[FFmpeg-devel] [PATCH]Simplify mlp_filter_channel_x86()

[Michael Niedermayer]

On Thu, Feb 19, 2015 at 05:13:19PM +0000, Carl Eugen Hoyos wrote:
> Hendrik Leppkes <h.leppkes <at> gmail.com> writes:
> 
> > > Attached patch by Francisco Blas Izquierdo Riera 
> > > fixes a compilation error in mlpdsp_init.c with 
> > > -fstack-check and some gcc compilers (I reproduced 
> > > the issue with gcc 4.7.3) by simplifying the code.
> > > I ran some benchmarks with a very large thd file, 
> > > 'time' confirms the results of '-benchmark'.
> > 
> > Please benchmark ASM changes using STAR/STOP_TIMER 
> > macros.
> 
> It's 5400 without vs 5500 decicyles with the patch 
> attached.
> 
> I (still) find it very hard to understand that 
> testing a few bytes of input data has more 
> meaning than running decoding several GBs 
> several times.
> 
> > Looking at the code, the change introduces one 
> > extra instruction in x64, and is identical in x86, 
> > so I don't really see how it can be faster?
> 
> I am not claiming it is faster.
> Just that a slowdown is not reproducible.

something like this can possibly be used to fix build of the file
until someone rewrites it to yasm

diff --git a/libavcodec/x86/Makefile b/libavcodec/x86/Makefile
index 7c4f4cd..b96b2ea 100644
--- a/libavcodec/x86/Makefile
+++ b/libavcodec/x86/Makefile
@@ -164,3 +164,5 @@ YASM-OBJS-$(CONFIG_VP9_DECODER)        += x86/vp9intrapred.o            \
                                           x86/vp9lpf.o                  \
                                           x86/vp9mc.o
 YASM-OBJS-$(CONFIG_WEBP_DECODER)       += x86/vp8dsp.o
+
+$(SUBDIR)x86/mlpdsp_init.o: CFLAGS := $(subst -fstack-check, -fno-stack-check, $(CFLAGS))

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

There will always be a question for which you do not know the correct answer.
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