gcc/tree-ssanames.c

   1 /* Generic routines for manipulating SSA_NAME expressions
   2    Copyright (C) 2003-2015 Free Software Foundation, Inc.
   3
   4 This file is part of GCC.
   5
   6 GCC is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 3, or (at your option)
   9 any later version.
  10
  11 GCC is distributed in the hope that it will be useful,
  12 but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 GNU General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GCC; see the file COPYING3.  If not see
  18 <http://www.gnu.org/licenses/>.  */
  19
  20 #include "config.h"
  21 #include "system.h"
  22 #include "coretypes.h"
  23 #include "backend.h"
  24 #include "tree.h"
  25 #include "gimple.h"
  26 #include "gimple-iterator.h"
  27 #include "hard-reg-set.h"
  28 #include "ssa.h"
  29 #include "alias.h"
  30 #include "fold-const.h"
  31 #include "stor-layout.h"
  32 #include "internal-fn.h"
  33 #include "tree-into-ssa.h"
  34 #include "tree-ssa.h"
  35 #include "tree-pass.h"
  36
  37 /* Rewriting a function into SSA form can create a huge number of SSA_NAMEs,
  38    many of which may be thrown away shortly after their creation if jumps
  39    were threaded through PHI nodes.
  40
  41    While our garbage collection mechanisms will handle this situation, it
  42    is extremely wasteful to create nodes and throw them away, especially
  43    when the nodes can be reused.
  44
  45    For PR 8361, we can significantly reduce the number of nodes allocated
  46    and thus the total amount of memory allocated by managing SSA_NAMEs a
  47    little.  This additionally helps reduce the amount of work done by the
  48    garbage collector.  Similar results have been seen on a wider variety
  49    of tests (such as the compiler itself).
  50
  51    Right now we maintain our free list on a per-function basis.  It may
  52    or may not make sense to maintain the free list for the duration of
  53    a compilation unit.
  54
  55    External code should rely solely upon HIGHEST_SSA_VERSION and the
  56    externally defined functions.  External code should not know about
  57    the details of the free list management.
  58
  59    External code should also not assume the version number on nodes is
  60    monotonically increasing.  We reuse the version number when we
  61    reuse an SSA_NAME expression.  This helps keep arrays and bitmaps
  62    more compact.  */
  63
  64
  65 /* Version numbers with special meanings.  We start allocating new version
  66    numbers after the special ones.  */
  67 #define UNUSED_NAME_VERSION 0
  68
  69 unsigned int ssa_name_nodes_reused;
  70 unsigned int ssa_name_nodes_created;
  71
  72 #define FREE_SSANAMES(fun) (fun)->gimple_df->free_ssanames
  73 #define FREE_SSANAMES_QUEUE(fun) (fun)->gimple_df->free_ssanames_queue
  74
  75
  76 /* Initialize management of SSA_NAMEs to default SIZE.  If SIZE is
  77    zero use default.  */
  78
  79 void
  80 init_ssanames (struct function *fn, int size)
  81 {
  82   if (size < 50)
  83     size = 50;
  84
  85   vec_alloc (SSANAMES (fn), size);
  86
  87   /* Version 0 is special, so reserve the first slot in the table.  Though
  88      currently unused, we may use version 0 in alias analysis as part of
  89      the heuristics used to group aliases when the alias sets are too
  90      large.
