Mercurial > hg > CbC > CbC_gcc
comparison gcc/doc/tm.texi.in @ 68:561a7518be6b
update gcc-4.6
author | Nobuyasu Oshiro <dimolto@cr.ie.u-ryukyu.ac.jp> |
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date | Sun, 21 Aug 2011 07:07:55 +0900 |
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children | 04ced10e8804 |
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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. | |
6 | |
7 @node Target Macros | |
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 | |
13 | |
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. | |
27 | |
28 @menu | |
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. | |
60 @end menu | |
61 | |
62 @node Target Structure | |
63 @section The Global @code{targetm} Variable | |
64 @cindex target hooks | |
65 @cindex target functions | |
66 | |
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: | |
75 @smallexample | |
76 #include "target.h" | |
77 #include "target-def.h" | |
78 | |
79 /* @r{Initialize the GCC target structure.} */ | |
80 | |
81 #undef TARGET_COMP_TYPE_ATTRIBUTES | |
82 #define TARGET_COMP_TYPE_ATTRIBUTES @var{machine}_comp_type_attributes | |
83 | |
84 struct gcc_target targetm = TARGET_INITIALIZER; | |
85 @end smallexample | |
86 @end deftypevar | |
87 | |
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. | |
93 | |
94 @node Driver | |
95 @section Controlling the Compilation Driver, @file{gcc} | |
96 @cindex driver | |
97 @cindex controlling the compilation driver | |
98 | |
99 @c prevent bad page break with this line | |
100 You can control the compilation driver. | |
101 | |
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. | |
105 | |
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. | |
112 | |
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. | |
116 | |
117 Do not define this macro if it does not need to do anything. | |
118 @end defmac | |
119 | |
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. | |
125 | |
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. | |
131 | |
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}. | |
135 | |
136 Do not define this macro if it does not need to do anything. | |
137 @end defmac | |
138 | |
139 @defmac CPP_SPEC | |
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@. | |
143 | |
144 Do not define this macro if it does not need to do anything. | |
145 @end defmac | |
146 | |
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. | |
151 @end defmac | |
152 | |
153 @defmac CC1_SPEC | |
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 | |
156 front ends. | |
157 It can also specify how to translate options you give to GCC into options | |
158 for GCC to pass to front ends. | |
159 | |
160 Do not define this macro if it does not need to do anything. | |
161 @end defmac | |
162 | |
163 @defmac CC1PLUS_SPEC | |
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}. | |
167 | |
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@. | |
172 @end defmac | |
173 | |
174 @defmac ASM_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. | |
179 | |
180 Do not define this macro if it does not need to do anything. | |
181 @end defmac | |
182 | |
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 | |
187 an example of this. | |
188 | |
189 Do not define this macro if it does not need to do anything. | |
190 @end defmac | |
191 | |
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. | |
198 | |
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. | |
203 @end defmac | |
204 | |
205 @defmac LINK_SPEC | |
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. | |
209 | |
210 Do not define this macro if it does not need to do anything. | |
211 @end defmac | |
212 | |
213 @defmac LIB_SPEC | |
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. | |
217 | |
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}. | |
220 @end defmac | |
221 | |
222 @defmac LIBGCC_SPEC | |
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}. | |
227 | |
228 If this macro is not defined, the GCC driver provides a default that | |
229 passes the string @option{-lgcc} to the linker. | |
230 @end defmac | |
231 | |
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. | |
242 @end defmac | |
243 | |
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}. | |
250 @end defmac | |
251 | |
252 @defmac LINK_EH_SPEC | |
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}. | |
257 @end defmac | |
258 | |
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. | |
263 | |
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}. | |
266 @end defmac | |
267 | |
268 @defmac ENDFILE_SPEC | |
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. | |
272 | |
273 Do not define this macro if it does not need to do anything. | |
274 @end defmac | |
275 | |
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}. | |
284 @end defmac | |
285 | |
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. | |
290 @end defmac | |
291 | |
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. | |
297 @end defmac | |
298 | |
299 @defmac EXTRA_SPECS | |
300 Define this macro to provide additional specifications to put in the | |
301 @file{specs} file that can be used in various specifications like | |
302 @code{CC1_SPEC}. | |
303 | |
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. | |
307 | |
308 Do not define this macro if it does not need to do anything. | |
309 | |
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 | |
313 these definitions. | |
314 | |
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 | |
318 used. | |
319 | |
320 The @file{config/rs6000/rs6000.h} target file defines: | |
321 | |
322 @smallexample | |
323 #define EXTRA_SPECS \ | |
324 @{ "cpp_sysv_default", CPP_SYSV_DEFAULT @}, | |
325 | |
326 #define CPP_SYS_DEFAULT "" | |
327 @end smallexample | |
328 | |
329 The @file{config/rs6000/sysv.h} target file defines: | |
330 @smallexample | |
331 #undef CPP_SPEC | |
332 #define CPP_SPEC \ | |
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@}" | |
337 | |
338 #undef CPP_SYSV_DEFAULT | |
339 #define CPP_SYSV_DEFAULT "-D_CALL_SYSV" | |
340 @end smallexample | |
341 | |
342 while the @file{config/rs6000/eabiaix.h} target file defines | |
343 @code{CPP_SYSV_DEFAULT} as: | |
344 | |
345 @smallexample | |
346 #undef CPP_SYSV_DEFAULT | |
347 #define CPP_SYSV_DEFAULT "-D_CALL_AIX" | |
348 @end smallexample | |
349 @end defmac | |
350 | |
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. | |
355 @end defmac | |
356 | |
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}. | |
360 @end defmac | |
361 | |
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. | |
370 @end defmac | |
371 | |
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. | |
376 @end defmac | |
377 | |
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}. | |
383 | |
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}. | |
388 @end defmac | |
389 | |
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. | |
394 @end defmac | |
395 | |
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}. | |
402 @end defmac | |
403 | |
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. | |
410 @end defmac | |
411 | |
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. | |
418 @end defmac | |
419 | |
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. | |
426 @end defmac | |
427 | |
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. | |
432 @end defmac | |
433 | |
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 | |
437 cross compiler. | |
438 @end defmac | |
439 | |
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. | |
445 @end defmac | |
446 | |
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. | |
452 | |
453 Cross compilers do not search either @file{/usr/local/include} or its | |
454 replacement. | |
455 @end defmac | |
456 | |
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. | |
462 | |
463 Cross compilers do not use this macro and do not search the directory | |
464 specified. | |
465 @end defmac | |
466 | |
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. | |
471 | |
472 Cross compilers ignore this macro and do not search either | |
473 @file{/usr/include} or its replacement. | |
474 @end defmac | |
475 | |
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. | |
480 @end defmac | |
481 | |
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. | |
491 | |
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. | |
499 | |
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}. | |
504 | |
505 For example, here is the definition used for VAX/VMS: | |
506 | |
507 @smallexample | |
508 #define INCLUDE_DEFAULTS \ | |
509 @{ \ | |
510 @{ "GNU_GXX_INCLUDE:", "G++", 1, 1@}, \ | |
511 @{ "GNU_CC_INCLUDE:", "GCC", 0, 0@}, \ | |
512 @{ "SYS$SYSROOT:[SYSLIB.]", 0, 0, 0@}, \ | |
513 @{ ".", 0, 0, 0@}, \ | |
514 @{ 0, 0, 0, 0@} \ | |
515 @} | |
516 @end smallexample | |
517 @end defmac | |
518 | |
519 Here is the order of prefixes tried for exec files: | |
520 | |
521 @enumerate | |
522 @item | |
523 Any prefixes specified by the user with @option{-B}. | |
524 | |
525 @item | |
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. | |
529 | |
530 @item | |
531 The directories specified by the environment variable @code{COMPILER_PATH}. | |
532 | |
533 @item | |
534 The macro @code{STANDARD_EXEC_PREFIX}, if the compiler has been installed | |
535 in the configured-time @var{prefix}. | |
536 | |
537 @item | |
538 The location @file{/usr/libexec/gcc/}, but only if this is a native compiler. | |
539 | |
540 @item | |
541 The location @file{/usr/lib/gcc/}, but only if this is a native compiler. | |
542 | |
543 @item | |
544 The macro @code{MD_EXEC_PREFIX}, if defined, but only if this is a native | |
545 compiler. | |
546 @end enumerate | |
547 | |
548 Here is the order of prefixes tried for startfiles: | |
549 | |
550 @enumerate | |
551 @item | |
552 Any prefixes specified by the user with @option{-B}. | |
553 | |
554 @item | |
555 The environment variable @code{GCC_EXEC_PREFIX} or its automatically determined | |
556 value based on the installed toolchain location. | |
557 | |
558 @item | |
559 The directories specified by the environment variable @code{LIBRARY_PATH} | |
560 (or port-specific name; native only, cross compilers do not use this). | |
561 | |
562 @item | |
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. | |
565 | |
566 @item | |
567 The location @file{/usr/lib/gcc/}, but only if this is a native compiler. | |
568 | |
569 @item | |
570 The macro @code{MD_EXEC_PREFIX}, if defined, but only if this is a native | |
571 compiler. | |
572 | |
573 @item | |
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. | |
576 | |
577 @item | |
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. | |
580 | |
581 @item | |
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. | |
585 | |
586 @item | |
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 | |
589 @file{/lib/}. | |
590 | |
591 @item | |
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 | |
594 @file{/usr/lib/}. | |
595 @end enumerate | |
596 | |
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 | |
602 | |
603 @c prevent bad page break with this line | |
604 Here are run-time target specifications. | |
605 | |
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 | |
613 results freely. | |
614 | |
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. | |
619 | |
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}. | |
630 | |
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 | |
639 preprocessing. | |
640 @end defmac | |
641 | |
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. | |
645 @end defmac | |
646 | |
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 | |
651 it yourself. | |
652 @end defmac | |
653 | |
654 @deftypevar {extern int} target_flags | |
655 This variable is declared in @file{options.h}, which is included before | |
656 any target-specific headers. | |
657 @end deftypevar | |
658 | |
659 @hook TARGET_DEFAULT_TARGET_FLAGS | |
660 This variable specifies the initial value of @code{target_flags}. | |
661 Its default setting is 0. | |
662 @end deftypevr | |
663 | |
664 @cindex optional hardware or system features | |
665 @cindex features, optional, in system conventions | |
666 | |
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. | |
673 | |
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. | |
682 @end deftypefn | |
683 | |
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. | |
691 | |
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. | |
696 @end deftypefn | |
697 | |
698 @hook TARGET_OBJC_CONSTRUCT_STRING_OBJECT | |
699 | |
700 @hook TARGET_STRING_OBJECT_REF_TYPE_P | |
701 | |
702 @hook TARGET_CHECK_STRING_OBJECT_FORMAT_ARG | |
703 | |
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: | |
708 | |
709 @smallexample | |
710 #ifdef MOTOROLA | |
711 #define TARGET_VERSION \ | |
712 fprintf (stderr, " (68k, Motorola syntax)"); | |
713 #else | |
714 #define TARGET_VERSION \ | |
715 fprintf (stderr, " (68k, MIT syntax)"); | |
716 #endif | |
717 @end smallexample | |
718 @end defmac | |
719 | |
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}. | |
728 @end deftypefn | |
729 | |
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 | |
735 frontends. | |
736 @end defmac | |
737 | |
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 explicitly. | |
746 | |
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. | |
750 @end deftypevr | |
751 | |
752 @hook TARGET_OPTION_INIT_STRUCT | |
753 | |
754 @hook TARGET_OPTION_DEFAULT_PARAMS | |
755 | |
756 @hook TARGET_HELP | |
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. | |
761 @end deftypefn | |
762 | |
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. | |
769 | |
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. | |
777 | |
778 Define this macro to 1 if your target needs this facility. The default | |
779 is 0. | |
780 @end defmac | |
781 | |
782 @node Per-Function Data | |
783 @section Defining data structures for per-function information. | |
784 @cindex per-function data | |
785 @cindex data structures | |
786 | |
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. | |
792 | |
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. | |
798 | |
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. | |
803 | |
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. | |
808 | |
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 | |
817 longer supported. | |
818 | |
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}. | |
824 @end defmac | |
825 | |
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. | |
832 | |
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. | |
836 @end deftypevar | |
837 | |
838 @node Storage Layout | |
839 @section Storage Layout | |
840 @cindex storage layout | |
841 | |
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}. | |
846 | |
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. | |
854 | |
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}. | |
857 @end defmac | |
858 | |
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. | |
862 @end defmac | |
863 | |
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. | |
870 @end defmac | |
871 | |
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. | |
877 | |
878 You need not define this macro if the ordering is the same as for | |
879 multi-word integers. | |
880 @end defmac | |
881 | |
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. | |
885 @end defmac | |
886 | |
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}. | |
890 @end defmac | |
891 | |
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. | |
896 @end defmac | |
897 | |
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. | |
901 @end defmac | |
902 | |
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. | |
907 @end defmac | |
908 | |
909 @defmac POINTER_SIZE | |
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}. | |
914 @end defmac | |
915 | |
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. | |
923 | |
924 You need not define this macro if the @code{ptr_mode}, @code{Pmode} | |
925 and @code{word_mode} are all the same width. | |
926 @end defmac | |
927 | |
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 | |
932 scalar type. | |
933 | |
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 | |
939 counterparts. | |
940 | |
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. | |
947 | |
948 Do not define this macro if it would never modify @var{m}. | |
949 @end defmac | |
950 | |
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 | |
956 pointer} types. | |
957 | |
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. | |
965 | |
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}. | |
969 @end deftypefn | |
970 | |
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 | |
975 size of an integer. | |
976 @end defmac | |
977 | |
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}. | |
984 @end defmac | |
985 | |
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}. | |
992 @end defmac | |
993 | |
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}. | |
998 @end defmac | |
999 | |
1000 @defmac FUNCTION_BOUNDARY | |
1001 Alignment required for a function entry point, in bits. | |
1002 @end defmac | |
1003 | |
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. | |
1008 @end defmac | |
1009 | |
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}. | |
1013 @end defmac | |
1014 | |
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}. | |
1018 @end defmac | |
1019 | |
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. | |
1025 @end defmac | |
1026 | |
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. | |
1032 @end defmac | |
1033 | |
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. | |
1041 @end defmac | |
1042 | |
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. | |
1046 | |
1047 If not defined, the default value is @code{STACK_BOUNDARY}. | |
1048 | |
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. | |
1053 @end defmac | |
1054 | |
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}. | |
1060 | |
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. | |
1066 @end defmac | |
1067 | |
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. | |
1073 | |
1074 If this macro is not defined, then @var{basic-align} is used. | |
1075 | |
1076 @findex strcpy | |
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. | |
1081 @end defmac | |
1082 | |
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 | |
1088 align the object. | |
1089 | |
1090 If this macro is not defined, then @var{basic-align} is used. | |
1091 | |
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. | |
1095 @end defmac | |
1096 | |
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. | |
1102 | |
1103 If this macro is not defined, then @var{basic-align} is used. | |
1104 | |
1105 One use of this macro is to increase alignment of medium-size data to | |
1106 make it all fit in fewer cache lines. | |
1107 | |
1108 If the value of this macro has a type, it should be an unsigned type. | |
1109 @end defmac | |
1110 | |
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 | |
1116 align the slot. | |
1117 | |
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 | |
1120 be used. | |
1121 | |
1122 This macro is to set alignment of stack slot to the maximum alignment | |
1123 of all possible modes which the slot may have. | |
1124 | |
1125 If the value of this macro has a type, it should be an unsigned type. | |
1126 @end defmac | |
1127 | |
1128 @defmac LOCAL_DECL_ALIGNMENT (@var{decl}) | |
1129 If defined, a C expression to compute the alignment for a local | |
1130 variable @var{decl}. | |
1131 | |
1132 If this macro is not defined, then | |
1133 @code{LOCAL_ALIGNMENT (TREE_TYPE (@var{decl}), DECL_ALIGN (@var{decl}))} | |
1134 is used. | |
1135 | |
1136 One use of this macro is to increase alignment of medium-size data to | |
1137 make it all fit in fewer cache lines. | |
1138 | |
1139 If the value of this macro has a type, it should be an unsigned type. | |
1140 @end defmac | |
1141 | |
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}. | |
1146 | |
1147 If this macro is not defined, then @var{align} will be used. | |
1148 @end defmac | |
1149 | |
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;}. | |
1153 | |
1154 If @code{PCC_BITFIELD_TYPE_MATTERS} is true, it overrides this macro. | |
1155 @end defmac | |
1156 | |
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. | |
1160 | |
1161 If you do not define this macro, the default is the same as | |
1162 @code{BITS_PER_UNIT}. | |
1163 @end defmac | |
1164 | |
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. | |
1169 @end defmac | |
1170 | |
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. | |
1174 | |
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. | |
1180 | |
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.) | |
1185 | |
1186 An unnamed bit-field will not affect the alignment of the containing | |
1187 structure. | |
1188 | |
1189 If the macro is defined, its definition should be a C expression; | |
1190 a nonzero value for the expression enables this behavior. | |
1191 | |
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. | |
1196 | |
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. | |
1200 | |
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. | |
1204 | |
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: | |
1208 | |
1209 @smallexample | |
1210 struct foo1 | |
1211 @{ | |
1212 char x; | |
1213 char :0; | |
1214 char y; | |
1215 @}; | |
1216 | |
1217 struct foo2 | |
1218 @{ | |
1219 char x; | |
1220 int :0; | |
1221 char y; | |
1222 @}; | |
1223 | |
1224 main () | |
1225 @{ | |
1226 printf ("Size of foo1 is %d\n", | |
1227 sizeof (struct foo1)); | |
1228 printf ("Size of foo2 is %d\n", | |
1229 sizeof (struct foo2)); | |
1230 exit (0); | |
1231 @} | |
1232 @end smallexample | |
1233 | |
1234 If this prints 2 and 5, then the compiler's behavior is what you would | |
1235 get from @code{PCC_BITFIELD_TYPE_MATTERS}. | |
1236 @end defmac | |
1237 | |
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. | |
1241 @end defmac | |
1242 | |
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. | |
1248 @end deftypefn | |
1249 | |
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. | |
1254 | |
1255 The default is @code{!TARGET_STRICT_ALIGN}. | |
1256 @end deftypefn | |
1257 | |
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 | |
1260 @code{BLKMODE}. | |
1261 | |
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. | |
1266 | |
1267 Normally, this is not needed. | |
1268 @end defmac | |
1269 | |
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 | |
1274 @var{specified}. | |
1275 | |
1276 The default is to use @var{specified} if it is larger; otherwise, use | |
1277 the smaller of @var{computed} and @code{BIGGEST_ALIGNMENT} | |
1278 @end defmac | |
1279 | |
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. | |
1286 @end defmac | |
1287 | |
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. | |
1295 | |
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 | |
1299 64-bit mode. | |
1300 @end defmac | |
1301 | |
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}). | |
1306 | |
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. | |
1310 @end defmac | |
1311 | |
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 | |
1316 targets. | |
1317 @end deftypefn | |
1318 | |
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 | |
1323 targets. | |
1324 @end deftypefn | |
1325 | |
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}. | |
1329 @end deftypefn | |
1330 | |
1331 @defmac ROUND_TOWARDS_ZERO | |
1332 If defined, this macro should be true if the prevailing rounding | |
1333 mode is towards zero. | |
1334 | |
1335 Defining this macro only affects the way @file{libgcc.a} emulates | |
1336 floating-point arithmetic. | |
1337 | |
1338 Not defining this macro is equivalent to returning zero. | |
1339 @end defmac | |
1340 | |
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. | |
1345 | |
1346 Defining this macro only affects the way @file{libgcc.a} emulates | |
1347 floating-point arithmetic. | |
1348 | |
1349 The default definition of this macro returns false for all sizes. | |
1350 @end defmac | |
1351 | |
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. | |
1364 | |
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. | |
1372 | |
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. | |
1378 @end deftypefn | |
1379 | |
1380 @hook TARGET_DECIMAL_FLOAT_SUPPORTED_P | |
1381 Returns true if the target supports decimal floating point. | |
1382 @end deftypefn | |
1383 | |
1384 @hook TARGET_FIXED_POINT_SUPPORTED_P | |
1385 Returns true if the target supports fixed-point arithmetic. | |
1386 @end deftypefn | |
1387 | |
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 | |
1394 usage. | |
1395 @end deftypefn | |
1396 | |
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. | |
1400 @end deftypefn | |
1401 | |
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 | |
1411 string constant. | |
1412 | |
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. | |
1425 | |
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} | |
1429 before mangling. | |
1430 | |
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 | |
1433 types. | |
1434 @end deftypefn | |
1435 | |
1436 @node Type Layout | |
1437 @section Layout of Source Language Data Types | |
1438 | |
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. | |
1443 | |
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. | |
1447 @end defmac | |
1448 | |
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 | |
1453 unit.) | |
1454 @end defmac | |
1455 | |
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. | |
1459 @end defmac | |
1460 | |
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}. | |
1467 @end defmac | |
1468 | |
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. | |
1474 @end defmac | |
1475 | |
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}. | |
1480 @end defmac | |
1481 | |
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}. | |
1486 @end defmac | |
1487 | |
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. | |
1491 @end defmac | |
1492 | |
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 | |
1496 words. | |
1497 @end defmac | |
1498 | |
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 | |
1502 words. | |
1503 @end defmac | |
1504 | |
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}. | |
1509 @end defmac | |
1510 | |
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}. | |
1515 @end defmac | |
1516 | |
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}. | |
1521 @end defmac | |
1522 | |
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}. | |
1527 @end defmac | |
1528 | |
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}. | |
1533 @end defmac | |
1534 | |
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}. | |
1539 @end defmac | |
1540 | |
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}. | |
1545 @end defmac | |
1546 | |
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}. | |
1551 @end defmac | |
1552 | |
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}. | |
1558 @end defmac | |
1559 | |
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, | |
1566 otherwise it is 0. | |
1567 @end defmac | |
1568 | |
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. | |
1574 @end defmac | |
1575 | |
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. | |
1581 @end defmac | |
1582 | |
1583 @defmac SF_SIZE | |
1584 @defmacx DF_SIZE | |
1585 @defmacx XF_SIZE | |
1586 @defmacx TF_SIZE | |
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. | |
1595 @end defmac | |
1596 | |
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. | |
1602 @end defmac | |
1603 | |
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} | |
1609 is the default. | |
1610 @end defmac | |
1611 | |
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}. | |
1617 @end defmac | |
1618 | |
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}. | |
1624 | |
1625 The default is to return false. | |
1626 @end deftypefn | |
1627 | |
1628 @defmac SIZE_TYPE | |
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. | |
1632 | |
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 | |
1639 crash on startup. | |
1640 | |
1641 If you don't define this macro, the default is @code{"long unsigned | |
1642 int"}. | |
1643 @end defmac | |
1644 | |
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. | |
1650 | |
1651 If you don't define this macro, the default is @code{"long int"}. | |
1652 @end defmac | |
1653 | |
1654 @defmac WCHAR_TYPE | |
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 | |
1658 information. | |
1659 | |
1660 If you don't define this macro, the default is @code{"int"}. | |
1661 @end defmac | |
1662 | |
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 | |
1666 @code{WCHAR_TYPE}. | |
1667 @end defmac | |
1668 | |
1669 @defmac WINT_TYPE | |
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 | |
1674 information. | |
1675 | |
1676 If you don't define this macro, the default is @code{"unsigned int"}. | |
1677 @end defmac | |
1678 | |
1679 @defmac INTMAX_TYPE | |
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. | |
1684 | |
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}. | |
1688 @end defmac | |
1689 | |
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. | |
1695 | |
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 | |
1699 int}. | |
1700 @end defmac | |
1701 | |
1702 @defmac SIG_ATOMIC_TYPE | |
1703 @defmacx INT8_TYPE | |
1704 @defmacx INT16_TYPE | |
1705 @defmacx INT32_TYPE | |
1706 @defmacx INT64_TYPE | |
1707 @defmacx UINT8_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. | |
1739 | |
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. | |
1745 @end defmac | |
1746 | |
1747 @defmac TARGET_PTRMEMFUNC_VBIT_LOCATION | |
1748 The C++ compiler represents a pointer-to-member-function with a struct | |
1749 that looks like: | |
1750 | |
1751 @smallexample | |
1752 struct @{ | |
1753 union @{ | |
1754 void (*fn)(); | |
1755 ptrdiff_t vtable_index; | |
1756 @}; | |
1757 ptrdiff_t delta; | |
1758 @}; | |
1759 @end smallexample | |
1760 | |
1761 @noindent | |
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. | |
1770 | |
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}. | |
1779 | |
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}. | |
1784 @end defmac | |
1785 | |
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. | |
1793 | |
1794 If vtables are used, the value of this macro should be the number | |
1795 of words that the function descriptor occupies. | |
1796 @end defmac | |
1797 | |
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. */ | |
1803 @end defmac | |
1804 | |
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. | |
1810 @end defmac | |
1811 | |
1812 @node Registers | |
1813 @section Register Usage | |
1814 @cindex register usage | |
1815 | |
1816 This section explains how to describe what registers the target machine | |
1817 has, and how (in general) they can be used. | |
1818 | |
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}. | |
1824 | |
1825 @menu | |
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. | |
1831 @end menu | |
1832 | |
1833 @node Register Basics | |
1834 @subsection Basic Characteristics of Registers | |
1835 | |
1836 @c prevent bad page break with this line | |
1837 Registers have various characteristics. | |
1838 | |
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}. | |
1844 @end defmac | |
1845 | |
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. | |
1855 | |
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. | |
1859 | |
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}}. | |
1865 @end defmac | |
1866 | |
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 | |
1875 function calls. | |
1876 | |
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. | |
1880 @end defmac | |
1881 | |
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}. | |
1891 @end defmac | |
1892 | |
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. | |
1902 @end defmac | |
1903 | |
1904 @findex fixed_regs | |
1905 @findex call_used_regs | |
1906 @findex global_regs | |
1907 @findex reg_names | |
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. | |
1924 | |
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. | |
1934 | |
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.) | |
1939 @end deftypefn | |
1940 | |
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 | |
1946 outbound register. | |
1947 @end defmac | |
1948 | |
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 | |
1954 register. | |
1955 @end defmac | |
1956 | |
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 | |
1962 gotos. | |
1963 @end defmac | |
1964 | |
1965 @defmac PC_REGNUM | |
1966 If the program counter has a register number, define this as that | |
1967 register number. Otherwise, do not define it. | |
1968 @end defmac | |
1969 | |
1970 @node Allocation Order | |
1971 @subsection Order of Allocation of Registers | |
1972 @cindex order of register allocation | |
1973 @cindex register allocation order | |
1974 | |
1975 @c prevent bad page break with this line | |
1976 Registers are allocated in order. | |
1977 | |
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). | |
1982 | |
1983 If this macro is not defined, registers are used lowest numbered first | |
1984 (all else being equal). | |
1985 | |
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. | |
1991 @end defmac | |
1992 | |
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. | |
1996 | |
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. | |
2000 | |
2001 The macro body should not assume anything about the contents of | |
2002 @code{reg_alloc_order} before execution of the macro. | |
2003 | |
2004 On most machines, it is not necessary to define this macro. | |
2005 @end defmac | |
2006 | |
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 | |
2013 should be defined. | |
2014 @end defmac | |
2015 | |
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}. | |
2024 | |
2025 On most machines, it is not necessary to define this macro. | |
2026 @end defmac | |
2027 | |
2028 @node Values in Registers | |
2029 @subsection How Values Fit in Registers | |
2030 | |
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. | |
2034 | |
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. | |
2041 | |
2042 On a machine where all registers are exactly one word, a suitable | |
2043 definition of this macro is | |
2044 | |
2045 @smallexample | |
2046 #define HARD_REGNO_NREGS(REGNO, MODE) \ | |
2047 ((GET_MODE_SIZE (MODE) + UNITS_PER_WORD - 1) \ | |
2048 / UNITS_PER_WORD) | |
2049 @end smallexample | |
2050 @end defmac | |
2051 | |
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. | |
2059 | |
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 | |
2062 nonzero. | |
2063 | |
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. | |
2070 @end defmac | |
2071 | |
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. | |
2077 @end defmac | |
2078 | |
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. | |
2086 @end defmac | |
2087 | |
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 | |
2093 | |
2094 @smallexample | |
2095 #define HARD_REGNO_MODE_OK(REGNO, MODE) 1 | |
2096 @end smallexample | |
2097 | |
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. | |
2100 | |
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. | |
2105 | |
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. | |
2110 | |
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 | |
2117 to be tieable. | |
2118 | |
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. | |
2125 | |
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. | |
2135 | |
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. | |
2141 | |
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. | |
2147 @end defmac | |
2148 | |
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}. | |
2152 | |
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 | |
2155 handler. | |
2156 | |
2157 The default is always nonzero. | |
2158 @end defmac | |
2159 | |
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. | |
2163 | |
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. | |
2170 | |
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 | |
2173 allocation. | |
2174 @end defmac | |
2175 | |
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. | |
2179 | |
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. | |
2182 | |
2183 The default version of this hook always returns @code{true}. | |
2184 @end deftypefn | |
2185 | |
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. | |
2190 @end defmac | |
2191 | |
2192 @node Leaf Functions | |
2193 @subsection Handling Leaf Functions | |
2194 | |
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 | |
2201 normally arrive. | |
2202 | |
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 | |
2208 functions''. | |
2209 | |
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 | |
2213 accomplish this. | |
2214 | |
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 | |
2218 function treatment. | |
2219 | |
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 | |
2224 in this vector. | |
2225 | |
2226 Define this macro only if the target machine offers a way to optimize | |
2227 the treatment of leaf functions. | |
2228 @end defmac | |
2229 | |
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. | |
2233 | |
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. | |
2237 | |
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 | |
2240 this. | |
2241 @end defmac | |
2242 | |
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 | |
2258 | |
2259 @node Stack Registers | |
2260 @subsection Registers That Form a Stack | |
2261 | |
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 | |
2265 stack. | |
2266 | |
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. | |
2274 | |
2275 @defmac STACK_REGS | |
2276 Define this if the machine has any stack-like registers. | |
2277 @end defmac | |
2278 | |
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. | |
2282 @end defmac | |
2283 | |
2284 @defmac FIRST_STACK_REG | |
2285 The number of the first stack-like register. This one is the top | |
2286 of the stack. | |
2287 @end defmac | |
2288 | |
2289 @defmac LAST_STACK_REG | |
2290 The number of the last stack-like register. This one is the bottom of | |
2291 the stack. | |
2292 @end defmac | |
2293 | |
2294 @node Register Classes | |
2295 @section Register Classes | |
2296 @cindex register class definitions | |
2297 @cindex class definitions, register | |
2298 | |
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}. | |
2303 | |
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. | |
2307 | |
2308 @findex ALL_REGS | |
2309 @findex NO_REGS | |
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. | |
2314 | |
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 | |
2320 to @code{ALL_REGS}. | |
2321 | |
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}. | |
2324 | |
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. | |
2329 | |
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, | |
2335 or even internal compiler errors when reload cannot find a register in the | |
2336 the class computed via @code{reg_class_subunion}. | |
2337 | |
2338 You must also specify certain redundant information about the register | |
2339 classes: for each class, which classes contain it and which ones are | |
2340 contained in it; for each pair of classes, the largest class contained | |
2341 in their union. | |
2342 | |
2343 When a value occupying several consecutive registers is expected in a | |
2344 certain class, all the registers used must belong to that class. | |
2345 Therefore, register classes cannot be used to enforce a requirement for | |
2346 a register pair to start with an even-numbered register. The way to | |
2347 specify this requirement is with @code{HARD_REGNO_MODE_OK}. | |
2348 | |
2349 Register classes used for input-operands of bitwise-and or shift | |
2350 instructions have a special requirement: each such class must have, for | |
2351 each fixed-point machine mode, a subclass whose registers can transfer that | |
2352 mode to or from memory. For example, on some machines, the operations for | |
2353 single-byte values (@code{QImode}) are limited to certain registers. When | |
2354 this is so, each register class that is used in a bitwise-and or shift | |
2355 instruction must have a subclass consisting of registers from which | |
2356 single-byte values can be loaded or stored. This is so that | |
2357 @code{PREFERRED_RELOAD_CLASS} can always have a possible value to return. | |
2358 | |
2359 @deftp {Data type} {enum reg_class} | |
2360 An enumerated type that must be defined with all the register class names | |
2361 as enumerated values. @code{NO_REGS} must be first. @code{ALL_REGS} | |
2362 must be the last register class, followed by one more enumerated value, | |
2363 @code{LIM_REG_CLASSES}, which is not a register class but rather | |
2364 tells how many classes there are. | |
2365 | |
2366 Each register class has a number, which is the value of casting | |
2367 the class name to type @code{int}. The number serves as an index | |
2368 in many of the tables described below. | |
2369 @end deftp | |
2370 | |
2371 @defmac N_REG_CLASSES | |
2372 The number of distinct register classes, defined as follows: | |
2373 | |
2374 @smallexample | |
2375 #define N_REG_CLASSES (int) LIM_REG_CLASSES | |
2376 @end smallexample | |
2377 @end defmac | |
2378 | |
2379 @defmac REG_CLASS_NAMES | |
2380 An initializer containing the names of the register classes as C string | |
2381 constants. These names are used in writing some of the debugging dumps. | |
2382 @end defmac | |
2383 | |
2384 @defmac REG_CLASS_CONTENTS | |
2385 An initializer containing the contents of the register classes, as integers | |
2386 which are bit masks. The @var{n}th integer specifies the contents of class | |
2387 @var{n}. The way the integer @var{mask} is interpreted is that | |
2388 register @var{r} is in the class if @code{@var{mask} & (1 << @var{r})} is 1. | |
2389 | |
2390 When the machine has more than 32 registers, an integer does not suffice. | |
2391 Then the integers are replaced by sub-initializers, braced groupings containing | |
2392 several integers. Each sub-initializer must be suitable as an initializer | |
2393 for the type @code{HARD_REG_SET} which is defined in @file{hard-reg-set.h}. | |
2394 In this situation, the first integer in each sub-initializer corresponds to | |
2395 registers 0 through 31, the second integer to registers 32 through 63, and | |
2396 so on. | |
2397 @end defmac | |
2398 | |
2399 @defmac REGNO_REG_CLASS (@var{regno}) | |
2400 A C expression whose value is a register class containing hard register | |
2401 @var{regno}. In general there is more than one such class; choose a class | |
2402 which is @dfn{minimal}, meaning that no smaller class also contains the | |
2403 register. | |
2404 @end defmac | |
2405 | |
2406 @defmac BASE_REG_CLASS | |
2407 A macro whose definition is the name of the class to which a valid | |
2408 base register must belong. A base register is one used in an address | |
2409 which is the register value plus a displacement. | |
2410 @end defmac | |
2411 | |
2412 @defmac MODE_BASE_REG_CLASS (@var{mode}) | |
2413 This is a variation of the @code{BASE_REG_CLASS} macro which allows | |
2414 the selection of a base register in a mode dependent manner. If | |
2415 @var{mode} is VOIDmode then it should return the same value as | |
2416 @code{BASE_REG_CLASS}. | |
2417 @end defmac | |
2418 | |
2419 @defmac MODE_BASE_REG_REG_CLASS (@var{mode}) | |
2420 A C expression whose value is the register class to which a valid | |
2421 base register must belong in order to be used in a base plus index | |
2422 register address. You should define this macro if base plus index | |
2423 addresses have different requirements than other base register uses. | |
2424 @end defmac | |
2425 | |
2426 @defmac MODE_CODE_BASE_REG_CLASS (@var{mode}, @var{outer_code}, @var{index_code}) | |
2427 A C expression whose value is the register class to which a valid | |
2428 base register must belong. @var{outer_code} and @var{index_code} define the | |
2429 context in which the base register occurs. @var{outer_code} is the code of | |
2430 the immediately enclosing expression (@code{MEM} for the top level of an | |
2431 address, @code{ADDRESS} for something that occurs in an | |
2432 @code{address_operand}). @var{index_code} is the code of the corresponding | |
2433 index expression if @var{outer_code} is @code{PLUS}; @code{SCRATCH} otherwise. | |
2434 @end defmac | |
2435 | |
2436 @defmac INDEX_REG_CLASS | |
2437 A macro whose definition is the name of the class to which a valid | |
2438 index register must belong. An index register is one used in an | |
2439 address where its value is either multiplied by a scale factor or | |
2440 added to another register (as well as added to a displacement). | |
2441 @end defmac | |
2442 | |
2443 @defmac REGNO_OK_FOR_BASE_P (@var{num}) | |
2444 A C expression which is nonzero if register number @var{num} is | |
2445 suitable for use as a base register in operand addresses. | |
2446 @end defmac | |
2447 | |
2448 @defmac REGNO_MODE_OK_FOR_BASE_P (@var{num}, @var{mode}) | |
2449 A C expression that is just like @code{REGNO_OK_FOR_BASE_P}, except that | |
2450 that expression may examine the mode of the memory reference in | |
2451 @var{mode}. You should define this macro if the mode of the memory | |
2452 reference affects whether a register may be used as a base register. If | |
2453 you define this macro, the compiler will use it instead of | |
2454 @code{REGNO_OK_FOR_BASE_P}. The mode may be @code{VOIDmode} for | |
2455 addresses that appear outside a @code{MEM}, i.e., as an | |
2456 @code{address_operand}. | |
2457 @end defmac | |
2458 | |
2459 @defmac REGNO_MODE_OK_FOR_REG_BASE_P (@var{num}, @var{mode}) | |
2460 A C expression which is nonzero if register number @var{num} is suitable for | |
2461 use as a base register in base plus index operand addresses, accessing | |
2462 memory in mode @var{mode}. It may be either a suitable hard register or a | |
2463 pseudo register that has been allocated such a hard register. You should | |
2464 define this macro if base plus index addresses have different requirements | |
2465 than other base register uses. | |
2466 | |
2467 Use of this macro is deprecated; please use the more general | |
2468 @code{REGNO_MODE_CODE_OK_FOR_BASE_P}. | |
2469 @end defmac | |
2470 | |
2471 @defmac REGNO_MODE_CODE_OK_FOR_BASE_P (@var{num}, @var{mode}, @var{outer_code}, @var{index_code}) | |
2472 A C expression that is just like @code{REGNO_MODE_OK_FOR_BASE_P}, except | |
2473 that that expression may examine the context in which the register | |
2474 appears in the memory reference. @var{outer_code} is the code of the | |
2475 immediately enclosing expression (@code{MEM} if at the top level of the | |
2476 address, @code{ADDRESS} for something that occurs in an | |
2477 @code{address_operand}). @var{index_code} is the code of the | |
2478 corresponding index expression if @var{outer_code} is @code{PLUS}; | |
2479 @code{SCRATCH} otherwise. The mode may be @code{VOIDmode} for addresses | |
2480 that appear outside a @code{MEM}, i.e., as an @code{address_operand}. | |
2481 @end defmac | |
2482 | |
2483 @defmac REGNO_OK_FOR_INDEX_P (@var{num}) | |
2484 A C expression which is nonzero if register number @var{num} is | |
2485 suitable for use as an index register in operand addresses. It may be | |
2486 either a suitable hard register or a pseudo register that has been | |
2487 allocated such a hard register. | |
2488 | |
2489 The difference between an index register and a base register is that | |
2490 the index register may be scaled. If an address involves the sum of | |
2491 two registers, neither one of them scaled, then either one may be | |
2492 labeled the ``base'' and the other the ``index''; but whichever | |
2493 labeling is used must fit the machine's constraints of which registers | |
2494 may serve in each capacity. The compiler will try both labelings, | |
2495 looking for one that is valid, and will reload one or both registers | |
2496 only if neither labeling works. | |
2497 @end defmac | |
2498 | |
2499 @hook TARGET_PREFERRED_RENAME_CLASS | |
2500 | |
2501 @hook TARGET_PREFERRED_RELOAD_CLASS | |
2502 A target hook that places additional restrictions on the register class | |
2503 to use when it is necessary to copy value @var{x} into a register in class | |
2504 @var{rclass}. The value is a register class; perhaps @var{rclass}, or perhaps | |
2505 another, smaller class. | |
2506 | |
2507 The default version of this hook always returns value of @code{rclass} argument. | |
2508 | |
2509 Sometimes returning a more restrictive class makes better code. For | |
2510 example, on the 68000, when @var{x} is an integer constant that is in range | |
2511 for a @samp{moveq} instruction, the value of this macro is always | |
2512 @code{DATA_REGS} as long as @var{rclass} includes the data registers. | |
2513 Requiring a data register guarantees that a @samp{moveq} will be used. | |
2514 | |
2515 One case where @code{TARGET_PREFERRED_RELOAD_CLASS} must not return | |
2516 @var{rclass} is if @var{x} is a legitimate constant which cannot be | |
2517 loaded into some register class. By returning @code{NO_REGS} you can | |
2518 force @var{x} into a memory location. For example, rs6000 can load | |
2519 immediate values into general-purpose registers, but does not have an | |
2520 instruction for loading an immediate value into a floating-point | |
2521 register, so @code{TARGET_PREFERRED_RELOAD_CLASS} returns @code{NO_REGS} when | |
2522 @var{x} is a floating-point constant. If the constant can't be loaded | |
2523 into any kind of register, code generation will be better if | |
2524 @code{LEGITIMATE_CONSTANT_P} makes the constant illegitimate instead | |
2525 of using @code{TARGET_PREFERRED_RELOAD_CLASS}. | |
2526 | |
2527 If an insn has pseudos in it after register allocation, reload will go | |
2528 through the alternatives and call repeatedly @code{TARGET_PREFERRED_RELOAD_CLASS} | |
2529 to find the best one. Returning @code{NO_REGS}, in this case, makes | |
2530 reload add a @code{!} in front of the constraint: the x86 back-end uses | |
2531 this feature to discourage usage of 387 registers when math is done in | |
2532 the SSE registers (and vice versa). | |
2533 @end deftypefn | |
2534 | |
2535 @defmac PREFERRED_RELOAD_CLASS (@var{x}, @var{class}) | |
2536 A C expression that places additional restrictions on the register class | |
2537 to use when it is necessary to copy value @var{x} into a register in class | |
2538 @var{class}. The value is a register class; perhaps @var{class}, or perhaps | |
2539 another, smaller class. On many machines, the following definition is | |
2540 safe: | |
2541 | |
2542 @smallexample | |
2543 #define PREFERRED_RELOAD_CLASS(X,CLASS) CLASS | |
2544 @end smallexample | |
2545 | |
2546 Sometimes returning a more restrictive class makes better code. For | |
2547 example, on the 68000, when @var{x} is an integer constant that is in range | |
2548 for a @samp{moveq} instruction, the value of this macro is always | |
2549 @code{DATA_REGS} as long as @var{class} includes the data registers. | |
2550 Requiring a data register guarantees that a @samp{moveq} will be used. | |
2551 | |
2552 One case where @code{PREFERRED_RELOAD_CLASS} must not return | |
2553 @var{class} is if @var{x} is a legitimate constant which cannot be | |
2554 loaded into some register class. By returning @code{NO_REGS} you can | |
2555 force @var{x} into a memory location. For example, rs6000 can load | |
2556 immediate values into general-purpose registers, but does not have an | |
2557 instruction for loading an immediate value into a floating-point | |
2558 register, so @code{PREFERRED_RELOAD_CLASS} returns @code{NO_REGS} when | |
2559 @var{x} is a floating-point constant. If the constant can't be loaded | |
2560 into any kind of register, code generation will be better if | |
2561 @code{LEGITIMATE_CONSTANT_P} makes the constant illegitimate instead | |
2562 of using @code{PREFERRED_RELOAD_CLASS}. | |
2563 | |
2564 If an insn has pseudos in it after register allocation, reload will go | |
2565 through the alternatives and call repeatedly @code{PREFERRED_RELOAD_CLASS} | |
2566 to find the best one. Returning @code{NO_REGS}, in this case, makes | |
2567 reload add a @code{!} in front of the constraint: the x86 back-end uses | |
2568 this feature to discourage usage of 387 registers when math is done in | |
2569 the SSE registers (and vice versa). | |
2570 @end defmac | |
2571 | |
2572 @defmac PREFERRED_OUTPUT_RELOAD_CLASS (@var{x}, @var{class}) | |
2573 Like @code{PREFERRED_RELOAD_CLASS}, but for output reloads instead of | |
2574 input reloads. If you don't define this macro, the default is to use | |
2575 @var{class}, unchanged. | |
2576 | |
2577 You can also use @code{PREFERRED_OUTPUT_RELOAD_CLASS} to discourage | |
2578 reload from using some alternatives, like @code{PREFERRED_RELOAD_CLASS}. | |
2579 @end defmac | |
2580 | |
2581 @hook TARGET_PREFERRED_OUTPUT_RELOAD_CLASS | |
2582 Like @code{TARGET_PREFERRED_RELOAD_CLASS}, but for output reloads instead of | |
2583 input reloads. | |
2584 | |
2585 The default version of this hook always returns value of @code{rclass} | |
2586 argument. | |
2587 | |
2588 You can also use @code{TARGET_PREFERRED_OUTPUT_RELOAD_CLASS} to discourage | |
2589 reload from using some alternatives, like @code{TARGET_PREFERRED_RELOAD_CLASS}. | |
2590 @end deftypefn | |
2591 | |
2592 @defmac LIMIT_RELOAD_CLASS (@var{mode}, @var{class}) | |
2593 A C expression that places additional restrictions on the register class | |
2594 to use when it is necessary to be able to hold a value of mode | |
2595 @var{mode} in a reload register for which class @var{class} would | |
2596 ordinarily be used. | |
2597 | |
2598 Unlike @code{PREFERRED_RELOAD_CLASS}, this macro should be used when | |
2599 there are certain modes that simply can't go in certain reload classes. | |
2600 | |
2601 The value is a register class; perhaps @var{class}, or perhaps another, | |
2602 smaller class. | |
2603 | |
2604 Don't define this macro unless the target machine has limitations which | |
2605 require the macro to do something nontrivial. | |
2606 @end defmac | |
2607 | |
2608 @hook TARGET_SECONDARY_RELOAD | |
2609 Many machines have some registers that cannot be copied directly to or | |
2610 from memory or even from other types of registers. An example is the | |
2611 @samp{MQ} register, which on most machines, can only be copied to or | |
2612 from general registers, but not memory. Below, we shall be using the | |
2613 term 'intermediate register' when a move operation cannot be performed | |
2614 directly, but has to be done by copying the source into the intermediate | |
2615 register first, and then copying the intermediate register to the | |
2616 destination. An intermediate register always has the same mode as | |
2617 source and destination. Since it holds the actual value being copied, | |
2618 reload might apply optimizations to re-use an intermediate register | |
2619 and eliding the copy from the source when it can determine that the | |
2620 intermediate register still holds the required value. | |
2621 | |
2622 Another kind of secondary reload is required on some machines which | |
2623 allow copying all registers to and from memory, but require a scratch | |
2624 register for stores to some memory locations (e.g., those with symbolic | |
2625 address on the RT, and those with certain symbolic address on the SPARC | |
2626 when compiling PIC)@. Scratch registers need not have the same mode | |
2627 as the value being copied, and usually hold a different value than | |
2628 that being copied. Special patterns in the md file are needed to | |
2629 describe how the copy is performed with the help of the scratch register; | |
2630 these patterns also describe the number, register class(es) and mode(s) | |
2631 of the scratch register(s). | |
2632 | |
2633 In some cases, both an intermediate and a scratch register are required. | |
2634 | |
2635 For input reloads, this target hook is called with nonzero @var{in_p}, | |
2636 and @var{x} is an rtx that needs to be copied to a register of class | |
2637 @var{reload_class} in @var{reload_mode}. For output reloads, this target | |
2638 hook is called with zero @var{in_p}, and a register of class @var{reload_class} | |
2639 needs to be copied to rtx @var{x} in @var{reload_mode}. | |
2640 | |
2641 If copying a register of @var{reload_class} from/to @var{x} requires | |
2642 an intermediate register, the hook @code{secondary_reload} should | |
2643 return the register class required for this intermediate register. | |
2644 If no intermediate register is required, it should return NO_REGS. | |
2645 If more than one intermediate register is required, describe the one | |
2646 that is closest in the copy chain to the reload register. | |
2647 | |
2648 If scratch registers are needed, you also have to describe how to | |
2649 perform the copy from/to the reload register to/from this | |
2650 closest intermediate register. Or if no intermediate register is | |
2651 required, but still a scratch register is needed, describe the | |
2652 copy from/to the reload register to/from the reload operand @var{x}. | |
2653 | |
2654 You do this by setting @code{sri->icode} to the instruction code of a pattern | |
2655 in the md file which performs the move. Operands 0 and 1 are the output | |
2656 and input of this copy, respectively. Operands from operand 2 onward are | |
2657 for scratch operands. These scratch operands must have a mode, and a | |
2658 single-register-class | |
2659 @c [later: or memory] | |
2660 output constraint. | |
2661 | |
2662 When an intermediate register is used, the @code{secondary_reload} | |
2663 hook will be called again to determine how to copy the intermediate | |
2664 register to/from the reload operand @var{x}, so your hook must also | |
2665 have code to handle the register class of the intermediate operand. | |
2666 | |
2667 @c [For later: maybe we'll allow multi-alternative reload patterns - | |
2668 @c the port maintainer could name a mov<mode> pattern that has clobbers - | |
2669 @c and match the constraints of input and output to determine the required | |
2670 @c alternative. A restriction would be that constraints used to match | |
2671 @c against reloads registers would have to be written as register class | |
2672 @c constraints, or we need a new target macro / hook that tells us if an | |
2673 @c arbitrary constraint can match an unknown register of a given class. | |
2674 @c Such a macro / hook would also be useful in other places.] | |
2675 | |
2676 | |
2677 @var{x} might be a pseudo-register or a @code{subreg} of a | |
2678 pseudo-register, which could either be in a hard register or in memory. | |
2679 Use @code{true_regnum} to find out; it will return @minus{}1 if the pseudo is | |
2680 in memory and the hard register number if it is in a register. | |
2681 | |
2682 Scratch operands in memory (constraint @code{"=m"} / @code{"=&m"}) are | |
2683 currently not supported. For the time being, you will have to continue | |
2684 to use @code{SECONDARY_MEMORY_NEEDED} for that purpose. | |
2685 | |
2686 @code{copy_cost} also uses this target hook to find out how values are | |
2687 copied. If you want it to include some extra cost for the need to allocate | |
2688 (a) scratch register(s), set @code{sri->extra_cost} to the additional cost. | |
2689 Or if two dependent moves are supposed to have a lower cost than the sum | |
2690 of the individual moves due to expected fortuitous scheduling and/or special | |
2691 forwarding logic, you can set @code{sri->extra_cost} to a negative amount. | |
2692 @end deftypefn | |
2693 | |
2694 @defmac SECONDARY_RELOAD_CLASS (@var{class}, @var{mode}, @var{x}) | |
2695 @defmacx SECONDARY_INPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x}) | |
2696 @defmacx SECONDARY_OUTPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x}) | |
2697 These macros are obsolete, new ports should use the target hook | |
2698 @code{TARGET_SECONDARY_RELOAD} instead. | |
2699 | |
2700 These are obsolete macros, replaced by the @code{TARGET_SECONDARY_RELOAD} | |
2701 target hook. Older ports still define these macros to indicate to the | |
2702 reload phase that it may | |
2703 need to allocate at least one register for a reload in addition to the | |
2704 register to contain the data. Specifically, if copying @var{x} to a | |
2705 register @var{class} in @var{mode} requires an intermediate register, | |
2706 you were supposed to define @code{SECONDARY_INPUT_RELOAD_CLASS} to return the | |
2707 largest register class all of whose registers can be used as | |
2708 intermediate registers or scratch registers. | |
2709 | |
2710 If copying a register @var{class} in @var{mode} to @var{x} requires an | |
2711 intermediate or scratch register, @code{SECONDARY_OUTPUT_RELOAD_CLASS} | |
2712 was supposed to be defined be defined to return the largest register | |
2713 class required. If the | |
2714 requirements for input and output reloads were the same, the macro | |
2715 @code{SECONDARY_RELOAD_CLASS} should have been used instead of defining both | |
2716 macros identically. | |
2717 | |
2718 The values returned by these macros are often @code{GENERAL_REGS}. | |
2719 Return @code{NO_REGS} if no spare register is needed; i.e., if @var{x} | |
2720 can be directly copied to or from a register of @var{class} in | |
2721 @var{mode} without requiring a scratch register. Do not define this | |
2722 macro if it would always return @code{NO_REGS}. | |
2723 | |
2724 If a scratch register is required (either with or without an | |
2725 intermediate register), you were supposed to define patterns for | |
2726 @samp{reload_in@var{m}} or @samp{reload_out@var{m}}, as required | |
2727 (@pxref{Standard Names}. These patterns, which were normally | |
2728 implemented with a @code{define_expand}, should be similar to the | |
2729 @samp{mov@var{m}} patterns, except that operand 2 is the scratch | |
2730 register. | |
2731 | |
2732 These patterns need constraints for the reload register and scratch | |
2733 register that | |
2734 contain a single register class. If the original reload register (whose | |
2735 class is @var{class}) can meet the constraint given in the pattern, the | |
2736 value returned by these macros is used for the class of the scratch | |
2737 register. Otherwise, two additional reload registers are required. | |
2738 Their classes are obtained from the constraints in the insn pattern. | |
2739 | |
2740 @var{x} might be a pseudo-register or a @code{subreg} of a | |
2741 pseudo-register, which could either be in a hard register or in memory. | |
2742 Use @code{true_regnum} to find out; it will return @minus{}1 if the pseudo is | |
2743 in memory and the hard register number if it is in a register. | |
2744 | |
2745 These macros should not be used in the case where a particular class of | |
2746 registers can only be copied to memory and not to another class of | |
2747 registers. In that case, secondary reload registers are not needed and | |
2748 would not be helpful. Instead, a stack location must be used to perform | |
2749 the copy and the @code{mov@var{m}} pattern should use memory as an | |
2750 intermediate storage. This case often occurs between floating-point and | |
2751 general registers. | |
2752 @end defmac | |
2753 | |
2754 @defmac SECONDARY_MEMORY_NEEDED (@var{class1}, @var{class2}, @var{m}) | |
2755 Certain machines have the property that some registers cannot be copied | |
2756 to some other registers without using memory. Define this macro on | |
2757 those machines to be a C expression that is nonzero if objects of mode | |
2758 @var{m} in registers of @var{class1} can only be copied to registers of | |
2759 class @var{class2} by storing a register of @var{class1} into memory | |
