[llvm-dev] Upgrading LLVM's minimum required CMake version

Siva Chandra via llvm-dev llvm-dev at lists.llvm.org
Thu Mar 26 13:38:48 PDT 2020

On Thu, Mar 26, 2020 at 1:26 PM Louis Dionne via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> > On Mar 26, 2020, at 16:07, Shoaib Meenai <smeenai at fb.com> wrote:
> >
> > We had this discussion a few months ago and it petered out, and it’s
> recently been revived in the context of upgrading the CMake version
> specifically for libc++ (at which point people suggested upgrading the
> CMake version used by all of LLVM), so let’s try to move this forward.
> I was going to create a new thread to ask LLVM as a whole, but you did it
> faster and better than I could have! Thanks a lot for all the research and
> context you added below. This is great.
> >
> > [...]
> >
> > Our build system is incredibly complex, and many of these features can
> be used to clean it up and make it much more maintainable. I would
> personally like us to at least bump up to CMake 3.12. I also do think it's
> worth establishing a policy and process around upgrading CMake versions,
> since newer versions keep on adding useful features (particularly better
> generator expression support), and we want to be able to keep taking
> advantage of them.
> I'd like to express very strong support for this. I believe 3.12 is
> reasonable, and it will give us a lot of features that can improve our life
> significantly, while still being old enough that some distributions will
> support it out of the box.

LLVM libc can live with 3.12. So, I lend my support for bumping to 3.12 at

> As far as establishing a policy goes, my preference would be to say that
> we systematically bump the requirement every release to e.g. the CMake
> released 12 months ago. I understand some people would rather have a
> detailed analysis of why we should upgrade every time, but I think it's
> unnecessary overhead because:
> 1. CMake keeps adding new features that can simplify the build system, so
> there's always "a reason" to upgrade
> 2. CMake is very easy to upgrade, so it makes sense to be more aggressive
> than for e.g. bumping compiler requirements
> Bumping systematically would have the benefit of lowering the effort to
> making these upgrades and avoiding situations where upgrade efforts are
> stalled for several years due to the effort of having to convince people
> over again. If we bumped systematically, it would also ensure that users
> and bot owners are trained to upgrade from time to time.
> However, no matter what the policy ends up being, I think it's important
> to at least bump it once soon, so I would be careful not to derail this
> effort in search of a perfect policy.
> Cheers,
> Louis
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