Once comp(x != 0) is removed for a bool x, `int n = b ? 1 : 0` becomes a
plain copy of the bool, and copy propagation replaced every load of n with
`(b ? 1 : 0)`. Refuse copies between bool and non-bool variables rather
than requiring identical types, which would also block legitimate copies
such as dynamic -> object or Derived[] -> Base[].
dualfroz
upstream