1 /* IPA visibility pass
2 Copyright (C) 2003-2018 Free Software Foundation, Inc.
3
4 This file is part of GCC.
5
6 GCC is free software; you can redistribute it and/or modify it under
7 the terms of the GNU General Public License as published by the Free
8 Software Foundation; either version 3, or (at your option) any later
9 version.
10
11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
12 WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 for more details.
15
16 You should have received a copy of the GNU General Public License
17 along with GCC; see the file COPYING3. If not see
18 <http://www.gnu.org/licenses/>. */
19
20 /* This file implements two related passes:
21
22 - pass_data_ipa_function_and_variable_visibility run just after
23 symbol table, references and callgraph are built
24
25 - pass_data_ipa_function_and_variable_visibility run as first
26 proper IPA pass (that is after early optimization, or, (with LTO)
27 as a first pass done at link-time.
28
29 Purpose of both passes is to set correctly visibility properties
30 of all symbols. This includes:
31
32 - Symbol privatization:
33
34 Some symbols that are declared public by frontend may be
35 turned local (either by -fwhole-program flag, by linker plugin feedback
36 or by other reasons)
37
38 - Discovery of local functions:
39
40 A local function is one whose calls can occur only in the current
41 compilation unit and all its calls are explicit, so we can change
42 its calling convention. We simply mark all static functions whose
43 address is not taken as local.
44
45 externally_visible flag is set for symbols that can not be privatized.
46 For privatized symbols we clear TREE_PUBLIC flag and dismantle comdat
47 group.
48
49 - Dismantling of comdat groups:
50
51 Comdat group represent a section that may be replaced by linker by
52 a different copy of the same section from other unit.
53 If we have resolution information (from linker plugin) and we know that
54 a given comdat gorup is prevailing, we can dismantle it and turn symbols
55 into normal symbols. If the resolution information says that the
56 section was previaled by copy from non-LTO code, we can also dismantle
57 it and turn all symbols into external.
58
59 - Local aliases:
60
61 Some symbols can be interposed by dynamic linker. Refering to these
62 symbols is expensive, since it needs to be overwritable by the dynamic
63 linker. In some cases we know that the interposition does not change
64 semantic and we can always refer to a local copy (as in the case of
65 inline function). In this case we produce a local alias and redirect
66 calls to it.
67
68 TODO: This should be done for references, too.
69
70 - Removal of static ocnstructors and destructors that have no side effects.
71
72 - Regularization of several oddities introduced by frontends that may
73 be impractical later in the optimization queue. */
74
75 #include "config.h"
76 #include "system.h"
77 #include "coretypes.h"
78 #include "tm.h"
79 #include "function.h"
80 #include "tree.h"
81 #include "gimple-expr.h"
82 #include "tree-pass.h"
83 #include "cgraph.h"
84 #include "calls.h"
85 #include "varasm.h"
86 #include "ipa-utils.h"
87 #include "stringpool.h"
88 #include "attribs.h"
89
90 /* Return true when NODE can not be local. Worker for cgraph_local_node_p. */
91
92 static bool
non_local_p(struct cgraph_node * node,void * data ATTRIBUTE_UNUSED)93 non_local_p (struct cgraph_node *node, void *data ATTRIBUTE_UNUSED)
94 {
95 return !(node->only_called_directly_or_aliased_p ()
96 /* i386 would need update to output thunk with local calling
97 conventions. */
98 && !node->thunk.thunk_p
99 && node->definition
100 && !DECL_EXTERNAL (node->decl)
101 && !lookup_attribute ("noipa", DECL_ATTRIBUTES (node->decl))
102 && !node->externally_visible
103 && !node->used_from_other_partition
104 && !node->in_other_partition
105 && node->get_availability () >= AVAIL_AVAILABLE);
106 }
107
108 /* Return true when function can be marked local. */
109
110 bool
local_p(void)111 cgraph_node::local_p (void)
112 {
113 cgraph_node *n = ultimate_alias_target ();
114
115 if (n->thunk.thunk_p)
116 return n->callees->callee->local_p ();
117 return !n->call_for_symbol_thunks_and_aliases (non_local_p,
118 NULL, true);
119
120 }
121
122 /* A helper for comdat_can_be_unshared_p. */
123
124 static bool
comdat_can_be_unshared_p_1(symtab_node * node)125 comdat_can_be_unshared_p_1 (symtab_node *node)
126 {
127 if (!node->externally_visible)
128 return true;
129 if (node->address_can_be_compared_p ())
130 {
131 struct ipa_ref *ref;
132
133 for (unsigned int i = 0; node->iterate_referring (i, ref); i++)
134 if (ref->address_matters_p ())
135 return false;
136 }
137
138 /* If the symbol is used in some weird way, better to not touch it. */
139 if (node->force_output)
140 return false;
141
142 /* Explicit instantiations needs to be output when possibly
143 used externally. */
144 if (node->forced_by_abi
145 && TREE_PUBLIC (node->decl)
146 && (node->resolution != LDPR_PREVAILING_DEF_IRONLY
147 && !flag_whole_program))
148 return false;
149
150 /* Non-readonly and volatile variables can not be duplicated. */
151 if (is_a <varpool_node *> (node)
152 && (!TREE_READONLY (node->decl)
153 || TREE_THIS_VOLATILE (node->decl)))
154 return false;
155 return true;
156 }
157
158 /* COMDAT functions must be shared only if they have address taken,
159 otherwise we can produce our own private implementation with
160 -fwhole-program.
