1 @c Copyright (C) 1988,1989,1992,1993,1994,1995,1996,1997,1998,1999,2000,2001,
2 @c 2002, 2003 Free Software Foundation, Inc.
3 @c This is part of the GCC manual.
4 @c For copying conditions, see the file gcc.texi.
7 @chapter Target Description Macros and Functions
8 @cindex machine description macros
9 @cindex target description macros
10 @cindex macros, target description
11 @cindex @file{tm.h} macros
13 In addition to the file @file{@var{machine}.md}, a machine description
14 includes a C header file conventionally given the name
15 @file{@var{machine}.h} and a C source file named @file{@var{machine}.c}.
16 The header file defines numerous macros that convey the information
17 about the target machine that does not fit into the scheme of the
18 @file{.md} file. The file @file{tm.h} should be a link to
19 @file{@var{machine}.h}. The header file @file{config.h} includes
20 @file{tm.h} and most compiler source files include @file{config.h}. The
21 source file defines a variable @code{targetm}, which is a structure
22 containing pointers to functions and data relating to the target
23 machine. @file{@var{machine}.c} should also contain their definitions,
24 if they are not defined elsewhere in GCC, and other functions called
25 through the macros defined in the @file{.h} file.
28 * Target Structure:: The @code{targetm} variable.
29 * Driver:: Controlling how the driver runs the compilation passes.
30 * Run-time Target:: Defining @samp{-m} options like @option{-m68000} and @option{-m68020}.
31 * Per-Function Data:: Defining data structures for per-function information.
32 * Storage Layout:: Defining sizes and alignments of data.
33 * Type Layout:: Defining sizes and properties of basic user data types.
34 * Escape Sequences:: Defining the value of target character escape sequences
35 * Registers:: Naming and describing the hardware registers.
36 * Register Classes:: Defining the classes of hardware registers.
37 * Stack and Calling:: Defining which way the stack grows and by how much.
38 * Varargs:: Defining the varargs macros.
39 * Trampolines:: Code set up at run time to enter a nested function.
40 * Library Calls:: Controlling how library routines are implicitly called.
41 * Addressing Modes:: Defining addressing modes valid for memory operands.
42 * Condition Code:: Defining how insns update the condition code.
43 * Costs:: Defining relative costs of different operations.
44 * Scheduling:: Adjusting the behavior of the instruction scheduler.
45 * Sections:: Dividing storage into text, data, and other sections.
46 * PIC:: Macros for position independent code.
47 * Assembler Format:: Defining how to write insns and pseudo-ops to output.
48 * Debugging Info:: Defining the format of debugging output.
49 * Floating Point:: Handling floating point for cross-compilers.
50 * Mode Switching:: Insertion of mode-switching instructions.
51 * Target Attributes:: Defining target-specific uses of @code{__attribute__}.
52 * MIPS Coprocessors:: MIPS coprocessor support and how to customize it.
53 * Misc:: Everything else.
56 @node Target Structure
57 @section The Global @code{targetm} Variable
59 @cindex target functions
61 @deftypevar {struct gcc_target} targetm
62 The target @file{.c} file must define the global @code{targetm} variable
63 which contains pointers to functions and data relating to the target
64 machine. The variable is declared in @file{target.h};
65 @file{target-def.h} defines the macro @code{TARGET_INITIALIZER} which is
66 used to initialize the variable, and macros for the default initializers
67 for elements of the structure. The @file{.c} file should override those
68 macros for which the default definition is inappropriate. For example:
71 #include "target-def.h"
73 /* @r{Initialize the GCC target structure.} */
75 #undef TARGET_COMP_TYPE_ATTRIBUTES
76 #define TARGET_COMP_TYPE_ATTRIBUTES @var{machine}_comp_type_attributes
78 struct gcc_target targetm = TARGET_INITIALIZER;
82 Where a macro should be defined in the @file{.c} file in this manner to
83 form part of the @code{targetm} structure, it is documented below as a
84 ``Target Hook'' with a prototype. Many macros will change in future
85 from being defined in the @file{.h} file to being part of the
86 @code{targetm} structure.
89 @section Controlling the Compilation Driver, @file{gcc}
91 @cindex controlling the compilation driver
93 @c prevent bad page break with this line
94 You can control the compilation driver.
96 @defmac SWITCH_TAKES_ARG (@var{char})
97 A C expression which determines whether the option @option{-@var{char}}
98 takes arguments. The value should be the number of arguments that
99 option takes--zero, for many options.
101 By default, this macro is defined as
102 @code{DEFAULT_SWITCH_TAKES_ARG}, which handles the standard options
103 properly. You need not define @code{SWITCH_TAKES_ARG} unless you
104 wish to add additional options which take arguments. Any redefinition
105 should call @code{DEFAULT_SWITCH_TAKES_ARG} and then check for
109 @defmac WORD_SWITCH_TAKES_ARG (@var{name})
110 A C expression which determines whether the option @option{-@var{name}}
111 takes arguments. The value should be the number of arguments that
112 option takes--zero, for many options. This macro rather than
113 @code{SWITCH_TAKES_ARG} is used for multi-character option names.
115 By default, this macro is defined as
116 @code{DEFAULT_WORD_SWITCH_TAKES_ARG}, which handles the standard options
117 properly. You need not define @code{WORD_SWITCH_TAKES_ARG} unless you
118 wish to add additional options which take arguments. Any redefinition
119 should call @code{DEFAULT_WORD_SWITCH_TAKES_ARG} and then check for
123 @defmac SWITCH_CURTAILS_COMPILATION (@var{char})
124 A C expression which determines whether the option @option{-@var{char}}
125 stops compilation before the generation of an executable. The value is
126 boolean, nonzero if the option does stop an executable from being
127 generated, zero otherwise.
129 By default, this macro is defined as
130 @code{DEFAULT_SWITCH_CURTAILS_COMPILATION}, which handles the standard
131 options properly. You need not define
132 @code{SWITCH_CURTAILS_COMPILATION} unless you wish to add additional
133 options which affect the generation of an executable. Any redefinition
134 should call @code{DEFAULT_SWITCH_CURTAILS_COMPILATION} and then check
135 for additional options.
138 @defmac SWITCHES_NEED_SPACES
139 A string-valued C expression which enumerates the options for which
140 the linker needs a space between the option and its argument.
142 If this macro is not defined, the default value is @code{""}.
145 @defmac TARGET_OPTION_TRANSLATE_TABLE
146 If defined, a list of pairs of strings, the first of which is a
147 potential command line target to the @file{gcc} driver program, and the
148 second of which is a space-separated (tabs and other whitespace are not
149 supported) list of options with which to replace the first option. The
150 target defining this list is responsible for assuring that the results
151 are valid. Replacement options may not be the @code{--opt} style, they
152 must be the @code{-opt} style. It is the intention of this macro to
153 provide a mechanism for substitution that affects the multilibs chosen,
154 such as one option that enables many options, some of which select
155 multilibs. Example nonsensical definition, where @code{-malt-abi},
156 @code{-EB}, and @code{-mspoo} cause different multilibs to be chosen:
159 #define TARGET_OPTION_TRANSLATE_TABLE \
160 @{ "-fast", "-march=fast-foo -malt-abi -I/usr/fast-foo" @}, \
161 @{ "-compat", "-EB -malign=4 -mspoo" @}
165 @defmac DRIVER_SELF_SPECS
166 A list of specs for the driver itself. It should be a suitable
167 initializer for an array of strings, with no surrounding braces.
169 The driver applies these specs to its own command line between loading
170 default @file{specs} files (but not command-line specified ones) and
171 choosing the multilib directory or running any subcommands. It
172 applies them in the order given, so each spec can depend on the
173 options added by earlier ones. It is also possible to remove options
174 using @samp{%<@var{option}} in the usual way.
176 This macro can be useful when a port has several interdependent target
177 options. It provides a way of standardizing the command line so
178 that the other specs are easier to write.
180 Do not define this macro if it does not need to do anything.
183 @defmac OPTION_DEFAULT_SPECS
184 A list of specs used to support configure-time default options (i.e.@:
185 @option{--with} options) in the driver. It should be a suitable initializer
186 for an array of structures, each containing two strings, without the
187 outermost pair of surrounding braces.
189 The first item in the pair is the name of the default. This must match
190 the code in @file{config.gcc} for the target. The second item is a spec
191 to apply if a default with this name was specified. The string
192 @samp{%(VALUE)} in the spec will be replaced by the value of the default
193 everywhere it occurs.
195 The driver will apply these specs to its own command line between loading
196 default @file{specs} files and processing @code{DRIVER_SELF_SPECS}, using
197 the same mechanism as @code{DRIVER_SELF_SPECS}.
199 Do not define this macro if it does not need to do anything.
203 A C string constant that tells the GCC driver program options to
204 pass to CPP@. It can also specify how to translate options you
205 give to GCC into options for GCC to pass to the CPP@.
207 Do not define this macro if it does not need to do anything.
210 @defmac CPLUSPLUS_CPP_SPEC
211 This macro is just like @code{CPP_SPEC}, but is used for C++, rather
212 than C@. If you do not define this macro, then the value of
213 @code{CPP_SPEC} (if any) will be used instead.
217 A C string constant that tells the GCC driver program options to
218 pass to @code{cc1}, @code{cc1plus}, @code{f771}, and the other language
220 It can also specify how to translate options you give to GCC into options
221 for GCC to pass to front ends.
223 Do not define this macro if it does not need to do anything.
227 A C string constant that tells the GCC driver program options to
228 pass to @code{cc1plus}. It can also specify how to translate options you
229 give to GCC into options for GCC to pass to the @code{cc1plus}.
231 Do not define this macro if it does not need to do anything.
232 Note that everything defined in CC1_SPEC is already passed to
233 @code{cc1plus} so there is no need to duplicate the contents of
234 CC1_SPEC in CC1PLUS_SPEC@.
238 A C string constant that tells the GCC driver program options to
239 pass to the assembler. It can also specify how to translate options
240 you give to GCC into options for GCC to pass to the assembler.
241 See the file @file{sun3.h} for an example of this.
243 Do not define this macro if it does not need to do anything.
246 @defmac ASM_FINAL_SPEC
247 A C string constant that tells the GCC driver program how to
248 run any programs which cleanup after the normal assembler.
249 Normally, this is not needed. See the file @file{mips.h} for
252 Do not define this macro if it does not need to do anything.
255 @defmac AS_NEEDS_DASH_FOR_PIPED_INPUT
256 Define this macro, with no value, if the driver should give the assembler
257 an argument consisting of a single dash, @option{-}, to instruct it to
258 read from its standard input (which will be a pipe connected to the
259 output of the compiler proper). This argument is given after any
260 @option{-o} option specifying the name of the output file.
262 If you do not define this macro, the assembler is assumed to read its
263 standard input if given no non-option arguments. If your assembler
264 cannot read standard input at all, use a @samp{%@{pipe:%e@}} construct;
265 see @file{mips.h} for instance.
269 A C string constant that tells the GCC driver program options to
270 pass to the linker. It can also specify how to translate options you
271 give to GCC into options for GCC to pass to the linker.
273 Do not define this macro if it does not need to do anything.
277 Another C string constant used much like @code{LINK_SPEC}. The difference
278 between the two is that @code{LIB_SPEC} is used at the end of the
279 command given to the linker.
281 If this macro is not defined, a default is provided that
282 loads the standard C library from the usual place. See @file{gcc.c}.
286 Another C string constant that tells the GCC driver program
287 how and when to place a reference to @file{libgcc.a} into the
288 linker command line. This constant is placed both before and after
289 the value of @code{LIB_SPEC}.
291 If this macro is not defined, the GCC driver provides a default that
292 passes the string @option{-lgcc} to the linker.
295 @defmac STARTFILE_SPEC
296 Another C string constant used much like @code{LINK_SPEC}. The
297 difference between the two is that @code{STARTFILE_SPEC} is used at
298 the very beginning of the command given to the linker.
300 If this macro is not defined, a default is provided that loads the
301 standard C startup file from the usual place. See @file{gcc.c}.
305 Another C string constant used much like @code{LINK_SPEC}. The
306 difference between the two is that @code{ENDFILE_SPEC} is used at
307 the very end of the command given to the linker.
309 Do not define this macro if it does not need to do anything.
312 @defmac THREAD_MODEL_SPEC
313 GCC @code{-v} will print the thread model GCC was configured to use.
314 However, this doesn't work on platforms that are multilibbed on thread
315 models, such as AIX 4.3. On such platforms, define
316 @code{THREAD_MODEL_SPEC} such that it evaluates to a string without
317 blanks that names one of the recognized thread models. @code{%*}, the
318 default value of this macro, will expand to the value of
319 @code{thread_file} set in @file{config.gcc}.
322 @defmac SYSROOT_SUFFIX_SPEC
323 Define this macro to add a suffix to the target sysroot when GCC is
324 configured with a sysroot. This will cause GCC to search for usr/lib,
325 et al, within sysroot+suffix.
328 @defmac SYSROOT_HEADERS_SUFFIX_SPEC
329 Define this macro to add a headers_suffix to the target sysroot when
330 GCC is configured with a sysroot. This will cause GCC to pass the
331 updated sysroot+headers_suffix to CPP@, causing it to search for
332 usr/include, et al, within sysroot+headers_suffix.
336 Define this macro to provide additional specifications to put in the
337 @file{specs} file that can be used in various specifications like
340 The definition should be an initializer for an array of structures,
341 containing a string constant, that defines the specification name, and a
342 string constant that provides the specification.
344 Do not define this macro if it does not need to do anything.
346 @code{EXTRA_SPECS} is useful when an architecture contains several
347 related targets, which have various @code{@dots{}_SPECS} which are similar
348 to each other, and the maintainer would like one central place to keep
351 For example, the PowerPC System V.4 targets use @code{EXTRA_SPECS} to
352 define either @code{_CALL_SYSV} when the System V calling sequence is
353 used or @code{_CALL_AIX} when the older AIX-based calling sequence is
356 The @file{config/rs6000/rs6000.h} target file defines:
359 #define EXTRA_SPECS \
360 @{ "cpp_sysv_default", CPP_SYSV_DEFAULT @},
362 #define CPP_SYS_DEFAULT ""
365 The @file{config/rs6000/sysv.h} target file defines:
369 "%@{posix: -D_POSIX_SOURCE @} \
370 %@{mcall-sysv: -D_CALL_SYSV @} \
371 %@{!mcall-sysv: %(cpp_sysv_default) @} \
372 %@{msoft-float: -D_SOFT_FLOAT@} %@{mcpu=403: -D_SOFT_FLOAT@}"
374 #undef CPP_SYSV_DEFAULT
375 #define CPP_SYSV_DEFAULT "-D_CALL_SYSV"
378 while the @file{config/rs6000/eabiaix.h} target file defines
379 @code{CPP_SYSV_DEFAULT} as:
382 #undef CPP_SYSV_DEFAULT
383 #define CPP_SYSV_DEFAULT "-D_CALL_AIX"
387 @defmac LINK_LIBGCC_SPECIAL
388 Define this macro if the driver program should find the library
389 @file{libgcc.a} itself and should not pass @option{-L} options to the
390 linker. If you do not define this macro, the driver program will pass
391 the argument @option{-lgcc} to tell the linker to do the search and will
392 pass @option{-L} options to it.
395 @defmac LINK_LIBGCC_SPECIAL_1
396 Define this macro if the driver program should find the library
397 @file{libgcc.a}. If you do not define this macro, the driver program will pass
398 the argument @option{-lgcc} to tell the linker to do the search.
399 This macro is similar to @code{LINK_LIBGCC_SPECIAL}, except that it does
400 not affect @option{-L} options.
403 @defmac LINK_GCC_C_SEQUENCE_SPEC
404 The sequence in which libgcc and libc are specified to the linker.
405 By default this is @code{%G %L %G}.
408 @defmac LINK_COMMAND_SPEC
409 A C string constant giving the complete command line need to execute the
410 linker. When you do this, you will need to update your port each time a
411 change is made to the link command line within @file{gcc.c}. Therefore,
412 define this macro only if you need to completely redefine the command
413 line for invoking the linker and there is no other way to accomplish
414 the effect you need. Overriding this macro may be avoidable by overriding
415 @code{LINK_GCC_C_SEQUENCE_SPEC} instead.
418 @defmac LINK_ELIMINATE_DUPLICATE_LDIRECTORIES
419 A nonzero value causes @command{collect2} to remove duplicate @option{-L@var{directory}} search
420 directories from linking commands. Do not give it a nonzero value if
421 removing duplicate search directories changes the linker's semantics.
424 @defmac MULTILIB_DEFAULTS
425 Define this macro as a C expression for the initializer of an array of
426 string to tell the driver program which options are defaults for this
427 target and thus do not need to be handled specially when using
428 @code{MULTILIB_OPTIONS}.
430 Do not define this macro if @code{MULTILIB_OPTIONS} is not defined in
431 the target makefile fragment or if none of the options listed in
432 @code{MULTILIB_OPTIONS} are set by default.
433 @xref{Target Fragment}.
436 @defmac RELATIVE_PREFIX_NOT_LINKDIR
437 Define this macro to tell @command{gcc} that it should only translate
438 a @option{-B} prefix into a @option{-L} linker option if the prefix
439 indicates an absolute file name.
442 @defmac STANDARD_EXEC_PREFIX
443 Define this macro as a C string constant if you wish to override the
444 standard choice of @file{/usr/local/lib/gcc-lib/} as the default prefix to
445 try when searching for the executable files of the compiler.
448 @defmac MD_EXEC_PREFIX
449 If defined, this macro is an additional prefix to try after
450 @code{STANDARD_EXEC_PREFIX}. @code{MD_EXEC_PREFIX} is not searched
451 when the @option{-b} option is used, or the compiler is built as a cross
452 compiler. If you define @code{MD_EXEC_PREFIX}, then be sure to add it
453 to the list of directories used to find the assembler in @file{configure.in}.
456 @defmac STANDARD_STARTFILE_PREFIX
457 Define this macro as a C string constant if you wish to override the
458 standard choice of @file{/usr/local/lib/} as the default prefix to
459 try when searching for startup files such as @file{crt0.o}.
462 @defmac MD_STARTFILE_PREFIX
463 If defined, this macro supplies an additional prefix to try after the
464 standard prefixes. @code{MD_EXEC_PREFIX} is not searched when the
465 @option{-b} option is used, or when the compiler is built as a cross
469 @defmac MD_STARTFILE_PREFIX_1
470 If defined, this macro supplies yet another prefix to try after the
471 standard prefixes. It is not searched when the @option{-b} option is
472 used, or when the compiler is built as a cross compiler.
475 @defmac INIT_ENVIRONMENT
476 Define this macro as a C string constant if you wish to set environment
477 variables for programs called by the driver, such as the assembler and
478 loader. The driver passes the value of this macro to @code{putenv} to
479 initialize the necessary environment variables.
482 @defmac LOCAL_INCLUDE_DIR
483 Define this macro as a C string constant if you wish to override the
484 standard choice of @file{/usr/local/include} as the default prefix to
485 try when searching for local header files. @code{LOCAL_INCLUDE_DIR}
486 comes before @code{SYSTEM_INCLUDE_DIR} in the search order.
488 Cross compilers do not search either @file{/usr/local/include} or its
492 @defmac MODIFY_TARGET_NAME
493 Define this macro if you wish to define command-line switches that
494 modify the default target name.
496 For each switch, you can include a string to be appended to the first
497 part of the configuration name or a string to be deleted from the
498 configuration name, if present. The definition should be an initializer
499 for an array of structures. Each array element should have three
500 elements: the switch name (a string constant, including the initial
501 dash), one of the enumeration codes @code{ADD} or @code{DELETE} to
502 indicate whether the string should be inserted or deleted, and the string
503 to be inserted or deleted (a string constant).
505 For example, on a machine where @samp{64} at the end of the
506 configuration name denotes a 64-bit target and you want the @option{-32}
507 and @option{-64} switches to select between 32- and 64-bit targets, you would
511 #define MODIFY_TARGET_NAME \
512 @{ @{ "-32", DELETE, "64"@}, \
513 @{"-64", ADD, "64"@}@}
517 @defmac SYSTEM_INCLUDE_DIR
518 Define this macro as a C string constant if you wish to specify a
519 system-specific directory to search for header files before the standard
520 directory. @code{SYSTEM_INCLUDE_DIR} comes before
521 @code{STANDARD_INCLUDE_DIR} in the search order.
523 Cross compilers do not use this macro and do not search the directory
527 @defmac STANDARD_INCLUDE_DIR
528 Define this macro as a C string constant if you wish to override the
529 standard choice of @file{/usr/include} as the default prefix to
530 try when searching for header files.
532 Cross compilers ignore this macro and do not search either
533 @file{/usr/include} or its replacement.
536 @defmac STANDARD_INCLUDE_COMPONENT
537 The ``component'' corresponding to @code{STANDARD_INCLUDE_DIR}.
538 See @code{INCLUDE_DEFAULTS}, below, for the description of components.
539 If you do not define this macro, no component is used.
542 @defmac INCLUDE_DEFAULTS
543 Define this macro if you wish to override the entire default search path
544 for include files. For a native compiler, the default search path
545 usually consists of @code{GCC_INCLUDE_DIR}, @code{LOCAL_INCLUDE_DIR},
546 @code{SYSTEM_INCLUDE_DIR}, @code{GPLUSPLUS_INCLUDE_DIR}, and
547 @code{STANDARD_INCLUDE_DIR}. In addition, @code{GPLUSPLUS_INCLUDE_DIR}
548 and @code{GCC_INCLUDE_DIR} are defined automatically by @file{Makefile},
549 and specify private search areas for GCC@. The directory
550 @code{GPLUSPLUS_INCLUDE_DIR} is used only for C++ programs.
552 The definition should be an initializer for an array of structures.
553 Each array element should have four elements: the directory name (a
554 string constant), the component name (also a string constant), a flag
555 for C++-only directories,
556 and a flag showing that the includes in the directory don't need to be
557 wrapped in @code{extern @samp{C}} when compiling C++. Mark the end of
558 the array with a null element.
560 The component name denotes what GNU package the include file is part of,
561 if any, in all upper-case letters. For example, it might be @samp{GCC}
562 or @samp{BINUTILS}. If the package is part of a vendor-supplied
563 operating system, code the component name as @samp{0}.
565 For example, here is the definition used for VAX/VMS:
568 #define INCLUDE_DEFAULTS \
570 @{ "GNU_GXX_INCLUDE:", "G++", 1, 1@}, \
571 @{ "GNU_CC_INCLUDE:", "GCC", 0, 0@}, \
572 @{ "SYS$SYSROOT:[SYSLIB.]", 0, 0, 0@}, \
579 Here is the order of prefixes tried for exec files:
583 Any prefixes specified by the user with @option{-B}.
586 The environment variable @code{GCC_EXEC_PREFIX}, if any.
589 The directories specified by the environment variable @code{COMPILER_PATH}.
592 The macro @code{STANDARD_EXEC_PREFIX}.
595 @file{/usr/lib/gcc/}.
598 The macro @code{MD_EXEC_PREFIX}, if any.
601 Here is the order of prefixes tried for startfiles:
605 Any prefixes specified by the user with @option{-B}.
608 The environment variable @code{GCC_EXEC_PREFIX}, if any.
611 The directories specified by the environment variable @code{LIBRARY_PATH}
612 (or port-specific name; native only, cross compilers do not use this).
615 The macro @code{STANDARD_EXEC_PREFIX}.
618 @file{/usr/lib/gcc/}.
621 The macro @code{MD_EXEC_PREFIX}, if any.
624 The macro @code{MD_STARTFILE_PREFIX}, if any.
627 The macro @code{STANDARD_STARTFILE_PREFIX}.
636 @node Run-time Target
637 @section Run-time Target Specification
638 @cindex run-time target specification
639 @cindex predefined macros
640 @cindex target specifications
642 @c prevent bad page break with this line
643 Here are run-time target specifications.
645 @defmac TARGET_CPU_CPP_BUILTINS ()
646 This function-like macro expands to a block of code that defines
647 built-in preprocessor macros and assertions for the target cpu, using
648 the functions @code{builtin_define}, @code{builtin_define_std} and
649 @code{builtin_assert}. When the front end
650 calls this macro it provides a trailing semicolon, and since it has
651 finished command line option processing your code can use those
654 @code{builtin_assert} takes a string in the form you pass to the
655 command-line option @option{-A}, such as @code{cpu=mips}, and creates
656 the assertion. @code{builtin_define} takes a string in the form
657 accepted by option @option{-D} and unconditionally defines the macro.
659 @code{builtin_define_std} takes a string representing the name of an
660 object-like macro. If it doesn't lie in the user's namespace,
661 @code{builtin_define_std} defines it unconditionally. Otherwise, it
662 defines a version with two leading underscores, and another version
663 with two leading and trailing underscores, and defines the original
664 only if an ISO standard was not requested on the command line. For
665 example, passing @code{unix} defines @code{__unix}, @code{__unix__}
666 and possibly @code{unix}; passing @code{_mips} defines @code{__mips},
667 @code{__mips__} and possibly @code{_mips}, and passing @code{_ABI64}
668 defines only @code{_ABI64}.
670 You can also test for the C dialect being compiled. The variable
671 @code{c_language} is set to one of @code{clk_c}, @code{clk_cplusplus}
672 or @code{clk_objective_c}. Note that if we are preprocessing
673 assembler, this variable will be @code{clk_c} but the function-like
674 macro @code{preprocessing_asm_p()} will return true, so you might want
675 to check for that first. If you need to check for strict ANSI, the
676 variable @code{flag_iso} can be used. The function-like macro
677 @code{preprocessing_trad_p()} can be used to check for traditional
681 @defmac TARGET_OS_CPP_BUILTINS ()
682 Similarly to @code{TARGET_CPU_CPP_BUILTINS} but this macro is optional
683 and is used for the target operating system instead.
686 @defmac TARGET_OBJFMT_CPP_BUILTINS ()
687 Similarly to @code{TARGET_CPU_CPP_BUILTINS} but this macro is optional
688 and is used for the target object format. @file{elfos.h} uses this
689 macro to define @code{__ELF__}, so you probably do not need to define
693 @deftypevar {extern int} target_flags
694 This declaration should be present.
697 @cindex optional hardware or system features
698 @cindex features, optional, in system conventions
700 @defmac TARGET_@var{featurename}
701 This series of macros is to allow compiler command arguments to
702 enable or disable the use of optional features of the target machine.
703 For example, one machine description serves both the 68000 and
704 the 68020; a command argument tells the compiler whether it should
705 use 68020-only instructions or not. This command argument works
706 by means of a macro @code{TARGET_68020} that tests a bit in
709 Define a macro @code{TARGET_@var{featurename}} for each such option.
710 Its definition should test a bit in @code{target_flags}. It is
711 recommended that a helper macro @code{MASK_@var{featurename}}
712 is defined for each bit-value to test, and used in
713 @code{TARGET_@var{featurename}} and @code{TARGET_SWITCHES}. For
717 #define TARGET_MASK_68020 1
718 #define TARGET_68020 (target_flags & MASK_68020)
721 One place where these macros are used is in the condition-expressions
722 of instruction patterns. Note how @code{TARGET_68020} appears
723 frequently in the 68000 machine description file, @file{m68k.md}.
724 Another place they are used is in the definitions of the other
725 macros in the @file{@var{machine}.h} file.
728 @defmac TARGET_SWITCHES
729 This macro defines names of command options to set and clear
730 bits in @code{target_flags}. Its definition is an initializer
731 with a subgrouping for each command option.
733 Each subgrouping contains a string constant, that defines the option
734 name, a number, which contains the bits to set in
735 @code{target_flags}, and a second string which is the description
736 displayed by @option{--help}. If the number is negative then the bits specified
737 by the number are cleared instead of being set. If the description
738 string is present but empty, then no help information will be displayed
739 for that option, but it will not count as an undocumented option. The
740 actual option name is made by appending @samp{-m} to the specified name.
741 Non-empty description strings should be marked with @code{N_(@dots{})} for
742 @command{xgettext}. Please do not mark empty strings because the empty
743 string is reserved by GNU gettext. @code{gettext("")} returns the header entry
744 of the message catalog with meta information, not the empty string.
746 In addition to the description for @option{--help},
747 more detailed documentation for each option should be added to
750 One of the subgroupings should have a null string. The number in
751 this grouping is the default value for @code{target_flags}. Any
752 target options act starting with that value.
754 Here is an example which defines @option{-m68000} and @option{-m68020}
755 with opposite meanings, and picks the latter as the default:
758 #define TARGET_SWITCHES \
759 @{ @{ "68020", MASK_68020, "" @}, \
760 @{ "68000", -MASK_68020, \
761 N_("Compile for the 68000") @}, \
762 @{ "", MASK_68020, "" @}, \
767 @defmac TARGET_OPTIONS
768 This macro is similar to @code{TARGET_SWITCHES} but defines names of command
769 options that have values. Its definition is an initializer with a
770 subgrouping for each command option.
772 Each subgrouping contains a string constant, that defines the option
773 name, the address of a variable, a description string, and a value.
774 Non-empty description strings should be marked with @code{N_(@dots{})}
775 for @command{xgettext}. Please do not mark empty strings because the
776 empty string is reserved by GNU gettext. @code{gettext("")} returns the
777 header entry of the message catalog with meta information, not the empty
780 If the value listed in the table is @code{NULL}, then the variable, type
781 @code{char *}, is set to the variable part of the given option if the
782 fixed part matches. In other words, if the first part of the option
783 matches what's in the table, the variable will be set to point to the
784 rest of the option. This allows the user to specify a value for that
785 option. The actual option name is made by appending @samp{-m} to the
786 specified name. Again, each option should also be documented in
789 If the value listed in the table is non-@code{NULL}, then the option
790 must match the option in the table exactly (with @samp{-m}), and the
791 variable is set to point to the value listed in the table.
793 Here is an example which defines @option{-mshort-data-@var{number}}. If the
794 given option is @option{-mshort-data-512}, the variable @code{m88k_short_data}
795 will be set to the string @code{"512"}.
798 extern char *m88k_short_data;
799 #define TARGET_OPTIONS \
800 @{ @{ "short-data-", &m88k_short_data, \
801 N_("Specify the size of the short data section"), 0 @} @}
804 Here is a variant of the above that allows the user to also specify
805 just @option{-mshort-data} where a default of @code{"64"} is used.
808 extern char *m88k_short_data;
809 #define TARGET_OPTIONS \
810 @{ @{ "short-data-", &m88k_short_data, \
811 N_("Specify the size of the short data section"), 0 @} \
812 @{ "short-data", &m88k_short_data, "", "64" @},
816 Here is an example which defines @option{-mno-alu}, @option{-malu1}, and
817 @option{-malu2} as a three-state switch, along with suitable macros for
818 checking the state of the option (documentation is elided for brevity).
822 char *chip_alu = ""; /* Specify default here. */
825 extern char *chip_alu;
826 #define TARGET_OPTIONS \
827 @{ @{ "no-alu", &chip_alu, "", "" @}, \
828 @{ "alu1", &chip_alu, "", "1" @}, \
829 @{ "alu2", &chip_alu, "", "2" @}, @}
830 #define TARGET_ALU (chip_alu[0] != '\0')
831 #define TARGET_ALU1 (chip_alu[0] == '1')
832 #define TARGET_ALU2 (chip_alu[0] == '2')
836 @defmac TARGET_VERSION
837 This macro is a C statement to print on @code{stderr} a string
838 describing the particular machine description choice. Every machine
839 description should define @code{TARGET_VERSION}. For example:
843 #define TARGET_VERSION \
844 fprintf (stderr, " (68k, Motorola syntax)");
846 #define TARGET_VERSION \
847 fprintf (stderr, " (68k, MIT syntax)");
852 @defmac OVERRIDE_OPTIONS
853 Sometimes certain combinations of command options do not make sense on
854 a particular target machine. You can define a macro
855 @code{OVERRIDE_OPTIONS} to take account of this. This macro, if
856 defined, is executed once just after all the command options have been
859 Don't use this macro to turn on various extra optimizations for
860 @option{-O}. That is what @code{OPTIMIZATION_OPTIONS} is for.
863 @defmac OPTIMIZATION_OPTIONS (@var{level}, @var{size})
864 Some machines may desire to change what optimizations are performed for
865 various optimization levels. This macro, if defined, is executed once
866 just after the optimization level is determined and before the remainder
867 of the command options have been parsed. Values set in this macro are
868 used as the default values for the other command line options.
870 @var{level} is the optimization level specified; 2 if @option{-O2} is
871 specified, 1 if @option{-O} is specified, and 0 if neither is specified.
873 @var{size} is nonzero if @option{-Os} is specified and zero otherwise.
875 You should not use this macro to change options that are not
876 machine-specific. These should uniformly selected by the same
877 optimization level on all supported machines. Use this macro to enable
878 machine-specific optimizations.
880 @strong{Do not examine @code{write_symbols} in
881 this macro!} The debugging options are not supposed to alter the
885 @defmac CAN_DEBUG_WITHOUT_FP
886 Define this macro if debugging can be performed even without a frame
887 pointer. If this macro is defined, GCC will turn on the
888 @option{-fomit-frame-pointer} option whenever @option{-O} is specified.
891 @node Per-Function Data
892 @section Defining data structures for per-function information.
893 @cindex per-function data
894 @cindex data structures
896 If the target needs to store information on a per-function basis, GCC
897 provides a macro and a couple of variables to allow this. Note, just
898 using statics to store the information is a bad idea, since GCC supports
899 nested functions, so you can be halfway through encoding one function
900 when another one comes along.
902 GCC defines a data structure called @code{struct function} which
903 contains all of the data specific to an individual function. This
904 structure contains a field called @code{machine} whose type is
905 @code{struct machine_function *}, which can be used by targets to point
906 to their own specific data.
908 If a target needs per-function specific data it should define the type
909 @code{struct machine_function} and also the macro @code{INIT_EXPANDERS}.
910 This macro should be used to initialize the function pointer
911 @code{init_machine_status}. This pointer is explained below.
913 One typical use of per-function, target specific data is to create an
914 RTX to hold the register containing the function's return address. This
915 RTX can then be used to implement the @code{__builtin_return_address}
916 function, for level 0.
918 Note---earlier implementations of GCC used a single data area to hold
919 all of the per-function information. Thus when processing of a nested
920 function began the old per-function data had to be pushed onto a
921 stack, and when the processing was finished, it had to be popped off the
922 stack. GCC used to provide function pointers called
923 @code{save_machine_status} and @code{restore_machine_status} to handle
924 the saving and restoring of the target specific information. Since the
925 single data area approach is no longer used, these pointers are no
928 @defmac INIT_EXPANDERS
929 Macro called to initialize any target specific information. This macro
930 is called once per function, before generation of any RTL has begun.
931 The intention of this macro is to allow the initialization of the
932 function pointer @code{init_machine_status}.
935 @deftypevar {void (*)(struct function *)} init_machine_status
936 If this function pointer is non-@code{NULL} it will be called once per
937 function, before function compilation starts, in order to allow the
938 target to perform any target specific initialization of the
939 @code{struct function} structure. It is intended that this would be
940 used to initialize the @code{machine} of that structure.
942 @code{struct machine_function} structures are expected to be freed by GC.
943 Generally, any memory that they reference must be allocated by using
944 @code{ggc_alloc}, including the structure itself.
948 @section Storage Layout
949 @cindex storage layout
951 Note that the definitions of the macros in this table which are sizes or
952 alignments measured in bits do not need to be constant. They can be C
953 expressions that refer to static variables, such as the @code{target_flags}.
954 @xref{Run-time Target}.
956 @defmac BITS_BIG_ENDIAN
957 Define this macro to have the value 1 if the most significant bit in a
958 byte has the lowest number; otherwise define it to have the value zero.
959 This means that bit-field instructions count from the most significant
960 bit. If the machine has no bit-field instructions, then this must still
961 be defined, but it doesn't matter which value it is defined to. This
962 macro need not be a constant.
964 This macro does not affect the way structure fields are packed into
965 bytes or words; that is controlled by @code{BYTES_BIG_ENDIAN}.
968 @defmac BYTES_BIG_ENDIAN
969 Define this macro to have the value 1 if the most significant byte in a
970 word has the lowest number. This macro need not be a constant.
973 @defmac WORDS_BIG_ENDIAN
974 Define this macro to have the value 1 if, in a multiword object, the
975 most significant word has the lowest number. This applies to both
976 memory locations and registers; GCC fundamentally assumes that the
977 order of words in memory is the same as the order in registers. This
978 macro need not be a constant.
981 @defmac LIBGCC2_WORDS_BIG_ENDIAN
982 Define this macro if @code{WORDS_BIG_ENDIAN} is not constant. This must be a
983 constant value with the same meaning as @code{WORDS_BIG_ENDIAN}, which will be
984 used only when compiling @file{libgcc2.c}. Typically the value will be set
985 based on preprocessor defines.
988 @defmac FLOAT_WORDS_BIG_ENDIAN
989 Define this macro to have the value 1 if @code{DFmode}, @code{XFmode} or
990 @code{TFmode} floating point numbers are stored in memory with the word
991 containing the sign bit at the lowest address; otherwise define it to
992 have the value 0. This macro need not be a constant.
994 You need not define this macro if the ordering is the same as for
998 @defmac BITS_PER_UNIT
999 Define this macro to be the number of bits in an addressable storage
1000 unit (byte). If you do not define this macro the default is 8.
1003 @defmac BITS_PER_WORD
1004 Number of bits in a word. If you do not define this macro, the default
1005 is @code{BITS_PER_UNIT * UNITS_PER_WORD}.
1008 @defmac MAX_BITS_PER_WORD
1009 Maximum number of bits in a word. If this is undefined, the default is
1010 @code{BITS_PER_WORD}. Otherwise, it is the constant value that is the
1011 largest value that @code{BITS_PER_WORD} can have at run-time.
1014 @defmac UNITS_PER_WORD
1015 Number of storage units in a word; normally 4.
1018 @defmac MIN_UNITS_PER_WORD
1019 Minimum number of units in a word. If this is undefined, the default is
1020 @code{UNITS_PER_WORD}. Otherwise, it is the constant value that is the
1021 smallest value that @code{UNITS_PER_WORD} can have at run-time.
1024 @defmac POINTER_SIZE
1025 Width of a pointer, in bits. You must specify a value no wider than the
1026 width of @code{Pmode}. If it is not equal to the width of @code{Pmode},
1027 you must define @code{POINTERS_EXTEND_UNSIGNED}. If you do not specify
1028 a value the default is @code{BITS_PER_WORD}.
1031 @defmac POINTERS_EXTEND_UNSIGNED
1032 A C expression whose value is greater than zero if pointers that need to be
1033 extended from being @code{POINTER_SIZE} bits wide to @code{Pmode} are to
1034 be zero-extended and zero if they are to be sign-extended. If the value
1035 is less then zero then there must be an "ptr_extend" instruction that
1036 extends a pointer from @code{POINTER_SIZE} to @code{Pmode}.
1038 You need not define this macro if the @code{POINTER_SIZE} is equal
1039 to the width of @code{Pmode}.
1042 @defmac PROMOTE_MODE (@var{m}, @var{unsignedp}, @var{type})
1043 A macro to update @var{m} and @var{unsignedp} when an object whose type
1044 is @var{type} and which has the specified mode and signedness is to be
1045 stored in a register. This macro is only called when @var{type} is a
1048 On most RISC machines, which only have operations that operate on a full
1049 register, define this macro to set @var{m} to @code{word_mode} if
1050 @var{m} is an integer mode narrower than @code{BITS_PER_WORD}. In most
1051 cases, only integer modes should be widened because wider-precision
1052 floating-point operations are usually more expensive than their narrower
1055 For most machines, the macro definition does not change @var{unsignedp}.
1056 However, some machines, have instructions that preferentially handle
1057 either signed or unsigned quantities of certain modes. For example, on
1058 the DEC Alpha, 32-bit loads from memory and 32-bit add instructions
1059 sign-extend the result to 64 bits. On such machines, set
1060 @var{unsignedp} according to which kind of extension is more efficient.
1062 Do not define this macro if it would never modify @var{m}.
1065 @defmac PROMOTE_FUNCTION_ARGS
1066 Define this macro if the promotion described by @code{PROMOTE_MODE}
1067 should also be done for outgoing function arguments.
1070 @defmac PROMOTE_FUNCTION_RETURN
1071 Define this macro if the promotion described by @code{PROMOTE_MODE}
1072 should also be done for the return value of functions.
1074 If this macro is defined, @code{FUNCTION_VALUE} must perform the same
1075 promotions done by @code{PROMOTE_MODE}.
1078 @defmac PROMOTE_FOR_CALL_ONLY
1079 Define this macro if the promotion described by @code{PROMOTE_MODE}
1080 should @emph{only} be performed for outgoing function arguments or
1081 function return values, as specified by @code{PROMOTE_FUNCTION_ARGS}
1082 and @code{PROMOTE_FUNCTION_RETURN}, respectively.
1085 @defmac PARM_BOUNDARY
1086 Normal alignment required for function parameters on the stack, in
1087 bits. All stack parameters receive at least this much alignment
1088 regardless of data type. On most machines, this is the same as the
1092 @defmac STACK_BOUNDARY
1093 Define this macro to the minimum alignment enforced by hardware for the
1094 stack pointer on this machine. The definition is a C expression for the
1095 desired alignment (measured in bits). This value is used as a default
1096 if @code{PREFERRED_STACK_BOUNDARY} is not defined. On most machines,
1097 this should be the same as @code{PARM_BOUNDARY}.
1100 @defmac PREFERRED_STACK_BOUNDARY
1101 Define this macro if you wish to preserve a certain alignment for the
1102 stack pointer, greater than what the hardware enforces. The definition
1103 is a C expression for the desired alignment (measured in bits). This
1104 macro must evaluate to a value equal to or larger than
1105 @code{STACK_BOUNDARY}.
1108 @defmac FORCE_PREFERRED_STACK_BOUNDARY_IN_MAIN
1109 A C expression that evaluates true if @code{PREFERRED_STACK_BOUNDARY} is
1110 not guaranteed by the runtime and we should emit code to align the stack
1111 at the beginning of @code{main}.
1113 @cindex @code{PUSH_ROUNDING}, interaction with @code{PREFERRED_STACK_BOUNDARY}
1114 If @code{PUSH_ROUNDING} is not defined, the stack will always be aligned
1115 to the specified boundary. If @code{PUSH_ROUNDING} is defined and specifies
1116 a less strict alignment than @code{PREFERRED_STACK_BOUNDARY}, the stack may
1117 be momentarily unaligned while pushing arguments.
1120 @defmac FUNCTION_BOUNDARY
1121 Alignment required for a function entry point, in bits.
1124 @defmac BIGGEST_ALIGNMENT
1125 Biggest alignment that any data type can require on this machine, in bits.
1128 @defmac MINIMUM_ATOMIC_ALIGNMENT
1129 If defined, the smallest alignment, in bits, that can be given to an
1130 object that can be referenced in one operation, without disturbing any
1131 nearby object. Normally, this is @code{BITS_PER_UNIT}, but may be larger
1132 on machines that don't have byte or half-word store operations.
1135 @defmac BIGGEST_FIELD_ALIGNMENT
1136 Biggest alignment that any structure or union field can require on this
1137 machine, in bits. If defined, this overrides @code{BIGGEST_ALIGNMENT} for
1138 structure and union fields only, unless the field alignment has been set
1139 by the @code{__attribute__ ((aligned (@var{n})))} construct.
1142 @defmac ADJUST_FIELD_ALIGN (@var{field}, @var{computed})
1143 An expression for the alignment of a structure field @var{field} if the
1144 alignment computed in the usual way (including applying of
1145 @code{BIGGEST_ALIGNMENT} and @code{BIGGEST_FIELD_ALIGNMENT} to the
1146 alignment) is @var{computed}. It overrides alignment only if the
1147 field alignment has not been set by the
1148 @code{__attribute__ ((aligned (@var{n})))} construct.
1151 @defmac MAX_OFILE_ALIGNMENT
1152 Biggest alignment supported by the object file format of this machine.
1153 Use this macro to limit the alignment which can be specified using the
1154 @code{__attribute__ ((aligned (@var{n})))} construct. If not defined,
1155 the default value is @code{BIGGEST_ALIGNMENT}.
1158 @defmac DATA_ALIGNMENT (@var{type}, @var{basic-align})
1159 If defined, a C expression to compute the alignment for a variable in
1160 the static store. @var{type} is the data type, and @var{basic-align} is
1161 the alignment that the object would ordinarily have. The value of this
1162 macro is used instead of that alignment to align the object.
1164 If this macro is not defined, then @var{basic-align} is used.
1167 One use of this macro is to increase alignment of medium-size data to
1168 make it all fit in fewer cache lines. Another is to cause character
1169 arrays to be word-aligned so that @code{strcpy} calls that copy
1170 constants to character arrays can be done inline.
1173 @defmac CONSTANT_ALIGNMENT (@var{constant}, @var{basic-align})
1174 If defined, a C expression to compute the alignment given to a constant
1175 that is being placed in memory. @var{constant} is the constant and
1176 @var{basic-align} is the alignment that the object would ordinarily
1177 have. The value of this macro is used instead of that alignment to
1180 If this macro is not defined, then @var{basic-align} is used.
1182 The typical use of this macro is to increase alignment for string
1183 constants to be word aligned so that @code{strcpy} calls that copy
1184 constants can be done inline.
1187 @defmac LOCAL_ALIGNMENT (@var{type}, @var{basic-align})
1188 If defined, a C expression to compute the alignment for a variable in
1189 the local store. @var{type} is the data type, and @var{basic-align} is
1190 the alignment that the object would ordinarily have. The value of this
1191 macro is used instead of that alignment to align the object.
1193 If this macro is not defined, then @var{basic-align} is used.
1195 One use of this macro is to increase alignment of medium-size data to
1196 make it all fit in fewer cache lines.
1199 @defmac EMPTY_FIELD_BOUNDARY
1200 Alignment in bits to be given to a structure bit-field that follows an
1201 empty field such as @code{int : 0;}.
1203 If @code{PCC_BITFIELD_TYPE_MATTERS} is true, it overrides this macro.
1206 @defmac STRUCTURE_SIZE_BOUNDARY
1207 Number of bits which any structure or union's size must be a multiple of.
1208 Each structure or union's size is rounded up to a multiple of this.
1210 If you do not define this macro, the default is the same as
1211 @code{BITS_PER_UNIT}.
1214 @defmac STRICT_ALIGNMENT
1215 Define this macro to be the value 1 if instructions will fail to work
1216 if given data not on the nominal alignment. If instructions will merely
1217 go slower in that case, define this macro as 0.
1220 @defmac PCC_BITFIELD_TYPE_MATTERS
1221 Define this if you wish to imitate the way many other C compilers handle
1222 alignment of bit-fields and the structures that contain them.
1224 The behavior is that the type written for a named bit-field (@code{int},
1225 @code{short}, or other integer type) imposes an alignment for the entire
1226 structure, as if the structure really did contain an ordinary field of
1227 that type. In addition, the bit-field is placed within the structure so
1228 that it would fit within such a field, not crossing a boundary for it.
1230 Thus, on most machines, a named bit-field whose type is written as
1231 @code{int} would not cross a four-byte boundary, and would force
1232 four-byte alignment for the whole structure. (The alignment used may
1233 not be four bytes; it is controlled by the other alignment parameters.)
1235 An unnamed bit-field will not affect the alignment of the containing
1238 If the macro is defined, its definition should be a C expression;
1239 a nonzero value for the expression enables this behavior.
1241 Note that if this macro is not defined, or its value is zero, some
1242 bit-fields may cross more than one alignment boundary. The compiler can
1243 support such references if there are @samp{insv}, @samp{extv}, and
1244 @samp{extzv} insns that can directly reference memory.
1246 The other known way of making bit-fields work is to define
1247 @code{STRUCTURE_SIZE_BOUNDARY} as large as @code{BIGGEST_ALIGNMENT}.
1248 Then every structure can be accessed with fullwords.
1250 Unless the machine has bit-field instructions or you define
1251 @code{STRUCTURE_SIZE_BOUNDARY} that way, you must define
1252 @code{PCC_BITFIELD_TYPE_MATTERS} to have a nonzero value.
