@code_native just lets you look at generated code, but Julia also uses macros frequently to give the compiler hints about how to compile your code. Some examples are @inbounds which disables bounds checks, @fastmath which is the local version of C/Fortran's --math-mode=fast, @simd which lets the compiler assume it can re-order loops (it will do so anyway if it can prove you won't notice). If you need more fine grained control (which is very rare) you can also emit LLVM bytecode (or direct assembly) directly.