Improve comments and readability of scheduler.

src/compiler/scheduler.h

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COMPILER_SCHEDULER_H_
 #define V8_COMPILER_SCHEDULER_H_
 
 #include "src/v8.h"
 
 #include "src/compiler/opcodes.h"
 #include "src/compiler/schedule.h"
 #include "src/zone-containers.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 // Computes a schedule from a graph, placing nodes into basic blocks and
 // ordering the basic blocks in the special RPO order.
 class Scheduler {
  public:
-  // The complete scheduling algorithm.
-  // Create a new schedule and place all nodes from the graph into it.
+  // The complete scheduling algorithm. Creates a new schedule and places all
+  // nodes from the graph into it.
   static Schedule* ComputeSchedule(Graph* graph);
 
   // Compute the RPO of blocks in an existing schedule.
   static BasicBlockVector* ComputeSpecialRPO(Schedule* schedule);
 
-  // (Exposed for testing only)
-  // Build and connect the CFG for a node graph, but don't schedule nodes.
-  static void ComputeCFG(Graph* graph, Schedule* schedule);
-
  private:
   enum Placement { kUnknown, kSchedulable, kFixed };
 
   // Per-node data tracked during scheduling.
   struct SchedulerData {
     int unscheduled_count_;      // Number of unscheduled uses of this node.
     int minimum_rpo_;            // Minimum legal RPO placement.
     bool is_connected_control_;  // {true} if control-connected to the end node.
     bool is_floating_control_;   // {true} if control, but not control-connected
                                  // to the end node.
@@ skipping 11 matching lines @@
 
   Scheduler(Zone* zone, Graph* graph, Schedule* schedule);
 
   SchedulerData DefaultSchedulerData();
 
   SchedulerData* GetData(Node* node) {
     DCHECK(node->id() < static_cast<int>(node_data_.size()));
     return &node_data_[node->id()];
   }
 
-  void BuildCFG();
-
   Placement GetPlacement(Node* node);
 
   int GetRPONumber(BasicBlock* block) {
     DCHECK(block->rpo_number() >= 0 &&
            block->rpo_number() <
                static_cast<int>(schedule_->rpo_order_.size()));
     DCHECK(schedule_->rpo_order_[block->rpo_number()] == block);
     return block->rpo_number();
   }
 
-  void GenerateImmediateDominatorTree();
   BasicBlock* GetCommonDominator(BasicBlock* b1, BasicBlock* b2);
 
+  // Phase 1: Build control-flow graph and dominator tree.
   friend class CFGBuilder;
+  void BuildCFG();
+  void GenerateImmediateDominatorTree();
 
+  // Phase 2: Prepare use counts for nodes.
+  friend class PrepareUsesVisitor;
+  void PrepareUses();
+
+  // Phase 3: Schedule nodes early.
   friend class ScheduleEarlyNodeVisitor;
   void ScheduleEarly();
 
-  friend class PrepareUsesVisitor;
-  void PrepareUses();
-
+  // Phase 4: Schedule nodes late.
   friend class ScheduleLateNodeVisitor;
   void ScheduleLate();
 
   bool ConnectFloatingControl();
-
   void ConnectFloatingControlSubgraph(BasicBlock* block, Node* node);
 };
-}
-}
-}  // namespace v8::internal::compiler
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8
 
 #endif  // V8_COMPILER_SCHEDULER_H_