Depends on what you mean by optimization standards, I guess. But a bare minimum for any compiler that wants to call itself optimizing is register allocation on

Depends on what you mean by optimization standards, I guess. But a bare minimum for any compiler that wants to call itself optimizing is register allocation on whole functions. For that you need to build a representation of a whole function, do liveness analysis on it, then do the actual register assignment and spill code generation. That's at least three passes.