javadoc has gotten slower in JDK 9. Whilst we have not yet investigated this in detail, we have observed that one significant data structure, the VisibleMemberMap, is computed often and would benefit from caching.

The data structure as a whole should be examined and improved (later), but even without that, simply caching the instances shows a 50% improvement in performance compared to without the cache, and a 30% net improvement over JDK 8 javadoc.