[Accepted as a DR at the February, 2019 meeting.]

According to 6.3 [basic.def.odr] paragraph 3,

A function whose name appears as a potentially-evaluated expression is odr-used if it is the unique lookup result or the selected member of a set of overloaded functions (6.5 [basic.lookup], 12.2 [over.match], 12.3 [over.over]), unless it is a pure virtual function and its name is not explicitly qualified. [Note: This covers calls to named functions (7.6.1.3 [expr.call]), operator overloading (Clause 12 [over]), user-defined conversions (11.4.8.3 [class.conv.fct]), allocation function for placement new (7.6.2.8 [expr.new]), as well as non-default initialization (9.5 [dcl.init]). A constructor selected to copy or move an object of class type is odr-used even if the call is actually elided by the implementation (11.4.5.3 [class.copy.ctor]). —end note] An allocation or deallocation function for a class is odr-used by a new expression appearing in a potentially-evaluated expression as specified in 7.6.2.8 [expr.new] and 11.4.11 [class.free]. A deallocation function for a class is odr-used by a delete expression appearing in a potentially-evaluated expression as specified in 7.6.2.9 [expr.delete] and 11.4.11 [class.free].

There are a couple of problems with this specification. First, contrary to the note, the names of overloaded operators, conversion functions, etc., do not appear in potentially-evaluated expressions, so the normative text does not make the note true. Also, the “as specified in” references do not cover odr-use explicitly, only the invocation of the functions.

One possible way of addressing these deficiencies would be a blanket rule like,

A function is odr-used if it is invoked by a potentially-evaluated expression.

(The existing wording about appearing in a potentially-evaluated expression would still be needed for non-call references.)