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   if (node->same_body)
 225     {
 226       struct cgraph_node *alias;
 227
 228       for (alias = node->same_body; alias; alias = alias->next)
 229         if (DECL_ASSEMBLER_NAME_SET_P (alias->decl))
 230           {
 231             lto_symtab_entry_t se
 232               = lto_symtab_get (DECL_ASSEMBLER_NAME (alias->decl));
 233
 234             for (; se; se = se->next)
 235               if (se->node == node)
 236                 {
 237                   se->node = NULL;
 238                   break;
 239                 }
 240           }
 241     }
 242
 243   /* Finally remove the replaced node.  */
 244   cgraph_remove_node (node);
 245 }
 246
 247 /* Merge two variable or function symbol table entries PREVAILING and ENTRY.
 248    Return false if the symbols are not fully compatible and a diagnostic
 249    should be emitted.  */
 250
 251 static bool
 252 lto_symtab_merge (lto_symtab_entry_t prevailing, lto_symtab_entry_t entry)
 253 {
 254   tree prevailing_decl = prevailing->decl;
 255   tree decl = entry->decl;
 256   tree prevailing_type, type;
 257
 258   /* Merge decl state in both directions, we may still end up using
 259      the new decl.  */
 260   TREE_ADDRESSABLE (prevailing_decl) |= TREE_ADDRESSABLE (decl);
 261   TREE_ADDRESSABLE (decl) |= TREE_ADDRESSABLE (prevailing_decl);
 262
 263   /* The linker may ask us to combine two incompatible symbols.
 264      Detect this case and notify the caller of required diagnostics.  */
 265
 266   if (TREE_CODE (decl) == FUNCTION_DECL)
 267     {
 268       if (TREE_TYPE (prevailing_decl) != TREE_TYPE (decl))
 269         /* If we don't have a merged type yet...sigh.  The linker
 270            wouldn't complain if the types were mismatched, so we
 271            probably shouldn't either.  Just use the type from
 272            whichever decl appears to be associated with the
 273            definition.  If for some odd reason neither decl is, the
 274            older one wins.  */
 275         (void) 0;
 276
 277       return true;
 278     }
 279
 280   /* Now we exclusively deal with VAR_DECLs.  */
 281
 282   /* Sharing a global symbol is a strong hint that two types are
 283      compatible.  We could use this information to complete
 284      incomplete pointed-to types more aggressively here, ignoring
 285      mismatches in both field and tag names.  It's difficult though
 286      to guarantee that this does not have side-effects on merging
 287      more compatible types from other translation units though.  */
 288
 289   /* We can tolerate differences in type qualification, the
 290      qualification of the prevailing definition will prevail.
 291      ???  In principle we might want to only warn for structurally
 292      incompatible types here, but unless we have protective measures
 293      for TBAA in place that would hide useful information.  */
 294   prevailing_type = TYPE_MAIN_VARIANT (TREE_TYPE (prevailing_decl));
 295   type = TYPE_MAIN_VARIANT (TREE_TYPE (decl));
 296
 297   /* We have to register and fetch canonical types here as the global
 298      fixup process didn't yet run.  */
 299   prevailing_type = gimple_register_type (prevailing_type);
 300   type = gimple_register_type (type);
 301   if (prevailing_type != type)
 302     {
 303       if (COMPLETE_TYPE_P (type))
 304         return false;
 305
 306       /* If type is incomplete then avoid warnings in the cases
 307          that TBAA handles just fine.  */
 308
 309       if (TREE_CODE (prevailing_type) != TREE_CODE (type))
 310         return false;
 311
 312       if (TREE_CODE (prevailing_type) == ARRAY_TYPE)
 313         {
 314           tree tem1 = TREE_TYPE (prevailing_type);
 315           tree tem2 = TREE_TYPE (type);
 316           while (TREE_CODE (tem1) == ARRAY_TYPE
 317                  && TREE_CODE (tem2) == ARRAY_TYPE)
 318             {
 319               tem1 = TREE_TYPE (tem1);
 320               tem2 = TREE_TYPE (tem2);
 321             }
 322
 323           if (TREE_CODE (tem1) != TREE_CODE (tem2))
 324             return false;
 325
 326           if (gimple_register_type (tem1) != gimple_register_type (tem2))
 327             return false;
 328         }
 329
 330       /* Fallthru.  Compatible enough.  */
 331     }
 332
 333   /* ???  We might want to emit a warning here if type qualification
 334      differences were spotted.  Do not do this unconditionally though.  */
 335
 336   /* There is no point in comparing too many details of the decls here.
