launder pointers:

close #1570

`std::launder` must be used whenever placement-new of an unknown type
is performed and the result of the placement-new expression is discarded.

Signed-off-by: Damian Jarek <damian.jarek93@gmail.com>

CHANGELOG.md

@@ -2,6 +2,7 @@ Version 251:
 
 * Clean up CI scripts
 * detect_ssl uses bool
+* launder pointers
 
 --------------------------------------------------------------------------------
 

include/boost/beast/core/detail/type_traits.hpp

@@ -124,6 +124,18 @@ struct is_contiguous_container<T, E, void_t<
     >::type>>: std::true_type
 {};
 
+template <class T, class U>
+T launder_cast(U* u)
+{
+#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606
+    return std::launder(reinterpret_cast<T>(u));
+#elif defined(BOOST_GCC) && BOOST_GCC_VERSION > 80000
+    return __builtin_launder(reinterpret_cast<T>(u));
+#else
+    return reinterpret_cast<T>(u);
+#endif
+}
+
 } // detail
 } // beast
 } // boost

include/boost/beast/core/detail/variant.hpp

@@ -45,7 +45,7 @@ class variant
         {
             using T =
                 mp11::mp_at_c<variant, I::value - 1>;
-            reinterpret_cast<T&>(self.buf_).~T();
+            detail::launder_cast<T*>(&self.buf_)->~T();
         }
     };
 
@@ -64,7 +64,7 @@ class variant
             using T =
                 mp11::mp_at_c<variant, I::value - 1>;
             ::new(&self.buf_) T(
-                reinterpret_cast<T const&>(other.buf_));
+                *detail::launder_cast<T const*>(&other.buf_));
             self.i_ = I::value;
         }
     };
@@ -83,9 +83,9 @@ class variant
         {
             using T =
                 mp11::mp_at_c<variant, I::value - 1>;
-            ::new(&self.buf_) T(
+            ::new(&self.buf_) T(std::move(
-                reinterpret_cast<T&&>(other.buf_));
+                *detail::launder_cast<T*>(&other.buf_)));
-            reinterpret_cast<T&>(other.buf_).~T();
+            detail::launder_cast<T*>(&other.buf_)->~T();
             self.i_ = I::value;
         }
     };
@@ -106,8 +106,8 @@ class variant
             using T =
                 mp11::mp_at_c<variant, I::value - 1>;
             return
-                reinterpret_cast<T const&>(self.buf_) ==
+                *detail::launder_cast<T const*>(&self.buf_) ==
-                reinterpret_cast<T const&>(other.buf_);
+                *detail::launder_cast<T const*>(&other.buf_);
         }
     };
 
@@ -208,7 +208,7 @@ public:
     get()
     {
         BOOST_ASSERT(i_ == I);
-        return *reinterpret_cast<
+        return *detail::launder_cast<
             mp11::mp_at_c<variant, I - 1>*>(&buf_);
     }
 
@@ -217,7 +217,7 @@ public:
     get() const
     {
         BOOST_ASSERT(i_ == I);
-        return *reinterpret_cast<
+        return *detail::launder_cast<
             mp11::mp_at_c<variant, I - 1> const*>(&buf_);
     }
 

include/boost/beast/websocket/detail/decorator.hpp

@@ -213,7 +213,7 @@ struct decorator::vtable_impl<F, true>
     void
     move(storage& dst, storage& src) noexcept
     {
-        auto& f = *reinterpret_cast<F*>(&src.buf_);
+        auto& f = *beast::detail::launder_cast<F*>(&src.buf_);
         ::new (&dst.buf_) F(std::move(f));
     }
 
@@ -221,7 +221,7 @@ struct decorator::vtable_impl<F, true>
     void
     destroy(storage& dst) noexcept
     {
-        reinterpret_cast<F*>(&dst.buf_)->~F();
+        beast::detail::launder_cast<F*>(&dst.buf_)->~F();
     }
 
     static
@@ -229,7 +229,7 @@ struct decorator::vtable_impl<F, true>
     invoke_req(storage& dst, request_type& req)
     {
         maybe_invoke<F, request_type>{}(
-            *reinterpret_cast<F*>(&dst.buf_), req);
+            *beast::detail::launder_cast<F*>(&dst.buf_), req);
     }
 
     static
@@ -237,7 +237,7 @@ struct decorator::vtable_impl<F, true>
     invoke_res(storage& dst, response_type& res)
     {
         maybe_invoke<F, response_type>{}(
-            *reinterpret_cast<F*>(&dst.buf_), res);
+            *beast::detail::launder_cast<F*>(&dst.buf_), res);
     }
 
     static