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     = gimple_types_compatible_p (TREE_TYPE (TREE_TYPE (prevailing_node->decl)),
 247                                  TREE_TYPE (TREE_TYPE (node->decl)), GTC_DIAG);
 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 (!gimple_types_compatible_p (TREE_TYPE (prevailing_decl),
 364                                       TREE_TYPE (decl), GTC_DIAG))
 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   /* We have to register and fetch canonical types here as the global
 394      fixup process didn't yet run.  */
 395   prevailing_type = gimple_register_type (prevailing_type);
 396   type = gimple_register_type (type);
 397   if (!gimple_types_compatible_p (prevailing_type, type, GTC_DIAG))
 398     {
 399       if (COMPLETE_TYPE_P (type))
 400         return false;
 401
 402       /* If type is incomplete then avoid warnings in the cases
 403          that TBAA handles just fine.  */
 404
 405       if (TREE_CODE (prevailing_type) != TREE_CODE (type))
 406         return false;
 407
 408       if (TREE_CODE (prevailing_type) == ARRAY_TYPE)
 409         {
 410           tree tem1 = TREE_TYPE (prevailing_type);
 411           tree tem2 = TREE_TYPE (type);
 412           while (TREE_CODE (tem1) == ARRAY_TYPE
 413                  && TREE_CODE (tem2) == ARRAY_TYPE)
 414             {
 415               tem1 = TREE_TYPE (tem1);
 416               tem2 = TREE_TYPE (tem2);
 417             }
 418
 419           if (TREE_CODE (tem1) != TREE_CODE (tem2))
 420             return false;
 421
 422           if (!gimple_types_compatible_p (gimple_register_type (tem1),
 423                                           gimple_register_type (tem2),
 424                                           GTC_DIAG))
 425             return false;
 426         }
 427
 428       /* Fallthru.  Compatible enough.  */
 429     }
 430
 431   /* ???  We might want to emit a warning here if type qualification
 432      differences were spotted.  Do not do this unconditionally though.  */
 433
 434   /* There is no point in comparing too many details of the decls here.
 435      The type compatibility checks or the completing of types has properly
 436      dealt with most issues.  */
 437
 438   /* The following should all not invoke fatal errors as in non-LTO
 439      mode the linker wouldn't complain either.  Just emit warnings.  */
 440
 441   /* Report a warning if user-specified alignments do not match.  */
 442   if ((DECL_USER_ALIGN (prevailing_decl) && DECL_USER_ALIGN (decl))
 443       && DECL_ALIGN (prevailing_decl) < DECL_ALIGN (decl))
 444     return false;
 445
 446   return true;
 447 }
 448
 449 /* Return true if the symtab entry E can be replaced by another symtab
 450    entry.  */
 451
 452 static bool
 453 lto_symtab_resolve_replaceable_p (lto_symtab_entry_t e)
 454 {
 455   if (DECL_EXTERNAL (e->decl)
 456       || DECL_COMDAT (e->decl)
 457       || DECL_ONE_ONLY (e->decl)
 458       || DECL_WEAK (e->decl))
 459     return true;
 460
 461   if (TREE_CODE (e->decl) == VAR_DECL)
 462     return (DECL_COMMON (e->decl)
 463             || (!flag_no_common && !DECL_INITIAL (e->decl)));
 464
 465   return false;
 466 }
 467
 468 /* Return true if the symtab entry E can be the prevailing one.  */
 469
 470 static bool
 471 lto_symtab_resolve_can_prevail_p (lto_symtab_entry_t e)
