Unable to achieve aligned writes

I am trying to implement an efficient memory move operation for a specific usage pattern: https://play.rust-lang.org/?gist=6ddd4e11d7f7b0f6503ddd398f0e665f&version=nightly&backtrace=1

In release mode, the loop in move_items() in the above example is compiled into a series of unaligned reads followed by unaligned writes, despite my efforts to have the writes aligned.
