gcc/lto-symtab.c

   1 /* LTO symbol table.
   2    Copyright 2009, 2010 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 "tree.h"
  26 #include "gimple.h"
  27 #include "ggc.h"
  28 #include "hashtab.h"
  29 #include "plugin-api.h"
  30 #include "lto-streamer.h"
  31
  32 /* Vector to keep track of external variables we've seen so far.  */
  33 VEC(tree,gc) *lto_global_var_decls;
  34
  35 /* Symbol table entry.  */
  36
  37 struct GTY(()) lto_symtab_entry_def
  38 {
  39   /* The symbol table entry key, an IDENTIFIER.  */
  40   tree id;
  41   /* The symbol table entry, a DECL.  */
  42   tree decl;
  43   /* The cgraph node if decl is a function decl.  Filled in during the
  44      merging process.  */
  45   struct cgraph_node *node;
  46   /* The varpool node if decl is a variable decl.  Filled in during the
  47      merging process.  */
  48   struct varpool_node *vnode;
  49   /* LTO file-data and symbol resolution for this decl.  */
  50   struct lto_file_decl_data * GTY((skip (""))) file_data;
  51   enum ld_plugin_symbol_resolution resolution;
  52   /* True when resolution was guessed and not read from the file.  */
  53   bool guessed;
  54   /* Pointer to the next entry with the same key.  Before decl merging
  55      this links all symbols from the different TUs.  After decl merging
  56      this links merged but incompatible decls, thus all prevailing ones
  57      remaining.  */
  58   struct lto_symtab_entry_def *next;
  59 };
  60 typedef struct lto_symtab_entry_def *lto_symtab_entry_t;
  61
  62 /* A poor man's symbol table. This hashes identifier to prevailing DECL
  63    if there is one. */
  64
  65 static GTY ((if_marked ("lto_symtab_entry_marked_p"),
  66              param_is (struct lto_symtab_entry_def)))
  67   htab_t lto_symtab_identifiers;
  68
  69 /* Free symtab hashtable.  */
  70
  71 void
  72 lto_symtab_free (void)
  73 {
  74   htab_delete (lto_symtab_identifiers);
  75   lto_symtab_identifiers = NULL;
  76 }
  77
  78 /* Return the hash value of an lto_symtab_entry_t object pointed to by P.  */
  79
  80 static hashval_t
  81 lto_symtab_entry_hash (const void *p)
  82 {
  83   const struct lto_symtab_entry_def *base =
  84     (const struct lto_symtab_entry_def *) p;
  85   return IDENTIFIER_HASH_VALUE (base->id);
  86 }
  87
  88 /* Return non-zero if P1 and P2 points to lto_symtab_entry_def structs
  89    corresponding to the same symbol.  */
  90
  91 static int
  92 lto_symtab_entry_eq (const void *p1, const void *p2)
  93 {
  94   const struct lto_symtab_entry_def *base1 =
  95      (const struct lto_symtab_entry_def *) p1;
  96   const struct lto_symtab_entry_def *base2 =
  97      (const struct lto_symtab_entry_def *) p2;
  98   return (base1->id == base2->id);
  99 }
 100
 101 /* Returns non-zero if P points to an lto_symtab_entry_def struct that needs
 102    to be marked for GC.  */
 103
 104 static int
 105 lto_symtab_entry_marked_p (const void *p)
 106 {
 107   const struct lto_symtab_entry_def *base =
 108      (const struct lto_symtab_entry_def *) p;
 109
 110   /* Keep this only if the common IDENTIFIER_NODE of the symtab chain
 111      is marked which it will be if at least one of the DECLs in the
 112      chain is marked.  */
 113   return ggc_marked_p (base->id);
 114 }
 115
 116 /* Lazily initialize resolution hash tables.  */
 117
 118 static void
 119 lto_symtab_maybe_init_hash_table (void)
 120 {
 121   if (lto_symtab_identifiers)
 122     return;
 123
 124   lto_symtab_identifiers =
 125     htab_create_ggc (1021, lto_symtab_entry_hash,
 126                      lto_symtab_entry_eq, NULL);
 127 }
 128
 129 /* Registers DECL with the LTO symbol table as having resolution RESOLUTION
 130    and read from FILE_DATA. */
 131
 132 void
 133 lto_symtab_register_decl (tree decl,
 134                           ld_plugin_symbol_resolution_t resolution,
 135                           struct lto_file_decl_data *file_data)
 136 {
 137   lto_symtab_entry_t new_entry;
 138   void **slot;
 139
 140   /* Check that declarations reaching this function do not have
 141      properties inconsistent with having external linkage.  If any of
 142      these asertions fail, then the object file reader has failed to
 143      detect these cases and issue appropriate error messages.  */
 144   gcc_assert (decl
 145               && TREE_PUBLIC (decl)
 146               && (TREE_CODE (decl) == VAR_DECL
 147                   || TREE_CODE (decl) == FUNCTION_DECL)
 148               && DECL_ASSEMBLER_NAME_SET_P (decl));
 149   if (TREE_CODE (decl) == VAR_DECL
 150       && DECL_INITIAL (decl))
 151     gcc_assert (!DECL_EXTERNAL (decl)
 152                 || (TREE_STATIC (decl) && TREE_READONLY (decl)));
 153   if (TREE_CODE (decl) == FUNCTION_DECL)
 154     gcc_assert (!DECL_ABSTRACT (decl));
 155
 156   new_entry = ggc_alloc_cleared_lto_symtab_entry_def ();
 157   new_entry->id = (*targetm.asm_out.mangle_assembler_name)
 158                   (IDENTIFIER_POINTER (DECL_ASSEMBLER_NAME (decl)));
 159   new_entry->decl = decl;
 160   new_entry->resolution = resolution;
 161   new_entry->file_data = file_data;
 162
 163   lto_symtab_maybe_init_hash_table ();
 164   slot = htab_find_slot (lto_symtab_identifiers, new_entry, INSERT);
 165   new_entry->next = (lto_symtab_entry_t) *slot;
 166   *slot = new_entry;
 167 }
 168
 169 /* Get the lto_symtab_entry_def struct associated with ID
 170    if there is one.  */
 171
 172 static lto_symtab_entry_t
 173 lto_symtab_get (tree id)
 174 {
 175   struct lto_symtab_entry_def temp;
 176   void **slot;
 177
 178   lto_symtab_maybe_init_hash_table ();
 179   temp.id = id;
 180   slot = htab_find_slot (lto_symtab_identifiers, &temp, NO_INSERT);
 181   return slot ? (lto_symtab_entry_t) *slot : NULL;
 182 }
 183
 184 /* Get the linker resolution for DECL.  */
 185
 186 enum ld_plugin_symbol_resolution
 187 lto_symtab_get_resolution (tree decl)
 188 {
 189   lto_symtab_entry_t e;
 190
 191   gcc_assert (DECL_ASSEMBLER_NAME_SET_P (decl));
 192
 193   e = lto_symtab_get ((*targetm.asm_out.mangle_assembler_name)
 194                       (IDENTIFIER_POINTER (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 compatible_p;
 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 ((*targetm.asm_out.mangle_assembler_name)
 222                  (IDENTIFIER_POINTER (DECL_ASSEMBLER_NAME (node->symbol.decl)))));
 223     }
 224
 225   /* Merge node flags.  */
 226   if (node->needed)
 227     cgraph_mark_needed_node (prevailing_node);
 228   if (node->reachable)
 229     cgraph_mark_reachable_node (prevailing_node);
 230   if (node->symbol.address_taken)
 231     {
 232       gcc_assert (!prevailing_node->global.inlined_to);
 233       cgraph_mark_address_taken_node (prevailing_node);
 234     }
 235
 236   /* Redirect all incoming edges.  */
 237   compatible_p
 238     = types_compatible_p (TREE_TYPE (TREE_TYPE (prevailing_node->symbol.decl)),
 239                           TREE_TYPE (TREE_TYPE (node->symbol.decl)));
 240   for (e = node->callers; e; e = next)
 241     {
 242       next = e->next_caller;
 243       cgraph_redirect_edge_callee (e, prevailing_node);
 244       /* If there is a mismatch between the supposed callee return type and
 245          the real one do not attempt to inline this function.
