gcc/varpool.c

   1 /* Callgraph handling code.
   2    Copyright (C) 2003-2013 Free Software Foundation, Inc.
   3    Contributed by Jan Hubicka
   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 "tm.h"
  25 #include "tree.h"
  26 #include "cgraph.h"
  27 #include "langhooks.h"
  28 #include "diagnostic-core.h"
  29 #include "hashtab.h"
  30 #include "ggc.h"
  31 #include "timevar.h"
  32 #include "debug.h"
  33 #include "target.h"
  34 #include "output.h"
  35 #include "gimple.h"
  36 #include "tree-flow.h"
  37 #include "flags.h"
  38
  39 /* Allocate new callgraph node and insert it into basic data structures.  */
  40
  41 struct varpool_node *
  42 varpool_create_empty_node (void)
  43 {
  44   struct varpool_node *node = ggc_alloc_cleared_varpool_node ();
  45   node->symbol.type = SYMTAB_VARIABLE;
  46   return node;
  47 }
  48
  49 /* Return varpool node assigned to DECL.  Create new one when needed.  */
  50 struct varpool_node *
  51 varpool_node_for_decl (tree decl)
  52 {
  53   struct varpool_node *node = varpool_get_node (decl);
  54   gcc_checking_assert (TREE_CODE (decl) == VAR_DECL);
  55   if (node)
  56     return node;
  57
  58   node = varpool_create_empty_node ();
  59   node->symbol.decl = decl;
  60   symtab_register_node ((symtab_node)node);
  61   return node;
  62 }
  63
  64 /* Remove node from the varpool.  */
  65 void
  66 varpool_remove_node (struct varpool_node *node)
  67 {
  68   symtab_unregister_node ((symtab_node)node);
  69   tree init;
  70
  71   /* Because we remove references from external functions before final compilation,
  72      we may end up removing useful constructors.
  73      FIXME: We probably want to trace boundaries better.  */
  74   if ((init = ctor_for_folding (node->symbol.decl)) == error_mark_node)
  75     varpool_remove_initializer (node);
  76   else
  77     DECL_INITIAL (node->symbol.decl) = init;
  78   ggc_free (node);
  79 }
  80
  81 /* Renove node initializer when it is no longer needed.  */
  82 void
  83 varpool_remove_initializer (struct varpool_node *node)
  84 {
  85   if (DECL_INITIAL (node->symbol.decl)
  86       && !DECL_IN_CONSTANT_POOL (node->symbol.decl)
  87       /* Keep vtables for BINFO folding.  */
  88       && !DECL_VIRTUAL_P (node->symbol.decl)
  89       /* FIXME: http://gcc.gnu.org/PR55395 */
  90       && debug_info_level == DINFO_LEVEL_NONE
  91       /* When doing declaration merging we have duplicate
  92          entries for given decl.  Do not attempt to remove
  93          the boides, or we will end up remiving
  94          wrong one.  */
  95       && cgraph_state != CGRAPH_LTO_STREAMING)
  96     DECL_INITIAL (node->symbol.decl) = error_mark_node;
  97 }
  98
  99 /* Dump given cgraph node.  */
 100 void
 101 dump_varpool_node (FILE *f, struct varpool_node *node)
 102 {
 103   dump_symtab_base (f, (symtab_node)node);
 104   fprintf (f, "  Availability: %s\n",
 105            cgraph_function_flags_ready
 106            ? cgraph_availability_names[cgraph_variable_initializer_availability (node)]
 107            : "not-ready");
 108   fprintf (f, "  Varpool flags:");
 109   if (DECL_INITIAL (node->symbol.decl))
 110     fprintf (f, " initialized");
 111   if (node->output)
 112     fprintf (f, " output");
 113   if (TREE_READONLY (node->symbol.decl))
 114     fprintf (f, " read-only");
 115   if (ctor_for_folding (node->symbol.decl) != error_mark_node)
 116     fprintf (f, " const-value-known");
 117   fprintf (f, "\n");
 118 }
 119
 120 /* Dump the variable pool.  */
 121 void
 122 dump_varpool (FILE *f)
 123 {
 124   struct varpool_node *node;
 125
 126   fprintf (f, "variable pool:\n\n");
 127   FOR_EACH_VARIABLE (node)
 128     dump_varpool_node (f, node);
 129 }
 130
 131 /* Dump the variable pool to stderr.  */
 132
 133 DEBUG_FUNCTION void
 134 debug_varpool (void)
 135 {
 136   dump_varpool (stderr);
 137 }
 138
 139 /* Given an assembler name, lookup node.  */
 140 struct varpool_node *
 141 varpool_node_for_asm (tree asmname)
 142 {
 143   if (symtab_node node = symtab_node_for_asm (asmname))
 144     return dyn_cast <varpool_node> (node);
 145   else
 146     return NULL;
 147 }
 148
 149 /* Return if DECL is constant and its initial value is known (so we can do
 150    constant folding using DECL_INITIAL (decl)).
