[turbofan][x64] Use the root register for comparisons with certain roots.

src/compiler/instruction-selector.h

 // Copyright 2014 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_SELECTOR_H_
 #define V8_COMPILER_INSTRUCTION_SELECTOR_H_
 
 #include <map>
 
 #include "src/compiler/common-operator.h"
@@ skipping 186 matching lines @@
   // Gets the effect level of {node}.
   int GetEffectLevel(Node* node) const;
 
   int GetVirtualRegister(const Node* node);
   const std::map<NodeId, int> GetVirtualRegistersForTesting() const;
 
   // Check if we can generate loads and stores of ExternalConstants relative
   // to the roots register, i.e. if both a root register is available for this
   // compilation unit and the serializer is disabled.
   bool CanAddressRelativeToRootsRegister() const;
+  // Check if we can use the roots register to access GC roots.
+  bool CanUseRootsRegister() const;
 
   Isolate* isolate() const { return sequence()->isolate(); }
 
  private:
   friend class OperandGenerator;
 
   bool UseInstructionScheduling() const {
     return (enable_scheduling_ == kEnableScheduling) &&
            InstructionScheduler::SchedulerSupported();
   }
@@ skipping 148 matching lines @@
   EnableSerialization enable_serialization_;
   Frame* frame_;
   bool instruction_selection_failed_;
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_INSTRUCTION_SELECTOR_H_