 472 {
 473   /* The C++ frontend ends up neither setting TREE_STATIC nor
 474      DECL_EXTERNAL on virtual methods but only TREE_PUBLIC.
 475      So do not reject !TREE_STATIC here but only DECL_EXTERNAL.  */
 476   if (DECL_EXTERNAL (e->decl))
 477     return false;
 478
 479   /* For functions we need a non-discarded body.  */
 480   if (TREE_CODE (e->decl) == FUNCTION_DECL)
 481     return (e->node
 482             && (e->node->analyzed
 483                 || (e->node->same_body_alias && e->node->same_body->analyzed)));
 484
 485   /* A variable should have a size.  */
 486   else if (TREE_CODE (e->decl) == VAR_DECL)
 487     {
 488       if (!e->vnode)
 489         return false;
 490       if (e->vnode->finalized)
 491         return true;
 492       return e->vnode->alias && e->vnode->extra_name->finalized;
 493     }
 494
 495   gcc_unreachable ();
 496 }
 497
 498 /* Resolve the symbol with the candidates in the chain *SLOT and store
 499    their resolutions.  */
 500
 501 static void
 502 lto_symtab_resolve_symbols (void **slot)
 503 {
 504   lto_symtab_entry_t e;
 505   lto_symtab_entry_t prevailing = NULL;
 506
 507   /* Always set e->node so that edges are updated to reflect decl merging. */
 508   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 509     {
 510       if (TREE_CODE (e->decl) == FUNCTION_DECL)
 511         e->node = cgraph_get_node_or_alias (e->decl);
 512       else if (TREE_CODE (e->decl) == VAR_DECL)
 513         e->vnode = varpool_get_node (e->decl);
 514     }
 515
 516   e = (lto_symtab_entry_t) *slot;
 517
 518   /* If the chain is already resolved there is nothing else to do.  */
 519   if (e->resolution != LDPR_UNKNOWN)
 520     return;
 521
 522   /* Find the single non-replaceable prevailing symbol and
 523      diagnose ODR violations.  */
 524   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 525     {
 526       if (!lto_symtab_resolve_can_prevail_p (e))
 527         {
 528           e->resolution = LDPR_RESOLVED_IR;
 529           e->guessed = true;
 530           continue;
 531         }
 532
 533       /* Set a default resolution - the final prevailing one will get
 534          adjusted later.  */
 535       e->resolution = LDPR_PREEMPTED_IR;
 536       e->guessed = true;
 537       if (!lto_symtab_resolve_replaceable_p (e))
 538         {
 539           if (prevailing)
 540             {
 541               error_at (DECL_SOURCE_LOCATION (e->decl),
 542                         "%qD has already been defined", e->decl);
 543               inform (DECL_SOURCE_LOCATION (prevailing->decl),
 544                       "previously defined here");
 545             }
 546           prevailing = e;
 547         }
 548     }
 549   if (prevailing)
 550     goto found;
 551
 552   /* Do a second round choosing one from the replaceable prevailing decls.  */
 553   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 554     {
 555       if (e->resolution != LDPR_PREEMPTED_IR)
 556         continue;
 557
 558       /* Choose the first function that can prevail as prevailing.  */
 559       if (TREE_CODE (e->decl) == FUNCTION_DECL)
 560         {
 561           prevailing = e;
 562           break;
 563         }
 564
 565       /* From variables that can prevail choose the largest one.  */
 566       if (!prevailing
 567           || tree_int_cst_lt (DECL_SIZE (prevailing->decl),
 568                               DECL_SIZE (e->decl)))
 569         prevailing = e;
 570     }
 571
 572   if (!prevailing)
 573     return;
 574
 575 found:
 576   /* If current lto files represent the whole program,
 577     it is correct to use LDPR_PREVALING_DEF_IRONLY.
