Simon Farnsworth (simon.delete@this.farnz.org.uk) on May 18, 2022 3:03 am wrote:
> anon1 (anon.delete@this.anon.com) on May 18, 2022 2:44 am wrote:
> > --- (---.delete@this.redheron.com) on May 17, 2022 2:57 pm wrote:
> > > You think a company that has pulled off three highly successful ISA transitions, (and
> > > three separate 32 to 64b transitions) will have difficulty with a sub-ISA transition?
> > >
> > > OK, then.
> > >
> >
> > Still, it is a bit odd if they introduce SVE2 in the second-ten product, leaving
> > M1 in a bit of an odd spot. Unless they pull something unexpected like retroactively
> > adding SVE2 support for M1 with some sort of microcode update.
>
> Odd, but not the surprising sort of odd for Apple - see also early
> Intel Macs being 32 bit only, when they rapidly moved to 64 bit.
>
> Removing NEON in M2 would be surprising, but adding SVE2 would fit with past changes.


They were depending on Intel's release schedule, and there were no power efficient 64 bit Intel x86 when they introduced Intel Macs. They could have waited nine months or so for Core 2 Duo but the lack of advancement of PPC was already really jeopardizing the Mac's future so they may not have felt they could wait any longer. Absent that concern I think they made a mistake not launching with 64 bits as the default. It would have been so much cleaner.

Contrast with the launch of Apple Silicon Macs where Apple had complete control over what was in M1, so if they wanted it to include SVE2 it would have. If there was some unknown reason where they would have had to wait to make that happen it wouldn't really be a problem if there was one more year of rumors about ARM Macs added to the rest.

SVE2 isn't anything like 64 bits though, because you either are 64 bits or you are not. SVE2 is a moving target, the functionality that is in SVE2 today is a subset of functionality that will be in it a few years. This is like AVX512 which Intel has added stuff to so a CPU that supports "AVX512" doesn't mean it can run all AVX512 code. There are some AVX512 instructions that only a subset of AVX512 supporting CPUs can run.

So I wonder if there really would have been a point to drawing a line in the sand by having SVE2 in M1 to say "all Apple Silicon Macs support SVE2"? They would still support a subset of SVE2 functionality found in M2 or M3 as more SVE2 instructions are added over time.