1254 If your aim is to make GCC use the same conventions for laying out
1255 bit-fields as are used by another compiler, here is how to investigate
1256 what the other compiler does. Compile and run this program:
1275 printf ("Size of foo1 is %d\n",
1276 sizeof (struct foo1));
1277 printf ("Size of foo2 is %d\n",
1278 sizeof (struct foo2));
1283 If this prints 2 and 5, then the compiler's behavior is what you would
1284 get from @code{PCC_BITFIELD_TYPE_MATTERS}.
1287 @defmac BITFIELD_NBYTES_LIMITED
1288 Like @code{PCC_BITFIELD_TYPE_MATTERS} except that its effect is limited
1289 to aligning a bit-field within the structure.
1292 @defmac MEMBER_TYPE_FORCES_BLK (@var{field}, @var{mode})
1293 Return 1 if a structure or array containing @var{field} should be accessed using
1296 If @var{field} is the only field in the structure, @var{mode} is its
1297 mode, otherwise @var{mode} is VOIDmode. @var{mode} is provided in the
1298 case where structures of one field would require the structure's mode to
1299 retain the field's mode.
1301 Normally, this is not needed. See the file @file{c4x.h} for an example
1302 of how to use this macro to prevent a structure having a floating point
1303 field from being accessed in an integer mode.
1306 @defmac ROUND_TYPE_ALIGN (@var{type}, @var{computed}, @var{specified})
1307 Define this macro as an expression for the alignment of a type (given
1308 by @var{type} as a tree node) if the alignment computed in the usual
1309 way is @var{computed} and the alignment explicitly specified was
1312 The default is to use @var{specified} if it is larger; otherwise, use
1313 the smaller of @var{computed} and @code{BIGGEST_ALIGNMENT}
1316 @defmac MAX_FIXED_MODE_SIZE
1317 An integer expression for the size in bits of the largest integer
1318 machine mode that should actually be used. All integer machine modes of
1319 this size or smaller can be used for structures and unions with the
1320 appropriate sizes. If this macro is undefined, @code{GET_MODE_BITSIZE
1321 (DImode)} is assumed.
1324 @defmac VECTOR_MODE_SUPPORTED_P (@var{mode})
1325 Define this macro to be nonzero if the port is prepared to handle insns
1326 involving vector mode @var{mode}. At the very least, it must have move
1327 patterns for this mode.
1330 @defmac STACK_SAVEAREA_MODE (@var{save_level})
1331 If defined, an expression of type @code{enum machine_mode} that
1332 specifies the mode of the save area operand of a
1333 @code{save_stack_@var{level}} named pattern (@pxref{Standard Names}).
1334 @var{save_level} is one of @code{SAVE_BLOCK}, @code{SAVE_FUNCTION}, or
1335 @code{SAVE_NONLOCAL} and selects which of the three named patterns is
1336 having its mode specified.
1338 You need not define this macro if it always returns @code{Pmode}. You
1339 would most commonly define this macro if the
1340 @code{save_stack_@var{level}} patterns need to support both a 32- and a
1344 @defmac STACK_SIZE_MODE
1345 If defined, an expression of type @code{enum machine_mode} that
1346 specifies the mode of the size increment operand of an
1347 @code{allocate_stack} named pattern (@pxref{Standard Names}).
1349 You need not define this macro if it always returns @code{word_mode}.
1350 You would most commonly define this macro if the @code{allocate_stack}
1351 pattern needs to support both a 32- and a 64-bit mode.
1354 @defmac TARGET_FLOAT_FORMAT
1355 A code distinguishing the floating point format of the target machine.
1356 There are four defined values:
1359 @item IEEE_FLOAT_FORMAT
1360 This code indicates IEEE floating point. It is the default; there is no
1361 need to define @code{TARGET_FLOAT_FORMAT} when the format is IEEE@.
1363 @item VAX_FLOAT_FORMAT
1364 This code indicates the ``F float'' (for @code{float}) and ``D float''
1365 or ``G float'' formats (for @code{double}) used on the VAX and PDP-11@.
1367 @item IBM_FLOAT_FORMAT
1368 This code indicates the format used on the IBM System/370.
1370 @item C4X_FLOAT_FORMAT
1371 This code indicates the format used on the TMS320C3x/C4x.
1374 If your target uses a floating point format other than these, you must
1375 define a new @var{name}_FLOAT_FORMAT code for it, and add support for
1376 it to @file{real.c}.
1378 The ordering of the component words of floating point values stored in
1379 memory is controlled by @code{FLOAT_WORDS_BIG_ENDIAN}.
1382 @defmac MODE_HAS_NANS (@var{mode})
1383 When defined, this macro should be true if @var{mode} has a NaN
1384 representation. The compiler assumes that NaNs are not equal to
1385 anything (including themselves) and that addition, subtraction,
1386 multiplication and division all return NaNs when one operand is
1389 By default, this macro is true if @var{mode} is a floating-point
1390 mode and the target floating-point format is IEEE@.
1393 @defmac MODE_HAS_INFINITIES (@var{mode})
1394 This macro should be true if @var{mode} can represent infinity. At
1395 present, the compiler uses this macro to decide whether @samp{x - x}
1396 is always defined. By default, the macro is true when @var{mode}
1397 is a floating-point mode and the target format is IEEE@.
1400 @defmac MODE_HAS_SIGNED_ZEROS (@var{mode})
1401 True if @var{mode} distinguishes between positive and negative zero.
1402 The rules are expected to follow the IEEE standard:
1406 @samp{x + x} has the same sign as @samp{x}.
1409 If the sum of two values with opposite sign is zero, the result is
1410 positive for all rounding modes expect towards @minus{}infinity, for
1411 which it is negative.
1414 The sign of a product or quotient is negative when exactly one
1415 of the operands is negative.
1418 The default definition is true if @var{mode} is a floating-point
1419 mode and the target format is IEEE@.
1422 @defmac MODE_HAS_SIGN_DEPENDENT_ROUNDING (@var{mode})
1423 If defined, this macro should be true for @var{mode} if it has at
1424 least one rounding mode in which @samp{x} and @samp{-x} can be
1425 rounded to numbers of different magnitude. Two such modes are
1426 towards @minus{}infinity and towards +infinity.
1428 The default definition of this macro is true if @var{mode} is
1429 a floating-point mode and the target format is IEEE@.
1432 @defmac ROUND_TOWARDS_ZERO
1433 If defined, this macro should be true if the prevailing rounding
1434 mode is towards zero. A true value has the following effects:
1438 @code{MODE_HAS_SIGN_DEPENDENT_ROUNDING} will be false for all modes.
1441 @file{libgcc.a}'s floating-point emulator will round towards zero
1442 rather than towards nearest.
1445 The compiler's floating-point emulator will round towards zero after
1446 doing arithmetic, and when converting from the internal float format to
1450 The macro does not affect the parsing of string literals. When the
1451 primary rounding mode is towards zero, library functions like
1452 @code{strtod} might still round towards nearest, and the compiler's
1453 parser should behave like the target's @code{strtod} where possible.
1455 Not defining this macro is equivalent to returning zero.
1458 @defmac LARGEST_EXPONENT_IS_NORMAL (@var{size})
1459 This macro should return true if floats with @var{size}
1460 bits do not have a NaN or infinity representation, but use the largest
1461 exponent for normal numbers instead.
1463 Defining this macro to true for @var{size} causes @code{MODE_HAS_NANS}
1464 and @code{MODE_HAS_INFINITIES} to be false for @var{size}-bit modes.
1465 It also affects the way @file{libgcc.a} and @file{real.c} emulate
1466 floating-point arithmetic.
1468 The default definition of this macro returns false for all sizes.
1471 @deftypefn {Target Hook} bool TARGET_VECTOR_OPAQUE_P (tree @var{type})
1472 This target hook should return @code{true} a vector is opaque. That
1473 is, if no cast is needed when copying a vector value of type
1474 @var{type} into another vector lvalue of the same size. Vector opaque
1475 types cannot be initialized. The default is that there are no such
1479 @deftypefn {Target Hook} bool TARGET_MS_BITFIELD_LAYOUT_P (tree @var{record_type})
1480 This target hook returns @code{true} if bit-fields in the given
1481 @var{record_type} are to be laid out following the rules of Microsoft
1482 Visual C/C++, namely: (i) a bit-field won't share the same storage
1483 unit with the previous bit-field if their underlying types have
1484 different sizes, and the bit-field will be aligned to the highest
1485 alignment of the underlying types of itself and of the previous
1486 bit-field; (ii) a zero-sized bit-field will affect the alignment of
1487 the whole enclosing structure, even if it is unnamed; except that
1488 (iii) a zero-sized bit-field will be disregarded unless it follows
1489 another bit-field of nonzero size. If this hook returns @code{true},
1490 other macros that control bit-field layout are ignored.
1492 When a bit-field is inserted into a packed record, the whole size
1493 of the underlying type is used by one or more same-size adjacent
1494 bit-fields (that is, if its long:3, 32 bits is used in the record,
1495 and any additional adjacent long bit-fields are packed into the same
1496 chunk of 32 bits. However, if the size changes, a new field of that
1497 size is allocated). In an unpacked record, this is the same as using
1498 alignment, but not equivalent when packing.
1500 If both MS bit-fields and @samp{__attribute__((packed))} are used,
1501 the latter will take precedence. If @samp{__attribute__((packed))} is
1502 used on a single field when MS bit-fields are in use, it will take
1503 precedence for that field, but the alignment of the rest of the structure
1504 may affect its placement.
1508 @section Layout of Source Language Data Types
1510 These macros define the sizes and other characteristics of the standard
1511 basic data types used in programs being compiled. Unlike the macros in
1512 the previous section, these apply to specific features of C and related
1513 languages, rather than to fundamental aspects of storage layout.
1515 @defmac INT_TYPE_SIZE
1516 A C expression for the size in bits of the type @code{int} on the
1517 target machine. If you don't define this, the default is one word.
1520 @defmac SHORT_TYPE_SIZE
1521 A C expression for the size in bits of the type @code{short} on the
1522 target machine. If you don't define this, the default is half a word.
1523 (If this would be less than one storage unit, it is rounded up to one
1527 @defmac LONG_TYPE_SIZE
1528 A C expression for the size in bits of the type @code{long} on the
1529 target machine. If you don't define this, the default is one word.
1532 @defmac ADA_LONG_TYPE_SIZE
1533 On some machines, the size used for the Ada equivalent of the type
1534 @code{long} by a native Ada compiler differs from that used by C. In
1535 that situation, define this macro to be a C expression to be used for
1536 the size of that type. If you don't define this, the default is the
1537 value of @code{LONG_TYPE_SIZE}.
1540 @defmac MAX_LONG_TYPE_SIZE
1541 Maximum number for the size in bits of the type @code{long} on the
1542 target machine. If this is undefined, the default is
1543 @code{LONG_TYPE_SIZE}. Otherwise, it is the constant value that is the
1544 largest value that @code{LONG_TYPE_SIZE} can have at run-time. This is
1548 @defmac LONG_LONG_TYPE_SIZE
1549 A C expression for the size in bits of the type @code{long long} on the
1550 target machine. If you don't define this, the default is two
1551 words. If you want to support GNU Ada on your machine, the value of this
1552 macro must be at least 64.
1555 @defmac CHAR_TYPE_SIZE
1556 A C expression for the size in bits of the type @code{char} on the
1557 target machine. If you don't define this, the default is
1558 @code{BITS_PER_UNIT}.
1561 @defmac BOOL_TYPE_SIZE
1562 A C expression for the size in bits of the C++ type @code{bool} and
1563 C99 type @code{_Bool} on the target machine. If you don't define
1564 this, and you probably shouldn't, the default is @code{CHAR_TYPE_SIZE}.
1567 @defmac FLOAT_TYPE_SIZE
1568 A C expression for the size in bits of the type @code{float} on the
1569 target machine. If you don't define this, the default is one word.
1572 @defmac DOUBLE_TYPE_SIZE
1573 A C expression for the size in bits of the type @code{double} on the
1574 target machine. If you don't define this, the default is two
1578 @defmac LONG_DOUBLE_TYPE_SIZE
1579 A C expression for the size in bits of the type @code{long double} on
1580 the target machine. If you don't define this, the default is two
1584 @defmac MAX_LONG_DOUBLE_TYPE_SIZE
1585 Maximum number for the size in bits of the type @code{long double} on the
1586 target machine. If this is undefined, the default is
1587 @code{LONG_DOUBLE_TYPE_SIZE}. Otherwise, it is the constant value that is
1588 the largest value that @code{LONG_DOUBLE_TYPE_SIZE} can have at run-time.
1589 This is used in @code{cpp}.
1592 @defmac TARGET_FLT_EVAL_METHOD
1593 A C expression for the value for @code{FLT_EVAL_METHOD} in @file{float.h},
1594 assuming, if applicable, that the floating-point control word is in its
1595 default state. If you do not define this macro the value of
1596 @code{FLT_EVAL_METHOD} will be zero.
1599 @defmac WIDEST_HARDWARE_FP_SIZE
1600 A C expression for the size in bits of the widest floating-point format
1601 supported by the hardware. If you define this macro, you must specify a
1602 value less than or equal to the value of @code{LONG_DOUBLE_TYPE_SIZE}.
1603 If you do not define this macro, the value of @code{LONG_DOUBLE_TYPE_SIZE}
1607 @defmac DEFAULT_SIGNED_CHAR
1608 An expression whose value is 1 or 0, according to whether the type
1609 @code{char} should be signed or unsigned by default. The user can
1610 always override this default with the options @option{-fsigned-char}
1611 and @option{-funsigned-char}.
1614 @defmac DEFAULT_SHORT_ENUMS
1615 A C expression to determine whether to give an @code{enum} type
1616 only as many bytes as it takes to represent the range of possible values
1617 of that type. A nonzero value means to do that; a zero value means all
1618 @code{enum} types should be allocated like @code{int}.
1620 If you don't define the macro, the default is 0.
1624 A C expression for a string describing the name of the data type to use
1625 for size values. The typedef name @code{size_t} is defined using the
1626 contents of the string.
1628 The string can contain more than one keyword. If so, separate them with
1629 spaces, and write first any length keyword, then @code{unsigned} if
1630 appropriate, and finally @code{int}. The string must exactly match one
1631 of the data type names defined in the function
1632 @code{init_decl_processing} in the file @file{c-decl.c}. You may not
1633 omit @code{int} or change the order---that would cause the compiler to
1636 If you don't define this macro, the default is @code{"long unsigned
1640 @defmac PTRDIFF_TYPE
1641 A C expression for a string describing the name of the data type to use
1642 for the result of subtracting two pointers. The typedef name
1643 @code{ptrdiff_t} is defined using the contents of the string. See
1644 @code{SIZE_TYPE} above for more information.
1646 If you don't define this macro, the default is @code{"long int"}.
1650 A C expression for a string describing the name of the data type to use
1651 for wide characters. The typedef name @code{wchar_t} is defined using
1652 the contents of the string. See @code{SIZE_TYPE} above for more
1655 If you don't define this macro, the default is @code{"int"}.
1658 @defmac WCHAR_TYPE_SIZE
1659 A C expression for the size in bits of the data type for wide
1660 characters. This is used in @code{cpp}, which cannot make use of
1664 @defmac MAX_WCHAR_TYPE_SIZE
1665 Maximum number for the size in bits of the data type for wide
1666 characters. If this is undefined, the default is
1667 @code{WCHAR_TYPE_SIZE}. Otherwise, it is the constant value that is the
1668 largest value that @code{WCHAR_TYPE_SIZE} can have at run-time. This is
1672 @defmac GCOV_TYPE_SIZE
1673 A C expression for the size in bits of the type used for gcov counters on the
1674 target machine. If you don't define this, the default is one
1675 @code{LONG_TYPE_SIZE} in case it is greater or equal to 64-bit and
1676 @code{LONG_LONG_TYPE_SIZE} otherwise. You may want to re-define the type to
1677 ensure atomicity for counters in multithreaded programs.
1681 A C expression for a string describing the name of the data type to
1682 use for wide characters passed to @code{printf} and returned from
1683 @code{getwc}. The typedef name @code{wint_t} is defined using the
1684 contents of the string. See @code{SIZE_TYPE} above for more
1687 If you don't define this macro, the default is @code{"unsigned int"}.
1691 A C expression for a string describing the name of the data type that
1692 can represent any value of any standard or extended signed integer type.
1693 The typedef name @code{intmax_t} is defined using the contents of the
1694 string. See @code{SIZE_TYPE} above for more information.
1696 If you don't define this macro, the default is the first of
1697 @code{"int"}, @code{"long int"}, or @code{"long long int"} that has as
1698 much precision as @code{long long int}.
1701 @defmac UINTMAX_TYPE
1702 A C expression for a string describing the name of the data type that
1703 can represent any value of any standard or extended unsigned integer
1704 type. The typedef name @code{uintmax_t} is defined using the contents
1705 of the string. See @code{SIZE_TYPE} above for more information.
1707 If you don't define this macro, the default is the first of
1708 @code{"unsigned int"}, @code{"long unsigned int"}, or @code{"long long
1709 unsigned int"} that has as much precision as @code{long long unsigned
1713 @defmac TARGET_PTRMEMFUNC_VBIT_LOCATION
1714 The C++ compiler represents a pointer-to-member-function with a struct
1721 ptrdiff_t vtable_index;
1728 The C++ compiler must use one bit to indicate whether the function that
1729 will be called through a pointer-to-member-function is virtual.
1730 Normally, we assume that the low-order bit of a function pointer must
1731 always be zero. Then, by ensuring that the vtable_index is odd, we can
1732 distinguish which variant of the union is in use. But, on some
1733 platforms function pointers can be odd, and so this doesn't work. In
1734 that case, we use the low-order bit of the @code{delta} field, and shift
1735 the remainder of the @code{delta} field to the left.
1737 GCC will automatically make the right selection about where to store
1738 this bit using the @code{FUNCTION_BOUNDARY} setting for your platform.
1739 However, some platforms such as ARM/Thumb have @code{FUNCTION_BOUNDARY}
1740 set such that functions always start at even addresses, but the lowest
1741 bit of pointers to functions indicate whether the function at that
1742 address is in ARM or Thumb mode. If this is the case of your
1743 architecture, you should define this macro to
1744 @code{ptrmemfunc_vbit_in_delta}.
1746 In general, you should not have to define this macro. On architectures
1747 in which function addresses are always even, according to
1748 @code{FUNCTION_BOUNDARY}, GCC will automatically define this macro to
1749 @code{ptrmemfunc_vbit_in_pfn}.
1752 @defmac TARGET_VTABLE_USES_DESCRIPTORS
1753 Normally, the C++ compiler uses function pointers in vtables. This
1754 macro allows the target to change to use ``function descriptors''
1755 instead. Function descriptors are found on targets for whom a
1756 function pointer is actually a small data structure. Normally the
1757 data structure consists of the actual code address plus a data
1758 pointer to which the function's data is relative.
1760 If vtables are used, the value of this macro should be the number
1761 of words that the function descriptor occupies.
1764 @defmac TARGET_VTABLE_ENTRY_ALIGN
1765 By default, the vtable entries are void pointers, the so the alignment
1766 is the same as pointer alignment. The value of this macro specifies
1767 the alignment of the vtable entry in bits. It should be defined only
1768 when special alignment is necessary. */
1771 @defmac TARGET_VTABLE_DATA_ENTRY_DISTANCE
1772 There are a few non-descriptor entries in the vtable at offsets below
1773 zero. If these entries must be padded (say, to preserve the alignment
1774 specified by @code{TARGET_VTABLE_ENTRY_ALIGN}), set this to the number
1775 of words in each data entry.
1778 @node Escape Sequences
1779 @section Target Character Escape Sequences
1780 @cindex escape sequences
1782 By default, GCC assumes that the C character escape sequences take on
1783 their ASCII values for the target. If this is not correct, you must
1784 explicitly define all of the macros below. All of them must evaluate
1785 to constants; they are used in @code{case} statements.
1791 @findex TARGET_NEWLINE
1794 @multitable {@code{TARGET_NEWLINE}} {Escape} {ASCII character}
1795 @item Macro @tab Escape @tab ASCII character
1796 @item @code{TARGET_BELL} @tab @kbd{\a} @tab @code{07}, @code{BEL}
1797 @item @code{TARGET_CR} @tab @kbd{\r} @tab @code{0D}, @code{CR}
1798 @item @code{TARGET_ESC} @tab @kbd{\e}, @kbd{\E} @tab @code{1B}, @code{ESC}
1799 @item @code{TARGET_FF} @tab @kbd{\f} @tab @code{0C}, @code{FF}
1800 @item @code{TARGET_NEWLINE} @tab @kbd{\n} @tab @code{0A}, @code{LF}
1801 @item @code{TARGET_TAB} @tab @kbd{\t} @tab @code{09}, @code{HT}
1802 @item @code{TARGET_VT} @tab @kbd{\v} @tab @code{0B}, @code{VT}
1806 Note that the @kbd{\e} and @kbd{\E} escapes are GNU extensions, not
1807 part of the C standard.
1810 @section Register Usage
1811 @cindex register usage
1813 This section explains how to describe what registers the target machine
1814 has, and how (in general) they can be used.
1816 The description of which registers a specific instruction can use is
1817 done with register classes; see @ref{Register Classes}. For information
1818 on using registers to access a stack frame, see @ref{Frame Registers}.
1819 For passing values in registers, see @ref{Register Arguments}.
1820 For returning values in registers, see @ref{Scalar Return}.
1823 * Register Basics:: Number and kinds of registers.
1824 * Allocation Order:: Order in which registers are allocated.
1825 * Values in Registers:: What kinds of values each reg can hold.
1826 * Leaf Functions:: Renumbering registers for leaf functions.
1827 * Stack Registers:: Handling a register stack such as 80387.
1830 @node Register Basics
1831 @subsection Basic Characteristics of Registers
1833 @c prevent bad page break with this line
1834 Registers have various characteristics.
1836 @defmac FIRST_PSEUDO_REGISTER
1837 Number of hardware registers known to the compiler. They receive
1838 numbers 0 through @code{FIRST_PSEUDO_REGISTER-1}; thus, the first
1839 pseudo register's number really is assigned the number
1840 @code{FIRST_PSEUDO_REGISTER}.
1843 @defmac FIXED_REGISTERS
1844 @cindex fixed register
1845 An initializer that says which registers are used for fixed purposes
1846 all throughout the compiled code and are therefore not available for
1847 general allocation. These would include the stack pointer, the frame
1848 pointer (except on machines where that can be used as a general
1849 register when no frame pointer is needed), the program counter on
1850 machines where that is considered one of the addressable registers,
1851 and any other numbered register with a standard use.
1853 This information is expressed as a sequence of numbers, separated by
1854 commas and surrounded by braces. The @var{n}th number is 1 if
1855 register @var{n} is fixed, 0 otherwise.
1857 The table initialized from this macro, and the table initialized by
1858 the following one, may be overridden at run time either automatically,
1859 by the actions of the macro @code{CONDITIONAL_REGISTER_USAGE}, or by
1860 the user with the command options @option{-ffixed-@var{reg}},
1861 @option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}}.
1864 @defmac CALL_USED_REGISTERS
1865 @cindex call-used register
1866 @cindex call-clobbered register
1867 @cindex call-saved register
1868 Like @code{FIXED_REGISTERS} but has 1 for each register that is
1869 clobbered (in general) by function calls as well as for fixed
1870 registers. This macro therefore identifies the registers that are not
1871 available for general allocation of values that must live across
1874 If a register has 0 in @code{CALL_USED_REGISTERS}, the compiler
1875 automatically saves it on function entry and restores it on function
1876 exit, if the register is used within the function.
1879 @defmac CALL_REALLY_USED_REGISTERS
1880 @cindex call-used register
1881 @cindex call-clobbered register
1882 @cindex call-saved register
1883 Like @code{CALL_USED_REGISTERS} except this macro doesn't require
1884 that the entire set of @code{FIXED_REGISTERS} be included.
1885 (@code{CALL_USED_REGISTERS} must be a superset of @code{FIXED_REGISTERS}).
1886 This macro is optional. If not specified, it defaults to the value
1887 of @code{CALL_USED_REGISTERS}.
1890 @defmac HARD_REGNO_CALL_PART_CLOBBERED (@var{regno}, @var{mode})
1891 @cindex call-used register
1892 @cindex call-clobbered register
1893 @cindex call-saved register
1894 A C expression that is nonzero if it is not permissible to store a
1895 value of mode @var{mode} in hard register number @var{regno} across a
1896 call without some part of it being clobbered. For most machines this
1897 macro need not be defined. It is only required for machines that do not
1898 preserve the entire contents of a register across a call.
1902 @findex call_used_regs
1905 @findex reg_class_contents
1906 @defmac CONDITIONAL_REGISTER_USAGE
1907 Zero or more C statements that may conditionally modify five variables
1908 @code{fixed_regs}, @code{call_used_regs}, @code{global_regs},
1909 @code{reg_names}, and @code{reg_class_contents}, to take into account
1910 any dependence of these register sets on target flags. The first three
1911 of these are of type @code{char []} (interpreted as Boolean vectors).
1912 @code{global_regs} is a @code{const char *[]}, and
1913 @code{reg_class_contents} is a @code{HARD_REG_SET}. Before the macro is
1914 called, @code{fixed_regs}, @code{call_used_regs},
1915 @code{reg_class_contents}, and @code{reg_names} have been initialized
1916 from @code{FIXED_REGISTERS}, @code{CALL_USED_REGISTERS},
1917 @code{REG_CLASS_CONTENTS}, and @code{REGISTER_NAMES}, respectively.
1918 @code{global_regs} has been cleared, and any @option{-ffixed-@var{reg}},
1919 @option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}}
1920 command options have been applied.
1922 You need not define this macro if it has no work to do.
1924 @cindex disabling certain registers
1925 @cindex controlling register usage
1926 If the usage of an entire class of registers depends on the target
1927 flags, you may indicate this to GCC by using this macro to modify
1928 @code{fixed_regs} and @code{call_used_regs} to 1 for each of the
1929 registers in the classes which should not be used by GCC@. Also define
1930 the macro @code{REG_CLASS_FROM_LETTER} / @code{REG_CLASS_FROM_CONSTRAINT}
1931 to return @code{NO_REGS} if it
1932 is called with a letter for a class that shouldn't be used.
1934 (However, if this class is not included in @code{GENERAL_REGS} and all
1935 of the insn patterns whose constraints permit this class are
1936 controlled by target switches, then GCC will automatically avoid using
1937 these registers when the target switches are opposed to them.)
1940 @defmac NON_SAVING_SETJMP
1941 If this macro is defined and has a nonzero value, it means that
1942 @code{setjmp} and related functions fail to save the registers, or that
1943 @code{longjmp} fails to restore them. To compensate, the compiler
1944 avoids putting variables in registers in functions that use
1948 @defmac INCOMING_REGNO (@var{out})
1949 Define this macro if the target machine has register windows. This C
1950 expression returns the register number as seen by the called function
1951 corresponding to the register number @var{out} as seen by the calling
1952 function. Return @var{out} if register number @var{out} is not an
1956 @defmac OUTGOING_REGNO (@var{in})
1957 Define this macro if the target machine has register windows. This C
1958 expression returns the register number as seen by the calling function
1959 corresponding to the register number @var{in} as seen by the called
1960 function. Return @var{in} if register number @var{in} is not an inbound
1964 @defmac LOCAL_REGNO (@var{regno})
1965 Define this macro if the target machine has register windows. This C
1966 expression returns true if the register is call-saved but is in the
1967 register window. Unlike most call-saved registers, such registers
1968 need not be explicitly restored on function exit or during non-local
1973 If the program counter has a register number, define this as that
1974 register number. Otherwise, do not define it.
1977 @node Allocation Order
1978 @subsection Order of Allocation of Registers
1979 @cindex order of register allocation
1980 @cindex register allocation order
1982 @c prevent bad page break with this line
1983 Registers are allocated in order.
1985 @defmac REG_ALLOC_ORDER
1986 If defined, an initializer for a vector of integers, containing the
1987 numbers of hard registers in the order in which GCC should prefer
1988 to use them (from most preferred to least).
1990 If this macro is not defined, registers are used lowest numbered first
1991 (all else being equal).
1993 One use of this macro is on machines where the highest numbered
1994 registers must always be saved and the save-multiple-registers
1995 instruction supports only sequences of consecutive registers. On such
1996 machines, define @code{REG_ALLOC_ORDER} to be an initializer that lists
1997 the highest numbered allocable register first.
2000 @defmac ORDER_REGS_FOR_LOCAL_ALLOC
2001 A C statement (sans semicolon) to choose the order in which to allocate
2002 hard registers for pseudo-registers local to a basic block.
2004 Store the desired register order in the array @code{reg_alloc_order}.
2005 Element 0 should be the register to allocate first; element 1, the next
2006 register; and so on.
2008 The macro body should not assume anything about the contents of
2009 @code{reg_alloc_order} before execution of the macro.
2011 On most machines, it is not necessary to define this macro.
2014 @node Values in Registers
2015 @subsection How Values Fit in Registers
2017 This section discusses the macros that describe which kinds of values
2018 (specifically, which machine modes) each register can hold, and how many
2019 consecutive registers are needed for a given mode.
2021 @defmac HARD_REGNO_NREGS (@var{regno}, @var{mode})
2022 A C expression for the number of consecutive hard registers, starting
2023 at register number @var{regno}, required to hold a value of mode
2026 On a machine where all registers are exactly one word, a suitable
2027 definition of this macro is
2030 #define HARD_REGNO_NREGS(REGNO, MODE) \
2031 ((GET_MODE_SIZE (MODE) + UNITS_PER_WORD - 1) \
2036 @defmac HARD_REGNO_MODE_OK (@var{regno}, @var{mode})
2037 A C expression that is nonzero if it is permissible to store a value
2038 of mode @var{mode} in hard register number @var{regno} (or in several
2039 registers starting with that one). For a machine where all registers
2040 are equivalent, a suitable definition is
2043 #define HARD_REGNO_MODE_OK(REGNO, MODE) 1
2046 You need not include code to check for the numbers of fixed registers,
2047 because the allocation mechanism considers them to be always occupied.
2049 @cindex register pairs
2050 On some machines, double-precision values must be kept in even/odd
2051 register pairs. You can implement that by defining this macro to reject
2052 odd register numbers for such modes.
2054 The minimum requirement for a mode to be OK in a register is that the
2055 @samp{mov@var{mode}} instruction pattern support moves between the
2056 register and other hard register in the same class and that moving a
2057 value into the register and back out not alter it.
2059 Since the same instruction used to move @code{word_mode} will work for
2060 all narrower integer modes, it is not necessary on any machine for
2061 @code{HARD_REGNO_MODE_OK} to distinguish between these modes, provided
2062 you define patterns @samp{movhi}, etc., to take advantage of this. This
2063 is useful because of the interaction between @code{HARD_REGNO_MODE_OK}
2064 and @code{MODES_TIEABLE_P}; it is very desirable for all integer modes
2067 Many machines have special registers for floating point arithmetic.
2068 Often people assume that floating point machine modes are allowed only
2069 in floating point registers. This is not true. Any registers that
2070 can hold integers can safely @emph{hold} a floating point machine
2071 mode, whether or not floating arithmetic can be done on it in those
2072 registers. Integer move instructions can be used to move the values.
2074 On some machines, though, the converse is true: fixed-point machine
2075 modes may not go in floating registers. This is true if the floating
2076 registers normalize any value stored in them, because storing a
2077 non-floating value there would garble it. In this case,
2078 @code{HARD_REGNO_MODE_OK} should reject fixed-point machine modes in
2079 floating registers. But if the floating registers do not automatically
2080 normalize, if you can store any bit pattern in one and retrieve it
2081 unchanged without a trap, then any machine mode may go in a floating
2082 register, so you can define this macro to say so.
2084 The primary significance of special floating registers is rather that
2085 they are the registers acceptable in floating point arithmetic
2086 instructions. However, this is of no concern to
2087 @code{HARD_REGNO_MODE_OK}. You handle it by writing the proper
2088 constraints for those instructions.
2090 On some machines, the floating registers are especially slow to access,
2091 so that it is better to store a value in a stack frame than in such a
2092 register if floating point arithmetic is not being done. As long as the
2093 floating registers are not in class @code{GENERAL_REGS}, they will not
2094 be used unless some pattern's constraint asks for one.
2097 @defmac MODES_TIEABLE_P (@var{mode1}, @var{mode2})
2098 A C expression that is nonzero if a value of mode
2099 @var{mode1} is accessible in mode @var{mode2} without copying.
2101 If @code{HARD_REGNO_MODE_OK (@var{r}, @var{mode1})} and
2102 @code{HARD_REGNO_MODE_OK (@var{r}, @var{mode2})} are always the same for
2103 any @var{r}, then @code{MODES_TIEABLE_P (@var{mode1}, @var{mode2})}
2104 should be nonzero. If they differ for any @var{r}, you should define
2105 this macro to return zero unless some other mechanism ensures the
2106 accessibility of the value in a narrower mode.
2108 You should define this macro to return nonzero in as many cases as
2109 possible since doing so will allow GCC to perform better register
2113 @defmac AVOID_CCMODE_COPIES
2114 Define this macro if the compiler should avoid copies to/from @code{CCmode}
2115 registers. You should only define this macro if support for copying to/from
2116 @code{CCmode} is incomplete.
2119 @node Leaf Functions
2120 @subsection Handling Leaf Functions
2122 @cindex leaf functions
2123 @cindex functions, leaf
2124 On some machines, a leaf function (i.e., one which makes no calls) can run
2125 more efficiently if it does not make its own register window. Often this
2126 means it is required to receive its arguments in the registers where they
2127 are passed by the caller, instead of the registers where they would
2130 The special treatment for leaf functions generally applies only when
2131 other conditions are met; for example, often they may use only those
2132 registers for its own variables and temporaries. We use the term ``leaf
2133 function'' to mean a function that is suitable for this special
2134 handling, so that functions with no calls are not necessarily ``leaf
2137 GCC assigns register numbers before it knows whether the function is
2138 suitable for leaf function treatment. So it needs to renumber the
2139 registers in order to output a leaf function. The following macros
2142 @defmac LEAF_REGISTERS
2143 Name of a char vector, indexed by hard register number, which
2144 contains 1 for a register that is allowable in a candidate for leaf
2147 If leaf function treatment involves renumbering the registers, then the
2148 registers marked here should be the ones before renumbering---those that
2149 GCC would ordinarily allocate. The registers which will actually be
2150 used in the assembler code, after renumbering, should not be marked with 1
2153 Define this macro only if the target machine offers a way to optimize
2154 the treatment of leaf functions.
2157 @defmac LEAF_REG_REMAP (@var{regno})
2158 A C expression whose value is the register number to which @var{regno}
2159 should be renumbered, when a function is treated as a leaf function.
2161 If @var{regno} is a register number which should not appear in a leaf
2162 function before renumbering, then the expression should yield @minus{}1, which
2163 will cause the compiler to abort.
2165 Define this macro only if the target machine offers a way to optimize the
2166 treatment of leaf functions, and registers need to be renumbered to do
2170 @findex current_function_is_leaf
2171 @findex current_function_uses_only_leaf_regs
2172 @code{TARGET_ASM_FUNCTION_PROLOGUE} and
2173 @code{TARGET_ASM_FUNCTION_EPILOGUE} must usually treat leaf functions
2174 specially. They can test the C variable @code{current_function_is_leaf}
2175 which is nonzero for leaf functions. @code{current_function_is_leaf} is
2176 set prior to local register allocation and is valid for the remaining
2177 compiler passes. They can also test the C variable
2178 @code{current_function_uses_only_leaf_regs} which is nonzero for leaf
2179 functions which only use leaf registers.
2180 @code{current_function_uses_only_leaf_regs} is valid after reload and is
2181 only useful if @code{LEAF_REGISTERS} is defined.
2182 @c changed this to fix overfull. ALSO: why the "it" at the beginning
2183 @c of the next paragraph?! --mew 2feb93
2185 @node Stack Registers
2186 @subsection Registers That Form a Stack
2188 There are special features to handle computers where some of the
2189 ``registers'' form a stack. Stack registers are normally written by
2190 pushing onto the stack, and are numbered relative to the top of the
2193 Currently, GCC can only handle one group of stack-like registers, and
2194 they must be consecutively numbered. Furthermore, the existing
2195 support for stack-like registers is specific to the 80387 floating
2196 point coprocessor. If you have a new architecture that uses
2197 stack-like registers, you will need to do substantial work on
2198 @file{reg-stack.c} and write your machine description to cooperate
2199 with it, as well as defining these macros.
2202 Define this if the machine has any stack-like registers.
2205 @defmac FIRST_STACK_REG
2206 The number of the first stack-like register. This one is the top
2210 @defmac LAST_STACK_REG
2211 The number of the last stack-like register. This one is the bottom of
2215 @node Register Classes
2216 @section Register Classes
2217 @cindex register class definitions
2218 @cindex class definitions, register
2220 On many machines, the numbered registers are not all equivalent.
2221 For example, certain registers may not be allowed for indexed addressing;
2222 certain registers may not be allowed in some instructions. These machine
2223 restrictions are described to the compiler using @dfn{register classes}.
2225 You define a number of register classes, giving each one a name and saying
2226 which of the registers belong to it. Then you can specify register classes
2227 that are allowed as operands to particular instruction patterns.
2231 In general, each register will belong to several classes. In fact, one
2232 class must be named @code{ALL_REGS} and contain all the registers. Another
2233 class must be named @code{NO_REGS} and contain no registers. Often the
2234 union of two classes will be another class; however, this is not required.
2236 @findex GENERAL_REGS
2237 One of the classes must be named @code{GENERAL_REGS}. There is nothing
2238 terribly special about the name, but the operand constraint letters
2239 @samp{r} and @samp{g} specify this class. If @code{GENERAL_REGS} is
2240 the same as @code{ALL_REGS}, just define it as a macro which expands
2243 Order the classes so that if class @var{x} is contained in class @var{y}
2244 then @var{x} has a lower class number than @var{y}.
2246 The way classes other than @code{GENERAL_REGS} are specified in operand
2247 constraints is through machine-dependent operand constraint letters.
2248 You can define such letters to correspond to various classes, then use
2249 them in operand constraints.
2251 You should define a class for the union of two classes whenever some
2252 instruction allows both classes. For example, if an instruction allows
2253 either a floating point (coprocessor) register or a general register for a
2254 certain operand, you should define a class @code{FLOAT_OR_GENERAL_REGS}
2255 which includes both of them. Otherwise you will get suboptimal code.
2257 You must also specify certain redundant information about the register
2258 classes: for each class, which classes contain it and which ones are
2259 contained in it; for each pair of classes, the largest class contained
2262 When a value occupying several consecutive registers is expected in a
2263 certain class, all the registers used must belong to that class.
2264 Therefore, register classes cannot be used to enforce a requirement for
2265 a register pair to start with an even-numbered register. The way to
2266 specify this requirement is with @code{HARD_REGNO_MODE_OK}.
2268 Register classes used for input-operands of bitwise-and or shift
2269 instructions have a special requirement: each such class must have, for
2270 each fixed-point machine mode, a subclass whose registers can transfer that
2271 mode to or from memory. For example, on some machines, the operations for
2272 single-byte values (@code{QImode}) are limited to certain registers. When
2273 this is so, each register class that is used in a bitwise-and or shift
2274 instruction must have a subclass consisting of registers from which
2275 single-byte values can be loaded or stored. This is so that
2276 @code{PREFERRED_RELOAD_CLASS} can always have a possible value to return.
2278 @deftp {Data type} {enum reg_class}
2279 An enumeral type that must be defined with all the register class names
2280 as enumeral values. @code{NO_REGS} must be first. @code{ALL_REGS}
2281 must be the last register class, followed by one more enumeral value,
2282 @code{LIM_REG_CLASSES}, which is not a register class but rather
2283 tells how many classes there are.
2285 Each register class has a number, which is the value of casting
2286 the class name to type @code{int}. The number serves as an index
2287 in many of the tables described below.
2290 @defmac N_REG_CLASSES
2291 The number of distinct register classes, defined as follows:
2294 #define N_REG_CLASSES (int) LIM_REG_CLASSES
2298 @defmac REG_CLASS_NAMES
2299 An initializer containing the names of the register classes as C string
2300 constants. These names are used in writing some of the debugging dumps.
2303 @defmac REG_CLASS_CONTENTS
2304 An initializer containing the contents of the register classes, as integers
2305 which are bit masks. The @var{n}th integer specifies the contents of class
2306 @var{n}. The way the integer @var{mask} is interpreted is that
2307 register @var{r} is in the class if @code{@var{mask} & (1 << @var{r})} is 1.
2309 When the machine has more than 32 registers, an integer does not suffice.
2310 Then the integers are replaced by sub-initializers, braced groupings containing
2311 several integers. Each sub-initializer must be suitable as an initializer
2312 for the type @code{HARD_REG_SET} which is defined in @file{hard-reg-set.h}.
2313 In this situation, the first integer in each sub-initializer corresponds to
2314 registers 0 through 31, the second integer to registers 32 through 63, and
2318 @defmac REGNO_REG_CLASS (@var{regno})
2319 A C expression whose value is a register class containing hard register
2320 @var{regno}. In general there is more than one such class; choose a class
2321 which is @dfn{minimal}, meaning that no smaller class also contains the
2325 @defmac BASE_REG_CLASS
2326 A macro whose definition is the name of the class to which a valid
2327 base register must belong. A base register is one used in an address
2328 which is the register value plus a displacement.
2331 @defmac MODE_BASE_REG_CLASS (@var{mode})
2332 This is a variation of the @code{BASE_REG_CLASS} macro which allows
2333 the selection of a base register in a mode dependent manner. If
2334 @var{mode} is VOIDmode then it should return the same value as
2335 @code{BASE_REG_CLASS}.
2338 @defmac INDEX_REG_CLASS
2339 A macro whose definition is the name of the class to which a valid
2340 index register must belong. An index register is one used in an
2341 address where its value is either multiplied by a scale factor or
2342 added to another register (as well as added to a displacement).
2345 @defmac CONSTRAINT_LEN (@var{char}, @var{str})
2346 For the constraint at the start of @var{str}, which starts with the letter
2347 @var{c}, return the length. This allows you to have register class /
2348 constant / extra constraints that are longer than a single letter;
2349 you don't need to define this macro if you can do with single-letter
2350 constraints only. The definition of this macro should use
2351 DEFAULT_CONSTRAINT_LEN for all the characters that you don't want
2352 to handle specially.
2353 There are some sanity checks in genoutput.c that check the constraint lengths
2354 for the md file, so you can also use this macro to help you while you are
2355 transitioning from a byzantine single-letter-constraint scheme: when you
2356 return a negative length for a constraint you want to re-use, genoutput
2357 will complain about every instance where it is used in the md file.
2360 @defmac REG_CLASS_FROM_LETTER (@var{char})
2361 A C expression which defines the machine-dependent operand constraint
2362 letters for register classes. If @var{char} is such a letter, the
2363 value should be the register class corresponding to it. Otherwise,
2364 the value should be @code{NO_REGS}. The register letter @samp{r},
2365 corresponding to class @code{GENERAL_REGS}, will not be passed
2366 to this macro; you do not need to handle it.
2369 @defmac REG_CLASS_FROM_CONSTRAINT (@var{char}, @var{str})
2370 Like @code{REG_CLASS_FROM_LETTER}, but you also get the constraint string
2371 passed in @var{str}, so that you can use suffixes to distinguish between
2375 @defmac REGNO_OK_FOR_BASE_P (@var{num})
2376 A C expression which is nonzero if register number @var{num} is
2377 suitable for use as a base register in operand addresses. It may be
2378 either a suitable hard register or a pseudo register that has been
2379 allocated such a hard register.
2382 @defmac REGNO_MODE_OK_FOR_BASE_P (@var{num}, @var{mode})
2383 A C expression that is just like @code{REGNO_OK_FOR_BASE_P}, except that
2384 that expression may examine the mode of the memory reference in
2385 @var{mode}. You should define this macro if the mode of the memory
2386 reference affects whether a register may be used as a base register. If
2387 you define this macro, the compiler will use it instead of
2388 @code{REGNO_OK_FOR_BASE_P}.
2391 @defmac REGNO_OK_FOR_INDEX_P (@var{num})
2392 A C expression which is nonzero if register number @var{num} is
2393 suitable for use as an index register in operand addresses. It may be
2394 either a suitable hard register or a pseudo register that has been
2395 allocated such a hard register.
2397 The difference between an index register and a base register is that
2398 the index register may be scaled. If an address involves the sum of
2399 two registers, neither one of them scaled, then either one may be
2400 labeled the ``base'' and the other the ``index''; but whichever
2401 labeling is used must fit the machine's constraints of which registers
2402 may serve in each capacity. The compiler will try both labelings,
2403 looking for one that is valid, and will reload one or both registers
2404 only if neither labeling works.
2407 @defmac PREFERRED_RELOAD_CLASS (@var{x}, @var{class})
2408 A C expression that places additional restrictions on the register class
2409 to use when it is necessary to copy value @var{x} into a register in class
2410 @var{class}. The value is a register class; perhaps @var{class}, or perhaps
2411 another, smaller class. On many machines, the following definition is
2415 #define PREFERRED_RELOAD_CLASS(X,CLASS) CLASS
2418 Sometimes returning a more restrictive class makes better code. For
2419 example, on the 68000, when @var{x} is an integer constant that is in range
2420 for a @samp{moveq} instruction, the value of this macro is always
2421 @code{DATA_REGS} as long as @var{class} includes the data registers.
2422 Requiring a data register guarantees that a @samp{moveq} will be used.
2424 If @var{x} is a @code{const_double}, by returning @code{NO_REGS}
2425 you can force @var{x} into a memory constant. This is useful on
2426 certain machines where immediate floating values cannot be loaded into
2427 certain kinds of registers.
2430 @defmac PREFERRED_OUTPUT_RELOAD_CLASS (@var{x}, @var{class})
2431 Like @code{PREFERRED_RELOAD_CLASS}, but for output reloads instead of
2432 input reloads. If you don't define this macro, the default is to use
2433 @var{class}, unchanged.
2436 @defmac LIMIT_RELOAD_CLASS (@var{mode}, @var{class})
2437 A C expression that places additional restrictions on the register class
2438 to use when it is necessary to be able to hold a value of mode
2439 @var{mode} in a reload register for which class @var{class} would
2442 Unlike @code{PREFERRED_RELOAD_CLASS}, this macro should be used when
2443 there are certain modes that simply can't go in certain reload classes.
2445 The value is a register class; perhaps @var{class}, or perhaps another,
2448 Don't define this macro unless the target machine has limitations which
2449 require the macro to do something nontrivial.
2452 @defmac SECONDARY_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
2453 @defmacx SECONDARY_INPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
2454 @defmacx SECONDARY_OUTPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
2455 Many machines have some registers that cannot be copied directly to or
2456 from memory or even from other types of registers. An example is the
2457 @samp{MQ} register, which on most machines, can only be copied to or
2458 from general registers, but not memory. Some machines allow copying all
2459 registers to and from memory, but require a scratch register for stores
2460 to some memory locations (e.g., those with symbolic address on the RT,
2461 and those with certain symbolic address on the SPARC when compiling
2462 PIC)@. In some cases, both an intermediate and a scratch register are
2465 You should define these macros to indicate to the reload phase that it may
2466 need to allocate at least one register for a reload in addition to the
2467 register to contain the data. Specifically, if copying @var{x} to a
2468 register @var{class} in @var{mode} requires an intermediate register,
2469 you should define @code{SECONDARY_INPUT_RELOAD_CLASS} to return the
2470 largest register class all of whose registers can be used as
2471 intermediate registers or scratch registers.
2473 If copying a register @var{class} in @var{mode} to @var{x} requires an
2474 intermediate or scratch register, @code{SECONDARY_OUTPUT_RELOAD_CLASS}
2475 should be defined to return the largest register class required. If the
2476 requirements for input and output reloads are the same, the macro
2477 @code{SECONDARY_RELOAD_CLASS} should be used instead of defining both
2480 The values returned by these macros are often @code{GENERAL_REGS}.
2481 Return @code{NO_REGS} if no spare register is needed; i.e., if @var{x}
2482 can be directly copied to or from a register of @var{class} in
2483 @var{mode} without requiring a scratch register. Do not define this
2484 macro if it would always return @code{NO_REGS}.