 151    Return ERROR_MARK_NODE when value is unknown.  */
 152
 153 tree
 154 ctor_for_folding (tree decl)
 155 {
 156   struct varpool_node *node, *real_node;
 157   tree real_decl;
 158
 159   if (TREE_CODE (decl) != VAR_DECL
 160       && TREE_CODE (decl) != CONST_DECL)
 161     return error_mark_node;
 162
 163   if (TREE_CODE (decl) == CONST_DECL
 164       || DECL_IN_CONSTANT_POOL (decl))
 165     return DECL_INITIAL (decl);
 166
 167   if (TREE_THIS_VOLATILE (decl))
 168     return error_mark_node;
 169
 170   /* Do not care about automatic variables.  Those are never initialized
 171      anyway, because gimplifier exapnds the code*/
 172   if (!TREE_STATIC (decl) && !DECL_EXTERNAL (decl))
 173     {
 174       gcc_assert (!TREE_PUBLIC (decl));
 175       return error_mark_node;
 176     }
 177
 178   gcc_assert (TREE_CODE (decl) == VAR_DECL);
 179
 180   node = varpool_get_node (decl);
 181   if (node)
 182     {
 183       real_node = varpool_variable_node (node);
 184       real_decl = real_node->symbol.decl;
 185     }
 186   else
 187     real_decl = decl;
 188
 189   /* See if we are dealing with alias.
 190      In most cases alias is just alternative symbol pointing to a given
 191      constructor.  This allows us to use interposition rules of DECL
 192      constructor of REAL_NODE.  However weakrefs are special by being just
 193      alternative name of their target (if defined).  */
 194   if (decl != real_decl)
 195     {
 196       gcc_assert (!DECL_INITIAL (decl)
 197                   || DECL_INITIAL (decl) == error_mark_node);
 198       if (lookup_attribute ("weakref", DECL_ATTRIBUTES (decl)))
 199         {
 200           node = varpool_alias_target (node);
 201           decl = node->symbol.decl;
 202         }
 203     }
 204
 205   /* Vtables are defined by their types and must match no matter of interposition
 206      rules.  */
 207   if (DECL_VIRTUAL_P (real_decl))
 208     {
 209       gcc_checking_assert (TREE_READONLY (real_decl));
 210       return DECL_INITIAL (real_decl);
 211     }
 212
 213   /* If thre is no constructor, we have nothing to do.  */
 214   if (DECL_INITIAL (real_decl) == error_mark_node)
 215     return error_mark_node;
 216
 217   /* Non-readonly alias of readonly variable is also de-facto readonly,
 218      because the variable itself is in readonly section.
 219      We also honnor READONLY flag on alias assuming that user knows
 220      what he is doing.  */
 221   if (!TREE_READONLY (decl) && !TREE_READONLY (real_decl))
 222     return error_mark_node;
 223
 224   /* Variables declared 'const' without an initializer
 225      have zero as the initializer if they may not be
 226      overridden at link or run time.  */
 227   if (!DECL_INITIAL (real_decl)
 228       && (DECL_EXTERNAL (decl) || decl_replaceable_p (decl)))
 229     return error_mark_node;
 230
 231   /* Variables declared `const' with an initializer are considered
 232      to not be overwritable with different initializer by default.
 233
 234      ??? Previously we behaved so for scalar variables but not for array
 235      accesses.  */
 236   return DECL_INITIAL (real_decl);
 237 }
 238
 239 /* Add the variable DECL to the varpool.
