[AMDGPU] SIMachineScheduler: Add support for several MachineScheduler features

[jsilvanus]

Summary

The SI machine scheduler inherits from ScheduleDAGMI.
This patch adds support for a few features that are implemented
in ScheduleDAGMI (or its base classes) that were missing so far
because their support is implemented in overridden functions.

• Support cl::opt -view-misched-dags This option allows to open a graphical window of the scheduling DAG.

• Support cl::opt -misched-print-dags This option allows to print the scheduling DAG in text form.

• After constructing the scheduling DAG, call postprocessDAG() to apply any registered DAG mutations. Note that currently there are no mutations defined in AMDGPUTargetMachine.cpp in case SIScheduler is used. Still add this to avoid surprises in the future in case mutations are added.

Change-Id: Ie109f046b7691bdc7935da83f8767d0f685526af

[foad]

LGTM, thanks!

llvm/include/llvm/CodeGen/MachineScheduler.h

 
 namespace llvm {
 
 extern cl::opt<bool> ForceTopDown;
 extern cl::opt<bool> ForceBottomUp;
 extern cl::opt<bool> VerifyScheduling;
 #ifndef NDEBUG
 extern cl::opt<bool> ViewMISchedDAGs;
+extern cl::opt<bool> PrintDAGs;
 #else
 extern const bool ViewMISchedDAGs;
+extern const bool PrintDAGs;
 #endif
 
 class AAResults;
 class LiveIntervals;
 class MachineDominatorTree;
 class MachineFunction;
 class MachineInstr;
 class MachineLoopInfo;

llvm/lib/CodeGen/MachineScheduler.cpp

 cl::opt<bool> VerifyScheduling(
     "verify-misched", cl::Hidden,
     cl::desc("Verify machine instrs before and after machine scheduling"));
 
 #ifndef NDEBUG
 cl::opt<bool> ViewMISchedDAGs(
     "view-misched-dags", cl::Hidden,
     cl::desc("Pop up a window to show MISched dags after they are processed"));
+cl::opt<bool> PrintDAGs("misched-print-dags", cl::Hidden,
+                        cl::desc("Print schedule DAGs"));
 #else
 const bool ViewMISchedDAGs = false;
+const bool PrintDAGs = false;
 #endif // NDEBUG
 
 } // end namespace llvm
 
 #ifndef NDEBUG
 /// In some situations a few uninteresting nodes depend on nearly all other
 /// nodes in the graph, provide a cutoff to hide them.
 static cl::opt<unsigned> ViewMISchedCutoff("view-misched-cutoff", cl::Hidden,
   cl::desc("Hide nodes with more predecessor/successor than cutoff"));
 
 static cl::opt<unsigned> MISchedCutoff("misched-cutoff", cl::Hidden,
   cl::desc("Stop scheduling after N instructions"), cl::init(~0U));
 
 static cl::opt<std::string> SchedOnlyFunc("misched-only-func", cl::Hidden,
   cl::desc("Only schedule this function"));
 static cl::opt<unsigned> SchedOnlyBlock("misched-only-block", cl::Hidden,
                                         cl::desc("Only schedule this MBB#"));
-static cl::opt<bool> PrintDAGs("misched-print-dags", cl::Hidden,
-                              cl::desc("Print schedule DAGs"));
-#else
-static const bool PrintDAGs = false;
 #endif // NDEBUG
 
 /// Avoid quadratic complexity in unusually large basic blocks by limiting the
 /// size of the ready lists.
 static cl::opt<unsigned> ReadyListLimit("misched-limit", cl::Hidden,
   cl::desc("Limit ready list to N instructions"), cl::init(256));
 
 static cl::opt<bool> EnableRegPressure("misched-regpressure", cl::Hidden,

llvm/lib/Target/AMDGPU/SIMachineScheduler.cpp

 
 void SIScheduleDAGMI::schedule()
 {
   SmallVector<SUnit*, 8> TopRoots, BotRoots;
   SIScheduleBlockResult Best, Temp;
   LLVM_DEBUG(dbgs() << "Preparing Scheduling\n");
 
   buildDAGWithRegPressure();
+  postprocessDAG();
+
   LLVM_DEBUG(dump());
+  if (PrintDAGs)
+    dump();
+  if (ViewMISchedDAGs)
+    viewGraph();
 
   topologicalSort();
   findRootsAndBiasEdges(TopRoots, BotRoots);
   // We reuse several ScheduleDAGMI and ScheduleDAGMILive
   // functions, but to make them happy we must initialize
   // the default Scheduler implementation (even if we do not
   // run it)
   SchedImpl->initialize(this);