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 no_aliases_please = false;
 213   bool compatible_p;
 214
 215   if (cgraph_dump_file)
 216     {
 217       fprintf (cgraph_dump_file, "Replacing cgraph node %s/%i by %s/%i"
 218                " for symbol %s\n",
 219                cgraph_node_name (node), node->uid,
 220                cgraph_node_name (prevailing_node),
 221                prevailing_node->uid,
 222                IDENTIFIER_POINTER ((*targetm.asm_out.mangle_assembler_name)
 223                  (IDENTIFIER_POINTER (DECL_ASSEMBLER_NAME (node->decl)))));
 224     }
 225
 226   if (prevailing_node->same_body_alias)
 227     {
 228       if (prevailing_node->thunk.thunk_p)
 229         no_aliases_please = true;
 230       prevailing_node = prevailing_node->same_body;
 231     }
 232
 233   /* Merge node flags.  */
 234   if (node->needed)
 235     cgraph_mark_needed_node (prevailing_node);
 236   if (node->reachable)
 237     cgraph_mark_reachable_node (prevailing_node);
 238   if (node->address_taken)
 239     {
 240       gcc_assert (!prevailing_node->global.inlined_to);
 241       cgraph_mark_address_taken_node (prevailing_node);
 242     }
 243
 244   /* Redirect all incoming edges.  */
 245   compatible_p
 246     = types_compatible_p (TREE_TYPE (TREE_TYPE (prevailing_node->decl)),
 247                           TREE_TYPE (TREE_TYPE (node->decl)));
 248   for (e = node->callers; e; e = next)
 249     {
 250       next = e->next_caller;
 251       cgraph_redirect_edge_callee (e, prevailing_node);
 252       /* If there is a mismatch between the supposed callee return type and
 253          the real one do not attempt to inline this function.
 254          ???  We really need a way to match function signatures for ABI
 255          compatibility and perform related promotions at inlining time.  */
 256       if (!compatible_p)
 257         e->call_stmt_cannot_inline_p = 1;
 258     }
 259   /* Redirect incomming references.  */
 260   ipa_clone_refering (prevailing_node, NULL, &node->ref_list);
 261
 262   /* If we have aliases, redirect them to the prevailing node.  */
 263   if (!node->same_body_alias && node->same_body)
 264     {
 265       struct cgraph_node *alias, *last;
 266       /* We prevail aliases/tunks by a thunk.  This is doable but
 267          would need thunk combination.  Hopefully no ABI changes will
 268          every be crazy enough.  */
 269       gcc_assert (!no_aliases_please);
 270
 271       for (alias = node->same_body; alias; alias = alias->next)
 272         {
 273           last = alias;
 274           gcc_assert (alias->same_body_alias);
 275           alias->same_body = prevailing_node;
 276         }
 277       last->next = prevailing_node->same_body;
 278       /* Node with aliases is prevailed by alias.
 279          We could handle this, but combining thunks together will be tricky.
 280          Hopefully this does not happen.  */
 281       if (prevailing_node->same_body)
 282         prevailing_node->same_body->previous = last;
 283       prevailing_node->same_body = node->same_body;
 284       node->same_body = NULL;
 285     }
 286
 287   /* Finally remove the replaced node.  */
 288   if (node->same_body_alias)
 289     cgraph_remove_same_body_alias (node);
 290   else
 291     cgraph_remove_node (node);
 292 }
 293
 294 /* Replace the cgraph node NODE with PREVAILING_NODE in the cgraph, merging
 295    all edges and removing the old node.  */
 296
 297 static void
 298 lto_varpool_replace_node (struct varpool_node *vnode,
 299                           struct varpool_node *prevailing_node)
 300 {
 301   /* Merge node flags.  */
 302   if (vnode->needed)
 303     {
 304       gcc_assert (!vnode->analyzed || prevailing_node->analyzed);
 305       varpool_mark_needed_node (prevailing_node);
 306     }
 307   /* Relink aliases.  */
 308   if (vnode->extra_name && !vnode->alias)
 309     {
 310       struct varpool_node *alias, *last;
 311       for (alias = vnode->extra_name;
 312            alias; alias = alias->next)
 313         {
 314           last = alias;
 315           alias->extra_name = prevailing_node;
 316         }
 317
 318       if (prevailing_node->extra_name)
 319         {
 320           last->next = prevailing_node->extra_name;
 321           prevailing_node->extra_name->prev = last;
 322         }
 323       prevailing_node->extra_name = vnode->extra_name;
 324       vnode->extra_name = NULL;
 325     }
 326   gcc_assert (!vnode->finalized || prevailing_node->finalized);
 327   gcc_assert (!vnode->analyzed || prevailing_node->analyzed);
 328
 329   /* When replacing by an alias, the references goes to the original
 330      variable.  */
 331   if (prevailing_node->alias && prevailing_node->extra_name)
 332     prevailing_node = prevailing_node->extra_name;
 333   ipa_clone_refering (NULL, prevailing_node, &vnode->ref_list);
 334
 335   /* Be sure we can garbage collect the initializer.  */
 336   if (DECL_INITIAL (vnode->decl))
 337     DECL_INITIAL (vnode->decl) = error_mark_node;
 338   /* Finally remove the replaced node.  */
 339   varpool_remove_node (vnode);
 340 }
 341
 342 /* Merge two variable or function symbol table entries PREVAILING and ENTRY.
