gcc/tree-ssanames.c

   1 /* Generic routines for manipulating SSA_NAME expressions
   2    Copyright (C) 2003-2014 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 "stor-layout.h"
  26 #include "basic-block.h"
  27 #include "tree-ssa-alias.h"
  28 #include "internal-fn.h"
  29 #include "gimple-expr.h"
  30 #include "is-a.h"
  31 #include "gimple.h"
  32 #include "gimple-ssa.h"
  33 #include "tree-phinodes.h"
  34 #include "ssa-iterators.h"
  35 #include "stringpool.h"
  36 #include "tree-ssanames.h"
  37 #include "tree-into-ssa.h"
  38 #include "tree-ssa.h"
  39 #include "tree-pass.h"
  40
  41 /* Rewriting a function into SSA form can create a huge number of SSA_NAMEs,
  42    many of which may be thrown away shortly after their creation if jumps
  43    were threaded through PHI nodes.
  44
  45    While our garbage collection mechanisms will handle this situation, it
  46    is extremely wasteful to create nodes and throw them away, especially
  47    when the nodes can be reused.
  48
  49    For PR 8361, we can significantly reduce the number of nodes allocated
  50    and thus the total amount of memory allocated by managing SSA_NAMEs a
  51    little.  This additionally helps reduce the amount of work done by the
  52    garbage collector.  Similar results have been seen on a wider variety
  53    of tests (such as the compiler itself).
  54
  55    Right now we maintain our free list on a per-function basis.  It may
  56    or may not make sense to maintain the free list for the duration of
  57    a compilation unit.
  58
  59    External code should rely solely upon HIGHEST_SSA_VERSION and the
  60    externally defined functions.  External code should not know about
  61    the details of the free list management.
  62
  63    External code should also not assume the version number on nodes is
  64    monotonically increasing.  We reuse the version number when we
  65    reuse an SSA_NAME expression.  This helps keep arrays and bitmaps
  66    more compact.  */
  67
  68
  69 /* Version numbers with special meanings.  We start allocating new version
  70    numbers after the special ones.  */
  71 #define UNUSED_NAME_VERSION 0
  72
  73 unsigned int ssa_name_nodes_reused;
  74 unsigned int ssa_name_nodes_created;
  75
  76 #define FREE_SSANAMES(fun) (fun)->gimple_df->free_ssanames
  77
  78
  79 /* Initialize management of SSA_NAMEs to default SIZE.  If SIZE is
  80    zero use default.  */
  81
  82 void
  83 init_ssanames (struct function *fn, int size)
  84 {
  85   if (size < 50)
  86     size = 50;
  87
  88   vec_alloc (SSANAMES (fn), size);
  89
  90   /* Version 0 is special, so reserve the first slot in the table.  Though
  91      currently unused, we may use version 0 in alias analysis as part of
  92      the heuristics used to group aliases when the alias sets are too
  93      large.
