gcc/ipa-visibility.c

   1 /* IPA visibility pass
   2    Copyright (C) 2003-2019 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 cannot 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 cannot be local. Worker for cgraph_local_node_p.  */
  91
  92 static bool
  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
 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
 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 cannot 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 cannot 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
 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
 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 (fndecl_built_in_p (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   return false;
 249 }
 250
 251 /* Return true when variable should be considered externally visible.  */
 252
 253 bool
 254 varpool_node::externally_visible_p (void)
 255 {
 256   while (transparent_alias && definition)
 257     return get_alias_target ()->externally_visible_p ();
 258   if (DECL_EXTERNAL (decl))
 259     return true;
 260
 261   if (!TREE_PUBLIC (decl))
 262     return false;
 263
 264   /* If linker counts on us, we must preserve the function.  */
 265   if (used_from_object_file_p ())
 266     return true;
 267
 268   /* Bringing TLS variables local may cause dynamic linker failures
 269      on limits of static TLS vars.  */
 270   if (DECL_THREAD_LOCAL_P (decl)
 271       && (DECL_TLS_MODEL (decl) != TLS_MODEL_EMULATED
 272           && DECL_TLS_MODEL (decl) != TLS_MODEL_INITIAL_EXEC))
 273     return true;
 274
 275   if (DECL_HARD_REGISTER (decl))
 276     return true;
 277   if (DECL_PRESERVE_P (decl))
 278     return true;
 279   if (lookup_attribute ("externally_visible",
 280                         DECL_ATTRIBUTES (decl)))
 281     return true;
 282   if (TARGET_DLLIMPORT_DECL_ATTRIBUTES
 283       && lookup_attribute ("dllexport",
 284                            DECL_ATTRIBUTES (decl)))
 285     return true;
 286
 287   /* See if we have linker information about symbol not being used or
 288      if we need to make guess based on the declaration.
 289
 290      Even if the linker clams the symbol is unused, never bring internal
 291      symbols that are declared by user as used or externally visible.
 292      This is needed for i.e. references from asm statements.   */
 293   if (used_from_object_file_p ())
 294     return true;
 295   if (resolution == LDPR_PREVAILING_DEF_IRONLY)
 296     return false;
 297
 298   /* As a special case, the COMDAT virtual tables can be unshared.
 299      In LTO mode turn vtables into static variables.  The variable is readonly,
 300      so this does not enable more optimization, but referring static var
 301      is faster for dynamic linking.  Also this match logic hidding vtables
 302      from LTO symbol tables.  */
 303   if (((in_lto_p || flag_whole_program) && !flag_incremental_link)
 304       && DECL_COMDAT (decl)
 305       && comdat_can_be_unshared_p (this))
 306     return false;
 307
 308   /* When doing link time optimizations, hidden symbols become local.  */
 309   if (in_lto_p && !flag_incremental_link
 310       && (DECL_VISIBILITY (decl) == VISIBILITY_HIDDEN
 311           || DECL_VISIBILITY (decl) == VISIBILITY_INTERNAL)
 312       /* Be sure that node is defined in IR file, not in other object
 313          file.  In that case we don't set used_from_other_object_file.  */
 314       && definition)
 315     ;
 316   else if (!flag_whole_program)
 317     return true;
 318
 319   /* Do not attempt to privatize COMDATS by default.
 320      This would break linking with C++ libraries sharing
 321      inline definitions.
 322
 323      FIXME: We can do so for readonly vars with no address taken and
 324      possibly also for vtables since no direct pointer comparsion is done.
 325      It might be interesting to do so to reduce linking overhead.  */
 326   if (DECL_COMDAT (decl) || DECL_WEAK (decl))
 327     return true;
 328   return false;
 329 }
 330
 331 /* Return true if reference to NODE can be replaced by a local alias.
