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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/106602] riscv: suboptimal codegen for
 zero_extendsidi2_shifted w/o bitmanip
Date: Wed, 02 Nov 2022 01:35:06 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106602

--- Comment #16 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Vineet Gupta from comment #14)
> (In reply to Jeffrey A. Law from comment #13)
> > Trying 7, 8, 9 -> 10:
> >     7: r140:DI=3D0x1
> >     8: r141:DI=3Dr140:DI<<0x26
> >       REG_DEAD r140:DI
> >       REG_EQUAL 0x4000000000
> >     9: r139:DI=3Dr141:DI-0x40
> >       REG_DEAD r141:DI
> >       REG_EQUAL 0x3fffffffc0
> >    10: r137:DI=3Dr138:DI&r139:DI
> >       REG_DEAD r139:DI
> >       REG_DEAD r138:DI
> > Failed to match this instruction:
> > (set (reg:DI 137)
> >     (and:DI (reg:DI 138)
> >         (const_int 274877906880 [0x3fffffffc0])))
> >=20
> >=20
> > That's what we're looking for.  I think I had a wrong switch somewhere.=
=20
> > Match that with a define_split and you should be good to go.
>=20
> I think you are missing the original left shift 6.
> So insn 6 from my dumps is important if we are to match
> zero_extendsidi2_shifted which matches and+shift (iff 3>>2=3D=3D0xfffffff=
f).
>=20
> But it feels like you agree on using REG_EQUAL note (if avail) to created
> merged pattern in try_combine() as opposed to my original thinking of only
> doing it if regular pattern match failed.

So what Jeff is saying is you just need a define_split which matches that f=
inal
set.

Something like:
(define_split
  [(set (match_operand:DI 0 "register_operand" "")
        (and:SI (match_operand:SI 1 "register_operand" "")
                (match_operand:SI 2 "shifted_mask_operand" "")))]
  ""
  [(set (match_operand:DI 0 ....=