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 "tm.h"
  24 #include "hash-set.h"
  25 #include "machmode.h"
  26 #include "vec.h"
  27 #include "double-int.h"
  28 #include "input.h"
  29 #include "alias.h"
  30 #include "symtab.h"
  31 #include "wide-int.h"
  32 #include "inchash.h"
  33 #include "tree.h"
  34 #include "fold-const.h"
  35 #include "stor-layout.h"
  36 #include "predict.h"
  37 #include "hard-reg-set.h"
  38 #include "input.h"
  39 #include "function.h"
  40 #include "basic-block.h"
  41 #include "tree-ssa-alias.h"
  42 #include "internal-fn.h"
  43 #include "gimple-expr.h"
  44 #include "is-a.h"
  45 #include "gimple.h"
  46 #include "gimple-ssa.h"
  47 #include "gimple-iterator.h"
  48 #include "tree-phinodes.h"
  49 #include "ssa-iterators.h"
  50 #include "stringpool.h"
  51 #include "tree-ssanames.h"
  52 #include "tree-into-ssa.h"
  53 #include "tree-ssa.h"
  54 #include "tree-pass.h"
  55
  56 /* Rewriting a function into SSA form can create a huge number of SSA_NAMEs,
  57    many of which may be thrown away shortly after their creation if jumps
  58    were threaded through PHI nodes.
  59
  60    While our garbage collection mechanisms will handle this situation, it
  61    is extremely wasteful to create nodes and throw them away, especially
  62    when the nodes can be reused.
  63
  64    For PR 8361, we can significantly reduce the number of nodes allocated
  65    and thus the total amount of memory allocated by managing SSA_NAMEs a
  66    little.  This additionally helps reduce the amount of work done by the
  67    garbage collector.  Similar results have been seen on a wider variety
  68    of tests (such as the compiler itself).
  69
  70    Right now we maintain our free list on a per-function basis.  It may
  71    or may not make sense to maintain the free list for the duration of
  72    a compilation unit.
  73
  74    External code should rely solely upon HIGHEST_SSA_VERSION and the
  75    externally defined functions.  External code should not know about
  76    the details of the free list management.
  77
  78    External code should also not assume the version number on nodes is
  79    monotonically increasing.  We reuse the version number when we
  80    reuse an SSA_NAME expression.  This helps keep arrays and bitmaps
  81    more compact.  */
  82
  83
  84 /* Version numbers with special meanings.  We start allocating new version
  85    numbers after the special ones.  */
  86 #define UNUSED_NAME_VERSION 0
  87
  88 unsigned int ssa_name_nodes_reused;
  89 unsigned int ssa_name_nodes_created;
  90
  91 #define FREE_SSANAMES(fun) (fun)->gimple_df->free_ssanames
  92
  93
  94 /* Initialize management of SSA_NAMEs to default SIZE.  If SIZE is
  95    zero use default.  */
  96
  97 void
  98 init_ssanames (struct function *fn, int size)
  99 {
 100   if (size < 50)
 101     size = 50;
 102
 103   vec_alloc (SSANAMES (fn), size);
 104
 105   /* Version 0 is special, so reserve the first slot in the table.  Though
 106      currently unused, we may use version 0 in alias analysis as part of
 107      the heuristics used to group aliases when the alias sets are too
 108      large.