  91
  92      We use vec::quick_push here because we know that SSA_NAMES has at
  93      least 50 elements reserved in it.  */
  94   SSANAMES (fn)->quick_push (NULL_TREE);
  95   FREE_SSANAMES (fn) = NULL;
  96   FREE_SSANAMES_QUEUE (fn) = NULL;
  97
  98   fn->gimple_df->ssa_renaming_needed = 0;
  99   fn->gimple_df->rename_vops = 0;
 100 }
 101
 102 /* Finalize management of SSA_NAMEs.  */
 103
 104 void
 105 fini_ssanames (void)
 106 {
 107   vec_free (SSANAMES (cfun));
 108   vec_free (FREE_SSANAMES (cfun));
 109   vec_free (FREE_SSANAMES_QUEUE (cfun));
 110 }
 111
 112 /* Dump some simple statistics regarding the re-use of SSA_NAME nodes.  */
 113
 114 void
 115 ssanames_print_statistics (void)
 116 {
 117   fprintf (stderr, "SSA_NAME nodes allocated: %u\n", ssa_name_nodes_created);
 118   fprintf (stderr, "SSA_NAME nodes reused: %u\n", ssa_name_nodes_reused);
 119 }
 120
 121 /* Move all SSA_NAMEs from FREE_SSA_NAMES_QUEUE to FREE_SSA_NAMES.
 122
 123    We do not, but should have a mode to verify the state of the SSA_NAMEs
 124    lists.  In particular at this point every name must be in the IL,
 125    on the free list or in the queue.  Anything else is an error.  */
 126
 127 void
 128 flush_ssaname_freelist (void)
 129 {
 130   vec_safe_splice (FREE_SSANAMES (cfun), FREE_SSANAMES_QUEUE (cfun));
 131   vec_safe_truncate (FREE_SSANAMES_QUEUE (cfun), 0);
 132 }
 133
 134 /* Return an SSA_NAME node for variable VAR defined in statement STMT
 135    in function FN.  STMT may be an empty statement for artificial
 136    references (e.g., default definitions created when a variable is
 137    used without a preceding definition).  */
 138
 139 tree
 140 make_ssa_name_fn (struct function *fn, tree var, gimple *stmt)
 141 {
 142   tree t;
 143   use_operand_p imm;
 144
 145   gcc_assert (TREE_CODE (var) == VAR_DECL
 146               || TREE_CODE (var) == PARM_DECL
 147               || TREE_CODE (var) == RESULT_DECL
 148               || (TYPE_P (var) && is_gimple_reg_type (var)));
 149
 150   /* If our free list has an element, then use it.  */
 151   if (!vec_safe_is_empty (FREE_SSANAMES (fn)))
 152     {
 153       t = FREE_SSANAMES (fn)->pop ();
 154       if (GATHER_STATISTICS)
 155         ssa_name_nodes_reused++;
 156
 157       /* The node was cleared out when we put it on the free list, so
 158          there is no need to do so again here.  */
 159       gcc_assert ((*SSANAMES (fn))[SSA_NAME_VERSION (t)] == NULL);
 160       (*SSANAMES (fn))[SSA_NAME_VERSION (t)] = t;
 161     }
 162   else
 163     {
 164       t = make_node (SSA_NAME);
 165       SSA_NAME_VERSION (t) = SSANAMES (fn)->length ();
 166       vec_safe_push (SSANAMES (fn), t);
 167       if (GATHER_STATISTICS)
 168         ssa_name_nodes_created++;
 169     }
 170
 171   if (TYPE_P (var))
 172     {
 173       TREE_TYPE (t) = var;
 174       SET_SSA_NAME_VAR_OR_IDENTIFIER (t, NULL_TREE);
 175     }
 176   else
 177     {
 178       TREE_TYPE (t) = TREE_TYPE (var);
 179       SET_SSA_NAME_VAR_OR_IDENTIFIER (t, var);
 180     }
 181   SSA_NAME_DEF_STMT (t) = stmt;
 182   if (POINTER_TYPE_P (TREE_TYPE (t)))
 183     SSA_NAME_PTR_INFO (t) = NULL;
 184   else
 185     SSA_NAME_RANGE_INFO (t) = NULL;
 186
 187   SSA_NAME_IN_FREE_LIST (t) = 0;
 188   SSA_NAME_IS_DEFAULT_DEF (t) = 0;
 189   imm = &(SSA_NAME_IMM_USE_NODE (t));
 190   imm->use = NULL;
 191   imm->prev = imm;
 192   imm->next = imm;
 193   imm->loc.ssa_name = t;
 194
 195   return t;
 196 }
 197
 198 /* Store range information RANGE_TYPE, MIN, and MAX to tree ssa_name NAME.  */
 199
 200 void
 201 set_range_info (tree name, enum value_range_type range_type,
