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

[Vitaly Buka via libcxx-commits]

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

>From 65b62ad4ac4e9df6df84774532f898d0a4c078fc Mon Sep 17 00:00:00 2001
From: Vitaly Buka <vitalybuka at google.com>
Date: Wed, 24 Apr 2024 00:03:23 -0700
Subject: [PATCH 1/3] =?UTF-8?q?[=F0=9D=98=80=F0=9D=97=BD=F0=9D=97=BF]=20in?=
 =?UTF-8?q?itial=20version?=
MIME-Version: 1.0
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Created using spr 1.3.4
---
 libcxx/include/__utility/no_destroy.h | 28 ++++++++++-----------------
 1 file changed, 10 insertions(+), 18 deletions(-)

diff --git a/libcxx/include/__utility/no_destroy.h b/libcxx/include/__utility/no_destroy.h
index f9c1eb7bed4569..833e16116c42d7 100644
--- a/libcxx/include/__utility/no_destroy.h
+++ b/libcxx/include/__utility/no_destroy.h
@@ -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 (&__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 (&__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_);
+  }
 
 private:
-  union {
-    _Tp __obj_;
-    char __dummy_; // so we can initialize a member even with __uninitialized_tag for constexpr-friendliness
-  };
+  alignas(_Tp) unsigned char __obj_[sizeof(_Tp)] = {};
 };
 
 _LIBCPP_END_NAMESPACE_STD

>From 22acc7f96a1990dea096f16447641077e447994b Mon Sep 17 00:00:00 2001
From: Vitaly Buka <vitalybuka at google.com>
Date: Wed, 24 Apr 2024 00:15:55 -0700
Subject: [PATCH 2/3] fix 99

Created using spr 1.3.4
---
 libcxx/include/__utility/no_destroy.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libcxx/include/__utility/no_destroy.h b/libcxx/include/__utility/no_destroy.h
index 833e16116c42d7..1413256a07b11a 100644
--- a/libcxx/include/__utility/no_destroy.h
+++ b/libcxx/include/__utility/no_destroy.h
@@ -47,7 +47,7 @@ struct __no_destroy {
   }
 
 private:
-  alignas(_Tp) unsigned char __obj_[sizeof(_Tp)] = {};
+  _ALIGNAS_TYPE(_Tp) unsigned char __obj_[sizeof(_Tp)] = {};
 };
 
 _LIBCPP_END_NAMESPACE_STD

>From 06b50eeaba5c9396b06087298b517d35c6026827 Mon Sep 17 00:00:00 2001
From: Vitaly Buka <vitalybuka at google.com>
Date: Wed, 24 Apr 2024 00:29:31 -0700
Subject: [PATCH 3/3] cast to void*

Created using spr 1.3.4
---
 libcxx/include/__utility/no_destroy.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libcxx/include/__utility/no_destroy.h b/libcxx/include/__utility/no_destroy.h
index 1413256a07b11a..9234ad8813db95 100644
--- a/libcxx/include/__utility/no_destroy.h
+++ b/libcxx/include/__utility/no_destroy.h
@@ -33,12 +33,12 @@ struct __no_destroy {
 
   template <class... _Args>
   _LIBCPP_CONSTEXPR _LIBCPP_HIDE_FROM_ABI explicit __no_destroy(_Args&&... __args) {
-    new (&__obj_) _Tp(std::forward<_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) {
-    return *(new (&__obj_) _Tp(std::forward<_Args>(__args)...));
+    return *(::new ((void*)__obj_) _Tp(std::forward<_Args>(__args)...));
   }
 
   _LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI _Tp& __get() { return *reinterpret_cast<_Tp*>(__obj_); }