Merge 2024-06 CWG Motion 3

P2747R2 constexpr placement new

Author: tkoeppe

source/basic.tex

@@ -3437,13 +3437,15 @@
 \end{example}
 
 \pnum
-An operation that begins the lifetime of
+Except during constant evaluation,
+an operation that begins the lifetime of
 an array of \tcode{unsigned char} or \tcode{std::byte}
 implicitly creates objects within the region of storage occupied by the array.
 \begin{note}
 The array object provides storage for these objects.
 \end{note}
-Any implicit or explicit invocation of a function
+Except during constant evaluation,
+any implicit or explicit invocation of a function
 named \tcode{\keyword{operator} \keyword{new}} or \tcode{\keyword{operator} \keyword{new}[]}
 implicitly creates objects in the returned region of storage and
 returns a pointer to a suitable created object.

source/expressions.tex

@@ -5471,12 +5471,7 @@
 
 \pnum
 During an evaluation of a constant expression,
-a call to an allocation function is always omitted.
-\begin{note}
-Only \grammarterm{new-expression}{s} that would otherwise result in
-a call to a replaceable global allocation function
-can be evaluated in constant expressions\iref{expr.const}.
-\end{note}
+a call to a replaceable allocation function is always omitted\iref{expr.const}.
 
 \pnum
 The implementation may
@@ -7645,9 +7640,27 @@
 
 \item
 a \grammarterm{new-expression}\iref{expr.new},
-unless the selected allocation function is
+unless either
+\begin{itemize}
+\item
+the selected allocation function is
 a replaceable global allocation function\iref{new.delete.single,new.delete.array} and
-the allocated storage is deallocated within the evaluation of $E$;
+the allocated storage is deallocated within the evaluation of $E$, or
+\item
+the selected allocation function is
+a non-allocating form\iref{new.delete.placement}
+with an allocated type \tcode{T}, where
+\begin{itemize}
+\item
+the placement argument to the \grammarterm{new-expression} points to
+an object that is pointer-interconvertible with an object of type \tcode{T} or,
+if T is an array type,
+with the first element of an object of type \tcode{T}, and
+\item
+the placement argument points to storage
+whose duration began within the evaluation of $E$;
+\end{itemize}
+\end{itemize}
 
 \item
 a \grammarterm{delete-expression}\iref{expr.delete},
@@ -7780,14 +7793,6 @@
 the evaluation of the body of a member function of \tcode{std::allocator<T>}
 as defined in \ref{allocator.members}, where \tcode{T} is a literal type,
 is ignored.
-Similarly, the evaluation of the body of
-\tcode{std::construct_at} or
-\tcode{std::ranges::construct_at}
-is considered to include only
-the initialization of the \tcode{T} object
-if the first argument (of type \tcode{T*}) points
-to storage allocated with \tcode{std::allocator<T>} or
-to an object whose lifetime began within the evaluation of $E$.
 
 \pnum
 For the purposes of determining whether $E$ is a core constant expression,

source/preprocessor.tex

@@ -1848,7 +1848,7 @@
 \defnxname{cpp_char8_t}                           & \tcode{202207L} \\ \rowsep
 \defnxname{cpp_concepts}                          & \tcode{202002L} \\ \rowsep
 \defnxname{cpp_conditional_explicit}              & \tcode{201806L} \\ \rowsep
-\defnxname{cpp_constexpr}                         & \tcode{202306L} \\ \rowsep
+\defnxname{cpp_constexpr}                         & \tcode{202406L} \\ \rowsep
 \defnxname{cpp_constexpr_dynamic_alloc}           & \tcode{201907L} \\ \rowsep
 \defnxname{cpp_constexpr_in_decltype}             & \tcode{201711L} \\ \rowsep
 \defnxname{cpp_consteval}                         & \tcode{202211L} \\ \rowsep

source/support.tex

@@ -610,6 +610,7 @@
 #define @\defnlibxname{cpp_lib_constexpr_functional}@              201907L // freestanding, also in \libheader{functional}
 #define @\defnlibxname{cpp_lib_constexpr_iterator}@                201811L // freestanding, also in \libheader{iterator}
 #define @\defnlibxname{cpp_lib_constexpr_memory}@                  202202L // freestanding, also in \libheader{memory}
+#define @\defnlibxname{cpp_lib_constexpr_new}@                     202406L // freestanding, also in \libheader{new}
 #define @\defnlibxname{cpp_lib_constexpr_numeric}@                 201911L // also in \libheader{numeric}
 #define @\defnlibxname{cpp_lib_constexpr_string}@                  201907L // also in \libheader{string}
 #define @\defnlibxname{cpp_lib_constexpr_string_view}@             201811L // also in \libheader{string_view}
@@ -2302,8 +2303,8 @@
 void operator delete[](void* ptr, const std::nothrow_t&) noexcept;
 void operator delete[](void* ptr, std::align_val_t alignment, const std::nothrow_t&) noexcept;
 
-[[nodiscard]] void* operator new  (std::size_t size, void* ptr) noexcept;
-[[nodiscard]] void* operator new[](std::size_t size, void* ptr) noexcept;
+[[nodiscard]] constexpr void* operator new  (std::size_t size, void* ptr) noexcept;
+[[nodiscard]] constexpr void* operator new[](std::size_t size, void* ptr) noexcept;
 void operator delete  (void* ptr, void*) noexcept;
 void operator delete[](void* ptr, void*) noexcept;
 \end{codeblock}
@@ -2836,7 +2837,7 @@
 
 \indexlibrarymember{new}{operator}%
 \begin{itemdecl}
-[[nodiscard]] void* operator new(std::size_t size, void* ptr) noexcept;
+[[nodiscard]] constexpr void* operator new(std::size_t size, void* ptr) noexcept;
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -2861,7 +2862,7 @@
 
 \indexlibrarymember{new}{operator}%
 \begin{itemdecl}
-[[nodiscard]] void* operator new[](std::size_t size, void* ptr) noexcept;
+[[nodiscard]] constexpr void* operator new[](std::size_t size, void* ptr) noexcept;
 \end{itemdecl}
 
 \begin{itemdescr}