[9] RFR(XS): 8176513 Poor code quality for ByteBuffers

[Roland Westrelin]

> FYI I've just submitted the test batch.
>
> Slightly adjusted the fix as well:
>
> -          need_mem_bar = mismatched || can_access_non_heap;
> +          need_mem_bar = mismatched && !adr_type->isa_aryptr();

Thanks for fixing this and taking care of testing.

Roland.