[Bug tree-optimization/66873] New: fortran variant of outer-1.c not parallelized by autopar

["vries at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66873

            Bug ID: 66873
           Summary: fortran variant of outer-1.c not parallelized by
                    autopar
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

Consider this example, a fortran version of autopar/outer-1.c:
...
program main
  implicit none
  integer, parameter         :: n = 500
  integer, dimension (0:n-1, 0:n-1) :: x
  integer                    :: i, j, ii, jj

  do ii = 0, n - 1
     do jj = 0, n - 1
        x(ii, jj) = ii + jj + 3
     end do
  end do

  do i = 0, n - 1
     do j = 0, n - 1
        if (x(i, j) .ne. i + j + 3) call abort
     end do
  end do

end program main
...

When trying to parallelize this using -O2 -ftree-parallelize-loops=2, it fails
on the dependencies:
...
(Data Dep:
#(Data Ref:
#  bb: 4
#  stmt: x[_12] = _14;
#  ref: x[_12];
#  base_object: x;
#  Access function 0: {{0, +, 1}_3, +, 500}_4
#)
#(Data Ref:
#  bb: 4
#  stmt: x[_12] = _14;
#  ref: x[_12];
#  base_object: x;
#  Access function 0: {{0, +, 1}_3, +, 500}_4
#)
  access_fn_A: {{0, +, 1}_3, +, 500}_4
  access_fn_B: {{0, +, 1}_3, +, 500}_4

 (subscript
  iterations_that_access_an_element_twice_in_A: [0]
  last_conflict: scev_not_known
  iterations_that_access_an_element_twice_in_B: [0]
  last_conflict: scev_not_known
  (Subscript distance: 0 ))
  inner loop index: 0
  loop nest: (3 4 )
  distance_vector:   0   0
  distance_vector: 500  -1
  direction_vector:     =    =
  direction_vector:     +    -
)
  FAILED: data dependencies exist across iterations
...