2486 If a scratch register is required (either with or without an
2487 intermediate register), you should define patterns for
2488 @samp{reload_in@var{m}} or @samp{reload_out@var{m}}, as required
2489 (@pxref{Standard Names}. These patterns, which will normally be
2490 implemented with a @code{define_expand}, should be similar to the
2491 @samp{mov@var{m}} patterns, except that operand 2 is the scratch
2494 Define constraints for the reload register and scratch register that
2495 contain a single register class. If the original reload register (whose
2496 class is @var{class}) can meet the constraint given in the pattern, the
2497 value returned by these macros is used for the class of the scratch
2498 register. Otherwise, two additional reload registers are required.
2499 Their classes are obtained from the constraints in the insn pattern.
2501 @var{x} might be a pseudo-register or a @code{subreg} of a
2502 pseudo-register, which could either be in a hard register or in memory.
2503 Use @code{true_regnum} to find out; it will return @minus{}1 if the pseudo is
2504 in memory and the hard register number if it is in a register.
2506 These macros should not be used in the case where a particular class of
2507 registers can only be copied to memory and not to another class of
2508 registers. In that case, secondary reload registers are not needed and
2509 would not be helpful. Instead, a stack location must be used to perform
2510 the copy and the @code{mov@var{m}} pattern should use memory as an
2511 intermediate storage. This case often occurs between floating-point and
2515 @defmac SECONDARY_MEMORY_NEEDED (@var{class1}, @var{class2}, @var{m})
2516 Certain machines have the property that some registers cannot be copied
2517 to some other registers without using memory. Define this macro on
2518 those machines to be a C expression that is nonzero if objects of mode
2519 @var{m} in registers of @var{class1} can only be copied to registers of
2520 class @var{class2} by storing a register of @var{class1} into memory
2521 and loading that memory location into a register of @var{class2}.
2523 Do not define this macro if its value would always be zero.
2526 @defmac SECONDARY_MEMORY_NEEDED_RTX (@var{mode})
2527 Normally when @code{SECONDARY_MEMORY_NEEDED} is defined, the compiler
2528 allocates a stack slot for a memory location needed for register copies.
2529 If this macro is defined, the compiler instead uses the memory location
2530 defined by this macro.
2532 Do not define this macro if you do not define
2533 @code{SECONDARY_MEMORY_NEEDED}.
2536 @defmac SECONDARY_MEMORY_NEEDED_MODE (@var{mode})
2537 When the compiler needs a secondary memory location to copy between two
2538 registers of mode @var{mode}, it normally allocates sufficient memory to
2539 hold a quantity of @code{BITS_PER_WORD} bits and performs the store and
2540 load operations in a mode that many bits wide and whose class is the
2541 same as that of @var{mode}.
2543 This is right thing to do on most machines because it ensures that all
2544 bits of the register are copied and prevents accesses to the registers
2545 in a narrower mode, which some machines prohibit for floating-point
2548 However, this default behavior is not correct on some machines, such as
2549 the DEC Alpha, that store short integers in floating-point registers
2550 differently than in integer registers. On those machines, the default
2551 widening will not work correctly and you must define this macro to
2552 suppress that widening in some cases. See the file @file{alpha.h} for
2555 Do not define this macro if you do not define
2556 @code{SECONDARY_MEMORY_NEEDED} or if widening @var{mode} to a mode that
2557 is @code{BITS_PER_WORD} bits wide is correct for your machine.
2560 @defmac SMALL_REGISTER_CLASSES
2561 On some machines, it is risky to let hard registers live across arbitrary
2562 insns. Typically, these machines have instructions that require values
2563 to be in specific registers (like an accumulator), and reload will fail
2564 if the required hard register is used for another purpose across such an
2567 Define @code{SMALL_REGISTER_CLASSES} to be an expression with a nonzero
2568 value on these machines. When this macro has a nonzero value, the
2569 compiler will try to minimize the lifetime of hard registers.
2571 It is always safe to define this macro with a nonzero value, but if you
2572 unnecessarily define it, you will reduce the amount of optimizations
2573 that can be performed in some cases. If you do not define this macro
2574 with a nonzero value when it is required, the compiler will run out of
2575 spill registers and print a fatal error message. For most machines, you
2576 should not define this macro at all.
2579 @defmac CLASS_LIKELY_SPILLED_P (@var{class})
2580 A C expression whose value is nonzero if pseudos that have been assigned
2581 to registers of class @var{class} would likely be spilled because
2582 registers of @var{class} are needed for spill registers.
2584 The default value of this macro returns 1 if @var{class} has exactly one
2585 register and zero otherwise. On most machines, this default should be
2586 used. Only define this macro to some other expression if pseudos
2587 allocated by @file{local-alloc.c} end up in memory because their hard
2588 registers were needed for spill registers. If this macro returns nonzero
2589 for those classes, those pseudos will only be allocated by
2590 @file{global.c}, which knows how to reallocate the pseudo to another
2591 register. If there would not be another register available for
2592 reallocation, you should not change the definition of this macro since
2593 the only effect of such a definition would be to slow down register
2597 @defmac CLASS_MAX_NREGS (@var{class}, @var{mode})
2598 A C expression for the maximum number of consecutive registers
2599 of class @var{class} needed to hold a value of mode @var{mode}.
2601 This is closely related to the macro @code{HARD_REGNO_NREGS}. In fact,
2602 the value of the macro @code{CLASS_MAX_NREGS (@var{class}, @var{mode})}
2603 should be the maximum value of @code{HARD_REGNO_NREGS (@var{regno},
2604 @var{mode})} for all @var{regno} values in the class @var{class}.
2606 This macro helps control the handling of multiple-word values
2610 @defmac CANNOT_CHANGE_MODE_CLASS (@var{from}, @var{to}, @var{class})
2611 If defined, a C expression that returns nonzero for a @var{class} for which
2612 a change from mode @var{from} to mode @var{to} is invalid.
2614 For the example, loading 32-bit integer or floating-point objects into
2615 floating-point registers on the Alpha extends them to 64 bits.
2616 Therefore loading a 64-bit object and then storing it as a 32-bit object
2617 does not store the low-order 32 bits, as would be the case for a normal
2618 register. Therefore, @file{alpha.h} defines @code{CANNOT_CHANGE_MODE_CLASS}
2622 #define CANNOT_CHANGE_MODE_CLASS(FROM, TO, CLASS) \
2623 (GET_MODE_SIZE (FROM) != GET_MODE_SIZE (TO) \
2624 ? reg_classes_intersect_p (FLOAT_REGS, (CLASS)) : 0)
2628 Three other special macros describe which operands fit which constraint
2631 @defmac CONST_OK_FOR_LETTER_P (@var{value}, @var{c})
2632 A C expression that defines the machine-dependent operand constraint
2633 letters (@samp{I}, @samp{J}, @samp{K}, @dots{} @samp{P}) that specify
2634 particular ranges of integer values. If @var{c} is one of those
2635 letters, the expression should check that @var{value}, an integer, is in
2636 the appropriate range and return 1 if so, 0 otherwise. If @var{c} is
2637 not one of those letters, the value should be 0 regardless of
2641 @defmac CONST_OK_FOR_CONSTRAINT_P (@var{value}, @var{c}, @var{str})
2642 Like @code{CONST_OK_FOR_LETTER_P}, but you also get the constraint
2643 string passed in @var{str}, so that you can use suffixes to distinguish
2644 between different variants.
2647 @defmac CONST_DOUBLE_OK_FOR_LETTER_P (@var{value}, @var{c})
2648 A C expression that defines the machine-dependent operand constraint
2649 letters that specify particular ranges of @code{const_double} values
2650 (@samp{G} or @samp{H}).
2652 If @var{c} is one of those letters, the expression should check that
2653 @var{value}, an RTX of code @code{const_double}, is in the appropriate
2654 range and return 1 if so, 0 otherwise. If @var{c} is not one of those
2655 letters, the value should be 0 regardless of @var{value}.
2657 @code{const_double} is used for all floating-point constants and for
2658 @code{DImode} fixed-point constants. A given letter can accept either
2659 or both kinds of values. It can use @code{GET_MODE} to distinguish
2660 between these kinds.
2663 @defmac CONST_DOUBLE_OK_FOR_CONSTRAINT_P (@var{value}, @var{c}, @var{str})
2664 Like @code{CONST_DOUBLE_OK_FOR_LETTER_P}, but you also get the constraint
2665 string passed in @var{str}, so that you can use suffixes to distinguish
2666 between different variants.
2669 @defmac EXTRA_CONSTRAINT (@var{value}, @var{c})
2670 A C expression that defines the optional machine-dependent constraint
2671 letters that can be used to segregate specific types of operands, usually
2672 memory references, for the target machine. Any letter that is not
2673 elsewhere defined and not matched by @code{REG_CLASS_FROM_LETTER} /
2674 @code{REG_CLASS_FROM_CONSTRAINT}
2675 may be used. Normally this macro will not be defined.
2677 If it is required for a particular target machine, it should return 1
2678 if @var{value} corresponds to the operand type represented by the
2679 constraint letter @var{c}. If @var{c} is not defined as an extra
2680 constraint, the value returned should be 0 regardless of @var{value}.
2682 For example, on the ROMP, load instructions cannot have their output
2683 in r0 if the memory reference contains a symbolic address. Constraint
2684 letter @samp{Q} is defined as representing a memory address that does
2685 @emph{not} contain a symbolic address. An alternative is specified with
2686 a @samp{Q} constraint on the input and @samp{r} on the output. The next
2687 alternative specifies @samp{m} on the input and a register class that
2688 does not include r0 on the output.
2691 @defmac EXTRA_CONSTRAINT_STR (@var{value}, @var{c}, @var{str})
2692 Like @code{EXTRA_CONSTRAINT}, but you also get the constraint string passed
2693 in @var{str}, so that you can use suffixes to distinguish between different
2697 @defmac EXTRA_MEMORY_CONSTRAINT (@var{c}, @var{str})
2698 A C expression that defines the optional machine-dependent constraint
2699 letters, amongst those accepted by @code{EXTRA_CONSTRAINT}, that should
2700 be treated like memory constraints by the reload pass.
2702 It should return 1 if the operand type represented by the constraint
2703 at the start of @var{str}, the first letter of which is the letter @var{c},
2704 comprises a subset of all memory references including
2705 all those whose address is simply a base register. This allows the reload
2706 pass to reload an operand, if it does not directly correspond to the operand
2707 type of @var{c}, by copying its address into a base register.
2709 For example, on the S/390, some instructions do not accept arbitrary
2710 memory references, but only those that do not make use of an index
2711 register. The constraint letter @samp{Q} is defined via
2712 @code{EXTRA_CONSTRAINT} as representing a memory address of this type.
2713 If the letter @samp{Q} is marked as @code{EXTRA_MEMORY_CONSTRAINT},
2714 a @samp{Q} constraint can handle any memory operand, because the
2715 reload pass knows it can be reloaded by copying the memory address
2716 into a base register if required. This is analogous to the way
2717 a @samp{o} constraint can handle any memory operand.
2720 @defmac EXTRA_ADDRESS_CONSTRAINT (@var{c}, @var{str})
2721 A C expression that defines the optional machine-dependent constraint
2722 letters, amongst those accepted by @code{EXTRA_CONSTRAINT} /
2723 @code{EXTRA_CONSTRAINT_STR}, that should
2724 be treated like address constraints by the reload pass.
2726 It should return 1 if the operand type represented by the constraint
2727 at the start of @var{str}, which starts with the letter @var{c}, comprises
2728 a subset of all memory addresses including
2729 all those that consist of just a base register. This allows the reload
2730 pass to reload an operand, if it does not directly correspond to the operand
2731 type of @var{str}, by copying it into a base register.
2733 Any constraint marked as @code{EXTRA_ADDRESS_CONSTRAINT} can only
2734 be used with the @code{address_operand} predicate. It is treated
2735 analogously to the @samp{p} constraint.
2738 @node Stack and Calling
2739 @section Stack Layout and Calling Conventions
2740 @cindex calling conventions
2742 @c prevent bad page break with this line
2743 This describes the stack layout and calling conventions.
2747 * Exception Handling::
2752 * Register Arguments::
2754 * Aggregate Return::
2762 @subsection Basic Stack Layout
2763 @cindex stack frame layout
2764 @cindex frame layout
2766 @c prevent bad page break with this line
2767 Here is the basic stack layout.
2769 @defmac STACK_GROWS_DOWNWARD
2770 Define this macro if pushing a word onto the stack moves the stack
2771 pointer to a smaller address.
2773 When we say, ``define this macro if @dots{},'' it means that the
2774 compiler checks this macro only with @code{#ifdef} so the precise
2775 definition used does not matter.
2778 @defmac STACK_PUSH_CODE
2779 This macro defines the operation used when something is pushed
2780 on the stack. In RTL, a push operation will be
2781 @code{(set (mem (STACK_PUSH_CODE (reg sp))) @dots{})}
2783 The choices are @code{PRE_DEC}, @code{POST_DEC}, @code{PRE_INC},
2784 and @code{POST_INC}. Which of these is correct depends on
2785 the stack direction and on whether the stack pointer points
2786 to the last item on the stack or whether it points to the
2787 space for the next item on the stack.
2789 The default is @code{PRE_DEC} when @code{STACK_GROWS_DOWNWARD} is
2790 defined, which is almost always right, and @code{PRE_INC} otherwise,
2791 which is often wrong.
2794 @defmac FRAME_GROWS_DOWNWARD
2795 Define this macro if the addresses of local variable slots are at negative
2796 offsets from the frame pointer.
2799 @defmac ARGS_GROW_DOWNWARD
2800 Define this macro if successive arguments to a function occupy decreasing
2801 addresses on the stack.
2804 @defmac STARTING_FRAME_OFFSET
2805 Offset from the frame pointer to the first local variable slot to be allocated.
2807 If @code{FRAME_GROWS_DOWNWARD}, find the next slot's offset by
2808 subtracting the first slot's length from @code{STARTING_FRAME_OFFSET}.
2809 Otherwise, it is found by adding the length of the first slot to the
2810 value @code{STARTING_FRAME_OFFSET}.
2811 @c i'm not sure if the above is still correct.. had to change it to get
2812 @c rid of an overfull. --mew 2feb93
2815 @defmac STACK_ALIGNMENT_NEEDED
2816 Define to zero to disable final alignment of the stack during reload.
2817 The nonzero default for this macro is suitable for most ports.
2819 On ports where @code{STARTING_FRAME_OFFSET} is nonzero or where there
2820 is a register save block following the local block that doesn't require
2821 alignment to @code{STACK_BOUNDARY}, it may be beneficial to disable
2822 stack alignment and do it in the backend.
2825 @defmac STACK_POINTER_OFFSET
2826 Offset from the stack pointer register to the first location at which
2827 outgoing arguments are placed. If not specified, the default value of
2828 zero is used. This is the proper value for most machines.
2830 If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above
2831 the first location at which outgoing arguments are placed.
2834 @defmac FIRST_PARM_OFFSET (@var{fundecl})
2835 Offset from the argument pointer register to the first argument's
2836 address. On some machines it may depend on the data type of the
2839 If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above
2840 the first argument's address.
2843 @defmac STACK_DYNAMIC_OFFSET (@var{fundecl})
2844 Offset from the stack pointer register to an item dynamically allocated
2845 on the stack, e.g., by @code{alloca}.
2847 The default value for this macro is @code{STACK_POINTER_OFFSET} plus the
2848 length of the outgoing arguments. The default is correct for most
2849 machines. See @file{function.c} for details.
2852 @defmac DYNAMIC_CHAIN_ADDRESS (@var{frameaddr})
2853 A C expression whose value is RTL representing the address in a stack
2854 frame where the pointer to the caller's frame is stored. Assume that
2855 @var{frameaddr} is an RTL expression for the address of the stack frame
2858 If you don't define this macro, the default is to return the value
2859 of @var{frameaddr}---that is, the stack frame address is also the
2860 address of the stack word that points to the previous frame.
2863 @defmac SETUP_FRAME_ADDRESSES
2864 If defined, a C expression that produces the machine-specific code to
2865 setup the stack so that arbitrary frames can be accessed. For example,
2866 on the SPARC, we must flush all of the register windows to the stack
2867 before we can access arbitrary stack frames. You will seldom need to
2871 @defmac BUILTIN_SETJMP_FRAME_VALUE
2872 If defined, a C expression that contains an rtx that is used to store
2873 the address of the current frame into the built in @code{setjmp} buffer.
2874 The default value, @code{virtual_stack_vars_rtx}, is correct for most
2875 machines. One reason you may need to define this macro is if
2876 @code{hard_frame_pointer_rtx} is the appropriate value on your machine.
2879 @defmac RETURN_ADDR_RTX (@var{count}, @var{frameaddr})
2880 A C expression whose value is RTL representing the value of the return
2881 address for the frame @var{count} steps up from the current frame, after
2882 the prologue. @var{frameaddr} is the frame pointer of the @var{count}
2883 frame, or the frame pointer of the @var{count} @minus{} 1 frame if
2884 @code{RETURN_ADDR_IN_PREVIOUS_FRAME} is defined.
2886 The value of the expression must always be the correct address when
2887 @var{count} is zero, but may be @code{NULL_RTX} if there is not way to
2888 determine the return address of other frames.
2891 @defmac RETURN_ADDR_IN_PREVIOUS_FRAME
2892 Define this if the return address of a particular stack frame is accessed
2893 from the frame pointer of the previous stack frame.
2896 @defmac INCOMING_RETURN_ADDR_RTX
2897 A C expression whose value is RTL representing the location of the
2898 incoming return address at the beginning of any function, before the
2899 prologue. This RTL is either a @code{REG}, indicating that the return
2900 value is saved in @samp{REG}, or a @code{MEM} representing a location in
2903 You only need to define this macro if you want to support call frame
2904 debugging information like that provided by DWARF 2.
2906 If this RTL is a @code{REG}, you should also define
2907 @code{DWARF_FRAME_RETURN_COLUMN} to @code{DWARF_FRAME_REGNUM (REGNO)}.
2910 @defmac INCOMING_FRAME_SP_OFFSET
2911 A C expression whose value is an integer giving the offset, in bytes,
2912 from the value of the stack pointer register to the top of the stack
2913 frame at the beginning of any function, before the prologue. The top of
2914 the frame is defined to be the value of the stack pointer in the
2915 previous frame, just before the call instruction.
2917 You only need to define this macro if you want to support call frame
2918 debugging information like that provided by DWARF 2.
2921 @defmac ARG_POINTER_CFA_OFFSET (@var{fundecl})
2922 A C expression whose value is an integer giving the offset, in bytes,
2923 from the argument pointer to the canonical frame address (cfa). The
2924 final value should coincide with that calculated by
2925 @code{INCOMING_FRAME_SP_OFFSET}. Which is unfortunately not usable
2926 during virtual register instantiation.
2928 The default value for this macro is @code{FIRST_PARM_OFFSET (fundecl)},
2929 which is correct for most machines; in general, the arguments are found
2930 immediately before the stack frame. Note that this is not the case on
2931 some targets that save registers into the caller's frame, such as SPARC
2932 and rs6000, and so such targets need to define this macro.
2934 You only need to define this macro if the default is incorrect, and you
2935 want to support call frame debugging information like that provided by
2940 Define this macro if the stack size for the target is very small. This
2941 has the effect of disabling gcc's built-in @samp{alloca}, though
2942 @samp{__builtin_alloca} is not affected.
2945 @node Exception Handling
2946 @subsection Exception Handling Support
2947 @cindex exception handling
2949 @defmac EH_RETURN_DATA_REGNO (@var{N})
2950 A C expression whose value is the @var{N}th register number used for
2951 data by exception handlers, or @code{INVALID_REGNUM} if fewer than
2952 @var{N} registers are usable.
2954 The exception handling library routines communicate with the exception
2955 handlers via a set of agreed upon registers. Ideally these registers
2956 should be call-clobbered; it is possible to use call-saved registers,
2957 but may negatively impact code size. The target must support at least
2958 2 data registers, but should define 4 if there are enough free registers.
2960 You must define this macro if you want to support call frame exception
2961 handling like that provided by DWARF 2.
2964 @defmac EH_RETURN_STACKADJ_RTX
2965 A C expression whose value is RTL representing a location in which
2966 to store a stack adjustment to be applied before function return.
2967 This is used to unwind the stack to an exception handler's call frame.
2968 It will be assigned zero on code paths that return normally.
2970 Typically this is a call-clobbered hard register that is otherwise
2971 untouched by the epilogue, but could also be a stack slot.
2973 Do not define this macro if the stack pointer is saved and restored
2974 by the regular prolog and epilog code in the call frame itself; in
2975 this case, the exception handling library routines will update the
2976 stack location to be restored in place. Otherwise, you must define
2977 this macro if you want to support call frame exception handling like
2978 that provided by DWARF 2.
2981 @defmac EH_RETURN_HANDLER_RTX
2982 A C expression whose value is RTL representing a location in which
2983 to store the address of an exception handler to which we should
2984 return. It will not be assigned on code paths that return normally.
2986 Typically this is the location in the call frame at which the normal
2987 return address is stored. For targets that return by popping an
2988 address off the stack, this might be a memory address just below
2989 the @emph{target} call frame rather than inside the current call
2990 frame. If defined, @code{EH_RETURN_STACKADJ_RTX} will have already
2991 been assigned, so it may be used to calculate the location of the
2994 Some targets have more complex requirements than storing to an
2995 address calculable during initial code generation. In that case
2996 the @code{eh_return} instruction pattern should be used instead.
2998 If you want to support call frame exception handling, you must
2999 define either this macro or the @code{eh_return} instruction pattern.
3002 @defmac RETURN_ADDR_OFFSET
3003 If defined, an integer-valued C expression for which rtl will be generated
3004 to add it to the exception handler address before it is searched in the
3005 exception handling tables, and to subtract it again from the address before
3006 using it to return to the exception handler.
3009 @defmac ASM_PREFERRED_EH_DATA_FORMAT (@var{code}, @var{global})
3010 This macro chooses the encoding of pointers embedded in the exception
3011 handling sections. If at all possible, this should be defined such
3012 that the exception handling section will not require dynamic relocations,
3013 and so may be read-only.
3015 @var{code} is 0 for data, 1 for code labels, 2 for function pointers.
3016 @var{global} is true if the symbol may be affected by dynamic relocations.
3017 The macro should return a combination of the @code{DW_EH_PE_*} defines
3018 as found in @file{dwarf2.h}.
3020 If this macro is not defined, pointers will not be encoded but
3021 represented directly.
3024 @defmac ASM_MAYBE_OUTPUT_ENCODED_ADDR_RTX (@var{file}, @var{encoding}, @var{size}, @var{addr}, @var{done})
3025 This macro allows the target to emit whatever special magic is required
3026 to represent the encoding chosen by @code{ASM_PREFERRED_EH_DATA_FORMAT}.
3027 Generic code takes care of pc-relative and indirect encodings; this must
3028 be defined if the target uses text-relative or data-relative encodings.
3030 This is a C statement that branches to @var{done} if the format was
3031 handled. @var{encoding} is the format chosen, @var{size} is the number
3032 of bytes that the format occupies, @var{addr} is the @code{SYMBOL_REF}
3036 @defmac MD_FALLBACK_FRAME_STATE_FOR (@var{context}, @var{fs}, @var{success})
3037 This macro allows the target to add cpu and operating system specific
3038 code to the call-frame unwinder for use when there is no unwind data
3039 available. The most common reason to implement this macro is to unwind
3040 through signal frames.
3042 This macro is called from @code{uw_frame_state_for} in @file{unwind-dw2.c}
3043 and @file{unwind-ia64.c}. @var{context} is an @code{_Unwind_Context};
3044 @var{fs} is an @code{_Unwind_FrameState}. Examine @code{context->ra}
3045 for the address of the code being executed and @code{context->cfa} for
3046 the stack pointer value. If the frame can be decoded, the register save
3047 addresses should be updated in @var{fs} and the macro should branch to
3048 @var{success}. If the frame cannot be decoded, the macro should do
3051 For proper signal handling in Java this macro is accompanied by
3052 @code{MAKE_THROW_FRAME}, defined in @file{libjava/include/*-signal.h} headers.
3055 @node Stack Checking
3056 @subsection Specifying How Stack Checking is Done
3058 GCC will check that stack references are within the boundaries of
3059 the stack, if the @option{-fstack-check} is specified, in one of three ways:
3063 If the value of the @code{STACK_CHECK_BUILTIN} macro is nonzero, GCC
3064 will assume that you have arranged for stack checking to be done at
3065 appropriate places in the configuration files, e.g., in
3066 @code{TARGET_ASM_FUNCTION_PROLOGUE}. GCC will do not other special
3070 If @code{STACK_CHECK_BUILTIN} is zero and you defined a named pattern
3071 called @code{check_stack} in your @file{md} file, GCC will call that
3072 pattern with one argument which is the address to compare the stack
3073 value against. You must arrange for this pattern to report an error if
3074 the stack pointer is out of range.
3077 If neither of the above are true, GCC will generate code to periodically
3078 ``probe'' the stack pointer using the values of the macros defined below.
3081 Normally, you will use the default values of these macros, so GCC
3082 will use the third approach.
3084 @defmac STACK_CHECK_BUILTIN
3085 A nonzero value if stack checking is done by the configuration files in a
3086 machine-dependent manner. You should define this macro if stack checking
3087 is require by the ABI of your machine or if you would like to have to stack
3088 checking in some more efficient way than GCC's portable approach.
3089 The default value of this macro is zero.
3092 @defmac STACK_CHECK_PROBE_INTERVAL
3093 An integer representing the interval at which GCC must generate stack
3094 probe instructions. You will normally define this macro to be no larger
3095 than the size of the ``guard pages'' at the end of a stack area. The
3096 default value of 4096 is suitable for most systems.
3099 @defmac STACK_CHECK_PROBE_LOAD
3100 A integer which is nonzero if GCC should perform the stack probe
3101 as a load instruction and zero if GCC should use a store instruction.
3102 The default is zero, which is the most efficient choice on most systems.
3105 @defmac STACK_CHECK_PROTECT
3106 The number of bytes of stack needed to recover from a stack overflow,
3107 for languages where such a recovery is supported. The default value of
3108 75 words should be adequate for most machines.
3111 @defmac STACK_CHECK_MAX_FRAME_SIZE
3112 The maximum size of a stack frame, in bytes. GCC will generate probe
3113 instructions in non-leaf functions to ensure at least this many bytes of
3114 stack are available. If a stack frame is larger than this size, stack
3115 checking will not be reliable and GCC will issue a warning. The
3116 default is chosen so that GCC only generates one instruction on most
3117 systems. You should normally not change the default value of this macro.
3120 @defmac STACK_CHECK_FIXED_FRAME_SIZE
3121 GCC uses this value to generate the above warning message. It
3122 represents the amount of fixed frame used by a function, not including
3123 space for any callee-saved registers, temporaries and user variables.
3124 You need only specify an upper bound for this amount and will normally
3125 use the default of four words.
3128 @defmac STACK_CHECK_MAX_VAR_SIZE
3129 The maximum size, in bytes, of an object that GCC will place in the
3130 fixed area of the stack frame when the user specifies
3131 @option{-fstack-check}.
3132 GCC computed the default from the values of the above macros and you will
3133 normally not need to override that default.
3137 @node Frame Registers
3138 @subsection Registers That Address the Stack Frame
3140 @c prevent bad page break with this line
3141 This discusses registers that address the stack frame.
3143 @defmac STACK_POINTER_REGNUM
3144 The register number of the stack pointer register, which must also be a
3145 fixed register according to @code{FIXED_REGISTERS}. On most machines,
3146 the hardware determines which register this is.
3149 @defmac FRAME_POINTER_REGNUM
3150 The register number of the frame pointer register, which is used to
3151 access automatic variables in the stack frame. On some machines, the
3152 hardware determines which register this is. On other machines, you can
3153 choose any register you wish for this purpose.
3156 @defmac HARD_FRAME_POINTER_REGNUM
3157 On some machines the offset between the frame pointer and starting
3158 offset of the automatic variables is not known until after register
3159 allocation has been done (for example, because the saved registers are
3160 between these two locations). On those machines, define
3161 @code{FRAME_POINTER_REGNUM} the number of a special, fixed register to
3162 be used internally until the offset is known, and define
3163 @code{HARD_FRAME_POINTER_REGNUM} to be the actual hard register number
3164 used for the frame pointer.
3166 You should define this macro only in the very rare circumstances when it
3167 is not possible to calculate the offset between the frame pointer and
3168 the automatic variables until after register allocation has been
3169 completed. When this macro is defined, you must also indicate in your
3170 definition of @code{ELIMINABLE_REGS} how to eliminate
3171 @code{FRAME_POINTER_REGNUM} into either @code{HARD_FRAME_POINTER_REGNUM}
3172 or @code{STACK_POINTER_REGNUM}.
3174 Do not define this macro if it would be the same as
3175 @code{FRAME_POINTER_REGNUM}.
3178 @defmac ARG_POINTER_REGNUM
3179 The register number of the arg pointer register, which is used to access
3180 the function's argument list. On some machines, this is the same as the
3181 frame pointer register. On some machines, the hardware determines which
3182 register this is. On other machines, you can choose any register you
3183 wish for this purpose. If this is not the same register as the frame
3184 pointer register, then you must mark it as a fixed register according to
3185 @code{FIXED_REGISTERS}, or arrange to be able to eliminate it
3186 (@pxref{Elimination}).
3189 @defmac RETURN_ADDRESS_POINTER_REGNUM
3190 The register number of the return address pointer register, which is used to
3191 access the current function's return address from the stack. On some
3192 machines, the return address is not at a fixed offset from the frame
3193 pointer or stack pointer or argument pointer. This register can be defined
3194 to point to the return address on the stack, and then be converted by
3195 @code{ELIMINABLE_REGS} into either the frame pointer or stack pointer.
3197 Do not define this macro unless there is no other way to get the return
3198 address from the stack.
3201 @defmac STATIC_CHAIN_REGNUM
3202 @defmacx STATIC_CHAIN_INCOMING_REGNUM
3203 Register numbers used for passing a function's static chain pointer. If
3204 register windows are used, the register number as seen by the called
3205 function is @code{STATIC_CHAIN_INCOMING_REGNUM}, while the register
3206 number as seen by the calling function is @code{STATIC_CHAIN_REGNUM}. If
3207 these registers are the same, @code{STATIC_CHAIN_INCOMING_REGNUM} need
3210 The static chain register need not be a fixed register.
3212 If the static chain is passed in memory, these macros should not be
3213 defined; instead, the next two macros should be defined.
3216 @defmac STATIC_CHAIN
3217 @defmacx STATIC_CHAIN_INCOMING
3218 If the static chain is passed in memory, these macros provide rtx giving
3219 @code{mem} expressions that denote where they are stored.
3220 @code{STATIC_CHAIN} and @code{STATIC_CHAIN_INCOMING} give the locations
3221 as seen by the calling and called functions, respectively. Often the former
3222 will be at an offset from the stack pointer and the latter at an offset from
3225 @findex stack_pointer_rtx
3226 @findex frame_pointer_rtx
3227 @findex arg_pointer_rtx
3228 The variables @code{stack_pointer_rtx}, @code{frame_pointer_rtx}, and
3229 @code{arg_pointer_rtx} will have been initialized prior to the use of these
3230 macros and should be used to refer to those items.
3232 If the static chain is passed in a register, the two previous macros should
3236 @defmac DWARF_FRAME_REGISTERS
3237 This macro specifies the maximum number of hard registers that can be
3238 saved in a call frame. This is used to size data structures used in
3239 DWARF2 exception handling.
3241 Prior to GCC 3.0, this macro was needed in order to establish a stable
3242 exception handling ABI in the face of adding new hard registers for ISA
3243 extensions. In GCC 3.0 and later, the EH ABI is insulated from changes
3244 in the number of hard registers. Nevertheless, this macro can still be
3245 used to reduce the runtime memory requirements of the exception handling
3246 routines, which can be substantial if the ISA contains a lot of
3247 registers that are not call-saved.
3249 If this macro is not defined, it defaults to
3250 @code{FIRST_PSEUDO_REGISTER}.
3253 @defmac PRE_GCC3_DWARF_FRAME_REGISTERS
3255 This macro is similar to @code{DWARF_FRAME_REGISTERS}, but is provided
3256 for backward compatibility in pre GCC 3.0 compiled code.
3258 If this macro is not defined, it defaults to
3259 @code{DWARF_FRAME_REGISTERS}.
3262 @defmac DWARF_REG_TO_UNWIND_COLUMN (@var{regno})
3264 Define this macro if the target's representation for dwarf registers
3265 is different than the internal representation for unwind column.
3266 Given a dwarf register, this macro should return the internal unwind
3267 column number to use instead.
3269 See the PowerPC's SPE target for an example.
3273 @subsection Eliminating Frame Pointer and Arg Pointer
3275 @c prevent bad page break with this line
3276 This is about eliminating the frame pointer and arg pointer.
3278 @defmac FRAME_POINTER_REQUIRED
3279 A C expression which is nonzero if a function must have and use a frame
3280 pointer. This expression is evaluated in the reload pass. If its value is
3281 nonzero the function will have a frame pointer.
3283 The expression can in principle examine the current function and decide
3284 according to the facts, but on most machines the constant 0 or the
3285 constant 1 suffices. Use 0 when the machine allows code to be generated
3286 with no frame pointer, and doing so saves some time or space. Use 1
3287 when there is no possible advantage to avoiding a frame pointer.
3289 In certain cases, the compiler does not know how to produce valid code
3290 without a frame pointer. The compiler recognizes those cases and
3291 automatically gives the function a frame pointer regardless of what
3292 @code{FRAME_POINTER_REQUIRED} says. You don't need to worry about
3295 In a function that does not require a frame pointer, the frame pointer
3296 register can be allocated for ordinary usage, unless you mark it as a
3297 fixed register. See @code{FIXED_REGISTERS} for more information.
3300 @findex get_frame_size
3301 @defmac INITIAL_FRAME_POINTER_OFFSET (@var{depth-var})
3302 A C statement to store in the variable @var{depth-var} the difference
3303 between the frame pointer and the stack pointer values immediately after
3304 the function prologue. The value would be computed from information
3305 such as the result of @code{get_frame_size ()} and the tables of
3306 registers @code{regs_ever_live} and @code{call_used_regs}.
3308 If @code{ELIMINABLE_REGS} is defined, this macro will be not be used and
3309 need not be defined. Otherwise, it must be defined even if
3310 @code{FRAME_POINTER_REQUIRED} is defined to always be true; in that
3311 case, you may set @var{depth-var} to anything.
3314 @defmac ELIMINABLE_REGS
3315 If defined, this macro specifies a table of register pairs used to
3316 eliminate unneeded registers that point into the stack frame. If it is not
3317 defined, the only elimination attempted by the compiler is to replace
3318 references to the frame pointer with references to the stack pointer.
3320 The definition of this macro is a list of structure initializations, each
3321 of which specifies an original and replacement register.
3323 On some machines, the position of the argument pointer is not known until
3324 the compilation is completed. In such a case, a separate hard register
3325 must be used for the argument pointer. This register can be eliminated by
3326 replacing it with either the frame pointer or the argument pointer,
3327 depending on whether or not the frame pointer has been eliminated.
3329 In this case, you might specify:
3331 #define ELIMINABLE_REGS \
3332 @{@{ARG_POINTER_REGNUM, STACK_POINTER_REGNUM@}, \
3333 @{ARG_POINTER_REGNUM, FRAME_POINTER_REGNUM@}, \
3334 @{FRAME_POINTER_REGNUM, STACK_POINTER_REGNUM@}@}
3337 Note that the elimination of the argument pointer with the stack pointer is
3338 specified first since that is the preferred elimination.
3341 @defmac CAN_ELIMINATE (@var{from-reg}, @var{to-reg})
3342 A C expression that returns nonzero if the compiler is allowed to try
3343 to replace register number @var{from-reg} with register number
3344 @var{to-reg}. This macro need only be defined if @code{ELIMINABLE_REGS}
3345 is defined, and will usually be the constant 1, since most of the cases
3346 preventing register elimination are things that the compiler already
3350 @defmac INITIAL_ELIMINATION_OFFSET (@var{from-reg}, @var{to-reg}, @var{offset-var})
3351 This macro is similar to @code{INITIAL_FRAME_POINTER_OFFSET}. It
3352 specifies the initial difference between the specified pair of
3353 registers. This macro must be defined if @code{ELIMINABLE_REGS} is
3357 @node Stack Arguments
3358 @subsection Passing Function Arguments on the Stack
3359 @cindex arguments on stack
3360 @cindex stack arguments
3362 The macros in this section control how arguments are passed
3363 on the stack. See the following section for other macros that
3364 control passing certain arguments in registers.
3366 @defmac PROMOTE_PROTOTYPES
3367 A C expression whose value is nonzero if an argument declared in
3368 a prototype as an integral type smaller than @code{int} should
3369 actually be passed as an @code{int}. In addition to avoiding
3370 errors in certain cases of mismatch, it also makes for better
3371 code on certain machines. If the macro is not defined in target
3372 header files, it defaults to 0.
3376 A C expression. If nonzero, push insns will be used to pass
3378 If the target machine does not have a push instruction, set it to zero.
3379 That directs GCC to use an alternate strategy: to
3380 allocate the entire argument block and then store the arguments into
3381 it. When @code{PUSH_ARGS} is nonzero, @code{PUSH_ROUNDING} must be defined too.
3384 @defmac PUSH_ARGS_REVERSED
3385 A C expression. If nonzero, function arguments will be evaluated from
3386 last to first, rather than from first to last. If this macro is not
3387 defined, it defaults to @code{PUSH_ARGS} on targets where the stack
3388 and args grow in opposite directions, and 0 otherwise.
3391 @defmac PUSH_ROUNDING (@var{npushed})
3392 A C expression that is the number of bytes actually pushed onto the
3393 stack when an instruction attempts to push @var{npushed} bytes.
3395 On some machines, the definition
3398 #define PUSH_ROUNDING(BYTES) (BYTES)
3402 will suffice. But on other machines, instructions that appear
3403 to push one byte actually push two bytes in an attempt to maintain
3404 alignment. Then the definition should be
3407 #define PUSH_ROUNDING(BYTES) (((BYTES) + 1) & ~1)
3411 @findex current_function_outgoing_args_size
3412 @defmac ACCUMULATE_OUTGOING_ARGS
3413 A C expression. If nonzero, the maximum amount of space required for outgoing arguments
3414 will be computed and placed into the variable
3415 @code{current_function_outgoing_args_size}. No space will be pushed
3416 onto the stack for each call; instead, the function prologue should
3417 increase the stack frame size by this amount.
3419 Setting both @code{PUSH_ARGS} and @code{ACCUMULATE_OUTGOING_ARGS}
3423 @defmac REG_PARM_STACK_SPACE (@var{fndecl})
3424 Define this macro if functions should assume that stack space has been
3425 allocated for arguments even when their values are passed in
3428 The value of this macro is the size, in bytes, of the area reserved for
3429 arguments passed in registers for the function represented by @var{fndecl},
3430 which can be zero if GCC is calling a library function.
3432 This space can be allocated by the caller, or be a part of the
3433 machine-dependent stack frame: @code{OUTGOING_REG_PARM_STACK_SPACE} says
3436 @c above is overfull. not sure what to do. --mew 5feb93 did
3437 @c something, not sure if it looks good. --mew 10feb93
3439 @defmac MAYBE_REG_PARM_STACK_SPACE
3440 @defmacx FINAL_REG_PARM_STACK_SPACE (@var{const_size}, @var{var_size})
3441 Define these macros in addition to the one above if functions might
3442 allocate stack space for arguments even when their values are passed
3443 in registers. These should be used when the stack space allocated
3444 for arguments in registers is not a simple constant independent of the
3445 function declaration.
3447 The value of the first macro is the size, in bytes, of the area that
3448 we should initially assume would be reserved for arguments passed in registers.
3450 The value of the second macro is the actual size, in bytes, of the area
3451 that will be reserved for arguments passed in registers. This takes two
3452 arguments: an integer representing the number of bytes of fixed sized
3453 arguments on the stack, and a tree representing the number of bytes of
3454 variable sized arguments on the stack.
3456 When these macros are defined, @code{REG_PARM_STACK_SPACE} will only be
3457 called for libcall functions, the current function, or for a function
3458 being called when it is known that such stack space must be allocated.
3459 In each case this value can be easily computed.
3461 When deciding whether a called function needs such stack space, and how
3462 much space to reserve, GCC uses these two macros instead of
3463 @code{REG_PARM_STACK_SPACE}.
3466 @defmac OUTGOING_REG_PARM_STACK_SPACE
3467 Define this if it is the responsibility of the caller to allocate the area
3468 reserved for arguments passed in registers.
3470 If @code{ACCUMULATE_OUTGOING_ARGS} is defined, this macro controls
3471 whether the space for these arguments counts in the value of
3472 @code{current_function_outgoing_args_size}.
3475 @defmac STACK_PARMS_IN_REG_PARM_AREA
3476 Define this macro if @code{REG_PARM_STACK_SPACE} is defined, but the
3477 stack parameters don't skip the area specified by it.
3478 @c i changed this, makes more sens and it should have taken care of the
3479 @c overfull.. not as specific, tho. --mew 5feb93
3481 Normally, when a parameter is not passed in registers, it is placed on the
3482 stack beyond the @code{REG_PARM_STACK_SPACE} area. Defining this macro
3483 suppresses this behavior and causes the parameter to be passed on the
3484 stack in its natural location.
3487 @defmac RETURN_POPS_ARGS (@var{fundecl}, @var{funtype}, @var{stack-size})
3488 A C expression that should indicate the number of bytes of its own
3489 arguments that a function pops on returning, or 0 if the
3490 function pops no arguments and the caller must therefore pop them all
3491 after the function returns.
3493 @var{fundecl} is a C variable whose value is a tree node that describes
3494 the function in question. Normally it is a node of type
3495 @code{FUNCTION_DECL} that describes the declaration of the function.
3496 From this you can obtain the @code{DECL_ATTRIBUTES} of the function.
3498 @var{funtype} is a C variable whose value is a tree node that
3499 describes the function in question. Normally it is a node of type
3500 @code{FUNCTION_TYPE} that describes the data type of the function.
3501 From this it is possible to obtain the data types of the value and
3502 arguments (if known).
3504 When a call to a library function is being considered, @var{fundecl}
3505 will contain an identifier node for the library function. Thus, if
3506 you need to distinguish among various library functions, you can do so
3507 by their names. Note that ``library function'' in this context means
3508 a function used to perform arithmetic, whose name is known specially
3509 in the compiler and was not mentioned in the C code being compiled.
3511 @var{stack-size} is the number of bytes of arguments passed on the
3512 stack. If a variable number of bytes is passed, it is zero, and
3513 argument popping will always be the responsibility of the calling function.
3515 On the VAX, all functions always pop their arguments, so the definition
3516 of this macro is @var{stack-size}. On the 68000, using the standard
3517 calling convention, no functions pop their arguments, so the value of
3518 the macro is always 0 in this case. But an alternative calling
3519 convention is available in which functions that take a fixed number of
3520 arguments pop them but other functions (such as @code{printf}) pop
3521 nothing (the caller pops all). When this convention is in use,
3522 @var{funtype} is examined to determine whether a function takes a fixed
3523 number of arguments.
3526 @defmac CALL_POPS_ARGS (@var{cum})
3527 A C expression that should indicate the number of bytes a call sequence
3528 pops off the stack. It is added to the value of @code{RETURN_POPS_ARGS}
3529 when compiling a function call.
3531 @var{cum} is the variable in which all arguments to the called function
3532 have been accumulated.
3534 On certain architectures, such as the SH5, a call trampoline is used
3535 that pops certain registers off the stack, depending on the arguments
3536 that have been passed to the function. Since this is a property of the
3537 call site, not of the called function, @code{RETURN_POPS_ARGS} is not
3541 @node Register Arguments
3542 @subsection Passing Arguments in Registers
3543 @cindex arguments in registers
3544 @cindex registers arguments
3546 This section describes the macros which let you control how various
3547 types of arguments are passed in registers or how they are arranged in
3550 @defmac FUNCTION_ARG (@var{cum}, @var{mode}, @var{type}, @var{named})
3551 A C expression that controls whether a function argument is passed
3552 in a register, and which register.
3554 The arguments are @var{cum}, which summarizes all the previous
3555 arguments; @var{mode}, the machine mode of the argument; @var{type},
3556 the data type of the argument as a tree node or 0 if that is not known
3557 (which happens for C support library functions); and @var{named},
3558 which is 1 for an ordinary argument and 0 for nameless arguments that
3559 correspond to @samp{@dots{}} in the called function's prototype.
3560 @var{type} can be an incomplete type if a syntax error has previously
3563 The value of the expression is usually either a @code{reg} RTX for the
3564 hard register in which to pass the argument, or zero to pass the
3565 argument on the stack.
3567 For machines like the VAX and 68000, where normally all arguments are
3568 pushed, zero suffices as a definition.
3570 The value of the expression can also be a @code{parallel} RTX@. This is
3571 used when an argument is passed in multiple locations. The mode of the
3572 @code{parallel} should be the mode of the entire argument. The
3573 @code{parallel} holds any number of @code{expr_list} pairs; each one
3574 describes where part of the argument is passed. In each
3575 @code{expr_list} the first operand must be a @code{reg} RTX for the hard
3576 register in which to pass this part of the argument, and the mode of the
3577 register RTX indicates how large this part of the argument is. The
3578 second operand of the @code{expr_list} is a @code{const_int} which gives
3579 the offset in bytes into the entire argument of where this part starts.
3580 As a special exception the first @code{expr_list} in the @code{parallel}
3581 RTX may have a first operand of zero. This indicates that the entire
3582 argument is also stored on the stack.
3584 The last time this macro is called, it is called with @code{MODE ==
3585 VOIDmode}, and its result is passed to the @code{call} or @code{call_value}
3586 pattern as operands 2 and 3 respectively.
3588 @cindex @file{stdarg.h} and register arguments
3589 The usual way to make the ISO library @file{stdarg.h} work on a machine
3590 where some arguments are usually passed in registers, is to cause
3591 nameless arguments to be passed on the stack instead. This is done
3592 by making @code{FUNCTION_ARG} return 0 whenever @var{named} is 0.
3594 @cindex @code{MUST_PASS_IN_STACK}, and @code{FUNCTION_ARG}
3595 @cindex @code{REG_PARM_STACK_SPACE}, and @code{FUNCTION_ARG}
3596 You may use the macro @code{MUST_PASS_IN_STACK (@var{mode}, @var{type})}
3597 in the definition of this macro to determine if this argument is of a
3598 type that must be passed in the stack. If @code{REG_PARM_STACK_SPACE}
3599 is not defined and @code{FUNCTION_ARG} returns nonzero for such an
3600 argument, the compiler will abort. If @code{REG_PARM_STACK_SPACE} is
3601 defined, the argument will be computed in the stack and then loaded into
3605 @defmac MUST_PASS_IN_STACK (@var{mode}, @var{type})
3606 Define as a C expression that evaluates to nonzero if we do not know how
3607 to pass TYPE solely in registers. The file @file{expr.h} defines a
3608 definition that is usually appropriate, refer to @file{expr.h} for additional
3612 @defmac FUNCTION_INCOMING_ARG (@var{cum}, @var{mode}, @var{type}, @var{named})
3613 Define this macro if the target machine has ``register windows'', so
3614 that the register in which a function sees an arguments is not
3615 necessarily the same as the one in which the caller passed the
3618 For such machines, @code{FUNCTION_ARG} computes the register in which
3619 the caller passes the value, and @code{FUNCTION_INCOMING_ARG} should
3620 be defined in a similar fashion to tell the function being called
3621 where the arguments will arrive.
3623 If @code{FUNCTION_INCOMING_ARG} is not defined, @code{FUNCTION_ARG}
3624 serves both purposes.
3627 @defmac FUNCTION_ARG_PARTIAL_NREGS (@var{cum}, @var{mode}, @var{type}, @var{named})
3628 A C expression for the number of words, at the beginning of an
3629 argument, that must be put in registers. The value must be zero for
3630 arguments that are passed entirely in registers or that are entirely
3631 pushed on the stack.
