[llvm] [GenericCycle] Add a Cache for getExitBlocks in GenericCycle (PR #112290)

[via llvm-commits]

Chengjunp wrote:

I’ve been investigating a compiletime issue and discovered that adding a cache for the `getExitBlocks` function in `GenericCycle` improves compile time of the `UniformityAnalysis` pass for some cases. However, I’m unsure whether this change aligns with the design principles of `GenericCycle`. If this change breaks some rules in the design, I also have another version that add the cache in the `UnformityAnalysis` pass. Since that is an analysis pass and the IR will not change during the process, I think that one would be safer than this change.

https://github.com/llvm/llvm-project/pull/112290