gcc/ipa-visibility.c

   1 /* IPA visibility pass
   2    Copyright (C) 2003-2017 Free Software Foundation, Inc.
   3
   4 This file is part of GCC.
   5
   6 GCC is free software; you can redistribute it and/or modify it under
   7 the terms of the GNU General Public License as published by the Free
   8 Software Foundation; either version 3, or (at your option) any later
   9 version.
  10
  11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  12 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14 for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GCC; see the file COPYING3.  If not see
  18 <http://www.gnu.org/licenses/>.  */
  19
  20 /* This file implements two related passes:
  21
  22      - pass_data_ipa_function_and_variable_visibility run just after
  23        symbol table, references and callgraph are built
  24
  25      - pass_data_ipa_function_and_variable_visibility run as first
  26        proper IPA pass (that is after early optimization, or, (with LTO)
  27        as a first pass done at link-time.
  28
  29    Purpose of both passes is to set correctly visibility properties
  30    of all symbols.  This includes:
  31
  32     - Symbol privatization:
  33
  34       Some symbols that are declared public by frontend may be
  35       turned local (either by -fwhole-program flag, by linker plugin feedback
  36       or by other reasons)
  37
  38     - Discovery of local functions:
  39
  40       A local function is one whose calls can occur only in the current
  41       compilation unit and all its calls are explicit, so we can change
  42       its calling convention.  We simply mark all static functions whose
  43       address is not taken as local.
  44
  45       externally_visible flag is set for symbols that can not be privatized.
  46       For privatized symbols we clear TREE_PUBLIC flag and dismantle comdat
  47       group.
  48
  49     - Dismantling of comdat groups:
  50
  51       Comdat group represent a section that may be replaced by linker by
  52       a different copy of the same section from other unit.
  53       If we have resolution information (from linker plugin) and we know that
  54       a given comdat gorup is prevailing, we can dismantle it and turn symbols
  55       into normal symbols.  If the resolution information says that the
  56       section was previaled by copy from non-LTO code, we can also dismantle
  57       it and turn all symbols into external.
  58
  59     - Local aliases:
  60
  61       Some symbols can be interposed by dynamic linker. Refering to these
  62       symbols is expensive, since it needs to be overwritable by the dynamic
  63       linker.  In some cases we know that the interposition does not change
  64       semantic and we can always refer to a local copy (as in the case of
  65       inline function).  In this case we produce a local alias and redirect
  66       calls to it.
  67
  68       TODO: This should be done for references, too.
  69
  70     - Removal of static ocnstructors and destructors that have no side effects.
  71
  72     - Regularization of several oddities introduced by frontends that may
  73       be impractical later in the optimization queue.  */
  74
  75 #include "config.h"
  76 #include "system.h"
  77 #include "coretypes.h"
  78 #include "tm.h"
  79 #include "function.h"
  80 #include "tree.h"
  81 #include "gimple-expr.h"
  82 #include "tree-pass.h"
  83 #include "cgraph.h"
  84 #include "calls.h"
  85 #include "varasm.h"
  86
  87 /* Return true when NODE can not be local. Worker for cgraph_local_node_p.  */
  88
  89 static bool
  90 non_local_p (struct cgraph_node *node, void *data ATTRIBUTE_UNUSED)
  91 {
  92   return !(node->only_called_directly_or_aliased_p ()
  93            /* i386 would need update to output thunk with local calling
  94               convetions.  */
  95            && !node->thunk.thunk_p
  96            && node->definition
  97            && !DECL_EXTERNAL (node->decl)
  98            && !node->externally_visible
  99            && !node->used_from_other_partition
 100            && !node->in_other_partition);
 101 }
 102
 103 /* Return true when function can be marked local.  */
 104
 105 bool
 106 cgraph_node::local_p (void)
 107 {
 108    cgraph_node *n = ultimate_alias_target ();
 109
 110    if (n->thunk.thunk_p)
 111      return n->callees->callee->local_p ();
 112    return !n->call_for_symbol_thunks_and_aliases (non_local_p,
 113                                                   NULL, true);
 114
 115 }
 116
 117 /* A helper for comdat_can_be_unshared_p.  */
 118
 119 static bool
 120 comdat_can_be_unshared_p_1 (symtab_node *node)
 121 {
 122   if (!node->externally_visible)
 123     return true;
 124   if (node->address_can_be_compared_p ())
 125     {
 126       struct ipa_ref *ref;
 127
 128       for (unsigned int i = 0; node->iterate_referring (i, ref); i++)
 129         if (ref->address_matters_p ())
 130           return false;
 131     }
 132
 133   /* If the symbol is used in some weird way, better to not touch it.  */
 134   if (node->force_output)
 135     return false;
 136
 137   /* Explicit instantiations needs to be output when possibly
 138      used externally.  */
 139   if (node->forced_by_abi
 140       && TREE_PUBLIC (node->decl)
 141       && (node->resolution != LDPR_PREVAILING_DEF_IRONLY
 142           && !flag_whole_program))
 143     return false;
 144
 145   /* Non-readonly and volatile variables can not be duplicated.  */
 146   if (is_a <varpool_node *> (node)
 147       && (!TREE_READONLY (node->decl)
 148           || TREE_THIS_VOLATILE (node->decl)))
 149     return false;
 150   return true;
 151 }
 152
 153 /* COMDAT functions must be shared only if they have address taken,
 154    otherwise we can produce our own private implementation with
 155    -fwhole-program.
