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   /* The varpool node if decl is a variable decl.  Filled in during the
  48      merging process.  */
  49   struct varpool_node *vnode;
  50   /* LTO file-data and symbol resolution for this decl.  */
  51   struct lto_file_decl_data * GTY((skip (""))) file_data;
  52   enum ld_plugin_symbol_resolution resolution;
  53   /* Pointer to the next entry with the same key.  Before decl merging
  54      this links all symbols from the different TUs.  After decl merging
  55      this links merged but incompatible decls, thus all prevailing ones
  56      remaining.  */
  57   struct lto_symtab_entry_def *next;
  58 };
  59 typedef struct lto_symtab_entry_def *lto_symtab_entry_t;
  60
  61 /* A poor man's symbol table. This hashes identifier to prevailing DECL
  62    if there is one. */
  63
  64 static GTY ((if_marked ("lto_symtab_entry_marked_p"),
  65              param_is (struct lto_symtab_entry_def)))
  66   htab_t lto_symtab_identifiers;
  67
  68 /* Free symtab hashtable.  */
  69
  70 void
  71 lto_symtab_free (void)
  72 {
  73   htab_delete (lto_symtab_identifiers);
  74   lto_symtab_identifiers = NULL;
  75 }
  76
  77 /* Return the hash value of an lto_symtab_entry_t object pointed to by P.  */
  78
  79 static hashval_t
  80 lto_symtab_entry_hash (const void *p)
  81 {
  82   const struct lto_symtab_entry_def *base =
  83     (const struct lto_symtab_entry_def *) p;
  84   return htab_hash_string (IDENTIFIER_POINTER (base->id));
  85 }
  86
  87 /* Return non-zero if P1 and P2 points to lto_symtab_entry_def structs
  88    corresponding to the same symbol.  */
  89
  90 static int
  91 lto_symtab_entry_eq (const void *p1, const void *p2)
  92 {
  93   const struct lto_symtab_entry_def *base1 =
  94      (const struct lto_symtab_entry_def *) p1;
  95   const struct lto_symtab_entry_def *base2 =
  96      (const struct lto_symtab_entry_def *) p2;
  97   return (base1->id == base2->id);
  98 }
  99
 100 /* Returns non-zero if P points to an lto_symtab_entry_def struct that needs
 101    to be marked for GC.  */
 102
 103 static int
 104 lto_symtab_entry_marked_p (const void *p)
 105 {
 106   const struct lto_symtab_entry_def *base =
 107      (const struct lto_symtab_entry_def *) p;
 108
 109   /* Keep this only if the common IDENTIFIER_NODE of the symtab chain
 110      is marked which it will be if at least one of the DECLs in the
 111      chain is marked.  */
 112   return ggc_marked_p (base->id);
 113 }
 114
 115 /* Lazily initialize resolution hash tables.  */
 116
 117 static void
 118 lto_symtab_maybe_init_hash_table (void)
 119 {
 120   if (lto_symtab_identifiers)
 121     return;
 122
 123   lto_symtab_identifiers =
 124     htab_create_ggc (1021, lto_symtab_entry_hash,
 125                      lto_symtab_entry_eq, NULL);
 126 }
 127
 128 /* Registers DECL with the LTO symbol table as having resolution RESOLUTION
 129    and read from FILE_DATA. */
 130
 131 void
 132 lto_symtab_register_decl (tree decl,
 133                           ld_plugin_symbol_resolution_t resolution,
 134                           struct lto_file_decl_data *file_data)
 135 {
 136   lto_symtab_entry_t new_entry;
 137   void **slot;
 138
 139   /* Check that declarations reaching this function do not have
 140      properties inconsistent with having external linkage.  If any of
 141      these asertions fail, then the object file reader has failed to
 142      detect these cases and issue appropriate error messages.  */
 143   gcc_assert (decl
 144               && TREE_PUBLIC (decl)
 145               && (TREE_CODE (decl) == VAR_DECL
