[14] RFR (S): 8226411: C2: Avoid memory barriers around off-heap unsafe accesses

[Vladimir Ivanov]

Thanks for review, John.

> I wonder if there is a similar opportunity in 
> LibraryCallKit::inline_unsafe_load_store
> or inline_vector_mem_operation or inline_unsafe_copyMemory.  All of those
> also form unsafe addresses, and at least some seem to mention NULL_PTR 
> or IN_HEAP.
> Is it worth an explanatory comment or a tracking bug?

Good point. I think inline_vector_mem_operation and 
inline_unsafe_copyMemory can benefit from a similar optimization. Will 
file an RFE.

Best regards,
Vladimir Ivanov