`MaybeInvalid<T>` - separate concepts of uninitialized memory and invalid values

steffahn:

(In LLVM this corresponds to the value “undef”.)

Technically, poison, IIRC. (TBH, even though I read LLVM’s documentation about the difference between undef, poison, and freeze(poison) not all that long ago, I’ve already forgotten the details, other than the fact that they’re trying to move towards using poison.)