QStack: Add a simple benchmark.

This covers the only real additions over QVector: push and pop. Really, there
isn't too much specific to benchmark here, but we're interested in one specific
case: that of pushing and popping a single item repeatedly.

With the current QVector behavior, this causes constant deallocation, which
makes it morbidly slow. This behavior will be reviewed in a subsequent commit.

Results (not that anyone really cares) for me:
    PASS   : tst_QStack::qstack_push()
    RESULT : tst_QStack::qstack_push():
         1.9 msecs per iteration (total: 61, iterations: 32)
    PASS   : tst_QStack::qstack_pop()
    RESULT : tst_QStack::qstack_pop():
         8.2 msecs per iteration (total: 66, iterations: 8)
    PASS   : tst_QStack::qstack_pushpopone()
    RESULT : tst_QStack::qstack_pushpopone():
         80 msecs per iteration (total: 80, iterations: 1)

Change-Id: I3530888abbfcfcef39318d6be6d5b07306a4704e
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

tests/benchmarks/corelib/tools/qstack/main.cpp

@@ -0,0 +1,89 @@
+/****************************************************************************
+**
+** Copyright (C) 2015 Robin Burchell <robin.burchell@viroteck.net>
+** Contact: http://www.qt-project.org/legal
+**
+** 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 Digia. For licensing terms and
+** conditions see http://qt.digia.com/licensing. For further information
+** use the contact form at http://qt.digia.com/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.
+**
+** In addition, as a special exception, Digia gives you certain additional
+** rights. These rights are described in the Digia Qt LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <QStack>
+#include <QDebug>
+#include <QtTest>
+
+#include <vector>
+
+class tst_QStack: public QObject
+{
+    Q_OBJECT
+
+private slots:
+    void qstack_push();
+    void qstack_pop();
+    void qstack_pushpopone();
+};
+
+const int N = 1000000;
+
+void tst_QStack::qstack_push()
+{
+    QStack<int> v;
+    QBENCHMARK {
+        for (int i = 0; i != N; ++i)
+            v.push(i);
+        v = QStack<int>();
+    }
+}
+
+void tst_QStack::qstack_pop()
+{
+    QStack<int> v;
+    for (int i = 0; i != N; ++i)
+        v.push(i);
+
+    QBENCHMARK {
+        QStack<int> v2 = v;
+        for (int i = 0; i != N; ++i) {
+            v2.pop();
+        }
+    }
+}
+
+void tst_QStack::qstack_pushpopone()
+{
+    QBENCHMARK {
+        QStack<int> v;
+        for (int i = 0; i != N; ++i) {
+            v.push(0);
+            v.pop();
+        }
+    }
+}
+
+QTEST_MAIN(tst_QStack)
+
+#include "main.moc"

tests/benchmarks/corelib/tools/qstack/qstack.pro

@@ -0,0 +1,4 @@
+TARGET = tst_bench_stack
+QT = core testlib core-private
+SOURCES += main.cpp
+CONFIG += release

tests/benchmarks/corelib/tools/tools.pro

@@ -12,6 +12,7 @@ SUBDIRS = \
         qrect \
         qregexp \
         qringbuffer \
+        qstack \
         qstring \
         qstringbuilder \
         qstringlist \