V4: Pass scope around as parameters inside the runtime.

The implementation of many (or all) runtime functions consist of first
creating a QV4::Scope, which saves and restores the JS stack pointer.
It also prevents tail-calls because of that restoring behavior. In many
cases it suffices to do that at the entry-point of the runtime.

The return value of a JS function call is now also stored in the scope.
Previously, all return values were stored in a ScopedValue, got loaded
on return, and immediately stored in another ScopedValue in the caller.
This resulted in a lot of stores, where now there is only one store
needed, and no extra ScopedValue for every function.

Change-Id: I13d80fc0ce72c5702ef1536d41d12f710c5914fa
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

12 files changed, 39 insertions, 48 deletions

diff --git a/src/qml/qml/qqmlbinding.cpp b/src/qml/qml/qqmlbinding.cpp
index eacb928901..3940176107 100644
--- a/src/qml/qml/qqmlbinding.cpp
+++ b/src/qml/qml/qqmlbinding.cpp
@@ -189,11 +189,12 @@ void QQmlBinding::update(QQmlPropertyPrivate::WriteFlags flags)
 
         bool isUndefined = false;
 
-        QV4::ScopedValue result(scope, QQmlJavaScriptExpression::evaluate(&isUndefined));
+        QV4::ScopedCallData callData(scope);
+        QQmlJavaScriptExpression::evaluate(callData, &isUndefined, scope);
 
         bool error = false;
         if (!watcher.wasDeleted() && isAddedToObject() && !hasError())
-            error = !write(pd, result, isUndefined, flags);
+            error = !write(pd, scope.result, isUndefined, flags);
 
         if (!watcher.wasDeleted()) {
 
@@ -377,11 +378,12 @@ QVariant QQmlBinding::evaluate()
     bool isUndefined = false;
 
     QV4::Scope scope(ep->v4engine());
-    QV4::ScopedValue result(scope, QQmlJavaScriptExpression::evaluate(&isUndefined));
+    QV4::ScopedCallData callData(scope);
+    QQmlJavaScriptExpression::evaluate(callData, &isUndefined, scope);
 
     ep->dereferenceScarceResources();
 
-    return scope.engine->toVariant(result, qMetaTypeId<QList<QObject*> >());
+    return scope.engine->toVariant(scope.result, qMetaTypeId<QList<QObject*> >());
 }
 
 QString QQmlBinding::expressionIdentifier()
diff --git a/src/qml/qml/qqmlboundsignal.cpp b/src/qml/qml/qqmlboundsignal.cpp
index 7d6e1ffa1a..e3c4464584 100644
--- a/src/qml/qml/qqmlboundsignal.cpp
+++ b/src/qml/qml/qqmlboundsignal.cpp
@@ -234,7 +234,7 @@ void QQmlBoundSignalExpression::evaluate(void **a)
         }
     }
 
-    QQmlJavaScriptExpression::evaluate(callData, 0);
+    QQmlJavaScriptExpression::evaluate(callData, 0, scope);
 
     ep->dereferenceScarceResources(); // "release" scarce resources if top-level expression evaluation is complete.
 }
@@ -256,7 +256,7 @@ void QQmlBoundSignalExpression::evaluate(const QList<QVariant> &args)
         callData->args[ii] = scope.engine->fromVariant(args[ii]);
     }
 
-    QQmlJavaScriptExpression::evaluate(callData, 0);
+    QQmlJavaScriptExpression::evaluate(callData, 0, scope);
 
     ep->dereferenceScarceResources(); // "release" scarce resources if top-level expression evaluation is complete.
 }
diff --git a/src/qml/qml/qqmlcomponent.cpp b/src/qml/qml/qqmlcomponent.cpp
index 52f6837842..854090f20b 100644
--- a/src/qml/qml/qqmlcomponent.cpp
+++ b/src/qml/qml/qqmlcomponent.cpp
@@ -1527,7 +1527,7 @@ void QV4::QmlIncubatorObject::statusChanged(QQmlIncubator::Status s)
         QV4::ScopedCallData callData(scope, 1);
         callData->thisObject = this;
         callData->args[0] = QV4::Primitive::fromUInt32(s);
-        f->call(callData);
+        f->call(scope, callData);
         if (scope.hasException()) {
             QQmlError error = scope.engine->catchExceptionAsQmlError();
             QQmlEnginePrivate::warning(QQmlEnginePrivate::get(scope.engine->qmlEngine()), error);
diff --git a/src/qml/qml/qqmldelayedcallqueue.cpp b/src/qml/qml/qqmldelayedcallqueue.cpp
index b3a0baffb4..d10a8c7718 100644
--- a/src/qml/qml/qqmldelayedcallqueue.cpp
+++ b/src/qml/qml/qqmldelayedcallqueue.cpp
@@ -74,7 +74,7 @@ void QQmlDelayedCallQueue::DelayedFunctionCall::execute(QV4::ExecutionEngine *en
 
