It took me a minute, but yes I completely agree that whether more GPRs helps depends on the code & compiler, and that there’s plenty of code you can’t inline. Re: MMIX Yes! Theoretically it would help if the hardware could dynamically alias registers, and automatically handle spilling when the RF is full. I have heard such a thing physically exists and has been tried, but I don’t know which chip/arch it is (maybe AMD?) nor how well it works. I would bet that it can’t be super efficient with registers, and maybe the complexity doesn’t pay off in practice because it thwarts and undermines inlining.