[Libre-soc-dev] scalar instructions and SVP64

[Luke Kenneth Casson Leighton]

On Wednesday, March 10, 2021, Jacob Lifshay <programmerjake at gmail.com>
wrote:

> https://libre-soc.org/irclog/%23libre-soc.2021-03-10.log.
> html#t2021-03-10T00:11:21
>
> You see why we need VL to be ignored when there aren't any vector
> arguments?


late (1am), the short answer is no.

VL=0 is defined as "all and any sv ops are NOP".

scalar in SV is defined as "element zero of a vector"

not "scalar because it's scalar i.e. not a vector"

it's DEFINED as being "element zero of the Vector".

ALL sv instructions ARE vector.

the misnamed-thing-we-call-sv-scalar is not actually a scalar.

it *is* "the zeroth element of the vector".

therefore by definition it falls under the vector loop

therefore when VL=0 it shall be skipped because all sv instructions *are*
skipped when VL=0

Period.

if you want scalar instructions you do not put them into SV.

you use the v3.0B scalar instructions because those are categorically
scalar.

RVV has the exact same thing.

all RVV instructions categorically become NOPs when VL==0

l.



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