3633 On some machines, certain arguments must be passed partially in
3634 registers and partially in memory. On these machines, typically the
3635 first @var{n} words of arguments are passed in registers, and the rest
3636 on the stack. If a multi-word argument (a @code{double} or a
3637 structure) crosses that boundary, its first few words must be passed
3638 in registers and the rest must be pushed. This macro tells the
3639 compiler when this occurs, and how many of the words should go in
3642 @code{FUNCTION_ARG} for these arguments should return the first
3643 register to be used by the caller for this argument; likewise
3644 @code{FUNCTION_INCOMING_ARG}, for the called function.
3647 @defmac FUNCTION_ARG_PASS_BY_REFERENCE (@var{cum}, @var{mode}, @var{type}, @var{named})
3648 A C expression that indicates when an argument must be passed by reference.
3649 If nonzero for an argument, a copy of that argument is made in memory and a
3650 pointer to the argument is passed instead of the argument itself.
3651 The pointer is passed in whatever way is appropriate for passing a pointer
3654 On machines where @code{REG_PARM_STACK_SPACE} is not defined, a suitable
3655 definition of this macro might be
3657 #define FUNCTION_ARG_PASS_BY_REFERENCE\
3658 (CUM, MODE, TYPE, NAMED) \
3659 MUST_PASS_IN_STACK (MODE, TYPE)
3661 @c this is *still* too long. --mew 5feb93
3664 @defmac FUNCTION_ARG_CALLEE_COPIES (@var{cum}, @var{mode}, @var{type}, @var{named})
3665 If defined, a C expression that indicates when it is the called function's
3666 responsibility to make a copy of arguments passed by invisible reference.
3667 Normally, the caller makes a copy and passes the address of the copy to the
3668 routine being called. When @code{FUNCTION_ARG_CALLEE_COPIES} is defined and is
3669 nonzero, the caller does not make a copy. Instead, it passes a pointer to the
3670 ``live'' value. The called function must not modify this value. If it can be
3671 determined that the value won't be modified, it need not make a copy;
3672 otherwise a copy must be made.
3675 @defmac CUMULATIVE_ARGS
3676 A C type for declaring a variable that is used as the first argument of
3677 @code{FUNCTION_ARG} and other related values. For some target machines,
3678 the type @code{int} suffices and can hold the number of bytes of
3681 There is no need to record in @code{CUMULATIVE_ARGS} anything about the
3682 arguments that have been passed on the stack. The compiler has other
3683 variables to keep track of that. For target machines on which all
3684 arguments are passed on the stack, there is no need to store anything in
3685 @code{CUMULATIVE_ARGS}; however, the data structure must exist and
3686 should not be empty, so use @code{int}.
3689 @defmac INIT_CUMULATIVE_ARGS (@var{cum}, @var{fntype}, @var{libname}, @var{fndecl})
3690 A C statement (sans semicolon) for initializing the variable
3691 @var{cum} for the state at the beginning of the argument list. The
3692 variable has type @code{CUMULATIVE_ARGS}. The value of @var{fntype}
3693 is the tree node for the data type of the function which will receive
3694 the args, or 0 if the args are to a compiler support library function.
3695 For direct calls that are not libcalls, @var{fndecl} contain the
3696 declaration node of the function. @var{fndecl} is also set when
3697 @code{INIT_CUMULATIVE_ARGS} is used to find arguments for the function
3700 When processing a call to a compiler support library function,
3701 @var{libname} identifies which one. It is a @code{symbol_ref} rtx which
3702 contains the name of the function, as a string. @var{libname} is 0 when
3703 an ordinary C function call is being processed. Thus, each time this
3704 macro is called, either @var{libname} or @var{fntype} is nonzero, but
3705 never both of them at once.
3708 @defmac INIT_CUMULATIVE_LIBCALL_ARGS (@var{cum}, @var{mode}, @var{libname})
3709 Like @code{INIT_CUMULATIVE_ARGS} but only used for outgoing libcalls,
3710 it gets a @code{MODE} argument instead of @var{fntype}, that would be
3711 @code{NULL}. @var{indirect} would always be zero, too. If this macro
3712 is not defined, @code{INIT_CUMULATIVE_ARGS (cum, NULL_RTX, libname,
3713 0)} is used instead.
3716 @defmac INIT_CUMULATIVE_INCOMING_ARGS (@var{cum}, @var{fntype}, @var{libname})
3717 Like @code{INIT_CUMULATIVE_ARGS} but overrides it for the purposes of
3718 finding the arguments for the function being compiled. If this macro is
3719 undefined, @code{INIT_CUMULATIVE_ARGS} is used instead.
3721 The value passed for @var{libname} is always 0, since library routines
3722 with special calling conventions are never compiled with GCC@. The
3723 argument @var{libname} exists for symmetry with
3724 @code{INIT_CUMULATIVE_ARGS}.
3725 @c could use "this macro" in place of @code{INIT_CUMULATIVE_ARGS}, maybe.
3726 @c --mew 5feb93 i switched the order of the sentences. --mew 10feb93
3729 @defmac FUNCTION_ARG_ADVANCE (@var{cum}, @var{mode}, @var{type}, @var{named})
3730 A C statement (sans semicolon) to update the summarizer variable
3731 @var{cum} to advance past an argument in the argument list. The
3732 values @var{mode}, @var{type} and @var{named} describe that argument.
3733 Once this is done, the variable @var{cum} is suitable for analyzing
3734 the @emph{following} argument with @code{FUNCTION_ARG}, etc.
3736 This macro need not do anything if the argument in question was passed
3737 on the stack. The compiler knows how to track the amount of stack space
3738 used for arguments without any special help.
3741 @defmac FUNCTION_ARG_PADDING (@var{mode}, @var{type})
3742 If defined, a C expression which determines whether, and in which direction,
3743 to pad out an argument with extra space. The value should be of type
3744 @code{enum direction}: either @code{upward} to pad above the argument,
3745 @code{downward} to pad below, or @code{none} to inhibit padding.
3747 The @emph{amount} of padding is always just enough to reach the next
3748 multiple of @code{FUNCTION_ARG_BOUNDARY}; this macro does not control
3751 This macro has a default definition which is right for most systems.
3752 For little-endian machines, the default is to pad upward. For
3753 big-endian machines, the default is to pad downward for an argument of
3754 constant size shorter than an @code{int}, and upward otherwise.
3757 @defmac PAD_VARARGS_DOWN
3758 If defined, a C expression which determines whether the default
3759 implementation of va_arg will attempt to pad down before reading the
3760 next argument, if that argument is smaller than its aligned space as
3761 controlled by @code{PARM_BOUNDARY}. If this macro is not defined, all such
3762 arguments are padded down if @code{BYTES_BIG_ENDIAN} is true.
3765 @defmac FUNCTION_ARG_BOUNDARY (@var{mode}, @var{type})
3766 If defined, a C expression that gives the alignment boundary, in bits,
3767 of an argument with the specified mode and type. If it is not defined,
3768 @code{PARM_BOUNDARY} is used for all arguments.
3771 @defmac FUNCTION_ARG_REGNO_P (@var{regno})
3772 A C expression that is nonzero if @var{regno} is the number of a hard
3773 register in which function arguments are sometimes passed. This does
3774 @emph{not} include implicit arguments such as the static chain and
3775 the structure-value address. On many machines, no registers can be
3776 used for this purpose since all function arguments are pushed on the
3780 @defmac SPLIT_COMPLEX_ARGS
3782 Define this macro to a nonzero value if complex function arguments
3783 should be split into their corresponding components. By default, GCC
3784 will attempt to pack complex arguments into the target's word size.
3785 Some ABIs require complex arguments to be split and treated as their
3786 individual components. For example, on AIX64, complex floats should
3787 be passed in a pair of floating point registers, even though a complex
3788 float would fit in one 64-bit floating point register.
3791 @defmac LOAD_ARGS_REVERSED
3792 If defined, the order in which arguments are loaded into their
3793 respective argument registers is reversed so that the last
3794 argument is loaded first. This macro only affects arguments
3795 passed in registers.
3799 @subsection How Scalar Function Values Are Returned
3800 @cindex return values in registers
3801 @cindex values, returned by functions
3802 @cindex scalars, returned as values
3804 This section discusses the macros that control returning scalars as
3805 values---values that can fit in registers.
3807 @defmac FUNCTION_VALUE (@var{valtype}, @var{func})
3808 A C expression to create an RTX representing the place where a
3809 function returns a value of data type @var{valtype}. @var{valtype} is
3810 a tree node representing a data type. Write @code{TYPE_MODE
3811 (@var{valtype})} to get the machine mode used to represent that type.
3812 On many machines, only the mode is relevant. (Actually, on most
3813 machines, scalar values are returned in the same place regardless of
3816 The value of the expression is usually a @code{reg} RTX for the hard
3817 register where the return value is stored. The value can also be a
3818 @code{parallel} RTX, if the return value is in multiple places. See
3819 @code{FUNCTION_ARG} for an explanation of the @code{parallel} form.
3821 If @code{PROMOTE_FUNCTION_RETURN} is defined, you must apply the same
3822 promotion rules specified in @code{PROMOTE_MODE} if @var{valtype} is a
3825 If the precise function being called is known, @var{func} is a tree
3826 node (@code{FUNCTION_DECL}) for it; otherwise, @var{func} is a null
3827 pointer. This makes it possible to use a different value-returning
3828 convention for specific functions when all their calls are
3831 @code{FUNCTION_VALUE} is not used for return vales with aggregate data
3832 types, because these are returned in another way. See
3833 @code{STRUCT_VALUE_REGNUM} and related macros, below.
3836 @defmac FUNCTION_OUTGOING_VALUE (@var{valtype}, @var{func})
3837 Define this macro if the target machine has ``register windows''
3838 so that the register in which a function returns its value is not
3839 the same as the one in which the caller sees the value.
3841 For such machines, @code{FUNCTION_VALUE} computes the register in which
3842 the caller will see the value. @code{FUNCTION_OUTGOING_VALUE} should be
3843 defined in a similar fashion to tell the function where to put the
3846 If @code{FUNCTION_OUTGOING_VALUE} is not defined,
3847 @code{FUNCTION_VALUE} serves both purposes.
3849 @code{FUNCTION_OUTGOING_VALUE} is not used for return vales with
3850 aggregate data types, because these are returned in another way. See
3851 @code{STRUCT_VALUE_REGNUM} and related macros, below.
3854 @defmac LIBCALL_VALUE (@var{mode})
3855 A C expression to create an RTX representing the place where a library
3856 function returns a value of mode @var{mode}. If the precise function
3857 being called is known, @var{func} is a tree node
3858 (@code{FUNCTION_DECL}) for it; otherwise, @var{func} is a null
3859 pointer. This makes it possible to use a different value-returning
3860 convention for specific functions when all their calls are
3863 Note that ``library function'' in this context means a compiler
3864 support routine, used to perform arithmetic, whose name is known
3865 specially by the compiler and was not mentioned in the C code being
3868 The definition of @code{LIBRARY_VALUE} need not be concerned aggregate
3869 data types, because none of the library functions returns such types.
3872 @defmac FUNCTION_VALUE_REGNO_P (@var{regno})
3873 A C expression that is nonzero if @var{regno} is the number of a hard
3874 register in which the values of called function may come back.
3876 A register whose use for returning values is limited to serving as the
3877 second of a pair (for a value of type @code{double}, say) need not be
3878 recognized by this macro. So for most machines, this definition
3882 #define FUNCTION_VALUE_REGNO_P(N) ((N) == 0)
3885 If the machine has register windows, so that the caller and the called
3886 function use different registers for the return value, this macro
3887 should recognize only the caller's register numbers.
3890 @defmac APPLY_RESULT_SIZE
3891 Define this macro if @samp{untyped_call} and @samp{untyped_return}
3892 need more space than is implied by @code{FUNCTION_VALUE_REGNO_P} for
3893 saving and restoring an arbitrary return value.
3896 @node Aggregate Return
3897 @subsection How Large Values Are Returned
3898 @cindex aggregates as return values
3899 @cindex large return values
3900 @cindex returning aggregate values
3901 @cindex structure value address
3903 When a function value's mode is @code{BLKmode} (and in some other
3904 cases), the value is not returned according to @code{FUNCTION_VALUE}
3905 (@pxref{Scalar Return}). Instead, the caller passes the address of a
3906 block of memory in which the value should be stored. This address
3907 is called the @dfn{structure value address}.
3909 This section describes how to control returning structure values in
3912 @defmac RETURN_IN_MEMORY (@var{type})
3913 A C expression which can inhibit the returning of certain function
3914 values in registers, based on the type of value. A nonzero value says
3915 to return the function value in memory, just as large structures are
3916 always returned. Here @var{type} will be a C expression of type
3917 @code{tree}, representing the data type of the value.
3919 Note that values of mode @code{BLKmode} must be explicitly handled
3920 by this macro. Also, the option @option{-fpcc-struct-return}
3921 takes effect regardless of this macro. On most systems, it is
3922 possible to leave the macro undefined; this causes a default
3923 definition to be used, whose value is the constant 1 for @code{BLKmode}
3924 values, and 0 otherwise.
3926 Do not use this macro to indicate that structures and unions should always
3927 be returned in memory. You should instead use @code{DEFAULT_PCC_STRUCT_RETURN}
3931 @defmac DEFAULT_PCC_STRUCT_RETURN
3932 Define this macro to be 1 if all structure and union return values must be
3933 in memory. Since this results in slower code, this should be defined
3934 only if needed for compatibility with other compilers or with an ABI@.
3935 If you define this macro to be 0, then the conventions used for structure
3936 and union return values are decided by the @code{RETURN_IN_MEMORY} macro.
3938 If not defined, this defaults to the value 1.
3941 @defmac STRUCT_VALUE_REGNUM
3942 If the structure value address is passed in a register, then
3943 @code{STRUCT_VALUE_REGNUM} should be the number of that register.
3946 @defmac STRUCT_VALUE
3947 If the structure value address is not passed in a register, define
3948 @code{STRUCT_VALUE} as an expression returning an RTX for the place
3949 where the address is passed. If it returns 0, the address is passed as
3950 an ``invisible'' first argument.
3953 @defmac STRUCT_VALUE_INCOMING_REGNUM
3954 On some architectures the place where the structure value address
3955 is found by the called function is not the same place that the
3956 caller put it. This can be due to register windows, or it could
3957 be because the function prologue moves it to a different place.
3959 If the incoming location of the structure value address is in a
3960 register, define this macro as the register number.
3963 @defmac STRUCT_VALUE_INCOMING
3964 If the incoming location is not a register, then you should define
3965 @code{STRUCT_VALUE_INCOMING} as an expression for an RTX for where the
3966 called function should find the value. If it should find the value on
3967 the stack, define this to create a @code{mem} which refers to the frame
3968 pointer. A definition of 0 means that the address is passed as an
3969 ``invisible'' first argument.
3972 @defmac PCC_STATIC_STRUCT_RETURN
3973 Define this macro if the usual system convention on the target machine
3974 for returning structures and unions is for the called function to return
3975 the address of a static variable containing the value.
3977 Do not define this if the usual system convention is for the caller to
3978 pass an address to the subroutine.
3980 This macro has effect in @option{-fpcc-struct-return} mode, but it does
3981 nothing when you use @option{-freg-struct-return} mode.
3985 @subsection Caller-Saves Register Allocation
3987 If you enable it, GCC can save registers around function calls. This
3988 makes it possible to use call-clobbered registers to hold variables that
3989 must live across calls.
3991 @defmac DEFAULT_CALLER_SAVES
3992 Define this macro if function calls on the target machine do not preserve
3993 any registers; in other words, if @code{CALL_USED_REGISTERS} has 1
3994 for all registers. When defined, this macro enables @option{-fcaller-saves}
3995 by default for all optimization levels. It has no effect for optimization
3996 levels 2 and higher, where @option{-fcaller-saves} is the default.
3999 @defmac CALLER_SAVE_PROFITABLE (@var{refs}, @var{calls})
4000 A C expression to determine whether it is worthwhile to consider placing
4001 a pseudo-register in a call-clobbered hard register and saving and
4002 restoring it around each function call. The expression should be 1 when
4003 this is worth doing, and 0 otherwise.
4005 If you don't define this macro, a default is used which is good on most
4006 machines: @code{4 * @var{calls} < @var{refs}}.
4009 @defmac HARD_REGNO_CALLER_SAVE_MODE (@var{regno}, @var{nregs})
4010 A C expression specifying which mode is required for saving @var{nregs}
4011 of a pseudo-register in call-clobbered hard register @var{regno}. If
4012 @var{regno} is unsuitable for caller save, @code{VOIDmode} should be
4013 returned. For most machines this macro need not be defined since GCC
4014 will select the smallest suitable mode.
4017 @node Function Entry
4018 @subsection Function Entry and Exit
4019 @cindex function entry and exit
4023 This section describes the macros that output function entry
4024 (@dfn{prologue}) and exit (@dfn{epilogue}) code.
4026 @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_PROLOGUE (FILE *@var{file}, HOST_WIDE_INT @var{size})
4027 If defined, a function that outputs the assembler code for entry to a
4028 function. The prologue is responsible for setting up the stack frame,
4029 initializing the frame pointer register, saving registers that must be
4030 saved, and allocating @var{size} additional bytes of storage for the
4031 local variables. @var{size} is an integer. @var{file} is a stdio
4032 stream to which the assembler code should be output.
4034 The label for the beginning of the function need not be output by this
4035 macro. That has already been done when the macro is run.
4037 @findex regs_ever_live
4038 To determine which registers to save, the macro can refer to the array
4039 @code{regs_ever_live}: element @var{r} is nonzero if hard register
4040 @var{r} is used anywhere within the function. This implies the function
4041 prologue should save register @var{r}, provided it is not one of the
4042 call-used registers. (@code{TARGET_ASM_FUNCTION_EPILOGUE} must likewise use
4043 @code{regs_ever_live}.)
4045 On machines that have ``register windows'', the function entry code does
4046 not save on the stack the registers that are in the windows, even if
4047 they are supposed to be preserved by function calls; instead it takes
4048 appropriate steps to ``push'' the register stack, if any non-call-used
4049 registers are used in the function.
4051 @findex frame_pointer_needed
4052 On machines where functions may or may not have frame-pointers, the
4053 function entry code must vary accordingly; it must set up the frame
4054 pointer if one is wanted, and not otherwise. To determine whether a
4055 frame pointer is in wanted, the macro can refer to the variable
4056 @code{frame_pointer_needed}. The variable's value will be 1 at run
4057 time in a function that needs a frame pointer. @xref{Elimination}.
4059 The function entry code is responsible for allocating any stack space
4060 required for the function. This stack space consists of the regions
4061 listed below. In most cases, these regions are allocated in the
4062 order listed, with the last listed region closest to the top of the
4063 stack (the lowest address if @code{STACK_GROWS_DOWNWARD} is defined, and
4064 the highest address if it is not defined). You can use a different order
4065 for a machine if doing so is more convenient or required for
4066 compatibility reasons. Except in cases where required by standard
4067 or by a debugger, there is no reason why the stack layout used by GCC
4068 need agree with that used by other compilers for a machine.
4071 @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_END_PROLOGUE (FILE *@var{file})
4072 If defined, a function that outputs assembler code at the end of a
4073 prologue. This should be used when the function prologue is being
4074 emitted as RTL, and you have some extra assembler that needs to be
4075 emitted. @xref{prologue instruction pattern}.
4078 @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_BEGIN_EPILOGUE (FILE *@var{file})
4079 If defined, a function that outputs assembler code at the start of an
4080 epilogue. This should be used when the function epilogue is being
4081 emitted as RTL, and you have some extra assembler that needs to be
4082 emitted. @xref{epilogue instruction pattern}.
4085 @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_EPILOGUE (FILE *@var{file}, HOST_WIDE_INT @var{size})
4086 If defined, a function that outputs the assembler code for exit from a
4087 function. The epilogue is responsible for restoring the saved
4088 registers and stack pointer to their values when the function was
4089 called, and returning control to the caller. This macro takes the
4090 same arguments as the macro @code{TARGET_ASM_FUNCTION_PROLOGUE}, and the
4091 registers to restore are determined from @code{regs_ever_live} and
4092 @code{CALL_USED_REGISTERS} in the same way.
4094 On some machines, there is a single instruction that does all the work
4095 of returning from the function. On these machines, give that
4096 instruction the name @samp{return} and do not define the macro
4097 @code{TARGET_ASM_FUNCTION_EPILOGUE} at all.
4099 Do not define a pattern named @samp{return} if you want the
4100 @code{TARGET_ASM_FUNCTION_EPILOGUE} to be used. If you want the target
4101 switches to control whether return instructions or epilogues are used,
4102 define a @samp{return} pattern with a validity condition that tests the
4103 target switches appropriately. If the @samp{return} pattern's validity
4104 condition is false, epilogues will be used.
4106 On machines where functions may or may not have frame-pointers, the
4107 function exit code must vary accordingly. Sometimes the code for these
4108 two cases is completely different. To determine whether a frame pointer
4109 is wanted, the macro can refer to the variable
4110 @code{frame_pointer_needed}. The variable's value will be 1 when compiling
4111 a function that needs a frame pointer.
4113 Normally, @code{TARGET_ASM_FUNCTION_PROLOGUE} and
4114 @code{TARGET_ASM_FUNCTION_EPILOGUE} must treat leaf functions specially.
4115 The C variable @code{current_function_is_leaf} is nonzero for such a
4116 function. @xref{Leaf Functions}.
4118 On some machines, some functions pop their arguments on exit while
4119 others leave that for the caller to do. For example, the 68020 when
4120 given @option{-mrtd} pops arguments in functions that take a fixed
4121 number of arguments.
4123 @findex current_function_pops_args
4124 Your definition of the macro @code{RETURN_POPS_ARGS} decides which
4125 functions pop their own arguments. @code{TARGET_ASM_FUNCTION_EPILOGUE}
4126 needs to know what was decided. The variable that is called
4127 @code{current_function_pops_args} is the number of bytes of its
4128 arguments that a function should pop. @xref{Scalar Return}.
4129 @c what is the "its arguments" in the above sentence referring to, pray
4130 @c tell? --mew 5feb93
4135 @findex current_function_pretend_args_size
4136 A region of @code{current_function_pretend_args_size} bytes of
4137 uninitialized space just underneath the first argument arriving on the
4138 stack. (This may not be at the very start of the allocated stack region
4139 if the calling sequence has pushed anything else since pushing the stack
4140 arguments. But usually, on such machines, nothing else has been pushed
4141 yet, because the function prologue itself does all the pushing.) This
4142 region is used on machines where an argument may be passed partly in
4143 registers and partly in memory, and, in some cases to support the
4144 features in @code{<stdarg.h>}.
4147 An area of memory used to save certain registers used by the function.
4148 The size of this area, which may also include space for such things as
4149 the return address and pointers to previous stack frames, is
4150 machine-specific and usually depends on which registers have been used
4151 in the function. Machines with register windows often do not require
4155 A region of at least @var{size} bytes, possibly rounded up to an allocation
4156 boundary, to contain the local variables of the function. On some machines,
4157 this region and the save area may occur in the opposite order, with the
4158 save area closer to the top of the stack.
4161 @cindex @code{ACCUMULATE_OUTGOING_ARGS} and stack frames
4162 Optionally, when @code{ACCUMULATE_OUTGOING_ARGS} is defined, a region of
4163 @code{current_function_outgoing_args_size} bytes to be used for outgoing
4164 argument lists of the function. @xref{Stack Arguments}.
4167 Normally, it is necessary for the macros
4168 @code{TARGET_ASM_FUNCTION_PROLOGUE} and
4169 @code{TARGET_ASM_FUNCTION_EPILOGUE} to treat leaf functions specially.
4170 The C variable @code{current_function_is_leaf} is nonzero for such a
4173 @defmac EXIT_IGNORE_STACK
4174 Define this macro as a C expression that is nonzero if the return
4175 instruction or the function epilogue ignores the value of the stack
4176 pointer; in other words, if it is safe to delete an instruction to
4177 adjust the stack pointer before a return from the function.
4179 Note that this macro's value is relevant only for functions for which
4180 frame pointers are maintained. It is never safe to delete a final
4181 stack adjustment in a function that has no frame pointer, and the
4182 compiler knows this regardless of @code{EXIT_IGNORE_STACK}.
4185 @defmac EPILOGUE_USES (@var{regno})
4186 Define this macro as a C expression that is nonzero for registers that are
4187 used by the epilogue or the @samp{return} pattern. The stack and frame
4188 pointer registers are already be assumed to be used as needed.
4191 @defmac EH_USES (@var{regno})
4192 Define this macro as a C expression that is nonzero for registers that are
4193 used by the exception handling mechanism, and so should be considered live
4194 on entry to an exception edge.
4197 @defmac DELAY_SLOTS_FOR_EPILOGUE
4198 Define this macro if the function epilogue contains delay slots to which
4199 instructions from the rest of the function can be ``moved''. The
4200 definition should be a C expression whose value is an integer
4201 representing the number of delay slots there.
4204 @defmac ELIGIBLE_FOR_EPILOGUE_DELAY (@var{insn}, @var{n})
4205 A C expression that returns 1 if @var{insn} can be placed in delay
4206 slot number @var{n} of the epilogue.
4208 The argument @var{n} is an integer which identifies the delay slot now
4209 being considered (since different slots may have different rules of
4210 eligibility). It is never negative and is always less than the number
4211 of epilogue delay slots (what @code{DELAY_SLOTS_FOR_EPILOGUE} returns).
4212 If you reject a particular insn for a given delay slot, in principle, it
4213 may be reconsidered for a subsequent delay slot. Also, other insns may
4214 (at least in principle) be considered for the so far unfilled delay
4217 @findex current_function_epilogue_delay_list
4218 @findex final_scan_insn
4219 The insns accepted to fill the epilogue delay slots are put in an RTL
4220 list made with @code{insn_list} objects, stored in the variable
4221 @code{current_function_epilogue_delay_list}. The insn for the first
4222 delay slot comes first in the list. Your definition of the macro
4223 @code{TARGET_ASM_FUNCTION_EPILOGUE} should fill the delay slots by
4224 outputting the insns in this list, usually by calling
4225 @code{final_scan_insn}.
4227 You need not define this macro if you did not define
4228 @code{DELAY_SLOTS_FOR_EPILOGUE}.
4231 @deftypefn {Target Hook} void TARGET_ASM_OUTPUT_MI_THUNK (FILE *@var{file}, tree @var{thunk_fndecl}, HOST_WIDE_INT @var{delta}, tree @var{function})
4232 A function that outputs the assembler code for a thunk
4233 function, used to implement C++ virtual function calls with multiple
4234 inheritance. The thunk acts as a wrapper around a virtual function,
4235 adjusting the implicit object parameter before handing control off to
4238 First, emit code to add the integer @var{delta} to the location that
4239 contains the incoming first argument. Assume that this argument
4240 contains a pointer, and is the one used to pass the @code{this} pointer
4241 in C++. This is the incoming argument @emph{before} the function prologue,
4242 e.g.@: @samp{%o0} on a sparc. The addition must preserve the values of
4243 all other incoming arguments.
4245 After the addition, emit code to jump to @var{function}, which is a
4246 @code{FUNCTION_DECL}. This is a direct pure jump, not a call, and does
4247 not touch the return address. Hence returning from @var{FUNCTION} will
4248 return to whoever called the current @samp{thunk}.
4250 The effect must be as if @var{function} had been called directly with
4251 the adjusted first argument. This macro is responsible for emitting all
4252 of the code for a thunk function; @code{TARGET_ASM_FUNCTION_PROLOGUE}
4253 and @code{TARGET_ASM_FUNCTION_EPILOGUE} are not invoked.
4255 The @var{thunk_fndecl} is redundant. (@var{delta} and @var{function}
4256 have already been extracted from it.) It might possibly be useful on
4257 some targets, but probably not.
4259 If you do not define this macro, the target-independent code in the C++
4260 front end will generate a less efficient heavyweight thunk that calls
4261 @var{function} instead of jumping to it. The generic approach does
4262 not support varargs.
4265 @deftypefn {Target Hook} void TARGET_ASM_OUTPUT_MI_VCALL_THUNK (FILE *@var{file}, tree @var{thunk_fndecl}, HOST_WIDE_INT @var{delta}, int @var{vcall_offset}, tree @var{function})
4266 A function like @code{TARGET_ASM_OUTPUT_MI_THUNK}, except that if
4267 @var{vcall_offset} is nonzero, an additional adjustment should be made
4268 after adding @code{delta}. In particular, if @var{p} is the
4269 adjusted pointer, the following adjustment should be made:
4272 p += (*((ptrdiff_t **)p))[vcall_offset/sizeof(ptrdiff_t)]
4276 If this function is defined, it will always be used in place of
4277 @code{TARGET_ASM_OUTPUT_MI_THUNK}.
4281 @subsection Generating Code for Profiling
4282 @cindex profiling, code generation
4284 These macros will help you generate code for profiling.
4286 @defmac FUNCTION_PROFILER (@var{file}, @var{labelno})
4287 A C statement or compound statement to output to @var{file} some
4288 assembler code to call the profiling subroutine @code{mcount}.
4291 The details of how @code{mcount} expects to be called are determined by
4292 your operating system environment, not by GCC@. To figure them out,
4293 compile a small program for profiling using the system's installed C
4294 compiler and look at the assembler code that results.
4296 Older implementations of @code{mcount} expect the address of a counter
4297 variable to be loaded into some register. The name of this variable is
4298 @samp{LP} followed by the number @var{labelno}, so you would generate
4299 the name using @samp{LP%d} in a @code{fprintf}.
4302 @defmac PROFILE_HOOK
4303 A C statement or compound statement to output to @var{file} some assembly
4304 code to call the profiling subroutine @code{mcount} even the target does
4305 not support profiling.
4308 @defmac NO_PROFILE_COUNTERS
4309 Define this macro if the @code{mcount} subroutine on your system does
4310 not need a counter variable allocated for each function. This is true
4311 for almost all modern implementations. If you define this macro, you
4312 must not use the @var{labelno} argument to @code{FUNCTION_PROFILER}.
4315 @defmac PROFILE_BEFORE_PROLOGUE
4316 Define this macro if the code for function profiling should come before
4317 the function prologue. Normally, the profiling code comes after.
4321 @subsection Permitting tail calls
4324 @deftypefn {Target Hook} bool TARGET_FUNCTION_OK_FOR_SIBCALL (tree @var{decl}, tree @var{exp})
4325 True if it is ok to do sibling call optimization for the specified
4326 call expression @var{exp}. @var{decl} will be the called function,
4327 or @code{NULL} if this is an indirect call.
4329 It is not uncommon for limitations of calling conventions to prevent
4330 tail calls to functions outside the current unit of translation, or
4331 during PIC compilation. The hook is used to enforce these restrictions,
4332 as the @code{sibcall} md pattern can not fail, or fall over to a
4333 ``normal'' call. The criteria for successful sibling call optimization
4334 may vary greatly between different architectures.
4338 @section Implementing the Varargs Macros
4339 @cindex varargs implementation
4341 GCC comes with an implementation of @code{<varargs.h>} and
4342 @code{<stdarg.h>} that work without change on machines that pass arguments
4343 on the stack. Other machines require their own implementations of
4344 varargs, and the two machine independent header files must have
4345 conditionals to include it.
4347 ISO @code{<stdarg.h>} differs from traditional @code{<varargs.h>} mainly in
4348 the calling convention for @code{va_start}. The traditional
4349 implementation takes just one argument, which is the variable in which
4350 to store the argument pointer. The ISO implementation of
4351 @code{va_start} takes an additional second argument. The user is
4352 supposed to write the last named argument of the function here.
4354 However, @code{va_start} should not use this argument. The way to find
4355 the end of the named arguments is with the built-in functions described
4358 @defmac __builtin_saveregs ()
4359 Use this built-in function to save the argument registers in memory so
4360 that the varargs mechanism can access them. Both ISO and traditional
4361 versions of @code{va_start} must use @code{__builtin_saveregs}, unless
4362 you use @code{SETUP_INCOMING_VARARGS} (see below) instead.
4364 On some machines, @code{__builtin_saveregs} is open-coded under the
4365 control of the macro @code{EXPAND_BUILTIN_SAVEREGS}. On other machines,
4366 it calls a routine written in assembler language, found in
4369 Code generated for the call to @code{__builtin_saveregs} appears at the
4370 beginning of the function, as opposed to where the call to
4371 @code{__builtin_saveregs} is written, regardless of what the code is.
4372 This is because the registers must be saved before the function starts
4373 to use them for its own purposes.
4374 @c i rewrote the first sentence above to fix an overfull hbox. --mew
4378 @defmac __builtin_args_info (@var{category})
4379 Use this built-in function to find the first anonymous arguments in
4382 In general, a machine may have several categories of registers used for
4383 arguments, each for a particular category of data types. (For example,
4384 on some machines, floating-point registers are used for floating-point
4385 arguments while other arguments are passed in the general registers.)
4386 To make non-varargs functions use the proper calling convention, you
4387 have defined the @code{CUMULATIVE_ARGS} data type to record how many
4388 registers in each category have been used so far
4390 @code{__builtin_args_info} accesses the same data structure of type
4391 @code{CUMULATIVE_ARGS} after the ordinary argument layout is finished
4392 with it, with @var{category} specifying which word to access. Thus, the
4393 value indicates the first unused register in a given category.
4395 Normally, you would use @code{__builtin_args_info} in the implementation
4396 of @code{va_start}, accessing each category just once and storing the
4397 value in the @code{va_list} object. This is because @code{va_list} will
4398 have to update the values, and there is no way to alter the
4399 values accessed by @code{__builtin_args_info}.
4402 @defmac __builtin_next_arg (@var{lastarg})
4403 This is the equivalent of @code{__builtin_args_info}, for stack
4404 arguments. It returns the address of the first anonymous stack
4405 argument, as type @code{void *}. If @code{ARGS_GROW_DOWNWARD}, it
4406 returns the address of the location above the first anonymous stack
4407 argument. Use it in @code{va_start} to initialize the pointer for
4408 fetching arguments from the stack. Also use it in @code{va_start} to
4409 verify that the second parameter @var{lastarg} is the last named argument
4410 of the current function.
4413 @defmac __builtin_classify_type (@var{object})
4414 Since each machine has its own conventions for which data types are
4415 passed in which kind of register, your implementation of @code{va_arg}
4416 has to embody these conventions. The easiest way to categorize the
4417 specified data type is to use @code{__builtin_classify_type} together
4418 with @code{sizeof} and @code{__alignof__}.
4420 @code{__builtin_classify_type} ignores the value of @var{object},
4421 considering only its data type. It returns an integer describing what
4422 kind of type that is---integer, floating, pointer, structure, and so on.
4424 The file @file{typeclass.h} defines an enumeration that you can use to
4425 interpret the values of @code{__builtin_classify_type}.
4428 These machine description macros help implement varargs:
4430 @defmac EXPAND_BUILTIN_SAVEREGS ()
4431 If defined, is a C expression that produces the machine-specific code
4432 for a call to @code{__builtin_saveregs}. This code will be moved to the
4433 very beginning of the function, before any parameter access are made.
4434 The return value of this function should be an RTX that contains the
4435 value to use as the return of @code{__builtin_saveregs}.
4438 @defmac SETUP_INCOMING_VARARGS (@var{args_so_far}, @var{mode}, @var{type}, @var{pretend_args_size}, @var{second_time})
4439 This macro offers an alternative to using @code{__builtin_saveregs} and
4440 defining the macro @code{EXPAND_BUILTIN_SAVEREGS}. Use it to store the
4441 anonymous register arguments into the stack so that all the arguments
4442 appear to have been passed consecutively on the stack. Once this is
4443 done, you can use the standard implementation of varargs that works for
4444 machines that pass all their arguments on the stack.
4446 The argument @var{args_so_far} is the @code{CUMULATIVE_ARGS} data
4447 structure, containing the values that are obtained after processing the
4448 named arguments. The arguments @var{mode} and @var{type} describe the
4449 last named argument---its machine mode and its data type as a tree node.
4451 The macro implementation should do two things: first, push onto the
4452 stack all the argument registers @emph{not} used for the named
4453 arguments, and second, store the size of the data thus pushed into the
4454 @code{int}-valued variable whose name is supplied as the argument
4455 @var{pretend_args_size}. The value that you store here will serve as
4456 additional offset for setting up the stack frame.
4458 Because you must generate code to push the anonymous arguments at
4459 compile time without knowing their data types,
4460 @code{SETUP_INCOMING_VARARGS} is only useful on machines that have just
4461 a single category of argument register and use it uniformly for all data
4464 If the argument @var{second_time} is nonzero, it means that the
4465 arguments of the function are being analyzed for the second time. This
4466 happens for an inline function, which is not actually compiled until the
4467 end of the source file. The macro @code{SETUP_INCOMING_VARARGS} should
4468 not generate any instructions in this case.
4471 @defmac STRICT_ARGUMENT_NAMING
4472 Define this macro to be a nonzero value if the location where a function
4473 argument is passed depends on whether or not it is a named argument.
4475 This macro controls how the @var{named} argument to @code{FUNCTION_ARG}
4476 is set for varargs and stdarg functions. If this macro returns a
4477 nonzero value, the @var{named} argument is always true for named
4478 arguments, and false for unnamed arguments. If it returns a value of
4479 zero, but @code{SETUP_INCOMING_VARARGS} is defined, then all arguments
4480 are treated as named. Otherwise, all named arguments except the last
4481 are treated as named.
4483 You need not define this macro if it always returns zero.
4486 @defmac PRETEND_OUTGOING_VARARGS_NAMED
4487 If you need to conditionally change ABIs so that one works with
4488 @code{SETUP_INCOMING_VARARGS}, but the other works like neither
4489 @code{SETUP_INCOMING_VARARGS} nor @code{STRICT_ARGUMENT_NAMING} was
4490 defined, then define this macro to return nonzero if
4491 @code{SETUP_INCOMING_VARARGS} is used, zero otherwise.
4492 Otherwise, you should not define this macro.
4496 @section Trampolines for Nested Functions
4497 @cindex trampolines for nested functions
4498 @cindex nested functions, trampolines for
4500 A @dfn{trampoline} is a small piece of code that is created at run time
4501 when the address of a nested function is taken. It normally resides on
4502 the stack, in the stack frame of the containing function. These macros
4503 tell GCC how to generate code to allocate and initialize a
4506 The instructions in the trampoline must do two things: load a constant
4507 address into the static chain register, and jump to the real address of
4508 the nested function. On CISC machines such as the m68k, this requires
4509 two instructions, a move immediate and a jump. Then the two addresses
4510 exist in the trampoline as word-long immediate operands. On RISC
4511 machines, it is often necessary to load each address into a register in
4512 two parts. Then pieces of each address form separate immediate
4515 The code generated to initialize the trampoline must store the variable
4516 parts---the static chain value and the function address---into the
4517 immediate operands of the instructions. On a CISC machine, this is
4518 simply a matter of copying each address to a memory reference at the
4519 proper offset from the start of the trampoline. On a RISC machine, it
4520 may be necessary to take out pieces of the address and store them
4523 @defmac TRAMPOLINE_TEMPLATE (@var{file})
4524 A C statement to output, on the stream @var{file}, assembler code for a
4525 block of data that contains the constant parts of a trampoline. This
4526 code should not include a label---the label is taken care of
4529 If you do not define this macro, it means no template is needed
4530 for the target. Do not define this macro on systems where the block move
4531 code to copy the trampoline into place would be larger than the code
4532 to generate it on the spot.
4535 @defmac TRAMPOLINE_SECTION
4536 The name of a subroutine to switch to the section in which the
4537 trampoline template is to be placed (@pxref{Sections}). The default is
4538 a value of @samp{readonly_data_section}, which places the trampoline in
4539 the section containing read-only data.
4542 @defmac TRAMPOLINE_SIZE
4543 A C expression for the size in bytes of the trampoline, as an integer.
4546 @defmac TRAMPOLINE_ALIGNMENT
4547 Alignment required for trampolines, in bits.
4549 If you don't define this macro, the value of @code{BIGGEST_ALIGNMENT}
4550 is used for aligning trampolines.
4553 @defmac INITIALIZE_TRAMPOLINE (@var{addr}, @var{fnaddr}, @var{static_chain})
4554 A C statement to initialize the variable parts of a trampoline.
4555 @var{addr} is an RTX for the address of the trampoline; @var{fnaddr} is
4556 an RTX for the address of the nested function; @var{static_chain} is an
4557 RTX for the static chain value that should be passed to the function
4561 @defmac TRAMPOLINE_ADJUST_ADDRESS (@var{addr})
4562 A C statement that should perform any machine-specific adjustment in
4563 the address of the trampoline. Its argument contains the address that
4564 was passed to @code{INITIALIZE_TRAMPOLINE}. In case the address to be
4565 used for a function call should be different from the address in which
4566 the template was stored, the different address should be assigned to
4567 @var{addr}. If this macro is not defined, @var{addr} will be used for
4570 @cindex @code{TARGET_ASM_FUNCTION_EPILOGUE} and trampolines
4571 @cindex @code{TARGET_ASM_FUNCTION_PROLOGUE} and trampolines
4572 If this macro is not defined, by default the trampoline is allocated as
4573 a stack slot. This default is right for most machines. The exceptions
4574 are machines where it is impossible to execute instructions in the stack
4575 area. On such machines, you may have to implement a separate stack,
4576 using this macro in conjunction with @code{TARGET_ASM_FUNCTION_PROLOGUE}
4577 and @code{TARGET_ASM_FUNCTION_EPILOGUE}.
4579 @var{fp} points to a data structure, a @code{struct function}, which
4580 describes the compilation status of the immediate containing function of
4581 the function which the trampoline is for. The stack slot for the
4582 trampoline is in the stack frame of this containing function. Other
4583 allocation strategies probably must do something analogous with this
4587 Implementing trampolines is difficult on many machines because they have
4588 separate instruction and data caches. Writing into a stack location
4589 fails to clear the memory in the instruction cache, so when the program
4590 jumps to that location, it executes the old contents.
4592 Here are two possible solutions. One is to clear the relevant parts of
4593 the instruction cache whenever a trampoline is set up. The other is to
4594 make all trampolines identical, by having them jump to a standard
4595 subroutine. The former technique makes trampoline execution faster; the
4596 latter makes initialization faster.
4598 To clear the instruction cache when a trampoline is initialized, define
4599 the following macro.
4601 @defmac CLEAR_INSN_CACHE (@var{beg}, @var{end})
4602 If defined, expands to a C expression clearing the @emph{instruction
4603 cache} in the specified interval. The definition of this macro would
4604 typically be a series of @code{asm} statements. Both @var{beg} and
4605 @var{end} are both pointer expressions.
4608 To use a standard subroutine, define the following macro. In addition,
4609 you must make sure that the instructions in a trampoline fill an entire
4610 cache line with identical instructions, or else ensure that the
4611 beginning of the trampoline code is always aligned at the same point in
4612 its cache line. Look in @file{m68k.h} as a guide.
4614 @defmac TRANSFER_FROM_TRAMPOLINE
4615 Define this macro if trampolines need a special subroutine to do their
4616 work. The macro should expand to a series of @code{asm} statements
4617 which will be compiled with GCC@. They go in a library function named
4618 @code{__transfer_from_trampoline}.
4620 If you need to avoid executing the ordinary prologue code of a compiled
4621 C function when you jump to the subroutine, you can do so by placing a
4622 special label of your own in the assembler code. Use one @code{asm}
4623 statement to generate an assembler label, and another to make the label
4624 global. Then trampolines can use that label to jump directly to your
4625 special assembler code.
4629 @section Implicit Calls to Library Routines
4630 @cindex library subroutine names
4631 @cindex @file{libgcc.a}
4633 @c prevent bad page break with this line
4634 Here is an explanation of implicit calls to library routines.
4636 @defmac MULSI3_LIBCALL
4637 A C string constant giving the name of the function to call for
4638 multiplication of one signed full-word by another. If you do not
4639 define this macro, the default name is used, which is @code{__mulsi3},
4640 a function defined in @file{libgcc.a}.
4643 @defmac DIVSI3_LIBCALL
4644 A C string constant giving the name of the function to call for
4645 division of one signed full-word by another. If you do not define
4646 this macro, the default name is used, which is @code{__divsi3}, a
4647 function defined in @file{libgcc.a}.
4650 @defmac UDIVSI3_LIBCALL
4651 A C string constant giving the name of the function to call for
4652 division of one unsigned full-word by another. If you do not define
4653 this macro, the default name is used, which is @code{__udivsi3}, a
4654 function defined in @file{libgcc.a}.
4657 @defmac MODSI3_LIBCALL
4658 A C string constant giving the name of the function to call for the
4659 remainder in division of one signed full-word by another. If you do
4660 not define this macro, the default name is used, which is
4661 @code{__modsi3}, a function defined in @file{libgcc.a}.
4664 @defmac UMODSI3_LIBCALL
4665 A C string constant giving the name of the function to call for the
4666 remainder in division of one unsigned full-word by another. If you do
4667 not define this macro, the default name is used, which is
4668 @code{__umodsi3}, a function defined in @file{libgcc.a}.
4671 @defmac MULDI3_LIBCALL
4672 A C string constant giving the name of the function to call for
4673 multiplication of one signed double-word by another. If you do not
4674 define this macro, the default name is used, which is @code{__muldi3},
4675 a function defined in @file{libgcc.a}.
4678 @defmac DIVDI3_LIBCALL
4679 A C string constant giving the name of the function to call for
4680 division of one signed double-word by another. If you do not define
4681 this macro, the default name is used, which is @code{__divdi3}, a
4682 function defined in @file{libgcc.a}.
4685 @defmac UDIVDI3_LIBCALL
4686 A C string constant giving the name of the function to call for
4687 division of one unsigned full-word by another. If you do not define
4688 this macro, the default name is used, which is @code{__udivdi3}, a
4689 function defined in @file{libgcc.a}.
4692 @defmac MODDI3_LIBCALL
4693 A C string constant giving the name of the function to call for the
4694 remainder in division of one signed double-word by another. If you do
4695 not define this macro, the default name is used, which is
4696 @code{__moddi3}, a function defined in @file{libgcc.a}.
4699 @defmac UMODDI3_LIBCALL
4700 A C string constant giving the name of the function to call for the
4701 remainder in division of one unsigned full-word by another. If you do
4702 not define this macro, the default name is used, which is
4703 @code{__umoddi3}, a function defined in @file{libgcc.a}.
4706 @defmac DECLARE_LIBRARY_RENAMES
4707 This macro, if defined, should expand to a piece of C code that will get
4708 expanded when compiling functions for libgcc.a. It can be used to
4709 provide alternate names for gcc's internal library functions if there
4710 are ABI-mandated names that the compiler should provide.
4713 @defmac INIT_TARGET_OPTABS
4714 Define this macro as a C statement that declares additional library
4715 routines renames existing ones. @code{init_optabs} calls this macro after
4716 initializing all the normal library routines.
4719 @defmac FLOAT_LIB_COMPARE_RETURNS_BOOL (@var{mode}, @var{comparison})
4720 Define this macro as a C statement that returns nonzero if a call to
4721 the floating point comparison library function will return a boolean
4722 value that indicates the result of the comparison. It should return
4723 zero if one of gcc's own libgcc functions is called.
4725 Most ports don't need to define this macro.
4728 @cindex @code{EDOM}, implicit usage
4731 The value of @code{EDOM} on the target machine, as a C integer constant
4732 expression. If you don't define this macro, GCC does not attempt to
4733 deposit the value of @code{EDOM} into @code{errno} directly. Look in
4734 @file{/usr/include/errno.h} to find the value of @code{EDOM} on your
4737 If you do not define @code{TARGET_EDOM}, then compiled code reports
4738 domain errors by calling the library function and letting it report the
4739 error. If mathematical functions on your system use @code{matherr} when
4740 there is an error, then you should leave @code{TARGET_EDOM} undefined so
4741 that @code{matherr} is used normally.
4744 @cindex @code{errno}, implicit usage
4745 @defmac GEN_ERRNO_RTX
4746 Define this macro as a C expression to create an rtl expression that
4747 refers to the global ``variable'' @code{errno}. (On certain systems,
4748 @code{errno} may not actually be a variable.) If you don't define this
4749 macro, a reasonable default is used.
4752 @cindex @code{bcopy}, implicit usage
4753 @cindex @code{memcpy}, implicit usage
4754 @cindex @code{memmove}, implicit usage
4755 @cindex @code{bzero}, implicit usage
4756 @cindex @code{memset}, implicit usage
4757 @defmac TARGET_MEM_FUNCTIONS
4758 Define this macro if GCC should generate calls to the ISO C
4759 (and System V) library functions @code{memcpy}, @code{memmove} and
4760 @code{memset} rather than the BSD functions @code{bcopy} and @code{bzero}.
