the loop preheader. Add instructions which are already in the preheader block that
may be common expressions of those that are hoisted out. These does get a few more
instructions CSE'ed.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85799 91177308-0d34-0410-b5e6-96231b3b80d8