loop.c (simplify_giv_expr): Adding two invariants results in an invariant.

        * loop.c (simplify_giv_expr): Adding two invariants results
        in an invariant.

From-SVN: r16179

gcc/ChangeLog

+Sun Oct 26 09:21:40 1997  Jeffrey A Law  (law@cygnus.com)
+
+	* loop.c (simplify_giv_expr): Adding two invariants results
+	in an invariant.
+
 Sun Oct 26 09:15:15 1997  Richard Henderson  <rth@cygnus.com>
 
 	* expr.c (get_inner_reference): Remove the array bias after 

gcc/loop.c

@@ -5353,10 +5353,13 @@ simplify_giv_expr (x, benefit)
 	  case CONST_INT:
 	  case USE:
 	    /* Both invariant.  Only valid if sum is machine operand.
-	       First strip off possible USE on first operand.  */
+	       First strip off possible USE on the operands.  */
 	    if (GET_CODE (arg0) == USE)
 	      arg0 = XEXP (arg0, 0);
 
+	    if (GET_CODE (arg1) == USE)
+	      arg1 = XEXP (arg1, 0);
+
 	    tem = 0;
 	    if (CONSTANT_P (arg0) && GET_CODE (arg1) == CONST_INT)
 	      {
@@ -5364,6 +5367,13 @@ simplify_giv_expr (x, benefit)
 		if (GET_CODE (tem) != CONST_INT)
 		  tem = gen_rtx (USE, mode, tem);
 	      }
+	    else
+	      {
+		/* Adding two invariants must result in an invariant,
+		   so enclose addition operation inside a USE and
+		   return it.  */
+		tem = gen_rtx (USE, mode, gen_rtx (PLUS, mode, arg0, arg1));
+	      }
 
 	    return tem;