private APCMap <int> GetStackDepthMap(Subroutine subroutine)
{
APCMap <int> result;
var key = new TypedKey("stackDepthKey");
if (!subroutine.TryGetValue(key, out result))
{
result = ComputeStackDepthMap(subroutine);
subroutine.Add(key, result);
}
return(result);
}