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 /* Free list of SSA_NAMEs.  This list is wiped at the end of each function
  65    after we leave SSA form.  */
  66 static GTY (()) tree free_ssanames;
  67
  68 /* Version numbers with special meanings.  We start allocating new version
  69    numbers after the special ones.  */
  70 #define UNUSED_NAME_VERSION 0
  71
  72 #ifdef GATHER_STATISTICS
  73 unsigned int ssa_name_nodes_reused;
  74 unsigned int ssa_name_nodes_created;
  75 #endif
  76
  77 /* Initialize management of SSA_NAMEs.  */
  78
  79 void
  80 init_ssanames (void)
  81 {
  82   VARRAY_TREE_INIT (ssa_names, 50, "ssa_names table");
  83
  84   /* Version 0 is special, so reserve the first slot in the table.  Though
  85      currently unused, we may use version 0 in alias analysis as part of
  86      the heuristics used to group aliases when the alias sets are too
  87      large.  */
  88   VARRAY_PUSH_TREE (ssa_names, NULL_TREE);
  89   free_ssanames = NULL;
  90 }
  91
  92 /* Finalize management of SSA_NAMEs.  */
  93
  94 void
  95 fini_ssanames (void)
  96 {
  97   ggc_free (ssa_names);
  98   ssa_names = NULL;
  99   free_ssanames = NULL;
 100 }
 101
 102 /* Dump some simple statistics regarding the re-use of SSA_NAME nodes.  */
 103
 104 #ifdef GATHER_STATISTICS
 105 void
 106 ssanames_print_statistics (void)
 107 {
 108   fprintf (stderr, "SSA_NAME nodes allocated: %u\n", ssa_name_nodes_created);
 109   fprintf (stderr, "SSA_NAME nodes reused: %u\n", ssa_name_nodes_reused);
 110 }
 111 #endif
 112
 113 /* Return an SSA_NAME node for variable VAR defined in statement STMT.
 114    STMT may be an empty statement for artificial references (e.g., default
 115    definitions created when a variable is used without a preceding
 116    definition).  */
 117
 118 tree
 119 make_ssa_name (tree var, tree stmt)
 120 {
 121   tree t;
 122   ssa_imm_use_t *imm;
 123
 124   gcc_assert (DECL_P (var)
 125               || TREE_CODE (var) == INDIRECT_REF);
 126
 127   gcc_assert (!stmt || EXPR_P (stmt) || TREE_CODE (stmt) == PHI_NODE);
 128
 129   /* If our free list has an element, then use it.  */
 130   if (free_ssanames)
 131     {
 132       t = free_ssanames;
 133       free_ssanames = TREE_CHAIN (free_ssanames);
 134 #ifdef GATHER_STATISTICS
 135       ssa_name_nodes_reused++;
 136 #endif
 137
 138       /* The node was cleared out when we put it on the free list, so
 139          there is no need to do so again here.  */
 140       gcc_assert (ssa_name (SSA_NAME_VERSION (t)) == NULL);
 141       VARRAY_TREE (ssa_names, SSA_NAME_VERSION (t)) = t;
 142     }
 143   else
 144     {
 145       t = make_node (SSA_NAME);
 146       SSA_NAME_VERSION (t) = num_ssa_names;
 147       VARRAY_PUSH_TREE (ssa_names, t);
 148 #ifdef GATHER_STATISTICS
 149       ssa_name_nodes_created++;
 150 #endif
 151     }
 152
 153   TREE_TYPE (t) = TREE_TYPE (var);
 154   SSA_NAME_VAR (t) = var;
 155   SSA_NAME_DEF_STMT (t) = stmt;
 156   SSA_NAME_PTR_INFO (t) = NULL;
 157   SSA_NAME_IN_FREE_LIST (t) = 0;
 158   imm = &(SSA_NAME_IMM_USE_NODE (t));
 159   imm->use = NULL;
 160   imm->prev = imm;
 161   imm->next = imm;
 162   imm->stmt = t;
 163
 164   return t;
 165 }
 166
 167
 168 /* We no longer need the SSA_NAME expression VAR, release it so that
 169    it may be reused.
 170
 171    Note it is assumed that no calls to make_ssa_name will be made
 172    until all uses of the ssa name are released and that the only
 173    use of the SSA_NAME expression is to check its SSA_NAME_VAR.  All
 174    other fields must be assumed clobbered.  */
 175
 176 void
 177 release_ssa_name (tree var)
 178 {
 179   if (!var)
 180     return;
 181
 182   /* Never release the default definition for a symbol.  It's a
 183      special SSA name that should always exist once it's created.  */
 184   if (var == var_ann (SSA_NAME_VAR (var))->default_def)
 185     return;
 186
 187   /* If VAR has been registered for SSA updating, don't remove it.