 202                 const wide_int_ref &min, const wide_int_ref &max)
 203 {
 204   gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
 205   gcc_assert (range_type == VR_RANGE || range_type == VR_ANTI_RANGE);
 206   range_info_def *ri = SSA_NAME_RANGE_INFO (name);
 207   unsigned int precision = TYPE_PRECISION (TREE_TYPE (name));
 208
 209   /* Allocate if not available.  */
 210   if (ri == NULL)
 211     {
 212       size_t size = (sizeof (range_info_def)
 213                      + trailing_wide_ints <3>::extra_size (precision));
 214       ri = static_cast<range_info_def *> (ggc_internal_alloc (size));
 215       ri->ints.set_precision (precision);
 216       SSA_NAME_RANGE_INFO (name) = ri;
 217       ri->set_nonzero_bits (wi::shwi (-1, precision));
 218     }
 219
 220   /* Record the range type.  */
 221   if (SSA_NAME_RANGE_TYPE (name) != range_type)
 222     SSA_NAME_ANTI_RANGE_P (name) = (range_type == VR_ANTI_RANGE);
 223
 224   /* Set the values.  */
 225   ri->set_min (min);
 226   ri->set_max (max);
 227
 228   /* If it is a range, try to improve nonzero_bits from the min/max.  */
 229   if (range_type == VR_RANGE)
 230     {
 231       wide_int xorv = ri->get_min () ^ ri->get_max ();
 232       if (xorv != 0)
 233         xorv = wi::mask (precision - wi::clz (xorv), false, precision);
 234       ri->set_nonzero_bits (ri->get_nonzero_bits () & (ri->get_min () | xorv));
 235     }
 236 }
 237
 238
 239 /* Gets range information MIN, MAX and returns enum value_range_type
 240    corresponding to tree ssa_name NAME.  enum value_range_type returned
 241    is used to determine if MIN and MAX are valid values.  */
 242
 243 enum value_range_type
 244 get_range_info (const_tree name, wide_int *min, wide_int *max)
 245 {
 246   gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
 247   gcc_assert (min && max);
 248   range_info_def *ri = SSA_NAME_RANGE_INFO (name);
 249
 250   /* Return VR_VARYING for SSA_NAMEs with NULL RANGE_INFO or SSA_NAMEs
 251      with integral types width > 2 * HOST_BITS_PER_WIDE_INT precision.  */
 252   if (!ri || (GET_MODE_PRECISION (TYPE_MODE (TREE_TYPE (name)))
 253               > 2 * HOST_BITS_PER_WIDE_INT))
 254     return VR_VARYING;
 255
 256   *min = ri->get_min ();
 257   *max = ri->get_max ();
 258   return SSA_NAME_RANGE_TYPE (name);
 259 }
 260
 261 /* Change non-zero bits bitmask of NAME.  */
 262
 263 void
 264 set_nonzero_bits (tree name, const wide_int_ref &mask)
 265 {
 266   gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
 267   if (SSA_NAME_RANGE_INFO (name) == NULL)
 268     set_range_info (name, VR_RANGE,
 269                     TYPE_MIN_VALUE (TREE_TYPE (name)),
 270                     TYPE_MAX_VALUE (TREE_TYPE (name)));
 271   range_info_def *ri = SSA_NAME_RANGE_INFO (name);
 272   ri->set_nonzero_bits (mask);
 273 }
 274
 275 /* Return a widest_int with potentially non-zero bits in SSA_NAME
 276    NAME, or -1 if unknown.  */
 277
 278 wide_int
 279 get_nonzero_bits (const_tree name)
 280 {
 281   unsigned int precision = TYPE_PRECISION (TREE_TYPE (name));
 282   if (POINTER_TYPE_P (TREE_TYPE (name)))
 283     {
 284       struct ptr_info_def *pi = SSA_NAME_PTR_INFO (name);
 285       if (pi && pi->align)
 286         return wi::shwi (-(HOST_WIDE_INT) pi->align
 287                          | (HOST_WIDE_INT) pi->misalign, precision);
 288       return wi::shwi (-1, precision);
 289     }
 290
 291   range_info_def *ri = SSA_NAME_RANGE_INFO (name);
 292   if (!ri)
 293     return wi::shwi (-1, precision);
 294
 295   return ri->get_nonzero_bits ();
 296 }
 297
 298 /* We no longer need the SSA_NAME expression VAR, release it so that
 299    it may be reused.
