gcc/lto-symtab.c

   1 /* LTO symbol table.
   2    Copyright 2009 Free Software Foundation, Inc.
   3    Contributed by CodeSourcery, Inc.
   4
   5 This file is part of GCC.
   6
   7 GCC is free software; you can redistribute it and/or modify it under
   8 the terms of the GNU General Public License as published by the Free
   9 Software Foundation; either version 3, or (at your option) any later
  10 version.
  11
  12 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  13 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  14 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  15 for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GCC; see the file COPYING3.  If not see
  19 <http://www.gnu.org/licenses/>.  */
  20
  21 #include "config.h"
  22 #include "system.h"
  23 #include "coretypes.h"
  24 #include "toplev.h"
  25 #include "tree.h"
  26 #include "gimple.h"
  27 #include "ggc.h"        /* lambda.h needs this */
  28 #include "lambda.h"     /* gcd */
  29 #include "hashtab.h"
  30 #include "plugin-api.h"
  31 #include "lto-streamer.h"
  32
  33 /* Vector to keep track of external variables we've seen so far.  */
  34 VEC(tree,gc) *lto_global_var_decls;
  35
  36 /* Symbol table entry.  */
  37
  38 struct GTY(()) lto_symtab_entry_def
  39 {
  40   /* The symbol table entry key, an IDENTIFIER.  */
  41   tree id;
  42   /* The symbol table entry, a DECL.  */
  43   tree decl;
  44   /* The cgraph node if decl is a function decl.  Filled in during the
  45      merging process.  */
  46   struct cgraph_node *node;
  47   /* LTO file-data and symbol resolution for this decl.  */
  48   struct lto_file_decl_data * GTY((skip (""))) file_data;
  49   enum ld_plugin_symbol_resolution resolution;
  50   /* Pointer to the next entry with the same key.  Before decl merging
  51      this links all symbols from the different TUs.  After decl merging
  52      this links merged but incompatible decls, thus all prevailing ones
  53      remaining.  */
  54   struct lto_symtab_entry_def *next;
  55 };
  56 typedef struct lto_symtab_entry_def *lto_symtab_entry_t;
  57
  58 /* A poor man's symbol table. This hashes identifier to prevailing DECL
  59    if there is one. */
  60
  61 static GTY ((if_marked ("lto_symtab_entry_marked_p"),
  62              param_is (struct lto_symtab_entry_def)))
  63   htab_t lto_symtab_identifiers;
  64
  65 /* Return the hash value of an lto_symtab_entry_t object pointed to by P.  */
  66
  67 static hashval_t
  68 lto_symtab_entry_hash (const void *p)
  69 {
  70   const struct lto_symtab_entry_def *base =
  71     (const struct lto_symtab_entry_def *) p;
  72   return htab_hash_string (IDENTIFIER_POINTER (base->id));
  73 }
  74
  75 /* Return non-zero if P1 and P2 points to lto_symtab_entry_def structs
  76    corresponding to the same symbol.  */
  77
  78 static int
  79 lto_symtab_entry_eq (const void *p1, const void *p2)
  80 {
  81   const struct lto_symtab_entry_def *base1 =
  82      (const struct lto_symtab_entry_def *) p1;
  83   const struct lto_symtab_entry_def *base2 =
  84      (const struct lto_symtab_entry_def *) p2;
  85   return (base1->id == base2->id);
  86 }
  87
  88 /* Returns non-zero if P points to an lto_symtab_entry_def struct that needs
  89    to be marked for GC.  */
  90
  91 static int
  92 lto_symtab_entry_marked_p (const void *p)
  93 {
  94   const struct lto_symtab_entry_def *base =
  95      (const struct lto_symtab_entry_def *) p;
  96
  97   /* Keep this only if the decl or the chain is marked.  */
  98   return (ggc_marked_p (base->decl)
  99           || (base->next && ggc_marked_p (base->next)));
 100 }
 101
 102 /* Lazily initialize resolution hash tables.  */
 103
 104 static void
 105 lto_symtab_maybe_init_hash_table (void)
 106 {
 107   if (lto_symtab_identifiers)
 108     return;
 109
 110   lto_symtab_identifiers =
 111     htab_create_ggc (1021, lto_symtab_entry_hash,