 343    Return false if the symbols are not fully compatible and a diagnostic
 344    should be emitted.  */
 345
 346 static bool
 347 lto_symtab_merge (lto_symtab_entry_t prevailing, lto_symtab_entry_t entry)
 348 {
 349   tree prevailing_decl = prevailing->decl;
 350   tree decl = entry->decl;
 351   tree prevailing_type, type;
 352
 353   /* Merge decl state in both directions, we may still end up using
 354      the new decl.  */
 355   TREE_ADDRESSABLE (prevailing_decl) |= TREE_ADDRESSABLE (decl);
 356   TREE_ADDRESSABLE (decl) |= TREE_ADDRESSABLE (prevailing_decl);
 357
 358   /* The linker may ask us to combine two incompatible symbols.
 359      Detect this case and notify the caller of required diagnostics.  */
 360
 361   if (TREE_CODE (decl) == FUNCTION_DECL)
 362     {
 363       if (!types_compatible_p (TREE_TYPE (prevailing_decl),
 364                                TREE_TYPE (decl)))
 365         /* If we don't have a merged type yet...sigh.  The linker
 366            wouldn't complain if the types were mismatched, so we
 367            probably shouldn't either.  Just use the type from
 368            whichever decl appears to be associated with the
 369            definition.  If for some odd reason neither decl is, the
 370            older one wins.  */
 371         (void) 0;
 372
 373       return true;
 374     }
 375
 376   /* Now we exclusively deal with VAR_DECLs.  */
 377
 378   /* Sharing a global symbol is a strong hint that two types are
 379      compatible.  We could use this information to complete
 380      incomplete pointed-to types more aggressively here, ignoring
 381      mismatches in both field and tag names.  It's difficult though
 382      to guarantee that this does not have side-effects on merging
 383      more compatible types from other translation units though.  */
 384
 385   /* We can tolerate differences in type qualification, the
 386      qualification of the prevailing definition will prevail.
 387      ???  In principle we might want to only warn for structurally
 388      incompatible types here, but unless we have protective measures
 389      for TBAA in place that would hide useful information.  */
 390   prevailing_type = TYPE_MAIN_VARIANT (TREE_TYPE (prevailing_decl));
 391   type = TYPE_MAIN_VARIANT (TREE_TYPE (decl));
 392
 393   if (!types_compatible_p (prevailing_type, type))
 394     {
 395       if (COMPLETE_TYPE_P (type))
 396         return false;
 397
 398       /* If type is incomplete then avoid warnings in the cases
 399          that TBAA handles just fine.  */
 400
 401       if (TREE_CODE (prevailing_type) != TREE_CODE (type))
 402         return false;
 403
 404       if (TREE_CODE (prevailing_type) == ARRAY_TYPE)
 405         {
 406           tree tem1 = TREE_TYPE (prevailing_type);
 407           tree tem2 = TREE_TYPE (type);
 408           while (TREE_CODE (tem1) == ARRAY_TYPE
 409                  && TREE_CODE (tem2) == ARRAY_TYPE)
 410             {
 411               tem1 = TREE_TYPE (tem1);
 412               tem2 = TREE_TYPE (tem2);
 413             }
 414
 415           if (TREE_CODE (tem1) != TREE_CODE (tem2))
 416             return false;
 417
 418           if (!types_compatible_p (tem1, tem2))
 419             return false;
 420         }
 421
 422       /* Fallthru.  Compatible enough.  */
 423     }
 424
 425   /* ???  We might want to emit a warning here if type qualification
 426      differences were spotted.  Do not do this unconditionally though.  */
 427
 428   /* There is no point in comparing too many details of the decls here.
