[Bug fortran/108665] New: Depenency checking: Run-time loop reversal instead of creating a temporary

[Bug fortran/108665] New: Depenency checking: Run-time loop reversal instead of creating a temporary

[tkoenig at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108665

            Bug ID: 108665
           Summary: Depenency checking: Run-time loop reversal instead of
                    creating a temporary
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tkoenig at gcc dot gnu.org
  Target Milestone: ---

In the Fortran front end, we could sometimes reverse loops at runtime if
dependency analysis shows that either a forward or a backward loop would have
no dependencies.

Example code:

module x
  implicit none
contains
  subroutine foo(a,i,j,n)
    integer, intent(in) :: i, j, n
    real, dimension(:), intent(inout) :: a
    a(i:i+n-1) = a(j:j+n-1) + 10.
  end subroutine foo
  subroutine bar(a,i,j,n)
    real, dimension(:), intent(inout) :: a
    integer,intent(in) :: i, j, n
    integer :: k
    if (i <= j) then
       do k=0, n-1, 1
          a(i+k) = a(j+k) + 10.
       end do
    else
       do k=n-1,0,-1
          a(i+k) = a(j+k) + 10.   
       end do
    end if
  end subroutine bar
end module x

where we create a temporary in foo.