serious problems. This is a subset of the possible
5822 conversion warnings; for the full set use @option{-Wtraditional-conversion}.
5825 Use of ISO C style function definitions. This warning intentionally is
5826 @emph{not} issued for prototype declarations or variadic functions
5827 because these ISO C features appear in your code when using
5828 libiberty's traditional C compatibility macros, @code{PARAMS} and
5829 @code{VPARAMS}. This warning is also bypassed for nested functions
5830 because that feature is already a GCC extension and thus not relevant to
5831 traditional C compatibility.
5834 @item -Wtraditional-conversion @r{(C and Objective-C only)}
5835 @opindex Wtraditional-conversion
5836 @opindex Wno-traditional-conversion
5837 Warn if a prototype causes a type conversion that is different from what
5838 would happen to the same argument in the absence of a prototype. This
5839 includes conversions of fixed point to floating and vice versa, and
5840 conversions changing the width or signedness of a fixed-point argument
5841 except when the same as the default promotion.
5843 @item -Wdeclaration-after-statement @r{(C and Objective-C only)}
5844 @opindex Wdeclaration-after-statement
5845 @opindex Wno-declaration-after-statement
5846 Warn when a declaration is found after a statement in a block. This
5847 construct, known from C++, was introduced with ISO C99 and is by default
5848 allowed in GCC@. It is not supported by ISO C90. @xref{Mixed Declarations}.
5853 Warn whenever a local variable or type declaration shadows another
5854 variable, parameter, type, class member (in C++), or instance variable
5855 (in Objective-C) or whenever a built-in function is shadowed. Note
5856 that in C++, the compiler warns if a local variable shadows an
5857 explicit typedef, but not if it shadows a struct/class/enum.
5858 Same as @option{-Wshadow=global}.
5860 @item -Wno-shadow-ivar @r{(Objective-C only)}
5861 @opindex Wno-shadow-ivar
5862 @opindex Wshadow-ivar
5863 Do not warn whenever a local variable shadows an instance variable in an
5866 @item -Wshadow=global
5867 @opindex Wshadow=local
5868 The default for @option{-Wshadow}. Warns for any (global) shadowing.
5870 @item -Wshadow=local
5871 @opindex Wshadow=local
5872 Warn when a local variable shadows another local variable or parameter.
5873 This warning is enabled by @option{-Wshadow=global}.
5875 @item -Wshadow=compatible-local
5876 @opindex Wshadow=compatible-local
5877 Warn when a local variable shadows another local variable or parameter
5878 whose type is compatible with that of the shadowing variable. In C++,
5879 type compatibility here means the type of the shadowing variable can be
5880 converted to that of the shadowed variable. The creation of this flag
5881 (in addition to @option{-Wshadow=local}) is based on the idea that when
5882 a local variable shadows another one of incompatible type, it is most
5883 likely intentional, not a bug or typo, as shown in the following example:
5887 for (SomeIterator i = SomeObj.begin(); i != SomeObj.end(); ++i)
5889 for (int i = 0; i < N; ++i)
5898 Since the two variable @code{i} in the example above have incompatible types,
5899 enabling only @option{-Wshadow=compatible-local} will not emit a warning.
5900 Because their types are incompatible, if a programmer accidentally uses one
5901 in place of the other, type checking will catch that and emit an error or
5902 warning. So not warning (about shadowing) in this case will not lead to
5903 undetected bugs. Use of this flag instead of @option{-Wshadow=local} can
5904 possibly reduce the number of warnings triggered by intentional shadowing.
5906 This warning is enabled by @option{-Wshadow=local}.
5908 @item -Wlarger-than=@var{len}
5909 @opindex Wlarger-than=@var{len}
5910 @opindex Wlarger-than-@var{len}
5911 Warn whenever an object of larger than @var{len} bytes is defined.
5913 @item -Wframe-larger-than=@var{len}
5914 @opindex Wframe-larger-than
5915 Warn if the size of a function frame is larger than @var{len} bytes.
5916 The computation done to determine the stack frame size is approximate
5917 and not conservative.
5918 The actual requirements may be somewhat greater than @var{len}
5919 even if you do not get a warning. In addition, any space allocated
5920 via @code{alloca}, variable-length arrays, or related constructs
5921 is not included by the compiler when determining
5922 whether or not to issue a warning.
5924 @item -Wno-free-nonheap-object
5925 @opindex Wno-free-nonheap-object
5926 @opindex Wfree-nonheap-object
5927 Do not warn when attempting to free an object that was not allocated
5930 @item -Wstack-usage=@var{len}
5931 @opindex Wstack-usage
5932 Warn if the stack usage of a function might be larger than @var{len} bytes.
5933 The computation done to determine the stack usage is conservative.
5934 Any space allocated via @code{alloca}, variable-length arrays, or related
5935 constructs is included by the compiler when determining whether or not to
5938 The message is in keeping with the output of @option{-fstack-usage}.
5942 If the stack usage is fully static but exceeds the specified amount, it's:
5945 warning: stack usage is 1120 bytes
5948 If the stack usage is (partly) dynamic but bounded, it's:
5951 warning: stack usage might be 1648 bytes
5954 If the stack usage is (partly) dynamic and not bounded, it's:
5957 warning: stack usage might be unbounded
5961 @item -Wunsafe-loop-optimizations
5962 @opindex Wunsafe-loop-optimizations
5963 @opindex Wno-unsafe-loop-optimizations
5964 Warn if the loop cannot be optimized because the compiler cannot
5965 assume anything on the bounds of the loop indices. With
5966 @option{-funsafe-loop-optimizations} warn if the compiler makes
5969 @item -Wno-pedantic-ms-format @r{(MinGW targets only)}
5970 @opindex Wno-pedantic-ms-format
5971 @opindex Wpedantic-ms-format
5972 When used in combination with @option{-Wformat}
5973 and @option{-pedantic} without GNU extensions, this option
5974 disables the warnings about non-ISO @code{printf} / @code{scanf} format
5975 width specifiers @code{I32}, @code{I64}, and @code{I} used on Windows targets,
5976 which depend on the MS runtime.
5979 @opindex Waligned-new
5980 @opindex Wno-aligned-new
5981 Warn about a new-expression of a type that requires greater alignment
5982 than the @code{alignof(std::max_align_t)} but uses an allocation
5983 function without an explicit alignment parameter. This option is
5984 enabled by @option{-Wall}.
5986 Normally this only warns about global allocation functions, but
5987 @option{-Waligned-new=all} also warns about class member allocation
5990 @item -Wplacement-new
5991 @itemx -Wplacement-new=@var{n}
5992 @opindex Wplacement-new
5993 @opindex Wno-placement-new
5994 Warn about placement new expressions with undefined behavior, such as
5995 constructing an object in a buffer that is smaller than the type of
5996 the object. For example, the placement new expression below is diagnosed
5997 because it attempts to construct an array of 64 integers in a buffer only
6003 This warning is enabled by default.
6006 @item -Wplacement-new=1
6007 This is the default warning level of @option{-Wplacement-new}. At this
6008 level the warning is not issued for some strictly undefined constructs that
6009 GCC allows as extensions for compatibility with legacy code. For example,
6010 the following @code{new} expression is not diagnosed at this level even
6011 though it has undefined behavior according to the C++ standard because
6012 it writes past the end of the one-element array.
6014 struct S @{ int n, a[1]; @};
6015 S *s = (S *)malloc (sizeof *s + 31 * sizeof s->a[0]);
6016 new (s->a)int [32]();
6019 @item -Wplacement-new=2
6020 At this level, in addition to diagnosing all the same constructs as at level
6021 1, a diagnostic is also issued for placement new expressions that construct
6022 an object in the last member of structure whose type is an array of a single
6023 element and whose size is less than the size of the object being constructed.
6024 While the previous example would be diagnosed, the following construct makes
6025 use of the flexible member array extension to avoid the warning at level 2.
6027 struct S @{ int n, a[]; @};
6028 S *s = (S *)malloc (sizeof *s + 32 * sizeof s->a[0]);
6029 new (s->a)int [32]();
6034 @item -Wpointer-arith
6035 @opindex Wpointer-arith
6036 @opindex Wno-pointer-arith
6037 Warn about anything that depends on the ``size of'' a function type or
6038 of @code{void}. GNU C assigns these types a size of 1, for
6039 convenience in calculations with @code{void *} pointers and pointers
6040 to functions. In C++, warn also when an arithmetic operation involves
6041 @code{NULL}. This warning is also enabled by @option{-Wpedantic}.
6043 @item -Wpointer-compare
6044 @opindex Wpointer-compare
6045 @opindex Wno-pointer-compare
6046 Warn if a pointer is compared with a zero character constant. This usually
6047 means that the pointer was meant to be dereferenced. For example:
6050 const char *p = foo ();
6055 Note that the code above is invalid in C++11.
6057 This warning is enabled by default.
6060 @opindex Wtype-limits
6061 @opindex Wno-type-limits
6062 Warn if a comparison is always true or always false due to the limited
6063 range of the data type, but do not warn for constant expressions. For
6064 example, warn if an unsigned variable is compared against zero with
6065 @code{<} or @code{>=}. This warning is also enabled by
6068 @include cppwarnopts.texi
6070 @item -Wbad-function-cast @r{(C and Objective-C only)}
6071 @opindex Wbad-function-cast
6072 @opindex Wno-bad-function-cast
6073 Warn when a function call is cast to a non-matching type.
6074 For example, warn if a call to a function returning an integer type
6075 is cast to a pointer type.
6077 @item -Wc90-c99-compat @r{(C and Objective-C only)}
6078 @opindex Wc90-c99-compat
6079 @opindex Wno-c90-c99-compat
6080 Warn about features not present in ISO C90, but present in ISO C99.
6081 For instance, warn about use of variable length arrays, @code{long long}
6082 type, @code{bool} type, compound literals, designated initializers, and so
6083 on. This option is independent of the standards mode. Warnings are disabled
6084 in the expression that follows @code{__extension__}.
6086 @item -Wc99-c11-compat @r{(C and Objective-C only)}
6087 @opindex Wc99-c11-compat
6088 @opindex Wno-c99-c11-compat
6089 Warn about features not present in ISO C99, but present in ISO C11.
6090 For instance, warn about use of anonymous structures and unions,
6091 @code{_Atomic} type qualifier, @code{_Thread_local} storage-class specifier,
6092 @code{_Alignas} specifier, @code{Alignof} operator, @code{_Generic} keyword,
6093 and so on. This option is independent of the standards mode. Warnings are
6094 disabled in the expression that follows @code{__extension__}.
6096 @item -Wc++-compat @r{(C and Objective-C only)}
6097 @opindex Wc++-compat
6098 Warn about ISO C constructs that are outside of the common subset of
6099 ISO C and ISO C++, e.g.@: request for implicit conversion from
6100 @code{void *} to a pointer to non-@code{void} type.
6102 @item -Wc++11-compat @r{(C++ and Objective-C++ only)}
6103 @opindex Wc++11-compat
6104 Warn about C++ constructs whose meaning differs between ISO C++ 1998
6105 and ISO C++ 2011, e.g., identifiers in ISO C++ 1998 that are keywords
6106 in ISO C++ 2011. This warning turns on @option{-Wnarrowing} and is
6107 enabled by @option{-Wall}.
6109 @item -Wc++14-compat @r{(C++ and Objective-C++ only)}
6110 @opindex Wc++14-compat
6111 Warn about C++ constructs whose meaning differs between ISO C++ 2011
6112 and ISO C++ 2014. This warning is enabled by @option{-Wall}.
6114 @item -Wc++17-compat @r{(C++ and Objective-C++ only)}
6115 @opindex Wc++17-compat
6116 Warn about C++ constructs whose meaning differs between ISO C++ 2014
6117 and ISO C++ 2017. This warning is enabled by @option{-Wall}.
6121 @opindex Wno-cast-qual
6122 Warn whenever a pointer is cast so as to remove a type qualifier from
6123 the target type. For example, warn if a @code{const char *} is cast
6124 to an ordinary @code{char *}.
6126 Also warn when making a cast that introduces a type qualifier in an
6127 unsafe way. For example, casting @code{char **} to @code{const char **}
6128 is unsafe, as in this example:
6131 /* p is char ** value. */
6132 const char **q = (const char **) p;
6133 /* Assignment of readonly string to const char * is OK. */
6135 /* Now char** pointer points to read-only memory. */
6140 @opindex Wcast-align
6141 @opindex Wno-cast-align
6142 Warn whenever a pointer is cast such that the required alignment of the
6143 target is increased. For example, warn if a @code{char *} is cast to
6144 an @code{int *} on machines where integers can only be accessed at
6145 two- or four-byte boundaries.
6147 @item -Wcast-align=strict
6148 @opindex Wcast-align=strict
6149 Warn whenever a pointer is cast such that the required alignment of the
6150 target is increased. For example, warn if a @code{char *} is cast to
6151 an @code{int *} regardless of the target machine.
6153 @item -Wcast-function-type
6154 @opindex Wcast-function-type
6155 @opindex Wno-cast-function-type
6156 Warn when a function pointer is cast to an incompatible function pointer.
6157 In a cast involving function types with a variable argument list only
6158 the types of initial arguments that are provided are considered.
6159 Any parameter of pointer-type matches any other pointer-type. Any benign
6160 differences in integral types are ignored, like @code{int} vs. @code{long}
6161 on ILP32 targets. Likewise type qualifiers are ignored. The function
6162 type @code{void (*) (void)} is special and matches everything, which can
6163 be used to suppress this warning.
6164 In a cast involving pointer to member types this warning warns whenever
6165 the type cast is changing the pointer to member type.
6166 This warning is enabled by @option{-Wextra}.
6168 @item -Wwrite-strings
6169 @opindex Wwrite-strings
6170 @opindex Wno-write-strings
6171 When compiling C, give string constants the type @code{const
6172 char[@var{length}]} so that copying the address of one into a
6173 non-@code{const} @code{char *} pointer produces a warning. These
6174 warnings help you find at compile time code that can try to write
6175 into a string constant, but only if you have been very careful about
6176 using @code{const} in declarations and prototypes. Otherwise, it is
6177 just a nuisance. This is why we did not make @option{-Wall} request
6180 When compiling C++, warn about the deprecated conversion from string
6181 literals to @code{char *}. This warning is enabled by default for C++
6185 @itemx -Wcatch-value=@var{n} @r{(C++ and Objective-C++ only)}
6186 @opindex Wcatch-value
6187 @opindex Wno-catch-value
6188 Warn about catch handlers that do not catch via reference.
6189 With @option{-Wcatch-value=1} (or @option{-Wcatch-value} for short)
6190 warn about polymorphic class types that are caught by value.
6191 With @option{-Wcatch-value=2} warn about all class types that are caught
6192 by value. With @option{-Wcatch-value=3} warn about all types that are
6193 not caught by reference. @option{-Wcatch-value} is enabled by @option{-Wall}.
6197 @opindex Wno-clobbered
6198 Warn for variables that might be changed by @code{longjmp} or
6199 @code{vfork}. This warning is also enabled by @option{-Wextra}.
6201 @item -Wconditionally-supported @r{(C++ and Objective-C++ only)}
6202 @opindex Wconditionally-supported
6203 @opindex Wno-conditionally-supported
6204 Warn for conditionally-supported (C++11 [intro.defs]) constructs.
6207 @opindex Wconversion
6208 @opindex Wno-conversion
6209 Warn for implicit conversions that may alter a value. This includes
6210 conversions between real and integer, like @code{abs (x)} when
6211 @code{x} is @code{double}; conversions between signed and unsigned,
6212 like @code{unsigned ui = -1}; and conversions to smaller types, like
6213 @code{sqrtf (M_PI)}. Do not warn for explicit casts like @code{abs
6214 ((int) x)} and @code{ui = (unsigned) -1}, or if the value is not
6215 changed by the conversion like in @code{abs (2.0)}. Warnings about
6216 conversions between signed and unsigned integers can be disabled by
6217 using @option{-Wno-sign-conversion}.
6219 For C++, also warn for confusing overload resolution for user-defined
6220 conversions; and conversions that never use a type conversion
6221 operator: conversions to @code{void}, the same type, a base class or a
6222 reference to them. Warnings about conversions between signed and
6223 unsigned integers are disabled by default in C++ unless
6224 @option{-Wsign-conversion} is explicitly enabled.
6226 @item -Wno-conversion-null @r{(C++ and Objective-C++ only)}
6227 @opindex Wconversion-null
6228 @opindex Wno-conversion-null
6229 Do not warn for conversions between @code{NULL} and non-pointer
6230 types. @option{-Wconversion-null} is enabled by default.
6232 @item -Wzero-as-null-pointer-constant @r{(C++ and Objective-C++ only)}
6233 @opindex Wzero-as-null-pointer-constant
6234 @opindex Wno-zero-as-null-pointer-constant
6235 Warn when a literal @samp{0} is used as null pointer constant. This can
6236 be useful to facilitate the conversion to @code{nullptr} in C++11.
6238 @item -Wsubobject-linkage @r{(C++ and Objective-C++ only)}
6239 @opindex Wsubobject-linkage
6240 @opindex Wno-subobject-linkage
6241 Warn if a class type has a base or a field whose type uses the anonymous
6242 namespace or depends on a type with no linkage. If a type A depends on
6243 a type B with no or internal linkage, defining it in multiple
6244 translation units would be an ODR violation because the meaning of B
6245 is different in each translation unit. If A only appears in a single
6246 translation unit, the best way to silence the warning is to give it
6247 internal linkage by putting it in an anonymous namespace as well. The
6248 compiler doesn't give this warning for types defined in the main .C
6249 file, as those are unlikely to have multiple definitions.
6250 @option{-Wsubobject-linkage} is enabled by default.
6252 @item -Wdangling-else
6253 @opindex Wdangling-else
6254 @opindex Wno-dangling-else
6255 Warn about constructions where there may be confusion to which
6256 @code{if} statement an @code{else} branch belongs. Here is an example of
6271 In C/C++, every @code{else} branch belongs to the innermost possible
6272 @code{if} statement, which in this example is @code{if (b)}. This is
6273 often not what the programmer expected, as illustrated in the above
6274 example by indentation the programmer chose. When there is the
6275 potential for this confusion, GCC issues a warning when this flag
6276 is specified. To eliminate the warning, add explicit braces around
6277 the innermost @code{if} statement so there is no way the @code{else}
6278 can belong to the enclosing @code{if}. The resulting code
6295 This warning is enabled by @option{-Wparentheses}.
6299 @opindex Wno-date-time
6300 Warn when macros @code{__TIME__}, @code{__DATE__} or @code{__TIMESTAMP__}
6301 are encountered as they might prevent bit-wise-identical reproducible
6304 @item -Wdelete-incomplete @r{(C++ and Objective-C++ only)}
6305 @opindex Wdelete-incomplete
6306 @opindex Wno-delete-incomplete
6307 Warn when deleting a pointer to incomplete type, which may cause
6308 undefined behavior at runtime. This warning is enabled by default.
6310 @item -Wuseless-cast @r{(C++ and Objective-C++ only)}
6311 @opindex Wuseless-cast
6312 @opindex Wno-useless-cast
6313 Warn when an expression is casted to its own type.
6316 @opindex Wempty-body
6317 @opindex Wno-empty-body
6318 Warn if an empty body occurs in an @code{if}, @code{else} or @code{do
6319 while} statement. This warning is also enabled by @option{-Wextra}.
6321 @item -Wenum-compare
6322 @opindex Wenum-compare
6323 @opindex Wno-enum-compare
6324 Warn about a comparison between values of different enumerated types.
6325 In C++ enumerated type mismatches in conditional expressions are also
6326 diagnosed and the warning is enabled by default. In C this warning is
6327 enabled by @option{-Wall}.
6329 @item -Wextra-semi @r{(C++, Objective-C++ only)}
6330 @opindex Wextra-semi
6331 @opindex Wno-extra-semi
6332 Warn about redundant semicolon after in-class function definition.
6334 @item -Wjump-misses-init @r{(C, Objective-C only)}
6335 @opindex Wjump-misses-init
6336 @opindex Wno-jump-misses-init
6337 Warn if a @code{goto} statement or a @code{switch} statement jumps
6338 forward across the initialization of a variable, or jumps backward to a
6339 label after the variable has been initialized. This only warns about
6340 variables that are initialized when they are declared. This warning is
6341 only supported for C and Objective-C; in C++ this sort of branch is an
6344 @option{-Wjump-misses-init} is included in @option{-Wc++-compat}. It
6345 can be disabled with the @option{-Wno-jump-misses-init} option.
6347 @item -Wsign-compare
6348 @opindex Wsign-compare
6349 @opindex Wno-sign-compare
6350 @cindex warning for comparison of signed and unsigned values
6351 @cindex comparison of signed and unsigned values, warning
6352 @cindex signed and unsigned values, comparison warning
6353 Warn when a comparison between signed and unsigned values could produce
6354 an incorrect result when the signed value is converted to unsigned.
6355 In C++, this warning is also enabled by @option{-Wall}. In C, it is
6356 also enabled by @option{-Wextra}.
6358 @item -Wsign-conversion
6359 @opindex Wsign-conversion
6360 @opindex Wno-sign-conversion
6361 Warn for implicit conversions that may change the sign of an integer
6362 value, like assigning a signed integer expression to an unsigned
6363 integer variable. An explicit cast silences the warning. In C, this
6364 option is enabled also by @option{-Wconversion}.
6366 @item -Wfloat-conversion
6367 @opindex Wfloat-conversion
6368 @opindex Wno-float-conversion
6369 Warn for implicit conversions that reduce the precision of a real value.
6370 This includes conversions from real to integer, and from higher precision
6371 real to lower precision real values. This option is also enabled by
6372 @option{-Wconversion}.
6374 @item -Wno-scalar-storage-order
6375 @opindex -Wno-scalar-storage-order
6376 @opindex -Wscalar-storage-order
6377 Do not warn on suspicious constructs involving reverse scalar storage order.
6379 @item -Wsized-deallocation @r{(C++ and Objective-C++ only)}
6380 @opindex Wsized-deallocation
6381 @opindex Wno-sized-deallocation
6382 Warn about a definition of an unsized deallocation function
6384 void operator delete (void *) noexcept;
6385 void operator delete[] (void *) noexcept;
6387 without a definition of the corresponding sized deallocation function
6389 void operator delete (void *, std::size_t) noexcept;
6390 void operator delete[] (void *, std::size_t) noexcept;
6392 or vice versa. Enabled by @option{-Wextra} along with
6393 @option{-fsized-deallocation}.
6395 @item -Wsizeof-pointer-div
6396 @opindex Wsizeof-pointer-div
6397 @opindex Wno-sizeof-pointer-div
6398 Warn for suspicious divisions of two sizeof expressions that divide
6399 the pointer size by the element size, which is the usual way to compute
6400 the array size but won't work out correctly with pointers. This warning
6401 warns e.g.@: about @code{sizeof (ptr) / sizeof (ptr[0])} if @code{ptr} is
6402 not an array, but a pointer. This warning is enabled by @option{-Wall}.
6404 @item -Wsizeof-pointer-memaccess
6405 @opindex Wsizeof-pointer-memaccess
6406 @opindex Wno-sizeof-pointer-memaccess
6407 Warn for suspicious length parameters to certain string and memory built-in
6408 functions if the argument uses @code{sizeof}. This warning triggers for
6409 example for @code{memset (ptr, 0, sizeof (ptr));} if @code{ptr} is not
6410 an array, but a pointer, and suggests a possible fix, or about
6411 @code{memcpy (&foo, ptr, sizeof (&foo));}. @option{-Wsizeof-pointer-memaccess}
6412 also warns about calls to bounded string copy functions like @code{strncat}
6413 or @code{strncpy} that specify as the bound a @code{sizeof} expression of
6414 the source array. For example, in the following function the call to
6415 @code{strncat} specifies the size of the source string as the bound. That
6416 is almost certainly a mistake and so the call is diagnosed.
6418 void make_file (const char *name)
6420 char path[PATH_MAX];
6421 strncpy (path, name, sizeof path - 1);
6422 strncat (path, ".text", sizeof ".text");
6427 The @option{-Wsizeof-pointer-memaccess} option is enabled by @option{-Wall}.
6429 @item -Wsizeof-array-argument
6430 @opindex Wsizeof-array-argument
6431 @opindex Wno-sizeof-array-argument
6432 Warn when the @code{sizeof} operator is applied to a parameter that is
6433 declared as an array in a function definition. This warning is enabled by
6434 default for C and C++ programs.
6436 @item -Wmemset-elt-size
6437 @opindex Wmemset-elt-size
6438 @opindex Wno-memset-elt-size
6439 Warn for suspicious calls to the @code{memset} built-in function, if the
6440 first argument references an array, and the third argument is a number
6441 equal to the number of elements, but not equal to the size of the array
6442 in memory. This indicates that the user has omitted a multiplication by
6443 the element size. This warning is enabled by @option{-Wall}.
6445 @item -Wmemset-transposed-args
6446 @opindex Wmemset-transposed-args
6447 @opindex Wno-memset-transposed-args
6448 Warn for suspicious calls to the @code{memset} built-in function, if the
6449 second argument is not zero and the third argument is zero. This warns e.g.@
6450 about @code{memset (buf, sizeof buf, 0)} where most probably
6451 @code{memset (buf, 0, sizeof buf)} was meant instead. The diagnostics
6452 is only emitted if the third argument is literal zero. If it is some
6453 expression that is folded to zero, a cast of zero to some type, etc.,
6454 it is far less likely that the user has mistakenly exchanged the arguments
6455 and no warning is emitted. This warning is enabled by @option{-Wall}.
6459 @opindex Wno-address
6460 Warn about suspicious uses of memory addresses. These include using
6461 the address of a function in a conditional expression, such as
6462 @code{void func(void); if (func)}, and comparisons against the memory
6463 address of a string literal, such as @code{if (x == "abc")}. Such
6464 uses typically indicate a programmer error: the address of a function
6465 always evaluates to true, so their use in a conditional usually
6466 indicate that the programmer forgot the parentheses in a function
6467 call; and comparisons against string literals result in unspecified
6468 behavior and are not portable in C, so they usually indicate that the
6469 programmer intended to use @code{strcmp}. This warning is enabled by
6473 @opindex Wlogical-op
6474 @opindex Wno-logical-op
6475 Warn about suspicious uses of logical operators in expressions.
6476 This includes using logical operators in contexts where a
6477 bit-wise operator is likely to be expected. Also warns when
6478 the operands of a logical operator are the same:
6481 if (a < 0 && a < 0) @{ @dots{} @}
6484 @item -Wlogical-not-parentheses
6485 @opindex Wlogical-not-parentheses
6486 @opindex Wno-logical-not-parentheses
6487 Warn about logical not used on the left hand side operand of a comparison.
6488 This option does not warn if the right operand is considered to be a boolean
6489 expression. Its purpose is to detect suspicious code like the following:
6493 if (!a > 1) @{ @dots{} @}
6496 It is possible to suppress the warning by wrapping the LHS into
6499 if ((!a) > 1) @{ @dots{} @}
6502 This warning is enabled by @option{-Wall}.
6504 @item -Waggregate-return
6505 @opindex Waggregate-return
6506 @opindex Wno-aggregate-return
6507 Warn if any functions that return structures or unions are defined or
6508 called. (In languages where you can return an array, this also elicits
6511 @item -Wno-aggressive-loop-optimizations
6512 @opindex Wno-aggressive-loop-optimizations
6513 @opindex Waggressive-loop-optimizations
6514 Warn if in a loop with constant number of iterations the compiler detects
6515 undefined behavior in some statement during one or more of the iterations.
6517 @item -Wno-attributes
6518 @opindex Wno-attributes
6519 @opindex Wattributes
6520 Do not warn if an unexpected @code{__attribute__} is used, such as
6521 unrecognized attributes, function attributes applied to variables,
6522 etc. This does not stop errors for incorrect use of supported
6525 @item -Wno-builtin-declaration-mismatch
6526 @opindex Wno-builtin-declaration-mismatch
6527 @opindex Wbuiltin-declaration-mismatch
6528 Warn if a built-in function is declared with the wrong signature or
6530 This warning is enabled by default.
6532 @item -Wno-builtin-macro-redefined
6533 @opindex Wno-builtin-macro-redefined
6534 @opindex Wbuiltin-macro-redefined
6535 Do not warn if certain built-in macros are redefined. This suppresses
6536 warnings for redefinition of @code{__TIMESTAMP__}, @code{__TIME__},
6537 @code{__DATE__}, @code{__FILE__}, and @code{__BASE_FILE__}.
6539 @item -Wstrict-prototypes @r{(C and Objective-C only)}
6540 @opindex Wstrict-prototypes
6541 @opindex Wno-strict-prototypes
6542 Warn if a function is declared or defined without specifying the
6543 argument types. (An old-style function definition is permitted without
6544 a warning if preceded by a declaration that specifies the argument
6547 @item -Wold-style-declaration @r{(C and Objective-C only)}
6548 @opindex Wold-style-declaration
6549 @opindex Wno-old-style-declaration
6550 Warn for obsolescent usages, according to the C Standard, in a
6551 declaration. For example, warn if storage-class specifiers like
6552 @code{static} are not the first things in a declaration. This warning
6553 is also enabled by @option{-Wextra}.
6555 @item -Wold-style-definition @r{(C and Objective-C only)}
6556 @opindex Wold-style-definition
6557 @opindex Wno-old-style-definition
6558 Warn if an old-style function definition is used. A warning is given
6559 even if there is a previous prototype.
6561 @item -Wmissing-parameter-type @r{(C and Objective-C only)}
6562 @opindex Wmissing-parameter-type
6563 @opindex Wno-missing-parameter-type
6564 A function parameter is declared without a type specifier in K&R-style
6571 This warning is also enabled by @option{-Wextra}.
6573 @item -Wmissing-prototypes @r{(C and Objective-C only)}
6574 @opindex Wmissing-prototypes
6575 @opindex Wno-missing-prototypes
6576 Warn if a global function is defined without a previous prototype
6577 declaration. This warning is issued even if the definition itself
6578 provides a prototype. Use this option to detect global functions
6579 that do not have a matching prototype declaration in a header file.
6580 This option is not valid for C++ because all function declarations
6581 provide prototypes and a non-matching declaration declares an
6582 overload rather than conflict with an earlier declaration.
6583 Use @option{-Wmissing-declarations} to detect missing declarations in C++.
6585 @item -Wmissing-declarations
6586 @opindex Wmissing-declarations
6587 @opindex Wno-missing-declarations
6588 Warn if a global function is defined without a previous declaration.
6589 Do so even if the definition itself provides a prototype.
6590 Use this option to detect global functions that are not declared in
6591 header files. In C, no warnings are issued for functions with previous
6592 non-prototype declarations; use @option{-Wmissing-prototypes} to detect
6593 missing prototypes. In C++, no warnings are issued for function templates,
6594 or for inline functions, or for functions in anonymous namespaces.
6596 @item -Wmissing-field-initializers
6597 @opindex Wmissing-field-initializers
6598 @opindex Wno-missing-field-initializers
6602 Warn if a structure's initializer has some fields missing. For
6603 example, the following code causes such a warning, because
6604 @code{x.h} is implicitly zero:
6607 struct s @{ int f, g, h; @};
6608 struct s x = @{ 3, 4 @};
6611 This option does not warn about designated initializers, so the following
6612 modification does not trigger a warning:
6615 struct s @{ int f, g, h; @};
6616 struct s x = @{ .f = 3, .g = 4 @};
6619 In C this option does not warn about the universal zero initializer
6623 struct s @{ int f, g, h; @};
6624 struct s x = @{ 0 @};
6627 Likewise, in C++ this option does not warn about the empty @{ @}
6628 initializer, for example:
6631 struct s @{ int f, g, h; @};
6635 This warning is included in @option{-Wextra}. To get other @option{-Wextra}
6636 warnings without this one, use @option{-Wextra -Wno-missing-field-initializers}.
6638 @item -Wno-multichar
6639 @opindex Wno-multichar
6641 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
6642 Usually they indicate a typo in the user's code, as they have
6643 implementation-defined values, and should not be used in portable code.
6645 @item -Wnormalized=@r{[}none@r{|}id@r{|}nfc@r{|}nfkc@r{]}
6646 @opindex Wnormalized=
6647 @opindex Wnormalized
6648 @opindex Wno-normalized
6651 @cindex character set, input normalization
6652 In ISO C and ISO C++, two identifiers are different if they are
6653 different sequences of characters. However, sometimes when characters
6654 outside the basic ASCII character set are used, you can have two
6655 different character sequences that look the same. To avoid confusion,
6656 the ISO 10646 standard sets out some @dfn{normalization rules} which
6657 when applied ensure that two sequences that look the same are turned into
6658 the same sequence. GCC can warn you if you are using identifiers that
6659 have not been normalized; this option controls that warning.
6661 There are four levels of warning supported by GCC@. The default is
6662 @option{-Wnormalized=nfc}, which warns about any identifier that is
6663 not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the
6664 recommended form for most uses. It is equivalent to
6665 @option{-Wnormalized}.
6667 Unfortunately, there are some characters allowed in identifiers by
6668 ISO C and ISO C++ that, when turned into NFC, are not allowed in
6669 identifiers. That is, there's no way to use these symbols in portable
6670 ISO C or C++ and have all your identifiers in NFC@.
6671 @option{-Wnormalized=id} suppresses the warning for these characters.
6672 It is hoped that future versions of the standards involved will correct
6673 this, which is why this option is not the default.
6675 You can switch the warning off for all characters by writing
6676 @option{-Wnormalized=none} or @option{-Wno-normalized}. You should
6677 only do this if you are using some other normalization scheme (like
6678 ``D''), because otherwise you can easily create bugs that are
6679 literally impossible to see.
6681 Some characters in ISO 10646 have distinct meanings but look identical
6682 in some fonts or display methodologies, especially once formatting has
6683 been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL
6684 LETTER N'', displays just like a regular @code{n} that has been
6685 placed in a superscript. ISO 10646 defines the @dfn{NFKC}
6686 normalization scheme to convert all these into a standard form as
6687 well, and GCC warns if your code is not in NFKC if you use
6688 @option{-Wnormalized=nfkc}. This warning is comparable to warning
6689 about every identifier that contains the letter O because it might be
6690 confused with the digit 0, and so is not the default, but may be
6691 useful as a local coding convention if the programming environment
6692 cannot be fixed to display these characters distinctly.
6694 @item -Wno-deprecated
6695 @opindex Wno-deprecated
6696 @opindex Wdeprecated
6697 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
6699 @item -Wno-deprecated-declarations
6700 @opindex Wno-deprecated-declarations
6701 @opindex Wdeprecated-declarations
6702 Do not warn about uses of functions (@pxref{Function Attributes}),
6703 variables (@pxref{Variable Attributes}), and types (@pxref{Type
6704 Attributes}) marked as deprecated by using the @code{deprecated}
6708 @opindex Wno-overflow
6710 Do not warn about compile-time overflow in constant expressions.
6715 Warn about One Definition Rule violations during link-time optimization.
6716 Requires @option{-flto-odr-type-merging} to be enabled. Enabled by default.
6719 @opindex Wopenm-simd
6720 Warn if the vectorizer cost model overrides the OpenMP
6721 simd directive set by user. The @option{-fsimd-cost-model=unlimited}
6722 option can be used to relax the cost model.
6724 @item -Woverride-init @r{(C and Objective-C only)}
6725 @opindex Woverride-init
6726 @opindex Wno-override-init
6730 Warn if an initialized field without side effects is overridden when
6731 using designated initializers (@pxref{Designated Inits, , Designated
6734 This warning is included in @option{-Wextra}. To get other
6735 @option{-Wextra} warnings without this one, use @option{-Wextra
6736 -Wno-override-init}.
6738 @item -Woverride-init-side-effects @r{(C and Objective-C only)}
6739 @opindex Woverride-init-side-effects
6740 @opindex Wno-override-init-side-effects
6741 Warn if an initialized field with side effects is overridden when
6742 using designated initializers (@pxref{Designated Inits, , Designated
6743 Initializers}). This warning is enabled by default.
6748 Warn if a structure is given the packed attribute, but the packed
6749 attribute has no effect on the layout or size of the structure.
6750 Such structures may be mis-aligned for little benefit. For
6751 instance, in this code, the variable @code{f.x} in @code{struct bar}
6752 is misaligned even though @code{struct bar} does not itself
6753 have the packed attribute:
6760 @} __attribute__((packed));
6768 @item -Wpacked-bitfield-compat
6769 @opindex Wpacked-bitfield-compat
6770 @opindex Wno-packed-bitfield-compat
6771 The 4.1, 4.2 and 4.3 series of GCC ignore the @code{packed} attribute
6772 on bit-fields of type @code{char}. This has been fixed in GCC 4.4 but
6773 the change can lead to differences in the structure layout. GCC
6774 informs you when the offset of such a field has changed in GCC 4.4.
6775 For example there is no longer a 4-bit padding between field @code{a}
6776 and @code{b} in this structure:
6783 @} __attribute__ ((packed));
6786 This warning is enabled by default. Use
6787 @option{-Wno-packed-bitfield-compat} to disable this warning.
6789 @item -Wpacked-not-aligned @r{(C, C++, Objective-C and Objective-C++ only)}
6790 @opindex Wpacked-not-aligned
6791 @opindex Wno-packed-not-aligned
6792 Warn if a structure field with explicitly specified alignment in a
6793 packed struct or union is misaligned. For example, a warning will
6794 be issued on @code{struct S}, like, @code{warning: alignment 1 of
6795 'struct S' is less than 8}, in this code:
6799 struct __attribute__ ((aligned (8))) S8 @{ char a[8]; @};
6800 struct __attribute__ ((packed)) S @{
6806 This warning is enabled by @option{-Wall}.
6811 Warn if padding is included in a structure, either to align an element
6812 of the structure or to align the whole structure. Sometimes when this
6813 happens it is possible to rearrange the fields of the structure to
6814 reduce the padding and so make the structure smaller.
6816 @item -Wredundant-decls
6817 @opindex Wredundant-decls
6818 @opindex Wno-redundant-decls
6819 Warn if anything is declared more than once in the same scope, even in
6820 cases where multiple declaration is valid and changes nothing.
6824 @opindex Wno-restrict
6825 Warn when an object referenced by a @code{restrict}-qualified parameter
6826 (or, in C++, a @code{__restrict}-qualified parameter) is aliased by another
6827 argument, or when copies between such objects overlap. For example,
6828 the call to the @code{strcpy} function below attempts to truncate the string
6829 by replacing its initial characters with the last four. However, because
6830 the call writes the terminating NUL into @code{a[4]}, the copies overlap and
6831 the call is diagnosed.
6836 char a[] = "abcd1234";
6841 The @option{-Wrestrict} option detects some instances of simple overlap
6842 even without optimization but works best at @option{-O2} and above. It
6843 is included in @option{-Wall}.
6845 @item -Wnested-externs @r{(C and Objective-C only)}
6846 @opindex Wnested-externs
6847 @opindex Wno-nested-externs
6848 Warn if an @code{extern} declaration is encountered within a function.
6850 @item -Wno-inherited-variadic-ctor
6851 @opindex Winherited-variadic-ctor
6852 @opindex Wno-inherited-variadic-ctor
6853 Suppress warnings about use of C++11 inheriting constructors when the
6854 base class inherited from has a C variadic constructor; the warning is
6855 on by default because the ellipsis is not inherited.
6860 Warn if a function that is declared as inline cannot be inlined.
6861 Even with this option, the compiler does not warn about failures to
6862 inline functions declared in system headers.
6864 The compiler uses a variety of heuristics to determine whether or not
6865 to inline a function. For example, the compiler takes into account
6866 the size of the function being inlined and the amount of inlining
6867 that has already been done in the current function. Therefore,
6868 seemingly insignificant changes in the source program can cause the
6869 warnings produced by @option{-Winline} to appear or disappear.
6871 @item -Wno-invalid-offsetof @r{(C++ and Objective-C++ only)}
6872 @opindex Wno-invalid-offsetof
6873 @opindex Winvalid-offsetof
6874 Suppress warnings from applying the @code{offsetof} macro to a non-POD
6875 type. According to the 2014 ISO C++ standard, applying @code{offsetof}
6876 to a non-standard-layout type is undefined. In existing C++ implementations,
6877 however, @code{offsetof} typically gives meaningful results.
6878 This flag is for users who are aware that they are
6879 writing nonportable code and who have deliberately chosen to ignore the
6882 The restrictions on @code{offsetof} may be relaxed in a future version
6883 of the C++ standard.
6885 @item -Wint-in-bool-context
6886 @opindex Wint-in-bool-context
6887 @opindex Wno-int-in-bool-context
6888 Warn for suspicious use of integer values where boolean values are expected,
6889 such as conditional expressions (?:) using non-boolean integer constants in
6890 boolean context, like @code{if (a <= b ? 2 : 3)}. Or left shifting of signed
6891 integers in boolean context, like @code{for (a = 0; 1 << a; a++);}. Likewise
6892 for all kinds of multiplications regardless of the data type.
6893 This warning is enabled by @option{-Wall}.
6895 @item -Wno-int-to-pointer-cast
6896 @opindex Wno-int-to-pointer-cast
6897 @opindex Wint-to-pointer-cast
6898 Suppress warnings from casts to pointer type of an integer of a
6899 different size. In C++, casting to a pointer type of smaller size is
6900 an error. @option{Wint-to-pointer-cast} is enabled by default.
6903 @item -Wno-pointer-to-int-cast @r{(C and Objective-C only)}
6904 @opindex Wno-pointer-to-int-cast
6905 @opindex Wpointer-to-int-cast
6906 Suppress warnings from casts from a pointer to an integer type of a
6910 @opindex Winvalid-pch
6911 @opindex Wno-invalid-pch
6912 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
6913 the search path but cannot be used.
6917 @opindex Wno-long-long
6918 Warn if @code{long long} type is used. This is enabled by either
6919 @option{-Wpedantic} or @option{-Wtraditional} in ISO C90 and C++98
6920 modes. To inhibit the warning messages, use @option{-Wno-long-long}.
6922 @item -Wvariadic-macros
6923 @opindex Wvariadic-macros
6924 @opindex Wno-variadic-macros
6925 Warn if variadic macros are used in ISO C90 mode, or if the GNU
6926 alternate syntax is used in ISO C99 mode. This is enabled by either
6927 @option{-Wpedantic} or @option{-Wtraditional}. To inhibit the warning
6928 messages, use @option{-Wno-variadic-macros}.
6932 @opindex Wno-varargs
6933 Warn upon questionable usage of the macros used to handle variable
6934 arguments like @code{va_start}. This is default. To inhibit the
6935 warning messages, use @option{-Wno-varargs}.
6937 @item -Wvector-operation-performance
6938 @opindex Wvector-operation-performance
6939 @opindex Wno-vector-operation-performance
6940 Warn if vector operation is not implemented via SIMD capabilities of the
6941 architecture. Mainly useful for the performance tuning.
6942 Vector operation can be implemented @code{piecewise}, which means that the
6943 scalar operation is performed on every vector element;
6944 @code{in parallel}, which means that the vector operation is implemented
6945 using scalars of wider type, which normally is more performance efficient;
6946 and @code{as a single scalar}, which means that vector fits into a
6949 @item -Wno-virtual-move-assign
6950 @opindex Wvirtual-move-assign
6951 @opindex Wno-virtual-move-assign
6952 Suppress warnings about inheriting from a virtual base with a
6953 non-trivial C++11 move assignment operator. This is dangerous because
6954 if the virtual base is reachable along more than one path, it is
6955 moved multiple times, which can mean both objects end up in the
6956 moved-from state. If the move assignment operator is written to avoid
6957 moving from a moved-from object, this warning can be disabled.
6962 Warn if a variable-length array is used in the code.
6963 @option{-Wno-vla} prevents the @option{-Wpedantic} warning of
6964 the variable-length array.
6966 @item -Wvla-larger-than=@var{n}
6967 If this option is used, the compiler will warn on uses of
6968 variable-length arrays where the size is either unbounded, or bounded
6969 by an argument that can be larger than @var{n} bytes. This is similar
6970 to how @option{-Walloca-larger-than=@var{n}} works, but with
6971 variable-length arrays.
6973 Note that GCC may optimize small variable-length arrays of a known
6974 value into plain arrays, so this warning may not get triggered for
6977 This warning is not enabled by @option{-Wall}, and is only active when
6978 @option{-ftree-vrp} is active (default for @option{-O2} and above).
6980 See also @option{-Walloca-larger-than=@var{n}}.
6982 @item -Wvolatile-register-var
6983 @opindex Wvolatile-register-var
6984 @opindex Wno-volatile-register-var
6985 Warn if a register variable is declared volatile. The volatile
6986 modifier does not inhibit all optimizations that may eliminate reads
6987 and/or writes to register variables. This warning is enabled by
6990 @item -Wdisabled-optimization
6991 @opindex Wdisabled-optimization
6992 @opindex Wno-disabled-optimization
6993 Warn if a requested optimization pass is disabled. This warning does
6994 not generally indicate that there is anything wrong with your code; it
6995 merely indicates that GCC's optimizers are unable to handle the code
6996 effectively. Often, the problem is that your code is too big or too
6997 complex; GCC refuses to optimize programs when the optimization
6998 itself is likely to take inordinate amounts of time.
7000 @item -Wpointer-sign @r{(C and Objective-C only)}
7001 @opindex Wpointer-sign
7002 @opindex Wno-pointer-sign
7003 Warn for pointer argument passing or assignment with different signedness.
7004 This option is only supported for C and Objective-C@. It is implied by
7005 @option{-Wall} and by @option{-Wpedantic}, which can be disabled with
7006 @option{-Wno-pointer-sign}.
7008 @item -Wstack-protector
7009 @opindex Wstack-protector
7010 @opindex Wno-stack-protector
7011 This option is only active when @option{-fstack-protector} is active. It
7012 warns about functions that are not protected against stack smashing.
7014 @item -Woverlength-strings
7015 @opindex Woverlength-strings
7016 @opindex Wno-overlength-strings
7017 Warn about string constants that are longer than the ``minimum
7018 maximum'' length specified in the C standard. Modern compilers
7019 generally allow string constants that are much longer than the
7020 standard's minimum limit, but very portable programs should avoid
7021 using longer strings.
7023 The limit applies @emph{after} string constant concatenation, and does
7024 not count the trailing NUL@. In C90, the limit was 509 characters; in
7025 C99, it was raised to 4095. C++98 does not specify a normative
7026 minimum maximum, so we do not diagnose overlength strings in C++@.
7028 This option is implied by @option{-Wpedantic}, and can be disabled with
7029 @option{-Wno-overlength-strings}.
7031 @item -Wunsuffixed-float-constants @r{(C and Objective-C only)}
7032 @opindex Wunsuffixed-float-constants
7034 Issue a warning for any floating constant that does not have
7035 a suffix. When used together with @option{-Wsystem-headers} it
7036 warns about such constants in system header files. This can be useful
7037 when preparing code to use with the @code{FLOAT_CONST_DECIMAL64} pragma
7038 from the decimal floating-point extension to C99.
7040 @item -Wno-designated-init @r{(C and Objective-C only)}
7041 Suppress warnings when a positional initializer is used to initialize
7042 a structure that has been marked with the @code{designated_init}
7046 Issue a warning when HSAIL cannot be emitted for the compiled function or
7051 @node Debugging Options
7052 @section Options for Debugging Your Program
7053 @cindex options, debugging
7054 @cindex debugging information options
7056 To tell GCC to emit extra information for use by a debugger, in almost
7057 all cases you need only to add @option{-g} to your other options.
7059 GCC allows you to use @option{-g} with
7060 @option{-O}. The shortcuts taken by optimized code may occasionally
7061 be surprising: some variables you declared may not exist
7062 at all; flow of control may briefly move where you did not expect it;
7063 some statements may not be executed because they compute constant
7064 results or their values are already at hand; some statements may
7065 execute in different places because they have been moved out of loops.
7066 Nevertheless it is possible to debug optimized output. This makes
7067 it reasonable to use the optimizer for programs that might have bugs.
7069 If you are not using some other optimization option, consider
7070 using @option{-Og} (@pxref{Optimize Options}) with @option{-g}.
7071 With no @option{-O} option at all, some compiler passes that collect
7072 information useful for debugging do not run at all, so that
7073 @option{-Og} may result in a better debugging experience.
7078 Produce debugging information in the operating system's native format
7079 (stabs, COFF, XCOFF, or DWARF)@. GDB can work with this debugging
7082 On most systems that use stabs format, @option{-g} enables use of extra
7083 debugging information that only GDB can use; this extra information
7084 makes debugging work better in GDB but probably makes other debuggers
7086 refuse to read the program. If you want to control for certain whether
7087 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
7088 @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
7092 Produce debugging information for use by GDB@. This means to use the
7093 most expressive format available (DWARF, stabs, or the native format
7094 if neither of those are supported), including GDB extensions if at all
7098 @itemx -gdwarf-@var{version}
7100 Produce debugging information in DWARF format (if that is supported).
7101 The value of @var{version} may be either 2, 3, 4 or 5; the default version
7102 for most targets is 4. DWARF Version 5 is only experimental.
7104 Note that with DWARF Version 2, some ports require and always
7105 use some non-conflicting DWARF 3 extensions in the unwind tables.
7107 Version 4 may require GDB 7.0 and @option{-fvar-tracking-assignments}
7108 for maximum benefit.
7110 GCC no longer supports DWARF Version 1, which is substantially
7111 different than Version 2 and later. For historical reasons, some
7112 other DWARF-related options such as
7113 @option{-fno-dwarf2-cfi-asm}) retain a reference to DWARF Version 2
7114 in their names, but apply to all currently-supported versions of DWARF.
7118 Produce debugging information in stabs format (if that is supported),
7119 without GDB extensions. This is the format used by DBX on most BSD
7120 systems. On MIPS, Alpha and System V Release 4 systems this option
7121 produces stabs debugging output that is not understood by DBX@.
7122 On System V Release 4 systems this option requires the GNU assembler.
7126 Produce debugging information in stabs format (if that is supported),
7127 using GNU extensions understood only by the GNU debugger (GDB)@. The
7128 use of these extensions is likely to make other debuggers crash or
7129 refuse to read the program.
7133 Produce debugging information in XCOFF format (if that is supported).
7134 This is the format used by the DBX debugger on IBM RS/6000 systems.
7138 Produce debugging information in XCOFF format (if that is supported),
7139 using GNU extensions understood only by the GNU debugger (GDB)@. The
7140 use of these extensions is likely to make other debuggers crash or
7141 refuse to read the program, and may cause assemblers other than the GNU
7142 assembler (GAS) to fail with an error.
7146 Produce debugging information in Alpha/VMS debug format (if that is
7147 supported). This is the format used by DEBUG on Alpha/VMS systems.
7150 @itemx -ggdb@var{level}
7151 @itemx -gstabs@var{level}
7152 @itemx -gxcoff@var{level}
7153 @itemx -gvms@var{level}
7154 Request debugging information and also use @var{level} to specify how
7155 much information. The default level is 2.
7157 Level 0 produces no debug information at all. Thus, @option{-g0} negates
7160 Level 1 produces minimal information, enough for making backtraces in
7161 parts of the program that you don't plan to debug. This includes
7162 descriptions of functions and external variables, and line number
7163 tables, but no information about local variables.
7165 Level 3 includes extra information, such as all the macro definitions
7166 present in the program. Some debuggers support macro expansion when
7167 you use @option{-g3}.
7169 @option{-gdwarf} does not accept a concatenated debug level, to avoid
7170 confusion with @option{-gdwarf-@var{level}}.
7171 Instead use an additional @option{-g@var{level}} option to change the
7172 debug level for DWARF.
7174 @item -feliminate-unused-debug-symbols
7175 @opindex feliminate-unused-debug-symbols
7176 Produce debugging information in stabs format (if that is supported),
7177 for only symbols that are actually used.
7179 @item -femit-class-debug-always
7180 @opindex femit-class-debug-always
7181 Instead of emitting debugging information for a C++ class in only one
7182 object file, emit it in all object files using the class. This option
7183 should be used only with debuggers that are unable to handle the way GCC
7184 normally emits debugging information for classes because using this
7185 option increases the size of debugging information by as much as a
7188 @item -fno-merge-debug-strings
7189 @opindex fmerge-debug-strings
7190 @opindex fno-merge-debug-strings
7191 Direct the linker to not merge together strings in the debugging
7192 information that are identical in different object files. Merging is
7193 not supported by all assemblers or linkers. Merging decreases the size
7194 of the debug information in the output file at the cost of increasing
7195 link processing time. Merging is enabled by default.
7197 @item -fdebug-prefix-map=@var{old}=@var{new}
7198 @opindex fdebug-prefix-map
7199 When compiling files residing in directory @file{@var{old}}, record
7200 debugging information describing them as if the files resided in
7201 directory @file{@var{new}} instead. This can be used to replace a
7202 build-time path with an install-time path in the debug info. It can
7203 also be used to change an absolute path to a relative path by using
7204 @file{.} for @var{new}. This can give more reproducible builds, which
7205 are location independent, but may require an extra command to tell GDB
7206 where to find the source files. See also @option{-ffile-prefix-map}.
7208 @item -fvar-tracking
7209 @opindex fvar-tracking
7210 Run variable tracking pass. It computes where variables are stored at each
7211 position in code. Better debugging information is then generated
7212 (if the debugging information format supports this information).
7214 It is enabled by default when compiling with optimization (@option{-Os},
7215 @option{-O}, @option{-O2}, @dots{}), debugging information (@option{-g}) and
7216 the debug info format supports it.
7218 @item -fvar-tracking-assignments
7219 @opindex fvar-tracking-assignments
7220 @opindex fno-var-tracking-assignments
7221 Annotate assignments to user variables early in the compilation and
7222 attempt to carry the annotations over throughout the compilation all the
7223 way to the end, in an attempt to improve debug information while
7224 optimizing. Use of @option{-gdwarf-4} is recommended along with it.
7226 It can be enabled even if var-tracking is disabled, in which case
7227 annotations are created and maintained, but discarded at the end.
7228 By default, this flag is enabled together with @option{-fvar-tracking},
7229 except when selective scheduling is enabled.
7232 @opindex gsplit-dwarf
7233 Separate as much DWARF debugging information as possible into a
7234 separate output file with the extension @file{.dwo}. This option allows
7235 the build system to avoid linking files with debug information. To
7236 be useful, this option requires a debugger capable of reading @file{.dwo}
7241 Generate DWARF @code{.debug_pubnames} and @code{.debug_pubtypes} sections.
7243 @item -ggnu-pubnames
7244 @opindex ggnu-pubnames
7245 Generate @code{.debug_pubnames} and @code{.debug_pubtypes} sections in a format
7246 suitable for conversion into a GDB@ index. This option is only useful
7247 with a linker that can produce GDB@ index version 7.
7249 @item -fdebug-types-section
7250 @opindex fdebug-types-section
7251 @opindex fno-debug-types-section
7252 When using DWARF Version 4 or higher, type DIEs can be put into
7253 their own @code{.debug_types} section instead of making them part of the
7254 @code{.debug_info} section. It is more efficient to put them in a separate
7255 comdat sections since the linker can then remove duplicates.
7256 But not all DWARF consumers support @code{.debug_types} sections yet
7257 and on some objects @code{.debug_types} produces larger instead of smaller
7258 debugging information.
7260 @item -grecord-gcc-switches
7261 @itemx -gno-record-gcc-switches
7262 @opindex grecord-gcc-switches
7263 @opindex gno-record-gcc-switches
7264 This switch causes the command-line options used to invoke the
7265 compiler that may affect code generation to be appended to the
7266 DW_AT_producer attribute in DWARF debugging information. The options
7267 are concatenated with spaces separating them from each other and from
7268 the compiler version.
7269 It is enabled by default.
7270 See also @option{-frecord-gcc-switches} for another
7271 way of storing compiler options into the object file.
7273 @item -gstrict-dwarf
7274 @opindex gstrict-dwarf
7275 Disallow using extensions of later DWARF standard version than selected
7276 with @option{-gdwarf-@var{version}}. On most targets using non-conflicting
7277 DWARF extensions from later standard versions is allowed.
7279 @item -gno-strict-dwarf
7280 @opindex gno-strict-dwarf
7281 Allow using extensions of later DWARF standard version than selected with
7282 @option{-gdwarf-@var{version}}.
7284 @item -gas-loc-support
7285 @opindex gas-loc-support
7286 Inform the compiler that the assembler supports @code{.loc} directives.
7287 It may then use them for the assembler to generate DWARF2+ line number
7290 This is generally desirable, because assembler-generated line-number
7291 tables are a lot more compact than those the compiler can generate
7294 This option will be enabled by default if, at GCC configure time, the
7295 assembler was found to support such directives.
7297 @item -gno-as-loc-support
7298 @opindex gno-as-loc-support
7299 Force GCC to generate DWARF2+ line number tables internally, if DWARF2+
7300 line number tables are to be generated.
7302 @item gas-locview-support
7303 @opindex gas-locview-support
7304 Inform the compiler that the assembler supports @code{view} assignment
7305 and reset assertion checking in @code{.loc} directives.
7307 This option will be enabled by default if, at GCC configure time, the
7308 assembler was found to support them.
7310 @item gno-as-locview-support
7311 Force GCC to assign view numbers internally, if
7312 @option{-gvariable-location-views} are explicitly requested.
7315 @itemx -gno-column-info
7316 @opindex gcolumn-info
7317 @opindex gno-column-info
7318 Emit location column information into DWARF debugging information, rather
7319 than just file and line.
7320 This option is enabled by default.
7322 @item -gstatement-frontiers
7323 @itemx -gno-statement-frontiers
7324 @opindex gstatement-frontiers
7325 @opindex gno-statement-frontiers
7326 This option causes GCC to create markers in the internal representation
7327 at the beginning of statements, and to keep them roughly in place
7328 throughout compilation, using them to guide the output of @code{is_stmt}
7329 markers in the line number table. This is enabled by default when
7330 compiling with optimization (@option{-Os}, @option{-O}, @option{-O2},
7331 @dots{}), and outputting DWARF 2 debug information at the normal level.
7333 @item -gvariable-location-views
7334 @itemx -gvariable-location-views=incompat5
7335 @itemx -gno-variable-location-views
7336 @opindex gvariable-location-views
7337 @opindex gvariable-location-views=incompat5
7338 @opindex gno-variable-location-views
7339 Augment variable location lists with progressive view numbers implied
7340 from the line number table. This enables debug information consumers to
7341 inspect state at certain points of the program, even if no instructions
7342 associated with the corresponding source locations are present at that
7343 point. If the assembler lacks support for view numbers in line number
7344 tables, this will cause the compiler to emit the line number table,
7345 which generally makes them somewhat less compact. The augmented line
7346 number tables and location lists are fully backward-compatible, so they
7347 can be consumed by debug information consumers that are not aware of
7348 these augmentations, but they won't derive any benefit from them either.
7350 This is enabled by default when outputting DWARF 2 debug information at
7351 the normal level, as long as there is assembler support,
7352 @option{-fvar-tracking-assignments} is enabled and
7353 @option{-gstrict-dwarf} is not. When assembler support is not
7354 available, this may still be enabled, but it will force GCC to output
7355 internal line number tables, and if
7356 @option{-ginternal-reset-location-views} is not enabled, that will most
7357 certainly lead to silently mismatching location views.
7359 There is a proposed representation for view numbers that is not backward
7360 compatible with the location list format introduced in DWARF 5, that can
7361 be enabled with @option{-gvariable-location-views=incompat5}. This
7362 option may be removed in the future, is only provided as a reference
7363 implementation of the proposed representation. Debug information
7364 consumers are not expected to support this extended format, and they
7365 would be rendered unable to decode location lists using it.
7367 @item -ginternal-reset-location-views
7368 @itemx -gnointernal-reset-location-views
7369 @opindex ginternal-reset-location-views
7370 @opindex gno-internal-reset-location-views
7371 Attempt to determine location views that can be omitted from location
7372 view lists. This requires the compiler to have very accurate insn
7373 length estimates, which isn't always the case, and it may cause
7374 incorrect view lists to be generated silently when using an assembler
7375 that does not support location view lists. The GNU assembler will flag
7376 any such error as a @code{view number mismatch}. This is only enabled
7377 on ports that define a reliable estimation function.
7379 @item -ginline-points
7380 @itemx -gno-inline-points
7381 @opindex ginline-points
7382 @opindex gno-inline-points
7383 Generate extended debug information for inlined functions. Location
7384 view tracking markers are inserted at inlined entry points, so that
7385 address and view numbers can be computed and output in debug
7386 information. This can be enabled independently of location views, in
7387 which case the view numbers won't be output, but it can only be enabled
7388 along with statement frontiers, and it is only enabled by default if
7389 location views are enabled.
7391 @item -gz@r{[}=@var{type}@r{]}
7393 Produce compressed debug sections in DWARF format, if that is supported.
7394 If @var{type} is not given, the default type depends on the capabilities
7395 of the assembler and linker used. @var{type} may be one of
7396 @samp{none} (don't compress debug sections), @samp{zlib} (use zlib
7397 compression in ELF gABI format), or @samp{zlib-gnu} (use zlib
7398 compression in traditional GNU format). If the linker doesn't support
7399 writing compressed debug sections, the option is rejected. Otherwise,
7400 if the assembler does not support them, @option{-gz} is silently ignored
7401 when producing object files.
7403 @item -femit-struct-debug-baseonly
7404 @opindex femit-struct-debug-baseonly
7405 Emit debug information for struct-like types
7406 only when the base name of the compilation source file
7407 matches the base name of file in which the struct is defined.
7409 This option substantially reduces the size of debugging information,
7410 but at significant potential loss in type information to the debugger.
7411 See @option{-femit-struct-debug-reduced} for a less aggressive option.
7412 See @option{-femit-struct-debug-detailed} for more detailed control.
7414 This option works only with DWARF debug output.
7416 @item -femit-struct-debug-reduced
7417 @opindex femit-struct-debug-reduced
7418 Emit debug information for struct-like types
7419 only when the base name of the compilation source file
7420 matches the base name of file in which the type is defined,
7421 unless the struct is a template or defined in a system header.
7423 This option significantly reduces the size of debugging information,
7424 with some potential loss in type information to the debugger.
7425 See @option{-femit-struct-debug-baseonly} for a more aggressive option.
7426 See @option{-femit-struct-debug-detailed} for more detailed control.
7428 This option works only with DWARF debug output.
7430 @item -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]}
7431 @opindex femit-struct-debug-detailed
7432 Specify the struct-like types
7433 for which the compiler generates debug information.
7434 The intent is to reduce duplicate struct debug information
7435 between different object files within the same program.
7437 This option is a detailed version of
7438 @option{-femit-struct-debug-reduced} and @option{-femit-struct-debug-baseonly},
7439 which serves for most needs.
7441 A specification has the syntax@*
7442 [@samp{dir:}|@samp{ind:}][@samp{ord:}|@samp{gen:}](@samp{any}|@samp{sys}|@samp{base}|@samp{none})
7444 The optional first word limits the specification to
7445 structs that are used directly (@samp{dir:}) or used indirectly (@samp{ind:}).
7446 A struct type is used directly when it is the type of a variable, member.
7447 Indirect uses arise through pointers to structs.
7448 That is, when use of an incomplete struct is valid, the use is indirect.
7450 @samp{struct one direct; struct two * indirect;}.
7452 The optional second word limits the specification to
7453 ordinary structs (@samp{ord:}) or generic structs (@samp{gen:}).
7454 Generic structs are a bit complicated to explain.
7455 For C++, these are non-explicit specializations of template classes,
7456 or non-template classes within the above.
7457 Other programming languages have generics,
7458 but @option{-femit-struct-debug-detailed} does not yet implement them.
7460 The third word specifies the source files for those
7461 structs for which the compiler should emit debug information.
7462 The values @samp{none} and @samp{any} have the normal meaning.
7463 The value @samp{base} means that
7464 the base of name of the file in which the type declaration appears
7465 must match the base of the name of the main compilation file.
7466 In practice, this means that when compiling @file{foo.c}, debug information
7467 is generated for types declared in that file and @file{foo.h},
7468 but not other header files.
7469 The value @samp{sys} means those types satisfying @samp{base}
7470 or declared in system or compiler headers.
7472 You may need to experiment to determine the best settings for your application.
7474 The default is @option{-femit-struct-debug-detailed=all}.
7476 This option works only with DWARF debug output.
7478 @item -fno-dwarf2-cfi-asm
7479 @opindex fdwarf2-cfi-asm
7480 @opindex fno-dwarf2-cfi-asm
7481 Emit DWARF unwind info as compiler generated @code{.eh_frame} section
7482 instead of using GAS @code{.cfi_*} directives.
7484 @item -fno-eliminate-unused-debug-types
7485 @opindex feliminate-unused-debug-types
7486 @opindex fno-eliminate-unused-debug-types
7487 Normally, when producing DWARF output, GCC avoids producing debug symbol
7488 output for types that are nowhere used in the source file being compiled.
7489 Sometimes it is useful to have GCC emit debugging
7490 information for all types declared in a compilation
7491 unit, regardless of whether or not they are actually used
7492 in that compilation unit, for example
7493 if, in the debugger, you want to cast a value to a type that is
7494 not actually used in your program (but is declared). More often,
7495 however, this results in a significant amount of wasted space.
7498 @node Optimize Options
7499 @section Options That Control Optimization
7500 @cindex optimize options
7501 @cindex options, optimization
7503 These options control various sorts of optimizations.
7505 Without any optimization option, the compiler's goal is to reduce the
7506 cost of compilation and to make debugging produce the expected
7507 results. Statements are independent: if you stop the program with a
7508 breakpoint between statements, you can then assign a new value to any
7509 variable or change the program counter to any other statement in the
7510 function and get exactly the results you expect from the source
7513 Turning on optimization flags makes the compiler attempt to improve
7514 the performance and/or code size at the expense of compilation time
7515 and possibly the ability to debug the program.
7517 The compiler performs optimization based on the knowledge it has of the
7518 program. Compiling multiple files at once to a single output file mode allows
7519 the compiler to use information gained from all of the files when compiling
7522 Not all optimizations are controlled directly by a flag. Only
7523 optimizations that have a flag are listed in this section.
7525 Most optimizations are only enabled if an @option{-O} level is set on
7526 the command line. Otherwise they are disabled, even if individual
7527 optimization flags are specified.
7529 Depending on the target and how GCC was configured, a slightly different
7530 set of optimizations may be enabled at each @option{-O} level than
7531 those listed here. You can invoke GCC with @option{-Q --help=optimizers}
7532 to find out the exact set of optimizations that are enabled at each level.
7533 @xref{Overall Options}, for examples.
7540 Optimize. Optimizing compilation takes somewhat more time, and a lot
7541 more memory for a large function.
7543 With @option{-O}, the compiler tries to reduce code size and execution
7544 time, without performing any optimizations that take a great deal of
7547 @option{-O} turns on the following optimization flags:
7550 -fbranch-count-reg @gol
7551 -fcombine-stack-adjustments @gol
7553 -fcprop-registers @gol
7556 -fdelayed-branch @gol
7558 -fforward-propagate @gol
7559 -fguess-branch-probability @gol
7560 -fif-conversion2 @gol
7561 -fif-conversion @gol
7562 -finline-functions-called-once @gol
7563 -fipa-pure-const @gol
7565 -fipa-reference @gol
7566 -fmerge-constants @gol
7567 -fmove-loop-invariants @gol
7568 -fomit-frame-pointer @gol
7569 -freorder-blocks @gol
7571 -fshrink-wrap-separate @gol
7572 -fsplit-wide-types @gol
7578 -ftree-coalesce-vars @gol
7579 -ftree-copy-prop @gol
7581 -ftree-dominator-opts @gol
7583 -ftree-forwprop @gol
7595 Optimize even more. GCC performs nearly all supported optimizations
7596 that do not involve a space-speed tradeoff.
7597 As compared to @option{-O}, this option increases both compilation time
7598 and the performance of the generated code.
7600 @option{-O2} turns on all optimization flags specified by @option{-O}. It
7601 also turns on the following optimization flags:
7602 @gccoptlist{-fthread-jumps @gol
7603 -falign-functions -falign-jumps @gol
7604 -falign-loops -falign-labels @gol
7607 -fcse-follow-jumps -fcse-skip-blocks @gol
7608 -fdelete-null-pointer-checks @gol
7609 -fdevirtualize -fdevirtualize-speculatively @gol
7610 -fexpensive-optimizations @gol
7611 -fgcse -fgcse-lm @gol
7612 -fhoist-adjacent-loads @gol
7613 -finline-small-functions @gol
7614 -findirect-inlining @gol
7620 -fisolate-erroneous-paths-dereference @gol
7622 -foptimize-sibling-calls @gol
7623 -foptimize-strlen @gol
7624 -fpartial-inlining @gol
7626 -freorder-blocks-algorithm=stc @gol
7627 -freorder-blocks-and-partition -freorder-functions @gol
7628 -frerun-cse-after-loop @gol
7629 -fsched-interblock -fsched-spec @gol
7630 -fschedule-insns -fschedule-insns2 @gol
7631 -fstore-merging @gol
7632 -fstrict-aliasing @gol
7633 -ftree-builtin-call-dce @gol
7634 -ftree-switch-conversion -ftree-tail-merge @gol
7635 -fcode-hoisting @gol
7640 Please note the warning under @option{-fgcse} about
7641 invoking @option{-O2} on programs that use computed gotos.
7645 Optimize yet more. @option{-O3} turns on all optimizations specified
7646 by @option{-O2} and also turns on the following optimization flags:
7647 @gccoptlist{-finline-functions @gol
7648 -funswitch-loops @gol
7649 -fpredictive-commoning @gol
7650 -fgcse-after-reload @gol
7651 -ftree-loop-vectorize @gol
7652 -ftree-loop-distribution @gol
7653 -ftree-loop-distribute-patterns @gol
7654 -floop-interchange @gol
7655 -floop-unroll-and-jam @gol
7657 -ftree-slp-vectorize @gol
7658 -fvect-cost-model @gol
7659 -ftree-partial-pre @gol
7665 Reduce compilation time and make debugging produce the expected
7666 results. This is the default.
7670 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
7671 do not typically increase code size. It also performs further
7672 optimizations designed to reduce code size.
7674 @option{-Os} disables the following optimization flags:
7675 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
7676 -falign-labels -freorder-blocks -freorder-blocks-algorithm=stc @gol
7677 -freorder-blocks-and-partition -fprefetch-loop-arrays}
7681 Disregard strict standards compliance. @option{-Ofast} enables all
7682 @option{-O3} optimizations. It also enables optimizations that are not
7683 valid for all standard-compliant programs.
7684 It turns on @option{-ffast-math} and the Fortran-specific
7685 @option{-fstack-arrays}, unless @option{-fmax-stack-var-size} is
7686 specified, and @option{-fno-protect-parens}.
7690 Optimize debugging experience. @option{-Og} enables optimizations
7691 that do not interfere with debugging. It should be the optimization
7692 level of choice for the standard edit-compile-debug cycle, offering
7693 a reasonable level of optimization while maintaining fast compilation
7694 and a good debugging experience.
7697 If you use multiple @option{-O} options, with or without level numbers,
7698 the last such option is the one that is effective.
7700 Options of the form @option{-f@var{flag}} specify machine-independent
7701 flags. Most flags have both positive and negative forms; the negative
7702 form of @option{-ffoo} is @option{-fno-foo}. In the table
7703 below, only one of the forms is listed---the one you typically
7704 use. You can figure out the other form by either removing @samp{no-}
7707 The following options control specific optimizations. They are either
7708 activated by @option{-O} options or are related to ones that are. You
7709 can use the following flags in the rare cases when ``fine-tuning'' of
7710 optimizations to be performed is desired.
7713 @item -fno-defer-pop
7714 @opindex fno-defer-pop
7715 Always pop the arguments to each function call as soon as that function
7716 returns. For machines that must pop arguments after a function call,
7717 the compiler normally lets arguments accumulate on the stack for several
7718 function calls and pops them all at once.
7720 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
7722 @item -fforward-propagate
7723 @opindex fforward-propagate
7724 Perform a forward propagation pass on RTL@. The pass tries to combine two
7725 instructions and checks if the result can be simplified. If loop unrolling
7726 is active, two passes are performed and the second is scheduled after
7729 This option is enabled by default at optimization levels @option{-O},
7730 @option{-O2}, @option{-O3}, @option{-Os}.
7732 @item -ffp-contract=@var{style}
7733 @opindex ffp-contract
7734 @option{-ffp-contract=off} disables floating-point expression contraction.
7735 @option{-ffp-contract=fast} enables floating-point expression contraction
7736 such as forming of fused multiply-add operations if the target has
7737 native support for them.
7738 @option{-ffp-contract=on} enables floating-point expression contraction
7739 if allowed by the language standard. This is currently not implemented
7740 and treated equal to @option{-ffp-contract=off}.
7742 The default is @option{-ffp-contract=fast}.
7744 @item -fomit-frame-pointer
7745 @opindex fomit-frame-pointer
7746 Omit the frame pointer in functions that don't need one. This avoids the
7747 instructions to save, set up and restore the frame pointer; on many targets
7748 it also makes an extra register available.
7750 On some targets this flag has no effect because the standard calling sequence
7751 always uses a frame pointer, so it cannot be omitted.
7753 Note that @option{-fno-omit-frame-pointer} doesn't guarantee the frame pointer
7754 is used in all functions. Several targets always omit the frame pointer in
7757 Enabled by default at @option{-O} and higher.
7759 @item -foptimize-sibling-calls
7760 @opindex foptimize-sibling-calls
7761 Optimize sibling and tail recursive calls.
7763 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
7765 @item -foptimize-strlen
7766 @opindex foptimize-strlen
7767 Optimize various standard C string functions (e.g. @code{strlen},
7768 @code{strchr} or @code{strcpy}) and
7769 their @code{_FORTIFY_SOURCE} counterparts into faster alternatives.
7771 Enabled at levels @option{-O2}, @option{-O3}.
7775 Do not expand any functions inline apart from those marked with
7776 the @code{always_inline} attribute. This is the default when not
7779 Single functions can be exempted from inlining by marking them
7780 with the @code{noinline} attribute.
7782 @item -finline-small-functions
7783 @opindex finline-small-functions
7784 Integrate functions into their callers when their body is smaller than expected
7785 function call code (so overall size of program gets smaller). The compiler
7786 heuristically decides which functions are simple enough to be worth integrating
7787 in this way. This inlining applies to all functions, even those not declared
7790 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
7792 @item -findirect-inlining
7793 @opindex findirect-inlining
7794 Inline also indirect calls that are discovered to be known at compile
7795 time thanks to previous inlining. This option has any effect only
7796 when inlining itself is turned on by the @option{-finline-functions}
7797 or @option{-finline-small-functions} options.
7799 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
7801 @item -finline-functions
7802 @opindex finline-functions
7803 Consider all functions for inlining, even if they are not declared inline.
7804 The compiler heuristically decides which functions are worth integrating
7807 If all calls to a given function are integrated, and the function is
7808 declared @code{static}, then the function is normally not output as
7809 assembler code in its own right.
7811 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
7813 @item -finline-functions-called-once
7814 @opindex finline-functions-called-once
7815 Consider all @code{static} functions called once for inlining into their
7816 caller even if they are not marked @code{inline}. If a call to a given
7817 function is integrated, then the function is not output as assembler code
7820 Enabled at levels @option{-O1}, @option{-O2}, @option{-O3} and @option{-Os}.
7822 @item -fearly-inlining
7823 @opindex fearly-inlining
7824 Inline functions marked by @code{always_inline} and functions whose body seems
7825 smaller than the function call overhead early before doing
7826 @option{-fprofile-generate} instrumentation and real inlining pass. Doing so
7827 makes profiling significantly cheaper and usually inlining faster on programs
7828 having large chains of nested wrapper functions.
7834 Perform interprocedural scalar replacement of aggregates, removal of
7835 unused parameters and replacement of parameters passed by reference
7836 by parameters passed by value.
7838 Enabled at levels @option{-O2}, @option{-O3} and @option{-Os}.
7840 @item -finline-limit=@var{n}
7841 @opindex finline-limit
7842 By default, GCC limits the size of functions that can be inlined. This flag
7843 allows coarse control of this limit. @var{n} is the size of functions that
7844 can be inlined in number of pseudo instructions.
7846 Inlining is actually controlled by a number of parameters, which may be
7847 specified individually by using @option{--param @var{name}=@var{value}}.
7848 The @option{-finline-limit=@var{n}} option sets some of these parameters
7852 @item max-inline-insns-single
7853 is set to @var{n}/2.
7854 @item max-inline-insns-auto
7855 is set to @var{n}/2.
7858 See below for a documentation of the individual
7859 parameters controlling inlining and for the defaults of these parameters.
7861 @emph{Note:} there may be no value to @option{-finline-limit} that results
7862 in default behavior.
7864 @emph{Note:} pseudo instruction represents, in this particular context, an
7865 abstract measurement of function's size. In no way does it represent a count
7866 of assembly instructions and as such its exact meaning might change from one
7867 release to an another.
7869 @item -fno-keep-inline-dllexport
7870 @opindex fno-keep-inline-dllexport
7871 This is a more fine-grained version of @option{-fkeep-inline-functions},
7872 which applies only to functions that are declared using the @code{dllexport}
7873 attribute or declspec. @xref{Function Attributes,,Declaring Attributes of
7876 @item -fkeep-inline-functions
7877 @opindex fkeep-inline-functions
7878 In C, emit @code{static} functions that are declared @code{inline}
7879 into the object file, even if the function has been inlined into all
7880 of its callers. This switch does not affect functions using the
7881 @code{extern inline} extension in GNU C90@. In C++, emit any and all
7882 inline functions into the object file.
7884 @item -fkeep-static-functions
7885 @opindex fkeep-static-functions
7886 Emit @code{static} functions into the object file, even if the function
7889 @item -fkeep-static-consts
7890 @opindex fkeep-static-consts
7891 Emit variables declared @code{static const} when optimization isn't turned
7892 on, even if the variables aren't referenced.
7894 GCC enables this option by default. If you want to force the compiler to
7895 check if a variable is referenced, regardless of whether or not
7896 optimization is turned on, use the @option{-fno-keep-static-consts} option.
7898 @item -fmerge-constants
7899 @opindex fmerge-constants
7900 Attempt to merge identical constants (string constants and floating-point
7901 constants) across compilation units.
7903 This option is the default for optimized compilation if the assembler and
7904 linker support it. Use @option{-fno-merge-constants} to inhibit this
7907 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
7909 @item -fmerge-all-constants
7910 @opindex fmerge-all-constants
7911 Attempt to merge identical constants and identical variables.
7913 This option implies @option{-fmerge-constants}. In addition to
7914 @option{-fmerge-constants} this considers e.g.@: even constant initialized
7915 arrays or initialized constant variables with integral or floating-point
7916 types. Languages like C or C++ require each variable, including multiple
7917 instances of the same variable in recursive calls, to have distinct locations,
7918 so using this option results in non-conforming
7921 @item -fmodulo-sched
7922 @opindex fmodulo-sched
7923 Perform swing modulo scheduling immediately before the first scheduling
7924 pass. This pass looks at innermost loops and reorders their
7925 instructions by overlapping different iterations.
7927 @item -fmodulo-sched-allow-regmoves
7928 @opindex fmodulo-sched-allow-regmoves
7929 Perform more aggressive SMS-based modulo scheduling with register moves
7930 allowed. By setting this flag certain anti-dependences edges are
7931 deleted, which triggers the generation of reg-moves based on the
7932 life-range analysis. This option is effective only with
7933 @option{-fmodulo-sched} enabled.
7935 @item -fno-branch-count-reg
7936 @opindex fno-branch-count-reg
7937 Avoid running a pass scanning for opportunities to use ``decrement and
7938 branch'' instructions on a count register instead of generating sequences
7939 of instructions that decrement a register, compare it against zero, and
7940 then branch based upon the result. This option is only meaningful on
7941 architectures that support such instructions, which include x86, PowerPC,
7942 IA-64 and S/390. Note that the @option{-fno-branch-count-reg} option
7943 doesn't remove the decrement and branch instructions from the generated
7944 instruction stream introduced by other optimization passes.
7946 Enabled by default at @option{-O1} and higher.
7948 The default is @option{-fbranch-count-reg}.
7950 @item -fno-function-cse
7951 @opindex fno-function-cse
7952 Do not put function addresses in registers; make each instruction that
7953 calls a constant function contain the function's address explicitly.
7955 This option results in less efficient code, but some strange hacks
7956 that alter the assembler output may be confused by the optimizations
7957 performed when this option is not used.
7959 The default is @option{-ffunction-cse}
7961 @item -fno-zero-initialized-in-bss
7962 @opindex fno-zero-initialized-in-bss
7963 If the target supports a BSS section, GCC by default puts variables that
7964 are initialized to zero into BSS@. This can save space in the resulting
7967 This option turns off this behavior because some programs explicitly
7968 rely on variables going to the data section---e.g., so that the
7969 resulting executable can find the beginning of that section and/or make
7970 assumptions based on that.
7972 The default is @option{-fzero-initialized-in-bss}.
7974 @item -fthread-jumps
7975 @opindex fthread-jumps
7976 Perform optimizations that check to see if a jump branches to a
7977 location where another comparison subsumed by the first is found. If
7978 so, the first branch is redirected to either the destination of the
7979 second branch or a point immediately following it, depending on whether
7980 the condition is known to be true or false.
7982 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
7984 @item -fsplit-wide-types
7985 @opindex fsplit-wide-types
7986 When using a type that occupies multiple registers, such as @code{long
7987 long} on a 32-bit system, split the registers apart and allocate them
7988 independently. This normally generates better code for those types,
7989 but may make debugging more difficult.
7991 Enabled at levels @option{-O}, @option{-O2}, @option{-O3},
7994 @item -fcse-follow-jumps
7995 @opindex fcse-follow-jumps
7996 In common subexpression elimination (CSE), scan through jump instructions
7997 when the target of the jump is not reached by any other path. For
7998 example, when CSE encounters an @code{if} statement with an
7999 @code{else} clause, CSE follows the jump when the condition
8002 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
8004 @item -fcse-skip-blocks
8005 @opindex fcse-skip-blocks
8006 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
8007 follow jumps that conditionally skip over blocks. When CSE
8008 encounters a simple @code{if} statement with no else clause,
8009 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
8010 body of the @code{if}.
8012 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
8014 @item -frerun-cse-after-loop
8015 @opindex frerun-cse-after-loop
8016 Re-run common subexpression elimination after loop optimizations are
8019 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
8023 Perform a global common subexpression elimination pass.
8024 This pass also performs global constant and copy propagation.
8026 @emph{Note:} When compiling a program using computed gotos, a GCC
8027 extension, you may get better run-time performance if you disable
8028 the global common subexpression elimination pass by adding
8029 @option{-fno-gcse} to the command line.
8031 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
8035 When @option{-fgcse-lm} is enabled, global common subexpression elimination
8036 attempts to move loads that are only killed by stores into themselves. This
8037 allows a loop containing a load/store sequence to be changed to a load outside
8038 the loop, and a copy/store within the loop.
8040 Enabled by default when @option{-fgcse} is enabled.
8044 When @option{-fgcse-sm} is enabled, a store motion pass is run after
8045 global common subexpression elimination. This pass attempts to move
8046 stores out of loops. When used in conjunction with @option{-fgcse-lm},
8047 loops containing a load/store sequence can be changed to a load before
8048 the loop and a store after the loop.
8050 Not enabled at any optimization level.
8054 When @option{-fgcse-las} is enabled, the global common subexpression
8055 elimination pass eliminates redundant loads that come after stores to the
8056 same memory location (both partial and full redundancies).
8058 Not enabled at any optimization level.
8060 @item -fgcse-after-reload
8061 @opindex fgcse-after-reload
8062 When @option{-fgcse-after-reload} is enabled, a redundant load elimination
8063 pass is performed after reload. The purpose of this pass is to clean up
8066 @item -faggressive-loop-optimizations
8067 @opindex faggressive-loop-optimizations
8068 This option tells the loop optimizer to use language constraints to
8069 derive bounds for the number of iterations of a loop. This assumes that
8070 loop code does not invoke undefined behavior by for example causing signed
8071 integer overflows or out-of-bound array accesses. The bounds for the
8072 number of iterations of a loop are used to guide loop unrolling and peeling
8073 and loop exit test optimizations.
8074 This option is enabled by default.
8076 @item -funconstrained-commons
8077 @opindex funconstrained-commons
8078 This option tells the compiler that variables declared in common blocks
8079 (e.g. Fortran) may later be overridden with longer trailing arrays. This
8080 prevents certain optimizations that depend on knowing the array bounds.
8082 @item -fcrossjumping
8083 @opindex fcrossjumping
8084 Perform cross-jumping transformation.
8085 This transformation unifies equivalent code and saves code size. The
8086 resulting code may or may not perform better than without cross-jumping.
8088 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
8090 @item -fauto-inc-dec
8091 @opindex fauto-inc-dec
8092 Combine increments or decrements of addresses with memory accesses.
8093 This pass is always skipped on architectures that do not have
8094 instructions to support this. Enabled by default at @option{-O} and
8095 higher on architectures that support this.
8099 Perform dead code elimination (DCE) on RTL@.
8100 Enabled by default at @option{-O} and higher.
8104 Perform dead store elimination (DSE) on RTL@.
8105 Enabled by default at @option{-O} and higher.
8107 @item -fif-conversion
8108 @opindex fif-conversion
8109 Attempt to transform conditional jumps into branch-less equivalents. This
8110 includes use of conditional moves, min, max, set flags and abs instructions, and
8111 some tricks doable by standard arithmetics. The use of conditional execution
8112 on chips where it is available is controlled by @option{-fif-conversion2}.
8114 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
8116 @item -fif-conversion2
8117 @opindex fif-conversion2
8118 Use conditional execution (where available) to transform conditional jumps into
8119 branch-less equivalents.
8121 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
8123 @item -fdeclone-ctor-dtor
8124 @opindex fdeclone-ctor-dtor
8125 The C++ ABI requires multiple entry points for constructors and
8126 destructors: one for a base subobject, one for a complete object, and
8127 one for a virtual destructor that calls operator delete afterwards.
8128 For a hierarchy with virtual bases, the base and complete variants are
8129 clones, which means two copies of the function. With this option, the
8130 base and complete variants are changed to be thunks that call a common
8133 Enabled by @option{-Os}.
8135 @item -fdelete-null-pointer-checks
8136 @opindex fdelete-null-pointer-checks
8137 Assume that programs cannot safely dereference null pointers, and that
8138 no code or data element resides at address zero.
8139 This option enables simple constant
8140 folding optimizations at all optimization levels. In addition, other
8141 optimization passes in GCC use this flag to control global dataflow
8142 analyses that eliminate useless checks for null pointers; these assume
8143 that a memory access to address zero always results in a trap, so
8144 that if a pointer is checked after it has already been dereferenced,
8147 Note however that in some environments this assumption is not true.
8148 Use @option{-fno-delete-null-pointer-checks} to disable this optimization
8149 for programs that depend on that behavior.
8151 This option is enabled by default on most targets. On Nios II ELF, it
8152 defaults to off. On AVR, CR16, and MSP430, this option is completely disabled.
8154 Passes that use the dataflow information
8155 are enabled independently at different optimization levels.
8157 @item -fdevirtualize
8158 @opindex fdevirtualize
8159 Attempt to convert calls to virtual functions to direct calls. This
8160 is done both within a procedure and interprocedurally as part of
8161 indirect inlining (@option{-findirect-inlining}) and interprocedural constant
8162 propagation (@option{-fipa-cp}).
8163 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
8165 @item -fdevirtualize-speculatively
8166 @opindex fdevirtualize-speculatively
8167 Attempt to convert calls to virtual functions to speculative direct calls.
8168 Based on the analysis of the type inheritance graph, determine for a given call
8169 the set of likely targets. If the set is small, preferably of size 1, change
8170 the call into a conditional deciding between direct and indirect calls. The
8171 speculative calls enable more optimizations, such as inlining. When they seem
8172 useless after further optimization, they are converted back into original form.
8174 @item -fdevirtualize-at-ltrans
8175 @opindex fdevirtualize-at-ltrans
8176 Stream extra information needed for aggressive devirtualization when running
8177 the link-time optimizer in local transformation mode.
8178 This option enables more devirtualization but
8179 significantly increases the size of streamed data. For this reason it is
8180 disabled by default.
8182 @item -fexpensive-optimizations
8183 @opindex fexpensive-optimizations
8184 Perform a number of minor optimizations that are relatively expensive.
8186 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
8190 Attempt to remove redundant extension instructions. This is especially
8191 helpful for the x86-64 architecture, which implicitly zero-extends in 64-bit
8192 registers after writing to their lower 32-bit half.
8194 Enabled for Alpha, AArch64 and x86 at levels @option{-O2},
8195 @option{-O3}, @option{-Os}.
8197 @item -fno-lifetime-dse
8198 @opindex fno-lifetime-dse
8199 In C++ the value of an object is only affected by changes within its
8200 lifetime: when the constructor begins, the object has an indeterminate
8201 value, and any changes during the lifetime of the object are dead when
8202 the object is destroyed. Normally dead store elimination will take
8203 advantage of this; if your code relies on the value of the object
8204 storage persisting beyond the lifetime of the object, you can use this
8205 flag to disable this optimization. To preserve stores before the
8206 constructor starts (e.g. because your operator new clears the object
8207 storage) but still treat the object as dead after the destructor you,
8208 can use @option{-flifetime-dse=1}. The default behavior can be
8209 explicitly selected with @option{-flifetime-dse=2}.
8210 @option{-flifetime-dse=0} is equivalent to @option{-fno-lifetime-dse}.
8212 @item -flive-range-shrinkage
8213 @opindex flive-range-shrinkage
8214 Attempt to decrease register pressure through register live range
8215 shrinkage. This is helpful for fast processors with small or moderate
8218 @item -fira-algorithm=@var{algorithm}
8219 @opindex fira-algorithm
8220 Use the specified coloring algorithm for the integrated register
8221 allocator. The @var{algorithm} argument can be @samp{priority}, which
8222 specifies Chow's priority coloring, or @samp{CB}, which specifies
8223 Chaitin-Briggs coloring. Chaitin-Briggs coloring is not implemented
8224 for all architectures, but for those targets that do support it, it is
8225 the default because it generates better code.
8227 @item -fira-region=@var{region}
8228 @opindex fira-region
8229 Use specified regions for the integrated register allocator. The
8230 @var{region} argument should be one of the following:
8235 Use all loops as register allocation regions.
8236 This can give the best results for machines with a small and/or
8237 irregular register set.
8240 Use all loops except for loops with small register pressure
8241 as the regions. This value usually gives
8242 the best results in most cases and for most architectures,
8243 and is enabled by default when compiling with optimization for speed
8244 (@option{-O}, @option{-O2}, @dots{}).
8247 Use all functions as a single region.
8248 This typically results in the smallest code size, and is enabled by default for
8249 @option{-Os} or @option{-O0}.
8253 @item -fira-hoist-pressure
8254 @opindex fira-hoist-pressure
8255 Use IRA to evaluate register pressure in the code hoisting pass for
8256 decisions to hoist expressions. This option usually results in smaller
8257 code, but it can slow the compiler down.
8259 This option is enabled at level @option{-Os} for all targets.
8261 @item -fira-loop-pressure
8262 @opindex fira-loop-pressure
8263 Use IRA to evaluate register pressure in loops for decisions to move
8264 loop invariants. This option usually results in generation
8265 of faster and smaller code on machines with large register files (>= 32
8266 registers), but it can slow the compiler down.
8268 This option is enabled at level @option{-O3} for some targets.
8270 @item -fno-ira-share-save-slots
8271 @opindex fno-ira-share-save-slots
8272 Disable sharing of stack slots used for saving call-used hard
8273 registers living through a call. Each hard register gets a
8274 separate stack slot, and as a result function stack frames are
8277 @item -fno-ira-share-spill-slots
8278 @opindex fno-ira-share-spill-slots
8279 Disable sharing of stack slots allocated for pseudo-registers. Each
8280 pseudo-register that does not get a hard register gets a separate
8281 stack slot, and as a result function stack frames are larger.
8285 Enable CFG-sensitive rematerialization in LRA. Instead of loading
8286 values of spilled pseudos, LRA tries to rematerialize (recalculate)
8287 values if it is profitable.
8289 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
8291 @item -fdelayed-branch
8292 @opindex fdelayed-branch
8293 If supported for the target machine, attempt to reorder instructions
8294 to exploit instruction slots available after delayed branch
8297 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
8299 @item -fschedule-insns
8300 @opindex fschedule-insns
8301 If supported for the target machine, attempt to reorder instructions to
8302 eliminate execution stalls due to required data being unavailable. This
8303 helps machines that have slow floating point or memory load instructions
8304 by allowing other instructions to be issued until the result of the load
8305 or floating-point instruction is required.
8307 Enabled at levels @option{-O2}, @option{-O3}.
8309 @item -fschedule-insns2
8310 @opindex fschedule-insns2
8311 Similar to @option{-fschedule-insns}, but requests an additional pass of
8312 instruction scheduling after register allocation has been done. This is
8313 especially useful on machines with a relatively small number of
8314 registers and where memory load instructions take more than one cycle.
8316 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
8318 @item -fno-sched-interblock
8319 @opindex fno-sched-interblock
8320 Don't schedule instructions across basic blocks. This is normally
8321 enabled by default when scheduling before register allocation, i.e.@:
8322 with @option{-fschedule-insns} or at @option{-O2} or higher.
8324 @item -fno-sched-spec
8325 @opindex fno-sched-spec
8326 Don't allow speculative motion of non-load instructions. This is normally
8327 enabled by default when scheduling before register allocation, i.e.@:
8328 with @option{-fschedule-insns} or at @option{-O2} or higher.
8330 @item -fsched-pressure
8331 @opindex fsched-pressure
8332 Enable register pressure sensitive insn scheduling before register
8333 allocation. This only makes sense when scheduling before register
8334 allocation is enabled, i.e.@: with @option{-fschedule-insns} or at
8335 @option{-O2} or higher. Usage of this option can improve the
8336 generated code and decrease its size by preventing register pressure
8337 increase above the number of available hard registers and subsequent
8338 spills in register allocation.
8340 @item -fsched-spec-load
8341 @opindex fsched-spec-load
8342 Allow speculative motion of some load instructions. This only makes
8343 sense when scheduling before register allocation, i.e.@: with
8344 @option{-fschedule-insns} or at @option{-O2} or higher.
8346 @item -fsched-spec-load-dangerous
8347 @opindex fsched-spec-load-dangerous
8348 Allow speculative motion of more load instructions. This only makes
8349 sense when scheduling before register allocation, i.e.@: with
8350 @option{-fschedule-insns} or at @option{-O2} or higher.
8352 @item -fsched-stalled-insns
8353 @itemx -fsched-stalled-insns=@var{n}
8354 @opindex fsched-stalled-insns
8355 Define how many insns (if any) can be moved prematurely from the queue
8356 of stalled insns into the ready list during the second scheduling pass.
8357 @option{-fno-sched-stalled-insns} means that no insns are moved
8358 prematurely, @option{-fsched-stalled-insns=0} means there is no limit
8359 on how many queued insns can be moved prematurely.
8360 @option{-fsched-stalled-insns} without a value is equivalent to
8361 @option{-fsched-stalled-insns=1}.
8363 @item -fsched-stalled-insns-dep
8364 @itemx -fsched-stalled-insns-dep=@var{n}
8365 @opindex fsched-stalled-insns-dep
8366 Define how many insn groups (cycles) are examined for a dependency
8367 on a stalled insn that is a candidate for premature removal from the queue
8368 of stalled insns. This has an effect only during the second scheduling pass,
8369 and only if @option{-fsched-stalled-insns} is used.
8370 @option{-fno-sched-stalled-insns-dep} is equivalent to
8371 @option{-fsched-stalled-insns-dep=0}.
8372 @option{-fsched-stalled-insns-dep} without a value is equivalent to
8373 @option{-fsched-stalled-insns-dep=1}.
8375 @item -fsched2-use-superblocks
8376 @opindex fsched2-use-superblocks
8377 When scheduling after register allocation, use superblock scheduling.
8378 This allows motion across basic block boundaries,
8379 resulting in faster schedules. This option is experimental, as not all machine
8380 descriptions used by GCC model the CPU closely enough to avoid unreliable
8381 results from the algorithm.
8383 This only makes sense when scheduling after register allocation, i.e.@: with
8384 @option{-fschedule-insns2} or at @option{-O2} or higher.
8386 @item -fsched-group-heuristic
8387 @opindex fsched-group-heuristic
8388 Enable the group heuristic in the scheduler. This heuristic favors
8389 the instruction that belongs to a schedule group. This is enabled
8390 by default when scheduling is enabled, i.e.@: with @option{-fschedule-insns}
8391 or @option{-fschedule-insns2} or at @option{-O2} or higher.
8393 @item -fsched-critical-path-heuristic
8394 @opindex fsched-critical-path-heuristic
8395 Enable the critical-path heuristic in the scheduler. This heuristic favors
8396 instructions on the critical path. This is enabled by default when
8397 scheduling is enabled, i.e.@: with @option{-fschedule-insns}
8398 or @option{-fschedule-insns2} or at @option{-O2} or higher.
8400 @item -fsched-spec-insn-heuristic
8401 @opindex fsched-spec-insn-heuristic
8402 Enable the speculative instruction heuristic in the scheduler. This
8403 heuristic favors speculative instructions with greater dependency weakness.
8404 This is enabled by default when scheduling is enabled, i.e.@:
8405 with @option{-fschedule-insns} or @option{-fschedule-insns2}
8406 or at @option{-O2} or higher.
8408 @item -fsched-rank-heuristic
8409 @opindex fsched-rank-heuristic
8410 Enable the rank heuristic in the scheduler. This heuristic favors
8411 the instruction belonging to a basic block with greater size or frequency.
8412 This is enabled by default when scheduling is enabled, i.e.@:
8413 with @option{-fschedule-insns} or @option{-fschedule-insns2} or
8414 at @option{-O2} or higher.
8416 @item -fsched-last-insn-heuristic
8417 @opindex fsched-last-insn-heuristic
8418 Enable the last-instruction heuristic in the scheduler. This heuristic
8419 favors the instruction that is less dependent on the last instruction
8420 scheduled. This is enabled by default when scheduling is enabled,
8421 i.e.@: with @option{-fschedule-insns} or @option{-fschedule-insns2} or
8422 at @option{-O2} or higher.
8424 @item -fsched-dep-count-heuristic
8425 @opindex fsched-dep-count-heuristic
8426 Enable the dependent-count heuristic in the scheduler. This heuristic
8427 favors the instruction that has more instructions depending on it.
8428 This is enabled by default when scheduling is enabled, i.e.@:
8429 with @option{-fschedule-insns} or @option{-fschedule-insns2} or
8430 at @option{-O2} or higher.
8432 @item -freschedule-modulo-scheduled-loops
8433 @opindex freschedule-modulo-scheduled-loops
8434 Modulo scheduling is performed before traditional scheduling. If a loop
8435 is modulo scheduled, later scheduling passes may change its schedule.
8436 Use this option to control that behavior.
8438 @item -fselective-scheduling
8439 @opindex fselective-scheduling
8440 Schedule instructions using selective scheduling algorithm. Selective
8441 scheduling runs instead of the first scheduler pass.
8443 @item -fselective-scheduling2
8444 @opindex fselective-scheduling2
8445 Schedule instructions using selective scheduling algorithm. Selective
8446 scheduling runs instead of the second scheduler pass.
8448 @item -fsel-sched-pipelining
8449 @opindex fsel-sched-pipelining
8450 Enable software pipelining of innermost loops during selective scheduling.
8451 This option has no effect unless one of @option{-fselective-scheduling} or
8452 @option{-fselective-scheduling2} is turned on.
8454 @item -fsel-sched-pipelining-outer-loops
8455 @opindex fsel-sched-pipelining-outer-loops
8456 When pipelining loops during selective scheduling, also pipeline outer loops.
8457 This option has no effect unless @option{-fsel-sched-pipelining} is turned on.
8459 @item -fsemantic-interposition
8460 @opindex fsemantic-interposition
8461 Some object formats, like ELF, allow interposing of symbols by the
8463 This means that for symbols exported from the DSO, the compiler cannot perform
8464 interprocedural propagation, inlining and other optimizations in anticipation
8465 that the function or variable in question may change. While this feature is
8466 useful, for example, to rewrite memory allocation functions by a debugging
8467 implementation, it is expensive in the terms of code quality.
8468 With @option{-fno-semantic-interposition} the compiler assumes that
8469 if interposition happens for functions the overwriting function will have
8470 precisely the same semantics (and side effects).
8471 Similarly if interposition happens
8472 for variables, the constructor of the variable will be the same. The flag
8473 has no effect for functions explicitly declared inline
8474 (where it is never allowed for interposition to change semantics)
8475 and for symbols explicitly declared weak.
8478 @opindex fshrink-wrap
8479 Emit function prologues only before parts of the function that need it,
8480 rather than at the top of the function. This flag is enabled by default at
8481 @option{-O} and higher.
8483 @item -fshrink-wrap-separate
8484 @opindex fshrink-wrap-separate
8485 Shrink-wrap separate parts of the prologue and epilogue separately, so that
8486 those parts are only executed when needed.
8487 This option is on by default, but has no effect unless @option{-fshrink-wrap}
8488 is also turned on and the target supports this.
8490 @item -fcaller-saves
8491 @opindex fcaller-saves
8492 Enable allocation of values to registers that are clobbered by
8493 function calls, by emitting extra instructions to save and restore the
8494 registers around such calls. Such allocation is done only when it
8495 seems to result in better code.
8497 This option is always enabled by default on certain machines, usually
8498 those which have no call-preserved registers to use instead.
8500 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
8502 @item -fcombine-stack-adjustments
8503 @opindex fcombine-stack-adjustments
8504 Tracks stack adjustments (pushes and pops) and stack memory references
8505 and then tries to find ways to combine them.
8507 Enabled by default at @option{-O1} and higher.
8511 Use caller save registers for allocation if those registers are not used by
8512 any called function. In that case it is not necessary to save and restore
8513 them around calls. This is only possible if called functions are part of
8514 same compilation unit as current function and they are compiled before it.
8516 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}, however the option
8517 is disabled if generated code will be instrumented for profiling
8518 (@option{-p}, or @option{-pg}) or if callee's register usage cannot be known
8519 exactly (this happens on targets that do not expose prologues
8520 and epilogues in RTL).
8522 @item -fconserve-stack
8523 @opindex fconserve-stack
8524 Attempt to minimize stack usage. The compiler attempts to use less
8525 stack space, even if that makes the program slower. This option
8526 implies setting the @option{large-stack-frame} parameter to 100
8527 and the @option{large-stack-frame-growth} parameter to 400.