 578     If current lto files are part of whole program, internal
 579     resolver doesn't know if it is LDPR_PREVAILING_DEF
 580     or LDPR_PREVAILING_DEF_IRONLY.  Use IRONLY conforms to
 581     using -fwhole-program.  Otherwise, it doesn't
 582     matter using either LDPR_PREVAILING_DEF or
 583     LDPR_PREVAILING_DEF_IRONLY
 584
 585     FIXME: above workaround due to gold plugin makes some
 586     variables IRONLY, which are indeed PREVAILING_DEF in
 587     resolution file.  These variables still need manual
 588     externally_visible attribute.  */
 589     prevailing->resolution = LDPR_PREVAILING_DEF_IRONLY;
 590     prevailing->guessed = true;
 591 }
 592
 593 /* Merge all decls in the symbol table chain to the prevailing decl and
 594    issue diagnostics about type mismatches.  If DIAGNOSED_P is true
 595    do not issue further diagnostics.*/
 596
 597 static void
 598 lto_symtab_merge_decls_2 (void **slot, bool diagnosed_p)
 599 {
 600   lto_symtab_entry_t prevailing, e;
 601   VEC(tree, heap) *mismatches = NULL;
 602   unsigned i;
 603   tree decl;
 604
 605   /* Nothing to do for a single entry.  */
 606   prevailing = (lto_symtab_entry_t) *slot;
 607   if (!prevailing->next)
 608     return;
 609
 610   /* Try to merge each entry with the prevailing one.  */
 611   for (e = prevailing->next; e; e = e->next)
 612     {
 613       if (!lto_symtab_merge (prevailing, e)
 614           && !diagnosed_p)
 615         VEC_safe_push (tree, heap, mismatches, e->decl);
 616     }
 617   if (VEC_empty (tree, mismatches))
 618     return;
 619
 620   /* Diagnose all mismatched re-declarations.  */
 621   FOR_EACH_VEC_ELT (tree, mismatches, i, decl)
 622     {
 623       if (!gimple_types_compatible_p (TREE_TYPE (prevailing->decl),
 624                                       TREE_TYPE (decl), GTC_DIAG))
 625         diagnosed_p |= warning_at (DECL_SOURCE_LOCATION (decl), 0,
 626                                    "type of %qD does not match original "
 627                                    "declaration", decl);
 628
 629       else if ((DECL_USER_ALIGN (prevailing->decl) && DECL_USER_ALIGN (decl))
 630                && DECL_ALIGN (prevailing->decl) < DECL_ALIGN (decl))
 631         {
 632           diagnosed_p |= warning_at (DECL_SOURCE_LOCATION (decl), 0,
 633                                      "alignment of %qD is bigger than "
 634                                      "original declaration", decl);
 635         }
 636     }
 637   if (diagnosed_p)
 638     inform (DECL_SOURCE_LOCATION (prevailing->decl),
 639             "previously declared here");
 640
 641   VEC_free (tree, heap, mismatches);
 642 }
 643
 644 /* Helper to process the decl chain for the symbol table entry *SLOT.  */
 645
 646 static int
 647 lto_symtab_merge_decls_1 (void **slot, void *data ATTRIBUTE_UNUSED)
 648 {
 649   lto_symtab_entry_t e, prevailing;
 650   bool diagnosed_p = false;
 651
 652   /* Compute the symbol resolutions.  This is a no-op when using the
 653      linker plugin.  */
 654   lto_symtab_resolve_symbols (slot);
 655
 656   /* Find the prevailing decl.  */
 657   for (prevailing = (lto_symtab_entry_t) *slot;
 658        prevailing
 659        && prevailing->resolution != LDPR_PREVAILING_DEF_IRONLY
 660        && prevailing->resolution != LDPR_PREVAILING_DEF;
 661        prevailing = prevailing->next)
 662     ;
 663
 664   /* Assert it's the only one.  */
 665   if (prevailing)
 666     for (e = prevailing->next; e; e = e->next)
 667       {
 668         if (e->resolution == LDPR_PREVAILING_DEF_IRONLY
 669             || e->resolution == LDPR_PREVAILING_DEF)
 670           fatal_error ("multiple prevailing defs for %qE",
 671                        DECL_NAME (prevailing->decl));
 672       }
 673
 674   /* If there's not a prevailing symbol yet it's an external reference.
