The C++ code I am referring to was hand optimised and maintained for 10+ years before the compiler I am maintaining was fast enough to take over. I never looked at the C++ code myself. I simply use it as the milestone to beat. When I took over the maintenance of the compiler it was 25x slower than the C++ code. It took a lot of work to finally make it faster. I also used the C++ code to compare the output of the compiler and the C++ code. I found quite a few bugs in the C++ code doing that by the way.