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
 176   gcc_assert (DECL_P (var)
 177               || TREE_CODE (var) == INDIRECT_REF);
 178
 179   gcc_assert (!stmt || EXPR_P (stmt) || TREE_CODE (stmt) == PHI_NODE);
 180
 181   /* If our free list has an element, then use it.  */
 182   if (free_ssanames)
 183     {
 184       t = free_ssanames;
 185       free_ssanames = TREE_CHAIN (free_ssanames);
 186 #ifdef GATHER_STATISTICS
 187       ssa_name_nodes_reused++;
 188 #endif
 189
 190       /* The node was cleared out when we put it on the free list, so
 191          there is no need to do so again here.  */
 192       gcc_assert (ssa_name (SSA_NAME_VERSION (t)) == NULL);
 193       VARRAY_TREE (ssa_names, SSA_NAME_VERSION (t)) = t;
 194     }
 195   else
 196     {
 197       t = make_node (SSA_NAME);
 198       SSA_NAME_VERSION (t) = num_ssa_names;
 199       VARRAY_PUSH_TREE (ssa_names, t);
 200 #ifdef GATHER_STATISTICS
 201       ssa_name_nodes_created++;
 202 #endif
 203     }
 204
 205   TREE_TYPE (t) = TREE_TYPE (var);
 206   SSA_NAME_VAR (t) = var;
 207   SSA_NAME_DEF_STMT (t) = stmt;
 208   SSA_NAME_PTR_INFO (t) = NULL;
 209   SSA_NAME_IN_FREE_LIST (t) = 0;
 210
 211   return t;
 212 }
 213
 214
 215 /* We no longer need the SSA_NAME expression VAR, release it so that
 216    it may be reused.
 217
 218    Note it is assumed that no calls to make_ssa_name will be made
 219    until all uses of the ssa name are released and that the only
 220    use of the SSA_NAME expression is to check its SSA_NAME_VAR.  All
 221    other fields must be assumed clobbered.  */
 222
 223 void
 224 release_ssa_name (tree var)
 225 {
 226   if (!var)
 227     return;
 228
 229   /* Never release the default definition for a symbol.  It's a
 230      special SSA name that should always exist once it's created.  */
 231   if (var == var_ann (SSA_NAME_VAR (var))->default_def)
 232     return;
 233
 234   /* If the ssa name is marked for rewriting, it may have multiple definitions,
 235      but we may happen to remove just one of them.  So do not remove the
 236      ssa name now.  */
 237   if (marked_for_rewrite_p (var))
 238     return;
 239
 240   /* release_ssa_name can be called multiple times on a single SSA_NAME.
 241      However, it should only end up on our free list one time.   We
 242      keep a status bit in the SSA_NAME node itself to indicate it has
 243      been put on the free list.
 244
 245      Note that once on the freelist you can not reference the SSA_NAME's
 246      defining statement.  */
 247   if (! SSA_NAME_IN_FREE_LIST (var))
 248     {
 249       tree saved_ssa_name_var = SSA_NAME_VAR (var);
 250       int saved_ssa_name_version = SSA_NAME_VERSION (var);
 251
 252       VARRAY_TREE (ssa_names, SSA_NAME_VERSION (var)) = NULL;
 253       memset (var, 0, tree_size (var));
 254
 255       /* First put back the right tree node so that the tree checking
 256          macros do not complain.  */
 257       TREE_SET_CODE (var, SSA_NAME);
 258
 259       /* Restore the version number.  */
 260       SSA_NAME_VERSION (var) = saved_ssa_name_version;
 261
 262       /* Hopefully this can go away once we have the new incremental
 263          SSA updating code installed.  */
 264       SSA_NAME_VAR (var) = saved_ssa_name_var;
 265
 266       /* Note this SSA_NAME is now in the first list.  */
 267       SSA_NAME_IN_FREE_LIST (var) = 1;
 268
 269       /* And finally link it into the free list.  */
 270       TREE_CHAIN (var) = free_ssanames;
 271       free_ssanames = var;
 272     }
 273 }
 274
 275 /* Creates a duplicate of a ssa name NAME defined in statement STMT.  */
 276
 277 tree
 278 duplicate_ssa_name (tree name, tree stmt)
 279 {
 280   tree new_name = make_ssa_name (SSA_NAME_VAR (name), stmt);
 281   struct ptr_info_def *old_ptr_info = SSA_NAME_PTR_INFO (name);
 282   struct ptr_info_def *new_ptr_info;
 283
 284   if (!old_ptr_info)
 285     return new_name;
 286
 287   new_ptr_info = ggc_alloc (sizeof (struct ptr_info_def));
 288   *new_ptr_info = *old_ptr_info;
 289
 290   if (old_ptr_info->pt_vars)
 291     {
 292       new_ptr_info->pt_vars = BITMAP_GGC_ALLOC ();
 293       bitmap_copy (new_ptr_info->pt_vars, old_ptr_info->pt_vars);
 294     }
 295
 296   SSA_NAME_PTR_INFO (new_name) = new_ptr_info;
 297   return new_name;
 298 }
 299
 300
 301 /* Release all the SSA_NAMEs created by STMT.  */
 302
 303 void
 304 release_defs (tree stmt)
 305 {
 306   tree def;
 307   ssa_op_iter iter;
 308
 309   FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
 310     if (TREE_CODE (def) == SSA_NAME)
 311       release_ssa_name (def);
 312 }
 313
 314
 315 /* Replace the symbol associated with SSA_NAME with SYM.  */
 316
 317 void
 318 replace_ssa_name_symbol (tree ssa_name, tree sym)
 319 {
 320   SSA_NAME_VAR (ssa_name) = sym;
 321   TREE_TYPE (ssa_name) = TREE_TYPE (sym);
 322 }
 323
 324 #include "gt-tree-ssanames.h"