See D37528 for a previous (non-deferred) version of this patch and its description.
Preserves dominance in a deferred manner using a new class DeferredDominance. This reduces the performance impact of updating the DominatorTree at every edge insertion and deletion. A user may call DDT->flush() within JumpThreading for an up-to-date DT. This patch currently has one flush() at the end of runImpl() to ensure DT is preserved across the pass.
LVI is also preserved to help subsequent passes such as CorrelatedValuePropagation. LVI is simpler to maintain and is done immediately (not deferred). The code to perfom the preversation was minimally altered and was simply marked as preserved for the PassManager to be informed.
This extends the analysis available to JumpThreading for future enhancements. One example is loop boundary threading.