For everyone that enjoyed this, there's an entire free online MIT course called Performance Engineering of Software Systems[1] where you'll learn plenty more tricks and common pitfalls like these. You'll also learn how to use tools to debug the low level performance of your programs: looking at cache misses, cpu utilization, time spent per assembly operation and so on. It's pretty cool :)

[1] https://ocw.mit.edu/courses/electrical-engineering-and-compu...