[llvm] [RFC][BPF] Report Unreachable Behavior from IR (PR #126858)

[via llvm-commits]

yonghong-song wrote:

> Even though this is BPF-specific, it is introducing constraints on target-independent transforms: specifically, any transform which may introduce unreachable code is illegal.
> 
> As such, I think this needs an RFC to determine how to go forward. The needs to describe the general impact on transformations, and whether there are any existing transforms impacted by the constraint.

@efriedma-quic I marked this patch as RFC. I think the key thing is about when 'unreachable' is introduced today in middle end and what is the expected scenario 'unreachable' could be introduced in the future. For the 'unreachable' introduced in the future, I guess it should be okay. The BPF can be adjusted as necessary, similar to other transformations.

https://github.com/llvm/llvm-project/pull/126858