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.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 (tree decl)
 111 {
 112   struct varpool_node key, **slot;
 113
 114   gcc_assert (DECL_P (decl) && TREE_CODE (decl) != FUNCTION_DECL);
 115
 116   if (!varpool_hash)
 117     return NULL;
 118   key.decl = decl;
 119   slot = (struct varpool_node **)
 120     htab_find_slot (varpool_hash, &key, INSERT);
 121   return *slot;
 122 }
 123
 124 /* Return varpool node assigned to DECL.  Create new one when needed.  */
 125 struct varpool_node *
 126 varpool_node (tree decl)
 127 {
 128   struct varpool_node key, *node, **slot;
 129
 130   gcc_assert (DECL_P (decl) && TREE_CODE (decl) != FUNCTION_DECL);
 131
 132   if (!varpool_hash)
 133     varpool_hash = htab_create_ggc (10, hash_varpool_node,
 134                                            eq_varpool_node, NULL);
 135   key.decl = decl;
 136   slot = (struct varpool_node **)
 137     htab_find_slot (varpool_hash, &key, INSERT);
 138   if (*slot)
 139     return *slot;
 140   node = GGC_CNEW (struct varpool_node);
 141   node->decl = decl;
 142   node->order = cgraph_order++;
 143   node->next = varpool_nodes;
 144   ipa_empty_ref_list (&node->ref_list);
 145   if (varpool_nodes)
 146     varpool_nodes->prev = node;
 147   varpool_nodes = node;
 148   *slot = node;
 149   return node;
 150 }
 151
 152 /* Remove node from the varpool.  */
 153 void
 154 varpool_remove_node (struct varpool_node *node)
 155 {
 156   void **slot;
 157   slot = htab_find_slot (varpool_hash, node, NO_INSERT);
 158   gcc_assert (*slot == node);
 159   htab_clear_slot (varpool_hash, slot);
 160   gcc_assert (!varpool_assembled_nodes_queue);
 161   if (!node->alias)
 162     while (node->extra_name)
 163       varpool_remove_node (node->extra_name);
 164   if (node->next)
 165     node->next->prev = node->prev;
 166   if (node->prev)
 167     node->prev->next = node->next;
 168   else
 169     {
 170       if (node->alias)
 171         {
 172           gcc_assert (node->extra_name->extra_name == node);
 173           node->extra_name->extra_name = node->next;
 174         }
 175       else
 176         {
 177           gcc_assert (varpool_nodes == node);
 178           varpool_nodes = node->next;
 179         }
 180     }
 181   if (varpool_first_unanalyzed_node == node)
 182     varpool_first_unanalyzed_node = node->next_needed;
 183   if (node->next_needed)
 184     node->next_needed->prev_needed = node->prev_needed;
 185   else if (node->prev_needed)
 186     {
 187       gcc_assert (varpool_last_needed_node);
 188       varpool_last_needed_node = node->prev_needed;
 189     }
 190   if (node->prev_needed)
 191     node->prev_needed->next_needed = node->next_needed;
 192   else if (node->next_needed)
 193     {
 194       gcc_assert (varpool_nodes_queue == node);
 195       varpool_nodes_queue = node->next_needed;
 196     }
 197   ipa_remove_all_references (&node->ref_list);
 198   ipa_remove_all_refering (&node->ref_list);
 199   ggc_free (node);
 200 }
 201
 202 /* Dump given cgraph node.  */
 203 void
 204 dump_varpool_node (FILE *f, struct varpool_node *node)
 205 {
 206   fprintf (f, "%s:", varpool_node_name (node));
 207   fprintf (f, " availability:%s",
 208            cgraph_function_flags_ready
 209            ? cgraph_availability_names[cgraph_variable_initializer_availability (node)]
 210            : "not-ready");
 211   if (DECL_ASSEMBLER_NAME_SET_P (node->decl))
 212     fprintf (f, " (asm: %s)", IDENTIFIER_POINTER (DECL_ASSEMBLER_NAME (node->decl)));
 213   if (DECL_INITIAL (node->decl))
 214     fprintf (f, " initialized");
 215   if (TREE_ASM_WRITTEN (node->decl))
 216     fprintf (f, " (asm written)");
 217   if (node->needed)
 218     fprintf (f, " needed");
 219   if (node->analyzed)
