That's not the optimization in question here, though. C uses the stack pointer a lot if you use a lot of stack-local variables. Mark all your stuff "static" a

That's not the optimization in question here, though. C uses the stack pointer a lot if you use a lot of stack-local variables. Mark all your stuff "static" and it will use immediate addresses instead (which may or may not help you -- putting all the "local" stuff in a block referenced by one pointer is usually a good thing!). What's happening here is that C++ is the inheritor of decades of ponderous analysis about how code works with temporary results such that it can usually (.../often/sometimes/under-the-right-astrological-sign) optimize them away or arrange to have them magically appear in the right place. The return value optimization and all the move semantics nonsense is aimed at this space. As a result, C++ tends to put things on the stack "where they want to go", where I guess Rust is a little naive and needs to build them in one place just to copy them where they need to be.