gcc/ipa-visibility.cc

   1 /* IPA visibility pass
   2    Copyright (C) 2003-2023 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
  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)
 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
 224   /* Limitation of gas requires us to output targets of symver aliases as
 225      global symbols.  This is binutils PR 25295.  */
 226   ipa_ref *ref;
 227   FOR_EACH_ALIAS (node, ref)
 228     if (ref->referring->symver)
 229       return true;
 230
 231   if (node->resolution == LDPR_PREVAILING_DEF_IRONLY)
 232     return false;
 233   /* When doing LTO or whole program, we can bring COMDAT functions static.
 234      This improves code quality and we know we will duplicate them at most twice
 235      (in the case that we are not using plugin and link with object file
 236       implementing same COMDAT)  */
 237   if (((in_lto_p || whole_program) && !flag_incremental_link)
 238       && DECL_COMDAT (node->decl)
 239       && comdat_can_be_unshared_p (node))
 240     return false;
 241
 242   /* When doing link time optimizations, hidden symbols become local.  */
 243   if ((in_lto_p && !flag_incremental_link)
 244       && (DECL_VISIBILITY (node->decl) == VISIBILITY_HIDDEN
 245           || DECL_VISIBILITY (node->decl) == VISIBILITY_INTERNAL)
 246       /* Be sure that node is defined in IR file, not in other object
 247          file.  In that case we don't set used_from_other_object_file.  */
 248       && node->definition)
 249     ;
 250   else if (!whole_program)
 251     return true;
 252
 253   if (MAIN_NAME_P (DECL_NAME (node->decl)))
 254     return true;
 255
 256   return false;
 257 }
 258
 259 /* Return true when variable should be considered externally visible.  */
 260
 261 bool
 262 varpool_node::externally_visible_p (void)
 263 {
 264   while (transparent_alias && definition)
 265     return get_alias_target ()->externally_visible_p ();
 266   if (DECL_EXTERNAL (decl))
 267     return true;
 268
 269   if (!TREE_PUBLIC (decl))
 270     return false;
 271
 272   /* If linker counts on us, we must preserve the function.  */
 273   if (used_from_object_file_p ())
 274     return true;
 275
 276   /* Bringing TLS variables local may cause dynamic linker failures
 277      on limits of static TLS vars.  */
 278   if (DECL_THREAD_LOCAL_P (decl)
 279       && (DECL_TLS_MODEL (decl) != TLS_MODEL_EMULATED
 280           && DECL_TLS_MODEL (decl) != TLS_MODEL_INITIAL_EXEC))
 281     return true;
 282
 283   if (DECL_HARD_REGISTER (decl))
 284     return true;
 285   if (DECL_PRESERVE_P (decl))
 286     return true;
 287   if (lookup_attribute ("externally_visible",
 288                         DECL_ATTRIBUTES (decl)))
 289     return true;
 290   if (TARGET_DLLIMPORT_DECL_ATTRIBUTES
 291       && lookup_attribute ("dllexport",
 292                            DECL_ATTRIBUTES (decl)))
 293     return true;
 294
 295   /* Limitation of gas requires us to output targets of symver aliases as
 296      global symbols.  This is binutils PR 25295.  */
 297   ipa_ref *ref;
 298   FOR_EACH_ALIAS (this, ref)
 299     if (ref->referring->symver)
 300       return true;
 301
 302   if (resolution == LDPR_PREVAILING_DEF_IRONLY)
 303     return false;
 304
 305   /* As a special case, the COMDAT virtual tables can be unshared.
 306      In LTO mode turn vtables into static variables.  The variable is readonly,
 307      so this does not enable more optimization, but referring static var
 308      is faster for dynamic linking.  Also this match logic hidding vtables
 309      from LTO symbol tables.  */
 310   if (((in_lto_p || flag_whole_program) && !flag_incremental_link)
 311       && DECL_COMDAT (decl)
 312       && comdat_can_be_unshared_p (this))
 313     return false;
 314
 315   /* When doing link time optimizations, hidden symbols become local.  */
 316   if (in_lto_p && !flag_incremental_link
 317       && (DECL_VISIBILITY (decl) == VISIBILITY_HIDDEN
 318           || DECL_VISIBILITY (decl) == VISIBILITY_INTERNAL)
 319       /* Be sure that node is defined in IR file, not in other object
 320          file.  In that case we don't set used_from_other_object_file.  */
 321       && definition)
 322     ;
 323   else if (!flag_whole_program)
 324     return true;
 325
 326   /* Do not attempt to privatize COMDATS by default.
