Between discussion at #1137 and a few rounds of revision at #1159 we
arrived at an optimisation where tasks that are both heavily hit and
very likely to return in a completed state are checked for a status of
either RanToCompletion, Canceled or Faulted and a path is taken where
no await is needed for any of those.
The Canceled and Faulted tasks are returned immediately, allowing that
state to be passed to the caller.
However, these are exceptional cases, and if we just continued the
subsequent await would raise the appropriate exception. Checking for
all three cases instead of just RanToCompletion is optimising for those
execptional conditions at cost (in the form of a larger comparison
segment of code) to the more common cases of the task either being
completed or still running.
Simplify this back to a check just for RanToCompletion.
Jon Hanna
0ef9ec292b