3 ms·

You don't want to inline functions that haven't been parsed. If it hasn't been called by the time you are JITing, then it probably isn't going to be on a hot pa

• chrisseaton 8y ago
  If it's been JITed then the AST may well have been discarded after the JIT completed! Doesn't V8 work like that today? You'll need to pass it again even if you have already parsed it! It's not hard to think of worst-cases. Think about an enormous function that you would not want to inline. It's been JITed, or it's running in a byte code interpreter, and the AST has been discarded. In your scheme you'll have to parse it to find it's too big. Huge waste of time, if you can see it's too large from the source code.
  • MikeHolman 8y ago
    You can't throw away your interpreter bytecode, because the JIT code needs to be able to bailout if a guard fails (e.g. if you specialized a var as an int and you get a non-int). So you can always use the size of your bytecode as an inlining heuristic (which is what Chakra does). Of course that wouldn't work before v8 had an interpreter, but they could have used other heuristics. For example, they could have used the size of the AST as a heuristic and saved that even after the AST gets thrown away.