diff --git a/core/authorize.php b/core/authorize.php
index c6ba51d..904b038 100644
--- a/core/authorize.php
+++ b/core/authorize.php
@@ -80,7 +80,7 @@ global $conf;
 // display errors via the maintenance theme.
 $module_list['system']['filename'] = 'core/modules/system/system.module';
 $module_list['user']['filename'] = 'core/modules/user/user.module';
-module_list(TRUE, FALSE, FALSE, $module_list);
+module_list('module_enabled', $module_list);
 drupal_load('module', 'system');
 drupal_load('module', 'user');
 
diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index c26ec86..c094ab2 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -961,14 +961,7 @@ function drupal_page_is_cacheable($allow_caching = NULL) {
  * @see bootstrap_hooks()
  */
 function bootstrap_invoke_all($hook) {
-  // Bootstrap modules should have been loaded when this function is called, so
-  // we don't need to tell module_list() to reset its internal list (and we
-  // therefore leave the first parameter at its default value of FALSE). We
-  // still pass in TRUE for the second parameter, though; in case this is the
-  // first time during the bootstrap that module_list() is called, we want to
-  // make sure that its internal cache is primed with the bootstrap modules
-  // only.
-  foreach (module_list(FALSE, TRUE) as $module) {
+  foreach (module_list('bootstrap') as $module) {
     drupal_load('module', $module);
     module_invoke($module, $hook);
   }
diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index 07e25a0..52f7ff0 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -279,10 +279,11 @@ function install_begin_request(&$install_state) {
   drupal_language_initialize();
 
   require_once DRUPAL_ROOT . '/core/includes/ajax.inc';
+  // Override the module list with a minimal set of modules.
   $module_list['system']['filename'] = 'core/modules/system/system.module';
   $module_list['entity']['filename'] = 'core/modules/entity/entity.module';
   $module_list['user']['filename']   = 'core/modules/user/user.module';
-  module_list(TRUE, FALSE, FALSE, $module_list);
+  module_list('module_enabled', $module_list);
   drupal_load('module', 'system');
   drupal_load('module', 'entity');
   drupal_load('module', 'user');
@@ -1401,6 +1402,9 @@ function install_load_profile(&$install_state) {
  *   An array of information about the current installation state.
  */
 function install_bootstrap_full(&$install_state) {
+  // Clear the module list that was overriden earlier in the process.
+  // This will allow all freshly installed modules to be loaded.
+  drupal_static_reset('module_list');
   drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL);
 }
 
diff --git a/core/includes/module.inc b/core/includes/module.inc
index df9c138..49a38db 100644
--- a/core/includes/module.inc
+++ b/core/includes/module.inc
@@ -20,7 +20,8 @@ function module_load_all($bootstrap = FALSE) {
   static $has_run = FALSE;
 
