[brucehoult]

If you want to get the absolute most out of a specific CPU that is in your hands then you of course have to refer to the documentation for that specific CPU.

That process doesn't depend on whether it's an x86 or an Arm or a RISC-V.

That's why x86 people refer to the HUGE document maintained by Agner Fog.

If you want your code to run well on all standards-compliant implementations then you write according to the ISA documentation, in this case RVA23. Or ARMv9-A. Or x86_64 v3.

[bjourne]

Nope. I want to get the most out of all cpus that will run my code. This is a combinatorial problem that grows exponentially by the number of relevant extensions. So, yes, you need to know the hardware, but accounting for combinations of 5 features is way easier than accounting for combinations of 10 features.

Riscv is basically repeating the same mistake X11 did. A minimal base that could be varied endlessly by combining extensions. I didn't work for X11. Some extensions became de facto mandatory (shm) while others fell by the wayside. But you could never rely on the availability of a given extension because someone somewhere might not have had it or disabled it. Then Wayland came along and cleaned up the gazillion extensions mis-design because it was a huge PITA. Riscv will get there too, sooner or later.