Dan Luu

I only seriously studied this for ARMv7, haven't really looked into ARMv8, but I'd expect this to be a relatively small impact relative to other factors, at least for "high performance" chips (including chips used in high-end cell phones as "high performance".

When we implemented an ARMv7 decoder, it was larger than our x86 decoder. This is a little unfair, since the decoder would've been smaller if our backend had originally been designed for ARM, but ARMv7 has a bunch of gross stuff that's not trivial to handle regardless of backend.

I believe a lot of that stuff is gone in ARMv8, but people don't really talk about the ARMv7 penalty the way people talk about the x86 penalty even though I think these two things aren't really so different, so I think it's mostly cultural that people say this about x86.

I'm not saying you can't do better than x86. You can do better. But if I were trying to make a low power chip with at-least iPhone performance, x86 or not would be the low order bit behind having a good micro-arch, making sure we have good circuit designers, etc.

Do you think there is a future for risc V in the mobile space or otherwise?

IDK, I think that's more of a business question than a technical question and I have no particular insight into the business side of things. IMO, the technical side is almost irrelevant in terms of whether or not RISC-V will be a successful ISA.

I mean, for any particular market, someone will have to produce a chip that's not garbage technically, but whether or not that happens is really a business question and not a technical question, IMO. And whether or not that thing sells is also a business question.

Do you see RISC-V having any particular technical advantages over ARM, in terms of being a more power efficient or flexible architecture to develop against, given the choice?