There are several semantic differences between Cpp1 and Cpp2. Cpp2 moves from last use, which is the biggest one. In a contrived example, that could result in a "hello world" changing to "goodbye world" or any other arbitrary behavior change you want to demonstrate. Cpp2 also doesn't require you to order functions and types or declare prototypes, which means partial template specializations and function overloads can produce similar changes when migrating from Cpp1 to Cpp2.

I've written a little demo here: https://godbolt.org/z/xn1eqd5zb

You can see where CPPFront inserts a `cpp2::move` call automatically, and how that differs from a superficially equivalent Cpp1 function.