 337      The type compatibility checks or the completing of types has properly
 338      dealt with most issues.  */
 339
 340   /* The following should all not invoke fatal errors as in non-LTO
 341      mode the linker wouldn't complain either.  Just emit warnings.  */
 342
 343   /* Report a warning if user-specified alignments do not match.  */
 344   if ((DECL_USER_ALIGN (prevailing_decl) && DECL_USER_ALIGN (decl))
 345       && DECL_ALIGN (prevailing_decl) < DECL_ALIGN (decl))
 346     return false;
 347
 348   return true;
 349 }
 350
 351 /* Return true if the symtab entry E can be replaced by another symtab
 352    entry.  */
 353
 354 static bool
 355 lto_symtab_resolve_replaceable_p (lto_symtab_entry_t e)
 356 {
 357   if (DECL_EXTERNAL (e->decl)
 358       || DECL_COMDAT (e->decl)
 359       || DECL_WEAK (e->decl))
 360     return true;
 361
 362   if (TREE_CODE (e->decl) == VAR_DECL)
 363     return (DECL_COMMON (e->decl)
 364             || (!flag_no_common && !DECL_INITIAL (e->decl)));
 365
 366   return false;
 367 }
 368
 369 /* Return true if the symtab entry E can be the prevailing one.  */
 370
 371 static bool
 372 lto_symtab_resolve_can_prevail_p (lto_symtab_entry_t e)
 373 {
 374   if (!TREE_STATIC (e->decl))
 375     return false;
 376
 377   /* For functions we need a non-discarded body.  */
 378   if (TREE_CODE (e->decl) == FUNCTION_DECL)
 379     return (e->node && e->node->analyzed);
 380
 381   /* A variable should have a size.  */
 382   else if (TREE_CODE (e->decl) == VAR_DECL)
 383     return (DECL_SIZE (e->decl) != NULL_TREE
 384             /* The C++ frontend retains TREE_STATIC on the declaration
 385                of foo_ in struct Foo { static Foo *foo_; }; but it is
 386                not a definition.  g++.dg/lto/20090315_0.C.  */
 387             && !DECL_EXTERNAL (e->decl));
 388
 389   gcc_unreachable ();
 390 }
 391
 392 /* Resolve the symbol with the candidates in the chain *SLOT and store
 393    their resolutions.  */
 394
 395 static void
 396 lto_symtab_resolve_symbols (void **slot)
 397 {
 398   lto_symtab_entry_t e;
 399   lto_symtab_entry_t prevailing = NULL;
 400
 401   /* Always set e->node so that edges are updated to reflect decl merging. */
 402   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 403     {
 404       if (TREE_CODE (e->decl) == FUNCTION_DECL)
 405         e->node = cgraph_get_node (e->decl);
 406     }
 407
 408   e = (lto_symtab_entry_t) *slot;
 409
 410   /* If the chain is already resolved there is nothing else to do.  */
 411   if (e->resolution != LDPR_UNKNOWN)
 412     return;
 413
 414   /* Find the single non-replaceable prevailing symbol and
 415      diagnose ODR violations.  */
 416   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 417     {
 418       if (!lto_symtab_resolve_can_prevail_p (e))
 419         {
 420           e->resolution = LDPR_RESOLVED_IR;
 421           continue;
 422         }
 423
 424       /* Set a default resolution - the final prevailing one will get
 425          adjusted later.  */
 426       e->resolution = LDPR_PREEMPTED_IR;
 427       if (!lto_symtab_resolve_replaceable_p (e))
 428         {
 429           if (prevailing)
 430             {
 431               error_at (DECL_SOURCE_LOCATION (e->decl),
 432                         "%qD has already been defined", e->decl);
