Sun Studio 12: Fortran User's Guide The PIPELOOP=n Directive

The PIPELOOP=n directive requires that you specify SUN after C$PRAGMA.

This directive must appear immediately before a DO loop. n is a positive integer constant, or zero, and asserts to the optimizer a dependence between loop iterations. A value of zero indicates that the loop has no inter-iteration (loop-carried) dependencies and can be freely pipelined by the optimizer. A positive n value implies that the I-th iteration of the loop has a dependency on the (I-n)-th iteration, and can be pipelined at best for only n iterations at a time.

C    We know that the value of K is such that there can be no
C    cross-iteration dependencies (E.g. K>N)
      DO I=1,N
       A(I)=A(I+K) + D(I)
       B(I)=B(I) + A(I)
      END DO

For more information on optimization, see the Fortran Programming Guide.