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

[Eli Friedman via llvm-commits]

https://github.com/efriedma-quic requested changes to this pull request.

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.

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