[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! ;)

When I'm on vacation, I usually do something in the evening. If you want to revert it, you'd better ask @dtcxzyw. @dtcxzyw should be more familiar with the backend than I am. Perhaps he would like to look into this as well (but I'm sure he's on vacation as well). Happy too! :3

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