1 @c Copyright (C) 1988-2015 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{} 1988-2015 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), adb(1), dbx(1), sdb(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.
76 Other options are passed on to one stage of processing. Some options
77 control the preprocessor and others the compiler itself. Yet other
78 options control the assembler and linker; most of these are not
79 documented here, since you rarely need to use any of them.
81 @cindex C compilation options
82 Most of the command-line options that you can use with GCC are useful
83 for C programs; when an option is only useful with another language
84 (usually C++), the explanation says so explicitly. If the description
85 for a particular option does not mention a source language, you can use
86 that option with all supported languages.
88 @cindex C++ compilation options
89 @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
90 options for compiling C++ programs.
92 @cindex grouping options
93 @cindex options, grouping
94 The @command{gcc} program accepts options and file names as operands. Many
95 options have multi-letter names; therefore multiple single-letter options
96 may @emph{not} be grouped: @option{-dv} is very different from @w{@samp{-d
99 @cindex order of options
100 @cindex options, order
101 You can mix options and other arguments. For the most part, the order
102 you use doesn't matter. Order does matter when you use several
103 options of the same kind; for example, if you specify @option{-L} more
104 than once, the directories are searched in the order specified. Also,
105 the placement of the @option{-l} option is significant.
107 Many options have long names starting with @samp{-f} or with
108 @samp{-W}---for example,
109 @option{-fmove-loop-invariants}, @option{-Wformat} and so on. Most of
110 these have both positive and negative forms; the negative form of
111 @option{-ffoo} is @option{-fno-foo}. This manual documents
112 only one of these two forms, whichever one is not the default.
116 @xref{Option Index}, for an index to GCC's options.
119 * Option Summary:: Brief list of all options, without explanations.
120 * Overall Options:: Controlling the kind of output:
121 an executable, object files, assembler files,
122 or preprocessed source.
123 * Invoking G++:: Compiling C++ programs.
124 * C Dialect Options:: Controlling the variant of C language compiled.
125 * C++ Dialect Options:: Variations on C++.
126 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
128 * Language Independent Options:: Controlling how diagnostics should be
130 * Warning Options:: How picky should the compiler be?
131 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
132 * Optimize Options:: How much optimization?
133 * Preprocessor Options:: Controlling header files and macro definitions.
134 Also, getting dependency information for Make.
135 * Assembler Options:: Passing options to the assembler.
136 * Link Options:: Specifying libraries and so on.
137 * Directory Options:: Where to find header files and libraries.
138 Where to find the compiler executable files.
139 * Spec Files:: How to pass switches to sub-processes.
140 * Target Options:: Running a cross-compiler, or an old version of GCC.
141 * Submodel Options:: Specifying minor hardware or convention variations,
142 such as 68010 vs 68020.
143 * Code Gen Options:: Specifying conventions for function calls, data layout
145 * Environment Variables:: Env vars that affect GCC.
146 * Precompiled Headers:: Compiling a header once, and using it many times.
152 @section Option Summary
154 Here is a summary of all the options, grouped by type. Explanations are
155 in the following sections.
158 @item Overall Options
159 @xref{Overall Options,,Options Controlling the Kind of Output}.
160 @gccoptlist{-c -S -E -o @var{file} -no-canonical-prefixes @gol
161 -pipe -pass-exit-codes @gol
162 -x @var{language} -v -### --help@r{[}=@var{class}@r{[},@dots{}@r{]]} --target-help @gol
163 --version -wrapper @@@var{file} -fplugin=@var{file} -fplugin-arg-@var{name}=@var{arg} @gol
164 -fdump-ada-spec@r{[}-slim@r{]} -fada-spec-parent=@var{unit} -fdump-go-spec=@var{file}}
166 @item C Language Options
167 @xref{C Dialect Options,,Options Controlling C Dialect}.
168 @gccoptlist{-ansi -std=@var{standard} -fgnu89-inline @gol
169 -aux-info @var{filename} -fallow-parameterless-variadic-functions @gol
170 -fno-asm -fno-builtin -fno-builtin-@var{function} @gol
171 -fhosted -ffreestanding -fopenacc -fopenmp -fopenmp-simd @gol
172 -fms-extensions -fplan9-extensions -trigraphs -traditional -traditional-cpp @gol
173 -fallow-single-precision -fcond-mismatch -flax-vector-conversions @gol
174 -fsigned-bitfields -fsigned-char @gol
175 -funsigned-bitfields -funsigned-char}
177 @item C++ Language Options
178 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
179 @gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol
180 -fconstexpr-depth=@var{n} -ffriend-injection @gol
181 -fno-elide-constructors @gol
182 -fno-enforce-eh-specs @gol
183 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
184 -fno-implicit-templates @gol
185 -fno-implicit-inline-templates @gol
186 -fno-implement-inlines -fms-extensions @gol
187 -fno-nonansi-builtins -fnothrow-opt -fno-operator-names @gol
188 -fno-optional-diags -fpermissive @gol
189 -fno-pretty-templates @gol
190 -frepo -fno-rtti -fsized-deallocation @gol
191 -fstats -ftemplate-backtrace-limit=@var{n} @gol
192 -ftemplate-depth=@var{n} @gol
193 -fno-threadsafe-statics -fuse-cxa-atexit @gol
194 -fno-weak -nostdinc++ @gol
195 -fvisibility-inlines-hidden @gol
196 -fvtable-verify=@r{[}std@r{|}preinit@r{|}none@r{]} @gol
197 -fvtv-counts -fvtv-debug @gol
198 -fvisibility-ms-compat @gol
199 -fext-numeric-literals @gol
200 -Wabi=@var{n} -Wabi-tag -Wconversion-null -Wctor-dtor-privacy @gol
201 -Wdelete-non-virtual-dtor -Wliteral-suffix -Wnarrowing @gol
202 -Wnoexcept -Wnon-virtual-dtor -Wreorder @gol
203 -Weffc++ -Wstrict-null-sentinel @gol
204 -Wno-non-template-friend -Wold-style-cast @gol
205 -Woverloaded-virtual -Wno-pmf-conversions @gol
208 @item Objective-C and Objective-C++ Language Options
209 @xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling
210 Objective-C and Objective-C++ Dialects}.
211 @gccoptlist{-fconstant-string-class=@var{class-name} @gol
212 -fgnu-runtime -fnext-runtime @gol
213 -fno-nil-receivers @gol
214 -fobjc-abi-version=@var{n} @gol
215 -fobjc-call-cxx-cdtors @gol
216 -fobjc-direct-dispatch @gol
217 -fobjc-exceptions @gol
220 -fobjc-std=objc1 @gol
221 -fno-local-ivars @gol
222 -fivar-visibility=@r{[}public@r{|}protected@r{|}private@r{|}package@r{]} @gol
223 -freplace-objc-classes @gol
226 -Wassign-intercept @gol
227 -Wno-protocol -Wselector @gol
228 -Wstrict-selector-match @gol
229 -Wundeclared-selector}
231 @item Language Independent Options
232 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
233 @gccoptlist{-fmessage-length=@var{n} @gol
234 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]} @gol
235 -fdiagnostics-color=@r{[}auto@r{|}never@r{|}always@r{]} @gol
236 -fno-diagnostics-show-option -fno-diagnostics-show-caret}
238 @item Warning Options
239 @xref{Warning Options,,Options to Request or Suppress Warnings}.
240 @gccoptlist{-fsyntax-only -fmax-errors=@var{n} -Wpedantic @gol
241 -pedantic-errors @gol
242 -w -Wextra -Wall -Waddress -Waggregate-return @gol
243 -Waggressive-loop-optimizations -Warray-bounds -Warray-bounds=@var{n} @gol
245 -Wno-attributes -Wno-builtin-macro-redefined @gol
246 -Wc90-c99-compat -Wc99-c11-compat @gol
247 -Wc++-compat -Wc++11-compat -Wc++14-compat -Wcast-align -Wcast-qual @gol
248 -Wchar-subscripts -Wclobbered -Wcomment -Wconditionally-supported @gol
249 -Wconversion -Wcoverage-mismatch -Wdate-time -Wdelete-incomplete -Wno-cpp @gol
250 -Wno-deprecated -Wno-deprecated-declarations -Wno-designated-init @gol
251 -Wdisabled-optimization @gol
252 -Wno-discarded-qualifiers -Wno-discarded-array-qualifiers @gol
253 -Wno-div-by-zero -Wdouble-promotion -Wempty-body -Wenum-compare @gol
254 -Wno-endif-labels -Werror -Werror=* @gol
255 -Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 @gol
256 -Wno-format-contains-nul -Wno-format-extra-args -Wformat-nonliteral @gol
257 -Wformat-security -Wformat-signedness -Wformat-y2k @gol
258 -Wframe-larger-than=@var{len} -Wno-free-nonheap-object -Wjump-misses-init @gol
259 -Wignored-qualifiers -Wincompatible-pointer-types @gol
260 -Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol
261 -Winit-self -Winline -Wno-int-conversion @gol
262 -Wno-int-to-pointer-cast -Wno-invalid-offsetof @gol
263 -Winvalid-pch -Wlarger-than=@var{len} -Wunsafe-loop-optimizations @gol
264 -Wlogical-op -Wlogical-not-parentheses -Wlong-long @gol
265 -Wmain -Wmaybe-uninitialized -Wmemset-transposed-args @gol
266 -Wmisleading-indentation -Wmissing-braces @gol
267 -Wmissing-field-initializers -Wmissing-include-dirs @gol
268 -Wno-multichar -Wnonnull -Wnormalized=@r{[}none@r{|}id@r{|}nfc@r{|}nfkc@r{]} @gol
269 -Wodr -Wno-overflow -Wopenmp-simd @gol
270 -Woverride-init-side-effects @gol
271 -Woverlength-strings -Wpacked -Wpacked-bitfield-compat -Wpadded @gol
272 -Wparentheses -Wpedantic-ms-format -Wno-pedantic-ms-format @gol
273 -Wpointer-arith -Wno-pointer-to-int-cast @gol
274 -Wredundant-decls -Wno-return-local-addr @gol
275 -Wreturn-type -Wsequence-point -Wshadow -Wno-shadow-ivar @gol
276 -Wshift-count-negative -Wshift-count-overflow -Wshift-negative-value @gol
277 -Wsign-compare -Wsign-conversion -Wfloat-conversion @gol
278 -Wsizeof-pointer-memaccess -Wsizeof-array-argument @gol
279 -Wstack-protector -Wstack-usage=@var{len} -Wstrict-aliasing @gol
280 -Wstrict-aliasing=n @gol -Wstrict-overflow -Wstrict-overflow=@var{n} @gol
281 -Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{]} @gol
282 -Wsuggest-final-types @gol -Wsuggest-final-methods -Wsuggest-override @gol
283 -Wmissing-format-attribute @gol
284 -Wswitch -Wswitch-default -Wswitch-enum -Wswitch-bool -Wsync-nand @gol
285 -Wsystem-headers -Wtrampolines -Wtrigraphs -Wtype-limits -Wundef @gol
286 -Wuninitialized -Wunknown-pragmas -Wno-pragmas @gol
287 -Wunsuffixed-float-constants -Wunused -Wunused-function @gol
288 -Wunused-label -Wunused-local-typedefs -Wunused-parameter @gol
289 -Wno-unused-result -Wunused-value @gol -Wunused-variable @gol
290 -Wunused-but-set-parameter -Wunused-but-set-variable @gol
291 -Wuseless-cast -Wvariadic-macros -Wvector-operation-performance @gol
292 -Wvla -Wvolatile-register-var -Wwrite-strings @gol
293 -Wzero-as-null-pointer-constant}
295 @item C and Objective-C-only Warning Options
296 @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
297 -Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs @gol
298 -Wold-style-declaration -Wold-style-definition @gol
299 -Wstrict-prototypes -Wtraditional -Wtraditional-conversion @gol
300 -Wdeclaration-after-statement -Wpointer-sign}
302 @item Debugging Options
303 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
304 @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
305 -fsanitize=@var{style} -fsanitize-recover -fsanitize-recover=@var{style} @gol
306 -fasan-shadow-offset=@var{number} -fsanitize-sections=@var{s1},@var{s2},... @gol
307 -fsanitize-undefined-trap-on-error @gol
308 -fcheck-pointer-bounds -fchkp-check-incomplete-type @gol
309 -fchkp-first-field-has-own-bounds -fchkp-narrow-bounds @gol
310 -fchkp-narrow-to-innermost-array -fchkp-optimize @gol
311 -fchkp-use-fast-string-functions -fchkp-use-nochk-string-functions @gol
312 -fchkp-use-static-bounds -fchkp-use-static-const-bounds @gol
313 -fchkp-treat-zero-dynamic-size-as-infinite -fchkp-check-read @gol
314 -fchkp-check-read -fchkp-check-write -fchkp-store-bounds @gol
315 -fchkp-instrument-calls -fchkp-instrument-marked-only @gol
316 -fchkp-use-wrappers @gol
317 -fdbg-cnt-list -fdbg-cnt=@var{counter-value-list} @gol
318 -fdisable-ipa-@var{pass_name} @gol
319 -fdisable-rtl-@var{pass_name} @gol
320 -fdisable-rtl-@var{pass-name}=@var{range-list} @gol
321 -fdisable-tree-@var{pass_name} @gol
322 -fdisable-tree-@var{pass-name}=@var{range-list} @gol
323 -fdump-noaddr -fdump-unnumbered -fdump-unnumbered-links @gol
324 -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
325 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
326 -fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline @gol
328 -fdump-statistics @gol
330 -fdump-tree-original@r{[}-@var{n}@r{]} @gol
331 -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
332 -fdump-tree-cfg -fdump-tree-alias @gol
334 -fdump-tree-ssa@r{[}-@var{n}@r{]} -fdump-tree-pre@r{[}-@var{n}@r{]} @gol
335 -fdump-tree-ccp@r{[}-@var{n}@r{]} -fdump-tree-dce@r{[}-@var{n}@r{]} @gol
336 -fdump-tree-gimple@r{[}-raw@r{]} @gol
337 -fdump-tree-dom@r{[}-@var{n}@r{]} @gol
338 -fdump-tree-dse@r{[}-@var{n}@r{]} @gol
339 -fdump-tree-phiprop@r{[}-@var{n}@r{]} @gol
340 -fdump-tree-phiopt@r{[}-@var{n}@r{]} @gol
341 -fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
342 -fdump-tree-copyrename@r{[}-@var{n}@r{]} @gol
343 -fdump-tree-nrv -fdump-tree-vect @gol
344 -fdump-tree-sink @gol
345 -fdump-tree-sra@r{[}-@var{n}@r{]} @gol
346 -fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
347 -fdump-tree-fre@r{[}-@var{n}@r{]} @gol
348 -fdump-tree-vtable-verify @gol
349 -fdump-tree-vrp@r{[}-@var{n}@r{]} @gol
350 -fdump-tree-storeccp@r{[}-@var{n}@r{]} @gol
351 -fdump-final-insns=@var{file} @gol
352 -fcompare-debug@r{[}=@var{opts}@r{]} -fcompare-debug-second @gol
353 -feliminate-dwarf2-dups -fno-eliminate-unused-debug-types @gol
354 -feliminate-unused-debug-symbols -femit-class-debug-always @gol
355 -fenable-@var{kind}-@var{pass} @gol
356 -fenable-@var{kind}-@var{pass}=@var{range-list} @gol
357 -fdebug-types-section -fmem-report-wpa @gol
358 -fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report -fprofile-arcs @gol
360 -fopt-info-@var{options}@r{[}=@var{file}@r{]} @gol
361 -frandom-seed=@var{number} -fsched-verbose=@var{n} @gol
362 -fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose @gol
363 -fstack-usage -ftest-coverage -ftime-report -fvar-tracking @gol
364 -fvar-tracking-assignments -fvar-tracking-assignments-toggle @gol
365 -g -g@var{level} -gtoggle -gcoff -gdwarf-@var{version} @gol
366 -ggdb -grecord-gcc-switches -gno-record-gcc-switches @gol
367 -gstabs -gstabs+ -gstrict-dwarf -gno-strict-dwarf @gol
368 -gvms -gxcoff -gxcoff+ -gz@r{[}=@var{type}@r{]} @gol
369 -fno-merge-debug-strings -fno-dwarf2-cfi-asm @gol
370 -fdebug-prefix-map=@var{old}=@var{new} @gol
371 -femit-struct-debug-baseonly -femit-struct-debug-reduced @gol
372 -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} @gol
373 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
374 -print-multi-directory -print-multi-lib -print-multi-os-directory @gol
375 -print-prog-name=@var{program} -print-search-dirs -Q @gol
376 -print-sysroot -print-sysroot-headers-suffix @gol
377 -save-temps -save-temps=cwd -save-temps=obj -time@r{[}=@var{file}@r{]}}
379 @item Optimization Options
380 @xref{Optimize Options,,Options that Control Optimization}.
381 @gccoptlist{-faggressive-loop-optimizations -falign-functions[=@var{n}] @gol
382 -falign-jumps[=@var{n}] @gol
383 -falign-labels[=@var{n}] -falign-loops[=@var{n}] @gol
384 -fassociative-math -fauto-profile -fauto-profile[=@var{path}] @gol
385 -fauto-inc-dec -fbranch-probabilities @gol
386 -fbranch-target-load-optimize -fbranch-target-load-optimize2 @gol
387 -fbtr-bb-exclusive -fcaller-saves @gol
388 -fcheck-data-deps -fcombine-stack-adjustments -fconserve-stack @gol
389 -fcompare-elim -fcprop-registers -fcrossjumping @gol
390 -fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules @gol
391 -fcx-limited-range @gol
392 -fdata-sections -fdce -fdelayed-branch @gol
393 -fdelete-null-pointer-checks -fdevirtualize -fdevirtualize-speculatively @gol
394 -fdevirtualize-at-ltrans -fdse @gol
395 -fearly-inlining -fipa-sra -fexpensive-optimizations -ffat-lto-objects @gol
396 -ffast-math -ffinite-math-only -ffloat-store -fexcess-precision=@var{style} @gol
397 -fforward-propagate -ffp-contract=@var{style} -ffunction-sections @gol
398 -fgcse -fgcse-after-reload -fgcse-las -fgcse-lm -fgraphite-identity @gol
399 -fgcse-sm -fhoist-adjacent-loads -fif-conversion @gol
400 -fif-conversion2 -findirect-inlining @gol
401 -finline-functions -finline-functions-called-once -finline-limit=@var{n} @gol
402 -finline-small-functions -fipa-cp -fipa-cp-clone -fipa-cp-alignment @gol
403 -fipa-pta -fipa-profile -fipa-pure-const -fipa-reference -fipa-icf @gol
404 -fira-algorithm=@var{algorithm} @gol
405 -fira-region=@var{region} -fira-hoist-pressure @gol
406 -fira-loop-pressure -fno-ira-share-save-slots @gol
407 -fno-ira-share-spill-slots -fira-verbose=@var{n} @gol
408 -fisolate-erroneous-paths-dereference -fisolate-erroneous-paths-attribute @gol
409 -fivopts -fkeep-inline-functions -fkeep-static-consts @gol
410 -flive-range-shrinkage @gol
411 -floop-block -floop-interchange -floop-strip-mine @gol
412 -floop-unroll-and-jam -floop-nest-optimize @gol
413 -floop-parallelize-all -flra-remat -flto -flto-compression-level @gol
414 -flto-partition=@var{alg} -flto-report -flto-report-wpa -fmerge-all-constants @gol
415 -fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves @gol
416 -fmove-loop-invariants -fno-branch-count-reg @gol
417 -fno-defer-pop -fno-function-cse -fno-guess-branch-probability @gol
418 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
419 -fno-sched-interblock -fno-sched-spec -fno-signed-zeros @gol
420 -fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol
421 -fomit-frame-pointer -foptimize-sibling-calls @gol
422 -fpartial-inlining -fpeel-loops -fpredictive-commoning @gol
423 -fprefetch-loop-arrays -fprofile-report @gol
424 -fprofile-correction -fprofile-dir=@var{path} -fprofile-generate @gol
425 -fprofile-generate=@var{path} @gol
426 -fprofile-use -fprofile-use=@var{path} -fprofile-values @gol
427 -fprofile-reorder-functions @gol
428 -freciprocal-math -free -frename-registers -freorder-blocks @gol
429 -freorder-blocks-and-partition -freorder-functions @gol
430 -frerun-cse-after-loop -freschedule-modulo-scheduled-loops @gol
431 -frounding-math -fsched2-use-superblocks -fsched-pressure @gol
432 -fsched-spec-load -fsched-spec-load-dangerous @gol
433 -fsched-stalled-insns-dep[=@var{n}] -fsched-stalled-insns[=@var{n}] @gol
434 -fsched-group-heuristic -fsched-critical-path-heuristic @gol
435 -fsched-spec-insn-heuristic -fsched-rank-heuristic @gol
436 -fsched-last-insn-heuristic -fsched-dep-count-heuristic @gol
437 -fschedule-fusion @gol
438 -fschedule-insns -fschedule-insns2 -fsection-anchors @gol
439 -fselective-scheduling -fselective-scheduling2 @gol
440 -fsel-sched-pipelining -fsel-sched-pipelining-outer-loops @gol
441 -fsemantic-interposition @gol
442 -fshrink-wrap -fsignaling-nans -fsingle-precision-constant @gol
443 -fsplit-ivs-in-unroller -fsplit-wide-types -fssa-phiopt @gol
444 -fstack-protector -fstack-protector-all -fstack-protector-strong @gol
445 -fstack-protector-explicit -fstdarg-opt -fstrict-aliasing @gol
446 -fstrict-overflow -fthread-jumps -ftracer -ftree-bit-ccp @gol
447 -ftree-builtin-call-dce -ftree-ccp -ftree-ch @gol
448 -ftree-coalesce-inline-vars -ftree-coalesce-vars -ftree-copy-prop @gol
449 -ftree-copyrename -ftree-dce -ftree-dominator-opts -ftree-dse @gol
450 -ftree-forwprop -ftree-fre -ftree-loop-if-convert @gol
451 -ftree-loop-if-convert-stores -ftree-loop-im @gol
452 -ftree-phiprop -ftree-loop-distribution -ftree-loop-distribute-patterns @gol
453 -ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize @gol
454 -ftree-loop-vectorize @gol
455 -ftree-parallelize-loops=@var{n} -ftree-pre -ftree-partial-pre -ftree-pta @gol
456 -ftree-reassoc -ftree-sink -ftree-slsr -ftree-sra @gol
457 -ftree-switch-conversion -ftree-tail-merge -ftree-ter @gol
458 -ftree-vectorize -ftree-vrp @gol
459 -funit-at-a-time -funroll-all-loops -funroll-loops @gol
460 -funsafe-loop-optimizations -funsafe-math-optimizations -funswitch-loops @gol
461 -fipa-ra -fvariable-expansion-in-unroller -fvect-cost-model -fvpt @gol
462 -fweb -fwhole-program -fwpa -fuse-linker-plugin @gol
463 --param @var{name}=@var{value}
464 -O -O0 -O1 -O2 -O3 -Os -Ofast -Og}
466 @item Preprocessor Options
467 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
468 @gccoptlist{-A@var{question}=@var{answer} @gol
469 -A-@var{question}@r{[}=@var{answer}@r{]} @gol
470 -C -dD -dI -dM -dN @gol
471 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
472 -idirafter @var{dir} @gol
473 -include @var{file} -imacros @var{file} @gol
474 -iprefix @var{file} -iwithprefix @var{dir} @gol
475 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
476 -imultilib @var{dir} -isysroot @var{dir} @gol
477 -M -MM -MF -MG -MP -MQ -MT -nostdinc @gol
478 -P -fdebug-cpp -ftrack-macro-expansion -fworking-directory @gol
479 -remap -trigraphs -undef -U@var{macro} @gol
480 -Wp,@var{option} -Xpreprocessor @var{option} -no-integrated-cpp}
482 @item Assembler Option
483 @xref{Assembler Options,,Passing Options to the Assembler}.
484 @gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
487 @xref{Link Options,,Options for Linking}.
488 @gccoptlist{@var{object-file-name} -fuse-ld=@var{linker} -l@var{library} @gol
489 -nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic @gol
490 -s -static -static-libgcc -static-libstdc++ @gol
491 -static-libasan -static-libtsan -static-liblsan -static-libubsan @gol
492 -static-libmpx -static-libmpxwrappers @gol
493 -shared -shared-libgcc -symbolic @gol
494 -T @var{script} -Wl,@var{option} -Xlinker @var{option} @gol
495 -u @var{symbol} -z @var{keyword}}
497 @item Directory Options
498 @xref{Directory Options,,Options for Directory Search}.
499 @gccoptlist{-B@var{prefix} -I@var{dir} -iplugindir=@var{dir} @gol
500 -iquote@var{dir} -L@var{dir} -specs=@var{file} -I- @gol
501 --sysroot=@var{dir} --no-sysroot-suffix}
503 @item Machine Dependent Options
504 @xref{Submodel Options,,Hardware Models and Configurations}.
505 @c This list is ordered alphanumerically by subsection name.
506 @c Try and put the significant identifier (CPU or system) first,
507 @c so users have a clue at guessing where the ones they want will be.
509 @emph{AArch64 Options}
510 @gccoptlist{-mabi=@var{name} -mbig-endian -mlittle-endian @gol
511 -mgeneral-regs-only @gol
512 -mcmodel=tiny -mcmodel=small -mcmodel=large @gol
514 -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol
515 -mtls-dialect=desc -mtls-dialect=traditional @gol
516 -mfix-cortex-a53-835769 -mno-fix-cortex-a53-835769 @gol
517 -mfix-cortex-a53-843419 -mno-fix-cortex-a53-843419 @gol
518 -march=@var{name} -mcpu=@var{name} -mtune=@var{name}}
520 @emph{Adapteva Epiphany Options}
521 @gccoptlist{-mhalf-reg-file -mprefer-short-insn-regs @gol
522 -mbranch-cost=@var{num} -mcmove -mnops=@var{num} -msoft-cmpsf @gol
523 -msplit-lohi -mpost-inc -mpost-modify -mstack-offset=@var{num} @gol
524 -mround-nearest -mlong-calls -mshort-calls -msmall16 @gol
525 -mfp-mode=@var{mode} -mvect-double -max-vect-align=@var{num} @gol
526 -msplit-vecmove-early -m1reg-@var{reg}}
529 @gccoptlist{-mbarrel-shifter @gol
530 -mcpu=@var{cpu} -mA6 -mARC600 -mA7 -mARC700 @gol
531 -mdpfp -mdpfp-compact -mdpfp-fast -mno-dpfp-lrsr @gol
532 -mea -mno-mpy -mmul32x16 -mmul64 @gol
533 -mnorm -mspfp -mspfp-compact -mspfp-fast -msimd -msoft-float -mswap @gol
534 -mcrc -mdsp-packa -mdvbf -mlock -mmac-d16 -mmac-24 -mrtsc -mswape @gol
535 -mtelephony -mxy -misize -mannotate-align -marclinux -marclinux_prof @gol
536 -mepilogue-cfi -mlong-calls -mmedium-calls -msdata @gol
537 -mucb-mcount -mvolatile-cache @gol
538 -malign-call -mauto-modify-reg -mbbit-peephole -mno-brcc @gol
539 -mcase-vector-pcrel -mcompact-casesi -mno-cond-exec -mearly-cbranchsi @gol
540 -mexpand-adddi -mindexed-loads -mlra -mlra-priority-none @gol
541 -mlra-priority-compact mlra-priority-noncompact -mno-millicode @gol
542 -mmixed-code -mq-class -mRcq -mRcw -msize-level=@var{level} @gol
543 -mtune=@var{cpu} -mmultcost=@var{num} -munalign-prob-threshold=@var{probability}}
546 @gccoptlist{-mapcs-frame -mno-apcs-frame @gol
547 -mabi=@var{name} @gol
548 -mapcs-stack-check -mno-apcs-stack-check @gol
549 -mapcs-float -mno-apcs-float @gol
550 -mapcs-reentrant -mno-apcs-reentrant @gol
551 -msched-prolog -mno-sched-prolog @gol
552 -mlittle-endian -mbig-endian @gol
553 -mfloat-abi=@var{name} @gol
554 -mfp16-format=@var{name}
555 -mthumb-interwork -mno-thumb-interwork @gol
556 -mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol
557 -mtune=@var{name} -mprint-tune-info @gol
558 -mstructure-size-boundary=@var{n} @gol
559 -mabort-on-noreturn @gol
560 -mlong-calls -mno-long-calls @gol
561 -msingle-pic-base -mno-single-pic-base @gol
562 -mpic-register=@var{reg} @gol
563 -mnop-fun-dllimport @gol
564 -mpoke-function-name @gol
566 -mtpcs-frame -mtpcs-leaf-frame @gol
567 -mcaller-super-interworking -mcallee-super-interworking @gol
568 -mtp=@var{name} -mtls-dialect=@var{dialect} @gol
569 -mword-relocations @gol
570 -mfix-cortex-m3-ldrd @gol
571 -munaligned-access @gol
572 -mneon-for-64bits @gol
573 -mslow-flash-data @gol
574 -masm-syntax-unified @gol
578 @gccoptlist{-mmcu=@var{mcu} -maccumulate-args -mbranch-cost=@var{cost} @gol
579 -mcall-prologues -mint8 -mn_flash=@var{size} -mno-interrupts @gol
580 -mrelax -mrmw -mstrict-X -mtiny-stack -nodevicelib -Waddr-space-convert}
582 @emph{Blackfin Options}
583 @gccoptlist{-mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} @gol
584 -msim -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol
585 -mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol
586 -mlow-64k -mno-low64k -mstack-check-l1 -mid-shared-library @gol
587 -mno-id-shared-library -mshared-library-id=@var{n} @gol
588 -mleaf-id-shared-library -mno-leaf-id-shared-library @gol
589 -msep-data -mno-sep-data -mlong-calls -mno-long-calls @gol
590 -mfast-fp -minline-plt -mmulticore -mcorea -mcoreb -msdram @gol
594 @gccoptlist{-mbig-endian -mlittle-endian -march=@var{cpu} @gol
595 -msim -msdata=@var{sdata-type}}
598 @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
599 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
600 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
601 -mstack-align -mdata-align -mconst-align @gol
602 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
603 -melf -maout -melinux -mlinux -sim -sim2 @gol
604 -mmul-bug-workaround -mno-mul-bug-workaround}
607 @gccoptlist{-mmac @gol
608 -mcr16cplus -mcr16c @gol
609 -msim -mint32 -mbit-ops
610 -mdata-model=@var{model}}
612 @emph{Darwin Options}
613 @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
614 -arch_only -bind_at_load -bundle -bundle_loader @gol
615 -client_name -compatibility_version -current_version @gol
617 -dependency-file -dylib_file -dylinker_install_name @gol
618 -dynamic -dynamiclib -exported_symbols_list @gol
619 -filelist -flat_namespace -force_cpusubtype_ALL @gol
620 -force_flat_namespace -headerpad_max_install_names @gol
622 -image_base -init -install_name -keep_private_externs @gol
623 -multi_module -multiply_defined -multiply_defined_unused @gol
624 -noall_load -no_dead_strip_inits_and_terms @gol
625 -nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol
626 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
627 -private_bundle -read_only_relocs -sectalign @gol
628 -sectobjectsymbols -whyload -seg1addr @gol
629 -sectcreate -sectobjectsymbols -sectorder @gol
630 -segaddr -segs_read_only_addr -segs_read_write_addr @gol
631 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
632 -segprot -segs_read_only_addr -segs_read_write_addr @gol
633 -single_module -static -sub_library -sub_umbrella @gol
634 -twolevel_namespace -umbrella -undefined @gol
635 -unexported_symbols_list -weak_reference_mismatches @gol
636 -whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol
637 -mkernel -mone-byte-bool}
639 @emph{DEC Alpha Options}
640 @gccoptlist{-mno-fp-regs -msoft-float @gol
641 -mieee -mieee-with-inexact -mieee-conformant @gol
642 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
643 -mtrap-precision=@var{mode} -mbuild-constants @gol
644 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
645 -mbwx -mmax -mfix -mcix @gol
646 -mfloat-vax -mfloat-ieee @gol
647 -mexplicit-relocs -msmall-data -mlarge-data @gol
648 -msmall-text -mlarge-text @gol
649 -mmemory-latency=@var{time}}
652 @gccoptlist{-msmall-model -mno-lsim}
655 @gccoptlist{-msim -mlra}
658 @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
659 -mhard-float -msoft-float @gol
660 -malloc-cc -mfixed-cc -mdword -mno-dword @gol
661 -mdouble -mno-double @gol
662 -mmedia -mno-media -mmuladd -mno-muladd @gol
663 -mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol
664 -mlinked-fp -mlong-calls -malign-labels @gol
665 -mlibrary-pic -macc-4 -macc-8 @gol
666 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
667 -moptimize-membar -mno-optimize-membar @gol
668 -mscc -mno-scc -mcond-exec -mno-cond-exec @gol
669 -mvliw-branch -mno-vliw-branch @gol
670 -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
671 -mno-nested-cond-exec -mtomcat-stats @gol
675 @emph{GNU/Linux Options}
676 @gccoptlist{-mglibc -muclibc -mmusl -mbionic -mandroid @gol
677 -tno-android-cc -tno-android-ld}
679 @emph{H8/300 Options}
680 @gccoptlist{-mrelax -mh -ms -mn -mexr -mno-exr -mint32 -malign-300}
683 @gccoptlist{-march=@var{architecture-type} @gol
684 -mdisable-fpregs -mdisable-indexing @gol
685 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
686 -mfixed-range=@var{register-range} @gol
687 -mjump-in-delay -mlinker-opt -mlong-calls @gol
688 -mlong-load-store -mno-disable-fpregs @gol
689 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
690 -mno-jump-in-delay -mno-long-load-store @gol
691 -mno-portable-runtime -mno-soft-float @gol
692 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
693 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
694 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
695 -munix=@var{unix-std} -nolibdld -static -threads}
698 @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
699 -mvolatile-asm-stop -mregister-names -msdata -mno-sdata @gol
700 -mconstant-gp -mauto-pic -mfused-madd @gol
701 -minline-float-divide-min-latency @gol
702 -minline-float-divide-max-throughput @gol
703 -mno-inline-float-divide @gol
704 -minline-int-divide-min-latency @gol
705 -minline-int-divide-max-throughput @gol
706 -mno-inline-int-divide @gol
707 -minline-sqrt-min-latency -minline-sqrt-max-throughput @gol
708 -mno-inline-sqrt @gol
709 -mdwarf2-asm -mearly-stop-bits @gol
710 -mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol
711 -mtune=@var{cpu-type} -milp32 -mlp64 @gol
712 -msched-br-data-spec -msched-ar-data-spec -msched-control-spec @gol
713 -msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec @gol
714 -msched-spec-ldc -msched-spec-control-ldc @gol
715 -msched-prefer-non-data-spec-insns -msched-prefer-non-control-spec-insns @gol
716 -msched-stop-bits-after-every-cycle -msched-count-spec-in-critical-path @gol
717 -msel-sched-dont-check-control-spec -msched-fp-mem-deps-zero-cost @gol
718 -msched-max-memory-insns-hard-limit -msched-max-memory-insns=@var{max-insns}}
721 @gccoptlist{-mbarrel-shift-enabled -mdivide-enabled -mmultiply-enabled @gol
722 -msign-extend-enabled -muser-enabled}
724 @emph{M32R/D Options}
725 @gccoptlist{-m32r2 -m32rx -m32r @gol
727 -malign-loops -mno-align-loops @gol
728 -missue-rate=@var{number} @gol
729 -mbranch-cost=@var{number} @gol
730 -mmodel=@var{code-size-model-type} @gol
731 -msdata=@var{sdata-type} @gol
732 -mno-flush-func -mflush-func=@var{name} @gol
733 -mno-flush-trap -mflush-trap=@var{number} @gol
737 @gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}}
739 @emph{M680x0 Options}
740 @gccoptlist{-march=@var{arch} -mcpu=@var{cpu} -mtune=@var{tune} @gol
741 -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
742 -m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407 @gol
743 -mcfv4e -mbitfield -mno-bitfield -mc68000 -mc68020 @gol
744 -mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort @gol
745 -mno-short -mhard-float -m68881 -msoft-float -mpcrel @gol
746 -malign-int -mstrict-align -msep-data -mno-sep-data @gol
747 -mshared-library-id=n -mid-shared-library -mno-id-shared-library @gol
751 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
752 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
753 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
754 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
755 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
758 @gccoptlist{-mabsdiff -mall-opts -maverage -mbased=@var{n} -mbitops @gol
759 -mc=@var{n} -mclip -mconfig=@var{name} -mcop -mcop32 -mcop64 -mivc2 @gol
760 -mdc -mdiv -meb -mel -mio-volatile -ml -mleadz -mm -mminmax @gol
761 -mmult -mno-opts -mrepeat -ms -msatur -msdram -msim -msimnovec -mtf @gol
764 @emph{MicroBlaze Options}
765 @gccoptlist{-msoft-float -mhard-float -msmall-divides -mcpu=@var{cpu} @gol
766 -mmemcpy -mxl-soft-mul -mxl-soft-div -mxl-barrel-shift @gol
767 -mxl-pattern-compare -mxl-stack-check -mxl-gp-opt -mno-clearbss @gol
768 -mxl-multiply-high -mxl-float-convert -mxl-float-sqrt @gol
769 -mbig-endian -mlittle-endian -mxl-reorder -mxl-mode-@var{app-model}}
772 @gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol
773 -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips32r3 -mips32r5 @gol
774 -mips32r6 -mips64 -mips64r2 -mips64r3 -mips64r5 -mips64r6 @gol
775 -mips16 -mno-mips16 -mflip-mips16 @gol
776 -minterlink-compressed -mno-interlink-compressed @gol
777 -minterlink-mips16 -mno-interlink-mips16 @gol
778 -mabi=@var{abi} -mabicalls -mno-abicalls @gol
779 -mshared -mno-shared -mplt -mno-plt -mxgot -mno-xgot @gol
780 -mgp32 -mgp64 -mfp32 -mfpxx -mfp64 -mhard-float -msoft-float @gol
781 -mno-float -msingle-float -mdouble-float @gol
782 -modd-spreg -mno-odd-spreg @gol
783 -mabs=@var{mode} -mnan=@var{encoding} @gol
784 -mdsp -mno-dsp -mdspr2 -mno-dspr2 @gol
787 -mvirt -mno-virt @gol
789 -mmicromips -mno-micromips @gol
790 -mfpu=@var{fpu-type} @gol
791 -msmartmips -mno-smartmips @gol
792 -mpaired-single -mno-paired-single -mdmx -mno-mdmx @gol
793 -mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc @gol
794 -mlong64 -mlong32 -msym32 -mno-sym32 @gol
795 -G@var{num} -mlocal-sdata -mno-local-sdata @gol
796 -mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt @gol
797 -membedded-data -mno-embedded-data @gol
798 -muninit-const-in-rodata -mno-uninit-const-in-rodata @gol
799 -mcode-readable=@var{setting} @gol
800 -msplit-addresses -mno-split-addresses @gol
801 -mexplicit-relocs -mno-explicit-relocs @gol
802 -mcheck-zero-division -mno-check-zero-division @gol
803 -mdivide-traps -mdivide-breaks @gol
804 -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol
805 -mmad -mno-mad -mimadd -mno-imadd -mfused-madd -mno-fused-madd -nocpp @gol
806 -mfix-24k -mno-fix-24k @gol
807 -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol
808 -mfix-r10000 -mno-fix-r10000 -mfix-rm7000 -mno-fix-rm7000 @gol
809 -mfix-vr4120 -mno-fix-vr4120 @gol
810 -mfix-vr4130 -mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1 @gol
811 -mflush-func=@var{func} -mno-flush-func @gol
812 -mbranch-cost=@var{num} -mbranch-likely -mno-branch-likely @gol
813 -mfp-exceptions -mno-fp-exceptions @gol
814 -mvr4130-align -mno-vr4130-align -msynci -mno-synci @gol
815 -mrelax-pic-calls -mno-relax-pic-calls -mmcount-ra-address}
818 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
819 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
820 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
821 -mno-base-addresses -msingle-exit -mno-single-exit}
823 @emph{MN10300 Options}
824 @gccoptlist{-mmult-bug -mno-mult-bug @gol
825 -mno-am33 -mam33 -mam33-2 -mam34 @gol
826 -mtune=@var{cpu-type} @gol
827 -mreturn-pointer-on-d0 @gol
828 -mno-crt0 -mrelax -mliw -msetlb}
831 @gccoptlist{-meb -mel -mmul.x -mno-crt0}
833 @emph{MSP430 Options}
834 @gccoptlist{-msim -masm-hex -mmcu= -mcpu= -mlarge -msmall -mrelax @gol
835 -mcode-region= -mdata-region= @gol
839 @gccoptlist{-mbig-endian -mlittle-endian @gol
840 -mreduced-regs -mfull-regs @gol
841 -mcmov -mno-cmov @gol
842 -mperf-ext -mno-perf-ext @gol
843 -mv3push -mno-v3push @gol
844 -m16bit -mno-16bit @gol
845 -misr-vector-size=@var{num} @gol
846 -mcache-block-size=@var{num} @gol
847 -march=@var{arch} @gol
848 -mcmodel=@var{code-model} @gol
851 @emph{Nios II Options}
852 @gccoptlist{-G @var{num} -mgpopt=@var{option} -mgpopt -mno-gpopt @gol
854 -mno-bypass-cache -mbypass-cache @gol
855 -mno-cache-volatile -mcache-volatile @gol
856 -mno-fast-sw-div -mfast-sw-div @gol
857 -mhw-mul -mno-hw-mul -mhw-mulx -mno-hw-mulx -mno-hw-div -mhw-div @gol
858 -mcustom-@var{insn}=@var{N} -mno-custom-@var{insn} @gol
859 -mcustom-fpu-cfg=@var{name} @gol
860 -mhal -msmallc -msys-crt0=@var{name} -msys-lib=@var{name}}
862 @emph{Nvidia PTX Options}
863 @gccoptlist{-m32 -m64 -mmainkernel}
865 @emph{PDP-11 Options}
866 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
867 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
868 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
869 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
870 -mbranch-expensive -mbranch-cheap @gol
871 -munix-asm -mdec-asm}
873 @emph{picoChip Options}
874 @gccoptlist{-mae=@var{ae_type} -mvliw-lookahead=@var{N} @gol
875 -msymbol-as-address -mno-inefficient-warnings}
877 @emph{PowerPC Options}
878 See RS/6000 and PowerPC Options.
881 @gccoptlist{-msim -mmul=none -mmul=g13 -mmul=g14 -mallregs @gol
882 -mcpu=g10 -mcpu=g13 -mcpu=g14 -mg10 -mg13 -mg14 @gol
883 -m64bit-doubles -m32bit-doubles}
885 @emph{RS/6000 and PowerPC Options}
886 @gccoptlist{-mcpu=@var{cpu-type} @gol
887 -mtune=@var{cpu-type} @gol
888 -mcmodel=@var{code-model} @gol
890 -maltivec -mno-altivec @gol
891 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
892 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
893 -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mpopcntd -mno-popcntd @gol
894 -mfprnd -mno-fprnd @gol
895 -mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mhard-dfp -mno-hard-dfp @gol
896 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
897 -m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol
898 -malign-power -malign-natural @gol
899 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
900 -msingle-float -mdouble-float -msimple-fpu @gol
901 -mstring -mno-string -mupdate -mno-update @gol
902 -mavoid-indexed-addresses -mno-avoid-indexed-addresses @gol
903 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
904 -mstrict-align -mno-strict-align -mrelocatable @gol
905 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
906 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
907 -mdynamic-no-pic -maltivec -mswdiv -msingle-pic-base @gol
908 -mprioritize-restricted-insns=@var{priority} @gol
909 -msched-costly-dep=@var{dependence_type} @gol
910 -minsert-sched-nops=@var{scheme} @gol
911 -mcall-sysv -mcall-netbsd @gol
912 -maix-struct-return -msvr4-struct-return @gol
913 -mabi=@var{abi-type} -msecure-plt -mbss-plt @gol
914 -mblock-move-inline-limit=@var{num} @gol
915 -misel -mno-isel @gol
916 -misel=yes -misel=no @gol
918 -mspe=yes -mspe=no @gol
920 -mgen-cell-microcode -mwarn-cell-microcode @gol
921 -mvrsave -mno-vrsave @gol
922 -mmulhw -mno-mulhw @gol
923 -mdlmzb -mno-dlmzb @gol
924 -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol
925 -mprototype -mno-prototype @gol
926 -msim -mmvme -mads -myellowknife -memb -msdata @gol
927 -msdata=@var{opt} -mvxworks -G @var{num} -pthread @gol
928 -mrecip -mrecip=@var{opt} -mno-recip -mrecip-precision @gol
929 -mno-recip-precision @gol
930 -mveclibabi=@var{type} -mfriz -mno-friz @gol
931 -mpointers-to-nested-functions -mno-pointers-to-nested-functions @gol
932 -msave-toc-indirect -mno-save-toc-indirect @gol
933 -mpower8-fusion -mno-mpower8-fusion -mpower8-vector -mno-power8-vector @gol
934 -mcrypto -mno-crypto -mdirect-move -mno-direct-move @gol
935 -mquad-memory -mno-quad-memory @gol
936 -mquad-memory-atomic -mno-quad-memory-atomic @gol
937 -mcompat-align-parm -mno-compat-align-parm @gol
938 -mupper-regs-df -mno-upper-regs-df -mupper-regs-sf -mno-upper-regs-sf @gol
939 -mupper-regs -mno-upper-regs}
942 @gccoptlist{-m64bit-doubles -m32bit-doubles -fpu -nofpu@gol
944 -mbig-endian-data -mlittle-endian-data @gol
947 -mas100-syntax -mno-as100-syntax@gol
949 -mmax-constant-size=@gol
952 -mallow-string-insns -mno-allow-string-insns@gol
953 -mno-warn-multiple-fast-interrupts@gol
954 -msave-acc-in-interrupts}
956 @emph{S/390 and zSeries Options}
957 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
958 -mhard-float -msoft-float -mhard-dfp -mno-hard-dfp @gol
959 -mlong-double-64 -mlong-double-128 @gol
960 -mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol
961 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
962 -m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol
963 -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol
964 -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard @gol
965 -mhotpatch=@var{halfwords},@var{halfwords}}
968 @gccoptlist{-meb -mel @gol
972 -mscore5 -mscore5u -mscore7 -mscore7d}
975 @gccoptlist{-m1 -m2 -m2e @gol
976 -m2a-nofpu -m2a-single-only -m2a-single -m2a @gol
978 -m4-nofpu -m4-single-only -m4-single -m4 @gol
979 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol
980 -m5-64media -m5-64media-nofpu @gol
981 -m5-32media -m5-32media-nofpu @gol
982 -m5-compact -m5-compact-nofpu @gol
983 -mb -ml -mdalign -mrelax @gol
984 -mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol
985 -mieee -mno-ieee -mbitops -misize -minline-ic_invalidate -mpadstruct @gol
986 -mspace -mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol
987 -mdivsi3_libfunc=@var{name} -mfixed-range=@var{register-range} @gol
988 -mindexed-addressing -mgettrcost=@var{number} -mpt-fixed @gol
989 -maccumulate-outgoing-args -minvalid-symbols @gol
990 -matomic-model=@var{atomic-model} @gol
991 -mbranch-cost=@var{num} -mzdcbranch -mno-zdcbranch @gol
992 -mcbranch-force-delay-slot @gol
993 -mfused-madd -mno-fused-madd -mfsca -mno-fsca -mfsrra -mno-fsrra @gol
994 -mpretend-cmove -mtas}
996 @emph{Solaris 2 Options}
997 @gccoptlist{-mclear-hwcap -mno-clear-hwcap -mimpure-text -mno-impure-text @gol
1000 @emph{SPARC Options}
1001 @gccoptlist{-mcpu=@var{cpu-type} @gol
1002 -mtune=@var{cpu-type} @gol
1003 -mcmodel=@var{code-model} @gol
1004 -mmemory-model=@var{mem-model} @gol
1005 -m32 -m64 -mapp-regs -mno-app-regs @gol
1006 -mfaster-structs -mno-faster-structs -mflat -mno-flat @gol
1007 -mfpu -mno-fpu -mhard-float -msoft-float @gol
1008 -mhard-quad-float -msoft-quad-float @gol
1009 -mstack-bias -mno-stack-bias @gol
1010 -munaligned-doubles -mno-unaligned-doubles @gol
1011 -muser-mode -mno-user-mode @gol
1012 -mv8plus -mno-v8plus -mvis -mno-vis @gol
1013 -mvis2 -mno-vis2 -mvis3 -mno-vis3 @gol
1014 -mcbcond -mno-cbcond @gol
1015 -mfmaf -mno-fmaf -mpopc -mno-popc @gol
1016 -mfix-at697f -mfix-ut699}
1019 @gccoptlist{-mwarn-reloc -merror-reloc @gol
1020 -msafe-dma -munsafe-dma @gol
1022 -msmall-mem -mlarge-mem -mstdmain @gol
1023 -mfixed-range=@var{register-range} @gol
1025 -maddress-space-conversion -mno-address-space-conversion @gol
1026 -mcache-size=@var{cache-size} @gol
1027 -matomic-updates -mno-atomic-updates}
1029 @emph{System V Options}
1030 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
1032 @emph{TILE-Gx Options}
1033 @gccoptlist{-mcpu=CPU -m32 -m64 -mbig-endian -mlittle-endian @gol
1034 -mcmodel=@var{code-model}}
1036 @emph{TILEPro Options}
1037 @gccoptlist{-mcpu=@var{cpu} -m32}
1040 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
1041 -mprolog-function -mno-prolog-function -mspace @gol
1042 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
1043 -mapp-regs -mno-app-regs @gol
1044 -mdisable-callt -mno-disable-callt @gol
1045 -mv850e2v3 -mv850e2 -mv850e1 -mv850es @gol
1046 -mv850e -mv850 -mv850e3v5 @gol
1057 @gccoptlist{-mg -mgnu -munix}
1059 @emph{Visium Options}
1060 @gccoptlist{-mdebug -msim -mfpu -mno-fpu -mhard-float -msoft-float @gol
1061 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} -msv-mode -muser-mode}
1064 @gccoptlist{-mvms-return-codes -mdebug-main=@var{prefix} -mmalloc64 @gol
1065 -mpointer-size=@var{size}}
1067 @emph{VxWorks Options}
1068 @gccoptlist{-mrtp -non-static -Bstatic -Bdynamic @gol
1069 -Xbind-lazy -Xbind-now}
1072 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
1073 -mtune-ctrl=@var{feature-list} -mdump-tune-features -mno-default @gol
1074 -mfpmath=@var{unit} @gol
1075 -masm=@var{dialect} -mno-fancy-math-387 @gol
1076 -mno-fp-ret-in-387 -msoft-float @gol
1077 -mno-wide-multiply -mrtd -malign-double @gol
1078 -mpreferred-stack-boundary=@var{num} @gol
1079 -mincoming-stack-boundary=@var{num} @gol
1080 -mcld -mcx16 -msahf -mmovbe -mcrc32 @gol
1081 -mrecip -mrecip=@var{opt} @gol
1082 -mvzeroupper -mprefer-avx128 @gol
1083 -mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx @gol
1084 -mavx2 -mavx512f -mavx512pf -mavx512er -mavx512cd -msha @gol
1085 -maes -mpclmul -mfsgsbase -mrdrnd -mf16c -mfma -mprefetchwt1 @gol
1086 -mclflushopt -mxsavec -mxsaves @gol
1087 -msse4a -m3dnow -mpopcnt -mabm -mbmi -mtbm -mfma4 -mxop -mlzcnt @gol
1088 -mbmi2 -mfxsr -mxsave -mxsaveopt -mrtm -mlwp -mmpx -mmwaitx -mthreads @gol
1089 -mno-align-stringops -minline-all-stringops @gol
1090 -minline-stringops-dynamically -mstringop-strategy=@var{alg} @gol
1091 -mmemcpy-strategy=@var{strategy} -mmemset-strategy=@var{strategy} @gol
1092 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
1093 -m96bit-long-double -mlong-double-64 -mlong-double-80 -mlong-double-128 @gol
1094 -mregparm=@var{num} -msseregparm @gol
1095 -mveclibabi=@var{type} -mvect8-ret-in-mem @gol
1096 -mpc32 -mpc64 -mpc80 -mstackrealign @gol
1097 -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol
1098 -mcmodel=@var{code-model} -mabi=@var{name} -maddress-mode=@var{mode} @gol
1099 -m32 -m64 -mx32 -m16 -mlarge-data-threshold=@var{num} @gol
1100 -msse2avx -mfentry -mrecord-mcount -mnop-mcount -m8bit-idiv @gol
1101 -mavx256-split-unaligned-load -mavx256-split-unaligned-store @gol
1102 -malign-data=@var{type} -mstack-protector-guard=@var{guard}}
1104 @emph{x86 Windows Options}
1105 @gccoptlist{-mconsole -mcygwin -mno-cygwin -mdll @gol
1106 -mnop-fun-dllimport -mthread @gol
1107 -municode -mwin32 -mwindows -fno-set-stack-executable}
1109 @emph{Xstormy16 Options}
1112 @emph{Xtensa Options}
1113 @gccoptlist{-mconst16 -mno-const16 @gol
1114 -mfused-madd -mno-fused-madd @gol
1116 -mserialize-volatile -mno-serialize-volatile @gol
1117 -mtext-section-literals -mno-text-section-literals @gol
1118 -mtarget-align -mno-target-align @gol
1119 -mlongcalls -mno-longcalls}
1121 @emph{zSeries Options}
1122 See S/390 and zSeries Options.
1124 @item Code Generation Options
1125 @xref{Code Gen Options,,Options for Code Generation Conventions}.
1126 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
1127 -ffixed-@var{reg} -fexceptions @gol
1128 -fnon-call-exceptions -fdelete-dead-exceptions -funwind-tables @gol
1129 -fasynchronous-unwind-tables @gol
1130 -fno-gnu-unique @gol
1131 -finhibit-size-directive -finstrument-functions @gol
1132 -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} @gol
1133 -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{} @gol
1134 -fno-common -fno-ident @gol
1135 -fpcc-struct-return -fpic -fPIC -fpie -fPIE -fno-plt @gol
1136 -fno-jump-tables @gol
1137 -frecord-gcc-switches @gol
1138 -freg-struct-return -fshort-enums @gol
1139 -fshort-double -fshort-wchar @gol
1140 -fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol
1141 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
1142 -fno-stack-limit -fsplit-stack @gol
1143 -fleading-underscore -ftls-model=@var{model} @gol
1144 -fstack-reuse=@var{reuse_level} @gol
1145 -ftrapv -fwrapv -fbounds-check @gol
1146 -fvisibility=@r{[}default@r{|}internal@r{|}hidden@r{|}protected@r{]} @gol
1147 -fstrict-volatile-bitfields -fsync-libcalls}
1151 @node Overall Options
1152 @section Options Controlling the Kind of Output
1154 Compilation can involve up to four stages: preprocessing, compilation
1155 proper, assembly and linking, always in that order. GCC is capable of
1156 preprocessing and compiling several files either into several
1157 assembler input files, or into one assembler input file; then each
1158 assembler input file produces an object file, and linking combines all
1159 the object files (those newly compiled, and those specified as input)
1160 into an executable file.
1162 @cindex file name suffix
1163 For any given input file, the file name suffix determines what kind of
1164 compilation is done:
1168 C source code that must be preprocessed.
1171 C source code that should not be preprocessed.
1174 C++ source code that should not be preprocessed.
1177 Objective-C source code. Note that you must link with the @file{libobjc}
1178 library to make an Objective-C program work.
1181 Objective-C source code that should not be preprocessed.
1185 Objective-C++ source code. Note that you must link with the @file{libobjc}
1186 library to make an Objective-C++ program work. Note that @samp{.M} refers
1187 to a literal capital M@.
1189 @item @var{file}.mii
1190 Objective-C++ source code that should not be preprocessed.
1193 C, C++, Objective-C or Objective-C++ header file to be turned into a
1194 precompiled header (default), or C, C++ header file to be turned into an
1195 Ada spec (via the @option{-fdump-ada-spec} switch).
1198 @itemx @var{file}.cp
1199 @itemx @var{file}.cxx
1200 @itemx @var{file}.cpp
1201 @itemx @var{file}.CPP
1202 @itemx @var{file}.c++
1204 C++ source code that must be preprocessed. Note that in @samp{.cxx},
1205 the last two letters must both be literally @samp{x}. Likewise,
1206 @samp{.C} refers to a literal capital C@.
1210 Objective-C++ source code that must be preprocessed.
1212 @item @var{file}.mii
1213 Objective-C++ source code that should not be preprocessed.
1217 @itemx @var{file}.hp
1218 @itemx @var{file}.hxx
1219 @itemx @var{file}.hpp
1220 @itemx @var{file}.HPP
1221 @itemx @var{file}.h++
1222 @itemx @var{file}.tcc
1223 C++ header file to be turned into a precompiled header or Ada spec.
1226 @itemx @var{file}.for
1227 @itemx @var{file}.ftn
1228 Fixed form Fortran source code that should not be preprocessed.
1231 @itemx @var{file}.FOR
1232 @itemx @var{file}.fpp
1233 @itemx @var{file}.FPP
1234 @itemx @var{file}.FTN
1235 Fixed form Fortran source code that must be preprocessed (with the traditional
1238 @item @var{file}.f90
1239 @itemx @var{file}.f95
1240 @itemx @var{file}.f03
1241 @itemx @var{file}.f08
1242 Free form Fortran source code that should not be preprocessed.
1244 @item @var{file}.F90
1245 @itemx @var{file}.F95
1246 @itemx @var{file}.F03
1247 @itemx @var{file}.F08
1248 Free form Fortran source code that must be preprocessed (with the
1249 traditional preprocessor).
1254 @c FIXME: Descriptions of Java file types.
1260 @item @var{file}.ads
1261 Ada source code file that contains a library unit declaration (a
1262 declaration of a package, subprogram, or generic, or a generic
1263 instantiation), or a library unit renaming declaration (a package,
1264 generic, or subprogram renaming declaration). Such files are also
1267 @item @var{file}.adb
1268 Ada source code file containing a library unit body (a subprogram or
1269 package body). Such files are also called @dfn{bodies}.
1271 @c GCC also knows about some suffixes for languages not yet included:
1282 @itemx @var{file}.sx
1283 Assembler code that must be preprocessed.
1286 An object file to be fed straight into linking.
1287 Any file name with no recognized suffix is treated this way.
1291 You can specify the input language explicitly with the @option{-x} option:
1294 @item -x @var{language}
1295 Specify explicitly the @var{language} for the following input files
1296 (rather than letting the compiler choose a default based on the file
1297 name suffix). This option applies to all following input files until
1298 the next @option{-x} option. Possible values for @var{language} are:
1300 c c-header cpp-output
1301 c++ c++-header c++-cpp-output
1302 objective-c objective-c-header objective-c-cpp-output
1303 objective-c++ objective-c++-header objective-c++-cpp-output
1304 assembler assembler-with-cpp
1306 f77 f77-cpp-input f95 f95-cpp-input
1312 Turn off any specification of a language, so that subsequent files are
1313 handled according to their file name suffixes (as they are if @option{-x}
1314 has not been used at all).
1316 @item -pass-exit-codes
1317 @opindex pass-exit-codes
1318 Normally the @command{gcc} program exits with the code of 1 if any
1319 phase of the compiler returns a non-success return code. If you specify
1320 @option{-pass-exit-codes}, the @command{gcc} program instead returns with
1321 the numerically highest error produced by any phase returning an error
1322 indication. The C, C++, and Fortran front ends return 4 if an internal
1323 compiler error is encountered.
1326 If you only want some of the stages of compilation, you can use
1327 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
1328 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
1329 @command{gcc} is to stop. Note that some combinations (for example,
1330 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
1335 Compile or assemble the source files, but do not link. The linking
1336 stage simply is not done. The ultimate output is in the form of an
1337 object file for each source file.
1339 By default, the object file name for a source file is made by replacing
1340 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
1342 Unrecognized input files, not requiring compilation or assembly, are
1347 Stop after the stage of compilation proper; do not assemble. The output
1348 is in the form of an assembler code file for each non-assembler input
1351 By default, the assembler file name for a source file is made by
1352 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
1354 Input files that don't require compilation are ignored.
1358 Stop after the preprocessing stage; do not run the compiler proper. The
1359 output is in the form of preprocessed source code, which is sent to the
1362 Input files that don't require preprocessing are ignored.
1364 @cindex output file option
1367 Place output in file @var{file}. This applies to whatever
1368 sort of output is being produced, whether it be an executable file,
1369 an object file, an assembler file or preprocessed C code.
1371 If @option{-o} is not specified, the default is to put an executable
1372 file in @file{a.out}, the object file for
1373 @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its
1374 assembler file in @file{@var{source}.s}, a precompiled header file in
1375 @file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on
1380 Print (on standard error output) the commands executed to run the stages
1381 of compilation. Also print the version number of the compiler driver
1382 program and of the preprocessor and the compiler proper.
1386 Like @option{-v} except the commands are not executed and arguments
1387 are quoted unless they contain only alphanumeric characters or @code{./-_}.
1388 This is useful for shell scripts to capture the driver-generated command lines.
1392 Use pipes rather than temporary files for communication between the
1393 various stages of compilation. This fails to work on some systems where
1394 the assembler is unable to read from a pipe; but the GNU assembler has
1399 Print (on the standard output) a description of the command-line options
1400 understood by @command{gcc}. If the @option{-v} option is also specified
1401 then @option{--help} is also passed on to the various processes
1402 invoked by @command{gcc}, so that they can display the command-line options
1403 they accept. If the @option{-Wextra} option has also been specified
1404 (prior to the @option{--help} option), then command-line options that
1405 have no documentation associated with them are also displayed.
1408 @opindex target-help
1409 Print (on the standard output) a description of target-specific command-line
1410 options for each tool. For some targets extra target-specific
1411 information may also be printed.
1413 @item --help=@{@var{class}@r{|[}^@r{]}@var{qualifier}@}@r{[},@dots{}@r{]}
1414 Print (on the standard output) a description of the command-line
1415 options understood by the compiler that fit into all specified classes
1416 and qualifiers. These are the supported classes:
1419 @item @samp{optimizers}
1420 Display all of the optimization options supported by the
1423 @item @samp{warnings}
1424 Display all of the options controlling warning messages
1425 produced by the compiler.
1428 Display target-specific options. Unlike the
1429 @option{--target-help} option however, target-specific options of the
1430 linker and assembler are not displayed. This is because those
1431 tools do not currently support the extended @option{--help=} syntax.
1434 Display the values recognized by the @option{--param}
1437 @item @var{language}
1438 Display the options supported for @var{language}, where
1439 @var{language} is the name of one of the languages supported in this
1443 Display the options that are common to all languages.
1446 These are the supported qualifiers:
1449 @item @samp{undocumented}
1450 Display only those options that are undocumented.
1453 Display options taking an argument that appears after an equal
1454 sign in the same continuous piece of text, such as:
1455 @samp{--help=target}.
1457 @item @samp{separate}
1458 Display options taking an argument that appears as a separate word
1459 following the original option, such as: @samp{-o output-file}.
1462 Thus for example to display all the undocumented target-specific
1463 switches supported by the compiler, use:
1466 --help=target,undocumented
1469 The sense of a qualifier can be inverted by prefixing it with the
1470 @samp{^} character, so for example to display all binary warning
1471 options (i.e., ones that are either on or off and that do not take an
1472 argument) that have a description, use:
1475 --help=warnings,^joined,^undocumented
1478 The argument to @option{--help=} should not consist solely of inverted
1481 Combining several classes is possible, although this usually
1482 restricts the output so much that there is nothing to display. One
1483 case where it does work, however, is when one of the classes is
1484 @var{target}. For example, to display all the target-specific
1485 optimization options, use:
1488 --help=target,optimizers
1491 The @option{--help=} option can be repeated on the command line. Each
1492 successive use displays its requested class of options, skipping
1493 those that have already been displayed.
1495 If the @option{-Q} option appears on the command line before the
1496 @option{--help=} option, then the descriptive text displayed by
1497 @option{--help=} is changed. Instead of describing the displayed
1498 options, an indication is given as to whether the option is enabled,
1499 disabled or set to a specific value (assuming that the compiler
1500 knows this at the point where the @option{--help=} option is used).
1502 Here is a truncated example from the ARM port of @command{gcc}:
1505 % gcc -Q -mabi=2 --help=target -c
1506 The following options are target specific:
1508 -mabort-on-noreturn [disabled]
1512 The output is sensitive to the effects of previous command-line
1513 options, so for example it is possible to find out which optimizations
1514 are enabled at @option{-O2} by using:
1517 -Q -O2 --help=optimizers
1520 Alternatively you can discover which binary optimizations are enabled
1521 by @option{-O3} by using:
1524 gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
1525 gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
1526 diff /tmp/O2-opts /tmp/O3-opts | grep enabled
1529 @item -no-canonical-prefixes
1530 @opindex no-canonical-prefixes
1531 Do not expand any symbolic links, resolve references to @samp{/../}
1532 or @samp{/./}, or make the path absolute when generating a relative
1537 Display the version number and copyrights of the invoked GCC@.
1541 Invoke all subcommands under a wrapper program. The name of the
1542 wrapper program and its parameters are passed as a comma separated
1546 gcc -c t.c -wrapper gdb,--args
1550 This invokes all subprograms of @command{gcc} under
1551 @samp{gdb --args}, thus the invocation of @command{cc1} is
1552 @samp{gdb --args cc1 @dots{}}.
1554 @item -fplugin=@var{name}.so
1556 Load the plugin code in file @var{name}.so, assumed to be a
1557 shared object to be dlopen'd by the compiler. The base name of
1558 the shared object file is used to identify the plugin for the
1559 purposes of argument parsing (See
1560 @option{-fplugin-arg-@var{name}-@var{key}=@var{value}} below).
1561 Each plugin should define the callback functions specified in the
1564 @item -fplugin-arg-@var{name}-@var{key}=@var{value}
1565 @opindex fplugin-arg
1566 Define an argument called @var{key} with a value of @var{value}
1567 for the plugin called @var{name}.
1569 @item -fdump-ada-spec@r{[}-slim@r{]}
1570 @opindex fdump-ada-spec
1571 For C and C++ source and include files, generate corresponding Ada specs.
1572 @xref{Generating Ada Bindings for C and C++ headers,,, gnat_ugn,
1573 GNAT User's Guide}, which provides detailed documentation on this feature.
1575 @item -fada-spec-parent=@var{unit}
1576 @opindex fada-spec-parent
1577 In conjunction with @option{-fdump-ada-spec@r{[}-slim@r{]}} above, generate
1578 Ada specs as child units of parent @var{unit}.
1580 @item -fdump-go-spec=@var{file}
1581 @opindex fdump-go-spec
1582 For input files in any language, generate corresponding Go
1583 declarations in @var{file}. This generates Go @code{const},
1584 @code{type}, @code{var}, and @code{func} declarations which may be a
1585 useful way to start writing a Go interface to code written in some
1588 @include @value{srcdir}/../libiberty/at-file.texi
1592 @section Compiling C++ Programs
1594 @cindex suffixes for C++ source
1595 @cindex C++ source file suffixes
1596 C++ source files conventionally use one of the suffixes @samp{.C},
1597 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
1598 @samp{.cxx}; C++ header files often use @samp{.hh}, @samp{.hpp},
1599 @samp{.H}, or (for shared template code) @samp{.tcc}; and
1600 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
1601 files with these names and compiles them as C++ programs even if you
1602 call the compiler the same way as for compiling C programs (usually
1603 with the name @command{gcc}).
1607 However, the use of @command{gcc} does not add the C++ library.
1608 @command{g++} is a program that calls GCC and automatically specifies linking
1609 against the C++ library. It treats @samp{.c},
1610 @samp{.h} and @samp{.i} files as C++ source files instead of C source
1611 files unless @option{-x} is used. This program is also useful when
1612 precompiling a C header file with a @samp{.h} extension for use in C++
1613 compilations. On many systems, @command{g++} is also installed with
1614 the name @command{c++}.
1616 @cindex invoking @command{g++}
1617 When you compile C++ programs, you may specify many of the same
1618 command-line options that you use for compiling programs in any
1619 language; or command-line options meaningful for C and related
1620 languages; or options that are meaningful only for C++ programs.
1621 @xref{C Dialect Options,,Options Controlling C Dialect}, for
1622 explanations of options for languages related to C@.
1623 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
1624 explanations of options that are meaningful only for C++ programs.
1626 @node C Dialect Options
1627 @section Options Controlling C Dialect
1628 @cindex dialect options
1629 @cindex language dialect options
1630 @cindex options, dialect
1632 The following options control the dialect of C (or languages derived
1633 from C, such as C++, Objective-C and Objective-C++) that the compiler
1637 @cindex ANSI support
1641 In C mode, this is equivalent to @option{-std=c90}. In C++ mode, it is
1642 equivalent to @option{-std=c++98}.
1644 This turns off certain features of GCC that are incompatible with ISO
1645 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
1646 such as the @code{asm} and @code{typeof} keywords, and
1647 predefined macros such as @code{unix} and @code{vax} that identify the
1648 type of system you are using. It also enables the undesirable and
1649 rarely used ISO trigraph feature. For the C compiler,
1650 it disables recognition of C++ style @samp{//} comments as well as
1651 the @code{inline} keyword.
1653 The alternate keywords @code{__asm__}, @code{__extension__},
1654 @code{__inline__} and @code{__typeof__} continue to work despite
1655 @option{-ansi}. You would not want to use them in an ISO C program, of
1656 course, but it is useful to put them in header files that might be included
1657 in compilations done with @option{-ansi}. Alternate predefined macros
1658 such as @code{__unix__} and @code{__vax__} are also available, with or
1659 without @option{-ansi}.
1661 The @option{-ansi} option does not cause non-ISO programs to be
1662 rejected gratuitously. For that, @option{-Wpedantic} is required in
1663 addition to @option{-ansi}. @xref{Warning Options}.
1665 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1666 option is used. Some header files may notice this macro and refrain
1667 from declaring certain functions or defining certain macros that the
1668 ISO standard doesn't call for; this is to avoid interfering with any
1669 programs that might use these names for other things.
1671 Functions that are normally built in but do not have semantics
1672 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1673 functions when @option{-ansi} is used. @xref{Other Builtins,,Other
1674 built-in functions provided by GCC}, for details of the functions
1679 Determine the language standard. @xref{Standards,,Language Standards
1680 Supported by GCC}, for details of these standard versions. This option
1681 is currently only supported when compiling C or C++.
1683 The compiler can accept several base standards, such as @samp{c90} or
1684 @samp{c++98}, and GNU dialects of those standards, such as
1685 @samp{gnu90} or @samp{gnu++98}. When a base standard is specified, the
1686 compiler accepts all programs following that standard plus those
1687 using GNU extensions that do not contradict it. For example,
1688 @option{-std=c90} turns off certain features of GCC that are
1689 incompatible with ISO C90, such as the @code{asm} and @code{typeof}
1690 keywords, but not other GNU extensions that do not have a meaning in
1691 ISO C90, such as omitting the middle term of a @code{?:}
1692 expression. On the other hand, when a GNU dialect of a standard is
1693 specified, all features supported by the compiler are enabled, even when
1694 those features change the meaning of the base standard. As a result, some
1695 strict-conforming programs may be rejected. The particular standard
1696 is used by @option{-Wpedantic} to identify which features are GNU
1697 extensions given that version of the standard. For example
1698 @option{-std=gnu90 -Wpedantic} warns about C++ style @samp{//}
1699 comments, while @option{-std=gnu99 -Wpedantic} does not.
1701 A value for this option must be provided; possible values are
1707 Support all ISO C90 programs (certain GNU extensions that conflict
1708 with ISO C90 are disabled). Same as @option{-ansi} for C code.
1710 @item iso9899:199409
1711 ISO C90 as modified in amendment 1.
1717 ISO C99. This standard is substantially completely supported, modulo
1718 bugs and floating-point issues
1719 (mainly but not entirely relating to optional C99 features from
1720 Annexes F and G). See
1721 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1722 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1727 ISO C11, the 2011 revision of the ISO C standard. This standard is
1728 substantially completely supported, modulo bugs, floating-point issues
1729 (mainly but not entirely relating to optional C11 features from
1730 Annexes F and G) and the optional Annexes K (Bounds-checking
1731 interfaces) and L (Analyzability). The name @samp{c1x} is deprecated.
1735 GNU dialect of ISO C90 (including some C99 features).
1739 GNU dialect of ISO C99. The name @samp{gnu9x} is deprecated.
1743 GNU dialect of ISO C11. This is the default for C code.
1744 The name @samp{gnu1x} is deprecated.
1748 The 1998 ISO C++ standard plus the 2003 technical corrigendum and some
1749 additional defect reports. Same as @option{-ansi} for C++ code.
1753 GNU dialect of @option{-std=c++98}. This is the default for
1758 The 2011 ISO C++ standard plus amendments.
1759 The name @samp{c++0x} is deprecated.
1763 GNU dialect of @option{-std=c++11}.
1764 The name @samp{gnu++0x} is deprecated.
1768 The 2014 ISO C++ standard plus amendments.
1769 The name @samp{c++1y} is deprecated.
1773 GNU dialect of @option{-std=c++14}.
1774 The name @samp{gnu++1y} is deprecated.
1777 The next revision of the ISO C++ standard, tentatively planned for
1778 2017. Support is highly experimental, and will almost certainly
1779 change in incompatible ways in future releases.
1782 GNU dialect of @option{-std=c++1z}. Support is highly experimental,
1783 and will almost certainly change in incompatible ways in future
1787 @item -fgnu89-inline
1788 @opindex fgnu89-inline
1789 The option @option{-fgnu89-inline} tells GCC to use the traditional
1790 GNU semantics for @code{inline} functions when in C99 mode.
1791 @xref{Inline,,An Inline Function is As Fast As a Macro}.
1792 Using this option is roughly equivalent to adding the
1793 @code{gnu_inline} function attribute to all inline functions
1794 (@pxref{Function Attributes}).
1796 The option @option{-fno-gnu89-inline} explicitly tells GCC to use the
1797 C99 semantics for @code{inline} when in C99 or gnu99 mode (i.e., it
1798 specifies the default behavior).
1799 This option is not supported in @option{-std=c90} or
1800 @option{-std=gnu90} mode.
1802 The preprocessor macros @code{__GNUC_GNU_INLINE__} and
1803 @code{__GNUC_STDC_INLINE__} may be used to check which semantics are
1804 in effect for @code{inline} functions. @xref{Common Predefined
1805 Macros,,,cpp,The C Preprocessor}.
1807 @item -aux-info @var{filename}
1809 Output to the given filename prototyped declarations for all functions
1810 declared and/or defined in a translation unit, including those in header
1811 files. This option is silently ignored in any language other than C@.
1813 Besides declarations, the file indicates, in comments, the origin of
1814 each declaration (source file and line), whether the declaration was
1815 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1816 @samp{O} for old, respectively, in the first character after the line
1817 number and the colon), and whether it came from a declaration or a
1818 definition (@samp{C} or @samp{F}, respectively, in the following
1819 character). In the case of function definitions, a K&R-style list of
1820 arguments followed by their declarations is also provided, inside
1821 comments, after the declaration.
1823 @item -fallow-parameterless-variadic-functions
1824 @opindex fallow-parameterless-variadic-functions
1825 Accept variadic functions without named parameters.
1827 Although it is possible to define such a function, this is not very
1828 useful as it is not possible to read the arguments. This is only
1829 supported for C as this construct is allowed by C++.
1833 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1834 keyword, so that code can use these words as identifiers. You can use
1835 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1836 instead. @option{-ansi} implies @option{-fno-asm}.
1838 In C++, this switch only affects the @code{typeof} keyword, since
1839 @code{asm} and @code{inline} are standard keywords. You may want to
1840 use the @option{-fno-gnu-keywords} flag instead, which has the same
1841 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1842 switch only affects the @code{asm} and @code{typeof} keywords, since
1843 @code{inline} is a standard keyword in ISO C99.
1846 @itemx -fno-builtin-@var{function}
1847 @opindex fno-builtin
1848 @cindex built-in functions
1849 Don't recognize built-in functions that do not begin with
1850 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1851 functions provided by GCC}, for details of the functions affected,
1852 including those which are not built-in functions when @option{-ansi} or
1853 @option{-std} options for strict ISO C conformance are used because they
1854 do not have an ISO standard meaning.
1856 GCC normally generates special code to handle certain built-in functions
1857 more efficiently; for instance, calls to @code{alloca} may become single
1858 instructions which adjust the stack directly, and calls to @code{memcpy}
1859 may become inline copy loops. The resulting code is often both smaller
1860 and faster, but since the function calls no longer appear as such, you
1861 cannot set a breakpoint on those calls, nor can you change the behavior
1862 of the functions by linking with a different library. In addition,
1863 when a function is recognized as a built-in function, GCC may use
1864 information about that function to warn about problems with calls to
1865 that function, or to generate more efficient code, even if the
1866 resulting code still contains calls to that function. For example,
1867 warnings are given with @option{-Wformat} for bad calls to
1868 @code{printf} when @code{printf} is built in and @code{strlen} is
1869 known not to modify global memory.
1871 With the @option{-fno-builtin-@var{function}} option
1872 only the built-in function @var{function} is
1873 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1874 function is named that is not built-in in this version of GCC, this
1875 option is ignored. There is no corresponding
1876 @option{-fbuiltin-@var{function}} option; if you wish to enable
1877 built-in functions selectively when using @option{-fno-builtin} or
1878 @option{-ffreestanding}, you may define macros such as:
1881 #define abs(n) __builtin_abs ((n))
1882 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1887 @cindex hosted environment
1889 Assert that compilation targets a hosted environment. This implies
1890 @option{-fbuiltin}. A hosted environment is one in which the
1891 entire standard library is available, and in which @code{main} has a return
1892 type of @code{int}. Examples are nearly everything except a kernel.
1893 This is equivalent to @option{-fno-freestanding}.
1895 @item -ffreestanding
1896 @opindex ffreestanding
1897 @cindex hosted environment
1899 Assert that compilation targets a freestanding environment. This
1900 implies @option{-fno-builtin}. A freestanding environment
1901 is one in which the standard library may not exist, and program startup may
1902 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1903 This is equivalent to @option{-fno-hosted}.
1905 @xref{Standards,,Language Standards Supported by GCC}, for details of
1906 freestanding and hosted environments.
1910 @cindex OpenACC accelerator programming
1911 Enable handling of OpenACC directives @code{#pragma acc} in C/C++ and
1912 @code{!$acc} in Fortran. When @option{-fopenacc} is specified, the
1913 compiler generates accelerated code according to the OpenACC Application
1914 Programming Interface v2.0 @w{@uref{http://www.openacc.org/}}. This option
1915 implies @option{-pthread}, and thus is only supported on targets that
1916 have support for @option{-pthread}.
1918 Note that this is an experimental feature, incomplete, and subject to
1919 change in future versions of GCC. See
1920 @w{@uref{https://gcc.gnu.org/wiki/OpenACC}} for more information.
1924 @cindex OpenMP parallel
1925 Enable handling of OpenMP directives @code{#pragma omp} in C/C++ and
1926 @code{!$omp} in Fortran. When @option{-fopenmp} is specified, the
1927 compiler generates parallel code according to the OpenMP Application
1928 Program Interface v4.0 @w{@uref{http://www.openmp.org/}}. This option
1929 implies @option{-pthread}, and thus is only supported on targets that
1930 have support for @option{-pthread}. @option{-fopenmp} implies
1931 @option{-fopenmp-simd}.
1934 @opindex fopenmp-simd
1937 Enable handling of OpenMP's SIMD directives with @code{#pragma omp}
1938 in C/C++ and @code{!$omp} in Fortran. Other OpenMP directives
1943 @cindex Enable Cilk Plus
1944 Enable the usage of Cilk Plus language extension features for C/C++.
1945 When the option @option{-fcilkplus} is specified, enable the usage of
1946 the Cilk Plus Language extension features for C/C++. The present
1947 implementation follows ABI version 1.2. This is an experimental
1948 feature that is only partially complete, and whose interface may
1949 change in future versions of GCC as the official specification
1950 changes. Currently, all features but @code{_Cilk_for} have been
1955 When the option @option{-fgnu-tm} is specified, the compiler
1956 generates code for the Linux variant of Intel's current Transactional
1957 Memory ABI specification document (Revision 1.1, May 6 2009). This is
1958 an experimental feature whose interface may change in future versions
1959 of GCC, as the official specification changes. Please note that not
1960 all architectures are supported for this feature.
1962 For more information on GCC's support for transactional memory,
1963 @xref{Enabling libitm,,The GNU Transactional Memory Library,libitm,GNU
1964 Transactional Memory Library}.
1966 Note that the transactional memory feature is not supported with
1967 non-call exceptions (@option{-fnon-call-exceptions}).
1969 @item -fms-extensions
1970 @opindex fms-extensions
1971 Accept some non-standard constructs used in Microsoft header files.
1973 In C++ code, this allows member names in structures to be similar
1974 to previous types declarations.
1983 Some cases of unnamed fields in structures and unions are only
1984 accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union
1985 fields within structs/unions}, for details.
1987 Note that this option is off for all targets but x86
1988 targets using ms-abi.
1990 @item -fplan9-extensions
1991 @opindex fplan9-extensions
1992 Accept some non-standard constructs used in Plan 9 code.
1994 This enables @option{-fms-extensions}, permits passing pointers to
1995 structures with anonymous fields to functions that expect pointers to
1996 elements of the type of the field, and permits referring to anonymous
1997 fields declared using a typedef. @xref{Unnamed Fields,,Unnamed
1998 struct/union fields within structs/unions}, for details. This is only
1999 supported for C, not C++.
2003 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
2004 options for strict ISO C conformance) implies @option{-trigraphs}.
2006 @cindex traditional C language
2007 @cindex C language, traditional
2009 @itemx -traditional-cpp
2010 @opindex traditional-cpp
2011 @opindex traditional
2012 Formerly, these options caused GCC to attempt to emulate a pre-standard
2013 C compiler. They are now only supported with the @option{-E} switch.
2014 The preprocessor continues to support a pre-standard mode. See the GNU
2015 CPP manual for details.
2017 @item -fcond-mismatch
2018 @opindex fcond-mismatch
2019 Allow conditional expressions with mismatched types in the second and
2020 third arguments. The value of such an expression is void. This option
2021 is not supported for C++.
2023 @item -flax-vector-conversions
2024 @opindex flax-vector-conversions
2025 Allow implicit conversions between vectors with differing numbers of
2026 elements and/or incompatible element types. This option should not be
2029 @item -funsigned-char
2030 @opindex funsigned-char
2031 Let the type @code{char} be unsigned, like @code{unsigned char}.
2033 Each kind of machine has a default for what @code{char} should
2034 be. It is either like @code{unsigned char} by default or like
2035 @code{signed char} by default.
2037 Ideally, a portable program should always use @code{signed char} or
2038 @code{unsigned char} when it depends on the signedness of an object.
2039 But many programs have been written to use plain @code{char} and
2040 expect it to be signed, or expect it to be unsigned, depending on the
2041 machines they were written for. This option, and its inverse, let you
2042 make such a program work with the opposite default.
2044 The type @code{char} is always a distinct type from each of
2045 @code{signed char} or @code{unsigned char}, even though its behavior
2046 is always just like one of those two.
2049 @opindex fsigned-char
2050 Let the type @code{char} be signed, like @code{signed char}.
2052 Note that this is equivalent to @option{-fno-unsigned-char}, which is
2053 the negative form of @option{-funsigned-char}. Likewise, the option
2054 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
2056 @item -fsigned-bitfields
2057 @itemx -funsigned-bitfields
2058 @itemx -fno-signed-bitfields
2059 @itemx -fno-unsigned-bitfields
2060 @opindex fsigned-bitfields
2061 @opindex funsigned-bitfields
2062 @opindex fno-signed-bitfields
2063 @opindex fno-unsigned-bitfields
2064 These options control whether a bit-field is signed or unsigned, when the
2065 declaration does not use either @code{signed} or @code{unsigned}. By
2066 default, such a bit-field is signed, because this is consistent: the
2067 basic integer types such as @code{int} are signed types.
2070 @node C++ Dialect Options
2071 @section Options Controlling C++ Dialect
2073 @cindex compiler options, C++
2074 @cindex C++ options, command-line
2075 @cindex options, C++
2076 This section describes the command-line options that are only meaningful
2077 for C++ programs. You can also use most of the GNU compiler options
2078 regardless of what language your program is in. For example, you
2079 might compile a file @file{firstClass.C} like this:
2082 g++ -g -frepo -O -c firstClass.C
2086 In this example, only @option{-frepo} is an option meant
2087 only for C++ programs; you can use the other options with any
2088 language supported by GCC@.
2090 Here is a list of options that are @emph{only} for compiling C++ programs:
2094 @item -fabi-version=@var{n}
2095 @opindex fabi-version
2096 Use version @var{n} of the C++ ABI@. The default is version 0.
2098 Version 0 refers to the version conforming most closely to
2099 the C++ ABI specification. Therefore, the ABI obtained using version 0
2100 will change in different versions of G++ as ABI bugs are fixed.
2102 Version 1 is the version of the C++ ABI that first appeared in G++ 3.2.
2104 Version 2 is the version of the C++ ABI that first appeared in G++
2105 3.4, and was the default through G++ 4.9.
2107 Version 3 corrects an error in mangling a constant address as a
2110 Version 4, which first appeared in G++ 4.5, implements a standard
2111 mangling for vector types.
2113 Version 5, which first appeared in G++ 4.6, corrects the mangling of
2114 attribute const/volatile on function pointer types, decltype of a
2115 plain decl, and use of a function parameter in the declaration of
2118 Version 6, which first appeared in G++ 4.7, corrects the promotion
2119 behavior of C++11 scoped enums and the mangling of template argument
2120 packs, const/static_cast, prefix ++ and --, and a class scope function
2121 used as a template argument.
2123 Version 7, which first appeared in G++ 4.8, that treats nullptr_t as a
2124 builtin type and corrects the mangling of lambdas in default argument
2127 Version 8, which first appeared in G++ 4.9, corrects the substitution
2128 behavior of function types with function-cv-qualifiers.
2130 See also @option{-Wabi}.
2132 @item -fabi-compat-version=@var{n}
2133 @opindex fabi-compat-version
2134 On targets that support strong aliases, G++
2135 works around mangling changes by creating an alias with the correct
2136 mangled name when defining a symbol with an incorrect mangled name.
2137 This switch specifies which ABI version to use for the alias.
2139 With @option{-fabi-version=0} (the default), this defaults to 2. If
2140 another ABI version is explicitly selected, this defaults to 0.
2142 The compatibility version is also set by @option{-Wabi=@var{n}}.
2144 @item -fno-access-control
2145 @opindex fno-access-control
2146 Turn off all access checking. This switch is mainly useful for working
2147 around bugs in the access control code.
2151 Check that the pointer returned by @code{operator new} is non-null
2152 before attempting to modify the storage allocated. This check is
2153 normally unnecessary because the C++ standard specifies that
2154 @code{operator new} only returns @code{0} if it is declared
2155 @code{throw()}, in which case the compiler always checks the
2156 return value even without this option. In all other cases, when
2157 @code{operator new} has a non-empty exception specification, memory
2158 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
2159 @samp{new (nothrow)}.
2161 @item -fconstexpr-depth=@var{n}
2162 @opindex fconstexpr-depth
2163 Set the maximum nested evaluation depth for C++11 constexpr functions
2164 to @var{n}. A limit is needed to detect endless recursion during
2165 constant expression evaluation. The minimum specified by the standard
2168 @item -fdeduce-init-list
2169 @opindex fdeduce-init-list
2170 Enable deduction of a template type parameter as
2171 @code{std::initializer_list} from a brace-enclosed initializer list, i.e.@:
2174 template <class T> auto forward(T t) -> decltype (realfn (t))
2181 forward(@{1,2@}); // call forward<std::initializer_list<int>>
2185 This deduction was implemented as a possible extension to the
2186 originally proposed semantics for the C++11 standard, but was not part
2187 of the final standard, so it is disabled by default. This option is
2188 deprecated, and may be removed in a future version of G++.
2190 @item -ffriend-injection
2191 @opindex ffriend-injection
2192 Inject friend functions into the enclosing namespace, so that they are
2193 visible outside the scope of the class in which they are declared.
2194 Friend functions were documented to work this way in the old Annotated
2195 C++ Reference Manual.
2196 However, in ISO C++ a friend function that is not declared
2197 in an enclosing scope can only be found using argument dependent
2198 lookup. GCC defaults to the standard behavior.
2200 This option is for compatibility, and may be removed in a future
2203 @item -fno-elide-constructors
2204 @opindex fno-elide-constructors
2205 The C++ standard allows an implementation to omit creating a temporary
2206 that is only used to initialize another object of the same type.
2207 Specifying this option disables that optimization, and forces G++ to
2208 call the copy constructor in all cases.
2210 @item -fno-enforce-eh-specs
2211 @opindex fno-enforce-eh-specs
2212 Don't generate code to check for violation of exception specifications
2213 at run time. This option violates the C++ standard, but may be useful
2214 for reducing code size in production builds, much like defining
2215 @code{NDEBUG}. This does not give user code permission to throw
2216 exceptions in violation of the exception specifications; the compiler
2217 still optimizes based on the specifications, so throwing an
2218 unexpected exception results in undefined behavior at run time.
2220 @item -fextern-tls-init
2221 @itemx -fno-extern-tls-init
2222 @opindex fextern-tls-init
2223 @opindex fno-extern-tls-init
2224 The C++11 and OpenMP standards allow @code{thread_local} and
2225 @code{threadprivate} variables to have dynamic (runtime)
2226 initialization. To support this, any use of such a variable goes
2227 through a wrapper function that performs any necessary initialization.
2228 When the use and definition of the variable are in the same
2229 translation unit, this overhead can be optimized away, but when the
2230 use is in a different translation unit there is significant overhead
2231 even if the variable doesn't actually need dynamic initialization. If
2232 the programmer can be sure that no use of the variable in a
2233 non-defining TU needs to trigger dynamic initialization (either
2234 because the variable is statically initialized, or a use of the
2235 variable in the defining TU will be executed before any uses in
2236 another TU), they can avoid this overhead with the
2237 @option{-fno-extern-tls-init} option.
2239 On targets that support symbol aliases, the default is
2240 @option{-fextern-tls-init}. On targets that do not support symbol
2241 aliases, the default is @option{-fno-extern-tls-init}.
2244 @itemx -fno-for-scope
2246 @opindex fno-for-scope
2247 If @option{-ffor-scope} is specified, the scope of variables declared in
2248 a @i{for-init-statement} is limited to the @code{for} loop itself,
2249 as specified by the C++ standard.
2250 If @option{-fno-for-scope} is specified, the scope of variables declared in
2251 a @i{for-init-statement} extends to the end of the enclosing scope,
2252 as was the case in old versions of G++, and other (traditional)
2253 implementations of C++.
2255 If neither flag is given, the default is to follow the standard,
2256 but to allow and give a warning for old-style code that would
2257 otherwise be invalid, or have different behavior.
2259 @item -fno-gnu-keywords
2260 @opindex fno-gnu-keywords
2261 Do not recognize @code{typeof} as a keyword, so that code can use this
2262 word as an identifier. You can use the keyword @code{__typeof__} instead.
2263 @option{-ansi} implies @option{-fno-gnu-keywords}.
2265 @item -fno-implicit-templates
2266 @opindex fno-implicit-templates
2267 Never emit code for non-inline templates that are instantiated
2268 implicitly (i.e.@: by use); only emit code for explicit instantiations.
2269 @xref{Template Instantiation}, for more information.
2271 @item -fno-implicit-inline-templates
2272 @opindex fno-implicit-inline-templates
2273 Don't emit code for implicit instantiations of inline templates, either.
2274 The default is to handle inlines differently so that compiles with and
2275 without optimization need the same set of explicit instantiations.
2277 @item -fno-implement-inlines
2278 @opindex fno-implement-inlines
2279 To save space, do not emit out-of-line copies of inline functions
2280 controlled by @code{#pragma implementation}. This causes linker
2281 errors if these functions are not inlined everywhere they are called.
2283 @item -fms-extensions
2284 @opindex fms-extensions
2285 Disable Wpedantic warnings about constructs used in MFC, such as implicit
2286 int and getting a pointer to member function via non-standard syntax.
2288 @item -fno-nonansi-builtins
2289 @opindex fno-nonansi-builtins
2290 Disable built-in declarations of functions that are not mandated by
2291 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
2292 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
2295 @opindex fnothrow-opt
2296 Treat a @code{throw()} exception specification as if it were a
2297 @code{noexcept} specification to reduce or eliminate the text size
2298 overhead relative to a function with no exception specification. If
2299 the function has local variables of types with non-trivial
2300 destructors, the exception specification actually makes the
2301 function smaller because the EH cleanups for those variables can be
2302 optimized away. The semantic effect is that an exception thrown out of
2303 a function with such an exception specification results in a call
2304 to @code{terminate} rather than @code{unexpected}.
2306 @item -fno-operator-names
2307 @opindex fno-operator-names
2308 Do not treat the operator name keywords @code{and}, @code{bitand},
2309 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
2310 synonyms as keywords.
2312 @item -fno-optional-diags
2313 @opindex fno-optional-diags
2314 Disable diagnostics that the standard says a compiler does not need to
2315 issue. Currently, the only such diagnostic issued by G++ is the one for
2316 a name having multiple meanings within a class.
2319 @opindex fpermissive
2320 Downgrade some diagnostics about nonconformant code from errors to
2321 warnings. Thus, using @option{-fpermissive} allows some
2322 nonconforming code to compile.
2324 @item -fno-pretty-templates
2325 @opindex fno-pretty-templates
2326 When an error message refers to a specialization of a function
2327 template, the compiler normally prints the signature of the
2328 template followed by the template arguments and any typedefs or
2329 typenames in the signature (e.g. @code{void f(T) [with T = int]}
2330 rather than @code{void f(int)}) so that it's clear which template is
2331 involved. When an error message refers to a specialization of a class
2332 template, the compiler omits any template arguments that match
2333 the default template arguments for that template. If either of these
2334 behaviors make it harder to understand the error message rather than
2335 easier, you can use @option{-fno-pretty-templates} to disable them.
2339 Enable automatic template instantiation at link time. This option also
2340 implies @option{-fno-implicit-templates}. @xref{Template
2341 Instantiation}, for more information.
2345 Disable generation of information about every class with virtual
2346 functions for use by the C++ run-time type identification features
2347 (@code{dynamic_cast} and @code{typeid}). If you don't use those parts
2348 of the language, you can save some space by using this flag. Note that
2349 exception handling uses the same information, but G++ generates it as
2350 needed. The @code{dynamic_cast} operator can still be used for casts that
2351 do not require run-time type information, i.e.@: casts to @code{void *} or to
2352 unambiguous base classes.
2354 @item -fsized-deallocation
2355 @opindex fsized-deallocation
2356 Enable the built-in global declarations
2358 void operator delete (void *, std::size_t) noexcept;
2359 void operator delete[] (void *, std::size_t) noexcept;
2361 as introduced in C++14. This is useful for user-defined replacement
2362 deallocation functions that, for example, use the size of the object
2363 to make deallocation faster. Enabled by default under
2364 @option{-std=c++14} and above. The flag @option{-Wsized-deallocation}
2365 warns about places that might want to add a definition.
2369 Emit statistics about front-end processing at the end of the compilation.
2370 This information is generally only useful to the G++ development team.
2372 @item -fstrict-enums
2373 @opindex fstrict-enums
2374 Allow the compiler to optimize using the assumption that a value of
2375 enumerated type can only be one of the values of the enumeration (as
2376 defined in the C++ standard; basically, a value that can be
2377 represented in the minimum number of bits needed to represent all the
2378 enumerators). This assumption may not be valid if the program uses a
2379 cast to convert an arbitrary integer value to the enumerated type.
2381 @item -ftemplate-backtrace-limit=@var{n}
2382 @opindex ftemplate-backtrace-limit
2383 Set the maximum number of template instantiation notes for a single
2384 warning or error to @var{n}. The default value is 10.
2386 @item -ftemplate-depth=@var{n}
2387 @opindex ftemplate-depth
2388 Set the maximum instantiation depth for template classes to @var{n}.
2389 A limit on the template instantiation depth is needed to detect
2390 endless recursions during template class instantiation. ANSI/ISO C++
2391 conforming programs must not rely on a maximum depth greater than 17
2392 (changed to 1024 in C++11). The default value is 900, as the compiler
2393 can run out of stack space before hitting 1024 in some situations.
2395 @item -fno-threadsafe-statics
2396 @opindex fno-threadsafe-statics
2397 Do not emit the extra code to use the routines specified in the C++
2398 ABI for thread-safe initialization of local statics. You can use this
2399 option to reduce code size slightly in code that doesn't need to be
2402 @item -fuse-cxa-atexit
2403 @opindex fuse-cxa-atexit
2404 Register destructors for objects with static storage duration with the
2405 @code{__cxa_atexit} function rather than the @code{atexit} function.
2406 This option is required for fully standards-compliant handling of static
2407 destructors, but only works if your C library supports
2408 @code{__cxa_atexit}.
2410 @item -fno-use-cxa-get-exception-ptr
2411 @opindex fno-use-cxa-get-exception-ptr
2412 Don't use the @code{__cxa_get_exception_ptr} runtime routine. This
2413 causes @code{std::uncaught_exception} to be incorrect, but is necessary
2414 if the runtime routine is not available.
2416 @item -fvisibility-inlines-hidden
2417 @opindex fvisibility-inlines-hidden
2418 This switch declares that the user does not attempt to compare
2419 pointers to inline functions or methods where the addresses of the two functions
2420 are taken in different shared objects.
2422 The effect of this is that GCC may, effectively, mark inline methods with
2423 @code{__attribute__ ((visibility ("hidden")))} so that they do not
2424 appear in the export table of a DSO and do not require a PLT indirection
2425 when used within the DSO@. Enabling this option can have a dramatic effect
2426 on load and link times of a DSO as it massively reduces the size of the
2427 dynamic export table when the library makes heavy use of templates.
2429 The behavior of this switch is not quite the same as marking the
2430 methods as hidden directly, because it does not affect static variables
2431 local to the function or cause the compiler to deduce that
2432 the function is defined in only one shared object.
2434 You may mark a method as having a visibility explicitly to negate the
2435 effect of the switch for that method. For example, if you do want to
2436 compare pointers to a particular inline method, you might mark it as
2437 having default visibility. Marking the enclosing class with explicit
2438 visibility has no effect.
2440 Explicitly instantiated inline methods are unaffected by this option
2441 as their linkage might otherwise cross a shared library boundary.
2442 @xref{Template Instantiation}.
2444 @item -fvisibility-ms-compat
2445 @opindex fvisibility-ms-compat
2446 This flag attempts to use visibility settings to make GCC's C++
2447 linkage model compatible with that of Microsoft Visual Studio.
2449 The flag makes these changes to GCC's linkage model:
2453 It sets the default visibility to @code{hidden}, like
2454 @option{-fvisibility=hidden}.
2457 Types, but not their members, are not hidden by default.
2460 The One Definition Rule is relaxed for types without explicit
2461 visibility specifications that are defined in more than one
2462 shared object: those declarations are permitted if they are
2463 permitted when this option is not used.
2466 In new code it is better to use @option{-fvisibility=hidden} and
2467 export those classes that are intended to be externally visible.
2468 Unfortunately it is possible for code to rely, perhaps accidentally,
2469 on the Visual Studio behavior.
2471 Among the consequences of these changes are that static data members
2472 of the same type with the same name but defined in different shared
2473 objects are different, so changing one does not change the other;
2474 and that pointers to function members defined in different shared
2475 objects may not compare equal. When this flag is given, it is a
2476 violation of the ODR to define types with the same name differently.
2478 @item -fvtable-verify=@r{[}std@r{|}preinit@r{|}none@r{]}
2479 @opindex fvtable-verify
2480 Turn on (or off, if using @option{-fvtable-verify=none}) the security
2481 feature that verifies at run time, for every virtual call, that
2482 the vtable pointer through which the call is made is valid for the type of
2483 the object, and has not been corrupted or overwritten. If an invalid vtable
2484 pointer is detected at run time, an error is reported and execution of the
2485 program is immediately halted.
2487 This option causes run-time data structures to be built at program startup,
2488 which are used for verifying the vtable pointers.
2489 The options @samp{std} and @samp{preinit}
2490 control the timing of when these data structures are built. In both cases the
2491 data structures are built before execution reaches @code{main}. Using
2492 @option{-fvtable-verify=std} causes the data structures to be built after
2493 shared libraries have been loaded and initialized.
2494 @option{-fvtable-verify=preinit} causes them to be built before shared
2495 libraries have been loaded and initialized.
2497 If this option appears multiple times in the command line with different
2498 values specified, @samp{none} takes highest priority over both @samp{std} and
2499 @samp{preinit}; @samp{preinit} takes priority over @samp{std}.
2503 When used in conjunction with @option{-fvtable-verify=std} or
2504 @option{-fvtable-verify=preinit}, causes debug versions of the
2505 runtime functions for the vtable verification feature to be called.
2506 This flag also causes the compiler to log information about which
2507 vtable pointers it finds for each class.
2508 This information is written to a file named @file{vtv_set_ptr_data.log}
2509 in the directory named by the environment variable @env{VTV_LOGS_DIR}
2510 if that is defined or the current working directory otherwise.
2512 Note: This feature @emph{appends} data to the log file. If you want a fresh log
2513 file, be sure to delete any existing one.
2516 @opindex fvtv-counts
2517 This is a debugging flag. When used in conjunction with
2518 @option{-fvtable-verify=std} or @option{-fvtable-verify=preinit}, this
2519 causes the compiler to keep track of the total number of virtual calls
2520 it encounters and the number of verifications it inserts. It also
2521 counts the number of calls to certain run-time library functions
2522 that it inserts and logs this information for each compilation unit.
2523 The compiler writes this information to a file named
2524 @file{vtv_count_data.log} in the directory named by the environment
2525 variable @env{VTV_LOGS_DIR} if that is defined or the current working
2526 directory otherwise. It also counts the size of the vtable pointer sets
2527 for each class, and writes this information to @file{vtv_class_set_sizes.log}
2528 in the same directory.
2530 Note: This feature @emph{appends} data to the log files. To get fresh log
2531 files, be sure to delete any existing ones.
2535 Do not use weak symbol support, even if it is provided by the linker.
2536 By default, G++ uses weak symbols if they are available. This
2537 option exists only for testing, and should not be used by end-users;
2538 it results in inferior code and has no benefits. This option may
2539 be removed in a future release of G++.
2543 Do not search for header files in the standard directories specific to
2544 C++, but do still search the other standard directories. (This option
2545 is used when building the C++ library.)
2548 In addition, these optimization, warning, and code generation options
2549 have meanings only for C++ programs:
2552 @item -Wabi @r{(C, Objective-C, C++ and Objective-C++ only)}
2555 When an explicit @option{-fabi-version=@var{n}} option is used, causes
2556 G++ to warn when it generates code that is probably not compatible with the
2557 vendor-neutral C++ ABI@. Since G++ now defaults to
2558 @option{-fabi-version=0}, @option{-Wabi} has no effect unless either
2559 an older ABI version is selected (with @option{-fabi-version=@var{n}})
2560 or an older compatibility version is selected (with
2561 @option{-Wabi=@var{n}} or @option{-fabi-compat-version=@var{n}}).
2563 Although an effort has been made to warn about
2564 all such cases, there are probably some cases that are not warned about,
2565 even though G++ is generating incompatible code. There may also be
2566 cases where warnings are emitted even though the code that is generated
2569 You should rewrite your code to avoid these warnings if you are
2570 concerned about the fact that code generated by G++ may not be binary
2571 compatible with code generated by other compilers.
2573 @option{-Wabi} can also be used with an explicit version number to
2574 warn about compatibility with a particular @option{-fabi-version}
2575 level, e.g. @option{-Wabi=2} to warn about changes relative to
2576 @option{-fabi-version=2}. Specifying a version number also sets
2577 @option{-fabi-compat-version=@var{n}}.
2579 The known incompatibilities in @option{-fabi-version=2} (which was the
2580 default from GCC 3.4 to 4.9) include:
2585 A template with a non-type template parameter of reference type was
2586 mangled incorrectly:
2589 template <int &> struct S @{@};
2593 This was fixed in @option{-fabi-version=3}.
2596 SIMD vector types declared using @code{__attribute ((vector_size))} were
2597 mangled in a non-standard way that does not allow for overloading of
2598 functions taking vectors of different sizes.
2600 The mangling was changed in @option{-fabi-version=4}.
2603 @code{__attribute ((const))} and @code{noreturn} were mangled as type
2604 qualifiers, and @code{decltype} of a plain declaration was folded away.
2606 These mangling issues were fixed in @option{-fabi-version=5}.
2609 Scoped enumerators passed as arguments to a variadic function are
2610 promoted like unscoped enumerators, causing @code{va_arg} to complain.
2611 On most targets this does not actually affect the parameter passing
2612 ABI, as there is no way to pass an argument smaller than @code{int}.
2614 Also, the ABI changed the mangling of template argument packs,
2615 @code{const_cast}, @code{static_cast}, prefix increment/decrement, and
2616 a class scope function used as a template argument.
2618 These issues were corrected in @option{-fabi-version=6}.
2621 Lambdas in default argument scope were mangled incorrectly, and the
2622 ABI changed the mangling of @code{nullptr_t}.
2624 These issues were corrected in @option{-fabi-version=7}.
2627 When mangling a function type with function-cv-qualifiers, the
2628 un-qualified function type was incorrectly treated as a substitution
2631 This was fixed in @option{-fabi-version=8}.
2634 It also warns about psABI-related changes. The known psABI changes at this
2640 For SysV/x86-64, unions with @code{long double} members are
2641 passed in memory as specified in psABI. For example:
2651 @code{union U} is always passed in memory.
2655 @item -Wabi-tag @r{(C++ and Objective-C++ only)}
2658 Warn when a type with an ABI tag is used in a context that does not
2659 have that ABI tag. See @ref{C++ Attributes} for more information
2662 @item -Wctor-dtor-privacy @r{(C++ and Objective-C++ only)}
2663 @opindex Wctor-dtor-privacy
2664 @opindex Wno-ctor-dtor-privacy
2665 Warn when a class seems unusable because all the constructors or
2666 destructors in that class are private, and it has neither friends nor
2667 public static member functions. Also warn if there are no non-private
2668 methods, and there's at least one private member function that isn't
2669 a constructor or destructor.
2671 @item -Wdelete-non-virtual-dtor @r{(C++ and Objective-C++ only)}
2672 @opindex Wdelete-non-virtual-dtor
2673 @opindex Wno-delete-non-virtual-dtor
2674 Warn when @code{delete} is used to destroy an instance of a class that
2675 has virtual functions and non-virtual destructor. It is unsafe to delete
2676 an instance of a derived class through a pointer to a base class if the
2677 base class does not have a virtual destructor. This warning is enabled
2680 @item -Wliteral-suffix @r{(C++ and Objective-C++ only)}
2681 @opindex Wliteral-suffix
2682 @opindex Wno-literal-suffix
2683 Warn when a string or character literal is followed by a ud-suffix which does
2684 not begin with an underscore. As a conforming extension, GCC treats such
2685 suffixes as separate preprocessing tokens in order to maintain backwards
2686 compatibility with code that uses formatting macros from @code{<inttypes.h>}.
2690 #define __STDC_FORMAT_MACROS
2691 #include <inttypes.h>
2696 printf("My int64: %" PRId64"\n", i64);
2700 In this case, @code{PRId64} is treated as a separate preprocessing token.
2702 This warning is enabled by default.
2704 @item -Wlto-type-mismatch
2705 @opindex Wlto-type-mismatch
2706 @opindex Wno-lto-type-mistmach
2708 During the link-time optimization warn about type mismatches in between
2709 global declarations from different compilation units.
2710 Requires @option{-flto} to be enabled. Enabled by default.
2712 @item -Wnarrowing @r{(C++ and Objective-C++ only)}
2714 @opindex Wno-narrowing
2715 Warn when a narrowing conversion prohibited by C++11 occurs within
2719 int i = @{ 2.2 @}; // error: narrowing from double to int
2722 This flag is included in @option{-Wall} and @option{-Wc++11-compat}.
2724 With @option{-std=c++11}, @option{-Wno-narrowing} suppresses the diagnostic
2725 required by the standard. Note that this does not affect the meaning
2726 of well-formed code; narrowing conversions are still considered
2727 ill-formed in SFINAE context.
2729 @item -Wnoexcept @r{(C++ and Objective-C++ only)}
2731 @opindex Wno-noexcept
2732 Warn when a noexcept-expression evaluates to false because of a call
2733 to a function that does not have a non-throwing exception
2734 specification (i.e. @code{throw()} or @code{noexcept}) but is known by
2735 the compiler to never throw an exception.
2737 @item -Wnon-virtual-dtor @r{(C++ and Objective-C++ only)}
2738 @opindex Wnon-virtual-dtor
2739 @opindex Wno-non-virtual-dtor
2740 Warn when a class has virtual functions and an accessible non-virtual
2741 destructor itself or in an accessible polymorphic base class, in which
2742 case it is possible but unsafe to delete an instance of a derived
2743 class through a pointer to the class itself or base class. This
2744 warning is automatically enabled if @option{-Weffc++} is specified.
