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From: iyzsong@member.fsf.org (=?utf-8?B?5a6L5paH5q2m?=)
Subject: Re: [PATCH 2/2] gnu: zita-convolver: Drop the '-march=native'
	optimization.
Date: Thu, 07 Jan 2016 22:53:45 +0800
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In-Reply-To: <8737u9ttjh.fsf@gnu.org> ("Ludovic =?utf-8?Q?Court=C3=A8s=22'?=
	=?utf-8?Q?s?= message of "Thu, 07 Jan 2016 14:20:50 +0100")
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To: Ludovic =?utf-8?Q?Court=C3=A8s?= <ludo@gnu.org>
Cc: guix-devel@gnu.org

ludo@gnu.org (Ludovic Court=C3=A8s) writes:

> Ricardo Wurmus <rekado@elephly.net> skribis:
>
>> =E5=AE=8B=E6=96=87=E6=AD=A6 <iyzsong@member.fsf.org> writes:
>>
>>> Ricardo Wurmus <rekado@elephly.net> writes:
>>>
>>>>> +              (snippet
>>>>> +               ;; Don't optimize for a specific processor architectu=
re.
>>>>> +               '(substitute* "libs/Makefile"
>>>>> +                  (("^CXXFLAGS \\+=3D -march=3Dnative") "")))
>>>>> +              (modules '((guix build utils)))
>>>>
>>>> Is this to avoid that packages are optimised for the CPU of the build
>>>> slave?
>>> Yes, using that from hydra will crash guitarix for me.
>>> Same as: <https://bugs.archlinux.org/task/36248>.
>>
>> Guitarix also crashes for me on i686 =E2=80=94 and I thought it was some=
thing to
>> do with my machine or the broken build of eigen.
Pushed, hopefully this will fix it on i686 too.
>
> Eigen is a header-only library, so what matters is the optimization
> flags passed when building the software that uses Eigen.
>
>>>> If so, could we instead pass different optimisation flags for
>>>> different architectures?  For a convolver I=E2=80=99d prefer to have *=
some*
>>>> optimisation, even if it=E2=80=99s just the greatest common divisor.
>
> It=E2=80=99s likely that zita-convolver has -O2 or similar *in addition* =
to
> -march=3Dnative, because the latter is no substitute for the former.
>
> Could you check that in the makefiles?
Yes, it actually has:
  CXXFLAGS =3D+ -ffast-math -funroll-loops -O3