 146                   || TREE_CODE (decl) == FUNCTION_DECL)
 147               && DECL_ASSEMBLER_NAME_SET_P (decl));
 148   if (TREE_CODE (decl) == VAR_DECL
 149       && DECL_INITIAL (decl))
 150     gcc_assert (!DECL_EXTERNAL (decl)
 151                 || (TREE_STATIC (decl) && TREE_READONLY (decl)));
 152   if (TREE_CODE (decl) == FUNCTION_DECL)
 153     gcc_assert (!DECL_ABSTRACT (decl));
 154
 155   new_entry = GGC_CNEW (struct lto_symtab_entry_def);
 156   new_entry->id = DECL_ASSEMBLER_NAME (decl);
 157   new_entry->decl = decl;
 158   new_entry->resolution = resolution;
 159   new_entry->file_data = file_data;
 160
 161   lto_symtab_maybe_init_hash_table ();
 162   slot = htab_find_slot (lto_symtab_identifiers, new_entry, INSERT);
 163   new_entry->next = (lto_symtab_entry_t) *slot;
 164   *slot = new_entry;
 165 }
 166
 167 /* Get the lto_symtab_entry_def struct associated with ID
 168    if there is one.  */
 169
 170 static lto_symtab_entry_t
 171 lto_symtab_get (tree id)
 172 {
 173   struct lto_symtab_entry_def temp;
 174   void **slot;
 175
 176   lto_symtab_maybe_init_hash_table ();
 177   temp.id = id;
 178   slot = htab_find_slot (lto_symtab_identifiers, &temp, NO_INSERT);
 179   return slot ? (lto_symtab_entry_t) *slot : NULL;
 180 }
 181
 182 /* Get the linker resolution for DECL.  */
 183
 184 enum ld_plugin_symbol_resolution
 185 lto_symtab_get_resolution (tree decl)
 186 {
 187   lto_symtab_entry_t e;
 188
 189   gcc_assert (DECL_ASSEMBLER_NAME_SET_P (decl));
 190
 191   e = lto_symtab_get (DECL_ASSEMBLER_NAME (decl));
 192   while (e && e->decl != decl)
 193     e = e->next;
 194   if (!e)
 195     return LDPR_UNKNOWN;
 196
 197   return e->resolution;
 198 }
 199
 200
 201 /* Replace the cgraph node NODE with PREVAILING_NODE in the cgraph, merging
 202    all edges and removing the old node.  */
 203
 204 static void
 205 lto_cgraph_replace_node (struct cgraph_node *node,
 206                          struct cgraph_node *prevailing_node)
 207 {
 208   struct cgraph_edge *e, *next;
 209
 210   /* Merge node flags.  */
 211   if (node->needed)
 212     cgraph_mark_needed_node (prevailing_node);
 213   if (node->reachable)
 214     cgraph_mark_reachable_node (prevailing_node);
 215   if (node->address_taken)
 216     {
 217       gcc_assert (!prevailing_node->global.inlined_to);
 218       cgraph_mark_address_taken_node (prevailing_node);
 219     }
 220
 221   /* Redirect all incoming edges.  */
 222   for (e = node->callers; e; e = next)
 223     {
 224       next = e->next_caller;
 225       cgraph_redirect_edge_callee (e, prevailing_node);
 226     }
 227   /* Redirect incomming references.  */
 228   ipa_clone_refering (prevailing_node, NULL, &node->ref_list);
 229
 230   if (node->same_body)
 231     {
 232       struct cgraph_node *alias;
 233
 234       for (alias = node->same_body; alias; alias = alias->next)
 235         if (DECL_ASSEMBLER_NAME_SET_P (alias->decl))
 236           {
 237             lto_symtab_entry_t se
 238               = lto_symtab_get (DECL_ASSEMBLER_NAME (alias->decl));
 239
 240             for (; se; se = se->next)
 241               if (se->node == node)
 242                 {
 243                   se->node = NULL;
 244                   break;
 245                 }
 246           }
 247     }
 248
 249   /* Finally remove the replaced node.  */
 250   cgraph_remove_node (node);
 251 }
 252
 253 /* Replace the cgraph node NODE with PREVAILING_NODE in the cgraph, merging
 254    all edges and removing the old node.  */
 255
 256 static void
 257 lto_varpool_replace_node (struct varpool_node *vnode,
