[Patch] Fix aliasing (/alignment) issue in ext/pb_assoc

[Paolo Carlini <pcarlini at suse dot de>]

Hi all, hi Benjamin,

as pointed out by Chris here:

    http://gcc.gnu.org/ml/libstdc++/2005-12/msg00232.html

and discussed a bit here:

    http://gcc.gnu.org/ml/libstdc++/2006-01/msg00013.html

We have got this aliasing/alignment issue, which, as far as I can see,
is a perfect candidate for a neat use of
tr1::aligned_storage/alignment_of. Indeed, the below appear to work
well, and the warning is gone. Any objections to this approach? Would be
for 4.1 branch too.

Thanks,
Paolo.

///////////////

2006-01-17  Paolo Carlini  <pcarlini@suse.de>

	* include/ext/pb_assoc/detail/value_type_adapter/
	value_type_adapter.hpp: Include <tr1/type_traits>.
	* include/ext/pb_assoc/detail/value_type_adapter/
	it_value_type_traits.hpp (it_value_type_traits_<>::value_type_holder):
	Use tr1::aligned_storage and tr1::alignment_of.
	(it_value_type_traits_<>::buf_t): Remove.
	(it_value_type_traits_<>::make_valid, recast): Adjust.

Index: include/ext/pb_assoc/detail/value_type_adapter/value_type_adapter.hpp
===================================================================
--- include/ext/pb_assoc/detail/value_type_adapter/value_type_adapter.hpp	(revision 109795)
+++ include/ext/pb_assoc/detail/value_type_adapter/value_type_adapter.hpp	(working copy)
@@ -1,6 +1,6 @@
 // -*- C++ -*-
 
-// Copyright (C) 2005 Free Software Foundation, Inc.
+// Copyright (C) 2005, 2006 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
@@ -51,6 +51,7 @@
 #include <ext/pb_assoc/detail/type_utils.hpp>
 #include <utility>
 #include <algorithm>
+#include <tr1/type_traits>  // for aligned_storage/alignment_of
 
 namespace pb_assoc
 {
Index: include/ext/pb_assoc/detail/value_type_adapter/it_value_type_traits.hpp
===================================================================
--- include/ext/pb_assoc/detail/value_type_adapter/it_value_type_traits.hpp	(revision 109795)
+++ include/ext/pb_assoc/detail/value_type_adapter/it_value_type_traits.hpp	(working copy)
@@ -1,6 +1,6 @@
 // -*- C++ -*-
 
-// Copyright (C) 2005 Free Software Foundation, Inc.
+// Copyright (C) 2005, 2006 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
@@ -94,16 +94,13 @@
     value_type>::other::const_pointer
   const_pointer;
 
-  typedef
-  typename Allocator_::template rebind<
-    int* >::other::value_type
-  buf_t;
-
   struct value_type_holder
   {
-    buf_t m_a_key_buf[sizeof(key_ref_pair) / sizeof(buf_t) + 1];
+    typename std::tr1::aligned_storage<sizeof(key_ref_pair),
+      std::tr1::alignment_of<key_ref_pair>::value>::type  m_a_key_buf;
 
-    buf_t m_a_value_buf[sizeof(value_type) / sizeof(buf_t) + 1];
+    typename std::tr1::aligned_storage<sizeof(value_type),
+      std::tr1::alignment_of<value_type>::value>::type  m_a_value_buf;
   };
 
   typedef
@@ -114,7 +111,7 @@
   inline static pointer
   recast(value_type_hoder_valerence r_holder)
   {
-    return reinterpret_cast<pointer>(r_holder.m_a_value_buf);
+    return reinterpret_cast<pointer>(&r_holder.m_a_value_buf);
   }
 
   inline static void
@@ -125,7 +122,7 @@
       void* >::other::value_type
       void_pointer;
 
-    void_pointer p_target = r_holder.m_a_key_buf;
+    void_pointer p_target = &r_holder.m_a_key_buf;
 
     new (p_target) key_ref_pair(r_bk, r_val.first);
 
@@ -135,9 +132,9 @@
       key_ref_pair_pointer;
 
     key_ref_pair_pointer p_key =
-      reinterpret_cast<key_ref_pair_pointer>(r_holder.m_a_key_buf);
+      reinterpret_cast<key_ref_pair_pointer>(&r_holder.m_a_key_buf);
 
-    p_target = r_holder.m_a_value_buf;
+    p_target = &r_holder.m_a_value_buf;
 
     new (p_target) value_type(*p_key, r_val.second);
   }
@@ -185,16 +182,13 @@
     value_type>::other::const_pointer
   const_pointer;
 
-  typedef
-  typename Allocator_::template rebind<
-    int* >::other::value_type
-  buf_t;
-
   struct value_type_holder
   {
-    buf_t m_a_key_buf[sizeof(key_ref_pair) / sizeof(buf_t) + 1];
+    typename std::tr1::aligned_storage<sizeof(key_ref_pair),
+      std::tr1::alignment_of<key_ref_pair>::value>::type  m_a_key_buf;
 
-    buf_t m_a_value_buf[sizeof(value_type) / sizeof(buf_t) + 1];
+    typename std::tr1::aligned_storage<sizeof(value_type),
+      std::tr1::alignment_of<value_type>::value>::type  m_a_value_buf;
   };
 
   typedef
@@ -205,7 +199,7 @@
   inline static pointer
   recast(value_type_hoder_valerence r_holder)
   {
-    return reinterpret_cast<pointer>(r_holder.m_a_value_buf);
+    return reinterpret_cast<pointer>(&r_holder.m_a_value_buf);
   }
 
   inline static void
@@ -216,7 +210,7 @@
       void* >::other::value_type
       void_pointer;
 
-    void_pointer p_target = r_holder.m_a_value_buf;
+    void_pointer p_target = &r_holder.m_a_value_buf;
 
     new (p_target) key_ref_pair(r_bk, r_val.first);
   }