3 ms·
I've read that rationale, and it's, well, I'm not going to say it's lying, but it's insincere. By the time it was written, they already settled on 16-bit alignm
by Joker_vD 3mo ago
I've read that rationale, and it's, well, I'm not going to say it's lying, but it's insincere. By the time it was written, they already settled on 16-bit alignment, and fetching (and then decoding) 16-bit aligned 32-bit instructions is either inefficient, or hard, or requires extra circuitry (or an instruction cache).
- rwmj 3mo agoHigh performance RISC-V chips exist from Rivos, Ventana and others, and high performance variable length chips also exist in general (AMD, Intel). So in actual reality it increases complexity somewhat, but is not a problem.
- Joker_vD 3mo agosighs This kind of discussion is so annoying... I start with "RISC-V's decision to make 32-bit instructions only 16-bit aligned complicates instruction fetch and decoding", and the response is "For high performance RISC-V implementations, it's a trivial matter" (which is true), I response with "But then why even bother with mostly-fixed-but-not-quite instruction length, just make a properly variable length ISA, it'd even simplify the instructions", and the reply is "the low-end implementations would struggle with decoding that efficiently" — but they already struggle with instruction fetch when they implement C extension! Nah, it's fine, the high-end chips can cope with that. And round and around this discussion goes... Apparently, RISC-V has no downsides at any end of the price spectrum, what a marvelous ISA.
- rwmj 3mo agoIf you have some specific question I may be able to answer it, since I've been involved with RISC-V for over a decade, dealt with all the main companies involved, written papers, etc. but so far I see no actual question or concrete objection.