 327      This would break linking with C++ libraries sharing
 328      inline definitions.
 329
 330      FIXME: We can do so for readonly vars with no address taken and
 331      possibly also for vtables since no direct pointer comparsion is done.
 332      It might be interesting to do so to reduce linking overhead.  */
 333   if (DECL_COMDAT (decl) || DECL_WEAK (decl))
 334     return true;
 335   return false;
 336 }
 337
 338 /* Return true if reference to NODE can be replaced by a local alias.
 339    Local aliases save dynamic linking overhead and enable more optimizations.
 340  */
 341
 342 static bool
 343 can_replace_by_local_alias (symtab_node *node)
 344 {
 345   /* If aliases aren't supported, we can't do replacement.  */
 346   if (!TARGET_SUPPORTS_ALIASES)
 347     return false;
 348
 349   /* Weakrefs have a reason to be non-local.  Be sure we do not replace
 350      them.  */
 351   while (node->transparent_alias && node->definition && !node->weakref)
 352     node = node->get_alias_target ();
 353   if (node->weakref)
 354     return false;
 355
 356   return (node->get_availability () > AVAIL_INTERPOSABLE
 357           && !decl_binds_to_current_def_p (node->decl)
 358           && !node->can_be_discarded_p ());
 359 }
 360
 361 /* Return true if we can replace reference to NODE by local alias
 362    within a virtual table.  Generally we can replace function pointers
 363    and virtual table pointers.  */
 364
 365 static bool
 366 can_replace_by_local_alias_in_vtable (symtab_node *node)
 367 {
 368   if (is_a <varpool_node *> (node)
 369       && !DECL_VIRTUAL_P (node->decl))
 370     return false;
 371   return can_replace_by_local_alias (node);
 372 }
 373
 374 /* walk_tree callback that rewrites initializer references.   */
 375
 376 static tree
 377 update_vtable_references (tree *tp, int *walk_subtrees,
 378                           void *data ATTRIBUTE_UNUSED)
 379 {
 380   if (VAR_OR_FUNCTION_DECL_P (*tp))
 381     {
 382       if (can_replace_by_local_alias_in_vtable (symtab_node::get (*tp)))
 383         *tp = symtab_node::get (*tp)->noninterposable_alias ()->decl;
 384       *walk_subtrees = 0;
 385     }
 386   else if (IS_TYPE_OR_DECL_P (*tp))
 387     *walk_subtrees = 0;
 388   return NULL;
 389 }
 390
 391 /* In LTO we can remove COMDAT groups and weak symbols.
