misched: add a hook for custom DAG postprocessing.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@163915 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/MachineScheduler.h

@@ -179,6 +179,14 @@ public:
 #endif
 };
 
+/// Mutate the DAG as a postpass after normal DAG building.
+class ScheduleDAGMutation {
+public:
+  virtual ~ScheduleDAGMutation() {}
+
+  virtual void apply(ScheduleDAGMI *DAG) = 0;
+};
+
 /// ScheduleDAGMI is an implementation of ScheduleDAGInstrs that schedules
 /// machine instructions while updating LiveIntervals and tracking regpressure.
 class ScheduleDAGMI : public ScheduleDAGInstrs {
@@ -187,6 +195,9 @@ protected:
   RegisterClassInfo *RegClassInfo;
   MachineSchedStrategy *SchedImpl;
 
+  /// Ordered list of DAG postprocessing steps.
+  std::vector<ScheduleDAGMutation*> Mutations;
+
   MachineBasicBlock::iterator LiveRegionEnd;
 
   /// Register pressure in this region computed by buildSchedGraph.
@@ -229,6 +240,13 @@ public:
     delete SchedImpl;
   }
 
+  /// Add a postprocessing step to the DAG builder.
+  /// Mutations are applied in the order that they are added after normal DAG
+  /// building and before MachineSchedStrategy initialization.
+  void addMutation(ScheduleDAGMutation *Mutation) {
+    Mutations.push_back(Mutation);
+  }
+
   MachineBasicBlock::iterator top() const { return CurrentTop; }
   MachineBasicBlock::iterator bottom() const { return CurrentBottom; }
 
@@ -282,6 +300,10 @@ protected:
   /// bottom of the DAG region without covereing any unscheduled instruction.
   void buildDAGWithRegPressure();
 
+  /// Apply each ScheduleDAGMutation step in order. This allows different
+  /// instances of ScheduleDAGMI to perform custom DAG postprocessing.
+  void postprocessDAG();
+
   /// Identify DAG roots and setup scheduler queues.
   void initQueues();
 

lib/CodeGen/MachineScheduler.cpp

@@ -484,6 +484,8 @@ void ScheduleDAGMI::releaseRoots() {
 void ScheduleDAGMI::schedule() {
   buildDAGWithRegPressure();
 
+  postprocessDAG();
+
   DEBUG(for (unsigned su = 0, e = SUnits.size(); su != e; ++su)
           SUnits[su].dumpAll(this));
 
@@ -522,6 +524,13 @@ void ScheduleDAGMI::buildDAGWithRegPressure() {
   initRegPressure();
 }
 
+/// Apply each ScheduleDAGMutation step in order.
+void ScheduleDAGMI::postprocessDAG() {
+  for (unsigned i = 0, e = Mutations.size(); i < e; ++i) {
+    Mutations[i]->apply(this);
+  }
+}
+
 /// Identify DAG roots and setup scheduler queues.
 void ScheduleDAGMI::initQueues() {
   // Initialize the strategy before modifying the DAG.