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->symbol.force_output)
 227     cgraph_mark_force_output_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_referring ((symtab_node)prevailing_node, &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   gcc_assert (!vnode->finalized || prevailing_node->finalized);
 266   gcc_assert (!vnode->analyzed || prevailing_node->analyzed);
 267
 268   ipa_clone_referring ((symtab_node)prevailing_node, &vnode->symbol.ref_list);
 269
 270   /* Be sure we can garbage collect the initializer.  */
 271   if (DECL_INITIAL (vnode->symbol.decl))
 272     DECL_INITIAL (vnode->symbol.decl) = error_mark_node;
 273   /* Finally remove the replaced node.  */
 274   varpool_remove_node (vnode);
 275 }
 276
 277 /* Merge two variable or function symbol table entries PREVAILING and ENTRY.
 278    Return false if the symbols are not fully compatible and a diagnostic
 279    should be emitted.  */
 280
 281 static bool
 282 lto_symtab_merge (lto_symtab_entry_t prevailing, lto_symtab_entry_t entry)
 283 {
 284   tree prevailing_decl = prevailing->decl;
 285   tree decl = entry->decl;
 286   tree prevailing_type, type;
 287
 288   /* Merge decl state in both directions, we may still end up using
 289      the new decl.  */
 290   TREE_ADDRESSABLE (prevailing_decl) |= TREE_ADDRESSABLE (decl);
 291   TREE_ADDRESSABLE (decl) |= TREE_ADDRESSABLE (prevailing_decl);
 292
 293   /* The linker may ask us to combine two incompatible symbols.
 294      Detect this case and notify the caller of required diagnostics.  */
 295
 296   if (TREE_CODE (decl) == FUNCTION_DECL)
 297     {
 298       if (!types_compatible_p (TREE_TYPE (prevailing_decl),
 299                                TREE_TYPE (decl)))
 300         /* If we don't have a merged type yet...sigh.  The linker
 301            wouldn't complain if the types were mismatched, so we
 302            probably shouldn't either.  Just use the type from
 303            whichever decl appears to be associated with the
 304            definition.  If for some odd reason neither decl is, the
 305            older one wins.  */
 306         (void) 0;
 307
 308       return true;
 309     }
 310
 311   /* Now we exclusively deal with VAR_DECLs.  */
 312
 313   /* Sharing a global symbol is a strong hint that two types are
 314      compatible.  We could use this information to complete
 315      incomplete pointed-to types more aggressively here, ignoring
 316      mismatches in both field and tag names.  It's difficult though
 317      to guarantee that this does not have side-effects on merging
 318      more compatible types from other translation units though.  */
 319
 320   /* We can tolerate differences in type qualification, the
 321      qualification of the prevailing definition will prevail.
 322      ???  In principle we might want to only warn for structurally
 323      incompatible types here, but unless we have protective measures
 324      for TBAA in place that would hide useful information.  */
 325   prevailing_type = TYPE_MAIN_VARIANT (TREE_TYPE (prevailing_decl));
 326   type = TYPE_MAIN_VARIANT (TREE_TYPE (decl));
 327
 328   if (!types_compatible_p (prevailing_type, type))
 329     {
 330       if (COMPLETE_TYPE_P (type))
 331         return false;
 332
 333       /* If type is incomplete then avoid warnings in the cases
 334          that TBAA handles just fine.  */
 335
 336       if (TREE_CODE (prevailing_type) != TREE_CODE (type))
 337         return false;
 338
 339       if (TREE_CODE (prevailing_type) == ARRAY_TYPE)
 340         {
 341           tree tem1 = TREE_TYPE (prevailing_type);
 342           tree tem2 = TREE_TYPE (type);
 343           while (TREE_CODE (tem1) == ARRAY_TYPE
 344                  && TREE_CODE (tem2) == ARRAY_TYPE)
 345             {
 346               tem1 = TREE_TYPE (tem1);
 347               tem2 = TREE_TYPE (tem2);
 348             }
 349
 350           if (TREE_CODE (tem1) != TREE_CODE (tem2))
 351             return false;
 352
 353           if (!types_compatible_p (tem1, tem2))
 354             return false;
 355         }
 356
 357       /* Fallthru.  Compatible enough.  */
 358     }
 359
 360   /* ???  We might want to emit a warning here if type qualification
 361      differences were spotted.  Do not do this unconditionally though.  */
 362
 363   /* There is no point in comparing too many details of the decls here.
