QML: Do not register static QML dependencies on every call.

QML objects can be re-parented on the fly, resulting in different
dependencies for expressions like 'parent.width'. So, because of this,
dependencies are cleared and re-calculated after every binding
evaluation.

However, dependencies on properties of the scope and context objects
cannot change, because these objects do not get changed for the
life-time of a binding. So we can permanently register them. This is
only done for bindings, not for functions, because those might be
conditionally executed.

According to valgrind, this is a reduction of ~186 instructions on x86
for every evaluation of:
Item {
    height: width
}

Change-Id: Ib095497323d4f08caf712d480007e2627a176369
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

7 files changed, 50 insertions, 17 deletions

diff --git a/src/qml/compiler/qqmlirbuilder.cpp b/src/qml/compiler/qqmlirbuilder.cpp
index 4fa63e3c84..c31a7bce4f 100644
--- a/src/qml/compiler/qqmlirbuilder.cpp
+++ b/src/qml/compiler/qqmlirbuilder.cpp
@@ -1890,7 +1890,9 @@ QV4::IR::Expr *JSCodeGen::fallbackNameLookup(const QString &name, int line, int
     // Look for IDs first.
     foreach (const IdMapping &mapping, _idObjects)
         if (name == mapping.name) {
-            _function->idObjectDependencies.insert(mapping.idIndex);
+            if (_function->isQmlBinding)
+                _function->idObjectDependencies.insert(mapping.idIndex);
+
             QV4::IR::Expr *s = _block->MEMBER(_block->TEMP(_qmlContextTemp), _function->newString(name), 0, QV4::IR::Member::MemberOfIdObjectsArray, mapping.idIndex);
             QV4::IR::Temp *result = _block->TEMP(_block->newTemp());
             _block->MOVE(result, s);
diff --git a/src/qml/compiler/qv4codegen.cpp b/src/qml/compiler/qv4codegen.cpp
index 8711bc049a..7a444e8c57 100644
--- a/src/qml/compiler/qv4codegen.cpp
+++ b/src/qml/compiler/qv4codegen.cpp
@@ -1961,6 +1961,7 @@ int Codegen::defineFunction(const QString &name, AST::Node *ast,
     function->maxNumberOfArguments = qMax(_env->maxNumberOfArguments, (int)QV4::Global::ReservedArgumentCount);
     function->isStrict = _env->isStrict;
     function->isNamedExpression = _env->isNamedFunctionExpression;
+    function->isQmlBinding = _env->compilationMode == QmlBinding;
 
     AST::SourceLocation loc = ast->firstSourceLocation();
     function->line = loc.startLine;
diff --git a/src/qml/compiler/qv4jsir.cpp b/src/qml/compiler/qv4jsir.cpp
index b994d2f707..74c4f91f2b 100644
--- a/src/qml/compiler/qv4jsir.cpp
+++ b/src/qml/compiler/qv4jsir.cpp
@@ -368,6 +368,7 @@ Function::Function(Module *module, Function *outer, const QString &name)
     , isNamedExpression(false)
     , hasTry(false)
     , hasWith(false)
+    , isQmlBinding(false)
     , unused(0)
     , line(-1)
     , column(-1)
diff --git a/src/qml/compiler/qv4jsir_p.h b/src/qml/compiler/qv4jsir_p.h
index 0254ae224d..c196e8127b 100644
--- a/src/qml/compiler/qv4jsir_p.h
+++ b/src/qml/compiler/qv4jsir_p.h
@@ -1258,7 +1258,8 @@ struct Function {
     uint isNamedExpression : 1;
     uint hasTry: 1;
     uint hasWith: 1;
-    uint unused : 25;
+    uint isQmlBinding: 1;
+    uint unused : 24;
 
     // Location of declaration in source code (-1 if not specified)
     int line;
diff --git a/src/qml/jsruntime/qv4functionobject.cpp b/src/qml/jsruntime/qv4functionobject.cpp
index 041044930b..fce80c46eb 100644
--- a/src/qml/jsruntime/qv4functionobject.cpp
+++ b/src/qml/jsruntime/qv4functionobject.cpp
@@ -435,7 +435,7 @@ void ScriptFunction::construct(const Managed *that, Scope &scope, CallData *call
 
