Probably you already heard about HHVM . As on their website:
HHVM is an open-source virtual machine designed for executing programs written in Hack and PHP . HHVM uses a just-in-time (JIT) compilation approach to achieve superior performance while maintaining the development flexibility that PHP provides.
Using simple terms – HHVM allows you run scripts written in PHP but much, much more faster. Obviously you the main purpose of HHVM is to run HACK language, but it works pretty good with PHP itself.