 258                           struct varpool_node *prevailing_node)
 259 {
 260   /* Merge node flags.  */
 261   if (vnode->needed)
 262     {
 263       gcc_assert (!vnode->analyzed || prevailing_node->analyzed);
 264       varpool_mark_needed_node (prevailing_node);
 265     }
 266   /* Relink aliases.  */
 267   if (vnode->extra_name && !vnode->alias)
 268     {
 269       struct varpool_node *alias, *last;
 270       for (alias = vnode->extra_name;
 271            alias; alias = alias->next)
 272         {
 273           last = alias;
 274           alias->extra_name = prevailing_node;
 275         }
 276
 277       if (prevailing_node->extra_name)
 278         {
 279           last->next = prevailing_node->extra_name;
 280           prevailing_node->extra_name->prev = last;
 281         }
 282       prevailing_node->extra_name = vnode->extra_name;
 283       vnode->extra_name = NULL;
 284     }
 285   gcc_assert (!vnode->finalized || prevailing_node->finalized);
 286   gcc_assert (!vnode->analyzed || prevailing_node->analyzed);
 287
 288   /* When replacing by an alias, the references goes to the original
 289      variable.  */
 290   if (prevailing_node->alias && prevailing_node->extra_name)
 291     prevailing_node = prevailing_node->extra_name;
 292   ipa_clone_refering (NULL, prevailing_node, &vnode->ref_list);
 293
 294   /* Be sure we can garbage collect the initializer.  */
 295   if (DECL_INITIAL (vnode->decl))
 296     DECL_INITIAL (vnode->decl) = error_mark_node;
 297   /* Finally remove the replaced node.  */
 298   varpool_remove_node (vnode);
 299 }
 300
 301 /* Merge two variable or function symbol table entries PREVAILING and ENTRY.
 302    Return false if the symbols are not fully compatible and a diagnostic
 303    should be emitted.  */
 304
 305 static bool
 306 lto_symtab_merge (lto_symtab_entry_t prevailing, lto_symtab_entry_t entry)
 307 {
 308   tree prevailing_decl = prevailing->decl;
 309   tree decl = entry->decl;
 310   tree prevailing_type, type;
 311
 312   /* Merge decl state in both directions, we may still end up using
 313      the new decl.  */
 314   TREE_ADDRESSABLE (prevailing_decl) |= TREE_ADDRESSABLE (decl);
 315   TREE_ADDRESSABLE (decl) |= TREE_ADDRESSABLE (prevailing_decl);
 316
 317   /* The linker may ask us to combine two incompatible symbols.
 318      Detect this case and notify the caller of required diagnostics.  */
 319
 320   if (TREE_CODE (decl) == FUNCTION_DECL)
 321     {
 322       if (TREE_TYPE (prevailing_decl) != TREE_TYPE (decl))
 323         /* If we don't have a merged type yet...sigh.  The linker
 324            wouldn't complain if the types were mismatched, so we
 325            probably shouldn't either.  Just use the type from
 326            whichever decl appears to be associated with the
 327            definition.  If for some odd reason neither decl is, the
 328            older one wins.  */
 329         (void) 0;
 330
 331       return true;
 332     }
 333
 334   /* Now we exclusively deal with VAR_DECLs.  */
 335
 336   /* Sharing a global symbol is a strong hint that two types are
 337      compatible.  We could use this information to complete
 338      incomplete pointed-to types more aggressively here, ignoring
 339      mismatches in both field and tag names.  It's difficult though
 340      to guarantee that this does not have side-effects on merging
 341      more compatible types from other translation units though.  */
 342
 343   /* We can tolerate differences in type qualification, the
 344      qualification of the prevailing definition will prevail.
