https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101828
Bug ID: 101828 Summary: The invocation of a virtual function for an object that is not usable in constant expression is accepeted by GCC Product: gcc Version: 12.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: xmh970252187 at gmail dot com Target Milestone: --- struct A{ constexpr int virtual fun() const{ return 0; } }; A obj; constexpr A const& rf = obj; constexpr int v = rf.fun(); According to [expr.const#5.5] > An expression E is a core constant expression unless the evaluation of E, > following the rules of the abstract machine ([intro.execution]), would > evaluate one of the following: >> an invocation of a virtual function for an object unless >>> the object is usable in constant expressions or >>> its lifetime began within the evaluation of E; Since `obj` is not an object that is usable in constant expression as per [expr.const#4] and its lifetime has begun before the declaration of `v`, hence its full-expression of the initialization cannot be a constant expression. It should be ill-formed. https://godbolt.org/z/8hKWs3WEf