4763 @cindex C99 math functions, implicit usage
4764 @defmac TARGET_C99_FUNCTIONS
4765 When this macro is nonzero, GCC will implicitly optimize @code{sin} calls into
4766 @code{sinf} and similarly for other functions defined by C99 standard. The
4767 default is nonzero that should be proper value for most modern systems, however
4768 number of existing systems lacks support for these functions in the runtime so
4769 they needs this macro to be redefined to 0.
4772 @defmac LIBGCC_NEEDS_DOUBLE
4773 Define this macro if @code{float} arguments cannot be passed to library
4774 routines (so they must be converted to @code{double}). This macro
4775 affects both how library calls are generated and how the library
4776 routines in @file{libgcc.a} accept their arguments. It is useful on
4777 machines where floating and fixed point arguments are passed
4778 differently, such as the i860.
4781 @defmac NEXT_OBJC_RUNTIME
4782 Define this macro to generate code for Objective-C message sending using
4783 the calling convention of the NeXT system. This calling convention
4784 involves passing the object, the selector and the method arguments all
4785 at once to the method-lookup library function.
4787 The default calling convention passes just the object and the selector
4788 to the lookup function, which returns a pointer to the method.
4791 @node Addressing Modes
4792 @section Addressing Modes
4793 @cindex addressing modes
4795 @c prevent bad page break with this line
4796 This is about addressing modes.
4798 @defmac HAVE_PRE_INCREMENT
4799 @defmacx HAVE_PRE_DECREMENT
4800 @defmacx HAVE_POST_INCREMENT
4801 @defmacx HAVE_POST_DECREMENT
4802 A C expression that is nonzero if the machine supports pre-increment,
4803 pre-decrement, post-increment, or post-decrement addressing respectively.
4806 @defmac HAVE_PRE_MODIFY_DISP
4807 @defmacx HAVE_POST_MODIFY_DISP
4808 A C expression that is nonzero if the machine supports pre- or
4809 post-address side-effect generation involving constants other than
4810 the size of the memory operand.
4813 @defmac HAVE_PRE_MODIFY_REG
4814 @defmacx HAVE_POST_MODIFY_REG
4815 A C expression that is nonzero if the machine supports pre- or
4816 post-address side-effect generation involving a register displacement.
4819 @defmac CONSTANT_ADDRESS_P (@var{x})
4820 A C expression that is 1 if the RTX @var{x} is a constant which
4821 is a valid address. On most machines, this can be defined as
4822 @code{CONSTANT_P (@var{x})}, but a few machines are more restrictive
4823 in which constant addresses are supported.
4826 @defmac CONSTANT_P (@var{x})
4827 @code{CONSTANT_P}, which is defined by target-independent code,
4828 accepts integer-values expressions whose values are not explicitly
4829 known, such as @code{symbol_ref}, @code{label_ref}, and @code{high}
4830 expressions and @code{const} arithmetic expressions, in addition to
4831 @code{const_int} and @code{const_double} expressions.
4834 @defmac MAX_REGS_PER_ADDRESS
4835 A number, the maximum number of registers that can appear in a valid
4836 memory address. Note that it is up to you to specify a value equal to
4837 the maximum number that @code{GO_IF_LEGITIMATE_ADDRESS} would ever
4841 @defmac GO_IF_LEGITIMATE_ADDRESS (@var{mode}, @var{x}, @var{label})
4842 A C compound statement with a conditional @code{goto @var{label};}
4843 executed if @var{x} (an RTX) is a legitimate memory address on the
4844 target machine for a memory operand of mode @var{mode}.
4846 It usually pays to define several simpler macros to serve as
4847 subroutines for this one. Otherwise it may be too complicated to
4850 This macro must exist in two variants: a strict variant and a
4851 non-strict one. The strict variant is used in the reload pass. It
4852 must be defined so that any pseudo-register that has not been
4853 allocated a hard register is considered a memory reference. In
4854 contexts where some kind of register is required, a pseudo-register
4855 with no hard register must be rejected.
4857 The non-strict variant is used in other passes. It must be defined to
4858 accept all pseudo-registers in every context where some kind of
4859 register is required.
4861 @findex REG_OK_STRICT
4862 Compiler source files that want to use the strict variant of this
4863 macro define the macro @code{REG_OK_STRICT}. You should use an
4864 @code{#ifdef REG_OK_STRICT} conditional to define the strict variant
4865 in that case and the non-strict variant otherwise.
4867 Subroutines to check for acceptable registers for various purposes (one
4868 for base registers, one for index registers, and so on) are typically
4869 among the subroutines used to define @code{GO_IF_LEGITIMATE_ADDRESS}.
4870 Then only these subroutine macros need have two variants; the higher
4871 levels of macros may be the same whether strict or not.
4873 Normally, constant addresses which are the sum of a @code{symbol_ref}
4874 and an integer are stored inside a @code{const} RTX to mark them as
4875 constant. Therefore, there is no need to recognize such sums
4876 specifically as legitimate addresses. Normally you would simply
4877 recognize any @code{const} as legitimate.
4879 Usually @code{PRINT_OPERAND_ADDRESS} is not prepared to handle constant
4880 sums that are not marked with @code{const}. It assumes that a naked
4881 @code{plus} indicates indexing. If so, then you @emph{must} reject such
4882 naked constant sums as illegitimate addresses, so that none of them will
4883 be given to @code{PRINT_OPERAND_ADDRESS}.
4885 @cindex @code{TARGET_ENCODE_SECTION_INFO} and address validation
4886 On some machines, whether a symbolic address is legitimate depends on
4887 the section that the address refers to. On these machines, define the
4888 target hook @code{TARGET_ENCODE_SECTION_INFO} to store the information
4889 into the @code{symbol_ref}, and then check for it here. When you see a
4890 @code{const}, you will have to look inside it to find the
4891 @code{symbol_ref} in order to determine the section. @xref{Assembler
4895 @defmac REG_OK_FOR_BASE_P (@var{x})
4896 A C expression that is nonzero if @var{x} (assumed to be a @code{reg}
4897 RTX) is valid for use as a base register. For hard registers, it
4898 should always accept those which the hardware permits and reject the
4899 others. Whether the macro accepts or rejects pseudo registers must be
4900 controlled by @code{REG_OK_STRICT} as described above. This usually
4901 requires two variant definitions, of which @code{REG_OK_STRICT}
4902 controls the one actually used.
4905 @defmac REG_MODE_OK_FOR_BASE_P (@var{x}, @var{mode})
4906 A C expression that is just like @code{REG_OK_FOR_BASE_P}, except that
4907 that expression may examine the mode of the memory reference in
4908 @var{mode}. You should define this macro if the mode of the memory
4909 reference affects whether a register may be used as a base register. If
4910 you define this macro, the compiler will use it instead of
4911 @code{REG_OK_FOR_BASE_P}.
4914 @defmac REG_OK_FOR_INDEX_P (@var{x})
4915 A C expression that is nonzero if @var{x} (assumed to be a @code{reg}
4916 RTX) is valid for use as an index register.
4918 The difference between an index register and a base register is that
4919 the index register may be scaled. If an address involves the sum of
4920 two registers, neither one of them scaled, then either one may be
4921 labeled the ``base'' and the other the ``index''; but whichever
4922 labeling is used must fit the machine's constraints of which registers
4923 may serve in each capacity. The compiler will try both labelings,
4924 looking for one that is valid, and will reload one or both registers
4925 only if neither labeling works.
4928 @defmac FIND_BASE_TERM (@var{x})
4929 A C expression to determine the base term of address @var{x}.
4930 This macro is used in only one place: `find_base_term' in alias.c.
4932 It is always safe for this macro to not be defined. It exists so
4933 that alias analysis can understand machine-dependent addresses.
4935 The typical use of this macro is to handle addresses containing
4936 a label_ref or symbol_ref within an UNSPEC@.
4939 @defmac LEGITIMIZE_ADDRESS (@var{x}, @var{oldx}, @var{mode}, @var{win})
4940 A C compound statement that attempts to replace @var{x} with a valid
4941 memory address for an operand of mode @var{mode}. @var{win} will be a
4942 C statement label elsewhere in the code; the macro definition may use
4945 GO_IF_LEGITIMATE_ADDRESS (@var{mode}, @var{x}, @var{win});
4949 to avoid further processing if the address has become legitimate.
4951 @findex break_out_memory_refs
4952 @var{x} will always be the result of a call to @code{break_out_memory_refs},
4953 and @var{oldx} will be the operand that was given to that function to produce
4956 The code generated by this macro should not alter the substructure of
4957 @var{x}. If it transforms @var{x} into a more legitimate form, it
4958 should assign @var{x} (which will always be a C variable) a new value.
4960 It is not necessary for this macro to come up with a legitimate
4961 address. The compiler has standard ways of doing so in all cases. In
4962 fact, it is safe for this macro to do nothing. But often a
4963 machine-dependent strategy can generate better code.
4966 @defmac LEGITIMIZE_RELOAD_ADDRESS (@var{x}, @var{mode}, @var{opnum}, @var{type}, @var{ind_levels}, @var{win})
4967 A C compound statement that attempts to replace @var{x}, which is an address
4968 that needs reloading, with a valid memory address for an operand of mode
4969 @var{mode}. @var{win} will be a C statement label elsewhere in the code.
4970 It is not necessary to define this macro, but it might be useful for
4971 performance reasons.
4973 For example, on the i386, it is sometimes possible to use a single
4974 reload register instead of two by reloading a sum of two pseudo
4975 registers into a register. On the other hand, for number of RISC
4976 processors offsets are limited so that often an intermediate address
4977 needs to be generated in order to address a stack slot. By defining
4978 @code{LEGITIMIZE_RELOAD_ADDRESS} appropriately, the intermediate addresses
4979 generated for adjacent some stack slots can be made identical, and thus
4982 @emph{Note}: This macro should be used with caution. It is necessary
4983 to know something of how reload works in order to effectively use this,
4984 and it is quite easy to produce macros that build in too much knowledge
4985 of reload internals.
4987 @emph{Note}: This macro must be able to reload an address created by a
4988 previous invocation of this macro. If it fails to handle such addresses
4989 then the compiler may generate incorrect code or abort.
4992 The macro definition should use @code{push_reload} to indicate parts that
4993 need reloading; @var{opnum}, @var{type} and @var{ind_levels} are usually
4994 suitable to be passed unaltered to @code{push_reload}.
4996 The code generated by this macro must not alter the substructure of
4997 @var{x}. If it transforms @var{x} into a more legitimate form, it
4998 should assign @var{x} (which will always be a C variable) a new value.
4999 This also applies to parts that you change indirectly by calling
5002 @findex strict_memory_address_p
5003 The macro definition may use @code{strict_memory_address_p} to test if
5004 the address has become legitimate.
5007 If you want to change only a part of @var{x}, one standard way of doing
5008 this is to use @code{copy_rtx}. Note, however, that is unshares only a
5009 single level of rtl. Thus, if the part to be changed is not at the
5010 top level, you'll need to replace first the top level.
5011 It is not necessary for this macro to come up with a legitimate
5012 address; but often a machine-dependent strategy can generate better code.
5015 @defmac GO_IF_MODE_DEPENDENT_ADDRESS (@var{addr}, @var{label})
5016 A C statement or compound statement with a conditional @code{goto
5017 @var{label};} executed if memory address @var{x} (an RTX) can have
5018 different meanings depending on the machine mode of the memory
5019 reference it is used for or if the address is valid for some modes
5022 Autoincrement and autodecrement addresses typically have mode-dependent
5023 effects because the amount of the increment or decrement is the size
5024 of the operand being addressed. Some machines have other mode-dependent
5025 addresses. Many RISC machines have no mode-dependent addresses.
5027 You may assume that @var{addr} is a valid address for the machine.
5030 @defmac LEGITIMATE_CONSTANT_P (@var{x})
5031 A C expression that is nonzero if @var{x} is a legitimate constant for
5032 an immediate operand on the target machine. You can assume that
5033 @var{x} satisfies @code{CONSTANT_P}, so you need not check this. In fact,
5034 @samp{1} is a suitable definition for this macro on machines where
5035 anything @code{CONSTANT_P} is valid.
5038 @node Condition Code
5039 @section Condition Code Status
5040 @cindex condition code status
5042 @c prevent bad page break with this line
5043 This describes the condition code status.
5046 The file @file{conditions.h} defines a variable @code{cc_status} to
5047 describe how the condition code was computed (in case the interpretation of
5048 the condition code depends on the instruction that it was set by). This
5049 variable contains the RTL expressions on which the condition code is
5050 currently based, and several standard flags.
5052 Sometimes additional machine-specific flags must be defined in the machine
5053 description header file. It can also add additional machine-specific
5054 information by defining @code{CC_STATUS_MDEP}.
5056 @defmac CC_STATUS_MDEP
5057 C code for a data type which is used for declaring the @code{mdep}
5058 component of @code{cc_status}. It defaults to @code{int}.
5060 This macro is not used on machines that do not use @code{cc0}.
5063 @defmac CC_STATUS_MDEP_INIT
5064 A C expression to initialize the @code{mdep} field to ``empty''.
5065 The default definition does nothing, since most machines don't use
5066 the field anyway. If you want to use the field, you should probably
5067 define this macro to initialize it.
5069 This macro is not used on machines that do not use @code{cc0}.
5072 @defmac NOTICE_UPDATE_CC (@var{exp}, @var{insn})
5073 A C compound statement to set the components of @code{cc_status}
5074 appropriately for an insn @var{insn} whose body is @var{exp}. It is
5075 this macro's responsibility to recognize insns that set the condition
5076 code as a byproduct of other activity as well as those that explicitly
5079 This macro is not used on machines that do not use @code{cc0}.
5081 If there are insns that do not set the condition code but do alter
5082 other machine registers, this macro must check to see whether they
5083 invalidate the expressions that the condition code is recorded as
5084 reflecting. For example, on the 68000, insns that store in address
5085 registers do not set the condition code, which means that usually
5086 @code{NOTICE_UPDATE_CC} can leave @code{cc_status} unaltered for such
5087 insns. But suppose that the previous insn set the condition code
5088 based on location @samp{a4@@(102)} and the current insn stores a new
5089 value in @samp{a4}. Although the condition code is not changed by
5090 this, it will no longer be true that it reflects the contents of
5091 @samp{a4@@(102)}. Therefore, @code{NOTICE_UPDATE_CC} must alter
5092 @code{cc_status} in this case to say that nothing is known about the
5093 condition code value.
5095 The definition of @code{NOTICE_UPDATE_CC} must be prepared to deal
5096 with the results of peephole optimization: insns whose patterns are
5097 @code{parallel} RTXs containing various @code{reg}, @code{mem} or
5098 constants which are just the operands. The RTL structure of these
5099 insns is not sufficient to indicate what the insns actually do. What
5100 @code{NOTICE_UPDATE_CC} should do when it sees one is just to run
5101 @code{CC_STATUS_INIT}.
5103 A possible definition of @code{NOTICE_UPDATE_CC} is to call a function
5104 that looks at an attribute (@pxref{Insn Attributes}) named, for example,
5105 @samp{cc}. This avoids having detailed information about patterns in
5106 two places, the @file{md} file and in @code{NOTICE_UPDATE_CC}.
5109 @defmac EXTRA_CC_MODES
5110 Condition codes are represented in registers by machine modes of class
5111 @code{MODE_CC}. By default, there is just one mode, @code{CCmode}, with
5112 this class. If you need more such modes, create a file named
5113 @file{@var{machine}-modes.def} in your @file{config/@var{machine}}
5114 directory (@pxref{Back End, , Anatomy of a Target Back End}), containing
5115 a list of these modes. Each entry in the list should be a call to the
5116 macro @code{CC}. This macro takes one argument, which is the name of
5117 the mode: it should begin with @samp{CC}. Do not put quotation marks
5118 around the name, or include the trailing @samp{mode}; these are
5119 automatically added. There should not be anything else in the file
5122 A sample @file{@var{machine}-modes.def} file might look like this:
5125 CC (CC_NOOV) /* @r{Comparison only valid if there was no overflow.} */
5126 CC (CCFP) /* @r{Floating point comparison that cannot trap.} */
5127 CC (CCFPE) /* @r{Floating point comparison that may trap.} */
5130 When you create this file, the macro @code{EXTRA_CC_MODES} is
5131 automatically defined by @command{configure}, with value @samp{1}.
5134 @defmac SELECT_CC_MODE (@var{op}, @var{x}, @var{y})
5135 Returns a mode from class @code{MODE_CC} to be used when comparison
5136 operation code @var{op} is applied to rtx @var{x} and @var{y}. For
5137 example, on the SPARC, @code{SELECT_CC_MODE} is defined as (see
5138 @pxref{Jump Patterns} for a description of the reason for this
5142 #define SELECT_CC_MODE(OP,X,Y) \
5143 (GET_MODE_CLASS (GET_MODE (X)) == MODE_FLOAT \
5144 ? ((OP == EQ || OP == NE) ? CCFPmode : CCFPEmode) \
5145 : ((GET_CODE (X) == PLUS || GET_CODE (X) == MINUS \
5146 || GET_CODE (X) == NEG) \
5147 ? CC_NOOVmode : CCmode))
5150 You need not define this macro if @code{EXTRA_CC_MODES} is not defined.
5153 @defmac CANONICALIZE_COMPARISON (@var{code}, @var{op0}, @var{op1})
5154 On some machines not all possible comparisons are defined, but you can
5155 convert an invalid comparison into a valid one. For example, the Alpha
5156 does not have a @code{GT} comparison, but you can use an @code{LT}
5157 comparison instead and swap the order of the operands.
5159 On such machines, define this macro to be a C statement to do any
5160 required conversions. @var{code} is the initial comparison code
5161 and @var{op0} and @var{op1} are the left and right operands of the
5162 comparison, respectively. You should modify @var{code}, @var{op0}, and
5163 @var{op1} as required.
5165 GCC will not assume that the comparison resulting from this macro is
5166 valid but will see if the resulting insn matches a pattern in the
5169 You need not define this macro if it would never change the comparison
5173 @defmac REVERSIBLE_CC_MODE (@var{mode})
5174 A C expression whose value is one if it is always safe to reverse a
5175 comparison whose mode is @var{mode}. If @code{SELECT_CC_MODE}
5176 can ever return @var{mode} for a floating-point inequality comparison,
5177 then @code{REVERSIBLE_CC_MODE (@var{mode})} must be zero.
5179 You need not define this macro if it would always returns zero or if the
5180 floating-point format is anything other than @code{IEEE_FLOAT_FORMAT}.
5181 For example, here is the definition used on the SPARC, where floating-point
5182 inequality comparisons are always given @code{CCFPEmode}:
5185 #define REVERSIBLE_CC_MODE(MODE) ((MODE) != CCFPEmode)
5189 @defmac REVERSE_CONDITION (@var{code}, @var{mode})
5190 A C expression whose value is reversed condition code of the @var{code} for
5191 comparison done in CC_MODE @var{mode}. The macro is used only in case
5192 @code{REVERSIBLE_CC_MODE (@var{mode})} is nonzero. Define this macro in case
5193 machine has some non-standard way how to reverse certain conditionals. For
5194 instance in case all floating point conditions are non-trapping, compiler may
5195 freely convert unordered compares to ordered one. Then definition may look
5199 #define REVERSE_CONDITION(CODE, MODE) \
5200 ((MODE) != CCFPmode ? reverse_condition (CODE) \
5201 : reverse_condition_maybe_unordered (CODE))
5205 @defmac REVERSE_CONDEXEC_PREDICATES_P (@var{code1}, @var{code2})
5206 A C expression that returns true if the conditional execution predicate
5207 @var{code1} is the inverse of @var{code2} and vice versa. Define this to
5208 return 0 if the target has conditional execution predicates that cannot be
5209 reversed safely. If no expansion is specified, this macro is defined as
5213 #define REVERSE_CONDEXEC_PREDICATES_P (x, y) \
5214 ((x) == reverse_condition (y))
5219 @section Describing Relative Costs of Operations
5220 @cindex costs of instructions
5221 @cindex relative costs
5222 @cindex speed of instructions
5224 These macros let you describe the relative speed of various operations
5225 on the target machine.
5227 @defmac REGISTER_MOVE_COST (@var{mode}, @var{from}, @var{to})
5228 A C expression for the cost of moving data of mode @var{mode} from a
5229 register in class @var{from} to one in class @var{to}. The classes are
5230 expressed using the enumeration values such as @code{GENERAL_REGS}. A
5231 value of 2 is the default; other values are interpreted relative to
5234 It is not required that the cost always equal 2 when @var{from} is the
5235 same as @var{to}; on some machines it is expensive to move between
5236 registers if they are not general registers.
5238 If reload sees an insn consisting of a single @code{set} between two
5239 hard registers, and if @code{REGISTER_MOVE_COST} applied to their
5240 classes returns a value of 2, reload does not check to ensure that the
5241 constraints of the insn are met. Setting a cost of other than 2 will
5242 allow reload to verify that the constraints are met. You should do this
5243 if the @samp{mov@var{m}} pattern's constraints do not allow such copying.
5246 @defmac MEMORY_MOVE_COST (@var{mode}, @var{class}, @var{in})
5247 A C expression for the cost of moving data of mode @var{mode} between a
5248 register of class @var{class} and memory; @var{in} is zero if the value
5249 is to be written to memory, nonzero if it is to be read in. This cost
5250 is relative to those in @code{REGISTER_MOVE_COST}. If moving between
5251 registers and memory is more expensive than between two registers, you
5252 should define this macro to express the relative cost.
5254 If you do not define this macro, GCC uses a default cost of 4 plus
5255 the cost of copying via a secondary reload register, if one is
5256 needed. If your machine requires a secondary reload register to copy
5257 between memory and a register of @var{class} but the reload mechanism is
5258 more complex than copying via an intermediate, define this macro to
5259 reflect the actual cost of the move.
5261 GCC defines the function @code{memory_move_secondary_cost} if
5262 secondary reloads are needed. It computes the costs due to copying via
5263 a secondary register. If your machine copies from memory using a
5264 secondary register in the conventional way but the default base value of
5265 4 is not correct for your machine, define this macro to add some other
5266 value to the result of that function. The arguments to that function
5267 are the same as to this macro.
5271 A C expression for the cost of a branch instruction. A value of 1 is
5272 the default; other values are interpreted relative to that.
5275 Here are additional macros which do not specify precise relative costs,
5276 but only that certain actions are more expensive than GCC would
5279 @defmac SLOW_BYTE_ACCESS
5280 Define this macro as a C expression which is nonzero if accessing less
5281 than a word of memory (i.e.@: a @code{char} or a @code{short}) is no
5282 faster than accessing a word of memory, i.e., if such access
5283 require more than one instruction or if there is no difference in cost
5284 between byte and (aligned) word loads.
5286 When this macro is not defined, the compiler will access a field by
5287 finding the smallest containing object; when it is defined, a fullword
5288 load will be used if alignment permits. Unless bytes accesses are
5289 faster than word accesses, using word accesses is preferable since it
5290 may eliminate subsequent memory access if subsequent accesses occur to
5291 other fields in the same word of the structure, but to different bytes.
5294 @defmac SLOW_UNALIGNED_ACCESS (@var{mode}, @var{alignment})
5295 Define this macro to be the value 1 if memory accesses described by the
5296 @var{mode} and @var{alignment} parameters have a cost many times greater
5297 than aligned accesses, for example if they are emulated in a trap
5300 When this macro is nonzero, the compiler will act as if
5301 @code{STRICT_ALIGNMENT} were nonzero when generating code for block
5302 moves. This can cause significantly more instructions to be produced.
5303 Therefore, do not set this macro nonzero if unaligned accesses only add a
5304 cycle or two to the time for a memory access.
5306 If the value of this macro is always zero, it need not be defined. If
5307 this macro is defined, it should produce a nonzero value when
5308 @code{STRICT_ALIGNMENT} is nonzero.
5312 The threshold of number of scalar memory-to-memory move insns, @emph{below}
5313 which a sequence of insns should be generated instead of a
5314 string move insn or a library call. Increasing the value will always
5315 make code faster, but eventually incurs high cost in increased code size.
5317 Note that on machines where the corresponding move insn is a
5318 @code{define_expand} that emits a sequence of insns, this macro counts
5319 the number of such sequences.
5321 If you don't define this, a reasonable default is used.
5324 @defmac MOVE_BY_PIECES_P (@var{size}, @var{alignment})
5325 A C expression used to determine whether @code{move_by_pieces} will be used to
5326 copy a chunk of memory, or whether some other block move mechanism
5327 will be used. Defaults to 1 if @code{move_by_pieces_ninsns} returns less
5328 than @code{MOVE_RATIO}.
5331 @defmac MOVE_MAX_PIECES
5332 A C expression used by @code{move_by_pieces} to determine the largest unit
5333 a load or store used to copy memory is. Defaults to @code{MOVE_MAX}.
5337 The threshold of number of scalar move insns, @emph{below} which a sequence
5338 of insns should be generated to clear memory instead of a string clear insn
5339 or a library call. Increasing the value will always make code faster, but
5340 eventually incurs high cost in increased code size.
5342 If you don't define this, a reasonable default is used.
5345 @defmac CLEAR_BY_PIECES_P (@var{size}, @var{alignment})
5346 A C expression used to determine whether @code{clear_by_pieces} will be used
5347 to clear a chunk of memory, or whether some other block clear mechanism
5348 will be used. Defaults to 1 if @code{move_by_pieces_ninsns} returns less
5349 than @code{CLEAR_RATIO}.
5352 @defmac STORE_BY_PIECES_P (@var{size}, @var{alignment})
5353 A C expression used to determine whether @code{store_by_pieces} will be
5354 used to set a chunk of memory to a constant value, or whether some other
5355 mechanism will be used. Used by @code{__builtin_memset} when storing
5356 values other than constant zero and by @code{__builtin_strcpy} when
5357 when called with a constant source string.
5358 Defaults to @code{MOVE_BY_PIECES_P}.
5361 @defmac USE_LOAD_POST_INCREMENT (@var{mode})
5362 A C expression used to determine whether a load postincrement is a good
5363 thing to use for a given mode. Defaults to the value of
5364 @code{HAVE_POST_INCREMENT}.
5367 @defmac USE_LOAD_POST_DECREMENT (@var{mode})
5368 A C expression used to determine whether a load postdecrement is a good
5369 thing to use for a given mode. Defaults to the value of
5370 @code{HAVE_POST_DECREMENT}.
5373 @defmac USE_LOAD_PRE_INCREMENT (@var{mode})
5374 A C expression used to determine whether a load preincrement is a good
5375 thing to use for a given mode. Defaults to the value of
5376 @code{HAVE_PRE_INCREMENT}.
5379 @defmac USE_LOAD_PRE_DECREMENT (@var{mode})
5380 A C expression used to determine whether a load predecrement is a good
5381 thing to use for a given mode. Defaults to the value of
5382 @code{HAVE_PRE_DECREMENT}.
5385 @defmac USE_STORE_POST_INCREMENT (@var{mode})
5386 A C expression used to determine whether a store postincrement is a good
5387 thing to use for a given mode. Defaults to the value of
5388 @code{HAVE_POST_INCREMENT}.
5391 @defmac USE_STORE_POST_DECREMENT (@var{mode})
5392 A C expression used to determine whether a store postdecrement is a good
5393 thing to use for a given mode. Defaults to the value of
5394 @code{HAVE_POST_DECREMENT}.
5397 @defmac USE_STORE_PRE_INCREMENT (@var{mode})
5398 This macro is used to determine whether a store preincrement is a good
5399 thing to use for a given mode. Defaults to the value of
5400 @code{HAVE_PRE_INCREMENT}.
5403 @defmac USE_STORE_PRE_DECREMENT (@var{mode})
5404 This macro is used to determine whether a store predecrement is a good
5405 thing to use for a given mode. Defaults to the value of
5406 @code{HAVE_PRE_DECREMENT}.
5409 @defmac NO_FUNCTION_CSE
5410 Define this macro if it is as good or better to call a constant
5411 function address than to call an address kept in a register.
5414 @defmac NO_RECURSIVE_FUNCTION_CSE
5415 Define this macro if it is as good or better for a function to call
5416 itself with an explicit address than to call an address kept in a
5420 @defmac RANGE_TEST_NON_SHORT_CIRCUIT
5421 Define this macro if a non-short-circuit operation produced by
5422 @samp{fold_range_test ()} is optimal. This macro defaults to true if
5423 @code{BRANCH_COST} is greater than or equal to the value 2.
5426 @deftypefn {Target Hook} bool TARGET_RTX_COSTS (rtx @var{x}, int @var{code}, int @var{outer_code}, int *@var{total})
5427 This target hook describes the relative costs of RTL expressions.
5429 The cost may depend on the precise form of the expression, which is
5430 available for examination in @var{x}, and the rtx code of the expression
5431 in which it is contained, found in @var{outer_code}. @var{code} is the
5432 expression code---redundant, since it can be obtained with
5433 @code{GET_CODE (@var{x})}.
5435 In implementing this hook, you can use the construct
5436 @code{COSTS_N_INSNS (@var{n})} to specify a cost equal to @var{n} fast
5439 On entry to the hook, @code{*@var{total}} contains a default estimate
5440 for the cost of the expression. The hook should modify this value as
5443 The hook returns true when all subexpressions of @var{x} have been
5444 processed, and false when @code{rtx_cost} should recurse.
5447 @deftypefn {Target Hook} int TARGET_ADDRESS_COST (rtx @var{address})
5448 This hook computes the cost of an addressing mode that contains
5449 @var{address}. If not defined, the cost is computed from
5450 the @var{address} expression and the @code{TARGET_RTX_COST} hook.
5452 For most CISC machines, the default cost is a good approximation of the
5453 true cost of the addressing mode. However, on RISC machines, all
5454 instructions normally have the same length and execution time. Hence
5455 all addresses will have equal costs.
5457 In cases where more than one form of an address is known, the form with
5458 the lowest cost will be used. If multiple forms have the same, lowest,
5459 cost, the one that is the most complex will be used.
5461 For example, suppose an address that is equal to the sum of a register
5462 and a constant is used twice in the same basic block. When this macro
5463 is not defined, the address will be computed in a register and memory
5464 references will be indirect through that register. On machines where
5465 the cost of the addressing mode containing the sum is no higher than
5466 that of a simple indirect reference, this will produce an additional
5467 instruction and possibly require an additional register. Proper
5468 specification of this macro eliminates this overhead for such machines.
5470 This hook is never called with an invalid address.
5472 On machines where an address involving more than one register is as
5473 cheap as an address computation involving only one register, defining
5474 @code{TARGET_ADDRESS_COST} to reflect this can cause two registers to
5475 be live over a region of code where only one would have been if
5476 @code{TARGET_ADDRESS_COST} were not defined in that manner. This effect
5477 should be considered in the definition of this macro. Equivalent costs
5478 should probably only be given to addresses with different numbers of
5479 registers on machines with lots of registers.
5483 @section Adjusting the Instruction Scheduler
5485 The instruction scheduler may need a fair amount of machine-specific
5486 adjustment in order to produce good code. GCC provides several target
5487 hooks for this purpose. It is usually enough to define just a few of
5488 them: try the first ones in this list first.
5490 @deftypefn {Target Hook} int TARGET_SCHED_ISSUE_RATE (void)
5491 This hook returns the maximum number of instructions that can ever
5492 issue at the same time on the target machine. The default is one.
5493 Although the insn scheduler can define itself the possibility of issue
5494 an insn on the same cycle, the value can serve as an additional
5495 constraint to issue insns on the same simulated processor cycle (see
5496 hooks @samp{TARGET_SCHED_REORDER} and @samp{TARGET_SCHED_REORDER2}).
5497 This value must be constant over the entire compilation. If you need
5498 it to vary depending on what the instructions are, you must use
5499 @samp{TARGET_SCHED_VARIABLE_ISSUE}.
5501 For the automaton based pipeline interface, you could define this hook
5502 to return the value of the macro @code{MAX_DFA_ISSUE_RATE}.
5505 @deftypefn {Target Hook} int TARGET_SCHED_VARIABLE_ISSUE (FILE *@var{file}, int @var{verbose}, rtx @var{insn}, int @var{more})
5506 This hook is executed by the scheduler after it has scheduled an insn
5507 from the ready list. It should return the number of insns which can
5508 still be issued in the current cycle. The default is
5509 @samp{@w{@var{more} - 1}} for insns other than @code{CLOBBER} and
5510 @code{USE}, which normally are not counted against the issue rate.
5511 You should define this hook if some insns take more machine resources
5512 than others, so that fewer insns can follow them in the same cycle.
5513 @var{file} is either a null pointer, or a stdio stream to write any
5514 debug output to. @var{verbose} is the verbose level provided by
5515 @option{-fsched-verbose-@var{n}}. @var{insn} is the instruction that
5519 @deftypefn {Target Hook} int TARGET_SCHED_ADJUST_COST (rtx @var{insn}, rtx @var{link}, rtx @var{dep_insn}, int @var{cost})
5520 This function corrects the value of @var{cost} based on the
5521 relationship between @var{insn} and @var{dep_insn} through the
5522 dependence @var{link}. It should return the new value. The default
5523 is to make no adjustment to @var{cost}. This can be used for example
5524 to specify to the scheduler using the traditional pipeline description
5525 that an output- or anti-dependence does not incur the same cost as a
5526 data-dependence. If the scheduler using the automaton based pipeline
5527 description, the cost of anti-dependence is zero and the cost of
5528 output-dependence is maximum of one and the difference of latency
5529 times of the first and the second insns. If these values are not
5530 acceptable, you could use the hook to modify them too. See also
5531 @pxref{Automaton pipeline description}.
5534 @deftypefn {Target Hook} int TARGET_SCHED_ADJUST_PRIORITY (rtx @var{insn}, int @var{priority})
5535 This hook adjusts the integer scheduling priority @var{priority} of
5536 @var{insn}. It should return the new priority. Reduce the priority to
5537 execute @var{insn} earlier, increase the priority to execute @var{insn}
5538 later. Do not define this hook if you do not need to adjust the
5539 scheduling priorities of insns.
5542 @deftypefn {Target Hook} int TARGET_SCHED_REORDER (FILE *@var{file}, int @var{verbose}, rtx *@var{ready}, int *@var{n_readyp}, int @var{clock})
5543 This hook is executed by the scheduler after it has scheduled the ready
5544 list, to allow the machine description to reorder it (for example to
5545 combine two small instructions together on @samp{VLIW} machines).
5546 @var{file} is either a null pointer, or a stdio stream to write any
5547 debug output to. @var{verbose} is the verbose level provided by
5548 @option{-fsched-verbose-@var{n}}. @var{ready} is a pointer to the ready
5549 list of instructions that are ready to be scheduled. @var{n_readyp} is
5550 a pointer to the number of elements in the ready list. The scheduler
5551 reads the ready list in reverse order, starting with
5552 @var{ready}[@var{*n_readyp}-1] and going to @var{ready}[0]. @var{clock}
5553 is the timer tick of the scheduler. You may modify the ready list and
5554 the number of ready insns. The return value is the number of insns that
5555 can issue this cycle; normally this is just @code{issue_rate}. See also
5556 @samp{TARGET_SCHED_REORDER2}.
5559 @deftypefn {Target Hook} int TARGET_SCHED_REORDER2 (FILE *@var{file}, int @var{verbose}, rtx *@var{ready}, int *@var{n_ready}, @var{clock})
5560 Like @samp{TARGET_SCHED_REORDER}, but called at a different time. That
5561 function is called whenever the scheduler starts a new cycle. This one
5562 is called once per iteration over a cycle, immediately after
5563 @samp{TARGET_SCHED_VARIABLE_ISSUE}; it can reorder the ready list and
5564 return the number of insns to be scheduled in the same cycle. Defining
5565 this hook can be useful if there are frequent situations where
5566 scheduling one insn causes other insns to become ready in the same
5567 cycle. These other insns can then be taken into account properly.
5570 @deftypefn {Target Hook} void TARGET_SCHED_DEPENDENCIES_EVALUATION_HOOK (rtx @var{head}, rtx @var{tail})
5571 This hook is called after evaluation forward dependencies of insns in
5572 chain given by two parameter values (@var{head} and @var{tail}
5573 correspondingly) but before insns scheduling of the insn chain. For
5574 example, it can be used for better insn classification if it requires
5575 analysis of dependencies. This hook can use backward and forward
5576 dependencies of the insn scheduler because they are already
5580 @deftypefn {Target Hook} void TARGET_SCHED_INIT (FILE *@var{file}, int @var{verbose}, int @var{max_ready})
5581 This hook is executed by the scheduler at the beginning of each block of
5582 instructions that are to be scheduled. @var{file} is either a null
5583 pointer, or a stdio stream to write any debug output to. @var{verbose}
5584 is the verbose level provided by @option{-fsched-verbose-@var{n}}.
5585 @var{max_ready} is the maximum number of insns in the current scheduling
5586 region that can be live at the same time. This can be used to allocate
5587 scratch space if it is needed, e.g. by @samp{TARGET_SCHED_REORDER}.
5590 @deftypefn {Target Hook} void TARGET_SCHED_FINISH (FILE *@var{file}, int @var{verbose})
5591 This hook is executed by the scheduler at the end of each block of
5592 instructions that are to be scheduled. It can be used to perform
5593 cleanup of any actions done by the other scheduling hooks. @var{file}
5594 is either a null pointer, or a stdio stream to write any debug output
5595 to. @var{verbose} is the verbose level provided by
5596 @option{-fsched-verbose-@var{n}}.
5599 @deftypefn {Target Hook} int TARGET_SCHED_USE_DFA_PIPELINE_INTERFACE (void)
5600 This hook is called many times during insn scheduling. If the hook
5601 returns nonzero, the automaton based pipeline description is used for
5602 insn scheduling. Otherwise the traditional pipeline description is
5603 used. The default is usage of the traditional pipeline description.
5605 You should also remember that to simplify the insn scheduler sources
5606 an empty traditional pipeline description interface is generated even
5607 if there is no a traditional pipeline description in the @file{.md}
5608 file. The same is true for the automaton based pipeline description.
5609 That means that you should be accurate in defining the hook.
5612 @deftypefn {Target Hook} int TARGET_SCHED_DFA_PRE_CYCLE_INSN (void)
5613 The hook returns an RTL insn. The automaton state used in the
5614 pipeline hazard recognizer is changed as if the insn were scheduled
5615 when the new simulated processor cycle starts. Usage of the hook may
5616 simplify the automaton pipeline description for some @acronym{VLIW}
5617 processors. If the hook is defined, it is used only for the automaton
5618 based pipeline description. The default is not to change the state
5619 when the new simulated processor cycle starts.
5622 @deftypefn {Target Hook} void TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN (void)
5623 The hook can be used to initialize data used by the previous hook.
5626 @deftypefn {Target Hook} int TARGET_SCHED_DFA_POST_CYCLE_INSN (void)
5627 The hook is analogous to @samp{TARGET_SCHED_DFA_PRE_CYCLE_INSN} but used
5628 to changed the state as if the insn were scheduled when the new
5629 simulated processor cycle finishes.
5632 @deftypefn {Target Hook} void TARGET_SCHED_INIT_DFA_POST_CYCLE_INSN (void)
5633 The hook is analogous to @samp{TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN} but
5634 used to initialize data used by the previous hook.
5637 @deftypefn {Target Hook} int TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD (void)
5638 This hook controls better choosing an insn from the ready insn queue
5639 for the @acronym{DFA}-based insn scheduler. Usually the scheduler
5640 chooses the first insn from the queue. If the hook returns a positive
5641 value, an additional scheduler code tries all permutations of
5642 @samp{TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD ()}
5643 subsequent ready insns to choose an insn whose issue will result in
5644 maximal number of issued insns on the same cycle. For the
5645 @acronym{VLIW} processor, the code could actually solve the problem of
5646 packing simple insns into the @acronym{VLIW} insn. Of course, if the
5647 rules of @acronym{VLIW} packing are described in the automaton.
5649 This code also could be used for superscalar @acronym{RISC}
5650 processors. Let us consider a superscalar @acronym{RISC} processor
5651 with 3 pipelines. Some insns can be executed in pipelines @var{A} or
5652 @var{B}, some insns can be executed only in pipelines @var{B} or
5653 @var{C}, and one insn can be executed in pipeline @var{B}. The
5654 processor may issue the 1st insn into @var{A} and the 2nd one into
5655 @var{B}. In this case, the 3rd insn will wait for freeing @var{B}
5656 until the next cycle. If the scheduler issues the 3rd insn the first,
5657 the processor could issue all 3 insns per cycle.
5659 Actually this code demonstrates advantages of the automaton based
5660 pipeline hazard recognizer. We try quickly and easy many insn
5661 schedules to choose the best one.
5663 The default is no multipass scheduling.
5666 @deftypefn {Target Hook} int TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD (rtx)
5668 This hook controls what insns from the ready insn queue will be
5669 considered for the multipass insn scheduling. If the hook returns
5670 zero for insn passed as the parameter, the insn will be not chosen to
5673 The default is that any ready insns can be chosen to be issued.
5676 @deftypefn {Target Hook} int TARGET_SCHED_DFA_NEW_CYCLE (FILE *, int, rtx, int, int, int *)
5678 This hook is called by the insn scheduler before issuing insn passed
5679 as the third parameter on given cycle. If the hook returns nonzero,
5680 the insn is not issued on given processors cycle. Instead of that,
5681 the processor cycle is advanced. If the value passed through the last
5682 parameter is zero, the insn ready queue is not sorted on the new cycle
5683 start as usually. The first parameter passes file for debugging
5684 output. The second one passes the scheduler verbose level of the
5685 debugging output. The forth and the fifth parameter values are
5686 correspondingly processor cycle on which the previous insn has been
5687 issued and the current processor cycle.
5690 @deftypefn {Target Hook} void TARGET_SCHED_INIT_DFA_BUBBLES (void)
5691 The @acronym{DFA}-based scheduler could take the insertion of nop
5692 operations for better insn scheduling into account. It can be done
5693 only if the multi-pass insn scheduling works (see hook
5694 @samp{TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD}).
5696 Let us consider a @acronym{VLIW} processor insn with 3 slots. Each
5697 insn can be placed only in one of the three slots. We have 3 ready
5698 insns @var{A}, @var{B}, and @var{C}. @var{A} and @var{C} can be
5699 placed only in the 1st slot, @var{B} can be placed only in the 3rd
5700 slot. We described the automaton which does not permit empty slot
5701 gaps between insns (usually such description is simpler). Without
5702 this code the scheduler would place each insn in 3 separate
5703 @acronym{VLIW} insns. If the scheduler places a nop insn into the 2nd
5704 slot, it could place the 3 insns into 2 @acronym{VLIW} insns. What is
5705 the nop insn is returned by hook @samp{TARGET_SCHED_DFA_BUBBLE}. Hook
5706 @samp{TARGET_SCHED_INIT_DFA_BUBBLES} can be used to initialize or
5707 create the nop insns.
5709 You should remember that the scheduler does not insert the nop insns.
5710 It is not wise because of the following optimizations. The scheduler
5711 only considers such possibility to improve the result schedule. The
5712 nop insns should be inserted lately, e.g. on the final phase.
5715 @deftypefn {Target Hook} rtx TARGET_SCHED_DFA_BUBBLE (int @var{index})
5716 This hook @samp{FIRST_CYCLE_MULTIPASS_SCHEDULING} is used to insert
5717 nop operations for better insn scheduling when @acronym{DFA}-based
5718 scheduler makes multipass insn scheduling (see also description of
5719 hook @samp{TARGET_SCHED_INIT_DFA_BUBBLES}). This hook
5720 returns a nop insn with given @var{index}. The indexes start with
5721 zero. The hook should return @code{NULL} if there are no more nop
5722 insns with indexes greater than given index.
5725 Macros in the following table are generated by the program
5726 @file{genattr} and can be useful for writing the hooks.
5728 @defmac TRADITIONAL_PIPELINE_INTERFACE
5729 The macro definition is generated if there is a traditional pipeline
5730 description in @file{.md} file. You should also remember that to
5731 simplify the insn scheduler sources an empty traditional pipeline
5732 description interface is generated even if there is no a traditional
5733 pipeline description in the @file{.md} file. The macro can be used to
5734 distinguish the two types of the traditional interface.
5737 @defmac DFA_PIPELINE_INTERFACE
5738 The macro definition is generated if there is an automaton pipeline
5739 description in @file{.md} file. You should also remember that to
5740 simplify the insn scheduler sources an empty automaton pipeline
5741 description interface is generated even if there is no an automaton
5742 pipeline description in the @file{.md} file. The macro can be used to
5743 distinguish the two types of the automaton interface.
5746 @defmac MAX_DFA_ISSUE_RATE
5747 The macro definition is generated in the automaton based pipeline
5748 description interface. Its value is calculated from the automaton
5749 based pipeline description and is equal to maximal number of all insns
5750 described in constructions @samp{define_insn_reservation} which can be
5751 issued on the same processor cycle.
5755 @section Dividing the Output into Sections (Texts, Data, @dots{})
5756 @c the above section title is WAY too long. maybe cut the part between
5757 @c the (...)? --mew 10feb93
5759 An object file is divided into sections containing different types of
5760 data. In the most common case, there are three sections: the @dfn{text
5761 section}, which holds instructions and read-only data; the @dfn{data
5762 section}, which holds initialized writable data; and the @dfn{bss
5763 section}, which holds uninitialized data. Some systems have other kinds
5766 The compiler must tell the assembler when to switch sections. These
5767 macros control what commands to output to tell the assembler this. You
5768 can also define additional sections.
5770 @defmac TEXT_SECTION_ASM_OP
5771 A C expression whose value is a string, including spacing, containing the
5772 assembler operation that should precede instructions and read-only data.
5773 Normally @code{"\t.text"} is right.
5776 @defmac TEXT_SECTION
5777 A C statement that switches to the default section containing instructions.
5778 Normally this is not needed, as simply defining @code{TEXT_SECTION_ASM_OP}
5779 is enough. The MIPS port uses this to sort all functions after all data
5783 @defmac HOT_TEXT_SECTION_NAME
5784 If defined, a C string constant for the name of the section containing most
5785 frequently executed functions of the program. If not defined, GCC will provide
5786 a default definition if the target supports named sections.
5789 @defmac UNLIKELY_EXECUTED_TEXT_SECTION_NAME
5790 If defined, a C string constant for the name of the section containing unlikely
5791 executed functions in the program.
5794 @defmac DATA_SECTION_ASM_OP
5795 A C expression whose value is a string, including spacing, containing the
5796 assembler operation to identify the following data as writable initialized
5797 data. Normally @code{"\t.data"} is right.
5800 @defmac READONLY_DATA_SECTION_ASM_OP
5801 A C expression whose value is a string, including spacing, containing the
5802 assembler operation to identify the following data as read-only initialized
5806 @defmac READONLY_DATA_SECTION
5807 A macro naming a function to call to switch to the proper section for
5808 read-only data. The default is to use @code{READONLY_DATA_SECTION_ASM_OP}
5809 if defined, else fall back to @code{text_section}.
5811 The most common definition will be @code{data_section}, if the target
5812 does not have a special read-only data section, and does not put data
5813 in the text section.
5816 @defmac SHARED_SECTION_ASM_OP
5817 If defined, a C expression whose value is a string, including spacing,
5818 containing the assembler operation to identify the following data as
5819 shared data. If not defined, @code{DATA_SECTION_ASM_OP} will be used.
5822 @defmac BSS_SECTION_ASM_OP
5823 If defined, a C expression whose value is a string, including spacing,
5824 containing the assembler operation to identify the following data as
5825 uninitialized global data. If not defined, and neither
5826 @code{ASM_OUTPUT_BSS} nor @code{ASM_OUTPUT_ALIGNED_BSS} are defined,
5827 uninitialized global data will be output in the data section if
5828 @option{-fno-common} is passed, otherwise @code{ASM_OUTPUT_COMMON} will be
5832 @defmac SHARED_BSS_SECTION_ASM_OP
5833 If defined, a C expression whose value is a string, including spacing,
5834 containing the assembler operation to identify the following data as
5835 uninitialized global shared data. If not defined, and
5836 @code{BSS_SECTION_ASM_OP} is, the latter will be used.
