gcc/libgomp/testsuite/libgomp.oacc-fortran/kernels-acc-loop-reduction.f90

! { dg-do run }
!
program foo
  IMPLICIT NONE
  INTEGER :: vol = 0

  call bar (vol)

  if (vol .ne. 2) stop 1
end program foo

subroutine bar(vol)
  IMPLICIT NONE
  INTEGER :: vol
  INTEGER :: j

  !$ACC KERNELS
  !$ACC LOOP REDUCTION(+:vol)
  DO j=1,2
     vol = vol + 1
  ENDDO
  !$ACC END KERNELS
end subroutine bar