[Bug fortran/94578] New: Incorrect assignment of RESHAPE() result to a Fortran pointer

["howisjw at hotmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94578

            Bug ID: 94578
           Summary: Incorrect assignment of RESHAPE() result to a Fortran
                    pointer
           Product: gcc
           Version: 8.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: howisjw at hotmail dot com
  Target Milestone: ---

The other day, I tried to compile a large Fortran code using gcc 8.3.0. In the
code the reshape function is used and the resulting is assigned to a Fortran
pointer. The results are not what I expected to be. I am not sure if it a bug
or if I do something which is not according to the latest Fortran standard. I
created a simple program (see below) to demostrate the problem. 

If I use the tmp array, like

  tmp     = reshape(source=array2d, shape=shape(array1d))
  array1d = tmp

it all works. I have the impression that under-the-hood the result of the
reshape function is stored in array1d using a some kind of memory copy. This
works fine if array1d is contiguous in memory. However, if array1d is a Fortran
pointer (my case) do not have to be contiguous in memory.


program bug_reshape
  implicit none

  type :: value_and_derivatives
     real(kind=8) :: x,s,t,st,ss,tt
     logical      :: up_to_date
  end type value_and_derivatives

  type :: tsolution
     type(value_and_derivatives) :: x, y
  end type tsolution

  type(tsolution), dimension(3*4), target :: solution

  ! Locals
  integer                                            :: i, j
  type(value_and_derivatives), dimension(3,4)        :: array2d
  type(value_and_derivatives), dimension(:), pointer :: array1d
  type(value_and_derivatives), dimension(3*4)        :: tmp

  array1d => solution%x

  do j=1,4
     do i=1,3
        array2d(i,j) = value_and_derivatives(i*j, i, j, 0.1*i*j, 0.1*i, 0.1*j,
.true.)
     end do
  end do
  array1d = reshape(source=array2d, shape=shape(array1d))

  print*,"--- array2d ---"
  do j=1,4
     do i=1,3
        print '(2(i1,1x),6(e15.7,1x),l)',i,j,array2d(i,j)
     end do
  end do

  print*,"--- array1d ---"
  do i=1,12
     print '(i1,1x,6(e15.7,1x),l)',i,array1d(i)
  end do
end program bug_reshape

Jan-Willem