2746 @item -Wreorder @r{(C++ and Objective-C++ only)}
2748 @opindex Wno-reorder
2749 @cindex reordering, warning
2750 @cindex warning for reordering of member initializers
2751 Warn when the order of member initializers given in the code does not
2752 match the order in which they must be executed. For instance:
2758 A(): j (0), i (1) @{ @}
2763 The compiler rearranges the member initializers for @code{i}
2764 and @code{j} to match the declaration order of the members, emitting
2765 a warning to that effect. This warning is enabled by @option{-Wall}.
2767 @item -fext-numeric-literals @r{(C++ and Objective-C++ only)}
2768 @opindex fext-numeric-literals
2769 @opindex fno-ext-numeric-literals
2770 Accept imaginary, fixed-point, or machine-defined
2771 literal number suffixes as GNU extensions.
2772 When this option is turned off these suffixes are treated
2773 as C++11 user-defined literal numeric suffixes.
2774 This is on by default for all pre-C++11 dialects and all GNU dialects:
2775 @option{-std=c++98}, @option{-std=gnu++98}, @option{-std=gnu++11},
2776 @option{-std=gnu++14}.
2777 This option is off by default
2778 for ISO C++11 onwards (@option{-std=c++11}, ...).
2781 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
2784 @item -Weffc++ @r{(C++ and Objective-C++ only)}
2787 Warn about violations of the following style guidelines from Scott Meyers'
2788 @cite{Effective C++} series of books:
2792 Define a copy constructor and an assignment operator for classes
2793 with dynamically-allocated memory.
2796 Prefer initialization to assignment in constructors.
2799 Have @code{operator=} return a reference to @code{*this}.
2802 Don't try to return a reference when you must return an object.
2805 Distinguish between prefix and postfix forms of increment and
2806 decrement operators.
2809 Never overload @code{&&}, @code{||}, or @code{,}.
2813 This option also enables @option{-Wnon-virtual-dtor}, which is also
2814 one of the effective C++ recommendations. However, the check is
2815 extended to warn about the lack of virtual destructor in accessible
2816 non-polymorphic bases classes too.
2818 When selecting this option, be aware that the standard library
2819 headers do not obey all of these guidelines; use @samp{grep -v}
2820 to filter out those warnings.
2822 @item -Wstrict-null-sentinel @r{(C++ and Objective-C++ only)}
2823 @opindex Wstrict-null-sentinel
2824 @opindex Wno-strict-null-sentinel
2825 Warn about the use of an uncasted @code{NULL} as sentinel. When
2826 compiling only with GCC this is a valid sentinel, as @code{NULL} is defined
2827 to @code{__null}. Although it is a null pointer constant rather than a
2828 null pointer, it is guaranteed to be of the same size as a pointer.
2829 But this use is not portable across different compilers.
2831 @item -Wno-non-template-friend @r{(C++ and Objective-C++ only)}
2832 @opindex Wno-non-template-friend
2833 @opindex Wnon-template-friend
2834 Disable warnings when non-templatized friend functions are declared
2835 within a template. Since the advent of explicit template specification
2836 support in G++, if the name of the friend is an unqualified-id (i.e.,
2837 @samp{friend foo(int)}), the C++ language specification demands that the
2838 friend declare or define an ordinary, nontemplate function. (Section
2839 14.5.3). Before G++ implemented explicit specification, unqualified-ids
2840 could be interpreted as a particular specialization of a templatized
2841 function. Because this non-conforming behavior is no longer the default
2842 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
2843 check existing code for potential trouble spots and is on by default.
2844 This new compiler behavior can be turned off with
2845 @option{-Wno-non-template-friend}, which keeps the conformant compiler code
2846 but disables the helpful warning.
2848 @item -Wold-style-cast @r{(C++ and Objective-C++ only)}
2849 @opindex Wold-style-cast
2850 @opindex Wno-old-style-cast
2851 Warn if an old-style (C-style) cast to a non-void type is used within
2852 a C++ program. The new-style casts (@code{dynamic_cast},
2853 @code{static_cast}, @code{reinterpret_cast}, and @code{const_cast}) are
2854 less vulnerable to unintended effects and much easier to search for.
2856 @item -Woverloaded-virtual @r{(C++ and Objective-C++ only)}
2857 @opindex Woverloaded-virtual
2858 @opindex Wno-overloaded-virtual
2859 @cindex overloaded virtual function, warning
2860 @cindex warning for overloaded virtual function
2861 Warn when a function declaration hides virtual functions from a
2862 base class. For example, in:
2869 struct B: public A @{
2874 the @code{A} class version of @code{f} is hidden in @code{B}, and code
2885 @item -Wno-pmf-conversions @r{(C++ and Objective-C++ only)}
2886 @opindex Wno-pmf-conversions
2887 @opindex Wpmf-conversions
2888 Disable the diagnostic for converting a bound pointer to member function
2891 @item -Wsign-promo @r{(C++ and Objective-C++ only)}
2892 @opindex Wsign-promo
2893 @opindex Wno-sign-promo
2894 Warn when overload resolution chooses a promotion from unsigned or
2895 enumerated type to a signed type, over a conversion to an unsigned type of
2896 the same size. Previous versions of G++ tried to preserve
2897 unsignedness, but the standard mandates the current behavior.
2899 @item -Wno-terminate @r{(C++ and Objective-C++ only)}
2901 @opindex Wno-terminate
2902 Disable the warning about a throw-expression that will immediately
2903 result in a call to @code{terminate}.
2906 @node Objective-C and Objective-C++ Dialect Options
2907 @section Options Controlling Objective-C and Objective-C++ Dialects
2909 @cindex compiler options, Objective-C and Objective-C++
2910 @cindex Objective-C and Objective-C++ options, command-line
2911 @cindex options, Objective-C and Objective-C++
2912 (NOTE: This manual does not describe the Objective-C and Objective-C++
2913 languages themselves. @xref{Standards,,Language Standards
2914 Supported by GCC}, for references.)
2916 This section describes the command-line options that are only meaningful
2917 for Objective-C and Objective-C++ programs. You can also use most of
2918 the language-independent GNU compiler options.
2919 For example, you might compile a file @file{some_class.m} like this:
2922 gcc -g -fgnu-runtime -O -c some_class.m
2926 In this example, @option{-fgnu-runtime} is an option meant only for
2927 Objective-C and Objective-C++ programs; you can use the other options with
2928 any language supported by GCC@.
2930 Note that since Objective-C is an extension of the C language, Objective-C
2931 compilations may also use options specific to the C front-end (e.g.,
2932 @option{-Wtraditional}). Similarly, Objective-C++ compilations may use
2933 C++-specific options (e.g., @option{-Wabi}).
2935 Here is a list of options that are @emph{only} for compiling Objective-C
2936 and Objective-C++ programs:
2939 @item -fconstant-string-class=@var{class-name}
2940 @opindex fconstant-string-class
2941 Use @var{class-name} as the name of the class to instantiate for each
2942 literal string specified with the syntax @code{@@"@dots{}"}. The default
2943 class name is @code{NXConstantString} if the GNU runtime is being used, and
2944 @code{NSConstantString} if the NeXT runtime is being used (see below). The
2945 @option{-fconstant-cfstrings} option, if also present, overrides the
2946 @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
2947 to be laid out as constant CoreFoundation strings.
2950 @opindex fgnu-runtime
2951 Generate object code compatible with the standard GNU Objective-C
2952 runtime. This is the default for most types of systems.
2954 @item -fnext-runtime
2955 @opindex fnext-runtime
2956 Generate output compatible with the NeXT runtime. This is the default
2957 for NeXT-based systems, including Darwin and Mac OS X@. The macro
2958 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
2961 @item -fno-nil-receivers
2962 @opindex fno-nil-receivers
2963 Assume that all Objective-C message dispatches (@code{[receiver
2964 message:arg]}) in this translation unit ensure that the receiver is
2965 not @code{nil}. This allows for more efficient entry points in the
2966 runtime to be used. This option is only available in conjunction with
2967 the NeXT runtime and ABI version 0 or 1.
2969 @item -fobjc-abi-version=@var{n}
2970 @opindex fobjc-abi-version
2971 Use version @var{n} of the Objective-C ABI for the selected runtime.
2972 This option is currently supported only for the NeXT runtime. In that
2973 case, Version 0 is the traditional (32-bit) ABI without support for
2974 properties and other Objective-C 2.0 additions. Version 1 is the
2975 traditional (32-bit) ABI with support for properties and other
2976 Objective-C 2.0 additions. Version 2 is the modern (64-bit) ABI. If
2977 nothing is specified, the default is Version 0 on 32-bit target
2978 machines, and Version 2 on 64-bit target machines.
2980 @item -fobjc-call-cxx-cdtors
2981 @opindex fobjc-call-cxx-cdtors
2982 For each Objective-C class, check if any of its instance variables is a
2983 C++ object with a non-trivial default constructor. If so, synthesize a
2984 special @code{- (id) .cxx_construct} instance method which runs
2985 non-trivial default constructors on any such instance variables, in order,
2986 and then return @code{self}. Similarly, check if any instance variable
2987 is a C++ object with a non-trivial destructor, and if so, synthesize a
2988 special @code{- (void) .cxx_destruct} method which runs
2989 all such default destructors, in reverse order.
2991 The @code{- (id) .cxx_construct} and @code{- (void) .cxx_destruct}
2992 methods thusly generated only operate on instance variables
2993 declared in the current Objective-C class, and not those inherited
2994 from superclasses. It is the responsibility of the Objective-C
2995 runtime to invoke all such methods in an object's inheritance
2996 hierarchy. The @code{- (id) .cxx_construct} methods are invoked
2997 by the runtime immediately after a new object instance is allocated;
2998 the @code{- (void) .cxx_destruct} methods are invoked immediately
2999 before the runtime deallocates an object instance.
3001 As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has
3002 support for invoking the @code{- (id) .cxx_construct} and
3003 @code{- (void) .cxx_destruct} methods.
3005 @item -fobjc-direct-dispatch
3006 @opindex fobjc-direct-dispatch
3007 Allow fast jumps to the message dispatcher. On Darwin this is
3008 accomplished via the comm page.
3010 @item -fobjc-exceptions
3011 @opindex fobjc-exceptions
3012 Enable syntactic support for structured exception handling in
3013 Objective-C, similar to what is offered by C++ and Java. This option
3014 is required to use the Objective-C keywords @code{@@try},
3015 @code{@@throw}, @code{@@catch}, @code{@@finally} and
3016 @code{@@synchronized}. This option is available with both the GNU
3017 runtime and the NeXT runtime (but not available in conjunction with
3018 the NeXT runtime on Mac OS X 10.2 and earlier).
3022 Enable garbage collection (GC) in Objective-C and Objective-C++
3023 programs. This option is only available with the NeXT runtime; the
3024 GNU runtime has a different garbage collection implementation that
3025 does not require special compiler flags.
3027 @item -fobjc-nilcheck
3028 @opindex fobjc-nilcheck
3029 For the NeXT runtime with version 2 of the ABI, check for a nil
3030 receiver in method invocations before doing the actual method call.
3031 This is the default and can be disabled using
3032 @option{-fno-objc-nilcheck}. Class methods and super calls are never
3033 checked for nil in this way no matter what this flag is set to.
3034 Currently this flag does nothing when the GNU runtime, or an older
3035 version of the NeXT runtime ABI, is used.
3037 @item -fobjc-std=objc1
3039 Conform to the language syntax of Objective-C 1.0, the language
3040 recognized by GCC 4.0. This only affects the Objective-C additions to
3041 the C/C++ language; it does not affect conformance to C/C++ standards,
3042 which is controlled by the separate C/C++ dialect option flags. When
3043 this option is used with the Objective-C or Objective-C++ compiler,
3044 any Objective-C syntax that is not recognized by GCC 4.0 is rejected.
3045 This is useful if you need to make sure that your Objective-C code can
3046 be compiled with older versions of GCC@.
3048 @item -freplace-objc-classes
3049 @opindex freplace-objc-classes
3050 Emit a special marker instructing @command{ld(1)} not to statically link in
3051 the resulting object file, and allow @command{dyld(1)} to load it in at
3052 run time instead. This is used in conjunction with the Fix-and-Continue
3053 debugging mode, where the object file in question may be recompiled and
3054 dynamically reloaded in the course of program execution, without the need
3055 to restart the program itself. Currently, Fix-and-Continue functionality
3056 is only available in conjunction with the NeXT runtime on Mac OS X 10.3
3061 When compiling for the NeXT runtime, the compiler ordinarily replaces calls
3062 to @code{objc_getClass("@dots{}")} (when the name of the class is known at
3063 compile time) with static class references that get initialized at load time,
3064 which improves run-time performance. Specifying the @option{-fzero-link} flag
3065 suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
3066 to be retained. This is useful in Zero-Link debugging mode, since it allows
3067 for individual class implementations to be modified during program execution.
3068 The GNU runtime currently always retains calls to @code{objc_get_class("@dots{}")}
3069 regardless of command-line options.
3071 @item -fno-local-ivars
3072 @opindex fno-local-ivars
3073 @opindex flocal-ivars
3074 By default instance variables in Objective-C can be accessed as if
3075 they were local variables from within the methods of the class they're
3076 declared in. This can lead to shadowing between instance variables
3077 and other variables declared either locally inside a class method or
3078 globally with the same name. Specifying the @option{-fno-local-ivars}
3079 flag disables this behavior thus avoiding variable shadowing issues.
3081 @item -fivar-visibility=@r{[}public@r{|}protected@r{|}private@r{|}package@r{]}
3082 @opindex fivar-visibility
3083 Set the default instance variable visibility to the specified option
3084 so that instance variables declared outside the scope of any access
3085 modifier directives default to the specified visibility.
3089 Dump interface declarations for all classes seen in the source file to a
3090 file named @file{@var{sourcename}.decl}.
3092 @item -Wassign-intercept @r{(Objective-C and Objective-C++ only)}
3093 @opindex Wassign-intercept
3094 @opindex Wno-assign-intercept
3095 Warn whenever an Objective-C assignment is being intercepted by the
3098 @item -Wno-protocol @r{(Objective-C and Objective-C++ only)}
3099 @opindex Wno-protocol
3101 If a class is declared to implement a protocol, a warning is issued for
3102 every method in the protocol that is not implemented by the class. The
3103 default behavior is to issue a warning for every method not explicitly
3104 implemented in the class, even if a method implementation is inherited
3105 from the superclass. If you use the @option{-Wno-protocol} option, then
3106 methods inherited from the superclass are considered to be implemented,
3107 and no warning is issued for them.
3109 @item -Wselector @r{(Objective-C and Objective-C++ only)}
3111 @opindex Wno-selector
3112 Warn if multiple methods of different types for the same selector are
3113 found during compilation. The check is performed on the list of methods
3114 in the final stage of compilation. Additionally, a check is performed
3115 for each selector appearing in a @code{@@selector(@dots{})}
3116 expression, and a corresponding method for that selector has been found
3117 during compilation. Because these checks scan the method table only at
3118 the end of compilation, these warnings are not produced if the final
3119 stage of compilation is not reached, for example because an error is
3120 found during compilation, or because the @option{-fsyntax-only} option is
3123 @item -Wstrict-selector-match @r{(Objective-C and Objective-C++ only)}
3124 @opindex Wstrict-selector-match
3125 @opindex Wno-strict-selector-match
3126 Warn if multiple methods with differing argument and/or return types are
3127 found for a given selector when attempting to send a message using this
3128 selector to a receiver of type @code{id} or @code{Class}. When this flag
3129 is off (which is the default behavior), the compiler omits such warnings
3130 if any differences found are confined to types that share the same size
3133 @item -Wundeclared-selector @r{(Objective-C and Objective-C++ only)}
3134 @opindex Wundeclared-selector
3135 @opindex Wno-undeclared-selector
3136 Warn if a @code{@@selector(@dots{})} expression referring to an
3137 undeclared selector is found. A selector is considered undeclared if no
3138 method with that name has been declared before the
3139 @code{@@selector(@dots{})} expression, either explicitly in an
3140 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
3141 an @code{@@implementation} section. This option always performs its
3142 checks as soon as a @code{@@selector(@dots{})} expression is found,
3143 while @option{-Wselector} only performs its checks in the final stage of
3144 compilation. This also enforces the coding style convention
3145 that methods and selectors must be declared before being used.
3147 @item -print-objc-runtime-info
3148 @opindex print-objc-runtime-info
3149 Generate C header describing the largest structure that is passed by
3154 @node Language Independent Options
3155 @section Options to Control Diagnostic Messages Formatting
3156 @cindex options to control diagnostics formatting
3157 @cindex diagnostic messages
3158 @cindex message formatting
3160 Traditionally, diagnostic messages have been formatted irrespective of
3161 the output device's aspect (e.g.@: its width, @dots{}). You can use the
3162 options described below
3163 to control the formatting algorithm for diagnostic messages,
3164 e.g.@: how many characters per line, how often source location
3165 information should be reported. Note that some language front ends may not
3166 honor these options.
3169 @item -fmessage-length=@var{n}
3170 @opindex fmessage-length
3171 Try to format error messages so that they fit on lines of about
3172 @var{n} characters. If @var{n} is zero, then no line-wrapping is
3173 done; each error message appears on a single line. This is the
3174 default for all front ends.
3176 @item -fdiagnostics-show-location=once
3177 @opindex fdiagnostics-show-location
3178 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
3179 reporter to emit source location information @emph{once}; that is, in
3180 case the message is too long to fit on a single physical line and has to
3181 be wrapped, the source location won't be emitted (as prefix) again,
3182 over and over, in subsequent continuation lines. This is the default
3185 @item -fdiagnostics-show-location=every-line
3186 Only meaningful in line-wrapping mode. Instructs the diagnostic
3187 messages reporter to emit the same source location information (as
3188 prefix) for physical lines that result from the process of breaking
3189 a message which is too long to fit on a single line.
3191 @item -fdiagnostics-color[=@var{WHEN}]
3192 @itemx -fno-diagnostics-color
3193 @opindex fdiagnostics-color
3194 @cindex highlight, color, colour
3195 @vindex GCC_COLORS @r{environment variable}
3196 Use color in diagnostics. @var{WHEN} is @samp{never}, @samp{always},
3197 or @samp{auto}. The default depends on how the compiler has been configured,
3198 it can be any of the above @var{WHEN} options or also @samp{never}
3199 if @env{GCC_COLORS} environment variable isn't present in the environment,
3200 and @samp{auto} otherwise.
3201 @samp{auto} means to use color only when the standard error is a terminal.
3202 The forms @option{-fdiagnostics-color} and @option{-fno-diagnostics-color} are
3203 aliases for @option{-fdiagnostics-color=always} and
3204 @option{-fdiagnostics-color=never}, respectively.
3206 The colors are defined by the environment variable @env{GCC_COLORS}.
3207 Its value is a colon-separated list of capabilities and Select Graphic
3208 Rendition (SGR) substrings. SGR commands are interpreted by the
3209 terminal or terminal emulator. (See the section in the documentation
3210 of your text terminal for permitted values and their meanings as
3211 character attributes.) These substring values are integers in decimal
3212 representation and can be concatenated with semicolons.
3213 Common values to concatenate include
3215 @samp{4} for underline,
3217 @samp{7} for inverse,
3218 @samp{39} for default foreground color,
3219 @samp{30} to @samp{37} for foreground colors,
3220 @samp{90} to @samp{97} for 16-color mode foreground colors,
3221 @samp{38;5;0} to @samp{38;5;255}
3222 for 88-color and 256-color modes foreground colors,
3223 @samp{49} for default background color,
3224 @samp{40} to @samp{47} for background colors,
3225 @samp{100} to @samp{107} for 16-color mode background colors,
3226 and @samp{48;5;0} to @samp{48;5;255}
3227 for 88-color and 256-color modes background colors.
3229 The default @env{GCC_COLORS} is
3231 error=01;31:warning=01;35:note=01;36:caret=01;32:locus=01:quote=01
3234 where @samp{01;31} is bold red, @samp{01;35} is bold magenta,
3235 @samp{01;36} is bold cyan, @samp{01;32} is bold green and
3236 @samp{01} is bold. Setting @env{GCC_COLORS} to the empty
3237 string disables colors.
3238 Supported capabilities are as follows.
3242 @vindex error GCC_COLORS @r{capability}
3243 SGR substring for error: markers.
3246 @vindex warning GCC_COLORS @r{capability}
3247 SGR substring for warning: markers.
3250 @vindex note GCC_COLORS @r{capability}
3251 SGR substring for note: markers.
3254 @vindex caret GCC_COLORS @r{capability}
3255 SGR substring for caret line.
3258 @vindex locus GCC_COLORS @r{capability}
3259 SGR substring for location information, @samp{file:line} or
3260 @samp{file:line:column} etc.
3263 @vindex quote GCC_COLORS @r{capability}
3264 SGR substring for information printed within quotes.
3267 @item -fno-diagnostics-show-option
3268 @opindex fno-diagnostics-show-option
3269 @opindex fdiagnostics-show-option
3270 By default, each diagnostic emitted includes text indicating the
3271 command-line option that directly controls the diagnostic (if such an
3272 option is known to the diagnostic machinery). Specifying the
3273 @option{-fno-diagnostics-show-option} flag suppresses that behavior.
3275 @item -fno-diagnostics-show-caret
3276 @opindex fno-diagnostics-show-caret
3277 @opindex fdiagnostics-show-caret
3278 By default, each diagnostic emitted includes the original source line
3279 and a caret '^' indicating the column. This option suppresses this
3280 information. The source line is truncated to @var{n} characters, if
3281 the @option{-fmessage-length=n} option is given. When the output is done
3282 to the terminal, the width is limited to the width given by the
3283 @env{COLUMNS} environment variable or, if not set, to the terminal width.
3287 @node Warning Options
3288 @section Options to Request or Suppress Warnings
3289 @cindex options to control warnings
3290 @cindex warning messages
3291 @cindex messages, warning
3292 @cindex suppressing warnings
3294 Warnings are diagnostic messages that report constructions that
3295 are not inherently erroneous but that are risky or suggest there
3296 may have been an error.
3298 The following language-independent options do not enable specific
3299 warnings but control the kinds of diagnostics produced by GCC@.
3302 @cindex syntax checking
3304 @opindex fsyntax-only
3305 Check the code for syntax errors, but don't do anything beyond that.
3307 @item -fmax-errors=@var{n}
3308 @opindex fmax-errors
3309 Limits the maximum number of error messages to @var{n}, at which point
3310 GCC bails out rather than attempting to continue processing the source
3311 code. If @var{n} is 0 (the default), there is no limit on the number
3312 of error messages produced. If @option{-Wfatal-errors} is also
3313 specified, then @option{-Wfatal-errors} takes precedence over this
3318 Inhibit all warning messages.
3323 Make all warnings into errors.
3328 Make the specified warning into an error. The specifier for a warning
3329 is appended; for example @option{-Werror=switch} turns the warnings
3330 controlled by @option{-Wswitch} into errors. This switch takes a
3331 negative form, to be used to negate @option{-Werror} for specific
3332 warnings; for example @option{-Wno-error=switch} makes
3333 @option{-Wswitch} warnings not be errors, even when @option{-Werror}
3336 The warning message for each controllable warning includes the
3337 option that controls the warning. That option can then be used with
3338 @option{-Werror=} and @option{-Wno-error=} as described above.
3339 (Printing of the option in the warning message can be disabled using the
3340 @option{-fno-diagnostics-show-option} flag.)
3342 Note that specifying @option{-Werror=}@var{foo} automatically implies
3343 @option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not
3346 @item -Wfatal-errors
3347 @opindex Wfatal-errors
3348 @opindex Wno-fatal-errors
3349 This option causes the compiler to abort compilation on the first error
3350 occurred rather than trying to keep going and printing further error
3355 You can request many specific warnings with options beginning with
3356 @samp{-W}, for example @option{-Wimplicit} to request warnings on
3357 implicit declarations. Each of these specific warning options also
3358 has a negative form beginning @samp{-Wno-} to turn off warnings; for
3359 example, @option{-Wno-implicit}. This manual lists only one of the
3360 two forms, whichever is not the default. For further
3361 language-specific options also refer to @ref{C++ Dialect Options} and
3362 @ref{Objective-C and Objective-C++ Dialect Options}.
3364 Some options, such as @option{-Wall} and @option{-Wextra}, turn on other
3365 options, such as @option{-Wunused}, which may turn on further options,
3366 such as @option{-Wunused-value}. The combined effect of positive and
3367 negative forms is that more specific options have priority over less
3368 specific ones, independently of their position in the command-line. For
3369 options of the same specificity, the last one takes effect. Options
3370 enabled or disabled via pragmas (@pxref{Diagnostic Pragmas}) take effect
3371 as if they appeared at the end of the command-line.
3373 When an unrecognized warning option is requested (e.g.,
3374 @option{-Wunknown-warning}), GCC emits a diagnostic stating
3375 that the option is not recognized. However, if the @option{-Wno-} form
3376 is used, the behavior is slightly different: no diagnostic is
3377 produced for @option{-Wno-unknown-warning} unless other diagnostics
3378 are being produced. This allows the use of new @option{-Wno-} options
3379 with old compilers, but if something goes wrong, the compiler
3380 warns that an unrecognized option is present.
3387 Issue all the warnings demanded by strict ISO C and ISO C++;
3388 reject all programs that use forbidden extensions, and some other
3389 programs that do not follow ISO C and ISO C++. For ISO C, follows the
3390 version of the ISO C standard specified by any @option{-std} option used.
3392 Valid ISO C and ISO C++ programs should compile properly with or without
3393 this option (though a rare few require @option{-ansi} or a
3394 @option{-std} option specifying the required version of ISO C)@. However,
3395 without this option, certain GNU extensions and traditional C and C++
3396 features are supported as well. With this option, they are rejected.
3398 @option{-Wpedantic} does not cause warning messages for use of the
3399 alternate keywords whose names begin and end with @samp{__}. Pedantic
3400 warnings are also disabled in the expression that follows
3401 @code{__extension__}. However, only system header files should use
3402 these escape routes; application programs should avoid them.
3403 @xref{Alternate Keywords}.
3405 Some users try to use @option{-Wpedantic} to check programs for strict ISO
3406 C conformance. They soon find that it does not do quite what they want:
3407 it finds some non-ISO practices, but not all---only those for which
3408 ISO C @emph{requires} a diagnostic, and some others for which
3409 diagnostics have been added.
3411 A feature to report any failure to conform to ISO C might be useful in
3412 some instances, but would require considerable additional work and would
3413 be quite different from @option{-Wpedantic}. We don't have plans to
3414 support such a feature in the near future.
3416 Where the standard specified with @option{-std} represents a GNU
3417 extended dialect of C, such as @samp{gnu90} or @samp{gnu99}, there is a
3418 corresponding @dfn{base standard}, the version of ISO C on which the GNU
3419 extended dialect is based. Warnings from @option{-Wpedantic} are given
3420 where they are required by the base standard. (It does not make sense
3421 for such warnings to be given only for features not in the specified GNU
3422 C dialect, since by definition the GNU dialects of C include all
3423 features the compiler supports with the given option, and there would be
3424 nothing to warn about.)
3426 @item -pedantic-errors
3427 @opindex pedantic-errors
3428 Give an error whenever the @dfn{base standard} (see @option{-Wpedantic})
3429 requires a diagnostic, in some cases where there is undefined behavior
3430 at compile-time and in some other cases that do not prevent compilation
3431 of programs that are valid according to the standard. This is not
3432 equivalent to @option{-Werror=pedantic}, since there are errors enabled
3433 by this option and not enabled by the latter and vice versa.
3438 This enables all the warnings about constructions that some users
3439 consider questionable, and that are easy to avoid (or modify to
3440 prevent the warning), even in conjunction with macros. This also
3441 enables some language-specific warnings described in @ref{C++ Dialect
3442 Options} and @ref{Objective-C and Objective-C++ Dialect Options}.
3444 @option{-Wall} turns on the following warning flags:
3446 @gccoptlist{-Waddress @gol
3447 -Warray-bounds=1 @r{(only with} @option{-O2}@r{)} @gol
3448 -Wc++11-compat -Wc++14-compat@gol
3449 -Wchar-subscripts @gol
3450 -Wenum-compare @r{(in C/ObjC; this is on by default in C++)} @gol
3451 -Wimplicit-int @r{(C and Objective-C only)} @gol
3452 -Wimplicit-function-declaration @r{(C and Objective-C only)} @gol
3455 -Wmain @r{(only for C/ObjC and unless} @option{-ffreestanding}@r{)} @gol
3456 -Wmaybe-uninitialized @gol
3457 -Wmissing-braces @r{(only for C/ObjC)} @gol
3464 -Wsequence-point @gol
3465 -Wsign-compare @r{(only in C++)} @gol
3466 -Wstrict-aliasing @gol
3467 -Wstrict-overflow=1 @gol
3470 -Wuninitialized @gol
3471 -Wunknown-pragmas @gol
3472 -Wunused-function @gol
3475 -Wunused-variable @gol
3476 -Wvolatile-register-var @gol
3479 Note that some warning flags are not implied by @option{-Wall}. Some of
3480 them warn about constructions that users generally do not consider
3481 questionable, but which occasionally you might wish to check for;
3482 others warn about constructions that are necessary or hard to avoid in
3483 some cases, and there is no simple way to modify the code to suppress
3484 the warning. Some of them are enabled by @option{-Wextra} but many of
3485 them must be enabled individually.
3491 This enables some extra warning flags that are not enabled by
3492 @option{-Wall}. (This option used to be called @option{-W}. The older
3493 name is still supported, but the newer name is more descriptive.)
3495 @gccoptlist{-Wclobbered @gol
3497 -Wignored-qualifiers @gol
3498 -Wmissing-field-initializers @gol
3499 -Wmissing-parameter-type @r{(C only)} @gol
3500 -Wold-style-declaration @r{(C only)} @gol
3501 -Woverride-init @gol
3504 -Wuninitialized @gol
3505 -Wshift-negative-value @gol
3506 -Wunused-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol
3507 -Wunused-but-set-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol
3510 The option @option{-Wextra} also prints warning messages for the
3516 A pointer is compared against integer zero with @code{<}, @code{<=},
3517 @code{>}, or @code{>=}.
3520 (C++ only) An enumerator and a non-enumerator both appear in a
3521 conditional expression.
3524 (C++ only) Ambiguous virtual bases.
3527 (C++ only) Subscripting an array that has been declared @code{register}.
3530 (C++ only) Taking the address of a variable that has been declared
3534 (C++ only) A base class is not initialized in a derived class's copy
3539 @item -Wchar-subscripts
3540 @opindex Wchar-subscripts
3541 @opindex Wno-char-subscripts
3542 Warn if an array subscript has type @code{char}. This is a common cause
3543 of error, as programmers often forget that this type is signed on some
3545 This warning is enabled by @option{-Wall}.
3549 @opindex Wno-comment
3550 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
3551 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
3552 This warning is enabled by @option{-Wall}.
3554 @item -Wno-coverage-mismatch
3555 @opindex Wno-coverage-mismatch
3556 Warn if feedback profiles do not match when using the
3557 @option{-fprofile-use} option.
3558 If a source file is changed between compiling with @option{-fprofile-gen} and
3559 with @option{-fprofile-use}, the files with the profile feedback can fail
3560 to match the source file and GCC cannot use the profile feedback
3561 information. By default, this warning is enabled and is treated as an
3562 error. @option{-Wno-coverage-mismatch} can be used to disable the
3563 warning or @option{-Wno-error=coverage-mismatch} can be used to
3564 disable the error. Disabling the error for this warning can result in
3565 poorly optimized code and is useful only in the
3566 case of very minor changes such as bug fixes to an existing code-base.
3567 Completely disabling the warning is not recommended.
3570 @r{(C, Objective-C, C++, Objective-C++ and Fortran only)}
3572 Suppress warning messages emitted by @code{#warning} directives.
3574 @item -Wdouble-promotion @r{(C, C++, Objective-C and Objective-C++ only)}
3575 @opindex Wdouble-promotion
3576 @opindex Wno-double-promotion
3577 Give a warning when a value of type @code{float} is implicitly
3578 promoted to @code{double}. CPUs with a 32-bit ``single-precision''
3579 floating-point unit implement @code{float} in hardware, but emulate
3580 @code{double} in software. On such a machine, doing computations
3581 using @code{double} values is much more expensive because of the
3582 overhead required for software emulation.
3584 It is easy to accidentally do computations with @code{double} because
3585 floating-point literals are implicitly of type @code{double}. For
3589 float area(float radius)
3591 return 3.14159 * radius * radius;
3595 the compiler performs the entire computation with @code{double}
3596 because the floating-point literal is a @code{double}.
3599 @itemx -Wformat=@var{n}
3602 @opindex ffreestanding
3603 @opindex fno-builtin
3605 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
3606 the arguments supplied have types appropriate to the format string
3607 specified, and that the conversions specified in the format string make
3608 sense. This includes standard functions, and others specified by format
3609 attributes (@pxref{Function Attributes}), in the @code{printf},
3610 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
3611 not in the C standard) families (or other target-specific families).
3612 Which functions are checked without format attributes having been
3613 specified depends on the standard version selected, and such checks of
3614 functions without the attribute specified are disabled by
3615 @option{-ffreestanding} or @option{-fno-builtin}.
3617 The formats are checked against the format features supported by GNU
3618 libc version 2.2. These include all ISO C90 and C99 features, as well
3619 as features from the Single Unix Specification and some BSD and GNU
3620 extensions. Other library implementations may not support all these
3621 features; GCC does not support warning about features that go beyond a
3622 particular library's limitations. However, if @option{-Wpedantic} is used
3623 with @option{-Wformat}, warnings are given about format features not
3624 in the selected standard version (but not for @code{strfmon} formats,
3625 since those are not in any version of the C standard). @xref{C Dialect
3626 Options,,Options Controlling C Dialect}.
3633 Option @option{-Wformat} is equivalent to @option{-Wformat=1}, and
3634 @option{-Wno-format} is equivalent to @option{-Wformat=0}. Since
3635 @option{-Wformat} also checks for null format arguments for several
3636 functions, @option{-Wformat} also implies @option{-Wnonnull}. Some
3637 aspects of this level of format checking can be disabled by the
3638 options: @option{-Wno-format-contains-nul},
3639 @option{-Wno-format-extra-args}, and @option{-Wno-format-zero-length}.
3640 @option{-Wformat} is enabled by @option{-Wall}.
3642 @item -Wno-format-contains-nul
3643 @opindex Wno-format-contains-nul
3644 @opindex Wformat-contains-nul
3645 If @option{-Wformat} is specified, do not warn about format strings that
3648 @item -Wno-format-extra-args
3649 @opindex Wno-format-extra-args
3650 @opindex Wformat-extra-args
3651 If @option{-Wformat} is specified, do not warn about excess arguments to a
3652 @code{printf} or @code{scanf} format function. The C standard specifies
3653 that such arguments are ignored.
3655 Where the unused arguments lie between used arguments that are
3656 specified with @samp{$} operand number specifications, normally
3657 warnings are still given, since the implementation could not know what
3658 type to pass to @code{va_arg} to skip the unused arguments. However,
3659 in the case of @code{scanf} formats, this option suppresses the
3660 warning if the unused arguments are all pointers, since the Single
3661 Unix Specification says that such unused arguments are allowed.
3663 @item -Wno-format-zero-length
3664 @opindex Wno-format-zero-length
3665 @opindex Wformat-zero-length
3666 If @option{-Wformat} is specified, do not warn about zero-length formats.
3667 The C standard specifies that zero-length formats are allowed.
3672 Enable @option{-Wformat} plus additional format checks. Currently
3673 equivalent to @option{-Wformat -Wformat-nonliteral -Wformat-security
3676 @item -Wformat-nonliteral
3677 @opindex Wformat-nonliteral
3678 @opindex Wno-format-nonliteral
3679 If @option{-Wformat} is specified, also warn if the format string is not a
3680 string literal and so cannot be checked, unless the format function
3681 takes its format arguments as a @code{va_list}.
3683 @item -Wformat-security
3684 @opindex Wformat-security
3685 @opindex Wno-format-security
3686 If @option{-Wformat} is specified, also warn about uses of format
3687 functions that represent possible security problems. At present, this
3688 warns about calls to @code{printf} and @code{scanf} functions where the
3689 format string is not a string literal and there are no format arguments,
3690 as in @code{printf (foo);}. This may be a security hole if the format
3691 string came from untrusted input and contains @samp{%n}. (This is
3692 currently a subset of what @option{-Wformat-nonliteral} warns about, but
3693 in future warnings may be added to @option{-Wformat-security} that are not
3694 included in @option{-Wformat-nonliteral}.)
3696 @item -Wformat-signedness
3697 @opindex Wformat-signedness
3698 @opindex Wno-format-signedness
3699 If @option{-Wformat} is specified, also warn if the format string
3700 requires an unsigned argument and the argument is signed and vice versa.
3703 @opindex Wformat-y2k
3704 @opindex Wno-format-y2k
3705 If @option{-Wformat} is specified, also warn about @code{strftime}
3706 formats that may yield only a two-digit year.
3711 @opindex Wno-nonnull
3712 Warn about passing a null pointer for arguments marked as
3713 requiring a non-null value by the @code{nonnull} function attribute.
3715 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
3716 can be disabled with the @option{-Wno-nonnull} option.
3718 @item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
3720 @opindex Wno-init-self
3721 Warn about uninitialized variables that are initialized with themselves.
3722 Note this option can only be used with the @option{-Wuninitialized} option.
3724 For example, GCC warns about @code{i} being uninitialized in the
3725 following snippet only when @option{-Winit-self} has been specified:
3736 This warning is enabled by @option{-Wall} in C++.
3738 @item -Wimplicit-int @r{(C and Objective-C only)}
3739 @opindex Wimplicit-int
3740 @opindex Wno-implicit-int
3741 Warn when a declaration does not specify a type.
3742 This warning is enabled by @option{-Wall}.
3744 @item -Wimplicit-function-declaration @r{(C and Objective-C only)}
3745 @opindex Wimplicit-function-declaration
3746 @opindex Wno-implicit-function-declaration
3747 Give a warning whenever a function is used before being declared. In
3748 C99 mode (@option{-std=c99} or @option{-std=gnu99}), this warning is
3749 enabled by default and it is made into an error by
3750 @option{-pedantic-errors}. This warning is also enabled by
3753 @item -Wimplicit @r{(C and Objective-C only)}
3755 @opindex Wno-implicit
3756 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
3757 This warning is enabled by @option{-Wall}.
3759 @item -Wignored-qualifiers @r{(C and C++ only)}
3760 @opindex Wignored-qualifiers
3761 @opindex Wno-ignored-qualifiers
3762 Warn if the return type of a function has a type qualifier
3763 such as @code{const}. For ISO C such a type qualifier has no effect,
3764 since the value returned by a function is not an lvalue.
3765 For C++, the warning is only emitted for scalar types or @code{void}.
3766 ISO C prohibits qualified @code{void} return types on function
3767 definitions, so such return types always receive a warning
3768 even without this option.
3770 This warning is also enabled by @option{-Wextra}.
3775 Warn if the type of @code{main} is suspicious. @code{main} should be
3776 a function with external linkage, returning int, taking either zero
3777 arguments, two, or three arguments of appropriate types. This warning
3778 is enabled by default in C++ and is enabled by either @option{-Wall}
3779 or @option{-Wpedantic}.
3781 @item -Wmisleading-indentation @r{(C and C++ only)}
3782 @opindex Wmisleading-indentation
3783 @opindex Wno-misleading-indentation
3784 Warn when the indentation of the code does not reflect the block structure.
3785 Specifically, a warning is issued for @code{if}, @code{else}, @code{while}, and
3786 @code{for} clauses with a guarded statement that does not use braces,
3787 followed by an unguarded statement with the same indentation.
3789 This warning is disabled by default.
3791 In the following example, the call to ``bar'' is misleadingly indented as
3792 if it were guarded by the ``if'' conditional.
3795 if (some_condition ())
3797 bar (); /* Gotcha: this is not guarded by the "if". */
3800 In the case of mixed tabs and spaces, the warning uses the
3801 @option{-ftabstop=} option to determine if the statements line up
3804 The warning is not issued for code involving multiline preprocessor logic
3805 such as the following example.
3810 #if SOME_CONDITION_THAT_DOES_NOT_HOLD
3816 The warning is not issued after a @code{#line} directive, since this
3817 typically indicates autogenerated code, and no assumptions can be made
3818 about the layout of the file that the directive references.
3820 @item -Wmissing-braces
3821 @opindex Wmissing-braces
3822 @opindex Wno-missing-braces
3823 Warn if an aggregate or union initializer is not fully bracketed. In
3824 the following example, the initializer for @code{a} is not fully
3825 bracketed, but that for @code{b} is fully bracketed. This warning is
3826 enabled by @option{-Wall} in C.
3829 int a[2][2] = @{ 0, 1, 2, 3 @};
3830 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
3833 This warning is enabled by @option{-Wall}.
3835 @item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)}
3836 @opindex Wmissing-include-dirs
3837 @opindex Wno-missing-include-dirs
3838 Warn if a user-supplied include directory does not exist.
3841 @opindex Wparentheses
3842 @opindex Wno-parentheses
3843 Warn if parentheses are omitted in certain contexts, such
3844 as when there is an assignment in a context where a truth value
3845 is expected, or when operators are nested whose precedence people
3846 often get confused about.
3848 Also warn if a comparison like @code{x<=y<=z} appears; this is
3849 equivalent to @code{(x<=y ? 1 : 0) <= z}, which is a different
3850 interpretation from that of ordinary mathematical notation.
3852 Also warn about constructions where there may be confusion to which
3853 @code{if} statement an @code{else} branch belongs. Here is an example of
3868 In C/C++, every @code{else} branch belongs to the innermost possible
3869 @code{if} statement, which in this example is @code{if (b)}. This is
3870 often not what the programmer expected, as illustrated in the above
3871 example by indentation the programmer chose. When there is the
3872 potential for this confusion, GCC issues a warning when this flag
3873 is specified. To eliminate the warning, add explicit braces around
3874 the innermost @code{if} statement so there is no way the @code{else}
3875 can belong to the enclosing @code{if}. The resulting code
3892 Also warn for dangerous uses of the GNU extension to
3893 @code{?:} with omitted middle operand. When the condition
3894 in the @code{?}: operator is a boolean expression, the omitted value is
3895 always 1. Often programmers expect it to be a value computed
3896 inside the conditional expression instead.
3898 This warning is enabled by @option{-Wall}.
3900 @item -Wsequence-point
3901 @opindex Wsequence-point
3902 @opindex Wno-sequence-point
3903 Warn about code that may have undefined semantics because of violations
3904 of sequence point rules in the C and C++ standards.
3906 The C and C++ standards define the order in which expressions in a C/C++
3907 program are evaluated in terms of @dfn{sequence points}, which represent
3908 a partial ordering between the execution of parts of the program: those
3909 executed before the sequence point, and those executed after it. These
3910 occur after the evaluation of a full expression (one which is not part
3911 of a larger expression), after the evaluation of the first operand of a
3912 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
3913 function is called (but after the evaluation of its arguments and the
3914 expression denoting the called function), and in certain other places.
3915 Other than as expressed by the sequence point rules, the order of
3916 evaluation of subexpressions of an expression is not specified. All
3917 these rules describe only a partial order rather than a total order,
3918 since, for example, if two functions are called within one expression
3919 with no sequence point between them, the order in which the functions
3920 are called is not specified. However, the standards committee have
3921 ruled that function calls do not overlap.
3923 It is not specified when between sequence points modifications to the
3924 values of objects take effect. Programs whose behavior depends on this
3925 have undefined behavior; the C and C++ standards specify that ``Between
3926 the previous and next sequence point an object shall have its stored
3927 value modified at most once by the evaluation of an expression.
3928 Furthermore, the prior value shall be read only to determine the value
3929 to be stored.''. If a program breaks these rules, the results on any
3930 particular implementation are entirely unpredictable.
3932 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
3933 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
3934 diagnosed by this option, and it may give an occasional false positive
3935 result, but in general it has been found fairly effective at detecting
3936 this sort of problem in programs.
3938 The standard is worded confusingly, therefore there is some debate
3939 over the precise meaning of the sequence point rules in subtle cases.
3940 Links to discussions of the problem, including proposed formal
3941 definitions, may be found on the GCC readings page, at
3942 @uref{http://gcc.gnu.org/@/readings.html}.
3944 This warning is enabled by @option{-Wall} for C and C++.
3946 @item -Wno-return-local-addr
3947 @opindex Wno-return-local-addr
3948 @opindex Wreturn-local-addr
3949 Do not warn about returning a pointer (or in C++, a reference) to a
3950 variable that goes out of scope after the function returns.
3953 @opindex Wreturn-type
3954 @opindex Wno-return-type
3955 Warn whenever a function is defined with a return type that defaults
3956 to @code{int}. Also warn about any @code{return} statement with no
3957 return value in a function whose return type is not @code{void}
3958 (falling off the end of the function body is considered returning
3959 without a value), and about a @code{return} statement with an
3960 expression in a function whose return type is @code{void}.
3962 For C++, a function without return type always produces a diagnostic
3963 message, even when @option{-Wno-return-type} is specified. The only
3964 exceptions are @code{main} and functions defined in system headers.
3966 This warning is enabled by @option{-Wall}.
3968 @item -Wshift-count-negative
3969 @opindex Wshift-count-negative
3970 @opindex Wno-shift-count-negative
3971 Warn if shift count is negative. This warning is enabled by default.
3973 @item -Wshift-count-overflow
3974 @opindex Wshift-count-overflow
3975 @opindex Wno-shift-count-overflow
3976 Warn if shift count >= width of type. This warning is enabled by default.
3978 @item -Wshift-negative-value
3979 @opindex Wshift-negative-value
3980 @opindex Wno-shift-negative-value
3981 Warn if left shifting a negative value. This warning is enabled by
3982 @option{-Wextra} in C99 and C++11 modes (and newer).
3987 Warn whenever a @code{switch} statement has an index of enumerated type
3988 and lacks a @code{case} for one or more of the named codes of that
3989 enumeration. (The presence of a @code{default} label prevents this
3990 warning.) @code{case} labels outside the enumeration range also
3991 provoke warnings when this option is used (even if there is a
3992 @code{default} label).
3993 This warning is enabled by @option{-Wall}.
3995 @item -Wswitch-default
3996 @opindex Wswitch-default
3997 @opindex Wno-switch-default
3998 Warn whenever a @code{switch} statement does not have a @code{default}
4002 @opindex Wswitch-enum
4003 @opindex Wno-switch-enum
4004 Warn whenever a @code{switch} statement has an index of enumerated type
4005 and lacks a @code{case} for one or more of the named codes of that
4006 enumeration. @code{case} labels outside the enumeration range also
4007 provoke warnings when this option is used. The only difference
4008 between @option{-Wswitch} and this option is that this option gives a
4009 warning about an omitted enumeration code even if there is a
4010 @code{default} label.
4013 @opindex Wswitch-bool
4014 @opindex Wno-switch-bool
4015 Warn whenever a @code{switch} statement has an index of boolean type.
4016 It is possible to suppress this warning by casting the controlling
4017 expression to a type other than @code{bool}. For example:
4020 switch ((int) (a == 4))
4026 This warning is enabled by default for C and C++ programs.
4028 @item -Wsync-nand @r{(C and C++ only)}
4030 @opindex Wno-sync-nand
4031 Warn when @code{__sync_fetch_and_nand} and @code{__sync_nand_and_fetch}
4032 built-in functions are used. These functions changed semantics in GCC 4.4.
4036 @opindex Wno-trigraphs
4037 Warn if any trigraphs are encountered that might change the meaning of
4038 the program (trigraphs within comments are not warned about).
4039 This warning is enabled by @option{-Wall}.
4041 @item -Wunused-but-set-parameter
4042 @opindex Wunused-but-set-parameter
4043 @opindex Wno-unused-but-set-parameter
4044 Warn whenever a function parameter is assigned to, but otherwise unused
4045 (aside from its declaration).
4047 To suppress this warning use the @code{unused} attribute
4048 (@pxref{Variable Attributes}).
4050 This warning is also enabled by @option{-Wunused} together with
4053 @item -Wunused-but-set-variable
4054 @opindex Wunused-but-set-variable
4055 @opindex Wno-unused-but-set-variable
4056 Warn whenever a local variable is assigned to, but otherwise unused
4057 (aside from its declaration).
4058 This warning is enabled by @option{-Wall}.
4060 To suppress this warning use the @code{unused} attribute
4061 (@pxref{Variable Attributes}).
4063 This warning is also enabled by @option{-Wunused}, which is enabled
4066 @item -Wunused-function
4067 @opindex Wunused-function
4068 @opindex Wno-unused-function
4069 Warn whenever a static function is declared but not defined or a
4070 non-inline static function is unused.
4071 This warning is enabled by @option{-Wall}.
4073 @item -Wunused-label
4074 @opindex Wunused-label
4075 @opindex Wno-unused-label
4076 Warn whenever a label is declared but not used.
4077 This warning is enabled by @option{-Wall}.
4079 To suppress this warning use the @code{unused} attribute
4080 (@pxref{Variable Attributes}).
4082 @item -Wunused-local-typedefs @r{(C, Objective-C, C++ and Objective-C++ only)}
4083 @opindex Wunused-local-typedefs
4084 Warn when a typedef locally defined in a function is not used.
4085 This warning is enabled by @option{-Wall}.
4087 @item -Wunused-parameter
4088 @opindex Wunused-parameter
4089 @opindex Wno-unused-parameter
4090 Warn whenever a function parameter is unused aside from its declaration.
4092 To suppress this warning use the @code{unused} attribute
4093 (@pxref{Variable Attributes}).
4095 @item -Wno-unused-result
4096 @opindex Wunused-result
4097 @opindex Wno-unused-result
4098 Do not warn if a caller of a function marked with attribute
4099 @code{warn_unused_result} (@pxref{Function Attributes}) does not use
4100 its return value. The default is @option{-Wunused-result}.
4102 @item -Wunused-variable
4103 @opindex Wunused-variable
4104 @opindex Wno-unused-variable
4105 Warn whenever a local variable or non-constant static variable is unused
4106 aside from its declaration.
4107 This warning is enabled by @option{-Wall}.
4109 To suppress this warning use the @code{unused} attribute
4110 (@pxref{Variable Attributes}).
4112 @item -Wunused-value
4113 @opindex Wunused-value
4114 @opindex Wno-unused-value
4115 Warn whenever a statement computes a result that is explicitly not
4116 used. To suppress this warning cast the unused expression to
4117 @code{void}. This includes an expression-statement or the left-hand
4118 side of a comma expression that contains no side effects. For example,
4119 an expression such as @code{x[i,j]} causes a warning, while
4120 @code{x[(void)i,j]} does not.
4122 This warning is enabled by @option{-Wall}.
4127 All the above @option{-Wunused} options combined.
4129 In order to get a warning about an unused function parameter, you must
4130 either specify @option{-Wextra -Wunused} (note that @option{-Wall} implies
4131 @option{-Wunused}), or separately specify @option{-Wunused-parameter}.
4133 @item -Wuninitialized
4134 @opindex Wuninitialized
4135 @opindex Wno-uninitialized
4136 Warn if an automatic variable is used without first being initialized
4137 or if a variable may be clobbered by a @code{setjmp} call. In C++,
4138 warn if a non-static reference or non-static @code{const} member
4139 appears in a class without constructors.
4141 If you want to warn about code that uses the uninitialized value of the
4142 variable in its own initializer, use the @option{-Winit-self} option.
4144 These warnings occur for individual uninitialized or clobbered
4145 elements of structure, union or array variables as well as for
4146 variables that are uninitialized or clobbered as a whole. They do
4147 not occur for variables or elements declared @code{volatile}. Because
4148 these warnings depend on optimization, the exact variables or elements
4149 for which there are warnings depends on the precise optimization
4150 options and version of GCC used.
4152 Note that there may be no warning about a variable that is used only
4153 to compute a value that itself is never used, because such
4154 computations may be deleted by data flow analysis before the warnings
4157 @item -Wmaybe-uninitialized
4158 @opindex Wmaybe-uninitialized
4159 @opindex Wno-maybe-uninitialized
4160 For an automatic variable, if there exists a path from the function
4161 entry to a use of the variable that is initialized, but there exist
4162 some other paths for which the variable is not initialized, the compiler
4163 emits a warning if it cannot prove the uninitialized paths are not
4164 executed at run time. These warnings are made optional because GCC is
4165 not smart enough to see all the reasons why the code might be correct
4166 in spite of appearing to have an error. Here is one example of how
4187 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
4188 always initialized, but GCC doesn't know this. To suppress the
4189 warning, you need to provide a default case with assert(0) or
4192 @cindex @code{longjmp} warnings
4193 This option also warns when a non-volatile automatic variable might be
4194 changed by a call to @code{longjmp}. These warnings as well are possible
4195 only in optimizing compilation.
4197 The compiler sees only the calls to @code{setjmp}. It cannot know
4198 where @code{longjmp} will be called; in fact, a signal handler could
4199 call it at any point in the code. As a result, you may get a warning
4200 even when there is in fact no problem because @code{longjmp} cannot
4201 in fact be called at the place that would cause a problem.
4203 Some spurious warnings can be avoided if you declare all the functions
4204 you use that never return as @code{noreturn}. @xref{Function
4207 This warning is enabled by @option{-Wall} or @option{-Wextra}.
4209 @item -Wunknown-pragmas
4210 @opindex Wunknown-pragmas
4211 @opindex Wno-unknown-pragmas
4212 @cindex warning for unknown pragmas
4213 @cindex unknown pragmas, warning
4214 @cindex pragmas, warning of unknown
4215 Warn when a @code{#pragma} directive is encountered that is not understood by
4216 GCC@. If this command-line option is used, warnings are even issued
4217 for unknown pragmas in system header files. This is not the case if
4218 the warnings are only enabled by the @option{-Wall} command-line option.
4221 @opindex Wno-pragmas
4223 Do not warn about misuses of pragmas, such as incorrect parameters,
4224 invalid syntax, or conflicts between pragmas. See also
4225 @option{-Wunknown-pragmas}.
4227 @item -Wstrict-aliasing
4228 @opindex Wstrict-aliasing
4229 @opindex Wno-strict-aliasing
4230 This option is only active when @option{-fstrict-aliasing} is active.
4231 It warns about code that might break the strict aliasing rules that the
4232 compiler is using for optimization. The warning does not catch all
4233 cases, but does attempt to catch the more common pitfalls. It is
4234 included in @option{-Wall}.
4235 It is equivalent to @option{-Wstrict-aliasing=3}
4237 @item -Wstrict-aliasing=n
4238 @opindex Wstrict-aliasing=n
4239 This option is only active when @option{-fstrict-aliasing} is active.
4240 It warns about code that might break the strict aliasing rules that the
4241 compiler is using for optimization.
4242 Higher levels correspond to higher accuracy (fewer false positives).
4243 Higher levels also correspond to more effort, similar to the way @option{-O}
4245 @option{-Wstrict-aliasing} is equivalent to @option{-Wstrict-aliasing=3}.
4247 Level 1: Most aggressive, quick, least accurate.
4248 Possibly useful when higher levels
4249 do not warn but @option{-fstrict-aliasing} still breaks the code, as it has very few
4250 false negatives. However, it has many false positives.
4251 Warns for all pointer conversions between possibly incompatible types,
4252 even if never dereferenced. Runs in the front end only.
4254 Level 2: Aggressive, quick, not too precise.
4255 May still have many false positives (not as many as level 1 though),
4256 and few false negatives (but possibly more than level 1).
4257 Unlike level 1, it only warns when an address is taken. Warns about
4258 incomplete types. Runs in the front end only.
4260 Level 3 (default for @option{-Wstrict-aliasing}):
4261 Should have very few false positives and few false
4262 negatives. Slightly slower than levels 1 or 2 when optimization is enabled.
4263 Takes care of the common pun+dereference pattern in the front end:
4264 @code{*(int*)&some_float}.
4265 If optimization is enabled, it also runs in the back end, where it deals
4266 with multiple statement cases using flow-sensitive points-to information.
4267 Only warns when the converted pointer is dereferenced.
4268 Does not warn about incomplete types.
4270 @item -Wstrict-overflow
4271 @itemx -Wstrict-overflow=@var{n}
4272 @opindex Wstrict-overflow
4273 @opindex Wno-strict-overflow
4274 This option is only active when @option{-fstrict-overflow} is active.
4275 It warns about cases where the compiler optimizes based on the
4276 assumption that signed overflow does not occur. Note that it does not
4277 warn about all cases where the code might overflow: it only warns
4278 about cases where the compiler implements some optimization. Thus
4279 this warning depends on the optimization level.
4281 An optimization that assumes that signed overflow does not occur is
4282 perfectly safe if the values of the variables involved are such that
4283 overflow never does, in fact, occur. Therefore this warning can
4284 easily give a false positive: a warning about code that is not
4285 actually a problem. To help focus on important issues, several
4286 warning levels are defined. No warnings are issued for the use of
4287 undefined signed overflow when estimating how many iterations a loop
4288 requires, in particular when determining whether a loop will be
4292 @item -Wstrict-overflow=1
4293 Warn about cases that are both questionable and easy to avoid. For
4294 example, with @option{-fstrict-overflow}, the compiler simplifies
4295 @code{x + 1 > x} to @code{1}. This level of
4296 @option{-Wstrict-overflow} is enabled by @option{-Wall}; higher levels
4297 are not, and must be explicitly requested.
4299 @item -Wstrict-overflow=2
4300 Also warn about other cases where a comparison is simplified to a
4301 constant. For example: @code{abs (x) >= 0}. This can only be
4302 simplified when @option{-fstrict-overflow} is in effect, because
4303 @code{abs (INT_MIN)} overflows to @code{INT_MIN}, which is less than
4304 zero. @option{-Wstrict-overflow} (with no level) is the same as
4305 @option{-Wstrict-overflow=2}.
4307 @item -Wstrict-overflow=3
4308 Also warn about other cases where a comparison is simplified. For
4309 example: @code{x + 1 > 1} is simplified to @code{x > 0}.
4311 @item -Wstrict-overflow=4
4312 Also warn about other simplifications not covered by the above cases.
4313 For example: @code{(x * 10) / 5} is simplified to @code{x * 2}.
4315 @item -Wstrict-overflow=5
4316 Also warn about cases where the compiler reduces the magnitude of a
4317 constant involved in a comparison. For example: @code{x + 2 > y} is
4318 simplified to @code{x + 1 >= y}. This is reported only at the
4319 highest warning level because this simplification applies to many
4320 comparisons, so this warning level gives a very large number of
4324 @item -Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{]}
4325 @opindex Wsuggest-attribute=
4326 @opindex Wno-suggest-attribute=
4327 Warn for cases where adding an attribute may be beneficial. The
4328 attributes currently supported are listed below.
4331 @item -Wsuggest-attribute=pure
4332 @itemx -Wsuggest-attribute=const
4333 @itemx -Wsuggest-attribute=noreturn
4334 @opindex Wsuggest-attribute=pure
4335 @opindex Wno-suggest-attribute=pure
4336 @opindex Wsuggest-attribute=const
4337 @opindex Wno-suggest-attribute=const
4338 @opindex Wsuggest-attribute=noreturn
4339 @opindex Wno-suggest-attribute=noreturn
4341 Warn about functions that might be candidates for attributes
4342 @code{pure}, @code{const} or @code{noreturn}. The compiler only warns for
4343 functions visible in other compilation units or (in the case of @code{pure} and
4344 @code{const}) if it cannot prove that the function returns normally. A function
4345 returns normally if it doesn't contain an infinite loop or return abnormally
4346 by throwing, calling @code{abort} or trapping. This analysis requires option
4347 @option{-fipa-pure-const}, which is enabled by default at @option{-O} and
4348 higher. Higher optimization levels improve the accuracy of the analysis.
4350 @item -Wsuggest-attribute=format
4351 @itemx -Wmissing-format-attribute
4352 @opindex Wsuggest-attribute=format
4353 @opindex Wmissing-format-attribute
4354 @opindex Wno-suggest-attribute=format
4355 @opindex Wno-missing-format-attribute
4359 Warn about function pointers that might be candidates for @code{format}
4360 attributes. Note these are only possible candidates, not absolute ones.
4361 GCC guesses that function pointers with @code{format} attributes that
4362 are used in assignment, initialization, parameter passing or return
4363 statements should have a corresponding @code{format} attribute in the
4364 resulting type. I.e.@: the left-hand side of the assignment or
4365 initialization, the type of the parameter variable, or the return type
4366 of the containing function respectively should also have a @code{format}
4367 attribute to avoid the warning.
4369 GCC also warns about function definitions that might be
4370 candidates for @code{format} attributes. Again, these are only
4371 possible candidates. GCC guesses that @code{format} attributes
4372 might be appropriate for any function that calls a function like
4373 @code{vprintf} or @code{vscanf}, but this might not always be the
4374 case, and some functions for which @code{format} attributes are
4375 appropriate may not be detected.
4378 @item -Wsuggest-final-types
4379 @opindex Wno-suggest-final-types
4380 @opindex Wsuggest-final-types
4381 Warn about types with virtual methods where code quality would be improved
4382 if the type were declared with the C++11 @code{final} specifier,
4384 declared in an anonymous namespace. This allows GCC to more aggressively
4385 devirtualize the polymorphic calls. This warning is more effective with link
4386 time optimization, where the information about the class hierarchy graph is
4389 @item -Wsuggest-final-methods
4390 @opindex Wno-suggest-final-methods
4391 @opindex Wsuggest-final-methods
4392 Warn about virtual methods where code quality would be improved if the method
4393 were declared with the C++11 @code{final} specifier,
4394 or, if possible, its type were
4395 declared in an anonymous namespace or with the @code{final} specifier.
4397 more effective with link time optimization, where the information about the
4398 class hierarchy graph is more complete. It is recommended to first consider
4399 suggestions of @option{-Wsuggest-final-types} and then rebuild with new
4402 @item -Wsuggest-override
4403 Warn about overriding virtual functions that are not marked with the override
4406 @item -Warray-bounds
4407 @itemx -Warray-bounds=@var{n}
4408 @opindex Wno-array-bounds
4409 @opindex Warray-bounds
4410 This option is only active when @option{-ftree-vrp} is active
4411 (default for @option{-O2} and above). It warns about subscripts to arrays
4412 that are always out of bounds. This warning is enabled by @option{-Wall}.
4415 @item -Warray-bounds=1
4416 This is the warning level of @option{-Warray-bounds} and is enabled
4417 by @option{-Wall}; higher levels are not, and must be explicitly requested.
4419 @item -Warray-bounds=2
4420 This warning level also warns about out of bounds access for
4421 arrays at the end of a struct and for arrays accessed through
4422 pointers. This warning level may give a larger number of
4423 false positives and is deactivated by default.
4426 @item -Wbool-compare
4427 @opindex Wno-bool-compare
4428 @opindex Wbool-compare
4429 Warn about boolean expression compared with an integer value different from
4430 @code{true}/@code{false}. For instance, the following comparison is
4435 if ((n > 1) == 2) @{ @dots{} @}
4437 This warning is enabled by @option{-Wall}.
4439 @item -Wno-discarded-qualifiers @r{(C and Objective-C only)}
4440 @opindex Wno-discarded-qualifiers
4441 @opindex Wdiscarded-qualifiers
4442 Do not warn if type qualifiers on pointers are being discarded.
4443 Typically, the compiler warns if a @code{const char *} variable is
4444 passed to a function that takes a @code{char *} parameter. This option
4445 can be used to suppress such a warning.
4447 @item -Wno-discarded-array-qualifiers @r{(C and Objective-C only)}
4448 @opindex Wno-discarded-array-qualifiers
4449 @opindex Wdiscarded-array-qualifiers
4450 Do not warn if type qualifiers on arrays which are pointer targets
4451 are being discarded. Typically, the compiler warns if a
4452 @code{const int (*)[]} variable is passed to a function that
4453 takes a @code{int (*)[]} parameter. This option can be used to
4454 suppress such a warning.
4456 @item -Wno-incompatible-pointer-types @r{(C and Objective-C only)}
4457 @opindex Wno-incompatible-pointer-types
4458 @opindex Wincompatible-pointer-types
4459 Do not warn when there is a conversion between pointers that have incompatible
4460 types. This warning is for cases not covered by @option{-Wno-pointer-sign},
4461 which warns for pointer argument passing or assignment with different
4464 @item -Wno-int-conversion @r{(C and Objective-C only)}
4465 @opindex Wno-int-conversion
4466 @opindex Wint-conversion
4467 Do not warn about incompatible integer to pointer and pointer to integer
4468 conversions. This warning is about implicit conversions; for explicit
4469 conversions the warnings @option{-Wno-int-to-pointer-cast} and
4470 @option{-Wno-pointer-to-int-cast} may be used.
4472 @item -Wno-div-by-zero
4473 @opindex Wno-div-by-zero
4474 @opindex Wdiv-by-zero
4475 Do not warn about compile-time integer division by zero. Floating-point
4476 division by zero is not warned about, as it can be a legitimate way of
4477 obtaining infinities and NaNs.
4479 @item -Wsystem-headers
4480 @opindex Wsystem-headers
4481 @opindex Wno-system-headers
4482 @cindex warnings from system headers
4483 @cindex system headers, warnings from
4484 Print warning messages for constructs found in system header files.
4485 Warnings from system headers are normally suppressed, on the assumption
4486 that they usually do not indicate real problems and would only make the
4487 compiler output harder to read. Using this command-line option tells
4488 GCC to emit warnings from system headers as if they occurred in user
4489 code. However, note that using @option{-Wall} in conjunction with this
4490 option does @emph{not} warn about unknown pragmas in system
4491 headers---for that, @option{-Wunknown-pragmas} must also be used.
4494 @opindex Wtrampolines
4495 @opindex Wno-trampolines
4496 Warn about trampolines generated for pointers to nested functions.
4497 A trampoline is a small piece of data or code that is created at run
4498 time on the stack when the address of a nested function is taken, and is
4499 used to call the nested function indirectly. For some targets, it is
4500 made up of data only and thus requires no special treatment. But, for
4501 most targets, it is made up of code and thus requires the stack to be
4502 made executable in order for the program to work properly.
4505 @opindex Wfloat-equal
4506 @opindex Wno-float-equal
4507 Warn if floating-point values are used in equality comparisons.
4509 The idea behind this is that sometimes it is convenient (for the
4510 programmer) to consider floating-point values as approximations to
4511 infinitely precise real numbers. If you are doing this, then you need
4512 to compute (by analyzing the code, or in some other way) the maximum or
4513 likely maximum error that the computation introduces, and allow for it
4514 when performing comparisons (and when producing output, but that's a
4515 different problem). In particular, instead of testing for equality, you
4516 should check to see whether the two values have ranges that overlap; and
4517 this is done with the relational operators, so equality comparisons are
4520 @item -Wtraditional @r{(C and Objective-C only)}
4521 @opindex Wtraditional
4522 @opindex Wno-traditional
4523 Warn about certain constructs that behave differently in traditional and
4524 ISO C@. Also warn about ISO C constructs that have no traditional C
4525 equivalent, and/or problematic constructs that should be avoided.
4529 Macro parameters that appear within string literals in the macro body.
4530 In traditional C macro replacement takes place within string literals,
4531 but in ISO C it does not.
4534 In traditional C, some preprocessor directives did not exist.
4535 Traditional preprocessors only considered a line to be a directive
4536 if the @samp{#} appeared in column 1 on the line. Therefore
4537 @option{-Wtraditional} warns about directives that traditional C
4538 understands but ignores because the @samp{#} does not appear as the
4539 first character on the line. It also suggests you hide directives like
4540 @code{#pragma} not understood by traditional C by indenting them. Some
4541 traditional implementations do not recognize @code{#elif}, so this option
4542 suggests avoiding it altogether.
4545 A function-like macro that appears without arguments.
4548 The unary plus operator.
4551 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating-point
4552 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
4553 constants.) Note, these suffixes appear in macros defined in the system
4554 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
4555 Use of these macros in user code might normally lead to spurious
4556 warnings, however GCC's integrated preprocessor has enough context to
4557 avoid warning in these cases.
4560 A function declared external in one block and then used after the end of
4564 A @code{switch} statement has an operand of type @code{long}.
4567 A non-@code{static} function declaration follows a @code{static} one.
4568 This construct is not accepted by some traditional C compilers.
4571 The ISO type of an integer constant has a different width or
4572 signedness from its traditional type. This warning is only issued if
4573 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
4574 typically represent bit patterns, are not warned about.
4577 Usage of ISO string concatenation is detected.
4580 Initialization of automatic aggregates.
4583 Identifier conflicts with labels. Traditional C lacks a separate
4584 namespace for labels.
4587 Initialization of unions. If the initializer is zero, the warning is
4588 omitted. This is done under the assumption that the zero initializer in
4589 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
4590 initializer warnings and relies on default initialization to zero in the
4594 Conversions by prototypes between fixed/floating-point values and vice
4595 versa. The absence of these prototypes when compiling with traditional
4596 C causes serious problems. This is a subset of the possible
4597 conversion warnings; for the full set use @option{-Wtraditional-conversion}.
4600 Use of ISO C style function definitions. This warning intentionally is
4601 @emph{not} issued for prototype declarations or variadic functions
4602 because these ISO C features appear in your code when using
4603 libiberty's traditional C compatibility macros, @code{PARAMS} and
4604 @code{VPARAMS}. This warning is also bypassed for nested functions
4605 because that feature is already a GCC extension and thus not relevant to
4606 traditional C compatibility.
4609 @item -Wtraditional-conversion @r{(C and Objective-C only)}
4610 @opindex Wtraditional-conversion
4611 @opindex Wno-traditional-conversion
4612 Warn if a prototype causes a type conversion that is different from what
4613 would happen to the same argument in the absence of a prototype. This
4614 includes conversions of fixed point to floating and vice versa, and
4615 conversions changing the width or signedness of a fixed-point argument
4616 except when the same as the default promotion.
4618 @item -Wdeclaration-after-statement @r{(C and Objective-C only)}
4619 @opindex Wdeclaration-after-statement
4620 @opindex Wno-declaration-after-statement
4621 Warn when a declaration is found after a statement in a block. This
4622 construct, known from C++, was introduced with ISO C99 and is by default
4623 allowed in GCC@. It is not supported by ISO C90. @xref{Mixed Declarations}.
4628 Warn if an undefined identifier is evaluated in an @code{#if} directive.
4630 @item -Wno-endif-labels
4631 @opindex Wno-endif-labels
4632 @opindex Wendif-labels
4633 Do not warn whenever an @code{#else} or an @code{#endif} are followed by text.
4638 Warn whenever a local variable or type declaration shadows another
4639 variable, parameter, type, class member (in C++), or instance variable
4640 (in Objective-C) or whenever a built-in function is shadowed. Note
4641 that in C++, the compiler warns if a local variable shadows an
4642 explicit typedef, but not if it shadows a struct/class/enum.
4644 @item -Wno-shadow-ivar @r{(Objective-C only)}
4645 @opindex Wno-shadow-ivar
4646 @opindex Wshadow-ivar
4647 Do not warn whenever a local variable shadows an instance variable in an
4650 @item -Wlarger-than=@var{len}
4651 @opindex Wlarger-than=@var{len}
4652 @opindex Wlarger-than-@var{len}
4653 Warn whenever an object of larger than @var{len} bytes is defined.
4655 @item -Wframe-larger-than=@var{len}
4656 @opindex Wframe-larger-than
4657 Warn if the size of a function frame is larger than @var{len} bytes.
4658 The computation done to determine the stack frame size is approximate
4659 and not conservative.
4660 The actual requirements may be somewhat greater than @var{len}
4661 even if you do not get a warning. In addition, any space allocated
4662 via @code{alloca}, variable-length arrays, or related constructs
4663 is not included by the compiler when determining
4664 whether or not to issue a warning.
4666 @item -Wno-free-nonheap-object
4667 @opindex Wno-free-nonheap-object
4668 @opindex Wfree-nonheap-object
4669 Do not warn when attempting to free an object that was not allocated
4672 @item -Wstack-usage=@var{len}
4673 @opindex Wstack-usage
4674 Warn if the stack usage of a function might be larger than @var{len} bytes.
4675 The computation done to determine the stack usage is conservative.
4676 Any space allocated via @code{alloca}, variable-length arrays, or related
4677 constructs is included by the compiler when determining whether or not to
4680 The message is in keeping with the output of @option{-fstack-usage}.
4684 If the stack usage is fully static but exceeds the specified amount, it's:
4687 warning: stack usage is 1120 bytes
4690 If the stack usage is (partly) dynamic but bounded, it's:
4693 warning: stack usage might be 1648 bytes
4696 If the stack usage is (partly) dynamic and not bounded, it's:
4699 warning: stack usage might be unbounded
4703 @item -Wunsafe-loop-optimizations
4704 @opindex Wunsafe-loop-optimizations
4705 @opindex Wno-unsafe-loop-optimizations
4706 Warn if the loop cannot be optimized because the compiler cannot
4707 assume anything on the bounds of the loop indices. With
4708 @option{-funsafe-loop-optimizations} warn if the compiler makes
4711 @item -Wno-pedantic-ms-format @r{(MinGW targets only)}
4712 @opindex Wno-pedantic-ms-format
4713 @opindex Wpedantic-ms-format
4714 When used in combination with @option{-Wformat}
4715 and @option{-pedantic} without GNU extensions, this option
4716 disables the warnings about non-ISO @code{printf} / @code{scanf} format
4717 width specifiers @code{I32}, @code{I64}, and @code{I} used on Windows targets,
4718 which depend on the MS runtime.
4720 @item -Wpointer-arith
4721 @opindex Wpointer-arith
4722 @opindex Wno-pointer-arith
4723 Warn about anything that depends on the ``size of'' a function type or
4724 of @code{void}. GNU C assigns these types a size of 1, for
4725 convenience in calculations with @code{void *} pointers and pointers
4726 to functions. In C++, warn also when an arithmetic operation involves
4727 @code{NULL}. This warning is also enabled by @option{-Wpedantic}.
4730 @opindex Wtype-limits
4731 @opindex Wno-type-limits
4732 Warn if a comparison is always true or always false due to the limited
4733 range of the data type, but do not warn for constant expressions. For
4734 example, warn if an unsigned variable is compared against zero with
4735 @code{<} or @code{>=}. This warning is also enabled by
4738 @item -Wbad-function-cast @r{(C and Objective-C only)}
4739 @opindex Wbad-function-cast
4740 @opindex Wno-bad-function-cast
4741 Warn when a function call is cast to a non-matching type.
4742 For example, warn if a call to a function returning an integer type
4743 is cast to a pointer type.
4745 @item -Wc90-c99-compat @r{(C and Objective-C only)}
4746 @opindex Wc90-c99-compat
4747 @opindex Wno-c90-c99-compat
4748 Warn about features not present in ISO C90, but present in ISO C99.
4749 For instance, warn about use of variable length arrays, @code{long long}
4750 type, @code{bool} type, compound literals, designated initializers, and so
4751 on. This option is independent of the standards mode. Warnings are disabled
4752 in the expression that follows @code{__extension__}.
4754 @item -Wc99-c11-compat @r{(C and Objective-C only)}
4755 @opindex Wc99-c11-compat
4756 @opindex Wno-c99-c11-compat
4757 Warn about features not present in ISO C99, but present in ISO C11.
4758 For instance, warn about use of anonymous structures and unions,
4759 @code{_Atomic} type qualifier, @code{_Thread_local} storage-class specifier,
4760 @code{_Alignas} specifier, @code{Alignof} operator, @code{_Generic} keyword,
4761 and so on. This option is independent of the standards mode. Warnings are
4762 disabled in the expression that follows @code{__extension__}.
4764 @item -Wc++-compat @r{(C and Objective-C only)}
4765 @opindex Wc++-compat
4766 Warn about ISO C constructs that are outside of the common subset of
4767 ISO C and ISO C++, e.g.@: request for implicit conversion from
4768 @code{void *} to a pointer to non-@code{void} type.
4770 @item -Wc++11-compat @r{(C++ and Objective-C++ only)}
4771 @opindex Wc++11-compat
4772 Warn about C++ constructs whose meaning differs between ISO C++ 1998
4773 and ISO C++ 2011, e.g., identifiers in ISO C++ 1998 that are keywords
4774 in ISO C++ 2011. This warning turns on @option{-Wnarrowing} and is
4775 enabled by @option{-Wall}.
4777 @item -Wc++14-compat @r{(C++ and Objective-C++ only)}
4778 @opindex Wc++14-compat
4779 Warn about C++ constructs whose meaning differs between ISO C++ 2011
4780 and ISO C++ 2014. This warning is enabled by @option{-Wall}.
4784 @opindex Wno-cast-qual
4785 Warn whenever a pointer is cast so as to remove a type qualifier from
4786 the target type. For example, warn if a @code{const char *} is cast
4787 to an ordinary @code{char *}.
4789 Also warn when making a cast that introduces a type qualifier in an
4790 unsafe way. For example, casting @code{char **} to @code{const char **}
4791 is unsafe, as in this example:
4794 /* p is char ** value. */
4795 const char **q = (const char **) p;
4796 /* Assignment of readonly string to const char * is OK. */
4798 /* Now char** pointer points to read-only memory. */
4803 @opindex Wcast-align
4804 @opindex Wno-cast-align
4805 Warn whenever a pointer is cast such that the required alignment of the
4806 target is increased. For example, warn if a @code{char *} is cast to
4807 an @code{int *} on machines where integers can only be accessed at
4808 two- or four-byte boundaries.
4810 @item -Wwrite-strings
4811 @opindex Wwrite-strings
4812 @opindex Wno-write-strings
4813 When compiling C, give string constants the type @code{const
4814 char[@var{length}]} so that copying the address of one into a
4815 non-@code{const} @code{char *} pointer produces a warning. These
4816 warnings help you find at compile time code that can try to write
4817 into a string constant, but only if you have been very careful about
4818 using @code{const} in declarations and prototypes. Otherwise, it is
4819 just a nuisance. This is why we did not make @option{-Wall} request
4822 When compiling C++, warn about the deprecated conversion from string
4823 literals to @code{char *}. This warning is enabled by default for C++
4828 @opindex Wno-clobbered
4829 Warn for variables that might be changed by @code{longjmp} or
4830 @code{vfork}. This warning is also enabled by @option{-Wextra}.
4832 @item -Wconditionally-supported @r{(C++ and Objective-C++ only)}
4833 @opindex Wconditionally-supported
4834 @opindex Wno-conditionally-supported
4835 Warn for conditionally-supported (C++11 [intro.defs]) constructs.
4838 @opindex Wconversion
4839 @opindex Wno-conversion
4840 Warn for implicit conversions that may alter a value. This includes
4841 conversions between real and integer, like @code{abs (x)} when
4842 @code{x} is @code{double}; conversions between signed and unsigned,
4843 like @code{unsigned ui = -1}; and conversions to smaller types, like
4844 @code{sqrtf (M_PI)}. Do not warn for explicit casts like @code{abs
4845 ((int) x)} and @code{ui = (unsigned) -1}, or if the value is not
4846 changed by the conversion like in @code{abs (2.0)}. Warnings about
4847 conversions between signed and unsigned integers can be disabled by
4848 using @option{-Wno-sign-conversion}.
4850 For C++, also warn for confusing overload resolution for user-defined
4851 conversions; and conversions that never use a type conversion
4852 operator: conversions to @code{void}, the same type, a base class or a
4853 reference to them. Warnings about conversions between signed and
4854 unsigned integers are disabled by default in C++ unless
4855 @option{-Wsign-conversion} is explicitly enabled.
4857 @item -Wno-conversion-null @r{(C++ and Objective-C++ only)}
4858 @opindex Wconversion-null
4859 @opindex Wno-conversion-null
4860 Do not warn for conversions between @code{NULL} and non-pointer
4861 types. @option{-Wconversion-null} is enabled by default.
4863 @item -Wzero-as-null-pointer-constant @r{(C++ and Objective-C++ only)}
4864 @opindex Wzero-as-null-pointer-constant
4865 @opindex Wno-zero-as-null-pointer-constant
4866 Warn when a literal '0' is used as null pointer constant. This can
4867 be useful to facilitate the conversion to @code{nullptr} in C++11.
4871 @opindex Wno-date-time
4872 Warn when macros @code{__TIME__}, @code{__DATE__} or @code{__TIMESTAMP__}
4873 are encountered as they might prevent bit-wise-identical reproducible
4876 @item -Wdelete-incomplete @r{(C++ and Objective-C++ only)}
4877 @opindex Wdelete-incomplete
4878 @opindex Wno-delete-incomplete
4879 Warn when deleting a pointer to incomplete type, which may cause
4880 undefined behavior at runtime. This warning is enabled by default.
4882 @item -Wuseless-cast @r{(C++ and Objective-C++ only)}
4883 @opindex Wuseless-cast
4884 @opindex Wno-useless-cast
4885 Warn when an expression is casted to its own type.
4888 @opindex Wempty-body
4889 @opindex Wno-empty-body
4890 Warn if an empty body occurs in an @code{if}, @code{else} or @code{do
4891 while} statement. This warning is also enabled by @option{-Wextra}.
4893 @item -Wenum-compare
4894 @opindex Wenum-compare
4895 @opindex Wno-enum-compare
4896 Warn about a comparison between values of different enumerated types.
4897 In C++ enumeral mismatches in conditional expressions are also
4898 diagnosed and the warning is enabled by default. In C this warning is
4899 enabled by @option{-Wall}.
4901 @item -Wjump-misses-init @r{(C, Objective-C only)}
4902 @opindex Wjump-misses-init
4903 @opindex Wno-jump-misses-init
4904 Warn if a @code{goto} statement or a @code{switch} statement jumps
4905 forward across the initialization of a variable, or jumps backward to a
4906 label after the variable has been initialized. This only warns about
4907 variables that are initialized when they are declared. This warning is
4908 only supported for C and Objective-C; in C++ this sort of branch is an
4911 @option{-Wjump-misses-init} is included in @option{-Wc++-compat}. It
4912 can be disabled with the @option{-Wno-jump-misses-init} option.
4914 @item -Wsign-compare
4915 @opindex Wsign-compare
4916 @opindex Wno-sign-compare
4917 @cindex warning for comparison of signed and unsigned values
4918 @cindex comparison of signed and unsigned values, warning
4919 @cindex signed and unsigned values, comparison warning
4920 Warn when a comparison between signed and unsigned values could produce
4921 an incorrect result when the signed value is converted to unsigned.
4922 This warning is also enabled by @option{-Wextra}; to get the other warnings
4923 of @option{-Wextra} without this warning, use @option{-Wextra -Wno-sign-compare}.
4925 @item -Wsign-conversion
4926 @opindex Wsign-conversion
4927 @opindex Wno-sign-conversion
4928 Warn for implicit conversions that may change the sign of an integer
4929 value, like assigning a signed integer expression to an unsigned
4930 integer variable. An explicit cast silences the warning. In C, this
4931 option is enabled also by @option{-Wconversion}.
4933 @item -Wfloat-conversion
4934 @opindex Wfloat-conversion
4935 @opindex Wno-float-conversion
4936 Warn for implicit conversions that reduce the precision of a real value.
4937 This includes conversions from real to integer, and from higher precision
4938 real to lower precision real values. This option is also enabled by
4939 @option{-Wconversion}.
4941 @item -Wsized-deallocation @r{(C++ and Objective-C++ only)}
4942 @opindex Wsized-deallocation
4943 @opindex Wno-sized-deallocation
4944 Warn about a definition of an unsized deallocation function
4946 void operator delete (void *) noexcept;
4947 void operator delete[] (void *) noexcept;
4949 without a definition of the corresponding sized deallocation function
4951 void operator delete (void *, std::size_t) noexcept;
4952 void operator delete[] (void *, std::size_t) noexcept;
4954 or vice versa. Enabled by @option{-Wextra} along with
4955 @option{-fsized-deallocation}.
4957 @item -Wsizeof-pointer-memaccess
4958 @opindex Wsizeof-pointer-memaccess
4959 @opindex Wno-sizeof-pointer-memaccess
4960 Warn for suspicious length parameters to certain string and memory built-in
4961 functions if the argument uses @code{sizeof}. This warning warns e.g.@:
4962 about @code{memset (ptr, 0, sizeof (ptr));} if @code{ptr} is not an array,
4963 but a pointer, and suggests a possible fix, or about
4964 @code{memcpy (&foo, ptr, sizeof (&foo));}. This warning is enabled by
4967 @item -Wsizeof-array-argument
4968 @opindex Wsizeof-array-argument
4969 @opindex Wno-sizeof-array-argument
4970 Warn when the @code{sizeof} operator is applied to a parameter that is
4971 declared as an array in a function definition. This warning is enabled by
4972 default for C and C++ programs.
4974 @item -Wmemset-transposed-args
4975 @opindex Wmemset-transposed-args
4976 @opindex Wno-memset-transposed-args
4977 Warn for suspicious calls to the @code{memset} built-in function, if the
4978 second argument is not zero and the third argument is zero. This warns e.g.@
4979 about @code{memset (buf, sizeof buf, 0)} where most probably
4980 @code{memset (buf, 0, sizeof buf)} was meant instead. The diagnostics
4981 is only emitted if the third argument is literal zero. If it is some
4982 expression that is folded to zero, a cast of zero to some type, etc.,
4983 it is far less likely that the user has mistakenly exchanged the arguments
4984 and no warning is emitted. This warning is enabled by @option{-Wall}.
4988 @opindex Wno-address
4989 Warn about suspicious uses of memory addresses. These include using
4990 the address of a function in a conditional expression, such as
4991 @code{void func(void); if (func)}, and comparisons against the memory
4992 address of a string literal, such as @code{if (x == "abc")}. Such
4993 uses typically indicate a programmer error: the address of a function
4994 always evaluates to true, so their use in a conditional usually
4995 indicate that the programmer forgot the parentheses in a function
4996 call; and comparisons against string literals result in unspecified
4997 behavior and are not portable in C, so they usually indicate that the
4998 programmer intended to use @code{strcmp}. This warning is enabled by
5002 @opindex Wlogical-op
5003 @opindex Wno-logical-op
5004 Warn about suspicious uses of logical operators in expressions.
5005 This includes using logical operators in contexts where a
5006 bit-wise operator is likely to be expected. Also warns when
5007 the operands of a logical operator are the same:
5010 if (a < 0 && a < 0) @{ @dots{} @}
5013 @item -Wlogical-not-parentheses
5014 @opindex Wlogical-not-parentheses
5015 @opindex Wno-logical-not-parentheses
5016 Warn about logical not used on the left hand side operand of a comparison.
5017 This option does not warn if the RHS operand is of a boolean type. Its
5018 purpose is to detect suspicious code like the following:
5022 if (!a > 1) @{ @dots{} @}
5025 It is possible to suppress the warning by wrapping the LHS into
5028 if ((!a) > 1) @{ @dots{} @}
5031 This warning is enabled by @option{-Wall}.
5033 @item -Waggregate-return
5034 @opindex Waggregate-return
5035 @opindex Wno-aggregate-return
5036 Warn if any functions that return structures or unions are defined or
5037 called. (In languages where you can return an array, this also elicits
5040 @item -Wno-aggressive-loop-optimizations
5041 @opindex Wno-aggressive-loop-optimizations
5042 @opindex Waggressive-loop-optimizations
5043 Warn if in a loop with constant number of iterations the compiler detects
5044 undefined behavior in some statement during one or more of the iterations.
5046 @item -Wno-attributes
5047 @opindex Wno-attributes
5048 @opindex Wattributes
5049 Do not warn if an unexpected @code{__attribute__} is used, such as
5050 unrecognized attributes, function attributes applied to variables,
5051 etc. This does not stop errors for incorrect use of supported
5054 @item -Wno-builtin-macro-redefined
5055 @opindex Wno-builtin-macro-redefined
5056 @opindex Wbuiltin-macro-redefined
5057 Do not warn if certain built-in macros are redefined. This suppresses
5058 warnings for redefinition of @code{__TIMESTAMP__}, @code{__TIME__},
5059 @code{__DATE__}, @code{__FILE__}, and @code{__BASE_FILE__}.
5061 @item -Wstrict-prototypes @r{(C and Objective-C only)}
5062 @opindex Wstrict-prototypes
5063 @opindex Wno-strict-prototypes
5064 Warn if a function is declared or defined without specifying the
5065 argument types. (An old-style function definition is permitted without
5066 a warning if preceded by a declaration that specifies the argument
5069 @item -Wold-style-declaration @r{(C and Objective-C only)}
5070 @opindex Wold-style-declaration
5071 @opindex Wno-old-style-declaration
5072 Warn for obsolescent usages, according to the C Standard, in a
5073 declaration. For example, warn if storage-class specifiers like
5074 @code{static} are not the first things in a declaration. This warning
5075 is also enabled by @option{-Wextra}.
5077 @item -Wold-style-definition @r{(C and Objective-C only)}
5078 @opindex Wold-style-definition
5079 @opindex Wno-old-style-definition
5080 Warn if an old-style function definition is used. A warning is given
5081 even if there is a previous prototype.
5083 @item -Wmissing-parameter-type @r{(C and Objective-C only)}
5084 @opindex Wmissing-parameter-type
5085 @opindex Wno-missing-parameter-type
5086 A function parameter is declared without a type specifier in K&R-style
5093 This warning is also enabled by @option{-Wextra}.
5095 @item -Wmissing-prototypes @r{(C and Objective-C only)}
5096 @opindex Wmissing-prototypes
5097 @opindex Wno-missing-prototypes
5098 Warn if a global function is defined without a previous prototype
5099 declaration. This warning is issued even if the definition itself
5100 provides a prototype. Use this option to detect global functions
5101 that do not have a matching prototype declaration in a header file.
5102 This option is not valid for C++ because all function declarations
5103 provide prototypes and a non-matching declaration declares an
5104 overload rather than conflict with an earlier declaration.
5105 Use @option{-Wmissing-declarations} to detect missing declarations in C++.
5107 @item -Wmissing-declarations
5108 @opindex Wmissing-declarations
5109 @opindex Wno-missing-declarations
5110 Warn if a global function is defined without a previous declaration.
5111 Do so even if the definition itself provides a prototype.
5112 Use this option to detect global functions that are not declared in
5113 header files. In C, no warnings are issued for functions with previous
5114 non-prototype declarations; use @option{-Wmissing-prototypes} to detect
5115 missing prototypes. In C++, no warnings are issued for function templates,
5116 or for inline functions, or for functions in anonymous namespaces.
5118 @item -Wmissing-field-initializers
5119 @opindex Wmissing-field-initializers
5120 @opindex Wno-missing-field-initializers
5124 Warn if a structure's initializer has some fields missing. For
5125 example, the following code causes such a warning, because
5126 @code{x.h} is implicitly zero:
5129 struct s @{ int f, g, h; @};
5130 struct s x = @{ 3, 4 @};
5133 This option does not warn about designated initializers, so the following
5134 modification does not trigger a warning:
5137 struct s @{ int f, g, h; @};
5138 struct s x = @{ .f = 3, .g = 4 @};
5141 In C++ this option does not warn either about the empty @{ @}
5142 initializer, for example:
5145 struct s @{ int f, g, h; @};
5149 This warning is included in @option{-Wextra}. To get other @option{-Wextra}
5150 warnings without this one, use @option{-Wextra -Wno-missing-field-initializers}.
5152 @item -Wno-multichar
5153 @opindex Wno-multichar
5155 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
5156 Usually they indicate a typo in the user's code, as they have
5157 implementation-defined values, and should not be used in portable code.
5159 @item -Wnormalized@r{[}=@r{<}none@r{|}id@r{|}nfc@r{|}nfkc@r{>]}
5160 @opindex Wnormalized=
5161 @opindex Wnormalized
5162 @opindex Wno-normalized
5165 @cindex character set, input normalization
5166 In ISO C and ISO C++, two identifiers are different if they are
5167 different sequences of characters. However, sometimes when characters
5168 outside the basic ASCII character set are used, you can have two
5169 different character sequences that look the same. To avoid confusion,
5170 the ISO 10646 standard sets out some @dfn{normalization rules} which
5171 when applied ensure that two sequences that look the same are turned into
5172 the same sequence. GCC can warn you if you are using identifiers that
5173 have not been normalized; this option controls that warning.
5175 There are four levels of warning supported by GCC@. The default is
5176 @option{-Wnormalized=nfc}, which warns about any identifier that is
5177 not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the
5178 recommended form for most uses. It is equivalent to
5179 @option{-Wnormalized}.
5181 Unfortunately, there are some characters allowed in identifiers by
5182 ISO C and ISO C++ that, when turned into NFC, are not allowed in
5183 identifiers. That is, there's no way to use these symbols in portable
5184 ISO C or C++ and have all your identifiers in NFC@.
5185 @option{-Wnormalized=id} suppresses the warning for these characters.
5186 It is hoped that future versions of the standards involved will correct
5187 this, which is why this option is not the default.
5189 You can switch the warning off for all characters by writing
5190 @option{-Wnormalized=none} or @option{-Wno-normalized}. You should
5191 only do this if you are using some other normalization scheme (like
5192 ``D''), because otherwise you can easily create bugs that are
5193 literally impossible to see.
5195 Some characters in ISO 10646 have distinct meanings but look identical
5196 in some fonts or display methodologies, especially once formatting has
5197 been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL
5198 LETTER N'', displays just like a regular @code{n} that has been
5199 placed in a superscript. ISO 10646 defines the @dfn{NFKC}
5200 normalization scheme to convert all these into a standard form as
5201 well, and GCC warns if your code is not in NFKC if you use
5202 @option{-Wnormalized=nfkc}. This warning is comparable to warning
5203 about every identifier that contains the letter O because it might be
5204 confused with the digit 0, and so is not the default, but may be
5205 useful as a local coding convention if the programming environment
5206 cannot be fixed to display these characters distinctly.
5208 @item -Wno-deprecated
5209 @opindex Wno-deprecated
5210 @opindex Wdeprecated
5211 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
5213 @item -Wno-deprecated-declarations
5214 @opindex Wno-deprecated-declarations
5215 @opindex Wdeprecated-declarations
5216 Do not warn about uses of functions (@pxref{Function Attributes}),
5217 variables (@pxref{Variable Attributes}), and types (@pxref{Type
5218 Attributes}) marked as deprecated by using the @code{deprecated}
5222 @opindex Wno-overflow
5224 Do not warn about compile-time overflow in constant expressions.
5229 Warn about One Definition Rule violations during link-time optimization.
5230 Requires @option{-flto-odr-type-merging} to be enabled. Enabled by default.
5233 @opindex Wopenm-simd
5234 Warn if the vectorizer cost model overrides the OpenMP or the Cilk Plus
5235 simd directive set by user. The @option{-fsimd-cost-model=unlimited}
5236 option can be used to relax the cost model.
5238 @item -Woverride-init @r{(C and Objective-C only)}
5239 @opindex Woverride-init
5240 @opindex Wno-override-init
5244 Warn if an initialized field without side effects is overridden when
5245 using designated initializers (@pxref{Designated Inits, , Designated
5248 This warning is included in @option{-Wextra}. To get other
5249 @option{-Wextra} warnings without this one, use @option{-Wextra
5250 -Wno-override-init}.
5252 @item -Woverride-init-side-effects @r{(C and Objective-C only)}
5253 @opindex Woverride-init-side-effects
5254 @opindex Wno-override-init-side-effects
5255 Warn if an initialized field with side effects is overridden when
5256 using designated initializers (@pxref{Designated Inits, , Designated
5257 Initializers}). This warning is enabled by default.
5262 Warn if a structure is given the packed attribute, but the packed
5263 attribute has no effect on the layout or size of the structure.
5264 Such structures may be mis-aligned for little benefit. For
5265 instance, in this code, the variable @code{f.x} in @code{struct bar}
5266 is misaligned even though @code{struct bar} does not itself
5267 have the packed attribute:
5274 @} __attribute__((packed));
5282 @item -Wpacked-bitfield-compat
5283 @opindex Wpacked-bitfield-compat
5284 @opindex Wno-packed-bitfield-compat
5285 The 4.1, 4.2 and 4.3 series of GCC ignore the @code{packed} attribute
5286 on bit-fields of type @code{char}. This has been fixed in GCC 4.4 but
5287 the change can lead to differences in the structure layout. GCC
5288 informs you when the offset of such a field has changed in GCC 4.4.
5289 For example there is no longer a 4-bit padding between field @code{a}
5290 and @code{b} in this structure:
5297 @} __attribute__ ((packed));
5300 This warning is enabled by default. Use
5301 @option{-Wno-packed-bitfield-compat} to disable this warning.
5306 Warn if padding is included in a structure, either to align an element
5307 of the structure or to align the whole structure. Sometimes when this
5308 happens it is possible to rearrange the fields of the structure to
5309 reduce the padding and so make the structure smaller.
5311 @item -Wredundant-decls
5312 @opindex Wredundant-decls
5313 @opindex Wno-redundant-decls
5314 Warn if anything is declared more than once in the same scope, even in
5315 cases where multiple declaration is valid and changes nothing.
5317 @item -Wnested-externs @r{(C and Objective-C only)}
5318 @opindex Wnested-externs
5319 @opindex Wno-nested-externs
5320 Warn if an @code{extern} declaration is encountered within a function.
5322 @item -Wno-inherited-variadic-ctor
5323 @opindex Winherited-variadic-ctor
5324 @opindex Wno-inherited-variadic-ctor
5325 Suppress warnings about use of C++11 inheriting constructors when the
5326 base class inherited from has a C variadic constructor; the warning is
5327 on by default because the ellipsis is not inherited.
5332 Warn if a function that is declared as inline cannot be inlined.
5333 Even with this option, the compiler does not warn about failures to
5334 inline functions declared in system headers.
5336 The compiler uses a variety of heuristics to determine whether or not
5337 to inline a function. For example, the compiler takes into account
5338 the size of the function being inlined and the amount of inlining
5339 that has already been done in the current function. Therefore,
5340 seemingly insignificant changes in the source program can cause the
5341 warnings produced by @option{-Winline} to appear or disappear.
5343 @item -Wno-invalid-offsetof @r{(C++ and Objective-C++ only)}
5344 @opindex Wno-invalid-offsetof
5345 @opindex Winvalid-offsetof
5346 Suppress warnings from applying the @code{offsetof} macro to a non-POD
5347 type. According to the 2014 ISO C++ standard, applying @code{offsetof}
5348 to a non-standard-layout type is undefined. In existing C++ implementations,
5349 however, @code{offsetof} typically gives meaningful results.
5350 This flag is for users who are aware that they are
5351 writing nonportable code and who have deliberately chosen to ignore the
5354 The restrictions on @code{offsetof} may be relaxed in a future version
5355 of the C++ standard.
5357 @item -Wno-int-to-pointer-cast
5358 @opindex Wno-int-to-pointer-cast
5359 @opindex Wint-to-pointer-cast
5360 Suppress warnings from casts to pointer type of an integer of a
5361 different size. In C++, casting to a pointer type of smaller size is
5362 an error. @option{Wint-to-pointer-cast} is enabled by default.
5365 @item -Wno-pointer-to-int-cast @r{(C and Objective-C only)}
5366 @opindex Wno-pointer-to-int-cast
5367 @opindex Wpointer-to-int-cast
5368 Suppress warnings from casts from a pointer to an integer type of a
5372 @opindex Winvalid-pch
5373 @opindex Wno-invalid-pch
5374 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
5375 the search path but can't be used.
5379 @opindex Wno-long-long
5380 Warn if @code{long long} type is used. This is enabled by either
5381 @option{-Wpedantic} or @option{-Wtraditional} in ISO C90 and C++98
5382 modes. To inhibit the warning messages, use @option{-Wno-long-long}.
5384 @item -Wvariadic-macros
5385 @opindex Wvariadic-macros
5386 @opindex Wno-variadic-macros
5387 Warn if variadic macros are used in ISO C90 mode, or if the GNU
5388 alternate syntax is used in ISO C99 mode. This is enabled by either
5389 @option{-Wpedantic} or @option{-Wtraditional}. To inhibit the warning
5390 messages, use @option{-Wno-variadic-macros}.
5394 @opindex Wno-varargs
5395 Warn upon questionable usage of the macros used to handle variable
5396 arguments like @code{va_start}. This is default. To inhibit the
5397 warning messages, use @option{-Wno-varargs}.
5399 @item -Wvector-operation-performance
5400 @opindex Wvector-operation-performance
5401 @opindex Wno-vector-operation-performance
5402 Warn if vector operation is not implemented via SIMD capabilities of the
5403 architecture. Mainly useful for the performance tuning.
5404 Vector operation can be implemented @code{piecewise}, which means that the
5405 scalar operation is performed on every vector element;
5406 @code{in parallel}, which means that the vector operation is implemented
5407 using scalars of wider type, which normally is more performance efficient;
5408 and @code{as a single scalar}, which means that vector fits into a
5411 @item -Wno-virtual-move-assign
5412 @opindex Wvirtual-move-assign
5413 @opindex Wno-virtual-move-assign
5414 Suppress warnings about inheriting from a virtual base with a
5415 non-trivial C++11 move assignment operator. This is dangerous because
5416 if the virtual base is reachable along more than one path, it is
5417 moved multiple times, which can mean both objects end up in the
5418 moved-from state. If the move assignment operator is written to avoid
5419 moving from a moved-from object, this warning can be disabled.
5424 Warn if variable length array is used in the code.
5425 @option{-Wno-vla} prevents the @option{-Wpedantic} warning of
5426 the variable length array.
5428 @item -Wvolatile-register-var
5429 @opindex Wvolatile-register-var
5430 @opindex Wno-volatile-register-var
5431 Warn if a register variable is declared volatile. The volatile
5432 modifier does not inhibit all optimizations that may eliminate reads
5433 and/or writes to register variables. This warning is enabled by
5436 @item -Wdisabled-optimization
5437 @opindex Wdisabled-optimization
5438 @opindex Wno-disabled-optimization
5439 Warn if a requested optimization pass is disabled. This warning does
5440 not generally indicate that there is anything wrong with your code; it
5441 merely indicates that GCC's optimizers are unable to handle the code
5442 effectively. Often, the problem is that your code is too big or too
5443 complex; GCC refuses to optimize programs when the optimization
5444 itself is likely to take inordinate amounts of time.
5446 @item -Wpointer-sign @r{(C and Objective-C only)}
5447 @opindex Wpointer-sign
5448 @opindex Wno-pointer-sign
5449 Warn for pointer argument passing or assignment with different signedness.
5450 This option is only supported for C and Objective-C@. It is implied by
5451 @option{-Wall} and by @option{-Wpedantic}, which can be disabled with
5452 @option{-Wno-pointer-sign}.
5454 @item -Wstack-protector
5455 @opindex Wstack-protector
5456 @opindex Wno-stack-protector
5457 This option is only active when @option{-fstack-protector} is active. It
5458 warns about functions that are not protected against stack smashing.
5460 @item -Woverlength-strings
5461 @opindex Woverlength-strings
5462 @opindex Wno-overlength-strings
5463 Warn about string constants that are longer than the ``minimum
5464 maximum'' length specified in the C standard. Modern compilers
5465 generally allow string constants that are much longer than the
5466 standard's minimum limit, but very portable programs should avoid
5467 using longer strings.
5469 The limit applies @emph{after} string constant concatenation, and does
5470 not count the trailing NUL@. In C90, the limit was 509 characters; in
5471 C99, it was raised to 4095. C++98 does not specify a normative
5472 minimum maximum, so we do not diagnose overlength strings in C++@.
5474 This option is implied by @option{-Wpedantic}, and can be disabled with
5475 @option{-Wno-overlength-strings}.
5477 @item -Wunsuffixed-float-constants @r{(C and Objective-C only)}
5478 @opindex Wunsuffixed-float-constants
5480 Issue a warning for any floating constant that does not have
5481 a suffix. When used together with @option{-Wsystem-headers} it
5482 warns about such constants in system header files. This can be useful
5483 when preparing code to use with the @code{FLOAT_CONST_DECIMAL64} pragma
5484 from the decimal floating-point extension to C99.
5486 @item -Wno-designated-init @r{(C and Objective-C only)}
5487 Suppress warnings when a positional initializer is used to initialize
5488 a structure that has been marked with the @code{designated_init}
5493 @node Debugging Options
5494 @section Options for Debugging Your Program or GCC
5495 @cindex options, debugging
5496 @cindex debugging information options
5498 GCC has various special options that are used for debugging
5499 either your program or GCC:
5504 Produce debugging information in the operating system's native format
5505 (stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging
5508 On most systems that use stabs format, @option{-g} enables use of extra
5509 debugging information that only GDB can use; this extra information
5510 makes debugging work better in GDB but probably makes other debuggers
5512 refuse to read the program. If you want to control for certain whether
5513 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
5514 @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
5516 GCC allows you to use @option{-g} with
5517 @option{-O}. The shortcuts taken by optimized code may occasionally
5518 produce surprising results: some variables you declared may not exist
5519 at all; flow of control may briefly move where you did not expect it;
5520 some statements may not be executed because they compute constant
5521 results or their values are already at hand; some statements may
5522 execute in different places because they have been moved out of loops.
5524 Nevertheless it proves possible to debug optimized output. This makes
5525 it reasonable to use the optimizer for programs that might have bugs.
5527 The following options are useful when GCC is generated with the
5528 capability for more than one debugging format.
5531 @opindex gsplit-dwarf
5532 Separate as much dwarf debugging information as possible into a
5533 separate output file with the extension .dwo. This option allows
5534 the build system to avoid linking files with debug information. To
5535 be useful, this option requires a debugger capable of reading .dwo
5540 Produce debugging information for use by GDB@. This means to use the
5541 most expressive format available (DWARF 2, stabs, or the native format
5542 if neither of those are supported), including GDB extensions if at all
5547 Generate dwarf .debug_pubnames and .debug_pubtypes sections.
5549 @item -ggnu-pubnames
5550 @opindex ggnu-pubnames
5551 Generate .debug_pubnames and .debug_pubtypes sections in a format
5552 suitable for conversion into a GDB@ index. This option is only useful
5553 with a linker that can produce GDB@ index version 7.
5557 Produce debugging information in stabs format (if that is supported),
5558 without GDB extensions. This is the format used by DBX on most BSD
5559 systems. On MIPS, Alpha and System V Release 4 systems this option
5560 produces stabs debugging output that is not understood by DBX or SDB@.
5561 On System V Release 4 systems this option requires the GNU assembler.
5563 @item -feliminate-unused-debug-symbols
5564 @opindex feliminate-unused-debug-symbols
5565 Produce debugging information in stabs format (if that is supported),
5566 for only symbols that are actually used.
5568 @item -femit-class-debug-always
5569 @opindex femit-class-debug-always
5570 Instead of emitting debugging information for a C++ class in only one
5571 object file, emit it in all object files using the class. This option
5572 should be used only with debuggers that are unable to handle the way GCC
5573 normally emits debugging information for classes because using this
5574 option increases the size of debugging information by as much as a
5577 @item -fdebug-types-section
5578 @opindex fdebug-types-section
5579 @opindex fno-debug-types-section
5580 When using DWARF Version 4 or higher, type DIEs can be put into
5581 their own @code{.debug_types} section instead of making them part of the
5582 @code{.debug_info} section. It is more efficient to put them in a separate
5583 comdat sections since the linker can then remove duplicates.
5584 But not all DWARF consumers support @code{.debug_types} sections yet
5585 and on some objects @code{.debug_types} produces larger instead of smaller
5586 debugging information.
5590 Produce debugging information in stabs format (if that is supported),
5591 using GNU extensions understood only by the GNU debugger (GDB)@. The
5592 use of these extensions is likely to make other debuggers crash or
5593 refuse to read the program.
5597 Produce debugging information in COFF format (if that is supported).
5598 This is the format used by SDB on most System V systems prior to
5603 Produce debugging information in XCOFF format (if that is supported).
5604 This is the format used by the DBX debugger on IBM RS/6000 systems.
5608 Produce debugging information in XCOFF format (if that is supported),
5609 using GNU extensions understood only by the GNU debugger (GDB)@. The
5610 use of these extensions is likely to make other debuggers crash or
5611 refuse to read the program, and may cause assemblers other than the GNU
5612 assembler (GAS) to fail with an error.
5614 @item -gdwarf-@var{version}
5615 @opindex gdwarf-@var{version}
5616 Produce debugging information in DWARF format (if that is supported).
5617 The value of @var{version} may be either 2, 3, 4 or 5; the default version
5618 for most targets is 4. DWARF Version 5 is only experimental.
5620 Note that with DWARF Version 2, some ports require and always
5621 use some non-conflicting DWARF 3 extensions in the unwind tables.
5623 Version 4 may require GDB 7.0 and @option{-fvar-tracking-assignments}
5624 for maximum benefit.
5626 @item -grecord-gcc-switches
5627 @opindex grecord-gcc-switches
5628 This switch causes the command-line options used to invoke the
5629 compiler that may affect code generation to be appended to the
5630 DW_AT_producer attribute in DWARF debugging information. The options
5631 are concatenated with spaces separating them from each other and from
5632 the compiler version. See also @option{-frecord-gcc-switches} for another
5633 way of storing compiler options into the object file. This is the default.
5635 @item -gno-record-gcc-switches
5636 @opindex gno-record-gcc-switches
5637 Disallow appending command-line options to the DW_AT_producer attribute
5638 in DWARF debugging information.
5640 @item -gstrict-dwarf
5641 @opindex gstrict-dwarf
5642 Disallow using extensions of later DWARF standard version than selected
5643 with @option{-gdwarf-@var{version}}. On most targets using non-conflicting
5644 DWARF extensions from later standard versions is allowed.
5646 @item -gno-strict-dwarf
5647 @opindex gno-strict-dwarf
5648 Allow using extensions of later DWARF standard version than selected with
5649 @option{-gdwarf-@var{version}}.