 240    Unlike varpool_finalize_decl function is intended to be used
 241    by middle end and allows insertion of new variable at arbitrary point
 242    of compilation.  */
 243 void
 244 varpool_add_new_variable (tree decl)
 245 {
 246   struct varpool_node *node;
 247   varpool_finalize_decl (decl);
 248   node = varpool_node_for_decl (decl);
 249   if (varpool_externally_visible_p (node))
 250     node->symbol.externally_visible = true;
 251 }
 252
 253 /* Return variable availability.  See cgraph.h for description of individual
 254    return values.  */
 255 enum availability
 256 cgraph_variable_initializer_availability (struct varpool_node *node)
 257 {
 258   gcc_assert (cgraph_function_flags_ready);
 259   if (!node->symbol.definition)
 260     return AVAIL_NOT_AVAILABLE;
 261   if (!TREE_PUBLIC (node->symbol.decl))
 262     return AVAIL_AVAILABLE;
 263   /* If the variable can be overwritten, return OVERWRITABLE.  Takes
 264      care of at least one notable extension - the COMDAT variables
 265      used to share template instantiations in C++.  */
 266   if (!decl_replaceable_p (node->symbol.decl))
 267     return AVAIL_OVERWRITABLE;
 268   return AVAIL_AVAILABLE;
 269 }
 270
 271 void
 272 varpool_analyze_node (struct varpool_node *node)
 273 {
 274   tree decl = node->symbol.decl;
 275
 276   /* When reading back varpool at LTO time, we re-construct the queue in order
 277      to have "needed" list right by inserting all needed nodes into varpool.
 278      We however don't want to re-analyze already analyzed nodes.  */
 279   if (!node->symbol.analyzed)
 280     {
 281       gcc_assert (!in_lto_p || cgraph_function_flags_ready);
 282       /* Compute the alignment early so function body expanders are
 283          already informed about increased alignment.  */
 284       align_variable (decl, 0);
 285     }
 286   if (node->symbol.alias)
 287     symtab_resolve_alias
 288        ((symtab_node) node, (symtab_node) varpool_get_node (node->symbol.alias_target));
 289   else if (DECL_INITIAL (decl))
 290     record_references_in_initializer (decl, node->symbol.analyzed);
 291   node->symbol.analyzed = true;
 292 }
 293
 294 /* Assemble thunks and aliases associated to NODE.  */
 295
 296 static void
 297 assemble_aliases (struct varpool_node *node)
 298 {
 299   int i;
 300   struct ipa_ref *ref;
 301   for (i = 0; ipa_ref_list_referring_iterate (&node->symbol.ref_list, i, ref); i++)
 302     if (ref->use == IPA_REF_ALIAS)
 303       {
 304         struct varpool_node *alias = ipa_ref_referring_varpool_node (ref);
 305         do_assemble_alias (alias->symbol.decl,
 306                            DECL_ASSEMBLER_NAME (node->symbol.decl));
 307         assemble_aliases (alias);
 308       }
 309 }
 310
 311 /* Output one variable, if necessary.  Return whether we output it.  */
 312
 313 bool
 314 varpool_assemble_decl (struct varpool_node *node)
 315 {
 316   tree decl = node->symbol.decl;
 317
 318   /* Aliases are outout when their target is produced or by
 319      output_weakrefs.  */
 320   if (node->symbol.alias)
 321     return false;
 322
 323   /* Constant pool is output from RTL land when the reference
 324      survive till this level.  */
 325   if (DECL_IN_CONSTANT_POOL (decl) && TREE_ASM_WRITTEN (decl))
 326     return false;
 327
 328   /* Decls with VALUE_EXPR should not be in the varpool at all.  They
 329      are not real variables, but just info for debugging and codegen.
 330      Unfortunately at the moment emutls is not updating varpool correctly
 331      after turning real vars into value_expr vars.  */
 332   if (DECL_HAS_VALUE_EXPR_P (decl)
 333       && !targetm.have_tls)
 334     return false;
 335
 336   /* Hard register vars do not need to be output.  */
 337   if (DECL_HARD_REGISTER (decl))
 338     return false;
 339
 340   gcc_checking_assert (!TREE_ASM_WRITTEN (decl)
 341                        && TREE_CODE (decl) == VAR_DECL
 342                        && !DECL_HAS_VALUE_EXPR_P (decl));
 343
 344   if (!node->symbol.in_other_partition
 345       && !DECL_EXTERNAL (decl))
 346     {
 347       assemble_variable (decl, 0, 1, 0);
 348       gcc_assert (TREE_ASM_WRITTEN (decl));
 349       node->symbol.definition = true;
 350       assemble_aliases (node);
 351       return true;
 352     }
 353
 354   return false;
 355 }
 356
 357 /* Add NODE to queue starting at FIRST.