 332    Local aliases save dynamic linking overhead and enable more optimizations.
 333  */
 334
 335 static bool
 336 can_replace_by_local_alias (symtab_node *node)
 337 {
 338   /* If aliases aren't supported, we can't do replacement.  */
 339   if (!TARGET_SUPPORTS_ALIASES)
 340     return false;
 341
 342   /* Weakrefs have a reason to be non-local.  Be sure we do not replace
 343      them.  */
 344   while (node->transparent_alias && node->definition && !node->weakref)
 345     node = node->get_alias_target ();
 346   if (node->weakref)
 347     return false;
 348
 349   return (node->get_availability () > AVAIL_INTERPOSABLE
 350           && !decl_binds_to_current_def_p (node->decl)
 351           && !node->can_be_discarded_p ());
 352 }
 353
 354 /* Return true if we can replace reference to NODE by local alias
 355    within a virtual table.  Generally we can replace function pointers
 356    and virtual table pointers.  */
 357
 358 static bool
 359 can_replace_by_local_alias_in_vtable (symtab_node *node)
 360 {
 361   if (is_a <varpool_node *> (node)
 362       && !DECL_VIRTUAL_P (node->decl))
 363     return false;
 364   return can_replace_by_local_alias (node);
 365 }
 366
 367 /* walk_tree callback that rewrites initializer references.   */
 368
 369 static tree
 370 update_vtable_references (tree *tp, int *walk_subtrees,
 371                           void *data ATTRIBUTE_UNUSED)
 372 {
 373   if (VAR_OR_FUNCTION_DECL_P (*tp))
 374     {
 375       if (can_replace_by_local_alias_in_vtable (symtab_node::get (*tp)))
 376         *tp = symtab_node::get (*tp)->noninterposable_alias ()->decl;
 377       *walk_subtrees = 0;
 378     }
 379   else if (IS_TYPE_OR_DECL_P (*tp))
 380     *walk_subtrees = 0;
 381   return NULL;
 382 }
 383
 384 /* In LTO we can remove COMDAT groups and weak symbols.
 385    Either turn them into normal symbols or external symbol depending on
 386    resolution info.  */
 387
 388 static void
 389 update_visibility_by_resolution_info (symtab_node * node)
 390 {
 391   bool define;
 392
 393   if (!node->externally_visible
 394       || (!DECL_WEAK (node->decl) && !DECL_ONE_ONLY (node->decl))
 395       || node->resolution == LDPR_UNKNOWN)
 396     return;
 397
 398   define = (node->resolution == LDPR_PREVAILING_DEF_IRONLY
 399             || node->resolution == LDPR_PREVAILING_DEF
 400             || node->resolution == LDPR_UNDEF
 401             || node->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP);
 402
 403   /* The linker decisions ought to agree in the whole group.  */
 404   if (node->same_comdat_group)
 405     for (symtab_node *next = node->same_comdat_group;
 406          next != node; next = next->same_comdat_group)
 407       {
 408         if (!next->externally_visible || next->transparent_alias)
 409           continue;
 410
 411         bool same_def
 412           = define == (next->resolution == LDPR_PREVAILING_DEF_IRONLY
 413                        || next->resolution == LDPR_PREVAILING_DEF
 414                        || next->resolution == LDPR_UNDEF
 415                        || next->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP);
 416         gcc_assert (in_lto_p || same_def);
 417         if (!same_def)
 418           return;
 419       }
 420
 421   if (node->same_comdat_group)
 422     for (symtab_node *next = node->same_comdat_group;
 423          next != node; next = next->same_comdat_group)
 424       {
 425         /* During incremental linking we need to keep symbol weak for future
 426            linking.  We can still drop definition if we know non-LTO world
 427            prevails.  */
 428         if (!flag_incremental_link)
 429           {
 430             DECL_WEAK (next->decl) = false;
 431             next->set_comdat_group (NULL);
 432           }
 433         if (!define)
 434           {
 435             if (next->externally_visible)
 436               DECL_EXTERNAL (next->decl) = true;
 437             next->set_comdat_group (NULL);
 438           }
 439       }
 440
 441   /* During incremental linking we need to keep symbol weak for future
 442      linking.  We can still drop definition if we know non-LTO world prevails.  */
 443   if (!flag_incremental_link)
 444     {
 445       DECL_WEAK (node->decl) = false;
 446       node->set_comdat_group (NULL);
 447       node->dissolve_same_comdat_group_list ();
 448     }
 449   if (!define)
 450     {
 451       DECL_EXTERNAL (node->decl) = true;
 452       node->set_comdat_group (NULL);
 453       node->dissolve_same_comdat_group_list ();
 454     }
 455 }
 456
 457 /* Try to get rid of weakref.  */