 109
 110      We use vec::quick_push here because we know that SSA_NAMES has at
 111      least 50 elements reserved in it.  */
 112   SSANAMES (fn)->quick_push (NULL_TREE);
 113   FREE_SSANAMES (fn) = NULL;
 114
 115   fn->gimple_df->ssa_renaming_needed = 0;
 116   fn->gimple_df->rename_vops = 0;
 117 }
 118
 119 /* Finalize management of SSA_NAMEs.  */
 120
 121 void
 122 fini_ssanames (void)
 123 {
 124   vec_free (SSANAMES (cfun));
 125   vec_free (FREE_SSANAMES (cfun));
 126 }
 127
 128 /* Dump some simple statistics regarding the re-use of SSA_NAME nodes.  */
 129
 130 void
 131 ssanames_print_statistics (void)
 132 {
 133   fprintf (stderr, "SSA_NAME nodes allocated: %u\n", ssa_name_nodes_created);
 134   fprintf (stderr, "SSA_NAME nodes reused: %u\n", ssa_name_nodes_reused);
 135 }
 136
 137 /* Return an SSA_NAME node for variable VAR defined in statement STMT
 138    in function FN.  STMT may be an empty statement for artificial
 139    references (e.g., default definitions created when a variable is
 140    used without a preceding definition).  */
 141
 142 tree
 143 make_ssa_name_fn (struct function *fn, tree var, gimple stmt)
 144 {
 145   tree t;
 146   use_operand_p imm;
 147
 148   gcc_assert (TREE_CODE (var) == VAR_DECL
 149               || TREE_CODE (var) == PARM_DECL
 150               || TREE_CODE (var) == RESULT_DECL
 151               || (TYPE_P (var) && is_gimple_reg_type (var)));
 152
 153   /* If our free list has an element, then use it.  */
 154   if (!vec_safe_is_empty (FREE_SSANAMES (fn)))
 155     {
 156       t = FREE_SSANAMES (fn)->pop ();
 157       if (GATHER_STATISTICS)
 158         ssa_name_nodes_reused++;
 159
 160       /* The node was cleared out when we put it on the free list, so
 161          there is no need to do so again here.  */
 162       gcc_assert ((*SSANAMES (fn))[SSA_NAME_VERSION (t)] == NULL);
 163       (*SSANAMES (fn))[SSA_NAME_VERSION (t)] = t;
 164     }
 165   else
 166     {
 167       t = make_node (SSA_NAME);
 168       SSA_NAME_VERSION (t) = SSANAMES (fn)->length ();
 169       vec_safe_push (SSANAMES (fn), t);
 170       if (GATHER_STATISTICS)
 171         ssa_name_nodes_created++;
 172     }
 173
 174   if (TYPE_P (var))
 175     {
 176       TREE_TYPE (t) = var;
 177       SET_SSA_NAME_VAR_OR_IDENTIFIER (t, NULL_TREE);
 178     }
 179   else
 180     {
 181       TREE_TYPE (t) = TREE_TYPE (var);
 182       SET_SSA_NAME_VAR_OR_IDENTIFIER (t, var);
 183     }
 184   SSA_NAME_DEF_STMT (t) = stmt;
 185   if (POINTER_TYPE_P (TREE_TYPE (t)))
 186     SSA_NAME_PTR_INFO (t) = NULL;
 187   else
 188     SSA_NAME_RANGE_INFO (t) = NULL;
 189
 190   SSA_NAME_IN_FREE_LIST (t) = 0;
 191   SSA_NAME_IS_DEFAULT_DEF (t) = 0;
 192   imm = &(SSA_NAME_IMM_USE_NODE (t));
 193   imm->use = NULL;
 194   imm->prev = imm;
 195   imm->next = imm;
 196   imm->loc.ssa_name = t;
 197
 198   return t;
 199 }
 200
 201 /* Store range information RANGE_TYPE, MIN, and MAX to tree ssa_name NAME.  */
 202
 203 void
 204 set_range_info (tree name, enum value_range_type range_type,
 205                 const wide_int_ref &min, const wide_int_ref &max)
 206 {
 207   gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
 208   gcc_assert (range_type == VR_RANGE || range_type == VR_ANTI_RANGE);
 209   range_info_def *ri = SSA_NAME_RANGE_INFO (name);
 210   unsigned int precision = TYPE_PRECISION (TREE_TYPE (name));
 211
 212   /* Allocate if not available.  */
 213   if (ri == NULL)
 214     {
 215       size_t size = (sizeof (range_info_def)
 216                      + trailing_wide_ints <3>::extra_size (precision));
 217       ri = static_cast<range_info_def *> (ggc_internal_alloc (size));
 218       ri->ints.set_precision (precision);
 219       SSA_NAME_RANGE_INFO (name) = ri;
 220       ri->set_nonzero_bits (wi::shwi (-1, precision));
 221     }
 222
 223   /* Record the range type.  */
 224   if (SSA_NAME_RANGE_TYPE (name) != range_type)
