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 (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 /* Similarly, but we know that we're propagating into an ASM_EXPR.  */
 160
 161 bool
 162 may_propagate_copy_into_asm (tree dest)
 163 {
 164   /* Hard register operands of asms are special.  Do not bypass.  */
 165   return !(TREE_CODE (dest) == SSA_NAME
 166            && DECL_HARD_REGISTER (SSA_NAME_VAR (dest)));
 167 }
 168
 169
 170 /* Given two SSA_NAMEs pointers ORIG and NEW such that we are copy
 171    propagating NEW into ORIG, consolidate aliasing information so that
 172    they both share the same memory tags.  */
 173
 174 static void
 175 merge_alias_info (tree orig, tree new)
 176 {
 177   tree new_sym = SSA_NAME_VAR (new);
 178   tree orig_sym = SSA_NAME_VAR (orig);
 179   var_ann_t new_ann = var_ann (new_sym);
 180   var_ann_t orig_ann = var_ann (orig_sym);
 181
 182   gcc_assert (POINTER_TYPE_P (TREE_TYPE (orig)));
 183   gcc_assert (POINTER_TYPE_P (TREE_TYPE (new)));
 184 #if defined ENABLE_CHECKING
 185   gcc_assert (lang_hooks.types_compatible_p (TREE_TYPE (orig),
 186                                              TREE_TYPE (new)));
 187
 188   /* If the pointed-to alias sets are different, these two pointers
 189      would never have the same memory tag.  In this case, NEW should
 190      not have been propagated into ORIG.  */
 191   gcc_assert (get_alias_set (TREE_TYPE (TREE_TYPE (new_sym)))
 192               == get_alias_set (TREE_TYPE (TREE_TYPE (orig_sym))));
 193 #endif
 194
 195   /* Merge type-based alias info.  */
 196   if (new_ann->type_mem_tag == NULL_TREE)
 197     new_ann->type_mem_tag = orig_ann->type_mem_tag;
 198   else if (orig_ann->type_mem_tag == NULL_TREE)
 199     orig_ann->type_mem_tag = new_ann->type_mem_tag;
 200   else
 201     gcc_assert (new_ann->type_mem_tag == orig_ann->type_mem_tag);
 202 }
 203
 204
 205 /* Common code for propagate_value and replace_exp.
 206
 207    Replace use operand OP_P with VAL.  FOR_PROPAGATION indicates if the
 208    replacement is done to propagate a value or not.  */
 209
 210 static void
 211 replace_exp_1 (use_operand_p op_p, tree val,
 212                bool for_propagation ATTRIBUTE_UNUSED)
 213 {
 214   tree op = USE_FROM_PTR (op_p);
 215
 216 #if defined ENABLE_CHECKING
 217   gcc_assert (!(for_propagation
 218                 && TREE_CODE (op) == SSA_NAME
 219                 && TREE_CODE (val) == SSA_NAME
 220                 && !may_propagate_copy (op, val)));
 221 #endif
 222
 223   if (TREE_CODE (val) == SSA_NAME)
 224     {
 225       if (TREE_CODE (op) == SSA_NAME && POINTER_TYPE_P (TREE_TYPE (op)))
 226         merge_alias_info (op, val);
 227       SET_USE (op_p, val);
 228     }
 229   else
 230     SET_USE (op_p, unsave_expr_now (val));
 231 }
 232
 233
 234 /* Propagate the value VAL (assumed to be a constant or another SSA_NAME)
 235    into the operand pointed by OP_P.
 236
 237    Use this version for const/copy propagation as it will perform additional
 238    checks to ensure validity of the const/copy propagation.  */
 239
 240 void
 241 propagate_value (use_operand_p op_p, tree val)
 242 {
 243   replace_exp_1 (op_p, val, true);
 244 }
 245
 246
 247 /* Propagate the value VAL (assumed to be a constant or another SSA_NAME)
 248    into the tree pointed by OP_P.
 249
 250    Use this version for const/copy propagation when SSA operands are not
 251    available.  It will perform the additional checks to ensure validity of
 252    the const/copy propagation, but will not update any operand information.
 253    Be sure to mark the stmt as modified.  */
 254
 255 void
 256 propagate_tree_value (tree *op_p, tree val)
 257 {
 258 #if defined ENABLE_CHECKING
 259   gcc_assert (!(TREE_CODE (val) == SSA_NAME
 260                 && TREE_CODE (*op_p) == SSA_NAME
 261                 && !may_propagate_copy (*op_p, val)));
 262 #endif
 263
 264   if (TREE_CODE (val) == SSA_NAME)
 265     {
 266       if (TREE_CODE (*op_p) == SSA_NAME && POINTER_TYPE_P (TREE_TYPE (*op_p)))
 267         merge_alias_info (*op_p, val);
 268       *op_p = val;
 269     }
 270   else
 271     *op_p = unsave_expr_now (val);
 272 }
 273
 274
 275 /* Replace *OP_P with value VAL (assumed to be a constant or another SSA_NAME).
 276
 277    Use this version when not const/copy propagating values.  For example,
 278    PRE uses this version when building expressions as they would appear
 279    in specific blocks taking into account actions of PHI nodes.  */
 280
 281 void
 282 replace_exp (use_operand_p op_p, tree val)
 283 {
 284   replace_exp_1 (op_p, val, false);
 285 }