         const QV4::FunctionObject *callback = m_function.as<QV4::FunctionObject>();
         Q_ASSERT(callback);
-        callback->call(callData);
+        callback->call(scope, callData);
 
         if (scope.engine->hasException) {
             QQmlError error = scope.engine->catchExceptionAsQmlError();
diff --git a/src/qml/qml/qqmlexpression.cpp b/src/qml/qml/qqmlexpression.cpp
index d48b6ad1d3..6afbd05e3e 100644
--- a/src/qml/qml/qqmlexpression.cpp
+++ b/src/qml/qml/qqmlexpression.cpp
@@ -245,14 +245,15 @@ void QQmlExpression::setExpression(const QString &expression)
 }
 
 // Must be called with a valid handle scope
-QV4::ReturnedValue QQmlExpressionPrivate::v4value(bool *isUndefined)
+void QQmlExpressionPrivate::v4value(bool *isUndefined, QV4::Scope &scope)
 {
     if (!expressionFunctionValid) {
         createQmlBinding(context(), scopeObject(), expression, url, line);
         expressionFunctionValid = true;
     }
 
-    return evaluate(isUndefined);
+    QV4::ScopedCallData callData(scope);
+    evaluate(callData, isUndefined, scope);
 }
 
 QVariant QQmlExpressionPrivate::value(bool *isUndefined)
@@ -271,9 +272,9 @@ QVariant QQmlExpressionPrivate::value(bool *isUndefined)
 
     {
         QV4::Scope scope(QV8Engine::getV4(ep->v8engine()));
-        QV4::ScopedValue result(scope, v4value(isUndefined));
+        v4value(isUndefined, scope);
         if (!hasError())
-            rv = scope.engine->toVariant(result, -1);
+            rv = scope.engine->toVariant(scope.result, -1);
     }
 
     ep->dereferenceScarceResources(); // "release" scarce resources if top-level expression evaluation is complete.
diff --git a/src/qml/qml/qqmlexpression_p.h b/src/qml/qml/qqmlexpression_p.h
index ccc629a3a3..741c25e206 100644
--- a/src/qml/qml/qqmlexpression_p.h
+++ b/src/qml/qml/qqmlexpression_p.h
@@ -76,7 +76,7 @@ public:
 
     QVariant value(bool *isUndefined = 0);
 
-    QV4::ReturnedValue v4value(bool *isUndefined = 0);
+    void v4value(bool *isUndefined, QV4::Scope &scope);
 
     static inline QQmlExpressionPrivate *get(QQmlExpression *expr);
     static inline QQmlExpression *get(QQmlExpressionPrivate *expr);
diff --git a/src/qml/qml/qqmljavascriptexpression.cpp b/src/qml/qml/qqmljavascriptexpression.cpp
index 8ba4b5eba1..eff1a6e039 100644
--- a/src/qml/qml/qqmljavascriptexpression.cpp
+++ b/src/qml/qml/qqmljavascriptexpression.cpp
@@ -147,16 +147,9 @@ void QQmlJavaScriptExpression::refresh()
 {
 }
 
-QV4::ReturnedValue QQmlJavaScriptExpression::evaluate(bool *isUndefined)
-{
-    QV4::ExecutionEngine *v4 = QV8Engine::getV4(m_context->engine);
-    QV4::Scope scope(v4);
-    QV4::ScopedCallData callData(scope);
 
-    return evaluate(callData, isUndefined);
-}
 
-QV4::ReturnedValue QQmlJavaScriptExpression::evaluate(QV4::CallData *callData, bool *isUndefined)
+void QQmlJavaScriptExpression::evaluate(QV4::CallData *callData, bool *isUndefined, QV4::Scope &scope)
 {
     Q_ASSERT(m_context && m_context->engine);
 
@@ -164,7 +157,7 @@ QV4::ReturnedValue QQmlJavaScriptExpression::evaluate(QV4::CallData *callData, b
     if (!f || f->isUndefined()) {
         if (isUndefined)
             *isUndefined = true;
-        return QV4::Encode::undefined();
+        return;
     }
 
     QQmlEnginePrivate *ep = QQmlEnginePrivate::get(m_context->engine);
@@ -184,8 +177,7 @@ QV4::ReturnedValue QQmlJavaScriptExpression::evaluate(QV4::CallData *callData, b
         capture.guards.copyAndClearPrepend(activeGuards);
 
