Make std::addressof constexpr in C++17 (Clang only).

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@263688 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/utilities/memory/specialized.algorithms/specialized.addressof/constexpr_addressof.pass.cpp

@@ -0,0 +1,42 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+// XFAIL: gcc
+
+// <memory>
+
+// template <ObjectType T> constexpr T* addressof(T& r);
+
+#include <memory>
+#include <cassert>
+
+struct Pointer {
+  constexpr Pointer(void* v) : value(v) {}
+  void* value;
+};
+
+struct A
+{
+    constexpr A() : n(42) {}
+    void operator&() const { }
+    int n;
+};
+
+constexpr int i = 0;
+constexpr double d = 0.0;
+constexpr A a{};
+
+int main()
+{
+    static_assert(std::addressof(i) == &i, "");
+    static_assert(std::addressof(d) == &d, "");
+    constexpr const A* ap = std::addressof(a);
+    static_assert(&ap->n == &a.n, "");
+}