161 Return true when turning COMDAT function static can not lead to wrong
162 code when the resulting object links with a library defining same COMDAT.
163
164 Virtual functions do have their addresses taken from the vtables,
165 but in C++ there is no way to compare their addresses for equality. */
166
167 static bool
comdat_can_be_unshared_p(symtab_node * node)168 comdat_can_be_unshared_p (symtab_node *node)
169 {
170 if (!comdat_can_be_unshared_p_1 (node))
171 return false;
172 if (node->same_comdat_group)
173 {
174 symtab_node *next;
175
176 /* If more than one function is in the same COMDAT group, it must
177 be shared even if just one function in the comdat group has
178 address taken. */
179 for (next = node->same_comdat_group;
180 next != node; next = next->same_comdat_group)
181 if (!comdat_can_be_unshared_p_1 (next))
182 return false;
183 }
184 return true;
185 }
186
187 /* Return true when function NODE should be considered externally visible. */
188
189 static bool
cgraph_externally_visible_p(struct cgraph_node * node,bool whole_program)190 cgraph_externally_visible_p (struct cgraph_node *node,
191 bool whole_program)
192 {
193 while (node->transparent_alias && node->definition)
194 node = node->get_alias_target ();
195 if (!node->definition)
196 return false;
197 if (!TREE_PUBLIC (node->decl)
198 || DECL_EXTERNAL (node->decl))
199 return false;
200
201 /* Do not try to localize built-in functions yet. One of problems is that we
202 end up mangling their asm for WHOPR that makes it impossible to call them
203 using the implicit built-in declarations anymore. Similarly this enables
204 us to remove them as unreachable before actual calls may appear during
205 expansion or folding. */
206 if (DECL_BUILT_IN (node->decl))
207 return true;
208
209 /* If linker counts on us, we must preserve the function. */
210 if (node->used_from_object_file_p ())
211 return true;
212 if (DECL_PRESERVE_P (node->decl))
213 return true;
214 if (lookup_attribute ("externally_visible",
215 DECL_ATTRIBUTES (node->decl)))
216 return true;
217 if (lookup_attribute ("noipa", DECL_ATTRIBUTES (node->decl)))
218 return true;
219 if (TARGET_DLLIMPORT_DECL_ATTRIBUTES
220 && lookup_attribute ("dllexport",
221 DECL_ATTRIBUTES (node->decl)))
222 return true;
223 if (node->resolution == LDPR_PREVAILING_DEF_IRONLY)
224 return false;
225 /* When doing LTO or whole program, we can bring COMDAT functoins static.
226 This improves code quality and we know we will duplicate them at most twice
227 (in the case that we are not using plugin and link with object file
228 implementing same COMDAT) */
229 if (((in_lto_p || whole_program) && !flag_incremental_link)
230 && DECL_COMDAT (node->decl)
231 && comdat_can_be_unshared_p (node))
232 return false;
233
234 /* When doing link time optimizations, hidden symbols become local. */
235 if ((in_lto_p && !flag_incremental_link)
236 && (DECL_VISIBILITY (node->decl) == VISIBILITY_HIDDEN
237 || DECL_VISIBILITY (node->decl) == VISIBILITY_INTERNAL)
238 /* Be sure that node is defined in IR file, not in other object
239 file. In that case we don't set used_from_other_object_file. */
240 && node->definition)
241 ;
242 else if (!whole_program)
243 return true;
244
245 if (MAIN_NAME_P (DECL_NAME (node->decl)))
246 return true;
247
248 if (node->instrumentation_clone
249 && MAIN_NAME_P (DECL_NAME (node->orig_decl)))
250 return true;
251
252 return false;
253 }
254
255 /* Return true when variable should be considered externally visible. */
256
257 bool
externally_visible_p(void)258 varpool_node::externally_visible_p (void)
259 {
260 while (transparent_alias && definition)
261 return get_alias_target ()->externally_visible_p ();
262 if (DECL_EXTERNAL (decl))
263 return true;
264
265 if (!TREE_PUBLIC (decl))
266 return false;
267
268 /* If linker counts on us, we must preserve the function. */
269 if (used_from_object_file_p ())
270 return true;
271
272 /* Bringing TLS variables local may cause dynamic linker failures
273 on limits of static TLS vars. */
274 if (DECL_THREAD_LOCAL_P (decl)
275 && (DECL_TLS_MODEL (decl) != TLS_MODEL_EMULATED
276 && DECL_TLS_MODEL (decl) != TLS_MODEL_INITIAL_EXEC))
277 return true;
278
279 if (DECL_HARD_REGISTER (decl))
280 return true;
281 if (DECL_PRESERVE_P (decl))
282 return true;
283 if (lookup_attribute ("externally_visible",
284 DECL_ATTRIBUTES (decl)))
285 return true;
286 if (TARGET_DLLIMPORT_DECL_ATTRIBUTES
287 && lookup_attribute ("dllexport",
288 DECL_ATTRIBUTES (decl)))
289 return true;
290
291 /* See if we have linker information about symbol not being used or
292 if we need to make guess based on the declaration.
