Optionally using more advanced CPU features

[Ricardo Wurmus]

Hi Guix,

I was wondering how we should go about optionally building software for
more advanced CPU features.  Currently, we build software for the lowest
common feature set among x86_64 CPUs.  That’s good for portability, but
not so good for performance.

Enabling CPU features often happens through configure flags, but
expressing support at that level in our package definitions seems bad.
How can we make it possible for users to build their software for
different CPUs?

We can cross-compile for other architectures on the command line with
“--target” and “--system”; can we allow for compilation with special CPU
features across the graph with “--features”?  Build system abstractions
or package definitions would then be changed to recognize these features
and modify the corresponding flags as needed.

If we had a larger build farm we could also offer substitutes for more
modern CPUs.

--
Ricardo

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