Re: [FFmpeg-devel] [PATCH 1/3] avutil/avassert: Add av_assert_unreachable()

[epirat07@gmail.com]

On 13 Jul 2024, at 2:47, Andreas Rheinhardt wrote:

> Marvin Scholz:
>> ---
>>  libavutil/avassert.h | 12 ++++++++++++
>>  1 file changed, 12 insertions(+)
>>
>> diff --git a/libavutil/avassert.h b/libavutil/avassert.h
>> index 1895fb7551..cdab912fe4 100644
>> --- a/libavutil/avassert.h
>> +++ b/libavutil/avassert.h
>> @@ -75,4 +75,16 @@
>>   */
>>  void av_assert0_fpu(void);
>>
>> +/**
>> + * Assert this can not be reached
>> + */
>> +#if AV_HAS_BUILTIN(__builtin_unreachable)
>> +#define av_assert_unreachable() do {   \
>> +    av_assert2(0);                      \
>> +    __builtin_unreachable();            \
>> +} while (0)
>> +#else
>> +#define av_assert_unreachable() av_assert2(0)
>> +#endif
>> +
>>  #endif /* AVUTIL_AVASSERT_H */
>>
>> base-commit: 85706f5136cf7c88f95843b2634dd3f7d7d2cb6d
>
> You are not the first one with this idea:
> https://ffmpeg.org/pipermail/ffmpeg-devel/2024-May/328116.html
> But Michael Niedermayer thinks that adding a new macro instead of
> directly reusing av_assert is more complicated.
>
Oh I did not notice that one, thanks…

I definitely think an av_assert_unreachable() is clearer than
av_assert0(!"reached") too, obviously, else I would not propose it.

(Somewhat proven by these two cases fixed by the patch where we use
av_assert1/2(0) variants which then result in the compiler not knowing
these are unreachable cases when the assert is not enabled.)

If this approach is rejected, I can submit a version that uses
av_assert0(!"reached“).

> - Andreas
>
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