--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/g++.dg/cpp2a/constexpr-new6.C	Thu Feb 13 11:34:05 2020 +0900
@@ -0,0 +1,83 @@
+// P0784R7
+// { dg-do compile { target c++2a } }
+
+namespace std
+{
+  inline namespace _8 { }
+  namespace _8 {
+
+    typedef __SIZE_TYPE__ size_t;
+
+    template <typename T>
+    struct allocator
+    {
+      constexpr allocator () noexcept {}
+
+      constexpr T *allocate (size_t n)
+      { return static_cast<T *> (::operator new (n * sizeof(T))); }
+
+      constexpr void
+      deallocate (T *p, size_t n)
+      { ::operator delete (p); }
+    };
+
+    template <typename T, typename U = T &&>
+    U __declval (int);
+    template <typename T>
+    T __declval (long);
+    template <typename T>
+    auto declval () noexcept -> decltype (__declval<T> (0));
+
+    template <typename T>
+    struct remove_reference
+    { typedef T type; };
+    template <typename T>
+    struct remove_reference<T &>
+    { typedef T type; };
+    template <typename T>
+    struct remove_reference<T &&>
+    { typedef T type; };
+
+    template <typename T>
+    constexpr T &&
+    forward (typename std::remove_reference<T>::type &t) noexcept
+    { return static_cast<T&&> (t); }
+
+    template<typename T>
+    constexpr T &&
+    forward (typename std::remove_reference<T>::type &&t) noexcept
+    { return static_cast<T&&> (t); }
+
+    template <typename T, typename... A>
+    constexpr auto
+    construct_at (T *l, A &&... a)
+    noexcept (noexcept (::new ((void *) 0) T (std::declval<A> ()...)))
+    -> decltype (::new ((void *) 0) T (std::declval<A> ()...))
+    { return ::new ((void *) l) T (std::forward<A> (a)...); }
+
+    template <typename T>
+    constexpr inline void
+    destroy_at (T *l)
+    { l->~T (); }
+  }
+}
+
+inline void *operator new (std::size_t, void *p) noexcept
+{ return p; }
+
+constexpr bool
+foo ()
+{
+  std::allocator<int> a;
+  auto p = a.allocate (2);
+  std::construct_at (p, 1);
+  std::construct_at (p + 1, 2);
+  if (p[0] != 1 || p[1] != 2)
+    throw 1;
+  std::destroy_at (p);
+  std::destroy_at (p + 1);
+  a.deallocate (p, 2);
+  return true;
+}
+
+static_assert (foo ());