[clang] [llvm] [Clang] C++20 Coroutines: Introduce Frontend Attribute [[clang::coro_await_elidable]] (PR #99282)

[Yuxuan Chen via cfe-commits]

================
@@ -8119,6 +8119,35 @@ but do not pass them to the underlying coroutine or pass them by value.
 }];
 }
 
+def CoroAwaitElidableDoc : Documentation {
+  let Category = DocCatDecl;
+  let Content = [{
+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.
----------------
yuxuanchen1997 wrote:

> What I am concerning is, actually we don't care if it is prvalue or not at all.

I am actually using `isPRValue()` in Sema for this case. The right-hand side of `co_await` being a prvalue is a crucial requirement of this design. If the right-hand side is not a prvalue, we cannot do the elide safely. 



https://github.com/llvm/llvm-project/pull/99282