  94
  95      We use vec::quick_push here because we know that SSA_NAMES has at
  96      least 50 elements reserved in it.  */
  97   SSANAMES (fn)->quick_push (NULL_TREE);
  98   FREE_SSANAMES (fn) = NULL;
  99
 100   fn->gimple_df->ssa_renaming_needed = 0;
 101   fn->gimple_df->rename_vops = 0;
 102 }
 103
 104 /* Finalize management of SSA_NAMEs.  */
 105
 106 void
 107 fini_ssanames (void)
 108 {
 109   vec_free (SSANAMES (cfun));
 110   vec_free (FREE_SSANAMES (cfun));
 111 }
 112
 113 /* Dump some simple statistics regarding the re-use of SSA_NAME nodes.  */
 114
 115 void
 116 ssanames_print_statistics (void)
 117 {
 118   fprintf (stderr, "SSA_NAME nodes allocated: %u\n", ssa_name_nodes_created);
 119   fprintf (stderr, "SSA_NAME nodes reused: %u\n", ssa_name_nodes_reused);
 120 }
 121
 122 /* Return an SSA_NAME node for variable VAR defined in statement STMT
 123    in function FN.  STMT may be an empty statement for artificial
 124    references (e.g., default definitions created when a variable is
 125    used without a preceding definition).  */
 126
 127 tree
 128 make_ssa_name_fn (struct function *fn, tree var, gimple stmt)
 129 {
 130   tree t;
 131   use_operand_p imm;
 132
 133   gcc_assert (TREE_CODE (var) == VAR_DECL
 134               || TREE_CODE (var) == PARM_DECL
 135               || TREE_CODE (var) == RESULT_DECL
 136               || (TYPE_P (var) && is_gimple_reg_type (var)));
 137
 138   /* If our free list has an element, then use it.  */
 139   if (!vec_safe_is_empty (FREE_SSANAMES (fn)))
 140     {
 141       t = FREE_SSANAMES (fn)->pop ();
 142       if (GATHER_STATISTICS)
 143         ssa_name_nodes_reused++;
 144
 145       /* The node was cleared out when we put it on the free list, so
 146          there is no need to do so again here.  */
 147       gcc_assert ((*SSANAMES (fn))[SSA_NAME_VERSION (t)] == NULL);
 148       (*SSANAMES (fn))[SSA_NAME_VERSION (t)] = t;
 149     }
 150   else
 151     {
 152       t = make_node (SSA_NAME);
 153       SSA_NAME_VERSION (t) = SSANAMES (fn)->length ();
 154       vec_safe_push (SSANAMES (fn), t);
 155       if (GATHER_STATISTICS)
 156         ssa_name_nodes_created++;
 157     }
 158
 159   if (TYPE_P (var))
 160     {
 161       TREE_TYPE (t) = var;
 162       SET_SSA_NAME_VAR_OR_IDENTIFIER (t, NULL_TREE);
 163     }
 164   else
 165     {
 166       TREE_TYPE (t) = TREE_TYPE (var);
 167       SET_SSA_NAME_VAR_OR_IDENTIFIER (t, var);
 168     }
 169   SSA_NAME_DEF_STMT (t) = stmt;
 170   if (POINTER_TYPE_P (TREE_TYPE (t)))
 171     SSA_NAME_PTR_INFO (t) = NULL;
 172   else
 173     SSA_NAME_RANGE_INFO (t) = NULL;
 174
 175   SSA_NAME_IN_FREE_LIST (t) = 0;
 176   SSA_NAME_IS_DEFAULT_DEF (t) = 0;
 177   imm = &(SSA_NAME_IMM_USE_NODE (t));
 178   imm->use = NULL;
 179   imm->prev = imm;
 180   imm->next = imm;
 181   imm->loc.ssa_name = t;
 182
 183   return t;
 184 }
 185
 186 /* Store range information RANGE_TYPE, MIN, and MAX to tree ssa_name NAME.  */
 187
 188 void
 189 set_range_info (tree name, enum value_range_type range_type,
 190                 const wide_int_ref &min, const wide_int_ref &max)
 191 {
 192   gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
 193   gcc_assert (range_type == VR_RANGE || range_type == VR_ANTI_RANGE);
 194   range_info_def *ri = SSA_NAME_RANGE_INFO (name);
 195   unsigned int precision = TYPE_PRECISION (TREE_TYPE (name));
 196
 197   /* Allocate if not available.  */
 198   if (ri == NULL)
 199     {
 200       size_t size = (sizeof (range_info_def)
 201                      + trailing_wide_ints <3>::extra_size (precision));
 202       ri = ggc_alloc_range_info_def (size);
 203       ri->ints.set_precision (precision);
 204       SSA_NAME_RANGE_INFO (name) = ri;
 205       ri->set_nonzero_bits (wi::shwi (-1, precision));
 206     }
