[llvm] AMDGPU: Add some leaf intrinsics to isAlwaysUniform (PR #101925)

[Sameer Sahasrabuddhe via llvm-commits]

ssahasra wrote:

> These would always be uniform anyway, but it shouldn't hurt to mark them as always uniform. This will help use TTI::isAlwaysUniform in place of proper uniformity analysis in trivial situations.

I don't think that so much justification is required. Things that are known to be uniform should be marked as such, liberally.

https://github.com/llvm/llvm-project/pull/101925