JIT Compiling Code in 5μs

Reminds me of the 2024 blog post Look ma, I wrote a new JIT compiler for PostgreSQL [0]. Both articles lament that Postgres's LLVM-based JIT [1] takes a while to generate code.

> The rarity of JIT compilers makes me believe that implementing a JIT compiler historically was too difficult for it to be worthwhile.

That's only true of writing a JIT from scratch. There's no rarity of JITs, it's just that LLVM (and other frameworks) are often used. Every major interpreter has a JIT compiler. PCRE2 has a JIT compiler. There are JIT frameworks out there with much faster code-generation than LLVM: Cranelift, GNU Lightning, Mir. I doubt they could do code-generation faster than a custom copy-and-patch JIT, but they'd be much faster than LLVM.

[0] https://www.pinaraf.info/2024/03/look-ma-i-wrote-a-new-jit-c... , discussed: https://news.ycombinator.com/item?id=39742916

[1] https://www.postgresql.org/docs/current/jit-reason.html

I recommend Russ Cox's articles on implementing a regex engine: https://swtch.com/~rsc/regexp/

It is very relevant

This is perhaps a little meta, but this was a pleasant read. It’s refreshing to read an article about using an LLM that doesn’t read like it was also written by that LLM.

I might use this approach to generate the stencils for a JIT firewall I’ve been experimenting with.

It also occurs to me that this could be used to generate eBPF byte code on the fly as well

Uhm, Common Lisp, where JIT is not only available but is also manageable: the programmer can decide what deserves to be compiled and what does not.

Besides run time, JIT is available also when the code is compiled or loaded for execution (i.e., do you have a compilation or loading speed-up in mind? no problem, you can also compile that speed-up into native machine code, and so ad infinitum...).

The problem with the approach is that it's not real JIT-compilation, it's just assembly templates with basic substitutions.

By not using LLVM, you're missing all the optimizations it does.

Author here. Let me know if you have any questions about the post or about pgrust.

pgrust sounds very interesting, but with the deep changes there’s no viable path to upstream it - is the end goal to be robust enough that it’ll get wide adoption?

It uses copy-and-patch compilation to archive that

Didn't know that

There’s been a meme circulating about how AI doesn’t help because “code was never the hard part.” I think that’s true in some domains, but in others, writing the code absolutely was the hard part. JIT compilers are a great example of that.

Tcc be like

Nice

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JIT compilation is unsecure.