 246          ???  We really need a way to match function signatures for ABI
 247          compatibility and perform related promotions at inlining time.  */
 248       if (!compatible_p)
 249         e->call_stmt_cannot_inline_p = 1;
 250     }
 251   /* Redirect incomming references.  */
 252   ipa_clone_refering (prevailing_node, NULL, &node->symbol.ref_list);
 253
 254   /* Finally remove the replaced node.  */
 255   cgraph_remove_node (node);
 256 }
 257
 258 /* Replace the cgraph node NODE with PREVAILING_NODE in the cgraph, merging
 259    all edges and removing the old node.  */
 260
 261 static void
 262 lto_varpool_replace_node (struct varpool_node *vnode,
 263                           struct varpool_node *prevailing_node)
 264 {
 265   /* Merge node flags.  */
 266   if (vnode->needed)
 267     {
 268       gcc_assert (!vnode->analyzed || prevailing_node->analyzed);
 269       varpool_mark_needed_node (prevailing_node);
 270     }
 271   gcc_assert (!vnode->finalized || prevailing_node->finalized);
 272   gcc_assert (!vnode->analyzed || prevailing_node->analyzed);
 273
 274   ipa_clone_refering (NULL, prevailing_node, &vnode->symbol.ref_list);
 275
 276   /* Be sure we can garbage collect the initializer.  */
 277   if (DECL_INITIAL (vnode->symbol.decl))
 278     DECL_INITIAL (vnode->symbol.decl) = error_mark_node;
 279   /* Finally remove the replaced node.  */
 280   varpool_remove_node (vnode);
 281 }
 282
 283 /* Merge two variable or function symbol table entries PREVAILING and ENTRY.
 284    Return false if the symbols are not fully compatible and a diagnostic
 285    should be emitted.  */
 286
 287 static bool
 288 lto_symtab_merge (lto_symtab_entry_t prevailing, lto_symtab_entry_t entry)
 289 {
 290   tree prevailing_decl = prevailing->decl;
 291   tree decl = entry->decl;
 292   tree prevailing_type, type;
 293
 294   /* Merge decl state in both directions, we may still end up using
 295      the new decl.  */
 296   TREE_ADDRESSABLE (prevailing_decl) |= TREE_ADDRESSABLE (decl);
 297   TREE_ADDRESSABLE (decl) |= TREE_ADDRESSABLE (prevailing_decl);
 298
 299   /* The linker may ask us to combine two incompatible symbols.
 300      Detect this case and notify the caller of required diagnostics.  */
 301
 302   if (TREE_CODE (decl) == FUNCTION_DECL)
 303     {
 304       if (!types_compatible_p (TREE_TYPE (prevailing_decl),
 305                                TREE_TYPE (decl)))
 306         /* If we don't have a merged type yet...sigh.  The linker
 307            wouldn't complain if the types were mismatched, so we
 308            probably shouldn't either.  Just use the type from
 309            whichever decl appears to be associated with the
 310            definition.  If for some odd reason neither decl is, the
 311            older one wins.  */
 312         (void) 0;
 313
 314       return true;
 315     }
 316
 317   /* Now we exclusively deal with VAR_DECLs.  */
 318
 319   /* Sharing a global symbol is a strong hint that two types are
 320      compatible.  We could use this information to complete
 321      incomplete pointed-to types more aggressively here, ignoring
 322      mismatches in both field and tag names.  It's difficult though
 323      to guarantee that this does not have side-effects on merging
 324      more compatible types from other translation units though.  */
 325
 326   /* We can tolerate differences in type qualification, the
 327      qualification of the prevailing definition will prevail.
