gcc/tree-ssanames.c

   1 /* Generic routines for manipulating SSA_NAME expressions
   2    Copyright (C) 2003, 2004, 2005 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 2, 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 COPYING.  If not, write to
  18 the Free Software Foundation, 59 Temple Place - Suite 330,
  19 Boston, MA 02111-1307, USA.  */
  20
  21 #include "config.h"
  22 #include "system.h"
  23 #include "coretypes.h"
  24 #include "tm.h"
  25 #include "tree.h"
  26 #include "varray.h"
  27 #include "ggc.h"
  28 #include "tree-flow.h"
  29
  30 /* Rewriting a function into SSA form can create a huge number of SSA_NAMEs,
  31    many of which may be thrown away shortly after their creation if jumps
  32    were threaded through PHI nodes.
  33
  34    While our garbage collection mechanisms will handle this situation, it
  35    is extremely wasteful to create nodes and throw them away, especially
  36    when the nodes can be reused.
  37
  38    For PR 8361, we can significantly reduce the number of nodes allocated
  39    and thus the total amount of memory allocated by managing SSA_NAMEs a
  40    little.  This additionally helps reduce the amount of work done by the
  41    garbage collector.  Similar results have been seen on a wider variety
  42    of tests (such as the compiler itself).
  43
  44    Right now we maintain our free list on a per-function basis.  It may
  45    or may not make sense to maintain the free list for the duration of
  46    a compilation unit.
  47
  48    External code should rely solely upon HIGHEST_SSA_VERSION and the
  49    externally defined functions.  External code should not know about
  50    the details of the free list management.
  51
  52    External code should also not assume the version number on nodes is
  53    monotonically increasing.  We reuse the version number when we
  54    reuse an SSA_NAME expression.  This helps keep arrays and bitmaps
  55    more compact.
  56
  57    We could also use a zone allocator for these objects since they have
  58    a very well defined lifetime.  If someone wants to experiment with that
  59    this is the place to try it.  */
  60
  61 /* Array of all SSA_NAMEs used in the function.  */
  62 varray_type ssa_names;
  63
  64 /* Bitmap of ssa names marked for rewriting.  */
  65 static bitmap ssa_names_to_rewrite;
  66
  67 /* Free list of SSA_NAMEs.  This list is wiped at the end of each function
  68    after we leave SSA form.  */
  69 static GTY (()) tree free_ssanames;
  70
  71 /* Version numbers with special meanings.  We start allocating new version
  72    numbers after the special ones.  */
  73 #define UNUSED_NAME_VERSION 0
  74
  75 #ifdef GATHER_STATISTICS
  76 unsigned int ssa_name_nodes_reused;
  77 unsigned int ssa_name_nodes_created;
  78 #endif
  79
  80 /* Returns true if ssa name VAR is marked for rewrite.  */
  81
  82 bool
  83 marked_for_rewrite_p (tree var)
  84 {
  85   return bitmap_bit_p (ssa_names_to_rewrite, SSA_NAME_VERSION (var));
  86 }
  87
  88 /* Returns true if any ssa name is marked for rewrite.  */
  89
  90 bool
  91 any_marked_for_rewrite_p (void)
  92 {
  93   if (!ssa_names_to_rewrite)
  94     return false;
  95
  96   return !bitmap_empty_p (ssa_names_to_rewrite);
  97 }
  98
  99 /* Mark ssa name VAR for rewriting.  */
 100
 101 void
 102 mark_for_rewrite (tree var)
 103 {
 104   bitmap_set_bit (ssa_names_to_rewrite, SSA_NAME_VERSION (var));
 105 }
 106
 107 /* Unmark all ssa names marked for rewrite.  */
 108
 109 void
 110 unmark_all_for_rewrite (void)
 111 {
 112   bitmap_clear (ssa_names_to_rewrite);
 113 }
 114
 115 /* Return the bitmap of ssa names to rewrite.  Copy the bitmap,
 116    so that the optimizers cannot access internals directly  */
 117
 118 bitmap
 119 marked_ssa_names (void)
 120 {
 121   bitmap ret = BITMAP_ALLOC (NULL);
 122
 123   bitmap_copy (ret, ssa_names_to_rewrite);
