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 "tree-flow.h"
  26 #include "tree-pass.h"
  27
  28 /* Rewriting a function into SSA form can create a huge number of SSA_NAMEs,
  29    many of which may be thrown away shortly after their creation if jumps
  30    were threaded through PHI nodes.
  31
  32    While our garbage collection mechanisms will handle this situation, it
  33    is extremely wasteful to create nodes and throw them away, especially
  34    when the nodes can be reused.
  35
  36    For PR 8361, we can significantly reduce the number of nodes allocated
  37    and thus the total amount of memory allocated by managing SSA_NAMEs a
  38    little.  This additionally helps reduce the amount of work done by the
  39    garbage collector.  Similar results have been seen on a wider variety
  40    of tests (such as the compiler itself).
  41
  42    Right now we maintain our free list on a per-function basis.  It may
  43    or may not make sense to maintain the free list for the duration of
  44    a compilation unit.
  45
  46    External code should rely solely upon HIGHEST_SSA_VERSION and the
  47    externally defined functions.  External code should not know about
  48    the details of the free list management.
  49
  50    External code should also not assume the version number on nodes is
  51    monotonically increasing.  We reuse the version number when we
  52    reuse an SSA_NAME expression.  This helps keep arrays and bitmaps
  53    more compact.
  54
  55    We could also use a zone allocator for these objects since they have
  56    a very well defined lifetime.  If someone wants to experiment with that
  57    this is the place to try it.  */
  58
  59 /* Version numbers with special meanings.  We start allocating new version
  60    numbers after the special ones.  */
  61 #define UNUSED_NAME_VERSION 0
  62
  63 unsigned int ssa_name_nodes_reused;
  64 unsigned int ssa_name_nodes_created;
  65
  66 /* Initialize management of SSA_NAMEs to default SIZE.  If SIZE is
  67    zero use default.  */
  68
  69 void
  70 init_ssanames (struct function *fn, int size)
  71 {
  72   if (size < 50)
  73     size = 50;
  74
  75   vec_alloc (SSANAMES (fn), size);
  76
  77   /* Version 0 is special, so reserve the first slot in the table.  Though
  78      currently unused, we may use version 0 in alias analysis as part of
  79      the heuristics used to group aliases when the alias sets are too
  80      large.
  81
  82      We use vec::quick_push here because we know that SSA_NAMES has at
  83      least 50 elements reserved in it.  */
  84   SSANAMES (fn)->quick_push (NULL_TREE);
  85   FREE_SSANAMES (fn) = NULL;
  86
  87   fn->gimple_df->ssa_renaming_needed = 0;
  88   fn->gimple_df->rename_vops = 0;
  89 }
  90
  91 /* Finalize management of SSA_NAMEs.  */
  92
  93 void
  94 fini_ssanames (void)
  95 {
  96   vec_free (SSANAMES (cfun));
  97   vec_free (FREE_SSANAMES (cfun));
  98 }
  99
 100 /* Dump some simple statistics regarding the re-use of SSA_NAME nodes.  */
 101
 102 void
 103 ssanames_print_statistics (void)
 104 {
 105   fprintf (stderr, "SSA_NAME nodes allocated: %u\n", ssa_name_nodes_created);
 106   fprintf (stderr, "SSA_NAME nodes reused: %u\n", ssa_name_nodes_reused);
 107 }
 108
 109 /* Return an SSA_NAME node for variable VAR defined in statement STMT
 110    in function FN.  STMT may be an empty statement for artificial
 111    references (e.g., default definitions created when a variable is
 112    used without a preceding definition).  */
 113
 114 tree
 115 make_ssa_name_fn (struct function *fn, tree var, gimple stmt)
 116 {
 117   tree t;
 118   use_operand_p imm;
 119
 120   gcc_assert (TREE_CODE (var) == VAR_DECL
