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 MD_EXEC_PREFIX
443 If defined, this macro is an additional prefix to try after
444 @code{STANDARD_EXEC_PREFIX}. @code{MD_EXEC_PREFIX} is not searched
445 when the @option{-b} option is used, or the compiler is built as a cross
446 compiler. If you define @code{MD_EXEC_PREFIX}, then be sure to add it
447 to the list of directories used to find the assembler in @file{configure.in}.
450 @defmac STANDARD_STARTFILE_PREFIX
451 Define this macro as a C string constant if you wish to override the
452 standard choice of @code{libdir} as the default prefix to
453 try when searching for startup files such as @file{crt0.o}.
454 @code{STANDARD_STARTFILE_PREFIX} is not searched when the compiler
455 is built as a cross compiler.
458 @defmac MD_STARTFILE_PREFIX
459 If defined, this macro supplies an additional prefix to try after the
460 standard prefixes. @code{MD_EXEC_PREFIX} is not searched when the
461 @option{-b} option is used, or when the compiler is built as a cross
465 @defmac MD_STARTFILE_PREFIX_1
466 If defined, this macro supplies yet another prefix to try after the
467 standard prefixes. It is not searched when the @option{-b} option is
468 used, or when the compiler is built as a cross compiler.
471 @defmac INIT_ENVIRONMENT
472 Define this macro as a C string constant if you wish to set environment
473 variables for programs called by the driver, such as the assembler and
474 loader. The driver passes the value of this macro to @code{putenv} to
475 initialize the necessary environment variables.
478 @defmac LOCAL_INCLUDE_DIR
479 Define this macro as a C string constant if you wish to override the
480 standard choice of @file{/usr/local/include} as the default prefix to
481 try when searching for local header files. @code{LOCAL_INCLUDE_DIR}
482 comes before @code{SYSTEM_INCLUDE_DIR} in the search order.
484 Cross compilers do not search either @file{/usr/local/include} or its
488 @defmac MODIFY_TARGET_NAME
489 Define this macro if you wish to define command-line switches that
490 modify the default target name.
492 For each switch, you can include a string to be appended to the first
493 part of the configuration name or a string to be deleted from the
494 configuration name, if present. The definition should be an initializer
495 for an array of structures. Each array element should have three
496 elements: the switch name (a string constant, including the initial
497 dash), one of the enumeration codes @code{ADD} or @code{DELETE} to
498 indicate whether the string should be inserted or deleted, and the string
499 to be inserted or deleted (a string constant).
501 For example, on a machine where @samp{64} at the end of the
502 configuration name denotes a 64-bit target and you want the @option{-32}
503 and @option{-64} switches to select between 32- and 64-bit targets, you would
507 #define MODIFY_TARGET_NAME \
508 @{ @{ "-32", DELETE, "64"@}, \
509 @{"-64", ADD, "64"@}@}
513 @defmac SYSTEM_INCLUDE_DIR
514 Define this macro as a C string constant if you wish to specify a
515 system-specific directory to search for header files before the standard
516 directory. @code{SYSTEM_INCLUDE_DIR} comes before
517 @code{STANDARD_INCLUDE_DIR} in the search order.
519 Cross compilers do not use this macro and do not search the directory
523 @defmac STANDARD_INCLUDE_DIR
524 Define this macro as a C string constant if you wish to override the
525 standard choice of @file{/usr/include} as the default prefix to
526 try when searching for header files.
528 Cross compilers ignore this macro and do not search either
529 @file{/usr/include} or its replacement.
532 @defmac STANDARD_INCLUDE_COMPONENT
533 The ``component'' corresponding to @code{STANDARD_INCLUDE_DIR}.
534 See @code{INCLUDE_DEFAULTS}, below, for the description of components.
535 If you do not define this macro, no component is used.
538 @defmac INCLUDE_DEFAULTS
539 Define this macro if you wish to override the entire default search path
540 for include files. For a native compiler, the default search path
541 usually consists of @code{GCC_INCLUDE_DIR}, @code{LOCAL_INCLUDE_DIR},
542 @code{SYSTEM_INCLUDE_DIR}, @code{GPLUSPLUS_INCLUDE_DIR}, and
543 @code{STANDARD_INCLUDE_DIR}. In addition, @code{GPLUSPLUS_INCLUDE_DIR}
544 and @code{GCC_INCLUDE_DIR} are defined automatically by @file{Makefile},
545 and specify private search areas for GCC@. The directory
546 @code{GPLUSPLUS_INCLUDE_DIR} is used only for C++ programs.
548 The definition should be an initializer for an array of structures.
549 Each array element should have four elements: the directory name (a
550 string constant), the component name (also a string constant), a flag
551 for C++-only directories,
552 and a flag showing that the includes in the directory don't need to be
553 wrapped in @code{extern @samp{C}} when compiling C++. Mark the end of
554 the array with a null element.
556 The component name denotes what GNU package the include file is part of,
557 if any, in all uppercase letters. For example, it might be @samp{GCC}
558 or @samp{BINUTILS}. If the package is part of a vendor-supplied
559 operating system, code the component name as @samp{0}.
561 For example, here is the definition used for VAX/VMS:
564 #define INCLUDE_DEFAULTS \
566 @{ "GNU_GXX_INCLUDE:", "G++", 1, 1@}, \
567 @{ "GNU_CC_INCLUDE:", "GCC", 0, 0@}, \
568 @{ "SYS$SYSROOT:[SYSLIB.]", 0, 0, 0@}, \
575 Here is the order of prefixes tried for exec files:
579 Any prefixes specified by the user with @option{-B}.
582 The environment variable @code{GCC_EXEC_PREFIX}, if any.
585 The directories specified by the environment variable @code{COMPILER_PATH}.
588 The macro @code{STANDARD_EXEC_PREFIX}.
591 @file{/usr/lib/gcc/}.
594 The macro @code{MD_EXEC_PREFIX}, if any.
597 Here is the order of prefixes tried for startfiles:
601 Any prefixes specified by the user with @option{-B}.
604 The environment variable @code{GCC_EXEC_PREFIX}, if any.
607 The directories specified by the environment variable @code{LIBRARY_PATH}
608 (or port-specific name; native only, cross compilers do not use this).
611 The macro @code{STANDARD_EXEC_PREFIX}.
614 @file{/usr/lib/gcc/}.
617 The macro @code{MD_EXEC_PREFIX}, if any.
620 The macro @code{MD_STARTFILE_PREFIX}, if any.
623 The macro @code{STANDARD_STARTFILE_PREFIX}.
632 @node Run-time Target
633 @section Run-time Target Specification
634 @cindex run-time target specification
635 @cindex predefined macros
636 @cindex target specifications
638 @c prevent bad page break with this line
639 Here are run-time target specifications.
641 @defmac TARGET_CPU_CPP_BUILTINS ()
642 This function-like macro expands to a block of code that defines
643 built-in preprocessor macros and assertions for the target cpu, using
644 the functions @code{builtin_define}, @code{builtin_define_std} and
645 @code{builtin_assert}. When the front end
646 calls this macro it provides a trailing semicolon, and since it has
647 finished command line option processing your code can use those
650 @code{builtin_assert} takes a string in the form you pass to the
651 command-line option @option{-A}, such as @code{cpu=mips}, and creates
652 the assertion. @code{builtin_define} takes a string in the form
653 accepted by option @option{-D} and unconditionally defines the macro.
655 @code{builtin_define_std} takes a string representing the name of an
656 object-like macro. If it doesn't lie in the user's namespace,
657 @code{builtin_define_std} defines it unconditionally. Otherwise, it
658 defines a version with two leading underscores, and another version
659 with two leading and trailing underscores, and defines the original
660 only if an ISO standard was not requested on the command line. For
661 example, passing @code{unix} defines @code{__unix}, @code{__unix__}
662 and possibly @code{unix}; passing @code{_mips} defines @code{__mips},
663 @code{__mips__} and possibly @code{_mips}, and passing @code{_ABI64}
664 defines only @code{_ABI64}.
666 You can also test for the C dialect being compiled. The variable
667 @code{c_language} is set to one of @code{clk_c}, @code{clk_cplusplus}
668 or @code{clk_objective_c}. Note that if we are preprocessing
669 assembler, this variable will be @code{clk_c} but the function-like
670 macro @code{preprocessing_asm_p()} will return true, so you might want
671 to check for that first. If you need to check for strict ANSI, the
672 variable @code{flag_iso} can be used. The function-like macro
673 @code{preprocessing_trad_p()} can be used to check for traditional
677 @defmac TARGET_OS_CPP_BUILTINS ()
678 Similarly to @code{TARGET_CPU_CPP_BUILTINS} but this macro is optional
679 and is used for the target operating system instead.
682 @defmac TARGET_OBJFMT_CPP_BUILTINS ()
683 Similarly to @code{TARGET_CPU_CPP_BUILTINS} but this macro is optional
684 and is used for the target object format. @file{elfos.h} uses this
685 macro to define @code{__ELF__}, so you probably do not need to define
689 @deftypevar {extern int} target_flags
690 This declaration should be present.
693 @cindex optional hardware or system features
694 @cindex features, optional, in system conventions
696 @defmac TARGET_@var{featurename}
697 This series of macros is to allow compiler command arguments to
698 enable or disable the use of optional features of the target machine.
699 For example, one machine description serves both the 68000 and
700 the 68020; a command argument tells the compiler whether it should
701 use 68020-only instructions or not. This command argument works
702 by means of a macro @code{TARGET_68020} that tests a bit in
705 Define a macro @code{TARGET_@var{featurename}} for each such option.
706 Its definition should test a bit in @code{target_flags}. It is
707 recommended that a helper macro @code{MASK_@var{featurename}}
708 is defined for each bit-value to test, and used in
709 @code{TARGET_@var{featurename}} and @code{TARGET_SWITCHES}. For
713 #define TARGET_MASK_68020 1
714 #define TARGET_68020 (target_flags & MASK_68020)
717 One place where these macros are used is in the condition-expressions
718 of instruction patterns. Note how @code{TARGET_68020} appears
719 frequently in the 68000 machine description file, @file{m68k.md}.
720 Another place they are used is in the definitions of the other
721 macros in the @file{@var{machine}.h} file.
724 @defmac TARGET_SWITCHES
725 This macro defines names of command options to set and clear
726 bits in @code{target_flags}. Its definition is an initializer
727 with a subgrouping for each command option.
729 Each subgrouping contains a string constant, that defines the option
730 name, a number, which contains the bits to set in
731 @code{target_flags}, and a second string which is the description
732 displayed by @option{--help}. If the number is negative then the bits specified
733 by the number are cleared instead of being set. If the description
734 string is present but empty, then no help information will be displayed
735 for that option, but it will not count as an undocumented option. The
736 actual option name is made by appending @samp{-m} to the specified name.
737 Non-empty description strings should be marked with @code{N_(@dots{})} for
738 @command{xgettext}. Please do not mark empty strings because the empty
739 string is reserved by GNU gettext. @code{gettext("")} returns the header entry
740 of the message catalog with meta information, not the empty string.
742 In addition to the description for @option{--help},
743 more detailed documentation for each option should be added to
746 One of the subgroupings should have a null string. The number in
747 this grouping is the default value for @code{target_flags}. Any
748 target options act starting with that value.
750 Here is an example which defines @option{-m68000} and @option{-m68020}
751 with opposite meanings, and picks the latter as the default:
754 #define TARGET_SWITCHES \
755 @{ @{ "68020", MASK_68020, "" @}, \
756 @{ "68000", -MASK_68020, \
757 N_("Compile for the 68000") @}, \
758 @{ "", MASK_68020, "" @}, \
763 @defmac TARGET_OPTIONS
764 This macro is similar to @code{TARGET_SWITCHES} but defines names of command
765 options that have values. Its definition is an initializer with a
766 subgrouping for each command option.
768 Each subgrouping contains a string constant, that defines the option
769 name, the address of a variable, a description string, and a value.
770 Non-empty description strings should be marked with @code{N_(@dots{})}
771 for @command{xgettext}. Please do not mark empty strings because the
772 empty string is reserved by GNU gettext. @code{gettext("")} returns the
773 header entry of the message catalog with meta information, not the empty
776 If the value listed in the table is @code{NULL}, then the variable, type
777 @code{char *}, is set to the variable part of the given option if the
778 fixed part matches. In other words, if the first part of the option
779 matches what's in the table, the variable will be set to point to the
780 rest of the option. This allows the user to specify a value for that
781 option. The actual option name is made by appending @samp{-m} to the
782 specified name. Again, each option should also be documented in
785 If the value listed in the table is non-@code{NULL}, then the option
786 must match the option in the table exactly (with @samp{-m}), and the
787 variable is set to point to the value listed in the table.
789 Here is an example which defines @option{-mshort-data-@var{number}}. If the
790 given option is @option{-mshort-data-512}, the variable @code{m88k_short_data}
791 will be set to the string @code{"512"}.
794 extern char *m88k_short_data;
795 #define TARGET_OPTIONS \
796 @{ @{ "short-data-", &m88k_short_data, \
797 N_("Specify the size of the short data section"), 0 @} @}
800 Here is a variant of the above that allows the user to also specify
801 just @option{-mshort-data} where a default of @code{"64"} is used.
804 extern char *m88k_short_data;
805 #define TARGET_OPTIONS \
806 @{ @{ "short-data-", &m88k_short_data, \
807 N_("Specify the size of the short data section"), 0 @} \
808 @{ "short-data", &m88k_short_data, "", "64" @},
812 Here is an example which defines @option{-mno-alu}, @option{-malu1}, and
813 @option{-malu2} as a three-state switch, along with suitable macros for
814 checking the state of the option (documentation is elided for brevity).
818 char *chip_alu = ""; /* Specify default here. */
821 extern char *chip_alu;
822 #define TARGET_OPTIONS \
823 @{ @{ "no-alu", &chip_alu, "", "" @}, \
824 @{ "alu1", &chip_alu, "", "1" @}, \
825 @{ "alu2", &chip_alu, "", "2" @}, @}
826 #define TARGET_ALU (chip_alu[0] != '\0')
827 #define TARGET_ALU1 (chip_alu[0] == '1')
828 #define TARGET_ALU2 (chip_alu[0] == '2')
832 @defmac TARGET_VERSION
833 This macro is a C statement to print on @code{stderr} a string
834 describing the particular machine description choice. Every machine
835 description should define @code{TARGET_VERSION}. For example:
839 #define TARGET_VERSION \
840 fprintf (stderr, " (68k, Motorola syntax)");
842 #define TARGET_VERSION \
843 fprintf (stderr, " (68k, MIT syntax)");
848 @defmac OVERRIDE_OPTIONS
849 Sometimes certain combinations of command options do not make sense on
850 a particular target machine. You can define a macro
851 @code{OVERRIDE_OPTIONS} to take account of this. This macro, if
852 defined, is executed once just after all the command options have been
855 Don't use this macro to turn on various extra optimizations for
856 @option{-O}. That is what @code{OPTIMIZATION_OPTIONS} is for.
859 @defmac OPTIMIZATION_OPTIONS (@var{level}, @var{size})
860 Some machines may desire to change what optimizations are performed for
861 various optimization levels. This macro, if defined, is executed once
862 just after the optimization level is determined and before the remainder
863 of the command options have been parsed. Values set in this macro are
864 used as the default values for the other command line options.
866 @var{level} is the optimization level specified; 2 if @option{-O2} is
867 specified, 1 if @option{-O} is specified, and 0 if neither is specified.
869 @var{size} is nonzero if @option{-Os} is specified and zero otherwise.
871 You should not use this macro to change options that are not
872 machine-specific. These should uniformly selected by the same
873 optimization level on all supported machines. Use this macro to enable
874 machine-specific optimizations.
876 @strong{Do not examine @code{write_symbols} in
877 this macro!} The debugging options are not supposed to alter the
881 @defmac CAN_DEBUG_WITHOUT_FP
882 Define this macro if debugging can be performed even without a frame
883 pointer. If this macro is defined, GCC will turn on the
884 @option{-fomit-frame-pointer} option whenever @option{-O} is specified.
887 @node Per-Function Data
888 @section Defining data structures for per-function information.
889 @cindex per-function data
890 @cindex data structures
892 If the target needs to store information on a per-function basis, GCC
893 provides a macro and a couple of variables to allow this. Note, just
894 using statics to store the information is a bad idea, since GCC supports
895 nested functions, so you can be halfway through encoding one function
896 when another one comes along.
898 GCC defines a data structure called @code{struct function} which
899 contains all of the data specific to an individual function. This
900 structure contains a field called @code{machine} whose type is
901 @code{struct machine_function *}, which can be used by targets to point
902 to their own specific data.
904 If a target needs per-function specific data it should define the type
905 @code{struct machine_function} and also the macro @code{INIT_EXPANDERS}.
906 This macro should be used to initialize the function pointer
907 @code{init_machine_status}. This pointer is explained below.
909 One typical use of per-function, target specific data is to create an
910 RTX to hold the register containing the function's return address. This
911 RTX can then be used to implement the @code{__builtin_return_address}
912 function, for level 0.
914 Note---earlier implementations of GCC used a single data area to hold
915 all of the per-function information. Thus when processing of a nested
916 function began the old per-function data had to be pushed onto a
917 stack, and when the processing was finished, it had to be popped off the
918 stack. GCC used to provide function pointers called
919 @code{save_machine_status} and @code{restore_machine_status} to handle
920 the saving and restoring of the target specific information. Since the
921 single data area approach is no longer used, these pointers are no
924 @defmac INIT_EXPANDERS
925 Macro called to initialize any target specific information. This macro
926 is called once per function, before generation of any RTL has begun.
927 The intention of this macro is to allow the initialization of the
928 function pointer @code{init_machine_status}.
931 @deftypevar {void (*)(struct function *)} init_machine_status
932 If this function pointer is non-@code{NULL} it will be called once per
933 function, before function compilation starts, in order to allow the
934 target to perform any target specific initialization of the
935 @code{struct function} structure. It is intended that this would be
936 used to initialize the @code{machine} of that structure.
938 @code{struct machine_function} structures are expected to be freed by GC.
939 Generally, any memory that they reference must be allocated by using
940 @code{ggc_alloc}, including the structure itself.
944 @section Storage Layout
945 @cindex storage layout
947 Note that the definitions of the macros in this table which are sizes or
948 alignments measured in bits do not need to be constant. They can be C
949 expressions that refer to static variables, such as the @code{target_flags}.
950 @xref{Run-time Target}.
952 @defmac BITS_BIG_ENDIAN
953 Define this macro to have the value 1 if the most significant bit in a
954 byte has the lowest number; otherwise define it to have the value zero.
955 This means that bit-field instructions count from the most significant
956 bit. If the machine has no bit-field instructions, then this must still
957 be defined, but it doesn't matter which value it is defined to. This
958 macro need not be a constant.
960 This macro does not affect the way structure fields are packed into
961 bytes or words; that is controlled by @code{BYTES_BIG_ENDIAN}.
964 @defmac BYTES_BIG_ENDIAN
965 Define this macro to have the value 1 if the most significant byte in a
966 word has the lowest number. This macro need not be a constant.
969 @defmac WORDS_BIG_ENDIAN
970 Define this macro to have the value 1 if, in a multiword object, the
971 most significant word has the lowest number. This applies to both
972 memory locations and registers; GCC fundamentally assumes that the
973 order of words in memory is the same as the order in registers. This
974 macro need not be a constant.
977 @defmac LIBGCC2_WORDS_BIG_ENDIAN
978 Define this macro if @code{WORDS_BIG_ENDIAN} is not constant. This must be a
979 constant value with the same meaning as @code{WORDS_BIG_ENDIAN}, which will be
980 used only when compiling @file{libgcc2.c}. Typically the value will be set
981 based on preprocessor defines.
984 @defmac FLOAT_WORDS_BIG_ENDIAN
985 Define this macro to have the value 1 if @code{DFmode}, @code{XFmode} or
986 @code{TFmode} floating point numbers are stored in memory with the word
987 containing the sign bit at the lowest address; otherwise define it to
988 have the value 0. This macro need not be a constant.
990 You need not define this macro if the ordering is the same as for
994 @defmac BITS_PER_UNIT
995 Define this macro to be the number of bits in an addressable storage
996 unit (byte). If you do not define this macro the default is 8.
999 @defmac BITS_PER_WORD
1000 Number of bits in a word. If you do not define this macro, the default
1001 is @code{BITS_PER_UNIT * UNITS_PER_WORD}.
1004 @defmac MAX_BITS_PER_WORD
1005 Maximum number of bits in a word. If this is undefined, the default is
1006 @code{BITS_PER_WORD}. Otherwise, it is the constant value that is the
1007 largest value that @code{BITS_PER_WORD} can have at run-time.
1010 @defmac UNITS_PER_WORD
1011 Number of storage units in a word; normally 4.
1014 @defmac MIN_UNITS_PER_WORD
1015 Minimum number of units in a word. If this is undefined, the default is
1016 @code{UNITS_PER_WORD}. Otherwise, it is the constant value that is the
1017 smallest value that @code{UNITS_PER_WORD} can have at run-time.
1020 @defmac POINTER_SIZE
1021 Width of a pointer, in bits. You must specify a value no wider than the
1022 width of @code{Pmode}. If it is not equal to the width of @code{Pmode},
1023 you must define @code{POINTERS_EXTEND_UNSIGNED}. If you do not specify
1024 a value the default is @code{BITS_PER_WORD}.
1027 @defmac POINTERS_EXTEND_UNSIGNED
1028 A C expression whose value is greater than zero if pointers that need to be
1029 extended from being @code{POINTER_SIZE} bits wide to @code{Pmode} are to
1030 be zero-extended and zero if they are to be sign-extended. If the value
1031 is less then zero then there must be an "ptr_extend" instruction that
1032 extends a pointer from @code{POINTER_SIZE} to @code{Pmode}.
1034 You need not define this macro if the @code{POINTER_SIZE} is equal
1035 to the width of @code{Pmode}.
1038 @defmac PROMOTE_MODE (@var{m}, @var{unsignedp}, @var{type})
1039 A macro to update @var{m} and @var{unsignedp} when an object whose type
1040 is @var{type} and which has the specified mode and signedness is to be
1041 stored in a register. This macro is only called when @var{type} is a
1044 On most RISC machines, which only have operations that operate on a full
1045 register, define this macro to set @var{m} to @code{word_mode} if
1046 @var{m} is an integer mode narrower than @code{BITS_PER_WORD}. In most
1047 cases, only integer modes should be widened because wider-precision
1048 floating-point operations are usually more expensive than their narrower
1051 For most machines, the macro definition does not change @var{unsignedp}.
1052 However, some machines, have instructions that preferentially handle
1053 either signed or unsigned quantities of certain modes. For example, on
1054 the DEC Alpha, 32-bit loads from memory and 32-bit add instructions
1055 sign-extend the result to 64 bits. On such machines, set
1056 @var{unsignedp} according to which kind of extension is more efficient.
1058 Do not define this macro if it would never modify @var{m}.
1061 @deftypefn {Target Hook} bool TARGET_PROMOTE_FUNCTION_ARGS (tree @var{fntype})
1062 This target hook should return @code{true} if the promotion described by
1063 @code{PROMOTE_MODE} should also be done for outgoing function arguments.
1066 @deftypefn {Target Hook} bool TARGET_PROMOTE_FUNCTION_RETURN (tree @var{fntype})
1067 This target hook should return @code{true} if the promotion described by
1068 @code{PROMOTE_MODE} should also be done for the return value of
1071 If this target hook returns @code{true}, @code{FUNCTION_VALUE} must
1072 perform the same promotions done by @code{PROMOTE_MODE}.
1075 @defmac PROMOTE_FOR_CALL_ONLY
1076 Define this macro if the promotion described by @code{PROMOTE_MODE}
1077 should @emph{only} be performed for outgoing function arguments or
1078 function return values, as specified by @code{TARGET_PROMOTE_FUNCTION_ARGS}
1079 and @code{TARGET_PROMOTE_FUNCTION_RETURN}, respectively.
1082 @defmac PARM_BOUNDARY
1083 Normal alignment required for function parameters on the stack, in
1084 bits. All stack parameters receive at least this much alignment
1085 regardless of data type. On most machines, this is the same as the
1089 @defmac STACK_BOUNDARY
1090 Define this macro to the minimum alignment enforced by hardware for the
1091 stack pointer on this machine. The definition is a C expression for the
1092 desired alignment (measured in bits). This value is used as a default
1093 if @code{PREFERRED_STACK_BOUNDARY} is not defined. On most machines,
1094 this should be the same as @code{PARM_BOUNDARY}.
1097 @defmac PREFERRED_STACK_BOUNDARY
1098 Define this macro if you wish to preserve a certain alignment for the
1099 stack pointer, greater than what the hardware enforces. The definition
1100 is a C expression for the desired alignment (measured in bits). This
1101 macro must evaluate to a value equal to or larger than
1102 @code{STACK_BOUNDARY}.
1105 @defmac FORCE_PREFERRED_STACK_BOUNDARY_IN_MAIN
1106 A C expression that evaluates true if @code{PREFERRED_STACK_BOUNDARY} is
1107 not guaranteed by the runtime and we should emit code to align the stack
1108 at the beginning of @code{main}.
1110 @cindex @code{PUSH_ROUNDING}, interaction with @code{PREFERRED_STACK_BOUNDARY}
1111 If @code{PUSH_ROUNDING} is not defined, the stack will always be aligned
1112 to the specified boundary. If @code{PUSH_ROUNDING} is defined and specifies
1113 a less strict alignment than @code{PREFERRED_STACK_BOUNDARY}, the stack may
1114 be momentarily unaligned while pushing arguments.
1117 @defmac FUNCTION_BOUNDARY
1118 Alignment required for a function entry point, in bits.
1121 @defmac BIGGEST_ALIGNMENT
1122 Biggest alignment that any data type can require on this machine, in bits.
1125 @defmac MINIMUM_ATOMIC_ALIGNMENT
1126 If defined, the smallest alignment, in bits, that can be given to an
1127 object that can be referenced in one operation, without disturbing any
1128 nearby object. Normally, this is @code{BITS_PER_UNIT}, but may be larger
1129 on machines that don't have byte or half-word store operations.
1132 @defmac BIGGEST_FIELD_ALIGNMENT
1133 Biggest alignment that any structure or union field can require on this
1134 machine, in bits. If defined, this overrides @code{BIGGEST_ALIGNMENT} for
1135 structure and union fields only, unless the field alignment has been set
1136 by the @code{__attribute__ ((aligned (@var{n})))} construct.
1139 @defmac ADJUST_FIELD_ALIGN (@var{field}, @var{computed})
1140 An expression for the alignment of a structure field @var{field} if the
1141 alignment computed in the usual way (including applying of
1142 @code{BIGGEST_ALIGNMENT} and @code{BIGGEST_FIELD_ALIGNMENT} to the
1143 alignment) is @var{computed}. It overrides alignment only if the
1144 field alignment has not been set by the
1145 @code{__attribute__ ((aligned (@var{n})))} construct.
1148 @defmac MAX_OFILE_ALIGNMENT
1149 Biggest alignment supported by the object file format of this machine.
1150 Use this macro to limit the alignment which can be specified using the
1151 @code{__attribute__ ((aligned (@var{n})))} construct. If not defined,
1152 the default value is @code{BIGGEST_ALIGNMENT}.
1155 @defmac DATA_ALIGNMENT (@var{type}, @var{basic-align})
1156 If defined, a C expression to compute the alignment for a variable in
1157 the static store. @var{type} is the data type, and @var{basic-align} is
1158 the alignment that the object would ordinarily have. The value of this
1159 macro is used instead of that alignment to align the object.
1161 If this macro is not defined, then @var{basic-align} is used.
1164 One use of this macro is to increase alignment of medium-size data to
1165 make it all fit in fewer cache lines. Another is to cause character
1166 arrays to be word-aligned so that @code{strcpy} calls that copy
1167 constants to character arrays can be done inline.
1170 @defmac CONSTANT_ALIGNMENT (@var{constant}, @var{basic-align})
1171 If defined, a C expression to compute the alignment given to a constant
1172 that is being placed in memory. @var{constant} is the constant and
1173 @var{basic-align} is the alignment that the object would ordinarily
1174 have. The value of this macro is used instead of that alignment to
1177 If this macro is not defined, then @var{basic-align} is used.
1179 The typical use of this macro is to increase alignment for string
1180 constants to be word aligned so that @code{strcpy} calls that copy
1181 constants can be done inline.
1184 @defmac LOCAL_ALIGNMENT (@var{type}, @var{basic-align})
1185 If defined, a C expression to compute the alignment for a variable in
1186 the local store. @var{type} is the data type, and @var{basic-align} is
1187 the alignment that the object would ordinarily have. The value of this
1188 macro is used instead of that alignment to align the object.
1190 If this macro is not defined, then @var{basic-align} is used.
1192 One use of this macro is to increase alignment of medium-size data to
1193 make it all fit in fewer cache lines.
1196 @defmac EMPTY_FIELD_BOUNDARY
1197 Alignment in bits to be given to a structure bit-field that follows an
1198 empty field such as @code{int : 0;}.
1200 If @code{PCC_BITFIELD_TYPE_MATTERS} is true, it overrides this macro.
1203 @defmac STRUCTURE_SIZE_BOUNDARY
1204 Number of bits which any structure or union's size must be a multiple of.
1205 Each structure or union's size is rounded up to a multiple of this.
1207 If you do not define this macro, the default is the same as
1208 @code{BITS_PER_UNIT}.
1211 @defmac STRICT_ALIGNMENT
1212 Define this macro to be the value 1 if instructions will fail to work
1213 if given data not on the nominal alignment. If instructions will merely
1214 go slower in that case, define this macro as 0.
1217 @defmac PCC_BITFIELD_TYPE_MATTERS
1218 Define this if you wish to imitate the way many other C compilers handle
1219 alignment of bit-fields and the structures that contain them.
1221 The behavior is that the type written for a named bit-field (@code{int},
1222 @code{short}, or other integer type) imposes an alignment for the entire
1223 structure, as if the structure really did contain an ordinary field of
1224 that type. In addition, the bit-field is placed within the structure so
1225 that it would fit within such a field, not crossing a boundary for it.
1227 Thus, on most machines, a named bit-field whose type is written as
1228 @code{int} would not cross a four-byte boundary, and would force
1229 four-byte alignment for the whole structure. (The alignment used may
1230 not be four bytes; it is controlled by the other alignment parameters.)
1232 An unnamed bit-field will not affect the alignment of the containing
1235 If the macro is defined, its definition should be a C expression;
1236 a nonzero value for the expression enables this behavior.
1238 Note that if this macro is not defined, or its value is zero, some
1239 bit-fields may cross more than one alignment boundary. The compiler can
1240 support such references if there are @samp{insv}, @samp{extv}, and
1241 @samp{extzv} insns that can directly reference memory.
1243 The other known way of making bit-fields work is to define
1244 @code{STRUCTURE_SIZE_BOUNDARY} as large as @code{BIGGEST_ALIGNMENT}.
1245 Then every structure can be accessed with fullwords.
1247 Unless the machine has bit-field instructions or you define
1248 @code{STRUCTURE_SIZE_BOUNDARY} that way, you must define
1249 @code{PCC_BITFIELD_TYPE_MATTERS} to have a nonzero value.
1251 If your aim is to make GCC use the same conventions for laying out
1252 bit-fields as are used by another compiler, here is how to investigate
1253 what the other compiler does. Compile and run this program:
1272 printf ("Size of foo1 is %d\n",
1273 sizeof (struct foo1));
1274 printf ("Size of foo2 is %d\n",
1275 sizeof (struct foo2));
1280 If this prints 2 and 5, then the compiler's behavior is what you would
1281 get from @code{PCC_BITFIELD_TYPE_MATTERS}.
1284 @defmac BITFIELD_NBYTES_LIMITED
1285 Like @code{PCC_BITFIELD_TYPE_MATTERS} except that its effect is limited
1286 to aligning a bit-field within the structure.
1289 @defmac MEMBER_TYPE_FORCES_BLK (@var{field}, @var{mode})
1290 Return 1 if a structure or array containing @var{field} should be accessed using
1293 If @var{field} is the only field in the structure, @var{mode} is its
1294 mode, otherwise @var{mode} is VOIDmode. @var{mode} is provided in the
1295 case where structures of one field would require the structure's mode to
1296 retain the field's mode.
1298 Normally, this is not needed. See the file @file{c4x.h} for an example
1299 of how to use this macro to prevent a structure having a floating point
1300 field from being accessed in an integer mode.
1303 @defmac ROUND_TYPE_ALIGN (@var{type}, @var{computed}, @var{specified})
1304 Define this macro as an expression for the alignment of a type (given
1305 by @var{type} as a tree node) if the alignment computed in the usual
1306 way is @var{computed} and the alignment explicitly specified was
1309 The default is to use @var{specified} if it is larger; otherwise, use
1310 the smaller of @var{computed} and @code{BIGGEST_ALIGNMENT}
1313 @defmac MAX_FIXED_MODE_SIZE
1314 An integer expression for the size in bits of the largest integer
1315 machine mode that should actually be used. All integer machine modes of
1316 this size or smaller can be used for structures and unions with the
1317 appropriate sizes. If this macro is undefined, @code{GET_MODE_BITSIZE
1318 (DImode)} is assumed.
1321 @defmac VECTOR_MODE_SUPPORTED_P (@var{mode})
1322 Define this macro to be nonzero if the port is prepared to handle insns
1323 involving vector mode @var{mode}. At the very least, it must have move
1324 patterns for this mode.
1327 @defmac STACK_SAVEAREA_MODE (@var{save_level})
1328 If defined, an expression of type @code{enum machine_mode} that
1329 specifies the mode of the save area operand of a
1330 @code{save_stack_@var{level}} named pattern (@pxref{Standard Names}).
1331 @var{save_level} is one of @code{SAVE_BLOCK}, @code{SAVE_FUNCTION}, or
1332 @code{SAVE_NONLOCAL} and selects which of the three named patterns is
1333 having its mode specified.
1335 You need not define this macro if it always returns @code{Pmode}. You
1336 would most commonly define this macro if the
1337 @code{save_stack_@var{level}} patterns need to support both a 32- and a
1341 @defmac STACK_SIZE_MODE
1342 If defined, an expression of type @code{enum machine_mode} that
1343 specifies the mode of the size increment operand of an
1344 @code{allocate_stack} named pattern (@pxref{Standard Names}).
1346 You need not define this macro if it always returns @code{word_mode}.
1347 You would most commonly define this macro if the @code{allocate_stack}
1348 pattern needs to support both a 32- and a 64-bit mode.
1351 @defmac TARGET_FLOAT_FORMAT
1352 A code distinguishing the floating point format of the target machine.
1353 There are four defined values:
1356 @item IEEE_FLOAT_FORMAT
1357 This code indicates IEEE floating point. It is the default; there is no
1358 need to define @code{TARGET_FLOAT_FORMAT} when the format is IEEE@.
1360 @item VAX_FLOAT_FORMAT
1361 This code indicates the ``F float'' (for @code{float}) and ``D float''
1362 or ``G float'' formats (for @code{double}) used on the VAX and PDP-11@.
1364 @item IBM_FLOAT_FORMAT
1365 This code indicates the format used on the IBM System/370.
1367 @item C4X_FLOAT_FORMAT
1368 This code indicates the format used on the TMS320C3x/C4x.
1371 If your target uses a floating point format other than these, you must
1372 define a new @var{name}_FLOAT_FORMAT code for it, and add support for
1373 it to @file{real.c}.
1375 The ordering of the component words of floating point values stored in
1376 memory is controlled by @code{FLOAT_WORDS_BIG_ENDIAN}.
1379 @defmac MODE_HAS_NANS (@var{mode})
1380 When defined, this macro should be true if @var{mode} has a NaN
1381 representation. The compiler assumes that NaNs are not equal to
1382 anything (including themselves) and that addition, subtraction,
1383 multiplication and division all return NaNs when one operand is
1386 By default, this macro is true if @var{mode} is a floating-point
1387 mode and the target floating-point format is IEEE@.
1390 @defmac MODE_HAS_INFINITIES (@var{mode})
1391 This macro should be true if @var{mode} can represent infinity. At
1392 present, the compiler uses this macro to decide whether @samp{x - x}
1393 is always defined. By default, the macro is true when @var{mode}
1394 is a floating-point mode and the target format is IEEE@.
1397 @defmac MODE_HAS_SIGNED_ZEROS (@var{mode})
1398 True if @var{mode} distinguishes between positive and negative zero.
1399 The rules are expected to follow the IEEE standard:
1403 @samp{x + x} has the same sign as @samp{x}.
1406 If the sum of two values with opposite sign is zero, the result is
1407 positive for all rounding modes expect towards @minus{}infinity, for
1408 which it is negative.
1411 The sign of a product or quotient is negative when exactly one
1412 of the operands is negative.
1415 The default definition is true if @var{mode} is a floating-point
1416 mode and the target format is IEEE@.
1419 @defmac MODE_HAS_SIGN_DEPENDENT_ROUNDING (@var{mode})
1420 If defined, this macro should be true for @var{mode} if it has at
1421 least one rounding mode in which @samp{x} and @samp{-x} can be
1422 rounded to numbers of different magnitude. Two such modes are
1423 towards @minus{}infinity and towards +infinity.
1425 The default definition of this macro is true if @var{mode} is
1426 a floating-point mode and the target format is IEEE@.
1429 @defmac ROUND_TOWARDS_ZERO
1430 If defined, this macro should be true if the prevailing rounding
1431 mode is towards zero. A true value has the following effects:
1435 @code{MODE_HAS_SIGN_DEPENDENT_ROUNDING} will be false for all modes.
1438 @file{libgcc.a}'s floating-point emulator will round towards zero
1439 rather than towards nearest.
1442 The compiler's floating-point emulator will round towards zero after
1443 doing arithmetic, and when converting from the internal float format to
1447 The macro does not affect the parsing of string literals. When the
1448 primary rounding mode is towards zero, library functions like
1449 @code{strtod} might still round towards nearest, and the compiler's
1450 parser should behave like the target's @code{strtod} where possible.
1452 Not defining this macro is equivalent to returning zero.
1455 @defmac LARGEST_EXPONENT_IS_NORMAL (@var{size})
1456 This macro should return true if floats with @var{size}
1457 bits do not have a NaN or infinity representation, but use the largest
1458 exponent for normal numbers instead.
1460 Defining this macro to true for @var{size} causes @code{MODE_HAS_NANS}
1461 and @code{MODE_HAS_INFINITIES} to be false for @var{size}-bit modes.
1462 It also affects the way @file{libgcc.a} and @file{real.c} emulate
1463 floating-point arithmetic.
1465 The default definition of this macro returns false for all sizes.
1468 @deftypefn {Target Hook} bool TARGET_VECTOR_OPAQUE_P (tree @var{type})
1469 This target hook should return @code{true} a vector is opaque. That
1470 is, if no cast is needed when copying a vector value of type
1471 @var{type} into another vector lvalue of the same size. Vector opaque
1472 types cannot be initialized. The default is that there are no such
1476 @deftypefn {Target Hook} bool TARGET_MS_BITFIELD_LAYOUT_P (tree @var{record_type})
1477 This target hook returns @code{true} if bit-fields in the given
1478 @var{record_type} are to be laid out following the rules of Microsoft
1479 Visual C/C++, namely: (i) a bit-field won't share the same storage
1480 unit with the previous bit-field if their underlying types have
1481 different sizes, and the bit-field will be aligned to the highest
1482 alignment of the underlying types of itself and of the previous
1483 bit-field; (ii) a zero-sized bit-field will affect the alignment of
1484 the whole enclosing structure, even if it is unnamed; except that
1485 (iii) a zero-sized bit-field will be disregarded unless it follows
1486 another bit-field of nonzero size. If this hook returns @code{true},
1487 other macros that control bit-field layout are ignored.
1489 When a bit-field is inserted into a packed record, the whole size
1490 of the underlying type is used by one or more same-size adjacent
1491 bit-fields (that is, if its long:3, 32 bits is used in the record,
1492 and any additional adjacent long bit-fields are packed into the same
1493 chunk of 32 bits. However, if the size changes, a new field of that
1494 size is allocated). In an unpacked record, this is the same as using
1495 alignment, but not equivalent when packing.
1497 If both MS bit-fields and @samp{__attribute__((packed))} are used,
1498 the latter will take precedence. If @samp{__attribute__((packed))} is
1499 used on a single field when MS bit-fields are in use, it will take
1500 precedence for that field, but the alignment of the rest of the structure
1501 may affect its placement.
1505 @section Layout of Source Language Data Types
1507 These macros define the sizes and other characteristics of the standard
1508 basic data types used in programs being compiled. Unlike the macros in
1509 the previous section, these apply to specific features of C and related
1510 languages, rather than to fundamental aspects of storage layout.
1512 @defmac INT_TYPE_SIZE
1513 A C expression for the size in bits of the type @code{int} on the
1514 target machine. If you don't define this, the default is one word.
1517 @defmac SHORT_TYPE_SIZE
1518 A C expression for the size in bits of the type @code{short} on the
1519 target machine. If you don't define this, the default is half a word.
1520 (If this would be less than one storage unit, it is rounded up to one
1524 @defmac LONG_TYPE_SIZE
1525 A C expression for the size in bits of the type @code{long} on the
1526 target machine. If you don't define this, the default is one word.
1529 @defmac ADA_LONG_TYPE_SIZE
1530 On some machines, the size used for the Ada equivalent of the type
1531 @code{long} by a native Ada compiler differs from that used by C. In
1532 that situation, define this macro to be a C expression to be used for
1533 the size of that type. If you don't define this, the default is the
1534 value of @code{LONG_TYPE_SIZE}.
1537 @defmac MAX_LONG_TYPE_SIZE
1538 Maximum number for the size in bits of the type @code{long} on the
1539 target machine. If this is undefined, the default is
1540 @code{LONG_TYPE_SIZE}. Otherwise, it is the constant value that is the
1541 largest value that @code{LONG_TYPE_SIZE} can have at run-time. This is
1545 @defmac LONG_LONG_TYPE_SIZE
1546 A C expression for the size in bits of the type @code{long long} on the
1547 target machine. If you don't define this, the default is two
1548 words. If you want to support GNU Ada on your machine, the value of this
1549 macro must be at least 64.
1552 @defmac CHAR_TYPE_SIZE
1553 A C expression for the size in bits of the type @code{char} on the
1554 target machine. If you don't define this, the default is
1555 @code{BITS_PER_UNIT}.
1558 @defmac BOOL_TYPE_SIZE
1559 A C expression for the size in bits of the C++ type @code{bool} and
1560 C99 type @code{_Bool} on the target machine. If you don't define
1561 this, and you probably shouldn't, the default is @code{CHAR_TYPE_SIZE}.
1564 @defmac FLOAT_TYPE_SIZE
1565 A C expression for the size in bits of the type @code{float} on the
1566 target machine. If you don't define this, the default is one word.
1569 @defmac DOUBLE_TYPE_SIZE
1570 A C expression for the size in bits of the type @code{double} on the
1571 target machine. If you don't define this, the default is two
1575 @defmac LONG_DOUBLE_TYPE_SIZE
1576 A C expression for the size in bits of the type @code{long double} on
1577 the target machine. If you don't define this, the default is two
1581 @defmac MAX_LONG_DOUBLE_TYPE_SIZE
1582 Maximum number for the size in bits of the type @code{long double} on the
1583 target machine. If this is undefined, the default is
1584 @code{LONG_DOUBLE_TYPE_SIZE}. Otherwise, it is the constant value that is
1585 the largest value that @code{LONG_DOUBLE_TYPE_SIZE} can have at run-time.
1586 This is used in @code{cpp}.
1589 @defmac TARGET_FLT_EVAL_METHOD
1590 A C expression for the value for @code{FLT_EVAL_METHOD} in @file{float.h},
1591 assuming, if applicable, that the floating-point control word is in its
1592 default state. If you do not define this macro the value of
1593 @code{FLT_EVAL_METHOD} will be zero.
1596 @defmac WIDEST_HARDWARE_FP_SIZE
1597 A C expression for the size in bits of the widest floating-point format
1598 supported by the hardware. If you define this macro, you must specify a
1599 value less than or equal to the value of @code{LONG_DOUBLE_TYPE_SIZE}.
1600 If you do not define this macro, the value of @code{LONG_DOUBLE_TYPE_SIZE}
1604 @defmac DEFAULT_SIGNED_CHAR
1605 An expression whose value is 1 or 0, according to whether the type
1606 @code{char} should be signed or unsigned by default. The user can
1607 always override this default with the options @option{-fsigned-char}
1608 and @option{-funsigned-char}.
1611 @defmac DEFAULT_SHORT_ENUMS
1612 A C expression to determine whether to give an @code{enum} type
1613 only as many bytes as it takes to represent the range of possible values
1614 of that type. A nonzero value means to do that; a zero value means all
1615 @code{enum} types should be allocated like @code{int}.
1617 If you don't define the macro, the default is 0.
1621 A C expression for a string describing the name of the data type to use
1622 for size values. The typedef name @code{size_t} is defined using the
1623 contents of the string.
1625 The string can contain more than one keyword. If so, separate them with
1626 spaces, and write first any length keyword, then @code{unsigned} if
1627 appropriate, and finally @code{int}. The string must exactly match one
1628 of the data type names defined in the function
1629 @code{init_decl_processing} in the file @file{c-decl.c}. You may not
1630 omit @code{int} or change the order---that would cause the compiler to
1633 If you don't define this macro, the default is @code{"long unsigned
1637 @defmac PTRDIFF_TYPE
1638 A C expression for a string describing the name of the data type to use
1639 for the result of subtracting two pointers. The typedef name
1640 @code{ptrdiff_t} is defined using the contents of the string. See
1641 @code{SIZE_TYPE} above for more information.
