NFC: refactor replaceDominatedUsesWith

Summary:
Since I will post patch with some changes to
replaceDominatedUsesWith, it would be good to avoid
duplicating code again.

Reviewers: davide, dberlin

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D32798

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@302575 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed