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Currently iterators over EquivalenceClasses will iterate over std::set, which guarantees the order specified by the comperator. Unfortunately in many cases, EquivalenceClasses are used with pointers, so iterating over std::set of pointers will not be deterministic across runs. There are multiple places that explicitly try to sort the equivalence classes before using them to try to get a deterministic order (LowerTypeTests, SplitModule), but there are others that do not at the moment and this can result at least in non-determinstic value naming in Float2Int. This patch updates EquivalenceClasses to keep track of all members via a extra SmallVector and removes code from LowerTypeTests and SplitModule to sort the classes before processing. Overall it looks like compile-time slightly decreases in most cases, but close to noise: https://llvm-compile-time-tracker.com/compare.php?from=7d441d9892295a6eb8aaf481e1715f039f6f224f&to=b0c2ac67a88d3ef86987e2f82115ea0170675a17&stat=instructions PR: https://github.com/llvm/llvm-project/pull/134075