[cxx-abi-dev] Transfer modes for parameters and return values

[Jason Merrill]

David Vandevoorde wrote:
> Hello again,
> 
> In 3.1.1 and 3.1.4, the ABI specifies that "by value" class type 
> parameters and class type return values are passed via the address of a 
> reference if the class type has
>     (a) a nontrivial destructor, or
>     (b) a nontrivial copy constructor.
> 
> Should we now also add to that:
>     (c) a (nontrivial) move constructor
> ?

I'm not sure.  We need to pass by reference in the case of a nontrivial 
copy constructor because it's invalid to do a bitwise copy in that case. 
  We need to do it in the case of a nontrivial destructor so that the 
caller can control when the destructor is run depending on copy elision. 
  Neither of those really applies to the move constructor.

Jason