[FFmpeg-devel] [PATCH 2/2] Require compilers to support C17.

[Lynne]

Feb 8, 2024, 20:05 by jamrial at gmail.com:

> On 2/8/2024 3:52 PM, Sean McGovern wrote:
>
>> Hi developers,
>>
>> On Wed, Feb 7, 2024, 23:30 Jean-Baptiste Kempf <jb at videolan.org> wrote:
>>
>>> Hello,
>>>
>>> On Thu, 8 Feb 2024, at 01:36, Cosmin Stejerean via ffmpeg-devel wrote:
>>>
>>>>> There were simply no objections to moving to C11.
>>>>> The C17 plan came about later because it has important bugfixes.
>>>>> It doesn't really matter as compilers backported the new behaviour to
>>>>>
>>> C11
>>>
>>>>> (or rather, they consistently had the same behaviour, but now it became
>>>>>
>>> a standard).
>>>
>>>>>
>>>>>
>>>>
>>>> There were no objections to C11, however C17 was brought up and there
>>>> were objections that it's likely too soon and I believe JB proposed
>>>> holding off for a year on C17 (while adopting C11 immediately), which
>>>>
>>>
>>> My recommendation is still this:
>>> - move to C11 now
>>> - activate C17 on some Fate/CI targets
>>> - recommend C17 compilers modes
>>> - move to C17 at this mid-year when 7.1 is branched (LTS if we follow our
>>> plans)
>>>
>>
>>
>> I like this approach. It's a shame we can't get metrics on who might be
>> genuinely affected by a direct move to C17.
>>
>> I'd be more than willing to host one or more FATE nodes with C17 turned on.
>> Do let me know if this is desirable.
>>
>
> At least for GCC, -std=c11 is the same as -std=c17 except for the __STDC_VERSION__ value. As in, apparently all the fixes are implemented either way. And as far as i understand it, we would require c11 but use c17 if present (Meaning, test std=c17, fallback to std=c11, abort if not possible), so all FATE instances using a relatively recent compiler will invariably use c17.
>
> What we would need is instances with old compilers, pre-2017, to get actual c11 testing.
>

We have plenty of old compilers on FATE, don't we?
I think the point of bumping the build-time requirements is to get rid of them,
and maybe we could use the chance to also get higher-quality metrics on
whether we can use the chance to reenable stuff like tree vectorization again
without old compilers miscompiling.

I could live with C11 for 7.0, but I would prefer to bump to C17 soon after
this release is made, rather than waiting for the middle of the year to have
to discuss this again.