[RuntimeAsync] Live ref-like temps are seen crossing awaits in Debug/minopts codegen for IL that does not have that.

[VSadov]

Observed while enabling rt async in Libraires partition - #119432

This triggers asserts like assert(!layout->HasGCByRef()); in AsyncTransformation::LayOutContinuation

Also see discussion in: #119432 (comment)

The actual reason is not completely known and the assert may be seen when compiling methods like:

        public static Task WhenAll(params ReadOnlySpan<Task> tasks)
        {
            switch (tasks.Length)
            {
                case 0:
                    return CompletedTask;

                case 1:
                    Task t = tasks[0];
                    if (t is null)
                    {
                        ThrowHelper.ThrowArgumentException(ExceptionResource.Task_MultiTaskContinuation_NullTask, ExceptionArgument.tasks);
                    }
                    return t;

                default:
                    return new WhenAllPromise(tasks);
            }
        }

The method itself is not async, but we generate an async thunk for it, which has the same ref-like parameter.
The thunk is simply passes the parameter to the wrapped call and does not use the parameter after the call (that is true for all parameters) and therefore nothing ref-like, or perhaps nothing at all, should need capturing into a closure.

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[jakobbotsch]

Do you have a link to the failure for this?

[VSadov]

Do you have a link to the failure for this?

I saw it in a local run. There was more than one failure. I think it requires running with -rc Checked -lc Debug.

If we run such configuration in default CI, there should be failures due to this.

I'll try to search for some failures for this in earlier iterations of this PR.