QmlCompiler: Implement ConvertThisToObject and basic DTZ

We know that 'this' is a QObject* since the metatypes stack frame
mandates it. Whenever you pass 'this' to anything it's loaded from the
special 'This' stack slot which then triggers a DTZ check. A DTZ check
is a noop if we can prove that the type is statically known, though.

In QmlCompiler, if we have a valid register content, then the register
has been set in all code paths that lead to the instruction in question.

Fixes: QTBUG-111439
Change-Id: I81d1cd140eea63f85628c3bef3a8f6db0a12096d
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

src/qml/qml/qqml.cpp

@@ -804,6 +804,12 @@ void qmlRegisterTypeAndRevisions<QQmlTypeNotAvailable, void>(
     qmlregister(TypeAndRevisionsRegistration, &type);
 }
 
+QObject *AOTCompiledContext::thisObject() const
+{
+    return static_cast<QV4::MetaTypesStackFrame *>(engine->handle()->currentStackFrame)
+            ->thisObject();
+}
+
 QQmlEngine *AOTCompiledContext::qmlEngine() const
 {
     return qmlContext ? qmlContext->engine() : nullptr;

src/qml/qml/qqmlprivate.h

@@ -623,6 +623,7 @@ namespace QQmlPrivate
             qintptr extraData;
         };
 
+        QObject *thisObject() const;
         QQmlEngine *qmlEngine() const;
 
         QJSValue jsMetaType(int index) const;

src/qmlcompiler/qqmljscodegenerator.cpp

@@ -175,7 +175,9 @@ QT_WARNING_POP
             else
                 result.code += u' ';
 
-            if (!registerIsArgument && registerIndex != Accumulator
+            if (!registerIsArgument
+                    && registerIndex != Accumulator
+                    && registerIndex != This
                     && !m_typeResolver->registerIsStoredIn(
                         function->registerTypes[registerIndex - firstRegisterIndex()],
                         m_typeResolver->voidType())) {
@@ -1902,7 +1904,8 @@ void QQmlJSCodeGenerator::generate_UnwindToLabel(int level, int offset)
 void QQmlJSCodeGenerator::generate_DeadTemporalZoneCheck(int name)
 {
     Q_UNUSED(name)
-    BYTECODE_UNIMPLEMENTED();
+    // Nothing to do here. If we have statically asserted the dtz check in the type propagator
+    // the value cannot be empty. Otherwise we can't get here.
 }
 
 void QQmlJSCodeGenerator::generate_ThrowException()
@@ -2121,7 +2124,7 @@ void QQmlJSCodeGenerator::generate_CreateRestParameter(int argIndex)
 
 void QQmlJSCodeGenerator::generate_ConvertThisToObject()
 {
-    BYTECODE_UNIMPLEMENTED();
+    m_body += changedRegisterVariable() + u" = aotContext->thisObject();\n"_s;
 }
 
 void QQmlJSCodeGenerator::generate_LoadSuperConstructor()

src/qmlcompiler/qqmljscompilepass_p.h

@@ -32,6 +32,7 @@ public:
     enum RegisterShortcuts {
         InvalidRegister = -1,
         Accumulator = QV4::CallData::Accumulator,
+        This = QV4::CallData::This,
         FirstArgument = QV4::CallData::OffsetCount
     };
 

src/qmlcompiler/qqmljstypepropagator.cpp

@@ -1520,8 +1520,22 @@ void QQmlJSTypePropagator::generate_UnwindToLabel(int level, int offset)
 
 void QQmlJSTypePropagator::generate_DeadTemporalZoneCheck(int name)
 {
-    Q_UNUSED(name)
-    INSTR_PROLOGUE_NOT_IMPLEMENTED();
+    const auto fail = [this, name]() {
+        setError(u"Cannot statically assert the dead temporal zone check for %1"_s.arg(
+                name ? m_jsUnitGenerator->stringForIndex(name) : u"the anonymous accumulator"_s));
+    };
+
+    const QQmlJSRegisterContent in = m_state.accumulatorIn();
+    if (in.isConversion()) {
+        for (const QQmlJSScope::ConstPtr &origin : in.conversionOrigins()) {
+            if (!m_typeResolver->equals(origin, m_typeResolver->emptyType()))
+                continue;
+            fail();
+            break;
+        }
+    } else if (m_typeResolver->registerContains(in, m_typeResolver->emptyType())) {
+        fail();
+    }
 }
 
 void QQmlJSTypePropagator::generate_ThrowException()
@@ -1703,7 +1717,7 @@ void QQmlJSTypePropagator::generate_CreateRestParameter(int argIndex)
 
 void QQmlJSTypePropagator::generate_ConvertThisToObject()
 {
-    INSTR_PROLOGUE_NOT_IMPLEMENTED();
+    setRegister(This, m_typeResolver->globalType(m_typeResolver->qObjectType()));
 }
 
 void QQmlJSTypePropagator::generate_LoadSuperConstructor()
@@ -2161,9 +2175,8 @@ void QQmlJSTypePropagator::generate_Sub(int lhs)
 
