Address comments on last patch:

Address comments on last patch:

- Loosen the restrictions when checking of it branches to a landing pad.
- Make the loop more efficient by checking the '.insert' return value.
- Do cheaper checks first.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@91101 91177308-0d34-0410-b5e6-96231b3b80d8