 345      ???  In principle we might want to only warn for structurally
 346      incompatible types here, but unless we have protective measures
 347      for TBAA in place that would hide useful information.  */
 348   prevailing_type = TYPE_MAIN_VARIANT (TREE_TYPE (prevailing_decl));
 349   type = TYPE_MAIN_VARIANT (TREE_TYPE (decl));
 350
 351   /* We have to register and fetch canonical types here as the global
 352      fixup process didn't yet run.  */
 353   prevailing_type = gimple_register_type (prevailing_type);
 354   type = gimple_register_type (type);
 355   if (prevailing_type != type)
 356     {
 357       if (COMPLETE_TYPE_P (type))
 358         return false;
 359
 360       /* If type is incomplete then avoid warnings in the cases
 361          that TBAA handles just fine.  */
 362
 363       if (TREE_CODE (prevailing_type) != TREE_CODE (type))
 364         return false;
 365
 366       if (TREE_CODE (prevailing_type) == ARRAY_TYPE)
 367         {
 368           tree tem1 = TREE_TYPE (prevailing_type);
 369           tree tem2 = TREE_TYPE (type);
 370           while (TREE_CODE (tem1) == ARRAY_TYPE
 371                  && TREE_CODE (tem2) == ARRAY_TYPE)
 372             {
 373               tem1 = TREE_TYPE (tem1);
 374               tem2 = TREE_TYPE (tem2);
 375             }
 376
 377           if (TREE_CODE (tem1) != TREE_CODE (tem2))
 378             return false;
 379
 380           if (gimple_register_type (tem1) != gimple_register_type (tem2))
 381             return false;
 382         }
 383
 384       /* Fallthru.  Compatible enough.  */
 385     }
 386
 387   /* ???  We might want to emit a warning here if type qualification
 388      differences were spotted.  Do not do this unconditionally though.  */
 389
 390   /* There is no point in comparing too many details of the decls here.
 391      The type compatibility checks or the completing of types has properly
 392      dealt with most issues.  */
 393
 394   /* The following should all not invoke fatal errors as in non-LTO
 395      mode the linker wouldn't complain either.  Just emit warnings.  */
 396
 397   /* Report a warning if user-specified alignments do not match.  */
 398   if ((DECL_USER_ALIGN (prevailing_decl) && DECL_USER_ALIGN (decl))
 399       && DECL_ALIGN (prevailing_decl) < DECL_ALIGN (decl))
 400     return false;
 401
 402   return true;
 403 }
 404
 405 /* Return true if the symtab entry E can be replaced by another symtab
 406    entry.  */
 407
 408 static bool
 409 lto_symtab_resolve_replaceable_p (lto_symtab_entry_t e)
 410 {
 411   if (DECL_EXTERNAL (e->decl)
 412       || DECL_COMDAT (e->decl)
 413       || DECL_WEAK (e->decl))
 414     return true;
 415
 416   if (TREE_CODE (e->decl) == VAR_DECL)
 417     return (DECL_COMMON (e->decl)
 418             || (!flag_no_common && !DECL_INITIAL (e->decl)));
 419
 420   return false;
 421 }
 422
 423 /* Return true if the symtab entry E can be the prevailing one.  */
 424
 425 static bool
 426 lto_symtab_resolve_can_prevail_p (lto_symtab_entry_t e)
 427 {
 428   /* The C++ frontend ends up neither setting TREE_STATIC nor
 429      DECL_EXTERNAL on virtual methods but only TREE_PUBLIC.
 430      So do not reject !TREE_STATIC here but only DECL_EXTERNAL.  */
 431   if (DECL_EXTERNAL (e->decl))
 432     return false;
 433
 434   /* For functions we need a non-discarded body.  */
 435   if (TREE_CODE (e->decl) == FUNCTION_DECL)
 436     return (e->node && e->node->analyzed);
 437
 438   /* A variable should have a size.  */
 439   else if (TREE_CODE (e->decl) == VAR_DECL)
 440     {
 441       if (!e->vnode)
 442         return false;
 443       if (e->vnode->finalized)
 444         return true;
 445       return e->vnode->alias && e->vnode->extra_name->finalized;
 446     }
 447
 448   gcc_unreachable ();
 449 }
 450
 451 /* Resolve the symbol with the candidates in the chain *SLOT and store
 452    their resolutions.  */
 453
