[CFLAA] Refactor graph-building code. NFC.

This patch refactors CFLAA's graph building code. This makes keeping
track of common state (TargetLibraryInfo, ...) easier.

Patch by Jia Chen.

Differential Revision: http://reviews.llvm.org/D21261


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@272688 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed