gcc/tree-ssanames.c

   1 /* Generic routines for manipulating SSA_NAME expressions
   2    Copyright (C) 2003-2013 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 "tree.h"
  25 #include "tree-ssa.h"
  26 #include "tree-pass.h"
  27
  28 /* Rewriting a function into SSA form can create a huge number of SSA_NAMEs,
  29    many of which may be thrown away shortly after their creation if jumps
  30    were threaded through PHI nodes.
  31
  32    While our garbage collection mechanisms will handle this situation, it
  33    is extremely wasteful to create nodes and throw them away, especially
  34    when the nodes can be reused.
  35
  36    For PR 8361, we can significantly reduce the number of nodes allocated
  37    and thus the total amount of memory allocated by managing SSA_NAMEs a
  38    little.  This additionally helps reduce the amount of work done by the
  39    garbage collector.  Similar results have been seen on a wider variety
  40    of tests (such as the compiler itself).
  41
  42    Right now we maintain our free list on a per-function basis.  It may
  43    or may not make sense to maintain the free list for the duration of
  44    a compilation unit.
  45
  46    External code should rely solely upon HIGHEST_SSA_VERSION and the
  47    externally defined functions.  External code should not know about
  48    the details of the free list management.
  49
  50    External code should also not assume the version number on nodes is
  51    monotonically increasing.  We reuse the version number when we
  52    reuse an SSA_NAME expression.  This helps keep arrays and bitmaps
  53    more compact.  */
  54
  55
  56 /* Version numbers with special meanings.  We start allocating new version
  57    numbers after the special ones.  */
  58 #define UNUSED_NAME_VERSION 0
  59
  60 unsigned int ssa_name_nodes_reused;
  61 unsigned int ssa_name_nodes_created;
  62
  63 #define FREE_SSANAMES(fun) (fun)->gimple_df->free_ssanames
  64
  65
  66 /* Initialize management of SSA_NAMEs to default SIZE.  If SIZE is
  67    zero use default.  */
  68
  69 void
  70 init_ssanames (struct function *fn, int size)
  71 {
  72   if (size < 50)
  73     size = 50;
  74
  75   vec_alloc (SSANAMES (fn), size);
  76
  77   /* Version 0 is special, so reserve the first slot in the table.  Though
  78      currently unused, we may use version 0 in alias analysis as part of
  79      the heuristics used to group aliases when the alias sets are too
  80      large.
  81
  82      We use vec::quick_push here because we know that SSA_NAMES has at
  83      least 50 elements reserved in it.  */
  84   SSANAMES (fn)->quick_push (NULL_TREE);
  85   FREE_SSANAMES (fn) = NULL;
  86
  87   fn->gimple_df->ssa_renaming_needed = 0;
  88   fn->gimple_df->rename_vops = 0;
  89 }
  90
  91 /* Finalize management of SSA_NAMEs.  */
  92
  93 void
  94 fini_ssanames (void)
  95 {
  96   vec_free (SSANAMES (cfun));
  97   vec_free (FREE_SSANAMES (cfun));
  98 }
  99
 100 /* Dump some simple statistics regarding the re-use of SSA_NAME nodes.  */
 101
 102 void
 103 ssanames_print_statistics (void)
 104 {
 105   fprintf (stderr, "SSA_NAME nodes allocated: %u\n", ssa_name_nodes_created);
 106   fprintf (stderr, "SSA_NAME nodes reused: %u\n", ssa_name_nodes_reused);
 107 }
 108
 109 /* Return an SSA_NAME node for variable VAR defined in statement STMT
 110    in function FN.  STMT may be an empty statement for artificial
 111    references (e.g., default definitions created when a variable is
 112    used without a preceding definition).  */
 113
 114 tree
 115 make_ssa_name_fn (struct function *fn, tree var, gimple stmt)
 116 {
 117   tree t;
 118   use_operand_p imm;
 119
