[llvm] [Uniformity] Avoid marking all PHIs as divergent in join blocks (PR #157808)

[Pankaj Dwivedi via llvm-commits]

PankajDwivedi-25 wrote:

In the case when all the `divergent` path has the same value and `hasSingleValue = false', are we considering it as uniform?

https://github.com/llvm/llvm-project/pull/157808