293
294 Even if the linker clams the symbol is unused, never bring internal
295 symbols that are declared by user as used or externally visible.
296 This is needed for i.e. references from asm statements. */
297 if (used_from_object_file_p ())
298 return true;
299 if (resolution == LDPR_PREVAILING_DEF_IRONLY)
300 return false;
301
302 /* As a special case, the COMDAT virtual tables can be unshared.
303 In LTO mode turn vtables into static variables. The variable is readonly,
304 so this does not enable more optimization, but referring static var
305 is faster for dynamic linking. Also this match logic hidding vtables
306 from LTO symbol tables. */
307 if (((in_lto_p || flag_whole_program) && !flag_incremental_link)
308 && DECL_COMDAT (decl)
309 && comdat_can_be_unshared_p (this))
310 return false;
311
312 /* When doing link time optimizations, hidden symbols become local. */
313 if (in_lto_p && !flag_incremental_link
314 && (DECL_VISIBILITY (decl) == VISIBILITY_HIDDEN
315 || DECL_VISIBILITY (decl) == VISIBILITY_INTERNAL)
316 /* Be sure that node is defined in IR file, not in other object
317 file. In that case we don't set used_from_other_object_file. */
318 && definition)
319 ;
320 else if (!flag_whole_program)
321 return true;
322
323 /* Do not attempt to privatize COMDATS by default.
324 This would break linking with C++ libraries sharing
325 inline definitions.
326
327 FIXME: We can do so for readonly vars with no address taken and
328 possibly also for vtables since no direct pointer comparsion is done.
329 It might be interesting to do so to reduce linking overhead. */
330 if (DECL_COMDAT (decl) || DECL_WEAK (decl))
331 return true;
332 return false;
333 }
334
335 /* Return true if reference to NODE can be replaced by a local alias.
336 Local aliases save dynamic linking overhead and enable more optimizations.
337 */
338
339 static bool
can_replace_by_local_alias(symtab_node * node)340 can_replace_by_local_alias (symtab_node *node)
341 {
342 /* If aliases aren't supported, we can't do replacement. */
343 if (!TARGET_SUPPORTS_ALIASES)
344 return false;
345
346 /* Weakrefs have a reason to be non-local. Be sure we do not replace
347 them. */
348 while (node->transparent_alias && node->definition && !node->weakref)
349 node = node->get_alias_target ();
350 if (node->weakref)
351 return false;
352
353 return (node->get_availability () > AVAIL_INTERPOSABLE
354 && !decl_binds_to_current_def_p (node->decl)
355 && !node->can_be_discarded_p ());
356 }
357
358 /* Return true if we can replace reference to NODE by local alias
359 within a virtual table. Generally we can replace function pointers
360 and virtual table pointers. */
361
362 static bool
can_replace_by_local_alias_in_vtable(symtab_node * node)363 can_replace_by_local_alias_in_vtable (symtab_node *node)
364 {
365 if (is_a <varpool_node *> (node)
366 && !DECL_VIRTUAL_P (node->decl))
367 return false;
368 return can_replace_by_local_alias (node);
369 }
370
371 /* walk_tree callback that rewrites initializer references. */
372
373 static tree
update_vtable_references(tree * tp,int * walk_subtrees,void * data ATTRIBUTE_UNUSED)374 update_vtable_references (tree *tp, int *walk_subtrees,
375 void *data ATTRIBUTE_UNUSED)
376 {
377 if (VAR_OR_FUNCTION_DECL_P (*tp))
378 {
379 if (can_replace_by_local_alias_in_vtable (symtab_node::get (*tp)))
380 *tp = symtab_node::get (*tp)->noninterposable_alias ()->decl;
381 *walk_subtrees = 0;
382 }
383 else if (IS_TYPE_OR_DECL_P (*tp))
384 *walk_subtrees = 0;
385 return NULL;
386 }
387
388 /* In LTO we can remove COMDAT groups and weak symbols.
