On the PHPClasses.org blog today there's a new post that talks about source code compilers and a few of the popular PHP compilers to help you optimize your code.
Several PHP compilers existed since many years ago, but the fact that it is actually Facebook releasing their [HipHop] compiler made it a very relevant matter for PHP developers, as Facebook is currently the busiest site in the world that is developed mostly in PHP.
He briefly explains what compilers can do for you (with diagrams) and takes a look at some of the native machine code compilers like Roadsend, PHC Open Source Compiler and Facebook's HipHop. He's also run a few benchmarks to show the performance of the resulting compiled code from each compiler. Some general conclusions are also included like dynamic vs. static PHP, opcode caching and the effects of I/O operations on script execution.