1643 If you don't define this macro, the default is @code{"long int"}.
1647 A C expression for a string describing the name of the data type to use
1648 for wide characters. The typedef name @code{wchar_t} is defined using
1649 the contents of the string. See @code{SIZE_TYPE} above for more
1652 If you don't define this macro, the default is @code{"int"}.
1655 @defmac WCHAR_TYPE_SIZE
1656 A C expression for the size in bits of the data type for wide
1657 characters. This is used in @code{cpp}, which cannot make use of
1661 @defmac MAX_WCHAR_TYPE_SIZE
1662 Maximum number for the size in bits of the data type for wide
1663 characters. If this is undefined, the default is
1664 @code{WCHAR_TYPE_SIZE}. Otherwise, it is the constant value that is the
1665 largest value that @code{WCHAR_TYPE_SIZE} can have at run-time. This is
1669 @defmac GCOV_TYPE_SIZE
1670 A C expression for the size in bits of the type used for gcov counters on the
1671 target machine. If you don't define this, the default is one
1672 @code{LONG_TYPE_SIZE} in case it is greater or equal to 64-bit and
1673 @code{LONG_LONG_TYPE_SIZE} otherwise. You may want to re-define the type to
1674 ensure atomicity for counters in multithreaded programs.
1678 A C expression for a string describing the name of the data type to
1679 use for wide characters passed to @code{printf} and returned from
1680 @code{getwc}. The typedef name @code{wint_t} is defined using the
1681 contents of the string. See @code{SIZE_TYPE} above for more
1684 If you don't define this macro, the default is @code{"unsigned int"}.
1688 A C expression for a string describing the name of the data type that
1689 can represent any value of any standard or extended signed integer type.
1690 The typedef name @code{intmax_t} is defined using the contents of the
1691 string. See @code{SIZE_TYPE} above for more information.
1693 If you don't define this macro, the default is the first of
1694 @code{"int"}, @code{"long int"}, or @code{"long long int"} that has as
1695 much precision as @code{long long int}.
1698 @defmac UINTMAX_TYPE
1699 A C expression for a string describing the name of the data type that
1700 can represent any value of any standard or extended unsigned integer
1701 type. The typedef name @code{uintmax_t} is defined using the contents
1702 of the string. See @code{SIZE_TYPE} above for more information.
1704 If you don't define this macro, the default is the first of
1705 @code{"unsigned int"}, @code{"long unsigned int"}, or @code{"long long
1706 unsigned int"} that has as much precision as @code{long long unsigned
1710 @defmac TARGET_PTRMEMFUNC_VBIT_LOCATION
1711 The C++ compiler represents a pointer-to-member-function with a struct
1718 ptrdiff_t vtable_index;
1725 The C++ compiler must use one bit to indicate whether the function that
1726 will be called through a pointer-to-member-function is virtual.
1727 Normally, we assume that the low-order bit of a function pointer must
1728 always be zero. Then, by ensuring that the vtable_index is odd, we can
1729 distinguish which variant of the union is in use. But, on some
1730 platforms function pointers can be odd, and so this doesn't work. In
1731 that case, we use the low-order bit of the @code{delta} field, and shift
1732 the remainder of the @code{delta} field to the left.
1734 GCC will automatically make the right selection about where to store
1735 this bit using the @code{FUNCTION_BOUNDARY} setting for your platform.
1736 However, some platforms such as ARM/Thumb have @code{FUNCTION_BOUNDARY}
1737 set such that functions always start at even addresses, but the lowest
1738 bit of pointers to functions indicate whether the function at that
1739 address is in ARM or Thumb mode. If this is the case of your
1740 architecture, you should define this macro to
1741 @code{ptrmemfunc_vbit_in_delta}.
1743 In general, you should not have to define this macro. On architectures
1744 in which function addresses are always even, according to
1745 @code{FUNCTION_BOUNDARY}, GCC will automatically define this macro to
1746 @code{ptrmemfunc_vbit_in_pfn}.
1749 @defmac TARGET_VTABLE_USES_DESCRIPTORS
1750 Normally, the C++ compiler uses function pointers in vtables. This
1751 macro allows the target to change to use ``function descriptors''
1752 instead. Function descriptors are found on targets for whom a
1753 function pointer is actually a small data structure. Normally the
1754 data structure consists of the actual code address plus a data
1755 pointer to which the function's data is relative.
1757 If vtables are used, the value of this macro should be the number
1758 of words that the function descriptor occupies.
1761 @defmac TARGET_VTABLE_ENTRY_ALIGN
1762 By default, the vtable entries are void pointers, the so the alignment
1763 is the same as pointer alignment. The value of this macro specifies
1764 the alignment of the vtable entry in bits. It should be defined only
1765 when special alignment is necessary. */
1768 @defmac TARGET_VTABLE_DATA_ENTRY_DISTANCE
1769 There are a few non-descriptor entries in the vtable at offsets below
1770 zero. If these entries must be padded (say, to preserve the alignment
1771 specified by @code{TARGET_VTABLE_ENTRY_ALIGN}), set this to the number
1772 of words in each data entry.
1775 @node Escape Sequences
1776 @section Target Character Escape Sequences
1777 @cindex escape sequences
1779 By default, GCC assumes that the C character escape sequences take on
1780 their ASCII values for the target. If this is not correct, you must
1781 explicitly define all of the macros below. All of them must evaluate
1782 to constants; they are used in @code{case} statements.
1788 @findex TARGET_NEWLINE
1791 @multitable {@code{TARGET_NEWLINE}} {Escape} {ASCII character}
1792 @item Macro @tab Escape @tab ASCII character
1793 @item @code{TARGET_BELL} @tab @kbd{\a} @tab @code{07}, @code{BEL}
1794 @item @code{TARGET_CR} @tab @kbd{\r} @tab @code{0D}, @code{CR}
1795 @item @code{TARGET_ESC} @tab @kbd{\e}, @kbd{\E} @tab @code{1B}, @code{ESC}
1796 @item @code{TARGET_FF} @tab @kbd{\f} @tab @code{0C}, @code{FF}
1797 @item @code{TARGET_NEWLINE} @tab @kbd{\n} @tab @code{0A}, @code{LF}
1798 @item @code{TARGET_TAB} @tab @kbd{\t} @tab @code{09}, @code{HT}
1799 @item @code{TARGET_VT} @tab @kbd{\v} @tab @code{0B}, @code{VT}
1803 Note that the @kbd{\e} and @kbd{\E} escapes are GNU extensions, not
1804 part of the C standard.
1807 @section Register Usage
1808 @cindex register usage
1810 This section explains how to describe what registers the target machine
1811 has, and how (in general) they can be used.
1813 The description of which registers a specific instruction can use is
1814 done with register classes; see @ref{Register Classes}. For information
1815 on using registers to access a stack frame, see @ref{Frame Registers}.
1816 For passing values in registers, see @ref{Register Arguments}.
1817 For returning values in registers, see @ref{Scalar Return}.
1820 * Register Basics:: Number and kinds of registers.
1821 * Allocation Order:: Order in which registers are allocated.
1822 * Values in Registers:: What kinds of values each reg can hold.
1823 * Leaf Functions:: Renumbering registers for leaf functions.
1824 * Stack Registers:: Handling a register stack such as 80387.
1827 @node Register Basics
1828 @subsection Basic Characteristics of Registers
1830 @c prevent bad page break with this line
1831 Registers have various characteristics.
1833 @defmac FIRST_PSEUDO_REGISTER
1834 Number of hardware registers known to the compiler. They receive
1835 numbers 0 through @code{FIRST_PSEUDO_REGISTER-1}; thus, the first
1836 pseudo register's number really is assigned the number
1837 @code{FIRST_PSEUDO_REGISTER}.
1840 @defmac FIXED_REGISTERS
1841 @cindex fixed register
1842 An initializer that says which registers are used for fixed purposes
1843 all throughout the compiled code and are therefore not available for
1844 general allocation. These would include the stack pointer, the frame
1845 pointer (except on machines where that can be used as a general
1846 register when no frame pointer is needed), the program counter on
1847 machines where that is considered one of the addressable registers,
1848 and any other numbered register with a standard use.
1850 This information is expressed as a sequence of numbers, separated by
1851 commas and surrounded by braces. The @var{n}th number is 1 if
1852 register @var{n} is fixed, 0 otherwise.
1854 The table initialized from this macro, and the table initialized by
1855 the following one, may be overridden at run time either automatically,
1856 by the actions of the macro @code{CONDITIONAL_REGISTER_USAGE}, or by
1857 the user with the command options @option{-ffixed-@var{reg}},
1858 @option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}}.
1861 @defmac CALL_USED_REGISTERS
1862 @cindex call-used register
1863 @cindex call-clobbered register
1864 @cindex call-saved register
1865 Like @code{FIXED_REGISTERS} but has 1 for each register that is
1866 clobbered (in general) by function calls as well as for fixed
1867 registers. This macro therefore identifies the registers that are not
1868 available for general allocation of values that must live across
1871 If a register has 0 in @code{CALL_USED_REGISTERS}, the compiler
1872 automatically saves it on function entry and restores it on function
1873 exit, if the register is used within the function.
1876 @defmac CALL_REALLY_USED_REGISTERS
1877 @cindex call-used register
1878 @cindex call-clobbered register
1879 @cindex call-saved register
1880 Like @code{CALL_USED_REGISTERS} except this macro doesn't require
1881 that the entire set of @code{FIXED_REGISTERS} be included.
1882 (@code{CALL_USED_REGISTERS} must be a superset of @code{FIXED_REGISTERS}).
1883 This macro is optional. If not specified, it defaults to the value
1884 of @code{CALL_USED_REGISTERS}.
1887 @defmac HARD_REGNO_CALL_PART_CLOBBERED (@var{regno}, @var{mode})
1888 @cindex call-used register
1889 @cindex call-clobbered register
1890 @cindex call-saved register
1891 A C expression that is nonzero if it is not permissible to store a
1892 value of mode @var{mode} in hard register number @var{regno} across a
1893 call without some part of it being clobbered. For most machines this
1894 macro need not be defined. It is only required for machines that do not
1895 preserve the entire contents of a register across a call.
1899 @findex call_used_regs
1902 @findex reg_class_contents
1903 @defmac CONDITIONAL_REGISTER_USAGE
1904 Zero or more C statements that may conditionally modify five variables
1905 @code{fixed_regs}, @code{call_used_regs}, @code{global_regs},
1906 @code{reg_names}, and @code{reg_class_contents}, to take into account
1907 any dependence of these register sets on target flags. The first three
1908 of these are of type @code{char []} (interpreted as Boolean vectors).
1909 @code{global_regs} is a @code{const char *[]}, and
1910 @code{reg_class_contents} is a @code{HARD_REG_SET}. Before the macro is
1911 called, @code{fixed_regs}, @code{call_used_regs},
1912 @code{reg_class_contents}, and @code{reg_names} have been initialized
1913 from @code{FIXED_REGISTERS}, @code{CALL_USED_REGISTERS},
1914 @code{REG_CLASS_CONTENTS}, and @code{REGISTER_NAMES}, respectively.
1915 @code{global_regs} has been cleared, and any @option{-ffixed-@var{reg}},
1916 @option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}}
1917 command options have been applied.
1919 You need not define this macro if it has no work to do.
1921 @cindex disabling certain registers
1922 @cindex controlling register usage
1923 If the usage of an entire class of registers depends on the target
1924 flags, you may indicate this to GCC by using this macro to modify
1925 @code{fixed_regs} and @code{call_used_regs} to 1 for each of the
1926 registers in the classes which should not be used by GCC@. Also define
1927 the macro @code{REG_CLASS_FROM_LETTER} / @code{REG_CLASS_FROM_CONSTRAINT}
1928 to return @code{NO_REGS} if it
1929 is called with a letter for a class that shouldn't be used.
1931 (However, if this class is not included in @code{GENERAL_REGS} and all
1932 of the insn patterns whose constraints permit this class are
1933 controlled by target switches, then GCC will automatically avoid using
1934 these registers when the target switches are opposed to them.)
1937 @defmac NON_SAVING_SETJMP
1938 If this macro is defined and has a nonzero value, it means that
1939 @code{setjmp} and related functions fail to save the registers, or that
1940 @code{longjmp} fails to restore them. To compensate, the compiler
1941 avoids putting variables in registers in functions that use
1945 @defmac INCOMING_REGNO (@var{out})
1946 Define this macro if the target machine has register windows. This C
1947 expression returns the register number as seen by the called function
1948 corresponding to the register number @var{out} as seen by the calling
1949 function. Return @var{out} if register number @var{out} is not an
1953 @defmac OUTGOING_REGNO (@var{in})
1954 Define this macro if the target machine has register windows. This C
1955 expression returns the register number as seen by the calling function
1956 corresponding to the register number @var{in} as seen by the called
1957 function. Return @var{in} if register number @var{in} is not an inbound
1961 @defmac LOCAL_REGNO (@var{regno})
1962 Define this macro if the target machine has register windows. This C
1963 expression returns true if the register is call-saved but is in the
1964 register window. Unlike most call-saved registers, such registers
1965 need not be explicitly restored on function exit or during non-local
1970 If the program counter has a register number, define this as that
1971 register number. Otherwise, do not define it.
1974 @node Allocation Order
1975 @subsection Order of Allocation of Registers
1976 @cindex order of register allocation
1977 @cindex register allocation order
1979 @c prevent bad page break with this line
1980 Registers are allocated in order.
1982 @defmac REG_ALLOC_ORDER
1983 If defined, an initializer for a vector of integers, containing the
1984 numbers of hard registers in the order in which GCC should prefer
1985 to use them (from most preferred to least).
1987 If this macro is not defined, registers are used lowest numbered first
1988 (all else being equal).
1990 One use of this macro is on machines where the highest numbered
1991 registers must always be saved and the save-multiple-registers
1992 instruction supports only sequences of consecutive registers. On such
1993 machines, define @code{REG_ALLOC_ORDER} to be an initializer that lists
1994 the highest numbered allocable register first.
1997 @defmac ORDER_REGS_FOR_LOCAL_ALLOC
1998 A C statement (sans semicolon) to choose the order in which to allocate
1999 hard registers for pseudo-registers local to a basic block.
2001 Store the desired register order in the array @code{reg_alloc_order}.
2002 Element 0 should be the register to allocate first; element 1, the next
2003 register; and so on.
2005 The macro body should not assume anything about the contents of
2006 @code{reg_alloc_order} before execution of the macro.
2008 On most machines, it is not necessary to define this macro.
2011 @node Values in Registers
2012 @subsection How Values Fit in Registers
2014 This section discusses the macros that describe which kinds of values
2015 (specifically, which machine modes) each register can hold, and how many
2016 consecutive registers are needed for a given mode.
2018 @defmac HARD_REGNO_NREGS (@var{regno}, @var{mode})
2019 A C expression for the number of consecutive hard registers, starting
2020 at register number @var{regno}, required to hold a value of mode
2023 On a machine where all registers are exactly one word, a suitable
2024 definition of this macro is
2027 #define HARD_REGNO_NREGS(REGNO, MODE) \
2028 ((GET_MODE_SIZE (MODE) + UNITS_PER_WORD - 1) \
2033 @defmac HARD_REGNO_MODE_OK (@var{regno}, @var{mode})
2034 A C expression that is nonzero if it is permissible to store a value
2035 of mode @var{mode} in hard register number @var{regno} (or in several
2036 registers starting with that one). For a machine where all registers
2037 are equivalent, a suitable definition is
2040 #define HARD_REGNO_MODE_OK(REGNO, MODE) 1
2043 You need not include code to check for the numbers of fixed registers,
2044 because the allocation mechanism considers them to be always occupied.
2046 @cindex register pairs
2047 On some machines, double-precision values must be kept in even/odd
2048 register pairs. You can implement that by defining this macro to reject
2049 odd register numbers for such modes.
2051 The minimum requirement for a mode to be OK in a register is that the
2052 @samp{mov@var{mode}} instruction pattern support moves between the
2053 register and other hard register in the same class and that moving a
2054 value into the register and back out not alter it.
2056 Since the same instruction used to move @code{word_mode} will work for
2057 all narrower integer modes, it is not necessary on any machine for
2058 @code{HARD_REGNO_MODE_OK} to distinguish between these modes, provided
2059 you define patterns @samp{movhi}, etc., to take advantage of this. This
2060 is useful because of the interaction between @code{HARD_REGNO_MODE_OK}
2061 and @code{MODES_TIEABLE_P}; it is very desirable for all integer modes
2064 Many machines have special registers for floating point arithmetic.
2065 Often people assume that floating point machine modes are allowed only
2066 in floating point registers. This is not true. Any registers that
2067 can hold integers can safely @emph{hold} a floating point machine
2068 mode, whether or not floating arithmetic can be done on it in those
2069 registers. Integer move instructions can be used to move the values.
2071 On some machines, though, the converse is true: fixed-point machine
2072 modes may not go in floating registers. This is true if the floating
2073 registers normalize any value stored in them, because storing a
2074 non-floating value there would garble it. In this case,
2075 @code{HARD_REGNO_MODE_OK} should reject fixed-point machine modes in
2076 floating registers. But if the floating registers do not automatically
2077 normalize, if you can store any bit pattern in one and retrieve it
2078 unchanged without a trap, then any machine mode may go in a floating
2079 register, so you can define this macro to say so.
2081 The primary significance of special floating registers is rather that
2082 they are the registers acceptable in floating point arithmetic
2083 instructions. However, this is of no concern to
2084 @code{HARD_REGNO_MODE_OK}. You handle it by writing the proper
2085 constraints for those instructions.
2087 On some machines, the floating registers are especially slow to access,
2088 so that it is better to store a value in a stack frame than in such a
2089 register if floating point arithmetic is not being done. As long as the
2090 floating registers are not in class @code{GENERAL_REGS}, they will not
2091 be used unless some pattern's constraint asks for one.
2094 @defmac MODES_TIEABLE_P (@var{mode1}, @var{mode2})
2095 A C expression that is nonzero if a value of mode
2096 @var{mode1} is accessible in mode @var{mode2} without copying.
2098 If @code{HARD_REGNO_MODE_OK (@var{r}, @var{mode1})} and
2099 @code{HARD_REGNO_MODE_OK (@var{r}, @var{mode2})} are always the same for
2100 any @var{r}, then @code{MODES_TIEABLE_P (@var{mode1}, @var{mode2})}
2101 should be nonzero. If they differ for any @var{r}, you should define
2102 this macro to return zero unless some other mechanism ensures the
2103 accessibility of the value in a narrower mode.
2105 You should define this macro to return nonzero in as many cases as
2106 possible since doing so will allow GCC to perform better register
2110 @defmac AVOID_CCMODE_COPIES
2111 Define this macro if the compiler should avoid copies to/from @code{CCmode}
2112 registers. You should only define this macro if support for copying to/from
2113 @code{CCmode} is incomplete.
2116 @node Leaf Functions
2117 @subsection Handling Leaf Functions
2119 @cindex leaf functions
2120 @cindex functions, leaf
2121 On some machines, a leaf function (i.e., one which makes no calls) can run
2122 more efficiently if it does not make its own register window. Often this
2123 means it is required to receive its arguments in the registers where they
2124 are passed by the caller, instead of the registers where they would
2127 The special treatment for leaf functions generally applies only when
2128 other conditions are met; for example, often they may use only those
2129 registers for its own variables and temporaries. We use the term ``leaf
2130 function'' to mean a function that is suitable for this special
2131 handling, so that functions with no calls are not necessarily ``leaf
2134 GCC assigns register numbers before it knows whether the function is
2135 suitable for leaf function treatment. So it needs to renumber the
2136 registers in order to output a leaf function. The following macros
2139 @defmac LEAF_REGISTERS
2140 Name of a char vector, indexed by hard register number, which
2141 contains 1 for a register that is allowable in a candidate for leaf
2144 If leaf function treatment involves renumbering the registers, then the
2145 registers marked here should be the ones before renumbering---those that
2146 GCC would ordinarily allocate. The registers which will actually be
2147 used in the assembler code, after renumbering, should not be marked with 1
2150 Define this macro only if the target machine offers a way to optimize
2151 the treatment of leaf functions.
2154 @defmac LEAF_REG_REMAP (@var{regno})
2155 A C expression whose value is the register number to which @var{regno}
2156 should be renumbered, when a function is treated as a leaf function.
2158 If @var{regno} is a register number which should not appear in a leaf
2159 function before renumbering, then the expression should yield @minus{}1, which
2160 will cause the compiler to abort.
2162 Define this macro only if the target machine offers a way to optimize the
2163 treatment of leaf functions, and registers need to be renumbered to do
2167 @findex current_function_is_leaf
2168 @findex current_function_uses_only_leaf_regs
2169 @code{TARGET_ASM_FUNCTION_PROLOGUE} and
2170 @code{TARGET_ASM_FUNCTION_EPILOGUE} must usually treat leaf functions
2171 specially. They can test the C variable @code{current_function_is_leaf}
2172 which is nonzero for leaf functions. @code{current_function_is_leaf} is
2173 set prior to local register allocation and is valid for the remaining
2174 compiler passes. They can also test the C variable
2175 @code{current_function_uses_only_leaf_regs} which is nonzero for leaf
2176 functions which only use leaf registers.
2177 @code{current_function_uses_only_leaf_regs} is valid after reload and is
2178 only useful if @code{LEAF_REGISTERS} is defined.
2179 @c changed this to fix overfull. ALSO: why the "it" at the beginning
2180 @c of the next paragraph?! --mew 2feb93
2182 @node Stack Registers
2183 @subsection Registers That Form a Stack
2185 There are special features to handle computers where some of the
2186 ``registers'' form a stack. Stack registers are normally written by
2187 pushing onto the stack, and are numbered relative to the top of the
2190 Currently, GCC can only handle one group of stack-like registers, and
2191 they must be consecutively numbered. Furthermore, the existing
2192 support for stack-like registers is specific to the 80387 floating
2193 point coprocessor. If you have a new architecture that uses
2194 stack-like registers, you will need to do substantial work on
2195 @file{reg-stack.c} and write your machine description to cooperate
2196 with it, as well as defining these macros.
2199 Define this if the machine has any stack-like registers.
2202 @defmac FIRST_STACK_REG
2203 The number of the first stack-like register. This one is the top
2207 @defmac LAST_STACK_REG
2208 The number of the last stack-like register. This one is the bottom of
2212 @node Register Classes
2213 @section Register Classes
2214 @cindex register class definitions
2215 @cindex class definitions, register
2217 On many machines, the numbered registers are not all equivalent.
2218 For example, certain registers may not be allowed for indexed addressing;
2219 certain registers may not be allowed in some instructions. These machine
2220 restrictions are described to the compiler using @dfn{register classes}.
2222 You define a number of register classes, giving each one a name and saying
2223 which of the registers belong to it. Then you can specify register classes
2224 that are allowed as operands to particular instruction patterns.
2228 In general, each register will belong to several classes. In fact, one
2229 class must be named @code{ALL_REGS} and contain all the registers. Another
2230 class must be named @code{NO_REGS} and contain no registers. Often the
2231 union of two classes will be another class; however, this is not required.
2233 @findex GENERAL_REGS
2234 One of the classes must be named @code{GENERAL_REGS}. There is nothing
2235 terribly special about the name, but the operand constraint letters
2236 @samp{r} and @samp{g} specify this class. If @code{GENERAL_REGS} is
2237 the same as @code{ALL_REGS}, just define it as a macro which expands
2240 Order the classes so that if class @var{x} is contained in class @var{y}
2241 then @var{x} has a lower class number than @var{y}.
2243 The way classes other than @code{GENERAL_REGS} are specified in operand
2244 constraints is through machine-dependent operand constraint letters.
2245 You can define such letters to correspond to various classes, then use
2246 them in operand constraints.
2248 You should define a class for the union of two classes whenever some
2249 instruction allows both classes. For example, if an instruction allows
2250 either a floating point (coprocessor) register or a general register for a
2251 certain operand, you should define a class @code{FLOAT_OR_GENERAL_REGS}
2252 which includes both of them. Otherwise you will get suboptimal code.
2254 You must also specify certain redundant information about the register
2255 classes: for each class, which classes contain it and which ones are
2256 contained in it; for each pair of classes, the largest class contained
2259 When a value occupying several consecutive registers is expected in a
2260 certain class, all the registers used must belong to that class.
2261 Therefore, register classes cannot be used to enforce a requirement for
2262 a register pair to start with an even-numbered register. The way to
2263 specify this requirement is with @code{HARD_REGNO_MODE_OK}.
2265 Register classes used for input-operands of bitwise-and or shift
2266 instructions have a special requirement: each such class must have, for
2267 each fixed-point machine mode, a subclass whose registers can transfer that
2268 mode to or from memory. For example, on some machines, the operations for
2269 single-byte values (@code{QImode}) are limited to certain registers. When
2270 this is so, each register class that is used in a bitwise-and or shift
2271 instruction must have a subclass consisting of registers from which
2272 single-byte values can be loaded or stored. This is so that
2273 @code{PREFERRED_RELOAD_CLASS} can always have a possible value to return.
2275 @deftp {Data type} {enum reg_class}
2276 An enumeral type that must be defined with all the register class names
2277 as enumeral values. @code{NO_REGS} must be first. @code{ALL_REGS}
2278 must be the last register class, followed by one more enumeral value,
2279 @code{LIM_REG_CLASSES}, which is not a register class but rather
2280 tells how many classes there are.
2282 Each register class has a number, which is the value of casting
2283 the class name to type @code{int}. The number serves as an index
2284 in many of the tables described below.
2287 @defmac N_REG_CLASSES
2288 The number of distinct register classes, defined as follows:
2291 #define N_REG_CLASSES (int) LIM_REG_CLASSES
2295 @defmac REG_CLASS_NAMES
2296 An initializer containing the names of the register classes as C string
2297 constants. These names are used in writing some of the debugging dumps.
2300 @defmac REG_CLASS_CONTENTS
2301 An initializer containing the contents of the register classes, as integers
2302 which are bit masks. The @var{n}th integer specifies the contents of class
2303 @var{n}. The way the integer @var{mask} is interpreted is that
2304 register @var{r} is in the class if @code{@var{mask} & (1 << @var{r})} is 1.
2306 When the machine has more than 32 registers, an integer does not suffice.
2307 Then the integers are replaced by sub-initializers, braced groupings containing
2308 several integers. Each sub-initializer must be suitable as an initializer
2309 for the type @code{HARD_REG_SET} which is defined in @file{hard-reg-set.h}.
2310 In this situation, the first integer in each sub-initializer corresponds to
2311 registers 0 through 31, the second integer to registers 32 through 63, and
2315 @defmac REGNO_REG_CLASS (@var{regno})
2316 A C expression whose value is a register class containing hard register
2317 @var{regno}. In general there is more than one such class; choose a class
2318 which is @dfn{minimal}, meaning that no smaller class also contains the
2322 @defmac BASE_REG_CLASS
2323 A macro whose definition is the name of the class to which a valid
2324 base register must belong. A base register is one used in an address
2325 which is the register value plus a displacement.
2328 @defmac MODE_BASE_REG_CLASS (@var{mode})
2329 This is a variation of the @code{BASE_REG_CLASS} macro which allows
2330 the selection of a base register in a mode dependent manner. If
2331 @var{mode} is VOIDmode then it should return the same value as
2332 @code{BASE_REG_CLASS}.
2335 @defmac INDEX_REG_CLASS
2336 A macro whose definition is the name of the class to which a valid
2337 index register must belong. An index register is one used in an
2338 address where its value is either multiplied by a scale factor or
2339 added to another register (as well as added to a displacement).
2342 @defmac CONSTRAINT_LEN (@var{char}, @var{str})
2343 For the constraint at the start of @var{str}, which starts with the letter
2344 @var{c}, return the length. This allows you to have register class /
2345 constant / extra constraints that are longer than a single letter;
2346 you don't need to define this macro if you can do with single-letter
2347 constraints only. The definition of this macro should use
2348 DEFAULT_CONSTRAINT_LEN for all the characters that you don't want
2349 to handle specially.
2350 There are some sanity checks in genoutput.c that check the constraint lengths
2351 for the md file, so you can also use this macro to help you while you are
2352 transitioning from a byzantine single-letter-constraint scheme: when you
2353 return a negative length for a constraint you want to re-use, genoutput
2354 will complain about every instance where it is used in the md file.
2357 @defmac REG_CLASS_FROM_LETTER (@var{char})
2358 A C expression which defines the machine-dependent operand constraint
2359 letters for register classes. If @var{char} is such a letter, the
2360 value should be the register class corresponding to it. Otherwise,
2361 the value should be @code{NO_REGS}. The register letter @samp{r},
2362 corresponding to class @code{GENERAL_REGS}, will not be passed
2363 to this macro; you do not need to handle it.
2366 @defmac REG_CLASS_FROM_CONSTRAINT (@var{char}, @var{str})
2367 Like @code{REG_CLASS_FROM_LETTER}, but you also get the constraint string
2368 passed in @var{str}, so that you can use suffixes to distinguish between
2372 @defmac REGNO_OK_FOR_BASE_P (@var{num})
2373 A C expression which is nonzero if register number @var{num} is
2374 suitable for use as a base register in operand addresses. It may be
2375 either a suitable hard register or a pseudo register that has been
2376 allocated such a hard register.
2379 @defmac REGNO_MODE_OK_FOR_BASE_P (@var{num}, @var{mode})
2380 A C expression that is just like @code{REGNO_OK_FOR_BASE_P}, except that
2381 that expression may examine the mode of the memory reference in
2382 @var{mode}. You should define this macro if the mode of the memory
2383 reference affects whether a register may be used as a base register. If
2384 you define this macro, the compiler will use it instead of
2385 @code{REGNO_OK_FOR_BASE_P}.
2388 @defmac REGNO_OK_FOR_INDEX_P (@var{num})
2389 A C expression which is nonzero if register number @var{num} is
2390 suitable for use as an index register in operand addresses. It may be
2391 either a suitable hard register or a pseudo register that has been
2392 allocated such a hard register.
2394 The difference between an index register and a base register is that
2395 the index register may be scaled. If an address involves the sum of
2396 two registers, neither one of them scaled, then either one may be
2397 labeled the ``base'' and the other the ``index''; but whichever
2398 labeling is used must fit the machine's constraints of which registers
2399 may serve in each capacity. The compiler will try both labelings,
2400 looking for one that is valid, and will reload one or both registers
2401 only if neither labeling works.
2404 @defmac PREFERRED_RELOAD_CLASS (@var{x}, @var{class})
2405 A C expression that places additional restrictions on the register class
2406 to use when it is necessary to copy value @var{x} into a register in class
2407 @var{class}. The value is a register class; perhaps @var{class}, or perhaps
2408 another, smaller class. On many machines, the following definition is
2412 #define PREFERRED_RELOAD_CLASS(X,CLASS) CLASS
2415 Sometimes returning a more restrictive class makes better code. For
2416 example, on the 68000, when @var{x} is an integer constant that is in range
2417 for a @samp{moveq} instruction, the value of this macro is always
2418 @code{DATA_REGS} as long as @var{class} includes the data registers.
2419 Requiring a data register guarantees that a @samp{moveq} will be used.
2421 If @var{x} is a @code{const_double}, by returning @code{NO_REGS}
2422 you can force @var{x} into a memory constant. This is useful on
2423 certain machines where immediate floating values cannot be loaded into
2424 certain kinds of registers.
2427 @defmac PREFERRED_OUTPUT_RELOAD_CLASS (@var{x}, @var{class})
2428 Like @code{PREFERRED_RELOAD_CLASS}, but for output reloads instead of
2429 input reloads. If you don't define this macro, the default is to use
2430 @var{class}, unchanged.
2433 @defmac LIMIT_RELOAD_CLASS (@var{mode}, @var{class})
2434 A C expression that places additional restrictions on the register class
2435 to use when it is necessary to be able to hold a value of mode
2436 @var{mode} in a reload register for which class @var{class} would
2439 Unlike @code{PREFERRED_RELOAD_CLASS}, this macro should be used when
2440 there are certain modes that simply can't go in certain reload classes.
2442 The value is a register class; perhaps @var{class}, or perhaps another,
2445 Don't define this macro unless the target machine has limitations which
2446 require the macro to do something nontrivial.
2449 @defmac SECONDARY_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
2450 @defmacx SECONDARY_INPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
2451 @defmacx SECONDARY_OUTPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
2452 Many machines have some registers that cannot be copied directly to or
2453 from memory or even from other types of registers. An example is the
2454 @samp{MQ} register, which on most machines, can only be copied to or
2455 from general registers, but not memory. Some machines allow copying all
2456 registers to and from memory, but require a scratch register for stores
2457 to some memory locations (e.g., those with symbolic address on the RT,
2458 and those with certain symbolic address on the SPARC when compiling
2459 PIC)@. In some cases, both an intermediate and a scratch register are
2462 You should define these macros to indicate to the reload phase that it may
2463 need to allocate at least one register for a reload in addition to the
2464 register to contain the data. Specifically, if copying @var{x} to a
2465 register @var{class} in @var{mode} requires an intermediate register,
2466 you should define @code{SECONDARY_INPUT_RELOAD_CLASS} to return the
2467 largest register class all of whose registers can be used as
2468 intermediate registers or scratch registers.
2470 If copying a register @var{class} in @var{mode} to @var{x} requires an
2471 intermediate or scratch register, @code{SECONDARY_OUTPUT_RELOAD_CLASS}
2472 should be defined to return the largest register class required. If the
2473 requirements for input and output reloads are the same, the macro
2474 @code{SECONDARY_RELOAD_CLASS} should be used instead of defining both
2477 The values returned by these macros are often @code{GENERAL_REGS}.
2478 Return @code{NO_REGS} if no spare register is needed; i.e., if @var{x}
2479 can be directly copied to or from a register of @var{class} in
2480 @var{mode} without requiring a scratch register. Do not define this
2481 macro if it would always return @code{NO_REGS}.
2483 If a scratch register is required (either with or without an
2484 intermediate register), you should define patterns for
2485 @samp{reload_in@var{m}} or @samp{reload_out@var{m}}, as required
2486 (@pxref{Standard Names}. These patterns, which will normally be
2487 implemented with a @code{define_expand}, should be similar to the
2488 @samp{mov@var{m}} patterns, except that operand 2 is the scratch
2491 Define constraints for the reload register and scratch register that
2492 contain a single register class. If the original reload register (whose
2493 class is @var{class}) can meet the constraint given in the pattern, the
2494 value returned by these macros is used for the class of the scratch
2495 register. Otherwise, two additional reload registers are required.
2496 Their classes are obtained from the constraints in the insn pattern.
2498 @var{x} might be a pseudo-register or a @code{subreg} of a
2499 pseudo-register, which could either be in a hard register or in memory.
2500 Use @code{true_regnum} to find out; it will return @minus{}1 if the pseudo is
2501 in memory and the hard register number if it is in a register.
2503 These macros should not be used in the case where a particular class of
2504 registers can only be copied to memory and not to another class of
2505 registers. In that case, secondary reload registers are not needed and
2506 would not be helpful. Instead, a stack location must be used to perform
2507 the copy and the @code{mov@var{m}} pattern should use memory as an
2508 intermediate storage. This case often occurs between floating-point and
2512 @defmac SECONDARY_MEMORY_NEEDED (@var{class1}, @var{class2}, @var{m})
2513 Certain machines have the property that some registers cannot be copied
2514 to some other registers without using memory. Define this macro on
2515 those machines to be a C expression that is nonzero if objects of mode
2516 @var{m} in registers of @var{class1} can only be copied to registers of
2517 class @var{class2} by storing a register of @var{class1} into memory
2518 and loading that memory location into a register of @var{class2}.
2520 Do not define this macro if its value would always be zero.
2523 @defmac SECONDARY_MEMORY_NEEDED_RTX (@var{mode})
2524 Normally when @code{SECONDARY_MEMORY_NEEDED} is defined, the compiler
2525 allocates a stack slot for a memory location needed for register copies.
2526 If this macro is defined, the compiler instead uses the memory location
2527 defined by this macro.
2529 Do not define this macro if you do not define
2530 @code{SECONDARY_MEMORY_NEEDED}.
2533 @defmac SECONDARY_MEMORY_NEEDED_MODE (@var{mode})
2534 When the compiler needs a secondary memory location to copy between two
2535 registers of mode @var{mode}, it normally allocates sufficient memory to
2536 hold a quantity of @code{BITS_PER_WORD} bits and performs the store and
2537 load operations in a mode that many bits wide and whose class is the
2538 same as that of @var{mode}.
2540 This is right thing to do on most machines because it ensures that all
2541 bits of the register are copied and prevents accesses to the registers
2542 in a narrower mode, which some machines prohibit for floating-point
2545 However, this default behavior is not correct on some machines, such as
2546 the DEC Alpha, that store short integers in floating-point registers
2547 differently than in integer registers. On those machines, the default
2548 widening will not work correctly and you must define this macro to
2549 suppress that widening in some cases. See the file @file{alpha.h} for
2552 Do not define this macro if you do not define
2553 @code{SECONDARY_MEMORY_NEEDED} or if widening @var{mode} to a mode that
2554 is @code{BITS_PER_WORD} bits wide is correct for your machine.
2557 @defmac SMALL_REGISTER_CLASSES
2558 On some machines, it is risky to let hard registers live across arbitrary
2559 insns. Typically, these machines have instructions that require values
2560 to be in specific registers (like an accumulator), and reload will fail
2561 if the required hard register is used for another purpose across such an
2564 Define @code{SMALL_REGISTER_CLASSES} to be an expression with a nonzero
2565 value on these machines. When this macro has a nonzero value, the
2566 compiler will try to minimize the lifetime of hard registers.
2568 It is always safe to define this macro with a nonzero value, but if you
2569 unnecessarily define it, you will reduce the amount of optimizations
2570 that can be performed in some cases. If you do not define this macro
2571 with a nonzero value when it is required, the compiler will run out of
2572 spill registers and print a fatal error message. For most machines, you
2573 should not define this macro at all.
2576 @defmac CLASS_LIKELY_SPILLED_P (@var{class})
2577 A C expression whose value is nonzero if pseudos that have been assigned
2578 to registers of class @var{class} would likely be spilled because
2579 registers of @var{class} are needed for spill registers.
2581 The default value of this macro returns 1 if @var{class} has exactly one
2582 register and zero otherwise. On most machines, this default should be
2583 used. Only define this macro to some other expression if pseudos
2584 allocated by @file{local-alloc.c} end up in memory because their hard
2585 registers were needed for spill registers. If this macro returns nonzero
2586 for those classes, those pseudos will only be allocated by
2587 @file{global.c}, which knows how to reallocate the pseudo to another
2588 register. If there would not be another register available for
2589 reallocation, you should not change the definition of this macro since
2590 the only effect of such a definition would be to slow down register
2594 @defmac CLASS_MAX_NREGS (@var{class}, @var{mode})
2595 A C expression for the maximum number of consecutive registers
2596 of class @var{class} needed to hold a value of mode @var{mode}.
2598 This is closely related to the macro @code{HARD_REGNO_NREGS}. In fact,
2599 the value of the macro @code{CLASS_MAX_NREGS (@var{class}, @var{mode})}
2600 should be the maximum value of @code{HARD_REGNO_NREGS (@var{regno},
2601 @var{mode})} for all @var{regno} values in the class @var{class}.
2603 This macro helps control the handling of multiple-word values
2607 @defmac CANNOT_CHANGE_MODE_CLASS (@var{from}, @var{to}, @var{class})
2608 If defined, a C expression that returns nonzero for a @var{class} for which
2609 a change from mode @var{from} to mode @var{to} is invalid.
2611 For the example, loading 32-bit integer or floating-point objects into
2612 floating-point registers on the Alpha extends them to 64 bits.
2613 Therefore loading a 64-bit object and then storing it as a 32-bit object
2614 does not store the low-order 32 bits, as would be the case for a normal
2615 register. Therefore, @file{alpha.h} defines @code{CANNOT_CHANGE_MODE_CLASS}
2619 #define CANNOT_CHANGE_MODE_CLASS(FROM, TO, CLASS) \
2620 (GET_MODE_SIZE (FROM) != GET_MODE_SIZE (TO) \
2621 ? reg_classes_intersect_p (FLOAT_REGS, (CLASS)) : 0)
2625 Three other special macros describe which operands fit which constraint
2628 @defmac CONST_OK_FOR_LETTER_P (@var{value}, @var{c})
2629 A C expression that defines the machine-dependent operand constraint
2630 letters (@samp{I}, @samp{J}, @samp{K}, @dots{} @samp{P}) that specify
2631 particular ranges of integer values. If @var{c} is one of those
2632 letters, the expression should check that @var{value}, an integer, is in
2633 the appropriate range and return 1 if so, 0 otherwise. If @var{c} is
2634 not one of those letters, the value should be 0 regardless of
2638 @defmac CONST_OK_FOR_CONSTRAINT_P (@var{value}, @var{c}, @var{str})
2639 Like @code{CONST_OK_FOR_LETTER_P}, but you also get the constraint
2640 string passed in @var{str}, so that you can use suffixes to distinguish
2641 between different variants.
2644 @defmac CONST_DOUBLE_OK_FOR_LETTER_P (@var{value}, @var{c})
2645 A C expression that defines the machine-dependent operand constraint
2646 letters that specify particular ranges of @code{const_double} values
2647 (@samp{G} or @samp{H}).
2649 If @var{c} is one of those letters, the expression should check that
2650 @var{value}, an RTX of code @code{const_double}, is in the appropriate
2651 range and return 1 if so, 0 otherwise. If @var{c} is not one of those
2652 letters, the value should be 0 regardless of @var{value}.
2654 @code{const_double} is used for all floating-point constants and for
2655 @code{DImode} fixed-point constants. A given letter can accept either
2656 or both kinds of values. It can use @code{GET_MODE} to distinguish
2657 between these kinds.
2660 @defmac CONST_DOUBLE_OK_FOR_CONSTRAINT_P (@var{value}, @var{c}, @var{str})
2661 Like @code{CONST_DOUBLE_OK_FOR_LETTER_P}, but you also get the constraint
2662 string passed in @var{str}, so that you can use suffixes to distinguish
2663 between different variants.
2666 @defmac EXTRA_CONSTRAINT (@var{value}, @var{c})
2667 A C expression that defines the optional machine-dependent constraint
2668 letters that can be used to segregate specific types of operands, usually
2669 memory references, for the target machine. Any letter that is not
2670 elsewhere defined and not matched by @code{REG_CLASS_FROM_LETTER} /
2671 @code{REG_CLASS_FROM_CONSTRAINT}
2672 may be used. Normally this macro will not be defined.
2674 If it is required for a particular target machine, it should return 1
2675 if @var{value} corresponds to the operand type represented by the
2676 constraint letter @var{c}. If @var{c} is not defined as an extra
2677 constraint, the value returned should be 0 regardless of @var{value}.
2679 For example, on the ROMP, load instructions cannot have their output
2680 in r0 if the memory reference contains a symbolic address. Constraint
2681 letter @samp{Q} is defined as representing a memory address that does
2682 @emph{not} contain a symbolic address. An alternative is specified with
2683 a @samp{Q} constraint on the input and @samp{r} on the output. The next
2684 alternative specifies @samp{m} on the input and a register class that
2685 does not include r0 on the output.
2688 @defmac EXTRA_CONSTRAINT_STR (@var{value}, @var{c}, @var{str})
2689 Like @code{EXTRA_CONSTRAINT}, but you also get the constraint string passed
2690 in @var{str}, so that you can use suffixes to distinguish between different
2694 @defmac EXTRA_MEMORY_CONSTRAINT (@var{c}, @var{str})
2695 A C expression that defines the optional machine-dependent constraint
2696 letters, amongst those accepted by @code{EXTRA_CONSTRAINT}, that should
2697 be treated like memory constraints by the reload pass.
2699 It should return 1 if the operand type represented by the constraint
2700 at the start of @var{str}, the first letter of which is the letter @var{c},
2701 comprises a subset of all memory references including
2702 all those whose address is simply a base register. This allows the reload
2703 pass to reload an operand, if it does not directly correspond to the operand
2704 type of @var{c}, by copying its address into a base register.
2706 For example, on the S/390, some instructions do not accept arbitrary
2707 memory references, but only those that do not make use of an index
2708 register. The constraint letter @samp{Q} is defined via
2709 @code{EXTRA_CONSTRAINT} as representing a memory address of this type.
2710 If the letter @samp{Q} is marked as @code{EXTRA_MEMORY_CONSTRAINT},
2711 a @samp{Q} constraint can handle any memory operand, because the
2712 reload pass knows it can be reloaded by copying the memory address
2713 into a base register if required. This is analogous to the way
2714 a @samp{o} constraint can handle any memory operand.
2717 @defmac EXTRA_ADDRESS_CONSTRAINT (@var{c}, @var{str})
2718 A C expression that defines the optional machine-dependent constraint
2719 letters, amongst those accepted by @code{EXTRA_CONSTRAINT} /
2720 @code{EXTRA_CONSTRAINT_STR}, that should
2721 be treated like address constraints by the reload pass.
2723 It should return 1 if the operand type represented by the constraint
2724 at the start of @var{str}, which starts with the letter @var{c}, comprises
2725 a subset of all memory addresses including
2726 all those that consist of just a base register. This allows the reload
2727 pass to reload an operand, if it does not directly correspond to the operand
2728 type of @var{str}, by copying it into a base register.
2730 Any constraint marked as @code{EXTRA_ADDRESS_CONSTRAINT} can only
2731 be used with the @code{address_operand} predicate. It is treated
2732 analogously to the @samp{p} constraint.
2735 @node Stack and Calling
2736 @section Stack Layout and Calling Conventions
2737 @cindex calling conventions
2739 @c prevent bad page break with this line
2740 This describes the stack layout and calling conventions.
2744 * Exception Handling::
2749 * Register Arguments::
2751 * Aggregate Return::
2759 @subsection Basic Stack Layout
2760 @cindex stack frame layout
2761 @cindex frame layout
2763 @c prevent bad page break with this line
2764 Here is the basic stack layout.
2766 @defmac STACK_GROWS_DOWNWARD
2767 Define this macro if pushing a word onto the stack moves the stack
2768 pointer to a smaller address.
2770 When we say, ``define this macro if @dots{},'' it means that the
2771 compiler checks this macro only with @code{#ifdef} so the precise
2772 definition used does not matter.
2775 @defmac STACK_PUSH_CODE
2776 This macro defines the operation used when something is pushed
2777 on the stack. In RTL, a push operation will be
2778 @code{(set (mem (STACK_PUSH_CODE (reg sp))) @dots{})}
2780 The choices are @code{PRE_DEC}, @code{POST_DEC}, @code{PRE_INC},
2781 and @code{POST_INC}. Which of these is correct depends on
2782 the stack direction and on whether the stack pointer points
2783 to the last item on the stack or whether it points to the
2784 space for the next item on the stack.
