diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index 2b06429..0624722 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -408,8 +408,6 @@ function list_themes($refresh = FALSE) {
  * @see template_preprocess()
  */
 function _theme($hook, $variables = array()) {
-  static $default_attributes;
-
   $module_handler = \Drupal::moduleHandler();
 
   // If called before all modules are loaded, we do not necessarily have a full
@@ -615,19 +613,8 @@ function _theme($hook, $variables = array()) {
       template_preprocess($default_template_variables, $hook, $info);
       $variables += $default_template_variables;
     }
-    if (!isset($default_attributes)) {
-      $default_attributes = new Attribute();
-    }
-    foreach (array('attributes', 'title_attributes', 'content_attributes') as $key) {
-      if (isset($variables[$key]) && !($variables[$key] instanceof Attribute)) {
-        if ($variables[$key]) {
-          $variables[$key] = new Attribute($variables[$key]);
-        }
-        else {
-          // Create empty attributes.
-          $variables[$key] = clone $default_attributes;
-        }
-      }
+    if (isset($variables['attributes']) && !($variables['attributes'] instanceof Attribute)) {
+      $variables['attributes'] = new Attribute($variables['attributes']);
     }
 
     // Render the output using the template file.
@@ -1061,8 +1048,6 @@ function template_preprocess_datetime(&$variables) {
 
   // Add a 'datetime' class.
   $variables['attributes']['class'][] = 'datetime';
-
-  $variables['attributes'] = new Attribute($variables['attributes']);
 }
 
 /**
@@ -1891,8 +1876,6 @@ function _template_preprocess_default_variables() {
   // Variables that don't depend on a database connection.
   $variables = array(
     'attributes' => array(),
-    'title_attributes' => array(),
-    'content_attributes' => array(),
     'title_prefix' => array(),
     'title_suffix' => array(),
     'db_is_active' => !defined('MAINTENANCE_MODE'),
@@ -2387,11 +2370,6 @@ function template_preprocess_field(&$variables, $hook) {
     $variables['attributes']['class'][] = 'clearfix';
   }
 
-  static $default_attributes;
-  if (!isset($default_attributes)) {
-    $default_attributes = new Attribute;
-  }
-
   // Modules (e.g., rdf.module) can add field item attributes (to
   // $item->_attributes) within hook_entity_prepare_view(). Some field
   // formatters move those attributes into some nested formatter-specific
@@ -2400,7 +2378,7 @@ function template_preprocess_field(&$variables, $hook) {
   // formatters leave them within $element['#items'][$delta]['_attributes'] to
   // be rendered on the item wrappers provided by field.html.twig.
   foreach ($variables['items'] as $delta => $item) {
-    $variables['item_attributes'][$delta] = !empty($element['#items'][$delta]->_attributes) ? new Attribute($element['#items'][$delta]->_attributes) : clone($default_attributes);
+    $variables['item_attributes'][$delta] = !empty($element['#items'][$delta]->_attributes) ? new Attribute($element['#items'][$delta]->_attributes) : new Attribute();
   }
 }
 
diff --git a/core/modules/block/block.module b/core/modules/block/block.module
index 37b93bd..32b2554 100644
--- a/core/modules/block/block.module
+++ b/core/modules/block/block.module
@@ -8,6 +8,7 @@
 use Drupal\block\BlockInterface;
 use Drupal\language\Entity\Language;
 use Drupal\system\Entity\Menu;
+use Drupal\Core\Template\Attribute;
 use Symfony\Cmf\Component\Routing\RouteObjectInterface;
 use Symfony\Component\HttpFoundation\Request;
 
@@ -382,6 +383,10 @@ function template_preprocess_block(&$variables) {
   if ($id = $variables['elements']['#block']->id()) {
     $variables['attributes']['id'] = drupal_html_id('block-' . $id);
   }
+
+  // For best performance, we only instantiate Attribute objects when needed.
+  $variables['title_attributes'] = isset($variables['title_attributes']) ? new Attribute($variables['title_attributes']) : NULL;
+  $variables['content_attributes'] = isset($variables['content_attributes']) ? new Attribute($variables['content_attributes']) : NULL;
 }
 
