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 "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 (ssa_name (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 MIN, and MAX to tree ssa_name NAME.  */
 187
 188 void
 189 set_range_info (tree name, double_int min, double_int max)
 190 {
 191   gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
 192   range_info_def *ri = SSA_NAME_RANGE_INFO (name);
 193
 194   /* Allocate if not available.  */
 195   if (ri == NULL)
 196     {
 197       ri = ggc_alloc_cleared_range_info_def ();
 198       SSA_NAME_RANGE_INFO (name) = ri;
 199       ri->nonzero_bits = double_int::mask (TYPE_PRECISION (TREE_TYPE (name)));
 200     }
 201
 202   /* Set the values.  */
 203   ri->min = min;
 204   ri->max = max;
 205
 206   /* If it is a range, try to improve nonzero_bits from the min/max.  */
 207   if (min.cmp (max, TYPE_UNSIGNED (TREE_TYPE (name))) != 1)
 208     {
 209       int prec = TYPE_PRECISION (TREE_TYPE (name));
 210       double_int xorv;
 211
 212       min = min.zext (prec);
 213       max = max.zext (prec);
 214       xorv = min ^ max;
 215       if (xorv.high)
 216         xorv = double_int::mask (2 * HOST_BITS_PER_WIDE_INT
 217                                  - clz_hwi (xorv.high));
 218       else if (xorv.low)
 219         xorv = double_int::mask (HOST_BITS_PER_WIDE_INT
 220                                  - clz_hwi (xorv.low));
 221       ri->nonzero_bits = ri->nonzero_bits & (min | xorv);
 222     }
 223 }
 224
 225
 226 /* Gets range information MIN, MAX and returns enum value_range_type
 227    corresponding to tree ssa_name NAME.  enum value_range_type returned
 228    is used to determine if MIN and MAX are valid values.  */
 229
 230 enum value_range_type
 231 get_range_info (const_tree name, double_int *min, double_int *max)
 232 {
 233   enum value_range_type range_type;
 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   /* If min > max, it is VR_ANTI_RANGE.  */
 245   if (ri->min.cmp (ri->max, TYPE_UNSIGNED (TREE_TYPE (name))) == 1)
 246     {
 247       /* VR_ANTI_RANGE ~[min, max] is encoded as [max + 1, min - 1].  */
 248       range_type = VR_ANTI_RANGE;
 249       *min = ri->max + double_int_one;
 250       *max = ri->min - double_int_one;
 251     }
 252   else
 253   {
 254     /* Otherwise (when min <= max), it is VR_RANGE.  */
 255     range_type = VR_RANGE;
 256     *min = ri->min;
 257     *max = ri->max;
 258   }
 259   return range_type;
 260 }
 261
 262 /* Change non-zero bits bitmask of NAME.  */
 263
 264 void
 265 set_nonzero_bits (tree name, double_int mask)
 266 {
 267   gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
 268   if (SSA_NAME_RANGE_INFO (name) == NULL)
 269     set_range_info (name,
 270                     tree_to_double_int (TYPE_MIN_VALUE (TREE_TYPE (name))),
 271                     tree_to_double_int (TYPE_MAX_VALUE (TREE_TYPE (name))));
 272   range_info_def *ri = SSA_NAME_RANGE_INFO (name);
 273   ri->nonzero_bits
 274     = mask & double_int::mask (TYPE_PRECISION (TREE_TYPE (name)));
 275 }
 276
 277 /* Return a double_int with potentially non-zero bits in SSA_NAME
 278    NAME, or double_int_minus_one if unknown.  */
 279
 280 double_int
 281 get_nonzero_bits (const_tree name)
 282 {
 283   if (POINTER_TYPE_P (TREE_TYPE (name)))
 284     {
 285       struct ptr_info_def *pi = SSA_NAME_PTR_INFO (name);
 286       if (pi && pi->align)
 287         {
 288           double_int al = double_int::from_uhwi (pi->align - 1);
 289           return ((double_int::mask (TYPE_PRECISION (TREE_TYPE (name))) & ~al)
 290                   | double_int::from_uhwi (pi->misalign));
 291         }
 292       return double_int_minus_one;
 293     }
 294
 295   range_info_def *ri = SSA_NAME_RANGE_INFO (name);
 296   if (!ri || (GET_MODE_PRECISION (TYPE_MODE (TREE_TYPE (name)))
 297               > 2 * HOST_BITS_PER_WIDE_INT))
 298     return double_int_minus_one;
 299
 300   return ri->nonzero_bits;
 301 }
 302
 303 /* We no longer need the SSA_NAME expression VAR, release it so that
 304    it may be reused.
