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From: "liuhongt at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/114591] [12/13/14 Regression] register allocators
 introduce an extra load operation since gcc-12
Date: Wed, 10 Apr 2024 08:17:21 +0000
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X-Bugzilla-Type: changed
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X-Bugzilla-Product: gcc
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X-Bugzilla-Keywords: missed-optimization, ra
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114591

Hongtao Liu <liuhongt at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |liuhongt at gcc dot gnu.org

--- Comment #4 from Hongtao Liu <liuhongt at gcc dot gnu.org> ---
(In reply to Uro=C5=A1 Bizjak from comment #3)
> (In reply to Jakub Jelinek from comment #2)
> > This changed with r12-5584-gca5667e867252db3c8642ee90f55427149cd92b6
>=20
> Strange, if I revert the constraints to the previous setting with:=20
>=20
> --cut here--
> diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
> index 10ae3113ae8..262dd25a8e0 100644
> --- a/gcc/config/i386/i386.md
> +++ b/gcc/config/i386/i386.md
> @@ -2870,9 +2870,9 @@ (define_peephole2
>=20=20
>  (define_insn "*movhi_internal"
>    [(set (match_operand:HI 0 "nonimmediate_operand"
> -    "=3Dr,r,r,m ,*k,*k ,r ,m ,*k ,?r,?*v,*Yv,*v,*v,jm,m")
> +    "=3Dr,r,r,m ,*k,*k ,*r ,*m ,*k ,?r,?v,*Yv,*v,*v,*jm,*m")
>         (match_operand:HI 1 "general_operand"
> -    "r ,n,m,rn,r ,*km,*k,*k,CBC,*v,r  ,C  ,*v,m ,*x,*v"))]
> +    "r ,n,m,rn,*r ,*km,*k,*k,CBC,v,r  ,C  ,v,m ,x,v"))]
>    "!(MEM_P (operands[0]) && MEM_P (operands[1]))
>     && ix86_hardreg_mov_ok (operands[0], operands[1])"
>  {
> --cut here--
>=20
> I still get:
>=20
>         movl    v1(%rip), %eax  # 6     [c=3D6 l=3D6]  *zero_extendsidi2/3
>         movq    %rax, v2(%rip)  # 16    [c=3D4 l=3D7]  *movdi_internal/5
>         movzwl  v1(%rip), %eax  # 7     [c=3D5 l=3D7]  *movhi_internal/2

My experience is memory cost for the operand with rm or separate r, m is
different which impacts RA decision.

https://gcc.gnu.org/pipermail/gcc-patches/2022-May/595573.html=