 392    Either turn them into normal symbols or external symbol depending on
 393    resolution info.  */
 394
 395 static void
 396 update_visibility_by_resolution_info (symtab_node * node)
 397 {
 398   bool define;
 399
 400   if (!node->externally_visible
 401       || (!DECL_WEAK (node->decl) && !DECL_ONE_ONLY (node->decl))
 402       || node->resolution == LDPR_UNKNOWN)
 403     return;
 404
 405   define = (node->resolution == LDPR_PREVAILING_DEF_IRONLY
 406             || node->resolution == LDPR_PREVAILING_DEF
 407             || node->resolution == LDPR_UNDEF
 408             || node->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP);
 409
 410   /* The linker decisions ought to agree in the whole group.  */
 411   if (node->same_comdat_group)
 412     for (symtab_node *next = node->same_comdat_group;
 413          next != node; next = next->same_comdat_group)
 414       {
 415         if (!next->externally_visible || next->transparent_alias)
 416           continue;
 417
 418         bool same_def
 419           = define == (next->resolution == LDPR_PREVAILING_DEF_IRONLY
 420                        || next->resolution == LDPR_PREVAILING_DEF
 421                        || next->resolution == LDPR_UNDEF
 422                        || next->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP);
 423         gcc_assert (in_lto_p || same_def);
 424         if (!same_def)
 425           return;
 426       }
 427
 428   if (node->same_comdat_group)
 429     for (symtab_node *next = node->same_comdat_group;
 430          next != node; next = next->same_comdat_group)
 431       {
 432         /* During incremental linking we need to keep symbol weak for future
 433            linking.  We can still drop definition if we know non-LTO world
 434            prevails.  */
 435         if (!flag_incremental_link)
 436           {
 437             DECL_WEAK (next->decl) = false;
 438             next->set_comdat_group (NULL);
 439           }
 440         if (!define)
 441           {
 442             if (next->externally_visible)
 443               DECL_EXTERNAL (next->decl) = true;
 444             next->set_comdat_group (NULL);
 445           }
 446       }
 447
 448   /* During incremental linking we need to keep symbol weak for future
 449      linking.  We can still drop definition if we know non-LTO world prevails.  */
 450   if (!flag_incremental_link)
 451     {
 452       DECL_WEAK (node->decl) = false;
 453       node->set_comdat_group (NULL);
 454       node->dissolve_same_comdat_group_list ();
 455     }
 456   if (!define)
 457     {
 458       DECL_EXTERNAL (node->decl) = true;
 459       node->set_comdat_group (NULL);
 460       node->dissolve_same_comdat_group_list ();
 461     }
 462 }
 463
 464 /* Try to get rid of weakref.  */
 465
 466 static void
 467 optimize_weakref (symtab_node *node)
 468 {
 469   bool strip_weakref = false;
 470   bool static_alias = false;
 471
 472   gcc_assert (node->weakref);
 473
 474   /* Weakrefs with no target defined cannot be optimized.  */
 475   if (!node->analyzed)
 476     return;
 477   symtab_node *target = node->get_alias_target ();
 478
 479   /* Weakrefs to weakrefs can be optimized only if target can be.  */
 480   if (target->weakref)
 481     optimize_weakref (target);
 482   if (target->weakref)
 483     return;
 484
 485   /* If we have definition of weakref's target and we know it binds locally,
 486      we can turn weakref to static alias.  */
 487   if (TARGET_SUPPORTS_ALIASES
 488       && target->definition && decl_binds_to_current_def_p (target->decl))
 489     strip_weakref = static_alias = true;
 490   /* Otherwise we can turn weakref into transparent alias.  This transformation
 491      may break asm statements which directly refers to symbol name and expect
 492      GNU as to translate it via .weakref directive. So do not optimize when
 493      DECL_PRESERVED is set and .weakref is supported.  */
 494   else if ((!DECL_PRESERVE_P (target->decl)
 495             || IDENTIFIER_TRANSPARENT_ALIAS (DECL_ASSEMBLER_NAME (node->decl)))
 496            && !DECL_WEAK (target->decl)
 497            && !DECL_EXTERNAL (target->decl)
 498            && ((target->definition && !target->can_be_discarded_p ())
 499                || target->resolution != LDPR_UNDEF))
 500     strip_weakref = true;
 501   if (!strip_weakref)
 502     return;
 503   node->weakref = false;
 504   IDENTIFIER_TRANSPARENT_ALIAS (DECL_ASSEMBLER_NAME (node->decl)) = 0;
 505   TREE_CHAIN (DECL_ASSEMBLER_NAME (node->decl)) = NULL_TREE;
 506   DECL_ATTRIBUTES (node->decl) = remove_attribute ("weakref",
 507                                                    DECL_ATTRIBUTES
 508                                                          (node->decl));
 509
 510   if (dump_file)
 511     fprintf (dump_file, "Optimizing weakref %s %s\n",
 512              node->dump_name (),
 513              static_alias ? "as static alias" : "as transparent alias");
 514
 515   if (static_alias)
 516     {
 517       /* make_decl_local will shortcircuit if it doesn't see TREE_PUBLIC.
