[llvm] [UniformityAnalysis] Propagate label to cycle exit blocks (PR #216296)

[Jay Foad via llvm-commits]

jayfoad wrote:

This looks like a real bug and your fix seems to have the right effect. I can't comment on whether it's the _right_ fix; I'll leave that to Sameer.

I am slightly surprised to hear that UA already detects the case where a PHI has the same incoming value for two different predecessors.

https://github.com/llvm/llvm-project/pull/216296