JIT compiling C++ is definitely the slowest thing we do. However, we're working on two different codegen modes.

1. C++

2. LLVM IR

The IR is much faster to compile, but its perf isn't nearly as good. This is meant to be a nice trade off, during iteration, so that you can use C++ codegen for your release artifact, but stick with IR when you're REPLing. The IR gen is still unstable right now, for the alpha, but we'll have both solidified this year.