https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113031
--- Comment #2 from Nathaniel Shead <nathanieloshead at gmail dot com> ---
Reduced to:
template <typename> class variant;
template <typename _Types, typename _Tp>
auto __variant_cast(_Tp __rhs) { return static_cast<variant<_Types>&&>(__rhs);
}
template <typename _Types>
struct _Move_assign_base : _Types {
void operator=(_Move_assign_base __rhs) { __variant_cast<_Types>(__rhs); }
};
template <typename _Types>
struct variant : _Move_assign_base<_Types> {
void emplace() {
variant __tmp;
*this = __tmp;
}
};
struct _Undefined_class {
struct _Nocopy_types {
void (_Undefined_class::*_M_member_pointer)();
};
struct function : _Nocopy_types {
struct optional {
void test03() {
variant<function> v;
v.emplace();
}
};
};
};
The following patch seems to fix the immediate problem (but not yet fully
regtested):
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index e1b2d27fc36..051f73fb73f 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -5709,7 +5709,8 @@ cxx_fold_indirect_ref_1 (const constexpr_ctx *ctx,
location_t loc, tree type,
}
/* Handle conversion to "as base" type. */
- if (CLASSTYPE_AS_BASE (optype) == type)
+ if (CLASS_TYPE_P (optype)
+ && CLASSTYPE_AS_BASE (optype) == type)
return op;
/* Handle conversion to an empty base class, which is represented with a
