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 (struct function *fn)
 106 {
 107   vec_free (SSANAMES (fn));
 108   vec_free (FREE_SSANAMES (fn));
 109   vec_free (FREE_SSANAMES_QUEUE (fn));
 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       ssa_name_nodes_reused++;
 155
 156       /* The node was cleared out when we put it on the free list, so
 157          there is no need to do so again here.  */
 158       gcc_assert ((*SSANAMES (fn))[SSA_NAME_VERSION (t)] == NULL);
 159       (*SSANAMES (fn))[SSA_NAME_VERSION (t)] = t;
 160     }
 161   else
 162     {
 163       t = make_node (SSA_NAME);
 164       SSA_NAME_VERSION (t) = SSANAMES (fn)->length ();
 165       vec_safe_push (SSANAMES (fn), t);
 166       ssa_name_nodes_created++;
 167     }
 168
 169   if (TYPE_P (var))
 170     {
 171       TREE_TYPE (t) = var;
 172       SET_SSA_NAME_VAR_OR_IDENTIFIER (t, NULL_TREE);
 173     }
 174   else
 175     {
 176       TREE_TYPE (t) = TREE_TYPE (var);
 177       SET_SSA_NAME_VAR_OR_IDENTIFIER (t, var);
 178     }
 179   SSA_NAME_DEF_STMT (t) = stmt;
 180   if (POINTER_TYPE_P (TREE_TYPE (t)))
 181     SSA_NAME_PTR_INFO (t) = NULL;
 182   else
 183     SSA_NAME_RANGE_INFO (t) = NULL;
 184
 185   SSA_NAME_IN_FREE_LIST (t) = 0;
 186   SSA_NAME_IS_DEFAULT_DEF (t) = 0;
 187   imm = &(SSA_NAME_IMM_USE_NODE (t));
 188   imm->use = NULL;
 189   imm->prev = imm;
 190   imm->next = imm;
 191   imm->loc.ssa_name = t;
 192
 193   return t;
 194 }
 195
 196 /* Store range information RANGE_TYPE, MIN, and MAX to tree ssa_name NAME.  */
 197
 198 void
 199 set_range_info (tree name, enum value_range_type range_type,
 200                 const wide_int_ref &min, const wide_int_ref &max)
 201 {
 202   gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
 203   gcc_assert (range_type == VR_RANGE || range_type == VR_ANTI_RANGE);
 204   range_info_def *ri = SSA_NAME_RANGE_INFO (name);
 205   unsigned int precision = TYPE_PRECISION (TREE_TYPE (name));
 206
 207   /* Allocate if not available.  */
 208   if (ri == NULL)
 209     {
 210       size_t size = (sizeof (range_info_def)
 211                      + trailing_wide_ints <3>::extra_size (precision));
 212       ri = static_cast<range_info_def *> (ggc_internal_alloc (size));
 213       ri->ints.set_precision (precision);
 214       SSA_NAME_RANGE_INFO (name) = ri;
 215       ri->set_nonzero_bits (wi::shwi (-1, precision));
 216     }
 217
 218   /* Record the range type.  */
 219   if (SSA_NAME_RANGE_TYPE (name) != range_type)
 220     SSA_NAME_ANTI_RANGE_P (name) = (range_type == VR_ANTI_RANGE);
 221
 222   /* Set the values.  */
 223   ri->set_min (min);
 224   ri->set_max (max);
 225
 226   /* If it is a range, try to improve nonzero_bits from the min/max.  */
 227   if (range_type == VR_RANGE)
 228     {
 229       wide_int xorv = ri->get_min () ^ ri->get_max ();
 230       if (xorv != 0)
 231         xorv = wi::mask (precision - wi::clz (xorv), false, precision);
 232       ri->set_nonzero_bits (ri->get_nonzero_bits () & (ri->get_min () | xorv));
 233     }
 234 }
 235
 236
 237 /* Gets range information MIN, MAX and returns enum value_range_type
 238    corresponding to tree ssa_name NAME.  enum value_range_type returned