389 Either turn them into normal symbols or external symbol depending on
390 resolution info. */
391
392 static void
update_visibility_by_resolution_info(symtab_node * node)393 update_visibility_by_resolution_info (symtab_node * node)
394 {
395 bool define;
396
397 if (!node->externally_visible
398 || (!DECL_WEAK (node->decl) && !DECL_ONE_ONLY (node->decl))
399 || node->resolution == LDPR_UNKNOWN)
400 return;
401
402 define = (node->resolution == LDPR_PREVAILING_DEF_IRONLY
403 || node->resolution == LDPR_PREVAILING_DEF
404 || node->resolution == LDPR_UNDEF
405 || node->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP);
406
407 /* The linker decisions ought to agree in the whole group. */
408 if (node->same_comdat_group)
409 for (symtab_node *next = node->same_comdat_group;
410 next != node; next = next->same_comdat_group)
411 {
412 if (!next->externally_visible || next->transparent_alias)
413 continue;
414
415 bool same_def
416 = define == (next->resolution == LDPR_PREVAILING_DEF_IRONLY
417 || next->resolution == LDPR_PREVAILING_DEF
418 || next->resolution == LDPR_UNDEF
419 || next->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP);
420 gcc_assert (in_lto_p || same_def);
421 if (!same_def)
422 return;
423 }
424
425 if (node->same_comdat_group)
426 for (symtab_node *next = node->same_comdat_group;
427 next != node; next = next->same_comdat_group)
428 {
429 /* During incremental linking we need to keep symbol weak for future
430 linking. We can still drop definition if we know non-LTO world
431 prevails. */
432 if (!flag_incremental_link)
433 {
434 DECL_WEAK (next->decl) = false;
435 next->set_comdat_group (NULL);
436 }
437 if (!define)
438 {
439 if (next->externally_visible)
440 DECL_EXTERNAL (next->decl) = true;
441 next->set_comdat_group (NULL);
442 }
443 }
444
445 /* During incremental linking we need to keep symbol weak for future
446 linking. We can still drop definition if we know non-LTO world prevails. */
447 if (!flag_incremental_link)
448 {
449 DECL_WEAK (node->decl) = false;
450 node->set_comdat_group (NULL);
451 node->dissolve_same_comdat_group_list ();
452 }
453 if (!define)
454 {
455 DECL_EXTERNAL (node->decl) = true;
456 node->set_comdat_group (NULL);
457 node->dissolve_same_comdat_group_list ();
458 }
459 }
460
461 /* Try to get rid of weakref. */
462
463 static void
optimize_weakref(symtab_node * node)464 optimize_weakref (symtab_node *node)
465 {
466 bool strip_weakref = false;
467 bool static_alias = false;
468
469 gcc_assert (node->weakref);
470
471 /* Weakrefs with no target defined can not be optimized. */
472 if (!node->analyzed)
473 return;
474 symtab_node *target = node->get_alias_target ();
475
476 /* Weakrefs to weakrefs can be optimized only if target can be. */
477 if (target->weakref)
478 optimize_weakref (target);
479 if (target->weakref)
480 return;
481
482 /* If we have definition of weakref's target and we know it binds locally,
483 we can turn weakref to static alias. */
484 if (TARGET_SUPPORTS_ALIASES
485 && target->definition && decl_binds_to_current_def_p (target->decl))
486 strip_weakref = static_alias = true;
487 /* Otherwise we can turn weakref into transparent alias. This transformation
488 may break asm statements which directly refers to symbol name and expect
489 GNU as to translate it via .weakref directive. So do not optimize when
490 DECL_PRESERVED is set and .weakref is supported. */
491 else if ((!DECL_PRESERVE_P (target->decl)
492 || IDENTIFIER_TRANSPARENT_ALIAS (DECL_ASSEMBLER_NAME (node->decl)))
493 && !DECL_WEAK (target->decl)
494 && !DECL_EXTERNAL (target->decl)
495 && ((target->definition && !target->can_be_discarded_p ())
496 || target->resolution != LDPR_UNDEF))
497 strip_weakref = true;
498 if (!strip_weakref)
499 return;
500 node->weakref = false;
501 IDENTIFIER_TRANSPARENT_ALIAS (DECL_ASSEMBLER_NAME (node->decl)) = 0;
502 TREE_CHAIN (DECL_ASSEMBLER_NAME (node->decl)) = NULL_TREE;
503 DECL_ATTRIBUTES (node->decl) = remove_attribute ("weakref",
504 DECL_ATTRIBUTES
505 (node->decl));
506
507 if (dump_file)
508 fprintf (dump_file, "Optimizing weakref %s %s\n",
509 node->name(),
510 static_alias ? "as static alias" : "as transparent alias");
511
512 if (static_alias)
513 {
514 /* make_decl_local will shortcircuit if it doesn't see TREE_PUBLIC.