8529 @item -ftree-reassoc
8530 @opindex ftree-reassoc
8531 Perform reassociation on trees. This flag is enabled by default
8532 at @option{-O} and higher.
8534 @item -fcode-hoisting
8535 @opindex fcode-hoisting
8536 Perform code hoisting. Code hoisting tries to move the
8537 evaluation of expressions executed on all paths to the function exit
8538 as early as possible. This is especially useful as a code size
8539 optimization, but it often helps for code speed as well.
8540 This flag is enabled by default at @option{-O2} and higher.
8544 Perform partial redundancy elimination (PRE) on trees. This flag is
8545 enabled by default at @option{-O2} and @option{-O3}.
8547 @item -ftree-partial-pre
8548 @opindex ftree-partial-pre
8549 Make partial redundancy elimination (PRE) more aggressive. This flag is
8550 enabled by default at @option{-O3}.
8552 @item -ftree-forwprop
8553 @opindex ftree-forwprop
8554 Perform forward propagation on trees. This flag is enabled by default
8555 at @option{-O} and higher.
8559 Perform full redundancy elimination (FRE) on trees. The difference
8560 between FRE and PRE is that FRE only considers expressions
8561 that are computed on all paths leading to the redundant computation.
8562 This analysis is faster than PRE, though it exposes fewer redundancies.
8563 This flag is enabled by default at @option{-O} and higher.
8565 @item -ftree-phiprop
8566 @opindex ftree-phiprop
8567 Perform hoisting of loads from conditional pointers on trees. This
8568 pass is enabled by default at @option{-O} and higher.
8570 @item -fhoist-adjacent-loads
8571 @opindex fhoist-adjacent-loads
8572 Speculatively hoist loads from both branches of an if-then-else if the
8573 loads are from adjacent locations in the same structure and the target
8574 architecture has a conditional move instruction. This flag is enabled
8575 by default at @option{-O2} and higher.
8577 @item -ftree-copy-prop
8578 @opindex ftree-copy-prop
8579 Perform copy propagation on trees. This pass eliminates unnecessary
8580 copy operations. This flag is enabled by default at @option{-O} and
8583 @item -fipa-pure-const
8584 @opindex fipa-pure-const
8585 Discover which functions are pure or constant.
8586 Enabled by default at @option{-O} and higher.
8588 @item -fipa-reference
8589 @opindex fipa-reference
8590 Discover which static variables do not escape the
8592 Enabled by default at @option{-O} and higher.
8596 Perform interprocedural pointer analysis and interprocedural modification
8597 and reference analysis. This option can cause excessive memory and
8598 compile-time usage on large compilation units. It is not enabled by
8599 default at any optimization level.
8602 @opindex fipa-profile
8603 Perform interprocedural profile propagation. The functions called only from
8604 cold functions are marked as cold. Also functions executed once (such as
8605 @code{cold}, @code{noreturn}, static constructors or destructors) are identified. Cold
8606 functions and loop less parts of functions executed once are then optimized for
8608 Enabled by default at @option{-O} and higher.
8612 Perform interprocedural constant propagation.
8613 This optimization analyzes the program to determine when values passed
8614 to functions are constants and then optimizes accordingly.
8615 This optimization can substantially increase performance
8616 if the application has constants passed to functions.
8617 This flag is enabled by default at @option{-O2}, @option{-Os} and @option{-O3}.
8619 @item -fipa-cp-clone
8620 @opindex fipa-cp-clone
8621 Perform function cloning to make interprocedural constant propagation stronger.
8622 When enabled, interprocedural constant propagation performs function cloning
8623 when externally visible function can be called with constant arguments.
8624 Because this optimization can create multiple copies of functions,
8625 it may significantly increase code size
8626 (see @option{--param ipcp-unit-growth=@var{value}}).
8627 This flag is enabled by default at @option{-O3}.
8630 @opindex -fipa-bit-cp
8631 When enabled, perform interprocedural bitwise constant
8632 propagation. This flag is enabled by default at @option{-O2}. It
8633 requires that @option{-fipa-cp} is enabled.
8637 When enabled, perform interprocedural propagation of value
8638 ranges. This flag is enabled by default at @option{-O2}. It requires
8639 that @option{-fipa-cp} is enabled.
8643 Perform Identical Code Folding for functions and read-only variables.
8644 The optimization reduces code size and may disturb unwind stacks by replacing
8645 a function by equivalent one with a different name. The optimization works
8646 more effectively with link-time optimization enabled.
8648 Nevertheless the behavior is similar to Gold Linker ICF optimization, GCC ICF
8649 works on different levels and thus the optimizations are not same - there are
8650 equivalences that are found only by GCC and equivalences found only by Gold.
8652 This flag is enabled by default at @option{-O2} and @option{-Os}.
8654 @item -fisolate-erroneous-paths-dereference
8655 @opindex fisolate-erroneous-paths-dereference
8656 Detect paths that trigger erroneous or undefined behavior due to
8657 dereferencing a null pointer. Isolate those paths from the main control
8658 flow and turn the statement with erroneous or undefined behavior into a trap.
8659 This flag is enabled by default at @option{-O2} and higher and depends on
8660 @option{-fdelete-null-pointer-checks} also being enabled.
8662 @item -fisolate-erroneous-paths-attribute
8663 @opindex fisolate-erroneous-paths-attribute
8664 Detect paths that trigger erroneous or undefined behavior due to a null value
8665 being used in a way forbidden by a @code{returns_nonnull} or @code{nonnull}
8666 attribute. Isolate those paths from the main control flow and turn the
8667 statement with erroneous or undefined behavior into a trap. This is not
8668 currently enabled, but may be enabled by @option{-O2} in the future.
8672 Perform forward store motion on trees. This flag is
8673 enabled by default at @option{-O} and higher.
8675 @item -ftree-bit-ccp
8676 @opindex ftree-bit-ccp
8677 Perform sparse conditional bit constant propagation on trees and propagate
8678 pointer alignment information.
8679 This pass only operates on local scalar variables and is enabled by default
8680 at @option{-O} and higher. It requires that @option{-ftree-ccp} is enabled.
8684 Perform sparse conditional constant propagation (CCP) on trees. This
8685 pass only operates on local scalar variables and is enabled by default
8686 at @option{-O} and higher.
8688 @item -fssa-backprop
8689 @opindex fssa-backprop
8690 Propagate information about uses of a value up the definition chain
8691 in order to simplify the definitions. For example, this pass strips
8692 sign operations if the sign of a value never matters. The flag is
8693 enabled by default at @option{-O} and higher.
8696 @opindex fssa-phiopt
8697 Perform pattern matching on SSA PHI nodes to optimize conditional
8698 code. This pass is enabled by default at @option{-O} and higher.
8700 @item -ftree-switch-conversion
8701 @opindex ftree-switch-conversion
8702 Perform conversion of simple initializations in a switch to
8703 initializations from a scalar array. This flag is enabled by default
8704 at @option{-O2} and higher.
8706 @item -ftree-tail-merge
8707 @opindex ftree-tail-merge
8708 Look for identical code sequences. When found, replace one with a jump to the
8709 other. This optimization is known as tail merging or cross jumping. This flag
8710 is enabled by default at @option{-O2} and higher. The compilation time
8712 be limited using @option{max-tail-merge-comparisons} parameter and
8713 @option{max-tail-merge-iterations} parameter.
8717 Perform dead code elimination (DCE) on trees. This flag is enabled by
8718 default at @option{-O} and higher.
8720 @item -ftree-builtin-call-dce
8721 @opindex ftree-builtin-call-dce
8722 Perform conditional dead code elimination (DCE) for calls to built-in functions
8723 that may set @code{errno} but are otherwise free of side effects. This flag is
8724 enabled by default at @option{-O2} and higher if @option{-Os} is not also
8727 @item -ftree-dominator-opts
8728 @opindex ftree-dominator-opts
8729 Perform a variety of simple scalar cleanups (constant/copy
8730 propagation, redundancy elimination, range propagation and expression
8731 simplification) based on a dominator tree traversal. This also
8732 performs jump threading (to reduce jumps to jumps). This flag is
8733 enabled by default at @option{-O} and higher.
8737 Perform dead store elimination (DSE) on trees. A dead store is a store into
8738 a memory location that is later overwritten by another store without
8739 any intervening loads. In this case the earlier store can be deleted. This
8740 flag is enabled by default at @option{-O} and higher.
8744 Perform loop header copying on trees. This is beneficial since it increases
8745 effectiveness of code motion optimizations. It also saves one jump. This flag
8746 is enabled by default at @option{-O} and higher. It is not enabled
8747 for @option{-Os}, since it usually increases code size.
8749 @item -ftree-loop-optimize
8750 @opindex ftree-loop-optimize
8751 Perform loop optimizations on trees. This flag is enabled by default
8752 at @option{-O} and higher.
8754 @item -ftree-loop-linear
8755 @itemx -floop-strip-mine
8757 @opindex ftree-loop-linear
8758 @opindex floop-strip-mine
8759 @opindex floop-block
8760 Perform loop nest optimizations. Same as
8761 @option{-floop-nest-optimize}. To use this code transformation, GCC has
8762 to be configured with @option{--with-isl} to enable the Graphite loop
8763 transformation infrastructure.
8765 @item -fgraphite-identity
8766 @opindex fgraphite-identity
8767 Enable the identity transformation for graphite. For every SCoP we generate
8768 the polyhedral representation and transform it back to gimple. Using
8769 @option{-fgraphite-identity} we can check the costs or benefits of the
8770 GIMPLE -> GRAPHITE -> GIMPLE transformation. Some minimal optimizations
8771 are also performed by the code generator isl, like index splitting and
8772 dead code elimination in loops.
8774 @item -floop-nest-optimize
8775 @opindex floop-nest-optimize
8776 Enable the isl based loop nest optimizer. This is a generic loop nest
8777 optimizer based on the Pluto optimization algorithms. It calculates a loop
8778 structure optimized for data-locality and parallelism. This option
8781 @item -floop-parallelize-all
8782 @opindex floop-parallelize-all
8783 Use the Graphite data dependence analysis to identify loops that can
8784 be parallelized. Parallelize all the loops that can be analyzed to
8785 not contain loop carried dependences without checking that it is
8786 profitable to parallelize the loops.
8788 @item -ftree-coalesce-vars
8789 @opindex ftree-coalesce-vars
8790 While transforming the program out of the SSA representation, attempt to
8791 reduce copying by coalescing versions of different user-defined
8792 variables, instead of just compiler temporaries. This may severely
8793 limit the ability to debug an optimized program compiled with
8794 @option{-fno-var-tracking-assignments}. In the negated form, this flag
8795 prevents SSA coalescing of user variables. This option is enabled by
8796 default if optimization is enabled, and it does very little otherwise.
8798 @item -ftree-loop-if-convert
8799 @opindex ftree-loop-if-convert
8800 Attempt to transform conditional jumps in the innermost loops to
8801 branch-less equivalents. The intent is to remove control-flow from
8802 the innermost loops in order to improve the ability of the
8803 vectorization pass to handle these loops. This is enabled by default
8804 if vectorization is enabled.
8806 @item -ftree-loop-distribution
8807 @opindex ftree-loop-distribution
8808 Perform loop distribution. This flag can improve cache performance on
8809 big loop bodies and allow further loop optimizations, like
8810 parallelization or vectorization, to take place. For example, the loop
8827 @item -ftree-loop-distribute-patterns
8828 @opindex ftree-loop-distribute-patterns
8829 Perform loop distribution of patterns that can be code generated with
8830 calls to a library. This flag is enabled by default at @option{-O3}.
8832 This pass distributes the initialization loops and generates a call to
8833 memset zero. For example, the loop
8849 and the initialization loop is transformed into a call to memset zero.
8851 @item -floop-interchange
8852 @opindex floop-interchange
8853 Perform loop interchange outside of graphite. This flag can improve cache
8854 performance on loop nest and allow further loop optimizations, like
8855 vectorization, to take place. For example, the loop
8857 for (int i = 0; i < N; i++)
8858 for (int j = 0; j < N; j++)
8859 for (int k = 0; k < N; k++)
8860 c[i][j] = c[i][j] + a[i][k]*b[k][j];
8864 for (int i = 0; i < N; i++)
8865 for (int k = 0; k < N; k++)
8866 for (int j = 0; j < N; j++)
8867 c[i][j] = c[i][j] + a[i][k]*b[k][j];
8870 @item -ftree-loop-im
8871 @opindex ftree-loop-im
8872 Perform loop invariant motion on trees. This pass moves only invariants that
8873 are hard to handle at RTL level (function calls, operations that expand to
8874 nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
8875 operands of conditions that are invariant out of the loop, so that we can use
8876 just trivial invariantness analysis in loop unswitching. The pass also includes
8879 @item -ftree-loop-ivcanon
8880 @opindex ftree-loop-ivcanon
8881 Create a canonical counter for number of iterations in loops for which
8882 determining number of iterations requires complicated analysis. Later
8883 optimizations then may determine the number easily. Useful especially
8884 in connection with unrolling.
8888 Perform induction variable optimizations (strength reduction, induction
8889 variable merging and induction variable elimination) on trees.
8891 @item -ftree-parallelize-loops=n
8892 @opindex ftree-parallelize-loops
8893 Parallelize loops, i.e., split their iteration space to run in n threads.
8894 This is only possible for loops whose iterations are independent
8895 and can be arbitrarily reordered. The optimization is only
8896 profitable on multiprocessor machines, for loops that are CPU-intensive,
8897 rather than constrained e.g.@: by memory bandwidth. This option
8898 implies @option{-pthread}, and thus is only supported on targets
8899 that have support for @option{-pthread}.
8903 Perform function-local points-to analysis on trees. This flag is
8904 enabled by default at @option{-O} and higher.
8908 Perform scalar replacement of aggregates. This pass replaces structure
8909 references with scalars to prevent committing structures to memory too
8910 early. This flag is enabled by default at @option{-O} and higher.
8912 @item -fstore-merging
8913 @opindex fstore-merging
8914 Perform merging of narrow stores to consecutive memory addresses. This pass
8915 merges contiguous stores of immediate values narrower than a word into fewer
8916 wider stores to reduce the number of instructions. This is enabled by default
8917 at @option{-O2} and higher as well as @option{-Os}.
8921 Perform temporary expression replacement during the SSA->normal phase. Single
8922 use/single def temporaries are replaced at their use location with their
8923 defining expression. This results in non-GIMPLE code, but gives the expanders
8924 much more complex trees to work on resulting in better RTL generation. This is
8925 enabled by default at @option{-O} and higher.
8929 Perform straight-line strength reduction on trees. This recognizes related
8930 expressions involving multiplications and replaces them by less expensive
8931 calculations when possible. This is enabled by default at @option{-O} and
8934 @item -ftree-vectorize
8935 @opindex ftree-vectorize
8936 Perform vectorization on trees. This flag enables @option{-ftree-loop-vectorize}
8937 and @option{-ftree-slp-vectorize} if not explicitly specified.
8939 @item -ftree-loop-vectorize
8940 @opindex ftree-loop-vectorize
8941 Perform loop vectorization on trees. This flag is enabled by default at
8942 @option{-O3} and when @option{-ftree-vectorize} is enabled.
8944 @item -ftree-slp-vectorize
8945 @opindex ftree-slp-vectorize
8946 Perform basic block vectorization on trees. This flag is enabled by default at
8947 @option{-O3} and when @option{-ftree-vectorize} is enabled.
8949 @item -fvect-cost-model=@var{model}
8950 @opindex fvect-cost-model
8951 Alter the cost model used for vectorization. The @var{model} argument
8952 should be one of @samp{unlimited}, @samp{dynamic} or @samp{cheap}.
8953 With the @samp{unlimited} model the vectorized code-path is assumed
8954 to be profitable while with the @samp{dynamic} model a runtime check
8955 guards the vectorized code-path to enable it only for iteration
8956 counts that will likely execute faster than when executing the original
8957 scalar loop. The @samp{cheap} model disables vectorization of
8958 loops where doing so would be cost prohibitive for example due to
8959 required runtime checks for data dependence or alignment but otherwise
8960 is equal to the @samp{dynamic} model.
8961 The default cost model depends on other optimization flags and is
8962 either @samp{dynamic} or @samp{cheap}.
8964 @item -fsimd-cost-model=@var{model}
8965 @opindex fsimd-cost-model
8966 Alter the cost model used for vectorization of loops marked with the OpenMP
8967 simd directive. The @var{model} argument should be one of
8968 @samp{unlimited}, @samp{dynamic}, @samp{cheap}. All values of @var{model}
8969 have the same meaning as described in @option{-fvect-cost-model} and by
8970 default a cost model defined with @option{-fvect-cost-model} is used.
8974 Perform Value Range Propagation on trees. This is similar to the
8975 constant propagation pass, but instead of values, ranges of values are
8976 propagated. This allows the optimizers to remove unnecessary range
8977 checks like array bound checks and null pointer checks. This is
8978 enabled by default at @option{-O2} and higher. Null pointer check
8979 elimination is only done if @option{-fdelete-null-pointer-checks} is
8983 @opindex fsplit-paths
8984 Split paths leading to loop backedges. This can improve dead code
8985 elimination and common subexpression elimination. This is enabled by
8986 default at @option{-O2} and above.
8988 @item -fsplit-ivs-in-unroller
8989 @opindex fsplit-ivs-in-unroller
8990 Enables expression of values of induction variables in later iterations
8991 of the unrolled loop using the value in the first iteration. This breaks
8992 long dependency chains, thus improving efficiency of the scheduling passes.
8994 A combination of @option{-fweb} and CSE is often sufficient to obtain the
8995 same effect. However, that is not reliable in cases where the loop body
8996 is more complicated than a single basic block. It also does not work at all
8997 on some architectures due to restrictions in the CSE pass.
8999 This optimization is enabled by default.
9001 @item -fvariable-expansion-in-unroller
9002 @opindex fvariable-expansion-in-unroller
9003 With this option, the compiler creates multiple copies of some
9004 local variables when unrolling a loop, which can result in superior code.
9006 @item -fpartial-inlining
9007 @opindex fpartial-inlining
9008 Inline parts of functions. This option has any effect only
9009 when inlining itself is turned on by the @option{-finline-functions}
9010 or @option{-finline-small-functions} options.
9012 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
9014 @item -fpredictive-commoning
9015 @opindex fpredictive-commoning
9016 Perform predictive commoning optimization, i.e., reusing computations
9017 (especially memory loads and stores) performed in previous
9018 iterations of loops.
9020 This option is enabled at level @option{-O3}.
9022 @item -fprefetch-loop-arrays
9023 @opindex fprefetch-loop-arrays
9024 If supported by the target machine, generate instructions to prefetch
9025 memory to improve the performance of loops that access large arrays.
9027 This option may generate better or worse code; results are highly
9028 dependent on the structure of loops within the source code.
9030 Disabled at level @option{-Os}.
9032 @item -fno-printf-return-value
9033 @opindex fno-printf-return-value
9034 Do not substitute constants for known return value of formatted output
9035 functions such as @code{sprintf}, @code{snprintf}, @code{vsprintf}, and
9036 @code{vsnprintf} (but not @code{printf} of @code{fprintf}). This
9037 transformation allows GCC to optimize or even eliminate branches based
9038 on the known return value of these functions called with arguments that
9039 are either constant, or whose values are known to be in a range that
9040 makes determining the exact return value possible. For example, when
9041 @option{-fprintf-return-value} is in effect, both the branch and the
9042 body of the @code{if} statement (but not the call to @code{snprint})
9043 can be optimized away when @code{i} is a 32-bit or smaller integer
9044 because the return value is guaranteed to be at most 8.
9048 if (snprintf (buf, "%08x", i) >= sizeof buf)
9052 The @option{-fprintf-return-value} option relies on other optimizations
9053 and yields best results with @option{-O2} and above. It works in tandem
9054 with the @option{-Wformat-overflow} and @option{-Wformat-truncation}
9055 options. The @option{-fprintf-return-value} option is enabled by default.
9058 @itemx -fno-peephole2
9059 @opindex fno-peephole
9060 @opindex fno-peephole2
9061 Disable any machine-specific peephole optimizations. The difference
9062 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
9063 are implemented in the compiler; some targets use one, some use the
9064 other, a few use both.
9066 @option{-fpeephole} is enabled by default.
9067 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
9069 @item -fno-guess-branch-probability
9070 @opindex fno-guess-branch-probability
9071 Do not guess branch probabilities using heuristics.
9073 GCC uses heuristics to guess branch probabilities if they are
9074 not provided by profiling feedback (@option{-fprofile-arcs}). These
9075 heuristics are based on the control flow graph. If some branch probabilities
9076 are specified by @code{__builtin_expect}, then the heuristics are
9077 used to guess branch probabilities for the rest of the control flow graph,
9078 taking the @code{__builtin_expect} info into account. The interactions
9079 between the heuristics and @code{__builtin_expect} can be complex, and in
9080 some cases, it may be useful to disable the heuristics so that the effects
9081 of @code{__builtin_expect} are easier to understand.
9083 The default is @option{-fguess-branch-probability} at levels
9084 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
9086 @item -freorder-blocks
9087 @opindex freorder-blocks
9088 Reorder basic blocks in the compiled function in order to reduce number of
9089 taken branches and improve code locality.
9091 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
9093 @item -freorder-blocks-algorithm=@var{algorithm}
9094 @opindex freorder-blocks-algorithm
9095 Use the specified algorithm for basic block reordering. The
9096 @var{algorithm} argument can be @samp{simple}, which does not increase
9097 code size (except sometimes due to secondary effects like alignment),
9098 or @samp{stc}, the ``software trace cache'' algorithm, which tries to
9099 put all often executed code together, minimizing the number of branches
9100 executed by making extra copies of code.
9102 The default is @samp{simple} at levels @option{-O}, @option{-Os}, and
9103 @samp{stc} at levels @option{-O2}, @option{-O3}.
9105 @item -freorder-blocks-and-partition
9106 @opindex freorder-blocks-and-partition
9107 In addition to reordering basic blocks in the compiled function, in order
9108 to reduce number of taken branches, partitions hot and cold basic blocks
9109 into separate sections of the assembly and @file{.o} files, to improve
9110 paging and cache locality performance.
9112 This optimization is automatically turned off in the presence of
9113 exception handling or unwind tables (on targets using setjump/longjump or target specific scheme), for linkonce sections, for functions with a user-defined
9114 section attribute and on any architecture that does not support named
9115 sections. When @option{-fsplit-stack} is used this option is not
9116 enabled by default (to avoid linker errors), but may be enabled
9117 explicitly (if using a working linker).
9119 Enabled for x86 at levels @option{-O2}, @option{-O3}, @option{-Os}.
9121 @item -freorder-functions
9122 @opindex freorder-functions
9123 Reorder functions in the object file in order to
9124 improve code locality. This is implemented by using special
9125 subsections @code{.text.hot} for most frequently executed functions and
9126 @code{.text.unlikely} for unlikely executed functions. Reordering is done by
9127 the linker so object file format must support named sections and linker must
9128 place them in a reasonable way.
9130 Also profile feedback must be available to make this option effective. See
9131 @option{-fprofile-arcs} for details.
9133 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
9135 @item -fstrict-aliasing
9136 @opindex fstrict-aliasing
9137 Allow the compiler to assume the strictest aliasing rules applicable to
9138 the language being compiled. For C (and C++), this activates
9139 optimizations based on the type of expressions. In particular, an
9140 object of one type is assumed never to reside at the same address as an
9141 object of a different type, unless the types are almost the same. For
9142 example, an @code{unsigned int} can alias an @code{int}, but not a
9143 @code{void*} or a @code{double}. A character type may alias any other
9146 @anchor{Type-punning}Pay special attention to code like this:
9159 The practice of reading from a different union member than the one most
9160 recently written to (called ``type-punning'') is common. Even with
9161 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
9162 is accessed through the union type. So, the code above works as
9163 expected. @xref{Structures unions enumerations and bit-fields
9164 implementation}. However, this code might not:
9175 Similarly, access by taking the address, casting the resulting pointer
9176 and dereferencing the result has undefined behavior, even if the cast
9177 uses a union type, e.g.:
9181 return ((union a_union *) &d)->i;
9185 The @option{-fstrict-aliasing} option is enabled at levels
9186 @option{-O2}, @option{-O3}, @option{-Os}.
9188 @item -falign-functions
9189 @itemx -falign-functions=@var{n}
9190 @opindex falign-functions
9191 Align the start of functions to the next power-of-two greater than
9192 @var{n}, skipping up to @var{n} bytes. For instance,
9193 @option{-falign-functions=32} aligns functions to the next 32-byte
9194 boundary, but @option{-falign-functions=24} aligns to the next
9195 32-byte boundary only if this can be done by skipping 23 bytes or less.
9197 @option{-fno-align-functions} and @option{-falign-functions=1} are
9198 equivalent and mean that functions are not aligned.
9200 Some assemblers only support this flag when @var{n} is a power of two;
9201 in that case, it is rounded up.
9203 If @var{n} is not specified or is zero, use a machine-dependent default.
9204 The maximum allowed @var{n} option value is 65536.
9206 Enabled at levels @option{-O2}, @option{-O3}.
9208 @item -flimit-function-alignment
9209 If this option is enabled, the compiler tries to avoid unnecessarily
9210 overaligning functions. It attempts to instruct the assembler to align
9211 by the amount specified by @option{-falign-functions}, but not to
9212 skip more bytes than the size of the function.
9214 @item -falign-labels
9215 @itemx -falign-labels=@var{n}
9216 @opindex falign-labels
9217 Align all branch targets to a power-of-two boundary, skipping up to
9218 @var{n} bytes like @option{-falign-functions}. This option can easily
9219 make code slower, because it must insert dummy operations for when the
9220 branch target is reached in the usual flow of the code.
9222 @option{-fno-align-labels} and @option{-falign-labels=1} are
9223 equivalent and mean that labels are not aligned.
9225 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
9226 are greater than this value, then their values are used instead.
9228 If @var{n} is not specified or is zero, use a machine-dependent default
9229 which is very likely to be @samp{1}, meaning no alignment.
9230 The maximum allowed @var{n} option value is 65536.
9232 Enabled at levels @option{-O2}, @option{-O3}.
9235 @itemx -falign-loops=@var{n}
9236 @opindex falign-loops
9237 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
9238 like @option{-falign-functions}. If the loops are
9239 executed many times, this makes up for any execution of the dummy
9242 @option{-fno-align-loops} and @option{-falign-loops=1} are
9243 equivalent and mean that loops are not aligned.
9244 The maximum allowed @var{n} option value is 65536.
9246 If @var{n} is not specified or is zero, use a machine-dependent default.
9248 Enabled at levels @option{-O2}, @option{-O3}.
9251 @itemx -falign-jumps=@var{n}
9252 @opindex falign-jumps
9253 Align branch targets to a power-of-two boundary, for branch targets
9254 where the targets can only be reached by jumping, skipping up to @var{n}
9255 bytes like @option{-falign-functions}. In this case, no dummy operations
9258 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
9259 equivalent and mean that loops are not aligned.
9261 If @var{n} is not specified or is zero, use a machine-dependent default.
9262 The maximum allowed @var{n} option value is 65536.
9264 Enabled at levels @option{-O2}, @option{-O3}.
9266 @item -funit-at-a-time
9267 @opindex funit-at-a-time
9268 This option is left for compatibility reasons. @option{-funit-at-a-time}
9269 has no effect, while @option{-fno-unit-at-a-time} implies
9270 @option{-fno-toplevel-reorder} and @option{-fno-section-anchors}.
9274 @item -fno-toplevel-reorder
9275 @opindex fno-toplevel-reorder
9276 Do not reorder top-level functions, variables, and @code{asm}
9277 statements. Output them in the same order that they appear in the
9278 input file. When this option is used, unreferenced static variables
9279 are not removed. This option is intended to support existing code
9280 that relies on a particular ordering. For new code, it is better to
9281 use attributes when possible.
9283 Enabled at level @option{-O0}. When disabled explicitly, it also implies
9284 @option{-fno-section-anchors}, which is otherwise enabled at @option{-O0} on some
9289 Constructs webs as commonly used for register allocation purposes and assign
9290 each web individual pseudo register. This allows the register allocation pass
9291 to operate on pseudos directly, but also strengthens several other optimization
9292 passes, such as CSE, loop optimizer and trivial dead code remover. It can,
9293 however, make debugging impossible, since variables no longer stay in a
9296 Enabled by default with @option{-funroll-loops}.
9298 @item -fwhole-program
9299 @opindex fwhole-program
9300 Assume that the current compilation unit represents the whole program being
9301 compiled. All public functions and variables with the exception of @code{main}
9302 and those merged by attribute @code{externally_visible} become static functions
9303 and in effect are optimized more aggressively by interprocedural optimizers.
9305 This option should not be used in combination with @option{-flto}.
9306 Instead relying on a linker plugin should provide safer and more precise
9309 @item -flto[=@var{n}]
9311 This option runs the standard link-time optimizer. When invoked
9312 with source code, it generates GIMPLE (one of GCC's internal
9313 representations) and writes it to special ELF sections in the object
9314 file. When the object files are linked together, all the function
9315 bodies are read from these ELF sections and instantiated as if they
9316 had been part of the same translation unit.
9318 To use the link-time optimizer, @option{-flto} and optimization
9319 options should be specified at compile time and during the final link.
9320 It is recommended that you compile all the files participating in the
9321 same link with the same options and also specify those options at
9326 gcc -c -O2 -flto foo.c
9327 gcc -c -O2 -flto bar.c
9328 gcc -o myprog -flto -O2 foo.o bar.o
9331 The first two invocations to GCC save a bytecode representation
9332 of GIMPLE into special ELF sections inside @file{foo.o} and
9333 @file{bar.o}. The final invocation reads the GIMPLE bytecode from
9334 @file{foo.o} and @file{bar.o}, merges the two files into a single
9335 internal image, and compiles the result as usual. Since both
9336 @file{foo.o} and @file{bar.o} are merged into a single image, this
9337 causes all the interprocedural analyses and optimizations in GCC to
9338 work across the two files as if they were a single one. This means,
9339 for example, that the inliner is able to inline functions in
9340 @file{bar.o} into functions in @file{foo.o} and vice-versa.
9342 Another (simpler) way to enable link-time optimization is:
9345 gcc -o myprog -flto -O2 foo.c bar.c
9348 The above generates bytecode for @file{foo.c} and @file{bar.c},
9349 merges them together into a single GIMPLE representation and optimizes
9350 them as usual to produce @file{myprog}.
9352 The only important thing to keep in mind is that to enable link-time
9353 optimizations you need to use the GCC driver to perform the link step.
9354 GCC then automatically performs link-time optimization if any of the
9355 objects involved were compiled with the @option{-flto} command-line option.
9357 should specify the optimization options to be used for link-time
9358 optimization though GCC tries to be clever at guessing an
9359 optimization level to use from the options used at compile time
9360 if you fail to specify one at link time. You can always override
9361 the automatic decision to do link-time optimization
9362 by passing @option{-fno-lto} to the link command.
9364 To make whole program optimization effective, it is necessary to make
9365 certain whole program assumptions. The compiler needs to know
9366 what functions and variables can be accessed by libraries and runtime
9367 outside of the link-time optimized unit. When supported by the linker,
9368 the linker plugin (see @option{-fuse-linker-plugin}) passes information
9369 to the compiler about used and externally visible symbols. When
9370 the linker plugin is not available, @option{-fwhole-program} should be
9371 used to allow the compiler to make these assumptions, which leads
9372 to more aggressive optimization decisions.
9374 When @option{-fuse-linker-plugin} is not enabled, when a file is
9375 compiled with @option{-flto}, the generated object file is larger than
9376 a regular object file because it contains GIMPLE bytecodes and the usual
9377 final code (see @option{-ffat-lto-objects}. This means that
9378 object files with LTO information can be linked as normal object
9379 files; if @option{-fno-lto} is passed to the linker, no
9380 interprocedural optimizations are applied. Note that when
9381 @option{-fno-fat-lto-objects} is enabled the compile stage is faster
9382 but you cannot perform a regular, non-LTO link on them.
9384 Additionally, the optimization flags used to compile individual files
9385 are not necessarily related to those used at link time. For instance,
9388 gcc -c -O0 -ffat-lto-objects -flto foo.c
9389 gcc -c -O0 -ffat-lto-objects -flto bar.c
9390 gcc -o myprog -O3 foo.o bar.o
9393 This produces individual object files with unoptimized assembler
9394 code, but the resulting binary @file{myprog} is optimized at
9395 @option{-O3}. If, instead, the final binary is generated with
9396 @option{-fno-lto}, then @file{myprog} is not optimized.
9398 When producing the final binary, GCC only
9399 applies link-time optimizations to those files that contain bytecode.
9400 Therefore, you can mix and match object files and libraries with
9401 GIMPLE bytecodes and final object code. GCC automatically selects
9402 which files to optimize in LTO mode and which files to link without
9405 There are some code generation flags preserved by GCC when
9406 generating bytecodes, as they need to be used during the final link
9407 stage. Generally options specified at link time override those
9408 specified at compile time.
9410 If you do not specify an optimization level option @option{-O} at
9411 link time, then GCC uses the highest optimization level
9412 used when compiling the object files.
9414 Currently, the following options and their settings are taken from
9415 the first object file that explicitly specifies them:
9416 @option{-fPIC}, @option{-fpic}, @option{-fpie}, @option{-fcommon},
9417 @option{-fexceptions}, @option{-fnon-call-exceptions}, @option{-fgnu-tm}
9418 and all the @option{-m} target flags.
9420 Certain ABI-changing flags are required to match in all compilation units,
9421 and trying to override this at link time with a conflicting value
9422 is ignored. This includes options such as @option{-freg-struct-return}
9423 and @option{-fpcc-struct-return}.
9425 Other options such as @option{-ffp-contract}, @option{-fno-strict-overflow},
9426 @option{-fwrapv}, @option{-fno-trapv} or @option{-fno-strict-aliasing}
9427 are passed through to the link stage and merged conservatively for
9428 conflicting translation units. Specifically
9429 @option{-fno-strict-overflow}, @option{-fwrapv} and @option{-fno-trapv} take
9430 precedence; and for example @option{-ffp-contract=off} takes precedence
9431 over @option{-ffp-contract=fast}. You can override them at link time.
9433 If LTO encounters objects with C linkage declared with incompatible
9434 types in separate translation units to be linked together (undefined
9435 behavior according to ISO C99 6.2.7), a non-fatal diagnostic may be
9436 issued. The behavior is still undefined at run time. Similar
9437 diagnostics may be raised for other languages.
9439 Another feature of LTO is that it is possible to apply interprocedural
9440 optimizations on files written in different languages:
9445 gfortran -c -flto baz.f90
9446 g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran
9449 Notice that the final link is done with @command{g++} to get the C++
9450 runtime libraries and @option{-lgfortran} is added to get the Fortran
9451 runtime libraries. In general, when mixing languages in LTO mode, you
9452 should use the same link command options as when mixing languages in a
9453 regular (non-LTO) compilation.
9455 If object files containing GIMPLE bytecode are stored in a library archive, say
9456 @file{libfoo.a}, it is possible to extract and use them in an LTO link if you
9457 are using a linker with plugin support. To create static libraries suitable
9458 for LTO, use @command{gcc-ar} and @command{gcc-ranlib} instead of @command{ar}
9459 and @command{ranlib};
9460 to show the symbols of object files with GIMPLE bytecode, use
9461 @command{gcc-nm}. Those commands require that @command{ar}, @command{ranlib}
9462 and @command{nm} have been compiled with plugin support. At link time, use the the
9463 flag @option{-fuse-linker-plugin} to ensure that the library participates in
9464 the LTO optimization process:
9467 gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo
9470 With the linker plugin enabled, the linker extracts the needed
9471 GIMPLE files from @file{libfoo.a} and passes them on to the running GCC
9472 to make them part of the aggregated GIMPLE image to be optimized.
9474 If you are not using a linker with plugin support and/or do not
9475 enable the linker plugin, then the objects inside @file{libfoo.a}
9476 are extracted and linked as usual, but they do not participate
9477 in the LTO optimization process. In order to make a static library suitable
9478 for both LTO optimization and usual linkage, compile its object files with
9479 @option{-flto} @option{-ffat-lto-objects}.
9481 Link-time optimizations do not require the presence of the whole program to
9482 operate. If the program does not require any symbols to be exported, it is
9483 possible to combine @option{-flto} and @option{-fwhole-program} to allow
9484 the interprocedural optimizers to use more aggressive assumptions which may
9485 lead to improved optimization opportunities.
9486 Use of @option{-fwhole-program} is not needed when linker plugin is
9487 active (see @option{-fuse-linker-plugin}).
9489 The current implementation of LTO makes no
9490 attempt to generate bytecode that is portable between different
9491 types of hosts. The bytecode files are versioned and there is a
9492 strict version check, so bytecode files generated in one version of
9493 GCC do not work with an older or newer version of GCC.
9495 Link-time optimization does not work well with generation of debugging
9496 information on systems other than those using a combination of ELF and
9499 If you specify the optional @var{n}, the optimization and code
9500 generation done at link time is executed in parallel using @var{n}
9501 parallel jobs by utilizing an installed @command{make} program. The
9502 environment variable @env{MAKE} may be used to override the program
9503 used. The default value for @var{n} is 1.
9505 You can also specify @option{-flto=jobserver} to use GNU make's
9506 job server mode to determine the number of parallel jobs. This
9507 is useful when the Makefile calling GCC is already executing in parallel.
9508 You must prepend a @samp{+} to the command recipe in the parent Makefile
9509 for this to work. This option likely only works if @env{MAKE} is
9512 @item -flto-partition=@var{alg}
9513 @opindex flto-partition
9514 Specify the partitioning algorithm used by the link-time optimizer.
9515 The value is either @samp{1to1} to specify a partitioning mirroring
9516 the original source files or @samp{balanced} to specify partitioning
9517 into equally sized chunks (whenever possible) or @samp{max} to create
9518 new partition for every symbol where possible. Specifying @samp{none}
9519 as an algorithm disables partitioning and streaming completely.
9520 The default value is @samp{balanced}. While @samp{1to1} can be used
9521 as an workaround for various code ordering issues, the @samp{max}
9522 partitioning is intended for internal testing only.
9523 The value @samp{one} specifies that exactly one partition should be
9524 used while the value @samp{none} bypasses partitioning and executes
9525 the link-time optimization step directly from the WPA phase.
9527 @item -flto-odr-type-merging
9528 @opindex flto-odr-type-merging
9529 Enable streaming of mangled types names of C++ types and their unification
9530 at link time. This increases size of LTO object files, but enables
9531 diagnostics about One Definition Rule violations.
9533 @item -flto-compression-level=@var{n}
9534 @opindex flto-compression-level
9535 This option specifies the level of compression used for intermediate
9536 language written to LTO object files, and is only meaningful in
9537 conjunction with LTO mode (@option{-flto}). Valid
9538 values are 0 (no compression) to 9 (maximum compression). Values
9539 outside this range are clamped to either 0 or 9. If the option is not
9540 given, a default balanced compression setting is used.
9542 @item -fuse-linker-plugin
9543 @opindex fuse-linker-plugin
9544 Enables the use of a linker plugin during link-time optimization. This
9545 option relies on plugin support in the linker, which is available in gold
9546 or in GNU ld 2.21 or newer.
9548 This option enables the extraction of object files with GIMPLE bytecode out
9549 of library archives. This improves the quality of optimization by exposing
9550 more code to the link-time optimizer. This information specifies what
9551 symbols can be accessed externally (by non-LTO object or during dynamic
9552 linking). Resulting code quality improvements on binaries (and shared
9553 libraries that use hidden visibility) are similar to @option{-fwhole-program}.
9554 See @option{-flto} for a description of the effect of this flag and how to
9557 This option is enabled by default when LTO support in GCC is enabled
9558 and GCC was configured for use with
9559 a linker supporting plugins (GNU ld 2.21 or newer or gold).
9561 @item -ffat-lto-objects
9562 @opindex ffat-lto-objects
9563 Fat LTO objects are object files that contain both the intermediate language
9564 and the object code. This makes them usable for both LTO linking and normal
9565 linking. This option is effective only when compiling with @option{-flto}
9566 and is ignored at link time.
9568 @option{-fno-fat-lto-objects} improves compilation time over plain LTO, but
9569 requires the complete toolchain to be aware of LTO. It requires a linker with
9570 linker plugin support for basic functionality. Additionally,
9571 @command{nm}, @command{ar} and @command{ranlib}
9572 need to support linker plugins to allow a full-featured build environment
9573 (capable of building static libraries etc). GCC provides the @command{gcc-ar},
9574 @command{gcc-nm}, @command{gcc-ranlib} wrappers to pass the right options
9575 to these tools. With non fat LTO makefiles need to be modified to use them.
9577 Note that modern binutils provide plugin auto-load mechanism.
9578 Installing the linker plugin into @file{$libdir/bfd-plugins} has the same
9579 effect as usage of the command wrappers (@command{gcc-ar}, @command{gcc-nm} and
9580 @command{gcc-ranlib}).
9582 The default is @option{-fno-fat-lto-objects} on targets with linker plugin
9585 @item -fcompare-elim
9586 @opindex fcompare-elim
9587 After register allocation and post-register allocation instruction splitting,
9588 identify arithmetic instructions that compute processor flags similar to a
9589 comparison operation based on that arithmetic. If possible, eliminate the
9590 explicit comparison operation.
9592 This pass only applies to certain targets that cannot explicitly represent
9593 the comparison operation before register allocation is complete.
9595 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
9597 @item -fcprop-registers
9598 @opindex fcprop-registers
9599 After register allocation and post-register allocation instruction splitting,
9600 perform a copy-propagation pass to try to reduce scheduling dependencies
9601 and occasionally eliminate the copy.
9603 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
9605 @item -fprofile-correction
9606 @opindex fprofile-correction
9607 Profiles collected using an instrumented binary for multi-threaded programs may
9608 be inconsistent due to missed counter updates. When this option is specified,
9609 GCC uses heuristics to correct or smooth out such inconsistencies. By
9610 default, GCC emits an error message when an inconsistent profile is detected.
9613 @itemx -fprofile-use=@var{path}
9614 @opindex fprofile-use
9615 Enable profile feedback-directed optimizations,
9616 and the following optimizations
9617 which are generally profitable only with profile feedback available:
9618 @option{-fbranch-probabilities}, @option{-fvpt},
9619 @option{-funroll-loops}, @option{-fpeel-loops}, @option{-ftracer},
9620 @option{-ftree-vectorize}, and @option{ftree-loop-distribute-patterns}.
9622 Before you can use this option, you must first generate profiling information.
9623 @xref{Instrumentation Options}, for information about the
9624 @option{-fprofile-generate} option.
9626 By default, GCC emits an error message if the feedback profiles do not
9627 match the source code. This error can be turned into a warning by using
9628 @option{-Wcoverage-mismatch}. Note this may result in poorly optimized
9631 If @var{path} is specified, GCC looks at the @var{path} to find
9632 the profile feedback data files. See @option{-fprofile-dir}.
9634 @item -fauto-profile
9635 @itemx -fauto-profile=@var{path}
9636 @opindex fauto-profile
9637 Enable sampling-based feedback-directed optimizations,
9638 and the following optimizations
9639 which are generally profitable only with profile feedback available:
9640 @option{-fbranch-probabilities}, @option{-fvpt},
9641 @option{-funroll-loops}, @option{-fpeel-loops}, @option{-ftracer},
9642 @option{-ftree-vectorize},
9643 @option{-finline-functions}, @option{-fipa-cp}, @option{-fipa-cp-clone},
9644 @option{-fpredictive-commoning}, @option{-funswitch-loops},
9645 @option{-fgcse-after-reload}, and @option{-ftree-loop-distribute-patterns}.
9647 @var{path} is the name of a file containing AutoFDO profile information.
9648 If omitted, it defaults to @file{fbdata.afdo} in the current directory.
9650 Producing an AutoFDO profile data file requires running your program
9651 with the @command{perf} utility on a supported GNU/Linux target system.
9652 For more information, see @uref{https://perf.wiki.kernel.org/}.
9656 perf record -e br_inst_retired:near_taken -b -o perf.data \
9660 Then use the @command{create_gcov} tool to convert the raw profile data
9661 to a format that can be used by GCC.@ You must also supply the
9662 unstripped binary for your program to this tool.
9663 See @uref{https://github.com/google/autofdo}.
9667 create_gcov --binary=your_program.unstripped --profile=perf.data \
9672 The following options control compiler behavior regarding floating-point
9673 arithmetic. These options trade off between speed and
9674 correctness. All must be specifically enabled.
9678 @opindex ffloat-store
9679 Do not store floating-point variables in registers, and inhibit other
9680 options that might change whether a floating-point value is taken from a
9683 @cindex floating-point precision
9684 This option prevents undesirable excess precision on machines such as
9685 the 68000 where the floating registers (of the 68881) keep more
9686 precision than a @code{double} is supposed to have. Similarly for the
9687 x86 architecture. For most programs, the excess precision does only
9688 good, but a few programs rely on the precise definition of IEEE floating
9689 point. Use @option{-ffloat-store} for such programs, after modifying
9690 them to store all pertinent intermediate computations into variables.
9692 @item -fexcess-precision=@var{style}
9693 @opindex fexcess-precision
9694 This option allows further control over excess precision on machines
9695 where floating-point operations occur in a format with more precision or
9696 range than the IEEE standard and interchange floating-point types. By
9697 default, @option{-fexcess-precision=fast} is in effect; this means that
9698 operations may be carried out in a wider precision than the types specified
9699 in the source if that would result in faster code, and it is unpredictable
9700 when rounding to the types specified in the source code takes place.
9701 When compiling C, if @option{-fexcess-precision=standard} is specified then
9702 excess precision follows the rules specified in ISO C99; in particular,
9703 both casts and assignments cause values to be rounded to their
9704 semantic types (whereas @option{-ffloat-store} only affects
9705 assignments). This option is enabled by default for C if a strict
9706 conformance option such as @option{-std=c99} is used.
9707 @option{-ffast-math} enables @option{-fexcess-precision=fast} by default
9708 regardless of whether a strict conformance option is used.
9711 @option{-fexcess-precision=standard} is not implemented for languages
9712 other than C. On the x86, it has no effect if @option{-mfpmath=sse}
9713 or @option{-mfpmath=sse+387} is specified; in the former case, IEEE
9714 semantics apply without excess precision, and in the latter, rounding
9719 Sets the options @option{-fno-math-errno}, @option{-funsafe-math-optimizations},
9720 @option{-ffinite-math-only}, @option{-fno-rounding-math},
9721 @option{-fno-signaling-nans}, @option{-fcx-limited-range} and
9722 @option{-fexcess-precision=fast}.
9724 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
9726 This option is not turned on by any @option{-O} option besides
9727 @option{-Ofast} since it can result in incorrect output for programs
9728 that depend on an exact implementation of IEEE or ISO rules/specifications
9729 for math functions. It may, however, yield faster code for programs
9730 that do not require the guarantees of these specifications.
9732 @item -fno-math-errno
9733 @opindex fno-math-errno
9734 Do not set @code{errno} after calling math functions that are executed
9735 with a single instruction, e.g., @code{sqrt}. A program that relies on
9736 IEEE exceptions for math error handling may want to use this flag
9737 for speed while maintaining IEEE arithmetic compatibility.
9739 This option is not turned on by any @option{-O} option since
9740 it can result in incorrect output for programs that depend on
9741 an exact implementation of IEEE or ISO rules/specifications for
9742 math functions. It may, however, yield faster code for programs
9743 that do not require the guarantees of these specifications.
9745 The default is @option{-fmath-errno}.
9747 On Darwin systems, the math library never sets @code{errno}. There is
9748 therefore no reason for the compiler to consider the possibility that
9749 it might, and @option{-fno-math-errno} is the default.
9751 @item -funsafe-math-optimizations
9752 @opindex funsafe-math-optimizations
9754 Allow optimizations for floating-point arithmetic that (a) assume
9755 that arguments and results are valid and (b) may violate IEEE or
9756 ANSI standards. When used at link time, it may include libraries
9757 or startup files that change the default FPU control word or other
9758 similar optimizations.
9760 This option is not turned on by any @option{-O} option since
9761 it can result in incorrect output for programs that depend on
9762 an exact implementation of IEEE or ISO rules/specifications for
9763 math functions. It may, however, yield faster code for programs
9764 that do not require the guarantees of these specifications.
9765 Enables @option{-fno-signed-zeros}, @option{-fno-trapping-math},
9766 @option{-fassociative-math} and @option{-freciprocal-math}.
9768 The default is @option{-fno-unsafe-math-optimizations}.
9770 @item -fassociative-math
9771 @opindex fassociative-math
9773 Allow re-association of operands in series of floating-point operations.
9774 This violates the ISO C and C++ language standard by possibly changing
9775 computation result. NOTE: re-ordering may change the sign of zero as
9776 well as ignore NaNs and inhibit or create underflow or overflow (and
9777 thus cannot be used on code that relies on rounding behavior like
9778 @code{(x + 2**52) - 2**52}. May also reorder floating-point comparisons
9779 and thus may not be used when ordered comparisons are required.
9780 This option requires that both @option{-fno-signed-zeros} and
9781 @option{-fno-trapping-math} be in effect. Moreover, it doesn't make
9782 much sense with @option{-frounding-math}. For Fortran the option
9783 is automatically enabled when both @option{-fno-signed-zeros} and
9784 @option{-fno-trapping-math} are in effect.
9786 The default is @option{-fno-associative-math}.
9788 @item -freciprocal-math
9789 @opindex freciprocal-math
9791 Allow the reciprocal of a value to be used instead of dividing by
9792 the value if this enables optimizations. For example @code{x / y}
9793 can be replaced with @code{x * (1/y)}, which is useful if @code{(1/y)}
9794 is subject to common subexpression elimination. Note that this loses
9795 precision and increases the number of flops operating on the value.
9797 The default is @option{-fno-reciprocal-math}.
9799 @item -ffinite-math-only
9800 @opindex ffinite-math-only
9801 Allow optimizations for floating-point arithmetic that assume
9802 that arguments and results are not NaNs or +-Infs.
9804 This option is not turned on by any @option{-O} option since
9805 it can result in incorrect output for programs that depend on
9806 an exact implementation of IEEE or ISO rules/specifications for
9807 math functions. It may, however, yield faster code for programs
9808 that do not require the guarantees of these specifications.
9810 The default is @option{-fno-finite-math-only}.
9812 @item -fno-signed-zeros
9813 @opindex fno-signed-zeros
9814 Allow optimizations for floating-point arithmetic that ignore the
9815 signedness of zero. IEEE arithmetic specifies the behavior of
9816 distinct +0.0 and @minus{}0.0 values, which then prohibits simplification
9817 of expressions such as x+0.0 or 0.0*x (even with @option{-ffinite-math-only}).
9818 This option implies that the sign of a zero result isn't significant.
9820 The default is @option{-fsigned-zeros}.
9822 @item -fno-trapping-math
9823 @opindex fno-trapping-math
9824 Compile code assuming that floating-point operations cannot generate
9825 user-visible traps. These traps include division by zero, overflow,
9826 underflow, inexact result and invalid operation. This option requires
9827 that @option{-fno-signaling-nans} be in effect. Setting this option may
9828 allow faster code if one relies on ``non-stop'' IEEE arithmetic, for example.
9830 This option should never be turned on by any @option{-O} option since
9831 it can result in incorrect output for programs that depend on
9832 an exact implementation of IEEE or ISO rules/specifications for
9835 The default is @option{-ftrapping-math}.
9837 @item -frounding-math
9838 @opindex frounding-math
9839 Disable transformations and optimizations that assume default floating-point
9840 rounding behavior. This is round-to-zero for all floating point
9841 to integer conversions, and round-to-nearest for all other arithmetic
9842 truncations. This option should be specified for programs that change
9843 the FP rounding mode dynamically, or that may be executed with a
9844 non-default rounding mode. This option disables constant folding of
9845 floating-point expressions at compile time (which may be affected by
9846 rounding mode) and arithmetic transformations that are unsafe in the
9847 presence of sign-dependent rounding modes.
9849 The default is @option{-fno-rounding-math}.
9851 This option is experimental and does not currently guarantee to
9852 disable all GCC optimizations that are affected by rounding mode.
9853 Future versions of GCC may provide finer control of this setting
9854 using C99's @code{FENV_ACCESS} pragma. This command-line option
9855 will be used to specify the default state for @code{FENV_ACCESS}.
9857 @item -fsignaling-nans
9858 @opindex fsignaling-nans
9859 Compile code assuming that IEEE signaling NaNs may generate user-visible
9860 traps during floating-point operations. Setting this option disables
9861 optimizations that may change the number of exceptions visible with
9862 signaling NaNs. This option implies @option{-ftrapping-math}.
9864 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
9867 The default is @option{-fno-signaling-nans}.
9869 This option is experimental and does not currently guarantee to
9870 disable all GCC optimizations that affect signaling NaN behavior.
9872 @item -fno-fp-int-builtin-inexact
9873 @opindex fno-fp-int-builtin-inexact
9874 Do not allow the built-in functions @code{ceil}, @code{floor},
9875 @code{round} and @code{trunc}, and their @code{float} and @code{long
9876 double} variants, to generate code that raises the ``inexact''
9877 floating-point exception for noninteger arguments. ISO C99 and C11
9878 allow these functions to raise the ``inexact'' exception, but ISO/IEC
9879 TS 18661-1:2014, the C bindings to IEEE 754-2008, does not allow these
9882 The default is @option{-ffp-int-builtin-inexact}, allowing the
9883 exception to be raised. This option does nothing unless
9884 @option{-ftrapping-math} is in effect.
9886 Even if @option{-fno-fp-int-builtin-inexact} is used, if the functions
9887 generate a call to a library function then the ``inexact'' exception
9888 may be raised if the library implementation does not follow TS 18661.
9890 @item -fsingle-precision-constant
9891 @opindex fsingle-precision-constant
9892 Treat floating-point constants as single precision instead of
9893 implicitly converting them to double-precision constants.
9895 @item -fcx-limited-range
9896 @opindex fcx-limited-range
9897 When enabled, this option states that a range reduction step is not
9898 needed when performing complex division. Also, there is no checking
9899 whether the result of a complex multiplication or division is @code{NaN
9900 + I*NaN}, with an attempt to rescue the situation in that case. The
9901 default is @option{-fno-cx-limited-range}, but is enabled by
9902 @option{-ffast-math}.
9904 This option controls the default setting of the ISO C99
9905 @code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to
9908 @item -fcx-fortran-rules
9909 @opindex fcx-fortran-rules
9910 Complex multiplication and division follow Fortran rules. Range
9911 reduction is done as part of complex division, but there is no checking
9912 whether the result of a complex multiplication or division is @code{NaN
9913 + I*NaN}, with an attempt to rescue the situation in that case.
9915 The default is @option{-fno-cx-fortran-rules}.
9919 The following options control optimizations that may improve
9920 performance, but are not enabled by any @option{-O} options. This
9921 section includes experimental options that may produce broken code.
9924 @item -fbranch-probabilities
9925 @opindex fbranch-probabilities
9926 After running a program compiled with @option{-fprofile-arcs}
9927 (@pxref{Instrumentation Options}),
9928 you can compile it a second time using
9929 @option{-fbranch-probabilities}, to improve optimizations based on
9930 the number of times each branch was taken. When a program
9931 compiled with @option{-fprofile-arcs} exits, it saves arc execution
9932 counts to a file called @file{@var{sourcename}.gcda} for each source
9933 file. The information in this data file is very dependent on the
9934 structure of the generated code, so you must use the same source code
9935 and the same optimization options for both compilations.
9937 With @option{-fbranch-probabilities}, GCC puts a
9938 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
9939 These can be used to improve optimization. Currently, they are only
9940 used in one place: in @file{reorg.c}, instead of guessing which path a
9941 branch is most likely to take, the @samp{REG_BR_PROB} values are used to
9942 exactly determine which path is taken more often.
9944 @item -fprofile-values
9945 @opindex fprofile-values
9946 If combined with @option{-fprofile-arcs}, it adds code so that some
9947 data about values of expressions in the program is gathered.
9949 With @option{-fbranch-probabilities}, it reads back the data gathered
9950 from profiling values of expressions for usage in optimizations.
9952 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
9954 @item -fprofile-reorder-functions
9955 @opindex fprofile-reorder-functions
9956 Function reordering based on profile instrumentation collects
9957 first time of execution of a function and orders these functions
9960 Enabled with @option{-fprofile-use}.
9964 If combined with @option{-fprofile-arcs}, this option instructs the compiler
9965 to add code to gather information about values of expressions.
9967 With @option{-fbranch-probabilities}, it reads back the data gathered
9968 and actually performs the optimizations based on them.
9969 Currently the optimizations include specialization of division operations
9970 using the knowledge about the value of the denominator.
9972 @item -frename-registers
9973 @opindex frename-registers
9974 Attempt to avoid false dependencies in scheduled code by making use
9975 of registers left over after register allocation. This optimization
9976 most benefits processors with lots of registers. Depending on the
9977 debug information format adopted by the target, however, it can
9978 make debugging impossible, since variables no longer stay in
9979 a ``home register''.
9981 Enabled by default with @option{-funroll-loops}.
9983 @item -fschedule-fusion
9984 @opindex fschedule-fusion
9985 Performs a target dependent pass over the instruction stream to schedule
9986 instructions of same type together because target machine can execute them
9987 more efficiently if they are adjacent to each other in the instruction flow.
9989 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
9993 Perform tail duplication to enlarge superblock size. This transformation
9994 simplifies the control flow of the function allowing other optimizations to do
9997 Enabled with @option{-fprofile-use}.
9999 @item -funroll-loops
10000 @opindex funroll-loops
10001 Unroll loops whose number of iterations can be determined at compile time or
10002 upon entry to the loop. @option{-funroll-loops} implies
10003 @option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}.
10004 It also turns on complete loop peeling (i.e.@: complete removal of loops with
10005 a small constant number of iterations). This option makes code larger, and may
10006 or may not make it run faster.
10008 Enabled with @option{-fprofile-use}.
10010 @item -funroll-all-loops
10011 @opindex funroll-all-loops
10012 Unroll all loops, even if their number of iterations is uncertain when
10013 the loop is entered. This usually makes programs run more slowly.
10014 @option{-funroll-all-loops} implies the same options as
10015 @option{-funroll-loops}.
10018 @opindex fpeel-loops
10019 Peels loops for which there is enough information that they do not
10020 roll much (from profile feedback or static analysis). It also turns on
10021 complete loop peeling (i.e.@: complete removal of loops with small constant
10022 number of iterations).
10024 Enabled with @option{-O3} and/or @option{-fprofile-use}.
10026 @item -fmove-loop-invariants
10027 @opindex fmove-loop-invariants
10028 Enables the loop invariant motion pass in the RTL loop optimizer. Enabled
10029 at level @option{-O1}
10031 @item -fsplit-loops
10032 @opindex fsplit-loops
10033 Split a loop into two if it contains a condition that's always true
10034 for one side of the iteration space and false for the other.
10036 @item -funswitch-loops
10037 @opindex funswitch-loops
10038 Move branches with loop invariant conditions out of the loop, with duplicates
10039 of the loop on both branches (modified according to result of the condition).
10041 @item -floop-unroll-and-jam
10042 @opindex floop-unroll-and-jam
10043 Apply unroll and jam transformations on feasible loops. In a loop
10044 nest this unrolls the outer loop by some factor and fuses the resulting
10045 multiple inner loops.
10047 @item -ffunction-sections
10048 @itemx -fdata-sections
10049 @opindex ffunction-sections
10050 @opindex fdata-sections
10051 Place each function or data item into its own section in the output
10052 file if the target supports arbitrary sections. The name of the
10053 function or the name of the data item determines the section's name
10054 in the output file.
10056 Use these options on systems where the linker can perform optimizations to
10057 improve locality of reference in the instruction space. Most systems using the
10058 ELF object format have linkers with such optimizations. On AIX, the linker
10059 rearranges sections (CSECTs) based on the call graph. The performance impact
10062 Together with a linker garbage collection (linker @option{--gc-sections}
10063 option) these options may lead to smaller statically-linked executables (after
10066 On ELF/DWARF systems these options do not degenerate the quality of the debug
10067 information. There could be issues with other object files/debug info formats.
10069 Only use these options when there are significant benefits from doing so. When
10070 you specify these options, the assembler and linker create larger object and
10071 executable files and are also slower. These options affect code generation.
10072 They prevent optimizations by the compiler and assembler using relative
10073 locations inside a translation unit since the locations are unknown until
10074 link time. An example of such an optimization is relaxing calls to short call
10077 @item -fbranch-target-load-optimize
10078 @opindex fbranch-target-load-optimize
10079 Perform branch target register load optimization before prologue / epilogue
10081 The use of target registers can typically be exposed only during reload,
10082 thus hoisting loads out of loops and doing inter-block scheduling needs
10083 a separate optimization pass.
10085 @item -fbranch-target-load-optimize2
10086 @opindex fbranch-target-load-optimize2
10087 Perform branch target register load optimization after prologue / epilogue
10090 @item -fbtr-bb-exclusive
10091 @opindex fbtr-bb-exclusive
10092 When performing branch target register load optimization, don't reuse
10093 branch target registers within any basic block.
10096 @opindex fstdarg-opt
10097 Optimize the prologue of variadic argument functions with respect to usage of
10100 @item -fsection-anchors
10101 @opindex fsection-anchors
10102 Try to reduce the number of symbolic address calculations by using
10103 shared ``anchor'' symbols to address nearby objects. This transformation
10104 can help to reduce the number of GOT entries and GOT accesses on some
10107 For example, the implementation of the following function @code{foo}:
10110 static int a, b, c;
10111 int foo (void) @{ return a + b + c; @}
10115 usually calculates the addresses of all three variables, but if you
10116 compile it with @option{-fsection-anchors}, it accesses the variables
10117 from a common anchor point instead. The effect is similar to the
10118 following pseudocode (which isn't valid C):
10123 register int *xr = &x;
10124 return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
10128 Not all targets support this option.
10130 @item --param @var{name}=@var{value}
10132 In some places, GCC uses various constants to control the amount of
10133 optimization that is done. For example, GCC does not inline functions
10134 that contain more than a certain number of instructions. You can
10135 control some of these constants on the command line using the
10136 @option{--param} option.
10138 The names of specific parameters, and the meaning of the values, are
10139 tied to the internals of the compiler, and are subject to change
10140 without notice in future releases.
10142 In each case, the @var{value} is an integer. The allowable choices for
10146 @item predictable-branch-outcome
10147 When branch is predicted to be taken with probability lower than this threshold
10148 (in percent), then it is considered well predictable. The default is 10.
10150 @item max-rtl-if-conversion-insns
10151 RTL if-conversion tries to remove conditional branches around a block and
10152 replace them with conditionally executed instructions. This parameter
10153 gives the maximum number of instructions in a block which should be
10154 considered for if-conversion. The default is 10, though the compiler will
10155 also use other heuristics to decide whether if-conversion is likely to be
10158 @item max-rtl-if-conversion-predictable-cost
10159 @itemx max-rtl-if-conversion-unpredictable-cost
10160 RTL if-conversion will try to remove conditional branches around a block
10161 and replace them with conditionally executed instructions. These parameters
10162 give the maximum permissible cost for the sequence that would be generated
10163 by if-conversion depending on whether the branch is statically determined
10164 to be predictable or not. The units for this parameter are the same as
10165 those for the GCC internal seq_cost metric. The compiler will try to
10166 provide a reasonable default for this parameter using the BRANCH_COST
10169 @item max-crossjump-edges
10170 The maximum number of incoming edges to consider for cross-jumping.
10171 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
10172 the number of edges incoming to each block. Increasing values mean
10173 more aggressive optimization, making the compilation time increase with
10174 probably small improvement in executable size.
10176 @item min-crossjump-insns
10177 The minimum number of instructions that must be matched at the end
10178 of two blocks before cross-jumping is performed on them. This
10179 value is ignored in the case where all instructions in the block being
10180 cross-jumped from are matched. The default value is 5.
10182 @item max-grow-copy-bb-insns
10183 The maximum code size expansion factor when copying basic blocks
10184 instead of jumping. The expansion is relative to a jump instruction.
10185 The default value is 8.
10187 @item max-goto-duplication-insns
10188 The maximum number of instructions to duplicate to a block that jumps
10189 to a computed goto. To avoid @math{O(N^2)} behavior in a number of
10190 passes, GCC factors computed gotos early in the compilation process,
10191 and unfactors them as late as possible. Only computed jumps at the
10192 end of a basic blocks with no more than max-goto-duplication-insns are
10193 unfactored. The default value is 8.
10195 @item max-delay-slot-insn-search
10196 The maximum number of instructions to consider when looking for an
10197 instruction to fill a delay slot. If more than this arbitrary number of
10198 instructions are searched, the time savings from filling the delay slot
10199 are minimal, so stop searching. Increasing values mean more
10200 aggressive optimization, making the compilation time increase with probably
10201 small improvement in execution time.
10203 @item max-delay-slot-live-search
10204 When trying to fill delay slots, the maximum number of instructions to
10205 consider when searching for a block with valid live register
10206 information. Increasing this arbitrarily chosen value means more
10207 aggressive optimization, increasing the compilation time. This parameter
10208 should be removed when the delay slot code is rewritten to maintain the
10209 control-flow graph.
10211 @item max-gcse-memory
10212 The approximate maximum amount of memory that can be allocated in
10213 order to perform the global common subexpression elimination
10214 optimization. If more memory than specified is required, the
10215 optimization is not done.
10217 @item max-gcse-insertion-ratio
10218 If the ratio of expression insertions to deletions is larger than this value
10219 for any expression, then RTL PRE inserts or removes the expression and thus
10220 leaves partially redundant computations in the instruction stream. The default value is 20.
10222 @item max-pending-list-length
10223 The maximum number of pending dependencies scheduling allows
10224 before flushing the current state and starting over. Large functions
10225 with few branches or calls can create excessively large lists which
10226 needlessly consume memory and resources.
10228 @item max-modulo-backtrack-attempts
10229 The maximum number of backtrack attempts the scheduler should make
10230 when modulo scheduling a loop. Larger values can exponentially increase
10233 @item max-inline-insns-single
10234 Several parameters control the tree inliner used in GCC@.
10235 This number sets the maximum number of instructions (counted in GCC's
10236 internal representation) in a single function that the tree inliner
10237 considers for inlining. This only affects functions declared
10238 inline and methods implemented in a class declaration (C++).
10239 The default value is 400.
10241 @item max-inline-insns-auto
10242 When you use @option{-finline-functions} (included in @option{-O3}),
10243 a lot of functions that would otherwise not be considered for inlining
10244 by the compiler are investigated. To those functions, a different
10245 (more restrictive) limit compared to functions declared inline can
10247 The default value is 30.
10249 @item inline-min-speedup
10250 When estimated performance improvement of caller + callee runtime exceeds this
10251 threshold (in percent), the function can be inlined regardless of the limit on
10252 @option{--param max-inline-insns-single} and @option{--param
10253 max-inline-insns-auto}.
10254 The default value is 15.
10256 @item large-function-insns
10257 The limit specifying really large functions. For functions larger than this
10258 limit after inlining, inlining is constrained by
10259 @option{--param large-function-growth}. This parameter is useful primarily
10260 to avoid extreme compilation time caused by non-linear algorithms used by the
10262 The default value is 2700.
10264 @item large-function-growth
10265 Specifies maximal growth of large function caused by inlining in percents.
10266 The default value is 100 which limits large function growth to 2.0 times
10269 @item large-unit-insns
10270 The limit specifying large translation unit. Growth caused by inlining of
10271 units larger than this limit is limited by @option{--param inline-unit-growth}.
10272 For small units this might be too tight.
10273 For example, consider a unit consisting of function A
10274 that is inline and B that just calls A three times. If B is small relative to
10275 A, the growth of unit is 300\% and yet such inlining is very sane. For very
10276 large units consisting of small inlineable functions, however, the overall unit
10277 growth limit is needed to avoid exponential explosion of code size. Thus for
10278 smaller units, the size is increased to @option{--param large-unit-insns}
10279 before applying @option{--param inline-unit-growth}. The default is 10000.
10281 @item inline-unit-growth
10282 Specifies maximal overall growth of the compilation unit caused by inlining.
10283 The default value is 20 which limits unit growth to 1.2 times the original
10284 size. Cold functions (either marked cold via an attribute or by profile
10285 feedback) are not accounted into the unit size.
10287 @item ipcp-unit-growth
10288 Specifies maximal overall growth of the compilation unit caused by
10289 interprocedural constant propagation. The default value is 10 which limits
10290 unit growth to 1.1 times the original size.
10292 @item large-stack-frame
10293 The limit specifying large stack frames. While inlining the algorithm is trying
10294 to not grow past this limit too much. The default value is 256 bytes.
10296 @item large-stack-frame-growth
10297 Specifies maximal growth of large stack frames caused by inlining in percents.
10298 The default value is 1000 which limits large stack frame growth to 11 times
10301 @item max-inline-insns-recursive
10302 @itemx max-inline-insns-recursive-auto
10303 Specifies the maximum number of instructions an out-of-line copy of a
10304 self-recursive inline
10305 function can grow into by performing recursive inlining.
10307 @option{--param max-inline-insns-recursive} applies to functions
10309 For functions not declared inline, recursive inlining
10310 happens only when @option{-finline-functions} (included in @option{-O3}) is
10311 enabled; @option{--param max-inline-insns-recursive-auto} applies instead. The
10312 default value is 450.
10314 @item max-inline-recursive-depth
10315 @itemx max-inline-recursive-depth-auto
10316 Specifies the maximum recursion depth used for recursive inlining.
10318 @option{--param max-inline-recursive-depth} applies to functions
10319 declared inline. For functions not declared inline, recursive inlining
10320 happens only when @option{-finline-functions} (included in @option{-O3}) is
10321 enabled; @option{--param max-inline-recursive-depth-auto} applies instead. The
10322 default value is 8.
10324 @item min-inline-recursive-probability
10325 Recursive inlining is profitable only for function having deep recursion
10326 in average and can hurt for function having little recursion depth by
10327 increasing the prologue size or complexity of function body to other
10330 When profile feedback is available (see @option{-fprofile-generate}) the actual
10331 recursion depth can be guessed from the probability that function recurses
10332 via a given call expression. This parameter limits inlining only to call
10333 expressions whose probability exceeds the given threshold (in percents).
10334 The default value is 10.
10336 @item early-inlining-insns
10337 Specify growth that the early inliner can make. In effect it increases
10338 the amount of inlining for code having a large abstraction penalty.
10339 The default value is 14.
10341 @item max-early-inliner-iterations
10342 Limit of iterations of the early inliner. This basically bounds
10343 the number of nested indirect calls the early inliner can resolve.
10344 Deeper chains are still handled by late inlining.
10346 @item comdat-sharing-probability
10347 Probability (in percent) that C++ inline function with comdat visibility
10348 are shared across multiple compilation units. The default value is 20.
10350 @item profile-func-internal-id
10351 A parameter to control whether to use function internal id in profile
10352 database lookup. If the value is 0, the compiler uses an id that
10353 is based on function assembler name and filename, which makes old profile
10354 data more tolerant to source changes such as function reordering etc.
10355 The default value is 0.
10357 @item min-vect-loop-bound
10358 The minimum number of iterations under which loops are not vectorized
10359 when @option{-ftree-vectorize} is used. The number of iterations after
10360 vectorization needs to be greater than the value specified by this option
10361 to allow vectorization. The default value is 0.
10363 @item gcse-cost-distance-ratio
10364 Scaling factor in calculation of maximum distance an expression
10365 can be moved by GCSE optimizations. This is currently supported only in the
10366 code hoisting pass. The bigger the ratio, the more aggressive code hoisting
10367 is with simple expressions, i.e., the expressions that have cost
10368 less than @option{gcse-unrestricted-cost}. Specifying 0 disables
10369 hoisting of simple expressions. The default value is 10.
10371 @item gcse-unrestricted-cost
10372 Cost, roughly measured as the cost of a single typical machine
10373 instruction, at which GCSE optimizations do not constrain
10374 the distance an expression can travel. This is currently
10375 supported only in the code hoisting pass. The lesser the cost,
10376 the more aggressive code hoisting is. Specifying 0
10377 allows all expressions to travel unrestricted distances.
10378 The default value is 3.
10380 @item max-hoist-depth
10381 The depth of search in the dominator tree for expressions to hoist.
10382 This is used to avoid quadratic behavior in hoisting algorithm.
10383 The value of 0 does not limit on the search, but may slow down compilation
10384 of huge functions. The default value is 30.
10386 @item max-tail-merge-comparisons
10387 The maximum amount of similar bbs to compare a bb with. This is used to
10388 avoid quadratic behavior in tree tail merging. The default value is 10.
10390 @item max-tail-merge-iterations
10391 The maximum amount of iterations of the pass over the function. This is used to
10392 limit compilation time in tree tail merging. The default value is 2.
10394 @item store-merging-allow-unaligned
10395 Allow the store merging pass to introduce unaligned stores if it is legal to
10396 do so. The default value is 1.
10398 @item max-stores-to-merge
10399 The maximum number of stores to attempt to merge into wider stores in the store
10400 merging pass. The minimum value is 2 and the default is 64.
10402 @item max-unrolled-insns
10403 The maximum number of instructions that a loop may have to be unrolled.
10404 If a loop is unrolled, this parameter also determines how many times
10405 the loop code is unrolled.
10407 @item max-average-unrolled-insns
10408 The maximum number of instructions biased by probabilities of their execution
10409 that a loop may have to be unrolled. If a loop is unrolled,
10410 this parameter also determines how many times the loop code is unrolled.
10412 @item max-unroll-times
10413 The maximum number of unrollings of a single loop.
10415 @item max-peeled-insns
10416 The maximum number of instructions that a loop may have to be peeled.
10417 If a loop is peeled, this parameter also determines how many times
10418 the loop code is peeled.
10420 @item max-peel-times
10421 The maximum number of peelings of a single loop.
10423 @item max-peel-branches
10424 The maximum number of branches on the hot path through the peeled sequence.
10426 @item max-completely-peeled-insns
10427 The maximum number of insns of a completely peeled loop.
10429 @item max-completely-peel-times
10430 The maximum number of iterations of a loop to be suitable for complete peeling.
10432 @item max-completely-peel-loop-nest-depth
10433 The maximum depth of a loop nest suitable for complete peeling.
10435 @item max-unswitch-insns
10436 The maximum number of insns of an unswitched loop.
10438 @item max-unswitch-level
10439 The maximum number of branches unswitched in a single loop.
10441 @item max-loop-headers-insns
10442 The maximum number of insns in loop header duplicated by the copy loop headers
10445 @item lim-expensive
10446 The minimum cost of an expensive expression in the loop invariant motion.
10448 @item iv-consider-all-candidates-bound
10449 Bound on number of candidates for induction variables, below which
10450 all candidates are considered for each use in induction variable
10451 optimizations. If there are more candidates than this,
10452 only the most relevant ones are considered to avoid quadratic time complexity.
10454 @item iv-max-considered-uses
10455 The induction variable optimizations give up on loops that contain more
10456 induction variable uses.
10458 @item iv-always-prune-cand-set-bound
10459 If the number of candidates in the set is smaller than this value,
10460 always try to remove unnecessary ivs from the set
10461 when adding a new one.
10463 @item avg-loop-niter
10464 Average number of iterations of a loop.
10466 @item dse-max-object-size
10467 Maximum size (in bytes) of objects tracked bytewise by dead store elimination.
10468 Larger values may result in larger compilation times.
10470 @item scev-max-expr-size
10471 Bound on size of expressions used in the scalar evolutions analyzer.
10472 Large expressions slow the analyzer.
10474 @item scev-max-expr-complexity
10475 Bound on the complexity of the expressions in the scalar evolutions analyzer.
10476 Complex expressions slow the analyzer.
10478 @item max-tree-if-conversion-phi-args
10479 Maximum number of arguments in a PHI supported by TREE if conversion
10480 unless the loop is marked with simd pragma.
10482 @item vect-max-version-for-alignment-checks
10483 The maximum number of run-time checks that can be performed when
10484 doing loop versioning for alignment in the vectorizer.
10486 @item vect-max-version-for-alias-checks
10487 The maximum number of run-time checks that can be performed when
10488 doing loop versioning for alias in the vectorizer.
10490 @item vect-max-peeling-for-alignment
10491 The maximum number of loop peels to enhance access alignment
10492 for vectorizer. Value -1 means no limit.
10494 @item max-iterations-to-track
10495 The maximum number of iterations of a loop the brute-force algorithm
10496 for analysis of the number of iterations of the loop tries to evaluate.
10498 @item hot-bb-count-ws-permille
10499 A basic block profile count is considered hot if it contributes to
10500 the given permillage (i.e. 0...1000) of the entire profiled execution.
10502 @item hot-bb-frequency-fraction
10503 Select fraction of the entry block frequency of executions of basic block in
10504 function given basic block needs to have to be considered hot.
10506 @item max-predicted-iterations
10507 The maximum number of loop iterations we predict statically. This is useful
10508 in cases where a function contains a single loop with known bound and
10509 another loop with unknown bound.
10510 The known number of iterations is predicted correctly, while
10511 the unknown number of iterations average to roughly 10. This means that the
10512 loop without bounds appears artificially cold relative to the other one.
10514 @item builtin-expect-probability
10515 Control the probability of the expression having the specified value. This
10516 parameter takes a percentage (i.e. 0 ... 100) as input.
10517 The default probability of 90 is obtained empirically.
10519 @item align-threshold
10521 Select fraction of the maximal frequency of executions of a basic block in
10522 a function to align the basic block.
10524 @item align-loop-iterations
10526 A loop expected to iterate at least the selected number of iterations is
10529 @item tracer-dynamic-coverage
10530 @itemx tracer-dynamic-coverage-feedback
10532 This value is used to limit superblock formation once the given percentage of
10533 executed instructions is covered. This limits unnecessary code size
10536 The @option{tracer-dynamic-coverage-feedback} parameter
10537 is used only when profile
10538 feedback is available. The real profiles (as opposed to statically estimated
10539 ones) are much less balanced allowing the threshold to be larger value.
10541 @item tracer-max-code-growth
10542 Stop tail duplication once code growth has reached given percentage. This is
10543 a rather artificial limit, as most of the duplicates are eliminated later in
10544 cross jumping, so it may be set to much higher values than is the desired code
10547 @item tracer-min-branch-ratio
10549 Stop reverse growth when the reverse probability of best edge is less than this
10550 threshold (in percent).
10552 @item tracer-min-branch-probability
10553 @itemx tracer-min-branch-probability-feedback
10555 Stop forward growth if the best edge has probability lower than this
10558 Similarly to @option{tracer-dynamic-coverage} two parameters are
10559 provided. @option{tracer-min-branch-probability-feedback} is used for
10560 compilation with profile feedback and @option{tracer-min-branch-probability}
10561 compilation without. The value for compilation with profile feedback
10562 needs to be more conservative (higher) in order to make tracer
10565 @item stack-clash-protection-guard-size
10566 Specify the size of the operating system provided stack guard as
10567 2 raised to @var{num} bytes. The default value is 12 (4096 bytes).
10568 Acceptable values are between 12 and 30. Higher values may reduce the
10569 number of explicit probes, but a value larger than the operating system
10570 provided guard will leave code vulnerable to stack clash style attacks.
10572 @item stack-clash-protection-probe-interval
10573 Stack clash protection involves probing stack space as it is allocated. This
10574 param controls the maximum distance between probes into the stack as 2 raised
10575 to @var{num} bytes. Acceptable values are between 10 and 16 and defaults to
10576 12. Higher values may reduce the number of explicit probes, but a value
10577 larger than the operating system provided guard will leave code vulnerable to
10578 stack clash style attacks.
10580 @item max-cse-path-length
10582 The maximum number of basic blocks on path that CSE considers.
10585 @item max-cse-insns
10586 The maximum number of instructions CSE processes before flushing.
10587 The default is 1000.
10589 @item ggc-min-expand
10591 GCC uses a garbage collector to manage its own memory allocation. This
10592 parameter specifies the minimum percentage by which the garbage
10593 collector's heap should be allowed to expand between collections.
10594 Tuning this may improve compilation speed; it has no effect on code
10597 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
10598 RAM >= 1GB@. If @code{getrlimit} is available, the notion of ``RAM'' is
10599 the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If
10600 GCC is not able to calculate RAM on a particular platform, the lower
10601 bound of 30% is used. Setting this parameter and
10602 @option{ggc-min-heapsize} to zero causes a full collection to occur at
10603 every opportunity. This is extremely slow, but can be useful for
10606 @item ggc-min-heapsize
10608 Minimum size of the garbage collector's heap before it begins bothering
10609 to collect garbage. The first collection occurs after the heap expands
10610 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
10611 tuning this may improve compilation speed, and has no effect on code
10614 The default is the smaller of RAM/8, RLIMIT_RSS, or a limit that
10615 tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
10616 with a lower bound of 4096 (four megabytes) and an upper bound of
10617 131072 (128 megabytes). If GCC is not able to calculate RAM on a
10618 particular platform, the lower bound is used. Setting this parameter
10619 very large effectively disables garbage collection. Setting this
10620 parameter and @option{ggc-min-expand} to zero causes a full collection
10621 to occur at every opportunity.
10623 @item max-reload-search-insns
10624 The maximum number of instruction reload should look backward for equivalent
10625 register. Increasing values mean more aggressive optimization, making the
10626 compilation time increase with probably slightly better performance.
10627 The default value is 100.
10629 @item max-cselib-memory-locations
10630 The maximum number of memory locations cselib should take into account.
10631 Increasing values mean more aggressive optimization, making the compilation time
10632 increase with probably slightly better performance. The default value is 500.
10634 @item max-sched-ready-insns
10635 The maximum number of instructions ready to be issued the scheduler should
10636 consider at any given time during the first scheduling pass. Increasing
10637 values mean more thorough searches, making the compilation time increase
10638 with probably little benefit. The default value is 100.
10640 @item max-sched-region-blocks
10641 The maximum number of blocks in a region to be considered for
10642 interblock scheduling. The default value is 10.
10644 @item max-pipeline-region-blocks
10645 The maximum number of blocks in a region to be considered for
10646 pipelining in the selective scheduler. The default value is 15.
10648 @item max-sched-region-insns
10649 The maximum number of insns in a region to be considered for
10650 interblock scheduling. The default value is 100.
10652 @item max-pipeline-region-insns
10653 The maximum number of insns in a region to be considered for
10654 pipelining in the selective scheduler. The default value is 200.
10656 @item min-spec-prob
10657 The minimum probability (in percents) of reaching a source block
10658 for interblock speculative scheduling. The default value is 40.
10660 @item max-sched-extend-regions-iters
10661 The maximum number of iterations through CFG to extend regions.
10662 A value of 0 (the default) disables region extensions.
10664 @item max-sched-insn-conflict-delay
10665 The maximum conflict delay for an insn to be considered for speculative motion.
10666 The default value is 3.
10668 @item sched-spec-prob-cutoff
10669 The minimal probability of speculation success (in percents), so that
10670 speculative insns are scheduled.
10671 The default value is 40.
10673 @item sched-state-edge-prob-cutoff
10674 The minimum probability an edge must have for the scheduler to save its
10676 The default value is 10.
10678 @item sched-mem-true-dep-cost
10679 Minimal distance (in CPU cycles) between store and load targeting same
10680 memory locations. The default value is 1.
10682 @item selsched-max-lookahead
10683 The maximum size of the lookahead window of selective scheduling. It is a
10684 depth of search for available instructions.
10685 The default value is 50.
10687 @item selsched-max-sched-times
10688 The maximum number of times that an instruction is scheduled during
10689 selective scheduling. This is the limit on the number of iterations
10690 through which the instruction may be pipelined. The default value is 2.
10692 @item selsched-insns-to-rename
10693 The maximum number of best instructions in the ready list that are considered
10694 for renaming in the selective scheduler. The default value is 2.
10697 The minimum value of stage count that swing modulo scheduler
10698 generates. The default value is 2.
10700 @item max-last-value-rtl
10701 The maximum size measured as number of RTLs that can be recorded in an expression
10702 in combiner for a pseudo register as last known value of that register. The default
10705 @item max-combine-insns
10706 The maximum number of instructions the RTL combiner tries to combine.
10707 The default value is 2 at @option{-Og} and 4 otherwise.
10709 @item integer-share-limit
10710 Small integer constants can use a shared data structure, reducing the
10711 compiler's memory usage and increasing its speed. This sets the maximum
10712 value of a shared integer constant. The default value is 256.
10714 @item ssp-buffer-size
10715 The minimum size of buffers (i.e.@: arrays) that receive stack smashing
10716 protection when @option{-fstack-protection} is used.
10718 @item min-size-for-stack-sharing
10719 The minimum size of variables taking part in stack slot sharing when not
10720 optimizing. The default value is 32.
10722 @item max-jump-thread-duplication-stmts
10723 Maximum number of statements allowed in a block that needs to be
10724 duplicated when threading jumps.
10726 @item max-fields-for-field-sensitive
10727 Maximum number of fields in a structure treated in
10728 a field sensitive manner during pointer analysis. The default is zero
10729 for @option{-O0} and @option{-O1},
10730 and 100 for @option{-Os}, @option{-O2}, and @option{-O3}.
10732 @item prefetch-latency
10733 Estimate on average number of instructions that are executed before
10734 prefetch finishes. The distance prefetched ahead is proportional
10735 to this constant. Increasing this number may also lead to less
10736 streams being prefetched (see @option{simultaneous-prefetches}).
10738 @item simultaneous-prefetches
10739 Maximum number of prefetches that can run at the same time.
10741 @item l1-cache-line-size
10742 The size of cache line in L1 cache, in bytes.
10744 @item l1-cache-size
10745 The size of L1 cache, in kilobytes.
10747 @item l2-cache-size
10748 The size of L2 cache, in kilobytes.
10750 @item loop-interchange-max-num-stmts
10751 The maximum number of stmts in a loop to be interchanged.
10753 @item loop-interchange-stride-ratio
10754 The minimum ratio between stride of two loops for interchange to be profitable.
10756 @item min-insn-to-prefetch-ratio
10757 The minimum ratio between the number of instructions and the
10758 number of prefetches to enable prefetching in a loop.
10760 @item prefetch-min-insn-to-mem-ratio
10761 The minimum ratio between the number of instructions and the
10762 number of memory references to enable prefetching in a loop.
10764 @item use-canonical-types
10765 Whether the compiler should use the ``canonical'' type system. By
10766 default, this should always be 1, which uses a more efficient internal
10767 mechanism for comparing types in C++ and Objective-C++. However, if
10768 bugs in the canonical type system are causing compilation failures,
10769 set this value to 0 to disable canonical types.
10771 @item switch-conversion-max-branch-ratio
10772 Switch initialization conversion refuses to create arrays that are
10773 bigger than @option{switch-conversion-max-branch-ratio} times the number of
10774 branches in the switch.
10776 @item max-partial-antic-length
10777 Maximum length of the partial antic set computed during the tree
10778 partial redundancy elimination optimization (@option{-ftree-pre}) when
10779 optimizing at @option{-O3} and above. For some sorts of source code
10780 the enhanced partial redundancy elimination optimization can run away,
10781 consuming all of the memory available on the host machine. This
10782 parameter sets a limit on the length of the sets that are computed,
10783 which prevents the runaway behavior. Setting a value of 0 for
10784 this parameter allows an unlimited set length.
10786 @item sccvn-max-scc-size
10787 Maximum size of a strongly connected component (SCC) during SCCVN
10788 processing. If this limit is hit, SCCVN processing for the whole
10789 function is not done and optimizations depending on it are
10790 disabled. The default maximum SCC size is 10000.
10792 @item sccvn-max-alias-queries-per-access
10793 Maximum number of alias-oracle queries we perform when looking for
10794 redundancies for loads and stores. If this limit is hit the search
10795 is aborted and the load or store is not considered redundant. The
10796 number of queries is algorithmically limited to the number of
10797 stores on all paths from the load to the function entry.
10798 The default maximum number of queries is 1000.
10800 @item ira-max-loops-num
10801 IRA uses regional register allocation by default. If a function
10802 contains more loops than the number given by this parameter, only at most
10803 the given number of the most frequently-executed loops form regions
10804 for regional register allocation. The default value of the
10807 @item ira-max-conflict-table-size
10808 Although IRA uses a sophisticated algorithm to compress the conflict
10809 table, the table can still require excessive amounts of memory for
10810 huge functions. If the conflict table for a function could be more
10811 than the size in MB given by this parameter, the register allocator
10812 instead uses a faster, simpler, and lower-quality
10813 algorithm that does not require building a pseudo-register conflict table.
10814 The default value of the parameter is 2000.
10816 @item ira-loop-reserved-regs
10817 IRA can be used to evaluate more accurate register pressure in loops
10818 for decisions to move loop invariants (see @option{-O3}). The number
10819 of available registers reserved for some other purposes is given
10820 by this parameter. The default value of the parameter is 2, which is
10821 the minimal number of registers needed by typical instructions.
10822 This value is the best found from numerous experiments.
10824 @item lra-inheritance-ebb-probability-cutoff
10825 LRA tries to reuse values reloaded in registers in subsequent insns.
10826 This optimization is called inheritance. EBB is used as a region to
10827 do this optimization. The parameter defines a minimal fall-through
10828 edge probability in percentage used to add BB to inheritance EBB in
10829 LRA. The default value of the parameter is 40. The value was chosen
10830 from numerous runs of SPEC2000 on x86-64.
10832 @item loop-invariant-max-bbs-in-loop
10833 Loop invariant motion can be very expensive, both in compilation time and
10834 in amount of needed compile-time memory, with very large loops. Loops
10835 with more basic blocks than this parameter won't have loop invariant
10836 motion optimization performed on them. The default value of the
10837 parameter is 1000 for @option{-O1} and 10000 for @option{-O2} and above.
10839 @item loop-max-datarefs-for-datadeps
10840 Building data dependencies is expensive for very large loops. This
10841 parameter limits the number of data references in loops that are
10842 considered for data dependence analysis. These large loops are no
10843 handled by the optimizations using loop data dependencies.
10844 The default value is 1000.
10846 @item max-vartrack-size
10847 Sets a maximum number of hash table slots to use during variable
10848 tracking dataflow analysis of any function. If this limit is exceeded
10849 with variable tracking at assignments enabled, analysis for that
10850 function is retried without it, after removing all debug insns from
10851 the function. If the limit is exceeded even without debug insns, var
10852 tracking analysis is completely disabled for the function. Setting
10853 the parameter to zero makes it unlimited.
10855 @item max-vartrack-expr-depth
10856 Sets a maximum number of recursion levels when attempting to map
10857 variable names or debug temporaries to value expressions. This trades
10858 compilation time for more complete debug information. If this is set too
10859 low, value expressions that are available and could be represented in
10860 debug information may end up not being used; setting this higher may
10861 enable the compiler to find more complex debug expressions, but compile
10862 time and memory use may grow. The default is 12.
10864 @item max-debug-marker-count
10865 Sets a threshold on the number of debug markers (e.g. begin stmt
10866 markers) to avoid complexity explosion at inlining or expanding to RTL.
10867 If a function has more such gimple stmts than the set limit, such stmts
10868 will be dropped from the inlined copy of a function, and from its RTL
10869 expansion. The default is 100000.
10871 @item min-nondebug-insn-uid
10872 Use uids starting at this parameter for nondebug insns. The range below
10873 the parameter is reserved exclusively for debug insns created by
10874 @option{-fvar-tracking-assignments}, but debug insns may get
10875 (non-overlapping) uids above it if the reserved range is exhausted.
10877 @item ipa-sra-ptr-growth-factor
10878 IPA-SRA replaces a pointer to an aggregate with one or more new
10879 parameters only when their cumulative size is less or equal to
10880 @option{ipa-sra-ptr-growth-factor} times the size of the original
10883 @item sra-max-scalarization-size-Ospeed
10884 @itemx sra-max-scalarization-size-Osize
10885 The two Scalar Reduction of Aggregates passes (SRA and IPA-SRA) aim to
10886 replace scalar parts of aggregates with uses of independent scalar
10887 variables. These parameters control the maximum size, in storage units,
10888 of aggregate which is considered for replacement when compiling for
10890 (@option{sra-max-scalarization-size-Ospeed}) or size
10891 (@option{sra-max-scalarization-size-Osize}) respectively.
10893 @item tm-max-aggregate-size
10894 When making copies of thread-local variables in a transaction, this
10895 parameter specifies the size in bytes after which variables are
10896 saved with the logging functions as opposed to save/restore code
10897 sequence pairs. This option only applies when using
10900 @item graphite-max-nb-scop-params
10901 To avoid exponential effects in the Graphite loop transforms, the
10902 number of parameters in a Static Control Part (SCoP) is bounded. The
10903 default value is 10 parameters, a value of zero can be used to lift
10904 the bound. A variable whose value is unknown at compilation time and
10905 defined outside a SCoP is a parameter of the SCoP.
10907 @item loop-block-tile-size
10908 Loop blocking or strip mining transforms, enabled with
10909 @option{-floop-block} or @option{-floop-strip-mine}, strip mine each
10910 loop in the loop nest by a given number of iterations. The strip
10911 length can be changed using the @option{loop-block-tile-size}
10912 parameter. The default value is 51 iterations.
10914 @item loop-unroll-jam-size
10915 Specify the unroll factor for the @option{-floop-unroll-and-jam} option. The
10916 default value is 4.
10918 @item loop-unroll-jam-depth
10919 Specify the dimension to be unrolled (counting from the most inner loop)
10920 for the @option{-floop-unroll-and-jam}. The default value is 2.
10922 @item ipa-cp-value-list-size
10923 IPA-CP attempts to track all possible values and types passed to a function's
10924 parameter in order to propagate them and perform devirtualization.
10925 @option{ipa-cp-value-list-size} is the maximum number of values and types it
10926 stores per one formal parameter of a function.
10928 @item ipa-cp-eval-threshold
10929 IPA-CP calculates its own score of cloning profitability heuristics
10930 and performs those cloning opportunities with scores that exceed
10931 @option{ipa-cp-eval-threshold}.
10933 @item ipa-cp-recursion-penalty
10934 Percentage penalty the recursive functions will receive when they
10935 are evaluated for cloning.
10937 @item ipa-cp-single-call-penalty
10938 Percentage penalty functions containing a single call to another
10939 function will receive when they are evaluated for cloning.
10942 @item ipa-max-agg-items
10943 IPA-CP is also capable to propagate a number of scalar values passed
10944 in an aggregate. @option{ipa-max-agg-items} controls the maximum
10945 number of such values per one parameter.
10947 @item ipa-cp-loop-hint-bonus
10948 When IPA-CP determines that a cloning candidate would make the number
10949 of iterations of a loop known, it adds a bonus of
10950 @option{ipa-cp-loop-hint-bonus} to the profitability score of
10953 @item ipa-cp-array-index-hint-bonus
10954 When IPA-CP determines that a cloning candidate would make the index of
10955 an array access known, it adds a bonus of
10956 @option{ipa-cp-array-index-hint-bonus} to the profitability
10957 score of the candidate.
10959 @item ipa-max-aa-steps
10960 During its analysis of function bodies, IPA-CP employs alias analysis
10961 in order to track values pointed to by function parameters. In order
10962 not spend too much time analyzing huge functions, it gives up and
10963 consider all memory clobbered after examining
10964 @option{ipa-max-aa-steps} statements modifying memory.
10966 @item lto-partitions
10967 Specify desired number of partitions produced during WHOPR compilation.
10968 The number of partitions should exceed the number of CPUs used for compilation.
10969 The default value is 32.
10971 @item lto-min-partition
10972 Size of minimal partition for WHOPR (in estimated instructions).
10973 This prevents expenses of splitting very small programs into too many
10976 @item lto-max-partition
10977 Size of max partition for WHOPR (in estimated instructions).
10978 to provide an upper bound for individual size of partition.
10979 Meant to be used only with balanced partitioning.
10981 @item cxx-max-namespaces-for-diagnostic-help
10982 The maximum number of namespaces to consult for suggestions when C++
10983 name lookup fails for an identifier. The default is 1000.
10985 @item sink-frequency-threshold
10986 The maximum relative execution frequency (in percents) of the target block
10987 relative to a statement's original block to allow statement sinking of a
10988 statement. Larger numbers result in more aggressive statement sinking.
10989 The default value is 75. A small positive adjustment is applied for
10990 statements with memory operands as those are even more profitable so sink.
10992 @item max-stores-to-sink
10993 The maximum number of conditional store pairs that can be sunk. Set to 0
10994 if either vectorization (@option{-ftree-vectorize}) or if-conversion
10995 (@option{-ftree-loop-if-convert}) is disabled. The default is 2.
10997 @item allow-store-data-races
10998 Allow optimizers to introduce new data races on stores.
10999 Set to 1 to allow, otherwise to 0. This option is enabled by default
11000 at optimization level @option{-Ofast}.
11002 @item case-values-threshold
11003 The smallest number of different values for which it is best to use a
11004 jump-table instead of a tree of conditional branches. If the value is
11005 0, use the default for the machine. The default is 0.
11007 @item tree-reassoc-width
11008 Set the maximum number of instructions executed in parallel in
11009 reassociated tree. This parameter overrides target dependent
11010 heuristics used by default if has non zero value.
11012 @item sched-pressure-algorithm
11013 Choose between the two available implementations of
11014 @option{-fsched-pressure}. Algorithm 1 is the original implementation
11015 and is the more likely to prevent instructions from being reordered.
11016 Algorithm 2 was designed to be a compromise between the relatively
11017 conservative approach taken by algorithm 1 and the rather aggressive
11018 approach taken by the default scheduler. It relies more heavily on
11019 having a regular register file and accurate register pressure classes.
11020 See @file{haifa-sched.c} in the GCC sources for more details.
11022 The default choice depends on the target.
11024 @item max-slsr-cand-scan
11025 Set the maximum number of existing candidates that are considered when
11026 seeking a basis for a new straight-line strength reduction candidate.
11029 Enable buffer overflow detection for global objects. This kind
11030 of protection is enabled by default if you are using
11031 @option{-fsanitize=address} option.
11032 To disable global objects protection use @option{--param asan-globals=0}.
11035 Enable buffer overflow detection for stack objects. This kind of
11036 protection is enabled by default when using @option{-fsanitize=address}.
11037 To disable stack protection use @option{--param asan-stack=0} option.
11039 @item asan-instrument-reads
11040 Enable buffer overflow detection for memory reads. This kind of
11041 protection is enabled by default when using @option{-fsanitize=address}.
11042 To disable memory reads protection use
11043 @option{--param asan-instrument-reads=0}.
11045 @item asan-instrument-writes
11046 Enable buffer overflow detection for memory writes. This kind of
11047 protection is enabled by default when using @option{-fsanitize=address}.
11048 To disable memory writes protection use
11049 @option{--param asan-instrument-writes=0} option.
11051 @item asan-memintrin
11052 Enable detection for built-in functions. This kind of protection
11053 is enabled by default when using @option{-fsanitize=address}.
11054 To disable built-in functions protection use
11055 @option{--param asan-memintrin=0}.
11057 @item asan-use-after-return
11058 Enable detection of use-after-return. This kind of protection
11059 is enabled by default when using the @option{-fsanitize=address} option.
11060 To disable it use @option{--param asan-use-after-return=0}.
11062 Note: By default the check is disabled at run time. To enable it,
11063 add @code{detect_stack_use_after_return=1} to the environment variable
11064 @env{ASAN_OPTIONS}.
11066 @item asan-instrumentation-with-call-threshold
11067 If number of memory accesses in function being instrumented
11068 is greater or equal to this number, use callbacks instead of inline checks.
11069 E.g. to disable inline code use
11070 @option{--param asan-instrumentation-with-call-threshold=0}.
11072 @item use-after-scope-direct-emission-threshold
11073 If the size of a local variable in bytes is smaller or equal to this
11074 number, directly poison (or unpoison) shadow memory instead of using
11075 run-time callbacks. The default value is 256.
11077 @item chkp-max-ctor-size
11078 Static constructors generated by Pointer Bounds Checker may become very
11079 large and significantly increase compile time at optimization level
11080 @option{-O1} and higher. This parameter is a maximum number of statements
11081 in a single generated constructor. Default value is 5000.
11083 @item max-fsm-thread-path-insns
11084 Maximum number of instructions to copy when duplicating blocks on a
11085 finite state automaton jump thread path. The default is 100.
11087 @item max-fsm-thread-length
11088 Maximum number of basic blocks on a finite state automaton jump thread
11089 path. The default is 10.
11091 @item max-fsm-thread-paths
11092 Maximum number of new jump thread paths to create for a finite state
11093 automaton. The default is 50.
11095 @item parloops-chunk-size
11096 Chunk size of omp schedule for loops parallelized by parloops. The default
11099 @item parloops-schedule
11100 Schedule type of omp schedule for loops parallelized by parloops (static,
11101 dynamic, guided, auto, runtime). The default is static.
11103 @item parloops-min-per-thread
11104 The minimum number of iterations per thread of an innermost parallelized
11105 loop for which the parallelized variant is prefered over the single threaded
11106 one. The default is 100. Note that for a parallelized loop nest the
11107 minimum number of iterations of the outermost loop per thread is two.
11109 @item max-ssa-name-query-depth
11110 Maximum depth of recursion when querying properties of SSA names in things
11111 like fold routines. One level of recursion corresponds to following a
11114 @item hsa-gen-debug-stores
11115 Enable emission of special debug stores within HSA kernels which are
11116 then read and reported by libgomp plugin. Generation of these stores
11117 is disabled by default, use @option{--param hsa-gen-debug-stores=1} to
11120 @item max-speculative-devirt-maydefs
11121 The maximum number of may-defs we analyze when looking for a must-def
11122 specifying the dynamic type of an object that invokes a virtual call
11123 we may be able to devirtualize speculatively.
11125 @item max-vrp-switch-assertions
11126 The maximum number of assertions to add along the default edge of a switch
11127 statement during VRP. The default is 10.
11129 @item unroll-jam-min-percent
11130 The minimum percentage of memory references that must be optimized
11131 away for the unroll-and-jam transformation to be considered profitable.
11133 @item unroll-jam-max-unroll
11134 The maximum number of times the outer loop should be unrolled by
11135 the unroll-and-jam transformation.
11139 @node Instrumentation Options
11140 @section Program Instrumentation Options
11141 @cindex instrumentation options
11142 @cindex program instrumentation options
11143 @cindex run-time error checking options
11144 @cindex profiling options
11145 @cindex options, program instrumentation
11146 @cindex options, run-time error checking
11147 @cindex options, profiling
11149 GCC supports a number of command-line options that control adding
11150 run-time instrumentation to the code it normally generates.
11151 For example, one purpose of instrumentation is collect profiling
11152 statistics for use in finding program hot spots, code coverage
11153 analysis, or profile-guided optimizations.
