[FFmpeg-devel] [PATCH] h264: mark xmm registers as clobbered in h264 qpel sse functions

[Michael Niedermayer]

On Thu, Oct 07, 2010 at 06:26:59PM -0300, Ramiro Polla wrote:
> $subj, fixes h264 for win64

>  h264_qpel_mmx.c |   21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> f7a94ad1d2ef7ffec9ce1a219ad9c9c4efc0e8d7  xmm_clobbers_h264_qpel_mmx.diff
> Index: libavcodec/x86/h264_qpel_mmx.c
> ===================================================================
> --- libavcodec/x86/h264_qpel_mmx.c	(revision 25401)
> +++ libavcodec/x86/h264_qpel_mmx.c	(working copy)
> @@ -677,6 +677,10 @@
>          : "D"((x86_reg)src2Stride), "S"((x86_reg)dstStride),\
>            "m"(ff_pw_5), "m"(ff_pw_16)\
>          : "memory"\
> +          XMM_CLOBBERS(, "%xmm0", "%xmm1", "%xmm2", "%xmm3", \
> +                         "%xmm4", "%xmm5", "%xmm6", "%xmm7", \
> +                         "%xmm8", "%xmm9", "%xmm10", "%xmm11", \
> +                         "%xmm12", "%xmm13", "%xmm14", "%xmm15") \
>      );\
>  }
>  #else // ARCH_X86_64

> @@ -699,6 +703,7 @@
>          "pxor %%xmm7, %%xmm7        \n\t"\
>          "movdqa %0, %%xmm6          \n\t"\
>          :: "m"(ff_pw_5)\
> +        XMM_CLOBBERS_ONLY("%xmm6", "%xmm7") \
>      );\
>      do{\


this is wrong
6/7 are read after the asm
correct is to either merge the asm blocks or to put manual store restore code
for the xmm registers there under appropriate ifdef

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

It is not what we do, but why we do it that matters.
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