   if (isset($bootstrap)) {
-    foreach (module_list(TRUE, $bootstrap) as $module) {
+    $type = $bootstrap ? 'bootstrap' : 'module_enabled';
+    foreach (module_list($type) as $module) {
       drupal_load('module', $module);
     }
     // $has_run will be TRUE if $bootstrap is FALSE.
@@ -33,70 +34,51 @@ function module_load_all($bootstrap = FALSE) {
 /**
  * Returns a list of currently active modules.
  *
- * Usually, this returns a list of all enabled modules. When called early on in
- * the bootstrap, it will return a list of vital modules only (those needed to
- * generate cached pages).
+ * Acts as a wrapper around system_list(), returning either a list of all
+ * enabled modules, or just modules needed for bootstrap.
+ * An optional parameter allows an alternative module list to be provided,
+ * which is then stored and used in subsequent calls instead of the one
+ * provided by system_list().
  *
- * All parameters to this function are optional and should generally not be
- * changed from their defaults.
- *
- * @param $refresh
- *   (optional) Whether to force the module list to be regenerated (such as
- *   after the administrator has changed the system settings). Defaults to
- *   FALSE.
- * @param $bootstrap_refresh
- *   (optional) When $refresh is TRUE, setting $bootstrap_refresh to TRUE forces
- *   the module list to be regenerated using the reduced set of modules loaded
- *   in "bootstrap mode" for cached pages. Otherwise, setting $refresh to TRUE
- *   generates the complete list of enabled modules.
- * @param $sort
- *   (optional) By default, modules are ordered by weight and module name. Set
- *   this option to TRUE to return a module list ordered only by module name.
+ * @param $type
+ *   The type of list to return:
+ *   - module_enabled: All enabled modules.
+ *   - bootstrap: All enabled modules required for bootstrap.
  * @param $fixed_list
  *   (optional) If an array of module names is provided, this will override the
  *   module list with the given set of modules. This will persist until the next
- *   call with $refresh set to TRUE or with a new $fixed_list passed in. This
- *   parameter is primarily intended for internal use (e.g., in install.php and
- *   update.php).
+ *   call with a new $fixed_list passed in. This parameter is primarily
+ *   intended for internal use (e.g., in install.php and update.php).
  *
  * @return
  *   An associative array whose keys and values are the names of the modules in
  *   the list.
  */
-function module_list($refresh = FALSE, $bootstrap_refresh = FALSE, $sort = FALSE, $fixed_list = NULL) {
-  static $list = array(), $sorted_list;
-
-  if (empty($list) || $refresh || $fixed_list) {
-    $list = array();
-    $sorted_list = NULL;
-    if ($fixed_list) {
-      foreach ($fixed_list as $name => $module) {
-        drupal_get_filename('module', $name, $module['filename']);
-        $list[$name] = $name;
-      }
-    }
-    else {
-      if ($refresh) {
-        // For the $refresh case, make sure that system_list() returns fresh
-        // data.
-        drupal_static_reset('system_list');
-      }
-      if ($bootstrap_refresh) {
-        $list = system_list('bootstrap');
-      }
-      else {
-        // Not using drupal_map_assoc() here as that requires common.inc.
-        $list = array_keys(system_list('module_enabled'));
-        $list = (!empty($list) ? array_combine($list, $list) : array());
-      }
+function module_list($type = 'module_enabled', $fixed_list = NULL) {
+  // Tracks data acquired from $fixed_list.
+  $module_list = &drupal_static(__FUNCTION__, array());
+
+  // The list that will be be returned. Separate from $module_list in order
+  // to avoid statically caching data acquired from system_list(), since
+  // that function already has its own static cache.
+  $list = $module_list;
+
+  if (isset($fixed_list)) {
+    foreach ($fixed_list as $name => $module) {
+      drupal_get_filename('module', $name, $module['filename']);
+      $module_list[$name] = $name;
     }
+    $list = $module_list;
   }
-  if ($sort) {
-    if (!isset($sorted_list)) {
-      $sorted_list = $list;
-      ksort($sorted_list);
+  elseif (empty($module_list)) {
+    if ($type == 'bootstrap') {
+      $list = system_list('bootstrap');
+    }
+    else {
+      // Not using drupal_map_assoc() here as that requires common.inc.
+      $list = array_keys(system_list($type));
+      $list = (!empty($list) ? array_combine($list, $list) : array());
     }
-    return $sorted_list;
   }
   return $list;
 }
@@ -443,7 +425,6 @@ function module_enable($module_list, $enable_dependencies = TRUE) {
         ->execute();
       // Refresh the module list to include it.
       system_list_reset();
-      module_list(TRUE);
       module_implements_reset();
       _system_update_bootstrap_status();
       // Update the registry to include it.
@@ -564,7 +545,6 @@ function module_disable($module_list, $disable_dependents = TRUE) {
   if (!empty($invoke_modules)) {
     // Refresh the module list to exclude the disabled modules.
     system_list_reset();
-    module_list(TRUE);
     module_implements_reset();
     // Invoke hook_modules_disabled before disabling modules,
     // so we can still call module hooks to get information.
@@ -636,16 +616,13 @@ function module_hook($module, $hook) {
  *
  * @param $hook
  *   The name of the hook (e.g. "help" or "menu").
- * @param $sort
- *   By default, modules are ordered by weight and filename, settings this option
- *   to TRUE, module list will be ordered by module name.
  *
  * @return
  *   An array with the names of the modules which are implementing this hook.
  *
  * @see module_implements_write_cache()
  */
-function module_implements($hook, $sort = FALSE) {
+function module_implements($hook) {
   // Use the advanced drupal_static() pattern, since this is called very often.
   static $drupal_static_fast;
   if (!isset($drupal_static_fast)) {
@@ -670,7 +647,7 @@ function module_implements($hook, $sort = FALSE) {
     $implementations['#write_cache'] = TRUE;
     $hook_info = module_hook_info();
     $implementations[$hook] = array();
-    $list = module_list(FALSE, FALSE, $sort);
+    $list = module_list();
     foreach ($list as $module) {
       $include_file = isset($hook_info[$hook]['group']) && module_load_include('inc', $module, $module . '.' . $hook_info[$hook]['group']);
       // Since module_hook() may needlessly try to load the include file again,
diff --git a/core/includes/schema.inc b/core/includes/schema.inc
index 18fab75..77ceb47 100644
--- a/core/includes/schema.inc
+++ b/core/includes/schema.inc
@@ -70,10 +70,10 @@ function drupal_get_complete_schema($rebuild = FALSE) {
       // been completed, so we force the functions we need to load just in case.
       if (function_exists('module_load_all_includes')) {
         // This function can be called very early in the bootstrap process, so
-        // we force the module_list() cache to be refreshed to ensure that it
-        // contains the complete list of modules before we go on to call
+        // we force the system_list() static cache to be refreshed to ensure
+        // that it contains the complete list of modules before we go on to call
         // module_load_all_includes().
-        module_list(TRUE);
+        drupal_static_reset('system_list');
         module_load_all_includes('install');
       }
 
