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 "diagnostic-core.h"
  25 #include "toplev.h"
  26 #include "tree.h"
  27 #include "gimple.h"
  28 #include "ggc.h"
  29 #include "lambda.h"     /* gcd */
  30 #include "hashtab.h"
  31 #include "plugin-api.h"
  32 #include "lto-streamer.h"
  33
  34 /* Vector to keep track of external variables we've seen so far.  */
  35 VEC(tree,gc) *lto_global_var_decls;
  36
  37 /* Symbol table entry.  */
  38
  39 struct GTY(()) lto_symtab_entry_def
  40 {
  41   /* The symbol table entry key, an IDENTIFIER.  */
  42   tree id;
  43   /* The symbol table entry, a DECL.  */
  44   tree decl;
  45   /* The cgraph node if decl is a function decl.  Filled in during the
  46      merging process.  */
  47   struct cgraph_node *node;
  48   /* The varpool node if decl is a variable decl.  Filled in during the
  49      merging process.  */
  50   struct varpool_node *vnode;
  51   /* LTO file-data and symbol resolution for this decl.  */
  52   struct lto_file_decl_data * GTY((skip (""))) file_data;
  53   enum ld_plugin_symbol_resolution resolution;
  54   /* True when resolution was guessed and not read from the file.  */
  55   bool guessed;
  56   /* Pointer to the next entry with the same key.  Before decl merging
  57      this links all symbols from the different TUs.  After decl merging
  58      this links merged but incompatible decls, thus all prevailing ones
  59      remaining.  */
  60   struct lto_symtab_entry_def *next;
  61 };
  62 typedef struct lto_symtab_entry_def *lto_symtab_entry_t;
  63
  64 /* A poor man's symbol table. This hashes identifier to prevailing DECL
  65    if there is one. */
  66
  67 static GTY ((if_marked ("lto_symtab_entry_marked_p"),
  68              param_is (struct lto_symtab_entry_def)))
  69   htab_t lto_symtab_identifiers;
  70
  71 /* Free symtab hashtable.  */
  72
  73 void
  74 lto_symtab_free (void)
  75 {
  76   htab_delete (lto_symtab_identifiers);
  77   lto_symtab_identifiers = NULL;
  78 }
  79
  80 /* Return the hash value of an lto_symtab_entry_t object pointed to by P.  */
  81
  82 static hashval_t
  83 lto_symtab_entry_hash (const void *p)
  84 {
  85   const struct lto_symtab_entry_def *base =
  86     (const struct lto_symtab_entry_def *) p;
  87   return IDENTIFIER_HASH_VALUE (base->id);
  88 }
  89
  90 /* Return non-zero if P1 and P2 points to lto_symtab_entry_def structs
  91    corresponding to the same symbol.  */
  92
  93 static int
  94 lto_symtab_entry_eq (const void *p1, const void *p2)
  95 {
  96   const struct lto_symtab_entry_def *base1 =
  97      (const struct lto_symtab_entry_def *) p1;
  98   const struct lto_symtab_entry_def *base2 =
  99      (const struct lto_symtab_entry_def *) p2;
 100   return (base1->id == base2->id);
 101 }
 102
 103 /* Returns non-zero if P points to an lto_symtab_entry_def struct that needs
 104    to be marked for GC.  */
 105
 106 static int
 107 lto_symtab_entry_marked_p (const void *p)
 108 {
 109   const struct lto_symtab_entry_def *base =
 110      (const struct lto_symtab_entry_def *) p;
 111
 112   /* Keep this only if the common IDENTIFIER_NODE of the symtab chain
 113      is marked which it will be if at least one of the DECLs in the
 114      chain is marked.  */
 115   return ggc_marked_p (base->id);
 116 }
 117
 118 /* Lazily initialize resolution hash tables.  */
 119
 120 static void
 121 lto_symtab_maybe_init_hash_table (void)
 122 {
 123   if (lto_symtab_identifiers)
 124     return;
 125
 126   lto_symtab_identifiers =
 127     htab_create_ggc (1021, lto_symtab_entry_hash,
 128                      lto_symtab_entry_eq, NULL);
 129 }
 130
