[llvm-branch-commits] [llvm] AMDGPU: Replace unused update.dpp inputs with poison instead of undef (PR #131287)

[Nuno Lopes via llvm-branch-commits]

nunoplopes wrote:

We don't propagate poison through intrinsics blindly. We do it when the semantics allow it.
Using poison as placeholder for unused lanes, don't care bits, etc is fine. But you are right that then we cannot make the intrinsic return poison because those arguments are poison.

We already do similar things with vector instructions and several intrinsics.

https://github.com/llvm/llvm-project/pull/131287