QQmlRefCount: de-virtualize dtor

Now that QQmlRefCounted ensures no-one uses ~QQmlRefCount() directly
anymore, we can make it non-virtual, shrinking the
sizeof(QQmlRefCount) from 8/16 to 4/4 bytes (32/64 bit platforms).

This requires moving the release() function from QQmlRefCount down
into QQmlRefCounted<T>, and static_cast'ing *this to T before calling
delete.

We need to be careful, of course, that no derived class relied on the
implied virtualness of ~QQmlRefCount() making their dtors virtual, so
require that all classes that use QQmlRefCounted are either final or
have a virtual destructor.

Update the toolsupport test and the TypeInformationVersion, as
sizeof(QQmlRefCount) was one the items checked.

Fixes: QTBUG-114817
Change-Id: I69afd36ec5b63313842c1438e0244503603ed96f
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

1 files changed, 3 insertions, 2 deletions

diff --git a/src/qml/qml/qqmltype_p_p.h b/src/qml/qml/qqmltype_p_p.h
index ab73da7a6b..73567b5a22 100644
--- a/src/qml/qml/qqmltype_p_p.h
+++ b/src/qml/qml/qqmltype_p_p.h
@@ -26,7 +26,7 @@
 
 QT_BEGIN_NAMESPACE
 
-class QQmlTypePrivate : public QQmlRefCounted<QQmlTypePrivate>
+class QQmlTypePrivate final : public QQmlRefCounted<QQmlTypePrivate>
 {
     Q_DISABLE_COPY_MOVE(QQmlTypePrivate)
 public:
@@ -145,7 +145,8 @@ public:
     void setName(const QString &uri, const QString &element);
 
 private:
-    ~QQmlTypePrivate() override;
+    ~QQmlTypePrivate();
+    friend class QQmlRefCounted<QQmlTypePrivate>;
 
     struct EnumInfo {
         QStringList path;