[clang] [llvm] [Clang][Coroutines] Improve CoroElide with [[clang::coro_structured_concurrency]] attribute for C++ (PR #94693)

[Chuanqi Xu via cfe-commits]

ChuanqiXu9 wrote:

> Thanks for the feedback. This patch is the first iteration to model this idea as quickly as I can. In general, I agree with your comments.
> 
> > * I feel the name containing `concurrency` is not proper
> 
> The name is bikesheddable as always. I was also thinking around the line of `[[clang::coro_inplace_awaitable_task]]`.
> 
> > * Every time we add or change IR related to coroutines, we need to update https://llvm.org/docs/Coroutines.html. So that we can understand the semantics of the proposed `llvm.coro.safe.elide` much easier.
> 
> Will do once we agree on a design.

It would be helpful for reviewers to understand the design ahead of time. For example, I can't be sure I understand your design 100% right now.

https://github.com/llvm/llvm-project/pull/94693