SDISel. This optimization was causing simplifylibcalls to
introduce type-unsafe nastiness. This is the first step, I'll be
expanding the memcmp optimizations shortly, covering things that
we really really wouldn't want simplifylibcalls to do.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@92098 91177308-0d34-0410-b5e6-96231b3b80d8
