Eliminate the loop that walks the critical path. Instead, just track the

Eliminate the loop that walks the critical path. Instead, just track the
position in the critical path during the main instruction walk.  This
eliminates the need for the CritialAntiDep DenseMap.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@61096 91177308-0d34-0410-b5e6-96231b3b80d8