gcc/varpool.c

   1 /* Callgraph handling code.
   2    Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2010
   3    Free Software Foundation, Inc.
   4    Contributed by Jan Hubicka
   5
   6 This file is part of GCC.
   7
   8 GCC is free software; you can redistribute it and/or modify it under
   9 the terms of the GNU General Public License as published by the Free
  10 Software Foundation; either version 3, or (at your option) any later
  11 version.
  12
  13 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  14 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  15 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  16 for more details.
  17
  18 You should have received a copy of the GNU General Public License
  19 along with GCC; see the file COPYING3.  If not see
  20 <http://www.gnu.org/licenses/>.  */
  21
  22 #include "config.h"
  23 #include "system.h"
  24 #include "coretypes.h"
  25 #include "tm.h"
  26 #include "tree.h"
  27 #include "cgraph.h"
  28 #include "langhooks.h"
  29 #include "diagnostic-core.h"
  30 #include "hashtab.h"
  31 #include "ggc.h"
  32 #include "timevar.h"
  33 #include "debug.h"
  34 #include "target.h"
  35 #include "output.h"
  36 #include "gimple.h"
  37 #include "tree-flow.h"
  38 #include "flags.h"
  39
  40 /*  This file contains basic routines manipulating variable pool.
  41
  42     Varpool acts as interface in between the front-end and middle-end
  43     and drives the decision process on what variables and when are
  44     going to be compiled.
  45
  46     The varpool nodes are allocated lazily for declarations
  47     either by frontend or at callgraph construction time.
  48     All variables supposed to be output into final file needs to be
  49     explicitly marked by frontend via VARPOOL_FINALIZE_DECL function.  */
  50
  51 /* Hash table used to convert declarations into nodes.  */
  52 static GTY((param_is (struct varpool_node))) htab_t varpool_hash;
  53
  54 /* The linked list of cgraph varpool nodes.
  55    Linked via node->next pointer.  */
  56 struct varpool_node *varpool_nodes;
  57
  58 /* Queue of cgraph nodes scheduled to be lowered and output.
  59    The queue is maintained via mark_needed_node, linked via node->next_needed
  60    pointer.
  61
  62    LAST_NEEDED_NODE points to the end of queue, so it can be
  63    maintained in forward order.  GTY is needed to make it friendly to
  64    PCH.
  65
  66    During compilation we construct the queue of needed variables
  67    twice: first time it is during cgraph construction, second time it is at the
  68    end of compilation in VARPOOL_REMOVE_UNREFERENCED_DECLS so we can avoid
  69    optimized out variables being output.
  70
  71    Each variable is thus first analyzed and then later possibly output.
  72    FIRST_UNANALYZED_NODE points to first node in queue that was not analyzed
  73    yet and is moved via VARPOOL_ANALYZE_PENDING_DECLS.  */
  74
  75 struct varpool_node *varpool_nodes_queue;
  76 static GTY(()) struct varpool_node *varpool_last_needed_node;
  77 static GTY(()) struct varpool_node *varpool_first_unanalyzed_node;
  78
  79 /* Lists all assembled variables to be sent to debugger output later on.  */
  80 static GTY(()) struct varpool_node *varpool_assembled_nodes_queue;
  81
  82 /* Return name of the node used in debug output.  */
  83 const char *
  84 varpool_node_name (struct varpool_node *node)
  85 {
