> It's worth a shot.

yeah. it is never too late to revert all the changes anyway. ;-) i'm not trying to stop you from implementing that, just thinking out loudly.

> To be clear, I mean that the pattern
> should be converted into regexp inside the URLFilter::MatchUrlPattern(), after all the
> preselection steps. I have no idea how much overhead would regexp
> creation introduce.

quite a lot. any decent regexp engine compiles expression into internal bytecode of some kind (possibly building kickstart and quick reject tables too), so it is better to at least cache created regexps.

> And its speed would depend hugely on the regexp engine.

here i think we should use the one that is used by Opera Core itself (modules/regexp). it is even JITed, as far as i can see.

> But don't forget that Boyer-Moore doesn't come for free either.

yea, but it is fast enough for small strings. and we can switch to b-m codepath only if we have some «big enough» amount of matches to check (after all possible early rejections).