2760 and loading that memory location into a register of @var{class2}. | |
2761 | |
2762 Do not define this macro if its value would always be zero. | |
2763 @end defmac | |
2764 | |
2765 @defmac SECONDARY_MEMORY_NEEDED_RTX (@var{mode}) | |
2766 Normally when @code{SECONDARY_MEMORY_NEEDED} is defined, the compiler | |
2767 allocates a stack slot for a memory location needed for register copies. | |
2768 If this macro is defined, the compiler instead uses the memory location | |
2769 defined by this macro. | |
2770 | |
2771 Do not define this macro if you do not define | |
2772 @code{SECONDARY_MEMORY_NEEDED}. | |
2773 @end defmac | |
2774 | |
2775 @defmac SECONDARY_MEMORY_NEEDED_MODE (@var{mode}) | |
2776 When the compiler needs a secondary memory location to copy between two | |
2777 registers of mode @var{mode}, it normally allocates sufficient memory to | |
2778 hold a quantity of @code{BITS_PER_WORD} bits and performs the store and | |
2779 load operations in a mode that many bits wide and whose class is the | |
2780 same as that of @var{mode}. | |
2781 | |
2782 This is right thing to do on most machines because it ensures that all | |
2783 bits of the register are copied and prevents accesses to the registers | |
2784 in a narrower mode, which some machines prohibit for floating-point | |
2785 registers. | |
2786 | |
2787 However, this default behavior is not correct on some machines, such as | |
2788 the DEC Alpha, that store short integers in floating-point registers | |
2789 differently than in integer registers. On those machines, the default | |
2790 widening will not work correctly and you must define this macro to | |
2791 suppress that widening in some cases. See the file @file{alpha.h} for | |
2792 details. | |
2793 | |
2794 Do not define this macro if you do not define | |
2795 @code{SECONDARY_MEMORY_NEEDED} or if widening @var{mode} to a mode that | |
2796 is @code{BITS_PER_WORD} bits wide is correct for your machine. | |
2797 @end defmac | |
2798 | |
2799 @hook TARGET_CLASS_LIKELY_SPILLED_P | |
2800 A target hook which returns @code{true} if pseudos that have been assigned | |
2801 to registers of class @var{rclass} would likely be spilled because | |
2802 registers of @var{rclass} are needed for spill registers. | |
2803 | |
2804 The default version of this target hook returns @code{true} if @var{rclass} | |
2805 has exactly one register and @code{false} otherwise. On most machines, this | |
2806 default should be used. Only use this target hook to some other expression | |
2807 if pseudos allocated by @file{local-alloc.c} end up in memory because their | |
2808 hard registers were needed for spill registers. If this target hook returns | |
2809 @code{false} for those classes, those pseudos will only be allocated by | |
2810 @file{global.c}, which knows how to reallocate the pseudo to another | |
2811 register. If there would not be another register available for reallocation, | |
2812 you should not change the implementation of this target hook since | |
2813 the only effect of such implementation would be to slow down register | |
2814 allocation. | |
2815 @end deftypefn | |
2816 | |
2817 @defmac CLASS_MAX_NREGS (@var{class}, @var{mode}) | |
2818 A C expression for the maximum number of consecutive registers | |
2819 of class @var{class} needed to hold a value of mode @var{mode}. | |
2820 | |
2821 This is closely related to the macro @code{HARD_REGNO_NREGS}. In fact, | |
2822 the value of the macro @code{CLASS_MAX_NREGS (@var{class}, @var{mode})} | |
2823 should be the maximum value of @code{HARD_REGNO_NREGS (@var{regno}, | |
2824 @var{mode})} for all @var{regno} values in the class @var{class}. | |
2825 | |
2826 This macro helps control the handling of multiple-word values | |
2827 in the reload pass. | |
2828 @end defmac | |
2829 | |
2830 @defmac CANNOT_CHANGE_MODE_CLASS (@var{from}, @var{to}, @var{class}) | |
2831 If defined, a C expression that returns nonzero for a @var{class} for which | |
2832 a change from mode @var{from} to mode @var{to} is invalid. | |
2833 | |
2834 For the example, loading 32-bit integer or floating-point objects into | |
2835 floating-point registers on the Alpha extends them to 64 bits. | |
2836 Therefore loading a 64-bit object and then storing it as a 32-bit object | |
2837 does not store the low-order 32 bits, as would be the case for a normal | |
2838 register. Therefore, @file{alpha.h} defines @code{CANNOT_CHANGE_MODE_CLASS} | |
2839 as below: | |
2840 | |
2841 @smallexample | |
2842 #define CANNOT_CHANGE_MODE_CLASS(FROM, TO, CLASS) \ | |
2843 (GET_MODE_SIZE (FROM) != GET_MODE_SIZE (TO) \ | |
2844 ? reg_classes_intersect_p (FLOAT_REGS, (CLASS)) : 0) | |
2845 @end smallexample | |
2846 @end defmac | |
2847 | |
2848 @hook TARGET_IRA_COVER_CLASSES | |
2849 Return an array of cover classes for the Integrated Register Allocator | |
2850 (@acronym{IRA}). Cover classes are a set of non-intersecting register | |
2851 classes covering all hard registers used for register allocation | |
2852 purposes. If a move between two registers in the same cover class is | |
2853 possible, it should be cheaper than a load or store of the registers. | |
2854 The array is terminated by a @code{LIM_REG_CLASSES} element. | |
2855 | |
2856 The order of cover classes in the array is important. If two classes | |
2857 have the same cost of usage for a pseudo, the class occurred first in | |
2858 the array is chosen for the pseudo. | |
2859 | |
2860 This hook is called once at compiler startup, after the command-line | |
2861 options have been processed. It is then re-examined by every call to | |
2862 @code{target_reinit}. | |
2863 | |
2864 The default implementation returns @code{IRA_COVER_CLASSES}, if defined, | |
2865 otherwise there is no default implementation. You must define either this | |
2866 macro or @code{IRA_COVER_CLASSES} in order to use the integrated register | |
2867 allocator with Chaitin-Briggs coloring. If the macro is not defined, | |
2868 the only available coloring algorithm is Chow's priority coloring. | |
2869 | |
2870 This hook must not be modified from @code{NULL} to non-@code{NULL} or | |
2871 vice versa by command-line option processing. | |
2872 @end deftypefn | |
2873 | |
2874 @defmac IRA_COVER_CLASSES | |
2875 See the documentation for @code{TARGET_IRA_COVER_CLASSES}. | |
2876 @end defmac | |
2877 | |
2878 @node Old Constraints | |
2879 @section Obsolete Macros for Defining Constraints | |
2880 @cindex defining constraints, obsolete method | |
2881 @cindex constraints, defining, obsolete method | |
2882 | |
2883 Machine-specific constraints can be defined with these macros instead | |
2884 of the machine description constructs described in @ref{Define | |
2885 Constraints}. This mechanism is obsolete. New ports should not use | |
2886 it; old ports should convert to the new mechanism. | |
2887 | |
2888 @defmac CONSTRAINT_LEN (@var{char}, @var{str}) | |
2889 For the constraint at the start of @var{str}, which starts with the letter | |
2890 @var{c}, return the length. This allows you to have register class / | |
2891 constant / extra constraints that are longer than a single letter; | |
2892 you don't need to define this macro if you can do with single-letter | |
2893 constraints only. The definition of this macro should use | |
2894 DEFAULT_CONSTRAINT_LEN for all the characters that you don't want | |
2895 to handle specially. | |
2896 There are some sanity checks in genoutput.c that check the constraint lengths | |
2897 for the md file, so you can also use this macro to help you while you are | |
2898 transitioning from a byzantine single-letter-constraint scheme: when you | |
2899 return a negative length for a constraint you want to re-use, genoutput | |
2900 will complain about every instance where it is used in the md file. | |
2901 @end defmac | |
2902 | |
2903 @defmac REG_CLASS_FROM_LETTER (@var{char}) | |
2904 A C expression which defines the machine-dependent operand constraint | |
2905 letters for register classes. If @var{char} is such a letter, the | |
2906 value should be the register class corresponding to it. Otherwise, | |
2907 the value should be @code{NO_REGS}. The register letter @samp{r}, | |
2908 corresponding to class @code{GENERAL_REGS}, will not be passed | |
2909 to this macro; you do not need to handle it. | |
2910 @end defmac | |
2911 | |
2912 @defmac REG_CLASS_FROM_CONSTRAINT (@var{char}, @var{str}) | |
2913 Like @code{REG_CLASS_FROM_LETTER}, but you also get the constraint string | |
2914 passed in @var{str}, so that you can use suffixes to distinguish between | |
2915 different variants. | |
2916 @end defmac | |
2917 | |
2918 @defmac CONST_OK_FOR_LETTER_P (@var{value}, @var{c}) | |
2919 A C expression that defines the machine-dependent operand constraint | |
2920 letters (@samp{I}, @samp{J}, @samp{K}, @dots{} @samp{P}) that specify | |
2921 particular ranges of integer values. If @var{c} is one of those | |
2922 letters, the expression should check that @var{value}, an integer, is in | |
2923 the appropriate range and return 1 if so, 0 otherwise. If @var{c} is | |
2924 not one of those letters, the value should be 0 regardless of | |
2925 @var{value}. | |
2926 @end defmac | |
2927 | |
2928 @defmac CONST_OK_FOR_CONSTRAINT_P (@var{value}, @var{c}, @var{str}) | |
2929 Like @code{CONST_OK_FOR_LETTER_P}, but you also get the constraint | |
2930 string passed in @var{str}, so that you can use suffixes to distinguish | |
2931 between different variants. | |
2932 @end defmac | |
2933 | |
2934 @defmac CONST_DOUBLE_OK_FOR_LETTER_P (@var{value}, @var{c}) | |
2935 A C expression that defines the machine-dependent operand constraint | |
2936 letters that specify particular ranges of @code{const_double} values | |
2937 (@samp{G} or @samp{H}). | |
2938 | |
2939 If @var{c} is one of those letters, the expression should check that | |
2940 @var{value}, an RTX of code @code{const_double}, is in the appropriate | |
2941 range and return 1 if so, 0 otherwise. If @var{c} is not one of those | |
2942 letters, the value should be 0 regardless of @var{value}. | |
2943 | |
2944 @code{const_double} is used for all floating-point constants and for | |
2945 @code{DImode} fixed-point constants. A given letter can accept either | |
2946 or both kinds of values. It can use @code{GET_MODE} to distinguish | |
2947 between these kinds. | |
2948 @end defmac | |
2949 | |
2950 @defmac CONST_DOUBLE_OK_FOR_CONSTRAINT_P (@var{value}, @var{c}, @var{str}) | |
2951 Like @code{CONST_DOUBLE_OK_FOR_LETTER_P}, but you also get the constraint | |
2952 string passed in @var{str}, so that you can use suffixes to distinguish | |
2953 between different variants. | |
2954 @end defmac | |
2955 | |
2956 @defmac EXTRA_CONSTRAINT (@var{value}, @var{c}) | |
2957 A C expression that defines the optional machine-dependent constraint | |
2958 letters that can be used to segregate specific types of operands, usually | |
2959 memory references, for the target machine. Any letter that is not | |
2960 elsewhere defined and not matched by @code{REG_CLASS_FROM_LETTER} / | |
2961 @code{REG_CLASS_FROM_CONSTRAINT} | |
2962 may be used. Normally this macro will not be defined. | |
2963 | |
2964 If it is required for a particular target machine, it should return 1 | |
2965 if @var{value} corresponds to the operand type represented by the | |
2966 constraint letter @var{c}. If @var{c} is not defined as an extra | |
2967 constraint, the value returned should be 0 regardless of @var{value}. | |
2968 | |
2969 For example, on the ROMP, load instructions cannot have their output | |
2970 in r0 if the memory reference contains a symbolic address. Constraint | |
2971 letter @samp{Q} is defined as representing a memory address that does | |
2972 @emph{not} contain a symbolic address. An alternative is specified with | |
2973 a @samp{Q} constraint on the input and @samp{r} on the output. The next | |
2974 alternative specifies @samp{m} on the input and a register class that | |
2975 does not include r0 on the output. | |
2976 @end defmac | |
2977 | |
2978 @defmac EXTRA_CONSTRAINT_STR (@var{value}, @var{c}, @var{str}) | |
2979 Like @code{EXTRA_CONSTRAINT}, but you also get the constraint string passed | |
2980 in @var{str}, so that you can use suffixes to distinguish between different | |
2981 variants. | |
2982 @end defmac | |
2983 | |
2984 @defmac EXTRA_MEMORY_CONSTRAINT (@var{c}, @var{str}) | |
2985 A C expression that defines the optional machine-dependent constraint | |
2986 letters, amongst those accepted by @code{EXTRA_CONSTRAINT}, that should | |
2987 be treated like memory constraints by the reload pass. | |
2988 | |
2989 It should return 1 if the operand type represented by the constraint | |
2990 at the start of @var{str}, the first letter of which is the letter @var{c}, | |
2991 comprises a subset of all memory references including | |
2992 all those whose address is simply a base register. This allows the reload | |
2993 pass to reload an operand, if it does not directly correspond to the operand | |
2994 type of @var{c}, by copying its address into a base register. | |
2995 | |
2996 For example, on the S/390, some instructions do not accept arbitrary | |
2997 memory references, but only those that do not make use of an index | |
2998 register. The constraint letter @samp{Q} is defined via | |
2999 @code{EXTRA_CONSTRAINT} as representing a memory address of this type. | |
3000 If the letter @samp{Q} is marked as @code{EXTRA_MEMORY_CONSTRAINT}, | |
3001 a @samp{Q} constraint can handle any memory operand, because the | |
3002 reload pass knows it can be reloaded by copying the memory address | |
3003 into a base register if required. This is analogous to the way | |
3004 an @samp{o} constraint can handle any memory operand. | |
3005 @end defmac | |
3006 | |
3007 @defmac EXTRA_ADDRESS_CONSTRAINT (@var{c}, @var{str}) | |
3008 A C expression that defines the optional machine-dependent constraint | |
3009 letters, amongst those accepted by @code{EXTRA_CONSTRAINT} / | |
3010 @code{EXTRA_CONSTRAINT_STR}, that should | |
3011 be treated like address constraints by the reload pass. | |
3012 | |
3013 It should return 1 if the operand type represented by the constraint | |
3014 at the start of @var{str}, which starts with the letter @var{c}, comprises | |
3015 a subset of all memory addresses including | |
3016 all those that consist of just a base register. This allows the reload | |
3017 pass to reload an operand, if it does not directly correspond to the operand | |
3018 type of @var{str}, by copying it into a base register. | |
3019 | |
3020 Any constraint marked as @code{EXTRA_ADDRESS_CONSTRAINT} can only | |
3021 be used with the @code{address_operand} predicate. It is treated | |
3022 analogously to the @samp{p} constraint. | |
3023 @end defmac | |
3024 | |
3025 @node Stack and Calling | |
3026 @section Stack Layout and Calling Conventions | |
3027 @cindex calling conventions | |
3028 | |
3029 @c prevent bad page break with this line | |
3030 This describes the stack layout and calling conventions. | |
3031 | |
3032 @menu | |
3033 * Frame Layout:: | |
3034 * Exception Handling:: | |
3035 * Stack Checking:: | |
3036 * Frame Registers:: | |
3037 * Elimination:: | |
3038 * Stack Arguments:: | |
3039 * Register Arguments:: | |
3040 * Scalar Return:: | |
3041 * Aggregate Return:: | |
3042 * Caller Saves:: | |
3043 * Function Entry:: | |
3044 * Profiling:: | |
3045 * Tail Calls:: | |
3046 * Stack Smashing Protection:: | |
3047 @end menu | |
3048 | |
3049 @node Frame Layout | |
3050 @subsection Basic Stack Layout | |
3051 @cindex stack frame layout | |
3052 @cindex frame layout | |
3053 | |
3054 @c prevent bad page break with this line | |
3055 Here is the basic stack layout. | |
3056 | |
3057 @defmac STACK_GROWS_DOWNWARD | |
3058 Define this macro if pushing a word onto the stack moves the stack | |
3059 pointer to a smaller address. | |
3060 | |
3061 When we say, ``define this macro if @dots{}'', it means that the | |
3062 compiler checks this macro only with @code{#ifdef} so the precise | |
3063 definition used does not matter. | |
3064 @end defmac | |
3065 | |
3066 @defmac STACK_PUSH_CODE | |
3067 This macro defines the operation used when something is pushed | |
3068 on the stack. In RTL, a push operation will be | |
3069 @code{(set (mem (STACK_PUSH_CODE (reg sp))) @dots{})} | |
3070 | |
3071 The choices are @code{PRE_DEC}, @code{POST_DEC}, @code{PRE_INC}, | |
3072 and @code{POST_INC}. Which of these is correct depends on | |
3073 the stack direction and on whether the stack pointer points | |
3074 to the last item on the stack or whether it points to the | |
3075 space for the next item on the stack. | |
3076 | |
3077 The default is @code{PRE_DEC} when @code{STACK_GROWS_DOWNWARD} is | |
3078 defined, which is almost always right, and @code{PRE_INC} otherwise, | |
3079 which is often wrong. | |
3080 @end defmac | |
3081 | |
3082 @defmac FRAME_GROWS_DOWNWARD | |
3083 Define this macro to nonzero value if the addresses of local variable slots | |
3084 are at negative offsets from the frame pointer. | |
3085 @end defmac | |
3086 | |
3087 @defmac ARGS_GROW_DOWNWARD | |
3088 Define this macro if successive arguments to a function occupy decreasing | |
3089 addresses on the stack. | |
3090 @end defmac | |
3091 | |
3092 @defmac STARTING_FRAME_OFFSET | |
3093 Offset from the frame pointer to the first local variable slot to be allocated. | |
3094 | |
3095 If @code{FRAME_GROWS_DOWNWARD}, find the next slot's offset by | |
3096 subtracting the first slot's length from @code{STARTING_FRAME_OFFSET}. | |
3097 Otherwise, it is found by adding the length of the first slot to the | |
3098 value @code{STARTING_FRAME_OFFSET}. | |
3099 @c i'm not sure if the above is still correct.. had to change it to get | |
3100 @c rid of an overfull. --mew 2feb93 | |
3101 @end defmac | |
3102 | |
3103 @defmac STACK_ALIGNMENT_NEEDED | |
3104 Define to zero to disable final alignment of the stack during reload. | |
3105 The nonzero default for this macro is suitable for most ports. | |
3106 | |
3107 On ports where @code{STARTING_FRAME_OFFSET} is nonzero or where there | |
3108 is a register save block following the local block that doesn't require | |
3109 alignment to @code{STACK_BOUNDARY}, it may be beneficial to disable | |
3110 stack alignment and do it in the backend. | |
3111 @end defmac | |
3112 | |
3113 @defmac STACK_POINTER_OFFSET | |
3114 Offset from the stack pointer register to the first location at which | |
3115 outgoing arguments are placed. If not specified, the default value of | |
3116 zero is used. This is the proper value for most machines. | |
3117 | |
3118 If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above | |
3119 the first location at which outgoing arguments are placed. | |
3120 @end defmac | |
3121 | |
3122 @defmac FIRST_PARM_OFFSET (@var{fundecl}) | |
3123 Offset from the argument pointer register to the first argument's | |
3124 address. On some machines it may depend on the data type of the | |
3125 function. | |
3126 | |
3127 If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above | |
3128 the first argument's address. | |
3129 @end defmac | |
3130 | |
3131 @defmac STACK_DYNAMIC_OFFSET (@var{fundecl}) | |
3132 Offset from the stack pointer register to an item dynamically allocated | |
3133 on the stack, e.g., by @code{alloca}. | |
3134 | |
3135 The default value for this macro is @code{STACK_POINTER_OFFSET} plus the | |
3136 length of the outgoing arguments. The default is correct for most | |
3137 machines. See @file{function.c} for details. | |
3138 @end defmac | |
3139 | |
3140 @defmac INITIAL_FRAME_ADDRESS_RTX | |
3141 A C expression whose value is RTL representing the address of the initial | |
3142 stack frame. This address is passed to @code{RETURN_ADDR_RTX} and | |
3143 @code{DYNAMIC_CHAIN_ADDRESS}. If you don't define this macro, a reasonable | |
3144 default value will be used. Define this macro in order to make frame pointer | |
3145 elimination work in the presence of @code{__builtin_frame_address (count)} and | |
3146 @code{__builtin_return_address (count)} for @code{count} not equal to zero. | |
3147 @end defmac | |
3148 | |
3149 @defmac DYNAMIC_CHAIN_ADDRESS (@var{frameaddr}) | |
3150 A C expression whose value is RTL representing the address in a stack | |
3151 frame where the pointer to the caller's frame is stored. Assume that | |
3152 @var{frameaddr} is an RTL expression for the address of the stack frame | |
3153 itself. | |
3154 | |
3155 If you don't define this macro, the default is to return the value | |
3156 of @var{frameaddr}---that is, the stack frame address is also the | |
3157 address of the stack word that points to the previous frame. | |
3158 @end defmac | |
3159 | |
3160 @defmac SETUP_FRAME_ADDRESSES | |
3161 If defined, a C expression that produces the machine-specific code to | |
3162 setup the stack so that arbitrary frames can be accessed. For example, | |
3163 on the SPARC, we must flush all of the register windows to the stack | |
3164 before we can access arbitrary stack frames. You will seldom need to | |
3165 define this macro. | |
3166 @end defmac | |
3167 | |
3168 @hook TARGET_BUILTIN_SETJMP_FRAME_VALUE | |
3169 This target hook should return an rtx that is used to store | |
3170 the address of the current frame into the built in @code{setjmp} buffer. | |
3171 The default value, @code{virtual_stack_vars_rtx}, is correct for most | |
3172 machines. One reason you may need to define this target hook is if | |
3173 @code{hard_frame_pointer_rtx} is the appropriate value on your machine. | |
3174 @end deftypefn | |
3175 | |
3176 @defmac FRAME_ADDR_RTX (@var{frameaddr}) | |
3177 A C expression whose value is RTL representing the value of the frame | |
3178 address for the current frame. @var{frameaddr} is the frame pointer | |
3179 of the current frame. This is used for __builtin_frame_address. | |
3180 You need only define this macro if the frame address is not the same | |
3181 as the frame pointer. Most machines do not need to define it. | |
3182 @end defmac | |
3183 | |
3184 @defmac RETURN_ADDR_RTX (@var{count}, @var{frameaddr}) | |
3185 A C expression whose value is RTL representing the value of the return | |
3186 address for the frame @var{count} steps up from the current frame, after | |
3187 the prologue. @var{frameaddr} is the frame pointer of the @var{count} | |
3188 frame, or the frame pointer of the @var{count} @minus{} 1 frame if | |
3189 @code{RETURN_ADDR_IN_PREVIOUS_FRAME} is defined. | |
3190 | |
3191 The value of the expression must always be the correct address when | |
3192 @var{count} is zero, but may be @code{NULL_RTX} if there is no way to | |
3193 determine the return address of other frames. | |
3194 @end defmac | |
3195 | |
3196 @defmac RETURN_ADDR_IN_PREVIOUS_FRAME | |
3197 Define this if the return address of a particular stack frame is accessed | |
3198 from the frame pointer of the previous stack frame. | |
3199 @end defmac | |
3200 | |
3201 @defmac INCOMING_RETURN_ADDR_RTX | |
3202 A C expression whose value is RTL representing the location of the | |
3203 incoming return address at the beginning of any function, before the | |
3204 prologue. This RTL is either a @code{REG}, indicating that the return | |
3205 value is saved in @samp{REG}, or a @code{MEM} representing a location in | |
3206 the stack. | |
3207 | |
3208 You only need to define this macro if you want to support call frame | |
3209 debugging information like that provided by DWARF 2. | |
3210 | |
3211 If this RTL is a @code{REG}, you should also define | |
3212 @code{DWARF_FRAME_RETURN_COLUMN} to @code{DWARF_FRAME_REGNUM (REGNO)}. | |
3213 @end defmac | |
3214 | |
3215 @defmac DWARF_ALT_FRAME_RETURN_COLUMN | |
3216 A C expression whose value is an integer giving a DWARF 2 column | |
3217 number that may be used as an alternative return column. The column | |
3218 must not correspond to any gcc hard register (that is, it must not | |
3219 be in the range of @code{DWARF_FRAME_REGNUM}). | |
3220 | |
3221 This macro can be useful if @code{DWARF_FRAME_RETURN_COLUMN} is set to a | |
3222 general register, but an alternative column needs to be used for signal | |
3223 frames. Some targets have also used different frame return columns | |
3224 over time. | |
3225 @end defmac | |
3226 | |
3227 @defmac DWARF_ZERO_REG | |
3228 A C expression whose value is an integer giving a DWARF 2 register | |
3229 number that is considered to always have the value zero. This should | |
3230 only be defined if the target has an architected zero register, and | |
3231 someone decided it was a good idea to use that register number to | |
3232 terminate the stack backtrace. New ports should avoid this. | |
3233 @end defmac | |
3234 | |
3235 @hook TARGET_DWARF_HANDLE_FRAME_UNSPEC | |
3236 This target hook allows the backend to emit frame-related insns that | |
3237 contain UNSPECs or UNSPEC_VOLATILEs. The DWARF 2 call frame debugging | |
3238 info engine will invoke it on insns of the form | |
3239 @smallexample | |
3240 (set (reg) (unspec [@dots{}] UNSPEC_INDEX)) | |
3241 @end smallexample | |
3242 and | |
3243 @smallexample | |
3244 (set (reg) (unspec_volatile [@dots{}] UNSPECV_INDEX)). | |
3245 @end smallexample | |
3246 to let the backend emit the call frame instructions. @var{label} is | |
3247 the CFI label attached to the insn, @var{pattern} is the pattern of | |
3248 the insn and @var{index} is @code{UNSPEC_INDEX} or @code{UNSPECV_INDEX}. | |
3249 @end deftypefn | |
3250 | |
3251 @defmac INCOMING_FRAME_SP_OFFSET | |
3252 A C expression whose value is an integer giving the offset, in bytes, | |
3253 from the value of the stack pointer register to the top of the stack | |
3254 frame at the beginning of any function, before the prologue. The top of | |
3255 the frame is defined to be the value of the stack pointer in the | |
3256 previous frame, just before the call instruction. | |
3257 | |
3258 You only need to define this macro if you want to support call frame | |
3259 debugging information like that provided by DWARF 2. | |
3260 @end defmac | |
3261 | |
3262 @defmac ARG_POINTER_CFA_OFFSET (@var{fundecl}) | |
3263 A C expression whose value is an integer giving the offset, in bytes, | |
3264 from the argument pointer to the canonical frame address (cfa). The | |
3265 final value should coincide with that calculated by | |
3266 @code{INCOMING_FRAME_SP_OFFSET}. Which is unfortunately not usable | |
3267 during virtual register instantiation. | |
3268 | |
3269 The default value for this macro is | |
3270 @code{FIRST_PARM_OFFSET (fundecl) + crtl->args.pretend_args_size}, | |
3271 which is correct for most machines; in general, the arguments are found | |
3272 immediately before the stack frame. Note that this is not the case on | |
3273 some targets that save registers into the caller's frame, such as SPARC | |
3274 and rs6000, and so such targets need to define this macro. | |
3275 | |
3276 You only need to define this macro if the default is incorrect, and you | |
3277 want to support call frame debugging information like that provided by | |
3278 DWARF 2. | |
3279 @end defmac | |
3280 | |
3281 @defmac FRAME_POINTER_CFA_OFFSET (@var{fundecl}) | |
3282 If defined, a C expression whose value is an integer giving the offset | |
3283 in bytes from the frame pointer to the canonical frame address (cfa). | |
3284 The final value should coincide with that calculated by | |
3285 @code{INCOMING_FRAME_SP_OFFSET}. | |
3286 | |
3287 Normally the CFA is calculated as an offset from the argument pointer, | |
3288 via @code{ARG_POINTER_CFA_OFFSET}, but if the argument pointer is | |
3289 variable due to the ABI, this may not be possible. If this macro is | |
3290 defined, it implies that the virtual register instantiation should be | |
3291 based on the frame pointer instead of the argument pointer. Only one | |
3292 of @code{FRAME_POINTER_CFA_OFFSET} and @code{ARG_POINTER_CFA_OFFSET} | |
3293 should be defined. | |
3294 @end defmac | |
3295 | |
3296 @defmac CFA_FRAME_BASE_OFFSET (@var{fundecl}) | |
3297 If defined, a C expression whose value is an integer giving the offset | |
3298 in bytes from the canonical frame address (cfa) to the frame base used | |
3299 in DWARF 2 debug information. The default is zero. A different value | |
3300 may reduce the size of debug information on some ports. | |
3301 @end defmac | |
3302 | |
3303 @node Exception Handling | |
3304 @subsection Exception Handling Support | |
3305 @cindex exception handling | |
3306 | |
3307 @defmac EH_RETURN_DATA_REGNO (@var{N}) | |
3308 A C expression whose value is the @var{N}th register number used for | |
3309 data by exception handlers, or @code{INVALID_REGNUM} if fewer than | |
3310 @var{N} registers are usable. | |
3311 | |
3312 The exception handling library routines communicate with the exception | |
3313 handlers via a set of agreed upon registers. Ideally these registers | |
3314 should be call-clobbered; it is possible to use call-saved registers, | |
3315 but may negatively impact code size. The target must support at least | |
3316 2 data registers, but should define 4 if there are enough free registers. | |
3317 | |
3318 You must define this macro if you want to support call frame exception | |
3319 handling like that provided by DWARF 2. | |
3320 @end defmac | |
3321 | |
3322 @defmac EH_RETURN_STACKADJ_RTX | |
3323 A C expression whose value is RTL representing a location in which | |
3324 to store a stack adjustment to be applied before function return. | |
3325 This is used to unwind the stack to an exception handler's call frame. | |
3326 It will be assigned zero on code paths that return normally. | |
3327 | |
3328 Typically this is a call-clobbered hard register that is otherwise | |
3329 untouched by the epilogue, but could also be a stack slot. | |
3330 | |
3331 Do not define this macro if the stack pointer is saved and restored | |
3332 by the regular prolog and epilog code in the call frame itself; in | |
3333 this case, the exception handling library routines will update the | |
3334 stack location to be restored in place. Otherwise, you must define | |
3335 this macro if you want to support call frame exception handling like | |
3336 that provided by DWARF 2. | |
3337 @end defmac | |
3338 | |
3339 @defmac EH_RETURN_HANDLER_RTX | |
3340 A C expression whose value is RTL representing a location in which | |
3341 to store the address of an exception handler to which we should | |
3342 return. It will not be assigned on code paths that return normally. | |
3343 | |
3344 Typically this is the location in the call frame at which the normal | |
3345 return address is stored. For targets that return by popping an | |
3346 address off the stack, this might be a memory address just below | |
3347 the @emph{target} call frame rather than inside the current call | |
3348 frame. If defined, @code{EH_RETURN_STACKADJ_RTX} will have already | |
3349 been assigned, so it may be used to calculate the location of the | |
3350 target call frame. | |
3351 | |
3352 Some targets have more complex requirements than storing to an | |
3353 address calculable during initial code generation. In that case | |
3354 the @code{eh_return} instruction pattern should be used instead. | |
3355 | |
3356 If you want to support call frame exception handling, you must | |
3357 define either this macro or the @code{eh_return} instruction pattern. | |
3358 @end defmac | |
3359 | |
3360 @defmac RETURN_ADDR_OFFSET | |
3361 If defined, an integer-valued C expression for which rtl will be generated | |
3362 to add it to the exception handler address before it is searched in the | |
3363 exception handling tables, and to subtract it again from the address before | |
3364 using it to return to the exception handler. | |
3365 @end defmac | |
3366 | |
3367 @defmac ASM_PREFERRED_EH_DATA_FORMAT (@var{code}, @var{global}) | |
3368 This macro chooses the encoding of pointers embedded in the exception | |
3369 handling sections. If at all possible, this should be defined such | |
3370 that the exception handling section will not require dynamic relocations, | |
3371 and so may be read-only. | |
3372 | |
3373 @var{code} is 0 for data, 1 for code labels, 2 for function pointers. | |
3374 @var{global} is true if the symbol may be affected by dynamic relocations. | |
3375 The macro should return a combination of the @code{DW_EH_PE_*} defines | |
3376 as found in @file{dwarf2.h}. | |
3377 | |
3378 If this macro is not defined, pointers will not be encoded but | |
3379 represented directly. | |
3380 @end defmac | |
3381 | |
3382 @defmac ASM_MAYBE_OUTPUT_ENCODED_ADDR_RTX (@var{file}, @var{encoding}, @var{size}, @var{addr}, @var{done}) | |
3383 This macro allows the target to emit whatever special magic is required | |
3384 to represent the encoding chosen by @code{ASM_PREFERRED_EH_DATA_FORMAT}. | |
3385 Generic code takes care of pc-relative and indirect encodings; this must | |
3386 be defined if the target uses text-relative or data-relative encodings. | |
3387 | |
3388 This is a C statement that branches to @var{done} if the format was | |
3389 handled. @var{encoding} is the format chosen, @var{size} is the number | |
3390 of bytes that the format occupies, @var{addr} is the @code{SYMBOL_REF} | |
3391 to be emitted. | |
3392 @end defmac | |
3393 | |
3394 @defmac MD_UNWIND_SUPPORT | |
3395 A string specifying a file to be #include'd in unwind-dw2.c. The file | |
3396 so included typically defines @code{MD_FALLBACK_FRAME_STATE_FOR}. | |
3397 @end defmac | |
3398 | |
3399 @defmac MD_FALLBACK_FRAME_STATE_FOR (@var{context}, @var{fs}) | |
3400 This macro allows the target to add CPU and operating system specific | |
3401 code to the call-frame unwinder for use when there is no unwind data | |
3402 available. The most common reason to implement this macro is to unwind | |
3403 through signal frames. | |
3404 | |
3405 This macro is called from @code{uw_frame_state_for} in | |
3406 @file{unwind-dw2.c}, @file{unwind-dw2-xtensa.c} and | |
3407 @file{unwind-ia64.c}. @var{context} is an @code{_Unwind_Context}; | |
3408 @var{fs} is an @code{_Unwind_FrameState}. Examine @code{context->ra} | |
3409 for the address of the code being executed and @code{context->cfa} for | |
3410 the stack pointer value. If the frame can be decoded, the register | |
3411 save addresses should be updated in @var{fs} and the macro should | |
3412 evaluate to @code{_URC_NO_REASON}. If the frame cannot be decoded, | |
3413 the macro should evaluate to @code{_URC_END_OF_STACK}. | |
3414 | |
3415 For proper signal handling in Java this macro is accompanied by | |
3416 @code{MAKE_THROW_FRAME}, defined in @file{libjava/include/*-signal.h} headers. | |
3417 @end defmac | |
3418 | |
3419 @defmac MD_HANDLE_UNWABI (@var{context}, @var{fs}) | |
3420 This macro allows the target to add operating system specific code to the | |
3421 call-frame unwinder to handle the IA-64 @code{.unwabi} unwinding directive, | |
3422 usually used for signal or interrupt frames. | |
3423 | |
3424 This macro is called from @code{uw_update_context} in @file{unwind-ia64.c}. | |
3425 @var{context} is an @code{_Unwind_Context}; | |
3426 @var{fs} is an @code{_Unwind_FrameState}. Examine @code{fs->unwabi} | |
3427 for the abi and context in the @code{.unwabi} directive. If the | |
3428 @code{.unwabi} directive can be handled, the register save addresses should | |
3429 be updated in @var{fs}. | |
3430 @end defmac | |
3431 | |
3432 @defmac TARGET_USES_WEAK_UNWIND_INFO | |
3433 A C expression that evaluates to true if the target requires unwind | |
3434 info to be given comdat linkage. Define it to be @code{1} if comdat | |
3435 linkage is necessary. The default is @code{0}. | |
3436 @end defmac | |
3437 | |
3438 @node Stack Checking | |
3439 @subsection Specifying How Stack Checking is Done | |
3440 | |
3441 GCC will check that stack references are within the boundaries of the | |
3442 stack, if the option @option{-fstack-check} is specified, in one of | |
3443 three ways: | |
3444 | |
3445 @enumerate | |
3446 @item | |
3447 If the value of the @code{STACK_CHECK_BUILTIN} macro is nonzero, GCC | |
3448 will assume that you have arranged for full stack checking to be done | |
3449 at appropriate places in the configuration files. GCC will not do | |
3450 other special processing. | |
3451 | |
3452 @item | |
3453 If @code{STACK_CHECK_BUILTIN} is zero and the value of the | |
3454 @code{STACK_CHECK_STATIC_BUILTIN} macro is nonzero, GCC will assume | |
3455 that you have arranged for static stack checking (checking of the | |
3456 static stack frame of functions) to be done at appropriate places | |
3457 in the configuration files. GCC will only emit code to do dynamic | |
3458 stack checking (checking on dynamic stack allocations) using the third | |
3459 approach below. | |
3460 | |
3461 @item | |
3462 If neither of the above are true, GCC will generate code to periodically | |
3463 ``probe'' the stack pointer using the values of the macros defined below. | |
3464 @end enumerate | |
3465 | |
3466 If neither STACK_CHECK_BUILTIN nor STACK_CHECK_STATIC_BUILTIN is defined, | |
3467 GCC will change its allocation strategy for large objects if the option | |
3468 @option{-fstack-check} is specified: they will always be allocated | |
3469 dynamically if their size exceeds @code{STACK_CHECK_MAX_VAR_SIZE} bytes. | |
3470 | |
3471 @defmac STACK_CHECK_BUILTIN | |
3472 A nonzero value if stack checking is done by the configuration files in a | |
3473 machine-dependent manner. You should define this macro if stack checking | |
3474 is required by the ABI of your machine or if you would like to do stack | |
3475 checking in some more efficient way than the generic approach. The default | |
3476 value of this macro is zero. | |
3477 @end defmac | |
3478 | |
3479 @defmac STACK_CHECK_STATIC_BUILTIN | |
3480 A nonzero value if static stack checking is done by the configuration files | |
3481 in a machine-dependent manner. You should define this macro if you would | |
3482 like to do static stack checking in some more efficient way than the generic | |
3483 approach. The default value of this macro is zero. | |
3484 @end defmac | |
3485 | |
3486 @defmac STACK_CHECK_PROBE_INTERVAL_EXP | |
3487 An integer specifying the interval at which GCC must generate stack probe | |
3488 instructions, defined as 2 raised to this integer. You will normally | |
3489 define this macro so that the interval be no larger than the size of | |
3490 the ``guard pages'' at the end of a stack area. The default value | |
3491 of 12 (4096-byte interval) is suitable for most systems. | |
3492 @end defmac | |
3493 | |
3494 @defmac STACK_CHECK_MOVING_SP | |
3495 An integer which is nonzero if GCC should move the stack pointer page by page | |
3496 when doing probes. This can be necessary on systems where the stack pointer | |
3497 contains the bottom address of the memory area accessible to the executing | |
3498 thread at any point in time. In this situation an alternate signal stack | |
3499 is required in order to be able to recover from a stack overflow. The | |
3500 default value of this macro is zero. | |
3501 @end defmac | |
3502 | |
3503 @defmac STACK_CHECK_PROTECT | |
3504 The number of bytes of stack needed to recover from a stack overflow, for | |
3505 languages where such a recovery is supported. The default value of 75 words | |
3506 with the @code{setjmp}/@code{longjmp}-based exception handling mechanism and | |
3507 8192 bytes with other exception handling mechanisms should be adequate for | |
3508 most machines. | |
3509 @end defmac | |
3510 | |
3511 The following macros are relevant only if neither STACK_CHECK_BUILTIN | |
3512 nor STACK_CHECK_STATIC_BUILTIN is defined; you can omit them altogether | |
3513 in the opposite case. | |
3514 | |
3515 @defmac STACK_CHECK_MAX_FRAME_SIZE | |
3516 The maximum size of a stack frame, in bytes. GCC will generate probe | |
3517 instructions in non-leaf functions to ensure at least this many bytes of | |
3518 stack are available. If a stack frame is larger than this size, stack | |
3519 checking will not be reliable and GCC will issue a warning. The | |
3520 default is chosen so that GCC only generates one instruction on most | |
3521 systems. You should normally not change the default value of this macro. | |
3522 @end defmac | |
3523 | |
3524 @defmac STACK_CHECK_FIXED_FRAME_SIZE | |
3525 GCC uses this value to generate the above warning message. It | |
3526 represents the amount of fixed frame used by a function, not including | |
3527 space for any callee-saved registers, temporaries and user variables. | |
3528 You need only specify an upper bound for this amount and will normally | |
3529 use the default of four words. | |
3530 @end defmac | |
3531 | |
3532 @defmac STACK_CHECK_MAX_VAR_SIZE | |
3533 The maximum size, in bytes, of an object that GCC will place in the | |
3534 fixed area of the stack frame when the user specifies | |
3535 @option{-fstack-check}. | |
3536 GCC computed the default from the values of the above macros and you will | |
3537 normally not need to override that default. | |
3538 @end defmac | |
3539 | |
3540 @need 2000 | |
3541 @node Frame Registers | |
3542 @subsection Registers That Address the Stack Frame | |
3543 | |
3544 @c prevent bad page break with this line | |
3545 This discusses registers that address the stack frame. | |
3546 | |
3547 @defmac STACK_POINTER_REGNUM | |
3548 The register number of the stack pointer register, which must also be a | |
3549 fixed register according to @code{FIXED_REGISTERS}. On most machines, | |
3550 the hardware determines which register this is. | |
3551 @end defmac | |
3552 | |
3553 @defmac FRAME_POINTER_REGNUM | |
3554 The register number of the frame pointer register, which is used to | |
3555 access automatic variables in the stack frame. On some machines, the | |
3556 hardware determines which register this is. On other machines, you can | |
3557 choose any register you wish for this purpose. | |
3558 @end defmac | |
3559 | |
3560 @defmac HARD_FRAME_POINTER_REGNUM | |
3561 On some machines the offset between the frame pointer and starting | |
3562 offset of the automatic variables is not known until after register | |
3563 allocation has been done (for example, because the saved registers are | |
3564 between these two locations). On those machines, define | |
3565 @code{FRAME_POINTER_REGNUM} the number of a special, fixed register to | |
3566 be used internally until the offset is known, and define | |
3567 @code{HARD_FRAME_POINTER_REGNUM} to be the actual hard register number | |
3568 used for the frame pointer. | |
3569 | |
3570 You should define this macro only in the very rare circumstances when it | |
3571 is not possible to calculate the offset between the frame pointer and | |
3572 the automatic variables until after register allocation has been | |
3573 completed. When this macro is defined, you must also indicate in your | |
3574 definition of @code{ELIMINABLE_REGS} how to eliminate | |
3575 @code{FRAME_POINTER_REGNUM} into either @code{HARD_FRAME_POINTER_REGNUM} | |
3576 or @code{STACK_POINTER_REGNUM}. | |
3577 | |
3578 Do not define this macro if it would be the same as | |
3579 @code{FRAME_POINTER_REGNUM}. | |
3580 @end defmac | |
3581 | |
3582 @defmac ARG_POINTER_REGNUM | |
3583 The register number of the arg pointer register, which is used to access | |
3584 the function's argument list. On some machines, this is the same as the | |
3585 frame pointer register. On some machines, the hardware determines which | |
3586 register this is. On other machines, you can choose any register you | |
3587 wish for this purpose. If this is not the same register as the frame | |
3588 pointer register, then you must mark it as a fixed register according to | |
3589 @code{FIXED_REGISTERS}, or arrange to be able to eliminate it | |
3590 (@pxref{Elimination}). | |
3591 @end defmac | |
3592 | |
3593 @defmac HARD_FRAME_POINTER_IS_FRAME_POINTER | |
3594 Define this to a preprocessor constant that is nonzero if | |
3595 @code{hard_frame_pointer_rtx} and @code{frame_pointer_rtx} should be | |
3596 the same. The default definition is @samp{(HARD_FRAME_POINTER_REGNUM | |
3597 == FRAME_POINTER_REGNUM)}; you only need to define this macro if that | |
3598 definition is not suitable for use in preprocessor conditionals. | |
3599 @end defmac | |
3600 | |
3601 @defmac HARD_FRAME_POINTER_IS_ARG_POINTER | |
3602 Define this to a preprocessor constant that is nonzero if | |
3603 @code{hard_frame_pointer_rtx} and @code{arg_pointer_rtx} should be the | |
3604 same. The default definition is @samp{(HARD_FRAME_POINTER_REGNUM == | |
3605 ARG_POINTER_REGNUM)}; you only need to define this macro if that | |
3606 definition is not suitable for use in preprocessor conditionals. | |
3607 @end defmac | |
3608 | |
3609 @defmac RETURN_ADDRESS_POINTER_REGNUM | |
3610 The register number of the return address pointer register, which is used to | |
3611 access the current function's return address from the stack. On some | |
3612 machines, the return address is not at a fixed offset from the frame | |
3613 pointer or stack pointer or argument pointer. This register can be defined | |
3614 to point to the return address on the stack, and then be converted by | |
3615 @code{ELIMINABLE_REGS} into either the frame pointer or stack pointer. | |
3616 | |
3617 Do not define this macro unless there is no other way to get the return | |
3618 address from the stack. | |
3619 @end defmac | |
3620 | |
3621 @defmac STATIC_CHAIN_REGNUM | |
3622 @defmacx STATIC_CHAIN_INCOMING_REGNUM | |
3623 Register numbers used for passing a function's static chain pointer. If | |
3624 register windows are used, the register number as seen by the called | |
3625 function is @code{STATIC_CHAIN_INCOMING_REGNUM}, while the register | |
3626 number as seen by the calling function is @code{STATIC_CHAIN_REGNUM}. If | |
3627 these registers are the same, @code{STATIC_CHAIN_INCOMING_REGNUM} need | |
3628 not be defined. | |
3629 | |
3630 The static chain register need not be a fixed register. | |
3631 | |
3632 If the static chain is passed in memory, these macros should not be | |
3633 defined; instead, the @code{TARGET_STATIC_CHAIN} hook should be used. | |
3634 @end defmac | |
3635 | |
3636 @hook TARGET_STATIC_CHAIN | |
3637 This hook replaces the use of @code{STATIC_CHAIN_REGNUM} et al for | |
3638 targets that may use different static chain locations for different | |
3639 nested functions. This may be required if the target has function | |
3640 attributes that affect the calling conventions of the function and | |
3641 those calling conventions use different static chain locations. | |
3642 | |
3643 The default version of this hook uses @code{STATIC_CHAIN_REGNUM} et al. | |
3644 | |
3645 If the static chain is passed in memory, this hook should be used to | |
3646 provide rtx giving @code{mem} expressions that denote where they are stored. | |
3647 Often the @code{mem} expression as seen by the caller will be at an offset | |
3648 from the stack pointer and the @code{mem} expression as seen by the callee | |
3649 will be at an offset from the frame pointer. | |
3650 @findex stack_pointer_rtx | |
3651 @findex frame_pointer_rtx | |
3652 @findex arg_pointer_rtx | |
3653 The variables @code{stack_pointer_rtx}, @code{frame_pointer_rtx}, and | |
3654 @code{arg_pointer_rtx} will have been initialized and should be used | |
3655 to refer to those items. | |
3656 @end deftypefn | |
3657 | |
3658 @defmac DWARF_FRAME_REGISTERS | |
3659 This macro specifies the maximum number of hard registers that can be | |
3660 saved in a call frame. This is used to size data structures used in | |
3661 DWARF2 exception handling. | |
3662 | |
3663 Prior to GCC 3.0, this macro was needed in order to establish a stable | |
3664 exception handling ABI in the face of adding new hard registers for ISA | |
3665 extensions. In GCC 3.0 and later, the EH ABI is insulated from changes | |
3666 in the number of hard registers. Nevertheless, this macro can still be | |
3667 used to reduce the runtime memory requirements of the exception handling | |
3668 routines, which can be substantial if the ISA contains a lot of | |
3669 registers that are not call-saved. | |
3670 | |
3671 If this macro is not defined, it defaults to | |
3672 @code{FIRST_PSEUDO_REGISTER}. | |
3673 @end defmac | |
3674 | |
3675 @defmac PRE_GCC3_DWARF_FRAME_REGISTERS | |
3676 | |
3677 This macro is similar to @code{DWARF_FRAME_REGISTERS}, but is provided | |
3678 for backward compatibility in pre GCC 3.0 compiled code. | |
3679 | |
3680 If this macro is not defined, it defaults to | |
3681 @code{DWARF_FRAME_REGISTERS}. | |
3682 @end defmac | |
3683 | |
3684 @defmac DWARF_REG_TO_UNWIND_COLUMN (@var{regno}) | |
3685 | |
3686 Define this macro if the target's representation for dwarf registers | |
3687 is different than the internal representation for unwind column. | |
3688 Given a dwarf register, this macro should return the internal unwind | |
3689 column number to use instead. | |
3690 | |
3691 See the PowerPC's SPE target for an example. | |
3692 @end defmac | |
3693 | |
3694 @defmac DWARF_FRAME_REGNUM (@var{regno}) | |
3695 | |
3696 Define this macro if the target's representation for dwarf registers | |
3697 used in .eh_frame or .debug_frame is different from that used in other | |
3698 debug info sections. Given a GCC hard register number, this macro | |
3699 should return the .eh_frame register number. The default is | |
3700 @code{DBX_REGISTER_NUMBER (@var{regno})}. | |
3701 | |
3702 @end defmac | |
3703 | |
3704 @defmac DWARF2_FRAME_REG_OUT (@var{regno}, @var{for_eh}) | |
3705 | |
3706 Define this macro to map register numbers held in the call frame info | |
3707 that GCC has collected using @code{DWARF_FRAME_REGNUM} to those that | |
3708 should be output in .debug_frame (@code{@var{for_eh}} is zero) and | |
3709 .eh_frame (@code{@var{for_eh}} is nonzero). The default is to | |
3710 return @code{@var{regno}}. | |
3711 | |
3712 @end defmac | |
3713 | |
3714 @node Elimination | |
3715 @subsection Eliminating Frame Pointer and Arg Pointer | |
3716 | |
3717 @c prevent bad page break with this line | |
3718 This is about eliminating the frame pointer and arg pointer. | |
3719 | |
3720 @hook TARGET_FRAME_POINTER_REQUIRED | |
3721 This target hook should return @code{true} if a function must have and use | |
3722 a frame pointer. This target hook is called in the reload pass. If its return | |
3723 value is @code{true} the function will have a frame pointer. | |
3724 | |
3725 This target hook can in principle examine the current function and decide | |
3726 according to the facts, but on most machines the constant @code{false} or the | |
3727 constant @code{true} suffices. Use @code{false} when the machine allows code | |
3728 to be generated with no frame pointer, and doing so saves some time or space. | |
3729 Use @code{true} when there is no possible advantage to avoiding a frame | |
3730 pointer. | |
3731 | |
3732 In certain cases, the compiler does not know how to produce valid code | |
3733 without a frame pointer. The compiler recognizes those cases and | |
3734 automatically gives the function a frame pointer regardless of what | |
3735 @code{TARGET_FRAME_POINTER_REQUIRED} returns. You don't need to worry about | |
3736 them. | |
3737 | |
3738 In a function that does not require a frame pointer, the frame pointer | |
3739 register can be allocated for ordinary usage, unless you mark it as a | |
3740 fixed register. See @code{FIXED_REGISTERS} for more information. | |
3741 | |
3742 Default return value is @code{false}. | |
3743 @end deftypefn | |
3744 | |
3745 @findex get_frame_size | |
3746 @defmac INITIAL_FRAME_POINTER_OFFSET (@var{depth-var}) | |
3747 A C statement to store in the variable @var{depth-var} the difference | |
3748 between the frame pointer and the stack pointer values immediately after | |
3749 the function prologue. The value would be computed from information | |
3750 such as the result of @code{get_frame_size ()} and the tables of | |
3751 registers @code{regs_ever_live} and @code{call_used_regs}. | |
3752 | |
3753 If @code{ELIMINABLE_REGS} is defined, this macro will be not be used and | |
3754 need not be defined. Otherwise, it must be defined even if | |
3755 @code{TARGET_FRAME_POINTER_REQUIRED} always returns true; in that | |
3756 case, you may set @var{depth-var} to anything. | |
3757 @end defmac | |
3758 | |
3759 @defmac ELIMINABLE_REGS | |
3760 If defined, this macro specifies a table of register pairs used to | |
3761 eliminate unneeded registers that point into the stack frame. If it is not | |
3762 defined, the only elimination attempted by the compiler is to replace | |
3763 references to the frame pointer with references to the stack pointer. | |
3764 | |
3765 The definition of this macro is a list of structure initializations, each | |
3766 of which specifies an original and replacement register. | |
3767 | |
3768 On some machines, the position of the argument pointer is not known until | |
3769 the compilation is completed. In such a case, a separate hard register | |
3770 must be used for the argument pointer. This register can be eliminated by | |
3771 replacing it with either the frame pointer or the argument pointer, | |
3772 depending on whether or not the frame pointer has been eliminated. | |
3773 | |
3774 In this case, you might specify: | |
3775 @smallexample | |
3776 #define ELIMINABLE_REGS \ | |
3777 @{@{ARG_POINTER_REGNUM, STACK_POINTER_REGNUM@}, \ | |
3778 @{ARG_POINTER_REGNUM, FRAME_POINTER_REGNUM@}, \ | |
3779 @{FRAME_POINTER_REGNUM, STACK_POINTER_REGNUM@}@} | |
3780 @end smallexample | |
3781 | |
3782 Note that the elimination of the argument pointer with the stack pointer is | |
3783 specified first since that is the preferred elimination. | |
3784 @end defmac | |
3785 | |
3786 @hook TARGET_CAN_ELIMINATE | |
3787 This target hook should returns @code{true} if the compiler is allowed to | |
3788 try to replace register number @var{from_reg} with register number | |
3789 @var{to_reg}. This target hook need only be defined if @code{ELIMINABLE_REGS} | |
3790 is defined, and will usually be @code{true}, since most of the cases | |
3791 preventing register elimination are things that the compiler already | |
3792 knows about. | |
3793 | |
3794 Default return value is @code{true}. | |
3795 @end deftypefn | |
3796 | |
3797 @defmac INITIAL_ELIMINATION_OFFSET (@var{from-reg}, @var{to-reg}, @var{offset-var}) | |
3798 This macro is similar to @code{INITIAL_FRAME_POINTER_OFFSET}. It | |
3799 specifies the initial difference between the specified pair of | |
3800 registers. This macro must be defined if @code{ELIMINABLE_REGS} is | |
3801 defined. | |
3802 @end defmac | |
3803 | |
3804 @node Stack Arguments | |
3805 @subsection Passing Function Arguments on the Stack | |
3806 @cindex arguments on stack | |
3807 @cindex stack arguments | |
3808 | |
3809 The macros in this section control how arguments are passed | |
3810 on the stack. See the following section for other macros that | |
3811 control passing certain arguments in registers. | |
3812 | |
3813 @hook TARGET_PROMOTE_PROTOTYPES | |
3814 This target hook returns @code{true} if an argument declared in a | |
3815 prototype as an integral type smaller than @code{int} should actually be | |
3816 passed as an @code{int}. In addition to avoiding errors in certain | |
3817 cases of mismatch, it also makes for better code on certain machines. | |
3818 The default is to not promote prototypes. | |
3819 @end deftypefn | |
3820 | |
3821 @defmac PUSH_ARGS | |
3822 A C expression. If nonzero, push insns will be used to pass | |
3823 outgoing arguments. | |
3824 If the target machine does not have a push instruction, set it to zero. | |
3825 That directs GCC to use an alternate strategy: to | |
3826 allocate the entire argument block and then store the arguments into | |
3827 it. When @code{PUSH_ARGS} is nonzero, @code{PUSH_ROUNDING} must be defined too. | |
3828 @end defmac | |
3829 | |
3830 @defmac PUSH_ARGS_REVERSED | |
3831 A C expression. If nonzero, function arguments will be evaluated from | |
3832 last to first, rather than from first to last. If this macro is not | |
3833 defined, it defaults to @code{PUSH_ARGS} on targets where the stack | |
3834 and args grow in opposite directions, and 0 otherwise. | |
3835 @end defmac | |
3836 | |
3837 @defmac PUSH_ROUNDING (@var{npushed}) | |
3838 A C expression that is the number of bytes actually pushed onto the | |
3839 stack when an instruction attempts to push @var{npushed} bytes. | |
3840 | |
3841 On some machines, the definition | |
3842 | |
3843 @smallexample | |
3844 #define PUSH_ROUNDING(BYTES) (BYTES) | |
3845 @end smallexample | |
3846 | |
3847 @noindent | |
3848 will suffice. But on other machines, instructions that appear | |
3849 to push one byte actually push two bytes in an attempt to maintain | |
3850 alignment. Then the definition should be | |
3851 | |
3852 @smallexample | |
3853 #define PUSH_ROUNDING(BYTES) (((BYTES) + 1) & ~1) | |
3854 @end smallexample | |
3855 | |
3856 If the value of this macro has a type, it should be an unsigned type. | |
3857 @end defmac | |
3858 | |
3859 @findex current_function_outgoing_args_size | |
3860 @defmac ACCUMULATE_OUTGOING_ARGS | |
3861 A C expression. If nonzero, the maximum amount of space required for outgoing arguments | |
3862 will be computed and placed into the variable | |
3863 @code{current_function_outgoing_args_size}. No space will be pushed | |
3864 onto the stack for each call; instead, the function prologue should | |
3865 increase the stack frame size by this amount. | |
3866 | |
3867 Setting both @code{PUSH_ARGS} and @code{ACCUMULATE_OUTGOING_ARGS} | |
3868 is not proper. | |
3869 @end defmac | |
3870 | |
3871 @defmac REG_PARM_STACK_SPACE (@var{fndecl}) | |
3872 Define this macro if functions should assume that stack space has been | |
3873 allocated for arguments even when their values are passed in | |
3874 registers. | |
3875 | |
3876 The value of this macro is the size, in bytes, of the area reserved for | |
3877 arguments passed in registers for the function represented by @var{fndecl}, | |
3878 which can be zero if GCC is calling a library function. | |
3879 The argument @var{fndecl} can be the FUNCTION_DECL, or the type itself | |
3880 of the function. | |
3881 | |
3882 This space can be allocated by the caller, or be a part of the | |
3883 machine-dependent stack frame: @code{OUTGOING_REG_PARM_STACK_SPACE} says | |
3884 which. | |
3885 @end defmac | |
3886 @c above is overfull. not sure what to do. --mew 5feb93 did | |
3887 @c something, not sure if it looks good. --mew 10feb93 | |
3888 | |
3889 @defmac OUTGOING_REG_PARM_STACK_SPACE (@var{fntype}) | |
3890 Define this to a nonzero value if it is the responsibility of the | |
3891 caller to allocate the area reserved for arguments passed in registers | |
3892 when calling a function of @var{fntype}. @var{fntype} may be NULL | |
3893 if the function called is a library function. | |
3894 | |
3895 If @code{ACCUMULATE_OUTGOING_ARGS} is defined, this macro controls | |
3896 whether the space for these arguments counts in the value of | |
3897 @code{current_function_outgoing_args_size}. | |
3898 @end defmac | |
3899 | |
3900 @defmac STACK_PARMS_IN_REG_PARM_AREA | |
3901 Define this macro if @code{REG_PARM_STACK_SPACE} is defined, but the | |
3902 stack parameters don't skip the area specified by it. | |
3903 @c i changed this, makes more sens and it should have taken care of the | |
3904 @c overfull.. not as specific, tho. --mew 5feb93 | |
3905 | |
3906 Normally, when a parameter is not passed in registers, it is placed on the | |
3907 stack beyond the @code{REG_PARM_STACK_SPACE} area. Defining this macro | |
3908 suppresses this behavior and causes the parameter to be passed on the | |
3909 stack in its natural location. | |
3910 @end defmac | |
3911 | |
3912 @hook TARGET_RETURN_POPS_ARGS | |
3913 This target hook returns the number of bytes of its own arguments that | |
3914 a function pops on returning, or 0 if the function pops no arguments | |
3915 and the caller must therefore pop them all after the function returns. | |
3916 | |
3917 @var{fundecl} is a C variable whose value is a tree node that describes | |
3918 the function in question. Normally it is a node of type | |
3919 @code{FUNCTION_DECL} that describes the declaration of the function. | |
3920 From this you can obtain the @code{DECL_ATTRIBUTES} of the function. | |
3921 | |
3922 @var{funtype} is a C variable whose value is a tree node that | |
3923 describes the function in question. Normally it is a node of type | |
3924 @code{FUNCTION_TYPE} that describes the data type of the function. | |
3925 From this it is possible to obtain the data types of the value and | |
3926 arguments (if known). | |
3927 | |
3928 When a call to a library function is being considered, @var{fundecl} | |
3929 will contain an identifier node for the library function. Thus, if | |
3930 you need to distinguish among various library functions, you can do so | |
3931 by their names. Note that ``library function'' in this context means | |
3932 a function used to perform arithmetic, whose name is known specially | |
3933 in the compiler and was not mentioned in the C code being compiled. | |
3934 | |
3935 @var{size} is the number of bytes of arguments passed on the | |
3936 stack. If a variable number of bytes is passed, it is zero, and | |
3937 argument popping will always be the responsibility of the calling function. | |
3938 | |
3939 On the VAX, all functions always pop their arguments, so the definition | |
3940 of this macro is @var{size}. On the 68000, using the standard | |
3941 calling convention, no functions pop their arguments, so the value of | |
3942 the macro is always 0 in this case. But an alternative calling | |
3943 convention is available in which functions that take a fixed number of | |
3944 arguments pop them but other functions (such as @code{printf}) pop | |
3945 nothing (the caller pops all). When this convention is in use, | |
3946 @var{funtype} is examined to determine whether a function takes a fixed | |
3947 number of arguments. | |
3948 @end deftypefn | |
3949 | |
3950 @defmac CALL_POPS_ARGS (@var{cum}) | |
3951 A C expression that should indicate the number of bytes a call sequence | |
3952 pops off the stack. It is added to the value of @code{RETURN_POPS_ARGS} | |
3953 when compiling a function call. | |
3954 | |
3955 @var{cum} is the variable in which all arguments to the called function | |
3956 have been accumulated. | |
3957 | |
3958 On certain architectures, such as the SH5, a call trampoline is used | |
3959 that pops certain registers off the stack, depending on the arguments | |
3960 that have been passed to the function. Since this is a property of the | |
3961 call site, not of the called function, @code{RETURN_POPS_ARGS} is not | |
3962 appropriate. | |
3963 @end defmac | |
3964 | |
3965 @node Register Arguments | |
3966 @subsection Passing Arguments in Registers | |
3967 @cindex arguments in registers | |
3968 @cindex registers arguments | |
3969 | |
3970 This section describes the macros which let you control how various | |
3971 types of arguments are passed in registers or how they are arranged in | |
3972 the stack. | |
3973 | |
3974 @defmac FUNCTION_ARG (@var{cum}, @var{mode}, @var{type}, @var{named}) | |
3975 A C expression that controls whether a function argument is passed | |
3976 in a register, and which register. | |
3977 | |
3978 The arguments are @var{cum}, which summarizes all the previous | |
3979 arguments; @var{mode}, the machine mode of the argument; @var{type}, | |
3980 the data type of the argument as a tree node or 0 if that is not known | |
3981 (which happens for C support library functions); and @var{named}, | |
3982 which is 1 for an ordinary argument and 0 for nameless arguments that | |
3983 correspond to @samp{@dots{}} in the called function's prototype. | |
3984 @var{type} can be an incomplete type if a syntax error has previously | |
3985 occurred. | |
3986 | |
3987 The value of the expression is usually either a @code{reg} RTX for the | |
3988 hard register in which to pass the argument, or zero to pass the | |
3989 argument on the stack. | |
