Re: Earliest version of gcc the project should support as stage1 for gcc 17?

On 20/03/2026 17:27, Jonathan Wakely wrote:
> On Fri, 20 Mar 2026 at 15:58, Christophe Lyon via Gcc <[email protected]> wrote:
>>
>>
>>
>> On 3/20/26 11:15, Jakub Jelinek via Gcc wrote:
>>> On Fri, Mar 20, 2026 at 09:47:08AM +0000, Claudio Bantaloukas via Gcc wrote:
>>>> Title says it all really.
>>>>
>>>> Why am I asking? I'd like to try writing a build that checks stage1 works
>>>> with the earliest version of gcc the project wants to support.
>>>>
>>>> https://gcc.gnu.org/install/prerequisites.html currently says:
>>>> - GCC 5.4 or newer has sufficient support for used C++14 features.
>>>> - If you need to build an intermediate version of GCC in order to bootstrap
>>>> current GCC, consider GCC 9.5
>>>>
>>>> Should it use gcc 5.4? Is it time to increase that version?
>>>
>>> Yes. No.
>>>
>>> We don't increase the minimum requirement just for fun, but when it gives
>>> significant benefits for the codebase and the earliest supported gcc is
>>> still old enough (unlike especially rustc but also LLVM we try not to
>>> require too recent stuff for building).
>>> The reason to go to gcc 5.4 [1] (which already causes significant pain, several
>>> CompilerFarm machines still have system gcc 4.8.5) was to be able to use
>>> C++14 and so not be as limited in constexpr functions as in C++11.
>>
>> I believe Claudio is aiming at adding such builds in the forge CI (happy
>> to help btw ;-) ), so I suppose a follow-up question is what distro &
>> version should a container use?  Claudio shared a list in his message,
>> none of which matches the exact 5.4 requirement.
>>
>> Does this mean starting with an ubuntu-16.04 (ships gcc-5.3.1) and
>> build/install gcc-5.4.0 in it, and use the resulting image?

Cristophe, you're right, I've been wanting to add such a check for a 
while. But I'd like to add a twist to it. Rather than use an unsupported 
operating system, requiring vsyscall emulation, I'd rather try and build 
an older version of gcc on top of a new distribution.

> Well based on what Jakub said, the Ubuntu 5.3.1 might be OK to build trunk.
> 
> Until a few weeks ago, I was building every trunk snapshot using the
> Ubuntu 16:04 system compiler. I switched to 18:04 because something
> was failing, but I don't know if it was a temporary breakage on trunk.

I guess we'll find out at some point :)

Cheers,
Claudio