QML: Introduce write accessors to QQmlAccessors

Same idea as the read accessors, but with a slight difference: the
property setters do emit signals, so we can't do a direct property write
and have to call the setter. However, it does circumvent the meta-calls.

There is one gotcha: if a property is intercepted (e.g. by a Behavior),
we still have to do the meta-call in order to dispatch the write to the
interceptor.

According to valgrind, this saves 138 instructions on x86 for every
"accessible" property write.

Change-Id: I07dbac95613415559ffa1691734a5af7c84721fc
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

1 files changed, 9 insertions, 0 deletions

diff --git a/src/qml/qml/qqmlabstractbinding_p.h b/src/qml/qml/qqmlabstractbinding_p.h
index 45221a4bcd..d25c0c6288 100644
--- a/src/qml/qml/qqmlabstractbinding_p.h
+++ b/src/qml/qml/qqmlabstractbinding_p.h
@@ -91,6 +91,8 @@ public:
 
     inline QQmlAbstractBinding *nextBinding() const;
 
+    inline bool canUseAccessor() const
+    { return m_nextBinding.flag2(); }
 
     struct RefCount {
         RefCount() : refCount(0) {}
@@ -112,8 +114,15 @@ protected:
     inline void setNextBinding(QQmlAbstractBinding *);
 
     int m_targetIndex;
+
+    // Pointer is the target object to which the binding binds
+    // flag1 is the updating flag
+    // flag2 is the enabled flag
     QFlagPointer<QObject> m_target;
+
     // Pointer to the next binding in the linked list of bindings.
+    // flag1 is used for addedToObject
+    // flag2 indicates if an accessor is can be used (i.e. there is no interceptor on the target)
     QFlagPointer<QQmlAbstractBinding> m_nextBinding;
 };