 518          be sure it really clears the WEAK flag.  */
 519       TREE_PUBLIC (node->decl) = true;
 520       node->make_decl_local ();
 521       node->forced_by_abi = false;
 522       node->resolution = LDPR_PREVAILING_DEF_IRONLY;
 523       node->externally_visible = false;
 524       gcc_assert (!DECL_WEAK (node->decl));
 525       node->transparent_alias = false;
 526     }
 527   else
 528     {
 529       symtab->change_decl_assembler_name
 530         (node->decl, DECL_ASSEMBLER_NAME (node->get_alias_target ()->decl));
 531       node->transparent_alias = true;
 532       node->copy_visibility_from (target);
 533     }
 534   gcc_assert (node->alias);
 535 }
 536
 537 /* NODE is an externally visible definition, which we've discovered is
 538    not needed externally.  Make it local to this compilation.  */
 539
 540 static void
 541 localize_node (bool whole_program, symtab_node *node)
 542 {
 543   gcc_assert (whole_program || in_lto_p || !TREE_PUBLIC (node->decl));
 544
 545   /* It is possible that one comdat group contains both hidden and non-hidden
 546      symbols.  In this case we can privatize all hidden symbol but we need
 547      to keep non-hidden exported.  */
 548   if (node->same_comdat_group
 549       && (node->resolution == LDPR_PREVAILING_DEF_IRONLY
 550           || node->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP))
 551     {
 552       symtab_node *next;
 553       for (next = node->same_comdat_group;
 554            next != node; next = next->same_comdat_group)
 555         if (next->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP
 556             || next->resolution == LDPR_PREVAILING_DEF)
 557           break;
 558       if (node != next)
 559         {
 560           if (!node->transparent_alias)
 561             {
 562               node->resolution = LDPR_PREVAILING_DEF_IRONLY;
 563               node->make_decl_local ();
 564               if (!flag_incremental_link)
 565                 node->unique_name |= true;
 566               return;
 567             }
 568         }
 569     }
 570   /* For similar reason do not privatize whole comdat when seeing comdat
 571      local.  Wait for non-comdat symbol to be privatized first.  */
 572   if (node->comdat_local_p ())
 573     return;
 574
 575   if (node->same_comdat_group && TREE_PUBLIC (node->decl))
 576     {
 577       for (symtab_node *next = node->same_comdat_group;
 578            next != node; next = next->same_comdat_group)
 579         {
 580           next->set_comdat_group (NULL);
 581           if (!next->alias)
 582             next->set_section (NULL);
 583           if (!next->transparent_alias)
 584             next->make_decl_local ();
 585           next->unique_name
 586             |= ((next->resolution == LDPR_PREVAILING_DEF_IRONLY
 587                  || next->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP)
 588                 && TREE_PUBLIC (next->decl)
 589                 && !flag_incremental_link);
 590         }
 591
 592       /* Now everything's localized, the grouping has no meaning, and
 593          will cause crashes if we keep it around.  */
 594       node->dissolve_same_comdat_group_list ();
 595     }
 596
 597   node->unique_name
 598     |= ((node->resolution == LDPR_PREVAILING_DEF_IRONLY
 599          || node->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP)
 600         && TREE_PUBLIC (node->decl)
 601         && !flag_incremental_link);
 602
 603   if (TREE_PUBLIC (node->decl))
 604     node->set_comdat_group (NULL);
 605   if (DECL_COMDAT (node->decl) && !node->alias)
 606     node->set_section (NULL);
 607   if (!node->transparent_alias)
 608     {
 609       node->resolution = LDPR_PREVAILING_DEF_IRONLY;
 610       node->make_decl_local ();
 611     }
 612 }
 613
 614 /* Decide on visibility of all symbols.  */
 615
 616 static unsigned int
 617 function_and_variable_visibility (bool whole_program)
 618 {
 619   struct cgraph_node *node;
 620   varpool_node *vnode;
 621
 622   /* All aliases should be processed at this point.  */
 623   gcc_checking_assert (!alias_pairs || !alias_pairs->length ());
 624
 625   if (TARGET_SUPPORTS_ALIASES)
 626     {
 627       FOR_EACH_DEFINED_FUNCTION (node)
 628         {
 629           if (node->get_availability () != AVAIL_INTERPOSABLE
 630               || DECL_EXTERNAL (node->decl)
 631               || node->has_aliases_p ()
 632               || lookup_attribute ("noipa", DECL_ATTRIBUTES (node->decl)))
 633             continue;
 634
