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, 51 Franklin Street, Fifth Floor,
  19 Boston, MA 02110-1301, 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 /* Version numbers with special meanings.  We start allocating new version
  62    numbers after the special ones.  */
  63 #define UNUSED_NAME_VERSION 0
  64
  65 #ifdef GATHER_STATISTICS
  66 unsigned int ssa_name_nodes_reused;
  67 unsigned int ssa_name_nodes_created;
  68 #endif
  69
  70 /* Initialize management of SSA_NAMEs.  */
  71
  72 void
  73 init_ssanames (void)
  74 {
  75   SSANAMES (cfun) = VEC_alloc (tree, gc, 50);
  76
  77   /* Version 0 is special, so reserve the first slot in the table.  Though
  78      currently unused, we may use version 0 in alias analysis as part of
  79      the heuristics used to group aliases when the alias sets are too
  80      large.
  81
  82      We use VEC_quick_push here because we know that SSA_NAMES has at
  83      least 50 elements reserved in it.  */
  84   VEC_quick_push (tree, SSANAMES (cfun), NULL_TREE);
  85   FREE_SSANAMES (cfun) = NULL;
  86 }
  87
  88 /* Finalize management of SSA_NAMEs.  */
  89
  90 void
  91 fini_ssanames (void)
  92 {
  93   VEC_free (tree, gc, SSANAMES (cfun));
  94   FREE_SSANAMES (cfun) = NULL;
  95 }
  96
  97 /* Dump some simple statistics regarding the re-use of SSA_NAME nodes.  */
  98
  99 #ifdef GATHER_STATISTICS
 100 void
 101 ssanames_print_statistics (void)
 102 {
 103   fprintf (stderr, "SSA_NAME nodes allocated: %u\n", ssa_name_nodes_created);
 104   fprintf (stderr, "SSA_NAME nodes reused: %u\n", ssa_name_nodes_reused);
 105 }
 106 #endif
 107
 108 /* Return an SSA_NAME node for variable VAR defined in statement STMT.
 109    STMT may be an empty statement for artificial references (e.g., default
 110    definitions created when a variable is used without a preceding
 111    definition).  */
 112
 113 tree
 114 make_ssa_name (tree var, tree stmt)
 115 {
 116   tree t;
 117   use_operand_p imm;
 118
 119   gcc_assert (DECL_P (var)
 120               || TREE_CODE (var) == INDIRECT_REF);
 121
 122   gcc_assert (!stmt
 123               || EXPR_P (stmt) || GIMPLE_STMT_P (stmt)
 124               || TREE_CODE (stmt) == PHI_NODE);
 125
 126   /* If our free list has an element, then use it.  */
 127   if (FREE_SSANAMES (cfun))
 128     {
 129       t = FREE_SSANAMES (cfun);
 130       FREE_SSANAMES (cfun) = TREE_CHAIN (FREE_SSANAMES (cfun));
 131 #ifdef GATHER_STATISTICS
 132       ssa_name_nodes_reused++;
 133 #endif
 134
 135       /* The node was cleared out when we put it on the free list, so
 136          there is no need to do so again here.  */
 137       gcc_assert (ssa_name (SSA_NAME_VERSION (t)) == NULL);
 138       VEC_replace (tree, SSANAMES (cfun), SSA_NAME_VERSION (t), t);
 139     }
 140   else
 141     {
 142       t = make_node (SSA_NAME);
 143       SSA_NAME_VERSION (t) = num_ssa_names;
 144       VEC_safe_push (tree, gc, SSANAMES (cfun), t);
 145 #ifdef GATHER_STATISTICS
 146       ssa_name_nodes_created++;
 147 #endif
 148     }
 149
 150   TREE_TYPE (t) = TREE_TYPE (var);
 151   SSA_NAME_VAR (t) = var;
 152   SSA_NAME_DEF_STMT (t) = stmt;
 153   SSA_NAME_PTR_INFO (t) = NULL;
 154   SSA_NAME_IN_FREE_LIST (t) = 0;
 155   imm = &(SSA_NAME_IMM_USE_NODE (t));
 156   imm->use = NULL;
 157   imm->prev = imm;
 158   imm->next = imm;
 159   imm->stmt = t;
 160
 161   return t;
 162 }
 163
 164
 165 /* We no longer need the SSA_NAME expression VAR, release it so that
 166    it may be reused.
 167
 168    Note it is assumed that no calls to make_ssa_name will be made
 169    until all uses of the ssa name are released and that the only
 170    use of the SSA_NAME expression is to check its SSA_NAME_VAR.  All
 171    other fields must be assumed clobbered.  */
 172
 173 void
 174 release_ssa_name (tree var)
 175 {
 176   if (!var)
 177     return;
 178
 179   /* Never release the default definition for a symbol.  It's a
 180      special SSA name that should always exist once it's created.  */
 181   if (var == gimple_default_def (cfun, SSA_NAME_VAR (var)))
 182     return;
 183
 184   /* If VAR has been registered for SSA updating, don't remove it.
