1 @c Copyright (C) 1988,1989,1992,1993,1994,1995,1996,1997,1998,1999,2000,2001,
2 @c 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
3 @c Free Software Foundation, Inc.
4 @c This is part of the GCC manual.
5 @c For copying conditions, see the file gcc.texi.
8 @chapter Target Description Macros and Functions
9 @cindex machine description macros
10 @cindex target description macros
11 @cindex macros, target description
12 @cindex @file{tm.h} macros
14 In addition to the file @file{@var{machine}.md}, a machine description
15 includes a C header file conventionally given the name
16 @file{@var{machine}.h} and a C source file named @file{@var{machine}.c}.
17 The header file defines numerous macros that convey the information
18 about the target machine that does not fit into the scheme of the
19 @file{.md} file. The file @file{tm.h} should be a link to
20 @file{@var{machine}.h}. The header file @file{config.h} includes
21 @file{tm.h} and most compiler source files include @file{config.h}. The
22 source file defines a variable @code{targetm}, which is a structure
23 containing pointers to functions and data relating to the target
24 machine. @file{@var{machine}.c} should also contain their definitions,
25 if they are not defined elsewhere in GCC, and other functions called
26 through the macros defined in the @file{.h} file.
29 * Target Structure:: The @code{targetm} variable.
30 * Driver:: Controlling how the driver runs the compilation passes.
31 * Run-time Target:: Defining @samp{-m} options like @option{-m68000} and @option{-m68020}.
32 * Per-Function Data:: Defining data structures for per-function information.
33 * Storage Layout:: Defining sizes and alignments of data.
34 * Type Layout:: Defining sizes and properties of basic user data types.
35 * Registers:: Naming and describing the hardware registers.
36 * Register Classes:: Defining the classes of hardware registers.
37 * Old Constraints:: The old way to define machine-specific constraints.
38 * Stack and Calling:: Defining which way the stack grows and by how much.
39 * Varargs:: Defining the varargs macros.
40 * Trampolines:: Code set up at run time to enter a nested function.
41 * Library Calls:: Controlling how library routines are implicitly called.
42 * Addressing Modes:: Defining addressing modes valid for memory operands.
43 * Anchored Addresses:: Defining how @option{-fsection-anchors} should work.
44 * Condition Code:: Defining how insns update the condition code.
45 * Costs:: Defining relative costs of different operations.
46 * Scheduling:: Adjusting the behavior of the instruction scheduler.
47 * Sections:: Dividing storage into text, data, and other sections.
48 * PIC:: Macros for position independent code.
49 * Assembler Format:: Defining how to write insns and pseudo-ops to output.
50 * Debugging Info:: Defining the format of debugging output.
51 * Floating Point:: Handling floating point for cross-compilers.
52 * Mode Switching:: Insertion of mode-switching instructions.
53 * Target Attributes:: Defining target-specific uses of @code{__attribute__}.
54 * Emulated TLS:: Emulated TLS support.
55 * MIPS Coprocessors:: MIPS coprocessor support and how to customize it.
56 * PCH Target:: Validity checking for precompiled headers.
57 * C++ ABI:: Controlling C++ ABI changes.
58 * Named Address Spaces:: Adding support for named address spaces
59 * Misc:: Everything else.
62 @node Target Structure
63 @section The Global @code{targetm} Variable
65 @cindex target functions
67 @deftypevar {struct gcc_target} targetm
68 The target @file{.c} file must define the global @code{targetm} variable
69 which contains pointers to functions and data relating to the target
70 machine. The variable is declared in @file{target.h};
71 @file{target-def.h} defines the macro @code{TARGET_INITIALIZER} which is
72 used to initialize the variable, and macros for the default initializers
73 for elements of the structure. The @file{.c} file should override those
74 macros for which the default definition is inappropriate. For example:
77 #include "target-def.h"
79 /* @r{Initialize the GCC target structure.} */
81 #undef TARGET_COMP_TYPE_ATTRIBUTES
82 #define TARGET_COMP_TYPE_ATTRIBUTES @var{machine}_comp_type_attributes
84 struct gcc_target targetm = TARGET_INITIALIZER;
88 Where a macro should be defined in the @file{.c} file in this manner to
89 form part of the @code{targetm} structure, it is documented below as a
90 ``Target Hook'' with a prototype. Many macros will change in future
91 from being defined in the @file{.h} file to being part of the
92 @code{targetm} structure.
95 @section Controlling the Compilation Driver, @file{gcc}
97 @cindex controlling the compilation driver
99 @c prevent bad page break with this line
100 You can control the compilation driver.
102 @defmac DRIVER_SELF_SPECS
103 A list of specs for the driver itself. It should be a suitable
104 initializer for an array of strings, with no surrounding braces.
106 The driver applies these specs to its own command line between loading
107 default @file{specs} files (but not command-line specified ones) and
108 choosing the multilib directory or running any subcommands. It
109 applies them in the order given, so each spec can depend on the
110 options added by earlier ones. It is also possible to remove options
111 using @samp{%<@var{option}} in the usual way.
113 This macro can be useful when a port has several interdependent target
114 options. It provides a way of standardizing the command line so
115 that the other specs are easier to write.
117 Do not define this macro if it does not need to do anything.
120 @defmac OPTION_DEFAULT_SPECS
121 A list of specs used to support configure-time default options (i.e.@:
122 @option{--with} options) in the driver. It should be a suitable initializer
123 for an array of structures, each containing two strings, without the
124 outermost pair of surrounding braces.
126 The first item in the pair is the name of the default. This must match
127 the code in @file{config.gcc} for the target. The second item is a spec
128 to apply if a default with this name was specified. The string
129 @samp{%(VALUE)} in the spec will be replaced by the value of the default
130 everywhere it occurs.
132 The driver will apply these specs to its own command line between loading
133 default @file{specs} files and processing @code{DRIVER_SELF_SPECS}, using
134 the same mechanism as @code{DRIVER_SELF_SPECS}.
136 Do not define this macro if it does not need to do anything.
140 A C string constant that tells the GCC driver program options to
141 pass to CPP@. It can also specify how to translate options you
142 give to GCC into options for GCC to pass to the CPP@.
144 Do not define this macro if it does not need to do anything.
147 @defmac CPLUSPLUS_CPP_SPEC
148 This macro is just like @code{CPP_SPEC}, but is used for C++, rather
149 than C@. If you do not define this macro, then the value of
150 @code{CPP_SPEC} (if any) will be used instead.
154 A C string constant that tells the GCC driver program options to
155 pass to @code{cc1}, @code{cc1plus}, @code{f771}, and the other language
157 It can also specify how to translate options you give to GCC into options
158 for GCC to pass to front ends.
160 Do not define this macro if it does not need to do anything.
164 A C string constant that tells the GCC driver program options to
165 pass to @code{cc1plus}. It can also specify how to translate options you
166 give to GCC into options for GCC to pass to the @code{cc1plus}.
168 Do not define this macro if it does not need to do anything.
169 Note that everything defined in CC1_SPEC is already passed to
170 @code{cc1plus} so there is no need to duplicate the contents of
171 CC1_SPEC in CC1PLUS_SPEC@.
175 A C string constant that tells the GCC driver program options to
176 pass to the assembler. It can also specify how to translate options
177 you give to GCC into options for GCC to pass to the assembler.
178 See the file @file{sun3.h} for an example of this.
180 Do not define this macro if it does not need to do anything.
183 @defmac ASM_FINAL_SPEC
184 A C string constant that tells the GCC driver program how to
185 run any programs which cleanup after the normal assembler.
186 Normally, this is not needed. See the file @file{mips.h} for
189 Do not define this macro if it does not need to do anything.
192 @defmac AS_NEEDS_DASH_FOR_PIPED_INPUT
193 Define this macro, with no value, if the driver should give the assembler
194 an argument consisting of a single dash, @option{-}, to instruct it to
195 read from its standard input (which will be a pipe connected to the
196 output of the compiler proper). This argument is given after any
197 @option{-o} option specifying the name of the output file.
199 If you do not define this macro, the assembler is assumed to read its
200 standard input if given no non-option arguments. If your assembler
201 cannot read standard input at all, use a @samp{%@{pipe:%e@}} construct;
202 see @file{mips.h} for instance.
206 A C string constant that tells the GCC driver program options to
207 pass to the linker. It can also specify how to translate options you
208 give to GCC into options for GCC to pass to the linker.
210 Do not define this macro if it does not need to do anything.
214 Another C string constant used much like @code{LINK_SPEC}. The difference
215 between the two is that @code{LIB_SPEC} is used at the end of the
216 command given to the linker.
218 If this macro is not defined, a default is provided that
219 loads the standard C library from the usual place. See @file{gcc.c}.
223 Another C string constant that tells the GCC driver program
224 how and when to place a reference to @file{libgcc.a} into the
225 linker command line. This constant is placed both before and after
226 the value of @code{LIB_SPEC}.
228 If this macro is not defined, the GCC driver provides a default that
229 passes the string @option{-lgcc} to the linker.
232 @defmac REAL_LIBGCC_SPEC
233 By default, if @code{ENABLE_SHARED_LIBGCC} is defined, the
234 @code{LIBGCC_SPEC} is not directly used by the driver program but is
235 instead modified to refer to different versions of @file{libgcc.a}
236 depending on the values of the command line flags @option{-static},
237 @option{-shared}, @option{-static-libgcc}, and @option{-shared-libgcc}. On
238 targets where these modifications are inappropriate, define
239 @code{REAL_LIBGCC_SPEC} instead. @code{REAL_LIBGCC_SPEC} tells the
240 driver how to place a reference to @file{libgcc} on the link command
241 line, but, unlike @code{LIBGCC_SPEC}, it is used unmodified.
244 @defmac USE_LD_AS_NEEDED
245 A macro that controls the modifications to @code{LIBGCC_SPEC}
246 mentioned in @code{REAL_LIBGCC_SPEC}. If nonzero, a spec will be
247 generated that uses --as-needed and the shared libgcc in place of the
248 static exception handler library, when linking without any of
249 @code{-static}, @code{-static-libgcc}, or @code{-shared-libgcc}.
253 If defined, this C string constant is added to @code{LINK_SPEC}.
254 When @code{USE_LD_AS_NEEDED} is zero or undefined, it also affects
255 the modifications to @code{LIBGCC_SPEC} mentioned in
256 @code{REAL_LIBGCC_SPEC}.
259 @defmac STARTFILE_SPEC
260 Another C string constant used much like @code{LINK_SPEC}. The
261 difference between the two is that @code{STARTFILE_SPEC} is used at
262 the very beginning of the command given to the linker.
264 If this macro is not defined, a default is provided that loads the
265 standard C startup file from the usual place. See @file{gcc.c}.
269 Another C string constant used much like @code{LINK_SPEC}. The
270 difference between the two is that @code{ENDFILE_SPEC} is used at
271 the very end of the command given to the linker.
273 Do not define this macro if it does not need to do anything.
276 @defmac THREAD_MODEL_SPEC
277 GCC @code{-v} will print the thread model GCC was configured to use.
278 However, this doesn't work on platforms that are multilibbed on thread
279 models, such as AIX 4.3. On such platforms, define
280 @code{THREAD_MODEL_SPEC} such that it evaluates to a string without
281 blanks that names one of the recognized thread models. @code{%*}, the
282 default value of this macro, will expand to the value of
283 @code{thread_file} set in @file{config.gcc}.
286 @defmac SYSROOT_SUFFIX_SPEC
287 Define this macro to add a suffix to the target sysroot when GCC is
288 configured with a sysroot. This will cause GCC to search for usr/lib,
289 et al, within sysroot+suffix.
292 @defmac SYSROOT_HEADERS_SUFFIX_SPEC
293 Define this macro to add a headers_suffix to the target sysroot when
294 GCC is configured with a sysroot. This will cause GCC to pass the
295 updated sysroot+headers_suffix to CPP, causing it to search for
296 usr/include, et al, within sysroot+headers_suffix.
300 Define this macro to provide additional specifications to put in the
301 @file{specs} file that can be used in various specifications like
304 The definition should be an initializer for an array of structures,
305 containing a string constant, that defines the specification name, and a
306 string constant that provides the specification.
308 Do not define this macro if it does not need to do anything.
310 @code{EXTRA_SPECS} is useful when an architecture contains several
311 related targets, which have various @code{@dots{}_SPECS} which are similar
312 to each other, and the maintainer would like one central place to keep
315 For example, the PowerPC System V.4 targets use @code{EXTRA_SPECS} to
316 define either @code{_CALL_SYSV} when the System V calling sequence is
317 used or @code{_CALL_AIX} when the older AIX-based calling sequence is
320 The @file{config/rs6000/rs6000.h} target file defines:
323 #define EXTRA_SPECS \
324 @{ "cpp_sysv_default", CPP_SYSV_DEFAULT @},
326 #define CPP_SYS_DEFAULT ""
329 The @file{config/rs6000/sysv.h} target file defines:
333 "%@{posix: -D_POSIX_SOURCE @} \
334 %@{mcall-sysv: -D_CALL_SYSV @} \
335 %@{!mcall-sysv: %(cpp_sysv_default) @} \
336 %@{msoft-float: -D_SOFT_FLOAT@} %@{mcpu=403: -D_SOFT_FLOAT@}"
338 #undef CPP_SYSV_DEFAULT
339 #define CPP_SYSV_DEFAULT "-D_CALL_SYSV"
342 while the @file{config/rs6000/eabiaix.h} target file defines
343 @code{CPP_SYSV_DEFAULT} as:
346 #undef CPP_SYSV_DEFAULT
347 #define CPP_SYSV_DEFAULT "-D_CALL_AIX"
351 @defmac LINK_LIBGCC_SPECIAL_1
352 Define this macro if the driver program should find the library
353 @file{libgcc.a}. If you do not define this macro, the driver program will pass
354 the argument @option{-lgcc} to tell the linker to do the search.
357 @defmac LINK_GCC_C_SEQUENCE_SPEC
358 The sequence in which libgcc and libc are specified to the linker.
359 By default this is @code{%G %L %G}.
362 @defmac LINK_COMMAND_SPEC
363 A C string constant giving the complete command line need to execute the
364 linker. When you do this, you will need to update your port each time a
365 change is made to the link command line within @file{gcc.c}. Therefore,
366 define this macro only if you need to completely redefine the command
367 line for invoking the linker and there is no other way to accomplish
368 the effect you need. Overriding this macro may be avoidable by overriding
369 @code{LINK_GCC_C_SEQUENCE_SPEC} instead.
372 @defmac LINK_ELIMINATE_DUPLICATE_LDIRECTORIES
373 A nonzero value causes @command{collect2} to remove duplicate @option{-L@var{directory}} search
374 directories from linking commands. Do not give it a nonzero value if
375 removing duplicate search directories changes the linker's semantics.
378 @defmac MULTILIB_DEFAULTS
379 Define this macro as a C expression for the initializer of an array of
380 string to tell the driver program which options are defaults for this
381 target and thus do not need to be handled specially when using
382 @code{MULTILIB_OPTIONS}.
384 Do not define this macro if @code{MULTILIB_OPTIONS} is not defined in
385 the target makefile fragment or if none of the options listed in
386 @code{MULTILIB_OPTIONS} are set by default.
387 @xref{Target Fragment}.
390 @defmac RELATIVE_PREFIX_NOT_LINKDIR
391 Define this macro to tell @command{gcc} that it should only translate
392 a @option{-B} prefix into a @option{-L} linker option if the prefix
393 indicates an absolute file name.
396 @defmac MD_EXEC_PREFIX
397 If defined, this macro is an additional prefix to try after
398 @code{STANDARD_EXEC_PREFIX}. @code{MD_EXEC_PREFIX} is not searched
399 when the compiler is built as a cross
400 compiler. If you define @code{MD_EXEC_PREFIX}, then be sure to add it
401 to the list of directories used to find the assembler in @file{configure.in}.
404 @defmac STANDARD_STARTFILE_PREFIX
405 Define this macro as a C string constant if you wish to override the
406 standard choice of @code{libdir} as the default prefix to
407 try when searching for startup files such as @file{crt0.o}.
408 @code{STANDARD_STARTFILE_PREFIX} is not searched when the compiler
409 is built as a cross compiler.
412 @defmac STANDARD_STARTFILE_PREFIX_1
413 Define this macro as a C string constant if you wish to override the
414 standard choice of @code{/lib} as a prefix to try after the default prefix
415 when searching for startup files such as @file{crt0.o}.
416 @code{STANDARD_STARTFILE_PREFIX_1} is not searched when the compiler
417 is built as a cross compiler.
420 @defmac STANDARD_STARTFILE_PREFIX_2
421 Define this macro as a C string constant if you wish to override the
422 standard choice of @code{/lib} as yet another prefix to try after the
423 default prefix when searching for startup files such as @file{crt0.o}.
424 @code{STANDARD_STARTFILE_PREFIX_2} is not searched when the compiler
425 is built as a cross compiler.
428 @defmac MD_STARTFILE_PREFIX
429 If defined, this macro supplies an additional prefix to try after the
430 standard prefixes. @code{MD_EXEC_PREFIX} is not searched when the
431 compiler is built as a cross compiler.
434 @defmac MD_STARTFILE_PREFIX_1
435 If defined, this macro supplies yet another prefix to try after the
436 standard prefixes. It is not searched when the compiler is built as a
440 @defmac INIT_ENVIRONMENT
441 Define this macro as a C string constant if you wish to set environment
442 variables for programs called by the driver, such as the assembler and
443 loader. The driver passes the value of this macro to @code{putenv} to
444 initialize the necessary environment variables.
447 @defmac LOCAL_INCLUDE_DIR
448 Define this macro as a C string constant if you wish to override the
449 standard choice of @file{/usr/local/include} as the default prefix to
450 try when searching for local header files. @code{LOCAL_INCLUDE_DIR}
451 comes before @code{SYSTEM_INCLUDE_DIR} in the search order.
453 Cross compilers do not search either @file{/usr/local/include} or its
457 @defmac SYSTEM_INCLUDE_DIR
458 Define this macro as a C string constant if you wish to specify a
459 system-specific directory to search for header files before the standard
460 directory. @code{SYSTEM_INCLUDE_DIR} comes before
461 @code{STANDARD_INCLUDE_DIR} in the search order.
463 Cross compilers do not use this macro and do not search the directory
467 @defmac STANDARD_INCLUDE_DIR
468 Define this macro as a C string constant if you wish to override the
469 standard choice of @file{/usr/include} as the default prefix to
470 try when searching for header files.
472 Cross compilers ignore this macro and do not search either
473 @file{/usr/include} or its replacement.
476 @defmac STANDARD_INCLUDE_COMPONENT
477 The ``component'' corresponding to @code{STANDARD_INCLUDE_DIR}.
478 See @code{INCLUDE_DEFAULTS}, below, for the description of components.
479 If you do not define this macro, no component is used.
482 @defmac INCLUDE_DEFAULTS
483 Define this macro if you wish to override the entire default search path
484 for include files. For a native compiler, the default search path
485 usually consists of @code{GCC_INCLUDE_DIR}, @code{LOCAL_INCLUDE_DIR},
486 @code{SYSTEM_INCLUDE_DIR}, @code{GPLUSPLUS_INCLUDE_DIR}, and
487 @code{STANDARD_INCLUDE_DIR}. In addition, @code{GPLUSPLUS_INCLUDE_DIR}
488 and @code{GCC_INCLUDE_DIR} are defined automatically by @file{Makefile},
489 and specify private search areas for GCC@. The directory
490 @code{GPLUSPLUS_INCLUDE_DIR} is used only for C++ programs.
492 The definition should be an initializer for an array of structures.
493 Each array element should have four elements: the directory name (a
494 string constant), the component name (also a string constant), a flag
495 for C++-only directories,
496 and a flag showing that the includes in the directory don't need to be
497 wrapped in @code{extern @samp{C}} when compiling C++. Mark the end of
498 the array with a null element.
500 The component name denotes what GNU package the include file is part of,
501 if any, in all uppercase letters. For example, it might be @samp{GCC}
502 or @samp{BINUTILS}. If the package is part of a vendor-supplied
503 operating system, code the component name as @samp{0}.
505 For example, here is the definition used for VAX/VMS:
508 #define INCLUDE_DEFAULTS \
510 @{ "GNU_GXX_INCLUDE:", "G++", 1, 1@}, \
511 @{ "GNU_CC_INCLUDE:", "GCC", 0, 0@}, \
512 @{ "SYS$SYSROOT:[SYSLIB.]", 0, 0, 0@}, \
519 Here is the order of prefixes tried for exec files:
523 Any prefixes specified by the user with @option{-B}.
526 The environment variable @code{GCC_EXEC_PREFIX} or, if @code{GCC_EXEC_PREFIX}
527 is not set and the compiler has not been installed in the configure-time
528 @var{prefix}, the location in which the compiler has actually been installed.
531 The directories specified by the environment variable @code{COMPILER_PATH}.
534 The macro @code{STANDARD_EXEC_PREFIX}, if the compiler has been installed
535 in the configured-time @var{prefix}.
538 The location @file{/usr/libexec/gcc/}, but only if this is a native compiler.
541 The location @file{/usr/lib/gcc/}, but only if this is a native compiler.
544 The macro @code{MD_EXEC_PREFIX}, if defined, but only if this is a native
548 Here is the order of prefixes tried for startfiles:
552 Any prefixes specified by the user with @option{-B}.
555 The environment variable @code{GCC_EXEC_PREFIX} or its automatically determined
556 value based on the installed toolchain location.
559 The directories specified by the environment variable @code{LIBRARY_PATH}
560 (or port-specific name; native only, cross compilers do not use this).
563 The macro @code{STANDARD_EXEC_PREFIX}, but only if the toolchain is installed
564 in the configured @var{prefix} or this is a native compiler.
567 The location @file{/usr/lib/gcc/}, but only if this is a native compiler.
570 The macro @code{MD_EXEC_PREFIX}, if defined, but only if this is a native
574 The macro @code{MD_STARTFILE_PREFIX}, if defined, but only if this is a
575 native compiler, or we have a target system root.
578 The macro @code{MD_STARTFILE_PREFIX_1}, if defined, but only if this is a
579 native compiler, or we have a target system root.
582 The macro @code{STANDARD_STARTFILE_PREFIX}, with any sysroot modifications.
583 If this path is relative it will be prefixed by @code{GCC_EXEC_PREFIX} and
584 the machine suffix or @code{STANDARD_EXEC_PREFIX} and the machine suffix.
587 The macro @code{STANDARD_STARTFILE_PREFIX_1}, but only if this is a native
588 compiler, or we have a target system root. The default for this macro is
592 The macro @code{STANDARD_STARTFILE_PREFIX_2}, but only if this is a native
593 compiler, or we have a target system root. The default for this macro is
597 @node Run-time Target
598 @section Run-time Target Specification
599 @cindex run-time target specification
600 @cindex predefined macros
601 @cindex target specifications
603 @c prevent bad page break with this line
604 Here are run-time target specifications.
606 @defmac TARGET_CPU_CPP_BUILTINS ()
607 This function-like macro expands to a block of code that defines
608 built-in preprocessor macros and assertions for the target CPU, using
609 the functions @code{builtin_define}, @code{builtin_define_std} and
610 @code{builtin_assert}. When the front end
611 calls this macro it provides a trailing semicolon, and since it has
612 finished command line option processing your code can use those
615 @code{builtin_assert} takes a string in the form you pass to the
616 command-line option @option{-A}, such as @code{cpu=mips}, and creates
617 the assertion. @code{builtin_define} takes a string in the form
618 accepted by option @option{-D} and unconditionally defines the macro.
620 @code{builtin_define_std} takes a string representing the name of an
621 object-like macro. If it doesn't lie in the user's namespace,
622 @code{builtin_define_std} defines it unconditionally. Otherwise, it
623 defines a version with two leading underscores, and another version
624 with two leading and trailing underscores, and defines the original
625 only if an ISO standard was not requested on the command line. For
626 example, passing @code{unix} defines @code{__unix}, @code{__unix__}
627 and possibly @code{unix}; passing @code{_mips} defines @code{__mips},
628 @code{__mips__} and possibly @code{_mips}, and passing @code{_ABI64}
629 defines only @code{_ABI64}.
631 You can also test for the C dialect being compiled. The variable
632 @code{c_language} is set to one of @code{clk_c}, @code{clk_cplusplus}
633 or @code{clk_objective_c}. Note that if we are preprocessing
634 assembler, this variable will be @code{clk_c} but the function-like
635 macro @code{preprocessing_asm_p()} will return true, so you might want
636 to check for that first. If you need to check for strict ANSI, the
637 variable @code{flag_iso} can be used. The function-like macro
638 @code{preprocessing_trad_p()} can be used to check for traditional
642 @defmac TARGET_OS_CPP_BUILTINS ()
643 Similarly to @code{TARGET_CPU_CPP_BUILTINS} but this macro is optional
644 and is used for the target operating system instead.
647 @defmac TARGET_OBJFMT_CPP_BUILTINS ()
648 Similarly to @code{TARGET_CPU_CPP_BUILTINS} but this macro is optional
649 and is used for the target object format. @file{elfos.h} uses this
650 macro to define @code{__ELF__}, so you probably do not need to define
654 @deftypevar {extern int} target_flags
655 This variable is declared in @file{options.h}, which is included before
656 any target-specific headers.
659 @hook TARGET_DEFAULT_TARGET_FLAGS
660 This variable specifies the initial value of @code{target_flags}.
661 Its default setting is 0.
664 @cindex optional hardware or system features
665 @cindex features, optional, in system conventions
667 @hook TARGET_HANDLE_OPTION
668 This hook is called whenever the user specifies one of the
669 target-specific options described by the @file{.opt} definition files
670 (@pxref{Options}). It has the opportunity to do some option-specific
671 processing and should return true if the option is valid. The default
672 definition does nothing but return true.
674 @var{code} specifies the @code{OPT_@var{name}} enumeration value
675 associated with the selected option; @var{name} is just a rendering of
676 the option name in which non-alphanumeric characters are replaced by
677 underscores. @var{arg} specifies the string argument and is null if
678 no argument was given. If the option is flagged as a @code{UInteger}
679 (@pxref{Option properties}), @var{value} is the numeric value of the
680 argument. Otherwise @var{value} is 1 if the positive form of the
681 option was used and 0 if the ``no-'' form was.
684 @hook TARGET_HANDLE_C_OPTION
685 This target hook is called whenever the user specifies one of the
686 target-specific C language family options described by the @file{.opt}
687 definition files(@pxref{Options}). It has the opportunity to do some
688 option-specific processing and should return true if the option is
689 valid. The arguments are like for @code{TARGET_HANDLE_OPTION}. The
690 default definition does nothing but return false.
692 In general, you should use @code{TARGET_HANDLE_OPTION} to handle
693 options. However, if processing an option requires routines that are
694 only available in the C (and related language) front ends, then you
695 should use @code{TARGET_HANDLE_C_OPTION} instead.
698 @hook TARGET_OBJC_CONSTRUCT_STRING_OBJECT
700 @hook TARGET_STRING_OBJECT_REF_TYPE_P
702 @hook TARGET_CHECK_STRING_OBJECT_FORMAT_ARG
704 @defmac TARGET_VERSION
705 This macro is a C statement to print on @code{stderr} a string
706 describing the particular machine description choice. Every machine
707 description should define @code{TARGET_VERSION}. For example:
711 #define TARGET_VERSION \
712 fprintf (stderr, " (68k, Motorola syntax)");
714 #define TARGET_VERSION \
715 fprintf (stderr, " (68k, MIT syntax)");
720 @hook TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE
721 This target function is similar to the hook @code{TARGET_OPTION_OVERRIDE}
722 but is called when the optimize level is changed via an attribute or
723 pragma or when it is reset at the end of the code affected by the
724 attribute or pragma. It is not called at the beginning of compilation
725 when @code{TARGET_OPTION_OVERRIDE} is called so if you want to perform these
726 actions then, you should have @code{TARGET_OPTION_OVERRIDE} call
727 @code{TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE}.
730 @defmac C_COMMON_OVERRIDE_OPTIONS
731 This is similar to the @code{TARGET_OPTION_OVERRIDE} hook
732 but is only used in the C
733 language frontends (C, Objective-C, C++, Objective-C++) and so can be
734 used to alter option flag variables which only exist in those
738 @hook TARGET_OPTION_OPTIMIZATION_TABLE
739 Some machines may desire to change what optimizations are performed for
740 various optimization levels. This variable, if defined, describes
741 options to enable at particular sets of optimization levels. These
742 options are processed once
743 just after the optimization level is determined and before the remainder
744 of the command options have been parsed, so may be overridden by other
745 options passed explicily.
747 This processing is run once at program startup and when the optimization
748 options are changed via @code{#pragma GCC optimize} or by using the
749 @code{optimize} attribute.
752 @hook TARGET_OPTION_INIT_STRUCT
754 @hook TARGET_OPTION_DEFAULT_PARAMS
757 This hook is called in response to the user invoking
758 @option{--target-help} on the command line. It gives the target a
759 chance to display extra information on the target specific command
760 line options found in its @file{.opt} file.
763 @defmac SWITCHABLE_TARGET
764 Some targets need to switch between substantially different subtargets
765 during compilation. For example, the MIPS target has one subtarget for
766 the traditional MIPS architecture and another for MIPS16. Source code
767 can switch between these two subarchitectures using the @code{mips16}
768 and @code{nomips16} attributes.
770 Such subtargets can differ in things like the set of available
771 registers, the set of available instructions, the costs of various
772 operations, and so on. GCC caches a lot of this type of information
773 in global variables, and recomputing them for each subtarget takes a
774 significant amount of time. The compiler therefore provides a facility
775 for maintaining several versions of the global variables and quickly
776 switching between them; see @file{target-globals.h} for details.
778 Define this macro to 1 if your target needs this facility. The default
782 @node Per-Function Data
783 @section Defining data structures for per-function information.
784 @cindex per-function data
785 @cindex data structures
787 If the target needs to store information on a per-function basis, GCC
788 provides a macro and a couple of variables to allow this. Note, just
789 using statics to store the information is a bad idea, since GCC supports
790 nested functions, so you can be halfway through encoding one function
791 when another one comes along.
793 GCC defines a data structure called @code{struct function} which
794 contains all of the data specific to an individual function. This
795 structure contains a field called @code{machine} whose type is
796 @code{struct machine_function *}, which can be used by targets to point
797 to their own specific data.
799 If a target needs per-function specific data it should define the type
800 @code{struct machine_function} and also the macro @code{INIT_EXPANDERS}.
801 This macro should be used to initialize the function pointer
802 @code{init_machine_status}. This pointer is explained below.
804 One typical use of per-function, target specific data is to create an
805 RTX to hold the register containing the function's return address. This
806 RTX can then be used to implement the @code{__builtin_return_address}
807 function, for level 0.
809 Note---earlier implementations of GCC used a single data area to hold
810 all of the per-function information. Thus when processing of a nested
811 function began the old per-function data had to be pushed onto a
812 stack, and when the processing was finished, it had to be popped off the
813 stack. GCC used to provide function pointers called
814 @code{save_machine_status} and @code{restore_machine_status} to handle
815 the saving and restoring of the target specific information. Since the
816 single data area approach is no longer used, these pointers are no
819 @defmac INIT_EXPANDERS
820 Macro called to initialize any target specific information. This macro
821 is called once per function, before generation of any RTL has begun.
822 The intention of this macro is to allow the initialization of the
823 function pointer @code{init_machine_status}.
826 @deftypevar {void (*)(struct function *)} init_machine_status
827 If this function pointer is non-@code{NULL} it will be called once per
828 function, before function compilation starts, in order to allow the
829 target to perform any target specific initialization of the
830 @code{struct function} structure. It is intended that this would be
831 used to initialize the @code{machine} of that structure.
833 @code{struct machine_function} structures are expected to be freed by GC@.
834 Generally, any memory that they reference must be allocated by using
835 GC allocation, including the structure itself.
839 @section Storage Layout
840 @cindex storage layout
842 Note that the definitions of the macros in this table which are sizes or
843 alignments measured in bits do not need to be constant. They can be C
844 expressions that refer to static variables, such as the @code{target_flags}.
845 @xref{Run-time Target}.
847 @defmac BITS_BIG_ENDIAN
848 Define this macro to have the value 1 if the most significant bit in a
849 byte has the lowest number; otherwise define it to have the value zero.
850 This means that bit-field instructions count from the most significant
851 bit. If the machine has no bit-field instructions, then this must still
852 be defined, but it doesn't matter which value it is defined to. This
853 macro need not be a constant.
855 This macro does not affect the way structure fields are packed into
856 bytes or words; that is controlled by @code{BYTES_BIG_ENDIAN}.
859 @defmac BYTES_BIG_ENDIAN
860 Define this macro to have the value 1 if the most significant byte in a
861 word has the lowest number. This macro need not be a constant.
864 @defmac WORDS_BIG_ENDIAN
865 Define this macro to have the value 1 if, in a multiword object, the
866 most significant word has the lowest number. This applies to both
867 memory locations and registers; GCC fundamentally assumes that the
868 order of words in memory is the same as the order in registers. This
869 macro need not be a constant.
872 @defmac FLOAT_WORDS_BIG_ENDIAN
873 Define this macro to have the value 1 if @code{DFmode}, @code{XFmode} or
874 @code{TFmode} floating point numbers are stored in memory with the word
875 containing the sign bit at the lowest address; otherwise define it to
876 have the value 0. This macro need not be a constant.
878 You need not define this macro if the ordering is the same as for
882 @defmac BITS_PER_UNIT
883 Define this macro to be the number of bits in an addressable storage
884 unit (byte). If you do not define this macro the default is 8.
887 @defmac BITS_PER_WORD
888 Number of bits in a word. If you do not define this macro, the default
889 is @code{BITS_PER_UNIT * UNITS_PER_WORD}.
892 @defmac MAX_BITS_PER_WORD
893 Maximum number of bits in a word. If this is undefined, the default is
894 @code{BITS_PER_WORD}. Otherwise, it is the constant value that is the
895 largest value that @code{BITS_PER_WORD} can have at run-time.
898 @defmac UNITS_PER_WORD
899 Number of storage units in a word; normally the size of a general-purpose
900 register, a power of two from 1 or 8.
903 @defmac MIN_UNITS_PER_WORD
904 Minimum number of units in a word. If this is undefined, the default is
905 @code{UNITS_PER_WORD}. Otherwise, it is the constant value that is the
906 smallest value that @code{UNITS_PER_WORD} can have at run-time.
910 Width of a pointer, in bits. You must specify a value no wider than the
911 width of @code{Pmode}. If it is not equal to the width of @code{Pmode},
912 you must define @code{POINTERS_EXTEND_UNSIGNED}. If you do not specify
913 a value the default is @code{BITS_PER_WORD}.
916 @defmac POINTERS_EXTEND_UNSIGNED
917 A C expression that determines how pointers should be extended from
918 @code{ptr_mode} to either @code{Pmode} or @code{word_mode}. It is
919 greater than zero if pointers should be zero-extended, zero if they
920 should be sign-extended, and negative if some other sort of conversion
921 is needed. In the last case, the extension is done by the target's
922 @code{ptr_extend} instruction.
924 You need not define this macro if the @code{ptr_mode}, @code{Pmode}
925 and @code{word_mode} are all the same width.
928 @defmac PROMOTE_MODE (@var{m}, @var{unsignedp}, @var{type})
929 A macro to update @var{m} and @var{unsignedp} when an object whose type
930 is @var{type} and which has the specified mode and signedness is to be
931 stored in a register. This macro is only called when @var{type} is a
934 On most RISC machines, which only have operations that operate on a full
935 register, define this macro to set @var{m} to @code{word_mode} if
936 @var{m} is an integer mode narrower than @code{BITS_PER_WORD}. In most
937 cases, only integer modes should be widened because wider-precision
938 floating-point operations are usually more expensive than their narrower
941 For most machines, the macro definition does not change @var{unsignedp}.
942 However, some machines, have instructions that preferentially handle
943 either signed or unsigned quantities of certain modes. For example, on
944 the DEC Alpha, 32-bit loads from memory and 32-bit add instructions
945 sign-extend the result to 64 bits. On such machines, set
946 @var{unsignedp} according to which kind of extension is more efficient.
948 Do not define this macro if it would never modify @var{m}.
951 @hook TARGET_PROMOTE_FUNCTION_MODE
952 Like @code{PROMOTE_MODE}, but it is applied to outgoing function arguments or
953 function return values. The target hook should return the new mode
954 and possibly change @code{*@var{punsignedp}} if the promotion should
955 change signedness. This function is called only for scalar @emph{or
958 @var{for_return} allows to distinguish the promotion of arguments and
959 return values. If it is @code{1}, a return value is being promoted and
960 @code{TARGET_FUNCTION_VALUE} must perform the same promotions done here.
961 If it is @code{2}, the returned mode should be that of the register in
962 which an incoming parameter is copied, or the outgoing result is computed;
963 then the hook should return the same mode as @code{promote_mode}, though
964 the signedness may be different.
966 The default is to not promote arguments and return values. You can
967 also define the hook to @code{default_promote_function_mode_always_promote}
968 if you would like to apply the same rules given by @code{PROMOTE_MODE}.
971 @defmac PARM_BOUNDARY
972 Normal alignment required for function parameters on the stack, in
973 bits. All stack parameters receive at least this much alignment
974 regardless of data type. On most machines, this is the same as the
978 @defmac STACK_BOUNDARY
979 Define this macro to the minimum alignment enforced by hardware for the
980 stack pointer on this machine. The definition is a C expression for the
981 desired alignment (measured in bits). This value is used as a default
982 if @code{PREFERRED_STACK_BOUNDARY} is not defined. On most machines,
983 this should be the same as @code{PARM_BOUNDARY}.
986 @defmac PREFERRED_STACK_BOUNDARY
987 Define this macro if you wish to preserve a certain alignment for the
988 stack pointer, greater than what the hardware enforces. The definition
989 is a C expression for the desired alignment (measured in bits). This
990 macro must evaluate to a value equal to or larger than
991 @code{STACK_BOUNDARY}.
994 @defmac INCOMING_STACK_BOUNDARY
995 Define this macro if the incoming stack boundary may be different
996 from @code{PREFERRED_STACK_BOUNDARY}. This macro must evaluate
997 to a value equal to or larger than @code{STACK_BOUNDARY}.
1000 @defmac FUNCTION_BOUNDARY
1001 Alignment required for a function entry point, in bits.
1004 @defmac BIGGEST_ALIGNMENT
1005 Biggest alignment that any data type can require on this machine, in
1006 bits. Note that this is not the biggest alignment that is supported,
1007 just the biggest alignment that, when violated, may cause a fault.
1010 @defmac MALLOC_ABI_ALIGNMENT
1011 Alignment, in bits, a C conformant malloc implementation has to
1012 provide. If not defined, the default value is @code{BITS_PER_WORD}.
1015 @defmac ATTRIBUTE_ALIGNED_VALUE
1016 Alignment used by the @code{__attribute__ ((aligned))} construct. If
1017 not defined, the default value is @code{BIGGEST_ALIGNMENT}.
1020 @defmac MINIMUM_ATOMIC_ALIGNMENT
1021 If defined, the smallest alignment, in bits, that can be given to an
1022 object that can be referenced in one operation, without disturbing any
1023 nearby object. Normally, this is @code{BITS_PER_UNIT}, but may be larger
1024 on machines that don't have byte or half-word store operations.
1027 @defmac BIGGEST_FIELD_ALIGNMENT
1028 Biggest alignment that any structure or union field can require on this
1029 machine, in bits. If defined, this overrides @code{BIGGEST_ALIGNMENT} for
1030 structure and union fields only, unless the field alignment has been set
1031 by the @code{__attribute__ ((aligned (@var{n})))} construct.
1034 @defmac ADJUST_FIELD_ALIGN (@var{field}, @var{computed})
1035 An expression for the alignment of a structure field @var{field} if the
1036 alignment computed in the usual way (including applying of
1037 @code{BIGGEST_ALIGNMENT} and @code{BIGGEST_FIELD_ALIGNMENT} to the
1038 alignment) is @var{computed}. It overrides alignment only if the
1039 field alignment has not been set by the
1040 @code{__attribute__ ((aligned (@var{n})))} construct.
1043 @defmac MAX_STACK_ALIGNMENT
1044 Biggest stack alignment guaranteed by the backend. Use this macro
1045 to specify the maximum alignment of a variable on stack.
1047 If not defined, the default value is @code{STACK_BOUNDARY}.
1049 @c FIXME: The default should be @code{PREFERRED_STACK_BOUNDARY}.
1050 @c But the fix for PR 32893 indicates that we can only guarantee
1051 @c maximum stack alignment on stack up to @code{STACK_BOUNDARY}, not
1052 @c @code{PREFERRED_STACK_BOUNDARY}, if stack alignment isn't supported.
1055 @defmac MAX_OFILE_ALIGNMENT
1056 Biggest alignment supported by the object file format of this machine.
1057 Use this macro to limit the alignment which can be specified using the
1058 @code{__attribute__ ((aligned (@var{n})))} construct. If not defined,
1059 the default value is @code{BIGGEST_ALIGNMENT}.
1061 On systems that use ELF, the default (in @file{config/elfos.h}) is
1062 the largest supported 32-bit ELF section alignment representable on
1063 a 32-bit host e.g. @samp{(((unsigned HOST_WIDEST_INT) 1 << 28) * 8)}.
1064 On 32-bit ELF the largest supported section alignment in bits is
1065 @samp{(0x80000000 * 8)}, but this is not representable on 32-bit hosts.
1068 @defmac DATA_ALIGNMENT (@var{type}, @var{basic-align})
1069 If defined, a C expression to compute the alignment for a variable in
1070 the static store. @var{type} is the data type, and @var{basic-align} is
1071 the alignment that the object would ordinarily have. The value of this
1072 macro is used instead of that alignment to align the object.
1074 If this macro is not defined, then @var{basic-align} is used.
1077 One use of this macro is to increase alignment of medium-size data to
1078 make it all fit in fewer cache lines. Another is to cause character
1079 arrays to be word-aligned so that @code{strcpy} calls that copy
1080 constants to character arrays can be done inline.
1083 @defmac CONSTANT_ALIGNMENT (@var{constant}, @var{basic-align})
1084 If defined, a C expression to compute the alignment given to a constant
1085 that is being placed in memory. @var{constant} is the constant and
1086 @var{basic-align} is the alignment that the object would ordinarily
1087 have. The value of this macro is used instead of that alignment to
1090 If this macro is not defined, then @var{basic-align} is used.
1092 The typical use of this macro is to increase alignment for string
1093 constants to be word aligned so that @code{strcpy} calls that copy
1094 constants can be done inline.
1097 @defmac LOCAL_ALIGNMENT (@var{type}, @var{basic-align})
1098 If defined, a C expression to compute the alignment for a variable in
1099 the local store. @var{type} is the data type, and @var{basic-align} is
1100 the alignment that the object would ordinarily have. The value of this
1101 macro is used instead of that alignment to align the object.
1103 If this macro is not defined, then @var{basic-align} is used.
1105 One use of this macro is to increase alignment of medium-size data to
1106 make it all fit in fewer cache lines.
1108 If the value of this macro has a type, it should be an unsigned type.
1111 @defmac STACK_SLOT_ALIGNMENT (@var{type}, @var{mode}, @var{basic-align})
1112 If defined, a C expression to compute the alignment for stack slot.
1113 @var{type} is the data type, @var{mode} is the widest mode available,
1114 and @var{basic-align} is the alignment that the slot would ordinarily
1115 have. The value of this macro is used instead of that alignment to
1118 If this macro is not defined, then @var{basic-align} is used when
1119 @var{type} is @code{NULL}. Otherwise, @code{LOCAL_ALIGNMENT} will
1122 This macro is to set alignment of stack slot to the maximum alignment
1123 of all possible modes which the slot may have.
1125 If the value of this macro has a type, it should be an unsigned type.
1128 @defmac LOCAL_DECL_ALIGNMENT (@var{decl})
1129 If defined, a C expression to compute the alignment for a local
1130 variable @var{decl}.
1132 If this macro is not defined, then
1133 @code{LOCAL_ALIGNMENT (TREE_TYPE (@var{decl}), DECL_ALIGN (@var{decl}))}
1136 One use of this macro is to increase alignment of medium-size data to
1137 make it all fit in fewer cache lines.
1139 If the value of this macro has a type, it should be an unsigned type.
1142 @defmac MINIMUM_ALIGNMENT (@var{exp}, @var{mode}, @var{align})
1143 If defined, a C expression to compute the minimum required alignment
1144 for dynamic stack realignment purposes for @var{exp} (a type or decl),
1145 @var{mode}, assuming normal alignment @var{align}.
1147 If this macro is not defined, then @var{align} will be used.
1150 @defmac EMPTY_FIELD_BOUNDARY
1151 Alignment in bits to be given to a structure bit-field that follows an
1152 empty field such as @code{int : 0;}.
1154 If @code{PCC_BITFIELD_TYPE_MATTERS} is true, it overrides this macro.
1157 @defmac STRUCTURE_SIZE_BOUNDARY
1158 Number of bits which any structure or union's size must be a multiple of.
1159 Each structure or union's size is rounded up to a multiple of this.
1161 If you do not define this macro, the default is the same as
1162 @code{BITS_PER_UNIT}.
1165 @defmac STRICT_ALIGNMENT
1166 Define this macro to be the value 1 if instructions will fail to work
1167 if given data not on the nominal alignment. If instructions will merely
1168 go slower in that case, define this macro as 0.
1171 @defmac PCC_BITFIELD_TYPE_MATTERS
1172 Define this if you wish to imitate the way many other C compilers handle
1173 alignment of bit-fields and the structures that contain them.
1175 The behavior is that the type written for a named bit-field (@code{int},
1176 @code{short}, or other integer type) imposes an alignment for the entire
1177 structure, as if the structure really did contain an ordinary field of
1178 that type. In addition, the bit-field is placed within the structure so
1179 that it would fit within such a field, not crossing a boundary for it.
1181 Thus, on most machines, a named bit-field whose type is written as
1182 @code{int} would not cross a four-byte boundary, and would force
1183 four-byte alignment for the whole structure. (The alignment used may
1184 not be four bytes; it is controlled by the other alignment parameters.)
1186 An unnamed bit-field will not affect the alignment of the containing
1189 If the macro is defined, its definition should be a C expression;
1190 a nonzero value for the expression enables this behavior.
1192 Note that if this macro is not defined, or its value is zero, some
1193 bit-fields may cross more than one alignment boundary. The compiler can
1194 support such references if there are @samp{insv}, @samp{extv}, and
1195 @samp{extzv} insns that can directly reference memory.
1197 The other known way of making bit-fields work is to define
1198 @code{STRUCTURE_SIZE_BOUNDARY} as large as @code{BIGGEST_ALIGNMENT}.
1199 Then every structure can be accessed with fullwords.
1201 Unless the machine has bit-field instructions or you define
1202 @code{STRUCTURE_SIZE_BOUNDARY} that way, you must define
1203 @code{PCC_BITFIELD_TYPE_MATTERS} to have a nonzero value.
1205 If your aim is to make GCC use the same conventions for laying out
1206 bit-fields as are used by another compiler, here is how to investigate
1207 what the other compiler does. Compile and run this program:
1226 printf ("Size of foo1 is %d\n",
1227 sizeof (struct foo1));
1228 printf ("Size of foo2 is %d\n",
1229 sizeof (struct foo2));
1234 If this prints 2 and 5, then the compiler's behavior is what you would
1235 get from @code{PCC_BITFIELD_TYPE_MATTERS}.
1238 @defmac BITFIELD_NBYTES_LIMITED
1239 Like @code{PCC_BITFIELD_TYPE_MATTERS} except that its effect is limited
1240 to aligning a bit-field within the structure.
1243 @hook TARGET_ALIGN_ANON_BITFIELD
1244 When @code{PCC_BITFIELD_TYPE_MATTERS} is true this hook will determine
1245 whether unnamed bitfields affect the alignment of the containing
1246 structure. The hook should return true if the structure should inherit
1247 the alignment requirements of an unnamed bitfield's type.
1250 @hook TARGET_NARROW_VOLATILE_BITFIELD
1251 This target hook should return @code{true} if accesses to volatile bitfields
1252 should use the narrowest mode possible. It should return @code{false} if
1253 these accesses should use the bitfield container type.
1255 The default is @code{!TARGET_STRICT_ALIGN}.
1258 @defmac MEMBER_TYPE_FORCES_BLK (@var{field}, @var{mode})
1259 Return 1 if a structure or array containing @var{field} should be accessed using
1262 If @var{field} is the only field in the structure, @var{mode} is its
1263 mode, otherwise @var{mode} is VOIDmode. @var{mode} is provided in the
1264 case where structures of one field would require the structure's mode to
1265 retain the field's mode.
1267 Normally, this is not needed.
1270 @defmac ROUND_TYPE_ALIGN (@var{type}, @var{computed}, @var{specified})
1271 Define this macro as an expression for the alignment of a type (given
1272 by @var{type} as a tree node) if the alignment computed in the usual
1273 way is @var{computed} and the alignment explicitly specified was
1276 The default is to use @var{specified} if it is larger; otherwise, use
1277 the smaller of @var{computed} and @code{BIGGEST_ALIGNMENT}
1280 @defmac MAX_FIXED_MODE_SIZE
1281 An integer expression for the size in bits of the largest integer
1282 machine mode that should actually be used. All integer machine modes of
1283 this size or smaller can be used for structures and unions with the
1284 appropriate sizes. If this macro is undefined, @code{GET_MODE_BITSIZE
1285 (DImode)} is assumed.
1288 @defmac STACK_SAVEAREA_MODE (@var{save_level})
1289 If defined, an expression of type @code{enum machine_mode} that
1290 specifies the mode of the save area operand of a
1291 @code{save_stack_@var{level}} named pattern (@pxref{Standard Names}).
1292 @var{save_level} is one of @code{SAVE_BLOCK}, @code{SAVE_FUNCTION}, or
1293 @code{SAVE_NONLOCAL} and selects which of the three named patterns is
1294 having its mode specified.
1296 You need not define this macro if it always returns @code{Pmode}. You
1297 would most commonly define this macro if the
1298 @code{save_stack_@var{level}} patterns need to support both a 32- and a
1302 @defmac STACK_SIZE_MODE
1303 If defined, an expression of type @code{enum machine_mode} that
1304 specifies the mode of the size increment operand of an
1305 @code{allocate_stack} named pattern (@pxref{Standard Names}).
1307 You need not define this macro if it always returns @code{word_mode}.
1308 You would most commonly define this macro if the @code{allocate_stack}
1309 pattern needs to support both a 32- and a 64-bit mode.
1312 @hook TARGET_LIBGCC_CMP_RETURN_MODE
1313 This target hook should return the mode to be used for the return value
1314 of compare instructions expanded to libgcc calls. If not defined
1315 @code{word_mode} is returned which is the right choice for a majority of
1319 @hook TARGET_LIBGCC_SHIFT_COUNT_MODE
1320 This target hook should return the mode to be used for the shift count operand
1321 of shift instructions expanded to libgcc calls. If not defined
1322 @code{word_mode} is returned which is the right choice for a majority of
1326 @hook TARGET_UNWIND_WORD_MODE
1327 Return machine mode to be used for @code{_Unwind_Word} type.
1328 The default is to use @code{word_mode}.
1331 @defmac ROUND_TOWARDS_ZERO
1332 If defined, this macro should be true if the prevailing rounding
1333 mode is towards zero.
1335 Defining this macro only affects the way @file{libgcc.a} emulates
1336 floating-point arithmetic.
1338 Not defining this macro is equivalent to returning zero.
1341 @defmac LARGEST_EXPONENT_IS_NORMAL (@var{size})
1342 This macro should return true if floats with @var{size}
1343 bits do not have a NaN or infinity representation, but use the largest
1344 exponent for normal numbers instead.
1346 Defining this macro only affects the way @file{libgcc.a} emulates
1347 floating-point arithmetic.
1349 The default definition of this macro returns false for all sizes.
1352 @hook TARGET_MS_BITFIELD_LAYOUT_P
1353 This target hook returns @code{true} if bit-fields in the given
1354 @var{record_type} are to be laid out following the rules of Microsoft
1355 Visual C/C++, namely: (i) a bit-field won't share the same storage
1356 unit with the previous bit-field if their underlying types have
1357 different sizes, and the bit-field will be aligned to the highest
1358 alignment of the underlying types of itself and of the previous
1359 bit-field; (ii) a zero-sized bit-field will affect the alignment of
1360 the whole enclosing structure, even if it is unnamed; except that
1361 (iii) a zero-sized bit-field will be disregarded unless it follows
1362 another bit-field of nonzero size. If this hook returns @code{true},
1363 other macros that control bit-field layout are ignored.
1365 When a bit-field is inserted into a packed record, the whole size
1366 of the underlying type is used by one or more same-size adjacent
1367 bit-fields (that is, if its long:3, 32 bits is used in the record,
1368 and any additional adjacent long bit-fields are packed into the same
1369 chunk of 32 bits. However, if the size changes, a new field of that
1370 size is allocated). In an unpacked record, this is the same as using
1371 alignment, but not equivalent when packing.
1373 If both MS bit-fields and @samp{__attribute__((packed))} are used,
1374 the latter will take precedence. If @samp{__attribute__((packed))} is
1375 used on a single field when MS bit-fields are in use, it will take
1376 precedence for that field, but the alignment of the rest of the structure
1377 may affect its placement.
1380 @hook TARGET_DECIMAL_FLOAT_SUPPORTED_P
1381 Returns true if the target supports decimal floating point.
1384 @hook TARGET_FIXED_POINT_SUPPORTED_P
1385 Returns true if the target supports fixed-point arithmetic.
1388 @hook TARGET_EXPAND_TO_RTL_HOOK
1389 This hook is called just before expansion into rtl, allowing the target
1390 to perform additional initializations or analysis before the expansion.
1391 For example, the rs6000 port uses it to allocate a scratch stack slot
1392 for use in copying SDmode values between memory and floating point
1393 registers whenever the function being expanded has any SDmode
1397 @hook TARGET_INSTANTIATE_DECLS
1398 This hook allows the backend to perform additional instantiations on rtl
1399 that are not actually in any insns yet, but will be later.
1402 @hook TARGET_MANGLE_TYPE
1403 If your target defines any fundamental types, or any types your target
1404 uses should be mangled differently from the default, define this hook
1405 to return the appropriate encoding for these types as part of a C++
1406 mangled name. The @var{type} argument is the tree structure representing
1407 the type to be mangled. The hook may be applied to trees which are
1408 not target-specific fundamental types; it should return @code{NULL}
1409 for all such types, as well as arguments it does not recognize. If the
1410 return value is not @code{NULL}, it must point to a statically-allocated
1413 Target-specific fundamental types might be new fundamental types or
1414 qualified versions of ordinary fundamental types. Encode new
1415 fundamental types as @samp{@w{u @var{n} @var{name}}}, where @var{name}
1416 is the name used for the type in source code, and @var{n} is the
1417 length of @var{name} in decimal. Encode qualified versions of
1418 ordinary types as @samp{@w{U @var{n} @var{name} @var{code}}}, where
1419 @var{name} is the name used for the type qualifier in source code,
1420 @var{n} is the length of @var{name} as above, and @var{code} is the
1421 code used to represent the unqualified version of this type. (See
1422 @code{write_builtin_type} in @file{cp/mangle.c} for the list of
1423 codes.) In both cases the spaces are for clarity; do not include any
1424 spaces in your string.
1426 This hook is applied to types prior to typedef resolution. If the mangled
1427 name for a particular type depends only on that type's main variant, you
1428 can perform typedef resolution yourself using @code{TYPE_MAIN_VARIANT}
1431 The default version of this hook always returns @code{NULL}, which is
1432 appropriate for a target that does not define any new fundamental
1437 @section Layout of Source Language Data Types
1439 These macros define the sizes and other characteristics of the standard
1440 basic data types used in programs being compiled. Unlike the macros in
1441 the previous section, these apply to specific features of C and related
1442 languages, rather than to fundamental aspects of storage layout.
1444 @defmac INT_TYPE_SIZE
1445 A C expression for the size in bits of the type @code{int} on the
1446 target machine. If you don't define this, the default is one word.
1449 @defmac SHORT_TYPE_SIZE
1450 A C expression for the size in bits of the type @code{short} on the
1451 target machine. If you don't define this, the default is half a word.
1452 (If this would be less than one storage unit, it is rounded up to one
1456 @defmac LONG_TYPE_SIZE
1457 A C expression for the size in bits of the type @code{long} on the
1458 target machine. If you don't define this, the default is one word.
1461 @defmac ADA_LONG_TYPE_SIZE
1462 On some machines, the size used for the Ada equivalent of the type
1463 @code{long} by a native Ada compiler differs from that used by C@. In
1464 that situation, define this macro to be a C expression to be used for
1465 the size of that type. If you don't define this, the default is the
1466 value of @code{LONG_TYPE_SIZE}.
1469 @defmac LONG_LONG_TYPE_SIZE
1470 A C expression for the size in bits of the type @code{long long} on the
1471 target machine. If you don't define this, the default is two
1472 words. If you want to support GNU Ada on your machine, the value of this
1473 macro must be at least 64.
1476 @defmac CHAR_TYPE_SIZE
1477 A C expression for the size in bits of the type @code{char} on the
1478 target machine. If you don't define this, the default is
1479 @code{BITS_PER_UNIT}.
1482 @defmac BOOL_TYPE_SIZE
1483 A C expression for the size in bits of the C++ type @code{bool} and
1484 C99 type @code{_Bool} on the target machine. If you don't define
1485 this, and you probably shouldn't, the default is @code{CHAR_TYPE_SIZE}.
1488 @defmac FLOAT_TYPE_SIZE
1489 A C expression for the size in bits of the type @code{float} on the
1490 target machine. If you don't define this, the default is one word.
1493 @defmac DOUBLE_TYPE_SIZE
1494 A C expression for the size in bits of the type @code{double} on the
1495 target machine. If you don't define this, the default is two
1499 @defmac LONG_DOUBLE_TYPE_SIZE
1500 A C expression for the size in bits of the type @code{long double} on
1501 the target machine. If you don't define this, the default is two
1505 @defmac SHORT_FRACT_TYPE_SIZE
1506 A C expression for the size in bits of the type @code{short _Fract} on
1507 the target machine. If you don't define this, the default is
1508 @code{BITS_PER_UNIT}.
1511 @defmac FRACT_TYPE_SIZE
1512 A C expression for the size in bits of the type @code{_Fract} on
1513 the target machine. If you don't define this, the default is
1514 @code{BITS_PER_UNIT * 2}.
1517 @defmac LONG_FRACT_TYPE_SIZE
1518 A C expression for the size in bits of the type @code{long _Fract} on
1519 the target machine. If you don't define this, the default is
1520 @code{BITS_PER_UNIT * 4}.
1523 @defmac LONG_LONG_FRACT_TYPE_SIZE
1524 A C expression for the size in bits of the type @code{long long _Fract} on
1525 the target machine. If you don't define this, the default is
1526 @code{BITS_PER_UNIT * 8}.
1529 @defmac SHORT_ACCUM_TYPE_SIZE
1530 A C expression for the size in bits of the type @code{short _Accum} on
1531 the target machine. If you don't define this, the default is
1532 @code{BITS_PER_UNIT * 2}.
1535 @defmac ACCUM_TYPE_SIZE
1536 A C expression for the size in bits of the type @code{_Accum} on
1537 the target machine. If you don't define this, the default is
1538 @code{BITS_PER_UNIT * 4}.
1541 @defmac LONG_ACCUM_TYPE_SIZE
1542 A C expression for the size in bits of the type @code{long _Accum} on
1543 the target machine. If you don't define this, the default is
1544 @code{BITS_PER_UNIT * 8}.