 225     SSA_NAME_ANTI_RANGE_P (name) = (range_type == VR_ANTI_RANGE);
 226
 227   /* Set the values.  */
 228   ri->set_min (min);
 229   ri->set_max (max);
 230
 231   /* If it is a range, try to improve nonzero_bits from the min/max.  */
 232   if (range_type == VR_RANGE)
 233     {
 234       wide_int xorv = ri->get_min () ^ ri->get_max ();
 235       if (xorv != 0)
 236         xorv = wi::mask (precision - wi::clz (xorv), false, precision);
 237       ri->set_nonzero_bits (ri->get_nonzero_bits () & (ri->get_min () | xorv));
 238     }
 239 }
 240
 241
 242 /* Gets range information MIN, MAX and returns enum value_range_type
 243    corresponding to tree ssa_name NAME.  enum value_range_type returned
 244    is used to determine if MIN and MAX are valid values.  */
 245
 246 enum value_range_type
 247 get_range_info (const_tree name, wide_int *min, wide_int *max)
 248 {
 249   gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
 250   gcc_assert (min && max);
 251   range_info_def *ri = SSA_NAME_RANGE_INFO (name);
 252
 253   /* Return VR_VARYING for SSA_NAMEs with NULL RANGE_INFO or SSA_NAMEs
 254      with integral types width > 2 * HOST_BITS_PER_WIDE_INT precision.  */
 255   if (!ri || (GET_MODE_PRECISION (TYPE_MODE (TREE_TYPE (name)))
 256               > 2 * HOST_BITS_PER_WIDE_INT))
 257     return VR_VARYING;
 258
 259   *min = ri->get_min ();
 260   *max = ri->get_max ();
 261   return SSA_NAME_RANGE_TYPE (name);
 262 }
 263
 264 /* Change non-zero bits bitmask of NAME.  */
 265
 266 void
 267 set_nonzero_bits (tree name, const wide_int_ref &mask)
 268 {
 269   gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
 270   if (SSA_NAME_RANGE_INFO (name) == NULL)
 271     set_range_info (name, VR_RANGE,
 272                     TYPE_MIN_VALUE (TREE_TYPE (name)),
 273                     TYPE_MAX_VALUE (TREE_TYPE (name)));
 274   range_info_def *ri = SSA_NAME_RANGE_INFO (name);
 275   ri->set_nonzero_bits (mask);
 276 }
 277
 278 /* Return a widest_int with potentially non-zero bits in SSA_NAME
 279    NAME, or -1 if unknown.  */
 280
 281 wide_int
 282 get_nonzero_bits (const_tree name)
 283 {
 284   unsigned int precision = TYPE_PRECISION (TREE_TYPE (name));
 285   if (POINTER_TYPE_P (TREE_TYPE (name)))
 286     {
 287       struct ptr_info_def *pi = SSA_NAME_PTR_INFO (name);
 288       if (pi && pi->align)
 289         return wi::shwi (-(HOST_WIDE_INT) pi->align
 290                          | (HOST_WIDE_INT) pi->misalign, precision);
 291       return wi::shwi (-1, precision);
 292     }
 293
 294   range_info_def *ri = SSA_NAME_RANGE_INFO (name);
 295   if (!ri)
 296     return wi::shwi (-1, precision);
 297
 298   return ri->get_nonzero_bits ();
 299 }
 300
 301 /* We no longer need the SSA_NAME expression VAR, release it so that
 302    it may be reused.
 303
 304    Note it is assumed that no calls to make_ssa_name will be made
 305    until all uses of the ssa name are released and that the only
 306    use of the SSA_NAME expression is to check its SSA_NAME_VAR.  All
 307    other fields must be assumed clobbered.  */
 308
 309 void
 310 release_ssa_name_fn (struct function *fn, tree var)
 311 {
 312   if (!var)
 313     return;
 314
 315   /* Never release the default definition for a symbol.  It's a
 316      special SSA name that should always exist once it's created.  */
 317   if (SSA_NAME_IS_DEFAULT_DEF (var))
 318     return;
 319
 320   /* If VAR has been registered for SSA updating, don't remove it.
 321      After update_ssa has run, the name will be released.  */
 322   if (name_registered_for_update_p (var))
 323     {
 324       release_ssa_name_after_update_ssa (var);
 325       return;
 326     }
 327
 328   /* release_ssa_name can be called multiple times on a single SSA_NAME.
 329      However, it should only end up on our free list one time.   We
 330      keep a status bit in the SSA_NAME node itself to indicate it has
 331      been put on the free list.
