PHP isn't even a good compilation target. There's no native FFI (you can't write pure PHP code that makes arbitrary syscalls), the extension interface exposes extremely brittle guts of the interpreter, it performs very poorly (compared to, e.g., JVM bytecode), and calling user-defined functions to work around the stupid misbehavior of the builtins (e.g., == which isn't even an equivalence relation) is only going to make its performance worse.