 364      The type compatibility checks or the completing of types has properly
 365      dealt with most issues.  */
 366
 367   /* The following should all not invoke fatal errors as in non-LTO
 368      mode the linker wouldn't complain either.  Just emit warnings.  */
 369
 370   /* Report a warning if user-specified alignments do not match.  */
 371   if ((DECL_USER_ALIGN (prevailing_decl) && DECL_USER_ALIGN (decl))
 372       && DECL_ALIGN (prevailing_decl) < DECL_ALIGN (decl))
 373     return false;
 374
 375   return true;
 376 }
 377
 378 /* Return true if the symtab entry E can be replaced by another symtab
 379    entry.  */
 380
 381 static bool
 382 lto_symtab_resolve_replaceable_p (lto_symtab_entry_t e)
 383 {
 384   if (DECL_EXTERNAL (e->decl)
 385       || DECL_COMDAT (e->decl)
 386       || DECL_ONE_ONLY (e->decl)
 387       || DECL_WEAK (e->decl))
 388     return true;
 389
 390   if (TREE_CODE (e->decl) == VAR_DECL)
 391     return (DECL_COMMON (e->decl)
 392             || (!flag_no_common && !DECL_INITIAL (e->decl)));
 393
 394   return false;
 395 }
 396
 397 /* Return true if the symtab entry E can be the prevailing one.  */
 398
 399 static bool
 400 lto_symtab_resolve_can_prevail_p (lto_symtab_entry_t e)
 401 {
 402   /* The C++ frontend ends up neither setting TREE_STATIC nor
 403      DECL_EXTERNAL on virtual methods but only TREE_PUBLIC.
 404      So do not reject !TREE_STATIC here but only DECL_EXTERNAL.  */
 405   if (DECL_EXTERNAL (e->decl))
 406     return false;
 407
 408   /* For functions we need a non-discarded body.  */
 409   if (TREE_CODE (e->decl) == FUNCTION_DECL)
 410     return (e->node && e->node->analyzed);
 411
 412   else if (TREE_CODE (e->decl) == VAR_DECL)
 413     {
 414       if (!e->vnode)
 415         return false;
 416       return e->vnode->finalized;
 417     }
 418
 419   gcc_unreachable ();
 420 }
 421
 422 /* Resolve the symbol with the candidates in the chain *SLOT and store
 423    their resolutions.  */
 424
 425 static void
 426 lto_symtab_resolve_symbols (void **slot)
 427 {
 428   lto_symtab_entry_t e;
 429   lto_symtab_entry_t prevailing = NULL;
 430
 431   /* Always set e->node so that edges are updated to reflect decl merging. */
 432   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 433     {
 434       if (TREE_CODE (e->decl) == FUNCTION_DECL)
 435         e->node = cgraph_get_node (e->decl);
 436       else if (TREE_CODE (e->decl) == VAR_DECL)
 437         e->vnode = varpool_get_node (e->decl);
 438       if (e->resolution == LDPR_PREVAILING_DEF_IRONLY
 439           || e->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP
 440           || e->resolution == LDPR_PREVAILING_DEF)
 441         prevailing = e;
 442     }
 443
 444   /* If the chain is already resolved there is nothing else to do.  */
 445   if (prevailing)
 446     return;
 447
 448   /* Find the single non-replaceable prevailing symbol and
 449      diagnose ODR violations.  */
 450   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 451     {
 452       if (!lto_symtab_resolve_can_prevail_p (e))
 453         {
 454           e->resolution = LDPR_RESOLVED_IR;
 455           e->guessed = true;
 456           continue;
 457         }
 458
 459       /* Set a default resolution - the final prevailing one will get
 460          adjusted later.  */
 461       e->resolution = LDPR_PREEMPTED_IR;
 462       e->guessed = true;
 463       if (!lto_symtab_resolve_replaceable_p (e))
 464         {
 465           if (prevailing)
 466             {
 467               error_at (DECL_SOURCE_LOCATION (e->decl),
 468                         "%qD has already been defined", e->decl);
 469               inform (DECL_SOURCE_LOCATION (prevailing->decl),
 470                       "previously defined here");
 471             }
 472           prevailing = e;
 473         }
 474     }
 475   if (prevailing)
 476     goto found;
 477
 478   /* Do a second round choosing one from the replaceable prevailing decls.  */
 479   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 480     {
 481       if (e->resolution != LDPR_PREEMPTED_IR)
 482         continue;
 483
 484       /* Choose the first function that can prevail as prevailing.  */
 485       if (TREE_CODE (e->decl) == FUNCTION_DECL)
 486         {
 487           prevailing = e;
 488           break;
 489         }
 490
 491       /* From variables that can prevail choose the largest one.  */
 492       if (!prevailing
 493           || tree_int_cst_lt (DECL_SIZE (prevailing->decl),
 494                               DECL_SIZE (e->decl)))
 495         prevailing = e;
 496     }
 497
 498   if (!prevailing)
 499     return;
 500
 501 found:
 502   /* If current lto files represent the whole program,
 503     it is correct to use LDPR_PREVALING_DEF_IRONLY.
