[FFmpeg-devel] [PATCH] Revert "libavcodec/mips: Fix specification of instruction name"

[Jiaxun Yang]

在 2021/7/22 下午4:00, yinshiyou-hf at loongson.cn 写道:
> > -----原始邮件-----
> > 发件人: "Jiaxun Yang" <jiaxun.yang at flygoat.com>
> > 发送时间: 2021-07-21 17:39:22 (星期三)
> > 收件人: ffmpeg-devel at ffmpeg.org
> > 抄送: yinshiyou-hf at loongson.cn, "Jin Bo" <jinbo at loongson.cn>, "Jiaxun Yang" <jiaxun.yang at flygoat.com>
> > 主题: [FFmpeg-devel] [PATCH] Revert "libavcodec/mips: Fix specification of instruction name"
> >
> > This reverts commit ebedd26eefe2ff4bbf5a358907c4e8e4b0d62eae.
> >
> > The original commit states that "gcc supports both of them,
> > clang only supports the second type", it's obviousely not ture.
> >
> > Error: opcode not supported on this processor: loongson3a(mips64r2) `pxor $f3,$f3,$f3'
> >
> > Tested with latest GCC11 and binutils 2.37.
> >
> > The statement is not true. I guess you may have a internal toolchain modified
> > for this purpose, but you're not the sole user of FFmpeg, you're breaking
> > other users like Debian. Also I can't find clang with Loongson extention
> > support every where.
> >
> > I'm reverting this for now. If you would like to implement it, another approach
> > could be make it as marco in mmiutils.h and filter it with #if define(__clang__).
> >
> > Signed-off-by: Jiaxun Yang <jiaxun.yang at flygoat.com>
> > Cc: Jin Bo <jinbo at loongson.cn>
> > Cc: yinshiyou-hf at loongson.cn
>
> Thank you for your feedback, following are my opinions:
> 1）according to the instruction mannul, we should use 'pxor' to operate float register.

Hi all,

+ Paul Hua for toolchain stuff

I wonder if it's available for general public?

> 2) MMI is loongson media extention，compiler from upstream not supported yet is true.
>   If you are using FFmpeg on loongson platform, you can try to get compiler from
>   http://www.loongnix.org/index.php/GCC or use loongson repository download.
>   Loongnix-1.0 :http://ftp.loongnix.org/os/loongnix/1.0/os/
>   Loongnix-20-mips64el:http://ftp.loongnix.org/os/loongnix/20/mips64el

No that's not true, Loongson-MMI had upstream toolchain support for 
Loongson-3A since 2019, which is binutils-2.32 and GCC-9.

And these instruction naming (and or xor) is available since 2008 for 
Loongson-2F.

> 3) If you are using on other mips platform which MMI is unsupported, and MMI havn't disabled automaticlly.
>   we will fix it soon.

MMI should be enable for generic MIPS platform as they intend to run on 
Loongson as well.


> 4) on the safe side, I suggest to add pxor instruction check in configure check.

Or ifdef for clang only?

Thanks.

- Jiaxun

> </jinbo at loongson.cn></jiaxun.yang at flygoat.com></jiaxun.yang at flygoat.com></jinbo at loongson.cn></jiaxun.yang at flygoat.com>