gcc/tree-ssanames.c

   1 /* Generic routines for manipulating SSA_NAME expressions
   2    Copyright (C) 2003, 2004, 2005, 2007, 2008, 2009, 2010
   3    Free Software Foundation, Inc.
   4
   5 This file is part of GCC.
   6
   7 GCC is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation; either version 3, or (at your option)
  10 any later version.
  11
  12 GCC is distributed in the hope that it will be useful,
  13 but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 GNU General Public License for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GCC; see the file COPYING3.  If not see
  19 <http://www.gnu.org/licenses/>.  */
  20
  21 #include "config.h"
  22 #include "system.h"
  23 #include "coretypes.h"
  24 #include "tm.h"
  25 #include "tree.h"
  26 #include "tree-flow.h"
  27 #include "tree-pass.h"
  28
  29 /* Rewriting a function into SSA form can create a huge number of SSA_NAMEs,
  30    many of which may be thrown away shortly after their creation if jumps
  31    were threaded through PHI nodes.
  32
  33    While our garbage collection mechanisms will handle this situation, it
  34    is extremely wasteful to create nodes and throw them away, especially
  35    when the nodes can be reused.
  36
  37    For PR 8361, we can significantly reduce the number of nodes allocated
  38    and thus the total amount of memory allocated by managing SSA_NAMEs a
  39    little.  This additionally helps reduce the amount of work done by the
  40    garbage collector.  Similar results have been seen on a wider variety
  41    of tests (such as the compiler itself).
  42
  43    Right now we maintain our free list on a per-function basis.  It may
  44    or may not make sense to maintain the free list for the duration of
  45    a compilation unit.
  46
  47    External code should rely solely upon HIGHEST_SSA_VERSION and the
  48    externally defined functions.  External code should not know about
  49    the details of the free list management.
  50
  51    External code should also not assume the version number on nodes is
  52    monotonically increasing.  We reuse the version number when we
  53    reuse an SSA_NAME expression.  This helps keep arrays and bitmaps
  54    more compact.
  55
  56    We could also use a zone allocator for these objects since they have
  57    a very well defined lifetime.  If someone wants to experiment with that
  58    this is the place to try it.  */
  59
  60 /* Version numbers with special meanings.  We start allocating new version
  61    numbers after the special ones.  */
  62 #define UNUSED_NAME_VERSION 0
  63
  64 unsigned int ssa_name_nodes_reused;
  65 unsigned int ssa_name_nodes_created;
  66
  67 /* Initialize management of SSA_NAMEs to default SIZE.  If SIZE is
  68    zero use default.  */
  69
  70 void
  71 init_ssanames (struct function *fn, int size)
  72 {
  73   if (size < 50)
  74     size = 50;
  75
  76   vec_alloc (SSANAMES (fn), size);
  77
  78   /* Version 0 is special, so reserve the first slot in the table.  Though
  79      currently unused, we may use version 0 in alias analysis as part of
  80      the heuristics used to group aliases when the alias sets are too
  81      large.
  82
  83      We use vec::quick_push here because we know that SSA_NAMES has at
  84      least 50 elements reserved in it.  */
  85   SSANAMES (fn)->quick_push (NULL_TREE);
  86   FREE_SSANAMES (fn) = NULL;
  87
  88   fn->gimple_df->ssa_renaming_needed = 0;
  89   fn->gimple_df->rename_vops = 0;
  90 }
  91
  92 /* Finalize management of SSA_NAMEs.  */
  93
  94 void
  95 fini_ssanames (void)