 332
 333      Note that once on the freelist you can not reference the SSA_NAME's
 334      defining statement.  */
 335   if (! SSA_NAME_IN_FREE_LIST (var))
 336     {
 337       tree saved_ssa_name_var = SSA_NAME_VAR (var);
 338       int saved_ssa_name_version = SSA_NAME_VERSION (var);
 339       use_operand_p imm = &(SSA_NAME_IMM_USE_NODE (var));
 340
 341       if (MAY_HAVE_DEBUG_STMTS)
 342         insert_debug_temp_for_var_def (NULL, var);
 343
 344 #ifdef ENABLE_CHECKING
 345       verify_imm_links (stderr, var);
 346 #endif
 347       while (imm->next != imm)
 348         delink_imm_use (imm->next);
 349
 350       (*SSANAMES (fn))[SSA_NAME_VERSION (var)] = NULL_TREE;
 351       memset (var, 0, tree_size (var));
 352
 353       imm->prev = imm;
 354       imm->next = imm;
 355       imm->loc.ssa_name = var;
 356
 357       /* First put back the right tree node so that the tree checking
 358          macros do not complain.  */
 359       TREE_SET_CODE (var, SSA_NAME);
 360
 361       /* Restore the version number.  */
 362       SSA_NAME_VERSION (var) = saved_ssa_name_version;
 363
 364       /* Hopefully this can go away once we have the new incremental
 365          SSA updating code installed.  */
 366       SET_SSA_NAME_VAR_OR_IDENTIFIER (var, saved_ssa_name_var);
 367
 368       /* Note this SSA_NAME is now in the first list.  */
 369       SSA_NAME_IN_FREE_LIST (var) = 1;
 370
 371       /* And finally put it on the free list.  */
 372       vec_safe_push (FREE_SSANAMES (fn), var);
 373     }
 374 }
 375
 376 /* If the alignment of the pointer described by PI is known, return true and
 377    store the alignment and the deviation from it into *ALIGNP and *MISALIGNP
 378    respectively.  Otherwise return false.  */
 379
 380 bool
 381 get_ptr_info_alignment (struct ptr_info_def *pi, unsigned int *alignp,
 382                         unsigned int *misalignp)
 383 {
 384   if (pi->align)
 385     {
 386       *alignp = pi->align;
 387       *misalignp = pi->misalign;
 388       return true;
 389     }
 390   else
 391     return false;
 392 }
 393
 394 /* State that the pointer described by PI has unknown alignment.  */
 395
 396 void
 397 mark_ptr_info_alignment_unknown (struct ptr_info_def *pi)
 398 {
 399   pi->align = 0;
 400   pi->misalign = 0;
 401 }
 402
 403 /* Store the the power-of-two byte alignment and the deviation from that
 404    alignment of pointer described by PI to ALIOGN and MISALIGN
 405    respectively.  */
 406
 407 void
 408 set_ptr_info_alignment (struct ptr_info_def *pi, unsigned int align,
 409                             unsigned int misalign)
 410 {
 411   gcc_checking_assert (align != 0);
 412   gcc_assert ((align & (align - 1)) == 0);
 413   gcc_assert ((misalign & ~(align - 1)) == 0);
 414
 415   pi->align = align;
 416   pi->misalign = misalign;
 417 }
 418
 419 /* If pointer described by PI has known alignment, increase its known
 420    misalignment by INCREMENT modulo its current alignment.  */
 421
 422 void
 423 adjust_ptr_info_misalignment (struct ptr_info_def *pi,
 424                               unsigned int increment)
 425 {
 426   if (pi->align != 0)
 427     {
 428       pi->misalign += increment;
 429       pi->misalign &= (pi->align - 1);
 430     }
 431 }
 432
 433 /* Return the alias information associated with pointer T.  It creates a
 434    new instance if none existed.  */
 435
 436 struct ptr_info_def *
 437 get_ptr_info (tree t)
 438 {
 439   struct ptr_info_def *pi;
 440
 441   gcc_assert (POINTER_TYPE_P (TREE_TYPE (t)));
 442
 443   pi = SSA_NAME_PTR_INFO (t);
 444   if (pi == NULL)
 445     {
 446       pi = ggc_cleared_alloc<ptr_info_def> ();
 447       pt_solution_reset (&pi->pt);
 448       mark_ptr_info_alignment_unknown (pi);
 449       SSA_NAME_PTR_INFO (t) = pi;
 450     }
 451
 452   return pi;
 453 }
 454
 455
 456 /* Creates a new SSA name using the template NAME tobe defined by
 457    statement STMT in function FN.  */
 458
 459 tree
 460 copy_ssa_name_fn (struct function *fn, tree name, gimple stmt)
 461 {
 462   tree new_name;
 463
 464   if (SSA_NAME_VAR (name))
 465     new_name = make_ssa_name_fn (fn, SSA_NAME_VAR (name), stmt);
 466   else
 467     {
 468       new_name = make_ssa_name_fn (fn, TREE_TYPE (name), stmt);
 469       SET_SSA_NAME_VAR_OR_IDENTIFIER (new_name, SSA_NAME_IDENTIFIER (name));
 470     }
 471
 472   return new_name;
 473 }
 474
 475
 476 /* Creates a duplicate of the ptr_info_def at PTR_INFO for use by
 477    the SSA name NAME.  */
 478
 479 void
 480 duplicate_ssa_name_ptr_info (tree name, struct ptr_info_def *ptr_info)
 481 {
 482   struct ptr_info_def *new_ptr_info;
 483
 484   gcc_assert (POINTER_TYPE_P (TREE_TYPE (name)));
 485   gcc_assert (!SSA_NAME_PTR_INFO (name));
 486
 487   if (!ptr_info)
 488     return;
 489
 490   new_ptr_info = ggc_alloc<ptr_info_def> ();
 491   *new_ptr_info = *ptr_info;
 492
 493   SSA_NAME_PTR_INFO (name) = new_ptr_info;
 494 }
 495
 496 /* Creates a duplicate of the range_info_def at RANGE_INFO of type
 497    RANGE_TYPE for use by the SSA name NAME.  */
 498 void
 499 duplicate_ssa_name_range_info (tree name, enum value_range_type range_type,
 500                                struct range_info_def *range_info)
 501 {
 502   struct range_info_def *new_range_info;
 503
 504   gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
 505   gcc_assert (!SSA_NAME_RANGE_INFO (name));
 506
 507   if (!range_info)
 508     return;
 509
 510   unsigned int precision = TYPE_PRECISION (TREE_TYPE (name));
 511   size_t size = (sizeof (range_info_def)
 512                  + trailing_wide_ints <3>::extra_size (precision));
 513   new_range_info = static_cast<range_info_def *> (ggc_internal_alloc (size));
 514   memcpy (new_range_info, range_info, size);
 515
 516   gcc_assert (range_type == VR_RANGE || range_type == VR_ANTI_RANGE);
 517   SSA_NAME_ANTI_RANGE_P (name) = (range_type == VR_ANTI_RANGE);
 518   SSA_NAME_RANGE_INFO (name) = new_range_info;
 519 }
 520
 521
 522
 523 /* Creates a duplicate of a ssa name NAME tobe defined by statement STMT
 524    in function FN.  */
 525
 526 tree
 527 duplicate_ssa_name_fn (struct function *fn, tree name, gimple stmt)
 528 {
 529   tree new_name = copy_ssa_name_fn (fn, name, stmt);
 530   if (POINTER_TYPE_P (TREE_TYPE (name)))
 531     {
 532       struct ptr_info_def *old_ptr_info = SSA_NAME_PTR_INFO (name);
 533
 534       if (old_ptr_info)
 535         duplicate_ssa_name_ptr_info (new_name, old_ptr_info);
 536     }
 537   else
 538     {
 539       struct range_info_def *old_range_info = SSA_NAME_RANGE_INFO (name);
 540
 541       if (old_range_info)
 542         duplicate_ssa_name_range_info (new_name, SSA_NAME_RANGE_TYPE (name),
 543                                        old_range_info);
 544     }
 545
 546   return new_name;
 547 }
 548
 549
 550 /* Reset all flow sensitive data on NAME such as range-info, nonzero
 551    bits and alignment.  */
 552
 553 void
 554 reset_flow_sensitive_info (tree name)
 555 {
 556   if (POINTER_TYPE_P (TREE_TYPE (name)))
 557     {
 558       /* points-to info is not flow-sensitive.  */
 559       if (SSA_NAME_PTR_INFO (name))
 560         mark_ptr_info_alignment_unknown (SSA_NAME_PTR_INFO (name));
 561     }
 562   else
 563     SSA_NAME_RANGE_INFO (name) = NULL;
 564 }
 565
