XCode is a solution for app development only. Occasionally I dig around looking for quotes, but AFAICT Apple has never claimed they're using clang for all of iOS and OS X. I suspect most of the internals are still built with gcc. Does anyone have evidence either way?
"Apple shipped the Mac OS X 10.8 and iOS 6 releases, and they were built virtually entirely with Clang - llvm-gcc is obsolete."
Another interesting thing:
"We invested major effort into compiler implementation and tuning for the custom Apple CPU design known as the "Apple A6". The exceptional CPU performance of the iPhone 5 was a result of a joint effort between the Apple silicon and LLVM teams."
Good quote, but that "virtually" is interesting. What parts are still using gcc? And is the interpretation that everything using the LLVM backend and not the GNU one?
The A6 quote doesn't mean much. All compilers work hard on device-specific optimizations; you can find similar press releases from Intel every few months.
The components of iOS that are written in C, C++ and Objective-C are all compiled with Clang. The few components that are written in other languages are not.