diff --git a/core/includes/theme.maintenance.inc b/core/includes/theme.maintenance.inc
index 3fd60c9..e769a11 100644
--- a/core/includes/theme.maintenance.inc
+++ b/core/includes/theme.maintenance.inc
@@ -56,7 +56,7 @@ function _drupal_maintenance_theme() {
   // Ensure that system.module is loaded.
   if (!function_exists('_system_rebuild_theme_data')) {
     $module_list['system']['filename'] = 'core/modules/system/system.module';
-    module_list(TRUE, FALSE, FALSE, $module_list);
+    module_list('module_enabled', $module_list);
     drupal_load('module', 'system');
   }
 
diff --git a/core/modules/dashboard/dashboard.test b/core/modules/dashboard/dashboard.test
index ff37d57..8707788 100644
--- a/core/modules/dashboard/dashboard.test
+++ b/core/modules/dashboard/dashboard.test
@@ -92,13 +92,13 @@ class DashboardBlocksTestCase extends DrupalWebTestCase {
     $this->drupalPost('admin/modules', $edit, t('Save configuration'));
     $this->assertText(t('The configuration options have been saved.'), t('Modules status has been updated.'));
     $this->assertNoRaw('assigned to the invalid region', t('Dashboard blocks gracefully disabled.'));
-    module_list(TRUE);
+    drupal_static_reset('system_list');
     $this->assertFalse(module_exists('dashboard'), t('Dashboard disabled.'));
 
     $edit['modules[Core][dashboard][enable]'] = 'dashboard';
     $this->drupalPost('admin/modules', $edit, t('Save configuration'));
     $this->assertText(t('The configuration options have been saved.'), t('Modules status has been updated.'));
-    module_list(TRUE);
+    drupal_static_reset('system_list');
     $this->assertTrue(module_exists('dashboard'), t('Dashboard enabled.'));
 
     $this->drupalGet('admin/dashboard');
diff --git a/core/modules/forum/forum.test b/core/modules/forum/forum.test
index b5b8ae4..7165c36 100644
--- a/core/modules/forum/forum.test
+++ b/core/modules/forum/forum.test
@@ -63,7 +63,7 @@ class ForumTestCase extends DrupalWebTestCase {
     $edit['modules[Core][forum][enable]'] = FALSE;
     $this->drupalPost('admin/modules', $edit, t('Save configuration'));
     $this->assertText(t('The configuration options have been saved.'), t('Modules status has been updated.'));
-    module_list(TRUE);
+    drupal_static_reset('system_list');
     $this->assertFalse(module_exists('forum'), t('Forum module is not enabled.'));
 
     // Attempt to re-enable the forum module and ensure it does not try to
@@ -72,7 +72,7 @@ class ForumTestCase extends DrupalWebTestCase {
     $edit['modules[Core][forum][enable]'] = 'forum';
     $this->drupalPost('admin/modules', $edit, t('Save configuration'));
     $this->assertText(t('The configuration options have been saved.'), t('Modules status has been updated.'));
-    module_list(TRUE);
+    drupal_static_reset('system_list');
     $this->assertTrue(module_exists('forum'), t('Forum module is enabled.'));
   }
 
diff --git a/core/modules/help/help.admin.inc b/core/modules/help/help.admin.inc
index 81cd224..0a8e147 100644
--- a/core/modules/help/help.admin.inc
+++ b/core/modules/help/help.admin.inc
@@ -64,7 +64,7 @@ function help_links_as_list() {
   $module_info = system_rebuild_module_data();
 
