gcc/tree-ssa-copy.c

   1 /* Const/copy propagation and SSA_NAME replacement support routines.
   2    Copyright (C) 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 "flags.h"
  27 #include "rtl.h"
  28 #include "tm_p.h"
  29 #include "ggc.h"
  30 #include "basic-block.h"
  31 #include "output.h"
  32 #include "errors.h"
  33 #include "expr.h"
  34 #include "function.h"
  35 #include "diagnostic.h"
  36 #include "timevar.h"
  37 #include "tree-dump.h"
  38 #include "tree-flow.h"
  39 #include "tree-pass.h"
  40 #include "langhooks.h"
  41
  42 /* This file provides a handful of interfaces for performing const/copy
  43    propagation and simple expression replacement which keep variable
  44    annotations up-to-date.
  45
  46    We require that for any copy operation where the RHS and LHS have
  47    a non-null memory tag that the memory tag be the same.   It is OK
  48    for one or both of the memory tags to be NULL.
  49
  50    We also require tracking if a variable is dereferenced in a load or
  51    store operation.
  52
  53    We enforce these requirements by having all copy propagation and
  54    replacements of one SSA_NAME with a different SSA_NAME to use the
  55    APIs defined in this file.  */
  56
  57
  58 /* Return true if we may propagate ORIG into DEST, false otherwise.  */
  59
  60 bool
  61 may_propagate_copy (tree dest, tree orig)
  62 {
  63   tree type_d = TREE_TYPE (dest);
  64   tree type_o = TREE_TYPE (orig);
  65
  66   /* Do not copy between types for which we *do* need a conversion.  */
  67   if (!tree_ssa_useless_type_conversion_1 (type_d, type_o))
  68     return false;
  69
  70   /* FIXME.  GIMPLE is allowing pointer assignments and comparisons of
  71      pointers that have different alias sets.  This means that these
  72      pointers will have different memory tags associated to them.
  73
  74      If we allow copy propagation in these cases, statements de-referencing
  75      the new pointer will now have a reference to a different memory tag
  76      with potentially incorrect SSA information.
  77
  78      This was showing up in libjava/java/util/zip/ZipFile.java with code
  79      like:
  80
  81         struct java.io.BufferedInputStream *T.660;
  82         struct java.io.BufferedInputStream *T.647;
  83         struct java.io.InputStream *is;
  84         struct java.io.InputStream *is.662;
  85         [ ... ]
  86         T.660 = T.647;
  87         is = T.660;     <-- This ought to be type-casted
  88         is.662 = is;
  89
  90      Also, f/name.c exposed a similar problem with a COND_EXPR predicate
  91      that was causing DOM to generate and equivalence with two pointers of
  92      alias-incompatible types:
  93
  94         struct _ffename_space *n;
  95         struct _ffename *ns;
  96         [ ... ]
  97         if (n == ns)
  98           goto lab;
  99         ...
 100         lab:
 101         return n;
 102
 103      I think that GIMPLE should emit the appropriate type-casts.  For the
 104      time being, blocking copy-propagation in these cases is the safe thing
 105      to do.  */
 106   if (TREE_CODE (dest) == SSA_NAME && TREE_CODE (orig) == SSA_NAME
 107       && POINTER_TYPE_P (type_d) && POINTER_TYPE_P (type_o))
 108     {
 109       tree mt_dest = var_ann (SSA_NAME_VAR (dest))->type_mem_tag;
 110       tree mt_orig = var_ann (SSA_NAME_VAR (orig))->type_mem_tag;
 111       if (mt_dest && mt_orig && mt_dest != mt_orig)
 112         return false;
 113       else if (!lang_hooks.types_compatible_p (type_d, type_o))
 114         return false;
 115       else if (!alias_sets_conflict_p (get_alias_set (type_d),
 116                                        get_alias_set (type_o)))
 117         return false;
 118     }
 119
 120   /* If the destination is a SSA_NAME for a virtual operand, then we have
 121      some special cases to handle.  */
 122   if (TREE_CODE (dest) == SSA_NAME && !is_gimple_reg (dest))
 123     {
 124       /* If both operands are SSA_NAMEs referring to virtual operands, then
 125          we can always propagate.  */
 126       if (TREE_CODE (orig) == SSA_NAME)
 127         {
 128           if (!is_gimple_reg (orig))
 129             return true;
 130
 131 #ifdef ENABLE_CHECKING
 132           /* If we have one real and one virtual operand, then something has
 133              gone terribly wrong.  */
 134           if (is_gimple_reg (orig))
 135             abort ();
 136 #endif
 137         }
 138
 139       /* We have a "copy" from something like a constant into a virtual
 140          operand.  Reject these.  */
 141       return false;
 142     }
 143
 144   /* If ORIG flows in from an abnormal edge, it cannot be propagated.  */