11154 Another class of program instrumentation is adding run-time checking
11155 to detect programming errors like invalid pointer
11156 dereferences or out-of-bounds array accesses, as well as deliberately
11157 hostile attacks such as stack smashing or C++ vtable hijacking.
11158 There is also a general hook which can be used to implement other
11159 forms of tracing or function-level instrumentation for debug or
11160 program analysis purposes.
11163 @cindex @command{prof}
11166 Generate extra code to write profile information suitable for the
11167 analysis program @command{prof}. You must use this option when compiling
11168 the source files you want data about, and you must also use it when
11171 @cindex @command{gprof}
11174 Generate extra code to write profile information suitable for the
11175 analysis program @command{gprof}. You must use this option when compiling
11176 the source files you want data about, and you must also use it when
11179 @item -fprofile-arcs
11180 @opindex fprofile-arcs
11181 Add code so that program flow @dfn{arcs} are instrumented. During
11182 execution the program records how many times each branch and call is
11183 executed and how many times it is taken or returns. On targets that support
11184 constructors with priority support, profiling properly handles constructors,
11185 destructors and C++ constructors (and destructors) of classes which are used
11186 as a type of a global variable.
11189 program exits it saves this data to a file called
11190 @file{@var{auxname}.gcda} for each source file. The data may be used for
11191 profile-directed optimizations (@option{-fbranch-probabilities}), or for
11192 test coverage analysis (@option{-ftest-coverage}). Each object file's
11193 @var{auxname} is generated from the name of the output file, if
11194 explicitly specified and it is not the final executable, otherwise it is
11195 the basename of the source file. In both cases any suffix is removed
11196 (e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
11197 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
11198 @xref{Cross-profiling}.
11200 @cindex @command{gcov}
11204 This option is used to compile and link code instrumented for coverage
11205 analysis. The option is a synonym for @option{-fprofile-arcs}
11206 @option{-ftest-coverage} (when compiling) and @option{-lgcov} (when
11207 linking). See the documentation for those options for more details.
11212 Compile the source files with @option{-fprofile-arcs} plus optimization
11213 and code generation options. For test coverage analysis, use the
11214 additional @option{-ftest-coverage} option. You do not need to profile
11215 every source file in a program.
11218 Compile the source files additionally with @option{-fprofile-abs-path}
11219 to create absolute path names in the @file{.gcno} files. This allows
11220 @command{gcov} to find the correct sources in projects where compilations
11221 occur with different working directories.
11224 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
11225 (the latter implies the former).
11228 Run the program on a representative workload to generate the arc profile
11229 information. This may be repeated any number of times. You can run
11230 concurrent instances of your program, and provided that the file system
11231 supports locking, the data files will be correctly updated. Unless
11232 a strict ISO C dialect option is in effect, @code{fork} calls are
11233 detected and correctly handled without double counting.
11236 For profile-directed optimizations, compile the source files again with
11237 the same optimization and code generation options plus
11238 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
11239 Control Optimization}).
11242 For test coverage analysis, use @command{gcov} to produce human readable
11243 information from the @file{.gcno} and @file{.gcda} files. Refer to the
11244 @command{gcov} documentation for further information.
11248 With @option{-fprofile-arcs}, for each function of your program GCC
11249 creates a program flow graph, then finds a spanning tree for the graph.
11250 Only arcs that are not on the spanning tree have to be instrumented: the
11251 compiler adds code to count the number of times that these arcs are
11252 executed. When an arc is the only exit or only entrance to a block, the
11253 instrumentation code can be added to the block; otherwise, a new basic
11254 block must be created to hold the instrumentation code.
11257 @item -ftest-coverage
11258 @opindex ftest-coverage
11259 Produce a notes file that the @command{gcov} code-coverage utility
11260 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
11261 show program coverage. Each source file's note file is called
11262 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
11263 above for a description of @var{auxname} and instructions on how to
11264 generate test coverage data. Coverage data matches the source files
11265 more closely if you do not optimize.
11267 @item -fprofile-abs-path
11268 @opindex fprofile-abs-path
11269 Automatically convert relative source file names to absolute path names
11270 in the @file{.gcno} files. This allows @command{gcov} to find the correct
11271 sources in projects where compilations occur with different working
11274 @item -fprofile-dir=@var{path}
11275 @opindex fprofile-dir
11277 Set the directory to search for the profile data files in to @var{path}.
11278 This option affects only the profile data generated by
11279 @option{-fprofile-generate}, @option{-ftest-coverage}, @option{-fprofile-arcs}
11280 and used by @option{-fprofile-use} and @option{-fbranch-probabilities}
11281 and its related options. Both absolute and relative paths can be used.
11282 By default, GCC uses the current directory as @var{path}, thus the
11283 profile data file appears in the same directory as the object file.
11285 @item -fprofile-generate
11286 @itemx -fprofile-generate=@var{path}
11287 @opindex fprofile-generate
11289 Enable options usually used for instrumenting application to produce
11290 profile useful for later recompilation with profile feedback based
11291 optimization. You must use @option{-fprofile-generate} both when
11292 compiling and when linking your program.
11294 The following options are enabled: @option{-fprofile-arcs}, @option{-fprofile-values}, @option{-fvpt}.
11296 If @var{path} is specified, GCC looks at the @var{path} to find
11297 the profile feedback data files. See @option{-fprofile-dir}.
11299 To optimize the program based on the collected profile information, use
11300 @option{-fprofile-use}. @xref{Optimize Options}, for more information.
11302 @item -fprofile-update=@var{method}
11303 @opindex fprofile-update
11305 Alter the update method for an application instrumented for profile
11306 feedback based optimization. The @var{method} argument should be one of
11307 @samp{single}, @samp{atomic} or @samp{prefer-atomic}.
11308 The first one is useful for single-threaded applications,
11309 while the second one prevents profile corruption by emitting thread-safe code.
11311 @strong{Warning:} When an application does not properly join all threads
11312 (or creates an detached thread), a profile file can be still corrupted.
11314 Using @samp{prefer-atomic} would be transformed either to @samp{atomic},
11315 when supported by a target, or to @samp{single} otherwise. The GCC driver
11316 automatically selects @samp{prefer-atomic} when @option{-pthread}
11317 is present in the command line.
11319 @item -fsanitize=address
11320 @opindex fsanitize=address
11321 Enable AddressSanitizer, a fast memory error detector.
11322 Memory access instructions are instrumented to detect
11323 out-of-bounds and use-after-free bugs.
11324 The option enables @option{-fsanitize-address-use-after-scope}.
11325 See @uref{https://github.com/google/sanitizers/wiki/AddressSanitizer} for
11326 more details. The run-time behavior can be influenced using the
11327 @env{ASAN_OPTIONS} environment variable. When set to @code{help=1},
11328 the available options are shown at startup of the instrumented program. See
11329 @url{https://github.com/google/sanitizers/wiki/AddressSanitizerFlags#run-time-flags}
11330 for a list of supported options.
11331 The option cannot be combined with @option{-fsanitize=thread}
11332 and/or @option{-fcheck-pointer-bounds}.
11334 @item -fsanitize=kernel-address
11335 @opindex fsanitize=kernel-address
11336 Enable AddressSanitizer for Linux kernel.
11337 See @uref{https://github.com/google/kasan/wiki} for more details.
11338 The option cannot be combined with @option{-fcheck-pointer-bounds}.
11340 @item -fsanitize=pointer-compare
11341 @opindex fsanitize=pointer-compare
11342 Instrument comparison operation (<, <=, >, >=) with pointer operands.
11343 The option must be combined with either @option{-fsanitize=kernel-address} or
11344 @option{-fsanitize=address}
11345 The option cannot be combined with @option{-fsanitize=thread}
11346 and/or @option{-fcheck-pointer-bounds}.
11347 Note: By default the check is disabled at run time. To enable it,
11348 add @code{detect_invalid_pointer_pairs=2} to the environment variable
11349 @env{ASAN_OPTIONS}. Using @code{detect_invalid_pointer_pairs=1} detects
11350 invalid operation only when both pointers are non-null.
11352 @item -fsanitize=pointer-subtract
11353 @opindex fsanitize=pointer-subtract
11354 Instrument subtraction with pointer operands.
11355 The option must be combined with either @option{-fsanitize=kernel-address} or
11356 @option{-fsanitize=address}
11357 The option cannot be combined with @option{-fsanitize=thread}
11358 and/or @option{-fcheck-pointer-bounds}.
11359 Note: By default the check is disabled at run time. To enable it,
11360 add @code{detect_invalid_pointer_pairs=2} to the environment variable
11361 @env{ASAN_OPTIONS}. Using @code{detect_invalid_pointer_pairs=1} detects
11362 invalid operation only when both pointers are non-null.
11364 @item -fsanitize=thread
11365 @opindex fsanitize=thread
11366 Enable ThreadSanitizer, a fast data race detector.
11367 Memory access instructions are instrumented to detect
11368 data race bugs. See @uref{https://github.com/google/sanitizers/wiki#threadsanitizer} for more
11369 details. The run-time behavior can be influenced using the @env{TSAN_OPTIONS}
11370 environment variable; see
11371 @url{https://github.com/google/sanitizers/wiki/ThreadSanitizerFlags} for a list of
11373 The option cannot be combined with @option{-fsanitize=address},
11374 @option{-fsanitize=leak} and/or @option{-fcheck-pointer-bounds}.
11376 Note that sanitized atomic builtins cannot throw exceptions when
11377 operating on invalid memory addresses with non-call exceptions
11378 (@option{-fnon-call-exceptions}).
11380 @item -fsanitize=leak
11381 @opindex fsanitize=leak
11382 Enable LeakSanitizer, a memory leak detector.
11383 This option only matters for linking of executables and
11384 the executable is linked against a library that overrides @code{malloc}
11385 and other allocator functions. See
11386 @uref{https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer} for more
11387 details. The run-time behavior can be influenced using the
11388 @env{LSAN_OPTIONS} environment variable.
11389 The option cannot be combined with @option{-fsanitize=thread}.
11391 @item -fsanitize=undefined
11392 @opindex fsanitize=undefined
11393 Enable UndefinedBehaviorSanitizer, a fast undefined behavior detector.
11394 Various computations are instrumented to detect undefined behavior
11395 at runtime. Current suboptions are:
11399 @item -fsanitize=shift
11400 @opindex fsanitize=shift
11401 This option enables checking that the result of a shift operation is
11402 not undefined. Note that what exactly is considered undefined differs
11403 slightly between C and C++, as well as between ISO C90 and C99, etc.
11404 This option has two suboptions, @option{-fsanitize=shift-base} and
11405 @option{-fsanitize=shift-exponent}.
11407 @item -fsanitize=shift-exponent
11408 @opindex fsanitize=shift-exponent
11409 This option enables checking that the second argument of a shift operation
11410 is not negative and is smaller than the precision of the promoted first
11413 @item -fsanitize=shift-base
11414 @opindex fsanitize=shift-base
11415 If the second argument of a shift operation is within range, check that the
11416 result of a shift operation is not undefined. Note that what exactly is
11417 considered undefined differs slightly between C and C++, as well as between
11418 ISO C90 and C99, etc.
11420 @item -fsanitize=integer-divide-by-zero
11421 @opindex fsanitize=integer-divide-by-zero
11422 Detect integer division by zero as well as @code{INT_MIN / -1} division.
11424 @item -fsanitize=unreachable
11425 @opindex fsanitize=unreachable
11426 With this option, the compiler turns the @code{__builtin_unreachable}
11427 call into a diagnostics message call instead. When reaching the
11428 @code{__builtin_unreachable} call, the behavior is undefined.
11430 @item -fsanitize=vla-bound
11431 @opindex fsanitize=vla-bound
11432 This option instructs the compiler to check that the size of a variable
11433 length array is positive.
11435 @item -fsanitize=null
11436 @opindex fsanitize=null
11437 This option enables pointer checking. Particularly, the application
11438 built with this option turned on will issue an error message when it
11439 tries to dereference a NULL pointer, or if a reference (possibly an
11440 rvalue reference) is bound to a NULL pointer, or if a method is invoked
11441 on an object pointed by a NULL pointer.
11443 @item -fsanitize=return
11444 @opindex fsanitize=return
11445 This option enables return statement checking. Programs
11446 built with this option turned on will issue an error message
11447 when the end of a non-void function is reached without actually
11448 returning a value. This option works in C++ only.
11450 @item -fsanitize=signed-integer-overflow
11451 @opindex fsanitize=signed-integer-overflow
11452 This option enables signed integer overflow checking. We check that
11453 the result of @code{+}, @code{*}, and both unary and binary @code{-}
11454 does not overflow in the signed arithmetics. Note, integer promotion
11455 rules must be taken into account. That is, the following is not an
11458 signed char a = SCHAR_MAX;
11462 @item -fsanitize=bounds
11463 @opindex fsanitize=bounds
11464 This option enables instrumentation of array bounds. Various out of bounds
11465 accesses are detected. Flexible array members, flexible array member-like
11466 arrays, and initializers of variables with static storage are not instrumented.
11467 The option cannot be combined with @option{-fcheck-pointer-bounds}.
11469 @item -fsanitize=bounds-strict
11470 @opindex fsanitize=bounds-strict
11471 This option enables strict instrumentation of array bounds. Most out of bounds
11472 accesses are detected, including flexible array members and flexible array
11473 member-like arrays. Initializers of variables with static storage are not
11474 instrumented. The option cannot be combined
11475 with @option{-fcheck-pointer-bounds}.
11477 @item -fsanitize=alignment
11478 @opindex fsanitize=alignment
11480 This option enables checking of alignment of pointers when they are
11481 dereferenced, or when a reference is bound to insufficiently aligned target,
11482 or when a method or constructor is invoked on insufficiently aligned object.
11484 @item -fsanitize=object-size
11485 @opindex fsanitize=object-size
11486 This option enables instrumentation of memory references using the
11487 @code{__builtin_object_size} function. Various out of bounds pointer
11488 accesses are detected.
11490 @item -fsanitize=float-divide-by-zero
11491 @opindex fsanitize=float-divide-by-zero
11492 Detect floating-point division by zero. Unlike other similar options,
11493 @option{-fsanitize=float-divide-by-zero} is not enabled by
11494 @option{-fsanitize=undefined}, since floating-point division by zero can
11495 be a legitimate way of obtaining infinities and NaNs.
11497 @item -fsanitize=float-cast-overflow
11498 @opindex fsanitize=float-cast-overflow
11499 This option enables floating-point type to integer conversion checking.
11500 We check that the result of the conversion does not overflow.
11501 Unlike other similar options, @option{-fsanitize=float-cast-overflow} is
11502 not enabled by @option{-fsanitize=undefined}.
11503 This option does not work well with @code{FE_INVALID} exceptions enabled.
11505 @item -fsanitize=nonnull-attribute
11506 @opindex fsanitize=nonnull-attribute
11508 This option enables instrumentation of calls, checking whether null values
11509 are not passed to arguments marked as requiring a non-null value by the
11510 @code{nonnull} function attribute.
11512 @item -fsanitize=returns-nonnull-attribute
11513 @opindex fsanitize=returns-nonnull-attribute
11515 This option enables instrumentation of return statements in functions
11516 marked with @code{returns_nonnull} function attribute, to detect returning
11517 of null values from such functions.
11519 @item -fsanitize=bool
11520 @opindex fsanitize=bool
11522 This option enables instrumentation of loads from bool. If a value other
11523 than 0/1 is loaded, a run-time error is issued.
11525 @item -fsanitize=enum
11526 @opindex fsanitize=enum
11528 This option enables instrumentation of loads from an enum type. If
11529 a value outside the range of values for the enum type is loaded,
11530 a run-time error is issued.
11532 @item -fsanitize=vptr
11533 @opindex fsanitize=vptr
11535 This option enables instrumentation of C++ member function calls, member
11536 accesses and some conversions between pointers to base and derived classes,
11537 to verify the referenced object has the correct dynamic type.
11539 @item -fsanitize=pointer-overflow
11540 @opindex fsanitize=pointer-overflow
11542 This option enables instrumentation of pointer arithmetics. If the pointer
11543 arithmetics overflows, a run-time error is issued.
11545 @item -fsanitize=builtin
11546 @opindex fsanitize=builtin
11548 This option enables instrumentation of arguments to selected builtin
11549 functions. If an invalid value is passed to such arguments, a run-time
11550 error is issued. E.g.@ passing 0 as the argument to @code{__builtin_ctz}
11551 or @code{__builtin_clz} invokes undefined behavior and is diagnosed
11556 While @option{-ftrapv} causes traps for signed overflows to be emitted,
11557 @option{-fsanitize=undefined} gives a diagnostic message.
11558 This currently works only for the C family of languages.
11560 @item -fno-sanitize=all
11561 @opindex fno-sanitize=all
11563 This option disables all previously enabled sanitizers.
11564 @option{-fsanitize=all} is not allowed, as some sanitizers cannot be used
11567 @item -fasan-shadow-offset=@var{number}
11568 @opindex fasan-shadow-offset
11569 This option forces GCC to use custom shadow offset in AddressSanitizer checks.
11570 It is useful for experimenting with different shadow memory layouts in
11571 Kernel AddressSanitizer.
11573 @item -fsanitize-sections=@var{s1},@var{s2},...
11574 @opindex fsanitize-sections
11575 Sanitize global variables in selected user-defined sections. @var{si} may
11578 @item -fsanitize-recover@r{[}=@var{opts}@r{]}
11579 @opindex fsanitize-recover
11580 @opindex fno-sanitize-recover
11581 @option{-fsanitize-recover=} controls error recovery mode for sanitizers
11582 mentioned in comma-separated list of @var{opts}. Enabling this option
11583 for a sanitizer component causes it to attempt to continue
11584 running the program as if no error happened. This means multiple
11585 runtime errors can be reported in a single program run, and the exit
11586 code of the program may indicate success even when errors
11587 have been reported. The @option{-fno-sanitize-recover=} option
11588 can be used to alter
11589 this behavior: only the first detected error is reported
11590 and program then exits with a non-zero exit code.
11592 Currently this feature only works for @option{-fsanitize=undefined} (and its suboptions
11593 except for @option{-fsanitize=unreachable} and @option{-fsanitize=return}),
11594 @option{-fsanitize=float-cast-overflow}, @option{-fsanitize=float-divide-by-zero},
11595 @option{-fsanitize=bounds-strict},
11596 @option{-fsanitize=kernel-address} and @option{-fsanitize=address}.
11597 For these sanitizers error recovery is turned on by default,
11598 except @option{-fsanitize=address}, for which this feature is experimental.
11599 @option{-fsanitize-recover=all} and @option{-fno-sanitize-recover=all} is also
11600 accepted, the former enables recovery for all sanitizers that support it,
11601 the latter disables recovery for all sanitizers that support it.
11603 Even if a recovery mode is turned on the compiler side, it needs to be also
11604 enabled on the runtime library side, otherwise the failures are still fatal.
11605 The runtime library defaults to @code{halt_on_error=0} for
11606 ThreadSanitizer and UndefinedBehaviorSanitizer, while default value for
11607 AddressSanitizer is @code{halt_on_error=1}. This can be overridden through
11608 setting the @code{halt_on_error} flag in the corresponding environment variable.
11610 Syntax without an explicit @var{opts} parameter is deprecated. It is
11611 equivalent to specifying an @var{opts} list of:
11614 undefined,float-cast-overflow,float-divide-by-zero,bounds-strict
11617 @item -fsanitize-address-use-after-scope
11618 @opindex fsanitize-address-use-after-scope
11619 Enable sanitization of local variables to detect use-after-scope bugs.
11620 The option sets @option{-fstack-reuse} to @samp{none}.
11622 @item -fsanitize-undefined-trap-on-error
11623 @opindex fsanitize-undefined-trap-on-error
11624 The @option{-fsanitize-undefined-trap-on-error} option instructs the compiler to
11625 report undefined behavior using @code{__builtin_trap} rather than
11626 a @code{libubsan} library routine. The advantage of this is that the
11627 @code{libubsan} library is not needed and is not linked in, so this
11628 is usable even in freestanding environments.
11630 @item -fsanitize-coverage=trace-pc
11631 @opindex fsanitize-coverage=trace-pc
11632 Enable coverage-guided fuzzing code instrumentation.
11633 Inserts a call to @code{__sanitizer_cov_trace_pc} into every basic block.
11635 @item -fsanitize-coverage=trace-cmp
11636 @opindex fsanitize-coverage=trace-cmp
11637 Enable dataflow guided fuzzing code instrumentation.
11638 Inserts a call to @code{__sanitizer_cov_trace_cmp1},
11639 @code{__sanitizer_cov_trace_cmp2}, @code{__sanitizer_cov_trace_cmp4} or
11640 @code{__sanitizer_cov_trace_cmp8} for integral comparison with both operands
11641 variable or @code{__sanitizer_cov_trace_const_cmp1},
11642 @code{__sanitizer_cov_trace_const_cmp2},
11643 @code{__sanitizer_cov_trace_const_cmp4} or
11644 @code{__sanitizer_cov_trace_const_cmp8} for integral comparison with one
11645 operand constant, @code{__sanitizer_cov_trace_cmpf} or
11646 @code{__sanitizer_cov_trace_cmpd} for float or double comparisons and
11647 @code{__sanitizer_cov_trace_switch} for switch statements.
11649 @item -fbounds-check
11650 @opindex fbounds-check
11651 For front ends that support it, generate additional code to check that
11652 indices used to access arrays are within the declared range. This is
11653 currently only supported by the Fortran front end, where this option
11656 @item -fcheck-pointer-bounds
11657 @opindex fcheck-pointer-bounds
11658 @opindex fno-check-pointer-bounds
11659 @cindex Pointer Bounds Checker options
11660 Enable Pointer Bounds Checker instrumentation. Each memory reference
11661 is instrumented with checks of the pointer used for memory access against
11662 bounds associated with that pointer.
11665 is only an implementation for Intel MPX available, thus x86 GNU/Linux target
11666 and @option{-mmpx} are required to enable this feature.
11667 MPX-based instrumentation requires
11668 a runtime library to enable MPX in hardware and handle bounds
11669 violation signals. By default when @option{-fcheck-pointer-bounds}
11670 and @option{-mmpx} options are used to link a program, the GCC driver
11671 links against the @file{libmpx} and @file{libmpxwrappers} libraries.
11672 Bounds checking on calls to dynamic libraries requires a linker
11673 with @option{-z bndplt} support; if GCC was configured with a linker
11674 without support for this option (including the Gold linker and older
11675 versions of ld), a warning is given if you link with @option{-mmpx}
11676 without also specifying @option{-static}, since the overall effectiveness
11677 of the bounds checking protection is reduced.
11678 See also @option{-static-libmpxwrappers}.
11680 MPX-based instrumentation
11681 may be used for debugging and also may be included in production code
11682 to increase program security. Depending on usage, you may
11683 have different requirements for the runtime library. The current version
11684 of the MPX runtime library is more oriented for use as a debugging
11685 tool. MPX runtime library usage implies @option{-lpthread}. See
11686 also @option{-static-libmpx}. The runtime library behavior can be
11687 influenced using various @env{CHKP_RT_*} environment variables. See
11688 @uref{https://gcc.gnu.org/wiki/Intel%20MPX%20support%20in%20the%20GCC%20compiler}
11691 Generated instrumentation may be controlled by various
11692 @option{-fchkp-*} options and by the @code{bnd_variable_size}
11693 structure field attribute (@pxref{Type Attributes}) and
11694 @code{bnd_legacy}, and @code{bnd_instrument} function attributes
11695 (@pxref{Function Attributes}). GCC also provides a number of built-in
11696 functions for controlling the Pointer Bounds Checker. @xref{Pointer
11697 Bounds Checker builtins}, for more information.
11699 @item -fchkp-check-incomplete-type
11700 @opindex fchkp-check-incomplete-type
11701 @opindex fno-chkp-check-incomplete-type
11702 Generate pointer bounds checks for variables with incomplete type.
11703 Enabled by default.
11705 @item -fchkp-narrow-bounds
11706 @opindex fchkp-narrow-bounds
11707 @opindex fno-chkp-narrow-bounds
11708 Controls bounds used by Pointer Bounds Checker for pointers to object
11709 fields. If narrowing is enabled then field bounds are used. Otherwise
11710 object bounds are used. See also @option{-fchkp-narrow-to-innermost-array}
11711 and @option{-fchkp-first-field-has-own-bounds}. Enabled by default.
11713 @item -fchkp-first-field-has-own-bounds
11714 @opindex fchkp-first-field-has-own-bounds
11715 @opindex fno-chkp-first-field-has-own-bounds
11716 Forces Pointer Bounds Checker to use narrowed bounds for the address of the
11717 first field in the structure. By default a pointer to the first field has
11718 the same bounds as a pointer to the whole structure.
11720 @item -fchkp-flexible-struct-trailing-arrays
11721 @opindex fchkp-flexible-struct-trailing-arrays
11722 @opindex fno-chkp-flexible-struct-trailing-arrays
11723 Forces Pointer Bounds Checker to treat all trailing arrays in structures as
11724 possibly flexible. By default only array fields with zero length or that are
11725 marked with attribute bnd_variable_size are treated as flexible.
11727 @item -fchkp-narrow-to-innermost-array
11728 @opindex fchkp-narrow-to-innermost-array
11729 @opindex fno-chkp-narrow-to-innermost-array
11730 Forces Pointer Bounds Checker to use bounds of the innermost arrays in
11731 case of nested static array access. By default this option is disabled and
11732 bounds of the outermost array are used.
11734 @item -fchkp-optimize
11735 @opindex fchkp-optimize
11736 @opindex fno-chkp-optimize
11737 Enables Pointer Bounds Checker optimizations. Enabled by default at
11738 optimization levels @option{-O}, @option{-O2}, @option{-O3}.
11740 @item -fchkp-use-fast-string-functions
11741 @opindex fchkp-use-fast-string-functions
11742 @opindex fno-chkp-use-fast-string-functions
11743 Enables use of @code{*_nobnd} versions of string functions (not copying bounds)
11744 by Pointer Bounds Checker. Disabled by default.
11746 @item -fchkp-use-nochk-string-functions
11747 @opindex fchkp-use-nochk-string-functions
11748 @opindex fno-chkp-use-nochk-string-functions
11749 Enables use of @code{*_nochk} versions of string functions (not checking bounds)
11750 by Pointer Bounds Checker. Disabled by default.
11752 @item -fchkp-use-static-bounds
11753 @opindex fchkp-use-static-bounds
11754 @opindex fno-chkp-use-static-bounds
11755 Allow Pointer Bounds Checker to generate static bounds holding
11756 bounds of static variables. Enabled by default.
11758 @item -fchkp-use-static-const-bounds
11759 @opindex fchkp-use-static-const-bounds
11760 @opindex fno-chkp-use-static-const-bounds
11761 Use statically-initialized bounds for constant bounds instead of
11762 generating them each time they are required. By default enabled when
11763 @option{-fchkp-use-static-bounds} is enabled.
11765 @item -fchkp-treat-zero-dynamic-size-as-infinite
11766 @opindex fchkp-treat-zero-dynamic-size-as-infinite
11767 @opindex fno-chkp-treat-zero-dynamic-size-as-infinite
11768 With this option, objects with incomplete type whose
11769 dynamically-obtained size is zero are treated as having infinite size
11770 instead by Pointer Bounds
11771 Checker. This option may be helpful if a program is linked with a library
11772 missing size information for some symbols. Disabled by default.
11774 @item -fchkp-check-read
11775 @opindex fchkp-check-read
11776 @opindex fno-chkp-check-read
11777 Instructs Pointer Bounds Checker to generate checks for all read
11778 accesses to memory. Enabled by default.
11780 @item -fchkp-check-write
11781 @opindex fchkp-check-write
11782 @opindex fno-chkp-check-write
11783 Instructs Pointer Bounds Checker to generate checks for all write
11784 accesses to memory. Enabled by default.
11786 @item -fchkp-store-bounds
11787 @opindex fchkp-store-bounds
11788 @opindex fno-chkp-store-bounds
11789 Instructs Pointer Bounds Checker to generate bounds stores for
11790 pointer writes. Enabled by default.
11792 @item -fchkp-instrument-calls
11793 @opindex fchkp-instrument-calls
11794 @opindex fno-chkp-instrument-calls
11795 Instructs Pointer Bounds Checker to pass pointer bounds to calls.
11796 Enabled by default.
11798 @item -fchkp-instrument-marked-only
11799 @opindex fchkp-instrument-marked-only
11800 @opindex fno-chkp-instrument-marked-only
11801 Instructs Pointer Bounds Checker to instrument only functions
11802 marked with the @code{bnd_instrument} attribute
11803 (@pxref{Function Attributes}). Disabled by default.
11805 @item -fchkp-use-wrappers
11806 @opindex fchkp-use-wrappers
11807 @opindex fno-chkp-use-wrappers
11808 Allows Pointer Bounds Checker to replace calls to built-in functions
11809 with calls to wrapper functions. When @option{-fchkp-use-wrappers}
11810 is used to link a program, the GCC driver automatically links
11811 against @file{libmpxwrappers}. See also @option{-static-libmpxwrappers}.
11812 Enabled by default.
11814 @item -fcf-protection=@r{[}full@r{|}branch@r{|}return@r{|}none@r{]}
11815 @opindex fcf-protection
11816 Enable code instrumentation of control-flow transfers to increase
11817 program security by checking that target addresses of control-flow
11818 transfer instructions (such as indirect function call, function return,
11819 indirect jump) are valid. This prevents diverting the flow of control
11820 to an unexpected target. This is intended to protect against such
11821 threats as Return-oriented Programming (ROP), and similarly
11822 call/jmp-oriented programming (COP/JOP).
11824 The value @code{branch} tells the compiler to implement checking of
11825 validity of control-flow transfer at the point of indirect branch
11826 instructions, i.e. call/jmp instructions. The value @code{return}
11827 implements checking of validity at the point of returning from a
11828 function. The value @code{full} is an alias for specifying both
11829 @code{branch} and @code{return}. The value @code{none} turns off
11832 The macro @code{__CET__} is defined when @option{-fcf-protection} is
11833 used. The first bit of @code{__CET__} is set to 1 for the value
11834 @code{branch} and the second bit of @code{__CET__} is set to 1 for
11837 You can also use the @code{nocf_check} attribute to identify
11838 which functions and calls should be skipped from instrumentation
11839 (@pxref{Function Attributes}).
11841 Currently the x86 GNU/Linux target provides an implementation based
11842 on Intel Control-flow Enforcement Technology (CET).
11844 @item -fstack-protector
11845 @opindex fstack-protector
11846 Emit extra code to check for buffer overflows, such as stack smashing
11847 attacks. This is done by adding a guard variable to functions with
11848 vulnerable objects. This includes functions that call @code{alloca}, and
11849 functions with buffers larger than 8 bytes. The guards are initialized
11850 when a function is entered and then checked when the function exits.
11851 If a guard check fails, an error message is printed and the program exits.
11853 @item -fstack-protector-all
11854 @opindex fstack-protector-all
11855 Like @option{-fstack-protector} except that all functions are protected.
11857 @item -fstack-protector-strong
11858 @opindex fstack-protector-strong
11859 Like @option{-fstack-protector} but includes additional functions to
11860 be protected --- those that have local array definitions, or have
11861 references to local frame addresses.
11863 @item -fstack-protector-explicit
11864 @opindex fstack-protector-explicit
11865 Like @option{-fstack-protector} but only protects those functions which
11866 have the @code{stack_protect} attribute.
11868 @item -fstack-check
11869 @opindex fstack-check
11870 Generate code to verify that you do not go beyond the boundary of the
11871 stack. You should specify this flag if you are running in an
11872 environment with multiple threads, but you only rarely need to specify it in
11873 a single-threaded environment since stack overflow is automatically
11874 detected on nearly all systems if there is only one stack.
11876 Note that this switch does not actually cause checking to be done; the
11877 operating system or the language runtime must do that. The switch causes
11878 generation of code to ensure that they see the stack being extended.
11880 You can additionally specify a string parameter: @samp{no} means no
11881 checking, @samp{generic} means force the use of old-style checking,
11882 @samp{specific} means use the best checking method and is equivalent
11883 to bare @option{-fstack-check}.
11885 Old-style checking is a generic mechanism that requires no specific
11886 target support in the compiler but comes with the following drawbacks:
11890 Modified allocation strategy for large objects: they are always
11891 allocated dynamically if their size exceeds a fixed threshold. Note this
11892 may change the semantics of some code.
11895 Fixed limit on the size of the static frame of functions: when it is
11896 topped by a particular function, stack checking is not reliable and
11897 a warning is issued by the compiler.
11900 Inefficiency: because of both the modified allocation strategy and the
11901 generic implementation, code performance is hampered.
11904 Note that old-style stack checking is also the fallback method for
11905 @samp{specific} if no target support has been added in the compiler.
11907 @samp{-fstack-check=} is designed for Ada's needs to detect infinite recursion
11908 and stack overflows. @samp{specific} is an excellent choice when compiling
11909 Ada code. It is not generally sufficient to protect against stack-clash
11910 attacks. To protect against those you want @samp{-fstack-clash-protection}.
11912 @item -fstack-clash-protection
11913 @opindex fstack-clash-protection
11914 Generate code to prevent stack clash style attacks. When this option is
11915 enabled, the compiler will only allocate one page of stack space at a time
11916 and each page is accessed immediately after allocation. Thus, it prevents
11917 allocations from jumping over any stack guard page provided by the
11920 Most targets do not fully support stack clash protection. However, on
11921 those targets @option{-fstack-clash-protection} will protect dynamic stack
11922 allocations. @option{-fstack-clash-protection} may also provide limited
11923 protection for static stack allocations if the target supports
11924 @option{-fstack-check=specific}.
11926 @item -fstack-limit-register=@var{reg}
11927 @itemx -fstack-limit-symbol=@var{sym}
11928 @itemx -fno-stack-limit
11929 @opindex fstack-limit-register
11930 @opindex fstack-limit-symbol
11931 @opindex fno-stack-limit
11932 Generate code to ensure that the stack does not grow beyond a certain value,
11933 either the value of a register or the address of a symbol. If a larger
11934 stack is required, a signal is raised at run time. For most targets,
11935 the signal is raised before the stack overruns the boundary, so
11936 it is possible to catch the signal without taking special precautions.
11938 For instance, if the stack starts at absolute address @samp{0x80000000}
11939 and grows downwards, you can use the flags
11940 @option{-fstack-limit-symbol=__stack_limit} and
11941 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
11942 of 128KB@. Note that this may only work with the GNU linker.
11944 You can locally override stack limit checking by using the
11945 @code{no_stack_limit} function attribute (@pxref{Function Attributes}).
11947 @item -fsplit-stack
11948 @opindex fsplit-stack
11949 Generate code to automatically split the stack before it overflows.
11950 The resulting program has a discontiguous stack which can only
11951 overflow if the program is unable to allocate any more memory. This
11952 is most useful when running threaded programs, as it is no longer
11953 necessary to calculate a good stack size to use for each thread. This
11954 is currently only implemented for the x86 targets running
11957 When code compiled with @option{-fsplit-stack} calls code compiled
11958 without @option{-fsplit-stack}, there may not be much stack space
11959 available for the latter code to run. If compiling all code,
11960 including library code, with @option{-fsplit-stack} is not an option,
11961 then the linker can fix up these calls so that the code compiled
11962 without @option{-fsplit-stack} always has a large stack. Support for
11963 this is implemented in the gold linker in GNU binutils release 2.21
11966 @item -fvtable-verify=@r{[}std@r{|}preinit@r{|}none@r{]}
11967 @opindex fvtable-verify
11968 This option is only available when compiling C++ code.
11969 It turns on (or off, if using @option{-fvtable-verify=none}) the security
11970 feature that verifies at run time, for every virtual call, that
11971 the vtable pointer through which the call is made is valid for the type of
11972 the object, and has not been corrupted or overwritten. If an invalid vtable
11973 pointer is detected at run time, an error is reported and execution of the
11974 program is immediately halted.
11976 This option causes run-time data structures to be built at program startup,
11977 which are used for verifying the vtable pointers.
11978 The options @samp{std} and @samp{preinit}
11979 control the timing of when these data structures are built. In both cases the
11980 data structures are built before execution reaches @code{main}. Using
11981 @option{-fvtable-verify=std} causes the data structures to be built after
11982 shared libraries have been loaded and initialized.
11983 @option{-fvtable-verify=preinit} causes them to be built before shared
11984 libraries have been loaded and initialized.
11986 If this option appears multiple times in the command line with different
11987 values specified, @samp{none} takes highest priority over both @samp{std} and
11988 @samp{preinit}; @samp{preinit} takes priority over @samp{std}.
11991 @opindex fvtv-debug
11992 When used in conjunction with @option{-fvtable-verify=std} or
11993 @option{-fvtable-verify=preinit}, causes debug versions of the
11994 runtime functions for the vtable verification feature to be called.
11995 This flag also causes the compiler to log information about which
11996 vtable pointers it finds for each class.
11997 This information is written to a file named @file{vtv_set_ptr_data.log}
11998 in the directory named by the environment variable @env{VTV_LOGS_DIR}
11999 if that is defined or the current working directory otherwise.
12001 Note: This feature @emph{appends} data to the log file. If you want a fresh log
12002 file, be sure to delete any existing one.
12005 @opindex fvtv-counts
12006 This is a debugging flag. When used in conjunction with
12007 @option{-fvtable-verify=std} or @option{-fvtable-verify=preinit}, this
12008 causes the compiler to keep track of the total number of virtual calls
12009 it encounters and the number of verifications it inserts. It also
12010 counts the number of calls to certain run-time library functions
12011 that it inserts and logs this information for each compilation unit.
12012 The compiler writes this information to a file named
12013 @file{vtv_count_data.log} in the directory named by the environment
12014 variable @env{VTV_LOGS_DIR} if that is defined or the current working
12015 directory otherwise. It also counts the size of the vtable pointer sets
12016 for each class, and writes this information to @file{vtv_class_set_sizes.log}
12017 in the same directory.
12019 Note: This feature @emph{appends} data to the log files. To get fresh log
12020 files, be sure to delete any existing ones.
12022 @item -finstrument-functions
12023 @opindex finstrument-functions
12024 Generate instrumentation calls for entry and exit to functions. Just
12025 after function entry and just before function exit, the following
12026 profiling functions are called with the address of the current
12027 function and its call site. (On some platforms,
12028 @code{__builtin_return_address} does not work beyond the current
12029 function, so the call site information may not be available to the
12030 profiling functions otherwise.)
12033 void __cyg_profile_func_enter (void *this_fn,
12035 void __cyg_profile_func_exit (void *this_fn,
12039 The first argument is the address of the start of the current function,
12040 which may be looked up exactly in the symbol table.
12042 This instrumentation is also done for functions expanded inline in other
12043 functions. The profiling calls indicate where, conceptually, the
12044 inline function is entered and exited. This means that addressable
12045 versions of such functions must be available. If all your uses of a
12046 function are expanded inline, this may mean an additional expansion of
12047 code size. If you use @code{extern inline} in your C code, an
12048 addressable version of such functions must be provided. (This is
12049 normally the case anyway, but if you get lucky and the optimizer always
12050 expands the functions inline, you might have gotten away without
12051 providing static copies.)
12053 A function may be given the attribute @code{no_instrument_function}, in
12054 which case this instrumentation is not done. This can be used, for
12055 example, for the profiling functions listed above, high-priority
12056 interrupt routines, and any functions from which the profiling functions
12057 cannot safely be called (perhaps signal handlers, if the profiling
12058 routines generate output or allocate memory).
12060 @item -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{}
12061 @opindex finstrument-functions-exclude-file-list
12063 Set the list of functions that are excluded from instrumentation (see
12064 the description of @option{-finstrument-functions}). If the file that
12065 contains a function definition matches with one of @var{file}, then
12066 that function is not instrumented. The match is done on substrings:
12067 if the @var{file} parameter is a substring of the file name, it is
12068 considered to be a match.
12073 -finstrument-functions-exclude-file-list=/bits/stl,include/sys
12077 excludes any inline function defined in files whose pathnames
12078 contain @file{/bits/stl} or @file{include/sys}.
12080 If, for some reason, you want to include letter @samp{,} in one of
12081 @var{sym}, write @samp{\,}. For example,
12082 @option{-finstrument-functions-exclude-file-list='\,\,tmp'}
12083 (note the single quote surrounding the option).
12085 @item -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{}
12086 @opindex finstrument-functions-exclude-function-list
12088 This is similar to @option{-finstrument-functions-exclude-file-list},
12089 but this option sets the list of function names to be excluded from
12090 instrumentation. The function name to be matched is its user-visible
12091 name, such as @code{vector<int> blah(const vector<int> &)}, not the
12092 internal mangled name (e.g., @code{_Z4blahRSt6vectorIiSaIiEE}). The
12093 match is done on substrings: if the @var{sym} parameter is a substring
12094 of the function name, it is considered to be a match. For C99 and C++
12095 extended identifiers, the function name must be given in UTF-8, not
12096 using universal character names.
12098 @item -fpatchable-function-entry=@var{N}[,@var{M}]
12099 @opindex fpatchable-function-entry
12100 Generate @var{N} NOPs right at the beginning
12101 of each function, with the function entry point before the @var{M}th NOP.
12102 If @var{M} is omitted, it defaults to @code{0} so the
12103 function entry points to the address just at the first NOP.
12104 The NOP instructions reserve extra space which can be used to patch in
12105 any desired instrumentation at run time, provided that the code segment
12106 is writable. The amount of space is controllable indirectly via
12107 the number of NOPs; the NOP instruction used corresponds to the instruction
12108 emitted by the internal GCC back-end interface @code{gen_nop}. This behavior
12109 is target-specific and may also depend on the architecture variant and/or
12110 other compilation options.
12112 For run-time identification, the starting addresses of these areas,
12113 which correspond to their respective function entries minus @var{M},
12114 are additionally collected in the @code{__patchable_function_entries}
12115 section of the resulting binary.
12117 Note that the value of @code{__attribute__ ((patchable_function_entry
12118 (N,M)))} takes precedence over command-line option
12119 @option{-fpatchable-function-entry=N,M}. This can be used to increase
12120 the area size or to remove it completely on a single function.
12121 If @code{N=0}, no pad location is recorded.
12123 The NOP instructions are inserted at---and maybe before, depending on
12124 @var{M}---the function entry address, even before the prologue.
12129 @node Preprocessor Options
12130 @section Options Controlling the Preprocessor
12131 @cindex preprocessor options
12132 @cindex options, preprocessor
12134 These options control the C preprocessor, which is run on each C source
12135 file before actual compilation.
12137 If you use the @option{-E} option, nothing is done except preprocessing.
12138 Some of these options make sense only together with @option{-E} because
12139 they cause the preprocessor output to be unsuitable for actual
12142 In addition to the options listed here, there are a number of options
12143 to control search paths for include files documented in
12144 @ref{Directory Options}.
12145 Options to control preprocessor diagnostics are listed in
12146 @ref{Warning Options}.
12149 @include cppopts.texi
12151 @item -Wp,@var{option}
12153 You can use @option{-Wp,@var{option}} to bypass the compiler driver
12154 and pass @var{option} directly through to the preprocessor. If
12155 @var{option} contains commas, it is split into multiple options at the
12156 commas. However, many options are modified, translated or interpreted
12157 by the compiler driver before being passed to the preprocessor, and
12158 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
12159 interface is undocumented and subject to change, so whenever possible
12160 you should avoid using @option{-Wp} and let the driver handle the
12163 @item -Xpreprocessor @var{option}
12164 @opindex Xpreprocessor
12165 Pass @var{option} as an option to the preprocessor. You can use this to
12166 supply system-specific preprocessor options that GCC does not
12169 If you want to pass an option that takes an argument, you must use
12170 @option{-Xpreprocessor} twice, once for the option and once for the argument.
12172 @item -no-integrated-cpp
12173 @opindex no-integrated-cpp
12174 Perform preprocessing as a separate pass before compilation.
12175 By default, GCC performs preprocessing as an integrated part of
12176 input tokenization and parsing.
12177 If this option is provided, the appropriate language front end
12178 (@command{cc1}, @command{cc1plus}, or @command{cc1obj} for C, C++,
12179 and Objective-C, respectively) is instead invoked twice,
12180 once for preprocessing only and once for actual compilation
12181 of the preprocessed input.
12182 This option may be useful in conjunction with the @option{-B} or
12183 @option{-wrapper} options to specify an alternate preprocessor or
12184 perform additional processing of the program source between
12185 normal preprocessing and compilation.
12189 @node Assembler Options
12190 @section Passing Options to the Assembler
12192 @c prevent bad page break with this line
12193 You can pass options to the assembler.
12196 @item -Wa,@var{option}
12198 Pass @var{option} as an option to the assembler. If @var{option}
12199 contains commas, it is split into multiple options at the commas.
12201 @item -Xassembler @var{option}
12202 @opindex Xassembler
12203 Pass @var{option} as an option to the assembler. You can use this to
12204 supply system-specific assembler options that GCC does not
12207 If you want to pass an option that takes an argument, you must use
12208 @option{-Xassembler} twice, once for the option and once for the argument.
12213 @section Options for Linking
12214 @cindex link options
12215 @cindex options, linking
12217 These options come into play when the compiler links object files into
12218 an executable output file. They are meaningless if the compiler is
12219 not doing a link step.
12223 @item @var{object-file-name}
12224 A file name that does not end in a special recognized suffix is
12225 considered to name an object file or library. (Object files are
12226 distinguished from libraries by the linker according to the file
12227 contents.) If linking is done, these object files are used as input
12236 If any of these options is used, then the linker is not run, and
12237 object file names should not be used as arguments. @xref{Overall
12241 @opindex fuse-ld=bfd
12242 Use the @command{bfd} linker instead of the default linker.
12244 @item -fuse-ld=gold
12245 @opindex fuse-ld=gold
12246 Use the @command{gold} linker instead of the default linker.
12249 @item -l@var{library}
12250 @itemx -l @var{library}
12252 Search the library named @var{library} when linking. (The second
12253 alternative with the library as a separate argument is only for
12254 POSIX compliance and is not recommended.)
12256 It makes a difference where in the command you write this option; the
12257 linker searches and processes libraries and object files in the order they
12258 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
12259 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
12260 to functions in @samp{z}, those functions may not be loaded.
12262 The linker searches a standard list of directories for the library,
12263 which is actually a file named @file{lib@var{library}.a}. The linker
12264 then uses this file as if it had been specified precisely by name.
12266 The directories searched include several standard system directories
12267 plus any that you specify with @option{-L}.
12269 Normally the files found this way are library files---archive files
12270 whose members are object files. The linker handles an archive file by
12271 scanning through it for members which define symbols that have so far
12272 been referenced but not defined. But if the file that is found is an
12273 ordinary object file, it is linked in the usual fashion. The only
12274 difference between using an @option{-l} option and specifying a file name
12275 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
12276 and searches several directories.
12280 You need this special case of the @option{-l} option in order to
12281 link an Objective-C or Objective-C++ program.
12283 @item -nostartfiles
12284 @opindex nostartfiles
12285 Do not use the standard system startup files when linking.
12286 The standard system libraries are used normally, unless @option{-nostdlib}
12287 or @option{-nodefaultlibs} is used.
12289 @item -nodefaultlibs
12290 @opindex nodefaultlibs
12291 Do not use the standard system libraries when linking.
12292 Only the libraries you specify are passed to the linker, and options
12293 specifying linkage of the system libraries, such as @option{-static-libgcc}
12294 or @option{-shared-libgcc}, are ignored.
12295 The standard startup files are used normally, unless @option{-nostartfiles}
12298 The compiler may generate calls to @code{memcmp},
12299 @code{memset}, @code{memcpy} and @code{memmove}.
12300 These entries are usually resolved by entries in
12301 libc. These entry points should be supplied through some other
12302 mechanism when this option is specified.
12306 Do not use the standard system startup files or libraries when linking.
12307 No startup files and only the libraries you specify are passed to
12308 the linker, and options specifying linkage of the system libraries, such as
12309 @option{-static-libgcc} or @option{-shared-libgcc}, are ignored.
12311 The compiler may generate calls to @code{memcmp}, @code{memset},
12312 @code{memcpy} and @code{memmove}.
12313 These entries are usually resolved by entries in
12314 libc. These entry points should be supplied through some other
12315 mechanism when this option is specified.
12317 @cindex @option{-lgcc}, use with @option{-nostdlib}
12318 @cindex @option{-nostdlib} and unresolved references
12319 @cindex unresolved references and @option{-nostdlib}
12320 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
12321 @cindex @option{-nodefaultlibs} and unresolved references
12322 @cindex unresolved references and @option{-nodefaultlibs}
12323 One of the standard libraries bypassed by @option{-nostdlib} and
12324 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
12325 which GCC uses to overcome shortcomings of particular machines, or special
12326 needs for some languages.
12327 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
12328 Collection (GCC) Internals},
12329 for more discussion of @file{libgcc.a}.)
12330 In most cases, you need @file{libgcc.a} even when you want to avoid
12331 other standard libraries. In other words, when you specify @option{-nostdlib}
12332 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
12333 This ensures that you have no unresolved references to internal GCC
12334 library subroutines.
12335 (An example of such an internal subroutine is @code{__main}, used to ensure C++
12336 constructors are called; @pxref{Collect2,,@code{collect2}, gccint,
12337 GNU Compiler Collection (GCC) Internals}.)
12341 Produce a dynamically linked position independent executable on targets
12342 that support it. For predictable results, you must also specify the same
12343 set of options used for compilation (@option{-fpie}, @option{-fPIE},
12344 or model suboptions) when you specify this linker option.
12348 Don't produce a dynamically linked position independent executable.
12351 @opindex static-pie
12352 Produce a static position independent executable on targets that support
12353 it. A static position independent executable is similar to a static
12354 executable, but can be loaded at any address without a dynamic linker.
12355 For predictable results, you must also specify the same set of options
12356 used for compilation (@option{-fpie}, @option{-fPIE}, or model
12357 suboptions) when you specify this linker option.
12361 Link with the POSIX threads library. This option is supported on
12362 GNU/Linux targets, most other Unix derivatives, and also on
12363 x86 Cygwin and MinGW targets. On some targets this option also sets
12364 flags for the preprocessor, so it should be used consistently for both
12365 compilation and linking.
12369 Pass the flag @option{-export-dynamic} to the ELF linker, on targets
12370 that support it. This instructs the linker to add all symbols, not
12371 only used ones, to the dynamic symbol table. This option is needed
12372 for some uses of @code{dlopen} or to allow obtaining backtraces
12373 from within a program.
12377 Remove all symbol table and relocation information from the executable.
12381 On systems that support dynamic linking, this overrides @option{-pie}
12382 and prevents linking with the shared libraries. On other systems, this
12383 option has no effect.
12387 Produce a shared object which can then be linked with other objects to
12388 form an executable. Not all systems support this option. For predictable
12389 results, you must also specify the same set of options used for compilation
12390 (@option{-fpic}, @option{-fPIC}, or model suboptions) when
12391 you specify this linker option.@footnote{On some systems, @samp{gcc -shared}
12392 needs to build supplementary stub code for constructors to work. On
12393 multi-libbed systems, @samp{gcc -shared} must select the correct support
12394 libraries to link against. Failing to supply the correct flags may lead
12395 to subtle defects. Supplying them in cases where they are not necessary
12398 @item -shared-libgcc
12399 @itemx -static-libgcc
12400 @opindex shared-libgcc
12401 @opindex static-libgcc
12402 On systems that provide @file{libgcc} as a shared library, these options
12403 force the use of either the shared or static version, respectively.
12404 If no shared version of @file{libgcc} was built when the compiler was
12405 configured, these options have no effect.
12407 There are several situations in which an application should use the
12408 shared @file{libgcc} instead of the static version. The most common
12409 of these is when the application wishes to throw and catch exceptions
12410 across different shared libraries. In that case, each of the libraries
12411 as well as the application itself should use the shared @file{libgcc}.
12413 Therefore, the G++ and driver automatically adds @option{-shared-libgcc}
12414 whenever you build a shared library or a main executable, because C++
12415 programs typically use exceptions, so this is the right thing to do.
12417 If, instead, you use the GCC driver to create shared libraries, you may
12418 find that they are not always linked with the shared @file{libgcc}.
12419 If GCC finds, at its configuration time, that you have a non-GNU linker
12420 or a GNU linker that does not support option @option{--eh-frame-hdr},
12421 it links the shared version of @file{libgcc} into shared libraries
12422 by default. Otherwise, it takes advantage of the linker and optimizes
12423 away the linking with the shared version of @file{libgcc}, linking with
12424 the static version of libgcc by default. This allows exceptions to
12425 propagate through such shared libraries, without incurring relocation
12426 costs at library load time.
12428 However, if a library or main executable is supposed to throw or catch
12429 exceptions, you must link it using the G++ driver, as appropriate
12430 for the languages used in the program, or using the option
12431 @option{-shared-libgcc}, such that it is linked with the shared
12434 @item -static-libasan
12435 @opindex static-libasan
12436 When the @option{-fsanitize=address} option is used to link a program,
12437 the GCC driver automatically links against @option{libasan}. If
12438 @file{libasan} is available as a shared library, and the @option{-static}
12439 option is not used, then this links against the shared version of
12440 @file{libasan}. The @option{-static-libasan} option directs the GCC
12441 driver to link @file{libasan} statically, without necessarily linking
12442 other libraries statically.
12444 @item -static-libtsan
12445 @opindex static-libtsan
12446 When the @option{-fsanitize=thread} option is used to link a program,
12447 the GCC driver automatically links against @option{libtsan}. If
12448 @file{libtsan} is available as a shared library, and the @option{-static}
12449 option is not used, then this links against the shared version of
12450 @file{libtsan}. The @option{-static-libtsan} option directs the GCC
12451 driver to link @file{libtsan} statically, without necessarily linking
12452 other libraries statically.
12454 @item -static-liblsan
12455 @opindex static-liblsan
12456 When the @option{-fsanitize=leak} option is used to link a program,
12457 the GCC driver automatically links against @option{liblsan}. If
12458 @file{liblsan} is available as a shared library, and the @option{-static}
12459 option is not used, then this links against the shared version of
12460 @file{liblsan}. The @option{-static-liblsan} option directs the GCC
12461 driver to link @file{liblsan} statically, without necessarily linking
12462 other libraries statically.
12464 @item -static-libubsan
12465 @opindex static-libubsan
12466 When the @option{-fsanitize=undefined} option is used to link a program,
12467 the GCC driver automatically links against @option{libubsan}. If
12468 @file{libubsan} is available as a shared library, and the @option{-static}
12469 option is not used, then this links against the shared version of
12470 @file{libubsan}. The @option{-static-libubsan} option directs the GCC
12471 driver to link @file{libubsan} statically, without necessarily linking
12472 other libraries statically.
12474 @item -static-libmpx
12475 @opindex static-libmpx
12476 When the @option{-fcheck-pointer bounds} and @option{-mmpx} options are
12477 used to link a program, the GCC driver automatically links against
12478 @file{libmpx}. If @file{libmpx} is available as a shared library,
12479 and the @option{-static} option is not used, then this links against
12480 the shared version of @file{libmpx}. The @option{-static-libmpx}
12481 option directs the GCC driver to link @file{libmpx} statically,
12482 without necessarily linking other libraries statically.
12484 @item -static-libmpxwrappers
12485 @opindex static-libmpxwrappers
12486 When the @option{-fcheck-pointer bounds} and @option{-mmpx} options are used
12487 to link a program without also using @option{-fno-chkp-use-wrappers}, the
12488 GCC driver automatically links against @file{libmpxwrappers}. If
12489 @file{libmpxwrappers} is available as a shared library, and the
12490 @option{-static} option is not used, then this links against the shared
12491 version of @file{libmpxwrappers}. The @option{-static-libmpxwrappers}
12492 option directs the GCC driver to link @file{libmpxwrappers} statically,
12493 without necessarily linking other libraries statically.
12495 @item -static-libstdc++
12496 @opindex static-libstdc++
12497 When the @command{g++} program is used to link a C++ program, it
12498 normally automatically links against @option{libstdc++}. If
12499 @file{libstdc++} is available as a shared library, and the
12500 @option{-static} option is not used, then this links against the
12501 shared version of @file{libstdc++}. That is normally fine. However, it
12502 is sometimes useful to freeze the version of @file{libstdc++} used by
12503 the program without going all the way to a fully static link. The
12504 @option{-static-libstdc++} option directs the @command{g++} driver to
12505 link @file{libstdc++} statically, without necessarily linking other
12506 libraries statically.
12510 Bind references to global symbols when building a shared object. Warn
12511 about any unresolved references (unless overridden by the link editor
12512 option @option{-Xlinker -z -Xlinker defs}). Only a few systems support
12515 @item -T @var{script}
12517 @cindex linker script
12518 Use @var{script} as the linker script. This option is supported by most
12519 systems using the GNU linker. On some targets, such as bare-board
12520 targets without an operating system, the @option{-T} option may be required
12521 when linking to avoid references to undefined symbols.
12523 @item -Xlinker @var{option}
12525 Pass @var{option} as an option to the linker. You can use this to
12526 supply system-specific linker options that GCC does not recognize.
12528 If you want to pass an option that takes a separate argument, you must use
12529 @option{-Xlinker} twice, once for the option and once for the argument.
12530 For example, to pass @option{-assert definitions}, you must write
12531 @option{-Xlinker -assert -Xlinker definitions}. It does not work to write
12532 @option{-Xlinker "-assert definitions"}, because this passes the entire
12533 string as a single argument, which is not what the linker expects.
12535 When using the GNU linker, it is usually more convenient to pass
12536 arguments to linker options using the @option{@var{option}=@var{value}}
12537 syntax than as separate arguments. For example, you can specify
12538 @option{-Xlinker -Map=output.map} rather than
12539 @option{-Xlinker -Map -Xlinker output.map}. Other linkers may not support
12540 this syntax for command-line options.
12542 @item -Wl,@var{option}
12544 Pass @var{option} as an option to the linker. If @var{option} contains
12545 commas, it is split into multiple options at the commas. You can use this
12546 syntax to pass an argument to the option.
12547 For example, @option{-Wl,-Map,output.map} passes @option{-Map output.map} to the
12548 linker. When using the GNU linker, you can also get the same effect with
12549 @option{-Wl,-Map=output.map}.
12551 @item -u @var{symbol}
12553 Pretend the symbol @var{symbol} is undefined, to force linking of
12554 library modules to define it. You can use @option{-u} multiple times with
12555 different symbols to force loading of additional library modules.
12557 @item -z @var{keyword}
12559 @option{-z} is passed directly on to the linker along with the keyword
12560 @var{keyword}. See the section in the documentation of your linker for
12561 permitted values and their meanings.
12564 @node Directory Options
12565 @section Options for Directory Search
12566 @cindex directory options
12567 @cindex options, directory search
12568 @cindex search path
12570 These options specify directories to search for header files, for
12571 libraries and for parts of the compiler:
12574 @include cppdiropts.texi
12576 @item -iplugindir=@var{dir}
12577 @opindex iplugindir=
12578 Set the directory to search for plugins that are passed
12579 by @option{-fplugin=@var{name}} instead of
12580 @option{-fplugin=@var{path}/@var{name}.so}. This option is not meant
12581 to be used by the user, but only passed by the driver.
12585 Add directory @var{dir} to the list of directories to be searched
12588 @item -B@var{prefix}
12590 This option specifies where to find the executables, libraries,
12591 include files, and data files of the compiler itself.
12593 The compiler driver program runs one or more of the subprograms
12594 @command{cpp}, @command{cc1}, @command{as} and @command{ld}. It tries
12595 @var{prefix} as a prefix for each program it tries to run, both with and
12596 without @samp{@var{machine}/@var{version}/} for the corresponding target
12597 machine and compiler version.
12599 For each subprogram to be run, the compiler driver first tries the
12600 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
12601 is not specified, the driver tries two standard prefixes,
12602 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
12603 those results in a file name that is found, the unmodified program
12604 name is searched for using the directories specified in your
12605 @env{PATH} environment variable.
12607 The compiler checks to see if the path provided by @option{-B}
12608 refers to a directory, and if necessary it adds a directory
12609 separator character at the end of the path.
12611 @option{-B} prefixes that effectively specify directory names also apply
12612 to libraries in the linker, because the compiler translates these
12613 options into @option{-L} options for the linker. They also apply to
12614 include files in the preprocessor, because the compiler translates these
12615 options into @option{-isystem} options for the preprocessor. In this case,
12616 the compiler appends @samp{include} to the prefix.
12618 The runtime support file @file{libgcc.a} can also be searched for using
12619 the @option{-B} prefix, if needed. If it is not found there, the two
12620 standard prefixes above are tried, and that is all. The file is left
12621 out of the link if it is not found by those means.
12623 Another way to specify a prefix much like the @option{-B} prefix is to use
12624 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
12627 As a special kludge, if the path provided by @option{-B} is
12628 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
12629 9, then it is replaced by @file{[dir/]include}. This is to help
12630 with boot-strapping the compiler.
12632 @item -no-canonical-prefixes
12633 @opindex no-canonical-prefixes
12634 Do not expand any symbolic links, resolve references to @samp{/../}
12635 or @samp{/./}, or make the path absolute when generating a relative
12638 @item --sysroot=@var{dir}
12640 Use @var{dir} as the logical root directory for headers and libraries.
12641 For example, if the compiler normally searches for headers in
12642 @file{/usr/include} and libraries in @file{/usr/lib}, it instead
12643 searches @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}.
12645 If you use both this option and the @option{-isysroot} option, then
12646 the @option{--sysroot} option applies to libraries, but the
12647 @option{-isysroot} option applies to header files.
12649 The GNU linker (beginning with version 2.16) has the necessary support
12650 for this option. If your linker does not support this option, the
12651 header file aspect of @option{--sysroot} still works, but the
12652 library aspect does not.
12654 @item --no-sysroot-suffix
12655 @opindex no-sysroot-suffix
12656 For some targets, a suffix is added to the root directory specified
12657 with @option{--sysroot}, depending on the other options used, so that
12658 headers may for example be found in
12659 @file{@var{dir}/@var{suffix}/usr/include} instead of
12660 @file{@var{dir}/usr/include}. This option disables the addition of
12665 @node Code Gen Options
12666 @section Options for Code Generation Conventions
12667 @cindex code generation conventions
12668 @cindex options, code generation
12669 @cindex run-time options
12671 These machine-independent options control the interface conventions
12672 used in code generation.
12674 Most of them have both positive and negative forms; the negative form
12675 of @option{-ffoo} is @option{-fno-foo}. In the table below, only
12676 one of the forms is listed---the one that is not the default. You
12677 can figure out the other form by either removing @samp{no-} or adding
12681 @item -fstack-reuse=@var{reuse-level}
12682 @opindex fstack_reuse
12683 This option controls stack space reuse for user declared local/auto variables
12684 and compiler generated temporaries. @var{reuse_level} can be @samp{all},
12685 @samp{named_vars}, or @samp{none}. @samp{all} enables stack reuse for all
12686 local variables and temporaries, @samp{named_vars} enables the reuse only for
12687 user defined local variables with names, and @samp{none} disables stack reuse
12688 completely. The default value is @samp{all}. The option is needed when the
12689 program extends the lifetime of a scoped local variable or a compiler generated
12690 temporary beyond the end point defined by the language. When a lifetime of
12691 a variable ends, and if the variable lives in memory, the optimizing compiler
12692 has the freedom to reuse its stack space with other temporaries or scoped
12693 local variables whose live range does not overlap with it. Legacy code extending
12694 local lifetime is likely to break with the stack reuse optimization.
12713 if (*p == 10) // out of scope use of local1
12724 A(int k) : i(k), j(k) @{ @}
12731 void foo(const A& ar)
12738 foo(A(10)); // temp object's lifetime ends when foo returns
12744 ap->i+= 10; // ap references out of scope temp whose space
12745 // is reused with a. What is the value of ap->i?
12750 The lifetime of a compiler generated temporary is well defined by the C++
12751 standard. When a lifetime of a temporary ends, and if the temporary lives
12752 in memory, the optimizing compiler has the freedom to reuse its stack
12753 space with other temporaries or scoped local variables whose live range
12754 does not overlap with it. However some of the legacy code relies on
12755 the behavior of older compilers in which temporaries' stack space is
12756 not reused, the aggressive stack reuse can lead to runtime errors. This
12757 option is used to control the temporary stack reuse optimization.
12761 This option generates traps for signed overflow on addition, subtraction,
12762 multiplication operations.
12763 The options @option{-ftrapv} and @option{-fwrapv} override each other, so using
12764 @option{-ftrapv} @option{-fwrapv} on the command-line results in
12765 @option{-fwrapv} being effective. Note that only active options override, so
12766 using @option{-ftrapv} @option{-fwrapv} @option{-fno-wrapv} on the command-line
12767 results in @option{-ftrapv} being effective.
12771 This option instructs the compiler to assume that signed arithmetic
12772 overflow of addition, subtraction and multiplication wraps around
12773 using twos-complement representation. This flag enables some optimizations
12774 and disables others.
12775 The options @option{-ftrapv} and @option{-fwrapv} override each other, so using
12776 @option{-ftrapv} @option{-fwrapv} on the command-line results in
12777 @option{-fwrapv} being effective. Note that only active options override, so
12778 using @option{-ftrapv} @option{-fwrapv} @option{-fno-wrapv} on the command-line
12779 results in @option{-ftrapv} being effective.
12781 @item -fwrapv-pointer
12782 @opindex fwrapv-pointer
12783 This option instructs the compiler to assume that pointer arithmetic
12784 overflow on addition and subtraction wraps around using twos-complement
12785 representation. This flag disables some optimizations which assume
12786 pointer overflow is invalid.
12788 @item -fstrict-overflow
12789 @opindex fstrict-overflow
12790 This option implies @option{-fno-wrapv} @option{-fno-wrapv-pointer} and when
12791 negated implies @option{-fwrapv} @option{-fwrapv-pointer}.
12794 @opindex fexceptions
12795 Enable exception handling. Generates extra code needed to propagate
12796 exceptions. For some targets, this implies GCC generates frame
12797 unwind information for all functions, which can produce significant data
12798 size overhead, although it does not affect execution. If you do not
12799 specify this option, GCC enables it by default for languages like
12800 C++ that normally require exception handling, and disables it for
12801 languages like C that do not normally require it. However, you may need
12802 to enable this option when compiling C code that needs to interoperate
12803 properly with exception handlers written in C++. You may also wish to
12804 disable this option if you are compiling older C++ programs that don't
12805 use exception handling.
12807 @item -fnon-call-exceptions
12808 @opindex fnon-call-exceptions
12809 Generate code that allows trapping instructions to throw exceptions.
12810 Note that this requires platform-specific runtime support that does
12811 not exist everywhere. Moreover, it only allows @emph{trapping}
12812 instructions to throw exceptions, i.e.@: memory references or floating-point
12813 instructions. It does not allow exceptions to be thrown from
12814 arbitrary signal handlers such as @code{SIGALRM}.
12816 @item -fdelete-dead-exceptions
12817 @opindex fdelete-dead-exceptions
12818 Consider that instructions that may throw exceptions but don't otherwise
12819 contribute to the execution of the program can be optimized away.
12820 This option is enabled by default for the Ada front end, as permitted by
12821 the Ada language specification.
12822 Optimization passes that cause dead exceptions to be removed are enabled independently at different optimization levels.
12824 @item -funwind-tables
12825 @opindex funwind-tables
12826 Similar to @option{-fexceptions}, except that it just generates any needed
12827 static data, but does not affect the generated code in any other way.
12828 You normally do not need to enable this option; instead, a language processor
12829 that needs this handling enables it on your behalf.
12831 @item -fasynchronous-unwind-tables
12832 @opindex fasynchronous-unwind-tables
12833 Generate unwind table in DWARF format, if supported by target machine. The
12834 table is exact at each instruction boundary, so it can be used for stack
12835 unwinding from asynchronous events (such as debugger or garbage collector).
12837 @item -fno-gnu-unique
12838 @opindex fno-gnu-unique
12839 On systems with recent GNU assembler and C library, the C++ compiler
12840 uses the @code{STB_GNU_UNIQUE} binding to make sure that definitions
12841 of template static data members and static local variables in inline
12842 functions are unique even in the presence of @code{RTLD_LOCAL}; this
12843 is necessary to avoid problems with a library used by two different
12844 @code{RTLD_LOCAL} plugins depending on a definition in one of them and
12845 therefore disagreeing with the other one about the binding of the
12846 symbol. But this causes @code{dlclose} to be ignored for affected
12847 DSOs; if your program relies on reinitialization of a DSO via
12848 @code{dlclose} and @code{dlopen}, you can use
12849 @option{-fno-gnu-unique}.
12851 @item -fpcc-struct-return
12852 @opindex fpcc-struct-return
12853 Return ``short'' @code{struct} and @code{union} values in memory like
12854 longer ones, rather than in registers. This convention is less
12855 efficient, but it has the advantage of allowing intercallability between
12856 GCC-compiled files and files compiled with other compilers, particularly
12857 the Portable C Compiler (pcc).
12859 The precise convention for returning structures in memory depends
12860 on the target configuration macros.
12862 Short structures and unions are those whose size and alignment match
12863 that of some integer type.
12865 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
12866 switch is not binary compatible with code compiled with the
12867 @option{-freg-struct-return} switch.
12868 Use it to conform to a non-default application binary interface.
12870 @item -freg-struct-return
12871 @opindex freg-struct-return
12872 Return @code{struct} and @code{union} values in registers when possible.
12873 This is more efficient for small structures than
12874 @option{-fpcc-struct-return}.
12876 If you specify neither @option{-fpcc-struct-return} nor
12877 @option{-freg-struct-return}, GCC defaults to whichever convention is
12878 standard for the target. If there is no standard convention, GCC
12879 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
12880 the principal compiler. In those cases, we can choose the standard, and
12881 we chose the more efficient register return alternative.
12883 @strong{Warning:} code compiled with the @option{-freg-struct-return}
12884 switch is not binary compatible with code compiled with the
12885 @option{-fpcc-struct-return} switch.
12886 Use it to conform to a non-default application binary interface.
12888 @item -fshort-enums
12889 @opindex fshort-enums
12890 Allocate to an @code{enum} type only as many bytes as it needs for the
12891 declared range of possible values. Specifically, the @code{enum} type
12892 is equivalent to the smallest integer type that has enough room.
12894 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
12895 code that is not binary compatible with code generated without that switch.
12896 Use it to conform to a non-default application binary interface.
12898 @item -fshort-wchar
12899 @opindex fshort-wchar
12900 Override the underlying type for @code{wchar_t} to be @code{short
12901 unsigned int} instead of the default for the target. This option is
12902 useful for building programs to run under WINE@.
12904 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
12905 code that is not binary compatible with code generated without that switch.
12906 Use it to conform to a non-default application binary interface.
12909 @opindex fno-common
12910 @cindex tentative definitions
12911 In C code, this option controls the placement of global variables
12912 defined without an initializer, known as @dfn{tentative definitions}
12913 in the C standard. Tentative definitions are distinct from declarations
12914 of a variable with the @code{extern} keyword, which do not allocate storage.
12916 Unix C compilers have traditionally allocated storage for
12917 uninitialized global variables in a common block. This allows the
12918 linker to resolve all tentative definitions of the same variable
12919 in different compilation units to the same object, or to a non-tentative
12921 This is the behavior specified by @option{-fcommon}, and is the default for
12922 GCC on most targets.
12923 On the other hand, this behavior is not required by ISO
12924 C, and on some targets may carry a speed or code size penalty on
12925 variable references.
12927 The @option{-fno-common} option specifies that the compiler should instead
12928 place uninitialized global variables in the data section of the object file.
12929 This inhibits the merging of tentative definitions by the linker so
12930 you get a multiple-definition error if the same
12931 variable is defined in more than one compilation unit.
12932 Compiling with @option{-fno-common} is useful on targets for which
12933 it provides better performance, or if you wish to verify that the
12934 program will work on other systems that always treat uninitialized
12935 variable definitions this way.
12939 Ignore the @code{#ident} directive.
12941 @item -finhibit-size-directive
12942 @opindex finhibit-size-directive
12943 Don't output a @code{.size} assembler directive, or anything else that
12944 would cause trouble if the function is split in the middle, and the
12945 two halves are placed at locations far apart in memory. This option is
12946 used when compiling @file{crtstuff.c}; you should not need to use it
12949 @item -fverbose-asm
12950 @opindex fverbose-asm
12951 Put extra commentary information in the generated assembly code to
12952 make it more readable. This option is generally only of use to those
12953 who actually need to read the generated assembly code (perhaps while
12954 debugging the compiler itself).
12956 @option{-fno-verbose-asm}, the default, causes the
12957 extra information to be omitted and is useful when comparing two assembler
12960 The added comments include:
12965 information on the compiler version and command-line options,
12968 the source code lines associated with the assembly instructions,
12969 in the form FILENAME:LINENUMBER:CONTENT OF LINE,
12972 hints on which high-level expressions correspond to
12973 the various assembly instruction operands.
12977 For example, given this C source file:
12985 for (i = 0; i < n; i++)
12992 compiling to (x86_64) assembly via @option{-S} and emitting the result
12993 direct to stdout via @option{-o} @option{-}
12996 gcc -S test.c -fverbose-asm -Os -o -
12999 gives output similar to this:
13003 # GNU C11 (GCC) version 7.0.0 20160809 (experimental) (x86_64-pc-linux-gnu)
13010 .type test, @@function
13014 # test.c:4: int total = 0;
13015 xorl %eax, %eax # <retval>
13016 # test.c:6: for (i = 0; i < n; i++)
13017 xorl %edx, %edx # i
13019 # test.c:6: for (i = 0; i < n; i++)
13020 cmpl %edi, %edx # n, i
13022 # test.c:7: total += i * i;
13023 movl %edx, %ecx # i, tmp92
13024 imull %edx, %ecx # i, tmp92
13025 # test.c:6: for (i = 0; i < n; i++)
13027 # test.c:7: total += i * i;
13028 addl %ecx, %eax # tmp92, <retval>
13036 .ident "GCC: (GNU) 7.0.0 20160809 (experimental)"
13037 .section .note.GNU-stack,"",@@progbits
13040 The comments are intended for humans rather than machines and hence the
13041 precise format of the comments is subject to change.
13043 @item -frecord-gcc-switches
13044 @opindex frecord-gcc-switches
13045 This switch causes the command line used to invoke the
13046 compiler to be recorded into the object file that is being created.
13047 This switch is only implemented on some targets and the exact format
13048 of the recording is target and binary file format dependent, but it
13049 usually takes the form of a section containing ASCII text. This
13050 switch is related to the @option{-fverbose-asm} switch, but that
13051 switch only records information in the assembler output file as
13052 comments, so it never reaches the object file.
13053 See also @option{-grecord-gcc-switches} for another
13054 way of storing compiler options into the object file.
13058 @cindex global offset table
13060 Generate position-independent code (PIC) suitable for use in a shared
13061 library, if supported for the target machine. Such code accesses all
13062 constant addresses through a global offset table (GOT)@. The dynamic
13063 loader resolves the GOT entries when the program starts (the dynamic
13064 loader is not part of GCC; it is part of the operating system). If
13065 the GOT size for the linked executable exceeds a machine-specific
13066 maximum size, you get an error message from the linker indicating that
13067 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
13068 instead. (These maximums are 8k on the SPARC, 28k on AArch64 and 32k
13069 on the m68k and RS/6000. The x86 has no such limit.)
13071 Position-independent code requires special support, and therefore works
13072 only on certain machines. For the x86, GCC supports PIC for System V
13073 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
13074 position-independent.
13076 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
13081 If supported for the target machine, emit position-independent code,
13082 suitable for dynamic linking and avoiding any limit on the size of the
13083 global offset table. This option makes a difference on AArch64, m68k,
13084 PowerPC and SPARC@.
13086 Position-independent code requires special support, and therefore works
13087 only on certain machines.
13089 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
13096 These options are similar to @option{-fpic} and @option{-fPIC}, but
13097 generated position independent code can be only linked into executables.
13098 Usually these options are used when @option{-pie} GCC option is
13099 used during linking.
13101 @option{-fpie} and @option{-fPIE} both define the macros
13102 @code{__pie__} and @code{__PIE__}. The macros have the value 1
13103 for @option{-fpie} and 2 for @option{-fPIE}.
13107 Do not use the PLT for external function calls in position-independent code.
13108 Instead, load the callee address at call sites from the GOT and branch to it.
13109 This leads to more efficient code by eliminating PLT stubs and exposing
13110 GOT loads to optimizations. On architectures such as 32-bit x86 where
13111 PLT stubs expect the GOT pointer in a specific register, this gives more
13112 register allocation freedom to the compiler.
13113 Lazy binding requires use of the PLT;
13114 with @option{-fno-plt} all external symbols are resolved at load time.
13116 Alternatively, the function attribute @code{noplt} can be used to avoid calls
13117 through the PLT for specific external functions.
13119 In position-dependent code, a few targets also convert calls to
13120 functions that are marked to not use the PLT to use the GOT instead.
13122 @item -fno-jump-tables
13123 @opindex fno-jump-tables
13124 Do not use jump tables for switch statements even where it would be
13125 more efficient than other code generation strategies. This option is
13126 of use in conjunction with @option{-fpic} or @option{-fPIC} for
13127 building code that forms part of a dynamic linker and cannot
13128 reference the address of a jump table. On some targets, jump tables
13129 do not require a GOT and this option is not needed.
13131 @item -ffixed-@var{reg}
13133 Treat the register named @var{reg} as a fixed register; generated code
13134 should never refer to it (except perhaps as a stack pointer, frame
13135 pointer or in some other fixed role).
13137 @var{reg} must be the name of a register. The register names accepted
13138 are machine-specific and are defined in the @code{REGISTER_NAMES}
13139 macro in the machine description macro file.
13141 This flag does not have a negative form, because it specifies a
13144 @item -fcall-used-@var{reg}
13145 @opindex fcall-used
13146 Treat the register named @var{reg} as an allocable register that is
13147 clobbered by function calls. It may be allocated for temporaries or
13148 variables that do not live across a call. Functions compiled this way
13149 do not save and restore the register @var{reg}.
13151 It is an error to use this flag with the frame pointer or stack pointer.
13152 Use of this flag for other registers that have fixed pervasive roles in
13153 the machine's execution model produces disastrous results.
13155 This flag does not have a negative form, because it specifies a
13158 @item -fcall-saved-@var{reg}
13159 @opindex fcall-saved
13160 Treat the register named @var{reg} as an allocable register saved by
13161 functions. It may be allocated even for temporaries or variables that
13162 live across a call. Functions compiled this way save and restore
13163 the register @var{reg} if they use it.
13165 It is an error to use this flag with the frame pointer or stack pointer.
13166 Use of this flag for other registers that have fixed pervasive roles in
13167 the machine's execution model produces disastrous results.
13169 A different sort of disaster results from the use of this flag for
13170 a register in which function values may be returned.
13172 This flag does not have a negative form, because it specifies a
13175 @item -fpack-struct[=@var{n}]
13176 @opindex fpack-struct
13177 Without a value specified, pack all structure members together without
13178 holes. When a value is specified (which must be a small power of two), pack
13179 structure members according to this value, representing the maximum
13180 alignment (that is, objects with default alignment requirements larger than
13181 this are output potentially unaligned at the next fitting location.
13183 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
13184 code that is not binary compatible with code generated without that switch.
13185 Additionally, it makes the code suboptimal.
13186 Use it to conform to a non-default application binary interface.
13188 @item -fleading-underscore
13189 @opindex fleading-underscore
13190 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
13191 change the way C symbols are represented in the object file. One use
13192 is to help link with legacy assembly code.
13194 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
13195 generate code that is not binary compatible with code generated without that
13196 switch. Use it to conform to a non-default application binary interface.
13197 Not all targets provide complete support for this switch.
13199 @item -ftls-model=@var{model}
13200 @opindex ftls-model
13201 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
13202 The @var{model} argument should be one of @samp{global-dynamic},
13203 @samp{local-dynamic}, @samp{initial-exec} or @samp{local-exec}.
13204 Note that the choice is subject to optimization: the compiler may use
13205 a more efficient model for symbols not visible outside of the translation
13206 unit, or if @option{-fpic} is not given on the command line.
13208 The default without @option{-fpic} is @samp{initial-exec}; with
13209 @option{-fpic} the default is @samp{global-dynamic}.
13211 @item -ftrampolines
13212 @opindex ftrampolines
13213 For targets that normally need trampolines for nested functions, always
13214 generate them instead of using descriptors. Otherwise, for targets that
13215 do not need them, like for example HP-PA or IA-64, do nothing.
13217 A trampoline is a small piece of code that is created at run time on the
13218 stack when the address of a nested function is taken, and is used to call
13219 the nested function indirectly. Therefore, it requires the stack to be
13220 made executable in order for the program to work properly.
13222 @option{-fno-trampolines} is enabled by default on a language by language
13223 basis to let the compiler avoid generating them, if it computes that this
13224 is safe, and replace them with descriptors. Descriptors are made up of data
13225 only, but the generated code must be prepared to deal with them. As of this
13226 writing, @option{-fno-trampolines} is enabled by default only for Ada.
13228 Moreover, code compiled with @option{-ftrampolines} and code compiled with
13229 @option{-fno-trampolines} are not binary compatible if nested functions are
13230 present. This option must therefore be used on a program-wide basis and be
13231 manipulated with extreme care.
13233 @item -fvisibility=@r{[}default@r{|}internal@r{|}hidden@r{|}protected@r{]}
13234 @opindex fvisibility
13235 Set the default ELF image symbol visibility to the specified option---all
13236 symbols are marked with this unless overridden within the code.
13237 Using this feature can very substantially improve linking and
13238 load times of shared object libraries, produce more optimized
13239 code, provide near-perfect API export and prevent symbol clashes.
13240 It is @strong{strongly} recommended that you use this in any shared objects
13243 Despite the nomenclature, @samp{default} always means public; i.e.,
13244 available to be linked against from outside the shared object.
13245 @samp{protected} and @samp{internal} are pretty useless in real-world
13246 usage so the only other commonly used option is @samp{hidden}.
13247 The default if @option{-fvisibility} isn't specified is
13248 @samp{default}, i.e., make every symbol public.
13250 A good explanation of the benefits offered by ensuring ELF
13251 symbols have the correct visibility is given by ``How To Write
13252 Shared Libraries'' by Ulrich Drepper (which can be found at
13253 @w{@uref{https://www.akkadia.org/drepper/}})---however a superior
13254 solution made possible by this option to marking things hidden when
13255 the default is public is to make the default hidden and mark things
13256 public. This is the norm with DLLs on Windows and with @option{-fvisibility=hidden}
13257 and @code{__attribute__ ((visibility("default")))} instead of
13258 @code{__declspec(dllexport)} you get almost identical semantics with
13259 identical syntax. This is a great boon to those working with
13260 cross-platform projects.
13262 For those adding visibility support to existing code, you may find
13263 @code{#pragma GCC visibility} of use. This works by you enclosing
13264 the declarations you wish to set visibility for with (for example)
13265 @code{#pragma GCC visibility push(hidden)} and
13266 @code{#pragma GCC visibility pop}.
13267 Bear in mind that symbol visibility should be viewed @strong{as
13268 part of the API interface contract} and thus all new code should
13269 always specify visibility when it is not the default; i.e., declarations
13270 only for use within the local DSO should @strong{always} be marked explicitly
13271 as hidden as so to avoid PLT indirection overheads---making this
13272 abundantly clear also aids readability and self-documentation of the code.
13273 Note that due to ISO C++ specification requirements, @code{operator new} and
13274 @code{operator delete} must always be of default visibility.
13276 Be aware that headers from outside your project, in particular system
13277 headers and headers from any other library you use, may not be
13278 expecting to be compiled with visibility other than the default. You
13279 may need to explicitly say @code{#pragma GCC visibility push(default)}
13280 before including any such headers.
13282 @code{extern} declarations are not affected by @option{-fvisibility}, so
13283 a lot of code can be recompiled with @option{-fvisibility=hidden} with
13284 no modifications. However, this means that calls to @code{extern}
13285 functions with no explicit visibility use the PLT, so it is more
13286 effective to use @code{__attribute ((visibility))} and/or
13287 @code{#pragma GCC visibility} to tell the compiler which @code{extern}
13288 declarations should be treated as hidden.
13290 Note that @option{-fvisibility} does affect C++ vague linkage
13291 entities. This means that, for instance, an exception class that is
13292 be thrown between DSOs must be explicitly marked with default
13293 visibility so that the @samp{type_info} nodes are unified between
13296 An overview of these techniques, their benefits and how to use them
13297 is at @uref{http://gcc.gnu.org/@/wiki/@/Visibility}.
13299 @item -fstrict-volatile-bitfields
13300 @opindex fstrict-volatile-bitfields
13301 This option should be used if accesses to volatile bit-fields (or other
13302 structure fields, although the compiler usually honors those types
13303 anyway) should use a single access of the width of the
13304 field's type, aligned to a natural alignment if possible. For
13305 example, targets with memory-mapped peripheral registers might require
13306 all such accesses to be 16 bits wide; with this flag you can
13307 declare all peripheral bit-fields as @code{unsigned short} (assuming short
13308 is 16 bits on these targets) to force GCC to use 16-bit accesses
13309 instead of, perhaps, a more efficient 32-bit access.
13311 If this option is disabled, the compiler uses the most efficient
13312 instruction. In the previous example, that might be a 32-bit load
13313 instruction, even though that accesses bytes that do not contain
13314 any portion of the bit-field, or memory-mapped registers unrelated to
13315 the one being updated.
13317 In some cases, such as when the @code{packed} attribute is applied to a
13318 structure field, it may not be possible to access the field with a single
13319 read or write that is correctly aligned for the target machine. In this
13320 case GCC falls back to generating multiple accesses rather than code that
13321 will fault or truncate the result at run time.
13323 Note: Due to restrictions of the C/C++11 memory model, write accesses are
13324 not allowed to touch non bit-field members. It is therefore recommended
13325 to define all bits of the field's type as bit-field members.
13327 The default value of this option is determined by the application binary
13328 interface for the target processor.
13330 @item -fsync-libcalls
13331 @opindex fsync-libcalls
13332 This option controls whether any out-of-line instance of the @code{__sync}
13333 family of functions may be used to implement the C++11 @code{__atomic}
13334 family of functions.
13336 The default value of this option is enabled, thus the only useful form
13337 of the option is @option{-fno-sync-libcalls}. This option is used in
13338 the implementation of the @file{libatomic} runtime library.
13342 @node Developer Options
13343 @section GCC Developer Options
13344 @cindex developer options
13345 @cindex debugging GCC
13346 @cindex debug dump options
13347 @cindex dump options
13348 @cindex compilation statistics
13350 This section describes command-line options that are primarily of
13351 interest to GCC developers, including options to support compiler
13352 testing and investigation of compiler bugs and compile-time
13353 performance problems. This includes options that produce debug dumps
13354 at various points in the compilation; that print statistics such as
13355 memory use and execution time; and that print information about GCC's
13356 configuration, such as where it searches for libraries. You should
13357 rarely need to use any of these options for ordinary compilation and
13362 @item -d@var{letters}
13363 @itemx -fdump-rtl-@var{pass}
13364 @itemx -fdump-rtl-@var{pass}=@var{filename}
13366 @opindex fdump-rtl-@var{pass}
13367 Says to make debugging dumps during compilation at times specified by
13368 @var{letters}. This is used for debugging the RTL-based passes of the
13369 compiler. The file names for most of the dumps are made by appending
13370 a pass number and a word to the @var{dumpname}, and the files are
13371 created in the directory of the output file. In case of
13372 @option{=@var{filename}} option, the dump is output on the given file
13373 instead of the pass numbered dump files. Note that the pass number is
13374 assigned as passes are registered into the pass manager. Most passes
13375 are registered in the order that they will execute and for these passes
13376 the number corresponds to the pass execution order. However, passes
13377 registered by plugins, passes specific to compilation targets, or
13378 passes that are otherwise registered after all the other passes are
13379 numbered higher than a pass named "final", even if they are executed
13380 earlier. @var{dumpname} is generated from the name of the output
13381 file if explicitly specified and not an executable, otherwise it is
13382 the basename of the source file.
13384 Some @option{-d@var{letters}} switches have different meaning when
13385 @option{-E} is used for preprocessing. @xref{Preprocessor Options},
13386 for information about preprocessor-specific dump options.
13388 Debug dumps can be enabled with a @option{-fdump-rtl} switch or some
13389 @option{-d} option @var{letters}. Here are the possible
13390 letters for use in @var{pass} and @var{letters}, and their meanings:
13394 @item -fdump-rtl-alignments
13395 @opindex fdump-rtl-alignments
13396 Dump after branch alignments have been computed.
13398 @item -fdump-rtl-asmcons
13399 @opindex fdump-rtl-asmcons
13400 Dump after fixing rtl statements that have unsatisfied in/out constraints.
13402 @item -fdump-rtl-auto_inc_dec
13403 @opindex fdump-rtl-auto_inc_dec
13404 Dump after auto-inc-dec discovery. This pass is only run on
13405 architectures that have auto inc or auto dec instructions.
13407 @item -fdump-rtl-barriers
13408 @opindex fdump-rtl-barriers
13409 Dump after cleaning up the barrier instructions.
13411 @item -fdump-rtl-bbpart
13412 @opindex fdump-rtl-bbpart
13413 Dump after partitioning hot and cold basic blocks.
13415 @item -fdump-rtl-bbro
13416 @opindex fdump-rtl-bbro
13417 Dump after block reordering.
13419 @item -fdump-rtl-btl1
13420 @itemx -fdump-rtl-btl2
13421 @opindex fdump-rtl-btl2
13422 @opindex fdump-rtl-btl2
13423 @option{-fdump-rtl-btl1} and @option{-fdump-rtl-btl2} enable dumping
13424 after the two branch
13425 target load optimization passes.
13427 @item -fdump-rtl-bypass
13428 @opindex fdump-rtl-bypass
13429 Dump after jump bypassing and control flow optimizations.
13431 @item -fdump-rtl-combine
13432 @opindex fdump-rtl-combine
13433 Dump after the RTL instruction combination pass.
13435 @item -fdump-rtl-compgotos
13436 @opindex fdump-rtl-compgotos
13437 Dump after duplicating the computed gotos.
13439 @item -fdump-rtl-ce1
13440 @itemx -fdump-rtl-ce2
13441 @itemx -fdump-rtl-ce3
13442 @opindex fdump-rtl-ce1
13443 @opindex fdump-rtl-ce2
13444 @opindex fdump-rtl-ce3
13445 @option{-fdump-rtl-ce1}, @option{-fdump-rtl-ce2}, and
13446 @option{-fdump-rtl-ce3} enable dumping after the three
13447 if conversion passes.
13449 @item -fdump-rtl-cprop_hardreg
13450 @opindex fdump-rtl-cprop_hardreg
13451 Dump after hard register copy propagation.
13453 @item -fdump-rtl-csa
13454 @opindex fdump-rtl-csa
13455 Dump after combining stack adjustments.
13457 @item -fdump-rtl-cse1
13458 @itemx -fdump-rtl-cse2
13459 @opindex fdump-rtl-cse1
13460 @opindex fdump-rtl-cse2
13461 @option{-fdump-rtl-cse1} and @option{-fdump-rtl-cse2} enable dumping after
13462 the two common subexpression elimination passes.
13464 @item -fdump-rtl-dce
13465 @opindex fdump-rtl-dce
13466 Dump after the standalone dead code elimination passes.
13468 @item -fdump-rtl-dbr
13469 @opindex fdump-rtl-dbr
13470 Dump after delayed branch scheduling.
13472 @item -fdump-rtl-dce1
13473 @itemx -fdump-rtl-dce2
13474 @opindex fdump-rtl-dce1
13475 @opindex fdump-rtl-dce2
13476 @option{-fdump-rtl-dce1} and @option{-fdump-rtl-dce2} enable dumping after
13477 the two dead store elimination passes.
13479 @item -fdump-rtl-eh
13480 @opindex fdump-rtl-eh
13481 Dump after finalization of EH handling code.
13483 @item -fdump-rtl-eh_ranges
13484 @opindex fdump-rtl-eh_ranges
13485 Dump after conversion of EH handling range regions.
13487 @item -fdump-rtl-expand
13488 @opindex fdump-rtl-expand
13489 Dump after RTL generation.
13491 @item -fdump-rtl-fwprop1
13492 @itemx -fdump-rtl-fwprop2
13493 @opindex fdump-rtl-fwprop1
13494 @opindex fdump-rtl-fwprop2
13495 @option{-fdump-rtl-fwprop1} and @option{-fdump-rtl-fwprop2} enable
13496 dumping after the two forward propagation passes.
13498 @item -fdump-rtl-gcse1
13499 @itemx -fdump-rtl-gcse2
13500 @opindex fdump-rtl-gcse1
13501 @opindex fdump-rtl-gcse2
13502 @option{-fdump-rtl-gcse1} and @option{-fdump-rtl-gcse2} enable dumping
13503 after global common subexpression elimination.
13505 @item -fdump-rtl-init-regs
13506 @opindex fdump-rtl-init-regs
13507 Dump after the initialization of the registers.
13509 @item -fdump-rtl-initvals
13510 @opindex fdump-rtl-initvals
13511 Dump after the computation of the initial value sets.
13513 @item -fdump-rtl-into_cfglayout
13514 @opindex fdump-rtl-into_cfglayout
13515 Dump after converting to cfglayout mode.
13517 @item -fdump-rtl-ira
13518 @opindex fdump-rtl-ira
13519 Dump after iterated register allocation.
13521 @item -fdump-rtl-jump
13522 @opindex fdump-rtl-jump
13523 Dump after the second jump optimization.
13525 @item -fdump-rtl-loop2
13526 @opindex fdump-rtl-loop2
13527 @option{-fdump-rtl-loop2} enables dumping after the rtl
13528 loop optimization passes.
13530 @item -fdump-rtl-mach
13531 @opindex fdump-rtl-mach
13532 Dump after performing the machine dependent reorganization pass, if that
13535 @item -fdump-rtl-mode_sw
13536 @opindex fdump-rtl-mode_sw
13537 Dump after removing redundant mode switches.
13539 @item -fdump-rtl-rnreg
13540 @opindex fdump-rtl-rnreg
13541 Dump after register renumbering.
13543 @item -fdump-rtl-outof_cfglayout
13544 @opindex fdump-rtl-outof_cfglayout
13545 Dump after converting from cfglayout mode.
13547 @item -fdump-rtl-peephole2
13548 @opindex fdump-rtl-peephole2
13549 Dump after the peephole pass.
13551 @item -fdump-rtl-postreload
13552 @opindex fdump-rtl-postreload
13553 Dump after post-reload optimizations.
13555 @item -fdump-rtl-pro_and_epilogue
13556 @opindex fdump-rtl-pro_and_epilogue
13557 Dump after generating the function prologues and epilogues.
13559 @item -fdump-rtl-sched1
13560 @itemx -fdump-rtl-sched2
13561 @opindex fdump-rtl-sched1
13562 @opindex fdump-rtl-sched2
13563 @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2} enable dumping
13564 after the basic block scheduling passes.
13566 @item -fdump-rtl-ree
13567 @opindex fdump-rtl-ree
13568 Dump after sign/zero extension elimination.
13570 @item -fdump-rtl-seqabstr
13571 @opindex fdump-rtl-seqabstr
13572 Dump after common sequence discovery.
13574 @item -fdump-rtl-shorten
13575 @opindex fdump-rtl-shorten
13576 Dump after shortening branches.
13578 @item -fdump-rtl-sibling
13579 @opindex fdump-rtl-sibling
13580 Dump after sibling call optimizations.
13582 @item -fdump-rtl-split1
13583 @itemx -fdump-rtl-split2
13584 @itemx -fdump-rtl-split3
13585 @itemx -fdump-rtl-split4
13586 @itemx -fdump-rtl-split5
13587 @opindex fdump-rtl-split1
13588 @opindex fdump-rtl-split2
13589 @opindex fdump-rtl-split3
13590 @opindex fdump-rtl-split4
13591 @opindex fdump-rtl-split5
13592 These options enable dumping after five rounds of
13593 instruction splitting.
13595 @item -fdump-rtl-sms
13596 @opindex fdump-rtl-sms
13597 Dump after modulo scheduling. This pass is only run on some
13600 @item -fdump-rtl-stack
13601 @opindex fdump-rtl-stack
13602 Dump after conversion from GCC's ``flat register file'' registers to the
13603 x87's stack-like registers. This pass is only run on x86 variants.
13605 @item -fdump-rtl-subreg1
13606 @itemx -fdump-rtl-subreg2
13607 @opindex fdump-rtl-subreg1
13608 @opindex fdump-rtl-subreg2
13609 @option{-fdump-rtl-subreg1} and @option{-fdump-rtl-subreg2} enable dumping after
13610 the two subreg expansion passes.
13612 @item -fdump-rtl-unshare
13613 @opindex fdump-rtl-unshare
13614 Dump after all rtl has been unshared.
13616 @item -fdump-rtl-vartrack
13617 @opindex fdump-rtl-vartrack
13618 Dump after variable tracking.
13620 @item -fdump-rtl-vregs
13621 @opindex fdump-rtl-vregs
13622 Dump after converting virtual registers to hard registers.
13624 @item -fdump-rtl-web
13625 @opindex fdump-rtl-web
13626 Dump after live range splitting.
13628 @item -fdump-rtl-regclass
13629 @itemx -fdump-rtl-subregs_of_mode_init
13630 @itemx -fdump-rtl-subregs_of_mode_finish
13631 @itemx -fdump-rtl-dfinit
13632 @itemx -fdump-rtl-dfinish
13633 @opindex fdump-rtl-regclass
13634 @opindex fdump-rtl-subregs_of_mode_init
13635 @opindex fdump-rtl-subregs_of_mode_finish
13636 @opindex fdump-rtl-dfinit
13637 @opindex fdump-rtl-dfinish
13638 These dumps are defined but always produce empty files.
13641 @itemx -fdump-rtl-all
13643 @opindex fdump-rtl-all
13644 Produce all the dumps listed above.
13648 Annotate the assembler output with miscellaneous debugging information.
13652 Dump all macro definitions, at the end of preprocessing, in addition to
13657 Produce a core dump whenever an error occurs.
13661 Annotate the assembler output with a comment indicating which
13662 pattern and alternative is used. The length and cost of each instruction are
13667 Dump the RTL in the assembler output as a comment before each instruction.
13668 Also turns on @option{-dp} annotation.
13672 Just generate RTL for a function instead of compiling it. Usually used
13673 with @option{-fdump-rtl-expand}.
13676 @item -fdump-noaddr
13677 @opindex fdump-noaddr
13678 When doing debugging dumps, suppress address output. This makes it more
13679 feasible to use diff on debugging dumps for compiler invocations with
13680 different compiler binaries and/or different
13681 text / bss / data / heap / stack / dso start locations.
13684 @opindex freport-bug
13685 Collect and dump debug information into a temporary file if an
13686 internal compiler error (ICE) occurs.
13688 @item -fdump-unnumbered
13689 @opindex fdump-unnumbered
13690 When doing debugging dumps, suppress instruction numbers and address output.
13691 This makes it more feasible to use diff on debugging dumps for compiler
13692 invocations with different options, in particular with and without
13695 @item -fdump-unnumbered-links
13696 @opindex fdump-unnumbered-links
13697 When doing debugging dumps (see @option{-d} option above), suppress
13698 instruction numbers for the links to the previous and next instructions
13701 @item -fdump-ipa-@var{switch}
13703 Control the dumping at various stages of inter-procedural analysis
13704 language tree to a file. The file name is generated by appending a
13705 switch specific suffix to the source file name, and the file is created
13706 in the same directory as the output file. The following dumps are
13711 Enables all inter-procedural analysis dumps.
13714 Dumps information about call-graph optimization, unused function removal,
13715 and inlining decisions.
13718 Dump after function inlining.
13722 @item -fdump-lang-all
13723 @itemx -fdump-lang-@var{switch}
13724 @itemx -fdump-lang-@var{switch}-@var{options}
13725 @itemx -fdump-lang-@var{switch}-@var{options}=@var{filename}
13726 @opindex fdump-lang-all
13727 @opindex fdump-lang
13728 Control the dumping of language-specific information. The @var{options}
13729 and @var{filename} portions behave as described in the
13730 @option{-fdump-tree} option. The following @var{switch} values are
13736 Enable all language-specific dumps.
13739 Dump class hierarchy information. Virtual table information is emitted
13740 unless '@option{slim}' is specified. This option is applicable to C++ only.
13743 Dump the raw internal tree data. This option is applicable to C++ only.
13747 @item -fdump-passes
13748 @opindex fdump-passes
13749 Print on @file{stderr} the list of optimization passes that are turned
13750 on and off by the current command-line options.
13752 @item -fdump-statistics-@var{option}
13753 @opindex fdump-statistics
13754 Enable and control dumping of pass statistics in a separate file. The
13755 file name is generated by appending a suffix ending in
13756 @samp{.statistics} to the source file name, and the file is created in
13757 the same directory as the output file. If the @samp{-@var{option}}
13758 form is used, @samp{-stats} causes counters to be summed over the
13759 whole compilation unit while @samp{-details} dumps every event as
13760 the passes generate them. The default with no option is to sum
13761 counters for each function compiled.
13763 @item -fdump-tree-all
13764 @itemx -fdump-tree-@var{switch}
13765 @itemx -fdump-tree-@var{switch}-@var{options}
13766 @itemx -fdump-tree-@var{switch}-@var{options}=@var{filename}
13767 @opindex fdump-tree-all
13768 @opindex fdump-tree
13769 Control the dumping at various stages of processing the intermediate
13770 language tree to a file. The file name is generated by appending a
13771 switch-specific suffix to the source file name, and the file is
13772 created in the same directory as the output file. In case of
13773 @option{=@var{filename}} option, the dump is output on the given file
13774 instead of the auto named dump files. If the @samp{-@var{options}}
13775 form is used, @var{options} is a list of @samp{-} separated options
13776 which control the details of the dump. Not all options are applicable
13777 to all dumps; those that are not meaningful are ignored. The
13778 following options are available
13782 Print the address of each node. Usually this is not meaningful as it
13783 changes according to the environment and source file. Its primary use
13784 is for tying up a dump file with a debug environment.
13786 If @code{DECL_ASSEMBLER_NAME} has been set for a given decl, use that
13787 in the dump instead of @code{DECL_NAME}. Its primary use is ease of
13788 use working backward from mangled names in the assembly file.
13790 When dumping front-end intermediate representations, inhibit dumping
13791 of members of a scope or body of a function merely because that scope
13792 has been reached. Only dump such items when they are directly reachable
13793 by some other path.
13795 When dumping pretty-printed trees, this option inhibits dumping the
13796 bodies of control structures.