 120   gcc_assert (TREE_CODE (var) == VAR_DECL
 121               || TREE_CODE (var) == PARM_DECL
 122               || TREE_CODE (var) == RESULT_DECL
 123               || (TYPE_P (var) && is_gimple_reg_type (var)));
 124
 125   /* If our free list has an element, then use it.  */
 126   if (!vec_safe_is_empty (FREE_SSANAMES (fn)))
 127     {
 128       t = FREE_SSANAMES (fn)->pop ();
 129       if (GATHER_STATISTICS)
 130         ssa_name_nodes_reused++;
 131
 132       /* The node was cleared out when we put it on the free list, so
 133          there is no need to do so again here.  */
 134       gcc_assert (ssa_name (SSA_NAME_VERSION (t)) == NULL);
 135       (*SSANAMES (fn))[SSA_NAME_VERSION (t)] = t;
 136     }
 137   else
 138     {
 139       t = make_node (SSA_NAME);
 140       SSA_NAME_VERSION (t) = SSANAMES (fn)->length ();
 141       vec_safe_push (SSANAMES (fn), t);
 142       if (GATHER_STATISTICS)
 143         ssa_name_nodes_created++;
 144     }
 145
 146   if (TYPE_P (var))
 147     {
 148       TREE_TYPE (t) = var;
 149       SET_SSA_NAME_VAR_OR_IDENTIFIER (t, NULL_TREE);
 150     }
 151   else
 152     {
 153       TREE_TYPE (t) = TREE_TYPE (var);
 154       SET_SSA_NAME_VAR_OR_IDENTIFIER (t, var);
 155     }
 156   SSA_NAME_DEF_STMT (t) = stmt;
 157   if (POINTER_TYPE_P (TREE_TYPE (t)))
 158     SSA_NAME_PTR_INFO (t) = NULL;
 159   else
 160     SSA_NAME_RANGE_INFO (t) = NULL;
 161
 162   SSA_NAME_IN_FREE_LIST (t) = 0;
 163   SSA_NAME_IS_DEFAULT_DEF (t) = 0;
 164   imm = &(SSA_NAME_IMM_USE_NODE (t));
 165   imm->use = NULL;
 166   imm->prev = imm;
 167   imm->next = imm;
 168   imm->loc.ssa_name = t;
 169
 170   return t;
 171 }
 172
 173 /* Store range information MIN, and MAX to tree ssa_name NAME.  */
 174
 175 void
 176 set_range_info (tree name, double_int min, double_int max)
 177 {
 178   gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
 179   range_info_def *ri = SSA_NAME_RANGE_INFO (name);
 180
 181   /* Allocate if not available.  */
 182   if (ri == NULL)
 183     {
 184       ri = ggc_alloc_cleared_range_info_def ();
 185       SSA_NAME_RANGE_INFO (name) = ri;
 186     }
 187
 188   /* Set the values.  */
 189   ri->min = min;
 190   ri->max = max;
 191 }
 192
 193
 194 /* Gets range information MIN, MAX and returns enum value_range_type
 195    corresponding to tree ssa_name NAME.  enum value_range_type returned
 196    is used to determine if MIN and MAX are valid values.  */
 197
 198 enum value_range_type
 199 get_range_info (tree name, double_int *min, double_int *max)
 200 {
 201   enum value_range_type range_type;
 202   gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
 203   gcc_assert (min && max);
 204   range_info_def *ri = SSA_NAME_RANGE_INFO (name);
 205
 206   /* Return VR_VARYING for SSA_NAMEs with NULL RANGE_INFO or SSA_NAMEs
 207      with integral types width > 2 * HOST_BITS_PER_WIDE_INT precision.  */
 208   if (!ri || (GET_MODE_PRECISION (TYPE_MODE (TREE_TYPE (name)))
 209               > 2 * HOST_BITS_PER_WIDE_INT))
 210     return VR_VARYING;
 211
 212   /* If min > max, it is VR_ANTI_RANGE.  */
 213   if (ri->min.cmp (ri->max, TYPE_UNSIGNED (TREE_TYPE (name))) == 1)
 214     {
 215       /* VR_ANTI_RANGE ~[min, max] is encoded as [max + 1, min - 1].  */
 216       range_type = VR_ANTI_RANGE;
 217       *min = ri->max + double_int_one;
 218       *max = ri->min - double_int_one;
 219     }
 220   else
 221   {
 222     /* Otherwise (when min <= max), it is VR_RANGE.  */
 223     range_type = VR_RANGE;
 224     *min = ri->min;
 225     *max = ri->max;
 226   }
 227   return range_type;
 228 }
 229
 230 /* We no longer need the SSA_NAME expression VAR, release it so that
 231    it may be reused.
