Macros are wonderful, but intuitively it seems very limited in scope wrt compile-time optimizations.

For example, how would you do dataflow analysis at compile-time (which is necessary for a plethora of optimizations) with just macros?

JVM does that for you. However you're free to do all sorts of kinds of optimizations that the JVM simply can't do. Think about a in-memory logic engine that's running during compilation - you can introduce relations which influence how code further down the line is compiled via macros.

Please explain?