Enable save button only when value different, or when input is dirty?

I see that a lot of frameworks for form validation have "is dirty" state check which tells if the user has ever modified input value.

But I don't see options that compare the original and current value of the input to check if it's actually different and needs to be saved.

So, in this use-case:

  1. Initial value: "my text"
  2. User changes to: "your text"
  3. Then the user changes it back to "my text"

Should the save button be enabled, or not?

My assumption is that the user might not remember what the original value was and would be looking for an option to save.

But if we only enable the save button when there's something to save - the user should recognize this and understand that his changes resulted in the starting value (back to the square one)?

Any opinions on that?