[llvm] [InstrRef] Add debug hint for not reachable blocks from entry (PR #77725)

[Jeremy Morse via llvm-commits]

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

This is a really interesting corner case -- thanks for having analysed it and added a reproducer / workaround! LGTM on the basis of the compiler should never crash; I think the side-effect of this bail-out will be false variable locations, which are strictly better than a crash.

Are there any LLVM issues opened about this where this can be discussed further? Something similar has happened in issue #62725, so we probably need to address a general problem here.

https://github.com/llvm/llvm-project/pull/77725