Fwd: Compile Fedora with auto-vectorization

[Florian Weimer]

FYI.

Please participate in the discussion on the devel list, as you see fit.

Thanks,
Florian

-------- Forwarded Message --------
Subject: Compile Fedora with auto-vectorization
Date: Mon, 5 Mar 2018 12:07:40 +0100
From: Florian Weimer <fweimer(a)redhat.com&gt;
Reply-To: Development discussions related to Fedora 
<devel(a)lists.fedoraproject.org&gt;
To: Development discussions related to Fedora 
<devel(a)lists.fedoraproject.org&gt;

Should we start compiling Fedora with auto-vectorization, either using 
-O3 or -O2 -ftree-loop-vectorize?

Downstream experimented with that for POWER 7 (the ppc64p7 packages). 
But if auto-vectorization is beneficial on POWER, it likely helps on 
other CPUs as well, given that SIMD support is quite common nowadays.

I really want to avoid a package-specific flag because I don't think 
discussions about per-package build policies are a good use of our time, 
and dependency changes invalidate previous decisions based on package 
use all the time.  (We saw a lot of that when we still had 
package-specific hardening flags.)

We currently have the RPM macro _performance_build for that: It's used 
in some Fedora spec files, but the redhat-rpm-config support have never 
be contributed to Fedora.  If we enable auto-vectorization globally, 
those packages could remove the _performance_build setting, a minor cleanup.

Thanks,
Florian
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