Use the new 'getSlotIndex' method to retrieve the attribute's slot index.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173499 91177308-0d34-0410-b5e6-96231b3b80d8
LoopVectorize: Refactor the code that vectorizes loads/stores to remove duplication.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173500 91177308-0d34-0410-b5e6-96231b3b80d8