[Bug fortran/53851] New: Automatic silent allocation/deallocation of allocatable variables in several instances

["liluli2011 at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53851

             Bug #: 53851
           Summary: Automatic silent allocation/deallocation of
                    allocatable variables in several instances
    Classification: Unclassified
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: liluli2011@gmail.com


I have found that gfortran (v4.6) performs implicit allocation and deallocation
of allocatable variables when these are assigned values using a constructor,
like in the example code below. I wonder whether this is intentional and
complying with the Fortran standard. I have checked with ifort and there seems
not to be such implicit allocation/deallocation for it (neither gfortran nor
ifort compilers give compilation or execution error messages in connection with
the example below, but the respective outputs are very different). 


   implicit none
   integer, allocatable, dimension(:)   :: vec
   integer, allocatable, dimension(:,:) :: aa
   integer :: i

!  allocate ( vec(20) )
   vec = (/ ( 1, -1, i = 1, 20 ) /)
   print*, "vector size", size(vec)

!  allocate ( aa(4,4) )
   aa = reshape ( vec , shape = (/ 4,4 /) ) ! It is like reshape implies a
silent previous allocation of an otherwise not explicitly allocated variable
   print*, "array shape", shape(aa)
   do i = 1, 4
     print*, aa(i,:)
   end do

!  deallocate ( aa ) ; allocate ( aa(5,5) )
   aa = reshape ( vec , shape = (/ 5,5 /) ) ! Now the variable is reallocated
implicitly to a new shape without having been explicitly deallocated
   print*, "new array shape", shape(aa)
   do i = 1, 5
     print*, aa(i,:)
   end do

   vec = (/ ( 1, -1, i = 1, 25 ) /)  ! same for this rank-1 array
   print*, "new vector size", size(vec)

   end program