 305
 306    Note it is assumed that no calls to make_ssa_name will be made
 307    until all uses of the ssa name are released and that the only
 308    use of the SSA_NAME expression is to check its SSA_NAME_VAR.  All
 309    other fields must be assumed clobbered.  */
 310
 311 void
 312 release_ssa_name (tree var)
 313 {
 314   if (!var)
 315     return;
 316
 317   /* Never release the default definition for a symbol.  It's a
 318      special SSA name that should always exist once it's created.  */
 319   if (SSA_NAME_IS_DEFAULT_DEF (var))
 320     return;
 321
 322   /* If VAR has been registered for SSA updating, don't remove it.
 323      After update_ssa has run, the name will be released.  */
 324   if (name_registered_for_update_p (var))
 325     {
 326       release_ssa_name_after_update_ssa (var);
 327       return;
 328     }
 329
 330   /* release_ssa_name can be called multiple times on a single SSA_NAME.
 331      However, it should only end up on our free list one time.   We
 332      keep a status bit in the SSA_NAME node itself to indicate it has
 333      been put on the free list.
 334
 335      Note that once on the freelist you can not reference the SSA_NAME's
 336      defining statement.  */
 337   if (! SSA_NAME_IN_FREE_LIST (var))
 338     {
 339       tree saved_ssa_name_var = SSA_NAME_VAR (var);
 340       int saved_ssa_name_version = SSA_NAME_VERSION (var);
 341       use_operand_p imm = &(SSA_NAME_IMM_USE_NODE (var));
 342
 343       if (MAY_HAVE_DEBUG_STMTS)
 344         insert_debug_temp_for_var_def (NULL, var);
 345
 346 #ifdef ENABLE_CHECKING
 347       verify_imm_links (stderr, var);
 348 #endif
 349       while (imm->next != imm)
 350         delink_imm_use (imm->next);
 351
 352       (*SSANAMES (cfun))[SSA_NAME_VERSION (var)] = NULL_TREE;
 353       memset (var, 0, tree_size (var));
 354
 355       imm->prev = imm;
 356       imm->next = imm;
 357       imm->loc.ssa_name = var;
 358
 359       /* First put back the right tree node so that the tree checking
 360          macros do not complain.  */
 361       TREE_SET_CODE (var, SSA_NAME);
 362
 363       /* Restore the version number.  */
 364       SSA_NAME_VERSION (var) = saved_ssa_name_version;
 365
 366       /* Hopefully this can go away once we have the new incremental
 367          SSA updating code installed.  */
 368       SET_SSA_NAME_VAR_OR_IDENTIFIER (var, saved_ssa_name_var);
 369
 370       /* Note this SSA_NAME is now in the first list.  */
 371       SSA_NAME_IN_FREE_LIST (var) = 1;
 372
 373       /* And finally put it on the free list.  */
 374       vec_safe_push (FREE_SSANAMES (cfun), var);
 375     }
 376 }
 377
 378 /* If the alignment of the pointer described by PI is known, return true and
 379    store the alignment and the deviation from it into *ALIGNP and *MISALIGNP
 380    respectively.  Otherwise return false.  */
 381
 382 bool
 383 get_ptr_info_alignment (struct ptr_info_def *pi, unsigned int *alignp,
 384                         unsigned int *misalignp)
 385 {
 386   if (pi->align)
 387     {
 388       *alignp = pi->align;
 389       *misalignp = pi->misalign;
 390       return true;
 391     }
 392   else
 393     return false;
 394 }
 395
 396 /* State that the pointer described by PI has unknown alignment.  */
 397
 398 void
 399 mark_ptr_info_alignment_unknown (struct ptr_info_def *pi)
 400 {
 401   pi->align = 0;
 402   pi->misalign = 0;
 403 }
 404
 405 /* Store the the power-of-two byte alignment and the deviation from that
