When determining whether temporary object is allowed to be created during passing or returning, triviality of assignment operators is ignored ([class.temporary]/3, so does Itanium C++ ABI), which is inconsistent with the definition of trivially copyable class in [class.prop]/1.
Perhaps we should replace the use of "trivially copyable" in [class.temporary]/(1.2) with a new term.

May be related to CWG2434.