 429      The type compatibility checks or the completing of types has properly
 430      dealt with most issues.  */
 431
 432   /* The following should all not invoke fatal errors as in non-LTO
 433      mode the linker wouldn't complain either.  Just emit warnings.  */
 434
 435   /* Report a warning if user-specified alignments do not match.  */
 436   if ((DECL_USER_ALIGN (prevailing_decl) && DECL_USER_ALIGN (decl))
 437       && DECL_ALIGN (prevailing_decl) < DECL_ALIGN (decl))
 438     return false;
 439
 440   return true;
 441 }
 442
 443 /* Return true if the symtab entry E can be replaced by another symtab
 444    entry.  */
 445
 446 static bool
 447 lto_symtab_resolve_replaceable_p (lto_symtab_entry_t e)
 448 {
 449   if (DECL_EXTERNAL (e->decl)
 450       || DECL_COMDAT (e->decl)
 451       || DECL_ONE_ONLY (e->decl)
 452       || DECL_WEAK (e->decl))
 453     return true;
 454
 455   if (TREE_CODE (e->decl) == VAR_DECL)
 456     return (DECL_COMMON (e->decl)
 457             || (!flag_no_common && !DECL_INITIAL (e->decl)));
 458
 459   return false;
 460 }
 461
 462 /* Return true if the symtab entry E can be the prevailing one.  */
 463
 464 static bool
 465 lto_symtab_resolve_can_prevail_p (lto_symtab_entry_t e)
 466 {
 467   /* The C++ frontend ends up neither setting TREE_STATIC nor
 468      DECL_EXTERNAL on virtual methods but only TREE_PUBLIC.
 469      So do not reject !TREE_STATIC here but only DECL_EXTERNAL.  */
 470   if (DECL_EXTERNAL (e->decl))
 471     return false;
 472
 473   /* For functions we need a non-discarded body.  */
 474   if (TREE_CODE (e->decl) == FUNCTION_DECL)
 475     return (e->node
 476             && (e->node->analyzed
 477                 || (e->node->same_body_alias && e->node->same_body->analyzed)));
 478
 479   /* A variable should have a size.  */
 480   else if (TREE_CODE (e->decl) == VAR_DECL)
 481     {
 482       if (!e->vnode)
 483         return false;
 484       if (e->vnode->finalized)
 485         return true;
 486       return e->vnode->alias && e->vnode->extra_name->finalized;
 487     }
 488
 489   gcc_unreachable ();
 490 }
 491
 492 /* Resolve the symbol with the candidates in the chain *SLOT and store
 493    their resolutions.  */
 494
 495 static void
 496 lto_symtab_resolve_symbols (void **slot)
 497 {
 498   lto_symtab_entry_t e;
 499   lto_symtab_entry_t prevailing = NULL;
 500
 501   /* Always set e->node so that edges are updated to reflect decl merging. */
 502   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 503     {
 504       if (TREE_CODE (e->decl) == FUNCTION_DECL)
 505         e->node = cgraph_get_node_or_alias (e->decl);
 506       else if (TREE_CODE (e->decl) == VAR_DECL)
 507         e->vnode = varpool_get_node (e->decl);
 508     }
 509
 510   e = (lto_symtab_entry_t) *slot;
 511
 512   /* If the chain is already resolved there is nothing else to do.  */
 513   if (e->resolution != LDPR_UNKNOWN)
 514     return;
 515
 516   /* Find the single non-replaceable prevailing symbol and
 517      diagnose ODR violations.  */
 518   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 519     {
 520       if (!lto_symtab_resolve_can_prevail_p (e))
 521         {
 522           e->resolution = LDPR_RESOLVED_IR;
 523           e->guessed = true;
 524           continue;
 525         }
 526
 527       /* Set a default resolution - the final prevailing one will get
 528          adjusted later.  */
 529       e->resolution = LDPR_PREEMPTED_IR;
 530       e->guessed = true;
 531       if (!lto_symtab_resolve_replaceable_p (e))
 532         {
 533           if (prevailing)
 534             {
 535               error_at (DECL_SOURCE_LOCATION (e->decl),
 536                         "%qD has already been defined", e->decl);
 537               inform (DECL_SOURCE_LOCATION (prevailing->decl),
 538                       "previously defined here");
 539             }
 540           prevailing = e;
 541         }
 542     }
 543   if (prevailing)
 544     goto found;
 545
 546   /* Do a second round choosing one from the replaceable prevailing decls.  */
 547   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 548     {
 549       if (e->resolution != LDPR_PREEMPTED_IR)
 550         continue;
 551
 552       /* Choose the first function that can prevail as prevailing.  */
 553       if (TREE_CODE (e->decl) == FUNCTION_DECL)
 554         {
 555           prevailing = e;
 556           break;
 557         }
 558
 559       /* From variables that can prevail choose the largest one.  */
 560       if (!prevailing
 561           || tree_int_cst_lt (DECL_SIZE (prevailing->decl),
 562                               DECL_SIZE (e->decl)))
 563         prevailing = e;
 564     }
 565
 566   if (!prevailing)
 567     return;
 568
 569 found:
 570   /* If current lto files represent the whole program,
 571     it is correct to use LDPR_PREVALING_DEF_IRONLY.
