[Bug fortran/31593] Invariant DO loop variables and subroutines

[tkoenig at gcc dot gnu dot org]

------- Comment #23 from tkoenig at gcc dot gnu dot org  2009-08-14 22:05 
-------
(In reply to comment #20)
> Created an attachment (id=18369)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=18369&action=view) [edit]
> updated patch
> 
> Corrected patch, I copied the variables in the wrong order on loop entry,
> clobbering the upper bound if it also happened to be the DO variable.

Hello Tobi,

your patch doesn't help a lot for this test case:

module foo                         
contains                           
  subroutine output(i1,i2,i3,i4,i5)
    print '(5(I0,:" "))',i1,i2,i3,i4,i5
  end subroutine output                
end module foo                         
program main                           
  use foo
  implicit none
  integer :: value
  integer :: p1, p2, p3, p4
  integer :: i

  do value = 750,800
     do i=1, 10
        do p1 = 1, value-2
           do p2 = p1 + 1, value - p1
              do p3 = p2 + 1, (value - (p1 + p2))/2
                 p4 = value - p1 - p2 - p3
                 if (p1 * p2 * p3 * p4 == value * 1000000) &
                 & call output(value,p1,p2,p3,p4)
              end do
           end do
        end do
     end do
  end do
end program main

Without your patch:

tkoe...@gcc16:~/Do$ gfortran -fdump-tree-original -O2 count-4.f90 && time
./a.out > /dev/null

real    0m8.448s
user    0m8.449s
sys     0m0.000s

With your patch:

tkoe...@gcc16:~/Do$ gfortran -fdump-tree-original -O2 count-4.f90 && time
./a.out > /dev/null

real    0m7.772s
user    0m7.768s
sys     0m0.004s

The test case

tkoe...@gcc16:~/Do$ cat count-5.f90
module foo                         
contains                           
  subroutine output(i1,i2,i3,i4,i5)
    print '(5(I0,:" "))',i1,i2,i3,i4,i5
  end subroutine output                
end module foo                         
program main                           
  use foo
  implicit none
  integer :: value
  integer :: p1, p2, p3, p4
  integer :: i

  do value = 750,800
     do i=1, 10
        do p1 = 1, value-2
           do p2 = p1 + 1, value - p1
              do p3 = p2 + 1, (value - (p1 + p2))/2
                 p4 = value - p1 - p2 - p3
                 if (p1 * p2 * p3 * p4 == value * 1000000) &
                 & call output((value),(p1),(p2),(p3),(p4))
              end do
           end do
        end do
     end do
  end do
end program main
tkoe...@gcc16:~/Do$ gfortran -fdump-tree-original -O2 count-5.f90 && time
./a.out > /dev/null

real    0m4.057s
user    0m4.056s

still produces much better code.

I think it would be better to use the original loop variable, and to create a
copy each time it is passed by reference.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31593