clang++: error: the clang compiler does not support '-march=native'

[Erich Dollansky]

Hi,

On Sat, 6 Feb 2016 21:01:13 -0700
Warner Losh <imp at bsdimp.com> wrote:

> On Sat, Feb 6, 2016 at 6:57 PM, Erich Dollansky
> <erichsfreebsdlist at alogt.com
> > wrote:  
> 
> > On Sat, 6 Feb 2016 15:49:14 -0700
> > Warner Losh <imp at bsdimp.com> wrote:
> >  
> > > On Sat, Feb 6, 2016 at 2:01 PM, Erich Dollansky
> > > <erichsfreebsdlist at alogt.com  
> > > > wrote:  
> > >  
> > > > compiling on a Raspberry Pi B 2 on FreeBSD 11 gives me above's
> > > > error message.
> > > >
> > > > A Internet search shows that this message does not exist.
> > > >
> > > > The program compiles using the same make file on FreeBSD 10
> > > > both on x86 and an Raspberry Pi B using the default compilers.
> > > >
> > > > Did support for 'march' get removed?
> > > >  
> > >
> > > As far as I can tell, it has never worked for either gcc or clang.
> > >  
> > this is what I would have liked to find out. Intel claims speed
> > gains of some 40% on their CPUs depending on the work load using
> > gcc.
> >
> > Getting a few per cent on a Raspberry for free would make a real
> > difference.
> >  
> 
> Well, the -march=<actual-cpu-here> args work, just not -march=native.
> The exact details of the core aren't exported from the kernel, so the
> compiler can't easily query them to guess at the best code generation
> to use. I think it would be a useful feature, but it just isn't one
> we have yet.
> 
> There are some -march values that get so aggressive about optimization
> that they reveal some alignment issues. However, I think we've kill
> them all. If not, we'd love to hear about it.
> 
> I know that the -march=arm1176 works well for the RPi B. Last time I
> tried it, the -march=cortex-a7 had some alignment issues. Since then
> I've seen fixes go into the tree and I haven't tried again. Reports
> from elsewhere indicate that this will give tens of percent in
> improvement depending on the workload.
> 
ok, I will try this then.

Is there a list of working architectures somewhere which really
applies for clang? I found only random information.

Erich