[FFmpeg-devel] [PATCH] remove gcc 3.3 workaround in swscale_template.c

Benoit Fouet benoit.fouet
Tue Sep 22 15:53:19 CEST 2009

On 2009-09-21 00:16, Diego Biurrun wrote:
> On Sun, Sep 20, 2009 at 09:02:46PM +0200, Reimar D?ffinger wrote:
>> On Sun, Sep 20, 2009 at 08:00:40PM +0200, Diego Biurrun wrote:
>>> On Sun, Sep 20, 2009 at 07:12:44PM +0200, Reimar D?ffinger wrote:
>>>> On Sun, Sep 20, 2009 at 06:53:36PM +0200, Diego Biurrun wrote:
>>>>> There's an ugly preprocessor gcc 3.3 workaround in swscale_template.c:
>>>>>   /* GCC 3.3 makes MPlayer crash on IA-32 machines when using "g" operand here,
>>>>>      which is needed to support GCC 4.0. */
>>>>>   #if ARCH_X86_64 && ((__GNUC__ > 3) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
>>>>>                   :: "m" (src1), "m" (dst), "g" (dstWidth), "m" (xInc_shr16), "m" (xInc_mask),
>>>>>   #else
>>>>>                   :: "m" (src1), "m" (dst), "m" (dstWidth), "m" (xInc_shr16), "m" (xInc_mask),
>>>>>   #endif
>>>>> At the very least it should be updated to use the AV_GCC_VERSION_AT_LEAST
>>>>> macro from libavutil.  However, I would prefer to get rid of it
>>>>> completely.  If I understand the comment correctly, deleting the whole
>>>>> #else clause would be the way to achieve this.  Since I know little
>>>>> enough assembler to have no real idea what "g" and "m" operands are all
>>>>> about I'd like to hear an informed opinion.
>>>> Huh? No, the upper line should give faster code but causes crashes due
>>>> to miscompilation with gcc 3.3
>>>> The lower line does not compile with gcc 4.0 on x86_64 but produces correct code
>>>> with 3.3.
>>>> At least that's what the comment says.
>>> OK, then I propose getting rid of the workaround completely.  I don't
>>> think x86_64 users with gcc 3.3 exist, so it's not worth the ugliness on
>>> our side.
>> Hm? Which do you consider a workaround? I think you might still need two cases,
>> one for x86_32 and one for x86_64 for gcc 4.x, you could only get rid of the
>> gcc version check.
> OK, I propose the attached patch.

which results in code as ugly, but with no support for gcc < 3.3 on x86_64
I'd say, if you really want to change that code, change it to use
AV_GCC_VERSION_AT_LEAST, and that should do, no ?


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