  86   return lang_hooks.decl_printable_name (node->decl, 2);
  87 }
  88
  89 /* Returns a hash code for P.  */
  90 static hashval_t
  91 hash_varpool_node (const void *p)
  92 {
  93   const struct varpool_node *n = (const struct varpool_node *) p;
  94   return (hashval_t) DECL_UID (n->decl);
  95 }
  96
  97 /* Returns nonzero if P1 and P2 are equal.  */
  98 static int
  99 eq_varpool_node (const void *p1, const void *p2)
 100 {
 101   const struct varpool_node *n1 =
 102     (const struct varpool_node *) p1;
 103   const struct varpool_node *n2 =
 104     (const struct varpool_node *) p2;
 105   return DECL_UID (n1->decl) == DECL_UID (n2->decl);
 106 }
 107
 108 /* Return varpool node assigned to DECL without creating new one.  */
 109 struct varpool_node *
 110 varpool_get_node (const_tree decl)
 111 {
 112   struct varpool_node key, **slot;
 113
 114   gcc_assert (TREE_CODE (decl) == VAR_DECL
 115               && (TREE_STATIC (decl) || DECL_EXTERNAL (decl)));
 116
 117   if (!varpool_hash)
 118     return NULL;
 119   key.decl = CONST_CAST2 (tree, const_tree, decl);
 120   slot = (struct varpool_node **)
 121     htab_find_slot (varpool_hash, &key, NO_INSERT);
 122   if (!slot)
 123     return NULL;
 124   return *slot;
 125 }
 126
 127 /* Return varpool node assigned to DECL.  Create new one when needed.  */
 128 struct varpool_node *
 129 varpool_node (tree decl)
 130 {
 131   struct varpool_node key, *node, **slot;
 132
 133   gcc_assert (TREE_CODE (decl) == VAR_DECL
 134               && (TREE_STATIC (decl) || DECL_EXTERNAL (decl)));
 135
 136   if (!varpool_hash)
 137     varpool_hash = htab_create_ggc (10, hash_varpool_node,
 138                                            eq_varpool_node, NULL);
 139   key.decl = decl;
 140   slot = (struct varpool_node **)
 141     htab_find_slot (varpool_hash, &key, INSERT);
 142   if (*slot)
 143     return *slot;
 144   node = ggc_alloc_cleared_varpool_node ();
 145   node->decl = decl;
 146   node->order = cgraph_order++;
 147   node->next = varpool_nodes;
 148   ipa_empty_ref_list (&node->ref_list);
 149   if (varpool_nodes)
 150     varpool_nodes->prev = node;
 151   varpool_nodes = node;
 152   *slot = node;
 153   return node;
 154 }
 155
 156 /* Remove node from the varpool.  */
 157 void
 158 varpool_remove_node (struct varpool_node *node)
 159 {
 160   void **slot;
 161   slot = htab_find_slot (varpool_hash, node, NO_INSERT);
 162   gcc_assert (*slot == node);
 163   htab_clear_slot (varpool_hash, slot);
 164   gcc_assert (!varpool_assembled_nodes_queue);
 165   if (!node->alias)
 166     while (node->extra_name)
 167       varpool_remove_node (node->extra_name);
 168   if (node->next)
 169     node->next->prev = node->prev;
 170   if (node->prev)
 171     node->prev->next = node->next;
 172   else
 173     {
 174       if (node->alias && node->extra_name)
 175         {
 176           gcc_assert (node->extra_name->extra_name == node);
 177           node->extra_name->extra_name = node->next;
 178         }
 179       else
 180         {
 181           gcc_assert (varpool_nodes == node);
 182           varpool_nodes = node->next;
 183         }
 184     }
 185   if (varpool_first_unanalyzed_node == node)
 186     varpool_first_unanalyzed_node = node->next_needed;
 187   if (node->next_needed)
 188     node->next_needed->prev_needed = node->prev_needed;
 189   else if (node->prev_needed)
 190     {