 232
 233    Note it is assumed that no calls to make_ssa_name will be made
 234    until all uses of the ssa name are released and that the only
 235    use of the SSA_NAME expression is to check its SSA_NAME_VAR.  All
 236    other fields must be assumed clobbered.  */
 237
 238 void
 239 release_ssa_name (tree var)
 240 {
 241   if (!var)
 242     return;
 243
 244   /* Never release the default definition for a symbol.  It's a
 245      special SSA name that should always exist once it's created.  */
 246   if (SSA_NAME_IS_DEFAULT_DEF (var))
 247     return;
 248
 249   /* If VAR has been registered for SSA updating, don't remove it.
 250      After update_ssa has run, the name will be released.  */
 251   if (name_registered_for_update_p (var))
 252     {
 253       release_ssa_name_after_update_ssa (var);
 254       return;
 255     }
 256
 257   /* release_ssa_name can be called multiple times on a single SSA_NAME.
 258      However, it should only end up on our free list one time.   We
 259      keep a status bit in the SSA_NAME node itself to indicate it has
 260      been put on the free list.
 261
 262      Note that once on the freelist you can not reference the SSA_NAME's
 263      defining statement.  */
 264   if (! SSA_NAME_IN_FREE_LIST (var))
 265     {
 266       tree saved_ssa_name_var = SSA_NAME_VAR (var);
 267       int saved_ssa_name_version = SSA_NAME_VERSION (var);
 268       use_operand_p imm = &(SSA_NAME_IMM_USE_NODE (var));
 269
 270       if (MAY_HAVE_DEBUG_STMTS)
 271         insert_debug_temp_for_var_def (NULL, var);
 272
 273 #ifdef ENABLE_CHECKING
 274       verify_imm_links (stderr, var);
 275 #endif
 276       while (imm->next != imm)
 277         delink_imm_use (imm->next);
 278
 279       (*SSANAMES (cfun))[SSA_NAME_VERSION (var)] = NULL_TREE;
 280       memset (var, 0, tree_size (var));
 281
 282       imm->prev = imm;
 283       imm->next = imm;
 284       imm->loc.ssa_name = var;
 285
 286       /* First put back the right tree node so that the tree checking
 287          macros do not complain.  */
 288       TREE_SET_CODE (var, SSA_NAME);
 289
 290       /* Restore the version number.  */
 291       SSA_NAME_VERSION (var) = saved_ssa_name_version;
 292
 293       /* Hopefully this can go away once we have the new incremental
 294          SSA updating code installed.  */
 295       SET_SSA_NAME_VAR_OR_IDENTIFIER (var, saved_ssa_name_var);
 296
 297       /* Note this SSA_NAME is now in the first list.  */
 298       SSA_NAME_IN_FREE_LIST (var) = 1;
 299
 300       /* And finally put it on the free list.  */
 301       vec_safe_push (FREE_SSANAMES (cfun), var);
 302     }
 303 }
 304
 305 /* If the alignment of the pointer described by PI is known, return true and
 306    store the alignment and the deviation from it into *ALIGNP and *MISALIGNP
 307    respectively.  Otherwise return false.  */
 308
 309 bool
 310 get_ptr_info_alignment (struct ptr_info_def *pi, unsigned int *alignp,
 311                         unsigned int *misalignp)
 312 {
 313   if (pi->align)
 314     {
 315       *alignp = pi->align;
 316       *misalignp = pi->misalign;
 317       return true;
 318     }
 319   else
 320     return false;
 321 }
 322
 323 /* State that the pointer described by PI has unknown alignment.  */
 324
 325 void
 326 mark_ptr_info_alignment_unknown (struct ptr_info_def *pi)
 327 {
 328   pi->align = 0;
 329   pi->misalign = 0;
 330 }
 331
 332 /* Store the the power-of-two byte alignment and the deviation from that