 328      ???  In principle we might want to only warn for structurally
 329      incompatible types here, but unless we have protective measures
 330      for TBAA in place that would hide useful information.  */
 331   prevailing_type = TYPE_MAIN_VARIANT (TREE_TYPE (prevailing_decl));
 332   type = TYPE_MAIN_VARIANT (TREE_TYPE (decl));
 333
 334   if (!types_compatible_p (prevailing_type, type))
 335     {
 336       if (COMPLETE_TYPE_P (type))
 337         return false;
 338
 339       /* If type is incomplete then avoid warnings in the cases
 340          that TBAA handles just fine.  */
 341
 342       if (TREE_CODE (prevailing_type) != TREE_CODE (type))
 343         return false;
 344
 345       if (TREE_CODE (prevailing_type) == ARRAY_TYPE)
 346         {
 347           tree tem1 = TREE_TYPE (prevailing_type);
 348           tree tem2 = TREE_TYPE (type);
 349           while (TREE_CODE (tem1) == ARRAY_TYPE
 350                  && TREE_CODE (tem2) == ARRAY_TYPE)
 351             {
 352               tem1 = TREE_TYPE (tem1);
 353               tem2 = TREE_TYPE (tem2);
 354             }
 355
 356           if (TREE_CODE (tem1) != TREE_CODE (tem2))
 357             return false;
 358
 359           if (!types_compatible_p (tem1, tem2))
 360             return false;
 361         }
 362
 363       /* Fallthru.  Compatible enough.  */
 364     }
 365
 366   /* ???  We might want to emit a warning here if type qualification
 367      differences were spotted.  Do not do this unconditionally though.  */
 368
 369   /* There is no point in comparing too many details of the decls here.
 370      The type compatibility checks or the completing of types has properly
 371      dealt with most issues.  */
 372
 373   /* The following should all not invoke fatal errors as in non-LTO
 374      mode the linker wouldn't complain either.  Just emit warnings.  */
 375
 376   /* Report a warning if user-specified alignments do not match.  */
 377   if ((DECL_USER_ALIGN (prevailing_decl) && DECL_USER_ALIGN (decl))
 378       && DECL_ALIGN (prevailing_decl) < DECL_ALIGN (decl))
 379     return false;
 380
 381   return true;
 382 }
 383
 384 /* Return true if the symtab entry E can be replaced by another symtab
 385    entry.  */
 386
 387 static bool
 388 lto_symtab_resolve_replaceable_p (lto_symtab_entry_t e)
 389 {
 390   if (DECL_EXTERNAL (e->decl)
 391       || DECL_COMDAT (e->decl)
 392       || DECL_ONE_ONLY (e->decl)
 393       || DECL_WEAK (e->decl))
 394     return true;
 395
 396   if (TREE_CODE (e->decl) == VAR_DECL)
 397     return (DECL_COMMON (e->decl)
 398             || (!flag_no_common && !DECL_INITIAL (e->decl)));
 399
 400   return false;
 401 }
 402
 403 /* Return true if the symtab entry E can be the prevailing one.  */
 404
 405 static bool
 406 lto_symtab_resolve_can_prevail_p (lto_symtab_entry_t e)
