Eric Fink (eric.delete@this.anon.com) on June 2, 2022 10:11 pm wrote:
> Heikki Kultala (heikk.i.kultal.a.delete@this.gmail.com) on June 2, 2022 12:04 pm wrote:
>
> > But everything else is not equal. Simpler decoder typically means either
> > 1) worse code density, worse cache hit rate, OR
> > 2) less expressive instructions, more instructions needed to perform the same task.
> >
> > So the argument "RISC is always better because it allows simpler decoder" is just stupid.
>
> I think though the argument might be (not sure, you guys are the expert) used for ARMv8.
> It does allow simpler decoding and it doesn't come with a code density disadvantage.
>

aarch64 code density is very good for a crippled fixed 32-bit instruction words, but it does not quite match Thumb2. According to my measurements, it does not even match RV64C, although it's not too far behind.
[According to my measurements] by now undisputed champ of code density in 32/64-bit world is nanoMIPS.
Unfortunately, it appears to be dead.

> It would be very interesting indeed to get a good measure on how decode
> complexity actually impacts CPU performance. Not that we every will :)