Stephan Tolksdorf: fixes the issue in the <atomic> header and adds corresponding tests. I've used macros to fall back to a user-provided default constructor if _LIBCPP_HAS_NO_DEFAULTED_FUNCTIONS (though I suspect that there won't be many users defining that macro).

The tests use placement new to check that atomic values get properly zero-initialized. I had to modify the atomic_is_lock_free test, because default initialization of an object of const type 'const A' (aka 'const atomic<int>') requires a user-provided default constructor.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@180945 91177308-0d34-0410-b5e6-96231b3b80d8

test/atomics/atomics.flag/default.pass.cpp

@@ -14,9 +14,18 @@
 // atomic_flag() = default;
 
 #include <atomic>
+#include <new>
 #include <cassert>
 
 int main()
 {
     std::atomic_flag f;
+
+    {
+        typedef std::atomic_flag A;
+        _ALIGNAS_TYPE(A) char storage[sizeof(A)] = {1};
+        A& zero = *new (storage) A();
+        assert(!zero.test_and_set());
+        zero.~A();
+    }
 }

test/atomics/atomics.types.generic/address.pass.cpp

@@ -66,6 +66,7 @@
 // };
 
 #include <atomic>
+#include <new>
 #include <type_traits>
 #include <cassert>
 
@@ -112,6 +113,13 @@ do_test()
     assert(obj == T(5*sizeof(X)));
     assert((obj -= std::ptrdiff_t(3)) == T(2*sizeof(X)));
     assert(obj == T(2*sizeof(X)));
+
+    {
+        _ALIGNAS_TYPE(A) char storage[sizeof(A)] = {23};
+        A& zero = *new (storage) A();    
+        assert(zero == 0);
+        zero.~A();
+    }
 }
 
 template <class A, class T>

test/atomics/atomics.types.generic/bool.pass.cpp

@@ -50,6 +50,7 @@
 // typedef atomic<bool> atomic_bool;
 
 #include <atomic>
+#include <new>
 #include <cassert>
 
 int main()
@@ -219,4 +220,11 @@ int main()
         assert((obj = true) == true);
         assert(obj == true);
     }
+    {
+        typedef std::atomic<bool> A;
+        _ALIGNAS_TYPE(A) char storage[sizeof(A)] = {1};
+        A& zero = *new (storage) A();    
+        assert(zero == false);
+        zero.~A();
+    }
 }

test/atomics/atomics.types.generic/integral.pass.cpp

@@ -85,6 +85,7 @@
 // };
 
 #include <atomic>
+#include <new>
 #include <cassert>
 
 template <class A, class T>
@@ -143,6 +144,13 @@ do_test()
     assert(obj == T(7));
     assert((obj ^= T(0xF)) == T(8));
     assert(obj == T(8));
+
+    {
+        _ALIGNAS_TYPE(A) char storage[sizeof(A)] = {23};
+        A& zero = *new (storage) A();    
+        assert(zero == 0);
+        zero.~A();
+    }
 }
 
 template <class A, class T>

test/atomics/atomics.types.operations/atomics.types.operations.req/atomic_is_lock_free.pass.cpp

@@ -24,10 +24,10 @@ void
 test()
 {
     typedef std::atomic<T> A;
-    const A ct;
-    bool b1 = std::atomic_is_lock_free(&ct);
-    const volatile A cvt;
-    bool b2 = std::atomic_is_lock_free(&cvt);
+    A t;
+    bool b1 = std::atomic_is_lock_free(static_cast<const A*>(&t));
+    volatile A vt;
+    bool b2 = std::atomic_is_lock_free(static_cast<const volatile A*>(&vt));
 }
 
 struct A