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From: "burnus at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/51284] New: [OOP] CLASS and VALUE attribute: No copy to temporary done
Date: Wed, 23 Nov 2011 16:44:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51284

             Bug #: 51284
           Summary: [OOP] CLASS and VALUE attribute: No copy to temporary
                    done
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: burnus@gcc.gnu.org
                CC: janus@gcc.gnu.org


The following program fails in several ways. As written, the program fails as
"test" modifies the value of a%i - but it shouldn't:

"A present dummy argument with the VALUE attribute becomes argument associated
with a definable anonymous data object whose initial value is the value of the
actual argument." (12.5.2.3 Argument association).

If one uncomments "test2", it fails with:
  Error: VALUE attribute conflicts with DIMENSION attribute at (1)
However, in Fortran 2008 this restriction is not present:

C557 An entity with the VALUE attribute shall be a dummy data object
     that is not an assumed-size array or a coarray, and does not have
     a coarray ultimate component.
C558 An entity with the VALUE attribute shall not have the ALLOCATABLE,
     INTENT (INOUT), INTENT (OUT), POINTER, or VOLATILE attributes.

Additionally, with the current polymorphic array draft patch the
  b(:)%i  (in "b(:)%i = 8" and "any(b(:)%i /= 8")
causes an ICE (segfault). Doing a "do i=1,8; b(i)%i = 8; done" had a similar
problem.

Finally, I think polymorphic arrays suffer from the same issue as scalar
polymorphic arrays.


Note: A deep copy has to be done, which takes the allocatable components into
account.


module m
  type t
    integer :: i
  end type t
contains
  subroutine test(x)
    class(t), VALUE :: x
    x%i = 5
  end subroutine test
!  subroutine test2(x)
!    class(t), VALUE :: x(:)
!    x(:)%i = 99
!  end subroutine test2
end module m

use m
class(t), allocatable :: a, b(:)
allocate ( t :: a, b(5))
a%i = 2
!b(:)%i = 8
call test(a)
!call test2(b)
if (a%i /= 2) call abort ()
!if (any(b(:)%i /= 8)) call abort ()
end