I know that PHP is compiled to byte code before it is run on the server, and then that byte code can be cached so that the whole script doesn't have to be re-interpreted with every web access.
But can you "compile" php and upload a binary-ish file, which will just be run by the byte code interpreter?
PHP doesn't really get compiled as with many programs. You can use Zend's encoder to make it unreadable though.
The short answer is "no".
The current implementation of PHP is that of an interpreted language. You can argue the theoretical aspects of the fact that any language can technically be interpreted or compiled, but as it stands, the current implementations are such that PHP code requires an interpreter to run, and the interpreter manages the executing environment.
To answer your question about uploading pre-compiled PHP bytecode, it's probably possible, but you'd have to implement a way for the PHP interpreter to read in such a file and work with it. With existing opcode caches out there already, it doesn't seem like a task that would reap much reward.
Googling "PHP compiler" turns up a number of 3rd party solutions:
http://www.roadsend.com/home/index.php?pageID=compiler
phc allows you to compile PHP programs into shared libraries, which can be uploaded to the server. The PHP program is compiled into binaries. It's done in such a way as to support evals, includes, and the entire PHP standard library.
Since the question was first asked, there has been a change to that answer from a flat out "no" to a "kind of"
http://github.com/facebook/hiphop-php/wiki
Hip Hop for PHP is a compiler that takes PHP code and turns it into highly optimized C++ Apparently, some functions are not supported (for example 'explode')
I found this question while looking for more information on how to implement HipHop and thought I'd speak up :)