13798 When dumping RTL, print the RTL in slim (condensed) form instead of
13799 the default LISP-like representation.
13801 Print a raw representation of the tree. By default, trees are
13802 pretty-printed into a C-like representation.
13804 Enable more detailed dumps (not honored by every dump option). Also
13805 include information from the optimization passes.
13807 Enable dumping various statistics about the pass (not honored by every dump
13810 Enable showing basic block boundaries (disabled in raw dumps).
13812 For each of the other indicated dump files (@option{-fdump-rtl-@var{pass}}),
13813 dump a representation of the control flow graph suitable for viewing with
13814 GraphViz to @file{@var{file}.@var{passid}.@var{pass}.dot}. Each function in
13815 the file is pretty-printed as a subgraph, so that GraphViz can render them
13816 all in a single plot.
13818 This option currently only works for RTL dumps, and the RTL is always
13819 dumped in slim form.
13821 Enable showing virtual operands for every statement.
13823 Enable showing line numbers for statements.
13825 Enable showing the unique ID (@code{DECL_UID}) for each variable.
13827 Enable showing the tree dump for each statement.
13829 Enable showing the EH region number holding each statement.
13831 Enable showing scalar evolution analysis details.
13833 Enable showing optimization information (only available in certain
13836 Enable showing missed optimization information (only available in certain
13839 Enable other detailed optimization information (only available in
13841 @item =@var{filename}
13842 Instead of an auto named dump file, output into the given file
13843 name. The file names @file{stdout} and @file{stderr} are treated
13844 specially and are considered already open standard streams. For
13848 gcc -O2 -ftree-vectorize -fdump-tree-vect-blocks=foo.dump
13849 -fdump-tree-pre=/dev/stderr file.c
13852 outputs vectorizer dump into @file{foo.dump}, while the PRE dump is
13853 output on to @file{stderr}. If two conflicting dump filenames are
13854 given for the same pass, then the latter option overrides the earlier
13858 Turn on all options, except @option{raw}, @option{slim}, @option{verbose}
13859 and @option{lineno}.
13862 Turn on all optimization options, i.e., @option{optimized},
13863 @option{missed}, and @option{note}.
13866 To determine what tree dumps are available or find the dump for a pass
13867 of interest follow the steps below.
13871 Invoke GCC with @option{-fdump-passes} and in the @file{stderr} output
13872 look for a code that corresponds to the pass you are interested in.
13873 For example, the codes @code{tree-evrp}, @code{tree-vrp1}, and
13874 @code{tree-vrp2} correspond to the three Value Range Propagation passes.
13875 The number at the end distinguishes distinct invocations of the same pass.
13877 To enable the creation of the dump file, append the pass code to
13878 the @option{-fdump-} option prefix and invoke GCC with it. For example,
13879 to enable the dump from the Early Value Range Propagation pass, invoke
13880 GCC with the @option{-fdump-tree-evrp} option. Optionally, you may
13881 specify the name of the dump file. If you don't specify one, GCC
13882 creates as described below.
13884 Find the pass dump in a file whose name is composed of three components
13885 separated by a period: the name of the source file GCC was invoked to
13886 compile, a numeric suffix indicating the pass number followed by the
13887 letter @samp{t} for tree passes (and the letter @samp{r} for RTL passes),
13888 and finally the pass code. For example, the Early VRP pass dump might
13889 be in a file named @file{myfile.c.038t.evrp} in the current working
13890 directory. Note that the numeric codes are not stable and may change
13891 from one version of GCC to another.
13895 @itemx -fopt-info-@var{options}
13896 @itemx -fopt-info-@var{options}=@var{filename}
13898 Controls optimization dumps from various optimization passes. If the
13899 @samp{-@var{options}} form is used, @var{options} is a list of
13900 @samp{-} separated option keywords to select the dump details and
13903 The @var{options} can be divided into two groups: options describing the
13904 verbosity of the dump, and options describing which optimizations
13905 should be included. The options from both the groups can be freely
13906 mixed as they are non-overlapping. However, in case of any conflicts,
13907 the later options override the earlier options on the command
13910 The following options control the dump verbosity:
13914 Print information when an optimization is successfully applied. It is
13915 up to a pass to decide which information is relevant. For example, the
13916 vectorizer passes print the source location of loops which are
13917 successfully vectorized.
13919 Print information about missed optimizations. Individual passes
13920 control which information to include in the output.
13922 Print verbose information about optimizations, such as certain
13923 transformations, more detailed messages about decisions etc.
13925 Print detailed optimization information. This includes
13926 @samp{optimized}, @samp{missed}, and @samp{note}.
13929 One or more of the following option keywords can be used to describe a
13930 group of optimizations:
13934 Enable dumps from all interprocedural optimizations.
13936 Enable dumps from all loop optimizations.
13938 Enable dumps from all inlining optimizations.
13940 Enable dumps from all OMP (Offloading and Multi Processing) optimizations.
13942 Enable dumps from all vectorization optimizations.
13944 Enable dumps from all optimizations. This is a superset of
13945 the optimization groups listed above.
13948 If @var{options} is
13949 omitted, it defaults to @samp{optimized-optall}, which means to dump all
13950 info about successful optimizations from all the passes.
13952 If the @var{filename} is provided, then the dumps from all the
13953 applicable optimizations are concatenated into the @var{filename}.
13954 Otherwise the dump is output onto @file{stderr}. Though multiple
13955 @option{-fopt-info} options are accepted, only one of them can include
13956 a @var{filename}. If other filenames are provided then all but the
13957 first such option are ignored.
13959 Note that the output @var{filename} is overwritten
13960 in case of multiple translation units. If a combined output from
13961 multiple translation units is desired, @file{stderr} should be used
13964 In the following example, the optimization info is output to
13973 gcc -O3 -fopt-info-missed=missed.all
13977 outputs missed optimization report from all the passes into
13978 @file{missed.all}, and this one:
13981 gcc -O2 -ftree-vectorize -fopt-info-vec-missed
13985 prints information about missed optimization opportunities from
13986 vectorization passes on @file{stderr}.
13987 Note that @option{-fopt-info-vec-missed} is equivalent to
13988 @option{-fopt-info-missed-vec}. The order of the optimization group
13989 names and message types listed after @option{-fopt-info} does not matter.
13991 As another example,
13993 gcc -O3 -fopt-info-inline-optimized-missed=inline.txt
13997 outputs information about missed optimizations as well as
13998 optimized locations from all the inlining passes into
14004 gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt
14008 Here the two output filenames @file{vec.miss} and @file{loop.opt} are
14009 in conflict since only one output file is allowed. In this case, only
14010 the first option takes effect and the subsequent options are
14011 ignored. Thus only @file{vec.miss} is produced which contains
14012 dumps from the vectorizer about missed opportunities.
14014 @item -fsched-verbose=@var{n}
14015 @opindex fsched-verbose
14016 On targets that use instruction scheduling, this option controls the
14017 amount of debugging output the scheduler prints to the dump files.
14019 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
14020 same information as @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2}.
14021 For @var{n} greater than one, it also output basic block probabilities,
14022 detailed ready list information and unit/insn info. For @var{n} greater
14023 than two, it includes RTL at abort point, control-flow and regions info.
14024 And for @var{n} over four, @option{-fsched-verbose} also includes
14029 @item -fenable-@var{kind}-@var{pass}
14030 @itemx -fdisable-@var{kind}-@var{pass}=@var{range-list}
14034 This is a set of options that are used to explicitly disable/enable
14035 optimization passes. These options are intended for use for debugging GCC.
14036 Compiler users should use regular options for enabling/disabling
14041 @item -fdisable-ipa-@var{pass}
14042 Disable IPA pass @var{pass}. @var{pass} is the pass name. If the same pass is
14043 statically invoked in the compiler multiple times, the pass name should be
14044 appended with a sequential number starting from 1.
14046 @item -fdisable-rtl-@var{pass}
14047 @itemx -fdisable-rtl-@var{pass}=@var{range-list}
14048 Disable RTL pass @var{pass}. @var{pass} is the pass name. If the same pass is
14049 statically invoked in the compiler multiple times, the pass name should be
14050 appended with a sequential number starting from 1. @var{range-list} is a
14051 comma-separated list of function ranges or assembler names. Each range is a number
14052 pair separated by a colon. The range is inclusive in both ends. If the range
14053 is trivial, the number pair can be simplified as a single number. If the
14054 function's call graph node's @var{uid} falls within one of the specified ranges,
14055 the @var{pass} is disabled for that function. The @var{uid} is shown in the
14056 function header of a dump file, and the pass names can be dumped by using
14057 option @option{-fdump-passes}.
14059 @item -fdisable-tree-@var{pass}
14060 @itemx -fdisable-tree-@var{pass}=@var{range-list}
14061 Disable tree pass @var{pass}. See @option{-fdisable-rtl} for the description of
14064 @item -fenable-ipa-@var{pass}
14065 Enable IPA pass @var{pass}. @var{pass} is the pass name. If the same pass is
14066 statically invoked in the compiler multiple times, the pass name should be
14067 appended with a sequential number starting from 1.
14069 @item -fenable-rtl-@var{pass}
14070 @itemx -fenable-rtl-@var{pass}=@var{range-list}
14071 Enable RTL pass @var{pass}. See @option{-fdisable-rtl} for option argument
14072 description and examples.
14074 @item -fenable-tree-@var{pass}
14075 @itemx -fenable-tree-@var{pass}=@var{range-list}
14076 Enable tree pass @var{pass}. See @option{-fdisable-rtl} for the description
14077 of option arguments.
14081 Here are some examples showing uses of these options.
14085 # disable ccp1 for all functions
14086 -fdisable-tree-ccp1
14087 # disable complete unroll for function whose cgraph node uid is 1
14088 -fenable-tree-cunroll=1
14089 # disable gcse2 for functions at the following ranges [1,1],
14090 # [300,400], and [400,1000]
14091 # disable gcse2 for functions foo and foo2
14092 -fdisable-rtl-gcse2=foo,foo2
14093 # disable early inlining
14094 -fdisable-tree-einline
14095 # disable ipa inlining
14096 -fdisable-ipa-inline
14097 # enable tree full unroll
14098 -fenable-tree-unroll
14103 @itemx -fchecking=@var{n}
14105 @opindex fno-checking
14106 Enable internal consistency checking. The default depends on
14107 the compiler configuration. @option{-fchecking=2} enables further
14108 internal consistency checking that might affect code generation.
14110 @item -frandom-seed=@var{string}
14111 @opindex frandom-seed
14112 This option provides a seed that GCC uses in place of
14113 random numbers in generating certain symbol names
14114 that have to be different in every compiled file. It is also used to
14115 place unique stamps in coverage data files and the object files that
14116 produce them. You can use the @option{-frandom-seed} option to produce
14117 reproducibly identical object files.
14119 The @var{string} can either be a number (decimal, octal or hex) or an
14120 arbitrary string (in which case it's converted to a number by
14123 The @var{string} should be different for every file you compile.
14126 @itemx -save-temps=cwd
14127 @opindex save-temps
14128 Store the usual ``temporary'' intermediate files permanently; place them
14129 in the current directory and name them based on the source file. Thus,
14130 compiling @file{foo.c} with @option{-c -save-temps} produces files
14131 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
14132 preprocessed @file{foo.i} output file even though the compiler now
14133 normally uses an integrated preprocessor.
14135 When used in combination with the @option{-x} command-line option,
14136 @option{-save-temps} is sensible enough to avoid over writing an
14137 input source file with the same extension as an intermediate file.
14138 The corresponding intermediate file may be obtained by renaming the
14139 source file before using @option{-save-temps}.
14141 If you invoke GCC in parallel, compiling several different source
14142 files that share a common base name in different subdirectories or the
14143 same source file compiled for multiple output destinations, it is
14144 likely that the different parallel compilers will interfere with each
14145 other, and overwrite the temporary files. For instance:
14148 gcc -save-temps -o outdir1/foo.o indir1/foo.c&
14149 gcc -save-temps -o outdir2/foo.o indir2/foo.c&
14152 may result in @file{foo.i} and @file{foo.o} being written to
14153 simultaneously by both compilers.
14155 @item -save-temps=obj
14156 @opindex save-temps=obj
14157 Store the usual ``temporary'' intermediate files permanently. If the
14158 @option{-o} option is used, the temporary files are based on the
14159 object file. If the @option{-o} option is not used, the
14160 @option{-save-temps=obj} switch behaves like @option{-save-temps}.
14165 gcc -save-temps=obj -c foo.c
14166 gcc -save-temps=obj -c bar.c -o dir/xbar.o
14167 gcc -save-temps=obj foobar.c -o dir2/yfoobar
14171 creates @file{foo.i}, @file{foo.s}, @file{dir/xbar.i},
14172 @file{dir/xbar.s}, @file{dir2/yfoobar.i}, @file{dir2/yfoobar.s}, and
14173 @file{dir2/yfoobar.o}.
14175 @item -time@r{[}=@var{file}@r{]}
14177 Report the CPU time taken by each subprocess in the compilation
14178 sequence. For C source files, this is the compiler proper and assembler
14179 (plus the linker if linking is done).
14181 Without the specification of an output file, the output looks like this:
14188 The first number on each line is the ``user time'', that is time spent
14189 executing the program itself. The second number is ``system time'',
14190 time spent executing operating system routines on behalf of the program.
14191 Both numbers are in seconds.
14193 With the specification of an output file, the output is appended to the
14194 named file, and it looks like this:
14197 0.12 0.01 cc1 @var{options}
14198 0.00 0.01 as @var{options}
14201 The ``user time'' and the ``system time'' are moved before the program
14202 name, and the options passed to the program are displayed, so that one
14203 can later tell what file was being compiled, and with which options.
14205 @item -fdump-final-insns@r{[}=@var{file}@r{]}
14206 @opindex fdump-final-insns
14207 Dump the final internal representation (RTL) to @var{file}. If the
14208 optional argument is omitted (or if @var{file} is @code{.}), the name
14209 of the dump file is determined by appending @code{.gkd} to the
14210 compilation output file name.
14212 @item -fcompare-debug@r{[}=@var{opts}@r{]}
14213 @opindex fcompare-debug
14214 @opindex fno-compare-debug
14215 If no error occurs during compilation, run the compiler a second time,
14216 adding @var{opts} and @option{-fcompare-debug-second} to the arguments
14217 passed to the second compilation. Dump the final internal
14218 representation in both compilations, and print an error if they differ.
14220 If the equal sign is omitted, the default @option{-gtoggle} is used.
14222 The environment variable @env{GCC_COMPARE_DEBUG}, if defined, non-empty
14223 and nonzero, implicitly enables @option{-fcompare-debug}. If
14224 @env{GCC_COMPARE_DEBUG} is defined to a string starting with a dash,
14225 then it is used for @var{opts}, otherwise the default @option{-gtoggle}
14228 @option{-fcompare-debug=}, with the equal sign but without @var{opts},
14229 is equivalent to @option{-fno-compare-debug}, which disables the dumping
14230 of the final representation and the second compilation, preventing even
14231 @env{GCC_COMPARE_DEBUG} from taking effect.
14233 To verify full coverage during @option{-fcompare-debug} testing, set
14234 @env{GCC_COMPARE_DEBUG} to say @option{-fcompare-debug-not-overridden},
14235 which GCC rejects as an invalid option in any actual compilation
14236 (rather than preprocessing, assembly or linking). To get just a
14237 warning, setting @env{GCC_COMPARE_DEBUG} to @samp{-w%n-fcompare-debug
14238 not overridden} will do.
14240 @item -fcompare-debug-second
14241 @opindex fcompare-debug-second
14242 This option is implicitly passed to the compiler for the second
14243 compilation requested by @option{-fcompare-debug}, along with options to
14244 silence warnings, and omitting other options that would cause the compiler
14245 to produce output to files or to standard output as a side effect. Dump
14246 files and preserved temporary files are renamed so as to contain the
14247 @code{.gk} additional extension during the second compilation, to avoid
14248 overwriting those generated by the first.
14250 When this option is passed to the compiler driver, it causes the
14251 @emph{first} compilation to be skipped, which makes it useful for little
14252 other than debugging the compiler proper.
14256 Turn off generation of debug info, if leaving out this option
14257 generates it, or turn it on at level 2 otherwise. The position of this
14258 argument in the command line does not matter; it takes effect after all
14259 other options are processed, and it does so only once, no matter how
14260 many times it is given. This is mainly intended to be used with
14261 @option{-fcompare-debug}.
14263 @item -fvar-tracking-assignments-toggle
14264 @opindex fvar-tracking-assignments-toggle
14265 @opindex fno-var-tracking-assignments-toggle
14266 Toggle @option{-fvar-tracking-assignments}, in the same way that
14267 @option{-gtoggle} toggles @option{-g}.
14271 Makes the compiler print out each function name as it is compiled, and
14272 print some statistics about each pass when it finishes.
14274 @item -ftime-report
14275 @opindex ftime-report
14276 Makes the compiler print some statistics about the time consumed by each
14277 pass when it finishes.
14279 @item -ftime-report-details
14280 @opindex ftime-report-details
14281 Record the time consumed by infrastructure parts separately for each pass.
14283 @item -fira-verbose=@var{n}
14284 @opindex fira-verbose
14285 Control the verbosity of the dump file for the integrated register allocator.
14286 The default value is 5. If the value @var{n} is greater or equal to 10,
14287 the dump output is sent to stderr using the same format as @var{n} minus 10.
14290 @opindex flto-report
14291 Prints a report with internal details on the workings of the link-time
14292 optimizer. The contents of this report vary from version to version.
14293 It is meant to be useful to GCC developers when processing object
14294 files in LTO mode (via @option{-flto}).
14296 Disabled by default.
14298 @item -flto-report-wpa
14299 @opindex flto-report-wpa
14300 Like @option{-flto-report}, but only print for the WPA phase of Link
14304 @opindex fmem-report
14305 Makes the compiler print some statistics about permanent memory
14306 allocation when it finishes.
14308 @item -fmem-report-wpa
14309 @opindex fmem-report-wpa
14310 Makes the compiler print some statistics about permanent memory
14311 allocation for the WPA phase only.
14313 @item -fpre-ipa-mem-report
14314 @opindex fpre-ipa-mem-report
14315 @item -fpost-ipa-mem-report
14316 @opindex fpost-ipa-mem-report
14317 Makes the compiler print some statistics about permanent memory
14318 allocation before or after interprocedural optimization.
14320 @item -fprofile-report
14321 @opindex fprofile-report
14322 Makes the compiler print some statistics about consistency of the
14323 (estimated) profile and effect of individual passes.
14325 @item -fstack-usage
14326 @opindex fstack-usage
14327 Makes the compiler output stack usage information for the program, on a
14328 per-function basis. The filename for the dump is made by appending
14329 @file{.su} to the @var{auxname}. @var{auxname} is generated from the name of
14330 the output file, if explicitly specified and it is not an executable,
14331 otherwise it is the basename of the source file. An entry is made up
14336 The name of the function.
14340 One or more qualifiers: @code{static}, @code{dynamic}, @code{bounded}.
14343 The qualifier @code{static} means that the function manipulates the stack
14344 statically: a fixed number of bytes are allocated for the frame on function
14345 entry and released on function exit; no stack adjustments are otherwise made
14346 in the function. The second field is this fixed number of bytes.
14348 The qualifier @code{dynamic} means that the function manipulates the stack
14349 dynamically: in addition to the static allocation described above, stack
14350 adjustments are made in the body of the function, for example to push/pop
14351 arguments around function calls. If the qualifier @code{bounded} is also
14352 present, the amount of these adjustments is bounded at compile time and
14353 the second field is an upper bound of the total amount of stack used by
14354 the function. If it is not present, the amount of these adjustments is
14355 not bounded at compile time and the second field only represents the
14360 Emit statistics about front-end processing at the end of the compilation.
14361 This option is supported only by the C++ front end, and
14362 the information is generally only useful to the G++ development team.
14364 @item -fdbg-cnt-list
14365 @opindex fdbg-cnt-list
14366 Print the name and the counter upper bound for all debug counters.
14369 @item -fdbg-cnt=@var{counter-value-list}
14371 Set the internal debug counter upper bound. @var{counter-value-list}
14372 is a comma-separated list of @var{name}:@var{value} pairs
14373 which sets the upper bound of each debug counter @var{name} to @var{value}.
14374 All debug counters have the initial upper bound of @code{UINT_MAX};
14375 thus @code{dbg_cnt} returns true always unless the upper bound
14376 is set by this option.
14377 For example, with @option{-fdbg-cnt=dce:10,tail_call:0},
14378 @code{dbg_cnt(dce)} returns true only for first 10 invocations.
14380 @item -print-file-name=@var{library}
14381 @opindex print-file-name
14382 Print the full absolute name of the library file @var{library} that
14383 would be used when linking---and don't do anything else. With this
14384 option, GCC does not compile or link anything; it just prints the
14387 @item -print-multi-directory
14388 @opindex print-multi-directory
14389 Print the directory name corresponding to the multilib selected by any
14390 other switches present in the command line. This directory is supposed
14391 to exist in @env{GCC_EXEC_PREFIX}.
14393 @item -print-multi-lib
14394 @opindex print-multi-lib
14395 Print the mapping from multilib directory names to compiler switches
14396 that enable them. The directory name is separated from the switches by
14397 @samp{;}, and each switch starts with an @samp{@@} instead of the
14398 @samp{-}, without spaces between multiple switches. This is supposed to
14399 ease shell processing.
14401 @item -print-multi-os-directory
14402 @opindex print-multi-os-directory
14403 Print the path to OS libraries for the selected
14404 multilib, relative to some @file{lib} subdirectory. If OS libraries are
14405 present in the @file{lib} subdirectory and no multilibs are used, this is
14406 usually just @file{.}, if OS libraries are present in @file{lib@var{suffix}}
14407 sibling directories this prints e.g.@: @file{../lib64}, @file{../lib} or
14408 @file{../lib32}, or if OS libraries are present in @file{lib/@var{subdir}}
14409 subdirectories it prints e.g.@: @file{amd64}, @file{sparcv9} or @file{ev6}.
14411 @item -print-multiarch
14412 @opindex print-multiarch
14413 Print the path to OS libraries for the selected multiarch,
14414 relative to some @file{lib} subdirectory.
14416 @item -print-prog-name=@var{program}
14417 @opindex print-prog-name
14418 Like @option{-print-file-name}, but searches for a program such as @command{cpp}.
14420 @item -print-libgcc-file-name
14421 @opindex print-libgcc-file-name
14422 Same as @option{-print-file-name=libgcc.a}.
14424 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
14425 but you do want to link with @file{libgcc.a}. You can do:
14428 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
14431 @item -print-search-dirs
14432 @opindex print-search-dirs
14433 Print the name of the configured installation directory and a list of
14434 program and library directories @command{gcc} searches---and don't do anything else.
14436 This is useful when @command{gcc} prints the error message
14437 @samp{installation problem, cannot exec cpp0: No such file or directory}.
14438 To resolve this you either need to put @file{cpp0} and the other compiler
14439 components where @command{gcc} expects to find them, or you can set the environment
14440 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
14441 Don't forget the trailing @samp{/}.
14442 @xref{Environment Variables}.
14444 @item -print-sysroot
14445 @opindex print-sysroot
14446 Print the target sysroot directory that is used during
14447 compilation. This is the target sysroot specified either at configure
14448 time or using the @option{--sysroot} option, possibly with an extra
14449 suffix that depends on compilation options. If no target sysroot is
14450 specified, the option prints nothing.
14452 @item -print-sysroot-headers-suffix
14453 @opindex print-sysroot-headers-suffix
14454 Print the suffix added to the target sysroot when searching for
14455 headers, or give an error if the compiler is not configured with such
14456 a suffix---and don't do anything else.
14459 @opindex dumpmachine
14460 Print the compiler's target machine (for example,
14461 @samp{i686-pc-linux-gnu})---and don't do anything else.
14464 @opindex dumpversion
14465 Print the compiler version (for example, @code{3.0}, @code{6.3.0} or @code{7})---and don't do
14466 anything else. This is the compiler version used in filesystem paths,
14467 specs, can be depending on how the compiler has been configured just
14468 a single number (major version), two numbers separated by dot (major and
14469 minor version) or three numbers separated by dots (major, minor and patchlevel
14472 @item -dumpfullversion
14473 @opindex dumpfullversion
14474 Print the full compiler version, always 3 numbers separated by dots,
14475 major, minor and patchlevel version.
14479 Print the compiler's built-in specs---and don't do anything else. (This
14480 is used when GCC itself is being built.) @xref{Spec Files}.
14483 @node Submodel Options
14484 @section Machine-Dependent Options
14485 @cindex submodel options
14486 @cindex specifying hardware config
14487 @cindex hardware models and configurations, specifying
14488 @cindex target-dependent options
14489 @cindex machine-dependent options
14491 Each target machine supported by GCC can have its own options---for
14492 example, to allow you to compile for a particular processor variant or
14493 ABI, or to control optimizations specific to that machine. By
14494 convention, the names of machine-specific options start with
14497 Some configurations of the compiler also support additional target-specific
14498 options, usually for compatibility with other compilers on the same
14501 @c This list is ordered alphanumerically by subsection name.
14502 @c It should be the same order and spelling as these options are listed
14503 @c in Machine Dependent Options
14506 * AArch64 Options::
14507 * Adapteva Epiphany Options::
14511 * Blackfin Options::
14516 * DEC Alpha Options::
14520 * GNU/Linux Options::
14530 * MicroBlaze Options::
14533 * MN10300 Options::
14537 * Nios II Options::
14538 * Nvidia PTX Options::
14540 * picoChip Options::
14541 * PowerPC Options::
14542 * PowerPC SPE Options::
14545 * RS/6000 and PowerPC Options::
14547 * S/390 and zSeries Options::
14550 * Solaris 2 Options::
14553 * System V Options::
14554 * TILE-Gx Options::
14555 * TILEPro Options::
14560 * VxWorks Options::
14562 * x86 Windows Options::
14563 * Xstormy16 Options::
14565 * zSeries Options::
14568 @node AArch64 Options
14569 @subsection AArch64 Options
14570 @cindex AArch64 Options
14572 These options are defined for AArch64 implementations:
14576 @item -mabi=@var{name}
14578 Generate code for the specified data model. Permissible values
14579 are @samp{ilp32} for SysV-like data model where int, long int and pointers
14580 are 32 bits, and @samp{lp64} for SysV-like data model where int is 32 bits,
14581 but long int and pointers are 64 bits.
14583 The default depends on the specific target configuration. Note that
14584 the LP64 and ILP32 ABIs are not link-compatible; you must compile your
14585 entire program with the same ABI, and link with a compatible set of libraries.
14588 @opindex mbig-endian
14589 Generate big-endian code. This is the default when GCC is configured for an
14590 @samp{aarch64_be-*-*} target.
14592 @item -mgeneral-regs-only
14593 @opindex mgeneral-regs-only
14594 Generate code which uses only the general-purpose registers. This will prevent
14595 the compiler from using floating-point and Advanced SIMD registers but will not
14596 impose any restrictions on the assembler.
14598 @item -mlittle-endian
14599 @opindex mlittle-endian
14600 Generate little-endian code. This is the default when GCC is configured for an
14601 @samp{aarch64-*-*} but not an @samp{aarch64_be-*-*} target.
14603 @item -mcmodel=tiny
14604 @opindex mcmodel=tiny
14605 Generate code for the tiny code model. The program and its statically defined
14606 symbols must be within 1MB of each other. Programs can be statically or
14607 dynamically linked.
14609 @item -mcmodel=small
14610 @opindex mcmodel=small
14611 Generate code for the small code model. The program and its statically defined
14612 symbols must be within 4GB of each other. Programs can be statically or
14613 dynamically linked. This is the default code model.
14615 @item -mcmodel=large
14616 @opindex mcmodel=large
14617 Generate code for the large code model. This makes no assumptions about
14618 addresses and sizes of sections. Programs can be statically linked only.
14620 @item -mstrict-align
14621 @opindex mstrict-align
14622 Avoid generating memory accesses that may not be aligned on a natural object
14623 boundary as described in the architecture specification.
14625 @item -momit-leaf-frame-pointer
14626 @itemx -mno-omit-leaf-frame-pointer
14627 @opindex momit-leaf-frame-pointer
14628 @opindex mno-omit-leaf-frame-pointer
14629 Omit or keep the frame pointer in leaf functions. The former behavior is the
14632 @item -mtls-dialect=desc
14633 @opindex mtls-dialect=desc
14634 Use TLS descriptors as the thread-local storage mechanism for dynamic accesses
14635 of TLS variables. This is the default.
14637 @item -mtls-dialect=traditional
14638 @opindex mtls-dialect=traditional
14639 Use traditional TLS as the thread-local storage mechanism for dynamic accesses
14642 @item -mtls-size=@var{size}
14644 Specify bit size of immediate TLS offsets. Valid values are 12, 24, 32, 48.
14645 This option requires binutils 2.26 or newer.
14647 @item -mfix-cortex-a53-835769
14648 @itemx -mno-fix-cortex-a53-835769
14649 @opindex mfix-cortex-a53-835769
14650 @opindex mno-fix-cortex-a53-835769
14651 Enable or disable the workaround for the ARM Cortex-A53 erratum number 835769.
14652 This involves inserting a NOP instruction between memory instructions and
14653 64-bit integer multiply-accumulate instructions.
14655 @item -mfix-cortex-a53-843419
14656 @itemx -mno-fix-cortex-a53-843419
14657 @opindex mfix-cortex-a53-843419
14658 @opindex mno-fix-cortex-a53-843419
14659 Enable or disable the workaround for the ARM Cortex-A53 erratum number 843419.
14660 This erratum workaround is made at link time and this will only pass the
14661 corresponding flag to the linker.
14663 @item -mlow-precision-recip-sqrt
14664 @itemx -mno-low-precision-recip-sqrt
14665 @opindex mlow-precision-recip-sqrt
14666 @opindex mno-low-precision-recip-sqrt
14667 Enable or disable the reciprocal square root approximation.
14668 This option only has an effect if @option{-ffast-math} or
14669 @option{-funsafe-math-optimizations} is used as well. Enabling this reduces
14670 precision of reciprocal square root results to about 16 bits for
14671 single precision and to 32 bits for double precision.
14673 @item -mlow-precision-sqrt
14674 @itemx -mno-low-precision-sqrt
14675 @opindex -mlow-precision-sqrt
14676 @opindex -mno-low-precision-sqrt
14677 Enable or disable the square root approximation.
14678 This option only has an effect if @option{-ffast-math} or
14679 @option{-funsafe-math-optimizations} is used as well. Enabling this reduces
14680 precision of square root results to about 16 bits for
14681 single precision and to 32 bits for double precision.
14682 If enabled, it implies @option{-mlow-precision-recip-sqrt}.
14684 @item -mlow-precision-div
14685 @itemx -mno-low-precision-div
14686 @opindex -mlow-precision-div
14687 @opindex -mno-low-precision-div
14688 Enable or disable the division approximation.
14689 This option only has an effect if @option{-ffast-math} or
14690 @option{-funsafe-math-optimizations} is used as well. Enabling this reduces
14691 precision of division results to about 16 bits for
14692 single precision and to 32 bits for double precision.
14694 @item -march=@var{name}
14696 Specify the name of the target architecture and, optionally, one or
14697 more feature modifiers. This option has the form
14698 @option{-march=@var{arch}@r{@{}+@r{[}no@r{]}@var{feature}@r{@}*}}.
14700 The permissible values for @var{arch} are @samp{armv8-a},
14701 @samp{armv8.1-a}, @samp{armv8.2-a}, @samp{armv8.3-a} or @samp{armv8.4-a}
14704 The value @samp{armv8.4-a} implies @samp{armv8.3-a} and enables compiler
14705 support for the ARMv8.4-A architecture extensions.
14707 The value @samp{armv8.3-a} implies @samp{armv8.2-a} and enables compiler
14708 support for the ARMv8.3-A architecture extensions.
14710 The value @samp{armv8.2-a} implies @samp{armv8.1-a} and enables compiler
14711 support for the ARMv8.2-A architecture extensions.
14713 The value @samp{armv8.1-a} implies @samp{armv8-a} and enables compiler
14714 support for the ARMv8.1-A architecture extension. In particular, it
14715 enables the @samp{+crc}, @samp{+lse}, and @samp{+rdma} features.
14717 The value @samp{native} is available on native AArch64 GNU/Linux and
14718 causes the compiler to pick the architecture of the host system. This
14719 option has no effect if the compiler is unable to recognize the
14720 architecture of the host system,
14722 The permissible values for @var{feature} are listed in the sub-section
14723 on @ref{aarch64-feature-modifiers,,@option{-march} and @option{-mcpu}
14724 Feature Modifiers}. Where conflicting feature modifiers are
14725 specified, the right-most feature is used.
14727 GCC uses @var{name} to determine what kind of instructions it can emit
14728 when generating assembly code. If @option{-march} is specified
14729 without either of @option{-mtune} or @option{-mcpu} also being
14730 specified, the code is tuned to perform well across a range of target
14731 processors implementing the target architecture.
14733 @item -mtune=@var{name}
14735 Specify the name of the target processor for which GCC should tune the
14736 performance of the code. Permissible values for this option are:
14737 @samp{generic}, @samp{cortex-a35}, @samp{cortex-a53}, @samp{cortex-a55},
14738 @samp{cortex-a57}, @samp{cortex-a72}, @samp{cortex-a73}, @samp{cortex-a75},
14739 @samp{exynos-m1}, @samp{falkor}, @samp{qdf24xx}, @samp{saphira},
14740 @samp{xgene1}, @samp{vulcan}, @samp{thunderx},
14741 @samp{thunderxt88}, @samp{thunderxt88p1}, @samp{thunderxt81},
14742 @samp{thunderxt83}, @samp{thunderx2t99}, @samp{cortex-a57.cortex-a53},
14743 @samp{cortex-a72.cortex-a53}, @samp{cortex-a73.cortex-a35},
14744 @samp{cortex-a73.cortex-a53}, @samp{cortex-a75.cortex-a55},
14747 The values @samp{cortex-a57.cortex-a53}, @samp{cortex-a72.cortex-a53},
14748 @samp{cortex-a73.cortex-a35}, @samp{cortex-a73.cortex-a53},
14749 @samp{cortex-a75.cortex-a55} specify that GCC should tune for a
14752 Additionally on native AArch64 GNU/Linux systems the value
14753 @samp{native} tunes performance to the host system. This option has no effect
14754 if the compiler is unable to recognize the processor of the host system.
14756 Where none of @option{-mtune=}, @option{-mcpu=} or @option{-march=}
14757 are specified, the code is tuned to perform well across a range
14758 of target processors.
14760 This option cannot be suffixed by feature modifiers.
14762 @item -mcpu=@var{name}
14764 Specify the name of the target processor, optionally suffixed by one
14765 or more feature modifiers. This option has the form
14766 @option{-mcpu=@var{cpu}@r{@{}+@r{[}no@r{]}@var{feature}@r{@}*}}, where
14767 the permissible values for @var{cpu} are the same as those available
14768 for @option{-mtune}. The permissible values for @var{feature} are
14769 documented in the sub-section on
14770 @ref{aarch64-feature-modifiers,,@option{-march} and @option{-mcpu}
14771 Feature Modifiers}. Where conflicting feature modifiers are
14772 specified, the right-most feature is used.
14774 GCC uses @var{name} to determine what kind of instructions it can emit when
14775 generating assembly code (as if by @option{-march}) and to determine
14776 the target processor for which to tune for performance (as if
14777 by @option{-mtune}). Where this option is used in conjunction
14778 with @option{-march} or @option{-mtune}, those options take precedence
14779 over the appropriate part of this option.
14781 @item -moverride=@var{string}
14783 Override tuning decisions made by the back-end in response to a
14784 @option{-mtune=} switch. The syntax, semantics, and accepted values
14785 for @var{string} in this option are not guaranteed to be consistent
14788 This option is only intended to be useful when developing GCC.
14790 @item -mverbose-cost-dump
14791 @opindex mverbose-cost-dump
14792 Enable verbose cost model dumping in the debug dump files. This option is
14793 provided for use in debugging the compiler.
14795 @item -mpc-relative-literal-loads
14796 @itemx -mno-pc-relative-literal-loads
14797 @opindex mpc-relative-literal-loads
14798 @opindex mno-pc-relative-literal-loads
14799 Enable or disable PC-relative literal loads. With this option literal pools are
14800 accessed using a single instruction and emitted after each function. This
14801 limits the maximum size of functions to 1MB. This is enabled by default for
14802 @option{-mcmodel=tiny}.
14804 @item -msign-return-address=@var{scope}
14805 @opindex msign-return-address
14806 Select the function scope on which return address signing will be applied.
14807 Permissible values are @samp{none}, which disables return address signing,
14808 @samp{non-leaf}, which enables pointer signing for functions which are not leaf
14809 functions, and @samp{all}, which enables pointer signing for all functions. The
14810 default value is @samp{none}.
14812 @item -msve-vector-bits=@var{bits}
14813 @opindex msve-vector-bits
14814 Specify the number of bits in an SVE vector register. This option only has
14815 an effect when SVE is enabled.
14817 GCC supports two forms of SVE code generation: ``vector-length
14818 agnostic'' output that works with any size of vector register and
14819 ``vector-length specific'' output that only works when the vector
14820 registers are a particular size. Replacing @var{bits} with
14821 @samp{scalable} selects vector-length agnostic output while
14822 replacing it with a number selects vector-length specific output.
14823 The possible lengths in the latter case are: 128, 256, 512, 1024
14824 and 2048. @samp{scalable} is the default.
14826 At present, @samp{-msve-vector-bits=128} produces the same output
14827 as @samp{-msve-vector-bits=scalable}.
14831 @subsubsection @option{-march} and @option{-mcpu} Feature Modifiers
14832 @anchor{aarch64-feature-modifiers}
14833 @cindex @option{-march} feature modifiers
14834 @cindex @option{-mcpu} feature modifiers
14835 Feature modifiers used with @option{-march} and @option{-mcpu} can be any of
14836 the following and their inverses @option{no@var{feature}}:
14840 Enable CRC extension. This is on by default for
14841 @option{-march=armv8.1-a}.
14843 Enable Crypto extension. This also enables Advanced SIMD and floating-point
14846 Enable floating-point instructions. This is on by default for all possible
14847 values for options @option{-march} and @option{-mcpu}.
14849 Enable Advanced SIMD instructions. This also enables floating-point
14850 instructions. This is on by default for all possible values for options
14851 @option{-march} and @option{-mcpu}.
14853 Enable Scalable Vector Extension instructions. This also enables Advanced
14854 SIMD and floating-point instructions.
14856 Enable Large System Extension instructions. This is on by default for
14857 @option{-march=armv8.1-a}.
14859 Enable Round Double Multiply Accumulate instructions. This is on by default
14860 for @option{-march=armv8.1-a}.
14862 Enable FP16 extension. This also enables floating-point instructions.
14864 Enable FP16 fmla extension. This also enables FP16 extensions and
14865 floating-point instructions. This option is enabled by default for @option{-march=armv8.4-a}. Use of this option with architectures prior to Armv8.2-A is not supported.
14868 Enable the RcPc extension. This does not change code generation from GCC,
14869 but is passed on to the assembler, enabling inline asm statements to use
14870 instructions from the RcPc extension.
14872 Enable the Dot Product extension. This also enables Advanced SIMD instructions.
14874 Enable the Armv8-a aes and pmull crypto extension. This also enables Advanced
14877 Enable the Armv8-a sha2 crypto extension. This also enables Advanced SIMD instructions.
14879 Enable the sha512 and sha3 crypto extension. This also enables Advanced SIMD
14880 instructions. Use of this option with architectures prior to Armv8.2-A is not supported.
14882 Enable the sm3 and sm4 crypto extension. This also enables Advanced SIMD instructions.
14883 Use of this option with architectures prior to Armv8.2-A is not supported.
14887 Feature @option{crypto} implies @option{aes}, @option{sha2}, and @option{simd},
14888 which implies @option{fp}.
14889 Conversely, @option{nofp} implies @option{nosimd}, which implies
14890 @option{nocrypto}, @option{noaes} and @option{nosha2}.
14892 @node Adapteva Epiphany Options
14893 @subsection Adapteva Epiphany Options
14895 These @samp{-m} options are defined for Adapteva Epiphany:
14898 @item -mhalf-reg-file
14899 @opindex mhalf-reg-file
14900 Don't allocate any register in the range @code{r32}@dots{}@code{r63}.
14901 That allows code to run on hardware variants that lack these registers.
14903 @item -mprefer-short-insn-regs
14904 @opindex mprefer-short-insn-regs
14905 Preferentially allocate registers that allow short instruction generation.
14906 This can result in increased instruction count, so this may either reduce or
14907 increase overall code size.
14909 @item -mbranch-cost=@var{num}
14910 @opindex mbranch-cost
14911 Set the cost of branches to roughly @var{num} ``simple'' instructions.
14912 This cost is only a heuristic and is not guaranteed to produce
14913 consistent results across releases.
14917 Enable the generation of conditional moves.
14919 @item -mnops=@var{num}
14921 Emit @var{num} NOPs before every other generated instruction.
14923 @item -mno-soft-cmpsf
14924 @opindex mno-soft-cmpsf
14925 For single-precision floating-point comparisons, emit an @code{fsub} instruction
14926 and test the flags. This is faster than a software comparison, but can
14927 get incorrect results in the presence of NaNs, or when two different small
14928 numbers are compared such that their difference is calculated as zero.
14929 The default is @option{-msoft-cmpsf}, which uses slower, but IEEE-compliant,
14930 software comparisons.
14932 @item -mstack-offset=@var{num}
14933 @opindex mstack-offset
14934 Set the offset between the top of the stack and the stack pointer.
14935 E.g., a value of 8 means that the eight bytes in the range @code{sp+0@dots{}sp+7}
14936 can be used by leaf functions without stack allocation.
14937 Values other than @samp{8} or @samp{16} are untested and unlikely to work.
14938 Note also that this option changes the ABI; compiling a program with a
14939 different stack offset than the libraries have been compiled with
14940 generally does not work.
14941 This option can be useful if you want to evaluate if a different stack
14942 offset would give you better code, but to actually use a different stack
14943 offset to build working programs, it is recommended to configure the
14944 toolchain with the appropriate @option{--with-stack-offset=@var{num}} option.
14946 @item -mno-round-nearest
14947 @opindex mno-round-nearest
14948 Make the scheduler assume that the rounding mode has been set to
14949 truncating. The default is @option{-mround-nearest}.
14952 @opindex mlong-calls
14953 If not otherwise specified by an attribute, assume all calls might be beyond
14954 the offset range of the @code{b} / @code{bl} instructions, and therefore load the
14955 function address into a register before performing a (otherwise direct) call.
14956 This is the default.
14958 @item -mshort-calls
14959 @opindex short-calls
14960 If not otherwise specified by an attribute, assume all direct calls are
14961 in the range of the @code{b} / @code{bl} instructions, so use these instructions
14962 for direct calls. The default is @option{-mlong-calls}.
14966 Assume addresses can be loaded as 16-bit unsigned values. This does not
14967 apply to function addresses for which @option{-mlong-calls} semantics
14970 @item -mfp-mode=@var{mode}
14972 Set the prevailing mode of the floating-point unit.
14973 This determines the floating-point mode that is provided and expected
14974 at function call and return time. Making this mode match the mode you
14975 predominantly need at function start can make your programs smaller and
14976 faster by avoiding unnecessary mode switches.
14978 @var{mode} can be set to one the following values:
14982 Any mode at function entry is valid, and retained or restored when
14983 the function returns, and when it calls other functions.
14984 This mode is useful for compiling libraries or other compilation units
14985 you might want to incorporate into different programs with different
14986 prevailing FPU modes, and the convenience of being able to use a single
14987 object file outweighs the size and speed overhead for any extra
14988 mode switching that might be needed, compared with what would be needed
14989 with a more specific choice of prevailing FPU mode.
14992 This is the mode used for floating-point calculations with
14993 truncating (i.e.@: round towards zero) rounding mode. That includes
14994 conversion from floating point to integer.
14996 @item round-nearest
14997 This is the mode used for floating-point calculations with
14998 round-to-nearest-or-even rounding mode.
15001 This is the mode used to perform integer calculations in the FPU, e.g.@:
15002 integer multiply, or integer multiply-and-accumulate.
15005 The default is @option{-mfp-mode=caller}
15007 @item -mnosplit-lohi
15008 @itemx -mno-postinc
15009 @itemx -mno-postmodify
15010 @opindex mnosplit-lohi
15011 @opindex mno-postinc
15012 @opindex mno-postmodify
15013 Code generation tweaks that disable, respectively, splitting of 32-bit
15014 loads, generation of post-increment addresses, and generation of
15015 post-modify addresses. The defaults are @option{msplit-lohi},
15016 @option{-mpost-inc}, and @option{-mpost-modify}.
15018 @item -mnovect-double
15019 @opindex mno-vect-double
15020 Change the preferred SIMD mode to SImode. The default is
15021 @option{-mvect-double}, which uses DImode as preferred SIMD mode.
15023 @item -max-vect-align=@var{num}
15024 @opindex max-vect-align
15025 The maximum alignment for SIMD vector mode types.
15026 @var{num} may be 4 or 8. The default is 8.
15027 Note that this is an ABI change, even though many library function
15028 interfaces are unaffected if they don't use SIMD vector modes
15029 in places that affect size and/or alignment of relevant types.
15031 @item -msplit-vecmove-early
15032 @opindex msplit-vecmove-early
15033 Split vector moves into single word moves before reload. In theory this
15034 can give better register allocation, but so far the reverse seems to be
15035 generally the case.
15037 @item -m1reg-@var{reg}
15039 Specify a register to hold the constant @minus{}1, which makes loading small negative
15040 constants and certain bitmasks faster.
15041 Allowable values for @var{reg} are @samp{r43} and @samp{r63},
15042 which specify use of that register as a fixed register,
15043 and @samp{none}, which means that no register is used for this
15044 purpose. The default is @option{-m1reg-none}.
15049 @subsection ARC Options
15050 @cindex ARC options
15052 The following options control the architecture variant for which code
15055 @c architecture variants
15058 @item -mbarrel-shifter
15059 @opindex mbarrel-shifter
15060 Generate instructions supported by barrel shifter. This is the default
15061 unless @option{-mcpu=ARC601} or @samp{-mcpu=ARCEM} is in effect.
15064 @opindex mjli-alawys
15065 Force to call a function using jli_s instruction. This option is
15066 valid only for ARCv2 architecture.
15068 @item -mcpu=@var{cpu}
15070 Set architecture type, register usage, and instruction scheduling
15071 parameters for @var{cpu}. There are also shortcut alias options
15072 available for backward compatibility and convenience. Supported
15073 values for @var{cpu} are
15079 Compile for ARC600. Aliases: @option{-mA6}, @option{-mARC600}.
15083 Compile for ARC601. Alias: @option{-mARC601}.
15088 Compile for ARC700. Aliases: @option{-mA7}, @option{-mARC700}.
15089 This is the default when configured with @option{--with-cpu=arc700}@.
15092 Compile for ARC EM.
15095 Compile for ARC HS.
15098 Compile for ARC EM CPU with no hardware extensions.
15101 Compile for ARC EM4 CPU.
15104 Compile for ARC EM4 DMIPS CPU.
15107 Compile for ARC EM4 DMIPS CPU with the single-precision floating-point
15111 Compile for ARC EM4 DMIPS CPU with single-precision floating-point and
15112 double assist instructions.
15115 Compile for ARC HS CPU with no hardware extensions except the atomic
15119 Compile for ARC HS34 CPU.
15122 Compile for ARC HS38 CPU.
15125 Compile for ARC HS38 CPU with all hardware extensions on.
15128 Compile for ARC 600 CPU with @code{norm} instructions enabled.
15130 @item arc600_mul32x16
15131 Compile for ARC 600 CPU with @code{norm} and 32x16-bit multiply
15132 instructions enabled.
15135 Compile for ARC 600 CPU with @code{norm} and @code{mul64}-family
15136 instructions enabled.
15139 Compile for ARC 601 CPU with @code{norm} instructions enabled.
15141 @item arc601_mul32x16
15142 Compile for ARC 601 CPU with @code{norm} and 32x16-bit multiply
15143 instructions enabled.
15146 Compile for ARC 601 CPU with @code{norm} and @code{mul64}-family
15147 instructions enabled.
15150 Compile for ARC 700 on NPS400 chip.
15153 Compile for ARC EM minimalist configuration featuring reduced register
15160 @itemx -mdpfp-compact
15161 @opindex mdpfp-compact
15162 Generate double-precision FPX instructions, tuned for the compact
15166 @opindex mdpfp-fast
15167 Generate double-precision FPX instructions, tuned for the fast
15170 @item -mno-dpfp-lrsr
15171 @opindex mno-dpfp-lrsr
15172 Disable @code{lr} and @code{sr} instructions from using FPX extension
15177 Generate extended arithmetic instructions. Currently only
15178 @code{divaw}, @code{adds}, @code{subs}, and @code{sat16} are
15179 supported. This is always enabled for @option{-mcpu=ARC700}.
15183 Do not generate @code{mpy}-family instructions for ARC700. This option is
15188 Generate 32x16-bit multiply and multiply-accumulate instructions.
15192 Generate @code{mul64} and @code{mulu64} instructions.
15193 Only valid for @option{-mcpu=ARC600}.
15197 Generate @code{norm} instructions. This is the default if @option{-mcpu=ARC700}
15202 @itemx -mspfp-compact
15203 @opindex mspfp-compact
15204 Generate single-precision FPX instructions, tuned for the compact
15208 @opindex mspfp-fast
15209 Generate single-precision FPX instructions, tuned for the fast
15214 Enable generation of ARC SIMD instructions via target-specific
15215 builtins. Only valid for @option{-mcpu=ARC700}.
15218 @opindex msoft-float
15219 This option ignored; it is provided for compatibility purposes only.
15220 Software floating-point code is emitted by default, and this default
15221 can overridden by FPX options; @option{-mspfp}, @option{-mspfp-compact}, or
15222 @option{-mspfp-fast} for single precision, and @option{-mdpfp},
15223 @option{-mdpfp-compact}, or @option{-mdpfp-fast} for double precision.
15227 Generate @code{swap} instructions.
15231 This enables use of the locked load/store conditional extension to implement
15232 atomic memory built-in functions. Not available for ARC 6xx or ARC
15237 Enable @code{div} and @code{rem} instructions for ARCv2 cores.
15239 @item -mcode-density
15240 @opindex mcode-density
15241 Enable code density instructions for ARC EM.
15242 This option is on by default for ARC HS.
15246 Enable double load/store operations for ARC HS cores.
15248 @item -mtp-regno=@var{regno}
15250 Specify thread pointer register number.
15252 @item -mmpy-option=@var{multo}
15253 @opindex mmpy-option
15254 Compile ARCv2 code with a multiplier design option. You can specify
15255 the option using either a string or numeric value for @var{multo}.
15256 @samp{wlh1} is the default value. The recognized values are:
15261 No multiplier available.
15265 16x16 multiplier, fully pipelined.
15266 The following instructions are enabled: @code{mpyw} and @code{mpyuw}.
15270 32x32 multiplier, fully
15271 pipelined (1 stage). The following instructions are additionally
15272 enabled: @code{mpy}, @code{mpyu}, @code{mpym}, @code{mpymu}, and @code{mpy_s}.
15276 32x32 multiplier, fully pipelined
15277 (2 stages). The following instructions are additionally enabled: @code{mpy},
15278 @code{mpyu}, @code{mpym}, @code{mpymu}, and @code{mpy_s}.
15282 Two 16x16 multipliers, blocking,
15283 sequential. The following instructions are additionally enabled: @code{mpy},
15284 @code{mpyu}, @code{mpym}, @code{mpymu}, and @code{mpy_s}.
15288 One 16x16 multiplier, blocking,
15289 sequential. The following instructions are additionally enabled: @code{mpy},
15290 @code{mpyu}, @code{mpym}, @code{mpymu}, and @code{mpy_s}.
15294 One 32x4 multiplier, blocking,
15295 sequential. The following instructions are additionally enabled: @code{mpy},
15296 @code{mpyu}, @code{mpym}, @code{mpymu}, and @code{mpy_s}.
15300 ARC HS SIMD support.
15304 ARC HS SIMD support.
15308 ARC HS SIMD support.
15312 This option is only available for ARCv2 cores@.
15314 @item -mfpu=@var{fpu}
15316 Enables support for specific floating-point hardware extensions for ARCv2
15317 cores. Supported values for @var{fpu} are:
15322 Enables support for single-precision floating-point hardware
15326 Enables support for double-precision floating-point hardware
15327 extensions. The single-precision floating-point extension is also
15328 enabled. Not available for ARC EM@.
15331 Enables support for double-precision floating-point hardware
15332 extensions using double-precision assist instructions. The single-precision
15333 floating-point extension is also enabled. This option is
15334 only available for ARC EM@.
15337 Enables support for double-precision floating-point hardware
15338 extensions using double-precision assist instructions.
15339 The single-precision floating-point, square-root, and divide
15340 extensions are also enabled. This option is
15341 only available for ARC EM@.
15344 Enables support for double-precision floating-point hardware
15345 extensions using double-precision assist instructions.
15346 The single-precision floating-point and fused multiply and add
15347 hardware extensions are also enabled. This option is
15348 only available for ARC EM@.
15351 Enables support for double-precision floating-point hardware
15352 extensions using double-precision assist instructions.
15353 All single-precision floating-point hardware extensions are also
15354 enabled. This option is only available for ARC EM@.
15357 Enables support for single-precision floating-point, square-root and divide
15358 hardware extensions@.
15361 Enables support for double-precision floating-point, square-root and divide
15362 hardware extensions. This option
15363 includes option @samp{fpus_div}. Not available for ARC EM@.
15366 Enables support for single-precision floating-point and
15367 fused multiply and add hardware extensions@.
15370 Enables support for double-precision floating-point and
15371 fused multiply and add hardware extensions. This option
15372 includes option @samp{fpus_fma}. Not available for ARC EM@.
15375 Enables support for all single-precision floating-point hardware
15379 Enables support for all single- and double-precision floating-point
15380 hardware extensions. Not available for ARC EM@.
15384 @item -mirq-ctrl-saved=@var{register-range}, @var{blink}, @var{lp_count}
15385 @opindex mirq-ctrl-saved
15386 Specifies general-purposes registers that the processor automatically
15387 saves/restores on interrupt entry and exit. @var{register-range} is
15388 specified as two registers separated by a dash. The register range
15389 always starts with @code{r0}, the upper limit is @code{fp} register.
15390 @var{blink} and @var{lp_count} are optional. This option is only
15391 valid for ARC EM and ARC HS cores.
15393 @item -mrgf-banked-regs=@var{number}
15394 @opindex mrgf-banked-regs
15395 Specifies the number of registers replicated in second register bank
15396 on entry to fast interrupt. Fast interrupts are interrupts with the
15397 highest priority level P0. These interrupts save only PC and STATUS32
15398 registers to avoid memory transactions during interrupt entry and exit
15399 sequences. Use this option when you are using fast interrupts in an
15400 ARC V2 family processor. Permitted values are 4, 8, 16, and 32.
15402 @item -mlpc-width=@var{width}
15403 @opindex mlpc-width
15404 Specify the width of the @code{lp_count} register. Valid values for
15405 @var{width} are 8, 16, 20, 24, 28 and 32 bits. The default width is
15406 fixed to 32 bits. If the width is less than 32, the compiler does not
15407 attempt to transform loops in your program to use the zero-delay loop
15408 mechanism unless it is known that the @code{lp_count} register can
15409 hold the required loop-counter value. Depending on the width
15410 specified, the compiler and run-time library might continue to use the
15411 loop mechanism for various needs. This option defines macro
15412 @code{__ARC_LPC_WIDTH__} with the value of @var{width}.
15416 This option instructs the compiler to generate code for a 16-entry
15417 register file. This option defines the @code{__ARC_RF16__}
15418 preprocessor macro.
15422 The following options are passed through to the assembler, and also
15423 define preprocessor macro symbols.
15425 @c Flags used by the assembler, but for which we define preprocessor
15426 @c macro symbols as well.
15429 @opindex mdsp-packa
15430 Passed down to the assembler to enable the DSP Pack A extensions.
15431 Also sets the preprocessor symbol @code{__Xdsp_packa}. This option is
15436 Passed down to the assembler to enable the dual Viterbi butterfly
15437 extension. Also sets the preprocessor symbol @code{__Xdvbf}. This
15438 option is deprecated.
15440 @c ARC700 4.10 extension instruction
15443 Passed down to the assembler to enable the locked load/store
15444 conditional extension. Also sets the preprocessor symbol
15449 Passed down to the assembler. Also sets the preprocessor symbol
15450 @code{__Xxmac_d16}. This option is deprecated.
15454 Passed down to the assembler. Also sets the preprocessor symbol
15455 @code{__Xxmac_24}. This option is deprecated.
15457 @c ARC700 4.10 extension instruction
15460 Passed down to the assembler to enable the 64-bit time-stamp counter
15461 extension instruction. Also sets the preprocessor symbol
15462 @code{__Xrtsc}. This option is deprecated.
15464 @c ARC700 4.10 extension instruction
15467 Passed down to the assembler to enable the swap byte ordering
15468 extension instruction. Also sets the preprocessor symbol
15472 @opindex mtelephony
15473 Passed down to the assembler to enable dual- and single-operand
15474 instructions for telephony. Also sets the preprocessor symbol
15475 @code{__Xtelephony}. This option is deprecated.
15479 Passed down to the assembler to enable the XY memory extension. Also
15480 sets the preprocessor symbol @code{__Xxy}.
15484 The following options control how the assembly code is annotated:
15486 @c Assembly annotation options
15490 Annotate assembler instructions with estimated addresses.
15492 @item -mannotate-align
15493 @opindex mannotate-align
15494 Explain what alignment considerations lead to the decision to make an
15495 instruction short or long.
15499 The following options are passed through to the linker:
15501 @c options passed through to the linker
15505 Passed through to the linker, to specify use of the @code{arclinux} emulation.
15506 This option is enabled by default in tool chains built for
15507 @w{@code{arc-linux-uclibc}} and @w{@code{arceb-linux-uclibc}} targets
15508 when profiling is not requested.
15510 @item -marclinux_prof
15511 @opindex marclinux_prof
15512 Passed through to the linker, to specify use of the
15513 @code{arclinux_prof} emulation. This option is enabled by default in
15514 tool chains built for @w{@code{arc-linux-uclibc}} and
15515 @w{@code{arceb-linux-uclibc}} targets when profiling is requested.
15519 The following options control the semantics of generated code:
15521 @c semantically relevant code generation options
15524 @opindex mlong-calls
15525 Generate calls as register indirect calls, thus providing access
15526 to the full 32-bit address range.
15528 @item -mmedium-calls
15529 @opindex mmedium-calls
15530 Don't use less than 25-bit addressing range for calls, which is the
15531 offset available for an unconditional branch-and-link
15532 instruction. Conditional execution of function calls is suppressed, to
15533 allow use of the 25-bit range, rather than the 21-bit range with
15534 conditional branch-and-link. This is the default for tool chains built
15535 for @w{@code{arc-linux-uclibc}} and @w{@code{arceb-linux-uclibc}} targets.
15539 Put definitions of externally-visible data in a small data section if
15540 that data is no bigger than @var{num} bytes. The default value of
15541 @var{num} is 4 for any ARC configuration, or 8 when we have double
15542 load/store operations.
15546 Do not generate sdata references. This is the default for tool chains
15547 built for @w{@code{arc-linux-uclibc}} and @w{@code{arceb-linux-uclibc}}
15550 @item -mvolatile-cache
15551 @opindex mvolatile-cache
15552 Use ordinarily cached memory accesses for volatile references. This is the
15555 @item -mno-volatile-cache
15556 @opindex mno-volatile-cache
15557 Enable cache bypass for volatile references.
15561 The following options fine tune code generation:
15562 @c code generation tuning options
15565 @opindex malign-call
15566 Do alignment optimizations for call instructions.
15568 @item -mauto-modify-reg
15569 @opindex mauto-modify-reg
15570 Enable the use of pre/post modify with register displacement.
15572 @item -mbbit-peephole
15573 @opindex mbbit-peephole
15574 Enable bbit peephole2.
15578 This option disables a target-specific pass in @file{arc_reorg} to
15579 generate compare-and-branch (@code{br@var{cc}}) instructions.
15580 It has no effect on
15581 generation of these instructions driven by the combiner pass.
15583 @item -mcase-vector-pcrel
15584 @opindex mcase-vector-pcrel
15585 Use PC-relative switch case tables to enable case table shortening.
15586 This is the default for @option{-Os}.
15588 @item -mcompact-casesi
15589 @opindex mcompact-casesi
15590 Enable compact @code{casesi} pattern. This is the default for @option{-Os},
15591 and only available for ARCv1 cores.
15593 @item -mno-cond-exec
15594 @opindex mno-cond-exec
15595 Disable the ARCompact-specific pass to generate conditional
15596 execution instructions.
15598 Due to delay slot scheduling and interactions between operand numbers,
15599 literal sizes, instruction lengths, and the support for conditional execution,
15600 the target-independent pass to generate conditional execution is often lacking,
15601 so the ARC port has kept a special pass around that tries to find more
15602 conditional execution generation opportunities after register allocation,
15603 branch shortening, and delay slot scheduling have been done. This pass
15604 generally, but not always, improves performance and code size, at the cost of
15605 extra compilation time, which is why there is an option to switch it off.
15606 If you have a problem with call instructions exceeding their allowable
15607 offset range because they are conditionalized, you should consider using
15608 @option{-mmedium-calls} instead.
15610 @item -mearly-cbranchsi
15611 @opindex mearly-cbranchsi
15612 Enable pre-reload use of the @code{cbranchsi} pattern.
15614 @item -mexpand-adddi
15615 @opindex mexpand-adddi
15616 Expand @code{adddi3} and @code{subdi3} at RTL generation time into
15617 @code{add.f}, @code{adc} etc. This option is deprecated.
15619 @item -mindexed-loads
15620 @opindex mindexed-loads
15621 Enable the use of indexed loads. This can be problematic because some
15622 optimizers then assume that indexed stores exist, which is not
15627 Enable Local Register Allocation. This is still experimental for ARC,
15628 so by default the compiler uses standard reload
15629 (i.e. @option{-mno-lra}).
15631 @item -mlra-priority-none
15632 @opindex mlra-priority-none
15633 Don't indicate any priority for target registers.
15635 @item -mlra-priority-compact
15636 @opindex mlra-priority-compact
15637 Indicate target register priority for r0..r3 / r12..r15.
15639 @item -mlra-priority-noncompact
15640 @opindex mlra-priority-noncompact
15641 Reduce target register priority for r0..r3 / r12..r15.
15643 @item -mno-millicode
15644 @opindex mno-millicode
15645 When optimizing for size (using @option{-Os}), prologues and epilogues
15646 that have to save or restore a large number of registers are often
15647 shortened by using call to a special function in libgcc; this is
15648 referred to as a @emph{millicode} call. As these calls can pose
15649 performance issues, and/or cause linking issues when linking in a
15650 nonstandard way, this option is provided to turn off millicode call
15654 @opindex mmixed-code
15655 Tweak register allocation to help 16-bit instruction generation.
15656 This generally has the effect of decreasing the average instruction size
15657 while increasing the instruction count.
15661 Enable @samp{q} instruction alternatives.
15662 This is the default for @option{-Os}.
15666 Enable @samp{Rcq} constraint handling.
15667 Most short code generation depends on this.
15668 This is the default.
15672 Enable @samp{Rcw} constraint handling.
15673 Most ccfsm condexec mostly depends on this.
15674 This is the default.
15676 @item -msize-level=@var{level}
15677 @opindex msize-level
15678 Fine-tune size optimization with regards to instruction lengths and alignment.
15679 The recognized values for @var{level} are:
15682 No size optimization. This level is deprecated and treated like @samp{1}.
15685 Short instructions are used opportunistically.
15688 In addition, alignment of loops and of code after barriers are dropped.
15691 In addition, optional data alignment is dropped, and the option @option{Os} is enabled.
15695 This defaults to @samp{3} when @option{-Os} is in effect. Otherwise,
15696 the behavior when this is not set is equivalent to level @samp{1}.
15698 @item -mtune=@var{cpu}
15700 Set instruction scheduling parameters for @var{cpu}, overriding any implied
15701 by @option{-mcpu=}.
15703 Supported values for @var{cpu} are
15707 Tune for ARC600 CPU.
15710 Tune for ARC601 CPU.
15713 Tune for ARC700 CPU with standard multiplier block.
15716 Tune for ARC700 CPU with XMAC block.
15719 Tune for ARC725D CPU.
15722 Tune for ARC750D CPU.
15726 @item -mmultcost=@var{num}
15728 Cost to assume for a multiply instruction, with @samp{4} being equal to a
15729 normal instruction.
15731 @item -munalign-prob-threshold=@var{probability}
15732 @opindex munalign-prob-threshold
15733 Set probability threshold for unaligning branches.
15734 When tuning for @samp{ARC700} and optimizing for speed, branches without
15735 filled delay slot are preferably emitted unaligned and long, unless
15736 profiling indicates that the probability for the branch to be taken
15737 is below @var{probability}. @xref{Cross-profiling}.
15738 The default is (REG_BR_PROB_BASE/2), i.e.@: 5000.
15742 The following options are maintained for backward compatibility, but
15743 are now deprecated and will be removed in a future release:
15745 @c Deprecated options
15753 @opindex mbig-endian
15756 Compile code for big-endian targets. Use of these options is now
15757 deprecated. Big-endian code is supported by configuring GCC to build
15758 @w{@code{arceb-elf32}} and @w{@code{arceb-linux-uclibc}} targets,
15759 for which big endian is the default.
15761 @item -mlittle-endian
15762 @opindex mlittle-endian
15765 Compile code for little-endian targets. Use of these options is now
15766 deprecated. Little-endian code is supported by configuring GCC to build
15767 @w{@code{arc-elf32}} and @w{@code{arc-linux-uclibc}} targets,
15768 for which little endian is the default.
15770 @item -mbarrel_shifter
15771 @opindex mbarrel_shifter
15772 Replaced by @option{-mbarrel-shifter}.
15774 @item -mdpfp_compact
15775 @opindex mdpfp_compact
15776 Replaced by @option{-mdpfp-compact}.
15779 @opindex mdpfp_fast
15780 Replaced by @option{-mdpfp-fast}.
15783 @opindex mdsp_packa
15784 Replaced by @option{-mdsp-packa}.
15788 Replaced by @option{-mea}.
15792 Replaced by @option{-mmac-24}.
15796 Replaced by @option{-mmac-d16}.
15798 @item -mspfp_compact
15799 @opindex mspfp_compact
15800 Replaced by @option{-mspfp-compact}.
15803 @opindex mspfp_fast
15804 Replaced by @option{-mspfp-fast}.
15806 @item -mtune=@var{cpu}
15808 Values @samp{arc600}, @samp{arc601}, @samp{arc700} and
15809 @samp{arc700-xmac} for @var{cpu} are replaced by @samp{ARC600},
15810 @samp{ARC601}, @samp{ARC700} and @samp{ARC700-xmac} respectively.
15812 @item -multcost=@var{num}
15814 Replaced by @option{-mmultcost}.
15819 @subsection ARM Options
15820 @cindex ARM options
15822 These @samp{-m} options are defined for the ARM port:
15825 @item -mabi=@var{name}
15827 Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu},
15828 @samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}.
15831 @opindex mapcs-frame
15832 Generate a stack frame that is compliant with the ARM Procedure Call
15833 Standard for all functions, even if this is not strictly necessary for
15834 correct execution of the code. Specifying @option{-fomit-frame-pointer}
15835 with this option causes the stack frames not to be generated for
15836 leaf functions. The default is @option{-mno-apcs-frame}.
15837 This option is deprecated.
15841 This is a synonym for @option{-mapcs-frame} and is deprecated.
15844 @c not currently implemented
15845 @item -mapcs-stack-check
15846 @opindex mapcs-stack-check
15847 Generate code to check the amount of stack space available upon entry to
15848 every function (that actually uses some stack space). If there is
15849 insufficient space available then either the function
15850 @code{__rt_stkovf_split_small} or @code{__rt_stkovf_split_big} is
15851 called, depending upon the amount of stack space required. The runtime
15852 system is required to provide these functions. The default is
15853 @option{-mno-apcs-stack-check}, since this produces smaller code.
15855 @c not currently implemented
15856 @item -mapcs-reentrant
15857 @opindex mapcs-reentrant
15858 Generate reentrant, position-independent code. The default is
15859 @option{-mno-apcs-reentrant}.
15862 @item -mthumb-interwork
15863 @opindex mthumb-interwork
15864 Generate code that supports calling between the ARM and Thumb
15865 instruction sets. Without this option, on pre-v5 architectures, the
15866 two instruction sets cannot be reliably used inside one program. The
15867 default is @option{-mno-thumb-interwork}, since slightly larger code
15868 is generated when @option{-mthumb-interwork} is specified. In AAPCS
15869 configurations this option is meaningless.
15871 @item -mno-sched-prolog
15872 @opindex mno-sched-prolog
15873 Prevent the reordering of instructions in the function prologue, or the
15874 merging of those instruction with the instructions in the function's
15875 body. This means that all functions start with a recognizable set
15876 of instructions (or in fact one of a choice from a small set of
15877 different function prologues), and this information can be used to
15878 locate the start of functions inside an executable piece of code. The
15879 default is @option{-msched-prolog}.
15881 @item -mfloat-abi=@var{name}
15882 @opindex mfloat-abi
15883 Specifies which floating-point ABI to use. Permissible values
15884 are: @samp{soft}, @samp{softfp} and @samp{hard}.
15886 Specifying @samp{soft} causes GCC to generate output containing
15887 library calls for floating-point operations.
15888 @samp{softfp} allows the generation of code using hardware floating-point
15889 instructions, but still uses the soft-float calling conventions.
15890 @samp{hard} allows generation of floating-point instructions
15891 and uses FPU-specific calling conventions.
15893 The default depends on the specific target configuration. Note that
15894 the hard-float and soft-float ABIs are not link-compatible; you must
15895 compile your entire program with the same ABI, and link with a
15896 compatible set of libraries.
15898 @item -mlittle-endian
15899 @opindex mlittle-endian
15900 Generate code for a processor running in little-endian mode. This is
15901 the default for all standard configurations.
15904 @opindex mbig-endian
15905 Generate code for a processor running in big-endian mode; the default is
15906 to compile code for a little-endian processor.
15911 When linking a big-endian image select between BE8 and BE32 formats.
15912 The option has no effect for little-endian images and is ignored. The
15913 default is dependent on the selected target architecture. For ARMv6
15914 and later architectures the default is BE8, for older architectures
15915 the default is BE32. BE32 format has been deprecated by ARM.
15917 @item -march=@var{name}@r{[}+extension@dots{}@r{]}
15919 This specifies the name of the target ARM architecture. GCC uses this
15920 name to determine what kind of instructions it can emit when generating
15921 assembly code. This option can be used in conjunction with or instead
15922 of the @option{-mcpu=} option.
15924 Permissible names are:
15926 @samp{armv5t}, @samp{armv5te},
15927 @samp{armv6}, @samp{armv6j}, @samp{armv6k}, @samp{armv6kz}, @samp{armv6t2},
15928 @samp{armv6z}, @samp{armv6zk},
15929 @samp{armv7}, @samp{armv7-a}, @samp{armv7ve},
15930 @samp{armv8-a}, @samp{armv8.1-a}, @samp{armv8.2-a}, @samp{armv8.3-a},
15934 @samp{armv6-m}, @samp{armv6s-m},
15935 @samp{armv7-m}, @samp{armv7e-m},
15936 @samp{armv8-m.base}, @samp{armv8-m.main},
15937 @samp{iwmmxt} and @samp{iwmmxt2}.
15939 Additionally, the following architectures, which lack support for the
15940 Thumb execution state, are recognized but support is deprecated:
15941 @samp{armv2}, @samp{armv2a}, @samp{armv3}, @samp{armv3m},
15942 @samp{armv4}, @samp{armv5} and @samp{armv5e}.
15944 Many of the architectures support extensions. These can be added by
15945 appending @samp{+@var{extension}} to the architecture name. Extension
15946 options are processed in order and capabilities accumulate. An extension
15947 will also enable any necessary base extensions
15948 upon which it depends. For example, the @samp{+crypto} extension
15949 will always enable the @samp{+simd} extension. The exception to the
15950 additive construction is for extensions that are prefixed with
15951 @samp{+no@dots{}}: these extensions disable the specified option and
15952 any other extensions that may depend on the presence of that
15955 For example, @samp{-march=armv7-a+simd+nofp+vfpv4} is equivalent to
15956 writing @samp{-march=armv7-a+vfpv4} since the @samp{+simd} option is
15957 entirely disabled by the @samp{+nofp} option that follows it.
15959 Most extension names are generically named, but have an effect that is
15960 dependent upon the architecture to which it is applied. For example,
15961 the @samp{+simd} option can be applied to both @samp{armv7-a} and
15962 @samp{armv8-a} architectures, but will enable the original ARMv7-A
15963 Advanced SIMD (Neon) extensions for @samp{armv7-a} and the ARMv8-A
15964 variant for @samp{armv8-a}.
15966 The table below lists the supported extensions for each architecture.
15967 Architectures not mentioned do not support any extensions.
15981 The VFPv2 floating-point instructions. The extension @samp{+vfpv2} can be
15982 used as an alias for this extension.
15985 Disable the floating-point instructions.
15989 The common subset of the ARMv7-A, ARMv7-R and ARMv7-M architectures.
15992 The VFPv3 floating-point instructions, with 16 double-precision
15993 registers. The extension @samp{+vfpv3-d16} can be used as an alias
15994 for this extension. Note that floating-point is not supported by the
15995 base ARMv7-M architecture, but is compatible with both the ARMv7-A and
15996 ARMv7-R architectures.
15999 Disable the floating-point instructions.
16005 The VFPv3 floating-point instructions, with 16 double-precision
16006 registers. The extension @samp{+vfpv3-d16} can be used as an alias
16007 for this extension.
16010 The Advanced SIMD (Neon) v1 and the VFPv3 floating-point instructions.
16011 The extensions @samp{+neon} and @samp{+neon-vfpv3} can be used as aliases
16012 for this extension.
16015 The VFPv3 floating-point instructions, with 32 double-precision
16018 @item +vfpv3-d16-fp16
16019 The VFPv3 floating-point instructions, with 16 double-precision
16020 registers and the half-precision floating-point conversion operations.
16023 The VFPv3 floating-point instructions, with 32 double-precision
16024 registers and the half-precision floating-point conversion operations.
16027 The VFPv4 floating-point instructions, with 16 double-precision
16031 The VFPv4 floating-point instructions, with 32 double-precision
16035 The Advanced SIMD (Neon) v1 and the VFPv3 floating-point instructions, with
16036 the half-precision floating-point conversion operations.
16039 The Advanced SIMD (Neon) v2 and the VFPv4 floating-point instructions.
16042 Disable the Advanced SIMD instructions (does not disable floating point).
16045 Disable the floating-point and Advanced SIMD instructions.
16049 The extended version of the ARMv7-A architecture with support for
16053 The VFPv4 floating-point instructions, with 16 double-precision registers.
16054 The extension @samp{+vfpv4-d16} can be used as an alias for this extension.
16057 The Advanced SIMD (Neon) v2 and the VFPv4 floating-point instructions. The
16058 extension @samp{+neon-vfpv4} can be used as an alias for this extension.
16061 The VFPv3 floating-point instructions, with 16 double-precision
16065 The VFPv3 floating-point instructions, with 32 double-precision
16068 @item +vfpv3-d16-fp16
16069 The VFPv3 floating-point instructions, with 16 double-precision
16070 registers and the half-precision floating-point conversion operations.
16073 The VFPv3 floating-point instructions, with 32 double-precision
16074 registers and the half-precision floating-point conversion operations.
16077 The VFPv4 floating-point instructions, with 16 double-precision
16081 The VFPv4 floating-point instructions, with 32 double-precision
16085 The Advanced SIMD (Neon) v1 and the VFPv3 floating-point instructions.
16086 The extension @samp{+neon-vfpv3} can be used as an alias for this extension.
16089 The Advanced SIMD (Neon) v1 and the VFPv3 floating-point instructions, with
16090 the half-precision floating-point conversion operations.
16093 Disable the Advanced SIMD instructions (does not disable floating point).
16096 Disable the floating-point and Advanced SIMD instructions.
16102 The Cyclic Redundancy Check (CRC) instructions.
16104 The ARMv8-A Advanced SIMD and floating-point instructions.
16106 The cryptographic instructions.
16108 Disable the cryptographic instructions.
16110 Disable the floating-point, Advanced SIMD and cryptographic instructions.
16116 The ARMv8.1-A Advanced SIMD and floating-point instructions.
16119 The cryptographic instructions. This also enables the Advanced SIMD and
16120 floating-point instructions.
16123 Disable the cryptographic instructions.
16126 Disable the floating-point, Advanced SIMD and cryptographic instructions.
16133 The half-precision floating-point data processing instructions.
16134 This also enables the Advanced SIMD and floating-point instructions.
16137 The half-precision floating-point fmla extension. This also enables
16138 the half-precision floating-point extension and Advanced SIMD and
16139 floating-point instructions.
16142 The ARMv8.1-A Advanced SIMD and floating-point instructions.
16145 The cryptographic instructions. This also enables the Advanced SIMD and
16146 floating-point instructions.
16149 Enable the Dot Product extension. This also enables Advanced SIMD instructions.
16152 Disable the cryptographic extension.
16155 Disable the floating-point, Advanced SIMD and cryptographic instructions.
16161 The half-precision floating-point data processing instructions.
16162 This also enables the Advanced SIMD and floating-point instructions as well
16163 as the Dot Product extension and the half-precision floating-point fmla
16167 The ARMv8.3-A Advanced SIMD and floating-point instructions as well as the
16168 Dot Product extension.
16171 The cryptographic instructions. This also enables the Advanced SIMD and
16172 floating-point instructions as well as the Dot Product extension.
16175 Disable the cryptographic extension.
16178 Disable the floating-point, Advanced SIMD and cryptographic instructions.
16184 The single-precision VFPv3 floating-point instructions. The extension
16185 @samp{+vfpv3xd} can be used as an alias for this extension.
16188 The VFPv3 floating-point instructions with 16 double-precision registers.
16189 The extension +vfpv3-d16 can be used as an alias for this extension.
16192 Disable the floating-point extension.
16195 The ARM-state integer division instructions.
16198 Disable the ARM-state integer division extension.
16204 The single-precision VFPv4 floating-point instructions.
16207 The single-precision FPv5 floating-point instructions.
16210 The single- and double-precision FPv5 floating-point instructions.
16213 Disable the floating-point extensions.
16219 The DSP instructions.
16222 Disable the DSP extension.
16225 The single-precision floating-point instructions.
16228 The single- and double-precision floating-point instructions.
16231 Disable the floating-point extension.
16237 The Cyclic Redundancy Check (CRC) instructions.
16239 The single-precision FPv5 floating-point instructions.
16241 The ARMv8-A Advanced SIMD and floating-point instructions.
16243 The cryptographic instructions.
16245 Disable the cryptographic instructions.
16247 Disable the floating-point, Advanced SIMD and cryptographic instructions.
16252 @option{-march=native} causes the compiler to auto-detect the architecture
16253 of the build computer. At present, this feature is only supported on
16254 GNU/Linux, and not all architectures are recognized. If the auto-detect
16255 is unsuccessful the option has no effect.
16257 @item -mtune=@var{name}
16259 This option specifies the name of the target ARM processor for
16260 which GCC should tune the performance of the code.
16261 For some ARM implementations better performance can be obtained by using
16263 Permissible names are: @samp{arm2}, @samp{arm250},
16264 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
16265 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
16266 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
16267 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
16269 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s},
16270 @samp{arm710t}, @samp{arm720t}, @samp{arm740t},
16271 @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
16272 @samp{strongarm1110},
16273 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
16274 @samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s},
16275 @samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi},
16276 @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s},
16277 @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e},
16278 @samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp},
16279 @samp{arm1156t2-s}, @samp{arm1156t2f-s}, @samp{arm1176jz-s}, @samp{arm1176jzf-s},
16280 @samp{generic-armv7-a}, @samp{cortex-a5}, @samp{cortex-a7}, @samp{cortex-a8},
16281 @samp{cortex-a9}, @samp{cortex-a12}, @samp{cortex-a15}, @samp{cortex-a17},
16282 @samp{cortex-a32}, @samp{cortex-a35}, @samp{cortex-a53}, @samp{cortex-a55},
16283 @samp{cortex-a57}, @samp{cortex-a72}, @samp{cortex-a73}, @samp{cortex-a75},
16284 @samp{cortex-r4}, @samp{cortex-r4f}, @samp{cortex-r5}, @samp{cortex-r7},
16285 @samp{cortex-r8}, @samp{cortex-r52},
16293 @samp{cortex-m0plus},
16294 @samp{cortex-m1.small-multiply},
16295 @samp{cortex-m0.small-multiply},
16296 @samp{cortex-m0plus.small-multiply},
16298 @samp{marvell-pj4},
16299 @samp{xscale}, @samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312},
16300 @samp{fa526}, @samp{fa626},
16301 @samp{fa606te}, @samp{fa626te}, @samp{fmp626}, @samp{fa726te},
16304 Additionally, this option can specify that GCC should tune the performance
16305 of the code for a big.LITTLE system. Permissible names are:
16306 @samp{cortex-a15.cortex-a7}, @samp{cortex-a17.cortex-a7},
16307 @samp{cortex-a57.cortex-a53}, @samp{cortex-a72.cortex-a53},
16308 @samp{cortex-a72.cortex-a35}, @samp{cortex-a73.cortex-a53},
16309 @samp{cortex-a75.cortex-a55}.
16311 @option{-mtune=generic-@var{arch}} specifies that GCC should tune the
16312 performance for a blend of processors within architecture @var{arch}.
16313 The aim is to generate code that run well on the current most popular
16314 processors, balancing between optimizations that benefit some CPUs in the
16315 range, and avoiding performance pitfalls of other CPUs. The effects of
16316 this option may change in future GCC versions as CPU models come and go.
16318 @option{-mtune} permits the same extension options as @option{-mcpu}, but
16319 the extension options do not affect the tuning of the generated code.
16321 @option{-mtune=native} causes the compiler to auto-detect the CPU
16322 of the build computer. At present, this feature is only supported on
16323 GNU/Linux, and not all architectures are recognized. If the auto-detect is
16324 unsuccessful the option has no effect.
16326 @item -mcpu=@var{name}@r{[}+extension@dots{}@r{]}
16328 This specifies the name of the target ARM processor. GCC uses this name
16329 to derive the name of the target ARM architecture (as if specified
16330 by @option{-march}) and the ARM processor type for which to tune for
16331 performance (as if specified by @option{-mtune}). Where this option
16332 is used in conjunction with @option{-march} or @option{-mtune},
16333 those options take precedence over the appropriate part of this option.
16335 Many of the supported CPUs implement optional architectural
16336 extensions. Where this is so the architectural extensions are
16337 normally enabled by default. If implementations that lack the
16338 extension exist, then the extension syntax can be used to disable
16339 those extensions that have been omitted. For floating-point and
16340 Advanced SIMD (Neon) instructions, the settings of the options
16341 @option{-mfloat-abi} and @option{-mfpu} must also be considered:
16342 floating-point and Advanced SIMD instructions will only be used if
16343 @option{-mfloat-abi} is not set to @samp{soft}; and any setting of
16344 @option{-mfpu} other than @samp{auto} will override the available
16345 floating-point and SIMD extension instructions.
16347 For example, @samp{cortex-a9} can be found in three major
16348 configurations: integer only, with just a floating-point unit or with
16349 floating-point and Advanced SIMD. The default is to enable all the
16350 instructions, but the extensions @samp{+nosimd} and @samp{+nofp} can
16351 be used to disable just the SIMD or both the SIMD and floating-point
16352 instructions respectively.
16354 Permissible names for this option are the same as those for
16357 The following extension options are common to the listed CPUs:
16361 Disable the DSP instructions on @samp{cortex-m33}.
16364 Disables the floating-point instructions on @samp{arm9e},
16365 @samp{arm946e-s}, @samp{arm966e-s}, @samp{arm968e-s}, @samp{arm10e},
16366 @samp{arm1020e}, @samp{arm1022e}, @samp{arm926ej-s},
16367 @samp{arm1026ej-s}, @samp{cortex-r5}, @samp{cortex-r7}, @samp{cortex-r8},
16368 @samp{cortex-m4}, @samp{cortex-m7} and @samp{cortex-m33}.
16369 Disables the floating-point and SIMD instructions on
16370 @samp{generic-armv7-a}, @samp{cortex-a5}, @samp{cortex-a7},
16371 @samp{cortex-a8}, @samp{cortex-a9}, @samp{cortex-a12},
16372 @samp{cortex-a15}, @samp{cortex-a17}, @samp{cortex-a15.cortex-a7},
16373 @samp{cortex-a17.cortex-a7}, @samp{cortex-a32}, @samp{cortex-a35},
16374 @samp{cortex-a53} and @samp{cortex-a55}.
16377 Disables the double-precision component of the floating-point instructions
16378 on @samp{cortex-r5}, @samp{cortex-r52} and @samp{cortex-m7}.
16381 Disables the SIMD (but not floating-point) instructions on
16382 @samp{generic-armv7-a}, @samp{cortex-a5}, @samp{cortex-a7}
16383 and @samp{cortex-a9}.
16386 Enables the cryptographic instructions on @samp{cortex-a32},
16387 @samp{cortex-a35}, @samp{cortex-a53}, @samp{cortex-a55}, @samp{cortex-a57},
16388 @samp{cortex-a72}, @samp{cortex-a73}, @samp{cortex-a75}, @samp{exynos-m1},
16389 @samp{xgene1}, @samp{cortex-a57.cortex-a53}, @samp{cortex-a72.cortex-a53},
16390 @samp{cortex-a73.cortex-a35}, @samp{cortex-a73.cortex-a53} and
16391 @samp{cortex-a75.cortex-a55}.
16394 Additionally the @samp{generic-armv7-a} pseudo target defaults to
16395 VFPv3 with 16 double-precision registers. It supports the following
16396 extension options: @samp{vfpv3-d16}, @samp{vfpv3},
16397 @samp{vfpv3-d16-fp16}, @samp{vfpv3-fp16}, @samp{vfpv4-d16},
16398 @samp{vfpv4}, @samp{neon}, @samp{neon-vfpv3}, @samp{neon-fp16},
16399 @samp{neon-vfpv4}. The meanings are the same as for the extensions to
16400 @option{-march=armv7-a}.
16402 @option{-mcpu=generic-@var{arch}} is also permissible, and is
16403 equivalent to @option{-march=@var{arch} -mtune=generic-@var{arch}}.
16404 See @option{-mtune} for more information.
16406 @option{-mcpu=native} causes the compiler to auto-detect the CPU
16407 of the build computer. At present, this feature is only supported on
16408 GNU/Linux, and not all architectures are recognized. If the auto-detect
16409 is unsuccessful the option has no effect.
16411 @item -mfpu=@var{name}
16413 This specifies what floating-point hardware (or hardware emulation) is
16414 available on the target. Permissible names are: @samp{auto}, @samp{vfpv2},
16416 @samp{vfpv3-fp16}, @samp{vfpv3-d16}, @samp{vfpv3-d16-fp16}, @samp{vfpv3xd},
16417 @samp{vfpv3xd-fp16}, @samp{neon-vfpv3}, @samp{neon-fp16}, @samp{vfpv4},
16418 @samp{vfpv4-d16}, @samp{fpv4-sp-d16}, @samp{neon-vfpv4},
16419 @samp{fpv5-d16}, @samp{fpv5-sp-d16},
16420 @samp{fp-armv8}, @samp{neon-fp-armv8} and @samp{crypto-neon-fp-armv8}.
16421 Note that @samp{neon} is an alias for @samp{neon-vfpv3} and @samp{vfp}
16422 is an alias for @samp{vfpv2}.
16424 The setting @samp{auto} is the default and is special. It causes the
16425 compiler to select the floating-point and Advanced SIMD instructions
16426 based on the settings of @option{-mcpu} and @option{-march}.
16428 If the selected floating-point hardware includes the NEON extension
16429 (e.g. @option{-mfpu=neon}), note that floating-point
16430 operations are not generated by GCC's auto-vectorization pass unless
16431 @option{-funsafe-math-optimizations} is also specified. This is
16432 because NEON hardware does not fully implement the IEEE 754 standard for
16433 floating-point arithmetic (in particular denormal values are treated as
16434 zero), so the use of NEON instructions may lead to a loss of precision.
16436 You can also set the fpu name at function level by using the @code{target("fpu=")} function attributes (@pxref{ARM Function Attributes}) or pragmas (@pxref{Function Specific Option Pragmas}).
16438 @item -mfp16-format=@var{name}
16439 @opindex mfp16-format
16440 Specify the format of the @code{__fp16} half-precision floating-point type.
16441 Permissible names are @samp{none}, @samp{ieee}, and @samp{alternative};
16442 the default is @samp{none}, in which case the @code{__fp16} type is not
16443 defined. @xref{Half-Precision}, for more information.
16445 @item -mstructure-size-boundary=@var{n}
16446 @opindex mstructure-size-boundary
16447 The sizes of all structures and unions are rounded up to a multiple
16448 of the number of bits set by this option. Permissible values are 8, 32
16449 and 64. The default value varies for different toolchains. For the COFF
16450 targeted toolchain the default value is 8. A value of 64 is only allowed
16451 if the underlying ABI supports it.
16453 Specifying a larger number can produce faster, more efficient code, but
16454 can also increase the size of the program. Different values are potentially
16455 incompatible. Code compiled with one value cannot necessarily expect to
16456 work with code or libraries compiled with another value, if they exchange
16457 information using structures or unions.
16459 This option is deprecated.
16461 @item -mabort-on-noreturn
16462 @opindex mabort-on-noreturn
16463 Generate a call to the function @code{abort} at the end of a
16464 @code{noreturn} function. It is executed if the function tries to
16468 @itemx -mno-long-calls
16469 @opindex mlong-calls
16470 @opindex mno-long-calls
16471 Tells the compiler to perform function calls by first loading the
16472 address of the function into a register and then performing a subroutine
16473 call on this register. This switch is needed if the target function
16474 lies outside of the 64-megabyte addressing range of the offset-based
16475 version of subroutine call instruction.
16477 Even if this switch is enabled, not all function calls are turned
16478 into long calls. The heuristic is that static functions, functions
16479 that have the @code{short_call} attribute, functions that are inside
16480 the scope of a @code{#pragma no_long_calls} directive, and functions whose
16481 definitions have already been compiled within the current compilation
16482 unit are not turned into long calls. The exceptions to this rule are
16483 that weak function definitions, functions with the @code{long_call}
16484 attribute or the @code{section} attribute, and functions that are within
16485 the scope of a @code{#pragma long_calls} directive are always
16486 turned into long calls.
16488 This feature is not enabled by default. Specifying
16489 @option{-mno-long-calls} restores the default behavior, as does
16490 placing the function calls within the scope of a @code{#pragma
16491 long_calls_off} directive. Note these switches have no effect on how
16492 the compiler generates code to handle function calls via function
16495 @item -msingle-pic-base
16496 @opindex msingle-pic-base
16497 Treat the register used for PIC addressing as read-only, rather than
16498 loading it in the prologue for each function. The runtime system is
16499 responsible for initializing this register with an appropriate value
16500 before execution begins.
16502 @item -mpic-register=@var{reg}
16503 @opindex mpic-register
16504 Specify the register to be used for PIC addressing.
16505 For standard PIC base case, the default is any suitable register
16506 determined by compiler. For single PIC base case, the default is
16507 @samp{R9} if target is EABI based or stack-checking is enabled,
16508 otherwise the default is @samp{R10}.
16510 @item -mpic-data-is-text-relative
16511 @opindex mpic-data-is-text-relative
16512 Assume that the displacement between the text and data segments is fixed
16513 at static link time. This permits using PC-relative addressing
16514 operations to access data known to be in the data segment. For
16515 non-VxWorks RTP targets, this option is enabled by default. When
16516 disabled on such targets, it will enable @option{-msingle-pic-base} by
16519 @item -mpoke-function-name
16520 @opindex mpoke-function-name
16521 Write the name of each function into the text section, directly
16522 preceding the function prologue. The generated code is similar to this:
16526 .ascii "arm_poke_function_name", 0
16529 .word 0xff000000 + (t1 - t0)
16530 arm_poke_function_name
16532 stmfd sp!, @{fp, ip, lr, pc@}
16536 When performing a stack backtrace, code can inspect the value of
16537 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
16538 location @code{pc - 12} and the top 8 bits are set, then we know that
16539 there is a function name embedded immediately preceding this location
16540 and has length @code{((pc[-3]) & 0xff000000)}.
16547 Select between generating code that executes in ARM and Thumb
16548 states. The default for most configurations is to generate code
16549 that executes in ARM state, but the default can be changed by
16550 configuring GCC with the @option{--with-mode=}@var{state}
16553 You can also override the ARM and Thumb mode for each function
16554 by using the @code{target("thumb")} and @code{target("arm")} function attributes
16555 (@pxref{ARM Function Attributes}) or pragmas (@pxref{Function Specific Option Pragmas}).
16558 @opindex mflip-thumb
16559 Switch ARM/Thumb modes on alternating functions.
16560 This option is provided for regression testing of mixed Thumb/ARM code
16561 generation, and is not intended for ordinary use in compiling code.
16564 @opindex mtpcs-frame
16565 Generate a stack frame that is compliant with the Thumb Procedure Call
16566 Standard for all non-leaf functions. (A leaf function is one that does
16567 not call any other functions.) The default is @option{-mno-tpcs-frame}.
16569 @item -mtpcs-leaf-frame
16570 @opindex mtpcs-leaf-frame
16571 Generate a stack frame that is compliant with the Thumb Procedure Call
16572 Standard for all leaf functions. (A leaf function is one that does
16573 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
16575 @item -mcallee-super-interworking
16576 @opindex mcallee-super-interworking
16577 Gives all externally visible functions in the file being compiled an ARM
16578 instruction set header which switches to Thumb mode before executing the
16579 rest of the function. This allows these functions to be called from
16580 non-interworking code. This option is not valid in AAPCS configurations
16581 because interworking is enabled by default.
16583 @item -mcaller-super-interworking
16584 @opindex mcaller-super-interworking
16585 Allows calls via function pointers (including virtual functions) to
16586 execute correctly regardless of whether the target code has been
16587 compiled for interworking or not. There is a small overhead in the cost
16588 of executing a function pointer if this option is enabled. This option
16589 is not valid in AAPCS configurations because interworking is enabled
16592 @item -mtp=@var{name}
16594 Specify the access model for the thread local storage pointer. The valid
16595 models are @samp{soft}, which generates calls to @code{__aeabi_read_tp},
16596 @samp{cp15}, which fetches the thread pointer from @code{cp15} directly
16597 (supported in the arm6k architecture), and @samp{auto}, which uses the
16598 best available method for the selected processor. The default setting is
16601 @item -mtls-dialect=@var{dialect}
16602 @opindex mtls-dialect
16603 Specify the dialect to use for accessing thread local storage. Two
16604 @var{dialect}s are supported---@samp{gnu} and @samp{gnu2}. The
16605 @samp{gnu} dialect selects the original GNU scheme for supporting
16606 local and global dynamic TLS models. The @samp{gnu2} dialect
16607 selects the GNU descriptor scheme, which provides better performance
16608 for shared libraries. The GNU descriptor scheme is compatible with
16609 the original scheme, but does require new assembler, linker and
16610 library support. Initial and local exec TLS models are unaffected by
16611 this option and always use the original scheme.
16613 @item -mword-relocations
16614 @opindex mword-relocations
16615 Only generate absolute relocations on word-sized values (i.e. R_ARM_ABS32).
16616 This is enabled by default on targets (uClinux, SymbianOS) where the runtime
16617 loader imposes this restriction, and when @option{-fpic} or @option{-fPIC}
16620 @item -mfix-cortex-m3-ldrd
16621 @opindex mfix-cortex-m3-ldrd
16622 Some Cortex-M3 cores can cause data corruption when @code{ldrd} instructions
16623 with overlapping destination and base registers are used. This option avoids
16624 generating these instructions. This option is enabled by default when
16625 @option{-mcpu=cortex-m3} is specified.
16627 @item -munaligned-access
16628 @itemx -mno-unaligned-access
16629 @opindex munaligned-access
16630 @opindex mno-unaligned-access
16631 Enables (or disables) reading and writing of 16- and 32- bit values
16632 from addresses that are not 16- or 32- bit aligned. By default
16633 unaligned access is disabled for all pre-ARMv6, all ARMv6-M and for
16634 ARMv8-M Baseline architectures, and enabled for all other
16635 architectures. If unaligned access is not enabled then words in packed
16636 data structures are accessed a byte at a time.
16638 The ARM attribute @code{Tag_CPU_unaligned_access} is set in the
16639 generated object file to either true or false, depending upon the
16640 setting of this option. If unaligned access is enabled then the
16641 preprocessor symbol @code{__ARM_FEATURE_UNALIGNED} is also
16644 @item -mneon-for-64bits
16645 @opindex mneon-for-64bits
16646 Enables using Neon to handle scalar 64-bits operations. This is
16647 disabled by default since the cost of moving data from core registers
16650 @item -mslow-flash-data
16651 @opindex mslow-flash-data
16652 Assume loading data from flash is slower than fetching instruction.
16653 Therefore literal load is minimized for better performance.
16654 This option is only supported when compiling for ARMv7 M-profile and
16657 @item -masm-syntax-unified
16658 @opindex masm-syntax-unified
16659 Assume inline assembler is using unified asm syntax. The default is
16660 currently off which implies divided syntax. This option has no impact
16661 on Thumb2. However, this may change in future releases of GCC.
16662 Divided syntax should be considered deprecated.
16664 @item -mrestrict-it
16665 @opindex mrestrict-it
16666 Restricts generation of IT blocks to conform to the rules of ARMv8-A.
16667 IT blocks can only contain a single 16-bit instruction from a select
16668 set of instructions. This option is on by default for ARMv8-A Thumb mode.
16670 @item -mprint-tune-info
16671 @opindex mprint-tune-info
16672 Print CPU tuning information as comment in assembler file. This is
16673 an option used only for regression testing of the compiler and not
16674 intended for ordinary use in compiling code. This option is disabled
16677 @item -mverbose-cost-dump
16678 @opindex mverbose-cost-dump
16679 Enable verbose cost model dumping in the debug dump files. This option is
16680 provided for use in debugging the compiler.
16683 @opindex mpure-code
16684 Do not allow constant data to be placed in code sections.
16685 Additionally, when compiling for ELF object format give all text sections the
16686 ELF processor-specific section attribute @code{SHF_ARM_PURECODE}. This option
16687 is only available when generating non-pic code for M-profile targets with the
16692 Generate secure code as per the "ARMv8-M Security Extensions: Requirements on
16693 Development Tools Engineering Specification", which can be found on
16694 @url{http://infocenter.arm.com/help/topic/com.arm.doc.ecm0359818/ECM0359818_armv8m_security_extensions_reqs_on_dev_tools_1_0.pdf}.
16698 @subsection AVR Options
16699 @cindex AVR Options
16701 These options are defined for AVR implementations:
16704 @item -mmcu=@var{mcu}
16706 Specify Atmel AVR instruction set architectures (ISA) or MCU type.
16708 The default for this option is@tie{}@samp{avr2}.
16710 GCC supports the following AVR devices and ISAs:
16712 @include avr-mmcu.texi
16717 Assume that all data in static storage can be accessed by LDS / STS
16718 instructions. This option has only an effect on reduced Tiny devices like
16719 ATtiny40. See also the @code{absdata}
16720 @ref{AVR Variable Attributes,variable attribute}.
16722 @item -maccumulate-args
16723 @opindex maccumulate-args
16724 Accumulate outgoing function arguments and acquire/release the needed
16725 stack space for outgoing function arguments once in function
16726 prologue/epilogue. Without this option, outgoing arguments are pushed
16727 before calling a function and popped afterwards.
16729 Popping the arguments after the function call can be expensive on
16730 AVR so that accumulating the stack space might lead to smaller
16731 executables because arguments need not be removed from the
16732 stack after such a function call.
16734 This option can lead to reduced code size for functions that perform
16735 several calls to functions that get their arguments on the stack like
16736 calls to printf-like functions.
16738 @item -mbranch-cost=@var{cost}
16739 @opindex mbranch-cost
16740 Set the branch costs for conditional branch instructions to
16741 @var{cost}. Reasonable values for @var{cost} are small, non-negative
16742 integers. The default branch cost is 0.
16744 @item -mcall-prologues
16745 @opindex mcall-prologues
16746 Functions prologues/epilogues are expanded as calls to appropriate
16747 subroutines. Code size is smaller.
16749 @item -mgas-isr-prologues
16750 @opindex mgas-isr-prologues
16751 Interrupt service routines (ISRs) may use the @code{__gcc_isr} pseudo
16752 instruction supported by GNU Binutils.
16753 If this option is on, the feature can still be disabled for individual
16754 ISRs by means of the @ref{AVR Function Attributes,,@code{no_gccisr}}
16755 function attribute. This feature is activated per default
16756 if optimization is on (but not with @option{-Og}, @pxref{Optimize Options}),
16757 and if GNU Binutils support @w{@uref{https://sourceware.org/PR21683,PR21683}}.
16761 Assume @code{int} to be 8-bit integer. This affects the sizes of all types: a
16762 @code{char} is 1 byte, an @code{int} is 1 byte, a @code{long} is 2 bytes,
16763 and @code{long long} is 4 bytes. Please note that this option does not
16764 conform to the C standards, but it results in smaller code
16767 @item -mmain-is-OS_task
16768 @opindex mmain-is-OS_task
16769 Do not save registers in @code{main}. The effect is the same like
16770 attaching attribute @ref{AVR Function Attributes,,@code{OS_task}}
16771 to @code{main}. It is activated per default if optimization is on.
16773 @item -mn-flash=@var{num}
16775 Assume that the flash memory has a size of
16776 @var{num} times 64@tie{}KiB.
16778 @item -mno-interrupts
16779 @opindex mno-interrupts
16780 Generated code is not compatible with hardware interrupts.
16781 Code size is smaller.
16785 Try to replace @code{CALL} resp.@: @code{JMP} instruction by the shorter
16786 @code{RCALL} resp.@: @code{RJMP} instruction if applicable.
16787 Setting @option{-mrelax} just adds the @option{--mlink-relax} option to
16788 the assembler's command line and the @option{--relax} option to the
16789 linker's command line.