 156    Return true when turning COMDAT function static can not lead to wrong
 157    code when the resulting object links with a library defining same COMDAT.
 158
 159    Virtual functions do have their addresses taken from the vtables,
 160    but in C++ there is no way to compare their addresses for equality.  */
 161
 162 static bool
 163 comdat_can_be_unshared_p (symtab_node *node)
 164 {
 165   if (!comdat_can_be_unshared_p_1 (node))
 166     return false;
 167   if (node->same_comdat_group)
 168     {
 169       symtab_node *next;
 170
 171       /* If more than one function is in the same COMDAT group, it must
 172          be shared even if just one function in the comdat group has
 173          address taken.  */
 174       for (next = node->same_comdat_group;
 175            next != node; next = next->same_comdat_group)
 176         if (!comdat_can_be_unshared_p_1 (next))
 177           return false;
 178     }
 179   return true;
 180 }
 181
 182 /* Return true when function NODE should be considered externally visible.  */
 183
 184 static bool
 185 cgraph_externally_visible_p (struct cgraph_node *node,
 186                              bool whole_program)
 187 {
 188   while (node->transparent_alias && node->definition)
 189     node = node->get_alias_target ();
 190   if (!node->definition)
 191     return false;
 192   if (!TREE_PUBLIC (node->decl)
 193       || DECL_EXTERNAL (node->decl))
 194     return false;
 195
 196   /* Do not try to localize built-in functions yet.  One of problems is that we
 197      end up mangling their asm for WHOPR that makes it impossible to call them
 198      using the implicit built-in declarations anymore.  Similarly this enables
 199      us to remove them as unreachable before actual calls may appear during
 200      expansion or folding.  */
 201   if (DECL_BUILT_IN (node->decl))
 202     return true;
 203
 204   /* If linker counts on us, we must preserve the function.  */
 205   if (node->used_from_object_file_p ())
 206     return true;
 207   if (DECL_PRESERVE_P (node->decl))
 208     return true;
 209   if (lookup_attribute ("externally_visible",
 210                         DECL_ATTRIBUTES (node->decl)))
 211     return true;
 212   if (TARGET_DLLIMPORT_DECL_ATTRIBUTES
 213       && lookup_attribute ("dllexport",
 214                            DECL_ATTRIBUTES (node->decl)))
 215     return true;
 216   if (node->resolution == LDPR_PREVAILING_DEF_IRONLY)
 217     return false;
 218   /* When doing LTO or whole program, we can bring COMDAT functoins static.
 219      This improves code quality and we know we will duplicate them at most twice
 220      (in the case that we are not using plugin and link with object file
 221       implementing same COMDAT)  */
 222   if (((in_lto_p || whole_program) && !flag_incremental_link)
 223       && DECL_COMDAT (node->decl)
 224       && comdat_can_be_unshared_p (node))
 225     return false;
 226
 227   /* When doing link time optimizations, hidden symbols become local.  */
 228   if ((in_lto_p && !flag_incremental_link)
 229       && (DECL_VISIBILITY (node->decl) == VISIBILITY_HIDDEN
 230           || DECL_VISIBILITY (node->decl) == VISIBILITY_INTERNAL)
 231       /* Be sure that node is defined in IR file, not in other object
 232          file.  In that case we don't set used_from_other_object_file.  */
 233       && node->definition)
 234     ;
 235   else if (!whole_program)
 236     return true;
 237
 238   if (MAIN_NAME_P (DECL_NAME (node->decl)))
 239     return true;
 240
 241   if (node->instrumentation_clone
 242       && MAIN_NAME_P (DECL_NAME (node->orig_decl)))
 243     return true;
 244
 245   return false;
 246 }
 247
 248 /* Return true when variable should be considered externally visible.  */
 249
 250 bool
 251 varpool_node::externally_visible_p (void)
 252 {
 253   while (transparent_alias && definition)
 254     return get_alias_target ()->externally_visible_p ();
 255   if (DECL_EXTERNAL (decl))
 256     return true;
 257
 258   if (!TREE_PUBLIC (decl))
 259     return false;
 260
 261   /* If linker counts on us, we must preserve the function.  */
 262   if (used_from_object_file_p ())
 263     return true;
 264
 265   /* Bringing TLS variables local may cause dynamic linker failures
 266      on limits of static TLS vars.  */
 267   if (DECL_THREAD_LOCAL_P (decl)
 268       && (DECL_TLS_MODEL (decl) != TLS_MODEL_EMULATED
 269           && DECL_TLS_MODEL (decl) != TLS_MODEL_INITIAL_EXEC))
 270     return true;
 271
 272   if (DECL_HARD_REGISTER (decl))
 273     return true;
 274   if (DECL_PRESERVE_P (decl))
 275     return true;
 276   if (lookup_attribute ("externally_visible",
 277                         DECL_ATTRIBUTES (decl)))
 278     return true;
 279   if (TARGET_DLLIMPORT_DECL_ATTRIBUTES
 280       && lookup_attribute ("dllexport",
 281                            DECL_ATTRIBUTES (decl)))
 282     return true;
 283
 284   /* See if we have linker information about symbol not being used or
 285      if we need to make guess based on the declaration.
