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