 131 /* Registers DECL with the LTO symbol table as having resolution RESOLUTION
 132    and read from FILE_DATA. */
 133
 134 void
 135 lto_symtab_register_decl (tree decl,
 136                           ld_plugin_symbol_resolution_t resolution,
 137                           struct lto_file_decl_data *file_data)
 138 {
 139   lto_symtab_entry_t new_entry;
 140   void **slot;
 141
 142   /* Check that declarations reaching this function do not have
 143      properties inconsistent with having external linkage.  If any of
 144      these asertions fail, then the object file reader has failed to
 145      detect these cases and issue appropriate error messages.  */
 146   gcc_assert (decl
 147               && TREE_PUBLIC (decl)
 148               && (TREE_CODE (decl) == VAR_DECL
 149                   || TREE_CODE (decl) == FUNCTION_DECL)
 150               && DECL_ASSEMBLER_NAME_SET_P (decl));
 151   if (TREE_CODE (decl) == VAR_DECL
 152       && DECL_INITIAL (decl))
 153     gcc_assert (!DECL_EXTERNAL (decl)
 154                 || (TREE_STATIC (decl) && TREE_READONLY (decl)));
 155   if (TREE_CODE (decl) == FUNCTION_DECL)
 156     gcc_assert (!DECL_ABSTRACT (decl));
 157
 158   new_entry = ggc_alloc_cleared_lto_symtab_entry_def ();
 159   new_entry->id = DECL_ASSEMBLER_NAME (decl);
 160   new_entry->decl = decl;
 161   new_entry->resolution = resolution;
 162   new_entry->file_data = file_data;
 163
 164   lto_symtab_maybe_init_hash_table ();
 165   slot = htab_find_slot (lto_symtab_identifiers, new_entry, INSERT);
 166   new_entry->next = (lto_symtab_entry_t) *slot;
 167   *slot = new_entry;
 168 }
 169
 170 /* Get the lto_symtab_entry_def struct associated with ID
 171    if there is one.  */
 172
 173 static lto_symtab_entry_t
 174 lto_symtab_get (tree id)
 175 {
 176   struct lto_symtab_entry_def temp;
 177   void **slot;
 178
 179   lto_symtab_maybe_init_hash_table ();
 180   temp.id = id;
 181   slot = htab_find_slot (lto_symtab_identifiers, &temp, NO_INSERT);
 182   return slot ? (lto_symtab_entry_t) *slot : NULL;
 183 }
 184
 185 /* Get the linker resolution for DECL.  */
 186
 187 enum ld_plugin_symbol_resolution
 188 lto_symtab_get_resolution (tree decl)
 189 {
 190   lto_symtab_entry_t e;
 191
 192   gcc_assert (DECL_ASSEMBLER_NAME_SET_P (decl));
 193
 194   e = lto_symtab_get (DECL_ASSEMBLER_NAME (decl));
 195   while (e && e->decl != decl)
 196     e = e->next;
 197   if (!e)
 198     return LDPR_UNKNOWN;
 199
 200   return e->resolution;
 201 }
 202
 203
 204 /* Replace the cgraph node NODE with PREVAILING_NODE in the cgraph, merging
 205    all edges and removing the old node.  */
 206
 207 static void
 208 lto_cgraph_replace_node (struct cgraph_node *node,
 209                          struct cgraph_node *prevailing_node)
 210 {
 211   struct cgraph_edge *e, *next;
 212   bool no_aliases_please = false;
 213
 214   if (cgraph_dump_file)
 215     {
 216       fprintf (cgraph_dump_file, "Replacing cgraph node %s/%i by %s/%i"
 217                " for symbol %s\n",
 218                cgraph_node_name (node), node->uid,
 219                cgraph_node_name (prevailing_node),
 220                prevailing_node->uid,
 221                IDENTIFIER_POINTER (DECL_ASSEMBLER_NAME (node->decl)));
 222     }
 223
 224   if (prevailing_node->same_body_alias)
 225     {
 226       if (prevailing_node->thunk.thunk_p)
 227         no_aliases_please = true;
 228       prevailing_node = prevailing_node->same_body;
 229     }
 230
 231   /* Merge node flags.  */
 232   if (node->needed)
 233     cgraph_mark_needed_node (prevailing_node);
 234   if (node->reachable)
 235     cgraph_mark_reachable_node (prevailing_node);
 236   if (node->address_taken)
 237     {