 191       gcc_assert (varpool_last_needed_node);
 192       varpool_last_needed_node = node->prev_needed;
 193     }
 194   if (node->prev_needed)
 195     node->prev_needed->next_needed = node->next_needed;
 196   else if (node->next_needed)
 197     {
 198       gcc_assert (varpool_nodes_queue == node);
 199       varpool_nodes_queue = node->next_needed;
 200     }
 201   if (node->same_comdat_group)
 202     {
 203       struct varpool_node *prev;
 204       for (prev = node->same_comdat_group;
 205            prev->same_comdat_group != node;
 206            prev = prev->same_comdat_group)
 207         ;
 208       if (node->same_comdat_group == prev)
 209         prev->same_comdat_group = NULL;
 210       else
 211         prev->same_comdat_group = node->same_comdat_group;
 212       node->same_comdat_group = NULL;
 213     }
 214   ipa_remove_all_references (&node->ref_list);
 215   ipa_remove_all_refering (&node->ref_list);
 216   ggc_free (node);
 217 }
 218
 219 /* Dump given cgraph node.  */
 220 void
 221 dump_varpool_node (FILE *f, struct varpool_node *node)
 222 {
 223   fprintf (f, "%s:", varpool_node_name (node));
 224   fprintf (f, " availability:%s",
 225            cgraph_function_flags_ready
 226            ? cgraph_availability_names[cgraph_variable_initializer_availability (node)]
 227            : "not-ready");
 228   if (DECL_ASSEMBLER_NAME_SET_P (node->decl))
 229     fprintf (f, " (asm: %s)", IDENTIFIER_POINTER (DECL_ASSEMBLER_NAME (node->decl)));
 230   if (DECL_INITIAL (node->decl))
 231     fprintf (f, " initialized");
 232   if (TREE_ASM_WRITTEN (node->decl))
 233     fprintf (f, " (asm written)");
 234   if (node->needed)
 235     fprintf (f, " needed");
 236   if (node->analyzed)
 237     fprintf (f, " analyzed");
 238   if (node->finalized)
 239     fprintf (f, " finalized");
 240   if (node->output)
 241     fprintf (f, " output");
 242   if (node->externally_visible)
 243     fprintf (f, " externally_visible");
 244   if (node->in_other_partition)
 245     fprintf (f, " in_other_partition");
 246   else if (node->used_from_other_partition)
 247     fprintf (f, " used_from_other_partition");
 248   fprintf (f, "\n");
 249   fprintf (f, "  References: ");
 250   ipa_dump_references (f, &node->ref_list);
 251   fprintf (f, "  Refering this var: ");
 252   ipa_dump_refering (f, &node->ref_list);
 253 }
 254
 255 /* Dump the variable pool.  */
 256 void
 257 dump_varpool (FILE *f)
 258 {
 259   struct varpool_node *node;
 260
 261   fprintf (f, "variable pool:\n\n");
 262   for (node = varpool_nodes; node; node = node->next)
 263     dump_varpool_node (f, node);
 264 }
 265
 266 /* Dump the variable pool to stderr.  */
 267
 268 DEBUG_FUNCTION void
 269 debug_varpool (void)
 270 {
 271   dump_varpool (stderr);
 272 }
 273
 274 /* Given an assembler name, lookup node.  */
 275 struct varpool_node *
 276 varpool_node_for_asm (tree asmname)
 277 {
 278   struct varpool_node *node;
 279
 280   for (node = varpool_nodes; node ; node = node->next)
 281     if (decl_assembler_name_equal (node->decl, asmname))
 282       return node;
 283
 284   return NULL;
 285 }
 286
 287 /* Helper function for finalization code - add node into lists so it will
 288    be analyzed and compiled.  */
 289 static void
 290 varpool_enqueue_needed_node (struct varpool_node *node)
 291 {
 292   if (varpool_last_needed_node)
 293     {
 294       varpool_last_needed_node->next_needed = node;
