The 70s era bit of this is the thinking that compilers 'sometimes re-write parts' of your program. Really they completely break your entire program down and then build it up from the ground again. Everything would show up as having been rewritten.
Taking that information into any sort of "yeah, this still represents the original intent of the author" highlight/lack of highlight/summary as it sounds like azinman2 wants might be a little more difficult. (After all, if you can implement that, why not have your compiler only emit 'sane' code in the first place?)