 635           cgraph_node *alias = 0;
 636           cgraph_edge *next_edge;
 637           for (cgraph_edge *e = node->callees; e; e = next_edge)
 638             {
 639               next_edge = e->next_callee;
 640               /* Recursive function calls usually can't be interposed.  */
 641
 642               if (!e->recursive_p ())
 643                 continue;
 644
 645               if (!alias)
 646                 {
 647                   alias
 648                     = dyn_cast<cgraph_node *> (node->noninterposable_alias ());
 649                   gcc_assert (alias && alias != node);
 650                 }
 651
 652               e->redirect_callee (alias);
 653               if (gimple_has_body_p (e->caller->decl))
 654                 {
 655                   push_cfun (DECL_STRUCT_FUNCTION (e->caller->decl));
 656                   cgraph_edge::redirect_call_stmt_to_callee (e);
 657                   pop_cfun ();
 658                 }
 659             }
 660         }
 661     }
 662
 663   FOR_EACH_FUNCTION (node)
 664     {
 665       int flags = flags_from_decl_or_type (node->decl);
 666
 667       /* Optimize away PURE and CONST constructors and destructors.  */
 668       if (node->analyzed
 669           && (DECL_STATIC_CONSTRUCTOR (node->decl)
 670               || DECL_STATIC_DESTRUCTOR (node->decl))
 671           && (flags & (ECF_CONST | ECF_PURE))
 672           && !(flags & ECF_LOOPING_CONST_OR_PURE)
 673           && opt_for_fn (node->decl, optimize))
 674         {
 675           DECL_STATIC_CONSTRUCTOR (node->decl) = 0;
 676           DECL_STATIC_DESTRUCTOR (node->decl) = 0;
 677         }
 678
 679       /* Frontends and alias code marks nodes as needed before parsing
 680          is finished.  We may end up marking as node external nodes
 681          where this flag is meaningless strip it.  */
 682       if (DECL_EXTERNAL (node->decl) || !node->definition)
 683         {
 684           node->force_output = 0;
 685           node->forced_by_abi = 0;
 686         }
 687
 688       /* C++ FE on lack of COMDAT support create local COMDAT functions
 689          (that ought to be shared but cannot due to object format
 690          limitations).  It is necessary to keep the flag to make rest of C++ FE
 691          happy.  Clear the flag here to avoid confusion in middle-end.  */
 692       if (DECL_COMDAT (node->decl) && !TREE_PUBLIC (node->decl))
 693         DECL_COMDAT (node->decl) = 0;
 694
 695       /* For external decls stop tracking same_comdat_group. It doesn't matter
 696          what comdat group they are in when they won't be emitted in this TU.
 697
 698          An exception is LTO where we may end up with both external
 699          and non-external declarations in the same comdat group in
 700          the case declarations was not merged.  */
 701       if (node->same_comdat_group && DECL_EXTERNAL (node->decl) && !in_lto_p)
 702         {
 703           if (flag_checking)
 704             {
 705               for (symtab_node *n = node->same_comdat_group;
 706                    n != node;
 707                    n = n->same_comdat_group)
 708                 /* If at least one of same comdat group functions is external,
 709                    all of them have to be, otherwise it is a front-end bug.  */
 710                 gcc_assert (DECL_EXTERNAL (n->decl));
 711             }
 712           node->dissolve_same_comdat_group_list ();
 713         }
 714       gcc_assert ((!DECL_WEAK (node->decl)
 715                   && !DECL_COMDAT (node->decl))
 716                   || TREE_PUBLIC (node->decl)
 717                   || node->weakref
 718                   || DECL_EXTERNAL (node->decl));
 719       if (cgraph_externally_visible_p (node, whole_program))
 720         {
 721           gcc_assert (!node->inlined_to);
 722           node->externally_visible = true;
 723         }
 724       else
 725         {
 726           node->externally_visible = false;
 727           node->forced_by_abi = false;
 728         }
 729       if (!node->externally_visible
 730           && node->definition && !node->weakref
 731           && !DECL_EXTERNAL (node->decl))
 732         localize_node (whole_program, node);
 733
 734       if (node->thunk
 735           && TREE_PUBLIC (node->decl))
 736         {
 737           struct cgraph_node *decl_node = node;
 738
 739           decl_node = decl_node->callees->callee->function_symbol ();
 740
 741           /* Thunks have the same visibility as function they are attached to.
