Unify some code. No functional change.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175409 91177308-0d34-0410-b5e6-96231b3b80d8
Grammar.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175410 91177308-0d34-0410-b5e6-96231b3b80d8
Clean up comment.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175411 91177308-0d34-0410-b5e6-96231b3b80d8
Add a comment.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175412 91177308-0d34-0410-b5e6-96231b3b80d8