[llvm] [InstSimplify] Make sure the simplified value doesn't generate poison in threadBinOpOverSelect (PR #87075)

[Nikita Popov via llvm-commits]

nikic wrote:

Can you please check what the impact of just deleting this special case entirely is? IIRC the last time I looked at this highly dubious code it didn't have any test coverage at all (though I might have added some at the time).

https://github.com/llvm/llvm-project/pull/87075