Avoid revocations when possible.

This is a small targeted fix for pr20119. The code needs quiet a bit of
refactoring and I added some FIXMEs about it, but I want to get the testcase
passing first.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212101 91177308-0d34-0410-b5e6-96231b3b80d8