I could be completely wrong but it looks like what this does is more like stack-caching. One operand, if it's the result of the last instruction, should already be in "virtual r0" which is already in a register. For the other operand of the opcode, it's an infinite set of "registers" at an offset from the stack pointer: https://github.com/wasm3/wasm3/tree/b1462d450ca367e39e4b2eb4...