Retrofitting JIT Compilers into C Interpreters

sgbeal

i tend to think of myself as a computing nerd, but posts like this one make me realize that i don't even rate on the computing nerd scale.

mwkaufma

TL;DR compile with a fork of LLVM that enables runtime IR tracing. Very clever!

fuhsnn

Took me a while to figure out whether it's interpreters for C programs or if there's a particular class of interpreters called "C". Turns out it's about interpreters implemented in C that they use modified LLVM to do the retrofitting, but couldn't it be applicable for other languages with LLVM IR, or other switch-in-a-loop patterns in C?

djwatson24

It's quite impressive they're able to take nearly arbitrary C and do this! Very similar to what pypy is doing here, but for C, and not a python subset. However not without downsides. It sounds like average code is only 2x faster than Lua, vs. LuaJit which is often 5-10x faster.

linzhangrun

It's truly a good thing to see a project like this in the era of Vibe Coding taking flight :)

measurablefunc

Why do they need to change LLVM? Why can't they make this another LLVM IR pass?

9fwfj9r

Those interested in this type of work can also visit https://cfallin.org/blog/2024/08/28/weval/ . The difference is that they use this technique to derive an AOT compiler.