[llvm] [UniformityAnalysis] Jump over reducible cycles when locating join blocks (PR #174938)

[Sameer Sahasrabuddhe via llvm-commits]

ssahasra wrote:

> What if the reducible cycle has no exits (infinite loop) is this expected?

If any cycle has no exits, it is itself an exit and hence not nested in any outer cycle. For a cycle `Inner` to be nested inside another cycle `Outer`, the blocks in `Outer` have to be reachable from `Inner` in order to form an SCC. Such an example does not trigger any of these issues.

https://github.com/llvm/llvm-project/pull/174938