gcc/varpool.c

   1 /* Callgraph handling code.
   2    Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008
   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->needed && node->finalized
 211       && !TREE_ASM_WRITTEN (node->decl))
 212     varpool_enqueue_needed_node (node);
 213   node->needed = 1;
 214 }
 215
 216 /* Reset the queue of needed nodes.  */
 217 static void
 218 varpool_reset_queue (void)
 219 {
 220   varpool_last_needed_node = NULL;
 221   varpool_nodes_queue = NULL;
 222   varpool_first_unanalyzed_node = NULL;
 223 }
 224
 225 /* Determine if variable DECL is needed.  That is, visible to something
 226    either outside this translation unit, something magic in the system
 227    configury */
 228 bool
 229 decide_is_variable_needed (struct varpool_node *node, tree decl)
 230 {
 231   /* If the user told us it is used, then it must be so.  */
 232   if ((node->externally_visible && !DECL_COMDAT (decl))
 233       || node->force_output)
 234     return true;
 235
 236   /* ??? If the assembler name is set by hand, it is possible to assemble
 237      the name later after finalizing the function and the fact is noticed
 238      in assemble_name then.  This is arguably a bug.  */
 239   if (DECL_ASSEMBLER_NAME_SET_P (decl)
 240       && TREE_SYMBOL_REFERENCED (DECL_ASSEMBLER_NAME (decl)))
 241     return true;
 242
 243   /* Externally visible variables must be output.  The exception is
 244      COMDAT variables that must be output only when they are needed.  */
 245   if (TREE_PUBLIC (decl)
 246       && !flag_whole_program
 247       && !flag_lto
 248       && !flag_whopr
 249       && !DECL_COMDAT (decl)
 250       && !DECL_EXTERNAL (decl))
 251     return true;
 252
 253   /* When emulating tls, we actually see references to the control
 254      variable, rather than the user-level variable.  */
 255   if (!targetm.have_tls
 256       && TREE_CODE (decl) == VAR_DECL
 257       && DECL_THREAD_LOCAL_P (decl))
 258     {
 259       tree control = emutls_decl (decl);
 260       if (decide_is_variable_needed (varpool_node (control), control))
 261         return true;
 262     }
 263
 264   /* When not reordering top level variables, we have to assume that
 265      we are going to keep everything.  */
 266   if (flag_toplevel_reorder)
 267     return false;
 268
 269   /* We want to emit COMDAT variables only when absolutely necessary.  */
 270   if (DECL_COMDAT (decl))
 271     return false;
 272   return true;
 273 }
 274
 275 /* Mark DECL as finalized.  By finalizing the declaration, frontend instruct the
 276    middle end to output the variable to asm file, if needed or externally
 277    visible.  */
 278 void
 279 varpool_finalize_decl (tree decl)
 280 {
 281   struct varpool_node *node = varpool_node (decl);
 282
 283   /* FIXME: We don't really stream varpool datastructure and instead rebuild it
 284      by varpool_finalize_decl.  This is not quite correct since this way we can't
 285      attach any info to varpool.  Eventually we will want to stream varpool nodes
 286      and the flags.
 287
 288      For the moment just prevent analysis of varpool nodes to happen again, so
 289      we will re-try to compute "address_taken" flag of varpool that breaks
 290      in presence of clones.  */
 291   if (in_lto_p)
 292     node->analyzed = true;
 293
 294   /* The first declaration of a variable that comes through this function
 295      decides whether it is global (in C, has external linkage)
 296      or local (in C, has internal linkage).  So do nothing more
 297      if this function has already run.  */
 298   if (node->finalized)
 299     {
 300       if (cgraph_global_info_ready)
 301         varpool_assemble_pending_decls ();
 302       return;
 303     }
 304   if (node->needed)
 305     varpool_enqueue_needed_node (node);
 306   node->finalized = true;
 307
 308   if (decide_is_variable_needed (node, decl))
 309     varpool_mark_needed_node (node);
 310   /* Since we reclaim unreachable nodes at the end of every language
 311      level unit, we need to be conservative about possible entry points
 312      there.  */
 313   else if (TREE_PUBLIC (decl) && !DECL_COMDAT (decl) && !DECL_EXTERNAL (decl))
 314     varpool_mark_needed_node (node);
 315   if (cgraph_global_info_ready)
 316     varpool_assemble_pending_decls ();
 317 }
 318
 319 /* Return variable availability.  See cgraph.h for description of individual
 320    return values.  */
 321 enum availability
 322 cgraph_variable_initializer_availability (struct varpool_node *node)
 323 {
 324   gcc_assert (cgraph_function_flags_ready);
 325   if (!node->finalized)
 326     return AVAIL_NOT_AVAILABLE;
 327   if (!TREE_PUBLIC (node->decl))
 328     return AVAIL_AVAILABLE;
 329   /* If the variable can be overwritten, return OVERWRITABLE.  Takes
 330      care of at least two notable extensions - the COMDAT variables
 331      used to share template instantiations in C++.  */
 332   if (!(*targetm.binds_local_p) (node->decl) && !DECL_COMDAT (node->decl))
 333     return AVAIL_OVERWRITABLE;
 334   return AVAIL_AVAILABLE;
 335 }
 336
 337 /* Walk the decls we marked as necessary and see if they reference new
 338    variables or functions and add them into the worklists.  */
 339 bool
 340 varpool_analyze_pending_decls (void)
 341 {
 342   bool changed = false;
 343   timevar_push (TV_CGRAPH);
 344
 345   while (varpool_first_unanalyzed_node)
 346     {
 347       tree decl = varpool_first_unanalyzed_node->decl;
 348       bool analyzed = varpool_first_unanalyzed_node->analyzed;
 349
 350       varpool_first_unanalyzed_node->analyzed = true;
 351
 352       varpool_first_unanalyzed_node = varpool_first_unanalyzed_node->next_needed;
 353
 354       /* When reading back varpool at LTO time, we re-construct the queue in order
 355          to have "needed" list right by inserting all needed nodes into varpool.
