Spamassassin supposedly can precompile rules to allow faster operation. It compiles an optimized matching automaton that will process all the regular expressions in parallel.

Anyway, in order to use it, you need to manuall install some dependencies. They probably can’t be introduced as real dependencies to not enforce them upon people who don’t want to use this feature. So far, I’ve identified

aptitude install re2c gcc libc6-dev make

I’m aware that many people will have the libc6-dev and gcc stuff already installed, and the re2c dependency is well-documented. But I actually had removed the C compiler from my mail server.