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Re: build system option to allow CPU optimizations?

From: Ludovic Courtès
Subject: Re: build system option to allow CPU optimizations?
Date: Mon, 20 Dec 2021 18:40:56 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux)


Ricardo Wurmus <> skribis:

> Ludovic Courtès <> writes:


> It may very well be the wrong approach in principle, but I also think
> that it’s a neat escape hatch for specific use cases. Separating
> reproducibility patching makes the package transformation mechanism
> more powerful and appealing.  Much like respecting TESTS? makes it
> easy for users of modified packages to bypass a failing test suite,
> making patching of Makefiles to remove CPU tuning conditional would
> make for much less complex custom package definitions.
>> I found one case though where this is not possible: C++ header-only
>> libraries such as Eigen contain hand-optimized vectorized routines,
>> selected at build time, but we end up compiling Eigen users as the
>> x86_64/AArch64 baseline, which is a waste.  (If you do know of other
>> problematic cases, I’m interested in taking a look!)
>> My solution to that is “package multi-versioning” via a
>> transformation
>> option.  Hopefully I’ll submit preliminary patches within a week or
>> so!
> Oh, exciting!

I forgot to mention it here, but it’s available for testing and probably
even ready to merge:

I think it makes an option to dismiss ‘-march’ removal unnecessary; or,
put differently, it achieves the same.

I’m interested in seeing which packages people would mark as “tunable”
and what performance gains it gives!


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