validity checksum behavior

[SamuelCupp]

At the hackathon, some discussion has come up regarding the correct behavior of PreSync. As part of this, the checksum currently only runs if the variable was already valid. Should this remain the same, or should it check the variable any time it doesn't write everywhere?

It is true that checksums on variables which were previously entirely invalid is somewhat slower, any code running with this on won't be efficient anyways. It is also true that we don't have to care about the checksum in this case, but strictly enforcing the READ/WRITE declarations could still be a good idea.