 572     If current lto files are part of whole program, internal
 573     resolver doesn't know if it is LDPR_PREVAILING_DEF
 574     or LDPR_PREVAILING_DEF_IRONLY.  Use IRONLY conforms to
 575     using -fwhole-program.  Otherwise, it doesn't
 576     matter using either LDPR_PREVAILING_DEF or
 577     LDPR_PREVAILING_DEF_IRONLY
 578
 579     FIXME: above workaround due to gold plugin makes some
 580     variables IRONLY, which are indeed PREVAILING_DEF in
 581     resolution file.  These variables still need manual
 582     externally_visible attribute.  */
 583     prevailing->resolution = LDPR_PREVAILING_DEF_IRONLY;
 584     prevailing->guessed = true;
 585 }
 586
 587 /* Merge all decls in the symbol table chain to the prevailing decl and
 588    issue diagnostics about type mismatches.  If DIAGNOSED_P is true
 589    do not issue further diagnostics.*/
 590
 591 static void
 592 lto_symtab_merge_decls_2 (void **slot, bool diagnosed_p)
 593 {
 594   lto_symtab_entry_t prevailing, e;
 595   VEC(tree, heap) *mismatches = NULL;
 596   unsigned i;
 597   tree decl;
 598
 599   /* Nothing to do for a single entry.  */
 600   prevailing = (lto_symtab_entry_t) *slot;
 601   if (!prevailing->next)
 602     return;
 603
 604   /* Try to merge each entry with the prevailing one.  */
 605   for (e = prevailing->next; e; e = e->next)
 606     {
 607       if (!lto_symtab_merge (prevailing, e)
 608           && !diagnosed_p)
 609         VEC_safe_push (tree, heap, mismatches, e->decl);
 610     }
 611   if (VEC_empty (tree, mismatches))
 612     return;
 613
 614   /* Diagnose all mismatched re-declarations.  */
 615   FOR_EACH_VEC_ELT (tree, mismatches, i, decl)
 616     {
 617       if (!types_compatible_p (TREE_TYPE (prevailing->decl), TREE_TYPE (decl)))
 618         diagnosed_p |= warning_at (DECL_SOURCE_LOCATION (decl), 0,
 619                                    "type of %qD does not match original "
 620                                    "declaration", decl);
 621
 622       else if ((DECL_USER_ALIGN (prevailing->decl) && DECL_USER_ALIGN (decl))
 623                && DECL_ALIGN (prevailing->decl) < DECL_ALIGN (decl))
 624         {
 625           diagnosed_p |= warning_at (DECL_SOURCE_LOCATION (decl), 0,
 626                                      "alignment of %qD is bigger than "
 627                                      "original declaration", decl);
 628         }
 629     }
 630   if (diagnosed_p)
 631     inform (DECL_SOURCE_LOCATION (prevailing->decl),
 632             "previously declared here");
 633
 634   VEC_free (tree, heap, mismatches);
 635 }
 636
 637 /* Helper to process the decl chain for the symbol table entry *SLOT.  */
 638
 639 static int
 640 lto_symtab_merge_decls_1 (void **slot, void *data ATTRIBUTE_UNUSED)
 641 {
 642   lto_symtab_entry_t e, prevailing;
 643   bool diagnosed_p = false;
 644
 645   /* Compute the symbol resolutions.  This is a no-op when using the
 646      linker plugin.  */
 647   lto_symtab_resolve_symbols (slot);
 648
 649   /* Find the prevailing decl.  */
 650   for (prevailing = (lto_symtab_entry_t) *slot;
 651        prevailing
 652        && prevailing->resolution != LDPR_PREVAILING_DEF_IRONLY
 653        && prevailing->resolution != LDPR_PREVAILING_DEF;
 654        prevailing = prevailing->next)
 655     ;
 656
 657   /* Assert it's the only one.  */
 658   if (prevailing)
 659     for (e = prevailing->next; e; e = e->next)
 660       {
 661         if (e->resolution == LDPR_PREVAILING_DEF_IRONLY
 662             || e->resolution == LDPR_PREVAILING_DEF)
 663           fatal_error ("multiple prevailing defs for %qE",
 664                        DECL_NAME (prevailing->decl));
 665       }
 666
 667   /* If there's not a prevailing symbol yet it's an external reference.
