Shift with const 4.

[r22034]

ir/be/test/am_test5.c

+struct s {
+	int m1;
+	int m2;
+	int m3;
+	int m4;
+};
+
+int i = 3;
+
+int main(int argc, char **argv) {
+	struct s a[100];
+	i = a[i].m1;
+
+
+	return 0;
+}