> Note that having TREE_TYPE(type)!=NULL does not imply that the type and the > base type are inequivalent. For example, if you declare a type Int as > follows: > subtype Int is Integer; > then TREE_TYPE(type_for_Int)=type_for_Integer, but the types are equivalent, > in particular they have the same TYPE_MIN_VALUE and TYPE_MAX_VALUE.
True, but there's still no harm in using the base type in that case (and I think the front end will). I think there are two very different things that need to be tested: (1) If fold wants to determine if it can safely remove a conversion, it needs to explicitly test whether the constant can fit into the (sub)type; it doesn't care whether it's a subtype of something or not. (2) If we're *generating* arithmetic, we can check TREE_TYPE (type) and, if nonzero, generate the conversions. Then fold can get rid of them if they turn out to be unnecessary. I think the above is the simplest mechanism that also is precisely correct; yes, we could do further checks in (2), but it seems unnecessary work: the issue isn't if the bounds are the same, but if the constant fits in the bounds.
