This is the mail archive of the mailing list for the GCC project.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: [i386, patch, RFC] HLE support in GCC

On Tue, Apr 10, 2012 at 9:34 AM, Andi Kleen <> wrote:
> "H.J. Lu" <> 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 |
>>> ?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.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]