[Mem2Reg] Simplify and micro optimize * Rearrange continu/break * BBNumbers.lookup(A) -> BBNumbers.find(A)->second BBNumbers has been computed, thus we can assume the value exists in the predicate. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@358351 91177308-0d34-0410-b5e6-96231b3b80d8