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 254D9385841B; Fri, 11 Feb 2022 21:52:06 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 254D9385841B
From: "qing.zhao at oracle dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/102586] [12 Regression] ICE in
 clear_padding_type, at gimple-fold.c:4798 since r12-3433-ga25e0b5e6ac8a77a
Date: Fri, 11 Feb 2022 21:52:05 +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: 12.0
X-Bugzilla-Keywords: ice-on-valid-code
X-Bugzilla-Severity: normal
X-Bugzilla-Who: qing.zhao at oracle dot com
X-Bugzilla-Status: NEW
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P1
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: 12.0
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-102586-4-Sk7T9YUVdF@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-102586-4@http.gcc.gnu.org/bugzilla/>
References: <bug-102586-4@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
X-BeenThere: gcc-bugs@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gcc-bugs mailing list <gcc-bugs.gcc.gnu.org>
List-Unsubscribe: <https://gcc.gnu.org/mailman/options/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-request@gcc.gnu.org?subject=help>
List-Subscribe: <https://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Fri, 11 Feb 2022 21:52:06 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102586

--- Comment #27 from Qing Zhao <qing.zhao at oracle dot com> ---
> On Feb 11, 2022, at 11:47 AM, jakub at gcc dot gnu.org <gcc-bugzilla@gcc.=
gnu.org> wrote:
> But if I do:
> struct C { char a; int b; char c; long d; C () : a (42), b (42), c (42), =
d (42)
> {} };
> void bar (C *);
> void
> foo ()
> {
>  C c;
>  bar (&c);
> }
> then *.gimple is:
>      c =3D .DEFERRED_INIT (24, 1, &"c"[0]);
>      __builtin_clear_padding (&c, 0B, 1);
>      C::C (&c);
>      bar (&c);
> ...
> void C::C (struct C * const this)
> {
>  *this =3D {CLOBBER};
>  {
>    this->a =3D 42;
>    this->b =3D 42;
>    this->c =3D 42;
>    this->d =3D 42;
>  }
> }
> After einline this is:
>  c =3D .DEFERRED_INIT (24, 1, &"c"[0]);
>  MEM <char[3]> [(struct C *)&c + 1B] =3D {};
>  MEM <char[7]> [(struct C *)&c + 9B] =3D {};
>  c =3D{v} {CLOBBER};
>  c.a =3D 42;
>  c.b =3D 42;
>  c.c =3D 42;
>  c.d =3D 42;
>  bar (&c);
> and that keeps until dse1 which optimizes that out:
>  c =3D{v} {CLOBBER};
>  c.a =3D 42;
>  c.b =3D 42;
>  c.c =3D 42;
>  c.d =3D 42;
>  bar (&c);
> so there is no zero padding initialization at all.

Does this issue only exist with -flifetime-dse=3D2?
When -flifetime-dse=3D2, the call to __builtin_clear_padding should be inse=
rted
AFTER the
start point of the constructor of the object, otherwise it=E2=80=99s dead a=
nd will be
eliminated by DSE.=20
And with -flifetime-dse=3D2, the padding initialization should be done by C=
++ FE
instead of middle end.
Is this understanding correct?=