1547 @defmac LONG_LONG_ACCUM_TYPE_SIZE
1548 A C expression for the size in bits of the type @code{long long _Accum} on
1549 the target machine. If you don't define this, the default is
1550 @code{BITS_PER_UNIT * 16}.
1553 @defmac LIBGCC2_LONG_DOUBLE_TYPE_SIZE
1554 Define this macro if @code{LONG_DOUBLE_TYPE_SIZE} is not constant or
1555 if you want routines in @file{libgcc2.a} for a size other than
1556 @code{LONG_DOUBLE_TYPE_SIZE}. If you don't define this, the
1557 default is @code{LONG_DOUBLE_TYPE_SIZE}.
1560 @defmac LIBGCC2_HAS_DF_MODE
1561 Define this macro if neither @code{DOUBLE_TYPE_SIZE} nor
1562 @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is
1563 @code{DFmode} but you want @code{DFmode} routines in @file{libgcc2.a}
1564 anyway. If you don't define this and either @code{DOUBLE_TYPE_SIZE}
1565 or @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is 64 then the default is 1,
1569 @defmac LIBGCC2_HAS_XF_MODE
1570 Define this macro if @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is not
1571 @code{XFmode} but you want @code{XFmode} routines in @file{libgcc2.a}
1572 anyway. If you don't define this and @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE}
1573 is 80 then the default is 1, otherwise it is 0.
1576 @defmac LIBGCC2_HAS_TF_MODE
1577 Define this macro if @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is not
1578 @code{TFmode} but you want @code{TFmode} routines in @file{libgcc2.a}
1579 anyway. If you don't define this and @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE}
1580 is 128 then the default is 1, otherwise it is 0.
1587 Define these macros to be the size in bits of the mantissa of
1588 @code{SFmode}, @code{DFmode}, @code{XFmode} and @code{TFmode} values,
1589 if the defaults in @file{libgcc2.h} are inappropriate. By default,
1590 @code{FLT_MANT_DIG} is used for @code{SF_SIZE}, @code{LDBL_MANT_DIG}
1591 for @code{XF_SIZE} and @code{TF_SIZE}, and @code{DBL_MANT_DIG} or
1592 @code{LDBL_MANT_DIG} for @code{DF_SIZE} according to whether
1593 @code{DOUBLE_TYPE_SIZE} or
1594 @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is 64.
1597 @defmac TARGET_FLT_EVAL_METHOD
1598 A C expression for the value for @code{FLT_EVAL_METHOD} in @file{float.h},
1599 assuming, if applicable, that the floating-point control word is in its
1600 default state. If you do not define this macro the value of
1601 @code{FLT_EVAL_METHOD} will be zero.
1604 @defmac WIDEST_HARDWARE_FP_SIZE
1605 A C expression for the size in bits of the widest floating-point format
1606 supported by the hardware. If you define this macro, you must specify a
1607 value less than or equal to the value of @code{LONG_DOUBLE_TYPE_SIZE}.
1608 If you do not define this macro, the value of @code{LONG_DOUBLE_TYPE_SIZE}
1612 @defmac DEFAULT_SIGNED_CHAR
1613 An expression whose value is 1 or 0, according to whether the type
1614 @code{char} should be signed or unsigned by default. The user can
1615 always override this default with the options @option{-fsigned-char}
1616 and @option{-funsigned-char}.
1619 @hook TARGET_DEFAULT_SHORT_ENUMS
1620 This target hook should return true if the compiler should give an
1621 @code{enum} type only as many bytes as it takes to represent the range
1622 of possible values of that type. It should return false if all
1623 @code{enum} types should be allocated like @code{int}.
1625 The default is to return false.
1629 A C expression for a string describing the name of the data type to use
1630 for size values. The typedef name @code{size_t} is defined using the
1631 contents of the string.
1633 The string can contain more than one keyword. If so, separate them with
1634 spaces, and write first any length keyword, then @code{unsigned} if
1635 appropriate, and finally @code{int}. The string must exactly match one
1636 of the data type names defined in the function
1637 @code{init_decl_processing} in the file @file{c-decl.c}. You may not
1638 omit @code{int} or change the order---that would cause the compiler to
1641 If you don't define this macro, the default is @code{"long unsigned
1645 @defmac PTRDIFF_TYPE
1646 A C expression for a string describing the name of the data type to use
1647 for the result of subtracting two pointers. The typedef name
1648 @code{ptrdiff_t} is defined using the contents of the string. See
1649 @code{SIZE_TYPE} above for more information.
1651 If you don't define this macro, the default is @code{"long int"}.
1655 A C expression for a string describing the name of the data type to use
1656 for wide characters. The typedef name @code{wchar_t} is defined using
1657 the contents of the string. See @code{SIZE_TYPE} above for more
1660 If you don't define this macro, the default is @code{"int"}.
1663 @defmac WCHAR_TYPE_SIZE
1664 A C expression for the size in bits of the data type for wide
1665 characters. This is used in @code{cpp}, which cannot make use of
1670 A C expression for a string describing the name of the data type to
1671 use for wide characters passed to @code{printf} and returned from
1672 @code{getwc}. The typedef name @code{wint_t} is defined using the
1673 contents of the string. See @code{SIZE_TYPE} above for more
1676 If you don't define this macro, the default is @code{"unsigned int"}.
1680 A C expression for a string describing the name of the data type that
1681 can represent any value of any standard or extended signed integer type.
1682 The typedef name @code{intmax_t} is defined using the contents of the
1683 string. See @code{SIZE_TYPE} above for more information.
1685 If you don't define this macro, the default is the first of
1686 @code{"int"}, @code{"long int"}, or @code{"long long int"} that has as
1687 much precision as @code{long long int}.
1690 @defmac UINTMAX_TYPE
1691 A C expression for a string describing the name of the data type that
1692 can represent any value of any standard or extended unsigned integer
1693 type. The typedef name @code{uintmax_t} is defined using the contents
1694 of the string. See @code{SIZE_TYPE} above for more information.
1696 If you don't define this macro, the default is the first of
1697 @code{"unsigned int"}, @code{"long unsigned int"}, or @code{"long long
1698 unsigned int"} that has as much precision as @code{long long unsigned
1702 @defmac SIG_ATOMIC_TYPE
1708 @defmacx UINT16_TYPE
1709 @defmacx UINT32_TYPE
1710 @defmacx UINT64_TYPE
1711 @defmacx INT_LEAST8_TYPE
1712 @defmacx INT_LEAST16_TYPE
1713 @defmacx INT_LEAST32_TYPE
1714 @defmacx INT_LEAST64_TYPE
1715 @defmacx UINT_LEAST8_TYPE
1716 @defmacx UINT_LEAST16_TYPE
1717 @defmacx UINT_LEAST32_TYPE
1718 @defmacx UINT_LEAST64_TYPE
1719 @defmacx INT_FAST8_TYPE
1720 @defmacx INT_FAST16_TYPE
1721 @defmacx INT_FAST32_TYPE
1722 @defmacx INT_FAST64_TYPE
1723 @defmacx UINT_FAST8_TYPE
1724 @defmacx UINT_FAST16_TYPE
1725 @defmacx UINT_FAST32_TYPE
1726 @defmacx UINT_FAST64_TYPE
1727 @defmacx INTPTR_TYPE
1728 @defmacx UINTPTR_TYPE
1729 C expressions for the standard types @code{sig_atomic_t},
1730 @code{int8_t}, @code{int16_t}, @code{int32_t}, @code{int64_t},
1731 @code{uint8_t}, @code{uint16_t}, @code{uint32_t}, @code{uint64_t},
1732 @code{int_least8_t}, @code{int_least16_t}, @code{int_least32_t},
1733 @code{int_least64_t}, @code{uint_least8_t}, @code{uint_least16_t},
1734 @code{uint_least32_t}, @code{uint_least64_t}, @code{int_fast8_t},
1735 @code{int_fast16_t}, @code{int_fast32_t}, @code{int_fast64_t},
1736 @code{uint_fast8_t}, @code{uint_fast16_t}, @code{uint_fast32_t},
1737 @code{uint_fast64_t}, @code{intptr_t}, and @code{uintptr_t}. See
1738 @code{SIZE_TYPE} above for more information.
1740 If any of these macros evaluates to a null pointer, the corresponding
1741 type is not supported; if GCC is configured to provide
1742 @code{<stdint.h>} in such a case, the header provided may not conform
1743 to C99, depending on the type in question. The defaults for all of
1744 these macros are null pointers.
1747 @defmac TARGET_PTRMEMFUNC_VBIT_LOCATION
1748 The C++ compiler represents a pointer-to-member-function with a struct
1755 ptrdiff_t vtable_index;
1762 The C++ compiler must use one bit to indicate whether the function that
1763 will be called through a pointer-to-member-function is virtual.
1764 Normally, we assume that the low-order bit of a function pointer must
1765 always be zero. Then, by ensuring that the vtable_index is odd, we can
1766 distinguish which variant of the union is in use. But, on some
1767 platforms function pointers can be odd, and so this doesn't work. In
1768 that case, we use the low-order bit of the @code{delta} field, and shift
1769 the remainder of the @code{delta} field to the left.
1771 GCC will automatically make the right selection about where to store
1772 this bit using the @code{FUNCTION_BOUNDARY} setting for your platform.
1773 However, some platforms such as ARM/Thumb have @code{FUNCTION_BOUNDARY}
1774 set such that functions always start at even addresses, but the lowest
1775 bit of pointers to functions indicate whether the function at that
1776 address is in ARM or Thumb mode. If this is the case of your
1777 architecture, you should define this macro to
1778 @code{ptrmemfunc_vbit_in_delta}.
1780 In general, you should not have to define this macro. On architectures
1781 in which function addresses are always even, according to
1782 @code{FUNCTION_BOUNDARY}, GCC will automatically define this macro to
1783 @code{ptrmemfunc_vbit_in_pfn}.
1786 @defmac TARGET_VTABLE_USES_DESCRIPTORS
1787 Normally, the C++ compiler uses function pointers in vtables. This
1788 macro allows the target to change to use ``function descriptors''
1789 instead. Function descriptors are found on targets for whom a
1790 function pointer is actually a small data structure. Normally the
1791 data structure consists of the actual code address plus a data
1792 pointer to which the function's data is relative.
1794 If vtables are used, the value of this macro should be the number
1795 of words that the function descriptor occupies.
1798 @defmac TARGET_VTABLE_ENTRY_ALIGN
1799 By default, the vtable entries are void pointers, the so the alignment
1800 is the same as pointer alignment. The value of this macro specifies
1801 the alignment of the vtable entry in bits. It should be defined only
1802 when special alignment is necessary. */
1805 @defmac TARGET_VTABLE_DATA_ENTRY_DISTANCE
1806 There are a few non-descriptor entries in the vtable at offsets below
1807 zero. If these entries must be padded (say, to preserve the alignment
1808 specified by @code{TARGET_VTABLE_ENTRY_ALIGN}), set this to the number
1809 of words in each data entry.
1813 @section Register Usage
1814 @cindex register usage
1816 This section explains how to describe what registers the target machine
1817 has, and how (in general) they can be used.
1819 The description of which registers a specific instruction can use is
1820 done with register classes; see @ref{Register Classes}. For information
1821 on using registers to access a stack frame, see @ref{Frame Registers}.
1822 For passing values in registers, see @ref{Register Arguments}.
1823 For returning values in registers, see @ref{Scalar Return}.
1826 * Register Basics:: Number and kinds of registers.
1827 * Allocation Order:: Order in which registers are allocated.
1828 * Values in Registers:: What kinds of values each reg can hold.
1829 * Leaf Functions:: Renumbering registers for leaf functions.
1830 * Stack Registers:: Handling a register stack such as 80387.
1833 @node Register Basics
1834 @subsection Basic Characteristics of Registers
1836 @c prevent bad page break with this line
1837 Registers have various characteristics.
1839 @defmac FIRST_PSEUDO_REGISTER
1840 Number of hardware registers known to the compiler. They receive
1841 numbers 0 through @code{FIRST_PSEUDO_REGISTER-1}; thus, the first
1842 pseudo register's number really is assigned the number
1843 @code{FIRST_PSEUDO_REGISTER}.
1846 @defmac FIXED_REGISTERS
1847 @cindex fixed register
1848 An initializer that says which registers are used for fixed purposes
1849 all throughout the compiled code and are therefore not available for
1850 general allocation. These would include the stack pointer, the frame
1851 pointer (except on machines where that can be used as a general
1852 register when no frame pointer is needed), the program counter on
1853 machines where that is considered one of the addressable registers,
1854 and any other numbered register with a standard use.
1856 This information is expressed as a sequence of numbers, separated by
1857 commas and surrounded by braces. The @var{n}th number is 1 if
1858 register @var{n} is fixed, 0 otherwise.
1860 The table initialized from this macro, and the table initialized by
1861 the following one, may be overridden at run time either automatically,
1862 by the actions of the macro @code{CONDITIONAL_REGISTER_USAGE}, or by
1863 the user with the command options @option{-ffixed-@var{reg}},
1864 @option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}}.
1867 @defmac CALL_USED_REGISTERS
1868 @cindex call-used register
1869 @cindex call-clobbered register
1870 @cindex call-saved register
1871 Like @code{FIXED_REGISTERS} but has 1 for each register that is
1872 clobbered (in general) by function calls as well as for fixed
1873 registers. This macro therefore identifies the registers that are not
1874 available for general allocation of values that must live across
1877 If a register has 0 in @code{CALL_USED_REGISTERS}, the compiler
1878 automatically saves it on function entry and restores it on function
1879 exit, if the register is used within the function.
1882 @defmac CALL_REALLY_USED_REGISTERS
1883 @cindex call-used register
1884 @cindex call-clobbered register
1885 @cindex call-saved register
1886 Like @code{CALL_USED_REGISTERS} except this macro doesn't require
1887 that the entire set of @code{FIXED_REGISTERS} be included.
1888 (@code{CALL_USED_REGISTERS} must be a superset of @code{FIXED_REGISTERS}).
1889 This macro is optional. If not specified, it defaults to the value
1890 of @code{CALL_USED_REGISTERS}.
1893 @defmac HARD_REGNO_CALL_PART_CLOBBERED (@var{regno}, @var{mode})
1894 @cindex call-used register
1895 @cindex call-clobbered register
1896 @cindex call-saved register
1897 A C expression that is nonzero if it is not permissible to store a
1898 value of mode @var{mode} in hard register number @var{regno} across a
1899 call without some part of it being clobbered. For most machines this
1900 macro need not be defined. It is only required for machines that do not
1901 preserve the entire contents of a register across a call.
1905 @findex call_used_regs
1908 @findex reg_class_contents
1909 @hook TARGET_CONDITIONAL_REGISTER_USAGE
1910 This hook may conditionally modify five variables
1911 @code{fixed_regs}, @code{call_used_regs}, @code{global_regs},
1912 @code{reg_names}, and @code{reg_class_contents}, to take into account
1913 any dependence of these register sets on target flags. The first three
1914 of these are of type @code{char []} (interpreted as Boolean vectors).
1915 @code{global_regs} is a @code{const char *[]}, and
1916 @code{reg_class_contents} is a @code{HARD_REG_SET}. Before the macro is
1917 called, @code{fixed_regs}, @code{call_used_regs},
1918 @code{reg_class_contents}, and @code{reg_names} have been initialized
1919 from @code{FIXED_REGISTERS}, @code{CALL_USED_REGISTERS},
1920 @code{REG_CLASS_CONTENTS}, and @code{REGISTER_NAMES}, respectively.
1921 @code{global_regs} has been cleared, and any @option{-ffixed-@var{reg}},
1922 @option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}}
1923 command options have been applied.
1925 @cindex disabling certain registers
1926 @cindex controlling register usage
1927 If the usage of an entire class of registers depends on the target
1928 flags, you may indicate this to GCC by using this macro to modify
1929 @code{fixed_regs} and @code{call_used_regs} to 1 for each of the
1930 registers in the classes which should not be used by GCC@. Also define
1931 the macro @code{REG_CLASS_FROM_LETTER} / @code{REG_CLASS_FROM_CONSTRAINT}
1932 to return @code{NO_REGS} if it
1933 is called with a letter for a class that shouldn't be used.
1935 (However, if this class is not included in @code{GENERAL_REGS} and all
1936 of the insn patterns whose constraints permit this class are
1937 controlled by target switches, then GCC will automatically avoid using
1938 these registers when the target switches are opposed to them.)
1941 @defmac INCOMING_REGNO (@var{out})
1942 Define this macro if the target machine has register windows. This C
1943 expression returns the register number as seen by the called function
1944 corresponding to the register number @var{out} as seen by the calling
1945 function. Return @var{out} if register number @var{out} is not an
1949 @defmac OUTGOING_REGNO (@var{in})
1950 Define this macro if the target machine has register windows. This C
1951 expression returns the register number as seen by the calling function
1952 corresponding to the register number @var{in} as seen by the called
1953 function. Return @var{in} if register number @var{in} is not an inbound
1957 @defmac LOCAL_REGNO (@var{regno})
1958 Define this macro if the target machine has register windows. This C
1959 expression returns true if the register is call-saved but is in the
1960 register window. Unlike most call-saved registers, such registers
1961 need not be explicitly restored on function exit or during non-local
1966 If the program counter has a register number, define this as that
1967 register number. Otherwise, do not define it.
1970 @node Allocation Order
1971 @subsection Order of Allocation of Registers
1972 @cindex order of register allocation
1973 @cindex register allocation order
1975 @c prevent bad page break with this line
1976 Registers are allocated in order.
1978 @defmac REG_ALLOC_ORDER
1979 If defined, an initializer for a vector of integers, containing the
1980 numbers of hard registers in the order in which GCC should prefer
1981 to use them (from most preferred to least).
1983 If this macro is not defined, registers are used lowest numbered first
1984 (all else being equal).
1986 One use of this macro is on machines where the highest numbered
1987 registers must always be saved and the save-multiple-registers
1988 instruction supports only sequences of consecutive registers. On such
1989 machines, define @code{REG_ALLOC_ORDER} to be an initializer that lists
1990 the highest numbered allocable register first.
1993 @defmac ADJUST_REG_ALLOC_ORDER
1994 A C statement (sans semicolon) to choose the order in which to allocate
1995 hard registers for pseudo-registers local to a basic block.
1997 Store the desired register order in the array @code{reg_alloc_order}.
1998 Element 0 should be the register to allocate first; element 1, the next
1999 register; and so on.
2001 The macro body should not assume anything about the contents of
2002 @code{reg_alloc_order} before execution of the macro.
2004 On most machines, it is not necessary to define this macro.
2007 @defmac HONOR_REG_ALLOC_ORDER
2008 Normally, IRA tries to estimate the costs for saving a register in the
2009 prologue and restoring it in the epilogue. This discourages it from
2010 using call-saved registers. If a machine wants to ensure that IRA
2011 allocates registers in the order given by REG_ALLOC_ORDER even if some
2012 call-saved registers appear earlier than call-used ones, this macro
2016 @defmac IRA_HARD_REGNO_ADD_COST_MULTIPLIER (@var{regno})
2017 In some case register allocation order is not enough for the
2018 Integrated Register Allocator (@acronym{IRA}) to generate a good code.
2019 If this macro is defined, it should return a floating point value
2020 based on @var{regno}. The cost of using @var{regno} for a pseudo will
2021 be increased by approximately the pseudo's usage frequency times the
2022 value returned by this macro. Not defining this macro is equivalent
2023 to having it always return @code{0.0}.
2025 On most machines, it is not necessary to define this macro.
2028 @node Values in Registers
2029 @subsection How Values Fit in Registers
2031 This section discusses the macros that describe which kinds of values
2032 (specifically, which machine modes) each register can hold, and how many
2033 consecutive registers are needed for a given mode.
2035 @defmac HARD_REGNO_NREGS (@var{regno}, @var{mode})
2036 A C expression for the number of consecutive hard registers, starting
2037 at register number @var{regno}, required to hold a value of mode
2038 @var{mode}. This macro must never return zero, even if a register
2039 cannot hold the requested mode - indicate that with HARD_REGNO_MODE_OK
2040 and/or CANNOT_CHANGE_MODE_CLASS instead.
2042 On a machine where all registers are exactly one word, a suitable
2043 definition of this macro is
2046 #define HARD_REGNO_NREGS(REGNO, MODE) \
2047 ((GET_MODE_SIZE (MODE) + UNITS_PER_WORD - 1) \
2052 @defmac HARD_REGNO_NREGS_HAS_PADDING (@var{regno}, @var{mode})
2053 A C expression that is nonzero if a value of mode @var{mode}, stored
2054 in memory, ends with padding that causes it to take up more space than
2055 in registers starting at register number @var{regno} (as determined by
2056 multiplying GCC's notion of the size of the register when containing
2057 this mode by the number of registers returned by
2058 @code{HARD_REGNO_NREGS}). By default this is zero.
2060 For example, if a floating-point value is stored in three 32-bit
2061 registers but takes up 128 bits in memory, then this would be
2064 This macros only needs to be defined if there are cases where
2065 @code{subreg_get_info}
2066 would otherwise wrongly determine that a @code{subreg} can be
2067 represented by an offset to the register number, when in fact such a
2068 @code{subreg} would contain some of the padding not stored in
2069 registers and so not be representable.
2072 @defmac HARD_REGNO_NREGS_WITH_PADDING (@var{regno}, @var{mode})
2073 For values of @var{regno} and @var{mode} for which
2074 @code{HARD_REGNO_NREGS_HAS_PADDING} returns nonzero, a C expression
2075 returning the greater number of registers required to hold the value
2076 including any padding. In the example above, the value would be four.
2079 @defmac REGMODE_NATURAL_SIZE (@var{mode})
2080 Define this macro if the natural size of registers that hold values
2081 of mode @var{mode} is not the word size. It is a C expression that
2082 should give the natural size in bytes for the specified mode. It is
2083 used by the register allocator to try to optimize its results. This
2084 happens for example on SPARC 64-bit where the natural size of
2085 floating-point registers is still 32-bit.
2088 @defmac HARD_REGNO_MODE_OK (@var{regno}, @var{mode})
2089 A C expression that is nonzero if it is permissible to store a value
2090 of mode @var{mode} in hard register number @var{regno} (or in several
2091 registers starting with that one). For a machine where all registers
2092 are equivalent, a suitable definition is
2095 #define HARD_REGNO_MODE_OK(REGNO, MODE) 1
2098 You need not include code to check for the numbers of fixed registers,
2099 because the allocation mechanism considers them to be always occupied.
2101 @cindex register pairs
2102 On some machines, double-precision values must be kept in even/odd
2103 register pairs. You can implement that by defining this macro to reject
2104 odd register numbers for such modes.
2106 The minimum requirement for a mode to be OK in a register is that the
2107 @samp{mov@var{mode}} instruction pattern support moves between the
2108 register and other hard register in the same class and that moving a
2109 value into the register and back out not alter it.
2111 Since the same instruction used to move @code{word_mode} will work for
2112 all narrower integer modes, it is not necessary on any machine for
2113 @code{HARD_REGNO_MODE_OK} to distinguish between these modes, provided
2114 you define patterns @samp{movhi}, etc., to take advantage of this. This
2115 is useful because of the interaction between @code{HARD_REGNO_MODE_OK}
2116 and @code{MODES_TIEABLE_P}; it is very desirable for all integer modes
2119 Many machines have special registers for floating point arithmetic.
2120 Often people assume that floating point machine modes are allowed only
2121 in floating point registers. This is not true. Any registers that
2122 can hold integers can safely @emph{hold} a floating point machine
2123 mode, whether or not floating arithmetic can be done on it in those
2124 registers. Integer move instructions can be used to move the values.
2126 On some machines, though, the converse is true: fixed-point machine
2127 modes may not go in floating registers. This is true if the floating
2128 registers normalize any value stored in them, because storing a
2129 non-floating value there would garble it. In this case,
2130 @code{HARD_REGNO_MODE_OK} should reject fixed-point machine modes in
2131 floating registers. But if the floating registers do not automatically
2132 normalize, if you can store any bit pattern in one and retrieve it
2133 unchanged without a trap, then any machine mode may go in a floating
2134 register, so you can define this macro to say so.
2136 The primary significance of special floating registers is rather that
2137 they are the registers acceptable in floating point arithmetic
2138 instructions. However, this is of no concern to
2139 @code{HARD_REGNO_MODE_OK}. You handle it by writing the proper
2140 constraints for those instructions.
2142 On some machines, the floating registers are especially slow to access,
2143 so that it is better to store a value in a stack frame than in such a
2144 register if floating point arithmetic is not being done. As long as the
2145 floating registers are not in class @code{GENERAL_REGS}, they will not
2146 be used unless some pattern's constraint asks for one.
2149 @defmac HARD_REGNO_RENAME_OK (@var{from}, @var{to})
2150 A C expression that is nonzero if it is OK to rename a hard register
2151 @var{from} to another hard register @var{to}.
2153 One common use of this macro is to prevent renaming of a register to
2154 another register that is not saved by a prologue in an interrupt
2157 The default is always nonzero.
2160 @defmac MODES_TIEABLE_P (@var{mode1}, @var{mode2})
2161 A C expression that is nonzero if a value of mode
2162 @var{mode1} is accessible in mode @var{mode2} without copying.
2164 If @code{HARD_REGNO_MODE_OK (@var{r}, @var{mode1})} and
2165 @code{HARD_REGNO_MODE_OK (@var{r}, @var{mode2})} are always the same for
2166 any @var{r}, then @code{MODES_TIEABLE_P (@var{mode1}, @var{mode2})}
2167 should be nonzero. If they differ for any @var{r}, you should define
2168 this macro to return zero unless some other mechanism ensures the
2169 accessibility of the value in a narrower mode.
2171 You should define this macro to return nonzero in as many cases as
2172 possible since doing so will allow GCC to perform better register
2176 @hook TARGET_HARD_REGNO_SCRATCH_OK
2177 This target hook should return @code{true} if it is OK to use a hard register
2178 @var{regno} as scratch reg in peephole2.
2180 One common use of this macro is to prevent using of a register that
2181 is not saved by a prologue in an interrupt handler.
2183 The default version of this hook always returns @code{true}.
2186 @defmac AVOID_CCMODE_COPIES
2187 Define this macro if the compiler should avoid copies to/from @code{CCmode}
2188 registers. You should only define this macro if support for copying to/from
2189 @code{CCmode} is incomplete.
2192 @node Leaf Functions
2193 @subsection Handling Leaf Functions
2195 @cindex leaf functions
2196 @cindex functions, leaf
2197 On some machines, a leaf function (i.e., one which makes no calls) can run
2198 more efficiently if it does not make its own register window. Often this
2199 means it is required to receive its arguments in the registers where they
2200 are passed by the caller, instead of the registers where they would
2203 The special treatment for leaf functions generally applies only when
2204 other conditions are met; for example, often they may use only those
2205 registers for its own variables and temporaries. We use the term ``leaf
2206 function'' to mean a function that is suitable for this special
2207 handling, so that functions with no calls are not necessarily ``leaf
2210 GCC assigns register numbers before it knows whether the function is
2211 suitable for leaf function treatment. So it needs to renumber the
2212 registers in order to output a leaf function. The following macros
2215 @defmac LEAF_REGISTERS
2216 Name of a char vector, indexed by hard register number, which
2217 contains 1 for a register that is allowable in a candidate for leaf
2220 If leaf function treatment involves renumbering the registers, then the
2221 registers marked here should be the ones before renumbering---those that
2222 GCC would ordinarily allocate. The registers which will actually be
2223 used in the assembler code, after renumbering, should not be marked with 1
2226 Define this macro only if the target machine offers a way to optimize
2227 the treatment of leaf functions.
2230 @defmac LEAF_REG_REMAP (@var{regno})
2231 A C expression whose value is the register number to which @var{regno}
2232 should be renumbered, when a function is treated as a leaf function.
2234 If @var{regno} is a register number which should not appear in a leaf
2235 function before renumbering, then the expression should yield @minus{}1, which
2236 will cause the compiler to abort.
2238 Define this macro only if the target machine offers a way to optimize the
2239 treatment of leaf functions, and registers need to be renumbered to do
2243 @findex current_function_is_leaf
2244 @findex current_function_uses_only_leaf_regs
2245 @code{TARGET_ASM_FUNCTION_PROLOGUE} and
2246 @code{TARGET_ASM_FUNCTION_EPILOGUE} must usually treat leaf functions
2247 specially. They can test the C variable @code{current_function_is_leaf}
2248 which is nonzero for leaf functions. @code{current_function_is_leaf} is
2249 set prior to local register allocation and is valid for the remaining
2250 compiler passes. They can also test the C variable
2251 @code{current_function_uses_only_leaf_regs} which is nonzero for leaf
2252 functions which only use leaf registers.
2253 @code{current_function_uses_only_leaf_regs} is valid after all passes
2254 that modify the instructions have been run and is only useful if
2255 @code{LEAF_REGISTERS} is defined.
2256 @c changed this to fix overfull. ALSO: why the "it" at the beginning
2257 @c of the next paragraph?! --mew 2feb93
2259 @node Stack Registers
2260 @subsection Registers That Form a Stack
2262 There are special features to handle computers where some of the
2263 ``registers'' form a stack. Stack registers are normally written by
2264 pushing onto the stack, and are numbered relative to the top of the
2267 Currently, GCC can only handle one group of stack-like registers, and
2268 they must be consecutively numbered. Furthermore, the existing
2269 support for stack-like registers is specific to the 80387 floating
2270 point coprocessor. If you have a new architecture that uses
2271 stack-like registers, you will need to do substantial work on
2272 @file{reg-stack.c} and write your machine description to cooperate
2273 with it, as well as defining these macros.
2276 Define this if the machine has any stack-like registers.
2279 @defmac STACK_REG_COVER_CLASS
2280 This is a cover class containing the stack registers. Define this if
2281 the machine has any stack-like registers.
2284 @defmac FIRST_STACK_REG
2285 The number of the first stack-like register. This one is the top
2289 @defmac LAST_STACK_REG
2290 The number of the last stack-like register. This one is the bottom of
2294 @node Register Classes
2295 @section Register Classes
2296 @cindex register class definitions
2297 @cindex class definitions, register
2299 On many machines, the numbered registers are not all equivalent.
2300 For example, certain registers may not be allowed for indexed addressing;
2301 certain registers may not be allowed in some instructions. These machine
2302 restrictions are described to the compiler using @dfn{register classes}.
2304 You define a number of register classes, giving each one a name and saying
2305 which of the registers belong to it. Then you can specify register classes
2306 that are allowed as operands to particular instruction patterns.
2310 In general, each register will belong to several classes. In fact, one
2311 class must be named @code{ALL_REGS} and contain all the registers. Another
2312 class must be named @code{NO_REGS} and contain no registers. Often the
2313 union of two classes will be another class; however, this is not required.
2315 @findex GENERAL_REGS
2316 One of the classes must be named @code{GENERAL_REGS}. There is nothing
2317 terribly special about the name, but the operand constraint letters
2318 @samp{r} and @samp{g} specify this class. If @code{GENERAL_REGS} is
2319 the same as @code{ALL_REGS}, just define it as a macro which expands
2322 Order the classes so that if class @var{x} is contained in class @var{y}
2323 then @var{x} has a lower class number than @var{y}.
2325 The way classes other than @code{GENERAL_REGS} are specified in operand
2326 constraints is through machine-dependent operand constraint letters.
2327 You can define such letters to correspond to various classes, then use
2328 them in operand constraints.
2330 You should define a class for the union of two classes whenever some
2331 instruction allows both classes. For example, if an instruction allows
2332 either a floating point (coprocessor) register or a general register for a
2333 certain operand, you should define a class @code{FLOAT_OR_GENERAL_REGS}
2334 which includes both of them. Otherwise you will get suboptimal code.
2336 You must also specify certain redundant information about the register
2337 classes: for each class, which classes contain it and which ones are
2338 contained in it; for each pair of classes, the largest class contained
2341 When a value occupying several consecutive registers is expected in a
2342 certain class, all the registers used must belong to that class.
2343 Therefore, register classes cannot be used to enforce a requirement for
2344 a register pair to start with an even-numbered register. The way to
2345 specify this requirement is with @code{HARD_REGNO_MODE_OK}.
2347 Register classes used for input-operands of bitwise-and or shift
2348 instructions have a special requirement: each such class must have, for
2349 each fixed-point machine mode, a subclass whose registers can transfer that
2350 mode to or from memory. For example, on some machines, the operations for
2351 single-byte values (@code{QImode}) are limited to certain registers. When
2352 this is so, each register class that is used in a bitwise-and or shift
2353 instruction must have a subclass consisting of registers from which
2354 single-byte values can be loaded or stored. This is so that
2355 @code{PREFERRED_RELOAD_CLASS} can always have a possible value to return.
2357 @deftp {Data type} {enum reg_class}
2358 An enumerated type that must be defined with all the register class names
2359 as enumerated values. @code{NO_REGS} must be first. @code{ALL_REGS}
2360 must be the last register class, followed by one more enumerated value,
2361 @code{LIM_REG_CLASSES}, which is not a register class but rather
2362 tells how many classes there are.
2364 Each register class has a number, which is the value of casting
2365 the class name to type @code{int}. The number serves as an index
2366 in many of the tables described below.
2369 @defmac N_REG_CLASSES
2370 The number of distinct register classes, defined as follows:
2373 #define N_REG_CLASSES (int) LIM_REG_CLASSES
2377 @defmac REG_CLASS_NAMES
2378 An initializer containing the names of the register classes as C string
2379 constants. These names are used in writing some of the debugging dumps.
2382 @defmac REG_CLASS_CONTENTS
2383 An initializer containing the contents of the register classes, as integers
2384 which are bit masks. The @var{n}th integer specifies the contents of class
2385 @var{n}. The way the integer @var{mask} is interpreted is that
2386 register @var{r} is in the class if @code{@var{mask} & (1 << @var{r})} is 1.
2388 When the machine has more than 32 registers, an integer does not suffice.
2389 Then the integers are replaced by sub-initializers, braced groupings containing
2390 several integers. Each sub-initializer must be suitable as an initializer
2391 for the type @code{HARD_REG_SET} which is defined in @file{hard-reg-set.h}.
2392 In this situation, the first integer in each sub-initializer corresponds to
2393 registers 0 through 31, the second integer to registers 32 through 63, and
2397 @defmac REGNO_REG_CLASS (@var{regno})
2398 A C expression whose value is a register class containing hard register
2399 @var{regno}. In general there is more than one such class; choose a class
2400 which is @dfn{minimal}, meaning that no smaller class also contains the
2404 @defmac BASE_REG_CLASS
2405 A macro whose definition is the name of the class to which a valid
2406 base register must belong. A base register is one used in an address
2407 which is the register value plus a displacement.
2410 @defmac MODE_BASE_REG_CLASS (@var{mode})
2411 This is a variation of the @code{BASE_REG_CLASS} macro which allows
2412 the selection of a base register in a mode dependent manner. If
2413 @var{mode} is VOIDmode then it should return the same value as
2414 @code{BASE_REG_CLASS}.
2417 @defmac MODE_BASE_REG_REG_CLASS (@var{mode})
2418 A C expression whose value is the register class to which a valid
2419 base register must belong in order to be used in a base plus index
2420 register address. You should define this macro if base plus index
2421 addresses have different requirements than other base register uses.
2424 @defmac MODE_CODE_BASE_REG_CLASS (@var{mode}, @var{outer_code}, @var{index_code})
2425 A C expression whose value is the register class to which a valid
2426 base register must belong. @var{outer_code} and @var{index_code} define the
2427 context in which the base register occurs. @var{outer_code} is the code of
2428 the immediately enclosing expression (@code{MEM} for the top level of an
2429 address, @code{ADDRESS} for something that occurs in an
2430 @code{address_operand}). @var{index_code} is the code of the corresponding
2431 index expression if @var{outer_code} is @code{PLUS}; @code{SCRATCH} otherwise.
2434 @defmac INDEX_REG_CLASS
2435 A macro whose definition is the name of the class to which a valid
2436 index register must belong. An index register is one used in an
2437 address where its value is either multiplied by a scale factor or
2438 added to another register (as well as added to a displacement).
2441 @defmac REGNO_OK_FOR_BASE_P (@var{num})
2442 A C expression which is nonzero if register number @var{num} is
2443 suitable for use as a base register in operand addresses.
2446 @defmac REGNO_MODE_OK_FOR_BASE_P (@var{num}, @var{mode})
2447 A C expression that is just like @code{REGNO_OK_FOR_BASE_P}, except that
2448 that expression may examine the mode of the memory reference in
2449 @var{mode}. You should define this macro if the mode of the memory
2450 reference affects whether a register may be used as a base register. If
2451 you define this macro, the compiler will use it instead of
2452 @code{REGNO_OK_FOR_BASE_P}. The mode may be @code{VOIDmode} for
2453 addresses that appear outside a @code{MEM}, i.e., as an
2454 @code{address_operand}.
2457 @defmac REGNO_MODE_OK_FOR_REG_BASE_P (@var{num}, @var{mode})
2458 A C expression which is nonzero if register number @var{num} is suitable for
2459 use as a base register in base plus index operand addresses, accessing
2460 memory in mode @var{mode}. It may be either a suitable hard register or a
2461 pseudo register that has been allocated such a hard register. You should
2462 define this macro if base plus index addresses have different requirements
2463 than other base register uses.
2465 Use of this macro is deprecated; please use the more general
2466 @code{REGNO_MODE_CODE_OK_FOR_BASE_P}.
2469 @defmac REGNO_MODE_CODE_OK_FOR_BASE_P (@var{num}, @var{mode}, @var{outer_code}, @var{index_code})
2470 A C expression that is just like @code{REGNO_MODE_OK_FOR_BASE_P}, except
2471 that that expression may examine the context in which the register
2472 appears in the memory reference. @var{outer_code} is the code of the
2473 immediately enclosing expression (@code{MEM} if at the top level of the
2474 address, @code{ADDRESS} for something that occurs in an
2475 @code{address_operand}). @var{index_code} is the code of the
2476 corresponding index expression if @var{outer_code} is @code{PLUS};
2477 @code{SCRATCH} otherwise. The mode may be @code{VOIDmode} for addresses
2478 that appear outside a @code{MEM}, i.e., as an @code{address_operand}.
2481 @defmac REGNO_OK_FOR_INDEX_P (@var{num})
2482 A C expression which is nonzero if register number @var{num} is
2483 suitable for use as an index register in operand addresses. It may be
2484 either a suitable hard register or a pseudo register that has been
2485 allocated such a hard register.
2487 The difference between an index register and a base register is that
2488 the index register may be scaled. If an address involves the sum of
2489 two registers, neither one of them scaled, then either one may be
2490 labeled the ``base'' and the other the ``index''; but whichever
2491 labeling is used must fit the machine's constraints of which registers
2492 may serve in each capacity. The compiler will try both labelings,
2493 looking for one that is valid, and will reload one or both registers
2494 only if neither labeling works.
2497 @hook TARGET_PREFERRED_RENAME_CLASS
2499 @hook TARGET_PREFERRED_RELOAD_CLASS
2500 A target hook that places additional restrictions on the register class
2501 to use when it is necessary to copy value @var{x} into a register in class
2502 @var{rclass}. The value is a register class; perhaps @var{rclass}, or perhaps
2503 another, smaller class.
2505 The default version of this hook always returns value of @code{rclass} argument.
2507 Sometimes returning a more restrictive class makes better code. For
2508 example, on the 68000, when @var{x} is an integer constant that is in range
2509 for a @samp{moveq} instruction, the value of this macro is always
2510 @code{DATA_REGS} as long as @var{rclass} includes the data registers.
2511 Requiring a data register guarantees that a @samp{moveq} will be used.
2513 One case where @code{TARGET_PREFERRED_RELOAD_CLASS} must not return
2514 @var{rclass} is if @var{x} is a legitimate constant which cannot be
2515 loaded into some register class. By returning @code{NO_REGS} you can
2516 force @var{x} into a memory location. For example, rs6000 can load
2517 immediate values into general-purpose registers, but does not have an
2518 instruction for loading an immediate value into a floating-point
2519 register, so @code{TARGET_PREFERRED_RELOAD_CLASS} returns @code{NO_REGS} when
2520 @var{x} is a floating-point constant. If the constant can't be loaded
2521 into any kind of register, code generation will be better if
2522 @code{LEGITIMATE_CONSTANT_P} makes the constant illegitimate instead
2523 of using @code{TARGET_PREFERRED_RELOAD_CLASS}.
2525 If an insn has pseudos in it after register allocation, reload will go
2526 through the alternatives and call repeatedly @code{TARGET_PREFERRED_RELOAD_CLASS}
2527 to find the best one. Returning @code{NO_REGS}, in this case, makes
2528 reload add a @code{!} in front of the constraint: the x86 back-end uses
2529 this feature to discourage usage of 387 registers when math is done in
2530 the SSE registers (and vice versa).
2533 @defmac PREFERRED_RELOAD_CLASS (@var{x}, @var{class})
2534 A C expression that places additional restrictions on the register class
2535 to use when it is necessary to copy value @var{x} into a register in class
2536 @var{class}. The value is a register class; perhaps @var{class}, or perhaps
2537 another, smaller class. On many machines, the following definition is
2541 #define PREFERRED_RELOAD_CLASS(X,CLASS) CLASS
2544 Sometimes returning a more restrictive class makes better code. For
2545 example, on the 68000, when @var{x} is an integer constant that is in range
2546 for a @samp{moveq} instruction, the value of this macro is always
2547 @code{DATA_REGS} as long as @var{class} includes the data registers.
2548 Requiring a data register guarantees that a @samp{moveq} will be used.
2550 One case where @code{PREFERRED_RELOAD_CLASS} must not return
2551 @var{class} is if @var{x} is a legitimate constant which cannot be
2552 loaded into some register class. By returning @code{NO_REGS} you can
2553 force @var{x} into a memory location. For example, rs6000 can load
2554 immediate values into general-purpose registers, but does not have an
2555 instruction for loading an immediate value into a floating-point
2556 register, so @code{PREFERRED_RELOAD_CLASS} returns @code{NO_REGS} when
2557 @var{x} is a floating-point constant. If the constant can't be loaded
2558 into any kind of register, code generation will be better if
2559 @code{LEGITIMATE_CONSTANT_P} makes the constant illegitimate instead
2560 of using @code{PREFERRED_RELOAD_CLASS}.
2562 If an insn has pseudos in it after register allocation, reload will go
2563 through the alternatives and call repeatedly @code{PREFERRED_RELOAD_CLASS}
2564 to find the best one. Returning @code{NO_REGS}, in this case, makes
2565 reload add a @code{!} in front of the constraint: the x86 back-end uses
2566 this feature to discourage usage of 387 registers when math is done in
2567 the SSE registers (and vice versa).
2570 @defmac PREFERRED_OUTPUT_RELOAD_CLASS (@var{x}, @var{class})
2571 Like @code{PREFERRED_RELOAD_CLASS}, but for output reloads instead of
2572 input reloads. If you don't define this macro, the default is to use
2573 @var{class}, unchanged.
2575 You can also use @code{PREFERRED_OUTPUT_RELOAD_CLASS} to discourage
2576 reload from using some alternatives, like @code{PREFERRED_RELOAD_CLASS}.
2579 @hook TARGET_PREFERRED_OUTPUT_RELOAD_CLASS
2580 Like @code{TARGET_PREFERRED_RELOAD_CLASS}, but for output reloads instead of
2583 The default version of this hook always returns value of @code{rclass}
2586 You can also use @code{TARGET_PREFERRED_OUTPUT_RELOAD_CLASS} to discourage
2587 reload from using some alternatives, like @code{TARGET_PREFERRED_RELOAD_CLASS}.
2590 @defmac LIMIT_RELOAD_CLASS (@var{mode}, @var{class})
2591 A C expression that places additional restrictions on the register class
2592 to use when it is necessary to be able to hold a value of mode
2593 @var{mode} in a reload register for which class @var{class} would
2596 Unlike @code{PREFERRED_RELOAD_CLASS}, this macro should be used when
2597 there are certain modes that simply can't go in certain reload classes.
2599 The value is a register class; perhaps @var{class}, or perhaps another,
2602 Don't define this macro unless the target machine has limitations which
2603 require the macro to do something nontrivial.
2606 @hook TARGET_SECONDARY_RELOAD
2607 Many machines have some registers that cannot be copied directly to or
2608 from memory or even from other types of registers. An example is the
2609 @samp{MQ} register, which on most machines, can only be copied to or
2610 from general registers, but not memory. Below, we shall be using the
2611 term 'intermediate register' when a move operation cannot be performed
2612 directly, but has to be done by copying the source into the intermediate
2613 register first, and then copying the intermediate register to the
2614 destination. An intermediate register always has the same mode as
2615 source and destination. Since it holds the actual value being copied,
2616 reload might apply optimizations to re-use an intermediate register
2617 and eliding the copy from the source when it can determine that the
2618 intermediate register still holds the required value.
2620 Another kind of secondary reload is required on some machines which
2621 allow copying all registers to and from memory, but require a scratch
2622 register for stores to some memory locations (e.g., those with symbolic
2623 address on the RT, and those with certain symbolic address on the SPARC
2624 when compiling PIC)@. Scratch registers need not have the same mode
2625 as the value being copied, and usually hold a different value than
2626 that being copied. Special patterns in the md file are needed to
2627 describe how the copy is performed with the help of the scratch register;
2628 these patterns also describe the number, register class(es) and mode(s)
2629 of the scratch register(s).
2631 In some cases, both an intermediate and a scratch register are required.
2633 For input reloads, this target hook is called with nonzero @var{in_p},
2634 and @var{x} is an rtx that needs to be copied to a register of class
2635 @var{reload_class} in @var{reload_mode}. For output reloads, this target
2636 hook is called with zero @var{in_p}, and a register of class @var{reload_class}
2637 needs to be copied to rtx @var{x} in @var{reload_mode}.
2639 If copying a register of @var{reload_class} from/to @var{x} requires
2640 an intermediate register, the hook @code{secondary_reload} should
2641 return the register class required for this intermediate register.
2642 If no intermediate register is required, it should return NO_REGS.
2643 If more than one intermediate register is required, describe the one
2644 that is closest in the copy chain to the reload register.
2646 If scratch registers are needed, you also have to describe how to
2647 perform the copy from/to the reload register to/from this
2648 closest intermediate register. Or if no intermediate register is
2649 required, but still a scratch register is needed, describe the
2650 copy from/to the reload register to/from the reload operand @var{x}.
2652 You do this by setting @code{sri->icode} to the instruction code of a pattern
2653 in the md file which performs the move. Operands 0 and 1 are the output
2654 and input of this copy, respectively. Operands from operand 2 onward are
2655 for scratch operands. These scratch operands must have a mode, and a
2656 single-register-class
2657 @c [later: or memory]
2660 When an intermediate register is used, the @code{secondary_reload}
2661 hook will be called again to determine how to copy the intermediate
2662 register to/from the reload operand @var{x}, so your hook must also
2663 have code to handle the register class of the intermediate operand.
2665 @c [For later: maybe we'll allow multi-alternative reload patterns -
2666 @c the port maintainer could name a mov<mode> pattern that has clobbers -
2667 @c and match the constraints of input and output to determine the required
2668 @c alternative. A restriction would be that constraints used to match
2669 @c against reloads registers would have to be written as register class
2670 @c constraints, or we need a new target macro / hook that tells us if an
2671 @c arbitrary constraint can match an unknown register of a given class.
2672 @c Such a macro / hook would also be useful in other places.]
2675 @var{x} might be a pseudo-register or a @code{subreg} of a
2676 pseudo-register, which could either be in a hard register or in memory.
2677 Use @code{true_regnum} to find out; it will return @minus{}1 if the pseudo is
2678 in memory and the hard register number if it is in a register.
2680 Scratch operands in memory (constraint @code{"=m"} / @code{"=&m"}) are
2681 currently not supported. For the time being, you will have to continue
2682 to use @code{SECONDARY_MEMORY_NEEDED} for that purpose.
2684 @code{copy_cost} also uses this target hook to find out how values are
2685 copied. If you want it to include some extra cost for the need to allocate
2686 (a) scratch register(s), set @code{sri->extra_cost} to the additional cost.
2687 Or if two dependent moves are supposed to have a lower cost than the sum
2688 of the individual moves due to expected fortuitous scheduling and/or special
2689 forwarding logic, you can set @code{sri->extra_cost} to a negative amount.
2692 @defmac SECONDARY_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
2693 @defmacx SECONDARY_INPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
2694 @defmacx SECONDARY_OUTPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
2695 These macros are obsolete, new ports should use the target hook
2696 @code{TARGET_SECONDARY_RELOAD} instead.
2698 These are obsolete macros, replaced by the @code{TARGET_SECONDARY_RELOAD}
2699 target hook. Older ports still define these macros to indicate to the
2700 reload phase that it may
2701 need to allocate at least one register for a reload in addition to the
2702 register to contain the data. Specifically, if copying @var{x} to a
2703 register @var{class} in @var{mode} requires an intermediate register,
2704 you were supposed to define @code{SECONDARY_INPUT_RELOAD_CLASS} to return the
2705 largest register class all of whose registers can be used as
2706 intermediate registers or scratch registers.
2708 If copying a register @var{class} in @var{mode} to @var{x} requires an
2709 intermediate or scratch register, @code{SECONDARY_OUTPUT_RELOAD_CLASS}
2710 was supposed to be defined be defined to return the largest register
2711 class required. If the
2712 requirements for input and output reloads were the same, the macro
2713 @code{SECONDARY_RELOAD_CLASS} should have been used instead of defining both
2716 The values returned by these macros are often @code{GENERAL_REGS}.
2717 Return @code{NO_REGS} if no spare register is needed; i.e., if @var{x}
2718 can be directly copied to or from a register of @var{class} in
2719 @var{mode} without requiring a scratch register. Do not define this
2720 macro if it would always return @code{NO_REGS}.
2722 If a scratch register is required (either with or without an
2723 intermediate register), you were supposed to define patterns for
2724 @samp{reload_in@var{m}} or @samp{reload_out@var{m}}, as required
2725 (@pxref{Standard Names}. These patterns, which were normally
2726 implemented with a @code{define_expand}, should be similar to the
2727 @samp{mov@var{m}} patterns, except that operand 2 is the scratch
2730 These patterns need constraints for the reload register and scratch
2732 contain a single register class. If the original reload register (whose
2733 class is @var{class}) can meet the constraint given in the pattern, the
2734 value returned by these macros is used for the class of the scratch
2735 register. Otherwise, two additional reload registers are required.
2736 Their classes are obtained from the constraints in the insn pattern.
2738 @var{x} might be a pseudo-register or a @code{subreg} of a
2739 pseudo-register, which could either be in a hard register or in memory.
2740 Use @code{true_regnum} to find out; it will return @minus{}1 if the pseudo is
2741 in memory and the hard register number if it is in a register.
2743 These macros should not be used in the case where a particular class of
2744 registers can only be copied to memory and not to another class of
2745 registers. In that case, secondary reload registers are not needed and
2746 would not be helpful. Instead, a stack location must be used to perform
2747 the copy and the @code{mov@var{m}} pattern should use memory as an
2748 intermediate storage. This case often occurs between floating-point and
2752 @defmac SECONDARY_MEMORY_NEEDED (@var{class1}, @var{class2}, @var{m})
2753 Certain machines have the property that some registers cannot be copied
2754 to some other registers without using memory. Define this macro on
2755 those machines to be a C expression that is nonzero if objects of mode
2756 @var{m} in registers of @var{class1} can only be copied to registers of
2757 class @var{class2} by storing a register of @var{class1} into memory
2758 and loading that memory location into a register of @var{class2}.
2760 Do not define this macro if its value would always be zero.
2763 @defmac SECONDARY_MEMORY_NEEDED_RTX (@var{mode})
2764 Normally when @code{SECONDARY_MEMORY_NEEDED} is defined, the compiler
2765 allocates a stack slot for a memory location needed for register copies.
2766 If this macro is defined, the compiler instead uses the memory location
2767 defined by this macro.
2769 Do not define this macro if you do not define
2770 @code{SECONDARY_MEMORY_NEEDED}.
2773 @defmac SECONDARY_MEMORY_NEEDED_MODE (@var{mode})
2774 When the compiler needs a secondary memory location to copy between two
2775 registers of mode @var{mode}, it normally allocates sufficient memory to
2776 hold a quantity of @code{BITS_PER_WORD} bits and performs the store and
2777 load operations in a mode that many bits wide and whose class is the
2778 same as that of @var{mode}.
2780 This is right thing to do on most machines because it ensures that all
2781 bits of the register are copied and prevents accesses to the registers
2782 in a narrower mode, which some machines prohibit for floating-point
2785 However, this default behavior is not correct on some machines, such as
2786 the DEC Alpha, that store short integers in floating-point registers
2787 differently than in integer registers. On those machines, the default
2788 widening will not work correctly and you must define this macro to
2789 suppress that widening in some cases. See the file @file{alpha.h} for
2792 Do not define this macro if you do not define
2793 @code{SECONDARY_MEMORY_NEEDED} or if widening @var{mode} to a mode that
2794 is @code{BITS_PER_WORD} bits wide is correct for your machine.
2797 @hook TARGET_CLASS_LIKELY_SPILLED_P
2798 A target hook which returns @code{true} if pseudos that have been assigned
2799 to registers of class @var{rclass} would likely be spilled because
2800 registers of @var{rclass} are needed for spill registers.
2802 The default version of this target hook returns @code{true} if @var{rclass}
2803 has exactly one register and @code{false} otherwise. On most machines, this
2804 default should be used. Only use this target hook to some other expression
2805 if pseudos allocated by @file{local-alloc.c} end up in memory because their
2806 hard registers were needed for spill registers. If this target hook returns
2807 @code{false} for those classes, those pseudos will only be allocated by
2808 @file{global.c}, which knows how to reallocate the pseudo to another
2809 register. If there would not be another register available for reallocation,
2810 you should not change the implementation of this target hook since
2811 the only effect of such implementation would be to slow down register
2815 @defmac CLASS_MAX_NREGS (@var{class}, @var{mode})
2816 A C expression for the maximum number of consecutive registers
2817 of class @var{class} needed to hold a value of mode @var{mode}.
2819 This is closely related to the macro @code{HARD_REGNO_NREGS}. In fact,
2820 the value of the macro @code{CLASS_MAX_NREGS (@var{class}, @var{mode})}
2821 should be the maximum value of @code{HARD_REGNO_NREGS (@var{regno},
2822 @var{mode})} for all @var{regno} values in the class @var{class}.
2824 This macro helps control the handling of multiple-word values
2828 @defmac CANNOT_CHANGE_MODE_CLASS (@var{from}, @var{to}, @var{class})
2829 If defined, a C expression that returns nonzero for a @var{class} for which
2830 a change from mode @var{from} to mode @var{to} is invalid.
2832 For the example, loading 32-bit integer or floating-point objects into
2833 floating-point registers on the Alpha extends them to 64 bits.
2834 Therefore loading a 64-bit object and then storing it as a 32-bit object
2835 does not store the low-order 32 bits, as would be the case for a normal
2836 register. Therefore, @file{alpha.h} defines @code{CANNOT_CHANGE_MODE_CLASS}
2840 #define CANNOT_CHANGE_MODE_CLASS(FROM, TO, CLASS) \
2841 (GET_MODE_SIZE (FROM) != GET_MODE_SIZE (TO) \
2842 ? reg_classes_intersect_p (FLOAT_REGS, (CLASS)) : 0)
2846 @hook TARGET_IRA_COVER_CLASSES
2847 Return an array of cover classes for the Integrated Register Allocator
2848 (@acronym{IRA}). Cover classes are a set of non-intersecting register
2849 classes covering all hard registers used for register allocation
2850 purposes. If a move between two registers in the same cover class is
2851 possible, it should be cheaper than a load or store of the registers.
2852 The array is terminated by a @code{LIM_REG_CLASSES} element.
2854 The order of cover classes in the array is important. If two classes
2855 have the same cost of usage for a pseudo, the class occurred first in
2856 the array is chosen for the pseudo.
2858 This hook is called once at compiler startup, after the command-line
2859 options have been processed. It is then re-examined by every call to
2860 @code{target_reinit}.
2862 The default implementation returns @code{IRA_COVER_CLASSES}, if defined,
2863 otherwise there is no default implementation. You must define either this
2864 macro or @code{IRA_COVER_CLASSES} in order to use the integrated register
2865 allocator with Chaitin-Briggs coloring. If the macro is not defined,
2866 the only available coloring algorithm is Chow's priority coloring.
2868 This hook must not be modified from @code{NULL} to non-@code{NULL} or
2869 vice versa by command-line option processing.
2872 @defmac IRA_COVER_CLASSES
2873 See the documentation for @code{TARGET_IRA_COVER_CLASSES}.
2876 @node Old Constraints
2877 @section Obsolete Macros for Defining Constraints
2878 @cindex defining constraints, obsolete method
2879 @cindex constraints, defining, obsolete method
2881 Machine-specific constraints can be defined with these macros instead
2882 of the machine description constructs described in @ref{Define
2883 Constraints}. This mechanism is obsolete. New ports should not use
2884 it; old ports should convert to the new mechanism.
2886 @defmac CONSTRAINT_LEN (@var{char}, @var{str})
2887 For the constraint at the start of @var{str}, which starts with the letter
2888 @var{c}, return the length. This allows you to have register class /
2889 constant / extra constraints that are longer than a single letter;
2890 you don't need to define this macro if you can do with single-letter
2891 constraints only. The definition of this macro should use
2892 DEFAULT_CONSTRAINT_LEN for all the characters that you don't want
2893 to handle specially.
2894 There are some sanity checks in genoutput.c that check the constraint lengths
2895 for the md file, so you can also use this macro to help you while you are
2896 transitioning from a byzantine single-letter-constraint scheme: when you
2897 return a negative length for a constraint you want to re-use, genoutput
2898 will complain about every instance where it is used in the md file.
2901 @defmac REG_CLASS_FROM_LETTER (@var{char})
2902 A C expression which defines the machine-dependent operand constraint
2903 letters for register classes. If @var{char} is such a letter, the
2904 value should be the register class corresponding to it. Otherwise,
2905 the value should be @code{NO_REGS}. The register letter @samp{r},
2906 corresponding to class @code{GENERAL_REGS}, will not be passed
2907 to this macro; you do not need to handle it.
2910 @defmac REG_CLASS_FROM_CONSTRAINT (@var{char}, @var{str})
2911 Like @code{REG_CLASS_FROM_LETTER}, but you also get the constraint string
2912 passed in @var{str}, so that you can use suffixes to distinguish between
2916 @defmac CONST_OK_FOR_LETTER_P (@var{value}, @var{c})
2917 A C expression that defines the machine-dependent operand constraint
2918 letters (@samp{I}, @samp{J}, @samp{K}, @dots{} @samp{P}) that specify
2919 particular ranges of integer values. If @var{c} is one of those
2920 letters, the expression should check that @var{value}, an integer, is in
2921 the appropriate range and return 1 if so, 0 otherwise. If @var{c} is
2922 not one of those letters, the value should be 0 regardless of
2926 @defmac CONST_OK_FOR_CONSTRAINT_P (@var{value}, @var{c}, @var{str})
2927 Like @code{CONST_OK_FOR_LETTER_P}, but you also get the constraint
2928 string passed in @var{str}, so that you can use suffixes to distinguish
2929 between different variants.
2932 @defmac CONST_DOUBLE_OK_FOR_LETTER_P (@var{value}, @var{c})
2933 A C expression that defines the machine-dependent operand constraint
2934 letters that specify particular ranges of @code{const_double} values
2935 (@samp{G} or @samp{H}).
