perf($compile): only re-$interpolate attributes values if the value has changed

Author: jbedard

src/ng/compile.js

@@ -2273,7 +2273,10 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
 
 
     function addAttrInterpolateDirective(node, directives, value, name, allOrNothing) {
-      var interpolateFn = $interpolate(value, true);
+      var trustedContext = getTrustedContext(node, name);
+      allOrNothing = ALL_OR_NOTHING_ATTRS[name] || allOrNothing;
+
+      var interpolateFn = $interpolate(value, true, trustedContext, allOrNothing);
 
       // no interpolation found -> ignore
       if (!interpolateFn) return;
@@ -2298,19 +2301,21 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
               pre: function attrInterpolatePreLinkFn(scope, element, attr) {
                 var $$observers = (attr.$$observers || (attr.$$observers = {}));
 
-                // If the attribute was removed, then we are done
-                if (!attr[name]) {
-                  return;
-                }
+                // If the attribute has changed since compilation
+                if (attr[name] !== value) {
+                  // If the attribute was removed, then we are done
+                  if (!attr[name]) {
+                    return;
+                  }
 
-                // we need to interpolate again, in case the attribute value has been updated
-                // (e.g. by another directive's compile function)
-                interpolateFn = $interpolate(attr[name], true, getTrustedContext(node, name),
-                    ALL_OR_NOTHING_ATTRS[name] || allOrNothing);
+                  // we need to interpolate again, in case the attribute value has been updated
+                  // (e.g. by another directive's compile function)
+                  interpolateFn = $interpolate(value = attr[name], true, trustedContext, allOrNothing);
 
-                // if attribute was updated so that there is no interpolation going on we don't want to
-                // register any observers
-                if (!interpolateFn) return;
+                  // if attribute was updated so that there is no interpolation going on we don't want to
+                  // register any observers
+                  if (!interpolateFn) return;
+                }
 
                 // initialize attr object so that it's ready in case we need the value for isolate
                 // scope initialization, otherwise the value would not be available from isolate