gcc/ipa-visibility.c

   1 /* IPA visibility pass
   2    Copyright (C) 2003-2021 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 #ifdef ASM_OUTPUT_DEF
 626   FOR_EACH_DEFINED_FUNCTION (node)
 627     {
 628       if (node->get_availability () != AVAIL_INTERPOSABLE
 629           || DECL_EXTERNAL (node->decl)
 630           || node->has_aliases_p ()
 631           || lookup_attribute ("noipa", DECL_ATTRIBUTES (node->decl)))
 632         continue;
 633
 634       cgraph_node *alias = 0;
 635       cgraph_edge *next_edge;
 636       for (cgraph_edge *e = node->callees; e; e = next_edge)
 637         {
 638           next_edge = e->next_callee;
 639           /* Recursive function calls usually can't be interposed.  */
 640
 641           if (!e->recursive_p ())
 642             continue;
 643
 644           if (!alias)
 645             {
 646               alias = dyn_cast<cgraph_node *> (node->noninterposable_alias ());
 647               gcc_assert (alias && alias != node);
 648             }
 649
 650           e->redirect_callee (alias);
 651           if (gimple_has_body_p (e->caller->decl))
 652             {
 653               push_cfun (DECL_STRUCT_FUNCTION (e->caller->decl));
 654               cgraph_edge::redirect_call_stmt_to_callee (e);
 655               pop_cfun ();
 656             }
 657         }
 658     }
 659 #endif
 660
 661   FOR_EACH_FUNCTION (node)
 662     {
 663       int flags = flags_from_decl_or_type (node->decl);
 664
 665       /* Optimize away PURE and CONST constructors and destructors.  */
 666       if (node->analyzed
 667           && (DECL_STATIC_CONSTRUCTOR (node->decl)
 668               || DECL_STATIC_DESTRUCTOR (node->decl))
 669           && (flags & (ECF_CONST | ECF_PURE))
 670           && !(flags & ECF_LOOPING_CONST_OR_PURE)
 671           && opt_for_fn (node->decl, optimize))
 672         {
 673           DECL_STATIC_CONSTRUCTOR (node->decl) = 0;
 674           DECL_STATIC_DESTRUCTOR (node->decl) = 0;
 675         }
 676
 677       /* Frontends and alias code marks nodes as needed before parsing
 678          is finished.  We may end up marking as node external nodes
 679          where this flag is meaningless strip it.  */
 680       if (DECL_EXTERNAL (node->decl) || !node->definition)
 681         {
 682           node->force_output = 0;
 683           node->forced_by_abi = 0;
 684         }
 685
 686       /* C++ FE on lack of COMDAT support create local COMDAT functions
 687          (that ought to be shared but cannot due to object format
 688          limitations).  It is necessary to keep the flag to make rest of C++ FE
 689          happy.  Clear the flag here to avoid confusion in middle-end.  */
 690       if (DECL_COMDAT (node->decl) && !TREE_PUBLIC (node->decl))
 691         DECL_COMDAT (node->decl) = 0;
 692
 693       /* For external decls stop tracking same_comdat_group. It doesn't matter
 694          what comdat group they are in when they won't be emitted in this TU.
 695
 696          An exception is LTO where we may end up with both external
 697          and non-external declarations in the same comdat group in
 698          the case declarations was not merged.  */
 699       if (node->same_comdat_group && DECL_EXTERNAL (node->decl) && !in_lto_p)
 700         {
 701           if (flag_checking)
 702             {
 703               for (symtab_node *n = node->same_comdat_group;
 704                    n != node;
 705                    n = n->same_comdat_group)
 706                 /* If at least one of same comdat group functions is external,
 707                    all of them have to be, otherwise it is a front-end bug.  */
 708                 gcc_assert (DECL_EXTERNAL (n->decl));
 709             }
 710           node->dissolve_same_comdat_group_list ();
 711         }
 712       gcc_assert ((!DECL_WEAK (node->decl)
 713                   && !DECL_COMDAT (node->decl))
 714                   || TREE_PUBLIC (node->decl)
 715                   || node->weakref
 716                   || DECL_EXTERNAL (node->decl));
 717       if (cgraph_externally_visible_p (node, whole_program))
 718         {
 719           gcc_assert (!node->inlined_to);
 720           node->externally_visible = true;
 721         }
 722       else
 723         {
 724           node->externally_visible = false;
 725           node->forced_by_abi = false;
 726         }
 727       if (!node->externally_visible
 728           && node->definition && !node->weakref
 729           && !DECL_EXTERNAL (node->decl))
 730         localize_node (whole_program, node);
 731
 732       if (node->thunk
 733           && TREE_PUBLIC (node->decl))
 734         {
 735           struct cgraph_node *decl_node = node;
 736
 737           decl_node = decl_node->callees->callee->function_symbol ();
 738
 739           /* Thunks have the same visibility as function they are attached to.
