From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
	id ED9FF385843E; Fri, 26 May 2023 15:21:25 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org ED9FF385843E
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1685114485;
	bh=1E812tjfyEv+GR+8H+3mV3/zVHIlmb8ewjewzAYn2H4=;
	h=From:To:Subject:Date:In-Reply-To:References:From;
	b=hm8QHuL86BwZTx/gknbDxcBIQNQvyR2FCw4/ZO0H6o0lqyfQ1LXhlkj/3c+eR4fKW
	 uOQ/ECYwblHJJ0XsJI4OsEpyYUlbsQbKm0q90wP+qmDU7nWUdxKiDBCDuCA2wabeIe
	 QyIxLYobNxhfnxA8yIHh7RmEdcvgVc53fgvGihKg=
From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/109907] Missed optimization for bit extraction (uses
 shift instead of single bit-test)
Date: Fri, 26 May 2023 15:21:25 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: middle-end
X-Bugzilla-Version: 14.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: normal
X-Bugzilla-Who: pinskia at gcc dot gnu.org
X-Bugzilla-Status: NEW
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-109907-4-r8iQlsSvek@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-109907-4@http.gcc.gnu.org/bugzilla/>
References: <bug-109907-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
List-Id: <gcc-bugs.sourceware.org>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109907

--- Comment #22 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Georg-Johann Lay from comment #20)
> What then happens is:
>=20
> expr.cc::do_store_flag()
> expmed.cc::emit_store_flag_force()
> expmed.cc::emit_store_flag()
> expmed.cc::emit_store_flag_1()
>=20
> the latter then does:
>=20
>       if (STORE_FLAG_VALUE =3D=3D 1 || normalizep)
>         /* If we are supposed to produce a 0/1 value, we want to do
>            a logical shift from the sign bit to the low-order bit; for
>            a -1/0 value, we do an arithmetic shift.  */
>         op0 =3D expand_shift (RSHIFT_EXPR, int_mode, op0,
>                             GET_MODE_BITSIZE (int_mode) - 1,
>                             subtarget, normalizep !=3D -1);
>=20
> "normalizep" is true because ops->type has a precision of 1, and
> STORE_FLAG_VALUE is the default of 1.
>=20
> Nowhere is there any cost computation or consideration whether extzv could
> do the trick.

Thanks for tracking down where the shift is expanded to. Let me try to use
extract_bit_field there instead (which should produce the better code).=