[Dominators] Teach LoopUnswitch to use the incremental API
Summary:
This patch makes LoopUnswitch use new incremental API for updating dominators.
It also updates SplitCriticalEdge, as it is called in LoopUnswitch.
There doesn't seem to be any noticeable performance difference when bootstrapping clang with this patch.
Reviewers: dberlin, davide, sanjoy, grosser, chandlerc
Reviewed By: davide, grosser
Subscribers: mzolotukhin, llvm-commits
Differential Revision: https://reviews.llvm.org/D35528
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@311093
91177308-0d34-0410-b5e6-
96231b3b80d8