Facebook is releasing a source code transformer that boosts the performance of PHP. Its called HipHop and has been used to reduce the CPU usage on Facebook by about 50%.

How?

- HipHop transforms PHP’s runtime system and rewrites some of its common extensions.
- Transforms source code into optimized C++ and then uses g++ to compile it.

More here: http://www.computerworld.com/s/article/9151539/Facebook_tool_aims_to_speed_up_PHP