This is applied on top of https://reviews.llvm.org/D86844 "[LoopDeletion] Allows deletion of possibly infinite side-effect free loops".
This patch handles the case where the whole loop is not dead, but only a certain constant path through it. If this path is entered, the loop is in fact dead and an early exit could be made.
Before finalizing the patch by adding tests and also handling the new PM, I would like to get some feedback as to if this is looking to be the right approach. I have seen that this handles the omnetpp function printAddressTable() the same way as GCC does, which gives a nice improvement on the benchmark (SystemZ, output disabled).