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Re: Better performance on older version of GCC

On Fri, Aug 27, 2010 at 5:02 PM, Corey Kasten
<> 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
> 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.


> Thanks
> Corey

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