Use single-visitation in variant assignment and swap and relops.

Also use indices instead of types when checking whether
variants hold the same thing.
* include/std/variant (__do_visit): Add a template parameter
for index visitation, invoke with indices if index visitation
is used.
(__variant_idx_cookie): New.
(__visit_with_index): Likewise.
(_Copy_assign_base::operator=): Do single-visitation with
an index visitor.
(_Move_assign_base::operator=): Likewise.
(_Extra_visit_slot_needed): Adjust.
(__visit_invoke): Call with indices if it's an index visitor.
(relops): Do single-visitation with an index visitor.
(swap): Likewise.
(__visitor_result_type): New.

From-SVN: r270056

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 98c218b..0b3d0c2 100644 (file)
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,22 @@
+2019-04-01  Ville Voutilainen  <ville.voutilainen@gmail.com>
+
+       Use single-visitation in variant assignment and swap and relops.
+       Also use indices instead of types when checking whether
+       variants hold the same thing.
+       * include/std/variant (__do_visit): Add a template parameter
+       for index visitation, invoke with indices if index visitation
+       is used.
+       (__variant_idx_cookie): New.
+       (__visit_with_index): Likewise.
+       (_Copy_assign_base::operator=): Do single-visitation with
+       an index visitor.
+       (_Move_assign_base::operator=): Likewise.
+       (_Extra_visit_slot_needed): Adjust.
+       (__visit_invoke): Call with indices if it's an index visitor.
+       (relops): Do single-visitation with an index visitor.
+       (swap): Likewise.
+       (__visitor_result_type): New.
+
 2019-03-30  Eric Botcazou  <ebotcazou@adacore.com>
 
        * src/c++17/fs_ops.cc (fs::permissions): Use std::errc::not_supported.

diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant
index 7fd6947..a7cc206 100644 (file)
--- a/libstdc++-v3/include/std/variant
+++ b/libstdc++-v3/include/std/variant
@@ -138,7 +138,7 @@ namespace __variant
     constexpr variant_alternative_t<_Np, variant<_Types...>> const&&
     get(const variant<_Types...>&&);
 
-  template<typename _Visitor, typename... _Variants>
+  template<bool __use_index=false, typename _Visitor, typename... _Variants>
     constexpr decltype(auto)
     __do_visit(_Visitor&& __visitor, _Variants&&... __variants);
 
@@ -175,6 +175,10 @@ namespace __variant
 
   // used for raw visitation
   struct __variant_cookie {};
+  // used for raw visitation with indices passed in
+  struct __variant_idx_cookie {};
+  // a more explanatory name than 'true'
+  inline constexpr auto __visit_with_index = bool_constant<true>{};
 