3990 | |
3991 For machines like the VAX and 68000, where normally all arguments are | |
3992 pushed, zero suffices as a definition. | |
3993 | |
3994 The value of the expression can also be a @code{parallel} RTX@. This is | |
3995 used when an argument is passed in multiple locations. The mode of the | |
3996 @code{parallel} should be the mode of the entire argument. The | |
3997 @code{parallel} holds any number of @code{expr_list} pairs; each one | |
3998 describes where part of the argument is passed. In each | |
3999 @code{expr_list} the first operand must be a @code{reg} RTX for the hard | |
4000 register in which to pass this part of the argument, and the mode of the | |
4001 register RTX indicates how large this part of the argument is. The | |
4002 second operand of the @code{expr_list} is a @code{const_int} which gives | |
4003 the offset in bytes into the entire argument of where this part starts. | |
4004 As a special exception the first @code{expr_list} in the @code{parallel} | |
4005 RTX may have a first operand of zero. This indicates that the entire | |
4006 argument is also stored on the stack. | |
4007 | |
4008 The last time this macro is called, it is called with @code{MODE == | |
4009 VOIDmode}, and its result is passed to the @code{call} or @code{call_value} | |
4010 pattern as operands 2 and 3 respectively. | |
4011 | |
4012 @cindex @file{stdarg.h} and register arguments | |
4013 The usual way to make the ISO library @file{stdarg.h} work on a machine | |
4014 where some arguments are usually passed in registers, is to cause | |
4015 nameless arguments to be passed on the stack instead. This is done | |
4016 by making @code{FUNCTION_ARG} return 0 whenever @var{named} is 0. | |
4017 | |
4018 @cindex @code{TARGET_MUST_PASS_IN_STACK}, and @code{FUNCTION_ARG} | |
4019 @cindex @code{REG_PARM_STACK_SPACE}, and @code{FUNCTION_ARG} | |
4020 You may use the hook @code{targetm.calls.must_pass_in_stack} | |
4021 in the definition of this macro to determine if this argument is of a | |
4022 type that must be passed in the stack. If @code{REG_PARM_STACK_SPACE} | |
4023 is not defined and @code{FUNCTION_ARG} returns nonzero for such an | |
4024 argument, the compiler will abort. If @code{REG_PARM_STACK_SPACE} is | |
4025 defined, the argument will be computed in the stack and then loaded into | |
4026 a register. | |
4027 @end defmac | |
4028 | |
4029 @hook TARGET_MUST_PASS_IN_STACK | |
4030 This target hook should return @code{true} if we should not pass @var{type} | |
4031 solely in registers. The file @file{expr.h} defines a | |
4032 definition that is usually appropriate, refer to @file{expr.h} for additional | |
4033 documentation. | |
4034 @end deftypefn | |
4035 | |
4036 @defmac FUNCTION_INCOMING_ARG (@var{cum}, @var{mode}, @var{type}, @var{named}) | |
4037 Define this macro if the target machine has ``register windows'', so | |
4038 that the register in which a function sees an arguments is not | |
4039 necessarily the same as the one in which the caller passed the | |
4040 argument. | |
4041 | |
4042 For such machines, @code{FUNCTION_ARG} computes the register in which | |
4043 the caller passes the value, and @code{FUNCTION_INCOMING_ARG} should | |
4044 be defined in a similar fashion to tell the function being called | |
4045 where the arguments will arrive. | |
4046 | |
4047 If @code{FUNCTION_INCOMING_ARG} is not defined, @code{FUNCTION_ARG} | |
4048 serves both purposes. | |
4049 @end defmac | |
4050 | |
4051 @hook TARGET_ARG_PARTIAL_BYTES | |
4052 This target hook returns the number of bytes at the beginning of an | |
4053 argument that must be put in registers. The value must be zero for | |
4054 arguments that are passed entirely in registers or that are entirely | |
4055 pushed on the stack. | |
4056 | |
4057 On some machines, certain arguments must be passed partially in | |
4058 registers and partially in memory. On these machines, typically the | |
4059 first few words of arguments are passed in registers, and the rest | |
4060 on the stack. If a multi-word argument (a @code{double} or a | |
4061 structure) crosses that boundary, its first few words must be passed | |
4062 in registers and the rest must be pushed. This macro tells the | |
4063 compiler when this occurs, and how many bytes should go in registers. | |
4064 | |
4065 @code{FUNCTION_ARG} for these arguments should return the first | |
4066 register to be used by the caller for this argument; likewise | |
4067 @code{FUNCTION_INCOMING_ARG}, for the called function. | |
4068 @end deftypefn | |
4069 | |
4070 @hook TARGET_PASS_BY_REFERENCE | |
4071 This target hook should return @code{true} if an argument at the | |
4072 position indicated by @var{cum} should be passed by reference. This | |
4073 predicate is queried after target independent reasons for being | |
4074 passed by reference, such as @code{TREE_ADDRESSABLE (type)}. | |
4075 | |
4076 If the hook returns true, a copy of that argument is made in memory and a | |
4077 pointer to the argument is passed instead of the argument itself. | |
4078 The pointer is passed in whatever way is appropriate for passing a pointer | |
4079 to that type. | |
4080 @end deftypefn | |
4081 | |
4082 @hook TARGET_CALLEE_COPIES | |
4083 The function argument described by the parameters to this hook is | |
4084 known to be passed by reference. The hook should return true if the | |
4085 function argument should be copied by the callee instead of copied | |
4086 by the caller. | |
4087 | |
4088 For any argument for which the hook returns true, if it can be | |
4089 determined that the argument is not modified, then a copy need | |
4090 not be generated. | |
4091 | |
4092 The default version of this hook always returns false. | |
4093 @end deftypefn | |
4094 | |
4095 @defmac CUMULATIVE_ARGS | |
4096 A C type for declaring a variable that is used as the first argument of | |
4097 @code{FUNCTION_ARG} and other related values. For some target machines, | |
4098 the type @code{int} suffices and can hold the number of bytes of | |
4099 argument so far. | |
4100 | |
4101 There is no need to record in @code{CUMULATIVE_ARGS} anything about the | |
4102 arguments that have been passed on the stack. The compiler has other | |
4103 variables to keep track of that. For target machines on which all | |
4104 arguments are passed on the stack, there is no need to store anything in | |
4105 @code{CUMULATIVE_ARGS}; however, the data structure must exist and | |
4106 should not be empty, so use @code{int}. | |
4107 @end defmac | |
4108 | |
4109 @defmac OVERRIDE_ABI_FORMAT (@var{fndecl}) | |
4110 If defined, this macro is called before generating any code for a | |
4111 function, but after the @var{cfun} descriptor for the function has been | |
4112 created. The back end may use this macro to update @var{cfun} to | |
4113 reflect an ABI other than that which would normally be used by default. | |
4114 If the compiler is generating code for a compiler-generated function, | |
4115 @var{fndecl} may be @code{NULL}. | |
4116 @end defmac | |
4117 | |
4118 @defmac INIT_CUMULATIVE_ARGS (@var{cum}, @var{fntype}, @var{libname}, @var{fndecl}, @var{n_named_args}) | |
4119 A C statement (sans semicolon) for initializing the variable | |
4120 @var{cum} for the state at the beginning of the argument list. The | |
4121 variable has type @code{CUMULATIVE_ARGS}. The value of @var{fntype} | |
4122 is the tree node for the data type of the function which will receive | |
4123 the args, or 0 if the args are to a compiler support library function. | |
4124 For direct calls that are not libcalls, @var{fndecl} contain the | |
4125 declaration node of the function. @var{fndecl} is also set when | |
4126 @code{INIT_CUMULATIVE_ARGS} is used to find arguments for the function | |
4127 being compiled. @var{n_named_args} is set to the number of named | |
4128 arguments, including a structure return address if it is passed as a | |
4129 parameter, when making a call. When processing incoming arguments, | |
4130 @var{n_named_args} is set to @minus{}1. | |
4131 | |
4132 When processing a call to a compiler support library function, | |
4133 @var{libname} identifies which one. It is a @code{symbol_ref} rtx which | |
4134 contains the name of the function, as a string. @var{libname} is 0 when | |
4135 an ordinary C function call is being processed. Thus, each time this | |
4136 macro is called, either @var{libname} or @var{fntype} is nonzero, but | |
4137 never both of them at once. | |
4138 @end defmac | |
4139 | |
4140 @defmac INIT_CUMULATIVE_LIBCALL_ARGS (@var{cum}, @var{mode}, @var{libname}) | |
4141 Like @code{INIT_CUMULATIVE_ARGS} but only used for outgoing libcalls, | |
4142 it gets a @code{MODE} argument instead of @var{fntype}, that would be | |
4143 @code{NULL}. @var{indirect} would always be zero, too. If this macro | |
4144 is not defined, @code{INIT_CUMULATIVE_ARGS (cum, NULL_RTX, libname, | |
4145 0)} is used instead. | |
4146 @end defmac | |
4147 | |
4148 @defmac INIT_CUMULATIVE_INCOMING_ARGS (@var{cum}, @var{fntype}, @var{libname}) | |
4149 Like @code{INIT_CUMULATIVE_ARGS} but overrides it for the purposes of | |
4150 finding the arguments for the function being compiled. If this macro is | |
4151 undefined, @code{INIT_CUMULATIVE_ARGS} is used instead. | |
4152 | |
4153 The value passed for @var{libname} is always 0, since library routines | |
4154 with special calling conventions are never compiled with GCC@. The | |
4155 argument @var{libname} exists for symmetry with | |
4156 @code{INIT_CUMULATIVE_ARGS}. | |
4157 @c could use "this macro" in place of @code{INIT_CUMULATIVE_ARGS}, maybe. | |
4158 @c --mew 5feb93 i switched the order of the sentences. --mew 10feb93 | |
4159 @end defmac | |
4160 | |
4161 @defmac FUNCTION_ARG_ADVANCE (@var{cum}, @var{mode}, @var{type}, @var{named}) | |
4162 A C statement (sans semicolon) to update the summarizer variable | |
4163 @var{cum} to advance past an argument in the argument list. The | |
4164 values @var{mode}, @var{type} and @var{named} describe that argument. | |
4165 Once this is done, the variable @var{cum} is suitable for analyzing | |
4166 the @emph{following} argument with @code{FUNCTION_ARG}, etc. | |
4167 | |
4168 This macro need not do anything if the argument in question was passed | |
4169 on the stack. The compiler knows how to track the amount of stack space | |
4170 used for arguments without any special help. | |
4171 @end defmac | |
4172 | |
4173 @defmac FUNCTION_ARG_OFFSET (@var{mode}, @var{type}) | |
4174 If defined, a C expression that is the number of bytes to add to the | |
4175 offset of the argument passed in memory. This is needed for the SPU, | |
4176 which passes @code{char} and @code{short} arguments in the preferred | |
4177 slot that is in the middle of the quad word instead of starting at the | |
4178 top. | |
4179 @end defmac | |
4180 | |
4181 @defmac FUNCTION_ARG_PADDING (@var{mode}, @var{type}) | |
4182 If defined, a C expression which determines whether, and in which direction, | |
4183 to pad out an argument with extra space. The value should be of type | |
4184 @code{enum direction}: either @code{upward} to pad above the argument, | |
4185 @code{downward} to pad below, or @code{none} to inhibit padding. | |
4186 | |
4187 The @emph{amount} of padding is always just enough to reach the next | |
4188 multiple of @code{TARGET_FUNCTION_ARG_BOUNDARY}; this macro does not | |
4189 control it. | |
4190 | |
4191 This macro has a default definition which is right for most systems. | |
4192 For little-endian machines, the default is to pad upward. For | |
4193 big-endian machines, the default is to pad downward for an argument of | |
4194 constant size shorter than an @code{int}, and upward otherwise. | |
4195 @end defmac | |
4196 | |
4197 @defmac PAD_VARARGS_DOWN | |
4198 If defined, a C expression which determines whether the default | |
4199 implementation of va_arg will attempt to pad down before reading the | |
4200 next argument, if that argument is smaller than its aligned space as | |
4201 controlled by @code{PARM_BOUNDARY}. If this macro is not defined, all such | |
4202 arguments are padded down if @code{BYTES_BIG_ENDIAN} is true. | |
4203 @end defmac | |
4204 | |
4205 @defmac BLOCK_REG_PADDING (@var{mode}, @var{type}, @var{first}) | |
4206 Specify padding for the last element of a block move between registers and | |
4207 memory. @var{first} is nonzero if this is the only element. Defining this | |
4208 macro allows better control of register function parameters on big-endian | |
4209 machines, without using @code{PARALLEL} rtl. In particular, | |
4210 @code{MUST_PASS_IN_STACK} need not test padding and mode of types in | |
4211 registers, as there is no longer a "wrong" part of a register; For example, | |
4212 a three byte aggregate may be passed in the high part of a register if so | |
4213 required. | |
4214 @end defmac | |
4215 | |
4216 @hook TARGET_FUNCTION_ARG_BOUNDARY | |
4217 This hook returns the alignment boundary, in bits, of an argument | |
4218 with the specified mode and type. The default hook returns | |
4219 @code{PARM_BOUNDARY} for all arguments. | |
4220 @end deftypefn | |
4221 | |
4222 @defmac FUNCTION_ARG_REGNO_P (@var{regno}) | |
4223 A C expression that is nonzero if @var{regno} is the number of a hard | |
4224 register in which function arguments are sometimes passed. This does | |
4225 @emph{not} include implicit arguments such as the static chain and | |
4226 the structure-value address. On many machines, no registers can be | |
4227 used for this purpose since all function arguments are pushed on the | |
4228 stack. | |
4229 @end defmac | |
4230 | |
4231 @hook TARGET_SPLIT_COMPLEX_ARG | |
4232 This hook should return true if parameter of type @var{type} are passed | |
4233 as two scalar parameters. By default, GCC will attempt to pack complex | |
4234 arguments into the target's word size. Some ABIs require complex arguments | |
4235 to be split and treated as their individual components. For example, on | |
4236 AIX64, complex floats should be passed in a pair of floating point | |
4237 registers, even though a complex float would fit in one 64-bit floating | |
4238 point register. | |
4239 | |
4240 The default value of this hook is @code{NULL}, which is treated as always | |
4241 false. | |
4242 @end deftypefn | |
4243 | |
4244 @hook TARGET_BUILD_BUILTIN_VA_LIST | |
4245 This hook returns a type node for @code{va_list} for the target. | |
4246 The default version of the hook returns @code{void*}. | |
4247 @end deftypefn | |
4248 | |
4249 @hook TARGET_ENUM_VA_LIST_P | |
4250 This target hook is used in function @code{c_common_nodes_and_builtins} | |
4251 to iterate through the target specific builtin types for va_list. The | |
4252 variable @var{idx} is used as iterator. @var{pname} has to be a pointer | |
4253 to a @code{const char *} and @var{ptree} a pointer to a @code{tree} typed | |
4254 variable. | |
4255 The arguments @var{pname} and @var{ptree} are used to store the result of | |
4256 this macro and are set to the name of the va_list builtin type and its | |
4257 internal type. | |
4258 If the return value of this macro is zero, then there is no more element. | |
4259 Otherwise the @var{IDX} should be increased for the next call of this | |
4260 macro to iterate through all types. | |
4261 @end deftypefn | |
4262 | |
4263 @hook TARGET_FN_ABI_VA_LIST | |
4264 This hook returns the va_list type of the calling convention specified by | |
4265 @var{fndecl}. | |
4266 The default version of this hook returns @code{va_list_type_node}. | |
4267 @end deftypefn | |
4268 | |
4269 @hook TARGET_CANONICAL_VA_LIST_TYPE | |
4270 This hook returns the va_list type of the calling convention specified by the | |
4271 type of @var{type}. If @var{type} is not a valid va_list type, it returns | |
4272 @code{NULL_TREE}. | |
4273 @end deftypefn | |
4274 | |
4275 @hook TARGET_GIMPLIFY_VA_ARG_EXPR | |
4276 This hook performs target-specific gimplification of | |
4277 @code{VA_ARG_EXPR}. The first two parameters correspond to the | |
4278 arguments to @code{va_arg}; the latter two are as in | |
4279 @code{gimplify.c:gimplify_expr}. | |
4280 @end deftypefn | |
4281 | |
4282 @hook TARGET_VALID_POINTER_MODE | |
4283 Define this to return nonzero if the port can handle pointers | |
4284 with machine mode @var{mode}. The default version of this | |
4285 hook returns true for both @code{ptr_mode} and @code{Pmode}. | |
4286 @end deftypefn | |
4287 | |
4288 @hook TARGET_REF_MAY_ALIAS_ERRNO | |
4289 | |
4290 @hook TARGET_SCALAR_MODE_SUPPORTED_P | |
4291 Define this to return nonzero if the port is prepared to handle | |
4292 insns involving scalar mode @var{mode}. For a scalar mode to be | |
4293 considered supported, all the basic arithmetic and comparisons | |
4294 must work. | |
4295 | |
4296 The default version of this hook returns true for any mode | |
4297 required to handle the basic C types (as defined by the port). | |
4298 Included here are the double-word arithmetic supported by the | |
4299 code in @file{optabs.c}. | |
4300 @end deftypefn | |
4301 | |
4302 @hook TARGET_VECTOR_MODE_SUPPORTED_P | |
4303 Define this to return nonzero if the port is prepared to handle | |
4304 insns involving vector mode @var{mode}. At the very least, it | |
4305 must have move patterns for this mode. | |
4306 @end deftypefn | |
4307 | |
4308 @hook TARGET_SMALL_REGISTER_CLASSES_FOR_MODE_P | |
4309 Define this to return nonzero for machine modes for which the port has | |
4310 small register classes. If this target hook returns nonzero for a given | |
4311 @var{mode}, the compiler will try to minimize the lifetime of registers | |
4312 in @var{mode}. The hook may be called with @code{VOIDmode} as argument. | |
4313 In this case, the hook is expected to return nonzero if it returns nonzero | |
4314 for any mode. | |
4315 | |
4316 On some machines, it is risky to let hard registers live across arbitrary | |
4317 insns. Typically, these machines have instructions that require values | |
4318 to be in specific registers (like an accumulator), and reload will fail | |
4319 if the required hard register is used for another purpose across such an | |
4320 insn. | |
4321 | |
4322 Passes before reload do not know which hard registers will be used | |
4323 in an instruction, but the machine modes of the registers set or used in | |
4324 the instruction are already known. And for some machines, register | |
4325 classes are small for, say, integer registers but not for floating point | |
4326 registers. For example, the AMD x86-64 architecture requires specific | |
4327 registers for the legacy x86 integer instructions, but there are many | |
4328 SSE registers for floating point operations. On such targets, a good | |
4329 strategy may be to return nonzero from this hook for @code{INTEGRAL_MODE_P} | |
4330 machine modes but zero for the SSE register classes. | |
4331 | |
4332 The default version of this hook returns false for any mode. It is always | |
4333 safe to redefine this hook to return with a nonzero value. But if you | |
4334 unnecessarily define it, you will reduce the amount of optimizations | |
4335 that can be performed in some cases. If you do not define this hook | |
4336 to return a nonzero value when it is required, the compiler will run out | |
4337 of spill registers and print a fatal error message. | |
4338 @end deftypefn | |
4339 | |
4340 @hook TARGET_FLAGS_REGNUM | |
4341 | |
4342 @node Scalar Return | |
4343 @subsection How Scalar Function Values Are Returned | |
4344 @cindex return values in registers | |
4345 @cindex values, returned by functions | |
4346 @cindex scalars, returned as values | |
4347 | |
4348 This section discusses the macros that control returning scalars as | |
4349 values---values that can fit in registers. | |
4350 | |
4351 @hook TARGET_FUNCTION_VALUE | |
4352 | |
4353 Define this to return an RTX representing the place where a function | |
4354 returns or receives a value of data type @var{ret_type}, a tree node | |
4355 representing a data type. @var{fn_decl_or_type} is a tree node | |
4356 representing @code{FUNCTION_DECL} or @code{FUNCTION_TYPE} of a | |
4357 function being called. If @var{outgoing} is false, the hook should | |
4358 compute the register in which the caller will see the return value. | |
4359 Otherwise, the hook should return an RTX representing the place where | |
4360 a function returns a value. | |
4361 | |
4362 On many machines, only @code{TYPE_MODE (@var{ret_type})} is relevant. | |
4363 (Actually, on most machines, scalar values are returned in the same | |
4364 place regardless of mode.) The value of the expression is usually a | |
4365 @code{reg} RTX for the hard register where the return value is stored. | |
4366 The value can also be a @code{parallel} RTX, if the return value is in | |
4367 multiple places. See @code{FUNCTION_ARG} for an explanation of the | |
4368 @code{parallel} form. Note that the callee will populate every | |
4369 location specified in the @code{parallel}, but if the first element of | |
4370 the @code{parallel} contains the whole return value, callers will use | |
4371 that element as the canonical location and ignore the others. The m68k | |
4372 port uses this type of @code{parallel} to return pointers in both | |
4373 @samp{%a0} (the canonical location) and @samp{%d0}. | |
4374 | |
4375 If @code{TARGET_PROMOTE_FUNCTION_RETURN} returns true, you must apply | |
4376 the same promotion rules specified in @code{PROMOTE_MODE} if | |
4377 @var{valtype} is a scalar type. | |
4378 | |
4379 If the precise function being called is known, @var{func} is a tree | |
4380 node (@code{FUNCTION_DECL}) for it; otherwise, @var{func} is a null | |
4381 pointer. This makes it possible to use a different value-returning | |
4382 convention for specific functions when all their calls are | |
4383 known. | |
4384 | |
4385 Some target machines have ``register windows'' so that the register in | |
4386 which a function returns its value is not the same as the one in which | |
4387 the caller sees the value. For such machines, you should return | |
4388 different RTX depending on @var{outgoing}. | |
4389 | |
4390 @code{TARGET_FUNCTION_VALUE} is not used for return values with | |
4391 aggregate data types, because these are returned in another way. See | |
4392 @code{TARGET_STRUCT_VALUE_RTX} and related macros, below. | |
4393 @end deftypefn | |
4394 | |
4395 @defmac FUNCTION_VALUE (@var{valtype}, @var{func}) | |
4396 This macro has been deprecated. Use @code{TARGET_FUNCTION_VALUE} for | |
4397 a new target instead. | |
4398 @end defmac | |
4399 | |
4400 @defmac LIBCALL_VALUE (@var{mode}) | |
4401 A C expression to create an RTX representing the place where a library | |
4402 function returns a value of mode @var{mode}. | |
4403 | |
4404 Note that ``library function'' in this context means a compiler | |
4405 support routine, used to perform arithmetic, whose name is known | |
4406 specially by the compiler and was not mentioned in the C code being | |
4407 compiled. | |
4408 @end defmac | |
4409 | |
4410 @hook TARGET_LIBCALL_VALUE | |
4411 Define this hook if the back-end needs to know the name of the libcall | |
4412 function in order to determine where the result should be returned. | |
4413 | |
4414 The mode of the result is given by @var{mode} and the name of the called | |
4415 library function is given by @var{fun}. The hook should return an RTX | |
4416 representing the place where the library function result will be returned. | |
4417 | |
4418 If this hook is not defined, then LIBCALL_VALUE will be used. | |
4419 @end deftypefn | |
4420 | |
4421 @defmac FUNCTION_VALUE_REGNO_P (@var{regno}) | |
4422 A C expression that is nonzero if @var{regno} is the number of a hard | |
4423 register in which the values of called function may come back. | |
4424 | |
4425 A register whose use for returning values is limited to serving as the | |
4426 second of a pair (for a value of type @code{double}, say) need not be | |
4427 recognized by this macro. So for most machines, this definition | |
4428 suffices: | |
4429 | |
4430 @smallexample | |
4431 #define FUNCTION_VALUE_REGNO_P(N) ((N) == 0) | |
4432 @end smallexample | |
4433 | |
4434 If the machine has register windows, so that the caller and the called | |
4435 function use different registers for the return value, this macro | |
4436 should recognize only the caller's register numbers. | |
4437 | |
4438 This macro has been deprecated. Use @code{TARGET_FUNCTION_VALUE_REGNO_P} | |
4439 for a new target instead. | |
4440 @end defmac | |
4441 | |
4442 @hook TARGET_FUNCTION_VALUE_REGNO_P | |
4443 A target hook that return @code{true} if @var{regno} is the number of a hard | |
4444 register in which the values of called function may come back. | |
4445 | |
4446 A register whose use for returning values is limited to serving as the | |
4447 second of a pair (for a value of type @code{double}, say) need not be | |
4448 recognized by this target hook. | |
4449 | |
4450 If the machine has register windows, so that the caller and the called | |
4451 function use different registers for the return value, this target hook | |
4452 should recognize only the caller's register numbers. | |
4453 | |
4454 If this hook is not defined, then FUNCTION_VALUE_REGNO_P will be used. | |
4455 @end deftypefn | |
4456 | |
4457 @defmac APPLY_RESULT_SIZE | |
4458 Define this macro if @samp{untyped_call} and @samp{untyped_return} | |
4459 need more space than is implied by @code{FUNCTION_VALUE_REGNO_P} for | |
4460 saving and restoring an arbitrary return value. | |
4461 @end defmac | |
4462 | |
4463 @hook TARGET_RETURN_IN_MSB | |
4464 This hook should return true if values of type @var{type} are returned | |
4465 at the most significant end of a register (in other words, if they are | |
4466 padded at the least significant end). You can assume that @var{type} | |
4467 is returned in a register; the caller is required to check this. | |
4468 | |
4469 Note that the register provided by @code{TARGET_FUNCTION_VALUE} must | |
4470 be able to hold the complete return value. For example, if a 1-, 2- | |
4471 or 3-byte structure is returned at the most significant end of a | |
4472 4-byte register, @code{TARGET_FUNCTION_VALUE} should provide an | |
4473 @code{SImode} rtx. | |
4474 @end deftypefn | |
4475 | |
4476 @node Aggregate Return | |
4477 @subsection How Large Values Are Returned | |
4478 @cindex aggregates as return values | |
4479 @cindex large return values | |
4480 @cindex returning aggregate values | |
4481 @cindex structure value address | |
4482 | |
4483 When a function value's mode is @code{BLKmode} (and in some other | |
4484 cases), the value is not returned according to | |
4485 @code{TARGET_FUNCTION_VALUE} (@pxref{Scalar Return}). Instead, the | |
4486 caller passes the address of a block of memory in which the value | |
4487 should be stored. This address is called the @dfn{structure value | |
4488 address}. | |
4489 | |
4490 This section describes how to control returning structure values in | |
4491 memory. | |
4492 | |
4493 @hook TARGET_RETURN_IN_MEMORY | |
4494 This target hook should return a nonzero value to say to return the | |
4495 function value in memory, just as large structures are always returned. | |
4496 Here @var{type} will be the data type of the value, and @var{fntype} | |
4497 will be the type of the function doing the returning, or @code{NULL} for | |
4498 libcalls. | |
4499 | |
4500 Note that values of mode @code{BLKmode} must be explicitly handled | |
4501 by this function. Also, the option @option{-fpcc-struct-return} | |
4502 takes effect regardless of this macro. On most systems, it is | |
4503 possible to leave the hook undefined; this causes a default | |
4504 definition to be used, whose value is the constant 1 for @code{BLKmode} | |
4505 values, and 0 otherwise. | |
4506 | |
4507 Do not use this hook to indicate that structures and unions should always | |
4508 be returned in memory. You should instead use @code{DEFAULT_PCC_STRUCT_RETURN} | |
4509 to indicate this. | |
4510 @end deftypefn | |
4511 | |
4512 @defmac DEFAULT_PCC_STRUCT_RETURN | |
4513 Define this macro to be 1 if all structure and union return values must be | |
4514 in memory. Since this results in slower code, this should be defined | |
4515 only if needed for compatibility with other compilers or with an ABI@. | |
4516 If you define this macro to be 0, then the conventions used for structure | |
4517 and union return values are decided by the @code{TARGET_RETURN_IN_MEMORY} | |
4518 target hook. | |
4519 | |
4520 If not defined, this defaults to the value 1. | |
4521 @end defmac | |
4522 | |
4523 @hook TARGET_STRUCT_VALUE_RTX | |
4524 This target hook should return the location of the structure value | |
4525 address (normally a @code{mem} or @code{reg}), or 0 if the address is | |
4526 passed as an ``invisible'' first argument. Note that @var{fndecl} may | |
4527 be @code{NULL}, for libcalls. You do not need to define this target | |
4528 hook if the address is always passed as an ``invisible'' first | |
4529 argument. | |
4530 | |
4531 On some architectures the place where the structure value address | |
4532 is found by the called function is not the same place that the | |
4533 caller put it. This can be due to register windows, or it could | |
4534 be because the function prologue moves it to a different place. | |
4535 @var{incoming} is @code{1} or @code{2} when the location is needed in | |
4536 the context of the called function, and @code{0} in the context of | |
4537 the caller. | |
4538 | |
4539 If @var{incoming} is nonzero and the address is to be found on the | |
4540 stack, return a @code{mem} which refers to the frame pointer. If | |
4541 @var{incoming} is @code{2}, the result is being used to fetch the | |
4542 structure value address at the beginning of a function. If you need | |
4543 to emit adjusting code, you should do it at this point. | |
4544 @end deftypefn | |
4545 | |
4546 @defmac PCC_STATIC_STRUCT_RETURN | |
4547 Define this macro if the usual system convention on the target machine | |
4548 for returning structures and unions is for the called function to return | |
4549 the address of a static variable containing the value. | |
4550 | |
4551 Do not define this if the usual system convention is for the caller to | |
4552 pass an address to the subroutine. | |
4553 | |
4554 This macro has effect in @option{-fpcc-struct-return} mode, but it does | |
4555 nothing when you use @option{-freg-struct-return} mode. | |
4556 @end defmac | |
4557 | |
4558 @hook TARGET_GET_RAW_RESULT_MODE | |
4559 | |
4560 @hook TARGET_GET_RAW_ARG_MODE | |
4561 | |
4562 @node Caller Saves | |
4563 @subsection Caller-Saves Register Allocation | |
4564 | |
4565 If you enable it, GCC can save registers around function calls. This | |
4566 makes it possible to use call-clobbered registers to hold variables that | |
4567 must live across calls. | |
4568 | |
4569 @defmac CALLER_SAVE_PROFITABLE (@var{refs}, @var{calls}) | |
4570 A C expression to determine whether it is worthwhile to consider placing | |
4571 a pseudo-register in a call-clobbered hard register and saving and | |
4572 restoring it around each function call. The expression should be 1 when | |
4573 this is worth doing, and 0 otherwise. | |
4574 | |
4575 If you don't define this macro, a default is used which is good on most | |
4576 machines: @code{4 * @var{calls} < @var{refs}}. | |
4577 @end defmac | |
4578 | |
4579 @defmac HARD_REGNO_CALLER_SAVE_MODE (@var{regno}, @var{nregs}) | |
4580 A C expression specifying which mode is required for saving @var{nregs} | |
4581 of a pseudo-register in call-clobbered hard register @var{regno}. If | |
4582 @var{regno} is unsuitable for caller save, @code{VOIDmode} should be | |
4583 returned. For most machines this macro need not be defined since GCC | |
4584 will select the smallest suitable mode. | |
4585 @end defmac | |
4586 | |
4587 @node Function Entry | |
4588 @subsection Function Entry and Exit | |
4589 @cindex function entry and exit | |
4590 @cindex prologue | |
4591 @cindex epilogue | |
4592 | |
4593 This section describes the macros that output function entry | |
4594 (@dfn{prologue}) and exit (@dfn{epilogue}) code. | |
4595 | |
4596 @hook TARGET_ASM_FUNCTION_PROLOGUE | |
4597 If defined, a function that outputs the assembler code for entry to a | |
4598 function. The prologue is responsible for setting up the stack frame, | |
4599 initializing the frame pointer register, saving registers that must be | |
4600 saved, and allocating @var{size} additional bytes of storage for the | |
4601 local variables. @var{size} is an integer. @var{file} is a stdio | |
4602 stream to which the assembler code should be output. | |
4603 | |
4604 The label for the beginning of the function need not be output by this | |
4605 macro. That has already been done when the macro is run. | |
4606 | |
4607 @findex regs_ever_live | |
4608 To determine which registers to save, the macro can refer to the array | |
4609 @code{regs_ever_live}: element @var{r} is nonzero if hard register | |
4610 @var{r} is used anywhere within the function. This implies the function | |
4611 prologue should save register @var{r}, provided it is not one of the | |
4612 call-used registers. (@code{TARGET_ASM_FUNCTION_EPILOGUE} must likewise use | |
4613 @code{regs_ever_live}.) | |
4614 | |
4615 On machines that have ``register windows'', the function entry code does | |
4616 not save on the stack the registers that are in the windows, even if | |
4617 they are supposed to be preserved by function calls; instead it takes | |
4618 appropriate steps to ``push'' the register stack, if any non-call-used | |
4619 registers are used in the function. | |
4620 | |
4621 @findex frame_pointer_needed | |
4622 On machines where functions may or may not have frame-pointers, the | |
4623 function entry code must vary accordingly; it must set up the frame | |
4624 pointer if one is wanted, and not otherwise. To determine whether a | |
4625 frame pointer is in wanted, the macro can refer to the variable | |
4626 @code{frame_pointer_needed}. The variable's value will be 1 at run | |
4627 time in a function that needs a frame pointer. @xref{Elimination}. | |
4628 | |
4629 The function entry code is responsible for allocating any stack space | |
4630 required for the function. This stack space consists of the regions | |
4631 listed below. In most cases, these regions are allocated in the | |
4632 order listed, with the last listed region closest to the top of the | |
4633 stack (the lowest address if @code{STACK_GROWS_DOWNWARD} is defined, and | |
4634 the highest address if it is not defined). You can use a different order | |
4635 for a machine if doing so is more convenient or required for | |
4636 compatibility reasons. Except in cases where required by standard | |
4637 or by a debugger, there is no reason why the stack layout used by GCC | |
4638 need agree with that used by other compilers for a machine. | |
4639 @end deftypefn | |
4640 | |
4641 @hook TARGET_ASM_FUNCTION_END_PROLOGUE | |
4642 If defined, a function that outputs assembler code at the end of a | |
4643 prologue. This should be used when the function prologue is being | |
4644 emitted as RTL, and you have some extra assembler that needs to be | |
4645 emitted. @xref{prologue instruction pattern}. | |
4646 @end deftypefn | |
4647 | |
4648 @hook TARGET_ASM_FUNCTION_BEGIN_EPILOGUE | |
4649 If defined, a function that outputs assembler code at the start of an | |
4650 epilogue. This should be used when the function epilogue is being | |
4651 emitted as RTL, and you have some extra assembler that needs to be | |
4652 emitted. @xref{epilogue instruction pattern}. | |
4653 @end deftypefn | |
4654 | |
4655 @hook TARGET_ASM_FUNCTION_EPILOGUE | |
4656 If defined, a function that outputs the assembler code for exit from a | |
4657 function. The epilogue is responsible for restoring the saved | |
4658 registers and stack pointer to their values when the function was | |
4659 called, and returning control to the caller. This macro takes the | |
4660 same arguments as the macro @code{TARGET_ASM_FUNCTION_PROLOGUE}, and the | |
4661 registers to restore are determined from @code{regs_ever_live} and | |
4662 @code{CALL_USED_REGISTERS} in the same way. | |
4663 | |
4664 On some machines, there is a single instruction that does all the work | |
4665 of returning from the function. On these machines, give that | |
4666 instruction the name @samp{return} and do not define the macro | |
4667 @code{TARGET_ASM_FUNCTION_EPILOGUE} at all. | |
4668 | |
4669 Do not define a pattern named @samp{return} if you want the | |
4670 @code{TARGET_ASM_FUNCTION_EPILOGUE} to be used. If you want the target | |
4671 switches to control whether return instructions or epilogues are used, | |
4672 define a @samp{return} pattern with a validity condition that tests the | |
4673 target switches appropriately. If the @samp{return} pattern's validity | |
4674 condition is false, epilogues will be used. | |
4675 | |
4676 On machines where functions may or may not have frame-pointers, the | |
4677 function exit code must vary accordingly. Sometimes the code for these | |
4678 two cases is completely different. To determine whether a frame pointer | |
4679 is wanted, the macro can refer to the variable | |
4680 @code{frame_pointer_needed}. The variable's value will be 1 when compiling | |
4681 a function that needs a frame pointer. | |
4682 | |
4683 Normally, @code{TARGET_ASM_FUNCTION_PROLOGUE} and | |
4684 @code{TARGET_ASM_FUNCTION_EPILOGUE} must treat leaf functions specially. | |
4685 The C variable @code{current_function_is_leaf} is nonzero for such a | |
4686 function. @xref{Leaf Functions}. | |
4687 | |
4688 On some machines, some functions pop their arguments on exit while | |
4689 others leave that for the caller to do. For example, the 68020 when | |
4690 given @option{-mrtd} pops arguments in functions that take a fixed | |
4691 number of arguments. | |
4692 | |
4693 @findex current_function_pops_args | |
4694 Your definition of the macro @code{RETURN_POPS_ARGS} decides which | |
4695 functions pop their own arguments. @code{TARGET_ASM_FUNCTION_EPILOGUE} | |
4696 needs to know what was decided. The number of bytes of the current | |
4697 function's arguments that this function should pop is available in | |
4698 @code{crtl->args.pops_args}. @xref{Scalar Return}. | |
4699 @end deftypefn | |
4700 | |
4701 @itemize @bullet | |
4702 @item | |
4703 @findex current_function_pretend_args_size | |
4704 A region of @code{current_function_pretend_args_size} bytes of | |
4705 uninitialized space just underneath the first argument arriving on the | |
4706 stack. (This may not be at the very start of the allocated stack region | |
4707 if the calling sequence has pushed anything else since pushing the stack | |
4708 arguments. But usually, on such machines, nothing else has been pushed | |
4709 yet, because the function prologue itself does all the pushing.) This | |
4710 region is used on machines where an argument may be passed partly in | |
4711 registers and partly in memory, and, in some cases to support the | |
4712 features in @code{<stdarg.h>}. | |
4713 | |
4714 @item | |
4715 An area of memory used to save certain registers used by the function. | |
4716 The size of this area, which may also include space for such things as | |
4717 the return address and pointers to previous stack frames, is | |
4718 machine-specific and usually depends on which registers have been used | |
4719 in the function. Machines with register windows often do not require | |
4720 a save area. | |
4721 | |
4722 @item | |
4723 A region of at least @var{size} bytes, possibly rounded up to an allocation | |
4724 boundary, to contain the local variables of the function. On some machines, | |
4725 this region and the save area may occur in the opposite order, with the | |
4726 save area closer to the top of the stack. | |
4727 | |
4728 @item | |
4729 @cindex @code{ACCUMULATE_OUTGOING_ARGS} and stack frames | |
4730 Optionally, when @code{ACCUMULATE_OUTGOING_ARGS} is defined, a region of | |
4731 @code{current_function_outgoing_args_size} bytes to be used for outgoing | |
4732 argument lists of the function. @xref{Stack Arguments}. | |
4733 @end itemize | |
4734 | |
4735 @defmac EXIT_IGNORE_STACK | |
4736 Define this macro as a C expression that is nonzero if the return | |
4737 instruction or the function epilogue ignores the value of the stack | |
4738 pointer; in other words, if it is safe to delete an instruction to | |
4739 adjust the stack pointer before a return from the function. The | |
4740 default is 0. | |
4741 | |
4742 Note that this macro's value is relevant only for functions for which | |
4743 frame pointers are maintained. It is never safe to delete a final | |
4744 stack adjustment in a function that has no frame pointer, and the | |
4745 compiler knows this regardless of @code{EXIT_IGNORE_STACK}. | |
4746 @end defmac | |
4747 | |
4748 @defmac EPILOGUE_USES (@var{regno}) | |
4749 Define this macro as a C expression that is nonzero for registers that are | |
4750 used by the epilogue or the @samp{return} pattern. The stack and frame | |
4751 pointer registers are already assumed to be used as needed. | |
4752 @end defmac | |
4753 | |
4754 @defmac EH_USES (@var{regno}) | |
4755 Define this macro as a C expression that is nonzero for registers that are | |
4756 used by the exception handling mechanism, and so should be considered live | |
4757 on entry to an exception edge. | |
4758 @end defmac | |
4759 | |
4760 @defmac DELAY_SLOTS_FOR_EPILOGUE | |
4761 Define this macro if the function epilogue contains delay slots to which | |
4762 instructions from the rest of the function can be ``moved''. The | |
4763 definition should be a C expression whose value is an integer | |
4764 representing the number of delay slots there. | |
4765 @end defmac | |
4766 | |
4767 @defmac ELIGIBLE_FOR_EPILOGUE_DELAY (@var{insn}, @var{n}) | |
4768 A C expression that returns 1 if @var{insn} can be placed in delay | |
4769 slot number @var{n} of the epilogue. | |
4770 | |
4771 The argument @var{n} is an integer which identifies the delay slot now | |
4772 being considered (since different slots may have different rules of | |
4773 eligibility). It is never negative and is always less than the number | |
4774 of epilogue delay slots (what @code{DELAY_SLOTS_FOR_EPILOGUE} returns). | |
4775 If you reject a particular insn for a given delay slot, in principle, it | |
4776 may be reconsidered for a subsequent delay slot. Also, other insns may | |
4777 (at least in principle) be considered for the so far unfilled delay | |
4778 slot. | |
4779 | |
4780 @findex current_function_epilogue_delay_list | |
4781 @findex final_scan_insn | |
4782 The insns accepted to fill the epilogue delay slots are put in an RTL | |
4783 list made with @code{insn_list} objects, stored in the variable | |
4784 @code{current_function_epilogue_delay_list}. The insn for the first | |
4785 delay slot comes first in the list. Your definition of the macro | |
4786 @code{TARGET_ASM_FUNCTION_EPILOGUE} should fill the delay slots by | |
4787 outputting the insns in this list, usually by calling | |
4788 @code{final_scan_insn}. | |
4789 | |
4790 You need not define this macro if you did not define | |
4791 @code{DELAY_SLOTS_FOR_EPILOGUE}. | |
4792 @end defmac | |
4793 | |
4794 @hook TARGET_ASM_OUTPUT_MI_THUNK | |
4795 A function that outputs the assembler code for a thunk | |
4796 function, used to implement C++ virtual function calls with multiple | |
4797 inheritance. The thunk acts as a wrapper around a virtual function, | |
4798 adjusting the implicit object parameter before handing control off to | |
4799 the real function. | |
4800 | |
4801 First, emit code to add the integer @var{delta} to the location that | |
4802 contains the incoming first argument. Assume that this argument | |
4803 contains a pointer, and is the one used to pass the @code{this} pointer | |
4804 in C++. This is the incoming argument @emph{before} the function prologue, | |
4805 e.g.@: @samp{%o0} on a sparc. The addition must preserve the values of | |
4806 all other incoming arguments. | |
4807 | |
4808 Then, if @var{vcall_offset} is nonzero, an additional adjustment should be | |
4809 made after adding @code{delta}. In particular, if @var{p} is the | |
4810 adjusted pointer, the following adjustment should be made: | |
4811 | |
4812 @smallexample | |
4813 p += (*((ptrdiff_t **)p))[vcall_offset/sizeof(ptrdiff_t)] | |
4814 @end smallexample | |
4815 | |
4816 After the additions, emit code to jump to @var{function}, which is a | |
4817 @code{FUNCTION_DECL}. This is a direct pure jump, not a call, and does | |
4818 not touch the return address. Hence returning from @var{FUNCTION} will | |
4819 return to whoever called the current @samp{thunk}. | |
4820 | |
4821 The effect must be as if @var{function} had been called directly with | |
4822 the adjusted first argument. This macro is responsible for emitting all | |
4823 of the code for a thunk function; @code{TARGET_ASM_FUNCTION_PROLOGUE} | |
4824 and @code{TARGET_ASM_FUNCTION_EPILOGUE} are not invoked. | |
4825 | |
4826 The @var{thunk_fndecl} is redundant. (@var{delta} and @var{function} | |
4827 have already been extracted from it.) It might possibly be useful on | |
4828 some targets, but probably not. | |
4829 | |
4830 If you do not define this macro, the target-independent code in the C++ | |
4831 front end will generate a less efficient heavyweight thunk that calls | |
4832 @var{function} instead of jumping to it. The generic approach does | |
4833 not support varargs. | |
4834 @end deftypefn | |
4835 | |
4836 @hook TARGET_ASM_CAN_OUTPUT_MI_THUNK | |
4837 A function that returns true if TARGET_ASM_OUTPUT_MI_THUNK would be able | |
4838 to output the assembler code for the thunk function specified by the | |
4839 arguments it is passed, and false otherwise. In the latter case, the | |
4840 generic approach will be used by the C++ front end, with the limitations | |
4841 previously exposed. | |
4842 @end deftypefn | |
4843 | |
4844 @node Profiling | |
4845 @subsection Generating Code for Profiling | |
4846 @cindex profiling, code generation | |
4847 | |
4848 These macros will help you generate code for profiling. | |
4849 | |
4850 @defmac FUNCTION_PROFILER (@var{file}, @var{labelno}) | |
4851 A C statement or compound statement to output to @var{file} some | |
4852 assembler code to call the profiling subroutine @code{mcount}. | |
4853 | |
4854 @findex mcount | |
4855 The details of how @code{mcount} expects to be called are determined by | |
4856 your operating system environment, not by GCC@. To figure them out, | |
4857 compile a small program for profiling using the system's installed C | |
4858 compiler and look at the assembler code that results. | |
4859 | |
4860 Older implementations of @code{mcount} expect the address of a counter | |
4861 variable to be loaded into some register. The name of this variable is | |
4862 @samp{LP} followed by the number @var{labelno}, so you would generate | |
4863 the name using @samp{LP%d} in a @code{fprintf}. | |
4864 @end defmac | |
4865 | |
4866 @defmac PROFILE_HOOK | |
4867 A C statement or compound statement to output to @var{file} some assembly | |
4868 code to call the profiling subroutine @code{mcount} even the target does | |
4869 not support profiling. | |
4870 @end defmac | |
4871 | |
4872 @defmac NO_PROFILE_COUNTERS | |
4873 Define this macro to be an expression with a nonzero value if the | |
4874 @code{mcount} subroutine on your system does not need a counter variable | |
4875 allocated for each function. This is true for almost all modern | |
4876 implementations. If you define this macro, you must not use the | |
4877 @var{labelno} argument to @code{FUNCTION_PROFILER}. | |
4878 @end defmac | |
4879 | |
4880 @defmac PROFILE_BEFORE_PROLOGUE | |
4881 Define this macro if the code for function profiling should come before | |
4882 the function prologue. Normally, the profiling code comes after. | |
4883 @end defmac | |
4884 | |
4885 @node Tail Calls | |
4886 @subsection Permitting tail calls | |
4887 @cindex tail calls | |
4888 | |
4889 @hook TARGET_FUNCTION_OK_FOR_SIBCALL | |
4890 True if it is ok to do sibling call optimization for the specified | |
4891 call expression @var{exp}. @var{decl} will be the called function, | |
4892 or @code{NULL} if this is an indirect call. | |
4893 | |
4894 It is not uncommon for limitations of calling conventions to prevent | |
4895 tail calls to functions outside the current unit of translation, or | |
4896 during PIC compilation. The hook is used to enforce these restrictions, | |
4897 as the @code{sibcall} md pattern can not fail, or fall over to a | |
4898 ``normal'' call. The criteria for successful sibling call optimization | |
4899 may vary greatly between different architectures. | |
4900 @end deftypefn | |
4901 | |
4902 @hook TARGET_EXTRA_LIVE_ON_ENTRY | |
4903 Add any hard registers to @var{regs} that are live on entry to the | |
4904 function. This hook only needs to be defined to provide registers that | |
4905 cannot be found by examination of FUNCTION_ARG_REGNO_P, the callee saved | |
4906 registers, STATIC_CHAIN_INCOMING_REGNUM, STATIC_CHAIN_REGNUM, | |
4907 TARGET_STRUCT_VALUE_RTX, FRAME_POINTER_REGNUM, EH_USES, | |
4908 FRAME_POINTER_REGNUM, ARG_POINTER_REGNUM, and the PIC_OFFSET_TABLE_REGNUM. | |
4909 @end deftypefn | |
4910 | |
4911 @node Stack Smashing Protection | |
4912 @subsection Stack smashing protection | |
4913 @cindex stack smashing protection | |
4914 | |
4915 @hook TARGET_STACK_PROTECT_GUARD | |
4916 This hook returns a @code{DECL} node for the external variable to use | |
4917 for the stack protection guard. This variable is initialized by the | |
4918 runtime to some random value and is used to initialize the guard value | |
4919 that is placed at the top of the local stack frame. The type of this | |
4920 variable must be @code{ptr_type_node}. | |
4921 | |
4922 The default version of this hook creates a variable called | |
4923 @samp{__stack_chk_guard}, which is normally defined in @file{libgcc2.c}. | |
4924 @end deftypefn | |
4925 | |
4926 @hook TARGET_STACK_PROTECT_FAIL | |
4927 This hook returns a tree expression that alerts the runtime that the | |
4928 stack protect guard variable has been modified. This expression should | |
4929 involve a call to a @code{noreturn} function. | |
4930 | |
4931 The default version of this hook invokes a function called | |
4932 @samp{__stack_chk_fail}, taking no arguments. This function is | |
4933 normally defined in @file{libgcc2.c}. | |
4934 @end deftypefn | |
4935 | |
4936 @hook TARGET_SUPPORTS_SPLIT_STACK | |
4937 | |
4938 @node Varargs | |
4939 @section Implementing the Varargs Macros | |
4940 @cindex varargs implementation | |
4941 | |
4942 GCC comes with an implementation of @code{<varargs.h>} and | |
4943 @code{<stdarg.h>} that work without change on machines that pass arguments | |
4944 on the stack. Other machines require their own implementations of | |
4945 varargs, and the two machine independent header files must have | |
4946 conditionals to include it. | |
4947 | |
4948 ISO @code{<stdarg.h>} differs from traditional @code{<varargs.h>} mainly in | |
4949 the calling convention for @code{va_start}. The traditional | |
4950 implementation takes just one argument, which is the variable in which | |
4951 to store the argument pointer. The ISO implementation of | |
4952 @code{va_start} takes an additional second argument. The user is | |
4953 supposed to write the last named argument of the function here. | |
4954 | |
4955 However, @code{va_start} should not use this argument. The way to find | |
4956 the end of the named arguments is with the built-in functions described | |
4957 below. | |
4958 | |
4959 @defmac __builtin_saveregs () | |
4960 Use this built-in function to save the argument registers in memory so | |
4961 that the varargs mechanism can access them. Both ISO and traditional | |
4962 versions of @code{va_start} must use @code{__builtin_saveregs}, unless | |
4963 you use @code{TARGET_SETUP_INCOMING_VARARGS} (see below) instead. | |
4964 | |
4965 On some machines, @code{__builtin_saveregs} is open-coded under the | |
4966 control of the target hook @code{TARGET_EXPAND_BUILTIN_SAVEREGS}. On | |
4967 other machines, it calls a routine written in assembler language, | |
4968 found in @file{libgcc2.c}. | |
4969 | |
4970 Code generated for the call to @code{__builtin_saveregs} appears at the | |
4971 beginning of the function, as opposed to where the call to | |
4972 @code{__builtin_saveregs} is written, regardless of what the code is. | |
4973 This is because the registers must be saved before the function starts | |
4974 to use them for its own purposes. | |
4975 @c i rewrote the first sentence above to fix an overfull hbox. --mew | |
4976 @c 10feb93 | |
4977 @end defmac | |
4978 | |
4979 @defmac __builtin_next_arg (@var{lastarg}) | |
4980 This builtin returns the address of the first anonymous stack | |
4981 argument, as type @code{void *}. If @code{ARGS_GROW_DOWNWARD}, it | |
4982 returns the address of the location above the first anonymous stack | |
4983 argument. Use it in @code{va_start} to initialize the pointer for | |
4984 fetching arguments from the stack. Also use it in @code{va_start} to | |
4985 verify that the second parameter @var{lastarg} is the last named argument | |
4986 of the current function. | |
4987 @end defmac | |
4988 | |
4989 @defmac __builtin_classify_type (@var{object}) | |
4990 Since each machine has its own conventions for which data types are | |
4991 passed in which kind of register, your implementation of @code{va_arg} | |
4992 has to embody these conventions. The easiest way to categorize the | |
4993 specified data type is to use @code{__builtin_classify_type} together | |
4994 with @code{sizeof} and @code{__alignof__}. | |
4995 | |
4996 @code{__builtin_classify_type} ignores the value of @var{object}, | |
4997 considering only its data type. It returns an integer describing what | |
4998 kind of type that is---integer, floating, pointer, structure, and so on. | |
4999 | |
5000 The file @file{typeclass.h} defines an enumeration that you can use to | |
5001 interpret the values of @code{__builtin_classify_type}. | |
5002 @end defmac | |
5003 | |
5004 These machine description macros help implement varargs: | |
5005 | |
5006 @hook TARGET_EXPAND_BUILTIN_SAVEREGS | |
5007 If defined, this hook produces the machine-specific code for a call to | |
5008 @code{__builtin_saveregs}. This code will be moved to the very | |
5009 beginning of the function, before any parameter access are made. The | |
5010 return value of this function should be an RTX that contains the value | |
5011 to use as the return of @code{__builtin_saveregs}. | |
5012 @end deftypefn | |
5013 | |
5014 @hook TARGET_SETUP_INCOMING_VARARGS | |
5015 This target hook offers an alternative to using | |
5016 @code{__builtin_saveregs} and defining the hook | |
5017 @code{TARGET_EXPAND_BUILTIN_SAVEREGS}. Use it to store the anonymous | |
5018 register arguments into the stack so that all the arguments appear to | |
5019 have been passed consecutively on the stack. Once this is done, you can | |
5020 use the standard implementation of varargs that works for machines that | |
5021 pass all their arguments on the stack. | |
5022 | |
5023 The argument @var{args_so_far} points to the @code{CUMULATIVE_ARGS} data | |
5024 structure, containing the values that are obtained after processing the | |
5025 named arguments. The arguments @var{mode} and @var{type} describe the | |
5026 last named argument---its machine mode and its data type as a tree node. | |
5027 | |
5028 The target hook should do two things: first, push onto the stack all the | |
5029 argument registers @emph{not} used for the named arguments, and second, | |
5030 store the size of the data thus pushed into the @code{int}-valued | |
5031 variable pointed to by @var{pretend_args_size}. The value that you | |
5032 store here will serve as additional offset for setting up the stack | |
5033 frame. | |
5034 | |
5035 Because you must generate code to push the anonymous arguments at | |
5036 compile time without knowing their data types, | |
5037 @code{TARGET_SETUP_INCOMING_VARARGS} is only useful on machines that | |
5038 have just a single category of argument register and use it uniformly | |
5039 for all data types. | |
5040 | |
5041 If the argument @var{second_time} is nonzero, it means that the | |
5042 arguments of the function are being analyzed for the second time. This | |
5043 happens for an inline function, which is not actually compiled until the | |
5044 end of the source file. The hook @code{TARGET_SETUP_INCOMING_VARARGS} should | |
5045 not generate any instructions in this case. | |
5046 @end deftypefn | |
5047 | |
5048 @hook TARGET_STRICT_ARGUMENT_NAMING | |
5049 Define this hook to return @code{true} if the location where a function | |
5050 argument is passed depends on whether or not it is a named argument. | |
5051 | |
5052 This hook controls how the @var{named} argument to @code{FUNCTION_ARG} | |
5053 is set for varargs and stdarg functions. If this hook returns | |
5054 @code{true}, the @var{named} argument is always true for named | |
5055 arguments, and false for unnamed arguments. If it returns @code{false}, | |
5056 but @code{TARGET_PRETEND_OUTGOING_VARARGS_NAMED} returns @code{true}, | |
5057 then all arguments are treated as named. Otherwise, all named arguments | |
5058 except the last are treated as named. | |
5059 | |
5060 You need not define this hook if it always returns @code{false}. | |
5061 @end deftypefn | |
5062 | |
5063 @hook TARGET_PRETEND_OUTGOING_VARARGS_NAMED | |
5064 If you need to conditionally change ABIs so that one works with | |
5065 @code{TARGET_SETUP_INCOMING_VARARGS}, but the other works like neither | |
5066 @code{TARGET_SETUP_INCOMING_VARARGS} nor @code{TARGET_STRICT_ARGUMENT_NAMING} was | |
5067 defined, then define this hook to return @code{true} if | |
5068 @code{TARGET_SETUP_INCOMING_VARARGS} is used, @code{false} otherwise. | |
5069 Otherwise, you should not define this hook. | |
5070 @end deftypefn | |
5071 | |
5072 @node Trampolines | |
5073 @section Trampolines for Nested Functions | |
5074 @cindex trampolines for nested functions | |
5075 @cindex nested functions, trampolines for | |
5076 | |
5077 A @dfn{trampoline} is a small piece of code that is created at run time | |
5078 when the address of a nested function is taken. It normally resides on | |
5079 the stack, in the stack frame of the containing function. These macros | |
5080 tell GCC how to generate code to allocate and initialize a | |
5081 trampoline. | |
5082 | |
5083 The instructions in the trampoline must do two things: load a constant | |
5084 address into the static chain register, and jump to the real address of | |
5085 the nested function. On CISC machines such as the m68k, this requires | |
5086 two instructions, a move immediate and a jump. Then the two addresses | |
5087 exist in the trampoline as word-long immediate operands. On RISC | |
5088 machines, it is often necessary to load each address into a register in | |
5089 two parts. Then pieces of each address form separate immediate | |
5090 operands. | |
5091 | |
5092 The code generated to initialize the trampoline must store the variable | |
5093 parts---the static chain value and the function address---into the | |
5094 immediate operands of the instructions. On a CISC machine, this is | |
5095 simply a matter of copying each address to a memory reference at the | |
5096 proper offset from the start of the trampoline. On a RISC machine, it | |
5097 may be necessary to take out pieces of the address and store them | |
5098 separately. | |
5099 | |
5100 @hook TARGET_ASM_TRAMPOLINE_TEMPLATE | |
5101 This hook is called by @code{assemble_trampoline_template} to output, | |
5102 on the stream @var{f}, assembler code for a block of data that contains | |
5103 the constant parts of a trampoline. This code should not include a | |
5104 label---the label is taken care of automatically. | |
5105 | |
5106 If you do not define this hook, it means no template is needed | |
5107 for the target. Do not define this hook on systems where the block move | |
5108 code to copy the trampoline into place would be larger than the code | |
5109 to generate it on the spot. | |
5110 @end deftypefn | |
5111 | |
5112 @defmac TRAMPOLINE_SECTION | |
5113 Return the section into which the trampoline template is to be placed | |
5114 (@pxref{Sections}). The default value is @code{readonly_data_section}. | |
5115 @end defmac | |
5116 | |
5117 @defmac TRAMPOLINE_SIZE | |
5118 A C expression for the size in bytes of the trampoline, as an integer. | |
5119 @end defmac | |
5120 | |
5121 @defmac TRAMPOLINE_ALIGNMENT | |
5122 Alignment required for trampolines, in bits. | |
5123 | |
5124 If you don't define this macro, the value of @code{FUNCTION_ALIGNMENT} | |
5125 is used for aligning trampolines. | |
5126 @end defmac | |
5127 | |
5128 @hook TARGET_TRAMPOLINE_INIT | |
5129 This hook is called to initialize a trampoline. | |
5130 @var{m_tramp} is an RTX for the memory block for the trampoline; @var{fndecl} | |
5131 is the @code{FUNCTION_DECL} for the nested function; @var{static_chain} is an | |
5132 RTX for the static chain value that should be passed to the function | |
5133 when it is called. | |
5134 | |
5135 If the target defines @code{TARGET_ASM_TRAMPOLINE_TEMPLATE}, then the | |
5136 first thing this hook should do is emit a block move into @var{m_tramp} | |
5137 from the memory block returned by @code{assemble_trampoline_template}. | |
5138 Note that the block move need only cover the constant parts of the | |
5139 trampoline. If the target isolates the variable parts of the trampoline | |
5140 to the end, not all @code{TRAMPOLINE_SIZE} bytes need be copied. | |
5141 | |
5142 If the target requires any other actions, such as flushing caches or | |
5143 enabling stack execution, these actions should be performed after | |
5144 initializing the trampoline proper. | |
5145 @end deftypefn | |
5146 | |
5147 @hook TARGET_TRAMPOLINE_ADJUST_ADDRESS | |
5148 This hook should perform any machine-specific adjustment in | |
5149 the address of the trampoline. Its argument contains the address of the | |
5150 memory block that was passed to @code{TARGET_TRAMPOLINE_INIT}. In case | |
5151 the address to be used for a function call should be different from the | |
5152 address at which the template was stored, the different address should | |
5153 be returned; otherwise @var{addr} should be returned unchanged. | |
5154 If this hook is not defined, @var{addr} will be used for function calls. | |
5155 @end deftypefn | |
5156 | |
5157 Implementing trampolines is difficult on many machines because they have | |
5158 separate instruction and data caches. Writing into a stack location | |
5159 fails to clear the memory in the instruction cache, so when the program | |
5160 jumps to that location, it executes the old contents. | |
5161 | |
5162 Here are two possible solutions. One is to clear the relevant parts of | |
5163 the instruction cache whenever a trampoline is set up. The other is to | |
5164 make all trampolines identical, by having them jump to a standard | |
5165 subroutine. The former technique makes trampoline execution faster; the | |
5166 latter makes initialization faster. | |
5167 | |
5168 To clear the instruction cache when a trampoline is initialized, define | |
5169 the following macro. | |
5170 | |
5171 @defmac CLEAR_INSN_CACHE (@var{beg}, @var{end}) | |
5172 If defined, expands to a C expression clearing the @emph{instruction | |
5173 cache} in the specified interval. The definition of this macro would | |
5174 typically be a series of @code{asm} statements. Both @var{beg} and | |
5175 @var{end} are both pointer expressions. | |
5176 @end defmac | |
5177 | |
5178 The operating system may also require the stack to be made executable | |
5179 before calling the trampoline. To implement this requirement, define | |
5180 the following macro. | |
5181 | |
5182 @defmac ENABLE_EXECUTE_STACK | |