 207
 208   /* Record the range type.  */
 209   if (SSA_NAME_RANGE_TYPE (name) != range_type)
 210     SSA_NAME_ANTI_RANGE_P (name) = (range_type == VR_ANTI_RANGE);
 211
 212   /* Set the values.  */
 213   ri->set_min (min);
 214   ri->set_max (max);
 215
 216   /* If it is a range, try to improve nonzero_bits from the min/max.  */
 217   if (range_type == VR_RANGE)
 218     {
 219       wide_int xorv = ri->get_min () ^ ri->get_max ();
 220       if (xorv != 0)
 221         xorv = wi::mask (precision - wi::clz (xorv), false, precision);
 222       ri->set_nonzero_bits (ri->get_nonzero_bits () & (ri->get_min () | xorv));
 223     }
 224 }
 225
 226
 227 /* Gets range information MIN, MAX and returns enum value_range_type
 228    corresponding to tree ssa_name NAME.  enum value_range_type returned
 229    is used to determine if MIN and MAX are valid values.  */
 230
 231 enum value_range_type
 232 get_range_info (const_tree name, wide_int *min, wide_int *max)
 233 {
 234   gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
 235   gcc_assert (min && max);
 236   range_info_def *ri = SSA_NAME_RANGE_INFO (name);
 237
 238   /* Return VR_VARYING for SSA_NAMEs with NULL RANGE_INFO or SSA_NAMEs
 239      with integral types width > 2 * HOST_BITS_PER_WIDE_INT precision.  */
 240   if (!ri || (GET_MODE_PRECISION (TYPE_MODE (TREE_TYPE (name)))
 241               > 2 * HOST_BITS_PER_WIDE_INT))
 242     return VR_VARYING;
 243
 244   *min = ri->get_min ();
 245   *max = ri->get_max ();
 246   return SSA_NAME_RANGE_TYPE (name);
 247 }
 248
 249 /* Change non-zero bits bitmask of NAME.  */
 250
 251 void
 252 set_nonzero_bits (tree name, const wide_int_ref &mask)
 253 {
 254   gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
 255   if (SSA_NAME_RANGE_INFO (name) == NULL)
 256     set_range_info (name, VR_RANGE,
 257                     TYPE_MIN_VALUE (TREE_TYPE (name)),
 258                     TYPE_MAX_VALUE (TREE_TYPE (name)));
 259   range_info_def *ri = SSA_NAME_RANGE_INFO (name);
 260   ri->set_nonzero_bits (mask);
 261 }
 262
 263 /* Return a widest_int with potentially non-zero bits in SSA_NAME
 264    NAME, or -1 if unknown.  */
 265
 266 wide_int
 267 get_nonzero_bits (const_tree name)
 268 {
 269   unsigned int precision = TYPE_PRECISION (TREE_TYPE (name));
 270   if (POINTER_TYPE_P (TREE_TYPE (name)))
 271     {
 272       struct ptr_info_def *pi = SSA_NAME_PTR_INFO (name);
 273       if (pi && pi->align)
 274         return wi::shwi (-(int) pi->align | pi->misalign, precision);
 275       return wi::shwi (-1, precision);
 276     }
 277
 278   range_info_def *ri = SSA_NAME_RANGE_INFO (name);
 279   if (!ri)
 280     return wi::shwi (-1, precision);
 281
 282   return ri->get_nonzero_bits ();
 283 }
 284
 285 /* We no longer need the SSA_NAME expression VAR, release it so that
 286    it may be reused.
 287
 288    Note it is assumed that no calls to make_ssa_name will be made
 289    until all uses of the ssa name are released and that the only
 290    use of the SSA_NAME expression is to check its SSA_NAME_VAR.  All
 291    other fields must be assumed clobbered.  */
 292
 293 void
 294 release_ssa_name_fn (struct function *fn, tree var)
 295 {
 296   if (!var)
 297     return;
 298
 299   /* Never release the default definition for a symbol.  It's a
 300      special SSA name that should always exist once it's created.  */
 301   if (SSA_NAME_IS_DEFAULT_DEF (var))
 302     return;
 303
 304   /* If VAR has been registered for SSA updating, don't remove it.
 305      After update_ssa has run, the name will be released.  */
 306   if (name_registered_for_update_p (var))
 307     {
 308       release_ssa_name_after_update_ssa (var);
 309       return;
 310     }
 311
 312   /* release_ssa_name can be called multiple times on a single SSA_NAME.
