The page claims the C program can do 550 million loop iterations in one second. That's exactly what you would expect from an average laptop. So the loop clearly

The page claims the C program can do 550 million loop iterations in one second. That's exactly what you would expect from an average laptop. So the loop clearly isn't getting optimized out in the executable used by the authors. If you compile with -O0 you can confirm this for yourself. You can also see that in later examples printf() statements are added to stymie the optimizer.