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     }
 114
 115   /* If the destination is a SSA_NAME for a virtual operand, then we have
 116      some special cases to handle.  */
 117   if (TREE_CODE (dest) == SSA_NAME && !is_gimple_reg (dest))
 118     {
 119       /* If both operands are SSA_NAMEs referring to virtual operands, then
 120          we can always propagate.  */
 121       if (TREE_CODE (orig) == SSA_NAME)
 122         {
 123           if (!is_gimple_reg (orig))
 124             return true;
 125
 126 #ifdef ENABLE_CHECKING
 127           /* If we have one real and one virtual operand, then something has
 128              gone terribly wrong.  */
 129           if (is_gimple_reg (orig))
 130             abort ();
 131 #endif
 132         }
 133
 134       /* We have a "copy" from something like a constant into a virtual
 135          operand.  Reject these.  */
 136       return false;
 137     }
 138
 139   /* If ORIG flows in from an abnormal edge, it cannot be propagated.  */
 140   if (TREE_CODE (orig) == SSA_NAME
 141       && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (orig))
 142     return false;
 143
 144   /* If DEST is an SSA_NAME that flows from an abnormal edge or if it
 145      represents a hard register, then it cannot be replaced.  */
 146   if (TREE_CODE (dest) == SSA_NAME
 147       && (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (dest)
 148           || DECL_HARD_REGISTER (SSA_NAME_VAR (dest))))
 149     return false;
 150
 151   /* Anything else is OK.  */
 152   return true;
 153 }
 154
 155 /* Given two SSA_NAMEs, replace the annotations for the one referred to by OP
 156    with VAR's annotations.
 157
 158    If OP is a pointer, copy the memory tag used originally by OP into
 159    VAR.  This is needed in cases where VAR had never been dereferenced in the
 160    program.
 161
 162    If FOR_PROPAGATION is true, then perform additional checks to ensure
 163    that const/copy propagation of var for OP is valid.  */
 164
 165 static void
 166 replace_ssa_names_ann (tree op,
 167                    tree var,
 168                    bool for_propagation ATTRIBUTE_UNUSED)
 169 {
 170 #if defined ENABLE_CHECKING
 171   if (for_propagation && !may_propagate_copy (op, var))
 172     abort ();
 173 #endif
 174
 175   /* If VAR doesn't have a memory tag, copy the one from the original
 176      operand.  Also copy the dereferenced flags.  */
 177   if (POINTER_TYPE_P (TREE_TYPE (op)))
 178     {
 179       var_ann_t new_ann = var_ann (SSA_NAME_VAR (var));
 180       var_ann_t orig_ann = var_ann (SSA_NAME_VAR (op));
 181
 182       if (new_ann->type_mem_tag == NULL_TREE)
 183         new_ann->type_mem_tag = orig_ann->type_mem_tag;
 184       else if (orig_ann->type_mem_tag == NULL_TREE)
 185         orig_ann->type_mem_tag = new_ann->type_mem_tag;
 186       else if (new_ann->type_mem_tag != orig_ann->type_mem_tag)
 187         abort ();
 188     }
 189
 190 }
 191
 192
 193 /* Common code for propagate_value and replace_exp.
 194
 195    Replace use operand OP_P with VAL.  FOR_PROPAGATION indicates if the
 196    replacement is done to propagate a value or not.  */
 197
 198 static void
 199 replace_exp_1 (use_operand_p op_p, tree val, bool for_propagation)
 200 {
 201   if (TREE_CODE (val) == SSA_NAME)
 202     {
 203       if (TREE_CODE (USE_FROM_PTR (op_p)) == SSA_NAME)
 204         replace_ssa_names_ann (USE_FROM_PTR (op_p), val, for_propagation);
 205       SET_USE (op_p, val);
 206     }
 207   else
 208     SET_USE (op_p, lhd_unsave_expr_now (val));
 209 }
 210
 211
 212 /* Propagate the value VAL (assumed to be a constant or another SSA_NAME)
 213    into the operand pointed by OP_P.
 214
 215    Use this version for const/copy propagation as it will perform additional
 216    checks to ensure validity of the const/copy propagation.  */
 217
 218 void
 219 propagate_value (use_operand_p op_p, tree val)
 220 {
 221   replace_exp_1 (op_p, val, true);
 222 }
 223
 224
 225 /* Propagate the value VAL (assumed to be a constant or another SSA_NAME)
 226    into the tree pointed by OP_P.
 227
 228    Use this version for const/copy propagation when SSA operands are not
 229    available.  It will perform the additional checks to ensure validity of
 230    the const/copy propagation, but will not update any operand information.
 231    Be sure to mark the stmt as modified.  */
 232
 233 void
 234 propagate_tree_value (tree *op_p, tree val)
 235 {
 236   if (TREE_CODE (val) == SSA_NAME)
 237     {
 238       if (TREE_CODE (*op_p) == SSA_NAME)
 239         replace_ssa_names_ann (*op_p, val, true);
 240       *op_p = val;
 241     }
 242   else
 243     *op_p = lhd_unsave_expr_now (val);
 244 }
 245
 246
 247 /* Replace *OP_P with value VAL (assumed to be a constant or another SSA_NAME).
 248
 249    Use this version when not const/copy propagating values.  For example,
 250    PRE uses this version when building expressions as they would appear
 251    in specific blocks taking into account actions of PHI nodes.  */
 252
 253 void
 254 replace_exp (use_operand_p op_p, tree val)
 255 {
 256   replace_exp_1 (op_p, val, false);
 257 }