gcc/tree-ssanames.c

   1 /* Generic routines for manipulating SSA_NAME expressions
   2    Copyright (C) 2003, 2004 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 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   if (ssa_names_to_rewrite
  86       && bitmap_bit_p (ssa_names_to_rewrite, SSA_NAME_VERSION (var)))
  87     return true;
  88
  89   return false;
  90 }
  91
  92 /* Returns true if any ssa name is marked for rewrite.  */
  93
  94 bool
  95 any_marked_for_rewrite_p (void)
  96 {
  97   if (!ssa_names_to_rewrite)
  98     return false;
  99
 100   return bitmap_first_set_bit (ssa_names_to_rewrite) != -1;
 101 }
 102
 103 /* Mark ssa name VAR for rewriting.  */
 104
 105 void
 106 mark_for_rewrite (tree var)
 107 {
 108   if (!ssa_names_to_rewrite)
 109     ssa_names_to_rewrite = BITMAP_XMALLOC ();
 110
 111   bitmap_set_bit (ssa_names_to_rewrite, SSA_NAME_VERSION (var));
 112 }
 113
 114 /* Unmark all ssa names marked for rewrite.  */
 115
 116 void
 117 unmark_all_for_rewrite (void)
 118 {
 119   if (!ssa_names_to_rewrite)
 120     return;
 121
 122   bitmap_clear (ssa_names_to_rewrite);
 123 }
 124
 125 /* Return the bitmap of ssa names to rewrite.  Copy the bitmap,
 126    so that the optimizers cannot access internals directly  */
 127
 128 bitmap
 129 marked_ssa_names (void)
 130 {
 131   bitmap ret = BITMAP_XMALLOC ();
 132   if (ssa_names_to_rewrite)
 133     bitmap_copy (ret, ssa_names_to_rewrite);
 134
 135   return ret;
 136 }
 137
 138 /* Initialize management of SSA_NAMEs.  */
 139
 140 void
 141 init_ssanames (void)
 142 {
 143   VARRAY_TREE_INIT (ssa_names, 50, "ssa_names table");
 144
 145   /* Version 0 is special, so reserve the first slot in the table.  Though
 146      currently unused, we may use version 0 in alias analysis as part of
 147      the heuristics used to group aliases when the alias sets are too
 148      large.  */
 149   VARRAY_PUSH_TREE (ssa_names, NULL_TREE);
 150   free_ssanames = NULL;
 151 }
 152
 153 /* Finalize management of SSA_NAMEs.  */
 154
 155 void
 156 fini_ssanames (void)
 157 {
 158   ggc_free (ssa_names);
 159   ssa_names = NULL;
 160   free_ssanames = NULL;
 161 }
 162
 163 /* Dump some simple statistics regarding the re-use of SSA_NAME nodes.  */
 164
 165 #ifdef GATHER_STATISTICS
 166 void
 167 ssanames_print_statistics (void)
 168 {
 169   fprintf (stderr, "SSA_NAME nodes allocated: %u\n", ssa_name_nodes_created);
 170   fprintf (stderr, "SSA_NAME nodes reused: %u\n", ssa_name_nodes_reused);
 171 }
 172 #endif
 173
 174 /* Return an SSA_NAME node for variable VAR defined in statement STMT.
 175    STMT may be an empty statement for artificial references (e.g., default
 176    definitions created when a variable is used without a preceding
 177    definition).  */
 178
 179 tree
 180 make_ssa_name (tree var, tree stmt)
 181 {
 182   tree t;
 183
 184   gcc_assert (DECL_P (var)
 185               || TREE_CODE (var) == INDIRECT_REF);
 186
 187   gcc_assert (!stmt || EXPR_P (stmt) || TREE_CODE (stmt) == PHI_NODE);
 188
 189   /* If our free list has an element, then use it.  */
 190   if (free_ssanames)
 191     {
 192       t = free_ssanames;
 193       free_ssanames = TREE_CHAIN (free_ssanames);
 194 #ifdef GATHER_STATISTICS
 195       ssa_name_nodes_reused++;
 196 #endif
 197
 198       /* The node was cleared out when we put it on the free list, so
 199          there is no need to do so again here.  */
 200       gcc_assert (ssa_name (SSA_NAME_VERSION (t)) == NULL);
 201       VARRAY_TREE (ssa_names, SSA_NAME_VERSION (t)) = t;
 202     }
 203   else
 204     {
 205       t = make_node (SSA_NAME);
 206       SSA_NAME_VERSION (t) = num_ssa_names;
 207       VARRAY_PUSH_TREE (ssa_names, t);
 208 #ifdef GATHER_STATISTICS
 209       ssa_name_nodes_created++;
 210 #endif
 211     }
 212
 213   TREE_TYPE (t) = TREE_TYPE (var);
 214   SSA_NAME_VAR (t) = var;
 215   SSA_NAME_DEF_STMT (t) = stmt;
 216   SSA_NAME_PTR_INFO (t) = NULL;
 217   SSA_NAME_IN_FREE_LIST (t) = 0;
 218
 219   return t;
 220 }
 221
 222
 223 /* We no longer need the SSA_NAME expression VAR, release it so that
 224    it may be reused.
