[FFmpeg-devel] [PATCH v5] lavc/vvc_mc: R-V V avg w_avg

[Rémi Denis-Courmont]

Le maanantaina 1. heinäkuuta 2024, 19.09.01 EEST flow gg a écrit :
> I reviewed it again, the purpose of is_w is to limit lmul to a maximum of
> 1/4 of vlen,

1/4 of vlen? Do you mean limit to EMUL=1 for EEW=32 and EMUL=1/4 for EEW=8?

Limiting LMUL to less than 1 at maximum EEW is useless from a functional 
standpoint, since fractional registers cannot be addressed individually. (Of 
course it might still be useful for performance reasons.)

> to prevent vector register shortage, which can also be
> considered as vset limiting lmul. I renamed it to quarter_len_limit.

TBH, I don't really understand.

If a lower LMUL limit is reached, then specialisations for the corresponding 
VLEN are simply unncessary/infeasible and the code for lower VLEN should be 
used.

If a higher LMUL limit is reached due to register pressure (or the 8 hard 
limit), then the given VLEN cannot be supported at all, or requires some 
completely different code.

Either way, I don't really follow why vsetvlfixed macros need to be involved.

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雷米‧德尼-库尔蒙
http://www.remlab.net/