2786 The default is @code{PRE_DEC} when @code{STACK_GROWS_DOWNWARD} is
2787 defined, which is almost always right, and @code{PRE_INC} otherwise,
2788 which is often wrong.
2791 @defmac FRAME_GROWS_DOWNWARD
2792 Define this macro if the addresses of local variable slots are at negative
2793 offsets from the frame pointer.
2796 @defmac ARGS_GROW_DOWNWARD
2797 Define this macro if successive arguments to a function occupy decreasing
2798 addresses on the stack.
2801 @defmac STARTING_FRAME_OFFSET
2802 Offset from the frame pointer to the first local variable slot to be allocated.
2804 If @code{FRAME_GROWS_DOWNWARD}, find the next slot's offset by
2805 subtracting the first slot's length from @code{STARTING_FRAME_OFFSET}.
2806 Otherwise, it is found by adding the length of the first slot to the
2807 value @code{STARTING_FRAME_OFFSET}.
2808 @c i'm not sure if the above is still correct.. had to change it to get
2809 @c rid of an overfull. --mew 2feb93
2812 @defmac STACK_ALIGNMENT_NEEDED
2813 Define to zero to disable final alignment of the stack during reload.
2814 The nonzero default for this macro is suitable for most ports.
2816 On ports where @code{STARTING_FRAME_OFFSET} is nonzero or where there
2817 is a register save block following the local block that doesn't require
2818 alignment to @code{STACK_BOUNDARY}, it may be beneficial to disable
2819 stack alignment and do it in the backend.
2822 @defmac STACK_POINTER_OFFSET
2823 Offset from the stack pointer register to the first location at which
2824 outgoing arguments are placed. If not specified, the default value of
2825 zero is used. This is the proper value for most machines.
2827 If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above
2828 the first location at which outgoing arguments are placed.
2831 @defmac FIRST_PARM_OFFSET (@var{fundecl})
2832 Offset from the argument pointer register to the first argument's
2833 address. On some machines it may depend on the data type of the
2836 If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above
2837 the first argument's address.
2840 @defmac STACK_DYNAMIC_OFFSET (@var{fundecl})
2841 Offset from the stack pointer register to an item dynamically allocated
2842 on the stack, e.g., by @code{alloca}.
2844 The default value for this macro is @code{STACK_POINTER_OFFSET} plus the
2845 length of the outgoing arguments. The default is correct for most
2846 machines. See @file{function.c} for details.
2849 @defmac DYNAMIC_CHAIN_ADDRESS (@var{frameaddr})
2850 A C expression whose value is RTL representing the address in a stack
2851 frame where the pointer to the caller's frame is stored. Assume that
2852 @var{frameaddr} is an RTL expression for the address of the stack frame
2855 If you don't define this macro, the default is to return the value
2856 of @var{frameaddr}---that is, the stack frame address is also the
2857 address of the stack word that points to the previous frame.
2860 @defmac SETUP_FRAME_ADDRESSES
2861 If defined, a C expression that produces the machine-specific code to
2862 setup the stack so that arbitrary frames can be accessed. For example,
2863 on the SPARC, we must flush all of the register windows to the stack
2864 before we can access arbitrary stack frames. You will seldom need to
2868 @defmac BUILTIN_SETJMP_FRAME_VALUE
2869 If defined, a C expression that contains an rtx that is used to store
2870 the address of the current frame into the built in @code{setjmp} buffer.
2871 The default value, @code{virtual_stack_vars_rtx}, is correct for most
2872 machines. One reason you may need to define this macro is if
2873 @code{hard_frame_pointer_rtx} is the appropriate value on your machine.
2876 @defmac RETURN_ADDR_RTX (@var{count}, @var{frameaddr})
2877 A C expression whose value is RTL representing the value of the return
2878 address for the frame @var{count} steps up from the current frame, after
2879 the prologue. @var{frameaddr} is the frame pointer of the @var{count}
2880 frame, or the frame pointer of the @var{count} @minus{} 1 frame if
2881 @code{RETURN_ADDR_IN_PREVIOUS_FRAME} is defined.
2883 The value of the expression must always be the correct address when
2884 @var{count} is zero, but may be @code{NULL_RTX} if there is not way to
2885 determine the return address of other frames.
2888 @defmac RETURN_ADDR_IN_PREVIOUS_FRAME
2889 Define this if the return address of a particular stack frame is accessed
2890 from the frame pointer of the previous stack frame.
2893 @defmac INCOMING_RETURN_ADDR_RTX
2894 A C expression whose value is RTL representing the location of the
2895 incoming return address at the beginning of any function, before the
2896 prologue. This RTL is either a @code{REG}, indicating that the return
2897 value is saved in @samp{REG}, or a @code{MEM} representing a location in
2900 You only need to define this macro if you want to support call frame
2901 debugging information like that provided by DWARF 2.
2903 If this RTL is a @code{REG}, you should also define
2904 @code{DWARF_FRAME_RETURN_COLUMN} to @code{DWARF_FRAME_REGNUM (REGNO)}.
2907 @defmac INCOMING_FRAME_SP_OFFSET
2908 A C expression whose value is an integer giving the offset, in bytes,
2909 from the value of the stack pointer register to the top of the stack
2910 frame at the beginning of any function, before the prologue. The top of
2911 the frame is defined to be the value of the stack pointer in the
2912 previous frame, just before the call instruction.
2914 You only need to define this macro if you want to support call frame
2915 debugging information like that provided by DWARF 2.
2918 @defmac ARG_POINTER_CFA_OFFSET (@var{fundecl})
2919 A C expression whose value is an integer giving the offset, in bytes,
2920 from the argument pointer to the canonical frame address (cfa). The
2921 final value should coincide with that calculated by
2922 @code{INCOMING_FRAME_SP_OFFSET}. Which is unfortunately not usable
2923 during virtual register instantiation.
2925 The default value for this macro is @code{FIRST_PARM_OFFSET (fundecl)},
2926 which is correct for most machines; in general, the arguments are found
2927 immediately before the stack frame. Note that this is not the case on
2928 some targets that save registers into the caller's frame, such as SPARC
2929 and rs6000, and so such targets need to define this macro.
2931 You only need to define this macro if the default is incorrect, and you
2932 want to support call frame debugging information like that provided by
2936 @node Exception Handling
2937 @subsection Exception Handling Support
2938 @cindex exception handling
2940 @defmac EH_RETURN_DATA_REGNO (@var{N})
2941 A C expression whose value is the @var{N}th register number used for
2942 data by exception handlers, or @code{INVALID_REGNUM} if fewer than
2943 @var{N} registers are usable.
2945 The exception handling library routines communicate with the exception
2946 handlers via a set of agreed upon registers. Ideally these registers
2947 should be call-clobbered; it is possible to use call-saved registers,
2948 but may negatively impact code size. The target must support at least
2949 2 data registers, but should define 4 if there are enough free registers.
2951 You must define this macro if you want to support call frame exception
2952 handling like that provided by DWARF 2.
2955 @defmac EH_RETURN_STACKADJ_RTX
2956 A C expression whose value is RTL representing a location in which
2957 to store a stack adjustment to be applied before function return.
2958 This is used to unwind the stack to an exception handler's call frame.
2959 It will be assigned zero on code paths that return normally.
2961 Typically this is a call-clobbered hard register that is otherwise
2962 untouched by the epilogue, but could also be a stack slot.
2964 Do not define this macro if the stack pointer is saved and restored
2965 by the regular prolog and epilog code in the call frame itself; in
2966 this case, the exception handling library routines will update the
2967 stack location to be restored in place. Otherwise, you must define
2968 this macro if you want to support call frame exception handling like
2969 that provided by DWARF 2.
2972 @defmac EH_RETURN_HANDLER_RTX
2973 A C expression whose value is RTL representing a location in which
2974 to store the address of an exception handler to which we should
2975 return. It will not be assigned on code paths that return normally.
2977 Typically this is the location in the call frame at which the normal
2978 return address is stored. For targets that return by popping an
2979 address off the stack, this might be a memory address just below
2980 the @emph{target} call frame rather than inside the current call
2981 frame. If defined, @code{EH_RETURN_STACKADJ_RTX} will have already
2982 been assigned, so it may be used to calculate the location of the
2985 Some targets have more complex requirements than storing to an
2986 address calculable during initial code generation. In that case
2987 the @code{eh_return} instruction pattern should be used instead.
2989 If you want to support call frame exception handling, you must
2990 define either this macro or the @code{eh_return} instruction pattern.
2993 @defmac RETURN_ADDR_OFFSET
2994 If defined, an integer-valued C expression for which rtl will be generated
2995 to add it to the exception handler address before it is searched in the
2996 exception handling tables, and to subtract it again from the address before
2997 using it to return to the exception handler.
3000 @defmac ASM_PREFERRED_EH_DATA_FORMAT (@var{code}, @var{global})
3001 This macro chooses the encoding of pointers embedded in the exception
3002 handling sections. If at all possible, this should be defined such
3003 that the exception handling section will not require dynamic relocations,
3004 and so may be read-only.
3006 @var{code} is 0 for data, 1 for code labels, 2 for function pointers.
3007 @var{global} is true if the symbol may be affected by dynamic relocations.
3008 The macro should return a combination of the @code{DW_EH_PE_*} defines
3009 as found in @file{dwarf2.h}.
3011 If this macro is not defined, pointers will not be encoded but
3012 represented directly.
3015 @defmac ASM_MAYBE_OUTPUT_ENCODED_ADDR_RTX (@var{file}, @var{encoding}, @var{size}, @var{addr}, @var{done})
3016 This macro allows the target to emit whatever special magic is required
3017 to represent the encoding chosen by @code{ASM_PREFERRED_EH_DATA_FORMAT}.
3018 Generic code takes care of pc-relative and indirect encodings; this must
3019 be defined if the target uses text-relative or data-relative encodings.
3021 This is a C statement that branches to @var{done} if the format was
3022 handled. @var{encoding} is the format chosen, @var{size} is the number
3023 of bytes that the format occupies, @var{addr} is the @code{SYMBOL_REF}
3027 @defmac MD_FALLBACK_FRAME_STATE_FOR (@var{context}, @var{fs}, @var{success})
3028 This macro allows the target to add cpu and operating system specific
3029 code to the call-frame unwinder for use when there is no unwind data
3030 available. The most common reason to implement this macro is to unwind
3031 through signal frames.
3033 This macro is called from @code{uw_frame_state_for} in @file{unwind-dw2.c}
3034 and @file{unwind-ia64.c}. @var{context} is an @code{_Unwind_Context};
3035 @var{fs} is an @code{_Unwind_FrameState}. Examine @code{context->ra}
3036 for the address of the code being executed and @code{context->cfa} for
3037 the stack pointer value. If the frame can be decoded, the register save
3038 addresses should be updated in @var{fs} and the macro should branch to
3039 @var{success}. If the frame cannot be decoded, the macro should do
3042 For proper signal handling in Java this macro is accompanied by
3043 @code{MAKE_THROW_FRAME}, defined in @file{libjava/include/*-signal.h} headers.
3046 @node Stack Checking
3047 @subsection Specifying How Stack Checking is Done
3049 GCC will check that stack references are within the boundaries of
3050 the stack, if the @option{-fstack-check} is specified, in one of three ways:
3054 If the value of the @code{STACK_CHECK_BUILTIN} macro is nonzero, GCC
3055 will assume that you have arranged for stack checking to be done at
3056 appropriate places in the configuration files, e.g., in
3057 @code{TARGET_ASM_FUNCTION_PROLOGUE}. GCC will do not other special
3061 If @code{STACK_CHECK_BUILTIN} is zero and you defined a named pattern
3062 called @code{check_stack} in your @file{md} file, GCC will call that
3063 pattern with one argument which is the address to compare the stack
3064 value against. You must arrange for this pattern to report an error if
3065 the stack pointer is out of range.
3068 If neither of the above are true, GCC will generate code to periodically
3069 ``probe'' the stack pointer using the values of the macros defined below.
3072 Normally, you will use the default values of these macros, so GCC
3073 will use the third approach.
3075 @defmac STACK_CHECK_BUILTIN
3076 A nonzero value if stack checking is done by the configuration files in a
3077 machine-dependent manner. You should define this macro if stack checking
3078 is require by the ABI of your machine or if you would like to have to stack
3079 checking in some more efficient way than GCC's portable approach.
3080 The default value of this macro is zero.
3083 @defmac STACK_CHECK_PROBE_INTERVAL
3084 An integer representing the interval at which GCC must generate stack
3085 probe instructions. You will normally define this macro to be no larger
3086 than the size of the ``guard pages'' at the end of a stack area. The
3087 default value of 4096 is suitable for most systems.
3090 @defmac STACK_CHECK_PROBE_LOAD
3091 A integer which is nonzero if GCC should perform the stack probe
3092 as a load instruction and zero if GCC should use a store instruction.
3093 The default is zero, which is the most efficient choice on most systems.
3096 @defmac STACK_CHECK_PROTECT
3097 The number of bytes of stack needed to recover from a stack overflow,
3098 for languages where such a recovery is supported. The default value of
3099 75 words should be adequate for most machines.
3102 @defmac STACK_CHECK_MAX_FRAME_SIZE
3103 The maximum size of a stack frame, in bytes. GCC will generate probe
3104 instructions in non-leaf functions to ensure at least this many bytes of
3105 stack are available. If a stack frame is larger than this size, stack
3106 checking will not be reliable and GCC will issue a warning. The
3107 default is chosen so that GCC only generates one instruction on most
3108 systems. You should normally not change the default value of this macro.
3111 @defmac STACK_CHECK_FIXED_FRAME_SIZE
3112 GCC uses this value to generate the above warning message. It
3113 represents the amount of fixed frame used by a function, not including
3114 space for any callee-saved registers, temporaries and user variables.
3115 You need only specify an upper bound for this amount and will normally
3116 use the default of four words.
3119 @defmac STACK_CHECK_MAX_VAR_SIZE
3120 The maximum size, in bytes, of an object that GCC will place in the
3121 fixed area of the stack frame when the user specifies
3122 @option{-fstack-check}.
3123 GCC computed the default from the values of the above macros and you will
3124 normally not need to override that default.
3128 @node Frame Registers
3129 @subsection Registers That Address the Stack Frame
3131 @c prevent bad page break with this line
3132 This discusses registers that address the stack frame.
3134 @defmac STACK_POINTER_REGNUM
3135 The register number of the stack pointer register, which must also be a
3136 fixed register according to @code{FIXED_REGISTERS}. On most machines,
3137 the hardware determines which register this is.
3140 @defmac FRAME_POINTER_REGNUM
3141 The register number of the frame pointer register, which is used to
3142 access automatic variables in the stack frame. On some machines, the
3143 hardware determines which register this is. On other machines, you can
3144 choose any register you wish for this purpose.
3147 @defmac HARD_FRAME_POINTER_REGNUM
3148 On some machines the offset between the frame pointer and starting
3149 offset of the automatic variables is not known until after register
3150 allocation has been done (for example, because the saved registers are
3151 between these two locations). On those machines, define
3152 @code{FRAME_POINTER_REGNUM} the number of a special, fixed register to
3153 be used internally until the offset is known, and define
3154 @code{HARD_FRAME_POINTER_REGNUM} to be the actual hard register number
3155 used for the frame pointer.
3157 You should define this macro only in the very rare circumstances when it
3158 is not possible to calculate the offset between the frame pointer and
3159 the automatic variables until after register allocation has been
3160 completed. When this macro is defined, you must also indicate in your
3161 definition of @code{ELIMINABLE_REGS} how to eliminate
3162 @code{FRAME_POINTER_REGNUM} into either @code{HARD_FRAME_POINTER_REGNUM}
3163 or @code{STACK_POINTER_REGNUM}.
3165 Do not define this macro if it would be the same as
3166 @code{FRAME_POINTER_REGNUM}.
3169 @defmac ARG_POINTER_REGNUM
3170 The register number of the arg pointer register, which is used to access
3171 the function's argument list. On some machines, this is the same as the
3172 frame pointer register. On some machines, the hardware determines which
3173 register this is. On other machines, you can choose any register you
3174 wish for this purpose. If this is not the same register as the frame
3175 pointer register, then you must mark it as a fixed register according to
3176 @code{FIXED_REGISTERS}, or arrange to be able to eliminate it
3177 (@pxref{Elimination}).
3180 @defmac RETURN_ADDRESS_POINTER_REGNUM
3181 The register number of the return address pointer register, which is used to
3182 access the current function's return address from the stack. On some
3183 machines, the return address is not at a fixed offset from the frame
3184 pointer or stack pointer or argument pointer. This register can be defined
3185 to point to the return address on the stack, and then be converted by
3186 @code{ELIMINABLE_REGS} into either the frame pointer or stack pointer.
3188 Do not define this macro unless there is no other way to get the return
3189 address from the stack.
3192 @defmac STATIC_CHAIN_REGNUM
3193 @defmacx STATIC_CHAIN_INCOMING_REGNUM
3194 Register numbers used for passing a function's static chain pointer. If
3195 register windows are used, the register number as seen by the called
3196 function is @code{STATIC_CHAIN_INCOMING_REGNUM}, while the register
3197 number as seen by the calling function is @code{STATIC_CHAIN_REGNUM}. If
3198 these registers are the same, @code{STATIC_CHAIN_INCOMING_REGNUM} need
3201 The static chain register need not be a fixed register.
3203 If the static chain is passed in memory, these macros should not be
3204 defined; instead, the next two macros should be defined.
3207 @defmac STATIC_CHAIN
3208 @defmacx STATIC_CHAIN_INCOMING
3209 If the static chain is passed in memory, these macros provide rtx giving
3210 @code{mem} expressions that denote where they are stored.
3211 @code{STATIC_CHAIN} and @code{STATIC_CHAIN_INCOMING} give the locations
3212 as seen by the calling and called functions, respectively. Often the former
3213 will be at an offset from the stack pointer and the latter at an offset from
3216 @findex stack_pointer_rtx
3217 @findex frame_pointer_rtx
3218 @findex arg_pointer_rtx
3219 The variables @code{stack_pointer_rtx}, @code{frame_pointer_rtx}, and
3220 @code{arg_pointer_rtx} will have been initialized prior to the use of these
3221 macros and should be used to refer to those items.
3223 If the static chain is passed in a register, the two previous macros should
3227 @defmac DWARF_FRAME_REGISTERS
3228 This macro specifies the maximum number of hard registers that can be
3229 saved in a call frame. This is used to size data structures used in
3230 DWARF2 exception handling.
3232 Prior to GCC 3.0, this macro was needed in order to establish a stable
3233 exception handling ABI in the face of adding new hard registers for ISA
3234 extensions. In GCC 3.0 and later, the EH ABI is insulated from changes
3235 in the number of hard registers. Nevertheless, this macro can still be
3236 used to reduce the runtime memory requirements of the exception handling
3237 routines, which can be substantial if the ISA contains a lot of
3238 registers that are not call-saved.
3240 If this macro is not defined, it defaults to
3241 @code{FIRST_PSEUDO_REGISTER}.
3244 @defmac PRE_GCC3_DWARF_FRAME_REGISTERS
3246 This macro is similar to @code{DWARF_FRAME_REGISTERS}, but is provided
3247 for backward compatibility in pre GCC 3.0 compiled code.
3249 If this macro is not defined, it defaults to
3250 @code{DWARF_FRAME_REGISTERS}.
3253 @defmac DWARF_REG_TO_UNWIND_COLUMN (@var{regno})
3255 Define this macro if the target's representation for dwarf registers
3256 is different than the internal representation for unwind column.
3257 Given a dwarf register, this macro should return the internal unwind
3258 column number to use instead.
3260 See the PowerPC's SPE target for an example.
3264 @subsection Eliminating Frame Pointer and Arg Pointer
3266 @c prevent bad page break with this line
3267 This is about eliminating the frame pointer and arg pointer.
3269 @defmac FRAME_POINTER_REQUIRED
3270 A C expression which is nonzero if a function must have and use a frame
3271 pointer. This expression is evaluated in the reload pass. If its value is
3272 nonzero the function will have a frame pointer.
3274 The expression can in principle examine the current function and decide
3275 according to the facts, but on most machines the constant 0 or the
3276 constant 1 suffices. Use 0 when the machine allows code to be generated
3277 with no frame pointer, and doing so saves some time or space. Use 1
3278 when there is no possible advantage to avoiding a frame pointer.
3280 In certain cases, the compiler does not know how to produce valid code
3281 without a frame pointer. The compiler recognizes those cases and
3282 automatically gives the function a frame pointer regardless of what
3283 @code{FRAME_POINTER_REQUIRED} says. You don't need to worry about
3286 In a function that does not require a frame pointer, the frame pointer
3287 register can be allocated for ordinary usage, unless you mark it as a
3288 fixed register. See @code{FIXED_REGISTERS} for more information.
3291 @findex get_frame_size
3292 @defmac INITIAL_FRAME_POINTER_OFFSET (@var{depth-var})
3293 A C statement to store in the variable @var{depth-var} the difference
3294 between the frame pointer and the stack pointer values immediately after
3295 the function prologue. The value would be computed from information
3296 such as the result of @code{get_frame_size ()} and the tables of
3297 registers @code{regs_ever_live} and @code{call_used_regs}.
3299 If @code{ELIMINABLE_REGS} is defined, this macro will be not be used and
3300 need not be defined. Otherwise, it must be defined even if
3301 @code{FRAME_POINTER_REQUIRED} is defined to always be true; in that
3302 case, you may set @var{depth-var} to anything.
3305 @defmac ELIMINABLE_REGS
3306 If defined, this macro specifies a table of register pairs used to
3307 eliminate unneeded registers that point into the stack frame. If it is not
3308 defined, the only elimination attempted by the compiler is to replace
3309 references to the frame pointer with references to the stack pointer.
3311 The definition of this macro is a list of structure initializations, each
3312 of which specifies an original and replacement register.
3314 On some machines, the position of the argument pointer is not known until
3315 the compilation is completed. In such a case, a separate hard register
3316 must be used for the argument pointer. This register can be eliminated by
3317 replacing it with either the frame pointer or the argument pointer,
3318 depending on whether or not the frame pointer has been eliminated.
3320 In this case, you might specify:
3322 #define ELIMINABLE_REGS \
3323 @{@{ARG_POINTER_REGNUM, STACK_POINTER_REGNUM@}, \
3324 @{ARG_POINTER_REGNUM, FRAME_POINTER_REGNUM@}, \
3325 @{FRAME_POINTER_REGNUM, STACK_POINTER_REGNUM@}@}
3328 Note that the elimination of the argument pointer with the stack pointer is
3329 specified first since that is the preferred elimination.
3332 @defmac CAN_ELIMINATE (@var{from-reg}, @var{to-reg})
3333 A C expression that returns nonzero if the compiler is allowed to try
3334 to replace register number @var{from-reg} with register number
3335 @var{to-reg}. This macro need only be defined if @code{ELIMINABLE_REGS}
3336 is defined, and will usually be the constant 1, since most of the cases
3337 preventing register elimination are things that the compiler already
3341 @defmac INITIAL_ELIMINATION_OFFSET (@var{from-reg}, @var{to-reg}, @var{offset-var})
3342 This macro is similar to @code{INITIAL_FRAME_POINTER_OFFSET}. It
3343 specifies the initial difference between the specified pair of
3344 registers. This macro must be defined if @code{ELIMINABLE_REGS} is
3348 @node Stack Arguments
3349 @subsection Passing Function Arguments on the Stack
3350 @cindex arguments on stack
3351 @cindex stack arguments
3353 The macros in this section control how arguments are passed
3354 on the stack. See the following section for other macros that
3355 control passing certain arguments in registers.
3357 @deftypefn {Target Hook} bool TARGET_PROMOTE_PROTOTYPES (tree @var{fntype})
3358 This target hook returns @code{true} if an argument declared in a
3359 prototype as an integral type smaller than @code{int} should actually be
3360 passed as an @code{int}. In addition to avoiding errors in certain
3361 cases of mismatch, it also makes for better code on certain machines.
3362 The default is to not promote prototypes.
3366 A C expression. If nonzero, push insns will be used to pass
3368 If the target machine does not have a push instruction, set it to zero.
3369 That directs GCC to use an alternate strategy: to
3370 allocate the entire argument block and then store the arguments into
3371 it. When @code{PUSH_ARGS} is nonzero, @code{PUSH_ROUNDING} must be defined too.
3374 @defmac PUSH_ARGS_REVERSED
3375 A C expression. If nonzero, function arguments will be evaluated from
3376 last to first, rather than from first to last. If this macro is not
3377 defined, it defaults to @code{PUSH_ARGS} on targets where the stack
3378 and args grow in opposite directions, and 0 otherwise.
3381 @defmac PUSH_ROUNDING (@var{npushed})
3382 A C expression that is the number of bytes actually pushed onto the
3383 stack when an instruction attempts to push @var{npushed} bytes.
3385 On some machines, the definition
3388 #define PUSH_ROUNDING(BYTES) (BYTES)
3392 will suffice. But on other machines, instructions that appear
3393 to push one byte actually push two bytes in an attempt to maintain
3394 alignment. Then the definition should be
3397 #define PUSH_ROUNDING(BYTES) (((BYTES) + 1) & ~1)
3401 @findex current_function_outgoing_args_size
3402 @defmac ACCUMULATE_OUTGOING_ARGS
3403 A C expression. If nonzero, the maximum amount of space required for outgoing arguments
3404 will be computed and placed into the variable
3405 @code{current_function_outgoing_args_size}. No space will be pushed
3406 onto the stack for each call; instead, the function prologue should
3407 increase the stack frame size by this amount.
3409 Setting both @code{PUSH_ARGS} and @code{ACCUMULATE_OUTGOING_ARGS}
3413 @defmac REG_PARM_STACK_SPACE (@var{fndecl})
3414 Define this macro if functions should assume that stack space has been
3415 allocated for arguments even when their values are passed in
3418 The value of this macro is the size, in bytes, of the area reserved for
3419 arguments passed in registers for the function represented by @var{fndecl},
3420 which can be zero if GCC is calling a library function.
3422 This space can be allocated by the caller, or be a part of the
3423 machine-dependent stack frame: @code{OUTGOING_REG_PARM_STACK_SPACE} says
3426 @c above is overfull. not sure what to do. --mew 5feb93 did
3427 @c something, not sure if it looks good. --mew 10feb93
3429 @defmac MAYBE_REG_PARM_STACK_SPACE
3430 @defmacx FINAL_REG_PARM_STACK_SPACE (@var{const_size}, @var{var_size})
3431 Define these macros in addition to the one above if functions might
3432 allocate stack space for arguments even when their values are passed
3433 in registers. These should be used when the stack space allocated
3434 for arguments in registers is not a simple constant independent of the
3435 function declaration.
3437 The value of the first macro is the size, in bytes, of the area that
3438 we should initially assume would be reserved for arguments passed in registers.
3440 The value of the second macro is the actual size, in bytes, of the area
3441 that will be reserved for arguments passed in registers. This takes two
3442 arguments: an integer representing the number of bytes of fixed sized
3443 arguments on the stack, and a tree representing the number of bytes of
3444 variable sized arguments on the stack.
3446 When these macros are defined, @code{REG_PARM_STACK_SPACE} will only be
3447 called for libcall functions, the current function, or for a function
3448 being called when it is known that such stack space must be allocated.
3449 In each case this value can be easily computed.
3451 When deciding whether a called function needs such stack space, and how
3452 much space to reserve, GCC uses these two macros instead of
3453 @code{REG_PARM_STACK_SPACE}.
3456 @defmac OUTGOING_REG_PARM_STACK_SPACE
3457 Define this if it is the responsibility of the caller to allocate the area
3458 reserved for arguments passed in registers.
3460 If @code{ACCUMULATE_OUTGOING_ARGS} is defined, this macro controls
3461 whether the space for these arguments counts in the value of
3462 @code{current_function_outgoing_args_size}.
3465 @defmac STACK_PARMS_IN_REG_PARM_AREA
3466 Define this macro if @code{REG_PARM_STACK_SPACE} is defined, but the
3467 stack parameters don't skip the area specified by it.
3468 @c i changed this, makes more sens and it should have taken care of the
3469 @c overfull.. not as specific, tho. --mew 5feb93
3471 Normally, when a parameter is not passed in registers, it is placed on the
3472 stack beyond the @code{REG_PARM_STACK_SPACE} area. Defining this macro
3473 suppresses this behavior and causes the parameter to be passed on the
3474 stack in its natural location.
3477 @defmac RETURN_POPS_ARGS (@var{fundecl}, @var{funtype}, @var{stack-size})
3478 A C expression that should indicate the number of bytes of its own
3479 arguments that a function pops on returning, or 0 if the
3480 function pops no arguments and the caller must therefore pop them all
3481 after the function returns.
3483 @var{fundecl} is a C variable whose value is a tree node that describes
3484 the function in question. Normally it is a node of type
3485 @code{FUNCTION_DECL} that describes the declaration of the function.
3486 From this you can obtain the @code{DECL_ATTRIBUTES} of the function.
3488 @var{funtype} is a C variable whose value is a tree node that
3489 describes the function in question. Normally it is a node of type
3490 @code{FUNCTION_TYPE} that describes the data type of the function.
3491 From this it is possible to obtain the data types of the value and
3492 arguments (if known).
3494 When a call to a library function is being considered, @var{fundecl}
3495 will contain an identifier node for the library function. Thus, if
3496 you need to distinguish among various library functions, you can do so
3497 by their names. Note that ``library function'' in this context means
3498 a function used to perform arithmetic, whose name is known specially
3499 in the compiler and was not mentioned in the C code being compiled.
3501 @var{stack-size} is the number of bytes of arguments passed on the
3502 stack. If a variable number of bytes is passed, it is zero, and
3503 argument popping will always be the responsibility of the calling function.
3505 On the VAX, all functions always pop their arguments, so the definition
3506 of this macro is @var{stack-size}. On the 68000, using the standard
3507 calling convention, no functions pop their arguments, so the value of
3508 the macro is always 0 in this case. But an alternative calling
3509 convention is available in which functions that take a fixed number of
3510 arguments pop them but other functions (such as @code{printf}) pop
3511 nothing (the caller pops all). When this convention is in use,
3512 @var{funtype} is examined to determine whether a function takes a fixed
3513 number of arguments.
3516 @defmac CALL_POPS_ARGS (@var{cum})
3517 A C expression that should indicate the number of bytes a call sequence
3518 pops off the stack. It is added to the value of @code{RETURN_POPS_ARGS}
3519 when compiling a function call.
3521 @var{cum} is the variable in which all arguments to the called function
3522 have been accumulated.
3524 On certain architectures, such as the SH5, a call trampoline is used
3525 that pops certain registers off the stack, depending on the arguments
3526 that have been passed to the function. Since this is a property of the
3527 call site, not of the called function, @code{RETURN_POPS_ARGS} is not
3531 @node Register Arguments
3532 @subsection Passing Arguments in Registers
3533 @cindex arguments in registers
3534 @cindex registers arguments
3536 This section describes the macros which let you control how various
3537 types of arguments are passed in registers or how they are arranged in
3540 @defmac FUNCTION_ARG (@var{cum}, @var{mode}, @var{type}, @var{named})
3541 A C expression that controls whether a function argument is passed
3542 in a register, and which register.
3544 The arguments are @var{cum}, which summarizes all the previous
3545 arguments; @var{mode}, the machine mode of the argument; @var{type},
3546 the data type of the argument as a tree node or 0 if that is not known
3547 (which happens for C support library functions); and @var{named},
3548 which is 1 for an ordinary argument and 0 for nameless arguments that
3549 correspond to @samp{@dots{}} in the called function's prototype.
3550 @var{type} can be an incomplete type if a syntax error has previously
3553 The value of the expression is usually either a @code{reg} RTX for the
3554 hard register in which to pass the argument, or zero to pass the
3555 argument on the stack.
3557 For machines like the VAX and 68000, where normally all arguments are
3558 pushed, zero suffices as a definition.
3560 The value of the expression can also be a @code{parallel} RTX@. This is
3561 used when an argument is passed in multiple locations. The mode of the
3562 @code{parallel} should be the mode of the entire argument. The
3563 @code{parallel} holds any number of @code{expr_list} pairs; each one
3564 describes where part of the argument is passed. In each
3565 @code{expr_list} the first operand must be a @code{reg} RTX for the hard
3566 register in which to pass this part of the argument, and the mode of the
3567 register RTX indicates how large this part of the argument is. The
3568 second operand of the @code{expr_list} is a @code{const_int} which gives
3569 the offset in bytes into the entire argument of where this part starts.
3570 As a special exception the first @code{expr_list} in the @code{parallel}
3571 RTX may have a first operand of zero. This indicates that the entire
3572 argument is also stored on the stack.
3574 The last time this macro is called, it is called with @code{MODE ==
3575 VOIDmode}, and its result is passed to the @code{call} or @code{call_value}
3576 pattern as operands 2 and 3 respectively.
3578 @cindex @file{stdarg.h} and register arguments
3579 The usual way to make the ISO library @file{stdarg.h} work on a machine
3580 where some arguments are usually passed in registers, is to cause
3581 nameless arguments to be passed on the stack instead. This is done
3582 by making @code{FUNCTION_ARG} return 0 whenever @var{named} is 0.
3584 @cindex @code{MUST_PASS_IN_STACK}, and @code{FUNCTION_ARG}
3585 @cindex @code{REG_PARM_STACK_SPACE}, and @code{FUNCTION_ARG}
3586 You may use the macro @code{MUST_PASS_IN_STACK (@var{mode}, @var{type})}
3587 in the definition of this macro to determine if this argument is of a
3588 type that must be passed in the stack. If @code{REG_PARM_STACK_SPACE}
3589 is not defined and @code{FUNCTION_ARG} returns nonzero for such an
3590 argument, the compiler will abort. If @code{REG_PARM_STACK_SPACE} is
3591 defined, the argument will be computed in the stack and then loaded into
3595 @defmac MUST_PASS_IN_STACK (@var{mode}, @var{type})
3596 Define as a C expression that evaluates to nonzero if we do not know how
3597 to pass TYPE solely in registers. The file @file{expr.h} defines a
3598 definition that is usually appropriate, refer to @file{expr.h} for additional
3602 @defmac FUNCTION_INCOMING_ARG (@var{cum}, @var{mode}, @var{type}, @var{named})
3603 Define this macro if the target machine has ``register windows'', so
3604 that the register in which a function sees an arguments is not
3605 necessarily the same as the one in which the caller passed the
3608 For such machines, @code{FUNCTION_ARG} computes the register in which
3609 the caller passes the value, and @code{FUNCTION_INCOMING_ARG} should
3610 be defined in a similar fashion to tell the function being called
3611 where the arguments will arrive.
3613 If @code{FUNCTION_INCOMING_ARG} is not defined, @code{FUNCTION_ARG}
3614 serves both purposes.
3617 @defmac FUNCTION_ARG_PARTIAL_NREGS (@var{cum}, @var{mode}, @var{type}, @var{named})
3618 A C expression for the number of words, at the beginning of an
3619 argument, that must be put in registers. The value must be zero for
3620 arguments that are passed entirely in registers or that are entirely
3621 pushed on the stack.
3623 On some machines, certain arguments must be passed partially in
3624 registers and partially in memory. On these machines, typically the
3625 first @var{n} words of arguments are passed in registers, and the rest
3626 on the stack. If a multi-word argument (a @code{double} or a
3627 structure) crosses that boundary, its first few words must be passed
3628 in registers and the rest must be pushed. This macro tells the
3629 compiler when this occurs, and how many of the words should go in
3632 @code{FUNCTION_ARG} for these arguments should return the first
3633 register to be used by the caller for this argument; likewise
3634 @code{FUNCTION_INCOMING_ARG}, for the called function.
3637 @defmac FUNCTION_ARG_PASS_BY_REFERENCE (@var{cum}, @var{mode}, @var{type}, @var{named})
3638 A C expression that indicates when an argument must be passed by reference.
3639 If nonzero for an argument, a copy of that argument is made in memory and a
3640 pointer to the argument is passed instead of the argument itself.
3641 The pointer is passed in whatever way is appropriate for passing a pointer
3644 On machines where @code{REG_PARM_STACK_SPACE} is not defined, a suitable
3645 definition of this macro might be
3647 #define FUNCTION_ARG_PASS_BY_REFERENCE\
3648 (CUM, MODE, TYPE, NAMED) \
3649 MUST_PASS_IN_STACK (MODE, TYPE)
3651 @c this is *still* too long. --mew 5feb93
3654 @defmac FUNCTION_ARG_CALLEE_COPIES (@var{cum}, @var{mode}, @var{type}, @var{named})
3655 If defined, a C expression that indicates when it is the called function's
3656 responsibility to make a copy of arguments passed by invisible reference.
3657 Normally, the caller makes a copy and passes the address of the copy to the
3658 routine being called. When @code{FUNCTION_ARG_CALLEE_COPIES} is defined and is
3659 nonzero, the caller does not make a copy. Instead, it passes a pointer to the
3660 ``live'' value. The called function must not modify this value. If it can be
3661 determined that the value won't be modified, it need not make a copy;
3662 otherwise a copy must be made.
3665 @defmac CUMULATIVE_ARGS
3666 A C type for declaring a variable that is used as the first argument of
3667 @code{FUNCTION_ARG} and other related values. For some target machines,
3668 the type @code{int} suffices and can hold the number of bytes of
3671 There is no need to record in @code{CUMULATIVE_ARGS} anything about the
3672 arguments that have been passed on the stack. The compiler has other
3673 variables to keep track of that. For target machines on which all
3674 arguments are passed on the stack, there is no need to store anything in
3675 @code{CUMULATIVE_ARGS}; however, the data structure must exist and
3676 should not be empty, so use @code{int}.
3679 @defmac INIT_CUMULATIVE_ARGS (@var{cum}, @var{fntype}, @var{libname}, @var{fndecl})
3680 A C statement (sans semicolon) for initializing the variable
3681 @var{cum} for the state at the beginning of the argument list. The
3682 variable has type @code{CUMULATIVE_ARGS}. The value of @var{fntype}
3683 is the tree node for the data type of the function which will receive
3684 the args, or 0 if the args are to a compiler support library function.
3685 For direct calls that are not libcalls, @var{fndecl} contain the
3686 declaration node of the function. @var{fndecl} is also set when
3687 @code{INIT_CUMULATIVE_ARGS} is used to find arguments for the function
3690 When processing a call to a compiler support library function,
3691 @var{libname} identifies which one. It is a @code{symbol_ref} rtx which
3692 contains the name of the function, as a string. @var{libname} is 0 when
3693 an ordinary C function call is being processed. Thus, each time this
3694 macro is called, either @var{libname} or @var{fntype} is nonzero, but
3695 never both of them at once.
3698 @defmac INIT_CUMULATIVE_LIBCALL_ARGS (@var{cum}, @var{mode}, @var{libname})
3699 Like @code{INIT_CUMULATIVE_ARGS} but only used for outgoing libcalls,
3700 it gets a @code{MODE} argument instead of @var{fntype}, that would be
3701 @code{NULL}. @var{indirect} would always be zero, too. If this macro
3702 is not defined, @code{INIT_CUMULATIVE_ARGS (cum, NULL_RTX, libname,
3703 0)} is used instead.
3706 @defmac INIT_CUMULATIVE_INCOMING_ARGS (@var{cum}, @var{fntype}, @var{libname})
3707 Like @code{INIT_CUMULATIVE_ARGS} but overrides it for the purposes of
3708 finding the arguments for the function being compiled. If this macro is
3709 undefined, @code{INIT_CUMULATIVE_ARGS} is used instead.
3711 The value passed for @var{libname} is always 0, since library routines
3712 with special calling conventions are never compiled with GCC@. The
3713 argument @var{libname} exists for symmetry with
3714 @code{INIT_CUMULATIVE_ARGS}.
3715 @c could use "this macro" in place of @code{INIT_CUMULATIVE_ARGS}, maybe.
3716 @c --mew 5feb93 i switched the order of the sentences. --mew 10feb93
3719 @defmac FUNCTION_ARG_ADVANCE (@var{cum}, @var{mode}, @var{type}, @var{named})
3720 A C statement (sans semicolon) to update the summarizer variable
3721 @var{cum} to advance past an argument in the argument list. The
3722 values @var{mode}, @var{type} and @var{named} describe that argument.
3723 Once this is done, the variable @var{cum} is suitable for analyzing
3724 the @emph{following} argument with @code{FUNCTION_ARG}, etc.
3726 This macro need not do anything if the argument in question was passed
3727 on the stack. The compiler knows how to track the amount of stack space
3728 used for arguments without any special help.
3731 @defmac FUNCTION_ARG_PADDING (@var{mode}, @var{type})
3732 If defined, a C expression which determines whether, and in which direction,
3733 to pad out an argument with extra space. The value should be of type
3734 @code{enum direction}: either @code{upward} to pad above the argument,
3735 @code{downward} to pad below, or @code{none} to inhibit padding.
3737 The @emph{amount} of padding is always just enough to reach the next
3738 multiple of @code{FUNCTION_ARG_BOUNDARY}; this macro does not control
3741 This macro has a default definition which is right for most systems.
3742 For little-endian machines, the default is to pad upward. For
3743 big-endian machines, the default is to pad downward for an argument of
3744 constant size shorter than an @code{int}, and upward otherwise.
3747 @defmac PAD_VARARGS_DOWN
3748 If defined, a C expression which determines whether the default
3749 implementation of va_arg will attempt to pad down before reading the
3750 next argument, if that argument is smaller than its aligned space as
3751 controlled by @code{PARM_BOUNDARY}. If this macro is not defined, all such
3752 arguments are padded down if @code{BYTES_BIG_ENDIAN} is true.
3755 @defmac BLOCK_REG_PADDING (@var{mode}, @var{type}, @var{first})
3756 Specify padding for the last element of a block move between registers and
3757 memory. @var{first} is nonzero if this is the only element. Defining this
3758 macro allows better control of register function parameters on big-endian
3759 machines, without using @code{PARALLEL} rtl. In particular,
3760 @code{MUST_PASS_IN_STACK} need not test padding and mode of types in
3761 registers, as there is no longer a "wrong" part of a register; For example,
3762 a three byte aggregate may be passed in the high part of a register if so
3766 @defmac FUNCTION_ARG_BOUNDARY (@var{mode}, @var{type})
3767 If defined, a C expression that gives the alignment boundary, in bits,
3768 of an argument with the specified mode and type. If it is not defined,
3769 @code{PARM_BOUNDARY} is used for all arguments.
3772 @defmac FUNCTION_ARG_REGNO_P (@var{regno})
3773 A C expression that is nonzero if @var{regno} is the number of a hard
3774 register in which function arguments are sometimes passed. This does
3775 @emph{not} include implicit arguments such as the static chain and
3776 the structure-value address. On many machines, no registers can be
3777 used for this purpose since all function arguments are pushed on the
3781 @defmac SPLIT_COMPLEX_ARGS
3783 Define this macro to a nonzero value if complex function arguments
3784 should be split into their corresponding components. By default, GCC
3785 will attempt to pack complex arguments into the target's word size.
3786 Some ABIs require complex arguments to be split and treated as their
3787 individual components. For example, on AIX64, complex floats should
3788 be passed in a pair of floating point registers, even though a complex
3789 float would fit in one 64-bit floating point register.
3792 @defmac LOAD_ARGS_REVERSED
3793 If defined, the order in which arguments are loaded into their
3794 respective argument registers is reversed so that the last
3795 argument is loaded first. This macro only affects arguments
3796 passed in registers.
3800 @subsection How Scalar Function Values Are Returned
3801 @cindex return values in registers
3802 @cindex values, returned by functions
3803 @cindex scalars, returned as values
3805 This section discusses the macros that control returning scalars as
3806 values---values that can fit in registers.
3808 @defmac FUNCTION_VALUE (@var{valtype}, @var{func})
3809 A C expression to create an RTX representing the place where a
3810 function returns a value of data type @var{valtype}. @var{valtype} is
3811 a tree node representing a data type. Write @code{TYPE_MODE
3812 (@var{valtype})} to get the machine mode used to represent that type.
3813 On many machines, only the mode is relevant. (Actually, on most
3814 machines, scalar values are returned in the same place regardless of
3817 The value of the expression is usually a @code{reg} RTX for the hard
3818 register where the return value is stored. The value can also be a
3819 @code{parallel} RTX, if the return value is in multiple places. See
3820 @code{FUNCTION_ARG} for an explanation of the @code{parallel} form.
3822 If @code{TARGET_PROMOTE_FUNCTION_RETURN} is defined, you must apply the same
3823 promotion rules specified in @code{PROMOTE_MODE} if @var{valtype} is a
3826 If the precise function being called is known, @var{func} is a tree
3827 node (@code{FUNCTION_DECL}) for it; otherwise, @var{func} is a null
3828 pointer. This makes it possible to use a different value-returning
3829 convention for specific functions when all their calls are
3832 @code{FUNCTION_VALUE} is not used for return vales with aggregate data
3833 types, because these are returned in another way. See
3834 @code{STRUCT_VALUE_REGNUM} and related macros, below.
3837 @defmac FUNCTION_OUTGOING_VALUE (@var{valtype}, @var{func})
3838 Define this macro if the target machine has ``register windows''
3839 so that the register in which a function returns its value is not
3840 the same as the one in which the caller sees the value.
3842 For such machines, @code{FUNCTION_VALUE} computes the register in which
3843 the caller will see the value. @code{FUNCTION_OUTGOING_VALUE} should be
3844 defined in a similar fashion to tell the function where to put the
3847 If @code{FUNCTION_OUTGOING_VALUE} is not defined,
3848 @code{FUNCTION_VALUE} serves both purposes.
3850 @code{FUNCTION_OUTGOING_VALUE} is not used for return vales with
3851 aggregate data types, because these are returned in another way. See
3852 @code{STRUCT_VALUE_REGNUM} and related macros, below.