 358    The queue is linked via AUX pointers and terminated by pointer to 1.  */
 359
 360 static void
 361 enqueue_node (struct varpool_node *node, struct varpool_node **first)
 362 {
 363   if (node->symbol.aux)
 364     return;
 365   gcc_checking_assert (*first);
 366   node->symbol.aux = *first;
 367   *first = node;
 368 }
 369
 370 /* Optimization of function bodies might've rendered some variables as
 371    unnecessary so we want to avoid these from being compiled.  Re-do
 372    reachability starting from variables that are either externally visible
 373    or was referred from the asm output routines.  */
 374
 375 static void
 376 varpool_remove_unreferenced_decls (void)
 377 {
 378   struct varpool_node *next, *node;
 379   struct varpool_node *first = (struct varpool_node *)(void *)1;
 380   int i;
 381   struct ipa_ref *ref;
 382
 383   if (seen_error ())
 384     return;
 385
 386   if (cgraph_dump_file)
 387     fprintf (cgraph_dump_file, "Trivially needed variables:");
 388   FOR_EACH_DEFINED_VARIABLE (node)
 389     {
 390       if (node->symbol.analyzed
 391           && (!varpool_can_remove_if_no_refs (node)
 392               /* We just expanded all function bodies.  See if any of
 393                  them needed the variable.  */
 394               || DECL_RTL_SET_P (node->symbol.decl)))
 395         {
 396           enqueue_node (node, &first);
 397           if (cgraph_dump_file)
 398             fprintf (cgraph_dump_file, " %s", varpool_node_asm_name (node));
 399         }
 400     }
 401   while (first != (struct varpool_node *)(void *)1)
 402     {
 403       node = first;
 404       first = (struct varpool_node *)first->symbol.aux;
 405
 406       if (node->symbol.same_comdat_group)
 407         {
 408           symtab_node next;
 409           for (next = node->symbol.same_comdat_group;
 410                next != (symtab_node)node;
 411                next = next->symbol.same_comdat_group)
 412             {
 413               varpool_node *vnext = dyn_cast <varpool_node> (next);
 414               if (vnext && vnext->symbol.analyzed)
 415                 enqueue_node (vnext, &first);
 416             }
 417         }
 418       for (i = 0; ipa_ref_list_reference_iterate (&node->symbol.ref_list, i, ref); i++)
 419         {
 420           varpool_node *vnode = dyn_cast <varpool_node> (ref->referred);
 421           if (vnode
 422               && (!DECL_EXTERNAL (ref->referred->symbol.decl)
 423                   || vnode->symbol.alias)
 424               && vnode->symbol.analyzed)
 425             enqueue_node (vnode, &first);
 426         }
 427     }
 428   if (cgraph_dump_file)
 429     fprintf (cgraph_dump_file, "\nRemoving variables:");
 430   for (node = varpool_first_defined_variable (); node; node = next)
 431     {
 432       next = varpool_next_defined_variable (node);
 433       if (!node->symbol.aux)
 434         {
 435           if (cgraph_dump_file)
 436             fprintf (cgraph_dump_file, " %s", varpool_node_asm_name (node));
 437           varpool_remove_node (node);
 438         }
 439     }
 440   if (cgraph_dump_file)
 441     fprintf (cgraph_dump_file, "\n");
 442 }
 443
 444 /* For variables in named sections make sure get_variable_section
 445    is called before we switch to those sections.  Then section
 446    conflicts between read-only and read-only requiring relocations
 447    sections can be resolved.  */
 448 void
 449 varpool_finalize_named_section_flags (struct varpool_node *node)
 450 {
 451   if (!TREE_ASM_WRITTEN (node->symbol.decl)
 452       && !node->symbol.alias
 453       && !node->symbol.in_other_partition
 454       && !DECL_EXTERNAL (node->symbol.decl)
 455       && TREE_CODE (node->symbol.decl) == VAR_DECL
 456       && !DECL_HAS_VALUE_EXPR_P (node->symbol.decl)
 457       && DECL_SECTION_NAME (node->symbol.decl))
 458     get_variable_section (node->symbol.decl, false);
 459 }
 460
 461 /* Output all variables enqueued to be assembled.  */
 462 bool