 504     If current lto files are part of whole program, internal
 505     resolver doesn't know if it is LDPR_PREVAILING_DEF
 506     or LDPR_PREVAILING_DEF_IRONLY.  Use IRONLY conforms to
 507     using -fwhole-program.  Otherwise, it doesn't
 508     matter using either LDPR_PREVAILING_DEF or
 509     LDPR_PREVAILING_DEF_IRONLY
 510
 511     FIXME: above workaround due to gold plugin makes some
 512     variables IRONLY, which are indeed PREVAILING_DEF in
 513     resolution file.  These variables still need manual
 514     externally_visible attribute.  */
 515     prevailing->resolution = LDPR_PREVAILING_DEF_IRONLY;
 516     prevailing->guessed = true;
 517 }
 518
 519 /* Merge all decls in the symbol table chain to the prevailing decl and
 520    issue diagnostics about type mismatches.  If DIAGNOSED_P is true
 521    do not issue further diagnostics.*/
 522
 523 static void
 524 lto_symtab_merge_decls_2 (void **slot, bool diagnosed_p)
 525 {
 526   lto_symtab_entry_t prevailing, e;
 527   VEC(tree, heap) *mismatches = NULL;
 528   unsigned i;
 529   tree decl;
 530
 531   /* Nothing to do for a single entry.  */
 532   prevailing = (lto_symtab_entry_t) *slot;
 533   if (!prevailing->next)
 534     return;
 535
 536   /* Try to merge each entry with the prevailing one.  */
 537   for (e = prevailing->next; e; e = e->next)
 538     {
 539       if (!lto_symtab_merge (prevailing, e)
 540           && !diagnosed_p)
 541         VEC_safe_push (tree, heap, mismatches, e->decl);
 542     }
 543   if (VEC_empty (tree, mismatches))
 544     return;
 545
 546   /* Diagnose all mismatched re-declarations.  */
 547   FOR_EACH_VEC_ELT (tree, mismatches, i, decl)
 548     {
 549       if (!types_compatible_p (TREE_TYPE (prevailing->decl), TREE_TYPE (decl)))
 550         diagnosed_p |= warning_at (DECL_SOURCE_LOCATION (decl), 0,
 551                                    "type of %qD does not match original "
 552                                    "declaration", decl);
 553
 554       else if ((DECL_USER_ALIGN (prevailing->decl) && DECL_USER_ALIGN (decl))
 555                && DECL_ALIGN (prevailing->decl) < DECL_ALIGN (decl))
 556         {
 557           diagnosed_p |= warning_at (DECL_SOURCE_LOCATION (decl), 0,
 558                                      "alignment of %qD is bigger than "
 559                                      "original declaration", decl);
 560         }
 561     }
 562   if (diagnosed_p)
 563     inform (DECL_SOURCE_LOCATION (prevailing->decl),
 564             "previously declared here");
 565
 566   VEC_free (tree, heap, mismatches);
 567 }
 568
 569 /* Helper to process the decl chain for the symbol table entry *SLOT.  */
 570
 571 static int
 572 lto_symtab_merge_decls_1 (void **slot, void *data ATTRIBUTE_UNUSED)
 573 {
 574   lto_symtab_entry_t e, prevailing;
 575   bool diagnosed_p = false;
 576
 577   /* Compute the symbol resolutions.  This is a no-op when using the
 578      linker plugin.  */
 579   lto_symtab_resolve_symbols (slot);
 580
 581   /* Find the prevailing decl.  */
 582   for (prevailing = (lto_symtab_entry_t) *slot;
 583        prevailing
 584        && prevailing->resolution != LDPR_PREVAILING_DEF_IRONLY
 585        && prevailing->resolution != LDPR_PREVAILING_DEF_IRONLY_EXP
 586        && prevailing->resolution != LDPR_PREVAILING_DEF;
 587        prevailing = prevailing->next)
 588     ;
 589
 590   /* Assert it's the only one.  */
 591   if (prevailing)
 592     for (e = prevailing->next; e; e = e->next)
 593       {
 594         if (e->resolution == LDPR_PREVAILING_DEF_IRONLY
 595             || e->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP
 596             || e->resolution == LDPR_PREVAILING_DEF)
 597           fatal_error ("multiple prevailing defs for %qE",
 598                        DECL_NAME (prevailing->decl));
 599       }
 600
 601   /* If there's not a prevailing symbol yet it's an external reference.