 300
 301    Note it is assumed that no calls to make_ssa_name will be made
 302    until all uses of the ssa name are released and that the only
 303    use of the SSA_NAME expression is to check its SSA_NAME_VAR.  All
 304    other fields must be assumed clobbered.  */
 305
 306 void
 307 release_ssa_name_fn (struct function *fn, tree var)
 308 {
 309   if (!var)
 310     return;
 311
 312   /* Never release the default definition for a symbol.  It's a
 313      special SSA name that should always exist once it's created.  */
 314   if (SSA_NAME_IS_DEFAULT_DEF (var))
 315     return;
 316
 317   /* If VAR has been registered for SSA updating, don't remove it.
 318      After update_ssa has run, the name will be released.  */
 319   if (name_registered_for_update_p (var))
 320     {
 321       release_ssa_name_after_update_ssa (var);
 322       return;
 323     }
 324
 325   /* release_ssa_name can be called multiple times on a single SSA_NAME.
 326      However, it should only end up on our free list one time.   We
 327      keep a status bit in the SSA_NAME node itself to indicate it has
 328      been put on the free list.
 329
 330      Note that once on the freelist you can not reference the SSA_NAME's
 331      defining statement.  */
 332   if (! SSA_NAME_IN_FREE_LIST (var))
 333     {
 334       tree saved_ssa_name_var = SSA_NAME_VAR (var);
 335       int saved_ssa_name_version = SSA_NAME_VERSION (var);
 336       use_operand_p imm = &(SSA_NAME_IMM_USE_NODE (var));
 337
 338       if (MAY_HAVE_DEBUG_STMTS)
 339         insert_debug_temp_for_var_def (NULL, var);
 340
 341 #ifdef ENABLE_CHECKING
 342       verify_imm_links (stderr, var);
 343 #endif
 344       while (imm->next != imm)
 345         delink_imm_use (imm->next);
 346
 347       (*SSANAMES (fn))[SSA_NAME_VERSION (var)] = NULL_TREE;
 348       memset (var, 0, tree_size (var));
 349
 350       imm->prev = imm;
 351       imm->next = imm;
 352       imm->loc.ssa_name = var;
 353
 354       /* First put back the right tree node so that the tree checking
 355          macros do not complain.  */
 356       TREE_SET_CODE (var, SSA_NAME);
 357
 358       /* Restore the version number.  */
 359       SSA_NAME_VERSION (var) = saved_ssa_name_version;
 360
 361       /* Hopefully this can go away once we have the new incremental
 362          SSA updating code installed.  */
 363       SET_SSA_NAME_VAR_OR_IDENTIFIER (var, saved_ssa_name_var);
 364
 365       /* Note this SSA_NAME is now in the first list.  */
 366       SSA_NAME_IN_FREE_LIST (var) = 1;
 367
 368       /* And finally queue it so that it will be put on the free list.  */
 369       vec_safe_push (FREE_SSANAMES_QUEUE (fn), var);
 370     }
 371 }
 372
 373 /* If the alignment of the pointer described by PI is known, return true and
 374    store the alignment and the deviation from it into *ALIGNP and *MISALIGNP
 375    respectively.  Otherwise return false.  */
 376
 377 bool
 378 get_ptr_info_alignment (struct ptr_info_def *pi, unsigned int *alignp,
 379                         unsigned int *misalignp)
