[llvm] [llvm][UnifyLoopExits] Avoid optimization if no exit block is found (PR #165343)

[Dmitry Sidorov via llvm-commits]

https://github.com/MrSidims approved this pull request.

I've stumbled on the issue quite recently and keen to have the PR merged. My assessment lead to a similar change with a small addition - I would be an assertion for Outgoing size in https://github.com/llvm/llvm-project/blob/8dfec259742648c12cca4470eedf583c4e21801f/llvm/lib/Transforms/Utils/ControlFlowUtils.cpp#L294 .

@Saldivarcher do you plan to move forward with the PR?
@ssahasra please help with review.

https://github.com/llvm/llvm-project/pull/165343