QML: Make Heap::Object and all subclasses trivial

GCC6 might dead-store-eliminate out our secret write to Base::mmdata,
because it expects all memory content to be "undefined" before
constructor calls. Clang might take the same approach if the constructor
of Heap::Object is removed.

By making these structs trivial, it also makes them memcpy-able.

Change-Id: I055b2ad28311b997fbe059849ebda4d5894eaa9b
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

1 files changed, 9 insertions, 2 deletions

diff --git a/src/qml/qml/qqmllistwrapper_p.h b/src/qml/qml/qqmllistwrapper_p.h
index 18038d2a80..d01b332159 100644
--- a/src/qml/qml/qqmllistwrapper_p.h
+++ b/src/qml/qml/qqmllistwrapper_p.h
@@ -66,11 +66,18 @@ namespace QV4 {
 namespace Heap {
 
 struct QmlListWrapper : Object {
-    QmlListWrapper();
+    void init();
     void destroy();
     QQmlQPointer<QObject> object;
-    QQmlListProperty<QObject> property;
+
+    QQmlListProperty<QObject> &property() {
+        return *reinterpret_cast<QQmlListProperty<QObject>*>(propertyData);
+    }
+
     int propertyType;
+
+private:
+    void *propertyData[sizeof(QQmlListProperty<QObject>)/sizeof(void*)];
 };
 
 }