 112                      lto_symtab_entry_eq, NULL);
 113 }
 114
 115 /* Registers DECL with the LTO symbol table as having resolution RESOLUTION
 116    and read from FILE_DATA. */
 117
 118 void
 119 lto_symtab_register_decl (tree decl,
 120                           ld_plugin_symbol_resolution_t resolution,
 121                           struct lto_file_decl_data *file_data)
 122 {
 123   lto_symtab_entry_t new_entry;
 124   void **slot;
 125
 126   /* Check that declarations reaching this function do not have
 127      properties inconsistent with having external linkage.  If any of
 128      these asertions fail, then the object file reader has failed to
 129      detect these cases and issue appropriate error messages.  */
 130   gcc_assert (decl
 131               && TREE_PUBLIC (decl)
 132               && (TREE_CODE (decl) == VAR_DECL
 133                   || TREE_CODE (decl) == FUNCTION_DECL)
 134               && DECL_ASSEMBLER_NAME_SET_P (decl));
 135   if (TREE_CODE (decl) == VAR_DECL
 136       && DECL_INITIAL (decl))
 137     gcc_assert (!DECL_EXTERNAL (decl)
 138                 || (TREE_STATIC (decl) && TREE_READONLY (decl)));
 139   if (TREE_CODE (decl) == FUNCTION_DECL)
 140     gcc_assert (!DECL_ABSTRACT (decl));
 141
 142   new_entry = GGC_CNEW (struct lto_symtab_entry_def);
 143   new_entry->id = DECL_ASSEMBLER_NAME (decl);
 144   new_entry->decl = decl;
 145   new_entry->resolution = resolution;
 146   new_entry->file_data = file_data;
 147
 148   lto_symtab_maybe_init_hash_table ();
 149   slot = htab_find_slot (lto_symtab_identifiers, new_entry, INSERT);
 150   new_entry->next = (lto_symtab_entry_t) *slot;
 151   *slot = new_entry;
 152 }
 153
 154 /* Get the lto_symtab_entry_def struct associated with ID
 155    if there is one.  */
 156
 157 static lto_symtab_entry_t
 158 lto_symtab_get (tree id)
 159 {
 160   struct lto_symtab_entry_def temp;
 161   void **slot;
 162
 163   lto_symtab_maybe_init_hash_table ();
 164   temp.id = id;
 165   slot = htab_find_slot (lto_symtab_identifiers, &temp, NO_INSERT);
 166   return slot ? (lto_symtab_entry_t) *slot : NULL;
 167 }
 168
 169 /* Get the linker resolution for DECL.  */
 170
 171 enum ld_plugin_symbol_resolution
 172 lto_symtab_get_resolution (tree decl)
 173 {
 174   lto_symtab_entry_t e;
 175
 176   gcc_assert (DECL_ASSEMBLER_NAME_SET_P (decl));
 177
 178   e = lto_symtab_get (DECL_ASSEMBLER_NAME (decl));
 179   while (e && e->decl != decl)
 180     e = e->next;
 181   if (!e)
 182     return LDPR_UNKNOWN;
 183
 184   return e->resolution;
 185 }
 186
 187
 188 /* Replace the cgraph node NODE with PREVAILING_NODE in the cgraph, merging
 189    all edges and removing the old node.  */
 190
 191 static void
 192 lto_cgraph_replace_node (struct cgraph_node *node,
 193                          struct cgraph_node *prevailing_node)
 194 {
 195   struct cgraph_edge *e, *next;
 196
 197   /* Merge node flags.  */
 198   if (node->needed)
 199     cgraph_mark_needed_node (prevailing_node);
 200   if (node->reachable)
 201     cgraph_mark_reachable_node (prevailing_node);
 202   if (node->address_taken)
 203     {
 204       gcc_assert (!prevailing_node->global.inlined_to);
 205       cgraph_mark_address_taken_node (prevailing_node);
 206     }
 207
 208   /* Redirect all incoming edges.  */
 209   for (e = node->callers; e; e = next)
 210     {
 211       next = e->next_caller;
 212       cgraph_redirect_edge_callee (e, prevailing_node);
 213     }
 214
 215   /* There are not supposed to be any outgoing edges from a node we
 216      replace.  Still this can happen for multiple instances of weak
 217      functions.  */
 218   for (e = node->callees; e; e = next)
 219     {
 220       next = e->next_callee;
 221       cgraph_remove_edge (e);
 222     }
 223
 224   /* Finally remove the replaced node.  */
 225   cgraph_remove_node (node);
 226 }
 227
 228 /* Merge two variable or function symbol table entries PREVAILING and ENTRY.
