[CodeGen][MachineScheduler][NFC]Update some comments of scheduler

[shining1984]

The member functions of ScheduleDAGMI are called back from PostMachineScheduler::runOnMachineFunction, instead of MachineScheduler::runOnMachineFunction.

[wangpc-pp]

Is this true? I think both PostMachineScheduler and MachineScheduler call this.
Should it be MachineSchedulerBase::scheduleRegions?

[shining1984]

1. MachineScheduler::runOnMachineFunction and PostMachineScheduler::runOnMachineFunction all call the MachineSchedulerBase::scheduleRegions.
2. Then MachineSchedulerBase::scheduleRegions call the Scheduler.enterRegion and Scheduler.schedule.
3. The Scheduler in MachineSchedulerBase::scheduleRegions is from MachineScheduler::runOnMachineFunction or PostMachineScheduler::runOnMachineFunction.
4. When Scheduler is from the MachineScheduler::runOnMachineFunction, it is return from the MachineScheduler::createMachineScheduler(), which get a new ScheduleDAGMILive pointer from the PassConfig->createMachineScheduler(this) or createGenericSchedLive. Then the Scheduler is ScheduleDAGMILive , the Scheduler.enterRegion is ScheduleDAGMILive.enterRegion. So, we can say the ScheduleDAGMILive::enterRegion is called back from MachineScheduler::runOnMachineFunction. The ScheduleDAGMILive::schedule is same as the ScheduleDAGMILive::enterRegion.
5. When Scheduler is from the PostMachineScheduler::runOnMachineFunction, it is return from the PostMachineScheduler::createPostMachineScheduler(), which get a new ScheduleDAGMI pointer from the PassConfig->createPostMachineScheduler(this) or createGenericSchedPostRA. Then the Scheduler is ScheduleDAGMI , the Scheduler.enterRegion is ScheduleDAGMI.enterRegion. So, we can say the ScheduleDAGMI::enterRegion is called back from PostMachineScheduler::runOnMachineFunction.The ScheduleDAGMI::schedule is same as the ScheduleDAGMI::enterRegion.
6. I changed the two comments from MachineScheduler::runOnMachineFunction to PostMachineScheduler::runOnMachineFunction is according the "5".

[MaskRay]

The convention for new code is "Don’t duplicate function or class name at the beginning of the comment." https://llvm.org/docs/CodingStandards.html#commenting

[wangpc-pp]

The convention for new code is "Don’t duplicate function or class name at the beginning of the comment." https://llvm.org/docs/CodingStandards.html#commenting

I think this is a fix for existed comments. :-)

[shining1984]

The convention for new code is "Don’t duplicate function or class name at the beginning of the comment." https://llvm.org/docs/CodingStandards.html#commenting

This pr just fixs three existed comments.
There are many comments in the two files need to update, if follow the "Don’t duplicate function or class name at the beginning of the comment." Maybe need a new pr to update them.

[wangpc-pp]

LGTM! Thanks for the detailed explanation!