out, DAGISelEmitter can compute it in its ctor, which simplifies some code.
Now we can use CodegenDAGPatterns in other parts of tblgen that want access
to dag pattern info, woo!
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45636 91177308-0d34-0410-b5e6-96231b3b80d8