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 = static_cast<range_info_def *> (ggc_internal_alloc (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 (-(HOST_WIDE_INT) pi->align
 275                          | (HOST_WIDE_INT) pi->misalign, precision);
 276       return wi::shwi (-1, precision);
 277     }
 278
 279   range_info_def *ri = SSA_NAME_RANGE_INFO (name);
 280   if (!ri)
 281     return wi::shwi (-1, precision);
 282
 283   return ri->get_nonzero_bits ();
 284 }
 285
 286 /* We no longer need the SSA_NAME expression VAR, release it so that
 287    it may be reused.
 288
 289    Note it is assumed that no calls to make_ssa_name will be made
 290    until all uses of the ssa name are released and that the only
 291    use of the SSA_NAME expression is to check its SSA_NAME_VAR.  All
 292    other fields must be assumed clobbered.  */
 293
 294 void
 295 release_ssa_name_fn (struct function *fn, tree var)
 296 {
 297   if (!var)
 298     return;
 299
 300   /* Never release the default definition for a symbol.  It's a
 301      special SSA name that should always exist once it's created.  */
 302   if (SSA_NAME_IS_DEFAULT_DEF (var))
 303     return;
 304
 305   /* If VAR has been registered for SSA updating, don't remove it.
 306      After update_ssa has run, the name will be released.  */
 307   if (name_registered_for_update_p (var))
 308     {
 309       release_ssa_name_after_update_ssa (var);
 310       return;
 311     }
 312
 313   /* release_ssa_name can be called multiple times on a single SSA_NAME.
 314      However, it should only end up on our free list one time.   We
 315      keep a status bit in the SSA_NAME node itself to indicate it has
 316      been put on the free list.
 317
 318      Note that once on the freelist you can not reference the SSA_NAME's
 319      defining statement.  */
 320   if (! SSA_NAME_IN_FREE_LIST (var))
 321     {
 322       tree saved_ssa_name_var = SSA_NAME_VAR (var);
 323       int saved_ssa_name_version = SSA_NAME_VERSION (var);
 324       use_operand_p imm = &(SSA_NAME_IMM_USE_NODE (var));
 325
 326       if (MAY_HAVE_DEBUG_STMTS)
 327         insert_debug_temp_for_var_def (NULL, var);
 328
 329 #ifdef ENABLE_CHECKING
 330       verify_imm_links (stderr, var);
 331 #endif
 332       while (imm->next != imm)
 333         delink_imm_use (imm->next);
 334
 335       (*SSANAMES (fn))[SSA_NAME_VERSION (var)] = NULL_TREE;
 336       memset (var, 0, tree_size (var));
 337
 338       imm->prev = imm;
 339       imm->next = imm;
 340       imm->loc.ssa_name = var;
 341
 342       /* First put back the right tree node so that the tree checking
 343          macros do not complain.  */
 344       TREE_SET_CODE (var, SSA_NAME);
 345
 346       /* Restore the version number.  */
 347       SSA_NAME_VERSION (var) = saved_ssa_name_version;
 348
 349       /* Hopefully this can go away once we have the new incremental
 350          SSA updating code installed.  */
 351       SET_SSA_NAME_VAR_OR_IDENTIFIER (var, saved_ssa_name_var);
 352
 353       /* Note this SSA_NAME is now in the first list.  */
 354       SSA_NAME_IN_FREE_LIST (var) = 1;
 355
 356       /* And finally put it on the free list.  */
 357       vec_safe_push (FREE_SSANAMES (fn), var);
 358     }
 359 }
 360
 361 /* If the alignment of the pointer described by PI is known, return true and
 362    store the alignment and the deviation from it into *ALIGNP and *MISALIGNP
 363    respectively.  Otherwise return false.  */
 364
 365 bool
 366 get_ptr_info_alignment (struct ptr_info_def *pi, unsigned int *alignp,
 367                         unsigned int *misalignp)
 368 {
 369   if (pi->align)
 370     {
 371       *alignp = pi->align;
 372       *misalignp = pi->misalign;
 373       return true;
 374     }
 375   else
 376     return false;
 377 }
 378
 379 /* State that the pointer described by PI has unknown alignment.  */
