[Fwd: Re: Off topic - G5 question]

James Cownie jcownie at etnus.com
Mon Jun 30 05:30:37 EDT 2003


Toon Moene wrote :-
> Mark Hahn wrote:
> 
> > I still see users fling their code at a machine with 
> > 	g77 prog.f && ./a.out
> > and wonder why it's so slow.
> 
> Well, I could make -O2 -ffast-math -funroll-loops the default (but then, 
> I don't think I'll get this past the IEEE754 police @ gcc.gnu.org :-)

However there's nothing to stop Mark (assuming he has control of the
machine) from setting the system up so that the "g77" you get by
default is really a shell script which turns on appropriate
optimisation flags, and also providing a command either to compile
unoptimised, or to change the users $PATH so that they can get to a
"raw" g77.

I know that this is the approach used by Nick McLaren on the big Sun
machines at Cambridge. 
  http://www.hpcf.cam.ac.uk/prog_franklin_compilers.html

Depending on the interests of your users (are they interested in their
application domain, or in becoming compiler switch experts), they may 
prefer a system where someone has already defaulted the compiler to
use an apporpiate set of magic optimisation flags.

-- Jim 

James Cownie	<jcownie at etnus.com>
Etnus, LLC.     +44 117 9071438
http://www.etnus.com
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