5839 @defmac INIT_SECTION_ASM_OP
5840 If defined, a C expression whose value is a string, including spacing,
5841 containing the assembler operation to identify the following data as
5842 initialization code. If not defined, GCC will assume such a section does
5846 @defmac FINI_SECTION_ASM_OP
5847 If defined, a C expression whose value is a string, including spacing,
5848 containing the assembler operation to identify the following data as
5849 finalization code. If not defined, GCC will assume such a section does
5853 @defmac CRT_CALL_STATIC_FUNCTION (@var{section_op}, @var{function})
5854 If defined, an ASM statement that switches to a different section
5855 via @var{section_op}, calls @var{function}, and switches back to
5856 the text section. This is used in @file{crtstuff.c} if
5857 @code{INIT_SECTION_ASM_OP} or @code{FINI_SECTION_ASM_OP} to calls
5858 to initialization and finalization functions from the init and fini
5859 sections. By default, this macro uses a simple function call. Some
5860 ports need hand-crafted assembly code to avoid dependencies on
5861 registers initialized in the function prologue or to ensure that
5862 constant pools don't end up too far way in the text section.
5865 @defmac FORCE_CODE_SECTION_ALIGN
5866 If defined, an ASM statement that aligns a code section to some
5867 arbitrary boundary. This is used to force all fragments of the
5868 @code{.init} and @code{.fini} sections to have to same alignment
5869 and thus prevent the linker from having to add any padding.
5874 @defmac EXTRA_SECTIONS
5875 A list of names for sections other than the standard two, which are
5876 @code{in_text} and @code{in_data}. You need not define this macro
5877 on a system with no other sections (that GCC needs to use).
5880 @findex text_section
5881 @findex data_section
5882 @defmac EXTRA_SECTION_FUNCTIONS
5883 One or more functions to be defined in @file{varasm.c}. These
5884 functions should do jobs analogous to those of @code{text_section} and
5885 @code{data_section}, for your additional sections. Do not define this
5886 macro if you do not define @code{EXTRA_SECTIONS}.
5889 @defmac JUMP_TABLES_IN_TEXT_SECTION
5890 Define this macro to be an expression with a nonzero value if jump
5891 tables (for @code{tablejump} insns) should be output in the text
5892 section, along with the assembler instructions. Otherwise, the
5893 readonly data section is used.
5895 This macro is irrelevant if there is no separate readonly data section.
5898 @deftypefn {Target Hook} void TARGET_ASM_SELECT_SECTION (tree @var{exp}, int @var{reloc}, unsigned HOST_WIDE_INT @var{align})
5899 Switches to the appropriate section for output of @var{exp}. You can
5900 assume that @var{exp} is either a @code{VAR_DECL} node or a constant of
5901 some sort. @var{reloc} indicates whether the initial value of @var{exp}
5902 requires link-time relocations. Bit 0 is set when variable contains
5903 local relocations only, while bit 1 is set for global relocations.
5904 Select the section by calling @code{data_section} or one of the
5905 alternatives for other sections. @var{align} is the constant alignment
5908 The default version of this function takes care of putting read-only
5909 variables in @code{readonly_data_section}.
5912 @deftypefn {Target Hook} void TARGET_ASM_UNIQUE_SECTION (tree @var{decl}, int @var{reloc})
5913 Build up a unique section name, expressed as a @code{STRING_CST} node,
5914 and assign it to @samp{DECL_SECTION_NAME (@var{decl})}.
5915 As with @code{TARGET_ASM_SELECT_SECTION}, @var{reloc} indicates whether
5916 the initial value of @var{exp} requires link-time relocations.
5918 The default version of this function appends the symbol name to the
5919 ELF section name that would normally be used for the symbol. For
5920 example, the function @code{foo} would be placed in @code{.text.foo}.
5921 Whatever the actual target object format, this is often good enough.
5924 @deftypefn {Target Hook} void TARGET_ASM_SELECT_RTX_SECTION (enum machine_mode @var{mode}, rtx @var{x}, unsigned HOST_WIDE_INT @var{align})
5925 Switches to the appropriate section for output of constant pool entry
5926 @var{x} in @var{mode}. You can assume that @var{x} is some kind of
5927 constant in RTL@. The argument @var{mode} is redundant except in the
5928 case of a @code{const_int} rtx. Select the section by calling
5929 @code{readonly_data_section} or one of the alternatives for other
5930 sections. @var{align} is the constant alignment in bits.
5932 The default version of this function takes care of putting symbolic
5933 constants in @code{flag_pic} mode in @code{data_section} and everything
5934 else in @code{readonly_data_section}.
5937 @deftypefn {Target Hook} void TARGET_ENCODE_SECTION_INFO (tree @var{decl}, rtx @var{rtl}, int @var{new_decl_p})
5938 Define this hook if references to a symbol or a constant must be
5939 treated differently depending on something about the variable or
5940 function named by the symbol (such as what section it is in).
5942 The hook is executed immediately after rtl has been created for
5943 @var{decl}, which may be a variable or function declaration or
5944 an entry in the constant pool. In either case, @var{rtl} is the
5945 rtl in question. Do @emph{not} use @code{DECL_RTL (@var{decl})}
5946 in this hook; that field may not have been initialized yet.
5948 In the case of a constant, it is safe to assume that the rtl is
5949 a @code{mem} whose address is a @code{symbol_ref}. Most decls
5950 will also have this form, but that is not guaranteed. Global
5951 register variables, for instance, will have a @code{reg} for their
5952 rtl. (Normally the right thing to do with such unusual rtl is
5955 The @var{new_decl_p} argument will be true if this is the first time
5956 that @code{TARGET_ENCODE_SECTION_INFO} has been invoked on this decl. It will
5957 be false for subsequent invocations, which will happen for duplicate
5958 declarations. Whether or not anything must be done for the duplicate
5959 declaration depends on whether the hook examines @code{DECL_ATTRIBUTES}.
5960 @var{new_decl_p} is always true when the hook is called for a constant.
5962 @cindex @code{SYMBOL_REF_FLAG}, in @code{TARGET_ENCODE_SECTION_INFO}
5963 The usual thing for this hook to do is to record flags in the
5964 @code{symbol_ref}, using @code{SYMBOL_REF_FLAG} or @code{SYMBOL_REF_FLAGS}.
5965 Historically, the name string was modified if it was necessary to
5966 encode more than one bit of information, but this practice is now
5967 discouraged; use @code{SYMBOL_REF_FLAGS}.
5969 The default definition of this hook, @code{default_encode_section_info}
5970 in @file{varasm.c}, sets a number of commonly-useful bits in
5971 @code{SYMBOL_REF_FLAGS}. Check whether the default does what you need
5972 before overriding it.
5975 @deftypefn {Target Hook} const char *TARGET_STRIP_NAME_ENCODING (const char *name)
5976 Decode @var{name} and return the real name part, sans
5977 the characters that @code{TARGET_ENCODE_SECTION_INFO}
5981 @deftypefn {Target Hook} bool TARGET_IN_SMALL_DATA_P (tree @var{exp})
5982 Returns true if @var{exp} should be placed into a ``small data'' section.
5983 The default version of this hook always returns false.
5986 @deftypevar {Target Hook} bool TARGET_HAVE_SRODATA_SECTION
5987 Contains the value true if the target places read-only
5988 ``small data'' into a separate section. The default value is false.
5991 @deftypefn {Target Hook} bool TARGET_BINDS_LOCAL_P (tree @var{exp})
5992 Returns true if @var{exp} names an object for which name resolution
5993 rules must resolve to the current ``module'' (dynamic shared library
5994 or executable image).
5996 The default version of this hook implements the name resolution rules
5997 for ELF, which has a looser model of global name binding than other
5998 currently supported object file formats.
6001 @deftypevar {Target Hook} bool TARGET_HAVE_TLS
6002 Contains the value true if the target supports thread-local storage.
6003 The default value is false.
6008 @section Position Independent Code
6009 @cindex position independent code
6012 This section describes macros that help implement generation of position
6013 independent code. Simply defining these macros is not enough to
6014 generate valid PIC; you must also add support to the macros
6015 @code{GO_IF_LEGITIMATE_ADDRESS} and @code{PRINT_OPERAND_ADDRESS}, as
6016 well as @code{LEGITIMIZE_ADDRESS}. You must modify the definition of
6017 @samp{movsi} to do something appropriate when the source operand
6018 contains a symbolic address. You may also need to alter the handling of
6019 switch statements so that they use relative addresses.
6020 @c i rearranged the order of the macros above to try to force one of
6021 @c them to the next line, to eliminate an overfull hbox. --mew 10feb93
6023 @defmac PIC_OFFSET_TABLE_REGNUM
6024 The register number of the register used to address a table of static
6025 data addresses in memory. In some cases this register is defined by a
6026 processor's ``application binary interface'' (ABI)@. When this macro
6027 is defined, RTL is generated for this register once, as with the stack
6028 pointer and frame pointer registers. If this macro is not defined, it
6029 is up to the machine-dependent files to allocate such a register (if
6030 necessary). Note that this register must be fixed when in use (e.g.@:
6031 when @code{flag_pic} is true).
6034 @defmac PIC_OFFSET_TABLE_REG_CALL_CLOBBERED
6035 Define this macro if the register defined by
6036 @code{PIC_OFFSET_TABLE_REGNUM} is clobbered by calls. Do not define
6037 this macro if @code{PIC_OFFSET_TABLE_REGNUM} is not defined.
6040 @defmac FINALIZE_PIC
6041 By generating position-independent code, when two different programs (A
6042 and B) share a common library (libC.a), the text of the library can be
6043 shared whether or not the library is linked at the same address for both
6044 programs. In some of these environments, position-independent code
6045 requires not only the use of different addressing modes, but also
6046 special code to enable the use of these addressing modes.
6048 The @code{FINALIZE_PIC} macro serves as a hook to emit these special
6049 codes once the function is being compiled into assembly code, but not
6050 before. (It is not done before, because in the case of compiling an
6051 inline function, it would lead to multiple PIC prologues being
6052 included in functions which used inline functions and were compiled to
6056 @defmac LEGITIMATE_PIC_OPERAND_P (@var{x})
6057 A C expression that is nonzero if @var{x} is a legitimate immediate
6058 operand on the target machine when generating position independent code.
6059 You can assume that @var{x} satisfies @code{CONSTANT_P}, so you need not
6060 check this. You can also assume @var{flag_pic} is true, so you need not
6061 check it either. You need not define this macro if all constants
6062 (including @code{SYMBOL_REF}) can be immediate operands when generating
6063 position independent code.
6066 @node Assembler Format
6067 @section Defining the Output Assembler Language
6069 This section describes macros whose principal purpose is to describe how
6070 to write instructions in assembler language---rather than what the
6074 * File Framework:: Structural information for the assembler file.
6075 * Data Output:: Output of constants (numbers, strings, addresses).
6076 * Uninitialized Data:: Output of uninitialized variables.
6077 * Label Output:: Output and generation of labels.
6078 * Initialization:: General principles of initialization
6079 and termination routines.
6080 * Macros for Initialization::
6081 Specific macros that control the handling of
6082 initialization and termination routines.
6083 * Instruction Output:: Output of actual instructions.
6084 * Dispatch Tables:: Output of jump tables.
6085 * Exception Region Output:: Output of exception region code.
6086 * Alignment Output:: Pseudo ops for alignment and skipping data.
6089 @node File Framework
6090 @subsection The Overall Framework of an Assembler File
6091 @cindex assembler format
6092 @cindex output of assembler code
6094 @c prevent bad page break with this line
6095 This describes the overall framework of an assembly file.
6097 @deftypefn {Target Hook} void TARGET_ASM_FILE_START ()
6098 @findex default_file_start
6099 Output to @code{asm_out_file} any text which the assembler expects to
6100 find at the beginning of a file. The default behavior is controlled
6101 by two flags, documented below. Unless your target's assembler is
6102 quite unusual, if you override the default, you should call
6103 @code{default_file_start} at some point in your target hook. This
6104 lets other target files rely on these variables.
6107 @deftypevr {Target Hook} bool TARGET_ASM_FILE_START_APP_OFF
6108 If this flag is true, the text of the macro @code{ASM_APP_OFF} will be
6109 printed as the very first line in the assembly file, unless
6110 @option{-fverbose-asm} is in effect. (If that macro has been defined
6111 to the empty string, this variable has no effect.) With the normal
6112 definition of @code{ASM_APP_OFF}, the effect is to notify the GNU
6113 assembler that it need not bother stripping comments or extra
6114 whitespace from its input. This allows it to work a bit faster.
6116 The default is false. You should not set it to true unless you have
6117 verified that your port does not generate any extra whitespace or
6118 comments that will cause GAS to issue errors in NO_APP mode.
6121 @deftypevr {Target Hook} bool TARGET_ASM_FILE_START_FILE_DIRECTIVE
6122 If this flag is true, @code{output_file_directive} will be called
6123 for the primary source file, immediately after printing
6124 @code{ASM_APP_OFF} (if that is enabled). Most ELF assemblers expect
6125 this to be done. The default is false.
6128 @deftypefn {Target Hook} void TARGET_ASM_FILE_END ()
6129 Output to @code{asm_out_file} any text which the assembler expects
6130 to find at the end of a file. The default is to output nothing.
6133 @deftypefun void file_end_indicate_exec_stack ()
6134 Some systems use a common convention, the @samp{.note.GNU-stack}
6135 special section, to indicate whether or not an object file relies on
6136 the stack being executable. If your system uses this convention, you
6137 should define @code{TARGET_ASM_FILE_END} to this function. If you
6138 need to do other things in that hook, have your hook function call
6142 @defmac ASM_COMMENT_START
6143 A C string constant describing how to begin a comment in the target
6144 assembler language. The compiler assumes that the comment will end at
6145 the end of the line.
6149 A C string constant for text to be output before each @code{asm}
6150 statement or group of consecutive ones. Normally this is
6151 @code{"#APP"}, which is a comment that has no effect on most
6152 assemblers but tells the GNU assembler that it must check the lines
6153 that follow for all valid assembler constructs.
6157 A C string constant for text to be output after each @code{asm}
6158 statement or group of consecutive ones. Normally this is
6159 @code{"#NO_APP"}, which tells the GNU assembler to resume making the
6160 time-saving assumptions that are valid for ordinary compiler output.
6163 @defmac ASM_OUTPUT_SOURCE_FILENAME (@var{stream}, @var{name})
6164 A C statement to output COFF information or DWARF debugging information
6165 which indicates that filename @var{name} is the current source file to
6166 the stdio stream @var{stream}.
6168 This macro need not be defined if the standard form of output
6169 for the file format in use is appropriate.
6172 @defmac OUTPUT_QUOTED_STRING (@var{stream}, @var{string})
6173 A C statement to output the string @var{string} to the stdio stream
6174 @var{stream}. If you do not call the function @code{output_quoted_string}
6175 in your config files, GCC will only call it to output filenames to
6176 the assembler source. So you can use it to canonicalize the format
6177 of the filename using this macro.
6180 @defmac ASM_OUTPUT_SOURCE_LINE (@var{stream}, @var{line}, @var{counter})
6181 A C statement to output DBX or SDB debugging information before code
6182 for line number @var{line} of the current source file to the
6183 stdio stream @var{stream}. @var{counter} is the number of time the
6184 macro was invoked, including the current invocation; it is intended
6185 to generate unique labels in the assembly output.
6187 This macro need not be defined if the standard form of debugging
6188 information for the debugger in use is appropriate.
6191 @defmac ASM_OUTPUT_IDENT (@var{stream}, @var{string})
6192 A C statement to output something to the assembler file to handle a
6193 @samp{#ident} directive containing the text @var{string}. If this
6194 macro is not defined, nothing is output for a @samp{#ident} directive.
6197 @deftypefn {Target Hook} void TARGET_ASM_NAMED_SECTION (const char *@var{name}, unsigned int @var{flags}, unsigned int @var{align})
6198 Output assembly directives to switch to section @var{name}. The section
6199 should have attributes as specified by @var{flags}, which is a bit mask
6200 of the @code{SECTION_*} flags defined in @file{output.h}. If @var{align}
6201 is nonzero, it contains an alignment in bytes to be used for the section,
6202 otherwise some target default should be used. Only targets that must
6203 specify an alignment within the section directive need pay attention to
6204 @var{align} -- we will still use @code{ASM_OUTPUT_ALIGN}.
6207 @deftypefn {Target Hook} bool TARGET_HAVE_NAMED_SECTIONS
6208 This flag is true if the target supports @code{TARGET_ASM_NAMED_SECTION}.
6211 @deftypefn {Target Hook} {unsigned int} TARGET_SECTION_TYPE_FLAGS (tree @var{decl}, const char *@var{name}, int @var{reloc})
6212 Choose a set of section attributes for use by @code{TARGET_ASM_NAMED_SECTION}
6213 based on a variable or function decl, a section name, and whether or not the
6214 declaration's initializer may contain runtime relocations. @var{decl} may be
6215 null, in which case read-write data should be assumed.
6217 The default version if this function handles choosing code vs data,
6218 read-only vs read-write data, and @code{flag_pic}. You should only
6219 need to override this if your target has special flags that might be
6220 set via @code{__attribute__}.
6225 @subsection Output of Data
6228 @deftypevr {Target Hook} {const char *} TARGET_ASM_BYTE_OP
6229 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_HI_OP
6230 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_SI_OP
6231 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_DI_OP
6232 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_TI_OP
6233 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_HI_OP
6234 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_SI_OP
6235 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_DI_OP
6236 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_TI_OP
6237 These hooks specify assembly directives for creating certain kinds
6238 of integer object. The @code{TARGET_ASM_BYTE_OP} directive creates a
6239 byte-sized object, the @code{TARGET_ASM_ALIGNED_HI_OP} one creates an
6240 aligned two-byte object, and so on. Any of the hooks may be
6241 @code{NULL}, indicating that no suitable directive is available.
6243 The compiler will print these strings at the start of a new line,
6244 followed immediately by the object's initial value. In most cases,
6245 the string should contain a tab, a pseudo-op, and then another tab.
6248 @deftypefn {Target Hook} bool TARGET_ASM_INTEGER (rtx @var{x}, unsigned int @var{size}, int @var{aligned_p})
6249 The @code{assemble_integer} function uses this hook to output an
6250 integer object. @var{x} is the object's value, @var{size} is its size
6251 in bytes and @var{aligned_p} indicates whether it is aligned. The
6252 function should return @code{true} if it was able to output the
6253 object. If it returns false, @code{assemble_integer} will try to
6254 split the object into smaller parts.
6256 The default implementation of this hook will use the
6257 @code{TARGET_ASM_BYTE_OP} family of strings, returning @code{false}
6258 when the relevant string is @code{NULL}.
6261 @defmac OUTPUT_ADDR_CONST_EXTRA (@var{stream}, @var{x}, @var{fail})
6262 A C statement to recognize @var{rtx} patterns that
6263 @code{output_addr_const} can't deal with, and output assembly code to
6264 @var{stream} corresponding to the pattern @var{x}. This may be used to
6265 allow machine-dependent @code{UNSPEC}s to appear within constants.
6267 If @code{OUTPUT_ADDR_CONST_EXTRA} fails to recognize a pattern, it must
6268 @code{goto fail}, so that a standard error message is printed. If it
6269 prints an error message itself, by calling, for example,
6270 @code{output_operand_lossage}, it may just complete normally.
6273 @defmac ASM_OUTPUT_ASCII (@var{stream}, @var{ptr}, @var{len})
6274 A C statement to output to the stdio stream @var{stream} an assembler
6275 instruction to assemble a string constant containing the @var{len}
6276 bytes at @var{ptr}. @var{ptr} will be a C expression of type
6277 @code{char *} and @var{len} a C expression of type @code{int}.
6279 If the assembler has a @code{.ascii} pseudo-op as found in the
6280 Berkeley Unix assembler, do not define the macro
6281 @code{ASM_OUTPUT_ASCII}.
6284 @defmac ASM_OUTPUT_FDESC (@var{stream}, @var{decl}, @var{n})
6285 A C statement to output word @var{n} of a function descriptor for
6286 @var{decl}. This must be defined if @code{TARGET_VTABLE_USES_DESCRIPTORS}
6287 is defined, and is otherwise unused.
6290 @defmac CONSTANT_POOL_BEFORE_FUNCTION
6291 You may define this macro as a C expression. You should define the
6292 expression to have a nonzero value if GCC should output the constant
6293 pool for a function before the code for the function, or a zero value if
6294 GCC should output the constant pool after the function. If you do
6295 not define this macro, the usual case, GCC will output the constant
6296 pool before the function.
6299 @defmac ASM_OUTPUT_POOL_PROLOGUE (@var{file}, @var{funname}, @var{fundecl}, @var{size})
6300 A C statement to output assembler commands to define the start of the
6301 constant pool for a function. @var{funname} is a string giving
6302 the name of the function. Should the return type of the function
6303 be required, it can be obtained via @var{fundecl}. @var{size}
6304 is the size, in bytes, of the constant pool that will be written
6305 immediately after this call.
6307 If no constant-pool prefix is required, the usual case, this macro need
6311 @defmac ASM_OUTPUT_SPECIAL_POOL_ENTRY (@var{file}, @var{x}, @var{mode}, @var{align}, @var{labelno}, @var{jumpto})
6312 A C statement (with or without semicolon) to output a constant in the
6313 constant pool, if it needs special treatment. (This macro need not do
6314 anything for RTL expressions that can be output normally.)
6316 The argument @var{file} is the standard I/O stream to output the
6317 assembler code on. @var{x} is the RTL expression for the constant to
6318 output, and @var{mode} is the machine mode (in case @var{x} is a
6319 @samp{const_int}). @var{align} is the required alignment for the value
6320 @var{x}; you should output an assembler directive to force this much
6323 The argument @var{labelno} is a number to use in an internal label for
6324 the address of this pool entry. The definition of this macro is
6325 responsible for outputting the label definition at the proper place.
6326 Here is how to do this:
6329 @code{(*targetm.asm_out.internal_label)} (@var{file}, "LC", @var{labelno});
6332 When you output a pool entry specially, you should end with a
6333 @code{goto} to the label @var{jumpto}. This will prevent the same pool
6334 entry from being output a second time in the usual manner.
6336 You need not define this macro if it would do nothing.
6339 @defmac ASM_OUTPUT_POOL_EPILOGUE (@var{file} @var{funname} @var{fundecl} @var{size})
6340 A C statement to output assembler commands to at the end of the constant
6341 pool for a function. @var{funname} is a string giving the name of the
6342 function. Should the return type of the function be required, you can
6343 obtain it via @var{fundecl}. @var{size} is the size, in bytes, of the
6344 constant pool that GCC wrote immediately before this call.
6346 If no constant-pool epilogue is required, the usual case, you need not
6350 @defmac IS_ASM_LOGICAL_LINE_SEPARATOR (@var{C})
6351 Define this macro as a C expression which is nonzero if @var{C} is
6352 used as a logical line separator by the assembler.
6354 If you do not define this macro, the default is that only
6355 the character @samp{;} is treated as a logical line separator.
6358 @deftypevr {Target Hook} {const char *} TARGET_ASM_OPEN_PAREN
6359 @deftypevrx {Target Hook} {const char *} TARGET_ASM_CLOSE_PAREN
6360 These target hooks are C string constants, describing the syntax in the
6361 assembler for grouping arithmetic expressions. If not overridden, they
6362 default to normal parentheses, which is correct for most assemblers.
6365 These macros are provided by @file{real.h} for writing the definitions
6366 of @code{ASM_OUTPUT_DOUBLE} and the like:
6368 @defmac REAL_VALUE_TO_TARGET_SINGLE (@var{x}, @var{l})
6369 @defmacx REAL_VALUE_TO_TARGET_DOUBLE (@var{x}, @var{l})
6370 @defmacx REAL_VALUE_TO_TARGET_LONG_DOUBLE (@var{x}, @var{l})
6371 These translate @var{x}, of type @code{REAL_VALUE_TYPE}, to the target's
6372 floating point representation, and store its bit pattern in the variable
6373 @var{l}. For @code{REAL_VALUE_TO_TARGET_SINGLE}, this variable should
6374 be a simple @code{long int}. For the others, it should be an array of
6375 @code{long int}. The number of elements in this array is determined by
6376 the size of the desired target floating point data type: 32 bits of it
6377 go in each @code{long int} array element. Each array element holds 32
6378 bits of the result, even if @code{long int} is wider than 32 bits on the
6381 The array element values are designed so that you can print them out
6382 using @code{fprintf} in the order they should appear in the target
6386 @node Uninitialized Data
6387 @subsection Output of Uninitialized Variables
6389 Each of the macros in this section is used to do the whole job of
6390 outputting a single uninitialized variable.
6392 @defmac ASM_OUTPUT_COMMON (@var{stream}, @var{name}, @var{size}, @var{rounded})
6393 A C statement (sans semicolon) to output to the stdio stream
6394 @var{stream} the assembler definition of a common-label named
6395 @var{name} whose size is @var{size} bytes. The variable @var{rounded}
6396 is the size rounded up to whatever alignment the caller wants.
6398 Use the expression @code{assemble_name (@var{stream}, @var{name})} to
6399 output the name itself; before and after that, output the additional
6400 assembler syntax for defining the name, and a newline.
6402 This macro controls how the assembler definitions of uninitialized
6403 common global variables are output.
6406 @defmac ASM_OUTPUT_ALIGNED_COMMON (@var{stream}, @var{name}, @var{size}, @var{alignment})
6407 Like @code{ASM_OUTPUT_COMMON} except takes the required alignment as a
6408 separate, explicit argument. If you define this macro, it is used in
6409 place of @code{ASM_OUTPUT_COMMON}, and gives you more flexibility in
6410 handling the required alignment of the variable. The alignment is specified
6411 as the number of bits.
6414 @defmac ASM_OUTPUT_ALIGNED_DECL_COMMON (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
6415 Like @code{ASM_OUTPUT_ALIGNED_COMMON} except that @var{decl} of the
6416 variable to be output, if there is one, or @code{NULL_TREE} if there
6417 is no corresponding variable. If you define this macro, GCC will use it
6418 in place of both @code{ASM_OUTPUT_COMMON} and
6419 @code{ASM_OUTPUT_ALIGNED_COMMON}. Define this macro when you need to see
6420 the variable's decl in order to chose what to output.
6423 @defmac ASM_OUTPUT_SHARED_COMMON (@var{stream}, @var{name}, @var{size}, @var{rounded})
6424 If defined, it is similar to @code{ASM_OUTPUT_COMMON}, except that it
6425 is used when @var{name} is shared. If not defined, @code{ASM_OUTPUT_COMMON}
6429 @defmac ASM_OUTPUT_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{rounded})
6430 A C statement (sans semicolon) to output to the stdio stream
6431 @var{stream} the assembler definition of uninitialized global @var{decl} named
6432 @var{name} whose size is @var{size} bytes. The variable @var{rounded}
6433 is the size rounded up to whatever alignment the caller wants.
6435 Try to use function @code{asm_output_bss} defined in @file{varasm.c} when
6436 defining this macro. If unable, use the expression
6437 @code{assemble_name (@var{stream}, @var{name})} to output the name itself;
6438 before and after that, output the additional assembler syntax for defining
6439 the name, and a newline.
6441 This macro controls how the assembler definitions of uninitialized global
6442 variables are output. This macro exists to properly support languages like
6443 C++ which do not have @code{common} data. However, this macro currently
6444 is not defined for all targets. If this macro and
6445 @code{ASM_OUTPUT_ALIGNED_BSS} are not defined then @code{ASM_OUTPUT_COMMON}
6446 or @code{ASM_OUTPUT_ALIGNED_COMMON} or
6447 @code{ASM_OUTPUT_ALIGNED_DECL_COMMON} is used.
6450 @defmac ASM_OUTPUT_ALIGNED_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
6451 Like @code{ASM_OUTPUT_BSS} except takes the required alignment as a
6452 separate, explicit argument. If you define this macro, it is used in
6453 place of @code{ASM_OUTPUT_BSS}, and gives you more flexibility in
6454 handling the required alignment of the variable. The alignment is specified
6455 as the number of bits.
6457 Try to use function @code{asm_output_aligned_bss} defined in file
6458 @file{varasm.c} when defining this macro.
6461 @defmac ASM_OUTPUT_SHARED_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{rounded})
6462 If defined, it is similar to @code{ASM_OUTPUT_BSS}, except that it
6463 is used when @var{name} is shared. If not defined, @code{ASM_OUTPUT_BSS}
6467 @defmac ASM_OUTPUT_LOCAL (@var{stream}, @var{name}, @var{size}, @var{rounded})
6468 A C statement (sans semicolon) to output to the stdio stream
6469 @var{stream} the assembler definition of a local-common-label named
6470 @var{name} whose size is @var{size} bytes. The variable @var{rounded}
6471 is the size rounded up to whatever alignment the caller wants.
6473 Use the expression @code{assemble_name (@var{stream}, @var{name})} to
6474 output the name itself; before and after that, output the additional
6475 assembler syntax for defining the name, and a newline.
6477 This macro controls how the assembler definitions of uninitialized
6478 static variables are output.
6481 @defmac ASM_OUTPUT_ALIGNED_LOCAL (@var{stream}, @var{name}, @var{size}, @var{alignment})
6482 Like @code{ASM_OUTPUT_LOCAL} except takes the required alignment as a
6483 separate, explicit argument. If you define this macro, it is used in
6484 place of @code{ASM_OUTPUT_LOCAL}, and gives you more flexibility in
6485 handling the required alignment of the variable. The alignment is specified
6486 as the number of bits.
6489 @defmac ASM_OUTPUT_ALIGNED_DECL_LOCAL (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
6490 Like @code{ASM_OUTPUT_ALIGNED_DECL} except that @var{decl} of the
6491 variable to be output, if there is one, or @code{NULL_TREE} if there
6492 is no corresponding variable. If you define this macro, GCC will use it
6493 in place of both @code{ASM_OUTPUT_DECL} and
6494 @code{ASM_OUTPUT_ALIGNED_DECL}. Define this macro when you need to see
6495 the variable's decl in order to chose what to output.
6498 @defmac ASM_OUTPUT_SHARED_LOCAL (@var{stream}, @var{name}, @var{size}, @var{rounded})
6499 If defined, it is similar to @code{ASM_OUTPUT_LOCAL}, except that it
6500 is used when @var{name} is shared. If not defined, @code{ASM_OUTPUT_LOCAL}
6505 @subsection Output and Generation of Labels
6507 @c prevent bad page break with this line
6508 This is about outputting labels.
6510 @findex assemble_name
6511 @defmac ASM_OUTPUT_LABEL (@var{stream}, @var{name})
6512 A C statement (sans semicolon) to output to the stdio stream
6513 @var{stream} the assembler definition of a label named @var{name}.
6514 Use the expression @code{assemble_name (@var{stream}, @var{name})} to
6515 output the name itself; before and after that, output the additional
6516 assembler syntax for defining the name, and a newline. A default
6517 definition of this macro is provided which is correct for most systems.
6521 A C string containing the appropriate assembler directive to specify the
6522 size of a symbol, without any arguments. On systems that use ELF, the
6523 default (in @file{config/elfos.h}) is @samp{"\t.size\t"}; on other
6524 systems, the default is not to define this macro.
6526 Define this macro only if it is correct to use the default definitions
6527 of @code{ASM_OUTPUT_SIZE_DIRECTIVE} and @code{ASM_OUTPUT_MEASURED_SIZE}
6528 for your system. If you need your own custom definitions of those
6529 macros, or if you do not need explicit symbol sizes at all, do not
6533 @defmac ASM_OUTPUT_SIZE_DIRECTIVE (@var{stream}, @var{name}, @var{size})
6534 A C statement (sans semicolon) to output to the stdio stream
6535 @var{stream} a directive telling the assembler that the size of the
6536 symbol @var{name} is @var{size}. @var{size} is a @code{HOST_WIDE_INT}.
6537 If you define @code{SIZE_ASM_OP}, a default definition of this macro is
6541 @defmac ASM_OUTPUT_MEASURED_SIZE (@var{stream}, @var{name})
6542 A C statement (sans semicolon) to output to the stdio stream
6543 @var{stream} a directive telling the assembler to calculate the size of
6544 the symbol @var{name} by subtracting its address from the current
6547 If you define @code{SIZE_ASM_OP}, a default definition of this macro is
6548 provided. The default assumes that the assembler recognizes a special
6549 @samp{.} symbol as referring to the current address, and can calculate
6550 the difference between this and another symbol. If your assembler does
6551 not recognize @samp{.} or cannot do calculations with it, you will need
6552 to redefine @code{ASM_OUTPUT_MEASURED_SIZE} to use some other technique.
6556 A C string containing the appropriate assembler directive to specify the
6557 type of a symbol, without any arguments. On systems that use ELF, the
6558 default (in @file{config/elfos.h}) is @samp{"\t.type\t"}; on other
6559 systems, the default is not to define this macro.
6561 Define this macro only if it is correct to use the default definition of
6562 @code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own
6563 custom definition of this macro, or if you do not need explicit symbol
6564 types at all, do not define this macro.
6567 @defmac TYPE_OPERAND_FMT
6568 A C string which specifies (using @code{printf} syntax) the format of
6569 the second operand to @code{TYPE_ASM_OP}. On systems that use ELF, the
6570 default (in @file{config/elfos.h}) is @samp{"@@%s"}; on other systems,
6571 the default is not to define this macro.
6573 Define this macro only if it is correct to use the default definition of
6574 @code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own
6575 custom definition of this macro, or if you do not need explicit symbol
6576 types at all, do not define this macro.
6579 @defmac ASM_OUTPUT_TYPE_DIRECTIVE (@var{stream}, @var{type})
6580 A C statement (sans semicolon) to output to the stdio stream
6581 @var{stream} a directive telling the assembler that the type of the
6582 symbol @var{name} is @var{type}. @var{type} is a C string; currently,
6583 that string is always either @samp{"function"} or @samp{"object"}, but
6584 you should not count on this.
6586 If you define @code{TYPE_ASM_OP} and @code{TYPE_OPERAND_FMT}, a default
6587 definition of this macro is provided.
6590 @defmac ASM_DECLARE_FUNCTION_NAME (@var{stream}, @var{name}, @var{decl})
6591 A C statement (sans semicolon) to output to the stdio stream
6592 @var{stream} any text necessary for declaring the name @var{name} of a
6593 function which is being defined. This macro is responsible for
6594 outputting the label definition (perhaps using
6595 @code{ASM_OUTPUT_LABEL}). The argument @var{decl} is the
6596 @code{FUNCTION_DECL} tree node representing the function.
6598 If this macro is not defined, then the function name is defined in the
6599 usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}).
6601 You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in the definition
6605 @defmac ASM_DECLARE_FUNCTION_SIZE (@var{stream}, @var{name}, @var{decl})
6606 A C statement (sans semicolon) to output to the stdio stream
6607 @var{stream} any text necessary for declaring the size of a function
6608 which is being defined. The argument @var{name} is the name of the
6609 function. The argument @var{decl} is the @code{FUNCTION_DECL} tree node
6610 representing the function.
6612 If this macro is not defined, then the function size is not defined.
6614 You may wish to use @code{ASM_OUTPUT_MEASURED_SIZE} in the definition
6618 @defmac ASM_DECLARE_OBJECT_NAME (@var{stream}, @var{name}, @var{decl})
6619 A C statement (sans semicolon) to output to the stdio stream
6620 @var{stream} any text necessary for declaring the name @var{name} of an
6621 initialized variable which is being defined. This macro must output the
6622 label definition (perhaps using @code{ASM_OUTPUT_LABEL}). The argument
6623 @var{decl} is the @code{VAR_DECL} tree node representing the variable.
6625 If this macro is not defined, then the variable name is defined in the
6626 usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}).
6628 You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} and/or
6629 @code{ASM_OUTPUT_SIZE_DIRECTIVE} in the definition of this macro.
6632 @defmac ASM_DECLARE_REGISTER_GLOBAL (@var{stream}, @var{decl}, @var{regno}, @var{name})
6633 A C statement (sans semicolon) to output to the stdio stream
6634 @var{stream} any text necessary for claiming a register @var{regno}
6635 for a global variable @var{decl} with name @var{name}.
6637 If you don't define this macro, that is equivalent to defining it to do
6641 @defmac ASM_FINISH_DECLARE_OBJECT (@var{stream}, @var{decl}, @var{toplevel}, @var{atend})
6642 A C statement (sans semicolon) to finish up declaring a variable name
6643 once the compiler has processed its initializer fully and thus has had a
6644 chance to determine the size of an array when controlled by an
6645 initializer. This is used on systems where it's necessary to declare
6646 something about the size of the object.
6648 If you don't define this macro, that is equivalent to defining it to do
6651 You may wish to use @code{ASM_OUTPUT_SIZE_DIRECTIVE} and/or
6652 @code{ASM_OUTPUT_MEASURED_SIZE} in the definition of this macro.
6655 @deftypefn {Target Hook} void TARGET_ASM_GLOBALIZE_LABEL (FILE *@var{stream}, const char *@var{name})
6656 This target hook is a function to output to the stdio stream
6657 @var{stream} some commands that will make the label @var{name} global;
6658 that is, available for reference from other files.
6660 The default implementation relies on a proper definition of
6661 @code{GLOBAL_ASM_OP}.
6664 @defmac ASM_WEAKEN_LABEL (@var{stream}, @var{name})
6665 A C statement (sans semicolon) to output to the stdio stream
6666 @var{stream} some commands that will make the label @var{name} weak;
6667 that is, available for reference from other files but only used if
6668 no other definition is available. Use the expression
6669 @code{assemble_name (@var{stream}, @var{name})} to output the name
6670 itself; before and after that, output the additional assembler syntax
6671 for making that name weak, and a newline.
6673 If you don't define this macro or @code{ASM_WEAKEN_DECL}, GCC will not
6674 support weak symbols and you should not define the @code{SUPPORTS_WEAK}
6678 @defmac ASM_WEAKEN_DECL (@var{stream}, @var{decl}, @var{name}, @var{value})
6679 Combines (and replaces) the function of @code{ASM_WEAKEN_LABEL} and
6680 @code{ASM_OUTPUT_WEAK_ALIAS}, allowing access to the associated function
6681 or variable decl. If @var{value} is not @code{NULL}, this C statement
6682 should output to the stdio stream @var{stream} assembler code which
6683 defines (equates) the weak symbol @var{name} to have the value
6684 @var{value}. If @var{value} is @code{NULL}, it should output commands
6685 to make @var{name} weak.
6688 @defmac SUPPORTS_WEAK
6689 A C expression which evaluates to true if the target supports weak symbols.
6691 If you don't define this macro, @file{defaults.h} provides a default
6692 definition. If either @code{ASM_WEAKEN_LABEL} or @code{ASM_WEAKEN_DECL}
6693 is defined, the default definition is @samp{1}; otherwise, it is
6694 @samp{0}. Define this macro if you want to control weak symbol support
6695 with a compiler flag such as @option{-melf}.
6698 @defmac MAKE_DECL_ONE_ONLY (@var{decl})
6699 A C statement (sans semicolon) to mark @var{decl} to be emitted as a
6700 public symbol such that extra copies in multiple translation units will
6701 be discarded by the linker. Define this macro if your object file
6702 format provides support for this concept, such as the @samp{COMDAT}
6703 section flags in the Microsoft Windows PE/COFF format, and this support
6704 requires changes to @var{decl}, such as putting it in a separate section.
6707 @defmac SUPPORTS_ONE_ONLY
6708 A C expression which evaluates to true if the target supports one-only
6711 If you don't define this macro, @file{varasm.c} provides a default
6712 definition. If @code{MAKE_DECL_ONE_ONLY} is defined, the default
6713 definition is @samp{1}; otherwise, it is @samp{0}. Define this macro if
6714 you want to control one-only symbol support with a compiler flag, or if
6715 setting the @code{DECL_ONE_ONLY} flag is enough to mark a declaration to
6716 be emitted as one-only.
6719 @deftypefn {Target Hook} void TARGET_ASM_ASSEMBLE_VISIBILITY (tree @var{decl}, const char *@var{visibility})
6720 This target hook is a function to output to @var{asm_out_file} some
6721 commands that will make the symbol(s) associated with @var{decl} have
6722 hidden, protected or internal visibility as specified by @var{visibility}.
6725 @defmac ASM_OUTPUT_EXTERNAL (@var{stream}, @var{decl}, @var{name})
6726 A C statement (sans semicolon) to output to the stdio stream
6727 @var{stream} any text necessary for declaring the name of an external
6728 symbol named @var{name} which is referenced in this compilation but
6729 not defined. The value of @var{decl} is the tree node for the
6732 This macro need not be defined if it does not need to output anything.
6733 The GNU assembler and most Unix assemblers don't require anything.
6736 @defmac ASM_OUTPUT_EXTERNAL_LIBCALL (@var{stream}, @var{symref})
6737 A C statement (sans semicolon) to output on @var{stream} an assembler
6738 pseudo-op to declare a library function name external. The name of the
6739 library function is given by @var{symref}, which has type @code{rtx} and
6740 is a @code{symbol_ref}.
6742 This macro need not be defined if it does not need to output anything.
6743 The GNU assembler and most Unix assemblers don't require anything.
6746 @defmac ASM_OUTPUT_LABELREF (@var{stream}, @var{name})
6747 A C statement (sans semicolon) to output to the stdio stream
6748 @var{stream} a reference in assembler syntax to a label named
6749 @var{name}. This should add @samp{_} to the front of the name, if that
6750 is customary on your operating system, as it is in most Berkeley Unix
6751 systems. This macro is used in @code{assemble_name}.
6754 @defmac ASM_OUTPUT_SYMBOL_REF (@var{stream}, @var{sym})
6755 A C statement (sans semicolon) to output a reference to
6756 @code{SYMBOL_REF} @var{sym}. If not defined, @code{assemble_name}
6757 will be used to output the name of the symbol. This macro may be used
6758 to modify the way a symbol is referenced depending on information
6759 encoded by @code{TARGET_ENCODE_SECTION_INFO}.
6762 @defmac ASM_OUTPUT_LABEL_REF (@var{stream}, @var{buf})
6763 A C statement (sans semicolon) to output a reference to @var{buf}, the
6764 result of @code{ASM_GENERATE_INTERNAL_LABEL}. If not defined,
6765 @code{assemble_name} will be used to output the name of the symbol.
6766 This macro is not used by @code{output_asm_label}, or the @code{%l}
6767 specifier that calls it; the intention is that this macro should be set
6768 when it is necessary to output a label differently when its address is
6772 @deftypefn {Target Hook} void TARGET_ASM_INTERNAL_LABEL (FILE *@var{stream}, const char *@var{prefix}, unsigned long @var{labelno})
6773 A function to output to the stdio stream @var{stream} a label whose
6774 name is made from the string @var{prefix} and the number @var{labelno}.
6776 It is absolutely essential that these labels be distinct from the labels
6777 used for user-level functions and variables. Otherwise, certain programs
6778 will have name conflicts with internal labels.
6780 It is desirable to exclude internal labels from the symbol table of the
6781 object file. Most assemblers have a naming convention for labels that
6782 should be excluded; on many systems, the letter @samp{L} at the
6783 beginning of a label has this effect. You should find out what
6784 convention your system uses, and follow it.
6786 The default version of this function utilizes ASM_GENERATE_INTERNAL_LABEL.
6789 @defmac ASM_OUTPUT_DEBUG_LABEL (@var{stream}, @var{prefix}, @var{num})
6790 A C statement to output to the stdio stream @var{stream} a debug info
6791 label whose name is made from the string @var{prefix} and the number
6792 @var{num}. This is useful for VLIW targets, where debug info labels
6793 may need to be treated differently than branch target labels. On some
6794 systems, branch target labels must be at the beginning of instruction
6795 bundles, but debug info labels can occur in the middle of instruction
6798 If this macro is not defined, then @code{(*targetm.asm_out.internal_label)} will be
6802 @defmac ASM_GENERATE_INTERNAL_LABEL (@var{string}, @var{prefix}, @var{num})
6803 A C statement to store into the string @var{string} a label whose name
6804 is made from the string @var{prefix} and the number @var{num}.
6806 This string, when output subsequently by @code{assemble_name}, should
6807 produce the output that @code{(*targetm.asm_out.internal_label)} would produce
6808 with the same @var{prefix} and @var{num}.
6810 If the string begins with @samp{*}, then @code{assemble_name} will
6811 output the rest of the string unchanged. It is often convenient for
6812 @code{ASM_GENERATE_INTERNAL_LABEL} to use @samp{*} in this way. If the
6813 string doesn't start with @samp{*}, then @code{ASM_OUTPUT_LABELREF} gets
6814 to output the string, and may change it. (Of course,
6815 @code{ASM_OUTPUT_LABELREF} is also part of your machine description, so
6816 you should know what it does on your machine.)
6819 @defmac ASM_FORMAT_PRIVATE_NAME (@var{outvar}, @var{name}, @var{number})
6820 A C expression to assign to @var{outvar} (which is a variable of type
6821 @code{char *}) a newly allocated string made from the string
6822 @var{name} and the number @var{number}, with some suitable punctuation
6823 added. Use @code{alloca} to get space for the string.
6825 The string will be used as an argument to @code{ASM_OUTPUT_LABELREF} to
6826 produce an assembler label for an internal static variable whose name is
6827 @var{name}. Therefore, the string must be such as to result in valid
6828 assembler code. The argument @var{number} is different each time this
6829 macro is executed; it prevents conflicts between similarly-named
6830 internal static variables in different scopes.
6832 Ideally this string should not be a valid C identifier, to prevent any
6833 conflict with the user's own symbols. Most assemblers allow periods
6834 or percent signs in assembler symbols; putting at least one of these
6835 between the name and the number will suffice.
6837 If this macro is not defined, a default definition will be provided
6838 which is correct for most systems.
6841 @defmac ASM_OUTPUT_DEF (@var{stream}, @var{name}, @var{value})
6842 A C statement to output to the stdio stream @var{stream} assembler code
6843 which defines (equates) the symbol @var{name} to have the value @var{value}.
6846 If @code{SET_ASM_OP} is defined, a default definition is provided which is
6847 correct for most systems.
6850 @defmac ASM_OUTPUT_DEF_FROM_DECLS (@var{stream}, @var{decl_of_name}, @var{decl_of_value})
6851 A C statement to output to the stdio stream @var{stream} assembler code
6852 which defines (equates) the symbol whose tree node is @var{decl_of_name}
6853 to have the value of the tree node @var{decl_of_value}. This macro will
6854 be used in preference to @samp{ASM_OUTPUT_DEF} if it is defined and if
6855 the tree nodes are available.
6858 If @code{SET_ASM_OP} is defined, a default definition is provided which is
6859 correct for most systems.
6862 @defmac ASM_OUTPUT_WEAK_ALIAS (@var{stream}, @var{name}, @var{value})
6863 A C statement to output to the stdio stream @var{stream} assembler code
6864 which defines (equates) the weak symbol @var{name} to have the value
6865 @var{value}. If @var{value} is @code{NULL}, it defines @var{name} as
6866 an undefined weak symbol.
6868 Define this macro if the target only supports weak aliases; define
6869 @code{ASM_OUTPUT_DEF} instead if possible.
6872 @defmac OBJC_GEN_METHOD_LABEL (@var{buf}, @var{is_inst}, @var{class_name}, @var{cat_name}, @var{sel_name})
6873 Define this macro to override the default assembler names used for
6874 Objective-C methods.
6876 The default name is a unique method number followed by the name of the
6877 class (e.g.@: @samp{_1_Foo}). For methods in categories, the name of
6878 the category is also included in the assembler name (e.g.@:
6881 These names are safe on most systems, but make debugging difficult since
6882 the method's selector is not present in the name. Therefore, particular
6883 systems define other ways of computing names.
6885 @var{buf} is an expression of type @code{char *} which gives you a
6886 buffer in which to store the name; its length is as long as
6887 @var{class_name}, @var{cat_name} and @var{sel_name} put together, plus
6888 50 characters extra.
6890 The argument @var{is_inst} specifies whether the method is an instance
6891 method or a class method; @var{class_name} is the name of the class;
6892 @var{cat_name} is the name of the category (or @code{NULL} if the method is not
6893 in a category); and @var{sel_name} is the name of the selector.
