I haven’t tried compiling this myself, but gcc does different things with a -march=x flag compared to specifying -mavx2, directly, mostly because -march implies

I haven’t tried compiling this myself, but gcc does different things with a -march=x flag compared to specifying -mavx2, directly, mostly because -march implies -mtune. Trying -march=haswell might give closer results. On the other hand, if using an older gcc and it can’t identify your processor, march=native will result in mtune=generic and much head scratching with results.