[llvm] [AMDGPU] Enable vectorization of i8 values. (PR #134934)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

Can you fix the description to be more specific about what it enables vectorization of? Is this only for loads and stores? We already have the load/store vectorizer to mostly ignore the cost of vector operations. Most of the tests look like no-ops, can you split this to have a pre-commit adding the baseline tests? 

https://github.com/llvm/llvm-project/pull/134934