Re: [PATCH] math: x86: Use prefix for FP_INIT_ROUNDMODE

["H.J. Lu" <hjl.tools@gmail.com>]

On Thu, Sep 1, 2022 at 9:42 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Thu, Sep 1, 2022 at 6:03 AM Adhemerval Zanella via Libc-alpha
> <libc-alpha@sourceware.org> wrote:
> >
> > Not all compilers support the inline asm prefix '%v' to emit the avx
> > instruction if AVX is enable.  Use a prefix instead.
> >
> > Checked on x86_64-linux-gnu and i686-linux-gnu.
> > ---
> >  sysdeps/x86/fpu/sfp-machine.h | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/sysdeps/x86/fpu/sfp-machine.h b/sysdeps/x86/fpu/sfp-machine.h
> > index 5892f4f5fe..006eebe257 100644
> > --- a/sysdeps/x86/fpu/sfp-machine.h
> > +++ b/sysdeps/x86/fpu/sfp-machine.h
> > @@ -39,9 +39,15 @@ typedef unsigned int UTItype __attribute__ ((mode (TI)));
> >
> >  # define FP_RND_MASK           0x6000
> >
> > +# ifdef __AVX__
> > +#  define AVX_INSN_PREFIX      "v"
> > +# else
> > +#  define AVX_INSN_PREFIX      ""
> > +# endif
> > +
> >  # define FP_INIT_ROUNDMODE                                     \
> >    do {                                                         \
> > -    __asm__ __volatile__ ("%vstmxcsr\t%0" : "=m" (_fcw));      \
> > +    __asm__ __volatile__ (AVX_INSN_PREFIX "stmxcsr\t%0" : "=m" (_fcw)); \
> >    } while (0)
> >  #else
> >  # define _FP_W_TYPE_SIZE       32
> > --
> > 2.34.1
> >
>
> Should we use __builtin_ia32_stmxcsr instead?
>

__builtin_ia32_stmxcsr requires extra instructions.

-- 
H.J.