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

[via llvm-commits]

HaohaiWen wrote:

> 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.

I just opened a new issue (https://github.com/llvm/llvm-project/issues/77729). I guess InstrRef requires each block can be accessed via entry so I made a solution for BranchFolding to make sure meet InstrRef requirement.

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