From: Harald Anlauf <anlauf@gmx.de>
To: sgk@troutmask.apl.washington.edu,
"Thompson," Matt "(GSFC-610.1)[SCIENCE" SYSTEMS AND APPLICATIONS
"INC]" via Fortran <fortran@gcc.gnu.org>
Cc: Thomas Koenig <tkoenig@netcologne.de>
Subject: Re: [EXTERNAL] Re: Advice with finding speed between O2 and O3
Date: Thu, 25 May 2023 20:51:02 +0200 [thread overview]
Message-ID: <ae39a9bd-6eee-beea-8dbf-5663affe3732@gmx.de> (raw)
In-Reply-To: <ZG+UUqGfELQfcqGk@troutmask.apl.washington.edu>
Am 25.05.23 um 19:01 schrieb Steve Kargl:
> On Thu, May 25, 2023 at 04:05:11PM +0000, Thompson, Matt (GSFC-610.1)[SCIENCE SYSTEMS AND APPLICATIONS INC] via Fortran wrote:
>> Thomas,
>>
>> Well, the code did not change. Period. Neither did the compiler. It was 12.3. (We can't use GCC 13 because it seems not to like something in our advanced Fortran code (lots of OO, submodules, string fun...)).
>>
>> And I did a run with essentially all the GNU checks on (our Debug build mode) and it happily runs!
>>
>> That said, I did some further tests and I am *really* confused. This fails:
>>
>> -O3 -march=haswell -mtune=generic -funroll-loops -g
>>
>> And this works:
>>
>> -O2 -march=haswell -mtune=generic -funroll-loops -g
>>
>> Now I just tried:
>>
>> -O2 -fgcse-after-reload -fipa-cp-clone -floop-interchange -floop-unroll-and-jam -fpeel-loops -fpredictive-commoning -fsplit-loops -fsplit-paths -ftree-loop-distribution -ftree-partial-pre -funroll-completely-grow-size -funswitch-loops -fversion-loops-for-strides -march=haswell -mtune=generic -funroll-loops -g
>>
>> which as far as I can see from the gcc man page:
>>
>> -O3 Optimize yet more. -O3 turns on all optimizations specified by -O2 and also turns on the following optimization flags:
>>
>> -fgcse-after-reload -fipa-cp-clone -floop-interchange -floop-unroll-and-jam -fpeel-loops -fpredictive-commoning -fsplit-loops -fsplit-paths -ftree-loop-distribution -ftree-partial-pre -funswitch-loops
>> -fvect-cost-model=dynamic -fversion-loops-for-strides
>>
>> means I am running essentially -O3.
>>
>> But it works.
>>
>> I'm...baffled. Is there something that *gfortran* enables with -O3 that isn't visible from the *gcc* man page?
>>
When I look at the complete *difference* of
gfortran-12 -c -Q --help=optimizers
between -O2 and -O3, I see other differing parameters:
- -fvect-cost-model=[unlimited|dynamic|cheap|very-cheap] very-cheap
+ -fvect-cost-model=[unlimited|dynamic|cheap|very-cheap] dynamic
Could these be relevant?
Harald
prev parent reply other threads:[~2023-05-25 18:51 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-22 15:31 Thompson, Matt (GSFC-610.1)[SCIENCE SYSTEMS AND APPLICATIONS INC]
2023-05-22 21:36 ` Thomas Koenig
2023-05-25 16:05 ` [EXTERNAL] " Thompson, Matt (GSFC-610.1)[SCIENCE SYSTEMS AND APPLICATIONS INC]
2023-05-25 17:01 ` Steve Kargl
2023-05-25 18:51 ` Harald Anlauf [this message]
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