[llvm] [NaryReassociate] Teach NaryReassociate about UniformityAnalysis (PR #175167)

[Juan Manuel Martinez Caamaño via llvm-commits]

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

The original concerns I had with this patch are covered. So it's ok for me. But wait for other's approval.

https://github.com/llvm/llvm-project/pull/175167