[llvm] [JumpThreading] Remove deleted BB from Unreachable (PR #126984)

[Nikita Popov via llvm-commits]

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

LGTM, thanks for the explanation. I think what JumpThreading does with BPI/BFI is unnecessarily complicated (why do we ever compute a fresh BPI/BFI if we're only doing updates?) and could maybe be cleaned up to avoid this flush, but let's land this fix for now.

https://github.com/llvm/llvm-project/pull/126984