Hello all, I have hit a snag in my attempt to add a JIT backend to Guile: I don't know where to store the JITed code.
There was a discussion of this a few weeks ago in which it was decided to try to make a simple and quick JIT engine that would be invisible to Scheme, hoping to eventually make a full AOT compilation engine using GCC. I am working on this JIT engine. What I need in this is some way to stash the JIT code I've made for a procedure in such a way that I can get it back again if I need to run the same procedure again. My current attempt tries to put it in the struct scm_objcode structure as an extra pointer, but the trouble is that scm_objcodes are made directly from bytecode, by just casting the bytecode to a struct scm_objcode. That by itself wouldn't be a terrible problem, because I can rearrange things in memory behind-the-scenes to hide the extra pointer, but objcodes can also be embedded in other objcodes. In order to make this work correctly, I'd either have to scan every bytecode that becomes an objcode, find any embedded objcodes, and add space for the new pointer, or modify the bytecode compiler to leave extra room. Of these two, I think the second option would be best because it would be faster, but then the fact that the objcode structure has an extra pointer is trickling up to Scheme code, and I'm not sure where the abstraction leakage would stop. (Bytecode? Assembly code?) I could fix this by not allowing objcode slices, and instead having some sort of indirection, but that removes some efficiency that might be important. Another option is to store the JITed code with the procedure object, but a procedure is already four machine words, and making it any bigger could mess up the machine cache. Can anyone suggest a solution? Thanks Noah