 124
 125   return ret;
 126 }
 127
 128 /* Initialize management of SSA_NAMEs.  */
 129
 130 void
 131 init_ssanames (void)
 132 {
 133   VARRAY_TREE_INIT (ssa_names, 50, "ssa_names table");
 134
 135   /* Version 0 is special, so reserve the first slot in the table.  Though
 136      currently unused, we may use version 0 in alias analysis as part of
 137      the heuristics used to group aliases when the alias sets are too
 138      large.  */
 139   VARRAY_PUSH_TREE (ssa_names, NULL_TREE);
 140   free_ssanames = NULL;
 141   ssa_names_to_rewrite = BITMAP_ALLOC (NULL);
 142 }
 143
 144 /* Finalize management of SSA_NAMEs.  */
 145
 146 void
 147 fini_ssanames (void)
 148 {
 149   BITMAP_FREE (ssa_names_to_rewrite);
 150   ggc_free (ssa_names);
 151   ssa_names = NULL;
 152   free_ssanames = NULL;
 153 }
 154
 155 /* Dump some simple statistics regarding the re-use of SSA_NAME nodes.  */
 156
 157 #ifdef GATHER_STATISTICS
 158 void
 159 ssanames_print_statistics (void)
 160 {
 161   fprintf (stderr, "SSA_NAME nodes allocated: %u\n", ssa_name_nodes_created);
 162   fprintf (stderr, "SSA_NAME nodes reused: %u\n", ssa_name_nodes_reused);
 163 }
 164 #endif
 165
 166 /* Return an SSA_NAME node for variable VAR defined in statement STMT.
 167    STMT may be an empty statement for artificial references (e.g., default
 168    definitions created when a variable is used without a preceding
 169    definition).  */
 170
 171 tree
 172 make_ssa_name (tree var, tree stmt)
 173 {
 174   tree t;
 175   ssa_imm_use_t *imm;
 176
 177   gcc_assert (DECL_P (var)
 178               || TREE_CODE (var) == INDIRECT_REF);
 179
 180   gcc_assert (!stmt || EXPR_P (stmt) || TREE_CODE (stmt) == PHI_NODE);
 181
 182   /* If our free list has an element, then use it.  */
 183   if (free_ssanames)
 184     {
 185       t = free_ssanames;
 186       free_ssanames = TREE_CHAIN (free_ssanames);
 187 #ifdef GATHER_STATISTICS
 188       ssa_name_nodes_reused++;
 189 #endif
 190
 191       /* The node was cleared out when we put it on the free list, so
 192          there is no need to do so again here.  */
 193       gcc_assert (ssa_name (SSA_NAME_VERSION (t)) == NULL);
 194       VARRAY_TREE (ssa_names, SSA_NAME_VERSION (t)) = t;
 195     }
 196   else
 197     {
 198       t = make_node (SSA_NAME);
 199       SSA_NAME_VERSION (t) = num_ssa_names;
 200       VARRAY_PUSH_TREE (ssa_names, t);
 201 #ifdef GATHER_STATISTICS
 202       ssa_name_nodes_created++;
 203 #endif
 204     }
 205
 206   TREE_TYPE (t) = TREE_TYPE (var);
 207   SSA_NAME_VAR (t) = var;
 208   SSA_NAME_DEF_STMT (t) = stmt;
 209   SSA_NAME_PTR_INFO (t) = NULL;
 210   SSA_NAME_IN_FREE_LIST (t) = 0;
 211   imm = &(SSA_NAME_IMM_USE_NODE (t));
 212   imm->use = NULL;
 213   imm->prev = imm;
 214   imm->next = imm;
 215   imm->stmt = t;
 216
 217   return t;
 218 }
 219
 220
 221 /* We no longer need the SSA_NAME expression VAR, release it so that
 222    it may be reused.
 223
 224    Note it is assumed that no calls to make_ssa_name will be made
 225    until all uses of the ssa name are released and that the only
 226    use of the SSA_NAME expression is to check its SSA_NAME_VAR.  All
 227    other fields must be assumed clobbered.  */
 228
 229 void
 230 release_ssa_name (tree var)
 231 {
 232   if (!var)
 233     return;
 234
 235   /* Never release the default definition for a symbol.  It's a
 236      special SSA name that should always exist once it's created.  */
 237   if (var == var_ann (SSA_NAME_VAR (var))->default_def)
 238     return;
 239
 240   /* If the ssa name is marked for rewriting, it may have multiple definitions,
 241      but we may happen to remove just one of them.  So do not remove the
 242      ssa name now.  */
 243   if (marked_for_rewrite_p (var))
 244     return;
 245
 246   /* release_ssa_name can be called multiple times on a single SSA_NAME.