16791 Jump relaxing is performed by the linker because jump offsets are not
16792 known before code is located. Therefore, the assembler code generated by the
16793 compiler is the same, but the instructions in the executable may
16794 differ from instructions in the assembler code.
16796 Relaxing must be turned on if linker stubs are needed, see the
16797 section on @code{EIND} and linker stubs below.
16801 Assume that the device supports the Read-Modify-Write
16802 instructions @code{XCH}, @code{LAC}, @code{LAS} and @code{LAT}.
16804 @item -mshort-calls
16805 @opindex mshort-calls
16807 Assume that @code{RJMP} and @code{RCALL} can target the whole
16810 This option is used internally for multilib selection. It is
16811 not an optimization option, and you don't need to set it by hand.
16815 Treat the stack pointer register as an 8-bit register,
16816 i.e.@: assume the high byte of the stack pointer is zero.
16817 In general, you don't need to set this option by hand.
16819 This option is used internally by the compiler to select and
16820 build multilibs for architectures @code{avr2} and @code{avr25}.
16821 These architectures mix devices with and without @code{SPH}.
16822 For any setting other than @option{-mmcu=avr2} or @option{-mmcu=avr25}
16823 the compiler driver adds or removes this option from the compiler
16824 proper's command line, because the compiler then knows if the device
16825 or architecture has an 8-bit stack pointer and thus no @code{SPH}
16830 Use address register @code{X} in a way proposed by the hardware. This means
16831 that @code{X} is only used in indirect, post-increment or
16832 pre-decrement addressing.
16834 Without this option, the @code{X} register may be used in the same way
16835 as @code{Y} or @code{Z} which then is emulated by additional
16837 For example, loading a value with @code{X+const} addressing with a
16838 small non-negative @code{const < 64} to a register @var{Rn} is
16842 adiw r26, const ; X += const
16843 ld @var{Rn}, X ; @var{Rn} = *X
16844 sbiw r26, const ; X -= const
16848 @opindex mtiny-stack
16849 Only change the lower 8@tie{}bits of the stack pointer.
16851 @item -mfract-convert-truncate
16852 @opindex mfract-convert-truncate
16853 Allow to use truncation instead of rounding towards zero for fractional fixed-point types.
16856 @opindex nodevicelib
16857 Don't link against AVR-LibC's device specific library @code{lib<mcu>.a}.
16859 @item -Waddr-space-convert
16860 @opindex Waddr-space-convert
16861 Warn about conversions between address spaces in the case where the
16862 resulting address space is not contained in the incoming address space.
16864 @item -Wmisspelled-isr
16865 @opindex Wmisspelled-isr
16866 Warn if the ISR is misspelled, i.e. without __vector prefix.
16867 Enabled by default.
16870 @subsubsection @code{EIND} and Devices with More Than 128 Ki Bytes of Flash
16871 @cindex @code{EIND}
16872 Pointers in the implementation are 16@tie{}bits wide.
16873 The address of a function or label is represented as word address so
16874 that indirect jumps and calls can target any code address in the
16875 range of 64@tie{}Ki words.
16877 In order to facilitate indirect jump on devices with more than 128@tie{}Ki
16878 bytes of program memory space, there is a special function register called
16879 @code{EIND} that serves as most significant part of the target address
16880 when @code{EICALL} or @code{EIJMP} instructions are used.
16882 Indirect jumps and calls on these devices are handled as follows by
16883 the compiler and are subject to some limitations:
16888 The compiler never sets @code{EIND}.
16891 The compiler uses @code{EIND} implicitly in @code{EICALL}/@code{EIJMP}
16892 instructions or might read @code{EIND} directly in order to emulate an
16893 indirect call/jump by means of a @code{RET} instruction.
16896 The compiler assumes that @code{EIND} never changes during the startup
16897 code or during the application. In particular, @code{EIND} is not
16898 saved/restored in function or interrupt service routine
16902 For indirect calls to functions and computed goto, the linker
16903 generates @emph{stubs}. Stubs are jump pads sometimes also called
16904 @emph{trampolines}. Thus, the indirect call/jump jumps to such a stub.
16905 The stub contains a direct jump to the desired address.
16908 Linker relaxation must be turned on so that the linker generates
16909 the stubs correctly in all situations. See the compiler option
16910 @option{-mrelax} and the linker option @option{--relax}.
16911 There are corner cases where the linker is supposed to generate stubs
16912 but aborts without relaxation and without a helpful error message.
16915 The default linker script is arranged for code with @code{EIND = 0}.
16916 If code is supposed to work for a setup with @code{EIND != 0}, a custom
16917 linker script has to be used in order to place the sections whose
16918 name start with @code{.trampolines} into the segment where @code{EIND}
16922 The startup code from libgcc never sets @code{EIND}.
16923 Notice that startup code is a blend of code from libgcc and AVR-LibC.
16924 For the impact of AVR-LibC on @code{EIND}, see the
16925 @w{@uref{http://nongnu.org/avr-libc/user-manual/,AVR-LibC user manual}}.
16928 It is legitimate for user-specific startup code to set up @code{EIND}
16929 early, for example by means of initialization code located in
16930 section @code{.init3}. Such code runs prior to general startup code
16931 that initializes RAM and calls constructors, but after the bit
16932 of startup code from AVR-LibC that sets @code{EIND} to the segment
16933 where the vector table is located.
16935 #include <avr/io.h>
16938 __attribute__((section(".init3"),naked,used,no_instrument_function))
16939 init3_set_eind (void)
16941 __asm volatile ("ldi r24,pm_hh8(__trampolines_start)\n\t"
16942 "out %i0,r24" :: "n" (&EIND) : "r24","memory");
16947 The @code{__trampolines_start} symbol is defined in the linker script.
16950 Stubs are generated automatically by the linker if
16951 the following two conditions are met:
16954 @item The address of a label is taken by means of the @code{gs} modifier
16955 (short for @emph{generate stubs}) like so:
16957 LDI r24, lo8(gs(@var{func}))
16958 LDI r25, hi8(gs(@var{func}))
16960 @item The final location of that label is in a code segment
16961 @emph{outside} the segment where the stubs are located.
16965 The compiler emits such @code{gs} modifiers for code labels in the
16966 following situations:
16968 @item Taking address of a function or code label.
16969 @item Computed goto.
16970 @item If prologue-save function is used, see @option{-mcall-prologues}
16971 command-line option.
16972 @item Switch/case dispatch tables. If you do not want such dispatch
16973 tables you can specify the @option{-fno-jump-tables} command-line option.
16974 @item C and C++ constructors/destructors called during startup/shutdown.
16975 @item If the tools hit a @code{gs()} modifier explained above.
16979 Jumping to non-symbolic addresses like so is @emph{not} supported:
16984 /* Call function at word address 0x2 */
16985 return ((int(*)(void)) 0x2)();
16989 Instead, a stub has to be set up, i.e.@: the function has to be called
16990 through a symbol (@code{func_4} in the example):
16995 extern int func_4 (void);
16997 /* Call function at byte address 0x4 */
17002 and the application be linked with @option{-Wl,--defsym,func_4=0x4}.
17003 Alternatively, @code{func_4} can be defined in the linker script.
17006 @subsubsection Handling of the @code{RAMPD}, @code{RAMPX}, @code{RAMPY} and @code{RAMPZ} Special Function Registers
17007 @cindex @code{RAMPD}
17008 @cindex @code{RAMPX}
17009 @cindex @code{RAMPY}
17010 @cindex @code{RAMPZ}
17011 Some AVR devices support memories larger than the 64@tie{}KiB range
17012 that can be accessed with 16-bit pointers. To access memory locations
17013 outside this 64@tie{}KiB range, the content of a @code{RAMP}
17014 register is used as high part of the address:
17015 The @code{X}, @code{Y}, @code{Z} address register is concatenated
17016 with the @code{RAMPX}, @code{RAMPY}, @code{RAMPZ} special function
17017 register, respectively, to get a wide address. Similarly,
17018 @code{RAMPD} is used together with direct addressing.
17022 The startup code initializes the @code{RAMP} special function
17023 registers with zero.
17026 If a @ref{AVR Named Address Spaces,named address space} other than
17027 generic or @code{__flash} is used, then @code{RAMPZ} is set
17028 as needed before the operation.
17031 If the device supports RAM larger than 64@tie{}KiB and the compiler
17032 needs to change @code{RAMPZ} to accomplish an operation, @code{RAMPZ}
17033 is reset to zero after the operation.
17036 If the device comes with a specific @code{RAMP} register, the ISR
17037 prologue/epilogue saves/restores that SFR and initializes it with
17038 zero in case the ISR code might (implicitly) use it.
17041 RAM larger than 64@tie{}KiB is not supported by GCC for AVR targets.
17042 If you use inline assembler to read from locations outside the
17043 16-bit address range and change one of the @code{RAMP} registers,
17044 you must reset it to zero after the access.
17048 @subsubsection AVR Built-in Macros
17050 GCC defines several built-in macros so that the user code can test
17051 for the presence or absence of features. Almost any of the following
17052 built-in macros are deduced from device capabilities and thus
17053 triggered by the @option{-mmcu=} command-line option.
17055 For even more AVR-specific built-in macros see
17056 @ref{AVR Named Address Spaces} and @ref{AVR Built-in Functions}.
17061 Build-in macro that resolves to a decimal number that identifies the
17062 architecture and depends on the @option{-mmcu=@var{mcu}} option.
17063 Possible values are:
17065 @code{2}, @code{25}, @code{3}, @code{31}, @code{35},
17066 @code{4}, @code{5}, @code{51}, @code{6}
17068 for @var{mcu}=@code{avr2}, @code{avr25}, @code{avr3}, @code{avr31},
17069 @code{avr35}, @code{avr4}, @code{avr5}, @code{avr51}, @code{avr6},
17074 @code{102}, @code{103}, @code{104},
17075 @code{105}, @code{106}, @code{107}
17077 for @var{mcu}=@code{avrtiny},
17078 @code{avrxmega2}, @code{avrxmega3}, @code{avrxmega4},
17079 @code{avrxmega5}, @code{avrxmega6}, @code{avrxmega7}, respectively.
17080 If @var{mcu} specifies a device, this built-in macro is set
17081 accordingly. For example, with @option{-mmcu=atmega8} the macro is
17082 defined to @code{4}.
17084 @item __AVR_@var{Device}__
17085 Setting @option{-mmcu=@var{device}} defines this built-in macro which reflects
17086 the device's name. For example, @option{-mmcu=atmega8} defines the
17087 built-in macro @code{__AVR_ATmega8__}, @option{-mmcu=attiny261a} defines
17088 @code{__AVR_ATtiny261A__}, etc.
17090 The built-in macros' names follow
17091 the scheme @code{__AVR_@var{Device}__} where @var{Device} is
17092 the device name as from the AVR user manual. The difference between
17093 @var{Device} in the built-in macro and @var{device} in
17094 @option{-mmcu=@var{device}} is that the latter is always lowercase.
17096 If @var{device} is not a device but only a core architecture like
17097 @samp{avr51}, this macro is not defined.
17099 @item __AVR_DEVICE_NAME__
17100 Setting @option{-mmcu=@var{device}} defines this built-in macro to
17101 the device's name. For example, with @option{-mmcu=atmega8} the macro
17102 is defined to @code{atmega8}.
17104 If @var{device} is not a device but only a core architecture like
17105 @samp{avr51}, this macro is not defined.
17107 @item __AVR_XMEGA__
17108 The device / architecture belongs to the XMEGA family of devices.
17110 @item __AVR_HAVE_ELPM__
17111 The device has the @code{ELPM} instruction.
17113 @item __AVR_HAVE_ELPMX__
17114 The device has the @code{ELPM R@var{n},Z} and @code{ELPM
17115 R@var{n},Z+} instructions.
17117 @item __AVR_HAVE_MOVW__
17118 The device has the @code{MOVW} instruction to perform 16-bit
17119 register-register moves.
17121 @item __AVR_HAVE_LPMX__
17122 The device has the @code{LPM R@var{n},Z} and
17123 @code{LPM R@var{n},Z+} instructions.
17125 @item __AVR_HAVE_MUL__
17126 The device has a hardware multiplier.
17128 @item __AVR_HAVE_JMP_CALL__
17129 The device has the @code{JMP} and @code{CALL} instructions.
17130 This is the case for devices with more than 8@tie{}KiB of program
17133 @item __AVR_HAVE_EIJMP_EICALL__
17134 @itemx __AVR_3_BYTE_PC__
17135 The device has the @code{EIJMP} and @code{EICALL} instructions.
17136 This is the case for devices with more than 128@tie{}KiB of program memory.
17137 This also means that the program counter
17138 (PC) is 3@tie{}bytes wide.
17140 @item __AVR_2_BYTE_PC__
17141 The program counter (PC) is 2@tie{}bytes wide. This is the case for devices
17142 with up to 128@tie{}KiB of program memory.
17144 @item __AVR_HAVE_8BIT_SP__
17145 @itemx __AVR_HAVE_16BIT_SP__
17146 The stack pointer (SP) register is treated as 8-bit respectively
17147 16-bit register by the compiler.
17148 The definition of these macros is affected by @option{-mtiny-stack}.
17150 @item __AVR_HAVE_SPH__
17152 The device has the SPH (high part of stack pointer) special function
17153 register or has an 8-bit stack pointer, respectively.
17154 The definition of these macros is affected by @option{-mmcu=} and
17155 in the cases of @option{-mmcu=avr2} and @option{-mmcu=avr25} also
17158 @item __AVR_HAVE_RAMPD__
17159 @itemx __AVR_HAVE_RAMPX__
17160 @itemx __AVR_HAVE_RAMPY__
17161 @itemx __AVR_HAVE_RAMPZ__
17162 The device has the @code{RAMPD}, @code{RAMPX}, @code{RAMPY},
17163 @code{RAMPZ} special function register, respectively.
17165 @item __NO_INTERRUPTS__
17166 This macro reflects the @option{-mno-interrupts} command-line option.
17168 @item __AVR_ERRATA_SKIP__
17169 @itemx __AVR_ERRATA_SKIP_JMP_CALL__
17170 Some AVR devices (AT90S8515, ATmega103) must not skip 32-bit
17171 instructions because of a hardware erratum. Skip instructions are
17172 @code{SBRS}, @code{SBRC}, @code{SBIS}, @code{SBIC} and @code{CPSE}.
17173 The second macro is only defined if @code{__AVR_HAVE_JMP_CALL__} is also
17176 @item __AVR_ISA_RMW__
17177 The device has Read-Modify-Write instructions (XCH, LAC, LAS and LAT).
17179 @item __AVR_SFR_OFFSET__=@var{offset}
17180 Instructions that can address I/O special function registers directly
17181 like @code{IN}, @code{OUT}, @code{SBI}, etc.@: may use a different
17182 address as if addressed by an instruction to access RAM like @code{LD}
17183 or @code{STS}. This offset depends on the device architecture and has
17184 to be subtracted from the RAM address in order to get the
17185 respective I/O@tie{}address.
17187 @item __AVR_SHORT_CALLS__
17188 The @option{-mshort-calls} command line option is set.
17190 @item __AVR_PM_BASE_ADDRESS__=@var{addr}
17191 Some devices support reading from flash memory by means of @code{LD*}
17192 instructions. The flash memory is seen in the data address space
17193 at an offset of @code{__AVR_PM_BASE_ADDRESS__}. If this macro
17194 is not defined, this feature is not available. If defined,
17195 the address space is linear and there is no need to put
17196 @code{.rodata} into RAM. This is handled by the default linker
17197 description file, and is currently available for
17198 @code{avrtiny} and @code{avrxmega3}. Even more convenient,
17199 there is no need to use address spaces like @code{__flash} or
17200 features like attribute @code{progmem} and @code{pgm_read_*}.
17202 @item __WITH_AVRLIBC__
17203 The compiler is configured to be used together with AVR-Libc.
17204 See the @option{--with-avrlibc} configure option.
17208 @node Blackfin Options
17209 @subsection Blackfin Options
17210 @cindex Blackfin Options
17213 @item -mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]}
17215 Specifies the name of the target Blackfin processor. Currently, @var{cpu}
17216 can be one of @samp{bf512}, @samp{bf514}, @samp{bf516}, @samp{bf518},
17217 @samp{bf522}, @samp{bf523}, @samp{bf524}, @samp{bf525}, @samp{bf526},
17218 @samp{bf527}, @samp{bf531}, @samp{bf532}, @samp{bf533},
17219 @samp{bf534}, @samp{bf536}, @samp{bf537}, @samp{bf538}, @samp{bf539},
17220 @samp{bf542}, @samp{bf544}, @samp{bf547}, @samp{bf548}, @samp{bf549},
17221 @samp{bf542m}, @samp{bf544m}, @samp{bf547m}, @samp{bf548m}, @samp{bf549m},
17222 @samp{bf561}, @samp{bf592}.
17224 The optional @var{sirevision} specifies the silicon revision of the target
17225 Blackfin processor. Any workarounds available for the targeted silicon revision
17226 are enabled. If @var{sirevision} is @samp{none}, no workarounds are enabled.
17227 If @var{sirevision} is @samp{any}, all workarounds for the targeted processor
17228 are enabled. The @code{__SILICON_REVISION__} macro is defined to two
17229 hexadecimal digits representing the major and minor numbers in the silicon
17230 revision. If @var{sirevision} is @samp{none}, the @code{__SILICON_REVISION__}
17231 is not defined. If @var{sirevision} is @samp{any}, the
17232 @code{__SILICON_REVISION__} is defined to be @code{0xffff}.
17233 If this optional @var{sirevision} is not used, GCC assumes the latest known
17234 silicon revision of the targeted Blackfin processor.
17236 GCC defines a preprocessor macro for the specified @var{cpu}.
17237 For the @samp{bfin-elf} toolchain, this option causes the hardware BSP
17238 provided by libgloss to be linked in if @option{-msim} is not given.
17240 Without this option, @samp{bf532} is used as the processor by default.
17242 Note that support for @samp{bf561} is incomplete. For @samp{bf561},
17243 only the preprocessor macro is defined.
17247 Specifies that the program will be run on the simulator. This causes
17248 the simulator BSP provided by libgloss to be linked in. This option
17249 has effect only for @samp{bfin-elf} toolchain.
17250 Certain other options, such as @option{-mid-shared-library} and
17251 @option{-mfdpic}, imply @option{-msim}.
17253 @item -momit-leaf-frame-pointer
17254 @opindex momit-leaf-frame-pointer
17255 Don't keep the frame pointer in a register for leaf functions. This
17256 avoids the instructions to save, set up and restore frame pointers and
17257 makes an extra register available in leaf functions.
17259 @item -mspecld-anomaly
17260 @opindex mspecld-anomaly
17261 When enabled, the compiler ensures that the generated code does not
17262 contain speculative loads after jump instructions. If this option is used,
17263 @code{__WORKAROUND_SPECULATIVE_LOADS} is defined.
17265 @item -mno-specld-anomaly
17266 @opindex mno-specld-anomaly
17267 Don't generate extra code to prevent speculative loads from occurring.
17269 @item -mcsync-anomaly
17270 @opindex mcsync-anomaly
17271 When enabled, the compiler ensures that the generated code does not
17272 contain CSYNC or SSYNC instructions too soon after conditional branches.
17273 If this option is used, @code{__WORKAROUND_SPECULATIVE_SYNCS} is defined.
17275 @item -mno-csync-anomaly
17276 @opindex mno-csync-anomaly
17277 Don't generate extra code to prevent CSYNC or SSYNC instructions from
17278 occurring too soon after a conditional branch.
17282 When enabled, the compiler is free to take advantage of the knowledge that
17283 the entire program fits into the low 64k of memory.
17286 @opindex mno-low-64k
17287 Assume that the program is arbitrarily large. This is the default.
17289 @item -mstack-check-l1
17290 @opindex mstack-check-l1
17291 Do stack checking using information placed into L1 scratchpad memory by the
17294 @item -mid-shared-library
17295 @opindex mid-shared-library
17296 Generate code that supports shared libraries via the library ID method.
17297 This allows for execute in place and shared libraries in an environment
17298 without virtual memory management. This option implies @option{-fPIC}.
17299 With a @samp{bfin-elf} target, this option implies @option{-msim}.
17301 @item -mno-id-shared-library
17302 @opindex mno-id-shared-library
17303 Generate code that doesn't assume ID-based shared libraries are being used.
17304 This is the default.
17306 @item -mleaf-id-shared-library
17307 @opindex mleaf-id-shared-library
17308 Generate code that supports shared libraries via the library ID method,
17309 but assumes that this library or executable won't link against any other
17310 ID shared libraries. That allows the compiler to use faster code for jumps
17313 @item -mno-leaf-id-shared-library
17314 @opindex mno-leaf-id-shared-library
17315 Do not assume that the code being compiled won't link against any ID shared
17316 libraries. Slower code is generated for jump and call insns.
17318 @item -mshared-library-id=n
17319 @opindex mshared-library-id
17320 Specifies the identification number of the ID-based shared library being
17321 compiled. Specifying a value of 0 generates more compact code; specifying
17322 other values forces the allocation of that number to the current
17323 library but is no more space- or time-efficient than omitting this option.
17327 Generate code that allows the data segment to be located in a different
17328 area of memory from the text segment. This allows for execute in place in
17329 an environment without virtual memory management by eliminating relocations
17330 against the text section.
17332 @item -mno-sep-data
17333 @opindex mno-sep-data
17334 Generate code that assumes that the data segment follows the text segment.
17335 This is the default.
17338 @itemx -mno-long-calls
17339 @opindex mlong-calls
17340 @opindex mno-long-calls
17341 Tells the compiler to perform function calls by first loading the
17342 address of the function into a register and then performing a subroutine
17343 call on this register. This switch is needed if the target function
17344 lies outside of the 24-bit addressing range of the offset-based
17345 version of subroutine call instruction.
17347 This feature is not enabled by default. Specifying
17348 @option{-mno-long-calls} restores the default behavior. Note these
17349 switches have no effect on how the compiler generates code to handle
17350 function calls via function pointers.
17354 Link with the fast floating-point library. This library relaxes some of
17355 the IEEE floating-point standard's rules for checking inputs against
17356 Not-a-Number (NAN), in the interest of performance.
17359 @opindex minline-plt
17360 Enable inlining of PLT entries in function calls to functions that are
17361 not known to bind locally. It has no effect without @option{-mfdpic}.
17364 @opindex mmulticore
17365 Build a standalone application for multicore Blackfin processors.
17366 This option causes proper start files and link scripts supporting
17367 multicore to be used, and defines the macro @code{__BFIN_MULTICORE}.
17368 It can only be used with @option{-mcpu=bf561@r{[}-@var{sirevision}@r{]}}.
17370 This option can be used with @option{-mcorea} or @option{-mcoreb}, which
17371 selects the one-application-per-core programming model. Without
17372 @option{-mcorea} or @option{-mcoreb}, the single-application/dual-core
17373 programming model is used. In this model, the main function of Core B
17374 should be named as @code{coreb_main}.
17376 If this option is not used, the single-core application programming
17381 Build a standalone application for Core A of BF561 when using
17382 the one-application-per-core programming model. Proper start files
17383 and link scripts are used to support Core A, and the macro
17384 @code{__BFIN_COREA} is defined.
17385 This option can only be used in conjunction with @option{-mmulticore}.
17389 Build a standalone application for Core B of BF561 when using
17390 the one-application-per-core programming model. Proper start files
17391 and link scripts are used to support Core B, and the macro
17392 @code{__BFIN_COREB} is defined. When this option is used, @code{coreb_main}
17393 should be used instead of @code{main}.
17394 This option can only be used in conjunction with @option{-mmulticore}.
17398 Build a standalone application for SDRAM. Proper start files and
17399 link scripts are used to put the application into SDRAM, and the macro
17400 @code{__BFIN_SDRAM} is defined.
17401 The loader should initialize SDRAM before loading the application.
17405 Assume that ICPLBs are enabled at run time. This has an effect on certain
17406 anomaly workarounds. For Linux targets, the default is to assume ICPLBs
17407 are enabled; for standalone applications the default is off.
17411 @subsection C6X Options
17412 @cindex C6X Options
17415 @item -march=@var{name}
17417 This specifies the name of the target architecture. GCC uses this
17418 name to determine what kind of instructions it can emit when generating
17419 assembly code. Permissible names are: @samp{c62x},
17420 @samp{c64x}, @samp{c64x+}, @samp{c67x}, @samp{c67x+}, @samp{c674x}.
17423 @opindex mbig-endian
17424 Generate code for a big-endian target.
17426 @item -mlittle-endian
17427 @opindex mlittle-endian
17428 Generate code for a little-endian target. This is the default.
17432 Choose startup files and linker script suitable for the simulator.
17434 @item -msdata=default
17435 @opindex msdata=default
17436 Put small global and static data in the @code{.neardata} section,
17437 which is pointed to by register @code{B14}. Put small uninitialized
17438 global and static data in the @code{.bss} section, which is adjacent
17439 to the @code{.neardata} section. Put small read-only data into the
17440 @code{.rodata} section. The corresponding sections used for large
17441 pieces of data are @code{.fardata}, @code{.far} and @code{.const}.
17444 @opindex msdata=all
17445 Put all data, not just small objects, into the sections reserved for
17446 small data, and use addressing relative to the @code{B14} register to
17450 @opindex msdata=none
17451 Make no use of the sections reserved for small data, and use absolute
17452 addresses to access all data. Put all initialized global and static
17453 data in the @code{.fardata} section, and all uninitialized data in the
17454 @code{.far} section. Put all constant data into the @code{.const}
17459 @subsection CRIS Options
17460 @cindex CRIS Options
17462 These options are defined specifically for the CRIS ports.
17465 @item -march=@var{architecture-type}
17466 @itemx -mcpu=@var{architecture-type}
17469 Generate code for the specified architecture. The choices for
17470 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
17471 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@.
17472 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
17475 @item -mtune=@var{architecture-type}
17477 Tune to @var{architecture-type} everything applicable about the generated
17478 code, except for the ABI and the set of available instructions. The
17479 choices for @var{architecture-type} are the same as for
17480 @option{-march=@var{architecture-type}}.
17482 @item -mmax-stack-frame=@var{n}
17483 @opindex mmax-stack-frame
17484 Warn when the stack frame of a function exceeds @var{n} bytes.
17490 The options @option{-metrax4} and @option{-metrax100} are synonyms for
17491 @option{-march=v3} and @option{-march=v8} respectively.
17493 @item -mmul-bug-workaround
17494 @itemx -mno-mul-bug-workaround
17495 @opindex mmul-bug-workaround
17496 @opindex mno-mul-bug-workaround
17497 Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
17498 models where it applies. This option is active by default.
17502 Enable CRIS-specific verbose debug-related information in the assembly
17503 code. This option also has the effect of turning off the @samp{#NO_APP}
17504 formatted-code indicator to the assembler at the beginning of the
17509 Do not use condition-code results from previous instruction; always emit
17510 compare and test instructions before use of condition codes.
17512 @item -mno-side-effects
17513 @opindex mno-side-effects
17514 Do not emit instructions with side effects in addressing modes other than
17517 @item -mstack-align
17518 @itemx -mno-stack-align
17519 @itemx -mdata-align
17520 @itemx -mno-data-align
17521 @itemx -mconst-align
17522 @itemx -mno-const-align
17523 @opindex mstack-align
17524 @opindex mno-stack-align
17525 @opindex mdata-align
17526 @opindex mno-data-align
17527 @opindex mconst-align
17528 @opindex mno-const-align
17529 These options (@samp{no-} options) arrange (eliminate arrangements) for the
17530 stack frame, individual data and constants to be aligned for the maximum
17531 single data access size for the chosen CPU model. The default is to
17532 arrange for 32-bit alignment. ABI details such as structure layout are
17533 not affected by these options.
17541 Similar to the stack- data- and const-align options above, these options
17542 arrange for stack frame, writable data and constants to all be 32-bit,
17543 16-bit or 8-bit aligned. The default is 32-bit alignment.
17545 @item -mno-prologue-epilogue
17546 @itemx -mprologue-epilogue
17547 @opindex mno-prologue-epilogue
17548 @opindex mprologue-epilogue
17549 With @option{-mno-prologue-epilogue}, the normal function prologue and
17550 epilogue which set up the stack frame are omitted and no return
17551 instructions or return sequences are generated in the code. Use this
17552 option only together with visual inspection of the compiled code: no
17553 warnings or errors are generated when call-saved registers must be saved,
17554 or storage for local variables needs to be allocated.
17558 @opindex mno-gotplt
17560 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
17561 instruction sequences that load addresses for functions from the PLT part
17562 of the GOT rather than (traditional on other architectures) calls to the
17563 PLT@. The default is @option{-mgotplt}.
17567 Legacy no-op option only recognized with the cris-axis-elf and
17568 cris-axis-linux-gnu targets.
17572 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
17576 This option, recognized for the cris-axis-elf, arranges
17577 to link with input-output functions from a simulator library. Code,
17578 initialized data and zero-initialized data are allocated consecutively.
17582 Like @option{-sim}, but pass linker options to locate initialized data at
17583 0x40000000 and zero-initialized data at 0x80000000.
17587 @subsection CR16 Options
17588 @cindex CR16 Options
17590 These options are defined specifically for the CR16 ports.
17596 Enable the use of multiply-accumulate instructions. Disabled by default.
17600 @opindex mcr16cplus
17602 Generate code for CR16C or CR16C+ architecture. CR16C+ architecture
17607 Links the library libsim.a which is in compatible with simulator. Applicable
17608 to ELF compiler only.
17612 Choose integer type as 32-bit wide.
17616 Generates @code{sbit}/@code{cbit} instructions for bit manipulations.
17618 @item -mdata-model=@var{model}
17619 @opindex mdata-model
17620 Choose a data model. The choices for @var{model} are @samp{near},
17621 @samp{far} or @samp{medium}. @samp{medium} is default.
17622 However, @samp{far} is not valid with @option{-mcr16c}, as the
17623 CR16C architecture does not support the far data model.
17626 @node Darwin Options
17627 @subsection Darwin Options
17628 @cindex Darwin options
17630 These options are defined for all architectures running the Darwin operating
17633 FSF GCC on Darwin does not create ``fat'' object files; it creates
17634 an object file for the single architecture that GCC was built to
17635 target. Apple's GCC on Darwin does create ``fat'' files if multiple
17636 @option{-arch} options are used; it does so by running the compiler or
17637 linker multiple times and joining the results together with
17640 The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or
17641 @samp{i686}) is determined by the flags that specify the ISA
17642 that GCC is targeting, like @option{-mcpu} or @option{-march}. The
17643 @option{-force_cpusubtype_ALL} option can be used to override this.
17645 The Darwin tools vary in their behavior when presented with an ISA
17646 mismatch. The assembler, @file{as}, only permits instructions to
17647 be used that are valid for the subtype of the file it is generating,
17648 so you cannot put 64-bit instructions in a @samp{ppc750} object file.
17649 The linker for shared libraries, @file{/usr/bin/libtool}, fails
17650 and prints an error if asked to create a shared library with a less
17651 restrictive subtype than its input files (for instance, trying to put
17652 a @samp{ppc970} object file in a @samp{ppc7400} library). The linker
17653 for executables, @command{ld}, quietly gives the executable the most
17654 restrictive subtype of any of its input files.
17659 Add the framework directory @var{dir} to the head of the list of
17660 directories to be searched for header files. These directories are
17661 interleaved with those specified by @option{-I} options and are
17662 scanned in a left-to-right order.
17664 A framework directory is a directory with frameworks in it. A
17665 framework is a directory with a @file{Headers} and/or
17666 @file{PrivateHeaders} directory contained directly in it that ends
17667 in @file{.framework}. The name of a framework is the name of this
17668 directory excluding the @file{.framework}. Headers associated with
17669 the framework are found in one of those two directories, with
17670 @file{Headers} being searched first. A subframework is a framework
17671 directory that is in a framework's @file{Frameworks} directory.
17672 Includes of subframework headers can only appear in a header of a
17673 framework that contains the subframework, or in a sibling subframework
17674 header. Two subframeworks are siblings if they occur in the same
17675 framework. A subframework should not have the same name as a
17676 framework; a warning is issued if this is violated. Currently a
17677 subframework cannot have subframeworks; in the future, the mechanism
17678 may be extended to support this. The standard frameworks can be found
17679 in @file{/System/Library/Frameworks} and
17680 @file{/Library/Frameworks}. An example include looks like
17681 @code{#include <Framework/header.h>}, where @file{Framework} denotes
17682 the name of the framework and @file{header.h} is found in the
17683 @file{PrivateHeaders} or @file{Headers} directory.
17685 @item -iframework@var{dir}
17686 @opindex iframework
17687 Like @option{-F} except the directory is a treated as a system
17688 directory. The main difference between this @option{-iframework} and
17689 @option{-F} is that with @option{-iframework} the compiler does not
17690 warn about constructs contained within header files found via
17691 @var{dir}. This option is valid only for the C family of languages.
17695 Emit debugging information for symbols that are used. For stabs
17696 debugging format, this enables @option{-feliminate-unused-debug-symbols}.
17697 This is by default ON@.
17701 Emit debugging information for all symbols and types.
17703 @item -mmacosx-version-min=@var{version}
17704 The earliest version of MacOS X that this executable will run on
17705 is @var{version}. Typical values of @var{version} include @code{10.1},
17706 @code{10.2}, and @code{10.3.9}.
17708 If the compiler was built to use the system's headers by default,
17709 then the default for this option is the system version on which the
17710 compiler is running, otherwise the default is to make choices that
17711 are compatible with as many systems and code bases as possible.
17715 Enable kernel development mode. The @option{-mkernel} option sets
17716 @option{-static}, @option{-fno-common}, @option{-fno-use-cxa-atexit},
17717 @option{-fno-exceptions}, @option{-fno-non-call-exceptions},
17718 @option{-fapple-kext}, @option{-fno-weak} and @option{-fno-rtti} where
17719 applicable. This mode also sets @option{-mno-altivec},
17720 @option{-msoft-float}, @option{-fno-builtin} and
17721 @option{-mlong-branch} for PowerPC targets.
17723 @item -mone-byte-bool
17724 @opindex mone-byte-bool
17725 Override the defaults for @code{bool} so that @code{sizeof(bool)==1}.
17726 By default @code{sizeof(bool)} is @code{4} when compiling for
17727 Darwin/PowerPC and @code{1} when compiling for Darwin/x86, so this
17728 option has no effect on x86.
17730 @strong{Warning:} The @option{-mone-byte-bool} switch causes GCC
17731 to generate code that is not binary compatible with code generated
17732 without that switch. Using this switch may require recompiling all
17733 other modules in a program, including system libraries. Use this
17734 switch to conform to a non-default data model.
17736 @item -mfix-and-continue
17737 @itemx -ffix-and-continue
17738 @itemx -findirect-data
17739 @opindex mfix-and-continue
17740 @opindex ffix-and-continue
17741 @opindex findirect-data
17742 Generate code suitable for fast turnaround development, such as to
17743 allow GDB to dynamically load @file{.o} files into already-running
17744 programs. @option{-findirect-data} and @option{-ffix-and-continue}
17745 are provided for backwards compatibility.
17749 Loads all members of static archive libraries.
17750 See man ld(1) for more information.
17752 @item -arch_errors_fatal
17753 @opindex arch_errors_fatal
17754 Cause the errors having to do with files that have the wrong architecture
17757 @item -bind_at_load
17758 @opindex bind_at_load
17759 Causes the output file to be marked such that the dynamic linker will
17760 bind all undefined references when the file is loaded or launched.
17764 Produce a Mach-o bundle format file.
17765 See man ld(1) for more information.
17767 @item -bundle_loader @var{executable}
17768 @opindex bundle_loader
17769 This option specifies the @var{executable} that will load the build
17770 output file being linked. See man ld(1) for more information.
17773 @opindex dynamiclib
17774 When passed this option, GCC produces a dynamic library instead of
17775 an executable when linking, using the Darwin @file{libtool} command.
17777 @item -force_cpusubtype_ALL
17778 @opindex force_cpusubtype_ALL
17779 This causes GCC's output file to have the @samp{ALL} subtype, instead of
17780 one controlled by the @option{-mcpu} or @option{-march} option.
17782 @item -allowable_client @var{client_name}
17783 @itemx -client_name
17784 @itemx -compatibility_version
17785 @itemx -current_version
17787 @itemx -dependency-file
17789 @itemx -dylinker_install_name
17791 @itemx -exported_symbols_list
17794 @itemx -flat_namespace
17795 @itemx -force_flat_namespace
17796 @itemx -headerpad_max_install_names
17799 @itemx -install_name
17800 @itemx -keep_private_externs
17801 @itemx -multi_module
17802 @itemx -multiply_defined
17803 @itemx -multiply_defined_unused
17806 @itemx -no_dead_strip_inits_and_terms
17807 @itemx -nofixprebinding
17808 @itemx -nomultidefs
17810 @itemx -noseglinkedit
17811 @itemx -pagezero_size
17813 @itemx -prebind_all_twolevel_modules
17814 @itemx -private_bundle
17816 @itemx -read_only_relocs
17818 @itemx -sectobjectsymbols
17822 @itemx -sectobjectsymbols
17825 @itemx -segs_read_only_addr
17827 @itemx -segs_read_write_addr
17828 @itemx -seg_addr_table
17829 @itemx -seg_addr_table_filename
17830 @itemx -seglinkedit
17832 @itemx -segs_read_only_addr
17833 @itemx -segs_read_write_addr
17834 @itemx -single_module
17836 @itemx -sub_library
17838 @itemx -sub_umbrella
17839 @itemx -twolevel_namespace
17842 @itemx -unexported_symbols_list
17843 @itemx -weak_reference_mismatches
17844 @itemx -whatsloaded
17845 @opindex allowable_client
17846 @opindex client_name
17847 @opindex compatibility_version
17848 @opindex current_version
17849 @opindex dead_strip
17850 @opindex dependency-file
17851 @opindex dylib_file
17852 @opindex dylinker_install_name
17854 @opindex exported_symbols_list
17856 @opindex flat_namespace
17857 @opindex force_flat_namespace
17858 @opindex headerpad_max_install_names
17859 @opindex image_base
17861 @opindex install_name
17862 @opindex keep_private_externs
17863 @opindex multi_module
17864 @opindex multiply_defined
17865 @opindex multiply_defined_unused
17866 @opindex noall_load
17867 @opindex no_dead_strip_inits_and_terms
17868 @opindex nofixprebinding
17869 @opindex nomultidefs
17871 @opindex noseglinkedit
17872 @opindex pagezero_size
17874 @opindex prebind_all_twolevel_modules
17875 @opindex private_bundle
17876 @opindex read_only_relocs
17878 @opindex sectobjectsymbols
17881 @opindex sectcreate
17882 @opindex sectobjectsymbols
17885 @opindex segs_read_only_addr
17886 @opindex segs_read_write_addr
17887 @opindex seg_addr_table
17888 @opindex seg_addr_table_filename
17889 @opindex seglinkedit
17891 @opindex segs_read_only_addr
17892 @opindex segs_read_write_addr
17893 @opindex single_module
17895 @opindex sub_library
17896 @opindex sub_umbrella
17897 @opindex twolevel_namespace
17900 @opindex unexported_symbols_list
17901 @opindex weak_reference_mismatches
17902 @opindex whatsloaded
17903 These options are passed to the Darwin linker. The Darwin linker man page
17904 describes them in detail.
17907 @node DEC Alpha Options
17908 @subsection DEC Alpha Options
17910 These @samp{-m} options are defined for the DEC Alpha implementations:
17913 @item -mno-soft-float
17914 @itemx -msoft-float
17915 @opindex mno-soft-float
17916 @opindex msoft-float
17917 Use (do not use) the hardware floating-point instructions for
17918 floating-point operations. When @option{-msoft-float} is specified,
17919 functions in @file{libgcc.a} are used to perform floating-point
17920 operations. Unless they are replaced by routines that emulate the
17921 floating-point operations, or compiled in such a way as to call such
17922 emulations routines, these routines issue floating-point
17923 operations. If you are compiling for an Alpha without floating-point
17924 operations, you must ensure that the library is built so as not to call
17927 Note that Alpha implementations without floating-point operations are
17928 required to have floating-point registers.
17931 @itemx -mno-fp-regs
17933 @opindex mno-fp-regs
17934 Generate code that uses (does not use) the floating-point register set.
17935 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
17936 register set is not used, floating-point operands are passed in integer
17937 registers as if they were integers and floating-point results are passed
17938 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
17939 so any function with a floating-point argument or return value called by code
17940 compiled with @option{-mno-fp-regs} must also be compiled with that
17943 A typical use of this option is building a kernel that does not use,
17944 and hence need not save and restore, any floating-point registers.
17948 The Alpha architecture implements floating-point hardware optimized for
17949 maximum performance. It is mostly compliant with the IEEE floating-point
17950 standard. However, for full compliance, software assistance is
17951 required. This option generates code fully IEEE-compliant code
17952 @emph{except} that the @var{inexact-flag} is not maintained (see below).
17953 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
17954 defined during compilation. The resulting code is less efficient but is
17955 able to correctly support denormalized numbers and exceptional IEEE
17956 values such as not-a-number and plus/minus infinity. Other Alpha
17957 compilers call this option @option{-ieee_with_no_inexact}.
17959 @item -mieee-with-inexact
17960 @opindex mieee-with-inexact
17961 This is like @option{-mieee} except the generated code also maintains
17962 the IEEE @var{inexact-flag}. Turning on this option causes the
17963 generated code to implement fully-compliant IEEE math. In addition to
17964 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
17965 macro. On some Alpha implementations the resulting code may execute
17966 significantly slower than the code generated by default. Since there is
17967 very little code that depends on the @var{inexact-flag}, you should
17968 normally not specify this option. Other Alpha compilers call this
17969 option @option{-ieee_with_inexact}.
17971 @item -mfp-trap-mode=@var{trap-mode}
17972 @opindex mfp-trap-mode
17973 This option controls what floating-point related traps are enabled.
17974 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
17975 The trap mode can be set to one of four values:
17979 This is the default (normal) setting. The only traps that are enabled
17980 are the ones that cannot be disabled in software (e.g., division by zero
17984 In addition to the traps enabled by @samp{n}, underflow traps are enabled
17988 Like @samp{u}, but the instructions are marked to be safe for software
17989 completion (see Alpha architecture manual for details).
17992 Like @samp{su}, but inexact traps are enabled as well.
17995 @item -mfp-rounding-mode=@var{rounding-mode}
17996 @opindex mfp-rounding-mode
17997 Selects the IEEE rounding mode. Other Alpha compilers call this option
17998 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
18003 Normal IEEE rounding mode. Floating-point numbers are rounded towards
18004 the nearest machine number or towards the even machine number in case
18008 Round towards minus infinity.
18011 Chopped rounding mode. Floating-point numbers are rounded towards zero.
18014 Dynamic rounding mode. A field in the floating-point control register
18015 (@var{fpcr}, see Alpha architecture reference manual) controls the
18016 rounding mode in effect. The C library initializes this register for
18017 rounding towards plus infinity. Thus, unless your program modifies the
18018 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
18021 @item -mtrap-precision=@var{trap-precision}
18022 @opindex mtrap-precision
18023 In the Alpha architecture, floating-point traps are imprecise. This
18024 means without software assistance it is impossible to recover from a
18025 floating trap and program execution normally needs to be terminated.
18026 GCC can generate code that can assist operating system trap handlers
18027 in determining the exact location that caused a floating-point trap.
18028 Depending on the requirements of an application, different levels of
18029 precisions can be selected:
18033 Program precision. This option is the default and means a trap handler
18034 can only identify which program caused a floating-point exception.
18037 Function precision. The trap handler can determine the function that
18038 caused a floating-point exception.
18041 Instruction precision. The trap handler can determine the exact
18042 instruction that caused a floating-point exception.
18045 Other Alpha compilers provide the equivalent options called
18046 @option{-scope_safe} and @option{-resumption_safe}.
18048 @item -mieee-conformant
18049 @opindex mieee-conformant
18050 This option marks the generated code as IEEE conformant. You must not
18051 use this option unless you also specify @option{-mtrap-precision=i} and either
18052 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
18053 is to emit the line @samp{.eflag 48} in the function prologue of the
18054 generated assembly file.
18056 @item -mbuild-constants
18057 @opindex mbuild-constants
18058 Normally GCC examines a 32- or 64-bit integer constant to
18059 see if it can construct it from smaller constants in two or three
18060 instructions. If it cannot, it outputs the constant as a literal and
18061 generates code to load it from the data segment at run time.
18063 Use this option to require GCC to construct @emph{all} integer constants
18064 using code, even if it takes more instructions (the maximum is six).
18066 You typically use this option to build a shared library dynamic
18067 loader. Itself a shared library, it must relocate itself in memory
18068 before it can find the variables and constants in its own data segment.
18086 Indicate whether GCC should generate code to use the optional BWX,
18087 CIX, FIX and MAX instruction sets. The default is to use the instruction
18088 sets supported by the CPU type specified via @option{-mcpu=} option or that
18089 of the CPU on which GCC was built if none is specified.
18092 @itemx -mfloat-ieee
18093 @opindex mfloat-vax
18094 @opindex mfloat-ieee
18095 Generate code that uses (does not use) VAX F and G floating-point
18096 arithmetic instead of IEEE single and double precision.
18098 @item -mexplicit-relocs
18099 @itemx -mno-explicit-relocs
18100 @opindex mexplicit-relocs
18101 @opindex mno-explicit-relocs
18102 Older Alpha assemblers provided no way to generate symbol relocations
18103 except via assembler macros. Use of these macros does not allow
18104 optimal instruction scheduling. GNU binutils as of version 2.12
18105 supports a new syntax that allows the compiler to explicitly mark
18106 which relocations should apply to which instructions. This option
18107 is mostly useful for debugging, as GCC detects the capabilities of
18108 the assembler when it is built and sets the default accordingly.
18111 @itemx -mlarge-data
18112 @opindex msmall-data
18113 @opindex mlarge-data
18114 When @option{-mexplicit-relocs} is in effect, static data is
18115 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
18116 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
18117 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
18118 16-bit relocations off of the @code{$gp} register. This limits the
18119 size of the small data area to 64KB, but allows the variables to be
18120 directly accessed via a single instruction.
18122 The default is @option{-mlarge-data}. With this option the data area
18123 is limited to just below 2GB@. Programs that require more than 2GB of
18124 data must use @code{malloc} or @code{mmap} to allocate the data in the
18125 heap instead of in the program's data segment.
18127 When generating code for shared libraries, @option{-fpic} implies
18128 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
18131 @itemx -mlarge-text
18132 @opindex msmall-text
18133 @opindex mlarge-text
18134 When @option{-msmall-text} is used, the compiler assumes that the
18135 code of the entire program (or shared library) fits in 4MB, and is
18136 thus reachable with a branch instruction. When @option{-msmall-data}
18137 is used, the compiler can assume that all local symbols share the
18138 same @code{$gp} value, and thus reduce the number of instructions
18139 required for a function call from 4 to 1.
18141 The default is @option{-mlarge-text}.
18143 @item -mcpu=@var{cpu_type}
18145 Set the instruction set and instruction scheduling parameters for
18146 machine type @var{cpu_type}. You can specify either the @samp{EV}
18147 style name or the corresponding chip number. GCC supports scheduling
18148 parameters for the EV4, EV5 and EV6 family of processors and
18149 chooses the default values for the instruction set from the processor
18150 you specify. If you do not specify a processor type, GCC defaults
18151 to the processor on which the compiler was built.
18153 Supported values for @var{cpu_type} are
18159 Schedules as an EV4 and has no instruction set extensions.
18163 Schedules as an EV5 and has no instruction set extensions.
18167 Schedules as an EV5 and supports the BWX extension.
18172 Schedules as an EV5 and supports the BWX and MAX extensions.
18176 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
18180 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
18183 Native toolchains also support the value @samp{native},
18184 which selects the best architecture option for the host processor.
18185 @option{-mcpu=native} has no effect if GCC does not recognize
18188 @item -mtune=@var{cpu_type}
18190 Set only the instruction scheduling parameters for machine type
18191 @var{cpu_type}. The instruction set is not changed.
18193 Native toolchains also support the value @samp{native},
18194 which selects the best architecture option for the host processor.
18195 @option{-mtune=native} has no effect if GCC does not recognize
18198 @item -mmemory-latency=@var{time}
18199 @opindex mmemory-latency
18200 Sets the latency the scheduler should assume for typical memory
18201 references as seen by the application. This number is highly
18202 dependent on the memory access patterns used by the application
18203 and the size of the external cache on the machine.
18205 Valid options for @var{time} are
18209 A decimal number representing clock cycles.
18215 The compiler contains estimates of the number of clock cycles for
18216 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
18217 (also called Dcache, Scache, and Bcache), as well as to main memory.
18218 Note that L3 is only valid for EV5.
18224 @subsection FR30 Options
18225 @cindex FR30 Options
18227 These options are defined specifically for the FR30 port.
18231 @item -msmall-model
18232 @opindex msmall-model
18233 Use the small address space model. This can produce smaller code, but
18234 it does assume that all symbolic values and addresses fit into a
18239 Assume that runtime support has been provided and so there is no need
18240 to include the simulator library (@file{libsim.a}) on the linker
18246 @subsection FT32 Options
18247 @cindex FT32 Options
18249 These options are defined specifically for the FT32 port.
18255 Specifies that the program will be run on the simulator. This causes
18256 an alternate runtime startup and library to be linked.
18257 You must not use this option when generating programs that will run on
18258 real hardware; you must provide your own runtime library for whatever
18259 I/O functions are needed.
18263 Enable Local Register Allocation. This is still experimental for FT32,
18264 so by default the compiler uses standard reload.
18268 Do not use div and mod instructions.
18272 Enable use of the extended instructions of the FT32B processor.
18276 Compress all code using the Ft32B code compression scheme.
18280 Do not generate code that reads program memory.
18285 @subsection FRV Options
18286 @cindex FRV Options
18292 Only use the first 32 general-purpose registers.
18297 Use all 64 general-purpose registers.
18302 Use only the first 32 floating-point registers.
18307 Use all 64 floating-point registers.
18310 @opindex mhard-float
18312 Use hardware instructions for floating-point operations.
18315 @opindex msoft-float
18317 Use library routines for floating-point operations.
18322 Dynamically allocate condition code registers.
18327 Do not try to dynamically allocate condition code registers, only
18328 use @code{icc0} and @code{fcc0}.
18333 Change ABI to use double word insns.
18338 Do not use double word instructions.
18343 Use floating-point double instructions.
18346 @opindex mno-double
18348 Do not use floating-point double instructions.
18353 Use media instructions.
18358 Do not use media instructions.
18363 Use multiply and add/subtract instructions.
18366 @opindex mno-muladd
18368 Do not use multiply and add/subtract instructions.
18373 Select the FDPIC ABI, which uses function descriptors to represent
18374 pointers to functions. Without any PIC/PIE-related options, it
18375 implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it
18376 assumes GOT entries and small data are within a 12-bit range from the
18377 GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets
18378 are computed with 32 bits.
18379 With a @samp{bfin-elf} target, this option implies @option{-msim}.
18382 @opindex minline-plt
18384 Enable inlining of PLT entries in function calls to functions that are
18385 not known to bind locally. It has no effect without @option{-mfdpic}.
18386 It's enabled by default if optimizing for speed and compiling for
18387 shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an
18388 optimization option such as @option{-O3} or above is present in the
18394 Assume a large TLS segment when generating thread-local code.
18399 Do not assume a large TLS segment when generating thread-local code.
18404 Enable the use of @code{GPREL} relocations in the FDPIC ABI for data
18405 that is known to be in read-only sections. It's enabled by default,
18406 except for @option{-fpic} or @option{-fpie}: even though it may help
18407 make the global offset table smaller, it trades 1 instruction for 4.
18408 With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4,
18409 one of which may be shared by multiple symbols, and it avoids the need
18410 for a GOT entry for the referenced symbol, so it's more likely to be a
18411 win. If it is not, @option{-mno-gprel-ro} can be used to disable it.
18413 @item -multilib-library-pic
18414 @opindex multilib-library-pic
18416 Link with the (library, not FD) pic libraries. It's implied by
18417 @option{-mlibrary-pic}, as well as by @option{-fPIC} and
18418 @option{-fpic} without @option{-mfdpic}. You should never have to use
18422 @opindex mlinked-fp
18424 Follow the EABI requirement of always creating a frame pointer whenever
18425 a stack frame is allocated. This option is enabled by default and can
18426 be disabled with @option{-mno-linked-fp}.
18429 @opindex mlong-calls
18431 Use indirect addressing to call functions outside the current
18432 compilation unit. This allows the functions to be placed anywhere
18433 within the 32-bit address space.
18435 @item -malign-labels
18436 @opindex malign-labels
18438 Try to align labels to an 8-byte boundary by inserting NOPs into the
18439 previous packet. This option only has an effect when VLIW packing
18440 is enabled. It doesn't create new packets; it merely adds NOPs to
18443 @item -mlibrary-pic
18444 @opindex mlibrary-pic
18446 Generate position-independent EABI code.
18451 Use only the first four media accumulator registers.
18456 Use all eight media accumulator registers.
18461 Pack VLIW instructions.
18466 Do not pack VLIW instructions.
18469 @opindex mno-eflags
18471 Do not mark ABI switches in e_flags.
18474 @opindex mcond-move
18476 Enable the use of conditional-move instructions (default).
18478 This switch is mainly for debugging the compiler and will likely be removed
18479 in a future version.
18481 @item -mno-cond-move
18482 @opindex mno-cond-move
18484 Disable the use of conditional-move instructions.
18486 This switch is mainly for debugging the compiler and will likely be removed
18487 in a future version.
18492 Enable the use of conditional set instructions (default).
18494 This switch is mainly for debugging the compiler and will likely be removed
18495 in a future version.
18500 Disable the use of conditional set instructions.
18502 This switch is mainly for debugging the compiler and will likely be removed
18503 in a future version.
18506 @opindex mcond-exec
18508 Enable the use of conditional execution (default).
18510 This switch is mainly for debugging the compiler and will likely be removed
18511 in a future version.
18513 @item -mno-cond-exec
18514 @opindex mno-cond-exec
18516 Disable the use of conditional execution.
18518 This switch is mainly for debugging the compiler and will likely be removed
18519 in a future version.
18521 @item -mvliw-branch
18522 @opindex mvliw-branch
18524 Run a pass to pack branches into VLIW instructions (default).
18526 This switch is mainly for debugging the compiler and will likely be removed
18527 in a future version.
18529 @item -mno-vliw-branch
18530 @opindex mno-vliw-branch
18532 Do not run a pass to pack branches into VLIW instructions.
18534 This switch is mainly for debugging the compiler and will likely be removed
18535 in a future version.
18537 @item -mmulti-cond-exec
18538 @opindex mmulti-cond-exec
18540 Enable optimization of @code{&&} and @code{||} in conditional execution
18543 This switch is mainly for debugging the compiler and will likely be removed
18544 in a future version.
18546 @item -mno-multi-cond-exec
18547 @opindex mno-multi-cond-exec
18549 Disable optimization of @code{&&} and @code{||} in conditional execution.
18551 This switch is mainly for debugging the compiler and will likely be removed
18552 in a future version.
18554 @item -mnested-cond-exec
18555 @opindex mnested-cond-exec
18557 Enable nested conditional execution optimizations (default).
18559 This switch is mainly for debugging the compiler and will likely be removed
18560 in a future version.
18562 @item -mno-nested-cond-exec
18563 @opindex mno-nested-cond-exec
18565 Disable nested conditional execution optimizations.
18567 This switch is mainly for debugging the compiler and will likely be removed
18568 in a future version.
18570 @item -moptimize-membar
18571 @opindex moptimize-membar
18573 This switch removes redundant @code{membar} instructions from the
18574 compiler-generated code. It is enabled by default.
18576 @item -mno-optimize-membar
18577 @opindex mno-optimize-membar
18579 This switch disables the automatic removal of redundant @code{membar}
18580 instructions from the generated code.
18582 @item -mtomcat-stats
18583 @opindex mtomcat-stats
18585 Cause gas to print out tomcat statistics.
18587 @item -mcpu=@var{cpu}
18590 Select the processor type for which to generate code. Possible values are
18591 @samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450},
18592 @samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}.
18596 @node GNU/Linux Options
18597 @subsection GNU/Linux Options
18599 These @samp{-m} options are defined for GNU/Linux targets:
18604 Use the GNU C library. This is the default except
18605 on @samp{*-*-linux-*uclibc*}, @samp{*-*-linux-*musl*} and
18606 @samp{*-*-linux-*android*} targets.
18610 Use uClibc C library. This is the default on
18611 @samp{*-*-linux-*uclibc*} targets.
18615 Use the musl C library. This is the default on
18616 @samp{*-*-linux-*musl*} targets.
18620 Use Bionic C library. This is the default on
18621 @samp{*-*-linux-*android*} targets.
18625 Compile code compatible with Android platform. This is the default on
18626 @samp{*-*-linux-*android*} targets.
18628 When compiling, this option enables @option{-mbionic}, @option{-fPIC},
18629 @option{-fno-exceptions} and @option{-fno-rtti} by default. When linking,
18630 this option makes the GCC driver pass Android-specific options to the linker.
18631 Finally, this option causes the preprocessor macro @code{__ANDROID__}
18634 @item -tno-android-cc
18635 @opindex tno-android-cc
18636 Disable compilation effects of @option{-mandroid}, i.e., do not enable
18637 @option{-mbionic}, @option{-fPIC}, @option{-fno-exceptions} and
18638 @option{-fno-rtti} by default.
18640 @item -tno-android-ld
18641 @opindex tno-android-ld
18642 Disable linking effects of @option{-mandroid}, i.e., pass standard Linux
18643 linking options to the linker.
18647 @node H8/300 Options
18648 @subsection H8/300 Options
18650 These @samp{-m} options are defined for the H8/300 implementations:
18655 Shorten some address references at link time, when possible; uses the
18656 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
18657 ld, Using ld}, for a fuller description.
18661 Generate code for the H8/300H@.
18665 Generate code for the H8S@.
18669 Generate code for the H8S and H8/300H in the normal mode. This switch
18670 must be used either with @option{-mh} or @option{-ms}.
18674 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
18678 Extended registers are stored on stack before execution of function
18679 with monitor attribute. Default option is @option{-mexr}.
18680 This option is valid only for H8S targets.
18684 Extended registers are not stored on stack before execution of function
18685 with monitor attribute. Default option is @option{-mno-exr}.
18686 This option is valid only for H8S targets.
18690 Make @code{int} data 32 bits by default.
18693 @opindex malign-300
18694 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
18695 The default for the H8/300H and H8S is to align longs and floats on
18697 @option{-malign-300} causes them to be aligned on 2-byte boundaries.
18698 This option has no effect on the H8/300.
18702 @subsection HPPA Options
18703 @cindex HPPA Options
18705 These @samp{-m} options are defined for the HPPA family of computers:
18708 @item -march=@var{architecture-type}
18710 Generate code for the specified architecture. The choices for
18711 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
18712 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
18713 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
18714 architecture option for your machine. Code compiled for lower numbered
18715 architectures runs on higher numbered architectures, but not the
18718 @item -mpa-risc-1-0
18719 @itemx -mpa-risc-1-1
18720 @itemx -mpa-risc-2-0
18721 @opindex mpa-risc-1-0
18722 @opindex mpa-risc-1-1
18723 @opindex mpa-risc-2-0
18724 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
18726 @item -mcaller-copies
18727 @opindex mcaller-copies
18728 The caller copies function arguments passed by hidden reference. This
18729 option should be used with care as it is not compatible with the default
18730 32-bit runtime. However, only aggregates larger than eight bytes are
18731 passed by hidden reference and the option provides better compatibility
18734 @item -mjump-in-delay
18735 @opindex mjump-in-delay
18736 This option is ignored and provided for compatibility purposes only.
18738 @item -mdisable-fpregs
18739 @opindex mdisable-fpregs
18740 Prevent floating-point registers from being used in any manner. This is
18741 necessary for compiling kernels that perform lazy context switching of
18742 floating-point registers. If you use this option and attempt to perform
18743 floating-point operations, the compiler aborts.
18745 @item -mdisable-indexing
18746 @opindex mdisable-indexing
18747 Prevent the compiler from using indexing address modes. This avoids some
18748 rather obscure problems when compiling MIG generated code under MACH@.
18750 @item -mno-space-regs
18751 @opindex mno-space-regs
18752 Generate code that assumes the target has no space registers. This allows
18753 GCC to generate faster indirect calls and use unscaled index address modes.
18755 Such code is suitable for level 0 PA systems and kernels.
18757 @item -mfast-indirect-calls
18758 @opindex mfast-indirect-calls
18759 Generate code that assumes calls never cross space boundaries. This
18760 allows GCC to emit code that performs faster indirect calls.
18762 This option does not work in the presence of shared libraries or nested
18765 @item -mfixed-range=@var{register-range}
18766 @opindex mfixed-range
18767 Generate code treating the given register range as fixed registers.
18768 A fixed register is one that the register allocator cannot use. This is
18769 useful when compiling kernel code. A register range is specified as
18770 two registers separated by a dash. Multiple register ranges can be
18771 specified separated by a comma.
18773 @item -mlong-load-store
18774 @opindex mlong-load-store
18775 Generate 3-instruction load and store sequences as sometimes required by
18776 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
18779 @item -mportable-runtime
18780 @opindex mportable-runtime
18781 Use the portable calling conventions proposed by HP for ELF systems.
18785 Enable the use of assembler directives only GAS understands.
18787 @item -mschedule=@var{cpu-type}
18789 Schedule code according to the constraints for the machine type
18790 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
18791 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
18792 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
18793 proper scheduling option for your machine. The default scheduling is
18797 @opindex mlinker-opt
18798 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
18799 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
18800 linkers in which they give bogus error messages when linking some programs.
18803 @opindex msoft-float
18804 Generate output containing library calls for floating point.
18805 @strong{Warning:} the requisite libraries are not available for all HPPA
18806 targets. Normally the facilities of the machine's usual C compiler are
18807 used, but this cannot be done directly in cross-compilation. You must make
18808 your own arrangements to provide suitable library functions for
18811 @option{-msoft-float} changes the calling convention in the output file;
18812 therefore, it is only useful if you compile @emph{all} of a program with
18813 this option. In particular, you need to compile @file{libgcc.a}, the
18814 library that comes with GCC, with @option{-msoft-float} in order for
18819 Generate the predefine, @code{_SIO}, for server IO@. The default is
18820 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
18821 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These
18822 options are available under HP-UX and HI-UX@.
18826 Use options specific to GNU @command{ld}.
18827 This passes @option{-shared} to @command{ld} when
18828 building a shared library. It is the default when GCC is configured,
18829 explicitly or implicitly, with the GNU linker. This option does not
18830 affect which @command{ld} is called; it only changes what parameters
18831 are passed to that @command{ld}.
18832 The @command{ld} that is called is determined by the
18833 @option{--with-ld} configure option, GCC's program search path, and
18834 finally by the user's @env{PATH}. The linker used by GCC can be printed
18835 using @samp{which `gcc -print-prog-name=ld`}. This option is only available
18836 on the 64-bit HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}.
18840 Use options specific to HP @command{ld}.
18841 This passes @option{-b} to @command{ld} when building
18842 a shared library and passes @option{+Accept TypeMismatch} to @command{ld} on all
18843 links. It is the default when GCC is configured, explicitly or
18844 implicitly, with the HP linker. This option does not affect
18845 which @command{ld} is called; it only changes what parameters are passed to that
18847 The @command{ld} that is called is determined by the @option{--with-ld}
18848 configure option, GCC's program search path, and finally by the user's
18849 @env{PATH}. The linker used by GCC can be printed using @samp{which
18850 `gcc -print-prog-name=ld`}. This option is only available on the 64-bit
18851 HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}.
18854 @opindex mno-long-calls
18855 Generate code that uses long call sequences. This ensures that a call
18856 is always able to reach linker generated stubs. The default is to generate
18857 long calls only when the distance from the call site to the beginning
18858 of the function or translation unit, as the case may be, exceeds a
18859 predefined limit set by the branch type being used. The limits for
18860 normal calls are 7,600,000 and 240,000 bytes, respectively for the
18861 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
18864 Distances are measured from the beginning of functions when using the
18865 @option{-ffunction-sections} option, or when using the @option{-mgas}
18866 and @option{-mno-portable-runtime} options together under HP-UX with
18869 It is normally not desirable to use this option as it degrades
18870 performance. However, it may be useful in large applications,
18871 particularly when partial linking is used to build the application.
18873 The types of long calls used depends on the capabilities of the
18874 assembler and linker, and the type of code being generated. The
18875 impact on systems that support long absolute calls, and long pic
18876 symbol-difference or pc-relative calls should be relatively small.
18877 However, an indirect call is used on 32-bit ELF systems in pic code
18878 and it is quite long.
18880 @item -munix=@var{unix-std}
18882 Generate compiler predefines and select a startfile for the specified
18883 UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95}
18884 and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95}
18885 is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX
18886 11.11 and later. The default values are @samp{93} for HP-UX 10.00,
18887 @samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11
18890 @option{-munix=93} provides the same predefines as GCC 3.3 and 3.4.
18891 @option{-munix=95} provides additional predefines for @code{XOPEN_UNIX}
18892 and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}.
18893 @option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX},
18894 @code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and
18895 @code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}.
18897 It is @emph{important} to note that this option changes the interfaces
18898 for various library routines. It also affects the operational behavior
18899 of the C library. Thus, @emph{extreme} care is needed in using this
18902 Library code that is intended to operate with more than one UNIX
18903 standard must test, set and restore the variable @code{__xpg4_extended_mask}
18904 as appropriate. Most GNU software doesn't provide this capability.
18908 Suppress the generation of link options to search libdld.sl when the
18909 @option{-static} option is specified on HP-UX 10 and later.
18913 The HP-UX implementation of setlocale in libc has a dependency on
18914 libdld.sl. There isn't an archive version of libdld.sl. Thus,
18915 when the @option{-static} option is specified, special link options
18916 are needed to resolve this dependency.
18918 On HP-UX 10 and later, the GCC driver adds the necessary options to
18919 link with libdld.sl when the @option{-static} option is specified.
18920 This causes the resulting binary to be dynamic. On the 64-bit port,
18921 the linkers generate dynamic binaries by default in any case. The
18922 @option{-nolibdld} option can be used to prevent the GCC driver from
18923 adding these link options.
18927 Add support for multithreading with the @dfn{dce thread} library
18928 under HP-UX@. This option sets flags for both the preprocessor and
18932 @node IA-64 Options
18933 @subsection IA-64 Options
18934 @cindex IA-64 Options
18936 These are the @samp{-m} options defined for the Intel IA-64 architecture.
18940 @opindex mbig-endian
18941 Generate code for a big-endian target. This is the default for HP-UX@.
18943 @item -mlittle-endian
18944 @opindex mlittle-endian
18945 Generate code for a little-endian target. This is the default for AIX5
18951 @opindex mno-gnu-as
18952 Generate (or don't) code for the GNU assembler. This is the default.
18953 @c Also, this is the default if the configure option @option{--with-gnu-as}
18959 @opindex mno-gnu-ld
18960 Generate (or don't) code for the GNU linker. This is the default.
18961 @c Also, this is the default if the configure option @option{--with-gnu-ld}
18966 Generate code that does not use a global pointer register. The result
18967 is not position independent code, and violates the IA-64 ABI@.
18969 @item -mvolatile-asm-stop
18970 @itemx -mno-volatile-asm-stop
18971 @opindex mvolatile-asm-stop
18972 @opindex mno-volatile-asm-stop
18973 Generate (or don't) a stop bit immediately before and after volatile asm
18976 @item -mregister-names
18977 @itemx -mno-register-names
18978 @opindex mregister-names
18979 @opindex mno-register-names
18980 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
18981 the stacked registers. This may make assembler output more readable.
18987 Disable (or enable) optimizations that use the small data section. This may
18988 be useful for working around optimizer bugs.
18990 @item -mconstant-gp
18991 @opindex mconstant-gp
18992 Generate code that uses a single constant global pointer value. This is
18993 useful when compiling kernel code.
18997 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
18998 This is useful when compiling firmware code.
19000 @item -minline-float-divide-min-latency
19001 @opindex minline-float-divide-min-latency
19002 Generate code for inline divides of floating-point values
19003 using the minimum latency algorithm.
19005 @item -minline-float-divide-max-throughput
19006 @opindex minline-float-divide-max-throughput
19007 Generate code for inline divides of floating-point values
19008 using the maximum throughput algorithm.
19010 @item -mno-inline-float-divide
19011 @opindex mno-inline-float-divide
19012 Do not generate inline code for divides of floating-point values.
19014 @item -minline-int-divide-min-latency
19015 @opindex minline-int-divide-min-latency
19016 Generate code for inline divides of integer values
19017 using the minimum latency algorithm.
19019 @item -minline-int-divide-max-throughput
19020 @opindex minline-int-divide-max-throughput
19021 Generate code for inline divides of integer values
19022 using the maximum throughput algorithm.
19024 @item -mno-inline-int-divide
19025 @opindex mno-inline-int-divide
19026 Do not generate inline code for divides of integer values.
19028 @item -minline-sqrt-min-latency
19029 @opindex minline-sqrt-min-latency
19030 Generate code for inline square roots
19031 using the minimum latency algorithm.
19033 @item -minline-sqrt-max-throughput
19034 @opindex minline-sqrt-max-throughput
19035 Generate code for inline square roots
19036 using the maximum throughput algorithm.
19038 @item -mno-inline-sqrt
19039 @opindex mno-inline-sqrt
19040 Do not generate inline code for @code{sqrt}.
19043 @itemx -mno-fused-madd
19044 @opindex mfused-madd
19045 @opindex mno-fused-madd
19046 Do (don't) generate code that uses the fused multiply/add or multiply/subtract
19047 instructions. The default is to use these instructions.
19049 @item -mno-dwarf2-asm
19050 @itemx -mdwarf2-asm
19051 @opindex mno-dwarf2-asm
19052 @opindex mdwarf2-asm
19053 Don't (or do) generate assembler code for the DWARF line number debugging
19054 info. This may be useful when not using the GNU assembler.
19056 @item -mearly-stop-bits
19057 @itemx -mno-early-stop-bits
19058 @opindex mearly-stop-bits
19059 @opindex mno-early-stop-bits
19060 Allow stop bits to be placed earlier than immediately preceding the
19061 instruction that triggered the stop bit. This can improve instruction
19062 scheduling, but does not always do so.
19064 @item -mfixed-range=@var{register-range}
19065 @opindex mfixed-range
19066 Generate code treating the given register range as fixed registers.
19067 A fixed register is one that the register allocator cannot use. This is
19068 useful when compiling kernel code. A register range is specified as
19069 two registers separated by a dash. Multiple register ranges can be
19070 specified separated by a comma.
19072 @item -mtls-size=@var{tls-size}
19074 Specify bit size of immediate TLS offsets. Valid values are 14, 22, and
19077 @item -mtune=@var{cpu-type}
19079 Tune the instruction scheduling for a particular CPU, Valid values are
19080 @samp{itanium}, @samp{itanium1}, @samp{merced}, @samp{itanium2},
19081 and @samp{mckinley}.
19087 Generate code for a 32-bit or 64-bit environment.
19088 The 32-bit environment sets int, long and pointer to 32 bits.
19089 The 64-bit environment sets int to 32 bits and long and pointer
19090 to 64 bits. These are HP-UX specific flags.
19092 @item -mno-sched-br-data-spec
19093 @itemx -msched-br-data-spec
19094 @opindex mno-sched-br-data-spec
19095 @opindex msched-br-data-spec
19096 (Dis/En)able data speculative scheduling before reload.
19097 This results in generation of @code{ld.a} instructions and
19098 the corresponding check instructions (@code{ld.c} / @code{chk.a}).
19099 The default setting is disabled.
19101 @item -msched-ar-data-spec
19102 @itemx -mno-sched-ar-data-spec
19103 @opindex msched-ar-data-spec
19104 @opindex mno-sched-ar-data-spec
19105 (En/Dis)able data speculative scheduling after reload.
19106 This results in generation of @code{ld.a} instructions and
19107 the corresponding check instructions (@code{ld.c} / @code{chk.a}).
19108 The default setting is enabled.
19110 @item -mno-sched-control-spec
19111 @itemx -msched-control-spec
19112 @opindex mno-sched-control-spec
19113 @opindex msched-control-spec
19114 (Dis/En)able control speculative scheduling. This feature is
19115 available only during region scheduling (i.e.@: before reload).
19116 This results in generation of the @code{ld.s} instructions and
19117 the corresponding check instructions @code{chk.s}.
19118 The default setting is disabled.
19120 @item -msched-br-in-data-spec
19121 @itemx -mno-sched-br-in-data-spec
19122 @opindex msched-br-in-data-spec
19123 @opindex mno-sched-br-in-data-spec
19124 (En/Dis)able speculative scheduling of the instructions that
19125 are dependent on the data speculative loads before reload.
19126 This is effective only with @option{-msched-br-data-spec} enabled.
19127 The default setting is enabled.
19129 @item -msched-ar-in-data-spec
19130 @itemx -mno-sched-ar-in-data-spec
19131 @opindex msched-ar-in-data-spec
19132 @opindex mno-sched-ar-in-data-spec
19133 (En/Dis)able speculative scheduling of the instructions that
19134 are dependent on the data speculative loads after reload.
19135 This is effective only with @option{-msched-ar-data-spec} enabled.
19136 The default setting is enabled.
19138 @item -msched-in-control-spec
19139 @itemx -mno-sched-in-control-spec
19140 @opindex msched-in-control-spec
19141 @opindex mno-sched-in-control-spec
19142 (En/Dis)able speculative scheduling of the instructions that
19143 are dependent on the control speculative loads.
19144 This is effective only with @option{-msched-control-spec} enabled.
19145 The default setting is enabled.
19147 @item -mno-sched-prefer-non-data-spec-insns
19148 @itemx -msched-prefer-non-data-spec-insns
19149 @opindex mno-sched-prefer-non-data-spec-insns
19150 @opindex msched-prefer-non-data-spec-insns
19151 If enabled, data-speculative instructions are chosen for schedule
19152 only if there are no other choices at the moment. This makes
19153 the use of the data speculation much more conservative.
19154 The default setting is disabled.
19156 @item -mno-sched-prefer-non-control-spec-insns
19157 @itemx -msched-prefer-non-control-spec-insns
19158 @opindex mno-sched-prefer-non-control-spec-insns
19159 @opindex msched-prefer-non-control-spec-insns
19160 If enabled, control-speculative instructions are chosen for schedule
19161 only if there are no other choices at the moment. This makes
19162 the use of the control speculation much more conservative.
19163 The default setting is disabled.
19165 @item -mno-sched-count-spec-in-critical-path
19166 @itemx -msched-count-spec-in-critical-path
19167 @opindex mno-sched-count-spec-in-critical-path
19168 @opindex msched-count-spec-in-critical-path
19169 If enabled, speculative dependencies are considered during
19170 computation of the instructions priorities. This makes the use of the
19171 speculation a bit more conservative.
19172 The default setting is disabled.
19174 @item -msched-spec-ldc
19175 @opindex msched-spec-ldc
19176 Use a simple data speculation check. This option is on by default.
19178 @item -msched-control-spec-ldc
19179 @opindex msched-spec-ldc
19180 Use a simple check for control speculation. This option is on by default.
19182 @item -msched-stop-bits-after-every-cycle
19183 @opindex msched-stop-bits-after-every-cycle
19184 Place a stop bit after every cycle when scheduling. This option is on
19187 @item -msched-fp-mem-deps-zero-cost
19188 @opindex msched-fp-mem-deps-zero-cost
19189 Assume that floating-point stores and loads are not likely to cause a conflict
19190 when placed into the same instruction group. This option is disabled by
19193 @item -msel-sched-dont-check-control-spec
19194 @opindex msel-sched-dont-check-control-spec
19195 Generate checks for control speculation in selective scheduling.
19196 This flag is disabled by default.
19198 @item -msched-max-memory-insns=@var{max-insns}
19199 @opindex msched-max-memory-insns
19200 Limit on the number of memory insns per instruction group, giving lower
19201 priority to subsequent memory insns attempting to schedule in the same
19202 instruction group. Frequently useful to prevent cache bank conflicts.
19203 The default value is 1.
19205 @item -msched-max-memory-insns-hard-limit
19206 @opindex msched-max-memory-insns-hard-limit
19207 Makes the limit specified by @option{msched-max-memory-insns} a hard limit,
19208 disallowing more than that number in an instruction group.
19209 Otherwise, the limit is ``soft'', meaning that non-memory operations
19210 are preferred when the limit is reached, but memory operations may still
19216 @subsection LM32 Options
19217 @cindex LM32 options
19219 These @option{-m} options are defined for the LatticeMico32 architecture:
19222 @item -mbarrel-shift-enabled
19223 @opindex mbarrel-shift-enabled
19224 Enable barrel-shift instructions.
19226 @item -mdivide-enabled
19227 @opindex mdivide-enabled
19228 Enable divide and modulus instructions.
19230 @item -mmultiply-enabled
19231 @opindex multiply-enabled
19232 Enable multiply instructions.
19234 @item -msign-extend-enabled
19235 @opindex msign-extend-enabled
19236 Enable sign extend instructions.
19238 @item -muser-enabled
19239 @opindex muser-enabled
19240 Enable user-defined instructions.
19245 @subsection M32C Options
19246 @cindex M32C options
19249 @item -mcpu=@var{name}
19251 Select the CPU for which code is generated. @var{name} may be one of
19252 @samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to
19253 /60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for
19254 the M32C/80 series.
19258 Specifies that the program will be run on the simulator. This causes
19259 an alternate runtime library to be linked in which supports, for
19260 example, file I/O@. You must not use this option when generating
19261 programs that will run on real hardware; you must provide your own
19262 runtime library for whatever I/O functions are needed.
19264 @item -memregs=@var{number}
19266 Specifies the number of memory-based pseudo-registers GCC uses
19267 during code generation. These pseudo-registers are used like real
19268 registers, so there is a tradeoff between GCC's ability to fit the
19269 code into available registers, and the performance penalty of using
19270 memory instead of registers. Note that all modules in a program must
19271 be compiled with the same value for this option. Because of that, you
19272 must not use this option with GCC's default runtime libraries.
19276 @node M32R/D Options
19277 @subsection M32R/D Options
19278 @cindex M32R/D options
19280 These @option{-m} options are defined for Renesas M32R/D architectures:
19285 Generate code for the M32R/2@.
19289 Generate code for the M32R/X@.
19293 Generate code for the M32R@. This is the default.
19295 @item -mmodel=small
19296 @opindex mmodel=small
19297 Assume all objects live in the lower 16MB of memory (so that their addresses
19298 can be loaded with the @code{ld24} instruction), and assume all subroutines
19299 are reachable with the @code{bl} instruction.
19300 This is the default.
19302 The addressability of a particular object can be set with the
19303 @code{model} attribute.
19305 @item -mmodel=medium
19306 @opindex mmodel=medium
19307 Assume objects may be anywhere in the 32-bit address space (the compiler
19308 generates @code{seth/add3} instructions to load their addresses), and
19309 assume all subroutines are reachable with the @code{bl} instruction.
19311 @item -mmodel=large
19312 @opindex mmodel=large
19313 Assume objects may be anywhere in the 32-bit address space (the compiler
19314 generates @code{seth/add3} instructions to load their addresses), and
19315 assume subroutines may not be reachable with the @code{bl} instruction
19316 (the compiler generates the much slower @code{seth/add3/jl}
19317 instruction sequence).
19320 @opindex msdata=none
19321 Disable use of the small data area. Variables are put into
19322 one of @code{.data}, @code{.bss}, or @code{.rodata} (unless the
19323 @code{section} attribute has been specified).
19324 This is the default.
19326 The small data area consists of sections @code{.sdata} and @code{.sbss}.
19327 Objects may be explicitly put in the small data area with the
19328 @code{section} attribute using one of these sections.
19330 @item -msdata=sdata
19331 @opindex msdata=sdata
19332 Put small global and static data in the small data area, but do not
19333 generate special code to reference them.
19336 @opindex msdata=use
19337 Put small global and static data in the small data area, and generate
19338 special instructions to reference them.
19342 @cindex smaller data references
19343 Put global and static objects less than or equal to @var{num} bytes
19344 into the small data or BSS sections instead of the normal data or BSS
19345 sections. The default value of @var{num} is 8.
19346 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
19347 for this option to have any effect.
19349 All modules should be compiled with the same @option{-G @var{num}} value.
19350 Compiling with different values of @var{num} may or may not work; if it
19351 doesn't the linker gives an error message---incorrect code is not
19356 Makes the M32R-specific code in the compiler display some statistics
19357 that might help in debugging programs.
19359 @item -malign-loops
19360 @opindex malign-loops
19361 Align all loops to a 32-byte boundary.
19363 @item -mno-align-loops
19364 @opindex mno-align-loops
19365 Do not enforce a 32-byte alignment for loops. This is the default.
19367 @item -missue-rate=@var{number}
19368 @opindex missue-rate=@var{number}
19369 Issue @var{number} instructions per cycle. @var{number} can only be 1
19372 @item -mbranch-cost=@var{number}
19373 @opindex mbranch-cost=@var{number}
19374 @var{number} can only be 1 or 2. If it is 1 then branches are
19375 preferred over conditional code, if it is 2, then the opposite applies.
19377 @item -mflush-trap=@var{number}
19378 @opindex mflush-trap=@var{number}
19379 Specifies the trap number to use to flush the cache. The default is
19380 12. Valid numbers are between 0 and 15 inclusive.
19382 @item -mno-flush-trap
19383 @opindex mno-flush-trap
19384 Specifies that the cache cannot be flushed by using a trap.
19386 @item -mflush-func=@var{name}
19387 @opindex mflush-func=@var{name}
19388 Specifies the name of the operating system function to call to flush
19389 the cache. The default is @samp{_flush_cache}, but a function call
19390 is only used if a trap is not available.
19392 @item -mno-flush-func
19393 @opindex mno-flush-func
19394 Indicates that there is no OS function for flushing the cache.
19398 @node M680x0 Options
19399 @subsection M680x0 Options
19400 @cindex M680x0 options
19402 These are the @samp{-m} options defined for M680x0 and ColdFire processors.
19403 The default settings depend on which architecture was selected when
19404 the compiler was configured; the defaults for the most common choices
19408 @item -march=@var{arch}
19410 Generate code for a specific M680x0 or ColdFire instruction set
19411 architecture. Permissible values of @var{arch} for M680x0
19412 architectures are: @samp{68000}, @samp{68010}, @samp{68020},
19413 @samp{68030}, @samp{68040}, @samp{68060} and @samp{cpu32}. ColdFire
19414 architectures are selected according to Freescale's ISA classification
19415 and the permissible values are: @samp{isaa}, @samp{isaaplus},
19416 @samp{isab} and @samp{isac}.
19418 GCC defines a macro @code{__mcf@var{arch}__} whenever it is generating
19419 code for a ColdFire target. The @var{arch} in this macro is one of the
19420 @option{-march} arguments given above.
19422 When used together, @option{-march} and @option{-mtune} select code
19423 that runs on a family of similar processors but that is optimized
19424 for a particular microarchitecture.
19426 @item -mcpu=@var{cpu}
19428 Generate code for a specific M680x0 or ColdFire processor.
19429 The M680x0 @var{cpu}s are: @samp{68000}, @samp{68010}, @samp{68020},
19430 @samp{68030}, @samp{68040}, @samp{68060}, @samp{68302}, @samp{68332}
19431 and @samp{cpu32}. The ColdFire @var{cpu}s are given by the table
19432 below, which also classifies the CPUs into families:
19434 @multitable @columnfractions 0.20 0.80
19435 @item @strong{Family} @tab @strong{@samp{-mcpu} arguments}
19436 @item @samp{51} @tab @samp{51} @samp{51ac} @samp{51ag} @samp{51cn} @samp{51em} @samp{51je} @samp{51jf} @samp{51jg} @samp{51jm} @samp{51mm} @samp{51qe} @samp{51qm}
19437 @item @samp{5206} @tab @samp{5202} @samp{5204} @samp{5206}
19438 @item @samp{5206e} @tab @samp{5206e}
19439 @item @samp{5208} @tab @samp{5207} @samp{5208}
19440 @item @samp{5211a} @tab @samp{5210a} @samp{5211a}
19441 @item @samp{5213} @tab @samp{5211} @samp{5212} @samp{5213}
19442 @item @samp{5216} @tab @samp{5214} @samp{5216}
19443 @item @samp{52235} @tab @samp{52230} @samp{52231} @samp{52232} @samp{52233} @samp{52234} @samp{52235}
19444 @item @samp{5225} @tab @samp{5224} @samp{5225}
19445 @item @samp{52259} @tab @samp{52252} @samp{52254} @samp{52255} @samp{52256} @samp{52258} @samp{52259}
19446 @item @samp{5235} @tab @samp{5232} @samp{5233} @samp{5234} @samp{5235} @samp{523x}
19447 @item @samp{5249} @tab @samp{5249}
19448 @item @samp{5250} @tab @samp{5250}
19449 @item @samp{5271} @tab @samp{5270} @samp{5271}
19450 @item @samp{5272} @tab @samp{5272}
19451 @item @samp{5275} @tab @samp{5274} @samp{5275}
19452 @item @samp{5282} @tab @samp{5280} @samp{5281} @samp{5282} @samp{528x}
19453 @item @samp{53017} @tab @samp{53011} @samp{53012} @samp{53013} @samp{53014} @samp{53015} @samp{53016} @samp{53017}
19454 @item @samp{5307} @tab @samp{5307}
19455 @item @samp{5329} @tab @samp{5327} @samp{5328} @samp{5329} @samp{532x}
19456 @item @samp{5373} @tab @samp{5372} @samp{5373} @samp{537x}
19457 @item @samp{5407} @tab @samp{5407}
19458 @item @samp{5475} @tab @samp{5470} @samp{5471} @samp{5472} @samp{5473} @samp{5474} @samp{5475} @samp{547x} @samp{5480} @samp{5481} @samp{5482} @samp{5483} @samp{5484} @samp{5485}
19461 @option{-mcpu=@var{cpu}} overrides @option{-march=@var{arch}} if
19462 @var{arch} is compatible with @var{cpu}. Other combinations of
19463 @option{-mcpu} and @option{-march} are rejected.
19465 GCC defines the macro @code{__mcf_cpu_@var{cpu}} when ColdFire target
19466 @var{cpu} is selected. It also defines @code{__mcf_family_@var{family}},
19467 where the value of @var{family} is given by the table above.
19469 @item -mtune=@var{tune}
19471 Tune the code for a particular microarchitecture within the
19472 constraints set by @option{-march} and @option{-mcpu}.
19473 The M680x0 microarchitectures are: @samp{68000}, @samp{68010},
19474 @samp{68020}, @samp{68030}, @samp{68040}, @samp{68060}
19475 and @samp{cpu32}. The ColdFire microarchitectures
19476 are: @samp{cfv1}, @samp{cfv2}, @samp{cfv3}, @samp{cfv4} and @samp{cfv4e}.
19478 You can also use @option{-mtune=68020-40} for code that needs
19479 to run relatively well on 68020, 68030 and 68040 targets.
19480 @option{-mtune=68020-60} is similar but includes 68060 targets
19481 as well. These two options select the same tuning decisions as
19482 @option{-m68020-40} and @option{-m68020-60} respectively.
19484 GCC defines the macros @code{__mc@var{arch}} and @code{__mc@var{arch}__}
19485 when tuning for 680x0 architecture @var{arch}. It also defines
19486 @code{mc@var{arch}} unless either @option{-ansi} or a non-GNU @option{-std}
19487 option is used. If GCC is tuning for a range of architectures,
19488 as selected by @option{-mtune=68020-40} or @option{-mtune=68020-60},
19489 it defines the macros for every architecture in the range.
19491 GCC also defines the macro @code{__m@var{uarch}__} when tuning for
19492 ColdFire microarchitecture @var{uarch}, where @var{uarch} is one
19493 of the arguments given above.
19499 Generate output for a 68000. This is the default
19500 when the compiler is configured for 68000-based systems.
19501 It is equivalent to @option{-march=68000}.
19503 Use this option for microcontrollers with a 68000 or EC000 core,
19504 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
19508 Generate output for a 68010. This is the default
19509 when the compiler is configured for 68010-based systems.
19510 It is equivalent to @option{-march=68010}.
19516 Generate output for a 68020. This is the default
19517 when the compiler is configured for 68020-based systems.
19518 It is equivalent to @option{-march=68020}.
19522 Generate output for a 68030. This is the default when the compiler is
19523 configured for 68030-based systems. It is equivalent to
19524 @option{-march=68030}.
19528 Generate output for a 68040. This is the default when the compiler is
19529 configured for 68040-based systems. It is equivalent to
19530 @option{-march=68040}.
19532 This option inhibits the use of 68881/68882 instructions that have to be
19533 emulated by software on the 68040. Use this option if your 68040 does not
19534 have code to emulate those instructions.
19538 Generate output for a 68060. This is the default when the compiler is
19539 configured for 68060-based systems. It is equivalent to
19540 @option{-march=68060}.
19542 This option inhibits the use of 68020 and 68881/68882 instructions that
19543 have to be emulated by software on the 68060. Use this option if your 68060
19544 does not have code to emulate those instructions.
19548 Generate output for a CPU32. This is the default
19549 when the compiler is configured for CPU32-based systems.
19550 It is equivalent to @option{-march=cpu32}.
19552 Use this option for microcontrollers with a
19553 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
19554 68336, 68340, 68341, 68349 and 68360.
19558 Generate output for a 520X ColdFire CPU@. This is the default
19559 when the compiler is configured for 520X-based systems.
19560 It is equivalent to @option{-mcpu=5206}, and is now deprecated
19561 in favor of that option.
19563 Use this option for microcontroller with a 5200 core, including
19564 the MCF5202, MCF5203, MCF5204 and MCF5206.
19568 Generate output for a 5206e ColdFire CPU@. The option is now
19569 deprecated in favor of the equivalent @option{-mcpu=5206e}.
19573 Generate output for a member of the ColdFire 528X family.
19574 The option is now deprecated in favor of the equivalent
19575 @option{-mcpu=528x}.
19579 Generate output for a ColdFire 5307 CPU@. The option is now deprecated
19580 in favor of the equivalent @option{-mcpu=5307}.
19584 Generate output for a ColdFire 5407 CPU@. The option is now deprecated
19585 in favor of the equivalent @option{-mcpu=5407}.
19589 Generate output for a ColdFire V4e family CPU (e.g.@: 547x/548x).
19590 This includes use of hardware floating-point instructions.
19591 The option is equivalent to @option{-mcpu=547x}, and is now
19592 deprecated in favor of that option.
19596 Generate output for a 68040, without using any of the new instructions.
19597 This results in code that can run relatively efficiently on either a
19598 68020/68881 or a 68030 or a 68040. The generated code does use the
19599 68881 instructions that are emulated on the 68040.
19601 The option is equivalent to @option{-march=68020} @option{-mtune=68020-40}.
19605 Generate output for a 68060, without using any of the new instructions.
19606 This results in code that can run relatively efficiently on either a
19607 68020/68881 or a 68030 or a 68040. The generated code does use the
19608 68881 instructions that are emulated on the 68060.
19610 The option is equivalent to @option{-march=68020} @option{-mtune=68020-60}.
19614 @opindex mhard-float
19616 Generate floating-point instructions. This is the default for 68020
19617 and above, and for ColdFire devices that have an FPU@. It defines the
19618 macro @code{__HAVE_68881__} on M680x0 targets and @code{__mcffpu__}
19619 on ColdFire targets.
19622 @opindex msoft-float
19623 Do not generate floating-point instructions; use library calls instead.
19624 This is the default for 68000, 68010, and 68832 targets. It is also
19625 the default for ColdFire devices that have no FPU.
19631 Generate (do not generate) ColdFire hardware divide and remainder
19632 instructions. If @option{-march} is used without @option{-mcpu},
19633 the default is ``on'' for ColdFire architectures and ``off'' for M680x0
19634 architectures. Otherwise, the default is taken from the target CPU
19635 (either the default CPU, or the one specified by @option{-mcpu}). For
19636 example, the default is ``off'' for @option{-mcpu=5206} and ``on'' for
19637 @option{-mcpu=5206e}.
19639 GCC defines the macro @code{__mcfhwdiv__} when this option is enabled.
19643 Consider type @code{int} to be 16 bits wide, like @code{short int}.
19644 Additionally, parameters passed on the stack are also aligned to a
19645 16-bit boundary even on targets whose API mandates promotion to 32-bit.
19649 Do not consider type @code{int} to be 16 bits wide. This is the default.
19652 @itemx -mno-bitfield
19653 @opindex mnobitfield
19654 @opindex mno-bitfield
19655 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
19656 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
19660 Do use the bit-field instructions. The @option{-m68020} option implies
19661 @option{-mbitfield}. This is the default if you use a configuration
19662 designed for a 68020.
19666 Use a different function-calling convention, in which functions
19667 that take a fixed number of arguments return with the @code{rtd}
19668 instruction, which pops their arguments while returning. This
19669 saves one instruction in the caller since there is no need to pop
19670 the arguments there.
19672 This calling convention is incompatible with the one normally
19673 used on Unix, so you cannot use it if you need to call libraries
19674 compiled with the Unix compiler.
19676 Also, you must provide function prototypes for all functions that
19677 take variable numbers of arguments (including @code{printf});
19678 otherwise incorrect code is generated for calls to those
19681 In addition, seriously incorrect code results if you call a
19682 function with too many arguments. (Normally, extra arguments are
19683 harmlessly ignored.)
19685 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
19686 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
19690 Do not use the calling conventions selected by @option{-mrtd}.
19691 This is the default.
19694 @itemx -mno-align-int
19695 @opindex malign-int
19696 @opindex mno-align-int
19697 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
19698 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
19699 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
19700 Aligning variables on 32-bit boundaries produces code that runs somewhat
19701 faster on processors with 32-bit busses at the expense of more memory.
19703 @strong{Warning:} if you use the @option{-malign-int} switch, GCC
19704 aligns structures containing the above types differently than
19705 most published application binary interface specifications for the m68k.
19709 Use the pc-relative addressing mode of the 68000 directly, instead of
19710 using a global offset table. At present, this option implies @option{-fpic},
19711 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
19712 not presently supported with @option{-mpcrel}, though this could be supported for
19713 68020 and higher processors.
19715 @item -mno-strict-align
19716 @itemx -mstrict-align
19717 @opindex mno-strict-align
19718 @opindex mstrict-align
19719 Do not (do) assume that unaligned memory references are handled by
19723 Generate code that allows the data segment to be located in a different
19724 area of memory from the text segment. This allows for execute-in-place in
19725 an environment without virtual memory management. This option implies
19728 @item -mno-sep-data
19729 Generate code that assumes that the data segment follows the text segment.
19730 This is the default.
19732 @item -mid-shared-library
19733 Generate code that supports shared libraries via the library ID method.
19734 This allows for execute-in-place and shared libraries in an environment
19735 without virtual memory management. This option implies @option{-fPIC}.
19737 @item -mno-id-shared-library
19738 Generate code that doesn't assume ID-based shared libraries are being used.
19739 This is the default.
19741 @item -mshared-library-id=n
19742 Specifies the identification number of the ID-based shared library being
19743 compiled. Specifying a value of 0 generates more compact code; specifying
19744 other values forces the allocation of that number to the current
19745 library, but is no more space- or time-efficient than omitting this option.
19751 When generating position-independent code for ColdFire, generate code
19752 that works if the GOT has more than 8192 entries. This code is
19753 larger and slower than code generated without this option. On M680x0
19754 processors, this option is not needed; @option{-fPIC} suffices.
19756 GCC normally uses a single instruction to load values from the GOT@.
19757 While this is relatively efficient, it only works if the GOT
19758 is smaller than about 64k. Anything larger causes the linker
19759 to report an error such as:
19761 @cindex relocation truncated to fit (ColdFire)
19763 relocation truncated to fit: R_68K_GOT16O foobar
19766 If this happens, you should recompile your code with @option{-mxgot}.
19767 It should then work with very large GOTs. However, code generated with
19768 @option{-mxgot} is less efficient, since it takes 4 instructions to fetch
19769 the value of a global symbol.
19771 Note that some linkers, including newer versions of the GNU linker,
19772 can create multiple GOTs and sort GOT entries. If you have such a linker,
19773 you should only need to use @option{-mxgot} when compiling a single
19774 object file that accesses more than 8192 GOT entries. Very few do.
19776 These options have no effect unless GCC is generating
19777 position-independent code.
19779 @item -mlong-jump-table-offsets
19780 @opindex mlong-jump-table-offsets
19781 Use 32-bit offsets in @code{switch} tables. The default is to use
19786 @node MCore Options
19787 @subsection MCore Options
19788 @cindex MCore options
19790 These are the @samp{-m} options defined for the Motorola M*Core
19796 @itemx -mno-hardlit
19798 @opindex mno-hardlit
19799 Inline constants into the code stream if it can be done in two
19800 instructions or less.
19806 Use the divide instruction. (Enabled by default).
19808 @item -mrelax-immediate
19809 @itemx -mno-relax-immediate
19810 @opindex mrelax-immediate
19811 @opindex mno-relax-immediate
19812 Allow arbitrary-sized immediates in bit operations.
19814 @item -mwide-bitfields
19815 @itemx -mno-wide-bitfields
19816 @opindex mwide-bitfields
19817 @opindex mno-wide-bitfields
19818 Always treat bit-fields as @code{int}-sized.
19820 @item -m4byte-functions
19821 @itemx -mno-4byte-functions
19822 @opindex m4byte-functions
19823 @opindex mno-4byte-functions
19824 Force all functions to be aligned to a 4-byte boundary.
19826 @item -mcallgraph-data
19827 @itemx -mno-callgraph-data
19828 @opindex mcallgraph-data
19829 @opindex mno-callgraph-data
19830 Emit callgraph information.
19833 @itemx -mno-slow-bytes
19834 @opindex mslow-bytes
19835 @opindex mno-slow-bytes
19836 Prefer word access when reading byte quantities.
19838 @item -mlittle-endian
19839 @itemx -mbig-endian
19840 @opindex mlittle-endian
19841 @opindex mbig-endian
19842 Generate code for a little-endian target.
19848 Generate code for the 210 processor.
19852 Assume that runtime support has been provided and so omit the
19853 simulator library (@file{libsim.a)} from the linker command line.
19855 @item -mstack-increment=@var{size}
19856 @opindex mstack-increment
19857 Set the maximum amount for a single stack increment operation. Large
19858 values can increase the speed of programs that contain functions
19859 that need a large amount of stack space, but they can also trigger a
19860 segmentation fault if the stack is extended too much. The default
19866 @subsection MeP Options
19867 @cindex MeP options
19873 Enables the @code{abs} instruction, which is the absolute difference
19874 between two registers.
19878 Enables all the optional instructions---average, multiply, divide, bit
19879 operations, leading zero, absolute difference, min/max, clip, and
19885 Enables the @code{ave} instruction, which computes the average of two
19888 @item -mbased=@var{n}
19890 Variables of size @var{n} bytes or smaller are placed in the
19891 @code{.based} section by default. Based variables use the @code{$tp}
19892 register as a base register, and there is a 128-byte limit to the
19893 @code{.based} section.
19897 Enables the bit operation instructions---bit test (@code{btstm}), set
19898 (@code{bsetm}), clear (@code{bclrm}), invert (@code{bnotm}), and
19899 test-and-set (@code{tas}).
19901 @item -mc=@var{name}
19903 Selects which section constant data is placed in. @var{name} may
19904 be @samp{tiny}, @samp{near}, or @samp{far}.
19908 Enables the @code{clip} instruction. Note that @option{-mclip} is not
19909 useful unless you also provide @option{-mminmax}.
19911 @item -mconfig=@var{name}
19913 Selects one of the built-in core configurations. Each MeP chip has
19914 one or more modules in it; each module has a core CPU and a variety of
19915 coprocessors, optional instructions, and peripherals. The
19916 @code{MeP-Integrator} tool, not part of GCC, provides these
19917 configurations through this option; using this option is the same as
19918 using all the corresponding command-line options. The default
19919 configuration is @samp{default}.
19923 Enables the coprocessor instructions. By default, this is a 32-bit
19924 coprocessor. Note that the coprocessor is normally enabled via the
19925 @option{-mconfig=} option.
19929 Enables the 32-bit coprocessor's instructions.
19933 Enables the 64-bit coprocessor's instructions.
19937 Enables IVC2 scheduling. IVC2 is a 64-bit VLIW coprocessor.
19941 Causes constant variables to be placed in the @code{.near} section.
19945 Enables the @code{div} and @code{divu} instructions.
19949 Generate big-endian code.
19953 Generate little-endian code.
19955 @item -mio-volatile
19956 @opindex mio-volatile
19957 Tells the compiler that any variable marked with the @code{io}
19958 attribute is to be considered volatile.
19962 Causes variables to be assigned to the @code{.far} section by default.
19966 Enables the @code{leadz} (leading zero) instruction.
19970 Causes variables to be assigned to the @code{.near} section by default.
19974 Enables the @code{min} and @code{max} instructions.
19978 Enables the multiplication and multiply-accumulate instructions.
19982 Disables all the optional instructions enabled by @option{-mall-opts}.
19986 Enables the @code{repeat} and @code{erepeat} instructions, used for
19987 low-overhead looping.
19991 Causes all variables to default to the @code{.tiny} section. Note
19992 that there is a 65536-byte limit to this section. Accesses to these
19993 variables use the @code{%gp} base register.
19997 Enables the saturation instructions. Note that the compiler does not
19998 currently generate these itself, but this option is included for
19999 compatibility with other tools, like @code{as}.
20003 Link the SDRAM-based runtime instead of the default ROM-based runtime.
20007 Link the simulator run-time libraries.
20011 Link the simulator runtime libraries, excluding built-in support
20012 for reset and exception vectors and tables.
20016 Causes all functions to default to the @code{.far} section. Without
20017 this option, functions default to the @code{.near} section.
20019 @item -mtiny=@var{n}
20021 Variables that are @var{n} bytes or smaller are allocated to the
20022 @code{.tiny} section. These variables use the @code{$gp} base
20023 register. The default for this option is 4, but note that there's a
20024 65536-byte limit to the @code{.tiny} section.
