Among other reasons, I'd guess this is Apple's attempt at modernization. The GCC/libc/libstdc++ codebase has been around for ages, and has accumulated cruft. St

Among other reasons, I'd guess this is Apple's attempt at modernization. The GCC/libc/libstdc++ codebase has been around for ages, and has accumulated cruft. Starting from scratch isn't always a solution, but in cases like this I think it can be. Modernizing the compiler (via clang/LLVM) is a great step forward, but modernizing the C++ libraries to take advantage of the new compiler infrastructure is a sensible step 2. If they can in fact speed up compilation speed and memory requirements (both at compile-time and run-time), as well as providing link-time and run-time optimization, it could be a big win, especially for large C++ projects (such as Mozilla, KDE, Qt, etc.).