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Subject: Re: A question about coarrays and -Warray-temporaries
To: Jorge D'Elia <jdelia@cimec.unl.edu.ar>, Gfortran List <fortran@gcc.gnu.org>
References: <121178681.597.1612108263047.JavaMail.zimbra@intec.unl.edu.ar>
From: Thomas Koenig <tkoenig@netcologne.de>
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Date: Mon, 1 Feb 2021 08:42:19 +0100
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Hi Jorge,

> I have a question with -Warray-temporaries in the test below.
> 
> With the AA coarray that warning appears in the first loop (on its local part),
> but not with the BB array with the same task, i.e.
> 
> 
> $ gfortran --version
> GNU Fortran (GCC) 11.0.0 20210125 (experimental)
> Copyright (C) 2021 Free Software Foundation, Inc.
> 
> $ gfortran -march=native -mtune=native -Ofast -fcheck=all -fcoarray=single -std=f2018 -Wall -Wextra -Warray-temporaries -o test.exe test.f90
> test.f90:37:19:
> 
>     37 |     AA (k1:nn,j) = AA (k1:nn,j) - UU (k1:nn) * AA (k,j)
>        |                   1
> Warning: Creating array temporary at (1) [-Warray-temporaries]
> 
> 
> Why this difference in behavior? Is it ok?

It seems that dependency checking does not detect that no overlap
can exist in that case, and so generates a temporary.  Probably,
dependency checking was not updated when coarrays were introduced.

This is a missed optimization, not a correctness issue.

Best regards

	Thomas