Emit code that matches the incoming DAG pattern and checks predicates.

Emit code that matches the incoming DAG pattern and checks predicates.
This does not check that types match yet, but PPC only has one integer type
;-).

This also doesn't have the code to build the resultant dag.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@23414 91177308-0d34-0410-b5e6-96231b3b80d8