2937 If @var{c} is one of those letters, the expression should check that
2938 @var{value}, an RTX of code @code{const_double}, is in the appropriate
2939 range and return 1 if so, 0 otherwise. If @var{c} is not one of those
2940 letters, the value should be 0 regardless of @var{value}.
2942 @code{const_double} is used for all floating-point constants and for
2943 @code{DImode} fixed-point constants. A given letter can accept either
2944 or both kinds of values. It can use @code{GET_MODE} to distinguish
2945 between these kinds.
2948 @defmac CONST_DOUBLE_OK_FOR_CONSTRAINT_P (@var{value}, @var{c}, @var{str})
2949 Like @code{CONST_DOUBLE_OK_FOR_LETTER_P}, but you also get the constraint
2950 string passed in @var{str}, so that you can use suffixes to distinguish
2951 between different variants.
2954 @defmac EXTRA_CONSTRAINT (@var{value}, @var{c})
2955 A C expression that defines the optional machine-dependent constraint
2956 letters that can be used to segregate specific types of operands, usually
2957 memory references, for the target machine. Any letter that is not
2958 elsewhere defined and not matched by @code{REG_CLASS_FROM_LETTER} /
2959 @code{REG_CLASS_FROM_CONSTRAINT}
2960 may be used. Normally this macro will not be defined.
2962 If it is required for a particular target machine, it should return 1
2963 if @var{value} corresponds to the operand type represented by the
2964 constraint letter @var{c}. If @var{c} is not defined as an extra
2965 constraint, the value returned should be 0 regardless of @var{value}.
2967 For example, on the ROMP, load instructions cannot have their output
2968 in r0 if the memory reference contains a symbolic address. Constraint
2969 letter @samp{Q} is defined as representing a memory address that does
2970 @emph{not} contain a symbolic address. An alternative is specified with
2971 a @samp{Q} constraint on the input and @samp{r} on the output. The next
2972 alternative specifies @samp{m} on the input and a register class that
2973 does not include r0 on the output.
2976 @defmac EXTRA_CONSTRAINT_STR (@var{value}, @var{c}, @var{str})
2977 Like @code{EXTRA_CONSTRAINT}, but you also get the constraint string passed
2978 in @var{str}, so that you can use suffixes to distinguish between different
2982 @defmac EXTRA_MEMORY_CONSTRAINT (@var{c}, @var{str})
2983 A C expression that defines the optional machine-dependent constraint
2984 letters, amongst those accepted by @code{EXTRA_CONSTRAINT}, that should
2985 be treated like memory constraints by the reload pass.
2987 It should return 1 if the operand type represented by the constraint
2988 at the start of @var{str}, the first letter of which is the letter @var{c},
2989 comprises a subset of all memory references including
2990 all those whose address is simply a base register. This allows the reload
2991 pass to reload an operand, if it does not directly correspond to the operand
2992 type of @var{c}, by copying its address into a base register.
2994 For example, on the S/390, some instructions do not accept arbitrary
2995 memory references, but only those that do not make use of an index
2996 register. The constraint letter @samp{Q} is defined via
2997 @code{EXTRA_CONSTRAINT} as representing a memory address of this type.
2998 If the letter @samp{Q} is marked as @code{EXTRA_MEMORY_CONSTRAINT},
2999 a @samp{Q} constraint can handle any memory operand, because the
3000 reload pass knows it can be reloaded by copying the memory address
3001 into a base register if required. This is analogous to the way
3002 an @samp{o} constraint can handle any memory operand.
3005 @defmac EXTRA_ADDRESS_CONSTRAINT (@var{c}, @var{str})
3006 A C expression that defines the optional machine-dependent constraint
3007 letters, amongst those accepted by @code{EXTRA_CONSTRAINT} /
3008 @code{EXTRA_CONSTRAINT_STR}, that should
3009 be treated like address constraints by the reload pass.
3011 It should return 1 if the operand type represented by the constraint
3012 at the start of @var{str}, which starts with the letter @var{c}, comprises
3013 a subset of all memory addresses including
3014 all those that consist of just a base register. This allows the reload
3015 pass to reload an operand, if it does not directly correspond to the operand
3016 type of @var{str}, by copying it into a base register.
3018 Any constraint marked as @code{EXTRA_ADDRESS_CONSTRAINT} can only
3019 be used with the @code{address_operand} predicate. It is treated
3020 analogously to the @samp{p} constraint.
3023 @node Stack and Calling
3024 @section Stack Layout and Calling Conventions
3025 @cindex calling conventions
3027 @c prevent bad page break with this line
3028 This describes the stack layout and calling conventions.
3032 * Exception Handling::
3037 * Register Arguments::
3039 * Aggregate Return::
3044 * Stack Smashing Protection::
3048 @subsection Basic Stack Layout
3049 @cindex stack frame layout
3050 @cindex frame layout
3052 @c prevent bad page break with this line
3053 Here is the basic stack layout.
3055 @defmac STACK_GROWS_DOWNWARD
3056 Define this macro if pushing a word onto the stack moves the stack
3057 pointer to a smaller address.
3059 When we say, ``define this macro if @dots{}'', it means that the
3060 compiler checks this macro only with @code{#ifdef} so the precise
3061 definition used does not matter.
3064 @defmac STACK_PUSH_CODE
3065 This macro defines the operation used when something is pushed
3066 on the stack. In RTL, a push operation will be
3067 @code{(set (mem (STACK_PUSH_CODE (reg sp))) @dots{})}
3069 The choices are @code{PRE_DEC}, @code{POST_DEC}, @code{PRE_INC},
3070 and @code{POST_INC}. Which of these is correct depends on
3071 the stack direction and on whether the stack pointer points
3072 to the last item on the stack or whether it points to the
3073 space for the next item on the stack.
3075 The default is @code{PRE_DEC} when @code{STACK_GROWS_DOWNWARD} is
3076 defined, which is almost always right, and @code{PRE_INC} otherwise,
3077 which is often wrong.
3080 @defmac FRAME_GROWS_DOWNWARD
3081 Define this macro to nonzero value if the addresses of local variable slots
3082 are at negative offsets from the frame pointer.
3085 @defmac ARGS_GROW_DOWNWARD
3086 Define this macro if successive arguments to a function occupy decreasing
3087 addresses on the stack.
3090 @defmac STARTING_FRAME_OFFSET
3091 Offset from the frame pointer to the first local variable slot to be allocated.
3093 If @code{FRAME_GROWS_DOWNWARD}, find the next slot's offset by
3094 subtracting the first slot's length from @code{STARTING_FRAME_OFFSET}.
3095 Otherwise, it is found by adding the length of the first slot to the
3096 value @code{STARTING_FRAME_OFFSET}.
3097 @c i'm not sure if the above is still correct.. had to change it to get
3098 @c rid of an overfull. --mew 2feb93
3101 @defmac STACK_ALIGNMENT_NEEDED
3102 Define to zero to disable final alignment of the stack during reload.
3103 The nonzero default for this macro is suitable for most ports.
3105 On ports where @code{STARTING_FRAME_OFFSET} is nonzero or where there
3106 is a register save block following the local block that doesn't require
3107 alignment to @code{STACK_BOUNDARY}, it may be beneficial to disable
3108 stack alignment and do it in the backend.
3111 @defmac STACK_POINTER_OFFSET
3112 Offset from the stack pointer register to the first location at which
3113 outgoing arguments are placed. If not specified, the default value of
3114 zero is used. This is the proper value for most machines.
3116 If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above
3117 the first location at which outgoing arguments are placed.
3120 @defmac FIRST_PARM_OFFSET (@var{fundecl})
3121 Offset from the argument pointer register to the first argument's
3122 address. On some machines it may depend on the data type of the
3125 If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above
3126 the first argument's address.
3129 @defmac STACK_DYNAMIC_OFFSET (@var{fundecl})
3130 Offset from the stack pointer register to an item dynamically allocated
3131 on the stack, e.g., by @code{alloca}.
3133 The default value for this macro is @code{STACK_POINTER_OFFSET} plus the
3134 length of the outgoing arguments. The default is correct for most
3135 machines. See @file{function.c} for details.
3138 @defmac INITIAL_FRAME_ADDRESS_RTX
3139 A C expression whose value is RTL representing the address of the initial
3140 stack frame. This address is passed to @code{RETURN_ADDR_RTX} and
3141 @code{DYNAMIC_CHAIN_ADDRESS}. If you don't define this macro, a reasonable
3142 default value will be used. Define this macro in order to make frame pointer
3143 elimination work in the presence of @code{__builtin_frame_address (count)} and
3144 @code{__builtin_return_address (count)} for @code{count} not equal to zero.
3147 @defmac DYNAMIC_CHAIN_ADDRESS (@var{frameaddr})
3148 A C expression whose value is RTL representing the address in a stack
3149 frame where the pointer to the caller's frame is stored. Assume that
3150 @var{frameaddr} is an RTL expression for the address of the stack frame
3153 If you don't define this macro, the default is to return the value
3154 of @var{frameaddr}---that is, the stack frame address is also the
3155 address of the stack word that points to the previous frame.
3158 @defmac SETUP_FRAME_ADDRESSES
3159 If defined, a C expression that produces the machine-specific code to
3160 setup the stack so that arbitrary frames can be accessed. For example,
3161 on the SPARC, we must flush all of the register windows to the stack
3162 before we can access arbitrary stack frames. You will seldom need to
3166 @hook TARGET_BUILTIN_SETJMP_FRAME_VALUE
3167 This target hook should return an rtx that is used to store
3168 the address of the current frame into the built in @code{setjmp} buffer.
3169 The default value, @code{virtual_stack_vars_rtx}, is correct for most
3170 machines. One reason you may need to define this target hook is if
3171 @code{hard_frame_pointer_rtx} is the appropriate value on your machine.
3174 @defmac FRAME_ADDR_RTX (@var{frameaddr})
3175 A C expression whose value is RTL representing the value of the frame
3176 address for the current frame. @var{frameaddr} is the frame pointer
3177 of the current frame. This is used for __builtin_frame_address.
3178 You need only define this macro if the frame address is not the same
3179 as the frame pointer. Most machines do not need to define it.
3182 @defmac RETURN_ADDR_RTX (@var{count}, @var{frameaddr})
3183 A C expression whose value is RTL representing the value of the return
3184 address for the frame @var{count} steps up from the current frame, after
3185 the prologue. @var{frameaddr} is the frame pointer of the @var{count}
3186 frame, or the frame pointer of the @var{count} @minus{} 1 frame if
3187 @code{RETURN_ADDR_IN_PREVIOUS_FRAME} is defined.
3189 The value of the expression must always be the correct address when
3190 @var{count} is zero, but may be @code{NULL_RTX} if there is no way to
3191 determine the return address of other frames.
3194 @defmac RETURN_ADDR_IN_PREVIOUS_FRAME
3195 Define this if the return address of a particular stack frame is accessed
3196 from the frame pointer of the previous stack frame.
3199 @defmac INCOMING_RETURN_ADDR_RTX
3200 A C expression whose value is RTL representing the location of the
3201 incoming return address at the beginning of any function, before the
3202 prologue. This RTL is either a @code{REG}, indicating that the return
3203 value is saved in @samp{REG}, or a @code{MEM} representing a location in
3206 You only need to define this macro if you want to support call frame
3207 debugging information like that provided by DWARF 2.
3209 If this RTL is a @code{REG}, you should also define
3210 @code{DWARF_FRAME_RETURN_COLUMN} to @code{DWARF_FRAME_REGNUM (REGNO)}.
3213 @defmac DWARF_ALT_FRAME_RETURN_COLUMN
3214 A C expression whose value is an integer giving a DWARF 2 column
3215 number that may be used as an alternative return column. The column
3216 must not correspond to any gcc hard register (that is, it must not
3217 be in the range of @code{DWARF_FRAME_REGNUM}).
3219 This macro can be useful if @code{DWARF_FRAME_RETURN_COLUMN} is set to a
3220 general register, but an alternative column needs to be used for signal
3221 frames. Some targets have also used different frame return columns
3225 @defmac DWARF_ZERO_REG
3226 A C expression whose value is an integer giving a DWARF 2 register
3227 number that is considered to always have the value zero. This should
3228 only be defined if the target has an architected zero register, and
3229 someone decided it was a good idea to use that register number to
3230 terminate the stack backtrace. New ports should avoid this.
3233 @hook TARGET_DWARF_HANDLE_FRAME_UNSPEC
3234 This target hook allows the backend to emit frame-related insns that
3235 contain UNSPECs or UNSPEC_VOLATILEs. The DWARF 2 call frame debugging
3236 info engine will invoke it on insns of the form
3238 (set (reg) (unspec [@dots{}] UNSPEC_INDEX))
3242 (set (reg) (unspec_volatile [@dots{}] UNSPECV_INDEX)).
3244 to let the backend emit the call frame instructions. @var{label} is
3245 the CFI label attached to the insn, @var{pattern} is the pattern of
3246 the insn and @var{index} is @code{UNSPEC_INDEX} or @code{UNSPECV_INDEX}.
3249 @defmac INCOMING_FRAME_SP_OFFSET
3250 A C expression whose value is an integer giving the offset, in bytes,
3251 from the value of the stack pointer register to the top of the stack
3252 frame at the beginning of any function, before the prologue. The top of
3253 the frame is defined to be the value of the stack pointer in the
3254 previous frame, just before the call instruction.
3256 You only need to define this macro if you want to support call frame
3257 debugging information like that provided by DWARF 2.
3260 @defmac ARG_POINTER_CFA_OFFSET (@var{fundecl})
3261 A C expression whose value is an integer giving the offset, in bytes,
3262 from the argument pointer to the canonical frame address (cfa). The
3263 final value should coincide with that calculated by
3264 @code{INCOMING_FRAME_SP_OFFSET}. Which is unfortunately not usable
3265 during virtual register instantiation.
3267 The default value for this macro is
3268 @code{FIRST_PARM_OFFSET (fundecl) + crtl->args.pretend_args_size},
3269 which is correct for most machines; in general, the arguments are found
3270 immediately before the stack frame. Note that this is not the case on
3271 some targets that save registers into the caller's frame, such as SPARC
3272 and rs6000, and so such targets need to define this macro.
3274 You only need to define this macro if the default is incorrect, and you
3275 want to support call frame debugging information like that provided by
3279 @defmac FRAME_POINTER_CFA_OFFSET (@var{fundecl})
3280 If defined, a C expression whose value is an integer giving the offset
3281 in bytes from the frame pointer to the canonical frame address (cfa).
3282 The final value should coincide with that calculated by
3283 @code{INCOMING_FRAME_SP_OFFSET}.
3285 Normally the CFA is calculated as an offset from the argument pointer,
3286 via @code{ARG_POINTER_CFA_OFFSET}, but if the argument pointer is
3287 variable due to the ABI, this may not be possible. If this macro is
3288 defined, it implies that the virtual register instantiation should be
3289 based on the frame pointer instead of the argument pointer. Only one
3290 of @code{FRAME_POINTER_CFA_OFFSET} and @code{ARG_POINTER_CFA_OFFSET}
3294 @defmac CFA_FRAME_BASE_OFFSET (@var{fundecl})
3295 If defined, a C expression whose value is an integer giving the offset
3296 in bytes from the canonical frame address (cfa) to the frame base used
3297 in DWARF 2 debug information. The default is zero. A different value
3298 may reduce the size of debug information on some ports.
3301 @node Exception Handling
3302 @subsection Exception Handling Support
3303 @cindex exception handling
3305 @defmac EH_RETURN_DATA_REGNO (@var{N})
3306 A C expression whose value is the @var{N}th register number used for
3307 data by exception handlers, or @code{INVALID_REGNUM} if fewer than
3308 @var{N} registers are usable.
3310 The exception handling library routines communicate with the exception
3311 handlers via a set of agreed upon registers. Ideally these registers
3312 should be call-clobbered; it is possible to use call-saved registers,
3313 but may negatively impact code size. The target must support at least
3314 2 data registers, but should define 4 if there are enough free registers.
3316 You must define this macro if you want to support call frame exception
3317 handling like that provided by DWARF 2.
3320 @defmac EH_RETURN_STACKADJ_RTX
3321 A C expression whose value is RTL representing a location in which
3322 to store a stack adjustment to be applied before function return.
3323 This is used to unwind the stack to an exception handler's call frame.
3324 It will be assigned zero on code paths that return normally.
3326 Typically this is a call-clobbered hard register that is otherwise
3327 untouched by the epilogue, but could also be a stack slot.
3329 Do not define this macro if the stack pointer is saved and restored
3330 by the regular prolog and epilog code in the call frame itself; in
3331 this case, the exception handling library routines will update the
3332 stack location to be restored in place. Otherwise, you must define
3333 this macro if you want to support call frame exception handling like
3334 that provided by DWARF 2.
3337 @defmac EH_RETURN_HANDLER_RTX
3338 A C expression whose value is RTL representing a location in which
3339 to store the address of an exception handler to which we should
3340 return. It will not be assigned on code paths that return normally.
3342 Typically this is the location in the call frame at which the normal
3343 return address is stored. For targets that return by popping an
3344 address off the stack, this might be a memory address just below
3345 the @emph{target} call frame rather than inside the current call
3346 frame. If defined, @code{EH_RETURN_STACKADJ_RTX} will have already
3347 been assigned, so it may be used to calculate the location of the
3350 Some targets have more complex requirements than storing to an
3351 address calculable during initial code generation. In that case
3352 the @code{eh_return} instruction pattern should be used instead.
3354 If you want to support call frame exception handling, you must
3355 define either this macro or the @code{eh_return} instruction pattern.
3358 @defmac RETURN_ADDR_OFFSET
3359 If defined, an integer-valued C expression for which rtl will be generated
3360 to add it to the exception handler address before it is searched in the
3361 exception handling tables, and to subtract it again from the address before
3362 using it to return to the exception handler.
3365 @defmac ASM_PREFERRED_EH_DATA_FORMAT (@var{code}, @var{global})
3366 This macro chooses the encoding of pointers embedded in the exception
3367 handling sections. If at all possible, this should be defined such
3368 that the exception handling section will not require dynamic relocations,
3369 and so may be read-only.
3371 @var{code} is 0 for data, 1 for code labels, 2 for function pointers.
3372 @var{global} is true if the symbol may be affected by dynamic relocations.
3373 The macro should return a combination of the @code{DW_EH_PE_*} defines
3374 as found in @file{dwarf2.h}.
3376 If this macro is not defined, pointers will not be encoded but
3377 represented directly.
3380 @defmac ASM_MAYBE_OUTPUT_ENCODED_ADDR_RTX (@var{file}, @var{encoding}, @var{size}, @var{addr}, @var{done})
3381 This macro allows the target to emit whatever special magic is required
3382 to represent the encoding chosen by @code{ASM_PREFERRED_EH_DATA_FORMAT}.
3383 Generic code takes care of pc-relative and indirect encodings; this must
3384 be defined if the target uses text-relative or data-relative encodings.
3386 This is a C statement that branches to @var{done} if the format was
3387 handled. @var{encoding} is the format chosen, @var{size} is the number
3388 of bytes that the format occupies, @var{addr} is the @code{SYMBOL_REF}
3392 @defmac MD_UNWIND_SUPPORT
3393 A string specifying a file to be #include'd in unwind-dw2.c. The file
3394 so included typically defines @code{MD_FALLBACK_FRAME_STATE_FOR}.
3397 @defmac MD_FALLBACK_FRAME_STATE_FOR (@var{context}, @var{fs})
3398 This macro allows the target to add CPU and operating system specific
3399 code to the call-frame unwinder for use when there is no unwind data
3400 available. The most common reason to implement this macro is to unwind
3401 through signal frames.
3403 This macro is called from @code{uw_frame_state_for} in
3404 @file{unwind-dw2.c}, @file{unwind-dw2-xtensa.c} and
3405 @file{unwind-ia64.c}. @var{context} is an @code{_Unwind_Context};
3406 @var{fs} is an @code{_Unwind_FrameState}. Examine @code{context->ra}
3407 for the address of the code being executed and @code{context->cfa} for
3408 the stack pointer value. If the frame can be decoded, the register
3409 save addresses should be updated in @var{fs} and the macro should
3410 evaluate to @code{_URC_NO_REASON}. If the frame cannot be decoded,
3411 the macro should evaluate to @code{_URC_END_OF_STACK}.
3413 For proper signal handling in Java this macro is accompanied by
3414 @code{MAKE_THROW_FRAME}, defined in @file{libjava/include/*-signal.h} headers.
3417 @defmac MD_HANDLE_UNWABI (@var{context}, @var{fs})
3418 This macro allows the target to add operating system specific code to the
3419 call-frame unwinder to handle the IA-64 @code{.unwabi} unwinding directive,
3420 usually used for signal or interrupt frames.
3422 This macro is called from @code{uw_update_context} in @file{unwind-ia64.c}.
3423 @var{context} is an @code{_Unwind_Context};
3424 @var{fs} is an @code{_Unwind_FrameState}. Examine @code{fs->unwabi}
3425 for the abi and context in the @code{.unwabi} directive. If the
3426 @code{.unwabi} directive can be handled, the register save addresses should
3427 be updated in @var{fs}.
3430 @defmac TARGET_USES_WEAK_UNWIND_INFO
3431 A C expression that evaluates to true if the target requires unwind
3432 info to be given comdat linkage. Define it to be @code{1} if comdat
3433 linkage is necessary. The default is @code{0}.
3436 @node Stack Checking
3437 @subsection Specifying How Stack Checking is Done
3439 GCC will check that stack references are within the boundaries of the
3440 stack, if the option @option{-fstack-check} is specified, in one of
3445 If the value of the @code{STACK_CHECK_BUILTIN} macro is nonzero, GCC
3446 will assume that you have arranged for full stack checking to be done
3447 at appropriate places in the configuration files. GCC will not do
3448 other special processing.
3451 If @code{STACK_CHECK_BUILTIN} is zero and the value of the
3452 @code{STACK_CHECK_STATIC_BUILTIN} macro is nonzero, GCC will assume
3453 that you have arranged for static stack checking (checking of the
3454 static stack frame of functions) to be done at appropriate places
3455 in the configuration files. GCC will only emit code to do dynamic
3456 stack checking (checking on dynamic stack allocations) using the third
3460 If neither of the above are true, GCC will generate code to periodically
3461 ``probe'' the stack pointer using the values of the macros defined below.
3464 If neither STACK_CHECK_BUILTIN nor STACK_CHECK_STATIC_BUILTIN is defined,
3465 GCC will change its allocation strategy for large objects if the option
3466 @option{-fstack-check} is specified: they will always be allocated
3467 dynamically if their size exceeds @code{STACK_CHECK_MAX_VAR_SIZE} bytes.
3469 @defmac STACK_CHECK_BUILTIN
3470 A nonzero value if stack checking is done by the configuration files in a
3471 machine-dependent manner. You should define this macro if stack checking
3472 is required by the ABI of your machine or if you would like to do stack
3473 checking in some more efficient way than the generic approach. The default
3474 value of this macro is zero.
3477 @defmac STACK_CHECK_STATIC_BUILTIN
3478 A nonzero value if static stack checking is done by the configuration files
3479 in a machine-dependent manner. You should define this macro if you would
3480 like to do static stack checking in some more efficient way than the generic
3481 approach. The default value of this macro is zero.
3484 @defmac STACK_CHECK_PROBE_INTERVAL_EXP
3485 An integer specifying the interval at which GCC must generate stack probe
3486 instructions, defined as 2 raised to this integer. You will normally
3487 define this macro so that the interval be no larger than the size of
3488 the ``guard pages'' at the end of a stack area. The default value
3489 of 12 (4096-byte interval) is suitable for most systems.
3492 @defmac STACK_CHECK_MOVING_SP
3493 An integer which is nonzero if GCC should move the stack pointer page by page
3494 when doing probes. This can be necessary on systems where the stack pointer
3495 contains the bottom address of the memory area accessible to the executing
3496 thread at any point in time. In this situation an alternate signal stack
3497 is required in order to be able to recover from a stack overflow. The
3498 default value of this macro is zero.
3501 @defmac STACK_CHECK_PROTECT
3502 The number of bytes of stack needed to recover from a stack overflow, for
3503 languages where such a recovery is supported. The default value of 75 words
3504 with the @code{setjmp}/@code{longjmp}-based exception handling mechanism and
3505 8192 bytes with other exception handling mechanisms should be adequate for
3509 The following macros are relevant only if neither STACK_CHECK_BUILTIN
3510 nor STACK_CHECK_STATIC_BUILTIN is defined; you can omit them altogether
3511 in the opposite case.
3513 @defmac STACK_CHECK_MAX_FRAME_SIZE
3514 The maximum size of a stack frame, in bytes. GCC will generate probe
3515 instructions in non-leaf functions to ensure at least this many bytes of
3516 stack are available. If a stack frame is larger than this size, stack
3517 checking will not be reliable and GCC will issue a warning. The
3518 default is chosen so that GCC only generates one instruction on most
3519 systems. You should normally not change the default value of this macro.
3522 @defmac STACK_CHECK_FIXED_FRAME_SIZE
3523 GCC uses this value to generate the above warning message. It
3524 represents the amount of fixed frame used by a function, not including
3525 space for any callee-saved registers, temporaries and user variables.
3526 You need only specify an upper bound for this amount and will normally
3527 use the default of four words.
3530 @defmac STACK_CHECK_MAX_VAR_SIZE
3531 The maximum size, in bytes, of an object that GCC will place in the
3532 fixed area of the stack frame when the user specifies
3533 @option{-fstack-check}.
3534 GCC computed the default from the values of the above macros and you will
3535 normally not need to override that default.
3539 @node Frame Registers
3540 @subsection Registers That Address the Stack Frame
3542 @c prevent bad page break with this line
3543 This discusses registers that address the stack frame.
3545 @defmac STACK_POINTER_REGNUM
3546 The register number of the stack pointer register, which must also be a
3547 fixed register according to @code{FIXED_REGISTERS}. On most machines,
3548 the hardware determines which register this is.
3551 @defmac FRAME_POINTER_REGNUM
3552 The register number of the frame pointer register, which is used to
3553 access automatic variables in the stack frame. On some machines, the
3554 hardware determines which register this is. On other machines, you can
3555 choose any register you wish for this purpose.
3558 @defmac HARD_FRAME_POINTER_REGNUM
3559 On some machines the offset between the frame pointer and starting
3560 offset of the automatic variables is not known until after register
3561 allocation has been done (for example, because the saved registers are
3562 between these two locations). On those machines, define
3563 @code{FRAME_POINTER_REGNUM} the number of a special, fixed register to
3564 be used internally until the offset is known, and define
3565 @code{HARD_FRAME_POINTER_REGNUM} to be the actual hard register number
3566 used for the frame pointer.
3568 You should define this macro only in the very rare circumstances when it
3569 is not possible to calculate the offset between the frame pointer and
3570 the automatic variables until after register allocation has been
3571 completed. When this macro is defined, you must also indicate in your
3572 definition of @code{ELIMINABLE_REGS} how to eliminate
3573 @code{FRAME_POINTER_REGNUM} into either @code{HARD_FRAME_POINTER_REGNUM}
3574 or @code{STACK_POINTER_REGNUM}.
3576 Do not define this macro if it would be the same as
3577 @code{FRAME_POINTER_REGNUM}.
3580 @defmac ARG_POINTER_REGNUM
3581 The register number of the arg pointer register, which is used to access
3582 the function's argument list. On some machines, this is the same as the
3583 frame pointer register. On some machines, the hardware determines which
3584 register this is. On other machines, you can choose any register you
3585 wish for this purpose. If this is not the same register as the frame
3586 pointer register, then you must mark it as a fixed register according to
3587 @code{FIXED_REGISTERS}, or arrange to be able to eliminate it
3588 (@pxref{Elimination}).
3591 @defmac HARD_FRAME_POINTER_IS_FRAME_POINTER
3592 Define this to a preprocessor constant that is nonzero if
3593 @code{hard_frame_pointer_rtx} and @code{frame_pointer_rtx} should be
3594 the same. The default definition is @samp{(HARD_FRAME_POINTER_REGNUM
3595 == FRAME_POINTER_REGNUM)}; you only need to define this macro if that
3596 definition is not suitable for use in preprocessor conditionals.
3599 @defmac HARD_FRAME_POINTER_IS_ARG_POINTER
3600 Define this to a preprocessor constant that is nonzero if
3601 @code{hard_frame_pointer_rtx} and @code{arg_pointer_rtx} should be the
3602 same. The default definition is @samp{(HARD_FRAME_POINTER_REGNUM ==
3603 ARG_POINTER_REGNUM)}; you only need to define this macro if that
3604 definition is not suitable for use in preprocessor conditionals.
3607 @defmac RETURN_ADDRESS_POINTER_REGNUM
3608 The register number of the return address pointer register, which is used to
3609 access the current function's return address from the stack. On some
3610 machines, the return address is not at a fixed offset from the frame
3611 pointer or stack pointer or argument pointer. This register can be defined
3612 to point to the return address on the stack, and then be converted by
3613 @code{ELIMINABLE_REGS} into either the frame pointer or stack pointer.
3615 Do not define this macro unless there is no other way to get the return
3616 address from the stack.
3619 @defmac STATIC_CHAIN_REGNUM
3620 @defmacx STATIC_CHAIN_INCOMING_REGNUM
3621 Register numbers used for passing a function's static chain pointer. If
3622 register windows are used, the register number as seen by the called
3623 function is @code{STATIC_CHAIN_INCOMING_REGNUM}, while the register
3624 number as seen by the calling function is @code{STATIC_CHAIN_REGNUM}. If
3625 these registers are the same, @code{STATIC_CHAIN_INCOMING_REGNUM} need
3628 The static chain register need not be a fixed register.
3630 If the static chain is passed in memory, these macros should not be
3631 defined; instead, the @code{TARGET_STATIC_CHAIN} hook should be used.
3634 @hook TARGET_STATIC_CHAIN
3635 This hook replaces the use of @code{STATIC_CHAIN_REGNUM} et al for
3636 targets that may use different static chain locations for different
3637 nested functions. This may be required if the target has function
3638 attributes that affect the calling conventions of the function and
3639 those calling conventions use different static chain locations.
3641 The default version of this hook uses @code{STATIC_CHAIN_REGNUM} et al.
3643 If the static chain is passed in memory, this hook should be used to
3644 provide rtx giving @code{mem} expressions that denote where they are stored.
3645 Often the @code{mem} expression as seen by the caller will be at an offset
3646 from the stack pointer and the @code{mem} expression as seen by the callee
3647 will be at an offset from the frame pointer.
3648 @findex stack_pointer_rtx
3649 @findex frame_pointer_rtx
3650 @findex arg_pointer_rtx
3651 The variables @code{stack_pointer_rtx}, @code{frame_pointer_rtx}, and
3652 @code{arg_pointer_rtx} will have been initialized and should be used
3653 to refer to those items.
3656 @defmac DWARF_FRAME_REGISTERS
3657 This macro specifies the maximum number of hard registers that can be
3658 saved in a call frame. This is used to size data structures used in
3659 DWARF2 exception handling.
3661 Prior to GCC 3.0, this macro was needed in order to establish a stable
3662 exception handling ABI in the face of adding new hard registers for ISA
3663 extensions. In GCC 3.0 and later, the EH ABI is insulated from changes
3664 in the number of hard registers. Nevertheless, this macro can still be
3665 used to reduce the runtime memory requirements of the exception handling
3666 routines, which can be substantial if the ISA contains a lot of
3667 registers that are not call-saved.
3669 If this macro is not defined, it defaults to
3670 @code{FIRST_PSEUDO_REGISTER}.
3673 @defmac PRE_GCC3_DWARF_FRAME_REGISTERS
3675 This macro is similar to @code{DWARF_FRAME_REGISTERS}, but is provided
3676 for backward compatibility in pre GCC 3.0 compiled code.
3678 If this macro is not defined, it defaults to
3679 @code{DWARF_FRAME_REGISTERS}.
3682 @defmac DWARF_REG_TO_UNWIND_COLUMN (@var{regno})
3684 Define this macro if the target's representation for dwarf registers
3685 is different than the internal representation for unwind column.
3686 Given a dwarf register, this macro should return the internal unwind
3687 column number to use instead.
3689 See the PowerPC's SPE target for an example.
3692 @defmac DWARF_FRAME_REGNUM (@var{regno})
3694 Define this macro if the target's representation for dwarf registers
3695 used in .eh_frame or .debug_frame is different from that used in other
3696 debug info sections. Given a GCC hard register number, this macro
3697 should return the .eh_frame register number. The default is
3698 @code{DBX_REGISTER_NUMBER (@var{regno})}.
3702 @defmac DWARF2_FRAME_REG_OUT (@var{regno}, @var{for_eh})
3704 Define this macro to map register numbers held in the call frame info
3705 that GCC has collected using @code{DWARF_FRAME_REGNUM} to those that
3706 should be output in .debug_frame (@code{@var{for_eh}} is zero) and
3707 .eh_frame (@code{@var{for_eh}} is nonzero). The default is to
3708 return @code{@var{regno}}.
3713 @subsection Eliminating Frame Pointer and Arg Pointer
3715 @c prevent bad page break with this line
3716 This is about eliminating the frame pointer and arg pointer.
3718 @hook TARGET_FRAME_POINTER_REQUIRED
3719 This target hook should return @code{true} if a function must have and use
3720 a frame pointer. This target hook is called in the reload pass. If its return
3721 value is @code{true} the function will have a frame pointer.
3723 This target hook can in principle examine the current function and decide
3724 according to the facts, but on most machines the constant @code{false} or the
3725 constant @code{true} suffices. Use @code{false} when the machine allows code
3726 to be generated with no frame pointer, and doing so saves some time or space.
3727 Use @code{true} when there is no possible advantage to avoiding a frame
3730 In certain cases, the compiler does not know how to produce valid code
3731 without a frame pointer. The compiler recognizes those cases and
3732 automatically gives the function a frame pointer regardless of what
3733 @code{TARGET_FRAME_POINTER_REQUIRED} returns. You don't need to worry about
3736 In a function that does not require a frame pointer, the frame pointer
3737 register can be allocated for ordinary usage, unless you mark it as a
3738 fixed register. See @code{FIXED_REGISTERS} for more information.
3740 Default return value is @code{false}.
3743 @findex get_frame_size
3744 @defmac INITIAL_FRAME_POINTER_OFFSET (@var{depth-var})
3745 A C statement to store in the variable @var{depth-var} the difference
3746 between the frame pointer and the stack pointer values immediately after
3747 the function prologue. The value would be computed from information
3748 such as the result of @code{get_frame_size ()} and the tables of
3749 registers @code{regs_ever_live} and @code{call_used_regs}.
3751 If @code{ELIMINABLE_REGS} is defined, this macro will be not be used and
3752 need not be defined. Otherwise, it must be defined even if
3753 @code{TARGET_FRAME_POINTER_REQUIRED} always returns true; in that
3754 case, you may set @var{depth-var} to anything.
3757 @defmac ELIMINABLE_REGS
3758 If defined, this macro specifies a table of register pairs used to
3759 eliminate unneeded registers that point into the stack frame. If it is not
3760 defined, the only elimination attempted by the compiler is to replace
3761 references to the frame pointer with references to the stack pointer.
3763 The definition of this macro is a list of structure initializations, each
3764 of which specifies an original and replacement register.
3766 On some machines, the position of the argument pointer is not known until
3767 the compilation is completed. In such a case, a separate hard register
3768 must be used for the argument pointer. This register can be eliminated by
3769 replacing it with either the frame pointer or the argument pointer,
3770 depending on whether or not the frame pointer has been eliminated.
3772 In this case, you might specify:
3774 #define ELIMINABLE_REGS \
3775 @{@{ARG_POINTER_REGNUM, STACK_POINTER_REGNUM@}, \
3776 @{ARG_POINTER_REGNUM, FRAME_POINTER_REGNUM@}, \
3777 @{FRAME_POINTER_REGNUM, STACK_POINTER_REGNUM@}@}
3780 Note that the elimination of the argument pointer with the stack pointer is
3781 specified first since that is the preferred elimination.
3784 @hook TARGET_CAN_ELIMINATE
3785 This target hook should returns @code{true} if the compiler is allowed to
3786 try to replace register number @var{from_reg} with register number
3787 @var{to_reg}. This target hook need only be defined if @code{ELIMINABLE_REGS}
3788 is defined, and will usually be @code{true}, since most of the cases
3789 preventing register elimination are things that the compiler already
3792 Default return value is @code{true}.
3795 @defmac INITIAL_ELIMINATION_OFFSET (@var{from-reg}, @var{to-reg}, @var{offset-var})
3796 This macro is similar to @code{INITIAL_FRAME_POINTER_OFFSET}. It
3797 specifies the initial difference between the specified pair of
3798 registers. This macro must be defined if @code{ELIMINABLE_REGS} is
3802 @node Stack Arguments
3803 @subsection Passing Function Arguments on the Stack
3804 @cindex arguments on stack
3805 @cindex stack arguments
3807 The macros in this section control how arguments are passed
3808 on the stack. See the following section for other macros that
3809 control passing certain arguments in registers.
3811 @hook TARGET_PROMOTE_PROTOTYPES
3812 This target hook returns @code{true} if an argument declared in a
3813 prototype as an integral type smaller than @code{int} should actually be
3814 passed as an @code{int}. In addition to avoiding errors in certain
3815 cases of mismatch, it also makes for better code on certain machines.
3816 The default is to not promote prototypes.
3820 A C expression. If nonzero, push insns will be used to pass
3822 If the target machine does not have a push instruction, set it to zero.
3823 That directs GCC to use an alternate strategy: to
3824 allocate the entire argument block and then store the arguments into
3825 it. When @code{PUSH_ARGS} is nonzero, @code{PUSH_ROUNDING} must be defined too.
3828 @defmac PUSH_ARGS_REVERSED
3829 A C expression. If nonzero, function arguments will be evaluated from
3830 last to first, rather than from first to last. If this macro is not
3831 defined, it defaults to @code{PUSH_ARGS} on targets where the stack
3832 and args grow in opposite directions, and 0 otherwise.
3835 @defmac PUSH_ROUNDING (@var{npushed})
3836 A C expression that is the number of bytes actually pushed onto the
3837 stack when an instruction attempts to push @var{npushed} bytes.
3839 On some machines, the definition
3842 #define PUSH_ROUNDING(BYTES) (BYTES)
3846 will suffice. But on other machines, instructions that appear
3847 to push one byte actually push two bytes in an attempt to maintain
3848 alignment. Then the definition should be
3851 #define PUSH_ROUNDING(BYTES) (((BYTES) + 1) & ~1)
3854 If the value of this macro has a type, it should be an unsigned type.
3857 @findex current_function_outgoing_args_size
3858 @defmac ACCUMULATE_OUTGOING_ARGS
3859 A C expression. If nonzero, the maximum amount of space required for outgoing arguments
3860 will be computed and placed into the variable
3861 @code{current_function_outgoing_args_size}. No space will be pushed
3862 onto the stack for each call; instead, the function prologue should
3863 increase the stack frame size by this amount.
3865 Setting both @code{PUSH_ARGS} and @code{ACCUMULATE_OUTGOING_ARGS}
3869 @defmac REG_PARM_STACK_SPACE (@var{fndecl})
3870 Define this macro if functions should assume that stack space has been
3871 allocated for arguments even when their values are passed in
3874 The value of this macro is the size, in bytes, of the area reserved for
3875 arguments passed in registers for the function represented by @var{fndecl},
3876 which can be zero if GCC is calling a library function.
3877 The argument @var{fndecl} can be the FUNCTION_DECL, or the type itself
3880 This space can be allocated by the caller, or be a part of the
3881 machine-dependent stack frame: @code{OUTGOING_REG_PARM_STACK_SPACE} says
3884 @c above is overfull. not sure what to do. --mew 5feb93 did
3885 @c something, not sure if it looks good. --mew 10feb93
3887 @defmac OUTGOING_REG_PARM_STACK_SPACE (@var{fntype})
3888 Define this to a nonzero value if it is the responsibility of the
3889 caller to allocate the area reserved for arguments passed in registers
3890 when calling a function of @var{fntype}. @var{fntype} may be NULL
3891 if the function called is a library function.
3893 If @code{ACCUMULATE_OUTGOING_ARGS} is defined, this macro controls
3894 whether the space for these arguments counts in the value of
3895 @code{current_function_outgoing_args_size}.
3898 @defmac STACK_PARMS_IN_REG_PARM_AREA
3899 Define this macro if @code{REG_PARM_STACK_SPACE} is defined, but the
3900 stack parameters don't skip the area specified by it.
3901 @c i changed this, makes more sens and it should have taken care of the
3902 @c overfull.. not as specific, tho. --mew 5feb93
3904 Normally, when a parameter is not passed in registers, it is placed on the
3905 stack beyond the @code{REG_PARM_STACK_SPACE} area. Defining this macro
3906 suppresses this behavior and causes the parameter to be passed on the
3907 stack in its natural location.
3910 @hook TARGET_RETURN_POPS_ARGS
3911 This target hook returns the number of bytes of its own arguments that
3912 a function pops on returning, or 0 if the function pops no arguments
3913 and the caller must therefore pop them all after the function returns.
3915 @var{fundecl} is a C variable whose value is a tree node that describes
3916 the function in question. Normally it is a node of type
3917 @code{FUNCTION_DECL} that describes the declaration of the function.
3918 From this you can obtain the @code{DECL_ATTRIBUTES} of the function.
3920 @var{funtype} is a C variable whose value is a tree node that
3921 describes the function in question. Normally it is a node of type
3922 @code{FUNCTION_TYPE} that describes the data type of the function.
3923 From this it is possible to obtain the data types of the value and
3924 arguments (if known).
3926 When a call to a library function is being considered, @var{fundecl}
3927 will contain an identifier node for the library function. Thus, if
3928 you need to distinguish among various library functions, you can do so
3929 by their names. Note that ``library function'' in this context means
3930 a function used to perform arithmetic, whose name is known specially
3931 in the compiler and was not mentioned in the C code being compiled.
3933 @var{size} is the number of bytes of arguments passed on the
3934 stack. If a variable number of bytes is passed, it is zero, and
3935 argument popping will always be the responsibility of the calling function.
3937 On the VAX, all functions always pop their arguments, so the definition
3938 of this macro is @var{size}. On the 68000, using the standard
3939 calling convention, no functions pop their arguments, so the value of
3940 the macro is always 0 in this case. But an alternative calling
3941 convention is available in which functions that take a fixed number of
3942 arguments pop them but other functions (such as @code{printf}) pop
3943 nothing (the caller pops all). When this convention is in use,
3944 @var{funtype} is examined to determine whether a function takes a fixed
3945 number of arguments.
3948 @defmac CALL_POPS_ARGS (@var{cum})
3949 A C expression that should indicate the number of bytes a call sequence
3950 pops off the stack. It is added to the value of @code{RETURN_POPS_ARGS}
3951 when compiling a function call.
3953 @var{cum} is the variable in which all arguments to the called function
3954 have been accumulated.
3956 On certain architectures, such as the SH5, a call trampoline is used
3957 that pops certain registers off the stack, depending on the arguments
3958 that have been passed to the function. Since this is a property of the
3959 call site, not of the called function, @code{RETURN_POPS_ARGS} is not
3963 @node Register Arguments
3964 @subsection Passing Arguments in Registers
3965 @cindex arguments in registers
3966 @cindex registers arguments
3968 This section describes the macros which let you control how various
3969 types of arguments are passed in registers or how they are arranged in
3972 @defmac FUNCTION_ARG (@var{cum}, @var{mode}, @var{type}, @var{named})
3973 A C expression that controls whether a function argument is passed
3974 in a register, and which register.
3976 The arguments are @var{cum}, which summarizes all the previous
3977 arguments; @var{mode}, the machine mode of the argument; @var{type},
3978 the data type of the argument as a tree node or 0 if that is not known
3979 (which happens for C support library functions); and @var{named},
3980 which is 1 for an ordinary argument and 0 for nameless arguments that
3981 correspond to @samp{@dots{}} in the called function's prototype.
3982 @var{type} can be an incomplete type if a syntax error has previously
3985 The value of the expression is usually either a @code{reg} RTX for the
3986 hard register in which to pass the argument, or zero to pass the
3987 argument on the stack.
3989 For machines like the VAX and 68000, where normally all arguments are
3990 pushed, zero suffices as a definition.
3992 The value of the expression can also be a @code{parallel} RTX@. This is
3993 used when an argument is passed in multiple locations. The mode of the
3994 @code{parallel} should be the mode of the entire argument. The
3995 @code{parallel} holds any number of @code{expr_list} pairs; each one
3996 describes where part of the argument is passed. In each
3997 @code{expr_list} the first operand must be a @code{reg} RTX for the hard
3998 register in which to pass this part of the argument, and the mode of the
3999 register RTX indicates how large this part of the argument is. The
4000 second operand of the @code{expr_list} is a @code{const_int} which gives
4001 the offset in bytes into the entire argument of where this part starts.
4002 As a special exception the first @code{expr_list} in the @code{parallel}
4003 RTX may have a first operand of zero. This indicates that the entire
4004 argument is also stored on the stack.
4006 The last time this macro is called, it is called with @code{MODE ==
4007 VOIDmode}, and its result is passed to the @code{call} or @code{call_value}
4008 pattern as operands 2 and 3 respectively.
4010 @cindex @file{stdarg.h} and register arguments
4011 The usual way to make the ISO library @file{stdarg.h} work on a machine
4012 where some arguments are usually passed in registers, is to cause
4013 nameless arguments to be passed on the stack instead. This is done
4014 by making @code{FUNCTION_ARG} return 0 whenever @var{named} is 0.
4016 @cindex @code{TARGET_MUST_PASS_IN_STACK}, and @code{FUNCTION_ARG}
4017 @cindex @code{REG_PARM_STACK_SPACE}, and @code{FUNCTION_ARG}
4018 You may use the hook @code{targetm.calls.must_pass_in_stack}
4019 in the definition of this macro to determine if this argument is of a
4020 type that must be passed in the stack. If @code{REG_PARM_STACK_SPACE}
4021 is not defined and @code{FUNCTION_ARG} returns nonzero for such an
4022 argument, the compiler will abort. If @code{REG_PARM_STACK_SPACE} is
4023 defined, the argument will be computed in the stack and then loaded into
4027 @hook TARGET_MUST_PASS_IN_STACK
4028 This target hook should return @code{true} if we should not pass @var{type}
4029 solely in registers. The file @file{expr.h} defines a
4030 definition that is usually appropriate, refer to @file{expr.h} for additional
4034 @defmac FUNCTION_INCOMING_ARG (@var{cum}, @var{mode}, @var{type}, @var{named})
4035 Define this macro if the target machine has ``register windows'', so
4036 that the register in which a function sees an arguments is not
4037 necessarily the same as the one in which the caller passed the
4040 For such machines, @code{FUNCTION_ARG} computes the register in which
4041 the caller passes the value, and @code{FUNCTION_INCOMING_ARG} should
4042 be defined in a similar fashion to tell the function being called
4043 where the arguments will arrive.
4045 If @code{FUNCTION_INCOMING_ARG} is not defined, @code{FUNCTION_ARG}
4046 serves both purposes.
4049 @hook TARGET_ARG_PARTIAL_BYTES
4050 This target hook returns the number of bytes at the beginning of an
4051 argument that must be put in registers. The value must be zero for
4052 arguments that are passed entirely in registers or that are entirely
4053 pushed on the stack.
4055 On some machines, certain arguments must be passed partially in
4056 registers and partially in memory. On these machines, typically the
4057 first few words of arguments are passed in registers, and the rest
4058 on the stack. If a multi-word argument (a @code{double} or a
4059 structure) crosses that boundary, its first few words must be passed
4060 in registers and the rest must be pushed. This macro tells the
4061 compiler when this occurs, and how many bytes should go in registers.
4063 @code{FUNCTION_ARG} for these arguments should return the first
4064 register to be used by the caller for this argument; likewise
4065 @code{FUNCTION_INCOMING_ARG}, for the called function.
4068 @hook TARGET_PASS_BY_REFERENCE
4069 This target hook should return @code{true} if an argument at the
4070 position indicated by @var{cum} should be passed by reference. This
4071 predicate is queried after target independent reasons for being
4072 passed by reference, such as @code{TREE_ADDRESSABLE (type)}.
4074 If the hook returns true, a copy of that argument is made in memory and a
4075 pointer to the argument is passed instead of the argument itself.
4076 The pointer is passed in whatever way is appropriate for passing a pointer
4080 @hook TARGET_CALLEE_COPIES
4081 The function argument described by the parameters to this hook is
4082 known to be passed by reference. The hook should return true if the
4083 function argument should be copied by the callee instead of copied
4086 For any argument for which the hook returns true, if it can be
4087 determined that the argument is not modified, then a copy need
4090 The default version of this hook always returns false.
4093 @defmac CUMULATIVE_ARGS
4094 A C type for declaring a variable that is used as the first argument of
4095 @code{FUNCTION_ARG} and other related values. For some target machines,
4096 the type @code{int} suffices and can hold the number of bytes of
4099 There is no need to record in @code{CUMULATIVE_ARGS} anything about the
4100 arguments that have been passed on the stack. The compiler has other
4101 variables to keep track of that. For target machines on which all
4102 arguments are passed on the stack, there is no need to store anything in
4103 @code{CUMULATIVE_ARGS}; however, the data structure must exist and
4104 should not be empty, so use @code{int}.
4107 @defmac OVERRIDE_ABI_FORMAT (@var{fndecl})
4108 If defined, this macro is called before generating any code for a
4109 function, but after the @var{cfun} descriptor for the function has been
4110 created. The back end may use this macro to update @var{cfun} to
4111 reflect an ABI other than that which would normally be used by default.
4112 If the compiler is generating code for a compiler-generated function,
4113 @var{fndecl} may be @code{NULL}.
4116 @defmac INIT_CUMULATIVE_ARGS (@var{cum}, @var{fntype}, @var{libname}, @var{fndecl}, @var{n_named_args})
4117 A C statement (sans semicolon) for initializing the variable
4118 @var{cum} for the state at the beginning of the argument list. The
4119 variable has type @code{CUMULATIVE_ARGS}. The value of @var{fntype}
4120 is the tree node for the data type of the function which will receive
4121 the args, or 0 if the args are to a compiler support library function.
4122 For direct calls that are not libcalls, @var{fndecl} contain the
4123 declaration node of the function. @var{fndecl} is also set when
4124 @code{INIT_CUMULATIVE_ARGS} is used to find arguments for the function
4125 being compiled. @var{n_named_args} is set to the number of named
4126 arguments, including a structure return address if it is passed as a
4127 parameter, when making a call. When processing incoming arguments,
4128 @var{n_named_args} is set to @minus{}1.
4130 When processing a call to a compiler support library function,
4131 @var{libname} identifies which one. It is a @code{symbol_ref} rtx which
4132 contains the name of the function, as a string. @var{libname} is 0 when
4133 an ordinary C function call is being processed. Thus, each time this
4134 macro is called, either @var{libname} or @var{fntype} is nonzero, but
4135 never both of them at once.
4138 @defmac INIT_CUMULATIVE_LIBCALL_ARGS (@var{cum}, @var{mode}, @var{libname})
4139 Like @code{INIT_CUMULATIVE_ARGS} but only used for outgoing libcalls,
4140 it gets a @code{MODE} argument instead of @var{fntype}, that would be
4141 @code{NULL}. @var{indirect} would always be zero, too. If this macro
4142 is not defined, @code{INIT_CUMULATIVE_ARGS (cum, NULL_RTX, libname,
4143 0)} is used instead.
4146 @defmac INIT_CUMULATIVE_INCOMING_ARGS (@var{cum}, @var{fntype}, @var{libname})
4147 Like @code{INIT_CUMULATIVE_ARGS} but overrides it for the purposes of
4148 finding the arguments for the function being compiled. If this macro is
4149 undefined, @code{INIT_CUMULATIVE_ARGS} is used instead.
4151 The value passed for @var{libname} is always 0, since library routines
4152 with special calling conventions are never compiled with GCC@. The
4153 argument @var{libname} exists for symmetry with
4154 @code{INIT_CUMULATIVE_ARGS}.
4155 @c could use "this macro" in place of @code{INIT_CUMULATIVE_ARGS}, maybe.
4156 @c --mew 5feb93 i switched the order of the sentences. --mew 10feb93
4159 @defmac FUNCTION_ARG_ADVANCE (@var{cum}, @var{mode}, @var{type}, @var{named})
4160 A C statement (sans semicolon) to update the summarizer variable
4161 @var{cum} to advance past an argument in the argument list. The
4162 values @var{mode}, @var{type} and @var{named} describe that argument.
4163 Once this is done, the variable @var{cum} is suitable for analyzing
4164 the @emph{following} argument with @code{FUNCTION_ARG}, etc.
4166 This macro need not do anything if the argument in question was passed
4167 on the stack. The compiler knows how to track the amount of stack space
4168 used for arguments without any special help.
4171 @defmac FUNCTION_ARG_OFFSET (@var{mode}, @var{type})
4172 If defined, a C expression that is the number of bytes to add to the
4173 offset of the argument passed in memory. This is needed for the SPU,
4174 which passes @code{char} and @code{short} arguments in the preferred
4175 slot that is in the middle of the quad word instead of starting at the
4179 @defmac FUNCTION_ARG_PADDING (@var{mode}, @var{type})
4180 If defined, a C expression which determines whether, and in which direction,
4181 to pad out an argument with extra space. The value should be of type
4182 @code{enum direction}: either @code{upward} to pad above the argument,
4183 @code{downward} to pad below, or @code{none} to inhibit padding.
4185 The @emph{amount} of padding is always just enough to reach the next
4186 multiple of @code{TARGET_FUNCTION_ARG_BOUNDARY}; this macro does not
4189 This macro has a default definition which is right for most systems.
4190 For little-endian machines, the default is to pad upward. For
4191 big-endian machines, the default is to pad downward for an argument of
4192 constant size shorter than an @code{int}, and upward otherwise.
4195 @defmac PAD_VARARGS_DOWN
4196 If defined, a C expression which determines whether the default
4197 implementation of va_arg will attempt to pad down before reading the
4198 next argument, if that argument is smaller than its aligned space as
4199 controlled by @code{PARM_BOUNDARY}. If this macro is not defined, all such
4200 arguments are padded down if @code{BYTES_BIG_ENDIAN} is true.
4203 @defmac BLOCK_REG_PADDING (@var{mode}, @var{type}, @var{first})
4204 Specify padding for the last element of a block move between registers and
4205 memory. @var{first} is nonzero if this is the only element. Defining this
4206 macro allows better control of register function parameters on big-endian
4207 machines, without using @code{PARALLEL} rtl. In particular,
4208 @code{MUST_PASS_IN_STACK} need not test padding and mode of types in
4209 registers, as there is no longer a "wrong" part of a register; For example,
4210 a three byte aggregate may be passed in the high part of a register if so
4214 @hook TARGET_FUNCTION_ARG_BOUNDARY
4215 This hook returns the the alignment boundary, in bits, of an argument
4216 with the specified mode and type. The default hook returns
4217 @code{PARM_BOUNDARY} for all arguments.
4220 @defmac FUNCTION_ARG_REGNO_P (@var{regno})
4221 A C expression that is nonzero if @var{regno} is the number of a hard
4222 register in which function arguments are sometimes passed. This does
4223 @emph{not} include implicit arguments such as the static chain and
4224 the structure-value address. On many machines, no registers can be
4225 used for this purpose since all function arguments are pushed on the
4229 @hook TARGET_SPLIT_COMPLEX_ARG
4230 This hook should return true if parameter of type @var{type} are passed
4231 as two scalar parameters. By default, GCC will attempt to pack complex
4232 arguments into the target's word size. Some ABIs require complex arguments
4233 to be split and treated as their individual components. For example, on
4234 AIX64, complex floats should be passed in a pair of floating point
4235 registers, even though a complex float would fit in one 64-bit floating
4238 The default value of this hook is @code{NULL}, which is treated as always
4242 @hook TARGET_BUILD_BUILTIN_VA_LIST
4243 This hook returns a type node for @code{va_list} for the target.
4244 The default version of the hook returns @code{void*}.
4247 @hook TARGET_ENUM_VA_LIST_P
4248 This target hook is used in function @code{c_common_nodes_and_builtins}
4249 to iterate through the target specific builtin types for va_list. The
4250 variable @var{idx} is used as iterator. @var{pname} has to be a pointer
4251 to a @code{const char *} and @var{ptree} a pointer to a @code{tree} typed
4253 The arguments @var{pname} and @var{ptree} are used to store the result of
4254 this macro and are set to the name of the va_list builtin type and its
4256 If the return value of this macro is zero, then there is no more element.
4257 Otherwise the @var{IDX} should be increased for the next call of this
4258 macro to iterate through all types.
4261 @hook TARGET_FN_ABI_VA_LIST
4262 This hook returns the va_list type of the calling convention specified by
4264 The default version of this hook returns @code{va_list_type_node}.
4267 @hook TARGET_CANONICAL_VA_LIST_TYPE
4268 This hook returns the va_list type of the calling convention specified by the
4269 type of @var{type}. If @var{type} is not a valid va_list type, it returns
4273 @hook TARGET_GIMPLIFY_VA_ARG_EXPR
4274 This hook performs target-specific gimplification of
4275 @code{VA_ARG_EXPR}. The first two parameters correspond to the
4276 arguments to @code{va_arg}; the latter two are as in
4277 @code{gimplify.c:gimplify_expr}.
4280 @hook TARGET_VALID_POINTER_MODE
4281 Define this to return nonzero if the port can handle pointers
4282 with machine mode @var{mode}. The default version of this
4283 hook returns true for both @code{ptr_mode} and @code{Pmode}.
4286 @hook TARGET_SCALAR_MODE_SUPPORTED_P
4287 Define this to return nonzero if the port is prepared to handle
4288 insns involving scalar mode @var{mode}. For a scalar mode to be
4289 considered supported, all the basic arithmetic and comparisons
4292 The default version of this hook returns true for any mode
4293 required to handle the basic C types (as defined by the port).
4294 Included here are the double-word arithmetic supported by the
4295 code in @file{optabs.c}.
4298 @hook TARGET_VECTOR_MODE_SUPPORTED_P
4299 Define this to return nonzero if the port is prepared to handle
4300 insns involving vector mode @var{mode}. At the very least, it
4301 must have move patterns for this mode.
4304 @hook TARGET_SMALL_REGISTER_CLASSES_FOR_MODE_P
4305 Define this to return nonzero for machine modes for which the port has
4306 small register classes. If this target hook returns nonzero for a given
4307 @var{mode}, the compiler will try to minimize the lifetime of registers
4308 in @var{mode}. The hook may be called with @code{VOIDmode} as argument.
4309 In this case, the hook is expected to return nonzero if it returns nonzero
4312 On some machines, it is risky to let hard registers live across arbitrary
4313 insns. Typically, these machines have instructions that require values
4314 to be in specific registers (like an accumulator), and reload will fail
4315 if the required hard register is used for another purpose across such an
4318 Passes before reload do not know which hard registers will be used
4319 in an instruction, but the machine modes of the registers set or used in
4320 the instruction are already known. And for some machines, register
4321 classes are small for, say, integer registers but not for floating point
4322 registers. For example, the AMD x86-64 architecture requires specific
4323 registers for the legacy x86 integer instructions, but there are many
4324 SSE registers for floating point operations. On such targets, a good
4325 strategy may be to return nonzero from this hook for @code{INTEGRAL_MODE_P}
4326 machine modes but zero for the SSE register classes.
4328 The default version of this hook retuns false for any mode. It is always
4329 safe to redefine this hook to return with a nonzero value. But if you
4330 unnecessarily define it, you will reduce the amount of optimizations
4331 that can be performed in some cases. If you do not define this hook
4332 to return a nonzero value when it is required, the compiler will run out
4333 of spill registers and print a fatal error message.