  96 {
  97   vec_free (SSANAMES (cfun));
  98   vec_free (FREE_SSANAMES (cfun));
  99 }
 100
 101 /* Dump some simple statistics regarding the re-use of SSA_NAME nodes.  */
 102
 103 void
 104 ssanames_print_statistics (void)
 105 {
 106   fprintf (stderr, "SSA_NAME nodes allocated: %u\n", ssa_name_nodes_created);
 107   fprintf (stderr, "SSA_NAME nodes reused: %u\n", ssa_name_nodes_reused);
 108 }
 109
 110 /* Return an SSA_NAME node for variable VAR defined in statement STMT
 111    in function FN.  STMT may be an empty statement for artificial
 112    references (e.g., default definitions created when a variable is
 113    used without a preceding definition).  */
 114
 115 tree
 116 make_ssa_name_fn (struct function *fn, tree var, gimple stmt)
 117 {
 118   tree t;
 119   use_operand_p imm;
 120
 121   gcc_assert (TREE_CODE (var) == VAR_DECL
 122               || TREE_CODE (var) == PARM_DECL
 123               || TREE_CODE (var) == RESULT_DECL
 124               || (TYPE_P (var) && is_gimple_reg_type (var)));
 125
 126   /* If our free list has an element, then use it.  */
 127   if (!vec_safe_is_empty (FREE_SSANAMES (fn)))
 128     {
 129       t = FREE_SSANAMES (fn)->pop ();
 130       if (GATHER_STATISTICS)
 131         ssa_name_nodes_reused++;
 132
 133       /* The node was cleared out when we put it on the free list, so
 134          there is no need to do so again here.  */
 135       gcc_assert (ssa_name (SSA_NAME_VERSION (t)) == NULL);
 136       (*SSANAMES (fn))[SSA_NAME_VERSION (t)] = t;
 137     }
 138   else
 139     {
 140       t = make_node (SSA_NAME);
 141       SSA_NAME_VERSION (t) = SSANAMES (fn)->length ();
 142       vec_safe_push (SSANAMES (fn), t);
 143       if (GATHER_STATISTICS)
 144         ssa_name_nodes_created++;
 145     }
 146
 147   if (TYPE_P (var))
 148     {
 149       TREE_TYPE (t) = var;
 150       SET_SSA_NAME_VAR_OR_IDENTIFIER (t, NULL_TREE);
 151     }
 152   else
 153     {
 154       TREE_TYPE (t) = TREE_TYPE (var);
 155       SET_SSA_NAME_VAR_OR_IDENTIFIER (t, var);
 156     }
 157   SSA_NAME_DEF_STMT (t) = stmt;
 158   SSA_NAME_PTR_INFO (t) = NULL;
 159   SSA_NAME_IN_FREE_LIST (t) = 0;
 160   SSA_NAME_IS_DEFAULT_DEF (t) = 0;
 161   imm = &(SSA_NAME_IMM_USE_NODE (t));
 162   imm->use = NULL;
 163   imm->prev = imm;
 164   imm->next = imm;
 165   imm->loc.ssa_name = t;
 166
 167   return t;
 168 }
 169
 170
 171 /* We no longer need the SSA_NAME expression VAR, release it so that
 172    it may be reused.
 173
 174    Note it is assumed that no calls to make_ssa_name will be made
 175    until all uses of the ssa name are released and that the only
 176    use of the SSA_NAME expression is to check its SSA_NAME_VAR.  All
 177    other fields must be assumed clobbered.  */
 178
 179 void
 180 release_ssa_name (tree var)
 181 {
 182   if (!var)
 183     return;
 184
 185   /* Never release the default definition for a symbol.  It's a
 186      special SSA name that should always exist once it's created.  */
 187   if (SSA_NAME_IS_DEFAULT_DEF (var))
 188     return;
 189
 190   /* If VAR has been registered for SSA updating, don't remove it.
 191      After update_ssa has run, the name will be released.  */
 192   if (name_registered_for_update_p (var))
 193     {
 194       release_ssa_name_after_update_ssa (var);
 195       return;
 196     }
 197
 198   /* release_ssa_name can be called multiple times on a single SSA_NAME.
 199      However, it should only end up on our free list one time.   We
 200      keep a status bit in the SSA_NAME node itself to indicate it has
 201      been put on the free list.
