Is there (or are there any plans to add) a WebAssembly -> asm.js compiler, so that I can write some code by hand in WebAssembly and still get it to run fast in old browsers? Or are there features of WebAssembly that would be impossible to add in asm.js?

The reason I ask is that asm.js is really painful and cumbersome to write by hand and wasm seems substantially nicer, but I only have small bits of numerical hot loops which I want to use wasm/asm.js for, and I have no desire to bring a bunch of code written in C into my little project.