trippels@gcc2-power8 test % cat type_traits.ii
namespace std {
template <typename> struct __success_type;
template <typename> void declval();
template <typename> class decay {
public:
  typedef int type;
};
template <typename...> struct common_type;
struct A {
  template <typename, typename _Up>
  static __success_type<typename decay<decltype(declval<_Up>)>::type> _S_test;
};
template <typename _Tp, typename _Up> struct __common_type_impl : A {
  typedef decltype(_S_test<_Tp, _Up>) type;
};
template <typename _Tp, typename _Up>
struct common_type<_Tp, _Up> : __common_type_impl<_Tp, _Up> {};
}
template <typename> struct B { struct _; };
template <typename T> typename B<T>::_ type;
template <template <typename...> class> struct C;
template <template <typename...> class f> C<f> metafunction;
template <typename T> struct B<T>::_ {};
namespace detail {
template <typename> struct _decltype;
}
template <template <typename...> class F> struct C {
  template <typename... T>
  auto operator()(T...)
      -> decltype(type<typename F<detail::_decltype<T>...>::type>);
};
auto common_type = metafunction<std::common_type>(0, 0);


trippels@gcc2-power8 test % c++ -c type_traits.ii
type_traits.ii: In instantiation of ‘decltype (type<typename F<detail::_decltype<T>...>::type>) C< <template-parameter-1-1> >::operator()(T ...) [with T = {int, int}; F = std::common_type; decltype (type<typename F<detail::_decltype<T>...>::type>) = B<std::__success_type<int> >::_; typename F<detail::_decltype<T>...>::type = std::__success_type<int>]’:

type_traits.ii:29:8: internal compiler error: tree check: expected identifier_node, have template_decl in write_unqualified_id, at cp/mangle.c:1218
   auto operator()(T...)
        ^
0x10d2be23 tree_check_failed(tree_node const*, char const*, int, char const*, ...)
        ../../gcc/gcc/tree.c:9499
0x103d188f tree_check
        ../../gcc/gcc/tree.h:2858
0x103d188f write_unqualified_id
        ../../gcc/gcc/cp/mangle.c:1218
0x103cb5ab write_expression
        ../../gcc/gcc/cp/mangle.c:2828
0x103cf47f write_type
        ../../gcc/gcc/cp/mangle.c:2129
0x103d1ec7 write_bare_function_type
        ../../gcc/gcc/cp/mangle.c:2527
0x103d4a67 mangle_decl_string
        ../../gcc/gcc/cp/mangle.c:3498
0x103d4c7f get_mangled_id
        ../../gcc/gcc/cp/mangle.c:3520
0x103d504f mangle_decl(tree_node*)
        ../../gcc/gcc/cp/mangle.c:3587
0x10d2d30f decl_assembler_name(tree_node*)
        ../../gcc/gcc/tree.c:658
0x1056c583 symbol_table::insert_to_assembler_name_hash(symtab_node*, bool)
        ../../gcc/gcc/symtab.c:157
0x1056d86f symbol_table::symtab_initialize_asm_name_hash()
        ../../gcc/gcc/symtab.c:249
0x1058a3ff analyze_functions
        ../../gcc/gcc/cgraphunit.c:1175
0x1058b267 symbol_table::finalize_compilation_unit()
        ../../gcc/gcc/cgraphunit.c:2477
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