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