[Bug 1499564] Re: gcc-5.2.1 miscompiles moved-from deque with private allocator

[Matthias Klose]

** Bug watch added: GCC Bugzilla #67707
   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67707

** Also affects: gcc via
   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67707
   Importance: Unknown
       Status: Unknown

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Title:
  gcc-5.2.1 miscompiles moved-from deque with private allocator

Status in gcc:
  Unknown
Status in gcc-5 package in Ubuntu:
  New

Bug description:
  This is upstream bug
  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67707 with a fix already
  in upstream gcc.

  The following program:

  #include <stdio.h>
  #include <utility>
  #include <deque>
  #include <memory>

  template<typename T>
  struct my_allocator: public std::allocator<T>
  {
          typedef size_t size_type;
          typedef T * pointer;
          typedef const T * const_pointer;

          typedef std::false_type is_always_equal;

          template<typename _Tp1>
          struct rebind
          {
                  typedef my_allocator<_Tp1> other;
          };

          pointer allocate(size_type n, const void *hint = nullptr)
          {
                  return std::allocator<T>::allocate(n, hint);
          }

          void deallocate(pointer p, size_type n)
          {
                  return std::allocator<T>::deallocate(p, n);
          }

          size_type max_size() const
          {
                  return std::allocator<T>::max_size();
          }

          my_allocator() : std::allocator<T>() { }
          ~my_allocator() { }

          my_allocator(const my_allocator & a) : std::allocator<T>(a) { }
          template<typename U>
          my_allocator(const my_allocator<U> & a) : std::allocator<T>(a) { }
  };

  int main(int argc, char * argv[])
  {
          std::deque<int, my_allocator<int>> a;

          printf("empty %d size %zd\n", a.empty(), a.size());
          a.emplace_back(1);
          printf("empty %d size %zd\n", a.empty(), a.size());
          std::deque<int, my_allocator<int>> b = std::move(a);
          printf("empty %d size %zd\n", a.empty(), a.size());
          a = std::deque<int, my_allocator<int>>();
          printf("empty %d size %zd\n", a.empty(), a.size());

          return 0;
  }

  incorrectly corrupts deque state and crashes:

  $ g++-5 --std=c++11 a.cpp
  $ ./a.out
  empty 1 size 0
  empty 0 size 1
  empty 1 size -128
  Segmentation fault (core dumped)

  This is with:

  $ g++-5 --version
  g++-5 (Ubuntu 5.2.1-18ubuntu1) 5.2.1 20150922

  If at all possible it would be great to get the upstream fix into
  Ubuntu 15.10 before the final release.  The upstream patch is very
  small (one line plus test case and changelog).

  ProblemType: Bug
  DistroRelease: Ubuntu 15.10
  Package: gcc-5 5.2.1-18ubuntu1
  ProcVersionSignature: Ubuntu 4.2.0-10.12-generic 4.2.0
  Uname: Linux 4.2.0-10-generic x86_64
  ApportVersion: 2.18.1-0ubuntu1
  Architecture: amd64
  CurrentDesktop: Unity
  Date: Thu Sep 24 16:53:12 2015
  InstallationDate: Installed on 2014-01-11 (621 days ago)
  InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Alpha amd64 (20140109)
  SourcePackage: gcc-5
  UpgradeStatus: Upgraded to wily on 2015-09-18 (6 days ago)

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