 458
 459 static void
 460 optimize_weakref (symtab_node *node)
 461 {
 462   bool strip_weakref = false;
 463   bool static_alias = false;
 464
 465   gcc_assert (node->weakref);
 466
 467   /* Weakrefs with no target defined cannot be optimized.  */
 468   if (!node->analyzed)
 469     return;
 470   symtab_node *target = node->get_alias_target ();
 471
 472   /* Weakrefs to weakrefs can be optimized only if target can be.  */
 473   if (target->weakref)
 474     optimize_weakref (target);
 475   if (target->weakref)
 476     return;
 477
 478   /* If we have definition of weakref's target and we know it binds locally,
 479      we can turn weakref to static alias.  */
 480   if (TARGET_SUPPORTS_ALIASES
 481       && target->definition && decl_binds_to_current_def_p (target->decl))
 482     strip_weakref = static_alias = true;
 483   /* Otherwise we can turn weakref into transparent alias.  This transformation
 484      may break asm statements which directly refers to symbol name and expect
 485      GNU as to translate it via .weakref directive. So do not optimize when
 486      DECL_PRESERVED is set and .weakref is supported.  */
 487   else if ((!DECL_PRESERVE_P (target->decl)
 488             || IDENTIFIER_TRANSPARENT_ALIAS (DECL_ASSEMBLER_NAME (node->decl)))
 489            && !DECL_WEAK (target->decl)
 490            && !DECL_EXTERNAL (target->decl)
 491            && ((target->definition && !target->can_be_discarded_p ())
 492                || target->resolution != LDPR_UNDEF))
 493     strip_weakref = true;
 494   if (!strip_weakref)
 495     return;
 496   node->weakref = false;
 497   IDENTIFIER_TRANSPARENT_ALIAS (DECL_ASSEMBLER_NAME (node->decl)) = 0;
 498   TREE_CHAIN (DECL_ASSEMBLER_NAME (node->decl)) = NULL_TREE;
 499   DECL_ATTRIBUTES (node->decl) = remove_attribute ("weakref",
 500                                                    DECL_ATTRIBUTES
 501                                                          (node->decl));
 502
 503   if (dump_file)
 504     fprintf (dump_file, "Optimizing weakref %s %s\n",
 505              node->name(),
 506              static_alias ? "as static alias" : "as transparent alias");
 507
 508   if (static_alias)
 509     {
 510       /* make_decl_local will shortcircuit if it doesn't see TREE_PUBLIC.
 511          be sure it really clears the WEAK flag.  */
 512       TREE_PUBLIC (node->decl) = true;
 513       node->make_decl_local ();
 514       node->forced_by_abi = false;
 515       node->resolution = LDPR_PREVAILING_DEF_IRONLY;
 516       node->externally_visible = false;
 517       gcc_assert (!DECL_WEAK (node->decl));
 518       node->transparent_alias = false;
 519     }
 520   else
 521     {
 522       symtab->change_decl_assembler_name
 523         (node->decl, DECL_ASSEMBLER_NAME (node->get_alias_target ()->decl));
 524       node->transparent_alias = true;
 525       node->copy_visibility_from (target);
 526     }
 527   gcc_assert (node->alias);
 528 }
 529
 530 /* NODE is an externally visible definition, which we've discovered is
 531    not needed externally.  Make it local to this compilation.  */
 532
 533 static void
 534 localize_node (bool whole_program, symtab_node *node)
 535 {
 536   gcc_assert (whole_program || in_lto_p || !TREE_PUBLIC (node->decl));
 537
 538   /* It is possible that one comdat group contains both hidden and non-hidden
 539      symbols.  In this case we can privatize all hidden symbol but we need
 540      to keep non-hidden exported.  */
 541   if (node->same_comdat_group
 542       && (node->resolution == LDPR_PREVAILING_DEF_IRONLY
 543           || node->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP))
 544     {
 545       symtab_node *next;
 546       for (next = node->same_comdat_group;
 547            next != node; next = next->same_comdat_group)
 548         if (next->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP
 549             || next->resolution == LDPR_PREVAILING_DEF)
 550           break;
 551       if (node != next)
 552         {
 553           if (!node->transparent_alias)
 554             {
 555               node->resolution = LDPR_PREVAILING_DEF_IRONLY;
 556               node->make_decl_local ();
 557               if (!flag_incremental_link)
 558                 node->unique_name |= true;
 559               return;
 560             }
 561         }
 562     }
 563   /* For similar reason do not privatize whole comdat when seeing comdat
 564      local.  Wait for non-comdat symbol to be privatized first.  */
 565   if (node->comdat_local_p ())
 566     return;
 567