 239    is used to determine if MIN and MAX are valid values.  */
 240
 241 enum value_range_type
 242 get_range_info (const_tree name, wide_int *min, wide_int *max)
 243 {
 244   gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
 245   gcc_assert (min && max);
 246   range_info_def *ri = SSA_NAME_RANGE_INFO (name);
 247
 248   /* Return VR_VARYING for SSA_NAMEs with NULL RANGE_INFO or SSA_NAMEs
 249      with integral types width > 2 * HOST_BITS_PER_WIDE_INT precision.  */
 250   if (!ri || (GET_MODE_PRECISION (TYPE_MODE (TREE_TYPE (name)))
 251               > 2 * HOST_BITS_PER_WIDE_INT))
 252     return VR_VARYING;
 253
 254   *min = ri->get_min ();
 255   *max = ri->get_max ();
 256   return SSA_NAME_RANGE_TYPE (name);
 257 }
 258
 259 /* Change non-zero bits bitmask of NAME.  */
 260
 261 void
 262 set_nonzero_bits (tree name, const wide_int_ref &mask)
 263 {
 264   gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
 265   if (SSA_NAME_RANGE_INFO (name) == NULL)
 266     set_range_info (name, VR_RANGE,
 267                     TYPE_MIN_VALUE (TREE_TYPE (name)),
 268                     TYPE_MAX_VALUE (TREE_TYPE (name)));
 269   range_info_def *ri = SSA_NAME_RANGE_INFO (name);
 270   ri->set_nonzero_bits (mask);
 271 }
 272
 273 /* Return a widest_int with potentially non-zero bits in SSA_NAME
 274    NAME, or -1 if unknown.  */
 275
 276 wide_int
 277 get_nonzero_bits (const_tree name)
 278 {
 279   unsigned int precision = TYPE_PRECISION (TREE_TYPE (name));
 280   if (POINTER_TYPE_P (TREE_TYPE (name)))
 281     {
 282       struct ptr_info_def *pi = SSA_NAME_PTR_INFO (name);
 283       if (pi && pi->align)
 284         return wi::shwi (-(HOST_WIDE_INT) pi->align
 285                          | (HOST_WIDE_INT) pi->misalign, precision);
 286       return wi::shwi (-1, precision);
 287     }
 288
 289   range_info_def *ri = SSA_NAME_RANGE_INFO (name);
 290   if (!ri)
 291     return wi::shwi (-1, precision);
 292
 293   return ri->get_nonzero_bits ();
 294 }
 295
 296 /* We no longer need the SSA_NAME expression VAR, release it so that
 297    it may be reused.
 298
 299    Note it is assumed that no calls to make_ssa_name will be made
 300    until all uses of the ssa name are released and that the only
 301    use of the SSA_NAME expression is to check its SSA_NAME_VAR.  All
 302    other fields must be assumed clobbered.  */
 303
 304 void
 305 release_ssa_name_fn (struct function *fn, tree var)
 306 {
 307   if (!var)
 308     return;
 309
 310   /* Never release the default definition for a symbol.  It's a
 311      special SSA name that should always exist once it's created.  */
 312   if (SSA_NAME_IS_DEFAULT_DEF (var))
 313     return;
 314
 315   /* If VAR has been registered for SSA updating, don't remove it.
 316      After update_ssa has run, the name will be released.  */
 317   if (name_registered_for_update_p (var))
 318     {
 319       release_ssa_name_after_update_ssa (var);
 320       return;
 321     }
 322
 323   /* release_ssa_name can be called multiple times on a single SSA_NAME.
 324      However, it should only end up on our free list one time.   We
 325      keep a status bit in the SSA_NAME node itself to indicate it has
 326      been put on the free list.
