[turbofan] Refactoring around the instruction scheduler.

src/compiler/instruction-scheduler.h

Index: src/compiler/instruction-scheduler.h
diff --git a/src/compiler/instruction-scheduler.h b/src/compiler/instruction-scheduler.h
index fafbe47908019115d95f2dabfb3aec3f73c80b1f..104c0b97de8bd401d2a39c42d7bbfac81f38bec9 100644
--- a/src/compiler/instruction-scheduler.h
+++ b/src/compiler/instruction-scheduler.h
@@ -90,11 +90,66 @@ class InstructionScheduler final : public ZoneObject {
     int start_cycle_;
   };
 
-  // Compare the two nodes and return true if node1 is a better candidate than
-  // node2 (i.e. node1 should be scheduled before node2).
-  bool CompareNodes(ScheduleGraphNode *node1, ScheduleGraphNode *node2) const;
+  // Keep track of all nodes ready to be scheduled (i.e. all their dependencies
+  // have been scheduled. Note that this class is inteded to be extended by
+  // concrete implementation of the scheduling queue which define the policy
+  // to pop node from the queue.
+  class SchedulingQueueBase {
+   public:
+    explicit SchedulingQueueBase(InstructionScheduler* scheduler)
+      : scheduler_(scheduler),
+        nodes_(scheduler->zone()) {
+    }
+
+    void AddNode(ScheduleGraphNode* node) {
+      nodes_.push_back(node);
+    }
+
+    bool IsEmpty() const {
+      return nodes_.empty();
+    }
+
+   protected:
+    InstructionScheduler* scheduler_;
+    ZoneLinkedList<ScheduleGraphNode*> nodes_;
+  };
+
+  // A scheduling queue which prioritize nodes on the critical path (we look
+  // for the instruction with the highest latency on the path to reach the end
+  // of the graph).
+  class CriticalPathFirstQueue : public SchedulingQueueBase  {
+   public:
+    explicit CriticalPathFirstQueue(InstructionScheduler* scheduler)
+      : SchedulingQueueBase(scheduler) { }
+
+    // Look for the best candidate to schedule, remove it from the queue and
+    // return it.
+    ScheduleGraphNode* PopBestCandidate(int cycle);
+
+   private:
+    // Compare the two nodes and return true if node1 is a better candidate than
+    // node2 (i.e. node1 should be scheduled before node2).
+    bool CompareNodes(ScheduleGraphNode *node1, ScheduleGraphNode *node2) const;
+  };
+
+  // A queue which pop a random node from the queue to perform stress tests on
+  // the scheduler.
+  class StressSchedulerQueue : public SchedulingQueueBase  {
+   public:
+    explicit StressSchedulerQueue(InstructionScheduler* scheduler)
+      : SchedulingQueueBase(scheduler) { }
+
+    ScheduleGraphNode* PopBestCandidate(int cycle);
+
+   private:
+    Isolate *isolate() {
+      return scheduler_->isolate();
+    }
+  };
 
-  // Perform scheduling for the current block.
+  // Perform scheduling for the current block specifying the queue type to
+  // use to determine the next best candidate.
+  template <typename QueueType>
   void ScheduleBlock();
 
   // Return the scheduling properties of the given instruction.
@@ -134,6 +189,7 @@ class InstructionScheduler final : public ZoneObject {
 
   Zone* zone() { return zone_; }
   InstructionSequence* sequence() { return sequence_; }
+  Isolate* isolate() { return sequence()->isolate(); }
 
   Zone* zone_;
   InstructionSequence* sequence_;