 295       node->prev_needed = varpool_last_needed_node;
 296     }
 297   varpool_last_needed_node = node;
 298   node->next_needed = NULL;
 299   if (!varpool_nodes_queue)
 300     varpool_nodes_queue = node;
 301   if (!varpool_first_unanalyzed_node)
 302     varpool_first_unanalyzed_node = node;
 303   notice_global_symbol (node->decl);
 304 }
 305
 306 /* Notify finalize_compilation_unit that given node is reachable
 307    or needed.  */
 308 void
 309 varpool_mark_needed_node (struct varpool_node *node)
 310 {
 311   if (node->alias && node->extra_name)
 312     node = node->extra_name;
 313   if (!node->needed && node->finalized
 314       && !TREE_ASM_WRITTEN (node->decl))
 315     varpool_enqueue_needed_node (node);
 316   node->needed = 1;
 317 }
 318
 319 /* Reset the queue of needed nodes.  */
 320 void
 321 varpool_reset_queue (void)
 322 {
 323   varpool_last_needed_node = NULL;
 324   varpool_nodes_queue = NULL;
 325   varpool_first_unanalyzed_node = NULL;
 326 }
 327
 328 /* Determine if variable DECL is needed.  That is, visible to something
 329    either outside this translation unit, something magic in the system
 330    configury */
 331 bool
 332 decide_is_variable_needed (struct varpool_node *node, tree decl)
 333 {
 334   if (node->used_from_other_partition)
 335     return true;
 336   /* If the user told us it is used, then it must be so.  */
 337   if ((node->externally_visible && !DECL_COMDAT (decl))
 338       || node->force_output)
 339     return true;
 340
 341   /* Externally visible variables must be output.  The exception is
 342      COMDAT variables that must be output only when they are needed.  */
 343   if (TREE_PUBLIC (decl)
 344       && !flag_whole_program
 345       && !flag_lto
 346       && !DECL_COMDAT (decl)
 347       && !DECL_EXTERNAL (decl))
 348     return true;
 349
 350   /* When not reordering top level variables, we have to assume that
 351      we are going to keep everything.  */
 352   if (flag_toplevel_reorder)
 353     return false;
 354
 355   /* We want to emit COMDAT variables only when absolutely necessary.  */
 356   if (DECL_COMDAT (decl))
 357     return false;
 358   return true;
 359 }
 360
 361 /* Return if DECL is constant and its initial value is known (so we can do
 362    constant folding using DECL_INITIAL (decl)).  */
 363
 364 bool
 365 const_value_known_p (tree decl)
 366 {
 367   if (TREE_CODE (decl) != VAR_DECL
 368       &&TREE_CODE (decl) != CONST_DECL)
 369     return false;
 370
 371   if (TREE_CODE (decl) == CONST_DECL
 372       || DECL_IN_CONSTANT_POOL (decl))
 373     return true;
 374
 375   gcc_assert (TREE_CODE (decl) == VAR_DECL);
 376
 377   if (!TREE_READONLY (decl))
 378     return false;
 379
 380   /* Gimplifier takes away constructors of local vars  */
 381   if (!TREE_STATIC (decl) && !DECL_EXTERNAL (decl))
 382     return DECL_INITIAL (decl) != NULL;
 383
 384   gcc_assert (TREE_STATIC (decl) || DECL_EXTERNAL (decl));
 385
 386   /* Variables declared 'const' without an initializer
 387      have zero as the initializer if they may not be
 388      overridden at link or run time.  */
 389   if (!DECL_INITIAL (decl)
 390       && (DECL_EXTERNAL (decl)
 391           || decl_replaceable_p (decl)))
 392     return false;
 393
 394   /* Variables declared `const' with an initializer are considered
 395      to not be overwritable with different initializer by default.
