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, 3 deletions

diff --git a/src/qml/qml/qqmlpropertycache_p.h b/src/qml/qml/qqmlpropertycache_p.h
index 0f44533ef7..b261d1caca 100644
--- a/src/qml/qml/qqmlpropertycache_p.h
+++ b/src/qml/qml/qqmlpropertycache_p.h
@@ -105,7 +105,7 @@ private:
         Shared = 1
     };
 
-    struct SharedHolder : public QQmlRefCounted<SharedHolder>
+    struct SharedHolder final : public QQmlRefCounted<SharedHolder>
     {
         Q_DISABLE_COPY_MOVE(SharedHolder)
         SharedHolder(QMetaObject *shared) : metaObject(shared) {}
@@ -116,7 +116,7 @@ private:
     mutable QBasicAtomicInteger<quintptr> d = 0;
 };
 
-class Q_QML_PRIVATE_EXPORT QQmlPropertyCache
+class Q_QML_PRIVATE_EXPORT QQmlPropertyCache final
     : public QQmlRefCounted<QQmlPropertyCache>
 {
 public:
@@ -136,7 +136,7 @@ public:
             const QMetaObject *, QTypeRevision metaObjectRevision = QTypeRevision::zero());
 
     QQmlPropertyCache() = default;
-    ~QQmlPropertyCache() override;
+    ~QQmlPropertyCache();
 
     void update(const QMetaObject *);
     void invalidate(const QMetaObject *);