[turbofan] Use a map to cache values definition in instruction scheduler.

src/compiler/instruction-scheduler.h

 // Copyright 2015 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_INSTRUCTION_SCHEDULER_H_
 #define V8_COMPILER_INSTRUCTION_SCHEDULER_H_
 
 #include "src/compiler/instruction.h"
 #include "src/zone-containers.h"
 
@@ skipping 138 matching lines @@
 
   // 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.
   int GetInstructionFlags(const Instruction* instr) const;
   int GetTargetInstructionFlags(const Instruction* instr) const;
 
-  // Return true if instr2 uses any value defined by instr1.
-  bool HasOperandDependency(const Instruction* instr1,
-                            const Instruction* instr2) const;
-
   // Return true if the instruction is a basic block terminator.
   bool IsBlockTerminator(const Instruction* instr) const;
 
   // Check whether the given instruction has side effects (e.g. function call,
   // memory store).
   bool HasSideEffect(const Instruction* instr) const {
     return GetInstructionFlags(instr) & kHasSideEffect;
   }
 
   // Return true if the instruction is a memory load.
@@ skipping 34 matching lines @@
 
   // Live-in register markers are nop instructions which are emitted at the
   // beginning of a basic block so that the register allocator will find a
   // defining instruction for live-in values. They must not be moved.
   // All these nops are chained together and added as a predecessor of every
   // other instructions in the basic block.
   ScheduleGraphNode* last_live_in_reg_marker_;
 
   // Last deoptimization instruction encountered while building the graph.
   ScheduleGraphNode* last_deopt_;
+
+  // Keep track of definition points for virtual registers. This is used to
+  // record operand dependencies in the scheduling graph.
+  ZoneMap<int32_t, ScheduleGraphNode*> operands_map_;
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_INSTRUCTION_SCHEDULER_H_