     Scoped<ScriptFunction> f(scope, static_cast<const ScriptFunction *>(that));
 
-    InternalClass *ic = scope.engine->emptyClass;
+    InternalClass *ic = v4->emptyClass;
     ScopedObject proto(scope, f->protoForConstructor());
     ScopedObject obj(scope, v4->newObject(ic, proto));
 
diff --git a/src/qml/qml/qqmljavascriptexpression.cpp b/src/qml/qml/qqmljavascriptexpression.cpp
index eff1a6e039..7fb66a49bf 100644
--- a/src/qml/qml/qqmljavascriptexpression.cpp
+++ b/src/qml/qml/qqmljavascriptexpression.cpp
@@ -106,7 +106,8 @@ QQmlJavaScriptExpression::~QQmlJavaScriptExpression()
             m_nextExpression->m_prevExpression = m_prevExpression;
     }
 
-    clearGuards();
+    clearActiveGuards();
+    clearPermanentGuards();
     if (m_scopeObject.isT2()) // notify DeleteWatcher of our deletion.
         m_scopeObject.asT2()->_s = 0;
 }
@@ -114,12 +115,12 @@ QQmlJavaScriptExpression::~QQmlJavaScriptExpression()
 void QQmlJavaScriptExpression::setNotifyOnValueChanged(bool v)
 {
     activeGuards.setFlagValue(v);
-    if (!v) clearGuards();
+    if (!v) clearActiveGuards();
 }
 
 void QQmlJavaScriptExpression::resetNotifyOnValueChanged()
 {
-    clearGuards();
+    clearActiveGuards();
 }
 
 void QQmlJavaScriptExpression::setContext(QQmlContextData *context)
@@ -214,7 +215,7 @@ void QQmlJavaScriptExpression::evaluate(QV4::CallData *callData, bool *isUndefin
     ep->propertyCapture = lastPropertyCapture;
 }
 
-void QQmlPropertyCapture::captureProperty(QQmlNotifier *n)
+void QQmlPropertyCapture::captureProperty(QQmlNotifier *n, Duration duration)
 {
     if (watcher->wasDeleted())
         return;
@@ -234,14 +235,17 @@ void QQmlPropertyCapture::captureProperty(QQmlNotifier *n)
         g->connect(n);
     }
 
-    expression->activeGuards.prepend(g);
+    if (duration == OnlyOnce)
+        expression->permanentGuards.prepend(g);
+    else
+        expression->activeGuards.prepend(g);
 }
 
 /*! \internal
 
     \a n is in the signal index range (see QObjectPrivate::signalIndex()).
 */
-void QQmlPropertyCapture::captureProperty(QObject *o, int c, int n)
+void QQmlPropertyCapture::captureProperty(QObject *o, int c, int n, Duration duration)
 {
     if (watcher->wasDeleted())
         return;
@@ -280,7 +284,10 @@ void QQmlPropertyCapture::captureProperty(QObject *o, int c, int n)
             g->connect(o, n, engine);
         }
 
-        expression->activeGuards.prepend(g);
+        if (duration == Permanently)
+            expression->permanentGuards.prepend(g);
+        else
+            expression->activeGuards.prepend(g);
     }
 }
 
@@ -297,6 +304,11 @@ void QQmlPropertyCapture::registerQmlDependencies(const QV4::CompiledData::Funct
     if (!capture)
         return;
 
+    if (capture->expression->m_permanentDependenciesRegistered)
+        return;
+
+    capture->expression->m_permanentDependenciesRegistered = true;
+
     QV4::Scoped<QV4::QmlContext> context(scope, engine->qmlContext());
     QQmlContextData *qmlContext = context->qmlContext();
 
@@ -304,7 +316,8 @@ void QQmlPropertyCapture::registerQmlDependencies(const QV4::CompiledData::Funct
     const int idObjectDependencyCount = compiledFunction->nDependingIdObjects;
     for (int i = 0; i < idObjectDependencyCount; ++i, ++idObjectDependency) {
         Q_ASSERT(int(*idObjectDependency) < qmlContext->idValueCount);
-        capture->captureProperty(&qmlContext->idValues[*idObjectDependency].bindings);
+        capture->captureProperty(&qmlContext->idValues[*idObjectDependency].bindings,
+                                 QQmlPropertyCapture::Permanently);
     }
 
