This adds back the testcase from r225738, and adds to it. Looks like we
need both sides for now (the assertion was incorrect both ways, and
although it seemed reasonable (when written correctly) it wasn't
particularly important).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225745 91177308-0d34-0410-b5e6-96231b3b80d8