 238       gcc_assert (!prevailing_node->global.inlined_to);
 239       cgraph_mark_address_taken_node (prevailing_node);
 240     }
 241
 242   /* Redirect all incoming edges.  */
 243   for (e = node->callers; e; e = next)
 244     {
 245       next = e->next_caller;
 246       cgraph_redirect_edge_callee (e, prevailing_node);
 247     }
 248   /* Redirect incomming references.  */
 249   ipa_clone_refering (prevailing_node, NULL, &node->ref_list);
 250
 251   /* If we have aliases, redirect them to the prevailing node.  */
 252   if (!node->same_body_alias && node->same_body)
 253     {
 254       struct cgraph_node *alias, *last;
 255       /* We prevail aliases/tunks by a thunk.  This is doable but
 256          would need thunk combination.  Hopefully no ABI changes will
 257          every be crazy enough.  */
 258       gcc_assert (!no_aliases_please);
 259
 260       for (alias = node->same_body; alias; alias = alias->next)
 261         {
 262           last = alias;
 263           gcc_assert (alias->same_body_alias);
 264           alias->same_body = prevailing_node;
 265           alias->thunk.alias = prevailing_node->decl;
 266         }
 267       last->next = prevailing_node->same_body;
 268       /* Node with aliases is prevailed by alias.
 269          We could handle this, but combining thunks together will be tricky.
 270          Hopefully this does not happen.  */
 271       if (prevailing_node->same_body)
 272         prevailing_node->same_body->previous = last;
 273       prevailing_node->same_body = node->same_body;
 274       node->same_body = NULL;
 275     }
 276
 277   /* Finally remove the replaced node.  */
 278   if (node->same_body_alias)
 279     cgraph_remove_same_body_alias (node);
 280   else
 281     cgraph_remove_node (node);
 282 }
 283
 284 /* Replace the cgraph node NODE with PREVAILING_NODE in the cgraph, merging
 285    all edges and removing the old node.  */
 286
 287 static void
 288 lto_varpool_replace_node (struct varpool_node *vnode,
 289                           struct varpool_node *prevailing_node)
 290 {
 291   /* Merge node flags.  */
 292   if (vnode->needed)
 293     {
 294       gcc_assert (!vnode->analyzed || prevailing_node->analyzed);
 295       varpool_mark_needed_node (prevailing_node);
 296     }
 297   /* Relink aliases.  */
 298   if (vnode->extra_name && !vnode->alias)
 299     {
 300       struct varpool_node *alias, *last;
 301       for (alias = vnode->extra_name;
 302            alias; alias = alias->next)
 303         {
 304           last = alias;
 305           alias->extra_name = prevailing_node;
 306         }
 307
 308       if (prevailing_node->extra_name)
 309         {
 310           last->next = prevailing_node->extra_name;
 311           prevailing_node->extra_name->prev = last;
 312         }
 313       prevailing_node->extra_name = vnode->extra_name;
 314       vnode->extra_name = NULL;
 315     }
 316   gcc_assert (!vnode->finalized || prevailing_node->finalized);
 317   gcc_assert (!vnode->analyzed || prevailing_node->analyzed);
 318
 319   /* When replacing by an alias, the references goes to the original
 320      variable.  */
 321   if (prevailing_node->alias && prevailing_node->extra_name)
 322     prevailing_node = prevailing_node->extra_name;
 323   ipa_clone_refering (NULL, prevailing_node, &vnode->ref_list);
 324
 325   /* Be sure we can garbage collect the initializer.  */
 326   if (DECL_INITIAL (vnode->decl))
 327     DECL_INITIAL (vnode->decl) = error_mark_node;
 328   /* Finally remove the replaced node.  */
 329   varpool_remove_node (vnode);
 330 }
 331
 332 /* Merge two variable or function symbol table entries PREVAILING and ENTRY.
