4.5.14 /max_invariant_if_growth, /miifg, (/miifg=500)

When a loop contains an IF statement whose condition does not change from one iteration to another, the same test must be repeated for every iteration. The code can often be made more efficient by floating the IF outside the loop and putting the THEN and ELSE sections into their own loops.

This gets more complicated when there is other code in the loop, because a copy of it must be included in both the THEN and ELSE loops. The /max_invariant_if_growth qualifier allows you to limit the total number of additional lines of code generated in each program unit through invariant-IF restructuring.

The /miifg setting is the maximum number of lines to which a program unit may grow due to invariant-IF floating. If restructuring a loop with invariant IFs would cause the size of the program unit to exceed this limit, the restructuring will not be performed. For example, if /miifg=500 and the original size of a subroutine was 450 noncomment lines, then at most 50 additional lines may be added by invariant-IF floating. Since other KAP transformations can add or delete lines, the number of lines actually added by invariant-IF floating and the final size of a program unit may differ from what the /miifg value alone would cause.

This can be controlled on a loop-by-loop basis with the C*$* max_invariant_if_growth (<integer>) directive. The maximum amount of additional code generated in a single loop through invariant-IF floating can be limited with the /each_invariant_ if_growth qualifier.

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Command-Line Qualifiers