 145   if (TREE_CODE (orig) == SSA_NAME
 146       && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (orig))
 147     return false;
 148
 149   /* If DEST is an SSA_NAME that flows from an abnormal edge or if it
 150      represents a hard register, then it cannot be replaced.  */
 151   if (TREE_CODE (dest) == SSA_NAME
 152       && (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (dest)
 153           || DECL_HARD_REGISTER (SSA_NAME_VAR (dest))))
 154     return false;
 155
 156   /* Anything else is OK.  */
 157   return true;
 158 }
 159
 160
 161 /* Given two SSA_NAMEs pointers ORIG and NEW such that we are copy
 162    propagating NEW into ORIG, consolidate aliasing information so that
 163    they both share the same memory tags.  */
 164
 165 static void
 166 merge_alias_info (tree orig, tree new)
 167 {
 168   tree new_sym = SSA_NAME_VAR (new);
 169   tree orig_sym = SSA_NAME_VAR (orig);
 170   var_ann_t new_ann = var_ann (new_sym);
 171   var_ann_t orig_ann = var_ann (orig_sym);
 172
 173 #if defined ENABLE_CHECKING
 174   if (!POINTER_TYPE_P (TREE_TYPE (orig))
 175       || !POINTER_TYPE_P (TREE_TYPE (new))
 176       || !lang_hooks.types_compatible_p (TREE_TYPE (orig), TREE_TYPE (new)))
 177     abort ();
 178
 179   /* If the pointed-to alias sets are different, these two pointers
 180      would never have the same memory tag.  In this case, NEW should
 181      not have been propagated into ORIG.  */
 182   if (get_alias_set (TREE_TYPE (TREE_TYPE (new_sym)))
 183       != get_alias_set (TREE_TYPE (TREE_TYPE (orig_sym))))
 184     abort ();
 185 #endif
 186
 187   /* Merge type-based alias info.  */
 188   if (new_ann->type_mem_tag == NULL_TREE)
 189     new_ann->type_mem_tag = orig_ann->type_mem_tag;
 190   else if (orig_ann->type_mem_tag == NULL_TREE)
 191     orig_ann->type_mem_tag = new_ann->type_mem_tag;
 192   else if (new_ann->type_mem_tag != orig_ann->type_mem_tag)
 193     abort ();
 194 }
 195
 196
 197 /* Common code for propagate_value and replace_exp.
 198
 199    Replace use operand OP_P with VAL.  FOR_PROPAGATION indicates if the
 200    replacement is done to propagate a value or not.  */
 201
 202 static void
 203 replace_exp_1 (use_operand_p op_p, tree val,
 204                bool for_propagation ATTRIBUTE_UNUSED)
 205 {
 206   tree op = USE_FROM_PTR (op_p);
 207
 208 #if defined ENABLE_CHECKING
 209   if (for_propagation
 210       && TREE_CODE (op) == SSA_NAME
 211       && TREE_CODE (val) == SSA_NAME
 212       && !may_propagate_copy (op, val))
 213     abort ();
 214 #endif
 215
 216   if (TREE_CODE (val) == SSA_NAME)
 217     {
 218       if (TREE_CODE (op) == SSA_NAME && POINTER_TYPE_P (TREE_TYPE (op)))
 219         merge_alias_info (op, val);
 220       SET_USE (op_p, val);
 221     }
 222   else
 223     SET_USE (op_p, lhd_unsave_expr_now (val));
 224 }
 225
 226
 227 /* Propagate the value VAL (assumed to be a constant or another SSA_NAME)
 228    into the operand pointed by OP_P.
 229
 230    Use this version for const/copy propagation as it will perform additional
 231    checks to ensure validity of the const/copy propagation.  */
 232
 233 void
 234 propagate_value (use_operand_p op_p, tree val)
 235 {
 236   replace_exp_1 (op_p, val, true);
 237 }
 238
 239
 240 /* Propagate the value VAL (assumed to be a constant or another SSA_NAME)
 241    into the tree pointed by OP_P.
 242
 243    Use this version for const/copy propagation when SSA operands are not
 244    available.  It will perform the additional checks to ensure validity of
 245    the const/copy propagation, but will not update any operand information.
 246    Be sure to mark the stmt as modified.  */
 247
 248 void
 249 propagate_tree_value (tree *op_p, tree val)
 250 {
 251 #if defined ENABLE_CHECKING
 252   if (TREE_CODE (val) == SSA_NAME
 253       && TREE_CODE (*op_p) == SSA_NAME
 254       && !may_propagate_copy (*op_p, val))
 255     abort ();
 256 #endif
 257
 258   if (TREE_CODE (val) == SSA_NAME)
 259     {
 260       if (TREE_CODE (*op_p) == SSA_NAME && POINTER_TYPE_P (TREE_TYPE (*op_p)))
 261         merge_alias_info (*op_p, val);
 262       *op_p = val;
 263     }
 264   else
 265     *op_p = lhd_unsave_expr_now (val);
 266 }
 267
 268
 269 /* Replace *OP_P with value VAL (assumed to be a constant or another SSA_NAME).
 270
 271    Use this version when not const/copy propagating values.  For example,
 272    PRE uses this version when building expressions as they would appear
 273    in specific blocks taking into account actions of PHI nodes.  */
 274
 275 void
 276 replace_exp (use_operand_p op_p, tree val)
 277 {
 278   replace_exp_1 (op_p, val, false);
 279 }