re PR libstdc++/65147 (alignment of std::atomic object is not correct)

2015-04-09  Jonathan Wakely  <jwakely@redhat.com>
	    Richard Henderson  <rth@redhat.com>

	PR libstdc++/65147
	* include/bits/atomic_base.h (__atomic_base<_ITp>): Increase
	alignment.
	* include/std/atomic (atomic): For types with a power of two size set
	alignment to at least the size.
	* testsuite/29_atomics/atomic/60695.cc: Adjust dg-error line number.
	* testsuite/29_atomics/atomic/65147.cc: New.
	* testsuite/29_atomics/atomic_integral/65147.cc: New.

Co-Authored-By: Richard Henderson <rth@redhat.com>

From-SVN: r221945

libstdc++-v3/ChangeLog

+2015-04-09  Jonathan Wakely  <jwakely@redhat.com>
+	    Richard Henderson  <rth@redhat.com>
+
+	PR libstdc++/65147
+	* include/bits/atomic_base.h (__atomic_base<_ITp>): Increase
+	alignment.
+	* include/std/atomic (atomic): For types with a power of two size set
+	alignment to at least the size.
+	* testsuite/29_atomics/atomic/60695.cc: Adjust dg-error line number.
+	* testsuite/29_atomics/atomic/65147.cc: New.
+	* testsuite/29_atomics/atomic_integral/65147.cc: New.
+
 2015-04-09  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>
 
 	* config/abi/post/solaris2.10/baseline_symbols.txt: Regenerate.

libstdc++-v3/include/bits/atomic_base.h

@@ -240,7 +240,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     private:
       typedef _ITp 	__int_type;
 
-      __int_type 	_M_i;
+      static constexpr int _S_alignment =
+	sizeof(_ITp) > alignof(_ITp) ? sizeof(_ITp) : alignof(_ITp);
+
+      alignas(_S_alignment) __int_type _M_i;
 
     public:
       __atomic_base() noexcept = default;

libstdc++-v3/include/std/atomic

@@ -165,18 +165,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     struct atomic
     {
     private:
-      // Align 1/2/4/8/16-byte types the same as integer types of that size.
-      // This matches the alignment effects of the C11 _Atomic qualifier.
+      // Align 1/2/4/8/16-byte types to at least their size.
       static constexpr int _S_min_alignment
-	= sizeof(_Tp) == sizeof(char)	   ? alignof(char)
-	: sizeof(_Tp) == sizeof(short)	   ? alignof(short)
-	: sizeof(_Tp) == sizeof(int)	   ? alignof(int)
-	: sizeof(_Tp) == sizeof(long)	   ? alignof(long)
-	: sizeof(_Tp) == sizeof(long long) ? alignof(long long)
-#ifdef _GLIBCXX_USE_INT128
-	: sizeof(_Tp) == sizeof(__int128)  ? alignof(__int128)
-#endif
-	: 0;
+	= (sizeof(_Tp) & (sizeof(_Tp) - 1)) || sizeof(_Tp) > 16
+	? 0 : sizeof(_Tp);
 
       static constexpr int _S_alignment
         = _S_min_alignment > alignof(_Tp) ? _S_min_alignment : alignof(_Tp);

libstdc++-v3/testsuite/29_atomics/atomic/60695.cc

@@ -27,4 +27,4 @@ struct X {
   char stuff[0]; // GNU extension, type has zero size
 };
 
-std::atomic<X> a;  // { dg-error "not supported" "" { target *-*-* } 189 }
+std::atomic<X> a;  // { dg-error "not supported" "" { target *-*-* } 181 }

libstdc++-v3/testsuite/29_atomics/atomic/65147.cc

+// 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++11" }
+// { dg-do compile }
+
+#include <atomic>
+
+struct S16 {
+   char c[16];
+};
+
+static_assert( alignof(std::atomic<S16>) >= 16,
+    "atomic<S16> must be aligned to at least its size" );

libstdc++-v3/testsuite/29_atomics/atomic_integral/65147.cc

+// 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++11" }
+// { dg-do compile }
+
+#include <atomic>
+
+static_assert( alignof(std::atomic<char>) >= sizeof(char),
+    "atomic<char> must be aligned to at least its size" );
+static_assert( alignof(std::atomic<short>) >= sizeof(short),
+    "atomic<short> must be aligned to at least its size" );
+static_assert( alignof(std::atomic<int>) >= sizeof(int),
+    "atomic<int> must be aligned to at least its size" );
+static_assert( alignof(std::atomic<long>) >= sizeof(long),
+    "atomic<long> must be aligned to at least its size" );
+static_assert( alignof(std::atomic<long long>) >= sizeof(long long),
+    "atomic<long long> must be aligned to at least its size" );