[llvm-branch-commits] [llvm] AMDGPU: Replace unused permlane inputs with poison instead of undef (PR #131288)

[Matt Arsenault via llvm-branch-commits]

arsenm wrote:

> Then I think the poison-propagating rules for this intrinsic should be documented. They're not obvious and "it just does what the underlying instruction does" is no longer sufficient.

We're currently not propagating poison for these intrinsics, and this patch isn't changing any behavior. This is changing an implementation detail of the discard input that is already done 

https://github.com/llvm/llvm-project/pull/131288