5183 Define this macro if certain operations must be performed before executing | |
5184 code located on the stack. The macro should expand to a series of C | |
5185 file-scope constructs (e.g.@: functions) and provide a unique entry point | |
5186 named @code{__enable_execute_stack}. The target is responsible for | |
5187 emitting calls to the entry point in the code, for example from the | |
5188 @code{TARGET_TRAMPOLINE_INIT} hook. | |
5189 @end defmac | |
5190 | |
5191 To use a standard subroutine, define the following macro. In addition, | |
5192 you must make sure that the instructions in a trampoline fill an entire | |
5193 cache line with identical instructions, or else ensure that the | |
5194 beginning of the trampoline code is always aligned at the same point in | |
5195 its cache line. Look in @file{m68k.h} as a guide. | |
5196 | |
5197 @defmac TRANSFER_FROM_TRAMPOLINE | |
5198 Define this macro if trampolines need a special subroutine to do their | |
5199 work. The macro should expand to a series of @code{asm} statements | |
5200 which will be compiled with GCC@. They go in a library function named | |
5201 @code{__transfer_from_trampoline}. | |
5202 | |
5203 If you need to avoid executing the ordinary prologue code of a compiled | |
5204 C function when you jump to the subroutine, you can do so by placing a | |
5205 special label of your own in the assembler code. Use one @code{asm} | |
5206 statement to generate an assembler label, and another to make the label | |
5207 global. Then trampolines can use that label to jump directly to your | |
5208 special assembler code. | |
5209 @end defmac | |
5210 | |
5211 @node Library Calls | |
5212 @section Implicit Calls to Library Routines | |
5213 @cindex library subroutine names | |
5214 @cindex @file{libgcc.a} | |
5215 | |
5216 @c prevent bad page break with this line | |
5217 Here is an explanation of implicit calls to library routines. | |
5218 | |
5219 @defmac DECLARE_LIBRARY_RENAMES | |
5220 This macro, if defined, should expand to a piece of C code that will get | |
5221 expanded when compiling functions for libgcc.a. It can be used to | |
5222 provide alternate names for GCC's internal library functions if there | |
5223 are ABI-mandated names that the compiler should provide. | |
5224 @end defmac | |
5225 | |
5226 @findex set_optab_libfunc | |
5227 @findex init_one_libfunc | |
5228 @hook TARGET_INIT_LIBFUNCS | |
5229 This hook should declare additional library routines or rename | |
5230 existing ones, using the functions @code{set_optab_libfunc} and | |
5231 @code{init_one_libfunc} defined in @file{optabs.c}. | |
5232 @code{init_optabs} calls this macro after initializing all the normal | |
5233 library routines. | |
5234 | |
5235 The default is to do nothing. Most ports don't need to define this hook. | |
5236 @end deftypefn | |
5237 | |
5238 @defmac FLOAT_LIB_COMPARE_RETURNS_BOOL (@var{mode}, @var{comparison}) | |
5239 This macro should return @code{true} if the library routine that | |
5240 implements the floating point comparison operator @var{comparison} in | |
5241 mode @var{mode} will return a boolean, and @var{false} if it will | |
5242 return a tristate. | |
5243 | |
5244 GCC's own floating point libraries return tristates from the | |
5245 comparison operators, so the default returns false always. Most ports | |
5246 don't need to define this macro. | |
5247 @end defmac | |
5248 | |
5249 @defmac TARGET_LIB_INT_CMP_BIASED | |
5250 This macro should evaluate to @code{true} if the integer comparison | |
5251 functions (like @code{__cmpdi2}) return 0 to indicate that the first | |
5252 operand is smaller than the second, 1 to indicate that they are equal, | |
5253 and 2 to indicate that the first operand is greater than the second. | |
5254 If this macro evaluates to @code{false} the comparison functions return | |
5255 @minus{}1, 0, and 1 instead of 0, 1, and 2. If the target uses the routines | |
5256 in @file{libgcc.a}, you do not need to define this macro. | |
5257 @end defmac | |
5258 | |
5259 @cindex @code{EDOM}, implicit usage | |
5260 @findex matherr | |
5261 @defmac TARGET_EDOM | |
5262 The value of @code{EDOM} on the target machine, as a C integer constant | |
5263 expression. If you don't define this macro, GCC does not attempt to | |
5264 deposit the value of @code{EDOM} into @code{errno} directly. Look in | |
5265 @file{/usr/include/errno.h} to find the value of @code{EDOM} on your | |
5266 system. | |
5267 | |
5268 If you do not define @code{TARGET_EDOM}, then compiled code reports | |
5269 domain errors by calling the library function and letting it report the | |
5270 error. If mathematical functions on your system use @code{matherr} when | |
5271 there is an error, then you should leave @code{TARGET_EDOM} undefined so | |
5272 that @code{matherr} is used normally. | |
5273 @end defmac | |
5274 | |
5275 @cindex @code{errno}, implicit usage | |
5276 @defmac GEN_ERRNO_RTX | |
5277 Define this macro as a C expression to create an rtl expression that | |
5278 refers to the global ``variable'' @code{errno}. (On certain systems, | |
5279 @code{errno} may not actually be a variable.) If you don't define this | |
5280 macro, a reasonable default is used. | |
5281 @end defmac | |
5282 | |
5283 @cindex C99 math functions, implicit usage | |
5284 @defmac TARGET_C99_FUNCTIONS | |
5285 When this macro is nonzero, GCC will implicitly optimize @code{sin} calls into | |
5286 @code{sinf} and similarly for other functions defined by C99 standard. The | |
5287 default is zero because a number of existing systems lack support for these | |
5288 functions in their runtime so this macro needs to be redefined to one on | |
5289 systems that do support the C99 runtime. | |
5290 @end defmac | |
5291 | |
5292 @cindex sincos math function, implicit usage | |
5293 @defmac TARGET_HAS_SINCOS | |
5294 When this macro is nonzero, GCC will implicitly optimize calls to @code{sin} | |
5295 and @code{cos} with the same argument to a call to @code{sincos}. The | |
5296 default is zero. The target has to provide the following functions: | |
5297 @smallexample | |
5298 void sincos(double x, double *sin, double *cos); | |
5299 void sincosf(float x, float *sin, float *cos); | |
5300 void sincosl(long double x, long double *sin, long double *cos); | |
5301 @end smallexample | |
5302 @end defmac | |
5303 | |
5304 @defmac NEXT_OBJC_RUNTIME | |
5305 Define this macro to generate code for Objective-C message sending using | |
5306 the calling convention of the NeXT system. This calling convention | |
5307 involves passing the object, the selector and the method arguments all | |
5308 at once to the method-lookup library function. | |
5309 | |
5310 The default calling convention passes just the object and the selector | |
5311 to the lookup function, which returns a pointer to the method. | |
5312 @end defmac | |
5313 | |
5314 @node Addressing Modes | |
5315 @section Addressing Modes | |
5316 @cindex addressing modes | |
5317 | |
5318 @c prevent bad page break with this line | |
5319 This is about addressing modes. | |
5320 | |
5321 @defmac HAVE_PRE_INCREMENT | |
5322 @defmacx HAVE_PRE_DECREMENT | |
5323 @defmacx HAVE_POST_INCREMENT | |
5324 @defmacx HAVE_POST_DECREMENT | |
5325 A C expression that is nonzero if the machine supports pre-increment, | |
5326 pre-decrement, post-increment, or post-decrement addressing respectively. | |
5327 @end defmac | |
5328 | |
5329 @defmac HAVE_PRE_MODIFY_DISP | |
5330 @defmacx HAVE_POST_MODIFY_DISP | |
5331 A C expression that is nonzero if the machine supports pre- or | |
5332 post-address side-effect generation involving constants other than | |
5333 the size of the memory operand. | |
5334 @end defmac | |
5335 | |
5336 @defmac HAVE_PRE_MODIFY_REG | |
5337 @defmacx HAVE_POST_MODIFY_REG | |
5338 A C expression that is nonzero if the machine supports pre- or | |
5339 post-address side-effect generation involving a register displacement. | |
5340 @end defmac | |
5341 | |
5342 @defmac CONSTANT_ADDRESS_P (@var{x}) | |
5343 A C expression that is 1 if the RTX @var{x} is a constant which | |
5344 is a valid address. On most machines the default definition of | |
5345 @code{(CONSTANT_P (@var{x}) && GET_CODE (@var{x}) != CONST_DOUBLE)} | |
5346 is acceptable, but a few machines are more restrictive as to which | |
5347 constant addresses are supported. | |
5348 @end defmac | |
5349 | |
5350 @defmac CONSTANT_P (@var{x}) | |
5351 @code{CONSTANT_P}, which is defined by target-independent code, | |
5352 accepts integer-values expressions whose values are not explicitly | |
5353 known, such as @code{symbol_ref}, @code{label_ref}, and @code{high} | |
5354 expressions and @code{const} arithmetic expressions, in addition to | |
5355 @code{const_int} and @code{const_double} expressions. | |
5356 @end defmac | |
5357 | |
5358 @defmac MAX_REGS_PER_ADDRESS | |
5359 A number, the maximum number of registers that can appear in a valid | |
5360 memory address. Note that it is up to you to specify a value equal to | |
5361 the maximum number that @code{TARGET_LEGITIMATE_ADDRESS_P} would ever | |
5362 accept. | |
5363 @end defmac | |
5364 | |
5365 @hook TARGET_LEGITIMATE_ADDRESS_P | |
5366 A function that returns whether @var{x} (an RTX) is a legitimate memory | |
5367 address on the target machine for a memory operand of mode @var{mode}. | |
5368 | |
5369 Legitimate addresses are defined in two variants: a strict variant and a | |
5370 non-strict one. The @var{strict} parameter chooses which variant is | |
5371 desired by the caller. | |
5372 | |
5373 The strict variant is used in the reload pass. It must be defined so | |
5374 that any pseudo-register that has not been allocated a hard register is | |
5375 considered a memory reference. This is because in contexts where some | |
5376 kind of register is required, a pseudo-register with no hard register | |
5377 must be rejected. For non-hard registers, the strict variant should look | |
5378 up the @code{reg_renumber} array; it should then proceed using the hard | |
5379 register number in the array, or treat the pseudo as a memory reference | |
5380 if the array holds @code{-1}. | |
5381 | |
5382 The non-strict variant is used in other passes. It must be defined to | |
5383 accept all pseudo-registers in every context where some kind of | |
5384 register is required. | |
5385 | |
5386 Normally, constant addresses which are the sum of a @code{symbol_ref} | |
5387 and an integer are stored inside a @code{const} RTX to mark them as | |
5388 constant. Therefore, there is no need to recognize such sums | |
5389 specifically as legitimate addresses. Normally you would simply | |
5390 recognize any @code{const} as legitimate. | |
5391 | |
5392 Usually @code{PRINT_OPERAND_ADDRESS} is not prepared to handle constant | |
5393 sums that are not marked with @code{const}. It assumes that a naked | |
5394 @code{plus} indicates indexing. If so, then you @emph{must} reject such | |
5395 naked constant sums as illegitimate addresses, so that none of them will | |
5396 be given to @code{PRINT_OPERAND_ADDRESS}. | |
5397 | |
5398 @cindex @code{TARGET_ENCODE_SECTION_INFO} and address validation | |
5399 On some machines, whether a symbolic address is legitimate depends on | |
5400 the section that the address refers to. On these machines, define the | |
5401 target hook @code{TARGET_ENCODE_SECTION_INFO} to store the information | |
5402 into the @code{symbol_ref}, and then check for it here. When you see a | |
5403 @code{const}, you will have to look inside it to find the | |
5404 @code{symbol_ref} in order to determine the section. @xref{Assembler | |
5405 Format}. | |
5406 | |
5407 @cindex @code{GO_IF_LEGITIMATE_ADDRESS} | |
5408 Some ports are still using a deprecated legacy substitute for | |
5409 this hook, the @code{GO_IF_LEGITIMATE_ADDRESS} macro. This macro | |
5410 has this syntax: | |
5411 | |
5412 @example | |
5413 #define GO_IF_LEGITIMATE_ADDRESS (@var{mode}, @var{x}, @var{label}) | |
5414 @end example | |
5415 | |
5416 @noindent | |
5417 and should @code{goto @var{label}} if the address @var{x} is a valid | |
5418 address on the target machine for a memory operand of mode @var{mode}. | |
5419 | |
5420 @findex REG_OK_STRICT | |
5421 Compiler source files that want to use the strict variant of this | |
5422 macro define the macro @code{REG_OK_STRICT}. You should use an | |
5423 @code{#ifdef REG_OK_STRICT} conditional to define the strict variant in | |
5424 that case and the non-strict variant otherwise. | |
5425 | |
5426 Using the hook is usually simpler because it limits the number of | |
5427 files that are recompiled when changes are made. | |
5428 @end deftypefn | |
5429 | |
5430 @defmac TARGET_MEM_CONSTRAINT | |
5431 A single character to be used instead of the default @code{'m'} | |
5432 character for general memory addresses. This defines the constraint | |
5433 letter which matches the memory addresses accepted by | |
5434 @code{TARGET_LEGITIMATE_ADDRESS_P}. Define this macro if you want to | |
5435 support new address formats in your back end without changing the | |
5436 semantics of the @code{'m'} constraint. This is necessary in order to | |
5437 preserve functionality of inline assembly constructs using the | |
5438 @code{'m'} constraint. | |
5439 @end defmac | |
5440 | |
5441 @defmac FIND_BASE_TERM (@var{x}) | |
5442 A C expression to determine the base term of address @var{x}, | |
5443 or to provide a simplified version of @var{x} from which @file{alias.c} | |
5444 can easily find the base term. This macro is used in only two places: | |
5445 @code{find_base_value} and @code{find_base_term} in @file{alias.c}. | |
5446 | |
5447 It is always safe for this macro to not be defined. It exists so | |
5448 that alias analysis can understand machine-dependent addresses. | |
5449 | |
5450 The typical use of this macro is to handle addresses containing | |
5451 a label_ref or symbol_ref within an UNSPEC@. | |
5452 @end defmac | |
5453 | |
5454 @hook TARGET_LEGITIMIZE_ADDRESS | |
5455 This hook is given an invalid memory address @var{x} for an | |
5456 operand of mode @var{mode} and should try to return a valid memory | |
5457 address. | |
5458 | |
5459 @findex break_out_memory_refs | |
5460 @var{x} will always be the result of a call to @code{break_out_memory_refs}, | |
5461 and @var{oldx} will be the operand that was given to that function to produce | |
5462 @var{x}. | |
5463 | |
5464 The code of the hook should not alter the substructure of | |
5465 @var{x}. If it transforms @var{x} into a more legitimate form, it | |
5466 should return the new @var{x}. | |
5467 | |
5468 It is not necessary for this hook to come up with a legitimate address. | |
5469 The compiler has standard ways of doing so in all cases. In fact, it | |
5470 is safe to omit this hook or make it return @var{x} if it cannot find | |
5471 a valid way to legitimize the address. But often a machine-dependent | |
5472 strategy can generate better code. | |
5473 @end deftypefn | |
5474 | |
5475 @defmac LEGITIMIZE_RELOAD_ADDRESS (@var{x}, @var{mode}, @var{opnum}, @var{type}, @var{ind_levels}, @var{win}) | |
5476 A C compound statement that attempts to replace @var{x}, which is an address | |
5477 that needs reloading, with a valid memory address for an operand of mode | |
5478 @var{mode}. @var{win} will be a C statement label elsewhere in the code. | |
5479 It is not necessary to define this macro, but it might be useful for | |
5480 performance reasons. | |
5481 | |
5482 For example, on the i386, it is sometimes possible to use a single | |
5483 reload register instead of two by reloading a sum of two pseudo | |
5484 registers into a register. On the other hand, for number of RISC | |
5485 processors offsets are limited so that often an intermediate address | |
5486 needs to be generated in order to address a stack slot. By defining | |
5487 @code{LEGITIMIZE_RELOAD_ADDRESS} appropriately, the intermediate addresses | |
5488 generated for adjacent some stack slots can be made identical, and thus | |
5489 be shared. | |
5490 | |
5491 @emph{Note}: This macro should be used with caution. It is necessary | |
5492 to know something of how reload works in order to effectively use this, | |
5493 and it is quite easy to produce macros that build in too much knowledge | |
5494 of reload internals. | |
5495 | |
5496 @emph{Note}: This macro must be able to reload an address created by a | |
5497 previous invocation of this macro. If it fails to handle such addresses | |
5498 then the compiler may generate incorrect code or abort. | |
5499 | |
5500 @findex push_reload | |
5501 The macro definition should use @code{push_reload} to indicate parts that | |
5502 need reloading; @var{opnum}, @var{type} and @var{ind_levels} are usually | |
5503 suitable to be passed unaltered to @code{push_reload}. | |
5504 | |
5505 The code generated by this macro must not alter the substructure of | |
5506 @var{x}. If it transforms @var{x} into a more legitimate form, it | |
5507 should assign @var{x} (which will always be a C variable) a new value. | |
5508 This also applies to parts that you change indirectly by calling | |
5509 @code{push_reload}. | |
5510 | |
5511 @findex strict_memory_address_p | |
5512 The macro definition may use @code{strict_memory_address_p} to test if | |
5513 the address has become legitimate. | |
5514 | |
5515 @findex copy_rtx | |
5516 If you want to change only a part of @var{x}, one standard way of doing | |
5517 this is to use @code{copy_rtx}. Note, however, that it unshares only a | |
5518 single level of rtl. Thus, if the part to be changed is not at the | |
5519 top level, you'll need to replace first the top level. | |
5520 It is not necessary for this macro to come up with a legitimate | |
5521 address; but often a machine-dependent strategy can generate better code. | |
5522 @end defmac | |
5523 | |
5524 @hook TARGET_MODE_DEPENDENT_ADDRESS_P | |
5525 This hook returns @code{true} if memory address @var{addr} can have | |
5526 different meanings depending on the machine mode of the memory | |
5527 reference it is used for or if the address is valid for some modes | |
5528 but not others. | |
5529 | |
5530 Autoincrement and autodecrement addresses typically have mode-dependent | |
5531 effects because the amount of the increment or decrement is the size | |
5532 of the operand being addressed. Some machines have other mode-dependent | |
5533 addresses. Many RISC machines have no mode-dependent addresses. | |
5534 | |
5535 You may assume that @var{addr} is a valid address for the machine. | |
5536 | |
5537 The default version of this hook returns @code{false}. | |
5538 @end deftypefn | |
5539 | |
5540 @defmac GO_IF_MODE_DEPENDENT_ADDRESS (@var{addr}, @var{label}) | |
5541 A C statement or compound statement with a conditional @code{goto | |
5542 @var{label};} executed if memory address @var{x} (an RTX) can have | |
5543 different meanings depending on the machine mode of the memory | |
5544 reference it is used for or if the address is valid for some modes | |
5545 but not others. | |
5546 | |
5547 Autoincrement and autodecrement addresses typically have mode-dependent | |
5548 effects because the amount of the increment or decrement is the size | |
5549 of the operand being addressed. Some machines have other mode-dependent | |
5550 addresses. Many RISC machines have no mode-dependent addresses. | |
5551 | |
5552 You may assume that @var{addr} is a valid address for the machine. | |
5553 | |
5554 These are obsolete macros, replaced by the | |
5555 @code{TARGET_MODE_DEPENDENT_ADDRESS_P} target hook. | |
5556 @end defmac | |
5557 | |
5558 @defmac LEGITIMATE_CONSTANT_P (@var{x}) | |
5559 A C expression that is nonzero if @var{x} is a legitimate constant for | |
5560 an immediate operand on the target machine. You can assume that | |
5561 @var{x} satisfies @code{CONSTANT_P}, so you need not check this. In fact, | |
5562 @samp{1} is a suitable definition for this macro on machines where | |
5563 anything @code{CONSTANT_P} is valid. | |
5564 @end defmac | |
5565 | |
5566 @hook TARGET_DELEGITIMIZE_ADDRESS | |
5567 This hook is used to undo the possibly obfuscating effects of the | |
5568 @code{LEGITIMIZE_ADDRESS} and @code{LEGITIMIZE_RELOAD_ADDRESS} target | |
5569 macros. Some backend implementations of these macros wrap symbol | |
5570 references inside an @code{UNSPEC} rtx to represent PIC or similar | |
5571 addressing modes. This target hook allows GCC's optimizers to understand | |
5572 the semantics of these opaque @code{UNSPEC}s by converting them back | |
5573 into their original form. | |
5574 @end deftypefn | |
5575 | |
5576 @hook TARGET_CANNOT_FORCE_CONST_MEM | |
5577 This hook should return true if @var{x} is of a form that cannot (or | |
5578 should not) be spilled to the constant pool. The default version of | |
5579 this hook returns false. | |
5580 | |
5581 The primary reason to define this hook is to prevent reload from | |
5582 deciding that a non-legitimate constant would be better reloaded | |
5583 from the constant pool instead of spilling and reloading a register | |
5584 holding the constant. This restriction is often true of addresses | |
5585 of TLS symbols for various targets. | |
5586 @end deftypefn | |
5587 | |
5588 @hook TARGET_USE_BLOCKS_FOR_CONSTANT_P | |
5589 This hook should return true if pool entries for constant @var{x} can | |
5590 be placed in an @code{object_block} structure. @var{mode} is the mode | |
5591 of @var{x}. | |
5592 | |
5593 The default version returns false for all constants. | |
5594 @end deftypefn | |
5595 | |
5596 @hook TARGET_BUILTIN_RECIPROCAL | |
5597 This hook should return the DECL of a function that implements reciprocal of | |
5598 the builtin function with builtin function code @var{fn}, or | |
5599 @code{NULL_TREE} if such a function is not available. @var{md_fn} is true | |
5600 when @var{fn} is a code of a machine-dependent builtin function. When | |
5601 @var{sqrt} is true, additional optimizations that apply only to the reciprocal | |
5602 of a square root function are performed, and only reciprocals of @code{sqrt} | |
5603 function are valid. | |
5604 @end deftypefn | |
5605 | |
5606 @hook TARGET_VECTORIZE_BUILTIN_MASK_FOR_LOAD | |
5607 This hook should return the DECL of a function @var{f} that given an | |
5608 address @var{addr} as an argument returns a mask @var{m} that can be | |
5609 used to extract from two vectors the relevant data that resides in | |
5610 @var{addr} in case @var{addr} is not properly aligned. | |
5611 | |
5612 The autovectorizer, when vectorizing a load operation from an address | |
5613 @var{addr} that may be unaligned, will generate two vector loads from | |
5614 the two aligned addresses around @var{addr}. It then generates a | |
5615 @code{REALIGN_LOAD} operation to extract the relevant data from the | |
5616 two loaded vectors. The first two arguments to @code{REALIGN_LOAD}, | |
5617 @var{v1} and @var{v2}, are the two vectors, each of size @var{VS}, and | |
5618 the third argument, @var{OFF}, defines how the data will be extracted | |
5619 from these two vectors: if @var{OFF} is 0, then the returned vector is | |
5620 @var{v2}; otherwise, the returned vector is composed from the last | |
5621 @var{VS}-@var{OFF} elements of @var{v1} concatenated to the first | |
5622 @var{OFF} elements of @var{v2}. | |
5623 | |
5624 If this hook is defined, the autovectorizer will generate a call | |
5625 to @var{f} (using the DECL tree that this hook returns) and will | |
5626 use the return value of @var{f} as the argument @var{OFF} to | |
5627 @code{REALIGN_LOAD}. Therefore, the mask @var{m} returned by @var{f} | |
5628 should comply with the semantics expected by @code{REALIGN_LOAD} | |
5629 described above. | |
5630 If this hook is not defined, then @var{addr} will be used as | |
5631 the argument @var{OFF} to @code{REALIGN_LOAD}, in which case the low | |
5632 log2(@var{VS}) @minus{} 1 bits of @var{addr} will be considered. | |
5633 @end deftypefn | |
5634 | |
5635 @hook TARGET_VECTORIZE_BUILTIN_MUL_WIDEN_EVEN | |
5636 This hook should return the DECL of a function @var{f} that implements | |
5637 widening multiplication of the even elements of two input vectors of type @var{x}. | |
5638 | |
5639 If this hook is defined, the autovectorizer will use it along with the | |
5640 @code{TARGET_VECTORIZE_BUILTIN_MUL_WIDEN_ODD} target hook when vectorizing | |
5641 widening multiplication in cases that the order of the results does not have to be | |
5642 preserved (e.g.@: used only by a reduction computation). Otherwise, the | |
5643 @code{widen_mult_hi/lo} idioms will be used. | |
5644 @end deftypefn | |
5645 | |
5646 @hook TARGET_VECTORIZE_BUILTIN_MUL_WIDEN_ODD | |
5647 This hook should return the DECL of a function @var{f} that implements | |
5648 widening multiplication of the odd elements of two input vectors of type @var{x}. | |
5649 | |
5650 If this hook is defined, the autovectorizer will use it along with the | |
5651 @code{TARGET_VECTORIZE_BUILTIN_MUL_WIDEN_EVEN} target hook when vectorizing | |
5652 widening multiplication in cases that the order of the results does not have to be | |
5653 preserved (e.g.@: used only by a reduction computation). Otherwise, the | |
5654 @code{widen_mult_hi/lo} idioms will be used. | |
5655 @end deftypefn | |
5656 | |
5657 @hook TARGET_VECTORIZE_BUILTIN_VECTORIZATION_COST | |
5658 Returns cost of different scalar or vector statements for vectorization cost model. | |
5659 For vector memory operations the cost may depend on type (@var{vectype}) and | |
5660 misalignment value (@var{misalign}). | |
5661 @end deftypefn | |
5662 | |
5663 @hook TARGET_VECTORIZE_VECTOR_ALIGNMENT_REACHABLE | |
5664 Return true if vector alignment is reachable (by peeling N iterations) for the given type. | |
5665 @end deftypefn | |
5666 | |
5667 @hook TARGET_VECTORIZE_BUILTIN_VEC_PERM | |
5668 Target builtin that implements vector permute. | |
5669 @end deftypefn | |
5670 | |
5671 @hook TARGET_VECTORIZE_BUILTIN_VEC_PERM_OK | |
5672 Return true if a vector created for @code{builtin_vec_perm} is valid. | |
5673 @end deftypefn | |
5674 | |
5675 @hook TARGET_VECTORIZE_BUILTIN_CONVERSION | |
5676 This hook should return the DECL of a function that implements conversion of the | |
5677 input vector of type @var{src_type} to type @var{dest_type}. | |
5678 The value of @var{code} is one of the enumerators in @code{enum tree_code} and | |
5679 specifies how the conversion is to be applied | |
5680 (truncation, rounding, etc.). | |
5681 | |
5682 If this hook is defined, the autovectorizer will use the | |
5683 @code{TARGET_VECTORIZE_BUILTIN_CONVERSION} target hook when vectorizing | |
5684 conversion. Otherwise, it will return @code{NULL_TREE}. | |
5685 @end deftypefn | |
5686 | |
5687 @hook TARGET_VECTORIZE_BUILTIN_VECTORIZED_FUNCTION | |
5688 This hook should return the decl of a function that implements the | |
5689 vectorized variant of the builtin function with builtin function code | |
5690 @var{code} or @code{NULL_TREE} if such a function is not available. | |
5691 The value of @var{fndecl} is the builtin function declaration. The | |
5692 return type of the vectorized function shall be of vector type | |
5693 @var{vec_type_out} and the argument types should be @var{vec_type_in}. | |
5694 @end deftypefn | |
5695 | |
5696 @hook TARGET_VECTORIZE_SUPPORT_VECTOR_MISALIGNMENT | |
5697 This hook should return true if the target supports misaligned vector | |
5698 store/load of a specific factor denoted in the @var{misalignment} | |
5699 parameter. The vector store/load should be of machine mode @var{mode} and | |
5700 the elements in the vectors should be of type @var{type}. @var{is_packed} | |
5701 parameter is true if the memory access is defined in a packed struct. | |
5702 @end deftypefn | |
5703 | |
5704 @hook TARGET_VECTORIZE_PREFERRED_SIMD_MODE | |
5705 This hook should return the preferred mode for vectorizing scalar | |
5706 mode @var{mode}. The default is | |
5707 equal to @code{word_mode}, because the vectorizer can do some | |
5708 transformations even in absence of specialized @acronym{SIMD} hardware. | |
5709 @end deftypefn | |
5710 | |
5711 @hook TARGET_VECTORIZE_AUTOVECTORIZE_VECTOR_SIZES | |
5712 This hook should return a mask of sizes that should be iterated over | |
5713 after trying to autovectorize using the vector size derived from the | |
5714 mode returned by @code{TARGET_VECTORIZE_PREFERRED_SIMD_MODE}. | |
5715 The default is zero which means to not iterate over other vector sizes. | |
5716 @end deftypefn | |
5717 | |
5718 @node Anchored Addresses | |
5719 @section Anchored Addresses | |
5720 @cindex anchored addresses | |
5721 @cindex @option{-fsection-anchors} | |
5722 | |
5723 GCC usually addresses every static object as a separate entity. | |
5724 For example, if we have: | |
5725 | |
5726 @smallexample | |
5727 static int a, b, c; | |
5728 int foo (void) @{ return a + b + c; @} | |
5729 @end smallexample | |
5730 | |
5731 the code for @code{foo} will usually calculate three separate symbolic | |
5732 addresses: those of @code{a}, @code{b} and @code{c}. On some targets, | |
5733 it would be better to calculate just one symbolic address and access | |
5734 the three variables relative to it. The equivalent pseudocode would | |
5735 be something like: | |
5736 | |
5737 @smallexample | |
5738 int foo (void) | |
5739 @{ | |
5740 register int *xr = &x; | |
5741 return xr[&a - &x] + xr[&b - &x] + xr[&c - &x]; | |
5742 @} | |
5743 @end smallexample | |
5744 | |
5745 (which isn't valid C). We refer to shared addresses like @code{x} as | |
5746 ``section anchors''. Their use is controlled by @option{-fsection-anchors}. | |
5747 | |
5748 The hooks below describe the target properties that GCC needs to know | |
5749 in order to make effective use of section anchors. It won't use | |
5750 section anchors at all unless either @code{TARGET_MIN_ANCHOR_OFFSET} | |
5751 or @code{TARGET_MAX_ANCHOR_OFFSET} is set to a nonzero value. | |
5752 | |
5753 @hook TARGET_MIN_ANCHOR_OFFSET | |
5754 The minimum offset that should be applied to a section anchor. | |
5755 On most targets, it should be the smallest offset that can be | |
5756 applied to a base register while still giving a legitimate address | |
5757 for every mode. The default value is 0. | |
5758 @end deftypevr | |
5759 | |
5760 @hook TARGET_MAX_ANCHOR_OFFSET | |
5761 Like @code{TARGET_MIN_ANCHOR_OFFSET}, but the maximum (inclusive) | |
5762 offset that should be applied to section anchors. The default | |
5763 value is 0. | |
5764 @end deftypevr | |
5765 | |
5766 @hook TARGET_ASM_OUTPUT_ANCHOR | |
5767 Write the assembly code to define section anchor @var{x}, which is a | |
5768 @code{SYMBOL_REF} for which @samp{SYMBOL_REF_ANCHOR_P (@var{x})} is true. | |
5769 The hook is called with the assembly output position set to the beginning | |
5770 of @code{SYMBOL_REF_BLOCK (@var{x})}. | |
5771 | |
5772 If @code{ASM_OUTPUT_DEF} is available, the hook's default definition uses | |
5773 it to define the symbol as @samp{. + SYMBOL_REF_BLOCK_OFFSET (@var{x})}. | |
5774 If @code{ASM_OUTPUT_DEF} is not available, the hook's default definition | |
5775 is @code{NULL}, which disables the use of section anchors altogether. | |
5776 @end deftypefn | |
5777 | |
5778 @hook TARGET_USE_ANCHORS_FOR_SYMBOL_P | |
5779 Return true if GCC should attempt to use anchors to access @code{SYMBOL_REF} | |
5780 @var{x}. You can assume @samp{SYMBOL_REF_HAS_BLOCK_INFO_P (@var{x})} and | |
5781 @samp{!SYMBOL_REF_ANCHOR_P (@var{x})}. | |
5782 | |
5783 The default version is correct for most targets, but you might need to | |
5784 intercept this hook to handle things like target-specific attributes | |
5785 or target-specific sections. | |
5786 @end deftypefn | |
5787 | |
5788 @node Condition Code | |
5789 @section Condition Code Status | |
5790 @cindex condition code status | |
5791 | |
5792 The macros in this section can be split in two families, according to the | |
5793 two ways of representing condition codes in GCC. | |
5794 | |
5795 The first representation is the so called @code{(cc0)} representation | |
5796 (@pxref{Jump Patterns}), where all instructions can have an implicit | |
5797 clobber of the condition codes. The second is the condition code | |
5798 register representation, which provides better schedulability for | |
5799 architectures that do have a condition code register, but on which | |
5800 most instructions do not affect it. The latter category includes | |
5801 most RISC machines. | |
5802 | |
5803 The implicit clobbering poses a strong restriction on the placement of | |
5804 the definition and use of the condition code, which need to be in adjacent | |
5805 insns for machines using @code{(cc0)}. This can prevent important | |
5806 optimizations on some machines. For example, on the IBM RS/6000, there | |
5807 is a delay for taken branches unless the condition code register is set | |
5808 three instructions earlier than the conditional branch. The instruction | |
5809 scheduler cannot perform this optimization if it is not permitted to | |
5810 separate the definition and use of the condition code register. | |
5811 | |
5812 For this reason, it is possible and suggested to use a register to | |
5813 represent the condition code for new ports. If there is a specific | |
5814 condition code register in the machine, use a hard register. If the | |
5815 condition code or comparison result can be placed in any general register, | |
5816 or if there are multiple condition registers, use a pseudo register. | |
5817 Registers used to store the condition code value will usually have a mode | |
5818 that is in class @code{MODE_CC}. | |
5819 | |
5820 Alternatively, you can use @code{BImode} if the comparison operator is | |
5821 specified already in the compare instruction. In this case, you are not | |
5822 interested in most macros in this section. | |
5823 | |
5824 @menu | |
5825 * CC0 Condition Codes:: Old style representation of condition codes. | |
5826 * MODE_CC Condition Codes:: Modern representation of condition codes. | |
5827 * Cond Exec Macros:: Macros to control conditional execution. | |
5828 @end menu | |
5829 | |
5830 @node CC0 Condition Codes | |
5831 @subsection Representation of condition codes using @code{(cc0)} | |
5832 @findex cc0 | |
5833 | |
5834 @findex cc_status | |
5835 The file @file{conditions.h} defines a variable @code{cc_status} to | |
5836 describe how the condition code was computed (in case the interpretation of | |
5837 the condition code depends on the instruction that it was set by). This | |
5838 variable contains the RTL expressions on which the condition code is | |
5839 currently based, and several standard flags. | |
5840 | |
5841 Sometimes additional machine-specific flags must be defined in the machine | |
5842 description header file. It can also add additional machine-specific | |
5843 information by defining @code{CC_STATUS_MDEP}. | |
5844 | |
5845 @defmac CC_STATUS_MDEP | |
5846 C code for a data type which is used for declaring the @code{mdep} | |
5847 component of @code{cc_status}. It defaults to @code{int}. | |
5848 | |
5849 This macro is not used on machines that do not use @code{cc0}. | |
5850 @end defmac | |
5851 | |
5852 @defmac CC_STATUS_MDEP_INIT | |
5853 A C expression to initialize the @code{mdep} field to ``empty''. | |
5854 The default definition does nothing, since most machines don't use | |
5855 the field anyway. If you want to use the field, you should probably | |
5856 define this macro to initialize it. | |
5857 | |
5858 This macro is not used on machines that do not use @code{cc0}. | |
5859 @end defmac | |
5860 | |
5861 @defmac NOTICE_UPDATE_CC (@var{exp}, @var{insn}) | |
5862 A C compound statement to set the components of @code{cc_status} | |
5863 appropriately for an insn @var{insn} whose body is @var{exp}. It is | |
5864 this macro's responsibility to recognize insns that set the condition | |
5865 code as a byproduct of other activity as well as those that explicitly | |
5866 set @code{(cc0)}. | |
5867 | |
5868 This macro is not used on machines that do not use @code{cc0}. | |
5869 | |
5870 If there are insns that do not set the condition code but do alter | |
5871 other machine registers, this macro must check to see whether they | |
5872 invalidate the expressions that the condition code is recorded as | |
5873 reflecting. For example, on the 68000, insns that store in address | |
5874 registers do not set the condition code, which means that usually | |
5875 @code{NOTICE_UPDATE_CC} can leave @code{cc_status} unaltered for such | |
5876 insns. But suppose that the previous insn set the condition code | |
5877 based on location @samp{a4@@(102)} and the current insn stores a new | |
5878 value in @samp{a4}. Although the condition code is not changed by | |
5879 this, it will no longer be true that it reflects the contents of | |
5880 @samp{a4@@(102)}. Therefore, @code{NOTICE_UPDATE_CC} must alter | |
5881 @code{cc_status} in this case to say that nothing is known about the | |
5882 condition code value. | |
5883 | |
5884 The definition of @code{NOTICE_UPDATE_CC} must be prepared to deal | |
5885 with the results of peephole optimization: insns whose patterns are | |
5886 @code{parallel} RTXs containing various @code{reg}, @code{mem} or | |
5887 constants which are just the operands. The RTL structure of these | |
5888 insns is not sufficient to indicate what the insns actually do. What | |
5889 @code{NOTICE_UPDATE_CC} should do when it sees one is just to run | |
5890 @code{CC_STATUS_INIT}. | |
5891 | |
5892 A possible definition of @code{NOTICE_UPDATE_CC} is to call a function | |
5893 that looks at an attribute (@pxref{Insn Attributes}) named, for example, | |
5894 @samp{cc}. This avoids having detailed information about patterns in | |
5895 two places, the @file{md} file and in @code{NOTICE_UPDATE_CC}. | |
5896 @end defmac | |
5897 | |
5898 @node MODE_CC Condition Codes | |
5899 @subsection Representation of condition codes using registers | |
5900 @findex CCmode | |
5901 @findex MODE_CC | |
5902 | |
5903 @defmac SELECT_CC_MODE (@var{op}, @var{x}, @var{y}) | |
5904 On many machines, the condition code may be produced by other instructions | |
5905 than compares, for example the branch can use directly the condition | |
5906 code set by a subtract instruction. However, on some machines | |
5907 when the condition code is set this way some bits (such as the overflow | |
5908 bit) are not set in the same way as a test instruction, so that a different | |
5909 branch instruction must be used for some conditional branches. When | |
5910 this happens, use the machine mode of the condition code register to | |
5911 record different formats of the condition code register. Modes can | |
5912 also be used to record which compare instruction (e.g. a signed or an | |
5913 unsigned comparison) produced the condition codes. | |
5914 | |
5915 If other modes than @code{CCmode} are required, add them to | |
5916 @file{@var{machine}-modes.def} and define @code{SELECT_CC_MODE} to choose | |
5917 a mode given an operand of a compare. This is needed because the modes | |
5918 have to be chosen not only during RTL generation but also, for example, | |
5919 by instruction combination. The result of @code{SELECT_CC_MODE} should | |
5920 be consistent with the mode used in the patterns; for example to support | |
5921 the case of the add on the SPARC discussed above, we have the pattern | |
5922 | |
5923 @smallexample | |
5924 (define_insn "" | |
5925 [(set (reg:CC_NOOV 0) | |
5926 (compare:CC_NOOV | |
5927 (plus:SI (match_operand:SI 0 "register_operand" "%r") | |
5928 (match_operand:SI 1 "arith_operand" "rI")) | |
5929 (const_int 0)))] | |
5930 "" | |
5931 "@dots{}") | |
5932 @end smallexample | |
5933 | |
5934 @noindent | |
5935 together with a @code{SELECT_CC_MODE} that returns @code{CC_NOOVmode} | |
5936 for comparisons whose argument is a @code{plus}: | |
5937 | |
5938 @smallexample | |
5939 #define SELECT_CC_MODE(OP,X,Y) \ | |
5940 (GET_MODE_CLASS (GET_MODE (X)) == MODE_FLOAT \ | |
5941 ? ((OP == EQ || OP == NE) ? CCFPmode : CCFPEmode) \ | |
5942 : ((GET_CODE (X) == PLUS || GET_CODE (X) == MINUS \ | |
5943 || GET_CODE (X) == NEG) \ | |
5944 ? CC_NOOVmode : CCmode)) | |
5945 @end smallexample | |
5946 | |
5947 Another reason to use modes is to retain information on which operands | |
5948 were used by the comparison; see @code{REVERSIBLE_CC_MODE} later in | |
5949 this section. | |
5950 | |
5951 You should define this macro if and only if you define extra CC modes | |
5952 in @file{@var{machine}-modes.def}. | |
5953 @end defmac | |
5954 | |
5955 @defmac CANONICALIZE_COMPARISON (@var{code}, @var{op0}, @var{op1}) | |
5956 On some machines not all possible comparisons are defined, but you can | |
5957 convert an invalid comparison into a valid one. For example, the Alpha | |
5958 does not have a @code{GT} comparison, but you can use an @code{LT} | |
5959 comparison instead and swap the order of the operands. | |
5960 | |
5961 On such machines, define this macro to be a C statement to do any | |
5962 required conversions. @var{code} is the initial comparison code | |
5963 and @var{op0} and @var{op1} are the left and right operands of the | |
5964 comparison, respectively. You should modify @var{code}, @var{op0}, and | |
5965 @var{op1} as required. | |
5966 | |
5967 GCC will not assume that the comparison resulting from this macro is | |
5968 valid but will see if the resulting insn matches a pattern in the | |
5969 @file{md} file. | |
5970 | |
5971 You need not define this macro if it would never change the comparison | |
5972 code or operands. | |
5973 @end defmac | |
5974 | |
5975 @defmac REVERSIBLE_CC_MODE (@var{mode}) | |
5976 A C expression whose value is one if it is always safe to reverse a | |
5977 comparison whose mode is @var{mode}. If @code{SELECT_CC_MODE} | |
5978 can ever return @var{mode} for a floating-point inequality comparison, | |
5979 then @code{REVERSIBLE_CC_MODE (@var{mode})} must be zero. | |
5980 | |
5981 You need not define this macro if it would always returns zero or if the | |
5982 floating-point format is anything other than @code{IEEE_FLOAT_FORMAT}. | |
5983 For example, here is the definition used on the SPARC, where floating-point | |
5984 inequality comparisons are always given @code{CCFPEmode}: | |
5985 | |
5986 @smallexample | |
5987 #define REVERSIBLE_CC_MODE(MODE) ((MODE) != CCFPEmode) | |
5988 @end smallexample | |
5989 @end defmac | |
5990 | |
5991 @defmac REVERSE_CONDITION (@var{code}, @var{mode}) | |
5992 A C expression whose value is reversed condition code of the @var{code} for | |
5993 comparison done in CC_MODE @var{mode}. The macro is used only in case | |
5994 @code{REVERSIBLE_CC_MODE (@var{mode})} is nonzero. Define this macro in case | |
5995 machine has some non-standard way how to reverse certain conditionals. For | |
5996 instance in case all floating point conditions are non-trapping, compiler may | |
5997 freely convert unordered compares to ordered one. Then definition may look | |
5998 like: | |
5999 | |
6000 @smallexample | |
6001 #define REVERSE_CONDITION(CODE, MODE) \ | |
6002 ((MODE) != CCFPmode ? reverse_condition (CODE) \ | |
6003 : reverse_condition_maybe_unordered (CODE)) | |
6004 @end smallexample | |
6005 @end defmac | |
6006 | |
6007 @hook TARGET_FIXED_CONDITION_CODE_REGS | |
6008 On targets which do not use @code{(cc0)}, and which use a hard | |
6009 register rather than a pseudo-register to hold condition codes, the | |
6010 regular CSE passes are often not able to identify cases in which the | |
6011 hard register is set to a common value. Use this hook to enable a | |
6012 small pass which optimizes such cases. This hook should return true | |
6013 to enable this pass, and it should set the integers to which its | |
6014 arguments point to the hard register numbers used for condition codes. | |
6015 When there is only one such register, as is true on most systems, the | |
6016 integer pointed to by @var{p2} should be set to | |
6017 @code{INVALID_REGNUM}. | |
6018 | |
6019 The default version of this hook returns false. | |
6020 @end deftypefn | |
6021 | |
6022 @hook TARGET_CC_MODES_COMPATIBLE | |
6023 On targets which use multiple condition code modes in class | |
6024 @code{MODE_CC}, it is sometimes the case that a comparison can be | |
6025 validly done in more than one mode. On such a system, define this | |
6026 target hook to take two mode arguments and to return a mode in which | |
6027 both comparisons may be validly done. If there is no such mode, | |
6028 return @code{VOIDmode}. | |
6029 | |
6030 The default version of this hook checks whether the modes are the | |
6031 same. If they are, it returns that mode. If they are different, it | |
6032 returns @code{VOIDmode}. | |
6033 @end deftypefn | |
6034 | |
6035 @node Cond Exec Macros | |
6036 @subsection Macros to control conditional execution | |
6037 @findex conditional execution | |
6038 @findex predication | |
6039 | |
6040 There is one macro that may need to be defined for targets | |
6041 supporting conditional execution, independent of how they | |
6042 represent conditional branches. | |
6043 | |
6044 @defmac REVERSE_CONDEXEC_PREDICATES_P (@var{op1}, @var{op2}) | |
6045 A C expression that returns true if the conditional execution predicate | |
6046 @var{op1}, a comparison operation, is the inverse of @var{op2} and vice | |
6047 versa. Define this to return 0 if the target has conditional execution | |
6048 predicates that cannot be reversed safely. There is no need to validate | |
6049 that the arguments of op1 and op2 are the same, this is done separately. | |
6050 If no expansion is specified, this macro is defined as follows: | |
6051 | |
6052 @smallexample | |
6053 #define REVERSE_CONDEXEC_PREDICATES_P (x, y) \ | |
6054 (GET_CODE ((x)) == reversed_comparison_code ((y), NULL)) | |
6055 @end smallexample | |
6056 @end defmac | |
6057 | |
6058 @node Costs | |
6059 @section Describing Relative Costs of Operations | |
6060 @cindex costs of instructions | |
6061 @cindex relative costs | |
6062 @cindex speed of instructions | |
6063 | |
6064 These macros let you describe the relative speed of various operations | |
6065 on the target machine. | |
6066 | |
6067 @defmac REGISTER_MOVE_COST (@var{mode}, @var{from}, @var{to}) | |
6068 A C expression for the cost of moving data of mode @var{mode} from a | |
6069 register in class @var{from} to one in class @var{to}. The classes are | |
6070 expressed using the enumeration values such as @code{GENERAL_REGS}. A | |
6071 value of 2 is the default; other values are interpreted relative to | |
6072 that. | |
6073 | |
6074 It is not required that the cost always equal 2 when @var{from} is the | |
6075 same as @var{to}; on some machines it is expensive to move between | |
6076 registers if they are not general registers. | |
6077 | |
6078 If reload sees an insn consisting of a single @code{set} between two | |
6079 hard registers, and if @code{REGISTER_MOVE_COST} applied to their | |
6080 classes returns a value of 2, reload does not check to ensure that the | |
6081 constraints of the insn are met. Setting a cost of other than 2 will | |
6082 allow reload to verify that the constraints are met. You should do this | |
6083 if the @samp{mov@var{m}} pattern's constraints do not allow such copying. | |
6084 | |
6085 These macros are obsolete, new ports should use the target hook | |
6086 @code{TARGET_REGISTER_MOVE_COST} instead. | |
6087 @end defmac | |
6088 | |
6089 @hook TARGET_REGISTER_MOVE_COST | |
6090 This target hook should return the cost of moving data of mode @var{mode} | |
6091 from a register in class @var{from} to one in class @var{to}. The classes | |
6092 are expressed using the enumeration values such as @code{GENERAL_REGS}. | |
6093 A value of 2 is the default; other values are interpreted relative to | |
6094 that. | |
6095 | |
6096 It is not required that the cost always equal 2 when @var{from} is the | |
6097 same as @var{to}; on some machines it is expensive to move between | |
6098 registers if they are not general registers. | |
6099 | |
6100 If reload sees an insn consisting of a single @code{set} between two | |
6101 hard registers, and if @code{TARGET_REGISTER_MOVE_COST} applied to their | |
6102 classes returns a value of 2, reload does not check to ensure that the | |
6103 constraints of the insn are met. Setting a cost of other than 2 will | |
6104 allow reload to verify that the constraints are met. You should do this | |
6105 if the @samp{mov@var{m}} pattern's constraints do not allow such copying. | |
6106 | |
6107 The default version of this function returns 2. | |
6108 @end deftypefn | |
6109 | |
6110 @defmac MEMORY_MOVE_COST (@var{mode}, @var{class}, @var{in}) | |
6111 A C expression for the cost of moving data of mode @var{mode} between a | |
6112 register of class @var{class} and memory; @var{in} is zero if the value | |
6113 is to be written to memory, nonzero if it is to be read in. This cost | |
6114 is relative to those in @code{REGISTER_MOVE_COST}. If moving between | |
6115 registers and memory is more expensive than between two registers, you | |
6116 should define this macro to express the relative cost. | |
6117 | |
6118 If you do not define this macro, GCC uses a default cost of 4 plus | |
6119 the cost of copying via a secondary reload register, if one is | |
6120 needed. If your machine requires a secondary reload register to copy | |
6121 between memory and a register of @var{class} but the reload mechanism is | |
6122 more complex than copying via an intermediate, define this macro to | |
6123 reflect the actual cost of the move. | |
6124 | |
6125 GCC defines the function @code{memory_move_secondary_cost} if | |
6126 secondary reloads are needed. It computes the costs due to copying via | |
6127 a secondary register. If your machine copies from memory using a | |
6128 secondary register in the conventional way but the default base value of | |
6129 4 is not correct for your machine, define this macro to add some other | |
6130 value to the result of that function. The arguments to that function | |
6131 are the same as to this macro. | |
6132 | |
6133 These macros are obsolete, new ports should use the target hook | |
6134 @code{TARGET_MEMORY_MOVE_COST} instead. | |
6135 @end defmac | |
6136 | |
6137 @hook TARGET_MEMORY_MOVE_COST | |
6138 This target hook should return the cost of moving data of mode @var{mode} | |
6139 between a register of class @var{rclass} and memory; @var{in} is @code{false} | |
6140 if the value is to be written to memory, @code{true} if it is to be read in. | |
6141 This cost is relative to those in @code{TARGET_REGISTER_MOVE_COST}. | |
6142 If moving between registers and memory is more expensive than between two | |
6143 registers, you should add this target hook to express the relative cost. | |
6144 | |
6145 If you do not add this target hook, GCC uses a default cost of 4 plus | |
6146 the cost of copying via a secondary reload register, if one is | |
6147 needed. If your machine requires a secondary reload register to copy | |
6148 between memory and a register of @var{rclass} but the reload mechanism is | |
6149 more complex than copying via an intermediate, use this target hook to | |
6150 reflect the actual cost of the move. | |
6151 | |
6152 GCC defines the function @code{memory_move_secondary_cost} if | |
6153 secondary reloads are needed. It computes the costs due to copying via | |
6154 a secondary register. If your machine copies from memory using a | |
6155 secondary register in the conventional way but the default base value of | |
6156 4 is not correct for your machine, use this target hook to add some other | |
6157 value to the result of that function. The arguments to that function | |
6158 are the same as to this target hook. | |
6159 @end deftypefn | |
6160 | |
6161 @defmac BRANCH_COST (@var{speed_p}, @var{predictable_p}) | |
6162 A C expression for the cost of a branch instruction. A value of 1 is | |
6163 the default; other values are interpreted relative to that. Parameter | |
6164 @var{speed_p} is true when the branch in question should be optimized | |
6165 for speed. When it is false, @code{BRANCH_COST} should return a value | |
6166 optimal for code size rather than performance. @var{predictable_p} is | |
6167 true for well-predicted branches. On many architectures the | |
6168 @code{BRANCH_COST} can be reduced then. | |
6169 @end defmac | |
6170 | |
6171 Here are additional macros which do not specify precise relative costs, | |
6172 but only that certain actions are more expensive than GCC would | |
6173 ordinarily expect. | |
6174 | |
6175 @defmac SLOW_BYTE_ACCESS | |
6176 Define this macro as a C expression which is nonzero if accessing less | |
6177 than a word of memory (i.e.@: a @code{char} or a @code{short}) is no | |
6178 faster than accessing a word of memory, i.e., if such access | |
6179 require more than one instruction or if there is no difference in cost | |
6180 between byte and (aligned) word loads. | |
6181 | |
6182 When this macro is not defined, the compiler will access a field by | |
6183 finding the smallest containing object; when it is defined, a fullword | |
6184 load will be used if alignment permits. Unless bytes accesses are | |
6185 faster than word accesses, using word accesses is preferable since it | |
6186 may eliminate subsequent memory access if subsequent accesses occur to | |
6187 other fields in the same word of the structure, but to different bytes. | |
6188 @end defmac | |
6189 | |
6190 @defmac SLOW_UNALIGNED_ACCESS (@var{mode}, @var{alignment}) | |
6191 Define this macro to be the value 1 if memory accesses described by the | |
6192 @var{mode} and @var{alignment} parameters have a cost many times greater | |
6193 than aligned accesses, for example if they are emulated in a trap | |
6194 handler. | |
6195 | |
6196 When this macro is nonzero, the compiler will act as if | |
6197 @code{STRICT_ALIGNMENT} were nonzero when generating code for block | |
6198 moves. This can cause significantly more instructions to be produced. | |
6199 Therefore, do not set this macro nonzero if unaligned accesses only add a | |
6200 cycle or two to the time for a memory access. | |
6201 | |
6202 If the value of this macro is always zero, it need not be defined. If | |
6203 this macro is defined, it should produce a nonzero value when | |
6204 @code{STRICT_ALIGNMENT} is nonzero. | |
6205 @end defmac | |
6206 | |
6207 @defmac MOVE_RATIO (@var{speed}) | |
6208 The threshold of number of scalar memory-to-memory move insns, @emph{below} | |
6209 which a sequence of insns should be generated instead of a | |
6210 string move insn or a library call. Increasing the value will always | |
6211 make code faster, but eventually incurs high cost in increased code size. | |
6212 | |
6213 Note that on machines where the corresponding move insn is a | |
6214 @code{define_expand} that emits a sequence of insns, this macro counts | |
6215 the number of such sequences. | |
6216 | |
6217 The parameter @var{speed} is true if the code is currently being | |
6218 optimized for speed rather than size. | |
6219 | |
6220 If you don't define this, a reasonable default is used. | |
6221 @end defmac | |
6222 | |
6223 @defmac MOVE_BY_PIECES_P (@var{size}, @var{alignment}) | |
6224 A C expression used to determine whether @code{move_by_pieces} will be used to | |
6225 copy a chunk of memory, or whether some other block move mechanism | |
6226 will be used. Defaults to 1 if @code{move_by_pieces_ninsns} returns less | |
6227 than @code{MOVE_RATIO}. | |
6228 @end defmac | |
6229 | |
6230 @defmac MOVE_MAX_PIECES | |
6231 A C expression used by @code{move_by_pieces} to determine the largest unit | |
6232 a load or store used to copy memory is. Defaults to @code{MOVE_MAX}. | |
6233 @end defmac | |
6234 | |
6235 @defmac CLEAR_RATIO (@var{speed}) | |
6236 The threshold of number of scalar move insns, @emph{below} which a sequence | |
6237 of insns should be generated to clear memory instead of a string clear insn | |
6238 or a library call. Increasing the value will always make code faster, but | |
6239 eventually incurs high cost in increased code size. | |
6240 | |
6241 The parameter @var{speed} is true if the code is currently being | |
6242 optimized for speed rather than size. | |
6243 | |
6244 If you don't define this, a reasonable default is used. | |
6245 @end defmac | |
6246 | |
6247 @defmac CLEAR_BY_PIECES_P (@var{size}, @var{alignment}) | |
6248 A C expression used to determine whether @code{clear_by_pieces} will be used | |
6249 to clear a chunk of memory, or whether some other block clear mechanism | |
6250 will be used. Defaults to 1 if @code{move_by_pieces_ninsns} returns less | |
6251 than @code{CLEAR_RATIO}. | |
6252 @end defmac | |
6253 | |
6254 @defmac SET_RATIO (@var{speed}) | |
6255 The threshold of number of scalar move insns, @emph{below} which a sequence | |
6256 of insns should be generated to set memory to a constant value, instead of | |
6257 a block set insn or a library call. | |
6258 Increasing the value will always make code faster, but | |
6259 eventually incurs high cost in increased code size. | |
6260 | |
6261 The parameter @var{speed} is true if the code is currently being | |
6262 optimized for speed rather than size. | |
6263 | |
6264 If you don't define this, it defaults to the value of @code{MOVE_RATIO}. | |
6265 @end defmac | |
6266 | |
6267 @defmac SET_BY_PIECES_P (@var{size}, @var{alignment}) | |
6268 A C expression used to determine whether @code{store_by_pieces} will be | |
6269 used to set a chunk of memory to a constant value, or whether some | |
6270 other mechanism will be used. Used by @code{__builtin_memset} when | |
6271 storing values other than constant zero. | |
6272 Defaults to 1 if @code{move_by_pieces_ninsns} returns less | |
6273 than @code{SET_RATIO}. | |
6274 @end defmac | |
6275 | |
6276 @defmac STORE_BY_PIECES_P (@var{size}, @var{alignment}) | |
6277 A C expression used to determine whether @code{store_by_pieces} will be | |
6278 used to set a chunk of memory to a constant string value, or whether some | |
6279 other mechanism will be used. Used by @code{__builtin_strcpy} when | |
6280 called with a constant source string. | |
6281 Defaults to 1 if @code{move_by_pieces_ninsns} returns less | |
6282 than @code{MOVE_RATIO}. | |
6283 @end defmac | |
6284 | |
6285 @defmac USE_LOAD_POST_INCREMENT (@var{mode}) | |
6286 A C expression used to determine whether a load postincrement is a good | |
6287 thing to use for a given mode. Defaults to the value of | |
6288 @code{HAVE_POST_INCREMENT}. | |
6289 @end defmac | |
6290 | |
6291 @defmac USE_LOAD_POST_DECREMENT (@var{mode}) | |
6292 A C expression used to determine whether a load postdecrement is a good | |
6293 thing to use for a given mode. Defaults to the value of | |
6294 @code{HAVE_POST_DECREMENT}. | |
6295 @end defmac | |
6296 | |
6297 @defmac USE_LOAD_PRE_INCREMENT (@var{mode}) | |
6298 A C expression used to determine whether a load preincrement is a good | |
6299 thing to use for a given mode. Defaults to the value of | |
6300 @code{HAVE_PRE_INCREMENT}. | |
6301 @end defmac | |
6302 | |
6303 @defmac USE_LOAD_PRE_DECREMENT (@var{mode}) | |
6304 A C expression used to determine whether a load predecrement is a good | |
6305 thing to use for a given mode. Defaults to the value of | |
6306 @code{HAVE_PRE_DECREMENT}. | |
6307 @end defmac | |
6308 | |
6309 @defmac USE_STORE_POST_INCREMENT (@var{mode}) | |
6310 A C expression used to determine whether a store postincrement is a good | |
6311 thing to use for a given mode. Defaults to the value of | |
6312 @code{HAVE_POST_INCREMENT}. | |
6313 @end defmac | |
6314 | |
6315 @defmac USE_STORE_POST_DECREMENT (@var{mode}) | |
6316 A C expression used to determine whether a store postdecrement is a good | |
6317 thing to use for a given mode. Defaults to the value of | |
6318 @code{HAVE_POST_DECREMENT}. | |
6319 @end defmac | |
6320 | |
6321 @defmac USE_STORE_PRE_INCREMENT (@var{mode}) | |
6322 This macro is used to determine whether a store preincrement is a good | |
6323 thing to use for a given mode. Defaults to the value of | |
6324 @code{HAVE_PRE_INCREMENT}. | |
6325 @end defmac | |
6326 | |
6327 @defmac USE_STORE_PRE_DECREMENT (@var{mode}) | |
6328 This macro is used to determine whether a store predecrement is a good | |
6329 thing to use for a given mode. Defaults to the value of | |
6330 @code{HAVE_PRE_DECREMENT}. | |
6331 @end defmac | |
6332 | |
6333 @defmac NO_FUNCTION_CSE | |
6334 Define this macro if it is as good or better to call a constant | |
6335 function address than to call an address kept in a register. | |
6336 @end defmac | |
6337 | |
6338 @defmac RANGE_TEST_NON_SHORT_CIRCUIT | |
6339 Define this macro if a non-short-circuit operation produced by | |
6340 @samp{fold_range_test ()} is optimal. This macro defaults to true if | |
6341 @code{BRANCH_COST} is greater than or equal to the value 2. | |
6342 @end defmac | |
6343 | |
6344 @hook TARGET_RTX_COSTS | |
6345 This target hook describes the relative costs of RTL expressions. | |
6346 | |
6347 The cost may depend on the precise form of the expression, which is | |
6348 available for examination in @var{x}, and the rtx code of the expression | |
6349 in which it is contained, found in @var{outer_code}. @var{code} is the | |
6350 expression code---redundant, since it can be obtained with | |
6351 @code{GET_CODE (@var{x})}. | |
6352 | |
6353 In implementing this hook, you can use the construct | |
6354 @code{COSTS_N_INSNS (@var{n})} to specify a cost equal to @var{n} fast | |
6355 instructions. | |
6356 | |
6357 On entry to the hook, @code{*@var{total}} contains a default estimate | |
6358 for the cost of the expression. The hook should modify this value as | |
6359 necessary. Traditionally, the default costs are @code{COSTS_N_INSNS (5)} | |
6360 for multiplications, @code{COSTS_N_INSNS (7)} for division and modulus | |
6361 operations, and @code{COSTS_N_INSNS (1)} for all other operations. | |
6362 | |
6363 When optimizing for code size, i.e.@: when @code{speed} is | |
6364 false, this target hook should be used to estimate the relative | |
6365 size cost of an expression, again relative to @code{COSTS_N_INSNS}. | |
6366 | |
6367 The hook returns true when all subexpressions of @var{x} have been | |
6368 processed, and false when @code{rtx_cost} should recurse. | |
6369 @end deftypefn | |
6370 | |
6371 @hook TARGET_ADDRESS_COST | |
6372 This hook computes the cost of an addressing mode that contains | |
6373 @var{address}. If not defined, the cost is computed from | |
6374 the @var{address} expression and the @code{TARGET_RTX_COST} hook. | |
6375 | |
6376 For most CISC machines, the default cost is a good approximation of the | |
6377 true cost of the addressing mode. However, on RISC machines, all | |
6378 instructions normally have the same length and execution time. Hence | |
6379 all addresses will have equal costs. | |
6380 | |
6381 In cases where more than one form of an address is known, the form with | |
6382 the lowest cost will be used. If multiple forms have the same, lowest, | |
6383 cost, the one that is the most complex will be used. | |
6384 | |
6385 For example, suppose an address that is equal to the sum of a register | |
6386 and a constant is used twice in the same basic block. When this macro | |
6387 is not defined, the address will be computed in a register and memory | |
6388 references will be indirect through that register. On machines where | |
6389 the cost of the addressing mode containing the sum is no higher than | |
6390 that of a simple indirect reference, this will produce an additional | |
6391 instruction and possibly require an additional register. Proper | |
6392 specification of this macro eliminates this overhead for such machines. | |
6393 | |
6394 This hook is never called with an invalid address. | |
6395 | |
6396 On machines where an address involving more than one register is as | |
6397 cheap as an address computation involving only one register, defining | |
6398 @code{TARGET_ADDRESS_COST} to reflect this can cause two registers to | |
6399 be live over a region of code where only one would have been if | |
6400 @code{TARGET_ADDRESS_COST} were not defined in that manner. This effect | |