20028 @node MicroBlaze Options
20029 @subsection MicroBlaze Options
20030 @cindex MicroBlaze Options
20035 @opindex msoft-float
20036 Use software emulation for floating point (default).
20039 @opindex mhard-float
20040 Use hardware floating-point instructions.
20044 Do not optimize block moves, use @code{memcpy}.
20046 @item -mno-clearbss
20047 @opindex mno-clearbss
20048 This option is deprecated. Use @option{-fno-zero-initialized-in-bss} instead.
20050 @item -mcpu=@var{cpu-type}
20052 Use features of, and schedule code for, the given CPU.
20053 Supported values are in the format @samp{v@var{X}.@var{YY}.@var{Z}},
20054 where @var{X} is a major version, @var{YY} is the minor version, and
20055 @var{Z} is compatibility code. Example values are @samp{v3.00.a},
20056 @samp{v4.00.b}, @samp{v5.00.a}, @samp{v5.00.b}, @samp{v5.00.b}, @samp{v6.00.a}.
20058 @item -mxl-soft-mul
20059 @opindex mxl-soft-mul
20060 Use software multiply emulation (default).
20062 @item -mxl-soft-div
20063 @opindex mxl-soft-div
20064 Use software emulation for divides (default).
20066 @item -mxl-barrel-shift
20067 @opindex mxl-barrel-shift
20068 Use the hardware barrel shifter.
20070 @item -mxl-pattern-compare
20071 @opindex mxl-pattern-compare
20072 Use pattern compare instructions.
20074 @item -msmall-divides
20075 @opindex msmall-divides
20076 Use table lookup optimization for small signed integer divisions.
20078 @item -mxl-stack-check
20079 @opindex mxl-stack-check
20080 This option is deprecated. Use @option{-fstack-check} instead.
20083 @opindex mxl-gp-opt
20084 Use GP-relative @code{.sdata}/@code{.sbss} sections.
20086 @item -mxl-multiply-high
20087 @opindex mxl-multiply-high
20088 Use multiply high instructions for high part of 32x32 multiply.
20090 @item -mxl-float-convert
20091 @opindex mxl-float-convert
20092 Use hardware floating-point conversion instructions.
20094 @item -mxl-float-sqrt
20095 @opindex mxl-float-sqrt
20096 Use hardware floating-point square root instruction.
20099 @opindex mbig-endian
20100 Generate code for a big-endian target.
20102 @item -mlittle-endian
20103 @opindex mlittle-endian
20104 Generate code for a little-endian target.
20107 @opindex mxl-reorder
20108 Use reorder instructions (swap and byte reversed load/store).
20110 @item -mxl-mode-@var{app-model}
20111 Select application model @var{app-model}. Valid models are
20114 normal executable (default), uses startup code @file{crt0.o}.
20117 for use with Xilinx Microprocessor Debugger (XMD) based
20118 software intrusive debug agent called xmdstub. This uses startup file
20119 @file{crt1.o} and sets the start address of the program to 0x800.
20122 for applications that are loaded using a bootloader.
20123 This model uses startup file @file{crt2.o} which does not contain a processor
20124 reset vector handler. This is suitable for transferring control on a
20125 processor reset to the bootloader rather than the application.
20128 for applications that do not require any of the
20129 MicroBlaze vectors. This option may be useful for applications running
20130 within a monitoring application. This model uses @file{crt3.o} as a startup file.
20133 Option @option{-xl-mode-@var{app-model}} is a deprecated alias for
20134 @option{-mxl-mode-@var{app-model}}.
20139 @subsection MIPS Options
20140 @cindex MIPS options
20146 Generate big-endian code.
20150 Generate little-endian code. This is the default for @samp{mips*el-*-*}
20153 @item -march=@var{arch}
20155 Generate code that runs on @var{arch}, which can be the name of a
20156 generic MIPS ISA, or the name of a particular processor.
20158 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
20159 @samp{mips32}, @samp{mips32r2}, @samp{mips32r3}, @samp{mips32r5},
20160 @samp{mips32r6}, @samp{mips64}, @samp{mips64r2}, @samp{mips64r3},
20161 @samp{mips64r5} and @samp{mips64r6}.
20162 The processor names are:
20163 @samp{4kc}, @samp{4km}, @samp{4kp}, @samp{4ksc},
20164 @samp{4kec}, @samp{4kem}, @samp{4kep}, @samp{4ksd},
20165 @samp{5kc}, @samp{5kf},
20167 @samp{24kc}, @samp{24kf2_1}, @samp{24kf1_1},
20168 @samp{24kec}, @samp{24kef2_1}, @samp{24kef1_1},
20169 @samp{34kc}, @samp{34kf2_1}, @samp{34kf1_1}, @samp{34kn},
20170 @samp{74kc}, @samp{74kf2_1}, @samp{74kf1_1}, @samp{74kf3_2},
20171 @samp{1004kc}, @samp{1004kf2_1}, @samp{1004kf1_1},
20174 @samp{loongson2e}, @samp{loongson2f}, @samp{loongson3a},
20176 @samp{m14k}, @samp{m14kc}, @samp{m14ke}, @samp{m14kec},
20177 @samp{m5100}, @samp{m5101},
20178 @samp{octeon}, @samp{octeon+}, @samp{octeon2}, @samp{octeon3},
20181 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
20182 @samp{r4600}, @samp{r4650}, @samp{r4700}, @samp{r6000}, @samp{r8000},
20183 @samp{rm7000}, @samp{rm9000},
20184 @samp{r10000}, @samp{r12000}, @samp{r14000}, @samp{r16000},
20187 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300},
20188 @samp{vr5000}, @samp{vr5400}, @samp{vr5500},
20189 @samp{xlr} and @samp{xlp}.
20190 The special value @samp{from-abi} selects the
20191 most compatible architecture for the selected ABI (that is,
20192 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
20194 The native Linux/GNU toolchain also supports the value @samp{native},
20195 which selects the best architecture option for the host processor.
20196 @option{-march=native} has no effect if GCC does not recognize
20199 In processor names, a final @samp{000} can be abbreviated as @samp{k}
20200 (for example, @option{-march=r2k}). Prefixes are optional, and
20201 @samp{vr} may be written @samp{r}.
20203 Names of the form @samp{@var{n}f2_1} refer to processors with
20204 FPUs clocked at half the rate of the core, names of the form
20205 @samp{@var{n}f1_1} refer to processors with FPUs clocked at the same
20206 rate as the core, and names of the form @samp{@var{n}f3_2} refer to
20207 processors with FPUs clocked a ratio of 3:2 with respect to the core.
20208 For compatibility reasons, @samp{@var{n}f} is accepted as a synonym
20209 for @samp{@var{n}f2_1} while @samp{@var{n}x} and @samp{@var{b}fx} are
20210 accepted as synonyms for @samp{@var{n}f1_1}.
20212 GCC defines two macros based on the value of this option. The first
20213 is @code{_MIPS_ARCH}, which gives the name of target architecture, as
20214 a string. The second has the form @code{_MIPS_ARCH_@var{foo}},
20215 where @var{foo} is the capitalized value of @code{_MIPS_ARCH}@.
20216 For example, @option{-march=r2000} sets @code{_MIPS_ARCH}
20217 to @code{"r2000"} and defines the macro @code{_MIPS_ARCH_R2000}.
20219 Note that the @code{_MIPS_ARCH} macro uses the processor names given
20220 above. In other words, it has the full prefix and does not
20221 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
20222 the macro names the resolved architecture (either @code{"mips1"} or
20223 @code{"mips3"}). It names the default architecture when no
20224 @option{-march} option is given.
20226 @item -mtune=@var{arch}
20228 Optimize for @var{arch}. Among other things, this option controls
20229 the way instructions are scheduled, and the perceived cost of arithmetic
20230 operations. The list of @var{arch} values is the same as for
20233 When this option is not used, GCC optimizes for the processor
20234 specified by @option{-march}. By using @option{-march} and
20235 @option{-mtune} together, it is possible to generate code that
20236 runs on a family of processors, but optimize the code for one
20237 particular member of that family.
20239 @option{-mtune} defines the macros @code{_MIPS_TUNE} and
20240 @code{_MIPS_TUNE_@var{foo}}, which work in the same way as the
20241 @option{-march} ones described above.
20245 Equivalent to @option{-march=mips1}.
20249 Equivalent to @option{-march=mips2}.
20253 Equivalent to @option{-march=mips3}.
20257 Equivalent to @option{-march=mips4}.
20261 Equivalent to @option{-march=mips32}.
20265 Equivalent to @option{-march=mips32r3}.
20269 Equivalent to @option{-march=mips32r5}.
20273 Equivalent to @option{-march=mips32r6}.
20277 Equivalent to @option{-march=mips64}.
20281 Equivalent to @option{-march=mips64r2}.
20285 Equivalent to @option{-march=mips64r3}.
20289 Equivalent to @option{-march=mips64r5}.
20293 Equivalent to @option{-march=mips64r6}.
20298 @opindex mno-mips16
20299 Generate (do not generate) MIPS16 code. If GCC is targeting a
20300 MIPS32 or MIPS64 architecture, it makes use of the MIPS16e ASE@.
20302 MIPS16 code generation can also be controlled on a per-function basis
20303 by means of @code{mips16} and @code{nomips16} attributes.
20304 @xref{Function Attributes}, for more information.
20306 @item -mflip-mips16
20307 @opindex mflip-mips16
20308 Generate MIPS16 code on alternating functions. This option is provided
20309 for regression testing of mixed MIPS16/non-MIPS16 code generation, and is
20310 not intended for ordinary use in compiling user code.
20312 @item -minterlink-compressed
20313 @itemx -mno-interlink-compressed
20314 @opindex minterlink-compressed
20315 @opindex mno-interlink-compressed
20316 Require (do not require) that code using the standard (uncompressed) MIPS ISA
20317 be link-compatible with MIPS16 and microMIPS code, and vice versa.
20319 For example, code using the standard ISA encoding cannot jump directly
20320 to MIPS16 or microMIPS code; it must either use a call or an indirect jump.
20321 @option{-minterlink-compressed} therefore disables direct jumps unless GCC
20322 knows that the target of the jump is not compressed.
20324 @item -minterlink-mips16
20325 @itemx -mno-interlink-mips16
20326 @opindex minterlink-mips16
20327 @opindex mno-interlink-mips16
20328 Aliases of @option{-minterlink-compressed} and
20329 @option{-mno-interlink-compressed}. These options predate the microMIPS ASE
20330 and are retained for backwards compatibility.
20342 Generate code for the given ABI@.
20344 Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
20345 generates 64-bit code when you select a 64-bit architecture, but you
20346 can use @option{-mgp32} to get 32-bit code instead.
20348 For information about the O64 ABI, see
20349 @uref{http://gcc.gnu.org/@/projects/@/mipso64-abi.html}.
20351 GCC supports a variant of the o32 ABI in which floating-point registers
20352 are 64 rather than 32 bits wide. You can select this combination with
20353 @option{-mabi=32} @option{-mfp64}. This ABI relies on the @code{mthc1}
20354 and @code{mfhc1} instructions and is therefore only supported for
20355 MIPS32R2, MIPS32R3 and MIPS32R5 processors.
20357 The register assignments for arguments and return values remain the
20358 same, but each scalar value is passed in a single 64-bit register
20359 rather than a pair of 32-bit registers. For example, scalar
20360 floating-point values are returned in @samp{$f0} only, not a
20361 @samp{$f0}/@samp{$f1} pair. The set of call-saved registers also
20362 remains the same in that the even-numbered double-precision registers
20365 Two additional variants of the o32 ABI are supported to enable
20366 a transition from 32-bit to 64-bit registers. These are FPXX
20367 (@option{-mfpxx}) and FP64A (@option{-mfp64} @option{-mno-odd-spreg}).
20368 The FPXX extension mandates that all code must execute correctly
20369 when run using 32-bit or 64-bit registers. The code can be interlinked
20370 with either FP32 or FP64, but not both.
20371 The FP64A extension is similar to the FP64 extension but forbids the
20372 use of odd-numbered single-precision registers. This can be used
20373 in conjunction with the @code{FRE} mode of FPUs in MIPS32R5
20374 processors and allows both FP32 and FP64A code to interlink and
20375 run in the same process without changing FPU modes.
20378 @itemx -mno-abicalls
20380 @opindex mno-abicalls
20381 Generate (do not generate) code that is suitable for SVR4-style
20382 dynamic objects. @option{-mabicalls} is the default for SVR4-based
20387 Generate (do not generate) code that is fully position-independent,
20388 and that can therefore be linked into shared libraries. This option
20389 only affects @option{-mabicalls}.
20391 All @option{-mabicalls} code has traditionally been position-independent,
20392 regardless of options like @option{-fPIC} and @option{-fpic}. However,
20393 as an extension, the GNU toolchain allows executables to use absolute
20394 accesses for locally-binding symbols. It can also use shorter GP
20395 initialization sequences and generate direct calls to locally-defined
20396 functions. This mode is selected by @option{-mno-shared}.
20398 @option{-mno-shared} depends on binutils 2.16 or higher and generates
20399 objects that can only be linked by the GNU linker. However, the option
20400 does not affect the ABI of the final executable; it only affects the ABI
20401 of relocatable objects. Using @option{-mno-shared} generally makes
20402 executables both smaller and quicker.
20404 @option{-mshared} is the default.
20410 Assume (do not assume) that the static and dynamic linkers
20411 support PLTs and copy relocations. This option only affects
20412 @option{-mno-shared -mabicalls}. For the n64 ABI, this option
20413 has no effect without @option{-msym32}.
20415 You can make @option{-mplt} the default by configuring
20416 GCC with @option{--with-mips-plt}. The default is
20417 @option{-mno-plt} otherwise.
20423 Lift (do not lift) the usual restrictions on the size of the global
20426 GCC normally uses a single instruction to load values from the GOT@.
20427 While this is relatively efficient, it only works if the GOT
20428 is smaller than about 64k. Anything larger causes the linker
20429 to report an error such as:
20431 @cindex relocation truncated to fit (MIPS)
20433 relocation truncated to fit: R_MIPS_GOT16 foobar
20436 If this happens, you should recompile your code with @option{-mxgot}.
20437 This works with very large GOTs, although the code is also
20438 less efficient, since it takes three instructions to fetch the
20439 value of a global symbol.
20441 Note that some linkers can create multiple GOTs. If you have such a
20442 linker, you should only need to use @option{-mxgot} when a single object
20443 file accesses more than 64k's worth of GOT entries. Very few do.
20445 These options have no effect unless GCC is generating position
20450 Assume that general-purpose registers are 32 bits wide.
20454 Assume that general-purpose registers are 64 bits wide.
20458 Assume that floating-point registers are 32 bits wide.
20462 Assume that floating-point registers are 64 bits wide.
20466 Do not assume the width of floating-point registers.
20469 @opindex mhard-float
20470 Use floating-point coprocessor instructions.
20473 @opindex msoft-float
20474 Do not use floating-point coprocessor instructions. Implement
20475 floating-point calculations using library calls instead.
20479 Equivalent to @option{-msoft-float}, but additionally asserts that the
20480 program being compiled does not perform any floating-point operations.
20481 This option is presently supported only by some bare-metal MIPS
20482 configurations, where it may select a special set of libraries
20483 that lack all floating-point support (including, for example, the
20484 floating-point @code{printf} formats).
20485 If code compiled with @option{-mno-float} accidentally contains
20486 floating-point operations, it is likely to suffer a link-time
20487 or run-time failure.
20489 @item -msingle-float
20490 @opindex msingle-float
20491 Assume that the floating-point coprocessor only supports single-precision
20494 @item -mdouble-float
20495 @opindex mdouble-float
20496 Assume that the floating-point coprocessor supports double-precision
20497 operations. This is the default.
20500 @itemx -mno-odd-spreg
20501 @opindex modd-spreg
20502 @opindex mno-odd-spreg
20503 Enable the use of odd-numbered single-precision floating-point registers
20504 for the o32 ABI. This is the default for processors that are known to
20505 support these registers. When using the o32 FPXX ABI, @option{-mno-odd-spreg}
20509 @itemx -mabs=legacy
20511 @opindex mabs=legacy
20512 These options control the treatment of the special not-a-number (NaN)
20513 IEEE 754 floating-point data with the @code{abs.@i{fmt}} and
20514 @code{neg.@i{fmt}} machine instructions.
20516 By default or when @option{-mabs=legacy} is used the legacy
20517 treatment is selected. In this case these instructions are considered
20518 arithmetic and avoided where correct operation is required and the
20519 input operand might be a NaN. A longer sequence of instructions that
20520 manipulate the sign bit of floating-point datum manually is used
20521 instead unless the @option{-ffinite-math-only} option has also been
20524 The @option{-mabs=2008} option selects the IEEE 754-2008 treatment. In
20525 this case these instructions are considered non-arithmetic and therefore
20526 operating correctly in all cases, including in particular where the
20527 input operand is a NaN. These instructions are therefore always used
20528 for the respective operations.
20531 @itemx -mnan=legacy
20533 @opindex mnan=legacy
20534 These options control the encoding of the special not-a-number (NaN)
20535 IEEE 754 floating-point data.
20537 The @option{-mnan=legacy} option selects the legacy encoding. In this
20538 case quiet NaNs (qNaNs) are denoted by the first bit of their trailing
20539 significand field being 0, whereas signaling NaNs (sNaNs) are denoted
20540 by the first bit of their trailing significand field being 1.
20542 The @option{-mnan=2008} option selects the IEEE 754-2008 encoding. In
20543 this case qNaNs are denoted by the first bit of their trailing
20544 significand field being 1, whereas sNaNs are denoted by the first bit of
20545 their trailing significand field being 0.
20547 The default is @option{-mnan=legacy} unless GCC has been configured with
20548 @option{--with-nan=2008}.
20554 Use (do not use) @samp{ll}, @samp{sc}, and @samp{sync} instructions to
20555 implement atomic memory built-in functions. When neither option is
20556 specified, GCC uses the instructions if the target architecture
20559 @option{-mllsc} is useful if the runtime environment can emulate the
20560 instructions and @option{-mno-llsc} can be useful when compiling for
20561 nonstandard ISAs. You can make either option the default by
20562 configuring GCC with @option{--with-llsc} and @option{--without-llsc}
20563 respectively. @option{--with-llsc} is the default for some
20564 configurations; see the installation documentation for details.
20570 Use (do not use) revision 1 of the MIPS DSP ASE@.
20571 @xref{MIPS DSP Built-in Functions}. This option defines the
20572 preprocessor macro @code{__mips_dsp}. It also defines
20573 @code{__mips_dsp_rev} to 1.
20579 Use (do not use) revision 2 of the MIPS DSP ASE@.
20580 @xref{MIPS DSP Built-in Functions}. This option defines the
20581 preprocessor macros @code{__mips_dsp} and @code{__mips_dspr2}.
20582 It also defines @code{__mips_dsp_rev} to 2.
20585 @itemx -mno-smartmips
20586 @opindex msmartmips
20587 @opindex mno-smartmips
20588 Use (do not use) the MIPS SmartMIPS ASE.
20590 @item -mpaired-single
20591 @itemx -mno-paired-single
20592 @opindex mpaired-single
20593 @opindex mno-paired-single
20594 Use (do not use) paired-single floating-point instructions.
20595 @xref{MIPS Paired-Single Support}. This option requires
20596 hardware floating-point support to be enabled.
20602 Use (do not use) MIPS Digital Media Extension instructions.
20603 This option can only be used when generating 64-bit code and requires
20604 hardware floating-point support to be enabled.
20609 @opindex mno-mips3d
20610 Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}.
20611 The option @option{-mips3d} implies @option{-mpaired-single}.
20614 @itemx -mno-micromips
20615 @opindex mmicromips
20616 @opindex mno-mmicromips
20617 Generate (do not generate) microMIPS code.
20619 MicroMIPS code generation can also be controlled on a per-function basis
20620 by means of @code{micromips} and @code{nomicromips} attributes.
20621 @xref{Function Attributes}, for more information.
20627 Use (do not use) MT Multithreading instructions.
20633 Use (do not use) the MIPS MCU ASE instructions.
20639 Use (do not use) the MIPS Enhanced Virtual Addressing instructions.
20645 Use (do not use) the MIPS Virtualization (VZ) instructions.
20651 Use (do not use) the MIPS eXtended Physical Address (XPA) instructions.
20655 Force @code{long} types to be 64 bits wide. See @option{-mlong32} for
20656 an explanation of the default and the way that the pointer size is
20661 Force @code{long}, @code{int}, and pointer types to be 32 bits wide.
20663 The default size of @code{int}s, @code{long}s and pointers depends on
20664 the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI
20665 uses 64-bit @code{long}s, as does the 64-bit EABI; the others use
20666 32-bit @code{long}s. Pointers are the same size as @code{long}s,
20667 or the same size as integer registers, whichever is smaller.
20673 Assume (do not assume) that all symbols have 32-bit values, regardless
20674 of the selected ABI@. This option is useful in combination with
20675 @option{-mabi=64} and @option{-mno-abicalls} because it allows GCC
20676 to generate shorter and faster references to symbolic addresses.
20680 Put definitions of externally-visible data in a small data section
20681 if that data is no bigger than @var{num} bytes. GCC can then generate
20682 more efficient accesses to the data; see @option{-mgpopt} for details.
20684 The default @option{-G} option depends on the configuration.
20686 @item -mlocal-sdata
20687 @itemx -mno-local-sdata
20688 @opindex mlocal-sdata
20689 @opindex mno-local-sdata
20690 Extend (do not extend) the @option{-G} behavior to local data too,
20691 such as to static variables in C@. @option{-mlocal-sdata} is the
20692 default for all configurations.
20694 If the linker complains that an application is using too much small data,
20695 you might want to try rebuilding the less performance-critical parts with
20696 @option{-mno-local-sdata}. You might also want to build large
20697 libraries with @option{-mno-local-sdata}, so that the libraries leave
20698 more room for the main program.
20700 @item -mextern-sdata
20701 @itemx -mno-extern-sdata
20702 @opindex mextern-sdata
20703 @opindex mno-extern-sdata
20704 Assume (do not assume) that externally-defined data is in
20705 a small data section if the size of that data is within the @option{-G} limit.
20706 @option{-mextern-sdata} is the default for all configurations.
20708 If you compile a module @var{Mod} with @option{-mextern-sdata} @option{-G
20709 @var{num}} @option{-mgpopt}, and @var{Mod} references a variable @var{Var}
20710 that is no bigger than @var{num} bytes, you must make sure that @var{Var}
20711 is placed in a small data section. If @var{Var} is defined by another
20712 module, you must either compile that module with a high-enough
20713 @option{-G} setting or attach a @code{section} attribute to @var{Var}'s
20714 definition. If @var{Var} is common, you must link the application
20715 with a high-enough @option{-G} setting.
20717 The easiest way of satisfying these restrictions is to compile
20718 and link every module with the same @option{-G} option. However,
20719 you may wish to build a library that supports several different
20720 small data limits. You can do this by compiling the library with
20721 the highest supported @option{-G} setting and additionally using
20722 @option{-mno-extern-sdata} to stop the library from making assumptions
20723 about externally-defined data.
20729 Use (do not use) GP-relative accesses for symbols that are known to be
20730 in a small data section; see @option{-G}, @option{-mlocal-sdata} and
20731 @option{-mextern-sdata}. @option{-mgpopt} is the default for all
20734 @option{-mno-gpopt} is useful for cases where the @code{$gp} register
20735 might not hold the value of @code{_gp}. For example, if the code is
20736 part of a library that might be used in a boot monitor, programs that
20737 call boot monitor routines pass an unknown value in @code{$gp}.
20738 (In such situations, the boot monitor itself is usually compiled
20739 with @option{-G0}.)
20741 @option{-mno-gpopt} implies @option{-mno-local-sdata} and
20742 @option{-mno-extern-sdata}.
20744 @item -membedded-data
20745 @itemx -mno-embedded-data
20746 @opindex membedded-data
20747 @opindex mno-embedded-data
20748 Allocate variables to the read-only data section first if possible, then
20749 next in the small data section if possible, otherwise in data. This gives
20750 slightly slower code than the default, but reduces the amount of RAM required
20751 when executing, and thus may be preferred for some embedded systems.
20753 @item -muninit-const-in-rodata
20754 @itemx -mno-uninit-const-in-rodata
20755 @opindex muninit-const-in-rodata
20756 @opindex mno-uninit-const-in-rodata
20757 Put uninitialized @code{const} variables in the read-only data section.
20758 This option is only meaningful in conjunction with @option{-membedded-data}.
20760 @item -mcode-readable=@var{setting}
20761 @opindex mcode-readable
20762 Specify whether GCC may generate code that reads from executable sections.
20763 There are three possible settings:
20766 @item -mcode-readable=yes
20767 Instructions may freely access executable sections. This is the
20770 @item -mcode-readable=pcrel
20771 MIPS16 PC-relative load instructions can access executable sections,
20772 but other instructions must not do so. This option is useful on 4KSc
20773 and 4KSd processors when the code TLBs have the Read Inhibit bit set.
20774 It is also useful on processors that can be configured to have a dual
20775 instruction/data SRAM interface and that, like the M4K, automatically
20776 redirect PC-relative loads to the instruction RAM.
20778 @item -mcode-readable=no
20779 Instructions must not access executable sections. This option can be
20780 useful on targets that are configured to have a dual instruction/data
20781 SRAM interface but that (unlike the M4K) do not automatically redirect
20782 PC-relative loads to the instruction RAM.
20785 @item -msplit-addresses
20786 @itemx -mno-split-addresses
20787 @opindex msplit-addresses
20788 @opindex mno-split-addresses
20789 Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler
20790 relocation operators. This option has been superseded by
20791 @option{-mexplicit-relocs} but is retained for backwards compatibility.
20793 @item -mexplicit-relocs
20794 @itemx -mno-explicit-relocs
20795 @opindex mexplicit-relocs
20796 @opindex mno-explicit-relocs
20797 Use (do not use) assembler relocation operators when dealing with symbolic
20798 addresses. The alternative, selected by @option{-mno-explicit-relocs},
20799 is to use assembler macros instead.
20801 @option{-mexplicit-relocs} is the default if GCC was configured
20802 to use an assembler that supports relocation operators.
20804 @item -mcheck-zero-division
20805 @itemx -mno-check-zero-division
20806 @opindex mcheck-zero-division
20807 @opindex mno-check-zero-division
20808 Trap (do not trap) on integer division by zero.
20810 The default is @option{-mcheck-zero-division}.
20812 @item -mdivide-traps
20813 @itemx -mdivide-breaks
20814 @opindex mdivide-traps
20815 @opindex mdivide-breaks
20816 MIPS systems check for division by zero by generating either a
20817 conditional trap or a break instruction. Using traps results in
20818 smaller code, but is only supported on MIPS II and later. Also, some
20819 versions of the Linux kernel have a bug that prevents trap from
20820 generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to
20821 allow conditional traps on architectures that support them and
20822 @option{-mdivide-breaks} to force the use of breaks.
20824 The default is usually @option{-mdivide-traps}, but this can be
20825 overridden at configure time using @option{--with-divide=breaks}.
20826 Divide-by-zero checks can be completely disabled using
20827 @option{-mno-check-zero-division}.
20829 @item -mload-store-pairs
20830 @itemx -mno-load-store-pairs
20831 @opindex mload-store-pairs
20832 @opindex mno-load-store-pairs
20833 Enable (disable) an optimization that pairs consecutive load or store
20834 instructions to enable load/store bonding. This option is enabled by
20835 default but only takes effect when the selected architecture is known
20836 to support bonding.
20841 @opindex mno-memcpy
20842 Force (do not force) the use of @code{memcpy} for non-trivial block
20843 moves. The default is @option{-mno-memcpy}, which allows GCC to inline
20844 most constant-sized copies.
20847 @itemx -mno-long-calls
20848 @opindex mlong-calls
20849 @opindex mno-long-calls
20850 Disable (do not disable) use of the @code{jal} instruction. Calling
20851 functions using @code{jal} is more efficient but requires the caller
20852 and callee to be in the same 256 megabyte segment.
20854 This option has no effect on abicalls code. The default is
20855 @option{-mno-long-calls}.
20861 Enable (disable) use of the @code{mad}, @code{madu} and @code{mul}
20862 instructions, as provided by the R4650 ISA@.
20868 Enable (disable) use of the @code{madd} and @code{msub} integer
20869 instructions. The default is @option{-mimadd} on architectures
20870 that support @code{madd} and @code{msub} except for the 74k
20871 architecture where it was found to generate slower code.
20874 @itemx -mno-fused-madd
20875 @opindex mfused-madd
20876 @opindex mno-fused-madd
20877 Enable (disable) use of the floating-point multiply-accumulate
20878 instructions, when they are available. The default is
20879 @option{-mfused-madd}.
20881 On the R8000 CPU when multiply-accumulate instructions are used,
20882 the intermediate product is calculated to infinite precision
20883 and is not subject to the FCSR Flush to Zero bit. This may be
20884 undesirable in some circumstances. On other processors the result
20885 is numerically identical to the equivalent computation using
20886 separate multiply, add, subtract and negate instructions.
20890 Tell the MIPS assembler to not run its preprocessor over user
20891 assembler files (with a @samp{.s} suffix) when assembling them.
20894 @itemx -mno-fix-24k
20896 @opindex mno-fix-24k
20897 Work around the 24K E48 (lost data on stores during refill) errata.
20898 The workarounds are implemented by the assembler rather than by GCC@.
20901 @itemx -mno-fix-r4000
20902 @opindex mfix-r4000
20903 @opindex mno-fix-r4000
20904 Work around certain R4000 CPU errata:
20907 A double-word or a variable shift may give an incorrect result if executed
20908 immediately after starting an integer division.
20910 A double-word or a variable shift may give an incorrect result if executed
20911 while an integer multiplication is in progress.
20913 An integer division may give an incorrect result if started in a delay slot
20914 of a taken branch or a jump.
20918 @itemx -mno-fix-r4400
20919 @opindex mfix-r4400
20920 @opindex mno-fix-r4400
20921 Work around certain R4400 CPU errata:
20924 A double-word or a variable shift may give an incorrect result if executed
20925 immediately after starting an integer division.
20929 @itemx -mno-fix-r10000
20930 @opindex mfix-r10000
20931 @opindex mno-fix-r10000
20932 Work around certain R10000 errata:
20935 @code{ll}/@code{sc} sequences may not behave atomically on revisions
20936 prior to 3.0. They may deadlock on revisions 2.6 and earlier.
20939 This option can only be used if the target architecture supports
20940 branch-likely instructions. @option{-mfix-r10000} is the default when
20941 @option{-march=r10000} is used; @option{-mno-fix-r10000} is the default
20945 @itemx -mno-fix-rm7000
20946 @opindex mfix-rm7000
20947 Work around the RM7000 @code{dmult}/@code{dmultu} errata. The
20948 workarounds are implemented by the assembler rather than by GCC@.
20951 @itemx -mno-fix-vr4120
20952 @opindex mfix-vr4120
20953 Work around certain VR4120 errata:
20956 @code{dmultu} does not always produce the correct result.
20958 @code{div} and @code{ddiv} do not always produce the correct result if one
20959 of the operands is negative.
20961 The workarounds for the division errata rely on special functions in
20962 @file{libgcc.a}. At present, these functions are only provided by
20963 the @code{mips64vr*-elf} configurations.
20965 Other VR4120 errata require a NOP to be inserted between certain pairs of
20966 instructions. These errata are handled by the assembler, not by GCC itself.
20969 @opindex mfix-vr4130
20970 Work around the VR4130 @code{mflo}/@code{mfhi} errata. The
20971 workarounds are implemented by the assembler rather than by GCC,
20972 although GCC avoids using @code{mflo} and @code{mfhi} if the
20973 VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi}
20974 instructions are available instead.
20977 @itemx -mno-fix-sb1
20979 Work around certain SB-1 CPU core errata.
20980 (This flag currently works around the SB-1 revision 2
20981 ``F1'' and ``F2'' floating-point errata.)
20983 @item -mr10k-cache-barrier=@var{setting}
20984 @opindex mr10k-cache-barrier
20985 Specify whether GCC should insert cache barriers to avoid the
20986 side effects of speculation on R10K processors.
20988 In common with many processors, the R10K tries to predict the outcome
20989 of a conditional branch and speculatively executes instructions from
20990 the ``taken'' branch. It later aborts these instructions if the
20991 predicted outcome is wrong. However, on the R10K, even aborted
20992 instructions can have side effects.
20994 This problem only affects kernel stores and, depending on the system,
20995 kernel loads. As an example, a speculatively-executed store may load
20996 the target memory into cache and mark the cache line as dirty, even if
20997 the store itself is later aborted. If a DMA operation writes to the
20998 same area of memory before the ``dirty'' line is flushed, the cached
20999 data overwrites the DMA-ed data. See the R10K processor manual
21000 for a full description, including other potential problems.
21002 One workaround is to insert cache barrier instructions before every memory
21003 access that might be speculatively executed and that might have side
21004 effects even if aborted. @option{-mr10k-cache-barrier=@var{setting}}
21005 controls GCC's implementation of this workaround. It assumes that
21006 aborted accesses to any byte in the following regions does not have
21011 the memory occupied by the current function's stack frame;
21014 the memory occupied by an incoming stack argument;
21017 the memory occupied by an object with a link-time-constant address.
21020 It is the kernel's responsibility to ensure that speculative
21021 accesses to these regions are indeed safe.
21023 If the input program contains a function declaration such as:
21029 then the implementation of @code{foo} must allow @code{j foo} and
21030 @code{jal foo} to be executed speculatively. GCC honors this
21031 restriction for functions it compiles itself. It expects non-GCC
21032 functions (such as hand-written assembly code) to do the same.
21034 The option has three forms:
21037 @item -mr10k-cache-barrier=load-store
21038 Insert a cache barrier before a load or store that might be
21039 speculatively executed and that might have side effects even
21042 @item -mr10k-cache-barrier=store
21043 Insert a cache barrier before a store that might be speculatively
21044 executed and that might have side effects even if aborted.
21046 @item -mr10k-cache-barrier=none
21047 Disable the insertion of cache barriers. This is the default setting.
21050 @item -mflush-func=@var{func}
21051 @itemx -mno-flush-func
21052 @opindex mflush-func
21053 Specifies the function to call to flush the I and D caches, or to not
21054 call any such function. If called, the function must take the same
21055 arguments as the common @code{_flush_func}, that is, the address of the
21056 memory range for which the cache is being flushed, the size of the
21057 memory range, and the number 3 (to flush both caches). The default
21058 depends on the target GCC was configured for, but commonly is either
21059 @code{_flush_func} or @code{__cpu_flush}.
21061 @item mbranch-cost=@var{num}
21062 @opindex mbranch-cost
21063 Set the cost of branches to roughly @var{num} ``simple'' instructions.
21064 This cost is only a heuristic and is not guaranteed to produce
21065 consistent results across releases. A zero cost redundantly selects
21066 the default, which is based on the @option{-mtune} setting.
21068 @item -mbranch-likely
21069 @itemx -mno-branch-likely
21070 @opindex mbranch-likely
21071 @opindex mno-branch-likely
21072 Enable or disable use of Branch Likely instructions, regardless of the
21073 default for the selected architecture. By default, Branch Likely
21074 instructions may be generated if they are supported by the selected
21075 architecture. An exception is for the MIPS32 and MIPS64 architectures
21076 and processors that implement those architectures; for those, Branch
21077 Likely instructions are not be generated by default because the MIPS32
21078 and MIPS64 architectures specifically deprecate their use.
21080 @item -mcompact-branches=never
21081 @itemx -mcompact-branches=optimal
21082 @itemx -mcompact-branches=always
21083 @opindex mcompact-branches=never
21084 @opindex mcompact-branches=optimal
21085 @opindex mcompact-branches=always
21086 These options control which form of branches will be generated. The
21087 default is @option{-mcompact-branches=optimal}.
21089 The @option{-mcompact-branches=never} option ensures that compact branch
21090 instructions will never be generated.
21092 The @option{-mcompact-branches=always} option ensures that a compact
21093 branch instruction will be generated if available. If a compact branch
21094 instruction is not available, a delay slot form of the branch will be
21097 This option is supported from MIPS Release 6 onwards.
21099 The @option{-mcompact-branches=optimal} option will cause a delay slot
21100 branch to be used if one is available in the current ISA and the delay
21101 slot is successfully filled. If the delay slot is not filled, a compact
21102 branch will be chosen if one is available.
21104 @item -mfp-exceptions
21105 @itemx -mno-fp-exceptions
21106 @opindex mfp-exceptions
21107 Specifies whether FP exceptions are enabled. This affects how
21108 FP instructions are scheduled for some processors.
21109 The default is that FP exceptions are
21112 For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
21113 64-bit code, then we can use both FP pipes. Otherwise, we can only use one
21116 @item -mvr4130-align
21117 @itemx -mno-vr4130-align
21118 @opindex mvr4130-align
21119 The VR4130 pipeline is two-way superscalar, but can only issue two
21120 instructions together if the first one is 8-byte aligned. When this
21121 option is enabled, GCC aligns pairs of instructions that it
21122 thinks should execute in parallel.
21124 This option only has an effect when optimizing for the VR4130.
21125 It normally makes code faster, but at the expense of making it bigger.
21126 It is enabled by default at optimization level @option{-O3}.
21131 Enable (disable) generation of @code{synci} instructions on
21132 architectures that support it. The @code{synci} instructions (if
21133 enabled) are generated when @code{__builtin___clear_cache} is
21136 This option defaults to @option{-mno-synci}, but the default can be
21137 overridden by configuring GCC with @option{--with-synci}.
21139 When compiling code for single processor systems, it is generally safe
21140 to use @code{synci}. However, on many multi-core (SMP) systems, it
21141 does not invalidate the instruction caches on all cores and may lead
21142 to undefined behavior.
21144 @item -mrelax-pic-calls
21145 @itemx -mno-relax-pic-calls
21146 @opindex mrelax-pic-calls
21147 Try to turn PIC calls that are normally dispatched via register
21148 @code{$25} into direct calls. This is only possible if the linker can
21149 resolve the destination at link time and if the destination is within
21150 range for a direct call.
21152 @option{-mrelax-pic-calls} is the default if GCC was configured to use
21153 an assembler and a linker that support the @code{.reloc} assembly
21154 directive and @option{-mexplicit-relocs} is in effect. With
21155 @option{-mno-explicit-relocs}, this optimization can be performed by the
21156 assembler and the linker alone without help from the compiler.
21158 @item -mmcount-ra-address
21159 @itemx -mno-mcount-ra-address
21160 @opindex mmcount-ra-address
21161 @opindex mno-mcount-ra-address
21162 Emit (do not emit) code that allows @code{_mcount} to modify the
21163 calling function's return address. When enabled, this option extends
21164 the usual @code{_mcount} interface with a new @var{ra-address}
21165 parameter, which has type @code{intptr_t *} and is passed in register
21166 @code{$12}. @code{_mcount} can then modify the return address by
21167 doing both of the following:
21170 Returning the new address in register @code{$31}.
21172 Storing the new address in @code{*@var{ra-address}},
21173 if @var{ra-address} is nonnull.
21176 The default is @option{-mno-mcount-ra-address}.
21178 @item -mframe-header-opt
21179 @itemx -mno-frame-header-opt
21180 @opindex mframe-header-opt
21181 Enable (disable) frame header optimization in the o32 ABI. When using the
21182 o32 ABI, calling functions will allocate 16 bytes on the stack for the called
21183 function to write out register arguments. When enabled, this optimization
21184 will suppress the allocation of the frame header if it can be determined that
21187 This optimization is off by default at all optimization levels.
21190 @itemx -mno-lxc1-sxc1
21191 @opindex mlxc1-sxc1
21192 When applicable, enable (disable) the generation of @code{lwxc1},
21193 @code{swxc1}, @code{ldxc1}, @code{sdxc1} instructions. Enabled by default.
21198 When applicable, enable (disable) the generation of 4-operand @code{madd.s},
21199 @code{madd.d} and related instructions. Enabled by default.
21204 @subsection MMIX Options
21205 @cindex MMIX Options
21207 These options are defined for the MMIX:
21211 @itemx -mno-libfuncs
21213 @opindex mno-libfuncs
21214 Specify that intrinsic library functions are being compiled, passing all
21215 values in registers, no matter the size.
21218 @itemx -mno-epsilon
21220 @opindex mno-epsilon
21221 Generate floating-point comparison instructions that compare with respect
21222 to the @code{rE} epsilon register.
21224 @item -mabi=mmixware
21226 @opindex mabi=mmixware
21228 Generate code that passes function parameters and return values that (in
21229 the called function) are seen as registers @code{$0} and up, as opposed to
21230 the GNU ABI which uses global registers @code{$231} and up.
21232 @item -mzero-extend
21233 @itemx -mno-zero-extend
21234 @opindex mzero-extend
21235 @opindex mno-zero-extend
21236 When reading data from memory in sizes shorter than 64 bits, use (do not
21237 use) zero-extending load instructions by default, rather than
21238 sign-extending ones.
21241 @itemx -mno-knuthdiv
21243 @opindex mno-knuthdiv
21244 Make the result of a division yielding a remainder have the same sign as
21245 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
21246 remainder follows the sign of the dividend. Both methods are
21247 arithmetically valid, the latter being almost exclusively used.
21249 @item -mtoplevel-symbols
21250 @itemx -mno-toplevel-symbols
21251 @opindex mtoplevel-symbols
21252 @opindex mno-toplevel-symbols
21253 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
21254 code can be used with the @code{PREFIX} assembly directive.
21258 Generate an executable in the ELF format, rather than the default
21259 @samp{mmo} format used by the @command{mmix} simulator.
21261 @item -mbranch-predict
21262 @itemx -mno-branch-predict
21263 @opindex mbranch-predict
21264 @opindex mno-branch-predict
21265 Use (do not use) the probable-branch instructions, when static branch
21266 prediction indicates a probable branch.
21268 @item -mbase-addresses
21269 @itemx -mno-base-addresses
21270 @opindex mbase-addresses
21271 @opindex mno-base-addresses
21272 Generate (do not generate) code that uses @emph{base addresses}. Using a
21273 base address automatically generates a request (handled by the assembler
21274 and the linker) for a constant to be set up in a global register. The
21275 register is used for one or more base address requests within the range 0
21276 to 255 from the value held in the register. The generally leads to short
21277 and fast code, but the number of different data items that can be
21278 addressed is limited. This means that a program that uses lots of static
21279 data may require @option{-mno-base-addresses}.
21281 @item -msingle-exit
21282 @itemx -mno-single-exit
21283 @opindex msingle-exit
21284 @opindex mno-single-exit
21285 Force (do not force) generated code to have a single exit point in each
21289 @node MN10300 Options
21290 @subsection MN10300 Options
21291 @cindex MN10300 options
21293 These @option{-m} options are defined for Matsushita MN10300 architectures:
21298 Generate code to avoid bugs in the multiply instructions for the MN10300
21299 processors. This is the default.
21301 @item -mno-mult-bug
21302 @opindex mno-mult-bug
21303 Do not generate code to avoid bugs in the multiply instructions for the
21304 MN10300 processors.
21308 Generate code using features specific to the AM33 processor.
21312 Do not generate code using features specific to the AM33 processor. This
21317 Generate code using features specific to the AM33/2.0 processor.
21321 Generate code using features specific to the AM34 processor.
21323 @item -mtune=@var{cpu-type}
21325 Use the timing characteristics of the indicated CPU type when
21326 scheduling instructions. This does not change the targeted processor
21327 type. The CPU type must be one of @samp{mn10300}, @samp{am33},
21328 @samp{am33-2} or @samp{am34}.
21330 @item -mreturn-pointer-on-d0
21331 @opindex mreturn-pointer-on-d0
21332 When generating a function that returns a pointer, return the pointer
21333 in both @code{a0} and @code{d0}. Otherwise, the pointer is returned
21334 only in @code{a0}, and attempts to call such functions without a prototype
21335 result in errors. Note that this option is on by default; use
21336 @option{-mno-return-pointer-on-d0} to disable it.
21340 Do not link in the C run-time initialization object file.
21344 Indicate to the linker that it should perform a relaxation optimization pass
21345 to shorten branches, calls and absolute memory addresses. This option only
21346 has an effect when used on the command line for the final link step.
21348 This option makes symbolic debugging impossible.
21352 Allow the compiler to generate @emph{Long Instruction Word}
21353 instructions if the target is the @samp{AM33} or later. This is the
21354 default. This option defines the preprocessor macro @code{__LIW__}.
21358 Do not allow the compiler to generate @emph{Long Instruction Word}
21359 instructions. This option defines the preprocessor macro
21364 Allow the compiler to generate the @emph{SETLB} and @emph{Lcc}
21365 instructions if the target is the @samp{AM33} or later. This is the
21366 default. This option defines the preprocessor macro @code{__SETLB__}.
21370 Do not allow the compiler to generate @emph{SETLB} or @emph{Lcc}
21371 instructions. This option defines the preprocessor macro
21372 @code{__NO_SETLB__}.
21376 @node Moxie Options
21377 @subsection Moxie Options
21378 @cindex Moxie Options
21384 Generate big-endian code. This is the default for @samp{moxie-*-*}
21389 Generate little-endian code.
21393 Generate mul.x and umul.x instructions. This is the default for
21394 @samp{moxiebox-*-*} configurations.
21398 Do not link in the C run-time initialization object file.
21402 @node MSP430 Options
21403 @subsection MSP430 Options
21404 @cindex MSP430 Options
21406 These options are defined for the MSP430:
21412 Force assembly output to always use hex constants. Normally such
21413 constants are signed decimals, but this option is available for
21414 testsuite and/or aesthetic purposes.
21418 Select the MCU to target. This is used to create a C preprocessor
21419 symbol based upon the MCU name, converted to upper case and pre- and
21420 post-fixed with @samp{__}. This in turn is used by the
21421 @file{msp430.h} header file to select an MCU-specific supplementary
21424 The option also sets the ISA to use. If the MCU name is one that is
21425 known to only support the 430 ISA then that is selected, otherwise the
21426 430X ISA is selected. A generic MCU name of @samp{msp430} can also be
21427 used to select the 430 ISA. Similarly the generic @samp{msp430x} MCU
21428 name selects the 430X ISA.
21430 In addition an MCU-specific linker script is added to the linker
21431 command line. The script's name is the name of the MCU with
21432 @file{.ld} appended. Thus specifying @option{-mmcu=xxx} on the @command{gcc}
21433 command line defines the C preprocessor symbol @code{__XXX__} and
21434 cause the linker to search for a script called @file{xxx.ld}.
21436 This option is also passed on to the assembler.
21439 @itemx -mno-warn-mcu
21441 @opindex mno-warn-mcu
21442 This option enables or disables warnings about conflicts between the
21443 MCU name specified by the @option{-mmcu} option and the ISA set by the
21444 @option{-mcpu} option and/or the hardware multiply support set by the
21445 @option{-mhwmult} option. It also toggles warnings about unrecognized
21446 MCU names. This option is on by default.
21450 Specifies the ISA to use. Accepted values are @samp{msp430},
21451 @samp{msp430x} and @samp{msp430xv2}. This option is deprecated. The
21452 @option{-mmcu=} option should be used to select the ISA.
21456 Link to the simulator runtime libraries and linker script. Overrides
21457 any scripts that would be selected by the @option{-mmcu=} option.
21461 Use large-model addressing (20-bit pointers, 32-bit @code{size_t}).
21465 Use small-model addressing (16-bit pointers, 16-bit @code{size_t}).
21469 This option is passed to the assembler and linker, and allows the
21470 linker to perform certain optimizations that cannot be done until
21475 Describes the type of hardware multiply supported by the target.
21476 Accepted values are @samp{none} for no hardware multiply, @samp{16bit}
21477 for the original 16-bit-only multiply supported by early MCUs.
21478 @samp{32bit} for the 16/32-bit multiply supported by later MCUs and
21479 @samp{f5series} for the 16/32-bit multiply supported by F5-series MCUs.
21480 A value of @samp{auto} can also be given. This tells GCC to deduce
21481 the hardware multiply support based upon the MCU name provided by the
21482 @option{-mmcu} option. If no @option{-mmcu} option is specified or if
21483 the MCU name is not recognized then no hardware multiply support is
21484 assumed. @code{auto} is the default setting.
21486 Hardware multiplies are normally performed by calling a library
21487 routine. This saves space in the generated code. When compiling at
21488 @option{-O3} or higher however the hardware multiplier is invoked
21489 inline. This makes for bigger, but faster code.
21491 The hardware multiply routines disable interrupts whilst running and
21492 restore the previous interrupt state when they finish. This makes
21493 them safe to use inside interrupt handlers as well as in normal code.
21497 Enable the use of a minimum runtime environment - no static
21498 initializers or constructors. This is intended for memory-constrained
21499 devices. The compiler includes special symbols in some objects
21500 that tell the linker and runtime which code fragments are required.
21502 @item -mcode-region=
21503 @itemx -mdata-region=
21504 @opindex mcode-region
21505 @opindex mdata-region
21506 These options tell the compiler where to place functions and data that
21507 do not have one of the @code{lower}, @code{upper}, @code{either} or
21508 @code{section} attributes. Possible values are @code{lower},
21509 @code{upper}, @code{either} or @code{any}. The first three behave
21510 like the corresponding attribute. The fourth possible value -
21511 @code{any} - is the default. It leaves placement entirely up to the
21512 linker script and how it assigns the standard sections
21513 (@code{.text}, @code{.data}, etc) to the memory regions.
21515 @item -msilicon-errata=
21516 @opindex msilicon-errata
21517 This option passes on a request to assembler to enable the fixes for
21518 the named silicon errata.
21520 @item -msilicon-errata-warn=
21521 @opindex msilicon-errata-warn
21522 This option passes on a request to the assembler to enable warning
21523 messages when a silicon errata might need to be applied.
21527 @node NDS32 Options
21528 @subsection NDS32 Options
21529 @cindex NDS32 Options
21531 These options are defined for NDS32 implementations:
21536 @opindex mbig-endian
21537 Generate code in big-endian mode.
21539 @item -mlittle-endian
21540 @opindex mlittle-endian
21541 Generate code in little-endian mode.
21543 @item -mreduced-regs
21544 @opindex mreduced-regs
21545 Use reduced-set registers for register allocation.
21548 @opindex mfull-regs
21549 Use full-set registers for register allocation.
21553 Generate conditional move instructions.
21557 Do not generate conditional move instructions.
21561 Generate performance extension instructions.
21563 @item -mno-ext-perf
21564 @opindex mno-perf-ext
21565 Do not generate performance extension instructions.
21569 Generate performance extension 2 instructions.
21571 @item -mno-ext-perf2
21572 @opindex mno-perf-ext
21573 Do not generate performance extension 2 instructions.
21577 Generate string extension instructions.
21579 @item -mno-ext-string
21580 @opindex mno-perf-ext
21581 Do not generate string extension instructions.
21585 Generate v3 push25/pop25 instructions.
21588 @opindex mno-v3push
21589 Do not generate v3 push25/pop25 instructions.
21593 Generate 16-bit instructions.
21596 @opindex mno-16-bit
21597 Do not generate 16-bit instructions.
21599 @item -misr-vector-size=@var{num}
21600 @opindex misr-vector-size
21601 Specify the size of each interrupt vector, which must be 4 or 16.
21603 @item -mcache-block-size=@var{num}
21604 @opindex mcache-block-size
21605 Specify the size of each cache block,
21606 which must be a power of 2 between 4 and 512.
21608 @item -march=@var{arch}
21610 Specify the name of the target architecture.
21612 @item -mcmodel=@var{code-model}
21614 Set the code model to one of
21617 All the data and read-only data segments must be within 512KB addressing space.
21618 The text segment must be within 16MB addressing space.
21619 @item @samp{medium}
21620 The data segment must be within 512KB while the read-only data segment can be
21621 within 4GB addressing space. The text segment should be still within 16MB
21624 All the text and data segments can be within 4GB addressing space.
21628 @opindex mctor-dtor
21629 Enable constructor/destructor feature.
21633 Guide linker to relax instructions.
21637 @node Nios II Options
21638 @subsection Nios II Options
21639 @cindex Nios II options
21640 @cindex Altera Nios II options
21642 These are the options defined for the Altera Nios II processor.
21648 @cindex smaller data references
21649 Put global and static objects less than or equal to @var{num} bytes
21650 into the small data or BSS sections instead of the normal data or BSS
21651 sections. The default value of @var{num} is 8.
21653 @item -mgpopt=@var{option}
21658 Generate (do not generate) GP-relative accesses. The following
21659 @var{option} names are recognized:
21664 Do not generate GP-relative accesses.
21667 Generate GP-relative accesses for small data objects that are not
21668 external, weak, or uninitialized common symbols.
21669 Also use GP-relative addressing for objects that
21670 have been explicitly placed in a small data section via a @code{section}
21674 As for @samp{local}, but also generate GP-relative accesses for
21675 small data objects that are external, weak, or common. If you use this option,
21676 you must ensure that all parts of your program (including libraries) are
21677 compiled with the same @option{-G} setting.
21680 Generate GP-relative accesses for all data objects in the program. If you
21681 use this option, the entire data and BSS segments
21682 of your program must fit in 64K of memory and you must use an appropriate
21683 linker script to allocate them within the addressable range of the
21687 Generate GP-relative addresses for function pointers as well as data
21688 pointers. If you use this option, the entire text, data, and BSS segments
21689 of your program must fit in 64K of memory and you must use an appropriate
21690 linker script to allocate them within the addressable range of the
21695 @option{-mgpopt} is equivalent to @option{-mgpopt=local}, and
21696 @option{-mno-gpopt} is equivalent to @option{-mgpopt=none}.
21698 The default is @option{-mgpopt} except when @option{-fpic} or
21699 @option{-fPIC} is specified to generate position-independent code.
21700 Note that the Nios II ABI does not permit GP-relative accesses from
21703 You may need to specify @option{-mno-gpopt} explicitly when building
21704 programs that include large amounts of small data, including large
21705 GOT data sections. In this case, the 16-bit offset for GP-relative
21706 addressing may not be large enough to allow access to the entire
21707 small data section.
21709 @item -mgprel-sec=@var{regexp}
21710 @opindex mgprel-sec
21711 This option specifies additional section names that can be accessed via
21712 GP-relative addressing. It is most useful in conjunction with
21713 @code{section} attributes on variable declarations
21714 (@pxref{Common Variable Attributes}) and a custom linker script.
21715 The @var{regexp} is a POSIX Extended Regular Expression.
21717 This option does not affect the behavior of the @option{-G} option, and
21718 and the specified sections are in addition to the standard @code{.sdata}
21719 and @code{.sbss} small-data sections that are recognized by @option{-mgpopt}.
21721 @item -mr0rel-sec=@var{regexp}
21722 @opindex mr0rel-sec
21723 This option specifies names of sections that can be accessed via a
21724 16-bit offset from @code{r0}; that is, in the low 32K or high 32K
21725 of the 32-bit address space. It is most useful in conjunction with
21726 @code{section} attributes on variable declarations
21727 (@pxref{Common Variable Attributes}) and a custom linker script.
21728 The @var{regexp} is a POSIX Extended Regular Expression.
21730 In contrast to the use of GP-relative addressing for small data,
21731 zero-based addressing is never generated by default and there are no
21732 conventional section names used in standard linker scripts for sections
21733 in the low or high areas of memory.
21739 Generate little-endian (default) or big-endian (experimental) code,
21742 @item -march=@var{arch}
21744 This specifies the name of the target Nios II architecture. GCC uses this
21745 name to determine what kind of instructions it can emit when generating
21746 assembly code. Permissible names are: @samp{r1}, @samp{r2}.
21748 The preprocessor macro @code{__nios2_arch__} is available to programs,
21749 with value 1 or 2, indicating the targeted ISA level.
21751 @item -mbypass-cache
21752 @itemx -mno-bypass-cache
21753 @opindex mno-bypass-cache
21754 @opindex mbypass-cache
21755 Force all load and store instructions to always bypass cache by
21756 using I/O variants of the instructions. The default is not to
21759 @item -mno-cache-volatile
21760 @itemx -mcache-volatile
21761 @opindex mcache-volatile
21762 @opindex mno-cache-volatile
21763 Volatile memory access bypass the cache using the I/O variants of
21764 the load and store instructions. The default is not to bypass the cache.
21766 @item -mno-fast-sw-div
21767 @itemx -mfast-sw-div
21768 @opindex mno-fast-sw-div
21769 @opindex mfast-sw-div
21770 Do not use table-based fast divide for small numbers. The default
21771 is to use the fast divide at @option{-O3} and above.
21775 @itemx -mno-hw-mulx
21779 @opindex mno-hw-mul
21781 @opindex mno-hw-mulx
21783 @opindex mno-hw-div
21785 Enable or disable emitting @code{mul}, @code{mulx} and @code{div} family of
21786 instructions by the compiler. The default is to emit @code{mul}
21787 and not emit @code{div} and @code{mulx}.
21793 Enable or disable generation of Nios II R2 BMX (bit manipulation) and
21794 CDX (code density) instructions. Enabling these instructions also
21795 requires @option{-march=r2}. Since these instructions are optional
21796 extensions to the R2 architecture, the default is not to emit them.
21798 @item -mcustom-@var{insn}=@var{N}
21799 @itemx -mno-custom-@var{insn}
21800 @opindex mcustom-@var{insn}
21801 @opindex mno-custom-@var{insn}
21802 Each @option{-mcustom-@var{insn}=@var{N}} option enables use of a
21803 custom instruction with encoding @var{N} when generating code that uses
21804 @var{insn}. For example, @option{-mcustom-fadds=253} generates custom
21805 instruction 253 for single-precision floating-point add operations instead
21806 of the default behavior of using a library call.
21808 The following values of @var{insn} are supported. Except as otherwise
21809 noted, floating-point operations are expected to be implemented with
21810 normal IEEE 754 semantics and correspond directly to the C operators or the
21811 equivalent GCC built-in functions (@pxref{Other Builtins}).
21813 Single-precision floating point:
21816 @item @samp{fadds}, @samp{fsubs}, @samp{fdivs}, @samp{fmuls}
21817 Binary arithmetic operations.
21823 Unary absolute value.
21825 @item @samp{fcmpeqs}, @samp{fcmpges}, @samp{fcmpgts}, @samp{fcmples}, @samp{fcmplts}, @samp{fcmpnes}
21826 Comparison operations.
21828 @item @samp{fmins}, @samp{fmaxs}
21829 Floating-point minimum and maximum. These instructions are only
21830 generated if @option{-ffinite-math-only} is specified.
21832 @item @samp{fsqrts}
21833 Unary square root operation.
21835 @item @samp{fcoss}, @samp{fsins}, @samp{ftans}, @samp{fatans}, @samp{fexps}, @samp{flogs}
21836 Floating-point trigonometric and exponential functions. These instructions
21837 are only generated if @option{-funsafe-math-optimizations} is also specified.
21841 Double-precision floating point:
21844 @item @samp{faddd}, @samp{fsubd}, @samp{fdivd}, @samp{fmuld}
21845 Binary arithmetic operations.
21851 Unary absolute value.
21853 @item @samp{fcmpeqd}, @samp{fcmpged}, @samp{fcmpgtd}, @samp{fcmpled}, @samp{fcmpltd}, @samp{fcmpned}
21854 Comparison operations.
21856 @item @samp{fmind}, @samp{fmaxd}
21857 Double-precision minimum and maximum. These instructions are only
21858 generated if @option{-ffinite-math-only} is specified.
21860 @item @samp{fsqrtd}
21861 Unary square root operation.
21863 @item @samp{fcosd}, @samp{fsind}, @samp{ftand}, @samp{fatand}, @samp{fexpd}, @samp{flogd}
21864 Double-precision trigonometric and exponential functions. These instructions
21865 are only generated if @option{-funsafe-math-optimizations} is also specified.
21871 @item @samp{fextsd}
21872 Conversion from single precision to double precision.
21874 @item @samp{ftruncds}
21875 Conversion from double precision to single precision.
21877 @item @samp{fixsi}, @samp{fixsu}, @samp{fixdi}, @samp{fixdu}
21878 Conversion from floating point to signed or unsigned integer types, with
21879 truncation towards zero.
21882 Conversion from single-precision floating point to signed integer,
21883 rounding to the nearest integer and ties away from zero.
21884 This corresponds to the @code{__builtin_lroundf} function when
21885 @option{-fno-math-errno} is used.
21887 @item @samp{floatis}, @samp{floatus}, @samp{floatid}, @samp{floatud}
21888 Conversion from signed or unsigned integer types to floating-point types.
21892 In addition, all of the following transfer instructions for internal
21893 registers X and Y must be provided to use any of the double-precision
21894 floating-point instructions. Custom instructions taking two
21895 double-precision source operands expect the first operand in the
21896 64-bit register X. The other operand (or only operand of a unary
21897 operation) is given to the custom arithmetic instruction with the
21898 least significant half in source register @var{src1} and the most
21899 significant half in @var{src2}. A custom instruction that returns a
21900 double-precision result returns the most significant 32 bits in the
21901 destination register and the other half in 32-bit register Y.
21902 GCC automatically generates the necessary code sequences to write
21903 register X and/or read register Y when double-precision floating-point
21904 instructions are used.
21909 Write @var{src1} into the least significant half of X and @var{src2} into
21910 the most significant half of X.
21913 Write @var{src1} into Y.
21915 @item @samp{frdxhi}, @samp{frdxlo}
21916 Read the most or least (respectively) significant half of X and store it in
21920 Read the value of Y and store it into @var{dest}.
21923 Note that you can gain more local control over generation of Nios II custom
21924 instructions by using the @code{target("custom-@var{insn}=@var{N}")}
21925 and @code{target("no-custom-@var{insn}")} function attributes
21926 (@pxref{Function Attributes})
21927 or pragmas (@pxref{Function Specific Option Pragmas}).
21929 @item -mcustom-fpu-cfg=@var{name}
21930 @opindex mcustom-fpu-cfg
21932 This option enables a predefined, named set of custom instruction encodings
21933 (see @option{-mcustom-@var{insn}} above).
21934 Currently, the following sets are defined:
21936 @option{-mcustom-fpu-cfg=60-1} is equivalent to:
21937 @gccoptlist{-mcustom-fmuls=252 @gol
21938 -mcustom-fadds=253 @gol
21939 -mcustom-fsubs=254 @gol
21940 -fsingle-precision-constant}
21942 @option{-mcustom-fpu-cfg=60-2} is equivalent to:
21943 @gccoptlist{-mcustom-fmuls=252 @gol
21944 -mcustom-fadds=253 @gol
21945 -mcustom-fsubs=254 @gol
21946 -mcustom-fdivs=255 @gol
21947 -fsingle-precision-constant}
21949 @option{-mcustom-fpu-cfg=72-3} is equivalent to:
21950 @gccoptlist{-mcustom-floatus=243 @gol
21951 -mcustom-fixsi=244 @gol
21952 -mcustom-floatis=245 @gol
21953 -mcustom-fcmpgts=246 @gol
21954 -mcustom-fcmples=249 @gol
21955 -mcustom-fcmpeqs=250 @gol
21956 -mcustom-fcmpnes=251 @gol
21957 -mcustom-fmuls=252 @gol
21958 -mcustom-fadds=253 @gol
21959 -mcustom-fsubs=254 @gol
21960 -mcustom-fdivs=255 @gol
21961 -fsingle-precision-constant}
21963 Custom instruction assignments given by individual
21964 @option{-mcustom-@var{insn}=} options override those given by
21965 @option{-mcustom-fpu-cfg=}, regardless of the
21966 order of the options on the command line.
21968 Note that you can gain more local control over selection of a FPU
21969 configuration by using the @code{target("custom-fpu-cfg=@var{name}")}
21970 function attribute (@pxref{Function Attributes})
21971 or pragma (@pxref{Function Specific Option Pragmas}).
21975 These additional @samp{-m} options are available for the Altera Nios II
21976 ELF (bare-metal) target:
21982 Link with HAL BSP. This suppresses linking with the GCC-provided C runtime
21983 startup and termination code, and is typically used in conjunction with
21984 @option{-msys-crt0=} to specify the location of the alternate startup code
21985 provided by the HAL BSP.
21989 Link with a limited version of the C library, @option{-lsmallc}, rather than
21992 @item -msys-crt0=@var{startfile}
21994 @var{startfile} is the file name of the startfile (crt0) to use
21995 when linking. This option is only useful in conjunction with @option{-mhal}.
21997 @item -msys-lib=@var{systemlib}
21999 @var{systemlib} is the library name of the library that provides
22000 low-level system calls required by the C library,
22001 e.g. @code{read} and @code{write}.
22002 This option is typically used to link with a library provided by a HAL BSP.
22006 @node Nvidia PTX Options
22007 @subsection Nvidia PTX Options
22008 @cindex Nvidia PTX options
22009 @cindex nvptx options
22011 These options are defined for Nvidia PTX:
22019 Generate code for 32-bit or 64-bit ABI.
22022 @opindex mmainkernel
22023 Link in code for a __main kernel. This is for stand-alone instead of
22024 offloading execution.
22028 Apply partitioned execution optimizations. This is the default when any
22029 level of optimization is selected.
22032 @opindex msoft-stack
22033 Generate code that does not use @code{.local} memory
22034 directly for stack storage. Instead, a per-warp stack pointer is
22035 maintained explicitly. This enables variable-length stack allocation (with
22036 variable-length arrays or @code{alloca}), and when global memory is used for
22037 underlying storage, makes it possible to access automatic variables from other
22038 threads, or with atomic instructions. This code generation variant is used
22039 for OpenMP offloading, but the option is exposed on its own for the purpose
22040 of testing the compiler; to generate code suitable for linking into programs
22041 using OpenMP offloading, use option @option{-mgomp}.
22043 @item -muniform-simt
22044 @opindex muniform-simt
22045 Switch to code generation variant that allows to execute all threads in each
22046 warp, while maintaining memory state and side effects as if only one thread
22047 in each warp was active outside of OpenMP SIMD regions. All atomic operations
22048 and calls to runtime (malloc, free, vprintf) are conditionally executed (iff
22049 current lane index equals the master lane index), and the register being
22050 assigned is copied via a shuffle instruction from the master lane. Outside of
22051 SIMD regions lane 0 is the master; inside, each thread sees itself as the
22052 master. Shared memory array @code{int __nvptx_uni[]} stores all-zeros or
22053 all-ones bitmasks for each warp, indicating current mode (0 outside of SIMD
22054 regions). Each thread can bitwise-and the bitmask at position @code{tid.y}
22055 with current lane index to compute the master lane index.
22059 Generate code for use in OpenMP offloading: enables @option{-msoft-stack} and
22060 @option{-muniform-simt} options, and selects corresponding multilib variant.
22064 @node PDP-11 Options
22065 @subsection PDP-11 Options
22066 @cindex PDP-11 Options
22068 These options are defined for the PDP-11:
22073 Use hardware FPP floating point. This is the default. (FIS floating
22074 point on the PDP-11/40 is not supported.)
22077 @opindex msoft-float
22078 Do not use hardware floating point.
22082 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
22086 Return floating-point results in memory. This is the default.
22090 Generate code for a PDP-11/40.
22094 Generate code for a PDP-11/45. This is the default.
22098 Generate code for a PDP-11/10.
22100 @item -mbcopy-builtin
22101 @opindex mbcopy-builtin
22102 Use inline @code{movmemhi} patterns for copying memory. This is the
22107 Do not use inline @code{movmemhi} patterns for copying memory.
22113 Use 16-bit @code{int}. This is the default.
22119 Use 32-bit @code{int}.
22122 @itemx -mno-float32
22124 @opindex mno-float32
22125 Use 64-bit @code{float}. This is the default.
22128 @itemx -mno-float64
22130 @opindex mno-float64
22131 Use 32-bit @code{float}.
22135 Use @code{abshi2} pattern. This is the default.
22139 Do not use @code{abshi2} pattern.
22141 @item -mbranch-expensive
22142 @opindex mbranch-expensive
22143 Pretend that branches are expensive. This is for experimenting with
22144 code generation only.
22146 @item -mbranch-cheap
22147 @opindex mbranch-cheap
22148 Do not pretend that branches are expensive. This is the default.
22152 Use Unix assembler syntax. This is the default when configured for
22153 @samp{pdp11-*-bsd}.
22157 Use DEC assembler syntax. This is the default when configured for any
22158 PDP-11 target other than @samp{pdp11-*-bsd}.
22161 @node picoChip Options
22162 @subsection picoChip Options
22163 @cindex picoChip options
22165 These @samp{-m} options are defined for picoChip implementations:
22169 @item -mae=@var{ae_type}
22171 Set the instruction set, register set, and instruction scheduling
22172 parameters for array element type @var{ae_type}. Supported values
22173 for @var{ae_type} are @samp{ANY}, @samp{MUL}, and @samp{MAC}.
22175 @option{-mae=ANY} selects a completely generic AE type. Code
22176 generated with this option runs on any of the other AE types. The
22177 code is not as efficient as it would be if compiled for a specific
22178 AE type, and some types of operation (e.g., multiplication) do not
22179 work properly on all types of AE.
22181 @option{-mae=MUL} selects a MUL AE type. This is the most useful AE type
22182 for compiled code, and is the default.
22184 @option{-mae=MAC} selects a DSP-style MAC AE. Code compiled with this
22185 option may suffer from poor performance of byte (char) manipulation,
22186 since the DSP AE does not provide hardware support for byte load/stores.
22188 @item -msymbol-as-address
22189 Enable the compiler to directly use a symbol name as an address in a
22190 load/store instruction, without first loading it into a
22191 register. Typically, the use of this option generates larger
22192 programs, which run faster than when the option isn't used. However, the
22193 results vary from program to program, so it is left as a user option,
22194 rather than being permanently enabled.
22196 @item -mno-inefficient-warnings
22197 Disables warnings about the generation of inefficient code. These
22198 warnings can be generated, for example, when compiling code that
22199 performs byte-level memory operations on the MAC AE type. The MAC AE has
22200 no hardware support for byte-level memory operations, so all byte
22201 load/stores must be synthesized from word load/store operations. This is
22202 inefficient and a warning is generated to indicate
22203 that you should rewrite the code to avoid byte operations, or to target
22204 an AE type that has the necessary hardware support. This option disables
22209 @node PowerPC Options
22210 @subsection PowerPC Options
22211 @cindex PowerPC options
22213 These are listed under @xref{RS/6000 and PowerPC Options}.
22215 @node PowerPC SPE Options
22216 @subsection PowerPC SPE Options
22217 @cindex PowerPC SPE options
22219 These @samp{-m} options are defined for PowerPC SPE:
22224 @itemx -mno-popcntb
22228 @opindex mno-popcntb
22229 You use these options to specify which instructions are available on the
22230 processor you are using. The default value of these options is
22231 determined when configuring GCC@. Specifying the
22232 @option{-mcpu=@var{cpu_type}} overrides the specification of these
22233 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
22234 rather than the options listed above.
22236 The @option{-mmfcrf} option allows GCC to generate the move from
22237 condition register field instruction implemented on the POWER4
22238 processor and other processors that support the PowerPC V2.01
22240 The @option{-mpopcntb} option allows GCC to generate the popcount and
22241 double-precision FP reciprocal estimate instruction implemented on the
22242 POWER5 processor and other processors that support the PowerPC V2.02
22245 @item -mcpu=@var{cpu_type}
22247 Set architecture type, register usage, and
22248 instruction scheduling parameters for machine type @var{cpu_type}.
22249 Supported values for @var{cpu_type} are @samp{8540}, @samp{8548},
22252 @option{-mcpu=powerpc} specifies pure 32-bit PowerPC (either
22253 endian), with an appropriate, generic processor model assumed for
22254 scheduling purposes.
22256 Specifying @samp{native} as cpu type detects and selects the
22257 architecture option that corresponds to the host processor of the
22258 system performing the compilation.
22259 @option{-mcpu=native} has no effect if GCC does not recognize the
22262 The other options specify a specific processor. Code generated under
22263 those options runs best on that processor, and may not run at all on
22266 The @option{-mcpu} options automatically enable or disable the
22269 @gccoptlist{-mhard-float -mmfcrf -mmultiple @gol
22270 -mpopcntb -mpopcntd @gol
22271 -msingle-float -mdouble-float @gol
22274 The particular options set for any particular CPU varies between
22275 compiler versions, depending on what setting seems to produce optimal
22276 code for that CPU; it doesn't necessarily reflect the actual hardware's
22277 capabilities. If you wish to set an individual option to a particular
22278 value, you may specify it after the @option{-mcpu} option, like
22279 @option{-mcpu=8548}.
22281 @item -mtune=@var{cpu_type}
22283 Set the instruction scheduling parameters for machine type
22284 @var{cpu_type}, but do not set the architecture type or register usage,
22285 as @option{-mcpu=@var{cpu_type}} does. The same
22286 values for @var{cpu_type} are used for @option{-mtune} as for
22287 @option{-mcpu}. If both are specified, the code generated uses the
22288 architecture and registers set by @option{-mcpu}, but the
22289 scheduling parameters set by @option{-mtune}.
22292 @opindex msecure-plt
22293 Generate code that allows @command{ld} and @command{ld.so}
22294 to build executables and shared
22295 libraries with non-executable @code{.plt} and @code{.got} sections.
22297 32-bit SYSV ABI option.
22301 Generate code that uses a BSS @code{.plt} section that @command{ld.so}
22303 requires @code{.plt} and @code{.got}
22304 sections that are both writable and executable.
22305 This is a PowerPC 32-bit SYSV ABI option.
22311 This switch enables or disables the generation of ISEL instructions.
22313 @item -misel=@var{yes/no}
22314 This switch has been deprecated. Use @option{-misel} and
22315 @option{-mno-isel} instead.
22321 This switch enables or disables the generation of SPE simd
22324 @item -mspe=@var{yes/no}
22325 This option has been deprecated. Use @option{-mspe} and
22326 @option{-mno-spe} instead.
22329 @itemx -mno-float128
22331 @opindex mno-float128
22332 Enable/disable the @var{__float128} keyword for IEEE 128-bit floating point
22333 and use either software emulation for IEEE 128-bit floating point or
22334 hardware instructions.
22336 @item -mfloat-gprs=@var{yes/single/double/no}
22337 @itemx -mfloat-gprs
22338 @opindex mfloat-gprs
22339 This switch enables or disables the generation of floating-point
22340 operations on the general-purpose registers for architectures that
22343 The argument @samp{yes} or @samp{single} enables the use of
22344 single-precision floating-point operations.
22346 The argument @samp{double} enables the use of single and
22347 double-precision floating-point operations.
22349 The argument @samp{no} disables floating-point operations on the
22350 general-purpose registers.
22352 This option is currently only available on the MPC854x.
22355 @itemx -mno-fp-in-toc
22356 @itemx -mno-sum-in-toc
22357 @itemx -mminimal-toc
22359 @opindex mno-fp-in-toc
22360 @opindex mno-sum-in-toc
22361 @opindex mminimal-toc
22362 Modify generation of the TOC (Table Of Contents), which is created for
22363 every executable file. The @option{-mfull-toc} option is selected by
22364 default. In that case, GCC allocates at least one TOC entry for
22365 each unique non-automatic variable reference in your program. GCC
22366 also places floating-point constants in the TOC@. However, only
22367 16,384 entries are available in the TOC@.
22369 If you receive a linker error message that saying you have overflowed
22370 the available TOC space, you can reduce the amount of TOC space used
22371 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
22372 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
22373 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
22374 generate code to calculate the sum of an address and a constant at
22375 run time instead of putting that sum into the TOC@. You may specify one
22376 or both of these options. Each causes GCC to produce very slightly
22377 slower and larger code at the expense of conserving TOC space.
22379 If you still run out of space in the TOC even when you specify both of
22380 these options, specify @option{-mminimal-toc} instead. This option causes
22381 GCC to make only one TOC entry for every file. When you specify this
22382 option, GCC produces code that is slower and larger but which
22383 uses extremely little TOC space. You may wish to use this option
22384 only on files that contain less frequently-executed code.
22388 Disables the 64-bit ABI. GCC defaults to @option{-maix32}.
22391 @itemx -mno-xl-compat
22392 @opindex mxl-compat
22393 @opindex mno-xl-compat
22394 Produce code that conforms more closely to IBM XL compiler semantics
22395 when using AIX-compatible ABI@. Pass floating-point arguments to
22396 prototyped functions beyond the register save area (RSA) on the stack
22397 in addition to argument FPRs. Do not assume that most significant
22398 double in 128-bit long double value is properly rounded when comparing
22399 values and converting to double. Use XL symbol names for long double
22402 The AIX calling convention was extended but not initially documented to
22403 handle an obscure K&R C case of calling a function that takes the
22404 address of its arguments with fewer arguments than declared. IBM XL
22405 compilers access floating-point arguments that do not fit in the
22406 RSA from the stack when a subroutine is compiled without
22407 optimization. Because always storing floating-point arguments on the
22408 stack is inefficient and rarely needed, this option is not enabled by
22409 default and only is necessary when calling subroutines compiled by IBM
22410 XL compilers without optimization.
22412 @item -malign-natural
22413 @itemx -malign-power
22414 @opindex malign-natural
22415 @opindex malign-power
22416 On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
22417 @option{-malign-natural} overrides the ABI-defined alignment of larger
22418 types, such as floating-point doubles, on their natural size-based boundary.
22419 The option @option{-malign-power} instructs GCC to follow the ABI-specified
22420 alignment rules. GCC defaults to the standard alignment defined in the ABI@.
22422 On 64-bit Darwin, natural alignment is the default, and @option{-malign-power}
22426 @itemx -mhard-float
22427 @opindex msoft-float
22428 @opindex mhard-float
22429 Generate code that does not use (uses) the floating-point register set.
22430 Software floating-point emulation is provided if you use the
22431 @option{-msoft-float} option, and pass the option to GCC when linking.
22433 @item -msingle-float
22434 @itemx -mdouble-float
22435 @opindex msingle-float
22436 @opindex mdouble-float
22437 Generate code for single- or double-precision floating-point operations.
22438 @option{-mdouble-float} implies @option{-msingle-float}.
22441 @itemx -mno-multiple
22443 @opindex mno-multiple
22444 Generate code that uses (does not use) the load multiple word
22445 instructions and the store multiple word instructions. These
22446 instructions are generated by default on POWER systems, and not
22447 generated on PowerPC systems. Do not use @option{-mmultiple} on little-endian
22448 PowerPC systems, since those instructions do not work when the
22449 processor is in little-endian mode. The exceptions are PPC740 and
22450 PPC750 which permit these instructions in little-endian mode.
22455 @opindex mno-update
22456 Generate code that uses (does not use) the load or store instructions
22457 that update the base register to the address of the calculated memory
22458 location. These instructions are generated by default. If you use
22459 @option{-mno-update}, there is a small window between the time that the
22460 stack pointer is updated and the address of the previous frame is
22461 stored, which means code that walks the stack frame across interrupts or
22462 signals may get corrupted data.
22464 @item -mavoid-indexed-addresses
22465 @itemx -mno-avoid-indexed-addresses
22466 @opindex mavoid-indexed-addresses
22467 @opindex mno-avoid-indexed-addresses
22468 Generate code that tries to avoid (not avoid) the use of indexed load
22469 or store instructions. These instructions can incur a performance
22470 penalty on Power6 processors in certain situations, such as when
22471 stepping through large arrays that cross a 16M boundary. This option
22472 is enabled by default when targeting Power6 and disabled otherwise.
22475 @itemx -mno-fused-madd
22476 @opindex mfused-madd
22477 @opindex mno-fused-madd
22478 Generate code that uses (does not use) the floating-point multiply and
22479 accumulate instructions. These instructions are generated by default
22480 if hardware floating point is used. The machine-dependent
22481 @option{-mfused-madd} option is now mapped to the machine-independent
22482 @option{-ffp-contract=fast} option, and @option{-mno-fused-madd} is
22483 mapped to @option{-ffp-contract=off}.
22485 @item -mno-strict-align
22486 @itemx -mstrict-align
22487 @opindex mno-strict-align
22488 @opindex mstrict-align
22489 On System V.4 and embedded PowerPC systems do not (do) assume that
22490 unaligned memory references are handled by the system.
22492 @item -mrelocatable
22493 @itemx -mno-relocatable
22494 @opindex mrelocatable
22495 @opindex mno-relocatable
22496 Generate code that allows (does not allow) a static executable to be
22497 relocated to a different address at run time. A simple embedded
22498 PowerPC system loader should relocate the entire contents of
22499 @code{.got2} and 4-byte locations listed in the @code{.fixup} section,
22500 a table of 32-bit addresses generated by this option. For this to
22501 work, all objects linked together must be compiled with
22502 @option{-mrelocatable} or @option{-mrelocatable-lib}.
22503 @option{-mrelocatable} code aligns the stack to an 8-byte boundary.
22505 @item -mrelocatable-lib
22506 @itemx -mno-relocatable-lib
22507 @opindex mrelocatable-lib
22508 @opindex mno-relocatable-lib
22509 Like @option{-mrelocatable}, @option{-mrelocatable-lib} generates a
22510 @code{.fixup} section to allow static executables to be relocated at
22511 run time, but @option{-mrelocatable-lib} does not use the smaller stack
22512 alignment of @option{-mrelocatable}. Objects compiled with
22513 @option{-mrelocatable-lib} may be linked with objects compiled with
22514 any combination of the @option{-mrelocatable} options.
22520 On System V.4 and embedded PowerPC systems do not (do) assume that
22521 register 2 contains a pointer to a global area pointing to the addresses
22522 used in the program.
22525 @itemx -mlittle-endian
22527 @opindex mlittle-endian
22528 On System V.4 and embedded PowerPC systems compile code for the
22529 processor in little-endian mode. The @option{-mlittle-endian} option is
22530 the same as @option{-mlittle}.
22533 @itemx -mbig-endian
22535 @opindex mbig-endian
22536 On System V.4 and embedded PowerPC systems compile code for the
22537 processor in big-endian mode. The @option{-mbig-endian} option is
22538 the same as @option{-mbig}.
22540 @item -mdynamic-no-pic
22541 @opindex mdynamic-no-pic
22542 On Darwin and Mac OS X systems, compile code so that it is not
22543 relocatable, but that its external references are relocatable. The
22544 resulting code is suitable for applications, but not shared
22547 @item -msingle-pic-base
22548 @opindex msingle-pic-base
22549 Treat the register used for PIC addressing as read-only, rather than
22550 loading it in the prologue for each function. The runtime system is
22551 responsible for initializing this register with an appropriate value
22552 before execution begins.
22554 @item -mprioritize-restricted-insns=@var{priority}
22555 @opindex mprioritize-restricted-insns
22556 This option controls the priority that is assigned to
22557 dispatch-slot restricted instructions during the second scheduling
22558 pass. The argument @var{priority} takes the value @samp{0}, @samp{1},
22559 or @samp{2} to assign no, highest, or second-highest (respectively)
22560 priority to dispatch-slot restricted
22563 @item -msched-costly-dep=@var{dependence_type}
22564 @opindex msched-costly-dep
22565 This option controls which dependences are considered costly
22566 by the target during instruction scheduling. The argument
22567 @var{dependence_type} takes one of the following values:
22571 No dependence is costly.
22574 All dependences are costly.
22576 @item @samp{true_store_to_load}
22577 A true dependence from store to load is costly.
22579 @item @samp{store_to_load}
22580 Any dependence from store to load is costly.
22583 Any dependence for which the latency is greater than or equal to
22584 @var{number} is costly.
22587 @item -minsert-sched-nops=@var{scheme}
22588 @opindex minsert-sched-nops
22589 This option controls which NOP insertion scheme is used during
22590 the second scheduling pass. The argument @var{scheme} takes one of the
22598 Pad with NOPs any dispatch group that has vacant issue slots,
22599 according to the scheduler's grouping.
22601 @item @samp{regroup_exact}
22602 Insert NOPs to force costly dependent insns into
22603 separate groups. Insert exactly as many NOPs as needed to force an insn
22604 to a new group, according to the estimated processor grouping.
22607 Insert NOPs to force costly dependent insns into
22608 separate groups. Insert @var{number} NOPs to force an insn to a new group.
22612 @opindex mcall-sysv
22613 On System V.4 and embedded PowerPC systems compile code using calling
22614 conventions that adhere to the March 1995 draft of the System V
22615 Application Binary Interface, PowerPC processor supplement. This is the
22616 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
22618 @item -mcall-sysv-eabi
22620 @opindex mcall-sysv-eabi
22621 @opindex mcall-eabi
22622 Specify both @option{-mcall-sysv} and @option{-meabi} options.
22624 @item -mcall-sysv-noeabi
22625 @opindex mcall-sysv-noeabi
22626 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
22628 @item -mcall-aixdesc
22630 On System V.4 and embedded PowerPC systems compile code for the AIX
22634 @opindex mcall-linux
22635 On System V.4 and embedded PowerPC systems compile code for the
22636 Linux-based GNU system.
22638 @item -mcall-freebsd
22639 @opindex mcall-freebsd
22640 On System V.4 and embedded PowerPC systems compile code for the
22641 FreeBSD operating system.
22643 @item -mcall-netbsd
22644 @opindex mcall-netbsd
22645 On System V.4 and embedded PowerPC systems compile code for the
22646 NetBSD operating system.
22648 @item -mcall-openbsd
22649 @opindex mcall-netbsd
22650 On System V.4 and embedded PowerPC systems compile code for the
22651 OpenBSD operating system.
22653 @item -maix-struct-return
22654 @opindex maix-struct-return
22655 Return all structures in memory (as specified by the AIX ABI)@.
22657 @item -msvr4-struct-return
22658 @opindex msvr4-struct-return
22659 Return structures smaller than 8 bytes in registers (as specified by the
22662 @item -mabi=@var{abi-type}
22664 Extend the current ABI with a particular extension, or remove such extension.
22665 Valid values are @samp{altivec}, @samp{no-altivec}, @samp{spe},
22666 @samp{no-spe}, @samp{ibmlongdouble}, @samp{ieeelongdouble},
22667 @samp{elfv1}, @samp{elfv2}@.
22671 Extend the current ABI with SPE ABI extensions. This does not change
22672 the default ABI, instead it adds the SPE ABI extensions to the current
22676 @opindex mabi=no-spe
22677 Disable Book-E SPE ABI extensions for the current ABI@.
22679 @item -mabi=ibmlongdouble
22680 @opindex mabi=ibmlongdouble
22681 Change the current ABI to use IBM extended-precision long double.
22682 This is not likely to work if your system defaults to using IEEE
22683 extended-precision long double. If you change the long double type
22684 from IEEE extended-precision, the compiler will issue a warning unless
22685 you use the @option{-Wno-psabi} option.
22687 @item -mabi=ieeelongdouble
22688 @opindex mabi=ieeelongdouble
22689 Change the current ABI to use IEEE extended-precision long double.
22690 This is not likely to work if your system defaults to using IBM
22691 extended-precision long double. If you change the long double type
22692 from IBM extended-precision, the compiler will issue a warning unless
22693 you use the @option{-Wno-psabi} option.
22696 @opindex mabi=elfv1
22697 Change the current ABI to use the ELFv1 ABI.
22698 This is the default ABI for big-endian PowerPC 64-bit Linux.
22699 Overriding the default ABI requires special system support and is
22700 likely to fail in spectacular ways.
22703 @opindex mabi=elfv2
22704 Change the current ABI to use the ELFv2 ABI.
22705 This is the default ABI for little-endian PowerPC 64-bit Linux.
22706 Overriding the default ABI requires special system support and is
22707 likely to fail in spectacular ways.
22709 @item -mgnu-attribute
22710 @itemx -mno-gnu-attribute
22711 @opindex mgnu-attribute
22712 @opindex mno-gnu-attribute
22713 Emit .gnu_attribute assembly directives to set tag/value pairs in a
22714 .gnu.attributes section that specify ABI variations in function
22715 parameters or return values.
22718 @itemx -mno-prototype
22719 @opindex mprototype
22720 @opindex mno-prototype
22721 On System V.4 and embedded PowerPC systems assume that all calls to
22722 variable argument functions are properly prototyped. Otherwise, the
22723 compiler must insert an instruction before every non-prototyped call to
22724 set or clear bit 6 of the condition code register (@code{CR}) to
22725 indicate whether floating-point values are passed in the floating-point
22726 registers in case the function takes variable arguments. With
22727 @option{-mprototype}, only calls to prototyped variable argument functions
22728 set or clear the bit.
22732 On embedded PowerPC systems, assume that the startup module is called
22733 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
22734 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}
22739 On embedded PowerPC systems, assume that the startup module is called
22740 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
22745 On embedded PowerPC systems, assume that the startup module is called
22746 @file{crt0.o} and the standard C libraries are @file{libads.a} and
22749 @item -myellowknife
22750 @opindex myellowknife
22751 On embedded PowerPC systems, assume that the startup module is called
22752 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
22757 On System V.4 and embedded PowerPC systems, specify that you are
22758 compiling for a VxWorks system.
22762 On embedded PowerPC systems, set the @code{PPC_EMB} bit in the ELF flags
22763 header to indicate that @samp{eabi} extended relocations are used.
22769 On System V.4 and embedded PowerPC systems do (do not) adhere to the
22770 Embedded Applications Binary Interface (EABI), which is a set of
22771 modifications to the System V.4 specifications. Selecting @option{-meabi}
22772 means that the stack is aligned to an 8-byte boundary, a function
22773 @code{__eabi} is called from @code{main} to set up the EABI
22774 environment, and the @option{-msdata} option can use both @code{r2} and
22775 @code{r13} to point to two separate small data areas. Selecting
22776 @option{-mno-eabi} means that the stack is aligned to a 16-byte boundary,
22777 no EABI initialization function is called from @code{main}, and the
22778 @option{-msdata} option only uses @code{r13} to point to a single
22779 small data area. The @option{-meabi} option is on by default if you
22780 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
22783 @opindex msdata=eabi
22784 On System V.4 and embedded PowerPC systems, put small initialized
22785 @code{const} global and static data in the @code{.sdata2} section, which
22786 is pointed to by register @code{r2}. Put small initialized
22787 non-@code{const} global and static data in the @code{.sdata} section,
22788 which is pointed to by register @code{r13}. Put small uninitialized
22789 global and static data in the @code{.sbss} section, which is adjacent to
22790 the @code{.sdata} section. The @option{-msdata=eabi} option is
22791 incompatible with the @option{-mrelocatable} option. The
22792 @option{-msdata=eabi} option also sets the @option{-memb} option.
22795 @opindex msdata=sysv
22796 On System V.4 and embedded PowerPC systems, put small global and static
22797 data in the @code{.sdata} section, which is pointed to by register
22798 @code{r13}. Put small uninitialized global and static data in the
22799 @code{.sbss} section, which is adjacent to the @code{.sdata} section.
22800 The @option{-msdata=sysv} option is incompatible with the
22801 @option{-mrelocatable} option.
22803 @item -msdata=default
22805 @opindex msdata=default
22807 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
22808 compile code the same as @option{-msdata=eabi}, otherwise compile code the
22809 same as @option{-msdata=sysv}.
22812 @opindex msdata=data
22813 On System V.4 and embedded PowerPC systems, put small global
22814 data in the @code{.sdata} section. Put small uninitialized global
22815 data in the @code{.sbss} section. Do not use register @code{r13}
22816 to address small data however. This is the default behavior unless
22817 other @option{-msdata} options are used.
22821 @opindex msdata=none
22823 On embedded PowerPC systems, put all initialized global and static data
22824 in the @code{.data} section, and all uninitialized data in the
22825 @code{.bss} section.
22827 @item -mblock-move-inline-limit=@var{num}
22828 @opindex mblock-move-inline-limit
22829 Inline all block moves (such as calls to @code{memcpy} or structure
22830 copies) less than or equal to @var{num} bytes. The minimum value for
22831 @var{num} is 32 bytes on 32-bit targets and 64 bytes on 64-bit
22832 targets. The default value is target-specific.
22836 @cindex smaller data references (PowerPC)
22837 @cindex .sdata/.sdata2 references (PowerPC)
22838 On embedded PowerPC systems, put global and static items less than or
22839 equal to @var{num} bytes into the small data or BSS sections instead of
22840 the normal data or BSS section. By default, @var{num} is 8. The
22841 @option{-G @var{num}} switch is also passed to the linker.
22842 All modules should be compiled with the same @option{-G @var{num}} value.
22845 @itemx -mno-regnames
22847 @opindex mno-regnames
22848 On System V.4 and embedded PowerPC systems do (do not) emit register
22849 names in the assembly language output using symbolic forms.
22852 @itemx -mno-longcall
22854 @opindex mno-longcall
22855 By default assume that all calls are far away so that a longer and more
22856 expensive calling sequence is required. This is required for calls
22857 farther than 32 megabytes (33,554,432 bytes) from the current location.
22858 A short call is generated if the compiler knows
22859 the call cannot be that far away. This setting can be overridden by
22860 the @code{shortcall} function attribute, or by @code{#pragma
22863 Some linkers are capable of detecting out-of-range calls and generating
22864 glue code on the fly. On these systems, long calls are unnecessary and
22865 generate slower code. As of this writing, the AIX linker can do this,
22866 as can the GNU linker for PowerPC/64. It is planned to add this feature
22867 to the GNU linker for 32-bit PowerPC systems as well.
22869 In the future, GCC may ignore all longcall specifications
22870 when the linker is known to generate glue.
22872 @item -mtls-markers
22873 @itemx -mno-tls-markers
22874 @opindex mtls-markers
22875 @opindex mno-tls-markers
22876 Mark (do not mark) calls to @code{__tls_get_addr} with a relocation
22877 specifying the function argument. The relocation allows the linker to
22878 reliably associate function call with argument setup instructions for
22879 TLS optimization, which in turn allows GCC to better schedule the
22885 This option enables use of the reciprocal estimate and
22886 reciprocal square root estimate instructions with additional
22887 Newton-Raphson steps to increase precision instead of doing a divide or
22888 square root and divide for floating-point arguments. You should use
22889 the @option{-ffast-math} option when using @option{-mrecip} (or at
22890 least @option{-funsafe-math-optimizations},
22891 @option{-ffinite-math-only}, @option{-freciprocal-math} and
22892 @option{-fno-trapping-math}). Note that while the throughput of the
22893 sequence is generally higher than the throughput of the non-reciprocal
22894 instruction, the precision of the sequence can be decreased by up to 2
22895 ulp (i.e.@: the inverse of 1.0 equals 0.99999994) for reciprocal square
22898 @item -mrecip=@var{opt}
22899 @opindex mrecip=opt
22900 This option controls which reciprocal estimate instructions
22901 may be used. @var{opt} is a comma-separated list of options, which may
22902 be preceded by a @code{!} to invert the option:
22907 Enable all estimate instructions.
22910 Enable the default instructions, equivalent to @option{-mrecip}.
22913 Disable all estimate instructions, equivalent to @option{-mno-recip}.
22916 Enable the reciprocal approximation instructions for both
22917 single and double precision.
22920 Enable the single-precision reciprocal approximation instructions.
22923 Enable the double-precision reciprocal approximation instructions.
22926 Enable the reciprocal square root approximation instructions for both
22927 single and double precision.
22930 Enable the single-precision reciprocal square root approximation instructions.
22933 Enable the double-precision reciprocal square root approximation instructions.
22937 So, for example, @option{-mrecip=all,!rsqrtd} enables
22938 all of the reciprocal estimate instructions, except for the
22939 @code{FRSQRTE}, @code{XSRSQRTEDP}, and @code{XVRSQRTEDP} instructions
22940 which handle the double-precision reciprocal square root calculations.
22942 @item -mrecip-precision
22943 @itemx -mno-recip-precision
22944 @opindex mrecip-precision
22945 Assume (do not assume) that the reciprocal estimate instructions
22946 provide higher-precision estimates than is mandated by the PowerPC
22947 ABI. Selecting @option{-mcpu=power6}, @option{-mcpu=power7} or
22948 @option{-mcpu=power8} automatically selects @option{-mrecip-precision}.
22949 The double-precision square root estimate instructions are not generated by
22950 default on low-precision machines, since they do not provide an
22951 estimate that converges after three steps.
22953 @item -mpointers-to-nested-functions
22954 @itemx -mno-pointers-to-nested-functions
22955 @opindex mpointers-to-nested-functions
22956 Generate (do not generate) code to load up the static chain register
22957 (@code{r11}) when calling through a pointer on AIX and 64-bit Linux
22958 systems where a function pointer points to a 3-word descriptor giving
22959 the function address, TOC value to be loaded in register @code{r2}, and
22960 static chain value to be loaded in register @code{r11}. The
22961 @option{-mpointers-to-nested-functions} is on by default. You cannot
22962 call through pointers to nested functions or pointers
22963 to functions compiled in other languages that use the static chain if
22964 you use @option{-mno-pointers-to-nested-functions}.
22966 @item -msave-toc-indirect
22967 @itemx -mno-save-toc-indirect
22968 @opindex msave-toc-indirect
22969 Generate (do not generate) code to save the TOC value in the reserved
22970 stack location in the function prologue if the function calls through
22971 a pointer on AIX and 64-bit Linux systems. If the TOC value is not
22972 saved in the prologue, it is saved just before the call through the
22973 pointer. The @option{-mno-save-toc-indirect} option is the default.
22975 @item -mcompat-align-parm
22976 @itemx -mno-compat-align-parm
22977 @opindex mcompat-align-parm
22978 Generate (do not generate) code to pass structure parameters with a
22979 maximum alignment of 64 bits, for compatibility with older versions
22982 Older versions of GCC (prior to 4.9.0) incorrectly did not align a
22983 structure parameter on a 128-bit boundary when that structure contained
22984 a member requiring 128-bit alignment. This is corrected in more
22985 recent versions of GCC. This option may be used to generate code
22986 that is compatible with functions compiled with older versions of
22989 The @option{-mno-compat-align-parm} option is the default.
22991 @item -mstack-protector-guard=@var{guard}
22992 @itemx -mstack-protector-guard-reg=@var{reg}
22993 @itemx -mstack-protector-guard-offset=@var{offset}
22994 @itemx -mstack-protector-guard-symbol=@var{symbol}
22995 @opindex mstack-protector-guard
22996 @opindex mstack-protector-guard-reg
22997 @opindex mstack-protector-guard-offset
22998 @opindex mstack-protector-guard-symbol
22999 Generate stack protection code using canary at @var{guard}. Supported
23000 locations are @samp{global} for global canary or @samp{tls} for per-thread
23001 canary in the TLS block (the default with GNU libc version 2.4 or later).
23003 With the latter choice the options
23004 @option{-mstack-protector-guard-reg=@var{reg}} and
23005 @option{-mstack-protector-guard-offset=@var{offset}} furthermore specify
23006 which register to use as base register for reading the canary, and from what
23007 offset from that base register. The default for those is as specified in the
23008 relevant ABI. @option{-mstack-protector-guard-symbol=@var{symbol}} overrides
23009 the offset with a symbol reference to a canary in the TLS block.
23013 @node RISC-V Options
23014 @subsection RISC-V Options
23015 @cindex RISC-V Options
23017 These command-line options are defined for RISC-V targets:
23020 @item -mbranch-cost=@var{n}
23021 @opindex mbranch-cost
23022 Set the cost of branches to roughly @var{n} instructions.
23027 When generating PIC code, do or don't allow the use of PLTs. Ignored for
23028 non-PIC. The default is @option{-mplt}.
23030 @item -mabi=@var{ABI-string}
23032 Specify integer and floating-point calling convention. @var{ABI-string}
23033 contains two parts: the size of integer types and the registers used for
23034 floating-point types. For example @samp{-march=rv64ifd -mabi=lp64d} means that
23035 @samp{long} and pointers are 64-bit (implicitly defining @samp{int} to be
23036 32-bit), and that floating-point values up to 64 bits wide are passed in F
23037 registers. Contrast this with @samp{-march=rv64ifd -mabi=lp64f}, which still
23038 allows the compiler to generate code that uses the F and D extensions but only
23039 allows floating-point values up to 32 bits long to be passed in registers; or
23040 @samp{-march=rv64ifd -mabi=lp64}, in which no floating-point arguments will be
23041 passed in registers.
23043 The default for this argument is system dependent, users who want a specific
23044 calling convention should specify one explicitly. The valid calling
23045 conventions are: @samp{ilp32}, @samp{ilp32f}, @samp{ilp32d}, @samp{lp64},
23046 @samp{lp64f}, and @samp{lp64d}. Some calling conventions are impossible to
23047 implement on some ISAs: for example, @samp{-march=rv32if -mabi=ilp32d} is
23048 invalid because the ABI requires 64-bit values be passed in F registers, but F
23049 registers are only 32 bits wide.
23054 Do or don't use hardware floating-point divide and square root instructions.
23055 This requires the F or D extensions for floating-point registers. The default
23056 is to use them if the specified architecture has these instructions.
23061 Do or don't use hardware instructions for integer division. This requires the
23062 M extension. The default is to use them if the specified architecture has
23063 these instructions.
23065 @item -march=@var{ISA-string}
23067 Generate code for given RISC-V ISA (e.g.@ @samp{rv64im}). ISA strings must be
23068 lower-case. Examples include @samp{rv64i}, @samp{rv32g}, and @samp{rv32imaf}.
23070 @item -mtune=@var{processor-string}
23072 Optimize the output for the given processor, specified by microarchitecture
23075 @item -mpreferred-stack-boundary=@var{num}
23076 @opindex mpreferred-stack-boundary
23077 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
23078 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
23079 the default is 4 (16 bytes or 128-bits).
23081 @strong{Warning:} If you use this switch, then you must build all modules with
23082 the same value, including any libraries. This includes the system libraries
23083 and startup modules.
23085 @item -msmall-data-limit=@var{n}
23086 @opindex msmall-data-limit
23087 Put global and static data smaller than @var{n} bytes into a special section
23090 @item -msave-restore
23091 @itemx -mno-save-restore
23092 @opindex msave-restore
23093 Do or don't use smaller but slower prologue and epilogue code that uses
23094 library function calls. The default is to use fast inline prologues and
23097 @item -mstrict-align
23098 @itemx -mno-strict-align
23099 @opindex mstrict-align
23100 Do not or do generate unaligned memory accesses. The default is set depending
23101 on whether the processor we are optimizing for supports fast unaligned access
23104 @item -mcmodel=medlow
23105 @opindex mcmodel=medlow
23106 Generate code for the medium-low code model. The program and its statically
23107 defined symbols must lie within a single 2 GiB address range and must lie
23108 between absolute addresses @minus{}2 GiB and +2 GiB. Programs can be
23109 statically or dynamically linked. This is the default code model.
23111 @item -mcmodel=medany
23112 @opindex mcmodel=medany
23113 Generate code for the medium-any code model. The program and its statically
23114 defined symbols must be within any single 2 GiB address range. Programs can be
23115 statically or dynamically linked.
23117 @item -mexplicit-relocs
23118 @itemx -mno-exlicit-relocs
23119 Use or do not use assembler relocation operators when dealing with symbolic
23120 addresses. The alternative is to use assembler macros instead, which may
23121 limit optimization.
23125 Take advantage of linker relaxations to reduce the number of instructions
23126 required to materialize symbol addresses. The default is to take advantage of
23127 linker relaxations.