5651 @item -gz@r{[}=@var{type}@r{]}
5653 Produce compressed debug sections in DWARF format, if that is supported.
5654 If @var{type} is not given, the default type depends on the capabilities
5655 of the assembler and linker used. @var{type} may be one of
5656 @samp{none} (don't compress debug sections), @samp{zlib} (use zlib
5657 compression in ELF gABI format), or @samp{zlib-gnu} (use zlib
5658 compression in traditional GNU format). If the linker doesn't support
5659 writing compressed debug sections, the option is rejected. Otherwise,
5660 if the assembler does not support them, @option{-gz} is silently ignored
5661 when producing object files.
5665 Produce debugging information in Alpha/VMS debug format (if that is
5666 supported). This is the format used by DEBUG on Alpha/VMS systems.
5669 @itemx -ggdb@var{level}
5670 @itemx -gstabs@var{level}
5671 @itemx -gcoff@var{level}
5672 @itemx -gxcoff@var{level}
5673 @itemx -gvms@var{level}
5674 Request debugging information and also use @var{level} to specify how
5675 much information. The default level is 2.
5677 Level 0 produces no debug information at all. Thus, @option{-g0} negates
5680 Level 1 produces minimal information, enough for making backtraces in
5681 parts of the program that you don't plan to debug. This includes
5682 descriptions of functions and external variables, and line number
5683 tables, but no information about local variables.
5685 Level 3 includes extra information, such as all the macro definitions
5686 present in the program. Some debuggers support macro expansion when
5687 you use @option{-g3}.
5689 @option{-gdwarf-2} does not accept a concatenated debug level, because
5690 GCC used to support an option @option{-gdwarf} that meant to generate
5691 debug information in version 1 of the DWARF format (which is very
5692 different from version 2), and it would have been too confusing. That
5693 debug format is long obsolete, but the option cannot be changed now.
5694 Instead use an additional @option{-g@var{level}} option to change the
5695 debug level for DWARF.
5699 Turn off generation of debug info, if leaving out this option
5700 generates it, or turn it on at level 2 otherwise. The position of this
5701 argument in the command line does not matter; it takes effect after all
5702 other options are processed, and it does so only once, no matter how
5703 many times it is given. This is mainly intended to be used with
5704 @option{-fcompare-debug}.
5706 @item -fsanitize=address
5707 @opindex fsanitize=address
5708 Enable AddressSanitizer, a fast memory error detector.
5709 Memory access instructions are instrumented to detect
5710 out-of-bounds and use-after-free bugs.
5711 See @uref{http://code.google.com/p/address-sanitizer/} for
5712 more details. The run-time behavior can be influenced using the
5713 @env{ASAN_OPTIONS} environment variable; see
5714 @url{https://code.google.com/p/address-sanitizer/wiki/Flags#Run-time_flags} for
5715 a list of supported options.
5717 @item -fsanitize=kernel-address
5718 @opindex fsanitize=kernel-address
5719 Enable AddressSanitizer for Linux kernel.
5720 See @uref{http://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel} for more details.
5722 @item -fsanitize=thread
5723 @opindex fsanitize=thread
5724 Enable ThreadSanitizer, a fast data race detector.
5725 Memory access instructions are instrumented to detect
5726 data race bugs. See @uref{http://code.google.com/p/thread-sanitizer/} for more
5727 details. The run-time behavior can be influenced using the @env{TSAN_OPTIONS}
5728 environment variable; see
5729 @url{https://code.google.com/p/thread-sanitizer/wiki/Flags} for a list of
5732 @item -fsanitize=leak
5733 @opindex fsanitize=leak
5734 Enable LeakSanitizer, a memory leak detector.
5735 This option only matters for linking of executables and if neither
5736 @option{-fsanitize=address} nor @option{-fsanitize=thread} is used. In that
5737 case the executable is linked against a library that overrides @code{malloc}
5738 and other allocator functions. See
5739 @uref{https://code.google.com/p/address-sanitizer/wiki/LeakSanitizer} for more
5740 details. The run-time behavior can be influenced using the
5741 @env{LSAN_OPTIONS} environment variable.
5743 @item -fsanitize=undefined
5744 @opindex fsanitize=undefined
5745 Enable UndefinedBehaviorSanitizer, a fast undefined behavior detector.
5746 Various computations are instrumented to detect undefined behavior
5747 at runtime. Current suboptions are:
5751 @item -fsanitize=shift
5752 @opindex fsanitize=shift
5753 This option enables checking that the result of a shift operation is
5754 not undefined. Note that what exactly is considered undefined differs
5755 slightly between C and C++, as well as between ISO C90 and C99, etc.
5757 @item -fsanitize=integer-divide-by-zero
5758 @opindex fsanitize=integer-divide-by-zero
5759 Detect integer division by zero as well as @code{INT_MIN / -1} division.
5761 @item -fsanitize=unreachable
5762 @opindex fsanitize=unreachable
5763 With this option, the compiler turns the @code{__builtin_unreachable}
5764 call into a diagnostics message call instead. When reaching the
5765 @code{__builtin_unreachable} call, the behavior is undefined.
5767 @item -fsanitize=vla-bound
5768 @opindex fsanitize=vla-bound
5769 This option instructs the compiler to check that the size of a variable
5770 length array is positive.
5772 @item -fsanitize=null
5773 @opindex fsanitize=null
5774 This option enables pointer checking. Particularly, the application
5775 built with this option turned on will issue an error message when it
5776 tries to dereference a NULL pointer, or if a reference (possibly an
5777 rvalue reference) is bound to a NULL pointer, or if a method is invoked
5778 on an object pointed by a NULL pointer.
5780 @item -fsanitize=return
5781 @opindex fsanitize=return
5782 This option enables return statement checking. Programs
5783 built with this option turned on will issue an error message
5784 when the end of a non-void function is reached without actually
5785 returning a value. This option works in C++ only.
5787 @item -fsanitize=signed-integer-overflow
5788 @opindex fsanitize=signed-integer-overflow
5789 This option enables signed integer overflow checking. We check that
5790 the result of @code{+}, @code{*}, and both unary and binary @code{-}
5791 does not overflow in the signed arithmetics. Note, integer promotion
5792 rules must be taken into account. That is, the following is not an
5795 signed char a = SCHAR_MAX;
5799 @item -fsanitize=bounds
5800 @opindex fsanitize=bounds
5801 This option enables instrumentation of array bounds. Various out of bounds
5802 accesses are detected. Flexible array members, flexible array member-like
5803 arrays, and initializers of variables with static storage are not instrumented.
5805 @item -fsanitize=bounds-strict
5806 @opindex fsanitize=bounds-strict
5807 This option enables strict instrumentation of array bounds. Most out of bounds
5808 accesses are detected, including flexible array members and flexible array
5809 member-like arrays. Initializers of variables with static storage are not
5812 @item -fsanitize=alignment
5813 @opindex fsanitize=alignment
5815 This option enables checking of alignment of pointers when they are
5816 dereferenced, or when a reference is bound to insufficiently aligned target,
5817 or when a method or constructor is invoked on insufficiently aligned object.
5819 @item -fsanitize=object-size
5820 @opindex fsanitize=object-size
5821 This option enables instrumentation of memory references using the
5822 @code{__builtin_object_size} function. Various out of bounds pointer
5823 accesses are detected.
5825 @item -fsanitize=float-divide-by-zero
5826 @opindex fsanitize=float-divide-by-zero
5827 Detect floating-point division by zero. Unlike other similar options,
5828 @option{-fsanitize=float-divide-by-zero} is not enabled by
5829 @option{-fsanitize=undefined}, since floating-point division by zero can
5830 be a legitimate way of obtaining infinities and NaNs.
5832 @item -fsanitize=float-cast-overflow
5833 @opindex fsanitize=float-cast-overflow
5834 This option enables floating-point type to integer conversion checking.
5835 We check that the result of the conversion does not overflow.
5836 Unlike other similar options, @option{-fsanitize=float-cast-overflow} is
5837 not enabled by @option{-fsanitize=undefined}.
5838 This option does not work well with @code{FE_INVALID} exceptions enabled.
5840 @item -fsanitize=nonnull-attribute
5841 @opindex fsanitize=nonnull-attribute
5843 This option enables instrumentation of calls, checking whether null values
5844 are not passed to arguments marked as requiring a non-null value by the
5845 @code{nonnull} function attribute.
5847 @item -fsanitize=returns-nonnull-attribute
5848 @opindex fsanitize=returns-nonnull-attribute
5850 This option enables instrumentation of return statements in functions
5851 marked with @code{returns_nonnull} function attribute, to detect returning
5852 of null values from such functions.
5854 @item -fsanitize=bool
5855 @opindex fsanitize=bool
5857 This option enables instrumentation of loads from bool. If a value other
5858 than 0/1 is loaded, a run-time error is issued.
5860 @item -fsanitize=enum
5861 @opindex fsanitize=enum
5863 This option enables instrumentation of loads from an enum type. If
5864 a value outside the range of values for the enum type is loaded,
5865 a run-time error is issued.
5867 @item -fsanitize=vptr
5868 @opindex fsanitize=vptr
5870 This option enables instrumentation of C++ member function calls, member
5871 accesses and some conversions between pointers to base and derived classes,
5872 to verify the referenced object has the correct dynamic type.
5876 While @option{-ftrapv} causes traps for signed overflows to be emitted,
5877 @option{-fsanitize=undefined} gives a diagnostic message.
5878 This currently works only for the C family of languages.
5880 @item -fno-sanitize=all
5881 @opindex fno-sanitize=all
5883 This option disables all previously enabled sanitizers.
5884 @option{-fsanitize=all} is not allowed, as some sanitizers cannot be used
5887 @item -fasan-shadow-offset=@var{number}
5888 @opindex fasan-shadow-offset
5889 This option forces GCC to use custom shadow offset in AddressSanitizer checks.
5890 It is useful for experimenting with different shadow memory layouts in
5891 Kernel AddressSanitizer.
5893 @item -fsanitize-sections=@var{s1},@var{s2},...
5894 @opindex fsanitize-sections
5895 Sanitize global variables in selected user-defined sections. @var{si} may
5898 @item -fsanitize-recover@r{[}=@var{opts}@r{]}
5899 @opindex fsanitize-recover
5900 @opindex fno-sanitize-recover
5901 @option{-fsanitize-recover=} controls error recovery mode for sanitizers
5902 mentioned in comma-separated list of @var{opts}. Enabling this option
5903 for a sanitizer component causes it to attempt to continue
5904 running the program as if no error happened. This means multiple
5905 runtime errors can be reported in a single program run, and the exit
5906 code of the program may indicate success even when errors
5907 have been reported. The @option{-fno-sanitize-recover=} option
5908 can be used to alter
5909 this behavior: only the first detected error is reported
5910 and program then exits with a non-zero exit code.
5912 Currently this feature only works for @option{-fsanitize=undefined} (and its suboptions
5913 except for @option{-fsanitize=unreachable} and @option{-fsanitize=return}),
5914 @option{-fsanitize=float-cast-overflow}, @option{-fsanitize=float-divide-by-zero} and
5915 @option{-fsanitize=kernel-address}. For these sanitizers error recovery is turned on by default.
5916 @option{-fsanitize-recover=all} and @option{-fno-sanitize-recover=all} is also
5917 accepted, the former enables recovery for all sanitizers that support it,
5918 the latter disables recovery for all sanitizers that support it.
5920 Syntax without explicit @var{opts} parameter is deprecated. It is equivalent to
5922 -fsanitize-recover=undefined,float-cast-overflow,float-divide-by-zero
5925 Similarly @option{-fno-sanitize-recover} is equivalent to
5927 -fno-sanitize-recover=undefined,float-cast-overflow,float-divide-by-zero
5930 @item -fsanitize-undefined-trap-on-error
5931 @opindex fsanitize-undefined-trap-on-error
5932 The @option{-fsanitize-undefined-trap-on-error} option instructs the compiler to
5933 report undefined behavior using @code{__builtin_trap} rather than
5934 a @code{libubsan} library routine. The advantage of this is that the
5935 @code{libubsan} library is not needed and is not linked in, so this
5936 is usable even in freestanding environments.
5938 @item -fcheck-pointer-bounds
5939 @opindex fcheck-pointer-bounds
5940 @opindex fno-check-pointer-bounds
5941 @cindex Pointer Bounds Checker options
5942 Enable Pointer Bounds Checker instrumentation. Each memory reference
5943 is instrumented with checks of the pointer used for memory access against
5944 bounds associated with that pointer.
5947 is only an implementation for Intel MPX available, thus x86 target
5948 and @option{-mmpx} are required to enable this feature.
5949 MPX-based instrumentation requires
5950 a runtime library to enable MPX in hardware and handle bounds
5951 violation signals. By default when @option{-fcheck-pointer-bounds}
5952 and @option{-mmpx} options are used to link a program, the GCC driver
5953 links against the @file{libmpx} runtime library and @file{libmpxwrappers}
5954 library. It also passes '-z bndplt' to a linker in case it supports this
5955 option (which is checked on libmpx configuration). Note that old versions
5956 of linker may ignore option. Gold linker doesn't support '-z bndplt'
5957 option. With no '-z bndplt' support in linker all calls to dynamic libraries
5958 lose passed bounds reducing overall protection level. It's highly
5959 recommended to use linker with '-z bndplt' support. In case such linker
5960 is not available it is adviced to always use @option{-static-libmpxwrappers}
5961 for better protection level or use @option{-static} to completely avoid
5962 external calls to dynamic libraries. MPX-based instrumentation
5963 may be used for debugging and also may be included in production code
5964 to increase program security. Depending on usage, you may
5965 have different requirements for the runtime library. The current version
5966 of the MPX runtime library is more oriented for use as a debugging
5967 tool. MPX runtime library usage implies @option{-lpthread}. See
5968 also @option{-static-libmpx}. The runtime library behavior can be
5969 influenced using various @env{CHKP_RT_*} environment variables. See
5970 @uref{https://gcc.gnu.org/wiki/Intel%20MPX%20support%20in%20the%20GCC%20compiler}
5973 Generated instrumentation may be controlled by various
5974 @option{-fchkp-*} options and by the @code{bnd_variable_size}
5975 structure field attribute (@pxref{Type Attributes}) and
5976 @code{bnd_legacy}, and @code{bnd_instrument} function attributes
5977 (@pxref{Function Attributes}). GCC also provides a number of built-in
5978 functions for controlling the Pointer Bounds Checker. @xref{Pointer
5979 Bounds Checker builtins}, for more information.
5981 @item -fchkp-check-incomplete-type
5982 @opindex fchkp-check-incomplete-type
5983 @opindex fno-chkp-check-incomplete-type
5984 Generate pointer bounds checks for variables with incomplete type.
5987 @item -fchkp-narrow-bounds
5988 @opindex fchkp-narrow-bounds
5989 @opindex fno-chkp-narrow-bounds
5990 Controls bounds used by Pointer Bounds Checker for pointers to object
5991 fields. If narrowing is enabled then field bounds are used. Otherwise
5992 object bounds are used. See also @option{-fchkp-narrow-to-innermost-array}
5993 and @option{-fchkp-first-field-has-own-bounds}. Enabled by default.
5995 @item -fchkp-first-field-has-own-bounds
5996 @opindex fchkp-first-field-has-own-bounds
5997 @opindex fno-chkp-first-field-has-own-bounds
5998 Forces Pointer Bounds Checker to use narrowed bounds for the address of the
5999 first field in the structure. By default a pointer to the first field has
6000 the same bounds as a pointer to the whole structure.
6002 @item -fchkp-narrow-to-innermost-array
6003 @opindex fchkp-narrow-to-innermost-array
6004 @opindex fno-chkp-narrow-to-innermost-array
6005 Forces Pointer Bounds Checker to use bounds of the innermost arrays in
6006 case of nested static array access. By default this option is disabled and
6007 bounds of the outermost array are used.
6009 @item -fchkp-optimize
6010 @opindex fchkp-optimize
6011 @opindex fno-chkp-optimize
6012 Enables Pointer Bounds Checker optimizations. Enabled by default at
6013 optimization levels @option{-O}, @option{-O2}, @option{-O3}.
6015 @item -fchkp-use-fast-string-functions
6016 @opindex fchkp-use-fast-string-functions
6017 @opindex fno-chkp-use-fast-string-functions
6018 Enables use of @code{*_nobnd} versions of string functions (not copying bounds)
6019 by Pointer Bounds Checker. Disabled by default.
6021 @item -fchkp-use-nochk-string-functions
6022 @opindex fchkp-use-nochk-string-functions
6023 @opindex fno-chkp-use-nochk-string-functions
6024 Enables use of @code{*_nochk} versions of string functions (not checking bounds)
6025 by Pointer Bounds Checker. Disabled by default.
6027 @item -fchkp-use-static-bounds
6028 @opindex fchkp-use-static-bounds
6029 @opindex fno-chkp-use-static-bounds
6030 Allow Pointer Bounds Checker to generate static bounds holding
6031 bounds of static variables. Enabled by default.
6033 @item -fchkp-use-static-const-bounds
6034 @opindex fchkp-use-static-const-bounds
6035 @opindex fno-chkp-use-static-const-bounds
6036 Use statically-initialized bounds for constant bounds instead of
6037 generating them each time they are required. By default enabled when
6038 @option{-fchkp-use-static-bounds} is enabled.
6040 @item -fchkp-treat-zero-dynamic-size-as-infinite
6041 @opindex fchkp-treat-zero-dynamic-size-as-infinite
6042 @opindex fno-chkp-treat-zero-dynamic-size-as-infinite
6043 With this option, objects with incomplete type whose
6044 dynamically-obtained size is zero are treated as having infinite size
6045 instead by Pointer Bounds
6046 Checker. This option may be helpful if a program is linked with a library
6047 missing size information for some symbols. Disabled by default.
6049 @item -fchkp-check-read
6050 @opindex fchkp-check-read
6051 @opindex fno-chkp-check-read
6052 Instructs Pointer Bounds Checker to generate checks for all read
6053 accesses to memory. Enabled by default.
6055 @item -fchkp-check-write
6056 @opindex fchkp-check-write
6057 @opindex fno-chkp-check-write
6058 Instructs Pointer Bounds Checker to generate checks for all write
6059 accesses to memory. Enabled by default.
6061 @item -fchkp-store-bounds
6062 @opindex fchkp-store-bounds
6063 @opindex fno-chkp-store-bounds
6064 Instructs Pointer Bounds Checker to generate bounds stores for
6065 pointer writes. Enabled by default.
6067 @item -fchkp-instrument-calls
6068 @opindex fchkp-instrument-calls
6069 @opindex fno-chkp-instrument-calls
6070 Instructs Pointer Bounds Checker to pass pointer bounds to calls.
6073 @item -fchkp-instrument-marked-only
6074 @opindex fchkp-instrument-marked-only
6075 @opindex fno-chkp-instrument-marked-only
6076 Instructs Pointer Bounds Checker to instrument only functions
6077 marked with the @code{bnd_instrument} attribute
6078 (@pxref{Function Attributes}). Disabled by default.
6080 @item -fchkp-use-wrappers
6081 @opindex fchkp-use-wrappers
6082 @opindex fno-chkp-use-wrappers
6083 Allows Pointer Bounds Checker to replace calls to built-in functions
6084 with calls to wrapper functions. When @option{-fchkp-use-wrappers}
6085 is used to link a program, the GCC driver automatically links
6086 against @file{libmpxwrappers}. See also @option{-static-libmpxwrappers}.
6089 @item -fdump-final-insns@r{[}=@var{file}@r{]}
6090 @opindex fdump-final-insns
6091 Dump the final internal representation (RTL) to @var{file}. If the
6092 optional argument is omitted (or if @var{file} is @code{.}), the name
6093 of the dump file is determined by appending @code{.gkd} to the
6094 compilation output file name.
6096 @item -fcompare-debug@r{[}=@var{opts}@r{]}
6097 @opindex fcompare-debug
6098 @opindex fno-compare-debug
6099 If no error occurs during compilation, run the compiler a second time,
6100 adding @var{opts} and @option{-fcompare-debug-second} to the arguments
6101 passed to the second compilation. Dump the final internal
6102 representation in both compilations, and print an error if they differ.
6104 If the equal sign is omitted, the default @option{-gtoggle} is used.
6106 The environment variable @env{GCC_COMPARE_DEBUG}, if defined, non-empty
6107 and nonzero, implicitly enables @option{-fcompare-debug}. If
6108 @env{GCC_COMPARE_DEBUG} is defined to a string starting with a dash,
6109 then it is used for @var{opts}, otherwise the default @option{-gtoggle}
6112 @option{-fcompare-debug=}, with the equal sign but without @var{opts},
6113 is equivalent to @option{-fno-compare-debug}, which disables the dumping
6114 of the final representation and the second compilation, preventing even
6115 @env{GCC_COMPARE_DEBUG} from taking effect.
6117 To verify full coverage during @option{-fcompare-debug} testing, set
6118 @env{GCC_COMPARE_DEBUG} to say @option{-fcompare-debug-not-overridden},
6119 which GCC rejects as an invalid option in any actual compilation
6120 (rather than preprocessing, assembly or linking). To get just a
6121 warning, setting @env{GCC_COMPARE_DEBUG} to @samp{-w%n-fcompare-debug
6122 not overridden} will do.
6124 @item -fcompare-debug-second
6125 @opindex fcompare-debug-second
6126 This option is implicitly passed to the compiler for the second
6127 compilation requested by @option{-fcompare-debug}, along with options to
6128 silence warnings, and omitting other options that would cause
6129 side-effect compiler outputs to files or to the standard output. Dump
6130 files and preserved temporary files are renamed so as to contain the
6131 @code{.gk} additional extension during the second compilation, to avoid
6132 overwriting those generated by the first.
6134 When this option is passed to the compiler driver, it causes the
6135 @emph{first} compilation to be skipped, which makes it useful for little
6136 other than debugging the compiler proper.
6138 @item -feliminate-dwarf2-dups
6139 @opindex feliminate-dwarf2-dups
6140 Compress DWARF 2 debugging information by eliminating duplicated
6141 information about each symbol. This option only makes sense when
6142 generating DWARF 2 debugging information with @option{-gdwarf-2}.
6144 @item -femit-struct-debug-baseonly
6145 @opindex femit-struct-debug-baseonly
6146 Emit debug information for struct-like types
6147 only when the base name of the compilation source file
6148 matches the base name of file in which the struct is defined.
6150 This option substantially reduces the size of debugging information,
6151 but at significant potential loss in type information to the debugger.
6152 See @option{-femit-struct-debug-reduced} for a less aggressive option.
6153 See @option{-femit-struct-debug-detailed} for more detailed control.
6155 This option works only with DWARF 2.
6157 @item -femit-struct-debug-reduced
6158 @opindex femit-struct-debug-reduced
6159 Emit debug information for struct-like types
6160 only when the base name of the compilation source file
6161 matches the base name of file in which the type is defined,
6162 unless the struct is a template or defined in a system header.
6164 This option significantly reduces the size of debugging information,
6165 with some potential loss in type information to the debugger.
6166 See @option{-femit-struct-debug-baseonly} for a more aggressive option.
6167 See @option{-femit-struct-debug-detailed} for more detailed control.
6169 This option works only with DWARF 2.
6171 @item -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]}
6172 @opindex femit-struct-debug-detailed
6173 Specify the struct-like types
6174 for which the compiler generates debug information.
6175 The intent is to reduce duplicate struct debug information
6176 between different object files within the same program.
6178 This option is a detailed version of
6179 @option{-femit-struct-debug-reduced} and @option{-femit-struct-debug-baseonly},
6180 which serves for most needs.
6182 A specification has the syntax@*
6183 [@samp{dir:}|@samp{ind:}][@samp{ord:}|@samp{gen:}](@samp{any}|@samp{sys}|@samp{base}|@samp{none})
6185 The optional first word limits the specification to
6186 structs that are used directly (@samp{dir:}) or used indirectly (@samp{ind:}).
6187 A struct type is used directly when it is the type of a variable, member.
6188 Indirect uses arise through pointers to structs.
6189 That is, when use of an incomplete struct is valid, the use is indirect.
6191 @samp{struct one direct; struct two * indirect;}.
6193 The optional second word limits the specification to
6194 ordinary structs (@samp{ord:}) or generic structs (@samp{gen:}).
6195 Generic structs are a bit complicated to explain.
6196 For C++, these are non-explicit specializations of template classes,
6197 or non-template classes within the above.
6198 Other programming languages have generics,
6199 but @option{-femit-struct-debug-detailed} does not yet implement them.
6201 The third word specifies the source files for those
6202 structs for which the compiler should emit debug information.
6203 The values @samp{none} and @samp{any} have the normal meaning.
6204 The value @samp{base} means that
6205 the base of name of the file in which the type declaration appears
6206 must match the base of the name of the main compilation file.
6207 In practice, this means that when compiling @file{foo.c}, debug information
6208 is generated for types declared in that file and @file{foo.h},
6209 but not other header files.
6210 The value @samp{sys} means those types satisfying @samp{base}
6211 or declared in system or compiler headers.
6213 You may need to experiment to determine the best settings for your application.
6215 The default is @option{-femit-struct-debug-detailed=all}.
6217 This option works only with DWARF 2.
6219 @item -fno-merge-debug-strings
6220 @opindex fmerge-debug-strings
6221 @opindex fno-merge-debug-strings
6222 Direct the linker to not merge together strings in the debugging
6223 information that are identical in different object files. Merging is
6224 not supported by all assemblers or linkers. Merging decreases the size
6225 of the debug information in the output file at the cost of increasing
6226 link processing time. Merging is enabled by default.
6228 @item -fdebug-prefix-map=@var{old}=@var{new}
6229 @opindex fdebug-prefix-map
6230 When compiling files in directory @file{@var{old}}, record debugging
6231 information describing them as in @file{@var{new}} instead.
6233 @item -fno-dwarf2-cfi-asm
6234 @opindex fdwarf2-cfi-asm
6235 @opindex fno-dwarf2-cfi-asm
6236 Emit DWARF 2 unwind info as compiler generated @code{.eh_frame} section
6237 instead of using GAS @code{.cfi_*} directives.
6239 @cindex @command{prof}
6242 Generate extra code to write profile information suitable for the
6243 analysis program @command{prof}. You must use this option when compiling
6244 the source files you want data about, and you must also use it when
6247 @cindex @command{gprof}
6250 Generate extra code to write profile information suitable for the
6251 analysis program @command{gprof}. You must use this option when compiling
6252 the source files you want data about, and you must also use it when
6257 Makes the compiler print out each function name as it is compiled, and
6258 print some statistics about each pass when it finishes.
6261 @opindex ftime-report
6262 Makes the compiler print some statistics about the time consumed by each
6263 pass when it finishes.
6266 @opindex fmem-report
6267 Makes the compiler print some statistics about permanent memory
6268 allocation when it finishes.
6270 @item -fmem-report-wpa
6271 @opindex fmem-report-wpa
6272 Makes the compiler print some statistics about permanent memory
6273 allocation for the WPA phase only.
6275 @item -fpre-ipa-mem-report
6276 @opindex fpre-ipa-mem-report
6277 @item -fpost-ipa-mem-report
6278 @opindex fpost-ipa-mem-report
6279 Makes the compiler print some statistics about permanent memory
6280 allocation before or after interprocedural optimization.
6282 @item -fprofile-report
6283 @opindex fprofile-report
6284 Makes the compiler print some statistics about consistency of the
6285 (estimated) profile and effect of individual passes.
6288 @opindex fstack-usage
6289 Makes the compiler output stack usage information for the program, on a
6290 per-function basis. The filename for the dump is made by appending
6291 @file{.su} to the @var{auxname}. @var{auxname} is generated from the name of
6292 the output file, if explicitly specified and it is not an executable,
6293 otherwise it is the basename of the source file. An entry is made up
6298 The name of the function.
6302 One or more qualifiers: @code{static}, @code{dynamic}, @code{bounded}.
6305 The qualifier @code{static} means that the function manipulates the stack
6306 statically: a fixed number of bytes are allocated for the frame on function
6307 entry and released on function exit; no stack adjustments are otherwise made
6308 in the function. The second field is this fixed number of bytes.
6310 The qualifier @code{dynamic} means that the function manipulates the stack
6311 dynamically: in addition to the static allocation described above, stack
6312 adjustments are made in the body of the function, for example to push/pop
6313 arguments around function calls. If the qualifier @code{bounded} is also
6314 present, the amount of these adjustments is bounded at compile time and
6315 the second field is an upper bound of the total amount of stack used by
6316 the function. If it is not present, the amount of these adjustments is
6317 not bounded at compile time and the second field only represents the
6320 @item -fprofile-arcs
6321 @opindex fprofile-arcs
6322 Add code so that program flow @dfn{arcs} are instrumented. During
6323 execution the program records how many times each branch and call is
6324 executed and how many times it is taken or returns. When the compiled
6325 program exits it saves this data to a file called
6326 @file{@var{auxname}.gcda} for each source file. The data may be used for
6327 profile-directed optimizations (@option{-fbranch-probabilities}), or for
6328 test coverage analysis (@option{-ftest-coverage}). Each object file's
6329 @var{auxname} is generated from the name of the output file, if
6330 explicitly specified and it is not the final executable, otherwise it is
6331 the basename of the source file. In both cases any suffix is removed
6332 (e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
6333 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
6334 @xref{Cross-profiling}.
6336 @cindex @command{gcov}
6340 This option is used to compile and link code instrumented for coverage
6341 analysis. The option is a synonym for @option{-fprofile-arcs}
6342 @option{-ftest-coverage} (when compiling) and @option{-lgcov} (when
6343 linking). See the documentation for those options for more details.
6348 Compile the source files with @option{-fprofile-arcs} plus optimization
6349 and code generation options. For test coverage analysis, use the
6350 additional @option{-ftest-coverage} option. You do not need to profile
6351 every source file in a program.
6354 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
6355 (the latter implies the former).
6358 Run the program on a representative workload to generate the arc profile
6359 information. This may be repeated any number of times. You can run
6360 concurrent instances of your program, and provided that the file system
6361 supports locking, the data files will be correctly updated. Also
6362 @code{fork} calls are detected and correctly handled (double counting
6366 For profile-directed optimizations, compile the source files again with
6367 the same optimization and code generation options plus
6368 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
6369 Control Optimization}).
6372 For test coverage analysis, use @command{gcov} to produce human readable
6373 information from the @file{.gcno} and @file{.gcda} files. Refer to the
6374 @command{gcov} documentation for further information.
6378 With @option{-fprofile-arcs}, for each function of your program GCC
6379 creates a program flow graph, then finds a spanning tree for the graph.
6380 Only arcs that are not on the spanning tree have to be instrumented: the
6381 compiler adds code to count the number of times that these arcs are
6382 executed. When an arc is the only exit or only entrance to a block, the
6383 instrumentation code can be added to the block; otherwise, a new basic
6384 block must be created to hold the instrumentation code.
6387 @item -ftest-coverage
6388 @opindex ftest-coverage
6389 Produce a notes file that the @command{gcov} code-coverage utility
6390 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
6391 show program coverage. Each source file's note file is called
6392 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
6393 above for a description of @var{auxname} and instructions on how to
6394 generate test coverage data. Coverage data matches the source files
6395 more closely if you do not optimize.
6397 @item -fdbg-cnt-list
6398 @opindex fdbg-cnt-list
6399 Print the name and the counter upper bound for all debug counters.
6402 @item -fdbg-cnt=@var{counter-value-list}
6404 Set the internal debug counter upper bound. @var{counter-value-list}
6405 is a comma-separated list of @var{name}:@var{value} pairs
6406 which sets the upper bound of each debug counter @var{name} to @var{value}.
6407 All debug counters have the initial upper bound of @code{UINT_MAX};
6408 thus @code{dbg_cnt} returns true always unless the upper bound
6409 is set by this option.
6410 For example, with @option{-fdbg-cnt=dce:10,tail_call:0},
6411 @code{dbg_cnt(dce)} returns true only for first 10 invocations.
6413 @item -fenable-@var{kind}-@var{pass}
6414 @itemx -fdisable-@var{kind}-@var{pass}=@var{range-list}
6418 This is a set of options that are used to explicitly disable/enable
6419 optimization passes. These options are intended for use for debugging GCC.
6420 Compiler users should use regular options for enabling/disabling
6425 @item -fdisable-ipa-@var{pass}
6426 Disable IPA pass @var{pass}. @var{pass} is the pass name. If the same pass is
6427 statically invoked in the compiler multiple times, the pass name should be
6428 appended with a sequential number starting from 1.
6430 @item -fdisable-rtl-@var{pass}
6431 @itemx -fdisable-rtl-@var{pass}=@var{range-list}
6432 Disable RTL pass @var{pass}. @var{pass} is the pass name. If the same pass is
6433 statically invoked in the compiler multiple times, the pass name should be
6434 appended with a sequential number starting from 1. @var{range-list} is a
6435 comma-separated list of function ranges or assembler names. Each range is a number
6436 pair separated by a colon. The range is inclusive in both ends. If the range
6437 is trivial, the number pair can be simplified as a single number. If the
6438 function's call graph node's @var{uid} falls within one of the specified ranges,
6439 the @var{pass} is disabled for that function. The @var{uid} is shown in the
6440 function header of a dump file, and the pass names can be dumped by using
6441 option @option{-fdump-passes}.
6443 @item -fdisable-tree-@var{pass}
6444 @itemx -fdisable-tree-@var{pass}=@var{range-list}
6445 Disable tree pass @var{pass}. See @option{-fdisable-rtl} for the description of
6448 @item -fenable-ipa-@var{pass}
6449 Enable IPA pass @var{pass}. @var{pass} is the pass name. If the same pass is
6450 statically invoked in the compiler multiple times, the pass name should be
6451 appended with a sequential number starting from 1.
6453 @item -fenable-rtl-@var{pass}
6454 @itemx -fenable-rtl-@var{pass}=@var{range-list}
6455 Enable RTL pass @var{pass}. See @option{-fdisable-rtl} for option argument
6456 description and examples.
6458 @item -fenable-tree-@var{pass}
6459 @itemx -fenable-tree-@var{pass}=@var{range-list}
6460 Enable tree pass @var{pass}. See @option{-fdisable-rtl} for the description
6461 of option arguments.
6465 Here are some examples showing uses of these options.
6469 # disable ccp1 for all functions
6471 # disable complete unroll for function whose cgraph node uid is 1
6472 -fenable-tree-cunroll=1
6473 # disable gcse2 for functions at the following ranges [1,1],
6474 # [300,400], and [400,1000]
6475 # disable gcse2 for functions foo and foo2
6476 -fdisable-rtl-gcse2=foo,foo2
6477 # disable early inlining
6478 -fdisable-tree-einline
6479 # disable ipa inlining
6480 -fdisable-ipa-inline
6481 # enable tree full unroll
6482 -fenable-tree-unroll
6486 @item -d@var{letters}
6487 @itemx -fdump-rtl-@var{pass}
6488 @itemx -fdump-rtl-@var{pass}=@var{filename}
6490 @opindex fdump-rtl-@var{pass}
6491 Says to make debugging dumps during compilation at times specified by
6492 @var{letters}. This is used for debugging the RTL-based passes of the
6493 compiler. The file names for most of the dumps are made by appending
6494 a pass number and a word to the @var{dumpname}, and the files are
6495 created in the directory of the output file. In case of
6496 @option{=@var{filename}} option, the dump is output on the given file
6497 instead of the pass numbered dump files. Note that the pass number is
6498 computed statically as passes get registered into the pass manager.
6499 Thus the numbering is not related to the dynamic order of execution of
6500 passes. In particular, a pass installed by a plugin could have a
6501 number over 200 even if it executed quite early. @var{dumpname} is
6502 generated from the name of the output file, if explicitly specified
6503 and it is not an executable, otherwise it is the basename of the
6504 source file. These switches may have different effects when
6505 @option{-E} is used for preprocessing.
6507 Debug dumps can be enabled with a @option{-fdump-rtl} switch or some
6508 @option{-d} option @var{letters}. Here are the possible
6509 letters for use in @var{pass} and @var{letters}, and their meanings:
6513 @item -fdump-rtl-alignments
6514 @opindex fdump-rtl-alignments
6515 Dump after branch alignments have been computed.
6517 @item -fdump-rtl-asmcons
6518 @opindex fdump-rtl-asmcons
6519 Dump after fixing rtl statements that have unsatisfied in/out constraints.
6521 @item -fdump-rtl-auto_inc_dec
6522 @opindex fdump-rtl-auto_inc_dec
6523 Dump after auto-inc-dec discovery. This pass is only run on
6524 architectures that have auto inc or auto dec instructions.
6526 @item -fdump-rtl-barriers
6527 @opindex fdump-rtl-barriers
6528 Dump after cleaning up the barrier instructions.
6530 @item -fdump-rtl-bbpart
6531 @opindex fdump-rtl-bbpart
6532 Dump after partitioning hot and cold basic blocks.
6534 @item -fdump-rtl-bbro
6535 @opindex fdump-rtl-bbro
6536 Dump after block reordering.
6538 @item -fdump-rtl-btl1
6539 @itemx -fdump-rtl-btl2
6540 @opindex fdump-rtl-btl2
6541 @opindex fdump-rtl-btl2
6542 @option{-fdump-rtl-btl1} and @option{-fdump-rtl-btl2} enable dumping
6543 after the two branch
6544 target load optimization passes.
6546 @item -fdump-rtl-bypass
6547 @opindex fdump-rtl-bypass
6548 Dump after jump bypassing and control flow optimizations.
6550 @item -fdump-rtl-combine
6551 @opindex fdump-rtl-combine
6552 Dump after the RTL instruction combination pass.
6554 @item -fdump-rtl-compgotos
6555 @opindex fdump-rtl-compgotos
6556 Dump after duplicating the computed gotos.
6558 @item -fdump-rtl-ce1
6559 @itemx -fdump-rtl-ce2
6560 @itemx -fdump-rtl-ce3
6561 @opindex fdump-rtl-ce1
6562 @opindex fdump-rtl-ce2
6563 @opindex fdump-rtl-ce3
6564 @option{-fdump-rtl-ce1}, @option{-fdump-rtl-ce2}, and
6565 @option{-fdump-rtl-ce3} enable dumping after the three
6566 if conversion passes.
6568 @item -fdump-rtl-cprop_hardreg
6569 @opindex fdump-rtl-cprop_hardreg
6570 Dump after hard register copy propagation.
6572 @item -fdump-rtl-csa
6573 @opindex fdump-rtl-csa
6574 Dump after combining stack adjustments.
6576 @item -fdump-rtl-cse1
6577 @itemx -fdump-rtl-cse2
6578 @opindex fdump-rtl-cse1
6579 @opindex fdump-rtl-cse2
6580 @option{-fdump-rtl-cse1} and @option{-fdump-rtl-cse2} enable dumping after
6581 the two common subexpression elimination passes.
6583 @item -fdump-rtl-dce
6584 @opindex fdump-rtl-dce
6585 Dump after the standalone dead code elimination passes.
6587 @item -fdump-rtl-dbr
6588 @opindex fdump-rtl-dbr
6589 Dump after delayed branch scheduling.
6591 @item -fdump-rtl-dce1
6592 @itemx -fdump-rtl-dce2
6593 @opindex fdump-rtl-dce1
6594 @opindex fdump-rtl-dce2
6595 @option{-fdump-rtl-dce1} and @option{-fdump-rtl-dce2} enable dumping after
6596 the two dead store elimination passes.
6599 @opindex fdump-rtl-eh
6600 Dump after finalization of EH handling code.
6602 @item -fdump-rtl-eh_ranges
6603 @opindex fdump-rtl-eh_ranges
6604 Dump after conversion of EH handling range regions.
6606 @item -fdump-rtl-expand
6607 @opindex fdump-rtl-expand
6608 Dump after RTL generation.
6610 @item -fdump-rtl-fwprop1
6611 @itemx -fdump-rtl-fwprop2
6612 @opindex fdump-rtl-fwprop1
6613 @opindex fdump-rtl-fwprop2
6614 @option{-fdump-rtl-fwprop1} and @option{-fdump-rtl-fwprop2} enable
6615 dumping after the two forward propagation passes.
6617 @item -fdump-rtl-gcse1
6618 @itemx -fdump-rtl-gcse2
6619 @opindex fdump-rtl-gcse1
6620 @opindex fdump-rtl-gcse2
6621 @option{-fdump-rtl-gcse1} and @option{-fdump-rtl-gcse2} enable dumping
6622 after global common subexpression elimination.
6624 @item -fdump-rtl-init-regs
6625 @opindex fdump-rtl-init-regs
6626 Dump after the initialization of the registers.
6628 @item -fdump-rtl-initvals
6629 @opindex fdump-rtl-initvals
6630 Dump after the computation of the initial value sets.
6632 @item -fdump-rtl-into_cfglayout
6633 @opindex fdump-rtl-into_cfglayout
6634 Dump after converting to cfglayout mode.
6636 @item -fdump-rtl-ira
6637 @opindex fdump-rtl-ira
6638 Dump after iterated register allocation.
6640 @item -fdump-rtl-jump
6641 @opindex fdump-rtl-jump
6642 Dump after the second jump optimization.
6644 @item -fdump-rtl-loop2
6645 @opindex fdump-rtl-loop2
6646 @option{-fdump-rtl-loop2} enables dumping after the rtl
6647 loop optimization passes.
6649 @item -fdump-rtl-mach
6650 @opindex fdump-rtl-mach
6651 Dump after performing the machine dependent reorganization pass, if that
6654 @item -fdump-rtl-mode_sw
6655 @opindex fdump-rtl-mode_sw
6656 Dump after removing redundant mode switches.
6658 @item -fdump-rtl-rnreg
6659 @opindex fdump-rtl-rnreg
6660 Dump after register renumbering.
6662 @item -fdump-rtl-outof_cfglayout
6663 @opindex fdump-rtl-outof_cfglayout
6664 Dump after converting from cfglayout mode.
6666 @item -fdump-rtl-peephole2
6667 @opindex fdump-rtl-peephole2
6668 Dump after the peephole pass.
6670 @item -fdump-rtl-postreload
6671 @opindex fdump-rtl-postreload
6672 Dump after post-reload optimizations.
6674 @item -fdump-rtl-pro_and_epilogue
6675 @opindex fdump-rtl-pro_and_epilogue
6676 Dump after generating the function prologues and epilogues.
6678 @item -fdump-rtl-sched1
6679 @itemx -fdump-rtl-sched2
6680 @opindex fdump-rtl-sched1
6681 @opindex fdump-rtl-sched2
6682 @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2} enable dumping
6683 after the basic block scheduling passes.
6685 @item -fdump-rtl-ree
6686 @opindex fdump-rtl-ree
6687 Dump after sign/zero extension elimination.
6689 @item -fdump-rtl-seqabstr
6690 @opindex fdump-rtl-seqabstr
6691 Dump after common sequence discovery.
6693 @item -fdump-rtl-shorten
6694 @opindex fdump-rtl-shorten
6695 Dump after shortening branches.
6697 @item -fdump-rtl-sibling
6698 @opindex fdump-rtl-sibling
6699 Dump after sibling call optimizations.
6701 @item -fdump-rtl-split1
6702 @itemx -fdump-rtl-split2
6703 @itemx -fdump-rtl-split3
6704 @itemx -fdump-rtl-split4
6705 @itemx -fdump-rtl-split5
6706 @opindex fdump-rtl-split1
6707 @opindex fdump-rtl-split2
6708 @opindex fdump-rtl-split3
6709 @opindex fdump-rtl-split4
6710 @opindex fdump-rtl-split5
6711 These options enable dumping after five rounds of
6712 instruction splitting.
6714 @item -fdump-rtl-sms
6715 @opindex fdump-rtl-sms
6716 Dump after modulo scheduling. This pass is only run on some
6719 @item -fdump-rtl-stack
6720 @opindex fdump-rtl-stack
6721 Dump after conversion from GCC's ``flat register file'' registers to the
6722 x87's stack-like registers. This pass is only run on x86 variants.
6724 @item -fdump-rtl-subreg1
6725 @itemx -fdump-rtl-subreg2
6726 @opindex fdump-rtl-subreg1
6727 @opindex fdump-rtl-subreg2
6728 @option{-fdump-rtl-subreg1} and @option{-fdump-rtl-subreg2} enable dumping after
6729 the two subreg expansion passes.
6731 @item -fdump-rtl-unshare
6732 @opindex fdump-rtl-unshare
6733 Dump after all rtl has been unshared.
6735 @item -fdump-rtl-vartrack
6736 @opindex fdump-rtl-vartrack
6737 Dump after variable tracking.
6739 @item -fdump-rtl-vregs
6740 @opindex fdump-rtl-vregs
6741 Dump after converting virtual registers to hard registers.
6743 @item -fdump-rtl-web
6744 @opindex fdump-rtl-web
6745 Dump after live range splitting.
6747 @item -fdump-rtl-regclass
6748 @itemx -fdump-rtl-subregs_of_mode_init
6749 @itemx -fdump-rtl-subregs_of_mode_finish
6750 @itemx -fdump-rtl-dfinit
6751 @itemx -fdump-rtl-dfinish
6752 @opindex fdump-rtl-regclass
6753 @opindex fdump-rtl-subregs_of_mode_init
6754 @opindex fdump-rtl-subregs_of_mode_finish
6755 @opindex fdump-rtl-dfinit
6756 @opindex fdump-rtl-dfinish
6757 These dumps are defined but always produce empty files.
6760 @itemx -fdump-rtl-all
6762 @opindex fdump-rtl-all
6763 Produce all the dumps listed above.
6767 Annotate the assembler output with miscellaneous debugging information.
6771 Dump all macro definitions, at the end of preprocessing, in addition to
6776 Produce a core dump whenever an error occurs.
6780 Annotate the assembler output with a comment indicating which
6781 pattern and alternative is used. The length of each instruction is
6786 Dump the RTL in the assembler output as a comment before each instruction.
6787 Also turns on @option{-dp} annotation.
6791 Just generate RTL for a function instead of compiling it. Usually used
6792 with @option{-fdump-rtl-expand}.
6796 @opindex fdump-noaddr
6797 When doing debugging dumps, suppress address output. This makes it more
6798 feasible to use diff on debugging dumps for compiler invocations with
6799 different compiler binaries and/or different
6800 text / bss / data / heap / stack / dso start locations.
6803 @opindex freport-bug
6804 Collect and dump debug information into temporary file if ICE in C/C++
6807 @item -fdump-unnumbered
6808 @opindex fdump-unnumbered
6809 When doing debugging dumps, suppress instruction numbers and address output.
6810 This makes it more feasible to use diff on debugging dumps for compiler
6811 invocations with different options, in particular with and without
6814 @item -fdump-unnumbered-links
6815 @opindex fdump-unnumbered-links
6816 When doing debugging dumps (see @option{-d} option above), suppress
6817 instruction numbers for the links to the previous and next instructions
6820 @item -fdump-translation-unit @r{(C++ only)}
6821 @itemx -fdump-translation-unit-@var{options} @r{(C++ only)}
6822 @opindex fdump-translation-unit
6823 Dump a representation of the tree structure for the entire translation
6824 unit to a file. The file name is made by appending @file{.tu} to the
6825 source file name, and the file is created in the same directory as the
6826 output file. If the @samp{-@var{options}} form is used, @var{options}
6827 controls the details of the dump as described for the
6828 @option{-fdump-tree} options.
6830 @item -fdump-class-hierarchy @r{(C++ only)}
6831 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
6832 @opindex fdump-class-hierarchy
6833 Dump a representation of each class's hierarchy and virtual function
6834 table layout to a file. The file name is made by appending
6835 @file{.class} to the source file name, and the file is created in the
6836 same directory as the output file. If the @samp{-@var{options}} form
6837 is used, @var{options} controls the details of the dump as described
6838 for the @option{-fdump-tree} options.
6840 @item -fdump-ipa-@var{switch}
6842 Control the dumping at various stages of inter-procedural analysis
6843 language tree to a file. The file name is generated by appending a
6844 switch specific suffix to the source file name, and the file is created
6845 in the same directory as the output file. The following dumps are
6850 Enables all inter-procedural analysis dumps.
6853 Dumps information about call-graph optimization, unused function removal,
6854 and inlining decisions.
6857 Dump after function inlining.
6862 @opindex fdump-passes
6863 Dump the list of optimization passes that are turned on and off by
6864 the current command-line options.
6866 @item -fdump-statistics-@var{option}
6867 @opindex fdump-statistics
6868 Enable and control dumping of pass statistics in a separate file. The
6869 file name is generated by appending a suffix ending in
6870 @samp{.statistics} to the source file name, and the file is created in
6871 the same directory as the output file. If the @samp{-@var{option}}
6872 form is used, @samp{-stats} causes counters to be summed over the
6873 whole compilation unit while @samp{-details} dumps every event as
6874 the passes generate them. The default with no option is to sum
6875 counters for each function compiled.
6877 @item -fdump-tree-@var{switch}
6878 @itemx -fdump-tree-@var{switch}-@var{options}
6879 @itemx -fdump-tree-@var{switch}-@var{options}=@var{filename}
6881 Control the dumping at various stages of processing the intermediate
6882 language tree to a file. The file name is generated by appending a
6883 switch-specific suffix to the source file name, and the file is
6884 created in the same directory as the output file. In case of
6885 @option{=@var{filename}} option, the dump is output on the given file
6886 instead of the auto named dump files. If the @samp{-@var{options}}
6887 form is used, @var{options} is a list of @samp{-} separated options
6888 which control the details of the dump. Not all options are applicable
6889 to all dumps; those that are not meaningful are ignored. The
6890 following options are available
6894 Print the address of each node. Usually this is not meaningful as it
6895 changes according to the environment and source file. Its primary use
6896 is for tying up a dump file with a debug environment.
6898 If @code{DECL_ASSEMBLER_NAME} has been set for a given decl, use that
6899 in the dump instead of @code{DECL_NAME}. Its primary use is ease of
6900 use working backward from mangled names in the assembly file.
6902 When dumping front-end intermediate representations, inhibit dumping
6903 of members of a scope or body of a function merely because that scope
6904 has been reached. Only dump such items when they are directly reachable
6907 When dumping pretty-printed trees, this option inhibits dumping the
6908 bodies of control structures.
6910 When dumping RTL, print the RTL in slim (condensed) form instead of
6911 the default LISP-like representation.
6913 Print a raw representation of the tree. By default, trees are
6914 pretty-printed into a C-like representation.
6916 Enable more detailed dumps (not honored by every dump option). Also
6917 include information from the optimization passes.
6919 Enable dumping various statistics about the pass (not honored by every dump
6922 Enable showing basic block boundaries (disabled in raw dumps).
6924 For each of the other indicated dump files (@option{-fdump-rtl-@var{pass}}),
6925 dump a representation of the control flow graph suitable for viewing with
6926 GraphViz to @file{@var{file}.@var{passid}.@var{pass}.dot}. Each function in
6927 the file is pretty-printed as a subgraph, so that GraphViz can render them
6928 all in a single plot.
6930 This option currently only works for RTL dumps, and the RTL is always
6931 dumped in slim form.
6933 Enable showing virtual operands for every statement.
6935 Enable showing line numbers for statements.
6937 Enable showing the unique ID (@code{DECL_UID}) for each variable.
6939 Enable showing the tree dump for each statement.
6941 Enable showing the EH region number holding each statement.
6943 Enable showing scalar evolution analysis details.
6945 Enable showing optimization information (only available in certain
6948 Enable showing missed optimization information (only available in certain
6951 Enable other detailed optimization information (only available in
6953 @item =@var{filename}
6954 Instead of an auto named dump file, output into the given file
6955 name. The file names @file{stdout} and @file{stderr} are treated
6956 specially and are considered already open standard streams. For
6960 gcc -O2 -ftree-vectorize -fdump-tree-vect-blocks=foo.dump
6961 -fdump-tree-pre=stderr file.c
6964 outputs vectorizer dump into @file{foo.dump}, while the PRE dump is
6965 output on to @file{stderr}. If two conflicting dump filenames are
6966 given for the same pass, then the latter option overrides the earlier
6970 Turn on all options, except @option{raw}, @option{slim}, @option{verbose}
6971 and @option{lineno}.
6974 Turn on all optimization options, i.e., @option{optimized},
6975 @option{missed}, and @option{note}.
6978 The following tree dumps are possible:
6982 @opindex fdump-tree-original
6983 Dump before any tree based optimization, to @file{@var{file}.original}.
6986 @opindex fdump-tree-optimized
6987 Dump after all tree based optimization, to @file{@var{file}.optimized}.
6990 @opindex fdump-tree-gimple
6991 Dump each function before and after the gimplification pass to a file. The
6992 file name is made by appending @file{.gimple} to the source file name.
6995 @opindex fdump-tree-cfg
6996 Dump the control flow graph of each function to a file. The file name is
6997 made by appending @file{.cfg} to the source file name.
7000 @opindex fdump-tree-ch
7001 Dump each function after copying loop headers. The file name is made by
7002 appending @file{.ch} to the source file name.
7005 @opindex fdump-tree-ssa
7006 Dump SSA related information to a file. The file name is made by appending
7007 @file{.ssa} to the source file name.
7010 @opindex fdump-tree-alias
7011 Dump aliasing information for each function. The file name is made by
7012 appending @file{.alias} to the source file name.
7015 @opindex fdump-tree-ccp
7016 Dump each function after CCP@. The file name is made by appending
7017 @file{.ccp} to the source file name.
7020 @opindex fdump-tree-storeccp
7021 Dump each function after STORE-CCP@. The file name is made by appending
7022 @file{.storeccp} to the source file name.
7025 @opindex fdump-tree-pre
7026 Dump trees after partial redundancy elimination. The file name is made
7027 by appending @file{.pre} to the source file name.
7030 @opindex fdump-tree-fre
7031 Dump trees after full redundancy elimination. The file name is made
7032 by appending @file{.fre} to the source file name.
7035 @opindex fdump-tree-copyprop
7036 Dump trees after copy propagation. The file name is made
7037 by appending @file{.copyprop} to the source file name.
7039 @item store_copyprop
7040 @opindex fdump-tree-store_copyprop
7041 Dump trees after store copy-propagation. The file name is made
7042 by appending @file{.store_copyprop} to the source file name.
7045 @opindex fdump-tree-dce
7046 Dump each function after dead code elimination. The file name is made by
7047 appending @file{.dce} to the source file name.
7050 @opindex fdump-tree-sra
7051 Dump each function after performing scalar replacement of aggregates. The
7052 file name is made by appending @file{.sra} to the source file name.
7055 @opindex fdump-tree-sink
7056 Dump each function after performing code sinking. The file name is made
7057 by appending @file{.sink} to the source file name.
7060 @opindex fdump-tree-dom
7061 Dump each function after applying dominator tree optimizations. The file
7062 name is made by appending @file{.dom} to the source file name.
7065 @opindex fdump-tree-dse
7066 Dump each function after applying dead store elimination. The file
7067 name is made by appending @file{.dse} to the source file name.
7070 @opindex fdump-tree-phiopt
7071 Dump each function after optimizing PHI nodes into straightline code. The file
7072 name is made by appending @file{.phiopt} to the source file name.
7075 @opindex fdump-tree-forwprop
7076 Dump each function after forward propagating single use variables. The file
7077 name is made by appending @file{.forwprop} to the source file name.
7080 @opindex fdump-tree-copyrename
7081 Dump each function after applying the copy rename optimization. The file
7082 name is made by appending @file{.copyrename} to the source file name.
7085 @opindex fdump-tree-nrv
7086 Dump each function after applying the named return value optimization on
7087 generic trees. The file name is made by appending @file{.nrv} to the source
7091 @opindex fdump-tree-vect
7092 Dump each function after applying vectorization of loops. The file name is
7093 made by appending @file{.vect} to the source file name.
7096 @opindex fdump-tree-slp
7097 Dump each function after applying vectorization of basic blocks. The file name
7098 is made by appending @file{.slp} to the source file name.
7101 @opindex fdump-tree-vrp
7102 Dump each function after Value Range Propagation (VRP). The file name
7103 is made by appending @file{.vrp} to the source file name.
7106 @opindex fdump-tree-all
7107 Enable all the available tree dumps with the flags provided in this option.
7111 @itemx -fopt-info-@var{options}
7112 @itemx -fopt-info-@var{options}=@var{filename}
7114 Controls optimization dumps from various optimization passes. If the
7115 @samp{-@var{options}} form is used, @var{options} is a list of
7116 @samp{-} separated option keywords to select the dump details and
7119 The @var{options} can be divided into two groups: options describing the
7120 verbosity of the dump, and options describing which optimizations
7121 should be included. The options from both the groups can be freely
7122 mixed as they are non-overlapping. However, in case of any conflicts,
7123 the later options override the earlier options on the command
7126 The following options control the dump verbosity:
7130 Print information when an optimization is successfully applied. It is
7131 up to a pass to decide which information is relevant. For example, the
7132 vectorizer passes print the source location of loops which are
7133 successfully vectorized.
7135 Print information about missed optimizations. Individual passes
7136 control which information to include in the output.
7138 Print verbose information about optimizations, such as certain
7139 transformations, more detailed messages about decisions etc.
7141 Print detailed optimization information. This includes
7142 @samp{optimized}, @samp{missed}, and @samp{note}.
7145 One or more of the following option keywords can be used to describe a
7146 group of optimizations:
7150 Enable dumps from all interprocedural optimizations.
7152 Enable dumps from all loop optimizations.
7154 Enable dumps from all inlining optimizations.
7156 Enable dumps from all vectorization optimizations.
7158 Enable dumps from all optimizations. This is a superset of
7159 the optimization groups listed above.
7163 omitted, it defaults to @samp{optimized-optall}, which means to dump all
7164 info about successful optimizations from all the passes.
7166 If the @var{filename} is provided, then the dumps from all the
7167 applicable optimizations are concatenated into the @var{filename}.
7168 Otherwise the dump is output onto @file{stderr}. Though multiple
7169 @option{-fopt-info} options are accepted, only one of them can include
7170 a @var{filename}. If other filenames are provided then all but the
7171 first such option are ignored.
7173 Note that the output @var{filename} is overwritten
7174 in case of multiple translation units. If a combined output from
7175 multiple translation units is desired, @file{stderr} should be used
7178 In the following example, the optimization info is output to
7187 gcc -O3 -fopt-info-missed=missed.all
7191 outputs missed optimization report from all the passes into
7192 @file{missed.all}, and this one:
7195 gcc -O2 -ftree-vectorize -fopt-info-vec-missed
7199 prints information about missed optimization opportunities from
7200 vectorization passes on @file{stderr}.
7201 Note that @option{-fopt-info-vec-missed} is equivalent to
7202 @option{-fopt-info-missed-vec}.
7206 gcc -O3 -fopt-info-inline-optimized-missed=inline.txt
7210 outputs information about missed optimizations as well as
7211 optimized locations from all the inlining passes into
7217 gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt
7221 Here the two output filenames @file{vec.miss} and @file{loop.opt} are
7222 in conflict since only one output file is allowed. In this case, only
7223 the first option takes effect and the subsequent options are
7224 ignored. Thus only @file{vec.miss} is produced which contains
7225 dumps from the vectorizer about missed opportunities.
7227 @item -frandom-seed=@var{number}
7228 @opindex frandom-seed
7229 This option provides a seed that GCC uses in place of
7230 random numbers in generating certain symbol names
7231 that have to be different in every compiled file. It is also used to
7232 place unique stamps in coverage data files and the object files that
7233 produce them. You can use the @option{-frandom-seed} option to produce
7234 reproducibly identical object files.
7236 The @var{number} should be different for every file you compile.
7238 @item -fsched-verbose=@var{n}
7239 @opindex fsched-verbose
7240 On targets that use instruction scheduling, this option controls the
7241 amount of debugging output the scheduler prints. This information is
7242 written to standard error, unless @option{-fdump-rtl-sched1} or
7243 @option{-fdump-rtl-sched2} is specified, in which case it is output
7244 to the usual dump listing file, @file{.sched1} or @file{.sched2}
7245 respectively. However for @var{n} greater than nine, the output is
7246 always printed to standard error.
7248 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
7249 same information as @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2}.
7250 For @var{n} greater than one, it also output basic block probabilities,
7251 detailed ready list information and unit/insn info. For @var{n} greater
7252 than two, it includes RTL at abort point, control-flow and regions info.
7253 And for @var{n} over four, @option{-fsched-verbose} also includes
7257 @itemx -save-temps=cwd
7259 Store the usual ``temporary'' intermediate files permanently; place them
7260 in the current directory and name them based on the source file. Thus,
7261 compiling @file{foo.c} with @option{-c -save-temps} produces files
7262 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
7263 preprocessed @file{foo.i} output file even though the compiler now
7264 normally uses an integrated preprocessor.
7266 When used in combination with the @option{-x} command-line option,
7267 @option{-save-temps} is sensible enough to avoid over writing an
7268 input source file with the same extension as an intermediate file.
7269 The corresponding intermediate file may be obtained by renaming the
7270 source file before using @option{-save-temps}.
7272 If you invoke GCC in parallel, compiling several different source
7273 files that share a common base name in different subdirectories or the
7274 same source file compiled for multiple output destinations, it is
7275 likely that the different parallel compilers will interfere with each
7276 other, and overwrite the temporary files. For instance:
7279 gcc -save-temps -o outdir1/foo.o indir1/foo.c&
7280 gcc -save-temps -o outdir2/foo.o indir2/foo.c&
7283 may result in @file{foo.i} and @file{foo.o} being written to
7284 simultaneously by both compilers.
7286 @item -save-temps=obj
7287 @opindex save-temps=obj
7288 Store the usual ``temporary'' intermediate files permanently. If the
7289 @option{-o} option is used, the temporary files are based on the
7290 object file. If the @option{-o} option is not used, the
7291 @option{-save-temps=obj} switch behaves like @option{-save-temps}.
7296 gcc -save-temps=obj -c foo.c
7297 gcc -save-temps=obj -c bar.c -o dir/xbar.o
7298 gcc -save-temps=obj foobar.c -o dir2/yfoobar
7302 creates @file{foo.i}, @file{foo.s}, @file{dir/xbar.i},
7303 @file{dir/xbar.s}, @file{dir2/yfoobar.i}, @file{dir2/yfoobar.s}, and
7304 @file{dir2/yfoobar.o}.
7306 @item -time@r{[}=@var{file}@r{]}
7308 Report the CPU time taken by each subprocess in the compilation
7309 sequence. For C source files, this is the compiler proper and assembler
7310 (plus the linker if linking is done).
7312 Without the specification of an output file, the output looks like this:
7319 The first number on each line is the ``user time'', that is time spent
7320 executing the program itself. The second number is ``system time'',
7321 time spent executing operating system routines on behalf of the program.
7322 Both numbers are in seconds.
7324 With the specification of an output file, the output is appended to the
7325 named file, and it looks like this:
7328 0.12 0.01 cc1 @var{options}
7329 0.00 0.01 as @var{options}
7332 The ``user time'' and the ``system time'' are moved before the program
7333 name, and the options passed to the program are displayed, so that one
7334 can later tell what file was being compiled, and with which options.
7336 @item -fvar-tracking
7337 @opindex fvar-tracking
7338 Run variable tracking pass. It computes where variables are stored at each
7339 position in code. Better debugging information is then generated
7340 (if the debugging information format supports this information).
7342 It is enabled by default when compiling with optimization (@option{-Os},
7343 @option{-O}, @option{-O2}, @dots{}), debugging information (@option{-g}) and
7344 the debug info format supports it.
7346 @item -fvar-tracking-assignments
7347 @opindex fvar-tracking-assignments
7348 @opindex fno-var-tracking-assignments
7349 Annotate assignments to user variables early in the compilation and
7350 attempt to carry the annotations over throughout the compilation all the
7351 way to the end, in an attempt to improve debug information while
7352 optimizing. Use of @option{-gdwarf-4} is recommended along with it.
7354 It can be enabled even if var-tracking is disabled, in which case
7355 annotations are created and maintained, but discarded at the end.
7356 By default, this flag is enabled together with @option{-fvar-tracking},
7357 except when selective scheduling is enabled.
7359 @item -fvar-tracking-assignments-toggle
7360 @opindex fvar-tracking-assignments-toggle
7361 @opindex fno-var-tracking-assignments-toggle
7362 Toggle @option{-fvar-tracking-assignments}, in the same way that
7363 @option{-gtoggle} toggles @option{-g}.
7365 @item -print-file-name=@var{library}
7366 @opindex print-file-name
7367 Print the full absolute name of the library file @var{library} that
7368 would be used when linking---and don't do anything else. With this
7369 option, GCC does not compile or link anything; it just prints the
7372 @item -print-multi-directory
7373 @opindex print-multi-directory
7374 Print the directory name corresponding to the multilib selected by any
7375 other switches present in the command line. This directory is supposed
7376 to exist in @env{GCC_EXEC_PREFIX}.
7378 @item -print-multi-lib
7379 @opindex print-multi-lib
7380 Print the mapping from multilib directory names to compiler switches
7381 that enable them. The directory name is separated from the switches by
7382 @samp{;}, and each switch starts with an @samp{@@} instead of the
7383 @samp{-}, without spaces between multiple switches. This is supposed to
7384 ease shell processing.
7386 @item -print-multi-os-directory
7387 @opindex print-multi-os-directory
7388 Print the path to OS libraries for the selected
7389 multilib, relative to some @file{lib} subdirectory. If OS libraries are
7390 present in the @file{lib} subdirectory and no multilibs are used, this is
7391 usually just @file{.}, if OS libraries are present in @file{lib@var{suffix}}
7392 sibling directories this prints e.g.@: @file{../lib64}, @file{../lib} or
7393 @file{../lib32}, or if OS libraries are present in @file{lib/@var{subdir}}
7394 subdirectories it prints e.g.@: @file{amd64}, @file{sparcv9} or @file{ev6}.
7396 @item -print-multiarch
7397 @opindex print-multiarch
7398 Print the path to OS libraries for the selected multiarch,
7399 relative to some @file{lib} subdirectory.
7401 @item -print-prog-name=@var{program}
7402 @opindex print-prog-name
7403 Like @option{-print-file-name}, but searches for a program such as @command{cpp}.
7405 @item -print-libgcc-file-name
7406 @opindex print-libgcc-file-name
7407 Same as @option{-print-file-name=libgcc.a}.
7409 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
7410 but you do want to link with @file{libgcc.a}. You can do:
7413 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
7416 @item -print-search-dirs
7417 @opindex print-search-dirs
7418 Print the name of the configured installation directory and a list of
7419 program and library directories @command{gcc} searches---and don't do anything else.
7421 This is useful when @command{gcc} prints the error message
7422 @samp{installation problem, cannot exec cpp0: No such file or directory}.
7423 To resolve this you either need to put @file{cpp0} and the other compiler
7424 components where @command{gcc} expects to find them, or you can set the environment
7425 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
7426 Don't forget the trailing @samp{/}.
7427 @xref{Environment Variables}.
7429 @item -print-sysroot
7430 @opindex print-sysroot
7431 Print the target sysroot directory that is used during
7432 compilation. This is the target sysroot specified either at configure
7433 time or using the @option{--sysroot} option, possibly with an extra
7434 suffix that depends on compilation options. If no target sysroot is
7435 specified, the option prints nothing.
7437 @item -print-sysroot-headers-suffix
7438 @opindex print-sysroot-headers-suffix
7439 Print the suffix added to the target sysroot when searching for
7440 headers, or give an error if the compiler is not configured with such
7441 a suffix---and don't do anything else.
7444 @opindex dumpmachine
7445 Print the compiler's target machine (for example,
7446 @samp{i686-pc-linux-gnu})---and don't do anything else.
7449 @opindex dumpversion
7450 Print the compiler version (for example, @code{3.0})---and don't do
7455 Print the compiler's built-in specs---and don't do anything else. (This
7456 is used when GCC itself is being built.) @xref{Spec Files}.
7458 @item -fno-eliminate-unused-debug-types
7459 @opindex feliminate-unused-debug-types
7460 @opindex fno-eliminate-unused-debug-types
7461 Normally, when producing DWARF 2 output, GCC avoids producing debug symbol
7462 output for types that are nowhere used in the source file being compiled.
7463 Sometimes it is useful to have GCC emit debugging
7464 information for all types declared in a compilation
7465 unit, regardless of whether or not they are actually used
7466 in that compilation unit, for example
7467 if, in the debugger, you want to cast a value to a type that is
7468 not actually used in your program (but is declared). More often,
7469 however, this results in a significant amount of wasted space.
7472 @node Optimize Options
7473 @section Options That Control Optimization
7474 @cindex optimize options
7475 @cindex options, optimization
7477 These options control various sorts of optimizations.
7479 Without any optimization option, the compiler's goal is to reduce the
7480 cost of compilation and to make debugging produce the expected
7481 results. Statements are independent: if you stop the program with a
7482 breakpoint between statements, you can then assign a new value to any
7483 variable or change the program counter to any other statement in the
7484 function and get exactly the results you expect from the source
7487 Turning on optimization flags makes the compiler attempt to improve
7488 the performance and/or code size at the expense of compilation time
7489 and possibly the ability to debug the program.
7491 The compiler performs optimization based on the knowledge it has of the
7492 program. Compiling multiple files at once to a single output file mode allows
7493 the compiler to use information gained from all of the files when compiling
7496 Not all optimizations are controlled directly by a flag. Only
7497 optimizations that have a flag are listed in this section.
7499 Most optimizations are only enabled if an @option{-O} level is set on
7500 the command line. Otherwise they are disabled, even if individual
7501 optimization flags are specified.
7503 Depending on the target and how GCC was configured, a slightly different
7504 set of optimizations may be enabled at each @option{-O} level than
7505 those listed here. You can invoke GCC with @option{-Q --help=optimizers}
7506 to find out the exact set of optimizations that are enabled at each level.
7507 @xref{Overall Options}, for examples.
7514 Optimize. Optimizing compilation takes somewhat more time, and a lot
7515 more memory for a large function.
7517 With @option{-O}, the compiler tries to reduce code size and execution
7518 time, without performing any optimizations that take a great deal of
7521 @option{-O} turns on the following optimization flags:
7524 -fbranch-count-reg @gol
7525 -fcombine-stack-adjustments @gol
7527 -fcprop-registers @gol
7530 -fdelayed-branch @gol
7532 -fforward-propagate @gol
7533 -fguess-branch-probability @gol
7534 -fif-conversion2 @gol
7535 -fif-conversion @gol
7536 -finline-functions-called-once @gol
7537 -fipa-pure-const @gol
7539 -fipa-reference @gol
7540 -fmerge-constants @gol
7541 -fmove-loop-invariants @gol
7543 -fsplit-wide-types @gol
7548 -ftree-copy-prop @gol
7549 -ftree-copyrename @gol
7551 -ftree-dominator-opts @gol
7553 -ftree-forwprop @gol
7563 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
7564 where doing so does not interfere with debugging.
7568 Optimize even more. GCC performs nearly all supported optimizations
7569 that do not involve a space-speed tradeoff.
7570 As compared to @option{-O}, this option increases both compilation time
7571 and the performance of the generated code.
7573 @option{-O2} turns on all optimization flags specified by @option{-O}. It
7574 also turns on the following optimization flags:
7575 @gccoptlist{-fthread-jumps @gol
7576 -falign-functions -falign-jumps @gol
7577 -falign-loops -falign-labels @gol
7580 -fcse-follow-jumps -fcse-skip-blocks @gol
7581 -fdelete-null-pointer-checks @gol
7582 -fdevirtualize -fdevirtualize-speculatively @gol
7583 -fexpensive-optimizations @gol
7584 -fgcse -fgcse-lm @gol
7585 -fhoist-adjacent-loads @gol
7586 -finline-small-functions @gol
7587 -findirect-inlining @gol
7589 -fipa-cp-alignment @gol
7592 -fisolate-erroneous-paths-dereference @gol
7594 -foptimize-sibling-calls @gol
7595 -foptimize-strlen @gol
7596 -fpartial-inlining @gol
7598 -freorder-blocks -freorder-blocks-and-partition -freorder-functions @gol
7599 -frerun-cse-after-loop @gol
7600 -fsched-interblock -fsched-spec @gol
7601 -fschedule-insns -fschedule-insns2 @gol
7602 -fstrict-aliasing -fstrict-overflow @gol
7603 -ftree-builtin-call-dce @gol
7604 -ftree-switch-conversion -ftree-tail-merge @gol
7609 Please note the warning under @option{-fgcse} about
7610 invoking @option{-O2} on programs that use computed gotos.
7614 Optimize yet more. @option{-O3} turns on all optimizations specified
7615 by @option{-O2} and also turns on the @option{-finline-functions},
7616 @option{-funswitch-loops}, @option{-fpredictive-commoning},
7617 @option{-fgcse-after-reload}, @option{-ftree-loop-vectorize},
7618 @option{-ftree-loop-distribute-patterns},
7619 @option{-ftree-slp-vectorize}, @option{-fvect-cost-model},
7620 @option{-ftree-partial-pre} and @option{-fipa-cp-clone} options.
7624 Reduce compilation time and make debugging produce the expected
7625 results. This is the default.
7629 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
7630 do not typically increase code size. It also performs further
7631 optimizations designed to reduce code size.
7633 @option{-Os} disables the following optimization flags:
7634 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
7635 -falign-labels -freorder-blocks -freorder-blocks-and-partition @gol
7636 -fprefetch-loop-arrays}
7640 Disregard strict standards compliance. @option{-Ofast} enables all
7641 @option{-O3} optimizations. It also enables optimizations that are not
7642 valid for all standard-compliant programs.
7643 It turns on @option{-ffast-math} and the Fortran-specific
7644 @option{-fno-protect-parens} and @option{-fstack-arrays}.
7648 Optimize debugging experience. @option{-Og} enables optimizations
7649 that do not interfere with debugging. It should be the optimization
7650 level of choice for the standard edit-compile-debug cycle, offering
7651 a reasonable level of optimization while maintaining fast compilation
7652 and a good debugging experience.
7654 If you use multiple @option{-O} options, with or without level numbers,
7655 the last such option is the one that is effective.
7658 Options of the form @option{-f@var{flag}} specify machine-independent
7659 flags. Most flags have both positive and negative forms; the negative
7660 form of @option{-ffoo} is @option{-fno-foo}. In the table
7661 below, only one of the forms is listed---the one you typically
7662 use. You can figure out the other form by either removing @samp{no-}
7665 The following options control specific optimizations. They are either
7666 activated by @option{-O} options or are related to ones that are. You
7667 can use the following flags in the rare cases when ``fine-tuning'' of
7668 optimizations to be performed is desired.
7671 @item -fno-defer-pop
7672 @opindex fno-defer-pop
7673 Always pop the arguments to each function call as soon as that function
7674 returns. For machines that must pop arguments after a function call,
7675 the compiler normally lets arguments accumulate on the stack for several
7676 function calls and pops them all at once.
7678 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
7680 @item -fforward-propagate
7681 @opindex fforward-propagate
7682 Perform a forward propagation pass on RTL@. The pass tries to combine two
7683 instructions and checks if the result can be simplified. If loop unrolling
7684 is active, two passes are performed and the second is scheduled after
7687 This option is enabled by default at optimization levels @option{-O},
7688 @option{-O2}, @option{-O3}, @option{-Os}.
7690 @item -ffp-contract=@var{style}
7691 @opindex ffp-contract
7692 @option{-ffp-contract=off} disables floating-point expression contraction.
7693 @option{-ffp-contract=fast} enables floating-point expression contraction
7694 such as forming of fused multiply-add operations if the target has
7695 native support for them.
7696 @option{-ffp-contract=on} enables floating-point expression contraction
7697 if allowed by the language standard. This is currently not implemented
7698 and treated equal to @option{-ffp-contract=off}.
7700 The default is @option{-ffp-contract=fast}.
7702 @item -fomit-frame-pointer
7703 @opindex fomit-frame-pointer
7704 Don't keep the frame pointer in a register for functions that
7705 don't need one. This avoids the instructions to save, set up and
7706 restore frame pointers; it also makes an extra register available
7707 in many functions. @strong{It also makes debugging impossible on
7710 On some machines, such as the VAX, this flag has no effect, because
7711 the standard calling sequence automatically handles the frame pointer
7712 and nothing is saved by pretending it doesn't exist. The
7713 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
7714 whether a target machine supports this flag. @xref{Registers,,Register
7715 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
7717 The default setting (when not optimizing for
7718 size) for 32-bit GNU/Linux x86 and 32-bit Darwin x86 targets is
7719 @option{-fomit-frame-pointer}. You can configure GCC with the
7720 @option{--enable-frame-pointer} configure option to change the default.
7722 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
7724 @item -foptimize-sibling-calls
7725 @opindex foptimize-sibling-calls
7726 Optimize sibling and tail recursive calls.
7728 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
7730 @item -foptimize-strlen
7731 @opindex foptimize-strlen
7732 Optimize various standard C string functions (e.g. @code{strlen},
7733 @code{strchr} or @code{strcpy}) and
7734 their @code{_FORTIFY_SOURCE} counterparts into faster alternatives.
7736 Enabled at levels @option{-O2}, @option{-O3}.
7740 Do not expand any functions inline apart from those marked with
7741 the @code{always_inline} attribute. This is the default when not
7744 Single functions can be exempted from inlining by marking them
7745 with the @code{noinline} attribute.
7747 @item -finline-small-functions
7748 @opindex finline-small-functions
7749 Integrate functions into their callers when their body is smaller than expected
7750 function call code (so overall size of program gets smaller). The compiler
7751 heuristically decides which functions are simple enough to be worth integrating
7752 in this way. This inlining applies to all functions, even those not declared
7755 Enabled at level @option{-O2}.
7757 @item -findirect-inlining
7758 @opindex findirect-inlining
7759 Inline also indirect calls that are discovered to be known at compile
7760 time thanks to previous inlining. This option has any effect only
7761 when inlining itself is turned on by the @option{-finline-functions}
7762 or @option{-finline-small-functions} options.
7764 Enabled at level @option{-O2}.
7766 @item -finline-functions
7767 @opindex finline-functions
7768 Consider all functions for inlining, even if they are not declared inline.
7769 The compiler heuristically decides which functions are worth integrating
7772 If all calls to a given function are integrated, and the function is
7773 declared @code{static}, then the function is normally not output as
7774 assembler code in its own right.
7776 Enabled at level @option{-O3}.
7778 @item -finline-functions-called-once
7779 @opindex finline-functions-called-once
7780 Consider all @code{static} functions called once for inlining into their
7781 caller even if they are not marked @code{inline}. If a call to a given
7782 function is integrated, then the function is not output as assembler code
7785 Enabled at levels @option{-O1}, @option{-O2}, @option{-O3} and @option{-Os}.
7787 @item -fearly-inlining
7788 @opindex fearly-inlining
7789 Inline functions marked by @code{always_inline} and functions whose body seems
7790 smaller than the function call overhead early before doing
7791 @option{-fprofile-generate} instrumentation and real inlining pass. Doing so
7792 makes profiling significantly cheaper and usually inlining faster on programs
7793 having large chains of nested wrapper functions.
7799 Perform interprocedural scalar replacement of aggregates, removal of
7800 unused parameters and replacement of parameters passed by reference
7801 by parameters passed by value.
7803 Enabled at levels @option{-O2}, @option{-O3} and @option{-Os}.
7805 @item -finline-limit=@var{n}
7806 @opindex finline-limit
7807 By default, GCC limits the size of functions that can be inlined. This flag
7808 allows coarse control of this limit. @var{n} is the size of functions that
7809 can be inlined in number of pseudo instructions.
7811 Inlining is actually controlled by a number of parameters, which may be
7812 specified individually by using @option{--param @var{name}=@var{value}}.
7813 The @option{-finline-limit=@var{n}} option sets some of these parameters
7817 @item max-inline-insns-single
7818 is set to @var{n}/2.
7819 @item max-inline-insns-auto
7820 is set to @var{n}/2.
7823 See below for a documentation of the individual
7824 parameters controlling inlining and for the defaults of these parameters.
7826 @emph{Note:} there may be no value to @option{-finline-limit} that results
7827 in default behavior.
7829 @emph{Note:} pseudo instruction represents, in this particular context, an
7830 abstract measurement of function's size. In no way does it represent a count
7831 of assembly instructions and as such its exact meaning might change from one
7832 release to an another.
7834 @item -fno-keep-inline-dllexport
7835 @opindex fno-keep-inline-dllexport
7836 This is a more fine-grained version of @option{-fkeep-inline-functions},
7837 which applies only to functions that are declared using the @code{dllexport}
7838 attribute or declspec (@xref{Function Attributes,,Declaring Attributes of
7841 @item -fkeep-inline-functions
7842 @opindex fkeep-inline-functions
7843 In C, emit @code{static} functions that are declared @code{inline}
7844 into the object file, even if the function has been inlined into all
7845 of its callers. This switch does not affect functions using the
7846 @code{extern inline} extension in GNU C90@. In C++, emit any and all
7847 inline functions into the object file.
7849 @item -fkeep-static-consts
7850 @opindex fkeep-static-consts
7851 Emit variables declared @code{static const} when optimization isn't turned
7852 on, even if the variables aren't referenced.
7854 GCC enables this option by default. If you want to force the compiler to
7855 check if a variable is referenced, regardless of whether or not
7856 optimization is turned on, use the @option{-fno-keep-static-consts} option.
7858 @item -fmerge-constants
7859 @opindex fmerge-constants
7860 Attempt to merge identical constants (string constants and floating-point
7861 constants) across compilation units.
7863 This option is the default for optimized compilation if the assembler and
7864 linker support it. Use @option{-fno-merge-constants} to inhibit this
7867 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
7869 @item -fmerge-all-constants
7870 @opindex fmerge-all-constants
7871 Attempt to merge identical constants and identical variables.
7873 This option implies @option{-fmerge-constants}. In addition to
7874 @option{-fmerge-constants} this considers e.g.@: even constant initialized
7875 arrays or initialized constant variables with integral or floating-point
7876 types. Languages like C or C++ require each variable, including multiple
7877 instances of the same variable in recursive calls, to have distinct locations,
7878 so using this option results in non-conforming
7881 @item -fmodulo-sched
7882 @opindex fmodulo-sched
7883 Perform swing modulo scheduling immediately before the first scheduling
7884 pass. This pass looks at innermost loops and reorders their
7885 instructions by overlapping different iterations.
7887 @item -fmodulo-sched-allow-regmoves
7888 @opindex fmodulo-sched-allow-regmoves
7889 Perform more aggressive SMS-based modulo scheduling with register moves
7890 allowed. By setting this flag certain anti-dependences edges are
7891 deleted, which triggers the generation of reg-moves based on the
7892 life-range analysis. This option is effective only with
7893 @option{-fmodulo-sched} enabled.
7895 @item -fno-branch-count-reg
7896 @opindex fno-branch-count-reg
7897 Do not use ``decrement and branch'' instructions on a count register,
7898 but instead generate a sequence of instructions that decrement a
7899 register, compare it against zero, then branch based upon the result.
7900 This option is only meaningful on architectures that support such
7901 instructions, which include x86, PowerPC, IA-64 and S/390.
7903 Enabled by default at @option{-O1} and higher.
7905 The default is @option{-fbranch-count-reg}.
7907 @item -fno-function-cse
7908 @opindex fno-function-cse
7909 Do not put function addresses in registers; make each instruction that
7910 calls a constant function contain the function's address explicitly.
7912 This option results in less efficient code, but some strange hacks
7913 that alter the assembler output may be confused by the optimizations
7914 performed when this option is not used.
7916 The default is @option{-ffunction-cse}
7918 @item -fno-zero-initialized-in-bss
7919 @opindex fno-zero-initialized-in-bss
7920 If the target supports a BSS section, GCC by default puts variables that
7921 are initialized to zero into BSS@. This can save space in the resulting
7924 This option turns off this behavior because some programs explicitly
7925 rely on variables going to the data section---e.g., so that the
7926 resulting executable can find the beginning of that section and/or make
7927 assumptions based on that.
7929 The default is @option{-fzero-initialized-in-bss}.
7931 @item -fthread-jumps
7932 @opindex fthread-jumps
7933 Perform optimizations that check to see if a jump branches to a
7934 location where another comparison subsumed by the first is found. If
7935 so, the first branch is redirected to either the destination of the
7936 second branch or a point immediately following it, depending on whether
7937 the condition is known to be true or false.
7939 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
7941 @item -fsplit-wide-types
7942 @opindex fsplit-wide-types
7943 When using a type that occupies multiple registers, such as @code{long
7944 long} on a 32-bit system, split the registers apart and allocate them
7945 independently. This normally generates better code for those types,
7946 but may make debugging more difficult.
7948 Enabled at levels @option{-O}, @option{-O2}, @option{-O3},
7951 @item -fcse-follow-jumps
7952 @opindex fcse-follow-jumps
7953 In common subexpression elimination (CSE), scan through jump instructions
7954 when the target of the jump is not reached by any other path. For
7955 example, when CSE encounters an @code{if} statement with an
7956 @code{else} clause, CSE follows the jump when the condition
7959 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
7961 @item -fcse-skip-blocks
7962 @opindex fcse-skip-blocks
7963 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
7964 follow jumps that conditionally skip over blocks. When CSE
7965 encounters a simple @code{if} statement with no else clause,
7966 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
7967 body of the @code{if}.
7969 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
7971 @item -frerun-cse-after-loop
7972 @opindex frerun-cse-after-loop
7973 Re-run common subexpression elimination after loop optimizations are
7976 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
7980 Perform a global common subexpression elimination pass.
7981 This pass also performs global constant and copy propagation.
7983 @emph{Note:} When compiling a program using computed gotos, a GCC
7984 extension, you may get better run-time performance if you disable
7985 the global common subexpression elimination pass by adding
7986 @option{-fno-gcse} to the command line.
7988 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
7992 When @option{-fgcse-lm} is enabled, global common subexpression elimination
7993 attempts to move loads that are only killed by stores into themselves. This
7994 allows a loop containing a load/store sequence to be changed to a load outside
7995 the loop, and a copy/store within the loop.
7997 Enabled by default when @option{-fgcse} is enabled.
8001 When @option{-fgcse-sm} is enabled, a store motion pass is run after
8002 global common subexpression elimination. This pass attempts to move
8003 stores out of loops. When used in conjunction with @option{-fgcse-lm},
8004 loops containing a load/store sequence can be changed to a load before
8005 the loop and a store after the loop.
8007 Not enabled at any optimization level.
8011 When @option{-fgcse-las} is enabled, the global common subexpression
8012 elimination pass eliminates redundant loads that come after stores to the
8013 same memory location (both partial and full redundancies).
8015 Not enabled at any optimization level.
8017 @item -fgcse-after-reload
8018 @opindex fgcse-after-reload
8019 When @option{-fgcse-after-reload} is enabled, a redundant load elimination
8020 pass is performed after reload. The purpose of this pass is to clean up
8023 @item -faggressive-loop-optimizations
8024 @opindex faggressive-loop-optimizations
8025 This option tells the loop optimizer to use language constraints to
8026 derive bounds for the number of iterations of a loop. This assumes that
8027 loop code does not invoke undefined behavior by for example causing signed
8028 integer overflows or out-of-bound array accesses. The bounds for the
8029 number of iterations of a loop are used to guide loop unrolling and peeling
8030 and loop exit test optimizations.
8031 This option is enabled by default.
8033 @item -funsafe-loop-optimizations
8034 @opindex funsafe-loop-optimizations
8035 This option tells the loop optimizer to assume that loop indices do not
8036 overflow, and that loops with nontrivial exit condition are not
8037 infinite. This enables a wider range of loop optimizations even if
8038 the loop optimizer itself cannot prove that these assumptions are valid.
8039 If you use @option{-Wunsafe-loop-optimizations}, the compiler warns you
8040 if it finds this kind of loop.
8042 @item -fcrossjumping
8043 @opindex fcrossjumping
8044 Perform cross-jumping transformation.
8045 This transformation unifies equivalent code and saves code size. The
8046 resulting code may or may not perform better than without cross-jumping.
8048 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
8050 @item -fauto-inc-dec
8051 @opindex fauto-inc-dec
8052 Combine increments or decrements of addresses with memory accesses.
8053 This pass is always skipped on architectures that do not have
8054 instructions to support this. Enabled by default at @option{-O} and
8055 higher on architectures that support this.
8059 Perform dead code elimination (DCE) on RTL@.
8060 Enabled by default at @option{-O} and higher.
8064 Perform dead store elimination (DSE) on RTL@.
8065 Enabled by default at @option{-O} and higher.
8067 @item -fif-conversion
8068 @opindex fif-conversion
8069 Attempt to transform conditional jumps into branch-less equivalents. This
8070 includes use of conditional moves, min, max, set flags and abs instructions, and
8071 some tricks doable by standard arithmetics. The use of conditional execution
8072 on chips where it is available is controlled by @option{-fif-conversion2}.
8074 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
8076 @item -fif-conversion2
8077 @opindex fif-conversion2
8078 Use conditional execution (where available) to transform conditional jumps into
8079 branch-less equivalents.
8081 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
8083 @item -fdeclone-ctor-dtor
8084 @opindex fdeclone-ctor-dtor
8085 The C++ ABI requires multiple entry points for constructors and
8086 destructors: one for a base subobject, one for a complete object, and
8087 one for a virtual destructor that calls operator delete afterwards.
8088 For a hierarchy with virtual bases, the base and complete variants are
8089 clones, which means two copies of the function. With this option, the
8090 base and complete variants are changed to be thunks that call a common
8093 Enabled by @option{-Os}.
8095 @item -fdelete-null-pointer-checks
8096 @opindex fdelete-null-pointer-checks
8097 Assume that programs cannot safely dereference null pointers, and that
8098 no code or data element resides at address zero.
8099 This option enables simple constant
8100 folding optimizations at all optimization levels. In addition, other
8101 optimization passes in GCC use this flag to control global dataflow
8102 analyses that eliminate useless checks for null pointers; these assume
8103 that a memory access to address zero always results in a trap, so
8104 that if a pointer is checked after it has already been dereferenced,
8107 Note however that in some environments this assumption is not true.
8108 Use @option{-fno-delete-null-pointer-checks} to disable this optimization
8109 for programs that depend on that behavior.
8111 This option is enabled by default on most targets. On Nios II ELF, it
8112 defaults to off. On AVR and CR16, this option is completely disabled.
8114 Passes that use the dataflow information
8115 are enabled independently at different optimization levels.
8117 @item -fdevirtualize
8118 @opindex fdevirtualize
8119 Attempt to convert calls to virtual functions to direct calls. This
8120 is done both within a procedure and interprocedurally as part of
8121 indirect inlining (@option{-findirect-inlining}) and interprocedural constant
8122 propagation (@option{-fipa-cp}).
8123 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
8125 @item -fdevirtualize-speculatively
8126 @opindex fdevirtualize-speculatively
8127 Attempt to convert calls to virtual functions to speculative direct calls.
8128 Based on the analysis of the type inheritance graph, determine for a given call
8129 the set of likely targets. If the set is small, preferably of size 1, change
8130 the call into a conditional deciding between direct and indirect calls. The
8131 speculative calls enable more optimizations, such as inlining. When they seem
8132 useless after further optimization, they are converted back into original form.
8134 @item -fdevirtualize-at-ltrans
8135 @opindex fdevirtualize-at-ltrans
8136 Stream extra information needed for aggressive devirtualization when running
8137 the link-time optimizer in local transformation mode.
8138 This option enables more devirtualization but
8139 significantly increases the size of streamed data. For this reason it is
8140 disabled by default.
8142 @item -fexpensive-optimizations
8143 @opindex fexpensive-optimizations
8144 Perform a number of minor optimizations that are relatively expensive.
8146 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
8150 Attempt to remove redundant extension instructions. This is especially
8151 helpful for the x86-64 architecture, which implicitly zero-extends in 64-bit
8152 registers after writing to their lower 32-bit half.
8154 Enabled for Alpha, AArch64 and x86 at levels @option{-O2},
8155 @option{-O3}, @option{-Os}.
8157 @item -fno-lifetime-dse
8158 @opindex fno-lifetime-dse
8159 In C++ the value of an object is only affected by changes within its
8160 lifetime: when the constructor begins, the object has an indeterminate
8161 value, and any changes during the lifetime of the object are dead when
8162 the object is destroyed. Normally dead store elimination will take
8163 advantage of this; if your code relies on the value of the object
8164 storage persisting beyond the lifetime of the object, you can use this
8165 flag to disable this optimization.
8167 @item -flive-range-shrinkage
8168 @opindex flive-range-shrinkage
8169 Attempt to decrease register pressure through register live range
8170 shrinkage. This is helpful for fast processors with small or moderate
8173 @item -fira-algorithm=@var{algorithm}
8174 @opindex fira-algorithm
8175 Use the specified coloring algorithm for the integrated register
8176 allocator. The @var{algorithm} argument can be @samp{priority}, which
8177 specifies Chow's priority coloring, or @samp{CB}, which specifies
8178 Chaitin-Briggs coloring. Chaitin-Briggs coloring is not implemented
8179 for all architectures, but for those targets that do support it, it is
8180 the default because it generates better code.
8182 @item -fira-region=@var{region}
8183 @opindex fira-region
8184 Use specified regions for the integrated register allocator. The
8185 @var{region} argument should be one of the following:
8190 Use all loops as register allocation regions.
8191 This can give the best results for machines with a small and/or
8192 irregular register set.
8195 Use all loops except for loops with small register pressure
8196 as the regions. This value usually gives
8197 the best results in most cases and for most architectures,
8198 and is enabled by default when compiling with optimization for speed
8199 (@option{-O}, @option{-O2}, @dots{}).
8202 Use all functions as a single region.
8203 This typically results in the smallest code size, and is enabled by default for
8204 @option{-Os} or @option{-O0}.
8208 @item -fira-hoist-pressure
8209 @opindex fira-hoist-pressure
8210 Use IRA to evaluate register pressure in the code hoisting pass for
8211 decisions to hoist expressions. This option usually results in smaller
8212 code, but it can slow the compiler down.
8214 This option is enabled at level @option{-Os} for all targets.
8216 @item -fira-loop-pressure
8217 @opindex fira-loop-pressure
8218 Use IRA to evaluate register pressure in loops for decisions to move
8219 loop invariants. This option usually results in generation
8220 of faster and smaller code on machines with large register files (>= 32
8221 registers), but it can slow the compiler down.
8223 This option is enabled at level @option{-O3} for some targets.
8225 @item -fno-ira-share-save-slots
8226 @opindex fno-ira-share-save-slots
8227 Disable sharing of stack slots used for saving call-used hard
8228 registers living through a call. Each hard register gets a
8229 separate stack slot, and as a result function stack frames are
8232 @item -fno-ira-share-spill-slots
8233 @opindex fno-ira-share-spill-slots
8234 Disable sharing of stack slots allocated for pseudo-registers. Each
8235 pseudo-register that does not get a hard register gets a separate
8236 stack slot, and as a result function stack frames are larger.
8238 @item -fira-verbose=@var{n}
8239 @opindex fira-verbose
8240 Control the verbosity of the dump file for the integrated register allocator.
8241 The default value is 5. If the value @var{n} is greater or equal to 10,
8242 the dump output is sent to stderr using the same format as @var{n} minus 10.
8246 Enable CFG-sensitive rematerialization in LRA. Instead of loading
8247 values of spilled pseudos, LRA tries to rematerialize (recalculate)
8248 values if it is profitable.
8250 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
8252 @item -fdelayed-branch
8253 @opindex fdelayed-branch
8254 If supported for the target machine, attempt to reorder instructions
8255 to exploit instruction slots available after delayed branch
8258 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
8260 @item -fschedule-insns
8261 @opindex fschedule-insns
8262 If supported for the target machine, attempt to reorder instructions to
8263 eliminate execution stalls due to required data being unavailable. This
8264 helps machines that have slow floating point or memory load instructions
8265 by allowing other instructions to be issued until the result of the load
8266 or floating-point instruction is required.
8268 Enabled at levels @option{-O2}, @option{-O3}.
8270 @item -fschedule-insns2
8271 @opindex fschedule-insns2
8272 Similar to @option{-fschedule-insns}, but requests an additional pass of
8273 instruction scheduling after register allocation has been done. This is
8274 especially useful on machines with a relatively small number of
8275 registers and where memory load instructions take more than one cycle.
8277 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
8279 @item -fno-sched-interblock
8280 @opindex fno-sched-interblock
8281 Don't schedule instructions across basic blocks. This is normally
8282 enabled by default when scheduling before register allocation, i.e.@:
8283 with @option{-fschedule-insns} or at @option{-O2} or higher.
8285 @item -fno-sched-spec
8286 @opindex fno-sched-spec
8287 Don't allow speculative motion of non-load instructions. This is normally
8288 enabled by default when scheduling before register allocation, i.e.@:
8289 with @option{-fschedule-insns} or at @option{-O2} or higher.
8291 @item -fsched-pressure
8292 @opindex fsched-pressure
8293 Enable register pressure sensitive insn scheduling before register
8294 allocation. This only makes sense when scheduling before register
8295 allocation is enabled, i.e.@: with @option{-fschedule-insns} or at
8296 @option{-O2} or higher. Usage of this option can improve the
8297 generated code and decrease its size by preventing register pressure
8298 increase above the number of available hard registers and subsequent
8299 spills in register allocation.
8301 @item -fsched-spec-load
8302 @opindex fsched-spec-load
8303 Allow speculative motion of some load instructions. This only makes
8304 sense when scheduling before register allocation, i.e.@: with
8305 @option{-fschedule-insns} or at @option{-O2} or higher.
8307 @item -fsched-spec-load-dangerous
8308 @opindex fsched-spec-load-dangerous
8309 Allow speculative motion of more load instructions. This only makes
8310 sense when scheduling before register allocation, i.e.@: with
8311 @option{-fschedule-insns} or at @option{-O2} or higher.
8313 @item -fsched-stalled-insns
8314 @itemx -fsched-stalled-insns=@var{n}
8315 @opindex fsched-stalled-insns
8316 Define how many insns (if any) can be moved prematurely from the queue
8317 of stalled insns into the ready list during the second scheduling pass.
8318 @option{-fno-sched-stalled-insns} means that no insns are moved
8319 prematurely, @option{-fsched-stalled-insns=0} means there is no limit
8320 on how many queued insns can be moved prematurely.
8321 @option{-fsched-stalled-insns} without a value is equivalent to
8322 @option{-fsched-stalled-insns=1}.
8324 @item -fsched-stalled-insns-dep
8325 @itemx -fsched-stalled-insns-dep=@var{n}
8326 @opindex fsched-stalled-insns-dep
8327 Define how many insn groups (cycles) are examined for a dependency
8328 on a stalled insn that is a candidate for premature removal from the queue
8329 of stalled insns. This has an effect only during the second scheduling pass,
8330 and only if @option{-fsched-stalled-insns} is used.
8331 @option{-fno-sched-stalled-insns-dep} is equivalent to
8332 @option{-fsched-stalled-insns-dep=0}.
8333 @option{-fsched-stalled-insns-dep} without a value is equivalent to
8334 @option{-fsched-stalled-insns-dep=1}.
8336 @item -fsched2-use-superblocks
8337 @opindex fsched2-use-superblocks
8338 When scheduling after register allocation, use superblock scheduling.
8339 This allows motion across basic block boundaries,
8340 resulting in faster schedules. This option is experimental, as not all machine
8341 descriptions used by GCC model the CPU closely enough to avoid unreliable
8342 results from the algorithm.
8344 This only makes sense when scheduling after register allocation, i.e.@: with
8345 @option{-fschedule-insns2} or at @option{-O2} or higher.
8347 @item -fsched-group-heuristic
8348 @opindex fsched-group-heuristic
8349 Enable the group heuristic in the scheduler. This heuristic favors
8350 the instruction that belongs to a schedule group. This is enabled
8351 by default when scheduling is enabled, i.e.@: with @option{-fschedule-insns}
8352 or @option{-fschedule-insns2} or at @option{-O2} or higher.
8354 @item -fsched-critical-path-heuristic
8355 @opindex fsched-critical-path-heuristic
8356 Enable the critical-path heuristic in the scheduler. This heuristic favors
8357 instructions on the critical path. This is enabled by default when
8358 scheduling is enabled, i.e.@: with @option{-fschedule-insns}
8359 or @option{-fschedule-insns2} or at @option{-O2} or higher.
8361 @item -fsched-spec-insn-heuristic
8362 @opindex fsched-spec-insn-heuristic
8363 Enable the speculative instruction heuristic in the scheduler. This
8364 heuristic favors speculative instructions with greater dependency weakness.
8365 This is enabled by default when scheduling is enabled, i.e.@:
8366 with @option{-fschedule-insns} or @option{-fschedule-insns2}
8367 or at @option{-O2} or higher.
8369 @item -fsched-rank-heuristic
8370 @opindex fsched-rank-heuristic
8371 Enable the rank heuristic in the scheduler. This heuristic favors
8372 the instruction belonging to a basic block with greater size or frequency.
8373 This is enabled by default when scheduling is enabled, i.e.@:
8374 with @option{-fschedule-insns} or @option{-fschedule-insns2} or
8375 at @option{-O2} or higher.
8377 @item -fsched-last-insn-heuristic
8378 @opindex fsched-last-insn-heuristic
8379 Enable the last-instruction heuristic in the scheduler. This heuristic
8380 favors the instruction that is less dependent on the last instruction
8381 scheduled. This is enabled by default when scheduling is enabled,
8382 i.e.@: with @option{-fschedule-insns} or @option{-fschedule-insns2} or
8383 at @option{-O2} or higher.
8385 @item -fsched-dep-count-heuristic
8386 @opindex fsched-dep-count-heuristic
8387 Enable the dependent-count heuristic in the scheduler. This heuristic
8388 favors the instruction that has more instructions depending on it.
8389 This is enabled by default when scheduling is enabled, i.e.@:
8390 with @option{-fschedule-insns} or @option{-fschedule-insns2} or
8391 at @option{-O2} or higher.
8393 @item -freschedule-modulo-scheduled-loops
8394 @opindex freschedule-modulo-scheduled-loops
8395 Modulo scheduling is performed before traditional scheduling. If a loop
8396 is modulo scheduled, later scheduling passes may change its schedule.
8397 Use this option to control that behavior.
8399 @item -fselective-scheduling
8400 @opindex fselective-scheduling
8401 Schedule instructions using selective scheduling algorithm. Selective
8402 scheduling runs instead of the first scheduler pass.
8404 @item -fselective-scheduling2
8405 @opindex fselective-scheduling2
8406 Schedule instructions using selective scheduling algorithm. Selective
8407 scheduling runs instead of the second scheduler pass.
8409 @item -fsel-sched-pipelining
8410 @opindex fsel-sched-pipelining
8411 Enable software pipelining of innermost loops during selective scheduling.
8412 This option has no effect unless one of @option{-fselective-scheduling} or
8413 @option{-fselective-scheduling2} is turned on.
8415 @item -fsel-sched-pipelining-outer-loops
8416 @opindex fsel-sched-pipelining-outer-loops
8417 When pipelining loops during selective scheduling, also pipeline outer loops.
8418 This option has no effect unless @option{-fsel-sched-pipelining} is turned on.
8420 @item -fsemantic-interposition
8421 @opindex fsemantic-interposition
8422 Some object formats, like ELF, allow interposing of symbols by the
8424 This means that for symbols exported from the DSO, the compiler cannot perform
8425 interprocedural propagation, inlining and other optimizations in anticipation
8426 that the function or variable in question may change. While this feature is
8427 useful, for example, to rewrite memory allocation functions by a debugging
8428 implementation, it is expensive in the terms of code quality.
8429 With @option{-fno-semantic-interposition} the compiler assumes that
8430 if interposition happens for functions the overwriting function will have
8431 precisely the same semantics (and side effects).
8432 Similarly if interposition happens
8433 for variables, the constructor of the variable will be the same. The flag
8434 has no effect for functions explicitly declared inline
8435 (where it is never allowed for interposition to change semantics)
8436 and for symbols explicitly declared weak.
8439 @opindex fshrink-wrap
8440 Emit function prologues only before parts of the function that need it,
8441 rather than at the top of the function. This flag is enabled by default at
8442 @option{-O} and higher.
8444 @item -fcaller-saves
8445 @opindex fcaller-saves
8446 Enable allocation of values to registers that are clobbered by
8447 function calls, by emitting extra instructions to save and restore the
8448 registers around such calls. Such allocation is done only when it
8449 seems to result in better code.
8451 This option is always enabled by default on certain machines, usually
8452 those which have no call-preserved registers to use instead.
8454 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
8456 @item -fcombine-stack-adjustments
8457 @opindex fcombine-stack-adjustments
8458 Tracks stack adjustments (pushes and pops) and stack memory references
8459 and then tries to find ways to combine them.
8461 Enabled by default at @option{-O1} and higher.
8465 Use caller save registers for allocation if those registers are not used by
8466 any called function. In that case it is not necessary to save and restore
8467 them around calls. This is only possible if called functions are part of
8468 same compilation unit as current function and they are compiled before it.
8470 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
8472 @item -fconserve-stack
8473 @opindex fconserve-stack
8474 Attempt to minimize stack usage. The compiler attempts to use less
8475 stack space, even if that makes the program slower. This option
8476 implies setting the @option{large-stack-frame} parameter to 100
8477 and the @option{large-stack-frame-growth} parameter to 400.
8479 @item -ftree-reassoc
8480 @opindex ftree-reassoc
8481 Perform reassociation on trees. This flag is enabled by default
8482 at @option{-O} and higher.
8486 Perform partial redundancy elimination (PRE) on trees. This flag is
8487 enabled by default at @option{-O2} and @option{-O3}.
8489 @item -ftree-partial-pre
8490 @opindex ftree-partial-pre
8491 Make partial redundancy elimination (PRE) more aggressive. This flag is
8492 enabled by default at @option{-O3}.
8494 @item -ftree-forwprop
8495 @opindex ftree-forwprop
8496 Perform forward propagation on trees. This flag is enabled by default
8497 at @option{-O} and higher.
8501 Perform full redundancy elimination (FRE) on trees. The difference
8502 between FRE and PRE is that FRE only considers expressions
8503 that are computed on all paths leading to the redundant computation.
8504 This analysis is faster than PRE, though it exposes fewer redundancies.
8505 This flag is enabled by default at @option{-O} and higher.
8507 @item -ftree-phiprop
8508 @opindex ftree-phiprop
8509 Perform hoisting of loads from conditional pointers on trees. This
8510 pass is enabled by default at @option{-O} and higher.
8512 @item -fhoist-adjacent-loads
8513 @opindex fhoist-adjacent-loads
8514 Speculatively hoist loads from both branches of an if-then-else if the
8515 loads are from adjacent locations in the same structure and the target
8516 architecture has a conditional move instruction. This flag is enabled
8517 by default at @option{-O2} and higher.
8519 @item -ftree-copy-prop
8520 @opindex ftree-copy-prop
8521 Perform copy propagation on trees. This pass eliminates unnecessary
8522 copy operations. This flag is enabled by default at @option{-O} and
8525 @item -fipa-pure-const
8526 @opindex fipa-pure-const
8527 Discover which functions are pure or constant.
8528 Enabled by default at @option{-O} and higher.
8530 @item -fipa-reference
8531 @opindex fipa-reference
8532 Discover which static variables do not escape the
8534 Enabled by default at @option{-O} and higher.
8538 Perform interprocedural pointer analysis and interprocedural modification
8539 and reference analysis. This option can cause excessive memory and
8540 compile-time usage on large compilation units. It is not enabled by
8541 default at any optimization level.
8544 @opindex fipa-profile
8545 Perform interprocedural profile propagation. The functions called only from
8546 cold functions are marked as cold. Also functions executed once (such as
8547 @code{cold}, @code{noreturn}, static constructors or destructors) are identified. Cold
8548 functions and loop less parts of functions executed once are then optimized for
8550 Enabled by default at @option{-O} and higher.
8554 Perform interprocedural constant propagation.
8555 This optimization analyzes the program to determine when values passed
8556 to functions are constants and then optimizes accordingly.
8557 This optimization can substantially increase performance
8558 if the application has constants passed to functions.
8559 This flag is enabled by default at @option{-O2}, @option{-Os} and @option{-O3}.
8561 @item -fipa-cp-clone
8562 @opindex fipa-cp-clone
8563 Perform function cloning to make interprocedural constant propagation stronger.
8564 When enabled, interprocedural constant propagation performs function cloning
8565 when externally visible function can be called with constant arguments.
8566 Because this optimization can create multiple copies of functions,
8567 it may significantly increase code size
8568 (see @option{--param ipcp-unit-growth=@var{value}}).
8569 This flag is enabled by default at @option{-O3}.
8571 @item -fipa-cp-alignment
8572 @opindex -fipa-cp-alignment
8573 When enabled, this optimization propagates alignment of function
8574 parameters to support better vectorization and string operations.
8576 This flag is enabled by default at @option{-O2} and @option{-Os}. It
8577 requires that @option{-fipa-cp} is enabled.
8581 Perform Identical Code Folding for functions and read-only variables.
8582 The optimization reduces code size and may disturb unwind stacks by replacing
8583 a function by equivalent one with a different name. The optimization works
8584 more effectively with link time optimization enabled.
8586 Nevertheless the behavior is similar to Gold Linker ICF optimization, GCC ICF
8587 works on different levels and thus the optimizations are not same - there are
8588 equivalences that are found only by GCC and equivalences found only by Gold.
