[llvm] [Coroutines] Drop dead instructions more aggressively in addMustTailToCoroResumes() (PR #85271)

[Chuanqi Xu via llvm-commits]

https://github.com/ChuanqiXu9 requested changes to this pull request.

I like the previous one version. And if the problem comes from a C++ program (I believe it may be the case), we can add the (reduced) C++ program as a test. If it is not the case, I guess we shouldn't do this OR we need to revisit the motivation or the issue or the use cases of switching IR.

https://github.com/llvm/llvm-project/pull/85271