[llvm] [AMDGPU] Combine redundant ballot intrinsic calls (PR #218357)

[Anshil Gandhi via llvm-commits]

gandhi56 wrote:

> Tangential note - does this also work for `mbcnt` and the like?

Yup, it would be pretty straightforward to extend.

https://github.com/llvm/llvm-project/pull/218357