 380 {
 381   if (pi->align)
 382     {
 383       *alignp = pi->align;
 384       *misalignp = pi->misalign;
 385       return true;
 386     }
 387   else
 388     return false;
 389 }
 390
 391 /* State that the pointer described by PI has unknown alignment.  */
 392
 393 void
 394 mark_ptr_info_alignment_unknown (struct ptr_info_def *pi)
 395 {
 396   pi->align = 0;
 397   pi->misalign = 0;
 398 }
 399
 400 /* Store the power-of-two byte alignment and the deviation from that
 401    alignment of pointer described by PI to ALIOGN and MISALIGN
 402    respectively.  */
 403
 404 void
 405 set_ptr_info_alignment (struct ptr_info_def *pi, unsigned int align,
 406                             unsigned int misalign)
 407 {
 408   gcc_checking_assert (align != 0);
 409   gcc_assert ((align & (align - 1)) == 0);
 410   gcc_assert ((misalign & ~(align - 1)) == 0);
 411
 412   pi->align = align;
 413   pi->misalign = misalign;
 414 }
 415
 416 /* If pointer described by PI has known alignment, increase its known
 417    misalignment by INCREMENT modulo its current alignment.  */
 418
 419 void
 420 adjust_ptr_info_misalignment (struct ptr_info_def *pi,
 421                               unsigned int increment)
 422 {
 423   if (pi->align != 0)
 424     {
 425       pi->misalign += increment;
 426       pi->misalign &= (pi->align - 1);
 427     }
 428 }
 429
 430 /* Return the alias information associated with pointer T.  It creates a
 431    new instance if none existed.  */
 432
 433 struct ptr_info_def *
 434 get_ptr_info (tree t)
 435 {
 436   struct ptr_info_def *pi;
 437
 438   gcc_assert (POINTER_TYPE_P (TREE_TYPE (t)));
 439
 440   pi = SSA_NAME_PTR_INFO (t);
 441   if (pi == NULL)
 442     {
 443       pi = ggc_cleared_alloc<ptr_info_def> ();
 444       pt_solution_reset (&pi->pt);
 445       mark_ptr_info_alignment_unknown (pi);
 446       SSA_NAME_PTR_INFO (t) = pi;
 447     }
 448
 449   return pi;
 450 }
 451
 452
 453 /* Creates a new SSA name using the template NAME tobe defined by
 454    statement STMT in function FN.  */
 455
 456 tree
 457 copy_ssa_name_fn (struct function *fn, tree name, gimple *stmt)
 458 {
 459   tree new_name;
 460
 461   if (SSA_NAME_VAR (name))
 462     new_name = make_ssa_name_fn (fn, SSA_NAME_VAR (name), stmt);
 463   else
 464     {
 465       new_name = make_ssa_name_fn (fn, TREE_TYPE (name), stmt);
 466       SET_SSA_NAME_VAR_OR_IDENTIFIER (new_name, SSA_NAME_IDENTIFIER (name));
 467     }
 468
 469   return new_name;
 470 }
 471
 472
 473 /* Creates a duplicate of the ptr_info_def at PTR_INFO for use by
 474    the SSA name NAME.  */
 475
 476 void
 477 duplicate_ssa_name_ptr_info (tree name, struct ptr_info_def *ptr_info)
 478 {
 479   struct ptr_info_def *new_ptr_info;
 480
 481   gcc_assert (POINTER_TYPE_P (TREE_TYPE (name)));
 482   gcc_assert (!SSA_NAME_PTR_INFO (name));
 483
 484   if (!ptr_info)
 485     return;
 486
 487   new_ptr_info = ggc_alloc<ptr_info_def> ();
 488   *new_ptr_info = *ptr_info;
 489
 490   SSA_NAME_PTR_INFO (name) = new_ptr_info;
