Re: [FFmpeg-devel] [PATCH 1/3] lavu: detect RISC-V F extension (i.e. float)

["Rémi Denis-Courmont" <remi@remlab.net>]

Le keskiviikkona 14. syyskuuta 2022, 22.28.01 EEST Lynne a écrit :
> Sep 14, 2022, 19:50 by remi@remlab.net:
> > From: Rémi Denis-Courmont <remi@remlab.net>
> > 
> > This introduces compile-tim and run-time CPU detection on RISC-V. In
> > practice, I doubt that FFmpeg will ever see a RISC-V CPU without the F
> > extension, and if it does, it probably won't have run-time detection.
> > So the flag is essentially always set.
> > 
> > But as things stand, checkasm wants it that way, and we are nowhere
> > near running short on CPU flag bits on that platform.
> > ---
> > 
> >  libavutil/cpu.c           |  4 ++++
> >  libavutil/cpu.h           |  3 +++
> >  libavutil/cpu_internal.h  |  1 +
> >  libavutil/riscv/Makefile  |  1 +
> >  libavutil/riscv/cpu.c     | 44 +++++++++++++++++++++++++++++++++++++++
> >  tests/checkasm/checkasm.c |  2 ++
> >  6 files changed, 55 insertions(+)
> >  create mode 100644 libavutil/riscv/Makefile
> >  create mode 100644 libavutil/riscv/cpu.c
> > 
> > diff --git a/libavutil/cpu.c b/libavutil/cpu.c
> > index 0035e927a5..6e9b8c5f58 100644
> > --- a/libavutil/cpu.c
> > +++ b/libavutil/cpu.c
> > @@ -62,6 +62,8 @@ static int get_cpu_flags(void)
> > 
> >  return ff_get_cpu_flags_arm();
> >  #elif ARCH_PPC
> >  return ff_get_cpu_flags_ppc();
> > 
> > +#elif ARCH_RISCV
> > +    return ff_get_cpu_flags_riscv();
> > 
> >  #elif ARCH_X86
> >  return ff_get_cpu_flags_x86();
> >  #elif ARCH_LOONGARCH
> > 
> > @@ -178,6 +180,8 @@ int av_parse_cpu_caps(unsigned *flags, const char *s)
> > 
> >  #elif ARCH_LOONGARCH
> >  { "lsx",      NULL, 0, AV_OPT_TYPE_CONST, { .i64 = AV_CPU_FLAG_LSX     
> >  },    .unit = "flags" }, { "lasx",     NULL, 0, AV_OPT_TYPE_CONST, {
> >  .i64 = AV_CPU_FLAG_LASX     },    .unit = "flags" },> 
> > +#elif ARCH_RISCV
> > +        { "float",    NULL, 0, AV_OPT_TYPE_CONST, { .i64 = AV_CPU_FLAG_F 
> >       },    .unit = "flags" },> 
> >  #endif
> >  { NULL },
> >  };
> > 
> > diff --git a/libavutil/cpu.h b/libavutil/cpu.h
> > index 9711e574c5..71ae70bcbd 100644
> > --- a/libavutil/cpu.h
> > +++ b/libavutil/cpu.h
> > @@ -78,6 +78,9 @@
> > 
> >  #define AV_CPU_FLAG_LSX          (1 << 0)
> >  #define AV_CPU_FLAG_LASX         (1 << 1)
> > 
> > +// RISC-V Vector extension
> > +#define AV_CPU_FLAG_F            (1 << 0)
> 
> Can you prefix that with RV (FLAG_RVF) like the function?

I agree that the name is a bit unfortunate, and that's essentially because 
RISC-V is not making up cool marketing names for their ISA extensions.

But it is consistent with what other architectures do, and RVF wouldn't be. So 
I have mixed feelings here. Arguably, the correct approach would be to only 
define the flags on their respective target architectures (and leave it as just 
"F").

I guess I will change it to RVF if nobody else expresses a contradictory 
opinion.

-- 
Реми Дёни-Курмон
http://www.remlab.net/



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