In fact, there isn’t any obvious way to perform the action of comparing your edited picture to the original, unedited version. While reverting the image back to its original is sometimes a valid option, for the more sizable edits it can take a great deal of time for the changes to process.
While you’re viewing an edited photo, simply hit the Shift key and you will instantly see the original image appear for as long as you hold. It’s an instant change, so no more waiting for the program to catch up.
In the Edit panel that slides in from the right is the option to revert your image to its original form. This is fine if you’re unhappy with your edit and want to start over again, but it will take time to remove effects.