 333    Return false if the symbols are not fully compatible and a diagnostic
 334    should be emitted.  */
 335
 336 static bool
 337 lto_symtab_merge (lto_symtab_entry_t prevailing, lto_symtab_entry_t entry)
 338 {
 339   tree prevailing_decl = prevailing->decl;
 340   tree decl = entry->decl;
 341   tree prevailing_type, type;
 342
 343   /* Merge decl state in both directions, we may still end up using
 344      the new decl.  */
 345   TREE_ADDRESSABLE (prevailing_decl) |= TREE_ADDRESSABLE (decl);
 346   TREE_ADDRESSABLE (decl) |= TREE_ADDRESSABLE (prevailing_decl);
 347
 348   /* The linker may ask us to combine two incompatible symbols.
 349      Detect this case and notify the caller of required diagnostics.  */
 350
 351   if (TREE_CODE (decl) == FUNCTION_DECL)
 352     {
 353       if (!gimple_types_compatible_p (TREE_TYPE (prevailing_decl),
 354                                       TREE_TYPE (decl), GTC_DIAG))
 355         /* If we don't have a merged type yet...sigh.  The linker
 356            wouldn't complain if the types were mismatched, so we
 357            probably shouldn't either.  Just use the type from
 358            whichever decl appears to be associated with the
 359            definition.  If for some odd reason neither decl is, the
 360            older one wins.  */
 361         (void) 0;
 362
 363       return true;
 364     }
 365
 366   /* Now we exclusively deal with VAR_DECLs.  */
 367
 368   /* Sharing a global symbol is a strong hint that two types are
 369      compatible.  We could use this information to complete
 370      incomplete pointed-to types more aggressively here, ignoring
 371      mismatches in both field and tag names.  It's difficult though
 372      to guarantee that this does not have side-effects on merging
 373      more compatible types from other translation units though.  */
 374
 375   /* We can tolerate differences in type qualification, the
 376      qualification of the prevailing definition will prevail.
 377      ???  In principle we might want to only warn for structurally
 378      incompatible types here, but unless we have protective measures
 379      for TBAA in place that would hide useful information.  */
 380   prevailing_type = TYPE_MAIN_VARIANT (TREE_TYPE (prevailing_decl));
 381   type = TYPE_MAIN_VARIANT (TREE_TYPE (decl));
 382
 383   /* We have to register and fetch canonical types here as the global
 384      fixup process didn't yet run.  */
 385   prevailing_type = gimple_register_type (prevailing_type);
 386   type = gimple_register_type (type);
 387   if (!gimple_types_compatible_p (prevailing_type, type, GTC_DIAG))
 388     {
 389       if (COMPLETE_TYPE_P (type))
 390         return false;
 391
 392       /* If type is incomplete then avoid warnings in the cases
 393          that TBAA handles just fine.  */
 394
 395       if (TREE_CODE (prevailing_type) != TREE_CODE (type))
 396         return false;
 397
 398       if (TREE_CODE (prevailing_type) == ARRAY_TYPE)
 399         {
 400           tree tem1 = TREE_TYPE (prevailing_type);
 401           tree tem2 = TREE_TYPE (type);
 402           while (TREE_CODE (tem1) == ARRAY_TYPE
 403                  && TREE_CODE (tem2) == ARRAY_TYPE)
 404             {
 405               tem1 = TREE_TYPE (tem1);
 406               tem2 = TREE_TYPE (tem2);
 407             }
 408
 409           if (TREE_CODE (tem1) != TREE_CODE (tem2))
 410             return false;
 411
 412           if (!gimple_types_compatible_p (gimple_register_type (tem1),
 413                                           gimple_register_type (tem2),
 414                                           GTC_DIAG))
 415             return false;
 416         }
 417
 418       /* Fallthru.  Compatible enough.  */
 419     }
 420
 421   /* ???  We might want to emit a warning here if type qualification
 422      differences were spotted.  Do not do this unconditionally though.  */
 423
 424   /* There is no point in comparing too many details of the decls here.