 286
 287      Even if the linker clams the symbol is unused, never bring internal
 288      symbols that are declared by user as used or externally visible.
 289      This is needed for i.e. references from asm statements.   */
 290   if (used_from_object_file_p ())
 291     return true;
 292   if (resolution == LDPR_PREVAILING_DEF_IRONLY)
 293     return false;
 294
 295   /* As a special case, the COMDAT virtual tables can be unshared.
 296      In LTO mode turn vtables into static variables.  The variable is readonly,
 297      so this does not enable more optimization, but referring static var
 298      is faster for dynamic linking.  Also this match logic hidding vtables
 299      from LTO symbol tables.  */
 300   if (((in_lto_p || flag_whole_program) && !flag_incremental_link)
 301       && DECL_COMDAT (decl)
 302       && comdat_can_be_unshared_p (this))
 303     return false;
 304
 305   /* When doing link time optimizations, hidden symbols become local.  */
 306   if (in_lto_p && !flag_incremental_link
 307       && (DECL_VISIBILITY (decl) == VISIBILITY_HIDDEN
 308           || DECL_VISIBILITY (decl) == VISIBILITY_INTERNAL)
 309       /* Be sure that node is defined in IR file, not in other object
 310          file.  In that case we don't set used_from_other_object_file.  */
 311       && definition)
 312     ;
 313   else if (!flag_whole_program)
 314     return true;
 315
 316   /* Do not attempt to privatize COMDATS by default.
 317      This would break linking with C++ libraries sharing
 318      inline definitions.
 319
 320      FIXME: We can do so for readonly vars with no address taken and
 321      possibly also for vtables since no direct pointer comparsion is done.
 322      It might be interesting to do so to reduce linking overhead.  */
 323   if (DECL_COMDAT (decl) || DECL_WEAK (decl))
 324     return true;
 325   return false;
 326 }
 327
 328 /* Return true if reference to NODE can be replaced by a local alias.
 329    Local aliases save dynamic linking overhead and enable more optimizations.
 330  */
 331
 332 static bool
 333 can_replace_by_local_alias (symtab_node *node)
 334 {
 335 #ifndef ASM_OUTPUT_DEF
 336   /* If aliases aren't supported, we can't do replacement.  */
 337   return false;
 338 #endif
 339   /* Weakrefs have a reason to be non-local.  Be sure we do not replace
 340      them.  */
 341   while (node->transparent_alias && node->definition && !node->weakref)
 342     node = node->get_alias_target ();
 343   if (node->weakref)
 344     return false;
 345
 346   return (node->get_availability () > AVAIL_INTERPOSABLE
 347           && !decl_binds_to_current_def_p (node->decl)
 348           && !node->can_be_discarded_p ());
 349 }
 350
 351 /* Return true if we can replace reference to NODE by local alias
 352    within a virtual table.  Generally we can replace function pointers
 353    and virtual table pointers.  */
 354
 355 static bool
 356 can_replace_by_local_alias_in_vtable (symtab_node *node)
 357 {
 358   if (is_a <varpool_node *> (node)
 359       && !DECL_VIRTUAL_P (node->decl))
 360     return false;
 361   return can_replace_by_local_alias (node);
 362 }
 363
 364 /* walk_tree callback that rewrites initializer references.   */
 365
 366 static tree
 367 update_vtable_references (tree *tp, int *walk_subtrees,
 368                           void *data ATTRIBUTE_UNUSED)
 369 {
 370   if (VAR_OR_FUNCTION_DECL_P (*tp))
 371     {
 372       if (can_replace_by_local_alias_in_vtable (symtab_node::get (*tp)))
 373         *tp = symtab_node::get (*tp)->noninterposable_alias ()->decl;
 374       *walk_subtrees = 0;
 375     }
 376   else if (IS_TYPE_OR_DECL_P (*tp))
 377     *walk_subtrees = 0;
 378   return NULL;
 379 }
 380
 381 /* In LTO we can remove COMDAT groups and weak symbols.