8590 This flag is enabled by default at @option{-O2} and @option{-Os}.
8592 @item -fisolate-erroneous-paths-dereference
8593 @opindex fisolate-erroneous-paths-dereference
8594 Detect paths that trigger erroneous or undefined behavior due to
8595 dereferencing a null pointer. Isolate those paths from the main control
8596 flow and turn the statement with erroneous or undefined behavior into a trap.
8597 This flag is enabled by default at @option{-O2} and higher and depends on
8598 @option{-fdelete-null-pointer-checks} also being enabled.
8600 @item -fisolate-erroneous-paths-attribute
8601 @opindex fisolate-erroneous-paths-attribute
8602 Detect paths that trigger erroneous or undefined behavior due a null value
8603 being used in a way forbidden by a @code{returns_nonnull} or @code{nonnull}
8604 attribute. Isolate those paths from the main control flow and turn the
8605 statement with erroneous or undefined behavior into a trap. This is not
8606 currently enabled, but may be enabled by @option{-O2} in the future.
8610 Perform forward store motion on trees. This flag is
8611 enabled by default at @option{-O} and higher.
8613 @item -ftree-bit-ccp
8614 @opindex ftree-bit-ccp
8615 Perform sparse conditional bit constant propagation on trees and propagate
8616 pointer alignment information.
8617 This pass only operates on local scalar variables and is enabled by default
8618 at @option{-O} and higher. It requires that @option{-ftree-ccp} is enabled.
8622 Perform sparse conditional constant propagation (CCP) on trees. This
8623 pass only operates on local scalar variables and is enabled by default
8624 at @option{-O} and higher.
8627 @opindex fssa-phiopt
8628 Perform pattern matching on SSA PHI nodes to optimize conditional
8629 code. This pass is enabled by default at @option{-O} and higher.
8631 @item -ftree-switch-conversion
8632 @opindex ftree-switch-conversion
8633 Perform conversion of simple initializations in a switch to
8634 initializations from a scalar array. This flag is enabled by default
8635 at @option{-O2} and higher.
8637 @item -ftree-tail-merge
8638 @opindex ftree-tail-merge
8639 Look for identical code sequences. When found, replace one with a jump to the
8640 other. This optimization is known as tail merging or cross jumping. This flag
8641 is enabled by default at @option{-O2} and higher. The compilation time
8643 be limited using @option{max-tail-merge-comparisons} parameter and
8644 @option{max-tail-merge-iterations} parameter.
8648 Perform dead code elimination (DCE) on trees. This flag is enabled by
8649 default at @option{-O} and higher.
8651 @item -ftree-builtin-call-dce
8652 @opindex ftree-builtin-call-dce
8653 Perform conditional dead code elimination (DCE) for calls to built-in functions
8654 that may set @code{errno} but are otherwise side-effect free. This flag is
8655 enabled by default at @option{-O2} and higher if @option{-Os} is not also
8658 @item -ftree-dominator-opts
8659 @opindex ftree-dominator-opts
8660 Perform a variety of simple scalar cleanups (constant/copy
8661 propagation, redundancy elimination, range propagation and expression
8662 simplification) based on a dominator tree traversal. This also
8663 performs jump threading (to reduce jumps to jumps). This flag is
8664 enabled by default at @option{-O} and higher.
8668 Perform dead store elimination (DSE) on trees. A dead store is a store into
8669 a memory location that is later overwritten by another store without
8670 any intervening loads. In this case the earlier store can be deleted. This
8671 flag is enabled by default at @option{-O} and higher.
8675 Perform loop header copying on trees. This is beneficial since it increases
8676 effectiveness of code motion optimizations. It also saves one jump. This flag
8677 is enabled by default at @option{-O} and higher. It is not enabled
8678 for @option{-Os}, since it usually increases code size.
8680 @item -ftree-loop-optimize
8681 @opindex ftree-loop-optimize
8682 Perform loop optimizations on trees. This flag is enabled by default
8683 at @option{-O} and higher.
8685 @item -ftree-loop-linear
8686 @opindex ftree-loop-linear
8687 Perform loop interchange transformations on tree. Same as
8688 @option{-floop-interchange}. To use this code transformation, GCC has
8689 to be configured with @option{--with-isl} to enable the Graphite loop
8690 transformation infrastructure.
8692 @item -floop-interchange
8693 @opindex floop-interchange
8694 Perform loop interchange transformations on loops. Interchanging two
8695 nested loops switches the inner and outer loops. For example, given a
8700 A(J, I) = A(J, I) * C
8705 loop interchange transforms the loop as if it were written:
8709 A(J, I) = A(J, I) * C
8713 which can be beneficial when @code{N} is larger than the caches,
8714 because in Fortran, the elements of an array are stored in memory
8715 contiguously by column, and the original loop iterates over rows,
8716 potentially creating at each access a cache miss. This optimization
8717 applies to all the languages supported by GCC and is not limited to
8718 Fortran. To use this code transformation, GCC has to be configured
8719 with @option{--with-isl} to enable the Graphite loop transformation
8722 @item -floop-strip-mine
8723 @opindex floop-strip-mine
8724 Perform loop strip mining transformations on loops. Strip mining
8725 splits a loop into two nested loops. The outer loop has strides
8726 equal to the strip size and the inner loop has strides of the
8727 original loop within a strip. The strip length can be changed
8728 using the @option{loop-block-tile-size} parameter. For example,
8736 loop strip mining transforms the loop as if it were written:
8739 DO I = II, min (II + 50, N)
8744 This optimization applies to all the languages supported by GCC and is
8745 not limited to Fortran. To use this code transformation, GCC has to
8746 be configured with @option{--with-isl} to enable the Graphite loop
8747 transformation infrastructure.
8750 @opindex floop-block
8751 Perform loop blocking transformations on loops. Blocking strip mines
8752 each loop in the loop nest such that the memory accesses of the
8753 element loops fit inside caches. The strip length can be changed
8754 using the @option{loop-block-tile-size} parameter. For example, given
8759 A(J, I) = B(I) + C(J)
8764 loop blocking transforms the loop as if it were written:
8768 DO I = II, min (II + 50, N)
8769 DO J = JJ, min (JJ + 50, M)
8770 A(J, I) = B(I) + C(J)
8776 which can be beneficial when @code{M} is larger than the caches,
8777 because the innermost loop iterates over a smaller amount of data
8778 which can be kept in the caches. This optimization applies to all the
8779 languages supported by GCC and is not limited to Fortran. To use this
8780 code transformation, GCC has to be configured with @option{--with-isl}
8781 to enable the Graphite loop transformation infrastructure.
8783 @item -fgraphite-identity
8784 @opindex fgraphite-identity
8785 Enable the identity transformation for graphite. For every SCoP we generate
8786 the polyhedral representation and transform it back to gimple. Using
8787 @option{-fgraphite-identity} we can check the costs or benefits of the
8788 GIMPLE -> GRAPHITE -> GIMPLE transformation. Some minimal optimizations
8789 are also performed by the code generator ISL, like index splitting and
8790 dead code elimination in loops.
8792 @item -floop-nest-optimize
8793 @opindex floop-nest-optimize
8794 Enable the ISL based loop nest optimizer. This is a generic loop nest
8795 optimizer based on the Pluto optimization algorithms. It calculates a loop
8796 structure optimized for data-locality and parallelism. This option
8799 @item -floop-unroll-and-jam
8800 @opindex floop-unroll-and-jam
8801 Enable unroll and jam for the ISL based loop nest optimizer. The unroll
8802 factor can be changed using the @option{loop-unroll-jam-size} parameter.
8803 The unrolled dimension (counting from the most inner one) can be changed
8804 using the @option{loop-unroll-jam-depth} parameter. .
8806 @item -floop-parallelize-all
8807 @opindex floop-parallelize-all
8808 Use the Graphite data dependence analysis to identify loops that can
8809 be parallelized. Parallelize all the loops that can be analyzed to
8810 not contain loop carried dependences without checking that it is
8811 profitable to parallelize the loops.
8813 @item -fcheck-data-deps
8814 @opindex fcheck-data-deps
8815 Compare the results of several data dependence analyzers. This option
8816 is used for debugging the data dependence analyzers.
8818 @item -ftree-loop-if-convert
8819 @opindex ftree-loop-if-convert
8820 Attempt to transform conditional jumps in the innermost loops to
8821 branch-less equivalents. The intent is to remove control-flow from
8822 the innermost loops in order to improve the ability of the
8823 vectorization pass to handle these loops. This is enabled by default
8824 if vectorization is enabled.
8826 @item -ftree-loop-if-convert-stores
8827 @opindex ftree-loop-if-convert-stores
8828 Attempt to also if-convert conditional jumps containing memory writes.
8829 This transformation can be unsafe for multi-threaded programs as it
8830 transforms conditional memory writes into unconditional memory writes.
8833 for (i = 0; i < N; i++)
8839 for (i = 0; i < N; i++)
8840 A[i] = cond ? expr : A[i];
8842 potentially producing data races.
8844 @item -ftree-loop-distribution
8845 @opindex ftree-loop-distribution
8846 Perform loop distribution. This flag can improve cache performance on
8847 big loop bodies and allow further loop optimizations, like
8848 parallelization or vectorization, to take place. For example, the loop
8865 @item -ftree-loop-distribute-patterns
8866 @opindex ftree-loop-distribute-patterns
8867 Perform loop distribution of patterns that can be code generated with
8868 calls to a library. This flag is enabled by default at @option{-O3}.
8870 This pass distributes the initialization loops and generates a call to
8871 memset zero. For example, the loop
8887 and the initialization loop is transformed into a call to memset zero.
8889 @item -ftree-loop-im
8890 @opindex ftree-loop-im
8891 Perform loop invariant motion on trees. This pass moves only invariants that
8892 are hard to handle at RTL level (function calls, operations that expand to
8893 nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
8894 operands of conditions that are invariant out of the loop, so that we can use
8895 just trivial invariantness analysis in loop unswitching. The pass also includes
8898 @item -ftree-loop-ivcanon
8899 @opindex ftree-loop-ivcanon
8900 Create a canonical counter for number of iterations in loops for which
8901 determining number of iterations requires complicated analysis. Later
8902 optimizations then may determine the number easily. Useful especially
8903 in connection with unrolling.
8907 Perform induction variable optimizations (strength reduction, induction
8908 variable merging and induction variable elimination) on trees.
8910 @item -ftree-parallelize-loops=n
8911 @opindex ftree-parallelize-loops
8912 Parallelize loops, i.e., split their iteration space to run in n threads.
8913 This is only possible for loops whose iterations are independent
8914 and can be arbitrarily reordered. The optimization is only
8915 profitable on multiprocessor machines, for loops that are CPU-intensive,
8916 rather than constrained e.g.@: by memory bandwidth. This option
8917 implies @option{-pthread}, and thus is only supported on targets
8918 that have support for @option{-pthread}.
8922 Perform function-local points-to analysis on trees. This flag is
8923 enabled by default at @option{-O} and higher.
8927 Perform scalar replacement of aggregates. This pass replaces structure
8928 references with scalars to prevent committing structures to memory too
8929 early. This flag is enabled by default at @option{-O} and higher.
8931 @item -ftree-copyrename
8932 @opindex ftree-copyrename
8933 Perform copy renaming on trees. This pass attempts to rename compiler
8934 temporaries to other variables at copy locations, usually resulting in
8935 variable names which more closely resemble the original variables. This flag
8936 is enabled by default at @option{-O} and higher.
8938 @item -ftree-coalesce-inlined-vars
8939 @opindex ftree-coalesce-inlined-vars
8940 Tell the copyrename pass (see @option{-ftree-copyrename}) to attempt to
8941 combine small user-defined variables too, but only if they are inlined
8942 from other functions. It is a more limited form of
8943 @option{-ftree-coalesce-vars}. This may harm debug information of such
8944 inlined variables, but it keeps variables of the inlined-into
8945 function apart from each other, such that they are more likely to
8946 contain the expected values in a debugging session.
8948 @item -ftree-coalesce-vars
8949 @opindex ftree-coalesce-vars
8950 Tell the copyrename pass (see @option{-ftree-copyrename}) to attempt to
8951 combine small user-defined variables too, instead of just compiler
8952 temporaries. This may severely limit the ability to debug an optimized
8953 program compiled with @option{-fno-var-tracking-assignments}. In the
8954 negated form, this flag prevents SSA coalescing of user variables,
8955 including inlined ones. This option is enabled by default.
8959 Perform temporary expression replacement during the SSA->normal phase. Single
8960 use/single def temporaries are replaced at their use location with their
8961 defining expression. This results in non-GIMPLE code, but gives the expanders
8962 much more complex trees to work on resulting in better RTL generation. This is
8963 enabled by default at @option{-O} and higher.
8967 Perform straight-line strength reduction on trees. This recognizes related
8968 expressions involving multiplications and replaces them by less expensive
8969 calculations when possible. This is enabled by default at @option{-O} and
8972 @item -ftree-vectorize
8973 @opindex ftree-vectorize
8974 Perform vectorization on trees. This flag enables @option{-ftree-loop-vectorize}
8975 and @option{-ftree-slp-vectorize} if not explicitly specified.
8977 @item -ftree-loop-vectorize
8978 @opindex ftree-loop-vectorize
8979 Perform loop vectorization on trees. This flag is enabled by default at
8980 @option{-O3} and when @option{-ftree-vectorize} is enabled.
8982 @item -ftree-slp-vectorize
8983 @opindex ftree-slp-vectorize
8984 Perform basic block vectorization on trees. This flag is enabled by default at
8985 @option{-O3} and when @option{-ftree-vectorize} is enabled.
8987 @item -fvect-cost-model=@var{model}
8988 @opindex fvect-cost-model
8989 Alter the cost model used for vectorization. The @var{model} argument
8990 should be one of @samp{unlimited}, @samp{dynamic} or @samp{cheap}.
8991 With the @samp{unlimited} model the vectorized code-path is assumed
8992 to be profitable while with the @samp{dynamic} model a runtime check
8993 guards the vectorized code-path to enable it only for iteration
8994 counts that will likely execute faster than when executing the original
8995 scalar loop. The @samp{cheap} model disables vectorization of
8996 loops where doing so would be cost prohibitive for example due to
8997 required runtime checks for data dependence or alignment but otherwise
8998 is equal to the @samp{dynamic} model.
8999 The default cost model depends on other optimization flags and is
9000 either @samp{dynamic} or @samp{cheap}.
9002 @item -fsimd-cost-model=@var{model}
9003 @opindex fsimd-cost-model
9004 Alter the cost model used for vectorization of loops marked with the OpenMP
9005 or Cilk Plus simd directive. The @var{model} argument should be one of
9006 @samp{unlimited}, @samp{dynamic}, @samp{cheap}. All values of @var{model}
9007 have the same meaning as described in @option{-fvect-cost-model} and by
9008 default a cost model defined with @option{-fvect-cost-model} is used.
9012 Perform Value Range Propagation on trees. This is similar to the
9013 constant propagation pass, but instead of values, ranges of values are
9014 propagated. This allows the optimizers to remove unnecessary range
9015 checks like array bound checks and null pointer checks. This is
9016 enabled by default at @option{-O2} and higher. Null pointer check
9017 elimination is only done if @option{-fdelete-null-pointer-checks} is
9020 @item -fsplit-ivs-in-unroller
9021 @opindex fsplit-ivs-in-unroller
9022 Enables expression of values of induction variables in later iterations
9023 of the unrolled loop using the value in the first iteration. This breaks
9024 long dependency chains, thus improving efficiency of the scheduling passes.
9026 A combination of @option{-fweb} and CSE is often sufficient to obtain the
9027 same effect. However, that is not reliable in cases where the loop body
9028 is more complicated than a single basic block. It also does not work at all
9029 on some architectures due to restrictions in the CSE pass.
9031 This optimization is enabled by default.
9033 @item -fvariable-expansion-in-unroller
9034 @opindex fvariable-expansion-in-unroller
9035 With this option, the compiler creates multiple copies of some
9036 local variables when unrolling a loop, which can result in superior code.
9038 @item -fpartial-inlining
9039 @opindex fpartial-inlining
9040 Inline parts of functions. This option has any effect only
9041 when inlining itself is turned on by the @option{-finline-functions}
9042 or @option{-finline-small-functions} options.
9044 Enabled at level @option{-O2}.
9046 @item -fpredictive-commoning
9047 @opindex fpredictive-commoning
9048 Perform predictive commoning optimization, i.e., reusing computations
9049 (especially memory loads and stores) performed in previous
9050 iterations of loops.
9052 This option is enabled at level @option{-O3}.
9054 @item -fprefetch-loop-arrays
9055 @opindex fprefetch-loop-arrays
9056 If supported by the target machine, generate instructions to prefetch
9057 memory to improve the performance of loops that access large arrays.
9059 This option may generate better or worse code; results are highly
9060 dependent on the structure of loops within the source code.
9062 Disabled at level @option{-Os}.
9065 @itemx -fno-peephole2
9066 @opindex fno-peephole
9067 @opindex fno-peephole2
9068 Disable any machine-specific peephole optimizations. The difference
9069 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
9070 are implemented in the compiler; some targets use one, some use the
9071 other, a few use both.
9073 @option{-fpeephole} is enabled by default.
9074 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
9076 @item -fno-guess-branch-probability
9077 @opindex fno-guess-branch-probability
9078 Do not guess branch probabilities using heuristics.
9080 GCC uses heuristics to guess branch probabilities if they are
9081 not provided by profiling feedback (@option{-fprofile-arcs}). These
9082 heuristics are based on the control flow graph. If some branch probabilities
9083 are specified by @code{__builtin_expect}, then the heuristics are
9084 used to guess branch probabilities for the rest of the control flow graph,
9085 taking the @code{__builtin_expect} info into account. The interactions
9086 between the heuristics and @code{__builtin_expect} can be complex, and in
9087 some cases, it may be useful to disable the heuristics so that the effects
9088 of @code{__builtin_expect} are easier to understand.
9090 The default is @option{-fguess-branch-probability} at levels
9091 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
9093 @item -freorder-blocks
9094 @opindex freorder-blocks
9095 Reorder basic blocks in the compiled function in order to reduce number of
9096 taken branches and improve code locality.
9098 Enabled at levels @option{-O2}, @option{-O3}.
9100 @item -freorder-blocks-and-partition
9101 @opindex freorder-blocks-and-partition
9102 In addition to reordering basic blocks in the compiled function, in order
9103 to reduce number of taken branches, partitions hot and cold basic blocks
9104 into separate sections of the assembly and .o files, to improve
9105 paging and cache locality performance.
9107 This optimization is automatically turned off in the presence of
9108 exception handling, for linkonce sections, for functions with a user-defined
9109 section attribute and on any architecture that does not support named
9112 Enabled for x86 at levels @option{-O2}, @option{-O3}.
9114 @item -freorder-functions
9115 @opindex freorder-functions
9116 Reorder functions in the object file in order to
9117 improve code locality. This is implemented by using special
9118 subsections @code{.text.hot} for most frequently executed functions and
9119 @code{.text.unlikely} for unlikely executed functions. Reordering is done by
9120 the linker so object file format must support named sections and linker must
9121 place them in a reasonable way.
9123 Also profile feedback must be available to make this option effective. See
9124 @option{-fprofile-arcs} for details.
9126 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
9128 @item -fstrict-aliasing
9129 @opindex fstrict-aliasing
9130 Allow the compiler to assume the strictest aliasing rules applicable to
9131 the language being compiled. For C (and C++), this activates
9132 optimizations based on the type of expressions. In particular, an
9133 object of one type is assumed never to reside at the same address as an
9134 object of a different type, unless the types are almost the same. For
9135 example, an @code{unsigned int} can alias an @code{int}, but not a
9136 @code{void*} or a @code{double}. A character type may alias any other
9139 @anchor{Type-punning}Pay special attention to code like this:
9152 The practice of reading from a different union member than the one most
9153 recently written to (called ``type-punning'') is common. Even with
9154 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
9155 is accessed through the union type. So, the code above works as
9156 expected. @xref{Structures unions enumerations and bit-fields
9157 implementation}. However, this code might not:
9168 Similarly, access by taking the address, casting the resulting pointer
9169 and dereferencing the result has undefined behavior, even if the cast
9170 uses a union type, e.g.:
9174 return ((union a_union *) &d)->i;
9178 The @option{-fstrict-aliasing} option is enabled at levels
9179 @option{-O2}, @option{-O3}, @option{-Os}.
9181 @item -fstrict-overflow
9182 @opindex fstrict-overflow
9183 Allow the compiler to assume strict signed overflow rules, depending
9184 on the language being compiled. For C (and C++) this means that
9185 overflow when doing arithmetic with signed numbers is undefined, which
9186 means that the compiler may assume that it does not happen. This
9187 permits various optimizations. For example, the compiler assumes
9188 that an expression like @code{i + 10 > i} is always true for
9189 signed @code{i}. This assumption is only valid if signed overflow is
9190 undefined, as the expression is false if @code{i + 10} overflows when
9191 using twos complement arithmetic. When this option is in effect any
9192 attempt to determine whether an operation on signed numbers
9193 overflows must be written carefully to not actually involve overflow.
9195 This option also allows the compiler to assume strict pointer
9196 semantics: given a pointer to an object, if adding an offset to that
9197 pointer does not produce a pointer to the same object, the addition is
9198 undefined. This permits the compiler to conclude that @code{p + u >
9199 p} is always true for a pointer @code{p} and unsigned integer
9200 @code{u}. This assumption is only valid because pointer wraparound is
9201 undefined, as the expression is false if @code{p + u} overflows using
9202 twos complement arithmetic.
9204 See also the @option{-fwrapv} option. Using @option{-fwrapv} means
9205 that integer signed overflow is fully defined: it wraps. When
9206 @option{-fwrapv} is used, there is no difference between
9207 @option{-fstrict-overflow} and @option{-fno-strict-overflow} for
9208 integers. With @option{-fwrapv} certain types of overflow are
9209 permitted. For example, if the compiler gets an overflow when doing
9210 arithmetic on constants, the overflowed value can still be used with
9211 @option{-fwrapv}, but not otherwise.
9213 The @option{-fstrict-overflow} option is enabled at levels
9214 @option{-O2}, @option{-O3}, @option{-Os}.
9216 @item -falign-functions
9217 @itemx -falign-functions=@var{n}
9218 @opindex falign-functions
9219 Align the start of functions to the next power-of-two greater than
9220 @var{n}, skipping up to @var{n} bytes. For instance,
9221 @option{-falign-functions=32} aligns functions to the next 32-byte
9222 boundary, but @option{-falign-functions=24} aligns to the next
9223 32-byte boundary only if this can be done by skipping 23 bytes or less.
9225 @option{-fno-align-functions} and @option{-falign-functions=1} are
9226 equivalent and mean that functions are not aligned.
9228 Some assemblers only support this flag when @var{n} is a power of two;
9229 in that case, it is rounded up.
9231 If @var{n} is not specified or is zero, use a machine-dependent default.
9233 Enabled at levels @option{-O2}, @option{-O3}.
9235 @item -falign-labels
9236 @itemx -falign-labels=@var{n}
9237 @opindex falign-labels
9238 Align all branch targets to a power-of-two boundary, skipping up to
9239 @var{n} bytes like @option{-falign-functions}. This option can easily
9240 make code slower, because it must insert dummy operations for when the
9241 branch target is reached in the usual flow of the code.
9243 @option{-fno-align-labels} and @option{-falign-labels=1} are
9244 equivalent and mean that labels are not aligned.
9246 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
9247 are greater than this value, then their values are used instead.
9249 If @var{n} is not specified or is zero, use a machine-dependent default
9250 which is very likely to be @samp{1}, meaning no alignment.
9252 Enabled at levels @option{-O2}, @option{-O3}.
9255 @itemx -falign-loops=@var{n}
9256 @opindex falign-loops
9257 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
9258 like @option{-falign-functions}. If the loops are
9259 executed many times, this makes up for any execution of the dummy
9262 @option{-fno-align-loops} and @option{-falign-loops=1} are
9263 equivalent and mean that loops are not aligned.
9265 If @var{n} is not specified or is zero, use a machine-dependent default.
9267 Enabled at levels @option{-O2}, @option{-O3}.
9270 @itemx -falign-jumps=@var{n}
9271 @opindex falign-jumps
9272 Align branch targets to a power-of-two boundary, for branch targets
9273 where the targets can only be reached by jumping, skipping up to @var{n}
9274 bytes like @option{-falign-functions}. In this case, no dummy operations
9277 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
9278 equivalent and mean that loops are not aligned.
9280 If @var{n} is not specified or is zero, use a machine-dependent default.
9282 Enabled at levels @option{-O2}, @option{-O3}.
9284 @item -funit-at-a-time
9285 @opindex funit-at-a-time
9286 This option is left for compatibility reasons. @option{-funit-at-a-time}
9287 has no effect, while @option{-fno-unit-at-a-time} implies
9288 @option{-fno-toplevel-reorder} and @option{-fno-section-anchors}.
9292 @item -fno-toplevel-reorder
9293 @opindex fno-toplevel-reorder
9294 Do not reorder top-level functions, variables, and @code{asm}
9295 statements. Output them in the same order that they appear in the
9296 input file. When this option is used, unreferenced static variables
9297 are not removed. This option is intended to support existing code
9298 that relies on a particular ordering. For new code, it is better to
9299 use attributes when possible.
9301 Enabled at level @option{-O0}. When disabled explicitly, it also implies
9302 @option{-fno-section-anchors}, which is otherwise enabled at @option{-O0} on some
9307 Constructs webs as commonly used for register allocation purposes and assign
9308 each web individual pseudo register. This allows the register allocation pass
9309 to operate on pseudos directly, but also strengthens several other optimization
9310 passes, such as CSE, loop optimizer and trivial dead code remover. It can,
9311 however, make debugging impossible, since variables no longer stay in a
9314 Enabled by default with @option{-funroll-loops}.
9316 @item -fwhole-program
9317 @opindex fwhole-program
9318 Assume that the current compilation unit represents the whole program being
9319 compiled. All public functions and variables with the exception of @code{main}
9320 and those merged by attribute @code{externally_visible} become static functions
9321 and in effect are optimized more aggressively by interprocedural optimizers.
9323 This option should not be used in combination with @option{-flto}.
9324 Instead relying on a linker plugin should provide safer and more precise
9327 @item -flto[=@var{n}]
9329 This option runs the standard link-time optimizer. When invoked
9330 with source code, it generates GIMPLE (one of GCC's internal
9331 representations) and writes it to special ELF sections in the object
9332 file. When the object files are linked together, all the function
9333 bodies are read from these ELF sections and instantiated as if they
9334 had been part of the same translation unit.
9336 To use the link-time optimizer, @option{-flto} and optimization
9337 options should be specified at compile time and during the final link.
9341 gcc -c -O2 -flto foo.c
9342 gcc -c -O2 -flto bar.c
9343 gcc -o myprog -flto -O2 foo.o bar.o
9346 The first two invocations to GCC save a bytecode representation
9347 of GIMPLE into special ELF sections inside @file{foo.o} and
9348 @file{bar.o}. The final invocation reads the GIMPLE bytecode from
9349 @file{foo.o} and @file{bar.o}, merges the two files into a single
9350 internal image, and compiles the result as usual. Since both
9351 @file{foo.o} and @file{bar.o} are merged into a single image, this
9352 causes all the interprocedural analyses and optimizations in GCC to
9353 work across the two files as if they were a single one. This means,
9354 for example, that the inliner is able to inline functions in
9355 @file{bar.o} into functions in @file{foo.o} and vice-versa.
9357 Another (simpler) way to enable link-time optimization is:
9360 gcc -o myprog -flto -O2 foo.c bar.c
9363 The above generates bytecode for @file{foo.c} and @file{bar.c},
9364 merges them together into a single GIMPLE representation and optimizes
9365 them as usual to produce @file{myprog}.
9367 The only important thing to keep in mind is that to enable link-time
9368 optimizations you need to use the GCC driver to perform the link-step.
9369 GCC then automatically performs link-time optimization if any of the
9370 objects involved were compiled with the @option{-flto} command-line option.
9372 should specify the optimization options to be used for link-time
9373 optimization though GCC tries to be clever at guessing an
9374 optimization level to use from the options used at compile-time
9375 if you fail to specify one at link-time. You can always override
9376 the automatic decision to do link-time optimization at link-time
9377 by passing @option{-fno-lto} to the link command.
9379 To make whole program optimization effective, it is necessary to make
9380 certain whole program assumptions. The compiler needs to know
9381 what functions and variables can be accessed by libraries and runtime
9382 outside of the link-time optimized unit. When supported by the linker,
9383 the linker plugin (see @option{-fuse-linker-plugin}) passes information
9384 to the compiler about used and externally visible symbols. When
9385 the linker plugin is not available, @option{-fwhole-program} should be
9386 used to allow the compiler to make these assumptions, which leads
9387 to more aggressive optimization decisions.
9389 When @option{-fuse-linker-plugin} is not enabled then, when a file is
9390 compiled with @option{-flto}, the generated object file is larger than
9391 a regular object file because it contains GIMPLE bytecodes and the usual
9392 final code (see @option{-ffat-lto-objects}. This means that
9393 object files with LTO information can be linked as normal object
9394 files; if @option{-fno-lto} is passed to the linker, no
9395 interprocedural optimizations are applied. Note that when
9396 @option{-fno-fat-lto-objects} is enabled the compile-stage is faster
9397 but you cannot perform a regular, non-LTO link on them.
9399 Additionally, the optimization flags used to compile individual files
9400 are not necessarily related to those used at link time. For instance,
9403 gcc -c -O0 -ffat-lto-objects -flto foo.c
9404 gcc -c -O0 -ffat-lto-objects -flto bar.c
9405 gcc -o myprog -O3 foo.o bar.o
9408 This produces individual object files with unoptimized assembler
9409 code, but the resulting binary @file{myprog} is optimized at
9410 @option{-O3}. If, instead, the final binary is generated with
9411 @option{-fno-lto}, then @file{myprog} is not optimized.
9413 When producing the final binary, GCC only
9414 applies link-time optimizations to those files that contain bytecode.
9415 Therefore, you can mix and match object files and libraries with
9416 GIMPLE bytecodes and final object code. GCC automatically selects
9417 which files to optimize in LTO mode and which files to link without
9420 There are some code generation flags preserved by GCC when
9421 generating bytecodes, as they need to be used during the final link
9422 stage. Generally options specified at link-time override those
9423 specified at compile-time.
9425 If you do not specify an optimization level option @option{-O} at
9426 link-time then GCC computes one based on the optimization levels
9427 used when compiling the object files. The highest optimization
9430 Currently, the following options and their setting are take from
9431 the first object file that explicitely specified it:
9432 @option{-fPIC}, @option{-fpic}, @option{-fpie}, @option{-fcommon},
9433 @option{-fexceptions}, @option{-fnon-call-exceptions}, @option{-fgnu-tm}
9434 and all the @option{-m} target flags.
9436 Certain ABI changing flags are required to match in all compilation-units
9437 and trying to override this at link-time with a conflicting value
9438 is ignored. This includes options such as @option{-freg-struct-return}
9439 and @option{-fpcc-struct-return}.
9441 Other options such as @option{-ffp-contract}, @option{-fno-strict-overflow},
9442 @option{-fwrapv}, @option{-fno-trapv} or @option{-fno-strict-aliasing}
9443 are passed through to the link stage and merged conservatively for
9444 conflicting translation units. Specifically
9445 @option{-fno-strict-overflow}, @option{-fwrapv} and @option{-fno-trapv} take
9446 precedence and for example @option{-ffp-contract=off} takes precedence
9447 over @option{-ffp-contract=fast}. You can override them at linke-time.
9449 It is recommended that you compile all the files participating in the
9450 same link with the same options and also specify those options at
9453 If LTO encounters objects with C linkage declared with incompatible
9454 types in separate translation units to be linked together (undefined
9455 behavior according to ISO C99 6.2.7), a non-fatal diagnostic may be
9456 issued. The behavior is still undefined at run time. Similar
9457 diagnostics may be raised for other languages.
9459 Another feature of LTO is that it is possible to apply interprocedural
9460 optimizations on files written in different languages:
9465 gfortran -c -flto baz.f90
9466 g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran
9469 Notice that the final link is done with @command{g++} to get the C++
9470 runtime libraries and @option{-lgfortran} is added to get the Fortran
9471 runtime libraries. In general, when mixing languages in LTO mode, you
9472 should use the same link command options as when mixing languages in a
9473 regular (non-LTO) compilation.
9475 If object files containing GIMPLE bytecode are stored in a library archive, say
9476 @file{libfoo.a}, it is possible to extract and use them in an LTO link if you
9477 are using a linker with plugin support. To create static libraries suitable
9478 for LTO, use @command{gcc-ar} and @command{gcc-ranlib} instead of @command{ar}
9479 and @command{ranlib};
9480 to show the symbols of object files with GIMPLE bytecode, use
9481 @command{gcc-nm}. Those commands require that @command{ar}, @command{ranlib}
9482 and @command{nm} have been compiled with plugin support. At link time, use the the
9483 flag @option{-fuse-linker-plugin} to ensure that the library participates in
9484 the LTO optimization process:
9487 gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo
9490 With the linker plugin enabled, the linker extracts the needed
9491 GIMPLE files from @file{libfoo.a} and passes them on to the running GCC
9492 to make them part of the aggregated GIMPLE image to be optimized.
9494 If you are not using a linker with plugin support and/or do not
9495 enable the linker plugin, then the objects inside @file{libfoo.a}
9496 are extracted and linked as usual, but they do not participate
9497 in the LTO optimization process. In order to make a static library suitable
9498 for both LTO optimization and usual linkage, compile its object files with
9499 @option{-flto} @option{-ffat-lto-objects}.
9501 Link-time optimizations do not require the presence of the whole program to
9502 operate. If the program does not require any symbols to be exported, it is
9503 possible to combine @option{-flto} and @option{-fwhole-program} to allow
9504 the interprocedural optimizers to use more aggressive assumptions which may
9505 lead to improved optimization opportunities.
9506 Use of @option{-fwhole-program} is not needed when linker plugin is
9507 active (see @option{-fuse-linker-plugin}).
9509 The current implementation of LTO makes no
9510 attempt to generate bytecode that is portable between different
9511 types of hosts. The bytecode files are versioned and there is a
9512 strict version check, so bytecode files generated in one version of
9513 GCC do not work with an older or newer version of GCC.
9515 Link-time optimization does not work well with generation of debugging
9516 information. Combining @option{-flto} with
9517 @option{-g} is currently experimental and expected to produce unexpected
9520 If you specify the optional @var{n}, the optimization and code
9521 generation done at link time is executed in parallel using @var{n}
9522 parallel jobs by utilizing an installed @command{make} program. The
9523 environment variable @env{MAKE} may be used to override the program
9524 used. The default value for @var{n} is 1.
9526 You can also specify @option{-flto=jobserver} to use GNU make's
9527 job server mode to determine the number of parallel jobs. This
9528 is useful when the Makefile calling GCC is already executing in parallel.
9529 You must prepend a @samp{+} to the command recipe in the parent Makefile
9530 for this to work. This option likely only works if @env{MAKE} is
9533 @item -flto-partition=@var{alg}
9534 @opindex flto-partition
9535 Specify the partitioning algorithm used by the link-time optimizer.
9536 The value is either @samp{1to1} to specify a partitioning mirroring
9537 the original source files or @samp{balanced} to specify partitioning
9538 into equally sized chunks (whenever possible) or @samp{max} to create
9539 new partition for every symbol where possible. Specifying @samp{none}
9540 as an algorithm disables partitioning and streaming completely.
9541 The default value is @samp{balanced}. While @samp{1to1} can be used
9542 as an workaround for various code ordering issues, the @samp{max}
9543 partitioning is intended for internal testing only.
9544 The value @samp{one} specifies that exactly one partition should be
9545 used while the value @samp{none} bypasses partitioning and executes
9546 the link-time optimization step directly from the WPA phase.
9548 @item -flto-odr-type-merging
9549 @opindex flto-odr-type-merging
9550 Enable streaming of mangled types names of C++ types and their unification
9551 at linktime. This increases size of LTO object files, but enable
9552 diagnostics about One Definition Rule violations.
9554 @item -flto-compression-level=@var{n}
9555 @opindex flto-compression-level
9556 This option specifies the level of compression used for intermediate
9557 language written to LTO object files, and is only meaningful in
9558 conjunction with LTO mode (@option{-flto}). Valid
9559 values are 0 (no compression) to 9 (maximum compression). Values
9560 outside this range are clamped to either 0 or 9. If the option is not
9561 given, a default balanced compression setting is used.
9564 @opindex flto-report
9565 Prints a report with internal details on the workings of the link-time
9566 optimizer. The contents of this report vary from version to version.
9567 It is meant to be useful to GCC developers when processing object
9568 files in LTO mode (via @option{-flto}).
9570 Disabled by default.
9572 @item -flto-report-wpa
9573 @opindex flto-report-wpa
9574 Like @option{-flto-report}, but only print for the WPA phase of Link
9577 @item -fuse-linker-plugin
9578 @opindex fuse-linker-plugin
9579 Enables the use of a linker plugin during link-time optimization. This
9580 option relies on plugin support in the linker, which is available in gold
9581 or in GNU ld 2.21 or newer.
9583 This option enables the extraction of object files with GIMPLE bytecode out
9584 of library archives. This improves the quality of optimization by exposing
9585 more code to the link-time optimizer. This information specifies what
9586 symbols can be accessed externally (by non-LTO object or during dynamic
9587 linking). Resulting code quality improvements on binaries (and shared
9588 libraries that use hidden visibility) are similar to @option{-fwhole-program}.
9589 See @option{-flto} for a description of the effect of this flag and how to
9592 This option is enabled by default when LTO support in GCC is enabled
9593 and GCC was configured for use with
9594 a linker supporting plugins (GNU ld 2.21 or newer or gold).
9596 @item -ffat-lto-objects
9597 @opindex ffat-lto-objects
9598 Fat LTO objects are object files that contain both the intermediate language
9599 and the object code. This makes them usable for both LTO linking and normal
9600 linking. This option is effective only when compiling with @option{-flto}
9601 and is ignored at link time.
9603 @option{-fno-fat-lto-objects} improves compilation time over plain LTO, but
9604 requires the complete toolchain to be aware of LTO. It requires a linker with
9605 linker plugin support for basic functionality. Additionally,
9606 @command{nm}, @command{ar} and @command{ranlib}
9607 need to support linker plugins to allow a full-featured build environment
9608 (capable of building static libraries etc). GCC provides the @command{gcc-ar},
9609 @command{gcc-nm}, @command{gcc-ranlib} wrappers to pass the right options
9610 to these tools. With non fat LTO makefiles need to be modified to use them.
9612 The default is @option{-fno-fat-lto-objects} on targets with linker plugin
9615 @item -fcompare-elim
9616 @opindex fcompare-elim
9617 After register allocation and post-register allocation instruction splitting,
9618 identify arithmetic instructions that compute processor flags similar to a
9619 comparison operation based on that arithmetic. If possible, eliminate the
9620 explicit comparison operation.
9622 This pass only applies to certain targets that cannot explicitly represent
9623 the comparison operation before register allocation is complete.
9625 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
9627 @item -fcprop-registers
9628 @opindex fcprop-registers
9629 After register allocation and post-register allocation instruction splitting,
9630 perform a copy-propagation pass to try to reduce scheduling dependencies
9631 and occasionally eliminate the copy.
9633 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
9635 @item -fprofile-correction
9636 @opindex fprofile-correction
9637 Profiles collected using an instrumented binary for multi-threaded programs may
9638 be inconsistent due to missed counter updates. When this option is specified,
9639 GCC uses heuristics to correct or smooth out such inconsistencies. By
9640 default, GCC emits an error message when an inconsistent profile is detected.
9642 @item -fprofile-dir=@var{path}
9643 @opindex fprofile-dir
9645 Set the directory to search for the profile data files in to @var{path}.
9646 This option affects only the profile data generated by
9647 @option{-fprofile-generate}, @option{-ftest-coverage}, @option{-fprofile-arcs}
9648 and used by @option{-fprofile-use} and @option{-fbranch-probabilities}
9649 and its related options. Both absolute and relative paths can be used.
9650 By default, GCC uses the current directory as @var{path}, thus the
9651 profile data file appears in the same directory as the object file.
9653 @item -fprofile-generate
9654 @itemx -fprofile-generate=@var{path}
9655 @opindex fprofile-generate
9657 Enable options usually used for instrumenting application to produce
9658 profile useful for later recompilation with profile feedback based
9659 optimization. You must use @option{-fprofile-generate} both when
9660 compiling and when linking your program.
9662 The following options are enabled: @option{-fprofile-arcs}, @option{-fprofile-values}, @option{-fvpt}.
9664 If @var{path} is specified, GCC looks at the @var{path} to find
9665 the profile feedback data files. See @option{-fprofile-dir}.
9668 @itemx -fprofile-use=@var{path}
9669 @opindex fprofile-use
9670 Enable profile feedback-directed optimizations,
9671 and the following optimizations
9672 which are generally profitable only with profile feedback available:
9673 @option{-fbranch-probabilities}, @option{-fvpt},
9674 @option{-funroll-loops}, @option{-fpeel-loops}, @option{-ftracer},
9675 @option{-ftree-vectorize}, and @option{ftree-loop-distribute-patterns}.
9677 By default, GCC emits an error message if the feedback profiles do not
9678 match the source code. This error can be turned into a warning by using
9679 @option{-Wcoverage-mismatch}. Note this may result in poorly optimized
9682 If @var{path} is specified, GCC looks at the @var{path} to find
9683 the profile feedback data files. See @option{-fprofile-dir}.
9685 @item -fauto-profile
9686 @itemx -fauto-profile=@var{path}
9687 @opindex fauto-profile
9688 Enable sampling-based feedback-directed optimizations,
9689 and the following optimizations
9690 which are generally profitable only with profile feedback available:
9691 @option{-fbranch-probabilities}, @option{-fvpt},
9692 @option{-funroll-loops}, @option{-fpeel-loops}, @option{-ftracer},
9693 @option{-ftree-vectorize},
9694 @option{-finline-functions}, @option{-fipa-cp}, @option{-fipa-cp-clone},
9695 @option{-fpredictive-commoning}, @option{-funswitch-loops},
9696 @option{-fgcse-after-reload}, and @option{-ftree-loop-distribute-patterns}.
9698 @var{path} is the name of a file containing AutoFDO profile information.
9699 If omitted, it defaults to @file{fbdata.afdo} in the current directory.
9701 Producing an AutoFDO profile data file requires running your program
9702 with the @command{perf} utility on a supported GNU/Linux target system.
9703 For more information, see @uref{https://perf.wiki.kernel.org/}.
9707 perf record -e br_inst_retired:near_taken -b -o perf.data \
9711 Then use the @command{create_gcov} tool to convert the raw profile data
9712 to a format that can be used by GCC.@ You must also supply the
9713 unstripped binary for your program to this tool.
9714 See @uref{https://github.com/google/autofdo}.
9718 create_gcov --binary=your_program.unstripped --profile=perf.data \
9723 The following options control compiler behavior regarding floating-point
9724 arithmetic. These options trade off between speed and
9725 correctness. All must be specifically enabled.
9729 @opindex ffloat-store
9730 Do not store floating-point variables in registers, and inhibit other
9731 options that might change whether a floating-point value is taken from a
9734 @cindex floating-point precision
9735 This option prevents undesirable excess precision on machines such as
9736 the 68000 where the floating registers (of the 68881) keep more
9737 precision than a @code{double} is supposed to have. Similarly for the
9738 x86 architecture. For most programs, the excess precision does only
9739 good, but a few programs rely on the precise definition of IEEE floating
9740 point. Use @option{-ffloat-store} for such programs, after modifying
9741 them to store all pertinent intermediate computations into variables.
9743 @item -fexcess-precision=@var{style}
9744 @opindex fexcess-precision
9745 This option allows further control over excess precision on machines
9746 where floating-point registers have more precision than the IEEE
9747 @code{float} and @code{double} types and the processor does not
9748 support operations rounding to those types. By default,
9749 @option{-fexcess-precision=fast} is in effect; this means that
9750 operations are carried out in the precision of the registers and that
9751 it is unpredictable when rounding to the types specified in the source
9752 code takes place. When compiling C, if
9753 @option{-fexcess-precision=standard} is specified then excess
9754 precision follows the rules specified in ISO C99; in particular,
9755 both casts and assignments cause values to be rounded to their
9756 semantic types (whereas @option{-ffloat-store} only affects
9757 assignments). This option is enabled by default for C if a strict
9758 conformance option such as @option{-std=c99} is used.
9761 @option{-fexcess-precision=standard} is not implemented for languages
9762 other than C, and has no effect if
9763 @option{-funsafe-math-optimizations} or @option{-ffast-math} is
9764 specified. On the x86, it also has no effect if @option{-mfpmath=sse}
9765 or @option{-mfpmath=sse+387} is specified; in the former case, IEEE
9766 semantics apply without excess precision, and in the latter, rounding
9771 Sets the options @option{-fno-math-errno}, @option{-funsafe-math-optimizations},
9772 @option{-ffinite-math-only}, @option{-fno-rounding-math},
9773 @option{-fno-signaling-nans} and @option{-fcx-limited-range}.
9775 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
9777 This option is not turned on by any @option{-O} option besides
9778 @option{-Ofast} since it can result in incorrect output for programs
9779 that depend on an exact implementation of IEEE or ISO rules/specifications
9780 for math functions. It may, however, yield faster code for programs
9781 that do not require the guarantees of these specifications.
9783 @item -fno-math-errno
9784 @opindex fno-math-errno
9785 Do not set @code{errno} after calling math functions that are executed
9786 with a single instruction, e.g., @code{sqrt}. A program that relies on
9787 IEEE exceptions for math error handling may want to use this flag
9788 for speed while maintaining IEEE arithmetic compatibility.
9790 This option is not turned on by any @option{-O} option since
9791 it can result in incorrect output for programs that depend on
9792 an exact implementation of IEEE or ISO rules/specifications for
9793 math functions. It may, however, yield faster code for programs
9794 that do not require the guarantees of these specifications.
9796 The default is @option{-fmath-errno}.
9798 On Darwin systems, the math library never sets @code{errno}. There is
9799 therefore no reason for the compiler to consider the possibility that
9800 it might, and @option{-fno-math-errno} is the default.
9802 @item -funsafe-math-optimizations
9803 @opindex funsafe-math-optimizations
9805 Allow optimizations for floating-point arithmetic that (a) assume
9806 that arguments and results are valid and (b) may violate IEEE or
9807 ANSI standards. When used at link-time, it may include libraries
9808 or startup files that change the default FPU control word or other
9809 similar optimizations.
9811 This option is not turned on by any @option{-O} option since
9812 it can result in incorrect output for programs that depend on
9813 an exact implementation of IEEE or ISO rules/specifications for
9814 math functions. It may, however, yield faster code for programs
9815 that do not require the guarantees of these specifications.
9816 Enables @option{-fno-signed-zeros}, @option{-fno-trapping-math},
9817 @option{-fassociative-math} and @option{-freciprocal-math}.
9819 The default is @option{-fno-unsafe-math-optimizations}.
9821 @item -fassociative-math
9822 @opindex fassociative-math
9824 Allow re-association of operands in series of floating-point operations.
9825 This violates the ISO C and C++ language standard by possibly changing
9826 computation result. NOTE: re-ordering may change the sign of zero as
9827 well as ignore NaNs and inhibit or create underflow or overflow (and
9828 thus cannot be used on code that relies on rounding behavior like
9829 @code{(x + 2**52) - 2**52}. May also reorder floating-point comparisons
9830 and thus may not be used when ordered comparisons are required.
9831 This option requires that both @option{-fno-signed-zeros} and
9832 @option{-fno-trapping-math} be in effect. Moreover, it doesn't make
9833 much sense with @option{-frounding-math}. For Fortran the option
9834 is automatically enabled when both @option{-fno-signed-zeros} and
9835 @option{-fno-trapping-math} are in effect.
9837 The default is @option{-fno-associative-math}.
9839 @item -freciprocal-math
9840 @opindex freciprocal-math
9842 Allow the reciprocal of a value to be used instead of dividing by
9843 the value if this enables optimizations. For example @code{x / y}
9844 can be replaced with @code{x * (1/y)}, which is useful if @code{(1/y)}
9845 is subject to common subexpression elimination. Note that this loses
9846 precision and increases the number of flops operating on the value.
9848 The default is @option{-fno-reciprocal-math}.
9850 @item -ffinite-math-only
9851 @opindex ffinite-math-only
9852 Allow optimizations for floating-point arithmetic that assume
9853 that arguments and results are not NaNs or +-Infs.
9855 This option is not turned on by any @option{-O} option since
9856 it can result in incorrect output for programs that depend on
9857 an exact implementation of IEEE or ISO rules/specifications for
9858 math functions. It may, however, yield faster code for programs
9859 that do not require the guarantees of these specifications.
9861 The default is @option{-fno-finite-math-only}.
9863 @item -fno-signed-zeros
9864 @opindex fno-signed-zeros
9865 Allow optimizations for floating-point arithmetic that ignore the
9866 signedness of zero. IEEE arithmetic specifies the behavior of
9867 distinct +0.0 and @minus{}0.0 values, which then prohibits simplification
9868 of expressions such as x+0.0 or 0.0*x (even with @option{-ffinite-math-only}).
9869 This option implies that the sign of a zero result isn't significant.
9871 The default is @option{-fsigned-zeros}.
9873 @item -fno-trapping-math
9874 @opindex fno-trapping-math
9875 Compile code assuming that floating-point operations cannot generate
9876 user-visible traps. These traps include division by zero, overflow,
9877 underflow, inexact result and invalid operation. This option requires
9878 that @option{-fno-signaling-nans} be in effect. Setting this option may
9879 allow faster code if one relies on ``non-stop'' IEEE arithmetic, for example.
9881 This option should never be turned on by any @option{-O} option since
9882 it can result in incorrect output for programs that depend on
9883 an exact implementation of IEEE or ISO rules/specifications for
9886 The default is @option{-ftrapping-math}.
9888 @item -frounding-math
9889 @opindex frounding-math
9890 Disable transformations and optimizations that assume default floating-point
9891 rounding behavior. This is round-to-zero for all floating point
9892 to integer conversions, and round-to-nearest for all other arithmetic
9893 truncations. This option should be specified for programs that change
9894 the FP rounding mode dynamically, or that may be executed with a
9895 non-default rounding mode. This option disables constant folding of
9896 floating-point expressions at compile time (which may be affected by
9897 rounding mode) and arithmetic transformations that are unsafe in the
9898 presence of sign-dependent rounding modes.
9900 The default is @option{-fno-rounding-math}.
9902 This option is experimental and does not currently guarantee to
9903 disable all GCC optimizations that are affected by rounding mode.
9904 Future versions of GCC may provide finer control of this setting
9905 using C99's @code{FENV_ACCESS} pragma. This command-line option
9906 will be used to specify the default state for @code{FENV_ACCESS}.
9908 @item -fsignaling-nans
9909 @opindex fsignaling-nans
9910 Compile code assuming that IEEE signaling NaNs may generate user-visible
9911 traps during floating-point operations. Setting this option disables
9912 optimizations that may change the number of exceptions visible with
9913 signaling NaNs. This option implies @option{-ftrapping-math}.
9915 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
9918 The default is @option{-fno-signaling-nans}.
9920 This option is experimental and does not currently guarantee to
9921 disable all GCC optimizations that affect signaling NaN behavior.
9923 @item -fsingle-precision-constant
9924 @opindex fsingle-precision-constant
9925 Treat floating-point constants as single precision instead of
9926 implicitly converting them to double-precision constants.
9928 @item -fcx-limited-range
9929 @opindex fcx-limited-range
9930 When enabled, this option states that a range reduction step is not
9931 needed when performing complex division. Also, there is no checking
9932 whether the result of a complex multiplication or division is @code{NaN
9933 + I*NaN}, with an attempt to rescue the situation in that case. The
9934 default is @option{-fno-cx-limited-range}, but is enabled by
9935 @option{-ffast-math}.
9937 This option controls the default setting of the ISO C99
9938 @code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to
9941 @item -fcx-fortran-rules
9942 @opindex fcx-fortran-rules
9943 Complex multiplication and division follow Fortran rules. Range
9944 reduction is done as part of complex division, but there is no checking
9945 whether the result of a complex multiplication or division is @code{NaN
9946 + I*NaN}, with an attempt to rescue the situation in that case.
9948 The default is @option{-fno-cx-fortran-rules}.
9952 The following options control optimizations that may improve
9953 performance, but are not enabled by any @option{-O} options. This
9954 section includes experimental options that may produce broken code.
9957 @item -fbranch-probabilities
9958 @opindex fbranch-probabilities
9959 After running a program compiled with @option{-fprofile-arcs}
9960 (@pxref{Debugging Options,, Options for Debugging Your Program or
9961 @command{gcc}}), you can compile it a second time using
9962 @option{-fbranch-probabilities}, to improve optimizations based on
9963 the number of times each branch was taken. When a program
9964 compiled with @option{-fprofile-arcs} exits, it saves arc execution
9965 counts to a file called @file{@var{sourcename}.gcda} for each source
9966 file. The information in this data file is very dependent on the
9967 structure of the generated code, so you must use the same source code
9968 and the same optimization options for both compilations.
9970 With @option{-fbranch-probabilities}, GCC puts a
9971 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
9972 These can be used to improve optimization. Currently, they are only
9973 used in one place: in @file{reorg.c}, instead of guessing which path a
9974 branch is most likely to take, the @samp{REG_BR_PROB} values are used to
9975 exactly determine which path is taken more often.
9977 @item -fprofile-values
9978 @opindex fprofile-values
9979 If combined with @option{-fprofile-arcs}, it adds code so that some
9980 data about values of expressions in the program is gathered.
9982 With @option{-fbranch-probabilities}, it reads back the data gathered
9983 from profiling values of expressions for usage in optimizations.
9985 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
9987 @item -fprofile-reorder-functions
9988 @opindex fprofile-reorder-functions
9989 Function reordering based on profile instrumentation collects
9990 first time of execution of a function and orders these functions
9993 Enabled with @option{-fprofile-use}.
9997 If combined with @option{-fprofile-arcs}, this option instructs the compiler
9998 to add code to gather information about values of expressions.
10000 With @option{-fbranch-probabilities}, it reads back the data gathered
10001 and actually performs the optimizations based on them.
10002 Currently the optimizations include specialization of division operations
10003 using the knowledge about the value of the denominator.
10005 @item -frename-registers
10006 @opindex frename-registers
10007 Attempt to avoid false dependencies in scheduled code by making use
10008 of registers left over after register allocation. This optimization
10009 most benefits processors with lots of registers. Depending on the
10010 debug information format adopted by the target, however, it can
10011 make debugging impossible, since variables no longer stay in
10012 a ``home register''.
10014 Enabled by default with @option{-funroll-loops} and @option{-fpeel-loops}.
10016 @item -fschedule-fusion
10017 @opindex fschedule-fusion
10018 Performs a target dependent pass over the instruction stream to schedule
10019 instructions of same type together because target machine can execute them
10020 more efficiently if they are adjacent to each other in the instruction flow.
10022 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
10026 Perform tail duplication to enlarge superblock size. This transformation
10027 simplifies the control flow of the function allowing other optimizations to do
10030 Enabled with @option{-fprofile-use}.
10032 @item -funroll-loops
10033 @opindex funroll-loops
10034 Unroll loops whose number of iterations can be determined at compile time or
10035 upon entry to the loop. @option{-funroll-loops} implies
10036 @option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}.
10037 It also turns on complete loop peeling (i.e.@: complete removal of loops with
10038 a small constant number of iterations). This option makes code larger, and may
10039 or may not make it run faster.
10041 Enabled with @option{-fprofile-use}.
10043 @item -funroll-all-loops
10044 @opindex funroll-all-loops
10045 Unroll all loops, even if their number of iterations is uncertain when
10046 the loop is entered. This usually makes programs run more slowly.
10047 @option{-funroll-all-loops} implies the same options as
10048 @option{-funroll-loops}.
10051 @opindex fpeel-loops
10052 Peels loops for which there is enough information that they do not
10053 roll much (from profile feedback). It also turns on complete loop peeling
10054 (i.e.@: complete removal of loops with small constant number of iterations).
10056 Enabled with @option{-fprofile-use}.
10058 @item -fmove-loop-invariants
10059 @opindex fmove-loop-invariants
10060 Enables the loop invariant motion pass in the RTL loop optimizer. Enabled
10061 at level @option{-O1}
10063 @item -funswitch-loops
10064 @opindex funswitch-loops
10065 Move branches with loop invariant conditions out of the loop, with duplicates
10066 of the loop on both branches (modified according to result of the condition).
10068 @item -ffunction-sections
10069 @itemx -fdata-sections
10070 @opindex ffunction-sections
10071 @opindex fdata-sections
10072 Place each function or data item into its own section in the output
10073 file if the target supports arbitrary sections. The name of the
10074 function or the name of the data item determines the section's name
10075 in the output file.
10077 Use these options on systems where the linker can perform optimizations
10078 to improve locality of reference in the instruction space. Most systems
10079 using the ELF object format and SPARC processors running Solaris 2 have
10080 linkers with such optimizations. AIX may have these optimizations in
10083 Only use these options when there are significant benefits from doing
10084 so. When you specify these options, the assembler and linker
10085 create larger object and executable files and are also slower.
10086 You cannot use @command{gprof} on all systems if you
10087 specify this option, and you may have problems with debugging if
10088 you specify both this option and @option{-g}.
10090 @item -fbranch-target-load-optimize
10091 @opindex fbranch-target-load-optimize
10092 Perform branch target register load optimization before prologue / epilogue
10094 The use of target registers can typically be exposed only during reload,
10095 thus hoisting loads out of loops and doing inter-block scheduling needs
10096 a separate optimization pass.
10098 @item -fbranch-target-load-optimize2
10099 @opindex fbranch-target-load-optimize2
10100 Perform branch target register load optimization after prologue / epilogue
10103 @item -fbtr-bb-exclusive
10104 @opindex fbtr-bb-exclusive
10105 When performing branch target register load optimization, don't reuse
10106 branch target registers within any basic block.
10108 @item -fstack-protector
10109 @opindex fstack-protector
10110 Emit extra code to check for buffer overflows, such as stack smashing
10111 attacks. This is done by adding a guard variable to functions with
10112 vulnerable objects. This includes functions that call @code{alloca}, and
10113 functions with buffers larger than 8 bytes. The guards are initialized
10114 when a function is entered and then checked when the function exits.
10115 If a guard check fails, an error message is printed and the program exits.
10117 @item -fstack-protector-all
10118 @opindex fstack-protector-all
10119 Like @option{-fstack-protector} except that all functions are protected.
10121 @item -fstack-protector-strong
10122 @opindex fstack-protector-strong
10123 Like @option{-fstack-protector} but includes additional functions to
10124 be protected --- those that have local array definitions, or have
10125 references to local frame addresses.
10127 @item -fstack-protector-explicit
10128 @opindex fstack-protector-explicit
10129 Like @option{-fstack-protector} but only protects those functions which
10130 have the @code{stack_protect} attribute
10133 @opindex fstdarg-opt
10134 Optimize the prologue of variadic argument functions with respect to usage of
10137 @item -fsection-anchors
10138 @opindex fsection-anchors
10139 Try to reduce the number of symbolic address calculations by using
10140 shared ``anchor'' symbols to address nearby objects. This transformation
10141 can help to reduce the number of GOT entries and GOT accesses on some
10144 For example, the implementation of the following function @code{foo}:
10147 static int a, b, c;
10148 int foo (void) @{ return a + b + c; @}
10152 usually calculates the addresses of all three variables, but if you
10153 compile it with @option{-fsection-anchors}, it accesses the variables
10154 from a common anchor point instead. The effect is similar to the
10155 following pseudocode (which isn't valid C):
10160 register int *xr = &x;
10161 return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
10165 Not all targets support this option.
10167 @item --param @var{name}=@var{value}
10169 In some places, GCC uses various constants to control the amount of
10170 optimization that is done. For example, GCC does not inline functions
10171 that contain more than a certain number of instructions. You can
10172 control some of these constants on the command line using the
10173 @option{--param} option.
10175 The names of specific parameters, and the meaning of the values, are
10176 tied to the internals of the compiler, and are subject to change
10177 without notice in future releases.
10179 In each case, the @var{value} is an integer. The allowable choices for
10183 @item predictable-branch-outcome
10184 When branch is predicted to be taken with probability lower than this threshold
10185 (in percent), then it is considered well predictable. The default is 10.
10187 @item max-crossjump-edges
10188 The maximum number of incoming edges to consider for cross-jumping.
10189 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
10190 the number of edges incoming to each block. Increasing values mean
10191 more aggressive optimization, making the compilation time increase with
10192 probably small improvement in executable size.
10194 @item min-crossjump-insns
10195 The minimum number of instructions that must be matched at the end
10196 of two blocks before cross-jumping is performed on them. This
10197 value is ignored in the case where all instructions in the block being
10198 cross-jumped from are matched. The default value is 5.
10200 @item max-grow-copy-bb-insns
10201 The maximum code size expansion factor when copying basic blocks
10202 instead of jumping. The expansion is relative to a jump instruction.
10203 The default value is 8.
10205 @item max-goto-duplication-insns
10206 The maximum number of instructions to duplicate to a block that jumps
10207 to a computed goto. To avoid @math{O(N^2)} behavior in a number of
10208 passes, GCC factors computed gotos early in the compilation process,
10209 and unfactors them as late as possible. Only computed jumps at the
10210 end of a basic blocks with no more than max-goto-duplication-insns are
10211 unfactored. The default value is 8.
10213 @item max-delay-slot-insn-search
10214 The maximum number of instructions to consider when looking for an
10215 instruction to fill a delay slot. If more than this arbitrary number of
10216 instructions are searched, the time savings from filling the delay slot
10217 are minimal, so stop searching. Increasing values mean more
10218 aggressive optimization, making the compilation time increase with probably
10219 small improvement in execution time.
10221 @item max-delay-slot-live-search
10222 When trying to fill delay slots, the maximum number of instructions to
10223 consider when searching for a block with valid live register
10224 information. Increasing this arbitrarily chosen value means more
10225 aggressive optimization, increasing the compilation time. This parameter
10226 should be removed when the delay slot code is rewritten to maintain the
10227 control-flow graph.
10229 @item max-gcse-memory
10230 The approximate maximum amount of memory that can be allocated in
10231 order to perform the global common subexpression elimination
10232 optimization. If more memory than specified is required, the
10233 optimization is not done.
10235 @item max-gcse-insertion-ratio
10236 If the ratio of expression insertions to deletions is larger than this value
10237 for any expression, then RTL PRE inserts or removes the expression and thus
10238 leaves partially redundant computations in the instruction stream. The default value is 20.
10240 @item max-pending-list-length
10241 The maximum number of pending dependencies scheduling allows
10242 before flushing the current state and starting over. Large functions
10243 with few branches or calls can create excessively large lists which
10244 needlessly consume memory and resources.
10246 @item max-modulo-backtrack-attempts
10247 The maximum number of backtrack attempts the scheduler should make
10248 when modulo scheduling a loop. Larger values can exponentially increase
10251 @item max-inline-insns-single
10252 Several parameters control the tree inliner used in GCC@.
10253 This number sets the maximum number of instructions (counted in GCC's
10254 internal representation) in a single function that the tree inliner
10255 considers for inlining. This only affects functions declared
10256 inline and methods implemented in a class declaration (C++).
10257 The default value is 400.
10259 @item max-inline-insns-auto
10260 When you use @option{-finline-functions} (included in @option{-O3}),
10261 a lot of functions that would otherwise not be considered for inlining
10262 by the compiler are investigated. To those functions, a different
10263 (more restrictive) limit compared to functions declared inline can
10265 The default value is 40.
10267 @item inline-min-speedup
10268 When estimated performance improvement of caller + callee runtime exceeds this
10269 threshold (in precent), the function can be inlined regardless the limit on
10270 @option{--param max-inline-insns-single} and @option{--param
10271 max-inline-insns-auto}.
10273 @item large-function-insns
10274 The limit specifying really large functions. For functions larger than this
10275 limit after inlining, inlining is constrained by
10276 @option{--param large-function-growth}. This parameter is useful primarily
10277 to avoid extreme compilation time caused by non-linear algorithms used by the
10279 The default value is 2700.
10281 @item large-function-growth
10282 Specifies maximal growth of large function caused by inlining in percents.
10283 The default value is 100 which limits large function growth to 2.0 times
10286 @item large-unit-insns
10287 The limit specifying large translation unit. Growth caused by inlining of
10288 units larger than this limit is limited by @option{--param inline-unit-growth}.
10289 For small units this might be too tight.
10290 For example, consider a unit consisting of function A
10291 that is inline and B that just calls A three times. If B is small relative to
10292 A, the growth of unit is 300\% and yet such inlining is very sane. For very
10293 large units consisting of small inlineable functions, however, the overall unit
10294 growth limit is needed to avoid exponential explosion of code size. Thus for
10295 smaller units, the size is increased to @option{--param large-unit-insns}
10296 before applying @option{--param inline-unit-growth}. The default is 10000.
10298 @item inline-unit-growth
10299 Specifies maximal overall growth of the compilation unit caused by inlining.
10300 The default value is 20 which limits unit growth to 1.2 times the original
10301 size. Cold functions (either marked cold via an attribute or by profile
10302 feedback) are not accounted into the unit size.
10304 @item ipcp-unit-growth
10305 Specifies maximal overall growth of the compilation unit caused by
10306 interprocedural constant propagation. The default value is 10 which limits
10307 unit growth to 1.1 times the original size.
10309 @item large-stack-frame
10310 The limit specifying large stack frames. While inlining the algorithm is trying
10311 to not grow past this limit too much. The default value is 256 bytes.
10313 @item large-stack-frame-growth
10314 Specifies maximal growth of large stack frames caused by inlining in percents.
10315 The default value is 1000 which limits large stack frame growth to 11 times
10318 @item max-inline-insns-recursive
10319 @itemx max-inline-insns-recursive-auto
10320 Specifies the maximum number of instructions an out-of-line copy of a
10321 self-recursive inline
10322 function can grow into by performing recursive inlining.
10324 @option{--param max-inline-insns-recursive} applies to functions
10326 For functions not declared inline, recursive inlining
10327 happens only when @option{-finline-functions} (included in @option{-O3}) is
10328 enabled; @option{--param max-inline-insns-recursive-auto} applies instead. The
10329 default value is 450.
10331 @item max-inline-recursive-depth
10332 @itemx max-inline-recursive-depth-auto
10333 Specifies the maximum recursion depth used for recursive inlining.
10335 @option{--param max-inline-recursive-depth} applies to functions
10336 declared inline. For functions not declared inline, recursive inlining
10337 happens only when @option{-finline-functions} (included in @option{-O3}) is
10338 enabled; @option{--param max-inline-recursive-depth-auto} applies instead. The
10339 default value is 8.
10341 @item min-inline-recursive-probability
10342 Recursive inlining is profitable only for function having deep recursion
10343 in average and can hurt for function having little recursion depth by
10344 increasing the prologue size or complexity of function body to other
10347 When profile feedback is available (see @option{-fprofile-generate}) the actual
10348 recursion depth can be guessed from probability that function recurses via a
10349 given call expression. This parameter limits inlining only to call expressions
10350 whose probability exceeds the given threshold (in percents).
10351 The default value is 10.
10353 @item early-inlining-insns
10354 Specify growth that the early inliner can make. In effect it increases
10355 the amount of inlining for code having a large abstraction penalty.
10356 The default value is 14.
10358 @item max-early-inliner-iterations
10359 Limit of iterations of the early inliner. This basically bounds
10360 the number of nested indirect calls the early inliner can resolve.
10361 Deeper chains are still handled by late inlining.
10363 @item comdat-sharing-probability
10364 Probability (in percent) that C++ inline function with comdat visibility
10365 are shared across multiple compilation units. The default value is 20.
10367 @item profile-func-internal-id
10368 A parameter to control whether to use function internal id in profile
10369 database lookup. If the value is 0, the compiler uses an id that
10370 is based on function assembler name and filename, which makes old profile
10371 data more tolerant to source changes such as function reordering etc.
10372 The default value is 0.
10374 @item min-vect-loop-bound
10375 The minimum number of iterations under which loops are not vectorized
10376 when @option{-ftree-vectorize} is used. The number of iterations after
10377 vectorization needs to be greater than the value specified by this option
10378 to allow vectorization. The default value is 0.
10380 @item gcse-cost-distance-ratio
10381 Scaling factor in calculation of maximum distance an expression
10382 can be moved by GCSE optimizations. This is currently supported only in the
10383 code hoisting pass. The bigger the ratio, the more aggressive code hoisting
10384 is with simple expressions, i.e., the expressions that have cost
10385 less than @option{gcse-unrestricted-cost}. Specifying 0 disables
10386 hoisting of simple expressions. The default value is 10.
10388 @item gcse-unrestricted-cost
10389 Cost, roughly measured as the cost of a single typical machine
10390 instruction, at which GCSE optimizations do not constrain
10391 the distance an expression can travel. This is currently
10392 supported only in the code hoisting pass. The lesser the cost,
10393 the more aggressive code hoisting is. Specifying 0
10394 allows all expressions to travel unrestricted distances.
10395 The default value is 3.
10397 @item max-hoist-depth
10398 The depth of search in the dominator tree for expressions to hoist.
10399 This is used to avoid quadratic behavior in hoisting algorithm.
10400 The value of 0 does not limit on the search, but may slow down compilation
10401 of huge functions. The default value is 30.
10403 @item max-tail-merge-comparisons
10404 The maximum amount of similar bbs to compare a bb with. This is used to
10405 avoid quadratic behavior in tree tail merging. The default value is 10.
10407 @item max-tail-merge-iterations
10408 The maximum amount of iterations of the pass over the function. This is used to
10409 limit compilation time in tree tail merging. The default value is 2.
10411 @item max-unrolled-insns
10412 The maximum number of instructions that a loop may have to be unrolled.
10413 If a loop is unrolled, this parameter also determines how many times
10414 the loop code is unrolled.
10416 @item max-average-unrolled-insns
10417 The maximum number of instructions biased by probabilities of their execution
10418 that a loop may have to be unrolled. If a loop is unrolled,
10419 this parameter also determines how many times the loop code is unrolled.
10421 @item max-unroll-times
10422 The maximum number of unrollings of a single loop.
10424 @item max-peeled-insns
10425 The maximum number of instructions that a loop may have to be peeled.
10426 If a loop is peeled, this parameter also determines how many times
10427 the loop code is peeled.
10429 @item max-peel-times
10430 The maximum number of peelings of a single loop.
10432 @item max-peel-branches
10433 The maximum number of branches on the hot path through the peeled sequence.
10435 @item max-completely-peeled-insns
10436 The maximum number of insns of a completely peeled loop.
10438 @item max-completely-peel-times
10439 The maximum number of iterations of a loop to be suitable for complete peeling.
10441 @item max-completely-peel-loop-nest-depth
10442 The maximum depth of a loop nest suitable for complete peeling.
10444 @item max-unswitch-insns
10445 The maximum number of insns of an unswitched loop.
10447 @item max-unswitch-level
10448 The maximum number of branches unswitched in a single loop.
10450 @item lim-expensive
10451 The minimum cost of an expensive expression in the loop invariant motion.
10453 @item iv-consider-all-candidates-bound
10454 Bound on number of candidates for induction variables, below which
10455 all candidates are considered for each use in induction variable
10456 optimizations. If there are more candidates than this,
10457 only the most relevant ones are considered to avoid quadratic time complexity.
10459 @item iv-max-considered-uses
10460 The induction variable optimizations give up on loops that contain more
10461 induction variable uses.
10463 @item iv-always-prune-cand-set-bound
10464 If the number of candidates in the set is smaller than this value,
10465 always try to remove unnecessary ivs from the set
10466 when adding a new one.
10468 @item scev-max-expr-size
10469 Bound on size of expressions used in the scalar evolutions analyzer.
10470 Large expressions slow the analyzer.
10472 @item scev-max-expr-complexity
10473 Bound on the complexity of the expressions in the scalar evolutions analyzer.
10474 Complex expressions slow the analyzer.
10476 @item omega-max-vars
10477 The maximum number of variables in an Omega constraint system.
10478 The default value is 128.
10480 @item omega-max-geqs
10481 The maximum number of inequalities in an Omega constraint system.
10482 The default value is 256.
10484 @item omega-max-eqs
10485 The maximum number of equalities in an Omega constraint system.
10486 The default value is 128.
10488 @item omega-max-wild-cards
10489 The maximum number of wildcard variables that the Omega solver is
10490 able to insert. The default value is 18.
10492 @item omega-hash-table-size
10493 The size of the hash table in the Omega solver. The default value is
10496 @item omega-max-keys
10497 The maximal number of keys used by the Omega solver. The default
10500 @item omega-eliminate-redundant-constraints
10501 When set to 1, use expensive methods to eliminate all redundant
10502 constraints. The default value is 0.
10504 @item vect-max-version-for-alignment-checks
10505 The maximum number of run-time checks that can be performed when
10506 doing loop versioning for alignment in the vectorizer.
10508 @item vect-max-version-for-alias-checks
10509 The maximum number of run-time checks that can be performed when
10510 doing loop versioning for alias in the vectorizer.
10512 @item vect-max-peeling-for-alignment
10513 The maximum number of loop peels to enhance access alignment
10514 for vectorizer. Value -1 means 'no limit'.
10516 @item max-iterations-to-track
10517 The maximum number of iterations of a loop the brute-force algorithm
10518 for analysis of the number of iterations of the loop tries to evaluate.
10520 @item hot-bb-count-ws-permille
10521 A basic block profile count is considered hot if it contributes to
10522 the given permillage (i.e. 0...1000) of the entire profiled execution.
10524 @item hot-bb-frequency-fraction
10525 Select fraction of the entry block frequency of executions of basic block in
10526 function given basic block needs to have to be considered hot.
10528 @item max-predicted-iterations
10529 The maximum number of loop iterations we predict statically. This is useful
10530 in cases where a function contains a single loop with known bound and
10531 another loop with unknown bound.
10532 The known number of iterations is predicted correctly, while
10533 the unknown number of iterations average to roughly 10. This means that the
10534 loop without bounds appears artificially cold relative to the other one.
10536 @item builtin-expect-probability
10537 Control the probability of the expression having the specified value. This
10538 parameter takes a percentage (i.e. 0 ... 100) as input.
10539 The default probability of 90 is obtained empirically.
10541 @item align-threshold
10543 Select fraction of the maximal frequency of executions of a basic block in
10544 a function to align the basic block.
10546 @item align-loop-iterations
10548 A loop expected to iterate at least the selected number of iterations is
10551 @item tracer-dynamic-coverage
10552 @itemx tracer-dynamic-coverage-feedback
10554 This value is used to limit superblock formation once the given percentage of
10555 executed instructions is covered. This limits unnecessary code size
10558 The @option{tracer-dynamic-coverage-feedback} parameter
10559 is used only when profile
10560 feedback is available. The real profiles (as opposed to statically estimated
10561 ones) are much less balanced allowing the threshold to be larger value.
10563 @item tracer-max-code-growth
10564 Stop tail duplication once code growth has reached given percentage. This is
10565 a rather artificial limit, as most of the duplicates are eliminated later in
10566 cross jumping, so it may be set to much higher values than is the desired code
10569 @item tracer-min-branch-ratio
10571 Stop reverse growth when the reverse probability of best edge is less than this
10572 threshold (in percent).
10574 @item tracer-min-branch-ratio
10575 @itemx tracer-min-branch-ratio-feedback
10577 Stop forward growth if the best edge has probability lower than this
10580 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
10581 compilation for profile feedback and one for compilation without. The value
10582 for compilation with profile feedback needs to be more conservative (higher) in
10583 order to make tracer effective.
10585 @item max-cse-path-length
10587 The maximum number of basic blocks on path that CSE considers.
10590 @item max-cse-insns
10591 The maximum number of instructions CSE processes before flushing.
10592 The default is 1000.
10594 @item ggc-min-expand
10596 GCC uses a garbage collector to manage its own memory allocation. This
10597 parameter specifies the minimum percentage by which the garbage
10598 collector's heap should be allowed to expand between collections.
10599 Tuning this may improve compilation speed; it has no effect on code
10602 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
10603 RAM >= 1GB@. If @code{getrlimit} is available, the notion of ``RAM'' is
10604 the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If
10605 GCC is not able to calculate RAM on a particular platform, the lower
10606 bound of 30% is used. Setting this parameter and
10607 @option{ggc-min-heapsize} to zero causes a full collection to occur at
10608 every opportunity. This is extremely slow, but can be useful for
10611 @item ggc-min-heapsize
10613 Minimum size of the garbage collector's heap before it begins bothering
10614 to collect garbage. The first collection occurs after the heap expands
10615 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
10616 tuning this may improve compilation speed, and has no effect on code
10619 The default is the smaller of RAM/8, RLIMIT_RSS, or a limit that
10620 tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
10621 with a lower bound of 4096 (four megabytes) and an upper bound of
10622 131072 (128 megabytes). If GCC is not able to calculate RAM on a
10623 particular platform, the lower bound is used. Setting this parameter
10624 very large effectively disables garbage collection. Setting this
10625 parameter and @option{ggc-min-expand} to zero causes a full collection
10626 to occur at every opportunity.
10628 @item max-reload-search-insns
10629 The maximum number of instruction reload should look backward for equivalent
10630 register. Increasing values mean more aggressive optimization, making the
10631 compilation time increase with probably slightly better performance.
10632 The default value is 100.
10634 @item max-cselib-memory-locations
10635 The maximum number of memory locations cselib should take into account.
10636 Increasing values mean more aggressive optimization, making the compilation time
10637 increase with probably slightly better performance. The default value is 500.
10639 @item reorder-blocks-duplicate
10640 @itemx reorder-blocks-duplicate-feedback
10642 Used by the basic block reordering pass to decide whether to use unconditional
10643 branch or duplicate the code on its destination. Code is duplicated when its
10644 estimated size is smaller than this value multiplied by the estimated size of
10645 unconditional jump in the hot spots of the program.
10647 The @option{reorder-block-duplicate-feedback} parameter
10648 is used only when profile
10649 feedback is available. It may be set to higher values than
10650 @option{reorder-block-duplicate} since information about the hot spots is more
10653 @item max-sched-ready-insns
10654 The maximum number of instructions ready to be issued the scheduler should
10655 consider at any given time during the first scheduling pass. Increasing
10656 values mean more thorough searches, making the compilation time increase
10657 with probably little benefit. The default value is 100.
10659 @item max-sched-region-blocks
10660 The maximum number of blocks in a region to be considered for
10661 interblock scheduling. The default value is 10.
10663 @item max-pipeline-region-blocks
10664 The maximum number of blocks in a region to be considered for
10665 pipelining in the selective scheduler. The default value is 15.
10667 @item max-sched-region-insns
10668 The maximum number of insns in a region to be considered for
10669 interblock scheduling. The default value is 100.
10671 @item max-pipeline-region-insns
10672 The maximum number of insns in a region to be considered for
10673 pipelining in the selective scheduler. The default value is 200.
10675 @item min-spec-prob
10676 The minimum probability (in percents) of reaching a source block
10677 for interblock speculative scheduling. The default value is 40.
10679 @item max-sched-extend-regions-iters
10680 The maximum number of iterations through CFG to extend regions.
10681 A value of 0 (the default) disables region extensions.
10683 @item max-sched-insn-conflict-delay
10684 The maximum conflict delay for an insn to be considered for speculative motion.
10685 The default value is 3.
10687 @item sched-spec-prob-cutoff
10688 The minimal probability of speculation success (in percents), so that
10689 speculative insns are scheduled.
10690 The default value is 40.
10692 @item sched-spec-state-edge-prob-cutoff
10693 The minimum probability an edge must have for the scheduler to save its
10695 The default value is 10.
10697 @item sched-mem-true-dep-cost
10698 Minimal distance (in CPU cycles) between store and load targeting same
10699 memory locations. The default value is 1.
10701 @item selsched-max-lookahead
10702 The maximum size of the lookahead window of selective scheduling. It is a
10703 depth of search for available instructions.
10704 The default value is 50.
10706 @item selsched-max-sched-times
10707 The maximum number of times that an instruction is scheduled during
10708 selective scheduling. This is the limit on the number of iterations
10709 through which the instruction may be pipelined. The default value is 2.
10711 @item selsched-max-insns-to-rename
10712 The maximum number of best instructions in the ready list that are considered
10713 for renaming in the selective scheduler. The default value is 2.
10716 The minimum value of stage count that swing modulo scheduler
10717 generates. The default value is 2.
10719 @item max-last-value-rtl
10720 The maximum size measured as number of RTLs that can be recorded in an expression
10721 in combiner for a pseudo register as last known value of that register. The default
10724 @item max-combine-insns
10725 The maximum number of instructions the RTL combiner tries to combine.
10726 The default value is 2 at @option{-Og} and 4 otherwise.
10728 @item integer-share-limit
10729 Small integer constants can use a shared data structure, reducing the
10730 compiler's memory usage and increasing its speed. This sets the maximum
10731 value of a shared integer constant. The default value is 256.
10733 @item ssp-buffer-size
10734 The minimum size of buffers (i.e.@: arrays) that receive stack smashing
10735 protection when @option{-fstack-protection} is used.
10737 @item min-size-for-stack-sharing
10738 The minimum size of variables taking part in stack slot sharing when not
10739 optimizing. The default value is 32.
10741 @item max-jump-thread-duplication-stmts
10742 Maximum number of statements allowed in a block that needs to be
10743 duplicated when threading jumps.
10745 @item max-fields-for-field-sensitive
10746 Maximum number of fields in a structure treated in
10747 a field sensitive manner during pointer analysis. The default is zero
10748 for @option{-O0} and @option{-O1},
10749 and 100 for @option{-Os}, @option{-O2}, and @option{-O3}.
10751 @item prefetch-latency
10752 Estimate on average number of instructions that are executed before
10753 prefetch finishes. The distance prefetched ahead is proportional
10754 to this constant. Increasing this number may also lead to less
10755 streams being prefetched (see @option{simultaneous-prefetches}).
10757 @item simultaneous-prefetches
10758 Maximum number of prefetches that can run at the same time.
10760 @item l1-cache-line-size
10761 The size of cache line in L1 cache, in bytes.
10763 @item l1-cache-size
10764 The size of L1 cache, in kilobytes.
10766 @item l2-cache-size
10767 The size of L2 cache, in kilobytes.
10769 @item min-insn-to-prefetch-ratio
10770 The minimum ratio between the number of instructions and the
10771 number of prefetches to enable prefetching in a loop.
10773 @item prefetch-min-insn-to-mem-ratio
10774 The minimum ratio between the number of instructions and the
10775 number of memory references to enable prefetching in a loop.
10777 @item use-canonical-types
10778 Whether the compiler should use the ``canonical'' type system. By
10779 default, this should always be 1, which uses a more efficient internal
10780 mechanism for comparing types in C++ and Objective-C++. However, if
10781 bugs in the canonical type system are causing compilation failures,
10782 set this value to 0 to disable canonical types.
10784 @item switch-conversion-max-branch-ratio
10785 Switch initialization conversion refuses to create arrays that are
10786 bigger than @option{switch-conversion-max-branch-ratio} times the number of
10787 branches in the switch.
10789 @item max-partial-antic-length
10790 Maximum length of the partial antic set computed during the tree
10791 partial redundancy elimination optimization (@option{-ftree-pre}) when
10792 optimizing at @option{-O3} and above. For some sorts of source code
10793 the enhanced partial redundancy elimination optimization can run away,
10794 consuming all of the memory available on the host machine. This
10795 parameter sets a limit on the length of the sets that are computed,
10796 which prevents the runaway behavior. Setting a value of 0 for
10797 this parameter allows an unlimited set length.
10799 @item sccvn-max-scc-size
10800 Maximum size of a strongly connected component (SCC) during SCCVN
10801 processing. If this limit is hit, SCCVN processing for the whole
10802 function is not done and optimizations depending on it are
10803 disabled. The default maximum SCC size is 10000.
10805 @item sccvn-max-alias-queries-per-access
10806 Maximum number of alias-oracle queries we perform when looking for
10807 redundancies for loads and stores. If this limit is hit the search
10808 is aborted and the load or store is not considered redundant. The
10809 number of queries is algorithmically limited to the number of
10810 stores on all paths from the load to the function entry.
10811 The default maxmimum number of queries is 1000.
10813 @item ira-max-loops-num
10814 IRA uses regional register allocation by default. If a function
10815 contains more loops than the number given by this parameter, only at most
10816 the given number of the most frequently-executed loops form regions
10817 for regional register allocation. The default value of the
10820 @item ira-max-conflict-table-size
10821 Although IRA uses a sophisticated algorithm to compress the conflict
10822 table, the table can still require excessive amounts of memory for
10823 huge functions. If the conflict table for a function could be more
10824 than the size in MB given by this parameter, the register allocator
10825 instead uses a faster, simpler, and lower-quality
10826 algorithm that does not require building a pseudo-register conflict table.
10827 The default value of the parameter is 2000.
10829 @item ira-loop-reserved-regs
10830 IRA can be used to evaluate more accurate register pressure in loops
10831 for decisions to move loop invariants (see @option{-O3}). The number
10832 of available registers reserved for some other purposes is given
10833 by this parameter. The default value of the parameter is 2, which is
10834 the minimal number of registers needed by typical instructions.
10835 This value is the best found from numerous experiments.
10837 @item lra-inheritance-ebb-probability-cutoff
10838 LRA tries to reuse values reloaded in registers in subsequent insns.
10839 This optimization is called inheritance. EBB is used as a region to
10840 do this optimization. The parameter defines a minimal fall-through
10841 edge probability in percentage used to add BB to inheritance EBB in
10842 LRA. The default value of the parameter is 40. The value was chosen
10843 from numerous runs of SPEC2000 on x86-64.
10845 @item loop-invariant-max-bbs-in-loop
10846 Loop invariant motion can be very expensive, both in compilation time and
10847 in amount of needed compile-time memory, with very large loops. Loops
10848 with more basic blocks than this parameter won't have loop invariant
10849 motion optimization performed on them. The default value of the
10850 parameter is 1000 for @option{-O1} and 10000 for @option{-O2} and above.
10852 @item loop-max-datarefs-for-datadeps
10853 Building data dapendencies is expensive for very large loops. This
10854 parameter limits the number of data references in loops that are
10855 considered for data dependence analysis. These large loops are no
10856 handled by the optimizations using loop data dependencies.
10857 The default value is 1000.
10859 @item max-vartrack-size
10860 Sets a maximum number of hash table slots to use during variable
10861 tracking dataflow analysis of any function. If this limit is exceeded
10862 with variable tracking at assignments enabled, analysis for that
10863 function is retried without it, after removing all debug insns from
10864 the function. If the limit is exceeded even without debug insns, var
10865 tracking analysis is completely disabled for the function. Setting
10866 the parameter to zero makes it unlimited.
10868 @item max-vartrack-expr-depth
10869 Sets a maximum number of recursion levels when attempting to map
10870 variable names or debug temporaries to value expressions. This trades
10871 compilation time for more complete debug information. If this is set too
10872 low, value expressions that are available and could be represented in
10873 debug information may end up not being used; setting this higher may
10874 enable the compiler to find more complex debug expressions, but compile
10875 time and memory use may grow. The default is 12.
10877 @item min-nondebug-insn-uid
10878 Use uids starting at this parameter for nondebug insns. The range below
10879 the parameter is reserved exclusively for debug insns created by
10880 @option{-fvar-tracking-assignments}, but debug insns may get
10881 (non-overlapping) uids above it if the reserved range is exhausted.
10883 @item ipa-sra-ptr-growth-factor
10884 IPA-SRA replaces a pointer to an aggregate with one or more new
10885 parameters only when their cumulative size is less or equal to
10886 @option{ipa-sra-ptr-growth-factor} times the size of the original
10889 @item sra-max-scalarization-size-Ospeed
10890 @item sra-max-scalarization-size-Osize
10891 The two Scalar Reduction of Aggregates passes (SRA and IPA-SRA) aim to
10892 replace scalar parts of aggregates with uses of independent scalar
10893 variables. These parameters control the maximum size, in storage units,
10894 of aggregate which is considered for replacement when compiling for
10896 (@option{sra-max-scalarization-size-Ospeed}) or size
10897 (@option{sra-max-scalarization-size-Osize}) respectively.
10899 @item tm-max-aggregate-size
10900 When making copies of thread-local variables in a transaction, this
10901 parameter specifies the size in bytes after which variables are
10902 saved with the logging functions as opposed to save/restore code
10903 sequence pairs. This option only applies when using
10906 @item graphite-max-nb-scop-params
10907 To avoid exponential effects in the Graphite loop transforms, the
10908 number of parameters in a Static Control Part (SCoP) is bounded. The
10909 default value is 10 parameters. A variable whose value is unknown at
10910 compilation time and defined outside a SCoP is a parameter of the SCoP.
10912 @item graphite-max-bbs-per-function
10913 To avoid exponential effects in the detection of SCoPs, the size of
10914 the functions analyzed by Graphite is bounded. The default value is
10917 @item loop-block-tile-size
10918 Loop blocking or strip mining transforms, enabled with
10919 @option{-floop-block} or @option{-floop-strip-mine}, strip mine each
10920 loop in the loop nest by a given number of iterations. The strip
10921 length can be changed using the @option{loop-block-tile-size}
10922 parameter. The default value is 51 iterations.
10924 @item loop-unroll-jam-size
10925 Specify the unroll factor for the @option{-floop-unroll-and-jam} option. The
10926 default value is 4.
10928 @item loop-unroll-jam-depth
10929 Specify the dimension to be unrolled (counting from the most inner loop)
10930 for the @option{-floop-unroll-and-jam}. The default value is 2.
10932 @item ipa-cp-value-list-size
10933 IPA-CP attempts to track all possible values and types passed to a function's
10934 parameter in order to propagate them and perform devirtualization.
10935 @option{ipa-cp-value-list-size} is the maximum number of values and types it
10936 stores per one formal parameter of a function.
10938 @item ipa-cp-eval-threshold
10939 IPA-CP calculates its own score of cloning profitability heuristics
10940 and performs those cloning opportunities with scores that exceed
10941 @option{ipa-cp-eval-threshold}.
10943 @item ipa-cp-recursion-penalty
10944 Percentage penalty the recursive functions will receive when they
10945 are evaluated for cloning.
10947 @item ipa-cp-single-call-penalty
10948 Percentage penalty functions containg a single call to another
10949 function will receive when they are evaluated for cloning.
10952 @item ipa-max-agg-items
10953 IPA-CP is also capable to propagate a number of scalar values passed
10954 in an aggregate. @option{ipa-max-agg-items} controls the maximum
10955 number of such values per one parameter.
10957 @item ipa-cp-loop-hint-bonus
10958 When IPA-CP determines that a cloning candidate would make the number
10959 of iterations of a loop known, it adds a bonus of
10960 @option{ipa-cp-loop-hint-bonus} to the profitability score of
10963 @item ipa-cp-array-index-hint-bonus
10964 When IPA-CP determines that a cloning candidate would make the index of
10965 an array access known, it adds a bonus of
10966 @option{ipa-cp-array-index-hint-bonus} to the profitability
10967 score of the candidate.
10969 @item ipa-max-aa-steps
10970 During its analysis of function bodies, IPA-CP employs alias analysis
10971 in order to track values pointed to by function parameters. In order
10972 not spend too much time analyzing huge functions, it gives up and
10973 consider all memory clobbered after examining
10974 @option{ipa-max-aa-steps} statements modifying memory.
10976 @item lto-partitions
10977 Specify desired number of partitions produced during WHOPR compilation.
10978 The number of partitions should exceed the number of CPUs used for compilation.
10979 The default value is 32.
10981 @item lto-minpartition
10982 Size of minimal partition for WHOPR (in estimated instructions).
10983 This prevents expenses of splitting very small programs into too many
10986 @item cxx-max-namespaces-for-diagnostic-help
10987 The maximum number of namespaces to consult for suggestions when C++
10988 name lookup fails for an identifier. The default is 1000.
10990 @item sink-frequency-threshold
10991 The maximum relative execution frequency (in percents) of the target block
10992 relative to a statement's original block to allow statement sinking of a
10993 statement. Larger numbers result in more aggressive statement sinking.
10994 The default value is 75. A small positive adjustment is applied for
10995 statements with memory operands as those are even more profitable so sink.
10997 @item max-stores-to-sink
10998 The maximum number of conditional stores paires that can be sunk. Set to 0
10999 if either vectorization (@option{-ftree-vectorize}) or if-conversion
11000 (@option{-ftree-loop-if-convert}) is disabled. The default is 2.
11002 @item allow-store-data-races
11003 Allow optimizers to introduce new data races on stores.
11004 Set to 1 to allow, otherwise to 0. This option is enabled by default
11005 at optimization level @option{-Ofast}.
11007 @item case-values-threshold
11008 The smallest number of different values for which it is best to use a
11009 jump-table instead of a tree of conditional branches. If the value is
11010 0, use the default for the machine. The default is 0.
11012 @item tree-reassoc-width
11013 Set the maximum number of instructions executed in parallel in
11014 reassociated tree. This parameter overrides target dependent
11015 heuristics used by default if has non zero value.
11017 @item sched-pressure-algorithm
11018 Choose between the two available implementations of
11019 @option{-fsched-pressure}. Algorithm 1 is the original implementation
11020 and is the more likely to prevent instructions from being reordered.
11021 Algorithm 2 was designed to be a compromise between the relatively
11022 conservative approach taken by algorithm 1 and the rather aggressive
11023 approach taken by the default scheduler. It relies more heavily on
11024 having a regular register file and accurate register pressure classes.
11025 See @file{haifa-sched.c} in the GCC sources for more details.
11027 The default choice depends on the target.
11029 @item max-slsr-cand-scan
11030 Set the maximum number of existing candidates that are considered when
11031 seeking a basis for a new straight-line strength reduction candidate.
11034 Enable buffer overflow detection for global objects. This kind
11035 of protection is enabled by default if you are using
11036 @option{-fsanitize=address} option.
11037 To disable global objects protection use @option{--param asan-globals=0}.
11040 Enable buffer overflow detection for stack objects. This kind of
11041 protection is enabled by default when using@option{-fsanitize=address}.
11042 To disable stack protection use @option{--param asan-stack=0} option.
11044 @item asan-instrument-reads
11045 Enable buffer overflow detection for memory reads. This kind of
11046 protection is enabled by default when using @option{-fsanitize=address}.
11047 To disable memory reads protection use
11048 @option{--param asan-instrument-reads=0}.
11050 @item asan-instrument-writes
11051 Enable buffer overflow detection for memory writes. This kind of
11052 protection is enabled by default when using @option{-fsanitize=address}.
11053 To disable memory writes protection use
11054 @option{--param asan-instrument-writes=0} option.
11056 @item asan-memintrin
11057 Enable detection for built-in functions. This kind of protection
11058 is enabled by default when using @option{-fsanitize=address}.
11059 To disable built-in functions protection use
11060 @option{--param asan-memintrin=0}.
11062 @item asan-use-after-return
11063 Enable detection of use-after-return. This kind of protection
11064 is enabled by default when using @option{-fsanitize=address} option.
11065 To disable use-after-return detection use
11066 @option{--param asan-use-after-return=0}.
11068 @item asan-instrumentation-with-call-threshold
11069 If number of memory accesses in function being instrumented
11070 is greater or equal to this number, use callbacks instead of inline checks.
11071 E.g. to disable inline code use
11072 @option{--param asan-instrumentation-with-call-threshold=0}.
11074 @item chkp-max-ctor-size
11075 Static constructors generated by Pointer Bounds Checker may become very
11076 large and significantly increase compile time at optimization level
11077 @option{-O1} and higher. This parameter is a maximum nubmer of statements
11078 in a single generated constructor. Default value is 5000.
11080 @item max-fsm-thread-path-insns
11081 Maximum number of instructions to copy when duplicating blocks on a
11082 finite state automaton jump thread path. The default is 100.
11084 @item max-fsm-thread-length
11085 Maximum number of basic blocks on a finite state automaton jump thread
11086 path. The default is 10.
11088 @item max-fsm-thread-paths
11089 Maximum number of new jump thread paths to create for a finite state
11090 automaton. The default is 50.
11095 @node Preprocessor Options
11096 @section Options Controlling the Preprocessor
11097 @cindex preprocessor options
11098 @cindex options, preprocessor
11100 These options control the C preprocessor, which is run on each C source
11101 file before actual compilation.
11103 If you use the @option{-E} option, nothing is done except preprocessing.
11104 Some of these options make sense only together with @option{-E} because
11105 they cause the preprocessor output to be unsuitable for actual
11109 @item -Wp,@var{option}
11111 You can use @option{-Wp,@var{option}} to bypass the compiler driver
11112 and pass @var{option} directly through to the preprocessor. If
11113 @var{option} contains commas, it is split into multiple options at the
11114 commas. However, many options are modified, translated or interpreted
11115 by the compiler driver before being passed to the preprocessor, and
11116 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
11117 interface is undocumented and subject to change, so whenever possible
11118 you should avoid using @option{-Wp} and let the driver handle the
11121 @item -Xpreprocessor @var{option}
11122 @opindex Xpreprocessor
11123 Pass @var{option} as an option to the preprocessor. You can use this to
11124 supply system-specific preprocessor options that GCC does not
11127 If you want to pass an option that takes an argument, you must use
11128 @option{-Xpreprocessor} twice, once for the option and once for the argument.
11130 @item -no-integrated-cpp
11131 @opindex no-integrated-cpp
11132 Perform preprocessing as a separate pass before compilation.
11133 By default, GCC performs preprocessing as an integrated part of
11134 input tokenization and parsing.
11135 If this option is provided, the appropriate language front end
11136 (@command{cc1}, @command{cc1plus}, or @command{cc1obj} for C, C++,
11137 and Objective-C, respectively) is instead invoked twice,
11138 once for preprocessing only and once for actual compilation
11139 of the preprocessed input.
11140 This option may be useful in conjunction with the @option{-B} or
11141 @option{-wrapper} options to specify an alternate preprocessor or
11142 perform additional processing of the program source between
11143 normal preprocessing and compilation.
11146 @include cppopts.texi
11148 @node Assembler Options
11149 @section Passing Options to the Assembler
11151 @c prevent bad page break with this line
11152 You can pass options to the assembler.
11155 @item -Wa,@var{option}
11157 Pass @var{option} as an option to the assembler. If @var{option}
11158 contains commas, it is split into multiple options at the commas.
11160 @item -Xassembler @var{option}
11161 @opindex Xassembler
11162 Pass @var{option} as an option to the assembler. You can use this to
11163 supply system-specific assembler options that GCC does not
11166 If you want to pass an option that takes an argument, you must use
11167 @option{-Xassembler} twice, once for the option and once for the argument.
11172 @section Options for Linking
11173 @cindex link options
11174 @cindex options, linking
11176 These options come into play when the compiler links object files into
11177 an executable output file. They are meaningless if the compiler is
11178 not doing a link step.
11182 @item @var{object-file-name}
11183 A file name that does not end in a special recognized suffix is
11184 considered to name an object file or library. (Object files are
11185 distinguished from libraries by the linker according to the file
11186 contents.) If linking is done, these object files are used as input
11195 If any of these options is used, then the linker is not run, and
11196 object file names should not be used as arguments. @xref{Overall
11200 @opindex fuse-ld=bfd
11201 Use the @command{bfd} linker instead of the default linker.
11203 @item -fuse-ld=gold
11204 @opindex fuse-ld=gold
11205 Use the @command{gold} linker instead of the default linker.
11208 @item -l@var{library}
11209 @itemx -l @var{library}
11211 Search the library named @var{library} when linking. (The second
11212 alternative with the library as a separate argument is only for
11213 POSIX compliance and is not recommended.)
11215 It makes a difference where in the command you write this option; the
11216 linker searches and processes libraries and object files in the order they
11217 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
11218 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
11219 to functions in @samp{z}, those functions may not be loaded.
11221 The linker searches a standard list of directories for the library,
11222 which is actually a file named @file{lib@var{library}.a}. The linker
11223 then uses this file as if it had been specified precisely by name.
11225 The directories searched include several standard system directories
11226 plus any that you specify with @option{-L}.
11228 Normally the files found this way are library files---archive files
11229 whose members are object files. The linker handles an archive file by
11230 scanning through it for members which define symbols that have so far
11231 been referenced but not defined. But if the file that is found is an
11232 ordinary object file, it is linked in the usual fashion. The only
11233 difference between using an @option{-l} option and specifying a file name
11234 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
11235 and searches several directories.
11239 You need this special case of the @option{-l} option in order to
11240 link an Objective-C or Objective-C++ program.
11242 @item -nostartfiles
11243 @opindex nostartfiles
11244 Do not use the standard system startup files when linking.
11245 The standard system libraries are used normally, unless @option{-nostdlib}
11246 or @option{-nodefaultlibs} is used.
11248 @item -nodefaultlibs
11249 @opindex nodefaultlibs
11250 Do not use the standard system libraries when linking.
11251 Only the libraries you specify are passed to the linker, and options
11252 specifying linkage of the system libraries, such as @option{-static-libgcc}
11253 or @option{-shared-libgcc}, are ignored.
11254 The standard startup files are used normally, unless @option{-nostartfiles}
11257 The compiler may generate calls to @code{memcmp},
11258 @code{memset}, @code{memcpy} and @code{memmove}.
11259 These entries are usually resolved by entries in
11260 libc. These entry points should be supplied through some other
11261 mechanism when this option is specified.
11265 Do not use the standard system startup files or libraries when linking.
11266 No startup files and only the libraries you specify are passed to
11267 the linker, and options specifying linkage of the system libraries, such as
11268 @option{-static-libgcc} or @option{-shared-libgcc}, are ignored.
11270 The compiler may generate calls to @code{memcmp}, @code{memset},
11271 @code{memcpy} and @code{memmove}.
11272 These entries are usually resolved by entries in
11273 libc. These entry points should be supplied through some other
11274 mechanism when this option is specified.
11276 @cindex @option{-lgcc}, use with @option{-nostdlib}
11277 @cindex @option{-nostdlib} and unresolved references
11278 @cindex unresolved references and @option{-nostdlib}
11279 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
11280 @cindex @option{-nodefaultlibs} and unresolved references
11281 @cindex unresolved references and @option{-nodefaultlibs}
11282 One of the standard libraries bypassed by @option{-nostdlib} and
11283 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
11284 which GCC uses to overcome shortcomings of particular machines, or special
11285 needs for some languages.
11286 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
11287 Collection (GCC) Internals},
11288 for more discussion of @file{libgcc.a}.)
11289 In most cases, you need @file{libgcc.a} even when you want to avoid
11290 other standard libraries. In other words, when you specify @option{-nostdlib}
11291 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
11292 This ensures that you have no unresolved references to internal GCC
11293 library subroutines.
11294 (An example of such an internal subroutine is @code{__main}, used to ensure C++
11295 constructors are called; @pxref{Collect2,,@code{collect2}, gccint,
11296 GNU Compiler Collection (GCC) Internals}.)
11300 Produce a position independent executable on targets that support it.
11301 For predictable results, you must also specify the same set of options
11302 used for compilation (@option{-fpie}, @option{-fPIE},
11303 or model suboptions) when you specify this linker option.
11307 Don't produce a position independent executable.
11311 Pass the flag @option{-export-dynamic} to the ELF linker, on targets
11312 that support it. This instructs the linker to add all symbols, not
11313 only used ones, to the dynamic symbol table. This option is needed
11314 for some uses of @code{dlopen} or to allow obtaining backtraces
11315 from within a program.
11319 Remove all symbol table and relocation information from the executable.
11323 On systems that support dynamic linking, this prevents linking with the shared
11324 libraries. On other systems, this option has no effect.
11328 Produce a shared object which can then be linked with other objects to
11329 form an executable. Not all systems support this option. For predictable
11330 results, you must also specify the same set of options used for compilation
11331 (@option{-fpic}, @option{-fPIC}, or model suboptions) when
11332 you specify this linker option.@footnote{On some systems, @samp{gcc -shared}
11333 needs to build supplementary stub code for constructors to work. On
11334 multi-libbed systems, @samp{gcc -shared} must select the correct support
11335 libraries to link against. Failing to supply the correct flags may lead
11336 to subtle defects. Supplying them in cases where they are not necessary
11339 @item -shared-libgcc
11340 @itemx -static-libgcc
11341 @opindex shared-libgcc
11342 @opindex static-libgcc
11343 On systems that provide @file{libgcc} as a shared library, these options
11344 force the use of either the shared or static version, respectively.
11345 If no shared version of @file{libgcc} was built when the compiler was
11346 configured, these options have no effect.
11348 There are several situations in which an application should use the
11349 shared @file{libgcc} instead of the static version. The most common
11350 of these is when the application wishes to throw and catch exceptions
11351 across different shared libraries. In that case, each of the libraries
11352 as well as the application itself should use the shared @file{libgcc}.
11354 Therefore, the G++ and GCJ drivers automatically add
11355 @option{-shared-libgcc} whenever you build a shared library or a main
11356 executable, because C++ and Java programs typically use exceptions, so
11357 this is the right thing to do.
11359 If, instead, you use the GCC driver to create shared libraries, you may
11360 find that they are not always linked with the shared @file{libgcc}.
11361 If GCC finds, at its configuration time, that you have a non-GNU linker
11362 or a GNU linker that does not support option @option{--eh-frame-hdr},
11363 it links the shared version of @file{libgcc} into shared libraries
11364 by default. Otherwise, it takes advantage of the linker and optimizes
11365 away the linking with the shared version of @file{libgcc}, linking with
11366 the static version of libgcc by default. This allows exceptions to
11367 propagate through such shared libraries, without incurring relocation
11368 costs at library load time.
11370 However, if a library or main executable is supposed to throw or catch
11371 exceptions, you must link it using the G++ or GCJ driver, as appropriate
11372 for the languages used in the program, or using the option
11373 @option{-shared-libgcc}, such that it is linked with the shared
11376 @item -static-libasan
11377 @opindex static-libasan
11378 When the @option{-fsanitize=address} option is used to link a program,
11379 the GCC driver automatically links against @option{libasan}. If
11380 @file{libasan} is available as a shared library, and the @option{-static}
11381 option is not used, then this links against the shared version of
11382 @file{libasan}. The @option{-static-libasan} option directs the GCC
11383 driver to link @file{libasan} statically, without necessarily linking
11384 other libraries statically.
11386 @item -static-libtsan
11387 @opindex static-libtsan
11388 When the @option{-fsanitize=thread} option is used to link a program,
11389 the GCC driver automatically links against @option{libtsan}. If
11390 @file{libtsan} is available as a shared library, and the @option{-static}
11391 option is not used, then this links against the shared version of
11392 @file{libtsan}. The @option{-static-libtsan} option directs the GCC
11393 driver to link @file{libtsan} statically, without necessarily linking
11394 other libraries statically.
11396 @item -static-liblsan
11397 @opindex static-liblsan
11398 When the @option{-fsanitize=leak} option is used to link a program,
11399 the GCC driver automatically links against @option{liblsan}. If
11400 @file{liblsan} is available as a shared library, and the @option{-static}
11401 option is not used, then this links against the shared version of
11402 @file{liblsan}. The @option{-static-liblsan} option directs the GCC
11403 driver to link @file{liblsan} statically, without necessarily linking
11404 other libraries statically.
11406 @item -static-libubsan
11407 @opindex static-libubsan
11408 When the @option{-fsanitize=undefined} option is used to link a program,
11409 the GCC driver automatically links against @option{libubsan}. If
11410 @file{libubsan} is available as a shared library, and the @option{-static}
11411 option is not used, then this links against the shared version of
11412 @file{libubsan}. The @option{-static-libubsan} option directs the GCC
11413 driver to link @file{libubsan} statically, without necessarily linking
11414 other libraries statically.
11416 @item -static-libmpx
11417 @opindex static-libmpx
11418 When the @option{-fcheck-pointer bounds} and @option{-mmpx} options are
11419 used to link a program, the GCC driver automatically links against
11420 @file{libmpx}. If @file{libmpx} is available as a shared library,
11421 and the @option{-static} option is not used, then this links against
11422 the shared version of @file{libmpx}. The @option{-static-libmpx}
11423 option directs the GCC driver to link @file{libmpx} statically,
11424 without necessarily linking other libraries statically.
11426 @item -static-libmpxwrappers
11427 @opindex static-libmpxwrappers
11428 When the @option{-fcheck-pointer bounds} and @option{-mmpx} options are used
11429 to link a program without also using @option{-fno-chkp-use-wrappers}, the
11430 GCC driver automatically links against @file{libmpxwrappers}. If
11431 @file{libmpxwrappers} is available as a shared library, and the
11432 @option{-static} option is not used, then this links against the shared
11433 version of @file{libmpxwrappers}. The @option{-static-libmpxwrappers}
11434 option directs the GCC driver to link @file{libmpxwrappers} statically,
11435 without necessarily linking other libraries statically.
11437 @item -static-libstdc++
11438 @opindex static-libstdc++
11439 When the @command{g++} program is used to link a C++ program, it
11440 normally automatically links against @option{libstdc++}. If
11441 @file{libstdc++} is available as a shared library, and the
11442 @option{-static} option is not used, then this links against the
11443 shared version of @file{libstdc++}. That is normally fine. However, it
11444 is sometimes useful to freeze the version of @file{libstdc++} used by
11445 the program without going all the way to a fully static link. The
11446 @option{-static-libstdc++} option directs the @command{g++} driver to
11447 link @file{libstdc++} statically, without necessarily linking other
11448 libraries statically.