 220     fprintf (f, " analyzed");
 221   if (node->finalized)
 222     fprintf (f, " finalized");
 223   if (node->output)
 224     fprintf (f, " output");
 225   if (node->externally_visible)
 226     fprintf (f, " externally_visible");
 227   if (node->in_other_partition)
 228     fprintf (f, " in_other_partition");
 229   else if (node->used_from_other_partition)
 230     fprintf (f, " used_from_other_partition");
 231   fprintf (f, "\n");
 232   fprintf (f, "  References: ");
 233   ipa_dump_references (f, &node->ref_list);
 234   fprintf (f, "  Refering this var: ");
 235   ipa_dump_refering (f, &node->ref_list);
 236 }
 237
 238 /* Dump the variable pool.  */
 239 void
 240 dump_varpool (FILE *f)
 241 {
 242   struct varpool_node *node;
 243
 244   fprintf (f, "variable pool:\n\n");
 245   for (node = varpool_nodes; node; node = node->next)
 246     dump_varpool_node (f, node);
 247 }
 248
 249 /* Dump the variable pool to stderr.  */
 250
 251 void
 252 debug_varpool (void)
 253 {
 254   dump_varpool (stderr);
 255 }
 256
 257 /* Given an assembler name, lookup node.  */
 258 struct varpool_node *
 259 varpool_node_for_asm (tree asmname)
 260 {
 261   struct varpool_node *node;
 262
 263   for (node = varpool_nodes; node ; node = node->next)
 264     if (decl_assembler_name_equal (node->decl, asmname))
 265       return node;
 266
 267   return NULL;
 268 }
 269
 270 /* Helper function for finalization code - add node into lists so it will
 271    be analyzed and compiled.  */
 272 static void
 273 varpool_enqueue_needed_node (struct varpool_node *node)
 274 {
 275   if (varpool_last_needed_node)
 276     {
 277       varpool_last_needed_node->next_needed = node;
 278       node->prev_needed = varpool_last_needed_node;
 279     }
 280   varpool_last_needed_node = node;
 281   node->next_needed = NULL;
 282   if (!varpool_nodes_queue)
 283     varpool_nodes_queue = node;
 284   if (!varpool_first_unanalyzed_node)
 285     varpool_first_unanalyzed_node = node;
 286   notice_global_symbol (node->decl);
 287 }
 288
 289 /* Notify finalize_compilation_unit that given node is reachable
 290    or needed.  */
 291 void
 292 varpool_mark_needed_node (struct varpool_node *node)
 293 {
 294   if (node->alias && node->extra_name)
 295     node = node->extra_name;
 296   if (!node->needed && node->finalized
 297       && !TREE_ASM_WRITTEN (node->decl))
 298     varpool_enqueue_needed_node (node);
 299   node->needed = 1;
 300 }
 301
 302 /* Reset the queue of needed nodes.  */
 303 void
 304 varpool_reset_queue (void)
 305 {
 306   varpool_last_needed_node = NULL;
 307   varpool_nodes_queue = NULL;
 308   varpool_first_unanalyzed_node = NULL;
 309 }
 310
 311 /* Determine if variable DECL is needed.  That is, visible to something
 312    either outside this translation unit, something magic in the system
 313    configury */
 314 bool
 315 decide_is_variable_needed (struct varpool_node *node, tree decl)
 316 {
 317   if (node->used_from_other_partition)
 318     return true;
 319   /* If the user told us it is used, then it must be so.  */
 320   if ((node->externally_visible && !DECL_COMDAT (decl))
 321       || node->force_output)
 322     return true;
 323
 324   /* ??? If the assembler name is set by hand, it is possible to assemble
 325      the name later after finalizing the function and the fact is noticed
 326      in assemble_name then.  This is arguably a bug.  */
 327   if (DECL_ASSEMBLER_NAME_SET_P (decl)
 328       && TREE_SYMBOL_REFERENCED (DECL_ASSEMBLER_NAME (decl)))
 329     return true;
 330
 331   /* Externally visible variables must be output.  The exception is
 332      COMDAT variables that must be output only when they are needed.  */
 333   if (TREE_PUBLIC (decl)
 334       && !flag_whole_program
 335       && !flag_lto
 336       && !flag_whopr
