Fix grammar

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212379 91177308-0d34-0410-b5e6-96231b3b80d8
Use cast<> instead of dyn_cast + assert

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212380 91177308-0d34-0410-b5e6-96231b3b80d8