Fix PR24114 - std::atomic for non-Clang is not a literal type

Add _LIBCPP_CONSTEXPR to the implementation of __gcc_atomic_t.


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@242172 91177308-0d34-0410-b5e6-96231b3b80d8

include/atomic

@@ -554,7 +554,8 @@ namespace __gcc_atomic {
 template <typename _Tp>
 struct __gcc_atomic_t {
   __gcc_atomic_t() _NOEXCEPT {}
-  explicit __gcc_atomic_t(_Tp value) _NOEXCEPT : __a_value(value) {}
+  _LIBCPP_CONSTEXPR explicit __gcc_atomic_t(_Tp value) _NOEXCEPT
+    : __a_value(value) {}
   _Tp __a_value;
 };
 #define _Atomic(x) __gcc_atomic::__gcc_atomic_t<x>

test/std/atomics/atomics.types.operations/atomics.types.operations.req/ctor.pass.cpp

@@ -0,0 +1,56 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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: libcpp-has-no-threads
+// UNSUPPORTED: c++98, c++03
+
+// <atomic>
+
+// constexpr atomic<T>::atomic(T value)
+
+#include <atomic>
+#include <type_traits>
+#include <cassert>
+
+struct UserType {
+    int i;
+
+    UserType() noexcept {}
+    constexpr explicit UserType(int d) noexcept : i(d) {}
+
+    friend bool operator==(const UserType& x, const UserType& y) {
+        return x.i == y.i;
+    }
+};
+
+template <class Tp>
+void test() {
+    typedef std::atomic<Tp> Atomic;
+    static_assert(std::is_literal_type<Atomic>::value, "");
+    constexpr Tp t(42);
+    {
+        constexpr Atomic a(t);
+        assert(a == t);
+    }
+    {
+        constexpr Atomic a{t};
+        assert(a == t);
+    }
+    {
+        constexpr Atomic a = ATOMIC_VAR_INIT(t);
+        assert(a == t);
+    }
+}
+
+
+int main()
+{
+    test<int>();
+    test<UserType>();
+}