 337       && !DECL_COMDAT (decl)
 338       && !DECL_EXTERNAL (decl))
 339     return true;
 340
 341   /* When emulating tls, we actually see references to the control
 342      variable, rather than the user-level variable.  */
 343   if (!targetm.have_tls
 344       && TREE_CODE (decl) == VAR_DECL
 345       && DECL_THREAD_LOCAL_P (decl))
 346     {
 347       tree control = emutls_decl (decl);
 348       if (decide_is_variable_needed (varpool_node (control), control))
 349         return true;
 350     }
 351
 352   /* When not reordering top level variables, we have to assume that
 353      we are going to keep everything.  */
 354   if (flag_toplevel_reorder)
 355     return false;
 356
 357   /* We want to emit COMDAT variables only when absolutely necessary.  */
 358   if (DECL_COMDAT (decl))
 359     return false;
 360   return true;
 361 }
 362
 363 /* Mark DECL as finalized.  By finalizing the declaration, frontend instruct the
 364    middle end to output the variable to asm file, if needed or externally
 365    visible.  */
 366 void
 367 varpool_finalize_decl (tree decl)
 368 {
 369   struct varpool_node *node = varpool_node (decl);
 370
 371   /* The first declaration of a variable that comes through this function
 372      decides whether it is global (in C, has external linkage)
 373      or local (in C, has internal linkage).  So do nothing more
 374      if this function has already run.  */
 375   if (node->finalized)
 376     {
 377       if (cgraph_global_info_ready)
 378         varpool_assemble_pending_decls ();
 379       return;
 380     }
 381   if (node->needed)
 382     varpool_enqueue_needed_node (node);
 383   node->finalized = true;
 384   if (TREE_THIS_VOLATILE (decl))
 385     node->force_output = true;
 386
 387   if (decide_is_variable_needed (node, decl))
 388     varpool_mark_needed_node (node);
 389   /* Since we reclaim unreachable nodes at the end of every language
 390      level unit, we need to be conservative about possible entry points
 391      there.  */
 392   else if (TREE_PUBLIC (decl) && !DECL_COMDAT (decl) && !DECL_EXTERNAL (decl))
 393     varpool_mark_needed_node (node);
 394   if (cgraph_global_info_ready)
 395     varpool_assemble_pending_decls ();
 396 }
 397
 398 /* Return variable availability.  See cgraph.h for description of individual
 399    return values.  */
 400 enum availability
 401 cgraph_variable_initializer_availability (struct varpool_node *node)
 402 {
 403   gcc_assert (cgraph_function_flags_ready);
 404   if (!node->finalized)
 405     return AVAIL_NOT_AVAILABLE;
 406   if (!TREE_PUBLIC (node->decl))
 407     return AVAIL_AVAILABLE;
 408   /* If the variable can be overwritten, return OVERWRITABLE.  Takes
 409      care of at least two notable extensions - the COMDAT variables
 410      used to share template instantiations in C++.  */
 411   if (!(*targetm.binds_local_p) (node->decl) && !DECL_COMDAT (node->decl))
 412     return AVAIL_OVERWRITABLE;
 413   return AVAIL_AVAILABLE;
 414 }
 415
 416 /* Walk the decls we marked as necessary and see if they reference new
 417    variables or functions and add them into the worklists.  */
 418 bool
 419 varpool_analyze_pending_decls (void)
 420 {
 421   bool changed = false;
 422
 423   timevar_push (TV_VARPOOL);
 424   while (varpool_first_unanalyzed_node)
 425     {
 426       tree decl = varpool_first_unanalyzed_node->decl;
 427       bool analyzed = varpool_first_unanalyzed_node->analyzed;
 428
 429       varpool_first_unanalyzed_node->analyzed = true;
 430
 431       varpool_first_unanalyzed_node = varpool_first_unanalyzed_node->next_needed;
 432
 433       /* When reading back varpool at LTO time, we re-construct the queue in order
 434          to have "needed" list right by inserting all needed nodes into varpool.
