[llvm] [InstCombine] Return early for zext(bitcast half to i16) (PR #201815)

[Nikita Popov via llvm-commits]

================

----------------
nikic wrote:

Yeah, at least in principle this can apply to that pattern (if the sign bit of the half is known).

It's not immediately obvious to me why that particular pattern should be unusually expensive inside isKnownNonNegative().

https://github.com/llvm/llvm-project/pull/201815