"Six registers are not very much, but this restriction was forced by the need to target CISC architectures which, like the x86, are poor of registers; anyway, b

"Six registers are not very much, but this restriction was forced by the need to target CISC architectures which, like the x86, are poor of registers; anyway, backends can specify the actual number of available registers with the calls JIT_R_NUM (for caller-save registers) and JIT_V_NUM (for callee-save registers)." (https://www.gnu.org/software/lightning/manual/lightning.html#The-instruction-set https://www.gnu.org/software/lightning/manual/lightning.html...) There used to be a boardly similar library called libjit https://www.gnu.org/software/libjit/ https://www.gnu.org/software/libjit/ which was slightly higher level: It offered an arbitrary number of virtual registers. It took care of register allocation, I don't recall how sophisticated it was. The docs call it "global" allocation, i.e., taking the whole function into account at once, as opposed to local allocation that considers blocks in isolation.