   $modules = array();
-  foreach (module_implements('help', TRUE) as $module) {
+  foreach (module_implements('help') as $module) {
     if (module_invoke($module, 'help', "admin/help#$module", $empty_arg)) {
       $modules[$module] = $module_info[$module]->info['name'];
     }
diff --git a/core/modules/help/help.module b/core/modules/help/help.module
index 9e74751..c57e62f 100644
--- a/core/modules/help/help.module
+++ b/core/modules/help/help.module
@@ -18,7 +18,9 @@ function help_menu() {
     'file' => 'help.admin.inc',
   );
 
-  foreach (module_implements('help', TRUE) as $module) {
+  $modules = module_implements('help');
+  ksort($modules);
+  foreach ($modules as $module) {
     $items['admin/help/' . $module] = array(
       'title' => $module,
       'page callback' => 'help_page',
diff --git a/core/modules/simpletest/drupal_web_test_case.php b/core/modules/simpletest/drupal_web_test_case.php
index a5a27ec..4b0d59e 100644
--- a/core/modules/simpletest/drupal_web_test_case.php
+++ b/core/modules/simpletest/drupal_web_test_case.php
@@ -739,7 +739,7 @@ class DrupalUnitTestCase extends DrupalTestCase {
     if (isset($module_list['locale'])) {
       $this->originalModuleList = $module_list;
       unset($module_list['locale']);
-      module_list(TRUE, FALSE, FALSE, $module_list);
+      module_list('module_enabled', $module_list);
     }
     $this->setup = TRUE;
   }
@@ -754,7 +754,7 @@ class DrupalUnitTestCase extends DrupalTestCase {
     $conf['file_public_path'] = $this->originalFileDirectory;
     // Restore modules if necessary.
     if (isset($this->originalModuleList)) {
-      module_list(TRUE, FALSE, FALSE, $this->originalModuleList);
+      module_list('module_enabled', $this->originalModuleList);
     }
   }
 }
@@ -1494,7 +1494,7 @@ class DrupalWebTestCase extends DrupalTestCase {
     // Reset all static variables.
     drupal_static_reset();
     // Reset the list of enabled modules.
-    module_list(TRUE);
+    drupal_static_reset('system_list');
 
     // Reset cached schema for new database prefix. This must be done before
     // drupal_flush_all_caches() so rebuilds can make use of the schema of
@@ -1572,7 +1572,7 @@ class DrupalWebTestCase extends DrupalTestCase {
 
     // Reload module list and implementations to ensure that test module hooks
     // aren't called after tests.
-    module_list(TRUE);
+    drupal_static_reset('system_list');
     module_implements_reset();
 
     // Reset the Field API.
diff --git a/core/modules/simpletest/tests/module.test b/core/modules/simpletest/tests/module.test
index 19acf60..0e3cba8 100644
--- a/core/modules/simpletest/tests/module.test
+++ b/core/modules/simpletest/tests/module.test
@@ -51,7 +51,7 @@ class ModuleUnitTest extends DrupalWebTestCase {
       ->condition('type', 'module')
       ->execute();
     // Reset the module list.
-    module_list(TRUE);
+    drupal_static_reset('system_list');
     // Move contact to the end of the array.
     unset($module_list[array_search('contact', $module_list)]);
     $module_list[] = 'contact';
@@ -62,12 +62,12 @@ class ModuleUnitTest extends DrupalWebTestCase {
       'system' => array('filename' => drupal_get_path('module', 'system')),
       'menu' => array('filename' => drupal_get_path('module', 'menu')),
     );
-    module_list(FALSE, FALSE, FALSE, $fixed_list);
+    module_list('module_enabled', $fixed_list);
     $new_module_list = array_combine(array_keys($fixed_list), array_keys($fixed_list));
     $this->assertModuleList($new_module_list, t('When using a fixed list'));
 
     // Reset the module list.
-    module_list(TRUE);
+    drupal_static_reset('system_list');
     $this->assertModuleList($module_list, t('After reset'));
   }
 
