[Libre-soc-misc] How not to design instruction sets

[Jacob Lifshay]

On Mon, Dec 14, 2020, 11:43 Luke Kenneth Casson Leighton <lkcl at lkcl.net>
wrote:

> On 12/14/20, Jacob Lifshay <programmerjake at gmail.com> wrote:
> > I found this on the RISC-V mailing lists, looks interesting:
> > https://player.vimeo.com/video/450406346
> >
> > it's a talk by one of the x86 AVX512 instruction set designers covering
> the
> > benefits and mistakes of AVX512.
>
> oo fascinating.  nice find.
>

One important thing they mentioned is that swizzles should not be combined
with ALU ops. Combining them with load/stores is fine though.

I'm thinking that if we have the realignment network on the input of the
ALUs anyway to handle packing the ALUs fuller when doing predicated ops
(AVX512 doesn't do that), then swizzles might be fine to combine with ALU
ops anyway.

Jacob
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