--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated4.C	Thu Feb 13 11:34:05 2020 +0900
@@ -0,0 +1,19 @@
+// P0595R2
+// { dg-do compile { target c++14 } }
+
+namespace std {
+  constexpr inline bool
+  is_constant_evaluated () noexcept
+  {
+    return __builtin_is_constant_evaluated ();
+  }
+}
+
+constexpr int
+foo () noexcept
+{
+  return std::is_constant_evaluated () ? 5 : 12;
+}
+
+static_assert (std::is_constant_evaluated (), "");
+static_assert (foo () == 5, "");