 229    Return false if the symbols are not fully compatible and a diagnostic
 230    should be emitted.  */
 231
 232 static bool
 233 lto_symtab_merge (lto_symtab_entry_t prevailing, lto_symtab_entry_t entry)
 234 {
 235   tree prevailing_decl = prevailing->decl;
 236   tree decl = entry->decl;
 237   tree prevailing_type, type;
 238
 239   /* Merge decl state in both directions, we may still end up using
 240      the new decl.  */
 241   TREE_ADDRESSABLE (prevailing_decl) |= TREE_ADDRESSABLE (decl);
 242   TREE_ADDRESSABLE (decl) |= TREE_ADDRESSABLE (prevailing_decl);
 243
 244   /* The linker may ask us to combine two incompatible symbols.
 245      Detect this case and notify the caller of required diagnostics.  */
 246
 247   if (TREE_CODE (decl) == FUNCTION_DECL)
 248     {
 249       if (TREE_TYPE (prevailing_decl) != TREE_TYPE (decl))
 250         /* If we don't have a merged type yet...sigh.  The linker
 251            wouldn't complain if the types were mismatched, so we
 252            probably shouldn't either.  Just use the type from
 253            whichever decl appears to be associated with the
 254            definition.  If for some odd reason neither decl is, the
 255            older one wins.  */
 256         (void) 0;
 257
 258       return true;
 259     }
 260
 261   /* Now we exclusively deal with VAR_DECLs.  */
 262
 263   /* Sharing a global symbol is a strong hint that two types are
 264      compatible.  We could use this information to complete
 265      incomplete pointed-to types more aggressively here, ignoring
 266      mismatches in both field and tag names.  It's difficult though
 267      to guarantee that this does not have side-effects on merging
 268      more compatible types from other translation units though.  */
 269
 270   /* We can tolerate differences in type qualification, the
 271      qualification of the prevailing definition will prevail.
 272      ???  In principle we might want to only warn for structurally
 273      incompatible types here, but unless we have protective measures
 274      for TBAA in place that would hide useful information.  */
 275   prevailing_type = TYPE_MAIN_VARIANT (TREE_TYPE (prevailing_decl));
 276   type = TYPE_MAIN_VARIANT (TREE_TYPE (decl));
 277
 278   /* We have to register and fetch canonical types here as the global
 279      fixup process didn't yet run.  */
 280   prevailing_type = gimple_register_type (prevailing_type);
 281   type = gimple_register_type (type);
 282   if (prevailing_type != type)
 283     {
 284       if (COMPLETE_TYPE_P (type))
 285         return false;
 286
 287       /* If type is incomplete then avoid warnings in the cases
 288          that TBAA handles just fine.  */
 289
 290       if (TREE_CODE (prevailing_type) != TREE_CODE (type))
 291         return false;
 292
 293       if (TREE_CODE (prevailing_type) == ARRAY_TYPE)
 294         {
 295           tree tem1 = TREE_TYPE (prevailing_type);
 296           tree tem2 = TREE_TYPE (type);
 297           while (TREE_CODE (tem1) == ARRAY_TYPE
 298                  && TREE_CODE (tem2) == ARRAY_TYPE)
 299             {
 300               tem1 = TREE_TYPE (tem1);
 301               tem2 = TREE_TYPE (tem2);
 302             }
 303
 304           if (TREE_CODE (tem1) != TREE_CODE (tem2))
 305             return false;
 306
 307           if (gimple_register_type (tem1) != gimple_register_type (tem2))
 308             return false;
 309         }
 310
 311       /* Fallthru.  Compatible enough.  */
 312     }
 313
 314   /* ???  We might want to emit a warning here if type qualification
 315      differences were spotted.  Do not do this unconditionally though.  */
 316
 317   /* There is no point in comparing too many details of the decls here.