 382    Either turn them into normal symbols or external symbol depending on
 383    resolution info.  */
 384
 385 static void
 386 update_visibility_by_resolution_info (symtab_node * node)
 387 {
 388   bool define;
 389
 390   if (!node->externally_visible
 391       || (!DECL_WEAK (node->decl) && !DECL_ONE_ONLY (node->decl))
 392       || node->resolution == LDPR_UNKNOWN)
 393     return;
 394
 395   define = (node->resolution == LDPR_PREVAILING_DEF_IRONLY
 396             || node->resolution == LDPR_PREVAILING_DEF
 397             || node->resolution == LDPR_UNDEF
 398             || node->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP);
 399
 400   /* The linker decisions ought to agree in the whole group.  */
 401   if (node->same_comdat_group)
 402     for (symtab_node *next = node->same_comdat_group;
 403          next != node; next = next->same_comdat_group)
 404       {
 405         if (!next->externally_visible || next->transparent_alias)
 406           continue;
 407
 408         bool same_def
 409           = define == (next->resolution == LDPR_PREVAILING_DEF_IRONLY
 410                        || next->resolution == LDPR_PREVAILING_DEF
 411                        || next->resolution == LDPR_UNDEF
 412                        || next->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP);
 413         gcc_assert (in_lto_p || same_def);
 414         if (!same_def)
 415           return;
 416       }
 417
 418   if (node->same_comdat_group)
 419     for (symtab_node *next = node->same_comdat_group;
 420          next != node; next = next->same_comdat_group)
 421       {
 422         /* During incremental linking we need to keep symbol weak for future
 423            linking.  We can still drop definition if we know non-LTO world
 424            prevails.  */
 425         if (!flag_incremental_link)
 426           {
 427             DECL_WEAK (next->decl) = false;
 428             next->set_comdat_group (NULL);
 429           }
 430         if (!define)
 431           {
 432             if (next->externally_visible)
 433               DECL_EXTERNAL (next->decl) = true;
 434             next->set_comdat_group (NULL);
 435           }
 436       }
 437
 438   /* During incremental linking we need to keep symbol weak for future
 439      linking.  We can still drop definition if we know non-LTO world prevails.  */
 440   if (!flag_incremental_link)
 441     {
 442       DECL_WEAK (node->decl) = false;
 443       node->set_comdat_group (NULL);
 444       node->dissolve_same_comdat_group_list ();
 445     }
 446   if (!define)
 447     {
 448       DECL_EXTERNAL (node->decl) = true;
 449       node->set_comdat_group (NULL);
 450       node->dissolve_same_comdat_group_list ();
 451     }
 452 }
 453
 454 /* Try to get rid of weakref.  */
 455
 456 static void
 457 optimize_weakref (symtab_node *node)
 458 {
 459 #ifdef ASM_OUTPUT_DEF
 460   bool aliases_supported = true;
 461 #else
 462   bool aliases_supported = false;
 463 #endif
 464   bool strip_weakref = false;
 465   bool static_alias = false;
 466
 467   gcc_assert (node->weakref);
 468
 469   /* Weakrefs with no target defined can not be optimized.  */
 470   if (!node->analyzed)
 471     return;
 472   symtab_node *target = node->get_alias_target ();
 473
 474   /* Weakrefs to weakrefs can be optimized only if target can be.  */
 475   if (target->weakref)
 476     optimize_weakref (target);
 477   if (target->weakref)
 478     return;
 479
 480   /* If we have definition of weakref's target and we know it binds locally,
 481      we can turn weakref to static alias.  */
 482   if (target->definition && decl_binds_to_current_def_p (target->decl)
 483       && aliases_supported)
 484     strip_weakref = static_alias = true;
 485   /* Otherwise we can turn weakref into transparent alias.  This transformation
 486      may break asm statements which directly refers to symbol name and expect
 487      GNU as to translate it via .weakref directive. So do not optimize when
 488      DECL_PRESERVED is set and .weakref is supported.  */
 489   else if ((!DECL_PRESERVE_P (target->decl)
 490             || IDENTIFIER_TRANSPARENT_ALIAS (DECL_ASSEMBLER_NAME (node->decl)))
 491            && !DECL_WEAK (target->decl)
 492            && !DECL_EXTERNAL (target->decl)
 493            && ((target->definition && !target->can_be_discarded_p ())
 494                || target->resolution != LDPR_UNDEF))
 495     strip_weakref = true;
 496   if (!strip_weakref)
 497     return;
 498   node->weakref = false;
 499   IDENTIFIER_TRANSPARENT_ALIAS (DECL_ASSEMBLER_NAME (node->decl)) = 0;
 500   TREE_CHAIN (DECL_ASSEMBLER_NAME (node->decl)) = NULL_TREE;
 501   DECL_ATTRIBUTES (node->decl) = remove_attribute ("weakref",
 502                                                    DECL_ATTRIBUTES
 503                                                          (node->decl));
 504
 505   if (dump_file)
 506     fprintf (dump_file, "Optimizing weakref %s %s\n",
 507              node->name(),
 508              static_alias ? "as static alias" : "as transparent alias");
 509
 510   if (static_alias)
 511     {
 512       /* make_decl_local will shortcircuit if it doesn't see TREE_PUBLIC.
