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 DD57A3858C53; Sat, 26 Aug 2023 05:47:28 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org DD57A3858C53
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1693028848;
	bh=2xHi2wfXzqnmaEG/KOBp+MJoCO27gwbaP0aLbDU3Wxo=;
	h=From:To:Subject:Date:In-Reply-To:References:From;
	b=bwZ6bC9sIkpJMGJzv5D/I78LnLZxTd6v298JYlczK6TVwg0xRJlEX4mzpmaoN0jt8
	 PQnXbtKwPVVdOavBRNUn5QSZcnt+tEMW3rel1KdzBo/aFp0GgmnHb0kA2WQt3/RJUp
	 TcgKcXw0b44wbrBokIeQ7vyub4GLQtLwqY7Wyw98=
From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/38264] tree_forwarder_block_p says no to first basic
 block
Date: Sat, 26 Aug 2023 05:47:27 +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: 4.4.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: enhancement
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-38264-4-TWgGFETpLM@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-38264-4@http.gcc.gnu.org/bugzilla/>
References: <bug-38264-4@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=3D38264

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I actually just ran into a problem caused by having this check here.

I was modifying tree-ssa-ifcombine to optimize the case where we have the s=
ame
condition on both bb from a bb like:
```
int g();
int h();

int j, l;

int f(int a, int *b)
{
        if (a =3D=3D 0)
        {
                if (b =3D=3D &j) goto L9; else goto L7;
        }
        else
        {
                if (b =3D=3D &j) goto L9; else goto L7;
        }
L7: return g();
L9: return h();
}
```

I go and try to remove one of the bb (which have the same condition) and th=
at
should have updated dominators in a reasonable way because the removal shou=
ld
have done a forwarder from bb 2 to bb3. But instead of doing the forwarding=
 of
the bb, we end up with still bb3 and the dominator needs to be updated in
non-trival ways.=