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>

1 files changed, 89 insertions, 0 deletions

diff --git a/src/corelib/global/qvolatile_p.h b/src/corelib/global/qvolatile_p.h
new file mode 100644
index 0000000000..211cb3d90c
--- /dev/null
+++ b/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