@@ -91,6 +91,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
_GLIBCXX20_CONSTEXPR
inline _Tp
exchange(_Tp& __obj, _Up&& __new_val)
+ noexcept(__and_<is_nothrow_move_constructible<_Tp>,
+ is_nothrow_assignable<_Tp&, _Up>>::value)
{ return std::__exchange(__obj, std::forward<_Up>(__new_val)); }
#if __cplusplus >= 201703L
new file mode 100644
@@ -0,0 +1,39 @@
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <utility>
+
+// This is a GCC extension. std::exchange is not required to be noexcept.
+
+static_assert( noexcept( std::exchange(std::declval<int&>(), 1) ) );
+
+struct X
+{
+ X(const X&);
+ X(X&&) noexcept;
+ X& operator=(const X&);
+ X& operator=(X&&) noexcept;
+ X& operator=(int);
+};
+
+extern X x, x2;
+static_assert( noexcept( std::exchange(x, std::move(x2)) ) );
+static_assert( ! noexcept( std::exchange(x, 1) ) );
+
+struct Y
+{
+ Y(Y&&) noexcept;
+ Y& operator=(Y&&);
+};
+
+extern Y y, y2;
+static_assert( ! noexcept( std::exchange(y, std::move(y2)) ) );
+
+struct Z
+{
+ Z(Z&&)noexcept;
+ Z& operator=(Z&&) ;
+};
+
+extern Z z, z2;
+static_assert( ! noexcept( std::exchange(z, std::move(z2)) ) );