[llvm-dev] coro transformations insert unreachable in destroy fn?

[Andrew Kelley via llvm-dev]

Found the problem.

Instead of the Return block I needed to use the Suspend block, which has
the llvm.coro.end in it.

On Wed, Feb 28, 2018 at 5:34 PM, Andrew Kelley <superjoe30 at gmail.com> wrote:

> I have this input IR in the final cleanup block of my coroutine:
>
> // call the free function
>   call fastcc void %22(%Allocator* %20, %"[]u8"* byval %4), !dbg !244
>
> // based on whether this is an early return or a normal return, we want to
> // either return to the caller, or resume the handle of the awaiter
>   br i1 %19, label %Resume, label %Return, !dbg !244
>
> Resume:                                           ; preds = %CheckFree
>   %31 = load i8*, i8** %14, align 8, !dbg !244
>   call void @llvm.coro.resume(i8* %31), !dbg !244
>
> // after resuming the awaiter, we return to the caller
>   br label %Return, !dbg !244
>
> Return:                                           ; preds = %Resume,
> %CheckFree
>   ret i8* undef, !dbg !244
>
>
> When CoroSplit creates the destroy function for this coroutine, it
> generates this:
>
>   call fastcc void %2(%Allocator* %0, %"[]u8"* byval %.reload.addr4), !dbg
> !296
>   unreachable
>
>
> How did that unreachable get there? What happened to my code above to
> resume or return to the caller?
>
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