 327
 328      Note that once on the freelist you can not reference the SSA_NAME's
 329      defining statement.  */
 330   if (! SSA_NAME_IN_FREE_LIST (var))
 331     {
 332       tree saved_ssa_name_var = SSA_NAME_VAR (var);
 333       int saved_ssa_name_version = SSA_NAME_VERSION (var);
 334       use_operand_p imm = &(SSA_NAME_IMM_USE_NODE (var));
 335
 336       if (MAY_HAVE_DEBUG_STMTS)
 337         insert_debug_temp_for_var_def (NULL, var);
 338
 339       if (flag_checking)
 340         verify_imm_links (stderr, var);
 341       while (imm->next != imm)
 342         delink_imm_use (imm->next);
 343
 344       (*SSANAMES (fn))[SSA_NAME_VERSION (var)] = NULL_TREE;
 345       memset (var, 0, tree_size (var));
 346
 347       imm->prev = imm;
 348       imm->next = imm;
 349       imm->loc.ssa_name = var;
 350
 351       /* First put back the right tree node so that the tree checking
 352          macros do not complain.  */
 353       TREE_SET_CODE (var, SSA_NAME);
 354
 355       /* Restore the version number.  */
 356       SSA_NAME_VERSION (var) = saved_ssa_name_version;
 357
 358       /* Hopefully this can go away once we have the new incremental
 359          SSA updating code installed.  */
 360       SET_SSA_NAME_VAR_OR_IDENTIFIER (var, saved_ssa_name_var);
 361
 362       /* Note this SSA_NAME is now in the first list.  */
 363       SSA_NAME_IN_FREE_LIST (var) = 1;
 364
 365       /* And finally queue it so that it will be put on the free list.  */
 366       vec_safe_push (FREE_SSANAMES_QUEUE (fn), var);
 367     }
 368 }
 369
 370 /* If the alignment of the pointer described by PI is known, return true and
 371    store the alignment and the deviation from it into *ALIGNP and *MISALIGNP
 372    respectively.  Otherwise return false.  */
 373
 374 bool
 375 get_ptr_info_alignment (struct ptr_info_def *pi, unsigned int *alignp,
 376                         unsigned int *misalignp)
 377 {
 378   if (pi->align)
 379     {
 380       *alignp = pi->align;
 381       *misalignp = pi->misalign;
 382       return true;
 383     }
 384   else
 385     return false;
 386 }
 387
 388 /* State that the pointer described by PI has unknown alignment.  */
 389
 390 void
 391 mark_ptr_info_alignment_unknown (struct ptr_info_def *pi)
 392 {
 393   pi->align = 0;
 394   pi->misalign = 0;
 395 }
 396
 397 /* Store the power-of-two byte alignment and the deviation from that
 398    alignment of pointer described by PI to ALIOGN and MISALIGN
 399    respectively.  */
 400
 401 void
 402 set_ptr_info_alignment (struct ptr_info_def *pi, unsigned int align,
 403                             unsigned int misalign)
 404 {
 405   gcc_checking_assert (align != 0);
 406   gcc_assert ((align & (align - 1)) == 0);
 407   gcc_assert ((misalign & ~(align - 1)) == 0);
 408
 409   pi->align = align;
 410   pi->misalign = misalign;
 411 }
 412
 413 /* If pointer described by PI has known alignment, increase its known
 414    misalignment by INCREMENT modulo its current alignment.  */
 415
 416 void
 417 adjust_ptr_info_misalignment (struct ptr_info_def *pi,
 418                               unsigned int increment)
 419 {
 420   if (pi->align != 0)
 421     {
 422       pi->misalign += increment;
 423       pi->misalign &= (pi->align - 1);
 424     }
 425 }
 426
 427 /* Return the alias information associated with pointer T.  It creates a
 428    new instance if none existed.  */
 429
 430 struct ptr_info_def *
 431 get_ptr_info (tree t)
 432 {
 433   struct ptr_info_def *pi;
 434
 435   gcc_assert (POINTER_TYPE_P (TREE_TYPE (t)));
 436
 437   pi = SSA_NAME_PTR_INFO (t);
 438   if (pi == NULL)
 439     {
 440       pi = ggc_cleared_alloc<ptr_info_def> ();
