[llvm] [CVP] Check whether the default case is reachable (PR #79993)

[Quentin Dian via llvm-commits]

DianQK wrote:

> Thanks for looking! I'd say if it's not convenient to prepare a fix by around Tuesday, it would likely be better to revert (I can take care of this) until you're back from the holidays. Happy New Year, btw! ;)

I'll add you to #78582, and I'll update the follow-up here. The similarity between the two IRs is that the replicated BBs have many predecessors and successors. It's just that this IR is represented as a loop.

https://github.com/llvm/llvm-project/pull/79993