 406    alignment of pointer described by PI to ALIOGN and MISALIGN
 407    respectively.  */
 408
 409 void
 410 set_ptr_info_alignment (struct ptr_info_def *pi, unsigned int align,
 411                             unsigned int misalign)
 412 {
 413   gcc_checking_assert (align != 0);
 414   gcc_assert ((align & (align - 1)) == 0);
 415   gcc_assert ((misalign & ~(align - 1)) == 0);
 416
 417   pi->align = align;
 418   pi->misalign = misalign;
 419 }
 420
 421 /* If pointer described by PI has known alignment, increase its known
 422    misalignment by INCREMENT modulo its current alignment.  */
 423
 424 void
 425 adjust_ptr_info_misalignment (struct ptr_info_def *pi,
 426                               unsigned int increment)
 427 {
 428   if (pi->align != 0)
 429     {
 430       pi->misalign += increment;
 431       pi->misalign &= (pi->align - 1);
 432     }
 433 }
 434
 435 /* Return the alias information associated with pointer T.  It creates a
 436    new instance if none existed.  */
 437
 438 struct ptr_info_def *
 439 get_ptr_info (tree t)
 440 {
 441   struct ptr_info_def *pi;
 442
 443   gcc_assert (POINTER_TYPE_P (TREE_TYPE (t)));
 444
 445   pi = SSA_NAME_PTR_INFO (t);
 446   if (pi == NULL)
 447     {
 448       pi = ggc_alloc_cleared_ptr_info_def ();
 449       pt_solution_reset (&pi->pt);
 450       mark_ptr_info_alignment_unknown (pi);
 451       SSA_NAME_PTR_INFO (t) = pi;
 452     }
 453
 454   return pi;
 455 }
 456
 457
 458 /* Creates a new SSA name using the template NAME tobe defined by
 459    statement STMT in function FN.  */
 460
 461 tree
 462 copy_ssa_name_fn (struct function *fn, tree name, gimple stmt)
 463 {
 464   tree new_name;
 465
 466   if (SSA_NAME_VAR (name))
 467     new_name = make_ssa_name_fn (fn, SSA_NAME_VAR (name), stmt);
 468   else
 469     {
 470       new_name = make_ssa_name_fn (fn, TREE_TYPE (name), stmt);
 471       SET_SSA_NAME_VAR_OR_IDENTIFIER (new_name, SSA_NAME_IDENTIFIER (name));
 472     }
 473
 474   return new_name;
 475 }
 476
 477
 478 /* Creates a duplicate of the ptr_info_def at PTR_INFO for use by
 479    the SSA name NAME.  */
 480
 481 void
 482 duplicate_ssa_name_ptr_info (tree name, struct ptr_info_def *ptr_info)
 483 {
 484   struct ptr_info_def *new_ptr_info;
 485
 486   gcc_assert (POINTER_TYPE_P (TREE_TYPE (name)));
 487   gcc_assert (!SSA_NAME_PTR_INFO (name));
 488
 489   if (!ptr_info)
 490     return;
 491
 492   new_ptr_info = ggc_alloc_ptr_info_def ();
 493   *new_ptr_info = *ptr_info;
 494
 495   SSA_NAME_PTR_INFO (name) = new_ptr_info;
 496 }
 497
 498 /* Creates a duplicate of the range_info_def at RANGE_INFO for use by
 499    the SSA name NAME.  */
 500 void
 501 duplicate_ssa_name_range_info (tree name, struct range_info_def *range_info)
 502 {
 503   struct range_info_def *new_range_info;
 504
 505   gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
 506   gcc_assert (!SSA_NAME_RANGE_INFO (name));
 507
 508   if (!range_info)
 509     return;
 510
 511   new_range_info = ggc_alloc_range_info_def ();
 512   *new_range_info = *range_info;
 513
 514   SSA_NAME_RANGE_INFO (name) = new_range_info;
 515 }
 516
 517
 518
 519 /* Creates a duplicate of a ssa name NAME tobe defined by statement STMT
 520    in function FN.  */
 521
 522 tree
 523 duplicate_ssa_name_fn (struct function *fn, tree name, gimple stmt)
 524 {
 525   tree new_name = copy_ssa_name_fn (fn, name, stmt);
 526   if (POINTER_TYPE_P (TREE_TYPE (name)))
 527     {