 433               inform (DECL_SOURCE_LOCATION (prevailing->decl),
 434                       "previously defined here");
 435             }
 436           prevailing = e;
 437         }
 438     }
 439   if (prevailing)
 440     goto found;
 441
 442   /* Do a second round choosing one from the replaceable prevailing decls.  */
 443   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 444     {
 445       if (e->resolution != LDPR_PREEMPTED_IR)
 446         continue;
 447
 448       /* Choose the first function that can prevail as prevailing.  */
 449       if (TREE_CODE (e->decl) == FUNCTION_DECL)
 450         {
 451           prevailing = e;
 452           break;
 453         }
 454
 455       /* From variables that can prevail choose the largest one.  */
 456       if (!prevailing
 457           || tree_int_cst_lt (DECL_SIZE (prevailing->decl),
 458                               DECL_SIZE (e->decl)))
 459         prevailing = e;
 460     }
 461
 462   if (!prevailing)
 463     return;
 464
 465 found:
 466   if (TREE_CODE (prevailing->decl) == VAR_DECL
 467       && TREE_READONLY (prevailing->decl))
 468     prevailing->resolution = LDPR_PREVAILING_DEF_IRONLY;
 469   else
 470     prevailing->resolution = LDPR_PREVAILING_DEF;
 471 }
 472
 473 /* Merge all decls in the symbol table chain to the prevailing decl and
 474    issue diagnostics about type mismatches.  */
 475
 476 static void
 477 lto_symtab_merge_decls_2 (void **slot)
 478 {
 479   lto_symtab_entry_t prevailing, e;
 480   VEC(tree, heap) *mismatches = NULL;
 481   unsigned i;
 482   tree decl;
 483   bool diagnosed_p = false;
 484
 485   /* Nothing to do for a single entry.  */
 486   prevailing = (lto_symtab_entry_t) *slot;
 487   if (!prevailing->next)
 488     return;
 489
 490   /* Try to merge each entry with the prevailing one.  */
 491   for (e = prevailing->next; e; e = e->next)
 492     {
 493       if (!lto_symtab_merge (prevailing, e))
 494         VEC_safe_push (tree, heap, mismatches, e->decl);
 495     }
 496   if (VEC_empty (tree, mismatches))
 497     return;
 498
 499   /* Diagnose all mismatched re-declarations.  */
 500   for (i = 0; VEC_iterate (tree, mismatches, i, decl); ++i)
 501     {
 502       if (TREE_TYPE (prevailing->decl) != TREE_TYPE (decl))
 503         diagnosed_p |= warning_at (DECL_SOURCE_LOCATION (decl), 0,
 504                                    "type of %qD does not match original "
 505                                    "declaration", decl);
 506
 507       else if ((DECL_USER_ALIGN (prevailing->decl) && DECL_USER_ALIGN (decl))
 508                && DECL_ALIGN (prevailing->decl) < DECL_ALIGN (decl))
 509         {
 510           diagnosed_p |= warning_at (DECL_SOURCE_LOCATION (decl), 0,
 511                                      "alignment of %qD is bigger than "
 512                                      "original declaration", decl);
 513         }
 514     }
 515   if (diagnosed_p)
 516     inform (DECL_SOURCE_LOCATION (prevailing->decl),
 517             "previously declared here");
 518
 519   VEC_free (tree, heap, mismatches);
 520 }
 521
 522 /* Helper to process the decl chain for the symbol table entry *SLOT.  */
 523
 524 static int
 525 lto_symtab_merge_decls_1 (void **slot, void *data ATTRIBUTE_UNUSED)
 526 {
 527   lto_symtab_entry_t e, prevailing;