 121               || TREE_CODE (var) == PARM_DECL
 122               || TREE_CODE (var) == RESULT_DECL
 123               || (TYPE_P (var) && is_gimple_reg_type (var)));
 124
 125   /* If our free list has an element, then use it.  */
 126   if (!vec_safe_is_empty (FREE_SSANAMES (fn)))
 127     {
 128       t = FREE_SSANAMES (fn)->pop ();
 129       if (GATHER_STATISTICS)
 130         ssa_name_nodes_reused++;
 131
 132       /* The node was cleared out when we put it on the free list, so
 133          there is no need to do so again here.  */
 134       gcc_assert (ssa_name (SSA_NAME_VERSION (t)) == NULL);
 135       (*SSANAMES (fn))[SSA_NAME_VERSION (t)] = t;
 136     }
 137   else
 138     {
 139       t = make_node (SSA_NAME);
 140       SSA_NAME_VERSION (t) = SSANAMES (fn)->length ();
 141       vec_safe_push (SSANAMES (fn), t);
 142       if (GATHER_STATISTICS)
 143         ssa_name_nodes_created++;
 144     }
 145
 146   if (TYPE_P (var))
 147     {
 148       TREE_TYPE (t) = var;
 149       SET_SSA_NAME_VAR_OR_IDENTIFIER (t, NULL_TREE);
 150     }
 151   else
 152     {
 153       TREE_TYPE (t) = TREE_TYPE (var);
 154       SET_SSA_NAME_VAR_OR_IDENTIFIER (t, var);
 155     }
 156   SSA_NAME_DEF_STMT (t) = stmt;
 157   SSA_NAME_PTR_INFO (t) = NULL;
 158   SSA_NAME_IN_FREE_LIST (t) = 0;
 159   SSA_NAME_IS_DEFAULT_DEF (t) = 0;
 160   imm = &(SSA_NAME_IMM_USE_NODE (t));
 161   imm->use = NULL;
 162   imm->prev = imm;
 163   imm->next = imm;
 164   imm->loc.ssa_name = t;
 165
 166   return t;
 167 }
 168
 169
 170 /* We no longer need the SSA_NAME expression VAR, release it so that
 171    it may be reused.
 172
 173    Note it is assumed that no calls to make_ssa_name will be made
 174    until all uses of the ssa name are released and that the only
 175    use of the SSA_NAME expression is to check its SSA_NAME_VAR.  All
 176    other fields must be assumed clobbered.  */
 177
 178 void
 179 release_ssa_name (tree var)
 180 {
 181   if (!var)
 182     return;
 183
 184   /* Never release the default definition for a symbol.  It's a
 185      special SSA name that should always exist once it's created.  */
 186   if (SSA_NAME_IS_DEFAULT_DEF (var))
 187     return;
 188
 189   /* If VAR has been registered for SSA updating, don't remove it.
 190      After update_ssa has run, the name will be released.  */
 191   if (name_registered_for_update_p (var))
 192     {
 193       release_ssa_name_after_update_ssa (var);
 194       return;
 195     }
 196
 197   /* release_ssa_name can be called multiple times on a single SSA_NAME.
 198      However, it should only end up on our free list one time.   We
 199      keep a status bit in the SSA_NAME node itself to indicate it has
 200      been put on the free list.
 201
 202      Note that once on the freelist you can not reference the SSA_NAME's
 203      defining statement.  */
 204   if (! SSA_NAME_IN_FREE_LIST (var))
 205     {
 206       tree saved_ssa_name_var = SSA_NAME_VAR (var);
 207       int saved_ssa_name_version = SSA_NAME_VERSION (var);
 208       use_operand_p imm = &(SSA_NAME_IMM_USE_NODE (var));
 209
 210       if (MAY_HAVE_DEBUG_STMTS)
 211         insert_debug_temp_for_var_def (NULL, var);
 212
 213 #ifdef ENABLE_CHECKING
 214       verify_imm_links (stderr, var);
 215 #endif
 216       while (imm->next != imm)
 217         delink_imm_use (imm->next);
 218
 219       (*SSANAMES (cfun))[SSA_NAME_VERSION (var)] = NULL_TREE;
 220       memset (var, 0, tree_size (var));
 221
 222       imm->prev = imm;
 223       imm->next = imm;
 224       imm->loc.ssa_name = var;
 225
 226       /* First put back the right tree node so that the tree checking
 227          macros do not complain.  */