3855 @defmac LIBCALL_VALUE (@var{mode})
3856 A C expression to create an RTX representing the place where a library
3857 function returns a value of mode @var{mode}. If the precise function
3858 being called is known, @var{func} is a tree node
3859 (@code{FUNCTION_DECL}) for it; otherwise, @var{func} is a null
3860 pointer. This makes it possible to use a different value-returning
3861 convention for specific functions when all their calls are
3864 Note that ``library function'' in this context means a compiler
3865 support routine, used to perform arithmetic, whose name is known
3866 specially by the compiler and was not mentioned in the C code being
3869 The definition of @code{LIBRARY_VALUE} need not be concerned aggregate
3870 data types, because none of the library functions returns such types.
3873 @defmac FUNCTION_VALUE_REGNO_P (@var{regno})
3874 A C expression that is nonzero if @var{regno} is the number of a hard
3875 register in which the values of called function may come back.
3877 A register whose use for returning values is limited to serving as the
3878 second of a pair (for a value of type @code{double}, say) need not be
3879 recognized by this macro. So for most machines, this definition
3883 #define FUNCTION_VALUE_REGNO_P(N) ((N) == 0)
3886 If the machine has register windows, so that the caller and the called
3887 function use different registers for the return value, this macro
3888 should recognize only the caller's register numbers.
3891 @defmac APPLY_RESULT_SIZE
3892 Define this macro if @samp{untyped_call} and @samp{untyped_return}
3893 need more space than is implied by @code{FUNCTION_VALUE_REGNO_P} for
3894 saving and restoring an arbitrary return value.
3897 @node Aggregate Return
3898 @subsection How Large Values Are Returned
3899 @cindex aggregates as return values
3900 @cindex large return values
3901 @cindex returning aggregate values
3902 @cindex structure value address
3904 When a function value's mode is @code{BLKmode} (and in some other
3905 cases), the value is not returned according to @code{FUNCTION_VALUE}
3906 (@pxref{Scalar Return}). Instead, the caller passes the address of a
3907 block of memory in which the value should be stored. This address
3908 is called the @dfn{structure value address}.
3910 This section describes how to control returning structure values in
3913 @deftypefn {Target Hook} bool RETURN_IN_MEMORY (tree @var{type}, tree @var{fntype})
3914 This target hook should return a nonzero value to say to return the
3915 function value in memory, just as large structures are always returned.
3916 Here @var{type} will be the data type of the value, and @var{fntype}
3917 will be the type of the function doing the returning, or @code{NULL} for
3920 Note that values of mode @code{BLKmode} must be explicitly handled
3921 by this function. Also, the option @option{-fpcc-struct-return}
3922 takes effect regardless of this macro. On most systems, it is
3923 possible to leave the hook undefined; this causes a default
3924 definition to be used, whose value is the constant 1 for @code{BLKmode}
3925 values, and 0 otherwise.
3927 Do not use this hook to indicate that structures and unions should always
3928 be returned in memory. You should instead use @code{DEFAULT_PCC_STRUCT_RETURN}
3932 @defmac DEFAULT_PCC_STRUCT_RETURN
3933 Define this macro to be 1 if all structure and union return values must be
3934 in memory. Since this results in slower code, this should be defined
3935 only if needed for compatibility with other compilers or with an ABI@.
3936 If you define this macro to be 0, then the conventions used for structure
3937 and union return values are decided by the @code{RETURN_IN_MEMORY} macro.
3939 If not defined, this defaults to the value 1.
3942 @deftypefn {Target Hook} rtx TARGET_STRUCT_VALUE_RTX (tree @var{fndecl}, int @var{incoming})
3943 This target hook should return the location of the structure value
3944 address (normally a @code{mem} or @code{reg}), or 0 if the address is
3945 passed as an ``invisible'' first argument. Note that @var{fndecl} may
3946 be @code{NULL}, for libcalls.
3948 On some architectures the place where the structure value address
3949 is found by the called function is not the same place that the
3950 caller put it. This can be due to register windows, or it could
3951 be because the function prologue moves it to a different place.
3952 @var{incoming} is @code{true} when the location is needed in
3953 the context of the called function, and @code{false} in the context of
3956 If @var{incoming} is @code{true} and the address is to be found on the
3957 stack, return a @code{mem} which refers to the frame pointer.
3960 @defmac PCC_STATIC_STRUCT_RETURN
3961 Define this macro if the usual system convention on the target machine
3962 for returning structures and unions is for the called function to return
3963 the address of a static variable containing the value.
3965 Do not define this if the usual system convention is for the caller to
3966 pass an address to the subroutine.
3968 This macro has effect in @option{-fpcc-struct-return} mode, but it does
3969 nothing when you use @option{-freg-struct-return} mode.
3973 @subsection Caller-Saves Register Allocation
3975 If you enable it, GCC can save registers around function calls. This
3976 makes it possible to use call-clobbered registers to hold variables that
3977 must live across calls.
3979 @defmac DEFAULT_CALLER_SAVES
3980 Define this macro if function calls on the target machine do not preserve
3981 any registers; in other words, if @code{CALL_USED_REGISTERS} has 1
3982 for all registers. When defined, this macro enables @option{-fcaller-saves}
3983 by default for all optimization levels. It has no effect for optimization
3984 levels 2 and higher, where @option{-fcaller-saves} is the default.
3987 @defmac CALLER_SAVE_PROFITABLE (@var{refs}, @var{calls})
3988 A C expression to determine whether it is worthwhile to consider placing
3989 a pseudo-register in a call-clobbered hard register and saving and
3990 restoring it around each function call. The expression should be 1 when
3991 this is worth doing, and 0 otherwise.
3993 If you don't define this macro, a default is used which is good on most
3994 machines: @code{4 * @var{calls} < @var{refs}}.
3997 @defmac HARD_REGNO_CALLER_SAVE_MODE (@var{regno}, @var{nregs})
3998 A C expression specifying which mode is required for saving @var{nregs}
3999 of a pseudo-register in call-clobbered hard register @var{regno}. If
4000 @var{regno} is unsuitable for caller save, @code{VOIDmode} should be
4001 returned. For most machines this macro need not be defined since GCC
4002 will select the smallest suitable mode.
4005 @node Function Entry
4006 @subsection Function Entry and Exit
4007 @cindex function entry and exit
4011 This section describes the macros that output function entry
4012 (@dfn{prologue}) and exit (@dfn{epilogue}) code.
4014 @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_PROLOGUE (FILE *@var{file}, HOST_WIDE_INT @var{size})
4015 If defined, a function that outputs the assembler code for entry to a
4016 function. The prologue is responsible for setting up the stack frame,
4017 initializing the frame pointer register, saving registers that must be
4018 saved, and allocating @var{size} additional bytes of storage for the
4019 local variables. @var{size} is an integer. @var{file} is a stdio
4020 stream to which the assembler code should be output.
4022 The label for the beginning of the function need not be output by this
4023 macro. That has already been done when the macro is run.
4025 @findex regs_ever_live
4026 To determine which registers to save, the macro can refer to the array
4027 @code{regs_ever_live}: element @var{r} is nonzero if hard register
4028 @var{r} is used anywhere within the function. This implies the function
4029 prologue should save register @var{r}, provided it is not one of the
4030 call-used registers. (@code{TARGET_ASM_FUNCTION_EPILOGUE} must likewise use
4031 @code{regs_ever_live}.)
4033 On machines that have ``register windows'', the function entry code does
4034 not save on the stack the registers that are in the windows, even if
4035 they are supposed to be preserved by function calls; instead it takes
4036 appropriate steps to ``push'' the register stack, if any non-call-used
4037 registers are used in the function.
4039 @findex frame_pointer_needed
4040 On machines where functions may or may not have frame-pointers, the
4041 function entry code must vary accordingly; it must set up the frame
4042 pointer if one is wanted, and not otherwise. To determine whether a
4043 frame pointer is in wanted, the macro can refer to the variable
4044 @code{frame_pointer_needed}. The variable's value will be 1 at run
4045 time in a function that needs a frame pointer. @xref{Elimination}.
4047 The function entry code is responsible for allocating any stack space
4048 required for the function. This stack space consists of the regions
4049 listed below. In most cases, these regions are allocated in the
4050 order listed, with the last listed region closest to the top of the
4051 stack (the lowest address if @code{STACK_GROWS_DOWNWARD} is defined, and
4052 the highest address if it is not defined). You can use a different order
4053 for a machine if doing so is more convenient or required for
4054 compatibility reasons. Except in cases where required by standard
4055 or by a debugger, there is no reason why the stack layout used by GCC
4056 need agree with that used by other compilers for a machine.
4059 @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_END_PROLOGUE (FILE *@var{file})
4060 If defined, a function that outputs assembler code at the end of a
4061 prologue. This should be used when the function prologue is being
4062 emitted as RTL, and you have some extra assembler that needs to be
4063 emitted. @xref{prologue instruction pattern}.
4066 @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_BEGIN_EPILOGUE (FILE *@var{file})
4067 If defined, a function that outputs assembler code at the start of an
4068 epilogue. This should be used when the function epilogue is being
4069 emitted as RTL, and you have some extra assembler that needs to be
4070 emitted. @xref{epilogue instruction pattern}.
4073 @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_EPILOGUE (FILE *@var{file}, HOST_WIDE_INT @var{size})
4074 If defined, a function that outputs the assembler code for exit from a
4075 function. The epilogue is responsible for restoring the saved
4076 registers and stack pointer to their values when the function was
4077 called, and returning control to the caller. This macro takes the
4078 same arguments as the macro @code{TARGET_ASM_FUNCTION_PROLOGUE}, and the
4079 registers to restore are determined from @code{regs_ever_live} and
4080 @code{CALL_USED_REGISTERS} in the same way.
4082 On some machines, there is a single instruction that does all the work
4083 of returning from the function. On these machines, give that
4084 instruction the name @samp{return} and do not define the macro
4085 @code{TARGET_ASM_FUNCTION_EPILOGUE} at all.
4087 Do not define a pattern named @samp{return} if you want the
4088 @code{TARGET_ASM_FUNCTION_EPILOGUE} to be used. If you want the target
4089 switches to control whether return instructions or epilogues are used,
4090 define a @samp{return} pattern with a validity condition that tests the
4091 target switches appropriately. If the @samp{return} pattern's validity
4092 condition is false, epilogues will be used.
4094 On machines where functions may or may not have frame-pointers, the
4095 function exit code must vary accordingly. Sometimes the code for these
4096 two cases is completely different. To determine whether a frame pointer
4097 is wanted, the macro can refer to the variable
4098 @code{frame_pointer_needed}. The variable's value will be 1 when compiling
4099 a function that needs a frame pointer.
4101 Normally, @code{TARGET_ASM_FUNCTION_PROLOGUE} and
4102 @code{TARGET_ASM_FUNCTION_EPILOGUE} must treat leaf functions specially.
4103 The C variable @code{current_function_is_leaf} is nonzero for such a
4104 function. @xref{Leaf Functions}.
4106 On some machines, some functions pop their arguments on exit while
4107 others leave that for the caller to do. For example, the 68020 when
4108 given @option{-mrtd} pops arguments in functions that take a fixed
4109 number of arguments.
4111 @findex current_function_pops_args
4112 Your definition of the macro @code{RETURN_POPS_ARGS} decides which
4113 functions pop their own arguments. @code{TARGET_ASM_FUNCTION_EPILOGUE}
4114 needs to know what was decided. The variable that is called
4115 @code{current_function_pops_args} is the number of bytes of its
4116 arguments that a function should pop. @xref{Scalar Return}.
4117 @c what is the "its arguments" in the above sentence referring to, pray
4118 @c tell? --mew 5feb93
4123 @findex current_function_pretend_args_size
4124 A region of @code{current_function_pretend_args_size} bytes of
4125 uninitialized space just underneath the first argument arriving on the
4126 stack. (This may not be at the very start of the allocated stack region
4127 if the calling sequence has pushed anything else since pushing the stack
4128 arguments. But usually, on such machines, nothing else has been pushed
4129 yet, because the function prologue itself does all the pushing.) This
4130 region is used on machines where an argument may be passed partly in
4131 registers and partly in memory, and, in some cases to support the
4132 features in @code{<stdarg.h>}.
4135 An area of memory used to save certain registers used by the function.
4136 The size of this area, which may also include space for such things as
4137 the return address and pointers to previous stack frames, is
4138 machine-specific and usually depends on which registers have been used
4139 in the function. Machines with register windows often do not require
4143 A region of at least @var{size} bytes, possibly rounded up to an allocation
4144 boundary, to contain the local variables of the function. On some machines,
4145 this region and the save area may occur in the opposite order, with the
4146 save area closer to the top of the stack.
4149 @cindex @code{ACCUMULATE_OUTGOING_ARGS} and stack frames
4150 Optionally, when @code{ACCUMULATE_OUTGOING_ARGS} is defined, a region of
4151 @code{current_function_outgoing_args_size} bytes to be used for outgoing
4152 argument lists of the function. @xref{Stack Arguments}.
4155 Normally, it is necessary for the macros
4156 @code{TARGET_ASM_FUNCTION_PROLOGUE} and
4157 @code{TARGET_ASM_FUNCTION_EPILOGUE} to treat leaf functions specially.
4158 The C variable @code{current_function_is_leaf} is nonzero for such a
4161 @defmac EXIT_IGNORE_STACK
4162 Define this macro as a C expression that is nonzero if the return
4163 instruction or the function epilogue ignores the value of the stack
4164 pointer; in other words, if it is safe to delete an instruction to
4165 adjust the stack pointer before a return from the function.
4167 Note that this macro's value is relevant only for functions for which
4168 frame pointers are maintained. It is never safe to delete a final
4169 stack adjustment in a function that has no frame pointer, and the
4170 compiler knows this regardless of @code{EXIT_IGNORE_STACK}.
4173 @defmac EPILOGUE_USES (@var{regno})
4174 Define this macro as a C expression that is nonzero for registers that are
4175 used by the epilogue or the @samp{return} pattern. The stack and frame
4176 pointer registers are already be assumed to be used as needed.
4179 @defmac EH_USES (@var{regno})
4180 Define this macro as a C expression that is nonzero for registers that are
4181 used by the exception handling mechanism, and so should be considered live
4182 on entry to an exception edge.
4185 @defmac DELAY_SLOTS_FOR_EPILOGUE
4186 Define this macro if the function epilogue contains delay slots to which
4187 instructions from the rest of the function can be ``moved''. The
4188 definition should be a C expression whose value is an integer
4189 representing the number of delay slots there.
4192 @defmac ELIGIBLE_FOR_EPILOGUE_DELAY (@var{insn}, @var{n})
4193 A C expression that returns 1 if @var{insn} can be placed in delay
4194 slot number @var{n} of the epilogue.
4196 The argument @var{n} is an integer which identifies the delay slot now
4197 being considered (since different slots may have different rules of
4198 eligibility). It is never negative and is always less than the number
4199 of epilogue delay slots (what @code{DELAY_SLOTS_FOR_EPILOGUE} returns).
4200 If you reject a particular insn for a given delay slot, in principle, it
4201 may be reconsidered for a subsequent delay slot. Also, other insns may
4202 (at least in principle) be considered for the so far unfilled delay
4205 @findex current_function_epilogue_delay_list
4206 @findex final_scan_insn
4207 The insns accepted to fill the epilogue delay slots are put in an RTL
4208 list made with @code{insn_list} objects, stored in the variable
4209 @code{current_function_epilogue_delay_list}. The insn for the first
4210 delay slot comes first in the list. Your definition of the macro
4211 @code{TARGET_ASM_FUNCTION_EPILOGUE} should fill the delay slots by
4212 outputting the insns in this list, usually by calling
4213 @code{final_scan_insn}.
4215 You need not define this macro if you did not define
4216 @code{DELAY_SLOTS_FOR_EPILOGUE}.
4219 @deftypefn {Target Hook} void TARGET_ASM_OUTPUT_MI_THUNK (FILE *@var{file}, tree @var{thunk_fndecl}, HOST_WIDE_INT @var{delta}, tree @var{function})
4220 A function that outputs the assembler code for a thunk
4221 function, used to implement C++ virtual function calls with multiple
4222 inheritance. The thunk acts as a wrapper around a virtual function,
4223 adjusting the implicit object parameter before handing control off to
4226 First, emit code to add the integer @var{delta} to the location that
4227 contains the incoming first argument. Assume that this argument
4228 contains a pointer, and is the one used to pass the @code{this} pointer
4229 in C++. This is the incoming argument @emph{before} the function prologue,
4230 e.g.@: @samp{%o0} on a sparc. The addition must preserve the values of
4231 all other incoming arguments.
4233 After the addition, emit code to jump to @var{function}, which is a
4234 @code{FUNCTION_DECL}. This is a direct pure jump, not a call, and does
4235 not touch the return address. Hence returning from @var{FUNCTION} will
4236 return to whoever called the current @samp{thunk}.
4238 The effect must be as if @var{function} had been called directly with
4239 the adjusted first argument. This macro is responsible for emitting all
4240 of the code for a thunk function; @code{TARGET_ASM_FUNCTION_PROLOGUE}
4241 and @code{TARGET_ASM_FUNCTION_EPILOGUE} are not invoked.
4243 The @var{thunk_fndecl} is redundant. (@var{delta} and @var{function}
4244 have already been extracted from it.) It might possibly be useful on
4245 some targets, but probably not.
4247 If you do not define this macro, the target-independent code in the C++
4248 front end will generate a less efficient heavyweight thunk that calls
4249 @var{function} instead of jumping to it. The generic approach does
4250 not support varargs.
4253 @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})
4254 A function like @code{TARGET_ASM_OUTPUT_MI_THUNK}, except that if
4255 @var{vcall_offset} is nonzero, an additional adjustment should be made
4256 after adding @code{delta}. In particular, if @var{p} is the
4257 adjusted pointer, the following adjustment should be made:
4260 p += (*((ptrdiff_t **)p))[vcall_offset/sizeof(ptrdiff_t)]
4264 If this function is defined, it will always be used in place of
4265 @code{TARGET_ASM_OUTPUT_MI_THUNK}.
4269 @subsection Generating Code for Profiling
4270 @cindex profiling, code generation
4272 These macros will help you generate code for profiling.
4274 @defmac FUNCTION_PROFILER (@var{file}, @var{labelno})
4275 A C statement or compound statement to output to @var{file} some
4276 assembler code to call the profiling subroutine @code{mcount}.
4279 The details of how @code{mcount} expects to be called are determined by
4280 your operating system environment, not by GCC@. To figure them out,
4281 compile a small program for profiling using the system's installed C
4282 compiler and look at the assembler code that results.
4284 Older implementations of @code{mcount} expect the address of a counter
4285 variable to be loaded into some register. The name of this variable is
4286 @samp{LP} followed by the number @var{labelno}, so you would generate
4287 the name using @samp{LP%d} in a @code{fprintf}.
4290 @defmac PROFILE_HOOK
4291 A C statement or compound statement to output to @var{file} some assembly
4292 code to call the profiling subroutine @code{mcount} even the target does
4293 not support profiling.
4296 @defmac NO_PROFILE_COUNTERS
4297 Define this macro if the @code{mcount} subroutine on your system does
4298 not need a counter variable allocated for each function. This is true
4299 for almost all modern implementations. If you define this macro, you
4300 must not use the @var{labelno} argument to @code{FUNCTION_PROFILER}.
4303 @defmac PROFILE_BEFORE_PROLOGUE
4304 Define this macro if the code for function profiling should come before
4305 the function prologue. Normally, the profiling code comes after.
4309 @subsection Permitting tail calls
4312 @deftypefn {Target Hook} bool TARGET_FUNCTION_OK_FOR_SIBCALL (tree @var{decl}, tree @var{exp})
4313 True if it is ok to do sibling call optimization for the specified
4314 call expression @var{exp}. @var{decl} will be the called function,
4315 or @code{NULL} if this is an indirect call.
4317 It is not uncommon for limitations of calling conventions to prevent
4318 tail calls to functions outside the current unit of translation, or
4319 during PIC compilation. The hook is used to enforce these restrictions,
4320 as the @code{sibcall} md pattern can not fail, or fall over to a
4321 ``normal'' call. The criteria for successful sibling call optimization
4322 may vary greatly between different architectures.
4326 @section Implementing the Varargs Macros
4327 @cindex varargs implementation
4329 GCC comes with an implementation of @code{<varargs.h>} and
4330 @code{<stdarg.h>} that work without change on machines that pass arguments
4331 on the stack. Other machines require their own implementations of
4332 varargs, and the two machine independent header files must have
4333 conditionals to include it.
4335 ISO @code{<stdarg.h>} differs from traditional @code{<varargs.h>} mainly in
4336 the calling convention for @code{va_start}. The traditional
4337 implementation takes just one argument, which is the variable in which
4338 to store the argument pointer. The ISO implementation of
4339 @code{va_start} takes an additional second argument. The user is
4340 supposed to write the last named argument of the function here.
4342 However, @code{va_start} should not use this argument. The way to find
4343 the end of the named arguments is with the built-in functions described
4346 @defmac __builtin_saveregs ()
4347 Use this built-in function to save the argument registers in memory so
4348 that the varargs mechanism can access them. Both ISO and traditional
4349 versions of @code{va_start} must use @code{__builtin_saveregs}, unless
4350 you use @code{SETUP_INCOMING_VARARGS} (see below) instead.
4352 On some machines, @code{__builtin_saveregs} is open-coded under the
4353 control of the macro @code{EXPAND_BUILTIN_SAVEREGS}. On other machines,
4354 it calls a routine written in assembler language, found in
4357 Code generated for the call to @code{__builtin_saveregs} appears at the
4358 beginning of the function, as opposed to where the call to
4359 @code{__builtin_saveregs} is written, regardless of what the code is.
4360 This is because the registers must be saved before the function starts
4361 to use them for its own purposes.
4362 @c i rewrote the first sentence above to fix an overfull hbox. --mew
4366 @defmac __builtin_args_info (@var{category})
4367 Use this built-in function to find the first anonymous arguments in
4370 In general, a machine may have several categories of registers used for
4371 arguments, each for a particular category of data types. (For example,
4372 on some machines, floating-point registers are used for floating-point
4373 arguments while other arguments are passed in the general registers.)
4374 To make non-varargs functions use the proper calling convention, you
4375 have defined the @code{CUMULATIVE_ARGS} data type to record how many
4376 registers in each category have been used so far
4378 @code{__builtin_args_info} accesses the same data structure of type
4379 @code{CUMULATIVE_ARGS} after the ordinary argument layout is finished
4380 with it, with @var{category} specifying which word to access. Thus, the
4381 value indicates the first unused register in a given category.
4383 Normally, you would use @code{__builtin_args_info} in the implementation
4384 of @code{va_start}, accessing each category just once and storing the
4385 value in the @code{va_list} object. This is because @code{va_list} will
4386 have to update the values, and there is no way to alter the
4387 values accessed by @code{__builtin_args_info}.
4390 @defmac __builtin_next_arg (@var{lastarg})
4391 This is the equivalent of @code{__builtin_args_info}, for stack
4392 arguments. It returns the address of the first anonymous stack
4393 argument, as type @code{void *}. If @code{ARGS_GROW_DOWNWARD}, it
4394 returns the address of the location above the first anonymous stack
4395 argument. Use it in @code{va_start} to initialize the pointer for
4396 fetching arguments from the stack. Also use it in @code{va_start} to
4397 verify that the second parameter @var{lastarg} is the last named argument
4398 of the current function.
4401 @defmac __builtin_classify_type (@var{object})
4402 Since each machine has its own conventions for which data types are
4403 passed in which kind of register, your implementation of @code{va_arg}
4404 has to embody these conventions. The easiest way to categorize the
4405 specified data type is to use @code{__builtin_classify_type} together
4406 with @code{sizeof} and @code{__alignof__}.
4408 @code{__builtin_classify_type} ignores the value of @var{object},
4409 considering only its data type. It returns an integer describing what
4410 kind of type that is---integer, floating, pointer, structure, and so on.
4412 The file @file{typeclass.h} defines an enumeration that you can use to
4413 interpret the values of @code{__builtin_classify_type}.
4416 These machine description macros help implement varargs:
4418 @deftypefn {Target Hook} rtx TARGET_EXPAND_BUILTIN_SAVEREGS (void)
4419 If defined, this hook produces the machine-specific code for a call to
4420 @code{__builtin_saveregs}. This code will be moved to the very
4421 beginning of the function, before any parameter access are made. The
4422 return value of this function should be an RTX that contains the value
4423 to use as the return of @code{__builtin_saveregs}.
4426 @deftypefn {Target Hook} void TARGET_SETUP_INCOMING_VARARGS (CUMULATIVE_ARGS *@var{args_so_far}, enum machine_mode @var{mode}, tree @var{type}, int *@var{pretend_args_size}, int @var{second_time})
4427 This target hook offers an alternative to using
4428 @code{__builtin_saveregs} and defining the hook
4429 @code{TARGET_EXPAND_BUILTIN_SAVEREGS}. Use it to store the anonymous
4430 register arguments into the stack so that all the arguments appear to
4431 have been passed consecutively on the stack. Once this is done, you can
4432 use the standard implementation of varargs that works for machines that
4433 pass all their arguments on the stack.
4435 The argument @var{args_so_far} points to the @code{CUMULATIVE_ARGS} data
4436 structure, containing the values that are obtained after processing the
4437 named arguments. The arguments @var{mode} and @var{type} describe the
4438 last named argument---its machine mode and its data type as a tree node.
4440 The target hook should do two things: first, push onto the stack all the
4441 argument registers @emph{not} used for the named arguments, and second,
4442 store the size of the data thus pushed into the @code{int}-valued
4443 variable pointed to by @var{pretend_args_size}. The value that you
4444 store here will serve as additional offset for setting up the stack
4447 Because you must generate code to push the anonymous arguments at
4448 compile time without knowing their data types,
4449 @code{TARGET_SETUP_INCOMING_VARARGS} is only useful on machines that
4450 have just a single category of argument register and use it uniformly
4453 If the argument @var{second_time} is nonzero, it means that the
4454 arguments of the function are being analyzed for the second time. This
4455 happens for an inline function, which is not actually compiled until the
4456 end of the source file. The hook @code{TARGET_SETUP_INCOMING_VARARGS} should
4457 not generate any instructions in this case.
4460 @deftypefn {Target Hook} bool TARGET_STRICT_ARGUMENT_NAMING (CUMULATIVE_ARGS *@var{ca})
4461 Define this hook to return @code{true} if the location where a function
4462 argument is passed depends on whether or not it is a named argument.
4464 This hook controls how the @var{named} argument to @code{FUNCTION_ARG}
4465 is set for varargs and stdarg functions. If this hook returns
4466 @code{true}, the @var{named} argument is always true for named
4467 arguments, and false for unnamed arguments. If it returns @code{false},
4468 but @code{TARGET_PRETEND_OUTOGOING_VARARGS_NAMED} returns @code{true},
4469 then all arguments are treated as named. Otherwise, all named arguments
4470 except the last are treated as named.
4472 You need not define this hook if it always returns zero.
4475 @deftypefn {Target Hook} bool TARGET_PRETEND_OUTGOING_VARARGS_NAMED
4476 If you need to conditionally change ABIs so that one works with
4477 @code{TARGET_SETUP_INCOMING_VARARGS}, but the other works like neither
4478 @code{TARGET_SETUP_INCOMING_VARARGS} nor @code{TARGET_STRICT_ARGUMENT_NAMING} was
4479 defined, then define this hook to return @code{true} if
4480 @code{SETUP_INCOMING_VARARGS} is used, @code{false} otherwise.
4481 Otherwise, you should not define this hook.
4485 @section Trampolines for Nested Functions
4486 @cindex trampolines for nested functions
4487 @cindex nested functions, trampolines for
4489 A @dfn{trampoline} is a small piece of code that is created at run time
4490 when the address of a nested function is taken. It normally resides on
4491 the stack, in the stack frame of the containing function. These macros
4492 tell GCC how to generate code to allocate and initialize a
4495 The instructions in the trampoline must do two things: load a constant
4496 address into the static chain register, and jump to the real address of
4497 the nested function. On CISC machines such as the m68k, this requires
4498 two instructions, a move immediate and a jump. Then the two addresses
4499 exist in the trampoline as word-long immediate operands. On RISC
4500 machines, it is often necessary to load each address into a register in
4501 two parts. Then pieces of each address form separate immediate
4504 The code generated to initialize the trampoline must store the variable
4505 parts---the static chain value and the function address---into the
4506 immediate operands of the instructions. On a CISC machine, this is
4507 simply a matter of copying each address to a memory reference at the
4508 proper offset from the start of the trampoline. On a RISC machine, it
4509 may be necessary to take out pieces of the address and store them
4512 @defmac TRAMPOLINE_TEMPLATE (@var{file})
4513 A C statement to output, on the stream @var{file}, assembler code for a
4514 block of data that contains the constant parts of a trampoline. This
4515 code should not include a label---the label is taken care of
4518 If you do not define this macro, it means no template is needed
4519 for the target. Do not define this macro on systems where the block move
4520 code to copy the trampoline into place would be larger than the code
4521 to generate it on the spot.
4524 @defmac TRAMPOLINE_SECTION
4525 The name of a subroutine to switch to the section in which the
4526 trampoline template is to be placed (@pxref{Sections}). The default is
4527 a value of @samp{readonly_data_section}, which places the trampoline in
4528 the section containing read-only data.
4531 @defmac TRAMPOLINE_SIZE
4532 A C expression for the size in bytes of the trampoline, as an integer.
4535 @defmac TRAMPOLINE_ALIGNMENT
4536 Alignment required for trampolines, in bits.
4538 If you don't define this macro, the value of @code{BIGGEST_ALIGNMENT}
4539 is used for aligning trampolines.
4542 @defmac INITIALIZE_TRAMPOLINE (@var{addr}, @var{fnaddr}, @var{static_chain})
4543 A C statement to initialize the variable parts of a trampoline.
4544 @var{addr} is an RTX for the address of the trampoline; @var{fnaddr} is
4545 an RTX for the address of the nested function; @var{static_chain} is an
4546 RTX for the static chain value that should be passed to the function
4550 @defmac TRAMPOLINE_ADJUST_ADDRESS (@var{addr})
4551 A C statement that should perform any machine-specific adjustment in
4552 the address of the trampoline. Its argument contains the address that
4553 was passed to @code{INITIALIZE_TRAMPOLINE}. In case the address to be
4554 used for a function call should be different from the address in which
4555 the template was stored, the different address should be assigned to
4556 @var{addr}. If this macro is not defined, @var{addr} will be used for
4559 @cindex @code{TARGET_ASM_FUNCTION_EPILOGUE} and trampolines
4560 @cindex @code{TARGET_ASM_FUNCTION_PROLOGUE} and trampolines
4561 If this macro is not defined, by default the trampoline is allocated as
4562 a stack slot. This default is right for most machines. The exceptions
4563 are machines where it is impossible to execute instructions in the stack
4564 area. On such machines, you may have to implement a separate stack,
4565 using this macro in conjunction with @code{TARGET_ASM_FUNCTION_PROLOGUE}
4566 and @code{TARGET_ASM_FUNCTION_EPILOGUE}.
4568 @var{fp} points to a data structure, a @code{struct function}, which
4569 describes the compilation status of the immediate containing function of
4570 the function which the trampoline is for. The stack slot for the
4571 trampoline is in the stack frame of this containing function. Other
4572 allocation strategies probably must do something analogous with this
4576 Implementing trampolines is difficult on many machines because they have
4577 separate instruction and data caches. Writing into a stack location
4578 fails to clear the memory in the instruction cache, so when the program
4579 jumps to that location, it executes the old contents.
4581 Here are two possible solutions. One is to clear the relevant parts of
4582 the instruction cache whenever a trampoline is set up. The other is to
4583 make all trampolines identical, by having them jump to a standard
4584 subroutine. The former technique makes trampoline execution faster; the
4585 latter makes initialization faster.
4587 To clear the instruction cache when a trampoline is initialized, define
4588 the following macro.
4590 @defmac CLEAR_INSN_CACHE (@var{beg}, @var{end})
4591 If defined, expands to a C expression clearing the @emph{instruction
4592 cache} in the specified interval. The definition of this macro would
4593 typically be a series of @code{asm} statements. Both @var{beg} and
4594 @var{end} are both pointer expressions.
4597 To use a standard subroutine, define the following macro. In addition,
4598 you must make sure that the instructions in a trampoline fill an entire
4599 cache line with identical instructions, or else ensure that the
4600 beginning of the trampoline code is always aligned at the same point in
4601 its cache line. Look in @file{m68k.h} as a guide.
4603 @defmac TRANSFER_FROM_TRAMPOLINE
4604 Define this macro if trampolines need a special subroutine to do their
4605 work. The macro should expand to a series of @code{asm} statements
4606 which will be compiled with GCC@. They go in a library function named
4607 @code{__transfer_from_trampoline}.
4609 If you need to avoid executing the ordinary prologue code of a compiled
4610 C function when you jump to the subroutine, you can do so by placing a
4611 special label of your own in the assembler code. Use one @code{asm}
4612 statement to generate an assembler label, and another to make the label
4613 global. Then trampolines can use that label to jump directly to your
4614 special assembler code.
4618 @section Implicit Calls to Library Routines
4619 @cindex library subroutine names
4620 @cindex @file{libgcc.a}
4622 @c prevent bad page break with this line
4623 Here is an explanation of implicit calls to library routines.
4625 @defmac MULSI3_LIBCALL
4626 A C string constant giving the name of the function to call for
4627 multiplication of one signed full-word by another. If you do not
4628 define this macro, the default name is used, which is @code{__mulsi3},
4629 a function defined in @file{libgcc.a}.
4632 @defmac DIVSI3_LIBCALL
4633 A C string constant giving the name of the function to call for
4634 division of one signed full-word by another. If you do not define
4635 this macro, the default name is used, which is @code{__divsi3}, a
4636 function defined in @file{libgcc.a}.
4639 @defmac UDIVSI3_LIBCALL
4640 A C string constant giving the name of the function to call for
4641 division of one unsigned full-word by another. If you do not define
4642 this macro, the default name is used, which is @code{__udivsi3}, a
4643 function defined in @file{libgcc.a}.
4646 @defmac MODSI3_LIBCALL
4647 A C string constant giving the name of the function to call for the
4648 remainder in division of one signed full-word by another. If you do
4649 not define this macro, the default name is used, which is
4650 @code{__modsi3}, a function defined in @file{libgcc.a}.
4653 @defmac UMODSI3_LIBCALL
4654 A C string constant giving the name of the function to call for the
4655 remainder in division of one unsigned full-word by another. If you do
4656 not define this macro, the default name is used, which is
4657 @code{__umodsi3}, a function defined in @file{libgcc.a}.
4660 @defmac MULDI3_LIBCALL
4661 A C string constant giving the name of the function to call for
4662 multiplication of one signed double-word by another. If you do not
4663 define this macro, the default name is used, which is @code{__muldi3},
4664 a function defined in @file{libgcc.a}.
4667 @defmac DIVDI3_LIBCALL
4668 A C string constant giving the name of the function to call for
4669 division of one signed double-word by another. If you do not define
4670 this macro, the default name is used, which is @code{__divdi3}, a
4671 function defined in @file{libgcc.a}.
4674 @defmac UDIVDI3_LIBCALL
4675 A C string constant giving the name of the function to call for
4676 division of one unsigned full-word by another. If you do not define
4677 this macro, the default name is used, which is @code{__udivdi3}, a
4678 function defined in @file{libgcc.a}.
4681 @defmac MODDI3_LIBCALL
4682 A C string constant giving the name of the function to call for the
4683 remainder in division of one signed double-word by another. If you do
4684 not define this macro, the default name is used, which is
4685 @code{__moddi3}, a function defined in @file{libgcc.a}.
4688 @defmac UMODDI3_LIBCALL
4689 A C string constant giving the name of the function to call for the
4690 remainder in division of one unsigned full-word by another. If you do
4691 not define this macro, the default name is used, which is
4692 @code{__umoddi3}, a function defined in @file{libgcc.a}.
4695 @defmac DECLARE_LIBRARY_RENAMES
4696 This macro, if defined, should expand to a piece of C code that will get
4697 expanded when compiling functions for libgcc.a. It can be used to
4698 provide alternate names for gcc's internal library functions if there
4699 are ABI-mandated names that the compiler should provide.
4702 @defmac INIT_TARGET_OPTABS
4703 Define this macro as a C statement that declares additional library
4704 routines renames existing ones. @code{init_optabs} calls this macro after
4705 initializing all the normal library routines.
4708 @defmac FLOAT_LIB_COMPARE_RETURNS_BOOL (@var{mode}, @var{comparison})
4709 Define this macro as a C statement that returns nonzero if a call to
4710 the floating point comparison library function will return a boolean
4711 value that indicates the result of the comparison. It should return
4712 zero if one of gcc's own libgcc functions is called.
4714 Most ports don't need to define this macro.
4717 @cindex @code{EDOM}, implicit usage
4720 The value of @code{EDOM} on the target machine, as a C integer constant
4721 expression. If you don't define this macro, GCC does not attempt to
4722 deposit the value of @code{EDOM} into @code{errno} directly. Look in
4723 @file{/usr/include/errno.h} to find the value of @code{EDOM} on your
4726 If you do not define @code{TARGET_EDOM}, then compiled code reports
4727 domain errors by calling the library function and letting it report the
4728 error. If mathematical functions on your system use @code{matherr} when
4729 there is an error, then you should leave @code{TARGET_EDOM} undefined so
4730 that @code{matherr} is used normally.
4733 @cindex @code{errno}, implicit usage
4734 @defmac GEN_ERRNO_RTX
4735 Define this macro as a C expression to create an rtl expression that
4736 refers to the global ``variable'' @code{errno}. (On certain systems,
4737 @code{errno} may not actually be a variable.) If you don't define this
4738 macro, a reasonable default is used.
4741 @cindex @code{bcopy}, implicit usage
4742 @cindex @code{memcpy}, implicit usage
4743 @cindex @code{memmove}, implicit usage
4744 @cindex @code{bzero}, implicit usage
4745 @cindex @code{memset}, implicit usage
4746 @defmac TARGET_MEM_FUNCTIONS
4747 Define this macro if GCC should generate calls to the ISO C
4748 (and System V) library functions @code{memcpy}, @code{memmove} and
4749 @code{memset} rather than the BSD functions @code{bcopy} and @code{bzero}.
4752 @cindex C99 math functions, implicit usage
4753 @defmac TARGET_C99_FUNCTIONS
4754 When this macro is nonzero, GCC will implicitly optimize @code{sin} calls into
4755 @code{sinf} and similarly for other functions defined by C99 standard. The
4756 default is nonzero that should be proper value for most modern systems, however
4757 number of existing systems lacks support for these functions in the runtime so
4758 they needs this macro to be redefined to 0.
4761 @defmac NEXT_OBJC_RUNTIME
4762 Define this macro to generate code for Objective-C message sending using
4763 the calling convention of the NeXT system. This calling convention
4764 involves passing the object, the selector and the method arguments all
4765 at once to the method-lookup library function.
4767 The default calling convention passes just the object and the selector
4768 to the lookup function, which returns a pointer to the method.
4771 @node Addressing Modes
4772 @section Addressing Modes
4773 @cindex addressing modes
4775 @c prevent bad page break with this line
4776 This is about addressing modes.
4778 @defmac HAVE_PRE_INCREMENT
4779 @defmacx HAVE_PRE_DECREMENT
4780 @defmacx HAVE_POST_INCREMENT
4781 @defmacx HAVE_POST_DECREMENT
4782 A C expression that is nonzero if the machine supports pre-increment,
4783 pre-decrement, post-increment, or post-decrement addressing respectively.
4786 @defmac HAVE_PRE_MODIFY_DISP
4787 @defmacx HAVE_POST_MODIFY_DISP
4788 A C expression that is nonzero if the machine supports pre- or
4789 post-address side-effect generation involving constants other than
4790 the size of the memory operand.
4793 @defmac HAVE_PRE_MODIFY_REG
4794 @defmacx HAVE_POST_MODIFY_REG
4795 A C expression that is nonzero if the machine supports pre- or
4796 post-address side-effect generation involving a register displacement.
4799 @defmac CONSTANT_ADDRESS_P (@var{x})
4800 A C expression that is 1 if the RTX @var{x} is a constant which
4801 is a valid address. On most machines, this can be defined as
4802 @code{CONSTANT_P (@var{x})}, but a few machines are more restrictive
4803 in which constant addresses are supported.
4806 @defmac CONSTANT_P (@var{x})
4807 @code{CONSTANT_P}, which is defined by target-independent code,
4808 accepts integer-values expressions whose values are not explicitly
4809 known, such as @code{symbol_ref}, @code{label_ref}, and @code{high}
4810 expressions and @code{const} arithmetic expressions, in addition to
4811 @code{const_int} and @code{const_double} expressions.
4814 @defmac MAX_REGS_PER_ADDRESS
4815 A number, the maximum number of registers that can appear in a valid
4816 memory address. Note that it is up to you to specify a value equal to
4817 the maximum number that @code{GO_IF_LEGITIMATE_ADDRESS} would ever
4821 @defmac GO_IF_LEGITIMATE_ADDRESS (@var{mode}, @var{x}, @var{label})
4822 A C compound statement with a conditional @code{goto @var{label};}
4823 executed if @var{x} (an RTX) is a legitimate memory address on the
4824 target machine for a memory operand of mode @var{mode}.
4826 It usually pays to define several simpler macros to serve as
4827 subroutines for this one. Otherwise it may be too complicated to
4830 This macro must exist in two variants: a strict variant and a
4831 non-strict one. The strict variant is used in the reload pass. It
4832 must be defined so that any pseudo-register that has not been
4833 allocated a hard register is considered a memory reference. In
4834 contexts where some kind of register is required, a pseudo-register
4835 with no hard register must be rejected.
4837 The non-strict variant is used in other passes. It must be defined to
4838 accept all pseudo-registers in every context where some kind of
4839 register is required.
4841 @findex REG_OK_STRICT
4842 Compiler source files that want to use the strict variant of this
4843 macro define the macro @code{REG_OK_STRICT}. You should use an
4844 @code{#ifdef REG_OK_STRICT} conditional to define the strict variant
4845 in that case and the non-strict variant otherwise.
4847 Subroutines to check for acceptable registers for various purposes (one
4848 for base registers, one for index registers, and so on) are typically
4849 among the subroutines used to define @code{GO_IF_LEGITIMATE_ADDRESS}.
4850 Then only these subroutine macros need have two variants; the higher
4851 levels of macros may be the same whether strict or not.
4853 Normally, constant addresses which are the sum of a @code{symbol_ref}
4854 and an integer are stored inside a @code{const} RTX to mark them as
4855 constant. Therefore, there is no need to recognize such sums
4856 specifically as legitimate addresses. Normally you would simply
4857 recognize any @code{const} as legitimate.
4859 Usually @code{PRINT_OPERAND_ADDRESS} is not prepared to handle constant
4860 sums that are not marked with @code{const}. It assumes that a naked
4861 @code{plus} indicates indexing. If so, then you @emph{must} reject such
4862 naked constant sums as illegitimate addresses, so that none of them will
4863 be given to @code{PRINT_OPERAND_ADDRESS}.
4865 @cindex @code{TARGET_ENCODE_SECTION_INFO} and address validation
4866 On some machines, whether a symbolic address is legitimate depends on
4867 the section that the address refers to. On these machines, define the
4868 target hook @code{TARGET_ENCODE_SECTION_INFO} to store the information
4869 into the @code{symbol_ref}, and then check for it here. When you see a
4870 @code{const}, you will have to look inside it to find the
4871 @code{symbol_ref} in order to determine the section. @xref{Assembler
4875 @defmac REG_OK_FOR_BASE_P (@var{x})
4876 A C expression that is nonzero if @var{x} (assumed to be a @code{reg}
4877 RTX) is valid for use as a base register. For hard registers, it
4878 should always accept those which the hardware permits and reject the
4879 others. Whether the macro accepts or rejects pseudo registers must be
4880 controlled by @code{REG_OK_STRICT} as described above. This usually
4881 requires two variant definitions, of which @code{REG_OK_STRICT}
4882 controls the one actually used.
4885 @defmac REG_MODE_OK_FOR_BASE_P (@var{x}, @var{mode})
4886 A C expression that is just like @code{REG_OK_FOR_BASE_P}, except that
4887 that expression may examine the mode of the memory reference in
4888 @var{mode}. You should define this macro if the mode of the memory
4889 reference affects whether a register may be used as a base register. If
4890 you define this macro, the compiler will use it instead of
4891 @code{REG_OK_FOR_BASE_P}.
4894 @defmac REG_OK_FOR_INDEX_P (@var{x})
4895 A C expression that is nonzero if @var{x} (assumed to be a @code{reg}
4896 RTX) is valid for use as an index register.
4898 The difference between an index register and a base register is that
4899 the index register may be scaled. If an address involves the sum of
4900 two registers, neither one of them scaled, then either one may be
4901 labeled the ``base'' and the other the ``index''; but whichever
4902 labeling is used must fit the machine's constraints of which registers
4903 may serve in each capacity. The compiler will try both labelings,
4904 looking for one that is valid, and will reload one or both registers
4905 only if neither labeling works.
4908 @defmac FIND_BASE_TERM (@var{x})
4909 A C expression to determine the base term of address @var{x}.
4910 This macro is used in only one place: `find_base_term' in alias.c.
4912 It is always safe for this macro to not be defined. It exists so
4913 that alias analysis can understand machine-dependent addresses.
4915 The typical use of this macro is to handle addresses containing
4916 a label_ref or symbol_ref within an UNSPEC@.
4919 @defmac LEGITIMIZE_ADDRESS (@var{x}, @var{oldx}, @var{mode}, @var{win})
4920 A C compound statement that attempts to replace @var{x} with a valid
4921 memory address for an operand of mode @var{mode}. @var{win} will be a
4922 C statement label elsewhere in the code; the macro definition may use
4925 GO_IF_LEGITIMATE_ADDRESS (@var{mode}, @var{x}, @var{win});
4929 to avoid further processing if the address has become legitimate.
4931 @findex break_out_memory_refs
4932 @var{x} will always be the result of a call to @code{break_out_memory_refs},
4933 and @var{oldx} will be the operand that was given to that function to produce
4936 The code generated by this macro should not alter the substructure of
4937 @var{x}. If it transforms @var{x} into a more legitimate form, it
4938 should assign @var{x} (which will always be a C variable) a new value.
