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Comment by loeg | Hacker News Reader

And compilers will often create jump tables from large switch statements anyway.

Indeed. At least in my experience, Rust (or LLVM, presumably) will make jump tables from all sorts of nonsense, doing something efficient even when there are gaps in matched values. Manually creating jump tables seems to be a waste of time.

(Actually, it doesn't even need to be a switch statement... Just a succession of `if`s works fine.)

Tables made out of computed gotos (so not exactly function pointers) are supposedly speeding CPython up: https://eli.thegreenplace.net/2012/07/12/computed-goto-for-e...

I've also found this comment in Python 3.6 source code in ceval.c which is where opcode dispatch is: https://pastebin.com/kuV7UfG0

> At least in my experience, Rust (or LLVM, presumably) will make jump tables from all sorts of nonsense, doing something efficient even when there are gaps in matched values. Manually creating jump tables seems to be a waste of time.

I wouldn't say it is always a waste of time just because jump tables can be easier to read and manage when you have a decent number of opcodes. Being able to have all your opcodes in separate functions and then just have one single list that shows exactly what opcode maps to what instruction is really nice:

https://github.com/mkilgore/yaji/blob/master/src/op.c#L336

To each his own though, you're right it likely doesn't matter that much performance wise.

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