 /**
diff --git a/core/modules/block/src/Tests/BlockPreprocessUnitTest.php b/core/modules/block/src/Tests/BlockPreprocessUnitTest.php
index e343019..d12c88a 100644
--- a/core/modules/block/src/Tests/BlockPreprocessUnitTest.php
+++ b/core/modules/block/src/Tests/BlockPreprocessUnitTest.php
@@ -55,7 +55,8 @@ function testBlockClasses() {
     // Test adding a class to the block content.
     $variables['content_attributes']['class'][] = 'test-class';
     template_preprocess_block($variables);
-    $this->assertEqual($variables['content_attributes']['class'], array('test-class', 'content'), 'Default .content class added to block content_attributes');
+    $classes = $variables['content_attributes']['class']->value();
+    $this->assertEqual($classes, array('test-class', 'content'), 'Default .content class added to block content_attributes');
   }
 
 }
diff --git a/core/modules/comment/comment.module b/core/modules/comment/comment.module
index b09bfa8..8537b97 100644
--- a/core/modules/comment/comment.module
+++ b/core/modules/comment/comment.module
@@ -19,6 +19,7 @@
 use Drupal\Core\Entity\Display\EntityViewDisplayInterface;
 use Drupal\Core\Field\FieldDefinitionInterface;
 use Drupal\Core\Render\Element;
+use Drupal\Core\Template\Attribute;
 use Drupal\Core\Url;
 use Drupal\field\FieldInstanceConfigInterface;
 use Drupal\field\FieldConfigInterface;
@@ -1463,6 +1464,10 @@ function template_preprocess_comment(&$variables) {
   $variables['attributes']['data-comment-user-id'] = $comment->getOwnerId();
 
   $variables['content_attributes']['class'][] = 'content';
+  $variables['content_attributes'] = new Attribute($variables['content_attributes']);
+
+  $variables['title_attributes'] = isset($variables['title_attributes']) ? $variables['title_attributes'] : array();
+  $variables['title_attributes'] = new Attribute($variables['title_attributes']);
 }
 
 /**
diff --git a/core/modules/node/node.module b/core/modules/node/node.module
index 2253f71..f1b6f93 100644
--- a/core/modules/node/node.module
+++ b/core/modules/node/node.module
@@ -701,6 +701,8 @@ function template_preprocess_node(&$variables) {
     $variables['attributes']['class'][] = 'preview';
   }
   $variables['content_attributes']['class'][] = 'content';
+  $variables['content_attributes'] = new Attribute($variables['content_attributes']);
+  $variables['title_attributes'] = isset($variables['title_attributes']) ? new Attribute($variables['title_attributes']) : new Attribute();
 }
 
 /**
diff --git a/core/modules/search/search.pages.inc b/core/modules/search/search.pages.inc
index 34b235c..81e2644 100644
--- a/core/modules/search/search.pages.inc
+++ b/core/modules/search/search.pages.inc
@@ -6,6 +6,7 @@
  */
 
 use Drupal\Core\Language\Language;
+use Drupal\Core\Template\Attribute;
 
 /**
  * Implements hook_theme_suggestions_HOOK().
@@ -59,5 +60,8 @@ function template_preprocess_search_result(&$variables) {
   // Provide separated and grouped meta information..
   $variables['info_split'] = $info;
   $variables['info'] = implode(' - ', $info);
+
+  $variables['title_attributes'] = isset($variables['title_attributes']) ? new Attribute($variables['title_attributes']) : new Attribute();
+  $variables['content_attributes'] = isset($variables['content_attributes']) ? new Attribute($variables['content_attributes']) : new Attribute();
 }