QVariant: Use QMetaTypeInferface directly

There is no reason for QVariant to go through QMetaType when it can use
the QMetaTypeInterface directly. Without LTO, the QMetaType method calls
are opaque, and we therefore risk to lose optimizations.
Additionally, avoid constructing a QMetaType from a type id if we
already have the QMetaType.

Fixes: QTBUG-90673
Change-Id: I7069ff6aff70d5baecdf5cf5760014c3dda81784
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/kernel/qvariant.cpp

@@ -248,24 +248,32 @@ static qreal qConvertToRealNumber(const QVariant::Private *d, bool *ok)
 // the type of d has already been set, but other field are not set
 static void customConstruct(QVariant::Private *d, const void *copy)
 {
-    const QMetaType type = d->type();
-    const uint size = type.sizeOf();
-    if (!size) {
+    QtPrivate::QMetaTypeInterface *iface = d->typeInterface();
+    if (!(iface && iface->size)) {
         *d = QVariant::Private();
         return;
     }
 
-    if (QVariant::Private::canUseInternalSpace(type)) {
-        type.construct(&d->data, copy);
+    if (QVariant::Private::canUseInternalSpace(iface)) {
+        // QVariant requires type to be copy and default constructible
+        Q_ASSERT(iface->copyCtr);
+        Q_ASSERT(iface->defaultCtr);
+        if (copy)
+            iface->copyCtr(iface, &d->data, copy);
+        else
+            iface->defaultCtr(iface, &d->data);
         d->is_shared = false;
     } else {
-        d->data.shared = QVariant::PrivateShared::create(type);
-        type.construct(d->data.shared->data(), copy);
+        d->data.shared = QVariant::PrivateShared::create(iface);
+        if (copy)
+            iface->copyCtr(iface, d->data.shared->data(), copy);
+        else
+            iface->defaultCtr(iface, d->data.shared->data());
         d->is_shared = true;
     }
     // need to check for nullptr_t here, as this can get called by fromValue(nullptr). fromValue() uses
     // std::addressof(value) which in this case returns the address of the nullptr object.
-    d->is_null = !copy || type == QMetaType::fromType<std::nullptr_t>();
+    d->is_null = !copy || QMetaType(iface) == QMetaType::fromType<std::nullptr_t>();
 }
 
 static void customClear(QVariant::Private *d)
@@ -471,11 +479,23 @@ static void customClear(QVariant::Private *d)
 
     Constructs a variant private of type \a type, and initializes with \a copy if
     \a copy is not \nullptr.
-*/
 
+*/
+//### Qt 7: Remove in favor of QMetaType overload
 void QVariant::create(int type, const void *copy)
 {
-    d = Private(QMetaType(type));
+    create(QMetaType(type), copy);
+}
+
+/*!
+    \fn QVariant::create(int type, const void *copy)
+
+    \internal
+    \overload
+*/
+void QVariant::create(QMetaType type, const void *copy)
+{
+    d = Private(type);
     customConstruct(&d, copy);
 }
 
@@ -510,9 +530,14 @@ QVariant::QVariant(const QVariant &p)
         d.data.shared->ref.ref();
         return;
     }
-    QMetaType t = d.type();
-    if (t.isValid())
-        t.construct(&d, p.constData());
+    QtPrivate::QMetaTypeInterface *iface = d.typeInterface();
+    auto other = p.constData();
+    if (iface) {
+        if (other)
+            iface->copyCtr(iface, &d, other);
+        else
+            iface->defaultCtr(iface, &d);
+    }
 }
 
 /*!
@@ -995,9 +1020,14 @@ QVariant &QVariant::operator=(const QVariant &variant)
         d = variant.d;
     } else {
         d = variant.d;
-        QMetaType t = d.type();
-        if (t.isValid())
-            t.construct(&d, variant.constData());
+        QtPrivate::QMetaTypeInterface *iface = d.typeInterface();
+        const void *other = variant.constData();
+        if (iface) {
+            if (other)
+                iface->copyCtr(iface, &d, other);
+            else
+                iface->defaultCtr(iface, &d);
+        }
     }
 
     return *this;
@@ -2021,7 +2051,7 @@ bool QVariant::convert(QMetaType targetType)
     QVariant oldValue = *this;
 
     clear();
-    create(targetType.id(), nullptr);
+    create(targetType, nullptr);
     if (!oldValue.canConvert(targetType))
         return false;
 

src/corelib/kernel/qvariant.h

@@ -426,10 +426,11 @@ public:
     private:
         inline PrivateShared() : ref(1) { }
     public:
-        static PrivateShared *create(QMetaType type)
+        static PrivateShared *create(const QtPrivate::QMetaTypeInterface *type)
         {
-            size_t size = type.sizeOf();
-            size_t align = type.alignOf();
+            Q_ASSERT(type);
+            size_t size = type->size;
+            size_t align = type->alignment;
 
             size += sizeof(PrivateShared);
             if (align > sizeof(PrivateShared)) {
@@ -463,10 +464,11 @@ public:
         static constexpr size_t MaxInternalSize = 3*sizeof(void *);
         template<typename T>
         static constexpr bool CanUseInternalSpace = (QTypeInfo<T>::isRelocatable && sizeof(T) <= MaxInternalSize && alignof(T) <= alignof(double));
-        static constexpr bool canUseInternalSpace(QMetaType type)
+        static constexpr bool canUseInternalSpace(QtPrivate::QMetaTypeInterface *type)
         {
-            return type.flags() & QMetaType::RelocatableType &&
-                   size_t(type.sizeOf()) <= MaxInternalSize && size_t(type.alignOf()) <= alignof(double);
+            Q_ASSERT(type);
+            return QMetaType::TypeFlags(type->flags) & QMetaType::RelocatableType &&
+                   size_t(type->size) <= MaxInternalSize && size_t(type->alignment) <= alignof(double);
         }
 
         union
@@ -506,6 +508,12 @@ public:
         {
             return QMetaType(reinterpret_cast<QtPrivate::QMetaTypeInterface *>(packedType << 2));
         }
+
+        inline QtPrivate::QMetaTypeInterface * typeInterface() const
+        {
+            return reinterpret_cast<QtPrivate::QMetaTypeInterface *>(packedType << 2);
+        }
+
         inline int typeId() const
         {
             return type().id();
@@ -531,6 +539,7 @@ private:
 protected:
     Private d;
     void create(int type, const void *copy);
+    void create(QMetaType type, const void *copy);
     bool equals(const QVariant &other) const;
     bool convert(int type, void *ptr) const;
     bool view(int type, void *ptr);

src/corelib/kernel/qvariant_p.h

@@ -65,7 +65,7 @@ inline void v_construct(QVariant::Private *x, const T &t)
         new (&x->data) T(t);
         x->is_shared = false;
     } else {
-        x->data.shared = QVariant::PrivateShared::create(QMetaType::fromType<T>());
+        x->data.shared = QVariant::PrivateShared::create(QtPrivate::qMetaTypeInterfaceForType<T>());
         new (x->data.shared->data()) T(t);
         x->is_shared = true;
     }