[Patch] Fortran: Fix Array dependency with local coarrays [PR98913] (was: Re: A question about coarrays and -Warray-temporaries)

[Tobias Burnus <tobias@codesourcery.com>]

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Hi all,

the attached patch now handles -fcoarray=single and access to the local
image like no coarray access, using the same check a before.

Actually, I think we could remove the if (..coarray..) check completely:
For 'single', it is like no coarrays; for 'lib' both AA[remote] =... and
"AA = ... AA[remove]" will create a function call and uses already
temporaries. I don't know what 'native'/'threads' does – but either it
the image index is different, then no temporary is needed at all – or it
is the same (in particular: this_image / not present), but then the
noncoarray analysis would work.

(Knowing that for i != this_image(), AA and AA[i] – or i /= j for AA[i]
and AA[j] – we could further relax the checks, but I don't think that
that's needed.)

Hence: Is the patch OK for the trunk? Or should we completely get rid of
if-conditional block?

Tobias

On 01.02.21 12:52, Tobias Burnus wrote:

> On 01.02.21 08:42, Thomas Koenig via Fortran wrote:
>>> 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. [...]
>> 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.
> I have now filled https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98913
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Fortran: Fix Array dependency with local coarrays [PR98913]

gcc/fortran/ChangeLog:

	PR fortran/98913
	* dependency.c (gfc_dep_resolver): Treat local access
	to coarrays like any array access in dependency analysis.

gcc/testsuite/ChangeLog:

	PR fortran/98913
	* gfortran.dg/coarray/array_temporary.f90: New test.

 gcc/fortran/dependency.c                           | 11 +++-
 .../gfortran.dg/coarray/array_temporary.f90        | 74 ++++++++++++++++++++++
 2 files changed, 83 insertions(+), 2 deletions(-)

diff --git a/gcc/fortran/dependency.c b/gcc/fortran/dependency.c
index c9baca80cbc..0de5d093aab 100644
--- a/gcc/fortran/dependency.c
+++ b/gcc/fortran/dependency.c
@@ -30,6 +30,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "dependency.h"
 #include "constructor.h"
 #include "arith.h"
+#include "options.h"
 
 /* static declarations */
 /* Enums  */
@@ -2143,8 +2144,14 @@ gfc_dep_resolver (gfc_ref *lref, gfc_ref *rref, gfc_reverse *reverse,
 
 	case REF_ARRAY:
 
-	  /* For now, treat all coarrays as dangerous.  */
-	  if (lref->u.ar.codimen || rref->u.ar.codimen)
+	  /* For now, treat all nonlocal coarrays as dangerous.  */
+	  if (flag_coarray != GFC_FCOARRAY_SINGLE
+	      && ((lref->u.ar.codimen
+		   && lref->u.ar.dimen_type[lref->u.ar.dimen]
+		      != DIMEN_THIS_IMAGE)
+		  || (rref->u.ar.codimen
+		      && lref->u.ar.dimen_type[lref->u.ar.dimen]
+			 != DIMEN_THIS_IMAGE)))
 	    return 1;
 
 	  if (ref_same_as_full_array (lref, rref))
diff --git a/gcc/testsuite/gfortran.dg/coarray/array_temporary.f90 b/gcc/testsuite/gfortran.dg/coarray/array_temporary.f90
new file mode 100644
index 00000000000..86460a7c282
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/coarray/array_temporary.f90
@@ -0,0 +1,74 @@
+! { dg-do compile }
+! { dg-additional-options "-Warray-temporaries" }
+!
+! PR fortran/98913
+!
+! Contributed by Jorge D'Elia
+!
+! Did create an array temporary for local access to coarray
+! (but not for identical noncoarray use).
+!
+
+program test
+  implicit none
+  integer, parameter :: iin = kind (1)     
+  integer, parameter :: idp = kind (1.0d0) 
+  real    (kind=idp), allocatable :: AA (:,:)[:]
+  real    (kind=idp), allocatable :: BB (:,:)
+  real    (kind=idp), allocatable :: UU (:)
+  integer (kind=iin) :: nn, n1, n2
+  integer (kind=iin) :: j, k, k1
+  !
+  nn =  5
+  n1 =  1
+  n2 = 10
+  !
+  allocate (AA (1:nn,n1:n2)[*])
+  allocate (BB (1:nn,n1:n2))
+  allocate (UU (1:nn))
+  !
+  k  = 1
+  k1 = k + 1
+  !
+  AA = 1.0_idp
+  BB = 1.0_idp
+  UU = 2.0_idp
+
+  ! AA - coarrays
+  ! No temporary needed:
+  do  j = 1, nn
+    AA (k1:nn,j) = AA (k1:nn,j) - UU (k1:nn) * AA (k,j)  ! { dg-bogus "Creating array temporary" }
+  end do
+  do  j = 1, nn
+    AA (k1:nn,j) = AA (k1:nn,j) - UU (k1:nn) * AA (k,j) - UU(k) * AA (k1-1:nn-1,j)  ! { dg-bogus "Creating array temporary" }
+  end do
+  do  j = 1, nn
+    AA (k1:nn,j) = AA (k1:nn,j) - UU (k1:nn) * AA (k,j) - UU(k) * AA (k1+1:nn+1,j)  ! { dg-bogus "Creating array temporary" }
+  end do
+
+  ! But:
+  do  j = 1, nn
+    AA (k1:nn,j) = AA (k1-1:nn-1,j) - UU (k1:nn) * AA (k,j) - UU(k) * AA (k1+1:nn+1,j)  ! { dg-warning "Creating array temporary" }
+  end do
+
+  ! BB - no coarrays
+  ! No temporary needed:
+  do  j = 1, nn
+    BB (k1:nn,j) = BB (k1:nn,j) - UU (k1:nn) * BB (k,j)  ! { dg-bogus "Creating array temporary" }
+  end do
+  do  j = 1, nn
+    BB (k1:nn,j) = BB (k1:nn,j) - UU (k1:nn) * BB (k,j) - UU(k) * BB (k1-1:nn-1,j)  ! { dg-bogus "Creating array temporary" }
+  end do
+  do  j = 1, nn
+    BB (k1:nn,j) = BB (k1:nn,j) - UU (k1:nn) * BB (k,j) - UU(k) * BB (k1+1:nn+1,j)  ! { dg-bogus "Creating array temporary" }
+  end do
+
+  ! But:
+  do  j = 1, nn
+    BB (k1:nn,j) = BB (k1-1:nn-1,j) - UU (k1:nn) * BB (k,j) - UU(k) * BB (k1+1:nn+1,j)  ! { dg-warning "Creating array temporary" }
+  end do
+
+  deallocate (AA)
+  deallocate (BB)
+  deallocate (UU)
+end program test