 380
 381 void
 382 mark_ptr_info_alignment_unknown (struct ptr_info_def *pi)
 383 {
 384   pi->align = 0;
 385   pi->misalign = 0;
 386 }
 387
 388 /* Store the the power-of-two byte alignment and the deviation from that
 389    alignment of pointer described by PI to ALIOGN and MISALIGN
 390    respectively.  */
 391
 392 void
 393 set_ptr_info_alignment (struct ptr_info_def *pi, unsigned int align,
 394                             unsigned int misalign)
 395 {
 396   gcc_checking_assert (align != 0);
 397   gcc_assert ((align & (align - 1)) == 0);
 398   gcc_assert ((misalign & ~(align - 1)) == 0);
 399
 400   pi->align = align;
 401   pi->misalign = misalign;
 402 }
 403
 404 /* If pointer described by PI has known alignment, increase its known
 405    misalignment by INCREMENT modulo its current alignment.  */
 406
 407 void
 408 adjust_ptr_info_misalignment (struct ptr_info_def *pi,
 409                               unsigned int increment)
 410 {
 411   if (pi->align != 0)
 412     {
 413       pi->misalign += increment;
 414       pi->misalign &= (pi->align - 1);
 415     }
 416 }
 417
 418 /* Return the alias information associated with pointer T.  It creates a
 419    new instance if none existed.  */
 420
 421 struct ptr_info_def *
 422 get_ptr_info (tree t)
 423 {
 424   struct ptr_info_def *pi;
 425
 426   gcc_assert (POINTER_TYPE_P (TREE_TYPE (t)));
 427
 428   pi = SSA_NAME_PTR_INFO (t);
 429   if (pi == NULL)
 430     {
 431       pi = ggc_cleared_alloc<ptr_info_def> ();
 432       pt_solution_reset (&pi->pt);
 433       mark_ptr_info_alignment_unknown (pi);
 434       SSA_NAME_PTR_INFO (t) = pi;
 435     }
 436
 437   return pi;
 438 }
 439
 440
 441 /* Creates a new SSA name using the template NAME tobe defined by
 442    statement STMT in function FN.  */
 443
 444 tree
 445 copy_ssa_name_fn (struct function *fn, tree name, gimple stmt)
 446 {
 447   tree new_name;
 448
 449   if (SSA_NAME_VAR (name))
 450     new_name = make_ssa_name_fn (fn, SSA_NAME_VAR (name), stmt);
 451   else
 452     {
 453       new_name = make_ssa_name_fn (fn, TREE_TYPE (name), stmt);
 454       SET_SSA_NAME_VAR_OR_IDENTIFIER (new_name, SSA_NAME_IDENTIFIER (name));
 455     }
 456
 457   return new_name;
 458 }
 459
 460
 461 /* Creates a duplicate of the ptr_info_def at PTR_INFO for use by
 462    the SSA name NAME.  */
 463
 464 void
 465 duplicate_ssa_name_ptr_info (tree name, struct ptr_info_def *ptr_info)
 466 {
 467   struct ptr_info_def *new_ptr_info;
 468
 469   gcc_assert (POINTER_TYPE_P (TREE_TYPE (name)));
 470   gcc_assert (!SSA_NAME_PTR_INFO (name));
 471
 472   if (!ptr_info)
 473     return;
 474
 475   new_ptr_info = ggc_alloc<ptr_info_def> ();
 476   *new_ptr_info = *ptr_info;
 477
 478   SSA_NAME_PTR_INFO (name) = new_ptr_info;
 479 }
 480
 481 /* Creates a duplicate of the range_info_def at RANGE_INFO of type
 482    RANGE_TYPE for use by the SSA name NAME.  */
 483 void
 484 duplicate_ssa_name_range_info (tree name, enum value_range_type range_type,
 485                                struct range_info_def *range_info)
 486 {
 487   struct range_info_def *new_range_info;
 488
 489   gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
 490   gcc_assert (!SSA_NAME_RANGE_INFO (name));
 491   gcc_assert (!SSA_NAME_ANTI_RANGE_P (name));
 492
 493   if (!range_info)
 494     return;
 495
 496   unsigned int precision = TYPE_PRECISION (TREE_TYPE (name));
 497   size_t size = (sizeof (range_info_def)
 498                  + trailing_wide_ints <3>::extra_size (precision));
 499   new_range_info = static_cast<range_info_def *> (ggc_internal_alloc (size));
 500   memcpy (new_range_info, range_info, size);
 501
 502   gcc_assert (range_type == VR_RANGE || range_type == VR_ANTI_RANGE);
 503   SSA_NAME_ANTI_RANGE_P (name) = (range_type == VR_ANTI_RANGE);
 504   SSA_NAME_RANGE_INFO (name) = new_range_info;
