> something like boyer-moore, but for filters.

Well, before implementing custom substring search algorithm for URLFilter::MatchUrlPattern(), I would try to convert the pattern to a RegExp. It should be faster than current naive checker and as fast as any other custom algorithm. RegExps could be compiled on demand and cached.

For the preselection something that utilizes common filtering patterns could be used. The "domain as a dictionary lookup key" should take care of about 3/4 rules.

Additionally, some lookup by path parts as keys could be devised. Google does something similar: https://developers.google.com/safe-browsing/v4/urls-hashing#... .

Both of these lookups could be enabled based on the number of qualifying patterns.

For the rest, the current FilterURLList::Find() can be used. I don't think it differs significantly from the "shortcuts comparison" described here: https://adblockplus.org/en/faq_internal#filters . But either algorithm could be further improved, for example, by sorting those hashes/shortcuts.