This seems counter-intuitive to people who don't write compilers, but a language that compiles to C++ can perform "better than C++" because it can emit code that no human would bother writing, usually taking advantage of information available in the source language that couldn't be safely determined by the C++ compiler alone. Whole program optimization, for example, allows you to do a lot of aggressive reorganization of code that would be very ugly if done by hand (think of putting all your code in one file and putting everything in an anonymous namespace).