   // _Uninitialized<T> is guaranteed to be a literal type, even if T is not.
   // We have to do this, because [basic.types]p10.5.3 (n4606) is not implemented
@@ -570,45 +574,44 @@ namespace __variant
       operator=(const _Copy_assign_base& __rhs)
          noexcept(_Traits<_Types...>::_S_nothrow_copy_assign)
       {
-       __do_visit([this, &__rhs](auto&& __this_mem, auto&& __rhs_mem) mutable
-                  -> __detail::__variant::__variant_cookie
+       __do_visit<__visit_with_index>([this](auto&& __rhs_mem,
+                                             auto __rhs_index) mutable
+           -> __detail::__variant::__variant_idx_cookie
          {
-           if constexpr (is_same_v<
-                           remove_reference_t<decltype(__this_mem)>,
-                           remove_reference_t<decltype(__rhs_mem)>>)
+           if constexpr (__rhs_index != variant_npos)
              {
-               if constexpr (!is_same_v<
-                               remove_reference_t<decltype(__rhs_mem)>,
-                               __variant_cookie>)
-                 __this_mem = __rhs_mem;
-             }
-           else
-             {
-               if constexpr (!is_same_v<
-                               remove_reference_t<decltype(__rhs_mem)>,
-                               __variant_cookie>)
+               if (this->_M_index == __rhs_index)
                  {
-                   using __rhs_type =
-                     remove_reference_t<decltype(__rhs_mem)>;
-                   if constexpr (is_nothrow_copy_constructible_v<__rhs_type>
-                     || !is_nothrow_move_constructible_v<__rhs_type>)
+                   if constexpr (__rhs_index != variant_npos)
                      {
-                       this->_M_destructive_copy(__rhs._M_index, __rhs_mem);
+                       auto& __this_mem =
+                         __variant::__get<__rhs_index>(*this);
+                       if constexpr (is_same_v<
+                                     remove_reference_t<decltype(__this_mem)>,
+                                     remove_reference_t<decltype(__rhs_mem)>>)
+                         __this_mem = __rhs_mem;
                      }
+                 }
+               else
+                 {
+                   using __rhs_type =
+                     remove_reference_t<decltype(__rhs_mem)>;
+                   if constexpr
+                     (is_nothrow_copy_constructible_v<__rhs_type>
+                      || !is_nothrow_move_constructible_v<__rhs_type>)
+                       this->_M_destructive_copy(__rhs_index, __rhs_mem);
                    else
                      {
                        auto __tmp(__rhs_mem);
-                       this->_M_destructive_move(__rhs._M_index,
+                       this->_M_destructive_move(__rhs_index,
                                                  std::move(__tmp));
                      }
                  }
-               else
-                 {
-                   this->_M_reset();
-                 }
              }
-         return {};
-       }, __variant_cast<_Types...>(*this), __variant_cast<_Types...>(__rhs));
+           else
+             this->_M_reset();
+           return {};
+         }, __variant_cast<_Types...>(__rhs));
        __glibcxx_assert(this->_M_index == __rhs._M_index);
        return *this;
       }
@@ -641,25 +644,32 @@ namespace __variant
       operator=(_Move_assign_base&& __rhs)
          noexcept(_Traits<_Types...>::_S_nothrow_move_assign)
       {
-       __do_visit([this, &__rhs](auto&& __this_mem, auto&& __rhs_mem) mutable
-                  -> __detail::__variant::__variant_cookie
+       __do_visit<__visit_with_index>([this](auto&& __rhs_mem,
+                                             auto __rhs_index) mutable
+           -> __detail::__variant::__variant_idx_cookie
          {
-           if constexpr (is_same_v<
-                           remove_reference_t<decltype(__this_mem)>,
-                           remove_reference_t<decltype(__rhs_mem)>>)
+           if constexpr (__rhs_index != variant_npos)
              {
-               if constexpr (!is_same_v<
-                               remove_reference_t<decltype(__rhs_mem)>,
-                               __variant_cookie>)
-                 __this_mem = std::move(__rhs_mem);
+               if (this->_M_index == __rhs_index)
+                 {
+                   if constexpr (__rhs_index != variant_npos)
+                     {
+                       auto& __this_mem =
+                         __variant::__get<__rhs_index>(*this);
+                       if constexpr (is_same_v<
+                                     remove_reference_t<decltype(__this_mem)>,
+                                     remove_reference_t<decltype(__rhs_mem)>>)
+                         __this_mem = std::move(__rhs_mem);
+                     }
+                 }
+               else
+                 this->_M_destructive_move(__rhs_index,
+                                           std::move(__rhs_mem));
              }
            else
-             {
-               auto __tmp(std::move(__rhs_mem));
-               this->_M_destructive_move(__rhs._M_index, std::move(__tmp));
-             }
-         return {};
-       }, __variant_cast<_Types...>(*this), __variant_cast<_Types...>(__rhs));
+             this->_M_reset();
+           return {};
+         }, __variant_cast<_Types...>(__rhs));
        __glibcxx_assert(this->_M_index == __rhs._M_index);
        return *this;
       }
@@ -777,7 +787,8 @@ namespace __variant
       : bool_constant<__never_valueless<_Types...>()> {};
 
     static constexpr bool value =
-      is_same_v<_Maybe_variant_cookie, __variant_cookie>
+      (is_same_v<_Maybe_variant_cookie, __variant_cookie>
+       || is_same_v<_Maybe_variant_cookie, __variant_idx_cookie>)
       && !_Variant_never_valueless<__remove_cvref_t<_Variant>>::value;
   };
 