 602      Happens a lot during ltrans.  Choose the first symbol with a
 603      cgraph or a varpool node.  */
 604   if (!prevailing)
 605     {
 606       prevailing = (lto_symtab_entry_t) *slot;
 607       /* For functions choose one with a cgraph node.  */
 608       if (TREE_CODE (prevailing->decl) == FUNCTION_DECL)
 609         while (!prevailing->node
 610                && prevailing->next)
 611           prevailing = prevailing->next;
 612       /* For variables chose with a priority variant with vnode
 613          attached (i.e. from unit where external declaration of
 614          variable is actually used).
 615          When there are multiple variants, chose one with size.
 616          This is needed for C++ typeinfos, for example in
 617          lto/20081204-1 there are typeifos in both units, just
 618          one of them do have size.  */
 619       if (TREE_CODE (prevailing->decl) == VAR_DECL)
 620         {
 621           for (e = prevailing->next; e; e = e->next)
 622             if ((!prevailing->vnode && e->vnode)
 623                 || ((prevailing->vnode != NULL) == (e->vnode != NULL)
 624                     && !COMPLETE_TYPE_P (TREE_TYPE (prevailing->decl))
 625                     && COMPLETE_TYPE_P (TREE_TYPE (e->decl))))
 626               prevailing = e;
 627         }
 628     }
 629
 630   /* Move it first in the list.  */
 631   if ((lto_symtab_entry_t) *slot != prevailing)
 632     {
 633       for (e = (lto_symtab_entry_t) *slot; e->next != prevailing; e = e->next)
 634         ;
 635       e->next = prevailing->next;
 636       prevailing->next = (lto_symtab_entry_t) *slot;
 637       *slot = (void *) prevailing;
 638     }
 639
 640   /* Record the prevailing variable.  */
 641   if (TREE_CODE (prevailing->decl) == VAR_DECL)
 642     VEC_safe_push (tree, gc, lto_global_var_decls, prevailing->decl);
 643
 644   /* Diagnose mismatched objects.  */
 645   for (e = prevailing->next; e; e = e->next)
 646     {
 647       if (TREE_CODE (prevailing->decl) == TREE_CODE (e->decl))
 648         continue;
 649
 650       switch (TREE_CODE (prevailing->decl))
 651         {
 652         case VAR_DECL:
 653           gcc_assert (TREE_CODE (e->decl) == FUNCTION_DECL);
 654           error_at (DECL_SOURCE_LOCATION (e->decl),
 655                     "variable %qD redeclared as function", prevailing->decl);
 656           break;
 657
 658         case FUNCTION_DECL:
 659           gcc_assert (TREE_CODE (e->decl) == VAR_DECL);
 660           error_at (DECL_SOURCE_LOCATION (e->decl),
 661                     "function %qD redeclared as variable", prevailing->decl);
 662           break;
 663
 664         default:
 665           gcc_unreachable ();
 666         }
 667
 668       diagnosed_p = true;
 669     }
 670   if (diagnosed_p)
 671       inform (DECL_SOURCE_LOCATION (prevailing->decl),
 672               "previously declared here");
 673
 674   /* Merge the chain to the single prevailing decl and diagnose
 675      mismatches.  */
 676   lto_symtab_merge_decls_2 (slot, diagnosed_p);
 677
 678   /* Store resolution decision into the callgraph.
 679      In LTRANS don't overwrite information we stored into callgraph at
 680      WPA stage.
 681
 682      Do not bother to store guessed decisions.  Generic code knows how
 683      to handle UNKNOWN relocation well.
