QML: Store idObjectDependencies in a QVarLengthArray.

The number of id objects referenced from a function or binding is
often very small. So using a QSet that allocates hash nodes takes more
memory, and is actually slower than using an array.

Change-Id: Id9fa60a860314790284f66318593b3ef938e6eef
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

2 files changed, 19 insertions, 3 deletions

diff --git a/src/qml/compiler/qv4compiler.cpp b/src/qml/compiler/qv4compiler.cpp
index b801009f4e..55d2501024 100644
--- a/src/qml/compiler/qv4compiler.cpp
+++ b/src/qml/compiler/qv4compiler.cpp
@@ -382,8 +382,10 @@ int QV4::Compiler::JSUnitGenerator::writeFunction(char *f, QV4::IR::Function *ir
 
     // write QML dependencies
     quint32 *writtenDeps = (quint32 *)(f + function->dependingIdObjectsOffset);
-    foreach (int id, irFunction->idObjectDependencies)
-        *writtenDeps++ = id;
+    for (int id : irFunction->idObjectDependencies) {
+        Q_ASSERT(id >= 0);
+        *writtenDeps++ = static_cast<quint32>(id);
+    }
 
     writtenDeps = (quint32 *)(f + function->dependingContextPropertiesOffset);
     for (auto property : irFunction->contextObjectPropertyDependencies) {
diff --git a/src/qml/compiler/qv4jsir_p.h b/src/qml/compiler/qv4jsir_p.h
index c196e8127b..a2bd6ad044 100644
--- a/src/qml/compiler/qv4jsir_p.h
+++ b/src/qml/compiler/qv4jsir_p.h
@@ -1193,6 +1193,20 @@ private:
     unsigned _isRemoved : 1;
 };
 
+template <typename T>
+class SmallSet: public QVarLengthArray<T, 8>
+{
+public:
+    void insert(int value)
+    {
+        for (auto it : *this) {
+            if (it == value)
+                return;
+        }
+        this->append(value);
+    }
+};
+
 // Map from meta property index (existence implies dependency) to notify signal index
 struct KeyValuePair
 {
@@ -1266,7 +1280,7 @@ struct Function {
     int column;
 
     // Qml extension:
-    QSet<int> idObjectDependencies;
+    SmallSet<int> idObjectDependencies;
     PropertyDependencyMap contextObjectPropertyDependencies;
     PropertyDependencyMap scopeObjectPropertyDependencies;