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Re: Better performance on older version of GCC


On Fri, 2010-08-27 at 17:09 +0200, Richard Guenther wrote:
> On Fri, Aug 27, 2010 at 5:02 PM, Corey Kasten
> <corey@materialintelligencellc.com> wrote:
> > On Fri, 2010-08-27 at 06:50 -0700, Nathan Froyd wrote:
> >> On Fri, Aug 27, 2010 at 09:44:25AM -0400, Corey Kasten wrote:
> >> > I find that the executable compiled on system A runs faster (on both
> >> > systems) than the executable compiled on system B (on both system), by a
> >> > factor about approximately 4 times. I have attempted to play with the
> >> > GCC optimizer flags and have not been able to get System B (with the
> >> > later GCC version) to compile code with any better performance. Could
> >> > someone please help figure this out?
> >>
> >> It's almost impossible to tell what's going on without an actual
> >> testcase.  You might not be able to provide the actual code, but you
> >> could try distilling it down to something you could release.
> >>
> >> -Nathan
> >
> > Thanks for the reply Nathan.
> >
> > I have attached an archive with the test case code. The code is built by
> > build.sh and outputs the number of microseconds to complete the
> > processing.
> >
> > Compiling with GCC version "4.1.2 20070925 (Red Hat 4.1.2-33)" produces
> > code that runs in about 66% of the time than does GCC version "4.3.0
> > 20080428 (Red Hat 4.3.0-8)"
> 
> -fcx-limited-range or -fcx-fortran-rules.  4.3 now is more conforming than 4.1.
> 
> Richard.
> 
> > Thanks
> >
> > Corey
> >

Richard,

-fcx-limited-range worked great on both my real benchmark and my test
achive. GCC didn't recognize -fcx-fortran-rules, but obviously I don't
need it.

Thanks so much,
Corey

  


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