6401 should be considered in the definition of this macro. Equivalent costs | |
6402 should probably only be given to addresses with different numbers of | |
6403 registers on machines with lots of registers. | |
6404 @end deftypefn | |
6405 | |
6406 @node Scheduling | |
6407 @section Adjusting the Instruction Scheduler | |
6408 | |
6409 The instruction scheduler may need a fair amount of machine-specific | |
6410 adjustment in order to produce good code. GCC provides several target | |
6411 hooks for this purpose. It is usually enough to define just a few of | |
6412 them: try the first ones in this list first. | |
6413 | |
6414 @hook TARGET_SCHED_ISSUE_RATE | |
6415 This hook returns the maximum number of instructions that can ever | |
6416 issue at the same time on the target machine. The default is one. | |
6417 Although the insn scheduler can define itself the possibility of issue | |
6418 an insn on the same cycle, the value can serve as an additional | |
6419 constraint to issue insns on the same simulated processor cycle (see | |
6420 hooks @samp{TARGET_SCHED_REORDER} and @samp{TARGET_SCHED_REORDER2}). | |
6421 This value must be constant over the entire compilation. If you need | |
6422 it to vary depending on what the instructions are, you must use | |
6423 @samp{TARGET_SCHED_VARIABLE_ISSUE}. | |
6424 @end deftypefn | |
6425 | |
6426 @hook TARGET_SCHED_VARIABLE_ISSUE | |
6427 This hook is executed by the scheduler after it has scheduled an insn | |
6428 from the ready list. It should return the number of insns which can | |
6429 still be issued in the current cycle. The default is | |
6430 @samp{@w{@var{more} - 1}} for insns other than @code{CLOBBER} and | |
6431 @code{USE}, which normally are not counted against the issue rate. | |
6432 You should define this hook if some insns take more machine resources | |
6433 than others, so that fewer insns can follow them in the same cycle. | |
6434 @var{file} is either a null pointer, or a stdio stream to write any | |
6435 debug output to. @var{verbose} is the verbose level provided by | |
6436 @option{-fsched-verbose-@var{n}}. @var{insn} is the instruction that | |
6437 was scheduled. | |
6438 @end deftypefn | |
6439 | |
6440 @hook TARGET_SCHED_ADJUST_COST | |
6441 This function corrects the value of @var{cost} based on the | |
6442 relationship between @var{insn} and @var{dep_insn} through the | |
6443 dependence @var{link}. It should return the new value. The default | |
6444 is to make no adjustment to @var{cost}. This can be used for example | |
6445 to specify to the scheduler using the traditional pipeline description | |
6446 that an output- or anti-dependence does not incur the same cost as a | |
6447 data-dependence. If the scheduler using the automaton based pipeline | |
6448 description, the cost of anti-dependence is zero and the cost of | |
6449 output-dependence is maximum of one and the difference of latency | |
6450 times of the first and the second insns. If these values are not | |
6451 acceptable, you could use the hook to modify them too. See also | |
6452 @pxref{Processor pipeline description}. | |
6453 @end deftypefn | |
6454 | |
6455 @hook TARGET_SCHED_ADJUST_PRIORITY | |
6456 This hook adjusts the integer scheduling priority @var{priority} of | |
6457 @var{insn}. It should return the new priority. Increase the priority to | |
6458 execute @var{insn} earlier, reduce the priority to execute @var{insn} | |
6459 later. Do not define this hook if you do not need to adjust the | |
6460 scheduling priorities of insns. | |
6461 @end deftypefn | |
6462 | |
6463 @hook TARGET_SCHED_REORDER | |
6464 This hook is executed by the scheduler after it has scheduled the ready | |
6465 list, to allow the machine description to reorder it (for example to | |
6466 combine two small instructions together on @samp{VLIW} machines). | |
6467 @var{file} is either a null pointer, or a stdio stream to write any | |
6468 debug output to. @var{verbose} is the verbose level provided by | |
6469 @option{-fsched-verbose-@var{n}}. @var{ready} is a pointer to the ready | |
6470 list of instructions that are ready to be scheduled. @var{n_readyp} is | |
6471 a pointer to the number of elements in the ready list. The scheduler | |
6472 reads the ready list in reverse order, starting with | |
6473 @var{ready}[@var{*n_readyp} @minus{} 1] and going to @var{ready}[0]. @var{clock} | |
6474 is the timer tick of the scheduler. You may modify the ready list and | |
6475 the number of ready insns. The return value is the number of insns that | |
6476 can issue this cycle; normally this is just @code{issue_rate}. See also | |
6477 @samp{TARGET_SCHED_REORDER2}. | |
6478 @end deftypefn | |
6479 | |
6480 @hook TARGET_SCHED_REORDER2 | |
6481 Like @samp{TARGET_SCHED_REORDER}, but called at a different time. That | |
6482 function is called whenever the scheduler starts a new cycle. This one | |
6483 is called once per iteration over a cycle, immediately after | |
6484 @samp{TARGET_SCHED_VARIABLE_ISSUE}; it can reorder the ready list and | |
6485 return the number of insns to be scheduled in the same cycle. Defining | |
6486 this hook can be useful if there are frequent situations where | |
6487 scheduling one insn causes other insns to become ready in the same | |
6488 cycle. These other insns can then be taken into account properly. | |
6489 @end deftypefn | |
6490 | |
6491 @hook TARGET_SCHED_DEPENDENCIES_EVALUATION_HOOK | |
6492 This hook is called after evaluation forward dependencies of insns in | |
6493 chain given by two parameter values (@var{head} and @var{tail} | |
6494 correspondingly) but before insns scheduling of the insn chain. For | |
6495 example, it can be used for better insn classification if it requires | |
6496 analysis of dependencies. This hook can use backward and forward | |
6497 dependencies of the insn scheduler because they are already | |
6498 calculated. | |
6499 @end deftypefn | |
6500 | |
6501 @hook TARGET_SCHED_INIT | |
6502 This hook is executed by the scheduler at the beginning of each block of | |
6503 instructions that are to be scheduled. @var{file} is either a null | |
6504 pointer, or a stdio stream to write any debug output to. @var{verbose} | |
6505 is the verbose level provided by @option{-fsched-verbose-@var{n}}. | |
6506 @var{max_ready} is the maximum number of insns in the current scheduling | |
6507 region that can be live at the same time. This can be used to allocate | |
6508 scratch space if it is needed, e.g.@: by @samp{TARGET_SCHED_REORDER}. | |
6509 @end deftypefn | |
6510 | |
6511 @hook TARGET_SCHED_FINISH | |
6512 This hook is executed by the scheduler at the end of each block of | |
6513 instructions that are to be scheduled. It can be used to perform | |
6514 cleanup of any actions done by the other scheduling hooks. @var{file} | |
6515 is either a null pointer, or a stdio stream to write any debug output | |
6516 to. @var{verbose} is the verbose level provided by | |
6517 @option{-fsched-verbose-@var{n}}. | |
6518 @end deftypefn | |
6519 | |
6520 @hook TARGET_SCHED_INIT_GLOBAL | |
6521 This hook is executed by the scheduler after function level initializations. | |
6522 @var{file} is either a null pointer, or a stdio stream to write any debug output to. | |
6523 @var{verbose} is the verbose level provided by @option{-fsched-verbose-@var{n}}. | |
6524 @var{old_max_uid} is the maximum insn uid when scheduling begins. | |
6525 @end deftypefn | |
6526 | |
6527 @hook TARGET_SCHED_FINISH_GLOBAL | |
6528 This is the cleanup hook corresponding to @code{TARGET_SCHED_INIT_GLOBAL}. | |
6529 @var{file} is either a null pointer, or a stdio stream to write any debug output to. | |
6530 @var{verbose} is the verbose level provided by @option{-fsched-verbose-@var{n}}. | |
6531 @end deftypefn | |
6532 | |
6533 @hook TARGET_SCHED_DFA_PRE_CYCLE_INSN | |
6534 The hook returns an RTL insn. The automaton state used in the | |
6535 pipeline hazard recognizer is changed as if the insn were scheduled | |
6536 when the new simulated processor cycle starts. Usage of the hook may | |
6537 simplify the automaton pipeline description for some @acronym{VLIW} | |
6538 processors. If the hook is defined, it is used only for the automaton | |
6539 based pipeline description. The default is not to change the state | |
6540 when the new simulated processor cycle starts. | |
6541 @end deftypefn | |
6542 | |
6543 @hook TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN | |
6544 The hook can be used to initialize data used by the previous hook. | |
6545 @end deftypefn | |
6546 | |
6547 @hook TARGET_SCHED_DFA_POST_CYCLE_INSN | |
6548 The hook is analogous to @samp{TARGET_SCHED_DFA_PRE_CYCLE_INSN} but used | |
6549 to changed the state as if the insn were scheduled when the new | |
6550 simulated processor cycle finishes. | |
6551 @end deftypefn | |
6552 | |
6553 @hook TARGET_SCHED_INIT_DFA_POST_CYCLE_INSN | |
6554 The hook is analogous to @samp{TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN} but | |
6555 used to initialize data used by the previous hook. | |
6556 @end deftypefn | |
6557 | |
6558 @hook TARGET_SCHED_DFA_PRE_ADVANCE_CYCLE | |
6559 The hook to notify target that the current simulated cycle is about to finish. | |
6560 The hook is analogous to @samp{TARGET_SCHED_DFA_PRE_CYCLE_INSN} but used | |
6561 to change the state in more complicated situations - e.g., when advancing | |
6562 state on a single insn is not enough. | |
6563 @end deftypefn | |
6564 | |
6565 @hook TARGET_SCHED_DFA_POST_ADVANCE_CYCLE | |
6566 The hook to notify target that new simulated cycle has just started. | |
6567 The hook is analogous to @samp{TARGET_SCHED_DFA_POST_CYCLE_INSN} but used | |
6568 to change the state in more complicated situations - e.g., when advancing | |
6569 state on a single insn is not enough. | |
6570 @end deftypefn | |
6571 | |
6572 @hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD | |
6573 This hook controls better choosing an insn from the ready insn queue | |
6574 for the @acronym{DFA}-based insn scheduler. Usually the scheduler | |
6575 chooses the first insn from the queue. If the hook returns a positive | |
6576 value, an additional scheduler code tries all permutations of | |
6577 @samp{TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD ()} | |
6578 subsequent ready insns to choose an insn whose issue will result in | |
6579 maximal number of issued insns on the same cycle. For the | |
6580 @acronym{VLIW} processor, the code could actually solve the problem of | |
6581 packing simple insns into the @acronym{VLIW} insn. Of course, if the | |
6582 rules of @acronym{VLIW} packing are described in the automaton. | |
6583 | |
6584 This code also could be used for superscalar @acronym{RISC} | |
6585 processors. Let us consider a superscalar @acronym{RISC} processor | |
6586 with 3 pipelines. Some insns can be executed in pipelines @var{A} or | |
6587 @var{B}, some insns can be executed only in pipelines @var{B} or | |
6588 @var{C}, and one insn can be executed in pipeline @var{B}. The | |
6589 processor may issue the 1st insn into @var{A} and the 2nd one into | |
6590 @var{B}. In this case, the 3rd insn will wait for freeing @var{B} | |
6591 until the next cycle. If the scheduler issues the 3rd insn the first, | |
6592 the processor could issue all 3 insns per cycle. | |
6593 | |
6594 Actually this code demonstrates advantages of the automaton based | |
6595 pipeline hazard recognizer. We try quickly and easy many insn | |
6596 schedules to choose the best one. | |
6597 | |
6598 The default is no multipass scheduling. | |
6599 @end deftypefn | |
6600 | |
6601 @hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD | |
6602 | |
6603 This hook controls what insns from the ready insn queue will be | |
6604 considered for the multipass insn scheduling. If the hook returns | |
6605 zero for @var{insn}, the insn will be not chosen to | |
6606 be issued. | |
6607 | |
6608 The default is that any ready insns can be chosen to be issued. | |
6609 @end deftypefn | |
6610 | |
6611 @hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_BEGIN | |
6612 This hook prepares the target backend for a new round of multipass | |
6613 scheduling. | |
6614 @end deftypefn | |
6615 | |
6616 @hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_ISSUE | |
6617 This hook is called when multipass scheduling evaluates instruction INSN. | |
6618 @end deftypefn | |
6619 | |
6620 @hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_BACKTRACK | |
6621 This is called when multipass scheduling backtracks from evaluation of | |
6622 an instruction. | |
6623 @end deftypefn | |
6624 | |
6625 @hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_END | |
6626 This hook notifies the target about the result of the concluded current | |
6627 round of multipass scheduling. | |
6628 @end deftypefn | |
6629 | |
6630 @hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_INIT | |
6631 This hook initializes target-specific data used in multipass scheduling. | |
6632 @end deftypefn | |
6633 | |
6634 @hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_FINI | |
6635 This hook finalizes target-specific data used in multipass scheduling. | |
6636 @end deftypefn | |
6637 | |
6638 @hook TARGET_SCHED_DFA_NEW_CYCLE | |
6639 This hook is called by the insn scheduler before issuing @var{insn} | |
6640 on cycle @var{clock}. If the hook returns nonzero, | |
6641 @var{insn} is not issued on this processor cycle. Instead, | |
6642 the processor cycle is advanced. If *@var{sort_p} | |
6643 is zero, the insn ready queue is not sorted on the new cycle | |
6644 start as usually. @var{dump} and @var{verbose} specify the file and | |
6645 verbosity level to use for debugging output. | |
6646 @var{last_clock} and @var{clock} are, respectively, the | |
6647 processor cycle on which the previous insn has been issued, | |
6648 and the current processor cycle. | |
6649 @end deftypefn | |
6650 | |
6651 @hook TARGET_SCHED_IS_COSTLY_DEPENDENCE | |
6652 This hook is used to define which dependences are considered costly by | |
6653 the target, so costly that it is not advisable to schedule the insns that | |
6654 are involved in the dependence too close to one another. The parameters | |
6655 to this hook are as follows: The first parameter @var{_dep} is the dependence | |
6656 being evaluated. The second parameter @var{cost} is the cost of the | |
6657 dependence as estimated by the scheduler, and the third | |
6658 parameter @var{distance} is the distance in cycles between the two insns. | |
6659 The hook returns @code{true} if considering the distance between the two | |
6660 insns the dependence between them is considered costly by the target, | |
6661 and @code{false} otherwise. | |
6662 | |
6663 Defining this hook can be useful in multiple-issue out-of-order machines, | |
6664 where (a) it's practically hopeless to predict the actual data/resource | |
6665 delays, however: (b) there's a better chance to predict the actual grouping | |
6666 that will be formed, and (c) correctly emulating the grouping can be very | |
6667 important. In such targets one may want to allow issuing dependent insns | |
6668 closer to one another---i.e., closer than the dependence distance; however, | |
6669 not in cases of ``costly dependences'', which this hooks allows to define. | |
6670 @end deftypefn | |
6671 | |
6672 @hook TARGET_SCHED_H_I_D_EXTENDED | |
6673 This hook is called by the insn scheduler after emitting a new instruction to | |
6674 the instruction stream. The hook notifies a target backend to extend its | |
6675 per instruction data structures. | |
6676 @end deftypefn | |
6677 | |
6678 @hook TARGET_SCHED_ALLOC_SCHED_CONTEXT | |
6679 Return a pointer to a store large enough to hold target scheduling context. | |
6680 @end deftypefn | |
6681 | |
6682 @hook TARGET_SCHED_INIT_SCHED_CONTEXT | |
6683 Initialize store pointed to by @var{tc} to hold target scheduling context. | |
6684 It @var{clean_p} is true then initialize @var{tc} as if scheduler is at the | |
6685 beginning of the block. Otherwise, copy the current context into @var{tc}. | |
6686 @end deftypefn | |
6687 | |
6688 @hook TARGET_SCHED_SET_SCHED_CONTEXT | |
6689 Copy target scheduling context pointed to by @var{tc} to the current context. | |
6690 @end deftypefn | |
6691 | |
6692 @hook TARGET_SCHED_CLEAR_SCHED_CONTEXT | |
6693 Deallocate internal data in target scheduling context pointed to by @var{tc}. | |
6694 @end deftypefn | |
6695 | |
6696 @hook TARGET_SCHED_FREE_SCHED_CONTEXT | |
6697 Deallocate a store for target scheduling context pointed to by @var{tc}. | |
6698 @end deftypefn | |
6699 | |
6700 @hook TARGET_SCHED_SPECULATE_INSN | |
6701 This hook is called by the insn scheduler when @var{insn} has only | |
6702 speculative dependencies and therefore can be scheduled speculatively. | |
6703 The hook is used to check if the pattern of @var{insn} has a speculative | |
6704 version and, in case of successful check, to generate that speculative | |
6705 pattern. The hook should return 1, if the instruction has a speculative form, | |
6706 or @minus{}1, if it doesn't. @var{request} describes the type of requested | |
6707 speculation. If the return value equals 1 then @var{new_pat} is assigned | |
6708 the generated speculative pattern. | |
6709 @end deftypefn | |
6710 | |
6711 @hook TARGET_SCHED_NEEDS_BLOCK_P | |
6712 This hook is called by the insn scheduler during generation of recovery code | |
6713 for @var{insn}. It should return @code{true}, if the corresponding check | |
6714 instruction should branch to recovery code, or @code{false} otherwise. | |
6715 @end deftypefn | |
6716 | |
6717 @hook TARGET_SCHED_GEN_SPEC_CHECK | |
6718 This hook is called by the insn scheduler to generate a pattern for recovery | |
6719 check instruction. If @var{mutate_p} is zero, then @var{insn} is a | |
6720 speculative instruction for which the check should be generated. | |
6721 @var{label} is either a label of a basic block, where recovery code should | |
6722 be emitted, or a null pointer, when requested check doesn't branch to | |
6723 recovery code (a simple check). If @var{mutate_p} is nonzero, then | |
6724 a pattern for a branchy check corresponding to a simple check denoted by | |
6725 @var{insn} should be generated. In this case @var{label} can't be null. | |
6726 @end deftypefn | |
6727 | |
6728 @hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD_SPEC | |
6729 This hook is used as a workaround for | |
6730 @samp{TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD} not being | |
6731 called on the first instruction of the ready list. The hook is used to | |
6732 discard speculative instructions that stand first in the ready list from | |
6733 being scheduled on the current cycle. If the hook returns @code{false}, | |
6734 @var{insn} will not be chosen to be issued. | |
6735 For non-speculative instructions, | |
6736 the hook should always return @code{true}. For example, in the ia64 backend | |
6737 the hook is used to cancel data speculative insns when the ALAT table | |
6738 is nearly full. | |
6739 @end deftypefn | |
6740 | |
6741 @hook TARGET_SCHED_SET_SCHED_FLAGS | |
6742 This hook is used by the insn scheduler to find out what features should be | |
6743 enabled/used. | |
6744 The structure *@var{spec_info} should be filled in by the target. | |
6745 The structure describes speculation types that can be used in the scheduler. | |
6746 @end deftypefn | |
6747 | |
6748 @hook TARGET_SCHED_SMS_RES_MII | |
6749 This hook is called by the swing modulo scheduler to calculate a | |
6750 resource-based lower bound which is based on the resources available in | |
6751 the machine and the resources required by each instruction. The target | |
6752 backend can use @var{g} to calculate such bound. A very simple lower | |
6753 bound will be used in case this hook is not implemented: the total number | |
6754 of instructions divided by the issue rate. | |
6755 @end deftypefn | |
6756 | |
6757 @hook TARGET_SCHED_DISPATCH | |
6758 This hook is called by Haifa Scheduler. It returns true if dispatch scheduling | |
6759 is supported in hardware and the condition specified in the parameter is true. | |
6760 @end deftypefn | |
6761 | |
6762 @hook TARGET_SCHED_DISPATCH_DO | |
6763 This hook is called by Haifa Scheduler. It performs the operation specified | |
6764 in its second parameter. | |
6765 @end deftypefn | |
6766 | |
6767 @node Sections | |
6768 @section Dividing the Output into Sections (Texts, Data, @dots{}) | |
6769 @c the above section title is WAY too long. maybe cut the part between | |
6770 @c the (...)? --mew 10feb93 | |
6771 | |
6772 An object file is divided into sections containing different types of | |
6773 data. In the most common case, there are three sections: the @dfn{text | |
6774 section}, which holds instructions and read-only data; the @dfn{data | |
6775 section}, which holds initialized writable data; and the @dfn{bss | |
6776 section}, which holds uninitialized data. Some systems have other kinds | |
6777 of sections. | |
6778 | |
6779 @file{varasm.c} provides several well-known sections, such as | |
6780 @code{text_section}, @code{data_section} and @code{bss_section}. | |
6781 The normal way of controlling a @code{@var{foo}_section} variable | |
6782 is to define the associated @code{@var{FOO}_SECTION_ASM_OP} macro, | |
6783 as described below. The macros are only read once, when @file{varasm.c} | |
6784 initializes itself, so their values must be run-time constants. | |
6785 They may however depend on command-line flags. | |
6786 | |
6787 @emph{Note:} Some run-time files, such @file{crtstuff.c}, also make | |
6788 use of the @code{@var{FOO}_SECTION_ASM_OP} macros, and expect them | |
6789 to be string literals. | |
6790 | |
6791 Some assemblers require a different string to be written every time a | |
6792 section is selected. If your assembler falls into this category, you | |
6793 should define the @code{TARGET_ASM_INIT_SECTIONS} hook and use | |
6794 @code{get_unnamed_section} to set up the sections. | |
6795 | |
6796 You must always create a @code{text_section}, either by defining | |
6797 @code{TEXT_SECTION_ASM_OP} or by initializing @code{text_section} | |
6798 in @code{TARGET_ASM_INIT_SECTIONS}. The same is true of | |
6799 @code{data_section} and @code{DATA_SECTION_ASM_OP}. If you do not | |
6800 create a distinct @code{readonly_data_section}, the default is to | |
6801 reuse @code{text_section}. | |
6802 | |
6803 All the other @file{varasm.c} sections are optional, and are null | |
6804 if the target does not provide them. | |
6805 | |
6806 @defmac TEXT_SECTION_ASM_OP | |
6807 A C expression whose value is a string, including spacing, containing the | |
6808 assembler operation that should precede instructions and read-only data. | |
6809 Normally @code{"\t.text"} is right. | |
6810 @end defmac | |
6811 | |
6812 @defmac HOT_TEXT_SECTION_NAME | |
6813 If defined, a C string constant for the name of the section containing most | |
6814 frequently executed functions of the program. If not defined, GCC will provide | |
6815 a default definition if the target supports named sections. | |
6816 @end defmac | |
6817 | |
6818 @defmac UNLIKELY_EXECUTED_TEXT_SECTION_NAME | |
6819 If defined, a C string constant for the name of the section containing unlikely | |
6820 executed functions in the program. | |
6821 @end defmac | |
6822 | |
6823 @defmac DATA_SECTION_ASM_OP | |
6824 A C expression whose value is a string, including spacing, containing the | |
6825 assembler operation to identify the following data as writable initialized | |
6826 data. Normally @code{"\t.data"} is right. | |
6827 @end defmac | |
6828 | |
6829 @defmac SDATA_SECTION_ASM_OP | |
6830 If defined, a C expression whose value is a string, including spacing, | |
6831 containing the assembler operation to identify the following data as | |
6832 initialized, writable small data. | |
6833 @end defmac | |
6834 | |
6835 @defmac READONLY_DATA_SECTION_ASM_OP | |
6836 A C expression whose value is a string, including spacing, containing the | |
6837 assembler operation to identify the following data as read-only initialized | |
6838 data. | |
6839 @end defmac | |
6840 | |
6841 @defmac BSS_SECTION_ASM_OP | |
6842 If defined, a C expression whose value is a string, including spacing, | |
6843 containing the assembler operation to identify the following data as | |
6844 uninitialized global data. If not defined, and neither | |
6845 @code{ASM_OUTPUT_BSS} nor @code{ASM_OUTPUT_ALIGNED_BSS} are defined, | |
6846 uninitialized global data will be output in the data section if | |
6847 @option{-fno-common} is passed, otherwise @code{ASM_OUTPUT_COMMON} will be | |
6848 used. | |
6849 @end defmac | |
6850 | |
6851 @defmac SBSS_SECTION_ASM_OP | |
6852 If defined, a C expression whose value is a string, including spacing, | |
6853 containing the assembler operation to identify the following data as | |
6854 uninitialized, writable small data. | |
6855 @end defmac | |
6856 | |
6857 @defmac TLS_COMMON_ASM_OP | |
6858 If defined, a C expression whose value is a string containing the | |
6859 assembler operation to identify the following data as thread-local | |
6860 common data. The default is @code{".tls_common"}. | |
6861 @end defmac | |
6862 | |
6863 @defmac TLS_SECTION_ASM_FLAG | |
6864 If defined, a C expression whose value is a character constant | |
6865 containing the flag used to mark a section as a TLS section. The | |
6866 default is @code{'T'}. | |
6867 @end defmac | |
6868 | |
6869 @defmac INIT_SECTION_ASM_OP | |
6870 If defined, a C expression whose value is a string, including spacing, | |
6871 containing the assembler operation to identify the following data as | |
6872 initialization code. If not defined, GCC will assume such a section does | |
6873 not exist. This section has no corresponding @code{init_section} | |
6874 variable; it is used entirely in runtime code. | |
6875 @end defmac | |
6876 | |
6877 @defmac FINI_SECTION_ASM_OP | |
6878 If defined, a C expression whose value is a string, including spacing, | |
6879 containing the assembler operation to identify the following data as | |
6880 finalization code. If not defined, GCC will assume such a section does | |
6881 not exist. This section has no corresponding @code{fini_section} | |
6882 variable; it is used entirely in runtime code. | |
6883 @end defmac | |
6884 | |
6885 @defmac INIT_ARRAY_SECTION_ASM_OP | |
6886 If defined, a C expression whose value is a string, including spacing, | |
6887 containing the assembler operation to identify the following data as | |
6888 part of the @code{.init_array} (or equivalent) section. If not | |
6889 defined, GCC will assume such a section does not exist. Do not define | |
6890 both this macro and @code{INIT_SECTION_ASM_OP}. | |
6891 @end defmac | |
6892 | |
6893 @defmac FINI_ARRAY_SECTION_ASM_OP | |
6894 If defined, a C expression whose value is a string, including spacing, | |
6895 containing the assembler operation to identify the following data as | |
6896 part of the @code{.fini_array} (or equivalent) section. If not | |
6897 defined, GCC will assume such a section does not exist. Do not define | |
6898 both this macro and @code{FINI_SECTION_ASM_OP}. | |
6899 @end defmac | |
6900 | |
6901 @defmac CRT_CALL_STATIC_FUNCTION (@var{section_op}, @var{function}) | |
6902 If defined, an ASM statement that switches to a different section | |
6903 via @var{section_op}, calls @var{function}, and switches back to | |
6904 the text section. This is used in @file{crtstuff.c} if | |
6905 @code{INIT_SECTION_ASM_OP} or @code{FINI_SECTION_ASM_OP} to calls | |
6906 to initialization and finalization functions from the init and fini | |
6907 sections. By default, this macro uses a simple function call. Some | |
6908 ports need hand-crafted assembly code to avoid dependencies on | |
6909 registers initialized in the function prologue or to ensure that | |
6910 constant pools don't end up too far way in the text section. | |
6911 @end defmac | |
6912 | |
6913 @defmac TARGET_LIBGCC_SDATA_SECTION | |
6914 If defined, a string which names the section into which small | |
6915 variables defined in crtstuff and libgcc should go. This is useful | |
6916 when the target has options for optimizing access to small data, and | |
6917 you want the crtstuff and libgcc routines to be conservative in what | |
6918 they expect of your application yet liberal in what your application | |
6919 expects. For example, for targets with a @code{.sdata} section (like | |
6920 MIPS), you could compile crtstuff with @code{-G 0} so that it doesn't | |
6921 require small data support from your application, but use this macro | |
6922 to put small data into @code{.sdata} so that your application can | |
6923 access these variables whether it uses small data or not. | |
6924 @end defmac | |
6925 | |
6926 @defmac FORCE_CODE_SECTION_ALIGN | |
6927 If defined, an ASM statement that aligns a code section to some | |
6928 arbitrary boundary. This is used to force all fragments of the | |
6929 @code{.init} and @code{.fini} sections to have to same alignment | |
6930 and thus prevent the linker from having to add any padding. | |
6931 @end defmac | |
6932 | |
6933 @defmac JUMP_TABLES_IN_TEXT_SECTION | |
6934 Define this macro to be an expression with a nonzero value if jump | |
6935 tables (for @code{tablejump} insns) should be output in the text | |
6936 section, along with the assembler instructions. Otherwise, the | |
6937 readonly data section is used. | |
6938 | |
6939 This macro is irrelevant if there is no separate readonly data section. | |
6940 @end defmac | |
6941 | |
6942 @hook TARGET_ASM_INIT_SECTIONS | |
6943 Define this hook if you need to do something special to set up the | |
6944 @file{varasm.c} sections, or if your target has some special sections | |
6945 of its own that you need to create. | |
6946 | |
6947 GCC calls this hook after processing the command line, but before writing | |
6948 any assembly code, and before calling any of the section-returning hooks | |
6949 described below. | |
6950 @end deftypefn | |
6951 | |
6952 @hook TARGET_ASM_RELOC_RW_MASK | |
6953 Return a mask describing how relocations should be treated when | |
6954 selecting sections. Bit 1 should be set if global relocations | |
6955 should be placed in a read-write section; bit 0 should be set if | |
6956 local relocations should be placed in a read-write section. | |
6957 | |
6958 The default version of this function returns 3 when @option{-fpic} | |
6959 is in effect, and 0 otherwise. The hook is typically redefined | |
6960 when the target cannot support (some kinds of) dynamic relocations | |
6961 in read-only sections even in executables. | |
6962 @end deftypefn | |
6963 | |
6964 @hook TARGET_ASM_SELECT_SECTION | |
6965 Return the section into which @var{exp} should be placed. You can | |
6966 assume that @var{exp} is either a @code{VAR_DECL} node or a constant of | |
6967 some sort. @var{reloc} indicates whether the initial value of @var{exp} | |
6968 requires link-time relocations. Bit 0 is set when variable contains | |
6969 local relocations only, while bit 1 is set for global relocations. | |
6970 @var{align} is the constant alignment in bits. | |
6971 | |
6972 The default version of this function takes care of putting read-only | |
6973 variables in @code{readonly_data_section}. | |
6974 | |
6975 See also @var{USE_SELECT_SECTION_FOR_FUNCTIONS}. | |
6976 @end deftypefn | |
6977 | |
6978 @defmac USE_SELECT_SECTION_FOR_FUNCTIONS | |
6979 Define this macro if you wish TARGET_ASM_SELECT_SECTION to be called | |
6980 for @code{FUNCTION_DECL}s as well as for variables and constants. | |
6981 | |
6982 In the case of a @code{FUNCTION_DECL}, @var{reloc} will be zero if the | |
6983 function has been determined to be likely to be called, and nonzero if | |
6984 it is unlikely to be called. | |
6985 @end defmac | |
6986 | |
6987 @hook TARGET_ASM_UNIQUE_SECTION | |
6988 Build up a unique section name, expressed as a @code{STRING_CST} node, | |
6989 and assign it to @samp{DECL_SECTION_NAME (@var{decl})}. | |
6990 As with @code{TARGET_ASM_SELECT_SECTION}, @var{reloc} indicates whether | |
6991 the initial value of @var{exp} requires link-time relocations. | |
6992 | |
6993 The default version of this function appends the symbol name to the | |
6994 ELF section name that would normally be used for the symbol. For | |
6995 example, the function @code{foo} would be placed in @code{.text.foo}. | |
6996 Whatever the actual target object format, this is often good enough. | |
6997 @end deftypefn | |
6998 | |
6999 @hook TARGET_ASM_FUNCTION_RODATA_SECTION | |
7000 Return the readonly data section associated with | |
7001 @samp{DECL_SECTION_NAME (@var{decl})}. | |
7002 The default version of this function selects @code{.gnu.linkonce.r.name} if | |
7003 the function's section is @code{.gnu.linkonce.t.name}, @code{.rodata.name} | |
7004 if function is in @code{.text.name}, and the normal readonly-data section | |
7005 otherwise. | |
7006 @end deftypefn | |
7007 | |
7008 @hook TARGET_ASM_SELECT_RTX_SECTION | |
7009 Return the section into which a constant @var{x}, of mode @var{mode}, | |
7010 should be placed. You can assume that @var{x} is some kind of | |
7011 constant in RTL@. The argument @var{mode} is redundant except in the | |
7012 case of a @code{const_int} rtx. @var{align} is the constant alignment | |
7013 in bits. | |
7014 | |
7015 The default version of this function takes care of putting symbolic | |
7016 constants in @code{flag_pic} mode in @code{data_section} and everything | |
7017 else in @code{readonly_data_section}. | |
7018 @end deftypefn | |
7019 | |
7020 @hook TARGET_MANGLE_DECL_ASSEMBLER_NAME | |
7021 Define this hook if you need to postprocess the assembler name generated | |
7022 by target-independent code. The @var{id} provided to this hook will be | |
7023 the computed name (e.g., the macro @code{DECL_NAME} of the @var{decl} in C, | |
7024 or the mangled name of the @var{decl} in C++). The return value of the | |
7025 hook is an @code{IDENTIFIER_NODE} for the appropriate mangled name on | |
7026 your target system. The default implementation of this hook just | |
7027 returns the @var{id} provided. | |
7028 @end deftypefn | |
7029 | |
7030 @hook TARGET_ENCODE_SECTION_INFO | |
7031 Define this hook if references to a symbol or a constant must be | |
7032 treated differently depending on something about the variable or | |
7033 function named by the symbol (such as what section it is in). | |
7034 | |
7035 The hook is executed immediately after rtl has been created for | |
7036 @var{decl}, which may be a variable or function declaration or | |
7037 an entry in the constant pool. In either case, @var{rtl} is the | |
7038 rtl in question. Do @emph{not} use @code{DECL_RTL (@var{decl})} | |
7039 in this hook; that field may not have been initialized yet. | |
7040 | |
7041 In the case of a constant, it is safe to assume that the rtl is | |
7042 a @code{mem} whose address is a @code{symbol_ref}. Most decls | |
7043 will also have this form, but that is not guaranteed. Global | |
7044 register variables, for instance, will have a @code{reg} for their | |
7045 rtl. (Normally the right thing to do with such unusual rtl is | |
7046 leave it alone.) | |
7047 | |
7048 The @var{new_decl_p} argument will be true if this is the first time | |
7049 that @code{TARGET_ENCODE_SECTION_INFO} has been invoked on this decl. It will | |
7050 be false for subsequent invocations, which will happen for duplicate | |
7051 declarations. Whether or not anything must be done for the duplicate | |
7052 declaration depends on whether the hook examines @code{DECL_ATTRIBUTES}. | |
7053 @var{new_decl_p} is always true when the hook is called for a constant. | |
7054 | |
7055 @cindex @code{SYMBOL_REF_FLAG}, in @code{TARGET_ENCODE_SECTION_INFO} | |
7056 The usual thing for this hook to do is to record flags in the | |
7057 @code{symbol_ref}, using @code{SYMBOL_REF_FLAG} or @code{SYMBOL_REF_FLAGS}. | |
7058 Historically, the name string was modified if it was necessary to | |
7059 encode more than one bit of information, but this practice is now | |
7060 discouraged; use @code{SYMBOL_REF_FLAGS}. | |
7061 | |
7062 The default definition of this hook, @code{default_encode_section_info} | |
7063 in @file{varasm.c}, sets a number of commonly-useful bits in | |
7064 @code{SYMBOL_REF_FLAGS}. Check whether the default does what you need | |
7065 before overriding it. | |
7066 @end deftypefn | |
7067 | |
7068 @hook TARGET_STRIP_NAME_ENCODING | |
7069 Decode @var{name} and return the real name part, sans | |
7070 the characters that @code{TARGET_ENCODE_SECTION_INFO} | |
7071 may have added. | |
7072 @end deftypefn | |
7073 | |
7074 @hook TARGET_IN_SMALL_DATA_P | |
7075 Returns true if @var{exp} should be placed into a ``small data'' section. | |
7076 The default version of this hook always returns false. | |
7077 @end deftypefn | |
7078 | |
7079 @hook TARGET_HAVE_SRODATA_SECTION | |
7080 Contains the value true if the target places read-only | |
7081 ``small data'' into a separate section. The default value is false. | |
7082 @end deftypevr | |
7083 | |
7084 @hook TARGET_PROFILE_BEFORE_PROLOGUE | |
7085 | |
7086 @hook TARGET_BINDS_LOCAL_P | |
7087 Returns true if @var{exp} names an object for which name resolution | |
7088 rules must resolve to the current ``module'' (dynamic shared library | |
7089 or executable image). | |
7090 | |
7091 The default version of this hook implements the name resolution rules | |
7092 for ELF, which has a looser model of global name binding than other | |
7093 currently supported object file formats. | |
7094 @end deftypefn | |
7095 | |
7096 @hook TARGET_HAVE_TLS | |
7097 Contains the value true if the target supports thread-local storage. | |
7098 The default value is false. | |
7099 @end deftypevr | |
7100 | |
7101 | |
7102 @node PIC | |
7103 @section Position Independent Code | |
7104 @cindex position independent code | |
7105 @cindex PIC | |
7106 | |
7107 This section describes macros that help implement generation of position | |
7108 independent code. Simply defining these macros is not enough to | |
7109 generate valid PIC; you must also add support to the hook | |
7110 @code{TARGET_LEGITIMATE_ADDRESS_P} and to the macro | |
7111 @code{PRINT_OPERAND_ADDRESS}, as well as @code{LEGITIMIZE_ADDRESS}. You | |
7112 must modify the definition of @samp{movsi} to do something appropriate | |
7113 when the source operand contains a symbolic address. You may also | |
7114 need to alter the handling of switch statements so that they use | |
7115 relative addresses. | |
7116 @c i rearranged the order of the macros above to try to force one of | |
7117 @c them to the next line, to eliminate an overfull hbox. --mew 10feb93 | |
7118 | |
7119 @defmac PIC_OFFSET_TABLE_REGNUM | |
7120 The register number of the register used to address a table of static | |
7121 data addresses in memory. In some cases this register is defined by a | |
7122 processor's ``application binary interface'' (ABI)@. When this macro | |
7123 is defined, RTL is generated for this register once, as with the stack | |
7124 pointer and frame pointer registers. If this macro is not defined, it | |
7125 is up to the machine-dependent files to allocate such a register (if | |
7126 necessary). Note that this register must be fixed when in use (e.g.@: | |
7127 when @code{flag_pic} is true). | |
7128 @end defmac | |
7129 | |
7130 @defmac PIC_OFFSET_TABLE_REG_CALL_CLOBBERED | |
7131 A C expression that is nonzero if the register defined by | |
7132 @code{PIC_OFFSET_TABLE_REGNUM} is clobbered by calls. If not defined, | |
7133 the default is zero. Do not define | |
7134 this macro if @code{PIC_OFFSET_TABLE_REGNUM} is not defined. | |
7135 @end defmac | |
7136 | |
7137 @defmac LEGITIMATE_PIC_OPERAND_P (@var{x}) | |
7138 A C expression that is nonzero if @var{x} is a legitimate immediate | |
7139 operand on the target machine when generating position independent code. | |
7140 You can assume that @var{x} satisfies @code{CONSTANT_P}, so you need not | |
7141 check this. You can also assume @var{flag_pic} is true, so you need not | |
7142 check it either. You need not define this macro if all constants | |
7143 (including @code{SYMBOL_REF}) can be immediate operands when generating | |
7144 position independent code. | |
7145 @end defmac | |
7146 | |
7147 @node Assembler Format | |
7148 @section Defining the Output Assembler Language | |
7149 | |
7150 This section describes macros whose principal purpose is to describe how | |
7151 to write instructions in assembler language---rather than what the | |
7152 instructions do. | |
7153 | |
7154 @menu | |
7155 * File Framework:: Structural information for the assembler file. | |
7156 * Data Output:: Output of constants (numbers, strings, addresses). | |
7157 * Uninitialized Data:: Output of uninitialized variables. | |
7158 * Label Output:: Output and generation of labels. | |
7159 * Initialization:: General principles of initialization | |
7160 and termination routines. | |
7161 * Macros for Initialization:: | |
7162 Specific macros that control the handling of | |
7163 initialization and termination routines. | |
7164 * Instruction Output:: Output of actual instructions. | |
7165 * Dispatch Tables:: Output of jump tables. | |
7166 * Exception Region Output:: Output of exception region code. | |
7167 * Alignment Output:: Pseudo ops for alignment and skipping data. | |
7168 @end menu | |
7169 | |
7170 @node File Framework | |
7171 @subsection The Overall Framework of an Assembler File | |
7172 @cindex assembler format | |
7173 @cindex output of assembler code | |
7174 | |
7175 @c prevent bad page break with this line | |
7176 This describes the overall framework of an assembly file. | |
7177 | |
7178 @findex default_file_start | |
7179 @hook TARGET_ASM_FILE_START | |
7180 Output to @code{asm_out_file} any text which the assembler expects to | |
7181 find at the beginning of a file. The default behavior is controlled | |
7182 by two flags, documented below. Unless your target's assembler is | |
7183 quite unusual, if you override the default, you should call | |
7184 @code{default_file_start} at some point in your target hook. This | |
7185 lets other target files rely on these variables. | |
7186 @end deftypefn | |
7187 | |
7188 @hook TARGET_ASM_FILE_START_APP_OFF | |
7189 If this flag is true, the text of the macro @code{ASM_APP_OFF} will be | |
7190 printed as the very first line in the assembly file, unless | |
7191 @option{-fverbose-asm} is in effect. (If that macro has been defined | |
7192 to the empty string, this variable has no effect.) With the normal | |
7193 definition of @code{ASM_APP_OFF}, the effect is to notify the GNU | |
7194 assembler that it need not bother stripping comments or extra | |
7195 whitespace from its input. This allows it to work a bit faster. | |
7196 | |
7197 The default is false. You should not set it to true unless you have | |
7198 verified that your port does not generate any extra whitespace or | |
7199 comments that will cause GAS to issue errors in NO_APP mode. | |
7200 @end deftypevr | |
7201 | |
7202 @hook TARGET_ASM_FILE_START_FILE_DIRECTIVE | |
7203 If this flag is true, @code{output_file_directive} will be called | |
7204 for the primary source file, immediately after printing | |
7205 @code{ASM_APP_OFF} (if that is enabled). Most ELF assemblers expect | |
7206 this to be done. The default is false. | |
7207 @end deftypevr | |
7208 | |
7209 @hook TARGET_ASM_FILE_END | |
7210 Output to @code{asm_out_file} any text which the assembler expects | |
7211 to find at the end of a file. The default is to output nothing. | |
7212 @end deftypefn | |
7213 | |
7214 @deftypefun void file_end_indicate_exec_stack () | |
7215 Some systems use a common convention, the @samp{.note.GNU-stack} | |
7216 special section, to indicate whether or not an object file relies on | |
7217 the stack being executable. If your system uses this convention, you | |
7218 should define @code{TARGET_ASM_FILE_END} to this function. If you | |
7219 need to do other things in that hook, have your hook function call | |
7220 this function. | |
7221 @end deftypefun | |
7222 | |
7223 @hook TARGET_ASM_LTO_START | |
7224 Output to @code{asm_out_file} any text which the assembler expects | |
7225 to find at the start of an LTO section. The default is to output | |
7226 nothing. | |
7227 @end deftypefn | |
7228 | |
7229 @hook TARGET_ASM_LTO_END | |
7230 Output to @code{asm_out_file} any text which the assembler expects | |
7231 to find at the end of an LTO section. The default is to output | |
7232 nothing. | |
7233 @end deftypefn | |
7234 | |
7235 @hook TARGET_ASM_CODE_END | |
7236 Output to @code{asm_out_file} any text which is needed before emitting | |
7237 unwind info and debug info at the end of a file. Some targets emit | |
7238 here PIC setup thunks that cannot be emitted at the end of file, | |
7239 because they couldn't have unwind info then. The default is to output | |
7240 nothing. | |
7241 @end deftypefn | |
7242 | |
7243 @defmac ASM_COMMENT_START | |
7244 A C string constant describing how to begin a comment in the target | |
7245 assembler language. The compiler assumes that the comment will end at | |
7246 the end of the line. | |
7247 @end defmac | |
7248 | |
7249 @defmac ASM_APP_ON | |
7250 A C string constant for text to be output before each @code{asm} | |
7251 statement or group of consecutive ones. Normally this is | |
7252 @code{"#APP"}, which is a comment that has no effect on most | |
7253 assemblers but tells the GNU assembler that it must check the lines | |
7254 that follow for all valid assembler constructs. | |
7255 @end defmac | |
7256 | |
7257 @defmac ASM_APP_OFF | |
7258 A C string constant for text to be output after each @code{asm} | |
7259 statement or group of consecutive ones. Normally this is | |
7260 @code{"#NO_APP"}, which tells the GNU assembler to resume making the | |
7261 time-saving assumptions that are valid for ordinary compiler output. | |
7262 @end defmac | |
7263 | |
7264 @defmac ASM_OUTPUT_SOURCE_FILENAME (@var{stream}, @var{name}) | |
7265 A C statement to output COFF information or DWARF debugging information | |
7266 which indicates that filename @var{name} is the current source file to | |
7267 the stdio stream @var{stream}. | |
7268 | |
7269 This macro need not be defined if the standard form of output | |
7270 for the file format in use is appropriate. | |
7271 @end defmac | |
7272 | |
7273 @hook TARGET_ASM_OUTPUT_SOURCE_FILENAME | |
7274 | |
7275 @defmac OUTPUT_QUOTED_STRING (@var{stream}, @var{string}) | |
7276 A C statement to output the string @var{string} to the stdio stream | |
7277 @var{stream}. If you do not call the function @code{output_quoted_string} | |
7278 in your config files, GCC will only call it to output filenames to | |
7279 the assembler source. So you can use it to canonicalize the format | |
7280 of the filename using this macro. | |
7281 @end defmac | |
7282 | |
7283 @defmac ASM_OUTPUT_IDENT (@var{stream}, @var{string}) | |
7284 A C statement to output something to the assembler file to handle a | |
7285 @samp{#ident} directive containing the text @var{string}. If this | |
7286 macro is not defined, nothing is output for a @samp{#ident} directive. | |
7287 @end defmac | |
7288 | |
7289 @hook TARGET_ASM_NAMED_SECTION | |
7290 Output assembly directives to switch to section @var{name}. The section | |
7291 should have attributes as specified by @var{flags}, which is a bit mask | |
7292 of the @code{SECTION_*} flags defined in @file{output.h}. If @var{decl} | |
7293 is non-NULL, it is the @code{VAR_DECL} or @code{FUNCTION_DECL} with which | |
7294 this section is associated. | |
7295 @end deftypefn | |
7296 | |
7297 @hook TARGET_ASM_FUNCTION_SECTION | |
7298 Return preferred text (sub)section for function @var{decl}. | |
7299 Main purpose of this function is to separate cold, normal and hot | |
7300 functions. @var{startup} is true when function is known to be used only | |
7301 at startup (from static constructors or it is @code{main()}). | |
7302 @var{exit} is true when function is known to be used only at exit | |
7303 (from static destructors). | |
7304 Return NULL if function should go to default text section. | |
7305 @end deftypefn | |
7306 | |
7307 @hook TARGET_ASM_FUNCTION_SWITCHED_TEXT_SECTIONS | |
7308 | |
7309 @hook TARGET_HAVE_NAMED_SECTIONS | |
7310 This flag is true if the target supports @code{TARGET_ASM_NAMED_SECTION}. | |
7311 It must not be modified by command-line option processing. | |
7312 @end deftypevr | |
7313 | |
7314 @anchor{TARGET_HAVE_SWITCHABLE_BSS_SECTIONS} | |
7315 @hook TARGET_HAVE_SWITCHABLE_BSS_SECTIONS | |
7316 This flag is true if we can create zeroed data by switching to a BSS | |
7317 section and then using @code{ASM_OUTPUT_SKIP} to allocate the space. | |
7318 This is true on most ELF targets. | |
7319 @end deftypevr | |
7320 | |
7321 @hook TARGET_SECTION_TYPE_FLAGS | |
7322 Choose a set of section attributes for use by @code{TARGET_ASM_NAMED_SECTION} | |
7323 based on a variable or function decl, a section name, and whether or not the | |
7324 declaration's initializer may contain runtime relocations. @var{decl} may be | |
7325 null, in which case read-write data should be assumed. | |
7326 | |
7327 The default version of this function handles choosing code vs data, | |
7328 read-only vs read-write data, and @code{flag_pic}. You should only | |
7329 need to override this if your target has special flags that might be | |
7330 set via @code{__attribute__}. | |
7331 @end deftypefn | |
7332 | |
7333 @hook TARGET_ASM_RECORD_GCC_SWITCHES | |
7334 Provides the target with the ability to record the gcc command line | |
7335 switches that have been passed to the compiler, and options that are | |
7336 enabled. The @var{type} argument specifies what is being recorded. | |
7337 It can take the following values: | |
7338 | |
7339 @table @gcctabopt | |
7340 @item SWITCH_TYPE_PASSED | |
7341 @var{text} is a command line switch that has been set by the user. | |
7342 | |
7343 @item SWITCH_TYPE_ENABLED | |
7344 @var{text} is an option which has been enabled. This might be as a | |
7345 direct result of a command line switch, or because it is enabled by | |
7346 default or because it has been enabled as a side effect of a different | |
7347 command line switch. For example, the @option{-O2} switch enables | |
7348 various different individual optimization passes. | |
7349 | |
7350 @item SWITCH_TYPE_DESCRIPTIVE | |
7351 @var{text} is either NULL or some descriptive text which should be | |
7352 ignored. If @var{text} is NULL then it is being used to warn the | |
7353 target hook that either recording is starting or ending. The first | |
7354 time @var{type} is SWITCH_TYPE_DESCRIPTIVE and @var{text} is NULL, the | |
7355 warning is for start up and the second time the warning is for | |
7356 wind down. This feature is to allow the target hook to make any | |
7357 necessary preparations before it starts to record switches and to | |
7358 perform any necessary tidying up after it has finished recording | |
7359 switches. | |
7360 | |
7361 @item SWITCH_TYPE_LINE_START | |
7362 This option can be ignored by this target hook. | |
7363 | |
7364 @item SWITCH_TYPE_LINE_END | |
7365 This option can be ignored by this target hook. | |
7366 @end table | |
7367 | |
7368 The hook's return value must be zero. Other return values may be | |
7369 supported in the future. | |
7370 | |
7371 By default this hook is set to NULL, but an example implementation is | |
7372 provided for ELF based targets. Called @var{elf_record_gcc_switches}, | |
7373 it records the switches as ASCII text inside a new, string mergeable | |
7374 section in the assembler output file. The name of the new section is | |
7375 provided by the @code{TARGET_ASM_RECORD_GCC_SWITCHES_SECTION} target | |
7376 hook. | |
7377 @end deftypefn | |
7378 | |
7379 @hook TARGET_ASM_RECORD_GCC_SWITCHES_SECTION | |
7380 This is the name of the section that will be created by the example | |
7381 ELF implementation of the @code{TARGET_ASM_RECORD_GCC_SWITCHES} target | |
7382 hook. | |
7383 @end deftypevr | |
7384 | |
7385 @need 2000 | |
7386 @node Data Output | |
7387 @subsection Output of Data | |
7388 | |
7389 | |
7390 @hook TARGET_ASM_BYTE_OP | |
7391 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_HI_OP | |
7392 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_SI_OP | |
7393 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_DI_OP | |
7394 @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_TI_OP | |
7395 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_HI_OP | |
7396 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_SI_OP | |
7397 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_DI_OP | |
7398 @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_TI_OP | |
7399 These hooks specify assembly directives for creating certain kinds | |
7400 of integer object. The @code{TARGET_ASM_BYTE_OP} directive creates a | |
7401 byte-sized object, the @code{TARGET_ASM_ALIGNED_HI_OP} one creates an | |
7402 aligned two-byte object, and so on. Any of the hooks may be | |
7403 @code{NULL}, indicating that no suitable directive is available. | |
7404 | |
7405 The compiler will print these strings at the start of a new line, | |
7406 followed immediately by the object's initial value. In most cases, | |
7407 the string should contain a tab, a pseudo-op, and then another tab. | |
7408 @end deftypevr | |
7409 | |
7410 @hook TARGET_ASM_INTEGER | |
7411 The @code{assemble_integer} function uses this hook to output an | |
7412 integer object. @var{x} is the object's value, @var{size} is its size | |
7413 in bytes and @var{aligned_p} indicates whether it is aligned. The | |
7414 function should return @code{true} if it was able to output the | |
7415 object. If it returns false, @code{assemble_integer} will try to | |
7416 split the object into smaller parts. | |
7417 | |
7418 The default implementation of this hook will use the | |
7419 @code{TARGET_ASM_BYTE_OP} family of strings, returning @code{false} | |
7420 when the relevant string is @code{NULL}. | |
7421 @end deftypefn | |
7422 | |
7423 @hook TARGET_ASM_OUTPUT_ADDR_CONST_EXTRA | |
7424 A target hook to recognize @var{rtx} patterns that @code{output_addr_const} | |
7425 can't deal with, and output assembly code to @var{file} corresponding to | |
7426 the pattern @var{x}. This may be used to allow machine-dependent | |
7427 @code{UNSPEC}s to appear within constants. | |
7428 | |
7429 If target hook fails to recognize a pattern, it must return @code{false}, | |
7430 so that a standard error message is printed. If it prints an error message | |
7431 itself, by calling, for example, @code{output_operand_lossage}, it may just | |
7432 return @code{true}. | |
7433 @end deftypefn | |
7434 | |
7435 @defmac OUTPUT_ADDR_CONST_EXTRA (@var{stream}, @var{x}, @var{fail}) | |
7436 A C statement to recognize @var{rtx} patterns that | |
7437 @code{output_addr_const} can't deal with, and output assembly code to | |
7438 @var{stream} corresponding to the pattern @var{x}. This may be used to | |
7439 allow machine-dependent @code{UNSPEC}s to appear within constants. | |
7440 | |
7441 If @code{OUTPUT_ADDR_CONST_EXTRA} fails to recognize a pattern, it must | |
7442 @code{goto fail}, so that a standard error message is printed. If it | |
7443 prints an error message itself, by calling, for example, | |
7444 @code{output_operand_lossage}, it may just complete normally. | |
7445 @end defmac | |
7446 | |
7447 @defmac ASM_OUTPUT_ASCII (@var{stream}, @var{ptr}, @var{len}) | |
7448 A C statement to output to the stdio stream @var{stream} an assembler | |
7449 instruction to assemble a string constant containing the @var{len} | |
7450 bytes at @var{ptr}. @var{ptr} will be a C expression of type | |
7451 @code{char *} and @var{len} a C expression of type @code{int}. | |
7452 | |
7453 If the assembler has a @code{.ascii} pseudo-op as found in the | |
7454 Berkeley Unix assembler, do not define the macro | |
7455 @code{ASM_OUTPUT_ASCII}. | |
7456 @end defmac | |
7457 | |
7458 @defmac ASM_OUTPUT_FDESC (@var{stream}, @var{decl}, @var{n}) | |
7459 A C statement to output word @var{n} of a function descriptor for | |
7460 @var{decl}. This must be defined if @code{TARGET_VTABLE_USES_DESCRIPTORS} | |
7461 is defined, and is otherwise unused. | |
7462 @end defmac | |
7463 | |
7464 @defmac CONSTANT_POOL_BEFORE_FUNCTION | |
7465 You may define this macro as a C expression. You should define the | |
7466 expression to have a nonzero value if GCC should output the constant | |
7467 pool for a function before the code for the function, or a zero value if | |
7468 GCC should output the constant pool after the function. If you do | |
7469 not define this macro, the usual case, GCC will output the constant | |
7470 pool before the function. | |
7471 @end defmac | |
7472 | |
7473 @defmac ASM_OUTPUT_POOL_PROLOGUE (@var{file}, @var{funname}, @var{fundecl}, @var{size}) | |
7474 A C statement to output assembler commands to define the start of the | |
7475 constant pool for a function. @var{funname} is a string giving | |
7476 the name of the function. Should the return type of the function | |
7477 be required, it can be obtained via @var{fundecl}. @var{size} | |
7478 is the size, in bytes, of the constant pool that will be written | |
7479 immediately after this call. | |
7480 | |
7481 If no constant-pool prefix is required, the usual case, this macro need | |
7482 not be defined. | |
7483 @end defmac | |
7484 | |
7485 @defmac ASM_OUTPUT_SPECIAL_POOL_ENTRY (@var{file}, @var{x}, @var{mode}, @var{align}, @var{labelno}, @var{jumpto}) | |
7486 A C statement (with or without semicolon) to output a constant in the | |
7487 constant pool, if it needs special treatment. (This macro need not do | |
7488 anything for RTL expressions that can be output normally.) | |
7489 | |
7490 The argument @var{file} is the standard I/O stream to output the | |
7491 assembler code on. @var{x} is the RTL expression for the constant to | |
7492 output, and @var{mode} is the machine mode (in case @var{x} is a | |
7493 @samp{const_int}). @var{align} is the required alignment for the value | |
7494 @var{x}; you should output an assembler directive to force this much | |
7495 alignment. | |
7496 | |
7497 The argument @var{labelno} is a number to use in an internal label for | |
7498 the address of this pool entry. The definition of this macro is | |
7499 responsible for outputting the label definition at the proper place. | |
7500 Here is how to do this: | |
7501 | |
7502 @smallexample | |
7503 @code{(*targetm.asm_out.internal_label)} (@var{file}, "LC", @var{labelno}); | |
7504 @end smallexample | |
7505 | |
7506 When you output a pool entry specially, you should end with a | |
7507 @code{goto} to the label @var{jumpto}. This will prevent the same pool | |
7508 entry from being output a second time in the usual manner. | |
7509 | |
7510 You need not define this macro if it would do nothing. | |
7511 @end defmac | |
7512 | |
7513 @defmac ASM_OUTPUT_POOL_EPILOGUE (@var{file} @var{funname} @var{fundecl} @var{size}) | |
7514 A C statement to output assembler commands to at the end of the constant | |
7515 pool for a function. @var{funname} is a string giving the name of the | |
7516 function. Should the return type of the function be required, you can | |
7517 obtain it via @var{fundecl}. @var{size} is the size, in bytes, of the | |
7518 constant pool that GCC wrote immediately before this call. | |
7519 | |
7520 If no constant-pool epilogue is required, the usual case, you need not | |
7521 define this macro. | |
7522 @end defmac | |
7523 | |
7524 @defmac IS_ASM_LOGICAL_LINE_SEPARATOR (@var{C}, @var{STR}) | |
7525 Define this macro as a C expression which is nonzero if @var{C} is | |
7526 used as a logical line separator by the assembler. @var{STR} points | |
7527 to the position in the string where @var{C} was found; this can be used if | |
7528 a line separator uses multiple characters. | |
7529 | |
7530 If you do not define this macro, the default is that only | |
7531 the character @samp{;} is treated as a logical line separator. | |
7532 @end defmac | |
7533 | |
7534 @hook TARGET_ASM_OPEN_PAREN | |
7535 These target hooks are C string constants, describing the syntax in the | |
7536 assembler for grouping arithmetic expressions. If not overridden, they | |
7537 default to normal parentheses, which is correct for most assemblers. | |
7538 @end deftypevr | |
7539 | |
7540 These macros are provided by @file{real.h} for writing the definitions | |
7541 of @code{ASM_OUTPUT_DOUBLE} and the like: | |
7542 | |
7543 @defmac REAL_VALUE_TO_TARGET_SINGLE (@var{x}, @var{l}) | |
7544 @defmacx REAL_VALUE_TO_TARGET_DOUBLE (@var{x}, @var{l}) | |
7545 @defmacx REAL_VALUE_TO_TARGET_LONG_DOUBLE (@var{x}, @var{l}) | |
7546 @defmacx REAL_VALUE_TO_TARGET_DECIMAL32 (@var{x}, @var{l}) | |
7547 @defmacx REAL_VALUE_TO_TARGET_DECIMAL64 (@var{x}, @var{l}) | |
7548 @defmacx REAL_VALUE_TO_TARGET_DECIMAL128 (@var{x}, @var{l}) | |
7549 These translate @var{x}, of type @code{REAL_VALUE_TYPE}, to the | |
7550 target's floating point representation, and store its bit pattern in | |
7551 the variable @var{l}. For @code{REAL_VALUE_TO_TARGET_SINGLE} and | |
7552 @code{REAL_VALUE_TO_TARGET_DECIMAL32}, this variable should be a | |
7553 simple @code{long int}. For the others, it should be an array of | |
7554 @code{long int}. The number of elements in this array is determined | |
7555 by the size of the desired target floating point data type: 32 bits of | |
7556 it go in each @code{long int} array element. Each array element holds | |
7557 32 bits of the result, even if @code{long int} is wider than 32 bits | |
7558 on the host machine. | |
7559 | |
7560 The array element values are designed so that you can print them out | |
7561 using @code{fprintf} in the order they should appear in the target | |
7562 machine's memory. | |
7563 @end defmac | |
7564 | |
7565 @node Uninitialized Data | |
7566 @subsection Output of Uninitialized Variables | |
7567 | |
7568 Each of the macros in this section is used to do the whole job of | |
7569 outputting a single uninitialized variable. | |
7570 | |
7571 @defmac ASM_OUTPUT_COMMON (@var{stream}, @var{name}, @var{size}, @var{rounded}) | |
7572 A C statement (sans semicolon) to output to the stdio stream | |
7573 @var{stream} the assembler definition of a common-label named | |
7574 @var{name} whose size is @var{size} bytes. The variable @var{rounded} | |
7575 is the size rounded up to whatever alignment the caller wants. It is | |
7576 possible that @var{size} may be zero, for instance if a struct with no | |
7577 other member than a zero-length array is defined. In this case, the | |
7578 backend must output a symbol definition that allocates at least one | |
7579 byte, both so that the address of the resulting object does not compare | |
7580 equal to any other, and because some object formats cannot even express | |
7581 the concept of a zero-sized common symbol, as that is how they represent | |
7582 an ordinary undefined external. | |
7583 | |
7584 Use the expression @code{assemble_name (@var{stream}, @var{name})} to | |
7585 output the name itself; before and after that, output the additional | |
7586 assembler syntax for defining the name, and a newline. | |
7587 | |
7588 This macro controls how the assembler definitions of uninitialized | |
7589 common global variables are output. | |
7590 @end defmac | |
7591 | |
7592 @defmac ASM_OUTPUT_ALIGNED_COMMON (@var{stream}, @var{name}, @var{size}, @var{alignment}) | |
7593 Like @code{ASM_OUTPUT_COMMON} except takes the required alignment as a | |
7594 separate, explicit argument. If you define this macro, it is used in | |
7595 place of @code{ASM_OUTPUT_COMMON}, and gives you more flexibility in | |
7596 handling the required alignment of the variable. The alignment is specified | |
7597 as the number of bits. | |
7598 @end defmac | |
7599 | |
7600 @defmac ASM_OUTPUT_ALIGNED_DECL_COMMON (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment}) | |
7601 Like @code{ASM_OUTPUT_ALIGNED_COMMON} except that @var{decl} of the | |
7602 variable to be output, if there is one, or @code{NULL_TREE} if there | |