 568   if (node->same_comdat_group && TREE_PUBLIC (node->decl))
 569     {
 570       for (symtab_node *next = node->same_comdat_group;
 571            next != node; next = next->same_comdat_group)
 572         {
 573           next->set_comdat_group (NULL);
 574           if (!next->alias)
 575             next->set_section (NULL);
 576           if (!next->transparent_alias)
 577             next->make_decl_local ();
 578           next->unique_name
 579             |= ((next->resolution == LDPR_PREVAILING_DEF_IRONLY
 580                  || next->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP)
 581                 && TREE_PUBLIC (next->decl)
 582                 && !flag_incremental_link);
 583         }
 584
 585       /* Now everything's localized, the grouping has no meaning, and
 586          will cause crashes if we keep it around.  */
 587       node->dissolve_same_comdat_group_list ();
 588     }
 589
 590   node->unique_name
 591     |= ((node->resolution == LDPR_PREVAILING_DEF_IRONLY
 592          || node->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP)
 593         && TREE_PUBLIC (node->decl)
 594         && !flag_incremental_link);
 595
 596   if (TREE_PUBLIC (node->decl))
 597     node->set_comdat_group (NULL);
 598   if (DECL_COMDAT (node->decl) && !node->alias)
 599     node->set_section (NULL);
 600   if (!node->transparent_alias)
 601     {
 602       node->resolution = LDPR_PREVAILING_DEF_IRONLY;
 603       node->make_decl_local ();
 604     }
 605 }
 606
 607 /* Decide on visibility of all symbols.  */
 608
 609 static unsigned int
 610 function_and_variable_visibility (bool whole_program)
 611 {
 612   struct cgraph_node *node;
 613   varpool_node *vnode;
 614
 615   /* All aliases should be processed at this point.  */
 616   gcc_checking_assert (!alias_pairs || !alias_pairs->length ());
 617
 618 #ifdef ASM_OUTPUT_DEF
 619   FOR_EACH_DEFINED_FUNCTION (node)
 620     {
 621       if (node->get_availability () != AVAIL_INTERPOSABLE
 622           || DECL_EXTERNAL (node->decl)
 623           || node->has_aliases_p ()
 624           || lookup_attribute ("noipa", DECL_ATTRIBUTES (node->decl)))
 625         continue;
 626
 627       cgraph_node *alias = 0;
 628       for (cgraph_edge *e = node->callees; e; e = e->next_callee)
 629         {
 630           /* Recursive function calls usually can't be interposed.  */
 631
 632           if (!e->recursive_p ())
 633             continue;
 634
 635           if (!alias)
 636             {
 637               alias = dyn_cast<cgraph_node *> (node->noninterposable_alias ());
 638               gcc_assert (alias && alias != node);
 639             }
 640
 641           e->redirect_callee (alias);
 642           if (gimple_has_body_p (e->caller->decl))
 643             {
 644               push_cfun (DECL_STRUCT_FUNCTION (e->caller->decl));
 645               e->redirect_call_stmt_to_callee ();
 646               pop_cfun ();
 647             }
 648         }
 649     }
 650 #endif
 651
 652   FOR_EACH_FUNCTION (node)
 653     {
 654       int flags = flags_from_decl_or_type (node->decl);
 655
 656       /* Optimize away PURE and CONST constructors and destructors.  */
 657       if (node->analyzed
 658           && (DECL_STATIC_CONSTRUCTOR (node->decl)
 659               || DECL_STATIC_DESTRUCTOR (node->decl))
 660           && (flags & (ECF_CONST | ECF_PURE))
 661           && !(flags & ECF_LOOPING_CONST_OR_PURE)
 662           && opt_for_fn (node->decl, optimize))
 663         {
 664           DECL_STATIC_CONSTRUCTOR (node->decl) = 0;
 665           DECL_STATIC_DESTRUCTOR (node->decl) = 0;
 666         }
 667
 668       /* Frontends and alias code marks nodes as needed before parsing
 669          is finished.  We may end up marking as node external nodes
 670          where this flag is meaningless strip it.  */
 671       if (DECL_EXTERNAL (node->decl) || !node->definition)
 672         {
 673           node->force_output = 0;
 674           node->forced_by_abi = 0;
 675         }
 676
 677       /* C++ FE on lack of COMDAT support create local COMDAT functions
 678          (that ought to be shared but cannot due to object format
 679          limitations).  It is necessary to keep the flag to make rest of C++ FE
 680          happy.  Clear the flag here to avoid confusion in middle-end.  */
 681       if (DECL_COMDAT (node->decl) && !TREE_PUBLIC (node->decl))
 682         DECL_COMDAT (node->decl) = 0;
 683
 684       /* For external decls stop tracking same_comdat_group. It doesn't matter
 685          what comdat group they are in when they won't be emitted in this TU.
