trivial diff: vn_util.m simplifying shifts

[Simon Taylor]

Estimated hours taken: 0.1

compiler/vn_util.m:
	Use `unchecked_left_shift' instead of `<<' when simplifying
	a constant << binop rval. Same for >>.

Index: vn_util.m
===================================================================
RCS file: /home/staff/zs/imp/mercury/compiler/vn_util.m,v
retrieving revision 1.62
diff -u -u -r1.62 vn_util.m
--- vn_util.m	1998/07/20 10:01:50	1.62
+++ vn_util.m	1999/03/30 04:59:15
@@ -660,7 +660,7 @@
 			Vnrval1 = vn_const(int_const(I1)),
 			Vnrval2 = vn_const(int_const(I2))
 		->
-			I is I1 >> I2,
+			I = unchecked_right_shift(I1, I2),
 			Vnrval = vn_const(int_const(I)),
 			VnTables = VnTables0
 		;
@@ -679,7 +679,7 @@
 			Vnrval1 = vn_const(int_const(I1)),
 			Vnrval2 = vn_const(int_const(I2))
 		->
-			I is I1 << I2,
+			I = unchecked_left_shift(I1, I2),
 			Vnrval = vn_const(int_const(I)),
 			VnTables = VnTables0
 		;