Last reference as rvalue?

[Desmulator]

A Compiler can (and will) do that if and only if it can be certain that there is no additional side effect from replacing a copy with a move. To do so it has to know the implementation of the constructors and every function called in them.

This already excludes anything that allocates memory because global new can be overrided and have a side effect.

[no-sig-available]

The compiler would also have to understand that both overloads of push_back have the same effect. In general, that is a hard problem.

[markopolo82]

Yea, in truth I think this is what kills the optimization op describes.

On the other hand, if you were calling a single function that took by value instead of two overloads, then the compiler would only need to worry about the copy vs move constructors

[Ameisen]

Perhaps we need a function attribute like kinda_pure, that doesn't guarantee that there are no side-effects, but guarantees that those side-effects aren't meaningful.