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From: Uros Bizjak <ubizjak@gmail.com>
Date: Tue, 5 Jan 2021 08:19:58 +0100
Message-ID: <CAFULd4ZtYegmmO-CWR1A__p8UHss4BgvqK48msydc-9_qXpn3g@mail.gmail.com>
Subject: Re: [PATCH]i386: Optimize pmovskb on zero_extend of subreg HI of the
 result [PR98461]
To: Hongtao Liu <crazylht@gmail.com>
Cc: Jakub Jelinek <jakub@redhat.com>, GCC Patches <gcc-patches@gcc.gnu.org>, 
 Kirill Yukhin <kirill.yukhin@gmail.com>
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On Tue, Jan 5, 2021 at 8:04 AM Uros Bizjak <ubizjak@gmail.com> wrote:
> >
> > +(define_split
> > +  [(set (match_operand:SI 0 "register_operand")
> > +        (zero_extend:SI
> > +          (not:HI
> > +            (subreg:HI
> > +              (unspec:SI
> > +                [(match_operand:V16QI 1 "register_operand")]
> > +                UNSPEC_MOVMSK) 0))))]
> > +  "TARGET_SSE2"
> > +  [(set (match_dup 2)
> > +        (unspec:SI [(match_dup 1)] UNSPEC_MOVMSK))
> > +   (set (match_dup 0)
> > +        (match_dup 3))]
>
> Just write:
>
> (set (match_dup 0)
>     (xor:SI (match_dup 2)(const_int 65535))

BTW: This could be a universal combine splitter to simplify

unsigned int foo (unsigned short z)
{
    return (unsigned short)~z;
}

Trying 7 -> 8:
   7: r87:HI=~r88:SI#0
     REG_DEAD r88:SI
   8: r86:SI=zero_extend(r87:HI)
     REG_DEAD r87:HI
Failed to match this instruction:
(set (reg:SI 86)
   (zero_extend:SI (not:HI (subreg:HI (reg:SI 88) 0))))

But combine does not "split" to one insns.

Uros.