[llvm] [AMDGPU] Group multiple single use producers under one single use instruction. (PR #90713)

[Jay Foad via llvm-commits]

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

LGTM (I have previously reviewed this downstream) but please wait at least 24 hours for other comments.

https://github.com/llvm/llvm-project/pull/90713