7603 is no corresponding variable. If you define this macro, GCC will use it | |
7604 in place of both @code{ASM_OUTPUT_COMMON} and | |
7605 @code{ASM_OUTPUT_ALIGNED_COMMON}. Define this macro when you need to see | |
7606 the variable's decl in order to chose what to output. | |
7607 @end defmac | |
7608 | |
7609 @defmac ASM_OUTPUT_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{rounded}) | |
7610 A C statement (sans semicolon) to output to the stdio stream | |
7611 @var{stream} the assembler definition of uninitialized global @var{decl} named | |
7612 @var{name} whose size is @var{size} bytes. The variable @var{rounded} | |
7613 is the size rounded up to whatever alignment the caller wants. | |
7614 | |
7615 Try to use function @code{asm_output_bss} defined in @file{varasm.c} when | |
7616 defining this macro. If unable, use the expression | |
7617 @code{assemble_name (@var{stream}, @var{name})} to output the name itself; | |
7618 before and after that, output the additional assembler syntax for defining | |
7619 the name, and a newline. | |
7620 | |
7621 There are two ways of handling global BSS@. One is to define either | |
7622 this macro or its aligned counterpart, @code{ASM_OUTPUT_ALIGNED_BSS}. | |
7623 The other is to have @code{TARGET_ASM_SELECT_SECTION} return a | |
7624 switchable BSS section (@pxref{TARGET_HAVE_SWITCHABLE_BSS_SECTIONS}). | |
7625 You do not need to do both. | |
7626 | |
7627 Some languages do not have @code{common} data, and require a | |
7628 non-common form of global BSS in order to handle uninitialized globals | |
7629 efficiently. C++ is one example of this. However, if the target does | |
7630 not support global BSS, the front end may choose to make globals | |
7631 common in order to save space in the object file. | |
7632 @end defmac | |
7633 | |
7634 @defmac ASM_OUTPUT_ALIGNED_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment}) | |
7635 Like @code{ASM_OUTPUT_BSS} except takes the required alignment as a | |
7636 separate, explicit argument. If you define this macro, it is used in | |
7637 place of @code{ASM_OUTPUT_BSS}, and gives you more flexibility in | |
7638 handling the required alignment of the variable. The alignment is specified | |
7639 as the number of bits. | |
7640 | |
7641 Try to use function @code{asm_output_aligned_bss} defined in file | |
7642 @file{varasm.c} when defining this macro. | |
7643 @end defmac | |
7644 | |
7645 @defmac ASM_OUTPUT_LOCAL (@var{stream}, @var{name}, @var{size}, @var{rounded}) | |
7646 A C statement (sans semicolon) to output to the stdio stream | |
7647 @var{stream} the assembler definition of a local-common-label named | |
7648 @var{name} whose size is @var{size} bytes. The variable @var{rounded} | |
7649 is the size rounded up to whatever alignment the caller wants. | |
7650 | |
7651 Use the expression @code{assemble_name (@var{stream}, @var{name})} to | |
7652 output the name itself; before and after that, output the additional | |
7653 assembler syntax for defining the name, and a newline. | |
7654 | |
7655 This macro controls how the assembler definitions of uninitialized | |
7656 static variables are output. | |
7657 @end defmac | |
7658 | |
7659 @defmac ASM_OUTPUT_ALIGNED_LOCAL (@var{stream}, @var{name}, @var{size}, @var{alignment}) | |
7660 Like @code{ASM_OUTPUT_LOCAL} except takes the required alignment as a | |
7661 separate, explicit argument. If you define this macro, it is used in | |
7662 place of @code{ASM_OUTPUT_LOCAL}, and gives you more flexibility in | |
7663 handling the required alignment of the variable. The alignment is specified | |
7664 as the number of bits. | |
7665 @end defmac | |
7666 | |
7667 @defmac ASM_OUTPUT_ALIGNED_DECL_LOCAL (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment}) | |
7668 Like @code{ASM_OUTPUT_ALIGNED_DECL} except that @var{decl} of the | |
7669 variable to be output, if there is one, or @code{NULL_TREE} if there | |
7670 is no corresponding variable. If you define this macro, GCC will use it | |
7671 in place of both @code{ASM_OUTPUT_DECL} and | |
7672 @code{ASM_OUTPUT_ALIGNED_DECL}. Define this macro when you need to see | |
7673 the variable's decl in order to chose what to output. | |
7674 @end defmac | |
7675 | |
7676 @node Label Output | |
7677 @subsection Output and Generation of Labels | |
7678 | |
7679 @c prevent bad page break with this line | |
7680 This is about outputting labels. | |
7681 | |
7682 @findex assemble_name | |
7683 @defmac ASM_OUTPUT_LABEL (@var{stream}, @var{name}) | |
7684 A C statement (sans semicolon) to output to the stdio stream | |
7685 @var{stream} the assembler definition of a label named @var{name}. | |
7686 Use the expression @code{assemble_name (@var{stream}, @var{name})} to | |
7687 output the name itself; before and after that, output the additional | |
7688 assembler syntax for defining the name, and a newline. A default | |
7689 definition of this macro is provided which is correct for most systems. | |
7690 @end defmac | |
7691 | |
7692 @defmac ASM_OUTPUT_FUNCTION_LABEL (@var{stream}, @var{name}, @var{decl}) | |
7693 A C statement (sans semicolon) to output to the stdio stream | |
7694 @var{stream} the assembler definition of a label named @var{name} of | |
7695 a function. | |
7696 Use the expression @code{assemble_name (@var{stream}, @var{name})} to | |
7697 output the name itself; before and after that, output the additional | |
7698 assembler syntax for defining the name, and a newline. A default | |
7699 definition of this macro is provided which is correct for most systems. | |
7700 | |
7701 If this macro is not defined, then the function name is defined in the | |
7702 usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}). | |
7703 @end defmac | |
7704 | |
7705 @findex assemble_name_raw | |
7706 @defmac ASM_OUTPUT_INTERNAL_LABEL (@var{stream}, @var{name}) | |
7707 Identical to @code{ASM_OUTPUT_LABEL}, except that @var{name} is known | |
7708 to refer to a compiler-generated label. The default definition uses | |
7709 @code{assemble_name_raw}, which is like @code{assemble_name} except | |
7710 that it is more efficient. | |
7711 @end defmac | |
7712 | |
7713 @defmac SIZE_ASM_OP | |
7714 A C string containing the appropriate assembler directive to specify the | |
7715 size of a symbol, without any arguments. On systems that use ELF, the | |
7716 default (in @file{config/elfos.h}) is @samp{"\t.size\t"}; on other | |
7717 systems, the default is not to define this macro. | |
7718 | |
7719 Define this macro only if it is correct to use the default definitions | |
7720 of @code{ASM_OUTPUT_SIZE_DIRECTIVE} and @code{ASM_OUTPUT_MEASURED_SIZE} | |
7721 for your system. If you need your own custom definitions of those | |
7722 macros, or if you do not need explicit symbol sizes at all, do not | |
7723 define this macro. | |
7724 @end defmac | |
7725 | |
7726 @defmac ASM_OUTPUT_SIZE_DIRECTIVE (@var{stream}, @var{name}, @var{size}) | |
7727 A C statement (sans semicolon) to output to the stdio stream | |
7728 @var{stream} a directive telling the assembler that the size of the | |
7729 symbol @var{name} is @var{size}. @var{size} is a @code{HOST_WIDE_INT}. | |
7730 If you define @code{SIZE_ASM_OP}, a default definition of this macro is | |
7731 provided. | |
7732 @end defmac | |
7733 | |
7734 @defmac ASM_OUTPUT_MEASURED_SIZE (@var{stream}, @var{name}) | |
7735 A C statement (sans semicolon) to output to the stdio stream | |
7736 @var{stream} a directive telling the assembler to calculate the size of | |
7737 the symbol @var{name} by subtracting its address from the current | |
7738 address. | |
7739 | |
7740 If you define @code{SIZE_ASM_OP}, a default definition of this macro is | |
7741 provided. The default assumes that the assembler recognizes a special | |
7742 @samp{.} symbol as referring to the current address, and can calculate | |
7743 the difference between this and another symbol. If your assembler does | |
7744 not recognize @samp{.} or cannot do calculations with it, you will need | |
7745 to redefine @code{ASM_OUTPUT_MEASURED_SIZE} to use some other technique. | |
7746 @end defmac | |
7747 | |
7748 @defmac TYPE_ASM_OP | |
7749 A C string containing the appropriate assembler directive to specify the | |
7750 type of a symbol, without any arguments. On systems that use ELF, the | |
7751 default (in @file{config/elfos.h}) is @samp{"\t.type\t"}; on other | |
7752 systems, the default is not to define this macro. | |
7753 | |
7754 Define this macro only if it is correct to use the default definition of | |
7755 @code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own | |
7756 custom definition of this macro, or if you do not need explicit symbol | |
7757 types at all, do not define this macro. | |
7758 @end defmac | |
7759 | |
7760 @defmac TYPE_OPERAND_FMT | |
7761 A C string which specifies (using @code{printf} syntax) the format of | |
7762 the second operand to @code{TYPE_ASM_OP}. On systems that use ELF, the | |
7763 default (in @file{config/elfos.h}) is @samp{"@@%s"}; on other systems, | |
7764 the default is not to define this macro. | |
7765 | |
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. | |
7770 @end defmac | |
7771 | |
7772 @defmac ASM_OUTPUT_TYPE_DIRECTIVE (@var{stream}, @var{type}) | |
7773 A C statement (sans semicolon) to output to the stdio stream | |
7774 @var{stream} a directive telling the assembler that the type of the | |
7775 symbol @var{name} is @var{type}. @var{type} is a C string; currently, | |
7776 that string is always either @samp{"function"} or @samp{"object"}, but | |
7777 you should not count on this. | |
7778 | |
7779 If you define @code{TYPE_ASM_OP} and @code{TYPE_OPERAND_FMT}, a default | |
7780 definition of this macro is provided. | |
7781 @end defmac | |
7782 | |
7783 @defmac ASM_DECLARE_FUNCTION_NAME (@var{stream}, @var{name}, @var{decl}) | |
7784 A C statement (sans semicolon) to output to the stdio stream | |
7785 @var{stream} any text necessary for declaring the name @var{name} of a | |
7786 function which is being defined. This macro is responsible for | |
7787 outputting the label definition (perhaps using | |
7788 @code{ASM_OUTPUT_FUNCTION_LABEL}). The argument @var{decl} is the | |
7789 @code{FUNCTION_DECL} tree node representing the function. | |
7790 | |
7791 If this macro is not defined, then the function name is defined in the | |
7792 usual manner as a label (by means of @code{ASM_OUTPUT_FUNCTION_LABEL}). | |
7793 | |
7794 You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in the definition | |
7795 of this macro. | |
7796 @end defmac | |
7797 | |
7798 @defmac ASM_DECLARE_FUNCTION_SIZE (@var{stream}, @var{name}, @var{decl}) | |
7799 A C statement (sans semicolon) to output to the stdio stream | |
7800 @var{stream} any text necessary for declaring the size of a function | |
7801 which is being defined. The argument @var{name} is the name of the | |
7802 function. The argument @var{decl} is the @code{FUNCTION_DECL} tree node | |
7803 representing the function. | |
7804 | |
7805 If this macro is not defined, then the function size is not defined. | |
7806 | |
7807 You may wish to use @code{ASM_OUTPUT_MEASURED_SIZE} in the definition | |
7808 of this macro. | |
7809 @end defmac | |
7810 | |
7811 @defmac ASM_DECLARE_OBJECT_NAME (@var{stream}, @var{name}, @var{decl}) | |
7812 A C statement (sans semicolon) to output to the stdio stream | |
7813 @var{stream} any text necessary for declaring the name @var{name} of an | |
7814 initialized variable which is being defined. This macro must output the | |
7815 label definition (perhaps using @code{ASM_OUTPUT_LABEL}). The argument | |
7816 @var{decl} is the @code{VAR_DECL} tree node representing the variable. | |
7817 | |
7818 If this macro is not defined, then the variable name is defined in the | |
7819 usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}). | |
7820 | |
7821 You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} and/or | |
7822 @code{ASM_OUTPUT_SIZE_DIRECTIVE} in the definition of this macro. | |
7823 @end defmac | |
7824 | |
7825 @hook TARGET_ASM_DECLARE_CONSTANT_NAME | |
7826 A target hook to output to the stdio stream @var{file} any text necessary | |
7827 for declaring the name @var{name} of a constant which is being defined. This | |
7828 target hook is responsible for outputting the label definition (perhaps using | |
7829 @code{assemble_label}). The argument @var{exp} is the value of the constant, | |
7830 and @var{size} is the size of the constant in bytes. The @var{name} | |
7831 will be an internal label. | |
7832 | |
7833 The default version of this target hook, define the @var{name} in the | |
7834 usual manner as a label (by means of @code{assemble_label}). | |
7835 | |
7836 You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in this target hook. | |
7837 @end deftypefn | |
7838 | |
7839 @defmac ASM_DECLARE_REGISTER_GLOBAL (@var{stream}, @var{decl}, @var{regno}, @var{name}) | |
7840 A C statement (sans semicolon) to output to the stdio stream | |
7841 @var{stream} any text necessary for claiming a register @var{regno} | |
7842 for a global variable @var{decl} with name @var{name}. | |
7843 | |
7844 If you don't define this macro, that is equivalent to defining it to do | |
7845 nothing. | |
7846 @end defmac | |
7847 | |
7848 @defmac ASM_FINISH_DECLARE_OBJECT (@var{stream}, @var{decl}, @var{toplevel}, @var{atend}) | |
7849 A C statement (sans semicolon) to finish up declaring a variable name | |
7850 once the compiler has processed its initializer fully and thus has had a | |
7851 chance to determine the size of an array when controlled by an | |
7852 initializer. This is used on systems where it's necessary to declare | |
7853 something about the size of the object. | |
7854 | |
7855 If you don't define this macro, that is equivalent to defining it to do | |
7856 nothing. | |
7857 | |
7858 You may wish to use @code{ASM_OUTPUT_SIZE_DIRECTIVE} and/or | |
7859 @code{ASM_OUTPUT_MEASURED_SIZE} in the definition of this macro. | |
7860 @end defmac | |
7861 | |
7862 @hook TARGET_ASM_GLOBALIZE_LABEL | |
7863 This target hook is a function to output to the stdio stream | |
7864 @var{stream} some commands that will make the label @var{name} global; | |
7865 that is, available for reference from other files. | |
7866 | |
7867 The default implementation relies on a proper definition of | |
7868 @code{GLOBAL_ASM_OP}. | |
7869 @end deftypefn | |
7870 | |
7871 @hook TARGET_ASM_GLOBALIZE_DECL_NAME | |
7872 This target hook is a function to output to the stdio stream | |
7873 @var{stream} some commands that will make the name associated with @var{decl} | |
7874 global; that is, available for reference from other files. | |
7875 | |
7876 The default implementation uses the TARGET_ASM_GLOBALIZE_LABEL target hook. | |
7877 @end deftypefn | |
7878 | |
7879 @defmac ASM_WEAKEN_LABEL (@var{stream}, @var{name}) | |
7880 A C statement (sans semicolon) to output to the stdio stream | |
7881 @var{stream} some commands that will make the label @var{name} weak; | |
7882 that is, available for reference from other files but only used if | |
7883 no other definition is available. Use the expression | |
7884 @code{assemble_name (@var{stream}, @var{name})} to output the name | |
7885 itself; before and after that, output the additional assembler syntax | |
7886 for making that name weak, and a newline. | |
7887 | |
7888 If you don't define this macro or @code{ASM_WEAKEN_DECL}, GCC will not | |
7889 support weak symbols and you should not define the @code{SUPPORTS_WEAK} | |
7890 macro. | |
7891 @end defmac | |
7892 | |
7893 @defmac ASM_WEAKEN_DECL (@var{stream}, @var{decl}, @var{name}, @var{value}) | |
7894 Combines (and replaces) the function of @code{ASM_WEAKEN_LABEL} and | |
7895 @code{ASM_OUTPUT_WEAK_ALIAS}, allowing access to the associated function | |
7896 or variable decl. If @var{value} is not @code{NULL}, this C statement | |
7897 should output to the stdio stream @var{stream} assembler code which | |
7898 defines (equates) the weak symbol @var{name} to have the value | |
7899 @var{value}. If @var{value} is @code{NULL}, it should output commands | |
7900 to make @var{name} weak. | |
7901 @end defmac | |
7902 | |
7903 @defmac ASM_OUTPUT_WEAKREF (@var{stream}, @var{decl}, @var{name}, @var{value}) | |
7904 Outputs a directive that enables @var{name} to be used to refer to | |
7905 symbol @var{value} with weak-symbol semantics. @code{decl} is the | |
7906 declaration of @code{name}. | |
7907 @end defmac | |
7908 | |
7909 @defmac SUPPORTS_WEAK | |
7910 A preprocessor constant expression which evaluates to true if the target | |
7911 supports weak symbols. | |
7912 | |
7913 If you don't define this macro, @file{defaults.h} provides a default | |
7914 definition. If either @code{ASM_WEAKEN_LABEL} or @code{ASM_WEAKEN_DECL} | |
7915 is defined, the default definition is @samp{1}; otherwise, it is @samp{0}. | |
7916 @end defmac | |
7917 | |
7918 @defmac TARGET_SUPPORTS_WEAK | |
7919 A C expression which evaluates to true if the target supports weak symbols. | |
7920 | |
7921 If you don't define this macro, @file{defaults.h} provides a default | |
7922 definition. The default definition is @samp{(SUPPORTS_WEAK)}. Define | |
7923 this macro if you want to control weak symbol support with a compiler | |
7924 flag such as @option{-melf}. | |
7925 @end defmac | |
7926 | |
7927 @defmac MAKE_DECL_ONE_ONLY (@var{decl}) | |
7928 A C statement (sans semicolon) to mark @var{decl} to be emitted as a | |
7929 public symbol such that extra copies in multiple translation units will | |
7930 be discarded by the linker. Define this macro if your object file | |
7931 format provides support for this concept, such as the @samp{COMDAT} | |
7932 section flags in the Microsoft Windows PE/COFF format, and this support | |
7933 requires changes to @var{decl}, such as putting it in a separate section. | |
7934 @end defmac | |
7935 | |
7936 @defmac SUPPORTS_ONE_ONLY | |
7937 A C expression which evaluates to true if the target supports one-only | |
7938 semantics. | |
7939 | |
7940 If you don't define this macro, @file{varasm.c} provides a default | |
7941 definition. If @code{MAKE_DECL_ONE_ONLY} is defined, the default | |
7942 definition is @samp{1}; otherwise, it is @samp{0}. Define this macro if | |
7943 you want to control one-only symbol support with a compiler flag, or if | |
7944 setting the @code{DECL_ONE_ONLY} flag is enough to mark a declaration to | |
7945 be emitted as one-only. | |
7946 @end defmac | |
7947 | |
7948 @hook TARGET_ASM_ASSEMBLE_VISIBILITY | |
7949 This target hook is a function to output to @var{asm_out_file} some | |
7950 commands that will make the symbol(s) associated with @var{decl} have | |
7951 hidden, protected or internal visibility as specified by @var{visibility}. | |
7952 @end deftypefn | |
7953 | |
7954 @defmac TARGET_WEAK_NOT_IN_ARCHIVE_TOC | |
7955 A C expression that evaluates to true if the target's linker expects | |
7956 that weak symbols do not appear in a static archive's table of contents. | |
7957 The default is @code{0}. | |
7958 | |
7959 Leaving weak symbols out of an archive's table of contents means that, | |
7960 if a symbol will only have a definition in one translation unit and | |
7961 will have undefined references from other translation units, that | |
7962 symbol should not be weak. Defining this macro to be nonzero will | |
7963 thus have the effect that certain symbols that would normally be weak | |
7964 (explicit template instantiations, and vtables for polymorphic classes | |
7965 with noninline key methods) will instead be nonweak. | |
7966 | |
7967 The C++ ABI requires this macro to be zero. Define this macro for | |
7968 targets where full C++ ABI compliance is impossible and where linker | |
7969 restrictions require weak symbols to be left out of a static archive's | |
7970 table of contents. | |
7971 @end defmac | |
7972 | |
7973 @defmac ASM_OUTPUT_EXTERNAL (@var{stream}, @var{decl}, @var{name}) | |
7974 A C statement (sans semicolon) to output to the stdio stream | |
7975 @var{stream} any text necessary for declaring the name of an external | |
7976 symbol named @var{name} which is referenced in this compilation but | |
7977 not defined. The value of @var{decl} is the tree node for the | |
7978 declaration. | |
7979 | |
7980 This macro need not be defined if it does not need to output anything. | |
7981 The GNU assembler and most Unix assemblers don't require anything. | |
7982 @end defmac | |
7983 | |
7984 @hook TARGET_ASM_EXTERNAL_LIBCALL | |
7985 This target hook is a function to output to @var{asm_out_file} an assembler | |
7986 pseudo-op to declare a library function name external. The name of the | |
7987 library function is given by @var{symref}, which is a @code{symbol_ref}. | |
7988 @end deftypefn | |
7989 | |
7990 @hook TARGET_ASM_MARK_DECL_PRESERVED | |
7991 This target hook is a function to output to @var{asm_out_file} an assembler | |
7992 directive to annotate @var{symbol} as used. The Darwin target uses the | |
7993 .no_dead_code_strip directive. | |
7994 @end deftypefn | |
7995 | |
7996 @defmac ASM_OUTPUT_LABELREF (@var{stream}, @var{name}) | |
7997 A C statement (sans semicolon) to output to the stdio stream | |
7998 @var{stream} a reference in assembler syntax to a label named | |
7999 @var{name}. This should add @samp{_} to the front of the name, if that | |
8000 is customary on your operating system, as it is in most Berkeley Unix | |
8001 systems. This macro is used in @code{assemble_name}. | |
8002 @end defmac | |
8003 | |
8004 @hook TARGET_MANGLE_ASSEMBLER_NAME | |
8005 | |
8006 @defmac ASM_OUTPUT_SYMBOL_REF (@var{stream}, @var{sym}) | |
8007 A C statement (sans semicolon) to output a reference to | |
8008 @code{SYMBOL_REF} @var{sym}. If not defined, @code{assemble_name} | |
8009 will be used to output the name of the symbol. This macro may be used | |
8010 to modify the way a symbol is referenced depending on information | |
8011 encoded by @code{TARGET_ENCODE_SECTION_INFO}. | |
8012 @end defmac | |
8013 | |
8014 @defmac ASM_OUTPUT_LABEL_REF (@var{stream}, @var{buf}) | |
8015 A C statement (sans semicolon) to output a reference to @var{buf}, the | |
8016 result of @code{ASM_GENERATE_INTERNAL_LABEL}. If not defined, | |
8017 @code{assemble_name} will be used to output the name of the symbol. | |
8018 This macro is not used by @code{output_asm_label}, or the @code{%l} | |
8019 specifier that calls it; the intention is that this macro should be set | |
8020 when it is necessary to output a label differently when its address is | |
8021 being taken. | |
8022 @end defmac | |
8023 | |
8024 @hook TARGET_ASM_INTERNAL_LABEL | |
8025 A function to output to the stdio stream @var{stream} a label whose | |
8026 name is made from the string @var{prefix} and the number @var{labelno}. | |
8027 | |
8028 It is absolutely essential that these labels be distinct from the labels | |
8029 used for user-level functions and variables. Otherwise, certain programs | |
8030 will have name conflicts with internal labels. | |
8031 | |
8032 It is desirable to exclude internal labels from the symbol table of the | |
8033 object file. Most assemblers have a naming convention for labels that | |
8034 should be excluded; on many systems, the letter @samp{L} at the | |
8035 beginning of a label has this effect. You should find out what | |
8036 convention your system uses, and follow it. | |
8037 | |
8038 The default version of this function utilizes @code{ASM_GENERATE_INTERNAL_LABEL}. | |
8039 @end deftypefn | |
8040 | |
8041 @defmac ASM_OUTPUT_DEBUG_LABEL (@var{stream}, @var{prefix}, @var{num}) | |
8042 A C statement to output to the stdio stream @var{stream} a debug info | |
8043 label whose name is made from the string @var{prefix} and the number | |
8044 @var{num}. This is useful for VLIW targets, where debug info labels | |
8045 may need to be treated differently than branch target labels. On some | |
8046 systems, branch target labels must be at the beginning of instruction | |
8047 bundles, but debug info labels can occur in the middle of instruction | |
8048 bundles. | |
8049 | |
8050 If this macro is not defined, then @code{(*targetm.asm_out.internal_label)} will be | |
8051 used. | |
8052 @end defmac | |
8053 | |
8054 @defmac ASM_GENERATE_INTERNAL_LABEL (@var{string}, @var{prefix}, @var{num}) | |
8055 A C statement to store into the string @var{string} a label whose name | |
8056 is made from the string @var{prefix} and the number @var{num}. | |
8057 | |
8058 This string, when output subsequently by @code{assemble_name}, should | |
8059 produce the output that @code{(*targetm.asm_out.internal_label)} would produce | |
8060 with the same @var{prefix} and @var{num}. | |
8061 | |
8062 If the string begins with @samp{*}, then @code{assemble_name} will | |
8063 output the rest of the string unchanged. It is often convenient for | |
8064 @code{ASM_GENERATE_INTERNAL_LABEL} to use @samp{*} in this way. If the | |
8065 string doesn't start with @samp{*}, then @code{ASM_OUTPUT_LABELREF} gets | |
8066 to output the string, and may change it. (Of course, | |
8067 @code{ASM_OUTPUT_LABELREF} is also part of your machine description, so | |
8068 you should know what it does on your machine.) | |
8069 @end defmac | |
8070 | |
8071 @defmac ASM_FORMAT_PRIVATE_NAME (@var{outvar}, @var{name}, @var{number}) | |
8072 A C expression to assign to @var{outvar} (which is a variable of type | |
8073 @code{char *}) a newly allocated string made from the string | |
8074 @var{name} and the number @var{number}, with some suitable punctuation | |
8075 added. Use @code{alloca} to get space for the string. | |
8076 | |
8077 The string will be used as an argument to @code{ASM_OUTPUT_LABELREF} to | |
8078 produce an assembler label for an internal static variable whose name is | |
8079 @var{name}. Therefore, the string must be such as to result in valid | |
8080 assembler code. The argument @var{number} is different each time this | |
8081 macro is executed; it prevents conflicts between similarly-named | |
8082 internal static variables in different scopes. | |
8083 | |
8084 Ideally this string should not be a valid C identifier, to prevent any | |
8085 conflict with the user's own symbols. Most assemblers allow periods | |
8086 or percent signs in assembler symbols; putting at least one of these | |
8087 between the name and the number will suffice. | |
8088 | |
8089 If this macro is not defined, a default definition will be provided | |
8090 which is correct for most systems. | |
8091 @end defmac | |
8092 | |
8093 @defmac ASM_OUTPUT_DEF (@var{stream}, @var{name}, @var{value}) | |
8094 A C statement to output to the stdio stream @var{stream} assembler code | |
8095 which defines (equates) the symbol @var{name} to have the value @var{value}. | |
8096 | |
8097 @findex SET_ASM_OP | |
8098 If @code{SET_ASM_OP} is defined, a default definition is provided which is | |
8099 correct for most systems. | |
8100 @end defmac | |
8101 | |
8102 @defmac ASM_OUTPUT_DEF_FROM_DECLS (@var{stream}, @var{decl_of_name}, @var{decl_of_value}) | |
8103 A C statement to output to the stdio stream @var{stream} assembler code | |
8104 which defines (equates) the symbol whose tree node is @var{decl_of_name} | |
8105 to have the value of the tree node @var{decl_of_value}. This macro will | |
8106 be used in preference to @samp{ASM_OUTPUT_DEF} if it is defined and if | |
8107 the tree nodes are available. | |
8108 | |
8109 @findex SET_ASM_OP | |
8110 If @code{SET_ASM_OP} is defined, a default definition is provided which is | |
8111 correct for most systems. | |
8112 @end defmac | |
8113 | |
8114 @defmac TARGET_DEFERRED_OUTPUT_DEFS (@var{decl_of_name}, @var{decl_of_value}) | |
8115 A C statement that evaluates to true if the assembler code which defines | |
8116 (equates) the symbol whose tree node is @var{decl_of_name} to have the value | |
8117 of the tree node @var{decl_of_value} should be emitted near the end of the | |
8118 current compilation unit. The default is to not defer output of defines. | |
8119 This macro affects defines output by @samp{ASM_OUTPUT_DEF} and | |
8120 @samp{ASM_OUTPUT_DEF_FROM_DECLS}. | |
8121 @end defmac | |
8122 | |
8123 @defmac ASM_OUTPUT_WEAK_ALIAS (@var{stream}, @var{name}, @var{value}) | |
8124 A C statement to output to the stdio stream @var{stream} assembler code | |
8125 which defines (equates) the weak symbol @var{name} to have the value | |
8126 @var{value}. If @var{value} is @code{NULL}, it defines @var{name} as | |
8127 an undefined weak symbol. | |
8128 | |
8129 Define this macro if the target only supports weak aliases; define | |
8130 @code{ASM_OUTPUT_DEF} instead if possible. | |
8131 @end defmac | |
8132 | |
8133 @defmac OBJC_GEN_METHOD_LABEL (@var{buf}, @var{is_inst}, @var{class_name}, @var{cat_name}, @var{sel_name}) | |
8134 Define this macro to override the default assembler names used for | |
8135 Objective-C methods. | |
8136 | |
8137 The default name is a unique method number followed by the name of the | |
8138 class (e.g.@: @samp{_1_Foo}). For methods in categories, the name of | |
8139 the category is also included in the assembler name (e.g.@: | |
8140 @samp{_1_Foo_Bar}). | |
8141 | |
8142 These names are safe on most systems, but make debugging difficult since | |
8143 the method's selector is not present in the name. Therefore, particular | |
8144 systems define other ways of computing names. | |
8145 | |
8146 @var{buf} is an expression of type @code{char *} which gives you a | |
8147 buffer in which to store the name; its length is as long as | |
8148 @var{class_name}, @var{cat_name} and @var{sel_name} put together, plus | |
8149 50 characters extra. | |
8150 | |
8151 The argument @var{is_inst} specifies whether the method is an instance | |
8152 method or a class method; @var{class_name} is the name of the class; | |
8153 @var{cat_name} is the name of the category (or @code{NULL} if the method is not | |
8154 in a category); and @var{sel_name} is the name of the selector. | |
8155 | |
8156 On systems where the assembler can handle quoted names, you can use this | |
8157 macro to provide more human-readable names. | |
8158 @end defmac | |
8159 | |
8160 @defmac ASM_DECLARE_CLASS_REFERENCE (@var{stream}, @var{name}) | |
8161 A C statement (sans semicolon) to output to the stdio stream | |
8162 @var{stream} commands to declare that the label @var{name} is an | |
8163 Objective-C class reference. This is only needed for targets whose | |
8164 linkers have special support for NeXT-style runtimes. | |
8165 @end defmac | |
8166 | |
8167 @defmac ASM_DECLARE_UNRESOLVED_REFERENCE (@var{stream}, @var{name}) | |
8168 A C statement (sans semicolon) to output to the stdio stream | |
8169 @var{stream} commands to declare that the label @var{name} is an | |
8170 unresolved Objective-C class reference. This is only needed for targets | |
8171 whose linkers have special support for NeXT-style runtimes. | |
8172 @end defmac | |
8173 | |
8174 @node Initialization | |
8175 @subsection How Initialization Functions Are Handled | |
8176 @cindex initialization routines | |
8177 @cindex termination routines | |
8178 @cindex constructors, output of | |
8179 @cindex destructors, output of | |
8180 | |
8181 The compiled code for certain languages includes @dfn{constructors} | |
8182 (also called @dfn{initialization routines})---functions to initialize | |
8183 data in the program when the program is started. These functions need | |
8184 to be called before the program is ``started''---that is to say, before | |
8185 @code{main} is called. | |
8186 | |
8187 Compiling some languages generates @dfn{destructors} (also called | |
8188 @dfn{termination routines}) that should be called when the program | |
8189 terminates. | |
8190 | |
8191 To make the initialization and termination functions work, the compiler | |
8192 must output something in the assembler code to cause those functions to | |
8193 be called at the appropriate time. When you port the compiler to a new | |
8194 system, you need to specify how to do this. | |
8195 | |
8196 There are two major ways that GCC currently supports the execution of | |
8197 initialization and termination functions. Each way has two variants. | |
8198 Much of the structure is common to all four variations. | |
8199 | |
8200 @findex __CTOR_LIST__ | |
8201 @findex __DTOR_LIST__ | |
8202 The linker must build two lists of these functions---a list of | |
8203 initialization functions, called @code{__CTOR_LIST__}, and a list of | |
8204 termination functions, called @code{__DTOR_LIST__}. | |
8205 | |
8206 Each list always begins with an ignored function pointer (which may hold | |
8207 0, @minus{}1, or a count of the function pointers after it, depending on | |
8208 the environment). This is followed by a series of zero or more function | |
8209 pointers to constructors (or destructors), followed by a function | |
8210 pointer containing zero. | |
8211 | |
8212 Depending on the operating system and its executable file format, either | |
8213 @file{crtstuff.c} or @file{libgcc2.c} traverses these lists at startup | |
8214 time and exit time. Constructors are called in reverse order of the | |
8215 list; destructors in forward order. | |
8216 | |
8217 The best way to handle static constructors works only for object file | |
8218 formats which provide arbitrarily-named sections. A section is set | |
8219 aside for a list of constructors, and another for a list of destructors. | |
8220 Traditionally these are called @samp{.ctors} and @samp{.dtors}. Each | |
8221 object file that defines an initialization function also puts a word in | |
8222 the constructor section to point to that function. The linker | |
8223 accumulates all these words into one contiguous @samp{.ctors} section. | |
8224 Termination functions are handled similarly. | |
8225 | |
8226 This method will be chosen as the default by @file{target-def.h} if | |
8227 @code{TARGET_ASM_NAMED_SECTION} is defined. A target that does not | |
8228 support arbitrary sections, but does support special designated | |
8229 constructor and destructor sections may define @code{CTORS_SECTION_ASM_OP} | |
8230 and @code{DTORS_SECTION_ASM_OP} to achieve the same effect. | |
8231 | |
8232 When arbitrary sections are available, there are two variants, depending | |
8233 upon how the code in @file{crtstuff.c} is called. On systems that | |
8234 support a @dfn{.init} section which is executed at program startup, | |
8235 parts of @file{crtstuff.c} are compiled into that section. The | |
8236 program is linked by the @command{gcc} driver like this: | |
8237 | |
8238 @smallexample | |
8239 ld -o @var{output_file} crti.o crtbegin.o @dots{} -lgcc crtend.o crtn.o | |
8240 @end smallexample | |
8241 | |
8242 The prologue of a function (@code{__init}) appears in the @code{.init} | |
8243 section of @file{crti.o}; the epilogue appears in @file{crtn.o}. Likewise | |
8244 for the function @code{__fini} in the @dfn{.fini} section. Normally these | |
8245 files are provided by the operating system or by the GNU C library, but | |
8246 are provided by GCC for a few targets. | |
8247 | |
8248 The objects @file{crtbegin.o} and @file{crtend.o} are (for most targets) | |
8249 compiled from @file{crtstuff.c}. They contain, among other things, code | |
8250 fragments within the @code{.init} and @code{.fini} sections that branch | |
8251 to routines in the @code{.text} section. The linker will pull all parts | |
8252 of a section together, which results in a complete @code{__init} function | |
8253 that invokes the routines we need at startup. | |
8254 | |
8255 To use this variant, you must define the @code{INIT_SECTION_ASM_OP} | |
8256 macro properly. | |
8257 | |
8258 If no init section is available, when GCC compiles any function called | |
8259 @code{main} (or more accurately, any function designated as a program | |
8260 entry point by the language front end calling @code{expand_main_function}), | |
8261 it inserts a procedure call to @code{__main} as the first executable code | |
8262 after the function prologue. The @code{__main} function is defined | |
8263 in @file{libgcc2.c} and runs the global constructors. | |
8264 | |
8265 In file formats that don't support arbitrary sections, there are again | |
8266 two variants. In the simplest variant, the GNU linker (GNU @code{ld}) | |
8267 and an `a.out' format must be used. In this case, | |
8268 @code{TARGET_ASM_CONSTRUCTOR} is defined to produce a @code{.stabs} | |
8269 entry of type @samp{N_SETT}, referencing the name @code{__CTOR_LIST__}, | |
8270 and with the address of the void function containing the initialization | |
8271 code as its value. The GNU linker recognizes this as a request to add | |
8272 the value to a @dfn{set}; the values are accumulated, and are eventually | |
8273 placed in the executable as a vector in the format described above, with | |
8274 a leading (ignored) count and a trailing zero element. | |
8275 @code{TARGET_ASM_DESTRUCTOR} is handled similarly. Since no init | |
8276 section is available, the absence of @code{INIT_SECTION_ASM_OP} causes | |
8277 the compilation of @code{main} to call @code{__main} as above, starting | |
8278 the initialization process. | |
8279 | |
8280 The last variant uses neither arbitrary sections nor the GNU linker. | |
8281 This is preferable when you want to do dynamic linking and when using | |
8282 file formats which the GNU linker does not support, such as `ECOFF'@. In | |
8283 this case, @code{TARGET_HAVE_CTORS_DTORS} is false, initialization and | |
8284 termination functions are recognized simply by their names. This requires | |
8285 an extra program in the linkage step, called @command{collect2}. This program | |
8286 pretends to be the linker, for use with GCC; it does its job by running | |
8287 the ordinary linker, but also arranges to include the vectors of | |
8288 initialization and termination functions. These functions are called | |
8289 via @code{__main} as described above. In order to use this method, | |
8290 @code{use_collect2} must be defined in the target in @file{config.gcc}. | |
8291 | |
8292 @ifinfo | |
8293 The following section describes the specific macros that control and | |
8294 customize the handling of initialization and termination functions. | |
8295 @end ifinfo | |
8296 | |
8297 @node Macros for Initialization | |
8298 @subsection Macros Controlling Initialization Routines | |
8299 | |
8300 Here are the macros that control how the compiler handles initialization | |
8301 and termination functions: | |
8302 | |
8303 @defmac INIT_SECTION_ASM_OP | |
8304 If defined, a C string constant, including spacing, for the assembler | |
8305 operation to identify the following data as initialization code. If not | |
8306 defined, GCC will assume such a section does not exist. When you are | |
8307 using special sections for initialization and termination functions, this | |
8308 macro also controls how @file{crtstuff.c} and @file{libgcc2.c} arrange to | |
8309 run the initialization functions. | |
8310 @end defmac | |
8311 | |
8312 @defmac HAS_INIT_SECTION | |
8313 If defined, @code{main} will not call @code{__main} as described above. | |
8314 This macro should be defined for systems that control start-up code | |
8315 on a symbol-by-symbol basis, such as OSF/1, and should not | |
8316 be defined explicitly for systems that support @code{INIT_SECTION_ASM_OP}. | |
8317 @end defmac | |
8318 | |
8319 @defmac LD_INIT_SWITCH | |
8320 If defined, a C string constant for a switch that tells the linker that | |
8321 the following symbol is an initialization routine. | |
8322 @end defmac | |
8323 | |
8324 @defmac LD_FINI_SWITCH | |
8325 If defined, a C string constant for a switch that tells the linker that | |
8326 the following symbol is a finalization routine. | |
8327 @end defmac | |
8328 | |
8329 @defmac COLLECT_SHARED_INIT_FUNC (@var{stream}, @var{func}) | |
8330 If defined, a C statement that will write a function that can be | |
8331 automatically called when a shared library is loaded. The function | |
8332 should call @var{func}, which takes no arguments. If not defined, and | |
8333 the object format requires an explicit initialization function, then a | |
8334 function called @code{_GLOBAL__DI} will be generated. | |
8335 | |
8336 This function and the following one are used by collect2 when linking a | |
8337 shared library that needs constructors or destructors, or has DWARF2 | |
8338 exception tables embedded in the code. | |
8339 @end defmac | |
8340 | |
8341 @defmac COLLECT_SHARED_FINI_FUNC (@var{stream}, @var{func}) | |
8342 If defined, a C statement that will write a function that can be | |
8343 automatically called when a shared library is unloaded. The function | |
8344 should call @var{func}, which takes no arguments. If not defined, and | |
8345 the object format requires an explicit finalization function, then a | |
8346 function called @code{_GLOBAL__DD} will be generated. | |
8347 @end defmac | |
8348 | |
8349 @defmac INVOKE__main | |
8350 If defined, @code{main} will call @code{__main} despite the presence of | |
8351 @code{INIT_SECTION_ASM_OP}. This macro should be defined for systems | |
8352 where the init section is not actually run automatically, but is still | |
8353 useful for collecting the lists of constructors and destructors. | |
8354 @end defmac | |
8355 | |
8356 @defmac SUPPORTS_INIT_PRIORITY | |
8357 If nonzero, the C++ @code{init_priority} attribute is supported and the | |
8358 compiler should emit instructions to control the order of initialization | |
8359 of objects. If zero, the compiler will issue an error message upon | |
8360 encountering an @code{init_priority} attribute. | |
8361 @end defmac | |
8362 | |
8363 @hook TARGET_HAVE_CTORS_DTORS | |
8364 This value is true if the target supports some ``native'' method of | |
8365 collecting constructors and destructors to be run at startup and exit. | |
8366 It is false if we must use @command{collect2}. | |
8367 @end deftypevr | |
8368 | |
8369 @hook TARGET_ASM_CONSTRUCTOR | |
8370 If defined, a function that outputs assembler code to arrange to call | |
8371 the function referenced by @var{symbol} at initialization time. | |
8372 | |
8373 Assume that @var{symbol} is a @code{SYMBOL_REF} for a function taking | |
8374 no arguments and with no return value. If the target supports initialization | |
8375 priorities, @var{priority} is a value between 0 and @code{MAX_INIT_PRIORITY}; | |
8376 otherwise it must be @code{DEFAULT_INIT_PRIORITY}. | |
8377 | |
8378 If this macro is not defined by the target, a suitable default will | |
8379 be chosen if (1) the target supports arbitrary section names, (2) the | |
8380 target defines @code{CTORS_SECTION_ASM_OP}, or (3) @code{USE_COLLECT2} | |
8381 is not defined. | |
8382 @end deftypefn | |
8383 | |
8384 @hook TARGET_ASM_DESTRUCTOR | |
8385 This is like @code{TARGET_ASM_CONSTRUCTOR} but used for termination | |
8386 functions rather than initialization functions. | |
8387 @end deftypefn | |
8388 | |
8389 If @code{TARGET_HAVE_CTORS_DTORS} is true, the initialization routine | |
8390 generated for the generated object file will have static linkage. | |
8391 | |
8392 If your system uses @command{collect2} as the means of processing | |
8393 constructors, then that program normally uses @command{nm} to scan | |
8394 an object file for constructor functions to be called. | |
8395 | |
8396 On certain kinds of systems, you can define this macro to make | |
8397 @command{collect2} work faster (and, in some cases, make it work at all): | |
8398 | |
8399 @defmac OBJECT_FORMAT_COFF | |
8400 Define this macro if the system uses COFF (Common Object File Format) | |
8401 object files, so that @command{collect2} can assume this format and scan | |
8402 object files directly for dynamic constructor/destructor functions. | |
8403 | |
8404 This macro is effective only in a native compiler; @command{collect2} as | |
8405 part of a cross compiler always uses @command{nm} for the target machine. | |
8406 @end defmac | |
8407 | |
8408 @defmac REAL_NM_FILE_NAME | |
8409 Define this macro as a C string constant containing the file name to use | |
8410 to execute @command{nm}. The default is to search the path normally for | |
8411 @command{nm}. | |
8412 @end defmac | |
8413 | |
8414 @defmac NM_FLAGS | |
8415 @command{collect2} calls @command{nm} to scan object files for static | |
8416 constructors and destructors and LTO info. By default, @option{-n} is | |
8417 passed. Define @code{NM_FLAGS} to a C string constant if other options | |
8418 are needed to get the same output format as GNU @command{nm -n} | |
8419 produces. | |
8420 @end defmac | |
8421 | |
8422 If your system supports shared libraries and has a program to list the | |
8423 dynamic dependencies of a given library or executable, you can define | |
8424 these macros to enable support for running initialization and | |
8425 termination functions in shared libraries: | |
8426 | |
8427 @defmac LDD_SUFFIX | |
8428 Define this macro to a C string constant containing the name of the program | |
8429 which lists dynamic dependencies, like @command{ldd} under SunOS 4. | |
8430 @end defmac | |
8431 | |
8432 @defmac PARSE_LDD_OUTPUT (@var{ptr}) | |
8433 Define this macro to be C code that extracts filenames from the output | |
8434 of the program denoted by @code{LDD_SUFFIX}. @var{ptr} is a variable | |
8435 of type @code{char *} that points to the beginning of a line of output | |
8436 from @code{LDD_SUFFIX}. If the line lists a dynamic dependency, the | |
8437 code must advance @var{ptr} to the beginning of the filename on that | |
8438 line. Otherwise, it must set @var{ptr} to @code{NULL}. | |
8439 @end defmac | |
8440 | |
8441 @defmac SHLIB_SUFFIX | |
8442 Define this macro to a C string constant containing the default shared | |
8443 library extension of the target (e.g., @samp{".so"}). @command{collect2} | |
8444 strips version information after this suffix when generating global | |
8445 constructor and destructor names. This define is only needed on targets | |
8446 that use @command{collect2} to process constructors and destructors. | |
8447 @end defmac | |
8448 | |
8449 @node Instruction Output | |
8450 @subsection Output of Assembler Instructions | |
8451 | |
8452 @c prevent bad page break with this line | |
8453 This describes assembler instruction output. | |
8454 | |
8455 @defmac REGISTER_NAMES | |
8456 A C initializer containing the assembler's names for the machine | |
8457 registers, each one as a C string constant. This is what translates | |
8458 register numbers in the compiler into assembler language. | |
8459 @end defmac | |
8460 | |
8461 @defmac ADDITIONAL_REGISTER_NAMES | |
8462 If defined, a C initializer for an array of structures containing a name | |
8463 and a register number. This macro defines additional names for hard | |
8464 registers, thus allowing the @code{asm} option in declarations to refer | |
8465 to registers using alternate names. | |
8466 @end defmac | |
8467 | |
8468 @defmac OVERLAPPING_REGISTER_NAMES | |
8469 If defined, a C initializer for an array of structures containing a | |
8470 name, a register number and a count of the number of consecutive | |
8471 machine registers the name overlaps. This macro defines additional | |
8472 names for hard registers, thus allowing the @code{asm} option in | |
8473 declarations to refer to registers using alternate names. Unlike | |
8474 @code{ADDITIONAL_REGISTER_NAMES}, this macro should be used when the | |
8475 register name implies multiple underlying registers. | |
8476 | |
8477 This macro should be used when it is important that a clobber in an | |
8478 @code{asm} statement clobbers all the underlying values implied by the | |
8479 register name. For example, on ARM, clobbering the double-precision | |
8480 VFP register ``d0'' implies clobbering both single-precision registers | |
8481 ``s0'' and ``s1''. | |
8482 @end defmac | |
8483 | |
8484 @defmac ASM_OUTPUT_OPCODE (@var{stream}, @var{ptr}) | |
8485 Define this macro if you are using an unusual assembler that | |
8486 requires different names for the machine instructions. | |
8487 | |
8488 The definition is a C statement or statements which output an | |
8489 assembler instruction opcode to the stdio stream @var{stream}. The | |
8490 macro-operand @var{ptr} is a variable of type @code{char *} which | |
8491 points to the opcode name in its ``internal'' form---the form that is | |
8492 written in the machine description. The definition should output the | |
8493 opcode name to @var{stream}, performing any translation you desire, and | |
8494 increment the variable @var{ptr} to point at the end of the opcode | |
8495 so that it will not be output twice. | |
8496 | |
8497 In fact, your macro definition may process less than the entire opcode | |
8498 name, or more than the opcode name; but if you want to process text | |
8499 that includes @samp{%}-sequences to substitute operands, you must take | |
8500 care of the substitution yourself. Just be sure to increment | |
8501 @var{ptr} over whatever text should not be output normally. | |
8502 | |
8503 @findex recog_data.operand | |
8504 If you need to look at the operand values, they can be found as the | |
8505 elements of @code{recog_data.operand}. | |
8506 | |
8507 If the macro definition does nothing, the instruction is output | |
8508 in the usual way. | |
8509 @end defmac | |
8510 | |
8511 @defmac FINAL_PRESCAN_INSN (@var{insn}, @var{opvec}, @var{noperands}) | |
8512 If defined, a C statement to be executed just prior to the output of | |
8513 assembler code for @var{insn}, to modify the extracted operands so | |
8514 they will be output differently. | |
8515 | |
8516 Here the argument @var{opvec} is the vector containing the operands | |
8517 extracted from @var{insn}, and @var{noperands} is the number of | |
8518 elements of the vector which contain meaningful data for this insn. | |
8519 The contents of this vector are what will be used to convert the insn | |
8520 template into assembler code, so you can change the assembler output | |
8521 by changing the contents of the vector. | |
8522 | |
8523 This macro is useful when various assembler syntaxes share a single | |
8524 file of instruction patterns; by defining this macro differently, you | |
8525 can cause a large class of instructions to be output differently (such | |
8526 as with rearranged operands). Naturally, variations in assembler | |
8527 syntax affecting individual insn patterns ought to be handled by | |
8528 writing conditional output routines in those patterns. | |
8529 | |
8530 If this macro is not defined, it is equivalent to a null statement. | |
8531 @end defmac | |
8532 | |
8533 @hook TARGET_ASM_FINAL_POSTSCAN_INSN | |
8534 If defined, this target hook is a function which is executed just after the | |
8535 output of assembler code for @var{insn}, to change the mode of the assembler | |
8536 if necessary. | |
8537 | |
8538 Here the argument @var{opvec} is the vector containing the operands | |
8539 extracted from @var{insn}, and @var{noperands} is the number of | |
8540 elements of the vector which contain meaningful data for this insn. | |
8541 The contents of this vector are what was used to convert the insn | |
8542 template into assembler code, so you can change the assembler mode | |
8543 by checking the contents of the vector. | |
8544 @end deftypefn | |
8545 | |
8546 @defmac PRINT_OPERAND (@var{stream}, @var{x}, @var{code}) | |
8547 A C compound statement to output to stdio stream @var{stream} the | |
8548 assembler syntax for an instruction operand @var{x}. @var{x} is an | |
8549 RTL expression. | |
8550 | |
8551 @var{code} is a value that can be used to specify one of several ways | |
8552 of printing the operand. It is used when identical operands must be | |
8553 printed differently depending on the context. @var{code} comes from | |
8554 the @samp{%} specification that was used to request printing of the | |
8555 operand. If the specification was just @samp{%@var{digit}} then | |
8556 @var{code} is 0; if the specification was @samp{%@var{ltr} | |
8557 @var{digit}} then @var{code} is the ASCII code for @var{ltr}. | |
8558 | |
8559 @findex reg_names | |
8560 If @var{x} is a register, this macro should print the register's name. | |
8561 The names can be found in an array @code{reg_names} whose type is | |
8562 @code{char *[]}. @code{reg_names} is initialized from | |
8563 @code{REGISTER_NAMES}. | |
8564 | |
8565 When the machine description has a specification @samp{%@var{punct}} | |
8566 (a @samp{%} followed by a punctuation character), this macro is called | |
8567 with a null pointer for @var{x} and the punctuation character for | |
8568 @var{code}. | |
8569 @end defmac | |
8570 | |
8571 @defmac PRINT_OPERAND_PUNCT_VALID_P (@var{code}) | |
8572 A C expression which evaluates to true if @var{code} is a valid | |
8573 punctuation character for use in the @code{PRINT_OPERAND} macro. If | |
8574 @code{PRINT_OPERAND_PUNCT_VALID_P} is not defined, it means that no | |
8575 punctuation characters (except for the standard one, @samp{%}) are used | |
8576 in this way. | |
8577 @end defmac | |
8578 | |
8579 @defmac PRINT_OPERAND_ADDRESS (@var{stream}, @var{x}) | |
8580 A C compound statement to output to stdio stream @var{stream} the | |
8581 assembler syntax for an instruction operand that is a memory reference | |
8582 whose address is @var{x}. @var{x} is an RTL expression. | |
8583 | |
8584 @cindex @code{TARGET_ENCODE_SECTION_INFO} usage | |
8585 On some machines, the syntax for a symbolic address depends on the | |
8586 section that the address refers to. On these machines, define the hook | |
8587 @code{TARGET_ENCODE_SECTION_INFO} to store the information into the | |
8588 @code{symbol_ref}, and then check for it here. @xref{Assembler | |
8589 Format}. | |
8590 @end defmac | |
8591 | |
8592 @findex dbr_sequence_length | |
8593 @defmac DBR_OUTPUT_SEQEND (@var{file}) | |
8594 A C statement, to be executed after all slot-filler instructions have | |
8595 been output. If necessary, call @code{dbr_sequence_length} to | |
8596 determine the number of slots filled in a sequence (zero if not | |
8597 currently outputting a sequence), to decide how many no-ops to output, | |
8598 or whatever. | |
8599 | |
8600 Don't define this macro if it has nothing to do, but it is helpful in | |
8601 reading assembly output if the extent of the delay sequence is made | |
8602 explicit (e.g.@: with white space). | |
8603 @end defmac | |
8604 | |
8605 @findex final_sequence | |
8606 Note that output routines for instructions with delay slots must be | |
8607 prepared to deal with not being output as part of a sequence | |
8608 (i.e.@: when the scheduling pass is not run, or when no slot fillers could be | |
8609 found.) The variable @code{final_sequence} is null when not | |
8610 processing a sequence, otherwise it contains the @code{sequence} rtx | |
8611 being output. | |
8612 | |
8613 @findex asm_fprintf | |
8614 @defmac REGISTER_PREFIX | |
8615 @defmacx LOCAL_LABEL_PREFIX | |
8616 @defmacx USER_LABEL_PREFIX | |
8617 @defmacx IMMEDIATE_PREFIX | |
8618 If defined, C string expressions to be used for the @samp{%R}, @samp{%L}, | |
8619 @samp{%U}, and @samp{%I} options of @code{asm_fprintf} (see | |
8620 @file{final.c}). These are useful when a single @file{md} file must | |
8621 support multiple assembler formats. In that case, the various @file{tm.h} | |
8622 files can define these macros differently. | |
8623 @end defmac | |
8624 | |
8625 @defmac ASM_FPRINTF_EXTENSIONS (@var{file}, @var{argptr}, @var{format}) | |
8626 If defined this macro should expand to a series of @code{case} | |
8627 statements which will be parsed inside the @code{switch} statement of | |
8628 the @code{asm_fprintf} function. This allows targets to define extra | |
8629 printf formats which may useful when generating their assembler | |
8630 statements. Note that uppercase letters are reserved for future | |
8631 generic extensions to asm_fprintf, and so are not available to target | |
8632 specific code. The output file is given by the parameter @var{file}. | |
8633 The varargs input pointer is @var{argptr} and the rest of the format | |
8634 string, starting the character after the one that is being switched | |
8635 upon, is pointed to by @var{format}. | |
8636 @end defmac | |
8637 | |
8638 @defmac ASSEMBLER_DIALECT | |
8639 If your target supports multiple dialects of assembler language (such as | |
8640 different opcodes), define this macro as a C expression that gives the | |
8641 numeric index of the assembler language dialect to use, with zero as the | |
8642 first variant. | |
8643 | |
8644 If this macro is defined, you may use constructs of the form | |
8645 @smallexample | |
8646 @samp{@{option0|option1|option2@dots{}@}} | |
8647 @end smallexample | |
8648 @noindent | |
8649 in the output templates of patterns (@pxref{Output Template}) or in the | |
8650 first argument of @code{asm_fprintf}. This construct outputs | |
8651 @samp{option0}, @samp{option1}, @samp{option2}, etc., if the value of | |
8652 @code{ASSEMBLER_DIALECT} is zero, one, two, etc. Any special characters | |
8653 within these strings retain their usual meaning. If there are fewer | |
8654 alternatives within the braces than the value of | |
8655 @code{ASSEMBLER_DIALECT}, the construct outputs nothing. | |
8656 | |
8657 If you do not define this macro, the characters @samp{@{}, @samp{|} and | |
8658 @samp{@}} do not have any special meaning when used in templates or | |
8659 operands to @code{asm_fprintf}. | |
8660 | |
8661 Define the macros @code{REGISTER_PREFIX}, @code{LOCAL_LABEL_PREFIX}, | |
8662 @code{USER_LABEL_PREFIX} and @code{IMMEDIATE_PREFIX} if you can express | |
8663 the variations in assembler language syntax with that mechanism. Define | |
8664 @code{ASSEMBLER_DIALECT} and use the @samp{@{option0|option1@}} syntax | |
8665 if the syntax variant are larger and involve such things as different | |
8666 opcodes or operand order. | |
8667 @end defmac | |
8668 | |
8669 @defmac ASM_OUTPUT_REG_PUSH (@var{stream}, @var{regno}) | |
8670 A C expression to output to @var{stream} some assembler code | |
8671 which will push hard register number @var{regno} onto the stack. | |
8672 The code need not be optimal, since this macro is used only when | |
8673 profiling. | |
8674 @end defmac | |
8675 | |
8676 @defmac ASM_OUTPUT_REG_POP (@var{stream}, @var{regno}) | |
8677 A C expression to output to @var{stream} some assembler code | |
8678 which will pop hard register number @var{regno} off of the stack. | |
8679 The code need not be optimal, since this macro is used only when | |
8680 profiling. | |
8681 @end defmac | |
8682 | |
8683 @node Dispatch Tables | |
8684 @subsection Output of Dispatch Tables | |
8685 | |
8686 @c prevent bad page break with this line | |
8687 This concerns dispatch tables. | |
8688 | |
8689 @cindex dispatch table | |
8690 @defmac ASM_OUTPUT_ADDR_DIFF_ELT (@var{stream}, @var{body}, @var{value}, @var{rel}) | |
8691 A C statement to output to the stdio stream @var{stream} an assembler | |
8692 pseudo-instruction to generate a difference between two labels. | |
8693 @var{value} and @var{rel} are the numbers of two internal labels. The | |
8694 definitions of these labels are output using | |
8695 @code{(*targetm.asm_out.internal_label)}, and they must be printed in the same | |
8696 way here. For example, | |
8697 | |
8698 @smallexample | |
8699 fprintf (@var{stream}, "\t.word L%d-L%d\n", | |
8700 @var{value}, @var{rel}) | |
8701 @end smallexample | |
8702 | |
8703 You must provide this macro on machines where the addresses in a | |
8704 dispatch table are relative to the table's own address. If defined, GCC | |
8705 will also use this macro on all machines when producing PIC@. | |
8706 @var{body} is the body of the @code{ADDR_DIFF_VEC}; it is provided so that the | |
8707 mode and flags can be read. | |
8708 @end defmac | |
8709 | |
8710 @defmac ASM_OUTPUT_ADDR_VEC_ELT (@var{stream}, @var{value}) | |
8711 This macro should be provided on machines where the addresses | |
8712 in a dispatch table are absolute. | |
8713 | |
8714 The definition should be a C statement to output to the stdio stream | |
8715 @var{stream} an assembler pseudo-instruction to generate a reference to | |
8716 a label. @var{value} is the number of an internal label whose | |
8717 definition is output using @code{(*targetm.asm_out.internal_label)}. | |
8718 For example, | |
8719 | |
8720 @smallexample | |
8721 fprintf (@var{stream}, "\t.word L%d\n", @var{value}) | |
8722 @end smallexample | |
8723 @end defmac | |
8724 | |
8725 @defmac ASM_OUTPUT_CASE_LABEL (@var{stream}, @var{prefix}, @var{num}, @var{table}) | |
8726 Define this if the label before a jump-table needs to be output | |
8727 specially. The first three arguments are the same as for | |
8728 @code{(*targetm.asm_out.internal_label)}; the fourth argument is the | |
8729 jump-table which follows (a @code{jump_insn} containing an | |
8730 @code{addr_vec} or @code{addr_diff_vec}). | |
8731 | |
8732 This feature is used on system V to output a @code{swbeg} statement | |
8733 for the table. | |
8734 | |
8735 If this macro is not defined, these labels are output with | |
8736 @code{(*targetm.asm_out.internal_label)}. | |
8737 @end defmac | |
8738 | |
8739 @defmac ASM_OUTPUT_CASE_END (@var{stream}, @var{num}, @var{table}) | |
8740 Define this if something special must be output at the end of a | |
8741 jump-table. The definition should be a C statement to be executed | |
8742 after the assembler code for the table is written. It should write | |
8743 the appropriate code to stdio stream @var{stream}. The argument | |
8744 @var{table} is the jump-table insn, and @var{num} is the label-number | |
8745 of the preceding label. | |
8746 | |
8747 If this macro is not defined, nothing special is output at the end of | |
8748 the jump-table. | |
8749 @end defmac | |
8750 | |
8751 @hook TARGET_ASM_EMIT_UNWIND_LABEL | |
8752 This target hook emits a label at the beginning of each FDE@. It | |
8753 should be defined on targets where FDEs need special labels, and it | |
8754 should write the appropriate label, for the FDE associated with the | |
8755 function declaration @var{decl}, to the stdio stream @var{stream}. | |
8756 The third argument, @var{for_eh}, is a boolean: true if this is for an | |
8757 exception table. The fourth argument, @var{empty}, is a boolean: | |
8758 true if this is a placeholder label for an omitted FDE@. | |
8759 | |
8760 The default is that FDEs are not given nonlocal labels. | |
8761 @end deftypefn | |
8762 | |
8763 @hook TARGET_ASM_EMIT_EXCEPT_TABLE_LABEL | |
8764 This target hook emits a label at the beginning of the exception table. | |
8765 It should be defined on targets where it is desirable for the table | |
8766 to be broken up according to function. | |
8767 | |
8768 The default is that no label is emitted. | |
8769 @end deftypefn | |
8770 | |
8771 @hook TARGET_ASM_EMIT_EXCEPT_PERSONALITY | |
8772 | |
8773 @hook TARGET_ASM_UNWIND_EMIT | |
8774 This target hook emits assembly directives required to unwind the | |
8775 given instruction. This is only used when @code{TARGET_EXCEPT_UNWIND_INFO} | |
8776 returns @code{UI_TARGET}. | |
8777 @end deftypefn | |
8778 | |
8779 @hook TARGET_ASM_UNWIND_EMIT_BEFORE_INSN | |
8780 | |
8781 @node Exception Region Output | |
8782 @subsection Assembler Commands for Exception Regions | |
8783 | |
8784 @c prevent bad page break with this line | |
8785 | |
8786 This describes commands marking the start and the end of an exception | |
8787 region. | |
8788 | |
8789 @defmac EH_FRAME_SECTION_NAME | |
8790 If defined, a C string constant for the name of the section containing | |
8791 exception handling frame unwind information. If not defined, GCC will | |
8792 provide a default definition if the target supports named sections. | |
8793 @file{crtstuff.c} uses this macro to switch to the appropriate section. | |
8794 | |
8795 You should define this symbol if your target supports DWARF 2 frame | |
8796 unwind information and the default definition does not work. | |
8797 @end defmac | |
8798 | |
8799 @defmac EH_FRAME_IN_DATA_SECTION | |
8800 If defined, DWARF 2 frame unwind information will be placed in the | |
8801 data section even though the target supports named sections. This | |