 228       TREE_SET_CODE (var, SSA_NAME);
 229
 230       /* Restore the version number.  */
 231       SSA_NAME_VERSION (var) = saved_ssa_name_version;
 232
 233       /* Hopefully this can go away once we have the new incremental
 234          SSA updating code installed.  */
 235       SET_SSA_NAME_VAR_OR_IDENTIFIER (var, saved_ssa_name_var);
 236
 237       /* Note this SSA_NAME is now in the first list.  */
 238       SSA_NAME_IN_FREE_LIST (var) = 1;
 239
 240       /* And finally put it on the free list.  */
 241       vec_safe_push (FREE_SSANAMES (cfun), var);
 242     }
 243 }
 244
 245 /* If the alignment of the pointer described by PI is known, return true and
 246    store the alignment and the deviation from it into *ALIGNP and *MISALIGNP
 247    respectively.  Otherwise return false.  */
 248
 249 bool
 250 get_ptr_info_alignment (struct ptr_info_def *pi, unsigned int *alignp,
 251                         unsigned int *misalignp)
 252 {
 253   if (pi->align)
 254     {
 255       *alignp = pi->align;
 256       *misalignp = pi->misalign;
 257       return true;
 258     }
 259   else
 260     return false;
 261 }
 262
 263 /* State that the pointer described by PI has unknown alignment.  */
 264
 265 void
 266 mark_ptr_info_alignment_unknown (struct ptr_info_def *pi)
 267 {
 268   pi->align = 0;
 269   pi->misalign = 0;
 270 }
 271
 272 /* Store the the power-of-two byte alignment and the deviation from that
 273    alignment of pointer described by PI to ALIOGN and MISALIGN
 274    respectively.  */
 275
 276 void
 277 set_ptr_info_alignment (struct ptr_info_def *pi, unsigned int align,
 278                             unsigned int misalign)
 279 {
 280   gcc_checking_assert (align != 0);
 281   gcc_assert ((align & (align - 1)) == 0);
 282   gcc_assert ((misalign & ~(align - 1)) == 0);
 283
 284   pi->align = align;
 285   pi->misalign = misalign;
 286 }
 287
 288 /* If pointer described by PI has known alignment, increase its known
 289    misalignment by INCREMENT modulo its current alignment.  */
 290
 291 void
 292 adjust_ptr_info_misalignment (struct ptr_info_def *pi,
 293                               unsigned int increment)
 294 {
 295   if (pi->align != 0)
 296     {
 297       pi->misalign += increment;
 298       pi->misalign &= (pi->align - 1);
 299     }
 300 }
 301
 302 /* Return the alias information associated with pointer T.  It creates a
 303    new instance if none existed.  */
 304
 305 struct ptr_info_def *
 306 get_ptr_info (tree t)
 307 {
 308   struct ptr_info_def *pi;
 309
 310   gcc_assert (POINTER_TYPE_P (TREE_TYPE (t)));
 311
 312   pi = SSA_NAME_PTR_INFO (t);
 313   if (pi == NULL)
 314     {
 315       pi = ggc_alloc_cleared_ptr_info_def ();
 316       pt_solution_reset (&pi->pt);
 317       mark_ptr_info_alignment_unknown (pi);
 318       SSA_NAME_PTR_INFO (t) = pi;
 319     }
 320
 321   return pi;
 322 }
 323
 324
 325 /* Creates a new SSA name using the template NAME tobe defined by
 326    statement STMT in function FN.  */
 327
 328 tree
 329 copy_ssa_name_fn (struct function *fn, tree name, gimple stmt)
 330 {
 331   tree new_name;
 332
 333   if (SSA_NAME_VAR (name))
 334     new_name = make_ssa_name_fn (fn, SSA_NAME_VAR (name), stmt);
 335   else
 336     {
 337       new_name = make_ssa_name_fn (fn, TREE_TYPE (name), stmt);
 338       SET_SSA_NAME_VAR_OR_IDENTIFIER (new_name, SSA_NAME_IDENTIFIER (name));
 339     }
 340
 341   return new_name;
 342 }
 343
 344
 345 /* Creates a duplicate of the ptr_info_def at PTR_INFO for use by
 346    the SSA name NAME.  */
 347
 348 void
 349 duplicate_ssa_name_ptr_info (tree name, struct ptr_info_def *ptr_info)
 350 {
 351   struct ptr_info_def *new_ptr_info;
 352
