You can also refer to PHP vs KPHP vs C++.
KPHP isn't always faster than PHP, but it can be used to speed up your code:
Another essential KPHP aspect is “zero-cost abstractions”. Create an unlimited number of defines and constants — they don't exist at runtime. Simple functions like getters are inlined and have no overhead at all.
KPHP performance compared to PHP:
This situation is quite common. KPHP rarely compiles already existing code without errors. It usually takes some time to rewrite PHP code for it to be compilable with KPHP.
Read more about this in compiling an existing project.
You can organize your project in a way that one part of it would be compiled, and the other would work on PHP.
KPHP is distributed under the GPLv3 license, on behalf of VK.com (V Kontakte LLC).
To communicate with KPHP community, use GitHub issues or a Telegram chat.
You can also take a look at our FAQ page and Roadmap page.
If you've developed a useful PHP library that successfully compiles with KPHP, feel free to share it here.
If you want to contribute to KPHP itself, try to dig into its internals. They're quite hard to take in all at once. Learn about KPHP architecture and examine imaginary contribution scenarios.
Just follow the left menu. KPHP's documentation is organized in a natural learning order.