Summary:
Teach `isHighCostExpansion` to consider divisions by power-of-two
constants as cheap and add a test case. This change is needed for a new
user of `isHighCostExpansion` that will be added in a subsequent change.
Depends on D8995.
Reviewers: atrick
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D8993
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@234845 91177308-0d34-0410-b5e6-96231b3b80d8
