[Libre-soc-isa] [Bug 1077] evaluate removing /vec234 from instructions, move subvl to SVSTATE

bugzilla-daemon at libre-soc.org bugzilla-daemon at libre-soc.org
Wed May 3 10:01:11 BST 2023


--- Comment #12 from Luke Kenneth Casson Leighton <lkcl at lkcl.net> ---
(In reply to Jacob Lifshay from comment #2)
> imho it is not sensible to remove subvl from the prefix because GPU code
> often has subvl different in each instruction, so setvl or similar would
> need to be constantly reran just to change subvl, this would easily be many
> times more setvl ops because otherwise setvl is usually ran once per shader
> or once per function.

on its own that's a good enough reason for me.

> All of that is unless we do what some other GPU compilers do, which is to
> convert all code to scalar code and only then run the
> full-function-vectorization -- this essentially splits all subvl=2/3/4 ops
> into 2/3/4 copies of a subvl=1 op and never uses subvl=2/3/4, essentially
> removing subvl completely from generated code.

i have a feeling that this was what ultimately must have been decided
in RVV: early drafts (0.6) had subvl but i think it got dropped.  given
the GPU long-term goals i'm inclined to say "keep".

You are receiving this mail because:
You are on the CC list for the bug.

More information about the Libre-SOC-ISA mailing list