http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58043
Bug ID: 58043
Summary: Incorrect behaviour of polymorphic array
Product: gcc
Version: 4.8.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: fortran
Assignee: unassigned at gcc dot gnu.org
Reporter: frank.otto at pci dot uni-heidelberg.de
Created attachment 30580
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=30580&action=edit
test case
The following test case (also attached) produces incorrect output using
gfortran 4.8.1 (also tested: 4.8.0, 4.7.3). It uses a polymorphic array
[dofs(:)] where the polymorphic type [dof_t] contains an allocatable array
[grd(:)]. When accessed through an element of the polymorphic array, the
array descriptor of grd(:) seems wrong.
**** testcase.f90 ****
module types_m
implicit none
type,abstract :: dof_t
integer :: gdim
real(kind=8),allocatable :: grd(:)
contains
procedure(dofinit_if),deferred :: init
end type dof_t
type,extends(dof_t) :: adof_t
contains
procedure :: init => adofinit
end type adof_t
abstract interface
subroutine dofinit_if(dof,gdim,xi,xf)
import :: dof_t
class(dof_t) :: dof
integer :: gdim
real(kind=8) :: xi,xf
end subroutine dofinit_if
end interface
contains
subroutine adofinit(dof,gdim,xi,xf)
class(adof_t) :: dof
integer :: gdim,g
real(kind=8) :: xi,xf,dx
dof%gdim = gdim
allocate(dof%grd(gdim))
dx = (xf-xi)/(gdim-1)
do g=1,gdim
dof%grd(g) = xi + (g-1)*dx
enddo
write (*,'(a)') "---- grd in adofinit ----"
do g=1,gdim
write (*,'(i5,f12.4)') g, dof%grd(g)
enddo
end subroutine adofinit
end module types_m
program main
use types_m
implicit none
class(dof_t),pointer :: dofs(:)
integer :: g
allocate(adof_t :: dofs(1))
call dofs(1)%init(17, -8.d0, 8.d0)
write (*,'(a)') "---- grd in main ----"
do g=1,dofs(1)%gdim
write (*,'(i5,f12.4)') g, dofs(1)%grd(g)
enddo
end program main
**** gfortran version ****
$ gfortran -v
Using built-in specs.
COLLECT_GCC=gfortran
COLLECT_LTO_WRAPPER=/cvos/shared/apps/gcc/4.8.1/libexec/gcc/x86_64-unknown-linux-gnu/4.8.1/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-4.8.1/configure --prefix=/cvos/shared/apps/gcc/4.8.1
--enable-languages=c,c++,fortran,go,objc
--with-gmp=/cvos/shared/apps/gcc/4.8/support
--with-mpfr=/cvos/shared/apps/gcc/4.8/support
--with-mpc=/cvos/shared/apps/gcc/4.8/support
--with-isl=/cvos/shared/apps/gcc/4.8/support
--with-cloog=/cvos/shared/apps/gcc/4.8/support --disable-nls --enable-shared
--enable-threads=posix --with-system-zlib --with-tune=native
Thread model: posix
gcc version 4.8.1 (GCC)
**** Compilation ****
$ gfortran -Wall testcase.f90
(no messages)
**** Observed Output ****
$ ./a.out
---- grd in adofinit ----
1 -8.0000
2 -7.0000
3 -6.0000
4 -5.0000
5 -4.0000
6 -3.0000
7 -2.0000
8 -1.0000
9 0.0000
10 1.0000
11 2.0000
12 3.0000
13 4.0000
14 5.0000
15 6.0000
16 7.0000
17 8.0000
---- grd in main ----
1 -8.0000
2 -1.0000
3 6.0000
4 0.0000
5 0.0000
6 0.0000
7 0.0000
8 0.0000
9 0.0000
10 0.0000
11 0.0000
12 0.0000
13 0.0000
14 0.0000
15 0.0000
16 0.0000
17 0.0000
**** Expected Output ****
Both blocks of numbers should be the same.
When compiled with Intel Fortran 13.1.0, the test case produces the expected
output, and also no warnings are produced.
**** Comments ****
What also doesn't work:
* dof_t%grd as pointer instead of allocatable (same output)
* in main, dofs(:) as allocatable instead of pointer (same output)
What does work:
* Using a scalar [class(dof_t),pointer::dof] polymorphic variable instead
of the polymorphic array.
The observed behaviour looks like something is wrong with the array
descriptor of grd(:), because this array is (in main) traversed with
a too large stride -- only every 7th element is visited. In a larger
program, this behaviour eventually leads to invalid memory access.