 425      The type compatibility checks or the completing of types has properly
 426      dealt with most issues.  */
 427
 428   /* The following should all not invoke fatal errors as in non-LTO
 429      mode the linker wouldn't complain either.  Just emit warnings.  */
 430
 431   /* Report a warning if user-specified alignments do not match.  */
 432   if ((DECL_USER_ALIGN (prevailing_decl) && DECL_USER_ALIGN (decl))
 433       && DECL_ALIGN (prevailing_decl) < DECL_ALIGN (decl))
 434     return false;
 435
 436   return true;
 437 }
 438
 439 /* Return true if the symtab entry E can be replaced by another symtab
 440    entry.  */
 441
 442 static bool
 443 lto_symtab_resolve_replaceable_p (lto_symtab_entry_t e)
 444 {
 445   if (DECL_EXTERNAL (e->decl)
 446       || DECL_COMDAT (e->decl)
 447       || DECL_WEAK (e->decl))
 448     return true;
 449
 450   if (TREE_CODE (e->decl) == VAR_DECL)
 451     return (DECL_COMMON (e->decl)
 452             || (!flag_no_common && !DECL_INITIAL (e->decl)));
 453
 454   return false;
 455 }
 456
 457 /* Return true if the symtab entry E can be the prevailing one.  */
 458
 459 static bool
 460 lto_symtab_resolve_can_prevail_p (lto_symtab_entry_t e)
 461 {
 462   /* The C++ frontend ends up neither setting TREE_STATIC nor
 463      DECL_EXTERNAL on virtual methods but only TREE_PUBLIC.
 464      So do not reject !TREE_STATIC here but only DECL_EXTERNAL.  */
 465   if (DECL_EXTERNAL (e->decl))
 466     return false;
 467
 468   /* For functions we need a non-discarded body.  */
 469   if (TREE_CODE (e->decl) == FUNCTION_DECL)
 470     return (e->node
 471             && (e->node->analyzed
 472                 || (e->node->same_body_alias && e->node->same_body->analyzed)));
 473
 474   /* A variable should have a size.  */
 475   else if (TREE_CODE (e->decl) == VAR_DECL)
 476     {
 477       if (!e->vnode)
 478         return false;
 479       if (e->vnode->finalized)
 480         return true;
 481       return e->vnode->alias && e->vnode->extra_name->finalized;
 482     }
 483
 484   gcc_unreachable ();
 485 }
 486
 487 /* Resolve the symbol with the candidates in the chain *SLOT and store
 488    their resolutions.  */
 489
 490 static void
 491 lto_symtab_resolve_symbols (void **slot)
 492 {
 493   lto_symtab_entry_t e;
 494   lto_symtab_entry_t prevailing = NULL;
 495
 496   /* Always set e->node so that edges are updated to reflect decl merging. */
 497   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 498     {
 499       if (TREE_CODE (e->decl) == FUNCTION_DECL)
 500         e->node = cgraph_get_node_or_alias (e->decl);
 501       else if (TREE_CODE (e->decl) == VAR_DECL)
 502         e->vnode = varpool_get_node (e->decl);
 503     }
 504
 505   e = (lto_symtab_entry_t) *slot;
 506
 507   /* If the chain is already resolved there is nothing else to do.  */
 508   if (e->resolution != LDPR_UNKNOWN)
 509     return;
 510
 511   /* Find the single non-replaceable prevailing symbol and
 512      diagnose ODR violations.  */
 513   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 514     {
 515       if (!lto_symtab_resolve_can_prevail_p (e))
 516         {
 517           e->resolution = LDPR_RESOLVED_IR;
 518           e->guessed = true;
 519           continue;
 520         }
 521
 522       /* Set a default resolution - the final prevailing one will get
 523          adjusted later.  */
 524       e->resolution = LDPR_PREEMPTED_IR;
 525       e->guessed = true;
 526       if (!lto_symtab_resolve_replaceable_p (e))
 527         {
 528           if (prevailing)
 529             {
 530               error_at (DECL_SOURCE_LOCATION (e->decl),
 531                         "%qD has already been defined", e->decl);
 532               inform (DECL_SOURCE_LOCATION (prevailing->decl),
 533                       "previously defined here");
 534             }
 535           prevailing = e;
 536         }
 537     }
 538   if (prevailing)
 539     goto found;
 540
 541   /* Do a second round choosing one from the replaceable prevailing decls.  */
 542   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 543     {
 544       if (e->resolution != LDPR_PREEMPTED_IR)
 545         continue;
 546
 547       /* Choose the first function that can prevail as prevailing.  */
 548       if (TREE_CODE (e->decl) == FUNCTION_DECL)
 549         {
 550           prevailing = e;
 551           break;
 552         }
 553
 554       /* From variables that can prevail choose the largest one.  */
 555       if (!prevailing
 556           || tree_int_cst_lt (DECL_SIZE (prevailing->decl),
 557                               DECL_SIZE (e->decl)))
 558         prevailing = e;
 559     }
 560
 561   if (!prevailing)
 562     return;
 563
 564 found:
 565   /* If current lto files represent the whole program,
 566     it is correct to use LDPR_PREVALING_DEF_IRONLY.