 675      Happens a lot during ltrans.  Choose the first symbol with a
 676      cgraph or a varpool node.  */
 677   if (!prevailing)
 678     {
 679       prevailing = (lto_symtab_entry_t) *slot;
 680       /* For functions choose one with a cgraph node.  */
 681       if (TREE_CODE (prevailing->decl) == FUNCTION_DECL)
 682         while (!prevailing->node
 683                && prevailing->next)
 684           prevailing = prevailing->next;
 685       /* For variables chose with a priority variant with vnode
 686          attached (i.e. from unit where external declaration of
 687          variable is actually used).
 688          When there are multiple variants, chose one with size.
 689          This is needed for C++ typeinfos, for example in
 690          lto/20081204-1 there are typeifos in both units, just
 691          one of them do have size.  */
 692       if (TREE_CODE (prevailing->decl) == VAR_DECL)
 693         {
 694           for (e = prevailing->next; e; e = e->next)
 695             if ((!prevailing->vnode && e->vnode)
 696                 || ((prevailing->vnode != NULL) == (e->vnode != NULL)
 697                     && !COMPLETE_TYPE_P (TREE_TYPE (prevailing->decl))
 698                     && COMPLETE_TYPE_P (TREE_TYPE (e->decl))))
 699               prevailing = e;
 700         }
 701     }
 702
 703   /* Move it first in the list.  */
 704   if ((lto_symtab_entry_t) *slot != prevailing)
 705     {
 706       for (e = (lto_symtab_entry_t) *slot; e->next != prevailing; e = e->next)
 707         ;
 708       e->next = prevailing->next;
 709       prevailing->next = (lto_symtab_entry_t) *slot;
 710       *slot = (void *) prevailing;
 711     }
 712
 713   /* Record the prevailing variable.  */
 714   if (TREE_CODE (prevailing->decl) == VAR_DECL)
 715     VEC_safe_push (tree, gc, lto_global_var_decls, prevailing->decl);
 716
 717   /* Diagnose mismatched objects.  */
 718   for (e = prevailing->next; e; e = e->next)
 719     {
 720       if (TREE_CODE (prevailing->decl) == TREE_CODE (e->decl))
 721         continue;
 722
 723       switch (TREE_CODE (prevailing->decl))
 724         {
 725         case VAR_DECL:
 726           gcc_assert (TREE_CODE (e->decl) == FUNCTION_DECL);
 727           error_at (DECL_SOURCE_LOCATION (e->decl),
 728                     "variable %qD redeclared as function", prevailing->decl);
 729           break;
 730
 731         case FUNCTION_DECL:
 732           gcc_assert (TREE_CODE (e->decl) == VAR_DECL);
 733           error_at (DECL_SOURCE_LOCATION (e->decl),
 734                     "function %qD redeclared as variable", prevailing->decl);
 735           break;
 736
 737         default:
 738           gcc_unreachable ();
 739         }
 740
 741       diagnosed_p = true;
 742     }
 743   if (diagnosed_p)
 744       inform (DECL_SOURCE_LOCATION (prevailing->decl),
 745               "previously declared here");
 746
 747   /* Register and adjust types of the entries.  */
 748   for (e = (lto_symtab_entry_t) *slot; e; e = e->next)
 749     TREE_TYPE (e->decl) = gimple_register_type (TREE_TYPE (e->decl));
 750
 751   /* Merge the chain to the single prevailing decl and diagnose
 752      mismatches.  */
 753   lto_symtab_merge_decls_2 (slot, diagnosed_p);
 754
 755   /* Store resolution decision into the callgraph.
 756      In LTRANS don't overwrite information we stored into callgraph at
 757      WPA stage.
 758
 759      Do not bother to store guessed decisions.  Generic code knows how
 760      to handle UNKNOWN relocation well.
