[llvm] [AMDGPU][TTI] Add Target Hook for Instruction Uniformity (getInstructionUniformity) (PR #137639)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

Don't we already have special context dependent uniformity with the existing API? e.g. identifying math based on the work item ID 

https://github.com/llvm/llvm-project/pull/137639