 407 {
 408   /* The C++ frontend ends up neither setting TREE_STATIC nor
 409      DECL_EXTERNAL on virtual methods but only TREE_PUBLIC.
 410      So do not reject !TREE_STATIC here but only DECL_EXTERNAL.  */
 411   if (DECL_EXTERNAL (e->decl))
 412     return false;
 413
 414   /* For functions we need a non-discarded body.  */
 415   if (TREE_CODE (e->decl) == FUNCTION_DECL)
 416     return (e->node && e->node->analyzed);
 417
 418   else if (TREE_CODE (e->decl) == VAR_DECL)
 419     {
 420       if (!e->vnode)
 421         return false;
 422       return e->vnode->finalized;
 423     }
 424
 425   gcc_unreachable ();
 426 }
 427
 428 /* Resolve the symbol with the candidates in the chain *SLOT and store
 429    their resolutions.  */
 430
 431 static void
 432 lto_symtab_resolve_symbols (void **slot)
 433 {
 434   lto_symtab_entry_t e;
 435   lto_symtab_entry_t prevailing = NULL;
 436
 437   /* Always set e->node so that edges are updated to reflect decl merging. */
 438   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 439     {
 440       if (TREE_CODE (e->decl) == FUNCTION_DECL)
 441         e->node = cgraph_get_node (e->decl);
 442       else if (TREE_CODE (e->decl) == VAR_DECL)
 443         e->vnode = varpool_get_node (e->decl);
 444       if (e->resolution == LDPR_PREVAILING_DEF_IRONLY
 445           || e->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP
 446           || e->resolution == LDPR_PREVAILING_DEF)
 447         prevailing = e;
 448     }
 449
 450   /* If the chain is already resolved there is nothing else to do.  */
 451   if (prevailing)
 452     return;
 453
 454   /* Find the single non-replaceable prevailing symbol and
 455      diagnose ODR violations.  */
 456   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 457     {
 458       if (!lto_symtab_resolve_can_prevail_p (e))
 459         {
 460           e->resolution = LDPR_RESOLVED_IR;
 461           e->guessed = true;
 462           continue;
 463         }
 464
 465       /* Set a default resolution - the final prevailing one will get
 466          adjusted later.  */
 467       e->resolution = LDPR_PREEMPTED_IR;
 468       e->guessed = true;
 469       if (!lto_symtab_resolve_replaceable_p (e))
 470         {
 471           if (prevailing)
 472             {
 473               error_at (DECL_SOURCE_LOCATION (e->decl),
 474                         "%qD has already been defined", e->decl);
 475               inform (DECL_SOURCE_LOCATION (prevailing->decl),
 476                       "previously defined here");
 477             }
 478           prevailing = e;
 479         }
 480     }
 481   if (prevailing)
 482     goto found;
 483
 484   /* Do a second round choosing one from the replaceable prevailing decls.  */
 485   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 486     {
 487       if (e->resolution != LDPR_PREEMPTED_IR)
 488         continue;
 489
 490       /* Choose the first function that can prevail as prevailing.  */
 491       if (TREE_CODE (e->decl) == FUNCTION_DECL)
 492         {
 493           prevailing = e;
 494           break;
 495         }
 496
 497       /* From variables that can prevail choose the largest one.  */
 498       if (!prevailing
 499           || tree_int_cst_lt (DECL_SIZE (prevailing->decl),
 500                               DECL_SIZE (e->decl)))
 501         prevailing = e;
 502     }
 503
 504   if (!prevailing)
 505     return;
 506
 507 found:
 508   /* If current lto files represent the whole program,
 509     it is correct to use LDPR_PREVALING_DEF_IRONLY.