4940 It is not necessary for this macro to come up with a legitimate
4941 address. The compiler has standard ways of doing so in all cases. In
4942 fact, it is safe for this macro to do nothing. But often a
4943 machine-dependent strategy can generate better code.
4946 @defmac LEGITIMIZE_RELOAD_ADDRESS (@var{x}, @var{mode}, @var{opnum}, @var{type}, @var{ind_levels}, @var{win})
4947 A C compound statement that attempts to replace @var{x}, which is an address
4948 that needs reloading, with a valid memory address for an operand of mode
4949 @var{mode}. @var{win} will be a C statement label elsewhere in the code.
4950 It is not necessary to define this macro, but it might be useful for
4951 performance reasons.
4953 For example, on the i386, it is sometimes possible to use a single
4954 reload register instead of two by reloading a sum of two pseudo
4955 registers into a register. On the other hand, for number of RISC
4956 processors offsets are limited so that often an intermediate address
4957 needs to be generated in order to address a stack slot. By defining
4958 @code{LEGITIMIZE_RELOAD_ADDRESS} appropriately, the intermediate addresses
4959 generated for adjacent some stack slots can be made identical, and thus
4962 @emph{Note}: This macro should be used with caution. It is necessary
4963 to know something of how reload works in order to effectively use this,
4964 and it is quite easy to produce macros that build in too much knowledge
4965 of reload internals.
4967 @emph{Note}: This macro must be able to reload an address created by a
4968 previous invocation of this macro. If it fails to handle such addresses
4969 then the compiler may generate incorrect code or abort.
4972 The macro definition should use @code{push_reload} to indicate parts that
4973 need reloading; @var{opnum}, @var{type} and @var{ind_levels} are usually
4974 suitable to be passed unaltered to @code{push_reload}.
4976 The code generated by this macro must not alter the substructure of
4977 @var{x}. If it transforms @var{x} into a more legitimate form, it
4978 should assign @var{x} (which will always be a C variable) a new value.
4979 This also applies to parts that you change indirectly by calling
4982 @findex strict_memory_address_p
4983 The macro definition may use @code{strict_memory_address_p} to test if
4984 the address has become legitimate.
4987 If you want to change only a part of @var{x}, one standard way of doing
4988 this is to use @code{copy_rtx}. Note, however, that is unshares only a
4989 single level of rtl. Thus, if the part to be changed is not at the
4990 top level, you'll need to replace first the top level.
4991 It is not necessary for this macro to come up with a legitimate
4992 address; but often a machine-dependent strategy can generate better code.
4995 @defmac GO_IF_MODE_DEPENDENT_ADDRESS (@var{addr}, @var{label})
4996 A C statement or compound statement with a conditional @code{goto
4997 @var{label};} executed if memory address @var{x} (an RTX) can have
4998 different meanings depending on the machine mode of the memory
4999 reference it is used for or if the address is valid for some modes
5002 Autoincrement and autodecrement addresses typically have mode-dependent
5003 effects because the amount of the increment or decrement is the size
5004 of the operand being addressed. Some machines have other mode-dependent
5005 addresses. Many RISC machines have no mode-dependent addresses.
5007 You may assume that @var{addr} is a valid address for the machine.
5010 @defmac LEGITIMATE_CONSTANT_P (@var{x})
5011 A C expression that is nonzero if @var{x} is a legitimate constant for
5012 an immediate operand on the target machine. You can assume that
5013 @var{x} satisfies @code{CONSTANT_P}, so you need not check this. In fact,
5014 @samp{1} is a suitable definition for this macro on machines where
5015 anything @code{CONSTANT_P} is valid.
5018 @node Condition Code
5019 @section Condition Code Status
5020 @cindex condition code status
5022 @c prevent bad page break with this line
5023 This describes the condition code status.
5026 The file @file{conditions.h} defines a variable @code{cc_status} to
5027 describe how the condition code was computed (in case the interpretation of
5028 the condition code depends on the instruction that it was set by). This
5029 variable contains the RTL expressions on which the condition code is
5030 currently based, and several standard flags.
5032 Sometimes additional machine-specific flags must be defined in the machine
5033 description header file. It can also add additional machine-specific
5034 information by defining @code{CC_STATUS_MDEP}.
5036 @defmac CC_STATUS_MDEP
5037 C code for a data type which is used for declaring the @code{mdep}
5038 component of @code{cc_status}. It defaults to @code{int}.
5040 This macro is not used on machines that do not use @code{cc0}.
5043 @defmac CC_STATUS_MDEP_INIT
5044 A C expression to initialize the @code{mdep} field to ``empty''.
5045 The default definition does nothing, since most machines don't use
5046 the field anyway. If you want to use the field, you should probably
5047 define this macro to initialize it.
5049 This macro is not used on machines that do not use @code{cc0}.
5052 @defmac NOTICE_UPDATE_CC (@var{exp}, @var{insn})
5053 A C compound statement to set the components of @code{cc_status}
5054 appropriately for an insn @var{insn} whose body is @var{exp}. It is
5055 this macro's responsibility to recognize insns that set the condition
5056 code as a byproduct of other activity as well as those that explicitly
5059 This macro is not used on machines that do not use @code{cc0}.
5061 If there are insns that do not set the condition code but do alter
5062 other machine registers, this macro must check to see whether they
5063 invalidate the expressions that the condition code is recorded as
5064 reflecting. For example, on the 68000, insns that store in address
5065 registers do not set the condition code, which means that usually
5066 @code{NOTICE_UPDATE_CC} can leave @code{cc_status} unaltered for such
5067 insns. But suppose that the previous insn set the condition code
5068 based on location @samp{a4@@(102)} and the current insn stores a new
5069 value in @samp{a4}. Although the condition code is not changed by
5070 this, it will no longer be true that it reflects the contents of
5071 @samp{a4@@(102)}. Therefore, @code{NOTICE_UPDATE_CC} must alter
5072 @code{cc_status} in this case to say that nothing is known about the
5073 condition code value.
5075 The definition of @code{NOTICE_UPDATE_CC} must be prepared to deal
5076 with the results of peephole optimization: insns whose patterns are
5077 @code{parallel} RTXs containing various @code{reg}, @code{mem} or
5078 constants which are just the operands. The RTL structure of these
5079 insns is not sufficient to indicate what the insns actually do. What
5080 @code{NOTICE_UPDATE_CC} should do when it sees one is just to run
5081 @code{CC_STATUS_INIT}.
5083 A possible definition of @code{NOTICE_UPDATE_CC} is to call a function
5084 that looks at an attribute (@pxref{Insn Attributes}) named, for example,
5085 @samp{cc}. This avoids having detailed information about patterns in
5086 two places, the @file{md} file and in @code{NOTICE_UPDATE_CC}.
5089 @defmac EXTRA_CC_MODES
5090 Condition codes are represented in registers by machine modes of class
5091 @code{MODE_CC}. By default, there is just one mode, @code{CCmode}, with
5092 this class. If you need more such modes, create a file named
5093 @file{@var{machine}-modes.def} in your @file{config/@var{machine}}
5094 directory (@pxref{Back End, , Anatomy of a Target Back End}), containing
5095 a list of these modes. Each entry in the list should be a call to the
5096 macro @code{CC}. This macro takes one argument, which is the name of
5097 the mode: it should begin with @samp{CC}. Do not put quotation marks
5098 around the name, or include the trailing @samp{mode}; these are
5099 automatically added. There should not be anything else in the file
5102 A sample @file{@var{machine}-modes.def} file might look like this:
5105 CC (CC_NOOV) /* @r{Comparison only valid if there was no overflow.} */
5106 CC (CCFP) /* @r{Floating point comparison that cannot trap.} */
5107 CC (CCFPE) /* @r{Floating point comparison that may trap.} */
5110 When you create this file, the macro @code{EXTRA_CC_MODES} is
5111 automatically defined by @command{configure}, with value @samp{1}.
5114 @defmac SELECT_CC_MODE (@var{op}, @var{x}, @var{y})
5115 Returns a mode from class @code{MODE_CC} to be used when comparison
5116 operation code @var{op} is applied to rtx @var{x} and @var{y}. For
5117 example, on the SPARC, @code{SELECT_CC_MODE} is defined as (see
5118 @pxref{Jump Patterns} for a description of the reason for this
5122 #define SELECT_CC_MODE(OP,X,Y) \
5123 (GET_MODE_CLASS (GET_MODE (X)) == MODE_FLOAT \
5124 ? ((OP == EQ || OP == NE) ? CCFPmode : CCFPEmode) \
5125 : ((GET_CODE (X) == PLUS || GET_CODE (X) == MINUS \
5126 || GET_CODE (X) == NEG) \
5127 ? CC_NOOVmode : CCmode))
5130 You need not define this macro if @code{EXTRA_CC_MODES} is not defined.
5133 @defmac CANONICALIZE_COMPARISON (@var{code}, @var{op0}, @var{op1})
5134 On some machines not all possible comparisons are defined, but you can
5135 convert an invalid comparison into a valid one. For example, the Alpha
5136 does not have a @code{GT} comparison, but you can use an @code{LT}
5137 comparison instead and swap the order of the operands.
5139 On such machines, define this macro to be a C statement to do any
5140 required conversions. @var{code} is the initial comparison code
5141 and @var{op0} and @var{op1} are the left and right operands of the
5142 comparison, respectively. You should modify @var{code}, @var{op0}, and
5143 @var{op1} as required.
5145 GCC will not assume that the comparison resulting from this macro is
5146 valid but will see if the resulting insn matches a pattern in the
5149 You need not define this macro if it would never change the comparison
5153 @defmac REVERSIBLE_CC_MODE (@var{mode})
5154 A C expression whose value is one if it is always safe to reverse a
5155 comparison whose mode is @var{mode}. If @code{SELECT_CC_MODE}
5156 can ever return @var{mode} for a floating-point inequality comparison,
5157 then @code{REVERSIBLE_CC_MODE (@var{mode})} must be zero.
5159 You need not define this macro if it would always returns zero or if the
5160 floating-point format is anything other than @code{IEEE_FLOAT_FORMAT}.
5161 For example, here is the definition used on the SPARC, where floating-point
5162 inequality comparisons are always given @code{CCFPEmode}:
5165 #define REVERSIBLE_CC_MODE(MODE) ((MODE) != CCFPEmode)
5169 @defmac REVERSE_CONDITION (@var{code}, @var{mode})
5170 A C expression whose value is reversed condition code of the @var{code} for
5171 comparison done in CC_MODE @var{mode}. The macro is used only in case
5172 @code{REVERSIBLE_CC_MODE (@var{mode})} is nonzero. Define this macro in case
5173 machine has some non-standard way how to reverse certain conditionals. For
5174 instance in case all floating point conditions are non-trapping, compiler may
5175 freely convert unordered compares to ordered one. Then definition may look
5179 #define REVERSE_CONDITION(CODE, MODE) \
5180 ((MODE) != CCFPmode ? reverse_condition (CODE) \
5181 : reverse_condition_maybe_unordered (CODE))
5185 @defmac REVERSE_CONDEXEC_PREDICATES_P (@var{code1}, @var{code2})
5186 A C expression that returns true if the conditional execution predicate
5187 @var{code1} is the inverse of @var{code2} and vice versa. Define this to
5188 return 0 if the target has conditional execution predicates that cannot be
5189 reversed safely. If no expansion is specified, this macro is defined as
5193 #define REVERSE_CONDEXEC_PREDICATES_P (x, y) \
5194 ((x) == reverse_condition (y))
5199 @section Describing Relative Costs of Operations
5200 @cindex costs of instructions
5201 @cindex relative costs
5202 @cindex speed of instructions
5204 These macros let you describe the relative speed of various operations
5205 on the target machine.
5207 @defmac REGISTER_MOVE_COST (@var{mode}, @var{from}, @var{to})
5208 A C expression for the cost of moving data of mode @var{mode} from a
5209 register in class @var{from} to one in class @var{to}. The classes are
5210 expressed using the enumeration values such as @code{GENERAL_REGS}. A
5211 value of 2 is the default; other values are interpreted relative to
5214 It is not required that the cost always equal 2 when @var{from} is the
5215 same as @var{to}; on some machines it is expensive to move between
5216 registers if they are not general registers.
5218 If reload sees an insn consisting of a single @code{set} between two
5219 hard registers, and if @code{REGISTER_MOVE_COST} applied to their
5220 classes returns a value of 2, reload does not check to ensure that the
5221 constraints of the insn are met. Setting a cost of other than 2 will
5222 allow reload to verify that the constraints are met. You should do this
5223 if the @samp{mov@var{m}} pattern's constraints do not allow such copying.
5226 @defmac MEMORY_MOVE_COST (@var{mode}, @var{class}, @var{in})
5227 A C expression for the cost of moving data of mode @var{mode} between a
5228 register of class @var{class} and memory; @var{in} is zero if the value
5229 is to be written to memory, nonzero if it is to be read in. This cost
5230 is relative to those in @code{REGISTER_MOVE_COST}. If moving between
5231 registers and memory is more expensive than between two registers, you
5232 should define this macro to express the relative cost.
5234 If you do not define this macro, GCC uses a default cost of 4 plus
5235 the cost of copying via a secondary reload register, if one is
5236 needed. If your machine requires a secondary reload register to copy
5237 between memory and a register of @var{class} but the reload mechanism is
5238 more complex than copying via an intermediate, define this macro to
5239 reflect the actual cost of the move.
5241 GCC defines the function @code{memory_move_secondary_cost} if
5242 secondary reloads are needed. It computes the costs due to copying via
5243 a secondary register. If your machine copies from memory using a
5244 secondary register in the conventional way but the default base value of
5245 4 is not correct for your machine, define this macro to add some other
5246 value to the result of that function. The arguments to that function
5247 are the same as to this macro.
5251 A C expression for the cost of a branch instruction. A value of 1 is
5252 the default; other values are interpreted relative to that.
5255 Here are additional macros which do not specify precise relative costs,
5256 but only that certain actions are more expensive than GCC would
5259 @defmac SLOW_BYTE_ACCESS
5260 Define this macro as a C expression which is nonzero if accessing less
5261 than a word of memory (i.e.@: a @code{char} or a @code{short}) is no
5262 faster than accessing a word of memory, i.e., if such access
5263 require more than one instruction or if there is no difference in cost
5264 between byte and (aligned) word loads.
5266 When this macro is not defined, the compiler will access a field by
5267 finding the smallest containing object; when it is defined, a fullword
5268 load will be used if alignment permits. Unless bytes accesses are
5269 faster than word accesses, using word accesses is preferable since it
5270 may eliminate subsequent memory access if subsequent accesses occur to
5271 other fields in the same word of the structure, but to different bytes.
5274 @defmac SLOW_UNALIGNED_ACCESS (@var{mode}, @var{alignment})
5275 Define this macro to be the value 1 if memory accesses described by the
5276 @var{mode} and @var{alignment} parameters have a cost many times greater
5277 than aligned accesses, for example if they are emulated in a trap
5280 When this macro is nonzero, the compiler will act as if
5281 @code{STRICT_ALIGNMENT} were nonzero when generating code for block
5282 moves. This can cause significantly more instructions to be produced.
5283 Therefore, do not set this macro nonzero if unaligned accesses only add a
5284 cycle or two to the time for a memory access.
5286 If the value of this macro is always zero, it need not be defined. If
5287 this macro is defined, it should produce a nonzero value when
5288 @code{STRICT_ALIGNMENT} is nonzero.
5292 The threshold of number of scalar memory-to-memory move insns, @emph{below}
5293 which a sequence of insns should be generated instead of a
5294 string move insn or a library call. Increasing the value will always
5295 make code faster, but eventually incurs high cost in increased code size.
5297 Note that on machines where the corresponding move insn is a
5298 @code{define_expand} that emits a sequence of insns, this macro counts
5299 the number of such sequences.
5301 If you don't define this, a reasonable default is used.
5304 @defmac MOVE_BY_PIECES_P (@var{size}, @var{alignment})
5305 A C expression used to determine whether @code{move_by_pieces} will be used to
5306 copy a chunk of memory, or whether some other block move mechanism
5307 will be used. Defaults to 1 if @code{move_by_pieces_ninsns} returns less
5308 than @code{MOVE_RATIO}.
5311 @defmac MOVE_MAX_PIECES
5312 A C expression used by @code{move_by_pieces} to determine the largest unit
5313 a load or store used to copy memory is. Defaults to @code{MOVE_MAX}.
5317 The threshold of number of scalar move insns, @emph{below} which a sequence
5318 of insns should be generated to clear memory instead of a string clear insn
5319 or a library call. Increasing the value will always make code faster, but
5320 eventually incurs high cost in increased code size.
5322 If you don't define this, a reasonable default is used.
5325 @defmac CLEAR_BY_PIECES_P (@var{size}, @var{alignment})
5326 A C expression used to determine whether @code{clear_by_pieces} will be used
5327 to clear a chunk of memory, or whether some other block clear mechanism
5328 will be used. Defaults to 1 if @code{move_by_pieces_ninsns} returns less
5329 than @code{CLEAR_RATIO}.
5332 @defmac STORE_BY_PIECES_P (@var{size}, @var{alignment})
5333 A C expression used to determine whether @code{store_by_pieces} will be
5334 used to set a chunk of memory to a constant value, or whether some other
5335 mechanism will be used. Used by @code{__builtin_memset} when storing
5336 values other than constant zero and by @code{__builtin_strcpy} when
5337 when called with a constant source string.
5338 Defaults to @code{MOVE_BY_PIECES_P}.
5341 @defmac USE_LOAD_POST_INCREMENT (@var{mode})
5342 A C expression used to determine whether a load postincrement is a good
5343 thing to use for a given mode. Defaults to the value of
5344 @code{HAVE_POST_INCREMENT}.
5347 @defmac USE_LOAD_POST_DECREMENT (@var{mode})
5348 A C expression used to determine whether a load postdecrement is a good
5349 thing to use for a given mode. Defaults to the value of
5350 @code{HAVE_POST_DECREMENT}.
5353 @defmac USE_LOAD_PRE_INCREMENT (@var{mode})
5354 A C expression used to determine whether a load preincrement is a good
5355 thing to use for a given mode. Defaults to the value of
5356 @code{HAVE_PRE_INCREMENT}.
5359 @defmac USE_LOAD_PRE_DECREMENT (@var{mode})
5360 A C expression used to determine whether a load predecrement is a good
5361 thing to use for a given mode. Defaults to the value of
5362 @code{HAVE_PRE_DECREMENT}.
5365 @defmac USE_STORE_POST_INCREMENT (@var{mode})
5366 A C expression used to determine whether a store postincrement is a good
5367 thing to use for a given mode. Defaults to the value of
5368 @code{HAVE_POST_INCREMENT}.
5371 @defmac USE_STORE_POST_DECREMENT (@var{mode})
5372 A C expression used to determine whether a store postdecrement is a good
5373 thing to use for a given mode. Defaults to the value of
5374 @code{HAVE_POST_DECREMENT}.
5377 @defmac USE_STORE_PRE_INCREMENT (@var{mode})
5378 This macro is used to determine whether a store preincrement is a good
5379 thing to use for a given mode. Defaults to the value of
5380 @code{HAVE_PRE_INCREMENT}.
5383 @defmac USE_STORE_PRE_DECREMENT (@var{mode})
5384 This macro is used to determine whether a store predecrement is a good
5385 thing to use for a given mode. Defaults to the value of
5386 @code{HAVE_PRE_DECREMENT}.
5389 @defmac NO_FUNCTION_CSE
5390 Define this macro if it is as good or better to call a constant
5391 function address than to call an address kept in a register.
5394 @defmac NO_RECURSIVE_FUNCTION_CSE
5395 Define this macro if it is as good or better for a function to call
5396 itself with an explicit address than to call an address kept in a
5400 @defmac RANGE_TEST_NON_SHORT_CIRCUIT
5401 Define this macro if a non-short-circuit operation produced by
5402 @samp{fold_range_test ()} is optimal. This macro defaults to true if
5403 @code{BRANCH_COST} is greater than or equal to the value 2.
5406 @deftypefn {Target Hook} bool TARGET_RTX_COSTS (rtx @var{x}, int @var{code}, int @var{outer_code}, int *@var{total})
5407 This target hook describes the relative costs of RTL expressions.
5409 The cost may depend on the precise form of the expression, which is
5410 available for examination in @var{x}, and the rtx code of the expression
5411 in which it is contained, found in @var{outer_code}. @var{code} is the
5412 expression code---redundant, since it can be obtained with
5413 @code{GET_CODE (@var{x})}.
5415 In implementing this hook, you can use the construct
5416 @code{COSTS_N_INSNS (@var{n})} to specify a cost equal to @var{n} fast
5419 On entry to the hook, @code{*@var{total}} contains a default estimate
5420 for the cost of the expression. The hook should modify this value as
5423 The hook returns true when all subexpressions of @var{x} have been
5424 processed, and false when @code{rtx_cost} should recurse.
5427 @deftypefn {Target Hook} int TARGET_ADDRESS_COST (rtx @var{address})
5428 This hook computes the cost of an addressing mode that contains
5429 @var{address}. If not defined, the cost is computed from
5430 the @var{address} expression and the @code{TARGET_RTX_COST} hook.
5432 For most CISC machines, the default cost is a good approximation of the
5433 true cost of the addressing mode. However, on RISC machines, all
5434 instructions normally have the same length and execution time. Hence
5435 all addresses will have equal costs.
5437 In cases where more than one form of an address is known, the form with
5438 the lowest cost will be used. If multiple forms have the same, lowest,
5439 cost, the one that is the most complex will be used.
5441 For example, suppose an address that is equal to the sum of a register
5442 and a constant is used twice in the same basic block. When this macro
5443 is not defined, the address will be computed in a register and memory
5444 references will be indirect through that register. On machines where
5445 the cost of the addressing mode containing the sum is no higher than
5446 that of a simple indirect reference, this will produce an additional
5447 instruction and possibly require an additional register. Proper
5448 specification of this macro eliminates this overhead for such machines.
5450 This hook is never called with an invalid address.
5452 On machines where an address involving more than one register is as
5453 cheap as an address computation involving only one register, defining
5454 @code{TARGET_ADDRESS_COST} to reflect this can cause two registers to
5455 be live over a region of code where only one would have been if
5456 @code{TARGET_ADDRESS_COST} were not defined in that manner. This effect
5457 should be considered in the definition of this macro. Equivalent costs
5458 should probably only be given to addresses with different numbers of
5459 registers on machines with lots of registers.
5463 @section Adjusting the Instruction Scheduler
5465 The instruction scheduler may need a fair amount of machine-specific
5466 adjustment in order to produce good code. GCC provides several target
5467 hooks for this purpose. It is usually enough to define just a few of
5468 them: try the first ones in this list first.
5470 @deftypefn {Target Hook} int TARGET_SCHED_ISSUE_RATE (void)
5471 This hook returns the maximum number of instructions that can ever
5472 issue at the same time on the target machine. The default is one.
5473 Although the insn scheduler can define itself the possibility of issue
5474 an insn on the same cycle, the value can serve as an additional
5475 constraint to issue insns on the same simulated processor cycle (see
5476 hooks @samp{TARGET_SCHED_REORDER} and @samp{TARGET_SCHED_REORDER2}).
5477 This value must be constant over the entire compilation. If you need
5478 it to vary depending on what the instructions are, you must use
5479 @samp{TARGET_SCHED_VARIABLE_ISSUE}.
5481 For the automaton based pipeline interface, you could define this hook
5482 to return the value of the macro @code{MAX_DFA_ISSUE_RATE}.
5485 @deftypefn {Target Hook} int TARGET_SCHED_VARIABLE_ISSUE (FILE *@var{file}, int @var{verbose}, rtx @var{insn}, int @var{more})
5486 This hook is executed by the scheduler after it has scheduled an insn
5487 from the ready list. It should return the number of insns which can
5488 still be issued in the current cycle. The default is
5489 @samp{@w{@var{more} - 1}} for insns other than @code{CLOBBER} and
5490 @code{USE}, which normally are not counted against the issue rate.
5491 You should define this hook if some insns take more machine resources
5492 than others, so that fewer insns can follow them in the same cycle.
5493 @var{file} is either a null pointer, or a stdio stream to write any
5494 debug output to. @var{verbose} is the verbose level provided by
5495 @option{-fsched-verbose-@var{n}}. @var{insn} is the instruction that
5499 @deftypefn {Target Hook} int TARGET_SCHED_ADJUST_COST (rtx @var{insn}, rtx @var{link}, rtx @var{dep_insn}, int @var{cost})
5500 This function corrects the value of @var{cost} based on the
5501 relationship between @var{insn} and @var{dep_insn} through the
5502 dependence @var{link}. It should return the new value. The default
5503 is to make no adjustment to @var{cost}. This can be used for example
5504 to specify to the scheduler using the traditional pipeline description
5505 that an output- or anti-dependence does not incur the same cost as a
5506 data-dependence. If the scheduler using the automaton based pipeline
5507 description, the cost of anti-dependence is zero and the cost of
5508 output-dependence is maximum of one and the difference of latency
5509 times of the first and the second insns. If these values are not
5510 acceptable, you could use the hook to modify them too. See also
5511 @pxref{Automaton pipeline description}.
5514 @deftypefn {Target Hook} int TARGET_SCHED_ADJUST_PRIORITY (rtx @var{insn}, int @var{priority})
5515 This hook adjusts the integer scheduling priority @var{priority} of
5516 @var{insn}. It should return the new priority. Reduce the priority to
5517 execute @var{insn} earlier, increase the priority to execute @var{insn}
5518 later. Do not define this hook if you do not need to adjust the
5519 scheduling priorities of insns.
5522 @deftypefn {Target Hook} int TARGET_SCHED_REORDER (FILE *@var{file}, int @var{verbose}, rtx *@var{ready}, int *@var{n_readyp}, int @var{clock})
5523 This hook is executed by the scheduler after it has scheduled the ready
5524 list, to allow the machine description to reorder it (for example to
5525 combine two small instructions together on @samp{VLIW} machines).
5526 @var{file} is either a null pointer, or a stdio stream to write any
5527 debug output to. @var{verbose} is the verbose level provided by
5528 @option{-fsched-verbose-@var{n}}. @var{ready} is a pointer to the ready
5529 list of instructions that are ready to be scheduled. @var{n_readyp} is
5530 a pointer to the number of elements in the ready list. The scheduler
5531 reads the ready list in reverse order, starting with
5532 @var{ready}[@var{*n_readyp}-1] and going to @var{ready}[0]. @var{clock}
5533 is the timer tick of the scheduler. You may modify the ready list and
5534 the number of ready insns. The return value is the number of insns that
5535 can issue this cycle; normally this is just @code{issue_rate}. See also
5536 @samp{TARGET_SCHED_REORDER2}.
5539 @deftypefn {Target Hook} int TARGET_SCHED_REORDER2 (FILE *@var{file}, int @var{verbose}, rtx *@var{ready}, int *@var{n_ready}, @var{clock})
5540 Like @samp{TARGET_SCHED_REORDER}, but called at a different time. That
5541 function is called whenever the scheduler starts a new cycle. This one
5542 is called once per iteration over a cycle, immediately after
5543 @samp{TARGET_SCHED_VARIABLE_ISSUE}; it can reorder the ready list and
5544 return the number of insns to be scheduled in the same cycle. Defining
5545 this hook can be useful if there are frequent situations where
5546 scheduling one insn causes other insns to become ready in the same
5547 cycle. These other insns can then be taken into account properly.
5550 @deftypefn {Target Hook} void TARGET_SCHED_DEPENDENCIES_EVALUATION_HOOK (rtx @var{head}, rtx @var{tail})
5551 This hook is called after evaluation forward dependencies of insns in
5552 chain given by two parameter values (@var{head} and @var{tail}
5553 correspondingly) but before insns scheduling of the insn chain. For
5554 example, it can be used for better insn classification if it requires
5555 analysis of dependencies. This hook can use backward and forward
5556 dependencies of the insn scheduler because they are already
5560 @deftypefn {Target Hook} void TARGET_SCHED_INIT (FILE *@var{file}, int @var{verbose}, int @var{max_ready})
5561 This hook is executed by the scheduler at the beginning of each block of
5562 instructions that are to be scheduled. @var{file} is either a null
5563 pointer, or a stdio stream to write any debug output to. @var{verbose}
5564 is the verbose level provided by @option{-fsched-verbose-@var{n}}.
5565 @var{max_ready} is the maximum number of insns in the current scheduling
5566 region that can be live at the same time. This can be used to allocate
5567 scratch space if it is needed, e.g. by @samp{TARGET_SCHED_REORDER}.
5570 @deftypefn {Target Hook} void TARGET_SCHED_FINISH (FILE *@var{file}, int @var{verbose})
5571 This hook is executed by the scheduler at the end of each block of
5572 instructions that are to be scheduled. It can be used to perform
5573 cleanup of any actions done by the other scheduling hooks. @var{file}
5574 is either a null pointer, or a stdio stream to write any debug output
5575 to. @var{verbose} is the verbose level provided by
5576 @option{-fsched-verbose-@var{n}}.
5579 @deftypefn {Target Hook} int TARGET_SCHED_USE_DFA_PIPELINE_INTERFACE (void)
5580 This hook is called many times during insn scheduling. If the hook
5581 returns nonzero, the automaton based pipeline description is used for
5582 insn scheduling. Otherwise the traditional pipeline description is
5583 used. The default is usage of the traditional pipeline description.
5585 You should also remember that to simplify the insn scheduler sources
5586 an empty traditional pipeline description interface is generated even
5587 if there is no a traditional pipeline description in the @file{.md}
5588 file. The same is true for the automaton based pipeline description.
5589 That means that you should be accurate in defining the hook.
5592 @deftypefn {Target Hook} int TARGET_SCHED_DFA_PRE_CYCLE_INSN (void)
5593 The hook returns an RTL insn. The automaton state used in the
5594 pipeline hazard recognizer is changed as if the insn were scheduled
5595 when the new simulated processor cycle starts. Usage of the hook may
5596 simplify the automaton pipeline description for some @acronym{VLIW}
5597 processors. If the hook is defined, it is used only for the automaton
5598 based pipeline description. The default is not to change the state
5599 when the new simulated processor cycle starts.
5602 @deftypefn {Target Hook} void TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN (void)
5603 The hook can be used to initialize data used by the previous hook.
5606 @deftypefn {Target Hook} int TARGET_SCHED_DFA_POST_CYCLE_INSN (void)
5607 The hook is analogous to @samp{TARGET_SCHED_DFA_PRE_CYCLE_INSN} but used
5608 to changed the state as if the insn were scheduled when the new
5609 simulated processor cycle finishes.
5612 @deftypefn {Target Hook} void TARGET_SCHED_INIT_DFA_POST_CYCLE_INSN (void)
5613 The hook is analogous to @samp{TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN} but
5614 used to initialize data used by the previous hook.
5617 @deftypefn {Target Hook} int TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD (void)
5618 This hook controls better choosing an insn from the ready insn queue
5619 for the @acronym{DFA}-based insn scheduler. Usually the scheduler
5620 chooses the first insn from the queue. If the hook returns a positive
5621 value, an additional scheduler code tries all permutations of
5622 @samp{TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD ()}
5623 subsequent ready insns to choose an insn whose issue will result in
5624 maximal number of issued insns on the same cycle. For the
5625 @acronym{VLIW} processor, the code could actually solve the problem of
5626 packing simple insns into the @acronym{VLIW} insn. Of course, if the
5627 rules of @acronym{VLIW} packing are described in the automaton.
5629 This code also could be used for superscalar @acronym{RISC}
5630 processors. Let us consider a superscalar @acronym{RISC} processor
5631 with 3 pipelines. Some insns can be executed in pipelines @var{A} or
5632 @var{B}, some insns can be executed only in pipelines @var{B} or
5633 @var{C}, and one insn can be executed in pipeline @var{B}. The
5634 processor may issue the 1st insn into @var{A} and the 2nd one into
5635 @var{B}. In this case, the 3rd insn will wait for freeing @var{B}
5636 until the next cycle. If the scheduler issues the 3rd insn the first,
5637 the processor could issue all 3 insns per cycle.
5639 Actually this code demonstrates advantages of the automaton based
5640 pipeline hazard recognizer. We try quickly and easy many insn
5641 schedules to choose the best one.
5643 The default is no multipass scheduling.
5646 @deftypefn {Target Hook} int TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD (rtx)
5648 This hook controls what insns from the ready insn queue will be
5649 considered for the multipass insn scheduling. If the hook returns
5650 zero for insn passed as the parameter, the insn will be not chosen to
5653 The default is that any ready insns can be chosen to be issued.
5656 @deftypefn {Target Hook} int TARGET_SCHED_DFA_NEW_CYCLE (FILE *, int, rtx, int, int, int *)
5658 This hook is called by the insn scheduler before issuing insn passed
5659 as the third parameter on given cycle. If the hook returns nonzero,
5660 the insn is not issued on given processors cycle. Instead of that,
5661 the processor cycle is advanced. If the value passed through the last
5662 parameter is zero, the insn ready queue is not sorted on the new cycle
5663 start as usually. The first parameter passes file for debugging
5664 output. The second one passes the scheduler verbose level of the
5665 debugging output. The forth and the fifth parameter values are
5666 correspondingly processor cycle on which the previous insn has been
5667 issued and the current processor cycle.
5670 @deftypefn {Target Hook} void TARGET_SCHED_INIT_DFA_BUBBLES (void)
5671 The @acronym{DFA}-based scheduler could take the insertion of nop
5672 operations for better insn scheduling into account. It can be done
5673 only if the multi-pass insn scheduling works (see hook
5674 @samp{TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD}).
5676 Let us consider a @acronym{VLIW} processor insn with 3 slots. Each
5677 insn can be placed only in one of the three slots. We have 3 ready
5678 insns @var{A}, @var{B}, and @var{C}. @var{A} and @var{C} can be
5679 placed only in the 1st slot, @var{B} can be placed only in the 3rd
5680 slot. We described the automaton which does not permit empty slot
5681 gaps between insns (usually such description is simpler). Without
5682 this code the scheduler would place each insn in 3 separate
5683 @acronym{VLIW} insns. If the scheduler places a nop insn into the 2nd
5684 slot, it could place the 3 insns into 2 @acronym{VLIW} insns. What is
5685 the nop insn is returned by hook @samp{TARGET_SCHED_DFA_BUBBLE}. Hook
5686 @samp{TARGET_SCHED_INIT_DFA_BUBBLES} can be used to initialize or
5687 create the nop insns.
5689 You should remember that the scheduler does not insert the nop insns.
5690 It is not wise because of the following optimizations. The scheduler
5691 only considers such possibility to improve the result schedule. The
5692 nop insns should be inserted lately, e.g. on the final phase.
5695 @deftypefn {Target Hook} rtx TARGET_SCHED_DFA_BUBBLE (int @var{index})
5696 This hook @samp{FIRST_CYCLE_MULTIPASS_SCHEDULING} is used to insert
5697 nop operations for better insn scheduling when @acronym{DFA}-based
5698 scheduler makes multipass insn scheduling (see also description of
5699 hook @samp{TARGET_SCHED_INIT_DFA_BUBBLES}). This hook
5700 returns a nop insn with given @var{index}. The indexes start with
5701 zero. The hook should return @code{NULL} if there are no more nop
5702 insns with indexes greater than given index.
5705 Macros in the following table are generated by the program
5706 @file{genattr} and can be useful for writing the hooks.
5708 @defmac TRADITIONAL_PIPELINE_INTERFACE
5709 The macro definition is generated if there is a traditional pipeline
5710 description in @file{.md} file. You should also remember that to
5711 simplify the insn scheduler sources an empty traditional pipeline
5712 description interface is generated even if there is no a traditional
5713 pipeline description in the @file{.md} file. The macro can be used to
5714 distinguish the two types of the traditional interface.
5717 @defmac DFA_PIPELINE_INTERFACE
5718 The macro definition is generated if there is an automaton pipeline
5719 description in @file{.md} file. You should also remember that to
5720 simplify the insn scheduler sources an empty automaton pipeline
5721 description interface is generated even if there is no an automaton
5722 pipeline description in the @file{.md} file. The macro can be used to
5723 distinguish the two types of the automaton interface.
5726 @defmac MAX_DFA_ISSUE_RATE
5727 The macro definition is generated in the automaton based pipeline
5728 description interface. Its value is calculated from the automaton
5729 based pipeline description and is equal to maximal number of all insns
5730 described in constructions @samp{define_insn_reservation} which can be
5731 issued on the same processor cycle.
5735 @section Dividing the Output into Sections (Texts, Data, @dots{})
5736 @c the above section title is WAY too long. maybe cut the part between
5737 @c the (...)? --mew 10feb93
5739 An object file is divided into sections containing different types of
5740 data. In the most common case, there are three sections: the @dfn{text
5741 section}, which holds instructions and read-only data; the @dfn{data
5742 section}, which holds initialized writable data; and the @dfn{bss
5743 section}, which holds uninitialized data. Some systems have other kinds
5746 The compiler must tell the assembler when to switch sections. These
5747 macros control what commands to output to tell the assembler this. You
5748 can also define additional sections.
5750 @defmac TEXT_SECTION_ASM_OP
5751 A C expression whose value is a string, including spacing, containing the
5752 assembler operation that should precede instructions and read-only data.
5753 Normally @code{"\t.text"} is right.
5756 @defmac TEXT_SECTION
5757 A C statement that switches to the default section containing instructions.
5758 Normally this is not needed, as simply defining @code{TEXT_SECTION_ASM_OP}
5759 is enough. The MIPS port uses this to sort all functions after all data
5763 @defmac HOT_TEXT_SECTION_NAME
5764 If defined, a C string constant for the name of the section containing most
5765 frequently executed functions of the program. If not defined, GCC will provide
5766 a default definition if the target supports named sections.
5769 @defmac UNLIKELY_EXECUTED_TEXT_SECTION_NAME
5770 If defined, a C string constant for the name of the section containing unlikely
5771 executed functions in the program.
5774 @defmac DATA_SECTION_ASM_OP
5775 A C expression whose value is a string, including spacing, containing the
5776 assembler operation to identify the following data as writable initialized
5777 data. Normally @code{"\t.data"} is right.
5780 @defmac READONLY_DATA_SECTION_ASM_OP
5781 A C expression whose value is a string, including spacing, containing the
5782 assembler operation to identify the following data as read-only initialized
5786 @defmac READONLY_DATA_SECTION
5787 A macro naming a function to call to switch to the proper section for
5788 read-only data. The default is to use @code{READONLY_DATA_SECTION_ASM_OP}
5789 if defined, else fall back to @code{text_section}.
5791 The most common definition will be @code{data_section}, if the target
5792 does not have a special read-only data section, and does not put data
5793 in the text section.
5796 @defmac SHARED_SECTION_ASM_OP
5797 If defined, a C expression whose value is a string, including spacing,
5798 containing the assembler operation to identify the following data as
5799 shared data. If not defined, @code{DATA_SECTION_ASM_OP} will be used.
5802 @defmac BSS_SECTION_ASM_OP
5803 If defined, a C expression whose value is a string, including spacing,
5804 containing the assembler operation to identify the following data as
5805 uninitialized global data. If not defined, and neither
5806 @code{ASM_OUTPUT_BSS} nor @code{ASM_OUTPUT_ALIGNED_BSS} are defined,
5807 uninitialized global data will be output in the data section if
5808 @option{-fno-common} is passed, otherwise @code{ASM_OUTPUT_COMMON} will be
5812 @defmac SHARED_BSS_SECTION_ASM_OP
5813 If defined, a C expression whose value is a string, including spacing,
5814 containing the assembler operation to identify the following data as
5815 uninitialized global shared data. If not defined, and
5816 @code{BSS_SECTION_ASM_OP} is, the latter will be used.
5819 @defmac INIT_SECTION_ASM_OP
5820 If defined, a C expression whose value is a string, including spacing,
5821 containing the assembler operation to identify the following data as
5822 initialization code. If not defined, GCC will assume such a section does
5826 @defmac FINI_SECTION_ASM_OP
5827 If defined, a C expression whose value is a string, including spacing,
5828 containing the assembler operation to identify the following data as
5829 finalization code. If not defined, GCC will assume such a section does
5833 @defmac CRT_CALL_STATIC_FUNCTION (@var{section_op}, @var{function})
5834 If defined, an ASM statement that switches to a different section
5835 via @var{section_op}, calls @var{function}, and switches back to
5836 the text section. This is used in @file{crtstuff.c} if
5837 @code{INIT_SECTION_ASM_OP} or @code{FINI_SECTION_ASM_OP} to calls
5838 to initialization and finalization functions from the init and fini
5839 sections. By default, this macro uses a simple function call. Some
5840 ports need hand-crafted assembly code to avoid dependencies on
5841 registers initialized in the function prologue or to ensure that
5842 constant pools don't end up too far way in the text section.
5845 @defmac FORCE_CODE_SECTION_ALIGN
5846 If defined, an ASM statement that aligns a code section to some
5847 arbitrary boundary. This is used to force all fragments of the
5848 @code{.init} and @code{.fini} sections to have to same alignment
5849 and thus prevent the linker from having to add any padding.
5854 @defmac EXTRA_SECTIONS
5855 A list of names for sections other than the standard two, which are
5856 @code{in_text} and @code{in_data}. You need not define this macro
5857 on a system with no other sections (that GCC needs to use).
5860 @findex text_section
5861 @findex data_section
5862 @defmac EXTRA_SECTION_FUNCTIONS
5863 One or more functions to be defined in @file{varasm.c}. These
5864 functions should do jobs analogous to those of @code{text_section} and
5865 @code{data_section}, for your additional sections. Do not define this
5866 macro if you do not define @code{EXTRA_SECTIONS}.
5869 @defmac JUMP_TABLES_IN_TEXT_SECTION
5870 Define this macro to be an expression with a nonzero value if jump
5871 tables (for @code{tablejump} insns) should be output in the text
5872 section, along with the assembler instructions. Otherwise, the
5873 readonly data section is used.
5875 This macro is irrelevant if there is no separate readonly data section.
5878 @deftypefn {Target Hook} void TARGET_ASM_SELECT_SECTION (tree @var{exp}, int @var{reloc}, unsigned HOST_WIDE_INT @var{align})
5879 Switches to the appropriate section for output of @var{exp}. You can
5880 assume that @var{exp} is either a @code{VAR_DECL} node or a constant of
5881 some sort. @var{reloc} indicates whether the initial value of @var{exp}
5882 requires link-time relocations. Bit 0 is set when variable contains
5883 local relocations only, while bit 1 is set for global relocations.
5884 Select the section by calling @code{data_section} or one of the
5885 alternatives for other sections. @var{align} is the constant alignment
5888 The default version of this function takes care of putting read-only
5889 variables in @code{readonly_data_section}.
5892 @deftypefn {Target Hook} void TARGET_ASM_UNIQUE_SECTION (tree @var{decl}, int @var{reloc})
5893 Build up a unique section name, expressed as a @code{STRING_CST} node,
5894 and assign it to @samp{DECL_SECTION_NAME (@var{decl})}.
5895 As with @code{TARGET_ASM_SELECT_SECTION}, @var{reloc} indicates whether
5896 the initial value of @var{exp} requires link-time relocations.
5898 The default version of this function appends the symbol name to the
5899 ELF section name that would normally be used for the symbol. For
5900 example, the function @code{foo} would be placed in @code{.text.foo}.
5901 Whatever the actual target object format, this is often good enough.
5904 @deftypefn {Target Hook} void TARGET_ASM_SELECT_RTX_SECTION (enum machine_mode @var{mode}, rtx @var{x}, unsigned HOST_WIDE_INT @var{align})
5905 Switches to the appropriate section for output of constant pool entry
5906 @var{x} in @var{mode}. You can assume that @var{x} is some kind of
5907 constant in RTL@. The argument @var{mode} is redundant except in the
5908 case of a @code{const_int} rtx. Select the section by calling
5909 @code{readonly_data_section} or one of the alternatives for other
5910 sections. @var{align} is the constant alignment in bits.
5912 The default version of this function takes care of putting symbolic
5913 constants in @code{flag_pic} mode in @code{data_section} and everything
5914 else in @code{readonly_data_section}.
5917 @deftypefn {Target Hook} void TARGET_ENCODE_SECTION_INFO (tree @var{decl}, rtx @var{rtl}, int @var{new_decl_p})
5918 Define this hook if references to a symbol or a constant must be
5919 treated differently depending on something about the variable or
5920 function named by the symbol (such as what section it is in).
5922 The hook is executed immediately after rtl has been created for
5923 @var{decl}, which may be a variable or function declaration or
5924 an entry in the constant pool. In either case, @var{rtl} is the
5925 rtl in question. Do @emph{not} use @code{DECL_RTL (@var{decl})}
5926 in this hook; that field may not have been initialized yet.
5928 In the case of a constant, it is safe to assume that the rtl is
5929 a @code{mem} whose address is a @code{symbol_ref}. Most decls
5930 will also have this form, but that is not guaranteed. Global
5931 register variables, for instance, will have a @code{reg} for their
5932 rtl. (Normally the right thing to do with such unusual rtl is
5935 The @var{new_decl_p} argument will be true if this is the first time
5936 that @code{TARGET_ENCODE_SECTION_INFO} has been invoked on this decl. It will
5937 be false for subsequent invocations, which will happen for duplicate
5938 declarations. Whether or not anything must be done for the duplicate
5939 declaration depends on whether the hook examines @code{DECL_ATTRIBUTES}.
5940 @var{new_decl_p} is always true when the hook is called for a constant.
5942 @cindex @code{SYMBOL_REF_FLAG}, in @code{TARGET_ENCODE_SECTION_INFO}
5943 The usual thing for this hook to do is to record flags in the
5944 @code{symbol_ref}, using @code{SYMBOL_REF_FLAG} or @code{SYMBOL_REF_FLAGS}.
5945 Historically, the name string was modified if it was necessary to
5946 encode more than one bit of information, but this practice is now
5947 discouraged; use @code{SYMBOL_REF_FLAGS}.
5949 The default definition of this hook, @code{default_encode_section_info}
5950 in @file{varasm.c}, sets a number of commonly-useful bits in
5951 @code{SYMBOL_REF_FLAGS}. Check whether the default does what you need
5952 before overriding it.