 684
 685      The problem with storing guessed decision is whether to use
 686      PREVAILING_DEF, PREVAILING_DEF_IRONLY, PREVAILING_DEF_IRONLY_EXP.
 687      First one would disable some whole program optimizations, while
 688      ther second would imply to many whole program assumptions.  */
 689   if (prevailing->node && !flag_ltrans && !prevailing->guessed)
 690     prevailing->node->symbol.resolution = prevailing->resolution;
 691   else if (prevailing->vnode && !flag_ltrans && !prevailing->guessed)
 692     prevailing->vnode->symbol.resolution = prevailing->resolution;
 693   return 1;
 694 }
 695
 696 /* Resolve and merge all symbol table chains to a prevailing decl.  */
 697
 698 void
 699 lto_symtab_merge_decls (void)
 700 {
 701   lto_symtab_maybe_init_hash_table ();
 702   htab_traverse (lto_symtab_identifiers, lto_symtab_merge_decls_1, NULL);
 703 }
 704
 705 /* Helper to process the decl chain for the symbol table entry *SLOT.  */
 706
 707 static int
 708 lto_symtab_merge_cgraph_nodes_1 (void **slot, void *data ATTRIBUTE_UNUSED)
 709 {
 710   lto_symtab_entry_t e, prevailing = (lto_symtab_entry_t) *slot;
 711
 712   if (!prevailing->next)
 713     return 1;
 714
 715   /* Replace the cgraph node of each entry with the prevailing one.  */
 716   for (e = prevailing->next; e; e = e->next)
 717     {
 718       if (e->node != NULL)
 719         {
 720           /* In case we prevail funcion by an alias, we can run into case
 721              that the alias has no cgraph node attached, since it was
 722              previously unused.  Create the node.  */
 723           if (!prevailing->node)
 724             {
 725               prevailing->node = cgraph_create_node (prevailing->decl);
 726               prevailing->node->alias = true;
 727             }
 728           lto_cgraph_replace_node (e->node, prevailing->node);
 729         }
 730       if (e->vnode != NULL)
 731         {
 732           if (!prevailing->vnode)
 733             {
 734               prevailing->vnode = varpool_node (prevailing->decl);
 735               prevailing->vnode->alias = true;
 736             }
 737           lto_varpool_replace_node (e->vnode, prevailing->vnode);
 738         }
 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   struct cgraph_node *node;
 754   struct varpool_node *vnode;
 755   lto_symtab_maybe_init_hash_table ();
 756   htab_traverse (lto_symtab_identifiers, lto_symtab_merge_cgraph_nodes_1, NULL);
 757
 758   FOR_EACH_FUNCTION (node)
 759     if ((node->thunk.thunk_p || node->alias)
 760         && node->thunk.alias)
 761       node->thunk.alias = lto_symtab_prevailing_decl (node->thunk.alias);
 762   FOR_EACH_VARIABLE (vnode)
 763     if (vnode->alias_of)
 764       vnode->alias_of = lto_symtab_prevailing_decl (vnode->alias_of);
 765 }
 766
 767 /* Given the decl DECL, return the prevailing decl with the same name. */
 768
 769 tree
 770 lto_symtab_prevailing_decl (tree decl)
 771 {
 772   lto_symtab_entry_t ret;
 773
 774   /* Builtins and local symbols are their own prevailing decl.  */
 775   if (!TREE_PUBLIC (decl) || is_builtin_fn (decl))
 776     return decl;
 777
 778   /* DECL_ABSTRACTs are their own prevailng decl.  */
 779   if (TREE_CODE (decl) == FUNCTION_DECL && DECL_ABSTRACT (decl))
 780     return decl;
 781
 782   /* Ensure DECL_ASSEMBLER_NAME will not set assembler name.  */
 783   gcc_assert (DECL_ASSEMBLER_NAME_SET_P (decl));
 784
 785   /* Walk through the list of candidates and return the one we merged to.  */
 786   ret = lto_symtab_get ((*targetm.asm_out.mangle_assembler_name)
 787                         (IDENTIFIER_POINTER (DECL_ASSEMBLER_NAME (decl))));
 788   if (!ret)
 789     return NULL_TREE;
 790
 791   return ret->decl;
 792 }
 793
 794 #include "gt-lto-symtab.h"