This fixes the PR in another way as well, allowing as many capture
uses in the replacement expression as in the original one, avoiding
some spurious save_exprs that way (and not perform "CSE" within
the match-and-simplify framework).

Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.

Richard.

2015-12-01  Richard Biener  <rguent...@suse.de>

        PR middle-end/68590
        * genmatch.c (struct capture_info): Add match_use_count.
        (capture_info::walk_match): Increment match_use_count.
        (dt_simplify::gen_1): For GENERIC, only wrap multi-use
        replacements in a save_expr if they occur more often than
        in the original expression.

Index: gcc/genmatch.c
===================================================================
--- gcc/genmatch.c      (revision 231101)
+++ gcc/genmatch.c      (working copy)
@@ -1851,7 +1850,8 @@ struct capture_info
       bool force_single_use;
       bool cond_expr_cond_p;
       unsigned long toplevel_msk;
-      int result_use_count;
+      unsigned match_use_count;
+      unsigned result_use_count;
       unsigned same_as;
       capture *c;
     };
@@ -1901,6 +1901,7 @@ capture_info::walk_match (operand *o, un
   if (capture *c = dyn_cast <capture *> (o))
     {
       unsigned where = c->where;
+      info[where].match_use_count++;
       info[where].toplevel_msk |= 1 << toplevel_arg;
       info[where].force_no_side_effects_p |= conditional_p;
       info[where].cond_expr_cond_p |= cond_expr_cond_p;
@@ -3106,13 +3107,16 @@ dt_simplify::gen_1 (FILE *f, int indent,
          else if (is_a <predicate_id *> (opr))
            is_predicate = true;
          /* Search for captures used multiple times in the result expression
-            and dependent on TREE_SIDE_EFFECTS emit a SAVE_EXPR.  */
+            and wrap them in a SAVE_EXPR.  Allow as many uses as in the
+            original expression.  */
          if (!is_predicate)
            for (int i = 0; i < s->capture_max + 1; ++i)
              {
-               if (cinfo.info[i].same_as != (unsigned)i)
+               if (cinfo.info[i].same_as != (unsigned)i
+                   || cinfo.info[i].cse_p)
                  continue;
-               if (cinfo.info[i].result_use_count > 1)
+               if (cinfo.info[i].result_use_count
+                   > cinfo.info[i].match_use_count)
                  fprintf_indent (f, indent,
                                  "captures[%d] = save_expr (captures[%d]);\n",
                                  i, i);

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