23132 @subsection RL78 Options
23133 @cindex RL78 Options
23139 Links in additional target libraries to support operation within a
23148 Specifies the type of hardware multiplication and division support to
23149 be used. The simplest is @code{none}, which uses software for both
23150 multiplication and division. This is the default. The @code{g13}
23151 value is for the hardware multiply/divide peripheral found on the
23152 RL78/G13 (S2 core) targets. The @code{g14} value selects the use of
23153 the multiplication and division instructions supported by the RL78/G14
23154 (S3 core) parts. The value @code{rl78} is an alias for @code{g14} and
23155 the value @code{mg10} is an alias for @code{none}.
23157 In addition a C preprocessor macro is defined, based upon the setting
23158 of this option. Possible values are: @code{__RL78_MUL_NONE__},
23159 @code{__RL78_MUL_G13__} or @code{__RL78_MUL_G14__}.
23166 Specifies the RL78 core to target. The default is the G14 core, also
23167 known as an S3 core or just RL78. The G13 or S2 core does not have
23168 multiply or divide instructions, instead it uses a hardware peripheral
23169 for these operations. The G10 or S1 core does not have register
23170 banks, so it uses a different calling convention.
23172 If this option is set it also selects the type of hardware multiply
23173 support to use, unless this is overridden by an explicit
23174 @option{-mmul=none} option on the command line. Thus specifying
23175 @option{-mcpu=g13} enables the use of the G13 hardware multiply
23176 peripheral and specifying @option{-mcpu=g10} disables the use of
23177 hardware multiplications altogether.
23179 Note, although the RL78/G14 core is the default target, specifying
23180 @option{-mcpu=g14} or @option{-mcpu=rl78} on the command line does
23181 change the behavior of the toolchain since it also enables G14
23182 hardware multiply support. If these options are not specified on the
23183 command line then software multiplication routines will be used even
23184 though the code targets the RL78 core. This is for backwards
23185 compatibility with older toolchains which did not have hardware
23186 multiply and divide support.
23188 In addition a C preprocessor macro is defined, based upon the setting
23189 of this option. Possible values are: @code{__RL78_G10__},
23190 @code{__RL78_G13__} or @code{__RL78_G14__}.
23200 These are aliases for the corresponding @option{-mcpu=} option. They
23201 are provided for backwards compatibility.
23205 Allow the compiler to use all of the available registers. By default
23206 registers @code{r24..r31} are reserved for use in interrupt handlers.
23207 With this option enabled these registers can be used in ordinary
23210 @item -m64bit-doubles
23211 @itemx -m32bit-doubles
23212 @opindex m64bit-doubles
23213 @opindex m32bit-doubles
23214 Make the @code{double} data type be 64 bits (@option{-m64bit-doubles})
23215 or 32 bits (@option{-m32bit-doubles}) in size. The default is
23216 @option{-m32bit-doubles}.
23218 @item -msave-mduc-in-interrupts
23219 @itemx -mno-save-mduc-in-interrupts
23220 @opindex msave-mduc-in-interrupts
23221 @opindex mno-save-mduc-in-interrupts
23222 Specifies that interrupt handler functions should preserve the
23223 MDUC registers. This is only necessary if normal code might use
23224 the MDUC registers, for example because it performs multiplication
23225 and division operations. The default is to ignore the MDUC registers
23226 as this makes the interrupt handlers faster. The target option -mg13
23227 needs to be passed for this to work as this feature is only available
23228 on the G13 target (S2 core). The MDUC registers will only be saved
23229 if the interrupt handler performs a multiplication or division
23230 operation or it calls another function.
23234 @node RS/6000 and PowerPC Options
23235 @subsection IBM RS/6000 and PowerPC Options
23236 @cindex RS/6000 and PowerPC Options
23237 @cindex IBM RS/6000 and PowerPC Options
23239 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
23241 @item -mpowerpc-gpopt
23242 @itemx -mno-powerpc-gpopt
23243 @itemx -mpowerpc-gfxopt
23244 @itemx -mno-powerpc-gfxopt
23247 @itemx -mno-powerpc64
23251 @itemx -mno-popcntb
23253 @itemx -mno-popcntd
23262 @itemx -mno-hard-dfp
23263 @opindex mpowerpc-gpopt
23264 @opindex mno-powerpc-gpopt
23265 @opindex mpowerpc-gfxopt
23266 @opindex mno-powerpc-gfxopt
23267 @opindex mpowerpc64
23268 @opindex mno-powerpc64
23272 @opindex mno-popcntb
23274 @opindex mno-popcntd
23280 @opindex mno-mfpgpr
23282 @opindex mno-hard-dfp
23283 You use these options to specify which instructions are available on the
23284 processor you are using. The default value of these options is
23285 determined when configuring GCC@. Specifying the
23286 @option{-mcpu=@var{cpu_type}} overrides the specification of these
23287 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
23288 rather than the options listed above.
23290 Specifying @option{-mpowerpc-gpopt} allows
23291 GCC to use the optional PowerPC architecture instructions in the
23292 General Purpose group, including floating-point square root. Specifying
23293 @option{-mpowerpc-gfxopt} allows GCC to
23294 use the optional PowerPC architecture instructions in the Graphics
23295 group, including floating-point select.
23297 The @option{-mmfcrf} option allows GCC to generate the move from
23298 condition register field instruction implemented on the POWER4
23299 processor and other processors that support the PowerPC V2.01
23301 The @option{-mpopcntb} option allows GCC to generate the popcount and
23302 double-precision FP reciprocal estimate instruction implemented on the
23303 POWER5 processor and other processors that support the PowerPC V2.02
23305 The @option{-mpopcntd} option allows GCC to generate the popcount
23306 instruction implemented on the POWER7 processor and other processors
23307 that support the PowerPC V2.06 architecture.
23308 The @option{-mfprnd} option allows GCC to generate the FP round to
23309 integer instructions implemented on the POWER5+ processor and other
23310 processors that support the PowerPC V2.03 architecture.
23311 The @option{-mcmpb} option allows GCC to generate the compare bytes
23312 instruction implemented on the POWER6 processor and other processors
23313 that support the PowerPC V2.05 architecture.
23314 The @option{-mmfpgpr} option allows GCC to generate the FP move to/from
23315 general-purpose register instructions implemented on the POWER6X
23316 processor and other processors that support the extended PowerPC V2.05
23318 The @option{-mhard-dfp} option allows GCC to generate the decimal
23319 floating-point instructions implemented on some POWER processors.
23321 The @option{-mpowerpc64} option allows GCC to generate the additional
23322 64-bit instructions that are found in the full PowerPC64 architecture
23323 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
23324 @option{-mno-powerpc64}.
23326 @item -mcpu=@var{cpu_type}
23328 Set architecture type, register usage, and
23329 instruction scheduling parameters for machine type @var{cpu_type}.
23330 Supported values for @var{cpu_type} are @samp{401}, @samp{403},
23331 @samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{464}, @samp{464fp},
23332 @samp{476}, @samp{476fp}, @samp{505}, @samp{601}, @samp{602}, @samp{603},
23333 @samp{603e}, @samp{604}, @samp{604e}, @samp{620}, @samp{630}, @samp{740},
23334 @samp{7400}, @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
23335 @samp{860}, @samp{970}, @samp{8540}, @samp{a2}, @samp{e300c2},
23336 @samp{e300c3}, @samp{e500mc}, @samp{e500mc64}, @samp{e5500},
23337 @samp{e6500}, @samp{ec603e}, @samp{G3}, @samp{G4}, @samp{G5},
23338 @samp{titan}, @samp{power3}, @samp{power4}, @samp{power5}, @samp{power5+},
23339 @samp{power6}, @samp{power6x}, @samp{power7}, @samp{power8},
23340 @samp{power9}, @samp{powerpc}, @samp{powerpc64}, @samp{powerpc64le},
23341 @samp{rs64}, and @samp{native}.
23343 @option{-mcpu=powerpc}, @option{-mcpu=powerpc64}, and
23344 @option{-mcpu=powerpc64le} specify pure 32-bit PowerPC (either
23345 endian), 64-bit big endian PowerPC and 64-bit little endian PowerPC
23346 architecture machine types, with an appropriate, generic processor
23347 model assumed for scheduling purposes.
23349 Specifying @samp{native} as cpu type detects and selects the
23350 architecture option that corresponds to the host processor of the
23351 system performing the compilation.
23352 @option{-mcpu=native} has no effect if GCC does not recognize the
23355 The other options specify a specific processor. Code generated under
23356 those options runs best on that processor, and may not run at all on
23359 The @option{-mcpu} options automatically enable or disable the
23362 @gccoptlist{-maltivec -mfprnd -mhard-float -mmfcrf -mmultiple @gol
23363 -mpopcntb -mpopcntd -mpowerpc64 @gol
23364 -mpowerpc-gpopt -mpowerpc-gfxopt -msingle-float -mdouble-float @gol
23365 -msimple-fpu -mmulhw -mdlmzb -mmfpgpr -mvsx @gol
23366 -mcrypto -mhtm -mpower8-fusion -mpower8-vector @gol
23367 -mquad-memory -mquad-memory-atomic -mfloat128 -mfloat128-hardware}
23369 The particular options set for any particular CPU varies between
23370 compiler versions, depending on what setting seems to produce optimal
23371 code for that CPU; it doesn't necessarily reflect the actual hardware's
23372 capabilities. If you wish to set an individual option to a particular
23373 value, you may specify it after the @option{-mcpu} option, like
23374 @option{-mcpu=970 -mno-altivec}.
23376 On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are
23377 not enabled or disabled by the @option{-mcpu} option at present because
23378 AIX does not have full support for these options. You may still
23379 enable or disable them individually if you're sure it'll work in your
23382 @item -mtune=@var{cpu_type}
23384 Set the instruction scheduling parameters for machine type
23385 @var{cpu_type}, but do not set the architecture type or register usage,
23386 as @option{-mcpu=@var{cpu_type}} does. The same
23387 values for @var{cpu_type} are used for @option{-mtune} as for
23388 @option{-mcpu}. If both are specified, the code generated uses the
23389 architecture and registers set by @option{-mcpu}, but the
23390 scheduling parameters set by @option{-mtune}.
23392 @item -mcmodel=small
23393 @opindex mcmodel=small
23394 Generate PowerPC64 code for the small model: The TOC is limited to
23397 @item -mcmodel=medium
23398 @opindex mcmodel=medium
23399 Generate PowerPC64 code for the medium model: The TOC and other static
23400 data may be up to a total of 4G in size. This is the default for 64-bit
23403 @item -mcmodel=large
23404 @opindex mcmodel=large
23405 Generate PowerPC64 code for the large model: The TOC may be up to 4G
23406 in size. Other data and code is only limited by the 64-bit address
23410 @itemx -mno-altivec
23412 @opindex mno-altivec
23413 Generate code that uses (does not use) AltiVec instructions, and also
23414 enable the use of built-in functions that allow more direct access to
23415 the AltiVec instruction set. You may also need to set
23416 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
23419 When @option{-maltivec} is used, rather than @option{-maltivec=le} or
23420 @option{-maltivec=be}, the element order for AltiVec intrinsics such
23421 as @code{vec_splat}, @code{vec_extract}, and @code{vec_insert}
23422 match array element order corresponding to the endianness of the
23423 target. That is, element zero identifies the leftmost element in a
23424 vector register when targeting a big-endian platform, and identifies
23425 the rightmost element in a vector register when targeting a
23426 little-endian platform.
23429 @opindex maltivec=be
23430 Generate AltiVec instructions using big-endian element order,
23431 regardless of whether the target is big- or little-endian. This is
23432 the default when targeting a big-endian platform. Using this option
23433 is currently deprecated. Support for this feature will be removed in
23436 The element order is used to interpret element numbers in AltiVec
23437 intrinsics such as @code{vec_splat}, @code{vec_extract}, and
23438 @code{vec_insert}. By default, these match array element order
23439 corresponding to the endianness for the target.
23442 @opindex maltivec=le
23443 Generate AltiVec instructions using little-endian element order,
23444 regardless of whether the target is big- or little-endian. This is
23445 the default when targeting a little-endian platform. This option is
23446 currently ignored when targeting a big-endian platform.
23448 The element order is used to interpret element numbers in AltiVec
23449 intrinsics such as @code{vec_splat}, @code{vec_extract}, and
23450 @code{vec_insert}. By default, these match array element order
23451 corresponding to the endianness for the target.
23456 @opindex mno-vrsave
23457 Generate VRSAVE instructions when generating AltiVec code.
23460 @opindex msecure-plt
23461 Generate code that allows @command{ld} and @command{ld.so}
23462 to build executables and shared
23463 libraries with non-executable @code{.plt} and @code{.got} sections.
23465 32-bit SYSV ABI option.
23469 Generate code that uses a BSS @code{.plt} section that @command{ld.so}
23471 requires @code{.plt} and @code{.got}
23472 sections that are both writable and executable.
23473 This is a PowerPC 32-bit SYSV ABI option.
23479 This switch enables or disables the generation of ISEL instructions.
23481 @item -misel=@var{yes/no}
23482 This switch has been deprecated. Use @option{-misel} and
23483 @option{-mno-isel} instead.
23488 @opindex mno-paired
23489 This switch enables or disables the generation of PAIRED simd
23496 Generate code that uses (does not use) vector/scalar (VSX)
23497 instructions, and also enable the use of built-in functions that allow
23498 more direct access to the VSX instruction set.
23503 @opindex mno-crypto
23504 Enable the use (disable) of the built-in functions that allow direct
23505 access to the cryptographic instructions that were added in version
23506 2.07 of the PowerPC ISA.
23512 Enable (disable) the use of the built-in functions that allow direct
23513 access to the Hardware Transactional Memory (HTM) instructions that
23514 were added in version 2.07 of the PowerPC ISA.
23516 @item -mpower8-fusion
23517 @itemx -mno-power8-fusion
23518 @opindex mpower8-fusion
23519 @opindex mno-power8-fusion
23520 Generate code that keeps (does not keeps) some integer operations
23521 adjacent so that the instructions can be fused together on power8 and
23524 @item -mpower8-vector
23525 @itemx -mno-power8-vector
23526 @opindex mpower8-vector
23527 @opindex mno-power8-vector
23528 Generate code that uses (does not use) the vector and scalar
23529 instructions that were added in version 2.07 of the PowerPC ISA. Also
23530 enable the use of built-in functions that allow more direct access to
23531 the vector instructions.
23533 @item -mquad-memory
23534 @itemx -mno-quad-memory
23535 @opindex mquad-memory
23536 @opindex mno-quad-memory
23537 Generate code that uses (does not use) the non-atomic quad word memory
23538 instructions. The @option{-mquad-memory} option requires use of
23541 @item -mquad-memory-atomic
23542 @itemx -mno-quad-memory-atomic
23543 @opindex mquad-memory-atomic
23544 @opindex mno-quad-memory-atomic
23545 Generate code that uses (does not use) the atomic quad word memory
23546 instructions. The @option{-mquad-memory-atomic} option requires use of
23550 @itemx -mno-float128
23552 @opindex mno-float128
23553 Enable/disable the @var{__float128} keyword for IEEE 128-bit floating point
23554 and use either software emulation for IEEE 128-bit floating point or
23555 hardware instructions.
23557 The VSX instruction set (@option{-mvsx}, @option{-mcpu=power7},
23558 @option{-mcpu=power8}), or @option{-mcpu=power9} must be enabled to
23559 use the IEEE 128-bit floating point support. The IEEE 128-bit
23560 floating point support only works on PowerPC Linux systems.
23562 The default for @option{-mfloat128} is enabled on PowerPC Linux
23563 systems using the VSX instruction set, and disabled on other systems.
23565 If you use the ISA 3.0 instruction set (@option{-mpower9-vector} or
23566 @option{-mcpu=power9}) on a 64-bit system, the IEEE 128-bit floating
23567 point support will also enable the generation of ISA 3.0 IEEE 128-bit
23568 floating point instructions. Otherwise, if you do not specify to
23569 generate ISA 3.0 instructions or you are targeting a 32-bit big endian
23570 system, IEEE 128-bit floating point will be done with software
23573 @item -mfloat128-hardware
23574 @itemx -mno-float128-hardware
23575 @opindex mfloat128-hardware
23576 @opindex mno-float128-hardware
23577 Enable/disable using ISA 3.0 hardware instructions to support the
23578 @var{__float128} data type.
23580 The default for @option{-mfloat128-hardware} is enabled on PowerPC
23581 Linux systems using the ISA 3.0 instruction set, and disabled on other
23588 Generate code for 32-bit or 64-bit environments of Darwin and SVR4
23589 targets (including GNU/Linux). The 32-bit environment sets int, long
23590 and pointer to 32 bits and generates code that runs on any PowerPC
23591 variant. The 64-bit environment sets int to 32 bits and long and
23592 pointer to 64 bits, and generates code for PowerPC64, as for
23593 @option{-mpowerpc64}.
23596 @itemx -mno-fp-in-toc
23597 @itemx -mno-sum-in-toc
23598 @itemx -mminimal-toc
23600 @opindex mno-fp-in-toc
23601 @opindex mno-sum-in-toc
23602 @opindex mminimal-toc
23603 Modify generation of the TOC (Table Of Contents), which is created for
23604 every executable file. The @option{-mfull-toc} option is selected by
23605 default. In that case, GCC allocates at least one TOC entry for
23606 each unique non-automatic variable reference in your program. GCC
23607 also places floating-point constants in the TOC@. However, only
23608 16,384 entries are available in the TOC@.
23610 If you receive a linker error message that saying you have overflowed
23611 the available TOC space, you can reduce the amount of TOC space used
23612 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
23613 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
23614 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
23615 generate code to calculate the sum of an address and a constant at
23616 run time instead of putting that sum into the TOC@. You may specify one
23617 or both of these options. Each causes GCC to produce very slightly
23618 slower and larger code at the expense of conserving TOC space.
23620 If you still run out of space in the TOC even when you specify both of
23621 these options, specify @option{-mminimal-toc} instead. This option causes
23622 GCC to make only one TOC entry for every file. When you specify this
23623 option, GCC produces code that is slower and larger but which
23624 uses extremely little TOC space. You may wish to use this option
23625 only on files that contain less frequently-executed code.
23631 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
23632 @code{long} type, and the infrastructure needed to support them.
23633 Specifying @option{-maix64} implies @option{-mpowerpc64},
23634 while @option{-maix32} disables the 64-bit ABI and
23635 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
23638 @itemx -mno-xl-compat
23639 @opindex mxl-compat
23640 @opindex mno-xl-compat
23641 Produce code that conforms more closely to IBM XL compiler semantics
23642 when using AIX-compatible ABI@. Pass floating-point arguments to
23643 prototyped functions beyond the register save area (RSA) on the stack
23644 in addition to argument FPRs. Do not assume that most significant
23645 double in 128-bit long double value is properly rounded when comparing
23646 values and converting to double. Use XL symbol names for long double
23649 The AIX calling convention was extended but not initially documented to
23650 handle an obscure K&R C case of calling a function that takes the
23651 address of its arguments with fewer arguments than declared. IBM XL
23652 compilers access floating-point arguments that do not fit in the
23653 RSA from the stack when a subroutine is compiled without
23654 optimization. Because always storing floating-point arguments on the
23655 stack is inefficient and rarely needed, this option is not enabled by
23656 default and only is necessary when calling subroutines compiled by IBM
23657 XL compilers without optimization.
23661 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
23662 application written to use message passing with special startup code to
23663 enable the application to run. The system must have PE installed in the
23664 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
23665 must be overridden with the @option{-specs=} option to specify the
23666 appropriate directory location. The Parallel Environment does not
23667 support threads, so the @option{-mpe} option and the @option{-pthread}
23668 option are incompatible.
23670 @item -malign-natural
23671 @itemx -malign-power
23672 @opindex malign-natural
23673 @opindex malign-power
23674 On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
23675 @option{-malign-natural} overrides the ABI-defined alignment of larger
23676 types, such as floating-point doubles, on their natural size-based boundary.
23677 The option @option{-malign-power} instructs GCC to follow the ABI-specified
23678 alignment rules. GCC defaults to the standard alignment defined in the ABI@.
23680 On 64-bit Darwin, natural alignment is the default, and @option{-malign-power}
23684 @itemx -mhard-float
23685 @opindex msoft-float
23686 @opindex mhard-float
23687 Generate code that does not use (uses) the floating-point register set.
23688 Software floating-point emulation is provided if you use the
23689 @option{-msoft-float} option, and pass the option to GCC when linking.
23691 @item -msingle-float
23692 @itemx -mdouble-float
23693 @opindex msingle-float
23694 @opindex mdouble-float
23695 Generate code for single- or double-precision floating-point operations.
23696 @option{-mdouble-float} implies @option{-msingle-float}.
23699 @opindex msimple-fpu
23700 Do not generate @code{sqrt} and @code{div} instructions for hardware
23701 floating-point unit.
23703 @item -mfpu=@var{name}
23705 Specify type of floating-point unit. Valid values for @var{name} are
23706 @samp{sp_lite} (equivalent to @option{-msingle-float -msimple-fpu}),
23707 @samp{dp_lite} (equivalent to @option{-mdouble-float -msimple-fpu}),
23708 @samp{sp_full} (equivalent to @option{-msingle-float}),
23709 and @samp{dp_full} (equivalent to @option{-mdouble-float}).
23712 @opindex mxilinx-fpu
23713 Perform optimizations for the floating-point unit on Xilinx PPC 405/440.
23716 @itemx -mno-multiple
23718 @opindex mno-multiple
23719 Generate code that uses (does not use) the load multiple word
23720 instructions and the store multiple word instructions. These
23721 instructions are generated by default on POWER systems, and not
23722 generated on PowerPC systems. Do not use @option{-mmultiple} on little-endian
23723 PowerPC systems, since those instructions do not work when the
23724 processor is in little-endian mode. The exceptions are PPC740 and
23725 PPC750 which permit these instructions in little-endian mode.
23730 @opindex mno-update
23731 Generate code that uses (does not use) the load or store instructions
23732 that update the base register to the address of the calculated memory
23733 location. These instructions are generated by default. If you use
23734 @option{-mno-update}, there is a small window between the time that the
23735 stack pointer is updated and the address of the previous frame is
23736 stored, which means code that walks the stack frame across interrupts or
23737 signals may get corrupted data.
23739 @item -mavoid-indexed-addresses
23740 @itemx -mno-avoid-indexed-addresses
23741 @opindex mavoid-indexed-addresses
23742 @opindex mno-avoid-indexed-addresses
23743 Generate code that tries to avoid (not avoid) the use of indexed load
23744 or store instructions. These instructions can incur a performance
23745 penalty on Power6 processors in certain situations, such as when
23746 stepping through large arrays that cross a 16M boundary. This option
23747 is enabled by default when targeting Power6 and disabled otherwise.
23750 @itemx -mno-fused-madd
23751 @opindex mfused-madd
23752 @opindex mno-fused-madd
23753 Generate code that uses (does not use) the floating-point multiply and
23754 accumulate instructions. These instructions are generated by default
23755 if hardware floating point is used. The machine-dependent
23756 @option{-mfused-madd} option is now mapped to the machine-independent
23757 @option{-ffp-contract=fast} option, and @option{-mno-fused-madd} is
23758 mapped to @option{-ffp-contract=off}.
23764 Generate code that uses (does not use) the half-word multiply and
23765 multiply-accumulate instructions on the IBM 405, 440, 464 and 476 processors.
23766 These instructions are generated by default when targeting those
23773 Generate code that uses (does not use) the string-search @samp{dlmzb}
23774 instruction on the IBM 405, 440, 464 and 476 processors. This instruction is
23775 generated by default when targeting those processors.
23777 @item -mno-bit-align
23779 @opindex mno-bit-align
23780 @opindex mbit-align
23781 On System V.4 and embedded PowerPC systems do not (do) force structures
23782 and unions that contain bit-fields to be aligned to the base type of the
23785 For example, by default a structure containing nothing but 8
23786 @code{unsigned} bit-fields of length 1 is aligned to a 4-byte
23787 boundary and has a size of 4 bytes. By using @option{-mno-bit-align},
23788 the structure is aligned to a 1-byte boundary and is 1 byte in
23791 @item -mno-strict-align
23792 @itemx -mstrict-align
23793 @opindex mno-strict-align
23794 @opindex mstrict-align
23795 On System V.4 and embedded PowerPC systems do not (do) assume that
23796 unaligned memory references are handled by the system.
23798 @item -mrelocatable
23799 @itemx -mno-relocatable
23800 @opindex mrelocatable
23801 @opindex mno-relocatable
23802 Generate code that allows (does not allow) a static executable to be
23803 relocated to a different address at run time. A simple embedded
23804 PowerPC system loader should relocate the entire contents of
23805 @code{.got2} and 4-byte locations listed in the @code{.fixup} section,
23806 a table of 32-bit addresses generated by this option. For this to
23807 work, all objects linked together must be compiled with
23808 @option{-mrelocatable} or @option{-mrelocatable-lib}.
23809 @option{-mrelocatable} code aligns the stack to an 8-byte boundary.
23811 @item -mrelocatable-lib
23812 @itemx -mno-relocatable-lib
23813 @opindex mrelocatable-lib
23814 @opindex mno-relocatable-lib
23815 Like @option{-mrelocatable}, @option{-mrelocatable-lib} generates a
23816 @code{.fixup} section to allow static executables to be relocated at
23817 run time, but @option{-mrelocatable-lib} does not use the smaller stack
23818 alignment of @option{-mrelocatable}. Objects compiled with
23819 @option{-mrelocatable-lib} may be linked with objects compiled with
23820 any combination of the @option{-mrelocatable} options.
23826 On System V.4 and embedded PowerPC systems do not (do) assume that
23827 register 2 contains a pointer to a global area pointing to the addresses
23828 used in the program.
23831 @itemx -mlittle-endian
23833 @opindex mlittle-endian
23834 On System V.4 and embedded PowerPC systems compile code for the
23835 processor in little-endian mode. The @option{-mlittle-endian} option is
23836 the same as @option{-mlittle}.
23839 @itemx -mbig-endian
23841 @opindex mbig-endian
23842 On System V.4 and embedded PowerPC systems compile code for the
23843 processor in big-endian mode. The @option{-mbig-endian} option is
23844 the same as @option{-mbig}.
23846 @item -mdynamic-no-pic
23847 @opindex mdynamic-no-pic
23848 On Darwin and Mac OS X systems, compile code so that it is not
23849 relocatable, but that its external references are relocatable. The
23850 resulting code is suitable for applications, but not shared
23853 @item -msingle-pic-base
23854 @opindex msingle-pic-base
23855 Treat the register used for PIC addressing as read-only, rather than
23856 loading it in the prologue for each function. The runtime system is
23857 responsible for initializing this register with an appropriate value
23858 before execution begins.
23860 @item -mprioritize-restricted-insns=@var{priority}
23861 @opindex mprioritize-restricted-insns
23862 This option controls the priority that is assigned to
23863 dispatch-slot restricted instructions during the second scheduling
23864 pass. The argument @var{priority} takes the value @samp{0}, @samp{1},
23865 or @samp{2} to assign no, highest, or second-highest (respectively)
23866 priority to dispatch-slot restricted
23869 @item -msched-costly-dep=@var{dependence_type}
23870 @opindex msched-costly-dep
23871 This option controls which dependences are considered costly
23872 by the target during instruction scheduling. The argument
23873 @var{dependence_type} takes one of the following values:
23877 No dependence is costly.
23880 All dependences are costly.
23882 @item @samp{true_store_to_load}
23883 A true dependence from store to load is costly.
23885 @item @samp{store_to_load}
23886 Any dependence from store to load is costly.
23889 Any dependence for which the latency is greater than or equal to
23890 @var{number} is costly.
23893 @item -minsert-sched-nops=@var{scheme}
23894 @opindex minsert-sched-nops
23895 This option controls which NOP insertion scheme is used during
23896 the second scheduling pass. The argument @var{scheme} takes one of the
23904 Pad with NOPs any dispatch group that has vacant issue slots,
23905 according to the scheduler's grouping.
23907 @item @samp{regroup_exact}
23908 Insert NOPs to force costly dependent insns into
23909 separate groups. Insert exactly as many NOPs as needed to force an insn
23910 to a new group, according to the estimated processor grouping.
23913 Insert NOPs to force costly dependent insns into
23914 separate groups. Insert @var{number} NOPs to force an insn to a new group.
23918 @opindex mcall-sysv
23919 On System V.4 and embedded PowerPC systems compile code using calling
23920 conventions that adhere to the March 1995 draft of the System V
23921 Application Binary Interface, PowerPC processor supplement. This is the
23922 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
23924 @item -mcall-sysv-eabi
23926 @opindex mcall-sysv-eabi
23927 @opindex mcall-eabi
23928 Specify both @option{-mcall-sysv} and @option{-meabi} options.
23930 @item -mcall-sysv-noeabi
23931 @opindex mcall-sysv-noeabi
23932 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
23934 @item -mcall-aixdesc
23936 On System V.4 and embedded PowerPC systems compile code for the AIX
23940 @opindex mcall-linux
23941 On System V.4 and embedded PowerPC systems compile code for the
23942 Linux-based GNU system.
23944 @item -mcall-freebsd
23945 @opindex mcall-freebsd
23946 On System V.4 and embedded PowerPC systems compile code for the
23947 FreeBSD operating system.
23949 @item -mcall-netbsd
23950 @opindex mcall-netbsd
23951 On System V.4 and embedded PowerPC systems compile code for the
23952 NetBSD operating system.
23954 @item -mcall-openbsd
23955 @opindex mcall-netbsd
23956 On System V.4 and embedded PowerPC systems compile code for the
23957 OpenBSD operating system.
23959 @item -mtraceback=@var{traceback_type}
23960 @opindex mtraceback
23961 Select the type of traceback table. Valid values for @var{traceback_type}
23962 are @samp{full}, @samp{part}, and @samp{no}.
23964 @item -maix-struct-return
23965 @opindex maix-struct-return
23966 Return all structures in memory (as specified by the AIX ABI)@.
23968 @item -msvr4-struct-return
23969 @opindex msvr4-struct-return
23970 Return structures smaller than 8 bytes in registers (as specified by the
23973 @item -mabi=@var{abi-type}
23975 Extend the current ABI with a particular extension, or remove such extension.
23976 Valid values are @samp{altivec}, @samp{no-altivec}, @samp{spe},
23977 @samp{no-spe}, @samp{ibmlongdouble}, @samp{ieeelongdouble},
23978 @samp{elfv1}, @samp{elfv2}@.
23980 @item -mabi=ibmlongdouble
23981 @opindex mabi=ibmlongdouble
23982 Change the current ABI to use IBM extended-precision long double.
23983 This is not likely to work if your system defaults to using IEEE
23984 extended-precision long double. If you change the long double type
23985 from IEEE extended-precision, the compiler will issue a warning unless
23986 you use the @option{-Wno-psabi} option.
23988 @item -mabi=ieeelongdouble
23989 @opindex mabi=ieeelongdouble
23990 Change the current ABI to use IEEE extended-precision long double.
23991 This is not likely to work if your system defaults to using IBM
23992 extended-precision long double. If you change the long double type
23993 from IBM extended-precision, the compiler will issue a warning unless
23994 you use the @option{-Wno-psabi} option.
23997 @opindex mabi=elfv1
23998 Change the current ABI to use the ELFv1 ABI.
23999 This is the default ABI for big-endian PowerPC 64-bit Linux.
24000 Overriding the default ABI requires special system support and is
24001 likely to fail in spectacular ways.
24004 @opindex mabi=elfv2
24005 Change the current ABI to use the ELFv2 ABI.
24006 This is the default ABI for little-endian PowerPC 64-bit Linux.
24007 Overriding the default ABI requires special system support and is
24008 likely to fail in spectacular ways.
24010 @item -mgnu-attribute
24011 @itemx -mno-gnu-attribute
24012 @opindex mgnu-attribute
24013 @opindex mno-gnu-attribute
24014 Emit .gnu_attribute assembly directives to set tag/value pairs in a
24015 .gnu.attributes section that specify ABI variations in function
24016 parameters or return values.
24019 @itemx -mno-prototype
24020 @opindex mprototype
24021 @opindex mno-prototype
24022 On System V.4 and embedded PowerPC systems assume that all calls to
24023 variable argument functions are properly prototyped. Otherwise, the
24024 compiler must insert an instruction before every non-prototyped call to
24025 set or clear bit 6 of the condition code register (@code{CR}) to
24026 indicate whether floating-point values are passed in the floating-point
24027 registers in case the function takes variable arguments. With
24028 @option{-mprototype}, only calls to prototyped variable argument functions
24029 set or clear the bit.
24033 On embedded PowerPC systems, assume that the startup module is called
24034 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
24035 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}
24040 On embedded PowerPC systems, assume that the startup module is called
24041 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
24046 On embedded PowerPC systems, assume that the startup module is called
24047 @file{crt0.o} and the standard C libraries are @file{libads.a} and
24050 @item -myellowknife
24051 @opindex myellowknife
24052 On embedded PowerPC systems, assume that the startup module is called
24053 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
24058 On System V.4 and embedded PowerPC systems, specify that you are
24059 compiling for a VxWorks system.
24063 On embedded PowerPC systems, set the @code{PPC_EMB} bit in the ELF flags
24064 header to indicate that @samp{eabi} extended relocations are used.
24070 On System V.4 and embedded PowerPC systems do (do not) adhere to the
24071 Embedded Applications Binary Interface (EABI), which is a set of
24072 modifications to the System V.4 specifications. Selecting @option{-meabi}
24073 means that the stack is aligned to an 8-byte boundary, a function
24074 @code{__eabi} is called from @code{main} to set up the EABI
24075 environment, and the @option{-msdata} option can use both @code{r2} and
24076 @code{r13} to point to two separate small data areas. Selecting
24077 @option{-mno-eabi} means that the stack is aligned to a 16-byte boundary,
24078 no EABI initialization function is called from @code{main}, and the
24079 @option{-msdata} option only uses @code{r13} to point to a single
24080 small data area. The @option{-meabi} option is on by default if you
24081 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
24084 @opindex msdata=eabi
24085 On System V.4 and embedded PowerPC systems, put small initialized
24086 @code{const} global and static data in the @code{.sdata2} section, which
24087 is pointed to by register @code{r2}. Put small initialized
24088 non-@code{const} global and static data in the @code{.sdata} section,
24089 which is pointed to by register @code{r13}. Put small uninitialized
24090 global and static data in the @code{.sbss} section, which is adjacent to
24091 the @code{.sdata} section. The @option{-msdata=eabi} option is
24092 incompatible with the @option{-mrelocatable} option. The
24093 @option{-msdata=eabi} option also sets the @option{-memb} option.
24096 @opindex msdata=sysv
24097 On System V.4 and embedded PowerPC systems, put small global and static
24098 data in the @code{.sdata} section, which is pointed to by register
24099 @code{r13}. Put small uninitialized global and static data in the
24100 @code{.sbss} section, which is adjacent to the @code{.sdata} section.
24101 The @option{-msdata=sysv} option is incompatible with the
24102 @option{-mrelocatable} option.
24104 @item -msdata=default
24106 @opindex msdata=default
24108 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
24109 compile code the same as @option{-msdata=eabi}, otherwise compile code the
24110 same as @option{-msdata=sysv}.
24113 @opindex msdata=data
24114 On System V.4 and embedded PowerPC systems, put small global
24115 data in the @code{.sdata} section. Put small uninitialized global
24116 data in the @code{.sbss} section. Do not use register @code{r13}
24117 to address small data however. This is the default behavior unless
24118 other @option{-msdata} options are used.
24122 @opindex msdata=none
24124 On embedded PowerPC systems, put all initialized global and static data
24125 in the @code{.data} section, and all uninitialized data in the
24126 @code{.bss} section.
24128 @item -mreadonly-in-sdata
24129 @itemx -mreadonly-in-sdata
24130 @opindex mreadonly-in-sdata
24131 @opindex mno-readonly-in-sdata
24132 Put read-only objects in the @code{.sdata} section as well. This is the
24135 @item -mblock-move-inline-limit=@var{num}
24136 @opindex mblock-move-inline-limit
24137 Inline all block moves (such as calls to @code{memcpy} or structure
24138 copies) less than or equal to @var{num} bytes. The minimum value for
24139 @var{num} is 32 bytes on 32-bit targets and 64 bytes on 64-bit
24140 targets. The default value is target-specific.
24142 @item -mblock-compare-inline-limit=@var{num}
24143 @opindex mblock-compare-inline-limit
24144 Generate non-looping inline code for all block compares (such as calls
24145 to @code{memcmp} or structure compares) less than or equal to @var{num}
24146 bytes. If @var{num} is 0, all inline expansion (non-loop and loop) of
24147 block compare is disabled. The default value is target-specific.
24149 @item -mblock-compare-inline-loop-limit=@var{num}
24150 @opindex mblock-compare-inline-loop-limit
24151 Generate an inline expansion using loop code for all block compares that
24152 are less than or equal to @var{num} bytes, but greater than the limit
24153 for non-loop inline block compare expansion. If the block length is not
24154 constant, at most @var{num} bytes will be compared before @code{memcmp}
24155 is called to compare the remainder of the block. The default value is
24158 @item -mstring-compare-inline-limit=@var{num}
24159 @opindex mstring-compare-inline-limit
24160 Generate at most @var{num} pairs of load instructions to compare the
24161 string inline. If the difference or end of string is not found at the
24162 end of the inline compare a call to @code{strcmp} or @code{strncmp} will
24163 take care of the rest of the comparison. The default is 8 pairs of
24164 loads, which will compare 64 bytes on a 64-bit target and 32 bytes on a
24169 @cindex smaller data references (PowerPC)
24170 @cindex .sdata/.sdata2 references (PowerPC)
24171 On embedded PowerPC systems, put global and static items less than or
24172 equal to @var{num} bytes into the small data or BSS sections instead of
24173 the normal data or BSS section. By default, @var{num} is 8. The
24174 @option{-G @var{num}} switch is also passed to the linker.
24175 All modules should be compiled with the same @option{-G @var{num}} value.
24178 @itemx -mno-regnames
24180 @opindex mno-regnames
24181 On System V.4 and embedded PowerPC systems do (do not) emit register
24182 names in the assembly language output using symbolic forms.
24185 @itemx -mno-longcall
24187 @opindex mno-longcall
24188 By default assume that all calls are far away so that a longer and more
24189 expensive calling sequence is required. This is required for calls
24190 farther than 32 megabytes (33,554,432 bytes) from the current location.
24191 A short call is generated if the compiler knows
24192 the call cannot be that far away. This setting can be overridden by
24193 the @code{shortcall} function attribute, or by @code{#pragma
24196 Some linkers are capable of detecting out-of-range calls and generating
24197 glue code on the fly. On these systems, long calls are unnecessary and
24198 generate slower code. As of this writing, the AIX linker can do this,
24199 as can the GNU linker for PowerPC/64. It is planned to add this feature
24200 to the GNU linker for 32-bit PowerPC systems as well.
24202 On Darwin/PPC systems, @code{#pragma longcall} generates @code{jbsr
24203 callee, L42}, plus a @dfn{branch island} (glue code). The two target
24204 addresses represent the callee and the branch island. The
24205 Darwin/PPC linker prefers the first address and generates a @code{bl
24206 callee} if the PPC @code{bl} instruction reaches the callee directly;
24207 otherwise, the linker generates @code{bl L42} to call the branch
24208 island. The branch island is appended to the body of the
24209 calling function; it computes the full 32-bit address of the callee
24212 On Mach-O (Darwin) systems, this option directs the compiler emit to
24213 the glue for every direct call, and the Darwin linker decides whether
24214 to use or discard it.
24216 In the future, GCC may ignore all longcall specifications
24217 when the linker is known to generate glue.
24219 @item -mtls-markers
24220 @itemx -mno-tls-markers
24221 @opindex mtls-markers
24222 @opindex mno-tls-markers
24223 Mark (do not mark) calls to @code{__tls_get_addr} with a relocation
24224 specifying the function argument. The relocation allows the linker to
24225 reliably associate function call with argument setup instructions for
24226 TLS optimization, which in turn allows GCC to better schedule the
24232 This option enables use of the reciprocal estimate and
24233 reciprocal square root estimate instructions with additional
24234 Newton-Raphson steps to increase precision instead of doing a divide or
24235 square root and divide for floating-point arguments. You should use
24236 the @option{-ffast-math} option when using @option{-mrecip} (or at
24237 least @option{-funsafe-math-optimizations},
24238 @option{-ffinite-math-only}, @option{-freciprocal-math} and
24239 @option{-fno-trapping-math}). Note that while the throughput of the
24240 sequence is generally higher than the throughput of the non-reciprocal
24241 instruction, the precision of the sequence can be decreased by up to 2
24242 ulp (i.e.@: the inverse of 1.0 equals 0.99999994) for reciprocal square
24245 @item -mrecip=@var{opt}
24246 @opindex mrecip=opt
24247 This option controls which reciprocal estimate instructions
24248 may be used. @var{opt} is a comma-separated list of options, which may
24249 be preceded by a @code{!} to invert the option:
24254 Enable all estimate instructions.
24257 Enable the default instructions, equivalent to @option{-mrecip}.
24260 Disable all estimate instructions, equivalent to @option{-mno-recip}.
24263 Enable the reciprocal approximation instructions for both
24264 single and double precision.
24267 Enable the single-precision reciprocal approximation instructions.
24270 Enable the double-precision reciprocal approximation instructions.
24273 Enable the reciprocal square root approximation instructions for both
24274 single and double precision.
24277 Enable the single-precision reciprocal square root approximation instructions.
24280 Enable the double-precision reciprocal square root approximation instructions.
24284 So, for example, @option{-mrecip=all,!rsqrtd} enables
24285 all of the reciprocal estimate instructions, except for the
24286 @code{FRSQRTE}, @code{XSRSQRTEDP}, and @code{XVRSQRTEDP} instructions
24287 which handle the double-precision reciprocal square root calculations.
24289 @item -mrecip-precision
24290 @itemx -mno-recip-precision
24291 @opindex mrecip-precision
24292 Assume (do not assume) that the reciprocal estimate instructions
24293 provide higher-precision estimates than is mandated by the PowerPC
24294 ABI. Selecting @option{-mcpu=power6}, @option{-mcpu=power7} or
24295 @option{-mcpu=power8} automatically selects @option{-mrecip-precision}.
24296 The double-precision square root estimate instructions are not generated by
24297 default on low-precision machines, since they do not provide an
24298 estimate that converges after three steps.
24300 @item -mveclibabi=@var{type}
24301 @opindex mveclibabi
24302 Specifies the ABI type to use for vectorizing intrinsics using an
24303 external library. The only type supported at present is @samp{mass},
24304 which specifies to use IBM's Mathematical Acceleration Subsystem
24305 (MASS) libraries for vectorizing intrinsics using external libraries.
24306 GCC currently emits calls to @code{acosd2}, @code{acosf4},
24307 @code{acoshd2}, @code{acoshf4}, @code{asind2}, @code{asinf4},
24308 @code{asinhd2}, @code{asinhf4}, @code{atan2d2}, @code{atan2f4},
24309 @code{atand2}, @code{atanf4}, @code{atanhd2}, @code{atanhf4},
24310 @code{cbrtd2}, @code{cbrtf4}, @code{cosd2}, @code{cosf4},
24311 @code{coshd2}, @code{coshf4}, @code{erfcd2}, @code{erfcf4},
24312 @code{erfd2}, @code{erff4}, @code{exp2d2}, @code{exp2f4},
24313 @code{expd2}, @code{expf4}, @code{expm1d2}, @code{expm1f4},
24314 @code{hypotd2}, @code{hypotf4}, @code{lgammad2}, @code{lgammaf4},
24315 @code{log10d2}, @code{log10f4}, @code{log1pd2}, @code{log1pf4},
24316 @code{log2d2}, @code{log2f4}, @code{logd2}, @code{logf4},
24317 @code{powd2}, @code{powf4}, @code{sind2}, @code{sinf4}, @code{sinhd2},
24318 @code{sinhf4}, @code{sqrtd2}, @code{sqrtf4}, @code{tand2},
24319 @code{tanf4}, @code{tanhd2}, and @code{tanhf4} when generating code
24320 for power7. Both @option{-ftree-vectorize} and
24321 @option{-funsafe-math-optimizations} must also be enabled. The MASS
24322 libraries must be specified at link time.
24327 Generate (do not generate) the @code{friz} instruction when the
24328 @option{-funsafe-math-optimizations} option is used to optimize
24329 rounding of floating-point values to 64-bit integer and back to floating
24330 point. The @code{friz} instruction does not return the same value if
24331 the floating-point number is too large to fit in an integer.
24333 @item -mpointers-to-nested-functions
24334 @itemx -mno-pointers-to-nested-functions
24335 @opindex mpointers-to-nested-functions
24336 Generate (do not generate) code to load up the static chain register
24337 (@code{r11}) when calling through a pointer on AIX and 64-bit Linux
24338 systems where a function pointer points to a 3-word descriptor giving
24339 the function address, TOC value to be loaded in register @code{r2}, and
24340 static chain value to be loaded in register @code{r11}. The
24341 @option{-mpointers-to-nested-functions} is on by default. You cannot
24342 call through pointers to nested functions or pointers
24343 to functions compiled in other languages that use the static chain if
24344 you use @option{-mno-pointers-to-nested-functions}.
24346 @item -msave-toc-indirect
24347 @itemx -mno-save-toc-indirect
24348 @opindex msave-toc-indirect
24349 Generate (do not generate) code to save the TOC value in the reserved
24350 stack location in the function prologue if the function calls through
24351 a pointer on AIX and 64-bit Linux systems. If the TOC value is not
24352 saved in the prologue, it is saved just before the call through the
24353 pointer. The @option{-mno-save-toc-indirect} option is the default.
24355 @item -mcompat-align-parm
24356 @itemx -mno-compat-align-parm
24357 @opindex mcompat-align-parm
24358 Generate (do not generate) code to pass structure parameters with a
24359 maximum alignment of 64 bits, for compatibility with older versions
24362 Older versions of GCC (prior to 4.9.0) incorrectly did not align a
24363 structure parameter on a 128-bit boundary when that structure contained
24364 a member requiring 128-bit alignment. This is corrected in more
24365 recent versions of GCC. This option may be used to generate code
24366 that is compatible with functions compiled with older versions of
24369 The @option{-mno-compat-align-parm} option is the default.
24371 @item -mstack-protector-guard=@var{guard}
24372 @itemx -mstack-protector-guard-reg=@var{reg}
24373 @itemx -mstack-protector-guard-offset=@var{offset}
24374 @itemx -mstack-protector-guard-symbol=@var{symbol}
24375 @opindex mstack-protector-guard
24376 @opindex mstack-protector-guard-reg
24377 @opindex mstack-protector-guard-offset
24378 @opindex mstack-protector-guard-symbol
24379 Generate stack protection code using canary at @var{guard}. Supported
24380 locations are @samp{global} for global canary or @samp{tls} for per-thread
24381 canary in the TLS block (the default with GNU libc version 2.4 or later).
24383 With the latter choice the options
24384 @option{-mstack-protector-guard-reg=@var{reg}} and
24385 @option{-mstack-protector-guard-offset=@var{offset}} furthermore specify
24386 which register to use as base register for reading the canary, and from what
24387 offset from that base register. The default for those is as specified in the
24388 relevant ABI. @option{-mstack-protector-guard-symbol=@var{symbol}} overrides
24389 the offset with a symbol reference to a canary in the TLS block.
24393 @subsection RX Options
24396 These command-line options are defined for RX targets:
24399 @item -m64bit-doubles
24400 @itemx -m32bit-doubles
24401 @opindex m64bit-doubles
24402 @opindex m32bit-doubles
24403 Make the @code{double} data type be 64 bits (@option{-m64bit-doubles})
24404 or 32 bits (@option{-m32bit-doubles}) in size. The default is
24405 @option{-m32bit-doubles}. @emph{Note} RX floating-point hardware only
24406 works on 32-bit values, which is why the default is
24407 @option{-m32bit-doubles}.
24413 Enables (@option{-fpu}) or disables (@option{-nofpu}) the use of RX
24414 floating-point hardware. The default is enabled for the RX600
24415 series and disabled for the RX200 series.
24417 Floating-point instructions are only generated for 32-bit floating-point
24418 values, however, so the FPU hardware is not used for doubles if the
24419 @option{-m64bit-doubles} option is used.
24421 @emph{Note} If the @option{-fpu} option is enabled then
24422 @option{-funsafe-math-optimizations} is also enabled automatically.
24423 This is because the RX FPU instructions are themselves unsafe.
24425 @item -mcpu=@var{name}
24427 Selects the type of RX CPU to be targeted. Currently three types are
24428 supported, the generic @samp{RX600} and @samp{RX200} series hardware and
24429 the specific @samp{RX610} CPU. The default is @samp{RX600}.
24431 The only difference between @samp{RX600} and @samp{RX610} is that the
24432 @samp{RX610} does not support the @code{MVTIPL} instruction.
24434 The @samp{RX200} series does not have a hardware floating-point unit
24435 and so @option{-nofpu} is enabled by default when this type is
24438 @item -mbig-endian-data
24439 @itemx -mlittle-endian-data
24440 @opindex mbig-endian-data
24441 @opindex mlittle-endian-data
24442 Store data (but not code) in the big-endian format. The default is
24443 @option{-mlittle-endian-data}, i.e.@: to store data in the little-endian
24446 @item -msmall-data-limit=@var{N}
24447 @opindex msmall-data-limit
24448 Specifies the maximum size in bytes of global and static variables
24449 which can be placed into the small data area. Using the small data
24450 area can lead to smaller and faster code, but the size of area is
24451 limited and it is up to the programmer to ensure that the area does
24452 not overflow. Also when the small data area is used one of the RX's
24453 registers (usually @code{r13}) is reserved for use pointing to this
24454 area, so it is no longer available for use by the compiler. This
24455 could result in slower and/or larger code if variables are pushed onto
24456 the stack instead of being held in this register.
24458 Note, common variables (variables that have not been initialized) and
24459 constants are not placed into the small data area as they are assigned
24460 to other sections in the output executable.
24462 The default value is zero, which disables this feature. Note, this
24463 feature is not enabled by default with higher optimization levels
24464 (@option{-O2} etc) because of the potentially detrimental effects of
24465 reserving a register. It is up to the programmer to experiment and
24466 discover whether this feature is of benefit to their program. See the
24467 description of the @option{-mpid} option for a description of how the
24468 actual register to hold the small data area pointer is chosen.
24474 Use the simulator runtime. The default is to use the libgloss
24475 board-specific runtime.
24477 @item -mas100-syntax
24478 @itemx -mno-as100-syntax
24479 @opindex mas100-syntax
24480 @opindex mno-as100-syntax
24481 When generating assembler output use a syntax that is compatible with
24482 Renesas's AS100 assembler. This syntax can also be handled by the GAS
24483 assembler, but it has some restrictions so it is not generated by default.
24485 @item -mmax-constant-size=@var{N}
24486 @opindex mmax-constant-size
24487 Specifies the maximum size, in bytes, of a constant that can be used as
24488 an operand in a RX instruction. Although the RX instruction set does
24489 allow constants of up to 4 bytes in length to be used in instructions,
24490 a longer value equates to a longer instruction. Thus in some
24491 circumstances it can be beneficial to restrict the size of constants
24492 that are used in instructions. Constants that are too big are instead
24493 placed into a constant pool and referenced via register indirection.
24495 The value @var{N} can be between 0 and 4. A value of 0 (the default)
24496 or 4 means that constants of any size are allowed.
24500 Enable linker relaxation. Linker relaxation is a process whereby the
24501 linker attempts to reduce the size of a program by finding shorter
24502 versions of various instructions. Disabled by default.
24504 @item -mint-register=@var{N}
24505 @opindex mint-register
24506 Specify the number of registers to reserve for fast interrupt handler
24507 functions. The value @var{N} can be between 0 and 4. A value of 1
24508 means that register @code{r13} is reserved for the exclusive use
24509 of fast interrupt handlers. A value of 2 reserves @code{r13} and
24510 @code{r12}. A value of 3 reserves @code{r13}, @code{r12} and
24511 @code{r11}, and a value of 4 reserves @code{r13} through @code{r10}.
24512 A value of 0, the default, does not reserve any registers.
24514 @item -msave-acc-in-interrupts
24515 @opindex msave-acc-in-interrupts
24516 Specifies that interrupt handler functions should preserve the
24517 accumulator register. This is only necessary if normal code might use
24518 the accumulator register, for example because it performs 64-bit
24519 multiplications. The default is to ignore the accumulator as this
24520 makes the interrupt handlers faster.
24526 Enables the generation of position independent data. When enabled any
24527 access to constant data is done via an offset from a base address
24528 held in a register. This allows the location of constant data to be
24529 determined at run time without requiring the executable to be
24530 relocated, which is a benefit to embedded applications with tight
24531 memory constraints. Data that can be modified is not affected by this
24534 Note, using this feature reserves a register, usually @code{r13}, for
24535 the constant data base address. This can result in slower and/or
24536 larger code, especially in complicated functions.
24538 The actual register chosen to hold the constant data base address
24539 depends upon whether the @option{-msmall-data-limit} and/or the
24540 @option{-mint-register} command-line options are enabled. Starting
24541 with register @code{r13} and proceeding downwards, registers are
24542 allocated first to satisfy the requirements of @option{-mint-register},
24543 then @option{-mpid} and finally @option{-msmall-data-limit}. Thus it
24544 is possible for the small data area register to be @code{r8} if both
24545 @option{-mint-register=4} and @option{-mpid} are specified on the
24548 By default this feature is not enabled. The default can be restored
24549 via the @option{-mno-pid} command-line option.
24551 @item -mno-warn-multiple-fast-interrupts
24552 @itemx -mwarn-multiple-fast-interrupts
24553 @opindex mno-warn-multiple-fast-interrupts
24554 @opindex mwarn-multiple-fast-interrupts
24555 Prevents GCC from issuing a warning message if it finds more than one
24556 fast interrupt handler when it is compiling a file. The default is to
24557 issue a warning for each extra fast interrupt handler found, as the RX
24558 only supports one such interrupt.
24560 @item -mallow-string-insns
24561 @itemx -mno-allow-string-insns
24562 @opindex mallow-string-insns
24563 @opindex mno-allow-string-insns
24564 Enables or disables the use of the string manipulation instructions
24565 @code{SMOVF}, @code{SCMPU}, @code{SMOVB}, @code{SMOVU}, @code{SUNTIL}
24566 @code{SWHILE} and also the @code{RMPA} instruction. These
24567 instructions may prefetch data, which is not safe to do if accessing
24568 an I/O register. (See section 12.2.7 of the RX62N Group User's Manual
24569 for more information).
24571 The default is to allow these instructions, but it is not possible for
24572 GCC to reliably detect all circumstances where a string instruction
24573 might be used to access an I/O register, so their use cannot be
24574 disabled automatically. Instead it is reliant upon the programmer to
24575 use the @option{-mno-allow-string-insns} option if their program
24576 accesses I/O space.
24578 When the instructions are enabled GCC defines the C preprocessor
24579 symbol @code{__RX_ALLOW_STRING_INSNS__}, otherwise it defines the
24580 symbol @code{__RX_DISALLOW_STRING_INSNS__}.
24586 Use only (or not only) @code{JSR} instructions to access functions.
24587 This option can be used when code size exceeds the range of @code{BSR}
24588 instructions. Note that @option{-mno-jsr} does not mean to not use
24589 @code{JSR} but instead means that any type of branch may be used.
24592 @emph{Note:} The generic GCC command-line option @option{-ffixed-@var{reg}}
24593 has special significance to the RX port when used with the
24594 @code{interrupt} function attribute. This attribute indicates a
24595 function intended to process fast interrupts. GCC ensures
24596 that it only uses the registers @code{r10}, @code{r11}, @code{r12}
24597 and/or @code{r13} and only provided that the normal use of the
24598 corresponding registers have been restricted via the
24599 @option{-ffixed-@var{reg}} or @option{-mint-register} command-line
24602 @node S/390 and zSeries Options
24603 @subsection S/390 and zSeries Options
24604 @cindex S/390 and zSeries Options
24606 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
24610 @itemx -msoft-float
24611 @opindex mhard-float
24612 @opindex msoft-float
24613 Use (do not use) the hardware floating-point instructions and registers
24614 for floating-point operations. When @option{-msoft-float} is specified,
24615 functions in @file{libgcc.a} are used to perform floating-point
24616 operations. When @option{-mhard-float} is specified, the compiler
24617 generates IEEE floating-point instructions. This is the default.
24620 @itemx -mno-hard-dfp
24622 @opindex mno-hard-dfp
24623 Use (do not use) the hardware decimal-floating-point instructions for
24624 decimal-floating-point operations. When @option{-mno-hard-dfp} is
24625 specified, functions in @file{libgcc.a} are used to perform
24626 decimal-floating-point operations. When @option{-mhard-dfp} is
24627 specified, the compiler generates decimal-floating-point hardware
24628 instructions. This is the default for @option{-march=z9-ec} or higher.
24630 @item -mlong-double-64
24631 @itemx -mlong-double-128
24632 @opindex mlong-double-64
24633 @opindex mlong-double-128
24634 These switches control the size of @code{long double} type. A size
24635 of 64 bits makes the @code{long double} type equivalent to the @code{double}
24636 type. This is the default.
24639 @itemx -mno-backchain
24640 @opindex mbackchain
24641 @opindex mno-backchain
24642 Store (do not store) the address of the caller's frame as backchain pointer
24643 into the callee's stack frame.
24644 A backchain may be needed to allow debugging using tools that do not understand
24645 DWARF call frame information.
24646 When @option{-mno-packed-stack} is in effect, the backchain pointer is stored
24647 at the bottom of the stack frame; when @option{-mpacked-stack} is in effect,
24648 the backchain is placed into the topmost word of the 96/160 byte register
24651 In general, code compiled with @option{-mbackchain} is call-compatible with
24652 code compiled with @option{-mmo-backchain}; however, use of the backchain
24653 for debugging purposes usually requires that the whole binary is built with
24654 @option{-mbackchain}. Note that the combination of @option{-mbackchain},
24655 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
24656 to build a linux kernel use @option{-msoft-float}.
24658 The default is to not maintain the backchain.
24660 @item -mpacked-stack
24661 @itemx -mno-packed-stack
24662 @opindex mpacked-stack
24663 @opindex mno-packed-stack
24664 Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is
24665 specified, the compiler uses the all fields of the 96/160 byte register save
24666 area only for their default purpose; unused fields still take up stack space.
24667 When @option{-mpacked-stack} is specified, register save slots are densely
24668 packed at the top of the register save area; unused space is reused for other
24669 purposes, allowing for more efficient use of the available stack space.
24670 However, when @option{-mbackchain} is also in effect, the topmost word of
24671 the save area is always used to store the backchain, and the return address
24672 register is always saved two words below the backchain.
24674 As long as the stack frame backchain is not used, code generated with
24675 @option{-mpacked-stack} is call-compatible with code generated with
24676 @option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for
24677 S/390 or zSeries generated code that uses the stack frame backchain at run
24678 time, not just for debugging purposes. Such code is not call-compatible
24679 with code compiled with @option{-mpacked-stack}. Also, note that the
24680 combination of @option{-mbackchain},
24681 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
24682 to build a linux kernel use @option{-msoft-float}.
24684 The default is to not use the packed stack layout.
24687 @itemx -mno-small-exec
24688 @opindex msmall-exec
24689 @opindex mno-small-exec
24690 Generate (or do not generate) code using the @code{bras} instruction
24691 to do subroutine calls.
24692 This only works reliably if the total executable size does not
24693 exceed 64k. The default is to use the @code{basr} instruction instead,
24694 which does not have this limitation.
24700 When @option{-m31} is specified, generate code compliant to the
24701 GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate
24702 code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in
24703 particular to generate 64-bit instructions. For the @samp{s390}
24704 targets, the default is @option{-m31}, while the @samp{s390x}
24705 targets default to @option{-m64}.
24711 When @option{-mzarch} is specified, generate code using the
24712 instructions available on z/Architecture.
24713 When @option{-mesa} is specified, generate code using the
24714 instructions available on ESA/390. Note that @option{-mesa} is
24715 not possible with @option{-m64}.
24716 When generating code compliant to the GNU/Linux for S/390 ABI,
24717 the default is @option{-mesa}. When generating code compliant
24718 to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}.
24724 The @option{-mhtm} option enables a set of builtins making use of
24725 instructions available with the transactional execution facility
24726 introduced with the IBM zEnterprise EC12 machine generation
24727 @ref{S/390 System z Built-in Functions}.
24728 @option{-mhtm} is enabled by default when using @option{-march=zEC12}.
24734 When @option{-mvx} is specified, generate code using the instructions
24735 available with the vector extension facility introduced with the IBM
24736 z13 machine generation.
24737 This option changes the ABI for some vector type values with regard to
24738 alignment and calling conventions. In case vector type values are
24739 being used in an ABI-relevant context a GAS @samp{.gnu_attribute}
24740 command will be added to mark the resulting binary with the ABI used.
24741 @option{-mvx} is enabled by default when using @option{-march=z13}.
24744 @itemx -mno-zvector
24746 @opindex mno-zvector
24747 The @option{-mzvector} option enables vector language extensions and
24748 builtins using instructions available with the vector extension
24749 facility introduced with the IBM z13 machine generation.
24750 This option adds support for @samp{vector} to be used as a keyword to
24751 define vector type variables and arguments. @samp{vector} is only
24752 available when GNU extensions are enabled. It will not be expanded
24753 when requesting strict standard compliance e.g. with @option{-std=c99}.
24754 In addition to the GCC low-level builtins @option{-mzvector} enables
24755 a set of builtins added for compatibility with AltiVec-style
24756 implementations like Power and Cell. In order to make use of these
24757 builtins the header file @file{vecintrin.h} needs to be included.
24758 @option{-mzvector} is disabled by default.
24764 Generate (or do not generate) code using the @code{mvcle} instruction
24765 to perform block moves. When @option{-mno-mvcle} is specified,
24766 use a @code{mvc} loop instead. This is the default unless optimizing for
24773 Print (or do not print) additional debug information when compiling.
24774 The default is to not print debug information.
24776 @item -march=@var{cpu-type}
24778 Generate code that runs on @var{cpu-type}, which is the name of a
24779 system representing a certain processor type. Possible values for
24780 @var{cpu-type} are @samp{z900}/@samp{arch5}, @samp{z990}/@samp{arch6},
24781 @samp{z9-109}, @samp{z9-ec}/@samp{arch7}, @samp{z10}/@samp{arch8},
24782 @samp{z196}/@samp{arch9}, @samp{zEC12}, @samp{z13}/@samp{arch11}, and
24785 The default is @option{-march=z900}. @samp{g5}/@samp{arch3} and
24786 @samp{g6} are deprecated and will be removed with future releases.
24788 Specifying @samp{native} as cpu type can be used to select the best
24789 architecture option for the host processor.
24790 @option{-march=native} has no effect if GCC does not recognize the
24793 @item -mtune=@var{cpu-type}
24795 Tune to @var{cpu-type} everything applicable about the generated code,
24796 except for the ABI and the set of available instructions.
24797 The list of @var{cpu-type} values is the same as for @option{-march}.
24798 The default is the value used for @option{-march}.
24801 @itemx -mno-tpf-trace
24802 @opindex mtpf-trace
24803 @opindex mno-tpf-trace
24804 Generate code that adds (does not add) in TPF OS specific branches to trace
24805 routines in the operating system. This option is off by default, even
24806 when compiling for the TPF OS@.
24809 @itemx -mno-fused-madd
24810 @opindex mfused-madd
24811 @opindex mno-fused-madd
24812 Generate code that uses (does not use) the floating-point multiply and
24813 accumulate instructions. These instructions are generated by default if
24814 hardware floating point is used.
24816 @item -mwarn-framesize=@var{framesize}
24817 @opindex mwarn-framesize
24818 Emit a warning if the current function exceeds the given frame size. Because
24819 this is a compile-time check it doesn't need to be a real problem when the program
24820 runs. It is intended to identify functions that most probably cause
24821 a stack overflow. It is useful to be used in an environment with limited stack
24822 size e.g.@: the linux kernel.
24824 @item -mwarn-dynamicstack
24825 @opindex mwarn-dynamicstack
24826 Emit a warning if the function calls @code{alloca} or uses dynamically-sized
24827 arrays. This is generally a bad idea with a limited stack size.
24829 @item -mstack-guard=@var{stack-guard}
24830 @itemx -mstack-size=@var{stack-size}
24831 @opindex mstack-guard
24832 @opindex mstack-size
24833 If these options are provided the S/390 back end emits additional instructions in
24834 the function prologue that trigger a trap if the stack size is @var{stack-guard}
24835 bytes above the @var{stack-size} (remember that the stack on S/390 grows downward).
24836 If the @var{stack-guard} option is omitted the smallest power of 2 larger than
24837 the frame size of the compiled function is chosen.
24838 These options are intended to be used to help debugging stack overflow problems.
24839 The additionally emitted code causes only little overhead and hence can also be
24840 used in production-like systems without greater performance degradation. The given
24841 values have to be exact powers of 2 and @var{stack-size} has to be greater than
24842 @var{stack-guard} without exceeding 64k.
24843 In order to be efficient the extra code makes the assumption that the stack starts
24844 at an address aligned to the value given by @var{stack-size}.
24845 The @var{stack-guard} option can only be used in conjunction with @var{stack-size}.
24847 @item -mhotpatch=@var{pre-halfwords},@var{post-halfwords}
24849 If the hotpatch option is enabled, a ``hot-patching'' function
24850 prologue is generated for all functions in the compilation unit.
24851 The funtion label is prepended with the given number of two-byte
24852 NOP instructions (@var{pre-halfwords}, maximum 1000000). After
24853 the label, 2 * @var{post-halfwords} bytes are appended, using the
24854 largest NOP like instructions the architecture allows (maximum
24857 If both arguments are zero, hotpatching is disabled.
24859 This option can be overridden for individual functions with the
24860 @code{hotpatch} attribute.
24863 @node Score Options
24864 @subsection Score Options
24865 @cindex Score Options
24867 These options are defined for Score implementations:
24872 Compile code for big-endian mode. This is the default.
24876 Compile code for little-endian mode.
24880 Disable generation of @code{bcnz} instructions.
24884 Enable generation of unaligned load and store instructions.
24888 Enable the use of multiply-accumulate instructions. Disabled by default.
24892 Specify the SCORE5 as the target architecture.
24896 Specify the SCORE5U of the target architecture.
24900 Specify the SCORE7 as the target architecture. This is the default.
24904 Specify the SCORE7D as the target architecture.
24908 @subsection SH Options
24910 These @samp{-m} options are defined for the SH implementations:
24915 Generate code for the SH1.
24919 Generate code for the SH2.
24922 Generate code for the SH2e.
24926 Generate code for the SH2a without FPU, or for a SH2a-FPU in such a way
24927 that the floating-point unit is not used.
24929 @item -m2a-single-only
24930 @opindex m2a-single-only
24931 Generate code for the SH2a-FPU, in such a way that no double-precision
24932 floating-point operations are used.
24935 @opindex m2a-single
24936 Generate code for the SH2a-FPU assuming the floating-point unit is in
24937 single-precision mode by default.
24941 Generate code for the SH2a-FPU assuming the floating-point unit is in
24942 double-precision mode by default.
24946 Generate code for the SH3.
24950 Generate code for the SH3e.
24954 Generate code for the SH4 without a floating-point unit.
24956 @item -m4-single-only
24957 @opindex m4-single-only
24958 Generate code for the SH4 with a floating-point unit that only
24959 supports single-precision arithmetic.
24963 Generate code for the SH4 assuming the floating-point unit is in
24964 single-precision mode by default.
24968 Generate code for the SH4.
24972 Generate code for SH4-100.
24974 @item -m4-100-nofpu
24975 @opindex m4-100-nofpu
24976 Generate code for SH4-100 in such a way that the
24977 floating-point unit is not used.
24979 @item -m4-100-single
24980 @opindex m4-100-single
24981 Generate code for SH4-100 assuming the floating-point unit is in
24982 single-precision mode by default.
24984 @item -m4-100-single-only
24985 @opindex m4-100-single-only
24986 Generate code for SH4-100 in such a way that no double-precision
24987 floating-point operations are used.
24991 Generate code for SH4-200.
24993 @item -m4-200-nofpu
24994 @opindex m4-200-nofpu
24995 Generate code for SH4-200 without in such a way that the
24996 floating-point unit is not used.
24998 @item -m4-200-single
24999 @opindex m4-200-single
25000 Generate code for SH4-200 assuming the floating-point unit is in
25001 single-precision mode by default.
25003 @item -m4-200-single-only
25004 @opindex m4-200-single-only
25005 Generate code for SH4-200 in such a way that no double-precision
25006 floating-point operations are used.
25010 Generate code for SH4-300.
25012 @item -m4-300-nofpu
25013 @opindex m4-300-nofpu
25014 Generate code for SH4-300 without in such a way that the
25015 floating-point unit is not used.
25017 @item -m4-300-single
25018 @opindex m4-300-single
25019 Generate code for SH4-300 in such a way that no double-precision
25020 floating-point operations are used.
25022 @item -m4-300-single-only
25023 @opindex m4-300-single-only
25024 Generate code for SH4-300 in such a way that no double-precision
25025 floating-point operations are used.
25029 Generate code for SH4-340 (no MMU, no FPU).
25033 Generate code for SH4-500 (no FPU). Passes @option{-isa=sh4-nofpu} to the
25038 Generate code for the SH4al-dsp, or for a SH4a in such a way that the
25039 floating-point unit is not used.
25041 @item -m4a-single-only
25042 @opindex m4a-single-only
25043 Generate code for the SH4a, in such a way that no double-precision
25044 floating-point operations are used.
25047 @opindex m4a-single
25048 Generate code for the SH4a assuming the floating-point unit is in
25049 single-precision mode by default.
25053 Generate code for the SH4a.
25057 Same as @option{-m4a-nofpu}, except that it implicitly passes
25058 @option{-dsp} to the assembler. GCC doesn't generate any DSP
25059 instructions at the moment.
25063 Compile code for the processor in big-endian mode.
25067 Compile code for the processor in little-endian mode.
25071 Align doubles at 64-bit boundaries. Note that this changes the calling
25072 conventions, and thus some functions from the standard C library do
25073 not work unless you recompile it first with @option{-mdalign}.
25077 Shorten some address references at link time, when possible; uses the
25078 linker option @option{-relax}.
25082 Use 32-bit offsets in @code{switch} tables. The default is to use
25087 Enable the use of bit manipulation instructions on SH2A.
25091 Enable the use of the instruction @code{fmovd}. Check @option{-mdalign} for
25092 alignment constraints.
25096 Comply with the calling conventions defined by Renesas.
25099 @opindex mno-renesas
25100 Comply with the calling conventions defined for GCC before the Renesas
25101 conventions were available. This option is the default for all
25102 targets of the SH toolchain.
25105 @opindex mnomacsave
25106 Mark the @code{MAC} register as call-clobbered, even if
25107 @option{-mrenesas} is given.
25113 Control the IEEE compliance of floating-point comparisons, which affects the
25114 handling of cases where the result of a comparison is unordered. By default
25115 @option{-mieee} is implicitly enabled. If @option{-ffinite-math-only} is
25116 enabled @option{-mno-ieee} is implicitly set, which results in faster
25117 floating-point greater-equal and less-equal comparisons. The implicit settings
25118 can be overridden by specifying either @option{-mieee} or @option{-mno-ieee}.
25120 @item -minline-ic_invalidate
25121 @opindex minline-ic_invalidate
25122 Inline code to invalidate instruction cache entries after setting up
25123 nested function trampolines.
25124 This option has no effect if @option{-musermode} is in effect and the selected
25125 code generation option (e.g. @option{-m4}) does not allow the use of the @code{icbi}
25127 If the selected code generation option does not allow the use of the @code{icbi}
25128 instruction, and @option{-musermode} is not in effect, the inlined code
25129 manipulates the instruction cache address array directly with an associative
25130 write. This not only requires privileged mode at run time, but it also
25131 fails if the cache line had been mapped via the TLB and has become unmapped.
25135 Dump instruction size and location in the assembly code.
25138 @opindex mpadstruct
25139 This option is deprecated. It pads structures to multiple of 4 bytes,
25140 which is incompatible with the SH ABI@.
25142 @item -matomic-model=@var{model}
25143 @opindex matomic-model=@var{model}
25144 Sets the model of atomic operations and additional parameters as a comma
25145 separated list. For details on the atomic built-in functions see
25146 @ref{__atomic Builtins}. The following models and parameters are supported:
25151 Disable compiler generated atomic sequences and emit library calls for atomic
25152 operations. This is the default if the target is not @code{sh*-*-linux*}.
25155 Generate GNU/Linux compatible gUSA software atomic sequences for the atomic
25156 built-in functions. The generated atomic sequences require additional support
25157 from the interrupt/exception handling code of the system and are only suitable
25158 for SH3* and SH4* single-core systems. This option is enabled by default when
25159 the target is @code{sh*-*-linux*} and SH3* or SH4*. When the target is SH4A,
25160 this option also partially utilizes the hardware atomic instructions
25161 @code{movli.l} and @code{movco.l} to create more efficient code, unless
25162 @samp{strict} is specified.
25165 Generate software atomic sequences that use a variable in the thread control
25166 block. This is a variation of the gUSA sequences which can also be used on
25167 SH1* and SH2* targets. The generated atomic sequences require additional
25168 support from the interrupt/exception handling code of the system and are only
25169 suitable for single-core systems. When using this model, the @samp{gbr-offset=}
25170 parameter has to be specified as well.
25173 Generate software atomic sequences that temporarily disable interrupts by
25174 setting @code{SR.IMASK = 1111}. This model works only when the program runs
25175 in privileged mode and is only suitable for single-core systems. Additional
25176 support from the interrupt/exception handling code of the system is not
25177 required. This model is enabled by default when the target is
25178 @code{sh*-*-linux*} and SH1* or SH2*.
25181 Generate hardware atomic sequences using the @code{movli.l} and @code{movco.l}
25182 instructions only. This is only available on SH4A and is suitable for
25183 multi-core systems. Since the hardware instructions support only 32 bit atomic
25184 variables access to 8 or 16 bit variables is emulated with 32 bit accesses.
25185 Code compiled with this option is also compatible with other software
25186 atomic model interrupt/exception handling systems if executed on an SH4A
25187 system. Additional support from the interrupt/exception handling code of the
25188 system is not required for this model.
25191 This parameter specifies the offset in bytes of the variable in the thread
25192 control block structure that should be used by the generated atomic sequences
25193 when the @samp{soft-tcb} model has been selected. For other models this
25194 parameter is ignored. The specified value must be an integer multiple of four
25195 and in the range 0-1020.
25198 This parameter prevents mixed usage of multiple atomic models, even if they
25199 are compatible, and makes the compiler generate atomic sequences of the
25200 specified model only.
25206 Generate the @code{tas.b} opcode for @code{__atomic_test_and_set}.
25207 Notice that depending on the particular hardware and software configuration
25208 this can degrade overall performance due to the operand cache line flushes
25209 that are implied by the @code{tas.b} instruction. On multi-core SH4A
25210 processors the @code{tas.b} instruction must be used with caution since it
25211 can result in data corruption for certain cache configurations.
25214 @opindex mprefergot
25215 When generating position-independent code, emit function calls using
25216 the Global Offset Table instead of the Procedure Linkage Table.
25219 @itemx -mno-usermode
25221 @opindex mno-usermode
25222 Don't allow (allow) the compiler generating privileged mode code. Specifying
25223 @option{-musermode} also implies @option{-mno-inline-ic_invalidate} if the
25224 inlined code would not work in user mode. @option{-musermode} is the default
25225 when the target is @code{sh*-*-linux*}. If the target is SH1* or SH2*
25226 @option{-musermode} has no effect, since there is no user mode.
25228 @item -multcost=@var{number}
25229 @opindex multcost=@var{number}
25230 Set the cost to assume for a multiply insn.
25232 @item -mdiv=@var{strategy}
25233 @opindex mdiv=@var{strategy}
25234 Set the division strategy to be used for integer division operations.
25235 @var{strategy} can be one of:
25240 Calls a library function that uses the single-step division instruction
25241 @code{div1} to perform the operation. Division by zero calculates an
25242 unspecified result and does not trap. This is the default except for SH4,
25243 SH2A and SHcompact.
25246 Calls a library function that performs the operation in double precision
25247 floating point. Division by zero causes a floating-point exception. This is
25248 the default for SHcompact with FPU. Specifying this for targets that do not
25249 have a double precision FPU defaults to @code{call-div1}.
25252 Calls a library function that uses a lookup table for small divisors and
25253 the @code{div1} instruction with case distinction for larger divisors. Division
25254 by zero calculates an unspecified result and does not trap. This is the default
25255 for SH4. Specifying this for targets that do not have dynamic shift
25256 instructions defaults to @code{call-div1}.
25260 When a division strategy has not been specified the default strategy is
25261 selected based on the current target. For SH2A the default strategy is to
25262 use the @code{divs} and @code{divu} instructions instead of library function
25265 @item -maccumulate-outgoing-args
25266 @opindex maccumulate-outgoing-args
25267 Reserve space once for outgoing arguments in the function prologue rather
25268 than around each call. Generally beneficial for performance and size. Also
25269 needed for unwinding to avoid changing the stack frame around conditional code.
25271 @item -mdivsi3_libfunc=@var{name}
25272 @opindex mdivsi3_libfunc=@var{name}
25273 Set the name of the library function used for 32-bit signed division to
25275 This only affects the name used in the @samp{call} division strategies, and
25276 the compiler still expects the same sets of input/output/clobbered registers as
25277 if this option were not present.
25279 @item -mfixed-range=@var{register-range}
25280 @opindex mfixed-range
25281 Generate code treating the given register range as fixed registers.
25282 A fixed register is one that the register allocator can not use. This is
25283 useful when compiling kernel code. A register range is specified as
25284 two registers separated by a dash. Multiple register ranges can be
25285 specified separated by a comma.
25287 @item -mbranch-cost=@var{num}
25288 @opindex mbranch-cost=@var{num}
25289 Assume @var{num} to be the cost for a branch instruction. Higher numbers
25290 make the compiler try to generate more branch-free code if possible.
25291 If not specified the value is selected depending on the processor type that
25292 is being compiled for.
25295 @itemx -mno-zdcbranch
25296 @opindex mzdcbranch
25297 @opindex mno-zdcbranch
25298 Assume (do not assume) that zero displacement conditional branch instructions
25299 @code{bt} and @code{bf} are fast. If @option{-mzdcbranch} is specified, the
25300 compiler prefers zero displacement branch code sequences. This is
25301 enabled by default when generating code for SH4 and SH4A. It can be explicitly
25302 disabled by specifying @option{-mno-zdcbranch}.
25304 @item -mcbranch-force-delay-slot
25305 @opindex mcbranch-force-delay-slot
25306 Force the usage of delay slots for conditional branches, which stuffs the delay
25307 slot with a @code{nop} if a suitable instruction cannot be found. By default
25308 this option is disabled. It can be enabled to work around hardware bugs as
25309 found in the original SH7055.
25312 @itemx -mno-fused-madd
25313 @opindex mfused-madd
25314 @opindex mno-fused-madd
25315 Generate code that uses (does not use) the floating-point multiply and
25316 accumulate instructions. These instructions are generated by default
25317 if hardware floating point is used. The machine-dependent
25318 @option{-mfused-madd} option is now mapped to the machine-independent
25319 @option{-ffp-contract=fast} option, and @option{-mno-fused-madd} is
25320 mapped to @option{-ffp-contract=off}.
25326 Allow or disallow the compiler to emit the @code{fsca} instruction for sine
25327 and cosine approximations. The option @option{-mfsca} must be used in
25328 combination with @option{-funsafe-math-optimizations}. It is enabled by default
25329 when generating code for SH4A. Using @option{-mno-fsca} disables sine and cosine
25330 approximations even if @option{-funsafe-math-optimizations} is in effect.
25336 Allow or disallow the compiler to emit the @code{fsrra} instruction for
25337 reciprocal square root approximations. The option @option{-mfsrra} must be used
25338 in combination with @option{-funsafe-math-optimizations} and
25339 @option{-ffinite-math-only}. It is enabled by default when generating code for
25340 SH4A. Using @option{-mno-fsrra} disables reciprocal square root approximations
25341 even if @option{-funsafe-math-optimizations} and @option{-ffinite-math-only} are
25344 @item -mpretend-cmove
25345 @opindex mpretend-cmove
25346 Prefer zero-displacement conditional branches for conditional move instruction
25347 patterns. This can result in faster code on the SH4 processor.
25351 Generate code using the FDPIC ABI.
25355 @node Solaris 2 Options
25356 @subsection Solaris 2 Options
25357 @cindex Solaris 2 options
25359 These @samp{-m} options are supported on Solaris 2:
25362 @item -mclear-hwcap
25363 @opindex mclear-hwcap
25364 @option{-mclear-hwcap} tells the compiler to remove the hardware
25365 capabilities generated by the Solaris assembler. This is only necessary
25366 when object files use ISA extensions not supported by the current
25367 machine, but check at runtime whether or not to use them.
25369 @item -mimpure-text
25370 @opindex mimpure-text
25371 @option{-mimpure-text}, used in addition to @option{-shared}, tells
25372 the compiler to not pass @option{-z text} to the linker when linking a
25373 shared object. Using this option, you can link position-dependent
25374 code into a shared object.
25376 @option{-mimpure-text} suppresses the ``relocations remain against
25377 allocatable but non-writable sections'' linker error message.
25378 However, the necessary relocations trigger copy-on-write, and the
25379 shared object is not actually shared across processes. Instead of
25380 using @option{-mimpure-text}, you should compile all source code with
25381 @option{-fpic} or @option{-fPIC}.
25385 These switches are supported in addition to the above on Solaris 2:
25390 This is a synonym for @option{-pthread}.
25393 @node SPARC Options
25394 @subsection SPARC Options
25395 @cindex SPARC options
25397 These @samp{-m} options are supported on the SPARC:
25400 @item -mno-app-regs
25402 @opindex mno-app-regs
25404 Specify @option{-mapp-regs} to generate output using the global registers
25405 2 through 4, which the SPARC SVR4 ABI reserves for applications. Like the
25406 global register 1, each global register 2 through 4 is then treated as an
25407 allocable register that is clobbered by function calls. This is the default.
25409 To be fully SVR4 ABI-compliant at the cost of some performance loss,
25410 specify @option{-mno-app-regs}. You should compile libraries and system
25411 software with this option.
25417 With @option{-mflat}, the compiler does not generate save/restore instructions
25418 and uses a ``flat'' or single register window model. This model is compatible
25419 with the regular register window model. The local registers and the input
25420 registers (0--5) are still treated as ``call-saved'' registers and are
25421 saved on the stack as needed.
25423 With @option{-mno-flat} (the default), the compiler generates save/restore
25424 instructions (except for leaf functions). This is the normal operating mode.
25427 @itemx -mhard-float
25429 @opindex mhard-float
25430 Generate output containing floating-point instructions. This is the
25434 @itemx -msoft-float
25436 @opindex msoft-float
25437 Generate output containing library calls for floating point.
25438 @strong{Warning:} the requisite libraries are not available for all SPARC
25439 targets. Normally the facilities of the machine's usual C compiler are
25440 used, but this cannot be done directly in cross-compilation. You must make
25441 your own arrangements to provide suitable library functions for
25442 cross-compilation. The embedded targets @samp{sparc-*-aout} and
25443 @samp{sparclite-*-*} do provide software floating-point support.
25445 @option{-msoft-float} changes the calling convention in the output file;
25446 therefore, it is only useful if you compile @emph{all} of a program with
25447 this option. In particular, you need to compile @file{libgcc.a}, the
25448 library that comes with GCC, with @option{-msoft-float} in order for
25451 @item -mhard-quad-float
25452 @opindex mhard-quad-float
25453 Generate output containing quad-word (long double) floating-point
25456 @item -msoft-quad-float
25457 @opindex msoft-quad-float
25458 Generate output containing library calls for quad-word (long double)
25459 floating-point instructions. The functions called are those specified
25460 in the SPARC ABI@. This is the default.
25462 As of this writing, there are no SPARC implementations that have hardware
25463 support for the quad-word floating-point instructions. They all invoke
25464 a trap handler for one of these instructions, and then the trap handler
25465 emulates the effect of the instruction. Because of the trap handler overhead,
25466 this is much slower than calling the ABI library routines. Thus the
25467 @option{-msoft-quad-float} option is the default.
25469 @item -mno-unaligned-doubles
25470 @itemx -munaligned-doubles
25471 @opindex mno-unaligned-doubles
25472 @opindex munaligned-doubles
25473 Assume that doubles have 8-byte alignment. This is the default.
25475 With @option{-munaligned-doubles}, GCC assumes that doubles have 8-byte
25476 alignment only if they are contained in another type, or if they have an
25477 absolute address. Otherwise, it assumes they have 4-byte alignment.
25478 Specifying this option avoids some rare compatibility problems with code
25479 generated by other compilers. It is not the default because it results
25480 in a performance loss, especially for floating-point code.
25483 @itemx -mno-user-mode
25484 @opindex muser-mode
25485 @opindex mno-user-mode
25486 Do not generate code that can only run in supervisor mode. This is relevant
25487 only for the @code{casa} instruction emitted for the LEON3 processor. This
25490 @item -mfaster-structs
25491 @itemx -mno-faster-structs
25492 @opindex mfaster-structs
25493 @opindex mno-faster-structs
25494 With @option{-mfaster-structs}, the compiler assumes that structures
25495 should have 8-byte alignment. This enables the use of pairs of
25496 @code{ldd} and @code{std} instructions for copies in structure
25497 assignment, in place of twice as many @code{ld} and @code{st} pairs.
25498 However, the use of this changed alignment directly violates the SPARC
25499 ABI@. Thus, it's intended only for use on targets where the developer
25500 acknowledges that their resulting code is not directly in line with
25501 the rules of the ABI@.
25503 @item -mstd-struct-return
25504 @itemx -mno-std-struct-return
25505 @opindex mstd-struct-return
25506 @opindex mno-std-struct-return
25507 With @option{-mstd-struct-return}, the compiler generates checking code
25508 in functions returning structures or unions to detect size mismatches
25509 between the two sides of function calls, as per the 32-bit ABI@.
25511 The default is @option{-mno-std-struct-return}. This option has no effect
25518 Enable Local Register Allocation. This is the default for SPARC since GCC 7
25519 so @option{-mno-lra} needs to be passed to get old Reload.
25521 @item -mcpu=@var{cpu_type}
25523 Set the instruction set, register set, and instruction scheduling parameters
25524 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
25525 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{hypersparc},
25526 @samp{leon}, @samp{leon3}, @samp{leon3v7}, @samp{sparclite}, @samp{f930},
25527 @samp{f934}, @samp{sparclite86x}, @samp{sparclet}, @samp{tsc701}, @samp{v9},
25528 @samp{ultrasparc}, @samp{ultrasparc3}, @samp{niagara}, @samp{niagara2},
25529 @samp{niagara3}, @samp{niagara4}, @samp{niagara7} and @samp{m8}.
25531 Native Solaris and GNU/Linux toolchains also support the value @samp{native},
25532 which selects the best architecture option for the host processor.
25533 @option{-mcpu=native} has no effect if GCC does not recognize
25536 Default instruction scheduling parameters are used for values that select
25537 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
25538 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
25540 Here is a list of each supported architecture and their supported
25548 supersparc, hypersparc, leon, leon3
25551 f930, f934, sparclite86x
25557 ultrasparc, ultrasparc3, niagara, niagara2, niagara3, niagara4,
25561 By default (unless configured otherwise), GCC generates code for the V7
25562 variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler
25563 additionally optimizes it for the Cypress CY7C602 chip, as used in the
25564 SPARCStation/SPARCServer 3xx series. This is also appropriate for the older
25565 SPARCStation 1, 2, IPX etc.
25567 With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC
25568 architecture. The only difference from V7 code is that the compiler emits
25569 the integer multiply and integer divide instructions which exist in SPARC-V8
25570 but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally
25571 optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and
25574 With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of
25575 the SPARC architecture. This adds the integer multiply, integer divide step
25576 and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7.
25577 With @option{-mcpu=f930}, the compiler additionally optimizes it for the
25578 Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With
25579 @option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu
25580 MB86934 chip, which is the more recent SPARClite with FPU@.
25582 With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of
25583 the SPARC architecture. This adds the integer multiply, multiply/accumulate,
25584 integer divide step and scan (@code{ffs}) instructions which exist in SPARClet
25585 but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally
25586 optimizes it for the TEMIC SPARClet chip.
25588 With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC
25589 architecture. This adds 64-bit integer and floating-point move instructions,
25590 3 additional floating-point condition code registers and conditional move
25591 instructions. With @option{-mcpu=ultrasparc}, the compiler additionally
25592 optimizes it for the Sun UltraSPARC I/II/IIi chips. With
25593 @option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the
25594 Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With
25595 @option{-mcpu=niagara}, the compiler additionally optimizes it for
25596 Sun UltraSPARC T1 chips. With @option{-mcpu=niagara2}, the compiler
25597 additionally optimizes it for Sun UltraSPARC T2 chips. With
25598 @option{-mcpu=niagara3}, the compiler additionally optimizes it for Sun
25599 UltraSPARC T3 chips. With @option{-mcpu=niagara4}, the compiler
25600 additionally optimizes it for Sun UltraSPARC T4 chips. With
25601 @option{-mcpu=niagara7}, the compiler additionally optimizes it for
25602 Oracle SPARC M7 chips. With @option{-mcpu=m8}, the compiler
25603 additionally optimizes it for Oracle M8 chips.
25605 @item -mtune=@var{cpu_type}
25607 Set the instruction scheduling parameters for machine type
25608 @var{cpu_type}, but do not set the instruction set or register set that the
25609 option @option{-mcpu=@var{cpu_type}} does.
25611 The same values for @option{-mcpu=@var{cpu_type}} can be used for
25612 @option{-mtune=@var{cpu_type}}, but the only useful values are those
25613 that select a particular CPU implementation. Those are
25614 @samp{cypress}, @samp{supersparc}, @samp{hypersparc}, @samp{leon},
25615 @samp{leon3}, @samp{leon3v7}, @samp{f930}, @samp{f934},
25616 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc},
25617 @samp{ultrasparc3}, @samp{niagara}, @samp{niagara2}, @samp{niagara3},
25618 @samp{niagara4}, @samp{niagara7} and @samp{m8}. With native Solaris
25619 and GNU/Linux toolchains, @samp{native} can also be used.
25624 @opindex mno-v8plus
25625 With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The
25626 difference from the V8 ABI is that the global and out registers are
25627 considered 64 bits wide. This is enabled by default on Solaris in 32-bit
25628 mode for all SPARC-V9 processors.
25634 With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC
25635 Visual Instruction Set extensions. The default is @option{-mno-vis}.
25641 With @option{-mvis2}, GCC generates code that takes advantage of
25642 version 2.0 of the UltraSPARC Visual Instruction Set extensions. The
25643 default is @option{-mvis2} when targeting a cpu that supports such
25644 instructions, such as UltraSPARC-III and later. Setting @option{-mvis2}
25645 also sets @option{-mvis}.
25651 With @option{-mvis3}, GCC generates code that takes advantage of
25652 version 3.0 of the UltraSPARC Visual Instruction Set extensions. The
25653 default is @option{-mvis3} when targeting a cpu that supports such
25654 instructions, such as niagara-3 and later. Setting @option{-mvis3}
25655 also sets @option{-mvis2} and @option{-mvis}.
25661 With @option{-mvis4}, GCC generates code that takes advantage of
25662 version 4.0 of the UltraSPARC Visual Instruction Set extensions. The
25663 default is @option{-mvis4} when targeting a cpu that supports such
25664 instructions, such as niagara-7 and later. Setting @option{-mvis4}
25665 also sets @option{-mvis3}, @option{-mvis2} and @option{-mvis}.
25671 With @option{-mvis4b}, GCC generates code that takes advantage of
25672 version 4.0 of the UltraSPARC Visual Instruction Set extensions, plus
25673 the additional VIS instructions introduced in the Oracle SPARC
25674 Architecture 2017. The default is @option{-mvis4b} when targeting a
25675 cpu that supports such instructions, such as m8 and later. Setting
25676 @option{-mvis4b} also sets @option{-mvis4}, @option{-mvis3},
25677 @option{-mvis2} and @option{-mvis}.
25682 @opindex mno-cbcond
25683 With @option{-mcbcond}, GCC generates code that takes advantage of the UltraSPARC
25684 Compare-and-Branch-on-Condition instructions. The default is @option{-mcbcond}
25685 when targeting a CPU that supports such instructions, such as Niagara-4 and
25692 With @option{-mfmaf}, GCC generates code that takes advantage of the UltraSPARC
25693 Fused Multiply-Add Floating-point instructions. The default is @option{-mfmaf}
25694 when targeting a CPU that supports such instructions, such as Niagara-3 and
25700 @opindex mno-fsmuld
25701 With @option{-mfsmuld}, GCC generates code that takes advantage of the
25702 Floating-point Multiply Single to Double (FsMULd) instruction. The default is
25703 @option{-mfsmuld} when targeting a CPU supporting the architecture versions V8
25704 or V9 with FPU except @option{-mcpu=leon}.
25710 With @option{-mpopc}, GCC generates code that takes advantage of the UltraSPARC
25711 Population Count instruction. The default is @option{-mpopc}
25712 when targeting a CPU that supports such an instruction, such as Niagara-2 and
25719 With @option{-msubxc}, GCC generates code that takes advantage of the UltraSPARC
25720 Subtract-Extended-with-Carry instruction. The default is @option{-msubxc}
25721 when targeting a CPU that supports such an instruction, such as Niagara-7 and
25725 @opindex mfix-at697f
25726 Enable the documented workaround for the single erratum of the Atmel AT697F
25727 processor (which corresponds to erratum #13 of the AT697E processor).
25730 @opindex mfix-ut699
25731 Enable the documented workarounds for the floating-point errata and the data
25732 cache nullify errata of the UT699 processor.
25735 @opindex mfix-ut700
25736 Enable the documented workaround for the back-to-back store errata of
25737 the UT699E/UT700 processor.
25739 @item -mfix-gr712rc
25740 @opindex mfix-gr712rc
25741 Enable the documented workaround for the back-to-back store errata of
25742 the GR712RC processor.
25745 These @samp{-m} options are supported in addition to the above
25746 on SPARC-V9 processors in 64-bit environments:
25753 Generate code for a 32-bit or 64-bit environment.
25754 The 32-bit environment sets int, long and pointer to 32 bits.
25755 The 64-bit environment sets int to 32 bits and long and pointer
25758 @item -mcmodel=@var{which}
25760 Set the code model to one of
25764 The Medium/Low code model: 64-bit addresses, programs
25765 must be linked in the low 32 bits of memory. Programs can be statically
25766 or dynamically linked.
25769 The Medium/Middle code model: 64-bit addresses, programs
25770 must be linked in the low 44 bits of memory, the text and data segments must
25771 be less than 2GB in size and the data segment must be located within 2GB of
25775 The Medium/Anywhere code model: 64-bit addresses, programs
25776 may be linked anywhere in memory, the text and data segments must be less
25777 than 2GB in size and the data segment must be located within 2GB of the
25781 The Medium/Anywhere code model for embedded systems:
25782 64-bit addresses, the text and data segments must be less than 2GB in
25783 size, both starting anywhere in memory (determined at link time). The
25784 global register %g4 points to the base of the data segment. Programs
25785 are statically linked and PIC is not supported.
25788 @item -mmemory-model=@var{mem-model}
25789 @opindex mmemory-model
25790 Set the memory model in force on the processor to one of
25794 The default memory model for the processor and operating system.
25797 Relaxed Memory Order
25800 Partial Store Order
25806 Sequential Consistency
25809 These memory models are formally defined in Appendix D of the SPARC-V9
25810 architecture manual, as set in the processor's @code{PSTATE.MM} field.
25813 @itemx -mno-stack-bias
25814 @opindex mstack-bias
25815 @opindex mno-stack-bias
25816 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
25817 frame pointer if present, are offset by @minus{}2047 which must be added back
25818 when making stack frame references. This is the default in 64-bit mode.
25819 Otherwise, assume no such offset is present.
25823 @subsection SPU Options
25824 @cindex SPU options
25826 These @samp{-m} options are supported on the SPU:
25830 @itemx -merror-reloc
25831 @opindex mwarn-reloc
25832 @opindex merror-reloc
25834 The loader for SPU does not handle dynamic relocations. By default, GCC
25835 gives an error when it generates code that requires a dynamic
25836 relocation. @option{-mno-error-reloc} disables the error,
25837 @option{-mwarn-reloc} generates a warning instead.
25840 @itemx -munsafe-dma
25842 @opindex munsafe-dma
25844 Instructions that initiate or test completion of DMA must not be
25845 reordered with respect to loads and stores of the memory that is being
25847 With @option{-munsafe-dma} you must use the @code{volatile} keyword to protect
25848 memory accesses, but that can lead to inefficient code in places where the
25849 memory is known to not change. Rather than mark the memory as volatile,
25850 you can use @option{-msafe-dma} to tell the compiler to treat
25851 the DMA instructions as potentially affecting all memory.
25853 @item -mbranch-hints
25854 @opindex mbranch-hints
25856 By default, GCC generates a branch hint instruction to avoid
25857 pipeline stalls for always-taken or probably-taken branches. A hint
25858 is not generated closer than 8 instructions away from its branch.
25859 There is little reason to disable them, except for debugging purposes,
25860 or to make an object a little bit smaller.
25864 @opindex msmall-mem
25865 @opindex mlarge-mem
25867 By default, GCC generates code assuming that addresses are never larger
25868 than 18 bits. With @option{-mlarge-mem} code is generated that assumes
25869 a full 32-bit address.
25874 By default, GCC links against startup code that assumes the SPU-style
25875 main function interface (which has an unconventional parameter list).
25876 With @option{-mstdmain}, GCC links your program against startup
25877 code that assumes a C99-style interface to @code{main}, including a
25878 local copy of @code{argv} strings.
25880 @item -mfixed-range=@var{register-range}
25881 @opindex mfixed-range
25882 Generate code treating the given register range as fixed registers.
25883 A fixed register is one that the register allocator cannot use. This is
25884 useful when compiling kernel code. A register range is specified as
25885 two registers separated by a dash. Multiple register ranges can be
25886 specified separated by a comma.
25892 Compile code assuming that pointers to the PPU address space accessed
25893 via the @code{__ea} named address space qualifier are either 32 or 64
25894 bits wide. The default is 32 bits. As this is an ABI-changing option,
25895 all object code in an executable must be compiled with the same setting.
25897 @item -maddress-space-conversion
25898 @itemx -mno-address-space-conversion
25899 @opindex maddress-space-conversion
25900 @opindex mno-address-space-conversion
25901 Allow/disallow treating the @code{__ea} address space as superset
25902 of the generic address space. This enables explicit type casts
25903 between @code{__ea} and generic pointer as well as implicit
25904 conversions of generic pointers to @code{__ea} pointers. The
25905 default is to allow address space pointer conversions.
25907 @item -mcache-size=@var{cache-size}
25908 @opindex mcache-size
25909 This option controls the version of libgcc that the compiler links to an
25910 executable and selects a software-managed cache for accessing variables
25911 in the @code{__ea} address space with a particular cache size. Possible
25912 options for @var{cache-size} are @samp{8}, @samp{16}, @samp{32}, @samp{64}
25913 and @samp{128}. The default cache size is 64KB.
25915 @item -matomic-updates
25916 @itemx -mno-atomic-updates
25917 @opindex matomic-updates
25918 @opindex mno-atomic-updates
25919 This option controls the version of libgcc that the compiler links to an
25920 executable and selects whether atomic updates to the software-managed
25921 cache of PPU-side variables are used. If you use atomic updates, changes
25922 to a PPU variable from SPU code using the @code{__ea} named address space
25923 qualifier do not interfere with changes to other PPU variables residing
25924 in the same cache line from PPU code. If you do not use atomic updates,
25925 such interference may occur; however, writing back cache lines is
25926 more efficient. The default behavior is to use atomic updates.
25929 @itemx -mdual-nops=@var{n}
25930 @opindex mdual-nops
25931 By default, GCC inserts NOPs to increase dual issue when it expects
25932 it to increase performance. @var{n} can be a value from 0 to 10. A
25933 smaller @var{n} inserts fewer NOPs. 10 is the default, 0 is the
25934 same as @option{-mno-dual-nops}. Disabled with @option{-Os}.
25936 @item -mhint-max-nops=@var{n}
25937 @opindex mhint-max-nops
25938 Maximum number of NOPs to insert for a branch hint. A branch hint must
25939 be at least 8 instructions away from the branch it is affecting. GCC
25940 inserts up to @var{n} NOPs to enforce this, otherwise it does not
25941 generate the branch hint.
25943 @item -mhint-max-distance=@var{n}
25944 @opindex mhint-max-distance
25945 The encoding of the branch hint instruction limits the hint to be within
25946 256 instructions of the branch it is affecting. By default, GCC makes
25947 sure it is within 125.
25950 @opindex msafe-hints
25951 Work around a hardware bug that causes the SPU to stall indefinitely.
25952 By default, GCC inserts the @code{hbrp} instruction to make sure
25953 this stall won't happen.
25957 @node System V Options
25958 @subsection Options for System V
25960 These additional options are available on System V Release 4 for
25961 compatibility with other compilers on those systems:
25966 Create a shared object.
25967 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
25971 Identify the versions of each tool used by the compiler, in a
25972 @code{.ident} assembler directive in the output.
25976 Refrain from adding @code{.ident} directives to the output file (this is
25979 @item -YP,@var{dirs}
25981 Search the directories @var{dirs}, and no others, for libraries
25982 specified with @option{-l}.
25984 @item -Ym,@var{dir}
25986 Look in the directory @var{dir} to find the M4 preprocessor.
25987 The assembler uses this option.
25988 @c This is supposed to go with a -Yd for predefined M4 macro files, but
25989 @c the generic assembler that comes with Solaris takes just -Ym.
25992 @node TILE-Gx Options
25993 @subsection TILE-Gx Options
25994 @cindex TILE-Gx options
25996 These @samp{-m} options are supported on the TILE-Gx:
25999 @item -mcmodel=small
26000 @opindex mcmodel=small
26001 Generate code for the small model. The distance for direct calls is
26002 limited to 500M in either direction. PC-relative addresses are 32
26003 bits. Absolute addresses support the full address range.
26005 @item -mcmodel=large
26006 @opindex mcmodel=large
26007 Generate code for the large model. There is no limitation on call
26008 distance, pc-relative addresses, or absolute addresses.
26010 @item -mcpu=@var{name}
26012 Selects the type of CPU to be targeted. Currently the only supported
26013 type is @samp{tilegx}.
