[MBP] Code cleanup /NFC

This is one of the patches to clean up the code so that
it is in a better form to make future enhancements easier.

In htis patch, the logic to collect viable successors are
extrated as a helper to unclutter the caller which gets very
large recenty. Also cleaned up BP adjustment code.
 


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@272482 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed