InlineCost also treats them as free and the current implementation
can cause assertion failures if PHI nodes are moved outside the region
from entry BBs to the region.
It also updates the code to use the instructionsWithoutDebug iterator.
Reviewers: davidxl, davide, vsk, graham-yiu-huawei
Reviewed By: davidxl
Differential Revision: https://reviews.llvm.org/D54748
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@347683 91177308-0d34-0410-b5e6-96231b3b80d8
