loops, hoisting instructions all the way out in one step rather
than hoisting them one nest level at a time. Also, make a few
other code simplifications. This speeds up MachineLICM
by several fold.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@62283 91177308-0d34-0410-b5e6-96231b3b80d8