 313      However, it should only end up on our free list one time.   We
 314      keep a status bit in the SSA_NAME node itself to indicate it has
 315      been put on the free list.
 316
 317      Note that once on the freelist you can not reference the SSA_NAME's
 318      defining statement.  */
 319   if (! SSA_NAME_IN_FREE_LIST (var))
 320     {
 321       tree saved_ssa_name_var = SSA_NAME_VAR (var);
 322       int saved_ssa_name_version = SSA_NAME_VERSION (var);
 323       use_operand_p imm = &(SSA_NAME_IMM_USE_NODE (var));
 324
 325       if (MAY_HAVE_DEBUG_STMTS)
 326         insert_debug_temp_for_var_def (NULL, var);
 327
 328 #ifdef ENABLE_CHECKING
 329       verify_imm_links (stderr, var);
 330 #endif
 331       while (imm->next != imm)
 332         delink_imm_use (imm->next);
 333
 334       (*SSANAMES (fn))[SSA_NAME_VERSION (var)] = NULL_TREE;
 335       memset (var, 0, tree_size (var));
 336
 337       imm->prev = imm;
 338       imm->next = imm;
 339       imm->loc.ssa_name = var;
 340
 341       /* First put back the right tree node so that the tree checking
 342          macros do not complain.  */
 343       TREE_SET_CODE (var, SSA_NAME);
 344
 345       /* Restore the version number.  */
 346       SSA_NAME_VERSION (var) = saved_ssa_name_version;
 347
 348       /* Hopefully this can go away once we have the new incremental
 349          SSA updating code installed.  */
 350       SET_SSA_NAME_VAR_OR_IDENTIFIER (var, saved_ssa_name_var);
 351
 352       /* Note this SSA_NAME is now in the first list.  */
 353       SSA_NAME_IN_FREE_LIST (var) = 1;
 354
 355       /* And finally put it on the free list.  */
 356       vec_safe_push (FREE_SSANAMES (fn), var);
 357     }
 358 }
 359
 360 /* If the alignment of the pointer described by PI is known, return true and
 361    store the alignment and the deviation from it into *ALIGNP and *MISALIGNP
 362    respectively.  Otherwise return false.  */
 363
 364 bool
 365 get_ptr_info_alignment (struct ptr_info_def *pi, unsigned int *alignp,
 366                         unsigned int *misalignp)
 367 {
 368   if (pi->align)
 369     {
 370       *alignp = pi->align;
 371       *misalignp = pi->misalign;
 372       return true;
 373     }
 374   else
 375     return false;
 376 }
 377
 378 /* State that the pointer described by PI has unknown alignment.  */
 379
 380 void
 381 mark_ptr_info_alignment_unknown (struct ptr_info_def *pi)
 382 {
 383   pi->align = 0;
 384   pi->misalign = 0;
 385 }
 386
 387 /* Store the the power-of-two byte alignment and the deviation from that
 388    alignment of pointer described by PI to ALIOGN and MISALIGN
 389    respectively.  */
 390
 391 void
 392 set_ptr_info_alignment (struct ptr_info_def *pi, unsigned int align,
 393                             unsigned int misalign)
 394 {
 395   gcc_checking_assert (align != 0);
 396   gcc_assert ((align & (align - 1)) == 0);
 397   gcc_assert ((misalign & ~(align - 1)) == 0);
 398
 399   pi->align = align;
 400   pi->misalign = misalign;
 401 }
 402
 403 /* If pointer described by PI has known alignment, increase its known
 404    misalignment by INCREMENT modulo its current alignment.  */
 405
 406 void
 407 adjust_ptr_info_misalignment (struct ptr_info_def *pi,
 408                               unsigned int increment)
 409 {
 410   if (pi->align != 0)
 411     {
