Remove ParentMap. You can just ask the domnode for its parent. No functionality

Remove ParentMap. You can just ask the domnode for its parent. No functionality
change.

Move the "Not profitable, avoid CSE!" debug message next to where we fail the
check for profitability and use a different message for avoiding CSE due to
being in different register classes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159729 91177308-0d34-0410-b5e6-96231b3b80d8