 668      Happens a lot during ltrans.  Choose the first symbol with a
 669      cgraph or a varpool node.  */
 670   if (!prevailing)
 671     {
 672       prevailing = (lto_symtab_entry_t) *slot;
 673       /* For functions choose one with a cgraph node.  */
 674       if (TREE_CODE (prevailing->decl) == FUNCTION_DECL)
 675         while (!prevailing->node
 676                && prevailing->next)
 677           prevailing = prevailing->next;
 678       /* For variables chose with a priority variant with vnode
 679          attached (i.e. from unit where external declaration of
 680          variable is actually used).
 681          When there are multiple variants, chose one with size.
 682          This is needed for C++ typeinfos, for example in
 683          lto/20081204-1 there are typeifos in both units, just
 684          one of them do have size.  */
 685       if (TREE_CODE (prevailing->decl) == VAR_DECL)
 686         {
 687           for (e = prevailing->next; e; e = e->next)
 688             if ((!prevailing->vnode && e->vnode)
 689                 || ((prevailing->vnode != NULL) == (e->vnode != NULL)
 690                     && !COMPLETE_TYPE_P (TREE_TYPE (prevailing->decl))
 691                     && COMPLETE_TYPE_P (TREE_TYPE (e->decl))))
 692               prevailing = e;
 693         }
 694     }
 695
 696   /* Move it first in the list.  */
 697   if ((lto_symtab_entry_t) *slot != prevailing)
 698     {
 699       for (e = (lto_symtab_entry_t) *slot; e->next != prevailing; e = e->next)
 700         ;
 701       e->next = prevailing->next;
 702       prevailing->next = (lto_symtab_entry_t) *slot;
 703       *slot = (void *) prevailing;
 704     }
 705
 706   /* Record the prevailing variable.  */
 707   if (TREE_CODE (prevailing->decl) == VAR_DECL)
 708     VEC_safe_push (tree, gc, lto_global_var_decls, prevailing->decl);
 709
 710   /* Diagnose mismatched objects.  */
 711   for (e = prevailing->next; e; e = e->next)
 712     {
 713       if (TREE_CODE (prevailing->decl) == TREE_CODE (e->decl))
 714         continue;
 715
 716       switch (TREE_CODE (prevailing->decl))
 717         {
 718         case VAR_DECL:
 719           gcc_assert (TREE_CODE (e->decl) == FUNCTION_DECL);
 720           error_at (DECL_SOURCE_LOCATION (e->decl),
 721                     "variable %qD redeclared as function", prevailing->decl);
 722           break;
 723
 724         case FUNCTION_DECL:
 725           gcc_assert (TREE_CODE (e->decl) == VAR_DECL);
 726           error_at (DECL_SOURCE_LOCATION (e->decl),
 727                     "function %qD redeclared as variable", prevailing->decl);
 728           break;
 729
 730         default:
 731           gcc_unreachable ();
 732         }
 733
 734       diagnosed_p = true;
 735     }
 736   if (diagnosed_p)
 737       inform (DECL_SOURCE_LOCATION (prevailing->decl),
 738               "previously declared here");
 739
 740   /* Merge the chain to the single prevailing decl and diagnose
 741      mismatches.  */
 742   lto_symtab_merge_decls_2 (slot, diagnosed_p);
 743
 744   /* Store resolution decision into the callgraph.
 745      In LTRANS don't overwrite information we stored into callgraph at
 746      WPA stage.
 747
 748      Do not bother to store guessed decisions.  Generic code knows how
 749      to handle UNKNOWN relocation well.