 463 varpool_output_variables (void)
 464 {
 465   bool changed = false;
 466   struct varpool_node *node;
 467
 468   if (seen_error ())
 469     return false;
 470
 471   varpool_remove_unreferenced_decls ();
 472
 473   timevar_push (TV_VAROUT);
 474
 475   FOR_EACH_DEFINED_VARIABLE (node)
 476     varpool_finalize_named_section_flags (node);
 477
 478   FOR_EACH_DEFINED_VARIABLE (node)
 479     if (varpool_assemble_decl (node))
 480       changed = true;
 481   timevar_pop (TV_VAROUT);
 482   return changed;
 483 }
 484
 485 /* Create a new global variable of type TYPE.  */
 486 tree
 487 add_new_static_var (tree type)
 488 {
 489   tree new_decl;
 490   struct varpool_node *new_node;
 491
 492   new_decl = create_tmp_var_raw (type, NULL);
 493   DECL_NAME (new_decl) = create_tmp_var_name (NULL);
 494   TREE_READONLY (new_decl) = 0;
 495   TREE_STATIC (new_decl) = 1;
 496   TREE_USED (new_decl) = 1;
 497   DECL_CONTEXT (new_decl) = NULL_TREE;
 498   DECL_ABSTRACT (new_decl) = 0;
 499   lang_hooks.dup_lang_specific_decl (new_decl);
 500   new_node = varpool_node_for_decl (new_decl);
 501   varpool_finalize_decl (new_decl);
 502
 503   return new_node->symbol.decl;
 504 }
 505
 506 /* Attempt to mark ALIAS as an alias to DECL.  Return TRUE if successful.
 507    Extra name aliases are output whenever DECL is output.  */
 508
 509 struct varpool_node *
 510 varpool_create_variable_alias (tree alias, tree decl)
 511 {
 512   struct varpool_node *alias_node;
 513
 514   gcc_assert (TREE_CODE (decl) == VAR_DECL);
 515   gcc_assert (TREE_CODE (alias) == VAR_DECL);
 516   alias_node = varpool_node_for_decl (alias);
 517   alias_node->symbol.alias = true;
 518   alias_node->symbol.definition = true;
 519   alias_node->symbol.alias_target = decl;
 520   if (lookup_attribute ("weakref", DECL_ATTRIBUTES (alias)) != NULL)
 521     alias_node->symbol.weakref = true;
 522   return alias_node;
 523 }
 524
 525 /* Attempt to mark ALIAS as an alias to DECL.  Return TRUE if successful.
 526    Extra name aliases are output whenever DECL is output.  */
 527
 528 struct varpool_node *
 529 varpool_extra_name_alias (tree alias, tree decl)
 530 {
 531   struct varpool_node *alias_node;
 532
 533 #ifndef ASM_OUTPUT_DEF
 534   /* If aliases aren't supported by the assembler, fail.  */
 535   return NULL;
 536 #endif
 537   alias_node = varpool_create_variable_alias (alias, decl);
 538   alias_node->symbol.cpp_implicit_alias = true;
 539
 540   /* Extra name alias mechanizm creates aliases really late
 541      via DECL_ASSEMBLER_NAME mechanizm.
 542      This is unfortunate because they are not going through the
 543      standard channels.  Ensure they get output.  */
 544   if (cpp_implicit_aliases_done)
 545     symtab_resolve_alias ((symtab_node)alias_node,
 546                           (symtab_node)varpool_node_for_decl (decl));
 547   return alias_node;
 548 }
 549
 550 /* Call calback on NODE and aliases associated to NODE.
 551    When INCLUDE_OVERWRITABLE is false, overwritable aliases and thunks are
 552    skipped. */
 553
 554 bool
 555 varpool_for_node_and_aliases (struct varpool_node *node,
 556                               bool (*callback) (struct varpool_node *, void *),
 557                               void *data,
 558                               bool include_overwritable)
 559 {
 560   int i;
 561   struct ipa_ref *ref;
 562
 563   if (callback (node, data))
 564     return true;
 565   for (i = 0; ipa_ref_list_referring_iterate (&node->symbol.ref_list, i, ref); i++)
 566     if (ref->use == IPA_REF_ALIAS)
 567       {
 568         struct varpool_node *alias = ipa_ref_referring_varpool_node (ref);
 569         if (include_overwritable
 570             || cgraph_variable_initializer_availability (alias) > AVAIL_OVERWRITABLE)
 571           if (varpool_for_node_and_aliases (alias, callback, data,
 572                                            include_overwritable))
 573             return true;
 574       }
 575   return false;
 576 }