Re: [FFmpeg-devel] [PATCH 07/10] avfilter/vf_nlmeans: Move ff_nlmeans_init into a header

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Soft Works:
> 
> 
>> -----Original Message-----
>> From: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
>> Sent: Friday, May 13, 2022 10:27 AM
>> To: Soft Works <softworkz@hotmail.com>; FFmpeg development discussions
>> and patches <ffmpeg-devel@ffmpeg.org>
>> Subject: Re: [FFmpeg-devel] [PATCH 07/10] avfilter/vf_nlmeans: Move
>> ff_nlmeans_init into a header
>>
>> Soft Works:
>>>
>>>
>>>> -----Original Message-----
>>>> From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of
>>>> Andreas Rheinhardt
>>>> Sent: Tuesday, May 3, 2022 8:38 AM
>>>> To: ffmpeg-devel@ffmpeg.org
>>>> Cc: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
>>>> Subject: [FFmpeg-devel] [PATCH 07/10] avfilter/vf_nlmeans: Move
>>>> ff_nlmeans_init into a header
>>>>
>>>> This removes a dependency of checkasm on lavfi/vf_nlmeans.o
>>>> and also allows to inline ff_nlmeans_init() irrespectively of
>>>> interposing.
>>>>
>>>> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
>>>> ---
>>>
>>> [..]
>>>
>>>> +
>>>> +static av_unused void ff_nlmeans_init(NLMeansDSPContext *dsp)
>>>> +{
>>>> +    dsp->compute_safe_ssd_integral_image =
>>>> compute_safe_ssd_integral_image_c;
>>>> +    dsp->compute_weights_line = compute_weights_line_c;
>>>> +
>>>> +    if (ARCH_AARCH64)
>>>> +        ff_nlmeans_init_aarch64(dsp);
>>>
>>> Hi Andreas,
>>>
>>> the above breaks compilation for me:
>>>
>>> 1>libavfilterd.lib(libavfilter_vf_nlmeans.obj) : error LNK2019:
>> unresolved external symbol ff_nlmeans_init_aarch64 referenced in
>> function ff_nlmeans_init
>>>
>>> The reason is that I'm (obviously) not compiling stuff from the
>>> libavfilter\aarch64 subfolder.
>>>
>>> It might need an #ifdef ?
>>>
>>> I haven't taken a deeper look at it, though.
>>>
>>> Thanks,
>>> softworkz
>>>
>>>
>>
>> That surprises me: The earlier code did exactly the same; in fact,
>> using
>> if (ARCH_*) is our typical check for arches in dsp-init code.
> 
> I looked at this a bit further. It seems that the VS project 
> generation tool that I'm using is creating dummy definitions
> for such cases. In the previous workspace it had generated
> 
> void ff_nlmeans_init_aarch64(NLMeansDSPContext *dsp) {return;}
> 
> in a separate code file for being able to work with the ffmpeg
> code in VS without modifying any of the code.
> 
> Now that you have moved that code to a header file, this logic 
> doesn't work anymore.
> 

Why does your compiler not just eliminate dead code like all the others?
Is this MSVC -O0 behaviour?
I just sent the patch
https://ffmpeg.org/pipermail/ffmpeg-devel/2022-May/296380.html, but now
that I read this I have to agree with Hendrik: Why not update your tool
instead?

- Andreas
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