That is roughly the design that OdinMonkey, the Firefox asm.js compiler, uses: verify the type information, then dump it all onto the high performance JS compil

That is roughly the design that OdinMonkey, the Firefox asm.js compiler, uses: verify the type information, then dump it all onto the high performance JS compiler backend. Two big advantages of an AOT approach like OdinMonkey are: 1. Consistency. You don't have to worry that some critical bit of type information will suddenly start to fail to be propagated all the way through multiple stages. This isn't really a problem for standard benchmarks, which are closely watched for regressions, but can be a problem for random code in the wild. JIT heuristics are complex. 2. Startup speed. AOT does not have to go through all of the various warmup phases, which are needed by JITs both to avoid wasting time on optimizing code that is not important for perf and to get type hints.