 396
 397      ??? Previously we behaved so for scalar variables but not for array
 398      accesses.  */
 399   return true;
 400 }
 401
 402 /* Mark DECL as finalized.  By finalizing the declaration, frontend instruct the
 403    middle end to output the variable to asm file, if needed or externally
 404    visible.  */
 405 void
 406 varpool_finalize_decl (tree decl)
 407 {
 408   struct varpool_node *node = varpool_node (decl);
 409
 410   gcc_assert (TREE_STATIC (decl));
 411
 412   /* The first declaration of a variable that comes through this function
 413      decides whether it is global (in C, has external linkage)
 414      or local (in C, has internal linkage).  So do nothing more
 415      if this function has already run.  */
 416   if (node->finalized)
 417     {
 418       if (cgraph_global_info_ready)
 419         varpool_assemble_pending_decls ();
 420       return;
 421     }
 422   if (node->needed)
 423     varpool_enqueue_needed_node (node);
 424   node->finalized = true;
 425   if (TREE_THIS_VOLATILE (decl) || DECL_PRESERVE_P (decl))
 426     node->force_output = true;
 427
 428   if (decide_is_variable_needed (node, decl))
 429     varpool_mark_needed_node (node);
 430   /* Since we reclaim unreachable nodes at the end of every language
 431      level unit, we need to be conservative about possible entry points
 432      there.  */
 433   else if (TREE_PUBLIC (decl) && !DECL_COMDAT (decl) && !DECL_EXTERNAL (decl))
 434     varpool_mark_needed_node (node);
 435   if (cgraph_global_info_ready)
 436     varpool_assemble_pending_decls ();
 437 }
 438
 439 /* Return variable availability.  See cgraph.h for description of individual
 440    return values.  */
 441 enum availability
 442 cgraph_variable_initializer_availability (struct varpool_node *node)
 443 {
 444   gcc_assert (cgraph_function_flags_ready);
 445   if (!node->finalized)
 446     return AVAIL_NOT_AVAILABLE;
 447   if (!TREE_PUBLIC (node->decl))
 448     return AVAIL_AVAILABLE;
 449   /* If the variable can be overwritten, return OVERWRITABLE.  Takes
 450      care of at least two notable extensions - the COMDAT variables
 451      used to share template instantiations in C++.  */
 452   if (!decl_replaceable_p (node->decl))
 453     return AVAIL_OVERWRITABLE;
 454   return AVAIL_AVAILABLE;
 455 }
 456
 457 /* Walk the decls we marked as necessary and see if they reference new
 458    variables or functions and add them into the worklists.  */
 459 bool
 460 varpool_analyze_pending_decls (void)
 461 {
 462   bool changed = false;
 463
 464   timevar_push (TV_VARPOOL);
 465   while (varpool_first_unanalyzed_node)
 466     {
 467       struct varpool_node *node = varpool_first_unanalyzed_node, *next;
 468       tree decl = node->decl;
 469       bool analyzed = node->analyzed;
 470
 471       varpool_first_unanalyzed_node->analyzed = true;
 472
 473       varpool_first_unanalyzed_node = varpool_first_unanalyzed_node->next_needed;
 474
 475       /* When reading back varpool at LTO time, we re-construct the queue in order
 476          to have "needed" list right by inserting all needed nodes into varpool.
 477          We however don't want to re-analyze already analyzed nodes.  */
 478       if (!analyzed)
 479         {
 480           gcc_assert (!in_lto_p || cgraph_function_flags_ready);
 481           /* Compute the alignment early so function body expanders are
 482              already informed about increased alignment.  */
 483           align_variable (decl, 0);
 484         }
 485       if (DECL_INITIAL (decl))
 486         record_references_in_initializer (decl, analyzed);
 487       if (node->same_comdat_group)
 488         {
 489           for (next = node->same_comdat_group;
 490                next != node;
 491                next = next->same_comdat_group)
 492             varpool_mark_needed_node (next);
 493         }
