[llvm] [AMDGPU] Calc IsVALU correctly during UADDO/USUBO selection (PR #159814)

[Jay Foad via llvm-commits]

https://github.com/jayfoad approved this pull request.

I think this is OK, but you are enabling code that has not been tested before so please be alert for any breakages.

Also the code you are enabling does not make too much sense to me. If it is checking for a SALU op feeding into another SALU op, why does it generate extra code to convert from scc to a vcc-like representation of the carry? See inline comment.

https://github.com/llvm/llvm-project/pull/159814