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>

1 files changed, 7 insertions, 10 deletions

diff --git a/src/plugins/qmltooling/qmldbg_debugger/qqmlnativedebugservice.cpp b/src/plugins/qmltooling/qmldbg_debugger/qqmlnativedebugservice.cpp
index 43036e9c3c..d54bf98068 100644
--- a/src/plugins/qmltooling/qmldbg_debugger/qqmlnativedebugservice.cpp
+++ b/src/plugins/qmltooling/qmldbg_debugger/qqmlnativedebugservice.cpp
@@ -208,7 +208,7 @@ private:
 
     void handleDebuggerDeleted(QObject *debugger);
 
-    QV4::ReturnedValue evaluateExpression(QV4::Scope &scope, const QString &expression);
+    void evaluateExpression(QV4::Scope &scope, const QString &expression);
     bool checkCondition(const QString &expression);
 
     QStringList breakOnSignals;
@@ -241,12 +241,11 @@ private:
 bool NativeDebugger::checkCondition(const QString &expression)
 {
     QV4::Scope scope(m_engine);
-    QV4::ReturnedValue result = evaluateExpression(scope, expression);
-    QV4::ScopedValue val(scope, result);
-    return val->booleanValue();
+    evaluateExpression(scope, expression);
+    return scope.result.booleanValue();
 }
 
-QV4::ReturnedValue NativeDebugger::evaluateExpression(QV4::Scope &scope, const QString &expression)
+void NativeDebugger::evaluateExpression(QV4::Scope &scope, const QString &expression)
 {
     m_runningJob = true;
 
@@ -261,12 +260,10 @@ QV4::ReturnedValue NativeDebugger::evaluateExpression(QV4::Scope &scope, const Q
     // That is a side-effect of inheritContext.
     script.inheritContext = true;
     script.parse();
-    QV4::ScopedValue result(scope);
     if (!m_engine->hasException)
-        result = script.run();
+        scope.result = script.run();
 
     m_runningJob = false;
-    return result->asReturnedValue();
 }
 
 NativeDebugger::NativeDebugger(QQmlNativeDebugServiceImpl *service, QV4::ExecutionEngine *engine)
@@ -545,8 +542,8 @@ void NativeDebugger::handleExpressions(QJsonObject *response, const QJsonObject
         TRACE_PROTOCOL("Evaluate expression: " << expression);
         m_runningJob = true;
 
-        QV4::ReturnedValue eval = evaluateExpression(scope, expression);
-        QV4::ScopedValue result(scope, eval);
+        evaluateExpression(scope, expression);
+        QV4::ScopedValue result(scope, scope.result);
 
         m_runningJob = false;
         if (result->isUndefined()) {