see the offsetof operator. Previously, we were matching something like MOVrm
in the front-end and later matching MOVrr in the back-end. This change makes
things more consistent. It also fixes cases where we can't match against a
memory operand as the source (test cases coming).
Part of rdar://12470317
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@166592 91177308-0d34-0410-b5e6-96231b3b80d8