 567     If current lto files are part of whole program, internal
 568     resolver doesn't know if it is LDPR_PREVAILING_DEF
 569     or LDPR_PREVAILING_DEF_IRONLY.  Use IRONLY conforms to
 570     using -fwhole-program.  Otherwise, it doesn't
 571     matter using either LDPR_PREVAILING_DEF or
 572     LDPR_PREVAILING_DEF_IRONLY
 573
 574     FIXME: above workaround due to gold plugin makes some
 575     variables IRONLY, which are indeed PREVAILING_DEF in
 576     resolution file.  These variables still need manual
 577     externally_visible attribute.  */
 578     prevailing->resolution = LDPR_PREVAILING_DEF_IRONLY;
 579     prevailing->guessed = true;
 580 }
 581
 582 /* Merge all decls in the symbol table chain to the prevailing decl and
 583    issue diagnostics about type mismatches.  */
 584
 585 static void
 586 lto_symtab_merge_decls_2 (void **slot)
 587 {
 588   lto_symtab_entry_t prevailing, e;
 589   VEC(tree, heap) *mismatches = NULL;
 590   unsigned i;
 591   tree decl;
 592   bool diagnosed_p = false;
 593
 594   /* Nothing to do for a single entry.  */
 595   prevailing = (lto_symtab_entry_t) *slot;
 596   if (!prevailing->next)
 597     return;
 598
 599   /* Try to merge each entry with the prevailing one.  */
 600   for (e = prevailing->next; e; e = e->next)
 601     {
 602       if (!lto_symtab_merge (prevailing, e))
 603         VEC_safe_push (tree, heap, mismatches, e->decl);
 604     }
 605   if (VEC_empty (tree, mismatches))
 606     return;
 607
 608   /* Diagnose all mismatched re-declarations.  */
 609   FOR_EACH_VEC_ELT (tree, mismatches, i, decl)
 610     {
 611       if (!gimple_types_compatible_p (TREE_TYPE (prevailing->decl),
 612                                       TREE_TYPE (decl), GTC_DIAG))
 613         diagnosed_p |= warning_at (DECL_SOURCE_LOCATION (decl), 0,
 614                                    "type of %qD does not match original "
 615                                    "declaration", decl);
 616
 617       else if ((DECL_USER_ALIGN (prevailing->decl) && DECL_USER_ALIGN (decl))
 618                && DECL_ALIGN (prevailing->decl) < DECL_ALIGN (decl))
 619         {
 620           diagnosed_p |= warning_at (DECL_SOURCE_LOCATION (decl), 0,
 621                                      "alignment of %qD is bigger than "
 622                                      "original declaration", decl);
 623         }
 624     }
 625   if (diagnosed_p)
 626     inform (DECL_SOURCE_LOCATION (prevailing->decl),
 627             "previously declared here");
 628
 629   VEC_free (tree, heap, mismatches);
 630 }
 631
 632 /* Helper to process the decl chain for the symbol table entry *SLOT.  */
 633
 634 static int
 635 lto_symtab_merge_decls_1 (void **slot, void *data ATTRIBUTE_UNUSED)
 636 {
 637   lto_symtab_entry_t e, prevailing;
 638   bool diagnosed_p = false;
 639
 640   /* Compute the symbol resolutions.  This is a no-op when using the
 641      linker plugin.  */
 642   lto_symtab_resolve_symbols (slot);
 643
 644   /* Find the prevailing decl.  */
 645   for (prevailing = (lto_symtab_entry_t) *slot;
 646        prevailing
 647        && prevailing->resolution != LDPR_PREVAILING_DEF_IRONLY
 648        && prevailing->resolution != LDPR_PREVAILING_DEF;
 649        prevailing = prevailing->next)
 650     ;
 651
 652   /* Assert it's the only one.  */
 653   if (prevailing)
 654     for (e = prevailing->next; e; e = e->next)
 655       {
 656         if (e->resolution == LDPR_PREVAILING_DEF_IRONLY
 657             || e->resolution == LDPR_PREVAILING_DEF)
 658           fatal_error ("multiple prevailing defs for %qE",
 659                        DECL_NAME (prevailing->decl));
 660       }
 661
 662   /* If there's not a prevailing symbol yet it's an external reference.
