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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/89984] Extra register move
Date: Sat, 04 Sep 2021 06:41:09 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D89984

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #1)
> The problem is here:
> (define_insn_and_split "@xorsign<mode>3_1"
>   [(set (match_operand:MODEF 0 "register_operand" "=3DYv")
>         (unspec:MODEF
>           [(match_operand:MODEF 1 "register_operand" "Yv")
>            (match_operand:MODEF 2 "register_operand" "0")
>            (match_operand:<ssevecmode> 3 "nonimmediate_operand" "Yvm")]
>           UNSPEC_XORSIGN))]
>   "SSE_FLOAT_MODE_P (<MODE>mode) && TARGET_SSE_MATH"
>   "#"
>   "&& reload_completed"
>   [(const_int 0)]
>   "ix86_split_xorsign (operands); DONE;")
>=20
>=20
> for AVX operand 2 does not need to be the same as operand 0.
> Shouldn't be a hard change for someone starting out to improve this.

Right,  The way copysign is defined is like this:
(define_insn "@copysign<mode>3_var"
  [(set (match_operand:SSEMODEF 0 "register_operand" "=3DYv,Yv,Yv,Yv,Yv")
        (unspec:SSEMODEF
          [(match_operand:SSEMODEF 2 "register_operand" "Yv,0,0,Yv,Yv")
           (match_operand:SSEMODEF 3 "register_operand" "1,1,Yv,1,Yv")
           (match_operand:<ssevecmodef> 4
             "nonimmediate_operand" "X,Yvm,Yvm,0,0")
           (match_operand:<ssevecmodef> 5
             "nonimmediate_operand" "0,Yvm,1,Yvm,1")]
          UNSPEC_COPYSIGN))
   (clobber (match_scratch:<ssevecmodef> 1 "=3DYv,Yv,Yv,Yv,Yv"))]
  "(SSE_FLOAT_MODE_P (<MODE>mode) && TARGET_SSE_MATH)
   || (TARGET_SSE && (<MODE>mode =3D=3D TFmode))"
  "#")

I suspect xorsign should be improved similarlly.=