@@ -80,8 +80,6 @@ class ModuleUnitTest extends DrupalWebTestCase {
   protected function assertModuleList(Array $expected_values, $condition) {
     $expected_values = array_combine($expected_values, $expected_values);
     $this->assertEqual($expected_values, module_list(), t('@condition: module_list() returns correct results', array('@condition' => $condition)));
-    ksort($expected_values);
-    $this->assertIdentical($expected_values, module_list(FALSE, FALSE, TRUE), t('@condition: module_list() returns correctly sorted results', array('@condition' => $condition)));
   }
 
   /**
diff --git a/core/modules/simpletest/tests/upgrade/upgrade.test b/core/modules/simpletest/tests/upgrade/upgrade.test
index aafb642..b1ad1ae 100644
--- a/core/modules/simpletest/tests/upgrade/upgrade.test
+++ b/core/modules/simpletest/tests/upgrade/upgrade.test
@@ -178,7 +178,7 @@ abstract class UpgradePathTestCase extends DrupalWebTestCase {
 
     // Reload module list and implementations to ensure that test module hooks
     // aren't called after tests.
-    module_list(TRUE);
+    drupal_static_reset('system_list');
     module_implements_reset();
 
     // Reset the Field API.
diff --git a/core/modules/system/system.admin.inc b/core/modules/system/system.admin.inc
index 978b0f4..a6594da 100644
--- a/core/modules/system/system.admin.inc
+++ b/core/modules/system/system.admin.inc
@@ -1194,7 +1194,8 @@ function system_modules_submit($form, &$form_state) {
 
   // Gets module list after install process, flushes caches and displays a
   // message if there are changes.
-  $post_install_list = module_list(TRUE);
+  drupal_static_reset('system_list');
+  $post_install_list = module_list();
   if ($pre_install_list != $post_install_list) {
     drupal_flush_all_caches();
     drupal_set_message(t('The configuration options have been saved.'));
diff --git a/core/modules/system/system.install b/core/modules/system/system.install
index 905d11d..ad5c403 100644
--- a/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -499,7 +499,7 @@ function system_install() {
 
   // Clear out module list and hook implementation statics before calling
   // system_rebuild_theme_data().
-  module_list(TRUE);
+  drupal_static_reset('system_list');
   module_implements_reset();
 
   // Load system theme data appropriately.
diff --git a/core/modules/system/system.test b/core/modules/system/system.test
index 9287d16..e6069a5 100644
--- a/core/modules/system/system.test
+++ b/core/modules/system/system.test
@@ -81,7 +81,7 @@ class ModuleTestCase extends DrupalWebTestCase {
    *   Expected module state.
    */
   function assertModules(array $modules, $enabled) {
-    module_list(TRUE);
+    drupal_static_reset('system_list');
     foreach ($modules as $module) {
       if ($enabled) {
         $message = 'Module "@module" is enabled.';
@@ -1563,7 +1563,7 @@ class SystemMainContentFallback extends DrupalWebTestCase {
     $edit['modules[Core][block][enable]'] = FALSE;
     $this->drupalPost('admin/modules', $edit, t('Save configuration'));
     $this->assertText(t('The configuration options have been saved.'), t('Modules status has been updated.'));
-    module_list(TRUE);
+    drupal_static_reset('system_list');
     $this->assertFalse(module_exists('block'), t('Block module disabled.'));
 
     // At this point, no region is filled and fallback should be triggered.
@@ -1597,7 +1597,7 @@ class SystemMainContentFallback extends DrupalWebTestCase {
     $edit['modules[Core][block][enable]'] = 'block';
     $this->drupalPost('admin/modules', $edit, t('Save configuration'));
     $this->assertText(t('The configuration options have been saved.'), t('Modules status has been updated.'));
-    module_list(TRUE);
+    drupal_static_reset('system_list');
     $this->assertTrue(module_exists('block'), t('Block module re-enabled.'));
   }
 }
diff --git a/core/update.php b/core/update.php
index 3d858a2..444ca4f 100644
--- a/core/update.php
+++ b/core/update.php
@@ -395,7 +395,7 @@ if (empty($op) && update_access_allowed()) {
   // Load module basics.
   include_once DRUPAL_ROOT . '/core/includes/module.inc';
   $module_list['system']['filename'] = 'core/modules/system/system.module';
-  module_list(TRUE, FALSE, FALSE, $module_list);
+  module_list('module_enabled', $module_list);
   drupal_load('module', 'system');
 
   // Reset the module_implements() cache so that any new hook implementations