Mirror changes from dotnet/coreclr

[dotnet-bot]

This PR contains mirrored changes from dotnet/coreclr

Please REBASE this PR when merging

[stephentoub]

@jkotas, I just noticed that corert's AsyncTaskMethodBuilder<TResult>.Create is different from coreclr's. The one in coreclr just returns default(AsyncTaskMethodBuilder<TResult>), but the one in corert does additional work if the debugger is attached:

corert/src/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncMethodBuilder.cs

Lines 423 to 433 in ede07f2

	public static AsyncTaskMethodBuilder<TResult> Create()
	{
	AsyncTaskMethodBuilder<TResult> atmb = new AsyncTaskMethodBuilder<TResult>();
	// On ProjectN we will eagerly initalize the task and it's Id if the debugger is attached
	atmb.m_task = (Task<TResult>)atmb.GetTaskIfDebuggingEnabled();
	if (atmb.m_task != null)
	{
	int i = atmb.m_task.Id;
	}
	return atmb;
	}

Do you know why?

[jkotas]

Good catch. I guess that it is because of the ProjectN debugger is different today and it needs this to work. We should make the change in the shared file under #if CORECLR ifdef.

cc @dotnet/dotnet-diag

[stephentoub]

We should make the change in the shared file under #if CORECLR ifdef.

Ok, I'll submit another coreclr PR to do that.