INDEPENDENT Loops

HPF gives additional opportunities for parallel implementation by using the INDEPENDENT directive to assert that the iterations of a do-loop can be done independently---that is, in any order or concurrently---without affecting the result . In effect, this directive changes a do-loop from an implicitly parallel construct to an explicitly parallel construct.

 The INDEPENDENT directive must instantaneously precede the do-loop to which it applies. In its easiest form, it has no additional argument and asserts simply that no iteration of the do-loop can affect any other iteration.

Example 9

In the following code fragment, the directives indicate that the outer two loops are independent. The inner loop assigns the elements of A repeatedly and hence it is not independent.

!HPF$   INDEPENDENT

do i=1,n1  ! Loop over i independent

!HPF$   INDEPENDENT

do j=1,n2      ! Loop over j independent

do k=1,n3          ! Inner loop not independent

A(i,j) = A(i,j) + B(i,j,k)*C(i,j)

enddo enddo

enddo