 353   gcc_assert (POINTER_TYPE_P (TREE_TYPE (name)));
 354   gcc_assert (!SSA_NAME_PTR_INFO (name));
 355
 356   if (!ptr_info)
 357     return;
 358
 359   new_ptr_info = ggc_alloc_ptr_info_def ();
 360   *new_ptr_info = *ptr_info;
 361
 362   SSA_NAME_PTR_INFO (name) = new_ptr_info;
 363 }
 364
 365
 366 /* Creates a duplicate of a ssa name NAME tobe defined by statement STMT
 367    in function FN.  */
 368
 369 tree
 370 duplicate_ssa_name_fn (struct function *fn, tree name, gimple stmt)
 371 {
 372   tree new_name = copy_ssa_name_fn (fn, name, stmt);
 373   struct ptr_info_def *old_ptr_info = SSA_NAME_PTR_INFO (name);
 374
 375   if (old_ptr_info)
 376     duplicate_ssa_name_ptr_info (new_name, old_ptr_info);
 377
 378   return new_name;
 379 }
 380
 381
 382 /* Release all the SSA_NAMEs created by STMT.  */
 383
 384 void
 385 release_defs (gimple stmt)
 386 {
 387   tree def;
 388   ssa_op_iter iter;
 389
 390   /* Make sure that we are in SSA.  Otherwise, operand cache may point
 391      to garbage.  */
 392   gcc_assert (gimple_in_ssa_p (cfun));
 393
 394   FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
 395     if (TREE_CODE (def) == SSA_NAME)
 396       release_ssa_name (def);
 397 }
 398
 399
 400 /* Replace the symbol associated with SSA_NAME with SYM.  */
 401
 402 void
 403 replace_ssa_name_symbol (tree ssa_name, tree sym)
 404 {
 405   SET_SSA_NAME_VAR_OR_IDENTIFIER (ssa_name, sym);
 406   TREE_TYPE (ssa_name) = TREE_TYPE (sym);
 407 }
 408
 409 /* Return SSA names that are unused to GGC memory and compact the SSA
 410    version namespace.  This is used to keep footprint of compiler during
 411    interprocedural optimization.  */
 412 static unsigned int
 413 release_dead_ssa_names (void)
 414 {
 415   unsigned i, j;
 416   int n = vec_safe_length (FREE_SSANAMES (cfun));
 417
 418   /* Now release the freelist.  */
 419   vec_free (FREE_SSANAMES (cfun));
 420
 421   /* And compact the SSA number space.  We make sure to not change the
 422      relative order of SSA versions.  */
 423   for (i = 1, j = 1; i < cfun->gimple_df->ssa_names->length (); ++i)
 424     {
 425       tree name = ssa_name (i);
 426       if (name)
 427         {
 428           if (i != j)
 429             {
 430               SSA_NAME_VERSION (name) = j;
 431               (*cfun->gimple_df->ssa_names)[j] = name;
 432             }
 433           j++;
 434         }
 435     }
 436   cfun->gimple_df->ssa_names->truncate (j);
 437
 438   statistics_counter_event (cfun, "SSA names released", n);
 439   statistics_counter_event (cfun, "SSA name holes removed", i - j);
 440   if (dump_file)
 441     fprintf (dump_file, "Released %i names, %.2f%%, removed %i holes\n",
 442              n, n * 100.0 / num_ssa_names, i - j);
 443   return 0;
 444 }
 445
 446 struct gimple_opt_pass pass_release_ssa_names =
 447 {
 448  {
 449   GIMPLE_PASS,
 450   "release_ssa",                        /* name */
 451   OPTGROUP_NONE,                        /* optinfo_flags */
 452   NULL,                                 /* gate */
 453   release_dead_ssa_names,               /* execute */
 454   NULL,                                 /* sub */
 455   NULL,                                 /* next */
 456   0,                                    /* static_pass_number */
 457   TV_TREE_SSA_OTHER,                    /* tv_id */
 458   PROP_ssa,                             /* properties_required */
 459   0,                                    /* properties_provided */
 460   0,                                    /* properties_destroyed */
 461   0,                                    /* todo_flags_start */
 462   0                                     /* todo_flags_finish */
 463  }
 464 };