 510     If current lto files are part of whole program, internal
 511     resolver doesn't know if it is LDPR_PREVAILING_DEF
 512     or LDPR_PREVAILING_DEF_IRONLY.  Use IRONLY conforms to
 513     using -fwhole-program.  Otherwise, it doesn't
 514     matter using either LDPR_PREVAILING_DEF or
 515     LDPR_PREVAILING_DEF_IRONLY
 516
 517     FIXME: above workaround due to gold plugin makes some
 518     variables IRONLY, which are indeed PREVAILING_DEF in
 519     resolution file.  These variables still need manual
 520     externally_visible attribute.  */
 521     prevailing->resolution = LDPR_PREVAILING_DEF_IRONLY;
 522     prevailing->guessed = true;
 523 }
 524
 525 /* Merge all decls in the symbol table chain to the prevailing decl and
 526    issue diagnostics about type mismatches.  If DIAGNOSED_P is true
 527    do not issue further diagnostics.*/
 528
 529 static void
 530 lto_symtab_merge_decls_2 (void **slot, bool diagnosed_p)
 531 {
 532   lto_symtab_entry_t prevailing, e;
 533   VEC(tree, heap) *mismatches = NULL;
 534   unsigned i;
 535   tree decl;
 536
 537   /* Nothing to do for a single entry.  */
 538   prevailing = (lto_symtab_entry_t) *slot;
 539   if (!prevailing->next)
 540     return;
 541
 542   /* Try to merge each entry with the prevailing one.  */
 543   for (e = prevailing->next; e; e = e->next)
 544     {
 545       if (!lto_symtab_merge (prevailing, e)
 546           && !diagnosed_p)
 547         VEC_safe_push (tree, heap, mismatches, e->decl);
 548     }
 549   if (VEC_empty (tree, mismatches))
 550     return;
 551
 552   /* Diagnose all mismatched re-declarations.  */
 553   FOR_EACH_VEC_ELT (tree, mismatches, i, decl)
 554     {
 555       if (!types_compatible_p (TREE_TYPE (prevailing->decl), TREE_TYPE (decl)))
 556         diagnosed_p |= warning_at (DECL_SOURCE_LOCATION (decl), 0,
 557                                    "type of %qD does not match original "
 558                                    "declaration", decl);
 559
 560       else if ((DECL_USER_ALIGN (prevailing->decl) && DECL_USER_ALIGN (decl))
 561                && DECL_ALIGN (prevailing->decl) < DECL_ALIGN (decl))
 562         {
 563           diagnosed_p |= warning_at (DECL_SOURCE_LOCATION (decl), 0,
 564                                      "alignment of %qD is bigger than "
 565                                      "original declaration", decl);
 566         }
 567     }
 568   if (diagnosed_p)
 569     inform (DECL_SOURCE_LOCATION (prevailing->decl),
 570             "previously declared here");
 571
 572   VEC_free (tree, heap, mismatches);
 573 }
 574
 575 /* Helper to process the decl chain for the symbol table entry *SLOT.  */
 576
 577 static int
 578 lto_symtab_merge_decls_1 (void **slot, void *data ATTRIBUTE_UNUSED)
 579 {
 580   lto_symtab_entry_t e, prevailing;
 581   bool diagnosed_p = false;
 582
 583   /* Compute the symbol resolutions.  This is a no-op when using the
 584      linker plugin.  */
 585   lto_symtab_resolve_symbols (slot);
 586
 587   /* Find the prevailing decl.  */
 588   for (prevailing = (lto_symtab_entry_t) *slot;
 589        prevailing
 590        && prevailing->resolution != LDPR_PREVAILING_DEF_IRONLY
 591        && prevailing->resolution != LDPR_PREVAILING_DEF_IRONLY_EXP
 592        && prevailing->resolution != LDPR_PREVAILING_DEF;
 593        prevailing = prevailing->next)
 594     ;
 595
 596   /* Assert it's the only one.  */
 597   if (prevailing)
 598     for (e = prevailing->next; e; e = e->next)
 599       {
 600         if (e->resolution == LDPR_PREVAILING_DEF_IRONLY
 601             || e->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP
 602             || e->resolution == LDPR_PREVAILING_DEF)
 603           fatal_error ("multiple prevailing defs for %qE",
 604                        DECL_NAME (prevailing->decl));
 605       }
 606
 607   /* If there's not a prevailing symbol yet it's an external reference.
 608      Happens a lot during ltrans.  Choose the first symbol with a
 609      cgraph or a varpool node.  */
 610   if (!prevailing)
 611     {
 612       prevailing = (lto_symtab_entry_t) *slot;
 613       /* For functions choose one with a cgraph node.  */
 614       if (TREE_CODE (prevailing->decl) == FUNCTION_DECL)
 615         while (!prevailing->node
 616                && prevailing->next)
 617           prevailing = prevailing->next;
 618       /* For variables chose with a priority variant with vnode
 619          attached (i.e. from unit where external declaration of
 620          variable is actually used).