11452 Bind references to global symbols when building a shared object. Warn
11453 about any unresolved references (unless overridden by the link editor
11454 option @option{-Xlinker -z -Xlinker defs}). Only a few systems support
11457 @item -T @var{script}
11459 @cindex linker script
11460 Use @var{script} as the linker script. This option is supported by most
11461 systems using the GNU linker. On some targets, such as bare-board
11462 targets without an operating system, the @option{-T} option may be required
11463 when linking to avoid references to undefined symbols.
11465 @item -Xlinker @var{option}
11467 Pass @var{option} as an option to the linker. You can use this to
11468 supply system-specific linker options that GCC does not recognize.
11470 If you want to pass an option that takes a separate argument, you must use
11471 @option{-Xlinker} twice, once for the option and once for the argument.
11472 For example, to pass @option{-assert definitions}, you must write
11473 @option{-Xlinker -assert -Xlinker definitions}. It does not work to write
11474 @option{-Xlinker "-assert definitions"}, because this passes the entire
11475 string as a single argument, which is not what the linker expects.
11477 When using the GNU linker, it is usually more convenient to pass
11478 arguments to linker options using the @option{@var{option}=@var{value}}
11479 syntax than as separate arguments. For example, you can specify
11480 @option{-Xlinker -Map=output.map} rather than
11481 @option{-Xlinker -Map -Xlinker output.map}. Other linkers may not support
11482 this syntax for command-line options.
11484 @item -Wl,@var{option}
11486 Pass @var{option} as an option to the linker. If @var{option} contains
11487 commas, it is split into multiple options at the commas. You can use this
11488 syntax to pass an argument to the option.
11489 For example, @option{-Wl,-Map,output.map} passes @option{-Map output.map} to the
11490 linker. When using the GNU linker, you can also get the same effect with
11491 @option{-Wl,-Map=output.map}.
11493 @item -u @var{symbol}
11495 Pretend the symbol @var{symbol} is undefined, to force linking of
11496 library modules to define it. You can use @option{-u} multiple times with
11497 different symbols to force loading of additional library modules.
11499 @item -z @var{keyword}
11501 @option{-z} is passed directly on to the linker along with the keyword
11502 @var{keyword}. See the section in the documentation of your linker for
11503 permitted values and their meanings.
11506 @node Directory Options
11507 @section Options for Directory Search
11508 @cindex directory options
11509 @cindex options, directory search
11510 @cindex search path
11512 These options specify directories to search for header files, for
11513 libraries and for parts of the compiler:
11518 Add the directory @var{dir} to the head of the list of directories to be
11519 searched for header files. This can be used to override a system header
11520 file, substituting your own version, since these directories are
11521 searched before the system header file directories. However, you should
11522 not use this option to add directories that contain vendor-supplied
11523 system header files (use @option{-isystem} for that). If you use more than
11524 one @option{-I} option, the directories are scanned in left-to-right
11525 order; the standard system directories come after.
11527 If a standard system include directory, or a directory specified with
11528 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
11529 option is ignored. The directory is still searched but as a
11530 system directory at its normal position in the system include chain.
11531 This is to ensure that GCC's procedure to fix buggy system headers and
11532 the ordering for the @code{include_next} directive are not inadvertently changed.
11533 If you really need to change the search order for system directories,
11534 use the @option{-nostdinc} and/or @option{-isystem} options.
11536 @item -iplugindir=@var{dir}
11537 @opindex iplugindir=
11538 Set the directory to search for plugins that are passed
11539 by @option{-fplugin=@var{name}} instead of
11540 @option{-fplugin=@var{path}/@var{name}.so}. This option is not meant
11541 to be used by the user, but only passed by the driver.
11543 @item -iquote@var{dir}
11545 Add the directory @var{dir} to the head of the list of directories to
11546 be searched for header files only for the case of @code{#include
11547 "@var{file}"}; they are not searched for @code{#include <@var{file}>},
11548 otherwise just like @option{-I}.
11552 Add directory @var{dir} to the list of directories to be searched
11555 @item -B@var{prefix}
11557 This option specifies where to find the executables, libraries,
11558 include files, and data files of the compiler itself.
11560 The compiler driver program runs one or more of the subprograms
11561 @command{cpp}, @command{cc1}, @command{as} and @command{ld}. It tries
11562 @var{prefix} as a prefix for each program it tries to run, both with and
11563 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
11565 For each subprogram to be run, the compiler driver first tries the
11566 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
11567 is not specified, the driver tries two standard prefixes,
11568 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
11569 those results in a file name that is found, the unmodified program
11570 name is searched for using the directories specified in your
11571 @env{PATH} environment variable.
11573 The compiler checks to see if the path provided by @option{-B}
11574 refers to a directory, and if necessary it adds a directory
11575 separator character at the end of the path.
11577 @option{-B} prefixes that effectively specify directory names also apply
11578 to libraries in the linker, because the compiler translates these
11579 options into @option{-L} options for the linker. They also apply to
11580 include files in the preprocessor, because the compiler translates these
11581 options into @option{-isystem} options for the preprocessor. In this case,
11582 the compiler appends @samp{include} to the prefix.
11584 The runtime support file @file{libgcc.a} can also be searched for using
11585 the @option{-B} prefix, if needed. If it is not found there, the two
11586 standard prefixes above are tried, and that is all. The file is left
11587 out of the link if it is not found by those means.
11589 Another way to specify a prefix much like the @option{-B} prefix is to use
11590 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
11593 As a special kludge, if the path provided by @option{-B} is
11594 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
11595 9, then it is replaced by @file{[dir/]include}. This is to help
11596 with boot-strapping the compiler.
11598 @item -specs=@var{file}
11600 Process @var{file} after the compiler reads in the standard @file{specs}
11601 file, in order to override the defaults which the @command{gcc} driver
11602 program uses when determining what switches to pass to @command{cc1},
11603 @command{cc1plus}, @command{as}, @command{ld}, etc. More than one
11604 @option{-specs=@var{file}} can be specified on the command line, and they
11605 are processed in order, from left to right.
11607 @item --sysroot=@var{dir}
11609 Use @var{dir} as the logical root directory for headers and libraries.
11610 For example, if the compiler normally searches for headers in
11611 @file{/usr/include} and libraries in @file{/usr/lib}, it instead
11612 searches @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}.
11614 If you use both this option and the @option{-isysroot} option, then
11615 the @option{--sysroot} option applies to libraries, but the
11616 @option{-isysroot} option applies to header files.
11618 The GNU linker (beginning with version 2.16) has the necessary support
11619 for this option. If your linker does not support this option, the
11620 header file aspect of @option{--sysroot} still works, but the
11621 library aspect does not.
11623 @item --no-sysroot-suffix
11624 @opindex no-sysroot-suffix
11625 For some targets, a suffix is added to the root directory specified
11626 with @option{--sysroot}, depending on the other options used, so that
11627 headers may for example be found in
11628 @file{@var{dir}/@var{suffix}/usr/include} instead of
11629 @file{@var{dir}/usr/include}. This option disables the addition of
11634 This option has been deprecated. Please use @option{-iquote} instead for
11635 @option{-I} directories before the @option{-I-} and remove the @option{-I-}
11637 Any directories you specify with @option{-I} options before the @option{-I-}
11638 option are searched only for the case of @code{#include "@var{file}"};
11639 they are not searched for @code{#include <@var{file}>}.
11641 If additional directories are specified with @option{-I} options after
11642 the @option{-I-} option, these directories are searched for all @code{#include}
11643 directives. (Ordinarily @emph{all} @option{-I} directories are used
11646 In addition, the @option{-I-} option inhibits the use of the current
11647 directory (where the current input file came from) as the first search
11648 directory for @code{#include "@var{file}"}. There is no way to
11649 override this effect of @option{-I-}. With @option{-I.} you can specify
11650 searching the directory that is current when the compiler is
11651 invoked. That is not exactly the same as what the preprocessor does
11652 by default, but it is often satisfactory.
11654 @option{-I-} does not inhibit the use of the standard system directories
11655 for header files. Thus, @option{-I-} and @option{-nostdinc} are
11662 @section Specifying Subprocesses and the Switches to Pass to Them
11665 @command{gcc} is a driver program. It performs its job by invoking a
11666 sequence of other programs to do the work of compiling, assembling and
11667 linking. GCC interprets its command-line parameters and uses these to
11668 deduce which programs it should invoke, and which command-line options
11669 it ought to place on their command lines. This behavior is controlled
11670 by @dfn{spec strings}. In most cases there is one spec string for each
11671 program that GCC can invoke, but a few programs have multiple spec
11672 strings to control their behavior. The spec strings built into GCC can
11673 be overridden by using the @option{-specs=} command-line switch to specify
11676 @dfn{Spec files} are plaintext files that are used to construct spec
11677 strings. They consist of a sequence of directives separated by blank
11678 lines. The type of directive is determined by the first non-whitespace
11679 character on the line, which can be one of the following:
11682 @item %@var{command}
11683 Issues a @var{command} to the spec file processor. The commands that can
11687 @item %include <@var{file}>
11688 @cindex @code{%include}
11689 Search for @var{file} and insert its text at the current point in the
11692 @item %include_noerr <@var{file}>
11693 @cindex @code{%include_noerr}
11694 Just like @samp{%include}, but do not generate an error message if the include
11695 file cannot be found.
11697 @item %rename @var{old_name} @var{new_name}
11698 @cindex @code{%rename}
11699 Rename the spec string @var{old_name} to @var{new_name}.
11703 @item *[@var{spec_name}]:
11704 This tells the compiler to create, override or delete the named spec
11705 string. All lines after this directive up to the next directive or
11706 blank line are considered to be the text for the spec string. If this
11707 results in an empty string then the spec is deleted. (Or, if the
11708 spec did not exist, then nothing happens.) Otherwise, if the spec
11709 does not currently exist a new spec is created. If the spec does
11710 exist then its contents are overridden by the text of this
11711 directive, unless the first character of that text is the @samp{+}
11712 character, in which case the text is appended to the spec.
11714 @item [@var{suffix}]:
11715 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
11716 and up to the next directive or blank line are considered to make up the
11717 spec string for the indicated suffix. When the compiler encounters an
11718 input file with the named suffix, it processes the spec string in
11719 order to work out how to compile that file. For example:
11723 z-compile -input %i
11726 This says that any input file whose name ends in @samp{.ZZ} should be
11727 passed to the program @samp{z-compile}, which should be invoked with the
11728 command-line switch @option{-input} and with the result of performing the
11729 @samp{%i} substitution. (See below.)
11731 As an alternative to providing a spec string, the text following a
11732 suffix directive can be one of the following:
11735 @item @@@var{language}
11736 This says that the suffix is an alias for a known @var{language}. This is
11737 similar to using the @option{-x} command-line switch to GCC to specify a
11738 language explicitly. For example:
11745 Says that .ZZ files are, in fact, C++ source files.
11748 This causes an error messages saying:
11751 @var{name} compiler not installed on this system.
11755 GCC already has an extensive list of suffixes built into it.
11756 This directive adds an entry to the end of the list of suffixes, but
11757 since the list is searched from the end backwards, it is effectively
11758 possible to override earlier entries using this technique.
11762 GCC has the following spec strings built into it. Spec files can
11763 override these strings or create their own. Note that individual
11764 targets can also add their own spec strings to this list.
11767 asm Options to pass to the assembler
11768 asm_final Options to pass to the assembler post-processor
11769 cpp Options to pass to the C preprocessor
11770 cc1 Options to pass to the C compiler
11771 cc1plus Options to pass to the C++ compiler
11772 endfile Object files to include at the end of the link
11773 link Options to pass to the linker
11774 lib Libraries to include on the command line to the linker
11775 libgcc Decides which GCC support library to pass to the linker
11776 linker Sets the name of the linker
11777 predefines Defines to be passed to the C preprocessor
11778 signed_char Defines to pass to CPP to say whether @code{char} is signed
11780 startfile Object files to include at the start of the link
11783 Here is a small example of a spec file:
11786 %rename lib old_lib
11789 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
11792 This example renames the spec called @samp{lib} to @samp{old_lib} and
11793 then overrides the previous definition of @samp{lib} with a new one.
11794 The new definition adds in some extra command-line options before
11795 including the text of the old definition.
11797 @dfn{Spec strings} are a list of command-line options to be passed to their
11798 corresponding program. In addition, the spec strings can contain
11799 @samp{%}-prefixed sequences to substitute variable text or to
11800 conditionally insert text into the command line. Using these constructs
11801 it is possible to generate quite complex command lines.
11803 Here is a table of all defined @samp{%}-sequences for spec
11804 strings. Note that spaces are not generated automatically around the
11805 results of expanding these sequences. Therefore you can concatenate them
11806 together or combine them with constant text in a single argument.
11810 Substitute one @samp{%} into the program name or argument.
11813 Substitute the name of the input file being processed.
11816 Substitute the basename of the input file being processed.
11817 This is the substring up to (and not including) the last period
11818 and not including the directory.
11821 This is the same as @samp{%b}, but include the file suffix (text after
11825 Marks the argument containing or following the @samp{%d} as a
11826 temporary file name, so that that file is deleted if GCC exits
11827 successfully. Unlike @samp{%g}, this contributes no text to the
11830 @item %g@var{suffix}
11831 Substitute a file name that has suffix @var{suffix} and is chosen
11832 once per compilation, and mark the argument in the same way as
11833 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
11834 name is now chosen in a way that is hard to predict even when previously
11835 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
11836 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
11837 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
11838 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
11839 was simply substituted with a file name chosen once per compilation,
11840 without regard to any appended suffix (which was therefore treated
11841 just like ordinary text), making such attacks more likely to succeed.
11843 @item %u@var{suffix}
11844 Like @samp{%g}, but generates a new temporary file name
11845 each time it appears instead of once per compilation.
11847 @item %U@var{suffix}
11848 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
11849 new one if there is no such last file name. In the absence of any
11850 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
11851 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
11852 involves the generation of two distinct file names, one
11853 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
11854 simply substituted with a file name chosen for the previous @samp{%u},
11855 without regard to any appended suffix.
11857 @item %j@var{suffix}
11858 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
11859 writable, and if @option{-save-temps} is not used;
11860 otherwise, substitute the name
11861 of a temporary file, just like @samp{%u}. This temporary file is not
11862 meant for communication between processes, but rather as a junk
11863 disposal mechanism.
11865 @item %|@var{suffix}
11866 @itemx %m@var{suffix}
11867 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
11868 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
11869 all. These are the two most common ways to instruct a program that it
11870 should read from standard input or write to standard output. If you
11871 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
11872 construct: see for example @file{f/lang-specs.h}.
11874 @item %.@var{SUFFIX}
11875 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
11876 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
11877 terminated by the next space or %.
11880 Marks the argument containing or following the @samp{%w} as the
11881 designated output file of this compilation. This puts the argument
11882 into the sequence of arguments that @samp{%o} substitutes.
11885 Substitutes the names of all the output files, with spaces
11886 automatically placed around them. You should write spaces
11887 around the @samp{%o} as well or the results are undefined.
11888 @samp{%o} is for use in the specs for running the linker.
11889 Input files whose names have no recognized suffix are not compiled
11890 at all, but they are included among the output files, so they are
11894 Substitutes the suffix for object files. Note that this is
11895 handled specially when it immediately follows @samp{%g, %u, or %U},
11896 because of the need for those to form complete file names. The
11897 handling is such that @samp{%O} is treated exactly as if it had already
11898 been substituted, except that @samp{%g, %u, and %U} do not currently
11899 support additional @var{suffix} characters following @samp{%O} as they do
11900 following, for example, @samp{.o}.
11903 Substitutes the standard macro predefinitions for the
11904 current target machine. Use this when running @command{cpp}.
11907 Like @samp{%p}, but puts @samp{__} before and after the name of each
11908 predefined macro, except for macros that start with @samp{__} or with
11909 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
11913 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
11914 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}),
11915 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
11916 and @option{-imultilib} as necessary.
11919 Current argument is the name of a library or startup file of some sort.
11920 Search for that file in a standard list of directories and substitute
11921 the full name found. The current working directory is included in the
11922 list of directories scanned.
11925 Current argument is the name of a linker script. Search for that file
11926 in the current list of directories to scan for libraries. If the file
11927 is located insert a @option{--script} option into the command line
11928 followed by the full path name found. If the file is not found then
11929 generate an error message. Note: the current working directory is not
11933 Print @var{str} as an error message. @var{str} is terminated by a newline.
11934 Use this when inconsistent options are detected.
11936 @item %(@var{name})
11937 Substitute the contents of spec string @var{name} at this point.
11939 @item %x@{@var{option}@}
11940 Accumulate an option for @samp{%X}.
11943 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
11947 Output the accumulated assembler options specified by @option{-Wa}.
11950 Output the accumulated preprocessor options specified by @option{-Wp}.
11953 Process the @code{asm} spec. This is used to compute the
11954 switches to be passed to the assembler.
11957 Process the @code{asm_final} spec. This is a spec string for
11958 passing switches to an assembler post-processor, if such a program is
11962 Process the @code{link} spec. This is the spec for computing the
11963 command line passed to the linker. Typically it makes use of the
11964 @samp{%L %G %S %D and %E} sequences.
11967 Dump out a @option{-L} option for each directory that GCC believes might
11968 contain startup files. If the target supports multilibs then the
11969 current multilib directory is prepended to each of these paths.
11972 Process the @code{lib} spec. This is a spec string for deciding which
11973 libraries are included on the command line to the linker.
11976 Process the @code{libgcc} spec. This is a spec string for deciding
11977 which GCC support library is included on the command line to the linker.
11980 Process the @code{startfile} spec. This is a spec for deciding which
11981 object files are the first ones passed to the linker. Typically
11982 this might be a file named @file{crt0.o}.
11985 Process the @code{endfile} spec. This is a spec string that specifies
11986 the last object files that are passed to the linker.
11989 Process the @code{cpp} spec. This is used to construct the arguments
11990 to be passed to the C preprocessor.
11993 Process the @code{cc1} spec. This is used to construct the options to be
11994 passed to the actual C compiler (@command{cc1}).
11997 Process the @code{cc1plus} spec. This is used to construct the options to be
11998 passed to the actual C++ compiler (@command{cc1plus}).
12001 Substitute the variable part of a matched option. See below.
12002 Note that each comma in the substituted string is replaced by
12006 Remove all occurrences of @code{-S} from the command line. Note---this
12007 command is position dependent. @samp{%} commands in the spec string
12008 before this one see @code{-S}, @samp{%} commands in the spec string
12009 after this one do not.
12011 @item %:@var{function}(@var{args})
12012 Call the named function @var{function}, passing it @var{args}.
12013 @var{args} is first processed as a nested spec string, then split
12014 into an argument vector in the usual fashion. The function returns
12015 a string which is processed as if it had appeared literally as part
12016 of the current spec.
12018 The following built-in spec functions are provided:
12021 @item @code{getenv}
12022 The @code{getenv} spec function takes two arguments: an environment
12023 variable name and a string. If the environment variable is not
12024 defined, a fatal error is issued. Otherwise, the return value is the
12025 value of the environment variable concatenated with the string. For
12026 example, if @env{TOPDIR} is defined as @file{/path/to/top}, then:
12029 %:getenv(TOPDIR /include)
12032 expands to @file{/path/to/top/include}.
12034 @item @code{if-exists}
12035 The @code{if-exists} spec function takes one argument, an absolute
12036 pathname to a file. If the file exists, @code{if-exists} returns the
12037 pathname. Here is a small example of its usage:
12041 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
12044 @item @code{if-exists-else}
12045 The @code{if-exists-else} spec function is similar to the @code{if-exists}
12046 spec function, except that it takes two arguments. The first argument is
12047 an absolute pathname to a file. If the file exists, @code{if-exists-else}
12048 returns the pathname. If it does not exist, it returns the second argument.
12049 This way, @code{if-exists-else} can be used to select one file or another,
12050 based on the existence of the first. Here is a small example of its usage:
12054 crt0%O%s %:if-exists(crti%O%s) \
12055 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
12058 @item @code{replace-outfile}
12059 The @code{replace-outfile} spec function takes two arguments. It looks for the
12060 first argument in the outfiles array and replaces it with the second argument. Here
12061 is a small example of its usage:
12064 %@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
12067 @item @code{remove-outfile}
12068 The @code{remove-outfile} spec function takes one argument. It looks for the
12069 first argument in the outfiles array and removes it. Here is a small example
12073 %:remove-outfile(-lm)
12076 @item @code{pass-through-libs}
12077 The @code{pass-through-libs} spec function takes any number of arguments. It
12078 finds any @option{-l} options and any non-options ending in @file{.a} (which it
12079 assumes are the names of linker input library archive files) and returns a
12080 result containing all the found arguments each prepended by
12081 @option{-plugin-opt=-pass-through=} and joined by spaces. This list is
12082 intended to be passed to the LTO linker plugin.
12085 %:pass-through-libs(%G %L %G)
12088 @item @code{print-asm-header}
12089 The @code{print-asm-header} function takes no arguments and simply
12090 prints a banner like:
12096 Use "-Wa,OPTION" to pass "OPTION" to the assembler.
12099 It is used to separate compiler options from assembler options
12100 in the @option{--target-help} output.
12103 @item %@{@code{S}@}
12104 Substitutes the @code{-S} switch, if that switch is given to GCC@.
12105 If that switch is not specified, this substitutes nothing. Note that
12106 the leading dash is omitted when specifying this option, and it is
12107 automatically inserted if the substitution is performed. Thus the spec
12108 string @samp{%@{foo@}} matches the command-line option @option{-foo}
12109 and outputs the command-line option @option{-foo}.
12111 @item %W@{@code{S}@}
12112 Like %@{@code{S}@} but mark last argument supplied within as a file to be
12113 deleted on failure.
12115 @item %@{@code{S}*@}
12116 Substitutes all the switches specified to GCC whose names start
12117 with @code{-S}, but which also take an argument. This is used for
12118 switches like @option{-o}, @option{-D}, @option{-I}, etc.
12119 GCC considers @option{-o foo} as being
12120 one switch whose name starts with @samp{o}. %@{o*@} substitutes this
12121 text, including the space. Thus two arguments are generated.
12123 @item %@{@code{S}*&@code{T}*@}
12124 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
12125 (the order of @code{S} and @code{T} in the spec is not significant).
12126 There can be any number of ampersand-separated variables; for each the
12127 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
12129 @item %@{@code{S}:@code{X}@}
12130 Substitutes @code{X}, if the @option{-S} switch is given to GCC@.
12132 @item %@{!@code{S}:@code{X}@}
12133 Substitutes @code{X}, if the @option{-S} switch is @emph{not} given to GCC@.
12135 @item %@{@code{S}*:@code{X}@}
12136 Substitutes @code{X} if one or more switches whose names start with
12137 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
12138 once, no matter how many such switches appeared. However, if @code{%*}
12139 appears somewhere in @code{X}, then @code{X} is substituted once
12140 for each matching switch, with the @code{%*} replaced by the part of
12141 that switch matching the @code{*}.
12143 If @code{%*} appears as the last part of a spec sequence then a space
12144 is added after the end of the last substitution. If there is more
12145 text in the sequence, however, then a space is not generated. This
12146 allows the @code{%*} substitution to be used as part of a larger
12147 string. For example, a spec string like this:
12150 %@{mcu=*:--script=%*/memory.ld@}
12154 when matching an option like @option{-mcu=newchip} produces:
12157 --script=newchip/memory.ld
12160 @item %@{.@code{S}:@code{X}@}
12161 Substitutes @code{X}, if processing a file with suffix @code{S}.
12163 @item %@{!.@code{S}:@code{X}@}
12164 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
12166 @item %@{,@code{S}:@code{X}@}
12167 Substitutes @code{X}, if processing a file for language @code{S}.
12169 @item %@{!,@code{S}:@code{X}@}
12170 Substitutes @code{X}, if not processing a file for language @code{S}.
12172 @item %@{@code{S}|@code{P}:@code{X}@}
12173 Substitutes @code{X} if either @code{-S} or @code{-P} is given to
12174 GCC@. This may be combined with @samp{!}, @samp{.}, @samp{,}, and
12175 @code{*} sequences as well, although they have a stronger binding than
12176 the @samp{|}. If @code{%*} appears in @code{X}, all of the
12177 alternatives must be starred, and only the first matching alternative
12180 For example, a spec string like this:
12183 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
12187 outputs the following command-line options from the following input
12188 command-line options:
12193 -d fred.c -foo -baz -boggle
12194 -d jim.d -bar -baz -boggle
12197 @item %@{S:X; T:Y; :D@}
12199 If @code{S} is given to GCC, substitutes @code{X}; else if @code{T} is
12200 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
12201 be as many clauses as you need. This may be combined with @code{.},
12202 @code{,}, @code{!}, @code{|}, and @code{*} as needed.
12207 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
12208 construct may contain other nested @samp{%} constructs or spaces, or
12209 even newlines. They are processed as usual, as described above.
12210 Trailing white space in @code{X} is ignored. White space may also
12211 appear anywhere on the left side of the colon in these constructs,
12212 except between @code{.} or @code{*} and the corresponding word.
12214 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
12215 handled specifically in these constructs. If another value of
12216 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
12217 @option{-W} switch is found later in the command line, the earlier
12218 switch value is ignored, except with @{@code{S}*@} where @code{S} is
12219 just one letter, which passes all matching options.
12221 The character @samp{|} at the beginning of the predicate text is used to
12222 indicate that a command should be piped to the following command, but
12223 only if @option{-pipe} is specified.
12225 It is built into GCC which switches take arguments and which do not.
12226 (You might think it would be useful to generalize this to allow each
12227 compiler's spec to say which switches take arguments. But this cannot
12228 be done in a consistent fashion. GCC cannot even decide which input
12229 files have been specified without knowing which switches take arguments,
12230 and it must know which input files to compile in order to tell which
12233 GCC also knows implicitly that arguments starting in @option{-l} are to be
12234 treated as compiler output files, and passed to the linker in their
12235 proper position among the other output files.
12237 @c man begin OPTIONS
12239 @node Target Options
12240 @section Specifying Target Machine and Compiler Version
12241 @cindex target options
12242 @cindex cross compiling
12243 @cindex specifying machine version
12244 @cindex specifying compiler version and target machine
12245 @cindex compiler version, specifying
12246 @cindex target machine, specifying
12248 The usual way to run GCC is to run the executable called @command{gcc}, or
12249 @command{@var{machine}-gcc} when cross-compiling, or
12250 @command{@var{machine}-gcc-@var{version}} to run a version other than the
12251 one that was installed last.
12253 @node Submodel Options
12254 @section Hardware Models and Configurations
12255 @cindex submodel options
12256 @cindex specifying hardware config
12257 @cindex hardware models and configurations, specifying
12258 @cindex machine dependent options
12260 Each target machine types can have its own
12261 special options, starting with @samp{-m}, to choose among various
12262 hardware models or configurations---for example, 68010 vs 68020,
12263 floating coprocessor or none. A single installed version of the
12264 compiler can compile for any model or configuration, according to the
12267 Some configurations of the compiler also support additional special
12268 options, usually for compatibility with other compilers on the same
12271 @c This list is ordered alphanumerically by subsection name.
12272 @c It should be the same order and spelling as these options are listed
12273 @c in Machine Dependent Options
12276 * AArch64 Options::
12277 * Adapteva Epiphany Options::
12281 * Blackfin Options::
12286 * DEC Alpha Options::
12290 * GNU/Linux Options::
12300 * MicroBlaze Options::
12303 * MN10300 Options::
12307 * Nios II Options::
12308 * Nvidia PTX Options::
12310 * picoChip Options::
12311 * PowerPC Options::
12313 * RS/6000 and PowerPC Options::
12315 * S/390 and zSeries Options::
12318 * Solaris 2 Options::
12321 * System V Options::
12322 * TILE-Gx Options::
12323 * TILEPro Options::
12328 * VxWorks Options::
12330 * x86 Windows Options::
12331 * Xstormy16 Options::
12333 * zSeries Options::
12336 @node AArch64 Options
12337 @subsection AArch64 Options
12338 @cindex AArch64 Options
12340 These options are defined for AArch64 implementations:
12344 @item -mabi=@var{name}
12346 Generate code for the specified data model. Permissible values
12347 are @samp{ilp32} for SysV-like data model where int, long int and pointer
12348 are 32-bit, and @samp{lp64} for SysV-like data model where int is 32-bit,
12349 but long int and pointer are 64-bit.
12351 The default depends on the specific target configuration. Note that
12352 the LP64 and ILP32 ABIs are not link-compatible; you must compile your
12353 entire program with the same ABI, and link with a compatible set of libraries.
12356 @opindex mbig-endian
12357 Generate big-endian code. This is the default when GCC is configured for an
12358 @samp{aarch64_be-*-*} target.
12360 @item -mgeneral-regs-only
12361 @opindex mgeneral-regs-only
12362 Generate code which uses only the general-purpose registers. This is equivalent
12363 to feature modifier @option{nofp} of @option{-march} or @option{-mcpu}, except
12364 that @option{-mgeneral-regs-only} takes precedence over any conflicting feature
12365 modifier regardless of sequence.
12367 @item -mlittle-endian
12368 @opindex mlittle-endian
12369 Generate little-endian code. This is the default when GCC is configured for an
12370 @samp{aarch64-*-*} but not an @samp{aarch64_be-*-*} target.
12372 @item -mcmodel=tiny
12373 @opindex mcmodel=tiny
12374 Generate code for the tiny code model. The program and its statically defined
12375 symbols must be within 1GB of each other. Pointers are 64 bits. Programs can
12376 be statically or dynamically linked. This model is not fully implemented and
12377 mostly treated as @samp{small}.
12379 @item -mcmodel=small
12380 @opindex mcmodel=small
12381 Generate code for the small code model. The program and its statically defined
12382 symbols must be within 4GB of each other. Pointers are 64 bits. Programs can
12383 be statically or dynamically linked. This is the default code model.
12385 @item -mcmodel=large
12386 @opindex mcmodel=large
12387 Generate code for the large code model. This makes no assumptions about
12388 addresses and sizes of sections. Pointers are 64 bits. Programs can be
12389 statically linked only.
12391 @item -mstrict-align
12392 @opindex mstrict-align
12393 Do not assume that unaligned memory references are handled by the system.
12395 @item -momit-leaf-frame-pointer
12396 @itemx -mno-omit-leaf-frame-pointer
12397 @opindex momit-leaf-frame-pointer
12398 @opindex mno-omit-leaf-frame-pointer
12399 Omit or keep the frame pointer in leaf functions. The former behaviour is the
12402 @item -mtls-dialect=desc
12403 @opindex mtls-dialect=desc
12404 Use TLS descriptors as the thread-local storage mechanism for dynamic accesses
12405 of TLS variables. This is the default.
12407 @item -mtls-dialect=traditional
12408 @opindex mtls-dialect=traditional
12409 Use traditional TLS as the thread-local storage mechanism for dynamic accesses
12412 @item -mfix-cortex-a53-835769
12413 @itemx -mno-fix-cortex-a53-835769
12414 @opindex mfix-cortex-a53-835769
12415 @opindex mno-fix-cortex-a53-835769
12416 Enable or disable the workaround for the ARM Cortex-A53 erratum number 835769.
12417 This involves inserting a NOP instruction between memory instructions and
12418 64-bit integer multiply-accumulate instructions.
12420 @item -mfix-cortex-a53-843419
12421 @itemx -mno-fix-cortex-a53-843419
12422 @opindex mfix-cortex-a53-843419
12423 @opindex mno-fix-cortex-a53-843419
12424 Enable or disable the workaround for the ARM Cortex-A53 erratum number 843419.
12425 This erratum workaround is made at link time and this will only pass the
12426 corresponding flag to the linker.
12428 @item -march=@var{name}
12430 Specify the name of the target architecture, optionally suffixed by one or
12431 more feature modifiers. This option has the form
12432 @option{-march=@var{arch}@r{@{}+@r{[}no@r{]}@var{feature}@r{@}*}}, where the
12433 permissible values for @var{arch} are @samp{armv8-a} or @samp{armv8.1-a}.
12434 The permissible values for @var{feature} are documented in the sub-section
12435 below. Additionally on native AArch64 GNU/Linux systems the value
12436 @samp{native} is available. This option causes the compiler to pick the
12437 architecture of the host system. If the compiler is unable to recognize the
12438 architecture of the host system this option has no effect.
12440 Where conflicting feature modifiers are specified, the right-most feature is
12443 GCC uses this name to determine what kind of instructions it can emit when
12444 generating assembly code.
12446 Where @option{-march} is specified without either of @option{-mtune}
12447 or @option{-mcpu} also being specified, the code is tuned to perform
12448 well across a range of target processors implementing the target
12451 @item -mtune=@var{name}
12453 Specify the name of the target processor for which GCC should tune the
12454 performance of the code. Permissible values for this option are:
12455 @samp{generic}, @samp{cortex-a53}, @samp{cortex-a57}, @samp{cortex-a72},
12456 @samp{exynos-m1}, @samp{thunderx}, @samp{xgene1}.
12458 Additionally, this option can specify that GCC should tune the performance
12459 of the code for a big.LITTLE system. Permissible values for this
12460 option are: @samp{cortex-a57.cortex-a53}, @samp{cortex-a72.cortex-a53}.
12462 Additionally on native AArch64 GNU/Linux systems the value @samp{native}
12464 This option causes the compiler to pick the architecture of and tune the
12465 performance of the code for the processor of the host system.
12466 If the compiler is unable to recognize the processor of the host system
12467 this option has no effect.
12469 Where none of @option{-mtune=}, @option{-mcpu=} or @option{-march=}
12470 are specified, the code is tuned to perform well across a range
12471 of target processors.
12473 This option cannot be suffixed by feature modifiers.
12475 @item -mcpu=@var{name}
12477 Specify the name of the target processor, optionally suffixed by one or more
12478 feature modifiers. This option has the form
12479 @option{-mcpu=@var{cpu}@r{@{}+@r{[}no@r{]}@var{feature}@r{@}*}}, where the
12480 permissible values for @var{cpu} are the same as those available for
12481 @option{-mtune}. Additionally on native AArch64 GNU/Linux systems the
12482 value @samp{native} is available.
12483 This option causes the compiler to tune the performance of the code for the
12484 processor of the host system. If the compiler is unable to recognize the
12485 processor of the host system this option has no effect.
12487 The permissible values for @var{feature} are documented in the sub-section
12490 Where conflicting feature modifiers are specified, the right-most feature is
12493 GCC uses this name to determine what kind of instructions it can emit when
12494 generating assembly code (as if by @option{-march}) and to determine
12495 the target processor for which to tune for performance (as if
12496 by @option{-mtune}). Where this option is used in conjunction
12497 with @option{-march} or @option{-mtune}, those options take precedence
12498 over the appropriate part of this option.
12501 @subsubsection @option{-march} and @option{-mcpu} Feature Modifiers
12502 @cindex @option{-march} feature modifiers
12503 @cindex @option{-mcpu} feature modifiers
12504 Feature modifiers used with @option{-march} and @option{-mcpu} can be any of
12505 the following and their inverses @option{no@var{feature}}:
12509 Enable CRC extension.
12511 Enable Crypto extension. This also enables Advanced SIMD and floating-point
12514 Enable floating-point instructions. This is on by default for all possible
12515 values for options @option{-march} and @option{-mcpu}.
12517 Enable Advanced SIMD instructions. This also enables floating-point
12518 instructions. This is on by default for all possible values for options
12519 @option{-march} and @option{-mcpu}.
12521 Enable Large System Extension instructions.
12523 Enable Privileged Access Never support.
12525 Enable Limited Ordering Regions support.
12527 Enable ARMv8.1 Advanced SIMD instructions.
12529 @item -moverride=@var{string}
12531 Override tuning decisions made by the back-end in response to a
12532 @option{-mtune=} switch. The syntax, semantics, and accepted values
12533 for @var{string} in this option are not guaranteed to be consistent
12536 This option is only intended to be useful when developing GCC.
12539 That is, @option{crypto} implies @option{simd} implies @option{fp}.
12540 Conversely, @option{nofp} (or equivalently, @option{-mgeneral-regs-only})
12541 implies @option{nosimd} implies @option{nocrypto}.
12543 @node Adapteva Epiphany Options
12544 @subsection Adapteva Epiphany Options
12546 These @samp{-m} options are defined for Adapteva Epiphany:
12549 @item -mhalf-reg-file
12550 @opindex mhalf-reg-file
12551 Don't allocate any register in the range @code{r32}@dots{}@code{r63}.
12552 That allows code to run on hardware variants that lack these registers.
12554 @item -mprefer-short-insn-regs
12555 @opindex mprefer-short-insn-regs
12556 Preferrentially allocate registers that allow short instruction generation.
12557 This can result in increased instruction count, so this may either reduce or
12558 increase overall code size.
12560 @item -mbranch-cost=@var{num}
12561 @opindex mbranch-cost
12562 Set the cost of branches to roughly @var{num} ``simple'' instructions.
12563 This cost is only a heuristic and is not guaranteed to produce
12564 consistent results across releases.
12568 Enable the generation of conditional moves.
12570 @item -mnops=@var{num}
12572 Emit @var{num} NOPs before every other generated instruction.
12574 @item -mno-soft-cmpsf
12575 @opindex mno-soft-cmpsf
12576 For single-precision floating-point comparisons, emit an @code{fsub} instruction
12577 and test the flags. This is faster than a software comparison, but can
12578 get incorrect results in the presence of NaNs, or when two different small
12579 numbers are compared such that their difference is calculated as zero.
12580 The default is @option{-msoft-cmpsf}, which uses slower, but IEEE-compliant,
12581 software comparisons.
12583 @item -mstack-offset=@var{num}
12584 @opindex mstack-offset
12585 Set the offset between the top of the stack and the stack pointer.
12586 E.g., a value of 8 means that the eight bytes in the range @code{sp+0@dots{}sp+7}
12587 can be used by leaf functions without stack allocation.
12588 Values other than @samp{8} or @samp{16} are untested and unlikely to work.
12589 Note also that this option changes the ABI; compiling a program with a
12590 different stack offset than the libraries have been compiled with
12591 generally does not work.
12592 This option can be useful if you want to evaluate if a different stack
12593 offset would give you better code, but to actually use a different stack
12594 offset to build working programs, it is recommended to configure the
12595 toolchain with the appropriate @option{--with-stack-offset=@var{num}} option.
12597 @item -mno-round-nearest
12598 @opindex mno-round-nearest
12599 Make the scheduler assume that the rounding mode has been set to
12600 truncating. The default is @option{-mround-nearest}.
12603 @opindex mlong-calls
12604 If not otherwise specified by an attribute, assume all calls might be beyond
12605 the offset range of the @code{b} / @code{bl} instructions, and therefore load the
12606 function address into a register before performing a (otherwise direct) call.
12607 This is the default.
12609 @item -mshort-calls
12610 @opindex short-calls
12611 If not otherwise specified by an attribute, assume all direct calls are
12612 in the range of the @code{b} / @code{bl} instructions, so use these instructions
12613 for direct calls. The default is @option{-mlong-calls}.
12617 Assume addresses can be loaded as 16-bit unsigned values. This does not
12618 apply to function addresses for which @option{-mlong-calls} semantics
12621 @item -mfp-mode=@var{mode}
12623 Set the prevailing mode of the floating-point unit.
12624 This determines the floating-point mode that is provided and expected
12625 at function call and return time. Making this mode match the mode you
12626 predominantly need at function start can make your programs smaller and
12627 faster by avoiding unnecessary mode switches.
12629 @var{mode} can be set to one the following values:
12633 Any mode at function entry is valid, and retained or restored when
12634 the function returns, and when it calls other functions.
12635 This mode is useful for compiling libraries or other compilation units
12636 you might want to incorporate into different programs with different
12637 prevailing FPU modes, and the convenience of being able to use a single
12638 object file outweighs the size and speed overhead for any extra
12639 mode switching that might be needed, compared with what would be needed
12640 with a more specific choice of prevailing FPU mode.
12643 This is the mode used for floating-point calculations with
12644 truncating (i.e.@: round towards zero) rounding mode. That includes
12645 conversion from floating point to integer.
12647 @item round-nearest
12648 This is the mode used for floating-point calculations with
12649 round-to-nearest-or-even rounding mode.
12652 This is the mode used to perform integer calculations in the FPU, e.g.@:
12653 integer multiply, or integer multiply-and-accumulate.
12656 The default is @option{-mfp-mode=caller}
12658 @item -mnosplit-lohi
12659 @itemx -mno-postinc
12660 @itemx -mno-postmodify
12661 @opindex mnosplit-lohi
12662 @opindex mno-postinc
12663 @opindex mno-postmodify
12664 Code generation tweaks that disable, respectively, splitting of 32-bit
12665 loads, generation of post-increment addresses, and generation of
12666 post-modify addresses. The defaults are @option{msplit-lohi},
12667 @option{-mpost-inc}, and @option{-mpost-modify}.
12669 @item -mnovect-double
12670 @opindex mno-vect-double
12671 Change the preferred SIMD mode to SImode. The default is
12672 @option{-mvect-double}, which uses DImode as preferred SIMD mode.
12674 @item -max-vect-align=@var{num}
12675 @opindex max-vect-align
12676 The maximum alignment for SIMD vector mode types.
12677 @var{num} may be 4 or 8. The default is 8.
12678 Note that this is an ABI change, even though many library function
12679 interfaces are unaffected if they don't use SIMD vector modes
12680 in places that affect size and/or alignment of relevant types.
12682 @item -msplit-vecmove-early
12683 @opindex msplit-vecmove-early
12684 Split vector moves into single word moves before reload. In theory this
12685 can give better register allocation, but so far the reverse seems to be
12686 generally the case.
12688 @item -m1reg-@var{reg}
12690 Specify a register to hold the constant @minus{}1, which makes loading small negative
12691 constants and certain bitmasks faster.
12692 Allowable values for @var{reg} are @samp{r43} and @samp{r63},
12693 which specify use of that register as a fixed register,
12694 and @samp{none}, which means that no register is used for this
12695 purpose. The default is @option{-m1reg-none}.
12700 @subsection ARC Options
12701 @cindex ARC options
12703 The following options control the architecture variant for which code
12706 @c architecture variants
12709 @item -mbarrel-shifter
12710 @opindex mbarrel-shifter
12711 Generate instructions supported by barrel shifter. This is the default
12712 unless @option{-mcpu=ARC601} is in effect.
12714 @item -mcpu=@var{cpu}
12716 Set architecture type, register usage, and instruction scheduling
12717 parameters for @var{cpu}. There are also shortcut alias options
12718 available for backward compatibility and convenience. Supported
12719 values for @var{cpu} are
12725 Compile for ARC600. Aliases: @option{-mA6}, @option{-mARC600}.
12729 Compile for ARC601. Alias: @option{-mARC601}.
12734 Compile for ARC700. Aliases: @option{-mA7}, @option{-mARC700}.
12735 This is the default when configured with @option{--with-cpu=arc700}@.
12740 @itemx -mdpfp-compact
12741 @opindex mdpfp-compact
12742 FPX: Generate Double Precision FPX instructions, tuned for the compact
12746 @opindex mdpfp-fast
12747 FPX: Generate Double Precision FPX instructions, tuned for the fast
12750 @item -mno-dpfp-lrsr
12751 @opindex mno-dpfp-lrsr
12752 Disable LR and SR instructions from using FPX extension aux registers.
12756 Generate Extended arithmetic instructions. Currently only
12757 @code{divaw}, @code{adds}, @code{subs}, and @code{sat16} are
12758 supported. This is always enabled for @option{-mcpu=ARC700}.
12762 Do not generate mpy instructions for ARC700.
12766 Generate 32x16 bit multiply and mac instructions.
12770 Generate mul64 and mulu64 instructions. Only valid for @option{-mcpu=ARC600}.
12774 Generate norm instruction. This is the default if @option{-mcpu=ARC700}
12779 @itemx -mspfp-compact
12780 @opindex mspfp-compact
12781 FPX: Generate Single Precision FPX instructions, tuned for the compact
12785 @opindex mspfp-fast
12786 FPX: Generate Single Precision FPX instructions, tuned for the fast
12791 Enable generation of ARC SIMD instructions via target-specific
12792 builtins. Only valid for @option{-mcpu=ARC700}.
12795 @opindex msoft-float
12796 This option ignored; it is provided for compatibility purposes only.
12797 Software floating point code is emitted by default, and this default
12798 can overridden by FPX options; @samp{mspfp}, @samp{mspfp-compact}, or
12799 @samp{mspfp-fast} for single precision, and @samp{mdpfp},
12800 @samp{mdpfp-compact}, or @samp{mdpfp-fast} for double precision.
12804 Generate swap instructions.
12808 The following options are passed through to the assembler, and also
12809 define preprocessor macro symbols.
12811 @c Flags used by the assembler, but for which we define preprocessor
12812 @c macro symbols as well.
12815 @opindex mdsp-packa
12816 Passed down to the assembler to enable the DSP Pack A extensions.
12817 Also sets the preprocessor symbol @code{__Xdsp_packa}.
12821 Passed down to the assembler to enable the dual viterbi butterfly
12822 extension. Also sets the preprocessor symbol @code{__Xdvbf}.
12824 @c ARC700 4.10 extension instruction
12827 Passed down to the assembler to enable the Locked Load/Store
12828 Conditional extension. Also sets the preprocessor symbol
12833 Passed down to the assembler. Also sets the preprocessor symbol
12834 @code{__Xxmac_d16}.
12838 Passed down to the assembler. Also sets the preprocessor symbol
12841 @c ARC700 4.10 extension instruction
12844 Passed down to the assembler to enable the 64-bit Time-Stamp Counter
12845 extension instruction. Also sets the preprocessor symbol
12848 @c ARC700 4.10 extension instruction
12851 Passed down to the assembler to enable the swap byte ordering
12852 extension instruction. Also sets the preprocessor symbol
12856 @opindex mtelephony
12857 Passed down to the assembler to enable dual and single operand
12858 instructions for telephony. Also sets the preprocessor symbol
12859 @code{__Xtelephony}.
12863 Passed down to the assembler to enable the XY Memory extension. Also
12864 sets the preprocessor symbol @code{__Xxy}.
12868 The following options control how the assembly code is annotated:
12870 @c Assembly annotation options
12874 Annotate assembler instructions with estimated addresses.
12876 @item -mannotate-align
12877 @opindex mannotate-align
12878 Explain what alignment considerations lead to the decision to make an
12879 instruction short or long.
12883 The following options are passed through to the linker:
12885 @c options passed through to the linker
12889 Passed through to the linker, to specify use of the @code{arclinux} emulation.
12890 This option is enabled by default in tool chains built for
12891 @w{@code{arc-linux-uclibc}} and @w{@code{arceb-linux-uclibc}} targets
12892 when profiling is not requested.
12894 @item -marclinux_prof
12895 @opindex marclinux_prof
12896 Passed through to the linker, to specify use of the
12897 @code{arclinux_prof} emulation. This option is enabled by default in
12898 tool chains built for @w{@code{arc-linux-uclibc}} and
12899 @w{@code{arceb-linux-uclibc}} targets when profiling is requested.
12903 The following options control the semantics of generated code:
12905 @c semantically relevant code generation options
12907 @item -mepilogue-cfi
12908 @opindex mepilogue-cfi
12909 Enable generation of call frame information for epilogues.
12911 @item -mno-epilogue-cfi
12912 @opindex mno-epilogue-cfi
12913 Disable generation of call frame information for epilogues.
12916 @opindex mlong-calls
12917 Generate call insns as register indirect calls, thus providing access
12918 to the full 32-bit address range.
12920 @item -mmedium-calls
12921 @opindex mmedium-calls
12922 Don't use less than 25 bit addressing range for calls, which is the
12923 offset available for an unconditional branch-and-link
12924 instruction. Conditional execution of function calls is suppressed, to
12925 allow use of the 25-bit range, rather than the 21-bit range with
12926 conditional branch-and-link. This is the default for tool chains built
12927 for @w{@code{arc-linux-uclibc}} and @w{@code{arceb-linux-uclibc}} targets.
12931 Do not generate sdata references. This is the default for tool chains
12932 built for @w{@code{arc-linux-uclibc}} and @w{@code{arceb-linux-uclibc}}
12936 @opindex mucb-mcount
12937 Instrument with mcount calls as used in UCB code. I.e. do the
12938 counting in the callee, not the caller. By default ARC instrumentation
12939 counts in the caller.
12941 @item -mvolatile-cache
12942 @opindex mvolatile-cache
12943 Use ordinarily cached memory accesses for volatile references. This is the
12946 @item -mno-volatile-cache
12947 @opindex mno-volatile-cache
12948 Enable cache bypass for volatile references.
12952 The following options fine tune code generation:
12953 @c code generation tuning options
12956 @opindex malign-call
12957 Do alignment optimizations for call instructions.
12959 @item -mauto-modify-reg
12960 @opindex mauto-modify-reg
12961 Enable the use of pre/post modify with register displacement.
12963 @item -mbbit-peephole
12964 @opindex mbbit-peephole
12965 Enable bbit peephole2.
12969 This option disables a target-specific pass in @file{arc_reorg} to
12970 generate @code{BRcc} instructions. It has no effect on @code{BRcc}
12971 generation driven by the combiner pass.
12973 @item -mcase-vector-pcrel
12974 @opindex mcase-vector-pcrel
12975 Use pc-relative switch case tables - this enables case table shortening.
12976 This is the default for @option{-Os}.
12978 @item -mcompact-casesi
12979 @opindex mcompact-casesi
12980 Enable compact casesi pattern.
12981 This is the default for @option{-Os}.
12983 @item -mno-cond-exec
12984 @opindex mno-cond-exec
12985 Disable ARCompact specific pass to generate conditional execution instructions.
12986 Due to delay slot scheduling and interactions between operand numbers,
12987 literal sizes, instruction lengths, and the support for conditional execution,
12988 the target-independent pass to generate conditional execution is often lacking,
12989 so the ARC port has kept a special pass around that tries to find more
12990 conditional execution generating opportunities after register allocation,
12991 branch shortening, and delay slot scheduling have been done. This pass
12992 generally, but not always, improves performance and code size, at the cost of
12993 extra compilation time, which is why there is an option to switch it off.
12994 If you have a problem with call instructions exceeding their allowable
12995 offset range because they are conditionalized, you should consider using
12996 @option{-mmedium-calls} instead.
12998 @item -mearly-cbranchsi
12999 @opindex mearly-cbranchsi
13000 Enable pre-reload use of the cbranchsi pattern.
13002 @item -mexpand-adddi
13003 @opindex mexpand-adddi
13004 Expand @code{adddi3} and @code{subdi3} at rtl generation time into
13005 @code{add.f}, @code{adc} etc.
13007 @item -mindexed-loads
13008 @opindex mindexed-loads
13009 Enable the use of indexed loads. This can be problematic because some
13010 optimizers then assume that indexed stores exist, which is not
13015 Enable Local Register Allocation. This is still experimental for ARC,
13016 so by default the compiler uses standard reload
13017 (i.e. @option{-mno-lra}).
13019 @item -mlra-priority-none
13020 @opindex mlra-priority-none
13021 Don't indicate any priority for target registers.
13023 @item -mlra-priority-compact
13024 @opindex mlra-priority-compact
13025 Indicate target register priority for r0..r3 / r12..r15.
13027 @item -mlra-priority-noncompact
13028 @opindex mlra-priority-noncompact
13029 Reduce target regsiter priority for r0..r3 / r12..r15.
13031 @item -mno-millicode
13032 @opindex mno-millicode
13033 When optimizing for size (using @option{-Os}), prologues and epilogues
13034 that have to save or restore a large number of registers are often
13035 shortened by using call to a special function in libgcc; this is
13036 referred to as a @emph{millicode} call. As these calls can pose
13037 performance issues, and/or cause linking issues when linking in a
13038 nonstandard way, this option is provided to turn off millicode call
13042 @opindex mmixed-code
13043 Tweak register allocation to help 16-bit instruction generation.
13044 This generally has the effect of decreasing the average instruction size
13045 while increasing the instruction count.
13049 Enable 'q' instruction alternatives.
13050 This is the default for @option{-Os}.
13054 Enable Rcq constraint handling - most short code generation depends on this.
13055 This is the default.
13059 Enable Rcw constraint handling - ccfsm condexec mostly depends on this.
13060 This is the default.
13062 @item -msize-level=@var{level}
13063 @opindex msize-level
13064 Fine-tune size optimization with regards to instruction lengths and alignment.
13065 The recognized values for @var{level} are:
13068 No size optimization. This level is deprecated and treated like @samp{1}.
13071 Short instructions are used opportunistically.
13074 In addition, alignment of loops and of code after barriers are dropped.
13077 In addition, optional data alignment is dropped, and the option @option{Os} is enabled.
13081 This defaults to @samp{3} when @option{-Os} is in effect. Otherwise,
13082 the behavior when this is not set is equivalent to level @samp{1}.
13084 @item -mtune=@var{cpu}
13086 Set instruction scheduling parameters for @var{cpu}, overriding any implied
13087 by @option{-mcpu=}.
13089 Supported values for @var{cpu} are
13093 Tune for ARC600 cpu.
13096 Tune for ARC601 cpu.
13099 Tune for ARC700 cpu with standard multiplier block.
13102 Tune for ARC700 cpu with XMAC block.
13105 Tune for ARC725D cpu.
13108 Tune for ARC750D cpu.
13112 @item -mmultcost=@var{num}
13114 Cost to assume for a multiply instruction, with @samp{4} being equal to a
13115 normal instruction.
13117 @item -munalign-prob-threshold=@var{probability}
13118 @opindex munalign-prob-threshold
13119 Set probability threshold for unaligning branches.
13120 When tuning for @samp{ARC700} and optimizing for speed, branches without
13121 filled delay slot are preferably emitted unaligned and long, unless
13122 profiling indicates that the probability for the branch to be taken
13123 is below @var{probability}. @xref{Cross-profiling}.
13124 The default is (REG_BR_PROB_BASE/2), i.e.@: 5000.
13128 The following options are maintained for backward compatibility, but
13129 are now deprecated and will be removed in a future release:
13131 @c Deprecated options
13139 @opindex mbig-endian
13142 Compile code for big endian targets. Use of these options is now
13143 deprecated. Users wanting big-endian code, should use the
13144 @w{@code{arceb-elf32}} and @w{@code{arceb-linux-uclibc}} targets when
13145 building the tool chain, for which big-endian is the default.
13147 @item -mlittle-endian
13148 @opindex mlittle-endian
13151 Compile code for little endian targets. Use of these options is now
13152 deprecated. Users wanting little-endian code should use the
13153 @w{@code{arc-elf32}} and @w{@code{arc-linux-uclibc}} targets when
13154 building the tool chain, for which little-endian is the default.
13156 @item -mbarrel_shifter
13157 @opindex mbarrel_shifter
13158 Replaced by @option{-mbarrel-shifter}.
13160 @item -mdpfp_compact
13161 @opindex mdpfp_compact
13162 Replaced by @option{-mdpfp-compact}.
13165 @opindex mdpfp_fast
13166 Replaced by @option{-mdpfp-fast}.
13169 @opindex mdsp_packa
13170 Replaced by @option{-mdsp-packa}.
13174 Replaced by @option{-mea}.
13178 Replaced by @option{-mmac-24}.
13182 Replaced by @option{-mmac-d16}.
13184 @item -mspfp_compact
13185 @opindex mspfp_compact
13186 Replaced by @option{-mspfp-compact}.
13189 @opindex mspfp_fast
13190 Replaced by @option{-mspfp-fast}.
13192 @item -mtune=@var{cpu}
13194 Values @samp{arc600}, @samp{arc601}, @samp{arc700} and
13195 @samp{arc700-xmac} for @var{cpu} are replaced by @samp{ARC600},
13196 @samp{ARC601}, @samp{ARC700} and @samp{ARC700-xmac} respectively
13198 @item -multcost=@var{num}
13200 Replaced by @option{-mmultcost}.
13205 @subsection ARM Options
13206 @cindex ARM options
13208 These @samp{-m} options are defined for the ARM port:
13211 @item -mabi=@var{name}
13213 Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu},
13214 @samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}.
13217 @opindex mapcs-frame
13218 Generate a stack frame that is compliant with the ARM Procedure Call
13219 Standard for all functions, even if this is not strictly necessary for
13220 correct execution of the code. Specifying @option{-fomit-frame-pointer}
13221 with this option causes the stack frames not to be generated for
13222 leaf functions. The default is @option{-mno-apcs-frame}.
13223 This option is deprecated.
13227 This is a synonym for @option{-mapcs-frame} and is deprecated.
13230 @c not currently implemented
13231 @item -mapcs-stack-check
13232 @opindex mapcs-stack-check
13233 Generate code to check the amount of stack space available upon entry to
13234 every function (that actually uses some stack space). If there is
13235 insufficient space available then either the function
13236 @code{__rt_stkovf_split_small} or @code{__rt_stkovf_split_big} is
13237 called, depending upon the amount of stack space required. The runtime
13238 system is required to provide these functions. The default is
13239 @option{-mno-apcs-stack-check}, since this produces smaller code.
13241 @c not currently implemented
13243 @opindex mapcs-float
13244 Pass floating-point arguments using the floating-point registers. This is
13245 one of the variants of the APCS@. This option is recommended if the
13246 target hardware has a floating-point unit or if a lot of floating-point
13247 arithmetic is going to be performed by the code. The default is
13248 @option{-mno-apcs-float}, since the size of integer-only code is
13249 slightly increased if @option{-mapcs-float} is used.
13251 @c not currently implemented
13252 @item -mapcs-reentrant
13253 @opindex mapcs-reentrant
13254 Generate reentrant, position-independent code. The default is
13255 @option{-mno-apcs-reentrant}.
13258 @item -mthumb-interwork
13259 @opindex mthumb-interwork
13260 Generate code that supports calling between the ARM and Thumb
13261 instruction sets. Without this option, on pre-v5 architectures, the
13262 two instruction sets cannot be reliably used inside one program. The
13263 default is @option{-mno-thumb-interwork}, since slightly larger code
13264 is generated when @option{-mthumb-interwork} is specified. In AAPCS
13265 configurations this option is meaningless.
13267 @item -mno-sched-prolog
13268 @opindex mno-sched-prolog
13269 Prevent the reordering of instructions in the function prologue, or the
13270 merging of those instruction with the instructions in the function's
13271 body. This means that all functions start with a recognizable set
13272 of instructions (or in fact one of a choice from a small set of
13273 different function prologues), and this information can be used to
13274 locate the start of functions inside an executable piece of code. The
13275 default is @option{-msched-prolog}.
13277 @item -mfloat-abi=@var{name}
13278 @opindex mfloat-abi
13279 Specifies which floating-point ABI to use. Permissible values
13280 are: @samp{soft}, @samp{softfp} and @samp{hard}.
13282 Specifying @samp{soft} causes GCC to generate output containing
13283 library calls for floating-point operations.
13284 @samp{softfp} allows the generation of code using hardware floating-point
13285 instructions, but still uses the soft-float calling conventions.
13286 @samp{hard} allows generation of floating-point instructions
13287 and uses FPU-specific calling conventions.
13289 The default depends on the specific target configuration. Note that
13290 the hard-float and soft-float ABIs are not link-compatible; you must
13291 compile your entire program with the same ABI, and link with a
13292 compatible set of libraries.
13294 @item -mlittle-endian
13295 @opindex mlittle-endian
13296 Generate code for a processor running in little-endian mode. This is
13297 the default for all standard configurations.
13300 @opindex mbig-endian
13301 Generate code for a processor running in big-endian mode; the default is
13302 to compile code for a little-endian processor.
13304 @item -march=@var{name}
13306 This specifies the name of the target ARM architecture. GCC uses this
13307 name to determine what kind of instructions it can emit when generating
13308 assembly code. This option can be used in conjunction with or instead
13309 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
13310 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
13311 @samp{armv5}, @samp{armv5t}, @samp{armv5e}, @samp{armv5te},
13312 @samp{armv6}, @samp{armv6j},
13313 @samp{armv6t2}, @samp{armv6z}, @samp{armv6zk}, @samp{armv6-m},
13314 @samp{armv7}, @samp{armv7-a}, @samp{armv7-r}, @samp{armv7-m}, @samp{armv7e-m},
13315 @samp{armv7ve}, @samp{armv8-a}, @samp{armv8-a+crc},
13316 @samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}.
13318 @option{-march=armv7ve} is the armv7-a architecture with virtualization
13321 @option{-march=armv8-a+crc} enables code generation for the ARMv8-A
13322 architecture together with the optional CRC32 extensions.
13324 @option{-march=native} causes the compiler to auto-detect the architecture
13325 of the build computer. At present, this feature is only supported on
13326 GNU/Linux, and not all architectures are recognized. If the auto-detect
13327 is unsuccessful the option has no effect.
13329 @item -mtune=@var{name}
13331 This option specifies the name of the target ARM processor for
13332 which GCC should tune the performance of the code.
13333 For some ARM implementations better performance can be obtained by using
13335 Permissible names are: @samp{arm2}, @samp{arm250},
13336 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
13337 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
13338 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
13339 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
13341 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s},
13342 @samp{arm710t}, @samp{arm720t}, @samp{arm740t},
13343 @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
13344 @samp{strongarm1110},
13345 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
13346 @samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s},
13347 @samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi},
13348 @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s},
13349 @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e},
13350 @samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp},
13351 @samp{arm1156t2-s}, @samp{arm1156t2f-s}, @samp{arm1176jz-s}, @samp{arm1176jzf-s},
13352 @samp{generic-armv7-a}, @samp{cortex-a5}, @samp{cortex-a7}, @samp{cortex-a8},
13353 @samp{cortex-a9}, @samp{cortex-a12}, @samp{cortex-a15}, @samp{cortex-a17},
13354 @samp{cortex-a53}, @samp{cortex-a57}, @samp{cortex-a72},
13356 @samp{cortex-r4f}, @samp{cortex-r5}, @samp{cortex-r7}, @samp{cortex-m7},
13361 @samp{cortex-m0plus},
13362 @samp{cortex-m1.small-multiply},
13363 @samp{cortex-m0.small-multiply},
13364 @samp{cortex-m0plus.small-multiply},
13366 @samp{marvell-pj4},
13367 @samp{xscale}, @samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312},
13368 @samp{fa526}, @samp{fa626},
13369 @samp{fa606te}, @samp{fa626te}, @samp{fmp626}, @samp{fa726te},
13372 Additionally, this option can specify that GCC should tune the performance
13373 of the code for a big.LITTLE system. Permissible names are:
13374 @samp{cortex-a15.cortex-a7}, @samp{cortex-a17.cortex-a7},
13375 @samp{cortex-a57.cortex-a53}, @samp{cortex-a72.cortex-a53}.
13377 @option{-mtune=generic-@var{arch}} specifies that GCC should tune the
13378 performance for a blend of processors within architecture @var{arch}.
13379 The aim is to generate code that run well on the current most popular
13380 processors, balancing between optimizations that benefit some CPUs in the
13381 range, and avoiding performance pitfalls of other CPUs. The effects of
13382 this option may change in future GCC versions as CPU models come and go.
13384 @option{-mtune=native} causes the compiler to auto-detect the CPU
13385 of the build computer. At present, this feature is only supported on
13386 GNU/Linux, and not all architectures are recognized. If the auto-detect is
13387 unsuccessful the option has no effect.
13389 @item -mcpu=@var{name}
13391 This specifies the name of the target ARM processor. GCC uses this name
13392 to derive the name of the target ARM architecture (as if specified
13393 by @option{-march}) and the ARM processor type for which to tune for
13394 performance (as if specified by @option{-mtune}). Where this option
13395 is used in conjunction with @option{-march} or @option{-mtune},
13396 those options take precedence over the appropriate part of this option.
13398 Permissible names for this option are the same as those for
13401 @option{-mcpu=generic-@var{arch}} is also permissible, and is
13402 equivalent to @option{-march=@var{arch} -mtune=generic-@var{arch}}.
13403 See @option{-mtune} for more information.
13405 @option{-mcpu=native} causes the compiler to auto-detect the CPU
13406 of the build computer. At present, this feature is only supported on
13407 GNU/Linux, and not all architectures are recognized. If the auto-detect
13408 is unsuccessful the option has no effect.
13410 @item -mfpu=@var{name}
13412 This specifies what floating-point hardware (or hardware emulation) is
13413 available on the target. Permissible names are: @samp{vfp}, @samp{vfpv3},
13414 @samp{vfpv3-fp16}, @samp{vfpv3-d16}, @samp{vfpv3-d16-fp16}, @samp{vfpv3xd},
13415 @samp{vfpv3xd-fp16}, @samp{neon}, @samp{neon-fp16}, @samp{vfpv4},
13416 @samp{vfpv4-d16}, @samp{fpv4-sp-d16}, @samp{neon-vfpv4},
13417 @samp{fpv5-d16}, @samp{fpv5-sp-d16},
13418 @samp{fp-armv8}, @samp{neon-fp-armv8}, and @samp{crypto-neon-fp-armv8}.
13420 If @option{-msoft-float} is specified this specifies the format of
13421 floating-point values.
13423 If the selected floating-point hardware includes the NEON extension
13424 (e.g. @option{-mfpu}=@samp{neon}), note that floating-point
13425 operations are not generated by GCC's auto-vectorization pass unless
13426 @option{-funsafe-math-optimizations} is also specified. This is
13427 because NEON hardware does not fully implement the IEEE 754 standard for
13428 floating-point arithmetic (in particular denormal values are treated as
13429 zero), so the use of NEON instructions may lead to a loss of precision.
13431 @item -mfp16-format=@var{name}
13432 @opindex mfp16-format
13433 Specify the format of the @code{__fp16} half-precision floating-point type.
13434 Permissible names are @samp{none}, @samp{ieee}, and @samp{alternative};
13435 the default is @samp{none}, in which case the @code{__fp16} type is not
13436 defined. @xref{Half-Precision}, for more information.
13438 @item -mstructure-size-boundary=@var{n}
13439 @opindex mstructure-size-boundary
13440 The sizes of all structures and unions are rounded up to a multiple
13441 of the number of bits set by this option. Permissible values are 8, 32
13442 and 64. The default value varies for different toolchains. For the COFF
13443 targeted toolchain the default value is 8. A value of 64 is only allowed
13444 if the underlying ABI supports it.
13446 Specifying a larger number can produce faster, more efficient code, but
13447 can also increase the size of the program. Different values are potentially
13448 incompatible. Code compiled with one value cannot necessarily expect to
13449 work with code or libraries compiled with another value, if they exchange
13450 information using structures or unions.
13452 @item -mabort-on-noreturn
13453 @opindex mabort-on-noreturn
13454 Generate a call to the function @code{abort} at the end of a
13455 @code{noreturn} function. It is executed if the function tries to
13459 @itemx -mno-long-calls
13460 @opindex mlong-calls
13461 @opindex mno-long-calls
13462 Tells the compiler to perform function calls by first loading the
13463 address of the function into a register and then performing a subroutine
13464 call on this register. This switch is needed if the target function
13465 lies outside of the 64-megabyte addressing range of the offset-based
13466 version of subroutine call instruction.
13468 Even if this switch is enabled, not all function calls are turned
13469 into long calls. The heuristic is that static functions, functions
13470 that have the @code{short_call} attribute, functions that are inside
13471 the scope of a @code{#pragma no_long_calls} directive, and functions whose
13472 definitions have already been compiled within the current compilation
13473 unit are not turned into long calls. The exceptions to this rule are
13474 that weak function definitions, functions with the @code{long_call}
13475 attribute or the @code{section} attribute, and functions that are within
13476 the scope of a @code{#pragma long_calls} directive are always
13477 turned into long calls.
13479 This feature is not enabled by default. Specifying
13480 @option{-mno-long-calls} restores the default behavior, as does
13481 placing the function calls within the scope of a @code{#pragma
13482 long_calls_off} directive. Note these switches have no effect on how
13483 the compiler generates code to handle function calls via function
13486 @item -msingle-pic-base
13487 @opindex msingle-pic-base
13488 Treat the register used for PIC addressing as read-only, rather than
13489 loading it in the prologue for each function. The runtime system is
13490 responsible for initializing this register with an appropriate value
13491 before execution begins.
13493 @item -mpic-register=@var{reg}
13494 @opindex mpic-register
13495 Specify the register to be used for PIC addressing.
13496 For standard PIC base case, the default is any suitable register
13497 determined by compiler. For single PIC base case, the default is
13498 @samp{R9} if target is EABI based or stack-checking is enabled,
13499 otherwise the default is @samp{R10}.
13501 @item -mpic-data-is-text-relative
13502 @opindex mpic-data-is-text-relative
13503 Assume that each data segments are relative to text segment at load time.
13504 Therefore, it permits addressing data using PC-relative operations.
13505 This option is on by default for targets other than VxWorks RTP.
13507 @item -mpoke-function-name
13508 @opindex mpoke-function-name
13509 Write the name of each function into the text section, directly
13510 preceding the function prologue. The generated code is similar to this:
13514 .ascii "arm_poke_function_name", 0
13517 .word 0xff000000 + (t1 - t0)
13518 arm_poke_function_name
13520 stmfd sp!, @{fp, ip, lr, pc@}
13524 When performing a stack backtrace, code can inspect the value of
13525 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
13526 location @code{pc - 12} and the top 8 bits are set, then we know that
13527 there is a function name embedded immediately preceding this location
13528 and has length @code{((pc[-3]) & 0xff000000)}.
13535 Select between generating code that executes in ARM and Thumb
13536 states. The default for most configurations is to generate code
13537 that executes in ARM state, but the default can be changed by
13538 configuring GCC with the @option{--with-mode=}@var{state}
13541 You can also override the ARM and Thumb mode for each function
13542 by using the @code{target("thumb")} and @code{target("arm")} function attributes
13543 (@pxref{ARM Function Attributes}) or pragmas (@pxref{Function Specific Option Pragmas}).
13546 @opindex mtpcs-frame
13547 Generate a stack frame that is compliant with the Thumb Procedure Call
13548 Standard for all non-leaf functions. (A leaf function is one that does
13549 not call any other functions.) The default is @option{-mno-tpcs-frame}.
13551 @item -mtpcs-leaf-frame
13552 @opindex mtpcs-leaf-frame
13553 Generate a stack frame that is compliant with the Thumb Procedure Call
13554 Standard for all leaf functions. (A leaf function is one that does
13555 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
13557 @item -mcallee-super-interworking
13558 @opindex mcallee-super-interworking
13559 Gives all externally visible functions in the file being compiled an ARM
13560 instruction set header which switches to Thumb mode before executing the
13561 rest of the function. This allows these functions to be called from
13562 non-interworking code. This option is not valid in AAPCS configurations
13563 because interworking is enabled by default.
13565 @item -mcaller-super-interworking
13566 @opindex mcaller-super-interworking
13567 Allows calls via function pointers (including virtual functions) to
13568 execute correctly regardless of whether the target code has been
13569 compiled for interworking or not. There is a small overhead in the cost
13570 of executing a function pointer if this option is enabled. This option
13571 is not valid in AAPCS configurations because interworking is enabled
13574 @item -mtp=@var{name}
13576 Specify the access model for the thread local storage pointer. The valid
13577 models are @samp{soft}, which generates calls to @code{__aeabi_read_tp},
13578 @samp{cp15}, which fetches the thread pointer from @code{cp15} directly
13579 (supported in the arm6k architecture), and @samp{auto}, which uses the
13580 best available method for the selected processor. The default setting is
13583 @item -mtls-dialect=@var{dialect}
13584 @opindex mtls-dialect
13585 Specify the dialect to use for accessing thread local storage. Two
13586 @var{dialect}s are supported---@samp{gnu} and @samp{gnu2}. The
13587 @samp{gnu} dialect selects the original GNU scheme for supporting
13588 local and global dynamic TLS models. The @samp{gnu2} dialect
13589 selects the GNU descriptor scheme, which provides better performance
13590 for shared libraries. The GNU descriptor scheme is compatible with
13591 the original scheme, but does require new assembler, linker and
13592 library support. Initial and local exec TLS models are unaffected by
13593 this option and always use the original scheme.
13595 @item -mword-relocations
13596 @opindex mword-relocations
13597 Only generate absolute relocations on word-sized values (i.e. R_ARM_ABS32).
13598 This is enabled by default on targets (uClinux, SymbianOS) where the runtime
13599 loader imposes this restriction, and when @option{-fpic} or @option{-fPIC}
13602 @item -mfix-cortex-m3-ldrd
13603 @opindex mfix-cortex-m3-ldrd
13604 Some Cortex-M3 cores can cause data corruption when @code{ldrd} instructions
13605 with overlapping destination and base registers are used. This option avoids
13606 generating these instructions. This option is enabled by default when
13607 @option{-mcpu=cortex-m3} is specified.
13609 @item -munaligned-access
13610 @itemx -mno-unaligned-access
13611 @opindex munaligned-access
13612 @opindex mno-unaligned-access
13613 Enables (or disables) reading and writing of 16- and 32- bit values
13614 from addresses that are not 16- or 32- bit aligned. By default
13615 unaligned access is disabled for all pre-ARMv6 and all ARMv6-M
13616 architectures, and enabled for all other architectures. If unaligned
13617 access is not enabled then words in packed data structures are
13618 accessed a byte at a time.
13620 The ARM attribute @code{Tag_CPU_unaligned_access} is set in the
13621 generated object file to either true or false, depending upon the
13622 setting of this option. If unaligned access is enabled then the
13623 preprocessor symbol @code{__ARM_FEATURE_UNALIGNED} is also
13626 @item -mneon-for-64bits
13627 @opindex mneon-for-64bits
13628 Enables using Neon to handle scalar 64-bits operations. This is
13629 disabled by default since the cost of moving data from core registers
13632 @item -mslow-flash-data
13633 @opindex mslow-flash-data
13634 Assume loading data from flash is slower than fetching instruction.
13635 Therefore literal load is minimized for better performance.
13636 This option is only supported when compiling for ARMv7 M-profile and
13639 @item -masm-syntax-unified
13640 @opindex masm-syntax-unified
13641 Assume inline assembler is using unified asm syntax. The default is
13642 currently off which implies divided syntax. Currently this option is
13643 available only for Thumb1 and has no effect on ARM state and Thumb2.
13644 However, this may change in future releases of GCC. Divided syntax
13645 should be considered deprecated.
13647 @item -mrestrict-it
13648 @opindex mrestrict-it
13649 Restricts generation of IT blocks to conform to the rules of ARMv8.
13650 IT blocks can only contain a single 16-bit instruction from a select
13651 set of instructions. This option is on by default for ARMv8 Thumb mode.
13653 @item -mprint-tune-info
13654 @opindex mprint-tune-info
13655 Print CPU tuning information as comment in assembler file. This is
13656 an option used only for regression testing of the compiler and not
13657 intended for ordinary use in compiling code. This option is disabled
13662 @subsection AVR Options
13663 @cindex AVR Options
13665 These options are defined for AVR implementations:
13668 @item -mmcu=@var{mcu}
13670 Specify Atmel AVR instruction set architectures (ISA) or MCU type.
13672 The default for this option is@tie{}@samp{avr2}.
13674 GCC supports the following AVR devices and ISAs:
13676 @include avr-mmcu.texi
13678 @item -maccumulate-args
13679 @opindex maccumulate-args
13680 Accumulate outgoing function arguments and acquire/release the needed
13681 stack space for outgoing function arguments once in function
13682 prologue/epilogue. Without this option, outgoing arguments are pushed
13683 before calling a function and popped afterwards.
13685 Popping the arguments after the function call can be expensive on
13686 AVR so that accumulating the stack space might lead to smaller
13687 executables because arguments need not to be removed from the
13688 stack after such a function call.
13690 This option can lead to reduced code size for functions that perform
13691 several calls to functions that get their arguments on the stack like
13692 calls to printf-like functions.
13694 @item -mbranch-cost=@var{cost}
13695 @opindex mbranch-cost
13696 Set the branch costs for conditional branch instructions to
13697 @var{cost}. Reasonable values for @var{cost} are small, non-negative
13698 integers. The default branch cost is 0.
13700 @item -mcall-prologues
13701 @opindex mcall-prologues
13702 Functions prologues/epilogues are expanded as calls to appropriate
13703 subroutines. Code size is smaller.
13707 Assume @code{int} to be 8-bit integer. This affects the sizes of all types: a
13708 @code{char} is 1 byte, an @code{int} is 1 byte, a @code{long} is 2 bytes,
13709 and @code{long long} is 4 bytes. Please note that this option does not
13710 conform to the C standards, but it results in smaller code
13713 @item -mn-flash=@var{num}
13715 Assume that the flash memory has a size of
13716 @var{num} times 64@tie{}KiB.
13718 @item -mno-interrupts
13719 @opindex mno-interrupts
13720 Generated code is not compatible with hardware interrupts.
13721 Code size is smaller.
13725 Try to replace @code{CALL} resp.@: @code{JMP} instruction by the shorter
13726 @code{RCALL} resp.@: @code{RJMP} instruction if applicable.
13727 Setting @option{-mrelax} just adds the @option{--mlink-relax} option to
13728 the assembler's command line and the @option{--relax} option to the
13729 linker's command line.
13731 Jump relaxing is performed by the linker because jump offsets are not
13732 known before code is located. Therefore, the assembler code generated by the
13733 compiler is the same, but the instructions in the executable may
13734 differ from instructions in the assembler code.
13736 Relaxing must be turned on if linker stubs are needed, see the
13737 section on @code{EIND} and linker stubs below.
13741 Assume that the device supports the Read-Modify-Write
13742 instructions @code{XCH}, @code{LAC}, @code{LAS} and @code{LAT}.
13746 Treat the stack pointer register as an 8-bit register,
13747 i.e.@: assume the high byte of the stack pointer is zero.
13748 In general, you don't need to set this option by hand.
13750 This option is used internally by the compiler to select and
13751 build multilibs for architectures @code{avr2} and @code{avr25}.
13752 These architectures mix devices with and without @code{SPH}.
13753 For any setting other than @option{-mmcu=avr2} or @option{-mmcu=avr25}
13754 the compiler driver adds or removes this option from the compiler
13755 proper's command line, because the compiler then knows if the device
13756 or architecture has an 8-bit stack pointer and thus no @code{SPH}
13761 Use address register @code{X} in a way proposed by the hardware. This means
13762 that @code{X} is only used in indirect, post-increment or
13763 pre-decrement addressing.
13765 Without this option, the @code{X} register may be used in the same way
13766 as @code{Y} or @code{Z} which then is emulated by additional
13768 For example, loading a value with @code{X+const} addressing with a
13769 small non-negative @code{const < 64} to a register @var{Rn} is
13773 adiw r26, const ; X += const
13774 ld @var{Rn}, X ; @var{Rn} = *X
13775 sbiw r26, const ; X -= const
13779 @opindex mtiny-stack
13780 Only change the lower 8@tie{}bits of the stack pointer.
13783 @opindex nodevicelib
13784 Don't link against AVR-LibC's device specific library @code{libdev.a}.
13786 @item -Waddr-space-convert
13787 @opindex Waddr-space-convert
13788 Warn about conversions between address spaces in the case where the
13789 resulting address space is not contained in the incoming address space.
13792 @subsubsection @code{EIND} and Devices with More Than 128 Ki Bytes of Flash
13793 @cindex @code{EIND}
13794 Pointers in the implementation are 16@tie{}bits wide.
13795 The address of a function or label is represented as word address so
13796 that indirect jumps and calls can target any code address in the
13797 range of 64@tie{}Ki words.
13799 In order to facilitate indirect jump on devices with more than 128@tie{}Ki
13800 bytes of program memory space, there is a special function register called
13801 @code{EIND} that serves as most significant part of the target address
13802 when @code{EICALL} or @code{EIJMP} instructions are used.
13804 Indirect jumps and calls on these devices are handled as follows by
13805 the compiler and are subject to some limitations:
13810 The compiler never sets @code{EIND}.
13813 The compiler uses @code{EIND} implicitely in @code{EICALL}/@code{EIJMP}
13814 instructions or might read @code{EIND} directly in order to emulate an
13815 indirect call/jump by means of a @code{RET} instruction.
13818 The compiler assumes that @code{EIND} never changes during the startup
13819 code or during the application. In particular, @code{EIND} is not
13820 saved/restored in function or interrupt service routine
13824 For indirect calls to functions and computed goto, the linker
13825 generates @emph{stubs}. Stubs are jump pads sometimes also called
13826 @emph{trampolines}. Thus, the indirect call/jump jumps to such a stub.
13827 The stub contains a direct jump to the desired address.
13830 Linker relaxation must be turned on so that the linker generates
13831 the stubs correctly in all situations. See the compiler option
13832 @option{-mrelax} and the linker option @option{--relax}.
13833 There are corner cases where the linker is supposed to generate stubs
13834 but aborts without relaxation and without a helpful error message.
13837 The default linker script is arranged for code with @code{EIND = 0}.
13838 If code is supposed to work for a setup with @code{EIND != 0}, a custom
13839 linker script has to be used in order to place the sections whose
13840 name start with @code{.trampolines} into the segment where @code{EIND}
13844 The startup code from libgcc never sets @code{EIND}.
13845 Notice that startup code is a blend of code from libgcc and AVR-LibC.
13846 For the impact of AVR-LibC on @code{EIND}, see the
13847 @w{@uref{http://nongnu.org/avr-libc/user-manual/,AVR-LibC user manual}}.
13850 It is legitimate for user-specific startup code to set up @code{EIND}
13851 early, for example by means of initialization code located in
13852 section @code{.init3}. Such code runs prior to general startup code
13853 that initializes RAM and calls constructors, but after the bit
13854 of startup code from AVR-LibC that sets @code{EIND} to the segment
13855 where the vector table is located.
13857 #include <avr/io.h>
13860 __attribute__((section(".init3"),naked,used,no_instrument_function))
13861 init3_set_eind (void)
13863 __asm volatile ("ldi r24,pm_hh8(__trampolines_start)\n\t"
13864 "out %i0,r24" :: "n" (&EIND) : "r24","memory");
13869 The @code{__trampolines_start} symbol is defined in the linker script.
13872 Stubs are generated automatically by the linker if
13873 the following two conditions are met:
13876 @item The address of a label is taken by means of the @code{gs} modifier
13877 (short for @emph{generate stubs}) like so:
13879 LDI r24, lo8(gs(@var{func}))
13880 LDI r25, hi8(gs(@var{func}))
13882 @item The final location of that label is in a code segment
13883 @emph{outside} the segment where the stubs are located.
13887 The compiler emits such @code{gs} modifiers for code labels in the
13888 following situations:
13890 @item Taking address of a function or code label.
13891 @item Computed goto.
13892 @item If prologue-save function is used, see @option{-mcall-prologues}
13893 command-line option.
13894 @item Switch/case dispatch tables. If you do not want such dispatch
13895 tables you can specify the @option{-fno-jump-tables} command-line option.
13896 @item C and C++ constructors/destructors called during startup/shutdown.
13897 @item If the tools hit a @code{gs()} modifier explained above.
13901 Jumping to non-symbolic addresses like so is @emph{not} supported:
13906 /* Call function at word address 0x2 */
13907 return ((int(*)(void)) 0x2)();
13911 Instead, a stub has to be set up, i.e.@: the function has to be called
13912 through a symbol (@code{func_4} in the example):
13917 extern int func_4 (void);
13919 /* Call function at byte address 0x4 */
13924 and the application be linked with @option{-Wl,--defsym,func_4=0x4}.
13925 Alternatively, @code{func_4} can be defined in the linker script.
13928 @subsubsection Handling of the @code{RAMPD}, @code{RAMPX}, @code{RAMPY} and @code{RAMPZ} Special Function Registers
13929 @cindex @code{RAMPD}
13930 @cindex @code{RAMPX}
13931 @cindex @code{RAMPY}
13932 @cindex @code{RAMPZ}
13933 Some AVR devices support memories larger than the 64@tie{}KiB range
13934 that can be accessed with 16-bit pointers. To access memory locations
13935 outside this 64@tie{}KiB range, the contentent of a @code{RAMP}
13936 register is used as high part of the address:
13937 The @code{X}, @code{Y}, @code{Z} address register is concatenated
13938 with the @code{RAMPX}, @code{RAMPY}, @code{RAMPZ} special function
13939 register, respectively, to get a wide address. Similarly,
13940 @code{RAMPD} is used together with direct addressing.
13944 The startup code initializes the @code{RAMP} special function
13945 registers with zero.
13948 If a @ref{AVR Named Address Spaces,named address space} other than
13949 generic or @code{__flash} is used, then @code{RAMPZ} is set
13950 as needed before the operation.
13953 If the device supports RAM larger than 64@tie{}KiB and the compiler
13954 needs to change @code{RAMPZ} to accomplish an operation, @code{RAMPZ}
13955 is reset to zero after the operation.
13958 If the device comes with a specific @code{RAMP} register, the ISR
13959 prologue/epilogue saves/restores that SFR and initializes it with
13960 zero in case the ISR code might (implicitly) use it.
13963 RAM larger than 64@tie{}KiB is not supported by GCC for AVR targets.
13964 If you use inline assembler to read from locations outside the
13965 16-bit address range and change one of the @code{RAMP} registers,
13966 you must reset it to zero after the access.
13970 @subsubsection AVR Built-in Macros
13972 GCC defines several built-in macros so that the user code can test
13973 for the presence or absence of features. Almost any of the following
13974 built-in macros are deduced from device capabilities and thus
13975 triggered by the @option{-mmcu=} command-line option.
13977 For even more AVR-specific built-in macros see
13978 @ref{AVR Named Address Spaces} and @ref{AVR Built-in Functions}.
13983 Build-in macro that resolves to a decimal number that identifies the
13984 architecture and depends on the @option{-mmcu=@var{mcu}} option.
13985 Possible values are:
13987 @code{2}, @code{25}, @code{3}, @code{31}, @code{35},
13988 @code{4}, @code{5}, @code{51}, @code{6}
13990 for @var{mcu}=@code{avr2}, @code{avr25}, @code{avr3}, @code{avr31},
13991 @code{avr35}, @code{avr4}, @code{avr5}, @code{avr51}, @code{avr6},
13995 @code{100}, @code{102}, @code{104},
13996 @code{105}, @code{106}, @code{107}
13998 for @var{mcu}=@code{avrtiny}, @code{avrxmega2}, @code{avrxmega4},
13999 @code{avrxmega5}, @code{avrxmega6}, @code{avrxmega7}, respectively.
14000 If @var{mcu} specifies a device, this built-in macro is set
14001 accordingly. For example, with @option{-mmcu=atmega8} the macro is
14002 defined to @code{4}.
14004 @item __AVR_@var{Device}__
14005 Setting @option{-mmcu=@var{device}} defines this built-in macro which reflects
14006 the device's name. For example, @option{-mmcu=atmega8} defines the
14007 built-in macro @code{__AVR_ATmega8__}, @option{-mmcu=attiny261a} defines
14008 @code{__AVR_ATtiny261A__}, etc.
14010 The built-in macros' names follow
14011 the scheme @code{__AVR_@var{Device}__} where @var{Device} is
14012 the device name as from the AVR user manual. The difference between
14013 @var{Device} in the built-in macro and @var{device} in
14014 @option{-mmcu=@var{device}} is that the latter is always lowercase.
14016 If @var{device} is not a device but only a core architecture like
14017 @samp{avr51}, this macro is not defined.
14019 @item __AVR_DEVICE_NAME__
14020 Setting @option{-mmcu=@var{device}} defines this built-in macro to
14021 the device's name. For example, with @option{-mmcu=atmega8} the macro
14022 is defined to @code{atmega8}.
14024 If @var{device} is not a device but only a core architecture like
14025 @samp{avr51}, this macro is not defined.
14027 @item __AVR_XMEGA__
14028 The device / architecture belongs to the XMEGA family of devices.
14030 @item __AVR_HAVE_ELPM__
14031 The device has the the @code{ELPM} instruction.
14033 @item __AVR_HAVE_ELPMX__
14034 The device has the @code{ELPM R@var{n},Z} and @code{ELPM
14035 R@var{n},Z+} instructions.
14037 @item __AVR_HAVE_MOVW__
14038 The device has the @code{MOVW} instruction to perform 16-bit
14039 register-register moves.
14041 @item __AVR_HAVE_LPMX__
14042 The device has the @code{LPM R@var{n},Z} and
14043 @code{LPM R@var{n},Z+} instructions.
14045 @item __AVR_HAVE_MUL__
14046 The device has a hardware multiplier.
14048 @item __AVR_HAVE_JMP_CALL__
14049 The device has the @code{JMP} and @code{CALL} instructions.
14050 This is the case for devices with at least 16@tie{}KiB of program
14053 @item __AVR_HAVE_EIJMP_EICALL__
14054 @itemx __AVR_3_BYTE_PC__
14055 The device has the @code{EIJMP} and @code{EICALL} instructions.
14056 This is the case for devices with more than 128@tie{}KiB of program memory.
14057 This also means that the program counter
14058 (PC) is 3@tie{}bytes wide.
14060 @item __AVR_2_BYTE_PC__
14061 The program counter (PC) is 2@tie{}bytes wide. This is the case for devices
14062 with up to 128@tie{}KiB of program memory.
14064 @item __AVR_HAVE_8BIT_SP__
14065 @itemx __AVR_HAVE_16BIT_SP__
14066 The stack pointer (SP) register is treated as 8-bit respectively
14067 16-bit register by the compiler.
14068 The definition of these macros is affected by @option{-mtiny-stack}.
14070 @item __AVR_HAVE_SPH__
14072 The device has the SPH (high part of stack pointer) special function
14073 register or has an 8-bit stack pointer, respectively.
14074 The definition of these macros is affected by @option{-mmcu=} and
14075 in the cases of @option{-mmcu=avr2} and @option{-mmcu=avr25} also
14078 @item __AVR_HAVE_RAMPD__
14079 @itemx __AVR_HAVE_RAMPX__
14080 @itemx __AVR_HAVE_RAMPY__
14081 @itemx __AVR_HAVE_RAMPZ__
14082 The device has the @code{RAMPD}, @code{RAMPX}, @code{RAMPY},
14083 @code{RAMPZ} special function register, respectively.
14085 @item __NO_INTERRUPTS__
14086 This macro reflects the @option{-mno-interrupts} command-line option.
14088 @item __AVR_ERRATA_SKIP__
14089 @itemx __AVR_ERRATA_SKIP_JMP_CALL__
14090 Some AVR devices (AT90S8515, ATmega103) must not skip 32-bit
14091 instructions because of a hardware erratum. Skip instructions are
14092 @code{SBRS}, @code{SBRC}, @code{SBIS}, @code{SBIC} and @code{CPSE}.
14093 The second macro is only defined if @code{__AVR_HAVE_JMP_CALL__} is also
14096 @item __AVR_ISA_RMW__
14097 The device has Read-Modify-Write instructions (XCH, LAC, LAS and LAT).
14099 @item __AVR_SFR_OFFSET__=@var{offset}
14100 Instructions that can address I/O special function registers directly
14101 like @code{IN}, @code{OUT}, @code{SBI}, etc.@: may use a different
14102 address as if addressed by an instruction to access RAM like @code{LD}
14103 or @code{STS}. This offset depends on the device architecture and has
14104 to be subtracted from the RAM address in order to get the
14105 respective I/O@tie{}address.
14107 @item __WITH_AVRLIBC__
14108 The compiler is configured to be used together with AVR-Libc.
14109 See the @option{--with-avrlibc} configure option.
14113 @node Blackfin Options
14114 @subsection Blackfin Options
14115 @cindex Blackfin Options
14118 @item -mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]}
14120 Specifies the name of the target Blackfin processor. Currently, @var{cpu}
14121 can be one of @samp{bf512}, @samp{bf514}, @samp{bf516}, @samp{bf518},
14122 @samp{bf522}, @samp{bf523}, @samp{bf524}, @samp{bf525}, @samp{bf526},
14123 @samp{bf527}, @samp{bf531}, @samp{bf532}, @samp{bf533},
14124 @samp{bf534}, @samp{bf536}, @samp{bf537}, @samp{bf538}, @samp{bf539},
14125 @samp{bf542}, @samp{bf544}, @samp{bf547}, @samp{bf548}, @samp{bf549},
14126 @samp{bf542m}, @samp{bf544m}, @samp{bf547m}, @samp{bf548m}, @samp{bf549m},
14127 @samp{bf561}, @samp{bf592}.
14129 The optional @var{sirevision} specifies the silicon revision of the target
14130 Blackfin processor. Any workarounds available for the targeted silicon revision
14131 are enabled. If @var{sirevision} is @samp{none}, no workarounds are enabled.
14132 If @var{sirevision} is @samp{any}, all workarounds for the targeted processor
14133 are enabled. The @code{__SILICON_REVISION__} macro is defined to two
14134 hexadecimal digits representing the major and minor numbers in the silicon
14135 revision. If @var{sirevision} is @samp{none}, the @code{__SILICON_REVISION__}
14136 is not defined. If @var{sirevision} is @samp{any}, the
14137 @code{__SILICON_REVISION__} is defined to be @code{0xffff}.
14138 If this optional @var{sirevision} is not used, GCC assumes the latest known
14139 silicon revision of the targeted Blackfin processor.
14141 GCC defines a preprocessor macro for the specified @var{cpu}.
14142 For the @samp{bfin-elf} toolchain, this option causes the hardware BSP
14143 provided by libgloss to be linked in if @option{-msim} is not given.
14145 Without this option, @samp{bf532} is used as the processor by default.
14147 Note that support for @samp{bf561} is incomplete. For @samp{bf561},
14148 only the preprocessor macro is defined.
14152 Specifies that the program will be run on the simulator. This causes
14153 the simulator BSP provided by libgloss to be linked in. This option
14154 has effect only for @samp{bfin-elf} toolchain.
14155 Certain other options, such as @option{-mid-shared-library} and
14156 @option{-mfdpic}, imply @option{-msim}.
14158 @item -momit-leaf-frame-pointer
14159 @opindex momit-leaf-frame-pointer
14160 Don't keep the frame pointer in a register for leaf functions. This
14161 avoids the instructions to save, set up and restore frame pointers and
14162 makes an extra register available in leaf functions. The option
14163 @option{-fomit-frame-pointer} removes the frame pointer for all functions,
14164 which might make debugging harder.
14166 @item -mspecld-anomaly
14167 @opindex mspecld-anomaly
14168 When enabled, the compiler ensures that the generated code does not
14169 contain speculative loads after jump instructions. If this option is used,
14170 @code{__WORKAROUND_SPECULATIVE_LOADS} is defined.
14172 @item -mno-specld-anomaly
14173 @opindex mno-specld-anomaly
14174 Don't generate extra code to prevent speculative loads from occurring.
14176 @item -mcsync-anomaly
14177 @opindex mcsync-anomaly
14178 When enabled, the compiler ensures that the generated code does not
14179 contain CSYNC or SSYNC instructions too soon after conditional branches.
14180 If this option is used, @code{__WORKAROUND_SPECULATIVE_SYNCS} is defined.
14182 @item -mno-csync-anomaly
14183 @opindex mno-csync-anomaly
14184 Don't generate extra code to prevent CSYNC or SSYNC instructions from
14185 occurring too soon after a conditional branch.
14189 When enabled, the compiler is free to take advantage of the knowledge that
14190 the entire program fits into the low 64k of memory.
14193 @opindex mno-low-64k
14194 Assume that the program is arbitrarily large. This is the default.
14196 @item -mstack-check-l1
14197 @opindex mstack-check-l1
14198 Do stack checking using information placed into L1 scratchpad memory by the
14201 @item -mid-shared-library
14202 @opindex mid-shared-library
14203 Generate code that supports shared libraries via the library ID method.
14204 This allows for execute in place and shared libraries in an environment
14205 without virtual memory management. This option implies @option{-fPIC}.
14206 With a @samp{bfin-elf} target, this option implies @option{-msim}.
14208 @item -mno-id-shared-library
14209 @opindex mno-id-shared-library
14210 Generate code that doesn't assume ID-based shared libraries are being used.
14211 This is the default.
14213 @item -mleaf-id-shared-library
14214 @opindex mleaf-id-shared-library
14215 Generate code that supports shared libraries via the library ID method,
14216 but assumes that this library or executable won't link against any other
14217 ID shared libraries. That allows the compiler to use faster code for jumps
14220 @item -mno-leaf-id-shared-library
14221 @opindex mno-leaf-id-shared-library
14222 Do not assume that the code being compiled won't link against any ID shared
14223 libraries. Slower code is generated for jump and call insns.
14225 @item -mshared-library-id=n
14226 @opindex mshared-library-id
14227 Specifies the identification number of the ID-based shared library being
14228 compiled. Specifying a value of 0 generates more compact code; specifying
14229 other values forces the allocation of that number to the current
14230 library but is no more space- or time-efficient than omitting this option.
14234 Generate code that allows the data segment to be located in a different
14235 area of memory from the text segment. This allows for execute in place in
14236 an environment without virtual memory management by eliminating relocations
14237 against the text section.
14239 @item -mno-sep-data
14240 @opindex mno-sep-data
14241 Generate code that assumes that the data segment follows the text segment.
14242 This is the default.
14245 @itemx -mno-long-calls
14246 @opindex mlong-calls
14247 @opindex mno-long-calls
14248 Tells the compiler to perform function calls by first loading the
14249 address of the function into a register and then performing a subroutine
14250 call on this register. This switch is needed if the target function
14251 lies outside of the 24-bit addressing range of the offset-based
14252 version of subroutine call instruction.
14254 This feature is not enabled by default. Specifying
14255 @option{-mno-long-calls} restores the default behavior. Note these
14256 switches have no effect on how the compiler generates code to handle
14257 function calls via function pointers.
14261 Link with the fast floating-point library. This library relaxes some of
14262 the IEEE floating-point standard's rules for checking inputs against
14263 Not-a-Number (NAN), in the interest of performance.
14266 @opindex minline-plt
14267 Enable inlining of PLT entries in function calls to functions that are
14268 not known to bind locally. It has no effect without @option{-mfdpic}.
14271 @opindex mmulticore
14272 Build a standalone application for multicore Blackfin processors.
14273 This option causes proper start files and link scripts supporting
14274 multicore to be used, and defines the macro @code{__BFIN_MULTICORE}.
14275 It can only be used with @option{-mcpu=bf561@r{[}-@var{sirevision}@r{]}}.
14277 This option can be used with @option{-mcorea} or @option{-mcoreb}, which
14278 selects the one-application-per-core programming model. Without
14279 @option{-mcorea} or @option{-mcoreb}, the single-application/dual-core
14280 programming model is used. In this model, the main function of Core B
14281 should be named as @code{coreb_main}.
14283 If this option is not used, the single-core application programming
14288 Build a standalone application for Core A of BF561 when using
14289 the one-application-per-core programming model. Proper start files
14290 and link scripts are used to support Core A, and the macro
14291 @code{__BFIN_COREA} is defined.
14292 This option can only be used in conjunction with @option{-mmulticore}.
14296 Build a standalone application for Core B of BF561 when using
14297 the one-application-per-core programming model. Proper start files
14298 and link scripts are used to support Core B, and the macro
14299 @code{__BFIN_COREB} is defined. When this option is used, @code{coreb_main}
14300 should be used instead of @code{main}.
14301 This option can only be used in conjunction with @option{-mmulticore}.
14305 Build a standalone application for SDRAM. Proper start files and
14306 link scripts are used to put the application into SDRAM, and the macro
14307 @code{__BFIN_SDRAM} is defined.
14308 The loader should initialize SDRAM before loading the application.
14312 Assume that ICPLBs are enabled at run time. This has an effect on certain
14313 anomaly workarounds. For Linux targets, the default is to assume ICPLBs
14314 are enabled; for standalone applications the default is off.
14318 @subsection C6X Options
14319 @cindex C6X Options
14322 @item -march=@var{name}
14324 This specifies the name of the target architecture. GCC uses this
14325 name to determine what kind of instructions it can emit when generating
14326 assembly code. Permissible names are: @samp{c62x},
14327 @samp{c64x}, @samp{c64x+}, @samp{c67x}, @samp{c67x+}, @samp{c674x}.
14330 @opindex mbig-endian
14331 Generate code for a big-endian target.
14333 @item -mlittle-endian
14334 @opindex mlittle-endian
14335 Generate code for a little-endian target. This is the default.
14339 Choose startup files and linker script suitable for the simulator.
14341 @item -msdata=default
14342 @opindex msdata=default
14343 Put small global and static data in the @code{.neardata} section,
14344 which is pointed to by register @code{B14}. Put small uninitialized
14345 global and static data in the @code{.bss} section, which is adjacent
14346 to the @code{.neardata} section. Put small read-only data into the
14347 @code{.rodata} section. The corresponding sections used for large
14348 pieces of data are @code{.fardata}, @code{.far} and @code{.const}.
14351 @opindex msdata=all
14352 Put all data, not just small objects, into the sections reserved for
14353 small data, and use addressing relative to the @code{B14} register to
14357 @opindex msdata=none
14358 Make no use of the sections reserved for small data, and use absolute
14359 addresses to access all data. Put all initialized global and static
14360 data in the @code{.fardata} section, and all uninitialized data in the
14361 @code{.far} section. Put all constant data into the @code{.const}
14366 @subsection CRIS Options
14367 @cindex CRIS Options
14369 These options are defined specifically for the CRIS ports.
14372 @item -march=@var{architecture-type}
14373 @itemx -mcpu=@var{architecture-type}
14376 Generate code for the specified architecture. The choices for
14377 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
14378 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@.
14379 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
14382 @item -mtune=@var{architecture-type}
14384 Tune to @var{architecture-type} everything applicable about the generated
14385 code, except for the ABI and the set of available instructions. The
14386 choices for @var{architecture-type} are the same as for
14387 @option{-march=@var{architecture-type}}.
14389 @item -mmax-stack-frame=@var{n}
14390 @opindex mmax-stack-frame
14391 Warn when the stack frame of a function exceeds @var{n} bytes.
14397 The options @option{-metrax4} and @option{-metrax100} are synonyms for
14398 @option{-march=v3} and @option{-march=v8} respectively.
14400 @item -mmul-bug-workaround
14401 @itemx -mno-mul-bug-workaround
14402 @opindex mmul-bug-workaround
14403 @opindex mno-mul-bug-workaround
14404 Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
14405 models where it applies. This option is active by default.
14409 Enable CRIS-specific verbose debug-related information in the assembly
14410 code. This option also has the effect of turning off the @samp{#NO_APP}
14411 formatted-code indicator to the assembler at the beginning of the
14416 Do not use condition-code results from previous instruction; always emit
14417 compare and test instructions before use of condition codes.
14419 @item -mno-side-effects
14420 @opindex mno-side-effects
14421 Do not emit instructions with side effects in addressing modes other than
14424 @item -mstack-align
14425 @itemx -mno-stack-align
14426 @itemx -mdata-align
14427 @itemx -mno-data-align
14428 @itemx -mconst-align
14429 @itemx -mno-const-align
14430 @opindex mstack-align
14431 @opindex mno-stack-align
14432 @opindex mdata-align
14433 @opindex mno-data-align
14434 @opindex mconst-align
14435 @opindex mno-const-align
14436 These options (@samp{no-} options) arrange (eliminate arrangements) for the
14437 stack frame, individual data and constants to be aligned for the maximum
14438 single data access size for the chosen CPU model. The default is to
14439 arrange for 32-bit alignment. ABI details such as structure layout are
14440 not affected by these options.
14448 Similar to the stack- data- and const-align options above, these options
14449 arrange for stack frame, writable data and constants to all be 32-bit,
14450 16-bit or 8-bit aligned. The default is 32-bit alignment.
14452 @item -mno-prologue-epilogue
14453 @itemx -mprologue-epilogue
14454 @opindex mno-prologue-epilogue
14455 @opindex mprologue-epilogue
14456 With @option{-mno-prologue-epilogue}, the normal function prologue and
14457 epilogue which set up the stack frame are omitted and no return
14458 instructions or return sequences are generated in the code. Use this
14459 option only together with visual inspection of the compiled code: no
14460 warnings or errors are generated when call-saved registers must be saved,
14461 or storage for local variables needs to be allocated.
14465 @opindex mno-gotplt
14467 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
14468 instruction sequences that load addresses for functions from the PLT part
14469 of the GOT rather than (traditional on other architectures) calls to the
14470 PLT@. The default is @option{-mgotplt}.
14474 Legacy no-op option only recognized with the cris-axis-elf and
14475 cris-axis-linux-gnu targets.
14479 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
14483 This option, recognized for the cris-axis-elf, arranges
14484 to link with input-output functions from a simulator library. Code,
14485 initialized data and zero-initialized data are allocated consecutively.
14489 Like @option{-sim}, but pass linker options to locate initialized data at
14490 0x40000000 and zero-initialized data at 0x80000000.
14494 @subsection CR16 Options
14495 @cindex CR16 Options
14497 These options are defined specifically for the CR16 ports.
14503 Enable the use of multiply-accumulate instructions. Disabled by default.
14507 @opindex mcr16cplus
14509 Generate code for CR16C or CR16C+ architecture. CR16C+ architecture
14514 Links the library libsim.a which is in compatible with simulator. Applicable
14515 to ELF compiler only.
14519 Choose integer type as 32-bit wide.
14523 Generates @code{sbit}/@code{cbit} instructions for bit manipulations.
14525 @item -mdata-model=@var{model}
14526 @opindex mdata-model
14527 Choose a data model. The choices for @var{model} are @samp{near},
14528 @samp{far} or @samp{medium}. @samp{medium} is default.
14529 However, @samp{far} is not valid with @option{-mcr16c}, as the
14530 CR16C architecture does not support the far data model.
14533 @node Darwin Options
14534 @subsection Darwin Options
14535 @cindex Darwin options
14537 These options are defined for all architectures running the Darwin operating
14540 FSF GCC on Darwin does not create ``fat'' object files; it creates
14541 an object file for the single architecture that GCC was built to
14542 target. Apple's GCC on Darwin does create ``fat'' files if multiple
14543 @option{-arch} options are used; it does so by running the compiler or
14544 linker multiple times and joining the results together with
14547 The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or
14548 @samp{i686}) is determined by the flags that specify the ISA
14549 that GCC is targeting, like @option{-mcpu} or @option{-march}. The
14550 @option{-force_cpusubtype_ALL} option can be used to override this.
14552 The Darwin tools vary in their behavior when presented with an ISA
14553 mismatch. The assembler, @file{as}, only permits instructions to
14554 be used that are valid for the subtype of the file it is generating,
14555 so you cannot put 64-bit instructions in a @samp{ppc750} object file.
14556 The linker for shared libraries, @file{/usr/bin/libtool}, fails
14557 and prints an error if asked to create a shared library with a less
14558 restrictive subtype than its input files (for instance, trying to put
14559 a @samp{ppc970} object file in a @samp{ppc7400} library). The linker
14560 for executables, @command{ld}, quietly gives the executable the most
14561 restrictive subtype of any of its input files.
14566 Add the framework directory @var{dir} to the head of the list of
14567 directories to be searched for header files. These directories are
14568 interleaved with those specified by @option{-I} options and are
14569 scanned in a left-to-right order.
14571 A framework directory is a directory with frameworks in it. A
14572 framework is a directory with a @file{Headers} and/or
14573 @file{PrivateHeaders} directory contained directly in it that ends
14574 in @file{.framework}. The name of a framework is the name of this
14575 directory excluding the @file{.framework}. Headers associated with
14576 the framework are found in one of those two directories, with
14577 @file{Headers} being searched first. A subframework is a framework
14578 directory that is in a framework's @file{Frameworks} directory.
14579 Includes of subframework headers can only appear in a header of a
14580 framework that contains the subframework, or in a sibling subframework
14581 header. Two subframeworks are siblings if they occur in the same
14582 framework. A subframework should not have the same name as a
14583 framework; a warning is issued if this is violated. Currently a
14584 subframework cannot have subframeworks; in the future, the mechanism
14585 may be extended to support this. The standard frameworks can be found
14586 in @file{/System/Library/Frameworks} and
14587 @file{/Library/Frameworks}. An example include looks like
14588 @code{#include <Framework/header.h>}, where @file{Framework} denotes
14589 the name of the framework and @file{header.h} is found in the
14590 @file{PrivateHeaders} or @file{Headers} directory.
14592 @item -iframework@var{dir}
14593 @opindex iframework
14594 Like @option{-F} except the directory is a treated as a system
14595 directory. The main difference between this @option{-iframework} and
14596 @option{-F} is that with @option{-iframework} the compiler does not
14597 warn about constructs contained within header files found via
14598 @var{dir}. This option is valid only for the C family of languages.
14602 Emit debugging information for symbols that are used. For stabs
14603 debugging format, this enables @option{-feliminate-unused-debug-symbols}.
14604 This is by default ON@.
14608 Emit debugging information for all symbols and types.
14610 @item -mmacosx-version-min=@var{version}
14611 The earliest version of MacOS X that this executable will run on
14612 is @var{version}. Typical values of @var{version} include @code{10.1},
14613 @code{10.2}, and @code{10.3.9}.
14615 If the compiler was built to use the system's headers by default,
14616 then the default for this option is the system version on which the
14617 compiler is running, otherwise the default is to make choices that
14618 are compatible with as many systems and code bases as possible.
14622 Enable kernel development mode. The @option{-mkernel} option sets
14623 @option{-static}, @option{-fno-common}, @option{-fno-use-cxa-atexit},
14624 @option{-fno-exceptions}, @option{-fno-non-call-exceptions},
14625 @option{-fapple-kext}, @option{-fno-weak} and @option{-fno-rtti} where
14626 applicable. This mode also sets @option{-mno-altivec},
14627 @option{-msoft-float}, @option{-fno-builtin} and
14628 @option{-mlong-branch} for PowerPC targets.
