CWG2466 co_await should be a single evaluation

Author: jensmaurer

source/basic.tex

@@ -5674,24 +5674,26 @@
 \end{example}
 
 \pnum
-When calling a function (whether or not the function is inline), every
-\indextext{value computation}%
-value computation and
-\indextext{side effects}%
-side effect associated with any argument
-expression, or with the postfix expression designating the called
-function, is sequenced before execution of every expression or statement
+When invoking a function (whether or not the function is inline),
+every argument expression and
+the postfix expression designating the called function
+are sequenced before every expression or statement
 in the body of the called function.
-For each function invocation \placeholder{F},
-for every evaluation \placeholder{A} that occurs within \placeholder{F} and
-every evaluation \placeholder{B} that does not occur within \placeholder{F} but
-is evaluated on the same thread and as part of the same signal handler (if any),
-either \placeholder{A} is sequenced before \placeholder{B} or
-\placeholder{B} is sequenced before \placeholder{A}.
+For each function invocation or
+evaluation of an \grammarterm{await-expression} \placeholder{F},
+each evaluation that does not occur within \placeholder{F} but
+is evaluated on the same thread and as part of the same signal handler (if any)
+is either sequenced before all evaluations that occur within \placeholder{F}
+or sequenced after all evaluations that occur within \placeholder{F};
 \begin{footnote}
 In other words,
 function executions do not interleave with each other.
 \end{footnote}
+if \placeholder{F} invokes or resumes a coroutine\iref{expr.await},
+only evaluations
+subsequent to the previous suspension (if any) and
+prior to the next suspension (if any)
+are considered to occur within \placeholder{F}.
 \begin{note}
 If \placeholder{A} and \placeholder{B} would not otherwise be sequenced then they are
 indeterminately sequenced.

source/expressions.tex

@@ -4609,6 +4609,10 @@
 the \placeholder{await-resume} expression is evaluated, and
 its result is the result of the \grammarterm{await-expression}.
 \end{itemize}
+\begin{note}
+With respect to sequencing,
+an \grammarterm{await-expression} is indivisible\iref{intro.execution}.
+\end{note}
 
 \pnum
 \begin{example}