515 be sure it really clears the WEAK flag. */
516 TREE_PUBLIC (node->decl) = true;
517 node->make_decl_local ();
518 node->forced_by_abi = false;
519 node->resolution = LDPR_PREVAILING_DEF_IRONLY;
520 node->externally_visible = false;
521 gcc_assert (!DECL_WEAK (node->decl));
522 node->transparent_alias = false;
523 }
524 else
525 {
526 symtab->change_decl_assembler_name
527 (node->decl, DECL_ASSEMBLER_NAME (node->get_alias_target ()->decl));
528 node->transparent_alias = true;
529 node->copy_visibility_from (target);
530 }
531 gcc_assert (node->alias);
532 }
533
534 /* NODE is an externally visible definition, which we've discovered is
535 not needed externally. Make it local to this compilation. */
536
537 static void
localize_node(bool whole_program,symtab_node * node)538 localize_node (bool whole_program, symtab_node *node)
539 {
540 gcc_assert (whole_program || in_lto_p || !TREE_PUBLIC (node->decl));
541
542 /* It is possible that one comdat group contains both hidden and non-hidden
543 symbols. In this case we can privatize all hidden symbol but we need
544 to keep non-hidden exported. */
545 if (node->same_comdat_group
546 && (node->resolution == LDPR_PREVAILING_DEF_IRONLY
547 || node->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP))
548 {
549 symtab_node *next;
550 for (next = node->same_comdat_group;
551 next != node; next = next->same_comdat_group)
552 if (next->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP
553 || next->resolution == LDPR_PREVAILING_DEF)
554 break;
555 if (node != next)
556 {
557 if (!node->transparent_alias)
558 {
559 node->resolution = LDPR_PREVAILING_DEF_IRONLY;
560 node->make_decl_local ();
561 if (!flag_incremental_link)
562 node->unique_name |= true;
563 return;
564 }
565 }
566 }
567 /* For similar reason do not privatize whole comdat when seeing comdat
568 local. Wait for non-comdat symbol to be privatized first. */
569 if (node->comdat_local_p ())
570 return;
571
572 if (node->same_comdat_group && TREE_PUBLIC (node->decl))
573 {
574 for (symtab_node *next = node->same_comdat_group;
575 next != node; next = next->same_comdat_group)
576 {
577 next->set_comdat_group (NULL);
578 if (!next->alias)
579 next->set_section (NULL);
580 if (!next->transparent_alias)
581 next->make_decl_local ();
582 next->unique_name
583 |= ((next->resolution == LDPR_PREVAILING_DEF_IRONLY
584 || next->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP)
585 && TREE_PUBLIC (next->decl)
586 && !flag_incremental_link);
587 }
588
589 /* Now everything's localized, the grouping has no meaning, and
590 will cause crashes if we keep it around. */
591 node->dissolve_same_comdat_group_list ();
592 }
593
594 node->unique_name
595 |= ((node->resolution == LDPR_PREVAILING_DEF_IRONLY
596 || node->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP)
597 && TREE_PUBLIC (node->decl)
598 && !flag_incremental_link);
599
600 if (TREE_PUBLIC (node->decl))
601 node->set_comdat_group (NULL);
602 if (DECL_COMDAT (node->decl) && !node->alias)
603 node->set_section (NULL);
604 if (!node->transparent_alias)
605 {
606 node->resolution = LDPR_PREVAILING_DEF_IRONLY;
607 node->make_decl_local ();
608 }
609 }
610
611 /* Decide on visibility of all symbols. */
612
613 static unsigned int
function_and_variable_visibility(bool whole_program)614 function_and_variable_visibility (bool whole_program)
615 {
616 struct cgraph_node *node;
617 varpool_node *vnode;
618
619 /* All aliases should be processed at this point. */
620 gcc_checking_assert (!alias_pairs || !alias_pairs->length ());
621
622 #ifdef ASM_OUTPUT_DEF
623 FOR_EACH_DEFINED_FUNCTION (node)
