Comment by a_e_k

If you're on x86-64, the Agner Fog manuals are kind of the bible. Free and he's been keeping them up to date for years. ("Copyright © 2004 - 2026. Last updated 2026-09-10.") I don't know how he does it. And even if you're not on x86-64, you can probably still learn a lot.

https://www.agner.org/optimize/