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

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?

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.