 185      After update_ssa has run, the name will be released.  */
 186   if (name_registered_for_update_p (var))
 187     {
 188       release_ssa_name_after_update_ssa (var);
 189       return;
 190     }
 191
 192   /* release_ssa_name can be called multiple times on a single SSA_NAME.
 193      However, it should only end up on our free list one time.   We
 194      keep a status bit in the SSA_NAME node itself to indicate it has
 195      been put on the free list.
 196
 197      Note that once on the freelist you can not reference the SSA_NAME's
 198      defining statement.  */
 199   if (! SSA_NAME_IN_FREE_LIST (var))
 200     {
 201       tree saved_ssa_name_var = SSA_NAME_VAR (var);
 202       int saved_ssa_name_version = SSA_NAME_VERSION (var);
 203       use_operand_p imm = &(SSA_NAME_IMM_USE_NODE (var));
 204
 205 #ifdef ENABLE_CHECKING
 206       verify_imm_links (stderr, var);
 207 #endif
 208       while (imm->next != imm)
 209         delink_imm_use (imm->next);
 210
 211       VEC_replace (tree, SSANAMES (cfun),
 212                    SSA_NAME_VERSION (var), NULL_TREE);
 213       memset (var, 0, tree_size (var));
 214
 215       imm->prev = imm;
 216       imm->next = imm;
 217       imm->stmt = var;
 218       /* First put back the right tree node so that the tree checking
 219          macros do not complain.  */
 220       TREE_SET_CODE (var, SSA_NAME);
 221
 222       /* Restore the version number.  */
 223       SSA_NAME_VERSION (var) = saved_ssa_name_version;
 224
 225       /* Hopefully this can go away once we have the new incremental
 226          SSA updating code installed.  */
 227       SSA_NAME_VAR (var) = saved_ssa_name_var;
 228
 229       /* Note this SSA_NAME is now in the first list.  */
 230       SSA_NAME_IN_FREE_LIST (var) = 1;
 231
 232       /* And finally link it into the free list.  */
 233       TREE_CHAIN (var) = FREE_SSANAMES (cfun);
 234       FREE_SSANAMES (cfun) = var;
 235     }
 236 }
 237
 238 /* Creates a duplicate of a ssa name NAME defined in statement STMT.  */
 239
 240 tree
 241 duplicate_ssa_name (tree name, tree stmt)
 242 {
 243   tree new_name = make_ssa_name (SSA_NAME_VAR (name), stmt);
 244   struct ptr_info_def *old_ptr_info = SSA_NAME_PTR_INFO (name);
 245
 246   if (old_ptr_info)
 247     duplicate_ssa_name_ptr_info (new_name, old_ptr_info);
 248
 249   return new_name;
 250 }
 251
 252
 253 /* Creates a duplicate of the ptr_info_def at PTR_INFO for use by
 254    the SSA name NAME.  */
 255
 256 void
 257 duplicate_ssa_name_ptr_info (tree name, struct ptr_info_def *ptr_info)
 258 {
 259   struct ptr_info_def *new_ptr_info;
 260
 261   gcc_assert (POINTER_TYPE_P (TREE_TYPE (name)));
 262   gcc_assert (!SSA_NAME_PTR_INFO (name));
 263
 264   if (!ptr_info)
 265     return;
 266
 267   new_ptr_info = ggc_alloc (sizeof (struct ptr_info_def));
 268   *new_ptr_info = *ptr_info;
 269
 270   if (ptr_info->pt_vars)
 271     {
 272       new_ptr_info->pt_vars = BITMAP_GGC_ALLOC ();
 273       bitmap_copy (new_ptr_info->pt_vars, ptr_info->pt_vars);
 274     }
 275
 276   SSA_NAME_PTR_INFO (name) = new_ptr_info;
 277 }
 278
 279
 280 /* Release all the SSA_NAMEs created by STMT.  */
 281
 282 void
 283 release_defs (tree stmt)
 284 {
 285   tree def;
 286   ssa_op_iter iter;
 287
 288   /* Make sure that we are in SSA.  Otherwise, operand cache may point
 289      to garbage.  */
 290   gcc_assert (gimple_in_ssa_p (cfun));
 291
 292   FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
 293     if (TREE_CODE (def) == SSA_NAME)
 294       release_ssa_name (def);
 295 }
 296
 297
 298 /* Replace the symbol associated with SSA_NAME with SYM.  */
 299
 300 void
 301 replace_ssa_name_symbol (tree ssa_name, tree sym)
 302 {
 303   SSA_NAME_VAR (ssa_name) = sym;
 304   TREE_TYPE (ssa_name) = TREE_TYPE (sym);
 305 }