It’s not really copy and patch, the whole point of the copy patch is so you can inline that in your compilation output and it’s a fast baseline interpreter because individual builtin functions are optimized (via the compiler output you’re copying from) and inlined (which is why you need to patch to update what registers are being used. In this model you jit only control flow really, then inline the implementation of each bytecode operation (in contrast to sparkplug [https://v8.dev/blog/sparkplug] which just calls a builtin instead of copy/patch). It’s still JIT which is vastly different than an interpreter.
> JIT will be things of the past
Sorry no. JIT is not going anywhere. They mentioned in the article JIT would be better performance just more effort than they wanted to put in (a good tradeoff!) JIT powers Java, Wasm and Javascript VMs and are certainly the way to get the fastest code because you can give the CPU code that it can do a much better job predicting the next instruction. With interpreters you’re often limited by the indirection of loads when looking up the next function to call, and generating code for the control flow outside calling your “builtins” is precisely what Sparkplug is doing.
At the end of the day, like most of engineering, choose the right tool for the job, which in this case is simplicity (which is often the right choice!), but that doesn’t mean it’s always the right choice. For example if browsers did this then Javascript performance would tank compared to what we get today.
> JIT will be things of the past
Sorry no. JIT is not going anywhere. They mentioned in the article JIT would be better performance just more effort than they wanted to put in (a good tradeoff!) JIT powers Java, Wasm and Javascript VMs and are certainly the way to get the fastest code because you can give the CPU code that it can do a much better job predicting the next instruction. With interpreters you’re often limited by the indirection of loads when looking up the next function to call, and generating code for the control flow outside calling your “builtins” is precisely what Sparkplug is doing.
At the end of the day, like most of engineering, choose the right tool for the job, which in this case is simplicity (which is often the right choice!), but that doesn’t mean it’s always the right choice. For example if browsers did this then Javascript performance would tank compared to what we get today.