[Interpreter] Reduce temporary register usage in generated bytecode.

src/interpreter/bytecode-generator.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_INTERPRETER_BYTECODE_GENERATOR_H_
 #define V8_INTERPRETER_BYTECODE_GENERATOR_H_
 
 #include "src/ast.h"
 #include "src/interpreter/bytecode-array-builder.h"
 #include "src/interpreter/bytecodes.h"
@@ skipping 12 matching lines @@
 #define DECLARE_VISIT(type) void Visit##type(type* node) override;
   AST_NODE_LIST(DECLARE_VISIT)
 #undef DECLARE_VISIT
 
   // Visiting function for declarations list is overridden.
   void VisitDeclarations(ZoneList<Declaration*>* declarations) override;
 
  private:
   class ControlScope;
   class ControlScopeForIteration;
+  class ExpressionResultScope;
+  class AccumulatorResultScope;
+  class EffectResultScope;
+  class RegisterResultScope;
 
   DEFINE_AST_VISITOR_SUBCLASS_MEMBERS();
 
   void VisitArithmeticExpression(BinaryOperation* binop);
   void VisitPropertyLoad(Register obj, Property* expr);
   void VisitVariableLoad(Variable* variable, FeedbackVectorSlot slot);
   void VisitVariableAssignment(Variable* variable, FeedbackVectorSlot slot);
 
   // Dispatched from VisitUnaryOperation.
   void VisitVoid(UnaryOperation* expr);
   void VisitTypeOf(UnaryOperation* expr);
   void VisitNot(UnaryOperation* expr);
 
+  // Visitors for obtaining expression result in the accumulator, in a
+  // register, or just getting the effect.
+  void VisitForAccumulatorValue(Expression* expression);
+  MUST_USE_RESULT Register VisitForRegisterValue(
+      Expression* expression, TemporaryRegisterScope* temporary_register_scope);
+  void VisitForEffect(Expression* node);
+
+  void SetResultRegister(Register reg);
+  Register GetResultRegister();
+  bool ResultRegisterIsEmpty() const;
+
   inline BytecodeArrayBuilder* builder() { return &builder_; }
   inline Scope* scope() const { return scope_; }
   inline void set_scope(Scope* scope) { scope_ = scope; }
   inline ControlScope* control_scope() const { return control_scope_; }
   inline void set_control_scope(ControlScope* scope) { control_scope_ = scope; }
   inline CompilationInfo* info() const { return info_; }
   inline void set_info(CompilationInfo* info) { info_ = info; }
   ZoneVector<Handle<Object>>* globals() { return &globals_; }
+  inline void set_result_scope(ExpressionResultScope* result_scope) {
+    result_scope_ = result_scope;
+  }
+  inline ExpressionResultScope* result_scope() const { return result_scope_; }
 
   LanguageMode language_mode() const;
   Strength language_mode_strength() const;
   int feedback_index(FeedbackVectorSlot slot) const;
   Register current_context() const;
 
   BytecodeArrayBuilder builder_;
   CompilationInfo* info_;
   Scope* scope_;
   ZoneVector<Handle<Object>> globals_;
   ControlScope* control_scope_;
 
   // TODO(rmcilroy): Encapsulate this in an environment object.
   Register current_context_;
+  ExpressionResultScope* result_scope_;
+  Maybe<Register> result_register_;
 };
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_INTERPRETER_BYTECODE_GENERATOR_H_