Implemented smart intrinsic / builtin system.  When you use trivial math functions like "pow", if they don't exist as a builtin, the compiler will implement its own versions, likewise, if a compiler builtin depends on a function that exists, it will use it, likewise if it doesn't it will implement it.  If you explicitally use __builtin_ (prefixed) versions, the compiler again will select the best option it can, be it a combination of both builtins and compiler builtins, all compiler builtins, OR, all builtins (most performant).