 494       changed = true;
 495     }
 496   timevar_pop (TV_VARPOOL);
 497   return changed;
 498 }
 499
 500 /* Output one variable, if necessary.  Return whether we output it.  */
 501 bool
 502 varpool_assemble_decl (struct varpool_node *node)
 503 {
 504   tree decl = node->decl;
 505
 506   if (!TREE_ASM_WRITTEN (decl)
 507       && !node->alias
 508       && !node->in_other_partition
 509       && !DECL_EXTERNAL (decl)
 510       && (TREE_CODE (decl) != VAR_DECL || !DECL_HAS_VALUE_EXPR_P (decl)))
 511     {
 512       assemble_variable (decl, 0, 1, 0);
 513       if (TREE_ASM_WRITTEN (decl))
 514         {
 515           struct varpool_node *alias;
 516
 517           node->next_needed = varpool_assembled_nodes_queue;
 518           node->prev_needed = NULL;
 519           if (varpool_assembled_nodes_queue)
 520             varpool_assembled_nodes_queue->prev_needed = node;
 521           varpool_assembled_nodes_queue = node;
 522           node->finalized = 1;
 523
 524           /* Also emit any extra name aliases.  */
 525           for (alias = node->extra_name; alias; alias = alias->next)
 526             {
 527               /* Update linkage fields in case they've changed.  */
 528               DECL_WEAK (alias->decl) = DECL_WEAK (decl);
 529               TREE_PUBLIC (alias->decl) = TREE_PUBLIC (decl);
 530               DECL_VISIBILITY (alias->decl) = DECL_VISIBILITY (decl);
 531               assemble_alias (alias->decl, DECL_ASSEMBLER_NAME (decl));
 532             }
 533
 534           return true;
 535         }
 536     }
 537
 538   return false;
 539 }
 540
 541 /* Optimization of function bodies might've rendered some variables as
 542    unnecessary so we want to avoid these from being compiled.
 543
 544    This is done by pruning the queue and keeping only the variables that
 545    really appear needed (ie they are either externally visible or referenced
 546    by compiled function). Re-doing the reachability analysis on variables
 547    brings back the remaining variables referenced by these.  */
 548 void
 549 varpool_remove_unreferenced_decls (void)
 550 {
 551   struct varpool_node *next, *node = varpool_nodes_queue;
 552
 553   varpool_reset_queue ();
 554
 555   if (seen_error ())
 556     return;
 557
 558   while (node)
 559     {
 560       tree decl = node->decl;
 561       next = node->next_needed;
 562       node->needed = 0;
 563
 564       if (node->finalized
 565           && (decide_is_variable_needed (node, decl)
 566               /* ??? Cgraph does not yet rule the world with an iron hand,
 567                  and does not control the emission of debug information.
 568                  After a variable has its DECL_RTL set, we must assume that
 569                  it may be referenced by the debug information, and we can
 570                  no longer elide it.  */
 571               || DECL_RTL_SET_P (decl)))
 572         varpool_mark_needed_node (node);
 573
 574       node = next;
 575     }
 576   /* Make sure we mark alias targets as used targets.  */
 577   finish_aliases_1 ();
 578   varpool_analyze_pending_decls ();
 579 }
 580
 581 /* Output all variables enqueued to be assembled.  */
 582 bool
 583 varpool_assemble_pending_decls (void)
 584 {
 585   bool changed = false;
 586
 587   if (seen_error ())
 588     return false;
 589
 590   timevar_push (TV_VAROUT);
 591   /* EH might mark decls as needed during expansion.  This should be safe since
 592      we don't create references to new function, but it should not be used
 593      elsewhere.  */
 594   varpool_analyze_pending_decls ();
 595
 596   while (varpool_nodes_queue)
 597     {
 598       struct varpool_node *node = varpool_nodes_queue;
 599
 600       varpool_nodes_queue = varpool_nodes_queue->next_needed;
 601       if (varpool_assemble_decl (node))
 602         changed = true;
 603       else
 604         {