4337 @subsection How Scalar Function Values Are Returned
4338 @cindex return values in registers
4339 @cindex values, returned by functions
4340 @cindex scalars, returned as values
4342 This section discusses the macros that control returning scalars as
4343 values---values that can fit in registers.
4345 @hook TARGET_FUNCTION_VALUE
4347 Define this to return an RTX representing the place where a function
4348 returns or receives a value of data type @var{ret_type}, a tree node
4349 representing a data type. @var{fn_decl_or_type} is a tree node
4350 representing @code{FUNCTION_DECL} or @code{FUNCTION_TYPE} of a
4351 function being called. If @var{outgoing} is false, the hook should
4352 compute the register in which the caller will see the return value.
4353 Otherwise, the hook should return an RTX representing the place where
4354 a function returns a value.
4356 On many machines, only @code{TYPE_MODE (@var{ret_type})} is relevant.
4357 (Actually, on most machines, scalar values are returned in the same
4358 place regardless of mode.) The value of the expression is usually a
4359 @code{reg} RTX for the hard register where the return value is stored.
4360 The value can also be a @code{parallel} RTX, if the return value is in
4361 multiple places. See @code{FUNCTION_ARG} for an explanation of the
4362 @code{parallel} form. Note that the callee will populate every
4363 location specified in the @code{parallel}, but if the first element of
4364 the @code{parallel} contains the whole return value, callers will use
4365 that element as the canonical location and ignore the others. The m68k
4366 port uses this type of @code{parallel} to return pointers in both
4367 @samp{%a0} (the canonical location) and @samp{%d0}.
4369 If @code{TARGET_PROMOTE_FUNCTION_RETURN} returns true, you must apply
4370 the same promotion rules specified in @code{PROMOTE_MODE} if
4371 @var{valtype} is a scalar type.
4373 If the precise function being called is known, @var{func} is a tree
4374 node (@code{FUNCTION_DECL}) for it; otherwise, @var{func} is a null
4375 pointer. This makes it possible to use a different value-returning
4376 convention for specific functions when all their calls are
4379 Some target machines have ``register windows'' so that the register in
4380 which a function returns its value is not the same as the one in which
4381 the caller sees the value. For such machines, you should return
4382 different RTX depending on @var{outgoing}.
4384 @code{TARGET_FUNCTION_VALUE} is not used for return values with
4385 aggregate data types, because these are returned in another way. See
4386 @code{TARGET_STRUCT_VALUE_RTX} and related macros, below.
4389 @defmac FUNCTION_VALUE (@var{valtype}, @var{func})
4390 This macro has been deprecated. Use @code{TARGET_FUNCTION_VALUE} for
4391 a new target instead.
4394 @defmac LIBCALL_VALUE (@var{mode})
4395 A C expression to create an RTX representing the place where a library
4396 function returns a value of mode @var{mode}.
4398 Note that ``library function'' in this context means a compiler
4399 support routine, used to perform arithmetic, whose name is known
4400 specially by the compiler and was not mentioned in the C code being
4404 @hook TARGET_LIBCALL_VALUE
4405 Define this hook if the back-end needs to know the name of the libcall
4406 function in order to determine where the result should be returned.
4408 The mode of the result is given by @var{mode} and the name of the called
4409 library function is given by @var{fun}. The hook should return an RTX
4410 representing the place where the library function result will be returned.
4412 If this hook is not defined, then LIBCALL_VALUE will be used.
4415 @defmac FUNCTION_VALUE_REGNO_P (@var{regno})
4416 A C expression that is nonzero if @var{regno} is the number of a hard
4417 register in which the values of called function may come back.
4419 A register whose use for returning values is limited to serving as the
4420 second of a pair (for a value of type @code{double}, say) need not be
4421 recognized by this macro. So for most machines, this definition
4425 #define FUNCTION_VALUE_REGNO_P(N) ((N) == 0)
4428 If the machine has register windows, so that the caller and the called
4429 function use different registers for the return value, this macro
4430 should recognize only the caller's register numbers.
4432 This macro has been deprecated. Use @code{TARGET_FUNCTION_VALUE_REGNO_P}
4433 for a new target instead.
4436 @hook TARGET_FUNCTION_VALUE_REGNO_P
4437 A target hook that return @code{true} if @var{regno} is the number of a hard
4438 register in which the values of called function may come back.
4440 A register whose use for returning values is limited to serving as the
4441 second of a pair (for a value of type @code{double}, say) need not be
4442 recognized by this target hook.
4444 If the machine has register windows, so that the caller and the called
4445 function use different registers for the return value, this target hook
4446 should recognize only the caller's register numbers.
4448 If this hook is not defined, then FUNCTION_VALUE_REGNO_P will be used.
4451 @defmac APPLY_RESULT_SIZE
4452 Define this macro if @samp{untyped_call} and @samp{untyped_return}
4453 need more space than is implied by @code{FUNCTION_VALUE_REGNO_P} for
4454 saving and restoring an arbitrary return value.
4457 @hook TARGET_RETURN_IN_MSB
4458 This hook should return true if values of type @var{type} are returned
4459 at the most significant end of a register (in other words, if they are
4460 padded at the least significant end). You can assume that @var{type}
4461 is returned in a register; the caller is required to check this.
4463 Note that the register provided by @code{TARGET_FUNCTION_VALUE} must
4464 be able to hold the complete return value. For example, if a 1-, 2-
4465 or 3-byte structure is returned at the most significant end of a
4466 4-byte register, @code{TARGET_FUNCTION_VALUE} should provide an
4470 @node Aggregate Return
4471 @subsection How Large Values Are Returned
4472 @cindex aggregates as return values
4473 @cindex large return values
4474 @cindex returning aggregate values
4475 @cindex structure value address
4477 When a function value's mode is @code{BLKmode} (and in some other
4478 cases), the value is not returned according to
4479 @code{TARGET_FUNCTION_VALUE} (@pxref{Scalar Return}). Instead, the
4480 caller passes the address of a block of memory in which the value
4481 should be stored. This address is called the @dfn{structure value
4484 This section describes how to control returning structure values in
4487 @hook TARGET_RETURN_IN_MEMORY
4488 This target hook should return a nonzero value to say to return the
4489 function value in memory, just as large structures are always returned.
4490 Here @var{type} will be the data type of the value, and @var{fntype}
4491 will be the type of the function doing the returning, or @code{NULL} for
4494 Note that values of mode @code{BLKmode} must be explicitly handled
4495 by this function. Also, the option @option{-fpcc-struct-return}
4496 takes effect regardless of this macro. On most systems, it is
4497 possible to leave the hook undefined; this causes a default
4498 definition to be used, whose value is the constant 1 for @code{BLKmode}
4499 values, and 0 otherwise.
4501 Do not use this hook to indicate that structures and unions should always
4502 be returned in memory. You should instead use @code{DEFAULT_PCC_STRUCT_RETURN}
4506 @defmac DEFAULT_PCC_STRUCT_RETURN
4507 Define this macro to be 1 if all structure and union return values must be
4508 in memory. Since this results in slower code, this should be defined
4509 only if needed for compatibility with other compilers or with an ABI@.
4510 If you define this macro to be 0, then the conventions used for structure
4511 and union return values are decided by the @code{TARGET_RETURN_IN_MEMORY}
4514 If not defined, this defaults to the value 1.
4517 @hook TARGET_STRUCT_VALUE_RTX
4518 This target hook should return the location of the structure value
4519 address (normally a @code{mem} or @code{reg}), or 0 if the address is
4520 passed as an ``invisible'' first argument. Note that @var{fndecl} may
4521 be @code{NULL}, for libcalls. You do not need to define this target
4522 hook if the address is always passed as an ``invisible'' first
4525 On some architectures the place where the structure value address
4526 is found by the called function is not the same place that the
4527 caller put it. This can be due to register windows, or it could
4528 be because the function prologue moves it to a different place.
4529 @var{incoming} is @code{1} or @code{2} when the location is needed in
4530 the context of the called function, and @code{0} in the context of
4533 If @var{incoming} is nonzero and the address is to be found on the
4534 stack, return a @code{mem} which refers to the frame pointer. If
4535 @var{incoming} is @code{2}, the result is being used to fetch the
4536 structure value address at the beginning of a function. If you need
4537 to emit adjusting code, you should do it at this point.
4540 @defmac PCC_STATIC_STRUCT_RETURN
4541 Define this macro if the usual system convention on the target machine
4542 for returning structures and unions is for the called function to return
4543 the address of a static variable containing the value.
4545 Do not define this if the usual system convention is for the caller to
4546 pass an address to the subroutine.
4548 This macro has effect in @option{-fpcc-struct-return} mode, but it does
4549 nothing when you use @option{-freg-struct-return} mode.
4552 @hook TARGET_GET_RAW_RESULT_MODE
4554 @hook TARGET_GET_RAW_ARG_MODE
4557 @subsection Caller-Saves Register Allocation
4559 If you enable it, GCC can save registers around function calls. This
4560 makes it possible to use call-clobbered registers to hold variables that
4561 must live across calls.
4563 @defmac CALLER_SAVE_PROFITABLE (@var{refs}, @var{calls})
4564 A C expression to determine whether it is worthwhile to consider placing
4565 a pseudo-register in a call-clobbered hard register and saving and
4566 restoring it around each function call. The expression should be 1 when
4567 this is worth doing, and 0 otherwise.
4569 If you don't define this macro, a default is used which is good on most
4570 machines: @code{4 * @var{calls} < @var{refs}}.
4573 @defmac HARD_REGNO_CALLER_SAVE_MODE (@var{regno}, @var{nregs})
4574 A C expression specifying which mode is required for saving @var{nregs}
4575 of a pseudo-register in call-clobbered hard register @var{regno}. If
4576 @var{regno} is unsuitable for caller save, @code{VOIDmode} should be
4577 returned. For most machines this macro need not be defined since GCC
4578 will select the smallest suitable mode.
4581 @node Function Entry
4582 @subsection Function Entry and Exit
4583 @cindex function entry and exit
4587 This section describes the macros that output function entry
4588 (@dfn{prologue}) and exit (@dfn{epilogue}) code.
4590 @hook TARGET_ASM_FUNCTION_PROLOGUE
4591 If defined, a function that outputs the assembler code for entry to a
4592 function. The prologue is responsible for setting up the stack frame,
4593 initializing the frame pointer register, saving registers that must be
4594 saved, and allocating @var{size} additional bytes of storage for the
4595 local variables. @var{size} is an integer. @var{file} is a stdio
4596 stream to which the assembler code should be output.
4598 The label for the beginning of the function need not be output by this
4599 macro. That has already been done when the macro is run.
4601 @findex regs_ever_live
4602 To determine which registers to save, the macro can refer to the array
4603 @code{regs_ever_live}: element @var{r} is nonzero if hard register
4604 @var{r} is used anywhere within the function. This implies the function
4605 prologue should save register @var{r}, provided it is not one of the
4606 call-used registers. (@code{TARGET_ASM_FUNCTION_EPILOGUE} must likewise use
4607 @code{regs_ever_live}.)
4609 On machines that have ``register windows'', the function entry code does
4610 not save on the stack the registers that are in the windows, even if
4611 they are supposed to be preserved by function calls; instead it takes
4612 appropriate steps to ``push'' the register stack, if any non-call-used
4613 registers are used in the function.
4615 @findex frame_pointer_needed
4616 On machines where functions may or may not have frame-pointers, the
4617 function entry code must vary accordingly; it must set up the frame
4618 pointer if one is wanted, and not otherwise. To determine whether a
4619 frame pointer is in wanted, the macro can refer to the variable
4620 @code{frame_pointer_needed}. The variable's value will be 1 at run
4621 time in a function that needs a frame pointer. @xref{Elimination}.
4623 The function entry code is responsible for allocating any stack space
4624 required for the function. This stack space consists of the regions
4625 listed below. In most cases, these regions are allocated in the
4626 order listed, with the last listed region closest to the top of the
4627 stack (the lowest address if @code{STACK_GROWS_DOWNWARD} is defined, and
4628 the highest address if it is not defined). You can use a different order
4629 for a machine if doing so is more convenient or required for
4630 compatibility reasons. Except in cases where required by standard
4631 or by a debugger, there is no reason why the stack layout used by GCC
4632 need agree with that used by other compilers for a machine.
4635 @hook TARGET_ASM_FUNCTION_END_PROLOGUE
4636 If defined, a function that outputs assembler code at the end of a
4637 prologue. This should be used when the function prologue is being
4638 emitted as RTL, and you have some extra assembler that needs to be
4639 emitted. @xref{prologue instruction pattern}.
4642 @hook TARGET_ASM_FUNCTION_BEGIN_EPILOGUE
4643 If defined, a function that outputs assembler code at the start of an
4644 epilogue. This should be used when the function epilogue is being
4645 emitted as RTL, and you have some extra assembler that needs to be
4646 emitted. @xref{epilogue instruction pattern}.
4649 @hook TARGET_ASM_FUNCTION_EPILOGUE
4650 If defined, a function that outputs the assembler code for exit from a
4651 function. The epilogue is responsible for restoring the saved
4652 registers and stack pointer to their values when the function was
4653 called, and returning control to the caller. This macro takes the
4654 same arguments as the macro @code{TARGET_ASM_FUNCTION_PROLOGUE}, and the
4655 registers to restore are determined from @code{regs_ever_live} and
4656 @code{CALL_USED_REGISTERS} in the same way.
4658 On some machines, there is a single instruction that does all the work
4659 of returning from the function. On these machines, give that
4660 instruction the name @samp{return} and do not define the macro
4661 @code{TARGET_ASM_FUNCTION_EPILOGUE} at all.
4663 Do not define a pattern named @samp{return} if you want the
4664 @code{TARGET_ASM_FUNCTION_EPILOGUE} to be used. If you want the target
4665 switches to control whether return instructions or epilogues are used,
4666 define a @samp{return} pattern with a validity condition that tests the
4667 target switches appropriately. If the @samp{return} pattern's validity
4668 condition is false, epilogues will be used.
4670 On machines where functions may or may not have frame-pointers, the
4671 function exit code must vary accordingly. Sometimes the code for these
4672 two cases is completely different. To determine whether a frame pointer
4673 is wanted, the macro can refer to the variable
4674 @code{frame_pointer_needed}. The variable's value will be 1 when compiling
4675 a function that needs a frame pointer.
4677 Normally, @code{TARGET_ASM_FUNCTION_PROLOGUE} and
4678 @code{TARGET_ASM_FUNCTION_EPILOGUE} must treat leaf functions specially.
4679 The C variable @code{current_function_is_leaf} is nonzero for such a
4680 function. @xref{Leaf Functions}.
4682 On some machines, some functions pop their arguments on exit while
4683 others leave that for the caller to do. For example, the 68020 when
4684 given @option{-mrtd} pops arguments in functions that take a fixed
4685 number of arguments.
4687 @findex current_function_pops_args
4688 Your definition of the macro @code{RETURN_POPS_ARGS} decides which
4689 functions pop their own arguments. @code{TARGET_ASM_FUNCTION_EPILOGUE}
4690 needs to know what was decided. The number of bytes of the current
4691 function's arguments that this function should pop is available in
4692 @code{crtl->args.pops_args}. @xref{Scalar Return}.
4697 @findex current_function_pretend_args_size
4698 A region of @code{current_function_pretend_args_size} bytes of
4699 uninitialized space just underneath the first argument arriving on the
4700 stack. (This may not be at the very start of the allocated stack region
4701 if the calling sequence has pushed anything else since pushing the stack
4702 arguments. But usually, on such machines, nothing else has been pushed
4703 yet, because the function prologue itself does all the pushing.) This
4704 region is used on machines where an argument may be passed partly in
4705 registers and partly in memory, and, in some cases to support the
4706 features in @code{<stdarg.h>}.
4709 An area of memory used to save certain registers used by the function.
4710 The size of this area, which may also include space for such things as
4711 the return address and pointers to previous stack frames, is
4712 machine-specific and usually depends on which registers have been used
4713 in the function. Machines with register windows often do not require
4717 A region of at least @var{size} bytes, possibly rounded up to an allocation
4718 boundary, to contain the local variables of the function. On some machines,
4719 this region and the save area may occur in the opposite order, with the
4720 save area closer to the top of the stack.
4723 @cindex @code{ACCUMULATE_OUTGOING_ARGS} and stack frames
4724 Optionally, when @code{ACCUMULATE_OUTGOING_ARGS} is defined, a region of
4725 @code{current_function_outgoing_args_size} bytes to be used for outgoing
4726 argument lists of the function. @xref{Stack Arguments}.
4729 @defmac EXIT_IGNORE_STACK
4730 Define this macro as a C expression that is nonzero if the return
4731 instruction or the function epilogue ignores the value of the stack
4732 pointer; in other words, if it is safe to delete an instruction to
4733 adjust the stack pointer before a return from the function. The
4736 Note that this macro's value is relevant only for functions for which
4737 frame pointers are maintained. It is never safe to delete a final
4738 stack adjustment in a function that has no frame pointer, and the
4739 compiler knows this regardless of @code{EXIT_IGNORE_STACK}.
4742 @defmac EPILOGUE_USES (@var{regno})
4743 Define this macro as a C expression that is nonzero for registers that are
4744 used by the epilogue or the @samp{return} pattern. The stack and frame
4745 pointer registers are already assumed to be used as needed.
4748 @defmac EH_USES (@var{regno})
4749 Define this macro as a C expression that is nonzero for registers that are
4750 used by the exception handling mechanism, and so should be considered live
4751 on entry to an exception edge.
4754 @defmac DELAY_SLOTS_FOR_EPILOGUE
4755 Define this macro if the function epilogue contains delay slots to which
4756 instructions from the rest of the function can be ``moved''. The
4757 definition should be a C expression whose value is an integer
4758 representing the number of delay slots there.
4761 @defmac ELIGIBLE_FOR_EPILOGUE_DELAY (@var{insn}, @var{n})
4762 A C expression that returns 1 if @var{insn} can be placed in delay
4763 slot number @var{n} of the epilogue.
4765 The argument @var{n} is an integer which identifies the delay slot now
4766 being considered (since different slots may have different rules of
4767 eligibility). It is never negative and is always less than the number
4768 of epilogue delay slots (what @code{DELAY_SLOTS_FOR_EPILOGUE} returns).
4769 If you reject a particular insn for a given delay slot, in principle, it
4770 may be reconsidered for a subsequent delay slot. Also, other insns may
4771 (at least in principle) be considered for the so far unfilled delay
4774 @findex current_function_epilogue_delay_list
4775 @findex final_scan_insn
4776 The insns accepted to fill the epilogue delay slots are put in an RTL
4777 list made with @code{insn_list} objects, stored in the variable
4778 @code{current_function_epilogue_delay_list}. The insn for the first
4779 delay slot comes first in the list. Your definition of the macro
4780 @code{TARGET_ASM_FUNCTION_EPILOGUE} should fill the delay slots by
4781 outputting the insns in this list, usually by calling
4782 @code{final_scan_insn}.
4784 You need not define this macro if you did not define
4785 @code{DELAY_SLOTS_FOR_EPILOGUE}.
4788 @hook TARGET_ASM_OUTPUT_MI_THUNK
4789 A function that outputs the assembler code for a thunk
4790 function, used to implement C++ virtual function calls with multiple
4791 inheritance. The thunk acts as a wrapper around a virtual function,
4792 adjusting the implicit object parameter before handing control off to
4795 First, emit code to add the integer @var{delta} to the location that
4796 contains the incoming first argument. Assume that this argument
4797 contains a pointer, and is the one used to pass the @code{this} pointer
4798 in C++. This is the incoming argument @emph{before} the function prologue,
4799 e.g.@: @samp{%o0} on a sparc. The addition must preserve the values of
4800 all other incoming arguments.
4802 Then, if @var{vcall_offset} is nonzero, an additional adjustment should be
4803 made after adding @code{delta}. In particular, if @var{p} is the
4804 adjusted pointer, the following adjustment should be made:
4807 p += (*((ptrdiff_t **)p))[vcall_offset/sizeof(ptrdiff_t)]
4810 After the additions, emit code to jump to @var{function}, which is a
4811 @code{FUNCTION_DECL}. This is a direct pure jump, not a call, and does
4812 not touch the return address. Hence returning from @var{FUNCTION} will
4813 return to whoever called the current @samp{thunk}.
4815 The effect must be as if @var{function} had been called directly with
4816 the adjusted first argument. This macro is responsible for emitting all
4817 of the code for a thunk function; @code{TARGET_ASM_FUNCTION_PROLOGUE}
4818 and @code{TARGET_ASM_FUNCTION_EPILOGUE} are not invoked.
4820 The @var{thunk_fndecl} is redundant. (@var{delta} and @var{function}
4821 have already been extracted from it.) It might possibly be useful on
4822 some targets, but probably not.
4824 If you do not define this macro, the target-independent code in the C++
4825 front end will generate a less efficient heavyweight thunk that calls
4826 @var{function} instead of jumping to it. The generic approach does
4827 not support varargs.
4830 @hook TARGET_ASM_CAN_OUTPUT_MI_THUNK
4831 A function that returns true if TARGET_ASM_OUTPUT_MI_THUNK would be able
4832 to output the assembler code for the thunk function specified by the
4833 arguments it is passed, and false otherwise. In the latter case, the
4834 generic approach will be used by the C++ front end, with the limitations
4839 @subsection Generating Code for Profiling
4840 @cindex profiling, code generation
4842 These macros will help you generate code for profiling.
4844 @defmac FUNCTION_PROFILER (@var{file}, @var{labelno})
4845 A C statement or compound statement to output to @var{file} some
4846 assembler code to call the profiling subroutine @code{mcount}.
4849 The details of how @code{mcount} expects to be called are determined by
4850 your operating system environment, not by GCC@. To figure them out,
4851 compile a small program for profiling using the system's installed C
4852 compiler and look at the assembler code that results.
4854 Older implementations of @code{mcount} expect the address of a counter
4855 variable to be loaded into some register. The name of this variable is
4856 @samp{LP} followed by the number @var{labelno}, so you would generate
4857 the name using @samp{LP%d} in a @code{fprintf}.
4860 @defmac PROFILE_HOOK
4861 A C statement or compound statement to output to @var{file} some assembly
4862 code to call the profiling subroutine @code{mcount} even the target does
4863 not support profiling.
4866 @defmac NO_PROFILE_COUNTERS
4867 Define this macro to be an expression with a nonzero value if the
4868 @code{mcount} subroutine on your system does not need a counter variable
4869 allocated for each function. This is true for almost all modern
4870 implementations. If you define this macro, you must not use the
4871 @var{labelno} argument to @code{FUNCTION_PROFILER}.
4874 @defmac PROFILE_BEFORE_PROLOGUE
4875 Define this macro if the code for function profiling should come before
4876 the function prologue. Normally, the profiling code comes after.
4880 @subsection Permitting tail calls
4883 @hook TARGET_FUNCTION_OK_FOR_SIBCALL
4884 True if it is ok to do sibling call optimization for the specified
4885 call expression @var{exp}. @var{decl} will be the called function,
4886 or @code{NULL} if this is an indirect call.
4888 It is not uncommon for limitations of calling conventions to prevent
4889 tail calls to functions outside the current unit of translation, or
4890 during PIC compilation. The hook is used to enforce these restrictions,
4891 as the @code{sibcall} md pattern can not fail, or fall over to a
4892 ``normal'' call. The criteria for successful sibling call optimization
4893 may vary greatly between different architectures.
4896 @hook TARGET_EXTRA_LIVE_ON_ENTRY
4897 Add any hard registers to @var{regs} that are live on entry to the
4898 function. This hook only needs to be defined to provide registers that
4899 cannot be found by examination of FUNCTION_ARG_REGNO_P, the callee saved
4900 registers, STATIC_CHAIN_INCOMING_REGNUM, STATIC_CHAIN_REGNUM,
4901 TARGET_STRUCT_VALUE_RTX, FRAME_POINTER_REGNUM, EH_USES,
4902 FRAME_POINTER_REGNUM, ARG_POINTER_REGNUM, and the PIC_OFFSET_TABLE_REGNUM.
4905 @node Stack Smashing Protection
4906 @subsection Stack smashing protection
4907 @cindex stack smashing protection
4909 @hook TARGET_STACK_PROTECT_GUARD
4910 This hook returns a @code{DECL} node for the external variable to use
4911 for the stack protection guard. This variable is initialized by the
4912 runtime to some random value and is used to initialize the guard value
4913 that is placed at the top of the local stack frame. The type of this
4914 variable must be @code{ptr_type_node}.
4916 The default version of this hook creates a variable called
4917 @samp{__stack_chk_guard}, which is normally defined in @file{libgcc2.c}.
4920 @hook TARGET_STACK_PROTECT_FAIL
4921 This hook returns a tree expression that alerts the runtime that the
4922 stack protect guard variable has been modified. This expression should
4923 involve a call to a @code{noreturn} function.
4925 The default version of this hook invokes a function called
4926 @samp{__stack_chk_fail}, taking no arguments. This function is
4927 normally defined in @file{libgcc2.c}.
4930 @hook TARGET_SUPPORTS_SPLIT_STACK
4933 @section Implementing the Varargs Macros
4934 @cindex varargs implementation
4936 GCC comes with an implementation of @code{<varargs.h>} and
4937 @code{<stdarg.h>} that work without change on machines that pass arguments
4938 on the stack. Other machines require their own implementations of
4939 varargs, and the two machine independent header files must have
4940 conditionals to include it.
4942 ISO @code{<stdarg.h>} differs from traditional @code{<varargs.h>} mainly in
4943 the calling convention for @code{va_start}. The traditional
4944 implementation takes just one argument, which is the variable in which
4945 to store the argument pointer. The ISO implementation of
4946 @code{va_start} takes an additional second argument. The user is
4947 supposed to write the last named argument of the function here.
4949 However, @code{va_start} should not use this argument. The way to find
4950 the end of the named arguments is with the built-in functions described
4953 @defmac __builtin_saveregs ()
4954 Use this built-in function to save the argument registers in memory so
4955 that the varargs mechanism can access them. Both ISO and traditional
4956 versions of @code{va_start} must use @code{__builtin_saveregs}, unless
4957 you use @code{TARGET_SETUP_INCOMING_VARARGS} (see below) instead.
4959 On some machines, @code{__builtin_saveregs} is open-coded under the
4960 control of the target hook @code{TARGET_EXPAND_BUILTIN_SAVEREGS}. On
4961 other machines, it calls a routine written in assembler language,
4962 found in @file{libgcc2.c}.
4964 Code generated for the call to @code{__builtin_saveregs} appears at the
4965 beginning of the function, as opposed to where the call to
4966 @code{__builtin_saveregs} is written, regardless of what the code is.
4967 This is because the registers must be saved before the function starts
4968 to use them for its own purposes.
4969 @c i rewrote the first sentence above to fix an overfull hbox. --mew
4973 @defmac __builtin_next_arg (@var{lastarg})
4974 This builtin returns the address of the first anonymous stack
4975 argument, as type @code{void *}. If @code{ARGS_GROW_DOWNWARD}, it
4976 returns the address of the location above the first anonymous stack
4977 argument. Use it in @code{va_start} to initialize the pointer for
4978 fetching arguments from the stack. Also use it in @code{va_start} to
4979 verify that the second parameter @var{lastarg} is the last named argument
4980 of the current function.
4983 @defmac __builtin_classify_type (@var{object})
4984 Since each machine has its own conventions for which data types are
4985 passed in which kind of register, your implementation of @code{va_arg}
4986 has to embody these conventions. The easiest way to categorize the
4987 specified data type is to use @code{__builtin_classify_type} together
4988 with @code{sizeof} and @code{__alignof__}.
4990 @code{__builtin_classify_type} ignores the value of @var{object},
4991 considering only its data type. It returns an integer describing what
4992 kind of type that is---integer, floating, pointer, structure, and so on.
4994 The file @file{typeclass.h} defines an enumeration that you can use to
4995 interpret the values of @code{__builtin_classify_type}.
4998 These machine description macros help implement varargs:
5000 @hook TARGET_EXPAND_BUILTIN_SAVEREGS
5001 If defined, this hook produces the machine-specific code for a call to
5002 @code{__builtin_saveregs}. This code will be moved to the very
5003 beginning of the function, before any parameter access are made. The
5004 return value of this function should be an RTX that contains the value
5005 to use as the return of @code{__builtin_saveregs}.
5008 @hook TARGET_SETUP_INCOMING_VARARGS
5009 This target hook offers an alternative to using
5010 @code{__builtin_saveregs} and defining the hook
5011 @code{TARGET_EXPAND_BUILTIN_SAVEREGS}. Use it to store the anonymous
5012 register arguments into the stack so that all the arguments appear to
5013 have been passed consecutively on the stack. Once this is done, you can
5014 use the standard implementation of varargs that works for machines that
5015 pass all their arguments on the stack.
5017 The argument @var{args_so_far} points to the @code{CUMULATIVE_ARGS} data
5018 structure, containing the values that are obtained after processing the
5019 named arguments. The arguments @var{mode} and @var{type} describe the
5020 last named argument---its machine mode and its data type as a tree node.
5022 The target hook should do two things: first, push onto the stack all the
5023 argument registers @emph{not} used for the named arguments, and second,
5024 store the size of the data thus pushed into the @code{int}-valued
5025 variable pointed to by @var{pretend_args_size}. The value that you
5026 store here will serve as additional offset for setting up the stack
5029 Because you must generate code to push the anonymous arguments at
5030 compile time without knowing their data types,
5031 @code{TARGET_SETUP_INCOMING_VARARGS} is only useful on machines that
5032 have just a single category of argument register and use it uniformly
5035 If the argument @var{second_time} is nonzero, it means that the
5036 arguments of the function are being analyzed for the second time. This
5037 happens for an inline function, which is not actually compiled until the
5038 end of the source file. The hook @code{TARGET_SETUP_INCOMING_VARARGS} should
5039 not generate any instructions in this case.
5042 @hook TARGET_STRICT_ARGUMENT_NAMING
5043 Define this hook to return @code{true} if the location where a function
5044 argument is passed depends on whether or not it is a named argument.
5046 This hook controls how the @var{named} argument to @code{FUNCTION_ARG}
5047 is set for varargs and stdarg functions. If this hook returns
5048 @code{true}, the @var{named} argument is always true for named
5049 arguments, and false for unnamed arguments. If it returns @code{false},
5050 but @code{TARGET_PRETEND_OUTGOING_VARARGS_NAMED} returns @code{true},
5051 then all arguments are treated as named. Otherwise, all named arguments
5052 except the last are treated as named.
5054 You need not define this hook if it always returns @code{false}.
5057 @hook TARGET_PRETEND_OUTGOING_VARARGS_NAMED
5058 If you need to conditionally change ABIs so that one works with
5059 @code{TARGET_SETUP_INCOMING_VARARGS}, but the other works like neither
5060 @code{TARGET_SETUP_INCOMING_VARARGS} nor @code{TARGET_STRICT_ARGUMENT_NAMING} was
5061 defined, then define this hook to return @code{true} if
5062 @code{TARGET_SETUP_INCOMING_VARARGS} is used, @code{false} otherwise.
5063 Otherwise, you should not define this hook.
5067 @section Trampolines for Nested Functions
5068 @cindex trampolines for nested functions
5069 @cindex nested functions, trampolines for
5071 A @dfn{trampoline} is a small piece of code that is created at run time
5072 when the address of a nested function is taken. It normally resides on
5073 the stack, in the stack frame of the containing function. These macros
5074 tell GCC how to generate code to allocate and initialize a
5077 The instructions in the trampoline must do two things: load a constant
5078 address into the static chain register, and jump to the real address of
5079 the nested function. On CISC machines such as the m68k, this requires
5080 two instructions, a move immediate and a jump. Then the two addresses
5081 exist in the trampoline as word-long immediate operands. On RISC
5082 machines, it is often necessary to load each address into a register in
5083 two parts. Then pieces of each address form separate immediate
5086 The code generated to initialize the trampoline must store the variable
5087 parts---the static chain value and the function address---into the
5088 immediate operands of the instructions. On a CISC machine, this is
5089 simply a matter of copying each address to a memory reference at the
5090 proper offset from the start of the trampoline. On a RISC machine, it
5091 may be necessary to take out pieces of the address and store them
5094 @hook TARGET_ASM_TRAMPOLINE_TEMPLATE
5095 This hook is called by @code{assemble_trampoline_template} to output,
5096 on the stream @var{f}, assembler code for a block of data that contains
5097 the constant parts of a trampoline. This code should not include a
5098 label---the label is taken care of automatically.
5100 If you do not define this hook, it means no template is needed
5101 for the target. Do not define this hook on systems where the block move
5102 code to copy the trampoline into place would be larger than the code
5103 to generate it on the spot.
5106 @defmac TRAMPOLINE_SECTION
5107 Return the section into which the trampoline template is to be placed
5108 (@pxref{Sections}). The default value is @code{readonly_data_section}.
5111 @defmac TRAMPOLINE_SIZE
5112 A C expression for the size in bytes of the trampoline, as an integer.
5115 @defmac TRAMPOLINE_ALIGNMENT
5116 Alignment required for trampolines, in bits.
5118 If you don't define this macro, the value of @code{FUNCTION_ALIGNMENT}
5119 is used for aligning trampolines.
5122 @hook TARGET_TRAMPOLINE_INIT
5123 This hook is called to initialize a trampoline.
5124 @var{m_tramp} is an RTX for the memory block for the trampoline; @var{fndecl}
5125 is the @code{FUNCTION_DECL} for the nested function; @var{static_chain} is an
5126 RTX for the static chain value that should be passed to the function
5129 If the target defines @code{TARGET_ASM_TRAMPOLINE_TEMPLATE}, then the
5130 first thing this hook should do is emit a block move into @var{m_tramp}
5131 from the memory block returned by @code{assemble_trampoline_template}.
5132 Note that the block move need only cover the constant parts of the
5133 trampoline. If the target isolates the variable parts of the trampoline
5134 to the end, not all @code{TRAMPOLINE_SIZE} bytes need be copied.
5136 If the target requires any other actions, such as flushing caches or
5137 enabling stack execution, these actions should be performed after
5138 initializing the trampoline proper.
5141 @hook TARGET_TRAMPOLINE_ADJUST_ADDRESS
5142 This hook should perform any machine-specific adjustment in
5143 the address of the trampoline. Its argument contains the address of the
5144 memory block that was passed to @code{TARGET_TRAMPOLINE_INIT}. In case
5145 the address to be used for a function call should be different from the
5146 address at which the template was stored, the different address should
5147 be returned; otherwise @var{addr} should be returned unchanged.
5148 If this hook is not defined, @var{addr} will be used for function calls.
5151 Implementing trampolines is difficult on many machines because they have
5152 separate instruction and data caches. Writing into a stack location
5153 fails to clear the memory in the instruction cache, so when the program
5154 jumps to that location, it executes the old contents.
5156 Here are two possible solutions. One is to clear the relevant parts of
5157 the instruction cache whenever a trampoline is set up. The other is to
5158 make all trampolines identical, by having them jump to a standard
5159 subroutine. The former technique makes trampoline execution faster; the
5160 latter makes initialization faster.
5162 To clear the instruction cache when a trampoline is initialized, define
5163 the following macro.
5165 @defmac CLEAR_INSN_CACHE (@var{beg}, @var{end})
5166 If defined, expands to a C expression clearing the @emph{instruction
5167 cache} in the specified interval. The definition of this macro would
5168 typically be a series of @code{asm} statements. Both @var{beg} and
5169 @var{end} are both pointer expressions.
5172 The operating system may also require the stack to be made executable
5173 before calling the trampoline. To implement this requirement, define
5174 the following macro.
5176 @defmac ENABLE_EXECUTE_STACK
5177 Define this macro if certain operations must be performed before executing
5178 code located on the stack. The macro should expand to a series of C
5179 file-scope constructs (e.g.@: functions) and provide a unique entry point
5180 named @code{__enable_execute_stack}. The target is responsible for
5181 emitting calls to the entry point in the code, for example from the
5182 @code{TARGET_TRAMPOLINE_INIT} hook.
5185 To use a standard subroutine, define the following macro. In addition,
5186 you must make sure that the instructions in a trampoline fill an entire
5187 cache line with identical instructions, or else ensure that the
5188 beginning of the trampoline code is always aligned at the same point in
5189 its cache line. Look in @file{m68k.h} as a guide.
5191 @defmac TRANSFER_FROM_TRAMPOLINE
5192 Define this macro if trampolines need a special subroutine to do their
5193 work. The macro should expand to a series of @code{asm} statements
5194 which will be compiled with GCC@. They go in a library function named
5195 @code{__transfer_from_trampoline}.
5197 If you need to avoid executing the ordinary prologue code of a compiled
5198 C function when you jump to the subroutine, you can do so by placing a
5199 special label of your own in the assembler code. Use one @code{asm}
5200 statement to generate an assembler label, and another to make the label
5201 global. Then trampolines can use that label to jump directly to your
5202 special assembler code.
5206 @section Implicit Calls to Library Routines
5207 @cindex library subroutine names
5208 @cindex @file{libgcc.a}
5210 @c prevent bad page break with this line
5211 Here is an explanation of implicit calls to library routines.
5213 @defmac DECLARE_LIBRARY_RENAMES
5214 This macro, if defined, should expand to a piece of C code that will get
5215 expanded when compiling functions for libgcc.a. It can be used to
5216 provide alternate names for GCC's internal library functions if there
5217 are ABI-mandated names that the compiler should provide.
5220 @findex set_optab_libfunc
5221 @findex init_one_libfunc
5222 @hook TARGET_INIT_LIBFUNCS
5223 This hook should declare additional library routines or rename
5224 existing ones, using the functions @code{set_optab_libfunc} and
5225 @code{init_one_libfunc} defined in @file{optabs.c}.
5226 @code{init_optabs} calls this macro after initializing all the normal
5229 The default is to do nothing. Most ports don't need to define this hook.
5232 @defmac FLOAT_LIB_COMPARE_RETURNS_BOOL (@var{mode}, @var{comparison})
5233 This macro should return @code{true} if the library routine that
5234 implements the floating point comparison operator @var{comparison} in
5235 mode @var{mode} will return a boolean, and @var{false} if it will
5238 GCC's own floating point libraries return tristates from the
5239 comparison operators, so the default returns false always. Most ports
5240 don't need to define this macro.
5243 @defmac TARGET_LIB_INT_CMP_BIASED
5244 This macro should evaluate to @code{true} if the integer comparison
5245 functions (like @code{__cmpdi2}) return 0 to indicate that the first
5246 operand is smaller than the second, 1 to indicate that they are equal,
5247 and 2 to indicate that the first operand is greater than the second.
5248 If this macro evaluates to @code{false} the comparison functions return
5249 @minus{}1, 0, and 1 instead of 0, 1, and 2. If the target uses the routines
5250 in @file{libgcc.a}, you do not need to define this macro.
5253 @cindex US Software GOFAST, floating point emulation library
5254 @cindex floating point emulation library, US Software GOFAST
5255 @cindex GOFAST, floating point emulation library
5256 @findex gofast_maybe_init_libfuncs
5257 @defmac US_SOFTWARE_GOFAST
5258 Define this macro if your system C library uses the US Software GOFAST
5259 library to provide floating point emulation.
5261 In addition to defining this macro, your architecture must set
5262 @code{TARGET_INIT_LIBFUNCS} to @code{gofast_maybe_init_libfuncs}, or
5263 else call that function from its version of that hook. It is defined
5264 in @file{config/gofast.h}, which must be included by your
5265 architecture's @file{@var{cpu}.c} file. See @file{sparc/sparc.c} for
5268 If this macro is defined, the
5269 @code{TARGET_FLOAT_LIB_COMPARE_RETURNS_BOOL} target hook must return
5270 false for @code{SFmode} and @code{DFmode} comparisons.
5273 @cindex @code{EDOM}, implicit usage
5276 The value of @code{EDOM} on the target machine, as a C integer constant
5277 expression. If you don't define this macro, GCC does not attempt to
5278 deposit the value of @code{EDOM} into @code{errno} directly. Look in
5279 @file{/usr/include/errno.h} to find the value of @code{EDOM} on your
5282 If you do not define @code{TARGET_EDOM}, then compiled code reports
5283 domain errors by calling the library function and letting it report the
5284 error. If mathematical functions on your system use @code{matherr} when
5285 there is an error, then you should leave @code{TARGET_EDOM} undefined so
5286 that @code{matherr} is used normally.
5289 @cindex @code{errno}, implicit usage
5290 @defmac GEN_ERRNO_RTX
5291 Define this macro as a C expression to create an rtl expression that
5292 refers to the global ``variable'' @code{errno}. (On certain systems,
5293 @code{errno} may not actually be a variable.) If you don't define this
5294 macro, a reasonable default is used.
5297 @cindex C99 math functions, implicit usage
5298 @defmac TARGET_C99_FUNCTIONS
5299 When this macro is nonzero, GCC will implicitly optimize @code{sin} calls into
5300 @code{sinf} and similarly for other functions defined by C99 standard. The
5301 default is zero because a number of existing systems lack support for these
5302 functions in their runtime so this macro needs to be redefined to one on
5303 systems that do support the C99 runtime.
5306 @cindex sincos math function, implicit usage
5307 @defmac TARGET_HAS_SINCOS
5308 When this macro is nonzero, GCC will implicitly optimize calls to @code{sin}
5309 and @code{cos} with the same argument to a call to @code{sincos}. The
5310 default is zero. The target has to provide the following functions:
5312 void sincos(double x, double *sin, double *cos);
5313 void sincosf(float x, float *sin, float *cos);
5314 void sincosl(long double x, long double *sin, long double *cos);
5318 @defmac NEXT_OBJC_RUNTIME
5319 Define this macro to generate code for Objective-C message sending using
5320 the calling convention of the NeXT system. This calling convention
5321 involves passing the object, the selector and the method arguments all
5322 at once to the method-lookup library function.
5324 The default calling convention passes just the object and the selector
5325 to the lookup function, which returns a pointer to the method.
5328 @node Addressing Modes
5329 @section Addressing Modes
5330 @cindex addressing modes
5332 @c prevent bad page break with this line
5333 This is about addressing modes.
5335 @defmac HAVE_PRE_INCREMENT
5336 @defmacx HAVE_PRE_DECREMENT
5337 @defmacx HAVE_POST_INCREMENT
5338 @defmacx HAVE_POST_DECREMENT
5339 A C expression that is nonzero if the machine supports pre-increment,
5340 pre-decrement, post-increment, or post-decrement addressing respectively.
5343 @defmac HAVE_PRE_MODIFY_DISP
5344 @defmacx HAVE_POST_MODIFY_DISP
5345 A C expression that is nonzero if the machine supports pre- or
5346 post-address side-effect generation involving constants other than
5347 the size of the memory operand.
5350 @defmac HAVE_PRE_MODIFY_REG
5351 @defmacx HAVE_POST_MODIFY_REG
5352 A C expression that is nonzero if the machine supports pre- or
5353 post-address side-effect generation involving a register displacement.
5356 @defmac CONSTANT_ADDRESS_P (@var{x})
5357 A C expression that is 1 if the RTX @var{x} is a constant which
5358 is a valid address. On most machines the default definition of
5359 @code{(CONSTANT_P (@var{x}) && GET_CODE (@var{x}) != CONST_DOUBLE)}
5360 is acceptable, but a few machines are more restrictive as to which
5361 constant addresses are supported.
5364 @defmac CONSTANT_P (@var{x})
5365 @code{CONSTANT_P}, which is defined by target-independent code,
5366 accepts integer-values expressions whose values are not explicitly
5367 known, such as @code{symbol_ref}, @code{label_ref}, and @code{high}
5368 expressions and @code{const} arithmetic expressions, in addition to
5369 @code{const_int} and @code{const_double} expressions.
5372 @defmac MAX_REGS_PER_ADDRESS
5373 A number, the maximum number of registers that can appear in a valid
5374 memory address. Note that it is up to you to specify a value equal to
5375 the maximum number that @code{TARGET_LEGITIMATE_ADDRESS_P} would ever
5379 @hook TARGET_LEGITIMATE_ADDRESS_P
5380 A function that returns whether @var{x} (an RTX) is a legitimate memory
5381 address on the target machine for a memory operand of mode @var{mode}.
5383 Legitimate addresses are defined in two variants: a strict variant and a
5384 non-strict one. The @var{strict} parameter chooses which variant is
5385 desired by the caller.
5387 The strict variant is used in the reload pass. It must be defined so
5388 that any pseudo-register that has not been allocated a hard register is
5389 considered a memory reference. This is because in contexts where some
5390 kind of register is required, a pseudo-register with no hard register
5391 must be rejected. For non-hard registers, the strict variant should look
5392 up the @code{reg_renumber} array; it should then proceed using the hard
5393 register number in the array, or treat the pseudo as a memory reference
5394 if the array holds @code{-1}.
5396 The non-strict variant is used in other passes. It must be defined to
5397 accept all pseudo-registers in every context where some kind of
5398 register is required.
5400 Normally, constant addresses which are the sum of a @code{symbol_ref}
5401 and an integer are stored inside a @code{const} RTX to mark them as
5402 constant. Therefore, there is no need to recognize such sums
5403 specifically as legitimate addresses. Normally you would simply
5404 recognize any @code{const} as legitimate.
5406 Usually @code{PRINT_OPERAND_ADDRESS} is not prepared to handle constant
5407 sums that are not marked with @code{const}. It assumes that a naked
5408 @code{plus} indicates indexing. If so, then you @emph{must} reject such
5409 naked constant sums as illegitimate addresses, so that none of them will
5410 be given to @code{PRINT_OPERAND_ADDRESS}.
5412 @cindex @code{TARGET_ENCODE_SECTION_INFO} and address validation
5413 On some machines, whether a symbolic address is legitimate depends on
5414 the section that the address refers to. On these machines, define the
5415 target hook @code{TARGET_ENCODE_SECTION_INFO} to store the information
5416 into the @code{symbol_ref}, and then check for it here. When you see a
5417 @code{const}, you will have to look inside it to find the
5418 @code{symbol_ref} in order to determine the section. @xref{Assembler
5421 @cindex @code{GO_IF_LEGITIMATE_ADDRESS}
5422 Some ports are still using a deprecated legacy substitute for
5423 this hook, the @code{GO_IF_LEGITIMATE_ADDRESS} macro. This macro
5427 #define GO_IF_LEGITIMATE_ADDRESS (@var{mode}, @var{x}, @var{label})
5431 and should @code{goto @var{label}} if the address @var{x} is a valid
5432 address on the target machine for a memory operand of mode @var{mode}.
5434 @findex REG_OK_STRICT
5435 Compiler source files that want to use the strict variant of this
5436 macro define the macro @code{REG_OK_STRICT}. You should use an
5437 @code{#ifdef REG_OK_STRICT} conditional to define the strict variant in
5438 that case and the non-strict variant otherwise.
5440 Using the hook is usually simpler because it limits the number of
5441 files that are recompiled when changes are made.
5444 @defmac TARGET_MEM_CONSTRAINT
5445 A single character to be used instead of the default @code{'m'}
5446 character for general memory addresses. This defines the constraint
5447 letter which matches the memory addresses accepted by
5448 @code{TARGET_LEGITIMATE_ADDRESS_P}. Define this macro if you want to
5449 support new address formats in your back end without changing the
5450 semantics of the @code{'m'} constraint. This is necessary in order to
5451 preserve functionality of inline assembly constructs using the
5452 @code{'m'} constraint.
5455 @defmac FIND_BASE_TERM (@var{x})
5456 A C expression to determine the base term of address @var{x},
5457 or to provide a simplified version of @var{x} from which @file{alias.c}
5458 can easily find the base term. This macro is used in only two places:
5459 @code{find_base_value} and @code{find_base_term} in @file{alias.c}.
5461 It is always safe for this macro to not be defined. It exists so
5462 that alias analysis can understand machine-dependent addresses.
5464 The typical use of this macro is to handle addresses containing
5465 a label_ref or symbol_ref within an UNSPEC@.
5468 @hook TARGET_LEGITIMIZE_ADDRESS
5469 This hook is given an invalid memory address @var{x} for an
5470 operand of mode @var{mode} and should try to return a valid memory
5473 @findex break_out_memory_refs
5474 @var{x} will always be the result of a call to @code{break_out_memory_refs},
5475 and @var{oldx} will be the operand that was given to that function to produce
5478 The code of the hook should not alter the substructure of
5479 @var{x}. If it transforms @var{x} into a more legitimate form, it
5480 should return the new @var{x}.
5482 It is not necessary for this hook to come up with a legitimate address.
5483 The compiler has standard ways of doing so in all cases. In fact, it
5484 is safe to omit this hook or make it return @var{x} if it cannot find
5485 a valid way to legitimize the address. But often a machine-dependent
5486 strategy can generate better code.
5489 @defmac LEGITIMIZE_RELOAD_ADDRESS (@var{x}, @var{mode}, @var{opnum}, @var{type}, @var{ind_levels}, @var{win})
5490 A C compound statement that attempts to replace @var{x}, which is an address
5491 that needs reloading, with a valid memory address for an operand of mode
5492 @var{mode}. @var{win} will be a C statement label elsewhere in the code.
5493 It is not necessary to define this macro, but it might be useful for
5494 performance reasons.
5496 For example, on the i386, it is sometimes possible to use a single
5497 reload register instead of two by reloading a sum of two pseudo
5498 registers into a register. On the other hand, for number of RISC
5499 processors offsets are limited so that often an intermediate address
5500 needs to be generated in order to address a stack slot. By defining
5501 @code{LEGITIMIZE_RELOAD_ADDRESS} appropriately, the intermediate addresses
5502 generated for adjacent some stack slots can be made identical, and thus
5505 @emph{Note}: This macro should be used with caution. It is necessary
5506 to know something of how reload works in order to effectively use this,
5507 and it is quite easy to produce macros that build in too much knowledge
5508 of reload internals.
5510 @emph{Note}: This macro must be able to reload an address created by a
5511 previous invocation of this macro. If it fails to handle such addresses
5512 then the compiler may generate incorrect code or abort.
5515 The macro definition should use @code{push_reload} to indicate parts that
5516 need reloading; @var{opnum}, @var{type} and @var{ind_levels} are usually
5517 suitable to be passed unaltered to @code{push_reload}.
5519 The code generated by this macro must not alter the substructure of
5520 @var{x}. If it transforms @var{x} into a more legitimate form, it
5521 should assign @var{x} (which will always be a C variable) a new value.
5522 This also applies to parts that you change indirectly by calling
5525 @findex strict_memory_address_p
5526 The macro definition may use @code{strict_memory_address_p} to test if
5527 the address has become legitimate.
5530 If you want to change only a part of @var{x}, one standard way of doing
5531 this is to use @code{copy_rtx}. Note, however, that it unshares only a
5532 single level of rtl. Thus, if the part to be changed is not at the
5533 top level, you'll need to replace first the top level.
5534 It is not necessary for this macro to come up with a legitimate
5535 address; but often a machine-dependent strategy can generate better code.
5538 @hook TARGET_MODE_DEPENDENT_ADDRESS_P
5539 This hook returns @code{true} if memory address @var{addr} can have
5540 different meanings depending on the machine mode of the memory
5541 reference it is used for or if the address is valid for some modes
5544 Autoincrement and autodecrement addresses typically have mode-dependent
5545 effects because the amount of the increment or decrement is the size
5546 of the operand being addressed. Some machines have other mode-dependent
5547 addresses. Many RISC machines have no mode-dependent addresses.
5549 You may assume that @var{addr} is a valid address for the machine.
5551 The default version of this hook returns @code{false}.
5554 @defmac GO_IF_MODE_DEPENDENT_ADDRESS (@var{addr}, @var{label})
5555 A C statement or compound statement with a conditional @code{goto
5556 @var{label};} executed if memory address @var{x} (an RTX) can have
5557 different meanings depending on the machine mode of the memory
5558 reference it is used for or if the address is valid for some modes
5561 Autoincrement and autodecrement addresses typically have mode-dependent
5562 effects because the amount of the increment or decrement is the size
5563 of the operand being addressed. Some machines have other mode-dependent
5564 addresses. Many RISC machines have no mode-dependent addresses.
5566 You may assume that @var{addr} is a valid address for the machine.
5568 These are obsolete macros, replaced by the
5569 @code{TARGET_MODE_DEPENDENT_ADDRESS_P} target hook.
5572 @defmac LEGITIMATE_CONSTANT_P (@var{x})
5573 A C expression that is nonzero if @var{x} is a legitimate constant for
5574 an immediate operand on the target machine. You can assume that
5575 @var{x} satisfies @code{CONSTANT_P}, so you need not check this. In fact,
5576 @samp{1} is a suitable definition for this macro on machines where
5577 anything @code{CONSTANT_P} is valid.
5580 @hook TARGET_DELEGITIMIZE_ADDRESS
5581 This hook is used to undo the possibly obfuscating effects of the
5582 @code{LEGITIMIZE_ADDRESS} and @code{LEGITIMIZE_RELOAD_ADDRESS} target
5583 macros. Some backend implementations of these macros wrap symbol
5584 references inside an @code{UNSPEC} rtx to represent PIC or similar
5585 addressing modes. This target hook allows GCC's optimizers to understand
5586 the semantics of these opaque @code{UNSPEC}s by converting them back
5587 into their original form.
5590 @hook TARGET_CANNOT_FORCE_CONST_MEM
5591 This hook should return true if @var{x} is of a form that cannot (or
5592 should not) be spilled to the constant pool. The default version of
5593 this hook returns false.
5595 The primary reason to define this hook is to prevent reload from
5596 deciding that a non-legitimate constant would be better reloaded
5597 from the constant pool instead of spilling and reloading a register
5598 holding the constant. This restriction is often true of addresses
5599 of TLS symbols for various targets.
5602 @hook TARGET_USE_BLOCKS_FOR_CONSTANT_P
5603 This hook should return true if pool entries for constant @var{x} can
5604 be placed in an @code{object_block} structure. @var{mode} is the mode
5607 The default version returns false for all constants.
5610 @hook TARGET_BUILTIN_RECIPROCAL
5611 This hook should return the DECL of a function that implements reciprocal of
5612 the builtin function with builtin function code @var{fn}, or
5613 @code{NULL_TREE} if such a function is not available. @var{md_fn} is true
5614 when @var{fn} is a code of a machine-dependent builtin function. When
5615 @var{sqrt} is true, additional optimizations that apply only to the reciprocal
5616 of a square root function are performed, and only reciprocals of @code{sqrt}
5620 @hook TARGET_VECTORIZE_BUILTIN_MASK_FOR_LOAD
5621 This hook should return the DECL of a function @var{f} that given an
5622 address @var{addr} as an argument returns a mask @var{m} that can be
5623 used to extract from two vectors the relevant data that resides in
5624 @var{addr} in case @var{addr} is not properly aligned.
5626 The autovectorizer, when vectorizing a load operation from an address
5627 @var{addr} that may be unaligned, will generate two vector loads from
5628 the two aligned addresses around @var{addr}. It then generates a
5629 @code{REALIGN_LOAD} operation to extract the relevant data from the
5630 two loaded vectors. The first two arguments to @code{REALIGN_LOAD},
5631 @var{v1} and @var{v2}, are the two vectors, each of size @var{VS}, and
5632 the third argument, @var{OFF}, defines how the data will be extracted
5633 from these two vectors: if @var{OFF} is 0, then the returned vector is
5634 @var{v2}; otherwise, the returned vector is composed from the last
5635 @var{VS}-@var{OFF} elements of @var{v1} concatenated to the first
5636 @var{OFF} elements of @var{v2}.
5638 If this hook is defined, the autovectorizer will generate a call
5639 to @var{f} (using the DECL tree that this hook returns) and will
5640 use the return value of @var{f} as the argument @var{OFF} to
5641 @code{REALIGN_LOAD}. Therefore, the mask @var{m} returned by @var{f}
5642 should comply with the semantics expected by @code{REALIGN_LOAD}
5644 If this hook is not defined, then @var{addr} will be used as
5645 the argument @var{OFF} to @code{REALIGN_LOAD}, in which case the low
5646 log2(@var{VS}) @minus{} 1 bits of @var{addr} will be considered.
5649 @hook TARGET_VECTORIZE_BUILTIN_MUL_WIDEN_EVEN
5650 This hook should return the DECL of a function @var{f} that implements
5651 widening multiplication of the even elements of two input vectors of type @var{x}.
5653 If this hook is defined, the autovectorizer will use it along with the
5654 @code{TARGET_VECTORIZE_BUILTIN_MUL_WIDEN_ODD} target hook when vectorizing
5655 widening multiplication in cases that the order of the results does not have to be
5656 preserved (e.g.@: used only by a reduction computation). Otherwise, the
5657 @code{widen_mult_hi/lo} idioms will be used.
5660 @hook TARGET_VECTORIZE_BUILTIN_MUL_WIDEN_ODD
5661 This hook should return the DECL of a function @var{f} that implements
5662 widening multiplication of the odd elements of two input vectors of type @var{x}.
5664 If this hook is defined, the autovectorizer will use it along with the
5665 @code{TARGET_VECTORIZE_BUILTIN_MUL_WIDEN_EVEN} target hook when vectorizing
5666 widening multiplication in cases that the order of the results does not have to be
5667 preserved (e.g.@: used only by a reduction computation). Otherwise, the
5668 @code{widen_mult_hi/lo} idioms will be used.
5671 @hook TARGET_VECTORIZE_BUILTIN_VECTORIZATION_COST
5672 Returns cost of different scalar or vector statements for vectorization cost model.
5673 For vector memory operations the cost may depend on type (@var{vectype}) and
5674 misalignment value (@var{misalign}).
5677 @hook TARGET_VECTORIZE_VECTOR_ALIGNMENT_REACHABLE
5678 Return true if vector alignment is reachable (by peeling N iterations) for the given type.
5681 @hook TARGET_VECTORIZE_BUILTIN_VEC_PERM
5682 Target builtin that implements vector permute.
5685 @hook TARGET_VECTORIZE_BUILTIN_VEC_PERM_OK
5686 Return true if a vector created for @code{builtin_vec_perm} is valid.
5689 @hook TARGET_VECTORIZE_BUILTIN_CONVERSION
5690 This hook should return the DECL of a function that implements conversion of the
5691 input vector of type @var{src_type} to type @var{dest_type}.
5692 The value of @var{code} is one of the enumerators in @code{enum tree_code} and
5693 specifies how the conversion is to be applied
5694 (truncation, rounding, etc.).
5696 If this hook is defined, the autovectorizer will use the
5697 @code{TARGET_VECTORIZE_BUILTIN_CONVERSION} target hook when vectorizing
5698 conversion. Otherwise, it will return @code{NULL_TREE}.
5701 @hook TARGET_VECTORIZE_BUILTIN_VECTORIZED_FUNCTION
5702 This hook should return the decl of a function that implements the
5703 vectorized variant of the builtin function with builtin function code
5704 @var{code} or @code{NULL_TREE} if such a function is not available.
5705 The value of @var{fndecl} is the builtin function declaration. The
5706 return type of the vectorized function shall be of vector type
5707 @var{vec_type_out} and the argument types should be @var{vec_type_in}.
5710 @hook TARGET_VECTORIZE_SUPPORT_VECTOR_MISALIGNMENT
5711 This hook should return true if the target supports misaligned vector
5712 store/load of a specific factor denoted in the @var{misalignment}
5713 parameter. The vector store/load should be of machine mode @var{mode} and
5714 the elements in the vectors should be of type @var{type}. @var{is_packed}
5715 parameter is true if the memory access is defined in a packed struct.
