[PATCH] D108122: FunctionAttrs: do not mark coroutines with odd return path `noreturn`

[Tim Northover via Phabricator via llvm-commits]

t.p.northover added a comment.

I've looked into this some more, and the return inserted by `@llvm.coro.end` is not necessarily representable in this function. If it's a `@llvm.coro.id.retcon.once` coroutine then the return is always a `ret void`, regardless of this function's prototype.

So, what if we require a `ret undef` instead as about the closest we can get? The real return (in the non-once case) is usually roughly `{i8* null, <lots of undef>}` and importantly doesn't contain any values from the function so we won't be lying about dataflow by using `undef`.

That's a doc change, a bunch of tests, and probably an autoupgrade (as well as Swift adoption). I'll tentatively get started.


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  https://reviews.llvm.org/D108122/new/

https://reviews.llvm.org/D108122