fold-const.c (fold_truthop): When changing a one-bit comparison against zero…

fold-const.c (fold_truthop): When changing a one-bit comparison against zero into a comparison against mask...

	* fold-const.c (fold_truthop): When changing a one-bit comparison
	against zero into a comparison against mask, do a proper sign
	extension.

From-SVN: r16448

gcc/ChangeLog

+Thu Nov 13 00:06:58 1997  J"orn Rennecke <amylaar@cygnus.co.uk>
+
+	* fold-const.c (fold_truthop): When changing a one-bit comparison
+	against zero into a comparison against mask, do a proper sign
+	extension.
+
 Wed Nov 12 09:37:01 1997  Jeffrey A Law  (law@cygnus.com)
 
 	* except.c: Do not include "assert.h".

gcc/fold-const.c

@@ -3424,16 +3424,33 @@ fold_truthop (code, truth_type, lhs, rhs)
   if (lcode != wanted_code)
     {
       if (l_const && integer_zerop (l_const) && integer_pow2p (ll_mask))
+	{
+	  if (ll_unsignedp)
 	    l_const = ll_mask;
 	else
+	  /* Since ll_arg is a single bit bit mask, we can sign extend
+	     it appropriately with a NEGATE_EXPR.
+	     l_const is made a signed value here, but since for l_const != NULL
+	     lr_unsignedp is not used, we don't need to clear the latter.  */
+	  l_const = fold (build1 (NEGATE_EXPR, TREE_TYPE (ll_arg),
+				  convert (TREE_TYPE (ll_arg), ll_mask)));
+	}
+      else
 	return 0;
     }
 
   if (rcode != wanted_code)
     {
       if (r_const && integer_zerop (r_const) && integer_pow2p (rl_mask))
+	{
+	  if (rl_unsignedp)
 	    r_const = rl_mask;
 	else
+	  /* This is analogous to the code for l_const above.  */
+	  r_const = fold (build1 (NEGATE_EXPR, TREE_TYPE (rl_arg),
+				  convert (TREE_TYPE (rl_arg), rl_mask)));
+	}
+      else
 	return 0;
     }