8802 might be necessary, for instance, if the system linker does garbage | |
8803 collection and sections cannot be marked as not to be collected. | |
8804 | |
8805 Do not define this macro unless @code{TARGET_ASM_NAMED_SECTION} is | |
8806 also defined. | |
8807 @end defmac | |
8808 | |
8809 @defmac EH_TABLES_CAN_BE_READ_ONLY | |
8810 Define this macro to 1 if your target is such that no frame unwind | |
8811 information encoding used with non-PIC code will ever require a | |
8812 runtime relocation, but the linker may not support merging read-only | |
8813 and read-write sections into a single read-write section. | |
8814 @end defmac | |
8815 | |
8816 @defmac MASK_RETURN_ADDR | |
8817 An rtx used to mask the return address found via @code{RETURN_ADDR_RTX}, so | |
8818 that it does not contain any extraneous set bits in it. | |
8819 @end defmac | |
8820 | |
8821 @defmac DWARF2_UNWIND_INFO | |
8822 Define this macro to 0 if your target supports DWARF 2 frame unwind | |
8823 information, but it does not yet work with exception handling. | |
8824 Otherwise, if your target supports this information (if it defines | |
8825 @code{INCOMING_RETURN_ADDR_RTX} and either @code{UNALIGNED_INT_ASM_OP} | |
8826 or @code{OBJECT_FORMAT_ELF}), GCC will provide a default definition of 1. | |
8827 @end defmac | |
8828 | |
8829 @hook TARGET_EXCEPT_UNWIND_INFO | |
8830 This hook defines the mechanism that will be used for exception handling | |
8831 by the target. If the target has ABI specified unwind tables, the hook | |
8832 should return @code{UI_TARGET}. If the target is to use the | |
8833 @code{setjmp}/@code{longjmp}-based exception handling scheme, the hook | |
8834 should return @code{UI_SJLJ}. If the target supports DWARF 2 frame unwind | |
8835 information, the hook should return @code{UI_DWARF2}. | |
8836 | |
8837 A target may, if exceptions are disabled, choose to return @code{UI_NONE}. | |
8838 This may end up simplifying other parts of target-specific code. The | |
8839 default implementation of this hook never returns @code{UI_NONE}. | |
8840 | |
8841 Note that the value returned by this hook should be constant. It should | |
8842 not depend on anything except the command-line switches described by | |
8843 @var{opts}. In particular, the | |
8844 setting @code{UI_SJLJ} must be fixed at compiler start-up as C pre-processor | |
8845 macros and builtin functions related to exception handling are set up | |
8846 depending on this setting. | |
8847 | |
8848 The default implementation of the hook first honors the | |
8849 @option{--enable-sjlj-exceptions} configure option, then | |
8850 @code{DWARF2_UNWIND_INFO}, and finally defaults to @code{UI_SJLJ}. If | |
8851 @code{DWARF2_UNWIND_INFO} depends on command-line options, the target | |
8852 must define this hook so that @var{opts} is used correctly. | |
8853 @end deftypefn | |
8854 | |
8855 @hook TARGET_UNWIND_TABLES_DEFAULT | |
8856 This variable should be set to @code{true} if the target ABI requires unwinding | |
8857 tables even when exceptions are not used. It must not be modified by | |
8858 command-line option processing. | |
8859 @end deftypevr | |
8860 | |
8861 @defmac DONT_USE_BUILTIN_SETJMP | |
8862 Define this macro to 1 if the @code{setjmp}/@code{longjmp}-based scheme | |
8863 should use the @code{setjmp}/@code{longjmp} functions from the C library | |
8864 instead of the @code{__builtin_setjmp}/@code{__builtin_longjmp} machinery. | |
8865 @end defmac | |
8866 | |
8867 @defmac DWARF_CIE_DATA_ALIGNMENT | |
8868 This macro need only be defined if the target might save registers in the | |
8869 function prologue at an offset to the stack pointer that is not aligned to | |
8870 @code{UNITS_PER_WORD}. The definition should be the negative minimum | |
8871 alignment if @code{STACK_GROWS_DOWNWARD} is defined, and the positive | |
8872 minimum alignment otherwise. @xref{SDB and DWARF}. Only applicable if | |
8873 the target supports DWARF 2 frame unwind information. | |
8874 @end defmac | |
8875 | |
8876 @hook TARGET_TERMINATE_DW2_EH_FRAME_INFO | |
8877 Contains the value true if the target should add a zero word onto the | |
8878 end of a Dwarf-2 frame info section when used for exception handling. | |
8879 Default value is false if @code{EH_FRAME_SECTION_NAME} is defined, and | |
8880 true otherwise. | |
8881 @end deftypevr | |
8882 | |
8883 @hook TARGET_DWARF_REGISTER_SPAN | |
8884 Given a register, this hook should return a parallel of registers to | |
8885 represent where to find the register pieces. Define this hook if the | |
8886 register and its mode are represented in Dwarf in non-contiguous | |
8887 locations, or if the register should be represented in more than one | |
8888 register in Dwarf. Otherwise, this hook should return @code{NULL_RTX}. | |
8889 If not defined, the default is to return @code{NULL_RTX}. | |
8890 @end deftypefn | |
8891 | |
8892 @hook TARGET_INIT_DWARF_REG_SIZES_EXTRA | |
8893 If some registers are represented in Dwarf-2 unwind information in | |
8894 multiple pieces, define this hook to fill in information about the | |
8895 sizes of those pieces in the table used by the unwinder at runtime. | |
8896 It will be called by @code{expand_builtin_init_dwarf_reg_sizes} after | |
8897 filling in a single size corresponding to each hard register; | |
8898 @var{address} is the address of the table. | |
8899 @end deftypefn | |
8900 | |
8901 @hook TARGET_ASM_TTYPE | |
8902 This hook is used to output a reference from a frame unwinding table to | |
8903 the type_info object identified by @var{sym}. It should return @code{true} | |
8904 if the reference was output. Returning @code{false} will cause the | |
8905 reference to be output using the normal Dwarf2 routines. | |
8906 @end deftypefn | |
8907 | |
8908 @hook TARGET_ARM_EABI_UNWINDER | |
8909 This flag should be set to @code{true} on targets that use an ARM EABI | |
8910 based unwinding library, and @code{false} on other targets. This effects | |
8911 the format of unwinding tables, and how the unwinder in entered after | |
8912 running a cleanup. The default is @code{false}. | |
8913 @end deftypevr | |
8914 | |
8915 @node Alignment Output | |
8916 @subsection Assembler Commands for Alignment | |
8917 | |
8918 @c prevent bad page break with this line | |
8919 This describes commands for alignment. | |
8920 | |
8921 @defmac JUMP_ALIGN (@var{label}) | |
8922 The alignment (log base 2) to put in front of @var{label}, which is | |
8923 a common destination of jumps and has no fallthru incoming edge. | |
8924 | |
8925 This macro need not be defined if you don't want any special alignment | |
8926 to be done at such a time. Most machine descriptions do not currently | |
8927 define the macro. | |
8928 | |
8929 Unless it's necessary to inspect the @var{label} parameter, it is better | |
8930 to set the variable @var{align_jumps} in the target's | |
8931 @code{TARGET_OPTION_OVERRIDE}. Otherwise, you should try to honor the user's | |
8932 selection in @var{align_jumps} in a @code{JUMP_ALIGN} implementation. | |
8933 @end defmac | |
8934 | |
8935 @hook TARGET_ASM_JUMP_ALIGN_MAX_SKIP | |
8936 The maximum number of bytes to skip before @var{label} when applying | |
8937 @code{JUMP_ALIGN}. This works only if | |
8938 @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined. | |
8939 @end deftypefn | |
8940 | |
8941 @defmac LABEL_ALIGN_AFTER_BARRIER (@var{label}) | |
8942 The alignment (log base 2) to put in front of @var{label}, which follows | |
8943 a @code{BARRIER}. | |
8944 | |
8945 This macro need not be defined if you don't want any special alignment | |
8946 to be done at such a time. Most machine descriptions do not currently | |
8947 define the macro. | |
8948 @end defmac | |
8949 | |
8950 @hook TARGET_ASM_LABEL_ALIGN_AFTER_BARRIER_MAX_SKIP | |
8951 The maximum number of bytes to skip before @var{label} when applying | |
8952 @code{LABEL_ALIGN_AFTER_BARRIER}. This works only if | |
8953 @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined. | |
8954 @end deftypefn | |
8955 | |
8956 @defmac LOOP_ALIGN (@var{label}) | |
8957 The alignment (log base 2) to put in front of @var{label}, which follows | |
8958 a @code{NOTE_INSN_LOOP_BEG} note. | |
8959 | |
8960 This macro need not be defined if you don't want any special alignment | |
8961 to be done at such a time. Most machine descriptions do not currently | |
8962 define the macro. | |
8963 | |
8964 Unless it's necessary to inspect the @var{label} parameter, it is better | |
8965 to set the variable @code{align_loops} in the target's | |
8966 @code{TARGET_OPTION_OVERRIDE}. Otherwise, you should try to honor the user's | |
8967 selection in @code{align_loops} in a @code{LOOP_ALIGN} implementation. | |
8968 @end defmac | |
8969 | |
8970 @hook TARGET_ASM_LOOP_ALIGN_MAX_SKIP | |
8971 The maximum number of bytes to skip when applying @code{LOOP_ALIGN} to | |
8972 @var{label}. This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is | |
8973 defined. | |
8974 @end deftypefn | |
8975 | |
8976 @defmac LABEL_ALIGN (@var{label}) | |
8977 The alignment (log base 2) to put in front of @var{label}. | |
8978 If @code{LABEL_ALIGN_AFTER_BARRIER} / @code{LOOP_ALIGN} specify a different alignment, | |
8979 the maximum of the specified values is used. | |
8980 | |
8981 Unless it's necessary to inspect the @var{label} parameter, it is better | |
8982 to set the variable @code{align_labels} in the target's | |
8983 @code{TARGET_OPTION_OVERRIDE}. Otherwise, you should try to honor the user's | |
8984 selection in @code{align_labels} in a @code{LABEL_ALIGN} implementation. | |
8985 @end defmac | |
8986 | |
8987 @hook TARGET_ASM_LABEL_ALIGN_MAX_SKIP | |
8988 The maximum number of bytes to skip when applying @code{LABEL_ALIGN} | |
8989 to @var{label}. This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN} | |
8990 is defined. | |
8991 @end deftypefn | |
8992 | |
8993 @defmac ASM_OUTPUT_SKIP (@var{stream}, @var{nbytes}) | |
8994 A C statement to output to the stdio stream @var{stream} an assembler | |
8995 instruction to advance the location counter by @var{nbytes} bytes. | |
8996 Those bytes should be zero when loaded. @var{nbytes} will be a C | |
8997 expression of type @code{unsigned HOST_WIDE_INT}. | |
8998 @end defmac | |
8999 | |
9000 @defmac ASM_NO_SKIP_IN_TEXT | |
9001 Define this macro if @code{ASM_OUTPUT_SKIP} should not be used in the | |
9002 text section because it fails to put zeros in the bytes that are skipped. | |
9003 This is true on many Unix systems, where the pseudo--op to skip bytes | |
9004 produces no-op instructions rather than zeros when used in the text | |
9005 section. | |
9006 @end defmac | |
9007 | |
9008 @defmac ASM_OUTPUT_ALIGN (@var{stream}, @var{power}) | |
9009 A C statement to output to the stdio stream @var{stream} an assembler | |
9010 command to advance the location counter to a multiple of 2 to the | |
9011 @var{power} bytes. @var{power} will be a C expression of type @code{int}. | |
9012 @end defmac | |
9013 | |
9014 @defmac ASM_OUTPUT_ALIGN_WITH_NOP (@var{stream}, @var{power}) | |
9015 Like @code{ASM_OUTPUT_ALIGN}, except that the ``nop'' instruction is used | |
9016 for padding, if necessary. | |
9017 @end defmac | |
9018 | |
9019 @defmac ASM_OUTPUT_MAX_SKIP_ALIGN (@var{stream}, @var{power}, @var{max_skip}) | |
9020 A C statement to output to the stdio stream @var{stream} an assembler | |
9021 command to advance the location counter to a multiple of 2 to the | |
9022 @var{power} bytes, but only if @var{max_skip} or fewer bytes are needed to | |
9023 satisfy the alignment request. @var{power} and @var{max_skip} will be | |
9024 a C expression of type @code{int}. | |
9025 @end defmac | |
9026 | |
9027 @need 3000 | |
9028 @node Debugging Info | |
9029 @section Controlling Debugging Information Format | |
9030 | |
9031 @c prevent bad page break with this line | |
9032 This describes how to specify debugging information. | |
9033 | |
9034 @menu | |
9035 * All Debuggers:: Macros that affect all debugging formats uniformly. | |
9036 * DBX Options:: Macros enabling specific options in DBX format. | |
9037 * DBX Hooks:: Hook macros for varying DBX format. | |
9038 * File Names and DBX:: Macros controlling output of file names in DBX format. | |
9039 * SDB and DWARF:: Macros for SDB (COFF) and DWARF formats. | |
9040 * VMS Debug:: Macros for VMS debug format. | |
9041 @end menu | |
9042 | |
9043 @node All Debuggers | |
9044 @subsection Macros Affecting All Debugging Formats | |
9045 | |
9046 @c prevent bad page break with this line | |
9047 These macros affect all debugging formats. | |
9048 | |
9049 @defmac DBX_REGISTER_NUMBER (@var{regno}) | |
9050 A C expression that returns the DBX register number for the compiler | |
9051 register number @var{regno}. In the default macro provided, the value | |
9052 of this expression will be @var{regno} itself. But sometimes there are | |
9053 some registers that the compiler knows about and DBX does not, or vice | |
9054 versa. In such cases, some register may need to have one number in the | |
9055 compiler and another for DBX@. | |
9056 | |
9057 If two registers have consecutive numbers inside GCC, and they can be | |
9058 used as a pair to hold a multiword value, then they @emph{must} have | |
9059 consecutive numbers after renumbering with @code{DBX_REGISTER_NUMBER}. | |
9060 Otherwise, debuggers will be unable to access such a pair, because they | |
9061 expect register pairs to be consecutive in their own numbering scheme. | |
9062 | |
9063 If you find yourself defining @code{DBX_REGISTER_NUMBER} in way that | |
9064 does not preserve register pairs, then what you must do instead is | |
9065 redefine the actual register numbering scheme. | |
9066 @end defmac | |
9067 | |
9068 @defmac DEBUGGER_AUTO_OFFSET (@var{x}) | |
9069 A C expression that returns the integer offset value for an automatic | |
9070 variable having address @var{x} (an RTL expression). The default | |
9071 computation assumes that @var{x} is based on the frame-pointer and | |
9072 gives the offset from the frame-pointer. This is required for targets | |
9073 that produce debugging output for DBX or COFF-style debugging output | |
9074 for SDB and allow the frame-pointer to be eliminated when the | |
9075 @option{-g} options is used. | |
9076 @end defmac | |
9077 | |
9078 @defmac DEBUGGER_ARG_OFFSET (@var{offset}, @var{x}) | |
9079 A C expression that returns the integer offset value for an argument | |
9080 having address @var{x} (an RTL expression). The nominal offset is | |
9081 @var{offset}. | |
9082 @end defmac | |
9083 | |
9084 @defmac PREFERRED_DEBUGGING_TYPE | |
9085 A C expression that returns the type of debugging output GCC should | |
9086 produce when the user specifies just @option{-g}. Define | |
9087 this if you have arranged for GCC to support more than one format of | |
9088 debugging output. Currently, the allowable values are @code{DBX_DEBUG}, | |
9089 @code{SDB_DEBUG}, @code{DWARF_DEBUG}, @code{DWARF2_DEBUG}, | |
9090 @code{XCOFF_DEBUG}, @code{VMS_DEBUG}, and @code{VMS_AND_DWARF2_DEBUG}. | |
9091 | |
9092 When the user specifies @option{-ggdb}, GCC normally also uses the | |
9093 value of this macro to select the debugging output format, but with two | |
9094 exceptions. If @code{DWARF2_DEBUGGING_INFO} is defined, GCC uses the | |
9095 value @code{DWARF2_DEBUG}. Otherwise, if @code{DBX_DEBUGGING_INFO} is | |
9096 defined, GCC uses @code{DBX_DEBUG}. | |
9097 | |
9098 The value of this macro only affects the default debugging output; the | |
9099 user can always get a specific type of output by using @option{-gstabs}, | |
9100 @option{-gcoff}, @option{-gdwarf-2}, @option{-gxcoff}, or @option{-gvms}. | |
9101 @end defmac | |
9102 | |
9103 @node DBX Options | |
9104 @subsection Specific Options for DBX Output | |
9105 | |
9106 @c prevent bad page break with this line | |
9107 These are specific options for DBX output. | |
9108 | |
9109 @defmac DBX_DEBUGGING_INFO | |
9110 Define this macro if GCC should produce debugging output for DBX | |
9111 in response to the @option{-g} option. | |
9112 @end defmac | |
9113 | |
9114 @defmac XCOFF_DEBUGGING_INFO | |
9115 Define this macro if GCC should produce XCOFF format debugging output | |
9116 in response to the @option{-g} option. This is a variant of DBX format. | |
9117 @end defmac | |
9118 | |
9119 @defmac DEFAULT_GDB_EXTENSIONS | |
9120 Define this macro to control whether GCC should by default generate | |
9121 GDB's extended version of DBX debugging information (assuming DBX-format | |
9122 debugging information is enabled at all). If you don't define the | |
9123 macro, the default is 1: always generate the extended information | |
9124 if there is any occasion to. | |
9125 @end defmac | |
9126 | |
9127 @defmac DEBUG_SYMS_TEXT | |
9128 Define this macro if all @code{.stabs} commands should be output while | |
9129 in the text section. | |
9130 @end defmac | |
9131 | |
9132 @defmac ASM_STABS_OP | |
9133 A C string constant, including spacing, naming the assembler pseudo op to | |
9134 use instead of @code{"\t.stabs\t"} to define an ordinary debugging symbol. | |
9135 If you don't define this macro, @code{"\t.stabs\t"} is used. This macro | |
9136 applies only to DBX debugging information format. | |
9137 @end defmac | |
9138 | |
9139 @defmac ASM_STABD_OP | |
9140 A C string constant, including spacing, naming the assembler pseudo op to | |
9141 use instead of @code{"\t.stabd\t"} to define a debugging symbol whose | |
9142 value is the current location. If you don't define this macro, | |
9143 @code{"\t.stabd\t"} is used. This macro applies only to DBX debugging | |
9144 information format. | |
9145 @end defmac | |
9146 | |
9147 @defmac ASM_STABN_OP | |
9148 A C string constant, including spacing, naming the assembler pseudo op to | |
9149 use instead of @code{"\t.stabn\t"} to define a debugging symbol with no | |
9150 name. If you don't define this macro, @code{"\t.stabn\t"} is used. This | |
9151 macro applies only to DBX debugging information format. | |
9152 @end defmac | |
9153 | |
9154 @defmac DBX_NO_XREFS | |
9155 Define this macro if DBX on your system does not support the construct | |
9156 @samp{xs@var{tagname}}. On some systems, this construct is used to | |
9157 describe a forward reference to a structure named @var{tagname}. | |
9158 On other systems, this construct is not supported at all. | |
9159 @end defmac | |
9160 | |
9161 @defmac DBX_CONTIN_LENGTH | |
9162 A symbol name in DBX-format debugging information is normally | |
9163 continued (split into two separate @code{.stabs} directives) when it | |
9164 exceeds a certain length (by default, 80 characters). On some | |
9165 operating systems, DBX requires this splitting; on others, splitting | |
9166 must not be done. You can inhibit splitting by defining this macro | |
9167 with the value zero. You can override the default splitting-length by | |
9168 defining this macro as an expression for the length you desire. | |
9169 @end defmac | |
9170 | |
9171 @defmac DBX_CONTIN_CHAR | |
9172 Normally continuation is indicated by adding a @samp{\} character to | |
9173 the end of a @code{.stabs} string when a continuation follows. To use | |
9174 a different character instead, define this macro as a character | |
9175 constant for the character you want to use. Do not define this macro | |
9176 if backslash is correct for your system. | |
9177 @end defmac | |
9178 | |
9179 @defmac DBX_STATIC_STAB_DATA_SECTION | |
9180 Define this macro if it is necessary to go to the data section before | |
9181 outputting the @samp{.stabs} pseudo-op for a non-global static | |
9182 variable. | |
9183 @end defmac | |
9184 | |
9185 @defmac DBX_TYPE_DECL_STABS_CODE | |
9186 The value to use in the ``code'' field of the @code{.stabs} directive | |
9187 for a typedef. The default is @code{N_LSYM}. | |
9188 @end defmac | |
9189 | |
9190 @defmac DBX_STATIC_CONST_VAR_CODE | |
9191 The value to use in the ``code'' field of the @code{.stabs} directive | |
9192 for a static variable located in the text section. DBX format does not | |
9193 provide any ``right'' way to do this. The default is @code{N_FUN}. | |
9194 @end defmac | |
9195 | |
9196 @defmac DBX_REGPARM_STABS_CODE | |
9197 The value to use in the ``code'' field of the @code{.stabs} directive | |
9198 for a parameter passed in registers. DBX format does not provide any | |
9199 ``right'' way to do this. The default is @code{N_RSYM}. | |
9200 @end defmac | |
9201 | |
9202 @defmac DBX_REGPARM_STABS_LETTER | |
9203 The letter to use in DBX symbol data to identify a symbol as a parameter | |
9204 passed in registers. DBX format does not customarily provide any way to | |
9205 do this. The default is @code{'P'}. | |
9206 @end defmac | |
9207 | |
9208 @defmac DBX_FUNCTION_FIRST | |
9209 Define this macro if the DBX information for a function and its | |
9210 arguments should precede the assembler code for the function. Normally, | |
9211 in DBX format, the debugging information entirely follows the assembler | |
9212 code. | |
9213 @end defmac | |
9214 | |
9215 @defmac DBX_BLOCKS_FUNCTION_RELATIVE | |
9216 Define this macro, with value 1, if the value of a symbol describing | |
9217 the scope of a block (@code{N_LBRAC} or @code{N_RBRAC}) should be | |
9218 relative to the start of the enclosing function. Normally, GCC uses | |
9219 an absolute address. | |
9220 @end defmac | |
9221 | |
9222 @defmac DBX_LINES_FUNCTION_RELATIVE | |
9223 Define this macro, with value 1, if the value of a symbol indicating | |
9224 the current line number (@code{N_SLINE}) should be relative to the | |
9225 start of the enclosing function. Normally, GCC uses an absolute address. | |
9226 @end defmac | |
9227 | |
9228 @defmac DBX_USE_BINCL | |
9229 Define this macro if GCC should generate @code{N_BINCL} and | |
9230 @code{N_EINCL} stabs for included header files, as on Sun systems. This | |
9231 macro also directs GCC to output a type number as a pair of a file | |
9232 number and a type number within the file. Normally, GCC does not | |
9233 generate @code{N_BINCL} or @code{N_EINCL} stabs, and it outputs a single | |
9234 number for a type number. | |
9235 @end defmac | |
9236 | |
9237 @node DBX Hooks | |
9238 @subsection Open-Ended Hooks for DBX Format | |
9239 | |
9240 @c prevent bad page break with this line | |
9241 These are hooks for DBX format. | |
9242 | |
9243 @defmac DBX_OUTPUT_LBRAC (@var{stream}, @var{name}) | |
9244 Define this macro to say how to output to @var{stream} the debugging | |
9245 information for the start of a scope level for variable names. The | |
9246 argument @var{name} is the name of an assembler symbol (for use with | |
9247 @code{assemble_name}) whose value is the address where the scope begins. | |
9248 @end defmac | |
9249 | |
9250 @defmac DBX_OUTPUT_RBRAC (@var{stream}, @var{name}) | |
9251 Like @code{DBX_OUTPUT_LBRAC}, but for the end of a scope level. | |
9252 @end defmac | |
9253 | |
9254 @defmac DBX_OUTPUT_NFUN (@var{stream}, @var{lscope_label}, @var{decl}) | |
9255 Define this macro if the target machine requires special handling to | |
9256 output an @code{N_FUN} entry for the function @var{decl}. | |
9257 @end defmac | |
9258 | |
9259 @defmac DBX_OUTPUT_SOURCE_LINE (@var{stream}, @var{line}, @var{counter}) | |
9260 A C statement to output DBX debugging information before code for line | |
9261 number @var{line} of the current source file to the stdio stream | |
9262 @var{stream}. @var{counter} is the number of time the macro was | |
9263 invoked, including the current invocation; it is intended to generate | |
9264 unique labels in the assembly output. | |
9265 | |
9266 This macro should not be defined if the default output is correct, or | |
9267 if it can be made correct by defining @code{DBX_LINES_FUNCTION_RELATIVE}. | |
9268 @end defmac | |
9269 | |
9270 @defmac NO_DBX_FUNCTION_END | |
9271 Some stabs encapsulation formats (in particular ECOFF), cannot handle the | |
9272 @code{.stabs "",N_FUN,,0,0,Lscope-function-1} gdb dbx extension construct. | |
9273 On those machines, define this macro to turn this feature off without | |
9274 disturbing the rest of the gdb extensions. | |
9275 @end defmac | |
9276 | |
9277 @defmac NO_DBX_BNSYM_ENSYM | |
9278 Some assemblers cannot handle the @code{.stabd BNSYM/ENSYM,0,0} gdb dbx | |
9279 extension construct. On those machines, define this macro to turn this | |
9280 feature off without disturbing the rest of the gdb extensions. | |
9281 @end defmac | |
9282 | |
9283 @node File Names and DBX | |
9284 @subsection File Names in DBX Format | |
9285 | |
9286 @c prevent bad page break with this line | |
9287 This describes file names in DBX format. | |
9288 | |
9289 @defmac DBX_OUTPUT_MAIN_SOURCE_FILENAME (@var{stream}, @var{name}) | |
9290 A C statement to output DBX debugging information to the stdio stream | |
9291 @var{stream}, which indicates that file @var{name} is the main source | |
9292 file---the file specified as the input file for compilation. | |
9293 This macro is called only once, at the beginning of compilation. | |
9294 | |
9295 This macro need not be defined if the standard form of output | |
9296 for DBX debugging information is appropriate. | |
9297 | |
9298 It may be necessary to refer to a label equal to the beginning of the | |
9299 text section. You can use @samp{assemble_name (stream, ltext_label_name)} | |
9300 to do so. If you do this, you must also set the variable | |
9301 @var{used_ltext_label_name} to @code{true}. | |
9302 @end defmac | |
9303 | |
9304 @defmac NO_DBX_MAIN_SOURCE_DIRECTORY | |
9305 Define this macro, with value 1, if GCC should not emit an indication | |
9306 of the current directory for compilation and current source language at | |
9307 the beginning of the file. | |
9308 @end defmac | |
9309 | |
9310 @defmac NO_DBX_GCC_MARKER | |
9311 Define this macro, with value 1, if GCC should not emit an indication | |
9312 that this object file was compiled by GCC@. The default is to emit | |
9313 an @code{N_OPT} stab at the beginning of every source file, with | |
9314 @samp{gcc2_compiled.} for the string and value 0. | |
9315 @end defmac | |
9316 | |
9317 @defmac DBX_OUTPUT_MAIN_SOURCE_FILE_END (@var{stream}, @var{name}) | |
9318 A C statement to output DBX debugging information at the end of | |
9319 compilation of the main source file @var{name}. Output should be | |
9320 written to the stdio stream @var{stream}. | |
9321 | |
9322 If you don't define this macro, nothing special is output at the end | |
9323 of compilation, which is correct for most machines. | |
9324 @end defmac | |
9325 | |
9326 @defmac DBX_OUTPUT_NULL_N_SO_AT_MAIN_SOURCE_FILE_END | |
9327 Define this macro @emph{instead of} defining | |
9328 @code{DBX_OUTPUT_MAIN_SOURCE_FILE_END}, if what needs to be output at | |
9329 the end of compilation is an @code{N_SO} stab with an empty string, | |
9330 whose value is the highest absolute text address in the file. | |
9331 @end defmac | |
9332 | |
9333 @need 2000 | |
9334 @node SDB and DWARF | |
9335 @subsection Macros for SDB and DWARF Output | |
9336 | |
9337 @c prevent bad page break with this line | |
9338 Here are macros for SDB and DWARF output. | |
9339 | |
9340 @defmac SDB_DEBUGGING_INFO | |
9341 Define this macro if GCC should produce COFF-style debugging output | |
9342 for SDB in response to the @option{-g} option. | |
9343 @end defmac | |
9344 | |
9345 @defmac DWARF2_DEBUGGING_INFO | |
9346 Define this macro if GCC should produce dwarf version 2 format | |
9347 debugging output in response to the @option{-g} option. | |
9348 | |
9349 @hook TARGET_DWARF_CALLING_CONVENTION | |
9350 Define this to enable the dwarf attribute @code{DW_AT_calling_convention} to | |
9351 be emitted for each function. Instead of an integer return the enum | |
9352 value for the @code{DW_CC_} tag. | |
9353 @end deftypefn | |
9354 | |
9355 To support optional call frame debugging information, you must also | |
9356 define @code{INCOMING_RETURN_ADDR_RTX} and either set | |
9357 @code{RTX_FRAME_RELATED_P} on the prologue insns if you use RTL for the | |
9358 prologue, or call @code{dwarf2out_def_cfa} and @code{dwarf2out_reg_save} | |
9359 as appropriate from @code{TARGET_ASM_FUNCTION_PROLOGUE} if you don't. | |
9360 @end defmac | |
9361 | |
9362 @defmac DWARF2_FRAME_INFO | |
9363 Define this macro to a nonzero value if GCC should always output | |
9364 Dwarf 2 frame information. If @code{TARGET_EXCEPT_UNWIND_INFO} | |
9365 (@pxref{Exception Region Output}) returns @code{UI_DWARF2}, and | |
9366 exceptions are enabled, GCC will output this information not matter | |
9367 how you define @code{DWARF2_FRAME_INFO}. | |
9368 @end defmac | |
9369 | |
9370 @hook TARGET_DEBUG_UNWIND_INFO | |
9371 This hook defines the mechanism that will be used for describing frame | |
9372 unwind information to the debugger. Normally the hook will return | |
9373 @code{UI_DWARF2} if DWARF 2 debug information is enabled, and | |
9374 return @code{UI_NONE} otherwise. | |
9375 | |
9376 A target may return @code{UI_DWARF2} even when DWARF 2 debug information | |
9377 is disabled in order to always output DWARF 2 frame information. | |
9378 | |
9379 A target may return @code{UI_TARGET} if it has ABI specified unwind tables. | |
9380 This will suppress generation of the normal debug frame unwind information. | |
9381 @end deftypefn | |
9382 | |
9383 @defmac DWARF2_ASM_LINE_DEBUG_INFO | |
9384 Define this macro to be a nonzero value if the assembler can generate Dwarf 2 | |
9385 line debug info sections. This will result in much more compact line number | |
9386 tables, and hence is desirable if it works. | |
9387 @end defmac | |
9388 | |
9389 @hook TARGET_WANT_DEBUG_PUB_SECTIONS | |
9390 | |
9391 @defmac ASM_OUTPUT_DWARF_DELTA (@var{stream}, @var{size}, @var{label1}, @var{label2}) | |
9392 A C statement to issue assembly directives that create a difference | |
9393 @var{lab1} minus @var{lab2}, using an integer of the given @var{size}. | |
9394 @end defmac | |
9395 | |
9396 @defmac ASM_OUTPUT_DWARF_VMS_DELTA (@var{stream}, @var{size}, @var{label1}, @var{label2}) | |
9397 A C statement to issue assembly directives that create a difference | |
9398 between the two given labels in system defined units, e.g. instruction | |
9399 slots on IA64 VMS, using an integer of the given size. | |
9400 @end defmac | |
9401 | |
9402 @defmac ASM_OUTPUT_DWARF_OFFSET (@var{stream}, @var{size}, @var{label}, @var{section}) | |
9403 A C statement to issue assembly directives that create a | |
9404 section-relative reference to the given @var{label}, using an integer of the | |
9405 given @var{size}. The label is known to be defined in the given @var{section}. | |
9406 @end defmac | |
9407 | |
9408 @defmac ASM_OUTPUT_DWARF_PCREL (@var{stream}, @var{size}, @var{label}) | |
9409 A C statement to issue assembly directives that create a self-relative | |
9410 reference to the given @var{label}, using an integer of the given @var{size}. | |
9411 @end defmac | |
9412 | |
9413 @defmac ASM_OUTPUT_DWARF_TABLE_REF (@var{label}) | |
9414 A C statement to issue assembly directives that create a reference to | |
9415 the DWARF table identifier @var{label} from the current section. This | |
9416 is used on some systems to avoid garbage collecting a DWARF table which | |
9417 is referenced by a function. | |
9418 @end defmac | |
9419 | |
9420 @hook TARGET_ASM_OUTPUT_DWARF_DTPREL | |
9421 If defined, this target hook is a function which outputs a DTP-relative | |
9422 reference to the given TLS symbol of the specified size. | |
9423 @end deftypefn | |
9424 | |
9425 @defmac PUT_SDB_@dots{} | |
9426 Define these macros to override the assembler syntax for the special | |
9427 SDB assembler directives. See @file{sdbout.c} for a list of these | |
9428 macros and their arguments. If the standard syntax is used, you need | |
9429 not define them yourself. | |
9430 @end defmac | |
9431 | |
9432 @defmac SDB_DELIM | |
9433 Some assemblers do not support a semicolon as a delimiter, even between | |
9434 SDB assembler directives. In that case, define this macro to be the | |
9435 delimiter to use (usually @samp{\n}). It is not necessary to define | |
9436 a new set of @code{PUT_SDB_@var{op}} macros if this is the only change | |
9437 required. | |
9438 @end defmac | |
9439 | |
9440 @defmac SDB_ALLOW_UNKNOWN_REFERENCES | |
9441 Define this macro to allow references to unknown structure, | |
9442 union, or enumeration tags to be emitted. Standard COFF does not | |
9443 allow handling of unknown references, MIPS ECOFF has support for | |
9444 it. | |
9445 @end defmac | |
9446 | |
9447 @defmac SDB_ALLOW_FORWARD_REFERENCES | |
9448 Define this macro to allow references to structure, union, or | |
9449 enumeration tags that have not yet been seen to be handled. Some | |
9450 assemblers choke if forward tags are used, while some require it. | |
9451 @end defmac | |
9452 | |
9453 @defmac SDB_OUTPUT_SOURCE_LINE (@var{stream}, @var{line}) | |
9454 A C statement to output SDB debugging information before code for line | |
9455 number @var{line} of the current source file to the stdio stream | |
9456 @var{stream}. The default is to emit an @code{.ln} directive. | |
9457 @end defmac | |
9458 | |
9459 @need 2000 | |
9460 @node VMS Debug | |
9461 @subsection Macros for VMS Debug Format | |
9462 | |
9463 @c prevent bad page break with this line | |
9464 Here are macros for VMS debug format. | |
9465 | |
9466 @defmac VMS_DEBUGGING_INFO | |
9467 Define this macro if GCC should produce debugging output for VMS | |
9468 in response to the @option{-g} option. The default behavior for VMS | |
9469 is to generate minimal debug info for a traceback in the absence of | |
9470 @option{-g} unless explicitly overridden with @option{-g0}. This | |
9471 behavior is controlled by @code{TARGET_OPTION_OPTIMIZATION} and | |
9472 @code{TARGET_OPTION_OVERRIDE}. | |
9473 @end defmac | |
9474 | |
9475 @node Floating Point | |
9476 @section Cross Compilation and Floating Point | |
9477 @cindex cross compilation and floating point | |
9478 @cindex floating point and cross compilation | |
9479 | |
9480 While all modern machines use twos-complement representation for integers, | |
9481 there are a variety of representations for floating point numbers. This | |
9482 means that in a cross-compiler the representation of floating point numbers | |
9483 in the compiled program may be different from that used in the machine | |
9484 doing the compilation. | |
9485 | |
9486 Because different representation systems may offer different amounts of | |
9487 range and precision, all floating point constants must be represented in | |
9488 the target machine's format. Therefore, the cross compiler cannot | |
9489 safely use the host machine's floating point arithmetic; it must emulate | |
9490 the target's arithmetic. To ensure consistency, GCC always uses | |
9491 emulation to work with floating point values, even when the host and | |
9492 target floating point formats are identical. | |
9493 | |
9494 The following macros are provided by @file{real.h} for the compiler to | |
9495 use. All parts of the compiler which generate or optimize | |
9496 floating-point calculations must use these macros. They may evaluate | |
9497 their operands more than once, so operands must not have side effects. | |
9498 | |
9499 @defmac REAL_VALUE_TYPE | |
9500 The C data type to be used to hold a floating point value in the target | |
9501 machine's format. Typically this is a @code{struct} containing an | |
9502 array of @code{HOST_WIDE_INT}, but all code should treat it as an opaque | |
9503 quantity. | |
9504 @end defmac | |
9505 | |
9506 @deftypefn Macro int REAL_VALUES_EQUAL (REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y}) | |
9507 Compares for equality the two values, @var{x} and @var{y}. If the target | |
9508 floating point format supports negative zeroes and/or NaNs, | |
9509 @samp{REAL_VALUES_EQUAL (-0.0, 0.0)} is true, and | |
9510 @samp{REAL_VALUES_EQUAL (NaN, NaN)} is false. | |
9511 @end deftypefn | |
9512 | |
9513 @deftypefn Macro int REAL_VALUES_LESS (REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y}) | |
9514 Tests whether @var{x} is less than @var{y}. | |
9515 @end deftypefn | |
9516 | |
9517 @deftypefn Macro HOST_WIDE_INT REAL_VALUE_FIX (REAL_VALUE_TYPE @var{x}) | |
9518 Truncates @var{x} to a signed integer, rounding toward zero. | |
9519 @end deftypefn | |
9520 | |
9521 @deftypefn Macro {unsigned HOST_WIDE_INT} REAL_VALUE_UNSIGNED_FIX (REAL_VALUE_TYPE @var{x}) | |
9522 Truncates @var{x} to an unsigned integer, rounding toward zero. If | |
9523 @var{x} is negative, returns zero. | |
9524 @end deftypefn | |
9525 | |
9526 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ATOF (const char *@var{string}, enum machine_mode @var{mode}) | |
9527 Converts @var{string} into a floating point number in the target machine's | |
9528 representation for mode @var{mode}. This routine can handle both | |
9529 decimal and hexadecimal floating point constants, using the syntax | |
9530 defined by the C language for both. | |
9531 @end deftypefn | |
9532 | |
9533 @deftypefn Macro int REAL_VALUE_NEGATIVE (REAL_VALUE_TYPE @var{x}) | |
9534 Returns 1 if @var{x} is negative (including negative zero), 0 otherwise. | |
9535 @end deftypefn | |
9536 | |
9537 @deftypefn Macro int REAL_VALUE_ISINF (REAL_VALUE_TYPE @var{x}) | |
9538 Determines whether @var{x} represents infinity (positive or negative). | |
9539 @end deftypefn | |
9540 | |
9541 @deftypefn Macro int REAL_VALUE_ISNAN (REAL_VALUE_TYPE @var{x}) | |
9542 Determines whether @var{x} represents a ``NaN'' (not-a-number). | |
9543 @end deftypefn | |
9544 | |
9545 @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}) | |
9546 Calculates an arithmetic operation on the two floating point values | |
9547 @var{x} and @var{y}, storing the result in @var{output} (which must be a | |
9548 variable). | |
9549 | |
9550 The operation to be performed is specified by @var{code}. Only the | |
9551 following codes are supported: @code{PLUS_EXPR}, @code{MINUS_EXPR}, | |
9552 @code{MULT_EXPR}, @code{RDIV_EXPR}, @code{MAX_EXPR}, @code{MIN_EXPR}. | |
9553 | |
9554 If @code{REAL_ARITHMETIC} is asked to evaluate division by zero and the | |
9555 target's floating point format cannot represent infinity, it will call | |
9556 @code{abort}. Callers should check for this situation first, using | |
9557 @code{MODE_HAS_INFINITIES}. @xref{Storage Layout}. | |
9558 @end deftypefn | |
9559 | |
9560 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_NEGATE (REAL_VALUE_TYPE @var{x}) | |
9561 Returns the negative of the floating point value @var{x}. | |
9562 @end deftypefn | |
9563 | |
9564 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ABS (REAL_VALUE_TYPE @var{x}) | |
9565 Returns the absolute value of @var{x}. | |
9566 @end deftypefn | |
9567 | |
9568 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_TRUNCATE (REAL_VALUE_TYPE @var{mode}, enum machine_mode @var{x}) | |
9569 Truncates the floating point value @var{x} to fit in @var{mode}. The | |
9570 return value is still a full-size @code{REAL_VALUE_TYPE}, but it has an | |
9571 appropriate bit pattern to be output as a floating constant whose | |
9572 precision accords with mode @var{mode}. | |
9573 @end deftypefn | |
9574 | |
9575 @deftypefn Macro void REAL_VALUE_TO_INT (HOST_WIDE_INT @var{low}, HOST_WIDE_INT @var{high}, REAL_VALUE_TYPE @var{x}) | |
9576 Converts a floating point value @var{x} into a double-precision integer | |
9577 which is then stored into @var{low} and @var{high}. If the value is not | |
9578 integral, it is truncated. | |
9579 @end deftypefn | |
9580 | |
9581 @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}) | |
9582 Converts a double-precision integer found in @var{low} and @var{high}, | |
9583 into a floating point value which is then stored into @var{x}. The | |
9584 value is truncated to fit in mode @var{mode}. | |
9585 @end deftypefn | |
9586 | |
9587 @node Mode Switching | |
9588 @section Mode Switching Instructions | |
9589 @cindex mode switching | |
9590 The following macros control mode switching optimizations: | |
9591 | |
9592 @defmac OPTIMIZE_MODE_SWITCHING (@var{entity}) | |
9593 Define this macro if the port needs extra instructions inserted for mode | |
9594 switching in an optimizing compilation. | |
9595 | |
9596 For an example, the SH4 can perform both single and double precision | |
9597 floating point operations, but to perform a single precision operation, | |
9598 the FPSCR PR bit has to be cleared, while for a double precision | |
9599 operation, this bit has to be set. Changing the PR bit requires a general | |
9600 purpose register as a scratch register, hence these FPSCR sets have to | |
9601 be inserted before reload, i.e.@: you can't put this into instruction emitting | |
9602 or @code{TARGET_MACHINE_DEPENDENT_REORG}. | |
9603 | |
9604 You can have multiple entities that are mode-switched, and select at run time | |
9605 which entities actually need it. @code{OPTIMIZE_MODE_SWITCHING} should | |
9606 return nonzero for any @var{entity} that needs mode-switching. | |
9607 If you define this macro, you also have to define | |
9608 @code{NUM_MODES_FOR_MODE_SWITCHING}, @code{MODE_NEEDED}, | |
9609 @code{MODE_PRIORITY_TO_MODE} and @code{EMIT_MODE_SET}. | |
9610 @code{MODE_AFTER}, @code{MODE_ENTRY}, and @code{MODE_EXIT} | |
9611 are optional. | |
9612 @end defmac | |
9613 | |
9614 @defmac NUM_MODES_FOR_MODE_SWITCHING | |
9615 If you define @code{OPTIMIZE_MODE_SWITCHING}, you have to define this as | |
9616 initializer for an array of integers. Each initializer element | |
9617 N refers to an entity that needs mode switching, and specifies the number | |
9618 of different modes that might need to be set for this entity. | |
9619 The position of the initializer in the initializer---starting counting at | |
9620 zero---determines the integer that is used to refer to the mode-switched | |
9621 entity in question. | |
9622 In macros that take mode arguments / yield a mode result, modes are | |
9623 represented as numbers 0 @dots{} N @minus{} 1. N is used to specify that no mode | |
9624 switch is needed / supplied. | |
9625 @end defmac | |
9626 | |
9627 @defmac MODE_NEEDED (@var{entity}, @var{insn}) | |
9628 @var{entity} is an integer specifying a mode-switched entity. If | |
9629 @code{OPTIMIZE_MODE_SWITCHING} is defined, you must define this macro to | |
9630 return an integer value not larger than the corresponding element in | |
9631 @code{NUM_MODES_FOR_MODE_SWITCHING}, to denote the mode that @var{entity} must | |
9632 be switched into prior to the execution of @var{insn}. | |
9633 @end defmac | |
9634 | |
9635 @defmac MODE_AFTER (@var{mode}, @var{insn}) | |
9636 If this macro is defined, it is evaluated for every @var{insn} during | |
9637 mode switching. It determines the mode that an insn results in (if | |
9638 different from the incoming mode). | |
9639 @end defmac | |
9640 | |
9641 @defmac MODE_ENTRY (@var{entity}) | |
9642 If this macro is defined, it is evaluated for every @var{entity} that needs | |
9643 mode switching. It should evaluate to an integer, which is a mode that | |
9644 @var{entity} is assumed to be switched to at function entry. If @code{MODE_ENTRY} | |
9645 is defined then @code{MODE_EXIT} must be defined. | |
9646 @end defmac | |
9647 | |
9648 @defmac MODE_EXIT (@var{entity}) | |
9649 If this macro is defined, it is evaluated for every @var{entity} that needs | |
9650 mode switching. It should evaluate to an integer, which is a mode that | |
9651 @var{entity} is assumed to be switched to at function exit. If @code{MODE_EXIT} | |
9652 is defined then @code{MODE_ENTRY} must be defined. | |
9653 @end defmac | |
9654 | |
9655 @defmac MODE_PRIORITY_TO_MODE (@var{entity}, @var{n}) | |
9656 This macro specifies the order in which modes for @var{entity} are processed. | |
9657 0 is the highest priority, @code{NUM_MODES_FOR_MODE_SWITCHING[@var{entity}] - 1} the | |
9658 lowest. The value of the macro should be an integer designating a mode | |
9659 for @var{entity}. For any fixed @var{entity}, @code{mode_priority_to_mode} | |
9660 (@var{entity}, @var{n}) shall be a bijection in 0 @dots{} | |
9661 @code{num_modes_for_mode_switching[@var{entity}] - 1}. | |
9662 @end defmac | |
9663 | |
9664 @defmac EMIT_MODE_SET (@var{entity}, @var{mode}, @var{hard_regs_live}) | |
9665 Generate one or more insns to set @var{entity} to @var{mode}. | |
9666 @var{hard_reg_live} is the set of hard registers live at the point where | |
9667 the insn(s) are to be inserted. | |
9668 @end defmac | |
9669 | |
9670 @node Target Attributes | |
9671 @section Defining target-specific uses of @code{__attribute__} | |
9672 @cindex target attributes | |
9673 @cindex machine attributes | |
9674 @cindex attributes, target-specific | |
9675 | |
9676 Target-specific attributes may be defined for functions, data and types. | |
9677 These are described using the following target hooks; they also need to | |
9678 be documented in @file{extend.texi}. | |
9679 | |
9680 @hook TARGET_ATTRIBUTE_TABLE | |
9681 If defined, this target hook points to an array of @samp{struct | |
9682 attribute_spec} (defined in @file{tree.h}) specifying the machine | |
9683 specific attributes for this target and some of the restrictions on the | |
9684 entities to which these attributes are applied and the arguments they | |
9685 take. | |
9686 @end deftypevr | |
9687 | |
9688 @hook TARGET_ATTRIBUTE_TAKES_IDENTIFIER_P | |
9689 If defined, this target hook is a function which returns true if the | |
9690 machine-specific attribute named @var{name} expects an identifier | |
9691 given as its first argument to be passed on as a plain identifier, not | |
9692 subjected to name lookup. If this is not defined, the default is | |
9693 false for all machine-specific attributes. | |
9694 @end deftypefn | |
9695 | |
9696 @hook TARGET_COMP_TYPE_ATTRIBUTES | |
9697 If defined, this target hook is a function which returns zero if the attributes on | |
9698 @var{type1} and @var{type2} are incompatible, one if they are compatible, | |
9699 and two if they are nearly compatible (which causes a warning to be | |
9700 generated). If this is not defined, machine-specific attributes are | |
9701 supposed always to be compatible. | |
9702 @end deftypefn | |
9703 | |
9704 @hook TARGET_SET_DEFAULT_TYPE_ATTRIBUTES | |
9705 If defined, this target hook is a function which assigns default attributes to | |
9706 the newly defined @var{type}. | |
9707 @end deftypefn | |
9708 | |
9709 @hook TARGET_MERGE_TYPE_ATTRIBUTES | |
9710 Define this target hook if the merging of type attributes needs special | |
9711 handling. If defined, the result is a list of the combined | |
9712 @code{TYPE_ATTRIBUTES} of @var{type1} and @var{type2}. It is assumed | |
9713 that @code{comptypes} has already been called and returned 1. This | |
9714 function may call @code{merge_attributes} to handle machine-independent | |
9715 merging. | |
9716 @end deftypefn | |
9717 | |
9718 @hook TARGET_MERGE_DECL_ATTRIBUTES | |
9719 Define this target hook if the merging of decl attributes needs special | |
9720 handling. If defined, the result is a list of the combined | |
9721 @code{DECL_ATTRIBUTES} of @var{olddecl} and @var{newdecl}. | |
9722 @var{newdecl} is a duplicate declaration of @var{olddecl}. Examples of | |
9723 when this is needed are when one attribute overrides another, or when an | |
9724 attribute is nullified by a subsequent definition. This function may | |
9725 call @code{merge_attributes} to handle machine-independent merging. | |
9726 | |
9727 @findex TARGET_DLLIMPORT_DECL_ATTRIBUTES | |
9728 If the only target-specific handling you require is @samp{dllimport} | |
9729 for Microsoft Windows targets, you should define the macro | |
9730 @code{TARGET_DLLIMPORT_DECL_ATTRIBUTES} to @code{1}. The compiler | |
9731 will then define a function called | |
9732 @code{merge_dllimport_decl_attributes} which can then be defined as | |
9733 the expansion of @code{TARGET_MERGE_DECL_ATTRIBUTES}. You can also | |
9734 add @code{handle_dll_attribute} in the attribute table for your port | |
9735 to perform initial processing of the @samp{dllimport} and | |
9736 @samp{dllexport} attributes. This is done in @file{i386/cygwin.h} and | |
9737 @file{i386/i386.c}, for example. | |
9738 @end deftypefn | |
9739 | |
9740 @hook TARGET_VALID_DLLIMPORT_ATTRIBUTE_P | |
9741 | |
9742 @defmac TARGET_DECLSPEC | |
9743 Define this macro to a nonzero value if you want to treat | |
9744 @code{__declspec(X)} as equivalent to @code{__attribute((X))}. By | |
9745 default, this behavior is enabled only for targets that define | |
9746 @code{TARGET_DLLIMPORT_DECL_ATTRIBUTES}. The current implementation | |
9747 of @code{__declspec} is via a built-in macro, but you should not rely | |
9748 on this implementation detail. | |
9749 @end defmac | |
9750 | |
9751 @hook TARGET_INSERT_ATTRIBUTES | |
9752 Define this target hook if you want to be able to add attributes to a decl | |
9753 when it is being created. This is normally useful for back ends which | |
9754 wish to implement a pragma by using the attributes which correspond to | |
9755 the pragma's effect. The @var{node} argument is the decl which is being | |
9756 created. The @var{attr_ptr} argument is a pointer to the attribute list | |
9757 for this decl. The list itself should not be modified, since it may be | |
9758 shared with other decls, but attributes may be chained on the head of | |
9759 the list and @code{*@var{attr_ptr}} modified to point to the new | |
9760 attributes, or a copy of the list may be made if further changes are | |
9761 needed. | |
9762 @end deftypefn | |
9763 | |
9764 @hook TARGET_FUNCTION_ATTRIBUTE_INLINABLE_P | |
9765 @cindex inlining | |
9766 This target hook returns @code{true} if it is ok to inline @var{fndecl} | |
9767 into the current function, despite its having target-specific | |
9768 attributes, @code{false} otherwise. By default, if a function has a | |
9769 target specific attribute attached to it, it will not be inlined. | |
9770 @end deftypefn | |
9771 | |
9772 @hook TARGET_OPTION_VALID_ATTRIBUTE_P | |
9773 This hook is called to parse the @code{attribute(option("..."))}, and | |
9774 it allows the function to set different target machine compile time | |
9775 options for the current function that might be different than the | |
9776 options specified on the command line. The hook should return | |
9777 @code{true} if the options are valid. | |
9778 | |
9779 The hook should set the @var{DECL_FUNCTION_SPECIFIC_TARGET} field in | |
9780 the function declaration to hold a pointer to a target specific | |
9781 @var{struct cl_target_option} structure. | |
9782 @end deftypefn | |
9783 | |
9784 @hook TARGET_OPTION_SAVE | |
9785 This hook is called to save any additional target specific information | |
9786 in the @var{struct cl_target_option} structure for function specific | |
9787 options. | |
9788 @xref{Option file format}. | |
9789 @end deftypefn | |
9790 | |
9791 @hook TARGET_OPTION_RESTORE | |
9792 This hook is called to restore any additional target specific | |
9793 information in the @var{struct cl_target_option} structure for | |
9794 function specific options. | |
9795 @end deftypefn | |
9796 | |
9797 @hook TARGET_OPTION_PRINT | |
9798 This hook is called to print any additional target specific | |
9799 information in the @var{struct cl_target_option} structure for | |
9800 function specific options. | |
9801 @end deftypefn | |
9802 | |
9803 @hook TARGET_OPTION_PRAGMA_PARSE | |
9804 This target hook parses the options for @code{#pragma GCC option} to | |
9805 set the machine specific options for functions that occur later in the | |
9806 input stream. The options should be the same as handled by the | |
9807 @code{TARGET_OPTION_VALID_ATTRIBUTE_P} hook. | |
9808 @end deftypefn | |
9809 | |
9810 @hook TARGET_OPTION_OVERRIDE | |
9811 Sometimes certain combinations of command options do not make sense on | |
9812 a particular target machine. You can override the hook | |
9813 @code{TARGET_OPTION_OVERRIDE} to take account of this. This hooks is called | |
9814 once just after all the command options have been parsed. | |
9815 | |
9816 Don't use this hook to turn on various extra optimizations for | |
9817 @option{-O}. That is what @code{TARGET_OPTION_OPTIMIZATION} is for. | |
9818 | |
9819 If you need to do something whenever the optimization level is | |
9820 changed via the optimize attribute or pragma, see | |
9821 @code{TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE} | |
9822 @end deftypefn | |
9823 | |
9824 @hook TARGET_CAN_INLINE_P | |
9825 This target hook returns @code{false} if the @var{caller} function | |
9826 cannot inline @var{callee}, based on target specific information. By | |
9827 default, inlining is not allowed if the callee function has function | |
9828 specific target options and the caller does not use the same options. | |
9829 @end deftypefn | |
9830 | |
9831 @node Emulated TLS | |
9832 @section Emulating TLS | |
9833 @cindex Emulated TLS | |
9834 | |
9835 For targets whose psABI does not provide Thread Local Storage via | |
9836 specific relocations and instruction sequences, an emulation layer is | |
9837 used. A set of target hooks allows this emulation layer to be | |
9838 configured for the requirements of a particular target. For instance | |
9839 the psABI may in fact specify TLS support in terms of an emulation | |
9840 layer. | |
9841 | |
9842 The emulation layer works by creating a control object for every TLS | |
9843 object. To access the TLS object, a lookup function is provided | |
9844 which, when given the address of the control object, will return the | |
9845 address of the current thread's instance of the TLS object. | |
9846 | |
9847 @hook TARGET_EMUTLS_GET_ADDRESS | |
9848 Contains the name of the helper function that uses a TLS control | |
9849 object to locate a TLS instance. The default causes libgcc's | |
9850 emulated TLS helper function to be used. | |
9851 @end deftypevr | |
9852 | |
9853 @hook TARGET_EMUTLS_REGISTER_COMMON | |
9854 Contains the name of the helper function that should be used at | |
9855 program startup to register TLS objects that are implicitly | |
9856 initialized to zero. If this is @code{NULL}, all TLS objects will | |
9857 have explicit initializers. The default causes libgcc's emulated TLS | |
9858 registration function to be used. | |
9859 @end deftypevr | |
9860 | |
9861 @hook TARGET_EMUTLS_VAR_SECTION | |
9862 Contains the name of the section in which TLS control variables should | |
9863 be placed. The default of @code{NULL} allows these to be placed in | |
9864 any section. | |
9865 @end deftypevr | |
9866 | |
9867 @hook TARGET_EMUTLS_TMPL_SECTION | |
9868 Contains the name of the section in which TLS initializers should be | |
9869 placed. The default of @code{NULL} allows these to be placed in any | |
9870 section. | |
9871 @end deftypevr | |
9872 | |
9873 @hook TARGET_EMUTLS_VAR_PREFIX | |
9874 Contains the prefix to be prepended to TLS control variable names. | |
9875 The default of @code{NULL} uses a target-specific prefix. | |
9876 @end deftypevr | |
9877 | |
9878 @hook TARGET_EMUTLS_TMPL_PREFIX | |
9879 Contains the prefix to be prepended to TLS initializer objects. The | |
9880 default of @code{NULL} uses a target-specific prefix. | |
9881 @end deftypevr | |
9882 | |
9883 @hook TARGET_EMUTLS_VAR_FIELDS | |
9884 Specifies a function that generates the FIELD_DECLs for a TLS control | |
9885 object type. @var{type} is the RECORD_TYPE the fields are for and | |
9886 @var{name} should be filled with the structure tag, if the default of | |
9887 @code{__emutls_object} is unsuitable. The default creates a type suitable | |
9888 for libgcc's emulated TLS function. | |
9889 @end deftypefn | |
9890 | |
9891 @hook TARGET_EMUTLS_VAR_INIT | |
9892 Specifies a function that generates the CONSTRUCTOR to initialize a | |
9893 TLS control object. @var{var} is the TLS control object, @var{decl} | |
9894 is the TLS object and @var{tmpl_addr} is the address of the | |
9895 initializer. The default initializes libgcc's emulated TLS control object. | |
9896 @end deftypefn | |
9897 | |
9898 @hook TARGET_EMUTLS_VAR_ALIGN_FIXED | |
9899 Specifies whether the alignment of TLS control variable objects is | |
9900 fixed and should not be increased as some backends may do to optimize | |
9901 single objects. The default is false. | |
9902 @end deftypevr | |
9903 | |
9904 @hook TARGET_EMUTLS_DEBUG_FORM_TLS_ADDRESS | |
9905 Specifies whether a DWARF @code{DW_OP_form_tls_address} location descriptor | |
9906 may be used to describe emulated TLS control objects. | |
9907 @end deftypevr | |
9908 | |
9909 @node MIPS Coprocessors | |
9910 @section Defining coprocessor specifics for MIPS targets. | |
9911 @cindex MIPS coprocessor-definition macros | |
9912 | |
9913 The MIPS specification allows MIPS implementations to have as many as 4 | |
9914 coprocessors, each with as many as 32 private registers. GCC supports | |
9915 accessing these registers and transferring values between the registers | |
9916 and memory using asm-ized variables. For example: | |
9917 | |
9918 @smallexample | |
9919 register unsigned int cp0count asm ("c0r1"); | |
9920 unsigned int d; | |
9921 | |
9922 d = cp0count + 3; | |
9923 @end smallexample | |
9924 | |
9925 (``c0r1'' is the default name of register 1 in coprocessor 0; alternate | |
9926 names may be added as described below, or the default names may be | |
9927 overridden entirely in @code{SUBTARGET_CONDITIONAL_REGISTER_USAGE}.) | |
9928 | |
9929 Coprocessor registers are assumed to be epilogue-used; sets to them will | |
9930 be preserved even if it does not appear that the register is used again | |
9931 later in the function. | |
9932 | |
9933 Another note: according to the MIPS spec, coprocessor 1 (if present) is | |
9934 the FPU@. One accesses COP1 registers through standard mips | |
9935 floating-point support; they are not included in this mechanism. | |
9936 | |
9937 There is one macro used in defining the MIPS coprocessor interface which | |
9938 you may want to override in subtargets; it is described below. | |
9939 | |
9940 @defmac ALL_COP_ADDITIONAL_REGISTER_NAMES | |
9941 A comma-separated list (with leading comma) of pairs describing the | |
9942 alternate names of coprocessor registers. The format of each entry should be | |
9943 @smallexample | |
9944 @{ @var{alternatename}, @var{register_number}@} | |
9945 @end smallexample | |
9946 Default: empty. | |
9947 @end defmac | |
9948 | |
9949 @node PCH Target | |
9950 @section Parameters for Precompiled Header Validity Checking | |
9951 @cindex parameters, precompiled headers | |
9952 | |
9953 @hook TARGET_GET_PCH_VALIDITY | |
9954 This hook returns a pointer to the data needed by | |
9955 @code{TARGET_PCH_VALID_P} and sets | |
9956 @samp{*@var{sz}} to the size of the data in bytes. | |
9957 @end deftypefn | |
9958 | |
9959 @hook TARGET_PCH_VALID_P | |
9960 This hook checks whether the options used to create a PCH file are | |
9961 compatible with the current settings. It returns @code{NULL} | |
9962 if so and a suitable error message if not. Error messages will | |
9963 be presented to the user and must be localized using @samp{_(@var{msg})}. | |
9964 | |
9965 @var{data} is the data that was returned by @code{TARGET_GET_PCH_VALIDITY} | |
9966 when the PCH file was created and @var{sz} is the size of that data in bytes. | |
9967 It's safe to assume that the data was created by the same version of the | |
9968 compiler, so no format checking is needed. | |
9969 | |
9970 The default definition of @code{default_pch_valid_p} should be | |
9971 suitable for most targets. | |
9972 @end deftypefn | |
9973 | |
9974 @hook TARGET_CHECK_PCH_TARGET_FLAGS | |
9975 If this hook is nonnull, the default implementation of | |
9976 @code{TARGET_PCH_VALID_P} will use it to check for compatible values | |
9977 of @code{target_flags}. @var{pch_flags} specifies the value that | |
9978 @code{target_flags} had when the PCH file was created. The return | |
9979 value is the same as for @code{TARGET_PCH_VALID_P}. | |
9980 @end deftypefn | |
9981 | |
9982 @node C++ ABI | |
9983 @section C++ ABI parameters | |
9984 @cindex parameters, c++ abi | |
9985 | |
9986 @hook TARGET_CXX_GUARD_TYPE | |
9987 Define this hook to override the integer type used for guard variables. | |
9988 These are used to implement one-time construction of static objects. The | |
9989 default is long_long_integer_type_node. | |
9990 @end deftypefn | |
9991 | |
9992 @hook TARGET_CXX_GUARD_MASK_BIT | |
9993 This hook determines how guard variables are used. It should return | |
9994 @code{false} (the default) if the first byte should be used. A return value of | |
9995 @code{true} indicates that only the least significant bit should be used. | |
9996 @end deftypefn | |
9997 | |
9998 @hook TARGET_CXX_GET_COOKIE_SIZE | |
9999 This hook returns the size of the cookie to use when allocating an array | |
10000 whose elements have the indicated @var{type}. Assumes that it is already | |
10001 known that a cookie is needed. The default is | |
10002 @code{max(sizeof (size_t), alignof(type))}, as defined in section 2.7 of the | |
10003 IA64/Generic C++ ABI@. | |
10004 @end deftypefn | |
10005 | |
10006 @hook TARGET_CXX_COOKIE_HAS_SIZE | |
10007 This hook should return @code{true} if the element size should be stored in | |
10008 array cookies. The default is to return @code{false}. | |
10009 @end deftypefn | |
10010 | |
10011 @hook TARGET_CXX_IMPORT_EXPORT_CLASS | |
10012 If defined by a backend this hook allows the decision made to export | |
10013 class @var{type} to be overruled. Upon entry @var{import_export} | |
10014 will contain 1 if the class is going to be exported, @minus{}1 if it is going | |
10015 to be imported and 0 otherwise. This function should return the | |
10016 modified value and perform any other actions necessary to support the | |
10017 backend's targeted operating system. | |
10018 @end deftypefn | |
10019 | |
10020 @hook TARGET_CXX_CDTOR_RETURNS_THIS | |
10021 This hook should return @code{true} if constructors and destructors return | |
10022 the address of the object created/destroyed. The default is to return | |
10023 @code{false}. | |
10024 @end deftypefn | |
10025 | |
10026 @hook TARGET_CXX_KEY_METHOD_MAY_BE_INLINE | |
10027 This hook returns true if the key method for a class (i.e., the method | |
10028 which, if defined in the current translation unit, causes the virtual | |
10029 table to be emitted) may be an inline function. Under the standard | |
10030 Itanium C++ ABI the key method may be an inline function so long as | |
10031 the function is not declared inline in the class definition. Under | |
10032 some variants of the ABI, an inline function can never be the key | |
10033 method. The default is to return @code{true}. | |
10034 @end deftypefn | |
10035 | |
10036 @hook TARGET_CXX_DETERMINE_CLASS_DATA_VISIBILITY | |
10037 | |
10038 @hook TARGET_CXX_CLASS_DATA_ALWAYS_COMDAT | |
10039 This hook returns true (the default) if virtual tables and other | |
10040 similar implicit class data objects are always COMDAT if they have | |
10041 external linkage. If this hook returns false, then class data for | |
10042 classes whose virtual table will be emitted in only one translation | |
10043 unit will not be COMDAT. | |
10044 @end deftypefn | |
10045 | |
10046 @hook TARGET_CXX_LIBRARY_RTTI_COMDAT | |
10047 This hook returns true (the default) if the RTTI information for | |
10048 the basic types which is defined in the C++ runtime should always | |
10049 be COMDAT, false if it should not be COMDAT. | |
10050 @end deftypefn | |
10051 | |
10052 @hook TARGET_CXX_USE_AEABI_ATEXIT | |
10053 This hook returns true if @code{__aeabi_atexit} (as defined by the ARM EABI) | |
10054 should be used to register static destructors when @option{-fuse-cxa-atexit} | |
10055 is in effect. The default is to return false to use @code{__cxa_atexit}. | |
10056 @end deftypefn | |
10057 | |
10058 @hook TARGET_CXX_USE_ATEXIT_FOR_CXA_ATEXIT | |
10059 This hook returns true if the target @code{atexit} function can be used | |
10060 in the same manner as @code{__cxa_atexit} to register C++ static | |
10061 destructors. This requires that @code{atexit}-registered functions in | |
10062 shared libraries are run in the correct order when the libraries are | |
10063 unloaded. The default is to return false. | |
