[Libre-soc-dev] WASM flexible-vectors & SimpleV

[Luke Kenneth Casson Leighton]

On Fri, Apr 9, 2021 at 10:29 AM Jacob Lifshay <programmerjake at gmail.com> wrote:

> umm, that's actually not quite right...in RVV there is a runtime constant
> value MVL

MVL as i understand it is a hard-coded (architectural) constant that
cannot in any way be changed.  you can *read* it but you certainly
cannot set it. that's what i understood the spec to state.

> where if you request a VL <= MVL you will *always* get exactly
> what you requested

the last time i checked...

> On RVV you might get less than MVL *only* if your requested VL is more than
> MVL (that's for balancing purposes, to ensure you don't have 1 loop with
> only a few elements and/or for other microarchitectural optimizations).

oh god they didn't.

https://github.com/riscv/riscv-v-spec/blob/master/v-spec.adoc#constraints-on-setting-vl

urrr....