 225
 226    Note it is assumed that no calls to make_ssa_name will be made
 227    until all uses of the ssa name are released and that the only
 228    use of the SSA_NAME expression is to check its SSA_NAME_VAR.  All
 229    other fields must be assumed clobbered.  */
 230
 231 void
 232 release_ssa_name (tree var)
 233 {
 234   if (!var)
 235     return;
 236
 237   /* Never release the default definition for a symbol.  It's a
 238      special SSA name that should always exist once it's created.  */
 239   if (var == var_ann (SSA_NAME_VAR (var))->default_def)
 240     return;
 241
 242   /* If the ssa name is marked for rewriting, it may have multiple definitions,
 243      but we may happen to remove just one of them.  So do not remove the
 244      ssa name now.  */
 245   if (marked_for_rewrite_p (var))
 246     return;
 247
 248   /* release_ssa_name can be called multiple times on a single SSA_NAME.
 249      However, it should only end up on our free list one time.   We
 250      keep a status bit in the SSA_NAME node itself to indicate it has
 251      been put on the free list.
 252
 253      Note that once on the freelist you can not reference the SSA_NAME's
 254      defining statement.  */
 255   if (! SSA_NAME_IN_FREE_LIST (var))
 256     {
 257       tree saved_ssa_name_var = SSA_NAME_VAR (var);
 258       int saved_ssa_name_version = SSA_NAME_VERSION (var);
 259
 260       VARRAY_TREE (ssa_names, SSA_NAME_VERSION (var)) = NULL;
 261       memset (var, 0, tree_size (var));
 262
 263       /* First put back the right tree node so that the tree checking
 264          macros do not complain.  */
 265       TREE_SET_CODE (var, SSA_NAME);
 266
 267       /* Restore the version number.  */
 268       SSA_NAME_VERSION (var) = saved_ssa_name_version;
 269
 270       /* Hopefully this can go away once we have the new incremental
 271          SSA updating code installed.  */
 272       SSA_NAME_VAR (var) = saved_ssa_name_var;
 273
 274       /* Note this SSA_NAME is now in the first list.  */
 275       SSA_NAME_IN_FREE_LIST (var) = 1;
 276
 277       /* And finally link it into the free list.  */
 278       TREE_CHAIN (var) = free_ssanames;
 279       free_ssanames = var;
 280     }
 281 }
 282
 283 /* Creates a duplicate of a ssa name NAME defined in statement STMT.  */
 284
 285 tree
 286 duplicate_ssa_name (tree name, tree stmt)
 287 {
 288   tree new_name = make_ssa_name (SSA_NAME_VAR (name), stmt);
 289   struct ptr_info_def *old_ptr_info = SSA_NAME_PTR_INFO (name);
 290   struct ptr_info_def *new_ptr_info;
 291
 292   if (!old_ptr_info)
 293     return new_name;
 294
 295   new_ptr_info = ggc_alloc (sizeof (struct ptr_info_def));
 296   *new_ptr_info = *old_ptr_info;
 297
 298   if (old_ptr_info->pt_vars)
 299     {
 300       new_ptr_info->pt_vars = BITMAP_GGC_ALLOC ();
 301       bitmap_copy (new_ptr_info->pt_vars, old_ptr_info->pt_vars);
 302     }
 303
 304   SSA_NAME_PTR_INFO (new_name) = new_ptr_info;
 305   return new_name;
 306 }
 307
 308
 309 /* Release all the SSA_NAMEs created by STMT.  */
 310
 311 void
 312 release_defs (tree stmt)
 313 {
 314   tree def;
 315   ssa_op_iter iter;
 316
 317   FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
 318     if (TREE_CODE (def) == SSA_NAME)
 319       release_ssa_name (def);
 320 }
 321
 322
 323 /* Replace the symbol associated with SSA_NAME with SYM.  */
 324
 325 void
 326 replace_ssa_name_symbol (tree ssa_name, tree sym)
 327 {
 328   SSA_NAME_VAR (ssa_name) = sym;
 329   TREE_TYPE (ssa_name) = TREE_TYPE (sym);
 330 }
 331
 332 #include "gt-tree-ssanames.h"