 454 static void
 455 lto_symtab_resolve_symbols (void **slot)
 456 {
 457   lto_symtab_entry_t e;
 458   lto_symtab_entry_t prevailing = NULL;
 459
 460   /* Always set e->node so that edges are updated to reflect decl merging. */
 461   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 462     {
 463       if (TREE_CODE (e->decl) == FUNCTION_DECL)
 464         e->node = cgraph_get_node (e->decl);
 465       else if (TREE_CODE (e->decl) == VAR_DECL)
 466         e->vnode = varpool_get_node (e->decl);
 467     }
 468
 469   e = (lto_symtab_entry_t) *slot;
 470
 471   /* If the chain is already resolved there is nothing else to do.  */
 472   if (e->resolution != LDPR_UNKNOWN)
 473     return;
 474
 475   /* Find the single non-replaceable prevailing symbol and
 476      diagnose ODR violations.  */
 477   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 478     {
 479       if (!lto_symtab_resolve_can_prevail_p (e))
 480         {
 481           e->resolution = LDPR_RESOLVED_IR;
 482           continue;
 483         }
 484
 485       /* Set a default resolution - the final prevailing one will get
 486          adjusted later.  */
 487       e->resolution = LDPR_PREEMPTED_IR;
 488       if (!lto_symtab_resolve_replaceable_p (e))
 489         {
 490           if (prevailing)
 491             {
 492               error_at (DECL_SOURCE_LOCATION (e->decl),
 493                         "%qD has already been defined", e->decl);
 494               inform (DECL_SOURCE_LOCATION (prevailing->decl),
 495                       "previously defined here");
 496             }
 497           prevailing = e;
 498         }
 499     }
 500   if (prevailing)
 501     goto found;
 502
 503   /* Do a second round choosing one from the replaceable prevailing decls.  */
 504   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 505     {
 506       if (e->resolution != LDPR_PREEMPTED_IR)
 507         continue;
 508
 509       /* Choose the first function that can prevail as prevailing.  */
 510       if (TREE_CODE (e->decl) == FUNCTION_DECL)
 511         {
 512           prevailing = e;
 513           break;
 514         }
 515
 516       /* From variables that can prevail choose the largest one.  */
 517       if (!prevailing
 518           || tree_int_cst_lt (DECL_SIZE (prevailing->decl),
 519                               DECL_SIZE (e->decl)))
 520         prevailing = e;
 521     }
 522
 523   if (!prevailing)
 524     return;
 525
 526 found:
 527   if (TREE_CODE (prevailing->decl) == VAR_DECL
 528       && TREE_READONLY (prevailing->decl))
 529     prevailing->resolution = LDPR_PREVAILING_DEF_IRONLY;
 530   else
 531     prevailing->resolution = LDPR_PREVAILING_DEF;
 532 }
 533
 534 /* Merge all decls in the symbol table chain to the prevailing decl and
 535    issue diagnostics about type mismatches.  */
 536
 537 static void
 538 lto_symtab_merge_decls_2 (void **slot)
 539 {
 540   lto_symtab_entry_t prevailing, e;
 541   VEC(tree, heap) *mismatches = NULL;
 542   unsigned i;
 543   tree decl;
 544   bool diagnosed_p = false;
 545
 546   /* Nothing to do for a single entry.  */
 547   prevailing = (lto_symtab_entry_t) *slot;
 548   if (!prevailing->next)
 549     return;
 550
 551   /* Try to merge each entry with the prevailing one.  */
 552   for (e = prevailing->next; e; e = e->next)
 553     {
 554       if (!lto_symtab_merge (prevailing, e))
 555         VEC_safe_push (tree, heap, mismatches, e->decl);
 556     }
 557   if (VEC_empty (tree, mismatches))
 558     return;
 559
 560   /* Diagnose all mismatched re-declarations.  */
 561   for (i = 0; VEC_iterate (tree, mismatches, i, decl); ++i)
 562     {
 563       if (TREE_TYPE (prevailing->decl) != TREE_TYPE (decl))
 564         diagnosed_p |= warning_at (DECL_SOURCE_LOCATION (decl), 0,
 565                                    "type of %qD does not match original "
 566                                    "declaration", decl);
 567