5955 @deftypefn {Target Hook} const char *TARGET_STRIP_NAME_ENCODING (const char *name)
5956 Decode @var{name} and return the real name part, sans
5957 the characters that @code{TARGET_ENCODE_SECTION_INFO}
5961 @deftypefn {Target Hook} bool TARGET_IN_SMALL_DATA_P (tree @var{exp})
5962 Returns true if @var{exp} should be placed into a ``small data'' section.
5963 The default version of this hook always returns false.
5966 @deftypevar {Target Hook} bool TARGET_HAVE_SRODATA_SECTION
5967 Contains the value true if the target places read-only
5968 ``small data'' into a separate section. The default value is false.
5971 @deftypefn {Target Hook} bool TARGET_BINDS_LOCAL_P (tree @var{exp})
5972 Returns true if @var{exp} names an object for which name resolution
5973 rules must resolve to the current ``module'' (dynamic shared library
5974 or executable image).
5976 The default version of this hook implements the name resolution rules
5977 for ELF, which has a looser model of global name binding than other
5978 currently supported object file formats.
5981 @deftypevar {Target Hook} bool TARGET_HAVE_TLS
5982 Contains the value true if the target supports thread-local storage.
5983 The default value is false.
5988 @section Position Independent Code
5989 @cindex position independent code
5992 This section describes macros that help implement generation of position
5993 independent code. Simply defining these macros is not enough to
5994 generate valid PIC; you must also add support to the macros
5995 @code{GO_IF_LEGITIMATE_ADDRESS} and @code{PRINT_OPERAND_ADDRESS}, as
5996 well as @code{LEGITIMIZE_ADDRESS}. You must modify the definition of
5997 @samp{movsi} to do something appropriate when the source operand
5998 contains a symbolic address. You may also need to alter the handling of
5999 switch statements so that they use relative addresses.
6000 @c i rearranged the order of the macros above to try to force one of
6001 @c them to the next line, to eliminate an overfull hbox. --mew 10feb93
6003 @defmac PIC_OFFSET_TABLE_REGNUM
6004 The register number of the register used to address a table of static
6005 data addresses in memory. In some cases this register is defined by a
6006 processor's ``application binary interface'' (ABI)@. When this macro
6007 is defined, RTL is generated for this register once, as with the stack
6008 pointer and frame pointer registers. If this macro is not defined, it
6009 is up to the machine-dependent files to allocate such a register (if
6010 necessary). Note that this register must be fixed when in use (e.g.@:
6011 when @code{flag_pic} is true).
6014 @defmac PIC_OFFSET_TABLE_REG_CALL_CLOBBERED
6015 Define this macro if the register defined by
6016 @code{PIC_OFFSET_TABLE_REGNUM} is clobbered by calls. Do not define
6017 this macro if @code{PIC_OFFSET_TABLE_REGNUM} is not defined.
6020 @defmac FINALIZE_PIC
6021 By generating position-independent code, when two different programs (A
6022 and B) share a common library (libC.a), the text of the library can be
6023 shared whether or not the library is linked at the same address for both
6024 programs. In some of these environments, position-independent code
6025 requires not only the use of different addressing modes, but also
6026 special code to enable the use of these addressing modes.
6028 The @code{FINALIZE_PIC} macro serves as a hook to emit these special
6029 codes once the function is being compiled into assembly code, but not
6030 before. (It is not done before, because in the case of compiling an
6031 inline function, it would lead to multiple PIC prologues being
6032 included in functions which used inline functions and were compiled to
6036 @defmac LEGITIMATE_PIC_OPERAND_P (@var{x})
6037 A C expression that is nonzero if @var{x} is a legitimate immediate
6038 operand on the target machine when generating position independent code.
6039 You can assume that @var{x} satisfies @code{CONSTANT_P}, so you need not
6040 check this. You can also assume @var{flag_pic} is true, so you need not
6041 check it either. You need not define this macro if all constants
6042 (including @code{SYMBOL_REF}) can be immediate operands when generating
6043 position independent code.
6046 @node Assembler Format
6047 @section Defining the Output Assembler Language
6049 This section describes macros whose principal purpose is to describe how
6050 to write instructions in assembler language---rather than what the
6054 * File Framework:: Structural information for the assembler file.
6055 * Data Output:: Output of constants (numbers, strings, addresses).
6056 * Uninitialized Data:: Output of uninitialized variables.
6057 * Label Output:: Output and generation of labels.
6058 * Initialization:: General principles of initialization
6059 and termination routines.
6060 * Macros for Initialization::
6061 Specific macros that control the handling of
6062 initialization and termination routines.
6063 * Instruction Output:: Output of actual instructions.
6064 * Dispatch Tables:: Output of jump tables.
6065 * Exception Region Output:: Output of exception region code.
6066 * Alignment Output:: Pseudo ops for alignment and skipping data.
6069 @node File Framework
6070 @subsection The Overall Framework of an Assembler File
6071 @cindex assembler format
6072 @cindex output of assembler code
6074 @c prevent bad page break with this line
6075 This describes the overall framework of an assembly file.
6077 @deftypefn {Target Hook} void TARGET_ASM_FILE_START ()
6078 @findex default_file_start
6079 Output to @code{asm_out_file} any text which the assembler expects to
6080 find at the beginning of a file. The default behavior is controlled
6081 by two flags, documented below. Unless your target's assembler is
6082 quite unusual, if you override the default, you should call
6083 @code{default_file_start} at some point in your target hook. This
6084 lets other target files rely on these variables.
6087 @deftypevr {Target Hook} bool TARGET_ASM_FILE_START_APP_OFF
6088 If this flag is true, the text of the macro @code{ASM_APP_OFF} will be
6089 printed as the very first line in the assembly file, unless
6090 @option{-fverbose-asm} is in effect. (If that macro has been defined
6091 to the empty string, this variable has no effect.) With the normal
6092 definition of @code{ASM_APP_OFF}, the effect is to notify the GNU
6093 assembler that it need not bother stripping comments or extra
6094 whitespace from its input. This allows it to work a bit faster.
6096 The default is false. You should not set it to true unless you have
6097 verified that your port does not generate any extra whitespace or
6098 comments that will cause GAS to issue errors in NO_APP mode.
6101 @deftypevr {Target Hook} bool TARGET_ASM_FILE_START_FILE_DIRECTIVE
6102 If this flag is true, @code{output_file_directive} will be called
6103 for the primary source file, immediately after printing
6104 @code{ASM_APP_OFF} (if that is enabled). Most ELF assemblers expect
6105 this to be done. The default is false.
6108 @deftypefn {Target Hook} void TARGET_ASM_FILE_END ()
6109 Output to @code{asm_out_file} any text which the assembler expects
6110 to find at the end of a file. The default is to output nothing.
6113 @deftypefun void file_end_indicate_exec_stack ()
6114 Some systems use a common convention, the @samp{.note.GNU-stack}
6115 special section, to indicate whether or not an object file relies on
6116 the stack being executable. If your system uses this convention, you
6117 should define @code{TARGET_ASM_FILE_END} to this function. If you
6118 need to do other things in that hook, have your hook function call
6122 @defmac ASM_COMMENT_START
6123 A C string constant describing how to begin a comment in the target
6124 assembler language. The compiler assumes that the comment will end at
6125 the end of the line.
6129 A C string constant for text to be output before each @code{asm}
6130 statement or group of consecutive ones. Normally this is
6131 @code{"#APP"}, which is a comment that has no effect on most
6132 assemblers but tells the GNU assembler that it must check the lines
6133 that follow for all valid assembler constructs.
6137 A C string constant for text to be output after each @code{asm}
6138 statement or group of consecutive ones. Normally this is
6139 @code{"#NO_APP"}, which tells the GNU assembler to resume making the
6140 time-saving assumptions that are valid for ordinary compiler output.
6143 @defmac ASM_OUTPUT_SOURCE_FILENAME (@var{stream}, @var{name})
6144 A C statement to output COFF information or DWARF debugging information
6145 which indicates that filename @var{name} is the current source file to
6146 the stdio stream @var{stream}.
6148 This macro need not be defined if the standard form of output
6149 for the file format in use is appropriate.
6152 @defmac OUTPUT_QUOTED_STRING (@var{stream}, @var{string})
6153 A C statement to output the string @var{string} to the stdio stream
6154 @var{stream}. If you do not call the function @code{output_quoted_string}
6155 in your config files, GCC will only call it to output filenames to
6156 the assembler source. So you can use it to canonicalize the format
6157 of the filename using this macro.
6160 @defmac ASM_OUTPUT_SOURCE_LINE (@var{stream}, @var{line}, @var{counter})
6161 A C statement to output DBX or SDB debugging information before code
6162 for line number @var{line} of the current source file to the
6163 stdio stream @var{stream}. @var{counter} is the number of time the
6164 macro was invoked, including the current invocation; it is intended
6165 to generate unique labels in the assembly output.
6167 This macro need not be defined if the standard form of debugging
6168 information for the debugger in use is appropriate.
6171 @defmac ASM_OUTPUT_IDENT (@var{stream}, @var{string})
6172 A C statement to output something to the assembler file to handle a
6173 @samp{#ident} directive containing the text @var{string}. If this
6174 macro is not defined, nothing is output for a @samp{#ident} directive.
6177 @deftypefn {Target Hook} void TARGET_ASM_NAMED_SECTION (const char *@var{name}, unsigned int @var{flags}, unsigned int @var{align})
6178 Output assembly directives to switch to section @var{name}. The section
6179 should have attributes as specified by @var{flags}, which is a bit mask
6180 of the @code{SECTION_*} flags defined in @file{output.h}. If @var{align}
6181 is nonzero, it contains an alignment in bytes to be used for the section,
6182 otherwise some target default should be used. Only targets that must
6183 specify an alignment within the section directive need pay attention to
6184 @var{align} -- we will still use @code{ASM_OUTPUT_ALIGN}.
6187 @deftypefn {Target Hook} bool TARGET_HAVE_NAMED_SECTIONS
6188 This flag is true if the target supports @code{TARGET_ASM_NAMED_SECTION}.
6191 @deftypefn {Target Hook} {unsigned int} TARGET_SECTION_TYPE_FLAGS (tree @var{decl}, const char *@var{name}, int @var{reloc})
6192 Choose a set of section attributes for use by @code{TARGET_ASM_NAMED_SECTION}
6193 based on a variable or function decl, a section name, and whether or not the
6194 declaration's initializer may contain runtime relocations. @var{decl} may be
6195 null, in which case read-write data should be assumed.
6197 The default version if this function handles choosing code vs data,
6198 read-only vs read-write data, and @code{flag_pic}. You should only
6199 need to override this if your target has special flags that might be
6200 set via @code{__attribute__}.
6205 @subsection Output of Data
6208 @deftypevr {Target Hook} {const char *} TARGET_ASM_BYTE_OP
6209 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_HI_OP
6210 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_SI_OP
6211 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_DI_OP
6212 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_TI_OP
6213 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_HI_OP
6214 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_SI_OP
6215 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_DI_OP
6216 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_TI_OP
6217 These hooks specify assembly directives for creating certain kinds
6218 of integer object. The @code{TARGET_ASM_BYTE_OP} directive creates a
6219 byte-sized object, the @code{TARGET_ASM_ALIGNED_HI_OP} one creates an
6220 aligned two-byte object, and so on. Any of the hooks may be
6221 @code{NULL}, indicating that no suitable directive is available.
6223 The compiler will print these strings at the start of a new line,
6224 followed immediately by the object's initial value. In most cases,
6225 the string should contain a tab, a pseudo-op, and then another tab.
6228 @deftypefn {Target Hook} bool TARGET_ASM_INTEGER (rtx @var{x}, unsigned int @var{size}, int @var{aligned_p})
6229 The @code{assemble_integer} function uses this hook to output an
6230 integer object. @var{x} is the object's value, @var{size} is its size
6231 in bytes and @var{aligned_p} indicates whether it is aligned. The
6232 function should return @code{true} if it was able to output the
6233 object. If it returns false, @code{assemble_integer} will try to
6234 split the object into smaller parts.
6236 The default implementation of this hook will use the
6237 @code{TARGET_ASM_BYTE_OP} family of strings, returning @code{false}
6238 when the relevant string is @code{NULL}.
6241 @defmac OUTPUT_ADDR_CONST_EXTRA (@var{stream}, @var{x}, @var{fail})
6242 A C statement to recognize @var{rtx} patterns that
6243 @code{output_addr_const} can't deal with, and output assembly code to
6244 @var{stream} corresponding to the pattern @var{x}. This may be used to
6245 allow machine-dependent @code{UNSPEC}s to appear within constants.
6247 If @code{OUTPUT_ADDR_CONST_EXTRA} fails to recognize a pattern, it must
6248 @code{goto fail}, so that a standard error message is printed. If it
6249 prints an error message itself, by calling, for example,
6250 @code{output_operand_lossage}, it may just complete normally.
6253 @defmac ASM_OUTPUT_ASCII (@var{stream}, @var{ptr}, @var{len})
6254 A C statement to output to the stdio stream @var{stream} an assembler
6255 instruction to assemble a string constant containing the @var{len}
6256 bytes at @var{ptr}. @var{ptr} will be a C expression of type
6257 @code{char *} and @var{len} a C expression of type @code{int}.
6259 If the assembler has a @code{.ascii} pseudo-op as found in the
6260 Berkeley Unix assembler, do not define the macro
6261 @code{ASM_OUTPUT_ASCII}.
6264 @defmac ASM_OUTPUT_FDESC (@var{stream}, @var{decl}, @var{n})
6265 A C statement to output word @var{n} of a function descriptor for
6266 @var{decl}. This must be defined if @code{TARGET_VTABLE_USES_DESCRIPTORS}
6267 is defined, and is otherwise unused.
6270 @defmac CONSTANT_POOL_BEFORE_FUNCTION
6271 You may define this macro as a C expression. You should define the
6272 expression to have a nonzero value if GCC should output the constant
6273 pool for a function before the code for the function, or a zero value if
6274 GCC should output the constant pool after the function. If you do
6275 not define this macro, the usual case, GCC will output the constant
6276 pool before the function.
6279 @defmac ASM_OUTPUT_POOL_PROLOGUE (@var{file}, @var{funname}, @var{fundecl}, @var{size})
6280 A C statement to output assembler commands to define the start of the
6281 constant pool for a function. @var{funname} is a string giving
6282 the name of the function. Should the return type of the function
6283 be required, it can be obtained via @var{fundecl}. @var{size}
6284 is the size, in bytes, of the constant pool that will be written
6285 immediately after this call.
6287 If no constant-pool prefix is required, the usual case, this macro need
6291 @defmac ASM_OUTPUT_SPECIAL_POOL_ENTRY (@var{file}, @var{x}, @var{mode}, @var{align}, @var{labelno}, @var{jumpto})
6292 A C statement (with or without semicolon) to output a constant in the
6293 constant pool, if it needs special treatment. (This macro need not do
6294 anything for RTL expressions that can be output normally.)
6296 The argument @var{file} is the standard I/O stream to output the
6297 assembler code on. @var{x} is the RTL expression for the constant to
6298 output, and @var{mode} is the machine mode (in case @var{x} is a
6299 @samp{const_int}). @var{align} is the required alignment for the value
6300 @var{x}; you should output an assembler directive to force this much
6303 The argument @var{labelno} is a number to use in an internal label for
6304 the address of this pool entry. The definition of this macro is
6305 responsible for outputting the label definition at the proper place.
6306 Here is how to do this:
6309 @code{(*targetm.asm_out.internal_label)} (@var{file}, "LC", @var{labelno});
6312 When you output a pool entry specially, you should end with a
6313 @code{goto} to the label @var{jumpto}. This will prevent the same pool
6314 entry from being output a second time in the usual manner.
6316 You need not define this macro if it would do nothing.
6319 @defmac ASM_OUTPUT_POOL_EPILOGUE (@var{file} @var{funname} @var{fundecl} @var{size})
6320 A C statement to output assembler commands to at the end of the constant
6321 pool for a function. @var{funname} is a string giving the name of the
6322 function. Should the return type of the function be required, you can
6323 obtain it via @var{fundecl}. @var{size} is the size, in bytes, of the
6324 constant pool that GCC wrote immediately before this call.
6326 If no constant-pool epilogue is required, the usual case, you need not
6330 @defmac IS_ASM_LOGICAL_LINE_SEPARATOR (@var{C})
6331 Define this macro as a C expression which is nonzero if @var{C} is
6332 used as a logical line separator by the assembler.
6334 If you do not define this macro, the default is that only
6335 the character @samp{;} is treated as a logical line separator.
6338 @deftypevr {Target Hook} {const char *} TARGET_ASM_OPEN_PAREN
6339 @deftypevrx {Target Hook} {const char *} TARGET_ASM_CLOSE_PAREN
6340 These target hooks are C string constants, describing the syntax in the
6341 assembler for grouping arithmetic expressions. If not overridden, they
6342 default to normal parentheses, which is correct for most assemblers.
6345 These macros are provided by @file{real.h} for writing the definitions
6346 of @code{ASM_OUTPUT_DOUBLE} and the like:
6348 @defmac REAL_VALUE_TO_TARGET_SINGLE (@var{x}, @var{l})
6349 @defmacx REAL_VALUE_TO_TARGET_DOUBLE (@var{x}, @var{l})
6350 @defmacx REAL_VALUE_TO_TARGET_LONG_DOUBLE (@var{x}, @var{l})
6351 These translate @var{x}, of type @code{REAL_VALUE_TYPE}, to the target's
6352 floating point representation, and store its bit pattern in the variable
6353 @var{l}. For @code{REAL_VALUE_TO_TARGET_SINGLE}, this variable should
6354 be a simple @code{long int}. For the others, it should be an array of
6355 @code{long int}. The number of elements in this array is determined by
6356 the size of the desired target floating point data type: 32 bits of it
6357 go in each @code{long int} array element. Each array element holds 32
6358 bits of the result, even if @code{long int} is wider than 32 bits on the
6361 The array element values are designed so that you can print them out
6362 using @code{fprintf} in the order they should appear in the target
6366 @node Uninitialized Data
6367 @subsection Output of Uninitialized Variables
6369 Each of the macros in this section is used to do the whole job of
6370 outputting a single uninitialized variable.
6372 @defmac ASM_OUTPUT_COMMON (@var{stream}, @var{name}, @var{size}, @var{rounded})
6373 A C statement (sans semicolon) to output to the stdio stream
6374 @var{stream} the assembler definition of a common-label named
6375 @var{name} whose size is @var{size} bytes. The variable @var{rounded}
6376 is the size rounded up to whatever alignment the caller wants.
6378 Use the expression @code{assemble_name (@var{stream}, @var{name})} to
6379 output the name itself; before and after that, output the additional
6380 assembler syntax for defining the name, and a newline.
6382 This macro controls how the assembler definitions of uninitialized
6383 common global variables are output.
6386 @defmac ASM_OUTPUT_ALIGNED_COMMON (@var{stream}, @var{name}, @var{size}, @var{alignment})
6387 Like @code{ASM_OUTPUT_COMMON} except takes the required alignment as a
6388 separate, explicit argument. If you define this macro, it is used in
6389 place of @code{ASM_OUTPUT_COMMON}, and gives you more flexibility in
6390 handling the required alignment of the variable. The alignment is specified
6391 as the number of bits.
6394 @defmac ASM_OUTPUT_ALIGNED_DECL_COMMON (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
6395 Like @code{ASM_OUTPUT_ALIGNED_COMMON} except that @var{decl} of the
6396 variable to be output, if there is one, or @code{NULL_TREE} if there
6397 is no corresponding variable. If you define this macro, GCC will use it
6398 in place of both @code{ASM_OUTPUT_COMMON} and
6399 @code{ASM_OUTPUT_ALIGNED_COMMON}. Define this macro when you need to see
6400 the variable's decl in order to chose what to output.
6403 @defmac ASM_OUTPUT_SHARED_COMMON (@var{stream}, @var{name}, @var{size}, @var{rounded})
6404 If defined, it is similar to @code{ASM_OUTPUT_COMMON}, except that it
6405 is used when @var{name} is shared. If not defined, @code{ASM_OUTPUT_COMMON}
6409 @defmac ASM_OUTPUT_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{rounded})
6410 A C statement (sans semicolon) to output to the stdio stream
6411 @var{stream} the assembler definition of uninitialized global @var{decl} named
6412 @var{name} whose size is @var{size} bytes. The variable @var{rounded}
6413 is the size rounded up to whatever alignment the caller wants.
6415 Try to use function @code{asm_output_bss} defined in @file{varasm.c} when
6416 defining this macro. If unable, use the expression
6417 @code{assemble_name (@var{stream}, @var{name})} to output the name itself;
6418 before and after that, output the additional assembler syntax for defining
6419 the name, and a newline.
6421 This macro controls how the assembler definitions of uninitialized global
6422 variables are output. This macro exists to properly support languages like
6423 C++ which do not have @code{common} data. However, this macro currently
6424 is not defined for all targets. If this macro and
6425 @code{ASM_OUTPUT_ALIGNED_BSS} are not defined then @code{ASM_OUTPUT_COMMON}
6426 or @code{ASM_OUTPUT_ALIGNED_COMMON} or
6427 @code{ASM_OUTPUT_ALIGNED_DECL_COMMON} is used.
6430 @defmac ASM_OUTPUT_ALIGNED_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
6431 Like @code{ASM_OUTPUT_BSS} except takes the required alignment as a
6432 separate, explicit argument. If you define this macro, it is used in
6433 place of @code{ASM_OUTPUT_BSS}, and gives you more flexibility in
6434 handling the required alignment of the variable. The alignment is specified
6435 as the number of bits.
6437 Try to use function @code{asm_output_aligned_bss} defined in file
6438 @file{varasm.c} when defining this macro.
6441 @defmac ASM_OUTPUT_SHARED_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{rounded})
6442 If defined, it is similar to @code{ASM_OUTPUT_BSS}, except that it
6443 is used when @var{name} is shared. If not defined, @code{ASM_OUTPUT_BSS}
6447 @defmac ASM_OUTPUT_LOCAL (@var{stream}, @var{name}, @var{size}, @var{rounded})
6448 A C statement (sans semicolon) to output to the stdio stream
6449 @var{stream} the assembler definition of a local-common-label named
6450 @var{name} whose size is @var{size} bytes. The variable @var{rounded}
6451 is the size rounded up to whatever alignment the caller wants.
6453 Use the expression @code{assemble_name (@var{stream}, @var{name})} to
6454 output the name itself; before and after that, output the additional
6455 assembler syntax for defining the name, and a newline.
6457 This macro controls how the assembler definitions of uninitialized
6458 static variables are output.
6461 @defmac ASM_OUTPUT_ALIGNED_LOCAL (@var{stream}, @var{name}, @var{size}, @var{alignment})
6462 Like @code{ASM_OUTPUT_LOCAL} except takes the required alignment as a
6463 separate, explicit argument. If you define this macro, it is used in
6464 place of @code{ASM_OUTPUT_LOCAL}, and gives you more flexibility in
6465 handling the required alignment of the variable. The alignment is specified
6466 as the number of bits.
6469 @defmac ASM_OUTPUT_ALIGNED_DECL_LOCAL (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
6470 Like @code{ASM_OUTPUT_ALIGNED_DECL} except that @var{decl} of the
6471 variable to be output, if there is one, or @code{NULL_TREE} if there
6472 is no corresponding variable. If you define this macro, GCC will use it
6473 in place of both @code{ASM_OUTPUT_DECL} and
6474 @code{ASM_OUTPUT_ALIGNED_DECL}. Define this macro when you need to see
6475 the variable's decl in order to chose what to output.
6478 @defmac ASM_OUTPUT_SHARED_LOCAL (@var{stream}, @var{name}, @var{size}, @var{rounded})
6479 If defined, it is similar to @code{ASM_OUTPUT_LOCAL}, except that it
6480 is used when @var{name} is shared. If not defined, @code{ASM_OUTPUT_LOCAL}
6485 @subsection Output and Generation of Labels
6487 @c prevent bad page break with this line
6488 This is about outputting labels.
6490 @findex assemble_name
6491 @defmac ASM_OUTPUT_LABEL (@var{stream}, @var{name})
6492 A C statement (sans semicolon) to output to the stdio stream
6493 @var{stream} the assembler definition of a label named @var{name}.
6494 Use the expression @code{assemble_name (@var{stream}, @var{name})} to
6495 output the name itself; before and after that, output the additional
6496 assembler syntax for defining the name, and a newline. A default
6497 definition of this macro is provided which is correct for most systems.
6501 A C string containing the appropriate assembler directive to specify the
6502 size of a symbol, without any arguments. On systems that use ELF, the
6503 default (in @file{config/elfos.h}) is @samp{"\t.size\t"}; on other
6504 systems, the default is not to define this macro.
6506 Define this macro only if it is correct to use the default definitions
6507 of @code{ASM_OUTPUT_SIZE_DIRECTIVE} and @code{ASM_OUTPUT_MEASURED_SIZE}
6508 for your system. If you need your own custom definitions of those
6509 macros, or if you do not need explicit symbol sizes at all, do not
6513 @defmac ASM_OUTPUT_SIZE_DIRECTIVE (@var{stream}, @var{name}, @var{size})
6514 A C statement (sans semicolon) to output to the stdio stream
6515 @var{stream} a directive telling the assembler that the size of the
6516 symbol @var{name} is @var{size}. @var{size} is a @code{HOST_WIDE_INT}.
6517 If you define @code{SIZE_ASM_OP}, a default definition of this macro is
6521 @defmac ASM_OUTPUT_MEASURED_SIZE (@var{stream}, @var{name})
6522 A C statement (sans semicolon) to output to the stdio stream
6523 @var{stream} a directive telling the assembler to calculate the size of
6524 the symbol @var{name} by subtracting its address from the current
6527 If you define @code{SIZE_ASM_OP}, a default definition of this macro is
6528 provided. The default assumes that the assembler recognizes a special
6529 @samp{.} symbol as referring to the current address, and can calculate
6530 the difference between this and another symbol. If your assembler does
6531 not recognize @samp{.} or cannot do calculations with it, you will need
6532 to redefine @code{ASM_OUTPUT_MEASURED_SIZE} to use some other technique.
6536 A C string containing the appropriate assembler directive to specify the
6537 type of a symbol, without any arguments. On systems that use ELF, the
6538 default (in @file{config/elfos.h}) is @samp{"\t.type\t"}; on other
6539 systems, the default is not to define this macro.
6541 Define this macro only if it is correct to use the default definition of
6542 @code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own
6543 custom definition of this macro, or if you do not need explicit symbol
6544 types at all, do not define this macro.
6547 @defmac TYPE_OPERAND_FMT
6548 A C string which specifies (using @code{printf} syntax) the format of
6549 the second operand to @code{TYPE_ASM_OP}. On systems that use ELF, the
6550 default (in @file{config/elfos.h}) is @samp{"@@%s"}; on other systems,
6551 the default is not to define this macro.
6553 Define this macro only if it is correct to use the default definition of
6554 @code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own
6555 custom definition of this macro, or if you do not need explicit symbol
6556 types at all, do not define this macro.
6559 @defmac ASM_OUTPUT_TYPE_DIRECTIVE (@var{stream}, @var{type})
6560 A C statement (sans semicolon) to output to the stdio stream
6561 @var{stream} a directive telling the assembler that the type of the
6562 symbol @var{name} is @var{type}. @var{type} is a C string; currently,
6563 that string is always either @samp{"function"} or @samp{"object"}, but
6564 you should not count on this.
6566 If you define @code{TYPE_ASM_OP} and @code{TYPE_OPERAND_FMT}, a default
6567 definition of this macro is provided.
6570 @defmac ASM_DECLARE_FUNCTION_NAME (@var{stream}, @var{name}, @var{decl})
6571 A C statement (sans semicolon) to output to the stdio stream
6572 @var{stream} any text necessary for declaring the name @var{name} of a
6573 function which is being defined. This macro is responsible for
6574 outputting the label definition (perhaps using
6575 @code{ASM_OUTPUT_LABEL}). The argument @var{decl} is the
6576 @code{FUNCTION_DECL} tree node representing the function.
6578 If this macro is not defined, then the function name is defined in the
6579 usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}).
6581 You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in the definition
6585 @defmac ASM_DECLARE_FUNCTION_SIZE (@var{stream}, @var{name}, @var{decl})
6586 A C statement (sans semicolon) to output to the stdio stream
6587 @var{stream} any text necessary for declaring the size of a function
6588 which is being defined. The argument @var{name} is the name of the
6589 function. The argument @var{decl} is the @code{FUNCTION_DECL} tree node
6590 representing the function.
6592 If this macro is not defined, then the function size is not defined.
6594 You may wish to use @code{ASM_OUTPUT_MEASURED_SIZE} in the definition
6598 @defmac ASM_DECLARE_OBJECT_NAME (@var{stream}, @var{name}, @var{decl})
6599 A C statement (sans semicolon) to output to the stdio stream
6600 @var{stream} any text necessary for declaring the name @var{name} of an
6601 initialized variable which is being defined. This macro must output the
6602 label definition (perhaps using @code{ASM_OUTPUT_LABEL}). The argument
6603 @var{decl} is the @code{VAR_DECL} tree node representing the variable.
6605 If this macro is not defined, then the variable name is defined in the
6606 usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}).
6608 You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} and/or
6609 @code{ASM_OUTPUT_SIZE_DIRECTIVE} in the definition of this macro.
6612 @defmac ASM_DECLARE_CONSTANT_NAME (@var{stream}, @var{name}, @var{exp}, @var{size})
6613 A C statement (sans semicolon) to output to the stdio stream
6614 @var{stream} any text necessary for declaring the name @var{name} of a
6615 constant which is being defined. This macro is responsible for
6616 outputting the label definition (perhaps using
6617 @code{ASM_OUTPUT_LABEL}). The argument @var{exp} is the
6618 value of the constant, and @var{size} is the size of the constant
6619 in bytes. @var{name} will be an internal label.
6621 If this macro is not defined, then the @var{name} is defined in the
6622 usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}).
6624 You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in the definition
6628 @defmac ASM_DECLARE_REGISTER_GLOBAL (@var{stream}, @var{decl}, @var{regno}, @var{name})
6629 A C statement (sans semicolon) to output to the stdio stream
6630 @var{stream} any text necessary for claiming a register @var{regno}
6631 for a global variable @var{decl} with name @var{name}.
6633 If you don't define this macro, that is equivalent to defining it to do
6637 @defmac ASM_FINISH_DECLARE_OBJECT (@var{stream}, @var{decl}, @var{toplevel}, @var{atend})
6638 A C statement (sans semicolon) to finish up declaring a variable name
6639 once the compiler has processed its initializer fully and thus has had a
6640 chance to determine the size of an array when controlled by an
6641 initializer. This is used on systems where it's necessary to declare
6642 something about the size of the object.
6644 If you don't define this macro, that is equivalent to defining it to do
6647 You may wish to use @code{ASM_OUTPUT_SIZE_DIRECTIVE} and/or
6648 @code{ASM_OUTPUT_MEASURED_SIZE} in the definition of this macro.
6651 @deftypefn {Target Hook} void TARGET_ASM_GLOBALIZE_LABEL (FILE *@var{stream}, const char *@var{name})
6652 This target hook is a function to output to the stdio stream
6653 @var{stream} some commands that will make the label @var{name} global;
6654 that is, available for reference from other files.
6656 The default implementation relies on a proper definition of
6657 @code{GLOBAL_ASM_OP}.
6660 @defmac ASM_WEAKEN_LABEL (@var{stream}, @var{name})
6661 A C statement (sans semicolon) to output to the stdio stream
6662 @var{stream} some commands that will make the label @var{name} weak;
6663 that is, available for reference from other files but only used if
6664 no other definition is available. Use the expression
6665 @code{assemble_name (@var{stream}, @var{name})} to output the name
6666 itself; before and after that, output the additional assembler syntax
6667 for making that name weak, and a newline.
6669 If you don't define this macro or @code{ASM_WEAKEN_DECL}, GCC will not
6670 support weak symbols and you should not define the @code{SUPPORTS_WEAK}
6674 @defmac ASM_WEAKEN_DECL (@var{stream}, @var{decl}, @var{name}, @var{value})
6675 Combines (and replaces) the function of @code{ASM_WEAKEN_LABEL} and
6676 @code{ASM_OUTPUT_WEAK_ALIAS}, allowing access to the associated function
6677 or variable decl. If @var{value} is not @code{NULL}, this C statement
6678 should output to the stdio stream @var{stream} assembler code which
6679 defines (equates) the weak symbol @var{name} to have the value
6680 @var{value}. If @var{value} is @code{NULL}, it should output commands
6681 to make @var{name} weak.
6684 @defmac SUPPORTS_WEAK
6685 A C expression which evaluates to true if the target supports weak symbols.
6687 If you don't define this macro, @file{defaults.h} provides a default
6688 definition. If either @code{ASM_WEAKEN_LABEL} or @code{ASM_WEAKEN_DECL}
6689 is defined, the default definition is @samp{1}; otherwise, it is
6690 @samp{0}. Define this macro if you want to control weak symbol support
6691 with a compiler flag such as @option{-melf}.
6694 @defmac MAKE_DECL_ONE_ONLY (@var{decl})
6695 A C statement (sans semicolon) to mark @var{decl} to be emitted as a
6696 public symbol such that extra copies in multiple translation units will
6697 be discarded by the linker. Define this macro if your object file
6698 format provides support for this concept, such as the @samp{COMDAT}
6699 section flags in the Microsoft Windows PE/COFF format, and this support
6700 requires changes to @var{decl}, such as putting it in a separate section.
6703 @defmac SUPPORTS_ONE_ONLY
6704 A C expression which evaluates to true if the target supports one-only
6707 If you don't define this macro, @file{varasm.c} provides a default
6708 definition. If @code{MAKE_DECL_ONE_ONLY} is defined, the default
6709 definition is @samp{1}; otherwise, it is @samp{0}. Define this macro if
6710 you want to control one-only symbol support with a compiler flag, or if
6711 setting the @code{DECL_ONE_ONLY} flag is enough to mark a declaration to
6712 be emitted as one-only.
6715 @deftypefn {Target Hook} void TARGET_ASM_ASSEMBLE_VISIBILITY (tree @var{decl}, const char *@var{visibility})
6716 This target hook is a function to output to @var{asm_out_file} some
6717 commands that will make the symbol(s) associated with @var{decl} have
6718 hidden, protected or internal visibility as specified by @var{visibility}.
6721 @defmac ASM_OUTPUT_EXTERNAL (@var{stream}, @var{decl}, @var{name})
6722 A C statement (sans semicolon) to output to the stdio stream
6723 @var{stream} any text necessary for declaring the name of an external
6724 symbol named @var{name} which is referenced in this compilation but
6725 not defined. The value of @var{decl} is the tree node for the
6728 This macro need not be defined if it does not need to output anything.
6729 The GNU assembler and most Unix assemblers don't require anything.
6732 @defmac ASM_OUTPUT_EXTERNAL_LIBCALL (@var{stream}, @var{symref})
6733 A C statement (sans semicolon) to output on @var{stream} an assembler
6734 pseudo-op to declare a library function name external. The name of the
6735 library function is given by @var{symref}, which has type @code{rtx} and
6736 is a @code{symbol_ref}.
6738 This macro need not be defined if it does not need to output anything.
6739 The GNU assembler and most Unix assemblers don't require anything.
6742 @defmac ASM_OUTPUT_LABELREF (@var{stream}, @var{name})
6743 A C statement (sans semicolon) to output to the stdio stream
6744 @var{stream} a reference in assembler syntax to a label named
6745 @var{name}. This should add @samp{_} to the front of the name, if that
6746 is customary on your operating system, as it is in most Berkeley Unix
6747 systems. This macro is used in @code{assemble_name}.
6750 @defmac ASM_OUTPUT_SYMBOL_REF (@var{stream}, @var{sym})
6751 A C statement (sans semicolon) to output a reference to
6752 @code{SYMBOL_REF} @var{sym}. If not defined, @code{assemble_name}
6753 will be used to output the name of the symbol. This macro may be used
6754 to modify the way a symbol is referenced depending on information
6755 encoded by @code{TARGET_ENCODE_SECTION_INFO}.
6758 @defmac ASM_OUTPUT_LABEL_REF (@var{stream}, @var{buf})
6759 A C statement (sans semicolon) to output a reference to @var{buf}, the
6760 result of @code{ASM_GENERATE_INTERNAL_LABEL}. If not defined,
6761 @code{assemble_name} will be used to output the name of the symbol.
6762 This macro is not used by @code{output_asm_label}, or the @code{%l}
6763 specifier that calls it; the intention is that this macro should be set
6764 when it is necessary to output a label differently when its address is
6768 @deftypefn {Target Hook} void TARGET_ASM_INTERNAL_LABEL (FILE *@var{stream}, const char *@var{prefix}, unsigned long @var{labelno})
6769 A function to output to the stdio stream @var{stream} a label whose
6770 name is made from the string @var{prefix} and the number @var{labelno}.
6772 It is absolutely essential that these labels be distinct from the labels
6773 used for user-level functions and variables. Otherwise, certain programs
6774 will have name conflicts with internal labels.
6776 It is desirable to exclude internal labels from the symbol table of the
6777 object file. Most assemblers have a naming convention for labels that
6778 should be excluded; on many systems, the letter @samp{L} at the
6779 beginning of a label has this effect. You should find out what
6780 convention your system uses, and follow it.
6782 The default version of this function utilizes ASM_GENERATE_INTERNAL_LABEL.
6785 @defmac ASM_OUTPUT_DEBUG_LABEL (@var{stream}, @var{prefix}, @var{num})
6786 A C statement to output to the stdio stream @var{stream} a debug info
6787 label whose name is made from the string @var{prefix} and the number
6788 @var{num}. This is useful for VLIW targets, where debug info labels
6789 may need to be treated differently than branch target labels. On some
6790 systems, branch target labels must be at the beginning of instruction
6791 bundles, but debug info labels can occur in the middle of instruction
6794 If this macro is not defined, then @code{(*targetm.asm_out.internal_label)} will be
6798 @defmac ASM_GENERATE_INTERNAL_LABEL (@var{string}, @var{prefix}, @var{num})
6799 A C statement to store into the string @var{string} a label whose name
6800 is made from the string @var{prefix} and the number @var{num}.
6802 This string, when output subsequently by @code{assemble_name}, should
6803 produce the output that @code{(*targetm.asm_out.internal_label)} would produce
6804 with the same @var{prefix} and @var{num}.
6806 If the string begins with @samp{*}, then @code{assemble_name} will
6807 output the rest of the string unchanged. It is often convenient for
6808 @code{ASM_GENERATE_INTERNAL_LABEL} to use @samp{*} in this way. If the
6809 string doesn't start with @samp{*}, then @code{ASM_OUTPUT_LABELREF} gets
6810 to output the string, and may change it. (Of course,
6811 @code{ASM_OUTPUT_LABELREF} is also part of your machine description, so
6812 you should know what it does on your machine.)
6815 @defmac ASM_FORMAT_PRIVATE_NAME (@var{outvar}, @var{name}, @var{number})
6816 A C expression to assign to @var{outvar} (which is a variable of type
6817 @code{char *}) a newly allocated string made from the string
6818 @var{name} and the number @var{number}, with some suitable punctuation
6819 added. Use @code{alloca} to get space for the string.
6821 The string will be used as an argument to @code{ASM_OUTPUT_LABELREF} to
6822 produce an assembler label for an internal static variable whose name is
6823 @var{name}. Therefore, the string must be such as to result in valid
6824 assembler code. The argument @var{number} is different each time this
6825 macro is executed; it prevents conflicts between similarly-named
6826 internal static variables in different scopes.
6828 Ideally this string should not be a valid C identifier, to prevent any
6829 conflict with the user's own symbols. Most assemblers allow periods
6830 or percent signs in assembler symbols; putting at least one of these
6831 between the name and the number will suffice.
6833 If this macro is not defined, a default definition will be provided
6834 which is correct for most systems.
6837 @defmac ASM_OUTPUT_DEF (@var{stream}, @var{name}, @var{value})
6838 A C statement to output to the stdio stream @var{stream} assembler code
6839 which defines (equates) the symbol @var{name} to have the value @var{value}.
6842 If @code{SET_ASM_OP} is defined, a default definition is provided which is
6843 correct for most systems.
6846 @defmac ASM_OUTPUT_DEF_FROM_DECLS (@var{stream}, @var{decl_of_name}, @var{decl_of_value})
6847 A C statement to output to the stdio stream @var{stream} assembler code
6848 which defines (equates) the symbol whose tree node is @var{decl_of_name}
6849 to have the value of the tree node @var{decl_of_value}. This macro will
6850 be used in preference to @samp{ASM_OUTPUT_DEF} if it is defined and if
6851 the tree nodes are available.
6854 If @code{SET_ASM_OP} is defined, a default definition is provided which is
6855 correct for most systems.
6858 @defmac ASM_OUTPUT_WEAK_ALIAS (@var{stream}, @var{name}, @var{value})
6859 A C statement to output to the stdio stream @var{stream} assembler code
6860 which defines (equates) the weak symbol @var{name} to have the value
6861 @var{value}. If @var{value} is @code{NULL}, it defines @var{name} as
6862 an undefined weak symbol.
6864 Define this macro if the target only supports weak aliases; define
6865 @code{ASM_OUTPUT_DEF} instead if possible.
6868 @defmac OBJC_GEN_METHOD_LABEL (@var{buf}, @var{is_inst}, @var{class_name}, @var{cat_name}, @var{sel_name})
6869 Define this macro to override the default assembler names used for
6870 Objective-C methods.
6872 The default name is a unique method number followed by the name of the
6873 class (e.g.@: @samp{_1_Foo}). For methods in categories, the name of
6874 the category is also included in the assembler name (e.g.@:
6877 These names are safe on most systems, but make debugging difficult since
6878 the method's selector is not present in the name. Therefore, particular
6879 systems define other ways of computing names.
6881 @var{buf} is an expression of type @code{char *} which gives you a
6882 buffer in which to store the name; its length is as long as
6883 @var{class_name}, @var{cat_name} and @var{sel_name} put together, plus
6884 50 characters extra.
6886 The argument @var{is_inst} specifies whether the method is an instance
6887 method or a class method; @var{class_name} is the name of the class;
6888 @var{cat_name} is the name of the category (or @code{NULL} if the method is not
6889 in a category); and @var{sel_name} is the name of the selector.
6891 On systems where the assembler can handle quoted names, you can use this
6892 macro to provide more human-readable names.
6895 @defmac ASM_DECLARE_CLASS_REFERENCE (@var{stream}, @var{name})
6896 A C statement (sans semicolon) to output to the stdio stream
6897 @var{stream} commands to declare that the label @var{name} is an
6898 Objective-C class reference. This is only needed for targets whose
6899 linkers have special support for NeXT-style runtimes.
6902 @defmac ASM_DECLARE_UNRESOLVED_REFERENCE (@var{stream}, @var{name})
6903 A C statement (sans semicolon) to output to the stdio stream
6904 @var{stream} commands to declare that the label @var{name} is an
6905 unresolved Objective-C class reference. This is only needed for targets
6906 whose linkers have special support for NeXT-style runtimes.
6909 @node Initialization
6910 @subsection How Initialization Functions Are Handled
6911 @cindex initialization routines
6912 @cindex termination routines
6913 @cindex constructors, output of
6914 @cindex destructors, output of
6916 The compiled code for certain languages includes @dfn{constructors}
6917 (also called @dfn{initialization routines})---functions to initialize
6918 data in the program when the program is started. These functions need
6919 to be called before the program is ``started''---that is to say, before
6920 @code{main} is called.
6922 Compiling some languages generates @dfn{destructors} (also called
6923 @dfn{termination routines}) that should be called when the program
6926 To make the initialization and termination functions work, the compiler
6927 must output something in the assembler code to cause those functions to
6928 be called at the appropriate time. When you port the compiler to a new
6929 system, you need to specify how to do this.
6931 There are two major ways that GCC currently supports the execution of
6932 initialization and termination functions. Each way has two variants.
6933 Much of the structure is common to all four variations.
6935 @findex __CTOR_LIST__
6936 @findex __DTOR_LIST__
6937 The linker must build two lists of these functions---a list of
6938 initialization functions, called @code{__CTOR_LIST__}, and a list of
6939 termination functions, called @code{__DTOR_LIST__}.
6941 Each list always begins with an ignored function pointer (which may hold
6942 0, @minus{}1, or a count of the function pointers after it, depending on
6943 the environment). This is followed by a series of zero or more function
6944 pointers to constructors (or destructors), followed by a function
6945 pointer containing zero.
6947 Depending on the operating system and its executable file format, either
6948 @file{crtstuff.c} or @file{libgcc2.c} traverses these lists at startup
6949 time and exit time. Constructors are called in reverse order of the
6950 list; destructors in forward order.
6952 The best way to handle static constructors works only for object file
6953 formats which provide arbitrarily-named sections. A section is set
6954 aside for a list of constructors, and another for a list of destructors.
6955 Traditionally these are called @samp{.ctors} and @samp{.dtors}. Each
6956 object file that defines an initialization function also puts a word in
6957 the constructor section to point to that function. The linker
6958 accumulates all these words into one contiguous @samp{.ctors} section.
6959 Termination functions are handled similarly.
6961 This method will be chosen as the default by @file{target-def.h} if
6962 @code{TARGET_ASM_NAMED_SECTION} is defined. A target that does not
6963 support arbitrary sections, but does support special designated
6964 constructor and destructor sections may define @code{CTORS_SECTION_ASM_OP}
6965 and @code{DTORS_SECTION_ASM_OP} to achieve the same effect.
6967 When arbitrary sections are available, there are two variants, depending
6968 upon how the code in @file{crtstuff.c} is called. On systems that
6969 support a @dfn{.init} section which is executed at program startup,
6970 parts of @file{crtstuff.c} are compiled into that section. The
6971 program is linked by the @command{gcc} driver like this:
6974 ld -o @var{output_file} crti.o crtbegin.o @dots{} -lgcc crtend.o crtn.o
6977 The prologue of a function (@code{__init}) appears in the @code{.init}
6978 section of @file{crti.o}; the epilogue appears in @file{crtn.o}. Likewise
6979 for the function @code{__fini} in the @dfn{.fini} section. Normally these
6980 files are provided by the operating system or by the GNU C library, but
6981 are provided by GCC for a few targets.
