[llvm] [InstCombine] Propagate demanded elements through trivially-vectorizable intrinsics (PR #221495)

[Nikita Popov via llvm-commits]

nikic wrote:

Okay, I see there is some discussion about this above. But I don't really get it. You say "per-operand mask conflates undef and poison". Where does this happen? From a cursory look PoisonElts seems to be about just poison, though some comments/variable names refer to undef.

https://github.com/llvm/llvm-project/pull/221495