 441       pt_solution_reset (&pi->pt);
 442       mark_ptr_info_alignment_unknown (pi);
 443       SSA_NAME_PTR_INFO (t) = pi;
 444     }
 445
 446   return pi;
 447 }
 448
 449
 450 /* Creates a new SSA name using the template NAME tobe defined by
 451    statement STMT in function FN.  */
 452
 453 tree
 454 copy_ssa_name_fn (struct function *fn, tree name, gimple *stmt)
 455 {
 456   tree new_name;
 457
 458   if (SSA_NAME_VAR (name))
 459     new_name = make_ssa_name_fn (fn, SSA_NAME_VAR (name), stmt);
 460   else
 461     {
 462       new_name = make_ssa_name_fn (fn, TREE_TYPE (name), stmt);
 463       SET_SSA_NAME_VAR_OR_IDENTIFIER (new_name, SSA_NAME_IDENTIFIER (name));
 464     }
 465
 466   return new_name;
 467 }
 468
 469
 470 /* Creates a duplicate of the ptr_info_def at PTR_INFO for use by
 471    the SSA name NAME.  */
 472
 473 void
 474 duplicate_ssa_name_ptr_info (tree name, struct ptr_info_def *ptr_info)
 475 {
 476   struct ptr_info_def *new_ptr_info;
 477
 478   gcc_assert (POINTER_TYPE_P (TREE_TYPE (name)));
 479   gcc_assert (!SSA_NAME_PTR_INFO (name));
 480
 481   if (!ptr_info)
 482     return;
 483
 484   new_ptr_info = ggc_alloc<ptr_info_def> ();
 485   *new_ptr_info = *ptr_info;
 486
 487   SSA_NAME_PTR_INFO (name) = new_ptr_info;
 488 }
 489
 490 /* Creates a duplicate of the range_info_def at RANGE_INFO of type
 491    RANGE_TYPE for use by the SSA name NAME.  */
 492 void
 493 duplicate_ssa_name_range_info (tree name, enum value_range_type range_type,
 494                                struct range_info_def *range_info)
 495 {
 496   struct range_info_def *new_range_info;
 497
 498   gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
 499   gcc_assert (!SSA_NAME_RANGE_INFO (name));
 500
 501   if (!range_info)
 502     return;
 503
 504   unsigned int precision = TYPE_PRECISION (TREE_TYPE (name));
 505   size_t size = (sizeof (range_info_def)
 506                  + trailing_wide_ints <3>::extra_size (precision));
 507   new_range_info = static_cast<range_info_def *> (ggc_internal_alloc (size));
 508   memcpy (new_range_info, range_info, size);
 509
 510   gcc_assert (range_type == VR_RANGE || range_type == VR_ANTI_RANGE);
 511   SSA_NAME_ANTI_RANGE_P (name) = (range_type == VR_ANTI_RANGE);
 512   SSA_NAME_RANGE_INFO (name) = new_range_info;
 513 }
 514
 515
 516
 517 /* Creates a duplicate of a ssa name NAME tobe defined by statement STMT
 518    in function FN.  */
 519
 520 tree
 521 duplicate_ssa_name_fn (struct function *fn, tree name, gimple *stmt)
 522 {
 523   tree new_name = copy_ssa_name_fn (fn, name, stmt);
 524   if (POINTER_TYPE_P (TREE_TYPE (name)))
 525     {
 526       struct ptr_info_def *old_ptr_info = SSA_NAME_PTR_INFO (name);
 527
 528       if (old_ptr_info)
 529         duplicate_ssa_name_ptr_info (new_name, old_ptr_info);
 530     }
 531   else
 532     {
 533       struct range_info_def *old_range_info = SSA_NAME_RANGE_INFO (name);
 534
 535       if (old_range_info)
 536         duplicate_ssa_name_range_info (new_name, SSA_NAME_RANGE_TYPE (name),
 537                                        old_range_info);
 538     }
 539
 540   return new_name;
 541 }
 542
 543
 544 /* Reset all flow sensitive data on NAME such as range-info, nonzero
 545    bits and alignment.  */
 546
 547 void
 548 reset_flow_sensitive_info (tree name)
 549 {
 550   if (POINTER_TYPE_P (TREE_TYPE (name)))
 551     {
 552       /* points-to info is not flow-sensitive.  */
 553       if (SSA_NAME_PTR_INFO (name))
 554         mark_ptr_info_alignment_unknown (SSA_NAME_PTR_INFO (name));
 555     }
 556   else
 557     SSA_NAME_RANGE_INFO (name) = NULL;
 558 }
 559
