1 files changed, 46 insertions, 0 deletions
diff --git a/clang/test/SemaCXX/constant-expression-cxx1y.cpp b/clang/test/SemaCXX/constant-expression-cxx1y.cpp
index 07ef7974d11..fe69d105023 100644
--- a/clang/test/SemaCXX/constant-expression-cxx1y.cpp
+++ b/clang/test/SemaCXX/constant-expression-cxx1y.cpp
@@ -1159,3 +1159,49 @@ enum InEnum2 : int {
 enum class InEnum3 {
   THREE = indirect_builtin_constant_p("abc")
 };
+
+// [class.ctor]p4:
+//   A constructor can be invoked for a const, volatile or const volatile
+//   object. const and volatile semantics are not applied on an object under
+//   construction. They come into effect when the constructor for the most
+//   derived object ends.
+namespace ObjectsUnderConstruction {
+  struct A {
+    int n;
+    constexpr A() : n(1) { n = 2; }
+  };
+  struct B {
+    const A a;
+    constexpr B(bool mutate) {
+      if (mutate)
+        const_cast<A &>(a).n = 3; // expected-note {{modification of object of const-qualified type 'const int'}}
+    }
+  };
+  constexpr B b(false);
+  static_assert(b.a.n == 2, "");
+  constexpr B bad(true); // expected-error {{must be initialized by a constant expression}} expected-note {{in call to 'B(true)'}}
+
+  struct C {
+    int n;
+    constexpr C() : n(1) { n = 2; }
+  };
+  constexpr int f(bool get) {
+    volatile C c; // expected-note {{here}}
+    return get ? const_cast<int&>(c.n) : 0; // expected-note {{read of volatile object 'c'}}
+  }
+  static_assert(f(false) == 0, ""); // ok, can modify volatile c.n during c's initialization: it's not volatile then
+  static_assert(f(true) == 2, ""); // expected-error {{constant}} expected-note {{in call}}
+
+  struct Aggregate {
+    int x = 0;
+    int y = ++x;
+  };
+  constexpr Aggregate aggr1;
+  static_assert(aggr1.x == 1 && aggr1.y == 1, "");
+  // FIXME: This is not specified by the standard, but sanity requires it.
+  constexpr Aggregate aggr2 = {};
+  static_assert(aggr2.x == 1 && aggr2.y == 1, "");
+
+  // The lifetime of 'n' begins at the initialization, not before.
+  constexpr int n = ++const_cast<int&>(n); // expected-error {{constant expression}} expected-note {{modification}}
+}