[FFmpeg-devel] [PATCH] x86: use new gcc atomic built-ins if available

[Reimar Döffinger]

On 26.10.2014, at 02:32, James Almer <jamrial at gmail.com> wrote:
> __sync built-ins are considered legacy and will be deprecated.
> These new memory model aware built-ins have been available since GCC 4.7.0

To me this sounds like "except for tsan, these new functions are worse in every aspect, and that's with gcc 4.9, who knows what mess 4.7 will make of them".
That sounds like a very bad argument to use them by default.
Nothing against also supporting them, but to make them default I don't think any performance regressions are acceptable, and we need to either test 4.7 as well or there must be a measurable performance advantage.
IMHO.
Note that ARM might benefit a lot if you manage to use the less strict versions.
However since it might not make a difference on x86 testing that they work properly might be difficult.