Added a method XmlElement::prependChildElement(), and used this for a few optimisations.

modules/juce_audio_processors/scanning/juce_KnownPluginList.cpp

@@ -287,8 +287,8 @@ XmlElement* KnownPluginList::createXml() const
 {
     XmlElement* const e = new XmlElement ("KNOWNPLUGINS");
 
-    for (int i = 0; i < types.size(); ++i)
-        e->addChildElement (types.getUnchecked(i)->createXml());
+    for (int i = types.size(); --i >= 0;)
+        e->prependChildElement (types.getUnchecked(i)->createXml());
 
     for (int i = 0; i < blacklist.size(); ++i)
         e->createNewChildElement ("BLACKLISTED")->setAttribute ("id", blacklist[i]);

modules/juce_core/xml/juce_XmlElement.cpp

@@ -585,18 +585,36 @@ XmlElement* XmlElement::getChildByAttribute (StringRef attributeName, StringRef
 void XmlElement::addChildElement (XmlElement* const newNode) noexcept
 {
     if (newNode != nullptr)
+    {
+        // The element being added must not be a child of another node!
+        jassert (newNode->nextListItem == nullptr);
+
         firstChildElement.append (newNode);
+    }
 }
 
 void XmlElement::insertChildElement (XmlElement* const newNode, int indexToInsertAt) noexcept
 {
     if (newNode != nullptr)
     {
-        removeChildElement (newNode, false);
+        // The element being added must not be a child of another node!
+        jassert (newNode->nextListItem == nullptr);
+
         firstChildElement.insertAtIndex (indexToInsertAt, newNode);
     }
 }
 
+void XmlElement::prependChildElement (XmlElement* newNode) noexcept
+{
+    if (newNode != nullptr)
+    {
+        // The element being added must not be a child of another node!
+        jassert (newNode->nextListItem == nullptr);
+
+        firstChildElement.insertNext (newNode);
+    }
+}
+
 XmlElement* XmlElement::createNewChildElement (const String& childTagName)
 {
     XmlElement* const newElement = new XmlElement (childTagName);

modules/juce_core/xml/juce_XmlElement.h

@@ -504,6 +504,10 @@ public:
         make sure the object that you pass in will not be deleted by anything else,
         and make sure it's not already the child of another element.
 
+        Note that due to the XmlElement using a singly-linked-list, prependChildElement()
+        is an O(1) operation, but addChildElement() is an O(N) operation - so if
+        you're adding large number of elements, you may prefer to do so in reverse order!
+
         @see getFirstChildElement, getNextElement, getNumChildElements,
              getChildElement, removeChildElement
     */
@@ -523,6 +527,21 @@ public:
     void insertChildElement (XmlElement* newChildNode,
                              int indexToInsertAt) noexcept;
 
+    /** Inserts an element at the beginning of this element's list of children.
+
+        Child elements are deleted automatically when their parent is deleted, so
+        make sure the object that you pass in will not be deleted by anything else,
+        and make sure it's not already the child of another element.
+
+        Note that due to the XmlElement using a singly-linked-list, prependChildElement()
+        is an O(1) operation, but addChildElement() is an O(N) operation - so if
+        you're adding large number of elements, you may prefer to do so in reverse order!
+
+        @param newChildNode     the element to add
+        @see addChildElement, insertChildElement
+    */
+    void prependChildElement (XmlElement* newChildElement) noexcept;
+
     /** Creates a new element with the given name and returns it, after adding it
         as a child element.
 

modules/juce_data_structures/values/juce_ValueTree.cpp

@@ -412,8 +412,9 @@ public:
         XmlElement* const xml = new XmlElement (type.toString());
         properties.copyToXmlAttributes (*xml);
 
-        for (int i = 0; i < children.size(); ++i)
-            xml->addChildElement (children.getObjectPointerUnchecked(i)->createXml());
+        // (NB: it's faster to add nodes to XML elements in reverse order)
+        for (int i = children.size(); --i >= 0;)
+            xml->prependChildElement (children.getObjectPointerUnchecked(i)->createXml());
 
         return xml;
     }

modules/juce_gui_basics/widgets/juce_TreeView.cpp

@@ -1840,8 +1840,8 @@ XmlElement* TreeViewItem::getOpennessState (const bool canReturnNull) const
 
             e = new XmlElement ("OPEN");
 
-            for (int i = 0; i < subItems.size(); ++i)
-                e->addChildElement (subItems.getUnchecked(i)->getOpennessState (true));
+            for (int i = subItems.size(); --i >= 0;)
+                e->prependChildElement (subItems.getUnchecked(i)->getOpennessState (true));
         }
         else
         {