Your message dated Tue, 20 Sep 2016 22:15:11 +0000
with message-id <e1bmtjn-0005qy...@franck.debian.org>
and subject line Bug#838316: Removed package(s) from unstable
has caused the Debian Bug report #781060,
regarding g++-4.9: Broken optimization when move-constructing from virtual 
subclass
to be marked as done.

This means that you claim that the problem has been dealt with.
If this is not the case it is now your responsibility to reopen the
Bug report if necessary, and/or fix the problem forthwith.

(NB: If you are a system administrator and have no idea what this
message is talking about, this may indicate a serious mail system
misconfiguration somewhere. Please contact ow...@bugs.debian.org
immediately.)


-- 
781060: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=781060
Debian Bug Tracking System
Contact ow...@bugs.debian.org with problems
--- Begin Message ---
Package: g++-4.9
Version: 4.9.2-10

Using g++ 4.9.2-10 on amd64, the below program behaves differently
when compiled with -O2 vs. not. The non-optimized version is correct;
the program's output should be:

~A(): moved = true
~A(): moved = false

However, with the optimized version, the program incorrectly outputs:

~A(): moved = false
~A(): moved = false

I.e. the line `other.moved = true` has been elided, or perhaps written
to the wrong location in memory. In practice, given the typical use
cases for move constructors, this bug tends to cause double-frees and
use-after-frees. In praticular, this is breaking the Cap'n Proto
library, which I maintain.

The attached self-contained script will demonstrate the problem.

Both G++ 4.8.4-1 and Clang 3.5.0-10 produce the correct output.
Additionally, G++ "4.9.2 20150304 (prerelease)" on Arch Linux produces
the correct output, possibly suggesting that this bug is
Debian-specific. (You can test different compiler versions by passing
the compiler command to use as the script's first parameter. By
default it uses `g++`.)

-Kenton

=======Program text=======
#include <stdio.h>

class A {
public:
  bool moved = false;

  A() = default;
  A(A&& other) {
    other.moved = true;
  }
  ~A() {
    printf("~A(): moved = %s\n", moved ? "true" : "false");
  }
};
class B: virtual public A {};
class C: virtual public B {};
class D: public C {};

int main() {
  A a = D();
}
=========================

-- System Information:
Debian Release: 8.0
  APT prefers testing-updates
  APT policy: (500, 'testing-updates'), (500, 'testing')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 3.16.0-4-amd64 (SMP w/12 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages g++-4.9 depends on:
ii  gcc-4.9            4.9.2-10
ii  gcc-4.9-base       4.9.2-10
ii  libc6              2.19-15
ii  libcloog-isl4      0.18.2-1+b2
ii  libgmp10           2:6.0.0+dfsg-6
ii  libisl10           0.12.2-2
ii  libmpc3            1.0.2-1
ii  libmpfr4           3.1.2-2
ii  libstdc++-4.9-dev  4.9.2-10
ii  zlib1g             1:1.2.8.dfsg-2+b1

g++-4.9 recommends no packages.

Versions of packages g++-4.9 suggests:
ii  g++-4.9-multilib    4.9.2-10
pn  gcc-4.9-doc         <none>
pn  libstdc++6-4.9-dbg  <none>

-- no debconf information

Attachment: test-move-from-virtual-subclass.sh
Description: Bourne shell script


--- End Message ---
--- Begin Message ---
Version: 4.9.4-2+rm

Dear submitter,

as the package gcc-4.9 has just been removed from the Debian archive
unstable we hereby close the associated bug reports.  We are sorry
that we couldn't deal with your issue properly.

For details on the removal, please see https://bugs.debian.org/838316

The version of this package that was in Debian prior to this removal
can still be found using http://snapshot.debian.org/.

This message was generated automatically; if you believe that there is
a problem with it please contact the archive administrators by mailing
ftpmas...@ftp-master.debian.org.

Debian distribution maintenance software
pp.
Chris Lamb (the ftpmaster behind the curtain)

--- End Message ---

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