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devel / comp.lang.fortran / Optimization options

Optimization options

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Subject: Optimization options
From: beliavsky@aol.com (Beliavsky)
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by: Beliavsky - Wed, 27 Apr 2022 14:12 UTC

Regarding compiler options to maximize speed I may tweet

The ifort -fast and gfortran -O3 -march=native options can be used to
increase speed. Gfortran -Ofast turns on -ffast-math and can give a
further 2x speedup in some cases, but it can also give incorrect
results and should be used with care. Use gfortran -Og to debug.

That is 274 characters. If there is something wrong, please let me know.

Re: Optimization options

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From: steve@seesignature.invalid (Steve Lionel)
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Subject: Re: Optimization options
Date: Thu, 28 Apr 2022 09:01:51 -0400
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by: Steve Lionel - Thu, 28 Apr 2022 13:01 UTC

On 4/27/2022 10:12 AM, Beliavsky wrote:
> Regarding compiler options to maximize speed I may tweet
>
> The ifort -fast and gfortran -O3 -march=native options can be used to
> increase speed. Gfortran -Ofast turns on -ffast-math and can give a
> further 2x speedup in some cases, but it can also give incorrect
> results and should be used with care. Use gfortran -Og to debug.
>
> That is 274 characters. If there is something wrong, please let me know.By itself this is mostly OK, but for the ifort users I'll probably add a
comment that -fast also turns on -xHost, and is best used when compiling
and running on the same processor. Like the gfortran option, the things
turned on by -fast can also change results.

The suggestion of using -Og to debug differences caused by high
optimization isn't useful, in my opinion.

I'd also wonder if it's appropriate for these tweets to be about
individual compilers and not the language.

--
Steve Lionel
ISO/IEC JTC1/SC22/WG5 (Fortran) Convenor
Retired Intel Fortran developer/support
Email: firstname at firstnamelastname dot com
Twitter: @DoctorFortran
LinkedIn: https://www.linkedin.com/in/stevelionel
Blog: https://stevelionel.com/drfortran
WG5: https://wg5-fortran.org

Subject	Author
Optimization options	Beliavsky
Re: Optimization options	Steve Lionel