The "invariant.load" metadata indicates the memory unit being accessed is immutable.
A load annotated with this metadata can be moved across any store.
As I am not sure if it is legal to move such loads across barrier/fence, this
change dose not allow such transformation.
rdar://11311484
Thank Arnold for code review.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@176562 91177308-0d34-0410-b5e6-96231b3b80d8
