ScheduleDAG: Cleanup dumping code; NFC

- Instead of having both `SUnit::dump(ScheduleDAG*)` and
  `ScheduleDAG::dumpNode(ScheduleDAG*)`, just keep the latter around.
- Add `ScheduleDAG::dump()` and avoid code duplication in several
  places. Implement it for different ScheduleDAG variants.
- Add `ScheduleDAG::dumpNodeName()` in favor of the `SUnit::print()`
  functions. They were only ever used for debug dumping and putting the
  function into ScheduleDAG is consistent with the `dumpNode()` change.

llvm-svn: 342520
diff --git a/llvm/lib/Target/AMDGPU/R600MachineScheduler.cpp b/llvm/lib/Target/AMDGPU/R600MachineScheduler.cpp
index a1429a2..478a473 100644
--- a/llvm/lib/Target/AMDGPU/R600MachineScheduler.cpp
+++ b/llvm/lib/Target/AMDGPU/R600MachineScheduler.cpp
@@ -127,13 +127,13 @@
 
   LLVM_DEBUG(if (SU) {
     dbgs() << " ** Pick node **\n";
-    SU->dump(DAG);
+    DAG->dumpNode(*SU);
   } else {
     dbgs() << "NO NODE \n";
     for (unsigned i = 0; i < DAG->SUnits.size(); i++) {
       const SUnit &S = DAG->SUnits[i];
       if (!S.isScheduled)
-        S.dump(DAG);
+        DAG->dumpNode(S);
     }
   });
 
@@ -188,11 +188,11 @@
 }
 
 void R600SchedStrategy::releaseTopNode(SUnit *SU) {
-  LLVM_DEBUG(dbgs() << "Top Releasing "; SU->dump(DAG););
+  LLVM_DEBUG(dbgs() << "Top Releasing "; DAG->dumpNode(*SU));
 }
 
 void R600SchedStrategy::releaseBottomNode(SUnit *SU) {
-  LLVM_DEBUG(dbgs() << "Bottom Releasing "; SU->dump(DAG););
+  LLVM_DEBUG(dbgs() << "Bottom Releasing "; DAG->dumpNode(*SU));
   if (isPhysicalRegCopy(SU->getInstr())) {
     PhysicalRegCopy.push_back(SU);
     return;