> /* Return true if the conversion from INNER_TYPE to OUTER_TYPE is a > ! useless type conversion, otherwise return false. > ! This function implicitly defines the middle-end type system. The > ! following invariants shall be fulfilled: > ! > ! 1) tree_ssa_useless_type_conversion_1 is transitive. If > ! a < b and b < c then a < c. > ! > ! 2) tree_ssa_useless_type_conversion_1 is not communtative. > ! From a < b does not follow a > b. > ! > ! 3) Conversions are useless only if with the resulting type > ! can be used in a subset of the operations the original type > ! can be applied to. For example casts to void* are useless, > ! casts from void* not. Casts to const T* are useless, casts > ! from const T* to T* not.
My understanding is that it's a relation, not an operation, so the proper term for 2 would be "symmetric". For the sake of completeness, you could also add that it's reflexive: a < a holds. Which would suggest to find a better symbol than '<' for it. :-) -- Eric Botcazou
