On 24.10.2016 21:34, wm4 wrote: > On Mon, 24 Oct 2016 21:19:46 +0200 > Andreas Cadhalpun <andreas.cadhal...@googlemail.com> wrote: >> On 24.10.2016 16:14, Ronald S. Bultje wrote: >>> On Mon, Oct 24, 2016 at 8:47 AM, wm4 <nfx...@googlemail.com> wrote: >>>> The next safest assumption is that it's fine as long as we explicitly >>>> don't use floating point or call external functions that aren't >>>> MMX-aware. This would mean calling any libc functions or user callbacks >>>> (including indirectly through e.g. av_log) is not fine. >> >> This is probably OK in practice and likely has a significant performance >> benefit. > > Seems like it. > > The compiler still could generate code using the FPU state at any > point, though, unless maybe there is an inline asm block. No function > can put the FPU into MMX mode, because any MMX using function must have > called emms before returning. Consequently, only compiler-known > intrinsics or opaque inline asm block could clobber the FPU state. The > latter because the compiler doesn't inspect asm blocks.
I agree. However, I think that this is currently only a theoretical issue. At least I'm not aware of this causing problems with a real compiler. Best regards, Andreas _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
