The important bit is from the Safari guys: "We don't currently cache the bytecode (or the native code). It is an option we have considered, however, currently,

The important bit is from the Safari guys: "We don't currently cache the bytecode (or the native code). It is an option we have considered, however, currently, code generation is a trivial portion of JS execution time (< 2%), so we're not pursuing this at the moment." Basically, it's not going to be a bigger saver compared to all the other parts of the process (e.g. fetching the file over the network).