 void QQmlJSTypePropagator::generate_InitializeBlockDeadTemporalZone(int firstReg, int count)
 {
-    Q_UNUSED(firstReg)
-    Q_UNUSED(count)
-    // Ignore. We reject uninitialized values anyway.
+    for (int reg = firstReg, end = firstReg + count; reg < end; ++reg)
+        setRegister(reg, m_typeResolver->globalType(m_typeResolver->emptyType()));
 }
 
 void QQmlJSTypePropagator::generate_ThrowOnNullOrUndefined()
@@ -2270,6 +2283,8 @@ void QQmlJSTypePropagator::endInstruction(QV4::Moth::Instr::Type instr)
     case QV4::Moth::Instr::Type::PushCatchContext:
     case QV4::Moth::Instr::Type::UnwindDispatch:
     case QV4::Moth::Instr::Type::InitializeBlockDeadTemporalZone:
+    case QV4::Moth::Instr::Type::ConvertThisToObject:
+    case QV4::Moth::Instr::Type::DeadTemporalZoneCheck:
         if (m_state.changedRegisterIndex() == Accumulator && !m_error->isValid()) {
             setError(u"Instruction is not expected to populate the accumulator"_s);
             return;

src/qmlcompiler/qqmljstyperesolver.cpp

@@ -49,6 +49,7 @@ QQmlJSTypeResolver::QQmlJSTypeResolver(QQmlJSImporter *importer)
     m_varType = builtinTypes.type(u"QVariant"_s).scope;
     m_jsValueType = builtinTypes.type(u"QJSValue"_s).scope;
     m_listPropertyType = builtinTypes.type(u"QQmlListProperty<QObject>"_s).scope;
+    m_qObjectType = builtinTypes.type(u"QObject"_s).scope;
     m_qObjectListType = builtinTypes.type(u"QObjectList"_s).scope;
 
     QQmlJSScope::Ptr emptyType = QQmlJSScope::create();

src/qmlcompiler/qqmljstyperesolver_p.h

@@ -70,6 +70,7 @@ public:
     QQmlJSScope::ConstPtr metaObjectType() const { return m_metaObjectType; }
     QQmlJSScope::ConstPtr functionType() const { return m_functionType; }
     QQmlJSScope::ConstPtr jsGlobalObject() const { return m_jsGlobalObject; }
+    QQmlJSScope::ConstPtr qObjectType() const { return m_qObjectType; }
     QQmlJSScope::ConstPtr qObjectListType() const { return m_qObjectListType; }
 
     QQmlJSScope::ConstPtr scopeForLocation(const QV4::CompiledData::Location &location) const;
@@ -236,6 +237,7 @@ protected:
     QQmlJSScope::ConstPtr m_jsValueType;
     QQmlJSScope::ConstPtr m_jsPrimitiveType;
     QQmlJSScope::ConstPtr m_listPropertyType;
+    QQmlJSScope::ConstPtr m_qObjectType;
     QQmlJSScope::ConstPtr m_qObjectListType;
     QQmlJSScope::ConstPtr m_metaObjectType;
     QQmlJSScope::ConstPtr m_functionType;

tests/auto/qml/qmlcppcodegen/data/CMakeLists.txt

@@ -192,6 +192,7 @@ set(qml_files
     text.qml
     themerbad.qml
     themergood.qml
+    thisObject.qml
     throwObjectName.qml
     toString.qml
     translation.qml

tests/auto/qml/qmlcppcodegen/data/failures.qml

@@ -70,4 +70,18 @@ QtObject {
     function readTracks(metadataList : list<badType>): int {
         return metadataList.length
     }
+
+    function dtzFail() : int {
+        for (var a = 10; a < 20; ++a) {
+            switch (a) {
+            case 11:
+                let b = 5;
+                break;
+            case 10:
+                console.log(b);
+                break;
+            }
+        }
+        return a;
+    }
 }

tests/auto/qml/qmlcppcodegen/data/thisObject.qml

@@ -0,0 +1,11 @@
+pragma Strict
+import QtQml
+
+QtObject {
+    property QtObject warned
+
+    function f(arg: QtObject) { warned = arg }
+    function warn() { f(this) }
+
+    Component.onCompleted: warn()
+}

tests/auto/qml/qmlcppcodegen/tst_qmlcppcodegen.cpp

@@ -179,6 +179,7 @@ private slots:
     void boolPointerMerge();
     void mergedObjectReadWrite();
     void listConversion();
+    void thisObject();
 };
 
 void tst_QmlCppCodegen::initTestCase()
@@ -3611,7 +3612,16 @@ void tst_QmlCppCodegen::listConversion()
         QVariant::fromValue<qsizetype>(3),
         QVariant::fromValue<Person *>(nullptr)
     }));
+}
 
+void tst_QmlCppCodegen::thisObject()
+{
+    QQmlEngine e;
+    QQmlComponent c(&e, QUrl(u"qrc:/qt/qml/TestTypes/thisObject.qml"_s));
+    QVERIFY2(c.isReady(), qPrintable(c.errorString()));
+    QScopedPointer<QObject> o(c.create());
+    QVERIFY(!o.isNull());
+    QCOMPARE(o->property("warned").value<QObject *>(), o.data());
 }
 
 QTEST_MAIN(tst_QmlCppCodegen)