[libcxx-commits] [clang] [libcxx] Elide suspension points via [[clang::coro_await_suspend_destroy]] (PR #152623)

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snarkmaster wrote:

Thanks for the initial review! I'm glad you like the idea. I'll finish polishing the e2e test, and address your inline comments 1-by-1 above.

> split out libcxx change

Okay, I'll do that for the next update, no problem.

> ... can cover https://github.com/llvm/llvm-project/issues/148380, right? 

For the trivial example of `void await_suspend(auto handle) { handle.destroy(); }`, yes, the user could use the new attribute.

But, I think it's possible to have coros that **conditionally** destroy the passed-in handle. So, if the user had something more complicated (e.g. coro that returns a handle, that also destroys the current coro), then my thing wouldn't help.

> Could you have a test for this?

My current IR test verifies that there's no heap alloc across a few examples. Were you thinking of a different kind of test? Can you be very specific since I'm totally new to LLVM?

> if you want, may be you can implement similar attributes to not invoke AwaitSuspend intrinsic in different conditions.

I don't know when I'll next be able to make time to work on this, but if I do, my next target would be `std::suspend_never`. I hope this one could be done without an attribute, though.  Do you have other use-cases in mind?


https://github.com/llvm/llvm-project/pull/152623