The previous logic for detection of incompatible PHINodes was broken in
various different ways.
1. `return true` and `return false` were flipped, so it effectively did
the opposite of what it was expected to do
2. `std::numeri_limits<Value *>::max()` yielded 0, breaking the lookup.
This commit fixes the condition for incompatible PHINodes and adds a lot
of logging.
Pietro Fezzardi
a7aa3a0e1a