624 {
625 if (node->get_availability () != AVAIL_INTERPOSABLE
626 || DECL_EXTERNAL (node->decl)
627 || node->has_aliases_p ()
628 || lookup_attribute ("noipa", DECL_ATTRIBUTES (node->decl)))
629 continue;
630
631 cgraph_node *alias = 0;
632 for (cgraph_edge *e = node->callees; e; e = e->next_callee)
633 {
634 /* Recursive function calls usually can't be interposed. */
635
636 if (!e->recursive_p ())
637 continue;
638
639 if (!alias)
640 {
641 alias = dyn_cast<cgraph_node *> (node->noninterposable_alias ());
642 gcc_assert (alias && alias != node);
643 }
644
645 e->redirect_callee (alias);
646 if (gimple_has_body_p (e->caller->decl))
647 {
648 push_cfun (DECL_STRUCT_FUNCTION (e->caller->decl));
649 e->redirect_call_stmt_to_callee ();
650 pop_cfun ();
651 }
652 }
653 }
654 #endif
655
656 FOR_EACH_FUNCTION (node)
657 {
658 int flags = flags_from_decl_or_type (node->decl);
659
660 /* Optimize away PURE and CONST constructors and destructors. */
661 if (node->analyzed
662 && (DECL_STATIC_CONSTRUCTOR (node->decl)
663 || DECL_STATIC_DESTRUCTOR (node->decl))
664 && (flags & (ECF_CONST | ECF_PURE))
665 && !(flags & ECF_LOOPING_CONST_OR_PURE)
666 && opt_for_fn (node->decl, optimize))
667 {
668 DECL_STATIC_CONSTRUCTOR (node->decl) = 0;
669 DECL_STATIC_DESTRUCTOR (node->decl) = 0;
670 }
671
672 /* Frontends and alias code marks nodes as needed before parsing
673 is finished. We may end up marking as node external nodes
674 where this flag is meaningless strip it. */
675 if (DECL_EXTERNAL (node->decl) || !node->definition)
676 {
677 node->force_output = 0;
678 node->forced_by_abi = 0;
679 }
680
681 /* C++ FE on lack of COMDAT support create local COMDAT functions
682 (that ought to be shared but can not due to object format
683 limitations). It is necessary to keep the flag to make rest of C++ FE
684 happy. Clear the flag here to avoid confusion in middle-end. */
685 if (DECL_COMDAT (node->decl) && !TREE_PUBLIC (node->decl))
686 DECL_COMDAT (node->decl) = 0;
687
688 /* For external decls stop tracking same_comdat_group. It doesn't matter
689 what comdat group they are in when they won't be emitted in this TU.
690
691 An exception is LTO where we may end up with both external
692 and non-external declarations in the same comdat group in
693 the case declarations was not merged. */
694 if (node->same_comdat_group && DECL_EXTERNAL (node->decl) && !in_lto_p)
695 {
696 if (flag_checking)
697 {
698 for (symtab_node *n = node->same_comdat_group;
699 n != node;
700 n = n->same_comdat_group)
701 /* If at least one of same comdat group functions is external,
702 all of them have to be, otherwise it is a front-end bug. */
703 gcc_assert (DECL_EXTERNAL (n->decl));
704 }
705 node->dissolve_same_comdat_group_list ();
706 }
707 gcc_assert ((!DECL_WEAK (node->decl)
708 && !DECL_COMDAT (node->decl))
709 || TREE_PUBLIC (node->decl)
710 || node->weakref
711 || DECL_EXTERNAL (node->decl));
712 if (cgraph_externally_visible_p (node, whole_program))
713 {
714 gcc_assert (!node->global.inlined_to);
715 node->externally_visible = true;
716 }
717 else
718 {
719 node->externally_visible = false;
720 node->forced_by_abi = false;
721 }
722 if (!node->externally_visible
723 && node->definition && !node->weakref
724 && !DECL_EXTERNAL (node->decl))
725 localize_node (whole_program, node);
726
727 if (node->thunk.thunk_p
728 && !node->thunk.add_pointer_bounds_args
729 && TREE_PUBLIC (node->decl))
730 {
731 struct cgraph_node *decl_node = node;
732
733 decl_node = decl_node->callees->callee->function_symbol ();
734
735 /* Thunks have the same visibility as function they are attached to.
