[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 04:05:58 BST 2023


https://bugs.libre-soc.org/show_bug.cgi?id=1077

--- Comment #2 from Jacob Lifshay <programmerjake at gmail.com> ---
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.

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.

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