 742              Make sure the C++ front end set this up properly.  */
 743           if (DECL_ONE_ONLY (decl_node->decl))
 744             {
 745               gcc_checking_assert (DECL_COMDAT (node->decl)
 746                                    == DECL_COMDAT (decl_node->decl));
 747               gcc_checking_assert (node->in_same_comdat_group_p (decl_node));
 748               gcc_checking_assert (node->same_comdat_group);
 749             }
 750           node->forced_by_abi = decl_node->forced_by_abi;
 751           if (DECL_EXTERNAL (decl_node->decl))
 752             DECL_EXTERNAL (node->decl) = 1;
 753         }
 754
 755       update_visibility_by_resolution_info (node);
 756       if (node->weakref)
 757         optimize_weakref (node);
 758     }
 759   FOR_EACH_DEFINED_FUNCTION (node)
 760     {
 761       if (!node->local)
 762         node->local |= node->local_p ();
 763
 764       /* If we know that function cannot be overwritten by a
 765          different semantics and moreover its section cannot be
 766          discarded, replace all direct calls by calls to an
 767          noninterposable alias.  This make dynamic linking cheaper and
 768          enable more optimization.
 769
 770          TODO: We can also update virtual tables.  */
 771       if (node->callers
 772           && can_replace_by_local_alias (node))
 773         {
 774           cgraph_node *alias = dyn_cast<cgraph_node *>
 775             (node->noninterposable_alias ());
 776
 777           if (alias && alias != node)
 778             {
 779               while (node->callers)
 780                 {
 781                   struct cgraph_edge *e = node->callers;
 782
 783                   e->redirect_callee (alias);
 784                   if (gimple_has_body_p (e->caller->decl))
 785                     {
 786                       push_cfun (DECL_STRUCT_FUNCTION (e->caller->decl));
 787                       cgraph_edge::redirect_call_stmt_to_callee (e);
 788                       pop_cfun ();
 789                     }
 790                 }
 791             }
 792         }
 793     }
 794   FOR_EACH_VARIABLE (vnode)
 795     {
 796       /* weak flag makes no sense on local variables.  */
 797       gcc_assert (!DECL_WEAK (vnode->decl)
 798                   || vnode->weakref
 799                   || TREE_PUBLIC (vnode->decl)
 800                   || DECL_EXTERNAL (vnode->decl));
 801       /* In several cases declarations cannot be common:
 802
 803          - when declaration has initializer
 804          - when it is in weak
 805          - when it has specific section
 806          - when it resides in non-generic address space.
