[llvm] [FastISel] Support unreachable with NoTrapAfterNoReturn (PR #118296)

[Alexis Engelke via llvm-commits]

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

LGTM. Was there any concrete use case where this caused a noticeable amount of fallbacks?

https://github.com/llvm/llvm-project/pull/118296