rL340921 has been reverted by rL340923 due to linkage dependency
from Transform/Utils to Analysis which is not allowed. In this patch
this has been fixed, a new utility function moved to Analysis.
Differential Revision: https://reviews.llvm.org/D51152
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@341014 91177308-0d34-0410-b5e6-96231b3b80d8