14630 @item -mone-byte-bool
14631 @opindex mone-byte-bool
14632 Override the defaults for @code{bool} so that @code{sizeof(bool)==1}.
14633 By default @code{sizeof(bool)} is @code{4} when compiling for
14634 Darwin/PowerPC and @code{1} when compiling for Darwin/x86, so this
14635 option has no effect on x86.
14637 @strong{Warning:} The @option{-mone-byte-bool} switch causes GCC
14638 to generate code that is not binary compatible with code generated
14639 without that switch. Using this switch may require recompiling all
14640 other modules in a program, including system libraries. Use this
14641 switch to conform to a non-default data model.
14643 @item -mfix-and-continue
14644 @itemx -ffix-and-continue
14645 @itemx -findirect-data
14646 @opindex mfix-and-continue
14647 @opindex ffix-and-continue
14648 @opindex findirect-data
14649 Generate code suitable for fast turnaround development, such as to
14650 allow GDB to dynamically load @file{.o} files into already-running
14651 programs. @option{-findirect-data} and @option{-ffix-and-continue}
14652 are provided for backwards compatibility.
14656 Loads all members of static archive libraries.
14657 See man ld(1) for more information.
14659 @item -arch_errors_fatal
14660 @opindex arch_errors_fatal
14661 Cause the errors having to do with files that have the wrong architecture
14664 @item -bind_at_load
14665 @opindex bind_at_load
14666 Causes the output file to be marked such that the dynamic linker will
14667 bind all undefined references when the file is loaded or launched.
14671 Produce a Mach-o bundle format file.
14672 See man ld(1) for more information.
14674 @item -bundle_loader @var{executable}
14675 @opindex bundle_loader
14676 This option specifies the @var{executable} that will load the build
14677 output file being linked. See man ld(1) for more information.
14680 @opindex dynamiclib
14681 When passed this option, GCC produces a dynamic library instead of
14682 an executable when linking, using the Darwin @file{libtool} command.
14684 @item -force_cpusubtype_ALL
14685 @opindex force_cpusubtype_ALL
14686 This causes GCC's output file to have the @samp{ALL} subtype, instead of
14687 one controlled by the @option{-mcpu} or @option{-march} option.
14689 @item -allowable_client @var{client_name}
14690 @itemx -client_name
14691 @itemx -compatibility_version
14692 @itemx -current_version
14694 @itemx -dependency-file
14696 @itemx -dylinker_install_name
14698 @itemx -exported_symbols_list
14701 @itemx -flat_namespace
14702 @itemx -force_flat_namespace
14703 @itemx -headerpad_max_install_names
14706 @itemx -install_name
14707 @itemx -keep_private_externs
14708 @itemx -multi_module
14709 @itemx -multiply_defined
14710 @itemx -multiply_defined_unused
14713 @itemx -no_dead_strip_inits_and_terms
14714 @itemx -nofixprebinding
14715 @itemx -nomultidefs
14717 @itemx -noseglinkedit
14718 @itemx -pagezero_size
14720 @itemx -prebind_all_twolevel_modules
14721 @itemx -private_bundle
14723 @itemx -read_only_relocs
14725 @itemx -sectobjectsymbols
14729 @itemx -sectobjectsymbols
14732 @itemx -segs_read_only_addr
14734 @itemx -segs_read_write_addr
14735 @itemx -seg_addr_table
14736 @itemx -seg_addr_table_filename
14737 @itemx -seglinkedit
14739 @itemx -segs_read_only_addr
14740 @itemx -segs_read_write_addr
14741 @itemx -single_module
14743 @itemx -sub_library
14745 @itemx -sub_umbrella
14746 @itemx -twolevel_namespace
14749 @itemx -unexported_symbols_list
14750 @itemx -weak_reference_mismatches
14751 @itemx -whatsloaded
14752 @opindex allowable_client
14753 @opindex client_name
14754 @opindex compatibility_version
14755 @opindex current_version
14756 @opindex dead_strip
14757 @opindex dependency-file
14758 @opindex dylib_file
14759 @opindex dylinker_install_name
14761 @opindex exported_symbols_list
14763 @opindex flat_namespace
14764 @opindex force_flat_namespace
14765 @opindex headerpad_max_install_names
14766 @opindex image_base
14768 @opindex install_name
14769 @opindex keep_private_externs
14770 @opindex multi_module
14771 @opindex multiply_defined
14772 @opindex multiply_defined_unused
14773 @opindex noall_load
14774 @opindex no_dead_strip_inits_and_terms
14775 @opindex nofixprebinding
14776 @opindex nomultidefs
14778 @opindex noseglinkedit
14779 @opindex pagezero_size
14781 @opindex prebind_all_twolevel_modules
14782 @opindex private_bundle
14783 @opindex read_only_relocs
14785 @opindex sectobjectsymbols
14788 @opindex sectcreate
14789 @opindex sectobjectsymbols
14792 @opindex segs_read_only_addr
14793 @opindex segs_read_write_addr
14794 @opindex seg_addr_table
14795 @opindex seg_addr_table_filename
14796 @opindex seglinkedit
14798 @opindex segs_read_only_addr
14799 @opindex segs_read_write_addr
14800 @opindex single_module
14802 @opindex sub_library
14803 @opindex sub_umbrella
14804 @opindex twolevel_namespace
14807 @opindex unexported_symbols_list
14808 @opindex weak_reference_mismatches
14809 @opindex whatsloaded
14810 These options are passed to the Darwin linker. The Darwin linker man page
14811 describes them in detail.
14814 @node DEC Alpha Options
14815 @subsection DEC Alpha Options
14817 These @samp{-m} options are defined for the DEC Alpha implementations:
14820 @item -mno-soft-float
14821 @itemx -msoft-float
14822 @opindex mno-soft-float
14823 @opindex msoft-float
14824 Use (do not use) the hardware floating-point instructions for
14825 floating-point operations. When @option{-msoft-float} is specified,
14826 functions in @file{libgcc.a} are used to perform floating-point
14827 operations. Unless they are replaced by routines that emulate the
14828 floating-point operations, or compiled in such a way as to call such
14829 emulations routines, these routines issue floating-point
14830 operations. If you are compiling for an Alpha without floating-point
14831 operations, you must ensure that the library is built so as not to call
14834 Note that Alpha implementations without floating-point operations are
14835 required to have floating-point registers.
14838 @itemx -mno-fp-regs
14840 @opindex mno-fp-regs
14841 Generate code that uses (does not use) the floating-point register set.
14842 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
14843 register set is not used, floating-point operands are passed in integer
14844 registers as if they were integers and floating-point results are passed
14845 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
14846 so any function with a floating-point argument or return value called by code
14847 compiled with @option{-mno-fp-regs} must also be compiled with that
14850 A typical use of this option is building a kernel that does not use,
14851 and hence need not save and restore, any floating-point registers.
14855 The Alpha architecture implements floating-point hardware optimized for
14856 maximum performance. It is mostly compliant with the IEEE floating-point
14857 standard. However, for full compliance, software assistance is
14858 required. This option generates code fully IEEE-compliant code
14859 @emph{except} that the @var{inexact-flag} is not maintained (see below).
14860 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
14861 defined during compilation. The resulting code is less efficient but is
14862 able to correctly support denormalized numbers and exceptional IEEE
14863 values such as not-a-number and plus/minus infinity. Other Alpha
14864 compilers call this option @option{-ieee_with_no_inexact}.
14866 @item -mieee-with-inexact
14867 @opindex mieee-with-inexact
14868 This is like @option{-mieee} except the generated code also maintains
14869 the IEEE @var{inexact-flag}. Turning on this option causes the
14870 generated code to implement fully-compliant IEEE math. In addition to
14871 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
14872 macro. On some Alpha implementations the resulting code may execute
14873 significantly slower than the code generated by default. Since there is
14874 very little code that depends on the @var{inexact-flag}, you should
14875 normally not specify this option. Other Alpha compilers call this
14876 option @option{-ieee_with_inexact}.
14878 @item -mfp-trap-mode=@var{trap-mode}
14879 @opindex mfp-trap-mode
14880 This option controls what floating-point related traps are enabled.
14881 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
14882 The trap mode can be set to one of four values:
14886 This is the default (normal) setting. The only traps that are enabled
14887 are the ones that cannot be disabled in software (e.g., division by zero
14891 In addition to the traps enabled by @samp{n}, underflow traps are enabled
14895 Like @samp{u}, but the instructions are marked to be safe for software
14896 completion (see Alpha architecture manual for details).
14899 Like @samp{su}, but inexact traps are enabled as well.
14902 @item -mfp-rounding-mode=@var{rounding-mode}
14903 @opindex mfp-rounding-mode
14904 Selects the IEEE rounding mode. Other Alpha compilers call this option
14905 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
14910 Normal IEEE rounding mode. Floating-point numbers are rounded towards
14911 the nearest machine number or towards the even machine number in case
14915 Round towards minus infinity.
14918 Chopped rounding mode. Floating-point numbers are rounded towards zero.
14921 Dynamic rounding mode. A field in the floating-point control register
14922 (@var{fpcr}, see Alpha architecture reference manual) controls the
14923 rounding mode in effect. The C library initializes this register for
14924 rounding towards plus infinity. Thus, unless your program modifies the
14925 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
14928 @item -mtrap-precision=@var{trap-precision}
14929 @opindex mtrap-precision
14930 In the Alpha architecture, floating-point traps are imprecise. This
14931 means without software assistance it is impossible to recover from a
14932 floating trap and program execution normally needs to be terminated.
14933 GCC can generate code that can assist operating system trap handlers
14934 in determining the exact location that caused a floating-point trap.
14935 Depending on the requirements of an application, different levels of
14936 precisions can be selected:
14940 Program precision. This option is the default and means a trap handler
14941 can only identify which program caused a floating-point exception.
14944 Function precision. The trap handler can determine the function that
14945 caused a floating-point exception.
14948 Instruction precision. The trap handler can determine the exact
14949 instruction that caused a floating-point exception.
14952 Other Alpha compilers provide the equivalent options called
14953 @option{-scope_safe} and @option{-resumption_safe}.
14955 @item -mieee-conformant
14956 @opindex mieee-conformant
14957 This option marks the generated code as IEEE conformant. You must not
14958 use this option unless you also specify @option{-mtrap-precision=i} and either
14959 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
14960 is to emit the line @samp{.eflag 48} in the function prologue of the
14961 generated assembly file.
14963 @item -mbuild-constants
14964 @opindex mbuild-constants
14965 Normally GCC examines a 32- or 64-bit integer constant to
14966 see if it can construct it from smaller constants in two or three
14967 instructions. If it cannot, it outputs the constant as a literal and
14968 generates code to load it from the data segment at run time.
14970 Use this option to require GCC to construct @emph{all} integer constants
14971 using code, even if it takes more instructions (the maximum is six).
14973 You typically use this option to build a shared library dynamic
14974 loader. Itself a shared library, it must relocate itself in memory
14975 before it can find the variables and constants in its own data segment.
14993 Indicate whether GCC should generate code to use the optional BWX,
14994 CIX, FIX and MAX instruction sets. The default is to use the instruction
14995 sets supported by the CPU type specified via @option{-mcpu=} option or that
14996 of the CPU on which GCC was built if none is specified.
14999 @itemx -mfloat-ieee
15000 @opindex mfloat-vax
15001 @opindex mfloat-ieee
15002 Generate code that uses (does not use) VAX F and G floating-point
15003 arithmetic instead of IEEE single and double precision.
15005 @item -mexplicit-relocs
15006 @itemx -mno-explicit-relocs
15007 @opindex mexplicit-relocs
15008 @opindex mno-explicit-relocs
15009 Older Alpha assemblers provided no way to generate symbol relocations
15010 except via assembler macros. Use of these macros does not allow
15011 optimal instruction scheduling. GNU binutils as of version 2.12
15012 supports a new syntax that allows the compiler to explicitly mark
15013 which relocations should apply to which instructions. This option
15014 is mostly useful for debugging, as GCC detects the capabilities of
15015 the assembler when it is built and sets the default accordingly.
15018 @itemx -mlarge-data
15019 @opindex msmall-data
15020 @opindex mlarge-data
15021 When @option{-mexplicit-relocs} is in effect, static data is
15022 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
15023 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
15024 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
15025 16-bit relocations off of the @code{$gp} register. This limits the
15026 size of the small data area to 64KB, but allows the variables to be
15027 directly accessed via a single instruction.
15029 The default is @option{-mlarge-data}. With this option the data area
15030 is limited to just below 2GB@. Programs that require more than 2GB of
15031 data must use @code{malloc} or @code{mmap} to allocate the data in the
15032 heap instead of in the program's data segment.
15034 When generating code for shared libraries, @option{-fpic} implies
15035 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
15038 @itemx -mlarge-text
15039 @opindex msmall-text
15040 @opindex mlarge-text
15041 When @option{-msmall-text} is used, the compiler assumes that the
15042 code of the entire program (or shared library) fits in 4MB, and is
15043 thus reachable with a branch instruction. When @option{-msmall-data}
15044 is used, the compiler can assume that all local symbols share the
15045 same @code{$gp} value, and thus reduce the number of instructions
15046 required for a function call from 4 to 1.
15048 The default is @option{-mlarge-text}.
15050 @item -mcpu=@var{cpu_type}
15052 Set the instruction set and instruction scheduling parameters for
15053 machine type @var{cpu_type}. You can specify either the @samp{EV}
15054 style name or the corresponding chip number. GCC supports scheduling
15055 parameters for the EV4, EV5 and EV6 family of processors and
15056 chooses the default values for the instruction set from the processor
15057 you specify. If you do not specify a processor type, GCC defaults
15058 to the processor on which the compiler was built.
15060 Supported values for @var{cpu_type} are
15066 Schedules as an EV4 and has no instruction set extensions.
15070 Schedules as an EV5 and has no instruction set extensions.
15074 Schedules as an EV5 and supports the BWX extension.
15079 Schedules as an EV5 and supports the BWX and MAX extensions.
15083 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
15087 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
15090 Native toolchains also support the value @samp{native},
15091 which selects the best architecture option for the host processor.
15092 @option{-mcpu=native} has no effect if GCC does not recognize
15095 @item -mtune=@var{cpu_type}
15097 Set only the instruction scheduling parameters for machine type
15098 @var{cpu_type}. The instruction set is not changed.
15100 Native toolchains also support the value @samp{native},
15101 which selects the best architecture option for the host processor.
15102 @option{-mtune=native} has no effect if GCC does not recognize
15105 @item -mmemory-latency=@var{time}
15106 @opindex mmemory-latency
15107 Sets the latency the scheduler should assume for typical memory
15108 references as seen by the application. This number is highly
15109 dependent on the memory access patterns used by the application
15110 and the size of the external cache on the machine.
15112 Valid options for @var{time} are
15116 A decimal number representing clock cycles.
15122 The compiler contains estimates of the number of clock cycles for
15123 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
15124 (also called Dcache, Scache, and Bcache), as well as to main memory.
15125 Note that L3 is only valid for EV5.
15131 @subsection FR30 Options
15132 @cindex FR30 Options
15134 These options are defined specifically for the FR30 port.
15138 @item -msmall-model
15139 @opindex msmall-model
15140 Use the small address space model. This can produce smaller code, but
15141 it does assume that all symbolic values and addresses fit into a
15146 Assume that runtime support has been provided and so there is no need
15147 to include the simulator library (@file{libsim.a}) on the linker
15153 @subsection FT32 Options
15154 @cindex FT32 Options
15156 These options are defined specifically for the FT32 port.
15162 Specifies that the program will be run on the simulator. This causes
15163 an alternate runtime startup and library to be linked.
15164 You must not use this option when generating programs that will run on
15165 real hardware; you must provide your own runtime library for whatever
15166 I/O functions are needed.
15170 Enable Local Register Allocation. This is still experimental for FT32,
15171 so by default the compiler uses standard reload.
15176 @subsection FRV Options
15177 @cindex FRV Options
15183 Only use the first 32 general-purpose registers.
15188 Use all 64 general-purpose registers.
15193 Use only the first 32 floating-point registers.
15198 Use all 64 floating-point registers.
15201 @opindex mhard-float
15203 Use hardware instructions for floating-point operations.
15206 @opindex msoft-float
15208 Use library routines for floating-point operations.
15213 Dynamically allocate condition code registers.
15218 Do not try to dynamically allocate condition code registers, only
15219 use @code{icc0} and @code{fcc0}.
15224 Change ABI to use double word insns.
15229 Do not use double word instructions.
15234 Use floating-point double instructions.
15237 @opindex mno-double
15239 Do not use floating-point double instructions.
15244 Use media instructions.
15249 Do not use media instructions.
15254 Use multiply and add/subtract instructions.
15257 @opindex mno-muladd
15259 Do not use multiply and add/subtract instructions.
15264 Select the FDPIC ABI, which uses function descriptors to represent
15265 pointers to functions. Without any PIC/PIE-related options, it
15266 implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it
15267 assumes GOT entries and small data are within a 12-bit range from the
15268 GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets
15269 are computed with 32 bits.
15270 With a @samp{bfin-elf} target, this option implies @option{-msim}.
15273 @opindex minline-plt
15275 Enable inlining of PLT entries in function calls to functions that are
15276 not known to bind locally. It has no effect without @option{-mfdpic}.
15277 It's enabled by default if optimizing for speed and compiling for
15278 shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an
15279 optimization option such as @option{-O3} or above is present in the
15285 Assume a large TLS segment when generating thread-local code.
15290 Do not assume a large TLS segment when generating thread-local code.
15295 Enable the use of @code{GPREL} relocations in the FDPIC ABI for data
15296 that is known to be in read-only sections. It's enabled by default,
15297 except for @option{-fpic} or @option{-fpie}: even though it may help
15298 make the global offset table smaller, it trades 1 instruction for 4.
15299 With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4,
15300 one of which may be shared by multiple symbols, and it avoids the need
15301 for a GOT entry for the referenced symbol, so it's more likely to be a
15302 win. If it is not, @option{-mno-gprel-ro} can be used to disable it.
15304 @item -multilib-library-pic
15305 @opindex multilib-library-pic
15307 Link with the (library, not FD) pic libraries. It's implied by
15308 @option{-mlibrary-pic}, as well as by @option{-fPIC} and
15309 @option{-fpic} without @option{-mfdpic}. You should never have to use
15313 @opindex mlinked-fp
15315 Follow the EABI requirement of always creating a frame pointer whenever
15316 a stack frame is allocated. This option is enabled by default and can
15317 be disabled with @option{-mno-linked-fp}.
15320 @opindex mlong-calls
15322 Use indirect addressing to call functions outside the current
15323 compilation unit. This allows the functions to be placed anywhere
15324 within the 32-bit address space.
15326 @item -malign-labels
15327 @opindex malign-labels
15329 Try to align labels to an 8-byte boundary by inserting NOPs into the
15330 previous packet. This option only has an effect when VLIW packing
15331 is enabled. It doesn't create new packets; it merely adds NOPs to
15334 @item -mlibrary-pic
15335 @opindex mlibrary-pic
15337 Generate position-independent EABI code.
15342 Use only the first four media accumulator registers.
15347 Use all eight media accumulator registers.
15352 Pack VLIW instructions.
15357 Do not pack VLIW instructions.
15360 @opindex mno-eflags
15362 Do not mark ABI switches in e_flags.
15365 @opindex mcond-move
15367 Enable the use of conditional-move instructions (default).
15369 This switch is mainly for debugging the compiler and will likely be removed
15370 in a future version.
15372 @item -mno-cond-move
15373 @opindex mno-cond-move
15375 Disable the use of conditional-move instructions.
15377 This switch is mainly for debugging the compiler and will likely be removed
15378 in a future version.
15383 Enable the use of conditional set instructions (default).
15385 This switch is mainly for debugging the compiler and will likely be removed
15386 in a future version.
15391 Disable the use of conditional set instructions.
15393 This switch is mainly for debugging the compiler and will likely be removed
15394 in a future version.
15397 @opindex mcond-exec
15399 Enable the use of conditional execution (default).
15401 This switch is mainly for debugging the compiler and will likely be removed
15402 in a future version.
15404 @item -mno-cond-exec
15405 @opindex mno-cond-exec
15407 Disable the use of conditional execution.
15409 This switch is mainly for debugging the compiler and will likely be removed
15410 in a future version.
15412 @item -mvliw-branch
15413 @opindex mvliw-branch
15415 Run a pass to pack branches into VLIW instructions (default).
15417 This switch is mainly for debugging the compiler and will likely be removed
15418 in a future version.
15420 @item -mno-vliw-branch
15421 @opindex mno-vliw-branch
15423 Do not run a pass to pack branches into VLIW instructions.
15425 This switch is mainly for debugging the compiler and will likely be removed
15426 in a future version.
15428 @item -mmulti-cond-exec
15429 @opindex mmulti-cond-exec
15431 Enable optimization of @code{&&} and @code{||} in conditional execution
15434 This switch is mainly for debugging the compiler and will likely be removed
15435 in a future version.
15437 @item -mno-multi-cond-exec
15438 @opindex mno-multi-cond-exec
15440 Disable optimization of @code{&&} and @code{||} in conditional execution.
15442 This switch is mainly for debugging the compiler and will likely be removed
15443 in a future version.
15445 @item -mnested-cond-exec
15446 @opindex mnested-cond-exec
15448 Enable nested conditional execution optimizations (default).
15450 This switch is mainly for debugging the compiler and will likely be removed
15451 in a future version.
15453 @item -mno-nested-cond-exec
15454 @opindex mno-nested-cond-exec
15456 Disable nested conditional execution optimizations.
15458 This switch is mainly for debugging the compiler and will likely be removed
15459 in a future version.
15461 @item -moptimize-membar
15462 @opindex moptimize-membar
15464 This switch removes redundant @code{membar} instructions from the
15465 compiler-generated code. It is enabled by default.
15467 @item -mno-optimize-membar
15468 @opindex mno-optimize-membar
15470 This switch disables the automatic removal of redundant @code{membar}
15471 instructions from the generated code.
15473 @item -mtomcat-stats
15474 @opindex mtomcat-stats
15476 Cause gas to print out tomcat statistics.
15478 @item -mcpu=@var{cpu}
15481 Select the processor type for which to generate code. Possible values are
15482 @samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450},
15483 @samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}.
15487 @node GNU/Linux Options
15488 @subsection GNU/Linux Options
15490 These @samp{-m} options are defined for GNU/Linux targets:
15495 Use the GNU C library. This is the default except
15496 on @samp{*-*-linux-*uclibc*}, @samp{*-*-linux-*musl*} and
15497 @samp{*-*-linux-*android*} targets.
15501 Use uClibc C library. This is the default on
15502 @samp{*-*-linux-*uclibc*} targets.
15506 Use the musl C library. This is the default on
15507 @samp{*-*-linux-*musl*} targets.
15511 Use Bionic C library. This is the default on
15512 @samp{*-*-linux-*android*} targets.
15516 Compile code compatible with Android platform. This is the default on
15517 @samp{*-*-linux-*android*} targets.
15519 When compiling, this option enables @option{-mbionic}, @option{-fPIC},
15520 @option{-fno-exceptions} and @option{-fno-rtti} by default. When linking,
15521 this option makes the GCC driver pass Android-specific options to the linker.
15522 Finally, this option causes the preprocessor macro @code{__ANDROID__}
15525 @item -tno-android-cc
15526 @opindex tno-android-cc
15527 Disable compilation effects of @option{-mandroid}, i.e., do not enable
15528 @option{-mbionic}, @option{-fPIC}, @option{-fno-exceptions} and
15529 @option{-fno-rtti} by default.
15531 @item -tno-android-ld
15532 @opindex tno-android-ld
15533 Disable linking effects of @option{-mandroid}, i.e., pass standard Linux
15534 linking options to the linker.
15538 @node H8/300 Options
15539 @subsection H8/300 Options
15541 These @samp{-m} options are defined for the H8/300 implementations:
15546 Shorten some address references at link time, when possible; uses the
15547 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
15548 ld, Using ld}, for a fuller description.
15552 Generate code for the H8/300H@.
15556 Generate code for the H8S@.
15560 Generate code for the H8S and H8/300H in the normal mode. This switch
15561 must be used either with @option{-mh} or @option{-ms}.
15565 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
15569 Extended registers are stored on stack before execution of function
15570 with monitor attribute. Default option is @option{-mexr}.
15571 This option is valid only for H8S targets.
15575 Extended registers are not stored on stack before execution of function
15576 with monitor attribute. Default option is @option{-mno-exr}.
15577 This option is valid only for H8S targets.
15581 Make @code{int} data 32 bits by default.
15584 @opindex malign-300
15585 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
15586 The default for the H8/300H and H8S is to align longs and floats on
15588 @option{-malign-300} causes them to be aligned on 2-byte boundaries.
15589 This option has no effect on the H8/300.
15593 @subsection HPPA Options
15594 @cindex HPPA Options
15596 These @samp{-m} options are defined for the HPPA family of computers:
15599 @item -march=@var{architecture-type}
15601 Generate code for the specified architecture. The choices for
15602 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
15603 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
15604 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
15605 architecture option for your machine. Code compiled for lower numbered
15606 architectures runs on higher numbered architectures, but not the
15609 @item -mpa-risc-1-0
15610 @itemx -mpa-risc-1-1
15611 @itemx -mpa-risc-2-0
15612 @opindex mpa-risc-1-0
15613 @opindex mpa-risc-1-1
15614 @opindex mpa-risc-2-0
15615 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
15617 @item -mjump-in-delay
15618 @opindex mjump-in-delay
15619 This option is ignored and provided for compatibility purposes only.
15621 @item -mdisable-fpregs
15622 @opindex mdisable-fpregs
15623 Prevent floating-point registers from being used in any manner. This is
15624 necessary for compiling kernels that perform lazy context switching of
15625 floating-point registers. If you use this option and attempt to perform
15626 floating-point operations, the compiler aborts.
15628 @item -mdisable-indexing
15629 @opindex mdisable-indexing
15630 Prevent the compiler from using indexing address modes. This avoids some
15631 rather obscure problems when compiling MIG generated code under MACH@.
15633 @item -mno-space-regs
15634 @opindex mno-space-regs
15635 Generate code that assumes the target has no space registers. This allows
15636 GCC to generate faster indirect calls and use unscaled index address modes.
15638 Such code is suitable for level 0 PA systems and kernels.
15640 @item -mfast-indirect-calls
15641 @opindex mfast-indirect-calls
15642 Generate code that assumes calls never cross space boundaries. This
15643 allows GCC to emit code that performs faster indirect calls.
15645 This option does not work in the presence of shared libraries or nested
15648 @item -mfixed-range=@var{register-range}
15649 @opindex mfixed-range
15650 Generate code treating the given register range as fixed registers.
15651 A fixed register is one that the register allocator cannot use. This is
15652 useful when compiling kernel code. A register range is specified as
15653 two registers separated by a dash. Multiple register ranges can be
15654 specified separated by a comma.
15656 @item -mlong-load-store
15657 @opindex mlong-load-store
15658 Generate 3-instruction load and store sequences as sometimes required by
15659 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
15662 @item -mportable-runtime
15663 @opindex mportable-runtime
15664 Use the portable calling conventions proposed by HP for ELF systems.
15668 Enable the use of assembler directives only GAS understands.
15670 @item -mschedule=@var{cpu-type}
15672 Schedule code according to the constraints for the machine type
15673 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
15674 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
15675 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
15676 proper scheduling option for your machine. The default scheduling is
15680 @opindex mlinker-opt
15681 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
15682 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
15683 linkers in which they give bogus error messages when linking some programs.
15686 @opindex msoft-float
15687 Generate output containing library calls for floating point.
15688 @strong{Warning:} the requisite libraries are not available for all HPPA
15689 targets. Normally the facilities of the machine's usual C compiler are
15690 used, but this cannot be done directly in cross-compilation. You must make
15691 your own arrangements to provide suitable library functions for
15694 @option{-msoft-float} changes the calling convention in the output file;
15695 therefore, it is only useful if you compile @emph{all} of a program with
15696 this option. In particular, you need to compile @file{libgcc.a}, the
15697 library that comes with GCC, with @option{-msoft-float} in order for
15702 Generate the predefine, @code{_SIO}, for server IO@. The default is
15703 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
15704 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These
15705 options are available under HP-UX and HI-UX@.
15709 Use options specific to GNU @command{ld}.
15710 This passes @option{-shared} to @command{ld} when
15711 building a shared library. It is the default when GCC is configured,
15712 explicitly or implicitly, with the GNU linker. This option does not
15713 affect which @command{ld} is called; it only changes what parameters
15714 are passed to that @command{ld}.
15715 The @command{ld} that is called is determined by the
15716 @option{--with-ld} configure option, GCC's program search path, and
15717 finally by the user's @env{PATH}. The linker used by GCC can be printed
15718 using @samp{which `gcc -print-prog-name=ld`}. This option is only available
15719 on the 64-bit HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}.
15723 Use options specific to HP @command{ld}.
15724 This passes @option{-b} to @command{ld} when building
15725 a shared library and passes @option{+Accept TypeMismatch} to @command{ld} on all
15726 links. It is the default when GCC is configured, explicitly or
15727 implicitly, with the HP linker. This option does not affect
15728 which @command{ld} is called; it only changes what parameters are passed to that
15730 The @command{ld} that is called is determined by the @option{--with-ld}
15731 configure option, GCC's program search path, and finally by the user's
15732 @env{PATH}. The linker used by GCC can be printed using @samp{which
15733 `gcc -print-prog-name=ld`}. This option is only available on the 64-bit
15734 HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}.
15737 @opindex mno-long-calls
15738 Generate code that uses long call sequences. This ensures that a call
15739 is always able to reach linker generated stubs. The default is to generate
15740 long calls only when the distance from the call site to the beginning
15741 of the function or translation unit, as the case may be, exceeds a
15742 predefined limit set by the branch type being used. The limits for
15743 normal calls are 7,600,000 and 240,000 bytes, respectively for the
15744 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
15747 Distances are measured from the beginning of functions when using the
15748 @option{-ffunction-sections} option, or when using the @option{-mgas}
15749 and @option{-mno-portable-runtime} options together under HP-UX with
15752 It is normally not desirable to use this option as it degrades
15753 performance. However, it may be useful in large applications,
15754 particularly when partial linking is used to build the application.
15756 The types of long calls used depends on the capabilities of the
15757 assembler and linker, and the type of code being generated. The
15758 impact on systems that support long absolute calls, and long pic
15759 symbol-difference or pc-relative calls should be relatively small.
15760 However, an indirect call is used on 32-bit ELF systems in pic code
15761 and it is quite long.
15763 @item -munix=@var{unix-std}
15765 Generate compiler predefines and select a startfile for the specified
15766 UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95}
15767 and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95}
15768 is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX
15769 11.11 and later. The default values are @samp{93} for HP-UX 10.00,
15770 @samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11
15773 @option{-munix=93} provides the same predefines as GCC 3.3 and 3.4.
15774 @option{-munix=95} provides additional predefines for @code{XOPEN_UNIX}
15775 and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}.
15776 @option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX},
15777 @code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and
15778 @code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}.
15780 It is @emph{important} to note that this option changes the interfaces
15781 for various library routines. It also affects the operational behavior
15782 of the C library. Thus, @emph{extreme} care is needed in using this
15785 Library code that is intended to operate with more than one UNIX
15786 standard must test, set and restore the variable @code{__xpg4_extended_mask}
15787 as appropriate. Most GNU software doesn't provide this capability.
15791 Suppress the generation of link options to search libdld.sl when the
15792 @option{-static} option is specified on HP-UX 10 and later.
15796 The HP-UX implementation of setlocale in libc has a dependency on
15797 libdld.sl. There isn't an archive version of libdld.sl. Thus,
15798 when the @option{-static} option is specified, special link options
15799 are needed to resolve this dependency.
15801 On HP-UX 10 and later, the GCC driver adds the necessary options to
15802 link with libdld.sl when the @option{-static} option is specified.
15803 This causes the resulting binary to be dynamic. On the 64-bit port,
15804 the linkers generate dynamic binaries by default in any case. The
15805 @option{-nolibdld} option can be used to prevent the GCC driver from
15806 adding these link options.
15810 Add support for multithreading with the @dfn{dce thread} library
15811 under HP-UX@. This option sets flags for both the preprocessor and
15815 @node IA-64 Options
15816 @subsection IA-64 Options
15817 @cindex IA-64 Options
15819 These are the @samp{-m} options defined for the Intel IA-64 architecture.
15823 @opindex mbig-endian
15824 Generate code for a big-endian target. This is the default for HP-UX@.
15826 @item -mlittle-endian
15827 @opindex mlittle-endian
15828 Generate code for a little-endian target. This is the default for AIX5
15834 @opindex mno-gnu-as
15835 Generate (or don't) code for the GNU assembler. This is the default.
15836 @c Also, this is the default if the configure option @option{--with-gnu-as}
15842 @opindex mno-gnu-ld
15843 Generate (or don't) code for the GNU linker. This is the default.
15844 @c Also, this is the default if the configure option @option{--with-gnu-ld}
15849 Generate code that does not use a global pointer register. The result
15850 is not position independent code, and violates the IA-64 ABI@.
15852 @item -mvolatile-asm-stop
15853 @itemx -mno-volatile-asm-stop
15854 @opindex mvolatile-asm-stop
15855 @opindex mno-volatile-asm-stop
15856 Generate (or don't) a stop bit immediately before and after volatile asm
15859 @item -mregister-names
15860 @itemx -mno-register-names
15861 @opindex mregister-names
15862 @opindex mno-register-names
15863 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
15864 the stacked registers. This may make assembler output more readable.
15870 Disable (or enable) optimizations that use the small data section. This may
15871 be useful for working around optimizer bugs.
15873 @item -mconstant-gp
15874 @opindex mconstant-gp
15875 Generate code that uses a single constant global pointer value. This is
15876 useful when compiling kernel code.
15880 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
15881 This is useful when compiling firmware code.
15883 @item -minline-float-divide-min-latency
15884 @opindex minline-float-divide-min-latency
15885 Generate code for inline divides of floating-point values
15886 using the minimum latency algorithm.
15888 @item -minline-float-divide-max-throughput
15889 @opindex minline-float-divide-max-throughput
15890 Generate code for inline divides of floating-point values
15891 using the maximum throughput algorithm.
15893 @item -mno-inline-float-divide
15894 @opindex mno-inline-float-divide
15895 Do not generate inline code for divides of floating-point values.
15897 @item -minline-int-divide-min-latency
15898 @opindex minline-int-divide-min-latency
15899 Generate code for inline divides of integer values
15900 using the minimum latency algorithm.
15902 @item -minline-int-divide-max-throughput
15903 @opindex minline-int-divide-max-throughput
15904 Generate code for inline divides of integer values
15905 using the maximum throughput algorithm.
15907 @item -mno-inline-int-divide
15908 @opindex mno-inline-int-divide
15909 Do not generate inline code for divides of integer values.
15911 @item -minline-sqrt-min-latency
15912 @opindex minline-sqrt-min-latency
15913 Generate code for inline square roots
15914 using the minimum latency algorithm.
15916 @item -minline-sqrt-max-throughput
15917 @opindex minline-sqrt-max-throughput
15918 Generate code for inline square roots
15919 using the maximum throughput algorithm.
15921 @item -mno-inline-sqrt
15922 @opindex mno-inline-sqrt
15923 Do not generate inline code for @code{sqrt}.
15926 @itemx -mno-fused-madd
15927 @opindex mfused-madd
15928 @opindex mno-fused-madd
15929 Do (don't) generate code that uses the fused multiply/add or multiply/subtract
15930 instructions. The default is to use these instructions.
15932 @item -mno-dwarf2-asm
15933 @itemx -mdwarf2-asm
15934 @opindex mno-dwarf2-asm
15935 @opindex mdwarf2-asm
15936 Don't (or do) generate assembler code for the DWARF 2 line number debugging
15937 info. This may be useful when not using the GNU assembler.
15939 @item -mearly-stop-bits
15940 @itemx -mno-early-stop-bits
15941 @opindex mearly-stop-bits
15942 @opindex mno-early-stop-bits
15943 Allow stop bits to be placed earlier than immediately preceding the
15944 instruction that triggered the stop bit. This can improve instruction
15945 scheduling, but does not always do so.
15947 @item -mfixed-range=@var{register-range}
15948 @opindex mfixed-range
15949 Generate code treating the given register range as fixed registers.
15950 A fixed register is one that the register allocator cannot use. This is
15951 useful when compiling kernel code. A register range is specified as
15952 two registers separated by a dash. Multiple register ranges can be
15953 specified separated by a comma.
15955 @item -mtls-size=@var{tls-size}
15957 Specify bit size of immediate TLS offsets. Valid values are 14, 22, and
15960 @item -mtune=@var{cpu-type}
15962 Tune the instruction scheduling for a particular CPU, Valid values are
15963 @samp{itanium}, @samp{itanium1}, @samp{merced}, @samp{itanium2},
15964 and @samp{mckinley}.
15970 Generate code for a 32-bit or 64-bit environment.
15971 The 32-bit environment sets int, long and pointer to 32 bits.
15972 The 64-bit environment sets int to 32 bits and long and pointer
15973 to 64 bits. These are HP-UX specific flags.
15975 @item -mno-sched-br-data-spec
15976 @itemx -msched-br-data-spec
15977 @opindex mno-sched-br-data-spec
15978 @opindex msched-br-data-spec
15979 (Dis/En)able data speculative scheduling before reload.
15980 This results in generation of @code{ld.a} instructions and
15981 the corresponding check instructions (@code{ld.c} / @code{chk.a}).
15982 The default is 'disable'.
15984 @item -msched-ar-data-spec
15985 @itemx -mno-sched-ar-data-spec
15986 @opindex msched-ar-data-spec
15987 @opindex mno-sched-ar-data-spec
15988 (En/Dis)able data speculative scheduling after reload.
15989 This results in generation of @code{ld.a} instructions and
15990 the corresponding check instructions (@code{ld.c} / @code{chk.a}).
15991 The default is 'enable'.
15993 @item -mno-sched-control-spec
15994 @itemx -msched-control-spec
15995 @opindex mno-sched-control-spec
15996 @opindex msched-control-spec
15997 (Dis/En)able control speculative scheduling. This feature is
15998 available only during region scheduling (i.e.@: before reload).
15999 This results in generation of the @code{ld.s} instructions and
16000 the corresponding check instructions @code{chk.s}.
16001 The default is 'disable'.
16003 @item -msched-br-in-data-spec
16004 @itemx -mno-sched-br-in-data-spec
16005 @opindex msched-br-in-data-spec
16006 @opindex mno-sched-br-in-data-spec
16007 (En/Dis)able speculative scheduling of the instructions that
16008 are dependent on the data speculative loads before reload.
16009 This is effective only with @option{-msched-br-data-spec} enabled.
16010 The default is 'enable'.
16012 @item -msched-ar-in-data-spec
16013 @itemx -mno-sched-ar-in-data-spec
16014 @opindex msched-ar-in-data-spec
16015 @opindex mno-sched-ar-in-data-spec
16016 (En/Dis)able speculative scheduling of the instructions that
16017 are dependent on the data speculative loads after reload.
16018 This is effective only with @option{-msched-ar-data-spec} enabled.
16019 The default is 'enable'.
16021 @item -msched-in-control-spec
16022 @itemx -mno-sched-in-control-spec
16023 @opindex msched-in-control-spec
16024 @opindex mno-sched-in-control-spec
16025 (En/Dis)able speculative scheduling of the instructions that
16026 are dependent on the control speculative loads.
16027 This is effective only with @option{-msched-control-spec} enabled.
16028 The default is 'enable'.
16030 @item -mno-sched-prefer-non-data-spec-insns
16031 @itemx -msched-prefer-non-data-spec-insns
16032 @opindex mno-sched-prefer-non-data-spec-insns
16033 @opindex msched-prefer-non-data-spec-insns
16034 If enabled, data-speculative instructions are chosen for schedule
16035 only if there are no other choices at the moment. This makes
16036 the use of the data speculation much more conservative.
16037 The default is 'disable'.
16039 @item -mno-sched-prefer-non-control-spec-insns
16040 @itemx -msched-prefer-non-control-spec-insns
16041 @opindex mno-sched-prefer-non-control-spec-insns
16042 @opindex msched-prefer-non-control-spec-insns
16043 If enabled, control-speculative instructions are chosen for schedule
16044 only if there are no other choices at the moment. This makes
16045 the use of the control speculation much more conservative.
16046 The default is 'disable'.
16048 @item -mno-sched-count-spec-in-critical-path
16049 @itemx -msched-count-spec-in-critical-path
16050 @opindex mno-sched-count-spec-in-critical-path
16051 @opindex msched-count-spec-in-critical-path
16052 If enabled, speculative dependencies are considered during
16053 computation of the instructions priorities. This makes the use of the
16054 speculation a bit more conservative.
16055 The default is 'disable'.
16057 @item -msched-spec-ldc
16058 @opindex msched-spec-ldc
16059 Use a simple data speculation check. This option is on by default.
16061 @item -msched-control-spec-ldc
16062 @opindex msched-spec-ldc
16063 Use a simple check for control speculation. This option is on by default.
16065 @item -msched-stop-bits-after-every-cycle
16066 @opindex msched-stop-bits-after-every-cycle
16067 Place a stop bit after every cycle when scheduling. This option is on
16070 @item -msched-fp-mem-deps-zero-cost
16071 @opindex msched-fp-mem-deps-zero-cost
16072 Assume that floating-point stores and loads are not likely to cause a conflict
16073 when placed into the same instruction group. This option is disabled by
16076 @item -msel-sched-dont-check-control-spec
16077 @opindex msel-sched-dont-check-control-spec
16078 Generate checks for control speculation in selective scheduling.
16079 This flag is disabled by default.
16081 @item -msched-max-memory-insns=@var{max-insns}
16082 @opindex msched-max-memory-insns
16083 Limit on the number of memory insns per instruction group, giving lower
16084 priority to subsequent memory insns attempting to schedule in the same
16085 instruction group. Frequently useful to prevent cache bank conflicts.
16086 The default value is 1.
16088 @item -msched-max-memory-insns-hard-limit
16089 @opindex msched-max-memory-insns-hard-limit
16090 Makes the limit specified by @option{msched-max-memory-insns} a hard limit,
16091 disallowing more than that number in an instruction group.
16092 Otherwise, the limit is ``soft'', meaning that non-memory operations
16093 are preferred when the limit is reached, but memory operations may still
16099 @subsection LM32 Options
16100 @cindex LM32 options
16102 These @option{-m} options are defined for the LatticeMico32 architecture:
16105 @item -mbarrel-shift-enabled
16106 @opindex mbarrel-shift-enabled
16107 Enable barrel-shift instructions.
16109 @item -mdivide-enabled
16110 @opindex mdivide-enabled
16111 Enable divide and modulus instructions.
16113 @item -mmultiply-enabled
16114 @opindex multiply-enabled
16115 Enable multiply instructions.
16117 @item -msign-extend-enabled
16118 @opindex msign-extend-enabled
16119 Enable sign extend instructions.
16121 @item -muser-enabled
16122 @opindex muser-enabled
16123 Enable user-defined instructions.
16128 @subsection M32C Options
16129 @cindex M32C options
16132 @item -mcpu=@var{name}
16134 Select the CPU for which code is generated. @var{name} may be one of
16135 @samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to
16136 /60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for
16137 the M32C/80 series.
16141 Specifies that the program will be run on the simulator. This causes
16142 an alternate runtime library to be linked in which supports, for
16143 example, file I/O@. You must not use this option when generating
16144 programs that will run on real hardware; you must provide your own
16145 runtime library for whatever I/O functions are needed.
16147 @item -memregs=@var{number}
16149 Specifies the number of memory-based pseudo-registers GCC uses
16150 during code generation. These pseudo-registers are used like real
16151 registers, so there is a tradeoff between GCC's ability to fit the
16152 code into available registers, and the performance penalty of using
16153 memory instead of registers. Note that all modules in a program must
16154 be compiled with the same value for this option. Because of that, you
16155 must not use this option with GCC's default runtime libraries.
16159 @node M32R/D Options
16160 @subsection M32R/D Options
16161 @cindex M32R/D options
16163 These @option{-m} options are defined for Renesas M32R/D architectures:
16168 Generate code for the M32R/2@.
16172 Generate code for the M32R/X@.
16176 Generate code for the M32R@. This is the default.
16178 @item -mmodel=small
16179 @opindex mmodel=small
16180 Assume all objects live in the lower 16MB of memory (so that their addresses
16181 can be loaded with the @code{ld24} instruction), and assume all subroutines
16182 are reachable with the @code{bl} instruction.
16183 This is the default.
16185 The addressability of a particular object can be set with the
16186 @code{model} attribute.
16188 @item -mmodel=medium
16189 @opindex mmodel=medium
16190 Assume objects may be anywhere in the 32-bit address space (the compiler
16191 generates @code{seth/add3} instructions to load their addresses), and
16192 assume all subroutines are reachable with the @code{bl} instruction.
16194 @item -mmodel=large
16195 @opindex mmodel=large
16196 Assume objects may be anywhere in the 32-bit address space (the compiler
16197 generates @code{seth/add3} instructions to load their addresses), and
16198 assume subroutines may not be reachable with the @code{bl} instruction
16199 (the compiler generates the much slower @code{seth/add3/jl}
16200 instruction sequence).
16203 @opindex msdata=none
16204 Disable use of the small data area. Variables are put into
16205 one of @code{.data}, @code{.bss}, or @code{.rodata} (unless the
16206 @code{section} attribute has been specified).
16207 This is the default.
16209 The small data area consists of sections @code{.sdata} and @code{.sbss}.
16210 Objects may be explicitly put in the small data area with the
16211 @code{section} attribute using one of these sections.
16213 @item -msdata=sdata
16214 @opindex msdata=sdata
16215 Put small global and static data in the small data area, but do not
16216 generate special code to reference them.
16219 @opindex msdata=use
16220 Put small global and static data in the small data area, and generate
16221 special instructions to reference them.
16225 @cindex smaller data references
16226 Put global and static objects less than or equal to @var{num} bytes
16227 into the small data or BSS sections instead of the normal data or BSS
16228 sections. The default value of @var{num} is 8.
16229 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
16230 for this option to have any effect.
16232 All modules should be compiled with the same @option{-G @var{num}} value.
16233 Compiling with different values of @var{num} may or may not work; if it
16234 doesn't the linker gives an error message---incorrect code is not
16239 Makes the M32R-specific code in the compiler display some statistics
16240 that might help in debugging programs.
16242 @item -malign-loops
16243 @opindex malign-loops
16244 Align all loops to a 32-byte boundary.
16246 @item -mno-align-loops
16247 @opindex mno-align-loops
16248 Do not enforce a 32-byte alignment for loops. This is the default.
16250 @item -missue-rate=@var{number}
16251 @opindex missue-rate=@var{number}
16252 Issue @var{number} instructions per cycle. @var{number} can only be 1
16255 @item -mbranch-cost=@var{number}
16256 @opindex mbranch-cost=@var{number}
16257 @var{number} can only be 1 or 2. If it is 1 then branches are
16258 preferred over conditional code, if it is 2, then the opposite applies.
16260 @item -mflush-trap=@var{number}
16261 @opindex mflush-trap=@var{number}
16262 Specifies the trap number to use to flush the cache. The default is
16263 12. Valid numbers are between 0 and 15 inclusive.
16265 @item -mno-flush-trap
16266 @opindex mno-flush-trap
16267 Specifies that the cache cannot be flushed by using a trap.
16269 @item -mflush-func=@var{name}
16270 @opindex mflush-func=@var{name}
16271 Specifies the name of the operating system function to call to flush
16272 the cache. The default is @samp{_flush_cache}, but a function call
16273 is only used if a trap is not available.
16275 @item -mno-flush-func
16276 @opindex mno-flush-func
16277 Indicates that there is no OS function for flushing the cache.
16281 @node M680x0 Options
16282 @subsection M680x0 Options
16283 @cindex M680x0 options
16285 These are the @samp{-m} options defined for M680x0 and ColdFire processors.
16286 The default settings depend on which architecture was selected when
16287 the compiler was configured; the defaults for the most common choices
16291 @item -march=@var{arch}
16293 Generate code for a specific M680x0 or ColdFire instruction set
16294 architecture. Permissible values of @var{arch} for M680x0
16295 architectures are: @samp{68000}, @samp{68010}, @samp{68020},
16296 @samp{68030}, @samp{68040}, @samp{68060} and @samp{cpu32}. ColdFire
16297 architectures are selected according to Freescale's ISA classification
16298 and the permissible values are: @samp{isaa}, @samp{isaaplus},
16299 @samp{isab} and @samp{isac}.
16301 GCC defines a macro @code{__mcf@var{arch}__} whenever it is generating
16302 code for a ColdFire target. The @var{arch} in this macro is one of the
16303 @option{-march} arguments given above.
16305 When used together, @option{-march} and @option{-mtune} select code
16306 that runs on a family of similar processors but that is optimized
16307 for a particular microarchitecture.
16309 @item -mcpu=@var{cpu}
16311 Generate code for a specific M680x0 or ColdFire processor.
16312 The M680x0 @var{cpu}s are: @samp{68000}, @samp{68010}, @samp{68020},
16313 @samp{68030}, @samp{68040}, @samp{68060}, @samp{68302}, @samp{68332}
16314 and @samp{cpu32}. The ColdFire @var{cpu}s are given by the table
16315 below, which also classifies the CPUs into families:
16317 @multitable @columnfractions 0.20 0.80
16318 @item @strong{Family} @tab @strong{@samp{-mcpu} arguments}
16319 @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}
16320 @item @samp{5206} @tab @samp{5202} @samp{5204} @samp{5206}
16321 @item @samp{5206e} @tab @samp{5206e}
16322 @item @samp{5208} @tab @samp{5207} @samp{5208}
16323 @item @samp{5211a} @tab @samp{5210a} @samp{5211a}
16324 @item @samp{5213} @tab @samp{5211} @samp{5212} @samp{5213}
16325 @item @samp{5216} @tab @samp{5214} @samp{5216}
16326 @item @samp{52235} @tab @samp{52230} @samp{52231} @samp{52232} @samp{52233} @samp{52234} @samp{52235}
16327 @item @samp{5225} @tab @samp{5224} @samp{5225}
16328 @item @samp{52259} @tab @samp{52252} @samp{52254} @samp{52255} @samp{52256} @samp{52258} @samp{52259}
16329 @item @samp{5235} @tab @samp{5232} @samp{5233} @samp{5234} @samp{5235} @samp{523x}
16330 @item @samp{5249} @tab @samp{5249}
16331 @item @samp{5250} @tab @samp{5250}
16332 @item @samp{5271} @tab @samp{5270} @samp{5271}
16333 @item @samp{5272} @tab @samp{5272}
16334 @item @samp{5275} @tab @samp{5274} @samp{5275}
16335 @item @samp{5282} @tab @samp{5280} @samp{5281} @samp{5282} @samp{528x}
16336 @item @samp{53017} @tab @samp{53011} @samp{53012} @samp{53013} @samp{53014} @samp{53015} @samp{53016} @samp{53017}
16337 @item @samp{5307} @tab @samp{5307}
16338 @item @samp{5329} @tab @samp{5327} @samp{5328} @samp{5329} @samp{532x}
16339 @item @samp{5373} @tab @samp{5372} @samp{5373} @samp{537x}
16340 @item @samp{5407} @tab @samp{5407}
16341 @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}
16344 @option{-mcpu=@var{cpu}} overrides @option{-march=@var{arch}} if
16345 @var{arch} is compatible with @var{cpu}. Other combinations of
16346 @option{-mcpu} and @option{-march} are rejected.
16348 GCC defines the macro @code{__mcf_cpu_@var{cpu}} when ColdFire target
16349 @var{cpu} is selected. It also defines @code{__mcf_family_@var{family}},
16350 where the value of @var{family} is given by the table above.
16352 @item -mtune=@var{tune}
16354 Tune the code for a particular microarchitecture within the
16355 constraints set by @option{-march} and @option{-mcpu}.
16356 The M680x0 microarchitectures are: @samp{68000}, @samp{68010},
16357 @samp{68020}, @samp{68030}, @samp{68040}, @samp{68060}
16358 and @samp{cpu32}. The ColdFire microarchitectures
16359 are: @samp{cfv1}, @samp{cfv2}, @samp{cfv3}, @samp{cfv4} and @samp{cfv4e}.
16361 You can also use @option{-mtune=68020-40} for code that needs
16362 to run relatively well on 68020, 68030 and 68040 targets.
16363 @option{-mtune=68020-60} is similar but includes 68060 targets
16364 as well. These two options select the same tuning decisions as
16365 @option{-m68020-40} and @option{-m68020-60} respectively.
16367 GCC defines the macros @code{__mc@var{arch}} and @code{__mc@var{arch}__}
16368 when tuning for 680x0 architecture @var{arch}. It also defines
16369 @code{mc@var{arch}} unless either @option{-ansi} or a non-GNU @option{-std}
16370 option is used. If GCC is tuning for a range of architectures,
16371 as selected by @option{-mtune=68020-40} or @option{-mtune=68020-60},
16372 it defines the macros for every architecture in the range.
16374 GCC also defines the macro @code{__m@var{uarch}__} when tuning for
16375 ColdFire microarchitecture @var{uarch}, where @var{uarch} is one
16376 of the arguments given above.
16382 Generate output for a 68000. This is the default
16383 when the compiler is configured for 68000-based systems.
16384 It is equivalent to @option{-march=68000}.
16386 Use this option for microcontrollers with a 68000 or EC000 core,
16387 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
16391 Generate output for a 68010. This is the default
16392 when the compiler is configured for 68010-based systems.
16393 It is equivalent to @option{-march=68010}.
16399 Generate output for a 68020. This is the default
16400 when the compiler is configured for 68020-based systems.
16401 It is equivalent to @option{-march=68020}.
16405 Generate output for a 68030. This is the default when the compiler is
16406 configured for 68030-based systems. It is equivalent to
16407 @option{-march=68030}.
16411 Generate output for a 68040. This is the default when the compiler is
16412 configured for 68040-based systems. It is equivalent to
16413 @option{-march=68040}.
16415 This option inhibits the use of 68881/68882 instructions that have to be
16416 emulated by software on the 68040. Use this option if your 68040 does not
16417 have code to emulate those instructions.
16421 Generate output for a 68060. This is the default when the compiler is
16422 configured for 68060-based systems. It is equivalent to
16423 @option{-march=68060}.
16425 This option inhibits the use of 68020 and 68881/68882 instructions that
16426 have to be emulated by software on the 68060. Use this option if your 68060
16427 does not have code to emulate those instructions.
16431 Generate output for a CPU32. This is the default
16432 when the compiler is configured for CPU32-based systems.
16433 It is equivalent to @option{-march=cpu32}.
16435 Use this option for microcontrollers with a
16436 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
16437 68336, 68340, 68341, 68349 and 68360.
16441 Generate output for a 520X ColdFire CPU@. This is the default
16442 when the compiler is configured for 520X-based systems.
16443 It is equivalent to @option{-mcpu=5206}, and is now deprecated
16444 in favor of that option.
16446 Use this option for microcontroller with a 5200 core, including
16447 the MCF5202, MCF5203, MCF5204 and MCF5206.
16451 Generate output for a 5206e ColdFire CPU@. The option is now
16452 deprecated in favor of the equivalent @option{-mcpu=5206e}.
16456 Generate output for a member of the ColdFire 528X family.
16457 The option is now deprecated in favor of the equivalent
16458 @option{-mcpu=528x}.
16462 Generate output for a ColdFire 5307 CPU@. The option is now deprecated
16463 in favor of the equivalent @option{-mcpu=5307}.
16467 Generate output for a ColdFire 5407 CPU@. The option is now deprecated
16468 in favor of the equivalent @option{-mcpu=5407}.
16472 Generate output for a ColdFire V4e family CPU (e.g.@: 547x/548x).
16473 This includes use of hardware floating-point instructions.
16474 The option is equivalent to @option{-mcpu=547x}, and is now
16475 deprecated in favor of that option.
16479 Generate output for a 68040, without using any of the new instructions.
16480 This results in code that can run relatively efficiently on either a
16481 68020/68881 or a 68030 or a 68040. The generated code does use the
16482 68881 instructions that are emulated on the 68040.
16484 The option is equivalent to @option{-march=68020} @option{-mtune=68020-40}.
16488 Generate output for a 68060, without using any of the new instructions.
16489 This results in code that can run relatively efficiently on either a
16490 68020/68881 or a 68030 or a 68040. The generated code does use the
16491 68881 instructions that are emulated on the 68060.
16493 The option is equivalent to @option{-march=68020} @option{-mtune=68020-60}.
16497 @opindex mhard-float
16499 Generate floating-point instructions. This is the default for 68020
16500 and above, and for ColdFire devices that have an FPU@. It defines the
16501 macro @code{__HAVE_68881__} on M680x0 targets and @code{__mcffpu__}
16502 on ColdFire targets.
16505 @opindex msoft-float
16506 Do not generate floating-point instructions; use library calls instead.
16507 This is the default for 68000, 68010, and 68832 targets. It is also
16508 the default for ColdFire devices that have no FPU.
16514 Generate (do not generate) ColdFire hardware divide and remainder
16515 instructions. If @option{-march} is used without @option{-mcpu},
16516 the default is ``on'' for ColdFire architectures and ``off'' for M680x0
16517 architectures. Otherwise, the default is taken from the target CPU
16518 (either the default CPU, or the one specified by @option{-mcpu}). For
16519 example, the default is ``off'' for @option{-mcpu=5206} and ``on'' for
16520 @option{-mcpu=5206e}.
16522 GCC defines the macro @code{__mcfhwdiv__} when this option is enabled.
16526 Consider type @code{int} to be 16 bits wide, like @code{short int}.
16527 Additionally, parameters passed on the stack are also aligned to a
16528 16-bit boundary even on targets whose API mandates promotion to 32-bit.
16532 Do not consider type @code{int} to be 16 bits wide. This is the default.
16535 @itemx -mno-bitfield
16536 @opindex mnobitfield
16537 @opindex mno-bitfield
16538 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
16539 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
16543 Do use the bit-field instructions. The @option{-m68020} option implies
16544 @option{-mbitfield}. This is the default if you use a configuration
16545 designed for a 68020.
16549 Use a different function-calling convention, in which functions
16550 that take a fixed number of arguments return with the @code{rtd}
16551 instruction, which pops their arguments while returning. This
16552 saves one instruction in the caller since there is no need to pop
16553 the arguments there.
16555 This calling convention is incompatible with the one normally
16556 used on Unix, so you cannot use it if you need to call libraries
16557 compiled with the Unix compiler.
16559 Also, you must provide function prototypes for all functions that
16560 take variable numbers of arguments (including @code{printf});
16561 otherwise incorrect code is generated for calls to those
16564 In addition, seriously incorrect code results if you call a
16565 function with too many arguments. (Normally, extra arguments are
16566 harmlessly ignored.)
16568 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
16569 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
16573 Do not use the calling conventions selected by @option{-mrtd}.
16574 This is the default.
16577 @itemx -mno-align-int
16578 @opindex malign-int
16579 @opindex mno-align-int
16580 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
16581 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
16582 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
16583 Aligning variables on 32-bit boundaries produces code that runs somewhat
16584 faster on processors with 32-bit busses at the expense of more memory.
16586 @strong{Warning:} if you use the @option{-malign-int} switch, GCC
16587 aligns structures containing the above types differently than
16588 most published application binary interface specifications for the m68k.
16592 Use the pc-relative addressing mode of the 68000 directly, instead of
16593 using a global offset table. At present, this option implies @option{-fpic},
16594 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
16595 not presently supported with @option{-mpcrel}, though this could be supported for
16596 68020 and higher processors.
16598 @item -mno-strict-align
16599 @itemx -mstrict-align
16600 @opindex mno-strict-align
16601 @opindex mstrict-align
16602 Do not (do) assume that unaligned memory references are handled by
16606 Generate code that allows the data segment to be located in a different
16607 area of memory from the text segment. This allows for execute-in-place in
16608 an environment without virtual memory management. This option implies
16611 @item -mno-sep-data
16612 Generate code that assumes that the data segment follows the text segment.
16613 This is the default.
16615 @item -mid-shared-library
16616 Generate code that supports shared libraries via the library ID method.
16617 This allows for execute-in-place and shared libraries in an environment
16618 without virtual memory management. This option implies @option{-fPIC}.
16620 @item -mno-id-shared-library
16621 Generate code that doesn't assume ID-based shared libraries are being used.
16622 This is the default.
16624 @item -mshared-library-id=n
16625 Specifies the identification number of the ID-based shared library being
16626 compiled. Specifying a value of 0 generates more compact code; specifying
16627 other values forces the allocation of that number to the current
16628 library, but is no more space- or time-efficient than omitting this option.
16634 When generating position-independent code for ColdFire, generate code
16635 that works if the GOT has more than 8192 entries. This code is
16636 larger and slower than code generated without this option. On M680x0
16637 processors, this option is not needed; @option{-fPIC} suffices.
16639 GCC normally uses a single instruction to load values from the GOT@.
16640 While this is relatively efficient, it only works if the GOT
16641 is smaller than about 64k. Anything larger causes the linker
16642 to report an error such as:
16644 @cindex relocation truncated to fit (ColdFire)
16646 relocation truncated to fit: R_68K_GOT16O foobar
16649 If this happens, you should recompile your code with @option{-mxgot}.
16650 It should then work with very large GOTs. However, code generated with
16651 @option{-mxgot} is less efficient, since it takes 4 instructions to fetch
16652 the value of a global symbol.
16654 Note that some linkers, including newer versions of the GNU linker,
16655 can create multiple GOTs and sort GOT entries. If you have such a linker,
16656 you should only need to use @option{-mxgot} when compiling a single
16657 object file that accesses more than 8192 GOT entries. Very few do.
16659 These options have no effect unless GCC is generating
16660 position-independent code.
16664 @node MCore Options
16665 @subsection MCore Options
16666 @cindex MCore options
16668 These are the @samp{-m} options defined for the Motorola M*Core
16674 @itemx -mno-hardlit
16676 @opindex mno-hardlit
16677 Inline constants into the code stream if it can be done in two
16678 instructions or less.
16684 Use the divide instruction. (Enabled by default).
16686 @item -mrelax-immediate
16687 @itemx -mno-relax-immediate
16688 @opindex mrelax-immediate
16689 @opindex mno-relax-immediate
16690 Allow arbitrary-sized immediates in bit operations.
16692 @item -mwide-bitfields
16693 @itemx -mno-wide-bitfields
16694 @opindex mwide-bitfields
16695 @opindex mno-wide-bitfields
16696 Always treat bit-fields as @code{int}-sized.
16698 @item -m4byte-functions
16699 @itemx -mno-4byte-functions
16700 @opindex m4byte-functions
16701 @opindex mno-4byte-functions
16702 Force all functions to be aligned to a 4-byte boundary.
16704 @item -mcallgraph-data
16705 @itemx -mno-callgraph-data
16706 @opindex mcallgraph-data
16707 @opindex mno-callgraph-data
16708 Emit callgraph information.
16711 @itemx -mno-slow-bytes
16712 @opindex mslow-bytes
16713 @opindex mno-slow-bytes
16714 Prefer word access when reading byte quantities.
16716 @item -mlittle-endian
16717 @itemx -mbig-endian
16718 @opindex mlittle-endian
16719 @opindex mbig-endian
16720 Generate code for a little-endian target.
16726 Generate code for the 210 processor.
16730 Assume that runtime support has been provided and so omit the
16731 simulator library (@file{libsim.a)} from the linker command line.
16733 @item -mstack-increment=@var{size}
16734 @opindex mstack-increment
16735 Set the maximum amount for a single stack increment operation. Large
16736 values can increase the speed of programs that contain functions
16737 that need a large amount of stack space, but they can also trigger a
16738 segmentation fault if the stack is extended too much. The default
16744 @subsection MeP Options
16745 @cindex MeP options
16751 Enables the @code{abs} instruction, which is the absolute difference
16752 between two registers.
16756 Enables all the optional instructions---average, multiply, divide, bit
16757 operations, leading zero, absolute difference, min/max, clip, and
16763 Enables the @code{ave} instruction, which computes the average of two
16766 @item -mbased=@var{n}
16768 Variables of size @var{n} bytes or smaller are placed in the
16769 @code{.based} section by default. Based variables use the @code{$tp}
16770 register as a base register, and there is a 128-byte limit to the
16771 @code{.based} section.
16775 Enables the bit operation instructions---bit test (@code{btstm}), set
16776 (@code{bsetm}), clear (@code{bclrm}), invert (@code{bnotm}), and
16777 test-and-set (@code{tas}).
16779 @item -mc=@var{name}
16781 Selects which section constant data is placed in. @var{name} may
16782 be @samp{tiny}, @samp{near}, or @samp{far}.
16786 Enables the @code{clip} instruction. Note that @option{-mclip} is not
16787 useful unless you also provide @option{-mminmax}.
16789 @item -mconfig=@var{name}
16791 Selects one of the built-in core configurations. Each MeP chip has
16792 one or more modules in it; each module has a core CPU and a variety of
16793 coprocessors, optional instructions, and peripherals. The
16794 @code{MeP-Integrator} tool, not part of GCC, provides these
16795 configurations through this option; using this option is the same as
16796 using all the corresponding command-line options. The default
16797 configuration is @samp{default}.
16801 Enables the coprocessor instructions. By default, this is a 32-bit
16802 coprocessor. Note that the coprocessor is normally enabled via the
16803 @option{-mconfig=} option.
16807 Enables the 32-bit coprocessor's instructions.
16811 Enables the 64-bit coprocessor's instructions.
16815 Enables IVC2 scheduling. IVC2 is a 64-bit VLIW coprocessor.
16819 Causes constant variables to be placed in the @code{.near} section.
16823 Enables the @code{div} and @code{divu} instructions.
16827 Generate big-endian code.
16831 Generate little-endian code.
16833 @item -mio-volatile
16834 @opindex mio-volatile
16835 Tells the compiler that any variable marked with the @code{io}
16836 attribute is to be considered volatile.
16840 Causes variables to be assigned to the @code{.far} section by default.
16844 Enables the @code{leadz} (leading zero) instruction.
16848 Causes variables to be assigned to the @code{.near} section by default.
16852 Enables the @code{min} and @code{max} instructions.
16856 Enables the multiplication and multiply-accumulate instructions.
16860 Disables all the optional instructions enabled by @option{-mall-opts}.
16864 Enables the @code{repeat} and @code{erepeat} instructions, used for
16865 low-overhead looping.
16869 Causes all variables to default to the @code{.tiny} section. Note
16870 that there is a 65536-byte limit to this section. Accesses to these
16871 variables use the @code{%gp} base register.
16875 Enables the saturation instructions. Note that the compiler does not
16876 currently generate these itself, but this option is included for
16877 compatibility with other tools, like @code{as}.
16881 Link the SDRAM-based runtime instead of the default ROM-based runtime.
16885 Link the simulator run-time libraries.
16889 Link the simulator runtime libraries, excluding built-in support
16890 for reset and exception vectors and tables.
16894 Causes all functions to default to the @code{.far} section. Without
16895 this option, functions default to the @code{.near} section.
16897 @item -mtiny=@var{n}
16899 Variables that are @var{n} bytes or smaller are allocated to the
16900 @code{.tiny} section. These variables use the @code{$gp} base
16901 register. The default for this option is 4, but note that there's a
16902 65536-byte limit to the @code{.tiny} section.
16906 @node MicroBlaze Options
16907 @subsection MicroBlaze Options
16908 @cindex MicroBlaze Options
16913 @opindex msoft-float
16914 Use software emulation for floating point (default).
16917 @opindex mhard-float
16918 Use hardware floating-point instructions.
16922 Do not optimize block moves, use @code{memcpy}.
16924 @item -mno-clearbss
16925 @opindex mno-clearbss
16926 This option is deprecated. Use @option{-fno-zero-initialized-in-bss} instead.
16928 @item -mcpu=@var{cpu-type}
16930 Use features of, and schedule code for, the given CPU.
16931 Supported values are in the format @samp{v@var{X}.@var{YY}.@var{Z}},
16932 where @var{X} is a major version, @var{YY} is the minor version, and
16933 @var{Z} is compatibility code. Example values are @samp{v3.00.a},
16934 @samp{v4.00.b}, @samp{v5.00.a}, @samp{v5.00.b}, @samp{v5.00.b}, @samp{v6.00.a}.
16936 @item -mxl-soft-mul
16937 @opindex mxl-soft-mul
16938 Use software multiply emulation (default).
16940 @item -mxl-soft-div
16941 @opindex mxl-soft-div
16942 Use software emulation for divides (default).
16944 @item -mxl-barrel-shift
16945 @opindex mxl-barrel-shift
16946 Use the hardware barrel shifter.
16948 @item -mxl-pattern-compare
16949 @opindex mxl-pattern-compare
16950 Use pattern compare instructions.
16952 @item -msmall-divides
16953 @opindex msmall-divides
16954 Use table lookup optimization for small signed integer divisions.
16956 @item -mxl-stack-check
16957 @opindex mxl-stack-check
16958 This option is deprecated. Use @option{-fstack-check} instead.
16961 @opindex mxl-gp-opt
16962 Use GP-relative @code{.sdata}/@code{.sbss} sections.
16964 @item -mxl-multiply-high
16965 @opindex mxl-multiply-high
16966 Use multiply high instructions for high part of 32x32 multiply.
16968 @item -mxl-float-convert
16969 @opindex mxl-float-convert
16970 Use hardware floating-point conversion instructions.
16972 @item -mxl-float-sqrt
16973 @opindex mxl-float-sqrt
16974 Use hardware floating-point square root instruction.
16977 @opindex mbig-endian
16978 Generate code for a big-endian target.
16980 @item -mlittle-endian
16981 @opindex mlittle-endian
16982 Generate code for a little-endian target.
16985 @opindex mxl-reorder
16986 Use reorder instructions (swap and byte reversed load/store).
16988 @item -mxl-mode-@var{app-model}
16989 Select application model @var{app-model}. Valid models are
16992 normal executable (default), uses startup code @file{crt0.o}.
16995 for use with Xilinx Microprocessor Debugger (XMD) based
16996 software intrusive debug agent called xmdstub. This uses startup file
16997 @file{crt1.o} and sets the start address of the program to 0x800.
17000 for applications that are loaded using a bootloader.
17001 This model uses startup file @file{crt2.o} which does not contain a processor
17002 reset vector handler. This is suitable for transferring control on a
17003 processor reset to the bootloader rather than the application.
17006 for applications that do not require any of the
17007 MicroBlaze vectors. This option may be useful for applications running
17008 within a monitoring application. This model uses @file{crt3.o} as a startup file.
17011 Option @option{-xl-mode-@var{app-model}} is a deprecated alias for
17012 @option{-mxl-mode-@var{app-model}}.
17017 @subsection MIPS Options
17018 @cindex MIPS options
17024 Generate big-endian code.
17028 Generate little-endian code. This is the default for @samp{mips*el-*-*}
17031 @item -march=@var{arch}
17033 Generate code that runs on @var{arch}, which can be the name of a
17034 generic MIPS ISA, or the name of a particular processor.
17036 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
17037 @samp{mips32}, @samp{mips32r2}, @samp{mips32r3}, @samp{mips32r5},
17038 @samp{mips32r6}, @samp{mips64}, @samp{mips64r2}, @samp{mips64r3},
17039 @samp{mips64r5} and @samp{mips64r6}.
17040 The processor names are:
17041 @samp{4kc}, @samp{4km}, @samp{4kp}, @samp{4ksc},
17042 @samp{4kec}, @samp{4kem}, @samp{4kep}, @samp{4ksd},
17043 @samp{5kc}, @samp{5kf},
17045 @samp{24kc}, @samp{24kf2_1}, @samp{24kf1_1},
17046 @samp{24kec}, @samp{24kef2_1}, @samp{24kef1_1},
17047 @samp{34kc}, @samp{34kf2_1}, @samp{34kf1_1}, @samp{34kn},
17048 @samp{74kc}, @samp{74kf2_1}, @samp{74kf1_1}, @samp{74kf3_2},
17049 @samp{1004kc}, @samp{1004kf2_1}, @samp{1004kf1_1},
17050 @samp{loongson2e}, @samp{loongson2f}, @samp{loongson3a},
17052 @samp{m14k}, @samp{m14kc}, @samp{m14ke}, @samp{m14kec},
17053 @samp{octeon}, @samp{octeon+}, @samp{octeon2}, @samp{octeon3},
17056 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
17057 @samp{r4600}, @samp{r4650}, @samp{r4700}, @samp{r6000}, @samp{r8000},
17058 @samp{rm7000}, @samp{rm9000},
17059 @samp{r10000}, @samp{r12000}, @samp{r14000}, @samp{r16000},
17062 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300},
17063 @samp{vr5000}, @samp{vr5400}, @samp{vr5500},
17064 @samp{xlr} and @samp{xlp}.
17065 The special value @samp{from-abi} selects the
17066 most compatible architecture for the selected ABI (that is,
17067 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
17069 The native Linux/GNU toolchain also supports the value @samp{native},
17070 which selects the best architecture option for the host processor.
17071 @option{-march=native} has no effect if GCC does not recognize
17074 In processor names, a final @samp{000} can be abbreviated as @samp{k}
17075 (for example, @option{-march=r2k}). Prefixes are optional, and
17076 @samp{vr} may be written @samp{r}.
17078 Names of the form @samp{@var{n}f2_1} refer to processors with
17079 FPUs clocked at half the rate of the core, names of the form
17080 @samp{@var{n}f1_1} refer to processors with FPUs clocked at the same
17081 rate as the core, and names of the form @samp{@var{n}f3_2} refer to
17082 processors with FPUs clocked a ratio of 3:2 with respect to the core.
17083 For compatibility reasons, @samp{@var{n}f} is accepted as a synonym
17084 for @samp{@var{n}f2_1} while @samp{@var{n}x} and @samp{@var{b}fx} are
17085 accepted as synonyms for @samp{@var{n}f1_1}.
17087 GCC defines two macros based on the value of this option. The first
17088 is @code{_MIPS_ARCH}, which gives the name of target architecture, as
17089 a string. The second has the form @code{_MIPS_ARCH_@var{foo}},
17090 where @var{foo} is the capitalized value of @code{_MIPS_ARCH}@.
17091 For example, @option{-march=r2000} sets @code{_MIPS_ARCH}
17092 to @code{"r2000"} and defines the macro @code{_MIPS_ARCH_R2000}.
17094 Note that the @code{_MIPS_ARCH} macro uses the processor names given
17095 above. In other words, it has the full prefix and does not
17096 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
17097 the macro names the resolved architecture (either @code{"mips1"} or
17098 @code{"mips3"}). It names the default architecture when no
17099 @option{-march} option is given.
17101 @item -mtune=@var{arch}
17103 Optimize for @var{arch}. Among other things, this option controls
17104 the way instructions are scheduled, and the perceived cost of arithmetic
17105 operations. The list of @var{arch} values is the same as for
17108 When this option is not used, GCC optimizes for the processor
17109 specified by @option{-march}. By using @option{-march} and
17110 @option{-mtune} together, it is possible to generate code that
17111 runs on a family of processors, but optimize the code for one
17112 particular member of that family.
17114 @option{-mtune} defines the macros @code{_MIPS_TUNE} and
17115 @code{_MIPS_TUNE_@var{foo}}, which work in the same way as the
17116 @option{-march} ones described above.
17120 Equivalent to @option{-march=mips1}.
17124 Equivalent to @option{-march=mips2}.
17128 Equivalent to @option{-march=mips3}.
17132 Equivalent to @option{-march=mips4}.
17136 Equivalent to @option{-march=mips32}.
17140 Equivalent to @option{-march=mips32r3}.
17144 Equivalent to @option{-march=mips32r5}.
17148 Equivalent to @option{-march=mips32r6}.
17152 Equivalent to @option{-march=mips64}.
17156 Equivalent to @option{-march=mips64r2}.
17160 Equivalent to @option{-march=mips64r3}.
17164 Equivalent to @option{-march=mips64r5}.
17168 Equivalent to @option{-march=mips64r6}.
17173 @opindex mno-mips16
17174 Generate (do not generate) MIPS16 code. If GCC is targeting a
17175 MIPS32 or MIPS64 architecture, it makes use of the MIPS16e ASE@.
17177 MIPS16 code generation can also be controlled on a per-function basis
17178 by means of @code{mips16} and @code{nomips16} attributes.
17179 @xref{Function Attributes}, for more information.
17181 @item -mflip-mips16
17182 @opindex mflip-mips16
17183 Generate MIPS16 code on alternating functions. This option is provided
17184 for regression testing of mixed MIPS16/non-MIPS16 code generation, and is
17185 not intended for ordinary use in compiling user code.
17187 @item -minterlink-compressed
17188 @item -mno-interlink-compressed
17189 @opindex minterlink-compressed
17190 @opindex mno-interlink-compressed
17191 Require (do not require) that code using the standard (uncompressed) MIPS ISA
17192 be link-compatible with MIPS16 and microMIPS code, and vice versa.
17194 For example, code using the standard ISA encoding cannot jump directly
17195 to MIPS16 or microMIPS code; it must either use a call or an indirect jump.
17196 @option{-minterlink-compressed} therefore disables direct jumps unless GCC
17197 knows that the target of the jump is not compressed.
17199 @item -minterlink-mips16
17200 @itemx -mno-interlink-mips16
17201 @opindex minterlink-mips16
17202 @opindex mno-interlink-mips16
17203 Aliases of @option{-minterlink-compressed} and
17204 @option{-mno-interlink-compressed}. These options predate the microMIPS ASE
17205 and are retained for backwards compatibility.
17217 Generate code for the given ABI@.
17219 Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
17220 generates 64-bit code when you select a 64-bit architecture, but you
17221 can use @option{-mgp32} to get 32-bit code instead.
17223 For information about the O64 ABI, see
17224 @uref{http://gcc.gnu.org/@/projects/@/mipso64-abi.html}.
17226 GCC supports a variant of the o32 ABI in which floating-point registers
17227 are 64 rather than 32 bits wide. You can select this combination with
17228 @option{-mabi=32} @option{-mfp64}. This ABI relies on the @code{mthc1}
17229 and @code{mfhc1} instructions and is therefore only supported for
17230 MIPS32R2, MIPS32R3 and MIPS32R5 processors.
17232 The register assignments for arguments and return values remain the
17233 same, but each scalar value is passed in a single 64-bit register
17234 rather than a pair of 32-bit registers. For example, scalar
17235 floating-point values are returned in @samp{$f0} only, not a
17236 @samp{$f0}/@samp{$f1} pair. The set of call-saved registers also
17237 remains the same in that the even-numbered double-precision registers
17240 Two additional variants of the o32 ABI are supported to enable
17241 a transition from 32-bit to 64-bit registers. These are FPXX
17242 (@option{-mfpxx}) and FP64A (@option{-mfp64} @option{-mno-odd-spreg}).
17243 The FPXX extension mandates that all code must execute correctly
17244 when run using 32-bit or 64-bit registers. The code can be interlinked
17245 with either FP32 or FP64, but not both.
17246 The FP64A extension is similar to the FP64 extension but forbids the
17247 use of odd-numbered single-precision registers. This can be used
17248 in conjunction with the @code{FRE} mode of FPUs in MIPS32R5
17249 processors and allows both FP32 and FP64A code to interlink and
17250 run in the same process without changing FPU modes.
17253 @itemx -mno-abicalls
17255 @opindex mno-abicalls
17256 Generate (do not generate) code that is suitable for SVR4-style
17257 dynamic objects. @option{-mabicalls} is the default for SVR4-based
17262 Generate (do not generate) code that is fully position-independent,
17263 and that can therefore be linked into shared libraries. This option
17264 only affects @option{-mabicalls}.
17266 All @option{-mabicalls} code has traditionally been position-independent,
17267 regardless of options like @option{-fPIC} and @option{-fpic}. However,
17268 as an extension, the GNU toolchain allows executables to use absolute
17269 accesses for locally-binding symbols. It can also use shorter GP
17270 initialization sequences and generate direct calls to locally-defined
17271 functions. This mode is selected by @option{-mno-shared}.
17273 @option{-mno-shared} depends on binutils 2.16 or higher and generates
17274 objects that can only be linked by the GNU linker. However, the option
17275 does not affect the ABI of the final executable; it only affects the ABI
17276 of relocatable objects. Using @option{-mno-shared} generally makes
17277 executables both smaller and quicker.
17279 @option{-mshared} is the default.
17285 Assume (do not assume) that the static and dynamic linkers
17286 support PLTs and copy relocations. This option only affects
17287 @option{-mno-shared -mabicalls}. For the n64 ABI, this option
17288 has no effect without @option{-msym32}.
17290 You can make @option{-mplt} the default by configuring
17291 GCC with @option{--with-mips-plt}. The default is
17292 @option{-mno-plt} otherwise.
17298 Lift (do not lift) the usual restrictions on the size of the global
17301 GCC normally uses a single instruction to load values from the GOT@.
17302 While this is relatively efficient, it only works if the GOT
17303 is smaller than about 64k. Anything larger causes the linker
17304 to report an error such as:
17306 @cindex relocation truncated to fit (MIPS)
17308 relocation truncated to fit: R_MIPS_GOT16 foobar
17311 If this happens, you should recompile your code with @option{-mxgot}.
17312 This works with very large GOTs, although the code is also
17313 less efficient, since it takes three instructions to fetch the
17314 value of a global symbol.
17316 Note that some linkers can create multiple GOTs. If you have such a
17317 linker, you should only need to use @option{-mxgot} when a single object
17318 file accesses more than 64k's worth of GOT entries. Very few do.
17320 These options have no effect unless GCC is generating position
17325 Assume that general-purpose registers are 32 bits wide.
17329 Assume that general-purpose registers are 64 bits wide.
17333 Assume that floating-point registers are 32 bits wide.
17337 Assume that floating-point registers are 64 bits wide.
17341 Do not assume the width of floating-point registers.
17344 @opindex mhard-float
17345 Use floating-point coprocessor instructions.
17348 @opindex msoft-float
17349 Do not use floating-point coprocessor instructions. Implement
17350 floating-point calculations using library calls instead.
17354 Equivalent to @option{-msoft-float}, but additionally asserts that the
17355 program being compiled does not perform any floating-point operations.
17356 This option is presently supported only by some bare-metal MIPS
17357 configurations, where it may select a special set of libraries
17358 that lack all floating-point support (including, for example, the
17359 floating-point @code{printf} formats).
17360 If code compiled with @option{-mno-float} accidentally contains
17361 floating-point operations, it is likely to suffer a link-time
17362 or run-time failure.
17364 @item -msingle-float
17365 @opindex msingle-float
17366 Assume that the floating-point coprocessor only supports single-precision
17369 @item -mdouble-float
17370 @opindex mdouble-float
17371 Assume that the floating-point coprocessor supports double-precision
17372 operations. This is the default.
17375 @itemx -mno-odd-spreg
17376 @opindex modd-spreg
17377 @opindex mno-odd-spreg
17378 Enable the use of odd-numbered single-precision floating-point registers
17379 for the o32 ABI. This is the default for processors that are known to
17380 support these registers. When using the o32 FPXX ABI, @option{-mno-odd-spreg}
17384 @itemx -mabs=legacy
17386 @opindex mabs=legacy
17387 These options control the treatment of the special not-a-number (NaN)
17388 IEEE 754 floating-point data with the @code{abs.@i{fmt}} and
17389 @code{neg.@i{fmt}} machine instructions.
17391 By default or when @option{-mabs=legacy} is used the legacy
17392 treatment is selected. In this case these instructions are considered
17393 arithmetic and avoided where correct operation is required and the
17394 input operand might be a NaN. A longer sequence of instructions that
17395 manipulate the sign bit of floating-point datum manually is used
17396 instead unless the @option{-ffinite-math-only} option has also been
17399 The @option{-mabs=2008} option selects the IEEE 754-2008 treatment. In
17400 this case these instructions are considered non-arithmetic and therefore
17401 operating correctly in all cases, including in particular where the
17402 input operand is a NaN. These instructions are therefore always used
17403 for the respective operations.
17406 @itemx -mnan=legacy
17408 @opindex mnan=legacy
17409 These options control the encoding of the special not-a-number (NaN)
17410 IEEE 754 floating-point data.
17412 The @option{-mnan=legacy} option selects the legacy encoding. In this
17413 case quiet NaNs (qNaNs) are denoted by the first bit of their trailing
17414 significand field being 0, whereas signalling NaNs (sNaNs) are denoted
17415 by the first bit of their trailing significand field being 1.
17417 The @option{-mnan=2008} option selects the IEEE 754-2008 encoding. In
17418 this case qNaNs are denoted by the first bit of their trailing
17419 significand field being 1, whereas sNaNs are denoted by the first bit of
17420 their trailing significand field being 0.
17422 The default is @option{-mnan=legacy} unless GCC has been configured with
17423 @option{--with-nan=2008}.
17429 Use (do not use) @samp{ll}, @samp{sc}, and @samp{sync} instructions to
17430 implement atomic memory built-in functions. When neither option is
17431 specified, GCC uses the instructions if the target architecture
17434 @option{-mllsc} is useful if the runtime environment can emulate the
17435 instructions and @option{-mno-llsc} can be useful when compiling for
17436 nonstandard ISAs. You can make either option the default by
17437 configuring GCC with @option{--with-llsc} and @option{--without-llsc}
17438 respectively. @option{--with-llsc} is the default for some
17439 configurations; see the installation documentation for details.
17445 Use (do not use) revision 1 of the MIPS DSP ASE@.
17446 @xref{MIPS DSP Built-in Functions}. This option defines the
17447 preprocessor macro @code{__mips_dsp}. It also defines
17448 @code{__mips_dsp_rev} to 1.
17454 Use (do not use) revision 2 of the MIPS DSP ASE@.
17455 @xref{MIPS DSP Built-in Functions}. This option defines the
17456 preprocessor macros @code{__mips_dsp} and @code{__mips_dspr2}.
17457 It also defines @code{__mips_dsp_rev} to 2.
17460 @itemx -mno-smartmips
17461 @opindex msmartmips
17462 @opindex mno-smartmips
17463 Use (do not use) the MIPS SmartMIPS ASE.
17465 @item -mpaired-single
17466 @itemx -mno-paired-single
17467 @opindex mpaired-single
17468 @opindex mno-paired-single
17469 Use (do not use) paired-single floating-point instructions.
17470 @xref{MIPS Paired-Single Support}. This option requires
17471 hardware floating-point support to be enabled.
17477 Use (do not use) MIPS Digital Media Extension instructions.
17478 This option can only be used when generating 64-bit code and requires
17479 hardware floating-point support to be enabled.
17484 @opindex mno-mips3d
17485 Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}.
17486 The option @option{-mips3d} implies @option{-mpaired-single}.
17489 @itemx -mno-micromips
17490 @opindex mmicromips
17491 @opindex mno-mmicromips
17492 Generate (do not generate) microMIPS code.
17494 MicroMIPS code generation can also be controlled on a per-function basis
17495 by means of @code{micromips} and @code{nomicromips} attributes.
17496 @xref{Function Attributes}, for more information.
17502 Use (do not use) MT Multithreading instructions.
17508 Use (do not use) the MIPS MCU ASE instructions.
17514 Use (do not use) the MIPS Enhanced Virtual Addressing instructions.
17520 Use (do not use) the MIPS Virtualization Application Specific instructions.
17526 Use (do not use) the MIPS eXtended Physical Address (XPA) instructions.
17530 Force @code{long} types to be 64 bits wide. See @option{-mlong32} for
17531 an explanation of the default and the way that the pointer size is
17536 Force @code{long}, @code{int}, and pointer types to be 32 bits wide.
17538 The default size of @code{int}s, @code{long}s and pointers depends on
17539 the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI
17540 uses 64-bit @code{long}s, as does the 64-bit EABI; the others use
17541 32-bit @code{long}s. Pointers are the same size as @code{long}s,
17542 or the same size as integer registers, whichever is smaller.
17548 Assume (do not assume) that all symbols have 32-bit values, regardless
17549 of the selected ABI@. This option is useful in combination with
17550 @option{-mabi=64} and @option{-mno-abicalls} because it allows GCC
17551 to generate shorter and faster references to symbolic addresses.
17555 Put definitions of externally-visible data in a small data section
17556 if that data is no bigger than @var{num} bytes. GCC can then generate
17557 more efficient accesses to the data; see @option{-mgpopt} for details.
17559 The default @option{-G} option depends on the configuration.
17561 @item -mlocal-sdata
17562 @itemx -mno-local-sdata
17563 @opindex mlocal-sdata
17564 @opindex mno-local-sdata
17565 Extend (do not extend) the @option{-G} behavior to local data too,
17566 such as to static variables in C@. @option{-mlocal-sdata} is the
17567 default for all configurations.
17569 If the linker complains that an application is using too much small data,
17570 you might want to try rebuilding the less performance-critical parts with
17571 @option{-mno-local-sdata}. You might also want to build large
17572 libraries with @option{-mno-local-sdata}, so that the libraries leave
17573 more room for the main program.
17575 @item -mextern-sdata
17576 @itemx -mno-extern-sdata
17577 @opindex mextern-sdata
17578 @opindex mno-extern-sdata
17579 Assume (do not assume) that externally-defined data is in
17580 a small data section if the size of that data is within the @option{-G} limit.
17581 @option{-mextern-sdata} is the default for all configurations.
17583 If you compile a module @var{Mod} with @option{-mextern-sdata} @option{-G
17584 @var{num}} @option{-mgpopt}, and @var{Mod} references a variable @var{Var}
17585 that is no bigger than @var{num} bytes, you must make sure that @var{Var}
17586 is placed in a small data section. If @var{Var} is defined by another
17587 module, you must either compile that module with a high-enough
17588 @option{-G} setting or attach a @code{section} attribute to @var{Var}'s
17589 definition. If @var{Var} is common, you must link the application
17590 with a high-enough @option{-G} setting.
17592 The easiest way of satisfying these restrictions is to compile
17593 and link every module with the same @option{-G} option. However,
17594 you may wish to build a library that supports several different
17595 small data limits. You can do this by compiling the library with
17596 the highest supported @option{-G} setting and additionally using
17597 @option{-mno-extern-sdata} to stop the library from making assumptions
17598 about externally-defined data.
17604 Use (do not use) GP-relative accesses for symbols that are known to be
17605 in a small data section; see @option{-G}, @option{-mlocal-sdata} and
17606 @option{-mextern-sdata}. @option{-mgpopt} is the default for all
17609 @option{-mno-gpopt} is useful for cases where the @code{$gp} register
17610 might not hold the value of @code{_gp}. For example, if the code is
17611 part of a library that might be used in a boot monitor, programs that
17612 call boot monitor routines pass an unknown value in @code{$gp}.
17613 (In such situations, the boot monitor itself is usually compiled
17614 with @option{-G0}.)
17616 @option{-mno-gpopt} implies @option{-mno-local-sdata} and
17617 @option{-mno-extern-sdata}.
17619 @item -membedded-data
17620 @itemx -mno-embedded-data
17621 @opindex membedded-data
17622 @opindex mno-embedded-data
17623 Allocate variables to the read-only data section first if possible, then
17624 next in the small data section if possible, otherwise in data. This gives
17625 slightly slower code than the default, but reduces the amount of RAM required
17626 when executing, and thus may be preferred for some embedded systems.
17628 @item -muninit-const-in-rodata
17629 @itemx -mno-uninit-const-in-rodata
17630 @opindex muninit-const-in-rodata
17631 @opindex mno-uninit-const-in-rodata
17632 Put uninitialized @code{const} variables in the read-only data section.
17633 This option is only meaningful in conjunction with @option{-membedded-data}.
17635 @item -mcode-readable=@var{setting}
17636 @opindex mcode-readable
17637 Specify whether GCC may generate code that reads from executable sections.
17638 There are three possible settings:
17641 @item -mcode-readable=yes
17642 Instructions may freely access executable sections. This is the
17645 @item -mcode-readable=pcrel
17646 MIPS16 PC-relative load instructions can access executable sections,
17647 but other instructions must not do so. This option is useful on 4KSc
17648 and 4KSd processors when the code TLBs have the Read Inhibit bit set.
17649 It is also useful on processors that can be configured to have a dual
17650 instruction/data SRAM interface and that, like the M4K, automatically
17651 redirect PC-relative loads to the instruction RAM.
17653 @item -mcode-readable=no
17654 Instructions must not access executable sections. This option can be
17655 useful on targets that are configured to have a dual instruction/data
17656 SRAM interface but that (unlike the M4K) do not automatically redirect
17657 PC-relative loads to the instruction RAM.
17660 @item -msplit-addresses
17661 @itemx -mno-split-addresses
17662 @opindex msplit-addresses
17663 @opindex mno-split-addresses
17664 Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler
17665 relocation operators. This option has been superseded by
17666 @option{-mexplicit-relocs} but is retained for backwards compatibility.
17668 @item -mexplicit-relocs
17669 @itemx -mno-explicit-relocs
17670 @opindex mexplicit-relocs
17671 @opindex mno-explicit-relocs
17672 Use (do not use) assembler relocation operators when dealing with symbolic
17673 addresses. The alternative, selected by @option{-mno-explicit-relocs},
17674 is to use assembler macros instead.
17676 @option{-mexplicit-relocs} is the default if GCC was configured
17677 to use an assembler that supports relocation operators.
17679 @item -mcheck-zero-division
17680 @itemx -mno-check-zero-division
17681 @opindex mcheck-zero-division
17682 @opindex mno-check-zero-division
17683 Trap (do not trap) on integer division by zero.
17685 The default is @option{-mcheck-zero-division}.
17687 @item -mdivide-traps
17688 @itemx -mdivide-breaks
17689 @opindex mdivide-traps
17690 @opindex mdivide-breaks
17691 MIPS systems check for division by zero by generating either a
17692 conditional trap or a break instruction. Using traps results in
17693 smaller code, but is only supported on MIPS II and later. Also, some
17694 versions of the Linux kernel have a bug that prevents trap from
17695 generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to
17696 allow conditional traps on architectures that support them and
17697 @option{-mdivide-breaks} to force the use of breaks.
17699 The default is usually @option{-mdivide-traps}, but this can be
17700 overridden at configure time using @option{--with-divide=breaks}.
17701 Divide-by-zero checks can be completely disabled using
17702 @option{-mno-check-zero-division}.
17707 @opindex mno-memcpy
17708 Force (do not force) the use of @code{memcpy} for non-trivial block
17709 moves. The default is @option{-mno-memcpy}, which allows GCC to inline
17710 most constant-sized copies.
17713 @itemx -mno-long-calls
17714 @opindex mlong-calls
17715 @opindex mno-long-calls
17716 Disable (do not disable) use of the @code{jal} instruction. Calling
17717 functions using @code{jal} is more efficient but requires the caller
17718 and callee to be in the same 256 megabyte segment.
17720 This option has no effect on abicalls code. The default is
17721 @option{-mno-long-calls}.
17727 Enable (disable) use of the @code{mad}, @code{madu} and @code{mul}
17728 instructions, as provided by the R4650 ISA@.
17734 Enable (disable) use of the @code{madd} and @code{msub} integer
17735 instructions. The default is @option{-mimadd} on architectures
17736 that support @code{madd} and @code{msub} except for the 74k
17737 architecture where it was found to generate slower code.
17740 @itemx -mno-fused-madd
17741 @opindex mfused-madd
17742 @opindex mno-fused-madd
17743 Enable (disable) use of the floating-point multiply-accumulate
17744 instructions, when they are available. The default is
17745 @option{-mfused-madd}.
17747 On the R8000 CPU when multiply-accumulate instructions are used,
17748 the intermediate product is calculated to infinite precision
17749 and is not subject to the FCSR Flush to Zero bit. This may be
17750 undesirable in some circumstances. On other processors the result
17751 is numerically identical to the equivalent computation using
17752 separate multiply, add, subtract and negate instructions.
17756 Tell the MIPS assembler to not run its preprocessor over user
17757 assembler files (with a @samp{.s} suffix) when assembling them.
17762 @opindex mno-fix-24k
17763 Work around the 24K E48 (lost data on stores during refill) errata.
17764 The workarounds are implemented by the assembler rather than by GCC@.
17767 @itemx -mno-fix-r4000
17768 @opindex mfix-r4000
17769 @opindex mno-fix-r4000
17770 Work around certain R4000 CPU errata:
17773 A double-word or a variable shift may give an incorrect result if executed
17774 immediately after starting an integer division.
17776 A double-word or a variable shift may give an incorrect result if executed
17777 while an integer multiplication is in progress.
17779 An integer division may give an incorrect result if started in a delay slot
17780 of a taken branch or a jump.
17784 @itemx -mno-fix-r4400
17785 @opindex mfix-r4400
17786 @opindex mno-fix-r4400
17787 Work around certain R4400 CPU errata:
17790 A double-word or a variable shift may give an incorrect result if executed
17791 immediately after starting an integer division.
17795 @itemx -mno-fix-r10000
17796 @opindex mfix-r10000
17797 @opindex mno-fix-r10000
17798 Work around certain R10000 errata:
17801 @code{ll}/@code{sc} sequences may not behave atomically on revisions
17802 prior to 3.0. They may deadlock on revisions 2.6 and earlier.
17805 This option can only be used if the target architecture supports
17806 branch-likely instructions. @option{-mfix-r10000} is the default when
17807 @option{-march=r10000} is used; @option{-mno-fix-r10000} is the default
17811 @itemx -mno-fix-rm7000
17812 @opindex mfix-rm7000
17813 Work around the RM7000 @code{dmult}/@code{dmultu} errata. The
17814 workarounds are implemented by the assembler rather than by GCC@.
17817 @itemx -mno-fix-vr4120
17818 @opindex mfix-vr4120
17819 Work around certain VR4120 errata:
17822 @code{dmultu} does not always produce the correct result.
17824 @code{div} and @code{ddiv} do not always produce the correct result if one
17825 of the operands is negative.
17827 The workarounds for the division errata rely on special functions in
17828 @file{libgcc.a}. At present, these functions are only provided by
17829 the @code{mips64vr*-elf} configurations.
17831 Other VR4120 errata require a NOP to be inserted between certain pairs of
17832 instructions. These errata are handled by the assembler, not by GCC itself.
17835 @opindex mfix-vr4130
17836 Work around the VR4130 @code{mflo}/@code{mfhi} errata. The
17837 workarounds are implemented by the assembler rather than by GCC,
17838 although GCC avoids using @code{mflo} and @code{mfhi} if the
17839 VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi}
17840 instructions are available instead.
17843 @itemx -mno-fix-sb1
17845 Work around certain SB-1 CPU core errata.
17846 (This flag currently works around the SB-1 revision 2
17847 ``F1'' and ``F2'' floating-point errata.)
17849 @item -mr10k-cache-barrier=@var{setting}
17850 @opindex mr10k-cache-barrier
17851 Specify whether GCC should insert cache barriers to avoid the
17852 side-effects of speculation on R10K processors.
17854 In common with many processors, the R10K tries to predict the outcome
17855 of a conditional branch and speculatively executes instructions from
17856 the ``taken'' branch. It later aborts these instructions if the
17857 predicted outcome is wrong. However, on the R10K, even aborted
17858 instructions can have side effects.
17860 This problem only affects kernel stores and, depending on the system,
17861 kernel loads. As an example, a speculatively-executed store may load
17862 the target memory into cache and mark the cache line as dirty, even if
17863 the store itself is later aborted. If a DMA operation writes to the
17864 same area of memory before the ``dirty'' line is flushed, the cached
17865 data overwrites the DMA-ed data. See the R10K processor manual
17866 for a full description, including other potential problems.
17868 One workaround is to insert cache barrier instructions before every memory
17869 access that might be speculatively executed and that might have side
17870 effects even if aborted. @option{-mr10k-cache-barrier=@var{setting}}
17871 controls GCC's implementation of this workaround. It assumes that
17872 aborted accesses to any byte in the following regions does not have
17877 the memory occupied by the current function's stack frame;
17880 the memory occupied by an incoming stack argument;
17883 the memory occupied by an object with a link-time-constant address.
17886 It is the kernel's responsibility to ensure that speculative
17887 accesses to these regions are indeed safe.
17889 If the input program contains a function declaration such as:
17895 then the implementation of @code{foo} must allow @code{j foo} and
17896 @code{jal foo} to be executed speculatively. GCC honors this
17897 restriction for functions it compiles itself. It expects non-GCC
17898 functions (such as hand-written assembly code) to do the same.
17900 The option has three forms:
17903 @item -mr10k-cache-barrier=load-store
17904 Insert a cache barrier before a load or store that might be
17905 speculatively executed and that might have side effects even
17908 @item -mr10k-cache-barrier=store
17909 Insert a cache barrier before a store that might be speculatively
17910 executed and that might have side effects even if aborted.
17912 @item -mr10k-cache-barrier=none
17913 Disable the insertion of cache barriers. This is the default setting.
17916 @item -mflush-func=@var{func}
17917 @itemx -mno-flush-func
17918 @opindex mflush-func
17919 Specifies the function to call to flush the I and D caches, or to not
17920 call any such function. If called, the function must take the same
17921 arguments as the common @code{_flush_func}, that is, the address of the
17922 memory range for which the cache is being flushed, the size of the
17923 memory range, and the number 3 (to flush both caches). The default
17924 depends on the target GCC was configured for, but commonly is either
17925 @code{_flush_func} or @code{__cpu_flush}.
17927 @item mbranch-cost=@var{num}
17928 @opindex mbranch-cost
17929 Set the cost of branches to roughly @var{num} ``simple'' instructions.
17930 This cost is only a heuristic and is not guaranteed to produce
17931 consistent results across releases. A zero cost redundantly selects
17932 the default, which is based on the @option{-mtune} setting.
17934 @item -mbranch-likely
17935 @itemx -mno-branch-likely
17936 @opindex mbranch-likely
17937 @opindex mno-branch-likely
17938 Enable or disable use of Branch Likely instructions, regardless of the
17939 default for the selected architecture. By default, Branch Likely
17940 instructions may be generated if they are supported by the selected
17941 architecture. An exception is for the MIPS32 and MIPS64 architectures
17942 and processors that implement those architectures; for those, Branch
17943 Likely instructions are not be generated by default because the MIPS32
17944 and MIPS64 architectures specifically deprecate their use.
17946 @item -mfp-exceptions
17947 @itemx -mno-fp-exceptions
17948 @opindex mfp-exceptions
17949 Specifies whether FP exceptions are enabled. This affects how
17950 FP instructions are scheduled for some processors.
17951 The default is that FP exceptions are
17954 For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
17955 64-bit code, then we can use both FP pipes. Otherwise, we can only use one
17958 @item -mvr4130-align
17959 @itemx -mno-vr4130-align
17960 @opindex mvr4130-align
17961 The VR4130 pipeline is two-way superscalar, but can only issue two
17962 instructions together if the first one is 8-byte aligned. When this
17963 option is enabled, GCC aligns pairs of instructions that it
17964 thinks should execute in parallel.
17966 This option only has an effect when optimizing for the VR4130.
17967 It normally makes code faster, but at the expense of making it bigger.
17968 It is enabled by default at optimization level @option{-O3}.
17973 Enable (disable) generation of @code{synci} instructions on
17974 architectures that support it. The @code{synci} instructions (if
17975 enabled) are generated when @code{__builtin___clear_cache} is
17978 This option defaults to @option{-mno-synci}, but the default can be
17979 overridden by configuring GCC with @option{--with-synci}.
17981 When compiling code for single processor systems, it is generally safe
17982 to use @code{synci}. However, on many multi-core (SMP) systems, it
17983 does not invalidate the instruction caches on all cores and may lead
17984 to undefined behavior.
17986 @item -mrelax-pic-calls
17987 @itemx -mno-relax-pic-calls
17988 @opindex mrelax-pic-calls
17989 Try to turn PIC calls that are normally dispatched via register
17990 @code{$25} into direct calls. This is only possible if the linker can
17991 resolve the destination at link-time and if the destination is within
17992 range for a direct call.
17994 @option{-mrelax-pic-calls} is the default if GCC was configured to use
17995 an assembler and a linker that support the @code{.reloc} assembly
17996 directive and @option{-mexplicit-relocs} is in effect. With
17997 @option{-mno-explicit-relocs}, this optimization can be performed by the
17998 assembler and the linker alone without help from the compiler.
18000 @item -mmcount-ra-address
18001 @itemx -mno-mcount-ra-address
18002 @opindex mmcount-ra-address
18003 @opindex mno-mcount-ra-address
18004 Emit (do not emit) code that allows @code{_mcount} to modify the
18005 calling function's return address. When enabled, this option extends
18006 the usual @code{_mcount} interface with a new @var{ra-address}
18007 parameter, which has type @code{intptr_t *} and is passed in register
18008 @code{$12}. @code{_mcount} can then modify the return address by
18009 doing both of the following:
18012 Returning the new address in register @code{$31}.
18014 Storing the new address in @code{*@var{ra-address}},
18015 if @var{ra-address} is nonnull.
18018 The default is @option{-mno-mcount-ra-address}.
18023 @subsection MMIX Options
18024 @cindex MMIX Options
18026 These options are defined for the MMIX:
18030 @itemx -mno-libfuncs
18032 @opindex mno-libfuncs
18033 Specify that intrinsic library functions are being compiled, passing all
18034 values in registers, no matter the size.
18037 @itemx -mno-epsilon
18039 @opindex mno-epsilon
18040 Generate floating-point comparison instructions that compare with respect
18041 to the @code{rE} epsilon register.
18043 @item -mabi=mmixware
18045 @opindex mabi=mmixware
18047 Generate code that passes function parameters and return values that (in
18048 the called function) are seen as registers @code{$0} and up, as opposed to
18049 the GNU ABI which uses global registers @code{$231} and up.
18051 @item -mzero-extend
18052 @itemx -mno-zero-extend
18053 @opindex mzero-extend
18054 @opindex mno-zero-extend
18055 When reading data from memory in sizes shorter than 64 bits, use (do not
18056 use) zero-extending load instructions by default, rather than
18057 sign-extending ones.
18060 @itemx -mno-knuthdiv
18062 @opindex mno-knuthdiv
18063 Make the result of a division yielding a remainder have the same sign as
18064 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
18065 remainder follows the sign of the dividend. Both methods are
18066 arithmetically valid, the latter being almost exclusively used.
18068 @item -mtoplevel-symbols
18069 @itemx -mno-toplevel-symbols
18070 @opindex mtoplevel-symbols
18071 @opindex mno-toplevel-symbols
18072 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
18073 code can be used with the @code{PREFIX} assembly directive.
18077 Generate an executable in the ELF format, rather than the default
18078 @samp{mmo} format used by the @command{mmix} simulator.
18080 @item -mbranch-predict
18081 @itemx -mno-branch-predict
18082 @opindex mbranch-predict
18083 @opindex mno-branch-predict
18084 Use (do not use) the probable-branch instructions, when static branch
18085 prediction indicates a probable branch.
18087 @item -mbase-addresses
18088 @itemx -mno-base-addresses
18089 @opindex mbase-addresses
18090 @opindex mno-base-addresses
18091 Generate (do not generate) code that uses @emph{base addresses}. Using a
18092 base address automatically generates a request (handled by the assembler
18093 and the linker) for a constant to be set up in a global register. The
18094 register is used for one or more base address requests within the range 0
18095 to 255 from the value held in the register. The generally leads to short
18096 and fast code, but the number of different data items that can be
18097 addressed is limited. This means that a program that uses lots of static
18098 data may require @option{-mno-base-addresses}.
18100 @item -msingle-exit
18101 @itemx -mno-single-exit
18102 @opindex msingle-exit
18103 @opindex mno-single-exit
18104 Force (do not force) generated code to have a single exit point in each
18108 @node MN10300 Options
18109 @subsection MN10300 Options
18110 @cindex MN10300 options
18112 These @option{-m} options are defined for Matsushita MN10300 architectures:
18117 Generate code to avoid bugs in the multiply instructions for the MN10300
18118 processors. This is the default.
18120 @item -mno-mult-bug
18121 @opindex mno-mult-bug
18122 Do not generate code to avoid bugs in the multiply instructions for the
18123 MN10300 processors.
18127 Generate code using features specific to the AM33 processor.
18131 Do not generate code using features specific to the AM33 processor. This
18136 Generate code using features specific to the AM33/2.0 processor.
18140 Generate code using features specific to the AM34 processor.
18142 @item -mtune=@var{cpu-type}
18144 Use the timing characteristics of the indicated CPU type when
18145 scheduling instructions. This does not change the targeted processor
18146 type. The CPU type must be one of @samp{mn10300}, @samp{am33},
18147 @samp{am33-2} or @samp{am34}.
18149 @item -mreturn-pointer-on-d0
18150 @opindex mreturn-pointer-on-d0
18151 When generating a function that returns a pointer, return the pointer
18152 in both @code{a0} and @code{d0}. Otherwise, the pointer is returned
18153 only in @code{a0}, and attempts to call such functions without a prototype
18154 result in errors. Note that this option is on by default; use
18155 @option{-mno-return-pointer-on-d0} to disable it.
18159 Do not link in the C run-time initialization object file.
18163 Indicate to the linker that it should perform a relaxation optimization pass
18164 to shorten branches, calls and absolute memory addresses. This option only
18165 has an effect when used on the command line for the final link step.
18167 This option makes symbolic debugging impossible.
18171 Allow the compiler to generate @emph{Long Instruction Word}
18172 instructions if the target is the @samp{AM33} or later. This is the
18173 default. This option defines the preprocessor macro @code{__LIW__}.
18177 Do not allow the compiler to generate @emph{Long Instruction Word}
18178 instructions. This option defines the preprocessor macro
18183 Allow the compiler to generate the @emph{SETLB} and @emph{Lcc}
18184 instructions if the target is the @samp{AM33} or later. This is the
18185 default. This option defines the preprocessor macro @code{__SETLB__}.