6895 On systems where the assembler can handle quoted names, you can use this
6896 macro to provide more human-readable names.
6899 @defmac ASM_DECLARE_CLASS_REFERENCE (@var{stream}, @var{name})
6900 A C statement (sans semicolon) to output to the stdio stream
6901 @var{stream} commands to declare that the label @var{name} is an
6902 Objective-C class reference. This is only needed for targets whose
6903 linkers have special support for NeXT-style runtimes.
6906 @defmac ASM_DECLARE_UNRESOLVED_REFERENCE (@var{stream}, @var{name})
6907 A C statement (sans semicolon) to output to the stdio stream
6908 @var{stream} commands to declare that the label @var{name} is an
6909 unresolved Objective-C class reference. This is only needed for targets
6910 whose linkers have special support for NeXT-style runtimes.
6913 @node Initialization
6914 @subsection How Initialization Functions Are Handled
6915 @cindex initialization routines
6916 @cindex termination routines
6917 @cindex constructors, output of
6918 @cindex destructors, output of
6920 The compiled code for certain languages includes @dfn{constructors}
6921 (also called @dfn{initialization routines})---functions to initialize
6922 data in the program when the program is started. These functions need
6923 to be called before the program is ``started''---that is to say, before
6924 @code{main} is called.
6926 Compiling some languages generates @dfn{destructors} (also called
6927 @dfn{termination routines}) that should be called when the program
6930 To make the initialization and termination functions work, the compiler
6931 must output something in the assembler code to cause those functions to
6932 be called at the appropriate time. When you port the compiler to a new
6933 system, you need to specify how to do this.
6935 There are two major ways that GCC currently supports the execution of
6936 initialization and termination functions. Each way has two variants.
6937 Much of the structure is common to all four variations.
6939 @findex __CTOR_LIST__
6940 @findex __DTOR_LIST__
6941 The linker must build two lists of these functions---a list of
6942 initialization functions, called @code{__CTOR_LIST__}, and a list of
6943 termination functions, called @code{__DTOR_LIST__}.
6945 Each list always begins with an ignored function pointer (which may hold
6946 0, @minus{}1, or a count of the function pointers after it, depending on
6947 the environment). This is followed by a series of zero or more function
6948 pointers to constructors (or destructors), followed by a function
6949 pointer containing zero.
6951 Depending on the operating system and its executable file format, either
6952 @file{crtstuff.c} or @file{libgcc2.c} traverses these lists at startup
6953 time and exit time. Constructors are called in reverse order of the
6954 list; destructors in forward order.
6956 The best way to handle static constructors works only for object file
6957 formats which provide arbitrarily-named sections. A section is set
6958 aside for a list of constructors, and another for a list of destructors.
6959 Traditionally these are called @samp{.ctors} and @samp{.dtors}. Each
6960 object file that defines an initialization function also puts a word in
6961 the constructor section to point to that function. The linker
6962 accumulates all these words into one contiguous @samp{.ctors} section.
6963 Termination functions are handled similarly.
6965 This method will be chosen as the default by @file{target-def.h} if
6966 @code{TARGET_ASM_NAMED_SECTION} is defined. A target that does not
6967 support arbitrary sections, but does support special designated
6968 constructor and destructor sections may define @code{CTORS_SECTION_ASM_OP}
6969 and @code{DTORS_SECTION_ASM_OP} to achieve the same effect.
6971 When arbitrary sections are available, there are two variants, depending
6972 upon how the code in @file{crtstuff.c} is called. On systems that
6973 support a @dfn{.init} section which is executed at program startup,
6974 parts of @file{crtstuff.c} are compiled into that section. The
6975 program is linked by the @command{gcc} driver like this:
6978 ld -o @var{output_file} crti.o crtbegin.o @dots{} -lgcc crtend.o crtn.o
6981 The prologue of a function (@code{__init}) appears in the @code{.init}
6982 section of @file{crti.o}; the epilogue appears in @file{crtn.o}. Likewise
6983 for the function @code{__fini} in the @dfn{.fini} section. Normally these
6984 files are provided by the operating system or by the GNU C library, but
6985 are provided by GCC for a few targets.
6987 The objects @file{crtbegin.o} and @file{crtend.o} are (for most targets)
6988 compiled from @file{crtstuff.c}. They contain, among other things, code
6989 fragments within the @code{.init} and @code{.fini} sections that branch
6990 to routines in the @code{.text} section. The linker will pull all parts
6991 of a section together, which results in a complete @code{__init} function
6992 that invokes the routines we need at startup.
6994 To use this variant, you must define the @code{INIT_SECTION_ASM_OP}
6997 If no init section is available, when GCC compiles any function called
6998 @code{main} (or more accurately, any function designated as a program
6999 entry point by the language front end calling @code{expand_main_function}),
7000 it inserts a procedure call to @code{__main} as the first executable code
7001 after the function prologue. The @code{__main} function is defined
7002 in @file{libgcc2.c} and runs the global constructors.
7004 In file formats that don't support arbitrary sections, there are again
7005 two variants. In the simplest variant, the GNU linker (GNU @code{ld})
7006 and an `a.out' format must be used. In this case,
7007 @code{TARGET_ASM_CONSTRUCTOR} is defined to produce a @code{.stabs}
7008 entry of type @samp{N_SETT}, referencing the name @code{__CTOR_LIST__},
7009 and with the address of the void function containing the initialization
7010 code as its value. The GNU linker recognizes this as a request to add
7011 the value to a @dfn{set}; the values are accumulated, and are eventually
7012 placed in the executable as a vector in the format described above, with
7013 a leading (ignored) count and a trailing zero element.
7014 @code{TARGET_ASM_DESTRUCTOR} is handled similarly. Since no init
7015 section is available, the absence of @code{INIT_SECTION_ASM_OP} causes
7016 the compilation of @code{main} to call @code{__main} as above, starting
7017 the initialization process.
7019 The last variant uses neither arbitrary sections nor the GNU linker.
7020 This is preferable when you want to do dynamic linking and when using
7021 file formats which the GNU linker does not support, such as `ECOFF'@. In
7022 this case, @code{TARGET_HAVE_CTORS_DTORS} is false, initialization and
7023 termination functions are recognized simply by their names. This requires
7024 an extra program in the linkage step, called @command{collect2}. This program
7025 pretends to be the linker, for use with GCC; it does its job by running
7026 the ordinary linker, but also arranges to include the vectors of
7027 initialization and termination functions. These functions are called
7028 via @code{__main} as described above. In order to use this method,
7029 @code{use_collect2} must be defined in the target in @file{config.gcc}.
7032 The following section describes the specific macros that control and
7033 customize the handling of initialization and termination functions.
7036 @node Macros for Initialization
7037 @subsection Macros Controlling Initialization Routines
7039 Here are the macros that control how the compiler handles initialization
7040 and termination functions:
7042 @defmac INIT_SECTION_ASM_OP
7043 If defined, a C string constant, including spacing, for the assembler
7044 operation to identify the following data as initialization code. If not
7045 defined, GCC will assume such a section does not exist. When you are
7046 using special sections for initialization and termination functions, this
7047 macro also controls how @file{crtstuff.c} and @file{libgcc2.c} arrange to
7048 run the initialization functions.
7051 @defmac HAS_INIT_SECTION
7052 If defined, @code{main} will not call @code{__main} as described above.
7053 This macro should be defined for systems that control start-up code
7054 on a symbol-by-symbol basis, such as OSF/1, and should not
7055 be defined explicitly for systems that support @code{INIT_SECTION_ASM_OP}.
7058 @defmac LD_INIT_SWITCH
7059 If defined, a C string constant for a switch that tells the linker that
7060 the following symbol is an initialization routine.
7063 @defmac LD_FINI_SWITCH
7064 If defined, a C string constant for a switch that tells the linker that
7065 the following symbol is a finalization routine.
7068 @defmac COLLECT_SHARED_INIT_FUNC (@var{stream}, @var{func})
7069 If defined, a C statement that will write a function that can be
7070 automatically called when a shared library is loaded. The function
7071 should call @var{func}, which takes no arguments. If not defined, and
7072 the object format requires an explicit initialization function, then a
7073 function called @code{_GLOBAL__DI} will be generated.
7075 This function and the following one are used by collect2 when linking a
7076 shared library that needs constructors or destructors, or has DWARF2
7077 exception tables embedded in the code.
7080 @defmac COLLECT_SHARED_FINI_FUNC (@var{stream}, @var{func})
7081 If defined, a C statement that will write a function that can be
7082 automatically called when a shared library is unloaded. The function
7083 should call @var{func}, which takes no arguments. If not defined, and
7084 the object format requires an explicit finalization function, then a
7085 function called @code{_GLOBAL__DD} will be generated.
7088 @defmac INVOKE__main
7089 If defined, @code{main} will call @code{__main} despite the presence of
7090 @code{INIT_SECTION_ASM_OP}. This macro should be defined for systems
7091 where the init section is not actually run automatically, but is still
7092 useful for collecting the lists of constructors and destructors.
7095 @defmac SUPPORTS_INIT_PRIORITY
7096 If nonzero, the C++ @code{init_priority} attribute is supported and the
7097 compiler should emit instructions to control the order of initialization
7098 of objects. If zero, the compiler will issue an error message upon
7099 encountering an @code{init_priority} attribute.
7102 @deftypefn {Target Hook} bool TARGET_HAVE_CTORS_DTORS
7103 This value is true if the target supports some ``native'' method of
7104 collecting constructors and destructors to be run at startup and exit.
7105 It is false if we must use @command{collect2}.
7108 @deftypefn {Target Hook} void TARGET_ASM_CONSTRUCTOR (rtx @var{symbol}, int @var{priority})
7109 If defined, a function that outputs assembler code to arrange to call
7110 the function referenced by @var{symbol} at initialization time.
7112 Assume that @var{symbol} is a @code{SYMBOL_REF} for a function taking
7113 no arguments and with no return value. If the target supports initialization
7114 priorities, @var{priority} is a value between 0 and @code{MAX_INIT_PRIORITY};
7115 otherwise it must be @code{DEFAULT_INIT_PRIORITY}.
7117 If this macro is not defined by the target, a suitable default will
7118 be chosen if (1) the target supports arbitrary section names, (2) the
7119 target defines @code{CTORS_SECTION_ASM_OP}, or (3) @code{USE_COLLECT2}
7123 @deftypefn {Target Hook} void TARGET_ASM_DESTRUCTOR (rtx @var{symbol}, int @var{priority})
7124 This is like @code{TARGET_ASM_CONSTRUCTOR} but used for termination
7125 functions rather than initialization functions.
7128 If @code{TARGET_HAVE_CTORS_DTORS} is true, the initialization routine
7129 generated for the generated object file will have static linkage.
7131 If your system uses @command{collect2} as the means of processing
7132 constructors, then that program normally uses @command{nm} to scan
7133 an object file for constructor functions to be called.
7135 On certain kinds of systems, you can define this macro to make
7136 @command{collect2} work faster (and, in some cases, make it work at all):
7138 @defmac OBJECT_FORMAT_COFF
7139 Define this macro if the system uses COFF (Common Object File Format)
7140 object files, so that @command{collect2} can assume this format and scan
7141 object files directly for dynamic constructor/destructor functions.
7143 This macro is effective only in a native compiler; @command{collect2} as
7144 part of a cross compiler always uses @command{nm} for the target machine.
7147 @defmac REAL_NM_FILE_NAME
7148 Define this macro as a C string constant containing the file name to use
7149 to execute @command{nm}. The default is to search the path normally for
7152 If your system supports shared libraries and has a program to list the
7153 dynamic dependencies of a given library or executable, you can define
7154 these macros to enable support for running initialization and
7155 termination functions in shared libraries:
7159 Define this macro to a C string constant containing the name of the program
7160 which lists dynamic dependencies, like @command{"ldd"} under SunOS 4.
7163 @defmac PARSE_LDD_OUTPUT (@var{ptr})
7164 Define this macro to be C code that extracts filenames from the output
7165 of the program denoted by @code{LDD_SUFFIX}. @var{ptr} is a variable
7166 of type @code{char *} that points to the beginning of a line of output
7167 from @code{LDD_SUFFIX}. If the line lists a dynamic dependency, the
7168 code must advance @var{ptr} to the beginning of the filename on that
7169 line. Otherwise, it must set @var{ptr} to @code{NULL}.
7172 @node Instruction Output
7173 @subsection Output of Assembler Instructions
7175 @c prevent bad page break with this line
7176 This describes assembler instruction output.
7178 @defmac REGISTER_NAMES
7179 A C initializer containing the assembler's names for the machine
7180 registers, each one as a C string constant. This is what translates
7181 register numbers in the compiler into assembler language.
7184 @defmac ADDITIONAL_REGISTER_NAMES
7185 If defined, a C initializer for an array of structures containing a name
7186 and a register number. This macro defines additional names for hard
7187 registers, thus allowing the @code{asm} option in declarations to refer
7188 to registers using alternate names.
7191 @defmac ASM_OUTPUT_OPCODE (@var{stream}, @var{ptr})
7192 Define this macro if you are using an unusual assembler that
7193 requires different names for the machine instructions.
7195 The definition is a C statement or statements which output an
7196 assembler instruction opcode to the stdio stream @var{stream}. The
7197 macro-operand @var{ptr} is a variable of type @code{char *} which
7198 points to the opcode name in its ``internal'' form---the form that is
7199 written in the machine description. The definition should output the
7200 opcode name to @var{stream}, performing any translation you desire, and
7201 increment the variable @var{ptr} to point at the end of the opcode
7202 so that it will not be output twice.
7204 In fact, your macro definition may process less than the entire opcode
7205 name, or more than the opcode name; but if you want to process text
7206 that includes @samp{%}-sequences to substitute operands, you must take
7207 care of the substitution yourself. Just be sure to increment
7208 @var{ptr} over whatever text should not be output normally.
7210 @findex recog_data.operand
7211 If you need to look at the operand values, they can be found as the
7212 elements of @code{recog_data.operand}.
7214 If the macro definition does nothing, the instruction is output
7218 @defmac FINAL_PRESCAN_INSN (@var{insn}, @var{opvec}, @var{noperands})
7219 If defined, a C statement to be executed just prior to the output of
7220 assembler code for @var{insn}, to modify the extracted operands so
7221 they will be output differently.
7223 Here the argument @var{opvec} is the vector containing the operands
7224 extracted from @var{insn}, and @var{noperands} is the number of
7225 elements of the vector which contain meaningful data for this insn.
7226 The contents of this vector are what will be used to convert the insn
7227 template into assembler code, so you can change the assembler output
7228 by changing the contents of the vector.
7230 This macro is useful when various assembler syntaxes share a single
7231 file of instruction patterns; by defining this macro differently, you
7232 can cause a large class of instructions to be output differently (such
7233 as with rearranged operands). Naturally, variations in assembler
7234 syntax affecting individual insn patterns ought to be handled by
7235 writing conditional output routines in those patterns.
7237 If this macro is not defined, it is equivalent to a null statement.
7240 @defmac FINAL_PRESCAN_LABEL
7241 If defined, @code{FINAL_PRESCAN_INSN} will be called on each
7242 @code{CODE_LABEL}. In that case, @var{opvec} will be a null pointer and
7243 @var{noperands} will be zero.
7246 @defmac PRINT_OPERAND (@var{stream}, @var{x}, @var{code})
7247 A C compound statement to output to stdio stream @var{stream} the
7248 assembler syntax for an instruction operand @var{x}. @var{x} is an
7251 @var{code} is a value that can be used to specify one of several ways
7252 of printing the operand. It is used when identical operands must be
7253 printed differently depending on the context. @var{code} comes from
7254 the @samp{%} specification that was used to request printing of the
7255 operand. If the specification was just @samp{%@var{digit}} then
7256 @var{code} is 0; if the specification was @samp{%@var{ltr}
7257 @var{digit}} then @var{code} is the ASCII code for @var{ltr}.
7260 If @var{x} is a register, this macro should print the register's name.
7261 The names can be found in an array @code{reg_names} whose type is
7262 @code{char *[]}. @code{reg_names} is initialized from
7263 @code{REGISTER_NAMES}.
7265 When the machine description has a specification @samp{%@var{punct}}
7266 (a @samp{%} followed by a punctuation character), this macro is called
7267 with a null pointer for @var{x} and the punctuation character for
7271 @defmac PRINT_OPERAND_PUNCT_VALID_P (@var{code})
7272 A C expression which evaluates to true if @var{code} is a valid
7273 punctuation character for use in the @code{PRINT_OPERAND} macro. If
7274 @code{PRINT_OPERAND_PUNCT_VALID_P} is not defined, it means that no
7275 punctuation characters (except for the standard one, @samp{%}) are used
7279 @defmac PRINT_OPERAND_ADDRESS (@var{stream}, @var{x})
7280 A C compound statement to output to stdio stream @var{stream} the
7281 assembler syntax for an instruction operand that is a memory reference
7282 whose address is @var{x}. @var{x} is an RTL expression.
7284 @cindex @code{TARGET_ENCODE_SECTION_INFO} usage
7285 On some machines, the syntax for a symbolic address depends on the
7286 section that the address refers to. On these machines, define the hook
7287 @code{TARGET_ENCODE_SECTION_INFO} to store the information into the
7288 @code{symbol_ref}, and then check for it here. @xref{Assembler
7292 @findex dbr_sequence_length
7293 @defmac DBR_OUTPUT_SEQEND (@var{file})
7294 A C statement, to be executed after all slot-filler instructions have
7295 been output. If necessary, call @code{dbr_sequence_length} to
7296 determine the number of slots filled in a sequence (zero if not
7297 currently outputting a sequence), to decide how many no-ops to output,
7300 Don't define this macro if it has nothing to do, but it is helpful in
7301 reading assembly output if the extent of the delay sequence is made
7302 explicit (e.g.@: with white space).
7305 @findex final_sequence
7306 Note that output routines for instructions with delay slots must be
7307 prepared to deal with not being output as part of a sequence
7308 (i.e.@: when the scheduling pass is not run, or when no slot fillers could be
7309 found.) The variable @code{final_sequence} is null when not
7310 processing a sequence, otherwise it contains the @code{sequence} rtx
7314 @defmac REGISTER_PREFIX
7315 @defmacx LOCAL_LABEL_PREFIX
7316 @defmacx USER_LABEL_PREFIX
7317 @defmacx IMMEDIATE_PREFIX
7318 If defined, C string expressions to be used for the @samp{%R}, @samp{%L},
7319 @samp{%U}, and @samp{%I} options of @code{asm_fprintf} (see
7320 @file{final.c}). These are useful when a single @file{md} file must
7321 support multiple assembler formats. In that case, the various @file{tm.h}
7322 files can define these macros differently.
7325 @defmac ASM_FPRINTF_EXTENSIONS (@var{file}, @var{argptr}, @var{format})
7326 If defined this macro should expand to a series of @code{case}
7327 statements which will be parsed inside the @code{switch} statement of
7328 the @code{asm_fprintf} function. This allows targets to define extra
7329 printf formats which may useful when generating their assembler
7330 statements. Note that upper case letters are reserved for future
7331 generic extensions to asm_fprintf, and so are not available to target
7332 specific code. The output file is given by the parameter @var{file}.
7333 The varargs input pointer is @var{argptr} and the rest of the format
7334 string, starting the character after the one that is being switched
7335 upon, is pointed to by @var{format}.
7338 @defmac ASSEMBLER_DIALECT
7339 If your target supports multiple dialects of assembler language (such as
7340 different opcodes), define this macro as a C expression that gives the
7341 numeric index of the assembler language dialect to use, with zero as the
7344 If this macro is defined, you may use constructs of the form
7346 @samp{@{option0|option1|option2@dots{}@}}
7349 in the output templates of patterns (@pxref{Output Template}) or in the
7350 first argument of @code{asm_fprintf}. This construct outputs
7351 @samp{option0}, @samp{option1}, @samp{option2}, etc., if the value of
7352 @code{ASSEMBLER_DIALECT} is zero, one, two, etc. Any special characters
7353 within these strings retain their usual meaning. If there are fewer
7354 alternatives within the braces than the value of
7355 @code{ASSEMBLER_DIALECT}, the construct outputs nothing.
7357 If you do not define this macro, the characters @samp{@{}, @samp{|} and
7358 @samp{@}} do not have any special meaning when used in templates or
7359 operands to @code{asm_fprintf}.
7361 Define the macros @code{REGISTER_PREFIX}, @code{LOCAL_LABEL_PREFIX},
7362 @code{USER_LABEL_PREFIX} and @code{IMMEDIATE_PREFIX} if you can express
7363 the variations in assembler language syntax with that mechanism. Define
7364 @code{ASSEMBLER_DIALECT} and use the @samp{@{option0|option1@}} syntax
7365 if the syntax variant are larger and involve such things as different
7366 opcodes or operand order.
7369 @defmac ASM_OUTPUT_REG_PUSH (@var{stream}, @var{regno})
7370 A C expression to output to @var{stream} some assembler code
7371 which will push hard register number @var{regno} onto the stack.
7372 The code need not be optimal, since this macro is used only when
7376 @defmac ASM_OUTPUT_REG_POP (@var{stream}, @var{regno})
7377 A C expression to output to @var{stream} some assembler code
7378 which will pop hard register number @var{regno} off of the stack.
7379 The code need not be optimal, since this macro is used only when
7383 @node Dispatch Tables
7384 @subsection Output of Dispatch Tables
7386 @c prevent bad page break with this line
7387 This concerns dispatch tables.
7389 @cindex dispatch table
7390 @defmac ASM_OUTPUT_ADDR_DIFF_ELT (@var{stream}, @var{body}, @var{value}, @var{rel})
7391 A C statement to output to the stdio stream @var{stream} an assembler
7392 pseudo-instruction to generate a difference between two labels.
7393 @var{value} and @var{rel} are the numbers of two internal labels. The
7394 definitions of these labels are output using
7395 @code{(*targetm.asm_out.internal_label)}, and they must be printed in the same
7396 way here. For example,
7399 fprintf (@var{stream}, "\t.word L%d-L%d\n",
7400 @var{value}, @var{rel})
7403 You must provide this macro on machines where the addresses in a
7404 dispatch table are relative to the table's own address. If defined, GCC
7405 will also use this macro on all machines when producing PIC@.
7406 @var{body} is the body of the @code{ADDR_DIFF_VEC}; it is provided so that the
7407 mode and flags can be read.
7410 @defmac ASM_OUTPUT_ADDR_VEC_ELT (@var{stream}, @var{value})
7411 This macro should be provided on machines where the addresses
7412 in a dispatch table are absolute.
7414 The definition should be a C statement to output to the stdio stream
7415 @var{stream} an assembler pseudo-instruction to generate a reference to
7416 a label. @var{value} is the number of an internal label whose
7417 definition is output using @code{(*targetm.asm_out.internal_label)}.
7421 fprintf (@var{stream}, "\t.word L%d\n", @var{value})
7425 @defmac ASM_OUTPUT_CASE_LABEL (@var{stream}, @var{prefix}, @var{num}, @var{table})
7426 Define this if the label before a jump-table needs to be output
7427 specially. The first three arguments are the same as for
7428 @code{(*targetm.asm_out.internal_label)}; the fourth argument is the
7429 jump-table which follows (a @code{jump_insn} containing an
7430 @code{addr_vec} or @code{addr_diff_vec}).
7432 This feature is used on system V to output a @code{swbeg} statement
7435 If this macro is not defined, these labels are output with
7436 @code{(*targetm.asm_out.internal_label)}.
7439 @defmac ASM_OUTPUT_CASE_END (@var{stream}, @var{num}, @var{table})
7440 Define this if something special must be output at the end of a
7441 jump-table. The definition should be a C statement to be executed
7442 after the assembler code for the table is written. It should write
7443 the appropriate code to stdio stream @var{stream}. The argument
7444 @var{table} is the jump-table insn, and @var{num} is the label-number
7445 of the preceding label.
7447 If this macro is not defined, nothing special is output at the end of
7451 @node Exception Region Output
7452 @subsection Assembler Commands for Exception Regions
7454 @c prevent bad page break with this line
7456 This describes commands marking the start and the end of an exception
7459 @defmac EH_FRAME_SECTION_NAME
7460 If defined, a C string constant for the name of the section containing
7461 exception handling frame unwind information. If not defined, GCC will
7462 provide a default definition if the target supports named sections.
7463 @file{crtstuff.c} uses this macro to switch to the appropriate section.
7465 You should define this symbol if your target supports DWARF 2 frame
7466 unwind information and the default definition does not work.
7469 @defmac EH_FRAME_IN_DATA_SECTION
7470 If defined, DWARF 2 frame unwind information will be placed in the
7471 data section even though the target supports named sections. This
7472 might be necessary, for instance, if the system linker does garbage
7473 collection and sections cannot be marked as not to be collected.
7475 Do not define this macro unless @code{TARGET_ASM_NAMED_SECTION} is
7479 @defmac MASK_RETURN_ADDR
7480 An rtx used to mask the return address found via @code{RETURN_ADDR_RTX}, so
7481 that it does not contain any extraneous set bits in it.
7484 @defmac DWARF2_UNWIND_INFO
7485 Define this macro to 0 if your target supports DWARF 2 frame unwind
7486 information, but it does not yet work with exception handling.
7487 Otherwise, if your target supports this information (if it defines
7488 @samp{INCOMING_RETURN_ADDR_RTX} and either @samp{UNALIGNED_INT_ASM_OP}
7489 or @samp{OBJECT_FORMAT_ELF}), GCC will provide a default definition of
7492 If this macro is defined to 1, the DWARF 2 unwinder will be the default
7493 exception handling mechanism; otherwise, @code{setjmp}/@code{longjmp} will be used by
7496 If this macro is defined to anything, the DWARF 2 unwinder will be used
7497 instead of inline unwinders and @code{__unwind_function} in the non-@code{setjmp} case.
7500 @defmac DWARF_CIE_DATA_ALIGNMENT
7501 This macro need only be defined if the target might save registers in the
7502 function prologue at an offset to the stack pointer that is not aligned to
7503 @code{UNITS_PER_WORD}. The definition should be the negative minimum
7504 alignment if @code{STACK_GROWS_DOWNWARD} is defined, and the positive
7505 minimum alignment otherwise. @xref{SDB and DWARF}. Only applicable if
7506 the target supports DWARF 2 frame unwind information.
7509 @deftypefn {Target Hook} void TARGET_ASM_EXCEPTION_SECTION ()
7510 If defined, a function that switches to the section in which the main
7511 exception table is to be placed (@pxref{Sections}). The default is a
7512 function that switches to a section named @code{.gcc_except_table} on
7513 machines that support named sections via
7514 @code{TARGET_ASM_NAMED_SECTION}, otherwise if @option{-fpic} or
7515 @option{-fPIC} is in effect, the @code{data_section}, otherwise the
7516 @code{readonly_data_section}.
7519 @deftypefn {Target Hook} void TARGET_ASM_EH_FRAME_SECTION ()
7520 If defined, a function that switches to the section in which the DWARF 2
7521 frame unwind information to be placed (@pxref{Sections}). The default
7522 is a function that outputs a standard GAS section directive, if
7523 @code{EH_FRAME_SECTION_NAME} is defined, or else a data section
7524 directive followed by a synthetic label.
7527 @deftypevar {Target Hook} bool TARGET_TERMINATE_DW2_EH_FRAME_INFO
7528 Contains the value true if the target should add a zero word onto the
7529 end of a Dwarf-2 frame info section when used for exception handling.
7530 Default value is false if @code{EH_FRAME_SECTION_NAME} is defined, and
7534 @deftypefn {Target Hook} rtx TARGET_DWARF_REGISTER_SPAN (rtx @var{reg})
7535 Given a register, this hook should return a parallel of registers to
7536 represent where to find the register pieces. Define this hook if the
7537 register and its mode are represented in Dwarf in non-contiguous
7538 locations, or if the register should be represented in more than one
7539 register in Dwarf. Otherwise, this hook should return @code{NULL_RTX}.
7540 If not defined, the default is to return @code{NULL_RTX}.
7543 @node Alignment Output
7544 @subsection Assembler Commands for Alignment
7546 @c prevent bad page break with this line
7547 This describes commands for alignment.
7549 @defmac JUMP_ALIGN (@var{label})
7550 The alignment (log base 2) to put in front of @var{label}, which is
7551 a common destination of jumps and has no fallthru incoming edge.
7553 This macro need not be defined if you don't want any special alignment
7554 to be done at such a time. Most machine descriptions do not currently
7557 Unless it's necessary to inspect the @var{label} parameter, it is better
7558 to set the variable @var{align_jumps} in the target's
7559 @code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's
7560 selection in @var{align_jumps} in a @code{JUMP_ALIGN} implementation.
7563 @defmac LABEL_ALIGN_AFTER_BARRIER (@var{label})
7564 The alignment (log base 2) to put in front of @var{label}, which follows
7567 This macro need not be defined if you don't want any special alignment
7568 to be done at such a time. Most machine descriptions do not currently
7572 @defmac LABEL_ALIGN_AFTER_BARRIER_MAX_SKIP
7573 The maximum number of bytes to skip when applying
7574 @code{LABEL_ALIGN_AFTER_BARRIER}. This works only if
7575 @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined.
7578 @defmac LOOP_ALIGN (@var{label})
7579 The alignment (log base 2) to put in front of @var{label}, which follows
7580 a @code{NOTE_INSN_LOOP_BEG} note.
7582 This macro need not be defined if you don't want any special alignment
7583 to be done at such a time. Most machine descriptions do not currently
7586 Unless it's necessary to inspect the @var{label} parameter, it is better
7587 to set the variable @code{align_loops} in the target's
7588 @code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's
7589 selection in @code{align_loops} in a @code{LOOP_ALIGN} implementation.
7592 @defmac LOOP_ALIGN_MAX_SKIP
7593 The maximum number of bytes to skip when applying @code{LOOP_ALIGN}.
7594 This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined.
7597 @defmac LABEL_ALIGN (@var{label})
7598 The alignment (log base 2) to put in front of @var{label}.
7599 If @code{LABEL_ALIGN_AFTER_BARRIER} / @code{LOOP_ALIGN} specify a different alignment,
7600 the maximum of the specified values is used.
7602 Unless it's necessary to inspect the @var{label} parameter, it is better
7603 to set the variable @code{align_labels} in the target's
7604 @code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's
7605 selection in @code{align_labels} in a @code{LABEL_ALIGN} implementation.
7608 @defmac LABEL_ALIGN_MAX_SKIP
7609 The maximum number of bytes to skip when applying @code{LABEL_ALIGN}.
7610 This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined.
7613 @defmac ASM_OUTPUT_SKIP (@var{stream}, @var{nbytes})
7614 A C statement to output to the stdio stream @var{stream} an assembler
7615 instruction to advance the location counter by @var{nbytes} bytes.
7616 Those bytes should be zero when loaded. @var{nbytes} will be a C
7617 expression of type @code{int}.
7620 @defmac ASM_NO_SKIP_IN_TEXT
7621 Define this macro if @code{ASM_OUTPUT_SKIP} should not be used in the
7622 text section because it fails to put zeros in the bytes that are skipped.
7623 This is true on many Unix systems, where the pseudo--op to skip bytes
7624 produces no-op instructions rather than zeros when used in the text
7628 @defmac ASM_OUTPUT_ALIGN (@var{stream}, @var{power})
7629 A C statement to output to the stdio stream @var{stream} an assembler
7630 command to advance the location counter to a multiple of 2 to the
7631 @var{power} bytes. @var{power} will be a C expression of type @code{int}.
7634 @defmac ASM_OUTPUT_ALIGN_WITH_NOP (@var{stream}, @var{power})
7635 Like @code{ASM_OUTPUT_ALIGN}, except that the ``nop'' instruction is used
7636 for padding, if necessary.
7639 @defmac ASM_OUTPUT_MAX_SKIP_ALIGN (@var{stream}, @var{power}, @var{max_skip})
7640 A C statement to output to the stdio stream @var{stream} an assembler
7641 command to advance the location counter to a multiple of 2 to the
7642 @var{power} bytes, but only if @var{max_skip} or fewer bytes are needed to
7643 satisfy the alignment request. @var{power} and @var{max_skip} will be
7644 a C expression of type @code{int}.
7648 @node Debugging Info
7649 @section Controlling Debugging Information Format
7651 @c prevent bad page break with this line
7652 This describes how to specify debugging information.
7655 * All Debuggers:: Macros that affect all debugging formats uniformly.
7656 * DBX Options:: Macros enabling specific options in DBX format.
7657 * DBX Hooks:: Hook macros for varying DBX format.
7658 * File Names and DBX:: Macros controlling output of file names in DBX format.
7659 * SDB and DWARF:: Macros for SDB (COFF) and DWARF formats.
7660 * VMS Debug:: Macros for VMS debug format.
7664 @subsection Macros Affecting All Debugging Formats
7666 @c prevent bad page break with this line
7667 These macros affect all debugging formats.
7669 @defmac DBX_REGISTER_NUMBER (@var{regno})
7670 A C expression that returns the DBX register number for the compiler
7671 register number @var{regno}. In the default macro provided, the value
7672 of this expression will be @var{regno} itself. But sometimes there are
7673 some registers that the compiler knows about and DBX does not, or vice
7674 versa. In such cases, some register may need to have one number in the
7675 compiler and another for DBX@.
7677 If two registers have consecutive numbers inside GCC, and they can be
7678 used as a pair to hold a multiword value, then they @emph{must} have
7679 consecutive numbers after renumbering with @code{DBX_REGISTER_NUMBER}.
7680 Otherwise, debuggers will be unable to access such a pair, because they
7681 expect register pairs to be consecutive in their own numbering scheme.
7683 If you find yourself defining @code{DBX_REGISTER_NUMBER} in way that
7684 does not preserve register pairs, then what you must do instead is
7685 redefine the actual register numbering scheme.
7688 @defmac DEBUGGER_AUTO_OFFSET (@var{x})
7689 A C expression that returns the integer offset value for an automatic
7690 variable having address @var{x} (an RTL expression). The default
7691 computation assumes that @var{x} is based on the frame-pointer and
7692 gives the offset from the frame-pointer. This is required for targets
7693 that produce debugging output for DBX or COFF-style debugging output
7694 for SDB and allow the frame-pointer to be eliminated when the
7695 @option{-g} options is used.
7698 @defmac DEBUGGER_ARG_OFFSET (@var{offset}, @var{x})
7699 A C expression that returns the integer offset value for an argument
7700 having address @var{x} (an RTL expression). The nominal offset is
7704 @defmac PREFERRED_DEBUGGING_TYPE
7705 A C expression that returns the type of debugging output GCC should
7706 produce when the user specifies just @option{-g}. Define
7707 this if you have arranged for GCC to support more than one format of
7708 debugging output. Currently, the allowable values are @code{DBX_DEBUG},
7709 @code{SDB_DEBUG}, @code{DWARF_DEBUG}, @code{DWARF2_DEBUG},
7710 @code{XCOFF_DEBUG}, @code{VMS_DEBUG}, and @code{VMS_AND_DWARF2_DEBUG}.
7712 When the user specifies @option{-ggdb}, GCC normally also uses the
7713 value of this macro to select the debugging output format, but with two
7714 exceptions. If @code{DWARF2_DEBUGGING_INFO} is defined and
7715 @code{LINKER_DOES_NOT_WORK_WITH_DWARF2} is not defined, GCC uses the
7716 value @code{DWARF2_DEBUG}. Otherwise, if @code{DBX_DEBUGGING_INFO} is
7717 defined, GCC uses @code{DBX_DEBUG}.
7719 The value of this macro only affects the default debugging output; the
7720 user can always get a specific type of output by using @option{-gstabs},
7721 @option{-gcoff}, @option{-gdwarf-1}, @option{-gdwarf-2}, @option{-gxcoff},
7726 @subsection Specific Options for DBX Output
7728 @c prevent bad page break with this line
7729 These are specific options for DBX output.
7731 @defmac DBX_DEBUGGING_INFO
7732 Define this macro if GCC should produce debugging output for DBX
7733 in response to the @option{-g} option.
7736 @defmac XCOFF_DEBUGGING_INFO
7737 Define this macro if GCC should produce XCOFF format debugging output
7738 in response to the @option{-g} option. This is a variant of DBX format.
7741 @defmac DEFAULT_GDB_EXTENSIONS
7742 Define this macro to control whether GCC should by default generate
7743 GDB's extended version of DBX debugging information (assuming DBX-format
7744 debugging information is enabled at all). If you don't define the
7745 macro, the default is 1: always generate the extended information
7746 if there is any occasion to.
7749 @defmac DEBUG_SYMS_TEXT
7750 Define this macro if all @code{.stabs} commands should be output while
7751 in the text section.
7754 @defmac ASM_STABS_OP
7755 A C string constant, including spacing, naming the assembler pseudo op to
7756 use instead of @code{"\t.stabs\t"} to define an ordinary debugging symbol.
7757 If you don't define this macro, @code{"\t.stabs\t"} is used. This macro
7758 applies only to DBX debugging information format.
7761 @defmac ASM_STABD_OP
7762 A C string constant, including spacing, naming the assembler pseudo op to
7763 use instead of @code{"\t.stabd\t"} to define a debugging symbol whose
7764 value is the current location. If you don't define this macro,
7765 @code{"\t.stabd\t"} is used. This macro applies only to DBX debugging
7769 @defmac ASM_STABN_OP
7770 A C string constant, including spacing, naming the assembler pseudo op to
7771 use instead of @code{"\t.stabn\t"} to define a debugging symbol with no
7772 name. If you don't define this macro, @code{"\t.stabn\t"} is used. This
7773 macro applies only to DBX debugging information format.
7776 @defmac DBX_NO_XREFS
7777 Define this macro if DBX on your system does not support the construct
7778 @samp{xs@var{tagname}}. On some systems, this construct is used to
7779 describe a forward reference to a structure named @var{tagname}.
7780 On other systems, this construct is not supported at all.
7783 @defmac DBX_CONTIN_LENGTH
7784 A symbol name in DBX-format debugging information is normally
7785 continued (split into two separate @code{.stabs} directives) when it
7786 exceeds a certain length (by default, 80 characters). On some
7787 operating systems, DBX requires this splitting; on others, splitting
7788 must not be done. You can inhibit splitting by defining this macro
7789 with the value zero. You can override the default splitting-length by
7790 defining this macro as an expression for the length you desire.
7793 @defmac DBX_CONTIN_CHAR
7794 Normally continuation is indicated by adding a @samp{\} character to
7795 the end of a @code{.stabs} string when a continuation follows. To use
7796 a different character instead, define this macro as a character
7797 constant for the character you want to use. Do not define this macro
7798 if backslash is correct for your system.
7801 @defmac DBX_STATIC_STAB_DATA_SECTION
7802 Define this macro if it is necessary to go to the data section before
7803 outputting the @samp{.stabs} pseudo-op for a non-global static
7807 @defmac DBX_TYPE_DECL_STABS_CODE
7808 The value to use in the ``code'' field of the @code{.stabs} directive
7809 for a typedef. The default is @code{N_LSYM}.
7812 @defmac DBX_STATIC_CONST_VAR_CODE
7813 The value to use in the ``code'' field of the @code{.stabs} directive
7814 for a static variable located in the text section. DBX format does not
7815 provide any ``right'' way to do this. The default is @code{N_FUN}.
7818 @defmac DBX_REGPARM_STABS_CODE
7819 The value to use in the ``code'' field of the @code{.stabs} directive
7820 for a parameter passed in registers. DBX format does not provide any
7821 ``right'' way to do this. The default is @code{N_RSYM}.
7824 @defmac DBX_REGPARM_STABS_LETTER
7825 The letter to use in DBX symbol data to identify a symbol as a parameter
7826 passed in registers. DBX format does not customarily provide any way to
7827 do this. The default is @code{'P'}.
7830 @defmac DBX_MEMPARM_STABS_LETTER
7831 The letter to use in DBX symbol data to identify a symbol as a stack
7832 parameter. The default is @code{'p'}.
7835 @defmac DBX_FUNCTION_FIRST
7836 Define this macro if the DBX information for a function and its
7837 arguments should precede the assembler code for the function. Normally,
7838 in DBX format, the debugging information entirely follows the assembler
7842 @defmac DBX_BLOCKS_FUNCTION_RELATIVE
7843 Define this macro if the value of a symbol describing the scope of a
7844 block (@code{N_LBRAC} or @code{N_RBRAC}) should be relative to the start
7845 of the enclosing function. Normally, GCC uses an absolute address.
7848 @defmac DBX_USE_BINCL
7849 Define this macro if GCC should generate @code{N_BINCL} and
7850 @code{N_EINCL} stabs for included header files, as on Sun systems. This
7851 macro also directs GCC to output a type number as a pair of a file
7852 number and a type number within the file. Normally, GCC does not
7853 generate @code{N_BINCL} or @code{N_EINCL} stabs, and it outputs a single
7854 number for a type number.
7858 @subsection Open-Ended Hooks for DBX Format
7860 @c prevent bad page break with this line
7861 These are hooks for DBX format.
7863 @defmac DBX_OUTPUT_LBRAC (@var{stream}, @var{name})
7864 Define this macro to say how to output to @var{stream} the debugging
7865 information for the start of a scope level for variable names. The
7866 argument @var{name} is the name of an assembler symbol (for use with
7867 @code{assemble_name}) whose value is the address where the scope begins.
7870 @defmac DBX_OUTPUT_RBRAC (@var{stream}, @var{name})
7871 Like @code{DBX_OUTPUT_LBRAC}, but for the end of a scope level.
7874 @defmac DBX_OUTPUT_NFUN (@var{stream}, @var{lscope_label}, @var{decl})
7875 Define this macro if the target machine requires special handling to
7876 output an @code{N_FUN} entry for the function @var{decl}.
7879 @defmac DBX_OUTPUT_FUNCTION_END (@var{stream}, @var{function})
7880 Define this macro if the target machine requires special output at the
7881 end of the debugging information for a function. The definition should
7882 be a C statement (sans semicolon) to output the appropriate information
7883 to @var{stream}. @var{function} is the @code{FUNCTION_DECL} node for
7887 @defmac DBX_OUTPUT_STANDARD_TYPES (@var{syms})
7888 Define this macro if you need to control the order of output of the
7889 standard data types at the beginning of compilation. The argument
7890 @var{syms} is a @code{tree} which is a chain of all the predefined
7891 global symbols, including names of data types.
7893 Normally, DBX output starts with definitions of the types for integers
7894 and characters, followed by all the other predefined types of the
7895 particular language in no particular order.
7897 On some machines, it is necessary to output different particular types
7898 first. To do this, define @code{DBX_OUTPUT_STANDARD_TYPES} to output
7899 those symbols in the necessary order. Any predefined types that you
7900 don't explicitly output will be output afterward in no particular order.
7902 Be careful not to define this macro so that it works only for C@. There
7903 are no global variables to access most of the built-in types, because
7904 another language may have another set of types. The way to output a
7905 particular type is to look through @var{syms} to see if you can find it.
7911 for (decl = syms; decl; decl = TREE_CHAIN (decl))
7912 if (!strcmp (IDENTIFIER_POINTER (DECL_NAME (decl)),
7914 dbxout_symbol (decl);
7920 This does nothing if the expected type does not exist.
7922 See the function @code{init_decl_processing} in @file{c-decl.c} to find
7923 the names to use for all the built-in C types.
7925 Here is another way of finding a particular type:
7927 @c this is still overfull. --mew 10feb93
7931 for (decl = syms; decl; decl = TREE_CHAIN (decl))
7932 if (TREE_CODE (decl) == TYPE_DECL
7933 && (TREE_CODE (TREE_TYPE (decl))
7935 && TYPE_PRECISION (TREE_TYPE (decl)) == 16
7936 && TYPE_UNSIGNED (TREE_TYPE (decl)))
7938 /* @r{This must be @code{unsigned short}.} */
7939 dbxout_symbol (decl);
7946 @defmac NO_DBX_FUNCTION_END
7947 Some stabs encapsulation formats (in particular ECOFF), cannot handle the
7948 @code{.stabs "",N_FUN,,0,0,Lscope-function-1} gdb dbx extension construct.
7949 On those machines, define this macro to turn this feature off without
7950 disturbing the rest of the gdb extensions.
7953 @node File Names and DBX
7954 @subsection File Names in DBX Format
7956 @c prevent bad page break with this line
7957 This describes file names in DBX format.
7959 @defmac DBX_OUTPUT_MAIN_SOURCE_FILENAME (@var{stream}, @var{name})
7960 A C statement to output DBX debugging information to the stdio stream
7961 @var{stream} which indicates that file @var{name} is the main source
7962 file---the file specified as the input file for compilation.
7963 This macro is called only once, at the beginning of compilation.
7965 This macro need not be defined if the standard form of output
7966 for DBX debugging information is appropriate.
7969 @defmac DBX_OUTPUT_MAIN_SOURCE_DIRECTORY (@var{stream}, @var{name})
7970 A C statement to output DBX debugging information to the stdio stream
7971 @var{stream} which indicates that the current directory during
7972 compilation is named @var{name}.
7974 This macro need not be defined if the standard form of output
7975 for DBX debugging information is appropriate.
7978 @defmac DBX_OUTPUT_MAIN_SOURCE_FILE_END (@var{stream}, @var{name})
7979 A C statement to output DBX debugging information at the end of
7980 compilation of the main source file @var{name}.
7982 If you don't define this macro, nothing special is output at the end
7983 of compilation, which is correct for most machines.
7988 @subsection Macros for SDB and DWARF Output
7990 @c prevent bad page break with this line
7991 Here are macros for SDB and DWARF output.
7993 @defmac SDB_DEBUGGING_INFO
7994 Define this macro if GCC should produce COFF-style debugging output
7995 for SDB in response to the @option{-g} option.
7998 @defmac DWARF_DEBUGGING_INFO
7999 Define this macro if GCC should produce dwarf format debugging output
8000 in response to the @option{-g} option.
8003 @defmac DWARF2_DEBUGGING_INFO
8004 Define this macro if GCC should produce dwarf version 2 format
8005 debugging output in response to the @option{-g} option.
8007 To support optional call frame debugging information, you must also
8008 define @code{INCOMING_RETURN_ADDR_RTX} and either set
8009 @code{RTX_FRAME_RELATED_P} on the prologue insns if you use RTL for the
8010 prologue, or call @code{dwarf2out_def_cfa} and @code{dwarf2out_reg_save}
8011 as appropriate from @code{TARGET_ASM_FUNCTION_PROLOGUE} if you don't.
8014 @defmac DWARF2_FRAME_INFO
8015 Define this macro to a nonzero value if GCC should always output
8016 Dwarf 2 frame information. If @code{DWARF2_UNWIND_INFO}
8017 (@pxref{Exception Region Output} is nonzero, GCC will output this
8018 information not matter how you define @code{DWARF2_FRAME_INFO}.
8021 @defmac LINKER_DOES_NOT_WORK_WITH_DWARF2
8022 Define this macro if the linker does not work with Dwarf version 2.
8023 Normally, if the user specifies only @option{-ggdb} GCC will use Dwarf
8024 version 2 if available; this macro disables this. See the description
8025 of the @code{PREFERRED_DEBUGGING_TYPE} macro for more details.
8028 @defmac DWARF2_GENERATE_TEXT_SECTION_LABEL
8029 By default, the Dwarf 2 debugging information generator will generate a
8030 label to mark the beginning of the text section. If it is better simply
8031 to use the name of the text section itself, rather than an explicit label,
8032 to indicate the beginning of the text section, define this macro to zero.
8035 @defmac DWARF2_ASM_LINE_DEBUG_INFO
8036 Define this macro to be a nonzero value if the assembler can generate Dwarf 2
8037 line debug info sections. This will result in much more compact line number
8038 tables, and hence is desirable if it works.
8041 @defmac ASM_OUTPUT_DWARF_DELTA (@var{stream}, @var{size}, @var{label1}, @var{label2})
8042 A C statement to issue assembly directives that create a difference
8043 between the two given labels, using an integer of the given size.
8046 @defmac ASM_OUTPUT_DWARF_OFFSET (@var{stream}, @var{size}, @var{label})
8047 A C statement to issue assembly directives that create a
8048 section-relative reference to the given label, using an integer of the
8052 @defmac ASM_OUTPUT_DWARF_PCREL (@var{stream}, @var{size}, @var{label})
8053 A C statement to issue assembly directives that create a self-relative
8054 reference to the given label, using an integer of the given size.
