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 (TREE_TYPE (type_d)),
 116                                        get_alias_set (TREE_TYPE (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           gcc_assert (!is_gimple_reg (orig));
 135 #endif
 136         }
 137
 138       /* We have a "copy" from something like a constant into a virtual
 139          operand.  Reject these.  */
 140       return false;
 141     }
 142
 143   /* If ORIG flows in from an abnormal edge, it cannot be propagated.  */
 144   if (TREE_CODE (orig) == SSA_NAME
 145       && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (orig))
 146     return false;
 147
 148   /* If DEST is an SSA_NAME that flows from an abnormal edge or if it
 149      represents a hard register, then it cannot be replaced.  */
 150   if (TREE_CODE (dest) == SSA_NAME
 151       && (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (dest)
 152           || DECL_HARD_REGISTER (SSA_NAME_VAR (dest))))
 153     return false;
 154
 155   /* Anything else is OK.  */
 156   return true;
 157 }
 158
 159
 160 /* Given two SSA_NAMEs pointers ORIG and NEW such that we are copy
 161    propagating NEW into ORIG, consolidate aliasing information so that
 162    they both share the same memory tags.  */
 163
 164 static void
 165 merge_alias_info (tree orig, tree new)
 166 {
 167   tree new_sym = SSA_NAME_VAR (new);
 168   tree orig_sym = SSA_NAME_VAR (orig);
 169   var_ann_t new_ann = var_ann (new_sym);
 170   var_ann_t orig_ann = var_ann (orig_sym);
 171
 172   gcc_assert (POINTER_TYPE_P (TREE_TYPE (orig)));
 173   gcc_assert (POINTER_TYPE_P (TREE_TYPE (new)));
 174 #if defined ENABLE_CHECKING
 175   gcc_assert (lang_hooks.types_compatible_p (TREE_TYPE (orig),
 176                                              TREE_TYPE (new)));
 177
 178   /* If the pointed-to alias sets are different, these two pointers
 179      would never have the same memory tag.  In this case, NEW should
 180      not have been propagated into ORIG.  */
 181   gcc_assert (get_alias_set (TREE_TYPE (TREE_TYPE (new_sym)))
 182               == get_alias_set (TREE_TYPE (TREE_TYPE (orig_sym))));
 183 #endif
 184
 185   /* Merge type-based alias info.  */
 186   if (new_ann->type_mem_tag == NULL_TREE)
 187     new_ann->type_mem_tag = orig_ann->type_mem_tag;
 188   else if (orig_ann->type_mem_tag == NULL_TREE)
 189     orig_ann->type_mem_tag = new_ann->type_mem_tag;
 190   else
 191     gcc_assert (new_ann->type_mem_tag == orig_ann->type_mem_tag);
 192 }
 193
 194
 195 /* Common code for propagate_value and replace_exp.
 196
 197    Replace use operand OP_P with VAL.  FOR_PROPAGATION indicates if the
 198    replacement is done to propagate a value or not.  */
 199
 200 static void
 201 replace_exp_1 (use_operand_p op_p, tree val,
 202                bool for_propagation ATTRIBUTE_UNUSED)
 203 {
 204   tree op = USE_FROM_PTR (op_p);
 205
 206 #if defined ENABLE_CHECKING
 207   gcc_assert (!(for_propagation
 208                 && TREE_CODE (op) == SSA_NAME
 209                 && TREE_CODE (val) == SSA_NAME
 210                 && !may_propagate_copy (op, val)));
 211 #endif
 212
 213   if (TREE_CODE (val) == SSA_NAME)
 214     {
 215       if (TREE_CODE (op) == SSA_NAME && POINTER_TYPE_P (TREE_TYPE (op)))
 216         merge_alias_info (op, val);
 217       SET_USE (op_p, val);
 218     }
 219   else
 220     SET_USE (op_p, unsave_expr_now (val));
 221 }
 222
 223
 224 /* Propagate the value VAL (assumed to be a constant or another SSA_NAME)
 225    into the operand pointed by OP_P.
 226
 227    Use this version for const/copy propagation as it will perform additional
 228    checks to ensure validity of the const/copy propagation.  */
 229
 230 void
 231 propagate_value (use_operand_p op_p, tree val)
 232 {
 233   replace_exp_1 (op_p, val, true);
 234 }
 235
 236
 237 /* Propagate the value VAL (assumed to be a constant or another SSA_NAME)
 238    into the tree pointed by OP_P.
 239
 240    Use this version for const/copy propagation when SSA operands are not
 241    available.  It will perform the additional checks to ensure validity of
 242    the const/copy propagation, but will not update any operand information.
 243    Be sure to mark the stmt as modified.  */
 244
 245 void
 246 propagate_tree_value (tree *op_p, tree val)
 247 {
 248 #if defined ENABLE_CHECKING
 249   gcc_assert (!(TREE_CODE (val) == SSA_NAME
 250                 && TREE_CODE (*op_p) == SSA_NAME
 251                 && !may_propagate_copy (*op_p, val)));
 252 #endif
 253
 254   if (TREE_CODE (val) == SSA_NAME)
 255     {
 256       if (TREE_CODE (*op_p) == SSA_NAME && POINTER_TYPE_P (TREE_TYPE (*op_p)))
 257         merge_alias_info (*op_p, val);
 258       *op_p = val;
 259     }
 260   else
 261     *op_p = unsave_expr_now (val);
 262 }
 263
 264
 265 /* Replace *OP_P with value VAL (assumed to be a constant or another SSA_NAME).
 266
 267    Use this version when not const/copy propagating values.  For example,
 268    PRE uses this version when building expressions as they would appear
 269    in specific blocks taking into account actions of PHI nodes.  */
 270
 271 void
 272 replace_exp (use_operand_p op_p, tree val)
 273 {
 274   replace_exp_1 (op_p, val, false);
 275 }