18189 Do not allow the compiler to generate @emph{SETLB} or @emph{Lcc}
18190 instructions. This option defines the preprocessor macro
18191 @code{__NO_SETLB__}.
18195 @node Moxie Options
18196 @subsection Moxie Options
18197 @cindex Moxie Options
18203 Generate big-endian code. This is the default for @samp{moxie-*-*}
18208 Generate little-endian code.
18212 Generate mul.x and umul.x instructions. This is the default for
18213 @samp{moxiebox-*-*} configurations.
18217 Do not link in the C run-time initialization object file.
18221 @node MSP430 Options
18222 @subsection MSP430 Options
18223 @cindex MSP430 Options
18225 These options are defined for the MSP430:
18231 Force assembly output to always use hex constants. Normally such
18232 constants are signed decimals, but this option is available for
18233 testsuite and/or aesthetic purposes.
18237 Select the MCU to target. This is used to create a C preprocessor
18238 symbol based upon the MCU name, converted to upper case and pre- and
18239 post-fixed with @samp{__}. This in turn is used by the
18240 @file{msp430.h} header file to select an MCU-specific supplementary
18243 The option also sets the ISA to use. If the MCU name is one that is
18244 known to only support the 430 ISA then that is selected, otherwise the
18245 430X ISA is selected. A generic MCU name of @samp{msp430} can also be
18246 used to select the 430 ISA. Similarly the generic @samp{msp430x} MCU
18247 name selects the 430X ISA.
18249 In addition an MCU-specific linker script is added to the linker
18250 command line. The script's name is the name of the MCU with
18251 @file{.ld} appended. Thus specifying @option{-mmcu=xxx} on the @command{gcc}
18252 command line defines the C preprocessor symbol @code{__XXX__} and
18253 cause the linker to search for a script called @file{xxx.ld}.
18255 This option is also passed on to the assembler.
18259 Specifies the ISA to use. Accepted values are @samp{msp430},
18260 @samp{msp430x} and @samp{msp430xv2}. This option is deprecated. The
18261 @option{-mmcu=} option should be used to select the ISA.
18265 Link to the simulator runtime libraries and linker script. Overrides
18266 any scripts that would be selected by the @option{-mmcu=} option.
18270 Use large-model addressing (20-bit pointers, 32-bit @code{size_t}).
18274 Use small-model addressing (16-bit pointers, 16-bit @code{size_t}).
18278 This option is passed to the assembler and linker, and allows the
18279 linker to perform certain optimizations that cannot be done until
18284 Describes the type of hardware multiply supported by the target.
18285 Accepted values are @samp{none} for no hardware multiply, @samp{16bit}
18286 for the original 16-bit-only multiply supported by early MCUs.
18287 @samp{32bit} for the 16/32-bit multiply supported by later MCUs and
18288 @samp{f5series} for the 16/32-bit multiply supported by F5-series MCUs.
18289 A value of @samp{auto} can also be given. This tells GCC to deduce
18290 the hardware multiply support based upon the MCU name provided by the
18291 @option{-mmcu} option. If no @option{-mmcu} option is specified then
18292 @samp{32bit} hardware multiply support is assumed. @samp{auto} is the
18295 Hardware multiplies are normally performed by calling a library
18296 routine. This saves space in the generated code. When compiling at
18297 @option{-O3} or higher however the hardware multiplier is invoked
18298 inline. This makes for bigger, but faster code.
18300 The hardware multiply routines disable interrupts whilst running and
18301 restore the previous interrupt state when they finish. This makes
18302 them safe to use inside interrupt handlers as well as in normal code.
18306 Enable the use of a minimum runtime environment - no static
18307 initializers or constructors. This is intended for memory-constrained
18308 devices. The compiler includes special symbols in some objects
18309 that tell the linker and runtime which code fragments are required.
18311 @item -mcode-region=
18312 @itemx -mdata-region=
18313 @opindex mcode-region
18314 @opindex mdata-region
18315 These options tell the compiler where to place functions and data that
18316 do not have one of the @code{lower}, @code{upper}, @code{either} or
18317 @code{section} attributes. Possible values are @code{lower},
18318 @code{upper}, @code{either} or @code{any}. The first three behave
18319 like the corresponding attribute. The fourth possible value -
18320 @code{any} - is the default. It leaves placement entirely up to the
18321 linker script and how it assigns the standard sections (.text, .data
18322 etc) to the memory regions.
18326 @node NDS32 Options
18327 @subsection NDS32 Options
18328 @cindex NDS32 Options
18330 These options are defined for NDS32 implementations:
18335 @opindex mbig-endian
18336 Generate code in big-endian mode.
18338 @item -mlittle-endian
18339 @opindex mlittle-endian
18340 Generate code in little-endian mode.
18342 @item -mreduced-regs
18343 @opindex mreduced-regs
18344 Use reduced-set registers for register allocation.
18347 @opindex mfull-regs
18348 Use full-set registers for register allocation.
18352 Generate conditional move instructions.
18356 Do not generate conditional move instructions.
18360 Generate performance extension instructions.
18362 @item -mno-perf-ext
18363 @opindex mno-perf-ext
18364 Do not generate performance extension instructions.
18368 Generate v3 push25/pop25 instructions.
18371 @opindex mno-v3push
18372 Do not generate v3 push25/pop25 instructions.
18376 Generate 16-bit instructions.
18379 @opindex mno-16-bit
18380 Do not generate 16-bit instructions.
18382 @item -misr-vector-size=@var{num}
18383 @opindex misr-vector-size
18384 Specify the size of each interrupt vector, which must be 4 or 16.
18386 @item -mcache-block-size=@var{num}
18387 @opindex mcache-block-size
18388 Specify the size of each cache block,
18389 which must be a power of 2 between 4 and 512.
18391 @item -march=@var{arch}
18393 Specify the name of the target architecture.
18395 @item -mcmodel=@var{code-model}
18397 Set the code model to one of
18400 All the data and read-only data segments must be within 512KB addressing space.
18401 The text segment must be within 16MB addressing space.
18402 @item @samp{medium}
18403 The data segment must be within 512KB while the read-only data segment can be
18404 within 4GB addressing space. The text segment should be still within 16MB
18407 All the text and data segments can be within 4GB addressing space.
18411 @opindex mctor-dtor
18412 Enable constructor/destructor feature.
18416 Guide linker to relax instructions.
18420 @node Nios II Options
18421 @subsection Nios II Options
18422 @cindex Nios II options
18423 @cindex Altera Nios II options
18425 These are the options defined for the Altera Nios II processor.
18431 @cindex smaller data references
18432 Put global and static objects less than or equal to @var{num} bytes
18433 into the small data or BSS sections instead of the normal data or BSS
18434 sections. The default value of @var{num} is 8.
18436 @item -mgpopt=@var{option}
18441 Generate (do not generate) GP-relative accesses. The following
18442 @var{option} names are recognized:
18447 Do not generate GP-relative accesses.
18450 Generate GP-relative accesses for small data objects that are not
18451 external or weak. Also use GP-relative addressing for objects that
18452 have been explicitly placed in a small data section via a @code{section}
18456 As for @samp{local}, but also generate GP-relative accesses for
18457 small data objects that are external or weak. If you use this option,
18458 you must ensure that all parts of your program (including libraries) are
18459 compiled with the same @option{-G} setting.
18462 Generate GP-relative accesses for all data objects in the program. If you
18463 use this option, the entire data and BSS segments
18464 of your program must fit in 64K of memory and you must use an appropriate
18465 linker script to allocate them within the addressible range of the
18469 Generate GP-relative addresses for function pointers as well as data
18470 pointers. If you use this option, the entire text, data, and BSS segments
18471 of your program must fit in 64K of memory and you must use an appropriate
18472 linker script to allocate them within the addressible range of the
18477 @option{-mgpopt} is equivalent to @option{-mgpopt=local}, and
18478 @option{-mno-gpopt} is equivalent to @option{-mgpopt=none}.
18480 The default is @option{-mgpopt} except when @option{-fpic} or
18481 @option{-fPIC} is specified to generate position-independent code.
18482 Note that the Nios II ABI does not permit GP-relative accesses from
18485 You may need to specify @option{-mno-gpopt} explicitly when building
18486 programs that include large amounts of small data, including large
18487 GOT data sections. In this case, the 16-bit offset for GP-relative
18488 addressing may not be large enough to allow access to the entire
18489 small data section.
18495 Generate little-endian (default) or big-endian (experimental) code,
18498 @item -mbypass-cache
18499 @itemx -mno-bypass-cache
18500 @opindex mno-bypass-cache
18501 @opindex mbypass-cache
18502 Force all load and store instructions to always bypass cache by
18503 using I/O variants of the instructions. The default is not to
18506 @item -mno-cache-volatile
18507 @itemx -mcache-volatile
18508 @opindex mcache-volatile
18509 @opindex mno-cache-volatile
18510 Volatile memory access bypass the cache using the I/O variants of
18511 the load and store instructions. The default is not to bypass the cache.
18513 @item -mno-fast-sw-div
18514 @itemx -mfast-sw-div
18515 @opindex mno-fast-sw-div
18516 @opindex mfast-sw-div
18517 Do not use table-based fast divide for small numbers. The default
18518 is to use the fast divide at @option{-O3} and above.
18522 @itemx -mno-hw-mulx
18526 @opindex mno-hw-mul
18528 @opindex mno-hw-mulx
18530 @opindex mno-hw-div
18532 Enable or disable emitting @code{mul}, @code{mulx} and @code{div} family of
18533 instructions by the compiler. The default is to emit @code{mul}
18534 and not emit @code{div} and @code{mulx}.
18536 @item -mcustom-@var{insn}=@var{N}
18537 @itemx -mno-custom-@var{insn}
18538 @opindex mcustom-@var{insn}
18539 @opindex mno-custom-@var{insn}
18540 Each @option{-mcustom-@var{insn}=@var{N}} option enables use of a
18541 custom instruction with encoding @var{N} when generating code that uses
18542 @var{insn}. For example, @option{-mcustom-fadds=253} generates custom
18543 instruction 253 for single-precision floating-point add operations instead
18544 of the default behavior of using a library call.
18546 The following values of @var{insn} are supported. Except as otherwise
18547 noted, floating-point operations are expected to be implemented with
18548 normal IEEE 754 semantics and correspond directly to the C operators or the
18549 equivalent GCC built-in functions (@pxref{Other Builtins}).
18551 Single-precision floating point:
18554 @item @samp{fadds}, @samp{fsubs}, @samp{fdivs}, @samp{fmuls}
18555 Binary arithmetic operations.
18561 Unary absolute value.
18563 @item @samp{fcmpeqs}, @samp{fcmpges}, @samp{fcmpgts}, @samp{fcmples}, @samp{fcmplts}, @samp{fcmpnes}
18564 Comparison operations.
18566 @item @samp{fmins}, @samp{fmaxs}
18567 Floating-point minimum and maximum. These instructions are only
18568 generated if @option{-ffinite-math-only} is specified.
18570 @item @samp{fsqrts}
18571 Unary square root operation.
18573 @item @samp{fcoss}, @samp{fsins}, @samp{ftans}, @samp{fatans}, @samp{fexps}, @samp{flogs}
18574 Floating-point trigonometric and exponential functions. These instructions
18575 are only generated if @option{-funsafe-math-optimizations} is also specified.
18579 Double-precision floating point:
18582 @item @samp{faddd}, @samp{fsubd}, @samp{fdivd}, @samp{fmuld}
18583 Binary arithmetic operations.
18589 Unary absolute value.
18591 @item @samp{fcmpeqd}, @samp{fcmpged}, @samp{fcmpgtd}, @samp{fcmpled}, @samp{fcmpltd}, @samp{fcmpned}
18592 Comparison operations.
18594 @item @samp{fmind}, @samp{fmaxd}
18595 Double-precision minimum and maximum. These instructions are only
18596 generated if @option{-ffinite-math-only} is specified.
18598 @item @samp{fsqrtd}
18599 Unary square root operation.
18601 @item @samp{fcosd}, @samp{fsind}, @samp{ftand}, @samp{fatand}, @samp{fexpd}, @samp{flogd}
18602 Double-precision trigonometric and exponential functions. These instructions
18603 are only generated if @option{-funsafe-math-optimizations} is also specified.
18609 @item @samp{fextsd}
18610 Conversion from single precision to double precision.
18612 @item @samp{ftruncds}
18613 Conversion from double precision to single precision.
18615 @item @samp{fixsi}, @samp{fixsu}, @samp{fixdi}, @samp{fixdu}
18616 Conversion from floating point to signed or unsigned integer types, with
18617 truncation towards zero.
18620 Conversion from single-precision floating point to signed integer,
18621 rounding to the nearest integer and ties away from zero.
18622 This corresponds to the @code{__builtin_lroundf} function when
18623 @option{-fno-math-errno} is used.
18625 @item @samp{floatis}, @samp{floatus}, @samp{floatid}, @samp{floatud}
18626 Conversion from signed or unsigned integer types to floating-point types.
18630 In addition, all of the following transfer instructions for internal
18631 registers X and Y must be provided to use any of the double-precision
18632 floating-point instructions. Custom instructions taking two
18633 double-precision source operands expect the first operand in the
18634 64-bit register X. The other operand (or only operand of a unary
18635 operation) is given to the custom arithmetic instruction with the
18636 least significant half in source register @var{src1} and the most
18637 significant half in @var{src2}. A custom instruction that returns a
18638 double-precision result returns the most significant 32 bits in the
18639 destination register and the other half in 32-bit register Y.
18640 GCC automatically generates the necessary code sequences to write
18641 register X and/or read register Y when double-precision floating-point
18642 instructions are used.
18647 Write @var{src1} into the least significant half of X and @var{src2} into
18648 the most significant half of X.
18651 Write @var{src1} into Y.
18653 @item @samp{frdxhi}, @samp{frdxlo}
18654 Read the most or least (respectively) significant half of X and store it in
18658 Read the value of Y and store it into @var{dest}.
18661 Note that you can gain more local control over generation of Nios II custom
18662 instructions by using the @code{target("custom-@var{insn}=@var{N}")}
18663 and @code{target("no-custom-@var{insn}")} function attributes
18664 (@pxref{Function Attributes})
18665 or pragmas (@pxref{Function Specific Option Pragmas}).
18667 @item -mcustom-fpu-cfg=@var{name}
18668 @opindex mcustom-fpu-cfg
18670 This option enables a predefined, named set of custom instruction encodings
18671 (see @option{-mcustom-@var{insn}} above).
18672 Currently, the following sets are defined:
18674 @option{-mcustom-fpu-cfg=60-1} is equivalent to:
18675 @gccoptlist{-mcustom-fmuls=252 @gol
18676 -mcustom-fadds=253 @gol
18677 -mcustom-fsubs=254 @gol
18678 -fsingle-precision-constant}
18680 @option{-mcustom-fpu-cfg=60-2} is equivalent to:
18681 @gccoptlist{-mcustom-fmuls=252 @gol
18682 -mcustom-fadds=253 @gol
18683 -mcustom-fsubs=254 @gol
18684 -mcustom-fdivs=255 @gol
18685 -fsingle-precision-constant}
18687 @option{-mcustom-fpu-cfg=72-3} is equivalent to:
18688 @gccoptlist{-mcustom-floatus=243 @gol
18689 -mcustom-fixsi=244 @gol
18690 -mcustom-floatis=245 @gol
18691 -mcustom-fcmpgts=246 @gol
18692 -mcustom-fcmples=249 @gol
18693 -mcustom-fcmpeqs=250 @gol
18694 -mcustom-fcmpnes=251 @gol
18695 -mcustom-fmuls=252 @gol
18696 -mcustom-fadds=253 @gol
18697 -mcustom-fsubs=254 @gol
18698 -mcustom-fdivs=255 @gol
18699 -fsingle-precision-constant}
18701 Custom instruction assignments given by individual
18702 @option{-mcustom-@var{insn}=} options override those given by
18703 @option{-mcustom-fpu-cfg=}, regardless of the
18704 order of the options on the command line.
18706 Note that you can gain more local control over selection of a FPU
18707 configuration by using the @code{target("custom-fpu-cfg=@var{name}")}
18708 function attribute (@pxref{Function Attributes})
18709 or pragma (@pxref{Function Specific Option Pragmas}).
18713 These additional @samp{-m} options are available for the Altera Nios II
18714 ELF (bare-metal) target:
18720 Link with HAL BSP. This suppresses linking with the GCC-provided C runtime
18721 startup and termination code, and is typically used in conjunction with
18722 @option{-msys-crt0=} to specify the location of the alternate startup code
18723 provided by the HAL BSP.
18727 Link with a limited version of the C library, @option{-lsmallc}, rather than
18730 @item -msys-crt0=@var{startfile}
18732 @var{startfile} is the file name of the startfile (crt0) to use
18733 when linking. This option is only useful in conjunction with @option{-mhal}.
18735 @item -msys-lib=@var{systemlib}
18737 @var{systemlib} is the library name of the library that provides
18738 low-level system calls required by the C library,
18739 e.g. @code{read} and @code{write}.
18740 This option is typically used to link with a library provided by a HAL BSP.
18744 @node Nvidia PTX Options
18745 @subsection Nvidia PTX Options
18746 @cindex Nvidia PTX options
18747 @cindex nvptx options
18749 These options are defined for Nvidia PTX:
18757 Generate code for 32-bit or 64-bit ABI.
18760 @opindex mmainkernel
18761 Link in code for a __main kernel. This is for stand-alone instead of
18762 offloading execution.
18766 @node PDP-11 Options
18767 @subsection PDP-11 Options
18768 @cindex PDP-11 Options
18770 These options are defined for the PDP-11:
18775 Use hardware FPP floating point. This is the default. (FIS floating
18776 point on the PDP-11/40 is not supported.)
18779 @opindex msoft-float
18780 Do not use hardware floating point.
18784 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
18788 Return floating-point results in memory. This is the default.
18792 Generate code for a PDP-11/40.
18796 Generate code for a PDP-11/45. This is the default.
18800 Generate code for a PDP-11/10.
18802 @item -mbcopy-builtin
18803 @opindex mbcopy-builtin
18804 Use inline @code{movmemhi} patterns for copying memory. This is the
18809 Do not use inline @code{movmemhi} patterns for copying memory.
18815 Use 16-bit @code{int}. This is the default.
18821 Use 32-bit @code{int}.
18824 @itemx -mno-float32
18826 @opindex mno-float32
18827 Use 64-bit @code{float}. This is the default.
18830 @itemx -mno-float64
18832 @opindex mno-float64
18833 Use 32-bit @code{float}.
18837 Use @code{abshi2} pattern. This is the default.
18841 Do not use @code{abshi2} pattern.
18843 @item -mbranch-expensive
18844 @opindex mbranch-expensive
18845 Pretend that branches are expensive. This is for experimenting with
18846 code generation only.
18848 @item -mbranch-cheap
18849 @opindex mbranch-cheap
18850 Do not pretend that branches are expensive. This is the default.
18854 Use Unix assembler syntax. This is the default when configured for
18855 @samp{pdp11-*-bsd}.
18859 Use DEC assembler syntax. This is the default when configured for any
18860 PDP-11 target other than @samp{pdp11-*-bsd}.
18863 @node picoChip Options
18864 @subsection picoChip Options
18865 @cindex picoChip options
18867 These @samp{-m} options are defined for picoChip implementations:
18871 @item -mae=@var{ae_type}
18873 Set the instruction set, register set, and instruction scheduling
18874 parameters for array element type @var{ae_type}. Supported values
18875 for @var{ae_type} are @samp{ANY}, @samp{MUL}, and @samp{MAC}.
18877 @option{-mae=ANY} selects a completely generic AE type. Code
18878 generated with this option runs on any of the other AE types. The
18879 code is not as efficient as it would be if compiled for a specific
18880 AE type, and some types of operation (e.g., multiplication) do not
18881 work properly on all types of AE.
18883 @option{-mae=MUL} selects a MUL AE type. This is the most useful AE type
18884 for compiled code, and is the default.
18886 @option{-mae=MAC} selects a DSP-style MAC AE. Code compiled with this
18887 option may suffer from poor performance of byte (char) manipulation,
18888 since the DSP AE does not provide hardware support for byte load/stores.
18890 @item -msymbol-as-address
18891 Enable the compiler to directly use a symbol name as an address in a
18892 load/store instruction, without first loading it into a
18893 register. Typically, the use of this option generates larger
18894 programs, which run faster than when the option isn't used. However, the
18895 results vary from program to program, so it is left as a user option,
18896 rather than being permanently enabled.
18898 @item -mno-inefficient-warnings
18899 Disables warnings about the generation of inefficient code. These
18900 warnings can be generated, for example, when compiling code that
18901 performs byte-level memory operations on the MAC AE type. The MAC AE has
18902 no hardware support for byte-level memory operations, so all byte
18903 load/stores must be synthesized from word load/store operations. This is
18904 inefficient and a warning is generated to indicate
18905 that you should rewrite the code to avoid byte operations, or to target
18906 an AE type that has the necessary hardware support. This option disables
18911 @node PowerPC Options
18912 @subsection PowerPC Options
18913 @cindex PowerPC options
18915 These are listed under @xref{RS/6000 and PowerPC Options}.
18918 @subsection RL78 Options
18919 @cindex RL78 Options
18925 Links in additional target libraries to support operation within a
18934 Specifies the type of hardware multiplication and division support to
18935 be used. The simplest is @code{none}, which uses software for both
18936 multiplication and division. This is the default. The @code{g13}
18937 value is for the hardware multiply/divide peripheral found on the
18938 RL78/G13 (S2 core) targets. The @code{g14} value selects the use of
18939 the multiplication and division instructions supported by the RL78/G14
18940 (S3 core) parts. The value @code{rl78} is an alias for @code{g14} and
18941 the value @code{mg10} is an alias for @code{none}.
18943 In addition a C preprocessor macro is defined, based upon the setting
18944 of this option. Possible values are: @code{__RL78_MUL_NONE__},
18945 @code{__RL78_MUL_G13__} or @code{__RL78_MUL_G14__}.
18952 Specifies the RL78 core to target. The default is the G14 core, also
18953 known as an S3 core or just RL78. The G13 or S2 core does not have
18954 multiply or divide instructions, instead it uses a hardware peripheral
18955 for these operations. The G10 or S1 core does not have register
18956 banks, so it uses a different calling convention.
18958 If this option is set it also selects the type of hardware multiply
18959 support to use, unless this is overridden by an explicit
18960 @option{-mmul=none} option on the command line. Thus specifying
18961 @option{-mcpu=g13} enables the use of the G13 hardware multiply
18962 peripheral and specifying @option{-mcpu=g10} disables the use of
18963 hardware multipications altogether.
18965 Note, although the RL78/G14 core is the default target, specifying
18966 @option{-mcpu=g14} or @option{-mcpu=rl78} on the command line does
18967 change the behaviour of the toolchain since it also enables G14
18968 hardware multiply support. If these options are not specified on the
18969 command line then software multiplication routines will be used even
18970 though the code targets the RL78 core. This is for backwards
18971 compatibility with older toolchains which did not have hardware
18972 multiply and divide support.
18974 In addition a C preprocessor macro is defined, based upon the setting
18975 of this option. Possible values are: @code{__RL78_G10__},
18976 @code{__RL78_G13__} or @code{__RL78_G14__}.
18986 These are aliases for the corresponding @option{-mcpu=} option. They
18987 are provided for backwards compatibility.
18991 Allow the compiler to use all of the available registers. By default
18992 registers @code{r24..r31} are reserved for use in interrupt handlers.
18993 With this option enabled these registers can be used in ordinary
18996 @item -m64bit-doubles
18997 @itemx -m32bit-doubles
18998 @opindex m64bit-doubles
18999 @opindex m32bit-doubles
19000 Make the @code{double} data type be 64 bits (@option{-m64bit-doubles})
19001 or 32 bits (@option{-m32bit-doubles}) in size. The default is
19002 @option{-m32bit-doubles}.
19006 @node RS/6000 and PowerPC Options
19007 @subsection IBM RS/6000 and PowerPC Options
19008 @cindex RS/6000 and PowerPC Options
19009 @cindex IBM RS/6000 and PowerPC Options
19011 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
19013 @item -mpowerpc-gpopt
19014 @itemx -mno-powerpc-gpopt
19015 @itemx -mpowerpc-gfxopt
19016 @itemx -mno-powerpc-gfxopt
19019 @itemx -mno-powerpc64
19023 @itemx -mno-popcntb
19025 @itemx -mno-popcntd
19034 @itemx -mno-hard-dfp
19035 @opindex mpowerpc-gpopt
19036 @opindex mno-powerpc-gpopt
19037 @opindex mpowerpc-gfxopt
19038 @opindex mno-powerpc-gfxopt
19039 @opindex mpowerpc64
19040 @opindex mno-powerpc64
19044 @opindex mno-popcntb
19046 @opindex mno-popcntd
19052 @opindex mno-mfpgpr
19054 @opindex mno-hard-dfp
19055 You use these options to specify which instructions are available on the
19056 processor you are using. The default value of these options is
19057 determined when configuring GCC@. Specifying the
19058 @option{-mcpu=@var{cpu_type}} overrides the specification of these
19059 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
19060 rather than the options listed above.
19062 Specifying @option{-mpowerpc-gpopt} allows
19063 GCC to use the optional PowerPC architecture instructions in the
19064 General Purpose group, including floating-point square root. Specifying
19065 @option{-mpowerpc-gfxopt} allows GCC to
19066 use the optional PowerPC architecture instructions in the Graphics
19067 group, including floating-point select.
19069 The @option{-mmfcrf} option allows GCC to generate the move from
19070 condition register field instruction implemented on the POWER4
19071 processor and other processors that support the PowerPC V2.01
19073 The @option{-mpopcntb} option allows GCC to generate the popcount and
19074 double-precision FP reciprocal estimate instruction implemented on the
19075 POWER5 processor and other processors that support the PowerPC V2.02
19077 The @option{-mpopcntd} option allows GCC to generate the popcount
19078 instruction implemented on the POWER7 processor and other processors
19079 that support the PowerPC V2.06 architecture.
19080 The @option{-mfprnd} option allows GCC to generate the FP round to
19081 integer instructions implemented on the POWER5+ processor and other
19082 processors that support the PowerPC V2.03 architecture.
19083 The @option{-mcmpb} option allows GCC to generate the compare bytes
19084 instruction implemented on the POWER6 processor and other processors
19085 that support the PowerPC V2.05 architecture.
19086 The @option{-mmfpgpr} option allows GCC to generate the FP move to/from
19087 general-purpose register instructions implemented on the POWER6X
19088 processor and other processors that support the extended PowerPC V2.05
19090 The @option{-mhard-dfp} option allows GCC to generate the decimal
19091 floating-point instructions implemented on some POWER processors.
19093 The @option{-mpowerpc64} option allows GCC to generate the additional
19094 64-bit instructions that are found in the full PowerPC64 architecture
19095 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
19096 @option{-mno-powerpc64}.
19098 @item -mcpu=@var{cpu_type}
19100 Set architecture type, register usage, and
19101 instruction scheduling parameters for machine type @var{cpu_type}.
19102 Supported values for @var{cpu_type} are @samp{401}, @samp{403},
19103 @samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{464}, @samp{464fp},
19104 @samp{476}, @samp{476fp}, @samp{505}, @samp{601}, @samp{602}, @samp{603},
19105 @samp{603e}, @samp{604}, @samp{604e}, @samp{620}, @samp{630}, @samp{740},
19106 @samp{7400}, @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
19107 @samp{860}, @samp{970}, @samp{8540}, @samp{a2}, @samp{e300c2},
19108 @samp{e300c3}, @samp{e500mc}, @samp{e500mc64}, @samp{e5500},
19109 @samp{e6500}, @samp{ec603e}, @samp{G3}, @samp{G4}, @samp{G5},
19110 @samp{titan}, @samp{power3}, @samp{power4}, @samp{power5}, @samp{power5+},
19111 @samp{power6}, @samp{power6x}, @samp{power7}, @samp{power8}, @samp{powerpc},
19112 @samp{powerpc64}, @samp{powerpc64le}, and @samp{rs64}.
19114 @option{-mcpu=powerpc}, @option{-mcpu=powerpc64}, and
19115 @option{-mcpu=powerpc64le} specify pure 32-bit PowerPC (either
19116 endian), 64-bit big endian PowerPC and 64-bit little endian PowerPC
19117 architecture machine types, with an appropriate, generic processor
19118 model assumed for scheduling purposes.
19120 The other options specify a specific processor. Code generated under
19121 those options runs best on that processor, and may not run at all on
19124 The @option{-mcpu} options automatically enable or disable the
19127 @gccoptlist{-maltivec -mfprnd -mhard-float -mmfcrf -mmultiple @gol
19128 -mpopcntb -mpopcntd -mpowerpc64 @gol
19129 -mpowerpc-gpopt -mpowerpc-gfxopt -msingle-float -mdouble-float @gol
19130 -msimple-fpu -mstring -mmulhw -mdlmzb -mmfpgpr -mvsx @gol
19131 -mcrypto -mdirect-move -mpower8-fusion -mpower8-vector @gol
19132 -mquad-memory -mquad-memory-atomic}
19134 The particular options set for any particular CPU varies between
19135 compiler versions, depending on what setting seems to produce optimal
19136 code for that CPU; it doesn't necessarily reflect the actual hardware's
19137 capabilities. If you wish to set an individual option to a particular
19138 value, you may specify it after the @option{-mcpu} option, like
19139 @option{-mcpu=970 -mno-altivec}.
19141 On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are
19142 not enabled or disabled by the @option{-mcpu} option at present because
19143 AIX does not have full support for these options. You may still
19144 enable or disable them individually if you're sure it'll work in your
19147 @item -mtune=@var{cpu_type}
19149 Set the instruction scheduling parameters for machine type
19150 @var{cpu_type}, but do not set the architecture type or register usage,
19151 as @option{-mcpu=@var{cpu_type}} does. The same
19152 values for @var{cpu_type} are used for @option{-mtune} as for
19153 @option{-mcpu}. If both are specified, the code generated uses the
19154 architecture and registers set by @option{-mcpu}, but the
19155 scheduling parameters set by @option{-mtune}.
19157 @item -mcmodel=small
19158 @opindex mcmodel=small
19159 Generate PowerPC64 code for the small model: The TOC is limited to
19162 @item -mcmodel=medium
19163 @opindex mcmodel=medium
19164 Generate PowerPC64 code for the medium model: The TOC and other static
19165 data may be up to a total of 4G in size.
19167 @item -mcmodel=large
19168 @opindex mcmodel=large
19169 Generate PowerPC64 code for the large model: The TOC may be up to 4G
19170 in size. Other data and code is only limited by the 64-bit address
19174 @itemx -mno-altivec
19176 @opindex mno-altivec
19177 Generate code that uses (does not use) AltiVec instructions, and also
19178 enable the use of built-in functions that allow more direct access to
19179 the AltiVec instruction set. You may also need to set
19180 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
19183 When @option{-maltivec} is used, rather than @option{-maltivec=le} or
19184 @option{-maltivec=be}, the element order for Altivec intrinsics such
19185 as @code{vec_splat}, @code{vec_extract}, and @code{vec_insert}
19186 match array element order corresponding to the endianness of the
19187 target. That is, element zero identifies the leftmost element in a
19188 vector register when targeting a big-endian platform, and identifies
19189 the rightmost element in a vector register when targeting a
19190 little-endian platform.
19193 @opindex maltivec=be
19194 Generate Altivec instructions using big-endian element order,
19195 regardless of whether the target is big- or little-endian. This is
19196 the default when targeting a big-endian platform.
19198 The element order is used to interpret element numbers in Altivec
19199 intrinsics such as @code{vec_splat}, @code{vec_extract}, and
19200 @code{vec_insert}. By default, these match array element order
19201 corresponding to the endianness for the target.
19204 @opindex maltivec=le
19205 Generate Altivec instructions using little-endian element order,
19206 regardless of whether the target is big- or little-endian. This is
19207 the default when targeting a little-endian platform. This option is
19208 currently ignored when targeting a big-endian platform.
19210 The element order is used to interpret element numbers in Altivec
19211 intrinsics such as @code{vec_splat}, @code{vec_extract}, and
19212 @code{vec_insert}. By default, these match array element order
19213 corresponding to the endianness for the target.
19218 @opindex mno-vrsave
19219 Generate VRSAVE instructions when generating AltiVec code.
19221 @item -mgen-cell-microcode
19222 @opindex mgen-cell-microcode
19223 Generate Cell microcode instructions.
19225 @item -mwarn-cell-microcode
19226 @opindex mwarn-cell-microcode
19227 Warn when a Cell microcode instruction is emitted. An example
19228 of a Cell microcode instruction is a variable shift.
19231 @opindex msecure-plt
19232 Generate code that allows @command{ld} and @command{ld.so}
19233 to build executables and shared
19234 libraries with non-executable @code{.plt} and @code{.got} sections.
19236 32-bit SYSV ABI option.
19240 Generate code that uses a BSS @code{.plt} section that @command{ld.so}
19242 requires @code{.plt} and @code{.got}
19243 sections that are both writable and executable.
19244 This is a PowerPC 32-bit SYSV ABI option.
19250 This switch enables or disables the generation of ISEL instructions.
19252 @item -misel=@var{yes/no}
19253 This switch has been deprecated. Use @option{-misel} and
19254 @option{-mno-isel} instead.
19260 This switch enables or disables the generation of SPE simd
19266 @opindex mno-paired
19267 This switch enables or disables the generation of PAIRED simd
19270 @item -mspe=@var{yes/no}
19271 This option has been deprecated. Use @option{-mspe} and
19272 @option{-mno-spe} instead.
19278 Generate code that uses (does not use) vector/scalar (VSX)
19279 instructions, and also enable the use of built-in functions that allow
19280 more direct access to the VSX instruction set.
19285 @opindex mno-crypto
19286 Enable the use (disable) of the built-in functions that allow direct
19287 access to the cryptographic instructions that were added in version
19288 2.07 of the PowerPC ISA.
19290 @item -mdirect-move
19291 @itemx -mno-direct-move
19292 @opindex mdirect-move
19293 @opindex mno-direct-move
19294 Generate code that uses (does not use) the instructions to move data
19295 between the general purpose registers and the vector/scalar (VSX)
19296 registers that were added in version 2.07 of the PowerPC ISA.
19298 @item -mpower8-fusion
19299 @itemx -mno-power8-fusion
19300 @opindex mpower8-fusion
19301 @opindex mno-power8-fusion
19302 Generate code that keeps (does not keeps) some integer operations
19303 adjacent so that the instructions can be fused together on power8 and
19306 @item -mpower8-vector
19307 @itemx -mno-power8-vector
19308 @opindex mpower8-vector
19309 @opindex mno-power8-vector
19310 Generate code that uses (does not use) the vector and scalar
19311 instructions that were added in version 2.07 of the PowerPC ISA. Also
19312 enable the use of built-in functions that allow more direct access to
19313 the vector instructions.
19315 @item -mquad-memory
19316 @itemx -mno-quad-memory
19317 @opindex mquad-memory
19318 @opindex mno-quad-memory
19319 Generate code that uses (does not use) the non-atomic quad word memory
19320 instructions. The @option{-mquad-memory} option requires use of
19323 @item -mquad-memory-atomic
19324 @itemx -mno-quad-memory-atomic
19325 @opindex mquad-memory-atomic
19326 @opindex mno-quad-memory-atomic
19327 Generate code that uses (does not use) the atomic quad word memory
19328 instructions. The @option{-mquad-memory-atomic} option requires use of
19331 @item -mupper-regs-df
19332 @itemx -mno-upper-regs-df
19333 @opindex mupper-regs-df
19334 @opindex mno-upper-regs-df
19335 Generate code that uses (does not use) the scalar double precision
19336 instructions that target all 64 registers in the vector/scalar
19337 floating point register set that were added in version 2.06 of the
19338 PowerPC ISA. @option{-mupper-regs-df} is turned on by default if you
19339 use any of the @option{-mcpu=power7}, @option{-mcpu=power8}, or
19340 @option{-mvsx} options.
19342 @item -mupper-regs-sf
19343 @itemx -mno-upper-regs-sf
19344 @opindex mupper-regs-sf
19345 @opindex mno-upper-regs-sf
19346 Generate code that uses (does not use) the scalar single precision
19347 instructions that target all 64 registers in the vector/scalar
19348 floating point register set that were added in version 2.07 of the
19349 PowerPC ISA. @option{-mupper-regs-sf} is turned on by default if you
19350 use either of the @option{-mcpu=power8} or @option{-mpower8-vector}
19354 @itemx -mno-upper-regs
19355 @opindex mupper-regs
19356 @opindex mno-upper-regs
19357 Generate code that uses (does not use) the scalar
19358 instructions that target all 64 registers in the vector/scalar
19359 floating point register set, depending on the model of the machine.
19361 If the @option{-mno-upper-regs} option is used, it turns off both
19362 @option{-mupper-regs-sf} and @option{-mupper-regs-df} options.
19364 @item -mfloat-gprs=@var{yes/single/double/no}
19365 @itemx -mfloat-gprs
19366 @opindex mfloat-gprs
19367 This switch enables or disables the generation of floating-point
19368 operations on the general-purpose registers for architectures that
19371 The argument @samp{yes} or @samp{single} enables the use of
19372 single-precision floating-point operations.
19374 The argument @samp{double} enables the use of single and
19375 double-precision floating-point operations.
19377 The argument @samp{no} disables floating-point operations on the
19378 general-purpose registers.
19380 This option is currently only available on the MPC854x.
19386 Generate code for 32-bit or 64-bit environments of Darwin and SVR4
19387 targets (including GNU/Linux). The 32-bit environment sets int, long
19388 and pointer to 32 bits and generates code that runs on any PowerPC
19389 variant. The 64-bit environment sets int to 32 bits and long and
19390 pointer to 64 bits, and generates code for PowerPC64, as for
19391 @option{-mpowerpc64}.
19394 @itemx -mno-fp-in-toc
19395 @itemx -mno-sum-in-toc
19396 @itemx -mminimal-toc
19398 @opindex mno-fp-in-toc
19399 @opindex mno-sum-in-toc
19400 @opindex mminimal-toc
19401 Modify generation of the TOC (Table Of Contents), which is created for
19402 every executable file. The @option{-mfull-toc} option is selected by
19403 default. In that case, GCC allocates at least one TOC entry for
19404 each unique non-automatic variable reference in your program. GCC
19405 also places floating-point constants in the TOC@. However, only
19406 16,384 entries are available in the TOC@.
19408 If you receive a linker error message that saying you have overflowed
19409 the available TOC space, you can reduce the amount of TOC space used
19410 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
19411 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
19412 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
19413 generate code to calculate the sum of an address and a constant at
19414 run time instead of putting that sum into the TOC@. You may specify one
19415 or both of these options. Each causes GCC to produce very slightly
19416 slower and larger code at the expense of conserving TOC space.
19418 If you still run out of space in the TOC even when you specify both of
19419 these options, specify @option{-mminimal-toc} instead. This option causes
19420 GCC to make only one TOC entry for every file. When you specify this
19421 option, GCC produces code that is slower and larger but which
19422 uses extremely little TOC space. You may wish to use this option
19423 only on files that contain less frequently-executed code.
19429 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
19430 @code{long} type, and the infrastructure needed to support them.
19431 Specifying @option{-maix64} implies @option{-mpowerpc64},
19432 while @option{-maix32} disables the 64-bit ABI and
19433 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
19436 @itemx -mno-xl-compat
19437 @opindex mxl-compat
19438 @opindex mno-xl-compat
19439 Produce code that conforms more closely to IBM XL compiler semantics
19440 when using AIX-compatible ABI@. Pass floating-point arguments to
19441 prototyped functions beyond the register save area (RSA) on the stack
19442 in addition to argument FPRs. Do not assume that most significant
19443 double in 128-bit long double value is properly rounded when comparing
19444 values and converting to double. Use XL symbol names for long double
19447 The AIX calling convention was extended but not initially documented to
19448 handle an obscure K&R C case of calling a function that takes the
19449 address of its arguments with fewer arguments than declared. IBM XL
19450 compilers access floating-point arguments that do not fit in the
19451 RSA from the stack when a subroutine is compiled without
19452 optimization. Because always storing floating-point arguments on the
19453 stack is inefficient and rarely needed, this option is not enabled by
19454 default and only is necessary when calling subroutines compiled by IBM
19455 XL compilers without optimization.
19459 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
19460 application written to use message passing with special startup code to
19461 enable the application to run. The system must have PE installed in the
19462 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
19463 must be overridden with the @option{-specs=} option to specify the
19464 appropriate directory location. The Parallel Environment does not
19465 support threads, so the @option{-mpe} option and the @option{-pthread}
19466 option are incompatible.
19468 @item -malign-natural
19469 @itemx -malign-power
19470 @opindex malign-natural
19471 @opindex malign-power
19472 On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
19473 @option{-malign-natural} overrides the ABI-defined alignment of larger
19474 types, such as floating-point doubles, on their natural size-based boundary.
19475 The option @option{-malign-power} instructs GCC to follow the ABI-specified
19476 alignment rules. GCC defaults to the standard alignment defined in the ABI@.
19478 On 64-bit Darwin, natural alignment is the default, and @option{-malign-power}
19482 @itemx -mhard-float
19483 @opindex msoft-float
19484 @opindex mhard-float
19485 Generate code that does not use (uses) the floating-point register set.
19486 Software floating-point emulation is provided if you use the
19487 @option{-msoft-float} option, and pass the option to GCC when linking.
19489 @item -msingle-float
19490 @itemx -mdouble-float
19491 @opindex msingle-float
19492 @opindex mdouble-float
19493 Generate code for single- or double-precision floating-point operations.
19494 @option{-mdouble-float} implies @option{-msingle-float}.
19497 @opindex msimple-fpu
19498 Do not generate @code{sqrt} and @code{div} instructions for hardware
19499 floating-point unit.
19501 @item -mfpu=@var{name}
19503 Specify type of floating-point unit. Valid values for @var{name} are
19504 @samp{sp_lite} (equivalent to @option{-msingle-float -msimple-fpu}),
19505 @samp{dp_lite} (equivalent to @option{-mdouble-float -msimple-fpu}),
19506 @samp{sp_full} (equivalent to @option{-msingle-float}),
19507 and @samp{dp_full} (equivalent to @option{-mdouble-float}).
19510 @opindex mxilinx-fpu
19511 Perform optimizations for the floating-point unit on Xilinx PPC 405/440.
19514 @itemx -mno-multiple
19516 @opindex mno-multiple
19517 Generate code that uses (does not use) the load multiple word
19518 instructions and the store multiple word instructions. These
19519 instructions are generated by default on POWER systems, and not
19520 generated on PowerPC systems. Do not use @option{-mmultiple} on little-endian
19521 PowerPC systems, since those instructions do not work when the
19522 processor is in little-endian mode. The exceptions are PPC740 and
19523 PPC750 which permit these instructions in little-endian mode.
19528 @opindex mno-string
19529 Generate code that uses (does not use) the load string instructions
19530 and the store string word instructions to save multiple registers and
19531 do small block moves. These instructions are generated by default on
19532 POWER systems, and not generated on PowerPC systems. Do not use
19533 @option{-mstring} on little-endian PowerPC systems, since those
19534 instructions do not work when the processor is in little-endian mode.
19535 The exceptions are PPC740 and PPC750 which permit these instructions
19536 in little-endian mode.
19541 @opindex mno-update
19542 Generate code that uses (does not use) the load or store instructions
19543 that update the base register to the address of the calculated memory
19544 location. These instructions are generated by default. If you use
19545 @option{-mno-update}, there is a small window between the time that the
19546 stack pointer is updated and the address of the previous frame is
19547 stored, which means code that walks the stack frame across interrupts or
19548 signals may get corrupted data.
19550 @item -mavoid-indexed-addresses
19551 @itemx -mno-avoid-indexed-addresses
19552 @opindex mavoid-indexed-addresses
19553 @opindex mno-avoid-indexed-addresses
19554 Generate code that tries to avoid (not avoid) the use of indexed load
19555 or store instructions. These instructions can incur a performance
19556 penalty on Power6 processors in certain situations, such as when
19557 stepping through large arrays that cross a 16M boundary. This option
19558 is enabled by default when targeting Power6 and disabled otherwise.
19561 @itemx -mno-fused-madd
19562 @opindex mfused-madd
19563 @opindex mno-fused-madd
19564 Generate code that uses (does not use) the floating-point multiply and
19565 accumulate instructions. These instructions are generated by default
19566 if hardware floating point is used. The machine-dependent
19567 @option{-mfused-madd} option is now mapped to the machine-independent
19568 @option{-ffp-contract=fast} option, and @option{-mno-fused-madd} is
19569 mapped to @option{-ffp-contract=off}.
19575 Generate code that uses (does not use) the half-word multiply and
19576 multiply-accumulate instructions on the IBM 405, 440, 464 and 476 processors.
19577 These instructions are generated by default when targeting those
19584 Generate code that uses (does not use) the string-search @samp{dlmzb}
19585 instruction on the IBM 405, 440, 464 and 476 processors. This instruction is
19586 generated by default when targeting those processors.
19588 @item -mno-bit-align
19590 @opindex mno-bit-align
19591 @opindex mbit-align
19592 On System V.4 and embedded PowerPC systems do not (do) force structures
19593 and unions that contain bit-fields to be aligned to the base type of the
19596 For example, by default a structure containing nothing but 8
19597 @code{unsigned} bit-fields of length 1 is aligned to a 4-byte
19598 boundary and has a size of 4 bytes. By using @option{-mno-bit-align},
19599 the structure is aligned to a 1-byte boundary and is 1 byte in
19602 @item -mno-strict-align
19603 @itemx -mstrict-align
19604 @opindex mno-strict-align
19605 @opindex mstrict-align
19606 On System V.4 and embedded PowerPC systems do not (do) assume that
19607 unaligned memory references are handled by the system.
19609 @item -mrelocatable
19610 @itemx -mno-relocatable
19611 @opindex mrelocatable
19612 @opindex mno-relocatable
19613 Generate code that allows (does not allow) a static executable to be
19614 relocated to a different address at run time. A simple embedded
19615 PowerPC system loader should relocate the entire contents of
19616 @code{.got2} and 4-byte locations listed in the @code{.fixup} section,
19617 a table of 32-bit addresses generated by this option. For this to
19618 work, all objects linked together must be compiled with
19619 @option{-mrelocatable} or @option{-mrelocatable-lib}.
19620 @option{-mrelocatable} code aligns the stack to an 8-byte boundary.
19622 @item -mrelocatable-lib
19623 @itemx -mno-relocatable-lib
19624 @opindex mrelocatable-lib
19625 @opindex mno-relocatable-lib
19626 Like @option{-mrelocatable}, @option{-mrelocatable-lib} generates a
19627 @code{.fixup} section to allow static executables to be relocated at
19628 run time, but @option{-mrelocatable-lib} does not use the smaller stack
19629 alignment of @option{-mrelocatable}. Objects compiled with
19630 @option{-mrelocatable-lib} may be linked with objects compiled with
19631 any combination of the @option{-mrelocatable} options.
19637 On System V.4 and embedded PowerPC systems do not (do) assume that
19638 register 2 contains a pointer to a global area pointing to the addresses
19639 used in the program.
19642 @itemx -mlittle-endian
19644 @opindex mlittle-endian
19645 On System V.4 and embedded PowerPC systems compile code for the
19646 processor in little-endian mode. The @option{-mlittle-endian} option is
19647 the same as @option{-mlittle}.
19650 @itemx -mbig-endian
19652 @opindex mbig-endian
19653 On System V.4 and embedded PowerPC systems compile code for the
19654 processor in big-endian mode. The @option{-mbig-endian} option is
19655 the same as @option{-mbig}.
19657 @item -mdynamic-no-pic
19658 @opindex mdynamic-no-pic
19659 On Darwin and Mac OS X systems, compile code so that it is not
19660 relocatable, but that its external references are relocatable. The
19661 resulting code is suitable for applications, but not shared
19664 @item -msingle-pic-base
19665 @opindex msingle-pic-base
19666 Treat the register used for PIC addressing as read-only, rather than
19667 loading it in the prologue for each function. The runtime system is
19668 responsible for initializing this register with an appropriate value
19669 before execution begins.
19671 @item -mprioritize-restricted-insns=@var{priority}
19672 @opindex mprioritize-restricted-insns
19673 This option controls the priority that is assigned to
19674 dispatch-slot restricted instructions during the second scheduling
19675 pass. The argument @var{priority} takes the value @samp{0}, @samp{1},
19676 or @samp{2} to assign no, highest, or second-highest (respectively)
19677 priority to dispatch-slot restricted
19680 @item -msched-costly-dep=@var{dependence_type}
19681 @opindex msched-costly-dep
19682 This option controls which dependences are considered costly
19683 by the target during instruction scheduling. The argument
19684 @var{dependence_type} takes one of the following values:
19688 No dependence is costly.
19691 All dependences are costly.
19693 @item @samp{true_store_to_load}
19694 A true dependence from store to load is costly.
19696 @item @samp{store_to_load}
19697 Any dependence from store to load is costly.
19700 Any dependence for which the latency is greater than or equal to
19701 @var{number} is costly.
19704 @item -minsert-sched-nops=@var{scheme}
19705 @opindex minsert-sched-nops
19706 This option controls which NOP insertion scheme is used during
19707 the second scheduling pass. The argument @var{scheme} takes one of the
19715 Pad with NOPs any dispatch group that has vacant issue slots,
19716 according to the scheduler's grouping.
19718 @item @samp{regroup_exact}
19719 Insert NOPs to force costly dependent insns into
19720 separate groups. Insert exactly as many NOPs as needed to force an insn
19721 to a new group, according to the estimated processor grouping.
19724 Insert NOPs to force costly dependent insns into
19725 separate groups. Insert @var{number} NOPs to force an insn to a new group.
19729 @opindex mcall-sysv
19730 On System V.4 and embedded PowerPC systems compile code using calling
19731 conventions that adhere to the March 1995 draft of the System V
19732 Application Binary Interface, PowerPC processor supplement. This is the
19733 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
19735 @item -mcall-sysv-eabi
19737 @opindex mcall-sysv-eabi
19738 @opindex mcall-eabi
19739 Specify both @option{-mcall-sysv} and @option{-meabi} options.
19741 @item -mcall-sysv-noeabi
19742 @opindex mcall-sysv-noeabi
19743 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
19745 @item -mcall-aixdesc
19747 On System V.4 and embedded PowerPC systems compile code for the AIX
19751 @opindex mcall-linux
19752 On System V.4 and embedded PowerPC systems compile code for the
19753 Linux-based GNU system.
19755 @item -mcall-freebsd
19756 @opindex mcall-freebsd
19757 On System V.4 and embedded PowerPC systems compile code for the
19758 FreeBSD operating system.
19760 @item -mcall-netbsd
19761 @opindex mcall-netbsd
19762 On System V.4 and embedded PowerPC systems compile code for the
19763 NetBSD operating system.
19765 @item -mcall-openbsd
19766 @opindex mcall-netbsd
19767 On System V.4 and embedded PowerPC systems compile code for the
19768 OpenBSD operating system.
19770 @item -maix-struct-return
19771 @opindex maix-struct-return
19772 Return all structures in memory (as specified by the AIX ABI)@.
19774 @item -msvr4-struct-return
19775 @opindex msvr4-struct-return
19776 Return structures smaller than 8 bytes in registers (as specified by the
19779 @item -mabi=@var{abi-type}
19781 Extend the current ABI with a particular extension, or remove such extension.
19782 Valid values are @samp{altivec}, @samp{no-altivec}, @samp{spe},
19783 @samp{no-spe}, @samp{ibmlongdouble}, @samp{ieeelongdouble},
19784 @samp{elfv1}, @samp{elfv2}@.
19788 Extend the current ABI with SPE ABI extensions. This does not change
19789 the default ABI, instead it adds the SPE ABI extensions to the current
19793 @opindex mabi=no-spe
19794 Disable Book-E SPE ABI extensions for the current ABI@.
19796 @item -mabi=ibmlongdouble
19797 @opindex mabi=ibmlongdouble
19798 Change the current ABI to use IBM extended-precision long double.
19799 This is a PowerPC 32-bit SYSV ABI option.
19801 @item -mabi=ieeelongdouble
19802 @opindex mabi=ieeelongdouble
19803 Change the current ABI to use IEEE extended-precision long double.
19804 This is a PowerPC 32-bit Linux ABI option.
19807 @opindex mabi=elfv1
19808 Change the current ABI to use the ELFv1 ABI.
19809 This is the default ABI for big-endian PowerPC 64-bit Linux.
19810 Overriding the default ABI requires special system support and is
19811 likely to fail in spectacular ways.
19814 @opindex mabi=elfv2
19815 Change the current ABI to use the ELFv2 ABI.
19816 This is the default ABI for little-endian PowerPC 64-bit Linux.
19817 Overriding the default ABI requires special system support and is
19818 likely to fail in spectacular ways.
19821 @itemx -mno-prototype
19822 @opindex mprototype
19823 @opindex mno-prototype
19824 On System V.4 and embedded PowerPC systems assume that all calls to
19825 variable argument functions are properly prototyped. Otherwise, the
19826 compiler must insert an instruction before every non-prototyped call to
19827 set or clear bit 6 of the condition code register (@code{CR}) to
19828 indicate whether floating-point values are passed in the floating-point
19829 registers in case the function takes variable arguments. With
19830 @option{-mprototype}, only calls to prototyped variable argument functions
19831 set or clear the bit.
19835 On embedded PowerPC systems, assume that the startup module is called
19836 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
19837 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}
19842 On embedded PowerPC systems, assume that the startup module is called
19843 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
19848 On embedded PowerPC systems, assume that the startup module is called
19849 @file{crt0.o} and the standard C libraries are @file{libads.a} and
19852 @item -myellowknife
19853 @opindex myellowknife
19854 On embedded PowerPC systems, assume that the startup module is called
19855 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
19860 On System V.4 and embedded PowerPC systems, specify that you are
19861 compiling for a VxWorks system.
19865 On embedded PowerPC systems, set the @code{PPC_EMB} bit in the ELF flags
19866 header to indicate that @samp{eabi} extended relocations are used.
19872 On System V.4 and embedded PowerPC systems do (do not) adhere to the
19873 Embedded Applications Binary Interface (EABI), which is a set of
19874 modifications to the System V.4 specifications. Selecting @option{-meabi}
19875 means that the stack is aligned to an 8-byte boundary, a function
19876 @code{__eabi} is called from @code{main} to set up the EABI
19877 environment, and the @option{-msdata} option can use both @code{r2} and
19878 @code{r13} to point to two separate small data areas. Selecting
19879 @option{-mno-eabi} means that the stack is aligned to a 16-byte boundary,
19880 no EABI initialization function is called from @code{main}, and the
19881 @option{-msdata} option only uses @code{r13} to point to a single
19882 small data area. The @option{-meabi} option is on by default if you
19883 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
19886 @opindex msdata=eabi
19887 On System V.4 and embedded PowerPC systems, put small initialized
19888 @code{const} global and static data in the @code{.sdata2} section, which
19889 is pointed to by register @code{r2}. Put small initialized
19890 non-@code{const} global and static data in the @code{.sdata} section,
19891 which is pointed to by register @code{r13}. Put small uninitialized
19892 global and static data in the @code{.sbss} section, which is adjacent to
19893 the @code{.sdata} section. The @option{-msdata=eabi} option is
19894 incompatible with the @option{-mrelocatable} option. The
19895 @option{-msdata=eabi} option also sets the @option{-memb} option.
19898 @opindex msdata=sysv
19899 On System V.4 and embedded PowerPC systems, put small global and static
19900 data in the @code{.sdata} section, which is pointed to by register
19901 @code{r13}. Put small uninitialized global and static data in the
19902 @code{.sbss} section, which is adjacent to the @code{.sdata} section.
19903 The @option{-msdata=sysv} option is incompatible with the
19904 @option{-mrelocatable} option.
19906 @item -msdata=default
19908 @opindex msdata=default
19910 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
19911 compile code the same as @option{-msdata=eabi}, otherwise compile code the
19912 same as @option{-msdata=sysv}.
19915 @opindex msdata=data
19916 On System V.4 and embedded PowerPC systems, put small global
19917 data in the @code{.sdata} section. Put small uninitialized global
19918 data in the @code{.sbss} section. Do not use register @code{r13}
19919 to address small data however. This is the default behavior unless
19920 other @option{-msdata} options are used.
19924 @opindex msdata=none
19926 On embedded PowerPC systems, put all initialized global and static data
19927 in the @code{.data} section, and all uninitialized data in the
19928 @code{.bss} section.
19930 @item -mblock-move-inline-limit=@var{num}
19931 @opindex mblock-move-inline-limit
19932 Inline all block moves (such as calls to @code{memcpy} or structure
19933 copies) less than or equal to @var{num} bytes. The minimum value for
19934 @var{num} is 32 bytes on 32-bit targets and 64 bytes on 64-bit
19935 targets. The default value is target-specific.
19939 @cindex smaller data references (PowerPC)
19940 @cindex .sdata/.sdata2 references (PowerPC)
19941 On embedded PowerPC systems, put global and static items less than or
19942 equal to @var{num} bytes into the small data or BSS sections instead of
19943 the normal data or BSS section. By default, @var{num} is 8. The
19944 @option{-G @var{num}} switch is also passed to the linker.
19945 All modules should be compiled with the same @option{-G @var{num}} value.
19948 @itemx -mno-regnames
19950 @opindex mno-regnames
19951 On System V.4 and embedded PowerPC systems do (do not) emit register
19952 names in the assembly language output using symbolic forms.
19955 @itemx -mno-longcall
19957 @opindex mno-longcall
19958 By default assume that all calls are far away so that a longer and more
19959 expensive calling sequence is required. This is required for calls
19960 farther than 32 megabytes (33,554,432 bytes) from the current location.
19961 A short call is generated if the compiler knows
19962 the call cannot be that far away. This setting can be overridden by
19963 the @code{shortcall} function attribute, or by @code{#pragma
19966 Some linkers are capable of detecting out-of-range calls and generating
19967 glue code on the fly. On these systems, long calls are unnecessary and
19968 generate slower code. As of this writing, the AIX linker can do this,
19969 as can the GNU linker for PowerPC/64. It is planned to add this feature
19970 to the GNU linker for 32-bit PowerPC systems as well.
19972 On Darwin/PPC systems, @code{#pragma longcall} generates @code{jbsr
19973 callee, L42}, plus a @dfn{branch island} (glue code). The two target
19974 addresses represent the callee and the branch island. The
19975 Darwin/PPC linker prefers the first address and generates a @code{bl
19976 callee} if the PPC @code{bl} instruction reaches the callee directly;
19977 otherwise, the linker generates @code{bl L42} to call the branch
19978 island. The branch island is appended to the body of the
19979 calling function; it computes the full 32-bit address of the callee
19982 On Mach-O (Darwin) systems, this option directs the compiler emit to
19983 the glue for every direct call, and the Darwin linker decides whether
19984 to use or discard it.
19986 In the future, GCC may ignore all longcall specifications
19987 when the linker is known to generate glue.
19989 @item -mtls-markers
19990 @itemx -mno-tls-markers
19991 @opindex mtls-markers
19992 @opindex mno-tls-markers
19993 Mark (do not mark) calls to @code{__tls_get_addr} with a relocation
19994 specifying the function argument. The relocation allows the linker to
19995 reliably associate function call with argument setup instructions for
19996 TLS optimization, which in turn allows GCC to better schedule the
20001 Adds support for multithreading with the @dfn{pthreads} library.
20002 This option sets flags for both the preprocessor and linker.
20007 This option enables use of the reciprocal estimate and
20008 reciprocal square root estimate instructions with additional
20009 Newton-Raphson steps to increase precision instead of doing a divide or
20010 square root and divide for floating-point arguments. You should use
20011 the @option{-ffast-math} option when using @option{-mrecip} (or at
20012 least @option{-funsafe-math-optimizations},
20013 @option{-finite-math-only}, @option{-freciprocal-math} and
20014 @option{-fno-trapping-math}). Note that while the throughput of the
20015 sequence is generally higher than the throughput of the non-reciprocal
20016 instruction, the precision of the sequence can be decreased by up to 2
20017 ulp (i.e.@: the inverse of 1.0 equals 0.99999994) for reciprocal square
20020 @item -mrecip=@var{opt}
20021 @opindex mrecip=opt
20022 This option controls which reciprocal estimate instructions
20023 may be used. @var{opt} is a comma-separated list of options, which may
20024 be preceded by a @code{!} to invert the option:
20029 Enable all estimate instructions.
20032 Enable the default instructions, equivalent to @option{-mrecip}.
20035 Disable all estimate instructions, equivalent to @option{-mno-recip}.
20038 Enable the reciprocal approximation instructions for both
20039 single and double precision.
20042 Enable the single-precision reciprocal approximation instructions.
20045 Enable the double-precision reciprocal approximation instructions.
20048 Enable the reciprocal square root approximation instructions for both
20049 single and double precision.
20052 Enable the single-precision reciprocal square root approximation instructions.
20055 Enable the double-precision reciprocal square root approximation instructions.
20059 So, for example, @option{-mrecip=all,!rsqrtd} enables
20060 all of the reciprocal estimate instructions, except for the
20061 @code{FRSQRTE}, @code{XSRSQRTEDP}, and @code{XVRSQRTEDP} instructions
20062 which handle the double-precision reciprocal square root calculations.
20064 @item -mrecip-precision
20065 @itemx -mno-recip-precision
20066 @opindex mrecip-precision
20067 Assume (do not assume) that the reciprocal estimate instructions
20068 provide higher-precision estimates than is mandated by the PowerPC
20069 ABI. Selecting @option{-mcpu=power6}, @option{-mcpu=power7} or
20070 @option{-mcpu=power8} automatically selects @option{-mrecip-precision}.
20071 The double-precision square root estimate instructions are not generated by
20072 default on low-precision machines, since they do not provide an
20073 estimate that converges after three steps.
20075 @item -mveclibabi=@var{type}
20076 @opindex mveclibabi
20077 Specifies the ABI type to use for vectorizing intrinsics using an
20078 external library. The only type supported at present is @samp{mass},
20079 which specifies to use IBM's Mathematical Acceleration Subsystem
20080 (MASS) libraries for vectorizing intrinsics using external libraries.
20081 GCC currently emits calls to @code{acosd2}, @code{acosf4},
20082 @code{acoshd2}, @code{acoshf4}, @code{asind2}, @code{asinf4},
20083 @code{asinhd2}, @code{asinhf4}, @code{atan2d2}, @code{atan2f4},
20084 @code{atand2}, @code{atanf4}, @code{atanhd2}, @code{atanhf4},
20085 @code{cbrtd2}, @code{cbrtf4}, @code{cosd2}, @code{cosf4},
20086 @code{coshd2}, @code{coshf4}, @code{erfcd2}, @code{erfcf4},
20087 @code{erfd2}, @code{erff4}, @code{exp2d2}, @code{exp2f4},
20088 @code{expd2}, @code{expf4}, @code{expm1d2}, @code{expm1f4},
20089 @code{hypotd2}, @code{hypotf4}, @code{lgammad2}, @code{lgammaf4},
20090 @code{log10d2}, @code{log10f4}, @code{log1pd2}, @code{log1pf4},
20091 @code{log2d2}, @code{log2f4}, @code{logd2}, @code{logf4},
20092 @code{powd2}, @code{powf4}, @code{sind2}, @code{sinf4}, @code{sinhd2},
20093 @code{sinhf4}, @code{sqrtd2}, @code{sqrtf4}, @code{tand2},
20094 @code{tanf4}, @code{tanhd2}, and @code{tanhf4} when generating code
20095 for power7. Both @option{-ftree-vectorize} and
20096 @option{-funsafe-math-optimizations} must also be enabled. The MASS
20097 libraries must be specified at link time.
20102 Generate (do not generate) the @code{friz} instruction when the
20103 @option{-funsafe-math-optimizations} option is used to optimize
20104 rounding of floating-point values to 64-bit integer and back to floating
20105 point. The @code{friz} instruction does not return the same value if
20106 the floating-point number is too large to fit in an integer.
20108 @item -mpointers-to-nested-functions
20109 @itemx -mno-pointers-to-nested-functions
20110 @opindex mpointers-to-nested-functions
20111 Generate (do not generate) code to load up the static chain register
20112 (@code{r11}) when calling through a pointer on AIX and 64-bit Linux
20113 systems where a function pointer points to a 3-word descriptor giving
20114 the function address, TOC value to be loaded in register @code{r2}, and
20115 static chain value to be loaded in register @code{r11}. The
20116 @option{-mpointers-to-nested-functions} is on by default. You cannot
20117 call through pointers to nested functions or pointers
20118 to functions compiled in other languages that use the static chain if
20119 you use @option{-mno-pointers-to-nested-functions}.
20121 @item -msave-toc-indirect
20122 @itemx -mno-save-toc-indirect
20123 @opindex msave-toc-indirect
20124 Generate (do not generate) code to save the TOC value in the reserved
20125 stack location in the function prologue if the function calls through
20126 a pointer on AIX and 64-bit Linux systems. If the TOC value is not
20127 saved in the prologue, it is saved just before the call through the
20128 pointer. The @option{-mno-save-toc-indirect} option is the default.
20130 @item -mcompat-align-parm
20131 @itemx -mno-compat-align-parm
20132 @opindex mcompat-align-parm
20133 Generate (do not generate) code to pass structure parameters with a
20134 maximum alignment of 64 bits, for compatibility with older versions
20137 Older versions of GCC (prior to 4.9.0) incorrectly did not align a
20138 structure parameter on a 128-bit boundary when that structure contained
20139 a member requiring 128-bit alignment. This is corrected in more
20140 recent versions of GCC. This option may be used to generate code
20141 that is compatible with functions compiled with older versions of
20144 The @option{-mno-compat-align-parm} option is the default.
20148 @subsection RX Options
20151 These command-line options are defined for RX targets:
20154 @item -m64bit-doubles
20155 @itemx -m32bit-doubles
20156 @opindex m64bit-doubles
20157 @opindex m32bit-doubles
20158 Make the @code{double} data type be 64 bits (@option{-m64bit-doubles})
20159 or 32 bits (@option{-m32bit-doubles}) in size. The default is
20160 @option{-m32bit-doubles}. @emph{Note} RX floating-point hardware only
20161 works on 32-bit values, which is why the default is
20162 @option{-m32bit-doubles}.
20168 Enables (@option{-fpu}) or disables (@option{-nofpu}) the use of RX
20169 floating-point hardware. The default is enabled for the RX600
20170 series and disabled for the RX200 series.
20172 Floating-point instructions are only generated for 32-bit floating-point
20173 values, however, so the FPU hardware is not used for doubles if the
20174 @option{-m64bit-doubles} option is used.
20176 @emph{Note} If the @option{-fpu} option is enabled then
20177 @option{-funsafe-math-optimizations} is also enabled automatically.
20178 This is because the RX FPU instructions are themselves unsafe.
20180 @item -mcpu=@var{name}
20182 Selects the type of RX CPU to be targeted. Currently three types are
20183 supported, the generic @samp{RX600} and @samp{RX200} series hardware and
20184 the specific @samp{RX610} CPU. The default is @samp{RX600}.
20186 The only difference between @samp{RX600} and @samp{RX610} is that the
20187 @samp{RX610} does not support the @code{MVTIPL} instruction.
20189 The @samp{RX200} series does not have a hardware floating-point unit
20190 and so @option{-nofpu} is enabled by default when this type is
20193 @item -mbig-endian-data
20194 @itemx -mlittle-endian-data
20195 @opindex mbig-endian-data
20196 @opindex mlittle-endian-data
20197 Store data (but not code) in the big-endian format. The default is
20198 @option{-mlittle-endian-data}, i.e.@: to store data in the little-endian
20201 @item -msmall-data-limit=@var{N}
20202 @opindex msmall-data-limit
20203 Specifies the maximum size in bytes of global and static variables
20204 which can be placed into the small data area. Using the small data
20205 area can lead to smaller and faster code, but the size of area is
20206 limited and it is up to the programmer to ensure that the area does
20207 not overflow. Also when the small data area is used one of the RX's
20208 registers (usually @code{r13}) is reserved for use pointing to this
20209 area, so it is no longer available for use by the compiler. This
20210 could result in slower and/or larger code if variables are pushed onto
20211 the stack instead of being held in this register.
20213 Note, common variables (variables that have not been initialized) and
20214 constants are not placed into the small data area as they are assigned
20215 to other sections in the output executable.
20217 The default value is zero, which disables this feature. Note, this
20218 feature is not enabled by default with higher optimization levels
20219 (@option{-O2} etc) because of the potentially detrimental effects of
20220 reserving a register. It is up to the programmer to experiment and
20221 discover whether this feature is of benefit to their program. See the
20222 description of the @option{-mpid} option for a description of how the
20223 actual register to hold the small data area pointer is chosen.
20229 Use the simulator runtime. The default is to use the libgloss
20230 board-specific runtime.
20232 @item -mas100-syntax
20233 @itemx -mno-as100-syntax
20234 @opindex mas100-syntax
20235 @opindex mno-as100-syntax
20236 When generating assembler output use a syntax that is compatible with
20237 Renesas's AS100 assembler. This syntax can also be handled by the GAS
20238 assembler, but it has some restrictions so it is not generated by default.
20240 @item -mmax-constant-size=@var{N}
20241 @opindex mmax-constant-size
20242 Specifies the maximum size, in bytes, of a constant that can be used as
20243 an operand in a RX instruction. Although the RX instruction set does
20244 allow constants of up to 4 bytes in length to be used in instructions,
20245 a longer value equates to a longer instruction. Thus in some
20246 circumstances it can be beneficial to restrict the size of constants
20247 that are used in instructions. Constants that are too big are instead
20248 placed into a constant pool and referenced via register indirection.
20250 The value @var{N} can be between 0 and 4. A value of 0 (the default)
20251 or 4 means that constants of any size are allowed.
20255 Enable linker relaxation. Linker relaxation is a process whereby the
20256 linker attempts to reduce the size of a program by finding shorter
20257 versions of various instructions. Disabled by default.
20259 @item -mint-register=@var{N}
20260 @opindex mint-register
20261 Specify the number of registers to reserve for fast interrupt handler
20262 functions. The value @var{N} can be between 0 and 4. A value of 1
20263 means that register @code{r13} is reserved for the exclusive use
20264 of fast interrupt handlers. A value of 2 reserves @code{r13} and
20265 @code{r12}. A value of 3 reserves @code{r13}, @code{r12} and
20266 @code{r11}, and a value of 4 reserves @code{r13} through @code{r10}.
20267 A value of 0, the default, does not reserve any registers.
20269 @item -msave-acc-in-interrupts
20270 @opindex msave-acc-in-interrupts
20271 Specifies that interrupt handler functions should preserve the
20272 accumulator register. This is only necessary if normal code might use
20273 the accumulator register, for example because it performs 64-bit
20274 multiplications. The default is to ignore the accumulator as this
20275 makes the interrupt handlers faster.
20281 Enables the generation of position independent data. When enabled any
20282 access to constant data is done via an offset from a base address
20283 held in a register. This allows the location of constant data to be
20284 determined at run time without requiring the executable to be
20285 relocated, which is a benefit to embedded applications with tight
20286 memory constraints. Data that can be modified is not affected by this
20289 Note, using this feature reserves a register, usually @code{r13}, for
20290 the constant data base address. This can result in slower and/or
20291 larger code, especially in complicated functions.
20293 The actual register chosen to hold the constant data base address
20294 depends upon whether the @option{-msmall-data-limit} and/or the
20295 @option{-mint-register} command-line options are enabled. Starting
20296 with register @code{r13} and proceeding downwards, registers are
20297 allocated first to satisfy the requirements of @option{-mint-register},
20298 then @option{-mpid} and finally @option{-msmall-data-limit}. Thus it
20299 is possible for the small data area register to be @code{r8} if both
20300 @option{-mint-register=4} and @option{-mpid} are specified on the
20303 By default this feature is not enabled. The default can be restored
20304 via the @option{-mno-pid} command-line option.
20306 @item -mno-warn-multiple-fast-interrupts
20307 @itemx -mwarn-multiple-fast-interrupts
20308 @opindex mno-warn-multiple-fast-interrupts
20309 @opindex mwarn-multiple-fast-interrupts
20310 Prevents GCC from issuing a warning message if it finds more than one
20311 fast interrupt handler when it is compiling a file. The default is to
20312 issue a warning for each extra fast interrupt handler found, as the RX
20313 only supports one such interrupt.
20315 @item -mallow-string-insns
20316 @itemx -mno-allow-string-insns
20317 @opindex mallow-string-insns
20318 @opindex mno-allow-string-insns
20319 Enables or disables the use of the string manipulation instructions
20320 @code{SMOVF}, @code{SCMPU}, @code{SMOVB}, @code{SMOVU}, @code{SUNTIL}
20321 @code{SWHILE} and also the @code{RMPA} instruction. These
20322 instructions may prefetch data, which is not safe to do if accessing
20323 an I/O register. (See section 12.2.7 of the RX62N Group User's Manual
20324 for more information).
20326 The default is to allow these instructions, but it is not possible for
20327 GCC to reliably detect all circumstances where a string instruction
20328 might be used to access an I/O register, so their use cannot be
20329 disabled automatically. Instead it is reliant upon the programmer to
20330 use the @option{-mno-allow-string-insns} option if their program
20331 accesses I/O space.
20333 When the instructions are enabled GCC defines the C preprocessor
20334 symbol @code{__RX_ALLOW_STRING_INSNS__}, otherwise it defines the
20335 symbol @code{__RX_DISALLOW_STRING_INSNS__}.
20338 @emph{Note:} The generic GCC command-line option @option{-ffixed-@var{reg}}
20339 has special significance to the RX port when used with the
20340 @code{interrupt} function attribute. This attribute indicates a
20341 function intended to process fast interrupts. GCC ensures
20342 that it only uses the registers @code{r10}, @code{r11}, @code{r12}
20343 and/or @code{r13} and only provided that the normal use of the
20344 corresponding registers have been restricted via the
20345 @option{-ffixed-@var{reg}} or @option{-mint-register} command-line
20348 @node S/390 and zSeries Options
20349 @subsection S/390 and zSeries Options
20350 @cindex S/390 and zSeries Options
20352 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
20356 @itemx -msoft-float
20357 @opindex mhard-float
20358 @opindex msoft-float
20359 Use (do not use) the hardware floating-point instructions and registers
20360 for floating-point operations. When @option{-msoft-float} is specified,
20361 functions in @file{libgcc.a} are used to perform floating-point
20362 operations. When @option{-mhard-float} is specified, the compiler
20363 generates IEEE floating-point instructions. This is the default.
20366 @itemx -mno-hard-dfp
20368 @opindex mno-hard-dfp
20369 Use (do not use) the hardware decimal-floating-point instructions for
20370 decimal-floating-point operations. When @option{-mno-hard-dfp} is
20371 specified, functions in @file{libgcc.a} are used to perform
20372 decimal-floating-point operations. When @option{-mhard-dfp} is
20373 specified, the compiler generates decimal-floating-point hardware
20374 instructions. This is the default for @option{-march=z9-ec} or higher.
20376 @item -mlong-double-64
20377 @itemx -mlong-double-128
20378 @opindex mlong-double-64
20379 @opindex mlong-double-128
20380 These switches control the size of @code{long double} type. A size
20381 of 64 bits makes the @code{long double} type equivalent to the @code{double}
20382 type. This is the default.
20385 @itemx -mno-backchain
20386 @opindex mbackchain
20387 @opindex mno-backchain
20388 Store (do not store) the address of the caller's frame as backchain pointer
20389 into the callee's stack frame.
20390 A backchain may be needed to allow debugging using tools that do not understand
20391 DWARF 2 call frame information.
20392 When @option{-mno-packed-stack} is in effect, the backchain pointer is stored
20393 at the bottom of the stack frame; when @option{-mpacked-stack} is in effect,
20394 the backchain is placed into the topmost word of the 96/160 byte register
20397 In general, code compiled with @option{-mbackchain} is call-compatible with
20398 code compiled with @option{-mmo-backchain}; however, use of the backchain
20399 for debugging purposes usually requires that the whole binary is built with
20400 @option{-mbackchain}. Note that the combination of @option{-mbackchain},
20401 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
20402 to build a linux kernel use @option{-msoft-float}.
20404 The default is to not maintain the backchain.
20406 @item -mpacked-stack
20407 @itemx -mno-packed-stack
20408 @opindex mpacked-stack
20409 @opindex mno-packed-stack
20410 Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is
20411 specified, the compiler uses the all fields of the 96/160 byte register save
20412 area only for their default purpose; unused fields still take up stack space.
20413 When @option{-mpacked-stack} is specified, register save slots are densely
20414 packed at the top of the register save area; unused space is reused for other
20415 purposes, allowing for more efficient use of the available stack space.
20416 However, when @option{-mbackchain} is also in effect, the topmost word of
20417 the save area is always used to store the backchain, and the return address
20418 register is always saved two words below the backchain.
20420 As long as the stack frame backchain is not used, code generated with
20421 @option{-mpacked-stack} is call-compatible with code generated with
20422 @option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for
20423 S/390 or zSeries generated code that uses the stack frame backchain at run
20424 time, not just for debugging purposes. Such code is not call-compatible
20425 with code compiled with @option{-mpacked-stack}. Also, note that the
20426 combination of @option{-mbackchain},
20427 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
20428 to build a linux kernel use @option{-msoft-float}.
20430 The default is to not use the packed stack layout.
20433 @itemx -mno-small-exec
20434 @opindex msmall-exec
20435 @opindex mno-small-exec
20436 Generate (or do not generate) code using the @code{bras} instruction
20437 to do subroutine calls.
20438 This only works reliably if the total executable size does not
20439 exceed 64k. The default is to use the @code{basr} instruction instead,
20440 which does not have this limitation.
20446 When @option{-m31} is specified, generate code compliant to the
20447 GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate
20448 code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in
20449 particular to generate 64-bit instructions. For the @samp{s390}
20450 targets, the default is @option{-m31}, while the @samp{s390x}
20451 targets default to @option{-m64}.
20457 When @option{-mzarch} is specified, generate code using the
20458 instructions available on z/Architecture.
20459 When @option{-mesa} is specified, generate code using the
20460 instructions available on ESA/390. Note that @option{-mesa} is
20461 not possible with @option{-m64}.
20462 When generating code compliant to the GNU/Linux for S/390 ABI,
20463 the default is @option{-mesa}. When generating code compliant
20464 to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}.
20470 Generate (or do not generate) code using the @code{mvcle} instruction
20471 to perform block moves. When @option{-mno-mvcle} is specified,
20472 use a @code{mvc} loop instead. This is the default unless optimizing for
20479 Print (or do not print) additional debug information when compiling.
20480 The default is to not print debug information.
20482 @item -march=@var{cpu-type}
20484 Generate code that runs on @var{cpu-type}, which is the name of a system
20485 representing a certain processor type. Possible values for
20486 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, @samp{z990},
20487 @samp{z9-109}, @samp{z9-ec}, @samp{z10}, @samp{z196}, @samp{zEC12},
20489 When generating code using the instructions available on z/Architecture,
20490 the default is @option{-march=z900}. Otherwise, the default is
20491 @option{-march=g5}.
20493 @item -mtune=@var{cpu-type}
20495 Tune to @var{cpu-type} everything applicable about the generated code,
20496 except for the ABI and the set of available instructions.
20497 The list of @var{cpu-type} values is the same as for @option{-march}.
20498 The default is the value used for @option{-march}.
20501 @itemx -mno-tpf-trace
20502 @opindex mtpf-trace
20503 @opindex mno-tpf-trace
20504 Generate code that adds (does not add) in TPF OS specific branches to trace
20505 routines in the operating system. This option is off by default, even
20506 when compiling for the TPF OS@.
20509 @itemx -mno-fused-madd
20510 @opindex mfused-madd
20511 @opindex mno-fused-madd
20512 Generate code that uses (does not use) the floating-point multiply and
20513 accumulate instructions. These instructions are generated by default if
20514 hardware floating point is used.
20516 @item -mwarn-framesize=@var{framesize}
20517 @opindex mwarn-framesize
20518 Emit a warning if the current function exceeds the given frame size. Because
20519 this is a compile-time check it doesn't need to be a real problem when the program
20520 runs. It is intended to identify functions that most probably cause
20521 a stack overflow. It is useful to be used in an environment with limited stack
20522 size e.g.@: the linux kernel.
20524 @item -mwarn-dynamicstack
20525 @opindex mwarn-dynamicstack
20526 Emit a warning if the function calls @code{alloca} or uses dynamically-sized
20527 arrays. This is generally a bad idea with a limited stack size.
20529 @item -mstack-guard=@var{stack-guard}
20530 @itemx -mstack-size=@var{stack-size}
20531 @opindex mstack-guard
20532 @opindex mstack-size
20533 If these options are provided the S/390 back end emits additional instructions in
20534 the function prologue that trigger a trap if the stack size is @var{stack-guard}
20535 bytes above the @var{stack-size} (remember that the stack on S/390 grows downward).
20536 If the @var{stack-guard} option is omitted the smallest power of 2 larger than
20537 the frame size of the compiled function is chosen.
20538 These options are intended to be used to help debugging stack overflow problems.
20539 The additionally emitted code causes only little overhead and hence can also be
20540 used in production-like systems without greater performance degradation. The given
20541 values have to be exact powers of 2 and @var{stack-size} has to be greater than
20542 @var{stack-guard} without exceeding 64k.
20543 In order to be efficient the extra code makes the assumption that the stack starts
20544 at an address aligned to the value given by @var{stack-size}.
20545 The @var{stack-guard} option can only be used in conjunction with @var{stack-size}.
20547 @item -mhotpatch=@var{pre-halfwords},@var{post-halfwords}
20549 If the hotpatch option is enabled, a ``hot-patching'' function
20550 prologue is generated for all functions in the compilation unit.
20551 The funtion label is prepended with the given number of two-byte
20552 NOP instructions (@var{pre-halfwords}, maximum 1000000). After
20553 the label, 2 * @var{post-halfwords} bytes are appended, using the
20554 largest NOP like instructions the architecture allows (maximum
20557 If both arguments are zero, hotpatching is disabled.
20559 This option can be overridden for individual functions with the
20560 @code{hotpatch} attribute.
20563 @node Score Options
20564 @subsection Score Options
20565 @cindex Score Options
20567 These options are defined for Score implementations:
20572 Compile code for big-endian mode. This is the default.
20576 Compile code for little-endian mode.
20580 Disable generation of @code{bcnz} instructions.
20584 Enable generation of unaligned load and store instructions.
20588 Enable the use of multiply-accumulate instructions. Disabled by default.
20592 Specify the SCORE5 as the target architecture.
20596 Specify the SCORE5U of the target architecture.
20600 Specify the SCORE7 as the target architecture. This is the default.
20604 Specify the SCORE7D as the target architecture.
20608 @subsection SH Options
20610 These @samp{-m} options are defined for the SH implementations:
20615 Generate code for the SH1.
20619 Generate code for the SH2.
20622 Generate code for the SH2e.
20626 Generate code for the SH2a without FPU, or for a SH2a-FPU in such a way
20627 that the floating-point unit is not used.
20629 @item -m2a-single-only
20630 @opindex m2a-single-only
20631 Generate code for the SH2a-FPU, in such a way that no double-precision
20632 floating-point operations are used.
20635 @opindex m2a-single
20636 Generate code for the SH2a-FPU assuming the floating-point unit is in
20637 single-precision mode by default.
20641 Generate code for the SH2a-FPU assuming the floating-point unit is in
20642 double-precision mode by default.
20646 Generate code for the SH3.
20650 Generate code for the SH3e.
20654 Generate code for the SH4 without a floating-point unit.
20656 @item -m4-single-only
20657 @opindex m4-single-only
20658 Generate code for the SH4 with a floating-point unit that only
20659 supports single-precision arithmetic.
20663 Generate code for the SH4 assuming the floating-point unit is in
20664 single-precision mode by default.
20668 Generate code for the SH4.
20672 Generate code for SH4-100.
20674 @item -m4-100-nofpu
20675 @opindex m4-100-nofpu
20676 Generate code for SH4-100 in such a way that the
20677 floating-point unit is not used.
20679 @item -m4-100-single
20680 @opindex m4-100-single
20681 Generate code for SH4-100 assuming the floating-point unit is in
20682 single-precision mode by default.
20684 @item -m4-100-single-only
20685 @opindex m4-100-single-only
20686 Generate code for SH4-100 in such a way that no double-precision
20687 floating-point operations are used.
20691 Generate code for SH4-200.
20693 @item -m4-200-nofpu
20694 @opindex m4-200-nofpu
20695 Generate code for SH4-200 without in such a way that the
20696 floating-point unit is not used.
20698 @item -m4-200-single
20699 @opindex m4-200-single
20700 Generate code for SH4-200 assuming the floating-point unit is in
20701 single-precision mode by default.
20703 @item -m4-200-single-only
20704 @opindex m4-200-single-only
20705 Generate code for SH4-200 in such a way that no double-precision
20706 floating-point operations are used.
20710 Generate code for SH4-300.
20712 @item -m4-300-nofpu
20713 @opindex m4-300-nofpu
20714 Generate code for SH4-300 without in such a way that the
20715 floating-point unit is not used.
20717 @item -m4-300-single
20718 @opindex m4-300-single
20719 Generate code for SH4-300 in such a way that no double-precision
20720 floating-point operations are used.
20722 @item -m4-300-single-only
20723 @opindex m4-300-single-only
20724 Generate code for SH4-300 in such a way that no double-precision
20725 floating-point operations are used.
20729 Generate code for SH4-340 (no MMU, no FPU).
20733 Generate code for SH4-500 (no FPU). Passes @option{-isa=sh4-nofpu} to the
20738 Generate code for the SH4al-dsp, or for a SH4a in such a way that the
20739 floating-point unit is not used.
20741 @item -m4a-single-only
20742 @opindex m4a-single-only
20743 Generate code for the SH4a, in such a way that no double-precision
20744 floating-point operations are used.
20747 @opindex m4a-single
20748 Generate code for the SH4a assuming the floating-point unit is in
20749 single-precision mode by default.
20753 Generate code for the SH4a.
20757 Same as @option{-m4a-nofpu}, except that it implicitly passes
20758 @option{-dsp} to the assembler. GCC doesn't generate any DSP
20759 instructions at the moment.
20762 @opindex m5-32media
20763 Generate 32-bit code for SHmedia.
20765 @item -m5-32media-nofpu
20766 @opindex m5-32media-nofpu
20767 Generate 32-bit code for SHmedia in such a way that the
20768 floating-point unit is not used.
20771 @opindex m5-64media
20772 Generate 64-bit code for SHmedia.
20774 @item -m5-64media-nofpu
20775 @opindex m5-64media-nofpu
20776 Generate 64-bit code for SHmedia in such a way that the
20777 floating-point unit is not used.
20780 @opindex m5-compact
20781 Generate code for SHcompact.
20783 @item -m5-compact-nofpu
20784 @opindex m5-compact-nofpu
20785 Generate code for SHcompact in such a way that the
20786 floating-point unit is not used.
20790 Compile code for the processor in big-endian mode.
20794 Compile code for the processor in little-endian mode.
20798 Align doubles at 64-bit boundaries. Note that this changes the calling
20799 conventions, and thus some functions from the standard C library do
20800 not work unless you recompile it first with @option{-mdalign}.
20804 Shorten some address references at link time, when possible; uses the
20805 linker option @option{-relax}.
20809 Use 32-bit offsets in @code{switch} tables. The default is to use
20814 Enable the use of bit manipulation instructions on SH2A.
20818 Enable the use of the instruction @code{fmovd}. Check @option{-mdalign} for
20819 alignment constraints.
20823 Comply with the calling conventions defined by Renesas.
20826 @opindex mno-renesas
20827 Comply with the calling conventions defined for GCC before the Renesas
20828 conventions were available. This option is the default for all
20829 targets of the SH toolchain.
20832 @opindex mnomacsave
20833 Mark the @code{MAC} register as call-clobbered, even if
20834 @option{-mrenesas} is given.
20840 Control the IEEE compliance of floating-point comparisons, which affects the
20841 handling of cases where the result of a comparison is unordered. By default
20842 @option{-mieee} is implicitly enabled. If @option{-ffinite-math-only} is
20843 enabled @option{-mno-ieee} is implicitly set, which results in faster
20844 floating-point greater-equal and less-equal comparisons. The implcit settings
20845 can be overridden by specifying either @option{-mieee} or @option{-mno-ieee}.
20847 @item -minline-ic_invalidate
20848 @opindex minline-ic_invalidate
20849 Inline code to invalidate instruction cache entries after setting up
20850 nested function trampolines.
20851 This option has no effect if @option{-musermode} is in effect and the selected
20852 code generation option (e.g. @option{-m4}) does not allow the use of the @code{icbi}
20854 If the selected code generation option does not allow the use of the @code{icbi}
20855 instruction, and @option{-musermode} is not in effect, the inlined code
20856 manipulates the instruction cache address array directly with an associative
20857 write. This not only requires privileged mode at run time, but it also
20858 fails if the cache line had been mapped via the TLB and has become unmapped.
20862 Dump instruction size and location in the assembly code.
20865 @opindex mpadstruct
20866 This option is deprecated. It pads structures to multiple of 4 bytes,
20867 which is incompatible with the SH ABI@.
20869 @item -matomic-model=@var{model}
20870 @opindex matomic-model=@var{model}
20871 Sets the model of atomic operations and additional parameters as a comma
20872 separated list. For details on the atomic built-in functions see
20873 @ref{__atomic Builtins}. The following models and parameters are supported:
20878 Disable compiler generated atomic sequences and emit library calls for atomic
20879 operations. This is the default if the target is not @code{sh*-*-linux*}.
20882 Generate GNU/Linux compatible gUSA software atomic sequences for the atomic
20883 built-in functions. The generated atomic sequences require additional support
20884 from the interrupt/exception handling code of the system and are only suitable
20885 for SH3* and SH4* single-core systems. This option is enabled by default when
20886 the target is @code{sh*-*-linux*} and SH3* or SH4*. When the target is SH4A,
20887 this option also partially utilizes the hardware atomic instructions
20888 @code{movli.l} and @code{movco.l} to create more efficient code, unless
20889 @samp{strict} is specified.
20892 Generate software atomic sequences that use a variable in the thread control
20893 block. This is a variation of the gUSA sequences which can also be used on
20894 SH1* and SH2* targets. The generated atomic sequences require additional
20895 support from the interrupt/exception handling code of the system and are only
20896 suitable for single-core systems. When using this model, the @samp{gbr-offset=}
20897 parameter has to be specified as well.
20900 Generate software atomic sequences that temporarily disable interrupts by
20901 setting @code{SR.IMASK = 1111}. This model works only when the program runs
20902 in privileged mode and is only suitable for single-core systems. Additional
20903 support from the interrupt/exception handling code of the system is not
20904 required. This model is enabled by default when the target is
20905 @code{sh*-*-linux*} and SH1* or SH2*.
20908 Generate hardware atomic sequences using the @code{movli.l} and @code{movco.l}
20909 instructions only. This is only available on SH4A and is suitable for
20910 multi-core systems. Since the hardware instructions support only 32 bit atomic
20911 variables access to 8 or 16 bit variables is emulated with 32 bit accesses.
20912 Code compiled with this option is also compatible with other software
20913 atomic model interrupt/exception handling systems if executed on an SH4A
20914 system. Additional support from the interrupt/exception handling code of the
20915 system is not required for this model.
20918 This parameter specifies the offset in bytes of the variable in the thread
20919 control block structure that should be used by the generated atomic sequences
20920 when the @samp{soft-tcb} model has been selected. For other models this
20921 parameter is ignored. The specified value must be an integer multiple of four
20922 and in the range 0-1020.
20925 This parameter prevents mixed usage of multiple atomic models, even if they
20926 are compatible, and makes the compiler generate atomic sequences of the
20927 specified model only.
20933 Generate the @code{tas.b} opcode for @code{__atomic_test_and_set}.
20934 Notice that depending on the particular hardware and software configuration
20935 this can degrade overall performance due to the operand cache line flushes
20936 that are implied by the @code{tas.b} instruction. On multi-core SH4A
20937 processors the @code{tas.b} instruction must be used with caution since it
20938 can result in data corruption for certain cache configurations.
20941 @opindex mprefergot
20942 When generating position-independent code, emit function calls using
20943 the Global Offset Table instead of the Procedure Linkage Table.
20946 @itemx -mno-usermode
20948 @opindex mno-usermode
20949 Don't allow (allow) the compiler generating privileged mode code. Specifying
20950 @option{-musermode} also implies @option{-mno-inline-ic_invalidate} if the
20951 inlined code would not work in user mode. @option{-musermode} is the default
20952 when the target is @code{sh*-*-linux*}. If the target is SH1* or SH2*
20953 @option{-musermode} has no effect, since there is no user mode.
20955 @item -multcost=@var{number}
20956 @opindex multcost=@var{number}
20957 Set the cost to assume for a multiply insn.
20959 @item -mdiv=@var{strategy}
20960 @opindex mdiv=@var{strategy}
20961 Set the division strategy to be used for integer division operations.
20962 For SHmedia @var{strategy} can be one of:
20967 Performs the operation in floating point. This has a very high latency,
20968 but needs only a few instructions, so it might be a good choice if
20969 your code has enough easily-exploitable ILP to allow the compiler to
20970 schedule the floating-point instructions together with other instructions.
20971 Division by zero causes a floating-point exception.
20974 Uses integer operations to calculate the inverse of the divisor,
20975 and then multiplies the dividend with the inverse. This strategy allows
20976 CSE and hoisting of the inverse calculation. Division by zero calculates
20977 an unspecified result, but does not trap.
20980 A variant of @samp{inv} where, if no CSE or hoisting opportunities
20981 have been found, or if the entire operation has been hoisted to the same
20982 place, the last stages of the inverse calculation are intertwined with the
20983 final multiply to reduce the overall latency, at the expense of using a few
20984 more instructions, and thus offering fewer scheduling opportunities with
20988 Calls a library function that usually implements the @samp{inv:minlat}
20990 This gives high code density for @code{m5-*media-nofpu} compilations.
20993 Uses a different entry point of the same library function, where it
20994 assumes that a pointer to a lookup table has already been set up, which
20995 exposes the pointer load to CSE and code hoisting optimizations.
21000 Use the @samp{inv} algorithm for initial
21001 code generation, but if the code stays unoptimized, revert to the @samp{call},
21002 @samp{call2}, or @samp{fp} strategies, respectively. Note that the
21003 potentially-trapping side effect of division by zero is carried by a
21004 separate instruction, so it is possible that all the integer instructions
21005 are hoisted out, but the marker for the side effect stays where it is.
21006 A recombination to floating-point operations or a call is not possible
21011 Variants of the @samp{inv:minlat} strategy. In the case
21012 that the inverse calculation is not separated from the multiply, they speed
21013 up division where the dividend fits into 20 bits (plus sign where applicable)
21014 by inserting a test to skip a number of operations in this case; this test
21015 slows down the case of larger dividends. @samp{inv20u} assumes the case of a such
21016 a small dividend to be unlikely, and @samp{inv20l} assumes it to be likely.
21020 For targets other than SHmedia @var{strategy} can be one of:
21025 Calls a library function that uses the single-step division instruction
21026 @code{div1} to perform the operation. Division by zero calculates an
21027 unspecified result and does not trap. This is the default except for SH4,
21028 SH2A and SHcompact.
21031 Calls a library function that performs the operation in double precision
21032 floating point. Division by zero causes a floating-point exception. This is
21033 the default for SHcompact with FPU. Specifying this for targets that do not
21034 have a double precision FPU defaults to @code{call-div1}.
21037 Calls a library function that uses a lookup table for small divisors and
21038 the @code{div1} instruction with case distinction for larger divisors. Division
21039 by zero calculates an unspecified result and does not trap. This is the default
21040 for SH4. Specifying this for targets that do not have dynamic shift
21041 instructions defaults to @code{call-div1}.
21045 When a division strategy has not been specified the default strategy is
21046 selected based on the current target. For SH2A the default strategy is to
21047 use the @code{divs} and @code{divu} instructions instead of library function
21050 @item -maccumulate-outgoing-args
21051 @opindex maccumulate-outgoing-args
21052 Reserve space once for outgoing arguments in the function prologue rather
21053 than around each call. Generally beneficial for performance and size. Also
21054 needed for unwinding to avoid changing the stack frame around conditional code.
21056 @item -mdivsi3_libfunc=@var{name}
21057 @opindex mdivsi3_libfunc=@var{name}
21058 Set the name of the library function used for 32-bit signed division to
21060 This only affects the name used in the @samp{call} and @samp{inv:call}
21061 division strategies, and the compiler still expects the same
21062 sets of input/output/clobbered registers as if this option were not present.
21064 @item -mfixed-range=@var{register-range}
21065 @opindex mfixed-range
21066 Generate code treating the given register range as fixed registers.
21067 A fixed register is one that the register allocator can not use. This is
21068 useful when compiling kernel code. A register range is specified as
21069 two registers separated by a dash. Multiple register ranges can be
21070 specified separated by a comma.
21072 @item -mindexed-addressing
21073 @opindex mindexed-addressing
21074 Enable the use of the indexed addressing mode for SHmedia32/SHcompact.
21075 This is only safe if the hardware and/or OS implement 32-bit wrap-around
21076 semantics for the indexed addressing mode. The architecture allows the
21077 implementation of processors with 64-bit MMU, which the OS could use to
21078 get 32-bit addressing, but since no current hardware implementation supports
21079 this or any other way to make the indexed addressing mode safe to use in
21080 the 32-bit ABI, the default is @option{-mno-indexed-addressing}.
21082 @item -mgettrcost=@var{number}
21083 @opindex mgettrcost=@var{number}
21084 Set the cost assumed for the @code{gettr} instruction to @var{number}.
21085 The default is 2 if @option{-mpt-fixed} is in effect, 100 otherwise.
21089 Assume @code{pt*} instructions won't trap. This generally generates
21090 better-scheduled code, but is unsafe on current hardware.
21091 The current architecture
21092 definition says that @code{ptabs} and @code{ptrel} trap when the target
21094 This has the unintentional effect of making it unsafe to schedule these
21095 instructions before a branch, or hoist them out of a loop. For example,
21096 @code{__do_global_ctors}, a part of @file{libgcc}
21097 that runs constructors at program
21098 startup, calls functions in a list which is delimited by @minus{}1. With the
21099 @option{-mpt-fixed} option, the @code{ptabs} is done before testing against @minus{}1.
21100 That means that all the constructors run a bit more quickly, but when
21101 the loop comes to the end of the list, the program crashes because @code{ptabs}
21102 loads @minus{}1 into a target register.
21104 Since this option is unsafe for any
21105 hardware implementing the current architecture specification, the default
21106 is @option{-mno-pt-fixed}. Unless specified explicitly with
21107 @option{-mgettrcost}, @option{-mno-pt-fixed} also implies @option{-mgettrcost=100};
21108 this deters register allocation from using target registers for storing
21111 @item -minvalid-symbols
21112 @opindex minvalid-symbols
21113 Assume symbols might be invalid. Ordinary function symbols generated by
21114 the compiler are always valid to load with
21115 @code{movi}/@code{shori}/@code{ptabs} or
21116 @code{movi}/@code{shori}/@code{ptrel},
21117 but with assembler and/or linker tricks it is possible
21118 to generate symbols that cause @code{ptabs} or @code{ptrel} to trap.
21119 This option is only meaningful when @option{-mno-pt-fixed} is in effect.
21120 It prevents cross-basic-block CSE, hoisting and most scheduling
21121 of symbol loads. The default is @option{-mno-invalid-symbols}.
21123 @item -mbranch-cost=@var{num}
21124 @opindex mbranch-cost=@var{num}
21125 Assume @var{num} to be the cost for a branch instruction. Higher numbers
21126 make the compiler try to generate more branch-free code if possible.
21127 If not specified the value is selected depending on the processor type that
21128 is being compiled for.
21131 @itemx -mno-zdcbranch
21132 @opindex mzdcbranch
21133 @opindex mno-zdcbranch
21134 Assume (do not assume) that zero displacement conditional branch instructions
21135 @code{bt} and @code{bf} are fast. If @option{-mzdcbranch} is specified, the
21136 compiler prefers zero displacement branch code sequences. This is
21137 enabled by default when generating code for SH4 and SH4A. It can be explicitly
21138 disabled by specifying @option{-mno-zdcbranch}.
21140 @item -mcbranch-force-delay-slot
21141 @opindex mcbranch-force-delay-slot
21142 Force the usage of delay slots for conditional branches, which stuffs the delay
21143 slot with a @code{nop} if a suitable instruction can't be found. By default
21144 this option is disabled. It can be enabled to work around hardware bugs as
21145 found in the original SH7055.
21148 @itemx -mno-fused-madd
21149 @opindex mfused-madd
21150 @opindex mno-fused-madd
21151 Generate code that uses (does not use) the floating-point multiply and
21152 accumulate instructions. These instructions are generated by default
21153 if hardware floating point is used. The machine-dependent
21154 @option{-mfused-madd} option is now mapped to the machine-independent
21155 @option{-ffp-contract=fast} option, and @option{-mno-fused-madd} is
21156 mapped to @option{-ffp-contract=off}.
21162 Allow or disallow the compiler to emit the @code{fsca} instruction for sine
21163 and cosine approximations. The option @option{-mfsca} must be used in
21164 combination with @option{-funsafe-math-optimizations}. It is enabled by default
21165 when generating code for SH4A. Using @option{-mno-fsca} disables sine and cosine
21166 approximations even if @option{-funsafe-math-optimizations} is in effect.
21172 Allow or disallow the compiler to emit the @code{fsrra} instruction for
21173 reciprocal square root approximations. The option @option{-mfsrra} must be used
21174 in combination with @option{-funsafe-math-optimizations} and
21175 @option{-ffinite-math-only}. It is enabled by default when generating code for
21176 SH4A. Using @option{-mno-fsrra} disables reciprocal square root approximations
21177 even if @option{-funsafe-math-optimizations} and @option{-ffinite-math-only} are
21180 @item -mpretend-cmove
21181 @opindex mpretend-cmove
21182 Prefer zero-displacement conditional branches for conditional move instruction
21183 patterns. This can result in faster code on the SH4 processor.
21187 @node Solaris 2 Options
21188 @subsection Solaris 2 Options
21189 @cindex Solaris 2 options
21191 These @samp{-m} options are supported on Solaris 2:
21194 @item -mclear-hwcap
21195 @opindex mclear-hwcap
21196 @option{-mclear-hwcap} tells the compiler to remove the hardware
21197 capabilities generated by the Solaris assembler. This is only necessary
21198 when object files use ISA extensions not supported by the current
21199 machine, but check at runtime whether or not to use them.
21201 @item -mimpure-text
21202 @opindex mimpure-text
21203 @option{-mimpure-text}, used in addition to @option{-shared}, tells
21204 the compiler to not pass @option{-z text} to the linker when linking a
21205 shared object. Using this option, you can link position-dependent
21206 code into a shared object.
21208 @option{-mimpure-text} suppresses the ``relocations remain against
21209 allocatable but non-writable sections'' linker error message.
21210 However, the necessary relocations trigger copy-on-write, and the
21211 shared object is not actually shared across processes. Instead of
21212 using @option{-mimpure-text}, you should compile all source code with
21213 @option{-fpic} or @option{-fPIC}.
21217 These switches are supported in addition to the above on Solaris 2:
21222 Add support for multithreading using the POSIX threads library. This
21223 option sets flags for both the preprocessor and linker. This option does
21224 not affect the thread safety of object code produced by the compiler or
21225 that of libraries supplied with it.
21229 This is a synonym for @option{-pthreads}.
21232 @node SPARC Options
21233 @subsection SPARC Options
21234 @cindex SPARC options
21236 These @samp{-m} options are supported on the SPARC:
21239 @item -mno-app-regs
21241 @opindex mno-app-regs
21243 Specify @option{-mapp-regs} to generate output using the global registers
21244 2 through 4, which the SPARC SVR4 ABI reserves for applications. Like the
21245 global register 1, each global register 2 through 4 is then treated as an
21246 allocable register that is clobbered by function calls. This is the default.
21248 To be fully SVR4 ABI-compliant at the cost of some performance loss,
21249 specify @option{-mno-app-regs}. You should compile libraries and system
21250 software with this option.
21256 With @option{-mflat}, the compiler does not generate save/restore instructions
21257 and uses a ``flat'' or single register window model. This model is compatible
21258 with the regular register window model. The local registers and the input
21259 registers (0--5) are still treated as ``call-saved'' registers and are
21260 saved on the stack as needed.
21262 With @option{-mno-flat} (the default), the compiler generates save/restore
21263 instructions (except for leaf functions). This is the normal operating mode.
21266 @itemx -mhard-float
21268 @opindex mhard-float
21269 Generate output containing floating-point instructions. This is the
21273 @itemx -msoft-float
21275 @opindex msoft-float
21276 Generate output containing library calls for floating point.
21277 @strong{Warning:} the requisite libraries are not available for all SPARC
21278 targets. Normally the facilities of the machine's usual C compiler are
21279 used, but this cannot be done directly in cross-compilation. You must make
21280 your own arrangements to provide suitable library functions for
21281 cross-compilation. The embedded targets @samp{sparc-*-aout} and
21282 @samp{sparclite-*-*} do provide software floating-point support.
21284 @option{-msoft-float} changes the calling convention in the output file;
21285 therefore, it is only useful if you compile @emph{all} of a program with
21286 this option. In particular, you need to compile @file{libgcc.a}, the
21287 library that comes with GCC, with @option{-msoft-float} in order for
21290 @item -mhard-quad-float
21291 @opindex mhard-quad-float
21292 Generate output containing quad-word (long double) floating-point
21295 @item -msoft-quad-float
21296 @opindex msoft-quad-float
21297 Generate output containing library calls for quad-word (long double)
21298 floating-point instructions. The functions called are those specified
21299 in the SPARC ABI@. This is the default.
21301 As of this writing, there are no SPARC implementations that have hardware
21302 support for the quad-word floating-point instructions. They all invoke
21303 a trap handler for one of these instructions, and then the trap handler
21304 emulates the effect of the instruction. Because of the trap handler overhead,
21305 this is much slower than calling the ABI library routines. Thus the
21306 @option{-msoft-quad-float} option is the default.
21308 @item -mno-unaligned-doubles
21309 @itemx -munaligned-doubles
21310 @opindex mno-unaligned-doubles
21311 @opindex munaligned-doubles
21312 Assume that doubles have 8-byte alignment. This is the default.
21314 With @option{-munaligned-doubles}, GCC assumes that doubles have 8-byte
21315 alignment only if they are contained in another type, or if they have an
21316 absolute address. Otherwise, it assumes they have 4-byte alignment.
21317 Specifying this option avoids some rare compatibility problems with code
21318 generated by other compilers. It is not the default because it results
21319 in a performance loss, especially for floating-point code.
21322 @itemx -mno-user-mode
21323 @opindex muser-mode
21324 @opindex mno-user-mode
21325 Do not generate code that can only run in supervisor mode. This is relevant
21326 only for the @code{casa} instruction emitted for the LEON3 processor. The
21327 default is @option{-mno-user-mode}.
21329 @item -mno-faster-structs
21330 @itemx -mfaster-structs
21331 @opindex mno-faster-structs
21332 @opindex mfaster-structs
21333 With @option{-mfaster-structs}, the compiler assumes that structures
21334 should have 8-byte alignment. This enables the use of pairs of
21335 @code{ldd} and @code{std} instructions for copies in structure
21336 assignment, in place of twice as many @code{ld} and @code{st} pairs.
21337 However, the use of this changed alignment directly violates the SPARC
21338 ABI@. Thus, it's intended only for use on targets where the developer
21339 acknowledges that their resulting code is not directly in line with
21340 the rules of the ABI@.
21342 @item -mcpu=@var{cpu_type}
21344 Set the instruction set, register set, and instruction scheduling parameters
21345 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
21346 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{hypersparc},
21347 @samp{leon}, @samp{leon3}, @samp{leon3v7}, @samp{sparclite}, @samp{f930},
21348 @samp{f934}, @samp{sparclite86x}, @samp{sparclet}, @samp{tsc701}, @samp{v9},
21349 @samp{ultrasparc}, @samp{ultrasparc3}, @samp{niagara}, @samp{niagara2},
21350 @samp{niagara3} and @samp{niagara4}.
21352 Native Solaris and GNU/Linux toolchains also support the value @samp{native},
21353 which selects the best architecture option for the host processor.
21354 @option{-mcpu=native} has no effect if GCC does not recognize
21357 Default instruction scheduling parameters are used for values that select
21358 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
21359 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
21361 Here is a list of each supported architecture and their supported
21369 supersparc, hypersparc, leon, leon3
21372 f930, f934, sparclite86x
21378 ultrasparc, ultrasparc3, niagara, niagara2, niagara3, niagara4
21381 By default (unless configured otherwise), GCC generates code for the V7
21382 variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler
21383 additionally optimizes it for the Cypress CY7C602 chip, as used in the
21384 SPARCStation/SPARCServer 3xx series. This is also appropriate for the older
21385 SPARCStation 1, 2, IPX etc.
21387 With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC
21388 architecture. The only difference from V7 code is that the compiler emits
21389 the integer multiply and integer divide instructions which exist in SPARC-V8
21390 but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally
21391 optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and
21394 With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of
21395 the SPARC architecture. This adds the integer multiply, integer divide step
21396 and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7.
