Codegen had a bug where if you emit a block in astubs that has a getNext() which is also in astubs, it would omit the jump. However, it might visit another block in a first, which is allowed to put code in astubs. Generally the block order was just defined by the order that happened to be in the block list by the time we get there. Change it to emit blocks in the RPO defined by sortCfg for now, after partitioning them into groups for a and astubs. This fixes the bug, and at least makes codegen use a defined order. We later will probably want to see about whether we may be able to avoid more jumps with smarter layout.
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. Join us on #hhvm on freenode.
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 (pdf - print, sign, scan, link) must be signed.
Licence
HipHop VM is licensed under the PHP and Zend licenses except as otherwise noted.