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 B3579385842E; Sat, 20 May 2023 22:40:11 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org B3579385842E
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1684622411;
	bh=PHv/4JroCD7fyOLs5uzxGV1Fz7z8in9gCTe1bnqdR/Q=;
	h=From:To:Subject:Date:In-Reply-To:References:From;
	b=JItUYZntoXl7lurdWy+1GjRwgHd8wWl+MW2xJaQaNA5THDad+6hJ5cKYnVHkMuT1t
	 LECVHrV3UR414Gr7BlileediEWwqQE7ZF8iMKLxweSteKK6BGOGQAjnjNI4/TYTQNF
	 QLJI56Mxpz1wX7Fs7VB+OYZMbvwt+nXA9YFky1M4=
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: Sat, 20 May 2023 22:40:11 +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: dependson
Message-ID: <bug-109907-4-QRfu3yIUV8@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

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Depends on|108847                      |

--- Comment #14 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Actually I take back on what is going on those 3. But I will be looking into
it.


  x.0_1 =3D (signed long) x_4(D);
  _2 =3D x.0_1 >> 31;
  _3 =3D (unsigned char) _2;
  _5 =3D _3 & 1;

That is what is causing arithmetic shift but we only need the first bit in =
the
end.
If we optimized that to:
  x.0_1 =3D (unsigned long) x_4(D);
  _2 =3D x.0_1 >> 31;
  _3 =3D (unsigned char) _2;
  _5 =3D _3 & 1;

similar to:
uint8_t cset_32bit31_1 (uint32_t x)
{
    if (x & (1ull<<31))
      return 1;
  return 0;
}

Then there is still an issue. I have some ideas of how to handling the first
case but I might need a few weeks.

Note GCC 14 code generation here is similar now to GCC 4.5.x so that is the
good news that this part is not a regression.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108847
[Bug 108847] unnecessary bitwise AND on boolean types and shifting of the
"sign" bit=