 491 }
 492
 493 /* Creates a duplicate of the range_info_def at RANGE_INFO of type
 494    RANGE_TYPE for use by the SSA name NAME.  */
 495 void
 496 duplicate_ssa_name_range_info (tree name, enum value_range_type range_type,
 497                                struct range_info_def *range_info)
 498 {
 499   struct range_info_def *new_range_info;
 500
 501   gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
 502   gcc_assert (!SSA_NAME_RANGE_INFO (name));
 503
 504   if (!range_info)
 505     return;
 506
 507   unsigned int precision = TYPE_PRECISION (TREE_TYPE (name));
 508   size_t size = (sizeof (range_info_def)
 509                  + trailing_wide_ints <3>::extra_size (precision));
 510   new_range_info = static_cast<range_info_def *> (ggc_internal_alloc (size));
 511   memcpy (new_range_info, range_info, size);
 512
 513   gcc_assert (range_type == VR_RANGE || range_type == VR_ANTI_RANGE);
 514   SSA_NAME_ANTI_RANGE_P (name) = (range_type == VR_ANTI_RANGE);
 515   SSA_NAME_RANGE_INFO (name) = new_range_info;
 516 }
 517
 518
 519
 520 /* Creates a duplicate of a ssa name NAME tobe defined by statement STMT
 521    in function FN.  */
 522
 523 tree
 524 duplicate_ssa_name_fn (struct function *fn, tree name, gimple *stmt)
 525 {
 526   tree new_name = copy_ssa_name_fn (fn, name, stmt);
 527   if (POINTER_TYPE_P (TREE_TYPE (name)))
 528     {
 529       struct ptr_info_def *old_ptr_info = SSA_NAME_PTR_INFO (name);
 530
 531       if (old_ptr_info)
 532         duplicate_ssa_name_ptr_info (new_name, old_ptr_info);
 533     }
 534   else
 535     {
 536       struct range_info_def *old_range_info = SSA_NAME_RANGE_INFO (name);
 537
 538       if (old_range_info)
 539         duplicate_ssa_name_range_info (new_name, SSA_NAME_RANGE_TYPE (name),
 540                                        old_range_info);
 541     }
 542
 543   return new_name;
 544 }
 545
 546
 547 /* Reset all flow sensitive data on NAME such as range-info, nonzero
 548    bits and alignment.  */
 549
 550 void
 551 reset_flow_sensitive_info (tree name)
 552 {
 553   if (POINTER_TYPE_P (TREE_TYPE (name)))
 554     {
 555       /* points-to info is not flow-sensitive.  */
 556       if (SSA_NAME_PTR_INFO (name))
 557         mark_ptr_info_alignment_unknown (SSA_NAME_PTR_INFO (name));
 558     }
 559   else
 560     SSA_NAME_RANGE_INFO (name) = NULL;
 561 }
 562
 563 /* Clear all flow sensitive data from all statements and PHI definitions
 564    in BB.  */
 565
 566 void
 567 reset_flow_sensitive_info_in_bb (basic_block bb)
 568 {
 569   for (gimple_stmt_iterator gsi = gsi_start_bb (bb); !gsi_end_p (gsi);
 570        gsi_next (&gsi))
 571     {
 572       gimple *stmt = gsi_stmt (gsi);
 573       ssa_op_iter i;
 574       tree op;
 575       FOR_EACH_SSA_TREE_OPERAND (op, stmt, i, SSA_OP_DEF)
 576         reset_flow_sensitive_info (op);
 577     }
 578
 579   for (gphi_iterator gsi = gsi_start_phis (bb); !gsi_end_p (gsi);
 580        gsi_next (&gsi))
 581     {
 582       tree phi_def = gimple_phi_result (gsi.phi ());
