If every function is marked noexcept, does it make a difference? Either way, the point of C++ exceptions was to make the fast path even faster by moving error handling out of it. Since they had no idea what was wrong, the code evidently was running in the fast path since it was not terminating by throwing exceptions, yet it ran slower merely because of the C++ exception support.

In any case, my point is that C++ features often carry overhead that simply does not exist in C. Being able to get C++ code to run as fast as C code (possibly by not using any C++ features) does not change that.