Add benchmark for pathological O(N^2) behavior in QQmlChangeSet.

This patch is just here for documentation of this behavior and does not
come with a fix yet. This hotspot was found while profiling the example
code attached to QTBUG-34391. It is triggered by the repeated calls
to _q_itemsMoved in QQmlDelegateModel::_q_layoutChanged.

Change-Id: I758744b3650c3c47dc86b914b823c3e9f96ce81e
Reviewed-by: Albert Astals Cid <albert.astals@canonical.com>
Reviewed-by: Daniel Vrátil <daniel.vratil@kdab.com>
Reviewed-by: Christopher Adams <chris.adams@jollamobile.com>

3 files changed, 71 insertions, 0 deletions

diff --git a/tests/benchmarks/qml/qml.pro b/tests/benchmarks/qml/qml.pro
index d3ce69c713..5d48ec0067 100644
--- a/tests/benchmarks/qml/qml.pro
+++ b/tests/benchmarks/qml/qml.pro
@@ -5,6 +5,7 @@ SUBDIRS += \
            compilation \
            javascript \
            holistic \
+           qqmlchangeset \
            qqmlcomponent \
            qqmlimage \
            qqmlmetaproperty \
diff --git a/tests/benchmarks/qml/qqmlchangeset/qqmlchangeset.pro b/tests/benchmarks/qml/qqmlchangeset/qqmlchangeset.pro
new file mode 100644
index 0000000000..fc0ccdf8ed
--- /dev/null
+++ b/tests/benchmarks/qml/qqmlchangeset/qqmlchangeset.pro
@@ -0,0 +1,10 @@
+CONFIG += benchmark
+TEMPLATE = app
+TARGET = tst_qqmlchangeset
+QT += qml quick-private testlib
+osx:CONFIG -= app_bundle
+
+SOURCES += tst_qqmlchangeset.cpp
+
+DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0
+
diff --git a/tests/benchmarks/qml/qqmlchangeset/tst_qqmlchangeset.cpp b/tests/benchmarks/qml/qqmlchangeset/tst_qqmlchangeset.cpp
new file mode 100644
index 0000000000..bbfb52343c
--- /dev/null
+++ b/tests/benchmarks/qml/qqmlchangeset/tst_qqmlchangeset.cpp
@@ -0,0 +1,60 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Milian Wolff <milian.wolff@kdab.com>
+** Contact: http://www.qt.io/licensing/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL21$
+** 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 http://www.qt.io/terms-conditions. For further
+** information use the contact form at http://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 2.1 or version 3 as published by the Free
+** Software Foundation and appearing in the file LICENSE.LGPLv21 and
+** LICENSE.LGPLv3 included in the packaging of this file. Please review the
+** following information to ensure the GNU Lesser General Public License
+** requirements will be met: https://www.gnu.org/licenses/lgpl.html and
+** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** As a special exception, The Qt Company gives you certain additional
+** rights. These rights are described in The Qt Company LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <qtest.h>
+
+#include <QDebug>
+
+#include <private/qqmlchangeset_p.h>
+
+class tst_qqmlchangeset : public QObject
+{
+    Q_OBJECT
+
+private slots:
+    void move();
+};
+
+void tst_qqmlchangeset::move()
+{
+    QBENCHMARK {
+        QQmlChangeSet set;
+        const int MAX_ROWS = 30000;
+        for (int i = 0; i < MAX_ROWS; ++i) {
+            set.move(i, MAX_ROWS - 1 - i, 1, i);
+        }
+    }
+}
+
+QTEST_MAIN(tst_qqmlchangeset)
+#include "tst_qqmlchangeset.moc"