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

Måns Rullgård mans
Tue Sep 21 12:13:38 CEST 2010

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

M?ns Rullg?rd
mans at mansr.com

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