 513          be sure it really clears the WEAK flag.  */
 514       TREE_PUBLIC (node->decl) = true;
 515       node->make_decl_local ();
 516       node->forced_by_abi = false;
 517       node->resolution = LDPR_PREVAILING_DEF_IRONLY;
 518       node->externally_visible = false;
 519       gcc_assert (!DECL_WEAK (node->decl));
 520       node->transparent_alias = false;
 521     }
 522   else
 523     {
 524       symtab->change_decl_assembler_name
 525         (node->decl, DECL_ASSEMBLER_NAME (node->get_alias_target ()->decl));
 526       node->transparent_alias = true;
 527       node->copy_visibility_from (target);
 528     }
 529   gcc_assert (node->alias);
 530 }
 531
 532 /* NODE is an externally visible definition, which we've discovered is
 533    not needed externally.  Make it local to this compilation.  */
 534
 535 static void
 536 localize_node (bool whole_program, symtab_node *node)
 537 {
 538   gcc_assert (whole_program || in_lto_p || !TREE_PUBLIC (node->decl));
 539
 540   /* It is possible that one comdat group contains both hidden and non-hidden
 541      symbols.  In this case we can privatize all hidden symbol but we need
 542      to keep non-hidden exported.  */
 543   if (node->same_comdat_group
 544       && node->resolution == LDPR_PREVAILING_DEF_IRONLY)
 545     {
 546       symtab_node *next;
 547       for (next = node->same_comdat_group;
 548            next != node; next = next->same_comdat_group)
 549         if (next->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP
 550             || next->resolution == LDPR_PREVAILING_DEF)
 551           break;
 552       if (node != next)
 553         {
 554           if (!node->transparent_alias)
 555             {
 556               node->resolution = LDPR_PREVAILING_DEF_IRONLY;
 557               node->make_decl_local ();
 558               if (!flag_incremental_link)
 559                 node->unique_name |= true;
 560               return;
 561             }
 562         }
 563     }
 564   /* For similar reason do not privatize whole comdat when seeing comdat
 565      local.  Wait for non-comdat symbol to be privatized first.  */
 566   if (node->comdat_local_p ())
 567     return;
 568
 569   if (node->same_comdat_group && TREE_PUBLIC (node->decl))
 570     {
 571       for (symtab_node *next = node->same_comdat_group;
 572            next != node; next = next->same_comdat_group)
 573         {
 574           next->set_comdat_group (NULL);
 575           if (!next->alias)
 576             next->set_section (NULL);
 577           if (!next->transparent_alias)
 578             next->make_decl_local ();
 579           next->unique_name
 580             |= ((next->resolution == LDPR_PREVAILING_DEF_IRONLY
 581                  || next->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP)
 582                 && TREE_PUBLIC (next->decl)
 583                 && !flag_incremental_link);
 584         }
 585
 586       /* Now everything's localized, the grouping has no meaning, and
 587          will cause crashes if we keep it around.  */
 588       node->dissolve_same_comdat_group_list ();
 589     }
 590
 591   node->unique_name
 592     |= ((node->resolution == LDPR_PREVAILING_DEF_IRONLY
 593          || node->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP)
 594         && TREE_PUBLIC (node->decl)
 595         && !flag_incremental_link);
 596
 597   if (TREE_PUBLIC (node->decl))
 598     node->set_comdat_group (NULL);
 599   if (DECL_COMDAT (node->decl) && !node->alias)
 600     node->set_section (NULL);
 601   if (!node->transparent_alias)
 602     {
 603       node->resolution = LDPR_PREVAILING_DEF_IRONLY;
 604       node->make_decl_local ();
 605     }
 606 }
 607
 608 /* Decide on visibility of all symbols.  */
 609
 610 static unsigned int
 611 function_and_variable_visibility (bool whole_program)
 612 {
 613   struct cgraph_node *node;
 614   varpool_node *vnode;
 615
 616   /* All aliases should be procssed at this point.  */
 617   gcc_checking_assert (!alias_pairs || !alias_pairs->length ());
 618
 619   FOR_EACH_FUNCTION (node)
 620     {
 621       int flags = flags_from_decl_or_type (node->decl);
 622
 623       /* Optimize away PURE and CONST constructors and destructors.  */
 624       if (optimize
 625           && (flags & (ECF_CONST | ECF_PURE))
 626           && !(flags & ECF_LOOPING_CONST_OR_PURE))
