The pervasive view of software performance is that compilers are better than humans at optimizing code, but the few humans who optimize important bits of code to the maximum extent disagree Similarly, computer programs today are increasingly diverging into a state where there is a tiny amount of extremely performance critical code, and a large amount of code where performance is so good on our hardware today that even horribly unoptimized code has no noticeable effect on performance.
Thus, optimizing compilers are useless on the first type of code (humans are better), and useless on the second (performance doesn’t matter). So what good are they at all?