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This is a very sound approach. The main benefit is that all JVM languages can utilize optimizations if the optimizations are in the JVM, thus logic duplication is reduced.

Also, please note that both Clang and GCC use the same approach, except in their cases the programmer typically does not see the intermediary code (which is LLVM for Clang, and a family of intermediate languages for GCC).

http://en.wikipedia.org/wiki/Intermediate_language

Except that, as evidenced by this case, the JVM isn't doing the optimization either!

(Also: it's not a stupid approach. Due to the way the JVM loads things, most of the time you don't know that any particular method won't be overridden later by something that does, in fact, have side effects. There are very few optimizations that could actually be done by the Java compiler.)

The compiler doesn't (shouldn't) know what the runtime system will look like, so it cannot make optimizations as safely or effectively as the JVM can.

Except that, as evidenced by this case, the JVM isn't doing the optimization either!