5718 @hook TARGET_VECTORIZE_PREFERRED_SIMD_MODE
5719 This hook should return the preferred mode for vectorizing scalar
5720 mode @var{mode}. The default is
5721 equal to @code{word_mode}, because the vectorizer can do some
5722 transformations even in absence of specialized @acronym{SIMD} hardware.
5725 @hook TARGET_VECTORIZE_AUTOVECTORIZE_VECTOR_SIZES
5726 This hook should return a mask of sizes that should be iterated over
5727 after trying to autovectorize using the vector size derived from the
5728 mode returned by @code{TARGET_VECTORIZE_PREFERRED_SIMD_MODE}.
5729 The default is zero which means to not iterate over other vector sizes.
5732 @node Anchored Addresses
5733 @section Anchored Addresses
5734 @cindex anchored addresses
5735 @cindex @option{-fsection-anchors}
5737 GCC usually addresses every static object as a separate entity.
5738 For example, if we have:
5742 int foo (void) @{ return a + b + c; @}
5745 the code for @code{foo} will usually calculate three separate symbolic
5746 addresses: those of @code{a}, @code{b} and @code{c}. On some targets,
5747 it would be better to calculate just one symbolic address and access
5748 the three variables relative to it. The equivalent pseudocode would
5754 register int *xr = &x;
5755 return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
5759 (which isn't valid C). We refer to shared addresses like @code{x} as
5760 ``section anchors''. Their use is controlled by @option{-fsection-anchors}.
5762 The hooks below describe the target properties that GCC needs to know
5763 in order to make effective use of section anchors. It won't use
5764 section anchors at all unless either @code{TARGET_MIN_ANCHOR_OFFSET}
5765 or @code{TARGET_MAX_ANCHOR_OFFSET} is set to a nonzero value.
5767 @hook TARGET_MIN_ANCHOR_OFFSET
5768 The minimum offset that should be applied to a section anchor.
5769 On most targets, it should be the smallest offset that can be
5770 applied to a base register while still giving a legitimate address
5771 for every mode. The default value is 0.
5774 @hook TARGET_MAX_ANCHOR_OFFSET
5775 Like @code{TARGET_MIN_ANCHOR_OFFSET}, but the maximum (inclusive)
5776 offset that should be applied to section anchors. The default
5780 @hook TARGET_ASM_OUTPUT_ANCHOR
5781 Write the assembly code to define section anchor @var{x}, which is a
5782 @code{SYMBOL_REF} for which @samp{SYMBOL_REF_ANCHOR_P (@var{x})} is true.
5783 The hook is called with the assembly output position set to the beginning
5784 of @code{SYMBOL_REF_BLOCK (@var{x})}.
5786 If @code{ASM_OUTPUT_DEF} is available, the hook's default definition uses
5787 it to define the symbol as @samp{. + SYMBOL_REF_BLOCK_OFFSET (@var{x})}.
5788 If @code{ASM_OUTPUT_DEF} is not available, the hook's default definition
5789 is @code{NULL}, which disables the use of section anchors altogether.
5792 @hook TARGET_USE_ANCHORS_FOR_SYMBOL_P
5793 Return true if GCC should attempt to use anchors to access @code{SYMBOL_REF}
5794 @var{x}. You can assume @samp{SYMBOL_REF_HAS_BLOCK_INFO_P (@var{x})} and
5795 @samp{!SYMBOL_REF_ANCHOR_P (@var{x})}.
5797 The default version is correct for most targets, but you might need to
5798 intercept this hook to handle things like target-specific attributes
5799 or target-specific sections.
5802 @node Condition Code
5803 @section Condition Code Status
5804 @cindex condition code status
5806 The macros in this section can be split in two families, according to the
5807 two ways of representing condition codes in GCC.
5809 The first representation is the so called @code{(cc0)} representation
5810 (@pxref{Jump Patterns}), where all instructions can have an implicit
5811 clobber of the condition codes. The second is the condition code
5812 register representation, which provides better schedulability for
5813 architectures that do have a condition code register, but on which
5814 most instructions do not affect it. The latter category includes
5817 The implicit clobbering poses a strong restriction on the placement of
5818 the definition and use of the condition code, which need to be in adjacent
5819 insns for machines using @code{(cc0)}. This can prevent important
5820 optimizations on some machines. For example, on the IBM RS/6000, there
5821 is a delay for taken branches unless the condition code register is set
5822 three instructions earlier than the conditional branch. The instruction
5823 scheduler cannot perform this optimization if it is not permitted to
5824 separate the definition and use of the condition code register.
5826 For this reason, it is possible and suggested to use a register to
5827 represent the condition code for new ports. If there is a specific
5828 condition code register in the machine, use a hard register. If the
5829 condition code or comparison result can be placed in any general register,
5830 or if there are multiple condition registers, use a pseudo register.
5831 Registers used to store the condition code value will usually have a mode
5832 that is in class @code{MODE_CC}.
5834 Alternatively, you can use @code{BImode} if the comparison operator is
5835 specified already in the compare instruction. In this case, you are not
5836 interested in most macros in this section.
5839 * CC0 Condition Codes:: Old style representation of condition codes.
5840 * MODE_CC Condition Codes:: Modern representation of condition codes.
5841 * Cond Exec Macros:: Macros to control conditional execution.
5844 @node CC0 Condition Codes
5845 @subsection Representation of condition codes using @code{(cc0)}
5849 The file @file{conditions.h} defines a variable @code{cc_status} to
5850 describe how the condition code was computed (in case the interpretation of
5851 the condition code depends on the instruction that it was set by). This
5852 variable contains the RTL expressions on which the condition code is
5853 currently based, and several standard flags.
5855 Sometimes additional machine-specific flags must be defined in the machine
5856 description header file. It can also add additional machine-specific
5857 information by defining @code{CC_STATUS_MDEP}.
5859 @defmac CC_STATUS_MDEP
5860 C code for a data type which is used for declaring the @code{mdep}
5861 component of @code{cc_status}. It defaults to @code{int}.
5863 This macro is not used on machines that do not use @code{cc0}.
5866 @defmac CC_STATUS_MDEP_INIT
5867 A C expression to initialize the @code{mdep} field to ``empty''.
5868 The default definition does nothing, since most machines don't use
5869 the field anyway. If you want to use the field, you should probably
5870 define this macro to initialize it.
5872 This macro is not used on machines that do not use @code{cc0}.
5875 @defmac NOTICE_UPDATE_CC (@var{exp}, @var{insn})
5876 A C compound statement to set the components of @code{cc_status}
5877 appropriately for an insn @var{insn} whose body is @var{exp}. It is
5878 this macro's responsibility to recognize insns that set the condition
5879 code as a byproduct of other activity as well as those that explicitly
5882 This macro is not used on machines that do not use @code{cc0}.
5884 If there are insns that do not set the condition code but do alter
5885 other machine registers, this macro must check to see whether they
5886 invalidate the expressions that the condition code is recorded as
5887 reflecting. For example, on the 68000, insns that store in address
5888 registers do not set the condition code, which means that usually
5889 @code{NOTICE_UPDATE_CC} can leave @code{cc_status} unaltered for such
5890 insns. But suppose that the previous insn set the condition code
5891 based on location @samp{a4@@(102)} and the current insn stores a new
5892 value in @samp{a4}. Although the condition code is not changed by
5893 this, it will no longer be true that it reflects the contents of
5894 @samp{a4@@(102)}. Therefore, @code{NOTICE_UPDATE_CC} must alter
5895 @code{cc_status} in this case to say that nothing is known about the
5896 condition code value.
5898 The definition of @code{NOTICE_UPDATE_CC} must be prepared to deal
5899 with the results of peephole optimization: insns whose patterns are
5900 @code{parallel} RTXs containing various @code{reg}, @code{mem} or
5901 constants which are just the operands. The RTL structure of these
5902 insns is not sufficient to indicate what the insns actually do. What
5903 @code{NOTICE_UPDATE_CC} should do when it sees one is just to run
5904 @code{CC_STATUS_INIT}.
5906 A possible definition of @code{NOTICE_UPDATE_CC} is to call a function
5907 that looks at an attribute (@pxref{Insn Attributes}) named, for example,
5908 @samp{cc}. This avoids having detailed information about patterns in
5909 two places, the @file{md} file and in @code{NOTICE_UPDATE_CC}.
5912 @node MODE_CC Condition Codes
5913 @subsection Representation of condition codes using registers
5917 @defmac SELECT_CC_MODE (@var{op}, @var{x}, @var{y})
5918 On many machines, the condition code may be produced by other instructions
5919 than compares, for example the branch can use directly the condition
5920 code set by a subtract instruction. However, on some machines
5921 when the condition code is set this way some bits (such as the overflow
5922 bit) are not set in the same way as a test instruction, so that a different
5923 branch instruction must be used for some conditional branches. When
5924 this happens, use the machine mode of the condition code register to
5925 record different formats of the condition code register. Modes can
5926 also be used to record which compare instruction (e.g. a signed or an
5927 unsigned comparison) produced the condition codes.
5929 If other modes than @code{CCmode} are required, add them to
5930 @file{@var{machine}-modes.def} and define @code{SELECT_CC_MODE} to choose
5931 a mode given an operand of a compare. This is needed because the modes
5932 have to be chosen not only during RTL generation but also, for example,
5933 by instruction combination. The result of @code{SELECT_CC_MODE} should
5934 be consistent with the mode used in the patterns; for example to support
5935 the case of the add on the SPARC discussed above, we have the pattern
5939 [(set (reg:CC_NOOV 0)
5941 (plus:SI (match_operand:SI 0 "register_operand" "%r")
5942 (match_operand:SI 1 "arith_operand" "rI"))
5949 together with a @code{SELECT_CC_MODE} that returns @code{CC_NOOVmode}
5950 for comparisons whose argument is a @code{plus}:
5953 #define SELECT_CC_MODE(OP,X,Y) \
5954 (GET_MODE_CLASS (GET_MODE (X)) == MODE_FLOAT \
5955 ? ((OP == EQ || OP == NE) ? CCFPmode : CCFPEmode) \
5956 : ((GET_CODE (X) == PLUS || GET_CODE (X) == MINUS \
5957 || GET_CODE (X) == NEG) \
5958 ? CC_NOOVmode : CCmode))
5961 Another reason to use modes is to retain information on which operands
5962 were used by the comparison; see @code{REVERSIBLE_CC_MODE} later in
5965 You should define this macro if and only if you define extra CC modes
5966 in @file{@var{machine}-modes.def}.
5969 @defmac CANONICALIZE_COMPARISON (@var{code}, @var{op0}, @var{op1})
5970 On some machines not all possible comparisons are defined, but you can
5971 convert an invalid comparison into a valid one. For example, the Alpha
5972 does not have a @code{GT} comparison, but you can use an @code{LT}
5973 comparison instead and swap the order of the operands.
5975 On such machines, define this macro to be a C statement to do any
5976 required conversions. @var{code} is the initial comparison code
5977 and @var{op0} and @var{op1} are the left and right operands of the
5978 comparison, respectively. You should modify @var{code}, @var{op0}, and
5979 @var{op1} as required.
5981 GCC will not assume that the comparison resulting from this macro is
5982 valid but will see if the resulting insn matches a pattern in the
5985 You need not define this macro if it would never change the comparison
5989 @defmac REVERSIBLE_CC_MODE (@var{mode})
5990 A C expression whose value is one if it is always safe to reverse a
5991 comparison whose mode is @var{mode}. If @code{SELECT_CC_MODE}
5992 can ever return @var{mode} for a floating-point inequality comparison,
5993 then @code{REVERSIBLE_CC_MODE (@var{mode})} must be zero.
5995 You need not define this macro if it would always returns zero or if the
5996 floating-point format is anything other than @code{IEEE_FLOAT_FORMAT}.
5997 For example, here is the definition used on the SPARC, where floating-point
5998 inequality comparisons are always given @code{CCFPEmode}:
6001 #define REVERSIBLE_CC_MODE(MODE) ((MODE) != CCFPEmode)
6005 @defmac REVERSE_CONDITION (@var{code}, @var{mode})
6006 A C expression whose value is reversed condition code of the @var{code} for
6007 comparison done in CC_MODE @var{mode}. The macro is used only in case
6008 @code{REVERSIBLE_CC_MODE (@var{mode})} is nonzero. Define this macro in case
6009 machine has some non-standard way how to reverse certain conditionals. For
6010 instance in case all floating point conditions are non-trapping, compiler may
6011 freely convert unordered compares to ordered one. Then definition may look
6015 #define REVERSE_CONDITION(CODE, MODE) \
6016 ((MODE) != CCFPmode ? reverse_condition (CODE) \
6017 : reverse_condition_maybe_unordered (CODE))
6021 @hook TARGET_FIXED_CONDITION_CODE_REGS
6022 On targets which do not use @code{(cc0)}, and which use a hard
6023 register rather than a pseudo-register to hold condition codes, the
6024 regular CSE passes are often not able to identify cases in which the
6025 hard register is set to a common value. Use this hook to enable a
6026 small pass which optimizes such cases. This hook should return true
6027 to enable this pass, and it should set the integers to which its
6028 arguments point to the hard register numbers used for condition codes.
6029 When there is only one such register, as is true on most systems, the
6030 integer pointed to by @var{p2} should be set to
6031 @code{INVALID_REGNUM}.
6033 The default version of this hook returns false.
6036 @hook TARGET_CC_MODES_COMPATIBLE
6037 On targets which use multiple condition code modes in class
6038 @code{MODE_CC}, it is sometimes the case that a comparison can be
6039 validly done in more than one mode. On such a system, define this
6040 target hook to take two mode arguments and to return a mode in which
6041 both comparisons may be validly done. If there is no such mode,
6042 return @code{VOIDmode}.
6044 The default version of this hook checks whether the modes are the
6045 same. If they are, it returns that mode. If they are different, it
6046 returns @code{VOIDmode}.
6049 @node Cond Exec Macros
6050 @subsection Macros to control conditional execution
6051 @findex conditional execution
6054 There is one macro that may need to be defined for targets
6055 supporting conditional execution, independent of how they
6056 represent conditional branches.
6058 @defmac REVERSE_CONDEXEC_PREDICATES_P (@var{op1}, @var{op2})
6059 A C expression that returns true if the conditional execution predicate
6060 @var{op1}, a comparison operation, is the inverse of @var{op2} and vice
6061 versa. Define this to return 0 if the target has conditional execution
6062 predicates that cannot be reversed safely. There is no need to validate
6063 that the arguments of op1 and op2 are the same, this is done separately.
6064 If no expansion is specified, this macro is defined as follows:
6067 #define REVERSE_CONDEXEC_PREDICATES_P (x, y) \
6068 (GET_CODE ((x)) == reversed_comparison_code ((y), NULL))
6073 @section Describing Relative Costs of Operations
6074 @cindex costs of instructions
6075 @cindex relative costs
6076 @cindex speed of instructions
6078 These macros let you describe the relative speed of various operations
6079 on the target machine.
6081 @defmac REGISTER_MOVE_COST (@var{mode}, @var{from}, @var{to})
6082 A C expression for the cost of moving data of mode @var{mode} from a
6083 register in class @var{from} to one in class @var{to}. The classes are
6084 expressed using the enumeration values such as @code{GENERAL_REGS}. A
6085 value of 2 is the default; other values are interpreted relative to
6088 It is not required that the cost always equal 2 when @var{from} is the
6089 same as @var{to}; on some machines it is expensive to move between
6090 registers if they are not general registers.
6092 If reload sees an insn consisting of a single @code{set} between two
6093 hard registers, and if @code{REGISTER_MOVE_COST} applied to their
6094 classes returns a value of 2, reload does not check to ensure that the
6095 constraints of the insn are met. Setting a cost of other than 2 will
6096 allow reload to verify that the constraints are met. You should do this
6097 if the @samp{mov@var{m}} pattern's constraints do not allow such copying.
6099 These macros are obsolete, new ports should use the target hook
6100 @code{TARGET_REGISTER_MOVE_COST} instead.
6103 @hook TARGET_REGISTER_MOVE_COST
6104 This target hook should return the cost of moving data of mode @var{mode}
6105 from a register in class @var{from} to one in class @var{to}. The classes
6106 are expressed using the enumeration values such as @code{GENERAL_REGS}.
6107 A value of 2 is the default; other values are interpreted relative to
6110 It is not required that the cost always equal 2 when @var{from} is the
6111 same as @var{to}; on some machines it is expensive to move between
6112 registers if they are not general registers.
6114 If reload sees an insn consisting of a single @code{set} between two
6115 hard registers, and if @code{TARGET_REGISTER_MOVE_COST} applied to their
6116 classes returns a value of 2, reload does not check to ensure that the
6117 constraints of the insn are met. Setting a cost of other than 2 will
6118 allow reload to verify that the constraints are met. You should do this
6119 if the @samp{mov@var{m}} pattern's constraints do not allow such copying.
6121 The default version of this function returns 2.
6124 @defmac MEMORY_MOVE_COST (@var{mode}, @var{class}, @var{in})
6125 A C expression for the cost of moving data of mode @var{mode} between a
6126 register of class @var{class} and memory; @var{in} is zero if the value
6127 is to be written to memory, nonzero if it is to be read in. This cost
6128 is relative to those in @code{REGISTER_MOVE_COST}. If moving between
6129 registers and memory is more expensive than between two registers, you
6130 should define this macro to express the relative cost.
6132 If you do not define this macro, GCC uses a default cost of 4 plus
6133 the cost of copying via a secondary reload register, if one is
6134 needed. If your machine requires a secondary reload register to copy
6135 between memory and a register of @var{class} but the reload mechanism is
6136 more complex than copying via an intermediate, define this macro to
6137 reflect the actual cost of the move.
6139 GCC defines the function @code{memory_move_secondary_cost} if
6140 secondary reloads are needed. It computes the costs due to copying via
6141 a secondary register. If your machine copies from memory using a
6142 secondary register in the conventional way but the default base value of
6143 4 is not correct for your machine, define this macro to add some other
6144 value to the result of that function. The arguments to that function
6145 are the same as to this macro.
6147 These macros are obsolete, new ports should use the target hook
6148 @code{TARGET_MEMORY_MOVE_COST} instead.
6151 @hook TARGET_MEMORY_MOVE_COST
6152 This target hook should return the cost of moving data of mode @var{mode}
6153 between a register of class @var{rclass} and memory; @var{in} is @code{false}
6154 if the value is to be written to memory, @code{true} if it is to be read in.
6155 This cost is relative to those in @code{TARGET_REGISTER_MOVE_COST}.
6156 If moving between registers and memory is more expensive than between two
6157 registers, you should add this target hook to express the relative cost.
6159 If you do not add this target hook, GCC uses a default cost of 4 plus
6160 the cost of copying via a secondary reload register, if one is
6161 needed. If your machine requires a secondary reload register to copy
6162 between memory and a register of @var{rclass} but the reload mechanism is
6163 more complex than copying via an intermediate, use this target hook to
6164 reflect the actual cost of the move.
6166 GCC defines the function @code{memory_move_secondary_cost} if
6167 secondary reloads are needed. It computes the costs due to copying via
6168 a secondary register. If your machine copies from memory using a
6169 secondary register in the conventional way but the default base value of
6170 4 is not correct for your machine, use this target hook to add some other
6171 value to the result of that function. The arguments to that function
6172 are the same as to this target hook.
6175 @defmac BRANCH_COST (@var{speed_p}, @var{predictable_p})
6176 A C expression for the cost of a branch instruction. A value of 1 is the
6177 default; other values are interpreted relative to that. Parameter @var{speed_p}
6178 is true when the branch in question should be optimized for speed. When
6179 it is false, @code{BRANCH_COST} should be returning value optimal for code size
6180 rather then performance considerations. @var{predictable_p} is true for well
6181 predictable branches. On many architectures the @code{BRANCH_COST} can be
6185 Here are additional macros which do not specify precise relative costs,
6186 but only that certain actions are more expensive than GCC would
6189 @defmac SLOW_BYTE_ACCESS
6190 Define this macro as a C expression which is nonzero if accessing less
6191 than a word of memory (i.e.@: a @code{char} or a @code{short}) is no
6192 faster than accessing a word of memory, i.e., if such access
6193 require more than one instruction or if there is no difference in cost
6194 between byte and (aligned) word loads.
6196 When this macro is not defined, the compiler will access a field by
6197 finding the smallest containing object; when it is defined, a fullword
6198 load will be used if alignment permits. Unless bytes accesses are
6199 faster than word accesses, using word accesses is preferable since it
6200 may eliminate subsequent memory access if subsequent accesses occur to
6201 other fields in the same word of the structure, but to different bytes.
6204 @defmac SLOW_UNALIGNED_ACCESS (@var{mode}, @var{alignment})
6205 Define this macro to be the value 1 if memory accesses described by the
6206 @var{mode} and @var{alignment} parameters have a cost many times greater
6207 than aligned accesses, for example if they are emulated in a trap
6210 When this macro is nonzero, the compiler will act as if
6211 @code{STRICT_ALIGNMENT} were nonzero when generating code for block
6212 moves. This can cause significantly more instructions to be produced.
6213 Therefore, do not set this macro nonzero if unaligned accesses only add a
6214 cycle or two to the time for a memory access.
6216 If the value of this macro is always zero, it need not be defined. If
6217 this macro is defined, it should produce a nonzero value when
6218 @code{STRICT_ALIGNMENT} is nonzero.
6221 @defmac MOVE_RATIO (@var{speed})
6222 The threshold of number of scalar memory-to-memory move insns, @emph{below}
6223 which a sequence of insns should be generated instead of a
6224 string move insn or a library call. Increasing the value will always
6225 make code faster, but eventually incurs high cost in increased code size.
6227 Note that on machines where the corresponding move insn is a
6228 @code{define_expand} that emits a sequence of insns, this macro counts
6229 the number of such sequences.
6231 The parameter @var{speed} is true if the code is currently being
6232 optimized for speed rather than size.
6234 If you don't define this, a reasonable default is used.
6237 @defmac MOVE_BY_PIECES_P (@var{size}, @var{alignment})
6238 A C expression used to determine whether @code{move_by_pieces} will be used to
6239 copy a chunk of memory, or whether some other block move mechanism
6240 will be used. Defaults to 1 if @code{move_by_pieces_ninsns} returns less
6241 than @code{MOVE_RATIO}.
6244 @defmac MOVE_MAX_PIECES
6245 A C expression used by @code{move_by_pieces} to determine the largest unit
6246 a load or store used to copy memory is. Defaults to @code{MOVE_MAX}.
6249 @defmac CLEAR_RATIO (@var{speed})
6250 The threshold of number of scalar move insns, @emph{below} which a sequence
6251 of insns should be generated to clear memory instead of a string clear insn
6252 or a library call. Increasing the value will always make code faster, but
6253 eventually incurs high cost in increased code size.
6255 The parameter @var{speed} is true if the code is currently being
6256 optimized for speed rather than size.
6258 If you don't define this, a reasonable default is used.
6261 @defmac CLEAR_BY_PIECES_P (@var{size}, @var{alignment})
6262 A C expression used to determine whether @code{clear_by_pieces} will be used
6263 to clear a chunk of memory, or whether some other block clear mechanism
6264 will be used. Defaults to 1 if @code{move_by_pieces_ninsns} returns less
6265 than @code{CLEAR_RATIO}.
6268 @defmac SET_RATIO (@var{speed})
6269 The threshold of number of scalar move insns, @emph{below} which a sequence
6270 of insns should be generated to set memory to a constant value, instead of
6271 a block set insn or a library call.
6272 Increasing the value will always make code faster, but
6273 eventually incurs high cost in increased code size.
6275 The parameter @var{speed} is true if the code is currently being
6276 optimized for speed rather than size.
6278 If you don't define this, it defaults to the value of @code{MOVE_RATIO}.
6281 @defmac SET_BY_PIECES_P (@var{size}, @var{alignment})
6282 A C expression used to determine whether @code{store_by_pieces} will be
6283 used to set a chunk of memory to a constant value, or whether some
6284 other mechanism will be used. Used by @code{__builtin_memset} when
6285 storing values other than constant zero.
6286 Defaults to 1 if @code{move_by_pieces_ninsns} returns less
6287 than @code{SET_RATIO}.
6290 @defmac STORE_BY_PIECES_P (@var{size}, @var{alignment})
6291 A C expression used to determine whether @code{store_by_pieces} will be
6292 used to set a chunk of memory to a constant string value, or whether some
6293 other mechanism will be used. Used by @code{__builtin_strcpy} when
6294 called with a constant source string.
6295 Defaults to 1 if @code{move_by_pieces_ninsns} returns less
6296 than @code{MOVE_RATIO}.
6299 @defmac USE_LOAD_POST_INCREMENT (@var{mode})
6300 A C expression used to determine whether a load postincrement is a good
6301 thing to use for a given mode. Defaults to the value of
6302 @code{HAVE_POST_INCREMENT}.
6305 @defmac USE_LOAD_POST_DECREMENT (@var{mode})
6306 A C expression used to determine whether a load postdecrement is a good
6307 thing to use for a given mode. Defaults to the value of
6308 @code{HAVE_POST_DECREMENT}.
6311 @defmac USE_LOAD_PRE_INCREMENT (@var{mode})
6312 A C expression used to determine whether a load preincrement is a good
6313 thing to use for a given mode. Defaults to the value of
6314 @code{HAVE_PRE_INCREMENT}.
6317 @defmac USE_LOAD_PRE_DECREMENT (@var{mode})
6318 A C expression used to determine whether a load predecrement is a good
6319 thing to use for a given mode. Defaults to the value of
6320 @code{HAVE_PRE_DECREMENT}.
6323 @defmac USE_STORE_POST_INCREMENT (@var{mode})
6324 A C expression used to determine whether a store postincrement is a good
6325 thing to use for a given mode. Defaults to the value of
6326 @code{HAVE_POST_INCREMENT}.
6329 @defmac USE_STORE_POST_DECREMENT (@var{mode})
6330 A C expression used to determine whether a store postdecrement is a good
6331 thing to use for a given mode. Defaults to the value of
6332 @code{HAVE_POST_DECREMENT}.
6335 @defmac USE_STORE_PRE_INCREMENT (@var{mode})
6336 This macro is used to determine whether a store preincrement is a good
6337 thing to use for a given mode. Defaults to the value of
6338 @code{HAVE_PRE_INCREMENT}.
6341 @defmac USE_STORE_PRE_DECREMENT (@var{mode})
6342 This macro is used to determine whether a store predecrement is a good
6343 thing to use for a given mode. Defaults to the value of
6344 @code{HAVE_PRE_DECREMENT}.
6347 @defmac NO_FUNCTION_CSE
6348 Define this macro if it is as good or better to call a constant
6349 function address than to call an address kept in a register.
6352 @defmac RANGE_TEST_NON_SHORT_CIRCUIT
6353 Define this macro if a non-short-circuit operation produced by
6354 @samp{fold_range_test ()} is optimal. This macro defaults to true if
6355 @code{BRANCH_COST} is greater than or equal to the value 2.
6358 @hook TARGET_RTX_COSTS
6359 This target hook describes the relative costs of RTL expressions.
6361 The cost may depend on the precise form of the expression, which is
6362 available for examination in @var{x}, and the rtx code of the expression
6363 in which it is contained, found in @var{outer_code}. @var{code} is the
6364 expression code---redundant, since it can be obtained with
6365 @code{GET_CODE (@var{x})}.
6367 In implementing this hook, you can use the construct
6368 @code{COSTS_N_INSNS (@var{n})} to specify a cost equal to @var{n} fast
6371 On entry to the hook, @code{*@var{total}} contains a default estimate
6372 for the cost of the expression. The hook should modify this value as
6373 necessary. Traditionally, the default costs are @code{COSTS_N_INSNS (5)}
6374 for multiplications, @code{COSTS_N_INSNS (7)} for division and modulus
6375 operations, and @code{COSTS_N_INSNS (1)} for all other operations.
6377 When optimizing for code size, i.e.@: when @code{speed} is
6378 false, this target hook should be used to estimate the relative
6379 size cost of an expression, again relative to @code{COSTS_N_INSNS}.
6381 The hook returns true when all subexpressions of @var{x} have been
6382 processed, and false when @code{rtx_cost} should recurse.
6385 @hook TARGET_ADDRESS_COST
6386 This hook computes the cost of an addressing mode that contains
6387 @var{address}. If not defined, the cost is computed from
6388 the @var{address} expression and the @code{TARGET_RTX_COST} hook.
6390 For most CISC machines, the default cost is a good approximation of the
6391 true cost of the addressing mode. However, on RISC machines, all
6392 instructions normally have the same length and execution time. Hence
6393 all addresses will have equal costs.
6395 In cases where more than one form of an address is known, the form with
6396 the lowest cost will be used. If multiple forms have the same, lowest,
6397 cost, the one that is the most complex will be used.
6399 For example, suppose an address that is equal to the sum of a register
6400 and a constant is used twice in the same basic block. When this macro
6401 is not defined, the address will be computed in a register and memory
6402 references will be indirect through that register. On machines where
6403 the cost of the addressing mode containing the sum is no higher than
6404 that of a simple indirect reference, this will produce an additional
6405 instruction and possibly require an additional register. Proper
6406 specification of this macro eliminates this overhead for such machines.
6408 This hook is never called with an invalid address.
6410 On machines where an address involving more than one register is as
6411 cheap as an address computation involving only one register, defining
6412 @code{TARGET_ADDRESS_COST} to reflect this can cause two registers to
6413 be live over a region of code where only one would have been if
6414 @code{TARGET_ADDRESS_COST} were not defined in that manner. This effect
6415 should be considered in the definition of this macro. Equivalent costs
6416 should probably only be given to addresses with different numbers of
6417 registers on machines with lots of registers.
6421 @section Adjusting the Instruction Scheduler
6423 The instruction scheduler may need a fair amount of machine-specific
6424 adjustment in order to produce good code. GCC provides several target
6425 hooks for this purpose. It is usually enough to define just a few of
6426 them: try the first ones in this list first.
6428 @hook TARGET_SCHED_ISSUE_RATE
6429 This hook returns the maximum number of instructions that can ever
6430 issue at the same time on the target machine. The default is one.
6431 Although the insn scheduler can define itself the possibility of issue
6432 an insn on the same cycle, the value can serve as an additional
6433 constraint to issue insns on the same simulated processor cycle (see
6434 hooks @samp{TARGET_SCHED_REORDER} and @samp{TARGET_SCHED_REORDER2}).
6435 This value must be constant over the entire compilation. If you need
6436 it to vary depending on what the instructions are, you must use
6437 @samp{TARGET_SCHED_VARIABLE_ISSUE}.
6440 @hook TARGET_SCHED_VARIABLE_ISSUE
6441 This hook is executed by the scheduler after it has scheduled an insn
6442 from the ready list. It should return the number of insns which can
6443 still be issued in the current cycle. The default is
6444 @samp{@w{@var{more} - 1}} for insns other than @code{CLOBBER} and
6445 @code{USE}, which normally are not counted against the issue rate.
6446 You should define this hook if some insns take more machine resources
6447 than others, so that fewer insns can follow them in the same cycle.
6448 @var{file} is either a null pointer, or a stdio stream to write any
6449 debug output to. @var{verbose} is the verbose level provided by
6450 @option{-fsched-verbose-@var{n}}. @var{insn} is the instruction that
6454 @hook TARGET_SCHED_ADJUST_COST
6455 This function corrects the value of @var{cost} based on the
6456 relationship between @var{insn} and @var{dep_insn} through the
6457 dependence @var{link}. It should return the new value. The default
6458 is to make no adjustment to @var{cost}. This can be used for example
6459 to specify to the scheduler using the traditional pipeline description
6460 that an output- or anti-dependence does not incur the same cost as a
6461 data-dependence. If the scheduler using the automaton based pipeline
6462 description, the cost of anti-dependence is zero and the cost of
6463 output-dependence is maximum of one and the difference of latency
6464 times of the first and the second insns. If these values are not
6465 acceptable, you could use the hook to modify them too. See also
6466 @pxref{Processor pipeline description}.
6469 @hook TARGET_SCHED_ADJUST_PRIORITY
6470 This hook adjusts the integer scheduling priority @var{priority} of
6471 @var{insn}. It should return the new priority. Increase the priority to
6472 execute @var{insn} earlier, reduce the priority to execute @var{insn}
6473 later. Do not define this hook if you do not need to adjust the
6474 scheduling priorities of insns.
6477 @hook TARGET_SCHED_REORDER
6478 This hook is executed by the scheduler after it has scheduled the ready
6479 list, to allow the machine description to reorder it (for example to
6480 combine two small instructions together on @samp{VLIW} machines).
6481 @var{file} is either a null pointer, or a stdio stream to write any
6482 debug output to. @var{verbose} is the verbose level provided by
6483 @option{-fsched-verbose-@var{n}}. @var{ready} is a pointer to the ready
6484 list of instructions that are ready to be scheduled. @var{n_readyp} is
6485 a pointer to the number of elements in the ready list. The scheduler
6486 reads the ready list in reverse order, starting with
6487 @var{ready}[@var{*n_readyp} @minus{} 1] and going to @var{ready}[0]. @var{clock}
6488 is the timer tick of the scheduler. You may modify the ready list and
6489 the number of ready insns. The return value is the number of insns that
6490 can issue this cycle; normally this is just @code{issue_rate}. See also
6491 @samp{TARGET_SCHED_REORDER2}.
6494 @hook TARGET_SCHED_REORDER2
6495 Like @samp{TARGET_SCHED_REORDER}, but called at a different time. That
6496 function is called whenever the scheduler starts a new cycle. This one
6497 is called once per iteration over a cycle, immediately after
6498 @samp{TARGET_SCHED_VARIABLE_ISSUE}; it can reorder the ready list and
6499 return the number of insns to be scheduled in the same cycle. Defining
6500 this hook can be useful if there are frequent situations where
6501 scheduling one insn causes other insns to become ready in the same
6502 cycle. These other insns can then be taken into account properly.
6505 @hook TARGET_SCHED_DEPENDENCIES_EVALUATION_HOOK
6506 This hook is called after evaluation forward dependencies of insns in
6507 chain given by two parameter values (@var{head} and @var{tail}
6508 correspondingly) but before insns scheduling of the insn chain. For
6509 example, it can be used for better insn classification if it requires
6510 analysis of dependencies. This hook can use backward and forward
6511 dependencies of the insn scheduler because they are already
6515 @hook TARGET_SCHED_INIT
6516 This hook is executed by the scheduler at the beginning of each block of
6517 instructions that are to be scheduled. @var{file} is either a null
6518 pointer, or a stdio stream to write any debug output to. @var{verbose}
6519 is the verbose level provided by @option{-fsched-verbose-@var{n}}.
6520 @var{max_ready} is the maximum number of insns in the current scheduling
6521 region that can be live at the same time. This can be used to allocate
6522 scratch space if it is needed, e.g.@: by @samp{TARGET_SCHED_REORDER}.
6525 @hook TARGET_SCHED_FINISH
6526 This hook is executed by the scheduler at the end of each block of
6527 instructions that are to be scheduled. It can be used to perform
6528 cleanup of any actions done by the other scheduling hooks. @var{file}
6529 is either a null pointer, or a stdio stream to write any debug output
6530 to. @var{verbose} is the verbose level provided by
6531 @option{-fsched-verbose-@var{n}}.
6534 @hook TARGET_SCHED_INIT_GLOBAL
6535 This hook is executed by the scheduler after function level initializations.
6536 @var{file} is either a null pointer, or a stdio stream to write any debug output to.
6537 @var{verbose} is the verbose level provided by @option{-fsched-verbose-@var{n}}.
6538 @var{old_max_uid} is the maximum insn uid when scheduling begins.
6541 @hook TARGET_SCHED_FINISH_GLOBAL
6542 This is the cleanup hook corresponding to @code{TARGET_SCHED_INIT_GLOBAL}.
6543 @var{file} is either a null pointer, or a stdio stream to write any debug output to.
6544 @var{verbose} is the verbose level provided by @option{-fsched-verbose-@var{n}}.
6547 @hook TARGET_SCHED_DFA_PRE_CYCLE_INSN
6548 The hook returns an RTL insn. The automaton state used in the
6549 pipeline hazard recognizer is changed as if the insn were scheduled
6550 when the new simulated processor cycle starts. Usage of the hook may
6551 simplify the automaton pipeline description for some @acronym{VLIW}
6552 processors. If the hook is defined, it is used only for the automaton
6553 based pipeline description. The default is not to change the state
6554 when the new simulated processor cycle starts.
6557 @hook TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN
6558 The hook can be used to initialize data used by the previous hook.
6561 @hook TARGET_SCHED_DFA_POST_CYCLE_INSN
6562 The hook is analogous to @samp{TARGET_SCHED_DFA_PRE_CYCLE_INSN} but used
6563 to changed the state as if the insn were scheduled when the new
6564 simulated processor cycle finishes.
6567 @hook TARGET_SCHED_INIT_DFA_POST_CYCLE_INSN
6568 The hook is analogous to @samp{TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN} but
6569 used to initialize data used by the previous hook.
6572 @hook TARGET_SCHED_DFA_PRE_ADVANCE_CYCLE
6573 The hook to notify target that the current simulated cycle is about to finish.
6574 The hook is analogous to @samp{TARGET_SCHED_DFA_PRE_CYCLE_INSN} but used
6575 to change the state in more complicated situations - e.g., when advancing
6576 state on a single insn is not enough.
6579 @hook TARGET_SCHED_DFA_POST_ADVANCE_CYCLE
6580 The hook to notify target that new simulated cycle has just started.
6581 The hook is analogous to @samp{TARGET_SCHED_DFA_POST_CYCLE_INSN} but used
6582 to change the state in more complicated situations - e.g., when advancing
6583 state on a single insn is not enough.
6586 @hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD
6587 This hook controls better choosing an insn from the ready insn queue
6588 for the @acronym{DFA}-based insn scheduler. Usually the scheduler
6589 chooses the first insn from the queue. If the hook returns a positive
6590 value, an additional scheduler code tries all permutations of
6591 @samp{TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD ()}
6592 subsequent ready insns to choose an insn whose issue will result in
6593 maximal number of issued insns on the same cycle. For the
6594 @acronym{VLIW} processor, the code could actually solve the problem of
6595 packing simple insns into the @acronym{VLIW} insn. Of course, if the
6596 rules of @acronym{VLIW} packing are described in the automaton.
6598 This code also could be used for superscalar @acronym{RISC}
6599 processors. Let us consider a superscalar @acronym{RISC} processor
6600 with 3 pipelines. Some insns can be executed in pipelines @var{A} or
6601 @var{B}, some insns can be executed only in pipelines @var{B} or
6602 @var{C}, and one insn can be executed in pipeline @var{B}. The
6603 processor may issue the 1st insn into @var{A} and the 2nd one into
6604 @var{B}. In this case, the 3rd insn will wait for freeing @var{B}
6605 until the next cycle. If the scheduler issues the 3rd insn the first,
6606 the processor could issue all 3 insns per cycle.
6608 Actually this code demonstrates advantages of the automaton based
6609 pipeline hazard recognizer. We try quickly and easy many insn
6610 schedules to choose the best one.
6612 The default is no multipass scheduling.
6615 @hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD
6617 This hook controls what insns from the ready insn queue will be
6618 considered for the multipass insn scheduling. If the hook returns
6619 zero for @var{insn}, the insn will be not chosen to
6622 The default is that any ready insns can be chosen to be issued.
6625 @hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_BEGIN
6626 This hook prepares the target backend for a new round of multipass
6630 @hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_ISSUE
6631 This hook is called when multipass scheduling evaluates instruction INSN.
6634 @hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_BACKTRACK
6635 This is called when multipass scheduling backtracks from evaluation of
6639 @hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_END
6640 This hook notifies the target about the result of the concluded current
6641 round of multipass scheduling.
6644 @hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_INIT
6645 This hook initilizes target-specific data used in multipass scheduling.
6648 @hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_FINI
6649 This hook finilizes target-specific data used in multipass scheduling.
6652 @hook TARGET_SCHED_DFA_NEW_CYCLE
6653 This hook is called by the insn scheduler before issuing @var{insn}
6654 on cycle @var{clock}. If the hook returns nonzero,
6655 @var{insn} is not issued on this processor cycle. Instead,
6656 the processor cycle is advanced. If *@var{sort_p}
6657 is zero, the insn ready queue is not sorted on the new cycle
6658 start as usually. @var{dump} and @var{verbose} specify the file and
6659 verbosity level to use for debugging output.
6660 @var{last_clock} and @var{clock} are, respectively, the
6661 processor cycle on which the previous insn has been issued,
6662 and the current processor cycle.
6665 @hook TARGET_SCHED_IS_COSTLY_DEPENDENCE
6666 This hook is used to define which dependences are considered costly by
6667 the target, so costly that it is not advisable to schedule the insns that
6668 are involved in the dependence too close to one another. The parameters
6669 to this hook are as follows: The first parameter @var{_dep} is the dependence
6670 being evaluated. The second parameter @var{cost} is the cost of the
6671 dependence as estimated by the scheduler, and the third
6672 parameter @var{distance} is the distance in cycles between the two insns.
6673 The hook returns @code{true} if considering the distance between the two
6674 insns the dependence between them is considered costly by the target,
6675 and @code{false} otherwise.
6677 Defining this hook can be useful in multiple-issue out-of-order machines,
6678 where (a) it's practically hopeless to predict the actual data/resource
6679 delays, however: (b) there's a better chance to predict the actual grouping
6680 that will be formed, and (c) correctly emulating the grouping can be very
6681 important. In such targets one may want to allow issuing dependent insns
6682 closer to one another---i.e., closer than the dependence distance; however,
6683 not in cases of ``costly dependences'', which this hooks allows to define.
6686 @hook TARGET_SCHED_H_I_D_EXTENDED
6687 This hook is called by the insn scheduler after emitting a new instruction to
6688 the instruction stream. The hook notifies a target backend to extend its
6689 per instruction data structures.
6692 @hook TARGET_SCHED_ALLOC_SCHED_CONTEXT
6693 Return a pointer to a store large enough to hold target scheduling context.
6696 @hook TARGET_SCHED_INIT_SCHED_CONTEXT
6697 Initialize store pointed to by @var{tc} to hold target scheduling context.
6698 It @var{clean_p} is true then initialize @var{tc} as if scheduler is at the
6699 beginning of the block. Otherwise, copy the current context into @var{tc}.
6702 @hook TARGET_SCHED_SET_SCHED_CONTEXT
6703 Copy target scheduling context pointed to by @var{tc} to the current context.
6706 @hook TARGET_SCHED_CLEAR_SCHED_CONTEXT
6707 Deallocate internal data in target scheduling context pointed to by @var{tc}.
6710 @hook TARGET_SCHED_FREE_SCHED_CONTEXT
6711 Deallocate a store for target scheduling context pointed to by @var{tc}.
6714 @hook TARGET_SCHED_SPECULATE_INSN
6715 This hook is called by the insn scheduler when @var{insn} has only
6716 speculative dependencies and therefore can be scheduled speculatively.
6717 The hook is used to check if the pattern of @var{insn} has a speculative
6718 version and, in case of successful check, to generate that speculative
6719 pattern. The hook should return 1, if the instruction has a speculative form,
6720 or @minus{}1, if it doesn't. @var{request} describes the type of requested
6721 speculation. If the return value equals 1 then @var{new_pat} is assigned
6722 the generated speculative pattern.
6725 @hook TARGET_SCHED_NEEDS_BLOCK_P
6726 This hook is called by the insn scheduler during generation of recovery code
6727 for @var{insn}. It should return @code{true}, if the corresponding check
6728 instruction should branch to recovery code, or @code{false} otherwise.
6731 @hook TARGET_SCHED_GEN_SPEC_CHECK
6732 This hook is called by the insn scheduler to generate a pattern for recovery
6733 check instruction. If @var{mutate_p} is zero, then @var{insn} is a
6734 speculative instruction for which the check should be generated.
6735 @var{label} is either a label of a basic block, where recovery code should
6736 be emitted, or a null pointer, when requested check doesn't branch to
6737 recovery code (a simple check). If @var{mutate_p} is nonzero, then
6738 a pattern for a branchy check corresponding to a simple check denoted by
6739 @var{insn} should be generated. In this case @var{label} can't be null.
6742 @hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD_SPEC
6743 This hook is used as a workaround for
6744 @samp{TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD} not being
6745 called on the first instruction of the ready list. The hook is used to
6746 discard speculative instructions that stand first in the ready list from
6747 being scheduled on the current cycle. If the hook returns @code{false},
6748 @var{insn} will not be chosen to be issued.
6749 For non-speculative instructions,
6750 the hook should always return @code{true}. For example, in the ia64 backend
6751 the hook is used to cancel data speculative insns when the ALAT table
6755 @hook TARGET_SCHED_SET_SCHED_FLAGS
6756 This hook is used by the insn scheduler to find out what features should be
6758 The structure *@var{spec_info} should be filled in by the target.
6759 The structure describes speculation types that can be used in the scheduler.
6762 @hook TARGET_SCHED_SMS_RES_MII
6763 This hook is called by the swing modulo scheduler to calculate a
6764 resource-based lower bound which is based on the resources available in
6765 the machine and the resources required by each instruction. The target
6766 backend can use @var{g} to calculate such bound. A very simple lower
6767 bound will be used in case this hook is not implemented: the total number
6768 of instructions divided by the issue rate.
6771 @hook TARGET_SCHED_DISPATCH
6772 This hook is called by Haifa Scheduler. It returns true if dispatch scheduling
6773 is supported in hardware and the condition specified in the parameter is true.
6776 @hook TARGET_SCHED_DISPATCH_DO
6777 This hook is called by Haifa Scheduler. It performs the operation specified
6778 in its second parameter.
6782 @section Dividing the Output into Sections (Texts, Data, @dots{})
6783 @c the above section title is WAY too long. maybe cut the part between
6784 @c the (...)? --mew 10feb93
6786 An object file is divided into sections containing different types of
6787 data. In the most common case, there are three sections: the @dfn{text
6788 section}, which holds instructions and read-only data; the @dfn{data
6789 section}, which holds initialized writable data; and the @dfn{bss
6790 section}, which holds uninitialized data. Some systems have other kinds
6793 @file{varasm.c} provides several well-known sections, such as
6794 @code{text_section}, @code{data_section} and @code{bss_section}.
6795 The normal way of controlling a @code{@var{foo}_section} variable
6796 is to define the associated @code{@var{FOO}_SECTION_ASM_OP} macro,
6797 as described below. The macros are only read once, when @file{varasm.c}
6798 initializes itself, so their values must be run-time constants.
6799 They may however depend on command-line flags.
6801 @emph{Note:} Some run-time files, such @file{crtstuff.c}, also make
6802 use of the @code{@var{FOO}_SECTION_ASM_OP} macros, and expect them
6803 to be string literals.
6805 Some assemblers require a different string to be written every time a
6806 section is selected. If your assembler falls into this category, you
6807 should define the @code{TARGET_ASM_INIT_SECTIONS} hook and use
6808 @code{get_unnamed_section} to set up the sections.
6810 You must always create a @code{text_section}, either by defining
6811 @code{TEXT_SECTION_ASM_OP} or by initializing @code{text_section}
6812 in @code{TARGET_ASM_INIT_SECTIONS}. The same is true of
6813 @code{data_section} and @code{DATA_SECTION_ASM_OP}. If you do not
6814 create a distinct @code{readonly_data_section}, the default is to
6815 reuse @code{text_section}.
6817 All the other @file{varasm.c} sections are optional, and are null
6818 if the target does not provide them.
6820 @defmac TEXT_SECTION_ASM_OP
6821 A C expression whose value is a string, including spacing, containing the
6822 assembler operation that should precede instructions and read-only data.
6823 Normally @code{"\t.text"} is right.
6826 @defmac HOT_TEXT_SECTION_NAME
6827 If defined, a C string constant for the name of the section containing most
6828 frequently executed functions of the program. If not defined, GCC will provide
6829 a default definition if the target supports named sections.
6832 @defmac UNLIKELY_EXECUTED_TEXT_SECTION_NAME
6833 If defined, a C string constant for the name of the section containing unlikely
6834 executed functions in the program.
6837 @defmac DATA_SECTION_ASM_OP
6838 A C expression whose value is a string, including spacing, containing the
6839 assembler operation to identify the following data as writable initialized
6840 data. Normally @code{"\t.data"} is right.
6843 @defmac SDATA_SECTION_ASM_OP
6844 If defined, a C expression whose value is a string, including spacing,
6845 containing the assembler operation to identify the following data as
6846 initialized, writable small data.
6849 @defmac READONLY_DATA_SECTION_ASM_OP
6850 A C expression whose value is a string, including spacing, containing the
6851 assembler operation to identify the following data as read-only initialized
6855 @defmac BSS_SECTION_ASM_OP
6856 If defined, a C expression whose value is a string, including spacing,
6857 containing the assembler operation to identify the following data as
6858 uninitialized global data. If not defined, and neither
6859 @code{ASM_OUTPUT_BSS} nor @code{ASM_OUTPUT_ALIGNED_BSS} are defined,
6860 uninitialized global data will be output in the data section if
6861 @option{-fno-common} is passed, otherwise @code{ASM_OUTPUT_COMMON} will be
6865 @defmac SBSS_SECTION_ASM_OP
6866 If defined, a C expression whose value is a string, including spacing,
6867 containing the assembler operation to identify the following data as
6868 uninitialized, writable small data.
6871 @defmac TLS_COMMON_ASM_OP
6872 If defined, a C expression whose value is a string containing the
6873 assembler operation to identify the following data as thread-local
6874 common data. The default is @code{".tls_common"}.
6877 @defmac TLS_SECTION_ASM_FLAG
6878 If defined, a C expression whose value is a character constant
6879 containing the flag used to mark a section as a TLS section. The
6880 default is @code{'T'}.
6883 @defmac INIT_SECTION_ASM_OP
6884 If defined, a C expression whose value is a string, including spacing,
6885 containing the assembler operation to identify the following data as
6886 initialization code. If not defined, GCC will assume such a section does
6887 not exist. This section has no corresponding @code{init_section}
6888 variable; it is used entirely in runtime code.
6891 @defmac FINI_SECTION_ASM_OP
6892 If defined, a C expression whose value is a string, including spacing,
6893 containing the assembler operation to identify the following data as
6894 finalization code. If not defined, GCC will assume such a section does
6895 not exist. This section has no corresponding @code{fini_section}
6896 variable; it is used entirely in runtime code.
6899 @defmac INIT_ARRAY_SECTION_ASM_OP
6900 If defined, a C expression whose value is a string, including spacing,
6901 containing the assembler operation to identify the following data as
6902 part of the @code{.init_array} (or equivalent) section. If not
6903 defined, GCC will assume such a section does not exist. Do not define
6904 both this macro and @code{INIT_SECTION_ASM_OP}.
6907 @defmac FINI_ARRAY_SECTION_ASM_OP
6908 If defined, a C expression whose value is a string, including spacing,
6909 containing the assembler operation to identify the following data as
6910 part of the @code{.fini_array} (or equivalent) section. If not
6911 defined, GCC will assume such a section does not exist. Do not define
6912 both this macro and @code{FINI_SECTION_ASM_OP}.
6915 @defmac CRT_CALL_STATIC_FUNCTION (@var{section_op}, @var{function})
6916 If defined, an ASM statement that switches to a different section
6917 via @var{section_op}, calls @var{function}, and switches back to
6918 the text section. This is used in @file{crtstuff.c} if
6919 @code{INIT_SECTION_ASM_OP} or @code{FINI_SECTION_ASM_OP} to calls
6920 to initialization and finalization functions from the init and fini
6921 sections. By default, this macro uses a simple function call. Some
6922 ports need hand-crafted assembly code to avoid dependencies on
6923 registers initialized in the function prologue or to ensure that
6924 constant pools don't end up too far way in the text section.
6927 @defmac TARGET_LIBGCC_SDATA_SECTION
6928 If defined, a string which names the section into which small
6929 variables defined in crtstuff and libgcc should go. This is useful
6930 when the target has options for optimizing access to small data, and
6931 you want the crtstuff and libgcc routines to be conservative in what
6932 they expect of your application yet liberal in what your application
6933 expects. For example, for targets with a @code{.sdata} section (like
6934 MIPS), you could compile crtstuff with @code{-G 0} so that it doesn't
6935 require small data support from your application, but use this macro
6936 to put small data into @code{.sdata} so that your application can
6937 access these variables whether it uses small data or not.
6940 @defmac FORCE_CODE_SECTION_ALIGN
6941 If defined, an ASM statement that aligns a code section to some
6942 arbitrary boundary. This is used to force all fragments of the
6943 @code{.init} and @code{.fini} sections to have to same alignment
6944 and thus prevent the linker from having to add any padding.
6947 @defmac JUMP_TABLES_IN_TEXT_SECTION
6948 Define this macro to be an expression with a nonzero value if jump
6949 tables (for @code{tablejump} insns) should be output in the text
6950 section, along with the assembler instructions. Otherwise, the
6951 readonly data section is used.
6953 This macro is irrelevant if there is no separate readonly data section.
6956 @hook TARGET_ASM_INIT_SECTIONS
6957 Define this hook if you need to do something special to set up the
6958 @file{varasm.c} sections, or if your target has some special sections
6959 of its own that you need to create.
6961 GCC calls this hook after processing the command line, but before writing
6962 any assembly code, and before calling any of the section-returning hooks
6966 @hook TARGET_ASM_RELOC_RW_MASK
6967 Return a mask describing how relocations should be treated when
6968 selecting sections. Bit 1 should be set if global relocations
6969 should be placed in a read-write section; bit 0 should be set if
6970 local relocations should be placed in a read-write section.
6972 The default version of this function returns 3 when @option{-fpic}
6973 is in effect, and 0 otherwise. The hook is typically redefined
6974 when the target cannot support (some kinds of) dynamic relocations
6975 in read-only sections even in executables.
6978 @hook TARGET_ASM_SELECT_SECTION
6979 Return the section into which @var{exp} should be placed. You can
6980 assume that @var{exp} is either a @code{VAR_DECL} node or a constant of
6981 some sort. @var{reloc} indicates whether the initial value of @var{exp}
6982 requires link-time relocations. Bit 0 is set when variable contains
6983 local relocations only, while bit 1 is set for global relocations.
6984 @var{align} is the constant alignment in bits.
6986 The default version of this function takes care of putting read-only
6987 variables in @code{readonly_data_section}.
6989 See also @var{USE_SELECT_SECTION_FOR_FUNCTIONS}.
6992 @defmac USE_SELECT_SECTION_FOR_FUNCTIONS
6993 Define this macro if you wish TARGET_ASM_SELECT_SECTION to be called
6994 for @code{FUNCTION_DECL}s as well as for variables and constants.
6996 In the case of a @code{FUNCTION_DECL}, @var{reloc} will be zero if the
6997 function has been determined to be likely to be called, and nonzero if
6998 it is unlikely to be called.
7001 @hook TARGET_ASM_UNIQUE_SECTION
7002 Build up a unique section name, expressed as a @code{STRING_CST} node,
7003 and assign it to @samp{DECL_SECTION_NAME (@var{decl})}.
7004 As with @code{TARGET_ASM_SELECT_SECTION}, @var{reloc} indicates whether
7005 the initial value of @var{exp} requires link-time relocations.
7007 The default version of this function appends the symbol name to the
7008 ELF section name that would normally be used for the symbol. For
7009 example, the function @code{foo} would be placed in @code{.text.foo}.
7010 Whatever the actual target object format, this is often good enough.
7013 @hook TARGET_ASM_FUNCTION_RODATA_SECTION
7014 Return the readonly data section associated with
7015 @samp{DECL_SECTION_NAME (@var{decl})}.
7016 The default version of this function selects @code{.gnu.linkonce.r.name} if
7017 the function's section is @code{.gnu.linkonce.t.name}, @code{.rodata.name}
7018 if function is in @code{.text.name}, and the normal readonly-data section
7022 @hook TARGET_ASM_SELECT_RTX_SECTION
7023 Return the section into which a constant @var{x}, of mode @var{mode},
7024 should be placed. You can assume that @var{x} is some kind of
7025 constant in RTL@. The argument @var{mode} is redundant except in the
7026 case of a @code{const_int} rtx. @var{align} is the constant alignment
7029 The default version of this function takes care of putting symbolic
7030 constants in @code{flag_pic} mode in @code{data_section} and everything
7031 else in @code{readonly_data_section}.
7034 @hook TARGET_MANGLE_DECL_ASSEMBLER_NAME
7035 Define this hook if you need to postprocess the assembler name generated
7036 by target-independent code. The @var{id} provided to this hook will be
7037 the computed name (e.g., the macro @code{DECL_NAME} of the @var{decl} in C,
7038 or the mangled name of the @var{decl} in C++). The return value of the
7039 hook is an @code{IDENTIFIER_NODE} for the appropriate mangled name on
7040 your target system. The default implementation of this hook just
7041 returns the @var{id} provided.
7044 @hook TARGET_ENCODE_SECTION_INFO
7045 Define this hook if references to a symbol or a constant must be
7046 treated differently depending on something about the variable or
7047 function named by the symbol (such as what section it is in).
7049 The hook is executed immediately after rtl has been created for
7050 @var{decl}, which may be a variable or function declaration or
7051 an entry in the constant pool. In either case, @var{rtl} is the
7052 rtl in question. Do @emph{not} use @code{DECL_RTL (@var{decl})}
7053 in this hook; that field may not have been initialized yet.
7055 In the case of a constant, it is safe to assume that the rtl is
7056 a @code{mem} whose address is a @code{symbol_ref}. Most decls
7057 will also have this form, but that is not guaranteed. Global
7058 register variables, for instance, will have a @code{reg} for their
7059 rtl. (Normally the right thing to do with such unusual rtl is
7062 The @var{new_decl_p} argument will be true if this is the first time
7063 that @code{TARGET_ENCODE_SECTION_INFO} has been invoked on this decl. It will
7064 be false for subsequent invocations, which will happen for duplicate
7065 declarations. Whether or not anything must be done for the duplicate
7066 declaration depends on whether the hook examines @code{DECL_ATTRIBUTES}.
7067 @var{new_decl_p} is always true when the hook is called for a constant.
7069 @cindex @code{SYMBOL_REF_FLAG}, in @code{TARGET_ENCODE_SECTION_INFO}
7070 The usual thing for this hook to do is to record flags in the
7071 @code{symbol_ref}, using @code{SYMBOL_REF_FLAG} or @code{SYMBOL_REF_FLAGS}.
7072 Historically, the name string was modified if it was necessary to
7073 encode more than one bit of information, but this practice is now
7074 discouraged; use @code{SYMBOL_REF_FLAGS}.
7076 The default definition of this hook, @code{default_encode_section_info}
7077 in @file{varasm.c}, sets a number of commonly-useful bits in
7078 @code{SYMBOL_REF_FLAGS}. Check whether the default does what you need
7079 before overriding it.
7082 @hook TARGET_STRIP_NAME_ENCODING
7083 Decode @var{name} and return the real name part, sans
7084 the characters that @code{TARGET_ENCODE_SECTION_INFO}
7088 @hook TARGET_IN_SMALL_DATA_P
7089 Returns true if @var{exp} should be placed into a ``small data'' section.
7090 The default version of this hook always returns false.
7093 @hook TARGET_HAVE_SRODATA_SECTION
7094 Contains the value true if the target places read-only
7095 ``small data'' into a separate section. The default value is false.
7098 @hook TARGET_PROFILE_BEFORE_PROLOGUE
7100 @hook TARGET_BINDS_LOCAL_P
7101 Returns true if @var{exp} names an object for which name resolution
7102 rules must resolve to the current ``module'' (dynamic shared library
7103 or executable image).
7105 The default version of this hook implements the name resolution rules
7106 for ELF, which has a looser model of global name binding than other
7107 currently supported object file formats.
