While post body contains control flow, it can be simple arithmetic operation instead and it will lead to the similar result, so not the control flow itself causing this. It seems more complex closure blocks some optimizations here, thus quicksort having less instructions. I suspect that complex closure was outlined to a separate fn, and not copied to quicksort anymore.

thank you! Oh. it seems user is blocked on lemmy.ml or something like that, so i cannot participate in this discussion or even see the post and answers within my instance.

Since I cannot reply where, you can post my reply if you wish: 2 points:

1. more complex closure and not only control flow, it can be simple arithmetic expression as well, results in actually smaller assembly on arm-unknown-linux-gnueabihf target.
2. I don't think the loop unrolling plays a big role here. sort_unstable_by() is using quicksort and I suspect that complex closure was outlined to a separate fn, and not copied to quicksort anymore.