Add a set of atomics based on GCC intrinsics

With this implementation, we can have Qt run on any architecture that
GCC supports without having to write specialised code. However, on
some architectures, the code that GCC generates is not optimal: it
uses locking on ARMv5 and it's always fully-ordered. For that reason,
it appears after the Qt native assembly implementations (it's a
fallback, not an override).

Since they all have fully-ordered memory semantics, we define only the
xxxRelaxed functions. The exception is __sync_lock_and_test, which has
acquire semantics, so we need to define the Release and Ordered
versions too.

On some architectures, GCC can support atomics on types different than
32-bit and pointer-sized (like x86, x86-64, ARM and even
MIPS). However, there's no standardised way of telling: GCC seems to
define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_{1,2,4,8} if those operations
are present, but I couldn't find it on the ARM compiler (it was there
for i386, x86-64, IA-64 and MIPS).

Change-Id: I55ff7a7c0cfc6388b7ad8e2c0dedecffdf2a3e01
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>

3 files changed, 133 insertions, 1 deletions

diff --git a/src/corelib/arch/arch.pri b/src/corelib/arch/arch.pri
index e8699a27c6..ba6fc71e2f 100644
--- a/src/corelib/arch/arch.pri
+++ b/src/corelib/arch/arch.pri
@@ -30,7 +30,8 @@ integrity:HEADERS += arch/qatomic_integrity.h
                        arch/qatomic_x86_64.h \
                        arch/qatomic_sh.h \
                        arch/qatomic_sh4a.h \
-                       arch/qatomic_nacl.h
+                       arch/qatomic_nacl.h \
+                       arch/qatomic_gcc.h
 
