I have seen that is indeed possible to compile WordPress with HPHP and was wondering… how much faster does it actually make it? I know that HPHP works fastest when it comes to static sites but would it make running WordPress for major sites significantly faster?
I know at the same time that it makes the one-click-upgrade and theme development harder!
Last year, Rasmus Lerdorf, a core member of the PHP team, made this presentation at the Digg offices in which he tries to make WordPress compile under HPHP… after doing his own work to make it fast as he can.
You don’t need to watch the video, the slides are enlightening enough.
The tl;dr is that proof-based optimization of code using proper tools will get you a great speed increase without the hassle of HPHP. Oh, and you need to modify WordPress anyway to get it to compile, as it uses extensions that HPHP does not replicate.