 318      The type compatibility checks or the completing of types has properly
 319      dealt with most issues.  */
 320
 321   /* The following should all not invoke fatal errors as in non-LTO
 322      mode the linker wouldn't complain either.  Just emit warnings.  */
 323
 324   /* Report a warning if user-specified alignments do not match.  */
 325   if ((DECL_USER_ALIGN (prevailing_decl) && DECL_USER_ALIGN (decl))
 326       && DECL_ALIGN (prevailing_decl) < DECL_ALIGN (decl))
 327     return false;
 328
 329   return true;
 330 }
 331
 332 /* Return true if the symtab entry E can be replaced by another symtab
 333    entry.  */
 334
 335 static bool
 336 lto_symtab_resolve_replaceable_p (lto_symtab_entry_t e)
 337 {
 338   if (DECL_EXTERNAL (e->decl)
 339       || DECL_COMDAT (e->decl)
 340       || DECL_WEAK (e->decl))
 341     return true;
 342
 343   if (TREE_CODE (e->decl) == VAR_DECL)
 344     return (DECL_COMMON (e->decl)
 345             || (!flag_no_common && !DECL_INITIAL (e->decl)));
 346
 347   return false;
 348 }
 349
 350 /* Return true if the symtab entry E can be the prevailing one.  */
 351
 352 static bool
 353 lto_symtab_resolve_can_prevail_p (lto_symtab_entry_t e)
 354 {
 355   if (!TREE_STATIC (e->decl))
 356     return false;
 357
 358   /* For functions we need a non-discarded body.  */
 359   if (TREE_CODE (e->decl) == FUNCTION_DECL)
 360     return (e->node && e->node->analyzed);
 361
 362   /* A variable should have a size.  */
 363   else if (TREE_CODE (e->decl) == VAR_DECL)
 364     return (DECL_SIZE (e->decl) != NULL_TREE
 365             /* The C++ frontend retains TREE_STATIC on the declaration
 366                of foo_ in struct Foo { static Foo *foo_; }; but it is
 367                not a definition.  g++.dg/lto/20090315_0.C.  */
 368             && !DECL_EXTERNAL (e->decl));
 369
 370   gcc_unreachable ();
 371 }
 372
 373 /* Resolve the symbol with the candidates in the chain *SLOT and store
 374    their resolutions.  */
 375
 376 static void
 377 lto_symtab_resolve_symbols (void **slot)
 378 {
 379   lto_symtab_entry_t e = (lto_symtab_entry_t) *slot;
 380   lto_symtab_entry_t prevailing = NULL;
 381
 382   /* If the chain is already resolved there is nothing to do.  */
 383   if (e->resolution != LDPR_UNKNOWN)
 384     return;
 385
 386   /* Find the single non-replaceable prevailing symbol and
 387      diagnose ODR violations.  */
 388   for (; e; e = e->next)
 389     {
 390       if (TREE_CODE (e->decl) == FUNCTION_DECL)
 391         e->node = cgraph_get_node (e->decl);
 392
 393       if (!lto_symtab_resolve_can_prevail_p (e))
 394         {
 395           e->resolution = LDPR_RESOLVED_IR;
 396           continue;
 397         }
 398
 399       /* Set a default resolution - the final prevailing one will get
 400          adjusted later.  */
 401       e->resolution = LDPR_PREEMPTED_IR;
 402       if (!lto_symtab_resolve_replaceable_p (e))
 403         {
 404           if (prevailing)
 405             {
 406               error_at (DECL_SOURCE_LOCATION (e->decl),
 407                         "%qD has already been defined", e->decl);
 408               inform (DECL_SOURCE_LOCATION (prevailing->decl),
 409                       "previously defined here");
 410             }
 411           prevailing = e;
 412         }
 413     }
 414   if (prevailing)
 415     goto found;
 416
 417   /* Do a second round choosing one from the replaceable prevailing decls.  */
 418   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 419     {
 420       if (e->resolution != LDPR_PREEMPTED_IR)
 421         continue;
 422
 423       /* Choose the first function that can prevail as prevailing.  */
 424       if (TREE_CODE (e->decl) == FUNCTION_DECL)
 425         {
 426           prevailing = e;
 427           break;
 428         }
 429
 430       /* From variables that can prevail choose the largest one.  */
