Learning about how compilers optimize code isn't really knowledge that goes out of date. Yes, things get reshuffled or new ideas appear, but everything builds on what's already there.

You'd never want (except in extreme desperation) to use this knowledge to to justify undefined behavior in your code. You use it to make sure you don't have any UB around! Strategies like "I wrote a null pointer check, why isn't it showing up anywhere in the assembly?" can be really helpful to resolve problems.