6.3.4 C*$* assert do (serial)

The C*$* assert do (serial) assertion forces the loop immediately following this assertion to be serial. Additionally, it restricts optimization by forcing all enclosing loops to be serial. Inner loops and other loops inside the same enclosing loop nest, but not enclosing the serial loop, may be optimized. The following code example shows how C*$* assert do (serial) works:

 DO 100 I=1,N
    DO 100 J = 1, N
C*$* ASSERT DO (SERIAL)
          DO 200 K = 1, N
            X(I,J,K) = X(I,J,K) * Y(I,J)
200      CONTINUE
          DO 300 K = 1, N
            X(I,J,K) = X(I,J,K) + Z(I,K)
300      CONTINUE
100      CONTINUE

The assertion forces the DO 100 I loop, the DO 100 J loop, and the DO 200 K loop to be serial. The DO 300 K loop can still be parallelized. In this case, KAP does NOT distribute the I or J loops to try to get a larger optimizable loop.

The following loop code shows an example of when to use C*$* assert do (serial) . X and Y must not process in parallel because they are equivalenced and they overlap in memory. Using C*$* assert do (serial) stops parallel execution of the loop.

C*$*    ASSERT DO (SERIAL)
        DO I = 1,N
           X(I) = Y(I)
        ENDDO

See also the C*$* assert do prefer (concurrent) assertion, Section 6.3.5, and C*$* assert do prefer (serial) , Section 6.3.6.