Summary: This fixes the bug pointed out in review with non-trivial unswitching. This also provides a basis that should make it pretty easy to finish fleshing out a routine to scan an entire function body for irreducible control flow, but this patch remains minimal for disabling loop unswitch. Reviewers: sanjoy, fedor.sergeev Subscribers: mcrosier, hiraditya, llvm-commits Differential Revision: https://reviews.llvm.org/D45754 llvm-svn: 330357