Even when we don't create a remainder loop (that is, when we unroll by 2), we
may duplicate nested loops into the remainder. This is complicated by the fact
the remainder may itself be either inserted into an outer loop, or at the top
level. In the latter case, we may need to create new top-level loops.
Differential Revision: https://reviews.llvm.org/D29156
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@293124 91177308-0d34-0410-b5e6-96231b3b80d8
