Facebook HipHop & CodeIgniter ? What do you think?

[eluser]Michael Wales[/eluser]
It compiles PHP down into C++ (not C) and it's not recommended if you are on a shared host.

In all honesty, very few people will see any sort of performance gain out of HipHop. You have to have millions and millions of visitors concurrently for you to even start worrying about CPU usage. You'll be better served optimizing your input/output (database calls, caching, etc).

Additionally, HipHop only transforms a subset of the PHP language. Not sure if all of CI fits within this subset they have selected, the developers have said they only left out features that weren't commonly used (eval() for example).