That’s awesome, I didn’t know SQLite had a bytecode.
Based on my experience writing interpreters, I know that bytecode is faster to interpret.
(Source: I wrote JavaScriptCore’s interpreter and it’s optimizing JITs. I’ve also worked on other language implementations. I’ve seen the AST vs bytecode thing play out more than once.)
Maybe I'm missing something, but the bytecode approach seems really obviously better, just from a memory usage and locality point of view. Scanning an array of bytes or words is obviously going to be faster than traversing a tree of pointers.
So I'd be surprised to find a serious language implementation using a pure AST in its interpreter, without at the very least flattening it to an array!
Edit to add: of course there are some cases where you might actually want the AST approach, as the Sqlite doc is careful to point out. But not very many.
It’s fine to use an AST interpreter if you pair it with really great JITs.
That has its own problems though - using an AST as a shared source of truth for your JIT compilers is cumbersome for implementing stuff like OSR. But from a perf standpoint, it’s probably fine.
Also - say you want to optimize just for startup time, like if the code you’re running has minimal looping or reexecution. Then AST is better because you skip a step before first execution.
Based on my experience writing interpreters, I know that bytecode is faster to interpret.
(Source: I wrote JavaScriptCore’s interpreter and it’s optimizing JITs. I’ve also worked on other language implementations. I’ve seen the AST vs bytecode thing play out more than once.)