[FFmpeg-devel] [flamefest-start] A little something on MMX/SSE intrinsics

[Michael Niedermayer]

On Thu, Feb 28, 2008 at 12:39:20AM +0200, ?smail D?nmez wrote:
> Hi,
> 
> On Thu, Feb 28, 2008 at 12:30 AM, Michael Niedermayer <michaelni at gmx.at> wrote:
> >
> > On Thu, Feb 28, 2008 at 12:04:14AM +0200, ?smail D?nmez wrote:
> >  > On Wed, Feb 27, 2008 at 11:33 PM, M?ns Rullg?rd <mans at mansr.com> wrote:
> >  > > Michael Niedermayer <michaelni at gmx.at> writes:
> >  > >
> >  > >  > On Wed, Feb 27, 2008 at 03:29:56PM -0500, Alexander Strange wrote:
> >  > >
> >  > > >> I don't think anyone can get Altivec asm to work better than
> >  > >  >> intrinsics on more than one CPU - PPC is really, really
> >  > >  >> scheduling-sensitive, especially the G5 and Cell.
> >  > >  >
> >  > >  > Until i see benchmarks id guess gcc+intrinsics will be slower than
> >  > >  > unsheduled naively written asm()
> >  > >
> >  > >  That depends on the CPU.  Some CPUs are quite particular about
> >  > >  instruction scheduling.
> >  > >
> >  > >
> >  > >  >> I guess you can always try, though, but don't do anything to
> >  > >  >> discourage people who know altivec from adding more. There's still a
> >  > >  >> lot missing from H.264.
> >  > >  >
> >  > >  > Code is either well written or should be rejected.
> >  > >  > Intrinsics != well written.
> >  > >
> >  > >  That's where you're wrong.  Code using intrinsics can be well-written.
> >  > >  The problem is not the code, but the compiler.
> >  >
> >  > Intrinsics can also be analyzed easily by the compiler so they get
> >  > optimized easily where as its not possible for plain asm.
> >
> >  Thats like giving a painting from Leonardo da Vinci to a wild boar so it can
> >  correct the fine details.
> 
> That assumes every assembly coder is talented like Leonardo da Vinci,
> good luck with that assumption :-)

It just assumes that most asm coders who work on ffmpeg are better than gcc.
And i claim that this is true.

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Let us carefully observe those good qualities wherein our enemies excel us
and endeavor to excel them, by avoiding what is faulty, and imitating what
is excellent in them. -- Plutarch
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