 621          When there are multiple variants, chose one with size.
 622          This is needed for C++ typeinfos, for example in
 623          lto/20081204-1 there are typeifos in both units, just
 624          one of them do have size.  */
 625       if (TREE_CODE (prevailing->decl) == VAR_DECL)
 626         {
 627           for (e = prevailing->next; e; e = e->next)
 628             if ((!prevailing->vnode && e->vnode)
 629                 || ((prevailing->vnode != NULL) == (e->vnode != NULL)
 630                     && !COMPLETE_TYPE_P (TREE_TYPE (prevailing->decl))
 631                     && COMPLETE_TYPE_P (TREE_TYPE (e->decl))))
 632               prevailing = e;
 633         }
 634     }
 635
 636   /* Move it first in the list.  */
 637   if ((lto_symtab_entry_t) *slot != prevailing)
 638     {
 639       for (e = (lto_symtab_entry_t) *slot; e->next != prevailing; e = e->next)
 640         ;
 641       e->next = prevailing->next;
 642       prevailing->next = (lto_symtab_entry_t) *slot;
 643       *slot = (void *) prevailing;
 644     }
 645
 646   /* Record the prevailing variable.  */
 647   if (TREE_CODE (prevailing->decl) == VAR_DECL)
 648     VEC_safe_push (tree, gc, lto_global_var_decls, prevailing->decl);
 649
 650   /* Diagnose mismatched objects.  */
 651   for (e = prevailing->next; e; e = e->next)
 652     {
 653       if (TREE_CODE (prevailing->decl) == TREE_CODE (e->decl))
 654         continue;
 655
 656       switch (TREE_CODE (prevailing->decl))
 657         {
 658         case VAR_DECL:
 659           gcc_assert (TREE_CODE (e->decl) == FUNCTION_DECL);
 660           error_at (DECL_SOURCE_LOCATION (e->decl),
 661                     "variable %qD redeclared as function", prevailing->decl);
 662           break;
 663
 664         case FUNCTION_DECL:
 665           gcc_assert (TREE_CODE (e->decl) == VAR_DECL);
 666           error_at (DECL_SOURCE_LOCATION (e->decl),
 667                     "function %qD redeclared as variable", prevailing->decl);
 668           break;
 669
 670         default:
 671           gcc_unreachable ();
 672         }
 673
 674       diagnosed_p = true;
 675     }
 676   if (diagnosed_p)
 677       inform (DECL_SOURCE_LOCATION (prevailing->decl),
 678               "previously declared here");
 679
 680   /* Merge the chain to the single prevailing decl and diagnose
 681      mismatches.  */
 682   lto_symtab_merge_decls_2 (slot, diagnosed_p);
 683
 684   /* Store resolution decision into the callgraph.
 685      In LTRANS don't overwrite information we stored into callgraph at
 686      WPA stage.
 687
 688      Do not bother to store guessed decisions.  Generic code knows how
 689      to handle UNKNOWN relocation well.
