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, 5 insertions, 4 deletions

diff --git a/src/qml/qml/qqmlcomponent.cpp b/src/qml/qml/qqmlcomponent.cpp
index 9a993d4ec3..23b8e5a712 100644
--- a/src/qml/qml/qqmlcomponent.cpp
+++ b/src/qml/qml/qqmlcomponent.cpp
@@ -1058,7 +1058,7 @@ namespace QV4 {
 namespace Heap {
 
 struct QmlIncubatorObject : Object {
-    QmlIncubatorObject(QQmlIncubator::IncubationMode = QQmlIncubator::Asynchronous);
+    void init(QQmlIncubator::IncubationMode = QQmlIncubator::Asynchronous);
     inline void destroy();
     QQmlComponentIncubator *incubator;
     QQmlQPointer<QObject> parent;
@@ -1484,10 +1484,11 @@ QQmlComponentExtension::~QQmlComponentExtension()
 {
 }
 
-QV4::Heap::QmlIncubatorObject::QmlIncubatorObject(QQmlIncubator::IncubationMode m)
-    : valuemap(QV4::Primitive::undefinedValue())
-    , statusChanged(QV4::Primitive::undefinedValue())
+void QV4::Heap::QmlIncubatorObject::init(QQmlIncubator::IncubationMode m)
 {
+    Object::init();
+    valuemap = QV4::Primitive::undefinedValue();
+    statusChanged = QV4::Primitive::undefinedValue();
     parent.init();
     qmlContext = nullptr;
     incubator = new QQmlComponentIncubator(this, m);