tests/compiler/dart2js/cps_ir/input/argument_refinement_num_1.dart

main() {
  var x = int.parse('1233');
  var y = int.parse('1234');
  print(x is num);
  print(y is num);
  print(x - y);
  print(x is num);
  print(y is num); // will be compiled to `true` if we know the type of `y`.
}