HHVM is a just-in-time compiler for PHP used by Facebook to serve billions of requests each day. This talk will give a quick overview of HHVM's history and architecture, followed by a deep dive into what made C++ the language of choice for writing HHVM.
C++ hits a sweet spot between performance and control on one end, and safety, maintainability, and convenience on the other.
The topics we’ll cover will include:
- how to call into generated machine code from C++;
- taking advantage of C++'s power to control "unsafe" details with memory including how memory is allocated, field size and layout, unions, reinterpret_casts, bit-stealing;
- integrating generated machine code with C++ exception handling and C++ profiling tools;
- leveraging templates and using the X Macro technique to improve performance and maintainability;
- and taking advantage of new C++11 features like unrestricted unions and move constructors.
Finally, we'll go over some obstacles we encountered such as generating machine code that calls C++ virtual methods, and how C++'s superb flexibility allowed us to work around these obstacles.
