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, 10 insertions, 0 deletions

diff --git a/src/qml/qml/qqmlvmemetaobject_p.h b/src/qml/qml/qqmlvmemetaobject_p.h
index 5aa141d026..4a81fc50d2 100644
--- a/src/qml/qml/qqmlvmemetaobject_p.h
+++ b/src/qml/qml/qqmlvmemetaobject_p.h
@@ -72,6 +72,7 @@
 
 #include <private/qv4object_p.h>
 #include <private/qv4value_p.h>
+#include <private/qqmlpropertyvalueinterceptor_p.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -105,6 +106,15 @@ public:
     // Used by auto-tests for inspection
     QQmlPropertyCache *propertyCache() const { return cache; }
 
+    bool intercepts(int coreIndex) const
+    {
+        for (auto it = interceptors; it; it = it->m_next) {
+            if (it->m_coreIndex == coreIndex)
+                return true;
+        }
+        return false;
+    }
+
 protected:
     int metaCall(QObject *o, QMetaObject::Call c, int id, void **a) Q_DECL_OVERRIDE;
     bool intercept(QMetaObject::Call c, int id, void **a);