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

[James Almer]

On 5/1/2020 4:27 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?

> 
>> 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

> 
> Carl Eugen
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