[FFmpeg-devel] [PATCH 5/5] lavc/vp8dsp: factor R-V V EPEL functions for all lengths

[Rémi Denis-Courmont]

Le lauantaina 25. toukokuuta 2024, 21.16.22 EEST flow gg a écrit :
> Would it be better to replace the two vsetvlstatic8 and vsetvlstatic16 with
> two vsetvl?

The other option is to hard-code the most pessimistic multiplier. That would 
be easier to read and save two instructions in the head, it would most likely 
end up slower overall, due to increased latency from the vector unit in the 
main loop.

On the other hand, with vsetvl, we have the option to adjust the multiplier at 
run-time depending on hardware vector size. That will not be possible with 
vsetvli unless we patch the code live (yikes).

> This would require the previous patch and this one to work
> together,

Yes, patch order matters.

> increasing the number of lines of code

This is reducing code size by over 2 kib of code, or several hundreds of 
instructions.

> Additionally, I have a question about patch 4 'save one R-V GPR' and patch
> 5. Should they be submitted as a single patch? Because patch 4 looks
> similar to what I initially submitted, and you suggested changing it to
> save lines of code. If it is only for patch 5, shouldn't they be combined
> together?

I think people here like to have as small and many patches as possible, as is 
generally considered the right way to use Git. Since patch 4 is a very minor 
but still independent (from patch 5) improvement, it should be separate, as 
far as I understand FFmpeg's practices.

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