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[RFC] Do pointer comparison first in operand_equal_p

This patch implements what I asked in

The time savings are negligible but measurable in the tree passes
(saves about 1% of compile time in the tree optimizers).

Bootstrapped and tested x86, x86_64, ia64 and ppc64.

Jeff had some doubts about the approach.  Roger, what do you
think?  Any reason why this would be unsafe in general?

Thanks.  Diego.

	* fold-const.c (operand_equal_p): Do pointer comparison first
	for operands with no side effects.

Index: fold-const.c
RCS file: /cvs/gcc/gcc/gcc/fold-const.c,v
retrieving revision 1.578
diff -d -u -p -r1.578 fold-const.c
--- fold-const.c	11 May 2005 15:21:23 -0000	1.578
+++ fold-const.c	13 May 2005 14:50:55 -0000
@@ -2363,6 +2363,10 @@ truth_value_p (enum tree_code code)
 operand_equal_p (tree arg0, tree arg1, unsigned int flags)
+  /* An operand is always equal to itself if it doesn't side effects.  */
+  if (arg0 == arg1 && !TREE_SIDE_EFFECTS (arg0))
+    return 1;
   /* If either is ERROR_MARK, they aren't equal.  */
   if (TREE_CODE (arg0) == ERROR_MARK || TREE_CODE (arg1) == ERROR_MARK)
     return 0;

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