QMap - improve QMap stl-map ctor

We can insert directly on the most left-most Node.

We always enforce an insert here (unlike the insert call),
but that is not a problem since the keys in a std::map are unique.

Change-Id: Ib409b90ffc57a5a43dab4a4b08d34f6fdabd057f
Reviewed-by: Lars Knoll <lars.knoll@digia.com>

src/corelib/tools/qmap.h

@@ -939,7 +939,7 @@ Q_OUTOFLINE_TEMPLATE QMap<Key, T>::QMap(const std::map<Key, T> &other)
     typename std::map<Key,T>::const_iterator it = other.end();
     while (it != other.begin()) {
         --it;
-        insert((*it).first, (*it).second);
+        d->createNode((*it).first, (*it).second, d->begin(), true); // insert on most left node.
     }
 }
 

tests/auto/corelib/tools/qmap/tst_qmap.cpp

@@ -55,6 +55,7 @@ protected:
 public slots:
     void init();
 private slots:
+    void ctor();
     void count();
     void clear();
     void beginEnd();
@@ -146,6 +147,30 @@ void tst_QMap::init()
     MyClass::count = 0;
 }
 
+void tst_QMap::ctor()
+{
+    std::map<int, int> map;
+    for (int i = 0; i < 100000; ++i)
+        map.insert(std::pair<int, int>(i * 3, i * 7));
+
+    QMap<int, int> qmap(map); // ctor.
+
+    // Check that we have the same
+    std::map<int, int>::iterator j = map.begin();
+    QMap<int, int>::const_iterator i = qmap.constBegin();
+
+    while (i != qmap.constEnd()) {
+        QCOMPARE( (*j).first, i.key());
+        QCOMPARE( (*j).second, i.value());
+        ++i;
+        ++j;
+    }
+
+    QCOMPARE( (int) map.size(), qmap.size());
+}
+
+
+
 void tst_QMap::count()
 {
     {

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

@@ -62,6 +62,8 @@ private slots:
     void iteration();
     void toStdMap();
     void iterator_begin();
+
+    void ctorStdMap();
 };
 
 
@@ -189,6 +191,19 @@ void tst_QMap::iterator_begin()
     }
 }
 
+void tst_QMap::ctorStdMap()
+{
+    std::map<int, int> map;
+    for (int i = 0; i < 100000; ++i)
+        map.insert(std::pair<int, int>(i, i));
+
+    QBENCHMARK {
+        QMap<int, int> qmap(map);
+        qmap.constBegin();
+    }
+}
+
+
 QTEST_MAIN(tst_QMap)
 
 #include "main.moc"