 188      After update_ssa has run, the name will be released.  */
 189   if (name_registered_for_update_p (var))
 190     {
 191       release_ssa_name_after_update_ssa (var);
 192       return;
 193     }
 194
 195   /* release_ssa_name can be called multiple times on a single SSA_NAME.
 196      However, it should only end up on our free list one time.   We
 197      keep a status bit in the SSA_NAME node itself to indicate it has
 198      been put on the free list.
 199
 200      Note that once on the freelist you can not reference the SSA_NAME's
 201      defining statement.  */
 202   if (! SSA_NAME_IN_FREE_LIST (var))
 203     {
 204       tree saved_ssa_name_var = SSA_NAME_VAR (var);
 205       int saved_ssa_name_version = SSA_NAME_VERSION (var);
 206       ssa_imm_use_t *imm = &(SSA_NAME_IMM_USE_NODE (var));
 207
 208 #ifdef ENABLE_CHECKING
 209       verify_imm_links (stderr, var);
 210 #endif
 211       while (imm->next != imm)
 212         delink_imm_use (imm->next);
 213
 214       VARRAY_TREE (ssa_names, SSA_NAME_VERSION (var)) = NULL;
 215       memset (var, 0, tree_size (var));
 216
 217       imm->prev = imm;
 218       imm->next = imm;
 219       imm->stmt = var;
 220       /* First put back the right tree node so that the tree checking
 221          macros do not complain.  */
 222       TREE_SET_CODE (var, SSA_NAME);
 223
 224       /* Restore the version number.  */
 225       SSA_NAME_VERSION (var) = saved_ssa_name_version;
 226
 227       /* Hopefully this can go away once we have the new incremental
 228          SSA updating code installed.  */
 229       SSA_NAME_VAR (var) = saved_ssa_name_var;
 230
 231       /* Note this SSA_NAME is now in the first list.  */
 232       SSA_NAME_IN_FREE_LIST (var) = 1;
 233
 234       /* And finally link it into the free list.  */
 235       TREE_CHAIN (var) = free_ssanames;
 236       free_ssanames = var;
 237     }
 238 }
 239
 240 /* Creates a duplicate of a ssa name NAME defined in statement STMT.  */
 241
 242 tree
 243 duplicate_ssa_name (tree name, tree stmt)
 244 {
 245   tree new_name = make_ssa_name (SSA_NAME_VAR (name), stmt);
 246   struct ptr_info_def *old_ptr_info = SSA_NAME_PTR_INFO (name);
 247
 248   if (old_ptr_info)
 249     duplicate_ssa_name_ptr_info (new_name, old_ptr_info);
 250
 251   return new_name;
 252 }
 253
 254
 255 /* Creates a duplicate of the ptr_info_def at PTR_INFO for use by
 256    the SSA name NAME.  */
 257
 258 void
 259 duplicate_ssa_name_ptr_info (tree name, struct ptr_info_def *ptr_info)
 260 {
 261   struct ptr_info_def *new_ptr_info;
 262
 263   gcc_assert (POINTER_TYPE_P (TREE_TYPE (name)));
 264   gcc_assert (!SSA_NAME_PTR_INFO (name));
 265
 266   if (!ptr_info)
 267     return;
 268
 269   new_ptr_info = ggc_alloc (sizeof (struct ptr_info_def));
 270   *new_ptr_info = *ptr_info;
 271
 272   if (ptr_info->pt_vars)
 273     {
 274       new_ptr_info->pt_vars = BITMAP_GGC_ALLOC ();
 275       bitmap_copy (new_ptr_info->pt_vars, ptr_info->pt_vars);
 276     }
 277
 278   SSA_NAME_PTR_INFO (name) = new_ptr_info;
 279 }
 280
 281
 282 /* Release all the SSA_NAMEs created by STMT.  */
 283
 284 void
 285 release_defs (tree stmt)
 286 {
 287   tree def;
 288   ssa_op_iter iter;
 289
 290   FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
 291     if (TREE_CODE (def) == SSA_NAME)
 292       release_ssa_name (def);
 293 }
 294
 295
 296 /* Replace the symbol associated with SSA_NAME with SYM.  */
 297
 298 void
 299 replace_ssa_name_symbol (tree ssa_name, tree sym)
 300 {
 301   SSA_NAME_VAR (ssa_name) = sym;
 302   TREE_TYPE (ssa_name) = TREE_TYPE (sym);
 303 }
 304
 305 #include "gt-tree-ssanames.h"