21397 With @option{-mcpu=f930}, the compiler additionally optimizes it for the
21398 Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With
21399 @option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu
21400 MB86934 chip, which is the more recent SPARClite with FPU@.
21402 With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of
21403 the SPARC architecture. This adds the integer multiply, multiply/accumulate,
21404 integer divide step and scan (@code{ffs}) instructions which exist in SPARClet
21405 but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally
21406 optimizes it for the TEMIC SPARClet chip.
21408 With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC
21409 architecture. This adds 64-bit integer and floating-point move instructions,
21410 3 additional floating-point condition code registers and conditional move
21411 instructions. With @option{-mcpu=ultrasparc}, the compiler additionally
21412 optimizes it for the Sun UltraSPARC I/II/IIi chips. With
21413 @option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the
21414 Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With
21415 @option{-mcpu=niagara}, the compiler additionally optimizes it for
21416 Sun UltraSPARC T1 chips. With @option{-mcpu=niagara2}, the compiler
21417 additionally optimizes it for Sun UltraSPARC T2 chips. With
21418 @option{-mcpu=niagara3}, the compiler additionally optimizes it for Sun
21419 UltraSPARC T3 chips. With @option{-mcpu=niagara4}, the compiler
21420 additionally optimizes it for Sun UltraSPARC T4 chips.
21422 @item -mtune=@var{cpu_type}
21424 Set the instruction scheduling parameters for machine type
21425 @var{cpu_type}, but do not set the instruction set or register set that the
21426 option @option{-mcpu=@var{cpu_type}} does.
21428 The same values for @option{-mcpu=@var{cpu_type}} can be used for
21429 @option{-mtune=@var{cpu_type}}, but the only useful values are those
21430 that select a particular CPU implementation. Those are @samp{cypress},
21431 @samp{supersparc}, @samp{hypersparc}, @samp{leon}, @samp{leon3},
21432 @samp{leon3v7}, @samp{f930}, @samp{f934}, @samp{sparclite86x}, @samp{tsc701},
21433 @samp{ultrasparc}, @samp{ultrasparc3}, @samp{niagara}, @samp{niagara2},
21434 @samp{niagara3} and @samp{niagara4}. With native Solaris and GNU/Linux
21435 toolchains, @samp{native} can also be used.
21440 @opindex mno-v8plus
21441 With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The
21442 difference from the V8 ABI is that the global and out registers are
21443 considered 64 bits wide. This is enabled by default on Solaris in 32-bit
21444 mode for all SPARC-V9 processors.
21450 With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC
21451 Visual Instruction Set extensions. The default is @option{-mno-vis}.
21457 With @option{-mvis2}, GCC generates code that takes advantage of
21458 version 2.0 of the UltraSPARC Visual Instruction Set extensions. The
21459 default is @option{-mvis2} when targeting a cpu that supports such
21460 instructions, such as UltraSPARC-III and later. Setting @option{-mvis2}
21461 also sets @option{-mvis}.
21467 With @option{-mvis3}, GCC generates code that takes advantage of
21468 version 3.0 of the UltraSPARC Visual Instruction Set extensions. The
21469 default is @option{-mvis3} when targeting a cpu that supports such
21470 instructions, such as niagara-3 and later. Setting @option{-mvis3}
21471 also sets @option{-mvis2} and @option{-mvis}.
21476 @opindex mno-cbcond
21477 With @option{-mcbcond}, GCC generates code that takes advantage of
21478 compare-and-branch instructions, as defined in the Sparc Architecture 2011.
21479 The default is @option{-mcbcond} when targeting a cpu that supports such
21480 instructions, such as niagara-4 and later.
21486 With @option{-mpopc}, GCC generates code that takes advantage of the UltraSPARC
21487 population count instruction. The default is @option{-mpopc}
21488 when targeting a cpu that supports such instructions, such as Niagara-2 and
21495 With @option{-mfmaf}, GCC generates code that takes advantage of the UltraSPARC
21496 Fused Multiply-Add Floating-point extensions. The default is @option{-mfmaf}
21497 when targeting a cpu that supports such instructions, such as Niagara-3 and
21501 @opindex mfix-at697f
21502 Enable the documented workaround for the single erratum of the Atmel AT697F
21503 processor (which corresponds to erratum #13 of the AT697E processor).
21506 @opindex mfix-ut699
21507 Enable the documented workarounds for the floating-point errata and the data
21508 cache nullify errata of the UT699 processor.
21511 These @samp{-m} options are supported in addition to the above
21512 on SPARC-V9 processors in 64-bit environments:
21519 Generate code for a 32-bit or 64-bit environment.
21520 The 32-bit environment sets int, long and pointer to 32 bits.
21521 The 64-bit environment sets int to 32 bits and long and pointer
21524 @item -mcmodel=@var{which}
21526 Set the code model to one of
21530 The Medium/Low code model: 64-bit addresses, programs
21531 must be linked in the low 32 bits of memory. Programs can be statically
21532 or dynamically linked.
21535 The Medium/Middle code model: 64-bit addresses, programs
21536 must be linked in the low 44 bits of memory, the text and data segments must
21537 be less than 2GB in size and the data segment must be located within 2GB of
21541 The Medium/Anywhere code model: 64-bit addresses, programs
21542 may be linked anywhere in memory, the text and data segments must be less
21543 than 2GB in size and the data segment must be located within 2GB of the
21547 The Medium/Anywhere code model for embedded systems:
21548 64-bit addresses, the text and data segments must be less than 2GB in
21549 size, both starting anywhere in memory (determined at link time). The
21550 global register %g4 points to the base of the data segment. Programs
21551 are statically linked and PIC is not supported.
21554 @item -mmemory-model=@var{mem-model}
21555 @opindex mmemory-model
21556 Set the memory model in force on the processor to one of
21560 The default memory model for the processor and operating system.
21563 Relaxed Memory Order
21566 Partial Store Order
21572 Sequential Consistency
21575 These memory models are formally defined in Appendix D of the Sparc V9
21576 architecture manual, as set in the processor's @code{PSTATE.MM} field.
21579 @itemx -mno-stack-bias
21580 @opindex mstack-bias
21581 @opindex mno-stack-bias
21582 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
21583 frame pointer if present, are offset by @minus{}2047 which must be added back
21584 when making stack frame references. This is the default in 64-bit mode.
21585 Otherwise, assume no such offset is present.
21589 @subsection SPU Options
21590 @cindex SPU options
21592 These @samp{-m} options are supported on the SPU:
21596 @itemx -merror-reloc
21597 @opindex mwarn-reloc
21598 @opindex merror-reloc
21600 The loader for SPU does not handle dynamic relocations. By default, GCC
21601 gives an error when it generates code that requires a dynamic
21602 relocation. @option{-mno-error-reloc} disables the error,
21603 @option{-mwarn-reloc} generates a warning instead.
21606 @itemx -munsafe-dma
21608 @opindex munsafe-dma
21610 Instructions that initiate or test completion of DMA must not be
21611 reordered with respect to loads and stores of the memory that is being
21613 With @option{-munsafe-dma} you must use the @code{volatile} keyword to protect
21614 memory accesses, but that can lead to inefficient code in places where the
21615 memory is known to not change. Rather than mark the memory as volatile,
21616 you can use @option{-msafe-dma} to tell the compiler to treat
21617 the DMA instructions as potentially affecting all memory.
21619 @item -mbranch-hints
21620 @opindex mbranch-hints
21622 By default, GCC generates a branch hint instruction to avoid
21623 pipeline stalls for always-taken or probably-taken branches. A hint
21624 is not generated closer than 8 instructions away from its branch.
21625 There is little reason to disable them, except for debugging purposes,
21626 or to make an object a little bit smaller.
21630 @opindex msmall-mem
21631 @opindex mlarge-mem
21633 By default, GCC generates code assuming that addresses are never larger
21634 than 18 bits. With @option{-mlarge-mem} code is generated that assumes
21635 a full 32-bit address.
21640 By default, GCC links against startup code that assumes the SPU-style
21641 main function interface (which has an unconventional parameter list).
21642 With @option{-mstdmain}, GCC links your program against startup
21643 code that assumes a C99-style interface to @code{main}, including a
21644 local copy of @code{argv} strings.
21646 @item -mfixed-range=@var{register-range}
21647 @opindex mfixed-range
21648 Generate code treating the given register range as fixed registers.
21649 A fixed register is one that the register allocator cannot use. This is
21650 useful when compiling kernel code. A register range is specified as
21651 two registers separated by a dash. Multiple register ranges can be
21652 specified separated by a comma.
21658 Compile code assuming that pointers to the PPU address space accessed
21659 via the @code{__ea} named address space qualifier are either 32 or 64
21660 bits wide. The default is 32 bits. As this is an ABI-changing option,
21661 all object code in an executable must be compiled with the same setting.
21663 @item -maddress-space-conversion
21664 @itemx -mno-address-space-conversion
21665 @opindex maddress-space-conversion
21666 @opindex mno-address-space-conversion
21667 Allow/disallow treating the @code{__ea} address space as superset
21668 of the generic address space. This enables explicit type casts
21669 between @code{__ea} and generic pointer as well as implicit
21670 conversions of generic pointers to @code{__ea} pointers. The
21671 default is to allow address space pointer conversions.
21673 @item -mcache-size=@var{cache-size}
21674 @opindex mcache-size
21675 This option controls the version of libgcc that the compiler links to an
21676 executable and selects a software-managed cache for accessing variables
21677 in the @code{__ea} address space with a particular cache size. Possible
21678 options for @var{cache-size} are @samp{8}, @samp{16}, @samp{32}, @samp{64}
21679 and @samp{128}. The default cache size is 64KB.
21681 @item -matomic-updates
21682 @itemx -mno-atomic-updates
21683 @opindex matomic-updates
21684 @opindex mno-atomic-updates
21685 This option controls the version of libgcc that the compiler links to an
21686 executable and selects whether atomic updates to the software-managed
21687 cache of PPU-side variables are used. If you use atomic updates, changes
21688 to a PPU variable from SPU code using the @code{__ea} named address space
21689 qualifier do not interfere with changes to other PPU variables residing
21690 in the same cache line from PPU code. If you do not use atomic updates,
21691 such interference may occur; however, writing back cache lines is
21692 more efficient. The default behavior is to use atomic updates.
21695 @itemx -mdual-nops=@var{n}
21696 @opindex mdual-nops
21697 By default, GCC inserts nops to increase dual issue when it expects
21698 it to increase performance. @var{n} can be a value from 0 to 10. A
21699 smaller @var{n} inserts fewer nops. 10 is the default, 0 is the
21700 same as @option{-mno-dual-nops}. Disabled with @option{-Os}.
21702 @item -mhint-max-nops=@var{n}
21703 @opindex mhint-max-nops
21704 Maximum number of nops to insert for a branch hint. A branch hint must
21705 be at least 8 instructions away from the branch it is affecting. GCC
21706 inserts up to @var{n} nops to enforce this, otherwise it does not
21707 generate the branch hint.
21709 @item -mhint-max-distance=@var{n}
21710 @opindex mhint-max-distance
21711 The encoding of the branch hint instruction limits the hint to be within
21712 256 instructions of the branch it is affecting. By default, GCC makes
21713 sure it is within 125.
21716 @opindex msafe-hints
21717 Work around a hardware bug that causes the SPU to stall indefinitely.
21718 By default, GCC inserts the @code{hbrp} instruction to make sure
21719 this stall won't happen.
21723 @node System V Options
21724 @subsection Options for System V
21726 These additional options are available on System V Release 4 for
21727 compatibility with other compilers on those systems:
21732 Create a shared object.
21733 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
21737 Identify the versions of each tool used by the compiler, in a
21738 @code{.ident} assembler directive in the output.
21742 Refrain from adding @code{.ident} directives to the output file (this is
21745 @item -YP,@var{dirs}
21747 Search the directories @var{dirs}, and no others, for libraries
21748 specified with @option{-l}.
21750 @item -Ym,@var{dir}
21752 Look in the directory @var{dir} to find the M4 preprocessor.
21753 The assembler uses this option.
21754 @c This is supposed to go with a -Yd for predefined M4 macro files, but
21755 @c the generic assembler that comes with Solaris takes just -Ym.
21758 @node TILE-Gx Options
21759 @subsection TILE-Gx Options
21760 @cindex TILE-Gx options
21762 These @samp{-m} options are supported on the TILE-Gx:
21765 @item -mcmodel=small
21766 @opindex mcmodel=small
21767 Generate code for the small model. The distance for direct calls is
21768 limited to 500M in either direction. PC-relative addresses are 32
21769 bits. Absolute addresses support the full address range.
21771 @item -mcmodel=large
21772 @opindex mcmodel=large
21773 Generate code for the large model. There is no limitation on call
21774 distance, pc-relative addresses, or absolute addresses.
21776 @item -mcpu=@var{name}
21778 Selects the type of CPU to be targeted. Currently the only supported
21779 type is @samp{tilegx}.
21785 Generate code for a 32-bit or 64-bit environment. The 32-bit
21786 environment sets int, long, and pointer to 32 bits. The 64-bit
21787 environment sets int to 32 bits and long and pointer to 64 bits.
21790 @itemx -mlittle-endian
21791 @opindex mbig-endian
21792 @opindex mlittle-endian
21793 Generate code in big/little endian mode, respectively.
21796 @node TILEPro Options
21797 @subsection TILEPro Options
21798 @cindex TILEPro options
21800 These @samp{-m} options are supported on the TILEPro:
21803 @item -mcpu=@var{name}
21805 Selects the type of CPU to be targeted. Currently the only supported
21806 type is @samp{tilepro}.
21810 Generate code for a 32-bit environment, which sets int, long, and
21811 pointer to 32 bits. This is the only supported behavior so the flag
21812 is essentially ignored.
21816 @subsection V850 Options
21817 @cindex V850 Options
21819 These @samp{-m} options are defined for V850 implementations:
21823 @itemx -mno-long-calls
21824 @opindex mlong-calls
21825 @opindex mno-long-calls
21826 Treat all calls as being far away (near). If calls are assumed to be
21827 far away, the compiler always loads the function's address into a
21828 register, and calls indirect through the pointer.
21834 Do not optimize (do optimize) basic blocks that use the same index
21835 pointer 4 or more times to copy pointer into the @code{ep} register, and
21836 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
21837 option is on by default if you optimize.
21839 @item -mno-prolog-function
21840 @itemx -mprolog-function
21841 @opindex mno-prolog-function
21842 @opindex mprolog-function
21843 Do not use (do use) external functions to save and restore registers
21844 at the prologue and epilogue of a function. The external functions
21845 are slower, but use less code space if more than one function saves
21846 the same number of registers. The @option{-mprolog-function} option
21847 is on by default if you optimize.
21851 Try to make the code as small as possible. At present, this just turns
21852 on the @option{-mep} and @option{-mprolog-function} options.
21854 @item -mtda=@var{n}
21856 Put static or global variables whose size is @var{n} bytes or less into
21857 the tiny data area that register @code{ep} points to. The tiny data
21858 area can hold up to 256 bytes in total (128 bytes for byte references).
21860 @item -msda=@var{n}
21862 Put static or global variables whose size is @var{n} bytes or less into
21863 the small data area that register @code{gp} points to. The small data
21864 area can hold up to 64 kilobytes.
21866 @item -mzda=@var{n}
21868 Put static or global variables whose size is @var{n} bytes or less into
21869 the first 32 kilobytes of memory.
21873 Specify that the target processor is the V850.
21877 Specify that the target processor is the V850E3V5. The preprocessor
21878 constant @code{__v850e3v5__} is defined if this option is used.
21882 Specify that the target processor is the V850E3V5. This is an alias for
21883 the @option{-mv850e3v5} option.
21887 Specify that the target processor is the V850E2V3. The preprocessor
21888 constant @code{__v850e2v3__} is defined if this option is used.
21892 Specify that the target processor is the V850E2. The preprocessor
21893 constant @code{__v850e2__} is defined if this option is used.
21897 Specify that the target processor is the V850E1. The preprocessor
21898 constants @code{__v850e1__} and @code{__v850e__} are defined if
21899 this option is used.
21903 Specify that the target processor is the V850ES. This is an alias for
21904 the @option{-mv850e1} option.
21908 Specify that the target processor is the V850E@. The preprocessor
21909 constant @code{__v850e__} is defined if this option is used.
21911 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
21912 nor @option{-mv850e2} nor @option{-mv850e2v3} nor @option{-mv850e3v5}
21913 are defined then a default target processor is chosen and the
21914 relevant @samp{__v850*__} preprocessor constant is defined.
21916 The preprocessor constants @code{__v850} and @code{__v851__} are always
21917 defined, regardless of which processor variant is the target.
21919 @item -mdisable-callt
21920 @itemx -mno-disable-callt
21921 @opindex mdisable-callt
21922 @opindex mno-disable-callt
21923 This option suppresses generation of the @code{CALLT} instruction for the
21924 v850e, v850e1, v850e2, v850e2v3 and v850e3v5 flavors of the v850
21927 This option is enabled by default when the RH850 ABI is
21928 in use (see @option{-mrh850-abi}), and disabled by default when the
21929 GCC ABI is in use. If @code{CALLT} instructions are being generated
21930 then the C preprocessor symbol @code{__V850_CALLT__} is defined.
21936 Pass on (or do not pass on) the @option{-mrelax} command-line option
21940 @itemx -mno-long-jumps
21941 @opindex mlong-jumps
21942 @opindex mno-long-jumps
21943 Disable (or re-enable) the generation of PC-relative jump instructions.
21946 @itemx -mhard-float
21947 @opindex msoft-float
21948 @opindex mhard-float
21949 Disable (or re-enable) the generation of hardware floating point
21950 instructions. This option is only significant when the target
21951 architecture is @samp{V850E2V3} or higher. If hardware floating point
21952 instructions are being generated then the C preprocessor symbol
21953 @code{__FPU_OK__} is defined, otherwise the symbol
21954 @code{__NO_FPU__} is defined.
21958 Enables the use of the e3v5 LOOP instruction. The use of this
21959 instruction is not enabled by default when the e3v5 architecture is
21960 selected because its use is still experimental.
21964 @opindex mrh850-abi
21966 Enables support for the RH850 version of the V850 ABI. This is the
21967 default. With this version of the ABI the following rules apply:
21971 Integer sized structures and unions are returned via a memory pointer
21972 rather than a register.
21975 Large structures and unions (more than 8 bytes in size) are passed by
21979 Functions are aligned to 16-bit boundaries.
21982 The @option{-m8byte-align} command-line option is supported.
21985 The @option{-mdisable-callt} command-line option is enabled by
21986 default. The @option{-mno-disable-callt} command-line option is not
21990 When this version of the ABI is enabled the C preprocessor symbol
21991 @code{__V850_RH850_ABI__} is defined.
21995 Enables support for the old GCC version of the V850 ABI. With this
21996 version of the ABI the following rules apply:
22000 Integer sized structures and unions are returned in register @code{r10}.
22003 Large structures and unions (more than 8 bytes in size) are passed by
22007 Functions are aligned to 32-bit boundaries, unless optimizing for
22011 The @option{-m8byte-align} command-line option is not supported.
22014 The @option{-mdisable-callt} command-line option is supported but not
22015 enabled by default.
22018 When this version of the ABI is enabled the C preprocessor symbol
22019 @code{__V850_GCC_ABI__} is defined.
22021 @item -m8byte-align
22022 @itemx -mno-8byte-align
22023 @opindex m8byte-align
22024 @opindex mno-8byte-align
22025 Enables support for @code{double} and @code{long long} types to be
22026 aligned on 8-byte boundaries. The default is to restrict the
22027 alignment of all objects to at most 4-bytes. When
22028 @option{-m8byte-align} is in effect the C preprocessor symbol
22029 @code{__V850_8BYTE_ALIGN__} is defined.
22032 @opindex mbig-switch
22033 Generate code suitable for big switch tables. Use this option only if
22034 the assembler/linker complain about out of range branches within a switch
22039 This option causes r2 and r5 to be used in the code generated by
22040 the compiler. This setting is the default.
22042 @item -mno-app-regs
22043 @opindex mno-app-regs
22044 This option causes r2 and r5 to be treated as fixed registers.
22049 @subsection VAX Options
22050 @cindex VAX options
22052 These @samp{-m} options are defined for the VAX:
22057 Do not output certain jump instructions (@code{aobleq} and so on)
22058 that the Unix assembler for the VAX cannot handle across long
22063 Do output those jump instructions, on the assumption that the
22064 GNU assembler is being used.
22068 Output code for G-format floating-point numbers instead of D-format.
22071 @node Visium Options
22072 @subsection Visium Options
22073 @cindex Visium options
22079 A program which performs file I/O and is destined to run on an MCM target
22080 should be linked with this option. It causes the libraries libc.a and
22081 libdebug.a to be linked. The program should be run on the target under
22082 the control of the GDB remote debugging stub.
22086 A program which performs file I/O and is destined to run on the simulator
22087 should be linked with option. This causes libraries libc.a and libsim.a to
22091 @itemx -mhard-float
22093 @opindex mhard-float
22094 Generate code containing floating-point instructions. This is the
22098 @itemx -msoft-float
22100 @opindex msoft-float
22101 Generate code containing library calls for floating-point.
22103 @option{-msoft-float} changes the calling convention in the output file;
22104 therefore, it is only useful if you compile @emph{all} of a program with
22105 this option. In particular, you need to compile @file{libgcc.a}, the
22106 library that comes with GCC, with @option{-msoft-float} in order for
22109 @item -mcpu=@var{cpu_type}
22111 Set the instruction set, register set, and instruction scheduling parameters
22112 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
22113 @samp{mcm}, @samp{gr5} and @samp{gr6}.
22115 @samp{mcm} is a synonym of @samp{gr5} present for backward compatibility.
22117 By default (unless configured otherwise), GCC generates code for the GR5
22118 variant of the Visium architecture.
22120 With @option{-mcpu=gr6}, GCC generates code for the GR6 variant of the Visium
22121 architecture. The only difference from GR5 code is that the compiler will
22122 generate block move instructions.
22124 @item -mtune=@var{cpu_type}
22126 Set the instruction scheduling parameters for machine type @var{cpu_type},
22127 but do not set the instruction set or register set that the option
22128 @option{-mcpu=@var{cpu_type}} would.
22132 Generate code for the supervisor mode, where there are no restrictions on
22133 the access to general registers. This is the default.
22136 @opindex muser-mode
22137 Generate code for the user mode, where the access to some general registers
22138 is forbidden: on the GR5, registers r24 to r31 cannot be accessed in this
22139 mode; on the GR6, only registers r29 to r31 are affected.
22143 @subsection VMS Options
22145 These @samp{-m} options are defined for the VMS implementations:
22148 @item -mvms-return-codes
22149 @opindex mvms-return-codes
22150 Return VMS condition codes from @code{main}. The default is to return POSIX-style
22151 condition (e.g.@ error) codes.
22153 @item -mdebug-main=@var{prefix}
22154 @opindex mdebug-main=@var{prefix}
22155 Flag the first routine whose name starts with @var{prefix} as the main
22156 routine for the debugger.
22160 Default to 64-bit memory allocation routines.
22162 @item -mpointer-size=@var{size}
22163 @opindex mpointer-size=@var{size}
22164 Set the default size of pointers. Possible options for @var{size} are
22165 @samp{32} or @samp{short} for 32 bit pointers, @samp{64} or @samp{long}
22166 for 64 bit pointers, and @samp{no} for supporting only 32 bit pointers.
22167 The later option disables @code{pragma pointer_size}.
22170 @node VxWorks Options
22171 @subsection VxWorks Options
22172 @cindex VxWorks Options
22174 The options in this section are defined for all VxWorks targets.
22175 Options specific to the target hardware are listed with the other
22176 options for that target.
22181 GCC can generate code for both VxWorks kernels and real time processes
22182 (RTPs). This option switches from the former to the latter. It also
22183 defines the preprocessor macro @code{__RTP__}.
22186 @opindex non-static
22187 Link an RTP executable against shared libraries rather than static
22188 libraries. The options @option{-static} and @option{-shared} can
22189 also be used for RTPs (@pxref{Link Options}); @option{-static}
22196 These options are passed down to the linker. They are defined for
22197 compatibility with Diab.
22200 @opindex Xbind-lazy
22201 Enable lazy binding of function calls. This option is equivalent to
22202 @option{-Wl,-z,now} and is defined for compatibility with Diab.
22206 Disable lazy binding of function calls. This option is the default and
22207 is defined for compatibility with Diab.
22211 @subsection x86 Options
22212 @cindex x86 Options
22214 These @samp{-m} options are defined for the x86 family of computers.
22218 @item -march=@var{cpu-type}
22220 Generate instructions for the machine type @var{cpu-type}. In contrast to
22221 @option{-mtune=@var{cpu-type}}, which merely tunes the generated code
22222 for the specified @var{cpu-type}, @option{-march=@var{cpu-type}} allows GCC
22223 to generate code that may not run at all on processors other than the one
22224 indicated. Specifying @option{-march=@var{cpu-type}} implies
22225 @option{-mtune=@var{cpu-type}}.
22227 The choices for @var{cpu-type} are:
22231 This selects the CPU to generate code for at compilation time by determining
22232 the processor type of the compiling machine. Using @option{-march=native}
22233 enables all instruction subsets supported by the local machine (hence
22234 the result might not run on different machines). Using @option{-mtune=native}
22235 produces code optimized for the local machine under the constraints
22236 of the selected instruction set.
22239 Original Intel i386 CPU@.
22242 Intel i486 CPU@. (No scheduling is implemented for this chip.)
22246 Intel Pentium CPU with no MMX support.
22249 Intel Pentium MMX CPU, based on Pentium core with MMX instruction set support.
22252 Intel Pentium Pro CPU@.
22255 When used with @option{-march}, the Pentium Pro
22256 instruction set is used, so the code runs on all i686 family chips.
22257 When used with @option{-mtune}, it has the same meaning as @samp{generic}.
22260 Intel Pentium II CPU, based on Pentium Pro core with MMX instruction set
22265 Intel Pentium III CPU, based on Pentium Pro core with MMX and SSE instruction
22269 Intel Pentium M; low-power version of Intel Pentium III CPU
22270 with MMX, SSE and SSE2 instruction set support. Used by Centrino notebooks.
22274 Intel Pentium 4 CPU with MMX, SSE and SSE2 instruction set support.
22277 Improved version of Intel Pentium 4 CPU with MMX, SSE, SSE2 and SSE3 instruction
22281 Improved version of Intel Pentium 4 CPU with 64-bit extensions, MMX, SSE,
22282 SSE2 and SSE3 instruction set support.
22285 Intel Core 2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3
22286 instruction set support.
22289 Intel Nehalem CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3,
22290 SSE4.1, SSE4.2 and POPCNT instruction set support.
22293 Intel Westmere CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3,
22294 SSE4.1, SSE4.2, POPCNT, AES and PCLMUL instruction set support.
22297 Intel Sandy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3,
22298 SSE4.1, SSE4.2, POPCNT, AVX, AES and PCLMUL instruction set support.
22301 Intel Ivy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3,
22302 SSE4.1, SSE4.2, POPCNT, AVX, AES, PCLMUL, FSGSBASE, RDRND and F16C
22303 instruction set support.
22306 Intel Haswell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3,
22307 SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA,
22308 BMI, BMI2 and F16C instruction set support.
22311 Intel Broadwell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3,
22312 SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA,
22313 BMI, BMI2, F16C, RDSEED, ADCX and PREFETCHW instruction set support.
22316 Intel Bonnell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3 and SSSE3
22317 instruction set support.
22320 Intel Silvermont CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3,
22321 SSE4.1, SSE4.2, POPCNT, AES, PCLMUL and RDRND instruction set support.
22324 Intel Knight's Landing CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3,
22325 SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA,
22326 BMI, BMI2, F16C, RDSEED, ADCX, PREFETCHW, AVX512F, AVX512PF, AVX512ER and
22327 AVX512CD instruction set support.
22330 AMD K6 CPU with MMX instruction set support.
22334 Improved versions of AMD K6 CPU with MMX and 3DNow!@: instruction set support.
22337 @itemx athlon-tbird
22338 AMD Athlon CPU with MMX, 3dNOW!, enhanced 3DNow!@: and SSE prefetch instructions
22344 Improved AMD Athlon CPU with MMX, 3DNow!, enhanced 3DNow!@: and full SSE
22345 instruction set support.
22351 Processors based on the AMD K8 core with x86-64 instruction set support,
22352 including the AMD Opteron, Athlon 64, and Athlon 64 FX processors.
22353 (This supersets MMX, SSE, SSE2, 3DNow!, enhanced 3DNow!@: and 64-bit
22354 instruction set extensions.)
22357 @itemx opteron-sse3
22358 @itemx athlon64-sse3
22359 Improved versions of AMD K8 cores with SSE3 instruction set support.
22363 CPUs based on AMD Family 10h cores with x86-64 instruction set support. (This
22364 supersets MMX, SSE, SSE2, SSE3, SSE4A, 3DNow!, enhanced 3DNow!, ABM and 64-bit
22365 instruction set extensions.)
22368 CPUs based on AMD Family 15h cores with x86-64 instruction set support. (This
22369 supersets FMA4, AVX, XOP, LWP, AES, PCL_MUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A,
22370 SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.)
22372 AMD Family 15h core based CPUs with x86-64 instruction set support. (This
22373 supersets BMI, TBM, F16C, FMA, FMA4, AVX, XOP, LWP, AES, PCL_MUL, CX16, MMX,
22374 SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set
22377 AMD Family 15h core based CPUs with x86-64 instruction set support. (This
22378 supersets BMI, TBM, F16C, FMA, FMA4, FSGSBASE, AVX, XOP, LWP, AES,
22379 PCL_MUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and
22380 64-bit instruction set extensions.
22382 AMD Family 15h core based CPUs with x86-64 instruction set support. (This
22383 supersets BMI, BMI2, TBM, F16C, FMA, FMA4, FSGSBASE, AVX, AVX2, XOP, LWP,
22384 AES, PCL_MUL, CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1,
22385 SSE4.2, ABM and 64-bit instruction set extensions.
22388 CPUs based on AMD Family 14h cores with x86-64 instruction set support. (This
22389 supersets MMX, SSE, SSE2, SSE3, SSSE3, SSE4A, CX16, ABM and 64-bit
22390 instruction set extensions.)
22393 CPUs based on AMD Family 16h cores with x86-64 instruction set support. This
22394 includes MOVBE, F16C, BMI, AVX, PCL_MUL, AES, SSE4.2, SSE4.1, CX16, ABM,
22395 SSE4A, SSSE3, SSE3, SSE2, SSE, MMX and 64-bit instruction set extensions.
22398 IDT WinChip C6 CPU, dealt in same way as i486 with additional MMX instruction
22402 IDT WinChip 2 CPU, dealt in same way as i486 with additional MMX and 3DNow!@:
22403 instruction set support.
22406 VIA C3 CPU with MMX and 3DNow!@: instruction set support. (No scheduling is
22407 implemented for this chip.)
22410 VIA C3-2 (Nehemiah/C5XL) CPU with MMX and SSE instruction set support.
22412 implemented for this chip.)
22415 AMD Geode embedded processor with MMX and 3DNow!@: instruction set support.
22418 @item -mtune=@var{cpu-type}
22420 Tune to @var{cpu-type} everything applicable about the generated code, except
22421 for the ABI and the set of available instructions.
22422 While picking a specific @var{cpu-type} schedules things appropriately
22423 for that particular chip, the compiler does not generate any code that
22424 cannot run on the default machine type unless you use a
22425 @option{-march=@var{cpu-type}} option.
22426 For example, if GCC is configured for i686-pc-linux-gnu
22427 then @option{-mtune=pentium4} generates code that is tuned for Pentium 4
22428 but still runs on i686 machines.
22430 The choices for @var{cpu-type} are the same as for @option{-march}.
22431 In addition, @option{-mtune} supports 2 extra choices for @var{cpu-type}:
22435 Produce code optimized for the most common IA32/@/AMD64/@/EM64T processors.
22436 If you know the CPU on which your code will run, then you should use
22437 the corresponding @option{-mtune} or @option{-march} option instead of
22438 @option{-mtune=generic}. But, if you do not know exactly what CPU users
22439 of your application will have, then you should use this option.
22441 As new processors are deployed in the marketplace, the behavior of this
22442 option will change. Therefore, if you upgrade to a newer version of
22443 GCC, code generation controlled by this option will change to reflect
22445 that are most common at the time that version of GCC is released.
22447 There is no @option{-march=generic} option because @option{-march}
22448 indicates the instruction set the compiler can use, and there is no
22449 generic instruction set applicable to all processors. In contrast,
22450 @option{-mtune} indicates the processor (or, in this case, collection of
22451 processors) for which the code is optimized.
22454 Produce code optimized for the most current Intel processors, which are
22455 Haswell and Silvermont for this version of GCC. If you know the CPU
22456 on which your code will run, then you should use the corresponding
22457 @option{-mtune} or @option{-march} option instead of @option{-mtune=intel}.
22458 But, if you want your application performs better on both Haswell and
22459 Silvermont, then you should use this option.
22461 As new Intel processors are deployed in the marketplace, the behavior of
22462 this option will change. Therefore, if you upgrade to a newer version of
22463 GCC, code generation controlled by this option will change to reflect
22464 the most current Intel processors at the time that version of GCC is
22467 There is no @option{-march=intel} option because @option{-march} indicates
22468 the instruction set the compiler can use, and there is no common
22469 instruction set applicable to all processors. In contrast,
22470 @option{-mtune} indicates the processor (or, in this case, collection of
22471 processors) for which the code is optimized.
22474 @item -mcpu=@var{cpu-type}
22476 A deprecated synonym for @option{-mtune}.
22478 @item -mfpmath=@var{unit}
22480 Generate floating-point arithmetic for selected unit @var{unit}. The choices
22481 for @var{unit} are:
22485 Use the standard 387 floating-point coprocessor present on the majority of chips and
22486 emulated otherwise. Code compiled with this option runs almost everywhere.
22487 The temporary results are computed in 80-bit precision instead of the precision
22488 specified by the type, resulting in slightly different results compared to most
22489 of other chips. See @option{-ffloat-store} for more detailed description.
22491 This is the default choice for x86-32 targets.
22494 Use scalar floating-point instructions present in the SSE instruction set.
22495 This instruction set is supported by Pentium III and newer chips,
22496 and in the AMD line
22497 by Athlon-4, Athlon XP and Athlon MP chips. The earlier version of the SSE
22498 instruction set supports only single-precision arithmetic, thus the double and
22499 extended-precision arithmetic are still done using 387. A later version, present
22500 only in Pentium 4 and AMD x86-64 chips, supports double-precision
22503 For the x86-32 compiler, you must use @option{-march=@var{cpu-type}}, @option{-msse}
22504 or @option{-msse2} switches to enable SSE extensions and make this option
22505 effective. For the x86-64 compiler, these extensions are enabled by default.
22507 The resulting code should be considerably faster in the majority of cases and avoid
22508 the numerical instability problems of 387 code, but may break some existing
22509 code that expects temporaries to be 80 bits.
22511 This is the default choice for the x86-64 compiler.
22516 Attempt to utilize both instruction sets at once. This effectively doubles the
22517 amount of available registers, and on chips with separate execution units for
22518 387 and SSE the execution resources too. Use this option with care, as it is
22519 still experimental, because the GCC register allocator does not model separate
22520 functional units well, resulting in unstable performance.
22523 @item -masm=@var{dialect}
22524 @opindex masm=@var{dialect}
22525 Output assembly instructions using selected @var{dialect}. Also affects
22526 which dialect is used for basic @code{asm} (@pxref{Basic Asm}) and
22527 extended @code{asm} (@pxref{Extended Asm}). Supported choices (in dialect
22528 order) are @samp{att} or @samp{intel}. The default is @samp{att}. Darwin does
22529 not support @samp{intel}.
22532 @itemx -mno-ieee-fp
22534 @opindex mno-ieee-fp
22535 Control whether or not the compiler uses IEEE floating-point
22536 comparisons. These correctly handle the case where the result of a
22537 comparison is unordered.
22540 @opindex msoft-float
22541 Generate output containing library calls for floating point.
22543 @strong{Warning:} the requisite libraries are not part of GCC@.
22544 Normally the facilities of the machine's usual C compiler are used, but
22545 this can't be done directly in cross-compilation. You must make your
22546 own arrangements to provide suitable library functions for
22549 On machines where a function returns floating-point results in the 80387
22550 register stack, some floating-point opcodes may be emitted even if
22551 @option{-msoft-float} is used.
22553 @item -mno-fp-ret-in-387
22554 @opindex mno-fp-ret-in-387
22555 Do not use the FPU registers for return values of functions.
22557 The usual calling convention has functions return values of types
22558 @code{float} and @code{double} in an FPU register, even if there
22559 is no FPU@. The idea is that the operating system should emulate
22562 The option @option{-mno-fp-ret-in-387} causes such values to be returned
22563 in ordinary CPU registers instead.
22565 @item -mno-fancy-math-387
22566 @opindex mno-fancy-math-387
22567 Some 387 emulators do not support the @code{sin}, @code{cos} and
22568 @code{sqrt} instructions for the 387. Specify this option to avoid
22569 generating those instructions. This option is the default on FreeBSD,
22570 OpenBSD and NetBSD@. This option is overridden when @option{-march}
22571 indicates that the target CPU always has an FPU and so the
22572 instruction does not need emulation. These
22573 instructions are not generated unless you also use the
22574 @option{-funsafe-math-optimizations} switch.
22576 @item -malign-double
22577 @itemx -mno-align-double
22578 @opindex malign-double
22579 @opindex mno-align-double
22580 Control whether GCC aligns @code{double}, @code{long double}, and
22581 @code{long long} variables on a two-word boundary or a one-word
22582 boundary. Aligning @code{double} variables on a two-word boundary
22583 produces code that runs somewhat faster on a Pentium at the
22584 expense of more memory.
22586 On x86-64, @option{-malign-double} is enabled by default.
22588 @strong{Warning:} if you use the @option{-malign-double} switch,
22589 structures containing the above types are aligned differently than
22590 the published application binary interface specifications for the x86-32
22591 and are not binary compatible with structures in code compiled
22592 without that switch.
22594 @item -m96bit-long-double
22595 @itemx -m128bit-long-double
22596 @opindex m96bit-long-double
22597 @opindex m128bit-long-double
22598 These switches control the size of @code{long double} type. The x86-32
22599 application binary interface specifies the size to be 96 bits,
22600 so @option{-m96bit-long-double} is the default in 32-bit mode.
22602 Modern architectures (Pentium and newer) prefer @code{long double}
22603 to be aligned to an 8- or 16-byte boundary. In arrays or structures
22604 conforming to the ABI, this is not possible. So specifying
22605 @option{-m128bit-long-double} aligns @code{long double}
22606 to a 16-byte boundary by padding the @code{long double} with an additional
22609 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
22610 its ABI specifies that @code{long double} is aligned on 16-byte boundary.
22612 Notice that neither of these options enable any extra precision over the x87
22613 standard of 80 bits for a @code{long double}.
22615 @strong{Warning:} if you override the default value for your target ABI, this
22616 changes the size of
22617 structures and arrays containing @code{long double} variables,
22618 as well as modifying the function calling convention for functions taking
22619 @code{long double}. Hence they are not binary-compatible
22620 with code compiled without that switch.
22622 @item -mlong-double-64
22623 @itemx -mlong-double-80
22624 @itemx -mlong-double-128
22625 @opindex mlong-double-64
22626 @opindex mlong-double-80
22627 @opindex mlong-double-128
22628 These switches control the size of @code{long double} type. A size
22629 of 64 bits makes the @code{long double} type equivalent to the @code{double}
22630 type. This is the default for 32-bit Bionic C library. A size
22631 of 128 bits makes the @code{long double} type equivalent to the
22632 @code{__float128} type. This is the default for 64-bit Bionic C library.
22634 @strong{Warning:} if you override the default value for your target ABI, this
22635 changes the size of
22636 structures and arrays containing @code{long double} variables,
22637 as well as modifying the function calling convention for functions taking
22638 @code{long double}. Hence they are not binary-compatible
22639 with code compiled without that switch.
22641 @item -malign-data=@var{type}
22642 @opindex malign-data
22643 Control how GCC aligns variables. Supported values for @var{type} are
22644 @samp{compat} uses increased alignment value compatible uses GCC 4.8
22645 and earlier, @samp{abi} uses alignment value as specified by the
22646 psABI, and @samp{cacheline} uses increased alignment value to match
22647 the cache line size. @samp{compat} is the default.
22649 @item -mlarge-data-threshold=@var{threshold}
22650 @opindex mlarge-data-threshold
22651 When @option{-mcmodel=medium} is specified, data objects larger than
22652 @var{threshold} are placed in the large data section. This value must be the
22653 same across all objects linked into the binary, and defaults to 65535.
22657 Use a different function-calling convention, in which functions that
22658 take a fixed number of arguments return with the @code{ret @var{num}}
22659 instruction, which pops their arguments while returning. This saves one
22660 instruction in the caller since there is no need to pop the arguments
22663 You can specify that an individual function is called with this calling
22664 sequence with the function attribute @code{stdcall}. You can also
22665 override the @option{-mrtd} option by using the function attribute
22666 @code{cdecl}. @xref{Function Attributes}.
22668 @strong{Warning:} this calling convention is incompatible with the one
22669 normally used on Unix, so you cannot use it if you need to call
22670 libraries compiled with the Unix compiler.
22672 Also, you must provide function prototypes for all functions that
22673 take variable numbers of arguments (including @code{printf});
22674 otherwise incorrect code is generated for calls to those
22677 In addition, seriously incorrect code results if you call a
22678 function with too many arguments. (Normally, extra arguments are
22679 harmlessly ignored.)
22681 @item -mregparm=@var{num}
22683 Control how many registers are used to pass integer arguments. By
22684 default, no registers are used to pass arguments, and at most 3
22685 registers can be used. You can control this behavior for a specific
22686 function by using the function attribute @code{regparm}.
22687 @xref{Function Attributes}.
22689 @strong{Warning:} if you use this switch, and
22690 @var{num} is nonzero, then you must build all modules with the same
22691 value, including any libraries. This includes the system libraries and
22695 @opindex msseregparm
22696 Use SSE register passing conventions for float and double arguments
22697 and return values. You can control this behavior for a specific
22698 function by using the function attribute @code{sseregparm}.
22699 @xref{Function Attributes}.
22701 @strong{Warning:} if you use this switch then you must build all
22702 modules with the same value, including any libraries. This includes
22703 the system libraries and startup modules.
22705 @item -mvect8-ret-in-mem
22706 @opindex mvect8-ret-in-mem
22707 Return 8-byte vectors in memory instead of MMX registers. This is the
22708 default on Solaris@tie{}8 and 9 and VxWorks to match the ABI of the Sun
22709 Studio compilers until version 12. Later compiler versions (starting
22710 with Studio 12 Update@tie{}1) follow the ABI used by other x86 targets, which
22711 is the default on Solaris@tie{}10 and later. @emph{Only} use this option if
22712 you need to remain compatible with existing code produced by those
22713 previous compiler versions or older versions of GCC@.
22722 Set 80387 floating-point precision to 32, 64 or 80 bits. When @option{-mpc32}
22723 is specified, the significands of results of floating-point operations are
22724 rounded to 24 bits (single precision); @option{-mpc64} rounds the
22725 significands of results of floating-point operations to 53 bits (double
22726 precision) and @option{-mpc80} rounds the significands of results of
22727 floating-point operations to 64 bits (extended double precision), which is
22728 the default. When this option is used, floating-point operations in higher
22729 precisions are not available to the programmer without setting the FPU
22730 control word explicitly.
22732 Setting the rounding of floating-point operations to less than the default
22733 80 bits can speed some programs by 2% or more. Note that some mathematical
22734 libraries assume that extended-precision (80-bit) floating-point operations
22735 are enabled by default; routines in such libraries could suffer significant
22736 loss of accuracy, typically through so-called ``catastrophic cancellation'',
22737 when this option is used to set the precision to less than extended precision.
22739 @item -mstackrealign
22740 @opindex mstackrealign
22741 Realign the stack at entry. On the x86, the @option{-mstackrealign}
22742 option generates an alternate prologue and epilogue that realigns the
22743 run-time stack if necessary. This supports mixing legacy codes that keep
22744 4-byte stack alignment with modern codes that keep 16-byte stack alignment for
22745 SSE compatibility. See also the attribute @code{force_align_arg_pointer},
22746 applicable to individual functions.
22748 @item -mpreferred-stack-boundary=@var{num}
22749 @opindex mpreferred-stack-boundary
22750 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
22751 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
22752 the default is 4 (16 bytes or 128 bits).
22754 @strong{Warning:} When generating code for the x86-64 architecture with
22755 SSE extensions disabled, @option{-mpreferred-stack-boundary=3} can be
22756 used to keep the stack boundary aligned to 8 byte boundary. Since
22757 x86-64 ABI require 16 byte stack alignment, this is ABI incompatible and
22758 intended to be used in controlled environment where stack space is
22759 important limitation. This option leads to wrong code when functions
22760 compiled with 16 byte stack alignment (such as functions from a standard
22761 library) are called with misaligned stack. In this case, SSE
22762 instructions may lead to misaligned memory access traps. In addition,
22763 variable arguments are handled incorrectly for 16 byte aligned
22764 objects (including x87 long double and __int128), leading to wrong
22765 results. You must build all modules with
22766 @option{-mpreferred-stack-boundary=3}, including any libraries. This
22767 includes the system libraries and startup modules.
22769 @item -mincoming-stack-boundary=@var{num}
22770 @opindex mincoming-stack-boundary
22771 Assume the incoming stack is aligned to a 2 raised to @var{num} byte
22772 boundary. If @option{-mincoming-stack-boundary} is not specified,
22773 the one specified by @option{-mpreferred-stack-boundary} is used.
22775 On Pentium and Pentium Pro, @code{double} and @code{long double} values
22776 should be aligned to an 8-byte boundary (see @option{-malign-double}) or
22777 suffer significant run time performance penalties. On Pentium III, the
22778 Streaming SIMD Extension (SSE) data type @code{__m128} may not work
22779 properly if it is not 16-byte aligned.
22781 To ensure proper alignment of this values on the stack, the stack boundary
22782 must be as aligned as that required by any value stored on the stack.
22783 Further, every function must be generated such that it keeps the stack
22784 aligned. Thus calling a function compiled with a higher preferred
22785 stack boundary from a function compiled with a lower preferred stack
22786 boundary most likely misaligns the stack. It is recommended that
22787 libraries that use callbacks always use the default setting.
22789 This extra alignment does consume extra stack space, and generally
22790 increases code size. Code that is sensitive to stack space usage, such
22791 as embedded systems and operating system kernels, may want to reduce the
22792 preferred alignment to @option{-mpreferred-stack-boundary=2}.
22838 @opindex mclfushopt
22856 @itemx -mprefetchwt1
22857 @opindex mprefetchwt1
22908 These switches enable the use of instructions in the MMX, SSE,
22909 SSE2, SSE3, SSSE3, SSE4.1, AVX, AVX2, AVX512F, AVX512PF, AVX512ER, AVX512CD,
22910 SHA, AES, PCLMUL, FSGSBASE, RDRND, F16C, FMA, SSE4A, FMA4, XOP, LWP, ABM,
22911 BMI, BMI2, FXSR, XSAVE, XSAVEOPT, LZCNT, RTM, MPX, MWAITX or 3DNow!@:
22912 extended instruction sets. Each has a corresponding @option{-mno-} option
22913 to disable use of these instructions.
22915 These extensions are also available as built-in functions: see
22916 @ref{x86 Built-in Functions}, for details of the functions enabled and
22917 disabled by these switches.
22919 To generate SSE/SSE2 instructions automatically from floating-point
22920 code (as opposed to 387 instructions), see @option{-mfpmath=sse}.
22922 GCC depresses SSEx instructions when @option{-mavx} is used. Instead, it
22923 generates new AVX instructions or AVX equivalence for all SSEx instructions
22926 These options enable GCC to use these extended instructions in
22927 generated code, even without @option{-mfpmath=sse}. Applications that
22928 perform run-time CPU detection must compile separate files for each
22929 supported architecture, using the appropriate flags. In particular,
22930 the file containing the CPU detection code should be compiled without
22933 @item -mdump-tune-features
22934 @opindex mdump-tune-features
22935 This option instructs GCC to dump the names of the x86 performance
22936 tuning features and default settings. The names can be used in
22937 @option{-mtune-ctrl=@var{feature-list}}.
22939 @item -mtune-ctrl=@var{feature-list}
22940 @opindex mtune-ctrl=@var{feature-list}
22941 This option is used to do fine grain control of x86 code generation features.
22942 @var{feature-list} is a comma separated list of @var{feature} names. See also
22943 @option{-mdump-tune-features}. When specified, the @var{feature} is turned
22944 on if it is not preceded with @samp{^}, otherwise, it is turned off.
22945 @option{-mtune-ctrl=@var{feature-list}} is intended to be used by GCC
22946 developers. Using it may lead to code paths not covered by testing and can
22947 potentially result in compiler ICEs or runtime errors.
22950 @opindex mno-default
22951 This option instructs GCC to turn off all tunable features. See also
22952 @option{-mtune-ctrl=@var{feature-list}} and @option{-mdump-tune-features}.
22956 This option instructs GCC to emit a @code{cld} instruction in the prologue
22957 of functions that use string instructions. String instructions depend on
22958 the DF flag to select between autoincrement or autodecrement mode. While the
22959 ABI specifies the DF flag to be cleared on function entry, some operating
22960 systems violate this specification by not clearing the DF flag in their
22961 exception dispatchers. The exception handler can be invoked with the DF flag
22962 set, which leads to wrong direction mode when string instructions are used.
22963 This option can be enabled by default on 32-bit x86 targets by configuring
22964 GCC with the @option{--enable-cld} configure option. Generation of @code{cld}
22965 instructions can be suppressed with the @option{-mno-cld} compiler option
22969 @opindex mvzeroupper
22970 This option instructs GCC to emit a @code{vzeroupper} instruction
22971 before a transfer of control flow out of the function to minimize
22972 the AVX to SSE transition penalty as well as remove unnecessary @code{zeroupper}
22975 @item -mprefer-avx128
22976 @opindex mprefer-avx128
22977 This option instructs GCC to use 128-bit AVX instructions instead of
22978 256-bit AVX instructions in the auto-vectorizer.
22982 This option enables GCC to generate @code{CMPXCHG16B} instructions.
22983 @code{CMPXCHG16B} allows for atomic operations on 128-bit double quadword
22984 (or oword) data types.
22985 This is useful for high-resolution counters that can be updated
22986 by multiple processors (or cores). This instruction is generated as part of
22987 atomic built-in functions: see @ref{__sync Builtins} or
22988 @ref{__atomic Builtins} for details.
22992 This option enables generation of @code{SAHF} instructions in 64-bit code.
22993 Early Intel Pentium 4 CPUs with Intel 64 support,
22994 prior to the introduction of Pentium 4 G1 step in December 2005,
22995 lacked the @code{LAHF} and @code{SAHF} instructions
22996 which are supported by AMD64.
22997 These are load and store instructions, respectively, for certain status flags.
22998 In 64-bit mode, the @code{SAHF} instruction is used to optimize @code{fmod},
22999 @code{drem}, and @code{remainder} built-in functions;
23000 see @ref{Other Builtins} for details.
23004 This option enables use of the @code{movbe} instruction to implement
23005 @code{__builtin_bswap32} and @code{__builtin_bswap64}.
23009 This option enables built-in functions @code{__builtin_ia32_crc32qi},
23010 @code{__builtin_ia32_crc32hi}, @code{__builtin_ia32_crc32si} and
23011 @code{__builtin_ia32_crc32di} to generate the @code{crc32} machine instruction.
23015 This option enables use of @code{RCPSS} and @code{RSQRTSS} instructions
23016 (and their vectorized variants @code{RCPPS} and @code{RSQRTPS})
23017 with an additional Newton-Raphson step
23018 to increase precision instead of @code{DIVSS} and @code{SQRTSS}
23019 (and their vectorized
23020 variants) for single-precision floating-point arguments. These instructions
23021 are generated only when @option{-funsafe-math-optimizations} is enabled
23022 together with @option{-finite-math-only} and @option{-fno-trapping-math}.
23023 Note that while the throughput of the sequence is higher than the throughput
23024 of the non-reciprocal instruction, the precision of the sequence can be
23025 decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994).
23027 Note that GCC implements @code{1.0f/sqrtf(@var{x})} in terms of @code{RSQRTSS}
23028 (or @code{RSQRTPS}) already with @option{-ffast-math} (or the above option
23029 combination), and doesn't need @option{-mrecip}.
23031 Also note that GCC emits the above sequence with additional Newton-Raphson step
23032 for vectorized single-float division and vectorized @code{sqrtf(@var{x})}
23033 already with @option{-ffast-math} (or the above option combination), and
23034 doesn't need @option{-mrecip}.
23036 @item -mrecip=@var{opt}
23037 @opindex mrecip=opt
23038 This option controls which reciprocal estimate instructions
23039 may be used. @var{opt} is a comma-separated list of options, which may
23040 be preceded by a @samp{!} to invert the option:
23044 Enable all estimate instructions.
23047 Enable the default instructions, equivalent to @option{-mrecip}.
23050 Disable all estimate instructions, equivalent to @option{-mno-recip}.
23053 Enable the approximation for scalar division.
23056 Enable the approximation for vectorized division.
23059 Enable the approximation for scalar square root.
23062 Enable the approximation for vectorized square root.
23065 So, for example, @option{-mrecip=all,!sqrt} enables
23066 all of the reciprocal approximations, except for square root.
23068 @item -mveclibabi=@var{type}
23069 @opindex mveclibabi
23070 Specifies the ABI type to use for vectorizing intrinsics using an
23071 external library. Supported values for @var{type} are @samp{svml}
23072 for the Intel short
23073 vector math library and @samp{acml} for the AMD math core library.
23074 To use this option, both @option{-ftree-vectorize} and
23075 @option{-funsafe-math-optimizations} have to be enabled, and an SVML or ACML
23076 ABI-compatible library must be specified at link time.
23078 GCC currently emits calls to @code{vmldExp2},
23079 @code{vmldLn2}, @code{vmldLog102}, @code{vmldLog102}, @code{vmldPow2},
23080 @code{vmldTanh2}, @code{vmldTan2}, @code{vmldAtan2}, @code{vmldAtanh2},
23081 @code{vmldCbrt2}, @code{vmldSinh2}, @code{vmldSin2}, @code{vmldAsinh2},
23082 @code{vmldAsin2}, @code{vmldCosh2}, @code{vmldCos2}, @code{vmldAcosh2},
23083 @code{vmldAcos2}, @code{vmlsExp4}, @code{vmlsLn4}, @code{vmlsLog104},
23084 @code{vmlsLog104}, @code{vmlsPow4}, @code{vmlsTanh4}, @code{vmlsTan4},
23085 @code{vmlsAtan4}, @code{vmlsAtanh4}, @code{vmlsCbrt4}, @code{vmlsSinh4},
23086 @code{vmlsSin4}, @code{vmlsAsinh4}, @code{vmlsAsin4}, @code{vmlsCosh4},
23087 @code{vmlsCos4}, @code{vmlsAcosh4} and @code{vmlsAcos4} for corresponding
23088 function type when @option{-mveclibabi=svml} is used, and @code{__vrd2_sin},
23089 @code{__vrd2_cos}, @code{__vrd2_exp}, @code{__vrd2_log}, @code{__vrd2_log2},
23090 @code{__vrd2_log10}, @code{__vrs4_sinf}, @code{__vrs4_cosf},
23091 @code{__vrs4_expf}, @code{__vrs4_logf}, @code{__vrs4_log2f},
23092 @code{__vrs4_log10f} and @code{__vrs4_powf} for the corresponding function type
23093 when @option{-mveclibabi=acml} is used.
23095 @item -mabi=@var{name}
23097 Generate code for the specified calling convention. Permissible values
23098 are @samp{sysv} for the ABI used on GNU/Linux and other systems, and
23099 @samp{ms} for the Microsoft ABI. The default is to use the Microsoft
23100 ABI when targeting Microsoft Windows and the SysV ABI on all other systems.
23101 You can control this behavior for specific functions by
23102 using the function attributes @code{ms_abi} and @code{sysv_abi}.
23103 @xref{Function Attributes}.
23105 @item -mtls-dialect=@var{type}
23106 @opindex mtls-dialect
23107 Generate code to access thread-local storage using the @samp{gnu} or
23108 @samp{gnu2} conventions. @samp{gnu} is the conservative default;
23109 @samp{gnu2} is more efficient, but it may add compile- and run-time
23110 requirements that cannot be satisfied on all systems.
23113 @itemx -mno-push-args
23114 @opindex mpush-args
23115 @opindex mno-push-args
23116 Use PUSH operations to store outgoing parameters. This method is shorter
23117 and usually equally fast as method using SUB/MOV operations and is enabled
23118 by default. In some cases disabling it may improve performance because of
23119 improved scheduling and reduced dependencies.
23121 @item -maccumulate-outgoing-args
23122 @opindex maccumulate-outgoing-args
23123 If enabled, the maximum amount of space required for outgoing arguments is
23124 computed in the function prologue. This is faster on most modern CPUs
23125 because of reduced dependencies, improved scheduling and reduced stack usage
23126 when the preferred stack boundary is not equal to 2. The drawback is a notable
23127 increase in code size. This switch implies @option{-mno-push-args}.
23131 Support thread-safe exception handling on MinGW. Programs that rely
23132 on thread-safe exception handling must compile and link all code with the
23133 @option{-mthreads} option. When compiling, @option{-mthreads} defines
23134 @option{-D_MT}; when linking, it links in a special thread helper library
23135 @option{-lmingwthrd} which cleans up per-thread exception-handling data.
23137 @item -mno-align-stringops
23138 @opindex mno-align-stringops
23139 Do not align the destination of inlined string operations. This switch reduces
23140 code size and improves performance in case the destination is already aligned,
23141 but GCC doesn't know about it.
23143 @item -minline-all-stringops
23144 @opindex minline-all-stringops
23145 By default GCC inlines string operations only when the destination is
23146 known to be aligned to least a 4-byte boundary.
23147 This enables more inlining and increases code
23148 size, but may improve performance of code that depends on fast
23149 @code{memcpy}, @code{strlen},
23150 and @code{memset} for short lengths.
23152 @item -minline-stringops-dynamically
23153 @opindex minline-stringops-dynamically
23154 For string operations of unknown size, use run-time checks with
23155 inline code for small blocks and a library call for large blocks.
23157 @item -mstringop-strategy=@var{alg}
23158 @opindex mstringop-strategy=@var{alg}
23159 Override the internal decision heuristic for the particular algorithm to use
23160 for inlining string operations. The allowed values for @var{alg} are:
23166 Expand using i386 @code{rep} prefix of the specified size.
23170 @itemx unrolled_loop
23171 Expand into an inline loop.
23174 Always use a library call.
23177 @item -mmemcpy-strategy=@var{strategy}
23178 @opindex mmemcpy-strategy=@var{strategy}
23179 Override the internal decision heuristic to decide if @code{__builtin_memcpy}
23180 should be inlined and what inline algorithm to use when the expected size
23181 of the copy operation is known. @var{strategy}
23182 is a comma-separated list of @var{alg}:@var{max_size}:@var{dest_align} triplets.
23183 @var{alg} is specified in @option{-mstringop-strategy}, @var{max_size} specifies
23184 the max byte size with which inline algorithm @var{alg} is allowed. For the last
23185 triplet, the @var{max_size} must be @code{-1}. The @var{max_size} of the triplets
23186 in the list must be specified in increasing order. The minimal byte size for
23187 @var{alg} is @code{0} for the first triplet and @code{@var{max_size} + 1} of the
23190 @item -mmemset-strategy=@var{strategy}
23191 @opindex mmemset-strategy=@var{strategy}
23192 The option is similar to @option{-mmemcpy-strategy=} except that it is to control
23193 @code{__builtin_memset} expansion.
23195 @item -momit-leaf-frame-pointer
23196 @opindex momit-leaf-frame-pointer
23197 Don't keep the frame pointer in a register for leaf functions. This
23198 avoids the instructions to save, set up, and restore frame pointers and
23199 makes an extra register available in leaf functions. The option
23200 @option{-fomit-leaf-frame-pointer} removes the frame pointer for leaf functions,
23201 which might make debugging harder.
23203 @item -mtls-direct-seg-refs
23204 @itemx -mno-tls-direct-seg-refs
23205 @opindex mtls-direct-seg-refs
23206 Controls whether TLS variables may be accessed with offsets from the
23207 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
23208 or whether the thread base pointer must be added. Whether or not this
23209 is valid depends on the operating system, and whether it maps the
23210 segment to cover the entire TLS area.
23212 For systems that use the GNU C Library, the default is on.
23215 @itemx -mno-sse2avx
23217 Specify that the assembler should encode SSE instructions with VEX
23218 prefix. The option @option{-mavx} turns this on by default.
23223 If profiling is active (@option{-pg}), put the profiling
23224 counter call before the prologue.
23225 Note: On x86 architectures the attribute @code{ms_hook_prologue}
23226 isn't possible at the moment for @option{-mfentry} and @option{-pg}.
23228 @item -mrecord-mcount
23229 @itemx -mno-record-mcount
23230 @opindex mrecord-mcount
23231 If profiling is active (@option{-pg}), generate a __mcount_loc section
23232 that contains pointers to each profiling call. This is useful for
23233 automatically patching and out calls.
23236 @itemx -mno-nop-mcount
23237 @opindex mnop-mcount
23238 If profiling is active (@option{-pg}), generate the calls to
23239 the profiling functions as nops. This is useful when they
23240 should be patched in later dynamically. This is likely only
23241 useful together with @option{-mrecord-mcount}.
23243 @item -mskip-rax-setup
23244 @itemx -mno-skip-rax-setup
23245 @opindex mskip-rax-setup
23246 When generating code for the x86-64 architecture with SSE extensions
23247 disabled, @option{-skip-rax-setup} can be used to skip setting up RAX
23248 register when there are no variable arguments passed in vector registers.
23250 @strong{Warning:} Since RAX register is used to avoid unnecessarily
23251 saving vector registers on stack when passing variable arguments, the
23252 impacts of this option are callees may waste some stack space,
23253 misbehave or jump to a random location. GCC 4.4 or newer don't have
23254 those issues, regardless the RAX register value.
23257 @itemx -mno-8bit-idiv
23258 @opindex m8bit-idiv
23259 On some processors, like Intel Atom, 8-bit unsigned integer divide is
23260 much faster than 32-bit/64-bit integer divide. This option generates a
23261 run-time check. If both dividend and divisor are within range of 0
23262 to 255, 8-bit unsigned integer divide is used instead of
23263 32-bit/64-bit integer divide.
23265 @item -mavx256-split-unaligned-load
23266 @itemx -mavx256-split-unaligned-store
23267 @opindex mavx256-split-unaligned-load
23268 @opindex mavx256-split-unaligned-store
23269 Split 32-byte AVX unaligned load and store.
23271 @item -mstack-protector-guard=@var{guard}
23272 @opindex mstack-protector-guard=@var{guard}
23273 Generate stack protection code using canary at @var{guard}. Supported
23274 locations are @samp{global} for global canary or @samp{tls} for per-thread
23275 canary in the TLS block (the default). This option has effect only when
23276 @option{-fstack-protector} or @option{-fstack-protector-all} is specified.
23280 These @samp{-m} switches are supported in addition to the above
23281 on x86-64 processors in 64-bit environments.
23292 Generate code for a 16-bit, 32-bit or 64-bit environment.
23293 The @option{-m32} option sets @code{int}, @code{long}, and pointer types
23295 generates code that runs on any i386 system.
23297 The @option{-m64} option sets @code{int} to 32 bits and @code{long} and pointer
23298 types to 64 bits, and generates code for the x86-64 architecture.
23299 For Darwin only the @option{-m64} option also turns off the @option{-fno-pic}
23300 and @option{-mdynamic-no-pic} options.
23302 The @option{-mx32} option sets @code{int}, @code{long}, and pointer types
23304 generates code for the x86-64 architecture.
23306 The @option{-m16} option is the same as @option{-m32}, except for that
23307 it outputs the @code{.code16gcc} assembly directive at the beginning of
23308 the assembly output so that the binary can run in 16-bit mode.
23310 @item -mno-red-zone
23311 @opindex mno-red-zone
23312 Do not use a so-called ``red zone'' for x86-64 code. The red zone is mandated
23313 by the x86-64 ABI; it is a 128-byte area beyond the location of the
23314 stack pointer that is not modified by signal or interrupt handlers
23315 and therefore can be used for temporary data without adjusting the stack
23316 pointer. The flag @option{-mno-red-zone} disables this red zone.
23318 @item -mcmodel=small
23319 @opindex mcmodel=small
23320 Generate code for the small code model: the program and its symbols must
23321 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
23322 Programs can be statically or dynamically linked. This is the default
23325 @item -mcmodel=kernel
23326 @opindex mcmodel=kernel
23327 Generate code for the kernel code model. The kernel runs in the
23328 negative 2 GB of the address space.
23329 This model has to be used for Linux kernel code.
23331 @item -mcmodel=medium
23332 @opindex mcmodel=medium
23333 Generate code for the medium model: the program is linked in the lower 2
23334 GB of the address space. Small symbols are also placed there. Symbols
23335 with sizes larger than @option{-mlarge-data-threshold} are put into
23336 large data or BSS sections and can be located above 2GB. Programs can
23337 be statically or dynamically linked.
23339 @item -mcmodel=large
23340 @opindex mcmodel=large
23341 Generate code for the large model. This model makes no assumptions
23342 about addresses and sizes of sections.
23344 @item -maddress-mode=long
23345 @opindex maddress-mode=long
23346 Generate code for long address mode. This is only supported for 64-bit
23347 and x32 environments. It is the default address mode for 64-bit
23350 @item -maddress-mode=short
23351 @opindex maddress-mode=short
23352 Generate code for short address mode. This is only supported for 32-bit
23353 and x32 environments. It is the default address mode for 32-bit and
23357 @node x86 Windows Options
23358 @subsection x86 Windows Options
23359 @cindex x86 Windows Options
23360 @cindex Windows Options for x86
23362 These additional options are available for Microsoft Windows targets:
23368 specifies that a console application is to be generated, by
23369 instructing the linker to set the PE header subsystem type
23370 required for console applications.
23371 This option is available for Cygwin and MinGW targets and is
23372 enabled by default on those targets.
23376 This option is available for Cygwin and MinGW targets. It
23377 specifies that a DLL---a dynamic link library---is to be
23378 generated, enabling the selection of the required runtime
23379 startup object and entry point.
23381 @item -mnop-fun-dllimport
23382 @opindex mnop-fun-dllimport
23383 This option is available for Cygwin and MinGW targets. It
23384 specifies that the @code{dllimport} attribute should be ignored.
23388 This option is available for MinGW targets. It specifies
23389 that MinGW-specific thread support is to be used.
23393 This option is available for MinGW-w64 targets. It causes
23394 the @code{UNICODE} preprocessor macro to be predefined, and
23395 chooses Unicode-capable runtime startup code.
23399 This option is available for Cygwin and MinGW targets. It
23400 specifies that the typical Microsoft Windows predefined macros are to
23401 be set in the pre-processor, but does not influence the choice
23402 of runtime library/startup code.
23406 This option is available for Cygwin and MinGW targets. It
23407 specifies that a GUI application is to be generated by
23408 instructing the linker to set the PE header subsystem type
23411 @item -fno-set-stack-executable
23412 @opindex fno-set-stack-executable
23413 This option is available for MinGW targets. It specifies that
23414 the executable flag for the stack used by nested functions isn't
23415 set. This is necessary for binaries running in kernel mode of
23416 Microsoft Windows, as there the User32 API, which is used to set executable
23417 privileges, isn't available.
23419 @item -fwritable-relocated-rdata
23420 @opindex fno-writable-relocated-rdata
23421 This option is available for MinGW and Cygwin targets. It specifies
23422 that relocated-data in read-only section is put into .data
23423 section. This is a necessary for older runtimes not supporting
23424 modification of .rdata sections for pseudo-relocation.
23426 @item -mpe-aligned-commons
23427 @opindex mpe-aligned-commons
23428 This option is available for Cygwin and MinGW targets. It
23429 specifies that the GNU extension to the PE file format that
23430 permits the correct alignment of COMMON variables should be
23431 used when generating code. It is enabled by default if
23432 GCC detects that the target assembler found during configuration
23433 supports the feature.
23436 See also under @ref{x86 Options} for standard options.
23438 @node Xstormy16 Options
23439 @subsection Xstormy16 Options
23440 @cindex Xstormy16 Options
23442 These options are defined for Xstormy16:
23447 Choose startup files and linker script suitable for the simulator.
23450 @node Xtensa Options
23451 @subsection Xtensa Options
23452 @cindex Xtensa Options
23454 These options are supported for Xtensa targets:
23458 @itemx -mno-const16
23460 @opindex mno-const16
23461 Enable or disable use of @code{CONST16} instructions for loading
23462 constant values. The @code{CONST16} instruction is currently not a
23463 standard option from Tensilica. When enabled, @code{CONST16}
23464 instructions are always used in place of the standard @code{L32R}
23465 instructions. The use of @code{CONST16} is enabled by default only if
23466 the @code{L32R} instruction is not available.
23469 @itemx -mno-fused-madd
23470 @opindex mfused-madd
23471 @opindex mno-fused-madd
23472 Enable or disable use of fused multiply/add and multiply/subtract
23473 instructions in the floating-point option. This has no effect if the
23474 floating-point option is not also enabled. Disabling fused multiply/add
23475 and multiply/subtract instructions forces the compiler to use separate
23476 instructions for the multiply and add/subtract operations. This may be
23477 desirable in some cases where strict IEEE 754-compliant results are
23478 required: the fused multiply add/subtract instructions do not round the
23479 intermediate result, thereby producing results with @emph{more} bits of
23480 precision than specified by the IEEE standard. Disabling fused multiply
23481 add/subtract instructions also ensures that the program output is not
23482 sensitive to the compiler's ability to combine multiply and add/subtract
23485 @item -mserialize-volatile
23486 @itemx -mno-serialize-volatile
23487 @opindex mserialize-volatile
23488 @opindex mno-serialize-volatile
23489 When this option is enabled, GCC inserts @code{MEMW} instructions before
23490 @code{volatile} memory references to guarantee sequential consistency.
23491 The default is @option{-mserialize-volatile}. Use
23492 @option{-mno-serialize-volatile} to omit the @code{MEMW} instructions.
23494 @item -mforce-no-pic
23495 @opindex mforce-no-pic
23496 For targets, like GNU/Linux, where all user-mode Xtensa code must be
23497 position-independent code (PIC), this option disables PIC for compiling
23500 @item -mtext-section-literals
23501 @itemx -mno-text-section-literals
23502 @opindex mtext-section-literals
23503 @opindex mno-text-section-literals
23504 These options control the treatment of literal pools. The default is
23505 @option{-mno-text-section-literals}, which places literals in a separate
23506 section in the output file. This allows the literal pool to be placed
23507 in a data RAM/ROM, and it also allows the linker to combine literal
23508 pools from separate object files to remove redundant literals and
23509 improve code size. With @option{-mtext-section-literals}, the literals
23510 are interspersed in the text section in order to keep them as close as
23511 possible to their references. This may be necessary for large assembly
23514 @item -mtarget-align
23515 @itemx -mno-target-align
23516 @opindex mtarget-align
23517 @opindex mno-target-align
23518 When this option is enabled, GCC instructs the assembler to
23519 automatically align instructions to reduce branch penalties at the
23520 expense of some code density. The assembler attempts to widen density
23521 instructions to align branch targets and the instructions following call
23522 instructions. If there are not enough preceding safe density
23523 instructions to align a target, no widening is performed. The
23524 default is @option{-mtarget-align}. These options do not affect the
23525 treatment of auto-aligned instructions like @code{LOOP}, which the
23526 assembler always aligns, either by widening density instructions or
23527 by inserting NOP instructions.
23530 @itemx -mno-longcalls
23531 @opindex mlongcalls
23532 @opindex mno-longcalls
23533 When this option is enabled, GCC instructs the assembler to translate
23534 direct calls to indirect calls unless it can determine that the target
23535 of a direct call is in the range allowed by the call instruction. This
23536 translation typically occurs for calls to functions in other source
23537 files. Specifically, the assembler translates a direct @code{CALL}
23538 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
23539 The default is @option{-mno-longcalls}. This option should be used in
23540 programs where the call target can potentially be out of range. This
23541 option is implemented in the assembler, not the compiler, so the
23542 assembly code generated by GCC still shows direct call
23543 instructions---look at the disassembled object code to see the actual
23544 instructions. Note that the assembler uses an indirect call for
23545 every cross-file call, not just those that really are out of range.
23548 @node zSeries Options
23549 @subsection zSeries Options
23550 @cindex zSeries options
23552 These are listed under @xref{S/390 and zSeries Options}.
23554 @node Code Gen Options
23555 @section Options for Code Generation Conventions
23556 @cindex code generation conventions
23557 @cindex options, code generation
23558 @cindex run-time options
23560 These machine-independent options control the interface conventions
23561 used in code generation.
23563 Most of them have both positive and negative forms; the negative form
23564 of @option{-ffoo} is @option{-fno-foo}. In the table below, only
23565 one of the forms is listed---the one that is not the default. You
23566 can figure out the other form by either removing @samp{no-} or adding
23570 @item -fbounds-check
23571 @opindex fbounds-check
23572 For front ends that support it, generate additional code to check that
23573 indices used to access arrays are within the declared range. This is
23574 currently only supported by the Java and Fortran front ends, where
23575 this option defaults to true and false respectively.
23577 @item -fstack-reuse=@var{reuse-level}
23578 @opindex fstack_reuse
23579 This option controls stack space reuse for user declared local/auto variables
23580 and compiler generated temporaries. @var{reuse_level} can be @samp{all},
23581 @samp{named_vars}, or @samp{none}. @samp{all} enables stack reuse for all
23582 local variables and temporaries, @samp{named_vars} enables the reuse only for
23583 user defined local variables with names, and @samp{none} disables stack reuse
23584 completely. The default value is @samp{all}. The option is needed when the
23585 program extends the lifetime of a scoped local variable or a compiler generated
23586 temporary beyond the end point defined by the language. When a lifetime of
23587 a variable ends, and if the variable lives in memory, the optimizing compiler
23588 has the freedom to reuse its stack space with other temporaries or scoped
23589 local variables whose live range does not overlap with it. Legacy code extending
23590 local lifetime is likely to break with the stack reuse optimization.
23609 if (*p == 10) // out of scope use of local1
23620 A(int k) : i(k), j(k) @{ @}
23627 void foo(const A& ar)
23634 foo(A(10)); // temp object's lifetime ends when foo returns
23640 ap->i+= 10; // ap references out of scope temp whose space
23641 // is reused with a. What is the value of ap->i?
23646 The lifetime of a compiler generated temporary is well defined by the C++
23647 standard. When a lifetime of a temporary ends, and if the temporary lives
23648 in memory, the optimizing compiler has the freedom to reuse its stack
23649 space with other temporaries or scoped local variables whose live range
23650 does not overlap with it. However some of the legacy code relies on
23651 the behavior of older compilers in which temporaries' stack space is
23652 not reused, the aggressive stack reuse can lead to runtime errors. This
23653 option is used to control the temporary stack reuse optimization.
23657 This option generates traps for signed overflow on addition, subtraction,
23658 multiplication operations.
23662 This option instructs the compiler to assume that signed arithmetic
23663 overflow of addition, subtraction and multiplication wraps around
23664 using twos-complement representation. This flag enables some optimizations
23665 and disables others. This option is enabled by default for the Java
23666 front end, as required by the Java language specification.
23669 @opindex fexceptions
23670 Enable exception handling. Generates extra code needed to propagate
23671 exceptions. For some targets, this implies GCC generates frame
23672 unwind information for all functions, which can produce significant data
23673 size overhead, although it does not affect execution. If you do not
23674 specify this option, GCC enables it by default for languages like
23675 C++ that normally require exception handling, and disables it for
23676 languages like C that do not normally require it. However, you may need
23677 to enable this option when compiling C code that needs to interoperate
23678 properly with exception handlers written in C++. You may also wish to
23679 disable this option if you are compiling older C++ programs that don't
23680 use exception handling.
23682 @item -fnon-call-exceptions
23683 @opindex fnon-call-exceptions
23684 Generate code that allows trapping instructions to throw exceptions.
23685 Note that this requires platform-specific runtime support that does
23686 not exist everywhere. Moreover, it only allows @emph{trapping}
23687 instructions to throw exceptions, i.e.@: memory references or floating-point
23688 instructions. It does not allow exceptions to be thrown from
23689 arbitrary signal handlers such as @code{SIGALRM}.
23691 @item -fdelete-dead-exceptions
23692 @opindex fdelete-dead-exceptions
23693 Consider that instructions that may throw exceptions but don't otherwise
23694 contribute to the execution of the program can be optimized away.
23695 This option is enabled by default for the Ada front end, as permitted by
23696 the Ada language specification.
23697 Optimization passes that cause dead exceptions to be removed are enabled independently at different optimization levels.
23699 @item -funwind-tables
23700 @opindex funwind-tables
23701 Similar to @option{-fexceptions}, except that it just generates any needed
23702 static data, but does not affect the generated code in any other way.
23703 You normally do not need to enable this option; instead, a language processor
23704 that needs this handling enables it on your behalf.
23706 @item -fasynchronous-unwind-tables
23707 @opindex fasynchronous-unwind-tables
23708 Generate unwind table in DWARF 2 format, if supported by target machine. The
23709 table is exact at each instruction boundary, so it can be used for stack
23710 unwinding from asynchronous events (such as debugger or garbage collector).
23712 @item -fno-gnu-unique
23713 @opindex fno-gnu-unique
23714 On systems with recent GNU assembler and C library, the C++ compiler
23715 uses the @code{STB_GNU_UNIQUE} binding to make sure that definitions
23716 of template static data members and static local variables in inline
23717 functions are unique even in the presence of @code{RTLD_LOCAL}; this
23718 is necessary to avoid problems with a library used by two different
23719 @code{RTLD_LOCAL} plugins depending on a definition in one of them and
23720 therefore disagreeing with the other one about the binding of the
23721 symbol. But this causes @code{dlclose} to be ignored for affected
23722 DSOs; if your program relies on reinitialization of a DSO via
23723 @code{dlclose} and @code{dlopen}, you can use
23724 @option{-fno-gnu-unique}.
23726 @item -fpcc-struct-return
23727 @opindex fpcc-struct-return
23728 Return ``short'' @code{struct} and @code{union} values in memory like
23729 longer ones, rather than in registers. This convention is less
23730 efficient, but it has the advantage of allowing intercallability between
23731 GCC-compiled files and files compiled with other compilers, particularly
23732 the Portable C Compiler (pcc).
23734 The precise convention for returning structures in memory depends
23735 on the target configuration macros.
23737 Short structures and unions are those whose size and alignment match
23738 that of some integer type.
23740 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
23741 switch is not binary compatible with code compiled with the
23742 @option{-freg-struct-return} switch.
23743 Use it to conform to a non-default application binary interface.
23745 @item -freg-struct-return
23746 @opindex freg-struct-return
23747 Return @code{struct} and @code{union} values in registers when possible.
23748 This is more efficient for small structures than
23749 @option{-fpcc-struct-return}.
23751 If you specify neither @option{-fpcc-struct-return} nor
23752 @option{-freg-struct-return}, GCC defaults to whichever convention is
23753 standard for the target. If there is no standard convention, GCC
23754 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
23755 the principal compiler. In those cases, we can choose the standard, and
23756 we chose the more efficient register return alternative.
23758 @strong{Warning:} code compiled with the @option{-freg-struct-return}
23759 switch is not binary compatible with code compiled with the
23760 @option{-fpcc-struct-return} switch.
23761 Use it to conform to a non-default application binary interface.
23763 @item -fshort-enums
23764 @opindex fshort-enums
23765 Allocate to an @code{enum} type only as many bytes as it needs for the
23766 declared range of possible values. Specifically, the @code{enum} type
23767 is equivalent to the smallest integer type that has enough room.
23769 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
23770 code that is not binary compatible with code generated without that switch.
23771 Use it to conform to a non-default application binary interface.
23773 @item -fshort-double
23774 @opindex fshort-double
23775 Use the same size for @code{double} as for @code{float}.
23777 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
23778 code that is not binary compatible with code generated without that switch.
23779 Use it to conform to a non-default application binary interface.
23781 @item -fshort-wchar
23782 @opindex fshort-wchar
23783 Override the underlying type for @code{wchar_t} to be @code{short
23784 unsigned int} instead of the default for the target. This option is
23785 useful for building programs to run under WINE@.
23787 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
23788 code that is not binary compatible with code generated without that switch.
23789 Use it to conform to a non-default application binary interface.
23792 @opindex fno-common
23793 In C code, controls the placement of uninitialized global variables.
23794 Unix C compilers have traditionally permitted multiple definitions of
23795 such variables in different compilation units by placing the variables
23797 This is the behavior specified by @option{-fcommon}, and is the default
23798 for GCC on most targets.
23799 On the other hand, this behavior is not required by ISO C, and on some
23800 targets may carry a speed or code size penalty on variable references.
23801 The @option{-fno-common} option specifies that the compiler should place
23802 uninitialized global variables in the data section of the object file,
23803 rather than generating them as common blocks.
23804 This has the effect that if the same variable is declared
23805 (without @code{extern}) in two different compilations,
23806 you get a multiple-definition error when you link them.
23807 In this case, you must compile with @option{-fcommon} instead.
23808 Compiling with @option{-fno-common} is useful on targets for which
23809 it provides better performance, or if you wish to verify that the
23810 program will work on other systems that always treat uninitialized
23811 variable declarations this way.
23815 Ignore the @code{#ident} directive.
23817 @item -finhibit-size-directive
23818 @opindex finhibit-size-directive
23819 Don't output a @code{.size} assembler directive, or anything else that
23820 would cause trouble if the function is split in the middle, and the
23821 two halves are placed at locations far apart in memory. This option is
23822 used when compiling @file{crtstuff.c}; you should not need to use it
23825 @item -fverbose-asm
23826 @opindex fverbose-asm
23827 Put extra commentary information in the generated assembly code to
23828 make it more readable. This option is generally only of use to those
23829 who actually need to read the generated assembly code (perhaps while
23830 debugging the compiler itself).
23832 @option{-fno-verbose-asm}, the default, causes the
23833 extra information to be omitted and is useful when comparing two assembler
23836 @item -frecord-gcc-switches
23837 @opindex frecord-gcc-switches
23838 This switch causes the command line used to invoke the
23839 compiler to be recorded into the object file that is being created.
23840 This switch is only implemented on some targets and the exact format
23841 of the recording is target and binary file format dependent, but it
23842 usually takes the form of a section containing ASCII text. This
23843 switch is related to the @option{-fverbose-asm} switch, but that
23844 switch only records information in the assembler output file as
23845 comments, so it never reaches the object file.
23846 See also @option{-grecord-gcc-switches} for another
23847 way of storing compiler options into the object file.
23851 @cindex global offset table
23853 Generate position-independent code (PIC) suitable for use in a shared
23854 library, if supported for the target machine. Such code accesses all
23855 constant addresses through a global offset table (GOT)@. The dynamic
23856 loader resolves the GOT entries when the program starts (the dynamic
23857 loader is not part of GCC; it is part of the operating system). If
23858 the GOT size for the linked executable exceeds a machine-specific
23859 maximum size, you get an error message from the linker indicating that
23860 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
23861 instead. (These maximums are 8k on the SPARC and 32k
23862 on the m68k and RS/6000. The x86 has no such limit.)
23864 Position-independent code requires special support, and therefore works
23865 only on certain machines. For the x86, GCC supports PIC for System V
23866 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
23867 position-independent.
23869 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
23874 If supported for the target machine, emit position-independent code,
23875 suitable for dynamic linking and avoiding any limit on the size of the
23876 global offset table. This option makes a difference on the m68k,
23877 PowerPC and SPARC@.
23879 Position-independent code requires special support, and therefore works
23880 only on certain machines.
23882 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
23889 These options are similar to @option{-fpic} and @option{-fPIC}, but
23890 generated position independent code can be only linked into executables.
23891 Usually these options are used when @option{-pie} GCC option is
23892 used during linking.
23894 @option{-fpie} and @option{-fPIE} both define the macros
23895 @code{__pie__} and @code{__PIE__}. The macros have the value 1
23896 for @option{-fpie} and 2 for @option{-fPIE}.
23900 Do not use PLT for external function calls in position-independent code.
23901 Instead, load callee address at call site from GOT and branch to it.
23902 This leads to more efficient code by eliminating PLT stubs and exposing
23903 GOT load to optimizations. On architectures such as 32-bit x86 where
23904 PLT stubs expect GOT pointer in a specific register, this gives more
23905 register allocation freedom to the compiler. Lazy binding requires PLT:
23906 with @option{-fno-plt} all external symbols are resolved at load time.
23908 Alternatively, function attribute @code{noplt} can be used to avoid PLT
23909 for calls to specific external functions by marking those functions with
23912 Additionally, a few targets also convert calls to those functions that are
23913 marked to not use the PLT to use the GOT instead for non-position independent
23916 @item -fno-jump-tables
23917 @opindex fno-jump-tables
23918 Do not use jump tables for switch statements even where it would be
23919 more efficient than other code generation strategies. This option is
23920 of use in conjunction with @option{-fpic} or @option{-fPIC} for
23921 building code that forms part of a dynamic linker and cannot
23922 reference the address of a jump table. On some targets, jump tables
23923 do not require a GOT and this option is not needed.
23925 @item -ffixed-@var{reg}
23927 Treat the register named @var{reg} as a fixed register; generated code
23928 should never refer to it (except perhaps as a stack pointer, frame
23929 pointer or in some other fixed role).
23931 @var{reg} must be the name of a register. The register names accepted
23932 are machine-specific and are defined in the @code{REGISTER_NAMES}
23933 macro in the machine description macro file.
23935 This flag does not have a negative form, because it specifies a
23938 @item -fcall-used-@var{reg}
23939 @opindex fcall-used
23940 Treat the register named @var{reg} as an allocable register that is
23941 clobbered by function calls. It may be allocated for temporaries or
23942 variables that do not live across a call. Functions compiled this way
23943 do not save and restore the register @var{reg}.
23945 It is an error to use this flag with the frame pointer or stack pointer.
23946 Use of this flag for other registers that have fixed pervasive roles in
23947 the machine's execution model produces disastrous results.
23949 This flag does not have a negative form, because it specifies a
23952 @item -fcall-saved-@var{reg}
23953 @opindex fcall-saved
23954 Treat the register named @var{reg} as an allocable register saved by
23955 functions. It may be allocated even for temporaries or variables that
23956 live across a call. Functions compiled this way save and restore
23957 the register @var{reg} if they use it.
23959 It is an error to use this flag with the frame pointer or stack pointer.
23960 Use of this flag for other registers that have fixed pervasive roles in
23961 the machine's execution model produces disastrous results.
23963 A different sort of disaster results from the use of this flag for
23964 a register in which function values may be returned.
23966 This flag does not have a negative form, because it specifies a
23969 @item -fpack-struct[=@var{n}]
23970 @opindex fpack-struct
23971 Without a value specified, pack all structure members together without
23972 holes. When a value is specified (which must be a small power of two), pack
23973 structure members according to this value, representing the maximum
23974 alignment (that is, objects with default alignment requirements larger than
23975 this are output potentially unaligned at the next fitting location.
23977 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
23978 code that is not binary compatible with code generated without that switch.
23979 Additionally, it makes the code suboptimal.
23980 Use it to conform to a non-default application binary interface.
23982 @item -finstrument-functions
23983 @opindex finstrument-functions
23984 Generate instrumentation calls for entry and exit to functions. Just
23985 after function entry and just before function exit, the following
23986 profiling functions are called with the address of the current
23987 function and its call site. (On some platforms,
23988 @code{__builtin_return_address} does not work beyond the current
23989 function, so the call site information may not be available to the
23990 profiling functions otherwise.)
23993 void __cyg_profile_func_enter (void *this_fn,
23995 void __cyg_profile_func_exit (void *this_fn,
23999 The first argument is the address of the start of the current function,
24000 which may be looked up exactly in the symbol table.
24002 This instrumentation is also done for functions expanded inline in other
24003 functions. The profiling calls indicate where, conceptually, the
24004 inline function is entered and exited. This means that addressable
24005 versions of such functions must be available. If all your uses of a
24006 function are expanded inline, this may mean an additional expansion of
24007 code size. If you use @code{extern inline} in your C code, an
24008 addressable version of such functions must be provided. (This is
24009 normally the case anyway, but if you get lucky and the optimizer always
24010 expands the functions inline, you might have gotten away without
24011 providing static copies.)
24013 A function may be given the attribute @code{no_instrument_function}, in
24014 which case this instrumentation is not done. This can be used, for
24015 example, for the profiling functions listed above, high-priority
24016 interrupt routines, and any functions from which the profiling functions
24017 cannot safely be called (perhaps signal handlers, if the profiling
24018 routines generate output or allocate memory).
24020 @item -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{}
24021 @opindex finstrument-functions-exclude-file-list
24023 Set the list of functions that are excluded from instrumentation (see
24024 the description of @option{-finstrument-functions}). If the file that
24025 contains a function definition matches with one of @var{file}, then
24026 that function is not instrumented. The match is done on substrings:
24027 if the @var{file} parameter is a substring of the file name, it is
24028 considered to be a match.
24033 -finstrument-functions-exclude-file-list=/bits/stl,include/sys
24037 excludes any inline function defined in files whose pathnames
24038 contain @file{/bits/stl} or @file{include/sys}.
24040 If, for some reason, you want to include letter @samp{,} in one of
24041 @var{sym}, write @samp{\,}. For example,
24042 @option{-finstrument-functions-exclude-file-list='\,\,tmp'}
24043 (note the single quote surrounding the option).
24045 @item -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{}
24046 @opindex finstrument-functions-exclude-function-list
24048 This is similar to @option{-finstrument-functions-exclude-file-list},
24049 but this option sets the list of function names to be excluded from
24050 instrumentation. The function name to be matched is its user-visible
24051 name, such as @code{vector<int> blah(const vector<int> &)}, not the
24052 internal mangled name (e.g., @code{_Z4blahRSt6vectorIiSaIiEE}). The
24053 match is done on substrings: if the @var{sym} parameter is a substring
24054 of the function name, it is considered to be a match. For C99 and C++
24055 extended identifiers, the function name must be given in UTF-8, not
24056 using universal character names.
24058 @item -fstack-check
24059 @opindex fstack-check
24060 Generate code to verify that you do not go beyond the boundary of the
24061 stack. You should specify this flag if you are running in an
24062 environment with multiple threads, but you only rarely need to specify it in
24063 a single-threaded environment since stack overflow is automatically
24064 detected on nearly all systems if there is only one stack.
24066 Note that this switch does not actually cause checking to be done; the
24067 operating system or the language runtime must do that. The switch causes
24068 generation of code to ensure that they see the stack being extended.
24070 You can additionally specify a string parameter: @samp{no} means no
24071 checking, @samp{generic} means force the use of old-style checking,
24072 @samp{specific} means use the best checking method and is equivalent
24073 to bare @option{-fstack-check}.
24075 Old-style checking is a generic mechanism that requires no specific
24076 target support in the compiler but comes with the following drawbacks:
24080 Modified allocation strategy for large objects: they are always
24081 allocated dynamically if their size exceeds a fixed threshold.
24084 Fixed limit on the size of the static frame of functions: when it is
24085 topped by a particular function, stack checking is not reliable and
24086 a warning is issued by the compiler.
24089 Inefficiency: because of both the modified allocation strategy and the
24090 generic implementation, code performance is hampered.
24093 Note that old-style stack checking is also the fallback method for
24094 @samp{specific} if no target support has been added in the compiler.
24096 @item -fstack-limit-register=@var{reg}
24097 @itemx -fstack-limit-symbol=@var{sym}
24098 @itemx -fno-stack-limit
24099 @opindex fstack-limit-register
24100 @opindex fstack-limit-symbol
24101 @opindex fno-stack-limit
24102 Generate code to ensure that the stack does not grow beyond a certain value,
24103 either the value of a register or the address of a symbol. If a larger
24104 stack is required, a signal is raised at run time. For most targets,
24105 the signal is raised before the stack overruns the boundary, so
24106 it is possible to catch the signal without taking special precautions.
24108 For instance, if the stack starts at absolute address @samp{0x80000000}
24109 and grows downwards, you can use the flags
24110 @option{-fstack-limit-symbol=__stack_limit} and
24111 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
24112 of 128KB@. Note that this may only work with the GNU linker.
24114 @item -fsplit-stack
24115 @opindex fsplit-stack
24116 Generate code to automatically split the stack before it overflows.
24117 The resulting program has a discontiguous stack which can only
24118 overflow if the program is unable to allocate any more memory. This
24119 is most useful when running threaded programs, as it is no longer
24120 necessary to calculate a good stack size to use for each thread. This
24121 is currently only implemented for the x86 targets running
24124 When code compiled with @option{-fsplit-stack} calls code compiled
24125 without @option{-fsplit-stack}, there may not be much stack space
24126 available for the latter code to run. If compiling all code,
24127 including library code, with @option{-fsplit-stack} is not an option,
24128 then the linker can fix up these calls so that the code compiled
24129 without @option{-fsplit-stack} always has a large stack. Support for
24130 this is implemented in the gold linker in GNU binutils release 2.21
24133 @item -fleading-underscore
24134 @opindex fleading-underscore
24135 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
24136 change the way C symbols are represented in the object file. One use
24137 is to help link with legacy assembly code.
24139 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
24140 generate code that is not binary compatible with code generated without that
24141 switch. Use it to conform to a non-default application binary interface.
24142 Not all targets provide complete support for this switch.
24144 @item -ftls-model=@var{model}
24145 @opindex ftls-model
24146 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
24147 The @var{model} argument should be one of @samp{global-dynamic},
24148 @samp{local-dynamic}, @samp{initial-exec} or @samp{local-exec}.
24149 Note that the choice is subject to optimization: the compiler may use
24150 a more efficient model for symbols not visible outside of the translation
24151 unit, or if @option{-fpic} is not given on the command line.
24153 The default without @option{-fpic} is @samp{initial-exec}; with
24154 @option{-fpic} the default is @samp{global-dynamic}.
24156 @item -fvisibility=@r{[}default@r{|}internal@r{|}hidden@r{|}protected@r{]}
24157 @opindex fvisibility
24158 Set the default ELF image symbol visibility to the specified option---all
24159 symbols are marked with this unless overridden within the code.
24160 Using this feature can very substantially improve linking and
24161 load times of shared object libraries, produce more optimized
24162 code, provide near-perfect API export and prevent symbol clashes.
24163 It is @strong{strongly} recommended that you use this in any shared objects
24166 Despite the nomenclature, @samp{default} always means public; i.e.,
24167 available to be linked against from outside the shared object.
24168 @samp{protected} and @samp{internal} are pretty useless in real-world
24169 usage so the only other commonly used option is @samp{hidden}.
24170 The default if @option{-fvisibility} isn't specified is
24171 @samp{default}, i.e., make every symbol public.
24173 A good explanation of the benefits offered by ensuring ELF
24174 symbols have the correct visibility is given by ``How To Write
24175 Shared Libraries'' by Ulrich Drepper (which can be found at
24176 @w{@uref{http://www.akkadia.org/drepper/}})---however a superior
24177 solution made possible by this option to marking things hidden when
24178 the default is public is to make the default hidden and mark things
24179 public. This is the norm with DLLs on Windows and with @option{-fvisibility=hidden}
24180 and @code{__attribute__ ((visibility("default")))} instead of
24181 @code{__declspec(dllexport)} you get almost identical semantics with
24182 identical syntax. This is a great boon to those working with
24183 cross-platform projects.
24185 For those adding visibility support to existing code, you may find
24186 @code{#pragma GCC visibility} of use. This works by you enclosing
24187 the declarations you wish to set visibility for with (for example)
24188 @code{#pragma GCC visibility push(hidden)} and
24189 @code{#pragma GCC visibility pop}.
24190 Bear in mind that symbol visibility should be viewed @strong{as
24191 part of the API interface contract} and thus all new code should
24192 always specify visibility when it is not the default; i.e., declarations
24193 only for use within the local DSO should @strong{always} be marked explicitly
24194 as hidden as so to avoid PLT indirection overheads---making this
24195 abundantly clear also aids readability and self-documentation of the code.
24196 Note that due to ISO C++ specification requirements, @code{operator new} and
24197 @code{operator delete} must always be of default visibility.
24199 Be aware that headers from outside your project, in particular system
24200 headers and headers from any other library you use, may not be
24201 expecting to be compiled with visibility other than the default. You
24202 may need to explicitly say @code{#pragma GCC visibility push(default)}
24203 before including any such headers.
24205 @code{extern} declarations are not affected by @option{-fvisibility}, so
24206 a lot of code can be recompiled with @option{-fvisibility=hidden} with
24207 no modifications. However, this means that calls to @code{extern}
24208 functions with no explicit visibility use the PLT, so it is more
24209 effective to use @code{__attribute ((visibility))} and/or
24210 @code{#pragma GCC visibility} to tell the compiler which @code{extern}
24211 declarations should be treated as hidden.
24213 Note that @option{-fvisibility} does affect C++ vague linkage
24214 entities. This means that, for instance, an exception class that is
24215 be thrown between DSOs must be explicitly marked with default
24216 visibility so that the @samp{type_info} nodes are unified between
24219 An overview of these techniques, their benefits and how to use them
24220 is at @uref{http://gcc.gnu.org/@/wiki/@/Visibility}.
24222 @item -fstrict-volatile-bitfields
24223 @opindex fstrict-volatile-bitfields
24224 This option should be used if accesses to volatile bit-fields (or other
24225 structure fields, although the compiler usually honors those types
24226 anyway) should use a single access of the width of the
24227 field's type, aligned to a natural alignment if possible. For
24228 example, targets with memory-mapped peripheral registers might require
24229 all such accesses to be 16 bits wide; with this flag you can
24230 declare all peripheral bit-fields as @code{unsigned short} (assuming short
24231 is 16 bits on these targets) to force GCC to use 16-bit accesses
24232 instead of, perhaps, a more efficient 32-bit access.
24234 If this option is disabled, the compiler uses the most efficient
24235 instruction. In the previous example, that might be a 32-bit load
24236 instruction, even though that accesses bytes that do not contain
24237 any portion of the bit-field, or memory-mapped registers unrelated to
24238 the one being updated.
24240 In some cases, such as when the @code{packed} attribute is applied to a
24241 structure field, it may not be possible to access the field with a single
24242 read or write that is correctly aligned for the target machine. In this
24243 case GCC falls back to generating multiple accesses rather than code that
24244 will fault or truncate the result at run time.
24246 Note: Due to restrictions of the C/C++11 memory model, write accesses are
24247 not allowed to touch non bit-field members. It is therefore recommended
24248 to define all bits of the field's type as bit-field members.
24250 The default value of this option is determined by the application binary
24251 interface for the target processor.
24253 @item -fsync-libcalls
24254 @opindex fsync-libcalls
24255 This option controls whether any out-of-line instance of the @code{__sync}
24256 family of functions may be used to implement the C++11 @code{__atomic}
24257 family of functions.
24259 The default value of this option is enabled, thus the only useful form
24260 of the option is @option{-fno-sync-libcalls}. This option is used in
24261 the implementation of the @file{libatomic} runtime library.
24267 @node Environment Variables
24268 @section Environment Variables Affecting GCC
24269 @cindex environment variables
24271 @c man begin ENVIRONMENT
24272 This section describes several environment variables that affect how GCC
24273 operates. Some of them work by specifying directories or prefixes to use
24274 when searching for various kinds of files. Some are used to specify other
24275 aspects of the compilation environment.
24277 Note that you can also specify places to search using options such as
24278 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
24279 take precedence over places specified using environment variables, which
24280 in turn take precedence over those specified by the configuration of GCC@.
24281 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
24282 GNU Compiler Collection (GCC) Internals}.
24287 @c @itemx LC_COLLATE
24289 @c @itemx LC_MONETARY
24290 @c @itemx LC_NUMERIC
24295 @c @findex LC_COLLATE
24296 @findex LC_MESSAGES
24297 @c @findex LC_MONETARY
24298 @c @findex LC_NUMERIC
24302 These environment variables control the way that GCC uses
24303 localization information which allows GCC to work with different
24304 national conventions. GCC inspects the locale categories
24305 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
24306 so. These locale categories can be set to any value supported by your
24307 installation. A typical value is @samp{en_GB.UTF-8} for English in the United
24308 Kingdom encoded in UTF-8.
24310 The @env{LC_CTYPE} environment variable specifies character
24311 classification. GCC uses it to determine the character boundaries in
24312 a string; this is needed for some multibyte encodings that contain quote
24313 and escape characters that are otherwise interpreted as a string
24316 The @env{LC_MESSAGES} environment variable specifies the language to
24317 use in diagnostic messages.
24319 If the @env{LC_ALL} environment variable is set, it overrides the value
24320 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
24321 and @env{LC_MESSAGES} default to the value of the @env{LANG}
24322 environment variable. If none of these variables are set, GCC
24323 defaults to traditional C English behavior.
24327 If @env{TMPDIR} is set, it specifies the directory to use for temporary
24328 files. GCC uses temporary files to hold the output of one stage of
24329 compilation which is to be used as input to the next stage: for example,
24330 the output of the preprocessor, which is the input to the compiler
24333 @item GCC_COMPARE_DEBUG
24334 @findex GCC_COMPARE_DEBUG
24335 Setting @env{GCC_COMPARE_DEBUG} is nearly equivalent to passing
24336 @option{-fcompare-debug} to the compiler driver. See the documentation
24337 of this option for more details.
24339 @item GCC_EXEC_PREFIX
24340 @findex GCC_EXEC_PREFIX
24341 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
24342 names of the subprograms executed by the compiler. No slash is added
24343 when this prefix is combined with the name of a subprogram, but you can
24344 specify a prefix that ends with a slash if you wish.
24346 If @env{GCC_EXEC_PREFIX} is not set, GCC attempts to figure out
24347 an appropriate prefix to use based on the pathname it is invoked with.
24349 If GCC cannot find the subprogram using the specified prefix, it
24350 tries looking in the usual places for the subprogram.
24352 The default value of @env{GCC_EXEC_PREFIX} is
24353 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the prefix to
24354 the installed compiler. In many cases @var{prefix} is the value
24355 of @code{prefix} when you ran the @file{configure} script.
24357 Other prefixes specified with @option{-B} take precedence over this prefix.
24359 This prefix is also used for finding files such as @file{crt0.o} that are
24362 In addition, the prefix is used in an unusual way in finding the
24363 directories to search for header files. For each of the standard
24364 directories whose name normally begins with @samp{/usr/local/lib/gcc}
24365 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
24366 replacing that beginning with the specified prefix to produce an
24367 alternate directory name. Thus, with @option{-Bfoo/}, GCC searches
24368 @file{foo/bar} just before it searches the standard directory
24369 @file{/usr/local/lib/bar}.
24370 If a standard directory begins with the configured
24371 @var{prefix} then the value of @var{prefix} is replaced by
24372 @env{GCC_EXEC_PREFIX} when looking for header files.
24374 @item COMPILER_PATH
24375 @findex COMPILER_PATH
24376 The value of @env{COMPILER_PATH} is a colon-separated list of
24377 directories, much like @env{PATH}. GCC tries the directories thus
24378 specified when searching for subprograms, if it can't find the
24379 subprograms using @env{GCC_EXEC_PREFIX}.
24382 @findex LIBRARY_PATH
24383 The value of @env{LIBRARY_PATH} is a colon-separated list of
24384 directories, much like @env{PATH}. When configured as a native compiler,
24385 GCC tries the directories thus specified when searching for special
24386 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
24387 using GCC also uses these directories when searching for ordinary
24388 libraries for the @option{-l} option (but directories specified with
24389 @option{-L} come first).
24393 @cindex locale definition
24394 This variable is used to pass locale information to the compiler. One way in
24395 which this information is used is to determine the character set to be used
24396 when character literals, string literals and comments are parsed in C and C++.
24397 When the compiler is configured to allow multibyte characters,
24398 the following values for @env{LANG} are recognized:
24402 Recognize JIS characters.
24404 Recognize SJIS characters.
24406 Recognize EUCJP characters.
24409 If @env{LANG} is not defined, or if it has some other value, then the
24410 compiler uses @code{mblen} and @code{mbtowc} as defined by the default locale to
24411 recognize and translate multibyte characters.
24415 Some additional environment variables affect the behavior of the
24418 @include cppenv.texi
24422 @node Precompiled Headers
24423 @section Using Precompiled Headers
24424 @cindex precompiled headers
24425 @cindex speed of compilation
24427 Often large projects have many header files that are included in every
24428 source file. The time the compiler takes to process these header files
24429 over and over again can account for nearly all of the time required to
24430 build the project. To make builds faster, GCC allows you to
24431 @dfn{precompile} a header file.
24433 To create a precompiled header file, simply compile it as you would any
24434 other file, if necessary using the @option{-x} option to make the driver
24435 treat it as a C or C++ header file. You may want to use a
24436 tool like @command{make} to keep the precompiled header up-to-date when
24437 the headers it contains change.
24439 A precompiled header file is searched for when @code{#include} is
24440 seen in the compilation. As it searches for the included file
24441 (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
24442 compiler looks for a precompiled header in each directory just before it
24443 looks for the include file in that directory. The name searched for is
24444 the name specified in the @code{#include} with @samp{.gch} appended. If
24445 the precompiled header file can't be used, it is ignored.
24447 For instance, if you have @code{#include "all.h"}, and you have
24448 @file{all.h.gch} in the same directory as @file{all.h}, then the
24449 precompiled header file is used if possible, and the original
24450 header is used otherwise.
24452 Alternatively, you might decide to put the precompiled header file in a
24453 directory and use @option{-I} to ensure that directory is searched
24454 before (or instead of) the directory containing the original header.
24455 Then, if you want to check that the precompiled header file is always
24456 used, you can put a file of the same name as the original header in this
24457 directory containing an @code{#error} command.
24459 This also works with @option{-include}. So yet another way to use
24460 precompiled headers, good for projects not designed with precompiled
24461 header files in mind, is to simply take most of the header files used by
24462 a project, include them from another header file, precompile that header
24463 file, and @option{-include} the precompiled header. If the header files
24464 have guards against multiple inclusion, they are skipped because
24465 they've already been included (in the precompiled header).
24467 If you need to precompile the same header file for different
24468 languages, targets, or compiler options, you can instead make a
24469 @emph{directory} named like @file{all.h.gch}, and put each precompiled
24470 header in the directory, perhaps using @option{-o}. It doesn't matter
24471 what you call the files in the directory; every precompiled header in
24472 the directory is considered. The first precompiled header
24473 encountered in the directory that is valid for this compilation is
24474 used; they're searched in no particular order.
24476 There are many other possibilities, limited only by your imagination,
24477 good sense, and the constraints of your build system.
24479 A precompiled header file can be used only when these conditions apply:
24483 Only one precompiled header can be used in a particular compilation.
24486 A precompiled header can't be used once the first C token is seen. You
24487 can have preprocessor directives before a precompiled header; you cannot
24488 include a precompiled header from inside another header.
24491 The precompiled header file must be produced for the same language as
24492 the current compilation. You can't use a C precompiled header for a C++
24496 The precompiled header file must have been produced by the same compiler
24497 binary as the current compilation is using.
24500 Any macros defined before the precompiled header is included must
24501 either be defined in the same way as when the precompiled header was
24502 generated, or must not affect the precompiled header, which usually
24503 means that they don't appear in the precompiled header at all.
24505 The @option{-D} option is one way to define a macro before a
24506 precompiled header is included; using a @code{#define} can also do it.
24507 There are also some options that define macros implicitly, like
24508 @option{-O} and @option{-Wdeprecated}; the same rule applies to macros
24511 @item If debugging information is output when using the precompiled
24512 header, using @option{-g} or similar, the same kind of debugging information
24513 must have been output when building the precompiled header. However,
24514 a precompiled header built using @option{-g} can be used in a compilation
24515 when no debugging information is being output.
24517 @item The same @option{-m} options must generally be used when building
24518 and using the precompiled header. @xref{Submodel Options},
24519 for any cases where this rule is relaxed.
24521 @item Each of the following options must be the same when building and using
24522 the precompiled header:
24524 @gccoptlist{-fexceptions}
24527 Some other command-line options starting with @option{-f},
24528 @option{-p}, or @option{-O} must be defined in the same way as when
24529 the precompiled header was generated. At present, it's not clear
24530 which options are safe to change and which are not; the safest choice
24531 is to use exactly the same options when generating and using the
24532 precompiled header. The following are known to be safe:
24534 @gccoptlist{-fmessage-length= -fpreprocessed -fsched-interblock @gol
24535 -fsched-spec -fsched-spec-load -fsched-spec-load-dangerous @gol
24536 -fsched-verbose=@var{number} -fschedule-insns -fvisibility= @gol
24541 For all of these except the last, the compiler automatically
24542 ignores the precompiled header if the conditions aren't met. If you
24543 find an option combination that doesn't work and doesn't cause the
24544 precompiled header to be ignored, please consider filing a bug report,
24547 If you do use differing options when generating and using the
24548 precompiled header, the actual behavior is a mixture of the
24549 behavior for the options. For instance, if you use @option{-g} to
24550 generate the precompiled header but not when using it, you may or may
24551 not get debugging information for routines in the precompiled header.