     Q_ASSERT(qmlContext->contextObject);
@@ -313,7 +326,8 @@ void QQmlPropertyCapture::registerQmlDependencies(const QV4::CompiledData::Funct
     for (int i = 0; i < contextPropertyDependencyCount; ++i) {
         const int propertyIndex = *contextPropertyDependency++;
         const int notifyIndex = *contextPropertyDependency++;
-        capture->captureProperty(qmlContext->contextObject, propertyIndex, notifyIndex);
+        capture->captureProperty(qmlContext->contextObject, propertyIndex, notifyIndex,
+                                 QQmlPropertyCapture::Permanently);
     }
 
     QObject *scopeObject = context->qmlScope();
@@ -322,7 +336,8 @@ void QQmlPropertyCapture::registerQmlDependencies(const QV4::CompiledData::Funct
     for (int i = 0; i < scopePropertyDependencyCount; ++i) {
         const int propertyIndex = *scopePropertyDependency++;
         const int notifyIndex = *scopePropertyDependency++;
-        capture->captureProperty(scopeObject, propertyIndex, notifyIndex);
+        capture->captureProperty(scopeObject, propertyIndex, notifyIndex,
+                                 QQmlPropertyCapture::Permanently);
     }
 
 }
@@ -406,12 +421,18 @@ void QQmlJavaScriptExpression::createQmlBinding(QQmlContextData *ctxt, QObject *
 }
 
 
-void QQmlJavaScriptExpression::clearGuards()
+void QQmlJavaScriptExpression::clearActiveGuards()
 {
     while (QQmlJavaScriptExpressionGuard *g = activeGuards.takeFirst())
         g->Delete();
 }
 
+void QQmlJavaScriptExpression::clearPermanentGuards()
+{
+    while (QQmlJavaScriptExpressionGuard *g = permanentGuards.takeFirst())
+        g->Delete();
+}
+
 void QQmlJavaScriptExpressionGuard_callback(QQmlNotifierEndpoint *e, void **)
 {
     QQmlJavaScriptExpression *expression =
diff --git a/src/qml/qml/qqmljavascriptexpression_p.h b/src/qml/qml/qqmljavascriptexpression_p.h
index 4472a643ff..a5c7a80153 100644
--- a/src/qml/qml/qqmljavascriptexpression_p.h
+++ b/src/qml/qml/qqmljavascriptexpression_p.h
@@ -136,7 +136,8 @@ public:
     inline bool hasDelayedError() const;
     QQmlError error(QQmlEngine *) const;
     void clearError();
-    void clearGuards();
+    void clearActiveGuards();
+    void clearPermanentGuards();
     QQmlDelayedError *delayedError();
 
     static QV4::ReturnedValue evalFunction(QQmlContextData *ctxt, QObject *scope,
@@ -157,10 +158,12 @@ private:
     //    activeGuards:flag2  - useSharedContext
     QBiPointer<QObject, DeleteWatcher> m_scopeObject;
     QForwardFieldList<QQmlJavaScriptExpressionGuard, &QQmlJavaScriptExpressionGuard::next> activeGuards;
+    QForwardFieldList<QQmlJavaScriptExpressionGuard, &QQmlJavaScriptExpressionGuard::next> permanentGuards;
 
     QQmlContextData *m_context;
     QQmlJavaScriptExpression **m_prevExpression;
     QQmlJavaScriptExpression  *m_nextExpression;
+    bool m_permanentDependenciesRegistered = false;
 
 protected:
     QV4::PersistentValue m_function;
@@ -177,10 +180,14 @@ public:
         Q_ASSERT(errorString == 0);
     }
 
-    void captureProperty(QQmlNotifier *);
-    void captureProperty(QObject *, int, int);
+    enum Duration {
+        OnlyOnce,
+        Permanently
+    };
 
     static void registerQmlDependencies(const QV4::CompiledData::Function *compiledFunction, const QV4::Scope &scope);
+    void captureProperty(QQmlNotifier *, Duration duration = OnlyOnce);
+    void captureProperty(QObject *, int, int, Duration duration = OnlyOnce);
 
     QQmlEngine *engine;
     QQmlJavaScriptExpression *expression;