On Tue, Apr 10, 2012 at 9:34 AM, Andi Kleen <a...@firstfloor.org> wrote:
> "H.J. Lu" <hjl.to...@gmail.com> writes:
>
>>> So, to emit HLE prefix, it is possible to do:
>>> int
>>> foo2 (int *p, int oldv, int newv)
>>> {
>>> __atomic_compare_exchange_n (p, &oldv, newv, 0, __ATOMIC_ACQUIRE |
>>> __ATOMIC_USE_HLE, __ATOMIC_ACQUIRE);
>>> return oldv;
>>> }
>>
>> This is wrong since HLE ACQUIRE/RELEASE has nothing to do with
>> C++ atomic acquire/release. You can have HLE RELEASE with C++
>> atomic acquire.
>
> It makes sense to combine the two. On x86 C++ atomic acquire/release
> means the compiler cannot move references outside. For HLE
> we really want the same, otherwise some of the memory references
> inside the transaction may not be transactional.
>
> So I think HLE_ACQUIRE should imply C++ acquire
> and HLE_RELEASE imply C++ release.
>
If it is the case, can we generate HLE RELEASE/ACQUIRE
prefix automatically for C++ atomics via -mhle command line option.
Then you don't need to modify the source codes to enable HLE support.
--
H.J.
