I want to add a new argument to translateTracelet. Rather than plumbing it through the many functions in the translation stack, let's use an options struct. Dealing with the many bools we had flying around controlling hhir was complicating things, so I removed m_useHHIR and collapsed them all into an "interp" bool in TranslArgs. I removed any code that was clearly unreachable from these changes.
HipHop VM for PHP 
HipHop VM (HHVM) is a new open-source virtual machine designed for executing programs written in PHP. HHVM uses a just-in-time compilation approach to achieve superior performance while maintaining the flexibility that PHP developers are accustomed to. HipHop VM (and before it HPHPc) has realized > 5x increase in throughput for Facebook compared with Zend PHP 5.2.
HipHop is most commonly run as a standalone server, replacing both Apache and modphp.
Installing
You can install a prebuilt package or compile from source.
Running
You can run standalone programs just by passing them to hhvm: hhvm my_script.php.
HipHop bundles in a webserver. So if you want to run on port 80 with document root /var/www:
sudo hhvm -m server /var/www
For anything more complicated, you'll want to make a config.hdf and run sudo hhvm -m server -c config.hdf.
Contributing
We'd love to have your help in making HipHop better. If you run into problems, please open an issue, or better yet, fork us and send a pull request.
If you want to help but don't know where to start, try fixing some of the Zend tests that don't pass. You can run them with hphp/test/run. When they work, move them to zend/good and send a pull request.
Before changes can be accepted a Contributors Licensing Agreement must be signed.
Licence
HipHop VM is licensed under the PHP and Zend licenses except as otherwise noted.