26019 Generate code for a 32-bit or 64-bit environment. The 32-bit
26020 environment sets int, long, and pointer to 32 bits. The 64-bit
26021 environment sets int to 32 bits and long and pointer to 64 bits.
26024 @itemx -mlittle-endian
26025 @opindex mbig-endian
26026 @opindex mlittle-endian
26027 Generate code in big/little endian mode, respectively.
26030 @node TILEPro Options
26031 @subsection TILEPro Options
26032 @cindex TILEPro options
26034 These @samp{-m} options are supported on the TILEPro:
26037 @item -mcpu=@var{name}
26039 Selects the type of CPU to be targeted. Currently the only supported
26040 type is @samp{tilepro}.
26044 Generate code for a 32-bit environment, which sets int, long, and
26045 pointer to 32 bits. This is the only supported behavior so the flag
26046 is essentially ignored.
26050 @subsection V850 Options
26051 @cindex V850 Options
26053 These @samp{-m} options are defined for V850 implementations:
26057 @itemx -mno-long-calls
26058 @opindex mlong-calls
26059 @opindex mno-long-calls
26060 Treat all calls as being far away (near). If calls are assumed to be
26061 far away, the compiler always loads the function's address into a
26062 register, and calls indirect through the pointer.
26068 Do not optimize (do optimize) basic blocks that use the same index
26069 pointer 4 or more times to copy pointer into the @code{ep} register, and
26070 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
26071 option is on by default if you optimize.
26073 @item -mno-prolog-function
26074 @itemx -mprolog-function
26075 @opindex mno-prolog-function
26076 @opindex mprolog-function
26077 Do not use (do use) external functions to save and restore registers
26078 at the prologue and epilogue of a function. The external functions
26079 are slower, but use less code space if more than one function saves
26080 the same number of registers. The @option{-mprolog-function} option
26081 is on by default if you optimize.
26085 Try to make the code as small as possible. At present, this just turns
26086 on the @option{-mep} and @option{-mprolog-function} options.
26088 @item -mtda=@var{n}
26090 Put static or global variables whose size is @var{n} bytes or less into
26091 the tiny data area that register @code{ep} points to. The tiny data
26092 area can hold up to 256 bytes in total (128 bytes for byte references).
26094 @item -msda=@var{n}
26096 Put static or global variables whose size is @var{n} bytes or less into
26097 the small data area that register @code{gp} points to. The small data
26098 area can hold up to 64 kilobytes.
26100 @item -mzda=@var{n}
26102 Put static or global variables whose size is @var{n} bytes or less into
26103 the first 32 kilobytes of memory.
26107 Specify that the target processor is the V850.
26111 Specify that the target processor is the V850E3V5. The preprocessor
26112 constant @code{__v850e3v5__} is defined if this option is used.
26116 Specify that the target processor is the V850E3V5. This is an alias for
26117 the @option{-mv850e3v5} option.
26121 Specify that the target processor is the V850E2V3. The preprocessor
26122 constant @code{__v850e2v3__} is defined if this option is used.
26126 Specify that the target processor is the V850E2. The preprocessor
26127 constant @code{__v850e2__} is defined if this option is used.
26131 Specify that the target processor is the V850E1. The preprocessor
26132 constants @code{__v850e1__} and @code{__v850e__} are defined if
26133 this option is used.
26137 Specify that the target processor is the V850ES. This is an alias for
26138 the @option{-mv850e1} option.
26142 Specify that the target processor is the V850E@. The preprocessor
26143 constant @code{__v850e__} is defined if this option is used.
26145 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
26146 nor @option{-mv850e2} nor @option{-mv850e2v3} nor @option{-mv850e3v5}
26147 are defined then a default target processor is chosen and the
26148 relevant @samp{__v850*__} preprocessor constant is defined.
26150 The preprocessor constants @code{__v850} and @code{__v851__} are always
26151 defined, regardless of which processor variant is the target.
26153 @item -mdisable-callt
26154 @itemx -mno-disable-callt
26155 @opindex mdisable-callt
26156 @opindex mno-disable-callt
26157 This option suppresses generation of the @code{CALLT} instruction for the
26158 v850e, v850e1, v850e2, v850e2v3 and v850e3v5 flavors of the v850
26161 This option is enabled by default when the RH850 ABI is
26162 in use (see @option{-mrh850-abi}), and disabled by default when the
26163 GCC ABI is in use. If @code{CALLT} instructions are being generated
26164 then the C preprocessor symbol @code{__V850_CALLT__} is defined.
26170 Pass on (or do not pass on) the @option{-mrelax} command-line option
26174 @itemx -mno-long-jumps
26175 @opindex mlong-jumps
26176 @opindex mno-long-jumps
26177 Disable (or re-enable) the generation of PC-relative jump instructions.
26180 @itemx -mhard-float
26181 @opindex msoft-float
26182 @opindex mhard-float
26183 Disable (or re-enable) the generation of hardware floating point
26184 instructions. This option is only significant when the target
26185 architecture is @samp{V850E2V3} or higher. If hardware floating point
26186 instructions are being generated then the C preprocessor symbol
26187 @code{__FPU_OK__} is defined, otherwise the symbol
26188 @code{__NO_FPU__} is defined.
26192 Enables the use of the e3v5 LOOP instruction. The use of this
26193 instruction is not enabled by default when the e3v5 architecture is
26194 selected because its use is still experimental.
26198 @opindex mrh850-abi
26200 Enables support for the RH850 version of the V850 ABI. This is the
26201 default. With this version of the ABI the following rules apply:
26205 Integer sized structures and unions are returned via a memory pointer
26206 rather than a register.
26209 Large structures and unions (more than 8 bytes in size) are passed by
26213 Functions are aligned to 16-bit boundaries.
26216 The @option{-m8byte-align} command-line option is supported.
26219 The @option{-mdisable-callt} command-line option is enabled by
26220 default. The @option{-mno-disable-callt} command-line option is not
26224 When this version of the ABI is enabled the C preprocessor symbol
26225 @code{__V850_RH850_ABI__} is defined.
26229 Enables support for the old GCC version of the V850 ABI. With this
26230 version of the ABI the following rules apply:
26234 Integer sized structures and unions are returned in register @code{r10}.
26237 Large structures and unions (more than 8 bytes in size) are passed by
26241 Functions are aligned to 32-bit boundaries, unless optimizing for
26245 The @option{-m8byte-align} command-line option is not supported.
26248 The @option{-mdisable-callt} command-line option is supported but not
26249 enabled by default.
26252 When this version of the ABI is enabled the C preprocessor symbol
26253 @code{__V850_GCC_ABI__} is defined.
26255 @item -m8byte-align
26256 @itemx -mno-8byte-align
26257 @opindex m8byte-align
26258 @opindex mno-8byte-align
26259 Enables support for @code{double} and @code{long long} types to be
26260 aligned on 8-byte boundaries. The default is to restrict the
26261 alignment of all objects to at most 4-bytes. When
26262 @option{-m8byte-align} is in effect the C preprocessor symbol
26263 @code{__V850_8BYTE_ALIGN__} is defined.
26266 @opindex mbig-switch
26267 Generate code suitable for big switch tables. Use this option only if
26268 the assembler/linker complain about out of range branches within a switch
26273 This option causes r2 and r5 to be used in the code generated by
26274 the compiler. This setting is the default.
26276 @item -mno-app-regs
26277 @opindex mno-app-regs
26278 This option causes r2 and r5 to be treated as fixed registers.
26283 @subsection VAX Options
26284 @cindex VAX options
26286 These @samp{-m} options are defined for the VAX:
26291 Do not output certain jump instructions (@code{aobleq} and so on)
26292 that the Unix assembler for the VAX cannot handle across long
26297 Do output those jump instructions, on the assumption that the
26298 GNU assembler is being used.
26302 Output code for G-format floating-point numbers instead of D-format.
26305 @node Visium Options
26306 @subsection Visium Options
26307 @cindex Visium options
26313 A program which performs file I/O and is destined to run on an MCM target
26314 should be linked with this option. It causes the libraries libc.a and
26315 libdebug.a to be linked. The program should be run on the target under
26316 the control of the GDB remote debugging stub.
26320 A program which performs file I/O and is destined to run on the simulator
26321 should be linked with option. This causes libraries libc.a and libsim.a to
26325 @itemx -mhard-float
26327 @opindex mhard-float
26328 Generate code containing floating-point instructions. This is the
26332 @itemx -msoft-float
26334 @opindex msoft-float
26335 Generate code containing library calls for floating-point.
26337 @option{-msoft-float} changes the calling convention in the output file;
26338 therefore, it is only useful if you compile @emph{all} of a program with
26339 this option. In particular, you need to compile @file{libgcc.a}, the
26340 library that comes with GCC, with @option{-msoft-float} in order for
26343 @item -mcpu=@var{cpu_type}
26345 Set the instruction set, register set, and instruction scheduling parameters
26346 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
26347 @samp{mcm}, @samp{gr5} and @samp{gr6}.
26349 @samp{mcm} is a synonym of @samp{gr5} present for backward compatibility.
26351 By default (unless configured otherwise), GCC generates code for the GR5
26352 variant of the Visium architecture.
26354 With @option{-mcpu=gr6}, GCC generates code for the GR6 variant of the Visium
26355 architecture. The only difference from GR5 code is that the compiler will
26356 generate block move instructions.
26358 @item -mtune=@var{cpu_type}
26360 Set the instruction scheduling parameters for machine type @var{cpu_type},
26361 but do not set the instruction set or register set that the option
26362 @option{-mcpu=@var{cpu_type}} would.
26366 Generate code for the supervisor mode, where there are no restrictions on
26367 the access to general registers. This is the default.
26370 @opindex muser-mode
26371 Generate code for the user mode, where the access to some general registers
26372 is forbidden: on the GR5, registers r24 to r31 cannot be accessed in this
26373 mode; on the GR6, only registers r29 to r31 are affected.
26377 @subsection VMS Options
26379 These @samp{-m} options are defined for the VMS implementations:
26382 @item -mvms-return-codes
26383 @opindex mvms-return-codes
26384 Return VMS condition codes from @code{main}. The default is to return POSIX-style
26385 condition (e.g.@ error) codes.
26387 @item -mdebug-main=@var{prefix}
26388 @opindex mdebug-main=@var{prefix}
26389 Flag the first routine whose name starts with @var{prefix} as the main
26390 routine for the debugger.
26394 Default to 64-bit memory allocation routines.
26396 @item -mpointer-size=@var{size}
26397 @opindex mpointer-size=@var{size}
26398 Set the default size of pointers. Possible options for @var{size} are
26399 @samp{32} or @samp{short} for 32 bit pointers, @samp{64} or @samp{long}
26400 for 64 bit pointers, and @samp{no} for supporting only 32 bit pointers.
26401 The later option disables @code{pragma pointer_size}.
26404 @node VxWorks Options
26405 @subsection VxWorks Options
26406 @cindex VxWorks Options
26408 The options in this section are defined for all VxWorks targets.
26409 Options specific to the target hardware are listed with the other
26410 options for that target.
26415 GCC can generate code for both VxWorks kernels and real time processes
26416 (RTPs). This option switches from the former to the latter. It also
26417 defines the preprocessor macro @code{__RTP__}.
26420 @opindex non-static
26421 Link an RTP executable against shared libraries rather than static
26422 libraries. The options @option{-static} and @option{-shared} can
26423 also be used for RTPs (@pxref{Link Options}); @option{-static}
26430 These options are passed down to the linker. They are defined for
26431 compatibility with Diab.
26434 @opindex Xbind-lazy
26435 Enable lazy binding of function calls. This option is equivalent to
26436 @option{-Wl,-z,now} and is defined for compatibility with Diab.
26440 Disable lazy binding of function calls. This option is the default and
26441 is defined for compatibility with Diab.
26445 @subsection x86 Options
26446 @cindex x86 Options
26448 These @samp{-m} options are defined for the x86 family of computers.
26452 @item -march=@var{cpu-type}
26454 Generate instructions for the machine type @var{cpu-type}. In contrast to
26455 @option{-mtune=@var{cpu-type}}, which merely tunes the generated code
26456 for the specified @var{cpu-type}, @option{-march=@var{cpu-type}} allows GCC
26457 to generate code that may not run at all on processors other than the one
26458 indicated. Specifying @option{-march=@var{cpu-type}} implies
26459 @option{-mtune=@var{cpu-type}}.
26461 The choices for @var{cpu-type} are:
26465 This selects the CPU to generate code for at compilation time by determining
26466 the processor type of the compiling machine. Using @option{-march=native}
26467 enables all instruction subsets supported by the local machine (hence
26468 the result might not run on different machines). Using @option{-mtune=native}
26469 produces code optimized for the local machine under the constraints
26470 of the selected instruction set.
26473 A generic CPU with 64-bit extensions.
26476 Original Intel i386 CPU@.
26479 Intel i486 CPU@. (No scheduling is implemented for this chip.)
26483 Intel Pentium CPU with no MMX support.
26486 Intel Lakemont MCU, based on Intel Pentium CPU.
26489 Intel Pentium MMX CPU, based on Pentium core with MMX instruction set support.
26492 Intel Pentium Pro CPU@.
26495 When used with @option{-march}, the Pentium Pro
26496 instruction set is used, so the code runs on all i686 family chips.
26497 When used with @option{-mtune}, it has the same meaning as @samp{generic}.
26500 Intel Pentium II CPU, based on Pentium Pro core with MMX instruction set
26505 Intel Pentium III CPU, based on Pentium Pro core with MMX and SSE instruction
26509 Intel Pentium M; low-power version of Intel Pentium III CPU
26510 with MMX, SSE and SSE2 instruction set support. Used by Centrino notebooks.
26514 Intel Pentium 4 CPU with MMX, SSE and SSE2 instruction set support.
26517 Improved version of Intel Pentium 4 CPU with MMX, SSE, SSE2 and SSE3 instruction
26521 Improved version of Intel Pentium 4 CPU with 64-bit extensions, MMX, SSE,
26522 SSE2 and SSE3 instruction set support.
26525 Intel Core 2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3
26526 instruction set support.
26529 Intel Nehalem CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3,
26530 SSE4.1, SSE4.2 and POPCNT instruction set support.
26533 Intel Westmere CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3,
26534 SSE4.1, SSE4.2, POPCNT, AES and PCLMUL instruction set support.
26537 Intel Sandy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3,
26538 SSE4.1, SSE4.2, POPCNT, AVX, AES and PCLMUL instruction set support.
26541 Intel Ivy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3,
26542 SSE4.1, SSE4.2, POPCNT, AVX, AES, PCLMUL, FSGSBASE, RDRND and F16C
26543 instruction set support.
26546 Intel Haswell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3,
26547 SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA,
26548 BMI, BMI2 and F16C instruction set support.
26551 Intel Broadwell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3,
26552 SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA,
26553 BMI, BMI2, F16C, RDSEED, ADCX and PREFETCHW instruction set support.
26556 Intel Skylake CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3,
26557 SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA,
26558 BMI, BMI2, F16C, RDSEED, ADCX, PREFETCHW, CLFLUSHOPT, XSAVEC and
26559 XSAVES instruction set support.
26562 Intel Bonnell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3 and SSSE3
26563 instruction set support.
26566 Intel Silvermont CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3,
26567 SSE4.1, SSE4.2, POPCNT, AES, PCLMUL and RDRND instruction set support.
26570 Intel Knight's Landing CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3,
26571 SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA,
26572 BMI, BMI2, F16C, RDSEED, ADCX, PREFETCHW, AVX512F, AVX512PF, AVX512ER and
26573 AVX512CD instruction set support.
26576 Intel Knights Mill CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3,
26577 SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA,
26578 BMI, BMI2, F16C, RDSEED, ADCX, PREFETCHW, AVX512F, AVX512PF, AVX512ER, AVX512CD,
26579 AVX5124VNNIW, AVX5124FMAPS and AVX512VPOPCNTDQ instruction set support.
26581 @item skylake-avx512
26582 Intel Skylake Server CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3,
26583 SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA,
26584 BMI, BMI2, F16C, RDSEED, ADCX, PREFETCHW, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F,
26585 CLWB, AVX512VL, AVX512BW, AVX512DQ and AVX512CD instruction set support.
26588 Intel Cannonlake Server CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2,
26589 SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2, AES, PCLMUL, FSGSBASE,
26590 RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX, PREFETCHW, CLFLUSHOPT, XSAVEC,
26591 XSAVES, AVX512F, AVX512VL, AVX512BW, AVX512DQ, AVX512CD, AVX512VBMI,
26592 AVX512IFMA, SHA and UMIP instruction set support.
26594 @item icelake-client
26595 Intel Icelake Client CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2,
26596 SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2, AES, PCLMUL, FSGSBASE,
26597 RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX, PREFETCHW, CLFLUSHOPT, XSAVEC,
26598 XSAVES, AVX512F, AVX512VL, AVX512BW, AVX512DQ, AVX512CD, AVX512VBMI,
26599 AVX512IFMA, SHA, CLWB, UMIP, RDPID, GFNI, AVX512VBMI2, AVX512VPOPCNTDQ,
26600 AVX512BITALG, AVX512VNNI, VPCLMULQDQ, VAES instruction set support.
26602 @item icelake-server
26603 Intel Icelake Server CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2,
26604 SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2, AES, PCLMUL, FSGSBASE,
26605 RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX, PREFETCHW, CLFLUSHOPT, XSAVEC,
26606 XSAVES, AVX512F, AVX512VL, AVX512BW, AVX512DQ, AVX512CD, AVX512VBMI,
26607 AVX512IFMA, SHA, CLWB, UMIP, RDPID, GFNI, AVX512VBMI2, AVX512VPOPCNTDQ,
26608 AVX512BITALG, AVX512VNNI, VPCLMULQDQ, VAES, PCONFIG and WBNOINVD instruction
26612 AMD K6 CPU with MMX instruction set support.
26616 Improved versions of AMD K6 CPU with MMX and 3DNow!@: instruction set support.
26619 @itemx athlon-tbird
26620 AMD Athlon CPU with MMX, 3dNOW!, enhanced 3DNow!@: and SSE prefetch instructions
26626 Improved AMD Athlon CPU with MMX, 3DNow!, enhanced 3DNow!@: and full SSE
26627 instruction set support.
26633 Processors based on the AMD K8 core with x86-64 instruction set support,
26634 including the AMD Opteron, Athlon 64, and Athlon 64 FX processors.
26635 (This supersets MMX, SSE, SSE2, 3DNow!, enhanced 3DNow!@: and 64-bit
26636 instruction set extensions.)
26639 @itemx opteron-sse3
26640 @itemx athlon64-sse3
26641 Improved versions of AMD K8 cores with SSE3 instruction set support.
26645 CPUs based on AMD Family 10h cores with x86-64 instruction set support. (This
26646 supersets MMX, SSE, SSE2, SSE3, SSE4A, 3DNow!, enhanced 3DNow!, ABM and 64-bit
26647 instruction set extensions.)
26650 CPUs based on AMD Family 15h cores with x86-64 instruction set support. (This
26651 supersets FMA4, AVX, XOP, LWP, AES, PCL_MUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A,
26652 SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.)
26654 AMD Family 15h core based CPUs with x86-64 instruction set support. (This
26655 supersets BMI, TBM, F16C, FMA, FMA4, AVX, XOP, LWP, AES, PCL_MUL, CX16, MMX,
26656 SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set
26659 AMD Family 15h core based CPUs with x86-64 instruction set support. (This
26660 supersets BMI, TBM, F16C, FMA, FMA4, FSGSBASE, AVX, XOP, LWP, AES,
26661 PCL_MUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and
26662 64-bit instruction set extensions.
26664 AMD Family 15h core based CPUs with x86-64 instruction set support. (This
26665 supersets BMI, BMI2, TBM, F16C, FMA, FMA4, FSGSBASE, AVX, AVX2, XOP, LWP,
26666 AES, PCL_MUL, CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1,
26667 SSE4.2, ABM and 64-bit instruction set extensions.
26670 AMD Family 17h core based CPUs with x86-64 instruction set support. (This
26671 supersets BMI, BMI2, F16C, FMA, FSGSBASE, AVX, AVX2, ADCX, RDSEED, MWAITX,
26672 SHA, CLZERO, AES, PCL_MUL, CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3,
26673 SSE4.1, SSE4.2, ABM, XSAVEC, XSAVES, CLFLUSHOPT, POPCNT, and 64-bit
26674 instruction set extensions.
26677 CPUs based on AMD Family 14h cores with x86-64 instruction set support. (This
26678 supersets MMX, SSE, SSE2, SSE3, SSSE3, SSE4A, CX16, ABM and 64-bit
26679 instruction set extensions.)
26682 CPUs based on AMD Family 16h cores with x86-64 instruction set support. This
26683 includes MOVBE, F16C, BMI, AVX, PCL_MUL, AES, SSE4.2, SSE4.1, CX16, ABM,
26684 SSE4A, SSSE3, SSE3, SSE2, SSE, MMX and 64-bit instruction set extensions.
26687 IDT WinChip C6 CPU, dealt in same way as i486 with additional MMX instruction
26691 IDT WinChip 2 CPU, dealt in same way as i486 with additional MMX and 3DNow!@:
26692 instruction set support.
26695 VIA C3 CPU with MMX and 3DNow!@: instruction set support.
26696 (No scheduling is implemented for this chip.)
26699 VIA C3-2 (Nehemiah/C5XL) CPU with MMX and SSE instruction set support.
26700 (No scheduling is implemented for this chip.)
26703 VIA C7 (Esther) CPU with MMX, SSE, SSE2 and SSE3 instruction set support.
26704 (No scheduling is implemented for this chip.)
26707 VIA Eden Samuel 2 CPU with MMX and 3DNow!@: instruction set support.
26708 (No scheduling is implemented for this chip.)
26711 VIA Eden Nehemiah CPU with MMX and SSE instruction set support.
26712 (No scheduling is implemented for this chip.)
26715 VIA Eden Esther CPU with MMX, SSE, SSE2 and SSE3 instruction set support.
26716 (No scheduling is implemented for this chip.)
26719 VIA Eden X2 CPU with x86-64, MMX, SSE, SSE2 and SSE3 instruction set support.
26720 (No scheduling is implemented for this chip.)
26723 VIA Eden X4 CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2,
26724 AVX and AVX2 instruction set support.
26725 (No scheduling is implemented for this chip.)
26728 Generic VIA Nano CPU with x86-64, MMX, SSE, SSE2, SSE3 and SSSE3
26729 instruction set support.
26730 (No scheduling is implemented for this chip.)
26733 VIA Nano 1xxx CPU with x86-64, MMX, SSE, SSE2, SSE3 and SSSE3
26734 instruction set support.
26735 (No scheduling is implemented for this chip.)
26738 VIA Nano 2xxx CPU with x86-64, MMX, SSE, SSE2, SSE3 and SSSE3
26739 instruction set support.
26740 (No scheduling is implemented for this chip.)
26743 VIA Nano 3xxx CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3 and SSE4.1
26744 instruction set support.
26745 (No scheduling is implemented for this chip.)
26748 VIA Nano Dual Core CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3 and SSE4.1
26749 instruction set support.
26750 (No scheduling is implemented for this chip.)
26753 VIA Nano Quad Core CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3 and SSE4.1
26754 instruction set support.
26755 (No scheduling is implemented for this chip.)
26758 AMD Geode embedded processor with MMX and 3DNow!@: instruction set support.
26761 @item -mtune=@var{cpu-type}
26763 Tune to @var{cpu-type} everything applicable about the generated code, except
26764 for the ABI and the set of available instructions.
26765 While picking a specific @var{cpu-type} schedules things appropriately
26766 for that particular chip, the compiler does not generate any code that
26767 cannot run on the default machine type unless you use a
26768 @option{-march=@var{cpu-type}} option.
26769 For example, if GCC is configured for i686-pc-linux-gnu
26770 then @option{-mtune=pentium4} generates code that is tuned for Pentium 4
26771 but still runs on i686 machines.
26773 The choices for @var{cpu-type} are the same as for @option{-march}.
26774 In addition, @option{-mtune} supports 2 extra choices for @var{cpu-type}:
26778 Produce code optimized for the most common IA32/@/AMD64/@/EM64T processors.
26779 If you know the CPU on which your code will run, then you should use
26780 the corresponding @option{-mtune} or @option{-march} option instead of
26781 @option{-mtune=generic}. But, if you do not know exactly what CPU users
26782 of your application will have, then you should use this option.
26784 As new processors are deployed in the marketplace, the behavior of this
26785 option will change. Therefore, if you upgrade to a newer version of
26786 GCC, code generation controlled by this option will change to reflect
26788 that are most common at the time that version of GCC is released.
26790 There is no @option{-march=generic} option because @option{-march}
26791 indicates the instruction set the compiler can use, and there is no
26792 generic instruction set applicable to all processors. In contrast,
26793 @option{-mtune} indicates the processor (or, in this case, collection of
26794 processors) for which the code is optimized.
26797 Produce code optimized for the most current Intel processors, which are
26798 Haswell and Silvermont for this version of GCC. If you know the CPU
26799 on which your code will run, then you should use the corresponding
26800 @option{-mtune} or @option{-march} option instead of @option{-mtune=intel}.
26801 But, if you want your application performs better on both Haswell and
26802 Silvermont, then you should use this option.
26804 As new Intel processors are deployed in the marketplace, the behavior of
26805 this option will change. Therefore, if you upgrade to a newer version of
26806 GCC, code generation controlled by this option will change to reflect
26807 the most current Intel processors at the time that version of GCC is
26810 There is no @option{-march=intel} option because @option{-march} indicates
26811 the instruction set the compiler can use, and there is no common
26812 instruction set applicable to all processors. In contrast,
26813 @option{-mtune} indicates the processor (or, in this case, collection of
26814 processors) for which the code is optimized.
26817 @item -mcpu=@var{cpu-type}
26819 A deprecated synonym for @option{-mtune}.
26821 @item -mfpmath=@var{unit}
26823 Generate floating-point arithmetic for selected unit @var{unit}. The choices
26824 for @var{unit} are:
26828 Use the standard 387 floating-point coprocessor present on the majority of chips and
26829 emulated otherwise. Code compiled with this option runs almost everywhere.
26830 The temporary results are computed in 80-bit precision instead of the precision
26831 specified by the type, resulting in slightly different results compared to most
26832 of other chips. See @option{-ffloat-store} for more detailed description.
26834 This is the default choice for non-Darwin x86-32 targets.
26837 Use scalar floating-point instructions present in the SSE instruction set.
26838 This instruction set is supported by Pentium III and newer chips,
26839 and in the AMD line
26840 by Athlon-4, Athlon XP and Athlon MP chips. The earlier version of the SSE
26841 instruction set supports only single-precision arithmetic, thus the double and
26842 extended-precision arithmetic are still done using 387. A later version, present
26843 only in Pentium 4 and AMD x86-64 chips, supports double-precision
26846 For the x86-32 compiler, you must use @option{-march=@var{cpu-type}}, @option{-msse}
26847 or @option{-msse2} switches to enable SSE extensions and make this option
26848 effective. For the x86-64 compiler, these extensions are enabled by default.
26850 The resulting code should be considerably faster in the majority of cases and avoid
26851 the numerical instability problems of 387 code, but may break some existing
26852 code that expects temporaries to be 80 bits.
26854 This is the default choice for the x86-64 compiler, Darwin x86-32 targets,
26855 and the default choice for x86-32 targets with the SSE2 instruction set
26856 when @option{-ffast-math} is enabled.
26861 Attempt to utilize both instruction sets at once. This effectively doubles the
26862 amount of available registers, and on chips with separate execution units for
26863 387 and SSE the execution resources too. Use this option with care, as it is
26864 still experimental, because the GCC register allocator does not model separate
26865 functional units well, resulting in unstable performance.
26868 @item -masm=@var{dialect}
26869 @opindex masm=@var{dialect}
26870 Output assembly instructions using selected @var{dialect}. Also affects
26871 which dialect is used for basic @code{asm} (@pxref{Basic Asm}) and
26872 extended @code{asm} (@pxref{Extended Asm}). Supported choices (in dialect
26873 order) are @samp{att} or @samp{intel}. The default is @samp{att}. Darwin does
26874 not support @samp{intel}.
26877 @itemx -mno-ieee-fp
26879 @opindex mno-ieee-fp
26880 Control whether or not the compiler uses IEEE floating-point
26881 comparisons. These correctly handle the case where the result of a
26882 comparison is unordered.
26885 @itemx -mhard-float
26887 @opindex mhard-float
26888 Generate output containing 80387 instructions for floating point.
26891 @itemx -msoft-float
26893 @opindex msoft-float
26894 Generate output containing library calls for floating point.
26896 @strong{Warning:} the requisite libraries are not part of GCC@.
26897 Normally the facilities of the machine's usual C compiler are used, but
26898 this cannot be done directly in cross-compilation. You must make your
26899 own arrangements to provide suitable library functions for
26902 On machines where a function returns floating-point results in the 80387
26903 register stack, some floating-point opcodes may be emitted even if
26904 @option{-msoft-float} is used.
26906 @item -mno-fp-ret-in-387
26907 @opindex mno-fp-ret-in-387
26908 Do not use the FPU registers for return values of functions.
26910 The usual calling convention has functions return values of types
26911 @code{float} and @code{double} in an FPU register, even if there
26912 is no FPU@. The idea is that the operating system should emulate
26915 The option @option{-mno-fp-ret-in-387} causes such values to be returned
26916 in ordinary CPU registers instead.
26918 @item -mno-fancy-math-387
26919 @opindex mno-fancy-math-387
26920 Some 387 emulators do not support the @code{sin}, @code{cos} and
26921 @code{sqrt} instructions for the 387. Specify this option to avoid
26922 generating those instructions. This option is the default on
26923 OpenBSD and NetBSD@. This option is overridden when @option{-march}
26924 indicates that the target CPU always has an FPU and so the
26925 instruction does not need emulation. These
26926 instructions are not generated unless you also use the
26927 @option{-funsafe-math-optimizations} switch.
26929 @item -malign-double
26930 @itemx -mno-align-double
26931 @opindex malign-double
26932 @opindex mno-align-double
26933 Control whether GCC aligns @code{double}, @code{long double}, and
26934 @code{long long} variables on a two-word boundary or a one-word
26935 boundary. Aligning @code{double} variables on a two-word boundary
26936 produces code that runs somewhat faster on a Pentium at the
26937 expense of more memory.
26939 On x86-64, @option{-malign-double} is enabled by default.
26941 @strong{Warning:} if you use the @option{-malign-double} switch,
26942 structures containing the above types are aligned differently than
26943 the published application binary interface specifications for the x86-32
26944 and are not binary compatible with structures in code compiled
26945 without that switch.
26947 @item -m96bit-long-double
26948 @itemx -m128bit-long-double
26949 @opindex m96bit-long-double
26950 @opindex m128bit-long-double
26951 These switches control the size of @code{long double} type. The x86-32
26952 application binary interface specifies the size to be 96 bits,
26953 so @option{-m96bit-long-double} is the default in 32-bit mode.
26955 Modern architectures (Pentium and newer) prefer @code{long double}
26956 to be aligned to an 8- or 16-byte boundary. In arrays or structures
26957 conforming to the ABI, this is not possible. So specifying
26958 @option{-m128bit-long-double} aligns @code{long double}
26959 to a 16-byte boundary by padding the @code{long double} with an additional
26962 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
26963 its ABI specifies that @code{long double} is aligned on 16-byte boundary.
26965 Notice that neither of these options enable any extra precision over the x87
26966 standard of 80 bits for a @code{long double}.
26968 @strong{Warning:} if you override the default value for your target ABI, this
26969 changes the size of
26970 structures and arrays containing @code{long double} variables,
26971 as well as modifying the function calling convention for functions taking
26972 @code{long double}. Hence they are not binary-compatible
26973 with code compiled without that switch.
26975 @item -mlong-double-64
26976 @itemx -mlong-double-80
26977 @itemx -mlong-double-128
26978 @opindex mlong-double-64
26979 @opindex mlong-double-80
26980 @opindex mlong-double-128
26981 These switches control the size of @code{long double} type. A size
26982 of 64 bits makes the @code{long double} type equivalent to the @code{double}
26983 type. This is the default for 32-bit Bionic C library. A size
26984 of 128 bits makes the @code{long double} type equivalent to the
26985 @code{__float128} type. This is the default for 64-bit Bionic C library.
26987 @strong{Warning:} if you override the default value for your target ABI, this
26988 changes the size of
26989 structures and arrays containing @code{long double} variables,
26990 as well as modifying the function calling convention for functions taking
26991 @code{long double}. Hence they are not binary-compatible
26992 with code compiled without that switch.
26994 @item -malign-data=@var{type}
26995 @opindex malign-data
26996 Control how GCC aligns variables. Supported values for @var{type} are
26997 @samp{compat} uses increased alignment value compatible uses GCC 4.8
26998 and earlier, @samp{abi} uses alignment value as specified by the
26999 psABI, and @samp{cacheline} uses increased alignment value to match
27000 the cache line size. @samp{compat} is the default.
27002 @item -mlarge-data-threshold=@var{threshold}
27003 @opindex mlarge-data-threshold
27004 When @option{-mcmodel=medium} is specified, data objects larger than
27005 @var{threshold} are placed in the large data section. This value must be the
27006 same across all objects linked into the binary, and defaults to 65535.
27010 Use a different function-calling convention, in which functions that
27011 take a fixed number of arguments return with the @code{ret @var{num}}
27012 instruction, which pops their arguments while returning. This saves one
27013 instruction in the caller since there is no need to pop the arguments
27016 You can specify that an individual function is called with this calling
27017 sequence with the function attribute @code{stdcall}. You can also
27018 override the @option{-mrtd} option by using the function attribute
27019 @code{cdecl}. @xref{Function Attributes}.
27021 @strong{Warning:} this calling convention is incompatible with the one
27022 normally used on Unix, so you cannot use it if you need to call
27023 libraries compiled with the Unix compiler.
27025 Also, you must provide function prototypes for all functions that
27026 take variable numbers of arguments (including @code{printf});
27027 otherwise incorrect code is generated for calls to those
27030 In addition, seriously incorrect code results if you call a
27031 function with too many arguments. (Normally, extra arguments are
27032 harmlessly ignored.)
27034 @item -mregparm=@var{num}
27036 Control how many registers are used to pass integer arguments. By
27037 default, no registers are used to pass arguments, and at most 3
27038 registers can be used. You can control this behavior for a specific
27039 function by using the function attribute @code{regparm}.
27040 @xref{Function Attributes}.
27042 @strong{Warning:} if you use this switch, and
27043 @var{num} is nonzero, then you must build all modules with the same
27044 value, including any libraries. This includes the system libraries and
27048 @opindex msseregparm
27049 Use SSE register passing conventions for float and double arguments
27050 and return values. You can control this behavior for a specific
27051 function by using the function attribute @code{sseregparm}.
27052 @xref{Function Attributes}.
27054 @strong{Warning:} if you use this switch then you must build all
27055 modules with the same value, including any libraries. This includes
27056 the system libraries and startup modules.
27058 @item -mvect8-ret-in-mem
27059 @opindex mvect8-ret-in-mem
27060 Return 8-byte vectors in memory instead of MMX registers. This is the
27061 default on Solaris@tie{}8 and 9 and VxWorks to match the ABI of the Sun
27062 Studio compilers until version 12. Later compiler versions (starting
27063 with Studio 12 Update@tie{}1) follow the ABI used by other x86 targets, which
27064 is the default on Solaris@tie{}10 and later. @emph{Only} use this option if
27065 you need to remain compatible with existing code produced by those
27066 previous compiler versions or older versions of GCC@.
27075 Set 80387 floating-point precision to 32, 64 or 80 bits. When @option{-mpc32}
27076 is specified, the significands of results of floating-point operations are
27077 rounded to 24 bits (single precision); @option{-mpc64} rounds the
27078 significands of results of floating-point operations to 53 bits (double
27079 precision) and @option{-mpc80} rounds the significands of results of
27080 floating-point operations to 64 bits (extended double precision), which is
27081 the default. When this option is used, floating-point operations in higher
27082 precisions are not available to the programmer without setting the FPU
27083 control word explicitly.
27085 Setting the rounding of floating-point operations to less than the default
27086 80 bits can speed some programs by 2% or more. Note that some mathematical
27087 libraries assume that extended-precision (80-bit) floating-point operations
27088 are enabled by default; routines in such libraries could suffer significant
27089 loss of accuracy, typically through so-called ``catastrophic cancellation'',
27090 when this option is used to set the precision to less than extended precision.
27092 @item -mstackrealign
27093 @opindex mstackrealign
27094 Realign the stack at entry. On the x86, the @option{-mstackrealign}
27095 option generates an alternate prologue and epilogue that realigns the
27096 run-time stack if necessary. This supports mixing legacy codes that keep
27097 4-byte stack alignment with modern codes that keep 16-byte stack alignment for
27098 SSE compatibility. See also the attribute @code{force_align_arg_pointer},
27099 applicable to individual functions.
27101 @item -mpreferred-stack-boundary=@var{num}
27102 @opindex mpreferred-stack-boundary
27103 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
27104 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
27105 the default is 4 (16 bytes or 128 bits).
27107 @strong{Warning:} When generating code for the x86-64 architecture with
27108 SSE extensions disabled, @option{-mpreferred-stack-boundary=3} can be
27109 used to keep the stack boundary aligned to 8 byte boundary. Since
27110 x86-64 ABI require 16 byte stack alignment, this is ABI incompatible and
27111 intended to be used in controlled environment where stack space is
27112 important limitation. This option leads to wrong code when functions
27113 compiled with 16 byte stack alignment (such as functions from a standard
27114 library) are called with misaligned stack. In this case, SSE
27115 instructions may lead to misaligned memory access traps. In addition,
27116 variable arguments are handled incorrectly for 16 byte aligned
27117 objects (including x87 long double and __int128), leading to wrong
27118 results. You must build all modules with
27119 @option{-mpreferred-stack-boundary=3}, including any libraries. This
27120 includes the system libraries and startup modules.
27122 @item -mincoming-stack-boundary=@var{num}
27123 @opindex mincoming-stack-boundary
27124 Assume the incoming stack is aligned to a 2 raised to @var{num} byte
27125 boundary. If @option{-mincoming-stack-boundary} is not specified,
27126 the one specified by @option{-mpreferred-stack-boundary} is used.
27128 On Pentium and Pentium Pro, @code{double} and @code{long double} values
27129 should be aligned to an 8-byte boundary (see @option{-malign-double}) or
27130 suffer significant run time performance penalties. On Pentium III, the
27131 Streaming SIMD Extension (SSE) data type @code{__m128} may not work
27132 properly if it is not 16-byte aligned.
27134 To ensure proper alignment of this values on the stack, the stack boundary
27135 must be as aligned as that required by any value stored on the stack.
27136 Further, every function must be generated such that it keeps the stack
27137 aligned. Thus calling a function compiled with a higher preferred
27138 stack boundary from a function compiled with a lower preferred stack
27139 boundary most likely misaligns the stack. It is recommended that
27140 libraries that use callbacks always use the default setting.
27142 This extra alignment does consume extra stack space, and generally
27143 increases code size. Code that is sensitive to stack space usage, such
27144 as embedded systems and operating system kernels, may want to reduce the
27145 preferred alignment to @option{-mpreferred-stack-boundary=2}.
27202 @itemx -mavx512ifma
27203 @opindex mavx512ifma
27205 @itemx -mavx512vbmi
27206 @opindex mavx512vbmi
27217 @itemx -mclflushopt
27218 @opindex mclflushopt
27241 @itemx -mprefetchwt1
27242 @opindex mprefetchwt1
27303 @itemx -mavx512vbmi2
27304 @opindex mavx512vbmi2
27312 @itemx -mvpclmulqdq
27313 @opindex mvpclmulqdq
27315 @itemx -mavx512bitalg
27316 @opindex mavx512bitalg
27322 @opindex mmovdir64b
27324 @itemx -mavx512vpopcntdq
27325 @opindex mavx512vpopcntdq
27326 These switches enable the use of instructions in the MMX, SSE,
27327 SSE2, SSE3, SSSE3, SSE4.1, AVX, AVX2, AVX512F, AVX512PF, AVX512ER, AVX512CD,
27328 SHA, AES, PCLMUL, FSGSBASE, RDRND, F16C, FMA, SSE4A, FMA4, XOP, LWP, ABM,
27329 AVX512VL, AVX512BW, AVX512DQ, AVX512IFMA, AVX512VBMI, BMI, BMI2, VAES,
27330 FXSR, XSAVE, XSAVEOPT, LZCNT, RTM, MPX, MWAITX, PKU, IBT, SHSTK, AVX512VBMI2,
27331 GFNI, VPCLMULQDQ, AVX512BITALG, MOVDIRI, MOVDIR64B,
27332 AVX512VPOPCNTDQ3DNow!@: or enhanced 3DNow!@: extended instruction sets.
27333 Each has a corresponding @option{-mno-} option to disable use of these
27336 These extensions are also available as built-in functions: see
27337 @ref{x86 Built-in Functions}, for details of the functions enabled and
27338 disabled by these switches.
27340 To generate SSE/SSE2 instructions automatically from floating-point
27341 code (as opposed to 387 instructions), see @option{-mfpmath=sse}.
27343 GCC depresses SSEx instructions when @option{-mavx} is used. Instead, it
27344 generates new AVX instructions or AVX equivalence for all SSEx instructions
27347 These options enable GCC to use these extended instructions in
27348 generated code, even without @option{-mfpmath=sse}. Applications that
27349 perform run-time CPU detection must compile separate files for each
27350 supported architecture, using the appropriate flags. In particular,
27351 the file containing the CPU detection code should be compiled without
27354 @item -mdump-tune-features
27355 @opindex mdump-tune-features
27356 This option instructs GCC to dump the names of the x86 performance
27357 tuning features and default settings. The names can be used in
27358 @option{-mtune-ctrl=@var{feature-list}}.
27360 @item -mtune-ctrl=@var{feature-list}
27361 @opindex mtune-ctrl=@var{feature-list}
27362 This option is used to do fine grain control of x86 code generation features.
27363 @var{feature-list} is a comma separated list of @var{feature} names. See also
27364 @option{-mdump-tune-features}. When specified, the @var{feature} is turned
27365 on if it is not preceded with @samp{^}, otherwise, it is turned off.
27366 @option{-mtune-ctrl=@var{feature-list}} is intended to be used by GCC
27367 developers. Using it may lead to code paths not covered by testing and can
27368 potentially result in compiler ICEs or runtime errors.
27371 @opindex mno-default
27372 This option instructs GCC to turn off all tunable features. See also
27373 @option{-mtune-ctrl=@var{feature-list}} and @option{-mdump-tune-features}.
27377 This option instructs GCC to emit a @code{cld} instruction in the prologue
27378 of functions that use string instructions. String instructions depend on
27379 the DF flag to select between autoincrement or autodecrement mode. While the
27380 ABI specifies the DF flag to be cleared on function entry, some operating
27381 systems violate this specification by not clearing the DF flag in their
27382 exception dispatchers. The exception handler can be invoked with the DF flag
27383 set, which leads to wrong direction mode when string instructions are used.
27384 This option can be enabled by default on 32-bit x86 targets by configuring
27385 GCC with the @option{--enable-cld} configure option. Generation of @code{cld}
27386 instructions can be suppressed with the @option{-mno-cld} compiler option
27390 @opindex mvzeroupper
27391 This option instructs GCC to emit a @code{vzeroupper} instruction
27392 before a transfer of control flow out of the function to minimize
27393 the AVX to SSE transition penalty as well as remove unnecessary @code{zeroupper}
27396 @item -mprefer-avx128
27397 @opindex mprefer-avx128
27398 This option instructs GCC to use 128-bit AVX instructions instead of
27399 256-bit AVX instructions in the auto-vectorizer.
27401 @item -mprefer-vector-width=@var{opt}
27402 @opindex mprefer-vector-width
27403 This option instructs GCC to use @var{opt}-bit vector width in instructions
27404 instead of default on the selected platform.
27408 No extra limitations applied to GCC other than defined by the selected platform.
27411 Prefer 128-bit vector width for instructions.
27414 Prefer 256-bit vector width for instructions.
27417 Prefer 512-bit vector width for instructions.
27422 This option enables GCC to generate @code{CMPXCHG16B} instructions in 64-bit
27423 code to implement compare-and-exchange operations on 16-byte aligned 128-bit
27424 objects. This is useful for atomic updates of data structures exceeding one
27425 machine word in size. The compiler uses this instruction to implement
27426 @ref{__sync Builtins}. However, for @ref{__atomic Builtins} operating on
27427 128-bit integers, a library call is always used.
27431 This option enables generation of @code{SAHF} instructions in 64-bit code.
27432 Early Intel Pentium 4 CPUs with Intel 64 support,
27433 prior to the introduction of Pentium 4 G1 step in December 2005,
27434 lacked the @code{LAHF} and @code{SAHF} instructions
27435 which are supported by AMD64.
27436 These are load and store instructions, respectively, for certain status flags.
27437 In 64-bit mode, the @code{SAHF} instruction is used to optimize @code{fmod},
27438 @code{drem}, and @code{remainder} built-in functions;
27439 see @ref{Other Builtins} for details.
27443 This option enables use of the @code{movbe} instruction to implement
27444 @code{__builtin_bswap32} and @code{__builtin_bswap64}.
27448 The @option{-mshstk} option enables shadow stack built-in functions
27449 from x86 Control-flow Enforcement Technology (CET).
27453 This option enables built-in functions @code{__builtin_ia32_crc32qi},
27454 @code{__builtin_ia32_crc32hi}, @code{__builtin_ia32_crc32si} and
27455 @code{__builtin_ia32_crc32di} to generate the @code{crc32} machine instruction.
27459 This option enables use of @code{RCPSS} and @code{RSQRTSS} instructions
27460 (and their vectorized variants @code{RCPPS} and @code{RSQRTPS})
27461 with an additional Newton-Raphson step
27462 to increase precision instead of @code{DIVSS} and @code{SQRTSS}
27463 (and their vectorized
27464 variants) for single-precision floating-point arguments. These instructions
27465 are generated only when @option{-funsafe-math-optimizations} is enabled
27466 together with @option{-ffinite-math-only} and @option{-fno-trapping-math}.
27467 Note that while the throughput of the sequence is higher than the throughput
27468 of the non-reciprocal instruction, the precision of the sequence can be
27469 decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994).
27471 Note that GCC implements @code{1.0f/sqrtf(@var{x})} in terms of @code{RSQRTSS}
27472 (or @code{RSQRTPS}) already with @option{-ffast-math} (or the above option
27473 combination), and doesn't need @option{-mrecip}.
27475 Also note that GCC emits the above sequence with additional Newton-Raphson step
27476 for vectorized single-float division and vectorized @code{sqrtf(@var{x})}
27477 already with @option{-ffast-math} (or the above option combination), and
27478 doesn't need @option{-mrecip}.
27480 @item -mrecip=@var{opt}
27481 @opindex mrecip=opt
27482 This option controls which reciprocal estimate instructions
27483 may be used. @var{opt} is a comma-separated list of options, which may
27484 be preceded by a @samp{!} to invert the option:
27488 Enable all estimate instructions.
27491 Enable the default instructions, equivalent to @option{-mrecip}.
27494 Disable all estimate instructions, equivalent to @option{-mno-recip}.
27497 Enable the approximation for scalar division.
27500 Enable the approximation for vectorized division.
27503 Enable the approximation for scalar square root.
27506 Enable the approximation for vectorized square root.
27509 So, for example, @option{-mrecip=all,!sqrt} enables
27510 all of the reciprocal approximations, except for square root.
27512 @item -mveclibabi=@var{type}
27513 @opindex mveclibabi
27514 Specifies the ABI type to use for vectorizing intrinsics using an
27515 external library. Supported values for @var{type} are @samp{svml}
27516 for the Intel short
27517 vector math library and @samp{acml} for the AMD math core library.
27518 To use this option, both @option{-ftree-vectorize} and
27519 @option{-funsafe-math-optimizations} have to be enabled, and an SVML or ACML
27520 ABI-compatible library must be specified at link time.
27522 GCC currently emits calls to @code{vmldExp2},
27523 @code{vmldLn2}, @code{vmldLog102}, @code{vmldLog102}, @code{vmldPow2},
27524 @code{vmldTanh2}, @code{vmldTan2}, @code{vmldAtan2}, @code{vmldAtanh2},
27525 @code{vmldCbrt2}, @code{vmldSinh2}, @code{vmldSin2}, @code{vmldAsinh2},
27526 @code{vmldAsin2}, @code{vmldCosh2}, @code{vmldCos2}, @code{vmldAcosh2},
27527 @code{vmldAcos2}, @code{vmlsExp4}, @code{vmlsLn4}, @code{vmlsLog104},
27528 @code{vmlsLog104}, @code{vmlsPow4}, @code{vmlsTanh4}, @code{vmlsTan4},
27529 @code{vmlsAtan4}, @code{vmlsAtanh4}, @code{vmlsCbrt4}, @code{vmlsSinh4},
27530 @code{vmlsSin4}, @code{vmlsAsinh4}, @code{vmlsAsin4}, @code{vmlsCosh4},
27531 @code{vmlsCos4}, @code{vmlsAcosh4} and @code{vmlsAcos4} for corresponding
27532 function type when @option{-mveclibabi=svml} is used, and @code{__vrd2_sin},
27533 @code{__vrd2_cos}, @code{__vrd2_exp}, @code{__vrd2_log}, @code{__vrd2_log2},
27534 @code{__vrd2_log10}, @code{__vrs4_sinf}, @code{__vrs4_cosf},
27535 @code{__vrs4_expf}, @code{__vrs4_logf}, @code{__vrs4_log2f},
27536 @code{__vrs4_log10f} and @code{__vrs4_powf} for the corresponding function type
27537 when @option{-mveclibabi=acml} is used.
27539 @item -mabi=@var{name}
27541 Generate code for the specified calling convention. Permissible values
27542 are @samp{sysv} for the ABI used on GNU/Linux and other systems, and
27543 @samp{ms} for the Microsoft ABI. The default is to use the Microsoft
27544 ABI when targeting Microsoft Windows and the SysV ABI on all other systems.
27545 You can control this behavior for specific functions by
27546 using the function attributes @code{ms_abi} and @code{sysv_abi}.
27547 @xref{Function Attributes}.
27549 @item -mforce-indirect-call
27550 @opindex mforce-indirect-call
27551 Force all calls to functions to be indirect. This is useful
27552 when using Intel Processor Trace where it generates more precise timing
27553 information for function calls.
27555 @item -mcall-ms2sysv-xlogues
27556 @opindex mcall-ms2sysv-xlogues
27557 @opindex mno-call-ms2sysv-xlogues
27558 Due to differences in 64-bit ABIs, any Microsoft ABI function that calls a
27559 System V ABI function must consider RSI, RDI and XMM6-15 as clobbered. By
27560 default, the code for saving and restoring these registers is emitted inline,
27561 resulting in fairly lengthy prologues and epilogues. Using
27562 @option{-mcall-ms2sysv-xlogues} emits prologues and epilogues that
27563 use stubs in the static portion of libgcc to perform these saves and restores,
27564 thus reducing function size at the cost of a few extra instructions.
27566 @item -mtls-dialect=@var{type}
27567 @opindex mtls-dialect
27568 Generate code to access thread-local storage using the @samp{gnu} or
27569 @samp{gnu2} conventions. @samp{gnu} is the conservative default;
27570 @samp{gnu2} is more efficient, but it may add compile- and run-time
27571 requirements that cannot be satisfied on all systems.
27574 @itemx -mno-push-args
27575 @opindex mpush-args
27576 @opindex mno-push-args
27577 Use PUSH operations to store outgoing parameters. This method is shorter
27578 and usually equally fast as method using SUB/MOV operations and is enabled
27579 by default. In some cases disabling it may improve performance because of
27580 improved scheduling and reduced dependencies.
27582 @item -maccumulate-outgoing-args
27583 @opindex maccumulate-outgoing-args
27584 If enabled, the maximum amount of space required for outgoing arguments is
27585 computed in the function prologue. This is faster on most modern CPUs
27586 because of reduced dependencies, improved scheduling and reduced stack usage
27587 when the preferred stack boundary is not equal to 2. The drawback is a notable
27588 increase in code size. This switch implies @option{-mno-push-args}.
27592 Support thread-safe exception handling on MinGW. Programs that rely
27593 on thread-safe exception handling must compile and link all code with the
27594 @option{-mthreads} option. When compiling, @option{-mthreads} defines
27595 @option{-D_MT}; when linking, it links in a special thread helper library
27596 @option{-lmingwthrd} which cleans up per-thread exception-handling data.
27598 @item -mms-bitfields
27599 @itemx -mno-ms-bitfields
27600 @opindex mms-bitfields
27601 @opindex mno-ms-bitfields
27603 Enable/disable bit-field layout compatible with the native Microsoft
27606 If @code{packed} is used on a structure, or if bit-fields are used,
27607 it may be that the Microsoft ABI lays out the structure differently
27608 than the way GCC normally does. Particularly when moving packed
27609 data between functions compiled with GCC and the native Microsoft compiler
27610 (either via function call or as data in a file), it may be necessary to access
27613 This option is enabled by default for Microsoft Windows
27614 targets. This behavior can also be controlled locally by use of variable
27615 or type attributes. For more information, see @ref{x86 Variable Attributes}
27616 and @ref{x86 Type Attributes}.
27618 The Microsoft structure layout algorithm is fairly simple with the exception
27619 of the bit-field packing.
27620 The padding and alignment of members of structures and whether a bit-field
27621 can straddle a storage-unit boundary are determine by these rules:
27624 @item Structure members are stored sequentially in the order in which they are
27625 declared: the first member has the lowest memory address and the last member
27628 @item Every data object has an alignment requirement. The alignment requirement
27629 for all data except structures, unions, and arrays is either the size of the
27630 object or the current packing size (specified with either the
27631 @code{aligned} attribute or the @code{pack} pragma),
27632 whichever is less. For structures, unions, and arrays,
27633 the alignment requirement is the largest alignment requirement of its members.
27634 Every object is allocated an offset so that:
27637 offset % alignment_requirement == 0
27640 @item Adjacent bit-fields are packed into the same 1-, 2-, or 4-byte allocation
27641 unit if the integral types are the same size and if the next bit-field fits
27642 into the current allocation unit without crossing the boundary imposed by the
27643 common alignment requirements of the bit-fields.
27646 MSVC interprets zero-length bit-fields in the following ways:
27649 @item If a zero-length bit-field is inserted between two bit-fields that
27650 are normally coalesced, the bit-fields are not coalesced.
27657 unsigned long bf_1 : 12;
27659 unsigned long bf_2 : 12;
27664 The size of @code{t1} is 8 bytes with the zero-length bit-field. If the
27665 zero-length bit-field were removed, @code{t1}'s size would be 4 bytes.
27667 @item If a zero-length bit-field is inserted after a bit-field, @code{foo}, and the
27668 alignment of the zero-length bit-field is greater than the member that follows it,
27669 @code{bar}, @code{bar} is aligned as the type of the zero-length bit-field.
27690 For @code{t2}, @code{bar} is placed at offset 2, rather than offset 1.
27691 Accordingly, the size of @code{t2} is 4. For @code{t3}, the zero-length
27692 bit-field does not affect the alignment of @code{bar} or, as a result, the size
27695 Taking this into account, it is important to note the following:
27698 @item If a zero-length bit-field follows a normal bit-field, the type of the
27699 zero-length bit-field may affect the alignment of the structure as whole. For
27700 example, @code{t2} has a size of 4 bytes, since the zero-length bit-field follows a
27701 normal bit-field, and is of type short.
27703 @item Even if a zero-length bit-field is not followed by a normal bit-field, it may
27704 still affect the alignment of the structure:
27715 Here, @code{t4} takes up 4 bytes.
27718 @item Zero-length bit-fields following non-bit-field members are ignored:
27730 Here, @code{t5} takes up 2 bytes.
27734 @item -mno-align-stringops
27735 @opindex mno-align-stringops
27736 Do not align the destination of inlined string operations. This switch reduces
27737 code size and improves performance in case the destination is already aligned,
27738 but GCC doesn't know about it.
27740 @item -minline-all-stringops
27741 @opindex minline-all-stringops
27742 By default GCC inlines string operations only when the destination is
27743 known to be aligned to least a 4-byte boundary.
27744 This enables more inlining and increases code
27745 size, but may improve performance of code that depends on fast
27746 @code{memcpy}, @code{strlen},
27747 and @code{memset} for short lengths.
27749 @item -minline-stringops-dynamically
27750 @opindex minline-stringops-dynamically
27751 For string operations of unknown size, use run-time checks with
27752 inline code for small blocks and a library call for large blocks.
27754 @item -mstringop-strategy=@var{alg}
27755 @opindex mstringop-strategy=@var{alg}
27756 Override the internal decision heuristic for the particular algorithm to use
27757 for inlining string operations. The allowed values for @var{alg} are:
27763 Expand using i386 @code{rep} prefix of the specified size.
27767 @itemx unrolled_loop
27768 Expand into an inline loop.
27771 Always use a library call.
27774 @item -mmemcpy-strategy=@var{strategy}
27775 @opindex mmemcpy-strategy=@var{strategy}
27776 Override the internal decision heuristic to decide if @code{__builtin_memcpy}
27777 should be inlined and what inline algorithm to use when the expected size
27778 of the copy operation is known. @var{strategy}
27779 is a comma-separated list of @var{alg}:@var{max_size}:@var{dest_align} triplets.
27780 @var{alg} is specified in @option{-mstringop-strategy}, @var{max_size} specifies
27781 the max byte size with which inline algorithm @var{alg} is allowed. For the last
27782 triplet, the @var{max_size} must be @code{-1}. The @var{max_size} of the triplets
27783 in the list must be specified in increasing order. The minimal byte size for
27784 @var{alg} is @code{0} for the first triplet and @code{@var{max_size} + 1} of the
27787 @item -mmemset-strategy=@var{strategy}
27788 @opindex mmemset-strategy=@var{strategy}
27789 The option is similar to @option{-mmemcpy-strategy=} except that it is to control
27790 @code{__builtin_memset} expansion.
27792 @item -momit-leaf-frame-pointer
27793 @opindex momit-leaf-frame-pointer
27794 Don't keep the frame pointer in a register for leaf functions. This
27795 avoids the instructions to save, set up, and restore frame pointers and
27796 makes an extra register available in leaf functions. The option
27797 @option{-fomit-leaf-frame-pointer} removes the frame pointer for leaf functions,
27798 which might make debugging harder.
27800 @item -mtls-direct-seg-refs
27801 @itemx -mno-tls-direct-seg-refs
27802 @opindex mtls-direct-seg-refs
27803 Controls whether TLS variables may be accessed with offsets from the
27804 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
27805 or whether the thread base pointer must be added. Whether or not this
27806 is valid depends on the operating system, and whether it maps the
27807 segment to cover the entire TLS area.
27809 For systems that use the GNU C Library, the default is on.
27812 @itemx -mno-sse2avx
27814 Specify that the assembler should encode SSE instructions with VEX
27815 prefix. The option @option{-mavx} turns this on by default.
27820 If profiling is active (@option{-pg}), put the profiling
27821 counter call before the prologue.
27822 Note: On x86 architectures the attribute @code{ms_hook_prologue}
27823 isn't possible at the moment for @option{-mfentry} and @option{-pg}.
27825 @item -mrecord-mcount
27826 @itemx -mno-record-mcount
27827 @opindex mrecord-mcount
27828 If profiling is active (@option{-pg}), generate a __mcount_loc section
27829 that contains pointers to each profiling call. This is useful for
27830 automatically patching and out calls.
27833 @itemx -mno-nop-mcount
27834 @opindex mnop-mcount
27835 If profiling is active (@option{-pg}), generate the calls to
27836 the profiling functions as NOPs. This is useful when they
27837 should be patched in later dynamically. This is likely only
27838 useful together with @option{-mrecord-mcount}.
27840 @item -mskip-rax-setup
27841 @itemx -mno-skip-rax-setup
27842 @opindex mskip-rax-setup
27843 When generating code for the x86-64 architecture with SSE extensions
27844 disabled, @option{-mskip-rax-setup} can be used to skip setting up RAX
27845 register when there are no variable arguments passed in vector registers.
27847 @strong{Warning:} Since RAX register is used to avoid unnecessarily
27848 saving vector registers on stack when passing variable arguments, the
27849 impacts of this option are callees may waste some stack space,
27850 misbehave or jump to a random location. GCC 4.4 or newer don't have
27851 those issues, regardless the RAX register value.
27854 @itemx -mno-8bit-idiv
27855 @opindex m8bit-idiv
27856 On some processors, like Intel Atom, 8-bit unsigned integer divide is
27857 much faster than 32-bit/64-bit integer divide. This option generates a
27858 run-time check. If both dividend and divisor are within range of 0
27859 to 255, 8-bit unsigned integer divide is used instead of
27860 32-bit/64-bit integer divide.
27862 @item -mavx256-split-unaligned-load
27863 @itemx -mavx256-split-unaligned-store
27864 @opindex mavx256-split-unaligned-load
27865 @opindex mavx256-split-unaligned-store
27866 Split 32-byte AVX unaligned load and store.
27868 @item -mstack-protector-guard=@var{guard}
27869 @itemx -mstack-protector-guard-reg=@var{reg}
27870 @itemx -mstack-protector-guard-offset=@var{offset}
27871 @opindex mstack-protector-guard
27872 @opindex mstack-protector-guard-reg
27873 @opindex mstack-protector-guard-offset
27874 Generate stack protection code using canary at @var{guard}. Supported
27875 locations are @samp{global} for global canary or @samp{tls} for per-thread
27876 canary in the TLS block (the default). This option has effect only when
27877 @option{-fstack-protector} or @option{-fstack-protector-all} is specified.
27879 With the latter choice the options
27880 @option{-mstack-protector-guard-reg=@var{reg}} and
27881 @option{-mstack-protector-guard-offset=@var{offset}} furthermore specify
27882 which segment register (@code{%fs} or @code{%gs}) to use as base register
27883 for reading the canary, and from what offset from that base register.
27884 The default for those is as specified in the relevant ABI.
27886 @item -mmitigate-rop
27887 @opindex mmitigate-rop
27888 Try to avoid generating code sequences that contain unintended return
27889 opcodes, to mitigate against certain forms of attack. At the moment,
27890 this option is limited in what it can do and should not be relied
27891 on to provide serious protection.
27893 @item -mgeneral-regs-only
27894 @opindex mgeneral-regs-only
27895 Generate code that uses only the general-purpose registers. This
27896 prevents the compiler from using floating-point, vector, mask and bound
27899 @item -mindirect-branch=@var{choice}
27900 @opindex -mindirect-branch
27901 Convert indirect call and jump with @var{choice}. The default is
27902 @samp{keep}, which keeps indirect call and jump unmodified.
27903 @samp{thunk} converts indirect call and jump to call and return thunk.
27904 @samp{thunk-inline} converts indirect call and jump to inlined call
27905 and return thunk. @samp{thunk-extern} converts indirect call and jump
27906 to external call and return thunk provided in a separate object file.
27907 You can control this behavior for a specific function by using the
27908 function attribute @code{indirect_branch}. @xref{Function Attributes}.
27910 Note that @option{-mcmodel=large} is incompatible with
27911 @option{-mindirect-branch=thunk} and
27912 @option{-mindirect-branch=thunk-extern} since the thunk function may
27913 not be reachable in the large code model.
27915 Note that @option{-mindirect-branch=thunk-extern} is incompatible with
27916 @option{-fcf-protection=branch} and @option{-fcheck-pointer-bounds}
27917 since the external thunk can not be modified to disable control-flow
27920 @item -mfunction-return=@var{choice}
27921 @opindex -mfunction-return
27922 Convert function return with @var{choice}. The default is @samp{keep},
27923 which keeps function return unmodified. @samp{thunk} converts function
27924 return to call and return thunk. @samp{thunk-inline} converts function
27925 return to inlined call and return thunk. @samp{thunk-extern} converts
27926 function return to external call and return thunk provided in a separate
27927 object file. You can control this behavior for a specific function by
27928 using the function attribute @code{function_return}.
27929 @xref{Function Attributes}.
27931 Note that @option{-mcmodel=large} is incompatible with
27932 @option{-mfunction-return=thunk} and
27933 @option{-mfunction-return=thunk-extern} since the thunk function may
27934 not be reachable in the large code model.
27937 @item -mindirect-branch-register
27938 @opindex -mindirect-branch-register
27939 Force indirect call and jump via register.
27943 These @samp{-m} switches are supported in addition to the above
27944 on x86-64 processors in 64-bit environments.
27957 Generate code for a 16-bit, 32-bit or 64-bit environment.
27958 The @option{-m32} option sets @code{int}, @code{long}, and pointer types
27960 generates code that runs on any i386 system.
27962 The @option{-m64} option sets @code{int} to 32 bits and @code{long} and pointer
27963 types to 64 bits, and generates code for the x86-64 architecture.
27964 For Darwin only the @option{-m64} option also turns off the @option{-fno-pic}
27965 and @option{-mdynamic-no-pic} options.
27967 The @option{-mx32} option sets @code{int}, @code{long}, and pointer types
27969 generates code for the x86-64 architecture.
27971 The @option{-m16} option is the same as @option{-m32}, except for that
27972 it outputs the @code{.code16gcc} assembly directive at the beginning of
27973 the assembly output so that the binary can run in 16-bit mode.
27975 The @option{-miamcu} option generates code which conforms to Intel MCU
27976 psABI. It requires the @option{-m32} option to be turned on.
27978 @item -mno-red-zone
27979 @opindex mno-red-zone
27980 Do not use a so-called ``red zone'' for x86-64 code. The red zone is mandated
27981 by the x86-64 ABI; it is a 128-byte area beyond the location of the
27982 stack pointer that is not modified by signal or interrupt handlers
27983 and therefore can be used for temporary data without adjusting the stack
27984 pointer. The flag @option{-mno-red-zone} disables this red zone.
27986 @item -mcmodel=small
27987 @opindex mcmodel=small
27988 Generate code for the small code model: the program and its symbols must
27989 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
27990 Programs can be statically or dynamically linked. This is the default
27993 @item -mcmodel=kernel
27994 @opindex mcmodel=kernel
27995 Generate code for the kernel code model. The kernel runs in the
27996 negative 2 GB of the address space.
27997 This model has to be used for Linux kernel code.
27999 @item -mcmodel=medium
28000 @opindex mcmodel=medium
28001 Generate code for the medium model: the program is linked in the lower 2
28002 GB of the address space. Small symbols are also placed there. Symbols
28003 with sizes larger than @option{-mlarge-data-threshold} are put into
28004 large data or BSS sections and can be located above 2GB. Programs can
28005 be statically or dynamically linked.
28007 @item -mcmodel=large
28008 @opindex mcmodel=large
28009 Generate code for the large model. This model makes no assumptions
28010 about addresses and sizes of sections.
28012 @item -maddress-mode=long
28013 @opindex maddress-mode=long
28014 Generate code for long address mode. This is only supported for 64-bit
28015 and x32 environments. It is the default address mode for 64-bit
28018 @item -maddress-mode=short
28019 @opindex maddress-mode=short
28020 Generate code for short address mode. This is only supported for 32-bit
28021 and x32 environments. It is the default address mode for 32-bit and
28025 @node x86 Windows Options
28026 @subsection x86 Windows Options
28027 @cindex x86 Windows Options
28028 @cindex Windows Options for x86
28030 These additional options are available for Microsoft Windows targets:
28036 specifies that a console application is to be generated, by
28037 instructing the linker to set the PE header subsystem type
28038 required for console applications.
28039 This option is available for Cygwin and MinGW targets and is
28040 enabled by default on those targets.
28044 This option is available for Cygwin and MinGW targets. It
28045 specifies that a DLL---a dynamic link library---is to be
28046 generated, enabling the selection of the required runtime
28047 startup object and entry point.
28049 @item -mnop-fun-dllimport
28050 @opindex mnop-fun-dllimport
28051 This option is available for Cygwin and MinGW targets. It
28052 specifies that the @code{dllimport} attribute should be ignored.
28056 This option is available for MinGW targets. It specifies
28057 that MinGW-specific thread support is to be used.
28061 This option is available for MinGW-w64 targets. It causes
28062 the @code{UNICODE} preprocessor macro to be predefined, and
28063 chooses Unicode-capable runtime startup code.
28067 This option is available for Cygwin and MinGW targets. It
28068 specifies that the typical Microsoft Windows predefined macros are to
28069 be set in the pre-processor, but does not influence the choice
28070 of runtime library/startup code.
28074 This option is available for Cygwin and MinGW targets. It
28075 specifies that a GUI application is to be generated by
28076 instructing the linker to set the PE header subsystem type
28079 @item -fno-set-stack-executable
28080 @opindex fno-set-stack-executable
28081 This option is available for MinGW targets. It specifies that
28082 the executable flag for the stack used by nested functions isn't
28083 set. This is necessary for binaries running in kernel mode of
28084 Microsoft Windows, as there the User32 API, which is used to set executable
28085 privileges, isn't available.
28087 @item -fwritable-relocated-rdata
28088 @opindex fno-writable-relocated-rdata
28089 This option is available for MinGW and Cygwin targets. It specifies
28090 that relocated-data in read-only section is put into the @code{.data}
28091 section. This is a necessary for older runtimes not supporting
28092 modification of @code{.rdata} sections for pseudo-relocation.
28094 @item -mpe-aligned-commons
28095 @opindex mpe-aligned-commons
28096 This option is available for Cygwin and MinGW targets. It
28097 specifies that the GNU extension to the PE file format that
28098 permits the correct alignment of COMMON variables should be
28099 used when generating code. It is enabled by default if
28100 GCC detects that the target assembler found during configuration
28101 supports the feature.
28104 See also under @ref{x86 Options} for standard options.
28106 @node Xstormy16 Options
28107 @subsection Xstormy16 Options
28108 @cindex Xstormy16 Options
28110 These options are defined for Xstormy16:
28115 Choose startup files and linker script suitable for the simulator.
28118 @node Xtensa Options
28119 @subsection Xtensa Options
28120 @cindex Xtensa Options
28122 These options are supported for Xtensa targets:
28126 @itemx -mno-const16
28128 @opindex mno-const16
28129 Enable or disable use of @code{CONST16} instructions for loading
28130 constant values. The @code{CONST16} instruction is currently not a
28131 standard option from Tensilica. When enabled, @code{CONST16}
28132 instructions are always used in place of the standard @code{L32R}
28133 instructions. The use of @code{CONST16} is enabled by default only if
28134 the @code{L32R} instruction is not available.
28137 @itemx -mno-fused-madd
28138 @opindex mfused-madd
28139 @opindex mno-fused-madd
28140 Enable or disable use of fused multiply/add and multiply/subtract
28141 instructions in the floating-point option. This has no effect if the
28142 floating-point option is not also enabled. Disabling fused multiply/add
28143 and multiply/subtract instructions forces the compiler to use separate
28144 instructions for the multiply and add/subtract operations. This may be
28145 desirable in some cases where strict IEEE 754-compliant results are
28146 required: the fused multiply add/subtract instructions do not round the
28147 intermediate result, thereby producing results with @emph{more} bits of
28148 precision than specified by the IEEE standard. Disabling fused multiply
28149 add/subtract instructions also ensures that the program output is not
28150 sensitive to the compiler's ability to combine multiply and add/subtract
28153 @item -mserialize-volatile
28154 @itemx -mno-serialize-volatile
28155 @opindex mserialize-volatile
28156 @opindex mno-serialize-volatile
28157 When this option is enabled, GCC inserts @code{MEMW} instructions before
28158 @code{volatile} memory references to guarantee sequential consistency.
28159 The default is @option{-mserialize-volatile}. Use
28160 @option{-mno-serialize-volatile} to omit the @code{MEMW} instructions.
28162 @item -mforce-no-pic
28163 @opindex mforce-no-pic
28164 For targets, like GNU/Linux, where all user-mode Xtensa code must be
28165 position-independent code (PIC), this option disables PIC for compiling
28168 @item -mtext-section-literals
28169 @itemx -mno-text-section-literals
28170 @opindex mtext-section-literals
28171 @opindex mno-text-section-literals
28172 These options control the treatment of literal pools. The default is
28173 @option{-mno-text-section-literals}, which places literals in a separate
28174 section in the output file. This allows the literal pool to be placed
28175 in a data RAM/ROM, and it also allows the linker to combine literal
28176 pools from separate object files to remove redundant literals and
28177 improve code size. With @option{-mtext-section-literals}, the literals
28178 are interspersed in the text section in order to keep them as close as
28179 possible to their references. This may be necessary for large assembly
28180 files. Literals for each function are placed right before that function.
28182 @item -mauto-litpools
28183 @itemx -mno-auto-litpools
28184 @opindex mauto-litpools
28185 @opindex mno-auto-litpools
28186 These options control the treatment of literal pools. The default is
28187 @option{-mno-auto-litpools}, which places literals in a separate
28188 section in the output file unless @option{-mtext-section-literals} is
28189 used. With @option{-mauto-litpools} the literals are interspersed in
28190 the text section by the assembler. Compiler does not produce explicit
28191 @code{.literal} directives and loads literals into registers with
28192 @code{MOVI} instructions instead of @code{L32R} to let the assembler
28193 do relaxation and place literals as necessary. This option allows
28194 assembler to create several literal pools per function and assemble
28195 very big functions, which may not be possible with
28196 @option{-mtext-section-literals}.
28198 @item -mtarget-align
28199 @itemx -mno-target-align
28200 @opindex mtarget-align
28201 @opindex mno-target-align
28202 When this option is enabled, GCC instructs the assembler to
28203 automatically align instructions to reduce branch penalties at the
28204 expense of some code density. The assembler attempts to widen density
28205 instructions to align branch targets and the instructions following call
28206 instructions. If there are not enough preceding safe density
28207 instructions to align a target, no widening is performed. The
28208 default is @option{-mtarget-align}. These options do not affect the
28209 treatment of auto-aligned instructions like @code{LOOP}, which the
28210 assembler always aligns, either by widening density instructions or
28211 by inserting NOP instructions.
28214 @itemx -mno-longcalls
28215 @opindex mlongcalls
28216 @opindex mno-longcalls
28217 When this option is enabled, GCC instructs the assembler to translate
28218 direct calls to indirect calls unless it can determine that the target
28219 of a direct call is in the range allowed by the call instruction. This
28220 translation typically occurs for calls to functions in other source
28221 files. Specifically, the assembler translates a direct @code{CALL}
28222 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
28223 The default is @option{-mno-longcalls}. This option should be used in
28224 programs where the call target can potentially be out of range. This
28225 option is implemented in the assembler, not the compiler, so the
28226 assembly code generated by GCC still shows direct call
28227 instructions---look at the disassembled object code to see the actual
28228 instructions. Note that the assembler uses an indirect call for
28229 every cross-file call, not just those that really are out of range.
28232 @node zSeries Options
28233 @subsection zSeries Options
28234 @cindex zSeries options
28236 These are listed under @xref{S/390 and zSeries Options}.
28242 @section Specifying Subprocesses and the Switches to Pass to Them
28245 @command{gcc} is a driver program. It performs its job by invoking a
28246 sequence of other programs to do the work of compiling, assembling and
28247 linking. GCC interprets its command-line parameters and uses these to
28248 deduce which programs it should invoke, and which command-line options
28249 it ought to place on their command lines. This behavior is controlled
28250 by @dfn{spec strings}. In most cases there is one spec string for each
28251 program that GCC can invoke, but a few programs have multiple spec
28252 strings to control their behavior. The spec strings built into GCC can
28253 be overridden by using the @option{-specs=} command-line switch to specify
28256 @dfn{Spec files} are plain-text files that are used to construct spec
28257 strings. They consist of a sequence of directives separated by blank
28258 lines. The type of directive is determined by the first non-whitespace
28259 character on the line, which can be one of the following:
28262 @item %@var{command}
28263 Issues a @var{command} to the spec file processor. The commands that can
28267 @item %include <@var{file}>
28268 @cindex @code{%include}
28269 Search for @var{file} and insert its text at the current point in the
28272 @item %include_noerr <@var{file}>
28273 @cindex @code{%include_noerr}
28274 Just like @samp{%include}, but do not generate an error message if the include
28275 file cannot be found.
28277 @item %rename @var{old_name} @var{new_name}
28278 @cindex @code{%rename}
28279 Rename the spec string @var{old_name} to @var{new_name}.
28283 @item *[@var{spec_name}]:
28284 This tells the compiler to create, override or delete the named spec
28285 string. All lines after this directive up to the next directive or
28286 blank line are considered to be the text for the spec string. If this
28287 results in an empty string then the spec is deleted. (Or, if the
28288 spec did not exist, then nothing happens.) Otherwise, if the spec
28289 does not currently exist a new spec is created. If the spec does
28290 exist then its contents are overridden by the text of this
28291 directive, unless the first character of that text is the @samp{+}
28292 character, in which case the text is appended to the spec.
28294 @item [@var{suffix}]:
28295 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
28296 and up to the next directive or blank line are considered to make up the
28297 spec string for the indicated suffix. When the compiler encounters an
28298 input file with the named suffix, it processes the spec string in
28299 order to work out how to compile that file. For example:
28303 z-compile -input %i
28306 This says that any input file whose name ends in @samp{.ZZ} should be
28307 passed to the program @samp{z-compile}, which should be invoked with the
28308 command-line switch @option{-input} and with the result of performing the
28309 @samp{%i} substitution. (See below.)
28311 As an alternative to providing a spec string, the text following a
28312 suffix directive can be one of the following:
28315 @item @@@var{language}
28316 This says that the suffix is an alias for a known @var{language}. This is
28317 similar to using the @option{-x} command-line switch to GCC to specify a
28318 language explicitly. For example:
28325 Says that .ZZ files are, in fact, C++ source files.
28328 This causes an error messages saying:
28331 @var{name} compiler not installed on this system.
28335 GCC already has an extensive list of suffixes built into it.
28336 This directive adds an entry to the end of the list of suffixes, but
28337 since the list is searched from the end backwards, it is effectively
28338 possible to override earlier entries using this technique.
28342 GCC has the following spec strings built into it. Spec files can
28343 override these strings or create their own. Note that individual
28344 targets can also add their own spec strings to this list.
28347 asm Options to pass to the assembler
28348 asm_final Options to pass to the assembler post-processor
28349 cpp Options to pass to the C preprocessor
28350 cc1 Options to pass to the C compiler
28351 cc1plus Options to pass to the C++ compiler
28352 endfile Object files to include at the end of the link
28353 link Options to pass to the linker
28354 lib Libraries to include on the command line to the linker
28355 libgcc Decides which GCC support library to pass to the linker
28356 linker Sets the name of the linker
28357 predefines Defines to be passed to the C preprocessor
28358 signed_char Defines to pass to CPP to say whether @code{char} is signed
28360 startfile Object files to include at the start of the link
28363 Here is a small example of a spec file:
28366 %rename lib old_lib
28369 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
28372 This example renames the spec called @samp{lib} to @samp{old_lib} and
28373 then overrides the previous definition of @samp{lib} with a new one.
28374 The new definition adds in some extra command-line options before
28375 including the text of the old definition.
28377 @dfn{Spec strings} are a list of command-line options to be passed to their
28378 corresponding program. In addition, the spec strings can contain
28379 @samp{%}-prefixed sequences to substitute variable text or to
28380 conditionally insert text into the command line. Using these constructs
28381 it is possible to generate quite complex command lines.
28383 Here is a table of all defined @samp{%}-sequences for spec
28384 strings. Note that spaces are not generated automatically around the
28385 results of expanding these sequences. Therefore you can concatenate them
28386 together or combine them with constant text in a single argument.
28390 Substitute one @samp{%} into the program name or argument.
28393 Substitute the name of the input file being processed.
28396 Substitute the basename of the input file being processed.
28397 This is the substring up to (and not including) the last period
28398 and not including the directory.
28401 This is the same as @samp{%b}, but include the file suffix (text after
28405 Marks the argument containing or following the @samp{%d} as a
28406 temporary file name, so that that file is deleted if GCC exits
28407 successfully. Unlike @samp{%g}, this contributes no text to the
28410 @item %g@var{suffix}
28411 Substitute a file name that has suffix @var{suffix} and is chosen
28412 once per compilation, and mark the argument in the same way as
28413 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
28414 name is now chosen in a way that is hard to predict even when previously
28415 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
28416 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
28417 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
28418 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
28419 was simply substituted with a file name chosen once per compilation,
28420 without regard to any appended suffix (which was therefore treated
28421 just like ordinary text), making such attacks more likely to succeed.
28423 @item %u@var{suffix}
28424 Like @samp{%g}, but generates a new temporary file name
28425 each time it appears instead of once per compilation.
28427 @item %U@var{suffix}
28428 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
28429 new one if there is no such last file name. In the absence of any
28430 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
28431 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
28432 involves the generation of two distinct file names, one
28433 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
28434 simply substituted with a file name chosen for the previous @samp{%u},
28435 without regard to any appended suffix.
28437 @item %j@var{suffix}
28438 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
28439 writable, and if @option{-save-temps} is not used;
28440 otherwise, substitute the name
28441 of a temporary file, just like @samp{%u}. This temporary file is not
28442 meant for communication between processes, but rather as a junk
28443 disposal mechanism.
28445 @item %|@var{suffix}
28446 @itemx %m@var{suffix}
28447 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
28448 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
28449 all. These are the two most common ways to instruct a program that it
28450 should read from standard input or write to standard output. If you
28451 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
28452 construct: see for example @file{f/lang-specs.h}.
28454 @item %.@var{SUFFIX}
28455 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
28456 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
28457 terminated by the next space or %.
28460 Marks the argument containing or following the @samp{%w} as the
28461 designated output file of this compilation. This puts the argument
28462 into the sequence of arguments that @samp{%o} substitutes.
28465 Substitutes the names of all the output files, with spaces
28466 automatically placed around them. You should write spaces
28467 around the @samp{%o} as well or the results are undefined.
28468 @samp{%o} is for use in the specs for running the linker.
28469 Input files whose names have no recognized suffix are not compiled
28470 at all, but they are included among the output files, so they are
28474 Substitutes the suffix for object files. Note that this is
28475 handled specially when it immediately follows @samp{%g, %u, or %U},
28476 because of the need for those to form complete file names. The
28477 handling is such that @samp{%O} is treated exactly as if it had already
28478 been substituted, except that @samp{%g, %u, and %U} do not currently
28479 support additional @var{suffix} characters following @samp{%O} as they do
28480 following, for example, @samp{.o}.
28483 Substitutes the standard macro predefinitions for the
28484 current target machine. Use this when running @command{cpp}.
28487 Like @samp{%p}, but puts @samp{__} before and after the name of each
28488 predefined macro, except for macros that start with @samp{__} or with
28489 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
28493 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
28494 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}),
28495 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
28496 and @option{-imultilib} as necessary.
28499 Current argument is the name of a library or startup file of some sort.
28500 Search for that file in a standard list of directories and substitute
28501 the full name found. The current working directory is included in the
28502 list of directories scanned.
28505 Current argument is the name of a linker script. Search for that file
28506 in the current list of directories to scan for libraries. If the file
28507 is located insert a @option{--script} option into the command line
28508 followed by the full path name found. If the file is not found then
28509 generate an error message. Note: the current working directory is not
28513 Print @var{str} as an error message. @var{str} is terminated by a newline.
28514 Use this when inconsistent options are detected.
28516 @item %(@var{name})
28517 Substitute the contents of spec string @var{name} at this point.
28519 @item %x@{@var{option}@}
28520 Accumulate an option for @samp{%X}.
28523 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
28527 Output the accumulated assembler options specified by @option{-Wa}.
28530 Output the accumulated preprocessor options specified by @option{-Wp}.
28533 Process the @code{asm} spec. This is used to compute the
28534 switches to be passed to the assembler.
28537 Process the @code{asm_final} spec. This is a spec string for
28538 passing switches to an assembler post-processor, if such a program is
28542 Process the @code{link} spec. This is the spec for computing the
28543 command line passed to the linker. Typically it makes use of the
28544 @samp{%L %G %S %D and %E} sequences.
28547 Dump out a @option{-L} option for each directory that GCC believes might
28548 contain startup files. If the target supports multilibs then the
28549 current multilib directory is prepended to each of these paths.
28552 Process the @code{lib} spec. This is a spec string for deciding which
28553 libraries are included on the command line to the linker.
28556 Process the @code{libgcc} spec. This is a spec string for deciding
28557 which GCC support library is included on the command line to the linker.
28560 Process the @code{startfile} spec. This is a spec for deciding which
28561 object files are the first ones passed to the linker. Typically
28562 this might be a file named @file{crt0.o}.
28565 Process the @code{endfile} spec. This is a spec string that specifies
28566 the last object files that are passed to the linker.
28569 Process the @code{cpp} spec. This is used to construct the arguments
28570 to be passed to the C preprocessor.
28573 Process the @code{cc1} spec. This is used to construct the options to be
28574 passed to the actual C compiler (@command{cc1}).
28577 Process the @code{cc1plus} spec. This is used to construct the options to be
28578 passed to the actual C++ compiler (@command{cc1plus}).
28581 Substitute the variable part of a matched option. See below.
28582 Note that each comma in the substituted string is replaced by
28586 Remove all occurrences of @code{-S} from the command line. Note---this
28587 command is position dependent. @samp{%} commands in the spec string
28588 before this one see @code{-S}, @samp{%} commands in the spec string
28589 after this one do not.
28591 @item %:@var{function}(@var{args})
28592 Call the named function @var{function}, passing it @var{args}.
28593 @var{args} is first processed as a nested spec string, then split
28594 into an argument vector in the usual fashion. The function returns
28595 a string which is processed as if it had appeared literally as part
28596 of the current spec.
28598 The following built-in spec functions are provided:
28601 @item @code{getenv}
28602 The @code{getenv} spec function takes two arguments: an environment
28603 variable name and a string. If the environment variable is not
28604 defined, a fatal error is issued. Otherwise, the return value is the
28605 value of the environment variable concatenated with the string. For
28606 example, if @env{TOPDIR} is defined as @file{/path/to/top}, then:
28609 %:getenv(TOPDIR /include)
28612 expands to @file{/path/to/top/include}.
28614 @item @code{if-exists}
28615 The @code{if-exists} spec function takes one argument, an absolute
28616 pathname to a file. If the file exists, @code{if-exists} returns the
28617 pathname. Here is a small example of its usage:
28621 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
28624 @item @code{if-exists-else}
28625 The @code{if-exists-else} spec function is similar to the @code{if-exists}
28626 spec function, except that it takes two arguments. The first argument is
28627 an absolute pathname to a file. If the file exists, @code{if-exists-else}
28628 returns the pathname. If it does not exist, it returns the second argument.
28629 This way, @code{if-exists-else} can be used to select one file or another,
28630 based on the existence of the first. Here is a small example of its usage:
28634 crt0%O%s %:if-exists(crti%O%s) \
28635 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
28638 @item @code{replace-outfile}
28639 The @code{replace-outfile} spec function takes two arguments. It looks for the
28640 first argument in the outfiles array and replaces it with the second argument. Here
28641 is a small example of its usage:
28644 %@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
28647 @item @code{remove-outfile}
28648 The @code{remove-outfile} spec function takes one argument. It looks for the
28649 first argument in the outfiles array and removes it. Here is a small example
28653 %:remove-outfile(-lm)
28656 @item @code{pass-through-libs}
28657 The @code{pass-through-libs} spec function takes any number of arguments. It
28658 finds any @option{-l} options and any non-options ending in @file{.a} (which it
28659 assumes are the names of linker input library archive files) and returns a
28660 result containing all the found arguments each prepended by
28661 @option{-plugin-opt=-pass-through=} and joined by spaces. This list is
28662 intended to be passed to the LTO linker plugin.
28665 %:pass-through-libs(%G %L %G)
28668 @item @code{print-asm-header}
28669 The @code{print-asm-header} function takes no arguments and simply
28670 prints a banner like:
28676 Use "-Wa,OPTION" to pass "OPTION" to the assembler.
28679 It is used to separate compiler options from assembler options
28680 in the @option{--target-help} output.
28684 Substitutes the @code{-S} switch, if that switch is given to GCC@.
28685 If that switch is not specified, this substitutes nothing. Note that
28686 the leading dash is omitted when specifying this option, and it is
28687 automatically inserted if the substitution is performed. Thus the spec
28688 string @samp{%@{foo@}} matches the command-line option @option{-foo}
28689 and outputs the command-line option @option{-foo}.
28692 Like %@{@code{S}@} but mark last argument supplied within as a file to be
28693 deleted on failure.
28696 Substitutes all the switches specified to GCC whose names start
28697 with @code{-S}, but which also take an argument. This is used for
28698 switches like @option{-o}, @option{-D}, @option{-I}, etc.
28699 GCC considers @option{-o foo} as being
28700 one switch whose name starts with @samp{o}. %@{o*@} substitutes this
28701 text, including the space. Thus two arguments are generated.
28704 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
28705 (the order of @code{S} and @code{T} in the spec is not significant).
28706 There can be any number of ampersand-separated variables; for each the
28707 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
28710 Substitutes @code{X}, if the @option{-S} switch is given to GCC@.
28713 Substitutes @code{X}, if the @option{-S} switch is @emph{not} given to GCC@.
28716 Substitutes @code{X} if one or more switches whose names start with
28717 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
28718 once, no matter how many such switches appeared. However, if @code{%*}
28719 appears somewhere in @code{X}, then @code{X} is substituted once
28720 for each matching switch, with the @code{%*} replaced by the part of
28721 that switch matching the @code{*}.
28723 If @code{%*} appears as the last part of a spec sequence then a space
28724 is added after the end of the last substitution. If there is more
28725 text in the sequence, however, then a space is not generated. This
28726 allows the @code{%*} substitution to be used as part of a larger
28727 string. For example, a spec string like this:
28730 %@{mcu=*:--script=%*/memory.ld@}
28734 when matching an option like @option{-mcu=newchip} produces:
28737 --script=newchip/memory.ld
28741 Substitutes @code{X}, if processing a file with suffix @code{S}.
28744 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
28747 Substitutes @code{X}, if processing a file for language @code{S}.
28750 Substitutes @code{X}, if not processing a file for language @code{S}.
28753 Substitutes @code{X} if either @code{-S} or @code{-P} is given to
28754 GCC@. This may be combined with @samp{!}, @samp{.}, @samp{,}, and
28755 @code{*} sequences as well, although they have a stronger binding than
28756 the @samp{|}. If @code{%*} appears in @code{X}, all of the
28757 alternatives must be starred, and only the first matching alternative
28760 For example, a spec string like this:
28763 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
28767 outputs the following command-line options from the following input
28768 command-line options:
28773 -d fred.c -foo -baz -boggle
28774 -d jim.d -bar -baz -boggle
28777 @item %@{S:X; T:Y; :D@}
28779 If @code{S} is given to GCC, substitutes @code{X}; else if @code{T} is
28780 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
28781 be as many clauses as you need. This may be combined with @code{.},
28782 @code{,}, @code{!}, @code{|}, and @code{*} as needed.
28787 The switch matching text @code{S} in a @samp{%@{S@}}, @samp{%@{S:X@}}
28788 or similar construct can use a backslash to ignore the special meaning
28789 of the character following it, thus allowing literal matching of a
28790 character that is otherwise specially treated. For example,
28791 @samp{%@{std=iso9899\:1999:X@}} substitutes @code{X} if the
28792 @option{-std=iso9899:1999} option is given.
28794 The conditional text @code{X} in a @samp{%@{S:X@}} or similar
28795 construct may contain other nested @samp{%} constructs or spaces, or
28796 even newlines. They are processed as usual, as described above.
28797 Trailing white space in @code{X} is ignored. White space may also
28798 appear anywhere on the left side of the colon in these constructs,
28799 except between @code{.} or @code{*} and the corresponding word.
28801 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
28802 handled specifically in these constructs. If another value of
28803 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
28804 @option{-W} switch is found later in the command line, the earlier
28805 switch value is ignored, except with @{@code{S}*@} where @code{S} is
28806 just one letter, which passes all matching options.
28808 The character @samp{|} at the beginning of the predicate text is used to
28809 indicate that a command should be piped to the following command, but
28810 only if @option{-pipe} is specified.
28812 It is built into GCC which switches take arguments and which do not.
28813 (You might think it would be useful to generalize this to allow each
28814 compiler's spec to say which switches take arguments. But this cannot
28815 be done in a consistent fashion. GCC cannot even decide which input
28816 files have been specified without knowing which switches take arguments,
28817 and it must know which input files to compile in order to tell which
28820 GCC also knows implicitly that arguments starting in @option{-l} are to be
28821 treated as compiler output files, and passed to the linker in their
28822 proper position among the other output files.
28824 @node Environment Variables
28825 @section Environment Variables Affecting GCC
28826 @cindex environment variables
28828 @c man begin ENVIRONMENT
28829 This section describes several environment variables that affect how GCC
28830 operates. Some of them work by specifying directories or prefixes to use
28831 when searching for various kinds of files. Some are used to specify other
28832 aspects of the compilation environment.
28834 Note that you can also specify places to search using options such as
28835 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
28836 take precedence over places specified using environment variables, which
28837 in turn take precedence over those specified by the configuration of GCC@.
28838 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
28839 GNU Compiler Collection (GCC) Internals}.
28844 @c @itemx LC_COLLATE
28846 @c @itemx LC_MONETARY
28847 @c @itemx LC_NUMERIC
28852 @c @findex LC_COLLATE
28853 @findex LC_MESSAGES
28854 @c @findex LC_MONETARY
28855 @c @findex LC_NUMERIC
28859 These environment variables control the way that GCC uses
28860 localization information which allows GCC to work with different
28861 national conventions. GCC inspects the locale categories
28862 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
28863 so. These locale categories can be set to any value supported by your
28864 installation. A typical value is @samp{en_GB.UTF-8} for English in the United
28865 Kingdom encoded in UTF-8.
28867 The @env{LC_CTYPE} environment variable specifies character
28868 classification. GCC uses it to determine the character boundaries in
28869 a string; this is needed for some multibyte encodings that contain quote
28870 and escape characters that are otherwise interpreted as a string
28873 The @env{LC_MESSAGES} environment variable specifies the language to
28874 use in diagnostic messages.
28876 If the @env{LC_ALL} environment variable is set, it overrides the value
28877 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
28878 and @env{LC_MESSAGES} default to the value of the @env{LANG}
28879 environment variable. If none of these variables are set, GCC
28880 defaults to traditional C English behavior.
28884 If @env{TMPDIR} is set, it specifies the directory to use for temporary
28885 files. GCC uses temporary files to hold the output of one stage of
28886 compilation which is to be used as input to the next stage: for example,
28887 the output of the preprocessor, which is the input to the compiler
28890 @item GCC_COMPARE_DEBUG
28891 @findex GCC_COMPARE_DEBUG
28892 Setting @env{GCC_COMPARE_DEBUG} is nearly equivalent to passing
28893 @option{-fcompare-debug} to the compiler driver. See the documentation
28894 of this option for more details.
28896 @item GCC_EXEC_PREFIX
28897 @findex GCC_EXEC_PREFIX
28898 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
28899 names of the subprograms executed by the compiler. No slash is added
28900 when this prefix is combined with the name of a subprogram, but you can
28901 specify a prefix that ends with a slash if you wish.
28903 If @env{GCC_EXEC_PREFIX} is not set, GCC attempts to figure out
28904 an appropriate prefix to use based on the pathname it is invoked with.
28906 If GCC cannot find the subprogram using the specified prefix, it
28907 tries looking in the usual places for the subprogram.
28909 The default value of @env{GCC_EXEC_PREFIX} is
28910 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the prefix to
28911 the installed compiler. In many cases @var{prefix} is the value
28912 of @code{prefix} when you ran the @file{configure} script.
28914 Other prefixes specified with @option{-B} take precedence over this prefix.
28916 This prefix is also used for finding files such as @file{crt0.o} that are
28919 In addition, the prefix is used in an unusual way in finding the
28920 directories to search for header files. For each of the standard
28921 directories whose name normally begins with @samp{/usr/local/lib/gcc}
28922 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
28923 replacing that beginning with the specified prefix to produce an
28924 alternate directory name. Thus, with @option{-Bfoo/}, GCC searches
28925 @file{foo/bar} just before it searches the standard directory
28926 @file{/usr/local/lib/bar}.
28927 If a standard directory begins with the configured
28928 @var{prefix} then the value of @var{prefix} is replaced by
28929 @env{GCC_EXEC_PREFIX} when looking for header files.
28931 @item COMPILER_PATH
28932 @findex COMPILER_PATH
28933 The value of @env{COMPILER_PATH} is a colon-separated list of
28934 directories, much like @env{PATH}. GCC tries the directories thus
28935 specified when searching for subprograms, if it cannot find the
28936 subprograms using @env{GCC_EXEC_PREFIX}.
28939 @findex LIBRARY_PATH
28940 The value of @env{LIBRARY_PATH} is a colon-separated list of
28941 directories, much like @env{PATH}. When configured as a native compiler,
28942 GCC tries the directories thus specified when searching for special
28943 linker files, if it cannot find them using @env{GCC_EXEC_PREFIX}. Linking
28944 using GCC also uses these directories when searching for ordinary
28945 libraries for the @option{-l} option (but directories specified with
28946 @option{-L} come first).
28950 @cindex locale definition
28951 This variable is used to pass locale information to the compiler. One way in
28952 which this information is used is to determine the character set to be used
28953 when character literals, string literals and comments are parsed in C and C++.
28954 When the compiler is configured to allow multibyte characters,
28955 the following values for @env{LANG} are recognized:
28959 Recognize JIS characters.
28961 Recognize SJIS characters.
28963 Recognize EUCJP characters.
28966 If @env{LANG} is not defined, or if it has some other value, then the
28967 compiler uses @code{mblen} and @code{mbtowc} as defined by the default locale to
28968 recognize and translate multibyte characters.
28972 Some additional environment variables affect the behavior of the
28975 @include cppenv.texi
28979 @node Precompiled Headers
28980 @section Using Precompiled Headers
28981 @cindex precompiled headers
28982 @cindex speed of compilation
28984 Often large projects have many header files that are included in every
28985 source file. The time the compiler takes to process these header files
28986 over and over again can account for nearly all of the time required to
28987 build the project. To make builds faster, GCC allows you to
28988 @dfn{precompile} a header file.
28990 To create a precompiled header file, simply compile it as you would any
28991 other file, if necessary using the @option{-x} option to make the driver
28992 treat it as a C or C++ header file. You may want to use a
28993 tool like @command{make} to keep the precompiled header up-to-date when
28994 the headers it contains change.
28996 A precompiled header file is searched for when @code{#include} is
28997 seen in the compilation. As it searches for the included file
28998 (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
28999 compiler looks for a precompiled header in each directory just before it
29000 looks for the include file in that directory. The name searched for is
29001 the name specified in the @code{#include} with @samp{.gch} appended. If
29002 the precompiled header file cannot be used, it is ignored.
29004 For instance, if you have @code{#include "all.h"}, and you have
29005 @file{all.h.gch} in the same directory as @file{all.h}, then the
29006 precompiled header file is used if possible, and the original
29007 header is used otherwise.
29009 Alternatively, you might decide to put the precompiled header file in a
29010 directory and use @option{-I} to ensure that directory is searched
29011 before (or instead of) the directory containing the original header.
29012 Then, if you want to check that the precompiled header file is always
29013 used, you can put a file of the same name as the original header in this
29014 directory containing an @code{#error} command.
29016 This also works with @option{-include}. So yet another way to use
29017 precompiled headers, good for projects not designed with precompiled
29018 header files in mind, is to simply take most of the header files used by
29019 a project, include them from another header file, precompile that header
29020 file, and @option{-include} the precompiled header. If the header files
29021 have guards against multiple inclusion, they are skipped because
29022 they've already been included (in the precompiled header).
29024 If you need to precompile the same header file for different
29025 languages, targets, or compiler options, you can instead make a
29026 @emph{directory} named like @file{all.h.gch}, and put each precompiled
29027 header in the directory, perhaps using @option{-o}. It doesn't matter
29028 what you call the files in the directory; every precompiled header in
29029 the directory is considered. The first precompiled header
29030 encountered in the directory that is valid for this compilation is
29031 used; they're searched in no particular order.
29033 There are many other possibilities, limited only by your imagination,
29034 good sense, and the constraints of your build system.
29036 A precompiled header file can be used only when these conditions apply:
29040 Only one precompiled header can be used in a particular compilation.
29043 A precompiled header cannot be used once the first C token is seen. You
29044 can have preprocessor directives before a precompiled header; you cannot
29045 include a precompiled header from inside another header.
29048 The precompiled header file must be produced for the same language as
29049 the current compilation. You cannot use a C precompiled header for a C++
29053 The precompiled header file must have been produced by the same compiler
29054 binary as the current compilation is using.
29057 Any macros defined before the precompiled header is included must
29058 either be defined in the same way as when the precompiled header was
29059 generated, or must not affect the precompiled header, which usually
29060 means that they don't appear in the precompiled header at all.
29062 The @option{-D} option is one way to define a macro before a
29063 precompiled header is included; using a @code{#define} can also do it.
29064 There are also some options that define macros implicitly, like
29065 @option{-O} and @option{-Wdeprecated}; the same rule applies to macros
29068 @item If debugging information is output when using the precompiled
29069 header, using @option{-g} or similar, the same kind of debugging information
29070 must have been output when building the precompiled header. However,
29071 a precompiled header built using @option{-g} can be used in a compilation
29072 when no debugging information is being output.
29074 @item The same @option{-m} options must generally be used when building
29075 and using the precompiled header. @xref{Submodel Options},
29076 for any cases where this rule is relaxed.
29078 @item Each of the following options must be the same when building and using
29079 the precompiled header:
29081 @gccoptlist{-fexceptions}
29084 Some other command-line options starting with @option{-f},
29085 @option{-p}, or @option{-O} must be defined in the same way as when
29086 the precompiled header was generated. At present, it's not clear
29087 which options are safe to change and which are not; the safest choice
29088 is to use exactly the same options when generating and using the
29089 precompiled header. The following are known to be safe:
29091 @gccoptlist{-fmessage-length= -fpreprocessed -fsched-interblock @gol
29092 -fsched-spec -fsched-spec-load -fsched-spec-load-dangerous @gol
29093 -fsched-verbose=@var{number} -fschedule-insns -fvisibility= @gol
29098 For all of these except the last, the compiler automatically
29099 ignores the precompiled header if the conditions aren't met. If you
29100 find an option combination that doesn't work and doesn't cause the
29101 precompiled header to be ignored, please consider filing a bug report,
29104 If you do use differing options when generating and using the
29105 precompiled header, the actual behavior is a mixture of the
29106 behavior for the options. For instance, if you use @option{-g} to
29107 generate the precompiled header but not when using it, you may or may
29108 not get debugging information for routines in the precompiled header.