 435          We however don't want to re-analyze already analyzed nodes.  */
 436       if (!analyzed)
 437         {
 438           gcc_assert (!in_lto_p || cgraph_function_flags_ready);
 439           /* Compute the alignment early so function body expanders are
 440              already informed about increased alignment.  */
 441           align_variable (decl, 0);
 442         }
 443       if (DECL_INITIAL (decl))
 444         record_references_in_initializer (decl, analyzed);
 445       changed = true;
 446     }
 447   timevar_pop (TV_VARPOOL);
 448   return changed;
 449 }
 450
 451 /* Output one variable, if necessary.  Return whether we output it.  */
 452 bool
 453 varpool_assemble_decl (struct varpool_node *node)
 454 {
 455   tree decl = node->decl;
 456
 457   if (!TREE_ASM_WRITTEN (decl)
 458       && !node->alias
 459       && !node->in_other_partition
 460       && !DECL_EXTERNAL (decl)
 461       && (TREE_CODE (decl) != VAR_DECL || !DECL_HAS_VALUE_EXPR_P (decl)))
 462     {
 463       assemble_variable (decl, 0, 1, 0);
 464       if (TREE_ASM_WRITTEN (decl))
 465         {
 466           struct varpool_node *alias;
 467
 468           node->next_needed = varpool_assembled_nodes_queue;
 469           node->prev_needed = NULL;
 470           if (varpool_assembled_nodes_queue)
 471             varpool_assembled_nodes_queue->prev_needed = node;
 472           varpool_assembled_nodes_queue = node;
 473           node->finalized = 1;
 474
 475           /* Also emit any extra name aliases.  */
 476           for (alias = node->extra_name; alias; alias = alias->next)
 477             {
 478               /* Update linkage fields in case they've changed.  */
 479               DECL_WEAK (alias->decl) = DECL_WEAK (decl);
 480               TREE_PUBLIC (alias->decl) = TREE_PUBLIC (decl);
 481               DECL_VISIBILITY (alias->decl) = DECL_VISIBILITY (decl);
 482               assemble_alias (alias->decl, DECL_ASSEMBLER_NAME (decl));
 483             }
 484
 485           return true;
 486         }
 487     }
 488
 489   return false;
 490 }
 491
 492 /* Optimization of function bodies might've rendered some variables as
 493    unnecessary so we want to avoid these from being compiled.
 494
 495    This is done by pruning the queue and keeping only the variables that
 496    really appear needed (ie they are either externally visible or referenced
 497    by compiled function). Re-doing the reachability analysis on variables
 498    brings back the remaining variables referenced by these.  */
 499 void
 500 varpool_remove_unreferenced_decls (void)
 501 {
 502   struct varpool_node *next, *node = varpool_nodes_queue;
 503
 504   varpool_reset_queue ();
 505
 506   if (errorcount || sorrycount)
 507     return;
 508
 509   while (node)
 510     {
 511       tree decl = node->decl;
 512       next = node->next_needed;
 513       node->needed = 0;
 514
 515       if (node->finalized
 516           && (decide_is_variable_needed (node, decl)
 517               /* ??? Cgraph does not yet rule the world with an iron hand,
 518                  and does not control the emission of debug information.
