Re: [PATCH] x86: correct and improve "*vec_dupv2di"

[Hongtao Liu <crazylht@gmail.com>]

On Thu, Jun 15, 2023 at 3:07 PM Uros Bizjak via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> On Thu, Jun 15, 2023 at 8:03 AM Jan Beulich via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> >
> > The input constraint for the %vmovddup alternative was wrong, as the
> > upper 16 XMM registers require AVX512VL to be used with this insn. To
> > compensate, introduce a new alternative permitting all 32 registers, by
> > broadcasting to the full 512 bits in that case if AVX512VL is not
> > available.
> >
> > gcc/
> >
> >         * config/i386/sse.md (vec_dupv2di): Correct %vmovddup input
> >         constraint. Add new AVX512F alternative.
> > ---
> > Strictly speaking the new alternative could be enabled from AVX2
> > onwards, but vmovddup can frequently be a shorter encoding (VEX2
> > vs VEX3).
> >
> > --- a/gcc/config/i386/sse.md
> > +++ b/gcc/config/i386/sse.md
> > @@ -25851,19 +25851,39 @@
> >            (symbol_ref "true")))])
> >
> >  (define_insn "*vec_dupv2di"
> > -  [(set (match_operand:V2DI 0 "register_operand"     "=x,v,v,x")
> > +  [(set (match_operand:V2DI 0 "register_operand"     "=x,v,v,v,x")
> >         (vec_duplicate:V2DI
> > -         (match_operand:DI 1 "nonimmediate_operand" " 0,Yv,vm,0")))]
> > +         (match_operand:DI 1 "nonimmediate_operand" " 0,Yv,vm,Yvm,0")))]
> >    "TARGET_SSE"
> > -  "@
> > -   punpcklqdq\t%0, %0
> > -   vpunpcklqdq\t{%d1, %0|%0, %d1}
> > -   %vmovddup\t{%1, %0|%0, %1}
> > -   movlhps\t%0, %0"
> > -  [(set_attr "isa" "sse2_noavx,avx,sse3,noavx")
> > -   (set_attr "type" "sselog1,sselog1,sselog1,ssemov")
> > -   (set_attr "prefix" "orig,maybe_evex,maybe_vex,orig")
> > -   (set_attr "mode" "TI,TI,DF,V4SF")])
> > +{
> > +  switch (which_alternative)
> > +    {
> > +    case 0:
> > +      return "punpcklqdq\t%0, %0";
> > +    case 1:
> > +      return "vpunpcklqdq\t{%d1, %0|%0, %d1}";
> > +    case 2:
> > +      if (TARGET_AVX512VL)
> > +       return "vpbroadcastq\t{%1, %0|%0, %1}";
> > +      return "vpbroadcastq\t{%1, %g0|%g0, %1}";
>
> You can use
>
> * return TARGET_AVX512VL ? \"vpbroadcastq\t{%1, %0|%0, %1}\" :
> \"vpbroadcastq\t{%1, %g0|%g0, %1}\";
>
> directly in a multi-output insn template to avoid the above C code.
> See e.g. sse2_cvtpd2pi for an example.
>
> Uros.
>
> > +    case 3:
> > +      return "%vmovddup\t{%1, %0|%0, %1}";
> > +    case 4:
> > +      return "movlhps\t%0, %0";
> > +    default:
> > +      gcc_unreachable ();
> > +    }
> > +}
> > +  [(set_attr "isa" "sse2_noavx,avx,avx512f,sse3,noavx")
> > +   (set_attr "type" "sselog1,sselog1,ssemov,sselog1,ssemov")
> > +   (set_attr "prefix" "orig,maybe_evex,evex,maybe_vex,orig")
> > +   (set_attr "mode" "TI,TI,TI,DF,V4SF")
alternative 2 should be XImode when !TARGET_AVX512VL.
> > +   (set (attr "enabled")
> > +       (if_then_else
> > +         (eq_attr "alternative" "2")
> > +         (symbol_ref "TARGET_AVX512VL
> > +                      || (TARGET_AVX512F && !TARGET_PREFER_AVX256)")
> > +         (const_string "*")))])
> >
> >  (define_insn "avx2_vbroadcasti128_<mode>"
> >    [(set (match_operand:VI_256 0 "register_operand" "=x,v,v")



-- 
BR,
Hongtao