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Proposed resolution (January, 2019):

1. Change 6.3 [basic.def.odr] bullet 2.4 as follows:

An expression ispotentially evaluated unless itis an unevaluated operand (7.2 [expr.prop]) or asubexpression thereof. The set ofpotential resultsof an expressione is defined as follows:

• ...

• Ife is a pointer-to-member expression(7.6.4 [expr.mptr.oper])whose second operand is aconstant expression, the set contains the potential resultsof the object expression.

• ...

• Otherwise, the set is empty.

2. Change 6.3 [basic.def.odr] paragraph 4, converting therunning text into bullets, as follows:

A variablex whose name appears as apotentially-evaluated expressionex is odr-usedbyex unlessapplying the lvalue-to-rvalueconversion (7.3.2 [conv.lval]) tox yieldsa constant expression (7.7 [expr.const]) that doesnot invoke a function other than a trivial special memberfunction (11.4.4 [special]) and, ifx isan object,

• x is a reference that is usable inconstant expressions (7.7 [expr.const]), or

• x is a variable of non-reference typethat is usable in constant expressions and has no mutablesubobjects, andex is an elementof the set of potential results of anexpressione, where eitherofnon-volatile-qualified non-class type to which thelvalue-to-rvalue conversion (7.3.2 [conv.lval]) isappliedtoe, ore is

• x is a variable of non-reference type, ande is an element of the set of potential results ofa discarded-value expression (7.2 [expr.prop])to which the lvalue-to-rvalue conversion is notapplied.

This resolution also resolves issues2103and2170.

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

The resolution ofissue 1741 was notintended to cause odr-use to occur in cases where it did not do sopreviously. However, in an example like

  extern int globx;  int main() {    const int &x = globx;    struct A {     const int *foo() {       return &x;     }    } a;    return *a.foo();  }

x satisfies the requirements for appearing in aconstant expression, but applying the lvalue-to-rvalueconverstion tox does not yield a constant expression.Similarly,

  struct A {    int q;    constexpr A(int q) : q(q) { }    constexpr A(const A &a) : q(a.q * 2) { }  };  int main(void) {    constexpr A a(42);    constexpr int aq = a.q;    struct Q {     int foo() { return a.q; }    } q;    return q.foo();  }

a satisfies the requirements for appearing in a constantexpression, but applying the lvalue-to-rvalue conversion toainvokes a non-trivial function.