Example conversion for optional, using [[trivially_relocatable(bool)]].

Quuxplusone · Quuxplusone · commit 293784a734a6 · 2019-01-18T13:23:24.000-05:00
diff --git a/include/__config b/include/__config
@@ -1281,6 +1281,14 @@ _LIBCPP_FUNC_VIS extern "C" void __sanitizer_annotate_contiguous_container(
 #define _LIBCPP_HAS_NO_IS_AGGREGATE
 #endif
 
+#ifndef _LIBCPP_TRIVIALLY_RELOCATABLE
+#if __has_extension(trivially_relocatable)
+#define _LIBCPP_TRIVIALLY_RELOCATABLE(x) [[clang::trivially_relocatable(x)]]
+#else
+#define _LIBCPP_TRIVIALLY_RELOCATABLE(x)
+#endif
+#endif
+
 #if !defined(__cpp_coroutines) || __cpp_coroutines < 201703L
 #define _LIBCPP_HAS_NO_COROUTINES
 #endif
diff --git a/include/optional b/include/optional
@@ -581,7 +581,7 @@ using __optional_sfinae_assign_base_t = __sfinae_assign_base<
 >;
 
 template <class _Tp>
-class optional
+class _LIBCPP_TRIVIALLY_RELOCATABLE(is_trivially_relocatable<_Tp>::value) optional
     : private __optional_move_assign_base<_Tp>
     , private __optional_sfinae_ctor_base_t<_Tp>
     , private __optional_sfinae_assign_base_t<_Tp>