 686
 687          An exception is LTO where we may end up with both external
 688          and non-external declarations in the same comdat group in
 689          the case declarations was not merged.  */
 690       if (node->same_comdat_group && DECL_EXTERNAL (node->decl) && !in_lto_p)
 691         {
 692           if (flag_checking)
 693             {
 694               for (symtab_node *n = node->same_comdat_group;
 695                    n != node;
 696                    n = n->same_comdat_group)
 697                 /* If at least one of same comdat group functions is external,
 698                    all of them have to be, otherwise it is a front-end bug.  */
 699                 gcc_assert (DECL_EXTERNAL (n->decl));
 700             }
 701           node->dissolve_same_comdat_group_list ();
 702         }
 703       gcc_assert ((!DECL_WEAK (node->decl)
 704                   && !DECL_COMDAT (node->decl))
 705                   || TREE_PUBLIC (node->decl)
 706                   || node->weakref
 707                   || DECL_EXTERNAL (node->decl));
 708       if (cgraph_externally_visible_p (node, whole_program))
 709         {
 710           gcc_assert (!node->global.inlined_to);
 711           node->externally_visible = true;
 712         }
 713       else
 714         {
 715           node->externally_visible = false;
 716           node->forced_by_abi = false;
 717         }
 718       if (!node->externally_visible
 719           && node->definition && !node->weakref
 720           && !DECL_EXTERNAL (node->decl))
 721         localize_node (whole_program, node);
 722
 723       if (node->thunk.thunk_p
 724           && TREE_PUBLIC (node->decl))
 725         {
 726           struct cgraph_node *decl_node = node;
 727
 728           decl_node = decl_node->callees->callee->function_symbol ();
 729
 730           /* Thunks have the same visibility as function they are attached to.
 731              Make sure the C++ front end set this up properly.  */
 732           if (DECL_ONE_ONLY (decl_node->decl))
 733             {
 734               gcc_checking_assert (DECL_COMDAT (node->decl)
 735                                    == DECL_COMDAT (decl_node->decl));
 736               gcc_checking_assert (node->in_same_comdat_group_p (decl_node));
 737               gcc_checking_assert (node->same_comdat_group);
 738             }
 739           node->forced_by_abi = decl_node->forced_by_abi;
 740           if (DECL_EXTERNAL (decl_node->decl))
 741             DECL_EXTERNAL (node->decl) = 1;
 742         }
 743
 744       update_visibility_by_resolution_info (node);
 745       if (node->weakref)
 746         optimize_weakref (node);
 747     }
 748   FOR_EACH_DEFINED_FUNCTION (node)
 749     {
 750       if (!node->local.local)
 751         node->local.local |= node->local_p ();
 752
 753       /* If we know that function cannot be overwritten by a
 754          different semantics and moreover its section cannot be
 755          discarded, replace all direct calls by calls to an
 756          noninterposable alias.  This make dynamic linking cheaper and
 757          enable more optimization.