 412       pi->misalign += increment;
 413       pi->misalign &= (pi->align - 1);
 414     }
 415 }
 416
 417 /* Return the alias information associated with pointer T.  It creates a
 418    new instance if none existed.  */
 419
 420 struct ptr_info_def *
 421 get_ptr_info (tree t)
 422 {
 423   struct ptr_info_def *pi;
 424
 425   gcc_assert (POINTER_TYPE_P (TREE_TYPE (t)));
 426
 427   pi = SSA_NAME_PTR_INFO (t);
 428   if (pi == NULL)
 429     {
 430       pi = ggc_alloc_cleared_ptr_info_def ();
 431       pt_solution_reset (&pi->pt);
 432       mark_ptr_info_alignment_unknown (pi);
 433       SSA_NAME_PTR_INFO (t) = pi;
 434     }
 435
 436   return pi;
 437 }
 438
 439
 440 /* Creates a new SSA name using the template NAME tobe defined by
 441    statement STMT in function FN.  */
 442
 443 tree
 444 copy_ssa_name_fn (struct function *fn, tree name, gimple stmt)
 445 {
 446   tree new_name;
 447
 448   if (SSA_NAME_VAR (name))
 449     new_name = make_ssa_name_fn (fn, SSA_NAME_VAR (name), stmt);
 450   else
 451     {
 452       new_name = make_ssa_name_fn (fn, TREE_TYPE (name), stmt);
 453       SET_SSA_NAME_VAR_OR_IDENTIFIER (new_name, SSA_NAME_IDENTIFIER (name));
 454     }
 455
 456   return new_name;
 457 }
 458
 459
 460 /* Creates a duplicate of the ptr_info_def at PTR_INFO for use by
 461    the SSA name NAME.  */
 462
 463 void
 464 duplicate_ssa_name_ptr_info (tree name, struct ptr_info_def *ptr_info)
 465 {
 466   struct ptr_info_def *new_ptr_info;
 467
 468   gcc_assert (POINTER_TYPE_P (TREE_TYPE (name)));
 469   gcc_assert (!SSA_NAME_PTR_INFO (name));
 470
 471   if (!ptr_info)
 472     return;
 473
 474   new_ptr_info = ggc_alloc_ptr_info_def ();
 475   *new_ptr_info = *ptr_info;
 476
 477   SSA_NAME_PTR_INFO (name) = new_ptr_info;
 478 }
 479
 480 /* Creates a duplicate of the range_info_def at RANGE_INFO of type
 481    RANGE_TYPE for use by the SSA name NAME.  */
 482 void
 483 duplicate_ssa_name_range_info (tree name, enum value_range_type range_type,
 484                                struct range_info_def *range_info)
 485 {
 486   struct range_info_def *new_range_info;
 487
 488   gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
 489   gcc_assert (!SSA_NAME_RANGE_INFO (name));
 490   gcc_assert (!SSA_NAME_ANTI_RANGE_P (name));
 491
 492   if (!range_info)
 493     return;
 494
 495   unsigned int precision = TYPE_PRECISION (TREE_TYPE (name));
 496   size_t size = (sizeof (range_info_def)
 497                  + trailing_wide_ints <3>::extra_size (precision));
 498   new_range_info = ggc_alloc_range_info_def (size);
 499   memcpy (new_range_info, range_info, size);
 500
 501   gcc_assert (range_type == VR_RANGE || range_type == VR_ANTI_RANGE);
 502   SSA_NAME_ANTI_RANGE_P (name) = (range_type == VR_ANTI_RANGE);
 503   SSA_NAME_RANGE_INFO (name) = new_range_info;
 504 }
 505
 506
 507
 508 /* Creates a duplicate of a ssa name NAME tobe defined by statement STMT
 509    in function FN.  */
 510
 511 tree
 512 duplicate_ssa_name_fn (struct function *fn, tree name, gimple stmt)
 513 {
 514   tree new_name = copy_ssa_name_fn (fn, name, stmt);
 515   if (POINTER_TYPE_P (TREE_TYPE (name)))
 516     {
 517       struct ptr_info_def *old_ptr_info = SSA_NAME_PTR_INFO (name);
 518
 519       if (old_ptr_info)
 520         duplicate_ssa_name_ptr_info (new_name, old_ptr_info);
