alt Hacker NewsTo make a more specific example, if you malloc()/free() within a loop, it's unlikely that the compiler will fix that for you. However, moving those calls outside of the loop (plus maybe add some realloc()s within, only if needed) is probably going to perform better.
That is something that can be easily found and usually fixed with trivial profiling. I'm more talking about data locality instead of pointer chasing. Once you set up a pointer-chasing data infrastructure changing that means rewriting most of your application.