736 Make sure the C++ front end set this up properly. */
737 if (DECL_ONE_ONLY (decl_node->decl))
738 {
739 gcc_checking_assert (DECL_COMDAT (node->decl)
740 == DECL_COMDAT (decl_node->decl));
741 gcc_checking_assert (node->in_same_comdat_group_p (decl_node));
742 gcc_checking_assert (node->same_comdat_group);
743 }
744 node->forced_by_abi = decl_node->forced_by_abi;
745 if (DECL_EXTERNAL (decl_node->decl))
746 DECL_EXTERNAL (node->decl) = 1;
747 }
748
749 update_visibility_by_resolution_info (node);
750 if (node->weakref)
751 optimize_weakref (node);
752 }
753 FOR_EACH_DEFINED_FUNCTION (node)
754 {
755 if (!node->local.local)
756 node->local.local |= node->local_p ();
757
758 /* If we know that function can not be overwritten by a
759 different semantics and moreover its section can not be
760 discarded, replace all direct calls by calls to an
761 noninterposable alias. This make dynamic linking cheaper and
762 enable more optimization.
763
764 TODO: We can also update virtual tables. */
765 if (node->callers
766 && can_replace_by_local_alias (node))
767 {
768 cgraph_node *alias = dyn_cast<cgraph_node *>
769 (node->noninterposable_alias ());
770
771 if (alias && alias != node)
772 {
773 while (node->callers)
774 {
775 struct cgraph_edge *e = node->callers;
776
777 e->redirect_callee (alias);
778 if (gimple_has_body_p (e->caller->decl))
779 {
780 push_cfun (DECL_STRUCT_FUNCTION (e->caller->decl));
781 e->redirect_call_stmt_to_callee ();
782 pop_cfun ();
783 }
784 }
785 }
786 }
787 }
788 FOR_EACH_VARIABLE (vnode)
789 {
790 /* weak flag makes no sense on local variables. */
791 gcc_assert (!DECL_WEAK (vnode->decl)
792 || vnode->weakref
793 || TREE_PUBLIC (vnode->decl)
794 || DECL_EXTERNAL (vnode->decl));
795 /* In several cases declarations can not be common:
796
797 - when declaration has initializer
798 - when it is in weak
799 - when it has specific section
800 - when it resides in non-generic address space.
801 - if declaration is local, it will get into .local common section
802 so common flag is not needed. Frontends still produce these in
803 certain cases, such as for:
804
805 static int a __attribute__ ((common))
806
807 Canonicalize things here and clear the redundant flag. */
808 if (DECL_COMMON (vnode->decl)
809 && (!(TREE_PUBLIC (vnode->decl)
810 || DECL_EXTERNAL (vnode->decl))
811 || (DECL_INITIAL (vnode->decl)
812 && DECL_INITIAL (vnode->decl) != error_mark_node)
813 || DECL_WEAK (vnode->decl)
814 || DECL_SECTION_NAME (vnode->decl) != NULL
815 || ! (ADDR_SPACE_GENERIC_P
816 (TYPE_ADDR_SPACE (TREE_TYPE (vnode->decl))))))
817 DECL_COMMON (vnode->decl) = 0;
818 if (vnode->weakref)
819 optimize_weakref (vnode);
820 }
821 FOR_EACH_DEFINED_VARIABLE (vnode)
822 {
823 if (!vnode->definition)
824 continue;
825 if (vnode->externally_visible_p ())
826 vnode->externally_visible = true;
827 else
828 {
829 vnode->externally_visible = false;
830 vnode->forced_by_abi = false;
831 }
832 if (lookup_attribute ("no_reorder",
833 DECL_ATTRIBUTES (vnode->decl)))
834 vnode->no_reorder = 1;
835
836 if (!vnode->externally_visible
837 && !vnode->transparent_alias
838 && !DECL_EXTERNAL (vnode->decl))
839 localize_node (whole_program, vnode);
840
841 update_visibility_by_resolution_info (vnode);
842
843 /* Update virtual tables to point to local aliases where possible. */
844 if (DECL_VIRTUAL_P (vnode->decl)
845 && !DECL_EXTERNAL (vnode->decl))
846 {
847 int i;
848 struct ipa_ref *ref;
849 bool found = false;
850
851 /* See if there is something to update. */
852 for (i = 0; vnode->iterate_reference (i, ref); i++)
853 if (ref->use == IPA_REF_ADDR
854 && can_replace_by_local_alias_in_vtable (ref->referred))
855 {
856 found = true;
857 break;
858 }
859 if (found)
860 {
861 hash_set<tree> visited_nodes;
862
863 vnode->get_constructor ();
864 walk_tree (&DECL_INITIAL (vnode->decl),
865 update_vtable_references, NULL, &visited_nodes);
866 vnode->remove_all_references ();
867 record_references_in_initializer (vnode->decl, false);
868 }
869 }
870 }
871
872 if (dump_file)
873 {
874 fprintf (dump_file, "\nMarking local functions:");
