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

[Matt Arsenault via llvm-branch-commits]

arsenm wrote:

> I have a conceptual objection: I don't think we can do both of these things:
> 
> 1. Replace unused inputs of all intrinsics with poison
> 2. Propagate poison from any argument, for all intrinsics
> 
> So how should we handle this in general? Is it better to replace unused inputs with "freeze poison"?

2 is not true. Poison does not unconditionally propagate through all intrinsic operands. These are special cases, we know the operation does not read the input. These should remain a constant poison 

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