 663      Happens a lot during ltrans.  Choose the first symbol with a
 664      cgraph or a varpool node.  */
 665   if (!prevailing)
 666     {
 667       prevailing = (lto_symtab_entry_t) *slot;
 668       /* For functions choose one with a cgraph node.  */
 669       if (TREE_CODE (prevailing->decl) == FUNCTION_DECL)
 670         while (!prevailing->node
 671                && prevailing->next)
 672           prevailing = prevailing->next;
 673       /* For variables chose with a priority variant with vnode
 674          attached (i.e. from unit where external declaration of
 675          variable is actually used).
 676          When there are multiple variants, chose one with size.
 677          This is needed for C++ typeinfos, for example in
 678          lto/20081204-1 there are typeifos in both units, just
 679          one of them do have size.  */
 680       if (TREE_CODE (prevailing->decl) == VAR_DECL)
 681         {
 682           for (e = prevailing->next; e; e = e->next)
 683             if ((!prevailing->vnode && e->vnode)
 684                 || ((prevailing->vnode != NULL) == (e->vnode != NULL)
 685                     && !COMPLETE_TYPE_P (TREE_TYPE (prevailing->decl))
 686                     && COMPLETE_TYPE_P (TREE_TYPE (e->decl))))
 687               prevailing = e;
 688         }
 689     }
 690
 691   /* Move it first in the list.  */
 692   if ((lto_symtab_entry_t) *slot != prevailing)
 693     {
 694       for (e = (lto_symtab_entry_t) *slot; e->next != prevailing; e = e->next)
 695         ;
 696       e->next = prevailing->next;
 697       prevailing->next = (lto_symtab_entry_t) *slot;
 698       *slot = (void *) prevailing;
 699     }
 700
 701   /* Record the prevailing variable.  */
 702   if (TREE_CODE (prevailing->decl) == VAR_DECL)
 703     VEC_safe_push (tree, gc, lto_global_var_decls, prevailing->decl);
 704
 705   /* Diagnose mismatched objects.  */
 706   for (e = prevailing->next; e; e = e->next)
 707     {
 708       if (TREE_CODE (prevailing->decl) == TREE_CODE (e->decl))
 709         continue;
 710
 711       switch (TREE_CODE (prevailing->decl))
 712         {
 713         case VAR_DECL:
 714           gcc_assert (TREE_CODE (e->decl) == FUNCTION_DECL);
 715           error_at (DECL_SOURCE_LOCATION (e->decl),
 716                     "variable %qD redeclared as function", prevailing->decl);
 717           break;
 718
 719         case FUNCTION_DECL:
 720           gcc_assert (TREE_CODE (e->decl) == VAR_DECL);
 721           error_at (DECL_SOURCE_LOCATION (e->decl),
 722                     "function %qD redeclared as variable", prevailing->decl);
 723           break;
 724
 725         default:
 726           gcc_unreachable ();
 727         }
 728
 729       diagnosed_p = true;
 730     }
 731   if (diagnosed_p)
 732       inform (DECL_SOURCE_LOCATION (prevailing->decl),
 733               "previously declared here");
 734
 735   /* Register and adjust types of the entries.  */
 736   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 737     TREE_TYPE (e->decl) = gimple_register_type (TREE_TYPE (e->decl));
 738
 739   /* Merge the chain to the single prevailing decl and diagnose
 740      mismatches.  */
 741   lto_symtab_merge_decls_2 (slot);
 742
 743   /* Drop all but the prevailing decl from the symtab.  */
 744   if (TREE_CODE (prevailing->decl) != FUNCTION_DECL
 745       && TREE_CODE (prevailing->decl) != VAR_DECL)
 746     prevailing->next = NULL;
 747
 748   /* Store resolution decision into the callgraph.
