XL Fortran Enterprise Edition for AIX : User's Guide - IBM

-qstrict_induction Option
Syntax
-qSTRICT_INDUCtion | -qNOSTRICT_INDUCtion
Prevents the compiler from performing induction (loop counter) variable
optimizations. These optimizations may be unsafe (may alter the semantics of your
program) when there are integer overflow operations involving the induction
variables.
You should avoid specifying -qstrict_induction unless absolutely necessary, as it
may cause performance degradation.
Examples
Consider the following two examples:
Example 1
integer(1) :: i, j
! Variable i can hold a
j = 0 ! maximum value of 127.
do i = 1, 200
j = j + 1
enddo
! Integer overflow occurs when 128th
! iteration of loop is attempted.
Example 2
integer(1) :: i
i = 1_1
! Variable i can hold a maximum
! value of 127.
100 continue
if (i == -127) goto 200
i = i + 1_1 ! occurs and i == -127.
goto 100
200 continue
print *, i
end
! Go to label 200 once decimal overflow
If you compile these examples with the -qstrict_induction option, the compiler
does not perform induction variable optimizations, but the performance of the
code may be affected. If you compile the examples with the -qnostrict_induction
option, the compiler may perform optimizations that may alter the semantics of the
programs.
XL Fortran Compiler-Option Reference 243