 605           node->prev_needed = NULL;
 606           node->next_needed = NULL;
 607         }
 608     }
 609   /* varpool_nodes_queue is now empty, clear the pointer to the last element
 610      in the queue.  */
 611   varpool_last_needed_node = NULL;
 612   timevar_pop (TV_VAROUT);
 613   return changed;
 614 }
 615
 616 /* Remove all elements from the queue so we can re-use it for debug output.  */
 617 void
 618 varpool_empty_needed_queue (void)
 619 {
 620   /* EH might mark decls as needed during expansion.  This should be safe since
 621      we don't create references to new function, but it should not be used
 622      elsewhere.  */
 623   varpool_analyze_pending_decls ();
 624
 625   while (varpool_nodes_queue)
 626     {
 627       struct varpool_node *node = varpool_nodes_queue;
 628       varpool_nodes_queue = varpool_nodes_queue->next_needed;
 629       node->next_needed = NULL;
 630       node->prev_needed = NULL;
 631     }
 632   /* varpool_nodes_queue is now empty, clear the pointer to the last element
 633      in the queue.  */
 634   varpool_last_needed_node = NULL;
 635 }
 636
 637 /* Create a new global variable of type TYPE.  */
 638 tree
 639 add_new_static_var (tree type)
 640 {
 641   tree new_decl;
 642   struct varpool_node *new_node;
 643
 644   new_decl = create_tmp_var (type, NULL);
 645   DECL_NAME (new_decl) = create_tmp_var_name (NULL);
 646   TREE_READONLY (new_decl) = 0;
 647   TREE_STATIC (new_decl) = 1;
 648   TREE_USED (new_decl) = 1;
 649   DECL_CONTEXT (new_decl) = NULL_TREE;
 650   DECL_ABSTRACT (new_decl) = 0;
 651   lang_hooks.dup_lang_specific_decl (new_decl);
 652   create_var_ann (new_decl);
 653   new_node = varpool_node (new_decl);
 654   varpool_mark_needed_node (new_node);
 655   add_referenced_var (new_decl);
 656   varpool_finalize_decl (new_decl);
 657
 658   return new_node->decl;
 659 }
 660
 661 /* Attempt to mark ALIAS as an alias to DECL.  Return TRUE if successful.
 662    Extra name aliases are output whenever DECL is output.  */
 663
 664 struct varpool_node *
 665 varpool_extra_name_alias (tree alias, tree decl)
 666 {
 667   struct varpool_node key, *alias_node, *decl_node, **slot;
 668
 669 #ifndef ASM_OUTPUT_DEF
 670   /* If aliases aren't supported by the assembler, fail.  */
 671   return false;
 672 #endif
 673
 674   gcc_assert (TREE_CODE (decl) == VAR_DECL);
 675   gcc_assert (TREE_CODE (alias) == VAR_DECL);
 676   /* Make sure the hash table has been created.  */
 677   decl_node = varpool_node (decl);
 678
 679   key.decl = alias;
 680
 681   slot = (struct varpool_node **) htab_find_slot (varpool_hash, &key, INSERT);
 682
 683   /* If the varpool_node has been already created, fail.  */
 684   if (*slot)
 685     return NULL;
 686
 687   alias_node = ggc_alloc_cleared_varpool_node ();
 688   alias_node->decl = alias;
 689   alias_node->alias = 1;
 690   alias_node->extra_name = decl_node;
 691   alias_node->next = decl_node->extra_name;
 692   ipa_empty_ref_list (&alias_node->ref_list);
 693   if (decl_node->extra_name)
 694     decl_node->extra_name->prev = alias_node;
 695   decl_node->extra_name = alias_node;
 696   *slot = alias_node;
 697   return alias_node;
 698 }
 699
 700 /* Return true when NODE is known to be used from other (non-LTO) object file.
 701    Known only when doing LTO via linker plugin.  */
 702
 703 bool
 704 varpool_used_from_object_file_p (struct varpool_node *node)
 705 {
 706   struct varpool_node *alias;
 707
 708   if (!TREE_PUBLIC (node->decl))
 709     return false;
 710   if (resolution_used_from_other_file_p (node->resolution))
 711     return true;
 712   for (alias = node->extra_name; alias; alias = alias->next)
 713     if (TREE_PUBLIC (alias->decl)
 714         && resolution_used_from_other_file_p (alias->resolution))
 715       return true;
 716   return false;
 717 }
 718
 719 #include "gt-varpool.h"