 202
 203      Note that once on the freelist you can not reference the SSA_NAME's
 204      defining statement.  */
 205   if (! SSA_NAME_IN_FREE_LIST (var))
 206     {
 207       tree saved_ssa_name_var = SSA_NAME_VAR (var);
 208       int saved_ssa_name_version = SSA_NAME_VERSION (var);
 209       use_operand_p imm = &(SSA_NAME_IMM_USE_NODE (var));
 210
 211       if (MAY_HAVE_DEBUG_STMTS)
 212         insert_debug_temp_for_var_def (NULL, var);
 213
 214 #ifdef ENABLE_CHECKING
 215       verify_imm_links (stderr, var);
 216 #endif
 217       while (imm->next != imm)
 218         delink_imm_use (imm->next);
 219
 220       (*SSANAMES (cfun))[SSA_NAME_VERSION (var)] = NULL_TREE;
 221       memset (var, 0, tree_size (var));
 222
 223       imm->prev = imm;
 224       imm->next = imm;
 225       imm->loc.ssa_name = var;
 226
 227       /* First put back the right tree node so that the tree checking
 228          macros do not complain.  */
 229       TREE_SET_CODE (var, SSA_NAME);
 230
 231       /* Restore the version number.  */
 232       SSA_NAME_VERSION (var) = saved_ssa_name_version;
 233
 234       /* Hopefully this can go away once we have the new incremental
 235          SSA updating code installed.  */
 236       SET_SSA_NAME_VAR_OR_IDENTIFIER (var, saved_ssa_name_var);
 237
 238       /* Note this SSA_NAME is now in the first list.  */
 239       SSA_NAME_IN_FREE_LIST (var) = 1;
 240
 241       /* And finally put it on the free list.  */
 242       vec_safe_push (FREE_SSANAMES (cfun), var);
 243     }
 244 }
 245
 246 /* If the alignment of the pointer described by PI is known, return true and
 247    store the alignment and the deviation from it into *ALIGNP and *MISALIGNP
 248    respectively.  Otherwise return false.  */
 249
 250 bool
 251 get_ptr_info_alignment (struct ptr_info_def *pi, unsigned int *alignp,
 252                         unsigned int *misalignp)
 253 {
 254   if (pi->align)
 255     {
 256       *alignp = pi->align;
 257       *misalignp = pi->misalign;
 258       return true;
 259     }
 260   else
 261     return false;
 262 }
 263
 264 /* State that the pointer described by PI has unknown alignment.  */
 265
 266 void
 267 mark_ptr_info_alignment_unknown (struct ptr_info_def *pi)
 268 {
 269   pi->align = 0;
 270   pi->misalign = 0;
 271 }
 272
 273 /* Store the the power-of-two byte alignment and the deviation from that
 274    alignment of pointer described by PI to ALIOGN and MISALIGN
 275    respectively.  */
 276
 277 void
 278 set_ptr_info_alignment (struct ptr_info_def *pi, unsigned int align,
 279                             unsigned int misalign)
 280 {
 281   gcc_checking_assert (align != 0);
 282   gcc_assert ((align & (align - 1)) == 0);
 283   gcc_assert ((misalign & ~(align - 1)) == 0);
 284
 285   pi->align = align;
 286   pi->misalign = misalign;
 287 }
 288
 289 /* If pointer described by PI has known alignment, increase its known
 290    misalignment by INCREMENT modulo its current alignment.  */
 291
 292 void
 293 adjust_ptr_info_misalignment (struct ptr_info_def *pi,
 294                               unsigned int increment)
 295 {
 296   if (pi->align != 0)
 297     {
 298       pi->misalign += increment;
 299       pi->misalign &= (pi->align - 1);
 300     }
 301 }
 302
 303 /* Return the alias information associated with pointer T.  It creates a
 304    new instance if none existed.  */
 305
 306 struct ptr_info_def *
 307 get_ptr_info (tree t)
 308 {
 309   struct ptr_info_def *pi;
 310
 311   gcc_assert (POINTER_TYPE_P (TREE_TYPE (t)));
 312
 313   pi = SSA_NAME_PTR_INFO (t);
 314   if (pi == NULL)
 315     {
 316       pi = ggc_alloc_cleared_ptr_info_def ();
 317       pt_solution_reset (&pi->pt);
 318       mark_ptr_info_alignment_unknown (pi);
 319       SSA_NAME_PTR_INFO (t) = pi;
 320     }
 321
 322   return pi;
 323 }
 324
 325
 326 /* Creates a new SSA name using the template NAME tobe defined by
 327    statement STMT in function FN.  */
 328
 329 tree
 330 copy_ssa_name_fn (struct function *fn, tree name, gimple stmt)
 331 {
 332   tree new_name;
 333
 334   if (SSA_NAME_VAR (name))
 335     new_name = make_ssa_name_fn (fn, SSA_NAME_VAR (name), stmt);