7110 @hook TARGET_HAVE_TLS
7111 Contains the value true if the target supports thread-local storage.
7112 The default value is false.
7117 @section Position Independent Code
7118 @cindex position independent code
7121 This section describes macros that help implement generation of position
7122 independent code. Simply defining these macros is not enough to
7123 generate valid PIC; you must also add support to the hook
7124 @code{TARGET_LEGITIMATE_ADDRESS_P} and to the macro
7125 @code{PRINT_OPERAND_ADDRESS}, as well as @code{LEGITIMIZE_ADDRESS}. You
7126 must modify the definition of @samp{movsi} to do something appropriate
7127 when the source operand contains a symbolic address. You may also
7128 need to alter the handling of switch statements so that they use
7130 @c i rearranged the order of the macros above to try to force one of
7131 @c them to the next line, to eliminate an overfull hbox. --mew 10feb93
7133 @defmac PIC_OFFSET_TABLE_REGNUM
7134 The register number of the register used to address a table of static
7135 data addresses in memory. In some cases this register is defined by a
7136 processor's ``application binary interface'' (ABI)@. When this macro
7137 is defined, RTL is generated for this register once, as with the stack
7138 pointer and frame pointer registers. If this macro is not defined, it
7139 is up to the machine-dependent files to allocate such a register (if
7140 necessary). Note that this register must be fixed when in use (e.g.@:
7141 when @code{flag_pic} is true).
7144 @defmac PIC_OFFSET_TABLE_REG_CALL_CLOBBERED
7145 A C expression that is nonzero if the register defined by
7146 @code{PIC_OFFSET_TABLE_REGNUM} is clobbered by calls. If not defined,
7147 the default is zero. Do not define
7148 this macro if @code{PIC_OFFSET_TABLE_REGNUM} is not defined.
7151 @defmac LEGITIMATE_PIC_OPERAND_P (@var{x})
7152 A C expression that is nonzero if @var{x} is a legitimate immediate
7153 operand on the target machine when generating position independent code.
7154 You can assume that @var{x} satisfies @code{CONSTANT_P}, so you need not
7155 check this. You can also assume @var{flag_pic} is true, so you need not
7156 check it either. You need not define this macro if all constants
7157 (including @code{SYMBOL_REF}) can be immediate operands when generating
7158 position independent code.
7161 @node Assembler Format
7162 @section Defining the Output Assembler Language
7164 This section describes macros whose principal purpose is to describe how
7165 to write instructions in assembler language---rather than what the
7169 * File Framework:: Structural information for the assembler file.
7170 * Data Output:: Output of constants (numbers, strings, addresses).
7171 * Uninitialized Data:: Output of uninitialized variables.
7172 * Label Output:: Output and generation of labels.
7173 * Initialization:: General principles of initialization
7174 and termination routines.
7175 * Macros for Initialization::
7176 Specific macros that control the handling of
7177 initialization and termination routines.
7178 * Instruction Output:: Output of actual instructions.
7179 * Dispatch Tables:: Output of jump tables.
7180 * Exception Region Output:: Output of exception region code.
7181 * Alignment Output:: Pseudo ops for alignment and skipping data.
7184 @node File Framework
7185 @subsection The Overall Framework of an Assembler File
7186 @cindex assembler format
7187 @cindex output of assembler code
7189 @c prevent bad page break with this line
7190 This describes the overall framework of an assembly file.
7192 @findex default_file_start
7193 @hook TARGET_ASM_FILE_START
7194 Output to @code{asm_out_file} any text which the assembler expects to
7195 find at the beginning of a file. The default behavior is controlled
7196 by two flags, documented below. Unless your target's assembler is
7197 quite unusual, if you override the default, you should call
7198 @code{default_file_start} at some point in your target hook. This
7199 lets other target files rely on these variables.
7202 @hook TARGET_ASM_FILE_START_APP_OFF
7203 If this flag is true, the text of the macro @code{ASM_APP_OFF} will be
7204 printed as the very first line in the assembly file, unless
7205 @option{-fverbose-asm} is in effect. (If that macro has been defined
7206 to the empty string, this variable has no effect.) With the normal
7207 definition of @code{ASM_APP_OFF}, the effect is to notify the GNU
7208 assembler that it need not bother stripping comments or extra
7209 whitespace from its input. This allows it to work a bit faster.
7211 The default is false. You should not set it to true unless you have
7212 verified that your port does not generate any extra whitespace or
7213 comments that will cause GAS to issue errors in NO_APP mode.
7216 @hook TARGET_ASM_FILE_START_FILE_DIRECTIVE
7217 If this flag is true, @code{output_file_directive} will be called
7218 for the primary source file, immediately after printing
7219 @code{ASM_APP_OFF} (if that is enabled). Most ELF assemblers expect
7220 this to be done. The default is false.
7223 @hook TARGET_ASM_FILE_END
7224 Output to @code{asm_out_file} any text which the assembler expects
7225 to find at the end of a file. The default is to output nothing.
7228 @deftypefun void file_end_indicate_exec_stack ()
7229 Some systems use a common convention, the @samp{.note.GNU-stack}
7230 special section, to indicate whether or not an object file relies on
7231 the stack being executable. If your system uses this convention, you
7232 should define @code{TARGET_ASM_FILE_END} to this function. If you
7233 need to do other things in that hook, have your hook function call
7237 @hook TARGET_ASM_LTO_START
7238 Output to @code{asm_out_file} any text which the assembler expects
7239 to find at the start of an LTO section. The default is to output
7243 @hook TARGET_ASM_LTO_END
7244 Output to @code{asm_out_file} any text which the assembler expects
7245 to find at the end of an LTO section. The default is to output
7249 @hook TARGET_ASM_CODE_END
7250 Output to @code{asm_out_file} any text which is needed before emitting
7251 unwind info and debug info at the end of a file. Some targets emit
7252 here PIC setup thunks that cannot be emitted at the end of file,
7253 because they couldn't have unwind info then. The default is to output
7257 @defmac ASM_COMMENT_START
7258 A C string constant describing how to begin a comment in the target
7259 assembler language. The compiler assumes that the comment will end at
7260 the end of the line.
7264 A C string constant for text to be output before each @code{asm}
7265 statement or group of consecutive ones. Normally this is
7266 @code{"#APP"}, which is a comment that has no effect on most
7267 assemblers but tells the GNU assembler that it must check the lines
7268 that follow for all valid assembler constructs.
7272 A C string constant for text to be output after each @code{asm}
7273 statement or group of consecutive ones. Normally this is
7274 @code{"#NO_APP"}, which tells the GNU assembler to resume making the
7275 time-saving assumptions that are valid for ordinary compiler output.
7278 @defmac ASM_OUTPUT_SOURCE_FILENAME (@var{stream}, @var{name})
7279 A C statement to output COFF information or DWARF debugging information
7280 which indicates that filename @var{name} is the current source file to
7281 the stdio stream @var{stream}.
7283 This macro need not be defined if the standard form of output
7284 for the file format in use is appropriate.
7287 @hook TARGET_ASM_OUTPUT_SOURCE_FILENAME
7289 @defmac OUTPUT_QUOTED_STRING (@var{stream}, @var{string})
7290 A C statement to output the string @var{string} to the stdio stream
7291 @var{stream}. If you do not call the function @code{output_quoted_string}
7292 in your config files, GCC will only call it to output filenames to
7293 the assembler source. So you can use it to canonicalize the format
7294 of the filename using this macro.
7297 @defmac ASM_OUTPUT_IDENT (@var{stream}, @var{string})
7298 A C statement to output something to the assembler file to handle a
7299 @samp{#ident} directive containing the text @var{string}. If this
7300 macro is not defined, nothing is output for a @samp{#ident} directive.
7303 @hook TARGET_ASM_NAMED_SECTION
7304 Output assembly directives to switch to section @var{name}. The section
7305 should have attributes as specified by @var{flags}, which is a bit mask
7306 of the @code{SECTION_*} flags defined in @file{output.h}. If @var{decl}
7307 is non-NULL, it is the @code{VAR_DECL} or @code{FUNCTION_DECL} with which
7308 this section is associated.
7311 @hook TARGET_ASM_FUNCTION_SECTION
7312 Return preferred text (sub)section for function @var{decl}.
7313 Main purpose of this function is to separate cold, normal and hot
7314 functions. @var{startup} is true when function is known to be used only
7315 at startup (from static constructors or it is @code{main()}).
7316 @var{exit} is true when function is known to be used only at exit
7317 (from static destructors).
7318 Return NULL if function should go to default text section.
7321 @hook TARGET_HAVE_NAMED_SECTIONS
7322 This flag is true if the target supports @code{TARGET_ASM_NAMED_SECTION}.
7323 It must not be modified by command-line option processing.
7326 @anchor{TARGET_HAVE_SWITCHABLE_BSS_SECTIONS}
7327 @hook TARGET_HAVE_SWITCHABLE_BSS_SECTIONS
7328 This flag is true if we can create zeroed data by switching to a BSS
7329 section and then using @code{ASM_OUTPUT_SKIP} to allocate the space.
7330 This is true on most ELF targets.
7333 @hook TARGET_SECTION_TYPE_FLAGS
7334 Choose a set of section attributes for use by @code{TARGET_ASM_NAMED_SECTION}
7335 based on a variable or function decl, a section name, and whether or not the
7336 declaration's initializer may contain runtime relocations. @var{decl} may be
7337 null, in which case read-write data should be assumed.
7339 The default version of this function handles choosing code vs data,
7340 read-only vs read-write data, and @code{flag_pic}. You should only
7341 need to override this if your target has special flags that might be
7342 set via @code{__attribute__}.
7345 @hook TARGET_ASM_RECORD_GCC_SWITCHES
7346 Provides the target with the ability to record the gcc command line
7347 switches that have been passed to the compiler, and options that are
7348 enabled. The @var{type} argument specifies what is being recorded.
7349 It can take the following values:
7352 @item SWITCH_TYPE_PASSED
7353 @var{text} is a command line switch that has been set by the user.
7355 @item SWITCH_TYPE_ENABLED
7356 @var{text} is an option which has been enabled. This might be as a
7357 direct result of a command line switch, or because it is enabled by
7358 default or because it has been enabled as a side effect of a different
7359 command line switch. For example, the @option{-O2} switch enables
7360 various different individual optimization passes.
7362 @item SWITCH_TYPE_DESCRIPTIVE
7363 @var{text} is either NULL or some descriptive text which should be
7364 ignored. If @var{text} is NULL then it is being used to warn the
7365 target hook that either recording is starting or ending. The first
7366 time @var{type} is SWITCH_TYPE_DESCRIPTIVE and @var{text} is NULL, the
7367 warning is for start up and the second time the warning is for
7368 wind down. This feature is to allow the target hook to make any
7369 necessary preparations before it starts to record switches and to
7370 perform any necessary tidying up after it has finished recording
7373 @item SWITCH_TYPE_LINE_START
7374 This option can be ignored by this target hook.
7376 @item SWITCH_TYPE_LINE_END
7377 This option can be ignored by this target hook.
7380 The hook's return value must be zero. Other return values may be
7381 supported in the future.
7383 By default this hook is set to NULL, but an example implementation is
7384 provided for ELF based targets. Called @var{elf_record_gcc_switches},
7385 it records the switches as ASCII text inside a new, string mergeable
7386 section in the assembler output file. The name of the new section is
7387 provided by the @code{TARGET_ASM_RECORD_GCC_SWITCHES_SECTION} target
7391 @hook TARGET_ASM_RECORD_GCC_SWITCHES_SECTION
7392 This is the name of the section that will be created by the example
7393 ELF implementation of the @code{TARGET_ASM_RECORD_GCC_SWITCHES} target
7399 @subsection Output of Data
7402 @hook TARGET_ASM_BYTE_OP
7403 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_HI_OP
7404 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_SI_OP
7405 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_DI_OP
7406 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_TI_OP
7407 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_HI_OP
7408 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_SI_OP
7409 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_DI_OP
7410 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_TI_OP
7411 These hooks specify assembly directives for creating certain kinds
7412 of integer object. The @code{TARGET_ASM_BYTE_OP} directive creates a
7413 byte-sized object, the @code{TARGET_ASM_ALIGNED_HI_OP} one creates an
7414 aligned two-byte object, and so on. Any of the hooks may be
7415 @code{NULL}, indicating that no suitable directive is available.
7417 The compiler will print these strings at the start of a new line,
7418 followed immediately by the object's initial value. In most cases,
7419 the string should contain a tab, a pseudo-op, and then another tab.
7422 @hook TARGET_ASM_INTEGER
7423 The @code{assemble_integer} function uses this hook to output an
7424 integer object. @var{x} is the object's value, @var{size} is its size
7425 in bytes and @var{aligned_p} indicates whether it is aligned. The
7426 function should return @code{true} if it was able to output the
7427 object. If it returns false, @code{assemble_integer} will try to
7428 split the object into smaller parts.
7430 The default implementation of this hook will use the
7431 @code{TARGET_ASM_BYTE_OP} family of strings, returning @code{false}
7432 when the relevant string is @code{NULL}.
7435 @hook TARGET_ASM_OUTPUT_ADDR_CONST_EXTRA
7436 A target hook to recognize @var{rtx} patterns that @code{output_addr_const}
7437 can't deal with, and output assembly code to @var{file} corresponding to
7438 the pattern @var{x}. This may be used to allow machine-dependent
7439 @code{UNSPEC}s to appear within constants.
7441 If target hook fails to recognize a pattern, it must return @code{false},
7442 so that a standard error message is printed. If it prints an error message
7443 itself, by calling, for example, @code{output_operand_lossage}, it may just
7447 @defmac OUTPUT_ADDR_CONST_EXTRA (@var{stream}, @var{x}, @var{fail})
7448 A C statement to recognize @var{rtx} patterns that
7449 @code{output_addr_const} can't deal with, and output assembly code to
7450 @var{stream} corresponding to the pattern @var{x}. This may be used to
7451 allow machine-dependent @code{UNSPEC}s to appear within constants.
7453 If @code{OUTPUT_ADDR_CONST_EXTRA} fails to recognize a pattern, it must
7454 @code{goto fail}, so that a standard error message is printed. If it
7455 prints an error message itself, by calling, for example,
7456 @code{output_operand_lossage}, it may just complete normally.
7459 @defmac ASM_OUTPUT_ASCII (@var{stream}, @var{ptr}, @var{len})
7460 A C statement to output to the stdio stream @var{stream} an assembler
7461 instruction to assemble a string constant containing the @var{len}
7462 bytes at @var{ptr}. @var{ptr} will be a C expression of type
7463 @code{char *} and @var{len} a C expression of type @code{int}.
7465 If the assembler has a @code{.ascii} pseudo-op as found in the
7466 Berkeley Unix assembler, do not define the macro
7467 @code{ASM_OUTPUT_ASCII}.
7470 @defmac ASM_OUTPUT_FDESC (@var{stream}, @var{decl}, @var{n})
7471 A C statement to output word @var{n} of a function descriptor for
7472 @var{decl}. This must be defined if @code{TARGET_VTABLE_USES_DESCRIPTORS}
7473 is defined, and is otherwise unused.
7476 @defmac CONSTANT_POOL_BEFORE_FUNCTION
7477 You may define this macro as a C expression. You should define the
7478 expression to have a nonzero value if GCC should output the constant
7479 pool for a function before the code for the function, or a zero value if
7480 GCC should output the constant pool after the function. If you do
7481 not define this macro, the usual case, GCC will output the constant
7482 pool before the function.
7485 @defmac ASM_OUTPUT_POOL_PROLOGUE (@var{file}, @var{funname}, @var{fundecl}, @var{size})
7486 A C statement to output assembler commands to define the start of the
7487 constant pool for a function. @var{funname} is a string giving
7488 the name of the function. Should the return type of the function
7489 be required, it can be obtained via @var{fundecl}. @var{size}
7490 is the size, in bytes, of the constant pool that will be written
7491 immediately after this call.
7493 If no constant-pool prefix is required, the usual case, this macro need
7497 @defmac ASM_OUTPUT_SPECIAL_POOL_ENTRY (@var{file}, @var{x}, @var{mode}, @var{align}, @var{labelno}, @var{jumpto})
7498 A C statement (with or without semicolon) to output a constant in the
7499 constant pool, if it needs special treatment. (This macro need not do
7500 anything for RTL expressions that can be output normally.)
7502 The argument @var{file} is the standard I/O stream to output the
7503 assembler code on. @var{x} is the RTL expression for the constant to
7504 output, and @var{mode} is the machine mode (in case @var{x} is a
7505 @samp{const_int}). @var{align} is the required alignment for the value
7506 @var{x}; you should output an assembler directive to force this much
7509 The argument @var{labelno} is a number to use in an internal label for
7510 the address of this pool entry. The definition of this macro is
7511 responsible for outputting the label definition at the proper place.
7512 Here is how to do this:
7515 @code{(*targetm.asm_out.internal_label)} (@var{file}, "LC", @var{labelno});
7518 When you output a pool entry specially, you should end with a
7519 @code{goto} to the label @var{jumpto}. This will prevent the same pool
7520 entry from being output a second time in the usual manner.
7522 You need not define this macro if it would do nothing.
7525 @defmac ASM_OUTPUT_POOL_EPILOGUE (@var{file} @var{funname} @var{fundecl} @var{size})
7526 A C statement to output assembler commands to at the end of the constant
7527 pool for a function. @var{funname} is a string giving the name of the
7528 function. Should the return type of the function be required, you can
7529 obtain it via @var{fundecl}. @var{size} is the size, in bytes, of the
7530 constant pool that GCC wrote immediately before this call.
7532 If no constant-pool epilogue is required, the usual case, you need not
7536 @defmac IS_ASM_LOGICAL_LINE_SEPARATOR (@var{C}, @var{STR})
7537 Define this macro as a C expression which is nonzero if @var{C} is
7538 used as a logical line separator by the assembler. @var{STR} points
7539 to the position in the string where @var{C} was found; this can be used if
7540 a line separator uses multiple characters.
7542 If you do not define this macro, the default is that only
7543 the character @samp{;} is treated as a logical line separator.
7546 @hook TARGET_ASM_OPEN_PAREN
7547 These target hooks are C string constants, describing the syntax in the
7548 assembler for grouping arithmetic expressions. If not overridden, they
7549 default to normal parentheses, which is correct for most assemblers.
7552 These macros are provided by @file{real.h} for writing the definitions
7553 of @code{ASM_OUTPUT_DOUBLE} and the like:
7555 @defmac REAL_VALUE_TO_TARGET_SINGLE (@var{x}, @var{l})
7556 @defmacx REAL_VALUE_TO_TARGET_DOUBLE (@var{x}, @var{l})
7557 @defmacx REAL_VALUE_TO_TARGET_LONG_DOUBLE (@var{x}, @var{l})
7558 @defmacx REAL_VALUE_TO_TARGET_DECIMAL32 (@var{x}, @var{l})
7559 @defmacx REAL_VALUE_TO_TARGET_DECIMAL64 (@var{x}, @var{l})
7560 @defmacx REAL_VALUE_TO_TARGET_DECIMAL128 (@var{x}, @var{l})
7561 These translate @var{x}, of type @code{REAL_VALUE_TYPE}, to the
7562 target's floating point representation, and store its bit pattern in
7563 the variable @var{l}. For @code{REAL_VALUE_TO_TARGET_SINGLE} and
7564 @code{REAL_VALUE_TO_TARGET_DECIMAL32}, this variable should be a
7565 simple @code{long int}. For the others, it should be an array of
7566 @code{long int}. The number of elements in this array is determined
7567 by the size of the desired target floating point data type: 32 bits of
7568 it go in each @code{long int} array element. Each array element holds
7569 32 bits of the result, even if @code{long int} is wider than 32 bits
7570 on the host machine.
7572 The array element values are designed so that you can print them out
7573 using @code{fprintf} in the order they should appear in the target
7577 @node Uninitialized Data
7578 @subsection Output of Uninitialized Variables
7580 Each of the macros in this section is used to do the whole job of
7581 outputting a single uninitialized variable.
7583 @defmac ASM_OUTPUT_COMMON (@var{stream}, @var{name}, @var{size}, @var{rounded})
7584 A C statement (sans semicolon) to output to the stdio stream
7585 @var{stream} the assembler definition of a common-label named
7586 @var{name} whose size is @var{size} bytes. The variable @var{rounded}
7587 is the size rounded up to whatever alignment the caller wants. It is
7588 possible that @var{size} may be zero, for instance if a struct with no
7589 other member than a zero-length array is defined. In this case, the
7590 backend must output a symbol definition that allocates at least one
7591 byte, both so that the address of the resulting object does not compare
7592 equal to any other, and because some object formats cannot even express
7593 the concept of a zero-sized common symbol, as that is how they represent
7594 an ordinary undefined external.
7596 Use the expression @code{assemble_name (@var{stream}, @var{name})} to
7597 output the name itself; before and after that, output the additional
7598 assembler syntax for defining the name, and a newline.
7600 This macro controls how the assembler definitions of uninitialized
7601 common global variables are output.
7604 @defmac ASM_OUTPUT_ALIGNED_COMMON (@var{stream}, @var{name}, @var{size}, @var{alignment})
7605 Like @code{ASM_OUTPUT_COMMON} except takes the required alignment as a
7606 separate, explicit argument. If you define this macro, it is used in
7607 place of @code{ASM_OUTPUT_COMMON}, and gives you more flexibility in
7608 handling the required alignment of the variable. The alignment is specified
7609 as the number of bits.
7612 @defmac ASM_OUTPUT_ALIGNED_DECL_COMMON (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
7613 Like @code{ASM_OUTPUT_ALIGNED_COMMON} except that @var{decl} of the
7614 variable to be output, if there is one, or @code{NULL_TREE} if there
7615 is no corresponding variable. If you define this macro, GCC will use it
7616 in place of both @code{ASM_OUTPUT_COMMON} and
7617 @code{ASM_OUTPUT_ALIGNED_COMMON}. Define this macro when you need to see
7618 the variable's decl in order to chose what to output.
7621 @defmac ASM_OUTPUT_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{rounded})
7622 A C statement (sans semicolon) to output to the stdio stream
7623 @var{stream} the assembler definition of uninitialized global @var{decl} named
7624 @var{name} whose size is @var{size} bytes. The variable @var{rounded}
7625 is the size rounded up to whatever alignment the caller wants.
7627 Try to use function @code{asm_output_bss} defined in @file{varasm.c} when
7628 defining this macro. If unable, use the expression
7629 @code{assemble_name (@var{stream}, @var{name})} to output the name itself;
7630 before and after that, output the additional assembler syntax for defining
7631 the name, and a newline.
7633 There are two ways of handling global BSS@. One is to define either
7634 this macro or its aligned counterpart, @code{ASM_OUTPUT_ALIGNED_BSS}.
7635 The other is to have @code{TARGET_ASM_SELECT_SECTION} return a
7636 switchable BSS section (@pxref{TARGET_HAVE_SWITCHABLE_BSS_SECTIONS}).
7637 You do not need to do both.
7639 Some languages do not have @code{common} data, and require a
7640 non-common form of global BSS in order to handle uninitialized globals
7641 efficiently. C++ is one example of this. However, if the target does
7642 not support global BSS, the front end may choose to make globals
7643 common in order to save space in the object file.
7646 @defmac ASM_OUTPUT_ALIGNED_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
7647 Like @code{ASM_OUTPUT_BSS} except takes the required alignment as a
7648 separate, explicit argument. If you define this macro, it is used in
7649 place of @code{ASM_OUTPUT_BSS}, and gives you more flexibility in
7650 handling the required alignment of the variable. The alignment is specified
7651 as the number of bits.
7653 Try to use function @code{asm_output_aligned_bss} defined in file
7654 @file{varasm.c} when defining this macro.
7657 @defmac ASM_OUTPUT_LOCAL (@var{stream}, @var{name}, @var{size}, @var{rounded})
7658 A C statement (sans semicolon) to output to the stdio stream
7659 @var{stream} the assembler definition of a local-common-label named
7660 @var{name} whose size is @var{size} bytes. The variable @var{rounded}
7661 is the size rounded up to whatever alignment the caller wants.
7663 Use the expression @code{assemble_name (@var{stream}, @var{name})} to
7664 output the name itself; before and after that, output the additional
7665 assembler syntax for defining the name, and a newline.
7667 This macro controls how the assembler definitions of uninitialized
7668 static variables are output.
7671 @defmac ASM_OUTPUT_ALIGNED_LOCAL (@var{stream}, @var{name}, @var{size}, @var{alignment})
7672 Like @code{ASM_OUTPUT_LOCAL} except takes the required alignment as a
7673 separate, explicit argument. If you define this macro, it is used in
7674 place of @code{ASM_OUTPUT_LOCAL}, and gives you more flexibility in
7675 handling the required alignment of the variable. The alignment is specified
7676 as the number of bits.
7679 @defmac ASM_OUTPUT_ALIGNED_DECL_LOCAL (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
7680 Like @code{ASM_OUTPUT_ALIGNED_DECL} except that @var{decl} of the
7681 variable to be output, if there is one, or @code{NULL_TREE} if there
7682 is no corresponding variable. If you define this macro, GCC will use it
7683 in place of both @code{ASM_OUTPUT_DECL} and
7684 @code{ASM_OUTPUT_ALIGNED_DECL}. Define this macro when you need to see
7685 the variable's decl in order to chose what to output.
7689 @subsection Output and Generation of Labels
7691 @c prevent bad page break with this line
7692 This is about outputting labels.
7694 @findex assemble_name
7695 @defmac ASM_OUTPUT_LABEL (@var{stream}, @var{name})
7696 A C statement (sans semicolon) to output to the stdio stream
7697 @var{stream} the assembler definition of a label named @var{name}.
7698 Use the expression @code{assemble_name (@var{stream}, @var{name})} to
7699 output the name itself; before and after that, output the additional
7700 assembler syntax for defining the name, and a newline. A default
7701 definition of this macro is provided which is correct for most systems.
7704 @defmac ASM_OUTPUT_FUNCTION_LABEL (@var{stream}, @var{name}, @var{decl})
7705 A C statement (sans semicolon) to output to the stdio stream
7706 @var{stream} the assembler definition of a label named @var{name} of
7708 Use the expression @code{assemble_name (@var{stream}, @var{name})} to
7709 output the name itself; before and after that, output the additional
7710 assembler syntax for defining the name, and a newline. A default
7711 definition of this macro is provided which is correct for most systems.
7713 If this macro is not defined, then the function name is defined in the
7714 usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}).
7717 @findex assemble_name_raw
7718 @defmac ASM_OUTPUT_INTERNAL_LABEL (@var{stream}, @var{name})
7719 Identical to @code{ASM_OUTPUT_LABEL}, except that @var{name} is known
7720 to refer to a compiler-generated label. The default definition uses
7721 @code{assemble_name_raw}, which is like @code{assemble_name} except
7722 that it is more efficient.
7726 A C string containing the appropriate assembler directive to specify the
7727 size of a symbol, without any arguments. On systems that use ELF, the
7728 default (in @file{config/elfos.h}) is @samp{"\t.size\t"}; on other
7729 systems, the default is not to define this macro.
7731 Define this macro only if it is correct to use the default definitions
7732 of @code{ASM_OUTPUT_SIZE_DIRECTIVE} and @code{ASM_OUTPUT_MEASURED_SIZE}
7733 for your system. If you need your own custom definitions of those
7734 macros, or if you do not need explicit symbol sizes at all, do not
7738 @defmac ASM_OUTPUT_SIZE_DIRECTIVE (@var{stream}, @var{name}, @var{size})
7739 A C statement (sans semicolon) to output to the stdio stream
7740 @var{stream} a directive telling the assembler that the size of the
7741 symbol @var{name} is @var{size}. @var{size} is a @code{HOST_WIDE_INT}.
7742 If you define @code{SIZE_ASM_OP}, a default definition of this macro is
7746 @defmac ASM_OUTPUT_MEASURED_SIZE (@var{stream}, @var{name})
7747 A C statement (sans semicolon) to output to the stdio stream
7748 @var{stream} a directive telling the assembler to calculate the size of
7749 the symbol @var{name} by subtracting its address from the current
7752 If you define @code{SIZE_ASM_OP}, a default definition of this macro is
7753 provided. The default assumes that the assembler recognizes a special
7754 @samp{.} symbol as referring to the current address, and can calculate
7755 the difference between this and another symbol. If your assembler does
7756 not recognize @samp{.} or cannot do calculations with it, you will need
7757 to redefine @code{ASM_OUTPUT_MEASURED_SIZE} to use some other technique.
7761 A C string containing the appropriate assembler directive to specify the
7762 type of a symbol, without any arguments. On systems that use ELF, the
7763 default (in @file{config/elfos.h}) is @samp{"\t.type\t"}; on other
7764 systems, the default is not to define this macro.
7766 Define this macro only if it is correct to use the default definition of
7767 @code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own
7768 custom definition of this macro, or if you do not need explicit symbol
7769 types at all, do not define this macro.
7772 @defmac TYPE_OPERAND_FMT
7773 A C string which specifies (using @code{printf} syntax) the format of
7774 the second operand to @code{TYPE_ASM_OP}. On systems that use ELF, the
7775 default (in @file{config/elfos.h}) is @samp{"@@%s"}; on other systems,
7776 the default is not to define this macro.
7778 Define this macro only if it is correct to use the default definition of
7779 @code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own
7780 custom definition of this macro, or if you do not need explicit symbol
7781 types at all, do not define this macro.
7784 @defmac ASM_OUTPUT_TYPE_DIRECTIVE (@var{stream}, @var{type})
7785 A C statement (sans semicolon) to output to the stdio stream
7786 @var{stream} a directive telling the assembler that the type of the
7787 symbol @var{name} is @var{type}. @var{type} is a C string; currently,
7788 that string is always either @samp{"function"} or @samp{"object"}, but
7789 you should not count on this.
7791 If you define @code{TYPE_ASM_OP} and @code{TYPE_OPERAND_FMT}, a default
7792 definition of this macro is provided.
7795 @defmac ASM_DECLARE_FUNCTION_NAME (@var{stream}, @var{name}, @var{decl})
7796 A C statement (sans semicolon) to output to the stdio stream
7797 @var{stream} any text necessary for declaring the name @var{name} of a
7798 function which is being defined. This macro is responsible for
7799 outputting the label definition (perhaps using
7800 @code{ASM_OUTPUT_FUNCTION_LABEL}). The argument @var{decl} is the
7801 @code{FUNCTION_DECL} tree node representing the function.
7803 If this macro is not defined, then the function name is defined in the
7804 usual manner as a label (by means of @code{ASM_OUTPUT_FUNCTION_LABEL}).
7806 You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in the definition
7810 @defmac ASM_DECLARE_FUNCTION_SIZE (@var{stream}, @var{name}, @var{decl})
7811 A C statement (sans semicolon) to output to the stdio stream
7812 @var{stream} any text necessary for declaring the size of a function
7813 which is being defined. The argument @var{name} is the name of the
7814 function. The argument @var{decl} is the @code{FUNCTION_DECL} tree node
7815 representing the function.
7817 If this macro is not defined, then the function size is not defined.
7819 You may wish to use @code{ASM_OUTPUT_MEASURED_SIZE} in the definition
7823 @defmac ASM_DECLARE_OBJECT_NAME (@var{stream}, @var{name}, @var{decl})
7824 A C statement (sans semicolon) to output to the stdio stream
7825 @var{stream} any text necessary for declaring the name @var{name} of an
7826 initialized variable which is being defined. This macro must output the
7827 label definition (perhaps using @code{ASM_OUTPUT_LABEL}). The argument
7828 @var{decl} is the @code{VAR_DECL} tree node representing the variable.
7830 If this macro is not defined, then the variable name is defined in the
7831 usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}).
7833 You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} and/or
7834 @code{ASM_OUTPUT_SIZE_DIRECTIVE} in the definition of this macro.
7837 @hook TARGET_ASM_DECLARE_CONSTANT_NAME
7838 A target hook to output to the stdio stream @var{file} any text necessary
7839 for declaring the name @var{name} of a constant which is being defined. This
7840 target hook is responsible for outputting the label definition (perhaps using
7841 @code{assemble_label}). The argument @var{exp} is the value of the constant,
7842 and @var{size} is the size of the constant in bytes. The @var{name}
7843 will be an internal label.
7845 The default version of this target hook, define the @var{name} in the
7846 usual manner as a label (by means of @code{assemble_label}).
7848 You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in this target hook.
7851 @defmac ASM_DECLARE_REGISTER_GLOBAL (@var{stream}, @var{decl}, @var{regno}, @var{name})
7852 A C statement (sans semicolon) to output to the stdio stream
7853 @var{stream} any text necessary for claiming a register @var{regno}
7854 for a global variable @var{decl} with name @var{name}.
7856 If you don't define this macro, that is equivalent to defining it to do
7860 @defmac ASM_FINISH_DECLARE_OBJECT (@var{stream}, @var{decl}, @var{toplevel}, @var{atend})
7861 A C statement (sans semicolon) to finish up declaring a variable name
7862 once the compiler has processed its initializer fully and thus has had a
7863 chance to determine the size of an array when controlled by an
7864 initializer. This is used on systems where it's necessary to declare
7865 something about the size of the object.
7867 If you don't define this macro, that is equivalent to defining it to do
7870 You may wish to use @code{ASM_OUTPUT_SIZE_DIRECTIVE} and/or
7871 @code{ASM_OUTPUT_MEASURED_SIZE} in the definition of this macro.
7874 @hook TARGET_ASM_GLOBALIZE_LABEL
7875 This target hook is a function to output to the stdio stream
7876 @var{stream} some commands that will make the label @var{name} global;
7877 that is, available for reference from other files.
7879 The default implementation relies on a proper definition of
7880 @code{GLOBAL_ASM_OP}.
7883 @hook TARGET_ASM_GLOBALIZE_DECL_NAME
7884 This target hook is a function to output to the stdio stream
7885 @var{stream} some commands that will make the name associated with @var{decl}
7886 global; that is, available for reference from other files.
7888 The default implementation uses the TARGET_ASM_GLOBALIZE_LABEL target hook.
7891 @defmac ASM_WEAKEN_LABEL (@var{stream}, @var{name})
7892 A C statement (sans semicolon) to output to the stdio stream
7893 @var{stream} some commands that will make the label @var{name} weak;
7894 that is, available for reference from other files but only used if
7895 no other definition is available. Use the expression
7896 @code{assemble_name (@var{stream}, @var{name})} to output the name
7897 itself; before and after that, output the additional assembler syntax
7898 for making that name weak, and a newline.
7900 If you don't define this macro or @code{ASM_WEAKEN_DECL}, GCC will not
7901 support weak symbols and you should not define the @code{SUPPORTS_WEAK}
7905 @defmac ASM_WEAKEN_DECL (@var{stream}, @var{decl}, @var{name}, @var{value})
7906 Combines (and replaces) the function of @code{ASM_WEAKEN_LABEL} and
7907 @code{ASM_OUTPUT_WEAK_ALIAS}, allowing access to the associated function
7908 or variable decl. If @var{value} is not @code{NULL}, this C statement
7909 should output to the stdio stream @var{stream} assembler code which
7910 defines (equates) the weak symbol @var{name} to have the value
7911 @var{value}. If @var{value} is @code{NULL}, it should output commands
7912 to make @var{name} weak.
7915 @defmac ASM_OUTPUT_WEAKREF (@var{stream}, @var{decl}, @var{name}, @var{value})
7916 Outputs a directive that enables @var{name} to be used to refer to
7917 symbol @var{value} with weak-symbol semantics. @code{decl} is the
7918 declaration of @code{name}.
7921 @defmac SUPPORTS_WEAK
7922 A preprocessor constant expression which evaluates to true if the target
7923 supports weak symbols.
7925 If you don't define this macro, @file{defaults.h} provides a default
7926 definition. If either @code{ASM_WEAKEN_LABEL} or @code{ASM_WEAKEN_DECL}
7927 is defined, the default definition is @samp{1}; otherwise, it is @samp{0}.
7930 @defmac TARGET_SUPPORTS_WEAK
7931 A C expression which evaluates to true if the target supports weak symbols.
7933 If you don't define this macro, @file{defaults.h} provides a default
7934 definition. The default definition is @samp{(SUPPORTS_WEAK)}. Define
7935 this macro if you want to control weak symbol support with a compiler
7936 flag such as @option{-melf}.
7939 @defmac MAKE_DECL_ONE_ONLY (@var{decl})
7940 A C statement (sans semicolon) to mark @var{decl} to be emitted as a
7941 public symbol such that extra copies in multiple translation units will
7942 be discarded by the linker. Define this macro if your object file
7943 format provides support for this concept, such as the @samp{COMDAT}
7944 section flags in the Microsoft Windows PE/COFF format, and this support
7945 requires changes to @var{decl}, such as putting it in a separate section.
7948 @defmac SUPPORTS_ONE_ONLY
7949 A C expression which evaluates to true if the target supports one-only
7952 If you don't define this macro, @file{varasm.c} provides a default
7953 definition. If @code{MAKE_DECL_ONE_ONLY} is defined, the default
7954 definition is @samp{1}; otherwise, it is @samp{0}. Define this macro if
7955 you want to control one-only symbol support with a compiler flag, or if
7956 setting the @code{DECL_ONE_ONLY} flag is enough to mark a declaration to
7957 be emitted as one-only.
7960 @hook TARGET_ASM_ASSEMBLE_VISIBILITY
7961 This target hook is a function to output to @var{asm_out_file} some
7962 commands that will make the symbol(s) associated with @var{decl} have
7963 hidden, protected or internal visibility as specified by @var{visibility}.
7966 @defmac TARGET_WEAK_NOT_IN_ARCHIVE_TOC
7967 A C expression that evaluates to true if the target's linker expects
7968 that weak symbols do not appear in a static archive's table of contents.
7969 The default is @code{0}.
7971 Leaving weak symbols out of an archive's table of contents means that,
7972 if a symbol will only have a definition in one translation unit and
7973 will have undefined references from other translation units, that
7974 symbol should not be weak. Defining this macro to be nonzero will
7975 thus have the effect that certain symbols that would normally be weak
7976 (explicit template instantiations, and vtables for polymorphic classes
7977 with noninline key methods) will instead be nonweak.
7979 The C++ ABI requires this macro to be zero. Define this macro for
7980 targets where full C++ ABI compliance is impossible and where linker
7981 restrictions require weak symbols to be left out of a static archive's
7985 @defmac ASM_OUTPUT_EXTERNAL (@var{stream}, @var{decl}, @var{name})
7986 A C statement (sans semicolon) to output to the stdio stream
7987 @var{stream} any text necessary for declaring the name of an external
7988 symbol named @var{name} which is referenced in this compilation but
7989 not defined. The value of @var{decl} is the tree node for the
7992 This macro need not be defined if it does not need to output anything.
7993 The GNU assembler and most Unix assemblers don't require anything.
7996 @hook TARGET_ASM_EXTERNAL_LIBCALL
7997 This target hook is a function to output to @var{asm_out_file} an assembler
7998 pseudo-op to declare a library function name external. The name of the
7999 library function is given by @var{symref}, which is a @code{symbol_ref}.
8002 @hook TARGET_ASM_MARK_DECL_PRESERVED
8003 This target hook is a function to output to @var{asm_out_file} an assembler
8004 directive to annotate @var{symbol} as used. The Darwin target uses the
8005 .no_dead_code_strip directive.
8008 @defmac ASM_OUTPUT_LABELREF (@var{stream}, @var{name})
8009 A C statement (sans semicolon) to output to the stdio stream
8010 @var{stream} a reference in assembler syntax to a label named
8011 @var{name}. This should add @samp{_} to the front of the name, if that
8012 is customary on your operating system, as it is in most Berkeley Unix
8013 systems. This macro is used in @code{assemble_name}.
8016 @defmac ASM_OUTPUT_SYMBOL_REF (@var{stream}, @var{sym})
8017 A C statement (sans semicolon) to output a reference to
8018 @code{SYMBOL_REF} @var{sym}. If not defined, @code{assemble_name}
8019 will be used to output the name of the symbol. This macro may be used
8020 to modify the way a symbol is referenced depending on information
8021 encoded by @code{TARGET_ENCODE_SECTION_INFO}.
8024 @defmac ASM_OUTPUT_LABEL_REF (@var{stream}, @var{buf})
8025 A C statement (sans semicolon) to output a reference to @var{buf}, the
8026 result of @code{ASM_GENERATE_INTERNAL_LABEL}. If not defined,
8027 @code{assemble_name} will be used to output the name of the symbol.
8028 This macro is not used by @code{output_asm_label}, or the @code{%l}
8029 specifier that calls it; the intention is that this macro should be set
8030 when it is necessary to output a label differently when its address is
8034 @hook TARGET_ASM_INTERNAL_LABEL
8035 A function to output to the stdio stream @var{stream} a label whose
8036 name is made from the string @var{prefix} and the number @var{labelno}.
8038 It is absolutely essential that these labels be distinct from the labels
8039 used for user-level functions and variables. Otherwise, certain programs
8040 will have name conflicts with internal labels.
8042 It is desirable to exclude internal labels from the symbol table of the
8043 object file. Most assemblers have a naming convention for labels that
8044 should be excluded; on many systems, the letter @samp{L} at the
8045 beginning of a label has this effect. You should find out what
8046 convention your system uses, and follow it.
8048 The default version of this function utilizes @code{ASM_GENERATE_INTERNAL_LABEL}.
8051 @defmac ASM_OUTPUT_DEBUG_LABEL (@var{stream}, @var{prefix}, @var{num})
8052 A C statement to output to the stdio stream @var{stream} a debug info
8053 label whose name is made from the string @var{prefix} and the number
8054 @var{num}. This is useful for VLIW targets, where debug info labels
8055 may need to be treated differently than branch target labels. On some
8056 systems, branch target labels must be at the beginning of instruction
8057 bundles, but debug info labels can occur in the middle of instruction
8060 If this macro is not defined, then @code{(*targetm.asm_out.internal_label)} will be
8064 @defmac ASM_GENERATE_INTERNAL_LABEL (@var{string}, @var{prefix}, @var{num})
8065 A C statement to store into the string @var{string} a label whose name
8066 is made from the string @var{prefix} and the number @var{num}.
8068 This string, when output subsequently by @code{assemble_name}, should
8069 produce the output that @code{(*targetm.asm_out.internal_label)} would produce
8070 with the same @var{prefix} and @var{num}.
8072 If the string begins with @samp{*}, then @code{assemble_name} will
8073 output the rest of the string unchanged. It is often convenient for
8074 @code{ASM_GENERATE_INTERNAL_LABEL} to use @samp{*} in this way. If the
8075 string doesn't start with @samp{*}, then @code{ASM_OUTPUT_LABELREF} gets
8076 to output the string, and may change it. (Of course,
8077 @code{ASM_OUTPUT_LABELREF} is also part of your machine description, so
8078 you should know what it does on your machine.)
8081 @defmac ASM_FORMAT_PRIVATE_NAME (@var{outvar}, @var{name}, @var{number})
8082 A C expression to assign to @var{outvar} (which is a variable of type
8083 @code{char *}) a newly allocated string made from the string
8084 @var{name} and the number @var{number}, with some suitable punctuation
8085 added. Use @code{alloca} to get space for the string.
8087 The string will be used as an argument to @code{ASM_OUTPUT_LABELREF} to
8088 produce an assembler label for an internal static variable whose name is
8089 @var{name}. Therefore, the string must be such as to result in valid
8090 assembler code. The argument @var{number} is different each time this
8091 macro is executed; it prevents conflicts between similarly-named
8092 internal static variables in different scopes.
8094 Ideally this string should not be a valid C identifier, to prevent any
8095 conflict with the user's own symbols. Most assemblers allow periods
8096 or percent signs in assembler symbols; putting at least one of these
8097 between the name and the number will suffice.
8099 If this macro is not defined, a default definition will be provided
8100 which is correct for most systems.
8103 @defmac ASM_OUTPUT_DEF (@var{stream}, @var{name}, @var{value})
8104 A C statement to output to the stdio stream @var{stream} assembler code
8105 which defines (equates) the symbol @var{name} to have the value @var{value}.
8108 If @code{SET_ASM_OP} is defined, a default definition is provided which is
8109 correct for most systems.
8112 @defmac ASM_OUTPUT_DEF_FROM_DECLS (@var{stream}, @var{decl_of_name}, @var{decl_of_value})
8113 A C statement to output to the stdio stream @var{stream} assembler code
8114 which defines (equates) the symbol whose tree node is @var{decl_of_name}
8115 to have the value of the tree node @var{decl_of_value}. This macro will
8116 be used in preference to @samp{ASM_OUTPUT_DEF} if it is defined and if
8117 the tree nodes are available.
8120 If @code{SET_ASM_OP} is defined, a default definition is provided which is
8121 correct for most systems.
8124 @defmac TARGET_DEFERRED_OUTPUT_DEFS (@var{decl_of_name}, @var{decl_of_value})
8125 A C statement that evaluates to true if the assembler code which defines
8126 (equates) the symbol whose tree node is @var{decl_of_name} to have the value
8127 of the tree node @var{decl_of_value} should be emitted near the end of the
8128 current compilation unit. The default is to not defer output of defines.
8129 This macro affects defines output by @samp{ASM_OUTPUT_DEF} and
8130 @samp{ASM_OUTPUT_DEF_FROM_DECLS}.
8133 @defmac ASM_OUTPUT_WEAK_ALIAS (@var{stream}, @var{name}, @var{value})
8134 A C statement to output to the stdio stream @var{stream} assembler code
8135 which defines (equates) the weak symbol @var{name} to have the value
8136 @var{value}. If @var{value} is @code{NULL}, it defines @var{name} as
8137 an undefined weak symbol.
8139 Define this macro if the target only supports weak aliases; define
8140 @code{ASM_OUTPUT_DEF} instead if possible.
8143 @defmac OBJC_GEN_METHOD_LABEL (@var{buf}, @var{is_inst}, @var{class_name}, @var{cat_name}, @var{sel_name})
8144 Define this macro to override the default assembler names used for
8145 Objective-C methods.
8147 The default name is a unique method number followed by the name of the
8148 class (e.g.@: @samp{_1_Foo}). For methods in categories, the name of
8149 the category is also included in the assembler name (e.g.@:
8152 These names are safe on most systems, but make debugging difficult since
8153 the method's selector is not present in the name. Therefore, particular
8154 systems define other ways of computing names.
8156 @var{buf} is an expression of type @code{char *} which gives you a
8157 buffer in which to store the name; its length is as long as
8158 @var{class_name}, @var{cat_name} and @var{sel_name} put together, plus
8159 50 characters extra.
8161 The argument @var{is_inst} specifies whether the method is an instance
8162 method or a class method; @var{class_name} is the name of the class;
8163 @var{cat_name} is the name of the category (or @code{NULL} if the method is not
8164 in a category); and @var{sel_name} is the name of the selector.
8166 On systems where the assembler can handle quoted names, you can use this
8167 macro to provide more human-readable names.
8170 @defmac ASM_DECLARE_CLASS_REFERENCE (@var{stream}, @var{name})
8171 A C statement (sans semicolon) to output to the stdio stream
8172 @var{stream} commands to declare that the label @var{name} is an
8173 Objective-C class reference. This is only needed for targets whose
8174 linkers have special support for NeXT-style runtimes.
8177 @defmac ASM_DECLARE_UNRESOLVED_REFERENCE (@var{stream}, @var{name})
8178 A C statement (sans semicolon) to output to the stdio stream
8179 @var{stream} commands to declare that the label @var{name} is an
8180 unresolved Objective-C class reference. This is only needed for targets
8181 whose linkers have special support for NeXT-style runtimes.
8184 @node Initialization
8185 @subsection How Initialization Functions Are Handled
8186 @cindex initialization routines
8187 @cindex termination routines
8188 @cindex constructors, output of
8189 @cindex destructors, output of
8191 The compiled code for certain languages includes @dfn{constructors}
8192 (also called @dfn{initialization routines})---functions to initialize
8193 data in the program when the program is started. These functions need
8194 to be called before the program is ``started''---that is to say, before
8195 @code{main} is called.
8197 Compiling some languages generates @dfn{destructors} (also called
8198 @dfn{termination routines}) that should be called when the program
8201 To make the initialization and termination functions work, the compiler
8202 must output something in the assembler code to cause those functions to
8203 be called at the appropriate time. When you port the compiler to a new
8204 system, you need to specify how to do this.
8206 There are two major ways that GCC currently supports the execution of
8207 initialization and termination functions. Each way has two variants.
8208 Much of the structure is common to all four variations.
8210 @findex __CTOR_LIST__
8211 @findex __DTOR_LIST__
8212 The linker must build two lists of these functions---a list of
8213 initialization functions, called @code{__CTOR_LIST__}, and a list of
8214 termination functions, called @code{__DTOR_LIST__}.
8216 Each list always begins with an ignored function pointer (which may hold
8217 0, @minus{}1, or a count of the function pointers after it, depending on
8218 the environment). This is followed by a series of zero or more function
8219 pointers to constructors (or destructors), followed by a function
8220 pointer containing zero.
8222 Depending on the operating system and its executable file format, either
8223 @file{crtstuff.c} or @file{libgcc2.c} traverses these lists at startup
8224 time and exit time. Constructors are called in reverse order of the
8225 list; destructors in forward order.
8227 The best way to handle static constructors works only for object file
8228 formats which provide arbitrarily-named sections. A section is set
8229 aside for a list of constructors, and another for a list of destructors.
8230 Traditionally these are called @samp{.ctors} and @samp{.dtors}. Each
8231 object file that defines an initialization function also puts a word in
8232 the constructor section to point to that function. The linker
8233 accumulates all these words into one contiguous @samp{.ctors} section.
8234 Termination functions are handled similarly.
8236 This method will be chosen as the default by @file{target-def.h} if
8237 @code{TARGET_ASM_NAMED_SECTION} is defined. A target that does not
8238 support arbitrary sections, but does support special designated
8239 constructor and destructor sections may define @code{CTORS_SECTION_ASM_OP}
8240 and @code{DTORS_SECTION_ASM_OP} to achieve the same effect.
8242 When arbitrary sections are available, there are two variants, depending
8243 upon how the code in @file{crtstuff.c} is called. On systems that
8244 support a @dfn{.init} section which is executed at program startup,
8245 parts of @file{crtstuff.c} are compiled into that section. The
8246 program is linked by the @command{gcc} driver like this:
8249 ld -o @var{output_file} crti.o crtbegin.o @dots{} -lgcc crtend.o crtn.o
8252 The prologue of a function (@code{__init}) appears in the @code{.init}
8253 section of @file{crti.o}; the epilogue appears in @file{crtn.o}. Likewise
8254 for the function @code{__fini} in the @dfn{.fini} section. Normally these
8255 files are provided by the operating system or by the GNU C library, but
8256 are provided by GCC for a few targets.
8258 The objects @file{crtbegin.o} and @file{crtend.o} are (for most targets)
8259 compiled from @file{crtstuff.c}. They contain, among other things, code
8260 fragments within the @code{.init} and @code{.fini} sections that branch
8261 to routines in the @code{.text} section. The linker will pull all parts
8262 of a section together, which results in a complete @code{__init} function
8263 that invokes the routines we need at startup.
8265 To use this variant, you must define the @code{INIT_SECTION_ASM_OP}
8268 If no init section is available, when GCC compiles any function called
8269 @code{main} (or more accurately, any function designated as a program
8270 entry point by the language front end calling @code{expand_main_function}),
8271 it inserts a procedure call to @code{__main} as the first executable code
8272 after the function prologue. The @code{__main} function is defined
8273 in @file{libgcc2.c} and runs the global constructors.
8275 In file formats that don't support arbitrary sections, there are again
8276 two variants. In the simplest variant, the GNU linker (GNU @code{ld})
8277 and an `a.out' format must be used. In this case,
8278 @code{TARGET_ASM_CONSTRUCTOR} is defined to produce a @code{.stabs}
8279 entry of type @samp{N_SETT}, referencing the name @code{__CTOR_LIST__},
8280 and with the address of the void function containing the initialization
8281 code as its value. The GNU linker recognizes this as a request to add
8282 the value to a @dfn{set}; the values are accumulated, and are eventually
8283 placed in the executable as a vector in the format described above, with
8284 a leading (ignored) count and a trailing zero element.
8285 @code{TARGET_ASM_DESTRUCTOR} is handled similarly. Since no init
8286 section is available, the absence of @code{INIT_SECTION_ASM_OP} causes
8287 the compilation of @code{main} to call @code{__main} as above, starting
8288 the initialization process.
8290 The last variant uses neither arbitrary sections nor the GNU linker.
8291 This is preferable when you want to do dynamic linking and when using
8292 file formats which the GNU linker does not support, such as `ECOFF'@. In
8293 this case, @code{TARGET_HAVE_CTORS_DTORS} is false, initialization and
8294 termination functions are recognized simply by their names. This requires
8295 an extra program in the linkage step, called @command{collect2}. This program
8296 pretends to be the linker, for use with GCC; it does its job by running
8297 the ordinary linker, but also arranges to include the vectors of
8298 initialization and termination functions. These functions are called
8299 via @code{__main} as described above. In order to use this method,
8300 @code{use_collect2} must be defined in the target in @file{config.gcc}.
8303 The following section describes the specific macros that control and
8304 customize the handling of initialization and termination functions.
8307 @node Macros for Initialization
8308 @subsection Macros Controlling Initialization Routines
8310 Here are the macros that control how the compiler handles initialization
8311 and termination functions:
8313 @defmac INIT_SECTION_ASM_OP
8314 If defined, a C string constant, including spacing, for the assembler
8315 operation to identify the following data as initialization code. If not
8316 defined, GCC will assume such a section does not exist. When you are
8317 using special sections for initialization and termination functions, this
8318 macro also controls how @file{crtstuff.c} and @file{libgcc2.c} arrange to
8319 run the initialization functions.
8322 @defmac HAS_INIT_SECTION
8323 If defined, @code{main} will not call @code{__main} as described above.
8324 This macro should be defined for systems that control start-up code
8325 on a symbol-by-symbol basis, such as OSF/1, and should not
8326 be defined explicitly for systems that support @code{INIT_SECTION_ASM_OP}.
8329 @defmac LD_INIT_SWITCH
8330 If defined, a C string constant for a switch that tells the linker that
8331 the following symbol is an initialization routine.
8334 @defmac LD_FINI_SWITCH
8335 If defined, a C string constant for a switch that tells the linker that
8336 the following symbol is a finalization routine.
8339 @defmac COLLECT_SHARED_INIT_FUNC (@var{stream}, @var{func})
8340 If defined, a C statement that will write a function that can be
8341 automatically called when a shared library is loaded. The function
8342 should call @var{func}, which takes no arguments. If not defined, and
8343 the object format requires an explicit initialization function, then a
8344 function called @code{_GLOBAL__DI} will be generated.
8346 This function and the following one are used by collect2 when linking a
8347 shared library that needs constructors or destructors, or has DWARF2
8348 exception tables embedded in the code.
8351 @defmac COLLECT_SHARED_FINI_FUNC (@var{stream}, @var{func})
8352 If defined, a C statement that will write a function that can be
8353 automatically called when a shared library is unloaded. The function
8354 should call @var{func}, which takes no arguments. If not defined, and
8355 the object format requires an explicit finalization function, then a
8356 function called @code{_GLOBAL__DD} will be generated.
8359 @defmac INVOKE__main
8360 If defined, @code{main} will call @code{__main} despite the presence of
8361 @code{INIT_SECTION_ASM_OP}. This macro should be defined for systems
8362 where the init section is not actually run automatically, but is still
8363 useful for collecting the lists of constructors and destructors.
8366 @defmac SUPPORTS_INIT_PRIORITY
8367 If nonzero, the C++ @code{init_priority} attribute is supported and the
8368 compiler should emit instructions to control the order of initialization
8369 of objects. If zero, the compiler will issue an error message upon
8370 encountering an @code{init_priority} attribute.
8373 @hook TARGET_HAVE_CTORS_DTORS
8374 This value is true if the target supports some ``native'' method of
8375 collecting constructors and destructors to be run at startup and exit.
8376 It is false if we must use @command{collect2}.
8379 @hook TARGET_ASM_CONSTRUCTOR
8380 If defined, a function that outputs assembler code to arrange to call
8381 the function referenced by @var{symbol} at initialization time.
8383 Assume that @var{symbol} is a @code{SYMBOL_REF} for a function taking
8384 no arguments and with no return value. If the target supports initialization
8385 priorities, @var{priority} is a value between 0 and @code{MAX_INIT_PRIORITY};
8386 otherwise it must be @code{DEFAULT_INIT_PRIORITY}.
8388 If this macro is not defined by the target, a suitable default will
8389 be chosen if (1) the target supports arbitrary section names, (2) the
8390 target defines @code{CTORS_SECTION_ASM_OP}, or (3) @code{USE_COLLECT2}
8394 @hook TARGET_ASM_DESTRUCTOR
8395 This is like @code{TARGET_ASM_CONSTRUCTOR} but used for termination
8396 functions rather than initialization functions.
8399 If @code{TARGET_HAVE_CTORS_DTORS} is true, the initialization routine
8400 generated for the generated object file will have static linkage.
8402 If your system uses @command{collect2} as the means of processing
8403 constructors, then that program normally uses @command{nm} to scan
8404 an object file for constructor functions to be called.
8406 On certain kinds of systems, you can define this macro to make
8407 @command{collect2} work faster (and, in some cases, make it work at all):
8409 @defmac OBJECT_FORMAT_COFF
8410 Define this macro if the system uses COFF (Common Object File Format)
8411 object files, so that @command{collect2} can assume this format and scan
8412 object files directly for dynamic constructor/destructor functions.
8414 This macro is effective only in a native compiler; @command{collect2} as
8415 part of a cross compiler always uses @command{nm} for the target machine.
8418 @defmac REAL_NM_FILE_NAME
8419 Define this macro as a C string constant containing the file name to use
8420 to execute @command{nm}. The default is to search the path normally for
8425 @command{collect2} calls @command{nm} to scan object files for static
8426 constructors and destructors and LTO info. By default, @option{-n} is
8427 passed. Define @code{NM_FLAGS} to a C string constant if other options
8428 are needed to get the same output formut as GNU @command{nm -n}
8432 If your system supports shared libraries and has a program to list the
8433 dynamic dependencies of a given library or executable, you can define
8434 these macros to enable support for running initialization and
8435 termination functions in shared libraries:
8438 Define this macro to a C string constant containing the name of the program
8439 which lists dynamic dependencies, like @command{ldd} under SunOS 4.
8442 @defmac PARSE_LDD_OUTPUT (@var{ptr})
8443 Define this macro to be C code that extracts filenames from the output
8444 of the program denoted by @code{LDD_SUFFIX}. @var{ptr} is a variable
8445 of type @code{char *} that points to the beginning of a line of output
8446 from @code{LDD_SUFFIX}. If the line lists a dynamic dependency, the
8447 code must advance @var{ptr} to the beginning of the filename on that
8448 line. Otherwise, it must set @var{ptr} to @code{NULL}.
8451 @defmac SHLIB_SUFFIX
8452 Define this macro to a C string constant containing the default shared
8453 library extension of the target (e.g., @samp{".so"}). @command{collect2}
8454 strips version information after this suffix when generating global
8455 constructor and destructor names. This define is only needed on targets
8456 that use @command{collect2} to process constructors and destructors.
8459 @node Instruction Output
8460 @subsection Output of Assembler Instructions
8462 @c prevent bad page break with this line
8463 This describes assembler instruction output.
8465 @defmac REGISTER_NAMES
8466 A C initializer containing the assembler's names for the machine
8467 registers, each one as a C string constant. This is what translates
8468 register numbers in the compiler into assembler language.
