Avoid redundant runtime checks in std::visit

Calling std::get will check some static assertions and also do a runtime
check for a valid index before calling __detail::__variant::__get. The
std::visit function already handles the case where any variant has an
invalid index, so __get can be used directly in __visit_invoke.

	* include/std/variant (__gen_vtable_impl::__visit_invoke): Call __get
	directly instead of get, as caller ensures correct index is used.
	(holds_alternative, get, get_if): Remove redundant inline specifiers.
	(_VARIANT_RELATION_FUNCTION_TEMPLATE): Likewise.

From-SVN: r264786

libstdc++-v3/ChangeLog

+2018-10-02  Jonathan Wakely  <jwakely@redhat.com>
+
+	* include/std/variant (__gen_vtable_impl::__visit_invoke): Call __get
+	directly instead of get, as caller ensures correct index is used.
+	(holds_alternative, get, get_if): Remove redundant inline specifiers.
+	(_VARIANT_RELATION_FUNCTION_TEMPLATE): Likewise.
+
 2018-10-02  Joseph Myers  <joseph@codesourcery.com>
 
 	* testsuite/lib/libstdc++.exp (libstdc++_init): Use

libstdc++-v3/include/std/variant

@@ -811,9 +811,8 @@ namespace __variant
 	{
 	  using _Alternative = variant_alternative_t<__index, _Next>;
 	  __element = __gen_vtable_impl<
-	    remove_reference_t<
-	      decltype(__element)>, tuple<_Variants...>,
-	      std::index_sequence<__indices..., __index>>::_S_apply();
+	    remove_reference_t<decltype(__element)>, tuple<_Variants...>,
+	    std::index_sequence<__indices..., __index>>::_S_apply();
 	}
     };
 
@@ -826,11 +825,11 @@ namespace __variant
       using _Array_type =
 	  _Multi_array<_Result_type (*)(_Visitor&&, _Variants...)>;
 
-      decltype(auto)
-      static constexpr __visit_invoke(_Visitor&& __visitor, _Variants... __vars)
+      static constexpr decltype(auto)
+      __visit_invoke(_Visitor&& __visitor, _Variants... __vars)
       {
 	return std::__invoke(std::forward<_Visitor>(__visitor),
-	    std::get<__indices>(std::forward<_Variants>(__vars))...);
+	    __variant::__get<__indices>(std::forward<_Variants>(__vars))...);
       }
 
       static constexpr auto
@@ -871,8 +870,8 @@ namespace __variant
 } // namespace __detail
 
   template<typename _Tp, typename... _Types>
-    inline constexpr bool holds_alternative(const variant<_Types...>& __v)
-    noexcept
+    constexpr bool
+    holds_alternative(const variant<_Types...>& __v) noexcept
     {
       static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
 		    "T should occur for exactly once in alternatives");
@@ -880,7 +879,7 @@ namespace __variant
     }
 
   template<typename _Tp, typename... _Types>
-    constexpr inline _Tp& get(variant<_Types...>& __v)
+    constexpr _Tp& get(variant<_Types...>& __v)
     {
       static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
 		    "T should occur for exactly once in alternatives");
@@ -889,7 +888,7 @@ namespace __variant
     }
 
   template<typename _Tp, typename... _Types>
-    constexpr inline _Tp&& get(variant<_Types...>&& __v)
+    constexpr _Tp&& get(variant<_Types...>&& __v)
     {
       static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
 		    "T should occur for exactly once in alternatives");
@@ -899,7 +898,7 @@ namespace __variant
     }
 
   template<typename _Tp, typename... _Types>
-    constexpr inline const _Tp& get(const variant<_Types...>& __v)
+    constexpr const _Tp& get(const variant<_Types...>& __v)
     {
       static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
 		    "T should occur for exactly once in alternatives");
@@ -908,7 +907,7 @@ namespace __variant
     }
 
   template<typename _Tp, typename... _Types>
-    constexpr inline const _Tp&& get(const variant<_Types...>&& __v)
+    constexpr const _Tp&& get(const variant<_Types...>&& __v)
     {
       static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
 		    "T should occur for exactly once in alternatives");
@@ -918,8 +917,7 @@ namespace __variant
     }
 
   template<size_t _Np, typename... _Types>
-    constexpr inline
-    add_pointer_t<variant_alternative_t<_Np, variant<_Types...>>>
+    constexpr add_pointer_t<variant_alternative_t<_Np, variant<_Types...>>>
     get_if(variant<_Types...>* __ptr) noexcept
     {
       using _Alternative_type = variant_alternative_t<_Np, variant<_Types...>>;
@@ -932,7 +930,7 @@ namespace __variant
     }
 
   template<size_t _Np, typename... _Types>
-    constexpr inline
+    constexpr
     add_pointer_t<const variant_alternative_t<_Np, variant<_Types...>>>
     get_if(const variant<_Types...>* __ptr) noexcept
     {
@@ -946,7 +944,7 @@ namespace __variant
     }
 
   template<typename _Tp, typename... _Types>
-    constexpr inline add_pointer_t<_Tp>
+    constexpr add_pointer_t<_Tp>
     get_if(variant<_Types...>* __ptr) noexcept
     {
       static_assert(__detail::__variant::__exactly_once<_Tp, _Types...>,
@@ -957,7 +955,7 @@ namespace __variant
     }
 
   template<typename _Tp, typename... _Types>
-    constexpr inline add_pointer_t<const _Tp>
+    constexpr add_pointer_t<const _Tp>
     get_if(const variant<_Types...>* __ptr)
     noexcept
     {
@@ -1277,7 +1275,7 @@ namespace __variant
 	  { &__detail::__variant::__erased_##__NAME< \
 		const variant&, __indices>... }; \
       template<size_t... __indices> \
-	constexpr inline bool \
+	constexpr bool \
 	_M_##__NAME(const variant& __rhs, \
 		    std::index_sequence<__indices...>) const \
 	{ \