perf($compile): clone the nodeList during linking only if necessary

Author: IgorMinar

src/ng/compile.js

@@ -934,7 +934,7 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
     function compileNodes(nodeList, transcludeFn, $rootElement, maxPriority, ignoreDirective,
                             previousCompileContext) {
       var linkFns = [],
-          attrs, directives, nodeLinkFn, childNodes, childLinkFn, linkFnFound;
+          attrs, directives, nodeLinkFn, childNodes, childLinkFn, linkFnFound, nodeLinkFnFound;
 
       for (var i = 0; i < nodeList.length; i++) {
         attrs = new Attributes();
@@ -963,6 +963,8 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
 
         linkFns.push(nodeLinkFn, childLinkFn);
         linkFnFound = linkFnFound || nodeLinkFn || childLinkFn;
+        nodeLinkFnFound = nodeLinkFnFound || nodeLinkFn;
+
         //use the previous context only for the first element in the virtual group
         previousCompileContext = null;
       }
@@ -972,14 +974,23 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
 
       function compositeLinkFn(scope, nodeList, $rootElement, parentBoundTranscludeFn) {
         var nodeLinkFn, childLinkFn, node, childScope, i, ii, n, childBoundTranscludeFn;
+        var stableNodeList;
+
+
+        if (nodeLinkFnFound) {
+          // copy nodeList so that if a nodeLinkFn removes or adds an element at this DOM level our
+          // offsets don't get screwed up
+          var nodeListLength = nodeList.length;
+          stableNodeList = new Array(nodeListLength);
 
-        // copy nodeList so that linking doesn't break due to live list updates.
-        var nodeListLength = nodeList.length,
-            stableNodeList = new Array(nodeListLength);
-        for (i = 0; i < nodeListLength; i++) {
-          stableNodeList[i] = nodeList[i];
+          for (i = 0; i < nodeListLength; i++) {
+            stableNodeList[i] = nodeList[i];
+          }
+        } else {
+          stableNodeList = nodeList;
         }
 
+        // TODO(perf): when the DOM is sparsely annotated with directives, we spend a lot of time iterating over nulls here
         for(i = 0, n = 0, ii = linkFns.length; i < ii; n++) {
           node = stableNodeList[n];
           nodeLinkFn = linkFns[i++];