Currently, the SLP schedule has two containers of `ScheduleData`:
`ExtraScheduleDataMap` and `ScheduleDataMap`. However, the
`ScheduleData` in `ExtraScheduleDataMap` is only used to indicate
whether the instruction is processed or not and does not participate in
the schedule, which is useless. `ScheduleDataMap` is sufficient for this
purpose. The `OpValue` member is used only in `ExtraScheduleDataMap`,
which is also useless.
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