8057 @defmac PUT_SDB_@dots{}
8058 Define these macros to override the assembler syntax for the special
8059 SDB assembler directives. See @file{sdbout.c} for a list of these
8060 macros and their arguments. If the standard syntax is used, you need
8061 not define them yourself.
8065 Some assemblers do not support a semicolon as a delimiter, even between
8066 SDB assembler directives. In that case, define this macro to be the
8067 delimiter to use (usually @samp{\n}). It is not necessary to define
8068 a new set of @code{PUT_SDB_@var{op}} macros if this is the only change
8072 @defmac SDB_GENERATE_FAKE
8073 Define this macro to override the usual method of constructing a dummy
8074 name for anonymous structure and union types. See @file{sdbout.c} for
8078 @defmac SDB_ALLOW_UNKNOWN_REFERENCES
8079 Define this macro to allow references to unknown structure,
8080 union, or enumeration tags to be emitted. Standard COFF does not
8081 allow handling of unknown references, MIPS ECOFF has support for
8085 @defmac SDB_ALLOW_FORWARD_REFERENCES
8086 Define this macro to allow references to structure, union, or
8087 enumeration tags that have not yet been seen to be handled. Some
8088 assemblers choke if forward tags are used, while some require it.
8093 @subsection Macros for VMS Debug Format
8095 @c prevent bad page break with this line
8096 Here are macros for VMS debug format.
8098 @defmac VMS_DEBUGGING_INFO
8099 Define this macro if GCC should produce debugging output for VMS
8100 in response to the @option{-g} option. The default behavior for VMS
8101 is to generate minimal debug info for a traceback in the absence of
8102 @option{-g} unless explicitly overridden with @option{-g0}. This
8103 behavior is controlled by @code{OPTIMIZATION_OPTIONS} and
8104 @code{OVERRIDE_OPTIONS}.
8107 @node Floating Point
8108 @section Cross Compilation and Floating Point
8109 @cindex cross compilation and floating point
8110 @cindex floating point and cross compilation
8112 While all modern machines use twos-complement representation for integers,
8113 there are a variety of representations for floating point numbers. This
8114 means that in a cross-compiler the representation of floating point numbers
8115 in the compiled program may be different from that used in the machine
8116 doing the compilation.
8118 Because different representation systems may offer different amounts of
8119 range and precision, all floating point constants must be represented in
8120 the target machine's format. Therefore, the cross compiler cannot
8121 safely use the host machine's floating point arithmetic; it must emulate
8122 the target's arithmetic. To ensure consistency, GCC always uses
8123 emulation to work with floating point values, even when the host and
8124 target floating point formats are identical.
8126 The following macros are provided by @file{real.h} for the compiler to
8127 use. All parts of the compiler which generate or optimize
8128 floating-point calculations must use these macros. They may evaluate
8129 their operands more than once, so operands must not have side effects.
8131 @defmac REAL_VALUE_TYPE
8132 The C data type to be used to hold a floating point value in the target
8133 machine's format. Typically this is a @code{struct} containing an
8134 array of @code{HOST_WIDE_INT}, but all code should treat it as an opaque
8138 @deftypefn Macro int REAL_VALUES_EQUAL (REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y})
8139 Compares for equality the two values, @var{x} and @var{y}. If the target
8140 floating point format supports negative zeroes and/or NaNs,
8141 @samp{REAL_VALUES_EQUAL (-0.0, 0.0)} is true, and
8142 @samp{REAL_VALUES_EQUAL (NaN, NaN)} is false.
8145 @deftypefn Macro int REAL_VALUES_LESS (REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y})
8146 Tests whether @var{x} is less than @var{y}.
8149 @deftypefn Macro HOST_WIDE_INT REAL_VALUE_FIX (REAL_VALUE_TYPE @var{x})
8150 Truncates @var{x} to a signed integer, rounding toward zero.
8153 @deftypefn Macro {unsigned HOST_WIDE_INT} REAL_VALUE_UNSIGNED_FIX (REAL_VALUE_TYPE @var{x})
8154 Truncates @var{x} to an unsigned integer, rounding toward zero. If
8155 @var{x} is negative, returns zero.
8158 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ATOF (const char *@var{string}, enum machine_mode @var{mode})
8159 Converts @var{string} into a floating point number in the target machine's
8160 representation for mode @var{mode}. This routine can handle both
8161 decimal and hexadecimal floating point constants, using the syntax
8162 defined by the C language for both.
8165 @deftypefn Macro int REAL_VALUE_NEGATIVE (REAL_VALUE_TYPE @var{x})
8166 Returns 1 if @var{x} is negative (including negative zero), 0 otherwise.
8169 @deftypefn Macro int REAL_VALUE_ISINF (REAL_VALUE_TYPE @var{x})
8170 Determines whether @var{x} represents infinity (positive or negative).
8173 @deftypefn Macro int REAL_VALUE_ISNAN (REAL_VALUE_TYPE @var{x})
8174 Determines whether @var{x} represents a ``NaN'' (not-a-number).
8177 @deftypefn Macro void REAL_ARITHMETIC (REAL_VALUE_TYPE @var{output}, enum tree_code @var{code}, REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y})
8178 Calculates an arithmetic operation on the two floating point values
8179 @var{x} and @var{y}, storing the result in @var{output} (which must be a
8182 The operation to be performed is specified by @var{code}. Only the
8183 following codes are supported: @code{PLUS_EXPR}, @code{MINUS_EXPR},
8184 @code{MULT_EXPR}, @code{RDIV_EXPR}, @code{MAX_EXPR}, @code{MIN_EXPR}.
8186 If @code{REAL_ARITHMETIC} is asked to evaluate division by zero and the
8187 target's floating point format cannot represent infinity, it will call
8188 @code{abort}. Callers should check for this situation first, using
8189 @code{MODE_HAS_INFINITIES}. @xref{Storage Layout}.
8192 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_NEGATE (REAL_VALUE_TYPE @var{x})
8193 Returns the negative of the floating point value @var{x}.
8196 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ABS (REAL_VALUE_TYPE @var{x})
8197 Returns the absolute value of @var{x}.
8200 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_TRUNCATE (REAL_VALUE_TYPE @var{mode}, enum machine_mode @var{x})
8201 Truncates the floating point value @var{x} to fit in @var{mode}. The
8202 return value is still a full-size @code{REAL_VALUE_TYPE}, but it has an
8203 appropriate bit pattern to be output asa floating constant whose
8204 precision accords with mode @var{mode}.
8207 @deftypefn Macro void REAL_VALUE_TO_INT (HOST_WIDE_INT @var{low}, HOST_WIDE_INT @var{high}, REAL_VALUE_TYPE @var{x})
8208 Converts a floating point value @var{x} into a double-precision integer
8209 which is then stored into @var{low} and @var{high}. If the value is not
8210 integral, it is truncated.
8213 @deftypefn Macro void REAL_VALUE_FROM_INT (REAL_VALUE_TYPE @var{x}, HOST_WIDE_INT @var{low}, HOST_WIDE_INT @var{high}, enum machine_mode @var{mode})
8214 Converts a double-precision integer found in @var{low} and @var{high},
8215 into a floating point value which is then stored into @var{x}. The
8216 value is truncated to fit in mode @var{mode}.
8219 @node Mode Switching
8220 @section Mode Switching Instructions
8221 @cindex mode switching
8222 The following macros control mode switching optimizations:
8224 @defmac OPTIMIZE_MODE_SWITCHING (@var{entity})
8225 Define this macro if the port needs extra instructions inserted for mode
8226 switching in an optimizing compilation.
8228 For an example, the SH4 can perform both single and double precision
8229 floating point operations, but to perform a single precision operation,
8230 the FPSCR PR bit has to be cleared, while for a double precision
8231 operation, this bit has to be set. Changing the PR bit requires a general
8232 purpose register as a scratch register, hence these FPSCR sets have to
8233 be inserted before reload, i.e.@: you can't put this into instruction emitting
8234 or @code{TARGET_MACHINE_DEPENDENT_REORG}.
8236 You can have multiple entities that are mode-switched, and select at run time
8237 which entities actually need it. @code{OPTIMIZE_MODE_SWITCHING} should
8238 return nonzero for any @var{entity} that needs mode-switching.
8239 If you define this macro, you also have to define
8240 @code{NUM_MODES_FOR_MODE_SWITCHING}, @code{MODE_NEEDED},
8241 @code{MODE_PRIORITY_TO_MODE} and @code{EMIT_MODE_SET}.
8242 @code{NORMAL_MODE} is optional.
8245 @defmac NUM_MODES_FOR_MODE_SWITCHING
8246 If you define @code{OPTIMIZE_MODE_SWITCHING}, you have to define this as
8247 initializer for an array of integers. Each initializer element
8248 N refers to an entity that needs mode switching, and specifies the number
8249 of different modes that might need to be set for this entity.
8250 The position of the initializer in the initializer - starting counting at
8251 zero - determines the integer that is used to refer to the mode-switched
8253 In macros that take mode arguments / yield a mode result, modes are
8254 represented as numbers 0 @dots{} N @minus{} 1. N is used to specify that no mode
8255 switch is needed / supplied.
8258 @defmac MODE_NEEDED (@var{entity}, @var{insn})
8259 @var{entity} is an integer specifying a mode-switched entity. If
8260 @code{OPTIMIZE_MODE_SWITCHING} is defined, you must define this macro to
8261 return an integer value not larger than the corresponding element in
8262 @code{NUM_MODES_FOR_MODE_SWITCHING}, to denote the mode that @var{entity} must
8263 be switched into prior to the execution of @var{insn}.
8266 @defmac NORMAL_MODE (@var{entity})
8267 If this macro is defined, it is evaluated for every @var{entity} that needs
8268 mode switching. It should evaluate to an integer, which is a mode that
8269 @var{entity} is assumed to be switched to at function entry and exit.
8272 @defmac MODE_PRIORITY_TO_MODE (@var{entity}, @var{n})
8273 This macro specifies the order in which modes for @var{entity} are processed.
8274 0 is the highest priority, @code{NUM_MODES_FOR_MODE_SWITCHING[@var{entity}] - 1} the
8275 lowest. The value of the macro should be an integer designating a mode
8276 for @var{entity}. For any fixed @var{entity}, @code{mode_priority_to_mode}
8277 (@var{entity}, @var{n}) shall be a bijection in 0 @dots{}
8278 @code{num_modes_for_mode_switching[@var{entity}] - 1}.
8281 @defmac EMIT_MODE_SET (@var{entity}, @var{mode}, @var{hard_regs_live})
8282 Generate one or more insns to set @var{entity} to @var{mode}.
8283 @var{hard_reg_live} is the set of hard registers live at the point where
8284 the insn(s) are to be inserted.
8287 @node Target Attributes
8288 @section Defining target-specific uses of @code{__attribute__}
8289 @cindex target attributes
8290 @cindex machine attributes
8291 @cindex attributes, target-specific
8293 Target-specific attributes may be defined for functions, data and types.
8294 These are described using the following target hooks; they also need to
8295 be documented in @file{extend.texi}.
8297 @deftypevr {Target Hook} {const struct attribute_spec *} TARGET_ATTRIBUTE_TABLE
8298 If defined, this target hook points to an array of @samp{struct
8299 attribute_spec} (defined in @file{tree.h}) specifying the machine
8300 specific attributes for this target and some of the restrictions on the
8301 entities to which these attributes are applied and the arguments they
8305 @deftypefn {Target Hook} int TARGET_COMP_TYPE_ATTRIBUTES (tree @var{type1}, tree @var{type2})
8306 If defined, this target hook is a function which returns zero if the attributes on
8307 @var{type1} and @var{type2} are incompatible, one if they are compatible,
8308 and two if they are nearly compatible (which causes a warning to be
8309 generated). If this is not defined, machine-specific attributes are
8310 supposed always to be compatible.
8313 @deftypefn {Target Hook} void TARGET_SET_DEFAULT_TYPE_ATTRIBUTES (tree @var{type})
8314 If defined, this target hook is a function which assigns default attributes to
8315 newly defined @var{type}.
8318 @deftypefn {Target Hook} tree TARGET_MERGE_TYPE_ATTRIBUTES (tree @var{type1}, tree @var{type2})
8319 Define this target hook if the merging of type attributes needs special
8320 handling. If defined, the result is a list of the combined
8321 @code{TYPE_ATTRIBUTES} of @var{type1} and @var{type2}. It is assumed
8322 that @code{comptypes} has already been called and returned 1. This
8323 function may call @code{merge_attributes} to handle machine-independent
8327 @deftypefn {Target Hook} tree TARGET_MERGE_DECL_ATTRIBUTES (tree @var{olddecl}, tree @var{newdecl})
8328 Define this target hook if the merging of decl attributes needs special
8329 handling. If defined, the result is a list of the combined
8330 @code{DECL_ATTRIBUTES} of @var{olddecl} and @var{newdecl}.
8331 @var{newdecl} is a duplicate declaration of @var{olddecl}. Examples of
8332 when this is needed are when one attribute overrides another, or when an
8333 attribute is nullified by a subsequent definition. This function may
8334 call @code{merge_attributes} to handle machine-independent merging.
8336 @findex TARGET_DLLIMPORT_DECL_ATTRIBUTES
8337 If the only target-specific handling you require is @samp{dllimport} for
8338 Windows targets, you should define the macro
8339 @code{TARGET_DLLIMPORT_DECL_ATTRIBUTES}. This links in a function
8340 called @code{merge_dllimport_decl_attributes} which can then be defined
8341 as the expansion of @code{TARGET_MERGE_DECL_ATTRIBUTES}. This is done
8342 in @file{i386/cygwin.h} and @file{i386/i386.c}, for example.
8345 @deftypefn {Target Hook} void TARGET_INSERT_ATTRIBUTES (tree @var{node}, tree *@var{attr_ptr})
8346 Define this target hook if you want to be able to add attributes to a decl
8347 when it is being created. This is normally useful for back ends which
8348 wish to implement a pragma by using the attributes which correspond to
8349 the pragma's effect. The @var{node} argument is the decl which is being
8350 created. The @var{attr_ptr} argument is a pointer to the attribute list
8351 for this decl. The list itself should not be modified, since it may be
8352 shared with other decls, but attributes may be chained on the head of
8353 the list and @code{*@var{attr_ptr}} modified to point to the new
8354 attributes, or a copy of the list may be made if further changes are
8358 @deftypefn {Target Hook} bool TARGET_FUNCTION_ATTRIBUTE_INLINABLE_P (tree @var{fndecl})
8360 This target hook returns @code{true} if it is ok to inline @var{fndecl}
8361 into the current function, despite its having target-specific
8362 attributes, @code{false} otherwise. By default, if a function has a
8363 target specific attribute attached to it, it will not be inlined.
8366 @node MIPS Coprocessors
8367 @section Defining coprocessor specifics for MIPS targets.
8368 @cindex MIPS coprocessor-definition macros
8370 The MIPS specification allows MIPS implementations to have as many as 4
8371 coprocessors, each with as many as 32 private registers. gcc supports
8372 accessing these registers and transferring values between the registers
8373 and memory using asm-ized variables. For example:
8376 register unsigned int cp0count asm ("c0r1");
8382 (``c0r1'' is the default name of register 1 in coprocessor 0; alternate
8383 names may be added as described below, or the default names may be
8384 overridden entirely in @code{SUBTARGET_CONDITIONAL_REGISTER_USAGE}.)
8386 Coprocessor registers are assumed to be epilogue-used; sets to them will
8387 be preserved even if it does not appear that the register is used again
8388 later in the function.
8390 Another note: according to the MIPS spec, coprocessor 1 (if present) is
8391 the FPU. One accesses COP1 registers through standard mips
8392 floating-point support; they are not included in this mechanism.
8394 There is one macro used in defining the MIPS coprocessor interface which
8395 you may want to override in subtargets; it is described below.
8397 @defmac ALL_COP_ADDITIONAL_REGISTER_NAMES
8398 A comma-separated list (with leading comma) of pairs describing the
8399 alternate names of coprocessor registers. The format of each entry should be
8401 @{ @var{alternatename}, @var{register_number}@}
8407 @section Miscellaneous Parameters
8408 @cindex parameters, miscellaneous
8410 @c prevent bad page break with this line
8411 Here are several miscellaneous parameters.
8413 @defmac PREDICATE_CODES
8414 Define this if you have defined special-purpose predicates in the file
8415 @file{@var{machine}.c}. This macro is called within an initializer of an
8416 array of structures. The first field in the structure is the name of a
8417 predicate and the second field is an array of rtl codes. For each
8418 predicate, list all rtl codes that can be in expressions matched by the
8419 predicate. The list should have a trailing comma. Here is an example
8420 of two entries in the list for a typical RISC machine:
8423 #define PREDICATE_CODES \
8424 @{"gen_reg_rtx_operand", @{SUBREG, REG@}@}, \
8425 @{"reg_or_short_cint_operand", @{SUBREG, REG, CONST_INT@}@},
8428 Defining this macro does not affect the generated code (however,
8429 incorrect definitions that omit an rtl code that may be matched by the
8430 predicate can cause the compiler to malfunction). Instead, it allows
8431 the table built by @file{genrecog} to be more compact and efficient,
8432 thus speeding up the compiler. The most important predicates to include
8433 in the list specified by this macro are those used in the most insn
8436 For each predicate function named in @code{PREDICATE_CODES}, a
8437 declaration will be generated in @file{insn-codes.h}.
8440 @defmac SPECIAL_MODE_PREDICATES
8441 Define this if you have special predicates that know special things
8442 about modes. Genrecog will warn about certain forms of
8443 @code{match_operand} without a mode; if the operand predicate is
8444 listed in @code{SPECIAL_MODE_PREDICATES}, the warning will be
8447 Here is an example from the IA-32 port (@code{ext_register_operand}
8448 specially checks for @code{HImode} or @code{SImode} in preparation
8449 for a byte extraction from @code{%ah} etc.).
8452 #define SPECIAL_MODE_PREDICATES \
8453 "ext_register_operand",
8457 @defmac CASE_VECTOR_MODE
8458 An alias for a machine mode name. This is the machine mode that
8459 elements of a jump-table should have.
8462 @defmac CASE_VECTOR_SHORTEN_MODE (@var{min_offset}, @var{max_offset}, @var{body})
8463 Optional: return the preferred mode for an @code{addr_diff_vec}
8464 when the minimum and maximum offset are known. If you define this,
8465 it enables extra code in branch shortening to deal with @code{addr_diff_vec}.
8466 To make this work, you also have to define @code{INSN_ALIGN} and
8467 make the alignment for @code{addr_diff_vec} explicit.
8468 The @var{body} argument is provided so that the offset_unsigned and scale
8469 flags can be updated.
8472 @defmac CASE_VECTOR_PC_RELATIVE
8473 Define this macro to be a C expression to indicate when jump-tables
8474 should contain relative addresses. If jump-tables never contain
8475 relative addresses, then you need not define this macro.
8478 @defmac CASE_DROPS_THROUGH
8479 Define this if control falls through a @code{case} insn when the index
8480 value is out of range. This means the specified default-label is
8481 actually ignored by the @code{case} insn proper.
8484 @defmac CASE_VALUES_THRESHOLD
8485 Define this to be the smallest number of different values for which it
8486 is best to use a jump-table instead of a tree of conditional branches.
8487 The default is four for machines with a @code{casesi} instruction and
8488 five otherwise. This is best for most machines.
8491 @defmac CASE_USE_BIT_TESTS
8492 Define this macro to be a C expression to indicate whether C switch
8493 statements may be implemented by a sequence of bit tests. This is
8494 advantageous on processors that can efficiently implement left shift
8495 of 1 by the number of bits held in a register, but inappropriate on
8496 targets that would require a loop. By default, this macro returns
8497 @code{true} if the target defines an @code{ashlsi3} pattern, and
8498 @code{false} otherwise.
8501 @defmac WORD_REGISTER_OPERATIONS
8502 Define this macro if operations between registers with integral mode
8503 smaller than a word are always performed on the entire register.
8504 Most RISC machines have this property and most CISC machines do not.
8507 @defmac LOAD_EXTEND_OP (@var{mode})
8508 Define this macro to be a C expression indicating when insns that read
8509 memory in @var{mode}, an integral mode narrower than a word, set the
8510 bits outside of @var{mode} to be either the sign-extension or the
8511 zero-extension of the data read. Return @code{SIGN_EXTEND} for values
8512 of @var{mode} for which the
8513 insn sign-extends, @code{ZERO_EXTEND} for which it zero-extends, and
8514 @code{NIL} for other modes.
8516 This macro is not called with @var{mode} non-integral or with a width
8517 greater than or equal to @code{BITS_PER_WORD}, so you may return any
8518 value in this case. Do not define this macro if it would always return
8519 @code{NIL}. On machines where this macro is defined, you will normally
8520 define it as the constant @code{SIGN_EXTEND} or @code{ZERO_EXTEND}.
8523 @defmac SHORT_IMMEDIATES_SIGN_EXTEND
8524 Define this macro if loading short immediate values into registers sign
8528 @defmac FIXUNS_TRUNC_LIKE_FIX_TRUNC
8529 Define this macro if the same instructions that convert a floating
8530 point number to a signed fixed point number also convert validly to an
8535 The maximum number of bytes that a single instruction can move quickly
8536 between memory and registers or between two memory locations.
8539 @defmac MAX_MOVE_MAX
8540 The maximum number of bytes that a single instruction can move quickly
8541 between memory and registers or between two memory locations. If this
8542 is undefined, the default is @code{MOVE_MAX}. Otherwise, it is the
8543 constant value that is the largest value that @code{MOVE_MAX} can have
8547 @defmac SHIFT_COUNT_TRUNCATED
8548 A C expression that is nonzero if on this machine the number of bits
8549 actually used for the count of a shift operation is equal to the number
8550 of bits needed to represent the size of the object being shifted. When
8551 this macro is nonzero, the compiler will assume that it is safe to omit
8552 a sign-extend, zero-extend, and certain bitwise `and' instructions that
8553 truncates the count of a shift operation. On machines that have
8554 instructions that act on bit-fields at variable positions, which may
8555 include `bit test' instructions, a nonzero @code{SHIFT_COUNT_TRUNCATED}
8556 also enables deletion of truncations of the values that serve as
8557 arguments to bit-field instructions.
8559 If both types of instructions truncate the count (for shifts) and
8560 position (for bit-field operations), or if no variable-position bit-field
8561 instructions exist, you should define this macro.
8563 However, on some machines, such as the 80386 and the 680x0, truncation
8564 only applies to shift operations and not the (real or pretended)
8565 bit-field operations. Define @code{SHIFT_COUNT_TRUNCATED} to be zero on
8566 such machines. Instead, add patterns to the @file{md} file that include
8567 the implied truncation of the shift instructions.
8569 You need not define this macro if it would always have the value of zero.
8572 @defmac TRULY_NOOP_TRUNCATION (@var{outprec}, @var{inprec})
8573 A C expression which is nonzero if on this machine it is safe to
8574 ``convert'' an integer of @var{inprec} bits to one of @var{outprec}
8575 bits (where @var{outprec} is smaller than @var{inprec}) by merely
8576 operating on it as if it had only @var{outprec} bits.
8578 On many machines, this expression can be 1.
8580 @c rearranged this, removed the phrase "it is reported that". this was
8581 @c to fix an overfull hbox. --mew 10feb93
8582 When @code{TRULY_NOOP_TRUNCATION} returns 1 for a pair of sizes for
8583 modes for which @code{MODES_TIEABLE_P} is 0, suboptimal code can result.
8584 If this is the case, making @code{TRULY_NOOP_TRUNCATION} return 0 in
8585 such cases may improve things.
8588 @defmac STORE_FLAG_VALUE
8589 A C expression describing the value returned by a comparison operator
8590 with an integral mode and stored by a store-flag instruction
8591 (@samp{s@var{cond}}) when the condition is true. This description must
8592 apply to @emph{all} the @samp{s@var{cond}} patterns and all the
8593 comparison operators whose results have a @code{MODE_INT} mode.
8595 A value of 1 or @minus{}1 means that the instruction implementing the
8596 comparison operator returns exactly 1 or @minus{}1 when the comparison is true
8597 and 0 when the comparison is false. Otherwise, the value indicates
8598 which bits of the result are guaranteed to be 1 when the comparison is
8599 true. This value is interpreted in the mode of the comparison
8600 operation, which is given by the mode of the first operand in the
8601 @samp{s@var{cond}} pattern. Either the low bit or the sign bit of
8602 @code{STORE_FLAG_VALUE} be on. Presently, only those bits are used by
8605 If @code{STORE_FLAG_VALUE} is neither 1 or @minus{}1, the compiler will
8606 generate code that depends only on the specified bits. It can also
8607 replace comparison operators with equivalent operations if they cause
8608 the required bits to be set, even if the remaining bits are undefined.
8609 For example, on a machine whose comparison operators return an
8610 @code{SImode} value and where @code{STORE_FLAG_VALUE} is defined as
8611 @samp{0x80000000}, saying that just the sign bit is relevant, the
8615 (ne:SI (and:SI @var{x} (const_int @var{power-of-2})) (const_int 0))
8622 (ashift:SI @var{x} (const_int @var{n}))
8626 where @var{n} is the appropriate shift count to move the bit being
8627 tested into the sign bit.
8629 There is no way to describe a machine that always sets the low-order bit
8630 for a true value, but does not guarantee the value of any other bits,
8631 but we do not know of any machine that has such an instruction. If you
8632 are trying to port GCC to such a machine, include an instruction to
8633 perform a logical-and of the result with 1 in the pattern for the
8634 comparison operators and let us know at @email{gcc@@gcc.gnu.org}.
8636 Often, a machine will have multiple instructions that obtain a value
8637 from a comparison (or the condition codes). Here are rules to guide the
8638 choice of value for @code{STORE_FLAG_VALUE}, and hence the instructions
8643 Use the shortest sequence that yields a valid definition for
8644 @code{STORE_FLAG_VALUE}. It is more efficient for the compiler to
8645 ``normalize'' the value (convert it to, e.g., 1 or 0) than for the
8646 comparison operators to do so because there may be opportunities to
8647 combine the normalization with other operations.
8650 For equal-length sequences, use a value of 1 or @minus{}1, with @minus{}1 being
8651 slightly preferred on machines with expensive jumps and 1 preferred on
8655 As a second choice, choose a value of @samp{0x80000001} if instructions
8656 exist that set both the sign and low-order bits but do not define the
8660 Otherwise, use a value of @samp{0x80000000}.
8663 Many machines can produce both the value chosen for
8664 @code{STORE_FLAG_VALUE} and its negation in the same number of
8665 instructions. On those machines, you should also define a pattern for
8666 those cases, e.g., one matching
8669 (set @var{A} (neg:@var{m} (ne:@var{m} @var{B} @var{C})))
8672 Some machines can also perform @code{and} or @code{plus} operations on
8673 condition code values with less instructions than the corresponding
8674 @samp{s@var{cond}} insn followed by @code{and} or @code{plus}. On those
8675 machines, define the appropriate patterns. Use the names @code{incscc}
8676 and @code{decscc}, respectively, for the patterns which perform
8677 @code{plus} or @code{minus} operations on condition code values. See
8678 @file{rs6000.md} for some examples. The GNU Superoptizer can be used to
8679 find such instruction sequences on other machines.
8681 If this macro is not defined, the default value, 1, is used. You need
8682 not define @code{STORE_FLAG_VALUE} if the machine has no store-flag
8683 instructions, or if the value generated by these instructions is 1.
8686 @defmac FLOAT_STORE_FLAG_VALUE (@var{mode})
8687 A C expression that gives a nonzero @code{REAL_VALUE_TYPE} value that is
8688 returned when comparison operators with floating-point results are true.
8689 Define this macro on machine that have comparison operations that return
8690 floating-point values. If there are no such operations, do not define
8694 @defmac CLZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value})
8695 @defmacx CTZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value})
8696 A C expression that evaluates to true if the architecture defines a value
8697 for @code{clz} or @code{ctz} with a zero operand. If so, @var{value}
8698 should be set to this value. If this macro is not defined, the value of
8699 @code{clz} or @code{ctz} is assumed to be undefined.
8701 This macro must be defined if the target's expansion for @code{ffs}
8702 relies on a particular value to get correct results. Otherwise it
8703 is not necessary, though it may be used to optimize some corner cases.
8705 Note that regardless of this macro the ``definedness'' of @code{clz}
8706 and @code{ctz} at zero do @emph{not} extend to the builtin functions
8707 visible to the user. Thus one may be free to adjust the value at will
8708 to match the target expansion of these operations without fear of
8713 An alias for the machine mode for pointers. On most machines, define
8714 this to be the integer mode corresponding to the width of a hardware
8715 pointer; @code{SImode} on 32-bit machine or @code{DImode} on 64-bit machines.
8716 On some machines you must define this to be one of the partial integer
8717 modes, such as @code{PSImode}.
8719 The width of @code{Pmode} must be at least as large as the value of
8720 @code{POINTER_SIZE}. If it is not equal, you must define the macro
8721 @code{POINTERS_EXTEND_UNSIGNED} to specify how pointers are extended
8725 @defmac FUNCTION_MODE
8726 An alias for the machine mode used for memory references to functions
8727 being called, in @code{call} RTL expressions. On most machines this
8728 should be @code{QImode}.
8731 @defmac INTEGRATE_THRESHOLD (@var{decl})
8732 A C expression for the maximum number of instructions above which the
8733 function @var{decl} should not be inlined. @var{decl} is a
8734 @code{FUNCTION_DECL} node.
8736 The default definition of this macro is 64 plus 8 times the number of
8737 arguments that the function accepts. Some people think a larger
8738 threshold should be used on RISC machines.
8741 @defmac STDC_0_IN_SYSTEM_HEADERS
8742 In normal operation, the preprocessor expands @code{__STDC__} to the
8743 constant 1, to signify that GCC conforms to ISO Standard C@. On some
8744 hosts, like Solaris, the system compiler uses a different convention,
8745 where @code{__STDC__} is normally 0, but is 1 if the user specifies
8746 strict conformance to the C Standard.
8748 Defining @code{STDC_0_IN_SYSTEM_HEADERS} makes GNU CPP follows the host
8749 convention when processing system header files, but when processing user
8750 files @code{__STDC__} will always expand to 1.
8753 @defmac NO_IMPLICIT_EXTERN_C
8754 Define this macro if the system header files support C++ as well as C@.
8755 This macro inhibits the usual method of using system header files in
8756 C++, which is to pretend that the file's contents are enclosed in
8757 @samp{extern "C" @{@dots{}@}}.
8762 @defmac REGISTER_TARGET_PRAGMAS ()
8763 Define this macro if you want to implement any target-specific pragmas.
8764 If defined, it is a C expression which makes a series of calls to
8765 @code{c_register_pragma} for each pragma. The macro may also do any
8766 setup required for the pragmas.
8768 The primary reason to define this macro is to provide compatibility with
8769 other compilers for the same target. In general, we discourage
8770 definition of target-specific pragmas for GCC@.
8772 If the pragma can be implemented by attributes then you should consider
8773 defining the target hook @samp{TARGET_INSERT_ATTRIBUTES} as well.
8775 Preprocessor macros that appear on pragma lines are not expanded. All
8776 @samp{#pragma} directives that do not match any registered pragma are
8777 silently ignored, unless the user specifies @option{-Wunknown-pragmas}.
8780 @deftypefun void c_register_pragma (const char *@var{space}, const char *@var{name}, void (*@var{callback}) (struct cpp_reader *))
8782 Each call to @code{c_register_pragma} establishes one pragma. The
8783 @var{callback} routine will be called when the preprocessor encounters a
8787 #pragma [@var{space}] @var{name} @dots{}
8790 @var{space} is the case-sensitive namespace of the pragma, or
8791 @code{NULL} to put the pragma in the global namespace. The callback
8792 routine receives @var{pfile} as its first argument, which can be passed
8793 on to cpplib's functions if necessary. You can lex tokens after the
8794 @var{name} by calling @code{c_lex}. Tokens that are not read by the
8795 callback will be silently ignored. The end of the line is indicated by
8796 a token of type @code{CPP_EOF}
8798 For an example use of this routine, see @file{c4x.h} and the callback
8799 routines defined in @file{c4x-c.c}.
8801 Note that the use of @code{c_lex} is specific to the C and C++
8802 compilers. It will not work in the Java or Fortran compilers, or any
8803 other language compilers for that matter. Thus if @code{c_lex} is going
8804 to be called from target-specific code, it must only be done so when
8805 building the C and C++ compilers. This can be done by defining the
8806 variables @code{c_target_objs} and @code{cxx_target_objs} in the
8807 target entry in the @file{config.gcc} file. These variables should name
8808 the target-specific, language-specific object file which contains the
8809 code that uses @code{c_lex}. Note it will also be necessary to add a
8810 rule to the makefile fragment pointed to by @code{tmake_file} that shows
8811 how to build this object file.
8816 @defmac HANDLE_SYSV_PRAGMA
8817 Define this macro (to a value of 1) if you want the System V style
8818 pragmas @samp{#pragma pack(<n>)} and @samp{#pragma weak <name>
8819 [=<value>]} to be supported by gcc.
8821 The pack pragma specifies the maximum alignment (in bytes) of fields
8822 within a structure, in much the same way as the @samp{__aligned__} and
8823 @samp{__packed__} @code{__attribute__}s do. A pack value of zero resets
8824 the behavior to the default.
8826 A subtlety for Microsoft Visual C/C++ style bit-field packing
8827 (e.g. -mms-bitfields) for targets that support it:
8828 When a bit-field is inserted into a packed record, the whole size
8829 of the underlying type is used by one or more same-size adjacent
8830 bit-fields (that is, if its long:3, 32 bits is used in the record,
8831 and any additional adjacent long bit-fields are packed into the same
8832 chunk of 32 bits. However, if the size changes, a new field of that
8835 If both MS bit-fields and @samp{__attribute__((packed))} are used,
8836 the latter will take precedence. If @samp{__attribute__((packed))} is
8837 used on a single field when MS bit-fields are in use, it will take
8838 precedence for that field, but the alignment of the rest of the structure
8839 may affect its placement.
8841 The weak pragma only works if @code{SUPPORTS_WEAK} and
8842 @code{ASM_WEAKEN_LABEL} are defined. If enabled it allows the creation
8843 of specifically named weak labels, optionally with a value.
8848 @defmac HANDLE_PRAGMA_PACK_PUSH_POP
8849 Define this macro (to a value of 1) if you want to support the Win32
8850 style pragmas @samp{#pragma pack(push,@var{n})} and @samp{#pragma
8851 pack(pop)}. The @samp{pack(push,@var{n})} pragma specifies the maximum alignment
8852 (in bytes) of fields within a structure, in much the same way as the
8853 @samp{__aligned__} and @samp{__packed__} @code{__attribute__}s do. A
8854 pack value of zero resets the behavior to the default. Successive
8855 invocations of this pragma cause the previous values to be stacked, so
8856 that invocations of @samp{#pragma pack(pop)} will return to the previous
8860 @defmac DOLLARS_IN_IDENTIFIERS
8861 Define this macro to control use of the character @samp{$} in
8862 identifier names for the C family of languages. 0 means @samp{$} is
8863 not allowed by default; 1 means it is allowed. 1 is the default;
8864 there is no need to define this macro in that case.
8867 @defmac NO_DOLLAR_IN_LABEL
8868 Define this macro if the assembler does not accept the character
8869 @samp{$} in label names. By default constructors and destructors in
8870 G++ have @samp{$} in the identifiers. If this macro is defined,
8871 @samp{.} is used instead.
8874 @defmac NO_DOT_IN_LABEL
8875 Define this macro if the assembler does not accept the character
8876 @samp{.} in label names. By default constructors and destructors in G++
8877 have names that use @samp{.}. If this macro is defined, these names
8878 are rewritten to avoid @samp{.}.
8881 @defmac DEFAULT_MAIN_RETURN
8882 Define this macro if the target system expects every program's @code{main}
8883 function to return a standard ``success'' value by default (if no other
8884 value is explicitly returned).
8886 The definition should be a C statement (sans semicolon) to generate the
8887 appropriate rtl instructions. It is used only when compiling the end of
8891 @defmac INSN_SETS_ARE_DELAYED (@var{insn})
8892 Define this macro as a C expression that is nonzero if it is safe for the
8893 delay slot scheduler to place instructions in the delay slot of @var{insn},
8894 even if they appear to use a resource set or clobbered in @var{insn}.
8895 @var{insn} is always a @code{jump_insn} or an @code{insn}; GCC knows that
8896 every @code{call_insn} has this behavior. On machines where some @code{insn}
8897 or @code{jump_insn} is really a function call and hence has this behavior,
8898 you should define this macro.
8900 You need not define this macro if it would always return zero.
8903 @defmac INSN_REFERENCES_ARE_DELAYED (@var{insn})
8904 Define this macro as a C expression that is nonzero if it is safe for the
8905 delay slot scheduler to place instructions in the delay slot of @var{insn},
8906 even if they appear to set or clobber a resource referenced in @var{insn}.
8907 @var{insn} is always a @code{jump_insn} or an @code{insn}. On machines where
8908 some @code{insn} or @code{jump_insn} is really a function call and its operands
8909 are registers whose use is actually in the subroutine it calls, you should
8910 define this macro. Doing so allows the delay slot scheduler to move
8911 instructions which copy arguments into the argument registers into the delay
8914 You need not define this macro if it would always return zero.
8917 @defmac MULTIPLE_SYMBOL_SPACES
8918 Define this macro if in some cases global symbols from one translation
8919 unit may not be bound to undefined symbols in another translation unit
8920 without user intervention. For instance, under Microsoft Windows
8921 symbols must be explicitly imported from shared libraries (DLLs).
8924 @defmac MD_ASM_CLOBBERS (@var{clobbers})
8925 A C statement that adds to @var{clobbers} @code{STRING_CST} trees for
8926 any hard regs the port wishes to automatically clobber for all asms.
8929 @defmac MAX_INTEGER_COMPUTATION_MODE
8930 Define this to the largest integer machine mode which can be used for
8931 operations other than load, store and copy operations.
8933 You need only define this macro if the target holds values larger than
8934 @code{word_mode} in general purpose registers. Most targets should not define
8938 @defmac MATH_LIBRARY
8939 Define this macro as a C string constant for the linker argument to link
8940 in the system math library, or @samp{""} if the target does not have a
8941 separate math library.
8943 You need only define this macro if the default of @samp{"-lm"} is wrong.
8946 @defmac LIBRARY_PATH_ENV
8947 Define this macro as a C string constant for the environment variable that
8948 specifies where the linker should look for libraries.
8950 You need only define this macro if the default of @samp{"LIBRARY_PATH"}
8954 @defmac TARGET_HAS_F_SETLKW
8955 Define this macro if the target supports file locking with fcntl / F_SETLKW@.
8956 Note that this functionality is part of POSIX@.
8957 Defining @code{TARGET_HAS_F_SETLKW} will enable the test coverage code
8958 to use file locking when exiting a program, which avoids race conditions
8959 if the program has forked.
8962 @defmac MAX_CONDITIONAL_EXECUTE
8964 A C expression for the maximum number of instructions to execute via
8965 conditional execution instructions instead of a branch. A value of
8966 @code{BRANCH_COST}+1 is the default if the machine does not use cc0, and
8967 1 if it does use cc0.
8970 @defmac IFCVT_MODIFY_TESTS (@var{ce_info}, @var{true_expr}, @var{false_expr})
8971 Used if the target needs to perform machine-dependent modifications on the
8972 conditionals used for turning basic blocks into conditionally executed code.
8973 @var{ce_info} points to a data structure, @code{struct ce_if_block}, which
8974 contains information about the currently processed blocks. @var{true_expr}
8975 and @var{false_expr} are the tests that are used for converting the
8976 then-block and the else-block, respectively. Set either @var{true_expr} or
8977 @var{false_expr} to a null pointer if the tests cannot be converted.
8980 @defmac IFCVT_MODIFY_MULTIPLE_TESTS (@var{ce_info}, @var{bb}, @var{true_expr}, @var{false_expr})
8981 Like @code{IFCVT_MODIFY_TESTS}, but used when converting more complicated
8982 if-statements into conditions combined by @code{and} and @code{or} operations.
8983 @var{bb} contains the basic block that contains the test that is currently
8984 being processed and about to be turned into a condition.
8987 @defmac IFCVT_MODIFY_INSN (@var{ce_info}, @var{pattern}, @var{insn})
8988 A C expression to modify the @var{PATTERN} of an @var{INSN} that is to
8989 be converted to conditional execution format. @var{ce_info} points to
8990 a data structure, @code{struct ce_if_block}, which contains information
8991 about the currently processed blocks.
8994 @defmac IFCVT_MODIFY_FINAL (@var{ce_info})
8995 A C expression to perform any final machine dependent modifications in
8996 converting code to conditional execution. The involved basic blocks
8997 can be found in the @code{struct ce_if_block} structure that is pointed
8998 to by @var{ce_info}.
9001 @defmac IFCVT_MODIFY_CANCEL (@var{ce_info})
9002 A C expression to cancel any machine dependent modifications in
9003 converting code to conditional execution. The involved basic blocks
9004 can be found in the @code{struct ce_if_block} structure that is pointed
9005 to by @var{ce_info}.
9008 @defmac IFCVT_INIT_EXTRA_FIELDS (@var{ce_info})
9009 A C expression to initialize any extra fields in a @code{struct ce_if_block}
9010 structure, which are defined by the @code{IFCVT_EXTRA_FIELDS} macro.
9013 @defmac IFCVT_EXTRA_FIELDS
9014 If defined, it should expand to a set of field declarations that will be
9015 added to the @code{struct ce_if_block} structure. These should be initialized
9016 by the @code{IFCVT_INIT_EXTRA_FIELDS} macro.
9019 @deftypefn {Target Hook} void TARGET_MACHINE_DEPENDENT_REORG ()
9020 If non-null, this hook performs a target-specific pass over the
9021 instruction stream. The compiler will run it at all optimization levels,
9022 just before the point at which it normally does delayed-branch scheduling.
9024 The exact purpose of the hook varies from target to target. Some use
9025 it to do transformations that are necessary for correctness, such as
9026 laying out in-function constant pools or avoiding hardware hazards.
9027 Others use it as an opportunity to do some machine-dependent optimizations.
9029 You need not implement the hook if it has nothing to do. The default
9033 @deftypefn {Target Hook} void TARGET_INIT_BUILTINS ()
9034 Define this hook if you have any machine-specific built-in functions
9035 that need to be defined. It should be a function that performs the
9038 Machine specific built-in functions can be useful to expand special machine
9039 instructions that would otherwise not normally be generated because
9040 they have no equivalent in the source language (for example, SIMD vector
9041 instructions or prefetch instructions).
9043 To create a built-in function, call the function @code{builtin_function}
9044 which is defined by the language front end. You can use any type nodes set
9045 up by @code{build_common_tree_nodes} and @code{build_common_tree_nodes_2};
9046 only language front ends that use those two functions will call
9047 @samp{TARGET_INIT_BUILTINS}.
9050 @deftypefn {Target Hook} rtx TARGET_EXPAND_BUILTIN (tree @var{exp}, rtx @var{target}, rtx @var{subtarget}, enum machine_mode @var{mode}, int @var{ignore})
9052 Expand a call to a machine specific built-in function that was set up by
9053 @samp{TARGET_INIT_BUILTINS}. @var{exp} is the expression for the
9054 function call; the result should go to @var{target} if that is
9055 convenient, and have mode @var{mode} if that is convenient.
9056 @var{subtarget} may be used as the target for computing one of
9057 @var{exp}'s operands. @var{ignore} is nonzero if the value is to be
9058 ignored. This function should return the result of the call to the
9062 @defmac MD_CAN_REDIRECT_BRANCH (@var{branch1}, @var{branch2})
9064 Take a branch insn in @var{branch1} and another in @var{branch2}.
9065 Return true if redirecting @var{branch1} to the destination of
9066 @var{branch2} is possible.
9068 On some targets, branches may have a limited range. Optimizing the
9069 filling of delay slots can result in branches being redirected, and this
9070 may in turn cause a branch offset to overflow.
9073 @defmac ALLOCATE_INITIAL_VALUE (@var{hard_reg})
9075 When the initial value of a hard register has been copied in a pseudo
9076 register, it is often not necessary to actually allocate another register
9077 to this pseudo register, because the original hard register or a stack slot
9078 it has been saved into can be used. @code{ALLOCATE_INITIAL_VALUE}, if
9079 defined, is called at the start of register allocation once for each
9080 hard register that had its initial value copied by using
9081 @code{get_func_hard_reg_initial_val} or @code{get_hard_reg_initial_val}.
9082 Possible values are @code{NULL_RTX}, if you don't want
9083 to do any special allocation, a @code{REG} rtx---that would typically be
9084 the hard register itself, if it is known not to be clobbered---or a
9086 If you are returning a @code{MEM}, this is only a hint for the allocator;
9087 it might decide to use another register anyways.
9088 You may use @code{current_function_leaf_function} in the definition of the
9089 macro, functions that use @code{REG_N_SETS}, to determine if the hard
9090 register in question will not be clobbered.
9093 @defmac TARGET_OBJECT_SUFFIX
9094 Define this macro to be a C string representing the suffix for object
9095 files on your target machine. If you do not define this macro, GCC will
9096 use @samp{.o} as the suffix for object files.
9099 @defmac TARGET_EXECUTABLE_SUFFIX
9100 Define this macro to be a C string representing the suffix to be
9101 automatically added to executable files on your target machine. If you
9102 do not define this macro, GCC will use the null string as the suffix for
9106 @defmac COLLECT_EXPORT_LIST
9107 If defined, @code{collect2} will scan the individual object files
9108 specified on its command line and create an export list for the linker.
9109 Define this macro for systems like AIX, where the linker discards
9110 object files that are not referenced from @code{main} and uses export
9114 @defmac MODIFY_JNI_METHOD_CALL (@var{mdecl})
9115 Define this macro to a C expression representing a variant of the
9116 method call @var{mdecl}, if Java Native Interface (JNI) methods
9117 must be invoked differently from other methods on your target.
9118 For example, on 32-bit Windows, JNI methods must be invoked using
9119 the @code{stdcall} calling convention and this macro is then
9120 defined as this expression:
9123 build_type_attribute_variant (@var{mdecl},
9125 (get_identifier ("stdcall"),
9130 @deftypefn {Target Hook} bool TARGET_CANNOT_MODIFY_JUMPS_P (void)
9131 This target hook returns @code{true} past the point in which new jump
9132 instructions could be created. On machines that require a register for
9133 every jump such as the SHmedia ISA of SH5, this point would typically be
9134 reload, so this target hook should be defined to a function such as:
9138 cannot_modify_jumps_past_reload_p ()
9140 return (reload_completed || reload_in_progress);
9145 @deftypefn {Target Hook} int TARGET_BRANCH_TARGET_REGISTER_CLASS (void)
9146 This target hook returns a register class for which branch target register
9147 optimizations should be applied. All registers in this class should be
9148 usable interchangeably. After reload, registers in this class will be
9149 re-allocated and loads will be hoisted out of loops and be subjected
9150 to inter-block scheduling.
9153 @deftypefn {Target Hook} bool TARGET_BRANCH_TARGET_REGISTER_CALLEE_SAVED (bool @var{after_prologue_epilogue_gen})
9154 Branch target register optimization will by default exclude callee-saved
9156 that are not already live during the current function; if this target hook
9157 returns true, they will be included. The target code must than make sure
9158 that all target registers in the class returned by
9159 @samp{TARGET_BRANCH_TARGET_REGISTER_CLASS} that might need saving are
9160 saved. @var{after_prologue_epilogue_gen} indicates if prologues and
9161 epilogues have already been generated. Note, even if you only return
9162 true when @var{after_prologue_epilogue_gen} is false, you still are likely
9163 to have to make special provisions in @code{INITIAL_ELIMINATION_OFFSET}
9164 to reserve space for caller-saved target registers.
9167 @defmac POWI_MAX_MULTS
9168 If defined, this macro is interpreted as a signed integer C expression
9169 that specifies the maximum number of floating point multiplications
9170 that should be emitted when expanding exponentiation by an integer
9171 constant inline. When this value is defined, exponentiation requiring
9172 more than this number of multiplications is implemented by calling the
9173 system library's @code{pow}, @code{powf} or @code{powl} routines.
9174 The default value places no upper bound on the multiplication count.