 528       struct ptr_info_def *old_ptr_info = SSA_NAME_PTR_INFO (name);
 529
 530       if (old_ptr_info)
 531         duplicate_ssa_name_ptr_info (new_name, old_ptr_info);
 532     }
 533   else
 534     {
 535       struct range_info_def *old_range_info = SSA_NAME_RANGE_INFO (name);
 536
 537       if (old_range_info)
 538         duplicate_ssa_name_range_info (new_name, old_range_info);
 539     }
 540
 541   return new_name;
 542 }
 543
 544
 545 /* Release all the SSA_NAMEs created by STMT.  */
 546
 547 void
 548 release_defs (gimple stmt)
 549 {
 550   tree def;
 551   ssa_op_iter iter;
 552
 553   /* Make sure that we are in SSA.  Otherwise, operand cache may point
 554      to garbage.  */
 555   gcc_assert (gimple_in_ssa_p (cfun));
 556
 557   FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
 558     if (TREE_CODE (def) == SSA_NAME)
 559       release_ssa_name (def);
 560 }
 561
 562
 563 /* Replace the symbol associated with SSA_NAME with SYM.  */
 564
 565 void
 566 replace_ssa_name_symbol (tree ssa_name, tree sym)
 567 {
 568   SET_SSA_NAME_VAR_OR_IDENTIFIER (ssa_name, sym);
 569   TREE_TYPE (ssa_name) = TREE_TYPE (sym);
 570 }
 571
 572 /* Return SSA names that are unused to GGC memory and compact the SSA
 573    version namespace.  This is used to keep footprint of compiler during
 574    interprocedural optimization.  */
 575 static unsigned int
 576 release_dead_ssa_names (void)
 577 {
 578   unsigned i, j;
 579   int n = vec_safe_length (FREE_SSANAMES (cfun));
 580
 581   /* Now release the freelist.  */
 582   vec_free (FREE_SSANAMES (cfun));
 583
 584   /* And compact the SSA number space.  We make sure to not change the
 585      relative order of SSA versions.  */
 586   for (i = 1, j = 1; i < cfun->gimple_df->ssa_names->length (); ++i)
 587     {
 588       tree name = ssa_name (i);
 589       if (name)
 590         {
 591           if (i != j)
 592             {
 593               SSA_NAME_VERSION (name) = j;
 594               (*cfun->gimple_df->ssa_names)[j] = name;
 595             }
 596           j++;
 597         }
 598     }
 599   cfun->gimple_df->ssa_names->truncate (j);
 600
 601   statistics_counter_event (cfun, "SSA names released", n);
 602   statistics_counter_event (cfun, "SSA name holes removed", i - j);
 603   if (dump_file)
 604     fprintf (dump_file, "Released %i names, %.2f%%, removed %i holes\n",
 605              n, n * 100.0 / num_ssa_names, i - j);
 606   return 0;
 607 }
 608
 609 namespace {
 610
 611 const pass_data pass_data_release_ssa_names =
 612 {
 613   GIMPLE_PASS, /* type */
 614   "release_ssa", /* name */
 615   OPTGROUP_NONE, /* optinfo_flags */
 616   false, /* has_gate */
 617   true, /* has_execute */
 618   TV_TREE_SSA_OTHER, /* tv_id */
 619   PROP_ssa, /* properties_required */
 620   0, /* properties_provided */
 621   0, /* properties_destroyed */
 622   TODO_remove_unused_locals, /* todo_flags_start */
 623   0, /* todo_flags_finish */
 624 };
 625
 626 class pass_release_ssa_names : public gimple_opt_pass
 627 {
 628 public:
 629   pass_release_ssa_names (gcc::context *ctxt)
 630     : gimple_opt_pass (pass_data_release_ssa_names, ctxt)
 631   {}
 632
 633   /* opt_pass methods: */
 634   unsigned int execute () { return release_dead_ssa_names (); }
 635
 636 }; // class pass_release_ssa_names
 637
 638 } // anon namespace
 639
 640 gimple_opt_pass *
 641 make_pass_release_ssa_names (gcc::context *ctxt)
 642 {
 643   return new pass_release_ssa_names (ctxt);
 644 }