Copy constructor vs. return value optimization

The standard allows any level of copy omission here:

• construct a local temporary, copy-construct it into a return value, and copy-construct the return value into the local "c". OR
• construct a local temporary, and copy-construct that into "c". OR
• construct "c" with the arguments "i,d"

The standard says that the copy constructor need not be used - see section 12.8/15:

15 Whenever a temporary class object is copied using a copy constructor, and this object and the copy have the same cv-unqualified type, an implementation is permitted to treat the original and the copy as two different ways of referring to the same object and not perform a copy at all, even if the class copy constructor or destructor have side effects.

And much more in a similar vein.