 740              Make sure the C++ front end set this up properly.  */
 741           if (DECL_ONE_ONLY (decl_node->decl))
 742             {
 743               gcc_checking_assert (DECL_COMDAT (node->decl)
 744                                    == DECL_COMDAT (decl_node->decl));
 745               gcc_checking_assert (node->in_same_comdat_group_p (decl_node));
 746               gcc_checking_assert (node->same_comdat_group);
 747             }
 748           node->forced_by_abi = decl_node->forced_by_abi;
 749           if (DECL_EXTERNAL (decl_node->decl))
 750             DECL_EXTERNAL (node->decl) = 1;
 751         }
 752
 753       update_visibility_by_resolution_info (node);
 754       if (node->weakref)
 755         optimize_weakref (node);
 756     }
 757   FOR_EACH_DEFINED_FUNCTION (node)
 758     {
 759       if (!node->local)
 760         node->local |= node->local_p ();
 761
 762       /* If we know that function cannot be overwritten by a
 763          different semantics and moreover its section cannot be
 764          discarded, replace all direct calls by calls to an
 765          noninterposable alias.  This make dynamic linking cheaper and
 766          enable more optimization.
 767
 768          TODO: We can also update virtual tables.  */
 769       if (node->callers
 770           && can_replace_by_local_alias (node))
 771         {
 772           cgraph_node *alias = dyn_cast<cgraph_node *>
 773             (node->noninterposable_alias ());
 774
 775           if (alias && alias != node)
 776             {
 777               while (node->callers)
 778                 {
 779                   struct cgraph_edge *e = node->callers;
 780
 781                   e->redirect_callee (alias);
 782                   if (gimple_has_body_p (e->caller->decl))
 783                     {
 784                       push_cfun (DECL_STRUCT_FUNCTION (e->caller->decl));
 785                       cgraph_edge::redirect_call_stmt_to_callee (e);
 786                       pop_cfun ();
 787                     }
 788                 }
 789             }
 790         }
 791     }
 792   FOR_EACH_VARIABLE (vnode)
 793     {
 794       /* weak flag makes no sense on local variables.  */
 795       gcc_assert (!DECL_WEAK (vnode->decl)
 796                   || vnode->weakref
 797                   || TREE_PUBLIC (vnode->decl)
 798                   || DECL_EXTERNAL (vnode->decl));
 799       /* In several cases declarations cannot be common:
 800
 801          - when declaration has initializer
 802          - when it is in weak
 803          - when it has specific section
 804          - when it resides in non-generic address space.
 805          - if declaration is local, it will get into .local common section
 806            so common flag is not needed.  Frontends still produce these in
 807            certain cases, such as for:
 808
 809              static int a __attribute__ ((common))
 810
 811          Canonicalize things here and clear the redundant flag.  */
 812       if (DECL_COMMON (vnode->decl)
 813           && (!(TREE_PUBLIC (vnode->decl)
 814               || DECL_EXTERNAL (vnode->decl))
 815               || (DECL_INITIAL (vnode->decl)
 816                   && DECL_INITIAL (vnode->decl) != error_mark_node)
 817               || DECL_WEAK (vnode->decl)
 818               || DECL_SECTION_NAME (vnode->decl) != NULL
 819               || ! (ADDR_SPACE_GENERIC_P
 820                     (TYPE_ADDR_SPACE (TREE_TYPE (vnode->decl))))))
 821         DECL_COMMON (vnode->decl) = 0;
 822       if (vnode->weakref)
 823         optimize_weakref (vnode);
 824     }
 825   FOR_EACH_DEFINED_VARIABLE (vnode)
 826     {
 827       if (!vnode->definition)
 828         continue;
 829       if (vnode->externally_visible_p ())
 830         vnode->externally_visible = true;
 831       else
 832         {
 833           vnode->externally_visible = false;
 834           vnode->forced_by_abi = false;
 835         }
 836       if (lookup_attribute ("no_reorder",
 837                             DECL_ATTRIBUTES (vnode->decl)))
 838         vnode->no_reorder = 1;
 839
 840       if (!vnode->externally_visible
 841           && !vnode->transparent_alias
 842           && !DECL_EXTERNAL (vnode->decl))
 843         localize_node (whole_program, vnode);
 844
 845       update_visibility_by_resolution_info (vnode);
 846
 847       /* Update virtual tables to point to local aliases where possible.  */
 848       if (DECL_VIRTUAL_P (vnode->decl)
 849           && !DECL_EXTERNAL (vnode->decl))
 850         {
 851           int i;
 852           struct ipa_ref *ref;
 853           bool found = false;
 854
 855           /* See if there is something to update.  */
 856           for (i = 0; vnode->iterate_reference (i, ref); i++)
 857             if (ref->use == IPA_REF_ADDR
 858                 && can_replace_by_local_alias_in_vtable (ref->referred))
 859               {
 860                 found = true;