 761
 762      The problem with storing guessed decision is whether to use
 763      PREVAILING_DEF or PREVAILING_DEF_IRONLY.  First one would disable
 764      some whole program optimizations, while ther second would imply
 765      to many whole program assumptions.  */
 766   if (prevailing->node && !flag_ltrans && !prevailing->guessed)
 767     prevailing->node->resolution = prevailing->resolution;
 768   else if (prevailing->vnode && !flag_ltrans && !prevailing->guessed)
 769     prevailing->vnode->resolution = prevailing->resolution;
 770   return 1;
 771 }
 772
 773 /* Resolve and merge all symbol table chains to a prevailing decl.  */
 774
 775 void
 776 lto_symtab_merge_decls (void)
 777 {
 778   lto_symtab_maybe_init_hash_table ();
 779   htab_traverse (lto_symtab_identifiers, lto_symtab_merge_decls_1, NULL);
 780 }
 781
 782 /* Helper to process the decl chain for the symbol table entry *SLOT.  */
 783
 784 static int
 785 lto_symtab_merge_cgraph_nodes_1 (void **slot, void *data ATTRIBUTE_UNUSED)
 786 {
 787   lto_symtab_entry_t e, prevailing = (lto_symtab_entry_t) *slot;
 788
 789   if (!prevailing->next)
 790     return 1;
 791
 792   /* Replace the cgraph node of each entry with the prevailing one.  */
 793   for (e = prevailing->next; e; e = e->next)
 794     {
 795       if (e->node != NULL)
 796         {
 797           /* In case we prevail funcion by an alias, we can run into case
 798              that the alias has no cgraph node attached, since it was
 799              previously unused.  Create the node.  */
 800           if (!prevailing->node)
 801             {
 802               prevailing->node = cgraph_create_node (prevailing->decl);
 803               prevailing->node->alias = true;
 804             }
 805           lto_cgraph_replace_node (e->node, prevailing->node);
 806         }
 807       if (e->vnode != NULL)
 808         {
 809           if (!prevailing->vnode)
 810             {
 811               prevailing->vnode = varpool_node (prevailing->decl);
 812               prevailing->vnode->alias = true;
 813             }
 814           lto_varpool_replace_node (e->vnode, prevailing->vnode);
 815         }
 816     }
 817
 818   /* Drop all but the prevailing decl from the symtab.  */
 819   prevailing->next = NULL;
 820
 821   return 1;
 822 }
 823
 824 /* Merge cgraph nodes according to the symbol merging done by
 825    lto_symtab_merge_decls.  */
 826
 827 void
 828 lto_symtab_merge_cgraph_nodes (void)
 829 {
 830   struct cgraph_node *node, *alias, *next;
 831   lto_symtab_maybe_init_hash_table ();
 832   htab_traverse (lto_symtab_identifiers, lto_symtab_merge_cgraph_nodes_1, NULL);
 833
 834   for (node = cgraph_nodes; node; node = node->next)
 835     for (alias = node->same_body; alias; alias = next)
 836       {
 837         next = alias->next;
 838         alias->thunk.alias = lto_symtab_prevailing_decl (alias->thunk.alias);
 839       }
 840 }
 841
 842 /* Given the decl DECL, return the prevailing decl with the same name. */
 843
 844 tree
 845 lto_symtab_prevailing_decl (tree decl)
 846 {
 847   lto_symtab_entry_t ret;
 848
 849   /* Builtins and local symbols are their own prevailing decl.  */
 850   if (!TREE_PUBLIC (decl) || is_builtin_fn (decl))
 851     return decl;
 852
 853   /* DECL_ABSTRACTs are their own prevailng decl.  */
 854   if (TREE_CODE (decl) == FUNCTION_DECL && DECL_ABSTRACT (decl))
 855     return decl;
 856
 857   /* Ensure DECL_ASSEMBLER_NAME will not set assembler name.  */
 858   gcc_assert (DECL_ASSEMBLER_NAME_SET_P (decl));
 859
 860   /* Walk through the list of candidates and return the one we merged to.  */
 861   ret = lto_symtab_get ((*targetm.asm_out.mangle_assembler_name)
 862                         (IDENTIFIER_POINTER (DECL_ASSEMBLER_NAME (decl))));
 863   if (!ret)
 864     return NULL_TREE;
 865
 866   return ret->decl;
 867 }
 868
 869 #include "gt-lto-symtab.h"