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 CCA673858404; Tue, 10 Jan 2023 17:32:50 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org CCA673858404
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1673371970;
	bh=6nWrQ8E2BVCHqndlKCDM/asj5L9E6v9+WmGxb+Cx1eQ=;
	h=From:To:Subject:Date:In-Reply-To:References:From;
	b=EHXhusthlc9+o9JiIJOvkhD4t83i+04Y0AcysMBh1ziOcYYBCAVK2j9xQSUZlDMTn
	 XGsj6qT09++cQuOd1OKAwV7RwyIL+E9TYOCx+NE+d6ibxVahRgrvpZnYW44lj/15Sf
	 9OopENjkne1Is9an2g7kxSPX3b9xhk3RoytIP69I=
From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/108360] [13 Regression] Dead Code Elimination
 Regression at -Os since r13-2048-g418b71c0d535bf
Date: Tue, 10 Jan 2023 17:32:50 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 13.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: normal
X-Bugzilla-Who: jakub 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: 13.0
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-108360-4-yjy1lX2GH5@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-108360-4@http.gcc.gnu.org/bugzilla/>
References: <bug-108360-4@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=3D108360

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Seems it happens even with
short b;
static short c;
unsigned char e;
char f;
void foo();
short(a)(short h, short i) { return h + i; }
static short(d)(short h, int i) { return (h >=3D 32 || h > (7 >> i)) ? h : =
h <<
i; }
unsigned g(short h, short i) { return h + i; }
int main() {
  short j, k =3D -1;
  c =3D a(0 >=3D b, k);
  f =3D c <=3D 0xD315BEF1;
  e =3D f << 4;
  j =3D d(e, 5);
  if (3 >=3D g(j =3D=3D b, k))
    foo();
  b =3D 32;
}
where we can't assume anything about b's value initially.
Still in GCC 12 we decide to thread jump it based on whether e (h in inline=
d d)
is 0 or non-0 - h >=3D 32 is based on ranges clearly always false and as e =
has
[0, 16] range, h > 0 and h !=3D 0 are the same thing, if h !=3D 0, then d r=
eturns
h, otherwise h << 5.  Later on we correctly figure out that if h =3D=3D 0, =
then h
<< 5 is 0.  But what I really don't understand how threadfull1 in that case
decided that foo will not be called.=