Reduce size of QQmlAbstractBinding

The doubly-linked list is unnecessary.  Most bindings are created at
startup, and removed only when the object is destroyed.  In these cases
the double-link buys nothing other than wasted space.  Even when the
bindings are removed earlier, searching the list is not that slow.

Change-Id: I22e1376b78ba712dafd171c7447fbc6ed212b891
Reviewed-by: Roberto Raggi <roberto.raggi@nokia.com>

4 files changed, 86 insertions, 25 deletions

diff --git a/src/qml/qml/qqmlabstractbinding.cpp b/src/qml/qml/qqmlabstractbinding.cpp
index acc207e970..672e3f5bed 100644
--- a/src/qml/qml/qqmlabstractbinding.cpp
+++ b/src/qml/qml/qqmlabstractbinding.cpp
@@ -48,13 +48,14 @@
 QT_BEGIN_NAMESPACE
 
 QQmlAbstractBinding::QQmlAbstractBinding()
-: m_prevBinding(0), m_nextBinding(0)
+: m_nextBinding(0)
 {
 }
 
 QQmlAbstractBinding::~QQmlAbstractBinding()
 {
-    Q_ASSERT(m_prevBinding == 0);
+    Q_ASSERT(isAddedToObject() == false);
+    Q_ASSERT(m_nextBinding == 0);
     Q_ASSERT(*m_mePtr == 0);
 }
 
@@ -83,7 +84,8 @@ However, it does not enable the binding itself or call update() on it.
 */
 void QQmlAbstractBinding::addToObject()
 {
-    Q_ASSERT(!m_prevBinding);
+    Q_ASSERT(!m_nextBinding);
+    Q_ASSERT(isAddedToObject() == false);
 
     QObject *obj = object();
     Q_ASSERT(obj);
@@ -117,18 +119,16 @@ void QQmlAbstractBinding::addToObject()
         }
 
         m_nextBinding = proxy->m_bindings;
-        if (m_nextBinding) m_nextBinding->m_prevBinding = &m_nextBinding;
-        m_prevBinding = &proxy->m_bindings;
         proxy->m_bindings = this;
 
     } else {
         m_nextBinding = data->bindings;
-        if (m_nextBinding) m_nextBinding->m_prevBinding = &m_nextBinding;
-        m_prevBinding = &data->bindings;
         data->bindings = this;
 
         data->setBindingBit(obj, index);
     }
+
+    setAddedToObject(true);
 }
 
 /*!
@@ -136,22 +136,59 @@ Remove the binding from the object.
 */
 void QQmlAbstractBinding::removeFromObject()
 {
-    if (m_prevBinding) {
+    if (isAddedToObject()) {
+        QObject *obj = object();
         int index = propertyIndex();
 
-        *m_prevBinding = m_nextBinding;
-        if (m_nextBinding) m_nextBinding->m_prevBinding = m_prevBinding;
-        m_prevBinding = 0;
-        m_nextBinding = 0;
+        QQmlData *data = QQmlData::get(obj, false);
+        Q_ASSERT(data);
 
         if (index & 0xFF000000) {
+
+            // Find the value type binding
+            QQmlAbstractBinding *vtbinding = data->bindings;
+            while (vtbinding->propertyIndex() != (index & 0xFFFFFF)) {
+                vtbinding = vtbinding->m_nextBinding;
+                Q_ASSERT(vtbinding);
+            }
+            Q_ASSERT(vtbinding->bindingType() == QQmlAbstractBinding::ValueTypeProxy);
+
+            QQmlValueTypeProxyBinding *vtproxybinding =
+                static_cast<QQmlValueTypeProxyBinding *>(vtbinding);
+
+            QQmlAbstractBinding *binding = vtproxybinding->m_bindings;
+            if (binding == this) {
+                vtproxybinding->m_bindings = m_nextBinding;
+            } else {
+               while (binding->m_nextBinding != this) {
+                  binding = binding->m_nextBinding;
+                  Q_ASSERT(binding);
+               }
+               binding->m_nextBinding = m_nextBinding;
+            }
+
             // Value type - we don't remove the proxy from the object.  It will sit their happily
             // doing nothing until it is removed by a write, a binding change or it is reused
             // to hold more sub-bindings.
-        } else if (QObject *obj = object()) {
-            QQmlData *data = QQmlData::get(obj, false);
-            if (data) data->clearBindingBit(index);
+
+        } else {
+
+            if (data->bindings == this) {
+                data->bindings = m_nextBinding;
+            } else {
+                QQmlAbstractBinding *binding = data->bindings;
+                while (binding->m_nextBinding != this) {
+                    binding = binding->m_nextBinding;
+                    Q_ASSERT(binding);
+                }
+                binding->m_nextBinding = m_nextBinding;
+            }
+
+            data->clearBindingBit(index);
         }
+
+        m_nextBinding = 0;
+        setAddedToObject(false);
     }
 }
 
diff --git a/src/qml/qml/qqmlabstractbinding_p.h b/src/qml/qml/qqmlabstractbinding_p.h
index ed414964f8..f3071cf8bf 100644
--- a/src/qml/qml/qqmlabstractbinding_p.h
+++ b/src/qml/qml/qqmlabstractbinding_p.h
@@ -65,8 +65,6 @@ class Q_QML_PRIVATE_EXPORT QQmlAbstractBinding
 public:
     typedef QWeakPointer<QQmlAbstractBinding> Pointer;
 