 528   bool diagnosed_p = false;
 529
 530   /* Compute the symbol resolutions.  This is a no-op when using the
 531      linker plugin.  */
 532   lto_symtab_resolve_symbols (slot);
 533
 534   /* Find the prevailing decl.  */
 535   for (prevailing = (lto_symtab_entry_t) *slot;
 536        prevailing
 537        && prevailing->resolution != LDPR_PREVAILING_DEF_IRONLY
 538        && prevailing->resolution != LDPR_PREVAILING_DEF;
 539        prevailing = prevailing->next)
 540     ;
 541
 542   /* Assert it's the only one.  */
 543   if (prevailing)
 544     for (e = prevailing->next; e; e = e->next)
 545       gcc_assert (e->resolution != LDPR_PREVAILING_DEF_IRONLY
 546                   && e->resolution != LDPR_PREVAILING_DEF);
 547
 548   /* If there's not a prevailing symbol yet it's an external reference.
 549      Happens a lot during ltrans.  Choose the first symbol with a
 550      cgraph or a varpool node.  */
 551   if (!prevailing)
 552     {
 553       prevailing = (lto_symtab_entry_t) *slot;
 554       /* For functions choose one with a cgraph node.  */
 555       if (TREE_CODE (prevailing->decl) == FUNCTION_DECL)
 556         while (!prevailing->node
 557                && prevailing->next)
 558           prevailing = prevailing->next;
 559       /* We do not stream varpool nodes, so the first decl has to
 560          be good enough for now.
 561          ???  For QOI choose a variable with readonly initializer
 562          if there is one.  This matches C++
 563          struct Foo { static const int i = 1; }; without a real
 564          definition.  */
 565       if (TREE_CODE (prevailing->decl) == VAR_DECL)
 566         while (!(TREE_READONLY (prevailing->decl)
 567                  && DECL_INITIAL (prevailing->decl))
 568                && prevailing->next)
 569           prevailing = prevailing->next;
 570     }
 571
 572   /* Move it first in the list.  */
 573   if ((lto_symtab_entry_t) *slot != prevailing)
 574     {
 575       for (e = (lto_symtab_entry_t) *slot; e->next != prevailing; e = e->next)
 576         ;
 577       e->next = prevailing->next;
 578       prevailing->next = (lto_symtab_entry_t) *slot;
 579       *slot = (void *) prevailing;
 580     }
 581
 582   /* Record the prevailing variable.  */
 583   if (TREE_CODE (prevailing->decl) == VAR_DECL)
 584     VEC_safe_push (tree, gc, lto_global_var_decls, prevailing->decl);
 585
 586   /* Diagnose mismatched objects.  */
 587   for (e = prevailing->next; e; e = e->next)
 588     {
 589       if (TREE_CODE (prevailing->decl) == TREE_CODE (e->decl))
 590         continue;
 591
 592       switch (TREE_CODE (prevailing->decl))
 593         {
 594         case VAR_DECL:
 595           gcc_assert (TREE_CODE (e->decl) == FUNCTION_DECL);
 596           error_at (DECL_SOURCE_LOCATION (e->decl),
 597                     "variable %qD redeclared as function", prevailing->decl);
 598           break;
 599
 600         case FUNCTION_DECL:
 601           gcc_assert (TREE_CODE (e->decl) == VAR_DECL);
 602           error_at (DECL_SOURCE_LOCATION (e->decl),
 603                     "function %qD redeclared as variable", prevailing->decl);
 604           break;
 605
 606         default:
 607           gcc_unreachable ();
 608         }
 609
 610       diagnosed_p = true;
 611     }
 612   if (diagnosed_p)
 613       inform (DECL_SOURCE_LOCATION (prevailing->decl),
