In both ScheduleDAGInstrs and MachineScheduler, we call `BufferSize = 0`
as _reserved_ and `BufferSize = 1` as _unbuffered_. This convention is
stem from the fact that we set `SUnit::hasReservedResource` to true when
any of the SUnit's consumed resources has BufferSize equal to zero; set
`SUnit::isUnbuffered` to true when any of its consumed resources has
BufferSize equal to one.
However, `SchedBoundary::isUnbufferedGroup` doesn't really follow this
convention: it returns true when the resource in question is a
`ProcResGroup` and its BufferSize equals to **zero** rather than one.
This could be really confusing for the reader. This patch renames this
function to `isReservedGroup` in aligned with the convention mentioned
above.
NFC.
6d4e75cc93