 336   else
 337     {
 338       new_name = make_ssa_name_fn (fn, TREE_TYPE (name), stmt);
 339       SET_SSA_NAME_VAR_OR_IDENTIFIER (new_name, SSA_NAME_IDENTIFIER (name));
 340     }
 341
 342   return new_name;
 343 }
 344
 345
 346 /* Creates a duplicate of the ptr_info_def at PTR_INFO for use by
 347    the SSA name NAME.  */
 348
 349 void
 350 duplicate_ssa_name_ptr_info (tree name, struct ptr_info_def *ptr_info)
 351 {
 352   struct ptr_info_def *new_ptr_info;
 353
 354   gcc_assert (POINTER_TYPE_P (TREE_TYPE (name)));
 355   gcc_assert (!SSA_NAME_PTR_INFO (name));
 356
 357   if (!ptr_info)
 358     return;
 359
 360   new_ptr_info = ggc_alloc_ptr_info_def ();
 361   *new_ptr_info = *ptr_info;
 362
 363   SSA_NAME_PTR_INFO (name) = new_ptr_info;
 364 }
 365
 366
 367 /* Creates a duplicate of a ssa name NAME tobe defined by statement STMT
 368    in function FN.  */
 369
 370 tree
 371 duplicate_ssa_name_fn (struct function *fn, tree name, gimple stmt)
 372 {
 373   tree new_name = copy_ssa_name_fn (fn, name, stmt);
 374   struct ptr_info_def *old_ptr_info = SSA_NAME_PTR_INFO (name);
 375
 376   if (old_ptr_info)
 377     duplicate_ssa_name_ptr_info (new_name, old_ptr_info);
 378
 379   return new_name;
 380 }
 381
 382
 383 /* Release all the SSA_NAMEs created by STMT.  */
 384
 385 void
 386 release_defs (gimple stmt)
 387 {
 388   tree def;
 389   ssa_op_iter iter;
 390
 391   /* Make sure that we are in SSA.  Otherwise, operand cache may point
 392      to garbage.  */
 393   gcc_assert (gimple_in_ssa_p (cfun));
 394
 395   FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
 396     if (TREE_CODE (def) == SSA_NAME)
 397       release_ssa_name (def);
 398 }
 399
 400
 401 /* Replace the symbol associated with SSA_NAME with SYM.  */
 402
 403 void
 404 replace_ssa_name_symbol (tree ssa_name, tree sym)
 405 {
 406   SET_SSA_NAME_VAR_OR_IDENTIFIER (ssa_name, sym);
 407   TREE_TYPE (ssa_name) = TREE_TYPE (sym);
 408 }
 409
 410 /* Return SSA names that are unused to GGC memory and compact the SSA
 411    version namespace.  This is used to keep footprint of compiler during
 412    interprocedural optimization.  */
 413 static unsigned int
 414 release_dead_ssa_names (void)
 415 {
 416   unsigned i, j;
 417   int n = vec_safe_length (FREE_SSANAMES (cfun));
 418
 419   /* Now release the freelist.  */
 420   vec_free (FREE_SSANAMES (cfun));
 421
 422   /* And compact the SSA number space.  We make sure to not change the
 423      relative order of SSA versions.  */
 424   for (i = 1, j = 1; i < cfun->gimple_df->ssa_names->length (); ++i)
 425     {
 426       tree name = ssa_name (i);
 427       if (name)
 428         {
 429           if (i != j)
 430             {
 431               SSA_NAME_VERSION (name) = j;
 432               (*cfun->gimple_df->ssa_names)[j] = name;
 433             }
 434           j++;
 435         }
 436     }
 437   cfun->gimple_df->ssa_names->truncate (j);
 438
 439   statistics_counter_event (cfun, "SSA names released", n);
 440   statistics_counter_event (cfun, "SSA name holes removed", i - j);
 441   if (dump_file)
 442     fprintf (dump_file, "Released %i names, %.2f%%, removed %i holes\n",
 443              n, n * 100.0 / num_ssa_names, i - j);
 444   return 0;
 445 }
 446
 447 struct gimple_opt_pass pass_release_ssa_names =
 448 {
 449  {
 450   GIMPLE_PASS,
 451   "release_ssa",                        /* name */
 452   OPTGROUP_NONE,                        /* optinfo_flags */
 453   NULL,                                 /* gate */
 454   release_dead_ssa_names,               /* execute */
 455   NULL,                                 /* sub */
 456   NULL,                                 /* next */
 457   0,                                    /* static_pass_number */
 458   TV_TREE_SSA_OTHER,                    /* tv_id */
 459   PROP_ssa,                             /* properties_required */
 460   0,                                    /* properties_provided */
 461   0,                                    /* properties_destroyed */
 462   0,                                    /* todo_flags_start */
 463   0                                     /* todo_flags_finish */
 464  }
 465 };