 690
 691      The problem with storing guessed decision is whether to use
 692      PREVAILING_DEF, PREVAILING_DEF_IRONLY, PREVAILING_DEF_IRONLY_EXP.
 693      First one would disable some whole program optimizations, while
 694      ther second would imply to many whole program assumptions.  */
 695   if (prevailing->node && !flag_ltrans && !prevailing->guessed)
 696     prevailing->node->symbol.resolution = prevailing->resolution;
 697   else if (prevailing->vnode && !flag_ltrans && !prevailing->guessed)
 698     prevailing->vnode->symbol.resolution = prevailing->resolution;
 699   return 1;
 700 }
 701
 702 /* Resolve and merge all symbol table chains to a prevailing decl.  */
 703
 704 void
 705 lto_symtab_merge_decls (void)
 706 {
 707   lto_symtab_maybe_init_hash_table ();
 708   htab_traverse (lto_symtab_identifiers, lto_symtab_merge_decls_1, NULL);
 709 }
 710
 711 /* Helper to process the decl chain for the symbol table entry *SLOT.  */
 712
 713 static int
 714 lto_symtab_merge_cgraph_nodes_1 (void **slot, void *data ATTRIBUTE_UNUSED)
 715 {
 716   lto_symtab_entry_t e, prevailing = (lto_symtab_entry_t) *slot;
 717
 718   if (!prevailing->next)
 719     return 1;
 720
 721   /* Replace the cgraph node of each entry with the prevailing one.  */
 722   for (e = prevailing->next; e; e = e->next)
 723     {
 724       if (e->node != NULL)
 725         {
 726           /* In case we prevail funcion by an alias, we can run into case
 727              that the alias has no cgraph node attached, since it was
 728              previously unused.  Create the node.  */
 729           if (!prevailing->node)
 730             {
 731               prevailing->node = cgraph_create_node (prevailing->decl);
 732               prevailing->node->alias = true;
 733             }
 734           lto_cgraph_replace_node (e->node, prevailing->node);
 735         }
 736       if (e->vnode != NULL)
 737         {
 738           if (!prevailing->vnode)
 739             {
 740               prevailing->vnode = varpool_node (prevailing->decl);
 741               prevailing->vnode->alias = true;
 742             }
 743           lto_varpool_replace_node (e->vnode, prevailing->vnode);
 744         }
 745     }
 746
 747   /* Drop all but the prevailing decl from the symtab.  */
 748   prevailing->next = NULL;
 749
 750   return 1;
 751 }
 752
 753 /* Merge cgraph nodes according to the symbol merging done by
 754    lto_symtab_merge_decls.  */
 755
 756 void
 757 lto_symtab_merge_cgraph_nodes (void)
 758 {
 759   struct cgraph_node *node;
 760   struct varpool_node *vnode;
 761   lto_symtab_maybe_init_hash_table ();
 762   htab_traverse (lto_symtab_identifiers, lto_symtab_merge_cgraph_nodes_1, NULL);
 763
 764   for (node = cgraph_nodes; node; node = node->next)
 765     if ((node->thunk.thunk_p || node->alias)
 766         && node->thunk.alias)
 767       node->thunk.alias = lto_symtab_prevailing_decl (node->thunk.alias);
 768   for (vnode = varpool_nodes; vnode; vnode = vnode->next)
 769     if (vnode->alias_of)
 770       vnode->alias_of = lto_symtab_prevailing_decl (vnode->alias_of);
 771 }
 772
 773 /* Given the decl DECL, return the prevailing decl with the same name. */
 774
 775 tree
 776 lto_symtab_prevailing_decl (tree decl)
 777 {
 778   lto_symtab_entry_t ret;
 779
 780   /* Builtins and local symbols are their own prevailing decl.  */
 781   if (!TREE_PUBLIC (decl) || is_builtin_fn (decl))
 782     return decl;
 783
 784   /* DECL_ABSTRACTs are their own prevailng decl.  */
 785   if (TREE_CODE (decl) == FUNCTION_DECL && DECL_ABSTRACT (decl))
 786     return decl;
 787
 788   /* Ensure DECL_ASSEMBLER_NAME will not set assembler name.  */
 789   gcc_assert (DECL_ASSEMBLER_NAME_SET_P (decl));
 790
 791   /* Walk through the list of candidates and return the one we merged to.  */
 792   ret = lto_symtab_get ((*targetm.asm_out.mangle_assembler_name)
 793                         (IDENTIFIER_POINTER (DECL_ASSEMBLER_NAME (decl))));
 794   if (!ret)
 795     return NULL_TREE;
 796
 797   return ret->decl;
 798 }
 799
 800 #include "gt-lto-symtab.h"