 431       if (!prevailing
 432           || tree_int_cst_lt (DECL_SIZE (prevailing->decl),
 433                               DECL_SIZE (e->decl)))
 434         prevailing = e;
 435     }
 436
 437   if (!prevailing)
 438     return;
 439
 440 found:
 441   if (TREE_CODE (prevailing->decl) == VAR_DECL
 442       && TREE_READONLY (prevailing->decl))
 443     prevailing->resolution = LDPR_PREVAILING_DEF_IRONLY;
 444   else
 445     prevailing->resolution = LDPR_PREVAILING_DEF;
 446 }
 447
 448 /* Merge all decls in the symbol table chain to the prevailing decl and
 449    issue diagnostics about type mismatches.  */
 450
 451 static void
 452 lto_symtab_merge_decls_2 (void **slot)
 453 {
 454   lto_symtab_entry_t prevailing, e;
 455   VEC(tree, heap) *mismatches = NULL;
 456   unsigned i;
 457   tree decl;
 458   bool diagnosed_p = false;
 459
 460   /* Nothing to do for a single entry.  */
 461   prevailing = (lto_symtab_entry_t) *slot;
 462   if (!prevailing->next)
 463     return;
 464
 465   /* Try to merge each entry with the prevailing one.  */
 466   for (e = prevailing->next; e; e = e->next)
 467     {
 468       if (!lto_symtab_merge (prevailing, e))
 469         VEC_safe_push (tree, heap, mismatches, e->decl);
 470     }
 471   if (VEC_empty (tree, mismatches))
 472     return;
 473
 474   /* Diagnose all mismatched re-declarations.  */
 475   for (i = 0; VEC_iterate (tree, mismatches, i, decl); ++i)
 476     {
 477       if (TREE_TYPE (prevailing->decl) != TREE_TYPE (decl))
 478         diagnosed_p |= warning_at (DECL_SOURCE_LOCATION (decl), 0,
 479                                    "type of %qD does not match original "
 480                                    "declaration", decl);
 481
 482       else if ((DECL_USER_ALIGN (prevailing->decl) && DECL_USER_ALIGN (decl))
 483                && DECL_ALIGN (prevailing->decl) < DECL_ALIGN (decl))
 484         {
 485           diagnosed_p |= warning_at (DECL_SOURCE_LOCATION (decl), 0,
 486                                      "alignment of %qD is bigger than "
 487                                      "original declaration", decl);
 488         }
 489     }
 490   if (diagnosed_p)
 491     inform (DECL_SOURCE_LOCATION (prevailing->decl),
 492             "previously declared here");
 493
 494   VEC_free (tree, heap, mismatches);
 495 }
 496
 497 /* Helper to process the decl chain for the symbol table entry *SLOT.  */
 498
 499 static int
 500 lto_symtab_merge_decls_1 (void **slot, void *data ATTRIBUTE_UNUSED)
 501 {
 502   lto_symtab_entry_t e, prevailing;
 503   bool diagnosed_p = false;
 504
 505   /* Compute the symbol resolutions.  This is a no-op when using the
 506      linker plugin.  */
 507   lto_symtab_resolve_symbols (slot);
 508
 509   /* Find the prevailing decl.  */
 510   for (prevailing = (lto_symtab_entry_t) *slot;
 511        prevailing
 512        && prevailing->resolution != LDPR_PREVAILING_DEF_IRONLY
 513        && prevailing->resolution != LDPR_PREVAILING_DEF;
 514        prevailing = prevailing->next)
 515     ;
 516
 517   /* Assert it's the only one.  */
 518   if (prevailing)
 519     for (e = prevailing->next; e; e = e->next)
 520       gcc_assert (e->resolution != LDPR_PREVAILING_DEF_IRONLY
 521                   && e->resolution != LDPR_PREVAILING_DEF);
 522
 523   /* If there's not a prevailing symbol yet it's an external reference.
 524      Happens a lot during ltrans.  Choose the first symbol with a
 525      cgraph or a varpool node.  */
 526   if (!prevailing)
 527     {
 528       prevailing = (lto_symtab_entry_t) *slot;
 529       /* For functions choose one with a cgraph node.  */
 530       if (TREE_CODE (prevailing->decl) == FUNCTION_DECL)
 531         while (!prevailing->node
 532                && prevailing->next)
 533           prevailing = prevailing->next;
 534       /* We do not stream varpool nodes, so the first decl has to
 535          be good enough for now.