 627         {
 628           DECL_STATIC_CONSTRUCTOR (node->decl) = 0;
 629           DECL_STATIC_DESTRUCTOR (node->decl) = 0;
 630         }
 631
 632       /* Frontends and alias code marks nodes as needed before parsing
 633          is finished.  We may end up marking as node external nodes
 634          where this flag is meaningless strip it.  */
 635       if (DECL_EXTERNAL (node->decl) || !node->definition)
 636         {
 637           node->force_output = 0;
 638           node->forced_by_abi = 0;
 639         }
 640
 641       /* C++ FE on lack of COMDAT support create local COMDAT functions
 642          (that ought to be shared but can not due to object format
 643          limitations).  It is necessary to keep the flag to make rest of C++ FE
 644          happy.  Clear the flag here to avoid confusion in middle-end.  */
 645       if (DECL_COMDAT (node->decl) && !TREE_PUBLIC (node->decl))
 646         DECL_COMDAT (node->decl) = 0;
 647
 648       /* For external decls stop tracking same_comdat_group. It doesn't matter
 649          what comdat group they are in when they won't be emitted in this TU.
 650
 651          An exception is LTO where we may end up with both external
 652          and non-external declarations in the same comdat group in
 653          the case declarations was not merged.  */
 654       if (node->same_comdat_group && DECL_EXTERNAL (node->decl) && !in_lto_p)
 655         {
 656           if (flag_checking)
 657             {
 658               for (symtab_node *n = node->same_comdat_group;
 659                    n != node;
 660                    n = n->same_comdat_group)
 661                 /* If at least one of same comdat group functions is external,
 662                    all of them have to be, otherwise it is a front-end bug.  */
 663                 gcc_assert (DECL_EXTERNAL (n->decl));
 664             }
 665           node->dissolve_same_comdat_group_list ();
 666         }
 667       gcc_assert ((!DECL_WEAK (node->decl)
 668                   && !DECL_COMDAT (node->decl))
 669                   || TREE_PUBLIC (node->decl)
 670                   || node->weakref
 671                   || DECL_EXTERNAL (node->decl));
 672       if (cgraph_externally_visible_p (node, whole_program))
 673         {
 674           gcc_assert (!node->global.inlined_to);
 675           node->externally_visible = true;
 676         }
 677       else
 678         {
 679           node->externally_visible = false;
 680           node->forced_by_abi = false;
 681         }
 682       if (!node->externally_visible
 683           && node->definition && !node->weakref
 684           && !DECL_EXTERNAL (node->decl))
 685         localize_node (whole_program, node);
 686
 687       if (node->thunk.thunk_p
 688           && !node->thunk.add_pointer_bounds_args
 689           && TREE_PUBLIC (node->decl))
 690         {
 691           struct cgraph_node *decl_node = node;
 692
 693           decl_node = decl_node->callees->callee->function_symbol ();
 694
 695           /* Thunks have the same visibility as function they are attached to.
 696              Make sure the C++ front end set this up properly.  */
 697           if (DECL_ONE_ONLY (decl_node->decl))
 698             {
 699               gcc_checking_assert (DECL_COMDAT (node->decl)
 700                                    == DECL_COMDAT (decl_node->decl));
 701               gcc_checking_assert (node->in_same_comdat_group_p (decl_node));
 702               gcc_checking_assert (node->same_comdat_group);
 703             }
 704           node->forced_by_abi = decl_node->forced_by_abi;
 705           if (DECL_EXTERNAL (decl_node->decl))
 706             DECL_EXTERNAL (node->decl) = 1;
 707         }
 708
 709       update_visibility_by_resolution_info (node);
 710       if (node->weakref)
 711         optimize_weakref (node);
 712     }
 713   FOR_EACH_DEFINED_FUNCTION (node)
 714     {
 715       if (!node->local.local)
 716         node->local.local |= node->local_p ();
 717
 718       /* If we know that function can not be overwritten by a
 719          different semantics and moreover its section can not be
 720          discarded, replace all direct calls by calls to an
 721          noninterposable alias.  This make dynamic linking cheaper and
 722          enable more optimization.
