Shameless self promotion: I wrote hussar[0], a tool that uses HHVM for PHP static analysis in projects that can't run HHVM directly. Etsy says "getting [their] code to run on HHVM was relatively easy", but my experience has been the opposite. Previous discussion on HN here: https://news.ycombinator.com/item?id=9071854

[0]: https://github.com/wayfair/hussar