[patch] libstdc++/60695 - add static_assert to std::atomic

[Jonathan Wakely]

As I said in the PR comments, I see no useful reason to allow
std::atomic<> to support zero-sized types.

Tested x86_64-linux, committed to trunk.


commit 6835d5ad1694f54d16c4a0d63273b12cbed78852
Author: Jonathan Wakely <a...@kayari.org>
Date:   Tue Apr 15 13:19:32 2014 +0100

        PR libstdc++/60695
        * include/std/atomic (atomic<_Tp>): Add static assertion.
        * testsuite/29_atomics/atomic/60695.cc: New.

diff --git a/libstdc++-v3/include/std/atomic b/libstdc++-v3/include/std/atomic
index ece75a4..1b8e445 100644
--- a/libstdc++-v3/include/std/atomic
+++ b/libstdc++-v3/include/std/atomic
@@ -163,6 +163,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     private:
       _Tp _M_i;
 
+      // TODO: static_assert(is_trivially_copyable<_Tp>::value, "");
+
+      static_assert(sizeof(_Tp) > 0,
+                   "Incomplete or zero-sized types are not supported");
+
     public:
       atomic() noexcept = default;
       ~atomic() noexcept = default;
diff --git a/libstdc++-v3/testsuite/29_atomics/atomic/60695.cc 
b/libstdc++-v3/testsuite/29_atomics/atomic/60695.cc
new file mode 100644
index 0000000..27c0c8f
--- /dev/null
+++ b/libstdc++-v3/testsuite/29_atomics/atomic/60695.cc
@@ -0,0 +1,30 @@
+// { dg-require-atomic-builtins "" }
+// { dg-options "-std=gnu++11" }
+// { dg-do compile }
+
+// Copyright (C) 2014 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+#include <atomic>
+
+// libstdc++/60695
+
+struct X {
+  char stuff[0]; // GNU extension, type has zero size
+};
+
+std::atomic<X> a;  // { dg-error "not supported" "" { target *-*-* } 168 }