 247      However, it should only end up on our free list one time.   We
 248      keep a status bit in the SSA_NAME node itself to indicate it has
 249      been put on the free list.
 250
 251      Note that once on the freelist you can not reference the SSA_NAME's
 252      defining statement.  */
 253   if (! SSA_NAME_IN_FREE_LIST (var))
 254     {
 255       tree saved_ssa_name_var = SSA_NAME_VAR (var);
 256       int saved_ssa_name_version = SSA_NAME_VERSION (var);
 257       ssa_imm_use_t *imm = &(SSA_NAME_IMM_USE_NODE (var));
 258
 259 #ifdef ENABLE_CHECKING
 260       verify_imm_links (stderr, var);
 261 #endif
 262       while (imm->next != imm)
 263         {
 264           delink_imm_use (imm->next);
 265         }
 266 #ifdef ENABLE_CHECKING
 267       if (imm->next != imm)
 268         abort();
 269 #endif
 270
 271       VARRAY_TREE (ssa_names, SSA_NAME_VERSION (var)) = NULL;
 272       memset (var, 0, tree_size (var));
 273
 274       imm->prev = imm;
 275       imm->next = imm;
 276       imm->stmt = var;
 277       /* First put back the right tree node so that the tree checking
 278          macros do not complain.  */
 279       TREE_SET_CODE (var, SSA_NAME);
 280
 281       /* Restore the version number.  */
 282       SSA_NAME_VERSION (var) = saved_ssa_name_version;
 283
 284       /* Hopefully this can go away once we have the new incremental
 285          SSA updating code installed.  */
 286       SSA_NAME_VAR (var) = saved_ssa_name_var;
 287
 288       /* Note this SSA_NAME is now in the first list.  */
 289       SSA_NAME_IN_FREE_LIST (var) = 1;
 290
 291       /* And finally link it into the free list.  */
 292       TREE_CHAIN (var) = free_ssanames;
 293       free_ssanames = var;
 294     }
 295 }
 296
 297 /* Creates a duplicate of a ssa name NAME defined in statement STMT.  */
 298
 299 tree
 300 duplicate_ssa_name (tree name, tree stmt)
 301 {
 302   tree new_name = make_ssa_name (SSA_NAME_VAR (name), stmt);
 303   struct ptr_info_def *old_ptr_info = SSA_NAME_PTR_INFO (name);
 304
 305   if (old_ptr_info)
 306     duplicate_ssa_name_ptr_info (new_name, old_ptr_info);
 307
 308   return new_name;
 309 }
 310
 311
 312 /* Creates a duplicate of the ptr_info_def at PTR_INFO for use by
 313    the ssa name NAME.  */
 314
 315 void
 316 duplicate_ssa_name_ptr_info (tree name, struct ptr_info_def *ptr_info)
 317 {
 318   struct ptr_info_def *new_ptr_info;
 319
 320   gcc_assert (POINTER_TYPE_P (TREE_TYPE (name)));
 321   gcc_assert (!SSA_NAME_PTR_INFO (name));
 322
 323   if (!ptr_info)
 324     return;
 325
 326   new_ptr_info = ggc_alloc (sizeof (struct ptr_info_def));
 327   *new_ptr_info = *ptr_info;
 328
 329   if (ptr_info->pt_vars)
 330     {
 331       new_ptr_info->pt_vars = BITMAP_GGC_ALLOC ();
 332       bitmap_copy (new_ptr_info->pt_vars, ptr_info->pt_vars);
 333     }
 334
 335   SSA_NAME_PTR_INFO (name) = new_ptr_info;
 336 }
 337
 338
 339 /* Release all the SSA_NAMEs created by STMT.  */
 340
 341 void
 342 release_defs (tree stmt)
 343 {
 344   tree def;
 345   ssa_op_iter iter;
 346
 347   FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
 348     if (TREE_CODE (def) == SSA_NAME)
 349       release_ssa_name (def);
 350 }
 351
 352
 353 /* Replace the symbol associated with SSA_NAME with SYM.  */
 354
 355 void
 356 replace_ssa_name_symbol (tree ssa_name, tree sym)
 357 {
 358   SSA_NAME_VAR (ssa_name) = sym;
 359   TREE_TYPE (ssa_name) = TREE_TYPE (sym);
 360 }
 361
 362 #include "gt-tree-ssanames.h"