 723
 724          TODO: We can also update virtual tables.  */
 725       if (node->callers
 726           && can_replace_by_local_alias (node))
 727         {
 728           cgraph_node *alias = dyn_cast<cgraph_node *>
 729             (node->noninterposable_alias ());
 730
 731           if (alias && alias != node)
 732             {
 733               while (node->callers)
 734                 {
 735                   struct cgraph_edge *e = node->callers;
 736
 737                   e->redirect_callee (alias);
 738                   if (gimple_has_body_p (e->caller->decl))
 739                     {
 740                       push_cfun (DECL_STRUCT_FUNCTION (e->caller->decl));
 741                       e->redirect_call_stmt_to_callee ();
 742                       pop_cfun ();
 743                     }
 744                 }
 745             }
 746         }
 747     }
 748   FOR_EACH_VARIABLE (vnode)
 749     {
 750       /* weak flag makes no sense on local variables.  */
 751       gcc_assert (!DECL_WEAK (vnode->decl)
 752                   || vnode->weakref
 753                   || TREE_PUBLIC (vnode->decl)
 754                   || DECL_EXTERNAL (vnode->decl));
 755       /* In several cases declarations can not be common:
 756
 757          - when declaration has initializer
 758          - when it is in weak
 759          - when it has specific section
 760          - when it resides in non-generic address space.
 761          - if declaration is local, it will get into .local common section
 762            so common flag is not needed.  Frontends still produce these in
 763            certain cases, such as for:
 764
 765              static int a __attribute__ ((common))
 766
 767          Canonicalize things here and clear the redundant flag.  */
 768       if (DECL_COMMON (vnode->decl)
 769           && (!(TREE_PUBLIC (vnode->decl)
 770               || DECL_EXTERNAL (vnode->decl))
 771               || (DECL_INITIAL (vnode->decl)
 772                   && DECL_INITIAL (vnode->decl) != error_mark_node)
 773               || DECL_WEAK (vnode->decl)
 774               || DECL_SECTION_NAME (vnode->decl) != NULL
 775               || ! (ADDR_SPACE_GENERIC_P
 776                     (TYPE_ADDR_SPACE (TREE_TYPE (vnode->decl))))))
 777         DECL_COMMON (vnode->decl) = 0;
 778       if (vnode->weakref)
 779         optimize_weakref (vnode);
 780     }
 781   FOR_EACH_DEFINED_VARIABLE (vnode)
 782     {
 783       if (!vnode->definition)
 784         continue;
 785       if (vnode->externally_visible_p ())
 786         vnode->externally_visible = true;
 787       else
 788         {
 789           vnode->externally_visible = false;
 790           vnode->forced_by_abi = false;
 791         }
 792       if (lookup_attribute ("no_reorder",
 793                             DECL_ATTRIBUTES (vnode->decl)))
 794         vnode->no_reorder = 1;
 795
 796       if (!vnode->externally_visible
 797           && !vnode->transparent_alias
 798           && !DECL_EXTERNAL (vnode->decl))
 799         localize_node (whole_program, vnode);
 800
 801       update_visibility_by_resolution_info (vnode);
 802
 803       /* Update virtual tables to point to local aliases where possible.  */
 804       if (DECL_VIRTUAL_P (vnode->decl)
 805           && !DECL_EXTERNAL (vnode->decl))
 806         {
 807           int i;
 808           struct ipa_ref *ref;
 809           bool found = false;
 810
 811           /* See if there is something to update.  */
 812           for (i = 0; vnode->iterate_reference (i, ref); i++)
 813             if (ref->use == IPA_REF_ADDR
 814                 && can_replace_by_local_alias_in_vtable (ref->referred))
 815               {
 816                 found = true;
 817                 break;
 818               }
 819           if (found)
 820             {
 821               hash_set<tree> visited_nodes;
 822
 823               vnode->get_constructor ();
 824               walk_tree (&DECL_INITIAL (vnode->decl),
 825                          update_vtable_references, NULL, &visited_nodes);
 826               vnode->remove_all_references ();
 827               record_references_in_initializer (vnode->decl, false);
 828             }
 829         }
 830     }
 831
 832   if (dump_file)
 833     {
 834       fprintf (dump_file, "\nMarking local functions:");
