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Building a baseline JIT for Lua automatically
- djwatson24 3y agoDeegen is my research meta-compiler to make high-performance VMs easier to write. Deegen takes in a semantic description of the VM bytecodes in C++, and use it as the single source of truth to automatically generate a high-performance VM at build time
- celeritascelery 3y agoI don’t understand how you can remove the calls with copy-and-patch. It seems like you would have to inline evaluate_lhs and evaluate_rhs to remove calls completely.
- sillycross 3y agoLook at the CPS-version of the add.
- celeritascelery 3y agoI saw that. I think I understand a little better. The CPS is to remove the calls between bytecodes, but wouldn’t do anything about lua function calls.
- sillycross 3y agoThat's correct. Lua function calls are not that easy to remove, as function is first-class value in Lua so can be redefined at any time. To remove a function call, you need speculative compilation and OSR-exit, which is outside the job of the baseline JIT.
- russellsprouts 3y ago> To solve [forward branches], those bytecodes would push information about how the branch destination address shall be fixed up into a late-patch buffer. This reminds me of how Forth `if` and `then` can be compiled in a single pass -- `if` writes the branch instruction and pushes the current instruction pointer to the stack, and `then` pops it and patches the instruction to point to the current instruction pointer.
- sillycross 3y agoThat's an interesting approach :) Though it only works if the control flow in the language is exactly "paired" (no continue/break, no goto, etc), I guess?
- celeritascelery 3y agoGreat work! This was a very interesting read. A lot of clever approaches here to make a generic JIT. How would one try out deegen?