 614               "previously declared here");
 615
 616   /* Register and adjust types of the entries.  */
 617   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 618     TREE_TYPE (e->decl) = gimple_register_type (TREE_TYPE (e->decl));
 619
 620   /* Merge the chain to the single prevailing decl and diagnose
 621      mismatches.  */
 622   lto_symtab_merge_decls_2 (slot);
 623
 624   /* Drop all but the prevailing decl from the symtab.  */
 625   if (TREE_CODE (prevailing->decl) != FUNCTION_DECL)
 626     prevailing->next = NULL;
 627
 628   return 1;
 629 }
 630
 631 /* Resolve and merge all symbol table chains to a prevailing decl.  */
 632
 633 void
 634 lto_symtab_merge_decls (void)
 635 {
 636   lto_symtab_maybe_init_hash_table ();
 637   htab_traverse (lto_symtab_identifiers, lto_symtab_merge_decls_1, NULL);
 638 }
 639
 640 /* Helper to process the decl chain for the symbol table entry *SLOT.  */
 641
 642 static int
 643 lto_symtab_merge_cgraph_nodes_1 (void **slot, void *data ATTRIBUTE_UNUSED)
 644 {
 645   lto_symtab_entry_t e, prevailing = (lto_symtab_entry_t) *slot;
 646
 647   if (!prevailing->next)
 648     return 1;
 649
 650   gcc_assert (TREE_CODE (prevailing->decl) == FUNCTION_DECL);
 651
 652   /* Replace the cgraph node of each entry with the prevailing one.  */
 653   for (e = prevailing->next; e; e = e->next)
 654     {
 655       if (e->node != NULL)
 656         {
 657           if (e->node->decl != e->decl && e->node->same_body)
 658             {
 659               struct cgraph_node *alias;
 660
 661               for (alias = e->node->same_body; alias; alias = alias->next)
 662                 if (alias->decl == e->decl)
 663                   break;
 664               if (alias)
 665                 {
 666                   cgraph_remove_same_body_alias (alias);
 667                   continue;
 668                 }
 669             }
 670           lto_cgraph_replace_node (e->node, prevailing->node);
 671         }
 672     }
 673
 674   /* Drop all but the prevailing decl from the symtab.  */
 675   prevailing->next = NULL;
 676
 677   return 1;
 678 }
 679
 680 /* Merge cgraph nodes according to the symbol merging done by
 681    lto_symtab_merge_decls.  */
 682
 683 void
 684 lto_symtab_merge_cgraph_nodes (void)
 685 {
 686   lto_symtab_maybe_init_hash_table ();
 687   htab_traverse (lto_symtab_identifiers, lto_symtab_merge_cgraph_nodes_1, NULL);
 688 }
 689
 690 /* Given the decl DECL, return the prevailing decl with the same name. */
 691
 692 tree
 693 lto_symtab_prevailing_decl (tree decl)
 694 {
 695   lto_symtab_entry_t ret;
 696
 697   /* Builtins and local symbols are their own prevailing decl.  */
 698   if (!TREE_PUBLIC (decl) || is_builtin_fn (decl))
 699     return decl;
 700
 701   /* DECL_ABSTRACTs are their own prevailng decl.  */
 702   if (TREE_CODE (decl) == FUNCTION_DECL && DECL_ABSTRACT (decl))
 703     return decl;
 704
 705   /* Ensure DECL_ASSEMBLER_NAME will not set assembler name.  */
 706   gcc_assert (DECL_ASSEMBLER_NAME_SET_P (decl));
 707
 708   /* Walk through the list of candidates and return the one we merged to.  */
 709   ret = lto_symtab_get (DECL_ASSEMBLER_NAME (decl));
 710   if (!ret)
 711     return NULL_TREE;
 712
 713   return ret->decl;
 714 }
 715
 716 #include "gt-lto-symtab.h"