[PATCH] D40427: [ADT] Introduce Disjoint Set Union structure

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev created this revision.
Herald added a subscriber: mgorny.

This patch introduces a data structure - Disjoint Set Union - that allows to perform
operations on disjoint sets of elements:

1. Check whether two elements `X` and `Y` belong to one set;
2. Merge sets containing `X` and `Y` into one set.

If we have a transitive symmetrical equivalence function `F`, and we proved that `F(X, Y)`
and `F(Y,Z)` is `true`, then adding these two pairs to DSU will also allow us to prove that
`F(Z, X)` is `true` for cheap. One possible application of that is using it as cache for
comparators: if we proved that `X compareTo Y == 0` and `Y compareTo Z == 0`, then
DSU can easily prove that `X compareTo Z == 0`.


https://reviews.llvm.org/D40427

Files:
  include/llvm/ADT/DisjointSetUnion.h
  unittests/ADT/CMakeLists.txt
  unittests/ADT/DisjointSetUnionTest.cpp

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