Improve logic that decides if its profitable to commute when some of the virtual...

Improve logic that decides if its profitable to commute when some of the virtual registers involved have uses/defs chains connecting them to physical register. Fix up the tests that this change improves.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221336 91177308-0d34-0410-b5e6-96231b3b80d8