     QV4::ExecutionEngine *v4 = QV8Engine::getV4(ep->v8engine());
-    QV4::Scope scope(v4);
-    QV4::ScopedValue result(scope, QV4::Primitive::undefinedValue());
+    scope.result = QV4::Primitive::undefinedValue();
     callData->thisObject = v4->globalObject;
     if (scopeObject()) {
         QV4::ScopedValue value(scope, QV4::QObjectWrapper::wrap(v4, scopeObject()));
@@ -193,7 +185,7 @@ QV4::ReturnedValue QQmlJavaScriptExpression::evaluate(QV4::CallData *callData, b
             callData->thisObject = value;
     }
 
-    result = f->as<QV4::FunctionObject>()->call(callData);
+    f->as<QV4::FunctionObject>()->call(scope, callData);
     if (scope.hasException()) {
         if (watcher.wasDeleted())
             scope.engine->catchException(); // ignore exception
@@ -203,7 +195,7 @@ QV4::ReturnedValue QQmlJavaScriptExpression::evaluate(QV4::CallData *callData, b
             *isUndefined = true;
     } else {
         if (isUndefined)
-            *isUndefined = result->isUndefined();
+            *isUndefined = scope.result.isUndefined();
 
         if (!watcher.wasDeleted() && hasDelayedError())
             delayedError()->clearError();
@@ -220,8 +212,6 @@ QV4::ReturnedValue QQmlJavaScriptExpression::evaluate(QV4::CallData *callData, b
         g->Delete();
 
     ep->propertyCapture = lastPropertyCapture;
-
-    return result->asReturnedValue();
 }
 
 void QQmlPropertyCapture::captureProperty(QQmlNotifier *n)
@@ -294,11 +284,12 @@ void QQmlPropertyCapture::captureProperty(QObject *o, int c, int n)
     }
 }
 
-void QQmlPropertyCapture::registerQmlDependencies(QV4::ExecutionEngine *engine, const QV4::CompiledData::Function *compiledFunction)
+void QQmlPropertyCapture::registerQmlDependencies(const QV4::CompiledData::Function *compiledFunction, const QV4::Scope &scope)
 {
     // Let the caller check and avoid the function call :)
     Q_ASSERT(compiledFunction->hasQmlDependencies());
 
+    QV4::ExecutionEngine *engine = scope.engine;
     QQmlEnginePrivate *ep = QQmlEnginePrivate::get(engine->qmlEngine());
     if (!ep)
         return;
@@ -306,7 +297,6 @@ void QQmlPropertyCapture::registerQmlDependencies(QV4::ExecutionEngine *engine,
     if (!capture)
         return;
 
-    QV4::Scope scope(engine);
     QV4::Scoped<QV4::QmlContext> context(scope, engine->qmlContext());
     QQmlContextData *qmlContext = context->qmlContext();
 
diff --git a/src/qml/qml/qqmljavascriptexpression_p.h b/src/qml/qml/qqmljavascriptexpression_p.h
index 94479f6c5e..4472a643ff 100644
--- a/src/qml/qml/qqmljavascriptexpression_p.h
+++ b/src/qml/qml/qqmljavascriptexpression_p.h
@@ -103,8 +103,7 @@ public:
     virtual QString expressionIdentifier() = 0;
     virtual void expressionChanged() = 0;
 
-    QV4::ReturnedValue evaluate(bool *isUndefined);
-    QV4::ReturnedValue evaluate(QV4::CallData *callData, bool *isUndefined);
+    void evaluate(QV4::CallData *callData, bool *isUndefined, QV4::Scope &scope);
 
     inline bool notifyOnValueChanged() const;
 
@@ -181,7 +180,7 @@ public:
     void captureProperty(QQmlNotifier *);
     void captureProperty(QObject *, int, int);
 
-    static void registerQmlDependencies(QV4::ExecutionEngine *engine, const QV4::CompiledData::Function *compiledFunction);
+    static void registerQmlDependencies(const QV4::CompiledData::Function *compiledFunction, const QV4::Scope &scope);
 
     QQmlEngine *engine;
     QQmlJavaScriptExpression *expression;
diff --git a/src/qml/qml/qqmlvmemetaobject.cpp b/src/qml/qml/qqmlvmemetaobject.cpp
index 6907b26cd8..a9aec4cded 100644
--- a/src/qml/qml/qqmlvmemetaobject.cpp
+++ b/src/qml/qml/qqmlvmemetaobject.cpp
@@ -945,15 +945,14 @@ int QQmlVMEMetaObject::metaCall(QObject *o, QMetaObject::Call c, int _id, void *
                 for (uint ii = 0; ii < parameterCount; ++ii)
                     callData->args[ii] = scope.engine->fromVariant(*(QVariant *)a[ii + 1]);
 