 QT_ARCH_CPP = $$QT_SOURCE_TREE/src/corelib/arch/$$QT_ARCH
 DEPENDPATH += $$QT_ARCH_CPP
diff --git a/src/corelib/arch/qatomic_gcc.h b/src/corelib/arch/qatomic_gcc.h
new file mode 100644
index 0000000000..2788aaf59b
--- /dev/null
+++ b/src/corelib/arch/qatomic_gcc.h
@@ -0,0 +1,129 @@
+/****************************************************************************
+**
+** Copyright (C) 2011 Thiago Macieira <thiago@kde.org>
+** Contact: http://www.qt-project.org/
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** GNU Lesser General Public License Usage
+** This file may be used under the terms of the GNU Lesser General Public
+** License version 2.1 as published by the Free Software Foundation and
+** appearing in the file LICENSE.LGPL included in the packaging of this
+** file. Please review the following information to ensure the GNU Lesser
+** General Public License version 2.1 requirements will be met:
+** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Nokia gives you certain additional
+** rights. These rights are described in the Nokia Qt LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU General
+** Public License version 3.0 as published by the Free Software Foundation
+** and appearing in the file LICENSE.GPL included in the packaging of this
+** file. Please review the following information to ensure the GNU General
+** Public License version 3.0 requirements will be met:
+** http://www.gnu.org/copyleft/gpl.html.
+**
+** Other Usage
+** Alternatively, this file may be used in accordance with the terms and
+** conditions contained in a signed written agreement between you and Nokia.
+**
+**
+**
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QATOMIC_GCC_H
+#define QATOMIC_GCC_H
+
+#include <QtCore/qgenericatomic.h>
+
+QT_BEGIN_HEADER
+QT_BEGIN_NAMESPACE
+
+#if 0
+#pragma qt_sync_stop_processing
+#endif
+
+template<> struct QAtomicIntegerTraits<int> { enum { IsInteger = 1 }; };
+template<> struct QAtomicIntegerTraits<unsigned int> { enum { IsInteger = 1 }; };
+
+#define Q_ATOMIC_INT_REFERENCE_COUNTING_IS_SOMETIMES_NATIVE
+#define Q_ATOMIC_INT_TEST_AND_SET_IS_SOMETIMES_NATIVE
+#define Q_ATOMIC_INT_FETCH_AND_STORE_IS_SOMETIMES_NATIVE
+#define Q_ATOMIC_INT_FETCH_AND_ADD_IS_SOMETIMES_NATIVE
+
+#define Q_ATOMIC_INT32_IS_SUPPORTED
+#define Q_ATOMIC_INT32_REFERENCE_COUNTING_IS_SOMETIMES_NATIVE
+#define Q_ATOMIC_INT32_TEST_AND_SET_IS_SOMETIMES_NATIVE
+#define Q_ATOMIC_INT32_FETCH_AND_STORE_IS_SOMETIMES_NATIVE
+#define Q_ATOMIC_INT32_FETCH_AND_ADD_IS_SOMETIMES_NATIVE
+
+#define Q_ATOMIC_POINTER_REFERENCE_COUNTING_IS_SOMETIMES_NATIVE
+#define Q_ATOMIC_POINTER_TEST_AND_SET_IS_SOMETIMES_NATIVE
+#define Q_ATOMIC_POINTER_FETCH_AND_STORE_IS_SOMETIMES_NATIVE
+#define Q_ATOMIC_POINTER_FETCH_AND_ADD_IS_SOMETIMES_NATIVE
+
+template <typename T> struct QAtomicOps: QGenericAtomicOps<QAtomicOps<T> >
+{
+    // The GCC intrinsics all have fully-ordered memory semantics, so we define
+    // only the xxxRelaxed functions. The exception is __sync_lock_and_test,
+    // which has acquire semantics, so we need to define the Release and
+    // Ordered versions too.
+
+    typedef T Type;
+
+#ifndef __ia64__
+    static T loadAcquire(T &_q_value)
+    {
+        T tmp = _q_value;
+        __sync_synchronize();
+        return tmp;
+    }
+
+    static void storeRelease(T &_q_value, T newValue)
+    {
+        __sync_synchronize();
+        _q_value = newValue;
+    }
+#endif
+
+    static bool isTestAndSetNative() { return false; }
+    static bool isTestAndSetWaitFree() { return false; }
+    static bool testAndSetRelaxed(T &_q_value, T expectedValue, T newValue)
+    {
+        return __sync_bool_compare_and_swap(&_q_value, expectedValue, newValue);
+    }
+
+    static T fetchAndStoreRelaxed(T &_q_value, T newValue)
+    {
+        return __sync_lock_test_and_set(&_q_value, newValue);
+    }
+
+    static T fetchAndStoreRelease(T &_q_value, T newValue)
+    {
+        __sync_synchronize();
+        return __sync_lock_test_and_set(&_q_value, newValue);
+    }
+
+    static T fetchAndStoreOrdered(T &_q_value, T newValue)
+    {
+        return fetchAndStoreRelease(_q_value, newValue);
+    }
+
+    static
+    T fetchAndAddRelaxed(T &_q_value, typename QAtomicAdditiveType<T>::AdditiveT valueToAdd)
+    {
+        return __sync_fetch_and_add(&_q_value, valueToAdd * QAtomicAdditiveType<T>::AddScale);
+    }
+};
+
+QT_END_NAMESPACE
+QT_END_HEADER
+
+#endif // QATOMIC_GCC_H
diff --git a/src/corelib/thread/qbasicatomic.h b/src/corelib/thread/qbasicatomic.h
index a9a3fe92c6..18febd36de 100644
--- a/src/corelib/thread/qbasicatomic.h
+++ b/src/corelib/thread/qbasicatomic.h
@@ -58,6 +58,8 @@
 #  include "QtCore/qatomic_mips.h"
 #elif defined(__x86_64) || defined(__x86_64__) || defined(__amd64)
 #  include <QtCore/qatomic_x86_64.h>
+#elif defined(Q_CC_GNU)
+#  include <QtCore/qatomic_gcc.h>
 #else
 #  define QT_OLD_ATOMICS
 #endif