 758
 759          TODO: We can also update virtual tables.  */
 760       if (node->callers
 761           && can_replace_by_local_alias (node))
 762         {
 763           cgraph_node *alias = dyn_cast<cgraph_node *>
 764             (node->noninterposable_alias ());
 765
 766           if (alias && alias != node)
 767             {
 768               while (node->callers)
 769                 {
 770                   struct cgraph_edge *e = node->callers;
 771
 772                   e->redirect_callee (alias);
 773                   if (gimple_has_body_p (e->caller->decl))
 774                     {
 775                       push_cfun (DECL_STRUCT_FUNCTION (e->caller->decl));
 776                       e->redirect_call_stmt_to_callee ();
 777                       pop_cfun ();
 778                     }
 779                 }
 780             }
 781         }
 782     }
 783   FOR_EACH_VARIABLE (vnode)
 784     {
 785       /* weak flag makes no sense on local variables.  */
 786       gcc_assert (!DECL_WEAK (vnode->decl)
 787                   || vnode->weakref
 788                   || TREE_PUBLIC (vnode->decl)
 789                   || DECL_EXTERNAL (vnode->decl));
 790       /* In several cases declarations cannot be common:
 791
 792          - when declaration has initializer
 793          - when it is in weak
 794          - when it has specific section
 795          - when it resides in non-generic address space.
 796          - if declaration is local, it will get into .local common section
 797            so common flag is not needed.  Frontends still produce these in
 798            certain cases, such as for:
 799
 800              static int a __attribute__ ((common))
 801
 802          Canonicalize things here and clear the redundant flag.  */
 803       if (DECL_COMMON (vnode->decl)
 804           && (!(TREE_PUBLIC (vnode->decl)
 805               || DECL_EXTERNAL (vnode->decl))
 806               || (DECL_INITIAL (vnode->decl)
 807                   && DECL_INITIAL (vnode->decl) != error_mark_node)
 808               || DECL_WEAK (vnode->decl)
 809               || DECL_SECTION_NAME (vnode->decl) != NULL
 810               || ! (ADDR_SPACE_GENERIC_P
 811                     (TYPE_ADDR_SPACE (TREE_TYPE (vnode->decl))))))
 812         DECL_COMMON (vnode->decl) = 0;
 813       if (vnode->weakref)
 814         optimize_weakref (vnode);
 815     }
 816   FOR_EACH_DEFINED_VARIABLE (vnode)
 817     {
 818       if (!vnode->definition)
 819         continue;
 820       if (vnode->externally_visible_p ())
 821         vnode->externally_visible = true;
 822       else
 823         {
 824           vnode->externally_visible = false;
 825           vnode->forced_by_abi = false;
 826         }
 827       if (lookup_attribute ("no_reorder",
 828                             DECL_ATTRIBUTES (vnode->decl)))
 829         vnode->no_reorder = 1;
 830
 831       if (!vnode->externally_visible
 832           && !vnode->transparent_alias
 833           && !DECL_EXTERNAL (vnode->decl))
 834         localize_node (whole_program, vnode);
 835
 836       update_visibility_by_resolution_info (vnode);
 837
 838       /* Update virtual tables to point to local aliases where possible.  */
 839       if (DECL_VIRTUAL_P (vnode->decl)
 840           && !DECL_EXTERNAL (vnode->decl))
 841         {
 842           int i;
 843           struct ipa_ref *ref;
 844           bool found = false;
 845
 846           /* See if there is something to update.  */
 847           for (i = 0; vnode->iterate_reference (i, ref); i++)
 848             if (ref->use == IPA_REF_ADDR
 849                 && can_replace_by_local_alias_in_vtable (ref->referred))
 850               {
 851                 found = true;
 852                 break;
 853               }
 854           if (found)
 855             {
 856               hash_set<tree> visited_nodes;
 857
 858               vnode->get_constructor ();
 859               walk_tree (&DECL_INITIAL (vnode->decl),
 860                          update_vtable_references, NULL, &visited_nodes);
 861               vnode->remove_all_references ();
 862               record_references_in_initializer (vnode->decl, false);
 863             }
 864         }
 865     }
 866
 867   if (dump_file)
 868     {
 869       fprintf (dump_file, "\nMarking local functions:");
