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Date: Tue, 8 Nov 2011 22:32:53 +0100
From: Roman Divacky <rdivacky@freebsd.org>
To: Alexander Best <arundel@freebsd.org>
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Cc: freebsd-toolchain@freebsd.org, Dimitry Andric <dim@FreeBSD.org>
Subject: Re: CPUTYPE=native handling
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On Tue, Nov 08, 2011 at 09:23:52PM +0000, Alexander Best wrote:
> On Tue Nov  8 11, Roman Divacky wrote:
> > clang will use "core2" for family=6 and model=15
> > 
> > check llvm/lib/Support/Host.cpp
> > 
> > what is the problem? The fact that our gcc from the middle-ages
> > does not recognize that?
> 
> actually a few months ago quite a lot of gcc commits happend to add newer
> optimisations (such as core2) to gcc and some commits aimed at modifying gcc,
> so it would make the best -march=native choice there is.
> 
> what's the clang command (similar to gcc -march=native -E -v - </dev/null),
> one can use to check what actual optimisation clang turns "native" into?
 
clang -### -march=native will show something like

"-target-cpu" "k8-sse3"


> also there seem to be cross-compilation issues. when people are running i386
> and want to cross-compile for amd64 and put CPUTYPE=core2 (or any other amd64
> cpu) into their make.conf, this gets downgraded by bsd.cpu.mk to prescott.
> 
> see http://www.freebsd.org/cgi/query-pr.cgi?pr=conf/84800
> and
> http://www.mail-archive.com/freebsd-hackers@freebsd.org/msg161451.html

If gcc supports nocona now, the conf/84800 patch is ok. The same goes
with downgrading core2 -> prescott.

I have no idea what gcc supports these days. I think we should just skip
the downgrading completely for clang as it either supports everything or
can be made easily to support what it doesnt.

roman