Make ~mutex and ~condition_variable trivial on Windows.

The implementations of __libcpp_mutex_destroy and __libcpp_condvar_destroy
are already NOPs, so this optimization is safe to perform.

See r365273 and PR27658 for more information.

llvm-svn: 365281

3 files changed, 48 insertions, 4 deletions

diff --git a/libcxx/src/CMakeLists.txt b/libcxx/src/CMakeLists.txt
index 56d7b9888e3..c13f8901581 100644
--- a/libcxx/src/CMakeLists.txt
+++ b/libcxx/src/CMakeLists.txt
@@ -8,6 +8,7 @@ set(LIBCXX_SOURCES
   charconv.cpp
   chrono.cpp
   condition_variable.cpp
+  condition_variable_destructor.cpp
   debug.cpp
   exception.cpp
   functional.cpp
diff --git a/libcxx/src/condition_variable.cpp b/libcxx/src/condition_variable.cpp
index e9b373965e1..b8426c66fde 100644
--- a/libcxx/src/condition_variable.cpp
+++ b/libcxx/src/condition_variable.cpp
@@ -21,10 +21,7 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-condition_variable::~condition_variable()
-{
-    __libcpp_condvar_destroy(&__cv_);
-}
+// ~condition_variable is defined elsewhere.
 
 void
 condition_variable::notify_one() _NOEXCEPT
diff --git a/libcxx/src/condition_variable_destructor.cpp b/libcxx/src/condition_variable_destructor.cpp
new file mode 100644
index 00000000000..44fa240ba78
--- /dev/null
+++ b/libcxx/src/condition_variable_destructor.cpp
@@ -0,0 +1,46 @@
+//===---------------- condition_variable_destructor.cpp ------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// Define ~condition_variable.
+//
+// On some platforms ~condition_variable has been made trivial and the
+// definition is only provided for ABI compatibility.
+
+#include "__config"
+#include "__threading_support"
+
+#if !defined(_LIBCPP_HAS_NO_THREADS)
+# if _LIBCPP_ABI_VERSION == 1 || !defined(_LIBCPP_HAS_TRIVIAL_CONDVAR_DESTRUCTION)
+#   define NEEDS_CONDVAR_DESTRUCTOR
+# endif
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#ifdef NEEDS_CONDVAR_DESTRUCTOR
+
+class _LIBCPP_TYPE_VIS condition_variable
+{
+    __libcpp_condvar_t __cv_ = _LIBCPP_CONDVAR_INITIALIZER;
+public:
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr condition_variable() noexcept = default;
+
+    ~condition_variable();
+
+    condition_variable(const condition_variable&) = delete;
+    condition_variable& operator=(const condition_variable&)  = delete;
+};
+
+condition_variable::~condition_variable()
+{
+    __libcpp_condvar_destroy(&__cv_);
+}
+#endif
+
+_LIBCPP_END_NAMESPACE_STD