Fix PR3393, which amounts to a bug in the expensive

Fix PR3393, which amounts to a bug in the expensive
checking logic.  Rather than make the checking more
complicated, I've tweaked some logic to make things
conform to how the checking thought things ought to
be, since this results in a simpler "mental model".

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@63048 91177308-0d34-0410-b5e6-96231b3b80d8