[Bug fortran/89204] New: -floop-interchange has no effect on Fortran code

[chinoune.mehdi at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89204

            Bug ID: 89204
           Summary: -floop-interchange has no effect on Fortran code
           Product: gcc
           Version: 8.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: chinoune.mehdi at hotmail dot com
  Target Milestone: ---

On 7 Dec 2017 Bin Cheng had introduced a better implementation of
-floop-interchange
https://gcc.gnu.org/ml/gcc-patches/2017-12/msg00360.html

bou it looks like it doesn't affect Fortran

#define M 2048
int a[M][M], b[M][M], c[M][M];
void matrix_mul (int n)
{
      for (int k = 0; k < n; k++)
    for (int j = 0; j < n; j++)
  for (int i = 0; i < n; i++)
        c[i][j] = c[i][j] + a[i][k]*b[k][j];
}

static void init (int i)
{
  for (int j = 0; j < M; j++)
    {
      a[i][j] = i;
      b[i][j] = j;
      c[i][j] = 0;
    }
}

int main (void)
{
  for (int i = 0; i < M; ++i)
    init (i);

  matrix_mul (M);

  return 0;
}


gcc-8 -O2 -floop-interchange -fopt-info loop-interchange-7.c -o test           
     loop-interchange-7.c:11:7: note: loops interchanged in loop nest
time ./test                                                                    
                                                                               
                                                                          real 
  0m7.759s                                                                     
                                                               user    0m7.656s
                                                                               
                                                    sys     0m0.031s

module mod_
  implicit none
  integer, parameter :: m = 2048
  integer :: a(m,m), b(m,m), c(m,m)

contains

  subroutine matrix_mul(n)
    integer, intent(in) :: n
    integer :: i, j, k

    do i = 1, n
      do j = 1, n
        do k = 1, n
          c(i,j) = c(i,j) + a(i,k)*b(k,j)
        end do
      end do
    end do

  end subroutine matrix_mul

  subroutine init(i)
    integer, intent(in) :: i
    integer :: j

    a(i,:) = i
    do j = 1, m
      b(i,j) = j
    end do

  end subroutine init

end module mod_

program main
  use mod_
  implicit none
  integer :: i

  c = 0
  do i = 1, m
    call init(i)
  end do

  call matrix_mul(m)

end program main

gfortran-8 -O2 -floop-interchange -fopt-info loop-interchange-7.f90 -o test
time ./test                                                                    
                                                                               
                                                                          real 
  1m30.447s                                                                    
                                                               user   
1m30.266s                                                                      
                                                             sys     0m0.063s