[FFmpeg-devel] [PATCH] split-radix FFT
Tue Jul 29 17:57:21 CEST 2008
On Tue, 2008-07-29 at 17:41 +0200, Michael Niedermayer wrote:
> On Tue, Jul 29, 2008 at 06:26:49PM +0300, Uoti Urpala wrote:
> > On Tue, 2008-07-29 at 17:10 +0200, Michael Niedermayer wrote:
> > > And just to clarify, yes what i considered a good argument was the sentance
> > > above where my reply is. That is to use MANGLE in speed critical code.
> > > That way most textrels are avoided while minimizing the speed impact.
> > >
> > > I do not think you ever argued for that.
> > IIRC I did mention the possibility of omitting -fPIC for a subset of
> > files.
> > > I remember you strongly arguing
> > > toward replacing all MANGLE by "m" knowing that it would break gcc 2.95
> > > and not really caring that it would slow down code compiled with -fPIC.
> > Of course the code would be slower on x86. If you want it to be as fast
> > as possible then compile it with -fPIC on x86. I don't think it's
> > worthwhile to pick only the globals used inside asm for such special
> > treatment.
> x86-64 shared libs require -fPIC, unless that has been fixed.
> so the user does not always have the option to omit -fPIC
I didn't mean to include AMD64 in x86. -fPIC does not cause that much
slowdown on it. And anyway what shared libs on AMD64 require is *no
textrels* - generating them by some other method wouldn't work any
better. So you don't need MANGLE to force creating textrels, and if it
did that the result in fact wouldn't work. You can avoid GOT lookup by
adding visibility information (and then the compiler will avoid it for
ALL uses, not just those inside asm).
More information about the ffmpeg-devel