trans.c (build_binary_op_trapv): Avoid emitting overflow check for constant result.

	* gcc-interface/trans.c (build_binary_op_trapv): Avoid emitting
	overflow check for constant result.

From-SVN: r141666

gcc/ada/ChangeLog

 2008-11-07  Geert Bosch  <bosch@adacore.com>
 
+	* gcc-interface/trans.c (build_binary_op_trapv): Avoid emitting
+	overflow check for constant result.
+
+2008-11-07  Geert Bosch  <bosch@adacore.com>
+
 	* gcc-interface/trans.c (build_binary_op_trapv): Use more efficient
 	overflow check for addition/subtraction if neither operand is constant.
 

gcc/ada/gcc-interface/trans.c

@@ -6146,6 +6146,10 @@ build_binary_op_trapv (enum tree_code code,
 
   gnu_expr = build_binary_op (code, gnu_type, lhs, rhs);
 
+  /* If we can fold the expression to a constant, just return it.
+     The caller will deal with overflow, no need to generate a check. */
+  if (TREE_CONSTANT (gnu_expr)) return gnu_expr;
+
   check = fold_build3 (COND_EXPR, integer_type_node,
 		       rhs_lt_zero,  check_neg, check_pos);