The compiler used, Clang 13.0.0, does indeed optimize out everything except for the "return 0;" at the end unless you compile with -O0 to disable optimization.

The compiler used, Clang 13.0.0, does indeed optimize out everything except for the "return 0;" at the end unless you compile with -O0 to disable optimization. I'm not sure whether the author benchmarked with -O0 or benchmarked a no-op, but either one is probably a mistake.