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

2 files changed, 18 insertions, 15 deletions

diff --git a/libcxx/include/__config b/libcxx/include/__config
index 1ed51699932..1ecced9f479 100644
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -1098,13 +1098,22 @@ _LIBCPP_FUNC_VIS extern "C" void __sanitizer_annotate_contiguous_container(
 #endif
 
 // The Apple, glibc, and Bionic implementation of pthreads implements
-// pthread_mutex_destroy as nop for regular mutexes.
+// pthread_mutex_destroy as nop for regular mutexes. Additionally, Win32
+// mutexes have no destroy mechanism.
 // TODO(EricWF): Enable this optimization on Apple and Bionic platforms after
 // speaking to their respective stakeholders.
-#if defined(_LIBCPP_HAS_THREAD_API_PTHREAD) && defined(__GLIBC__)
+#if (defined(_LIBCPP_HAS_THREAD_API_PTHREAD) && defined(__GLIBC__)) \
+  || defined(_LIBCPP_HAS_THREAD_API_WIN32)
 # define _LIBCPP_HAS_TRIVIAL_MUTEX_DESTRUCTION
 #endif
 
+// Destroying a condvar is a nop on Windows.
+// TODO(EricWF): This is potentially true for some pthread implementations
+// as well.
+#if defined(_LIBCPP_HAS_THREAD_API_WIN32)
+# define _LIBCPP_HAS_TRIVIAL_CONDVAR_DESTRUCTION
+#endif
+
 // Systems that use capability-based security (FreeBSD with Capsicum,
 // Nuxi CloudABI) may only provide local filesystem access (using *at()).
 // Functions like open(), rename(), unlink() and stat() should not be
diff --git a/libcxx/include/__mutex_base b/libcxx/include/__mutex_base
index 61abae979ac..f828beaf780 100644
--- a/libcxx/include/__mutex_base
+++ b/libcxx/include/__mutex_base
@@ -282,26 +282,20 @@ _LIBCPP_DECLARE_STRONG_ENUM_EPILOG(cv_status)
 
 class _LIBCPP_TYPE_VIS condition_variable
 {
-#ifndef _LIBCPP_CXX03_LANG
     __libcpp_condvar_t __cv_ = _LIBCPP_CONDVAR_INITIALIZER;
-#else
-    __libcpp_condvar_t __cv_;
-#endif
-
 public:
     _LIBCPP_INLINE_VISIBILITY
-#ifndef _LIBCPP_CXX03_LANG
-    constexpr condition_variable() _NOEXCEPT = default;
+    _LIBCPP_CONSTEXPR condition_variable() _NOEXCEPT = default;
+
+#ifdef _LIBCPP_HAS_TRIVIAL_CONDVAR_DESTRUCTION
+    ~condition_variable() = default;
 #else
-    condition_variable() _NOEXCEPT {__cv_ = (__libcpp_condvar_t)_LIBCPP_CONDVAR_INITIALIZER;}
-#endif
     ~condition_variable();
+#endif
 
-private:
-    condition_variable(const condition_variable&); // = delete;
-    condition_variable& operator=(const condition_variable&); // = delete;
+    condition_variable(const condition_variable&) = delete;
+    condition_variable& operator=(const condition_variable&) = delete;
 
-public:
     void notify_one() _NOEXCEPT;
     void notify_all() _NOEXCEPT;