Factor out more code for computing register live-range informationfor
scheduling, and generalize is so that preserves state across
scheduling regions. This fixes incorrect live-range information around
terminators and labels, which are effective region boundaries.
In place of looking for terminators to anchor inter-block dependencies,
introduce special entry and exit scheduling units for this purpose.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@64254
91177308-0d34-0410-b5e6-
96231b3b80d8