 583       reset_flow_sensitive_info (phi_def);
 584     }
 585 }
 586
 587 /* Release all the SSA_NAMEs created by STMT.  */
 588
 589 void
 590 release_defs (gimple *stmt)
 591 {
 592   tree def;
 593   ssa_op_iter iter;
 594
 595   /* Make sure that we are in SSA.  Otherwise, operand cache may point
 596      to garbage.  */
 597   gcc_assert (gimple_in_ssa_p (cfun));
 598
 599   FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
 600     if (TREE_CODE (def) == SSA_NAME)
 601       release_ssa_name (def);
 602 }
 603
 604
 605 /* Replace the symbol associated with SSA_NAME with SYM.  */
 606
 607 void
 608 replace_ssa_name_symbol (tree ssa_name, tree sym)
 609 {
 610   SET_SSA_NAME_VAR_OR_IDENTIFIER (ssa_name, sym);
 611   TREE_TYPE (ssa_name) = TREE_TYPE (sym);
 612 }
 613
 614 /* Return SSA names that are unused to GGC memory and compact the SSA
 615    version namespace.  This is used to keep footprint of compiler during
 616    interprocedural optimization.  */
 617
 618 namespace {
 619
 620 const pass_data pass_data_release_ssa_names =
 621 {
 622   GIMPLE_PASS, /* type */
 623   "release_ssa", /* name */
 624   OPTGROUP_NONE, /* optinfo_flags */
 625   TV_TREE_SSA_OTHER, /* tv_id */
 626   PROP_ssa, /* properties_required */
 627   0, /* properties_provided */
 628   0, /* properties_destroyed */
 629   TODO_remove_unused_locals, /* todo_flags_start */
 630   0, /* todo_flags_finish */
 631 };
 632
 633 class pass_release_ssa_names : public gimple_opt_pass
 634 {
 635 public:
 636   pass_release_ssa_names (gcc::context *ctxt)
 637     : gimple_opt_pass (pass_data_release_ssa_names, ctxt)
 638   {}
 639
 640   /* opt_pass methods: */
 641   virtual unsigned int execute (function *);
 642
 643 }; // class pass_release_ssa_names
 644
 645 unsigned int
 646 pass_release_ssa_names::execute (function *fun)
 647 {
 648   unsigned i, j;
 649   flush_ssaname_freelist ();
 650   int n = vec_safe_length (FREE_SSANAMES (fun));
 651
 652   /* Now release the freelist.  */
 653   vec_free (FREE_SSANAMES (fun));
 654
 655   /* And compact the SSA number space.  We make sure to not change the
 656      relative order of SSA versions.  */
 657   for (i = 1, j = 1; i < fun->gimple_df->ssa_names->length (); ++i)
 658     {
 659       tree name = ssa_name (i);
 660       if (name)
 661         {
 662           if (i != j)
 663             {
 664               SSA_NAME_VERSION (name) = j;
 665               (*fun->gimple_df->ssa_names)[j] = name;
 666             }
 667           j++;
 668         }
 669     }
 670   fun->gimple_df->ssa_names->truncate (j);
 671
 672   statistics_counter_event (fun, "SSA names released", n);
 673   statistics_counter_event (fun, "SSA name holes removed", i - j);
 674   if (dump_file)
 675     fprintf (dump_file, "Released %i names, %.2f%%, removed %i holes\n",
 676              n, n * 100.0 / num_ssa_names, i - j);
 677   return 0;
 678 }
 679
 680 } // anon namespace
 681
 682 gimple_opt_pass *
 683 make_pass_release_ssa_names (gcc::context *ctxt)
 684 {
 685   return new pass_release_ssa_names (ctxt);
 686 }