Mark H Weaver <mhw@netris.org> writes:

> LLVM is an optional input for Mesa which enables the Gallium 'llvmpipe'
> driver, a fast software rasterizer that uses LLVM to do runtime code
> generation.
>
>   https://docs.mesa3d.org/gallium/drivers/llvmpipe.html
>
> Among other things, this allows use of the GNOME Shell on systems
> without hardware support for 3D graphics.
>
> GTK depends on Mesa.
>
> ...
>
> Alternatively, for those who do not wish to maintain their own private
> branch, here's a hybrid approach that might be workable: add a local
> variant of 'mesa' with 'llvm' removed from 'inputs' (and "-Dllvm=true"
> removed from the configure flags), then add a local variant of 'gtk+'
> that uses your local 'mesa', and finally add a local variant of 'emacs'
> that uses your local 'gtk+'.  I guess those last two steps could be
> replaced by deep package rewrites, although I've never used that
> functionality since I prefer the more flexible "private git branch"
> approach to customizing Guix to my preferences.

If I understand correctly, we could have a gtk-minimal that depends on
mesa-minimal which is built without LLVM.  If llvmpipe is only useful
for GNOME Shell and the like, it's very likely that Emacs and many other
packages don't need GTK-on-LLVM.

-- 
Pierre Neidhardt
https://ambrevar.xyz/