6983 The objects @file{crtbegin.o} and @file{crtend.o} are (for most targets)
6984 compiled from @file{crtstuff.c}. They contain, among other things, code
6985 fragments within the @code{.init} and @code{.fini} sections that branch
6986 to routines in the @code{.text} section. The linker will pull all parts
6987 of a section together, which results in a complete @code{__init} function
6988 that invokes the routines we need at startup.
6990 To use this variant, you must define the @code{INIT_SECTION_ASM_OP}
6993 If no init section is available, when GCC compiles any function called
6994 @code{main} (or more accurately, any function designated as a program
6995 entry point by the language front end calling @code{expand_main_function}),
6996 it inserts a procedure call to @code{__main} as the first executable code
6997 after the function prologue. The @code{__main} function is defined
6998 in @file{libgcc2.c} and runs the global constructors.
7000 In file formats that don't support arbitrary sections, there are again
7001 two variants. In the simplest variant, the GNU linker (GNU @code{ld})
7002 and an `a.out' format must be used. In this case,
7003 @code{TARGET_ASM_CONSTRUCTOR} is defined to produce a @code{.stabs}
7004 entry of type @samp{N_SETT}, referencing the name @code{__CTOR_LIST__},
7005 and with the address of the void function containing the initialization
7006 code as its value. The GNU linker recognizes this as a request to add
7007 the value to a @dfn{set}; the values are accumulated, and are eventually
7008 placed in the executable as a vector in the format described above, with
7009 a leading (ignored) count and a trailing zero element.
7010 @code{TARGET_ASM_DESTRUCTOR} is handled similarly. Since no init
7011 section is available, the absence of @code{INIT_SECTION_ASM_OP} causes
7012 the compilation of @code{main} to call @code{__main} as above, starting
7013 the initialization process.
7015 The last variant uses neither arbitrary sections nor the GNU linker.
7016 This is preferable when you want to do dynamic linking and when using
7017 file formats which the GNU linker does not support, such as `ECOFF'@. In
7018 this case, @code{TARGET_HAVE_CTORS_DTORS} is false, initialization and
7019 termination functions are recognized simply by their names. This requires
7020 an extra program in the linkage step, called @command{collect2}. This program
7021 pretends to be the linker, for use with GCC; it does its job by running
7022 the ordinary linker, but also arranges to include the vectors of
7023 initialization and termination functions. These functions are called
7024 via @code{__main} as described above. In order to use this method,
7025 @code{use_collect2} must be defined in the target in @file{config.gcc}.
7028 The following section describes the specific macros that control and
7029 customize the handling of initialization and termination functions.
7032 @node Macros for Initialization
7033 @subsection Macros Controlling Initialization Routines
7035 Here are the macros that control how the compiler handles initialization
7036 and termination functions:
7038 @defmac INIT_SECTION_ASM_OP
7039 If defined, a C string constant, including spacing, for the assembler
7040 operation to identify the following data as initialization code. If not
7041 defined, GCC will assume such a section does not exist. When you are
7042 using special sections for initialization and termination functions, this
7043 macro also controls how @file{crtstuff.c} and @file{libgcc2.c} arrange to
7044 run the initialization functions.
7047 @defmac HAS_INIT_SECTION
7048 If defined, @code{main} will not call @code{__main} as described above.
7049 This macro should be defined for systems that control start-up code
7050 on a symbol-by-symbol basis, such as OSF/1, and should not
7051 be defined explicitly for systems that support @code{INIT_SECTION_ASM_OP}.
7054 @defmac LD_INIT_SWITCH
7055 If defined, a C string constant for a switch that tells the linker that
7056 the following symbol is an initialization routine.
7059 @defmac LD_FINI_SWITCH
7060 If defined, a C string constant for a switch that tells the linker that
7061 the following symbol is a finalization routine.
7064 @defmac COLLECT_SHARED_INIT_FUNC (@var{stream}, @var{func})
7065 If defined, a C statement that will write a function that can be
7066 automatically called when a shared library is loaded. The function
7067 should call @var{func}, which takes no arguments. If not defined, and
7068 the object format requires an explicit initialization function, then a
7069 function called @code{_GLOBAL__DI} will be generated.
7071 This function and the following one are used by collect2 when linking a
7072 shared library that needs constructors or destructors, or has DWARF2
7073 exception tables embedded in the code.
7076 @defmac COLLECT_SHARED_FINI_FUNC (@var{stream}, @var{func})
7077 If defined, a C statement that will write a function that can be
7078 automatically called when a shared library is unloaded. The function
7079 should call @var{func}, which takes no arguments. If not defined, and
7080 the object format requires an explicit finalization function, then a
7081 function called @code{_GLOBAL__DD} will be generated.
7084 @defmac INVOKE__main
7085 If defined, @code{main} will call @code{__main} despite the presence of
7086 @code{INIT_SECTION_ASM_OP}. This macro should be defined for systems
7087 where the init section is not actually run automatically, but is still
7088 useful for collecting the lists of constructors and destructors.
7091 @defmac SUPPORTS_INIT_PRIORITY
7092 If nonzero, the C++ @code{init_priority} attribute is supported and the
7093 compiler should emit instructions to control the order of initialization
7094 of objects. If zero, the compiler will issue an error message upon
7095 encountering an @code{init_priority} attribute.
7098 @deftypefn {Target Hook} bool TARGET_HAVE_CTORS_DTORS
7099 This value is true if the target supports some ``native'' method of
7100 collecting constructors and destructors to be run at startup and exit.
7101 It is false if we must use @command{collect2}.
7104 @deftypefn {Target Hook} void TARGET_ASM_CONSTRUCTOR (rtx @var{symbol}, int @var{priority})
7105 If defined, a function that outputs assembler code to arrange to call
7106 the function referenced by @var{symbol} at initialization time.
7108 Assume that @var{symbol} is a @code{SYMBOL_REF} for a function taking
7109 no arguments and with no return value. If the target supports initialization
7110 priorities, @var{priority} is a value between 0 and @code{MAX_INIT_PRIORITY};
7111 otherwise it must be @code{DEFAULT_INIT_PRIORITY}.
7113 If this macro is not defined by the target, a suitable default will
7114 be chosen if (1) the target supports arbitrary section names, (2) the
7115 target defines @code{CTORS_SECTION_ASM_OP}, or (3) @code{USE_COLLECT2}
7119 @deftypefn {Target Hook} void TARGET_ASM_DESTRUCTOR (rtx @var{symbol}, int @var{priority})
7120 This is like @code{TARGET_ASM_CONSTRUCTOR} but used for termination
7121 functions rather than initialization functions.
7124 If @code{TARGET_HAVE_CTORS_DTORS} is true, the initialization routine
7125 generated for the generated object file will have static linkage.
7127 If your system uses @command{collect2} as the means of processing
7128 constructors, then that program normally uses @command{nm} to scan
7129 an object file for constructor functions to be called.
7131 On certain kinds of systems, you can define this macro to make
7132 @command{collect2} work faster (and, in some cases, make it work at all):
7134 @defmac OBJECT_FORMAT_COFF
7135 Define this macro if the system uses COFF (Common Object File Format)
7136 object files, so that @command{collect2} can assume this format and scan
7137 object files directly for dynamic constructor/destructor functions.
7139 This macro is effective only in a native compiler; @command{collect2} as
7140 part of a cross compiler always uses @command{nm} for the target machine.
7143 @defmac REAL_NM_FILE_NAME
7144 Define this macro as a C string constant containing the file name to use
7145 to execute @command{nm}. The default is to search the path normally for
7148 If your system supports shared libraries and has a program to list the
7149 dynamic dependencies of a given library or executable, you can define
7150 these macros to enable support for running initialization and
7151 termination functions in shared libraries:
7155 Define this macro to a C string constant containing the name of the program
7156 which lists dynamic dependencies, like @command{"ldd"} under SunOS 4.
7159 @defmac PARSE_LDD_OUTPUT (@var{ptr})
7160 Define this macro to be C code that extracts filenames from the output
7161 of the program denoted by @code{LDD_SUFFIX}. @var{ptr} is a variable
7162 of type @code{char *} that points to the beginning of a line of output
7163 from @code{LDD_SUFFIX}. If the line lists a dynamic dependency, the
7164 code must advance @var{ptr} to the beginning of the filename on that
7165 line. Otherwise, it must set @var{ptr} to @code{NULL}.
7168 @node Instruction Output
7169 @subsection Output of Assembler Instructions
7171 @c prevent bad page break with this line
7172 This describes assembler instruction output.
7174 @defmac REGISTER_NAMES
7175 A C initializer containing the assembler's names for the machine
7176 registers, each one as a C string constant. This is what translates
7177 register numbers in the compiler into assembler language.
7180 @defmac ADDITIONAL_REGISTER_NAMES
7181 If defined, a C initializer for an array of structures containing a name
7182 and a register number. This macro defines additional names for hard
7183 registers, thus allowing the @code{asm} option in declarations to refer
7184 to registers using alternate names.
7187 @defmac ASM_OUTPUT_OPCODE (@var{stream}, @var{ptr})
7188 Define this macro if you are using an unusual assembler that
7189 requires different names for the machine instructions.
7191 The definition is a C statement or statements which output an
7192 assembler instruction opcode to the stdio stream @var{stream}. The
7193 macro-operand @var{ptr} is a variable of type @code{char *} which
7194 points to the opcode name in its ``internal'' form---the form that is
7195 written in the machine description. The definition should output the
7196 opcode name to @var{stream}, performing any translation you desire, and
7197 increment the variable @var{ptr} to point at the end of the opcode
7198 so that it will not be output twice.
7200 In fact, your macro definition may process less than the entire opcode
7201 name, or more than the opcode name; but if you want to process text
7202 that includes @samp{%}-sequences to substitute operands, you must take
7203 care of the substitution yourself. Just be sure to increment
7204 @var{ptr} over whatever text should not be output normally.
7206 @findex recog_data.operand
7207 If you need to look at the operand values, they can be found as the
7208 elements of @code{recog_data.operand}.
7210 If the macro definition does nothing, the instruction is output
7214 @defmac FINAL_PRESCAN_INSN (@var{insn}, @var{opvec}, @var{noperands})
7215 If defined, a C statement to be executed just prior to the output of
7216 assembler code for @var{insn}, to modify the extracted operands so
7217 they will be output differently.
7219 Here the argument @var{opvec} is the vector containing the operands
7220 extracted from @var{insn}, and @var{noperands} is the number of
7221 elements of the vector which contain meaningful data for this insn.
7222 The contents of this vector are what will be used to convert the insn
7223 template into assembler code, so you can change the assembler output
7224 by changing the contents of the vector.
7226 This macro is useful when various assembler syntaxes share a single
7227 file of instruction patterns; by defining this macro differently, you
7228 can cause a large class of instructions to be output differently (such
7229 as with rearranged operands). Naturally, variations in assembler
7230 syntax affecting individual insn patterns ought to be handled by
7231 writing conditional output routines in those patterns.
7233 If this macro is not defined, it is equivalent to a null statement.
7236 @defmac FINAL_PRESCAN_LABEL
7237 If defined, @code{FINAL_PRESCAN_INSN} will be called on each
7238 @code{CODE_LABEL}. In that case, @var{opvec} will be a null pointer and
7239 @var{noperands} will be zero.
7242 @defmac PRINT_OPERAND (@var{stream}, @var{x}, @var{code})
7243 A C compound statement to output to stdio stream @var{stream} the
7244 assembler syntax for an instruction operand @var{x}. @var{x} is an
7247 @var{code} is a value that can be used to specify one of several ways
7248 of printing the operand. It is used when identical operands must be
7249 printed differently depending on the context. @var{code} comes from
7250 the @samp{%} specification that was used to request printing of the
7251 operand. If the specification was just @samp{%@var{digit}} then
7252 @var{code} is 0; if the specification was @samp{%@var{ltr}
7253 @var{digit}} then @var{code} is the ASCII code for @var{ltr}.
7256 If @var{x} is a register, this macro should print the register's name.
7257 The names can be found in an array @code{reg_names} whose type is
7258 @code{char *[]}. @code{reg_names} is initialized from
7259 @code{REGISTER_NAMES}.
7261 When the machine description has a specification @samp{%@var{punct}}
7262 (a @samp{%} followed by a punctuation character), this macro is called
7263 with a null pointer for @var{x} and the punctuation character for
7267 @defmac PRINT_OPERAND_PUNCT_VALID_P (@var{code})
7268 A C expression which evaluates to true if @var{code} is a valid
7269 punctuation character for use in the @code{PRINT_OPERAND} macro. If
7270 @code{PRINT_OPERAND_PUNCT_VALID_P} is not defined, it means that no
7271 punctuation characters (except for the standard one, @samp{%}) are used
7275 @defmac PRINT_OPERAND_ADDRESS (@var{stream}, @var{x})
7276 A C compound statement to output to stdio stream @var{stream} the
7277 assembler syntax for an instruction operand that is a memory reference
7278 whose address is @var{x}. @var{x} is an RTL expression.
7280 @cindex @code{TARGET_ENCODE_SECTION_INFO} usage
7281 On some machines, the syntax for a symbolic address depends on the
7282 section that the address refers to. On these machines, define the hook
7283 @code{TARGET_ENCODE_SECTION_INFO} to store the information into the
7284 @code{symbol_ref}, and then check for it here. @xref{Assembler
7288 @findex dbr_sequence_length
7289 @defmac DBR_OUTPUT_SEQEND (@var{file})
7290 A C statement, to be executed after all slot-filler instructions have
7291 been output. If necessary, call @code{dbr_sequence_length} to
7292 determine the number of slots filled in a sequence (zero if not
7293 currently outputting a sequence), to decide how many no-ops to output,
7296 Don't define this macro if it has nothing to do, but it is helpful in
7297 reading assembly output if the extent of the delay sequence is made
7298 explicit (e.g.@: with white space).
7301 @findex final_sequence
7302 Note that output routines for instructions with delay slots must be
7303 prepared to deal with not being output as part of a sequence
7304 (i.e.@: when the scheduling pass is not run, or when no slot fillers could be
7305 found.) The variable @code{final_sequence} is null when not
7306 processing a sequence, otherwise it contains the @code{sequence} rtx
7310 @defmac REGISTER_PREFIX
7311 @defmacx LOCAL_LABEL_PREFIX
7312 @defmacx USER_LABEL_PREFIX
7313 @defmacx IMMEDIATE_PREFIX
7314 If defined, C string expressions to be used for the @samp{%R}, @samp{%L},
7315 @samp{%U}, and @samp{%I} options of @code{asm_fprintf} (see
7316 @file{final.c}). These are useful when a single @file{md} file must
7317 support multiple assembler formats. In that case, the various @file{tm.h}
7318 files can define these macros differently.
7321 @defmac ASM_FPRINTF_EXTENSIONS (@var{file}, @var{argptr}, @var{format})
7322 If defined this macro should expand to a series of @code{case}
7323 statements which will be parsed inside the @code{switch} statement of
7324 the @code{asm_fprintf} function. This allows targets to define extra
7325 printf formats which may useful when generating their assembler
7326 statements. Note that uppercase letters are reserved for future
7327 generic extensions to asm_fprintf, and so are not available to target
7328 specific code. The output file is given by the parameter @var{file}.
7329 The varargs input pointer is @var{argptr} and the rest of the format
7330 string, starting the character after the one that is being switched
7331 upon, is pointed to by @var{format}.
7334 @defmac ASSEMBLER_DIALECT
7335 If your target supports multiple dialects of assembler language (such as
7336 different opcodes), define this macro as a C expression that gives the
7337 numeric index of the assembler language dialect to use, with zero as the
7340 If this macro is defined, you may use constructs of the form
7342 @samp{@{option0|option1|option2@dots{}@}}
7345 in the output templates of patterns (@pxref{Output Template}) or in the
7346 first argument of @code{asm_fprintf}. This construct outputs
7347 @samp{option0}, @samp{option1}, @samp{option2}, etc., if the value of
7348 @code{ASSEMBLER_DIALECT} is zero, one, two, etc. Any special characters
7349 within these strings retain their usual meaning. If there are fewer
7350 alternatives within the braces than the value of
7351 @code{ASSEMBLER_DIALECT}, the construct outputs nothing.
7353 If you do not define this macro, the characters @samp{@{}, @samp{|} and
7354 @samp{@}} do not have any special meaning when used in templates or
7355 operands to @code{asm_fprintf}.
7357 Define the macros @code{REGISTER_PREFIX}, @code{LOCAL_LABEL_PREFIX},
7358 @code{USER_LABEL_PREFIX} and @code{IMMEDIATE_PREFIX} if you can express
7359 the variations in assembler language syntax with that mechanism. Define
7360 @code{ASSEMBLER_DIALECT} and use the @samp{@{option0|option1@}} syntax
7361 if the syntax variant are larger and involve such things as different
7362 opcodes or operand order.
7365 @defmac ASM_OUTPUT_REG_PUSH (@var{stream}, @var{regno})
7366 A C expression to output to @var{stream} some assembler code
7367 which will push hard register number @var{regno} onto the stack.
7368 The code need not be optimal, since this macro is used only when
7372 @defmac ASM_OUTPUT_REG_POP (@var{stream}, @var{regno})
7373 A C expression to output to @var{stream} some assembler code
7374 which will pop hard register number @var{regno} off of the stack.
7375 The code need not be optimal, since this macro is used only when
7379 @node Dispatch Tables
7380 @subsection Output of Dispatch Tables
7382 @c prevent bad page break with this line
7383 This concerns dispatch tables.
7385 @cindex dispatch table
7386 @defmac ASM_OUTPUT_ADDR_DIFF_ELT (@var{stream}, @var{body}, @var{value}, @var{rel})
7387 A C statement to output to the stdio stream @var{stream} an assembler
7388 pseudo-instruction to generate a difference between two labels.
7389 @var{value} and @var{rel} are the numbers of two internal labels. The
7390 definitions of these labels are output using
7391 @code{(*targetm.asm_out.internal_label)}, and they must be printed in the same
7392 way here. For example,
7395 fprintf (@var{stream}, "\t.word L%d-L%d\n",
7396 @var{value}, @var{rel})
7399 You must provide this macro on machines where the addresses in a
7400 dispatch table are relative to the table's own address. If defined, GCC
7401 will also use this macro on all machines when producing PIC@.
7402 @var{body} is the body of the @code{ADDR_DIFF_VEC}; it is provided so that the
7403 mode and flags can be read.
7406 @defmac ASM_OUTPUT_ADDR_VEC_ELT (@var{stream}, @var{value})
7407 This macro should be provided on machines where the addresses
7408 in a dispatch table are absolute.
7410 The definition should be a C statement to output to the stdio stream
7411 @var{stream} an assembler pseudo-instruction to generate a reference to
7412 a label. @var{value} is the number of an internal label whose
7413 definition is output using @code{(*targetm.asm_out.internal_label)}.
7417 fprintf (@var{stream}, "\t.word L%d\n", @var{value})
7421 @defmac ASM_OUTPUT_CASE_LABEL (@var{stream}, @var{prefix}, @var{num}, @var{table})
7422 Define this if the label before a jump-table needs to be output
7423 specially. The first three arguments are the same as for
7424 @code{(*targetm.asm_out.internal_label)}; the fourth argument is the
7425 jump-table which follows (a @code{jump_insn} containing an
7426 @code{addr_vec} or @code{addr_diff_vec}).
7428 This feature is used on system V to output a @code{swbeg} statement
7431 If this macro is not defined, these labels are output with
7432 @code{(*targetm.asm_out.internal_label)}.
7435 @defmac ASM_OUTPUT_CASE_END (@var{stream}, @var{num}, @var{table})
7436 Define this if something special must be output at the end of a
7437 jump-table. The definition should be a C statement to be executed
7438 after the assembler code for the table is written. It should write
7439 the appropriate code to stdio stream @var{stream}. The argument
7440 @var{table} is the jump-table insn, and @var{num} is the label-number
7441 of the preceding label.
7443 If this macro is not defined, nothing special is output at the end of
7447 @node Exception Region Output
7448 @subsection Assembler Commands for Exception Regions
7450 @c prevent bad page break with this line
7452 This describes commands marking the start and the end of an exception
7455 @defmac EH_FRAME_SECTION_NAME
7456 If defined, a C string constant for the name of the section containing
7457 exception handling frame unwind information. If not defined, GCC will
7458 provide a default definition if the target supports named sections.
7459 @file{crtstuff.c} uses this macro to switch to the appropriate section.
7461 You should define this symbol if your target supports DWARF 2 frame
7462 unwind information and the default definition does not work.
7465 @defmac EH_FRAME_IN_DATA_SECTION
7466 If defined, DWARF 2 frame unwind information will be placed in the
7467 data section even though the target supports named sections. This
7468 might be necessary, for instance, if the system linker does garbage
7469 collection and sections cannot be marked as not to be collected.
7471 Do not define this macro unless @code{TARGET_ASM_NAMED_SECTION} is
7475 @defmac MASK_RETURN_ADDR
7476 An rtx used to mask the return address found via @code{RETURN_ADDR_RTX}, so
7477 that it does not contain any extraneous set bits in it.
7480 @defmac DWARF2_UNWIND_INFO
7481 Define this macro to 0 if your target supports DWARF 2 frame unwind
7482 information, but it does not yet work with exception handling.
7483 Otherwise, if your target supports this information (if it defines
7484 @samp{INCOMING_RETURN_ADDR_RTX} and either @samp{UNALIGNED_INT_ASM_OP}
7485 or @samp{OBJECT_FORMAT_ELF}), GCC will provide a default definition of
7488 If this macro is defined to 1, the DWARF 2 unwinder will be the default
7489 exception handling mechanism; otherwise, @code{setjmp}/@code{longjmp} will be used by
7492 If this macro is defined to anything, the DWARF 2 unwinder will be used
7493 instead of inline unwinders and @code{__unwind_function} in the non-@code{setjmp} case.
7496 @defmac DWARF_CIE_DATA_ALIGNMENT
7497 This macro need only be defined if the target might save registers in the
7498 function prologue at an offset to the stack pointer that is not aligned to
7499 @code{UNITS_PER_WORD}. The definition should be the negative minimum
7500 alignment if @code{STACK_GROWS_DOWNWARD} is defined, and the positive
7501 minimum alignment otherwise. @xref{SDB and DWARF}. Only applicable if
7502 the target supports DWARF 2 frame unwind information.
7505 @deftypefn {Target Hook} void TARGET_ASM_EXCEPTION_SECTION ()
7506 If defined, a function that switches to the section in which the main
7507 exception table is to be placed (@pxref{Sections}). The default is a
7508 function that switches to a section named @code{.gcc_except_table} on
7509 machines that support named sections via
7510 @code{TARGET_ASM_NAMED_SECTION}, otherwise if @option{-fpic} or
7511 @option{-fPIC} is in effect, the @code{data_section}, otherwise the
7512 @code{readonly_data_section}.
7515 @deftypefn {Target Hook} void TARGET_ASM_EH_FRAME_SECTION ()
7516 If defined, a function that switches to the section in which the DWARF 2
7517 frame unwind information to be placed (@pxref{Sections}). The default
7518 is a function that outputs a standard GAS section directive, if
7519 @code{EH_FRAME_SECTION_NAME} is defined, or else a data section
7520 directive followed by a synthetic label.
7523 @deftypevar {Target Hook} bool TARGET_TERMINATE_DW2_EH_FRAME_INFO
7524 Contains the value true if the target should add a zero word onto the
7525 end of a Dwarf-2 frame info section when used for exception handling.
7526 Default value is false if @code{EH_FRAME_SECTION_NAME} is defined, and
7530 @deftypefn {Target Hook} rtx TARGET_DWARF_REGISTER_SPAN (rtx @var{reg})
7531 Given a register, this hook should return a parallel of registers to
7532 represent where to find the register pieces. Define this hook if the
7533 register and its mode are represented in Dwarf in non-contiguous
7534 locations, or if the register should be represented in more than one
7535 register in Dwarf. Otherwise, this hook should return @code{NULL_RTX}.
7536 If not defined, the default is to return @code{NULL_RTX}.
7539 @node Alignment Output
7540 @subsection Assembler Commands for Alignment
7542 @c prevent bad page break with this line
7543 This describes commands for alignment.
7545 @defmac JUMP_ALIGN (@var{label})
7546 The alignment (log base 2) to put in front of @var{label}, which is
7547 a common destination of jumps and has no fallthru incoming edge.
7549 This macro need not be defined if you don't want any special alignment
7550 to be done at such a time. Most machine descriptions do not currently
7553 Unless it's necessary to inspect the @var{label} parameter, it is better
7554 to set the variable @var{align_jumps} in the target's
7555 @code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's
7556 selection in @var{align_jumps} in a @code{JUMP_ALIGN} implementation.
7559 @defmac LABEL_ALIGN_AFTER_BARRIER (@var{label})
7560 The alignment (log base 2) to put in front of @var{label}, which follows
7563 This macro need not be defined if you don't want any special alignment
7564 to be done at such a time. Most machine descriptions do not currently
7568 @defmac LABEL_ALIGN_AFTER_BARRIER_MAX_SKIP
7569 The maximum number of bytes to skip when applying
7570 @code{LABEL_ALIGN_AFTER_BARRIER}. This works only if
7571 @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined.
7574 @defmac LOOP_ALIGN (@var{label})
7575 The alignment (log base 2) to put in front of @var{label}, which follows
7576 a @code{NOTE_INSN_LOOP_BEG} note.
7578 This macro need not be defined if you don't want any special alignment
7579 to be done at such a time. Most machine descriptions do not currently
7582 Unless it's necessary to inspect the @var{label} parameter, it is better
7583 to set the variable @code{align_loops} in the target's
7584 @code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's
7585 selection in @code{align_loops} in a @code{LOOP_ALIGN} implementation.
7588 @defmac LOOP_ALIGN_MAX_SKIP
7589 The maximum number of bytes to skip when applying @code{LOOP_ALIGN}.
7590 This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined.
7593 @defmac LABEL_ALIGN (@var{label})
7594 The alignment (log base 2) to put in front of @var{label}.
7595 If @code{LABEL_ALIGN_AFTER_BARRIER} / @code{LOOP_ALIGN} specify a different alignment,
7596 the maximum of the specified values is used.
7598 Unless it's necessary to inspect the @var{label} parameter, it is better
7599 to set the variable @code{align_labels} in the target's
7600 @code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's
7601 selection in @code{align_labels} in a @code{LABEL_ALIGN} implementation.
7604 @defmac LABEL_ALIGN_MAX_SKIP
7605 The maximum number of bytes to skip when applying @code{LABEL_ALIGN}.
7606 This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined.
7609 @defmac ASM_OUTPUT_SKIP (@var{stream}, @var{nbytes})
7610 A C statement to output to the stdio stream @var{stream} an assembler
7611 instruction to advance the location counter by @var{nbytes} bytes.
7612 Those bytes should be zero when loaded. @var{nbytes} will be a C
7613 expression of type @code{int}.
7616 @defmac ASM_NO_SKIP_IN_TEXT
7617 Define this macro if @code{ASM_OUTPUT_SKIP} should not be used in the
7618 text section because it fails to put zeros in the bytes that are skipped.
7619 This is true on many Unix systems, where the pseudo--op to skip bytes
7620 produces no-op instructions rather than zeros when used in the text
7624 @defmac ASM_OUTPUT_ALIGN (@var{stream}, @var{power})
7625 A C statement to output to the stdio stream @var{stream} an assembler
7626 command to advance the location counter to a multiple of 2 to the
7627 @var{power} bytes. @var{power} will be a C expression of type @code{int}.
7630 @defmac ASM_OUTPUT_ALIGN_WITH_NOP (@var{stream}, @var{power})
7631 Like @code{ASM_OUTPUT_ALIGN}, except that the ``nop'' instruction is used
7632 for padding, if necessary.
7635 @defmac ASM_OUTPUT_MAX_SKIP_ALIGN (@var{stream}, @var{power}, @var{max_skip})
7636 A C statement to output to the stdio stream @var{stream} an assembler
7637 command to advance the location counter to a multiple of 2 to the
7638 @var{power} bytes, but only if @var{max_skip} or fewer bytes are needed to
7639 satisfy the alignment request. @var{power} and @var{max_skip} will be
7640 a C expression of type @code{int}.
7644 @node Debugging Info
7645 @section Controlling Debugging Information Format
7647 @c prevent bad page break with this line
7648 This describes how to specify debugging information.
7651 * All Debuggers:: Macros that affect all debugging formats uniformly.
7652 * DBX Options:: Macros enabling specific options in DBX format.
7653 * DBX Hooks:: Hook macros for varying DBX format.
7654 * File Names and DBX:: Macros controlling output of file names in DBX format.
7655 * SDB and DWARF:: Macros for SDB (COFF) and DWARF formats.
7656 * VMS Debug:: Macros for VMS debug format.
7660 @subsection Macros Affecting All Debugging Formats
7662 @c prevent bad page break with this line
7663 These macros affect all debugging formats.
7665 @defmac DBX_REGISTER_NUMBER (@var{regno})
7666 A C expression that returns the DBX register number for the compiler
7667 register number @var{regno}. In the default macro provided, the value
7668 of this expression will be @var{regno} itself. But sometimes there are
7669 some registers that the compiler knows about and DBX does not, or vice
7670 versa. In such cases, some register may need to have one number in the
7671 compiler and another for DBX@.
7673 If two registers have consecutive numbers inside GCC, and they can be
7674 used as a pair to hold a multiword value, then they @emph{must} have
7675 consecutive numbers after renumbering with @code{DBX_REGISTER_NUMBER}.
7676 Otherwise, debuggers will be unable to access such a pair, because they
7677 expect register pairs to be consecutive in their own numbering scheme.
7679 If you find yourself defining @code{DBX_REGISTER_NUMBER} in way that
7680 does not preserve register pairs, then what you must do instead is
7681 redefine the actual register numbering scheme.
7684 @defmac DEBUGGER_AUTO_OFFSET (@var{x})
7685 A C expression that returns the integer offset value for an automatic
7686 variable having address @var{x} (an RTL expression). The default
7687 computation assumes that @var{x} is based on the frame-pointer and
7688 gives the offset from the frame-pointer. This is required for targets
7689 that produce debugging output for DBX or COFF-style debugging output
7690 for SDB and allow the frame-pointer to be eliminated when the
7691 @option{-g} options is used.
7694 @defmac DEBUGGER_ARG_OFFSET (@var{offset}, @var{x})
7695 A C expression that returns the integer offset value for an argument
7696 having address @var{x} (an RTL expression). The nominal offset is
7700 @defmac PREFERRED_DEBUGGING_TYPE
7701 A C expression that returns the type of debugging output GCC should
7702 produce when the user specifies just @option{-g}. Define
7703 this if you have arranged for GCC to support more than one format of
7704 debugging output. Currently, the allowable values are @code{DBX_DEBUG},
7705 @code{SDB_DEBUG}, @code{DWARF_DEBUG}, @code{DWARF2_DEBUG},
7706 @code{XCOFF_DEBUG}, @code{VMS_DEBUG}, and @code{VMS_AND_DWARF2_DEBUG}.
7708 When the user specifies @option{-ggdb}, GCC normally also uses the
7709 value of this macro to select the debugging output format, but with two
7710 exceptions. If @code{DWARF2_DEBUGGING_INFO} is defined and
7711 @code{LINKER_DOES_NOT_WORK_WITH_DWARF2} is not defined, GCC uses the
7712 value @code{DWARF2_DEBUG}. Otherwise, if @code{DBX_DEBUGGING_INFO} is
7713 defined, GCC uses @code{DBX_DEBUG}.
7715 The value of this macro only affects the default debugging output; the
7716 user can always get a specific type of output by using @option{-gstabs},
7717 @option{-gcoff}, @option{-gdwarf-1}, @option{-gdwarf-2}, @option{-gxcoff},
7722 @subsection Specific Options for DBX Output
7724 @c prevent bad page break with this line
7725 These are specific options for DBX output.
7727 @defmac DBX_DEBUGGING_INFO
7728 Define this macro if GCC should produce debugging output for DBX
7729 in response to the @option{-g} option.
7732 @defmac XCOFF_DEBUGGING_INFO
7733 Define this macro if GCC should produce XCOFF format debugging output
7734 in response to the @option{-g} option. This is a variant of DBX format.
7737 @defmac DEFAULT_GDB_EXTENSIONS
7738 Define this macro to control whether GCC should by default generate
7739 GDB's extended version of DBX debugging information (assuming DBX-format
7740 debugging information is enabled at all). If you don't define the
7741 macro, the default is 1: always generate the extended information
7742 if there is any occasion to.
7745 @defmac DEBUG_SYMS_TEXT
7746 Define this macro if all @code{.stabs} commands should be output while
7747 in the text section.
7750 @defmac ASM_STABS_OP
7751 A C string constant, including spacing, naming the assembler pseudo op to
7752 use instead of @code{"\t.stabs\t"} to define an ordinary debugging symbol.
7753 If you don't define this macro, @code{"\t.stabs\t"} is used. This macro
7754 applies only to DBX debugging information format.
7757 @defmac ASM_STABD_OP
7758 A C string constant, including spacing, naming the assembler pseudo op to
7759 use instead of @code{"\t.stabd\t"} to define a debugging symbol whose
7760 value is the current location. If you don't define this macro,
7761 @code{"\t.stabd\t"} is used. This macro applies only to DBX debugging
7765 @defmac ASM_STABN_OP
7766 A C string constant, including spacing, naming the assembler pseudo op to
7767 use instead of @code{"\t.stabn\t"} to define a debugging symbol with no
7768 name. If you don't define this macro, @code{"\t.stabn\t"} is used. This
7769 macro applies only to DBX debugging information format.
7772 @defmac DBX_NO_XREFS
7773 Define this macro if DBX on your system does not support the construct
7774 @samp{xs@var{tagname}}. On some systems, this construct is used to
7775 describe a forward reference to a structure named @var{tagname}.
7776 On other systems, this construct is not supported at all.
7779 @defmac DBX_CONTIN_LENGTH
7780 A symbol name in DBX-format debugging information is normally
7781 continued (split into two separate @code{.stabs} directives) when it
7782 exceeds a certain length (by default, 80 characters). On some
7783 operating systems, DBX requires this splitting; on others, splitting
7784 must not be done. You can inhibit splitting by defining this macro
7785 with the value zero. You can override the default splitting-length by
7786 defining this macro as an expression for the length you desire.
7789 @defmac DBX_CONTIN_CHAR
7790 Normally continuation is indicated by adding a @samp{\} character to
7791 the end of a @code{.stabs} string when a continuation follows. To use
7792 a different character instead, define this macro as a character
7793 constant for the character you want to use. Do not define this macro
7794 if backslash is correct for your system.
7797 @defmac DBX_STATIC_STAB_DATA_SECTION
7798 Define this macro if it is necessary to go to the data section before
7799 outputting the @samp{.stabs} pseudo-op for a non-global static
7803 @defmac DBX_TYPE_DECL_STABS_CODE
7804 The value to use in the ``code'' field of the @code{.stabs} directive
7805 for a typedef. The default is @code{N_LSYM}.
7808 @defmac DBX_STATIC_CONST_VAR_CODE
7809 The value to use in the ``code'' field of the @code{.stabs} directive
7810 for a static variable located in the text section. DBX format does not
7811 provide any ``right'' way to do this. The default is @code{N_FUN}.
7814 @defmac DBX_REGPARM_STABS_CODE
7815 The value to use in the ``code'' field of the @code{.stabs} directive
7816 for a parameter passed in registers. DBX format does not provide any
7817 ``right'' way to do this. The default is @code{N_RSYM}.
7820 @defmac DBX_REGPARM_STABS_LETTER
7821 The letter to use in DBX symbol data to identify a symbol as a parameter
7822 passed in registers. DBX format does not customarily provide any way to
7823 do this. The default is @code{'P'}.
7826 @defmac DBX_MEMPARM_STABS_LETTER
7827 The letter to use in DBX symbol data to identify a symbol as a stack
7828 parameter. The default is @code{'p'}.
7831 @defmac DBX_FUNCTION_FIRST
7832 Define this macro if the DBX information for a function and its
7833 arguments should precede the assembler code for the function. Normally,
7834 in DBX format, the debugging information entirely follows the assembler
7838 @defmac DBX_BLOCKS_FUNCTION_RELATIVE
7839 Define this macro if the value of a symbol describing the scope of a
7840 block (@code{N_LBRAC} or @code{N_RBRAC}) should be relative to the start
7841 of the enclosing function. Normally, GCC uses an absolute address.
7844 @defmac DBX_USE_BINCL
7845 Define this macro if GCC should generate @code{N_BINCL} and
7846 @code{N_EINCL} stabs for included header files, as on Sun systems. This
7847 macro also directs GCC to output a type number as a pair of a file
7848 number and a type number within the file. Normally, GCC does not
7849 generate @code{N_BINCL} or @code{N_EINCL} stabs, and it outputs a single
7850 number for a type number.
7854 @subsection Open-Ended Hooks for DBX Format
7856 @c prevent bad page break with this line
7857 These are hooks for DBX format.
7859 @defmac DBX_OUTPUT_LBRAC (@var{stream}, @var{name})
7860 Define this macro to say how to output to @var{stream} the debugging
7861 information for the start of a scope level for variable names. The
7862 argument @var{name} is the name of an assembler symbol (for use with
7863 @code{assemble_name}) whose value is the address where the scope begins.
7866 @defmac DBX_OUTPUT_RBRAC (@var{stream}, @var{name})
7867 Like @code{DBX_OUTPUT_LBRAC}, but for the end of a scope level.
7870 @defmac DBX_OUTPUT_NFUN (@var{stream}, @var{lscope_label}, @var{decl})
7871 Define this macro if the target machine requires special handling to
7872 output an @code{N_FUN} entry for the function @var{decl}.
7875 @defmac DBX_OUTPUT_FUNCTION_END (@var{stream}, @var{function})
7876 Define this macro if the target machine requires special output at the
7877 end of the debugging information for a function. The definition should
7878 be a C statement (sans semicolon) to output the appropriate information
7879 to @var{stream}. @var{function} is the @code{FUNCTION_DECL} node for
7883 @defmac DBX_OUTPUT_STANDARD_TYPES (@var{syms})
7884 Define this macro if you need to control the order of output of the
7885 standard data types at the beginning of compilation. The argument
7886 @var{syms} is a @code{tree} which is a chain of all the predefined
7887 global symbols, including names of data types.
7889 Normally, DBX output starts with definitions of the types for integers
7890 and characters, followed by all the other predefined types of the
7891 particular language in no particular order.
7893 On some machines, it is necessary to output different particular types
7894 first. To do this, define @code{DBX_OUTPUT_STANDARD_TYPES} to output
7895 those symbols in the necessary order. Any predefined types that you
7896 don't explicitly output will be output afterward in no particular order.
7898 Be careful not to define this macro so that it works only for C@. There
7899 are no global variables to access most of the built-in types, because
7900 another language may have another set of types. The way to output a
7901 particular type is to look through @var{syms} to see if you can find it.
7907 for (decl = syms; decl; decl = TREE_CHAIN (decl))
7908 if (!strcmp (IDENTIFIER_POINTER (DECL_NAME (decl)),
7910 dbxout_symbol (decl);
7916 This does nothing if the expected type does not exist.
7918 See the function @code{init_decl_processing} in @file{c-decl.c} to find
7919 the names to use for all the built-in C types.
7921 Here is another way of finding a particular type:
7923 @c this is still overfull. --mew 10feb93
7927 for (decl = syms; decl; decl = TREE_CHAIN (decl))
7928 if (TREE_CODE (decl) == TYPE_DECL
7929 && (TREE_CODE (TREE_TYPE (decl))
7931 && TYPE_PRECISION (TREE_TYPE (decl)) == 16
7932 && TYPE_UNSIGNED (TREE_TYPE (decl)))
7934 /* @r{This must be @code{unsigned short}.} */
7935 dbxout_symbol (decl);
7942 @defmac NO_DBX_FUNCTION_END
7943 Some stabs encapsulation formats (in particular ECOFF), cannot handle the
7944 @code{.stabs "",N_FUN,,0,0,Lscope-function-1} gdb dbx extension construct.
7945 On those machines, define this macro to turn this feature off without
7946 disturbing the rest of the gdb extensions.
7949 @node File Names and DBX
7950 @subsection File Names in DBX Format
7952 @c prevent bad page break with this line
7953 This describes file names in DBX format.
7955 @defmac DBX_OUTPUT_MAIN_SOURCE_FILENAME (@var{stream}, @var{name})
7956 A C statement to output DBX debugging information to the stdio stream
7957 @var{stream} which indicates that file @var{name} is the main source
7958 file---the file specified as the input file for compilation.
7959 This macro is called only once, at the beginning of compilation.
7961 This macro need not be defined if the standard form of output
7962 for DBX debugging information is appropriate.
7965 @defmac DBX_OUTPUT_MAIN_SOURCE_DIRECTORY (@var{stream}, @var{name})
7966 A C statement to output DBX debugging information to the stdio stream
7967 @var{stream} which indicates that the current directory during
7968 compilation is named @var{name}.
7970 This macro need not be defined if the standard form of output
7971 for DBX debugging information is appropriate.
7974 @defmac DBX_OUTPUT_MAIN_SOURCE_FILE_END (@var{stream}, @var{name})
7975 A C statement to output DBX debugging information at the end of
7976 compilation of the main source file @var{name}.
7978 If you don't define this macro, nothing special is output at the end
7979 of compilation, which is correct for most machines.
7984 @subsection Macros for SDB and DWARF Output
7986 @c prevent bad page break with this line
7987 Here are macros for SDB and DWARF output.
7989 @defmac SDB_DEBUGGING_INFO
7990 Define this macro if GCC should produce COFF-style debugging output
7991 for SDB in response to the @option{-g} option.
7994 @defmac DWARF_DEBUGGING_INFO
7995 Define this macro if GCC should produce dwarf format debugging output
7996 in response to the @option{-g} option.
7999 @defmac DWARF2_DEBUGGING_INFO
8000 Define this macro if GCC should produce dwarf version 2 format
8001 debugging output in response to the @option{-g} option.
8003 To support optional call frame debugging information, you must also
8004 define @code{INCOMING_RETURN_ADDR_RTX} and either set
8005 @code{RTX_FRAME_RELATED_P} on the prologue insns if you use RTL for the
8006 prologue, or call @code{dwarf2out_def_cfa} and @code{dwarf2out_reg_save}
8007 as appropriate from @code{TARGET_ASM_FUNCTION_PROLOGUE} if you don't.
8010 @defmac DWARF2_FRAME_INFO
8011 Define this macro to a nonzero value if GCC should always output
8012 Dwarf 2 frame information. If @code{DWARF2_UNWIND_INFO}
8013 (@pxref{Exception Region Output} is nonzero, GCC will output this
8014 information not matter how you define @code{DWARF2_FRAME_INFO}.
8017 @defmac LINKER_DOES_NOT_WORK_WITH_DWARF2
8018 Define this macro if the linker does not work with Dwarf version 2.
8019 Normally, if the user specifies only @option{-ggdb} GCC will use Dwarf
8020 version 2 if available; this macro disables this. See the description
8021 of the @code{PREFERRED_DEBUGGING_TYPE} macro for more details.
8024 @defmac DWARF2_GENERATE_TEXT_SECTION_LABEL
8025 By default, the Dwarf 2 debugging information generator will generate a
8026 label to mark the beginning of the text section. If it is better simply
8027 to use the name of the text section itself, rather than an explicit label,
8028 to indicate the beginning of the text section, define this macro to zero.
8031 @defmac DWARF2_ASM_LINE_DEBUG_INFO
8032 Define this macro to be a nonzero value if the assembler can generate Dwarf 2
8033 line debug info sections. This will result in much more compact line number
8034 tables, and hence is desirable if it works.
8037 @defmac ASM_OUTPUT_DWARF_DELTA (@var{stream}, @var{size}, @var{label1}, @var{label2})
8038 A C statement to issue assembly directives that create a difference
8039 between the two given labels, using an integer of the given size.
8042 @defmac ASM_OUTPUT_DWARF_OFFSET (@var{stream}, @var{size}, @var{label})
8043 A C statement to issue assembly directives that create a
8044 section-relative reference to the given label, using an integer of the
8048 @defmac ASM_OUTPUT_DWARF_PCREL (@var{stream}, @var{size}, @var{label})
8049 A C statement to issue assembly directives that create a self-relative
8050 reference to the given label, using an integer of the given size.
8053 @defmac PUT_SDB_@dots{}
8054 Define these macros to override the assembler syntax for the special
8055 SDB assembler directives. See @file{sdbout.c} for a list of these
8056 macros and their arguments. If the standard syntax is used, you need
8057 not define them yourself.
8061 Some assemblers do not support a semicolon as a delimiter, even between
8062 SDB assembler directives. In that case, define this macro to be the
8063 delimiter to use (usually @samp{\n}). It is not necessary to define
8064 a new set of @code{PUT_SDB_@var{op}} macros if this is the only change
8068 @defmac SDB_GENERATE_FAKE
8069 Define this macro to override the usual method of constructing a dummy
8070 name for anonymous structure and union types. See @file{sdbout.c} for
8074 @defmac SDB_ALLOW_UNKNOWN_REFERENCES
8075 Define this macro to allow references to unknown structure,
8076 union, or enumeration tags to be emitted. Standard COFF does not
8077 allow handling of unknown references, MIPS ECOFF has support for
8081 @defmac SDB_ALLOW_FORWARD_REFERENCES
8082 Define this macro to allow references to structure, union, or
8083 enumeration tags that have not yet been seen to be handled. Some
8084 assemblers choke if forward tags are used, while some require it.
8089 @subsection Macros for VMS Debug Format
8091 @c prevent bad page break with this line
8092 Here are macros for VMS debug format.
8094 @defmac VMS_DEBUGGING_INFO
8095 Define this macro if GCC should produce debugging output for VMS
8096 in response to the @option{-g} option. The default behavior for VMS
8097 is to generate minimal debug info for a traceback in the absence of
8098 @option{-g} unless explicitly overridden with @option{-g0}. This
8099 behavior is controlled by @code{OPTIMIZATION_OPTIONS} and
8100 @code{OVERRIDE_OPTIONS}.