 536          ???  For QOI choose a variable with readonly initializer
 537          if there is one.  This matches C++
 538          struct Foo { static const int i = 1; }; without a real
 539          definition.  */
 540       if (TREE_CODE (prevailing->decl) == VAR_DECL)
 541         while (!(TREE_READONLY (prevailing->decl)
 542                  && DECL_INITIAL (prevailing->decl))
 543                && prevailing->next)
 544           prevailing = prevailing->next;
 545     }
 546
 547   /* Move it first in the list.  */
 548   if ((lto_symtab_entry_t) *slot != prevailing)
 549     {
 550       for (e = (lto_symtab_entry_t) *slot; e->next != prevailing; e = e->next)
 551         ;
 552       e->next = prevailing->next;
 553       prevailing->next = (lto_symtab_entry_t) *slot;
 554       *slot = (void *) prevailing;
 555     }
 556
 557   /* Record the prevailing variable.  */
 558   if (TREE_CODE (prevailing->decl) == VAR_DECL)
 559     VEC_safe_push (tree, gc, lto_global_var_decls, prevailing->decl);
 560
 561   /* Diagnose mismatched objects.  */
 562   for (e = prevailing->next; e; e = e->next)
 563     {
 564       if (TREE_CODE (prevailing->decl) == TREE_CODE (e->decl))
 565         continue;
 566
 567       switch (TREE_CODE (prevailing->decl))
 568         {
 569         case VAR_DECL:
 570           gcc_assert (TREE_CODE (e->decl) == FUNCTION_DECL);
 571           error_at (DECL_SOURCE_LOCATION (e->decl),
 572                     "variable %qD redeclared as function", prevailing->decl);
 573           break;
 574
 575         case FUNCTION_DECL:
 576           gcc_assert (TREE_CODE (e->decl) == VAR_DECL);
 577           error_at (DECL_SOURCE_LOCATION (e->decl),
 578                     "function %qD redeclared as variable", prevailing->decl);
 579           break;
 580
 581         default:
 582           gcc_unreachable ();
 583         }
 584
 585       diagnosed_p = true;
 586     }
 587   if (diagnosed_p)
 588       inform (DECL_SOURCE_LOCATION (prevailing->decl),
 589               "previously declared here");
 590
 591   /* Register and adjust types of the entries.  */
 592   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 593     TREE_TYPE (e->decl) = gimple_register_type (TREE_TYPE (e->decl));
 594
 595   /* Merge the chain to the single prevailing decl and diagnose
 596      mismatches.  */
 597   lto_symtab_merge_decls_2 (slot);
 598
 599   /* Drop all but the prevailing decl from the symtab.  */
 600   if (TREE_CODE (prevailing->decl) != FUNCTION_DECL)
 601     prevailing->next = NULL;
 602
 603   return 1;
 604 }
 605
 606 /* Resolve and merge all symbol table chains to a prevailing decl.  */
 607
 608 void
 609 lto_symtab_merge_decls (void)
 610 {
 611   lto_symtab_maybe_init_hash_table ();
 612   htab_traverse (lto_symtab_identifiers, lto_symtab_merge_decls_1, NULL);
 613 }
 614
 615 /* Helper to process the decl chain for the symbol table entry *SLOT.  */
 616
 617 static int
 618 lto_symtab_merge_cgraph_nodes_1 (void **slot, void *data ATTRIBUTE_UNUSED)
 619 {
 620   lto_symtab_entry_t e, prevailing = (lto_symtab_entry_t) *slot;
 621
 622   if (!prevailing->next)
 623     return 1;
 624
 625   gcc_assert (TREE_CODE (prevailing->decl) == FUNCTION_DECL);
 626
 627   /* Replace the cgraph node of each entry with the prevailing one.  */
 628   for (e = prevailing->next; e; e = e->next)
 629     {
 630       if (e->node != NULL)
 631         lto_cgraph_replace_node (e->node, prevailing->node);
 632     }
 633
 634   /* Drop all but the prevailing decl from the symtab.  */
 635   prevailing->next = NULL;
 636
 637   return 1;
 638 }
 639
 640 /* Merge cgraph nodes according to the symbol merging done by
 641    lto_symtab_merge_decls.  */
 642
 643 void
 644 lto_symtab_merge_cgraph_nodes (void)
 645 {
 646   lto_symtab_maybe_init_hash_table ();
 647   htab_traverse (lto_symtab_identifiers, lto_symtab_merge_cgraph_nodes_1, NULL);
 648 }
 649
 650 /* Given the decl DECL, return the prevailing decl with the same name. */
 651
 652 tree
 653 lto_symtab_prevailing_decl (tree decl)
 654 {
 655   lto_symtab_entry_t ret;
 656
 657   /* Builtins and local symbols are their own prevailing decl.  */
 658   if (!TREE_PUBLIC (decl) || is_builtin_fn (decl))
 659     return decl;
 660
 661   /* DECL_ABSTRACTs are their own prevailng decl.  */
 662   if (TREE_CODE (decl) == FUNCTION_DECL && DECL_ABSTRACT (decl))
 663     return decl;
 664
 665   /* Ensure DECL_ASSEMBLER_NAME will not set assembler name.  */
 666   gcc_assert (DECL_ASSEMBLER_NAME_SET_P (decl));
 667
 668   /* Walk through the list of candidates and return the one we merged to.  */
 669   ret = lto_symtab_get (DECL_ASSEMBLER_NAME (decl));
 670   if (!ret)
 671     return NULL_TREE;
 672
 673   return ret->decl;
 674 }
 675
 676 #include "gt-lto-symtab.h"