Merge 2025-06 LWG Motion 28

P3111R8 Atomic Reduction Operations

Author: tkoeppe

source/algorithms.tex

@@ -339,7 +339,8 @@
 A standard library function is \defn{vectorization-unsafe}
 if it is specified to synchronize with another function invocation, or
 another function invocation is specified to synchronize with it,
-and if it is not a memory allocation or deallocation function.
+and if it is not a memory allocation or deallocation function
+or lock-free atomic modify-write operation\iref{atomics.order}.
 \begin{note}
 Implementations must ensure that internal synchronization
 inside standard library functions does not prevent forward progress

source/basic.tex

@@ -6919,7 +6919,8 @@
 \item invoke the function \tcode{std::this_thread::yield}\iref{thread.thread.this},
 \item make a call to a library I/O function,
 \item perform an access through a volatile glvalue,
-\item perform a synchronization operation or an atomic operation, or
+\item perform an atomic or synchronization operation
+other than an atomic modify-write operation\iref{atomics.order}, or
 \item continue execution of a trivial infinite loop\iref{stmt.iter.general}.
 \end{itemize}
 \begin{note}
@@ -6976,9 +6977,10 @@
 an \defn{execution step}:
 \begin{itemize}
 \item termination of the thread of execution,
-\item performing an access through a volatile glvalue, or
-\item completion of a call to a library I/O function, a
-      synchronization operation, or an atomic operation.
+\item performing an access through a volatile glvalue,
+\item completion of a call to a library I/O function, or
+\item completion of an atomic or synchronization operation
+other than an atomic modify-write operation\iref{atomics.order}.
 \end{itemize}
 
 \pnum

source/support.tex

@@ -591,6 +591,7 @@
 #define @\defnlibxname{cpp_lib_atomic_is_always_lock_free}@        201603L // freestanding, also in \libheader{atomic}
 #define @\defnlibxname{cpp_lib_atomic_lock_free_type_aliases}@     201907L // also in \libheader{atomic}
 #define @\defnlibxname{cpp_lib_atomic_min_max}@                    202506L // freestanding, also in \libheader{atomic}
+#define @\defnlibxname{cpp_lib_atomic_reductions}@                 202506L // freestanding, also in \libheader{atomic}
 #define @\defnlibxname{cpp_lib_atomic_ref}@                        202411L // freestanding, also in \libheader{atomic}
 #define @\defnlibxname{cpp_lib_atomic_shared_ptr}@                 201711L // also in \libheader{memory}
 #define @\defnlibxname{cpp_lib_atomic_value_initialization}@       201911L // freestanding, also in \libheader{atomic}, \libheader{memory}