 835       FOR_EACH_DEFINED_FUNCTION (node)
 836         if (node->local.local)
 837           fprintf (dump_file, " %s", node->name ());
 838       fprintf (dump_file, "\n\n");
 839       fprintf (dump_file, "\nMarking externally visible functions:");
 840       FOR_EACH_DEFINED_FUNCTION (node)
 841         if (node->externally_visible)
 842           fprintf (dump_file, " %s", node->name ());
 843       fprintf (dump_file, "\n\n");
 844       fprintf (dump_file, "\nMarking externally visible variables:");
 845       FOR_EACH_DEFINED_VARIABLE (vnode)
 846         if (vnode->externally_visible)
 847           fprintf (dump_file, " %s", vnode->name ());
 848       fprintf (dump_file, "\n\n");
 849     }
 850   symtab->function_flags_ready = true;
 851   return 0;
 852 }
 853
 854 /* Local function pass handling visibilities.  This happens before LTO streaming
 855    so in particular -fwhole-program should be ignored at this level.  */
 856
 857 namespace {
 858
 859 const pass_data pass_data_ipa_function_and_variable_visibility =
 860 {
 861   SIMPLE_IPA_PASS, /* type */
 862   "visibility", /* name */
 863   OPTGROUP_NONE, /* optinfo_flags */
 864   TV_CGRAPHOPT, /* tv_id */
 865   0, /* properties_required */
 866   0, /* properties_provided */
 867   0, /* properties_destroyed */
 868   0, /* todo_flags_start */
 869   ( TODO_remove_functions | TODO_dump_symtab ), /* todo_flags_finish */
 870 };
 871
 872 /* Bring functions local at LTO time with -fwhole-program.  */
 873
 874 static unsigned int
 875 whole_program_function_and_variable_visibility (void)
 876 {
 877   function_and_variable_visibility (flag_whole_program);
 878   if (optimize)
 879     ipa_discover_readonly_nonaddressable_vars ();
 880   return 0;
 881 }
 882
 883 } // anon namespace
 884
 885 namespace {
 886
 887 const pass_data pass_data_ipa_whole_program_visibility =
 888 {
 889   IPA_PASS, /* type */
 890   "whole-program", /* name */
 891   OPTGROUP_NONE, /* optinfo_flags */
 892   TV_CGRAPHOPT, /* tv_id */
 893   0, /* properties_required */
 894   0, /* properties_provided */
 895   0, /* properties_destroyed */
 896   0, /* todo_flags_start */
 897   ( TODO_remove_functions | TODO_dump_symtab ), /* todo_flags_finish */
 898 };
 899
 900 class pass_ipa_whole_program_visibility : public ipa_opt_pass_d
 901 {
 902 public:
 903   pass_ipa_whole_program_visibility (gcc::context *ctxt)
 904     : ipa_opt_pass_d (pass_data_ipa_whole_program_visibility, ctxt,
 905                       NULL, /* generate_summary */
 906                       NULL, /* write_summary */
 907                       NULL, /* read_summary */
 908                       NULL, /* write_optimization_summary */
 909                       NULL, /* read_optimization_summary */
 910                       NULL, /* stmt_fixup */
 911                       0, /* function_transform_todo_flags_start */
 912                       NULL, /* function_transform */
 913                       NULL) /* variable_transform */
 914   {}
 915
 916   /* opt_pass methods: */
 917
 918   virtual bool gate (function *)
 919     {
 920       /* Do not re-run on ltrans stage.  */
 921       return !flag_ltrans;
 922     }
 923   virtual unsigned int execute (function *)
 924     {
 925       return whole_program_function_and_variable_visibility ();
 926     }
 927
 928 }; // class pass_ipa_whole_program_visibility
 929
 930 } // anon namespace
 931
 932 ipa_opt_pass_d *
 933 make_pass_ipa_whole_program_visibility (gcc::context *ctxt)
 934 {
 935   return new pass_ipa_whole_program_visibility (ctxt);
 936 }
 937
 938 class pass_ipa_function_and_variable_visibility : public simple_ipa_opt_pass
 939 {
 940 public:
 941   pass_ipa_function_and_variable_visibility (gcc::context *ctxt)
 942     : simple_ipa_opt_pass (pass_data_ipa_function_and_variable_visibility,
 943                            ctxt)
 944   {}
 945
 946   /* opt_pass methods: */
 947   virtual unsigned int execute (function *)
 948     {
 949       return function_and_variable_visibility (flag_whole_program && !flag_lto);
 950     }
 951
 952 }; // class pass_ipa_function_and_variable_visibility
 953
 954 simple_ipa_opt_pass *
 955 make_pass_ipa_function_and_variable_visibility (gcc::context *ctxt)
 956 {
 957   return new pass_ipa_function_and_variable_visibility (ctxt);
 958 }