[FFmpeg-devel] [PATCH 0/2] Fix strict aliasing violations in AAC and AC3 parsers

[Aurelien Jacobs]

Benoit Fouet wrote:

> On 12/15/2008 10:35 AM, M?ns Rullg?rd wrote:
> > M?ns Rullg?rd <mans at mansr.com> writes:
> >
> >> "Jason Garrett-Glaser" <darkshikari at gmail.com> writes:
> >>
> >>>> am i interperting this correctly, that the code is hugely faster with
> >>>> -fno-strict-aliasing
> >>>> ?
> >>>> and iam of course in favor of the faster variant for h264.c
> >>> Yes, but it makes absolutely no sense why it would be faster--the
> >>> oprofile says even the asm functions are faster which of course makes
> >>> no sense at all.
> >>>
> >>> Others in #ffmpeg-devel have reported small speed increases or
> >>> decreases, but nothing like what I posted.
> >> Changes in decoding time after adding -fno-strict-aliasing on ARM:
> >>
> >> H.264   -2.4%
> >> MPEG4   +0.14%
> >> MPEG2   -2.3%
> >> Vorbis  +0.08%
> >> Flac    +3.6%
> >> MP3     +2.6%
> >> AC3     +0.83%
> >> DTS     +0.81%
> >
> > BTW, that was with codesourcery gcc 4.2.1.
> >
> >> I will test with Jason's sample on Core2 and see if I get anything
> >> resembling his results.
> >
> > Tested on Core2, and I get no such numbers:
> >
> > vanilla              203.7867 s
> > -fno-strict-aliasing 204.2257 s
> >
> > This was with gcc 4.2.4.
> >
> 
> same with gcc 4.3.2 on a Core2:
> vanilla              245.095s
> -fno-strict-aliasing 247.687s

same with gcc 4.3.2 on Athlon64:
vanilla              308.219s
-fno-strict-aliasing 312.632s

Aurel