real function foo(i, y)
  implicit none (type, external)
  interface
    subroutine print_i(i); integer, intent(in) :: i; end
    subroutine bar(); end
  end interface 
  integer :: i
  real :: y
  foo = 0.0
  call print_i(i)
  i = 5
  call bar()  ! < this prevents optimizing the sin(y) away
  if (i == 5) return
  foo = sin(y)
end