[CodeGen][MachineScheduler][NFC]Update some comments of scheduler (#74705)

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

Author: shining1984

llvm/include/llvm/CodeGen/SchedulerRegistry.h

@@ -63,7 +63,7 @@ class RegisterScheduler
 ScheduleDAGSDNodes *createBURRListDAGScheduler(SelectionDAGISel *IS,
                                                CodeGenOptLevel OptLevel);
 
-/// createBURRListDAGScheduler - This creates a bottom up list scheduler that
+/// createSourceListDAGScheduler - This creates a bottom up list scheduler that
 /// schedules nodes in source code order when possible.
 ScheduleDAGSDNodes *createSourceListDAGScheduler(SelectionDAGISel *IS,
                                                  CodeGenOptLevel OptLevel);

llvm/lib/CodeGen/MachineScheduler.cpp

@@ -747,9 +747,9 @@ void ScheduleDAGMI::finishBlock() {
   ScheduleDAGInstrs::finishBlock();
 }
 
-/// enterRegion - Called back from MachineScheduler::runOnMachineFunction after
-/// crossing a scheduling boundary. [begin, end) includes all instructions in
-/// the region, including the boundary itself and single-instruction regions
+/// enterRegion - Called back from PostMachineScheduler::runOnMachineFunction
+/// after crossing a scheduling boundary. [begin, end) includes all instructions
+/// in the region, including the boundary itself and single-instruction regions
 /// that don't get scheduled.
 void ScheduleDAGMI::enterRegion(MachineBasicBlock *bb,
                                      MachineBasicBlock::iterator begin,
@@ -793,9 +793,9 @@ bool ScheduleDAGMI::checkSchedLimit() {
 }
 
 /// Per-region scheduling driver, called back from
-/// MachineScheduler::runOnMachineFunction. This is a simplified driver that
-/// does not consider liveness or register pressure. It is useful for PostRA
-/// scheduling and potentially other custom schedulers.
+/// PostMachineScheduler::runOnMachineFunction. This is a simplified driver
+/// that does not consider liveness or register pressure. It is useful for
+/// PostRA scheduling and potentially other custom schedulers.
 void ScheduleDAGMI::schedule() {
   LLVM_DEBUG(dbgs() << "ScheduleDAGMI::schedule starting\n");
   LLVM_DEBUG(SchedImpl->dumpPolicy());