--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated6.C	Thu Feb 13 11:34:05 2020 +0900
@@ -0,0 +1,29 @@
+// P0595R2
+// { dg-do compile { target c++14 } }
+
+namespace std {
+  constexpr inline bool
+  is_constant_evaluated () noexcept
+  {
+    return __builtin_is_constant_evaluated ();
+  }
+}
+
+int a;
+
+constexpr bool
+foo (int x)
+{
+  return __builtin_constant_p (x);
+}
+
+constexpr bool
+bar (int x)
+{
+  return __builtin_constant_p (x + a);
+}
+
+static_assert (__builtin_constant_p (0) + 2 * std::is_constant_evaluated () == 3, "");
+static_assert (__builtin_constant_p (a) + 2 * std::is_constant_evaluated () == 2, "");
+static_assert (foo (0) + 2 * std::is_constant_evaluated () == 3, "");
+static_assert (bar (0) + 2 * std::is_constant_evaluated () == 2, "");