 861                 break;
 862               }
 863           if (found)
 864             {
 865               hash_set<tree> visited_nodes;
 866
 867               vnode->get_constructor ();
 868               walk_tree (&DECL_INITIAL (vnode->decl),
 869                          update_vtable_references, NULL, &visited_nodes);
 870               vnode->remove_all_references ();
 871               record_references_in_initializer (vnode->decl, false);
 872             }
 873         }
 874     }
 875
 876   if (dump_file)
 877     {
 878       fprintf (dump_file, "\nMarking local functions:");
 879       FOR_EACH_DEFINED_FUNCTION (node)
 880         if (node->local)
 881           fprintf (dump_file, " %s", node->dump_name ());
 882       fprintf (dump_file, "\n\n");
 883       fprintf (dump_file, "\nMarking externally visible functions:");
 884       FOR_EACH_DEFINED_FUNCTION (node)
 885         if (node->externally_visible)
 886           fprintf (dump_file, " %s", node->dump_name ());
 887       fprintf (dump_file, "\n\n");
 888       fprintf (dump_file, "\nMarking externally visible variables:");
 889       FOR_EACH_DEFINED_VARIABLE (vnode)
 890         if (vnode->externally_visible)
 891           fprintf (dump_file, " %s", vnode->dump_name ());
 892       fprintf (dump_file, "\n\n");
 893     }
 894   symtab->function_flags_ready = true;
 895   return 0;
 896 }
 897
 898 /* Local function pass handling visibilities.  This happens before LTO streaming
 899    so in particular -fwhole-program should be ignored at this level.  */
 900
 901 namespace {
 902
 903 const pass_data pass_data_ipa_function_and_variable_visibility =
 904 {
 905   SIMPLE_IPA_PASS, /* type */
 906   "visibility", /* name */
 907   OPTGROUP_NONE, /* optinfo_flags */
 908   TV_CGRAPHOPT, /* tv_id */
 909   0, /* properties_required */
 910   0, /* properties_provided */
 911   0, /* properties_destroyed */
 912   0, /* todo_flags_start */
 913   ( TODO_remove_functions | TODO_dump_symtab ), /* todo_flags_finish */
 914 };
 915
 916 /* Bring functions local at LTO time with -fwhole-program.  */
 917
 918 static unsigned int
 919 whole_program_function_and_variable_visibility (void)
 920 {
 921   function_and_variable_visibility (flag_whole_program);
 922   if (optimize || in_lto_p)
 923     ipa_discover_variable_flags ();
 924   return 0;
 925 }
 926
 927 } // anon namespace
 928
 929 namespace {
 930
 931 const pass_data pass_data_ipa_whole_program_visibility =
 932 {
 933   IPA_PASS, /* type */
 934   "whole-program", /* name */
 935   OPTGROUP_NONE, /* optinfo_flags */
 936   TV_CGRAPHOPT, /* tv_id */
 937   0, /* properties_required */
 938   0, /* properties_provided */
 939   0, /* properties_destroyed */
 940   0, /* todo_flags_start */
 941   ( TODO_remove_functions | TODO_dump_symtab ), /* todo_flags_finish */
 942 };
 943
 944 class pass_ipa_whole_program_visibility : public ipa_opt_pass_d
 945 {
 946 public:
 947   pass_ipa_whole_program_visibility (gcc::context *ctxt)
 948     : ipa_opt_pass_d (pass_data_ipa_whole_program_visibility, ctxt,
 949                       NULL, /* generate_summary */
 950                       NULL, /* write_summary */
 951                       NULL, /* read_summary */
 952                       NULL, /* write_optimization_summary */
 953                       NULL, /* read_optimization_summary */
 954                       NULL, /* stmt_fixup */
 955                       0, /* function_transform_todo_flags_start */
 956                       NULL, /* function_transform */
 957                       NULL) /* variable_transform */
 958   {}
 959
 960   /* opt_pass methods: */
 961
 962   virtual bool gate (function *)
 963     {
 964       /* Do not re-run on ltrans stage.  */
 965       return !flag_ltrans;
 966     }
 967   virtual unsigned int execute (function *)
 968     {
 969       return whole_program_function_and_variable_visibility ();
 970     }
 971
 972 }; // class pass_ipa_whole_program_visibility
 973
 974 } // anon namespace
 975
 976 ipa_opt_pass_d *
 977 make_pass_ipa_whole_program_visibility (gcc::context *ctxt)
 978 {
 979   return new pass_ipa_whole_program_visibility (ctxt);
 980 }
 981
 982 class pass_ipa_function_and_variable_visibility : public simple_ipa_opt_pass
 983 {
 984 public:
 985   pass_ipa_function_and_variable_visibility (gcc::context *ctxt)
 986     : simple_ipa_opt_pass (pass_data_ipa_function_and_variable_visibility,
 987                            ctxt)
 988   {}
 989
 990   /* opt_pass methods: */
 991   virtual unsigned int execute (function *)
 992     {
 993       return function_and_variable_visibility (flag_whole_program && !flag_lto);
 994     }
 995
 996 }; // class pass_ipa_function_and_variable_visibility
 997
 998 simple_ipa_opt_pass *
 999 make_pass_ipa_function_and_variable_visibility (gcc::context *ctxt)
1000 {
1001   return new pass_ipa_function_and_variable_visibility (ctxt);
1002 }