8471 @defmac ADDITIONAL_REGISTER_NAMES
8472 If defined, a C initializer for an array of structures containing a name
8473 and a register number. This macro defines additional names for hard
8474 registers, thus allowing the @code{asm} option in declarations to refer
8475 to registers using alternate names.
8478 @defmac OVERLAPPING_REGISTER_NAMES
8479 If defined, a C initializer for an array of structures containing a
8480 name, a register number and a count of the number of consecutive
8481 machine registers the name overlaps. This macro defines additional
8482 names for hard registers, thus allowing the @code{asm} option in
8483 declarations to refer to registers using alternate names. Unlike
8484 @code{ADDITIONAL_REGISTER_NAMES}, this macro should be used when the
8485 register name implies multiple underlying registers.
8487 This macro should be used when it is important that a clobber in an
8488 @code{asm} statement clobbers all the underlying values implied by the
8489 register name. For example, on ARM, clobbering the double-precision
8490 VFP register ``d0'' implies clobbering both single-precision registers
8494 @defmac ASM_OUTPUT_OPCODE (@var{stream}, @var{ptr})
8495 Define this macro if you are using an unusual assembler that
8496 requires different names for the machine instructions.
8498 The definition is a C statement or statements which output an
8499 assembler instruction opcode to the stdio stream @var{stream}. The
8500 macro-operand @var{ptr} is a variable of type @code{char *} which
8501 points to the opcode name in its ``internal'' form---the form that is
8502 written in the machine description. The definition should output the
8503 opcode name to @var{stream}, performing any translation you desire, and
8504 increment the variable @var{ptr} to point at the end of the opcode
8505 so that it will not be output twice.
8507 In fact, your macro definition may process less than the entire opcode
8508 name, or more than the opcode name; but if you want to process text
8509 that includes @samp{%}-sequences to substitute operands, you must take
8510 care of the substitution yourself. Just be sure to increment
8511 @var{ptr} over whatever text should not be output normally.
8513 @findex recog_data.operand
8514 If you need to look at the operand values, they can be found as the
8515 elements of @code{recog_data.operand}.
8517 If the macro definition does nothing, the instruction is output
8521 @defmac FINAL_PRESCAN_INSN (@var{insn}, @var{opvec}, @var{noperands})
8522 If defined, a C statement to be executed just prior to the output of
8523 assembler code for @var{insn}, to modify the extracted operands so
8524 they will be output differently.
8526 Here the argument @var{opvec} is the vector containing the operands
8527 extracted from @var{insn}, and @var{noperands} is the number of
8528 elements of the vector which contain meaningful data for this insn.
8529 The contents of this vector are what will be used to convert the insn
8530 template into assembler code, so you can change the assembler output
8531 by changing the contents of the vector.
8533 This macro is useful when various assembler syntaxes share a single
8534 file of instruction patterns; by defining this macro differently, you
8535 can cause a large class of instructions to be output differently (such
8536 as with rearranged operands). Naturally, variations in assembler
8537 syntax affecting individual insn patterns ought to be handled by
8538 writing conditional output routines in those patterns.
8540 If this macro is not defined, it is equivalent to a null statement.
8543 @hook TARGET_ASM_FINAL_POSTSCAN_INSN
8544 If defined, this target hook is a function which is executed just after the
8545 output of assembler code for @var{insn}, to change the mode of the assembler
8548 Here the argument @var{opvec} is the vector containing the operands
8549 extracted from @var{insn}, and @var{noperands} is the number of
8550 elements of the vector which contain meaningful data for this insn.
8551 The contents of this vector are what was used to convert the insn
8552 template into assembler code, so you can change the assembler mode
8553 by checking the contents of the vector.
8556 @defmac PRINT_OPERAND (@var{stream}, @var{x}, @var{code})
8557 A C compound statement to output to stdio stream @var{stream} the
8558 assembler syntax for an instruction operand @var{x}. @var{x} is an
8561 @var{code} is a value that can be used to specify one of several ways
8562 of printing the operand. It is used when identical operands must be
8563 printed differently depending on the context. @var{code} comes from
8564 the @samp{%} specification that was used to request printing of the
8565 operand. If the specification was just @samp{%@var{digit}} then
8566 @var{code} is 0; if the specification was @samp{%@var{ltr}
8567 @var{digit}} then @var{code} is the ASCII code for @var{ltr}.
8570 If @var{x} is a register, this macro should print the register's name.
8571 The names can be found in an array @code{reg_names} whose type is
8572 @code{char *[]}. @code{reg_names} is initialized from
8573 @code{REGISTER_NAMES}.
8575 When the machine description has a specification @samp{%@var{punct}}
8576 (a @samp{%} followed by a punctuation character), this macro is called
8577 with a null pointer for @var{x} and the punctuation character for
8581 @defmac PRINT_OPERAND_PUNCT_VALID_P (@var{code})
8582 A C expression which evaluates to true if @var{code} is a valid
8583 punctuation character for use in the @code{PRINT_OPERAND} macro. If
8584 @code{PRINT_OPERAND_PUNCT_VALID_P} is not defined, it means that no
8585 punctuation characters (except for the standard one, @samp{%}) are used
8589 @defmac PRINT_OPERAND_ADDRESS (@var{stream}, @var{x})
8590 A C compound statement to output to stdio stream @var{stream} the
8591 assembler syntax for an instruction operand that is a memory reference
8592 whose address is @var{x}. @var{x} is an RTL expression.
8594 @cindex @code{TARGET_ENCODE_SECTION_INFO} usage
8595 On some machines, the syntax for a symbolic address depends on the
8596 section that the address refers to. On these machines, define the hook
8597 @code{TARGET_ENCODE_SECTION_INFO} to store the information into the
8598 @code{symbol_ref}, and then check for it here. @xref{Assembler
8602 @findex dbr_sequence_length
8603 @defmac DBR_OUTPUT_SEQEND (@var{file})
8604 A C statement, to be executed after all slot-filler instructions have
8605 been output. If necessary, call @code{dbr_sequence_length} to
8606 determine the number of slots filled in a sequence (zero if not
8607 currently outputting a sequence), to decide how many no-ops to output,
8610 Don't define this macro if it has nothing to do, but it is helpful in
8611 reading assembly output if the extent of the delay sequence is made
8612 explicit (e.g.@: with white space).
8615 @findex final_sequence
8616 Note that output routines for instructions with delay slots must be
8617 prepared to deal with not being output as part of a sequence
8618 (i.e.@: when the scheduling pass is not run, or when no slot fillers could be
8619 found.) The variable @code{final_sequence} is null when not
8620 processing a sequence, otherwise it contains the @code{sequence} rtx
8624 @defmac REGISTER_PREFIX
8625 @defmacx LOCAL_LABEL_PREFIX
8626 @defmacx USER_LABEL_PREFIX
8627 @defmacx IMMEDIATE_PREFIX
8628 If defined, C string expressions to be used for the @samp{%R}, @samp{%L},
8629 @samp{%U}, and @samp{%I} options of @code{asm_fprintf} (see
8630 @file{final.c}). These are useful when a single @file{md} file must
8631 support multiple assembler formats. In that case, the various @file{tm.h}
8632 files can define these macros differently.
8635 @defmac ASM_FPRINTF_EXTENSIONS (@var{file}, @var{argptr}, @var{format})
8636 If defined this macro should expand to a series of @code{case}
8637 statements which will be parsed inside the @code{switch} statement of
8638 the @code{asm_fprintf} function. This allows targets to define extra
8639 printf formats which may useful when generating their assembler
8640 statements. Note that uppercase letters are reserved for future
8641 generic extensions to asm_fprintf, and so are not available to target
8642 specific code. The output file is given by the parameter @var{file}.
8643 The varargs input pointer is @var{argptr} and the rest of the format
8644 string, starting the character after the one that is being switched
8645 upon, is pointed to by @var{format}.
8648 @defmac ASSEMBLER_DIALECT
8649 If your target supports multiple dialects of assembler language (such as
8650 different opcodes), define this macro as a C expression that gives the
8651 numeric index of the assembler language dialect to use, with zero as the
8654 If this macro is defined, you may use constructs of the form
8656 @samp{@{option0|option1|option2@dots{}@}}
8659 in the output templates of patterns (@pxref{Output Template}) or in the
8660 first argument of @code{asm_fprintf}. This construct outputs
8661 @samp{option0}, @samp{option1}, @samp{option2}, etc., if the value of
8662 @code{ASSEMBLER_DIALECT} is zero, one, two, etc. Any special characters
8663 within these strings retain their usual meaning. If there are fewer
8664 alternatives within the braces than the value of
8665 @code{ASSEMBLER_DIALECT}, the construct outputs nothing.
8667 If you do not define this macro, the characters @samp{@{}, @samp{|} and
8668 @samp{@}} do not have any special meaning when used in templates or
8669 operands to @code{asm_fprintf}.
8671 Define the macros @code{REGISTER_PREFIX}, @code{LOCAL_LABEL_PREFIX},
8672 @code{USER_LABEL_PREFIX} and @code{IMMEDIATE_PREFIX} if you can express
8673 the variations in assembler language syntax with that mechanism. Define
8674 @code{ASSEMBLER_DIALECT} and use the @samp{@{option0|option1@}} syntax
8675 if the syntax variant are larger and involve such things as different
8676 opcodes or operand order.
8679 @defmac ASM_OUTPUT_REG_PUSH (@var{stream}, @var{regno})
8680 A C expression to output to @var{stream} some assembler code
8681 which will push hard register number @var{regno} onto the stack.
8682 The code need not be optimal, since this macro is used only when
8686 @defmac ASM_OUTPUT_REG_POP (@var{stream}, @var{regno})
8687 A C expression to output to @var{stream} some assembler code
8688 which will pop hard register number @var{regno} off of the stack.
8689 The code need not be optimal, since this macro is used only when
8693 @node Dispatch Tables
8694 @subsection Output of Dispatch Tables
8696 @c prevent bad page break with this line
8697 This concerns dispatch tables.
8699 @cindex dispatch table
8700 @defmac ASM_OUTPUT_ADDR_DIFF_ELT (@var{stream}, @var{body}, @var{value}, @var{rel})
8701 A C statement to output to the stdio stream @var{stream} an assembler
8702 pseudo-instruction to generate a difference between two labels.
8703 @var{value} and @var{rel} are the numbers of two internal labels. The
8704 definitions of these labels are output using
8705 @code{(*targetm.asm_out.internal_label)}, and they must be printed in the same
8706 way here. For example,
8709 fprintf (@var{stream}, "\t.word L%d-L%d\n",
8710 @var{value}, @var{rel})
8713 You must provide this macro on machines where the addresses in a
8714 dispatch table are relative to the table's own address. If defined, GCC
8715 will also use this macro on all machines when producing PIC@.
8716 @var{body} is the body of the @code{ADDR_DIFF_VEC}; it is provided so that the
8717 mode and flags can be read.
8720 @defmac ASM_OUTPUT_ADDR_VEC_ELT (@var{stream}, @var{value})
8721 This macro should be provided on machines where the addresses
8722 in a dispatch table are absolute.
8724 The definition should be a C statement to output to the stdio stream
8725 @var{stream} an assembler pseudo-instruction to generate a reference to
8726 a label. @var{value} is the number of an internal label whose
8727 definition is output using @code{(*targetm.asm_out.internal_label)}.
8731 fprintf (@var{stream}, "\t.word L%d\n", @var{value})
8735 @defmac ASM_OUTPUT_CASE_LABEL (@var{stream}, @var{prefix}, @var{num}, @var{table})
8736 Define this if the label before a jump-table needs to be output
8737 specially. The first three arguments are the same as for
8738 @code{(*targetm.asm_out.internal_label)}; the fourth argument is the
8739 jump-table which follows (a @code{jump_insn} containing an
8740 @code{addr_vec} or @code{addr_diff_vec}).
8742 This feature is used on system V to output a @code{swbeg} statement
8745 If this macro is not defined, these labels are output with
8746 @code{(*targetm.asm_out.internal_label)}.
8749 @defmac ASM_OUTPUT_CASE_END (@var{stream}, @var{num}, @var{table})
8750 Define this if something special must be output at the end of a
8751 jump-table. The definition should be a C statement to be executed
8752 after the assembler code for the table is written. It should write
8753 the appropriate code to stdio stream @var{stream}. The argument
8754 @var{table} is the jump-table insn, and @var{num} is the label-number
8755 of the preceding label.
8757 If this macro is not defined, nothing special is output at the end of
8761 @hook TARGET_ASM_EMIT_UNWIND_LABEL
8762 This target hook emits a label at the beginning of each FDE@. It
8763 should be defined on targets where FDEs need special labels, and it
8764 should write the appropriate label, for the FDE associated with the
8765 function declaration @var{decl}, to the stdio stream @var{stream}.
8766 The third argument, @var{for_eh}, is a boolean: true if this is for an
8767 exception table. The fourth argument, @var{empty}, is a boolean:
8768 true if this is a placeholder label for an omitted FDE@.
8770 The default is that FDEs are not given nonlocal labels.
8773 @hook TARGET_ASM_EMIT_EXCEPT_TABLE_LABEL
8774 This target hook emits a label at the beginning of the exception table.
8775 It should be defined on targets where it is desirable for the table
8776 to be broken up according to function.
8778 The default is that no label is emitted.
8781 @hook TARGET_ASM_EMIT_EXCEPT_PERSONALITY
8783 @hook TARGET_ASM_UNWIND_EMIT
8784 This target hook emits assembly directives required to unwind the
8785 given instruction. This is only used when @code{TARGET_EXCEPT_UNWIND_INFO}
8786 returns @code{UI_TARGET}.
8789 @hook TARGET_ASM_UNWIND_EMIT_BEFORE_INSN
8791 @node Exception Region Output
8792 @subsection Assembler Commands for Exception Regions
8794 @c prevent bad page break with this line
8796 This describes commands marking the start and the end of an exception
8799 @defmac EH_FRAME_SECTION_NAME
8800 If defined, a C string constant for the name of the section containing
8801 exception handling frame unwind information. If not defined, GCC will
8802 provide a default definition if the target supports named sections.
8803 @file{crtstuff.c} uses this macro to switch to the appropriate section.
8805 You should define this symbol if your target supports DWARF 2 frame
8806 unwind information and the default definition does not work.
8809 @defmac EH_FRAME_IN_DATA_SECTION
8810 If defined, DWARF 2 frame unwind information will be placed in the
8811 data section even though the target supports named sections. This
8812 might be necessary, for instance, if the system linker does garbage
8813 collection and sections cannot be marked as not to be collected.
8815 Do not define this macro unless @code{TARGET_ASM_NAMED_SECTION} is
8819 @defmac EH_TABLES_CAN_BE_READ_ONLY
8820 Define this macro to 1 if your target is such that no frame unwind
8821 information encoding used with non-PIC code will ever require a
8822 runtime relocation, but the linker may not support merging read-only
8823 and read-write sections into a single read-write section.
8826 @defmac MASK_RETURN_ADDR
8827 An rtx used to mask the return address found via @code{RETURN_ADDR_RTX}, so
8828 that it does not contain any extraneous set bits in it.
8831 @defmac DWARF2_UNWIND_INFO
8832 Define this macro to 0 if your target supports DWARF 2 frame unwind
8833 information, but it does not yet work with exception handling.
8834 Otherwise, if your target supports this information (if it defines
8835 @code{INCOMING_RETURN_ADDR_RTX} and either @code{UNALIGNED_INT_ASM_OP}
8836 or @code{OBJECT_FORMAT_ELF}), GCC will provide a default definition of 1.
8839 @hook TARGET_EXCEPT_UNWIND_INFO
8840 This hook defines the mechanism that will be used for exception handling
8841 by the target. If the target has ABI specified unwind tables, the hook
8842 should return @code{UI_TARGET}. If the target is to use the
8843 @code{setjmp}/@code{longjmp}-based exception handling scheme, the hook
8844 should return @code{UI_SJLJ}. If the target supports DWARF 2 frame unwind
8845 information, the hook should return @code{UI_DWARF2}.
8847 A target may, if exceptions are disabled, choose to return @code{UI_NONE}.
8848 This may end up simplifying other parts of target-specific code. The
8849 default implementation of this hook never returns @code{UI_NONE}.
8851 Note that the value returned by this hook should be constant. It should
8852 not depend on anything except the command-line switches described by
8853 @var{opts}. In particular, the
8854 setting @code{UI_SJLJ} must be fixed at compiler start-up as C pre-processor
8855 macros and builtin functions related to exception handling are set up
8856 depending on this setting.
8858 The default implementation of the hook first honors the
8859 @option{--enable-sjlj-exceptions} configure option, then
8860 @code{DWARF2_UNWIND_INFO}, and finally defaults to @code{UI_SJLJ}. If
8861 @code{DWARF2_UNWIND_INFO} depends on command-line options, the target
8862 must define this hook so that @var{opts} is used correctly.
8865 @hook TARGET_UNWIND_TABLES_DEFAULT
8866 This variable should be set to @code{true} if the target ABI requires unwinding
8867 tables even when exceptions are not used. It must not be modified by
8868 command-line option processing.
8871 @defmac DONT_USE_BUILTIN_SETJMP
8872 Define this macro to 1 if the @code{setjmp}/@code{longjmp}-based scheme
8873 should use the @code{setjmp}/@code{longjmp} functions from the C library
8874 instead of the @code{__builtin_setjmp}/@code{__builtin_longjmp} machinery.
8877 @defmac DWARF_CIE_DATA_ALIGNMENT
8878 This macro need only be defined if the target might save registers in the
8879 function prologue at an offset to the stack pointer that is not aligned to
8880 @code{UNITS_PER_WORD}. The definition should be the negative minimum
8881 alignment if @code{STACK_GROWS_DOWNWARD} is defined, and the positive
8882 minimum alignment otherwise. @xref{SDB and DWARF}. Only applicable if
8883 the target supports DWARF 2 frame unwind information.
8886 @hook TARGET_TERMINATE_DW2_EH_FRAME_INFO
8887 Contains the value true if the target should add a zero word onto the
8888 end of a Dwarf-2 frame info section when used for exception handling.
8889 Default value is false if @code{EH_FRAME_SECTION_NAME} is defined, and
8893 @hook TARGET_DWARF_REGISTER_SPAN
8894 Given a register, this hook should return a parallel of registers to
8895 represent where to find the register pieces. Define this hook if the
8896 register and its mode are represented in Dwarf in non-contiguous
8897 locations, or if the register should be represented in more than one
8898 register in Dwarf. Otherwise, this hook should return @code{NULL_RTX}.
8899 If not defined, the default is to return @code{NULL_RTX}.
8902 @hook TARGET_INIT_DWARF_REG_SIZES_EXTRA
8903 If some registers are represented in Dwarf-2 unwind information in
8904 multiple pieces, define this hook to fill in information about the
8905 sizes of those pieces in the table used by the unwinder at runtime.
8906 It will be called by @code{expand_builtin_init_dwarf_reg_sizes} after
8907 filling in a single size corresponding to each hard register;
8908 @var{address} is the address of the table.
8911 @hook TARGET_ASM_TTYPE
8912 This hook is used to output a reference from a frame unwinding table to
8913 the type_info object identified by @var{sym}. It should return @code{true}
8914 if the reference was output. Returning @code{false} will cause the
8915 reference to be output using the normal Dwarf2 routines.
8918 @hook TARGET_ARM_EABI_UNWINDER
8919 This flag should be set to @code{true} on targets that use an ARM EABI
8920 based unwinding library, and @code{false} on other targets. This effects
8921 the format of unwinding tables, and how the unwinder in entered after
8922 running a cleanup. The default is @code{false}.
8925 @node Alignment Output
8926 @subsection Assembler Commands for Alignment
8928 @c prevent bad page break with this line
8929 This describes commands for alignment.
8931 @defmac JUMP_ALIGN (@var{label})
8932 The alignment (log base 2) to put in front of @var{label}, which is
8933 a common destination of jumps and has no fallthru incoming edge.
8935 This macro need not be defined if you don't want any special alignment
8936 to be done at such a time. Most machine descriptions do not currently
8939 Unless it's necessary to inspect the @var{label} parameter, it is better
8940 to set the variable @var{align_jumps} in the target's
8941 @code{TARGET_OPTION_OVERRIDE}. Otherwise, you should try to honor the user's
8942 selection in @var{align_jumps} in a @code{JUMP_ALIGN} implementation.
8945 @hook TARGET_ASM_JUMP_ALIGN_MAX_SKIP
8946 The maximum number of bytes to skip before @var{label} when applying
8947 @code{JUMP_ALIGN}. This works only if
8948 @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined.
8951 @defmac LABEL_ALIGN_AFTER_BARRIER (@var{label})
8952 The alignment (log base 2) to put in front of @var{label}, which follows
8955 This macro need not be defined if you don't want any special alignment
8956 to be done at such a time. Most machine descriptions do not currently
8960 @hook TARGET_ASM_LABEL_ALIGN_AFTER_BARRIER_MAX_SKIP
8961 The maximum number of bytes to skip before @var{label} when applying
8962 @code{LABEL_ALIGN_AFTER_BARRIER}. This works only if
8963 @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined.
8966 @defmac LOOP_ALIGN (@var{label})
8967 The alignment (log base 2) to put in front of @var{label}, which follows
8968 a @code{NOTE_INSN_LOOP_BEG} note.
8970 This macro need not be defined if you don't want any special alignment
8971 to be done at such a time. Most machine descriptions do not currently
8974 Unless it's necessary to inspect the @var{label} parameter, it is better
8975 to set the variable @code{align_loops} in the target's
8976 @code{TARGET_OPTION_OVERRIDE}. Otherwise, you should try to honor the user's
8977 selection in @code{align_loops} in a @code{LOOP_ALIGN} implementation.
8980 @hook TARGET_ASM_LOOP_ALIGN_MAX_SKIP
8981 The maximum number of bytes to skip when applying @code{LOOP_ALIGN} to
8982 @var{label}. This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is
8986 @defmac LABEL_ALIGN (@var{label})
8987 The alignment (log base 2) to put in front of @var{label}.
8988 If @code{LABEL_ALIGN_AFTER_BARRIER} / @code{LOOP_ALIGN} specify a different alignment,
8989 the maximum of the specified values is used.
8991 Unless it's necessary to inspect the @var{label} parameter, it is better
8992 to set the variable @code{align_labels} in the target's
8993 @code{TARGET_OPTION_OVERRIDE}. Otherwise, you should try to honor the user's
8994 selection in @code{align_labels} in a @code{LABEL_ALIGN} implementation.
8997 @hook TARGET_ASM_LABEL_ALIGN_MAX_SKIP
8998 The maximum number of bytes to skip when applying @code{LABEL_ALIGN}
8999 to @var{label}. This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN}
9003 @defmac ASM_OUTPUT_SKIP (@var{stream}, @var{nbytes})
9004 A C statement to output to the stdio stream @var{stream} an assembler
9005 instruction to advance the location counter by @var{nbytes} bytes.
9006 Those bytes should be zero when loaded. @var{nbytes} will be a C
9007 expression of type @code{unsigned HOST_WIDE_INT}.
9010 @defmac ASM_NO_SKIP_IN_TEXT
9011 Define this macro if @code{ASM_OUTPUT_SKIP} should not be used in the
9012 text section because it fails to put zeros in the bytes that are skipped.
9013 This is true on many Unix systems, where the pseudo--op to skip bytes
9014 produces no-op instructions rather than zeros when used in the text
9018 @defmac ASM_OUTPUT_ALIGN (@var{stream}, @var{power})
9019 A C statement to output to the stdio stream @var{stream} an assembler
9020 command to advance the location counter to a multiple of 2 to the
9021 @var{power} bytes. @var{power} will be a C expression of type @code{int}.
9024 @defmac ASM_OUTPUT_ALIGN_WITH_NOP (@var{stream}, @var{power})
9025 Like @code{ASM_OUTPUT_ALIGN}, except that the ``nop'' instruction is used
9026 for padding, if necessary.
9029 @defmac ASM_OUTPUT_MAX_SKIP_ALIGN (@var{stream}, @var{power}, @var{max_skip})
9030 A C statement to output to the stdio stream @var{stream} an assembler
9031 command to advance the location counter to a multiple of 2 to the
9032 @var{power} bytes, but only if @var{max_skip} or fewer bytes are needed to
9033 satisfy the alignment request. @var{power} and @var{max_skip} will be
9034 a C expression of type @code{int}.
9038 @node Debugging Info
9039 @section Controlling Debugging Information Format
9041 @c prevent bad page break with this line
9042 This describes how to specify debugging information.
9045 * All Debuggers:: Macros that affect all debugging formats uniformly.
9046 * DBX Options:: Macros enabling specific options in DBX format.
9047 * DBX Hooks:: Hook macros for varying DBX format.
9048 * File Names and DBX:: Macros controlling output of file names in DBX format.
9049 * SDB and DWARF:: Macros for SDB (COFF) and DWARF formats.
9050 * VMS Debug:: Macros for VMS debug format.
9054 @subsection Macros Affecting All Debugging Formats
9056 @c prevent bad page break with this line
9057 These macros affect all debugging formats.
9059 @defmac DBX_REGISTER_NUMBER (@var{regno})
9060 A C expression that returns the DBX register number for the compiler
9061 register number @var{regno}. In the default macro provided, the value
9062 of this expression will be @var{regno} itself. But sometimes there are
9063 some registers that the compiler knows about and DBX does not, or vice
9064 versa. In such cases, some register may need to have one number in the
9065 compiler and another for DBX@.
9067 If two registers have consecutive numbers inside GCC, and they can be
9068 used as a pair to hold a multiword value, then they @emph{must} have
9069 consecutive numbers after renumbering with @code{DBX_REGISTER_NUMBER}.
9070 Otherwise, debuggers will be unable to access such a pair, because they
9071 expect register pairs to be consecutive in their own numbering scheme.
9073 If you find yourself defining @code{DBX_REGISTER_NUMBER} in way that
9074 does not preserve register pairs, then what you must do instead is
9075 redefine the actual register numbering scheme.
9078 @defmac DEBUGGER_AUTO_OFFSET (@var{x})
9079 A C expression that returns the integer offset value for an automatic
9080 variable having address @var{x} (an RTL expression). The default
9081 computation assumes that @var{x} is based on the frame-pointer and
9082 gives the offset from the frame-pointer. This is required for targets
9083 that produce debugging output for DBX or COFF-style debugging output
9084 for SDB and allow the frame-pointer to be eliminated when the
9085 @option{-g} options is used.
9088 @defmac DEBUGGER_ARG_OFFSET (@var{offset}, @var{x})
9089 A C expression that returns the integer offset value for an argument
9090 having address @var{x} (an RTL expression). The nominal offset is
9094 @defmac PREFERRED_DEBUGGING_TYPE
9095 A C expression that returns the type of debugging output GCC should
9096 produce when the user specifies just @option{-g}. Define
9097 this if you have arranged for GCC to support more than one format of
9098 debugging output. Currently, the allowable values are @code{DBX_DEBUG},
9099 @code{SDB_DEBUG}, @code{DWARF_DEBUG}, @code{DWARF2_DEBUG},
9100 @code{XCOFF_DEBUG}, @code{VMS_DEBUG}, and @code{VMS_AND_DWARF2_DEBUG}.
9102 When the user specifies @option{-ggdb}, GCC normally also uses the
9103 value of this macro to select the debugging output format, but with two
9104 exceptions. If @code{DWARF2_DEBUGGING_INFO} is defined, GCC uses the
9105 value @code{DWARF2_DEBUG}. Otherwise, if @code{DBX_DEBUGGING_INFO} is
9106 defined, GCC uses @code{DBX_DEBUG}.
9108 The value of this macro only affects the default debugging output; the
9109 user can always get a specific type of output by using @option{-gstabs},
9110 @option{-gcoff}, @option{-gdwarf-2}, @option{-gxcoff}, or @option{-gvms}.
9114 @subsection Specific Options for DBX Output
9116 @c prevent bad page break with this line
9117 These are specific options for DBX output.
9119 @defmac DBX_DEBUGGING_INFO
9120 Define this macro if GCC should produce debugging output for DBX
9121 in response to the @option{-g} option.
9124 @defmac XCOFF_DEBUGGING_INFO
9125 Define this macro if GCC should produce XCOFF format debugging output
9126 in response to the @option{-g} option. This is a variant of DBX format.
9129 @defmac DEFAULT_GDB_EXTENSIONS
9130 Define this macro to control whether GCC should by default generate
9131 GDB's extended version of DBX debugging information (assuming DBX-format
9132 debugging information is enabled at all). If you don't define the
9133 macro, the default is 1: always generate the extended information
9134 if there is any occasion to.
9137 @defmac DEBUG_SYMS_TEXT
9138 Define this macro if all @code{.stabs} commands should be output while
9139 in the text section.
9142 @defmac ASM_STABS_OP
9143 A C string constant, including spacing, naming the assembler pseudo op to
9144 use instead of @code{"\t.stabs\t"} to define an ordinary debugging symbol.
9145 If you don't define this macro, @code{"\t.stabs\t"} is used. This macro
9146 applies only to DBX debugging information format.
9149 @defmac ASM_STABD_OP
9150 A C string constant, including spacing, naming the assembler pseudo op to
9151 use instead of @code{"\t.stabd\t"} to define a debugging symbol whose
9152 value is the current location. If you don't define this macro,
9153 @code{"\t.stabd\t"} is used. This macro applies only to DBX debugging
9157 @defmac ASM_STABN_OP
9158 A C string constant, including spacing, naming the assembler pseudo op to
9159 use instead of @code{"\t.stabn\t"} to define a debugging symbol with no
9160 name. If you don't define this macro, @code{"\t.stabn\t"} is used. This
9161 macro applies only to DBX debugging information format.
9164 @defmac DBX_NO_XREFS
9165 Define this macro if DBX on your system does not support the construct
9166 @samp{xs@var{tagname}}. On some systems, this construct is used to
9167 describe a forward reference to a structure named @var{tagname}.
9168 On other systems, this construct is not supported at all.
9171 @defmac DBX_CONTIN_LENGTH
9172 A symbol name in DBX-format debugging information is normally
9173 continued (split into two separate @code{.stabs} directives) when it
9174 exceeds a certain length (by default, 80 characters). On some
9175 operating systems, DBX requires this splitting; on others, splitting
9176 must not be done. You can inhibit splitting by defining this macro
9177 with the value zero. You can override the default splitting-length by
9178 defining this macro as an expression for the length you desire.
9181 @defmac DBX_CONTIN_CHAR
9182 Normally continuation is indicated by adding a @samp{\} character to
9183 the end of a @code{.stabs} string when a continuation follows. To use
9184 a different character instead, define this macro as a character
9185 constant for the character you want to use. Do not define this macro
9186 if backslash is correct for your system.
9189 @defmac DBX_STATIC_STAB_DATA_SECTION
9190 Define this macro if it is necessary to go to the data section before
9191 outputting the @samp{.stabs} pseudo-op for a non-global static
9195 @defmac DBX_TYPE_DECL_STABS_CODE
9196 The value to use in the ``code'' field of the @code{.stabs} directive
9197 for a typedef. The default is @code{N_LSYM}.
9200 @defmac DBX_STATIC_CONST_VAR_CODE
9201 The value to use in the ``code'' field of the @code{.stabs} directive
9202 for a static variable located in the text section. DBX format does not
9203 provide any ``right'' way to do this. The default is @code{N_FUN}.
9206 @defmac DBX_REGPARM_STABS_CODE
9207 The value to use in the ``code'' field of the @code{.stabs} directive
9208 for a parameter passed in registers. DBX format does not provide any
9209 ``right'' way to do this. The default is @code{N_RSYM}.
9212 @defmac DBX_REGPARM_STABS_LETTER
9213 The letter to use in DBX symbol data to identify a symbol as a parameter
9214 passed in registers. DBX format does not customarily provide any way to
9215 do this. The default is @code{'P'}.
9218 @defmac DBX_FUNCTION_FIRST
9219 Define this macro if the DBX information for a function and its
9220 arguments should precede the assembler code for the function. Normally,
9221 in DBX format, the debugging information entirely follows the assembler
9225 @defmac DBX_BLOCKS_FUNCTION_RELATIVE
9226 Define this macro, with value 1, if the value of a symbol describing
9227 the scope of a block (@code{N_LBRAC} or @code{N_RBRAC}) should be
9228 relative to the start of the enclosing function. Normally, GCC uses
9229 an absolute address.
9232 @defmac DBX_LINES_FUNCTION_RELATIVE
9233 Define this macro, with value 1, if the value of a symbol indicating
9234 the current line number (@code{N_SLINE}) should be relative to the
9235 start of the enclosing function. Normally, GCC uses an absolute address.
9238 @defmac DBX_USE_BINCL
9239 Define this macro if GCC should generate @code{N_BINCL} and
9240 @code{N_EINCL} stabs for included header files, as on Sun systems. This
9241 macro also directs GCC to output a type number as a pair of a file
9242 number and a type number within the file. Normally, GCC does not
9243 generate @code{N_BINCL} or @code{N_EINCL} stabs, and it outputs a single
9244 number for a type number.
9248 @subsection Open-Ended Hooks for DBX Format
9250 @c prevent bad page break with this line
9251 These are hooks for DBX format.
9253 @defmac DBX_OUTPUT_LBRAC (@var{stream}, @var{name})
9254 Define this macro to say how to output to @var{stream} the debugging
9255 information for the start of a scope level for variable names. The
9256 argument @var{name} is the name of an assembler symbol (for use with
9257 @code{assemble_name}) whose value is the address where the scope begins.
9260 @defmac DBX_OUTPUT_RBRAC (@var{stream}, @var{name})
9261 Like @code{DBX_OUTPUT_LBRAC}, but for the end of a scope level.
9264 @defmac DBX_OUTPUT_NFUN (@var{stream}, @var{lscope_label}, @var{decl})
9265 Define this macro if the target machine requires special handling to
9266 output an @code{N_FUN} entry for the function @var{decl}.
9269 @defmac DBX_OUTPUT_SOURCE_LINE (@var{stream}, @var{line}, @var{counter})
9270 A C statement to output DBX debugging information before code for line
9271 number @var{line} of the current source file to the stdio stream
9272 @var{stream}. @var{counter} is the number of time the macro was
9273 invoked, including the current invocation; it is intended to generate
9274 unique labels in the assembly output.
9276 This macro should not be defined if the default output is correct, or
9277 if it can be made correct by defining @code{DBX_LINES_FUNCTION_RELATIVE}.
9280 @defmac NO_DBX_FUNCTION_END
9281 Some stabs encapsulation formats (in particular ECOFF), cannot handle the
9282 @code{.stabs "",N_FUN,,0,0,Lscope-function-1} gdb dbx extension construct.
9283 On those machines, define this macro to turn this feature off without
9284 disturbing the rest of the gdb extensions.
9287 @defmac NO_DBX_BNSYM_ENSYM
9288 Some assemblers cannot handle the @code{.stabd BNSYM/ENSYM,0,0} gdb dbx
9289 extension construct. On those machines, define this macro to turn this
9290 feature off without disturbing the rest of the gdb extensions.
9293 @node File Names and DBX
9294 @subsection File Names in DBX Format
9296 @c prevent bad page break with this line
9297 This describes file names in DBX format.
9299 @defmac DBX_OUTPUT_MAIN_SOURCE_FILENAME (@var{stream}, @var{name})
9300 A C statement to output DBX debugging information to the stdio stream
9301 @var{stream}, which indicates that file @var{name} is the main source
9302 file---the file specified as the input file for compilation.
9303 This macro is called only once, at the beginning of compilation.
9305 This macro need not be defined if the standard form of output
9306 for DBX debugging information is appropriate.
9308 It may be necessary to refer to a label equal to the beginning of the
9309 text section. You can use @samp{assemble_name (stream, ltext_label_name)}
9310 to do so. If you do this, you must also set the variable
9311 @var{used_ltext_label_name} to @code{true}.
9314 @defmac NO_DBX_MAIN_SOURCE_DIRECTORY
9315 Define this macro, with value 1, if GCC should not emit an indication
9316 of the current directory for compilation and current source language at
9317 the beginning of the file.
9320 @defmac NO_DBX_GCC_MARKER
9321 Define this macro, with value 1, if GCC should not emit an indication
9322 that this object file was compiled by GCC@. The default is to emit
9323 an @code{N_OPT} stab at the beginning of every source file, with
9324 @samp{gcc2_compiled.} for the string and value 0.
9327 @defmac DBX_OUTPUT_MAIN_SOURCE_FILE_END (@var{stream}, @var{name})
9328 A C statement to output DBX debugging information at the end of
9329 compilation of the main source file @var{name}. Output should be
9330 written to the stdio stream @var{stream}.
9332 If you don't define this macro, nothing special is output at the end
9333 of compilation, which is correct for most machines.
9336 @defmac DBX_OUTPUT_NULL_N_SO_AT_MAIN_SOURCE_FILE_END
9337 Define this macro @emph{instead of} defining
9338 @code{DBX_OUTPUT_MAIN_SOURCE_FILE_END}, if what needs to be output at
9339 the end of compilation is an @code{N_SO} stab with an empty string,
9340 whose value is the highest absolute text address in the file.
9345 @subsection Macros for SDB and DWARF Output
9347 @c prevent bad page break with this line
9348 Here are macros for SDB and DWARF output.
9350 @defmac SDB_DEBUGGING_INFO
9351 Define this macro if GCC should produce COFF-style debugging output
9352 for SDB in response to the @option{-g} option.
9355 @defmac DWARF2_DEBUGGING_INFO
9356 Define this macro if GCC should produce dwarf version 2 format
9357 debugging output in response to the @option{-g} option.
9359 @hook TARGET_DWARF_CALLING_CONVENTION
9360 Define this to enable the dwarf attribute @code{DW_AT_calling_convention} to
9361 be emitted for each function. Instead of an integer return the enum
9362 value for the @code{DW_CC_} tag.
9365 To support optional call frame debugging information, you must also
9366 define @code{INCOMING_RETURN_ADDR_RTX} and either set
9367 @code{RTX_FRAME_RELATED_P} on the prologue insns if you use RTL for the
9368 prologue, or call @code{dwarf2out_def_cfa} and @code{dwarf2out_reg_save}
9369 as appropriate from @code{TARGET_ASM_FUNCTION_PROLOGUE} if you don't.
9372 @defmac DWARF2_FRAME_INFO
9373 Define this macro to a nonzero value if GCC should always output
9374 Dwarf 2 frame information. If @code{TARGET_EXCEPT_UNWIND_INFO}
9375 (@pxref{Exception Region Output}) returns @code{UI_DWARF2}, and
9376 exceptions are enabled, GCC will output this information not matter
9377 how you define @code{DWARF2_FRAME_INFO}.
9380 @hook TARGET_DEBUG_UNWIND_INFO
9381 This hook defines the mechanism that will be used for describing frame
9382 unwind information to the debugger. Normally the hook will return
9383 @code{UI_DWARF2} if DWARF 2 debug information is enabled, and
9384 return @code{UI_NONE} otherwise.
9386 A target may return @code{UI_DWARF2} even when DWARF 2 debug information
9387 is disabled in order to always output DWARF 2 frame information.
9389 A target may return @code{UI_TARGET} if it has ABI specified unwind tables.
9390 This will suppress generation of the normal debug frame unwind information.
9393 @defmac DWARF2_ASM_LINE_DEBUG_INFO
9394 Define this macro to be a nonzero value if the assembler can generate Dwarf 2
9395 line debug info sections. This will result in much more compact line number
9396 tables, and hence is desirable if it works.
9399 @hook TARGET_WANT_DEBUG_PUB_SECTIONS
9401 @defmac ASM_OUTPUT_DWARF_DELTA (@var{stream}, @var{size}, @var{label1}, @var{label2})
9402 A C statement to issue assembly directives that create a difference
9403 @var{lab1} minus @var{lab2}, using an integer of the given @var{size}.
9406 @defmac ASM_OUTPUT_DWARF_VMS_DELTA (@var{stream}, @var{size}, @var{label1}, @var{label2})
9407 A C statement to issue assembly directives that create a difference
9408 between the two given labels in system defined units, e.g. instruction
9409 slots on IA64 VMS, using an integer of the given size.
9412 @defmac ASM_OUTPUT_DWARF_OFFSET (@var{stream}, @var{size}, @var{label}, @var{section})
9413 A C statement to issue assembly directives that create a
9414 section-relative reference to the given @var{label}, using an integer of the
9415 given @var{size}. The label is known to be defined in the given @var{section}.
9418 @defmac ASM_OUTPUT_DWARF_PCREL (@var{stream}, @var{size}, @var{label})
9419 A C statement to issue assembly directives that create a self-relative
9420 reference to the given @var{label}, using an integer of the given @var{size}.
9423 @defmac ASM_OUTPUT_DWARF_TABLE_REF (@var{label})
9424 A C statement to issue assembly directives that create a reference to
9425 the DWARF table identifier @var{label} from the current section. This
9426 is used on some systems to avoid garbage collecting a DWARF table which
9427 is referenced by a function.
9430 @hook TARGET_ASM_OUTPUT_DWARF_DTPREL
9431 If defined, this target hook is a function which outputs a DTP-relative
9432 reference to the given TLS symbol of the specified size.
9435 @defmac PUT_SDB_@dots{}
9436 Define these macros to override the assembler syntax for the special
9437 SDB assembler directives. See @file{sdbout.c} for a list of these
9438 macros and their arguments. If the standard syntax is used, you need
9439 not define them yourself.
9443 Some assemblers do not support a semicolon as a delimiter, even between
9444 SDB assembler directives. In that case, define this macro to be the
9445 delimiter to use (usually @samp{\n}). It is not necessary to define
9446 a new set of @code{PUT_SDB_@var{op}} macros if this is the only change
9450 @defmac SDB_ALLOW_UNKNOWN_REFERENCES
9451 Define this macro to allow references to unknown structure,
9452 union, or enumeration tags to be emitted. Standard COFF does not
9453 allow handling of unknown references, MIPS ECOFF has support for
9457 @defmac SDB_ALLOW_FORWARD_REFERENCES
9458 Define this macro to allow references to structure, union, or
9459 enumeration tags that have not yet been seen to be handled. Some
9460 assemblers choke if forward tags are used, while some require it.
9463 @defmac SDB_OUTPUT_SOURCE_LINE (@var{stream}, @var{line})
9464 A C statement to output SDB debugging information before code for line
9465 number @var{line} of the current source file to the stdio stream
9466 @var{stream}. The default is to emit an @code{.ln} directive.
9471 @subsection Macros for VMS Debug Format
9473 @c prevent bad page break with this line
9474 Here are macros for VMS debug format.
9476 @defmac VMS_DEBUGGING_INFO
9477 Define this macro if GCC should produce debugging output for VMS
9478 in response to the @option{-g} option. The default behavior for VMS
9479 is to generate minimal debug info for a traceback in the absence of
9480 @option{-g} unless explicitly overridden with @option{-g0}. This
9481 behavior is controlled by @code{TARGET_OPTION_OPTIMIZATION} and
9482 @code{TARGET_OPTION_OVERRIDE}.
9485 @node Floating Point
9486 @section Cross Compilation and Floating Point
9487 @cindex cross compilation and floating point
9488 @cindex floating point and cross compilation
9490 While all modern machines use twos-complement representation for integers,
9491 there are a variety of representations for floating point numbers. This
9492 means that in a cross-compiler the representation of floating point numbers
9493 in the compiled program may be different from that used in the machine
9494 doing the compilation.
9496 Because different representation systems may offer different amounts of
9497 range and precision, all floating point constants must be represented in
9498 the target machine's format. Therefore, the cross compiler cannot
9499 safely use the host machine's floating point arithmetic; it must emulate
9500 the target's arithmetic. To ensure consistency, GCC always uses
9501 emulation to work with floating point values, even when the host and
9502 target floating point formats are identical.
9504 The following macros are provided by @file{real.h} for the compiler to
9505 use. All parts of the compiler which generate or optimize
9506 floating-point calculations must use these macros. They may evaluate
9507 their operands more than once, so operands must not have side effects.
9509 @defmac REAL_VALUE_TYPE
9510 The C data type to be used to hold a floating point value in the target
9511 machine's format. Typically this is a @code{struct} containing an
9512 array of @code{HOST_WIDE_INT}, but all code should treat it as an opaque
9516 @deftypefn Macro int REAL_VALUES_EQUAL (REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y})
9517 Compares for equality the two values, @var{x} and @var{y}. If the target
9518 floating point format supports negative zeroes and/or NaNs,
9519 @samp{REAL_VALUES_EQUAL (-0.0, 0.0)} is true, and
9520 @samp{REAL_VALUES_EQUAL (NaN, NaN)} is false.
9523 @deftypefn Macro int REAL_VALUES_LESS (REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y})
9524 Tests whether @var{x} is less than @var{y}.
9527 @deftypefn Macro HOST_WIDE_INT REAL_VALUE_FIX (REAL_VALUE_TYPE @var{x})
9528 Truncates @var{x} to a signed integer, rounding toward zero.
9531 @deftypefn Macro {unsigned HOST_WIDE_INT} REAL_VALUE_UNSIGNED_FIX (REAL_VALUE_TYPE @var{x})
9532 Truncates @var{x} to an unsigned integer, rounding toward zero. If
9533 @var{x} is negative, returns zero.
9536 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ATOF (const char *@var{string}, enum machine_mode @var{mode})
9537 Converts @var{string} into a floating point number in the target machine's
9538 representation for mode @var{mode}. This routine can handle both
9539 decimal and hexadecimal floating point constants, using the syntax
9540 defined by the C language for both.
9543 @deftypefn Macro int REAL_VALUE_NEGATIVE (REAL_VALUE_TYPE @var{x})
9544 Returns 1 if @var{x} is negative (including negative zero), 0 otherwise.
9547 @deftypefn Macro int REAL_VALUE_ISINF (REAL_VALUE_TYPE @var{x})
9548 Determines whether @var{x} represents infinity (positive or negative).
9551 @deftypefn Macro int REAL_VALUE_ISNAN (REAL_VALUE_TYPE @var{x})
9552 Determines whether @var{x} represents a ``NaN'' (not-a-number).
9555 @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})
9556 Calculates an arithmetic operation on the two floating point values
9557 @var{x} and @var{y}, storing the result in @var{output} (which must be a
9560 The operation to be performed is specified by @var{code}. Only the
9561 following codes are supported: @code{PLUS_EXPR}, @code{MINUS_EXPR},
9562 @code{MULT_EXPR}, @code{RDIV_EXPR}, @code{MAX_EXPR}, @code{MIN_EXPR}.
9564 If @code{REAL_ARITHMETIC} is asked to evaluate division by zero and the
9565 target's floating point format cannot represent infinity, it will call
9566 @code{abort}. Callers should check for this situation first, using
9567 @code{MODE_HAS_INFINITIES}. @xref{Storage Layout}.
9570 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_NEGATE (REAL_VALUE_TYPE @var{x})
9571 Returns the negative of the floating point value @var{x}.
9574 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ABS (REAL_VALUE_TYPE @var{x})
9575 Returns the absolute value of @var{x}.
9578 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_TRUNCATE (REAL_VALUE_TYPE @var{mode}, enum machine_mode @var{x})
9579 Truncates the floating point value @var{x} to fit in @var{mode}. The
9580 return value is still a full-size @code{REAL_VALUE_TYPE}, but it has an
9581 appropriate bit pattern to be output as a floating constant whose
9582 precision accords with mode @var{mode}.
9585 @deftypefn Macro void REAL_VALUE_TO_INT (HOST_WIDE_INT @var{low}, HOST_WIDE_INT @var{high}, REAL_VALUE_TYPE @var{x})
9586 Converts a floating point value @var{x} into a double-precision integer
9587 which is then stored into @var{low} and @var{high}. If the value is not
9588 integral, it is truncated.
9591 @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})
9592 Converts a double-precision integer found in @var{low} and @var{high},
9593 into a floating point value which is then stored into @var{x}. The
9594 value is truncated to fit in mode @var{mode}.
9597 @node Mode Switching
9598 @section Mode Switching Instructions
9599 @cindex mode switching
9600 The following macros control mode switching optimizations:
9602 @defmac OPTIMIZE_MODE_SWITCHING (@var{entity})
9603 Define this macro if the port needs extra instructions inserted for mode
9604 switching in an optimizing compilation.
9606 For an example, the SH4 can perform both single and double precision
9607 floating point operations, but to perform a single precision operation,
9608 the FPSCR PR bit has to be cleared, while for a double precision
9609 operation, this bit has to be set. Changing the PR bit requires a general
9610 purpose register as a scratch register, hence these FPSCR sets have to
9611 be inserted before reload, i.e.@: you can't put this into instruction emitting
9612 or @code{TARGET_MACHINE_DEPENDENT_REORG}.
9614 You can have multiple entities that are mode-switched, and select at run time
9615 which entities actually need it. @code{OPTIMIZE_MODE_SWITCHING} should
9616 return nonzero for any @var{entity} that needs mode-switching.
9617 If you define this macro, you also have to define
9618 @code{NUM_MODES_FOR_MODE_SWITCHING}, @code{MODE_NEEDED},
9619 @code{MODE_PRIORITY_TO_MODE} and @code{EMIT_MODE_SET}.
9620 @code{MODE_AFTER}, @code{MODE_ENTRY}, and @code{MODE_EXIT}
9624 @defmac NUM_MODES_FOR_MODE_SWITCHING
9625 If you define @code{OPTIMIZE_MODE_SWITCHING}, you have to define this as
9626 initializer for an array of integers. Each initializer element
9627 N refers to an entity that needs mode switching, and specifies the number
9628 of different modes that might need to be set for this entity.
9629 The position of the initializer in the initializer---starting counting at
9630 zero---determines the integer that is used to refer to the mode-switched
9632 In macros that take mode arguments / yield a mode result, modes are
9633 represented as numbers 0 @dots{} N @minus{} 1. N is used to specify that no mode
9634 switch is needed / supplied.
9637 @defmac MODE_NEEDED (@var{entity}, @var{insn})
9638 @var{entity} is an integer specifying a mode-switched entity. If
9639 @code{OPTIMIZE_MODE_SWITCHING} is defined, you must define this macro to
9640 return an integer value not larger than the corresponding element in
9641 @code{NUM_MODES_FOR_MODE_SWITCHING}, to denote the mode that @var{entity} must
9642 be switched into prior to the execution of @var{insn}.
9645 @defmac MODE_AFTER (@var{mode}, @var{insn})
9646 If this macro is defined, it is evaluated for every @var{insn} during
9647 mode switching. It determines the mode that an insn results in (if
9648 different from the incoming mode).
9651 @defmac MODE_ENTRY (@var{entity})
9652 If this macro is defined, it is evaluated for every @var{entity} that needs
9653 mode switching. It should evaluate to an integer, which is a mode that
9654 @var{entity} is assumed to be switched to at function entry. If @code{MODE_ENTRY}
9655 is defined then @code{MODE_EXIT} must be defined.
9658 @defmac MODE_EXIT (@var{entity})
9659 If this macro is defined, it is evaluated for every @var{entity} that needs
9660 mode switching. It should evaluate to an integer, which is a mode that
9661 @var{entity} is assumed to be switched to at function exit. If @code{MODE_EXIT}
9662 is defined then @code{MODE_ENTRY} must be defined.
9665 @defmac MODE_PRIORITY_TO_MODE (@var{entity}, @var{n})
9666 This macro specifies the order in which modes for @var{entity} are processed.
9667 0 is the highest priority, @code{NUM_MODES_FOR_MODE_SWITCHING[@var{entity}] - 1} the
9668 lowest. The value of the macro should be an integer designating a mode
9669 for @var{entity}. For any fixed @var{entity}, @code{mode_priority_to_mode}
9670 (@var{entity}, @var{n}) shall be a bijection in 0 @dots{}
9671 @code{num_modes_for_mode_switching[@var{entity}] - 1}.
9674 @defmac EMIT_MODE_SET (@var{entity}, @var{mode}, @var{hard_regs_live})
9675 Generate one or more insns to set @var{entity} to @var{mode}.
9676 @var{hard_reg_live} is the set of hard registers live at the point where
9677 the insn(s) are to be inserted.
9680 @node Target Attributes
9681 @section Defining target-specific uses of @code{__attribute__}
9682 @cindex target attributes
9683 @cindex machine attributes
9684 @cindex attributes, target-specific
9686 Target-specific attributes may be defined for functions, data and types.
9687 These are described using the following target hooks; they also need to
9688 be documented in @file{extend.texi}.
9690 @hook TARGET_ATTRIBUTE_TABLE
9691 If defined, this target hook points to an array of @samp{struct
9692 attribute_spec} (defined in @file{tree.h}) specifying the machine
9693 specific attributes for this target and some of the restrictions on the
9694 entities to which these attributes are applied and the arguments they
9698 @hook TARGET_ATTRIBUTE_TAKES_IDENTIFIER_P
9699 If defined, this target hook is a function which returns true if the
9700 machine-specific attribute named @var{name} expects an identifier
9701 given as its first argument to be passed on as a plain identifier, not
9702 subjected to name lookup. If this is not defined, the default is
9703 false for all machine-specific attributes.
9706 @hook TARGET_COMP_TYPE_ATTRIBUTES
9707 If defined, this target hook is a function which returns zero if the attributes on
9708 @var{type1} and @var{type2} are incompatible, one if they are compatible,
9709 and two if they are nearly compatible (which causes a warning to be
9710 generated). If this is not defined, machine-specific attributes are
9711 supposed always to be compatible.
9714 @hook TARGET_SET_DEFAULT_TYPE_ATTRIBUTES
9715 If defined, this target hook is a function which assigns default attributes to
9716 the newly defined @var{type}.
9719 @hook TARGET_MERGE_TYPE_ATTRIBUTES
9720 Define this target hook if the merging of type attributes needs special
9721 handling. If defined, the result is a list of the combined
9722 @code{TYPE_ATTRIBUTES} of @var{type1} and @var{type2}. It is assumed
9723 that @code{comptypes} has already been called and returned 1. This
9724 function may call @code{merge_attributes} to handle machine-independent
9728 @hook TARGET_MERGE_DECL_ATTRIBUTES
9729 Define this target hook if the merging of decl attributes needs special
9730 handling. If defined, the result is a list of the combined
9731 @code{DECL_ATTRIBUTES} of @var{olddecl} and @var{newdecl}.
9732 @var{newdecl} is a duplicate declaration of @var{olddecl}. Examples of
9733 when this is needed are when one attribute overrides another, or when an
9734 attribute is nullified by a subsequent definition. This function may
9735 call @code{merge_attributes} to handle machine-independent merging.
9737 @findex TARGET_DLLIMPORT_DECL_ATTRIBUTES
9738 If the only target-specific handling you require is @samp{dllimport}
9739 for Microsoft Windows targets, you should define the macro
9740 @code{TARGET_DLLIMPORT_DECL_ATTRIBUTES} to @code{1}. The compiler
9741 will then define a function called
9742 @code{merge_dllimport_decl_attributes} which can then be defined as
9743 the expansion of @code{TARGET_MERGE_DECL_ATTRIBUTES}. You can also
9744 add @code{handle_dll_attribute} in the attribute table for your port
9745 to perform initial processing of the @samp{dllimport} and
9746 @samp{dllexport} attributes. This is done in @file{i386/cygwin.h} and
9747 @file{i386/i386.c}, for example.
9750 @hook TARGET_VALID_DLLIMPORT_ATTRIBUTE_P
9752 @defmac TARGET_DECLSPEC
9753 Define this macro to a nonzero value if you want to treat
9754 @code{__declspec(X)} as equivalent to @code{__attribute((X))}. By
9755 default, this behavior is enabled only for targets that define
9756 @code{TARGET_DLLIMPORT_DECL_ATTRIBUTES}. The current implementation
9757 of @code{__declspec} is via a built-in macro, but you should not rely
9758 on this implementation detail.
9761 @hook TARGET_INSERT_ATTRIBUTES
9762 Define this target hook if you want to be able to add attributes to a decl
9763 when it is being created. This is normally useful for back ends which
9764 wish to implement a pragma by using the attributes which correspond to
9765 the pragma's effect. The @var{node} argument is the decl which is being
9766 created. The @var{attr_ptr} argument is a pointer to the attribute list
9767 for this decl. The list itself should not be modified, since it may be
9768 shared with other decls, but attributes may be chained on the head of
9769 the list and @code{*@var{attr_ptr}} modified to point to the new
9770 attributes, or a copy of the list may be made if further changes are
9774 @hook TARGET_FUNCTION_ATTRIBUTE_INLINABLE_P
9776 This target hook returns @code{true} if it is ok to inline @var{fndecl}
9777 into the current function, despite its having target-specific
9778 attributes, @code{false} otherwise. By default, if a function has a
9779 target specific attribute attached to it, it will not be inlined.
9782 @hook TARGET_OPTION_VALID_ATTRIBUTE_P
9783 This hook is called to parse the @code{attribute(option("..."))}, and
9784 it allows the function to set different target machine compile time
9785 options for the current function that might be different than the
9786 options specified on the command line. The hook should return
9787 @code{true} if the options are valid.
9789 The hook should set the @var{DECL_FUNCTION_SPECIFIC_TARGET} field in
9790 the function declaration to hold a pointer to a target specific
9791 @var{struct cl_target_option} structure.
9794 @hook TARGET_OPTION_SAVE
9795 This hook is called to save any additional target specific information
9796 in the @var{struct cl_target_option} structure for function specific
9798 @xref{Option file format}.
9801 @hook TARGET_OPTION_RESTORE
9802 This hook is called to restore any additional target specific
9803 information in the @var{struct cl_target_option} structure for
9804 function specific options.
9807 @hook TARGET_OPTION_PRINT
9808 This hook is called to print any additional target specific
9809 information in the @var{struct cl_target_option} structure for
9810 function specific options.
9813 @hook TARGET_OPTION_PRAGMA_PARSE
9814 This target hook parses the options for @code{#pragma GCC option} to
9815 set the machine specific options for functions that occur later in the
9816 input stream. The options should be the same as handled by the
9817 @code{TARGET_OPTION_VALID_ATTRIBUTE_P} hook.
9820 @hook TARGET_OPTION_OVERRIDE
9821 Sometimes certain combinations of command options do not make sense on
9822 a particular target machine. You can override the hook
9823 @code{TARGET_OPTION_OVERRIDE} to take account of this. This hooks is called
9824 once just after all the command options have been parsed.
9826 Don't use this hook to turn on various extra optimizations for
9827 @option{-O}. That is what @code{TARGET_OPTION_OPTIMIZATION} is for.
9829 If you need to do something whenever the optimization level is
9830 changed via the optimize attribute or pragma, see
9831 @code{TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE}
9834 @hook TARGET_CAN_INLINE_P
9835 This target hook returns @code{false} if the @var{caller} function
9836 cannot inline @var{callee}, based on target specific information. By
9837 default, inlining is not allowed if the callee function has function
9838 specific target options and the caller does not use the same options.
9842 @section Emulating TLS
9843 @cindex Emulated TLS
9845 For targets whose psABI does not provide Thread Local Storage via
9846 specific relocations and instruction sequences, an emulation layer is
9847 used. A set of target hooks allows this emulation layer to be
9848 configured for the requirements of a particular target. For instance
9849 the psABI may in fact specify TLS support in terms of an emulation
9852 The emulation layer works by creating a control object for every TLS
9853 object. To access the TLS object, a lookup function is provided
9854 which, when given the address of the control object, will return the
9855 address of the current thread's instance of the TLS object.
9857 @hook TARGET_EMUTLS_GET_ADDRESS
9858 Contains the name of the helper function that uses a TLS control
9859 object to locate a TLS instance. The default causes libgcc's
9860 emulated TLS helper function to be used.
9863 @hook TARGET_EMUTLS_REGISTER_COMMON
9864 Contains the name of the helper function that should be used at
9865 program startup to register TLS objects that are implicitly
9866 initialized to zero. If this is @code{NULL}, all TLS objects will
9867 have explicit initializers. The default causes libgcc's emulated TLS
9868 registration function to be used.
