We've fixed the case where this could return an instruction after the given instruction, but also means that we can falsely return a 'unique' def when they could be one coming from the backedge of loop.
nit: after some coding style discussion on the list, I believe it is preferred to put brackets there.
nit: produces -> producing?
If I am not mistaken, looks like we are actually return nullptr here, except for one case. Thus, can we simplify the above to this below?
if (Def->getParent() != Parent && Incoming.size() == 1) return Def; return nullptr;