[llvm] [mlir] [EquivalenceClasses] Use DenseMap instead of std::set. (NFC) (PR #134264)

[Nikita Popov via llvm-commits]

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

LGTM. Now that SCEV stopped using it I don't think we have really hot EquivalenceClasses uses anymore, but previously that std::set did show up in profiles, so it's nice to get rid of it.

Are there any operator< we can drop now?

https://github.com/llvm/llvm-project/pull/134264