@@ -925,7 +936,13 @@ namespace __variant
       static constexpr decltype(auto)
       __visit_invoke(_Visitor&& __visitor, _Variants... __vars)
       {
-       return std::__invoke(std::forward<_Visitor>(__visitor),
+       if constexpr (is_same_v<_Result_type, __variant_idx_cookie>)
+         return std::__invoke(std::forward<_Visitor>(__visitor),
+           __element_by_index_or_cookie<__indices>(
+             std::forward<_Variants>(__vars))...,
+             integral_constant<size_t, __indices>()...);
+       else
+         return std::__invoke(std::forward<_Visitor>(__visitor),
            __element_by_index_or_cookie<__indices>(
              std::forward<_Variants>(__vars))...);
       }
@@ -1082,25 +1099,25 @@ namespace __variant
                                 const variant<_Types...>& __rhs) \
     { \
       bool __ret = true; \
-      __do_visit([&__ret, &__lhs, __rhs] \
-                (auto&& __this_mem, auto&& __rhs_mem) mutable  \
-                  -> __detail::__variant::__variant_cookie \
+      __do_visit<__detail::__variant::__visit_with_index>( \
+        [&__ret, &__lhs, __rhs] \
+                (auto&& __rhs_mem, auto __rhs_index) mutable \
+                  -> __detail::__variant::__variant_idx_cookie \
         { \
-         if constexpr (!is_same_v< \
-                         remove_reference_t<decltype(__this_mem)>, \
-                         remove_reference_t<decltype(__rhs_mem)>> \
-                       || is_same_v<decltype(__this_mem), \
-                                    __detail::__variant::__variant_cookie>) \
-           __ret = (__lhs.index() + 1) __OP (__rhs.index() + 1); \
-         else if constexpr (is_same_v< \
-                              remove_reference_t<decltype(__this_mem)>, \
-                              remove_reference_t<decltype(__rhs_mem)>> \
-                             && !is_same_v< \
-                                 remove_reference_t<decltype(__this_mem)>, \
-                                 __detail::__variant::__variant_cookie>) \
-           __ret = __this_mem __OP __rhs_mem; \
+         if constexpr (__rhs_index != variant_npos) \
+           { \
+             if (__lhs.index() == __rhs_index) \
+               { \
+                 auto& __this_mem = std::get<__rhs_index>(__lhs);      \
+                  __ret = __this_mem __OP __rhs_mem; \
+                } \
+             else \
+               __ret = (__lhs.index() + 1) __OP (__rhs_index + 1); \
+            } \
+          else \
+            __ret = (__lhs.index() + 1) __OP (__rhs_index + 1); \
          return {}; \
-       }, __lhs, __rhs); \
+       }, __rhs); \
       return __ret; \
     } \
 \
@@ -1402,51 +1419,47 @@ namespace __variant
       noexcept((__is_nothrow_swappable<_Types>::value && ...)
               && is_nothrow_move_constructible_v<variant>)
       {
-       __do_visit([this, &__rhs](auto&& __this_mem, auto&& __rhs_mem) mutable
-                  -> __detail::__variant::__variant_cookie
+       __do_visit<__detail::__variant::__visit_with_index>(
+         [this, &__rhs](auto&& __rhs_mem,
+                        auto __rhs_index) mutable
+           -> __detail::__variant::__variant_idx_cookie
          {
-           if constexpr (is_same_v<
-                           remove_reference_t<decltype(__this_mem)>,
-                           remove_reference_t<decltype(__rhs_mem)>>)
+           if constexpr (__rhs_index != variant_npos)
              {
-               if constexpr (!is_same_v<
-                               remove_reference_t<decltype(__rhs_mem)>,
-                               __detail::__variant::__variant_cookie>)
+               if (this->index() == __rhs_index)
                  {
+                   auto& __this_mem =
+                     std::get<__rhs_index>(*this);
                    using std::swap;
                    swap(__this_mem, __rhs_mem);
                  }
+               else
+                 {
+                   if (this->index() != variant_npos)
+                     {
+                       auto __tmp(std::move(__rhs_mem));
+                       __rhs = std::move(*this);
+                       this->_M_destructive_move(__rhs_index,
+                                                 std::move(__tmp));
+                     }
+                   else
+                     {
+                       this->_M_destructive_move(__rhs_index,
+                                                 std::move(__rhs_mem));
+                       __rhs._M_reset();
+                     }
+                 }
              }
            else
              {
-               if constexpr (is_same_v<
-                               remove_reference_t<decltype(__this_mem)>,
-                               __detail::__variant::__variant_cookie>)
+               if (this->index() != variant_npos)
                  {
-                   this->_M_destructive_move(__rhs.index(),
-                                             std::move(__rhs_mem));
-                   __rhs._M_reset();
-                 }
-               else if constexpr (is_same_v<
-                                    remove_reference_t<decltype(__rhs_mem)>,
-                                    __detail::__variant::__variant_cookie>)
-                 {
-                   __rhs._M_destructive_move(this->index(),
-                                             std::move(__this_mem));
+                   __rhs = std::move(*this);
                    this->_M_reset();
                  }
-               else
-                 {
-                   auto __tmp(std::move(__rhs_mem));
-                   auto __idx = __rhs.index();
-                   __rhs._M_destructive_move(this->index(),
-                                             std::move(__this_mem));
-                   this->_M_destructive_move(__idx,
-                                             std::move(__tmp));
-                 }
              }
-         return {};
-       }, *this, __rhs);
+           return {};
+         }, __rhs);
       }
 
     private:
@@ -1523,13 +1536,25 @@ namespace __variant
       return __detail::__variant::__get<_Np>(std::move(__v));
     }
 
-  template<typename _Visitor, typename... _Variants>
+  template<bool __use_index, typename _Visitor, typename... _Variants>
+    decltype(auto)
+    __visitor_result_type(_Visitor&& __visitor, _Variants&&... __variants)
+    {
+      if constexpr(__use_index)
+        return __detail::__variant::__variant_idx_cookie{};
+      else
+       return std::forward<_Visitor>(__visitor)(
+         std::get<0>(std::forward<_Variants>(__variants))...);
+    }
+
+  template<bool __use_index, typename _Visitor, typename... _Variants>
     constexpr decltype(auto)
     __do_visit(_Visitor&& __visitor, _Variants&&... __variants)
     {
       using _Result_type =
-       decltype(std::forward<_Visitor>(__visitor)(
-           std::get<0>(std::forward<_Variants>(__variants))...));
+       decltype(__visitor_result_type<__use_index>(
+                  std::forward<_Visitor>(__visitor),
+                  std::forward<_Variants>(__variants)...));
 
       constexpr auto& __vtable = __detail::__variant::__gen_vtable<
        _Result_type, _Visitor&&, _Variants&&...>::_S_vtable;