Very very good points! Relatedly: for any performance sensitive code, reading the relevant version of the Intel Optimization manual + a book like Hacker's Deli

Very very good points! Relatedly: for any performance sensitive code, reading the relevant version of the Intel Optimization manual + a book like Hacker's Delight will lead to a lot of good understanding of these trick. (admission: i'm spending a lot of my time staring at ways to make it really really easy to write fast numerical codes, so thinking about the ports on modern CPUs is very very helpful)