10064 @end deftypefn | |
10065 | |
10066 @hook TARGET_CXX_ADJUST_CLASS_AT_DEFINITION | |
10067 | |
10068 @node Named Address Spaces | |
10069 @section Adding support for named address spaces | |
10070 @cindex named address spaces | |
10071 | |
10072 The draft technical report of the ISO/IEC JTC1 S22 WG14 N1275 | |
10073 standards committee, @cite{Programming Languages - C - Extensions to | |
10074 support embedded processors}, specifies a syntax for embedded | |
10075 processors to specify alternate address spaces. You can configure a | |
10076 GCC port to support section 5.1 of the draft report to add support for | |
10077 address spaces other than the default address space. These address | |
10078 spaces are new keywords that are similar to the @code{volatile} and | |
10079 @code{const} type attributes. | |
10080 | |
10081 Pointers to named address spaces can have a different size than | |
10082 pointers to the generic address space. | |
10083 | |
10084 For example, the SPU port uses the @code{__ea} address space to refer | |
10085 to memory in the host processor, rather than memory local to the SPU | |
10086 processor. Access to memory in the @code{__ea} address space involves | |
10087 issuing DMA operations to move data between the host processor and the | |
10088 local processor memory address space. Pointers in the @code{__ea} | |
10089 address space are either 32 bits or 64 bits based on the | |
10090 @option{-mea32} or @option{-mea64} switches (native SPU pointers are | |
10091 always 32 bits). | |
10092 | |
10093 Internally, address spaces are represented as a small integer in the | |
10094 range 0 to 15 with address space 0 being reserved for the generic | |
10095 address space. | |
10096 | |
10097 To register a named address space qualifier keyword with the C front end, | |
10098 the target may call the @code{c_register_addr_space} routine. For example, | |
10099 the SPU port uses the following to declare @code{__ea} as the keyword for | |
10100 named address space #1: | |
10101 @smallexample | |
10102 #define ADDR_SPACE_EA 1 | |
10103 c_register_addr_space ("__ea", ADDR_SPACE_EA); | |
10104 @end smallexample | |
10105 | |
10106 @hook TARGET_ADDR_SPACE_POINTER_MODE | |
10107 Define this to return the machine mode to use for pointers to | |
10108 @var{address_space} if the target supports named address spaces. | |
10109 The default version of this hook returns @code{ptr_mode} for the | |
10110 generic address space only. | |
10111 @end deftypefn | |
10112 | |
10113 @hook TARGET_ADDR_SPACE_ADDRESS_MODE | |
10114 Define this to return the machine mode to use for addresses in | |
10115 @var{address_space} if the target supports named address spaces. | |
10116 The default version of this hook returns @code{Pmode} for the | |
10117 generic address space only. | |
10118 @end deftypefn | |
10119 | |
10120 @hook TARGET_ADDR_SPACE_VALID_POINTER_MODE | |
10121 Define this to return nonzero if the port can handle pointers | |
10122 with machine mode @var{mode} to address space @var{as}. This target | |
10123 hook is the same as the @code{TARGET_VALID_POINTER_MODE} target hook, | |
10124 except that it includes explicit named address space support. The default | |
10125 version of this hook returns true for the modes returned by either the | |
10126 @code{TARGET_ADDR_SPACE_POINTER_MODE} or @code{TARGET_ADDR_SPACE_ADDRESS_MODE} | |
10127 target hooks for the given address space. | |
10128 @end deftypefn | |
10129 | |
10130 @hook TARGET_ADDR_SPACE_LEGITIMATE_ADDRESS_P | |
10131 Define this to return true if @var{exp} is a valid address for mode | |
10132 @var{mode} in the named address space @var{as}. The @var{strict} | |
10133 parameter says whether strict addressing is in effect after reload has | |
10134 finished. This target hook is the same as the | |
10135 @code{TARGET_LEGITIMATE_ADDRESS_P} target hook, except that it includes | |
10136 explicit named address space support. | |
10137 @end deftypefn | |
10138 | |
10139 @hook TARGET_ADDR_SPACE_LEGITIMIZE_ADDRESS | |
10140 Define this to modify an invalid address @var{x} to be a valid address | |
10141 with mode @var{mode} in the named address space @var{as}. This target | |
10142 hook is the same as the @code{TARGET_LEGITIMIZE_ADDRESS} target hook, | |
10143 except that it includes explicit named address space support. | |
10144 @end deftypefn | |
10145 | |
10146 @hook TARGET_ADDR_SPACE_SUBSET_P | |
10147 Define this to return whether the @var{subset} named address space is | |
10148 contained within the @var{superset} named address space. Pointers to | |
10149 a named address space that is a subset of another named address space | |
10150 will be converted automatically without a cast if used together in | |
10151 arithmetic operations. Pointers to a superset address space can be | |
10152 converted to pointers to a subset address space via explicit casts. | |
10153 @end deftypefn | |
10154 | |
10155 @hook TARGET_ADDR_SPACE_CONVERT | |
10156 Define this to convert the pointer expression represented by the RTL | |
10157 @var{op} with type @var{from_type} that points to a named address | |
10158 space to a new pointer expression with type @var{to_type} that points | |
10159 to a different named address space. When this hook it called, it is | |
10160 guaranteed that one of the two address spaces is a subset of the other, | |
10161 as determined by the @code{TARGET_ADDR_SPACE_SUBSET_P} target hook. | |
10162 @end deftypefn | |
10163 | |
10164 @node Misc | |
10165 @section Miscellaneous Parameters | |
10166 @cindex parameters, miscellaneous | |
10167 | |
10168 @c prevent bad page break with this line | |
10169 Here are several miscellaneous parameters. | |
10170 | |
10171 @defmac HAS_LONG_COND_BRANCH | |
10172 Define this boolean macro to indicate whether or not your architecture | |
10173 has conditional branches that can span all of memory. It is used in | |
10174 conjunction with an optimization that partitions hot and cold basic | |
10175 blocks into separate sections of the executable. If this macro is | |
10176 set to false, gcc will convert any conditional branches that attempt | |
10177 to cross between sections into unconditional branches or indirect jumps. | |
10178 @end defmac | |
10179 | |
10180 @defmac HAS_LONG_UNCOND_BRANCH | |
10181 Define this boolean macro to indicate whether or not your architecture | |
10182 has unconditional branches that can span all of memory. It is used in | |
10183 conjunction with an optimization that partitions hot and cold basic | |
10184 blocks into separate sections of the executable. If this macro is | |
10185 set to false, gcc will convert any unconditional branches that attempt | |
10186 to cross between sections into indirect jumps. | |
10187 @end defmac | |
10188 | |
10189 @defmac CASE_VECTOR_MODE | |
10190 An alias for a machine mode name. This is the machine mode that | |
10191 elements of a jump-table should have. | |
10192 @end defmac | |
10193 | |
10194 @defmac CASE_VECTOR_SHORTEN_MODE (@var{min_offset}, @var{max_offset}, @var{body}) | |
10195 Optional: return the preferred mode for an @code{addr_diff_vec} | |
10196 when the minimum and maximum offset are known. If you define this, | |
10197 it enables extra code in branch shortening to deal with @code{addr_diff_vec}. | |
10198 To make this work, you also have to define @code{INSN_ALIGN} and | |
10199 make the alignment for @code{addr_diff_vec} explicit. | |
10200 The @var{body} argument is provided so that the offset_unsigned and scale | |
10201 flags can be updated. | |
10202 @end defmac | |
10203 | |
10204 @defmac CASE_VECTOR_PC_RELATIVE | |
10205 Define this macro to be a C expression to indicate when jump-tables | |
10206 should contain relative addresses. You need not define this macro if | |
10207 jump-tables never contain relative addresses, or jump-tables should | |
10208 contain relative addresses only when @option{-fPIC} or @option{-fPIC} | |
10209 is in effect. | |
10210 @end defmac | |
10211 | |
10212 @hook TARGET_CASE_VALUES_THRESHOLD | |
10213 This function return the smallest number of different values for which it | |
10214 is best to use a jump-table instead of a tree of conditional branches. | |
10215 The default is four for machines with a @code{casesi} instruction and | |
10216 five otherwise. This is best for most machines. | |
10217 @end deftypefn | |
10218 | |
10219 @defmac CASE_USE_BIT_TESTS | |
10220 Define this macro to be a C expression to indicate whether C switch | |
10221 statements may be implemented by a sequence of bit tests. This is | |
10222 advantageous on processors that can efficiently implement left shift | |
10223 of 1 by the number of bits held in a register, but inappropriate on | |
10224 targets that would require a loop. By default, this macro returns | |
10225 @code{true} if the target defines an @code{ashlsi3} pattern, and | |
10226 @code{false} otherwise. | |
10227 @end defmac | |
10228 | |
10229 @defmac WORD_REGISTER_OPERATIONS | |
10230 Define this macro if operations between registers with integral mode | |
10231 smaller than a word are always performed on the entire register. | |
10232 Most RISC machines have this property and most CISC machines do not. | |
10233 @end defmac | |
10234 | |
10235 @defmac LOAD_EXTEND_OP (@var{mem_mode}) | |
10236 Define this macro to be a C expression indicating when insns that read | |
10237 memory in @var{mem_mode}, an integral mode narrower than a word, set the | |
10238 bits outside of @var{mem_mode} to be either the sign-extension or the | |
10239 zero-extension of the data read. Return @code{SIGN_EXTEND} for values | |
10240 of @var{mem_mode} for which the | |
10241 insn sign-extends, @code{ZERO_EXTEND} for which it zero-extends, and | |
10242 @code{UNKNOWN} for other modes. | |
10243 | |
10244 This macro is not called with @var{mem_mode} non-integral or with a width | |
10245 greater than or equal to @code{BITS_PER_WORD}, so you may return any | |
10246 value in this case. Do not define this macro if it would always return | |
10247 @code{UNKNOWN}. On machines where this macro is defined, you will normally | |
10248 define it as the constant @code{SIGN_EXTEND} or @code{ZERO_EXTEND}. | |
10249 | |
10250 You may return a non-@code{UNKNOWN} value even if for some hard registers | |
10251 the sign extension is not performed, if for the @code{REGNO_REG_CLASS} | |
10252 of these hard registers @code{CANNOT_CHANGE_MODE_CLASS} returns nonzero | |
10253 when the @var{from} mode is @var{mem_mode} and the @var{to} mode is any | |
10254 integral mode larger than this but not larger than @code{word_mode}. | |
10255 | |
10256 You must return @code{UNKNOWN} if for some hard registers that allow this | |
10257 mode, @code{CANNOT_CHANGE_MODE_CLASS} says that they cannot change to | |
10258 @code{word_mode}, but that they can change to another integral mode that | |
10259 is larger then @var{mem_mode} but still smaller than @code{word_mode}. | |
10260 @end defmac | |
10261 | |
10262 @defmac SHORT_IMMEDIATES_SIGN_EXTEND | |
10263 Define this macro if loading short immediate values into registers sign | |
10264 extends. | |
10265 @end defmac | |
10266 | |
10267 @defmac FIXUNS_TRUNC_LIKE_FIX_TRUNC | |
10268 Define this macro if the same instructions that convert a floating | |
10269 point number to a signed fixed point number also convert validly to an | |
10270 unsigned one. | |
10271 @end defmac | |
10272 | |
10273 @hook TARGET_MIN_DIVISIONS_FOR_RECIP_MUL | |
10274 When @option{-ffast-math} is in effect, GCC tries to optimize | |
10275 divisions by the same divisor, by turning them into multiplications by | |
10276 the reciprocal. This target hook specifies the minimum number of divisions | |
10277 that should be there for GCC to perform the optimization for a variable | |
10278 of mode @var{mode}. The default implementation returns 3 if the machine | |
10279 has an instruction for the division, and 2 if it does not. | |
10280 @end deftypefn | |
10281 | |
10282 @defmac MOVE_MAX | |
10283 The maximum number of bytes that a single instruction can move quickly | |
10284 between memory and registers or between two memory locations. | |
10285 @end defmac | |
10286 | |
10287 @defmac MAX_MOVE_MAX | |
10288 The maximum number of bytes that a single instruction can move quickly | |
10289 between memory and registers or between two memory locations. If this | |
10290 is undefined, the default is @code{MOVE_MAX}. Otherwise, it is the | |
10291 constant value that is the largest value that @code{MOVE_MAX} can have | |
10292 at run-time. | |
10293 @end defmac | |
10294 | |
10295 @defmac SHIFT_COUNT_TRUNCATED | |
10296 A C expression that is nonzero if on this machine the number of bits | |
10297 actually used for the count of a shift operation is equal to the number | |
10298 of bits needed to represent the size of the object being shifted. When | |
10299 this macro is nonzero, the compiler will assume that it is safe to omit | |
10300 a sign-extend, zero-extend, and certain bitwise `and' instructions that | |
10301 truncates the count of a shift operation. On machines that have | |
10302 instructions that act on bit-fields at variable positions, which may | |
10303 include `bit test' instructions, a nonzero @code{SHIFT_COUNT_TRUNCATED} | |
10304 also enables deletion of truncations of the values that serve as | |
10305 arguments to bit-field instructions. | |
10306 | |
10307 If both types of instructions truncate the count (for shifts) and | |
10308 position (for bit-field operations), or if no variable-position bit-field | |
10309 instructions exist, you should define this macro. | |
10310 | |
10311 However, on some machines, such as the 80386 and the 680x0, truncation | |
10312 only applies to shift operations and not the (real or pretended) | |
10313 bit-field operations. Define @code{SHIFT_COUNT_TRUNCATED} to be zero on | |
10314 such machines. Instead, add patterns to the @file{md} file that include | |
10315 the implied truncation of the shift instructions. | |
10316 | |
10317 You need not define this macro if it would always have the value of zero. | |
10318 @end defmac | |
10319 | |
10320 @anchor{TARGET_SHIFT_TRUNCATION_MASK} | |
10321 @hook TARGET_SHIFT_TRUNCATION_MASK | |
10322 This function describes how the standard shift patterns for @var{mode} | |
10323 deal with shifts by negative amounts or by more than the width of the mode. | |
10324 @xref{shift patterns}. | |
10325 | |
10326 On many machines, the shift patterns will apply a mask @var{m} to the | |
10327 shift count, meaning that a fixed-width shift of @var{x} by @var{y} is | |
10328 equivalent to an arbitrary-width shift of @var{x} by @var{y & m}. If | |
10329 this is true for mode @var{mode}, the function should return @var{m}, | |
10330 otherwise it should return 0. A return value of 0 indicates that no | |
10331 particular behavior is guaranteed. | |
10332 | |
10333 Note that, unlike @code{SHIFT_COUNT_TRUNCATED}, this function does | |
10334 @emph{not} apply to general shift rtxes; it applies only to instructions | |
10335 that are generated by the named shift patterns. | |
10336 | |
10337 The default implementation of this function returns | |
10338 @code{GET_MODE_BITSIZE (@var{mode}) - 1} if @code{SHIFT_COUNT_TRUNCATED} | |
10339 and 0 otherwise. This definition is always safe, but if | |
10340 @code{SHIFT_COUNT_TRUNCATED} is false, and some shift patterns | |
10341 nevertheless truncate the shift count, you may get better code | |
10342 by overriding it. | |
10343 @end deftypefn | |
10344 | |
10345 @defmac TRULY_NOOP_TRUNCATION (@var{outprec}, @var{inprec}) | |
10346 A C expression which is nonzero if on this machine it is safe to | |
10347 ``convert'' an integer of @var{inprec} bits to one of @var{outprec} | |
10348 bits (where @var{outprec} is smaller than @var{inprec}) by merely | |
10349 operating on it as if it had only @var{outprec} bits. | |
10350 | |
10351 On many machines, this expression can be 1. | |
10352 | |
10353 @c rearranged this, removed the phrase "it is reported that". this was | |
10354 @c to fix an overfull hbox. --mew 10feb93 | |
10355 When @code{TRULY_NOOP_TRUNCATION} returns 1 for a pair of sizes for | |
10356 modes for which @code{MODES_TIEABLE_P} is 0, suboptimal code can result. | |
10357 If this is the case, making @code{TRULY_NOOP_TRUNCATION} return 0 in | |
10358 such cases may improve things. | |
10359 @end defmac | |
10360 | |
10361 @hook TARGET_MODE_REP_EXTENDED | |
10362 The representation of an integral mode can be such that the values | |
10363 are always extended to a wider integral mode. Return | |
10364 @code{SIGN_EXTEND} if values of @var{mode} are represented in | |
10365 sign-extended form to @var{rep_mode}. Return @code{UNKNOWN} | |
10366 otherwise. (Currently, none of the targets use zero-extended | |
10367 representation this way so unlike @code{LOAD_EXTEND_OP}, | |
10368 @code{TARGET_MODE_REP_EXTENDED} is expected to return either | |
10369 @code{SIGN_EXTEND} or @code{UNKNOWN}. Also no target extends | |
10370 @var{mode} to @var{rep_mode} so that @var{rep_mode} is not the next | |
10371 widest integral mode and currently we take advantage of this fact.) | |
10372 | |
10373 Similarly to @code{LOAD_EXTEND_OP} you may return a non-@code{UNKNOWN} | |
10374 value even if the extension is not performed on certain hard registers | |
10375 as long as for the @code{REGNO_REG_CLASS} of these hard registers | |
10376 @code{CANNOT_CHANGE_MODE_CLASS} returns nonzero. | |
10377 | |
10378 Note that @code{TARGET_MODE_REP_EXTENDED} and @code{LOAD_EXTEND_OP} | |
10379 describe two related properties. If you define | |
10380 @code{TARGET_MODE_REP_EXTENDED (mode, word_mode)} you probably also want | |
10381 to define @code{LOAD_EXTEND_OP (mode)} to return the same type of | |
10382 extension. | |
10383 | |
10384 In order to enforce the representation of @code{mode}, | |
10385 @code{TRULY_NOOP_TRUNCATION} should return false when truncating to | |
10386 @code{mode}. | |
10387 @end deftypefn | |
10388 | |
10389 @defmac STORE_FLAG_VALUE | |
10390 A C expression describing the value returned by a comparison operator | |
10391 with an integral mode and stored by a store-flag instruction | |
10392 (@samp{cstore@var{mode}4}) when the condition is true. This description must | |
10393 apply to @emph{all} the @samp{cstore@var{mode}4} patterns and all the | |
10394 comparison operators whose results have a @code{MODE_INT} mode. | |
10395 | |
10396 A value of 1 or @minus{}1 means that the instruction implementing the | |
10397 comparison operator returns exactly 1 or @minus{}1 when the comparison is true | |
10398 and 0 when the comparison is false. Otherwise, the value indicates | |
10399 which bits of the result are guaranteed to be 1 when the comparison is | |
10400 true. This value is interpreted in the mode of the comparison | |
10401 operation, which is given by the mode of the first operand in the | |
10402 @samp{cstore@var{mode}4} pattern. Either the low bit or the sign bit of | |
10403 @code{STORE_FLAG_VALUE} be on. Presently, only those bits are used by | |
10404 the compiler. | |
10405 | |
10406 If @code{STORE_FLAG_VALUE} is neither 1 or @minus{}1, the compiler will | |
10407 generate code that depends only on the specified bits. It can also | |
10408 replace comparison operators with equivalent operations if they cause | |
10409 the required bits to be set, even if the remaining bits are undefined. | |
10410 For example, on a machine whose comparison operators return an | |
10411 @code{SImode} value and where @code{STORE_FLAG_VALUE} is defined as | |
10412 @samp{0x80000000}, saying that just the sign bit is relevant, the | |
10413 expression | |
10414 | |
10415 @smallexample | |
10416 (ne:SI (and:SI @var{x} (const_int @var{power-of-2})) (const_int 0)) | |
10417 @end smallexample | |
10418 | |
10419 @noindent | |
10420 can be converted to | |
10421 | |
10422 @smallexample | |
10423 (ashift:SI @var{x} (const_int @var{n})) | |
10424 @end smallexample | |
10425 | |
10426 @noindent | |
10427 where @var{n} is the appropriate shift count to move the bit being | |
10428 tested into the sign bit. | |
10429 | |
10430 There is no way to describe a machine that always sets the low-order bit | |
10431 for a true value, but does not guarantee the value of any other bits, | |
10432 but we do not know of any machine that has such an instruction. If you | |
10433 are trying to port GCC to such a machine, include an instruction to | |
10434 perform a logical-and of the result with 1 in the pattern for the | |
10435 comparison operators and let us know at @email{gcc@@gcc.gnu.org}. | |
10436 | |
10437 Often, a machine will have multiple instructions that obtain a value | |
10438 from a comparison (or the condition codes). Here are rules to guide the | |
10439 choice of value for @code{STORE_FLAG_VALUE}, and hence the instructions | |
10440 to be used: | |
10441 | |
10442 @itemize @bullet | |
10443 @item | |
10444 Use the shortest sequence that yields a valid definition for | |
10445 @code{STORE_FLAG_VALUE}. It is more efficient for the compiler to | |
10446 ``normalize'' the value (convert it to, e.g., 1 or 0) than for the | |
10447 comparison operators to do so because there may be opportunities to | |
10448 combine the normalization with other operations. | |
10449 | |
10450 @item | |
10451 For equal-length sequences, use a value of 1 or @minus{}1, with @minus{}1 being | |
10452 slightly preferred on machines with expensive jumps and 1 preferred on | |
10453 other machines. | |
10454 | |
10455 @item | |
10456 As a second choice, choose a value of @samp{0x80000001} if instructions | |
10457 exist that set both the sign and low-order bits but do not define the | |
10458 others. | |
10459 | |
10460 @item | |
10461 Otherwise, use a value of @samp{0x80000000}. | |
10462 @end itemize | |
10463 | |
10464 Many machines can produce both the value chosen for | |
10465 @code{STORE_FLAG_VALUE} and its negation in the same number of | |
10466 instructions. On those machines, you should also define a pattern for | |
10467 those cases, e.g., one matching | |
10468 | |
10469 @smallexample | |
10470 (set @var{A} (neg:@var{m} (ne:@var{m} @var{B} @var{C}))) | |
10471 @end smallexample | |
10472 | |
10473 Some machines can also perform @code{and} or @code{plus} operations on | |
10474 condition code values with less instructions than the corresponding | |
10475 @samp{cstore@var{mode}4} insn followed by @code{and} or @code{plus}. On those | |
10476 machines, define the appropriate patterns. Use the names @code{incscc} | |
10477 and @code{decscc}, respectively, for the patterns which perform | |
10478 @code{plus} or @code{minus} operations on condition code values. See | |
10479 @file{rs6000.md} for some examples. The GNU Superoptimizer can be used to | |
10480 find such instruction sequences on other machines. | |
10481 | |
10482 If this macro is not defined, the default value, 1, is used. You need | |
10483 not define @code{STORE_FLAG_VALUE} if the machine has no store-flag | |
10484 instructions, or if the value generated by these instructions is 1. | |
10485 @end defmac | |
10486 | |
10487 @defmac FLOAT_STORE_FLAG_VALUE (@var{mode}) | |
10488 A C expression that gives a nonzero @code{REAL_VALUE_TYPE} value that is | |
10489 returned when comparison operators with floating-point results are true. | |
10490 Define this macro on machines that have comparison operations that return | |
10491 floating-point values. If there are no such operations, do not define | |
10492 this macro. | |
10493 @end defmac | |
10494 | |
10495 @defmac VECTOR_STORE_FLAG_VALUE (@var{mode}) | |
10496 A C expression that gives a rtx representing the nonzero true element | |
10497 for vector comparisons. The returned rtx should be valid for the inner | |
10498 mode of @var{mode} which is guaranteed to be a vector mode. Define | |
10499 this macro on machines that have vector comparison operations that | |
10500 return a vector result. If there are no such operations, do not define | |
10501 this macro. Typically, this macro is defined as @code{const1_rtx} or | |
10502 @code{constm1_rtx}. This macro may return @code{NULL_RTX} to prevent | |
10503 the compiler optimizing such vector comparison operations for the | |
10504 given mode. | |
10505 @end defmac | |
10506 | |
10507 @defmac CLZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value}) | |
10508 @defmacx CTZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value}) | |
10509 A C expression that indicates whether the architecture defines a value | |
10510 for @code{clz} or @code{ctz} with a zero operand. | |
10511 A result of @code{0} indicates the value is undefined. | |
10512 If the value is defined for only the RTL expression, the macro should | |
10513 evaluate to @code{1}; if the value applies also to the corresponding optab | |
10514 entry (which is normally the case if it expands directly into | |
10515 the corresponding RTL), then the macro should evaluate to @code{2}. | |
10516 In the cases where the value is defined, @var{value} should be set to | |
10517 this value. | |
10518 | |
10519 If this macro is not defined, the value of @code{clz} or | |
10520 @code{ctz} at zero is assumed to be undefined. | |
10521 | |
10522 This macro must be defined if the target's expansion for @code{ffs} | |
10523 relies on a particular value to get correct results. Otherwise it | |
10524 is not necessary, though it may be used to optimize some corner cases, and | |
10525 to provide a default expansion for the @code{ffs} optab. | |
10526 | |
10527 Note that regardless of this macro the ``definedness'' of @code{clz} | |
10528 and @code{ctz} at zero do @emph{not} extend to the builtin functions | |
10529 visible to the user. Thus one may be free to adjust the value at will | |
10530 to match the target expansion of these operations without fear of | |
10531 breaking the API@. | |
10532 @end defmac | |
10533 | |
10534 @defmac Pmode | |
10535 An alias for the machine mode for pointers. On most machines, define | |
10536 this to be the integer mode corresponding to the width of a hardware | |
10537 pointer; @code{SImode} on 32-bit machine or @code{DImode} on 64-bit machines. | |
10538 On some machines you must define this to be one of the partial integer | |
10539 modes, such as @code{PSImode}. | |
10540 | |
10541 The width of @code{Pmode} must be at least as large as the value of | |
10542 @code{POINTER_SIZE}. If it is not equal, you must define the macro | |
10543 @code{POINTERS_EXTEND_UNSIGNED} to specify how pointers are extended | |
10544 to @code{Pmode}. | |
10545 @end defmac | |
10546 | |
10547 @defmac FUNCTION_MODE | |
10548 An alias for the machine mode used for memory references to functions | |
10549 being called, in @code{call} RTL expressions. On most CISC machines, | |
10550 where an instruction can begin at any byte address, this should be | |
10551 @code{QImode}. On most RISC machines, where all instructions have fixed | |
10552 size and alignment, this should be a mode with the same size and alignment | |
10553 as the machine instruction words - typically @code{SImode} or @code{HImode}. | |
10554 @end defmac | |
10555 | |
10556 @defmac STDC_0_IN_SYSTEM_HEADERS | |
10557 In normal operation, the preprocessor expands @code{__STDC__} to the | |
10558 constant 1, to signify that GCC conforms to ISO Standard C@. On some | |
10559 hosts, like Solaris, the system compiler uses a different convention, | |
10560 where @code{__STDC__} is normally 0, but is 1 if the user specifies | |
10561 strict conformance to the C Standard. | |
10562 | |
10563 Defining @code{STDC_0_IN_SYSTEM_HEADERS} makes GNU CPP follows the host | |
10564 convention when processing system header files, but when processing user | |
10565 files @code{__STDC__} will always expand to 1. | |
10566 @end defmac | |
10567 | |
10568 @defmac NO_IMPLICIT_EXTERN_C | |
10569 Define this macro if the system header files support C++ as well as C@. | |
10570 This macro inhibits the usual method of using system header files in | |
10571 C++, which is to pretend that the file's contents are enclosed in | |
10572 @samp{extern "C" @{@dots{}@}}. | |
10573 @end defmac | |
10574 | |
10575 @findex #pragma | |
10576 @findex pragma | |
10577 @defmac REGISTER_TARGET_PRAGMAS () | |
10578 Define this macro if you want to implement any target-specific pragmas. | |
10579 If defined, it is a C expression which makes a series of calls to | |
10580 @code{c_register_pragma} or @code{c_register_pragma_with_expansion} | |
10581 for each pragma. The macro may also do any | |
10582 setup required for the pragmas. | |
10583 | |
10584 The primary reason to define this macro is to provide compatibility with | |
10585 other compilers for the same target. In general, we discourage | |
10586 definition of target-specific pragmas for GCC@. | |
10587 | |
10588 If the pragma can be implemented by attributes then you should consider | |
10589 defining the target hook @samp{TARGET_INSERT_ATTRIBUTES} as well. | |
10590 | |
10591 Preprocessor macros that appear on pragma lines are not expanded. All | |
10592 @samp{#pragma} directives that do not match any registered pragma are | |
10593 silently ignored, unless the user specifies @option{-Wunknown-pragmas}. | |
10594 @end defmac | |
10595 | |
10596 @deftypefun void c_register_pragma (const char *@var{space}, const char *@var{name}, void (*@var{callback}) (struct cpp_reader *)) | |
10597 @deftypefunx void c_register_pragma_with_expansion (const char *@var{space}, const char *@var{name}, void (*@var{callback}) (struct cpp_reader *)) | |
10598 | |
10599 Each call to @code{c_register_pragma} or | |
10600 @code{c_register_pragma_with_expansion} establishes one pragma. The | |
10601 @var{callback} routine will be called when the preprocessor encounters a | |
10602 pragma of the form | |
10603 | |
10604 @smallexample | |
10605 #pragma [@var{space}] @var{name} @dots{} | |
10606 @end smallexample | |
10607 | |
10608 @var{space} is the case-sensitive namespace of the pragma, or | |
10609 @code{NULL} to put the pragma in the global namespace. The callback | |
10610 routine receives @var{pfile} as its first argument, which can be passed | |
10611 on to cpplib's functions if necessary. You can lex tokens after the | |
10612 @var{name} by calling @code{pragma_lex}. Tokens that are not read by the | |
10613 callback will be silently ignored. The end of the line is indicated by | |
10614 a token of type @code{CPP_EOF}. Macro expansion occurs on the | |
10615 arguments of pragmas registered with | |
10616 @code{c_register_pragma_with_expansion} but not on the arguments of | |
10617 pragmas registered with @code{c_register_pragma}. | |
10618 | |
10619 Note that the use of @code{pragma_lex} is specific to the C and C++ | |
10620 compilers. It will not work in the Java or Fortran compilers, or any | |
10621 other language compilers for that matter. Thus if @code{pragma_lex} is going | |
10622 to be called from target-specific code, it must only be done so when | |
10623 building the C and C++ compilers. This can be done by defining the | |
10624 variables @code{c_target_objs} and @code{cxx_target_objs} in the | |
10625 target entry in the @file{config.gcc} file. These variables should name | |
10626 the target-specific, language-specific object file which contains the | |
10627 code that uses @code{pragma_lex}. Note it will also be necessary to add a | |
10628 rule to the makefile fragment pointed to by @code{tmake_file} that shows | |
10629 how to build this object file. | |
10630 @end deftypefun | |
10631 | |
10632 @defmac HANDLE_PRAGMA_PACK_WITH_EXPANSION | |
10633 Define this macro if macros should be expanded in the | |
10634 arguments of @samp{#pragma pack}. | |
10635 @end defmac | |
10636 | |
10637 @hook TARGET_HANDLE_PRAGMA_EXTERN_PREFIX | |
10638 | |
10639 @defmac TARGET_DEFAULT_PACK_STRUCT | |
10640 If your target requires a structure packing default other than 0 (meaning | |
10641 the machine default), define this macro to the necessary value (in bytes). | |
10642 This must be a value that would also be valid to use with | |
10643 @samp{#pragma pack()} (that is, a small power of two). | |
10644 @end defmac | |
10645 | |
10646 @defmac DOLLARS_IN_IDENTIFIERS | |
10647 Define this macro to control use of the character @samp{$} in | |
10648 identifier names for the C family of languages. 0 means @samp{$} is | |
10649 not allowed by default; 1 means it is allowed. 1 is the default; | |
10650 there is no need to define this macro in that case. | |
10651 @end defmac | |
10652 | |
10653 @defmac NO_DOLLAR_IN_LABEL | |
10654 Define this macro if the assembler does not accept the character | |
10655 @samp{$} in label names. By default constructors and destructors in | |
10656 G++ have @samp{$} in the identifiers. If this macro is defined, | |
10657 @samp{.} is used instead. | |
10658 @end defmac | |
10659 | |
10660 @defmac NO_DOT_IN_LABEL | |
10661 Define this macro if the assembler does not accept the character | |
10662 @samp{.} in label names. By default constructors and destructors in G++ | |
10663 have names that use @samp{.}. If this macro is defined, these names | |
10664 are rewritten to avoid @samp{.}. | |
10665 @end defmac | |
10666 | |
10667 @defmac INSN_SETS_ARE_DELAYED (@var{insn}) | |
10668 Define this macro as a C expression that is nonzero if it is safe for the | |
10669 delay slot scheduler to place instructions in the delay slot of @var{insn}, | |
10670 even if they appear to use a resource set or clobbered in @var{insn}. | |
10671 @var{insn} is always a @code{jump_insn} or an @code{insn}; GCC knows that | |
10672 every @code{call_insn} has this behavior. On machines where some @code{insn} | |
10673 or @code{jump_insn} is really a function call and hence has this behavior, | |
10674 you should define this macro. | |
10675 | |
10676 You need not define this macro if it would always return zero. | |
10677 @end defmac | |
10678 | |
10679 @defmac INSN_REFERENCES_ARE_DELAYED (@var{insn}) | |
10680 Define this macro as a C expression that is nonzero if it is safe for the | |
10681 delay slot scheduler to place instructions in the delay slot of @var{insn}, | |
10682 even if they appear to set or clobber a resource referenced in @var{insn}. | |
10683 @var{insn} is always a @code{jump_insn} or an @code{insn}. On machines where | |
10684 some @code{insn} or @code{jump_insn} is really a function call and its operands | |
10685 are registers whose use is actually in the subroutine it calls, you should | |
10686 define this macro. Doing so allows the delay slot scheduler to move | |
10687 instructions which copy arguments into the argument registers into the delay | |
10688 slot of @var{insn}. | |
10689 | |
10690 You need not define this macro if it would always return zero. | |
10691 @end defmac | |
10692 | |
10693 @defmac MULTIPLE_SYMBOL_SPACES | |
10694 Define this macro as a C expression that is nonzero if, in some cases, | |
10695 global symbols from one translation unit may not be bound to undefined | |
10696 symbols in another translation unit without user intervention. For | |
10697 instance, under Microsoft Windows symbols must be explicitly imported | |
10698 from shared libraries (DLLs). | |
10699 | |
10700 You need not define this macro if it would always evaluate to zero. | |
10701 @end defmac | |
10702 | |
10703 @hook TARGET_MD_ASM_CLOBBERS | |
10704 This target hook should add to @var{clobbers} @code{STRING_CST} trees for | |
10705 any hard regs the port wishes to automatically clobber for an asm. | |
10706 It should return the result of the last @code{tree_cons} used to add a | |
10707 clobber. The @var{outputs}, @var{inputs} and @var{clobber} lists are the | |
10708 corresponding parameters to the asm and may be inspected to avoid | |
10709 clobbering a register that is an input or output of the asm. You can use | |
10710 @code{tree_overlaps_hard_reg_set}, declared in @file{tree.h}, to test | |
10711 for overlap with regards to asm-declared registers. | |
10712 @end deftypefn | |
10713 | |
10714 @defmac MATH_LIBRARY | |
10715 Define this macro as a C string constant for the linker argument to link | |
10716 in the system math library, minus the initial @samp{"-l"}, or | |
10717 @samp{""} if the target does not have a | |
10718 separate math library. | |
10719 | |
10720 You need only define this macro if the default of @samp{"m"} is wrong. | |
10721 @end defmac | |
10722 | |
10723 @defmac LIBRARY_PATH_ENV | |
10724 Define this macro as a C string constant for the environment variable that | |
10725 specifies where the linker should look for libraries. | |
10726 | |
10727 You need only define this macro if the default of @samp{"LIBRARY_PATH"} | |
10728 is wrong. | |
10729 @end defmac | |
10730 | |
10731 @defmac TARGET_POSIX_IO | |
10732 Define this macro if the target supports the following POSIX@ file | |
10733 functions, access, mkdir and file locking with fcntl / F_SETLKW@. | |
10734 Defining @code{TARGET_POSIX_IO} will enable the test coverage code | |
10735 to use file locking when exiting a program, which avoids race conditions | |
10736 if the program has forked. It will also create directories at run-time | |
10737 for cross-profiling. | |
10738 @end defmac | |
10739 | |
10740 @defmac MAX_CONDITIONAL_EXECUTE | |
10741 | |
10742 A C expression for the maximum number of instructions to execute via | |
10743 conditional execution instructions instead of a branch. A value of | |
10744 @code{BRANCH_COST}+1 is the default if the machine does not use cc0, and | |
10745 1 if it does use cc0. | |
10746 @end defmac | |
10747 | |
10748 @defmac IFCVT_MODIFY_TESTS (@var{ce_info}, @var{true_expr}, @var{false_expr}) | |
10749 Used if the target needs to perform machine-dependent modifications on the | |
10750 conditionals used for turning basic blocks into conditionally executed code. | |
10751 @var{ce_info} points to a data structure, @code{struct ce_if_block}, which | |
10752 contains information about the currently processed blocks. @var{true_expr} | |
10753 and @var{false_expr} are the tests that are used for converting the | |
10754 then-block and the else-block, respectively. Set either @var{true_expr} or | |
10755 @var{false_expr} to a null pointer if the tests cannot be converted. | |
10756 @end defmac | |
10757 | |
10758 @defmac IFCVT_MODIFY_MULTIPLE_TESTS (@var{ce_info}, @var{bb}, @var{true_expr}, @var{false_expr}) | |
10759 Like @code{IFCVT_MODIFY_TESTS}, but used when converting more complicated | |
10760 if-statements into conditions combined by @code{and} and @code{or} operations. | |
10761 @var{bb} contains the basic block that contains the test that is currently | |
10762 being processed and about to be turned into a condition. | |
10763 @end defmac | |
10764 | |
10765 @defmac IFCVT_MODIFY_INSN (@var{ce_info}, @var{pattern}, @var{insn}) | |
10766 A C expression to modify the @var{PATTERN} of an @var{INSN} that is to | |
10767 be converted to conditional execution format. @var{ce_info} points to | |
10768 a data structure, @code{struct ce_if_block}, which contains information | |
10769 about the currently processed blocks. | |
10770 @end defmac | |
10771 | |
10772 @defmac IFCVT_MODIFY_FINAL (@var{ce_info}) | |
10773 A C expression to perform any final machine dependent modifications in | |
10774 converting code to conditional execution. The involved basic blocks | |
10775 can be found in the @code{struct ce_if_block} structure that is pointed | |
10776 to by @var{ce_info}. | |
10777 @end defmac | |
10778 | |
10779 @defmac IFCVT_MODIFY_CANCEL (@var{ce_info}) | |
10780 A C expression to cancel any machine dependent modifications in | |
10781 converting code to conditional execution. The involved basic blocks | |
10782 can be found in the @code{struct ce_if_block} structure that is pointed | |
10783 to by @var{ce_info}. | |
10784 @end defmac | |
10785 | |
10786 @defmac IFCVT_INIT_EXTRA_FIELDS (@var{ce_info}) | |
10787 A C expression to initialize any extra fields in a @code{struct ce_if_block} | |
10788 structure, which are defined by the @code{IFCVT_EXTRA_FIELDS} macro. | |
10789 @end defmac | |
10790 | |
10791 @defmac IFCVT_EXTRA_FIELDS | |
10792 If defined, it should expand to a set of field declarations that will be | |
10793 added to the @code{struct ce_if_block} structure. These should be initialized | |
10794 by the @code{IFCVT_INIT_EXTRA_FIELDS} macro. | |
10795 @end defmac | |
10796 | |
10797 @hook TARGET_MACHINE_DEPENDENT_REORG | |
10798 If non-null, this hook performs a target-specific pass over the | |
10799 instruction stream. The compiler will run it at all optimization levels, | |
10800 just before the point at which it normally does delayed-branch scheduling. | |
10801 | |
10802 The exact purpose of the hook varies from target to target. Some use | |
10803 it to do transformations that are necessary for correctness, such as | |
10804 laying out in-function constant pools or avoiding hardware hazards. | |
10805 Others use it as an opportunity to do some machine-dependent optimizations. | |
10806 | |
10807 You need not implement the hook if it has nothing to do. The default | |
10808 definition is null. | |
10809 @end deftypefn | |
10810 | |
10811 @hook TARGET_INIT_BUILTINS | |
10812 Define this hook if you have any machine-specific built-in functions | |
10813 that need to be defined. It should be a function that performs the | |
10814 necessary setup. | |
10815 | |
10816 Machine specific built-in functions can be useful to expand special machine | |
10817 instructions that would otherwise not normally be generated because | |
10818 they have no equivalent in the source language (for example, SIMD vector | |
10819 instructions or prefetch instructions). | |
10820 | |
10821 To create a built-in function, call the function | |
10822 @code{lang_hooks.builtin_function} | |
10823 which is defined by the language front end. You can use any type nodes set | |
10824 up by @code{build_common_tree_nodes} and @code{build_common_tree_nodes_2}; | |
10825 only language front ends that use those two functions will call | |
10826 @samp{TARGET_INIT_BUILTINS}. | |
10827 @end deftypefn | |
10828 | |
10829 @hook TARGET_BUILTIN_DECL | |
10830 Define this hook if you have any machine-specific built-in functions | |
10831 that need to be defined. It should be a function that returns the | |
10832 builtin function declaration for the builtin function code @var{code}. | |
10833 If there is no such builtin and it cannot be initialized at this time | |
10834 if @var{initialize_p} is true the function should return @code{NULL_TREE}. | |
10835 If @var{code} is out of range the function should return | |
10836 @code{error_mark_node}. | |
10837 @end deftypefn | |
10838 | |
10839 @hook TARGET_EXPAND_BUILTIN | |
10840 | |
10841 Expand a call to a machine specific built-in function that was set up by | |
10842 @samp{TARGET_INIT_BUILTINS}. @var{exp} is the expression for the | |
10843 function call; the result should go to @var{target} if that is | |
10844 convenient, and have mode @var{mode} if that is convenient. | |
10845 @var{subtarget} may be used as the target for computing one of | |
10846 @var{exp}'s operands. @var{ignore} is nonzero if the value is to be | |
10847 ignored. This function should return the result of the call to the | |
10848 built-in function. | |
10849 @end deftypefn | |
10850 | |
10851 @hook TARGET_RESOLVE_OVERLOADED_BUILTIN | |
10852 Select a replacement for a machine specific built-in function that | |
10853 was set up by @samp{TARGET_INIT_BUILTINS}. This is done | |
10854 @emph{before} regular type checking, and so allows the target to | |
10855 implement a crude form of function overloading. @var{fndecl} is the | |
10856 declaration of the built-in function. @var{arglist} is the list of | |
10857 arguments passed to the built-in function. The result is a | |
10858 complete expression that implements the operation, usually | |
10859 another @code{CALL_EXPR}. | |
10860 @var{arglist} really has type @samp{VEC(tree,gc)*} | |
10861 @end deftypefn | |
10862 | |
10863 @hook TARGET_FOLD_BUILTIN | |
10864 Fold a call to a machine specific built-in function that was set up by | |
10865 @samp{TARGET_INIT_BUILTINS}. @var{fndecl} is the declaration of the | |
10866 built-in function. @var{n_args} is the number of arguments passed to | |
10867 the function; the arguments themselves are pointed to by @var{argp}. | |
10868 The result is another tree containing a simplified expression for the | |
10869 call's result. If @var{ignore} is true the value will be ignored. | |
10870 @end deftypefn | |
10871 | |
10872 @hook TARGET_INVALID_WITHIN_DOLOOP | |
10873 | |
10874 Take an instruction in @var{insn} and return NULL if it is valid within a | |
10875 low-overhead loop, otherwise return a string explaining why doloop | |
10876 could not be applied. | |
10877 | |
10878 Many targets use special registers for low-overhead looping. For any | |
10879 instruction that clobbers these this function should return a string indicating | |
10880 the reason why the doloop could not be applied. | |
10881 By default, the RTL loop optimizer does not use a present doloop pattern for | |
10882 loops containing function calls or branch on table instructions. | |
10883 @end deftypefn | |
10884 | |
10885 @defmac MD_CAN_REDIRECT_BRANCH (@var{branch1}, @var{branch2}) | |
10886 | |
10887 Take a branch insn in @var{branch1} and another in @var{branch2}. | |
10888 Return true if redirecting @var{branch1} to the destination of | |
10889 @var{branch2} is possible. | |
10890 | |
10891 On some targets, branches may have a limited range. Optimizing the | |
10892 filling of delay slots can result in branches being redirected, and this | |
10893 may in turn cause a branch offset to overflow. | |
10894 @end defmac | |
10895 | |
10896 @hook TARGET_COMMUTATIVE_P | |
10897 This target hook returns @code{true} if @var{x} is considered to be commutative. | |
10898 Usually, this is just COMMUTATIVE_P (@var{x}), but the HP PA doesn't consider | |
10899 PLUS to be commutative inside a MEM@. @var{outer_code} is the rtx code | |
10900 of the enclosing rtl, if known, otherwise it is UNKNOWN. | |
10901 @end deftypefn | |
10902 | |
10903 @hook TARGET_ALLOCATE_INITIAL_VALUE | |
10904 | |
10905 When the initial value of a hard register has been copied in a pseudo | |
10906 register, it is often not necessary to actually allocate another register | |
10907 to this pseudo register, because the original hard register or a stack slot | |
10908 it has been saved into can be used. @code{TARGET_ALLOCATE_INITIAL_VALUE} | |
10909 is called at the start of register allocation once for each hard register | |
10910 that had its initial value copied by using | |
10911 @code{get_func_hard_reg_initial_val} or @code{get_hard_reg_initial_val}. | |
10912 Possible values are @code{NULL_RTX}, if you don't want | |
10913 to do any special allocation, a @code{REG} rtx---that would typically be | |
10914 the hard register itself, if it is known not to be clobbered---or a | |
10915 @code{MEM}. | |
10916 If you are returning a @code{MEM}, this is only a hint for the allocator; | |
10917 it might decide to use another register anyways. | |
10918 You may use @code{current_function_leaf_function} in the hook, functions | |
10919 that use @code{REG_N_SETS}, to determine if the hard | |
10920 register in question will not be clobbered. | |
10921 The default value of this hook is @code{NULL}, which disables any special | |
10922 allocation. | |
10923 @end deftypefn | |
10924 | |
10925 @hook TARGET_UNSPEC_MAY_TRAP_P | |
10926 This target hook returns nonzero if @var{x}, an @code{unspec} or | |
10927 @code{unspec_volatile} operation, might cause a trap. Targets can use | |
10928 this hook to enhance precision of analysis for @code{unspec} and | |
10929 @code{unspec_volatile} operations. You may call @code{may_trap_p_1} | |
10930 to analyze inner elements of @var{x} in which case @var{flags} should be | |
10931 passed along. | |
10932 @end deftypefn | |
10933 | |
10934 @hook TARGET_SET_CURRENT_FUNCTION | |
10935 The compiler invokes this hook whenever it changes its current function | |
10936 context (@code{cfun}). You can define this function if | |
10937 the back end needs to perform any initialization or reset actions on a | |
10938 per-function basis. For example, it may be used to implement function | |
10939 attributes that affect register usage or code generation patterns. | |
10940 The argument @var{decl} is the declaration for the new function context, | |
10941 and may be null to indicate that the compiler has left a function context | |
10942 and is returning to processing at the top level. | |
10943 The default hook function does nothing. | |
10944 | |
10945 GCC sets @code{cfun} to a dummy function context during initialization of | |
10946 some parts of the back end. The hook function is not invoked in this | |
10947 situation; you need not worry about the hook being invoked recursively, | |
10948 or when the back end is in a partially-initialized state. | |
10949 @code{cfun} might be @code{NULL} to indicate processing at top level, | |
10950 outside of any function scope. | |
10951 @end deftypefn | |
10952 | |
10953 @defmac TARGET_OBJECT_SUFFIX | |
10954 Define this macro to be a C string representing the suffix for object | |
10955 files on your target machine. If you do not define this macro, GCC will | |
10956 use @samp{.o} as the suffix for object files. | |
10957 @end defmac | |
10958 | |
10959 @defmac TARGET_EXECUTABLE_SUFFIX | |
10960 Define this macro to be a C string representing the suffix to be | |
10961 automatically added to executable files on your target machine. If you | |
10962 do not define this macro, GCC will use the null string as the suffix for | |
10963 executable files. | |
10964 @end defmac | |
10965 | |
10966 @defmac COLLECT_EXPORT_LIST | |
10967 If defined, @code{collect2} will scan the individual object files | |
10968 specified on its command line and create an export list for the linker. | |
10969 Define this macro for systems like AIX, where the linker discards | |
10970 object files that are not referenced from @code{main} and uses export | |
10971 lists. | |
10972 @end defmac | |
10973 | |
10974 @defmac MODIFY_JNI_METHOD_CALL (@var{mdecl}) | |
10975 Define this macro to a C expression representing a variant of the | |
10976 method call @var{mdecl}, if Java Native Interface (JNI) methods | |
10977 must be invoked differently from other methods on your target. | |
10978 For example, on 32-bit Microsoft Windows, JNI methods must be invoked using | |
10979 the @code{stdcall} calling convention and this macro is then | |
10980 defined as this expression: | |
10981 | |
10982 @smallexample | |
10983 build_type_attribute_variant (@var{mdecl}, | |
10984 build_tree_list | |
10985 (get_identifier ("stdcall"), | |
10986 NULL)) | |
10987 @end smallexample | |
10988 @end defmac | |
10989 | |
10990 @hook TARGET_CANNOT_MODIFY_JUMPS_P | |
10991 This target hook returns @code{true} past the point in which new jump | |
10992 instructions could be created. On machines that require a register for | |
10993 every jump such as the SHmedia ISA of SH5, this point would typically be | |
10994 reload, so this target hook should be defined to a function such as: | |
10995 | |
10996 @smallexample | |
10997 static bool | |
10998 cannot_modify_jumps_past_reload_p () | |
10999 @{ | |
11000 return (reload_completed || reload_in_progress); | |
11001 @} | |
11002 @end smallexample | |
11003 @end deftypefn | |
11004 | |
11005 @hook TARGET_BRANCH_TARGET_REGISTER_CLASS | |
11006 This target hook returns a register class for which branch target register | |
11007 optimizations should be applied. All registers in this class should be | |
11008 usable interchangeably. After reload, registers in this class will be | |
11009 re-allocated and loads will be hoisted out of loops and be subjected | |
11010 to inter-block scheduling. | |
11011 @end deftypefn | |
11012 | |
11013 @hook TARGET_BRANCH_TARGET_REGISTER_CALLEE_SAVED | |
11014 Branch target register optimization will by default exclude callee-saved | |
11015 registers | |
11016 that are not already live during the current function; if this target hook | |
11017 returns true, they will be included. The target code must than make sure | |
11018 that all target registers in the class returned by | |
11019 @samp{TARGET_BRANCH_TARGET_REGISTER_CLASS} that might need saving are | |
11020 saved. @var{after_prologue_epilogue_gen} indicates if prologues and | |
11021 epilogues have already been generated. Note, even if you only return | |
11022 true when @var{after_prologue_epilogue_gen} is false, you still are likely | |
11023 to have to make special provisions in @code{INITIAL_ELIMINATION_OFFSET} | |
11024 to reserve space for caller-saved target registers. | |
11025 @end deftypefn | |
11026 | |
11027 @hook TARGET_HAVE_CONDITIONAL_EXECUTION | |
11028 This target hook returns true if the target supports conditional execution. | |
11029 This target hook is required only when the target has several different | |
11030 modes and they have different conditional execution capability, such as ARM. | |
11031 @end deftypefn | |
11032 | |
11033 @hook TARGET_LOOP_UNROLL_ADJUST | |
11034 This target hook returns a new value for the number of times @var{loop} | |
11035 should be unrolled. The parameter @var{nunroll} is the number of times | |
11036 the loop is to be unrolled. The parameter @var{loop} is a pointer to | |
11037 the loop, which is going to be checked for unrolling. This target hook | |
11038 is required only when the target has special constraints like maximum | |
11039 number of memory accesses. | |
11040 @end deftypefn | |
11041 | |
11042 @defmac POWI_MAX_MULTS | |
11043 If defined, this macro is interpreted as a signed integer C expression | |
11044 that specifies the maximum number of floating point multiplications | |
11045 that should be emitted when expanding exponentiation by an integer | |
11046 constant inline. When this value is defined, exponentiation requiring | |
11047 more than this number of multiplications is implemented by calling the | |
11048 system library's @code{pow}, @code{powf} or @code{powl} routines. | |
11049 The default value places no upper bound on the multiplication count. | |
11050 @end defmac | |
11051 | |
11052 @deftypefn Macro void TARGET_EXTRA_INCLUDES (const char *@var{sysroot}, const char *@var{iprefix}, int @var{stdinc}) | |
11053 This target hook should register any extra include files for the | |
11054 target. The parameter @var{stdinc} indicates if normal include files | |
11055 are present. The parameter @var{sysroot} is the system root directory. | |
11056 The parameter @var{iprefix} is the prefix for the gcc directory. | |
11057 @end deftypefn | |
11058 | |
11059 @deftypefn Macro void TARGET_EXTRA_PRE_INCLUDES (const char *@var{sysroot}, const char *@var{iprefix}, int @var{stdinc}) | |
11060 This target hook should register any extra include files for the | |
11061 target before any standard headers. The parameter @var{stdinc} | |
11062 indicates if normal include files are present. The parameter | |
11063 @var{sysroot} is the system root directory. The parameter | |
11064 @var{iprefix} is the prefix for the gcc directory. | |
11065 @end deftypefn | |
11066 | |
11067 @deftypefn Macro void TARGET_OPTF (char *@var{path}) | |
11068 This target hook should register special include paths for the target. | |
11069 The parameter @var{path} is the include to register. On Darwin | |
11070 systems, this is used for Framework includes, which have semantics | |
11071 that are different from @option{-I}. | |
11072 @end deftypefn | |
11073 | |
11074 @defmac bool TARGET_USE_LOCAL_THUNK_ALIAS_P (tree @var{fndecl}) | |
11075 This target macro returns @code{true} if it is safe to use a local alias | |
11076 for a virtual function @var{fndecl} when constructing thunks, | |
11077 @code{false} otherwise. By default, the macro returns @code{true} for all | |
11078 functions, if a target supports aliases (i.e.@: defines | |
11079 @code{ASM_OUTPUT_DEF}), @code{false} otherwise, | |
11080 @end defmac | |
11081 | |
11082 @defmac TARGET_FORMAT_TYPES | |
11083 If defined, this macro is the name of a global variable containing | |
11084 target-specific format checking information for the @option{-Wformat} | |
11085 option. The default is to have no target-specific format checks. | |
11086 @end defmac | |
11087 | |
11088 @defmac TARGET_N_FORMAT_TYPES | |
11089 If defined, this macro is the number of entries in | |
11090 @code{TARGET_FORMAT_TYPES}. | |
11091 @end defmac | |
11092 | |
11093 @defmac TARGET_OVERRIDES_FORMAT_ATTRIBUTES | |
11094 If defined, this macro is the name of a global variable containing | |
11095 target-specific format overrides for the @option{-Wformat} option. The | |
11096 default is to have no target-specific format overrides. If defined, | |
11097 @code{TARGET_FORMAT_TYPES} must be defined, too. | |
11098 @end defmac | |
11099 | |
11100 @defmac TARGET_OVERRIDES_FORMAT_ATTRIBUTES_COUNT | |
11101 If defined, this macro specifies the number of entries in | |
11102 @code{TARGET_OVERRIDES_FORMAT_ATTRIBUTES}. | |
11103 @end defmac | |
11104 | |
11105 @defmac TARGET_OVERRIDES_FORMAT_INIT | |
11106 If defined, this macro specifies the optional initialization | |
11107 routine for target specific customizations of the system printf | |
11108 and scanf formatter settings. | |
11109 @end defmac | |
11110 | |
11111 @hook TARGET_RELAXED_ORDERING | |
11112 If set to @code{true}, means that the target's memory model does not | |
11113 guarantee that loads which do not depend on one another will access | |
11114 main memory in the order of the instruction stream; if ordering is | |
11115 important, an explicit memory barrier must be used. This is true of | |
11116 many recent processors which implement a policy of ``relaxed,'' | |
11117 ``weak,'' or ``release'' memory consistency, such as Alpha, PowerPC, | |
11118 and ia64. The default is @code{false}. | |
11119 @end deftypevr | |
11120 | |
11121 @hook TARGET_INVALID_ARG_FOR_UNPROTOTYPED_FN | |
11122 If defined, this macro returns the diagnostic message when it is | |
11123 illegal to pass argument @var{val} to function @var{funcdecl} | |
11124 with prototype @var{typelist}. | |
11125 @end deftypefn | |
11126 | |
11127 @hook TARGET_INVALID_CONVERSION | |
11128 If defined, this macro returns the diagnostic message when it is | |
11129 invalid to convert from @var{fromtype} to @var{totype}, or @code{NULL} | |
11130 if validity should be determined by the front end. | |
11131 @end deftypefn | |
11132 | |
11133 @hook TARGET_INVALID_UNARY_OP | |
11134 If defined, this macro returns the diagnostic message when it is | |
11135 invalid to apply operation @var{op} (where unary plus is denoted by | |
11136 @code{CONVERT_EXPR}) to an operand of type @var{type}, or @code{NULL} | |
11137 if validity should be determined by the front end. | |
11138 @end deftypefn | |
11139 | |
11140 @hook TARGET_INVALID_BINARY_OP | |
11141 If defined, this macro returns the diagnostic message when it is | |
11142 invalid to apply operation @var{op} to operands of types @var{type1} | |
11143 and @var{type2}, or @code{NULL} if validity should be determined by | |
11144 the front end. | |
11145 @end deftypefn | |
11146 | |
11147 @hook TARGET_INVALID_PARAMETER_TYPE | |
11148 If defined, this macro returns the diagnostic message when it is | |
11149 invalid for functions to include parameters of type @var{type}, | |
11150 or @code{NULL} if validity should be determined by | |
11151 the front end. This is currently used only by the C and C++ front ends. | |
11152 @end deftypefn | |
11153 | |
11154 @hook TARGET_INVALID_RETURN_TYPE | |
11155 If defined, this macro returns the diagnostic message when it is | |
11156 invalid for functions to have return type @var{type}, | |
11157 or @code{NULL} if validity should be determined by | |
11158 the front end. This is currently used only by the C and C++ front ends. | |
11159 @end deftypefn | |
11160 | |
11161 @hook TARGET_PROMOTED_TYPE | |
11162 If defined, this target hook returns the type to which values of | |
11163 @var{type} should be promoted when they appear in expressions, | |
11164 analogous to the integer promotions, or @code{NULL_TREE} to use the | |
11165 front end's normal promotion rules. This hook is useful when there are | |
11166 target-specific types with special promotion rules. | |
11167 This is currently used only by the C and C++ front ends. | |
11168 @end deftypefn | |
11169 | |
11170 @hook TARGET_CONVERT_TO_TYPE | |
11171 If defined, this hook returns the result of converting @var{expr} to | |
11172 @var{type}. It should return the converted expression, | |
11173 or @code{NULL_TREE} to apply the front end's normal conversion rules. | |
11174 This hook is useful when there are target-specific types with special | |
11175 conversion rules. | |
11176 This is currently used only by the C and C++ front ends. | |
11177 @end deftypefn | |
11178 | |
11179 @defmac TARGET_USE_JCR_SECTION | |
11180 This macro determines whether to use the JCR section to register Java | |
11181 classes. By default, TARGET_USE_JCR_SECTION is defined to 1 if both | |
11182 SUPPORTS_WEAK and TARGET_HAVE_NAMED_SECTIONS are true, else 0. | |
11183 @end defmac | |
11184 | |
11185 @defmac OBJC_JBLEN | |
11186 This macro determines the size of the objective C jump buffer for the | |
11187 NeXT runtime. By default, OBJC_JBLEN is defined to an innocuous value. | |
11188 @end defmac | |
11189 | |
11190 @defmac LIBGCC2_UNWIND_ATTRIBUTE | |
11191 Define this macro if any target-specific attributes need to be attached | |
11192 to the functions in @file{libgcc} that provide low-level support for | |
11193 call stack unwinding. It is used in declarations in @file{unwind-generic.h} | |
11194 and the associated definitions of those functions. | |
11195 @end defmac | |
11196 | |
11197 @hook TARGET_UPDATE_STACK_BOUNDARY | |
11198 Define this macro to update the current function stack boundary if | |
11199 necessary. | |
11200 @end deftypefn | |
11201 | |
11202 @hook TARGET_GET_DRAP_RTX | |
11203 This hook should return an rtx for Dynamic Realign Argument Pointer (DRAP) if a | |
11204 different argument pointer register is needed to access the function's | |
11205 argument list due to stack realignment. Return @code{NULL} if no DRAP | |
11206 is needed. | |
11207 @end deftypefn | |
11208 | |
11209 @hook TARGET_ALLOCATE_STACK_SLOTS_FOR_ARGS | |
11210 When optimization is disabled, this hook indicates whether or not | |
11211 arguments should be allocated to stack slots. Normally, GCC allocates | |
11212 stacks slots for arguments when not optimizing in order to make | |
11213 debugging easier. However, when a function is declared with | |
11214 @code{__attribute__((naked))}, there is no stack frame, and the compiler | |
11215 cannot safely move arguments from the registers in which they are passed | |
11216 to the stack. Therefore, this hook should return true in general, but | |
11217 false for naked functions. The default implementation always returns true. | |
11218 @end deftypefn | |
11219 | |
11220 @hook TARGET_CONST_ANCHOR | |
11221 On some architectures it can take multiple instructions to synthesize | |
11222 a constant. If there is another constant already in a register that | |
11223 is close enough in value then it is preferable that the new constant | |
11224 is computed from this register using immediate addition or | |
11225 subtraction. We accomplish this through CSE. Besides the value of | |
11226 the constant we also add a lower and an upper constant anchor to the | |
11227 available expressions. These are then queried when encountering new | |
11228 constants. The anchors are computed by rounding the constant up and | |
11229 down to a multiple of the value of @code{TARGET_CONST_ANCHOR}. | |
11230 @code{TARGET_CONST_ANCHOR} should be the maximum positive value | |
11231 accepted by immediate-add plus one. We currently assume that the | |
11232 value of @code{TARGET_CONST_ANCHOR} is a power of 2. For example, on | |
11233 MIPS, where add-immediate takes a 16-bit signed value, | |
11234 @code{TARGET_CONST_ANCHOR} is set to @samp{0x8000}. The default value | |
11235 is zero, which disables this optimization. @end deftypevr |