[FFmpeg-devel] [PATCH 2/2] Use gcc/clang builtins for av_sat_(add|sub)_64_c if available.

[James Almer]

On 5/1/2020 4:37 PM, Carl Eugen Hoyos wrote:
> Am Fr., 1. Mai 2020 um 21:34 Uhr schrieb James Almer <jamrial at gmail.com>:
>>
>> On 5/1/2020 4:27 PM, Carl Eugen Hoyos wrote:
>>> Am Fr., 1. Mai 2020 um 20:22 Uhr schrieb James Almer <jamrial at gmail.com>:
>>>>
>>>> On 5/1/2020 3:07 PM, Carl Eugen Hoyos wrote:
>>>>> Am Fr., 1. Mai 2020 um 19:24 Uhr schrieb Dale Curtis <dalecurtis at chromium.org>:
>>>>>>
>>>>>> Signed-off-by: Dale Curtis <dalecurtis at chromium.org>
>>>>>> ---
>>>>>>  libavutil/common.h | 10 ++++++++++
>>>>>>  1 file changed, 10 insertions(+)
>>>>>
>>>>> Imo, this is guaranteed to break x86 compilation with some unusual
>>>>> toolchain.
>>>>> I looked carefully at all occurrences of AV_GCC_VERSION_AT_LEAST()
>>>>> and I believe they are in fact different (not for x86 or combined with other
>>>>> checks).
>>>>
>>>> Can you elaborate on this? AV_GCC_VERSION_AT_LEAST() is a public macro
>>>> used in public headers to choose one or another path depending on if the
>>>> compiler is a recent enough GCC, or something else.
>>>
>>>> What toolchain could this break
>>>
>>> It definitely breaks icc compilation on Linux.
>>
>> So ICC on Linux defines __GNUC__ >= 5 yet doesn't support these builtins?
> 
> No, but yes, this is the effect.

So that means ICC is broken, defining support for features it doesn't
really has.
We can workaround that with a !defined(__INTEL_COMPILER) check, i guess,
but perhaps we may want to stop supporting broken compilers.

> 
>>>> and why specifically x86?
>>>
>>> I mentioned x86 because afaics, all existing relevant uses of
>>> AV_GCC_VERSION_AT_LEAST() will not be triggered on x86.
>>
>> AV_GCC_VERSION_AT_LEAST is used in a lot of arch agnostic libavutil
>> headers, and in x86/intmath.h
> 
> This is exactly what I meant above with "carefully".

It would be nice if you could stop being so terse and explain what's on
your mind for once. You're not being clear at all, and i asked you to
elaborate, something you still haven't done.