-    QQmlAbstractBinding();
-
     virtual void destroy();
 
     virtual QString expression() const;
@@ -95,6 +93,7 @@ public:
     static void printBindingLoopError(QQmlProperty &prop);
 
 protected:
+    QQmlAbstractBinding();
     virtual ~QQmlAbstractBinding();
     void clear();
 
@@ -114,9 +113,13 @@ private:
 
     typedef QSharedPointer<QQmlAbstractBinding> SharedPointer;
     // To save memory, we also store the rarely used weakPointer() instance in here
+    // We also use the flag bits:
+    //    m_mePtr.flag1: added to object
     QPointerValuePair<QQmlAbstractBinding*, SharedPointer> m_mePtr;
 
-    QQmlAbstractBinding **m_prevBinding;
+    inline void setAddedToObject(bool v);
+    inline bool isAddedToObject() const;
+
     QQmlAbstractBinding  *m_nextBinding;
 };
 
@@ -126,6 +129,16 @@ QQmlAbstractBinding::getPointer(QQmlAbstractBinding *p)
     return p ? p->weakPointer() : Pointer();
 }
 
+void QQmlAbstractBinding::setAddedToObject(bool v)
+{
+    m_mePtr.setFlagValue(v);
+}
+
+bool QQmlAbstractBinding::isAddedToObject() const
+{
+    return m_mePtr.flag();
+}
+
 QT_END_NAMESPACE
 
 #endif // QQMLABSTRACTBINDING_P_H
diff --git a/src/qml/qml/qqmlengine.cpp b/src/qml/qml/qqmlengine.cpp
index 4a3e30793c..08dd845dd6 100644
--- a/src/qml/qml/qqmlengine.cpp
+++ b/src/qml/qml/qqmlengine.cpp
@@ -1293,7 +1293,7 @@ void QQmlData::destroyed(QObject *object)
     QQmlAbstractBinding *binding = bindings;
     while (binding) {
         QQmlAbstractBinding *next = binding->m_nextBinding;
-        binding->m_prevBinding = 0;
+        binding->setAddedToObject(false);
         binding->m_nextBinding = 0;
         binding->destroy();
         binding = next;
diff --git a/src/qml/qml/qqmlvaluetypeproxybinding.cpp b/src/qml/qml/qqmlvaluetypeproxybinding.cpp
index 2cc15a50f5..2b891dc4e1 100644
--- a/src/qml/qml/qqmlvaluetypeproxybinding.cpp
+++ b/src/qml/qml/qqmlvaluetypeproxybinding.cpp
@@ -50,10 +50,14 @@ QQmlValueTypeProxyBinding::QQmlValueTypeProxyBinding(QObject *o, int index)
 
 QQmlValueTypeProxyBinding::~QQmlValueTypeProxyBinding()
 {
-    while (m_bindings) {
-        QQmlAbstractBinding *binding = m_bindings;
-        binding->setEnabled(false, 0);
+    QQmlAbstractBinding *binding = m_bindings;
+    // This must be identical to the logic in QQmlData::destroyed()
+    while (binding) {
+        QQmlAbstractBinding *next = binding->m_nextBinding;
+        binding->setAddedToObject(false);
+        binding->m_nextBinding = 0;
         binding->destroy();
+        binding = next;
     }
 }
 
@@ -110,16 +114,23 @@ Removes a collection of bindings, corresponding to the set bits in \a mask.
 void QQmlValueTypeProxyBinding::removeBindings(quint32 mask)
 {
     QQmlAbstractBinding *binding = m_bindings;
+    QQmlAbstractBinding *lastBinding = 0;
+
     while (binding) {
         if (mask & (1 << (binding->propertyIndex() >> 24))) {
             QQmlAbstractBinding *remove = binding;
             binding = remove->m_nextBinding;
-            *remove->m_prevBinding = remove->m_nextBinding;
-            if (remove->m_nextBinding) remove->m_nextBinding->m_prevBinding = remove->m_prevBinding;
-            remove->m_prevBinding = 0;
+
+            if (lastBinding == 0)
+                m_bindings = remove->m_nextBinding;
+            else
+                lastBinding->m_nextBinding = remove->m_nextBinding;
+
+            remove->setAddedToObject(false);
             remove->m_nextBinding = 0;
             remove->destroy();
         } else {
+            lastBinding = binding;
             binding = binding->m_nextBinding;
         }
     }