[ADCE] Refactoring for new functionality (NFC)

Summary:
This is another refactoring to break up the one function into three logical components functions.
Another non-functional change before we start added in features.

Reviewers: nadav, mehdi_amini, majnemer

Subscribers: twoh, freik, llvm-commits

Differential Revision: https://reviews.llvm.org/D23102

llvm-svn: 277855