 333    alignment of pointer described by PI to ALIOGN and MISALIGN
 334    respectively.  */
 335
 336 void
 337 set_ptr_info_alignment (struct ptr_info_def *pi, unsigned int align,
 338                             unsigned int misalign)
 339 {
 340   gcc_checking_assert (align != 0);
 341   gcc_assert ((align & (align - 1)) == 0);
 342   gcc_assert ((misalign & ~(align - 1)) == 0);
 343
 344   pi->align = align;
 345   pi->misalign = misalign;
 346 }
 347
 348 /* If pointer described by PI has known alignment, increase its known
 349    misalignment by INCREMENT modulo its current alignment.  */
 350
 351 void
 352 adjust_ptr_info_misalignment (struct ptr_info_def *pi,
 353                               unsigned int increment)
 354 {
 355   if (pi->align != 0)
 356     {
 357       pi->misalign += increment;
 358       pi->misalign &= (pi->align - 1);
 359     }
 360 }
 361
 362 /* Return the alias information associated with pointer T.  It creates a
 363    new instance if none existed.  */
 364
 365 struct ptr_info_def *
 366 get_ptr_info (tree t)
 367 {
 368   struct ptr_info_def *pi;
 369
 370   gcc_assert (POINTER_TYPE_P (TREE_TYPE (t)));
 371
 372   pi = SSA_NAME_PTR_INFO (t);
 373   if (pi == NULL)
 374     {
 375       pi = ggc_alloc_cleared_ptr_info_def ();
 376       pt_solution_reset (&pi->pt);
 377       mark_ptr_info_alignment_unknown (pi);
 378       SSA_NAME_PTR_INFO (t) = pi;
 379     }
 380
 381   return pi;
 382 }
 383
 384
 385 /* Creates a new SSA name using the template NAME tobe defined by
 386    statement STMT in function FN.  */
 387
 388 tree
 389 copy_ssa_name_fn (struct function *fn, tree name, gimple stmt)
 390 {
 391   tree new_name;
 392
 393   if (SSA_NAME_VAR (name))
 394     new_name = make_ssa_name_fn (fn, SSA_NAME_VAR (name), stmt);
 395   else
 396     {
 397       new_name = make_ssa_name_fn (fn, TREE_TYPE (name), stmt);
 398       SET_SSA_NAME_VAR_OR_IDENTIFIER (new_name, SSA_NAME_IDENTIFIER (name));
 399     }
 400
 401   return new_name;
 402 }
 403
 404
 405 /* Creates a duplicate of the ptr_info_def at PTR_INFO for use by
 406    the SSA name NAME.  */
 407
 408 void
 409 duplicate_ssa_name_ptr_info (tree name, struct ptr_info_def *ptr_info)
 410 {
 411   struct ptr_info_def *new_ptr_info;
 412
 413   gcc_assert (POINTER_TYPE_P (TREE_TYPE (name)));
 414   gcc_assert (!SSA_NAME_PTR_INFO (name));
 415
 416   if (!ptr_info)
 417     return;
 418
 419   new_ptr_info = ggc_alloc_ptr_info_def ();
 420   *new_ptr_info = *ptr_info;
 421
 422   SSA_NAME_PTR_INFO (name) = new_ptr_info;
 423 }
 424
 425 /* Creates a duplicate of the range_info_def at RANGE_INFO for use by
 426    the SSA name NAME.  */
 427 void
 428 duplicate_ssa_name_range_info (tree name, struct range_info_def *range_info)
 429 {
 430   struct range_info_def *new_range_info;
 431
 432   gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
 433   gcc_assert (!SSA_NAME_RANGE_INFO (name));
 434
 435   if (!range_info)
 436     return;
 437
 438   new_range_info = ggc_alloc_range_info_def ();
 439   *new_range_info = *range_info;
 440
 441   SSA_NAME_RANGE_INFO (name) = new_range_info;
 442 }
 443
 444
 445
 446 /* Creates a duplicate of a ssa name NAME tobe defined by statement STMT
 447    in function FN.  */
 448
 449 tree
 450 duplicate_ssa_name_fn (struct function *fn, tree name, gimple stmt)
 451 {
 452   tree new_name = copy_ssa_name_fn (fn, name, stmt);
 453   if (POINTER_TYPE_P (TREE_TYPE (name)))
 454     {