 749      In LTRANS don't overwrite information we stored into callgraph at
 750      WPA stage.
 751
 752      Do not bother to store guessed decisions.  Generic code knows how
 753      to handle UNKNOWN relocation well.
 754
 755      The problem with storing guessed decision is whether to use
 756      PREVAILING_DEF or PREVAILING_DEF_IRONLY.  First one would disable
 757      some whole program optimizations, while ther second would imply
 758      to many whole program assumptions.  */
 759   if (prevailing->node && !flag_ltrans && !prevailing->guessed)
 760     prevailing->node->resolution = prevailing->resolution;
 761   else if (prevailing->vnode && !flag_ltrans && !prevailing->guessed)
 762     prevailing->vnode->resolution = prevailing->resolution;
 763   return 1;
 764 }
 765
 766 /* Resolve and merge all symbol table chains to a prevailing decl.  */
 767
 768 void
 769 lto_symtab_merge_decls (void)
 770 {
 771   lto_symtab_maybe_init_hash_table ();
 772   htab_traverse (lto_symtab_identifiers, lto_symtab_merge_decls_1, NULL);
 773 }
 774
 775 /* Helper to process the decl chain for the symbol table entry *SLOT.  */
 776
 777 static int
 778 lto_symtab_merge_cgraph_nodes_1 (void **slot, void *data ATTRIBUTE_UNUSED)
 779 {
 780   lto_symtab_entry_t e, prevailing = (lto_symtab_entry_t) *slot;
 781
 782   if (!prevailing->next)
 783     return 1;
 784
 785   /* Replace the cgraph node of each entry with the prevailing one.  */
 786   for (e = prevailing->next; e; e = e->next)
 787     {
 788       if (e->node != NULL)
 789         lto_cgraph_replace_node (e->node, prevailing->node);
 790       if (e->vnode != NULL)
 791         lto_varpool_replace_node (e->vnode, prevailing->vnode);
 792     }
 793
 794   /* Drop all but the prevailing decl from the symtab.  */
 795   prevailing->next = NULL;
 796
 797   return 1;
 798 }
 799
 800 /* Merge cgraph nodes according to the symbol merging done by
 801    lto_symtab_merge_decls.  */
 802
 803 void
 804 lto_symtab_merge_cgraph_nodes (void)
 805 {
 806   lto_symtab_maybe_init_hash_table ();
 807   htab_traverse (lto_symtab_identifiers, lto_symtab_merge_cgraph_nodes_1, NULL);
 808 }
 809
 810 /* Given the decl DECL, return the prevailing decl with the same name. */
 811
 812 tree
 813 lto_symtab_prevailing_decl (tree decl)
 814 {
 815   lto_symtab_entry_t ret;
 816
 817   /* Builtins and local symbols are their own prevailing decl.  */
 818   if (!TREE_PUBLIC (decl) || is_builtin_fn (decl))
 819     return decl;
 820
 821   /* DECL_ABSTRACTs are their own prevailng decl.  */
 822   if (TREE_CODE (decl) == FUNCTION_DECL && DECL_ABSTRACT (decl))
 823     return decl;
 824
 825   /* Ensure DECL_ASSEMBLER_NAME will not set assembler name.  */
 826   gcc_assert (DECL_ASSEMBLER_NAME_SET_P (decl));
 827
 828   /* Walk through the list of candidates and return the one we merged to.  */
 829   ret = lto_symtab_get (DECL_ASSEMBLER_NAME (decl));
 830   if (!ret)
 831     return NULL_TREE;
 832
 833   return ret->decl;
 834 }
 835
 836 #include "gt-lto-symtab.h"