alt Hacker NewsYes, fixed-length instructions are easier to decode, but that also means a hard upper limit on the number of instructions that could ever be supported. Which is obviously a problem for a future-proof architecture.
The rationale for this and also for confining the base set to 32 bit is explained here: https://docs.riscv.org/reference/isa/v20250508/unpriv/extend...
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dmitrygr • yesterday at 10:44 PM
> also means a hard upper limit on the number of instructions that could ever be supported. Which is obviously a problem for a future-proof architecture.
Yup, aarch64 is doomed. /s
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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).