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Re: [patch] Fix std::experimental::any for small, non-trivial objects


On 02/05/15 19:51 +0200, Daniel Krügler wrote:
2015-05-02 19:33 GMT+02:00 Jonathan Wakely <jwakely@redhat.com>:
Looking at it now, I think the _Internal alias template should also
check that alignof(_Tp) <= alignof(void*) so that it can safely be
stored in the _Storage.

Otherwise a type with sizeof(T) <= sizeof(void*) but
alignof(T) > alignof(void*) would not be correctly aligned when stored
in the buffer.

Yes, I agree.

Fixed like so, tested powerpc64le-linux and powerpc-aix, committed to
trunk. I'll do something similar on the gcc5 branch too, but not
today.
commit a29ec813a90122d1c23eb74af379ce6e0c416c8e
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Sat May 2 19:05:51 2015 +0100

    	* include/experimental/any (any::_Storage): Fix alignment of buffer.
    	(any::_Internal): Check alignment of type.
    	* testsuite/experimental/any/cons/aligned.cc: New.
    	* testsuite/experimental/any/misc/any_cast_neg.cc: Adjust dg-error.

diff --git a/libstdc++-v3/include/experimental/any b/libstdc++-v3/include/experimental/any
index b2d1b9c..7b5e5ec 100644
--- a/libstdc++-v3/include/experimental/any
+++ b/libstdc++-v3/include/experimental/any
@@ -98,11 +98,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       _Storage& operator=(const _Storage&) = delete;
 
       void* _M_ptr;
-      std::aligned_storage<sizeof(_M_ptr), sizeof(_M_ptr)>::type _M_buffer;
+      aligned_storage<sizeof(_M_ptr), alignof(void*)>::type _M_buffer;
     };
 
     template<typename _Tp, typename _Safe = is_nothrow_move_constructible<_Tp>,
-	     bool _Fits = (sizeof(_Tp) <= sizeof(_Storage))>
+	     bool _Fits = (sizeof(_Tp) <= sizeof(_Storage))
+			  && (alignof(_Tp) <= alignof(_Storage))>
       using _Internal = std::integral_constant<bool, _Safe::value && _Fits>;
 
     template<typename _Tp>
diff --git a/libstdc++-v3/testsuite/experimental/any/cons/aligned.cc b/libstdc++-v3/testsuite/experimental/any/cons/aligned.cc
new file mode 100644
index 0000000..3923994
--- /dev/null
+++ b/libstdc++-v3/testsuite/experimental/any/cons/aligned.cc
@@ -0,0 +1,52 @@
+// Copyright (C) 2015 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/>.
+
+// { dg-options "-std=gnu++14" }
+
+#include <experimental/any>
+#include <cstdint>
+#include <testsuite_hooks.h>
+
+// Alignment requiremnts of this type prevent it being stored in 'any'
+struct alignas(2 * alignof(void*)) X { };
+
+bool
+stored_internally(void* obj, const std::experimental::any& a)
+{
+  std::uintptr_t a_addr = reinterpret_cast<std::uintptr_t>(&a);
+  std::uintptr_t a_end = a_addr + sizeof(a);
+  std::uintptr_t obj_addr = reinterpret_cast<std::uintptr_t>(obj);
+  return (a_addr <= obj_addr) && (obj_addr < a_end);
+}
+
+void
+test01()
+{
+  std::experimental::any a = X{};
+  X& x = std::experimental::any_cast<X&>(a);
+  VERIFY( !stored_internally(&x, a) );
+
+  a = 'X';
+  char& c = std::experimental::any_cast<char&>(a);
+  VERIFY( stored_internally(&c, a) );
+}
+
+int
+main()
+{
+  test01();
+}
diff --git a/libstdc++-v3/testsuite/experimental/any/misc/any_cast_neg.cc b/libstdc++-v3/testsuite/experimental/any/misc/any_cast_neg.cc
index 5823175..39e3226 100644
--- a/libstdc++-v3/testsuite/experimental/any/misc/any_cast_neg.cc
+++ b/libstdc++-v3/testsuite/experimental/any/misc/any_cast_neg.cc
@@ -26,5 +26,5 @@ void test01()
   using std::experimental::any_cast;
 
   const any y(1);
-  any_cast<int&>(y); // { dg-error "qualifiers" "" { target { *-*-* } } 355 }
+  any_cast<int&>(y); // { dg-error "qualifiers" "" { target { *-*-* } } 356 }
 }

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