Try the following example with your compiler: DO I = 1,100 DO J = 1,100 DO K = 1,100 A(I,J,K) = B(I,J,K) + C(I,J,K) ENDDO ENDDO ENDDO And then DO K = 1,100 DO J = 1,100 DO I = 1,100 ...

Try the following example with your compiler:

DO I = 1,100

DO J = 1,100

DO K = 1,100

A(I,J,K) = B(I,J,K) + C(I,J,K)

ENDDO

ENDDO

ENDDO

And then

DO K = 1,100

DO J = 1,100

DO I = 1,100

A(I,J,K) = B(I,J,K) + C(I,J,K)

ENDDO

ENDDO

ENDDO

Does your compiler perform this optimization automatically?