================
@@ -8261,12 +8261,19 @@ def CoroAwaitElidableDoc : Documentation {
The ``[[clang::coro_await_elidable]]`` is a class attribute which can be
applied
to a coroutine return type.
-When a coroutine function that returns such a type calls another coroutine
function,
-the compiler performs heap allocation elision when the call to the coroutine
function
-is immediately co_awaited as a prvalue. In this case, the coroutine frame for
the
-callee will be a local variable within the enclosing braces in the caller's
stack
-frame. And the local variable, like other variables in coroutines, may be
collected
-into the coroutine frame, which may be allocated on the heap.
+When a coroutine function returns such a type, a direct call expression therein
+that returns a prvalue of a type attributed ``[[clang::coro_await_elidable]]``
+is said to be under a safe elide context if one of the following is true:
----------------
vogelsgesang wrote:
> When a coroutine function returns such a type, a direct call expression
> therein that returns a prvalue of a type attributed
> ``[[clang::coro_await_elidable]]`` [...]
If I am reading the code correctly, it is not actually a requirement that the
containing / callee coroutine itself is also annotated as
`coro_await_elidable`. Only the called coroutine needs to be annotated as
`coro_await_elidable`.
I.e., we would also apply HALO for something like
```
class [[clang::coro_await_elidable]] ElidableTask { ... };
class NonElidableTask { ... };
ElidableTask foo();
NonElidableTask bar() {
co_await foo(); // foo()'s coroutine frame on this line is elidable
}
```
Or did I misread the code?
Assuming I understood code correctly, I would propose something like
```
A call to a coroutine function returning such a type is said to be safe-to-elide
if one of the following is true:
- it is the immediate right-hand side operand to a co_await expression.
- it is an argument to a [[clang::coro_must_await]] parameter or parameter pack
of another safe-to-elide function call.
Do note that the safe-to-elide context applies only to the call expression
itself,
and the context does not transitively include any of its subexpressions unless
``[[clang::coro_must_await]]`` is used to opt-in to transivitely applying
safe-to-elide.
The compiler performs heap allocation elision on call expressions on
safe-to-elide
calls, if the callee is a coroutine.
```
https://github.com/llvm/llvm-project/pull/108474
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