KAP users should be aware that KAP assumes that the Fortran code that it processes conforms to the Fortran rules. Programs that violate these rules may behave differently after KAP transforms it.
As an example, the following is a program in which the loop control variable is modified during execution of the loop:
DIMENSION A(200) COMMON I J = 10 K = 100 L = 10 DO I=J,K,L A(I) = I CALL SETI ENDDO WRITE (6,*) I,A(I) END SUBROUTINE SETI COMMON I I = 20 END
The output of this program is as follows:
30 30.00000
When the Digital Fortran compiler does not know the value of the
"increment" parameter of a DO loop, it always computes a loop
iteration count, even if the value is subsequently determined by
value propagation. Thus, if the program illegally modifies the loop
control variable I , the loop will still complete in
the correct number of iterations. In this case, no compilation time
or run-time error message is given, even though the program violates
the Fortran 77 standard and language rules.
KAP produces the following when this program is processed:
DIMENSION A(200) COMMON I DO I=10,100,10 A(I) = I CALL SETI END DO WRITE (6, *) I, A(I) END SUBROUTINE SETI COMMON I I = 20 END
This program incurs an access violation at run time. Since
the Digital Fortran compiler sees that the increment value is
a constant, it uses I directly to test for loop
termination. Since I is modified in the loop just
before the test, the loop does not terminate, but at the top
of the loop I is given a new value appropriate
for the iteration number the loop has reached. Eventually
I exceeds 200 and the assignment statement accesses
past A(200) , resulting in the access violation.
A wide variety of incorrect behaviors can result from KAP transformations with "illegal" programs. This possibility (and others of like nature) will need to be considered when evaluating programs whose run-time behavior changes when KAP is used.