 807          - if declaration is local, it will get into .local common section
 808            so common flag is not needed.  Frontends still produce these in
 809            certain cases, such as for:
 810
 811              static int a __attribute__ ((common))
 812
 813          Canonicalize things here and clear the redundant flag.  */
 814       if (DECL_COMMON (vnode->decl)
 815           && (!(TREE_PUBLIC (vnode->decl)
 816               || DECL_EXTERNAL (vnode->decl))
 817               || (DECL_INITIAL (vnode->decl)
 818                   && DECL_INITIAL (vnode->decl) != error_mark_node)
 819               || DECL_WEAK (vnode->decl)
 820               || DECL_SECTION_NAME (vnode->decl) != NULL
 821               || ! (ADDR_SPACE_GENERIC_P
 822                     (TYPE_ADDR_SPACE (TREE_TYPE (vnode->decl))))))
 823         DECL_COMMON (vnode->decl) = 0;
 824       if (vnode->weakref)
 825         optimize_weakref (vnode);
 826     }
 827   FOR_EACH_DEFINED_VARIABLE (vnode)
 828     {
 829       if (!vnode->definition)
 830         continue;
 831       if (vnode->externally_visible_p ())
 832         vnode->externally_visible = true;
 833       else
 834         {
 835           vnode->externally_visible = false;
 836           vnode->forced_by_abi = false;
 837         }
 838       if (lookup_attribute ("no_reorder",
 839                             DECL_ATTRIBUTES (vnode->decl)))
 840         vnode->no_reorder = 1;
 841
 842       if (!vnode->externally_visible
 843           && !vnode->transparent_alias
 844           && !DECL_EXTERNAL (vnode->decl))
 845         localize_node (whole_program, vnode);
 846
 847       update_visibility_by_resolution_info (vnode);
 848
 849       /* Update virtual tables to point to local aliases where possible.  */
 850       if (DECL_VIRTUAL_P (vnode->decl)
 851           && !DECL_EXTERNAL (vnode->decl))
 852         {
 853           int i;
 854           struct ipa_ref *ref;
 855           bool found = false;
 856
 857           /* See if there is something to update.  */
 858           for (i = 0; vnode->iterate_reference (i, ref); i++)
 859             if (ref->use == IPA_REF_ADDR
 860                 && can_replace_by_local_alias_in_vtable (ref->referred))
 861               {
 862                 found = true;
 863                 break;
 864               }
 865           if (found)
 866             {
 867               hash_set<tree> visited_nodes;
 868
 869               vnode->get_constructor ();
 870               walk_tree (&DECL_INITIAL (vnode->decl),
 871                          update_vtable_references, NULL, &visited_nodes);
 872               vnode->remove_all_references ();
 873               record_references_in_initializer (vnode->decl, false);
 874             }
 875         }
 876     }
 877
 878   if (symtab->state >= IPA_SSA)
 879     {
 880       FOR_EACH_VARIABLE (vnode)
 881         {
 882           tree decl = vnode->decl;
 883
 884           /* Upgrade TLS access model based on optimized visibility status,
 885              unless it was specified explicitly or no references remain.  */
 886           if (DECL_THREAD_LOCAL_P (decl)
 887               && !lookup_attribute ("tls_model", DECL_ATTRIBUTES (decl))
 888               && vnode->ref_list.referring.length ())
 889             {
 890               enum tls_model new_model = decl_default_tls_model (decl);
 891               STATIC_ASSERT (TLS_MODEL_GLOBAL_DYNAMIC < TLS_MODEL_LOCAL_DYNAMIC);
 892               STATIC_ASSERT (TLS_MODEL_INITIAL_EXEC < TLS_MODEL_LOCAL_EXEC);
 893               /* We'd prefer to assert that recomputed model is not weaker than
 894                  what the front-end assigned, but cannot: see PR 107353.  */
 895               if (new_model >= decl_tls_model (decl))
 896                 set_decl_tls_model (decl, new_model);
 897             }
 898         }
 899     }
 900
 901   if (dump_file)
 902     {
 903       fprintf (dump_file, "\nMarking local functions:");
 904       FOR_EACH_DEFINED_FUNCTION (node)
 905         if (node->local)
 906           fprintf (dump_file, " %s", node->dump_name ());
 907       fprintf (dump_file, "\n\n");