 505 }
 506
 507
 508
 509 /* Creates a duplicate of a ssa name NAME tobe defined by statement STMT
 510    in function FN.  */
 511
 512 tree
 513 duplicate_ssa_name_fn (struct function *fn, tree name, gimple stmt)
 514 {
 515   tree new_name = copy_ssa_name_fn (fn, name, stmt);
 516   if (POINTER_TYPE_P (TREE_TYPE (name)))
 517     {
 518       struct ptr_info_def *old_ptr_info = SSA_NAME_PTR_INFO (name);
 519
 520       if (old_ptr_info)
 521         duplicate_ssa_name_ptr_info (new_name, old_ptr_info);
 522     }
 523   else
 524     {
 525       struct range_info_def *old_range_info = SSA_NAME_RANGE_INFO (name);
 526
 527       if (old_range_info)
 528         duplicate_ssa_name_range_info (new_name, SSA_NAME_RANGE_TYPE (name),
 529                                        old_range_info);
 530     }
 531
 532   return new_name;
 533 }
 534
 535
 536 /* Release all the SSA_NAMEs created by STMT.  */
 537
 538 void
 539 release_defs (gimple stmt)
 540 {
 541   tree def;
 542   ssa_op_iter iter;
 543
 544   /* Make sure that we are in SSA.  Otherwise, operand cache may point
 545      to garbage.  */
 546   gcc_assert (gimple_in_ssa_p (cfun));
 547
 548   FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
 549     if (TREE_CODE (def) == SSA_NAME)
 550       release_ssa_name (def);
 551 }
 552
 553
 554 /* Replace the symbol associated with SSA_NAME with SYM.  */
 555
 556 void
 557 replace_ssa_name_symbol (tree ssa_name, tree sym)
 558 {
 559   SET_SSA_NAME_VAR_OR_IDENTIFIER (ssa_name, sym);
 560   TREE_TYPE (ssa_name) = TREE_TYPE (sym);
 561 }
 562
 563 /* Return SSA names that are unused to GGC memory and compact the SSA
 564    version namespace.  This is used to keep footprint of compiler during
 565    interprocedural optimization.  */
 566
 567 namespace {
 568
 569 const pass_data pass_data_release_ssa_names =
 570 {
 571   GIMPLE_PASS, /* type */
 572   "release_ssa", /* name */
 573   OPTGROUP_NONE, /* optinfo_flags */
 574   true, /* has_execute */
 575   TV_TREE_SSA_OTHER, /* tv_id */
 576   PROP_ssa, /* properties_required */
 577   0, /* properties_provided */
 578   0, /* properties_destroyed */
 579   TODO_remove_unused_locals, /* todo_flags_start */
 580   0, /* todo_flags_finish */
 581 };
 582
 583 class pass_release_ssa_names : public gimple_opt_pass
 584 {
 585 public:
 586   pass_release_ssa_names (gcc::context *ctxt)
 587     : gimple_opt_pass (pass_data_release_ssa_names, ctxt)
 588   {}
 589
 590   /* opt_pass methods: */
 591   virtual unsigned int execute (function *);
 592
 593 }; // class pass_release_ssa_names
 594
 595 unsigned int
 596 pass_release_ssa_names::execute (function *fun)
 597 {
 598   unsigned i, j;
 599   int n = vec_safe_length (FREE_SSANAMES (fun));
 600
 601   /* Now release the freelist.  */
 602   vec_free (FREE_SSANAMES (fun));
 603
 604   /* And compact the SSA number space.  We make sure to not change the
 605      relative order of SSA versions.  */
 606   for (i = 1, j = 1; i < fun->gimple_df->ssa_names->length (); ++i)
 607     {
 608       tree name = ssa_name (i);
 609       if (name)
 610         {
 611           if (i != j)
 612             {
 613               SSA_NAME_VERSION (name) = j;
 614               (*fun->gimple_df->ssa_names)[j] = name;
 615             }
 616           j++;
 617         }
 618     }
 619   fun->gimple_df->ssa_names->truncate (j);
 620
 621   statistics_counter_event (fun, "SSA names released", n);
 622   statistics_counter_event (fun, "SSA name holes removed", i - j);
 623   if (dump_file)
 624     fprintf (dump_file, "Released %i names, %.2f%%, removed %i holes\n",
 625              n, n * 100.0 / num_ssa_names, i - j);
 626   return 0;
 627 }
 628
 629 } // anon namespace
 630
 631 gimple_opt_pass *
 632 make_pass_release_ssa_names (gcc::context *ctxt)
 633 {
 634   return new pass_release_ssa_names (ctxt);
 635 }