 566 /* Clear all flow sensitive data from all statements and PHI definitions
 567    in BB.  */
 568
 569 void
 570 reset_flow_sensitive_info_in_bb (basic_block bb)
 571 {
 572   for (gimple_stmt_iterator gsi = gsi_start_bb (bb); !gsi_end_p (gsi);
 573        gsi_next (&gsi))
 574     {
 575       gimple stmt = gsi_stmt (gsi);
 576       ssa_op_iter i;
 577       tree op;
 578       FOR_EACH_SSA_TREE_OPERAND (op, stmt, i, SSA_OP_DEF)
 579         reset_flow_sensitive_info (op);
 580     }
 581
 582   for (gphi_iterator gsi = gsi_start_phis (bb); !gsi_end_p (gsi);
 583        gsi_next (&gsi))
 584     {
 585       tree phi_def = gimple_phi_result (gsi.phi ());
 586       reset_flow_sensitive_info (phi_def);
 587     }
 588 }
 589
 590 /* Release all the SSA_NAMEs created by STMT.  */
 591
 592 void
 593 release_defs (gimple stmt)
 594 {
 595   tree def;
 596   ssa_op_iter iter;
 597
 598   /* Make sure that we are in SSA.  Otherwise, operand cache may point
 599      to garbage.  */
 600   gcc_assert (gimple_in_ssa_p (cfun));
 601
 602   FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
 603     if (TREE_CODE (def) == SSA_NAME)
 604       release_ssa_name (def);
 605 }
 606
 607
 608 /* Replace the symbol associated with SSA_NAME with SYM.  */
 609
 610 void
 611 replace_ssa_name_symbol (tree ssa_name, tree sym)
 612 {
 613   SET_SSA_NAME_VAR_OR_IDENTIFIER (ssa_name, sym);
 614   TREE_TYPE (ssa_name) = TREE_TYPE (sym);
 615 }
 616
 617 /* Return SSA names that are unused to GGC memory and compact the SSA
 618    version namespace.  This is used to keep footprint of compiler during
 619    interprocedural optimization.  */
 620
 621 namespace {
 622
 623 const pass_data pass_data_release_ssa_names =
 624 {
 625   GIMPLE_PASS, /* type */
 626   "release_ssa", /* name */
 627   OPTGROUP_NONE, /* optinfo_flags */
 628   TV_TREE_SSA_OTHER, /* tv_id */
 629   PROP_ssa, /* properties_required */
 630   0, /* properties_provided */
 631   0, /* properties_destroyed */
 632   TODO_remove_unused_locals, /* todo_flags_start */
 633   0, /* todo_flags_finish */
 634 };
 635
 636 class pass_release_ssa_names : public gimple_opt_pass
 637 {
 638 public:
 639   pass_release_ssa_names (gcc::context *ctxt)
 640     : gimple_opt_pass (pass_data_release_ssa_names, ctxt)
 641   {}
 642
 643   /* opt_pass methods: */
 644   virtual unsigned int execute (function *);
 645
 646 }; // class pass_release_ssa_names
 647
 648 unsigned int
 649 pass_release_ssa_names::execute (function *fun)
 650 {
 651   unsigned i, j;
 652   int n = vec_safe_length (FREE_SSANAMES (fun));
 653
 654   /* Now release the freelist.  */
 655   vec_free (FREE_SSANAMES (fun));
 656
 657   /* And compact the SSA number space.  We make sure to not change the
 658      relative order of SSA versions.  */
 659   for (i = 1, j = 1; i < fun->gimple_df->ssa_names->length (); ++i)
 660     {
 661       tree name = ssa_name (i);
 662       if (name)
 663         {
 664           if (i != j)
 665             {
 666               SSA_NAME_VERSION (name) = j;
 667               (*fun->gimple_df->ssa_names)[j] = name;
 668             }
 669           j++;
 670         }
 671     }
 672   fun->gimple_df->ssa_names->truncate (j);
 673
 674   statistics_counter_event (fun, "SSA names released", n);
 675   statistics_counter_event (fun, "SSA name holes removed", i - j);
 676   if (dump_file)
 677     fprintf (dump_file, "Released %i names, %.2f%%, removed %i holes\n",
 678              n, n * 100.0 / num_ssa_names, i - j);
 679   return 0;
 680 }
 681
 682 } // anon namespace
 683
 684 gimple_opt_pass *
 685 make_pass_release_ssa_names (gcc::context *ctxt)
 686 {
 687   return new pass_release_ssa_names (ctxt);
 688 }