c4 VS AoikC4x86Study

This part is not terribly difficult, though,—Forth implementations have long explored[1] the road from emiting a list of VM instructions (“token threading”) to emitting a list VM instruction implementation entry points (both “indirect” and “direct threading”, arguably) to emitting a stream of call instructions targeting said entry points (“subroutine threading”) to copying the implementation bodies there (“inline threading”).

With sufficient dedication, you can even obtain the machine code to inline by cutting it out of code compiled from a high-level implementation language, in the name of portability. Gforth does this[2] in the land of Forth, but the more well-known implementation is perhaps the dyngen code generator[3] used in Qemu before the switch to TCG in version 0.10.

Generating machine code isn’t difficult, and neither is modifying a (low-level) bytecode generator to do it[4]. Generaring good machine code is difficult.

[1] http://www.bradrodriguez.com/papers/moving1.htm

[2] https://www.complang.tuwien.ac.at/forth/gforth/Docs-html/Dyn...

[3] https://gitlab.com/qemu-project/qemu/-/blob/v0.9.1/qemu-tech..., rendered as https://web.archive.org/web/20081120011949if_/http://bellard...

[4] https://github.com/EarlGray/c4/blob/master/JIT.md