On 26/03/15 13:21 +0000, Jonathan Wakely wrote:
This includes your fix to avoid decreasing alignment, but I didn't add
a test for that as I couldn't make it fail on any of the targets I
test on.
commit f796769ad20c0353490b9f1a7e019e2f0c1771fb
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Wed Sep 3 15:39:53 2014 +0100
PR libstdc++/62259
PR libstdc++/65147
* include/std/atomic (atomic<T>): Increase alignment for types with
the same size as one of the integral types.
* testsuite/29_atomics/atomic/60695.cc: Adjust dg-error line number.
* testsuite/29_atomics/atomic/62259.cc: New.
My patch was not sufficient to fix 65147, because I didn't increase
the alignment of the std::atomic<integral type> specializations, and
std::atomic<16-byte type> is only aligned correctly if __int128 is
supported, which isn't true on x86 and other 32-bit targets.
This is the best I've come up with, does anyone have any better ideas
than the #else branch to hardcode alignment of 16-byte types to 16?
commit d0ccfb0523066c69f3d22d9cdd617a139c57f9e1
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Mon Mar 30 14:28:01 2015 +0100
PR libstdc++/65147
* include/bits/atomic_base.h (__atomic_base): Align as underlying
type.
* include/std/atomic (atomic<T>): Hardcode alignment for 16-byte
types when __int128 is not available.
* testsuite/29_atomics/atomic/60695.cc: Adjust dg-error line number.
* testsuite/29_atomics/atomic/65147.cc: New.
diff --git a/libstdc++-v3/include/bits/atomic_base.h b/libstdc++-v3/include/bits/atomic_base.h
index 8104c98..48931ac 100644
--- a/libstdc++-v3/include/bits/atomic_base.h
+++ b/libstdc++-v3/include/bits/atomic_base.h
@@ -235,7 +235,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// 8 bytes, since that is what GCC built-in functions for atomic
// memory access expect.
template<typename _ITp>
- struct __atomic_base
+ struct alignas(_ITp) __atomic_base
{
private:
typedef _ITp __int_type;
@@ -559,7 +559,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
/// Partial specialization for pointer types.
template<typename _PTp>
- struct __atomic_base<_PTp*>
+ struct alignas(_PTp*) __atomic_base<_PTp*>
{
private:
typedef _PTp* __pointer_type;
diff --git a/libstdc++-v3/include/std/atomic b/libstdc++-v3/include/std/atomic
index 88c8b17..2b09477 100644
--- a/libstdc++-v3/include/std/atomic
+++ b/libstdc++-v3/include/std/atomic
@@ -175,6 +175,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
: sizeof(_Tp) == sizeof(long long) ? alignof(long long)
#ifdef _GLIBCXX_USE_INT128
: sizeof(_Tp) == sizeof(__int128) ? alignof(__int128)
+#else
+ : sizeof(_Tp) == 16 ? 16
#endif
: 0;
diff --git a/libstdc++-v3/testsuite/29_atomics/atomic/60695.cc b/libstdc++-v3/testsuite/29_atomics/atomic/60695.cc
index 6f618a0..f755be0 100644
--- a/libstdc++-v3/testsuite/29_atomics/atomic/60695.cc
+++ b/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 *-*-* } 191 }
diff --git a/libstdc++-v3/testsuite/29_atomics/atomic/65147.cc b/libstdc++-v3/testsuite/29_atomics/atomic/65147.cc
new file mode 100644
index 0000000..bb92513
--- /dev/null
+++ b/libstdc++-v3/testsuite/29_atomics/atomic/65147.cc
@@ -0,0 +1,42 @@
+// 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 }
+
+// PR libstdc++65147
+
+#include <atomic>
+
+static_assert( alignof(std::atomic<short>) == alignof(short),
+ "atomic short must be aligned like short" );
+
+static_assert( alignof(std::atomic<int>) == alignof(int),
+ "atomic int must be aligned like int" );
+
+static_assert( alignof(std::atomic<long>) == alignof(long),
+ "atomic long must be aligned like long" );
+
+static_assert( alignof(std::atomic<long long>) == alignof(long long),
+ "atomic long long must be aligned like long long" );
+
+struct S {
+ char s[16];
+};
+
+static_assert( alignof(std::atomic<S>) > 1,
+ "atomic 16-byte struct must not be aligned like char" );