 750
 751      The problem with storing guessed decision is whether to use
 752      PREVAILING_DEF or PREVAILING_DEF_IRONLY.  First one would disable
 753      some whole program optimizations, while ther second would imply
 754      to many whole program assumptions.  */
 755   if (prevailing->node && !flag_ltrans && !prevailing->guessed)
 756     prevailing->node->resolution = prevailing->resolution;
 757   else if (prevailing->vnode && !flag_ltrans && !prevailing->guessed)
 758     prevailing->vnode->resolution = prevailing->resolution;
 759   return 1;
 760 }
 761
 762 /* Resolve and merge all symbol table chains to a prevailing decl.  */
 763
 764 void
 765 lto_symtab_merge_decls (void)
 766 {
 767   lto_symtab_maybe_init_hash_table ();
 768   htab_traverse (lto_symtab_identifiers, lto_symtab_merge_decls_1, NULL);
 769 }
 770
 771 /* Helper to process the decl chain for the symbol table entry *SLOT.  */
 772
 773 static int
 774 lto_symtab_merge_cgraph_nodes_1 (void **slot, void *data ATTRIBUTE_UNUSED)
 775 {
 776   lto_symtab_entry_t e, prevailing = (lto_symtab_entry_t) *slot;
 777
 778   if (!prevailing->next)
 779     return 1;
 780
 781   /* Replace the cgraph node of each entry with the prevailing one.  */
 782   for (e = prevailing->next; e; e = e->next)
 783     {
 784       if (e->node != NULL)
 785         {
 786           /* In case we prevail funcion by an alias, we can run into case
 787              that the alias has no cgraph node attached, since it was
 788              previously unused.  Create the node.  */
 789           if (!prevailing->node)
 790             {
 791               prevailing->node = cgraph_create_node (prevailing->decl);
 792               prevailing->node->alias = true;
 793             }
 794           lto_cgraph_replace_node (e->node, prevailing->node);
 795         }
 796       if (e->vnode != NULL)
 797         {
 798           if (!prevailing->vnode)
 799             {
 800               prevailing->vnode = varpool_node (prevailing->decl);
 801               prevailing->vnode->alias = true;
 802             }
 803           lto_varpool_replace_node (e->vnode, prevailing->vnode);
 804         }
 805     }
 806
 807   /* Drop all but the prevailing decl from the symtab.  */
 808   prevailing->next = NULL;
 809
 810   return 1;
 811 }
 812
 813 /* Merge cgraph nodes according to the symbol merging done by
 814    lto_symtab_merge_decls.  */
 815
 816 void
 817 lto_symtab_merge_cgraph_nodes (void)
 818 {
 819   struct cgraph_node *node, *alias, *next;
 820   lto_symtab_maybe_init_hash_table ();
 821   htab_traverse (lto_symtab_identifiers, lto_symtab_merge_cgraph_nodes_1, NULL);
 822
 823   for (node = cgraph_nodes; node; node = node->next)
 824     {
 825       if (node->thunk.thunk_p)
 826         node->thunk.alias = lto_symtab_prevailing_decl (node->thunk.alias);
 827       for (alias = node->same_body; alias; alias = next)
 828         {
 829           next = alias->next;
 830           alias->thunk.alias = lto_symtab_prevailing_decl (alias->thunk.alias);
 831         }
 832     }
 833 }
 834
 835 /* Given the decl DECL, return the prevailing decl with the same name. */
 836
 837 tree
 838 lto_symtab_prevailing_decl (tree decl)
 839 {
 840   lto_symtab_entry_t ret;
 841
 842   /* Builtins and local symbols are their own prevailing decl.  */
 843   if (!TREE_PUBLIC (decl) || is_builtin_fn (decl))
 844     return decl;
 845
 846   /* DECL_ABSTRACTs are their own prevailng decl.  */
 847   if (TREE_CODE (decl) == FUNCTION_DECL && DECL_ABSTRACT (decl))
 848     return decl;
 849
 850   /* Ensure DECL_ASSEMBLER_NAME will not set assembler name.  */
 851   gcc_assert (DECL_ASSEMBLER_NAME_SET_P (decl));
 852
 853   /* Walk through the list of candidates and return the one we merged to.  */
 854   ret = lto_symtab_get ((*targetm.asm_out.mangle_assembler_name)
 855                         (IDENTIFIER_POINTER (DECL_ASSEMBLER_NAME (decl))));
 856   if (!ret)
 857     return NULL_TREE;
 858
 859   return ret->decl;
 860 }
 861
 862 #include "gt-lto-symtab.h"