> assume that compilers have gotten a little better at optimization
Again: you're comparing the performance of different algorithms. A compiler won't turn bubblesort into quicksort.
Again: you're comparing the performance of different algorithms. A compiler won't turn bubblesort into quicksort.
If you show a modern compiler the typical idiomatic blob of code for counting the set bits in a word in a language like C, the compiler goes "Oh, popcount I know this" and when targeting modern CPUs it emits a single instruction, the popcount instruction for that CPU.
In APL idiom recognition was essential to making even a halfway decent compiler. It's easy, and idiomatic, to write APL which would be tremendously wasteful if implemented naively, while recognising common idioms could remove lots of that waste without needing the level of sophistication modern compilers have during optimisation.
Because the compiler knows about idioms you should not try to optimise your programs by writing non-idiomatic code until you've determined you have a performance problem and the non-idiomatic code is identified as a way to fix it. Otherwise it may be that the compiler improves and now your code is not only harder to maintain it also has worse performance than the idiomatic solution.
The programmer can understand these domain characteristics but the compiler certainly can't. If code isn't running qsort(), this could be a mistake, but may also be an optimization.
(But no, I'm not expecting AI driven compilers anytime soon)