Re: [FFmpeg-devel] [PATCH] lavc/aarch64: new optimization for 8-bit hevc_pel_uni_w_pixels, qpel_uni_w_h, qpel_uni_w_v, qpel_uni_w_hv and qpel_h

[myais <Logan.Lyu@myais.com.cn>]

Hi, Martin,

I saw your new opinions. Do you mean that the code of my current patch 
should be guard as follows?

C code：

/if (have_i8mm(cpu_flags)) {//
//}/

/asm code :/

/#if HAVE_I8MM/

/#endif/


I mean my current code base does not have those definitions, should I 
implement them directly as if they already exist?


other opinions is under modification..


在 2023/5/26 16:34, Martin Storsjö 写道:
> Hi,
>
> Overall these patches seem mostly ok, but I've got a few minor points 
> to make:
>
> - The usdot instruction requires the i8mm extension (part of 
> armv8.6-a), while udot or sdot would require the dotprod extension 
> (available in armv8.4-a). If you could manage with udot or sdot, these 
> functions would be usable on a wider set of CPUs.
>
> Therefore, the current guards are wrong. Also, I finally got support 
> implemented for optionally using these cpu extensions, even if the 
> baseline of the compile don't include it, by runtime enabling it. See 
> the patchset at 
> https://patchwork.ffmpeg.org/project/ffmpeg/list/?series=9009.
>
> To adapt your patches on top of this, see the two topmost commits at 
> https://github.com/mstorsjo/ffmpeg/commits/archext.
>
> - The indentation is inconsistent; in the first patch, you have some 
> instructions written like this:
>
> +        sqadd   v1.4s, v1.4s, v29.4s
>
> While you later use this style:
>
> +        dup             v1.16b, v28.b[1]
>
> The latter seems to match the style we commonly use; please reformat 
> your code to match that consistently.
>
> With some macro invocations in the first patch, you also seem to have 
> too much indentation in some places. See e.g. this:
>
> +1:      ldr             q23, [x2, x3]
> +        add             x2, x2, x3, lsl #1
> +        QPEL_FILTER_B     v26, v16, v17, v18, v19, v20, v21, v22, v23
> +        QPEL_FILTER_B2    v27, v16, v17, v18, v19, v20, v21, v22, v23
> +        QPEL_UNI_W_V_16
> +        subs            w4, w4, #1
> +        b.eq            2f
>
> (If the macro name is too long, that's ok, but here there's no need to 
> have those lines unaligned.)
>
> - In the third patch, you've got multiple parameters from the stack 
> like this:
>
> +        ldp             x14, x15, [sp]          // mx, my
> +        ldr             w13, [sp, #16]          // width
>
> I see that the mx an my parameters are intptr_t; that's good, since if 
> they would be 32 bit integers, the ABI for such parameters on the 
> stack differ between macOS/Darwin and Linux. But as long as they're 
> intptr_t they behave the same.
>
> - At the same place, you're backing up a bunch of registers:
>
> +        stp             x20, x21, [sp, #-16]!
> +        stp             x22, x23, [sp, #-16]!
> +        stp             x24, x25, [sp, #-16]!
> +        stp             x26, x27, [sp, #-16]!
> +        stp             x28, x30, [sp, #-16]!
>
> This is inefficient; instead, do this:
>
> +        stp             x28, x30, [sp, #-80]!
> +        stp             x20, x21, [sp, #16]
> +        stp             x22, x23, [sp, #32]
> +        stp             x24, x25, [sp, #48]
> +        stp             x26, x27, [sp, #64]
>
> Also, following that, I see that you back up the stack pointer in x28. 
> Why do you use x28 for that? Using x29 would be customary as frame 
> pointer.
>
> Aside for that, I think the rest of the patches is acceptable.
>
> // Martin
>
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