 356          We however don't want to re-analyze already analyzed nodes.  */
 357       if (!analyzed)
 358         {
 359           gcc_assert (!in_lto_p);
 360           /* Compute the alignment early so function body expanders are
 361              already informed about increased alignment.  */
 362           align_variable (decl, 0);
 363         }
 364       if (DECL_INITIAL (decl))
 365         record_references_in_initializer (decl, analyzed);
 366       changed = true;
 367     }
 368   timevar_pop (TV_CGRAPH);
 369   return changed;
 370 }
 371
 372 /* Output one variable, if necessary.  Return whether we output it.  */
 373 bool
 374 varpool_assemble_decl (struct varpool_node *node)
 375 {
 376   tree decl = node->decl;
 377
 378   if (!TREE_ASM_WRITTEN (decl)
 379       && !node->alias
 380       && !DECL_EXTERNAL (decl)
 381       && (TREE_CODE (decl) != VAR_DECL || !DECL_HAS_VALUE_EXPR_P (decl)))
 382     {
 383       assemble_variable (decl, 0, 1, 0);
 384       if (TREE_ASM_WRITTEN (decl))
 385         {
 386           node->next_needed = varpool_assembled_nodes_queue;
 387           varpool_assembled_nodes_queue = node;
 388           node->finalized = 1;
 389           return true;
 390         }
 391     }
 392
 393   return false;
 394 }
 395
 396 /* Optimization of function bodies might've rendered some variables as
 397    unnecessary so we want to avoid these from being compiled.
 398
 399    This is done by pruning the queue and keeping only the variables that
 400    really appear needed (ie they are either externally visible or referenced
 401    by compiled function). Re-doing the reachability analysis on variables
 402    brings back the remaining variables referenced by these.  */
 403 void
 404 varpool_remove_unreferenced_decls (void)
 405 {
 406   struct varpool_node *next, *node = varpool_nodes_queue;
 407
 408   varpool_reset_queue ();
 409
 410   if (errorcount || sorrycount)
 411     return;
 412
 413   while (node)
 414     {
 415       tree decl = node->decl;
 416       next = node->next_needed;
 417       node->needed = 0;
 418
 419       if (node->finalized
 420           && (decide_is_variable_needed (node, decl)
 421               /* ??? Cgraph does not yet rule the world with an iron hand,
 422                  and does not control the emission of debug information.
 423                  After a variable has its DECL_RTL set, we must assume that
 424                  it may be referenced by the debug information, and we can
 425                  no longer elide it.  */
 426               || DECL_RTL_SET_P (decl)))
 427         varpool_mark_needed_node (node);
 428
 429       node = next;
 430     }
 431   /* Make sure we mark alias targets as used targets.  */
 432   finish_aliases_1 ();
 433   varpool_analyze_pending_decls ();
 434 }
 435
 436 /* Output all variables enqueued to be assembled.  */
 437 bool
 438 varpool_assemble_pending_decls (void)
 439 {
 440   bool changed = false;
 441
 442   if (errorcount || sorrycount)
 443     return false;
 444
 445   /* EH might mark decls as needed during expansion.  This should be safe since
 446      we don't create references to new function, but it should not be used
 447      elsewhere.  */
 448   varpool_analyze_pending_decls ();
 449
 450   while (varpool_nodes_queue)
 451     {
 452       struct varpool_node *node = varpool_nodes_queue;
 453
 454       varpool_nodes_queue = varpool_nodes_queue->next_needed;
 455       if (varpool_assemble_decl (node))
 456         changed = true;
 457       else
 458         node->next_needed = NULL;
 459     }
 460   /* varpool_nodes_queue is now empty, clear the pointer to the last element
 461      in the queue.  */
 462   varpool_last_needed_node = NULL;
 463   return changed;
 464 }
 465
 466 /* Remove all elements from the queue so we can re-use it for debug output.  */
 467 void
 468 varpool_empty_needed_queue (void)
 469 {
 470   /* EH might mark decls as needed during expansion.  This should be safe since
 471      we don't create references to new function, but it should not be used
 472      elsewhere.  */
 473   varpool_analyze_pending_decls ();
 474
 475   while (varpool_nodes_queue)
 476     {
 477       struct varpool_node *node = varpool_nodes_queue;
 478       varpool_nodes_queue = varpool_nodes_queue->next_needed;
 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 }
 485
 486 /* Create a new global variable of type TYPE.  */
 487 tree
 488 add_new_static_var (tree type)
 489 {
 490   tree new_decl;
 491   struct varpool_node *new_node;
 492
 493   new_decl = create_tmp_var (type, NULL);
 494   DECL_NAME (new_decl) = create_tmp_var_name (NULL);
 495   TREE_READONLY (new_decl) = 0;
 496   TREE_STATIC (new_decl) = 1;
 497   TREE_USED (new_decl) = 1;
 498   DECL_CONTEXT (new_decl) = NULL_TREE;
 499   DECL_ABSTRACT (new_decl) = 0;
 500   lang_hooks.dup_lang_specific_decl (new_decl);
 501   create_var_ann (new_decl);
 502   new_node = varpool_node (new_decl);
 503   varpool_mark_needed_node (new_node);
 504   add_referenced_var (new_decl);
 505   varpool_finalize_decl (new_decl);
 506
 507   return new_node->decl;
 508 }
 509
 510 #include "gt-varpool.h"