 568       else if ((DECL_USER_ALIGN (prevailing->decl) && DECL_USER_ALIGN (decl))
 569                && DECL_ALIGN (prevailing->decl) < DECL_ALIGN (decl))
 570         {
 571           diagnosed_p |= warning_at (DECL_SOURCE_LOCATION (decl), 0,
 572                                      "alignment of %qD is bigger than "
 573                                      "original declaration", decl);
 574         }
 575     }
 576   if (diagnosed_p)
 577     inform (DECL_SOURCE_LOCATION (prevailing->decl),
 578             "previously declared here");
 579
 580   VEC_free (tree, heap, mismatches);
 581 }
 582
 583 /* Helper to process the decl chain for the symbol table entry *SLOT.  */
 584
 585 static int
 586 lto_symtab_merge_decls_1 (void **slot, void *data ATTRIBUTE_UNUSED)
 587 {
 588   lto_symtab_entry_t e, prevailing;
 589   bool diagnosed_p = false;
 590
 591   /* Compute the symbol resolutions.  This is a no-op when using the
 592      linker plugin.  */
 593   lto_symtab_resolve_symbols (slot);
 594
 595   /* Find the prevailing decl.  */
 596   for (prevailing = (lto_symtab_entry_t) *slot;
 597        prevailing
 598        && prevailing->resolution != LDPR_PREVAILING_DEF_IRONLY
 599        && prevailing->resolution != LDPR_PREVAILING_DEF;
 600        prevailing = prevailing->next)
 601     ;
 602
 603   /* Assert it's the only one.  */
 604   if (prevailing)
 605     for (e = prevailing->next; e; e = e->next)
 606       gcc_assert (e->resolution != LDPR_PREVAILING_DEF_IRONLY
 607                   && e->resolution != LDPR_PREVAILING_DEF);
 608
 609   /* If there's not a prevailing symbol yet it's an external reference.
 610      Happens a lot during ltrans.  Choose the first symbol with a
 611      cgraph or a varpool node.  */
 612   if (!prevailing)
 613     {
 614       prevailing = (lto_symtab_entry_t) *slot;
 615       /* For functions choose one with a cgraph node.  */
 616       if (TREE_CODE (prevailing->decl) == FUNCTION_DECL)
 617         while (!prevailing->node
 618                && prevailing->next)
 619           prevailing = prevailing->next;
 620       /* For variables chose with a priority variant with vnode
 621          attached (i.e. from unit where external declaration of
 622          variable is actually used).
 623          When there are multiple variants, chose one with size.
 624          This is needed for C++ typeinfos, for example in
 625          lto/20081204-1 there are typeifos in both units, just
 626          one of them do have size.  */
 627       if (TREE_CODE (prevailing->decl) == VAR_DECL)
 628         {
 629           for (e = prevailing->next; e; e = e->next)
 630             if ((!prevailing->vnode && e->vnode)
 631                 || ((prevailing->vnode != NULL) == (e->vnode != NULL)
 632                     && !COMPLETE_TYPE_P (TREE_TYPE (prevailing->decl))
 633                     && COMPLETE_TYPE_P (TREE_TYPE (e->decl))))
 634               prevailing = e;
 635         }
 636     }
 637
 638   /* Move it first in the list.  */
 639   if ((lto_symtab_entry_t) *slot != prevailing)
 640     {
 641       for (e = (lto_symtab_entry_t) *slot; e->next != prevailing; e = e->next)
 642         ;
 643       e->next = prevailing->next;
 644       prevailing->next = (lto_symtab_entry_t) *slot;
 645       *slot = (void *) prevailing;
 646     }
 647
 648   /* Record the prevailing variable.  */
 649   if (TREE_CODE (prevailing->decl) == VAR_DECL)
 650     VEC_safe_push (tree, gc, lto_global_var_decls, prevailing->decl);
 651
 652   /* Diagnose mismatched objects.  */
 653   for (e = prevailing->next; e; e = e->next)
 654     {
 655       if (TREE_CODE (prevailing->decl) == TREE_CODE (e->decl))
 656         continue;
 657
 658       switch (TREE_CODE (prevailing->decl))
 659         {
 660         case VAR_DECL:
 661           gcc_assert (TREE_CODE (e->decl) == FUNCTION_DECL);
 662           error_at (DECL_SOURCE_LOCATION (e->decl),
