I'd say that for languages such as Python or Javascript tracing JIT compilers are the only viable approach. Because the languages allow anything you can't make

I'd say that for languages such as Python or Javascript tracing JIT compilers are the only viable approach. Because the languages allow anything you can't make any sensible predictions about types and call graphs at compile time (people tried; didn't work well). The incremental-JIT approach (LuaJIT) has less information to work with, and it's not aware which parts of the program are bottlenecks, so it can't intelligently decide which parts parts need optimization most. The tracing JIT is such an obvious tactic that it should be part of any dynamic language. Measure which parts are slow, then optimize those parts using the parameter type information gathered at runtime. Fall back on original code on type mismatch. The implementation is hairy, but it's a no-brainer conceptually speaking. I suspect that dynamic languages will evolve over the next 10 years to allow for really efficient compilers, but for the current languages such as Javascript I doubt we're ever going to see massive performance improvements.