This is often true for SPEC, but not true for real world code. Or at least, we extensively tested this at Google, before, during, and after the move to LLVM.

This is often true for SPEC, but not true for real world code. Or at least, we extensively tested this at Google, before, during, and after the move to LLVM. On many thousands of libraries, binaries, etc, made up of hundreds of millions of lines of C++. While there were wins and losses, on average, LLVM was a consistent net positive. That was true despite having spent 5+ years of having a large team dedicated to doing nothing but finding places to improve performance of GCC compiled code (and contributing back patches), and doing so very successfully. That said, as time approaches infinity, the compilers are going to generate the best code for the things that someone took the time to analyze and make the compiler better at. There is, in the end, no magic that makes GCC better than LLVM or vice versa. The vast majority of it is tuning and improving things little by little for whatever targets someone is trying to improve.