tests: fix some -Wvolatile

C++20 deprecated compound volatile statements such as pre- and
post-increments, to stress that they're not atomic. So instead of

    volatile i;
    ~~~~;
    ++i;

you're now supposed to write

    volatile i;
    ~~~~;
    int j = i; // volatile load
    ++j;
    i = j; // volatile store

which matches more closely what hardware does.

Instead of fixing every use of volatile pre- or post-increment in this
fashion individually, and realising that probably a few more Qt
modules will have the same kind of code patterns in them, write
QtPrivate functions to do the job centrally.

Change-Id: I838097bd484ef2118c071726963f103c080d2ba5
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/corelib/CMakeLists.txt

@@ -60,6 +60,7 @@ qt_internal_add_module(Core
         global/qsysinfo.h
         global/qsystemdetection.h
         global/qtypeinfo.h
+        global/qvolatile_p.h
         io/qabstractfileengine.cpp io/qabstractfileengine_p.h
         io/qbuffer.cpp io/qbuffer.h
         io/qdataurl.cpp io/qdataurl_p.h

src/corelib/global/qvolatile_p.h

@@ -0,0 +1,89 @@
+/****************************************************************************
+**
+** Copyright (C) 2021 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Marc Mutz <marc.mutz@kdab.com>
+** Contact: http://www.qt.io/licensing/
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QVOLATILE_P_H
+#define QVOLATILE_P_H
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API.  It exists for the convenience
+// of a number of Qt sources files.  This header file may change from
+// version to version without notice, or even be removed.
+//
+// We mean it.
+//
+
+#include <QtCore/qglobal.h>
+
+QT_BEGIN_NAMESPACE
+
+namespace QtPrivate {
+template <typename T>
+using if_volatile = std::enable_if_t<std::is_volatile_v<T>, bool>;
+
+//
+// C++20-deprecated volatile compound operations, rewritten as separated operations
+//
+
+// these functions return `auto`, not `T`, to strip cv-qualifiers without having
+// to mention the `volatile` keyword
+
+template <typename T, QtPrivate::if_volatile<T> = true>
+auto volatilePreIncrement(T &x) {
+    auto y = x;
+    ++y;
+    x = y;
+    return y;
+}
+
+template <typename T, QtPrivate::if_volatile<T> = true>
+auto volatilePreDecrement(T &x)
+{
+    auto y = x;
+    --y;
+    x = y;
+    return y;
+}
+} // namespace QtPrivate
+
+QT_END_NAMESPACE
+
+#endif // QVOLATILE_H

tests/auto/corelib/thread/qmutex/CMakeLists.txt

@@ -7,12 +7,6 @@
 qt_internal_add_test(tst_qmutex
     SOURCES
         tst_qmutex.cpp
-)
-
-## Scopes:
-#####################################################################
-
-qt_internal_extend_target(tst_qmutex CONDITION WIN32
     PUBLIC_LIBRARIES
         Qt::CorePrivate
 )

tests/auto/corelib/thread/qmutex/tst_qmutex.cpp

@@ -36,6 +36,7 @@
 #include <qmutex.h>
 #include <qthread.h>
 #include <qwaitcondition.h>
+#include <private/qvolatile_p.h>
 
 class tst_QMutex : public QObject
 {
@@ -1191,9 +1192,9 @@ void tst_QMutex::tryLockDeadlock()
         {
             for (int i = 0; i < 100000; ++i) {
                 if (mut.tryLock(0)) {
-                    if ((++tryLockDeadlockCounter) != 1)
+                    if (QtPrivate::volatilePreIncrement(tryLockDeadlockCounter) != 1)
                         ++tryLockDeadlockFailureCount;
-                    if ((--tryLockDeadlockCounter) != 0)
+                    if (QtPrivate::volatilePreDecrement(tryLockDeadlockCounter) != 0)
                         ++tryLockDeadlockFailureCount;
                     mut.unlock();
                 }
@@ -1210,9 +1211,9 @@ void tst_QMutex::tryLockDeadlock()
 