875 FOR_EACH_DEFINED_FUNCTION (node)
876 if (node->local.local)
877 fprintf (dump_file, " %s", node->name ());
878 fprintf (dump_file, "\n\n");
879 fprintf (dump_file, "\nMarking externally visible functions:");
880 FOR_EACH_DEFINED_FUNCTION (node)
881 if (node->externally_visible)
882 fprintf (dump_file, " %s", node->name ());
883 fprintf (dump_file, "\n\n");
884 fprintf (dump_file, "\nMarking externally visible variables:");
885 FOR_EACH_DEFINED_VARIABLE (vnode)
886 if (vnode->externally_visible)
887 fprintf (dump_file, " %s", vnode->name ());
888 fprintf (dump_file, "\n\n");
889 }
890 symtab->function_flags_ready = true;
891 return 0;
892 }
893
894 /* Local function pass handling visibilities. This happens before LTO streaming
895 so in particular -fwhole-program should be ignored at this level. */
896
897 namespace {
898
899 const pass_data pass_data_ipa_function_and_variable_visibility =
900 {
901 SIMPLE_IPA_PASS, /* type */
902 "visibility", /* name */
903 OPTGROUP_NONE, /* optinfo_flags */
904 TV_CGRAPHOPT, /* tv_id */
905 0, /* properties_required */
906 0, /* properties_provided */
907 0, /* properties_destroyed */
908 0, /* todo_flags_start */
909 ( TODO_remove_functions | TODO_dump_symtab ), /* todo_flags_finish */
910 };
911
912 /* Bring functions local at LTO time with -fwhole-program. */
913
914 static unsigned int
whole_program_function_and_variable_visibility(void)915 whole_program_function_and_variable_visibility (void)
916 {
917 function_and_variable_visibility (flag_whole_program);
918 if (optimize || in_lto_p)
919 ipa_discover_readonly_nonaddressable_vars ();
920 return 0;
921 }
922
923 } // anon namespace
924
925 namespace {
926
927 const pass_data pass_data_ipa_whole_program_visibility =
928 {
929 IPA_PASS, /* type */
930 "whole-program", /* name */
931 OPTGROUP_NONE, /* optinfo_flags */
932 TV_CGRAPHOPT, /* tv_id */
933 0, /* properties_required */
934 0, /* properties_provided */
935 0, /* properties_destroyed */
936 0, /* todo_flags_start */
937 ( TODO_remove_functions | TODO_dump_symtab ), /* todo_flags_finish */
938 };
939
940 class pass_ipa_whole_program_visibility : public ipa_opt_pass_d
941 {
942 public:
pass_ipa_whole_program_visibility(gcc::context * ctxt)943 pass_ipa_whole_program_visibility (gcc::context *ctxt)
944 : ipa_opt_pass_d (pass_data_ipa_whole_program_visibility, ctxt,
945 NULL, /* generate_summary */
946 NULL, /* write_summary */
947 NULL, /* read_summary */
948 NULL, /* write_optimization_summary */
949 NULL, /* read_optimization_summary */
950 NULL, /* stmt_fixup */
951 0, /* function_transform_todo_flags_start */
952 NULL, /* function_transform */
953 NULL) /* variable_transform */
954 {}
955
956 /* opt_pass methods: */
957
gate(function *)958 virtual bool gate (function *)
959 {
960 /* Do not re-run on ltrans stage. */
961 return !flag_ltrans;
962 }
execute(function *)963 virtual unsigned int execute (function *)
964 {
965 return whole_program_function_and_variable_visibility ();
966 }
967
968 }; // class pass_ipa_whole_program_visibility
969
970 } // anon namespace
971
972 ipa_opt_pass_d *
make_pass_ipa_whole_program_visibility(gcc::context * ctxt)973 make_pass_ipa_whole_program_visibility (gcc::context *ctxt)
974 {
975 return new pass_ipa_whole_program_visibility (ctxt);
976 }
977
978 class pass_ipa_function_and_variable_visibility : public simple_ipa_opt_pass
979 {
980 public:
pass_ipa_function_and_variable_visibility(gcc::context * ctxt)981 pass_ipa_function_and_variable_visibility (gcc::context *ctxt)
982 : simple_ipa_opt_pass (pass_data_ipa_function_and_variable_visibility,
983 ctxt)
984 {}
985
986 /* opt_pass methods: */
execute(function *)987 virtual unsigned int execute (function *)
988 {
989 return function_and_variable_visibility (flag_whole_program && !flag_lto);
990 }
991
992 }; // class pass_ipa_function_and_variable_visibility
993
994 simple_ipa_opt_pass *
make_pass_ipa_function_and_variable_visibility(gcc::context * ctxt)995 make_pass_ipa_function_and_variable_visibility (gcc::context *ctxt)
996 {
997 return new pass_ipa_function_and_variable_visibility (ctxt);
998 }
999