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 248CE3858D37; Thu,  2 Mar 2023 18:12:37 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 248CE3858D37
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1677780757;
	bh=KpK/+Hcy0wSb2W3yBQoxiXHEJ6IBjr7ivKgpd11S8js=;
	h=From:To:Subject:Date:From;
	b=W4GxrAi6tkuKLBZH/3O8E3x99Xqd5leWq5eeLAE1w+yhhLzmiDkRRyfSOTuIgbviE
	 ybGGw4yduqROewcjFrTKbFRSZAt6mu0XIkpQR7MBQbReUmjhrNIpd7utn3oTT1TOUU
	 aeCSeTkTeqq3qdbPdawlF5WpR1CRAtQxq0Pas4sI=
From: "daniel.gotsch at bluerivertech dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/108993] New: Value initialization does not occur for
 derived class with -Os, for gcc versions > 5
Date: Thu, 02 Mar 2023 18:12:36 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: unknown
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: daniel.gotsch at bluerivertech dot com
X-Bugzilla-Status: UNCONFIRMED
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: bug_id short_desc product version bug_status
 bug_severity priority component assigned_to reporter target_milestone
Message-ID: <bug-108993-4@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=3D108993

            Bug ID: 108993
           Summary: Value initialization does not occur for derived class
                    with -Os, for gcc versions > 5
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: daniel.gotsch at bluerivertech dot com
  Target Milestone: ---

Minimal example:

#include <iostream>

struct Base {
    Base() {} // not a default constructor
    double x;
};

struct Derived : public Base {
    Derived() =3D default; // default constructor should lead to
zero-initialization
};

int main () {
    Base a{};=20
    std::cout << a.x; // Could be any value

    Derived b{};
    std::cout << b.x; // Should be set 0 but isn't set 0 when compiled with=
 -Os
flag
}


see compiler output https://godbolt.org/z/Ecr1K9cMM

The class Derived has a default constructor which satisfies (2) of
value-initalization meaning the object should be zero-initialized.
see https://en.cppreference.com/w/cpp/language/value_initialization

Zero-initialization should zero-out the base class too, see
https://en.cppreference.com/w/cpp/language/zero_initialization=