[llvm] [Semilattice] Introduce for dataflow analysis with KnownBits (PR #177616)

[Nikita Popov via llvm-commits]

nikic wrote:

This PR still leaves me very confused. As far as I can tell, you appear to be creating a copy of the use-def graph as a separate, explicit graph, and giving that the name of "semilattice". I don't understand why we need that copy of the graph, and I don't understand why that graph is being called a semilattice. While KnownBits do form a semilattice structure, I think that is only relevant insofar as sparse dataflow propagation over a semilattice with monotonic transitions will converge?

https://github.com/llvm/llvm-project/pull/177616