[FFmpeg-devel] [PATCH] update doc/optimization.txt

Michael Niedermayer michaelni
Tue Sep 21 13:27:51 CEST 2010

On Tue, Sep 21, 2010 at 11:13:38AM +0100, M?ns Rullg?rd wrote:
> Michael Niedermayer <michaelni at gmx.at> writes:
> > On Tue, Sep 21, 2010 at 10:36:02AM +0100, M?ns Rullg?rd wrote:
> >> Michael Niedermayer <michaelni at gmx.at> writes:
> >> 
> >> >> The function call overhead is exactly the same with yasm or C,
> >> >> assuming the C compiler doesn't generate ridiculous prologues and
> >> >> epilogues.  Please stop claiming anything else.  Nobody is talking
> >> >> about asm that actually gets inlined.
> >> >
> >> > thats not true, the split asm cases surely where inlined and a 1:1
> >> > conversion to yasm would have had additional call overhead.
> >> 
> >> Nobody ever suggested doing that.  We've always been talking about
> >> whole functions, be they written C or yasm.  Now stop making straw man
> >> arguments, please.
> >
> > you talk about optimizing C code to asm and converting inline
> > to yasm both in one patch and use it as argument why yasm is better.
> > But its the C->asm optimization that makes it better not inline->yasm
> The split inline asm in the SSE IMDCT could not have been merged.
> There was a function call to the FFT between the two parts, and on
> x86_64 it is not possible to do a function call from within inline asm
> (and it is a bad idea on any arch).  When the entire function is
> written in yasm, there is of course no problem with making function
> calls.

interresting strawman argument
noone was talking about cases that cannot easily be done in inline asm
not that calling from inline would be impossible or anything but i surely
agree that for these 0.1% of asm yasm is likely the better choice

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Incandescent light bulbs waste a lot of energy as heat so the EU forbids them.
Their replacement, compact fluorescent lamps, much more expensive, dont fit in
many old lamps, flicker, contain toxic mercury, produce a fraction of the light
that is claimed and in a unnatural spectrum rendering colors different than
in natural light. Ah and we now need to turn the heaters up more in winter to
compensate the lower wasted heat. Who wins? Not the environment, thats for sure
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