Revert "PERF: Recover `changes_applied` performance (#31698)"

This reverts commit a19e91f0fab13cca61acdb1f33e27be2323b9786.

2 files changed, 5 insertions, 2 deletions

diff --git a/activerecord/lib/active_record/attribute_methods/dirty.rb b/activerecord/lib/active_record/attribute_methods/dirty.rb
index df4c79b0f6..3de6fe566d 100644
--- a/activerecord/lib/active_record/attribute_methods/dirty.rb
+++ b/activerecord/lib/active_record/attribute_methods/dirty.rb
@@ -32,7 +32,9 @@ module ActiveRecord
       # <tt>reload</tt> the record and clears changed attributes.
       def reload(*)
         super.tap do
+          @previously_changed = ActiveSupport::HashWithIndifferentAccess.new
           @mutations_before_last_save = nil
+          @attributes_changed_by_setter = ActiveSupport::HashWithIndifferentAccess.new
           @mutations_from_database = nil
         end
       end
@@ -112,12 +114,12 @@ module ActiveRecord
 
       # Alias for +changed+
       def changed_attribute_names_to_save
-        mutations_from_database.changed_attribute_names
+        changes_to_save.keys
       end
 
       # Alias for +changed_attributes+
       def attributes_in_database
-        mutations_from_database.changed_values
+        changes_to_save.transform_values(&:first)
       end
 
       private
diff --git a/activerecord/lib/active_record/persistence.rb b/activerecord/lib/active_record/persistence.rb
index d4f4a5887a..6ec477c7f3 100644
--- a/activerecord/lib/active_record/persistence.rb
+++ b/activerecord/lib/active_record/persistence.rb
@@ -374,6 +374,7 @@ module ActiveRecord
       became.send(:initialize)
       became.instance_variable_set("@attributes", @attributes)
       became.instance_variable_set("@mutations_from_database", @mutations_from_database) if defined?(@mutations_from_database)
+      became.instance_variable_set("@changed_attributes", attributes_changed_by_setter)
       became.instance_variable_set("@new_record", new_record?)
       became.instance_variable_set("@destroyed", destroyed?)
       became.errors.copy!(errors)