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