| Message ID | CAFk2RUa=c0srwncHEirj1CPAM0rSKgYLucjnDm21nqDh5Kc5Ng@mail.gmail.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v3] PR libstdc++/89825 | expand |
Slight tweak, the condition for _M_valid and _Extra_visit_slot_needed
is now in sync.
2019-03-26 Ville Voutilainen <ville.voutilainen@gmail.com>
PR libstdc++/89825
Fix based on a suggestion by Antony Polukhin.
* include/std/variant (__never_valueless): New.
(_M_valid): Use it.
(_Extra_visit_slot_needed): New.
(_Multi_array): Use it.
(_S_apply_all_alts): Likewise.
diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant
index 3631463..3932a8a 100644
--- a/libstdc++-v3/include/std/variant
+++ b/libstdc++-v3/include/std/variant
@@ -323,6 +323,12 @@ namespace __variant
_Variadic_union<_Rest...> _M_rest;
};
+ template <typename... _Types>
+ constexpr bool __never_valueless()
+ {
+ return (is_trivially_copyable_v<_Types> && ...);
+ }
+
// Defines index and the dtor, possibly trivial.
template<bool __trivially_destructible, typename... _Types>
struct _Variant_storage;
@@ -408,7 +414,7 @@ namespace __variant
constexpr bool
_M_valid() const noexcept
{
- if constexpr ((is_trivially_copyable_v<_Types> && ...))
+ if constexpr (__never_valueless<_Types...>())
return true;
return this->_M_index != __index_type(variant_npos);
}
@@ -747,6 +753,20 @@ namespace __variant
void* __get_storage(_Variant&& __v)
{ return __v._M_storage(); }
+ template <typename _Maybe_variant_cookie, typename _Variant>
+ struct _Extra_visit_slot_needed
+ {
+ template <typename> struct _Variant_never_valueless;
+
+ template <typename... _Types>
+ struct _Variant_never_valueless<variant<_Types...>>
+ : bool_constant<__never_valueless<_Types...>()> {};
+
+ static constexpr bool value =
+ is_same_v<_Maybe_variant_cookie, __variant_cookie>
+ && !_Variant_never_valueless<__remove_cvref_t<_Variant>>::value;
+ };
+
// Used for storing multi-dimensional vtable.
template<typename _Tp, size_t... _Dimensions>
struct _Multi_array
@@ -764,8 +784,11 @@ namespace __variant
size_t __first, size_t... __rest>
struct _Multi_array<_Ret(*)(_Visitor, _Variants...), __first, __rest...>
{
+ static constexpr size_t __index =
+ sizeof...(_Variants) - sizeof...(__rest) - 1;
+ using _Variant = typename _Nth_type<__index, _Variants...>::type;
static constexpr int __do_cookie =
- is_same_v<_Ret, __variant_cookie> ? 1 : 0;
+ _Extra_visit_slot_needed<_Ret, _Variant>::value ? 1 : 0;
using _Tp = _Ret(*)(_Visitor, _Variants...);
template<typename... _Args>
constexpr const _Tp&
@@ -832,7 +855,7 @@ namespace __variant
_S_apply_all_alts(_Array_type& __vtable,
std::index_sequence<__var_indices...>)
{
- if constexpr (is_same_v<_Result_type, __variant_cookie>)
+ if constexpr (_Extra_visit_slot_needed<_Result_type, _Next>::value)
(_S_apply_single_alt<true, __var_indices>(
__vtable._M_arr[__var_indices + 1],
&(__vtable._M_arr[0])), ...);
On 26/03/19 16:48 +0200, Ville Voutilainen wrote: >Slight tweak, the condition for _M_valid and _Extra_visit_slot_needed >is now in sync. > OK, thanks. > > PR libstdc++/89825 > Fix based on a suggestion by Antony Polukhin. > * include/std/variant (__never_valueless): New. > (_M_valid): Use it. > (_Extra_visit_slot_needed): New. > (_Multi_array): Use it. > (_S_apply_all_alts): Likewise.
diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant index 3631463..27ea516 100644 --- a/libstdc++-v3/include/std/variant +++ b/libstdc++-v3/include/std/variant @@ -747,6 +747,20 @@ namespace __variant void* __get_storage(_Variant&& __v) { return __v._M_storage(); } + template <typename _Maybe_variant_cookie, typename _Variant> + struct _Extra_visit_slot_needed + { + template <typename> struct _Variant_never_valueless; + + template <typename... _Types> + struct _Variant_never_valueless<variant<_Types...>> + : bool_constant<(is_trivially_copyable_v<_Types>&&...)> {}; + + static constexpr bool value = + is_same_v<_Maybe_variant_cookie, __variant_cookie> + && !_Variant_never_valueless<__remove_cvref_t<_Variant>>::value; + }; + // Used for storing multi-dimensional vtable. template<typename _Tp, size_t... _Dimensions> struct _Multi_array @@ -764,8 +778,11 @@ namespace __variant size_t __first, size_t... __rest> struct _Multi_array<_Ret(*)(_Visitor, _Variants...), __first, __rest...> { + static constexpr size_t __index = + sizeof...(_Variants) - sizeof...(__rest) - 1; + using _Variant = typename _Nth_type<__index, _Variants...>::type; static constexpr int __do_cookie = - is_same_v<_Ret, __variant_cookie> ? 1 : 0; + _Extra_visit_slot_needed<_Ret, _Variant>::value ? 1 : 0; using _Tp = _Ret(*)(_Visitor, _Variants...); template<typename... _Args> constexpr const _Tp& @@ -832,7 +849,7 @@ namespace __variant _S_apply_all_alts(_Array_type& __vtable, std::index_sequence<__var_indices...>) { - if constexpr (is_same_v<_Result_type, __variant_cookie>) + if constexpr (_Extra_visit_slot_needed<_Result_type, _Next>::value) (_S_apply_single_alt<true, __var_indices>( __vtable._M_arr[__var_indices + 1], &(__vtable._M_arr[0])), ...);
2019-03-26 Ville Voutilainen <ville.voutilainen@gmail.com> PR libstdc++/89825 Fix based on a suggestion by Antony Polukhin. * include/std/variant (_Extra_visit_slot_needed): New. (_Multi_array): Use it. (_S_apply_all_alts): Likewise.