 455       struct ptr_info_def *old_ptr_info = SSA_NAME_PTR_INFO (name);
 456
 457       if (old_ptr_info)
 458         duplicate_ssa_name_ptr_info (new_name, old_ptr_info);
 459     }
 460   else
 461     {
 462       struct range_info_def *old_range_info = SSA_NAME_RANGE_INFO (name);
 463
 464       if (old_range_info)
 465         duplicate_ssa_name_range_info (new_name, old_range_info);
 466     }
 467
 468   return new_name;
 469 }
 470
 471
 472 /* Release all the SSA_NAMEs created by STMT.  */
 473
 474 void
 475 release_defs (gimple stmt)
 476 {
 477   tree def;
 478   ssa_op_iter iter;
 479
 480   /* Make sure that we are in SSA.  Otherwise, operand cache may point
 481      to garbage.  */
 482   gcc_assert (gimple_in_ssa_p (cfun));
 483
 484   FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
 485     if (TREE_CODE (def) == SSA_NAME)
 486       release_ssa_name (def);
 487 }
 488
 489
 490 /* Replace the symbol associated with SSA_NAME with SYM.  */
 491
 492 void
 493 replace_ssa_name_symbol (tree ssa_name, tree sym)
 494 {
 495   SET_SSA_NAME_VAR_OR_IDENTIFIER (ssa_name, sym);
 496   TREE_TYPE (ssa_name) = TREE_TYPE (sym);
 497 }
 498
 499 /* Return SSA names that are unused to GGC memory and compact the SSA
 500    version namespace.  This is used to keep footprint of compiler during
 501    interprocedural optimization.  */
 502 static unsigned int
 503 release_dead_ssa_names (void)
 504 {
 505   unsigned i, j;
 506   int n = vec_safe_length (FREE_SSANAMES (cfun));
 507
 508   /* Now release the freelist.  */
 509   vec_free (FREE_SSANAMES (cfun));
 510
 511   /* And compact the SSA number space.  We make sure to not change the
 512      relative order of SSA versions.  */
 513   for (i = 1, j = 1; i < cfun->gimple_df->ssa_names->length (); ++i)
 514     {
 515       tree name = ssa_name (i);
 516       if (name)
 517         {
 518           if (i != j)
 519             {
 520               SSA_NAME_VERSION (name) = j;
 521               (*cfun->gimple_df->ssa_names)[j] = name;
 522             }
 523           j++;
 524         }
 525     }
 526   cfun->gimple_df->ssa_names->truncate (j);
 527
 528   statistics_counter_event (cfun, "SSA names released", n);
 529   statistics_counter_event (cfun, "SSA name holes removed", i - j);
 530   if (dump_file)
 531     fprintf (dump_file, "Released %i names, %.2f%%, removed %i holes\n",
 532              n, n * 100.0 / num_ssa_names, i - j);
 533   return 0;
 534 }
 535
 536 namespace {
 537
 538 const pass_data pass_data_release_ssa_names =
 539 {
 540   GIMPLE_PASS, /* type */
 541   "release_ssa", /* name */
 542   OPTGROUP_NONE, /* optinfo_flags */
 543   false, /* has_gate */
 544   true, /* has_execute */
 545   TV_TREE_SSA_OTHER, /* tv_id */
 546   PROP_ssa, /* properties_required */
 547   0, /* properties_provided */
 548   0, /* properties_destroyed */
 549   TODO_remove_unused_locals, /* todo_flags_start */
 550   0, /* todo_flags_finish */
 551 };
 552
 553 class pass_release_ssa_names : public gimple_opt_pass
 554 {
 555 public:
 556   pass_release_ssa_names (gcc::context *ctxt)
 557     : gimple_opt_pass (pass_data_release_ssa_names, ctxt)
 558   {}
 559
 560   /* opt_pass methods: */
 561   unsigned int execute () { return release_dead_ssa_names (); }
 562
 563 }; // class pass_release_ssa_names
 564
 565 } // anon namespace
 566
 567 gimple_opt_pass *
 568 make_pass_release_ssa_names (gcc::context *ctxt)
 569 {
 570   return new pass_release_ssa_names (ctxt);
 571 }