 870       FOR_EACH_DEFINED_FUNCTION (node)
 871         if (node->local.local)
 872           fprintf (dump_file, " %s", node->name ());
 873       fprintf (dump_file, "\n\n");
 874       fprintf (dump_file, "\nMarking externally visible functions:");
 875       FOR_EACH_DEFINED_FUNCTION (node)
 876         if (node->externally_visible)
 877           fprintf (dump_file, " %s", node->name ());
 878       fprintf (dump_file, "\n\n");
 879       fprintf (dump_file, "\nMarking externally visible variables:");
 880       FOR_EACH_DEFINED_VARIABLE (vnode)
 881         if (vnode->externally_visible)
 882           fprintf (dump_file, " %s", vnode->name ());
 883       fprintf (dump_file, "\n\n");
 884     }
 885   symtab->function_flags_ready = true;
 886   return 0;
 887 }
 888
 889 /* Local function pass handling visibilities.  This happens before LTO streaming
 890    so in particular -fwhole-program should be ignored at this level.  */
 891
 892 namespace {
 893
 894 const pass_data pass_data_ipa_function_and_variable_visibility =
 895 {
 896   SIMPLE_IPA_PASS, /* type */
 897   "visibility", /* name */
 898   OPTGROUP_NONE, /* optinfo_flags */
 899   TV_CGRAPHOPT, /* tv_id */
 900   0, /* properties_required */
 901   0, /* properties_provided */
 902   0, /* properties_destroyed */
 903   0, /* todo_flags_start */
 904   ( TODO_remove_functions | TODO_dump_symtab ), /* todo_flags_finish */
 905 };
 906
 907 /* Bring functions local at LTO time with -fwhole-program.  */
 908
 909 static unsigned int
 910 whole_program_function_and_variable_visibility (void)
 911 {
 912   function_and_variable_visibility (flag_whole_program);
 913   if (optimize || in_lto_p)
 914     ipa_discover_variable_flags ();
 915   return 0;
 916 }
 917
 918 } // anon namespace
 919
 920 namespace {
 921
 922 const pass_data pass_data_ipa_whole_program_visibility =
 923 {
 924   IPA_PASS, /* type */
 925   "whole-program", /* name */
 926   OPTGROUP_NONE, /* optinfo_flags */
 927   TV_CGRAPHOPT, /* tv_id */
 928   0, /* properties_required */
 929   0, /* properties_provided */
 930   0, /* properties_destroyed */
 931   0, /* todo_flags_start */
 932   ( TODO_remove_functions | TODO_dump_symtab ), /* todo_flags_finish */
 933 };
 934
 935 class pass_ipa_whole_program_visibility : public ipa_opt_pass_d
 936 {
 937 public:
 938   pass_ipa_whole_program_visibility (gcc::context *ctxt)
 939     : ipa_opt_pass_d (pass_data_ipa_whole_program_visibility, ctxt,
 940                       NULL, /* generate_summary */
 941                       NULL, /* write_summary */
 942                       NULL, /* read_summary */
 943                       NULL, /* write_optimization_summary */
 944                       NULL, /* read_optimization_summary */
 945                       NULL, /* stmt_fixup */
 946                       0, /* function_transform_todo_flags_start */
 947                       NULL, /* function_transform */
 948                       NULL) /* variable_transform */
 949   {}
 950
 951   /* opt_pass methods: */
 952
 953   virtual bool gate (function *)
 954     {
 955       /* Do not re-run on ltrans stage.  */
 956       return !flag_ltrans;
 957     }
 958   virtual unsigned int execute (function *)
 959     {
 960       return whole_program_function_and_variable_visibility ();
 961     }
 962
 963 }; // class pass_ipa_whole_program_visibility
 964
 965 } // anon namespace
 966
 967 ipa_opt_pass_d *
 968 make_pass_ipa_whole_program_visibility (gcc::context *ctxt)
 969 {
 970   return new pass_ipa_whole_program_visibility (ctxt);
 971 }
 972
 973 class pass_ipa_function_and_variable_visibility : public simple_ipa_opt_pass
 974 {
 975 public:
 976   pass_ipa_function_and_variable_visibility (gcc::context *ctxt)
 977     : simple_ipa_opt_pass (pass_data_ipa_function_and_variable_visibility,
 978                            ctxt)
 979   {}
 980
 981   /* opt_pass methods: */
 982   virtual unsigned int execute (function *)
 983     {
 984       return function_and_variable_visibility (flag_whole_program && !flag_lto);
 985     }
 986
 987 }; // class pass_ipa_function_and_variable_visibility
 988
 989 simple_ipa_opt_pass *
 990 make_pass_ipa_function_and_variable_visibility (gcc::context *ctxt)
 991 {
 992   return new pass_ipa_function_and_variable_visibility (ctxt);
 993 }