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

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?

Thanks,

Christophe

> The next step would be to be able to use C++17 features (but which ones are
> the ones we can't live without in the sources right now?), but that
> would mean requiring GCC 9.  That is IMHO quite premature.
> We've switched to C++14 requirement in GCC 15 and between GCC 5 and 9 it
> is 4 years, so I'd expect switching roughly in GCC 19 rather than GCC 17.
> 
> [1] I think some 5.3.1 versions can be just fine too, depends on from when,
> there were some important C++14 bugfixes between 5.3.0 and 5.4.0.
> 
> 	Jakub
>