9871 @hook TARGET_EMUTLS_VAR_SECTION
9872 Contains the name of the section in which TLS control variables should
9873 be placed. The default of @code{NULL} allows these to be placed in
9877 @hook TARGET_EMUTLS_TMPL_SECTION
9878 Contains the name of the section in which TLS initializers should be
9879 placed. The default of @code{NULL} allows these to be placed in any
9883 @hook TARGET_EMUTLS_VAR_PREFIX
9884 Contains the prefix to be prepended to TLS control variable names.
9885 The default of @code{NULL} uses a target-specific prefix.
9888 @hook TARGET_EMUTLS_TMPL_PREFIX
9889 Contains the prefix to be prepended to TLS initializer objects. The
9890 default of @code{NULL} uses a target-specific prefix.
9893 @hook TARGET_EMUTLS_VAR_FIELDS
9894 Specifies a function that generates the FIELD_DECLs for a TLS control
9895 object type. @var{type} is the RECORD_TYPE the fields are for and
9896 @var{name} should be filled with the structure tag, if the default of
9897 @code{__emutls_object} is unsuitable. The default creates a type suitable
9898 for libgcc's emulated TLS function.
9901 @hook TARGET_EMUTLS_VAR_INIT
9902 Specifies a function that generates the CONSTRUCTOR to initialize a
9903 TLS control object. @var{var} is the TLS control object, @var{decl}
9904 is the TLS object and @var{tmpl_addr} is the address of the
9905 initializer. The default initializes libgcc's emulated TLS control object.
9908 @hook TARGET_EMUTLS_VAR_ALIGN_FIXED
9909 Specifies whether the alignment of TLS control variable objects is
9910 fixed and should not be increased as some backends may do to optimize
9911 single objects. The default is false.
9914 @hook TARGET_EMUTLS_DEBUG_FORM_TLS_ADDRESS
9915 Specifies whether a DWARF @code{DW_OP_form_tls_address} location descriptor
9916 may be used to describe emulated TLS control objects.
9919 @node MIPS Coprocessors
9920 @section Defining coprocessor specifics for MIPS targets.
9921 @cindex MIPS coprocessor-definition macros
9923 The MIPS specification allows MIPS implementations to have as many as 4
9924 coprocessors, each with as many as 32 private registers. GCC supports
9925 accessing these registers and transferring values between the registers
9926 and memory using asm-ized variables. For example:
9929 register unsigned int cp0count asm ("c0r1");
9935 (``c0r1'' is the default name of register 1 in coprocessor 0; alternate
9936 names may be added as described below, or the default names may be
9937 overridden entirely in @code{SUBTARGET_CONDITIONAL_REGISTER_USAGE}.)
9939 Coprocessor registers are assumed to be epilogue-used; sets to them will
9940 be preserved even if it does not appear that the register is used again
9941 later in the function.
9943 Another note: according to the MIPS spec, coprocessor 1 (if present) is
9944 the FPU@. One accesses COP1 registers through standard mips
9945 floating-point support; they are not included in this mechanism.
9947 There is one macro used in defining the MIPS coprocessor interface which
9948 you may want to override in subtargets; it is described below.
9950 @defmac ALL_COP_ADDITIONAL_REGISTER_NAMES
9951 A comma-separated list (with leading comma) of pairs describing the
9952 alternate names of coprocessor registers. The format of each entry should be
9954 @{ @var{alternatename}, @var{register_number}@}
9960 @section Parameters for Precompiled Header Validity Checking
9961 @cindex parameters, precompiled headers
9963 @hook TARGET_GET_PCH_VALIDITY
9964 This hook returns a pointer to the data needed by
9965 @code{TARGET_PCH_VALID_P} and sets
9966 @samp{*@var{sz}} to the size of the data in bytes.
9969 @hook TARGET_PCH_VALID_P
9970 This hook checks whether the options used to create a PCH file are
9971 compatible with the current settings. It returns @code{NULL}
9972 if so and a suitable error message if not. Error messages will
9973 be presented to the user and must be localized using @samp{_(@var{msg})}.
9975 @var{data} is the data that was returned by @code{TARGET_GET_PCH_VALIDITY}
9976 when the PCH file was created and @var{sz} is the size of that data in bytes.
9977 It's safe to assume that the data was created by the same version of the
9978 compiler, so no format checking is needed.
9980 The default definition of @code{default_pch_valid_p} should be
9981 suitable for most targets.
9984 @hook TARGET_CHECK_PCH_TARGET_FLAGS
9985 If this hook is nonnull, the default implementation of
9986 @code{TARGET_PCH_VALID_P} will use it to check for compatible values
9987 of @code{target_flags}. @var{pch_flags} specifies the value that
9988 @code{target_flags} had when the PCH file was created. The return
9989 value is the same as for @code{TARGET_PCH_VALID_P}.
9993 @section C++ ABI parameters
9994 @cindex parameters, c++ abi
9996 @hook TARGET_CXX_GUARD_TYPE
9997 Define this hook to override the integer type used for guard variables.
9998 These are used to implement one-time construction of static objects. The
9999 default is long_long_integer_type_node.
10002 @hook TARGET_CXX_GUARD_MASK_BIT
10003 This hook determines how guard variables are used. It should return
10004 @code{false} (the default) if the first byte should be used. A return value of
10005 @code{true} indicates that only the least significant bit should be used.
10008 @hook TARGET_CXX_GET_COOKIE_SIZE
10009 This hook returns the size of the cookie to use when allocating an array
10010 whose elements have the indicated @var{type}. Assumes that it is already
10011 known that a cookie is needed. The default is
10012 @code{max(sizeof (size_t), alignof(type))}, as defined in section 2.7 of the
10013 IA64/Generic C++ ABI@.
10016 @hook TARGET_CXX_COOKIE_HAS_SIZE
10017 This hook should return @code{true} if the element size should be stored in
10018 array cookies. The default is to return @code{false}.
10021 @hook TARGET_CXX_IMPORT_EXPORT_CLASS
10022 If defined by a backend this hook allows the decision made to export
10023 class @var{type} to be overruled. Upon entry @var{import_export}
10024 will contain 1 if the class is going to be exported, @minus{}1 if it is going
10025 to be imported and 0 otherwise. This function should return the
10026 modified value and perform any other actions necessary to support the
10027 backend's targeted operating system.
10030 @hook TARGET_CXX_CDTOR_RETURNS_THIS
10031 This hook should return @code{true} if constructors and destructors return
10032 the address of the object created/destroyed. The default is to return
10036 @hook TARGET_CXX_KEY_METHOD_MAY_BE_INLINE
10037 This hook returns true if the key method for a class (i.e., the method
10038 which, if defined in the current translation unit, causes the virtual
10039 table to be emitted) may be an inline function. Under the standard
10040 Itanium C++ ABI the key method may be an inline function so long as
10041 the function is not declared inline in the class definition. Under
10042 some variants of the ABI, an inline function can never be the key
10043 method. The default is to return @code{true}.
10046 @hook TARGET_CXX_DETERMINE_CLASS_DATA_VISIBILITY
10048 @hook TARGET_CXX_CLASS_DATA_ALWAYS_COMDAT
10049 This hook returns true (the default) if virtual tables and other
10050 similar implicit class data objects are always COMDAT if they have
10051 external linkage. If this hook returns false, then class data for
10052 classes whose virtual table will be emitted in only one translation
10053 unit will not be COMDAT.
10056 @hook TARGET_CXX_LIBRARY_RTTI_COMDAT
10057 This hook returns true (the default) if the RTTI information for
10058 the basic types which is defined in the C++ runtime should always
10059 be COMDAT, false if it should not be COMDAT.
10062 @hook TARGET_CXX_USE_AEABI_ATEXIT
10063 This hook returns true if @code{__aeabi_atexit} (as defined by the ARM EABI)
10064 should be used to register static destructors when @option{-fuse-cxa-atexit}
10065 is in effect. The default is to return false to use @code{__cxa_atexit}.
10068 @hook TARGET_CXX_USE_ATEXIT_FOR_CXA_ATEXIT
10069 This hook returns true if the target @code{atexit} function can be used
10070 in the same manner as @code{__cxa_atexit} to register C++ static
10071 destructors. This requires that @code{atexit}-registered functions in
10072 shared libraries are run in the correct order when the libraries are
10073 unloaded. The default is to return false.
10076 @hook TARGET_CXX_ADJUST_CLASS_AT_DEFINITION
10078 @node Named Address Spaces
10079 @section Adding support for named address spaces
10080 @cindex named address spaces
10082 The draft technical report of the ISO/IEC JTC1 S22 WG14 N1275
10083 standards committee, @cite{Programming Languages - C - Extensions to
10084 support embedded processors}, specifies a syntax for embedded
10085 processors to specify alternate address spaces. You can configure a
10086 GCC port to support section 5.1 of the draft report to add support for
10087 address spaces other than the default address space. These address
10088 spaces are new keywords that are similar to the @code{volatile} and
10089 @code{const} type attributes.
10091 Pointers to named address spaces can have a different size than
10092 pointers to the generic address space.
10094 For example, the SPU port uses the @code{__ea} address space to refer
10095 to memory in the host processor, rather than memory local to the SPU
10096 processor. Access to memory in the @code{__ea} address space involves
10097 issuing DMA operations to move data between the host processor and the
10098 local processor memory address space. Pointers in the @code{__ea}
10099 address space are either 32 bits or 64 bits based on the
10100 @option{-mea32} or @option{-mea64} switches (native SPU pointers are
10103 Internally, address spaces are represented as a small integer in the
10104 range 0 to 15 with address space 0 being reserved for the generic
10107 To register a named address space qualifier keyword with the C front end,
10108 the target may call the @code{c_register_addr_space} routine. For example,
10109 the SPU port uses the following to declare @code{__ea} as the keyword for
10110 named address space #1:
10112 #define ADDR_SPACE_EA 1
10113 c_register_addr_space ("__ea", ADDR_SPACE_EA);
10116 @hook TARGET_ADDR_SPACE_POINTER_MODE
10117 Define this to return the machine mode to use for pointers to
10118 @var{address_space} if the target supports named address spaces.
10119 The default version of this hook returns @code{ptr_mode} for the
10120 generic address space only.
10123 @hook TARGET_ADDR_SPACE_ADDRESS_MODE
10124 Define this to return the machine mode to use for addresses in
10125 @var{address_space} if the target supports named address spaces.
10126 The default version of this hook returns @code{Pmode} for the
10127 generic address space only.
10130 @hook TARGET_ADDR_SPACE_VALID_POINTER_MODE
10131 Define this to return nonzero if the port can handle pointers
10132 with machine mode @var{mode} to address space @var{as}. This target
10133 hook is the same as the @code{TARGET_VALID_POINTER_MODE} target hook,
10134 except that it includes explicit named address space support. The default
10135 version of this hook returns true for the modes returned by either the
10136 @code{TARGET_ADDR_SPACE_POINTER_MODE} or @code{TARGET_ADDR_SPACE_ADDRESS_MODE}
10137 target hooks for the given address space.
10140 @hook TARGET_ADDR_SPACE_LEGITIMATE_ADDRESS_P
10141 Define this to return true if @var{exp} is a valid address for mode
10142 @var{mode} in the named address space @var{as}. The @var{strict}
10143 parameter says whether strict addressing is in effect after reload has
10144 finished. This target hook is the same as the
10145 @code{TARGET_LEGITIMATE_ADDRESS_P} target hook, except that it includes
10146 explicit named address space support.
10149 @hook TARGET_ADDR_SPACE_LEGITIMIZE_ADDRESS
10150 Define this to modify an invalid address @var{x} to be a valid address
10151 with mode @var{mode} in the named address space @var{as}. This target
10152 hook is the same as the @code{TARGET_LEGITIMIZE_ADDRESS} target hook,
10153 except that it includes explicit named address space support.
10156 @hook TARGET_ADDR_SPACE_SUBSET_P
10157 Define this to return whether the @var{subset} named address space is
10158 contained within the @var{superset} named address space. Pointers to
10159 a named address space that is a subset of another named address space
10160 will be converted automatically without a cast if used together in
10161 arithmetic operations. Pointers to a superset address space can be
10162 converted to pointers to a subset address space via explicit casts.
10165 @hook TARGET_ADDR_SPACE_CONVERT
10166 Define this to convert the pointer expression represented by the RTL
10167 @var{op} with type @var{from_type} that points to a named address
10168 space to a new pointer expression with type @var{to_type} that points
10169 to a different named address space. When this hook it called, it is
10170 guaranteed that one of the two address spaces is a subset of the other,
10171 as determined by the @code{TARGET_ADDR_SPACE_SUBSET_P} target hook.
10175 @section Miscellaneous Parameters
10176 @cindex parameters, miscellaneous
10178 @c prevent bad page break with this line
10179 Here are several miscellaneous parameters.
10181 @defmac HAS_LONG_COND_BRANCH
10182 Define this boolean macro to indicate whether or not your architecture
10183 has conditional branches that can span all of memory. It is used in
10184 conjunction with an optimization that partitions hot and cold basic
10185 blocks into separate sections of the executable. If this macro is
10186 set to false, gcc will convert any conditional branches that attempt
10187 to cross between sections into unconditional branches or indirect jumps.
10190 @defmac HAS_LONG_UNCOND_BRANCH
10191 Define this boolean macro to indicate whether or not your architecture
10192 has unconditional branches that can span all of memory. It is used in
10193 conjunction with an optimization that partitions hot and cold basic
10194 blocks into separate sections of the executable. If this macro is
10195 set to false, gcc will convert any unconditional branches that attempt
10196 to cross between sections into indirect jumps.
10199 @defmac CASE_VECTOR_MODE
10200 An alias for a machine mode name. This is the machine mode that
10201 elements of a jump-table should have.
10204 @defmac CASE_VECTOR_SHORTEN_MODE (@var{min_offset}, @var{max_offset}, @var{body})
10205 Optional: return the preferred mode for an @code{addr_diff_vec}
10206 when the minimum and maximum offset are known. If you define this,
10207 it enables extra code in branch shortening to deal with @code{addr_diff_vec}.
10208 To make this work, you also have to define @code{INSN_ALIGN} and
10209 make the alignment for @code{addr_diff_vec} explicit.
10210 The @var{body} argument is provided so that the offset_unsigned and scale
10211 flags can be updated.
10214 @defmac CASE_VECTOR_PC_RELATIVE
10215 Define this macro to be a C expression to indicate when jump-tables
10216 should contain relative addresses. You need not define this macro if
10217 jump-tables never contain relative addresses, or jump-tables should
10218 contain relative addresses only when @option{-fPIC} or @option{-fPIC}
10222 @hook TARGET_CASE_VALUES_THRESHOLD
10223 This function return the smallest number of different values for which it
10224 is best to use a jump-table instead of a tree of conditional branches.
10225 The default is four for machines with a @code{casesi} instruction and
10226 five otherwise. This is best for most machines.
10229 @defmac CASE_USE_BIT_TESTS
10230 Define this macro to be a C expression to indicate whether C switch
10231 statements may be implemented by a sequence of bit tests. This is
10232 advantageous on processors that can efficiently implement left shift
10233 of 1 by the number of bits held in a register, but inappropriate on
10234 targets that would require a loop. By default, this macro returns
10235 @code{true} if the target defines an @code{ashlsi3} pattern, and
10236 @code{false} otherwise.
10239 @defmac WORD_REGISTER_OPERATIONS
10240 Define this macro if operations between registers with integral mode
10241 smaller than a word are always performed on the entire register.
10242 Most RISC machines have this property and most CISC machines do not.
10245 @defmac LOAD_EXTEND_OP (@var{mem_mode})
10246 Define this macro to be a C expression indicating when insns that read
10247 memory in @var{mem_mode}, an integral mode narrower than a word, set the
10248 bits outside of @var{mem_mode} to be either the sign-extension or the
10249 zero-extension of the data read. Return @code{SIGN_EXTEND} for values
10250 of @var{mem_mode} for which the
10251 insn sign-extends, @code{ZERO_EXTEND} for which it zero-extends, and
10252 @code{UNKNOWN} for other modes.
10254 This macro is not called with @var{mem_mode} non-integral or with a width
10255 greater than or equal to @code{BITS_PER_WORD}, so you may return any
10256 value in this case. Do not define this macro if it would always return
10257 @code{UNKNOWN}. On machines where this macro is defined, you will normally
10258 define it as the constant @code{SIGN_EXTEND} or @code{ZERO_EXTEND}.
10260 You may return a non-@code{UNKNOWN} value even if for some hard registers
10261 the sign extension is not performed, if for the @code{REGNO_REG_CLASS}
10262 of these hard registers @code{CANNOT_CHANGE_MODE_CLASS} returns nonzero
10263 when the @var{from} mode is @var{mem_mode} and the @var{to} mode is any
10264 integral mode larger than this but not larger than @code{word_mode}.
10266 You must return @code{UNKNOWN} if for some hard registers that allow this
10267 mode, @code{CANNOT_CHANGE_MODE_CLASS} says that they cannot change to
10268 @code{word_mode}, but that they can change to another integral mode that
10269 is larger then @var{mem_mode} but still smaller than @code{word_mode}.
10272 @defmac SHORT_IMMEDIATES_SIGN_EXTEND
10273 Define this macro if loading short immediate values into registers sign
10277 @defmac FIXUNS_TRUNC_LIKE_FIX_TRUNC
10278 Define this macro if the same instructions that convert a floating
10279 point number to a signed fixed point number also convert validly to an
10283 @hook TARGET_MIN_DIVISIONS_FOR_RECIP_MUL
10284 When @option{-ffast-math} is in effect, GCC tries to optimize
10285 divisions by the same divisor, by turning them into multiplications by
10286 the reciprocal. This target hook specifies the minimum number of divisions
10287 that should be there for GCC to perform the optimization for a variable
10288 of mode @var{mode}. The default implementation returns 3 if the machine
10289 has an instruction for the division, and 2 if it does not.
10293 The maximum number of bytes that a single instruction can move quickly
10294 between memory and registers or between two memory locations.
10297 @defmac MAX_MOVE_MAX
10298 The maximum number of bytes that a single instruction can move quickly
10299 between memory and registers or between two memory locations. If this
10300 is undefined, the default is @code{MOVE_MAX}. Otherwise, it is the
10301 constant value that is the largest value that @code{MOVE_MAX} can have
10305 @defmac SHIFT_COUNT_TRUNCATED
10306 A C expression that is nonzero if on this machine the number of bits
10307 actually used for the count of a shift operation is equal to the number
10308 of bits needed to represent the size of the object being shifted. When
10309 this macro is nonzero, the compiler will assume that it is safe to omit
10310 a sign-extend, zero-extend, and certain bitwise `and' instructions that
10311 truncates the count of a shift operation. On machines that have
10312 instructions that act on bit-fields at variable positions, which may
10313 include `bit test' instructions, a nonzero @code{SHIFT_COUNT_TRUNCATED}
10314 also enables deletion of truncations of the values that serve as
10315 arguments to bit-field instructions.
10317 If both types of instructions truncate the count (for shifts) and
10318 position (for bit-field operations), or if no variable-position bit-field
10319 instructions exist, you should define this macro.
10321 However, on some machines, such as the 80386 and the 680x0, truncation
10322 only applies to shift operations and not the (real or pretended)
10323 bit-field operations. Define @code{SHIFT_COUNT_TRUNCATED} to be zero on
10324 such machines. Instead, add patterns to the @file{md} file that include
10325 the implied truncation of the shift instructions.
10327 You need not define this macro if it would always have the value of zero.
10330 @anchor{TARGET_SHIFT_TRUNCATION_MASK}
10331 @hook TARGET_SHIFT_TRUNCATION_MASK
10332 This function describes how the standard shift patterns for @var{mode}
10333 deal with shifts by negative amounts or by more than the width of the mode.
10334 @xref{shift patterns}.
10336 On many machines, the shift patterns will apply a mask @var{m} to the
10337 shift count, meaning that a fixed-width shift of @var{x} by @var{y} is
10338 equivalent to an arbitrary-width shift of @var{x} by @var{y & m}. If
10339 this is true for mode @var{mode}, the function should return @var{m},
10340 otherwise it should return 0. A return value of 0 indicates that no
10341 particular behavior is guaranteed.
10343 Note that, unlike @code{SHIFT_COUNT_TRUNCATED}, this function does
10344 @emph{not} apply to general shift rtxes; it applies only to instructions
10345 that are generated by the named shift patterns.
10347 The default implementation of this function returns
10348 @code{GET_MODE_BITSIZE (@var{mode}) - 1} if @code{SHIFT_COUNT_TRUNCATED}
10349 and 0 otherwise. This definition is always safe, but if
10350 @code{SHIFT_COUNT_TRUNCATED} is false, and some shift patterns
10351 nevertheless truncate the shift count, you may get better code
10355 @defmac TRULY_NOOP_TRUNCATION (@var{outprec}, @var{inprec})
10356 A C expression which is nonzero if on this machine it is safe to
10357 ``convert'' an integer of @var{inprec} bits to one of @var{outprec}
10358 bits (where @var{outprec} is smaller than @var{inprec}) by merely
10359 operating on it as if it had only @var{outprec} bits.
10361 On many machines, this expression can be 1.
10363 @c rearranged this, removed the phrase "it is reported that". this was
10364 @c to fix an overfull hbox. --mew 10feb93
10365 When @code{TRULY_NOOP_TRUNCATION} returns 1 for a pair of sizes for
10366 modes for which @code{MODES_TIEABLE_P} is 0, suboptimal code can result.
10367 If this is the case, making @code{TRULY_NOOP_TRUNCATION} return 0 in
10368 such cases may improve things.
10371 @hook TARGET_MODE_REP_EXTENDED
10372 The representation of an integral mode can be such that the values
10373 are always extended to a wider integral mode. Return
10374 @code{SIGN_EXTEND} if values of @var{mode} are represented in
10375 sign-extended form to @var{rep_mode}. Return @code{UNKNOWN}
10376 otherwise. (Currently, none of the targets use zero-extended
10377 representation this way so unlike @code{LOAD_EXTEND_OP},
10378 @code{TARGET_MODE_REP_EXTENDED} is expected to return either
10379 @code{SIGN_EXTEND} or @code{UNKNOWN}. Also no target extends
10380 @var{mode} to @var{rep_mode} so that @var{rep_mode} is not the next
10381 widest integral mode and currently we take advantage of this fact.)
10383 Similarly to @code{LOAD_EXTEND_OP} you may return a non-@code{UNKNOWN}
10384 value even if the extension is not performed on certain hard registers
10385 as long as for the @code{REGNO_REG_CLASS} of these hard registers
10386 @code{CANNOT_CHANGE_MODE_CLASS} returns nonzero.
10388 Note that @code{TARGET_MODE_REP_EXTENDED} and @code{LOAD_EXTEND_OP}
10389 describe two related properties. If you define
10390 @code{TARGET_MODE_REP_EXTENDED (mode, word_mode)} you probably also want
10391 to define @code{LOAD_EXTEND_OP (mode)} to return the same type of
10394 In order to enforce the representation of @code{mode},
10395 @code{TRULY_NOOP_TRUNCATION} should return false when truncating to
10399 @defmac STORE_FLAG_VALUE
10400 A C expression describing the value returned by a comparison operator
10401 with an integral mode and stored by a store-flag instruction
10402 (@samp{cstore@var{mode}4}) when the condition is true. This description must
10403 apply to @emph{all} the @samp{cstore@var{mode}4} patterns and all the
10404 comparison operators whose results have a @code{MODE_INT} mode.
10406 A value of 1 or @minus{}1 means that the instruction implementing the
10407 comparison operator returns exactly 1 or @minus{}1 when the comparison is true
10408 and 0 when the comparison is false. Otherwise, the value indicates
10409 which bits of the result are guaranteed to be 1 when the comparison is
10410 true. This value is interpreted in the mode of the comparison
10411 operation, which is given by the mode of the first operand in the
10412 @samp{cstore@var{mode}4} pattern. Either the low bit or the sign bit of
10413 @code{STORE_FLAG_VALUE} be on. Presently, only those bits are used by
10416 If @code{STORE_FLAG_VALUE} is neither 1 or @minus{}1, the compiler will
10417 generate code that depends only on the specified bits. It can also
10418 replace comparison operators with equivalent operations if they cause
10419 the required bits to be set, even if the remaining bits are undefined.
10420 For example, on a machine whose comparison operators return an
10421 @code{SImode} value and where @code{STORE_FLAG_VALUE} is defined as
10422 @samp{0x80000000}, saying that just the sign bit is relevant, the
10426 (ne:SI (and:SI @var{x} (const_int @var{power-of-2})) (const_int 0))
10430 can be converted to
10433 (ashift:SI @var{x} (const_int @var{n}))
10437 where @var{n} is the appropriate shift count to move the bit being
10438 tested into the sign bit.
10440 There is no way to describe a machine that always sets the low-order bit
10441 for a true value, but does not guarantee the value of any other bits,
10442 but we do not know of any machine that has such an instruction. If you
10443 are trying to port GCC to such a machine, include an instruction to
10444 perform a logical-and of the result with 1 in the pattern for the
10445 comparison operators and let us know at @email{gcc@@gcc.gnu.org}.
10447 Often, a machine will have multiple instructions that obtain a value
10448 from a comparison (or the condition codes). Here are rules to guide the
10449 choice of value for @code{STORE_FLAG_VALUE}, and hence the instructions
10454 Use the shortest sequence that yields a valid definition for
10455 @code{STORE_FLAG_VALUE}. It is more efficient for the compiler to
10456 ``normalize'' the value (convert it to, e.g., 1 or 0) than for the
10457 comparison operators to do so because there may be opportunities to
10458 combine the normalization with other operations.
10461 For equal-length sequences, use a value of 1 or @minus{}1, with @minus{}1 being
10462 slightly preferred on machines with expensive jumps and 1 preferred on
10466 As a second choice, choose a value of @samp{0x80000001} if instructions
10467 exist that set both the sign and low-order bits but do not define the
10471 Otherwise, use a value of @samp{0x80000000}.
10474 Many machines can produce both the value chosen for
10475 @code{STORE_FLAG_VALUE} and its negation in the same number of
10476 instructions. On those machines, you should also define a pattern for
10477 those cases, e.g., one matching
10480 (set @var{A} (neg:@var{m} (ne:@var{m} @var{B} @var{C})))
10483 Some machines can also perform @code{and} or @code{plus} operations on
10484 condition code values with less instructions than the corresponding
10485 @samp{cstore@var{mode}4} insn followed by @code{and} or @code{plus}. On those
10486 machines, define the appropriate patterns. Use the names @code{incscc}
10487 and @code{decscc}, respectively, for the patterns which perform
10488 @code{plus} or @code{minus} operations on condition code values. See
10489 @file{rs6000.md} for some examples. The GNU Superoptizer can be used to
10490 find such instruction sequences on other machines.
10492 If this macro is not defined, the default value, 1, is used. You need
10493 not define @code{STORE_FLAG_VALUE} if the machine has no store-flag
10494 instructions, or if the value generated by these instructions is 1.
10497 @defmac FLOAT_STORE_FLAG_VALUE (@var{mode})
10498 A C expression that gives a nonzero @code{REAL_VALUE_TYPE} value that is
10499 returned when comparison operators with floating-point results are true.
10500 Define this macro on machines that have comparison operations that return
10501 floating-point values. If there are no such operations, do not define
10505 @defmac VECTOR_STORE_FLAG_VALUE (@var{mode})
10506 A C expression that gives a rtx representing the nonzero true element
10507 for vector comparisons. The returned rtx should be valid for the inner
10508 mode of @var{mode} which is guaranteed to be a vector mode. Define
10509 this macro on machines that have vector comparison operations that
10510 return a vector result. If there are no such operations, do not define
10511 this macro. Typically, this macro is defined as @code{const1_rtx} or
10512 @code{constm1_rtx}. This macro may return @code{NULL_RTX} to prevent
10513 the compiler optimizing such vector comparison operations for the
10517 @defmac CLZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value})
10518 @defmacx CTZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value})
10519 A C expression that indicates whether the architecture defines a value
10520 for @code{clz} or @code{ctz} with a zero operand.
10521 A result of @code{0} indicates the value is undefined.
10522 If the value is defined for only the RTL expression, the macro should
10523 evaluate to @code{1}; if the value applies also to the corresponding optab
10524 entry (which is normally the case if it expands directly into
10525 the corresponding RTL), then the macro should evaluate to @code{2}.
10526 In the cases where the value is defined, @var{value} should be set to
10529 If this macro is not defined, the value of @code{clz} or
10530 @code{ctz} at zero is assumed to be undefined.
10532 This macro must be defined if the target's expansion for @code{ffs}
10533 relies on a particular value to get correct results. Otherwise it
10534 is not necessary, though it may be used to optimize some corner cases, and
10535 to provide a default expansion for the @code{ffs} optab.
10537 Note that regardless of this macro the ``definedness'' of @code{clz}
10538 and @code{ctz} at zero do @emph{not} extend to the builtin functions
10539 visible to the user. Thus one may be free to adjust the value at will
10540 to match the target expansion of these operations without fear of
10545 An alias for the machine mode for pointers. On most machines, define
10546 this to be the integer mode corresponding to the width of a hardware
10547 pointer; @code{SImode} on 32-bit machine or @code{DImode} on 64-bit machines.
10548 On some machines you must define this to be one of the partial integer
10549 modes, such as @code{PSImode}.
10551 The width of @code{Pmode} must be at least as large as the value of
10552 @code{POINTER_SIZE}. If it is not equal, you must define the macro
10553 @code{POINTERS_EXTEND_UNSIGNED} to specify how pointers are extended
10557 @defmac FUNCTION_MODE
10558 An alias for the machine mode used for memory references to functions
10559 being called, in @code{call} RTL expressions. On most CISC machines,
10560 where an instruction can begin at any byte address, this should be
10561 @code{QImode}. On most RISC machines, where all instructions have fixed
10562 size and alignment, this should be a mode with the same size and alignment
10563 as the machine instruction words - typically @code{SImode} or @code{HImode}.
10566 @defmac STDC_0_IN_SYSTEM_HEADERS
10567 In normal operation, the preprocessor expands @code{__STDC__} to the
10568 constant 1, to signify that GCC conforms to ISO Standard C@. On some
10569 hosts, like Solaris, the system compiler uses a different convention,
10570 where @code{__STDC__} is normally 0, but is 1 if the user specifies
10571 strict conformance to the C Standard.
10573 Defining @code{STDC_0_IN_SYSTEM_HEADERS} makes GNU CPP follows the host
10574 convention when processing system header files, but when processing user
10575 files @code{__STDC__} will always expand to 1.
10578 @defmac NO_IMPLICIT_EXTERN_C
10579 Define this macro if the system header files support C++ as well as C@.
10580 This macro inhibits the usual method of using system header files in
10581 C++, which is to pretend that the file's contents are enclosed in
10582 @samp{extern "C" @{@dots{}@}}.
10587 @defmac REGISTER_TARGET_PRAGMAS ()
10588 Define this macro if you want to implement any target-specific pragmas.
10589 If defined, it is a C expression which makes a series of calls to
10590 @code{c_register_pragma} or @code{c_register_pragma_with_expansion}
10591 for each pragma. The macro may also do any
10592 setup required for the pragmas.
10594 The primary reason to define this macro is to provide compatibility with
10595 other compilers for the same target. In general, we discourage
10596 definition of target-specific pragmas for GCC@.
10598 If the pragma can be implemented by attributes then you should consider
10599 defining the target hook @samp{TARGET_INSERT_ATTRIBUTES} as well.
10601 Preprocessor macros that appear on pragma lines are not expanded. All
10602 @samp{#pragma} directives that do not match any registered pragma are
10603 silently ignored, unless the user specifies @option{-Wunknown-pragmas}.
10606 @deftypefun void c_register_pragma (const char *@var{space}, const char *@var{name}, void (*@var{callback}) (struct cpp_reader *))
10607 @deftypefunx void c_register_pragma_with_expansion (const char *@var{space}, const char *@var{name}, void (*@var{callback}) (struct cpp_reader *))
10609 Each call to @code{c_register_pragma} or
10610 @code{c_register_pragma_with_expansion} establishes one pragma. The
10611 @var{callback} routine will be called when the preprocessor encounters a
10615 #pragma [@var{space}] @var{name} @dots{}
10618 @var{space} is the case-sensitive namespace of the pragma, or
10619 @code{NULL} to put the pragma in the global namespace. The callback
10620 routine receives @var{pfile} as its first argument, which can be passed
10621 on to cpplib's functions if necessary. You can lex tokens after the
10622 @var{name} by calling @code{pragma_lex}. Tokens that are not read by the
10623 callback will be silently ignored. The end of the line is indicated by
10624 a token of type @code{CPP_EOF}. Macro expansion occurs on the
10625 arguments of pragmas registered with
10626 @code{c_register_pragma_with_expansion} but not on the arguments of
10627 pragmas registered with @code{c_register_pragma}.
10629 Note that the use of @code{pragma_lex} is specific to the C and C++
10630 compilers. It will not work in the Java or Fortran compilers, or any
10631 other language compilers for that matter. Thus if @code{pragma_lex} is going
10632 to be called from target-specific code, it must only be done so when
10633 building the C and C++ compilers. This can be done by defining the
10634 variables @code{c_target_objs} and @code{cxx_target_objs} in the
10635 target entry in the @file{config.gcc} file. These variables should name
10636 the target-specific, language-specific object file which contains the
10637 code that uses @code{pragma_lex}. Note it will also be necessary to add a
10638 rule to the makefile fragment pointed to by @code{tmake_file} that shows
10639 how to build this object file.
10642 @defmac HANDLE_PRAGMA_PACK_WITH_EXPANSION
10643 Define this macro if macros should be expanded in the
10644 arguments of @samp{#pragma pack}.
10647 @hook TARGET_HANDLE_PRAGMA_EXTERN_PREFIX
10649 @defmac TARGET_DEFAULT_PACK_STRUCT
10650 If your target requires a structure packing default other than 0 (meaning
10651 the machine default), define this macro to the necessary value (in bytes).
10652 This must be a value that would also be valid to use with
10653 @samp{#pragma pack()} (that is, a small power of two).
10656 @defmac DOLLARS_IN_IDENTIFIERS
10657 Define this macro to control use of the character @samp{$} in
10658 identifier names for the C family of languages. 0 means @samp{$} is
10659 not allowed by default; 1 means it is allowed. 1 is the default;
10660 there is no need to define this macro in that case.
10663 @defmac NO_DOLLAR_IN_LABEL
10664 Define this macro if the assembler does not accept the character
10665 @samp{$} in label names. By default constructors and destructors in
10666 G++ have @samp{$} in the identifiers. If this macro is defined,
10667 @samp{.} is used instead.
10670 @defmac NO_DOT_IN_LABEL
10671 Define this macro if the assembler does not accept the character
10672 @samp{.} in label names. By default constructors and destructors in G++
10673 have names that use @samp{.}. If this macro is defined, these names
10674 are rewritten to avoid @samp{.}.
10677 @defmac INSN_SETS_ARE_DELAYED (@var{insn})
10678 Define this macro as a C expression that is nonzero if it is safe for the
10679 delay slot scheduler to place instructions in the delay slot of @var{insn},
10680 even if they appear to use a resource set or clobbered in @var{insn}.
10681 @var{insn} is always a @code{jump_insn} or an @code{insn}; GCC knows that
10682 every @code{call_insn} has this behavior. On machines where some @code{insn}
10683 or @code{jump_insn} is really a function call and hence has this behavior,
10684 you should define this macro.
10686 You need not define this macro if it would always return zero.
10689 @defmac INSN_REFERENCES_ARE_DELAYED (@var{insn})
10690 Define this macro as a C expression that is nonzero if it is safe for the
10691 delay slot scheduler to place instructions in the delay slot of @var{insn},
10692 even if they appear to set or clobber a resource referenced in @var{insn}.
10693 @var{insn} is always a @code{jump_insn} or an @code{insn}. On machines where
10694 some @code{insn} or @code{jump_insn} is really a function call and its operands
10695 are registers whose use is actually in the subroutine it calls, you should
10696 define this macro. Doing so allows the delay slot scheduler to move
10697 instructions which copy arguments into the argument registers into the delay
10698 slot of @var{insn}.
10700 You need not define this macro if it would always return zero.
10703 @defmac MULTIPLE_SYMBOL_SPACES
10704 Define this macro as a C expression that is nonzero if, in some cases,
10705 global symbols from one translation unit may not be bound to undefined
10706 symbols in another translation unit without user intervention. For
10707 instance, under Microsoft Windows symbols must be explicitly imported
10708 from shared libraries (DLLs).
10710 You need not define this macro if it would always evaluate to zero.
10713 @hook TARGET_MD_ASM_CLOBBERS
10714 This target hook should add to @var{clobbers} @code{STRING_CST} trees for
10715 any hard regs the port wishes to automatically clobber for an asm.
10716 It should return the result of the last @code{tree_cons} used to add a
10717 clobber. The @var{outputs}, @var{inputs} and @var{clobber} lists are the
10718 corresponding parameters to the asm and may be inspected to avoid
10719 clobbering a register that is an input or output of the asm. You can use
10720 @code{tree_overlaps_hard_reg_set}, declared in @file{tree.h}, to test
10721 for overlap with regards to asm-declared registers.
10724 @defmac MATH_LIBRARY
10725 Define this macro as a C string constant for the linker argument to link
10726 in the system math library, minus the initial @samp{"-l"}, or
10727 @samp{""} if the target does not have a
10728 separate math library.
10730 You need only define this macro if the default of @samp{"m"} is wrong.
10733 @defmac LIBRARY_PATH_ENV
10734 Define this macro as a C string constant for the environment variable that
10735 specifies where the linker should look for libraries.
10737 You need only define this macro if the default of @samp{"LIBRARY_PATH"}
10741 @defmac TARGET_POSIX_IO
10742 Define this macro if the target supports the following POSIX@ file
10743 functions, access, mkdir and file locking with fcntl / F_SETLKW@.
10744 Defining @code{TARGET_POSIX_IO} will enable the test coverage code
10745 to use file locking when exiting a program, which avoids race conditions
10746 if the program has forked. It will also create directories at run-time
10747 for cross-profiling.
10750 @defmac MAX_CONDITIONAL_EXECUTE
10752 A C expression for the maximum number of instructions to execute via
10753 conditional execution instructions instead of a branch. A value of
10754 @code{BRANCH_COST}+1 is the default if the machine does not use cc0, and
10755 1 if it does use cc0.
10758 @defmac IFCVT_MODIFY_TESTS (@var{ce_info}, @var{true_expr}, @var{false_expr})
10759 Used if the target needs to perform machine-dependent modifications on the
10760 conditionals used for turning basic blocks into conditionally executed code.
10761 @var{ce_info} points to a data structure, @code{struct ce_if_block}, which
10762 contains information about the currently processed blocks. @var{true_expr}
10763 and @var{false_expr} are the tests that are used for converting the
10764 then-block and the else-block, respectively. Set either @var{true_expr} or
10765 @var{false_expr} to a null pointer if the tests cannot be converted.
10768 @defmac IFCVT_MODIFY_MULTIPLE_TESTS (@var{ce_info}, @var{bb}, @var{true_expr}, @var{false_expr})
10769 Like @code{IFCVT_MODIFY_TESTS}, but used when converting more complicated
10770 if-statements into conditions combined by @code{and} and @code{or} operations.
10771 @var{bb} contains the basic block that contains the test that is currently
10772 being processed and about to be turned into a condition.
10775 @defmac IFCVT_MODIFY_INSN (@var{ce_info}, @var{pattern}, @var{insn})
10776 A C expression to modify the @var{PATTERN} of an @var{INSN} that is to
10777 be converted to conditional execution format. @var{ce_info} points to
10778 a data structure, @code{struct ce_if_block}, which contains information
10779 about the currently processed blocks.
10782 @defmac IFCVT_MODIFY_FINAL (@var{ce_info})
10783 A C expression to perform any final machine dependent modifications in
10784 converting code to conditional execution. The involved basic blocks
10785 can be found in the @code{struct ce_if_block} structure that is pointed
10786 to by @var{ce_info}.
10789 @defmac IFCVT_MODIFY_CANCEL (@var{ce_info})
10790 A C expression to cancel any machine dependent modifications in
10791 converting code to conditional execution. The involved basic blocks
10792 can be found in the @code{struct ce_if_block} structure that is pointed
10793 to by @var{ce_info}.
10796 @defmac IFCVT_INIT_EXTRA_FIELDS (@var{ce_info})
10797 A C expression to initialize any extra fields in a @code{struct ce_if_block}
10798 structure, which are defined by the @code{IFCVT_EXTRA_FIELDS} macro.
10801 @defmac IFCVT_EXTRA_FIELDS
10802 If defined, it should expand to a set of field declarations that will be
10803 added to the @code{struct ce_if_block} structure. These should be initialized
10804 by the @code{IFCVT_INIT_EXTRA_FIELDS} macro.
10807 @hook TARGET_MACHINE_DEPENDENT_REORG
10808 If non-null, this hook performs a target-specific pass over the
10809 instruction stream. The compiler will run it at all optimization levels,
10810 just before the point at which it normally does delayed-branch scheduling.
10812 The exact purpose of the hook varies from target to target. Some use
10813 it to do transformations that are necessary for correctness, such as
10814 laying out in-function constant pools or avoiding hardware hazards.
10815 Others use it as an opportunity to do some machine-dependent optimizations.
10817 You need not implement the hook if it has nothing to do. The default
10818 definition is null.
10821 @hook TARGET_INIT_BUILTINS
10822 Define this hook if you have any machine-specific built-in functions
10823 that need to be defined. It should be a function that performs the
10826 Machine specific built-in functions can be useful to expand special machine
10827 instructions that would otherwise not normally be generated because
10828 they have no equivalent in the source language (for example, SIMD vector
10829 instructions or prefetch instructions).
10831 To create a built-in function, call the function
10832 @code{lang_hooks.builtin_function}
10833 which is defined by the language front end. You can use any type nodes set
10834 up by @code{build_common_tree_nodes} and @code{build_common_tree_nodes_2};
10835 only language front ends that use those two functions will call
10836 @samp{TARGET_INIT_BUILTINS}.
10839 @hook TARGET_BUILTIN_DECL
10840 Define this hook if you have any machine-specific built-in functions
10841 that need to be defined. It should be a function that returns the
10842 builtin function declaration for the builtin function code @var{code}.
10843 If there is no such builtin and it cannot be initialized at this time
10844 if @var{initialize_p} is true the function should return @code{NULL_TREE}.
10845 If @var{code} is out of range the function should return
10846 @code{error_mark_node}.
10849 @hook TARGET_EXPAND_BUILTIN
10851 Expand a call to a machine specific built-in function that was set up by
10852 @samp{TARGET_INIT_BUILTINS}. @var{exp} is the expression for the
10853 function call; the result should go to @var{target} if that is
10854 convenient, and have mode @var{mode} if that is convenient.
10855 @var{subtarget} may be used as the target for computing one of
10856 @var{exp}'s operands. @var{ignore} is nonzero if the value is to be
10857 ignored. This function should return the result of the call to the
10861 @hook TARGET_RESOLVE_OVERLOADED_BUILTIN
10862 Select a replacement for a machine specific built-in function that
10863 was set up by @samp{TARGET_INIT_BUILTINS}. This is done
10864 @emph{before} regular type checking, and so allows the target to
10865 implement a crude form of function overloading. @var{fndecl} is the
10866 declaration of the built-in function. @var{arglist} is the list of
10867 arguments passed to the built-in function. The result is a
10868 complete expression that implements the operation, usually
10869 another @code{CALL_EXPR}.
10870 @var{arglist} really has type @samp{VEC(tree,gc)*}
10873 @hook TARGET_FOLD_BUILTIN
10874 Fold a call to a machine specific built-in function that was set up by
10875 @samp{TARGET_INIT_BUILTINS}. @var{fndecl} is the declaration of the
10876 built-in function. @var{n_args} is the number of arguments passed to
10877 the function; the arguments themselves are pointed to by @var{argp}.
10878 The result is another tree containing a simplified expression for the
10879 call's result. If @var{ignore} is true the value will be ignored.
10882 @hook TARGET_INVALID_WITHIN_DOLOOP
10884 Take an instruction in @var{insn} and return NULL if it is valid within a
10885 low-overhead loop, otherwise return a string explaining why doloop
10886 could not be applied.
10888 Many targets use special registers for low-overhead looping. For any
10889 instruction that clobbers these this function should return a string indicating
10890 the reason why the doloop could not be applied.
10891 By default, the RTL loop optimizer does not use a present doloop pattern for
10892 loops containing function calls or branch on table instructions.
10895 @defmac MD_CAN_REDIRECT_BRANCH (@var{branch1}, @var{branch2})
10897 Take a branch insn in @var{branch1} and another in @var{branch2}.
10898 Return true if redirecting @var{branch1} to the destination of
10899 @var{branch2} is possible.
10901 On some targets, branches may have a limited range. Optimizing the
10902 filling of delay slots can result in branches being redirected, and this
10903 may in turn cause a branch offset to overflow.
10906 @hook TARGET_COMMUTATIVE_P
10907 This target hook returns @code{true} if @var{x} is considered to be commutative.
10908 Usually, this is just COMMUTATIVE_P (@var{x}), but the HP PA doesn't consider
10909 PLUS to be commutative inside a MEM@. @var{outer_code} is the rtx code
10910 of the enclosing rtl, if known, otherwise it is UNKNOWN.
10913 @hook TARGET_ALLOCATE_INITIAL_VALUE
10915 When the initial value of a hard register has been copied in a pseudo
10916 register, it is often not necessary to actually allocate another register
10917 to this pseudo register, because the original hard register or a stack slot
10918 it has been saved into can be used. @code{TARGET_ALLOCATE_INITIAL_VALUE}
10919 is called at the start of register allocation once for each hard register
10920 that had its initial value copied by using
10921 @code{get_func_hard_reg_initial_val} or @code{get_hard_reg_initial_val}.
10922 Possible values are @code{NULL_RTX}, if you don't want
10923 to do any special allocation, a @code{REG} rtx---that would typically be
10924 the hard register itself, if it is known not to be clobbered---or a
10926 If you are returning a @code{MEM}, this is only a hint for the allocator;
10927 it might decide to use another register anyways.
10928 You may use @code{current_function_leaf_function} in the hook, functions
10929 that use @code{REG_N_SETS}, to determine if the hard
10930 register in question will not be clobbered.
10931 The default value of this hook is @code{NULL}, which disables any special
10935 @hook TARGET_UNSPEC_MAY_TRAP_P
10936 This target hook returns nonzero if @var{x}, an @code{unspec} or
10937 @code{unspec_volatile} operation, might cause a trap. Targets can use
10938 this hook to enhance precision of analysis for @code{unspec} and
10939 @code{unspec_volatile} operations. You may call @code{may_trap_p_1}
10940 to analyze inner elements of @var{x} in which case @var{flags} should be
10944 @hook TARGET_SET_CURRENT_FUNCTION
10945 The compiler invokes this hook whenever it changes its current function
10946 context (@code{cfun}). You can define this function if
10947 the back end needs to perform any initialization or reset actions on a
10948 per-function basis. For example, it may be used to implement function
10949 attributes that affect register usage or code generation patterns.
10950 The argument @var{decl} is the declaration for the new function context,
10951 and may be null to indicate that the compiler has left a function context
10952 and is returning to processing at the top level.
10953 The default hook function does nothing.
10955 GCC sets @code{cfun} to a dummy function context during initialization of
10956 some parts of the back end. The hook function is not invoked in this
10957 situation; you need not worry about the hook being invoked recursively,
10958 or when the back end is in a partially-initialized state.
10959 @code{cfun} might be @code{NULL} to indicate processing at top level,
10960 outside of any function scope.
10963 @defmac TARGET_OBJECT_SUFFIX
10964 Define this macro to be a C string representing the suffix for object
10965 files on your target machine. If you do not define this macro, GCC will
10966 use @samp{.o} as the suffix for object files.
10969 @defmac TARGET_EXECUTABLE_SUFFIX
10970 Define this macro to be a C string representing the suffix to be
10971 automatically added to executable files on your target machine. If you
10972 do not define this macro, GCC will use the null string as the suffix for
10976 @defmac COLLECT_EXPORT_LIST
10977 If defined, @code{collect2} will scan the individual object files
10978 specified on its command line and create an export list for the linker.
10979 Define this macro for systems like AIX, where the linker discards
10980 object files that are not referenced from @code{main} and uses export
10984 @defmac MODIFY_JNI_METHOD_CALL (@var{mdecl})
10985 Define this macro to a C expression representing a variant of the
10986 method call @var{mdecl}, if Java Native Interface (JNI) methods
10987 must be invoked differently from other methods on your target.
10988 For example, on 32-bit Microsoft Windows, JNI methods must be invoked using
10989 the @code{stdcall} calling convention and this macro is then
10990 defined as this expression:
10993 build_type_attribute_variant (@var{mdecl},
10995 (get_identifier ("stdcall"),
11000 @hook TARGET_CANNOT_MODIFY_JUMPS_P
11001 This target hook returns @code{true} past the point in which new jump
11002 instructions could be created. On machines that require a register for
11003 every jump such as the SHmedia ISA of SH5, this point would typically be
11004 reload, so this target hook should be defined to a function such as:
11008 cannot_modify_jumps_past_reload_p ()
11010 return (reload_completed || reload_in_progress);
11015 @hook TARGET_BRANCH_TARGET_REGISTER_CLASS
11016 This target hook returns a register class for which branch target register
11017 optimizations should be applied. All registers in this class should be
11018 usable interchangeably. After reload, registers in this class will be
11019 re-allocated and loads will be hoisted out of loops and be subjected
11020 to inter-block scheduling.
11023 @hook TARGET_BRANCH_TARGET_REGISTER_CALLEE_SAVED
11024 Branch target register optimization will by default exclude callee-saved
11026 that are not already live during the current function; if this target hook
11027 returns true, they will be included. The target code must than make sure
11028 that all target registers in the class returned by
11029 @samp{TARGET_BRANCH_TARGET_REGISTER_CLASS} that might need saving are
11030 saved. @var{after_prologue_epilogue_gen} indicates if prologues and
11031 epilogues have already been generated. Note, even if you only return
11032 true when @var{after_prologue_epilogue_gen} is false, you still are likely
11033 to have to make special provisions in @code{INITIAL_ELIMINATION_OFFSET}
11034 to reserve space for caller-saved target registers.
11037 @hook TARGET_HAVE_CONDITIONAL_EXECUTION
11038 This target hook returns true if the target supports conditional execution.
11039 This target hook is required only when the target has several different
11040 modes and they have different conditional execution capability, such as ARM.
11043 @hook TARGET_LOOP_UNROLL_ADJUST
11044 This target hook returns a new value for the number of times @var{loop}
11045 should be unrolled. The parameter @var{nunroll} is the number of times
11046 the loop is to be unrolled. The parameter @var{loop} is a pointer to
11047 the loop, which is going to be checked for unrolling. This target hook
11048 is required only when the target has special constraints like maximum
11049 number of memory accesses.
11052 @defmac POWI_MAX_MULTS
11053 If defined, this macro is interpreted as a signed integer C expression
11054 that specifies the maximum number of floating point multiplications
11055 that should be emitted when expanding exponentiation by an integer
11056 constant inline. When this value is defined, exponentiation requiring
11057 more than this number of multiplications is implemented by calling the
11058 system library's @code{pow}, @code{powf} or @code{powl} routines.
11059 The default value places no upper bound on the multiplication count.
11062 @deftypefn Macro void TARGET_EXTRA_INCLUDES (const char *@var{sysroot}, const char *@var{iprefix}, int @var{stdinc})
11063 This target hook should register any extra include files for the
11064 target. The parameter @var{stdinc} indicates if normal include files
11065 are present. The parameter @var{sysroot} is the system root directory.
11066 The parameter @var{iprefix} is the prefix for the gcc directory.
11069 @deftypefn Macro void TARGET_EXTRA_PRE_INCLUDES (const char *@var{sysroot}, const char *@var{iprefix}, int @var{stdinc})
11070 This target hook should register any extra include files for the
11071 target before any standard headers. The parameter @var{stdinc}
11072 indicates if normal include files are present. The parameter
11073 @var{sysroot} is the system root directory. The parameter
11074 @var{iprefix} is the prefix for the gcc directory.
11077 @deftypefn Macro void TARGET_OPTF (char *@var{path})
11078 This target hook should register special include paths for the target.
11079 The parameter @var{path} is the include to register. On Darwin
11080 systems, this is used for Framework includes, which have semantics
11081 that are different from @option{-I}.
11084 @defmac bool TARGET_USE_LOCAL_THUNK_ALIAS_P (tree @var{fndecl})
11085 This target macro returns @code{true} if it is safe to use a local alias
11086 for a virtual function @var{fndecl} when constructing thunks,
11087 @code{false} otherwise. By default, the macro returns @code{true} for all
11088 functions, if a target supports aliases (i.e.@: defines
11089 @code{ASM_OUTPUT_DEF}), @code{false} otherwise,
11092 @defmac TARGET_FORMAT_TYPES
11093 If defined, this macro is the name of a global variable containing
11094 target-specific format checking information for the @option{-Wformat}
11095 option. The default is to have no target-specific format checks.
11098 @defmac TARGET_N_FORMAT_TYPES
11099 If defined, this macro is the number of entries in
11100 @code{TARGET_FORMAT_TYPES}.
11103 @defmac TARGET_OVERRIDES_FORMAT_ATTRIBUTES
11104 If defined, this macro is the name of a global variable containing
11105 target-specific format overrides for the @option{-Wformat} option. The
11106 default is to have no target-specific format overrides. If defined,
11107 @code{TARGET_FORMAT_TYPES} must be defined, too.
11110 @defmac TARGET_OVERRIDES_FORMAT_ATTRIBUTES_COUNT
11111 If defined, this macro specifies the number of entries in
11112 @code{TARGET_OVERRIDES_FORMAT_ATTRIBUTES}.
11115 @defmac TARGET_OVERRIDES_FORMAT_INIT
11116 If defined, this macro specifies the optional initialization
11117 routine for target specific customizations of the system printf
11118 and scanf formatter settings.
11121 @hook TARGET_RELAXED_ORDERING
11122 If set to @code{true}, means that the target's memory model does not
11123 guarantee that loads which do not depend on one another will access
11124 main memory in the order of the instruction stream; if ordering is
11125 important, an explicit memory barrier must be used. This is true of
11126 many recent processors which implement a policy of ``relaxed,''
11127 ``weak,'' or ``release'' memory consistency, such as Alpha, PowerPC,
11128 and ia64. The default is @code{false}.
11131 @hook TARGET_INVALID_ARG_FOR_UNPROTOTYPED_FN
11132 If defined, this macro returns the diagnostic message when it is
11133 illegal to pass argument @var{val} to function @var{funcdecl}
11134 with prototype @var{typelist}.
11137 @hook TARGET_INVALID_CONVERSION
11138 If defined, this macro returns the diagnostic message when it is
11139 invalid to convert from @var{fromtype} to @var{totype}, or @code{NULL}
11140 if validity should be determined by the front end.
11143 @hook TARGET_INVALID_UNARY_OP
11144 If defined, this macro returns the diagnostic message when it is
11145 invalid to apply operation @var{op} (where unary plus is denoted by
11146 @code{CONVERT_EXPR}) to an operand of type @var{type}, or @code{NULL}
11147 if validity should be determined by the front end.
11150 @hook TARGET_INVALID_BINARY_OP
11151 If defined, this macro returns the diagnostic message when it is
11152 invalid to apply operation @var{op} to operands of types @var{type1}
11153 and @var{type2}, or @code{NULL} if validity should be determined by
11157 @hook TARGET_INVALID_PARAMETER_TYPE
11158 If defined, this macro returns the diagnostic message when it is
11159 invalid for functions to include parameters of type @var{type},
11160 or @code{NULL} if validity should be determined by
11161 the front end. This is currently used only by the C and C++ front ends.
11164 @hook TARGET_INVALID_RETURN_TYPE
11165 If defined, this macro returns the diagnostic message when it is
11166 invalid for functions to have return type @var{type},
11167 or @code{NULL} if validity should be determined by
11168 the front end. This is currently used only by the C and C++ front ends.
11171 @hook TARGET_PROMOTED_TYPE
11172 If defined, this target hook returns the type to which values of
11173 @var{type} should be promoted when they appear in expressions,
11174 analogous to the integer promotions, or @code{NULL_TREE} to use the
11175 front end's normal promotion rules. This hook is useful when there are
11176 target-specific types with special promotion rules.
11177 This is currently used only by the C and C++ front ends.
11180 @hook TARGET_CONVERT_TO_TYPE
11181 If defined, this hook returns the result of converting @var{expr} to
11182 @var{type}. It should return the converted expression,
11183 or @code{NULL_TREE} to apply the front end's normal conversion rules.
11184 This hook is useful when there are target-specific types with special
11186 This is currently used only by the C and C++ front ends.
11189 @defmac TARGET_USE_JCR_SECTION
11190 This macro determines whether to use the JCR section to register Java
11191 classes. By default, TARGET_USE_JCR_SECTION is defined to 1 if both
11192 SUPPORTS_WEAK and TARGET_HAVE_NAMED_SECTIONS are true, else 0.
11196 This macro determines the size of the objective C jump buffer for the
11197 NeXT runtime. By default, OBJC_JBLEN is defined to an innocuous value.
11200 @defmac LIBGCC2_UNWIND_ATTRIBUTE
11201 Define this macro if any target-specific attributes need to be attached
11202 to the functions in @file{libgcc} that provide low-level support for
11203 call stack unwinding. It is used in declarations in @file{unwind-generic.h}
11204 and the associated definitions of those functions.
11207 @hook TARGET_UPDATE_STACK_BOUNDARY
11208 Define this macro to update the current function stack boundary if
11212 @hook TARGET_GET_DRAP_RTX
11213 This hook should return an rtx for Dynamic Realign Argument Pointer (DRAP) if a
11214 different argument pointer register is needed to access the function's
11215 argument list due to stack realignment. Return @code{NULL} if no DRAP
11219 @hook TARGET_ALLOCATE_STACK_SLOTS_FOR_ARGS
11220 When optimization is disabled, this hook indicates whether or not
11221 arguments should be allocated to stack slots. Normally, GCC allocates
11222 stacks slots for arguments when not optimizing in order to make
11223 debugging easier. However, when a function is declared with
11224 @code{__attribute__((naked))}, there is no stack frame, and the compiler
11225 cannot safely move arguments from the registers in which they are passed
11226 to the stack. Therefore, this hook should return true in general, but
11227 false for naked functions. The default implementation always returns true.
11230 @hook TARGET_CONST_ANCHOR
11231 On some architectures it can take multiple instructions to synthesize
11232 a constant. If there is another constant already in a register that
11233 is close enough in value then it is preferable that the new constant
11234 is computed from this register using immediate addition or
11235 subtraction. We accomplish this through CSE. Besides the value of
11236 the constant we also add a lower and an upper constant anchor to the
11237 available expressions. These are then queried when encountering new
11238 constants. The anchors are computed by rounding the constant up and
11239 down to a multiple of the value of @code{TARGET_CONST_ANCHOR}.
11240 @code{TARGET_CONST_ANCHOR} should be the maximum positive value
11241 accepted by immediate-add plus one. We currently assume that the
11242 value of @code{TARGET_CONST_ANCHOR} is a power of 2. For example, on
11243 MIPS, where add-immediate takes a 16-bit signed value,
11244 @code{TARGET_CONST_ANCHOR} is set to @samp{0x8000}. The default value
11245 is zero, which disables this optimization. @end deftypevr