[clang] [llvm] [EquivalenceClasses] Use SmallVector for deterministic iteration order. (PR #134075)

[Nikita Popov via llvm-commits]

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

This looks reasonable to me. We could keep the existing API with a custom iterator, but given the limited amount of uses this seems ok.

https://github.com/llvm/llvm-project/pull/134075