8103 @node Floating Point
8104 @section Cross Compilation and Floating Point
8105 @cindex cross compilation and floating point
8106 @cindex floating point and cross compilation
8108 While all modern machines use twos-complement representation for integers,
8109 there are a variety of representations for floating point numbers. This
8110 means that in a cross-compiler the representation of floating point numbers
8111 in the compiled program may be different from that used in the machine
8112 doing the compilation.
8114 Because different representation systems may offer different amounts of
8115 range and precision, all floating point constants must be represented in
8116 the target machine's format. Therefore, the cross compiler cannot
8117 safely use the host machine's floating point arithmetic; it must emulate
8118 the target's arithmetic. To ensure consistency, GCC always uses
8119 emulation to work with floating point values, even when the host and
8120 target floating point formats are identical.
8122 The following macros are provided by @file{real.h} for the compiler to
8123 use. All parts of the compiler which generate or optimize
8124 floating-point calculations must use these macros. They may evaluate
8125 their operands more than once, so operands must not have side effects.
8127 @defmac REAL_VALUE_TYPE
8128 The C data type to be used to hold a floating point value in the target
8129 machine's format. Typically this is a @code{struct} containing an
8130 array of @code{HOST_WIDE_INT}, but all code should treat it as an opaque
8134 @deftypefn Macro int REAL_VALUES_EQUAL (REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y})
8135 Compares for equality the two values, @var{x} and @var{y}. If the target
8136 floating point format supports negative zeroes and/or NaNs,
8137 @samp{REAL_VALUES_EQUAL (-0.0, 0.0)} is true, and
8138 @samp{REAL_VALUES_EQUAL (NaN, NaN)} is false.
8141 @deftypefn Macro int REAL_VALUES_LESS (REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y})
8142 Tests whether @var{x} is less than @var{y}.
8145 @deftypefn Macro HOST_WIDE_INT REAL_VALUE_FIX (REAL_VALUE_TYPE @var{x})
8146 Truncates @var{x} to a signed integer, rounding toward zero.
8149 @deftypefn Macro {unsigned HOST_WIDE_INT} REAL_VALUE_UNSIGNED_FIX (REAL_VALUE_TYPE @var{x})
8150 Truncates @var{x} to an unsigned integer, rounding toward zero. If
8151 @var{x} is negative, returns zero.
8154 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ATOF (const char *@var{string}, enum machine_mode @var{mode})
8155 Converts @var{string} into a floating point number in the target machine's
8156 representation for mode @var{mode}. This routine can handle both
8157 decimal and hexadecimal floating point constants, using the syntax
8158 defined by the C language for both.
8161 @deftypefn Macro int REAL_VALUE_NEGATIVE (REAL_VALUE_TYPE @var{x})
8162 Returns 1 if @var{x} is negative (including negative zero), 0 otherwise.
8165 @deftypefn Macro int REAL_VALUE_ISINF (REAL_VALUE_TYPE @var{x})
8166 Determines whether @var{x} represents infinity (positive or negative).
8169 @deftypefn Macro int REAL_VALUE_ISNAN (REAL_VALUE_TYPE @var{x})
8170 Determines whether @var{x} represents a ``NaN'' (not-a-number).
8173 @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})
8174 Calculates an arithmetic operation on the two floating point values
8175 @var{x} and @var{y}, storing the result in @var{output} (which must be a
8178 The operation to be performed is specified by @var{code}. Only the
8179 following codes are supported: @code{PLUS_EXPR}, @code{MINUS_EXPR},
8180 @code{MULT_EXPR}, @code{RDIV_EXPR}, @code{MAX_EXPR}, @code{MIN_EXPR}.
8182 If @code{REAL_ARITHMETIC} is asked to evaluate division by zero and the
8183 target's floating point format cannot represent infinity, it will call
8184 @code{abort}. Callers should check for this situation first, using
8185 @code{MODE_HAS_INFINITIES}. @xref{Storage Layout}.
8188 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_NEGATE (REAL_VALUE_TYPE @var{x})
8189 Returns the negative of the floating point value @var{x}.
8192 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ABS (REAL_VALUE_TYPE @var{x})
8193 Returns the absolute value of @var{x}.
8196 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_TRUNCATE (REAL_VALUE_TYPE @var{mode}, enum machine_mode @var{x})
8197 Truncates the floating point value @var{x} to fit in @var{mode}. The
8198 return value is still a full-size @code{REAL_VALUE_TYPE}, but it has an
8199 appropriate bit pattern to be output asa floating constant whose
8200 precision accords with mode @var{mode}.
8203 @deftypefn Macro void REAL_VALUE_TO_INT (HOST_WIDE_INT @var{low}, HOST_WIDE_INT @var{high}, REAL_VALUE_TYPE @var{x})
8204 Converts a floating point value @var{x} into a double-precision integer
8205 which is then stored into @var{low} and @var{high}. If the value is not
8206 integral, it is truncated.
8209 @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})
8210 Converts a double-precision integer found in @var{low} and @var{high},
8211 into a floating point value which is then stored into @var{x}. The
8212 value is truncated to fit in mode @var{mode}.
8215 @node Mode Switching
8216 @section Mode Switching Instructions
8217 @cindex mode switching
8218 The following macros control mode switching optimizations:
8220 @defmac OPTIMIZE_MODE_SWITCHING (@var{entity})
8221 Define this macro if the port needs extra instructions inserted for mode
8222 switching in an optimizing compilation.
8224 For an example, the SH4 can perform both single and double precision
8225 floating point operations, but to perform a single precision operation,
8226 the FPSCR PR bit has to be cleared, while for a double precision
8227 operation, this bit has to be set. Changing the PR bit requires a general
8228 purpose register as a scratch register, hence these FPSCR sets have to
8229 be inserted before reload, i.e.@: you can't put this into instruction emitting
8230 or @code{TARGET_MACHINE_DEPENDENT_REORG}.
8232 You can have multiple entities that are mode-switched, and select at run time
8233 which entities actually need it. @code{OPTIMIZE_MODE_SWITCHING} should
8234 return nonzero for any @var{entity} that needs mode-switching.
8235 If you define this macro, you also have to define
8236 @code{NUM_MODES_FOR_MODE_SWITCHING}, @code{MODE_NEEDED},
8237 @code{MODE_PRIORITY_TO_MODE} and @code{EMIT_MODE_SET}.
8238 @code{NORMAL_MODE} is optional.
8241 @defmac NUM_MODES_FOR_MODE_SWITCHING
8242 If you define @code{OPTIMIZE_MODE_SWITCHING}, you have to define this as
8243 initializer for an array of integers. Each initializer element
8244 N refers to an entity that needs mode switching, and specifies the number
8245 of different modes that might need to be set for this entity.
8246 The position of the initializer in the initializer - starting counting at
8247 zero - determines the integer that is used to refer to the mode-switched
8249 In macros that take mode arguments / yield a mode result, modes are
8250 represented as numbers 0 @dots{} N @minus{} 1. N is used to specify that no mode
8251 switch is needed / supplied.
8254 @defmac MODE_NEEDED (@var{entity}, @var{insn})
8255 @var{entity} is an integer specifying a mode-switched entity. If
8256 @code{OPTIMIZE_MODE_SWITCHING} is defined, you must define this macro to
8257 return an integer value not larger than the corresponding element in
8258 @code{NUM_MODES_FOR_MODE_SWITCHING}, to denote the mode that @var{entity} must
8259 be switched into prior to the execution of @var{insn}.
8262 @defmac NORMAL_MODE (@var{entity})
8263 If this macro is defined, it is evaluated for every @var{entity} that needs
8264 mode switching. It should evaluate to an integer, which is a mode that
8265 @var{entity} is assumed to be switched to at function entry and exit.
8268 @defmac MODE_PRIORITY_TO_MODE (@var{entity}, @var{n})
8269 This macro specifies the order in which modes for @var{entity} are processed.
8270 0 is the highest priority, @code{NUM_MODES_FOR_MODE_SWITCHING[@var{entity}] - 1} the
8271 lowest. The value of the macro should be an integer designating a mode
8272 for @var{entity}. For any fixed @var{entity}, @code{mode_priority_to_mode}
8273 (@var{entity}, @var{n}) shall be a bijection in 0 @dots{}
8274 @code{num_modes_for_mode_switching[@var{entity}] - 1}.
8277 @defmac EMIT_MODE_SET (@var{entity}, @var{mode}, @var{hard_regs_live})
8278 Generate one or more insns to set @var{entity} to @var{mode}.
8279 @var{hard_reg_live} is the set of hard registers live at the point where
8280 the insn(s) are to be inserted.
8283 @node Target Attributes
8284 @section Defining target-specific uses of @code{__attribute__}
8285 @cindex target attributes
8286 @cindex machine attributes
8287 @cindex attributes, target-specific
8289 Target-specific attributes may be defined for functions, data and types.
8290 These are described using the following target hooks; they also need to
8291 be documented in @file{extend.texi}.
8293 @deftypevr {Target Hook} {const struct attribute_spec *} TARGET_ATTRIBUTE_TABLE
8294 If defined, this target hook points to an array of @samp{struct
8295 attribute_spec} (defined in @file{tree.h}) specifying the machine
8296 specific attributes for this target and some of the restrictions on the
8297 entities to which these attributes are applied and the arguments they
8301 @deftypefn {Target Hook} int TARGET_COMP_TYPE_ATTRIBUTES (tree @var{type1}, tree @var{type2})
8302 If defined, this target hook is a function which returns zero if the attributes on
8303 @var{type1} and @var{type2} are incompatible, one if they are compatible,
8304 and two if they are nearly compatible (which causes a warning to be
8305 generated). If this is not defined, machine-specific attributes are
8306 supposed always to be compatible.
8309 @deftypefn {Target Hook} void TARGET_SET_DEFAULT_TYPE_ATTRIBUTES (tree @var{type})
8310 If defined, this target hook is a function which assigns default attributes to
8311 newly defined @var{type}.
8314 @deftypefn {Target Hook} tree TARGET_MERGE_TYPE_ATTRIBUTES (tree @var{type1}, tree @var{type2})
8315 Define this target hook if the merging of type attributes needs special
8316 handling. If defined, the result is a list of the combined
8317 @code{TYPE_ATTRIBUTES} of @var{type1} and @var{type2}. It is assumed
8318 that @code{comptypes} has already been called and returned 1. This
8319 function may call @code{merge_attributes} to handle machine-independent
8323 @deftypefn {Target Hook} tree TARGET_MERGE_DECL_ATTRIBUTES (tree @var{olddecl}, tree @var{newdecl})
8324 Define this target hook if the merging of decl attributes needs special
8325 handling. If defined, the result is a list of the combined
8326 @code{DECL_ATTRIBUTES} of @var{olddecl} and @var{newdecl}.
8327 @var{newdecl} is a duplicate declaration of @var{olddecl}. Examples of
8328 when this is needed are when one attribute overrides another, or when an
8329 attribute is nullified by a subsequent definition. This function may
8330 call @code{merge_attributes} to handle machine-independent merging.
8332 @findex TARGET_DLLIMPORT_DECL_ATTRIBUTES
8333 If the only target-specific handling you require is @samp{dllimport} for
8334 Windows targets, you should define the macro
8335 @code{TARGET_DLLIMPORT_DECL_ATTRIBUTES}. This links in a function
8336 called @code{merge_dllimport_decl_attributes} which can then be defined
8337 as the expansion of @code{TARGET_MERGE_DECL_ATTRIBUTES}. This is done
8338 in @file{i386/cygwin.h} and @file{i386/i386.c}, for example.
8341 @deftypefn {Target Hook} void TARGET_INSERT_ATTRIBUTES (tree @var{node}, tree *@var{attr_ptr})
8342 Define this target hook if you want to be able to add attributes to a decl
8343 when it is being created. This is normally useful for back ends which
8344 wish to implement a pragma by using the attributes which correspond to
8345 the pragma's effect. The @var{node} argument is the decl which is being
8346 created. The @var{attr_ptr} argument is a pointer to the attribute list
8347 for this decl. The list itself should not be modified, since it may be
8348 shared with other decls, but attributes may be chained on the head of
8349 the list and @code{*@var{attr_ptr}} modified to point to the new
8350 attributes, or a copy of the list may be made if further changes are
8354 @deftypefn {Target Hook} bool TARGET_FUNCTION_ATTRIBUTE_INLINABLE_P (tree @var{fndecl})
8356 This target hook returns @code{true} if it is ok to inline @var{fndecl}
8357 into the current function, despite its having target-specific
8358 attributes, @code{false} otherwise. By default, if a function has a
8359 target specific attribute attached to it, it will not be inlined.
8362 @node MIPS Coprocessors
8363 @section Defining coprocessor specifics for MIPS targets.
8364 @cindex MIPS coprocessor-definition macros
8366 The MIPS specification allows MIPS implementations to have as many as 4
8367 coprocessors, each with as many as 32 private registers. gcc supports
8368 accessing these registers and transferring values between the registers
8369 and memory using asm-ized variables. For example:
8372 register unsigned int cp0count asm ("c0r1");
8378 (``c0r1'' is the default name of register 1 in coprocessor 0; alternate
8379 names may be added as described below, or the default names may be
8380 overridden entirely in @code{SUBTARGET_CONDITIONAL_REGISTER_USAGE}.)
8382 Coprocessor registers are assumed to be epilogue-used; sets to them will
8383 be preserved even if it does not appear that the register is used again
8384 later in the function.
8386 Another note: according to the MIPS spec, coprocessor 1 (if present) is
8387 the FPU. One accesses COP1 registers through standard mips
8388 floating-point support; they are not included in this mechanism.
8390 There is one macro used in defining the MIPS coprocessor interface which
8391 you may want to override in subtargets; it is described below.
8393 @defmac ALL_COP_ADDITIONAL_REGISTER_NAMES
8394 A comma-separated list (with leading comma) of pairs describing the
8395 alternate names of coprocessor registers. The format of each entry should be
8397 @{ @var{alternatename}, @var{register_number}@}
8403 @section Miscellaneous Parameters
8404 @cindex parameters, miscellaneous
8406 @c prevent bad page break with this line
8407 Here are several miscellaneous parameters.
8409 @defmac PREDICATE_CODES
8410 Define this if you have defined special-purpose predicates in the file
8411 @file{@var{machine}.c}. This macro is called within an initializer of an
8412 array of structures. The first field in the structure is the name of a
8413 predicate and the second field is an array of rtl codes. For each
8414 predicate, list all rtl codes that can be in expressions matched by the
8415 predicate. The list should have a trailing comma. Here is an example
8416 of two entries in the list for a typical RISC machine:
8419 #define PREDICATE_CODES \
8420 @{"gen_reg_rtx_operand", @{SUBREG, REG@}@}, \
8421 @{"reg_or_short_cint_operand", @{SUBREG, REG, CONST_INT@}@},
8424 Defining this macro does not affect the generated code (however,
8425 incorrect definitions that omit an rtl code that may be matched by the
8426 predicate can cause the compiler to malfunction). Instead, it allows
8427 the table built by @file{genrecog} to be more compact and efficient,
8428 thus speeding up the compiler. The most important predicates to include
8429 in the list specified by this macro are those used in the most insn
8432 For each predicate function named in @code{PREDICATE_CODES}, a
8433 declaration will be generated in @file{insn-codes.h}.
8436 @defmac SPECIAL_MODE_PREDICATES
8437 Define this if you have special predicates that know special things
8438 about modes. Genrecog will warn about certain forms of
8439 @code{match_operand} without a mode; if the operand predicate is
8440 listed in @code{SPECIAL_MODE_PREDICATES}, the warning will be
8443 Here is an example from the IA-32 port (@code{ext_register_operand}
8444 specially checks for @code{HImode} or @code{SImode} in preparation
8445 for a byte extraction from @code{%ah} etc.).
8448 #define SPECIAL_MODE_PREDICATES \
8449 "ext_register_operand",
8453 @defmac CASE_VECTOR_MODE
8454 An alias for a machine mode name. This is the machine mode that
8455 elements of a jump-table should have.
8458 @defmac CASE_VECTOR_SHORTEN_MODE (@var{min_offset}, @var{max_offset}, @var{body})
8459 Optional: return the preferred mode for an @code{addr_diff_vec}
8460 when the minimum and maximum offset are known. If you define this,
8461 it enables extra code in branch shortening to deal with @code{addr_diff_vec}.
8462 To make this work, you also have to define @code{INSN_ALIGN} and
8463 make the alignment for @code{addr_diff_vec} explicit.
8464 The @var{body} argument is provided so that the offset_unsigned and scale
8465 flags can be updated.
8468 @defmac CASE_VECTOR_PC_RELATIVE
8469 Define this macro to be a C expression to indicate when jump-tables
8470 should contain relative addresses. If jump-tables never contain
8471 relative addresses, then you need not define this macro.
8474 @defmac CASE_DROPS_THROUGH
8475 Define this if control falls through a @code{case} insn when the index
8476 value is out of range. This means the specified default-label is
8477 actually ignored by the @code{case} insn proper.
8480 @defmac CASE_VALUES_THRESHOLD
8481 Define this to be the smallest number of different values for which it
8482 is best to use a jump-table instead of a tree of conditional branches.
8483 The default is four for machines with a @code{casesi} instruction and
8484 five otherwise. This is best for most machines.
8487 @defmac CASE_USE_BIT_TESTS
8488 Define this macro to be a C expression to indicate whether C switch
8489 statements may be implemented by a sequence of bit tests. This is
8490 advantageous on processors that can efficiently implement left shift
8491 of 1 by the number of bits held in a register, but inappropriate on
8492 targets that would require a loop. By default, this macro returns
8493 @code{true} if the target defines an @code{ashlsi3} pattern, and
8494 @code{false} otherwise.
8497 @defmac WORD_REGISTER_OPERATIONS
8498 Define this macro if operations between registers with integral mode
8499 smaller than a word are always performed on the entire register.
8500 Most RISC machines have this property and most CISC machines do not.
8503 @defmac LOAD_EXTEND_OP (@var{mode})
8504 Define this macro to be a C expression indicating when insns that read
8505 memory in @var{mode}, an integral mode narrower than a word, set the
8506 bits outside of @var{mode} to be either the sign-extension or the
8507 zero-extension of the data read. Return @code{SIGN_EXTEND} for values
8508 of @var{mode} for which the
8509 insn sign-extends, @code{ZERO_EXTEND} for which it zero-extends, and
8510 @code{NIL} for other modes.
8512 This macro is not called with @var{mode} non-integral or with a width
8513 greater than or equal to @code{BITS_PER_WORD}, so you may return any
8514 value in this case. Do not define this macro if it would always return
8515 @code{NIL}. On machines where this macro is defined, you will normally
8516 define it as the constant @code{SIGN_EXTEND} or @code{ZERO_EXTEND}.
8519 @defmac SHORT_IMMEDIATES_SIGN_EXTEND
8520 Define this macro if loading short immediate values into registers sign
8524 @defmac FIXUNS_TRUNC_LIKE_FIX_TRUNC
8525 Define this macro if the same instructions that convert a floating
8526 point number to a signed fixed point number also convert validly to an
8531 The maximum number of bytes that a single instruction can move quickly
8532 between memory and registers or between two memory locations.
8535 @defmac MAX_MOVE_MAX
8536 The maximum number of bytes that a single instruction can move quickly
8537 between memory and registers or between two memory locations. If this
8538 is undefined, the default is @code{MOVE_MAX}. Otherwise, it is the
8539 constant value that is the largest value that @code{MOVE_MAX} can have
8543 @defmac SHIFT_COUNT_TRUNCATED
8544 A C expression that is nonzero if on this machine the number of bits
8545 actually used for the count of a shift operation is equal to the number
8546 of bits needed to represent the size of the object being shifted. When
8547 this macro is nonzero, the compiler will assume that it is safe to omit
8548 a sign-extend, zero-extend, and certain bitwise `and' instructions that
8549 truncates the count of a shift operation. On machines that have
8550 instructions that act on bit-fields at variable positions, which may
8551 include `bit test' instructions, a nonzero @code{SHIFT_COUNT_TRUNCATED}
8552 also enables deletion of truncations of the values that serve as
8553 arguments to bit-field instructions.
8555 If both types of instructions truncate the count (for shifts) and
8556 position (for bit-field operations), or if no variable-position bit-field
8557 instructions exist, you should define this macro.
8559 However, on some machines, such as the 80386 and the 680x0, truncation
8560 only applies to shift operations and not the (real or pretended)
8561 bit-field operations. Define @code{SHIFT_COUNT_TRUNCATED} to be zero on
8562 such machines. Instead, add patterns to the @file{md} file that include
8563 the implied truncation of the shift instructions.
8565 You need not define this macro if it would always have the value of zero.
8568 @defmac TRULY_NOOP_TRUNCATION (@var{outprec}, @var{inprec})
8569 A C expression which is nonzero if on this machine it is safe to
8570 ``convert'' an integer of @var{inprec} bits to one of @var{outprec}
8571 bits (where @var{outprec} is smaller than @var{inprec}) by merely
8572 operating on it as if it had only @var{outprec} bits.
8574 On many machines, this expression can be 1.
8576 @c rearranged this, removed the phrase "it is reported that". this was
8577 @c to fix an overfull hbox. --mew 10feb93
8578 When @code{TRULY_NOOP_TRUNCATION} returns 1 for a pair of sizes for
8579 modes for which @code{MODES_TIEABLE_P} is 0, suboptimal code can result.
8580 If this is the case, making @code{TRULY_NOOP_TRUNCATION} return 0 in
8581 such cases may improve things.
8584 @defmac STORE_FLAG_VALUE
8585 A C expression describing the value returned by a comparison operator
8586 with an integral mode and stored by a store-flag instruction
8587 (@samp{s@var{cond}}) when the condition is true. This description must
8588 apply to @emph{all} the @samp{s@var{cond}} patterns and all the
8589 comparison operators whose results have a @code{MODE_INT} mode.
8591 A value of 1 or @minus{}1 means that the instruction implementing the
8592 comparison operator returns exactly 1 or @minus{}1 when the comparison is true
8593 and 0 when the comparison is false. Otherwise, the value indicates
8594 which bits of the result are guaranteed to be 1 when the comparison is
8595 true. This value is interpreted in the mode of the comparison
8596 operation, which is given by the mode of the first operand in the
8597 @samp{s@var{cond}} pattern. Either the low bit or the sign bit of
8598 @code{STORE_FLAG_VALUE} be on. Presently, only those bits are used by
8601 If @code{STORE_FLAG_VALUE} is neither 1 or @minus{}1, the compiler will
8602 generate code that depends only on the specified bits. It can also
8603 replace comparison operators with equivalent operations if they cause
8604 the required bits to be set, even if the remaining bits are undefined.
8605 For example, on a machine whose comparison operators return an
8606 @code{SImode} value and where @code{STORE_FLAG_VALUE} is defined as
8607 @samp{0x80000000}, saying that just the sign bit is relevant, the
8611 (ne:SI (and:SI @var{x} (const_int @var{power-of-2})) (const_int 0))
8618 (ashift:SI @var{x} (const_int @var{n}))
8622 where @var{n} is the appropriate shift count to move the bit being
8623 tested into the sign bit.
8625 There is no way to describe a machine that always sets the low-order bit
8626 for a true value, but does not guarantee the value of any other bits,
8627 but we do not know of any machine that has such an instruction. If you
8628 are trying to port GCC to such a machine, include an instruction to
8629 perform a logical-and of the result with 1 in the pattern for the
8630 comparison operators and let us know at @email{gcc@@gcc.gnu.org}.
8632 Often, a machine will have multiple instructions that obtain a value
8633 from a comparison (or the condition codes). Here are rules to guide the
8634 choice of value for @code{STORE_FLAG_VALUE}, and hence the instructions
8639 Use the shortest sequence that yields a valid definition for
8640 @code{STORE_FLAG_VALUE}. It is more efficient for the compiler to
8641 ``normalize'' the value (convert it to, e.g., 1 or 0) than for the
8642 comparison operators to do so because there may be opportunities to
8643 combine the normalization with other operations.
8646 For equal-length sequences, use a value of 1 or @minus{}1, with @minus{}1 being
8647 slightly preferred on machines with expensive jumps and 1 preferred on
8651 As a second choice, choose a value of @samp{0x80000001} if instructions
8652 exist that set both the sign and low-order bits but do not define the
8656 Otherwise, use a value of @samp{0x80000000}.
8659 Many machines can produce both the value chosen for
8660 @code{STORE_FLAG_VALUE} and its negation in the same number of
8661 instructions. On those machines, you should also define a pattern for
8662 those cases, e.g., one matching
8665 (set @var{A} (neg:@var{m} (ne:@var{m} @var{B} @var{C})))
8668 Some machines can also perform @code{and} or @code{plus} operations on
8669 condition code values with less instructions than the corresponding
8670 @samp{s@var{cond}} insn followed by @code{and} or @code{plus}. On those
8671 machines, define the appropriate patterns. Use the names @code{incscc}
8672 and @code{decscc}, respectively, for the patterns which perform
8673 @code{plus} or @code{minus} operations on condition code values. See
8674 @file{rs6000.md} for some examples. The GNU Superoptizer can be used to
8675 find such instruction sequences on other machines.
8677 If this macro is not defined, the default value, 1, is used. You need
8678 not define @code{STORE_FLAG_VALUE} if the machine has no store-flag
8679 instructions, or if the value generated by these instructions is 1.
8682 @defmac FLOAT_STORE_FLAG_VALUE (@var{mode})
8683 A C expression that gives a nonzero @code{REAL_VALUE_TYPE} value that is
8684 returned when comparison operators with floating-point results are true.
8685 Define this macro on machine that have comparison operations that return
8686 floating-point values. If there are no such operations, do not define
8690 @defmac CLZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value})
8691 @defmacx CTZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value})
8692 A C expression that evaluates to true if the architecture defines a value
8693 for @code{clz} or @code{ctz} with a zero operand. If so, @var{value}
8694 should be set to this value. If this macro is not defined, the value of
8695 @code{clz} or @code{ctz} is assumed to be undefined.
8697 This macro must be defined if the target's expansion for @code{ffs}
8698 relies on a particular value to get correct results. Otherwise it
8699 is not necessary, though it may be used to optimize some corner cases.
8701 Note that regardless of this macro the ``definedness'' of @code{clz}
8702 and @code{ctz} at zero do @emph{not} extend to the builtin functions
8703 visible to the user. Thus one may be free to adjust the value at will
8704 to match the target expansion of these operations without fear of
8709 An alias for the machine mode for pointers. On most machines, define
8710 this to be the integer mode corresponding to the width of a hardware
8711 pointer; @code{SImode} on 32-bit machine or @code{DImode} on 64-bit machines.
8712 On some machines you must define this to be one of the partial integer
8713 modes, such as @code{PSImode}.
8715 The width of @code{Pmode} must be at least as large as the value of
8716 @code{POINTER_SIZE}. If it is not equal, you must define the macro
8717 @code{POINTERS_EXTEND_UNSIGNED} to specify how pointers are extended
8721 @defmac FUNCTION_MODE
8722 An alias for the machine mode used for memory references to functions
8723 being called, in @code{call} RTL expressions. On most machines this
8724 should be @code{QImode}.
8727 @defmac INTEGRATE_THRESHOLD (@var{decl})
8728 A C expression for the maximum number of instructions above which the
8729 function @var{decl} should not be inlined. @var{decl} is a
8730 @code{FUNCTION_DECL} node.
8732 The default definition of this macro is 64 plus 8 times the number of
8733 arguments that the function accepts. Some people think a larger
8734 threshold should be used on RISC machines.
8737 @defmac STDC_0_IN_SYSTEM_HEADERS
8738 In normal operation, the preprocessor expands @code{__STDC__} to the
8739 constant 1, to signify that GCC conforms to ISO Standard C@. On some
8740 hosts, like Solaris, the system compiler uses a different convention,
8741 where @code{__STDC__} is normally 0, but is 1 if the user specifies
8742 strict conformance to the C Standard.
8744 Defining @code{STDC_0_IN_SYSTEM_HEADERS} makes GNU CPP follows the host
8745 convention when processing system header files, but when processing user
8746 files @code{__STDC__} will always expand to 1.
8749 @defmac NO_IMPLICIT_EXTERN_C
8750 Define this macro if the system header files support C++ as well as C@.
8751 This macro inhibits the usual method of using system header files in
8752 C++, which is to pretend that the file's contents are enclosed in
8753 @samp{extern "C" @{@dots{}@}}.
8758 @defmac REGISTER_TARGET_PRAGMAS ()
8759 Define this macro if you want to implement any target-specific pragmas.
8760 If defined, it is a C expression which makes a series of calls to
8761 @code{c_register_pragma} for each pragma. The macro may also do any
8762 setup required for the pragmas.
8764 The primary reason to define this macro is to provide compatibility with
8765 other compilers for the same target. In general, we discourage
8766 definition of target-specific pragmas for GCC@.
8768 If the pragma can be implemented by attributes then you should consider
8769 defining the target hook @samp{TARGET_INSERT_ATTRIBUTES} as well.
8771 Preprocessor macros that appear on pragma lines are not expanded. All
8772 @samp{#pragma} directives that do not match any registered pragma are
8773 silently ignored, unless the user specifies @option{-Wunknown-pragmas}.
8776 @deftypefun void c_register_pragma (const char *@var{space}, const char *@var{name}, void (*@var{callback}) (struct cpp_reader *))
8778 Each call to @code{c_register_pragma} establishes one pragma. The
8779 @var{callback} routine will be called when the preprocessor encounters a
8783 #pragma [@var{space}] @var{name} @dots{}
8786 @var{space} is the case-sensitive namespace of the pragma, or
8787 @code{NULL} to put the pragma in the global namespace. The callback
8788 routine receives @var{pfile} as its first argument, which can be passed
8789 on to cpplib's functions if necessary. You can lex tokens after the
8790 @var{name} by calling @code{c_lex}. Tokens that are not read by the
8791 callback will be silently ignored. The end of the line is indicated by
8792 a token of type @code{CPP_EOF}
8794 For an example use of this routine, see @file{c4x.h} and the callback
8795 routines defined in @file{c4x-c.c}.
8797 Note that the use of @code{c_lex} is specific to the C and C++
8798 compilers. It will not work in the Java or Fortran compilers, or any
8799 other language compilers for that matter. Thus if @code{c_lex} is going
8800 to be called from target-specific code, it must only be done so when
8801 building the C and C++ compilers. This can be done by defining the
8802 variables @code{c_target_objs} and @code{cxx_target_objs} in the
8803 target entry in the @file{config.gcc} file. These variables should name
8804 the target-specific, language-specific object file which contains the
8805 code that uses @code{c_lex}. Note it will also be necessary to add a
8806 rule to the makefile fragment pointed to by @code{tmake_file} that shows
8807 how to build this object file.
8812 @defmac HANDLE_SYSV_PRAGMA
8813 Define this macro (to a value of 1) if you want the System V style
8814 pragmas @samp{#pragma pack(<n>)} and @samp{#pragma weak <name>
8815 [=<value>]} to be supported by gcc.
8817 The pack pragma specifies the maximum alignment (in bytes) of fields
8818 within a structure, in much the same way as the @samp{__aligned__} and
8819 @samp{__packed__} @code{__attribute__}s do. A pack value of zero resets
8820 the behavior to the default.
8822 A subtlety for Microsoft Visual C/C++ style bit-field packing
8823 (e.g. -mms-bitfields) for targets that support it:
8824 When a bit-field is inserted into a packed record, the whole size
8825 of the underlying type is used by one or more same-size adjacent
8826 bit-fields (that is, if its long:3, 32 bits is used in the record,
8827 and any additional adjacent long bit-fields are packed into the same
8828 chunk of 32 bits. However, if the size changes, a new field of that
8831 If both MS bit-fields and @samp{__attribute__((packed))} are used,
8832 the latter will take precedence. If @samp{__attribute__((packed))} is
8833 used on a single field when MS bit-fields are in use, it will take
8834 precedence for that field, but the alignment of the rest of the structure
8835 may affect its placement.
8837 The weak pragma only works if @code{SUPPORTS_WEAK} and
8838 @code{ASM_WEAKEN_LABEL} are defined. If enabled it allows the creation
8839 of specifically named weak labels, optionally with a value.
8844 @defmac HANDLE_PRAGMA_PACK_PUSH_POP
8845 Define this macro (to a value of 1) if you want to support the Win32
8846 style pragmas @samp{#pragma pack(push,@var{n})} and @samp{#pragma
8847 pack(pop)}. The @samp{pack(push,@var{n})} pragma specifies the maximum alignment
8848 (in bytes) of fields within a structure, in much the same way as the
8849 @samp{__aligned__} and @samp{__packed__} @code{__attribute__}s do. A
8850 pack value of zero resets the behavior to the default. Successive
8851 invocations of this pragma cause the previous values to be stacked, so
8852 that invocations of @samp{#pragma pack(pop)} will return to the previous
8856 @defmac DOLLARS_IN_IDENTIFIERS
8857 Define this macro to control use of the character @samp{$} in
8858 identifier names for the C family of languages. 0 means @samp{$} is
8859 not allowed by default; 1 means it is allowed. 1 is the default;
8860 there is no need to define this macro in that case.
8863 @defmac NO_DOLLAR_IN_LABEL
8864 Define this macro if the assembler does not accept the character
8865 @samp{$} in label names. By default constructors and destructors in
8866 G++ have @samp{$} in the identifiers. If this macro is defined,
8867 @samp{.} is used instead.
8870 @defmac NO_DOT_IN_LABEL
8871 Define this macro if the assembler does not accept the character
8872 @samp{.} in label names. By default constructors and destructors in G++
8873 have names that use @samp{.}. If this macro is defined, these names
8874 are rewritten to avoid @samp{.}.
8877 @defmac DEFAULT_MAIN_RETURN
8878 Define this macro if the target system expects every program's @code{main}
8879 function to return a standard ``success'' value by default (if no other
8880 value is explicitly returned).
8882 The definition should be a C statement (sans semicolon) to generate the
8883 appropriate rtl instructions. It is used only when compiling the end of
8887 @defmac INSN_SETS_ARE_DELAYED (@var{insn})
8888 Define this macro as a C expression that is nonzero if it is safe for the
8889 delay slot scheduler to place instructions in the delay slot of @var{insn},
8890 even if they appear to use a resource set or clobbered in @var{insn}.
8891 @var{insn} is always a @code{jump_insn} or an @code{insn}; GCC knows that
8892 every @code{call_insn} has this behavior. On machines where some @code{insn}
8893 or @code{jump_insn} is really a function call and hence has this behavior,
8894 you should define this macro.
8896 You need not define this macro if it would always return zero.
8899 @defmac INSN_REFERENCES_ARE_DELAYED (@var{insn})
8900 Define this macro as a C expression that is nonzero if it is safe for the
8901 delay slot scheduler to place instructions in the delay slot of @var{insn},
8902 even if they appear to set or clobber a resource referenced in @var{insn}.
8903 @var{insn} is always a @code{jump_insn} or an @code{insn}. On machines where
8904 some @code{insn} or @code{jump_insn} is really a function call and its operands
8905 are registers whose use is actually in the subroutine it calls, you should
8906 define this macro. Doing so allows the delay slot scheduler to move
8907 instructions which copy arguments into the argument registers into the delay
8910 You need not define this macro if it would always return zero.
8913 @defmac MULTIPLE_SYMBOL_SPACES
8914 Define this macro if in some cases global symbols from one translation
8915 unit may not be bound to undefined symbols in another translation unit
8916 without user intervention. For instance, under Microsoft Windows
8917 symbols must be explicitly imported from shared libraries (DLLs).
8920 @defmac MD_ASM_CLOBBERS (@var{clobbers})
8921 A C statement that adds to @var{clobbers} @code{STRING_CST} trees for
8922 any hard regs the port wishes to automatically clobber for all asms.
8925 @defmac MAX_INTEGER_COMPUTATION_MODE
8926 Define this to the largest integer machine mode which can be used for
8927 operations other than load, store and copy operations.
8929 You need only define this macro if the target holds values larger than
8930 @code{word_mode} in general purpose registers. Most targets should not define
8934 @defmac MATH_LIBRARY
8935 Define this macro as a C string constant for the linker argument to link
8936 in the system math library, or @samp{""} if the target does not have a
8937 separate math library.
8939 You need only define this macro if the default of @samp{"-lm"} is wrong.
8942 @defmac LIBRARY_PATH_ENV
8943 Define this macro as a C string constant for the environment variable that
8944 specifies where the linker should look for libraries.
8946 You need only define this macro if the default of @samp{"LIBRARY_PATH"}
8950 @defmac TARGET_HAS_F_SETLKW
8951 Define this macro if the target supports file locking with fcntl / F_SETLKW@.
8952 Note that this functionality is part of POSIX@.
8953 Defining @code{TARGET_HAS_F_SETLKW} will enable the test coverage code
8954 to use file locking when exiting a program, which avoids race conditions
8955 if the program has forked.
8958 @defmac MAX_CONDITIONAL_EXECUTE
8960 A C expression for the maximum number of instructions to execute via
8961 conditional execution instructions instead of a branch. A value of
8962 @code{BRANCH_COST}+1 is the default if the machine does not use cc0, and
8963 1 if it does use cc0.
8966 @defmac IFCVT_MODIFY_TESTS (@var{ce_info}, @var{true_expr}, @var{false_expr})
8967 Used if the target needs to perform machine-dependent modifications on the
8968 conditionals used for turning basic blocks into conditionally executed code.
8969 @var{ce_info} points to a data structure, @code{struct ce_if_block}, which
8970 contains information about the currently processed blocks. @var{true_expr}
8971 and @var{false_expr} are the tests that are used for converting the
8972 then-block and the else-block, respectively. Set either @var{true_expr} or
8973 @var{false_expr} to a null pointer if the tests cannot be converted.
8976 @defmac IFCVT_MODIFY_MULTIPLE_TESTS (@var{ce_info}, @var{bb}, @var{true_expr}, @var{false_expr})
8977 Like @code{IFCVT_MODIFY_TESTS}, but used when converting more complicated
8978 if-statements into conditions combined by @code{and} and @code{or} operations.
8979 @var{bb} contains the basic block that contains the test that is currently
8980 being processed and about to be turned into a condition.
8983 @defmac IFCVT_MODIFY_INSN (@var{ce_info}, @var{pattern}, @var{insn})
8984 A C expression to modify the @var{PATTERN} of an @var{INSN} that is to
8985 be converted to conditional execution format. @var{ce_info} points to
8986 a data structure, @code{struct ce_if_block}, which contains information
8987 about the currently processed blocks.
8990 @defmac IFCVT_MODIFY_FINAL (@var{ce_info})
8991 A C expression to perform any final machine dependent modifications in
8992 converting code to conditional execution. The involved basic blocks
8993 can be found in the @code{struct ce_if_block} structure that is pointed
8994 to by @var{ce_info}.
8997 @defmac IFCVT_MODIFY_CANCEL (@var{ce_info})
8998 A C expression to cancel any machine dependent modifications in
8999 converting code to conditional execution. The involved basic blocks
9000 can be found in the @code{struct ce_if_block} structure that is pointed
9001 to by @var{ce_info}.
9004 @defmac IFCVT_INIT_EXTRA_FIELDS (@var{ce_info})
9005 A C expression to initialize any extra fields in a @code{struct ce_if_block}
9006 structure, which are defined by the @code{IFCVT_EXTRA_FIELDS} macro.
9009 @defmac IFCVT_EXTRA_FIELDS
9010 If defined, it should expand to a set of field declarations that will be
9011 added to the @code{struct ce_if_block} structure. These should be initialized
9012 by the @code{IFCVT_INIT_EXTRA_FIELDS} macro.
9015 @deftypefn {Target Hook} void TARGET_MACHINE_DEPENDENT_REORG ()
9016 If non-null, this hook performs a target-specific pass over the
9017 instruction stream. The compiler will run it at all optimization levels,
9018 just before the point at which it normally does delayed-branch scheduling.
9020 The exact purpose of the hook varies from target to target. Some use
9021 it to do transformations that are necessary for correctness, such as
9022 laying out in-function constant pools or avoiding hardware hazards.
9023 Others use it as an opportunity to do some machine-dependent optimizations.
9025 You need not implement the hook if it has nothing to do. The default
9029 @deftypefn {Target Hook} void TARGET_INIT_BUILTINS ()
9030 Define this hook if you have any machine-specific built-in functions
9031 that need to be defined. It should be a function that performs the
9034 Machine specific built-in functions can be useful to expand special machine
9035 instructions that would otherwise not normally be generated because
9036 they have no equivalent in the source language (for example, SIMD vector
9037 instructions or prefetch instructions).
9039 To create a built-in function, call the function @code{builtin_function}
9040 which is defined by the language front end. You can use any type nodes set
9041 up by @code{build_common_tree_nodes} and @code{build_common_tree_nodes_2};
9042 only language front ends that use those two functions will call
9043 @samp{TARGET_INIT_BUILTINS}.
9046 @deftypefn {Target Hook} rtx TARGET_EXPAND_BUILTIN (tree @var{exp}, rtx @var{target}, rtx @var{subtarget}, enum machine_mode @var{mode}, int @var{ignore})
9048 Expand a call to a machine specific built-in function that was set up by
9049 @samp{TARGET_INIT_BUILTINS}. @var{exp} is the expression for the
9050 function call; the result should go to @var{target} if that is
9051 convenient, and have mode @var{mode} if that is convenient.
9052 @var{subtarget} may be used as the target for computing one of
9053 @var{exp}'s operands. @var{ignore} is nonzero if the value is to be
9054 ignored. This function should return the result of the call to the
9058 @defmac MD_CAN_REDIRECT_BRANCH (@var{branch1}, @var{branch2})
9060 Take a branch insn in @var{branch1} and another in @var{branch2}.
9061 Return true if redirecting @var{branch1} to the destination of
9062 @var{branch2} is possible.
9064 On some targets, branches may have a limited range. Optimizing the
9065 filling of delay slots can result in branches being redirected, and this
9066 may in turn cause a branch offset to overflow.
9069 @defmac ALLOCATE_INITIAL_VALUE (@var{hard_reg})
9071 When the initial value of a hard register has been copied in a pseudo
9072 register, it is often not necessary to actually allocate another register
9073 to this pseudo register, because the original hard register or a stack slot
9074 it has been saved into can be used. @code{ALLOCATE_INITIAL_VALUE}, if
9075 defined, is called at the start of register allocation once for each
9076 hard register that had its initial value copied by using
9077 @code{get_func_hard_reg_initial_val} or @code{get_hard_reg_initial_val}.
9078 Possible values are @code{NULL_RTX}, if you don't want
9079 to do any special allocation, a @code{REG} rtx---that would typically be
9080 the hard register itself, if it is known not to be clobbered---or a
9082 If you are returning a @code{MEM}, this is only a hint for the allocator;
9083 it might decide to use another register anyways.
9084 You may use @code{current_function_leaf_function} in the definition of the
9085 macro, functions that use @code{REG_N_SETS}, to determine if the hard
9086 register in question will not be clobbered.
9089 @defmac TARGET_OBJECT_SUFFIX
9090 Define this macro to be a C string representing the suffix for object
9091 files on your target machine. If you do not define this macro, GCC will
9092 use @samp{.o} as the suffix for object files.
9095 @defmac TARGET_EXECUTABLE_SUFFIX
9096 Define this macro to be a C string representing the suffix to be
9097 automatically added to executable files on your target machine. If you
9098 do not define this macro, GCC will use the null string as the suffix for
9102 @defmac COLLECT_EXPORT_LIST
9103 If defined, @code{collect2} will scan the individual object files
9104 specified on its command line and create an export list for the linker.
9105 Define this macro for systems like AIX, where the linker discards
9106 object files that are not referenced from @code{main} and uses export
9110 @defmac MODIFY_JNI_METHOD_CALL (@var{mdecl})
9111 Define this macro to a C expression representing a variant of the
9112 method call @var{mdecl}, if Java Native Interface (JNI) methods
9113 must be invoked differently from other methods on your target.
9114 For example, on 32-bit Windows, JNI methods must be invoked using
9115 the @code{stdcall} calling convention and this macro is then
9116 defined as this expression:
9119 build_type_attribute_variant (@var{mdecl},
9121 (get_identifier ("stdcall"),
9126 @deftypefn {Target Hook} bool TARGET_CANNOT_MODIFY_JUMPS_P (void)
9127 This target hook returns @code{true} past the point in which new jump
9128 instructions could be created. On machines that require a register for
9129 every jump such as the SHmedia ISA of SH5, this point would typically be
9130 reload, so this target hook should be defined to a function such as:
9134 cannot_modify_jumps_past_reload_p ()
9136 return (reload_completed || reload_in_progress);
9141 @deftypefn {Target Hook} int TARGET_BRANCH_TARGET_REGISTER_CLASS (void)
9142 This target hook returns a register class for which branch target register
9143 optimizations should be applied. All registers in this class should be
9144 usable interchangeably. After reload, registers in this class will be
9145 re-allocated and loads will be hoisted out of loops and be subjected
9146 to inter-block scheduling.
9149 @deftypefn {Target Hook} bool TARGET_BRANCH_TARGET_REGISTER_CALLEE_SAVED (bool @var{after_prologue_epilogue_gen})
9150 Branch target register optimization will by default exclude callee-saved
9152 that are not already live during the current function; if this target hook
9153 returns true, they will be included. The target code must than make sure
9154 that all target registers in the class returned by
9155 @samp{TARGET_BRANCH_TARGET_REGISTER_CLASS} that might need saving are
9156 saved. @var{after_prologue_epilogue_gen} indicates if prologues and
9157 epilogues have already been generated. Note, even if you only return
9158 true when @var{after_prologue_epilogue_gen} is false, you still are likely
9159 to have to make special provisions in @code{INITIAL_ELIMINATION_OFFSET}
9160 to reserve space for caller-saved target registers.
9163 @defmac POWI_MAX_MULTS
9164 If defined, this macro is interpreted as a signed integer C expression
9165 that specifies the maximum number of floating point multiplications
9166 that should be emitted when expanding exponentiation by an integer
9167 constant inline. When this value is defined, exponentiation requiring
9168 more than this number of multiplications is implemented by calling the
9169 system library's @code{pow}, @code{powf} or @code{powl} routines.
9170 The default value places no upper bound on the multiplication count.