     for (int i = 0; i < 100000; ++i) {
         mut.lock();
-        if ((++tryLockDeadlockCounter) != 1)
+        if (QtPrivate::volatilePreIncrement(tryLockDeadlockCounter) != 1)
             ++tryLockDeadlockFailureCount;
-        if ((--tryLockDeadlockCounter) != 0)
+        if (QtPrivate::volatilePreDecrement(tryLockDeadlockCounter) != 0)
             ++tryLockDeadlockFailureCount;
         mut.unlock();
     }

tests/auto/corelib/thread/qreadwritelock/CMakeLists.txt

@@ -7,4 +7,6 @@
 qt_internal_add_test(tst_qreadwritelock
     SOURCES
         tst_qreadwritelock.cpp
+    PUBLIC_LIBRARIES
+        Qt::CorePrivate
 )

tests/auto/corelib/thread/qreadwritelock/tst_qreadwritelock.cpp

@@ -34,6 +34,7 @@
 #include <qmutex.h>
 #include <qthread.h>
 #include <qwaitcondition.h>
+#include <private/qvolatile_p.h>
 
 #ifdef Q_OS_UNIX
 #include <unistd.h>
@@ -587,12 +588,8 @@ public:
             if(count)
                 qFatal("Non-zero count at start of write! (%d)",count );
 //            printf(".");
-            int i;
+            for (int i = 0; i < maxval; ++i)
-            for(i=0; i<maxval; ++i) {
+                QtPrivate::volatilePreIncrement(count);
-                volatile int lc=count;
-                ++lc;
-                count=lc;
-            }
             count=0;
             testRwlock.unlock();
             msleep(ulong(waitTime));

tests/auto/corelib/tools/qsharedpointer/CMakeLists.txt

@@ -8,4 +8,6 @@ qt_internal_add_test(tst_qsharedpointer
         nontracked.cpp
         wrapper.cpp
         tst_qsharedpointer.cpp
+    PUBLIC_LIBRARIES
+        Qt::CorePrivate
 )

tests/auto/corelib/tools/qsharedpointer/tst_qsharedpointer.cpp

@@ -37,6 +37,7 @@
 #include <QtCore/QList>
 #include <QtCore/QMap>
 #include <QtCore/QThread>
+#include <QtCore/private/qvolatile_p.h>
 
 #include "forwarddeclared.h"
 #include "nontracked.h"
@@ -1944,7 +1945,7 @@ class ThreadData
     QAtomicInt * volatile ptr;
 public:
     ThreadData(QAtomicInt *p) : ptr(p) { }
-    ~ThreadData() { ++ptr; }
+    ~ThreadData() { QtPrivate::volatilePreIncrement(ptr); }
     void ref()
     {
         // if we're called after the destructor, we'll crash

tests/benchmarks/corelib/thread/qmutex/CMakeLists.txt

@@ -8,6 +8,7 @@ qt_internal_add_benchmark(tst_bench_qmutex
     SOURCES
         tst_qmutex.cpp
     PUBLIC_LIBRARIES
+        Qt::CorePrivate
         Qt::Test
 )
 

tests/benchmarks/corelib/thread/qmutex/tst_qmutex.cpp

@@ -28,6 +28,7 @@
 
 #include <QtCore/QtCore>
 #include <QTest>
+#include <QtCore/private/qvolatile_p.h>
 
 #include <math.h>
 
@@ -158,7 +159,7 @@ void tst_QMutex::noThread()
             QBENCHMARK {
                 count = 0;
                 for (int i = 0; i < N; i++) {
-                    count++;
+                    QtPrivate::volatilePreIncrement(count);
                 }
             }
             break;
@@ -167,7 +168,7 @@ void tst_QMutex::noThread()
                 count = 0;
                 for (int i = 0; i < N; i++) {
                     mtx.lock();
-                    count++;
+                    QtPrivate::volatilePreIncrement(count);
                     mtx.unlock();
                 }
             }
@@ -177,7 +178,7 @@ void tst_QMutex::noThread()
                 count = 0;
                 for (int i = 0; i < N; i++) {
                     QMutexLocker locker(&mtx);
-                    count++;
+                    QtPrivate::volatilePreIncrement(count);
                 }
             }
             break;