[libcxx-commits] [libcxx] [libcxx] Remove empty ~__no_destroy (PR #89882)

[A. Jiang via libcxx-commits]

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@@ -29,33 +29,25 @@ struct __uninitialized_tag {};
 // initialization using __emplace.
 template <class _Tp>
 struct __no_destroy {
-  _LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI explicit __no_destroy(__uninitialized_tag) : __dummy_() {
-    if (__libcpp_is_constant_evaluated()) {
-      __dummy_ = char();
-    }
-  }
-  _LIBCPP_HIDE_FROM_ABI ~__no_destroy() {
-    // nothing
-  }
+  _LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI explicit __no_destroy(__uninitialized_tag) {}
 
   template <class... _Args>
-  _LIBCPP_CONSTEXPR _LIBCPP_HIDE_FROM_ABI explicit __no_destroy(_Args&&... __args)
-      : __obj_(std::forward<_Args>(__args)...) {}
+  _LIBCPP_CONSTEXPR _LIBCPP_HIDE_FROM_ABI explicit __no_destroy(_Args&&... __args) {
+    ::new ((void*)__obj_) _Tp(std::forward<_Args>(__args)...);
+  }
 
   template <class... _Args>
   _LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI _Tp& __emplace(_Args&&... __args) {
-    new (&__obj_) _Tp(std::forward<_Args>(__args)...);
-    return __obj_;
+    return *(::new ((void*)__obj_) _Tp(std::forward<_Args>(__args)...));
   }
 
-  _LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI _Tp& __get() { return __obj_; }
-  _LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI _Tp const& __get() const { return __obj_; }
+  _LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI _Tp& __get() { return *reinterpret_cast<_Tp*>(__obj_); }
+  _LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI _Tp const& __get() const {
+    return *reinterpret_cast<const _Tp*>(__obj_);
+  }
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frederick-vs-ja wrote:

Likewise, `reinterpret_cast` makes the `constexpr` meaningless.

https://github.com/llvm/llvm-project/pull/89882