 521     }
 522   else
 523     {
 524       struct range_info_def *old_range_info = SSA_NAME_RANGE_INFO (name);
 525
 526       if (old_range_info)
 527         duplicate_ssa_name_range_info (new_name, SSA_NAME_RANGE_TYPE (name),
 528                                        old_range_info);
 529     }
 530
 531   return new_name;
 532 }
 533
 534
 535 /* Release all the SSA_NAMEs created by STMT.  */
 536
 537 void
 538 release_defs (gimple stmt)
 539 {
 540   tree def;
 541   ssa_op_iter iter;
 542
 543   /* Make sure that we are in SSA.  Otherwise, operand cache may point
 544      to garbage.  */
 545   gcc_assert (gimple_in_ssa_p (cfun));
 546
 547   FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
 548     if (TREE_CODE (def) == SSA_NAME)
 549       release_ssa_name (def);
 550 }
 551
 552
 553 /* Replace the symbol associated with SSA_NAME with SYM.  */
 554
 555 void
 556 replace_ssa_name_symbol (tree ssa_name, tree sym)
 557 {
 558   SET_SSA_NAME_VAR_OR_IDENTIFIER (ssa_name, sym);
 559   TREE_TYPE (ssa_name) = TREE_TYPE (sym);
 560 }
 561
 562 /* Return SSA names that are unused to GGC memory and compact the SSA
 563    version namespace.  This is used to keep footprint of compiler during
 564    interprocedural optimization.  */
 565
 566 namespace {
 567
 568 const pass_data pass_data_release_ssa_names =
 569 {
 570   GIMPLE_PASS, /* type */
 571   "release_ssa", /* name */
 572   OPTGROUP_NONE, /* optinfo_flags */
 573   true, /* has_execute */
 574   TV_TREE_SSA_OTHER, /* tv_id */
 575   PROP_ssa, /* properties_required */
 576   0, /* properties_provided */
 577   0, /* properties_destroyed */
 578   TODO_remove_unused_locals, /* todo_flags_start */
 579   0, /* todo_flags_finish */
 580 };
 581
 582 class pass_release_ssa_names : public gimple_opt_pass
 583 {
 584 public:
 585   pass_release_ssa_names (gcc::context *ctxt)
 586     : gimple_opt_pass (pass_data_release_ssa_names, ctxt)
 587   {}
 588
 589   /* opt_pass methods: */
 590   virtual unsigned int execute (function *);
 591
 592 }; // class pass_release_ssa_names
 593
 594 unsigned int
 595 pass_release_ssa_names::execute (function *fun)
 596 {
 597   unsigned i, j;
 598   int n = vec_safe_length (FREE_SSANAMES (fun));
 599
 600   /* Now release the freelist.  */
 601   vec_free (FREE_SSANAMES (fun));
 602
 603   /* And compact the SSA number space.  We make sure to not change the
 604      relative order of SSA versions.  */
 605   for (i = 1, j = 1; i < fun->gimple_df->ssa_names->length (); ++i)
 606     {
 607       tree name = ssa_name (i);
 608       if (name)
 609         {
 610           if (i != j)
 611             {
 612               SSA_NAME_VERSION (name) = j;
 613               (*fun->gimple_df->ssa_names)[j] = name;
 614             }
 615           j++;
 616         }
 617     }
 618   fun->gimple_df->ssa_names->truncate (j);
 619
 620   statistics_counter_event (fun, "SSA names released", n);
 621   statistics_counter_event (fun, "SSA name holes removed", i - j);
 622   if (dump_file)
 623     fprintf (dump_file, "Released %i names, %.2f%%, removed %i holes\n",
 624              n, n * 100.0 / num_ssa_names, i - j);
 625   return 0;
 626 }
 627
 628 } // anon namespace
 629
 630 gimple_opt_pass *
 631 make_pass_release_ssa_names (gcc::context *ctxt)
 632 {
 633   return new pass_release_ssa_names (ctxt);
 634 }