 519                  After a variable has its DECL_RTL set, we must assume that
 520                  it may be referenced by the debug information, and we can
 521                  no longer elide it.  */
 522               || DECL_RTL_SET_P (decl)))
 523         varpool_mark_needed_node (node);
 524
 525       node = next;
 526     }
 527   /* Make sure we mark alias targets as used targets.  */
 528   finish_aliases_1 ();
 529   varpool_analyze_pending_decls ();
 530 }
 531
 532 /* Output all variables enqueued to be assembled.  */
 533 bool
 534 varpool_assemble_pending_decls (void)
 535 {
 536   bool changed = false;
 537
 538   if (errorcount || sorrycount)
 539     return false;
 540
 541   timevar_push (TV_VAROUT);
 542   /* EH might mark decls as needed during expansion.  This should be safe since
 543      we don't create references to new function, but it should not be used
 544      elsewhere.  */
 545   varpool_analyze_pending_decls ();
 546
 547   while (varpool_nodes_queue)
 548     {
 549       struct varpool_node *node = varpool_nodes_queue;
 550
 551       varpool_nodes_queue = varpool_nodes_queue->next_needed;
 552       if (varpool_assemble_decl (node))
 553         changed = true;
 554       else
 555         {
 556           node->prev_needed = NULL;
 557           node->next_needed = NULL;
 558         }
 559     }
 560   /* varpool_nodes_queue is now empty, clear the pointer to the last element
 561      in the queue.  */
 562   varpool_last_needed_node = NULL;
 563   timevar_pop (TV_VAROUT);
 564   return changed;
 565 }
 566
 567 /* Remove all elements from the queue so we can re-use it for debug output.  */
 568 void
 569 varpool_empty_needed_queue (void)
 570 {
 571   /* EH might mark decls as needed during expansion.  This should be safe since
 572      we don't create references to new function, but it should not be used
 573      elsewhere.  */
 574   varpool_analyze_pending_decls ();
 575
 576   while (varpool_nodes_queue)
 577     {
 578       struct varpool_node *node = varpool_nodes_queue;
 579       varpool_nodes_queue = varpool_nodes_queue->next_needed;
 580       node->next_needed = NULL;
 581       node->prev_needed = NULL;
 582     }
 583   /* varpool_nodes_queue is now empty, clear the pointer to the last element
 584      in the queue.  */
 585   varpool_last_needed_node = NULL;
 586 }
 587
 588 /* Create a new global variable of type TYPE.  */
 589 tree
 590 add_new_static_var (tree type)
 591 {
 592   tree new_decl;
 593   struct varpool_node *new_node;
 594
 595   new_decl = create_tmp_var (type, NULL);
 596   DECL_NAME (new_decl) = create_tmp_var_name (NULL);
 597   TREE_READONLY (new_decl) = 0;
 598   TREE_STATIC (new_decl) = 1;
 599   TREE_USED (new_decl) = 1;
 600   DECL_CONTEXT (new_decl) = NULL_TREE;
 601   DECL_ABSTRACT (new_decl) = 0;
 602   lang_hooks.dup_lang_specific_decl (new_decl);
 603   create_var_ann (new_decl);
 604   new_node = varpool_node (new_decl);
 605   varpool_mark_needed_node (new_node);
 606   add_referenced_var (new_decl);
 607   varpool_finalize_decl (new_decl);
 608
 609   return new_node->decl;
 610 }
 611
 612 /* Attempt to mark ALIAS as an alias to DECL.  Return TRUE if successful.
 613    Extra name aliases are output whenever DECL is output.  */
 614
 615 bool
 616 varpool_extra_name_alias (tree alias, tree decl)
 617 {
 618   struct varpool_node key, *alias_node, *decl_node, **slot;
 619
 620 #ifndef ASM_OUTPUT_DEF
 621   /* If aliases aren't supported by the assembler, fail.  */
 622   return false;
 623 #endif
 624
 625   gcc_assert (TREE_CODE (decl) == VAR_DECL);
 626   gcc_assert (TREE_CODE (alias) == VAR_DECL);
 627   /* Make sure the hash table has been created.  */
 628   decl_node = varpool_node (decl);
 629
 630   key.decl = alias;
 631
 632   slot = (struct varpool_node **) htab_find_slot (varpool_hash, &key, INSERT);
 633
 634   /* If the varpool_node has been already created, fail.  */
 635   if (*slot)
 636     return false;
 637
 638   alias_node = GGC_CNEW (struct varpool_node);
 639   alias_node->decl = alias;
 640   alias_node->alias = 1;
 641   alias_node->extra_name = decl_node;
 642   alias_node->next = decl_node->extra_name;
 643   ipa_empty_ref_list (&alias_node->ref_list);
 644   if (decl_node->extra_name)
 645     decl_node->extra_name->prev = alias_node;
 646   decl_node->extra_name = alias_node;
 647   *slot = alias_node;
 648   return true;
 649 }
 650
 651 #include "gt-varpool.h"