llSubStringIndex and llListFindList with min=-1 allow optimizing this:
if (llListFindList(...) < 0) -> if (~llListFindList(...))
That has been implemented since long, but we didn't have the data.
This solves a long-standing issue where we needed more data about LSL functions than just whether it's side-effect-free.
There's still some debug code, which is kept for history purposes.