It may be reused in a different piece of logic.
LGTM. Don't see where you're going with this, but the patch is obvious correct and doesn't make anything particularly messy.
I need it for https://reviews.llvm.org/D50891
Tracking down instructions that write memory is pretty much the same as with control flow. Thinking about it even more, we can generalize much more things there.
Another application of that is that we can cache this method (its users don't change control flow, so the set of predecessors should remain unchanged).