 663                     "variable %qD redeclared as function", prevailing->decl);
 664           break;
 665
 666         case FUNCTION_DECL:
 667           gcc_assert (TREE_CODE (e->decl) == VAR_DECL);
 668           error_at (DECL_SOURCE_LOCATION (e->decl),
 669                     "function %qD redeclared as variable", prevailing->decl);
 670           break;
 671
 672         default:
 673           gcc_unreachable ();
 674         }
 675
 676       diagnosed_p = true;
 677     }
 678   if (diagnosed_p)
 679       inform (DECL_SOURCE_LOCATION (prevailing->decl),
 680               "previously declared here");
 681
 682   /* Register and adjust types of the entries.  */
 683   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 684     TREE_TYPE (e->decl) = gimple_register_type (TREE_TYPE (e->decl));
 685
 686   /* Merge the chain to the single prevailing decl and diagnose
 687      mismatches.  */
 688   lto_symtab_merge_decls_2 (slot);
 689
 690   /* Drop all but the prevailing decl from the symtab.  */
 691   if (TREE_CODE (prevailing->decl) != FUNCTION_DECL
 692       && TREE_CODE (prevailing->decl) != VAR_DECL)
 693     prevailing->next = NULL;
 694
 695   return 1;
 696 }
 697
 698 /* Resolve and merge all symbol table chains to a prevailing decl.  */
 699
 700 void
 701 lto_symtab_merge_decls (void)
 702 {
 703   lto_symtab_maybe_init_hash_table ();
 704   htab_traverse (lto_symtab_identifiers, lto_symtab_merge_decls_1, NULL);
 705 }
 706
 707 /* Helper to process the decl chain for the symbol table entry *SLOT.  */
 708
 709 static int
 710 lto_symtab_merge_cgraph_nodes_1 (void **slot, void *data ATTRIBUTE_UNUSED)
 711 {
 712   lto_symtab_entry_t e, prevailing = (lto_symtab_entry_t) *slot;
 713
 714   if (!prevailing->next)
 715     return 1;
 716
 717   /* Replace the cgraph node of each entry with the prevailing one.  */
 718   for (e = prevailing->next; e; e = e->next)
 719     {
 720       if (e->node != NULL)
 721         {
 722           if (e->node->decl != e->decl && e->node->same_body)
 723             {
 724               struct cgraph_node *alias;
 725
 726               for (alias = e->node->same_body; alias; alias = alias->next)
 727                 if (alias->decl == e->decl)
 728                   break;
 729               if (alias)
 730                 {
 731                   cgraph_remove_same_body_alias (alias);
 732                   continue;
 733                 }
 734             }
 735           lto_cgraph_replace_node (e->node, prevailing->node);
 736         }
 737       if (e->vnode != NULL)
 738         lto_varpool_replace_node (e->vnode, prevailing->vnode);
 739     }
 740
 741   /* Drop all but the prevailing decl from the symtab.  */
 742   prevailing->next = NULL;
 743
 744   return 1;
 745 }
 746
 747 /* Merge cgraph nodes according to the symbol merging done by
 748    lto_symtab_merge_decls.  */
 749
 750 void
 751 lto_symtab_merge_cgraph_nodes (void)
 752 {
 753   lto_symtab_maybe_init_hash_table ();
 754   htab_traverse (lto_symtab_identifiers, lto_symtab_merge_cgraph_nodes_1, NULL);
 755 }
 756
 757 /* Given the decl DECL, return the prevailing decl with the same name. */
 758
 759 tree
 760 lto_symtab_prevailing_decl (tree decl)
 761 {
 762   lto_symtab_entry_t ret;
 763
 764   /* Builtins and local symbols are their own prevailing decl.  */
 765   if (!TREE_PUBLIC (decl) || is_builtin_fn (decl))
 766     return decl;
 767
 768   /* DECL_ABSTRACTs are their own prevailng decl.  */
 769   if (TREE_CODE (decl) == FUNCTION_DECL && DECL_ABSTRACT (decl))
 770     return decl;
 771
 772   /* Ensure DECL_ASSEMBLER_NAME will not set assembler name.  */
 773   gcc_assert (DECL_ASSEMBLER_NAME_SET_P (decl));
 774
 775   /* Walk through the list of candidates and return the one we merged to.  */
 776   ret = lto_symtab_get (DECL_ASSEMBLER_NAME (decl));
 777   if (!ret)
 778     return NULL_TREE;
 779
 780   return ret->decl;
 781 }
 782
 783 #include "gt-lto-symtab.h"