-                QV4::ScopedValue result(scope);
-                result = function->call(callData);
+                function->call(scope, callData);
                 if (scope.hasException()) {
                     QQmlError error = scope.engine->catchExceptionAsQmlError();
                     if (error.isValid())
                         ep->warning(error);
                     if (a[0]) *(QVariant *)a[0] = QVariant();
                 } else {
-                    if (a[0]) *(QVariant *)a[0] = scope.engine->toVariant(result, 0);
+                    if (a[0]) *(QVariant *)a[0] = scope.engine->toVariant(scope.result, 0);
                 }
 
                 ep->dereferenceScarceResources(); // "release" scarce resources if top-level expression evaluation is complete.
diff --git a/src/qml/qml/qqmlxmlhttprequest.cpp b/src/qml/qml/qqmlxmlhttprequest.cpp
index e2784103b0..74de30c96c 100644
--- a/src/qml/qml/qqmlxmlhttprequest.cpp
+++ b/src/qml/qml/qqmlxmlhttprequest.cpp
@@ -1560,7 +1560,7 @@ void QQmlXMLHttpRequest::dispatchCallback(Object *thisObj, QQmlContextData *cont
 
     QV4::ScopedCallData callData(scope);
     callData->thisObject = Encode::undefined();
-    callback->call(callData);
+    callback->call(scope, callData);
 
     if (scope.engine->hasException) {
         QQmlError error = scope.engine->catchExceptionAsQmlError();
@@ -1621,22 +1621,23 @@ struct QQmlXMLHttpRequestCtor : public FunctionObject
             c->proto->mark(e);
         FunctionObject::markObjects(that, e);
     }
-    static ReturnedValue construct(const Managed *that, QV4::CallData *)
+    static void construct(const Managed *that, Scope &scope, QV4::CallData *)
     {
-        Scope scope(static_cast<const QQmlXMLHttpRequestCtor *>(that)->engine());
         Scoped<QQmlXMLHttpRequestCtor> ctor(scope, that->as<QQmlXMLHttpRequestCtor>());
-        if (!ctor)
-            return scope.engine->throwTypeError();
+        if (!ctor) {
+            scope.result = scope.engine->throwTypeError();
+            return;
+        }
 
         QQmlXMLHttpRequest *r = new QQmlXMLHttpRequest(scope.engine->v8Engine->networkAccessManager());
         Scoped<QQmlXMLHttpRequestWrapper> w(scope, scope.engine->memoryManager->allocObject<QQmlXMLHttpRequestWrapper>(r));
         ScopedObject proto(scope, ctor->d()->proto);
         w->setPrototype(proto);
-        return w.asReturnedValue();
+        scope.result = w.asReturnedValue();
     }
 
-    static ReturnedValue call(const Managed *, QV4::CallData *) {
-        return Primitive::undefinedValue().asReturnedValue();
+    static void call(const Managed *, Scope &scope, QV4::CallData *) {
+        scope.result = Primitive::undefinedValue();
     }
 
     void setupProto();
diff --git a/src/qml/qml/v8/qqmlbuiltinfunctions.cpp b/src/qml/qml/v8/qqmlbuiltinfunctions.cpp
index 482da31779..a0dff482b1 100644
--- a/src/qml/qml/v8/qqmlbuiltinfunctions.cpp
+++ b/src/qml/qml/v8/qqmlbuiltinfunctions.cpp
@@ -1285,11 +1285,10 @@ void QQmlBindingFunction::initBindingLocation()
     d()->bindingLocation.line = frame.line;
 }
 
-ReturnedValue QQmlBindingFunction::call(const Managed *that, CallData *callData)
+void QQmlBindingFunction::call(const Managed *that, Scope &scope, CallData *callData)
 {
-    Scope scope(static_cast<const QQmlBindingFunction*>(that)->engine());
     ScopedFunctionObject function(scope, static_cast<const QQmlBindingFunction*>(that)->d()->originalFunction);
-    return function->call(callData);
+    function->call(scope, callData);
 }
 
 void QQmlBindingFunction::markObjects(Heap::Base *that, ExecutionEngine *e)
diff --git a/src/qml/qml/v8/qqmlbuiltinfunctions_p.h b/src/qml/qml/v8/qqmlbuiltinfunctions_p.h
index 5404ab3616..d29983c476 100644
--- a/src/qml/qml/v8/qqmlbuiltinfunctions_p.h
+++ b/src/qml/qml/v8/qqmlbuiltinfunctions_p.h
@@ -188,7 +188,7 @@ struct QQmlBindingFunction : public QV4::FunctionObject
 
     void initBindingLocation(); // from caller stack trace
 
-    static ReturnedValue call(const Managed *that, CallData *callData);
+    static void call(const Managed *that, Scope &scope, CallData *callData);
 
     static void markObjects(Heap::Base *that, ExecutionEngine *e);
 };