[llvm] [InstCombine] Mark as unknown the branch weights of packed integer selecting shifts (PR #162726)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 approved this pull request.

LGTM. No existing data to pull from, and there's no way to have a reasonable guess about which why the select goes without instrumentation.

https://github.com/llvm/llvm-project/pull/162726