 908       fprintf (dump_file, "\nMarking externally visible functions:");
 909       FOR_EACH_DEFINED_FUNCTION (node)
 910         if (node->externally_visible)
 911           fprintf (dump_file, " %s", node->dump_name ());
 912       fprintf (dump_file, "\n\n");
 913       fprintf (dump_file, "\nMarking externally visible variables:");
 914       FOR_EACH_DEFINED_VARIABLE (vnode)
 915         if (vnode->externally_visible)
 916           fprintf (dump_file, " %s", vnode->dump_name ());
 917       fprintf (dump_file, "\n\n");
 918     }
 919   symtab->function_flags_ready = true;
 920   return 0;
 921 }
 922
 923 /* Local function pass handling visibilities.  This happens before LTO streaming
 924    so in particular -fwhole-program should be ignored at this level.  */
 925
 926 namespace {
 927
 928 const pass_data pass_data_ipa_function_and_variable_visibility =
 929 {
 930   SIMPLE_IPA_PASS, /* type */
 931   "visibility", /* name */
 932   OPTGROUP_NONE, /* optinfo_flags */
 933   TV_CGRAPHOPT, /* tv_id */
 934   0, /* properties_required */
 935   0, /* properties_provided */
 936   0, /* properties_destroyed */
 937   0, /* todo_flags_start */
 938   ( TODO_remove_functions | TODO_dump_symtab ), /* todo_flags_finish */
 939 };
 940
 941 /* Bring functions local at LTO time with -fwhole-program.  */
 942
 943 static unsigned int
 944 whole_program_function_and_variable_visibility (void)
 945 {
 946   function_and_variable_visibility (flag_whole_program);
 947   if (optimize || in_lto_p)
 948     ipa_discover_variable_flags ();
 949   return 0;
 950 }
 951
 952 } // anon namespace
 953
 954 namespace {
 955
 956 const pass_data pass_data_ipa_whole_program_visibility =
 957 {
 958   IPA_PASS, /* type */
 959   "whole-program", /* name */
 960   OPTGROUP_NONE, /* optinfo_flags */
 961   TV_CGRAPHOPT, /* tv_id */
 962   0, /* properties_required */
 963   0, /* properties_provided */
 964   0, /* properties_destroyed */
 965   0, /* todo_flags_start */
 966   ( TODO_remove_functions | TODO_dump_symtab ), /* todo_flags_finish */
 967 };
 968
 969 class pass_ipa_whole_program_visibility : public ipa_opt_pass_d
 970 {
 971 public:
 972   pass_ipa_whole_program_visibility (gcc::context *ctxt)
 973     : ipa_opt_pass_d (pass_data_ipa_whole_program_visibility, ctxt,
 974                       NULL, /* generate_summary */
 975                       NULL, /* write_summary */
 976                       NULL, /* read_summary */
 977                       NULL, /* write_optimization_summary */
 978                       NULL, /* read_optimization_summary */
 979                       NULL, /* stmt_fixup */
 980                       0, /* function_transform_todo_flags_start */
 981                       NULL, /* function_transform */
 982                       NULL) /* variable_transform */
 983   {}
 984
 985   /* opt_pass methods: */
 986
 987   bool gate (function *) final override
 988     {
 989       /* Do not re-run on ltrans stage.  */
 990       return !flag_ltrans;
 991     }
 992   unsigned int execute (function *) final override
 993     {
 994       return whole_program_function_and_variable_visibility ();
 995     }
 996
 997 }; // class pass_ipa_whole_program_visibility
 998
 999 } // anon namespace
1000
1001 ipa_opt_pass_d *
1002 make_pass_ipa_whole_program_visibility (gcc::context *ctxt)
1003 {
1004   return new pass_ipa_whole_program_visibility (ctxt);
1005 }
1006
1007 class pass_ipa_function_and_variable_visibility : public simple_ipa_opt_pass
1008 {
1009 public:
1010   pass_ipa_function_and_variable_visibility (gcc::context *ctxt)
1011     : simple_ipa_opt_pass (pass_data_ipa_function_and_variable_visibility,
1012                            ctxt)
1013   {}
1014
1015   /* opt_pass methods: */
1016   unsigned int execute (function *) final override
1017     {
1018       return function_and_variable_visibility (flag_whole_program && !flag_lto);
1019     }
1020
1021 }; // class pass_ipa_function_and_variable_visibility
1022
1023 simple_ipa_opt_pass *
1024 make_pass_ipa_function_and_variable_visibility (gcc::context *ctxt)
1025 {
1026   return new pass_ipa_function_and_variable_visibility (ctxt);
1027 }