 560 /* Clear all flow sensitive data from all statements and PHI definitions
 561    in BB.  */
 562
 563 void
 564 reset_flow_sensitive_info_in_bb (basic_block bb)
 565 {
 566   for (gimple_stmt_iterator gsi = gsi_start_bb (bb); !gsi_end_p (gsi);
 567        gsi_next (&gsi))
 568     {
 569       gimple *stmt = gsi_stmt (gsi);
 570       ssa_op_iter i;
 571       tree op;
 572       FOR_EACH_SSA_TREE_OPERAND (op, stmt, i, SSA_OP_DEF)
 573         reset_flow_sensitive_info (op);
 574     }
 575
 576   for (gphi_iterator gsi = gsi_start_phis (bb); !gsi_end_p (gsi);
 577        gsi_next (&gsi))
 578     {
 579       tree phi_def = gimple_phi_result (gsi.phi ());
 580       reset_flow_sensitive_info (phi_def);
 581     }
 582 }
 583
 584 /* Release all the SSA_NAMEs created by STMT.  */
 585
 586 void
 587 release_defs (gimple *stmt)
 588 {
 589   tree def;
 590   ssa_op_iter iter;
 591
 592   /* Make sure that we are in SSA.  Otherwise, operand cache may point
 593      to garbage.  */
 594   gcc_assert (gimple_in_ssa_p (cfun));
 595
 596   FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
 597     if (TREE_CODE (def) == SSA_NAME)
 598       release_ssa_name (def);
 599 }
 600
 601
 602 /* Replace the symbol associated with SSA_NAME with SYM.  */
 603
 604 void
 605 replace_ssa_name_symbol (tree ssa_name, tree sym)
 606 {
 607   SET_SSA_NAME_VAR_OR_IDENTIFIER (ssa_name, sym);
 608   TREE_TYPE (ssa_name) = TREE_TYPE (sym);
 609 }
 610
 611 /* Return SSA names that are unused to GGC memory and compact the SSA
 612    version namespace.  This is used to keep footprint of compiler during
 613    interprocedural optimization.  */
 614
 615 namespace {
 616
 617 const pass_data pass_data_release_ssa_names =
 618 {
 619   GIMPLE_PASS, /* type */
 620   "release_ssa", /* name */
 621   OPTGROUP_NONE, /* optinfo_flags */
 622   TV_TREE_SSA_OTHER, /* tv_id */
 623   PROP_ssa, /* properties_required */
 624   0, /* properties_provided */
 625   0, /* properties_destroyed */
 626   TODO_remove_unused_locals, /* todo_flags_start */
 627   0, /* todo_flags_finish */
 628 };
 629
 630 class pass_release_ssa_names : public gimple_opt_pass
 631 {
 632 public:
 633   pass_release_ssa_names (gcc::context *ctxt)
 634     : gimple_opt_pass (pass_data_release_ssa_names, ctxt)
 635   {}
 636
 637   /* opt_pass methods: */
 638   virtual unsigned int execute (function *);
 639
 640 }; // class pass_release_ssa_names
 641
 642 unsigned int
 643 pass_release_ssa_names::execute (function *fun)
 644 {
 645   unsigned i, j;
 646   int n = vec_safe_length (FREE_SSANAMES (fun));
 647
 648   /* Now release the freelist.  */
 649   vec_free (FREE_SSANAMES (fun));
 650
 651   /* And compact the SSA number space.  We make sure to not change the
 652      relative order of SSA versions.  */
 653   for (i = 1, j = 1; i < fun->gimple_df->ssa_names->length (); ++i)
 654     {
 655       tree name = ssa_name (i);
 656       if (name)
 657         {
 658           if (i != j)
 659             {
 660               SSA_NAME_VERSION (name) = j;
 661               (*fun->gimple_df->ssa_names)[j] = name;
 662             }
 663           j++;
 664         }
 665     }
 666   fun->gimple_df->ssa_names->truncate (j);
 667
 668   statistics_counter_event (fun, "SSA names released", n);
 669   statistics_counter_event (fun, "SSA name holes removed", i - j);
 670   if (dump_file)
 671     fprintf (dump_file, "Released %i names, %.2f%%, removed %i holes\n",
 672              n, n * 100.0 / num_ssa_names, i - j);
 673   return 0;
 674 }
 675
 676 } // anon namespace
 677
 678 gimple_opt_pass *
 679 make_pass_release_ssa_names (gcc::context *ctxt)
 680 {
 681   return new pass_release_ssa_names (ctxt);
 682 }