Switch scheduler to iterative floating control placement.

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"
@@ skipping 11 matching lines @@
  public:
   // The complete scheduling algorithm. Creates a new schedule and places all
   // nodes from the graph into it.
   static Schedule* ComputeSchedule(ZonePool* zone_pool, Graph* graph);
 
   // Compute the RPO of blocks in an existing schedule.
   static BasicBlockVector* ComputeSpecialRPO(ZonePool* zone_pool,
                                              Schedule* schedule);
 
  private:
-  enum Placement { kUnknown, kSchedulable, kFixed, kCoupled };
+  // Placement of a node changes during scheduling. The placement state
+  // transitions over time while the scheduler is choosing a position:
+  //
+  //                   +---------------------+-----+----> kFixed
+  //                  /                     /     /
+  //    kUnknown ----+------> kCoupled ----+     /
+  //                  \                         /
+  //                   +----> kSchedulable ----+--------> kScheduled
+  //
+  // 1) GetPlacement(): kUnknown -> kCoupled|kSchedulable|kFixed
+  // 2) UpdatePlacement(): kCoupled|kSchedulable -> kFixed|kScheduled
+  enum Placement { kUnknown, kSchedulable, kFixed, kCoupled, kScheduled };
 
   // Per-node data tracked during scheduling.
   struct SchedulerData {
     BasicBlock* minimum_block_;  // Minimum legal RPO placement.
     int unscheduled_count_;      // Number of unscheduled uses of this node.
     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.
     Placement placement_;        // Whether the node is fixed, schedulable,
                                  // coupled to another node, or not yet known.
   };
 
   Zone* zone_;
   Graph* graph_;
   Schedule* schedule_;
   NodeVectorVector scheduled_nodes_;     // Per-block list of nodes in reverse.
   NodeVector schedule_root_nodes_;       // Fixed root nodes seed the worklist.
   ZoneQueue<Node*> schedule_queue_;      // Worklist of schedulable nodes.
   ZoneVector<SchedulerData> node_data_;  // Per-node data for all nodes.
-  bool has_floating_control_;
 
   Scheduler(Zone* zone, Graph* graph, Schedule* schedule);
 
   inline SchedulerData DefaultSchedulerData();
   inline SchedulerData* GetData(Node* node);
 
   Placement GetPlacement(Node* node);
+  void UpdatePlacement(Node* node, Placement placement);
 
   void IncrementUnscheduledUseCount(Node* node, Node* from);
   void DecrementUnscheduledUseCount(Node* node, Node* from);
 
   inline int GetRPONumber(BasicBlock* block);
   BasicBlock* GetCommonDominator(BasicBlock* b1, BasicBlock* b2);
 
   // Phase 1: Build control-flow graph.
   friend class CFGBuilder;
   void BuildCFG();
 
   // Phase 2: Compute special RPO and dominator tree.
   friend class SpecialRPONumberer;
   void ComputeSpecialRPONumbering();
   void GenerateImmediateDominatorTree();
 
   // Phase 3: Prepare use counts for nodes.
   friend class PrepareUsesVisitor;
   void PrepareUses();
 
   // Phase 4: Schedule nodes early.
   friend class ScheduleEarlyNodeVisitor;
   void ScheduleEarly();
 
   // Phase 5: Schedule nodes late.
   friend class ScheduleLateNodeVisitor;
   void ScheduleLate();
 
-  bool ConnectFloatingControl();
-  void ConnectFloatingControlSubgraph(BasicBlock* block, Node* node);
+  void FuseFloatingControl(BasicBlock* block, Node* node);
+  void MovePlannedNodes(BasicBlock* from, BasicBlock* to);
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_SCHEDULER_H_