[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 13 matching lines @@
   AST_NODE_LIST(DECLARE_VISIT)
 #undef DECLARE_VISIT
 
   // Visiting function for declarations list is overridden.
   void VisitDeclarations(ZoneList<Declaration*>* declarations) override;
 
  private:
   class ContextScope;
   class ControlScope;
   class ControlScopeForIteration;
+  class ExpressionResultScope;
+  class TopLevelResultScope;
+  class AccumulatorResultScope;
+  class EffectResultScope;
+  class RegisterResultScope;
 
   void MakeBytecodeBody();
   Register NextContextRegister() const;
 
   DEFINE_AST_VISITOR_SUBCLASS_MEMBERS();
 
-  Register VisitArguments(ZoneList<Expression*>* arguments,
-                          TemporaryRegisterScope* caller_scope);
+  Register VisitArguments(ZoneList<Expression*>* arguments);
   void VisitArithmeticExpression(BinaryOperation* binop);
   void VisitCommaExpression(BinaryOperation* binop);
   void VisitLogicalOrExpression(BinaryOperation* binop);
   void VisitLogicalAndExpression(BinaryOperation* binop);
   void VisitPropertyLoad(Register obj, Property* expr);
   void VisitVariableLoad(Variable* variable, FeedbackVectorSlot slot);
   void VisitVariableAssignment(Variable* variable, FeedbackVectorSlot slot);
   void VisitNewLocalFunctionContext();
   void VisitBuildLocalActivationContext();
   void VisitNewLocalBlockContext(Scope* scope);
   void VisitFunctionClosureForContext();
   void VisitSetHomeObject(Register value, Register home_object,
                           ObjectLiteralProperty* property, int slot_number = 0);
   void VisitObjectLiteralAccessor(Register home_object,
                                   ObjectLiteralProperty* property,
                                   Register value_out);
 
   // 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);
+  void VisitForEffect(Expression* node);
+
+  // Binary expression state machine and load-store tracking.
+  void PrepareForBinaryExpression();
+  Register LoadForBinaryExpression(Register reg);
+  void StoreForBinaryExpression(Register reg);
+  void CompleteBinaryExpression();
+
   inline BytecodeArrayBuilder* builder() { return &builder_; }
 
   inline Isolate* isolate() const { return isolate_; }
   inline Zone* zone() const { return zone_; }
 
   inline Scope* scope() const { return scope_; }
   inline void set_scope(Scope* scope) { scope_ = scope; }
   inline CompilationInfo* info() const { return info_; }
   inline void set_info(CompilationInfo* info) { info_ = info; }
 
   inline ControlScope* execution_control() const { return execution_control_; }
   inline void set_execution_control(ControlScope* scope) {
     execution_control_ = scope;
   }
   inline ContextScope* execution_context() const { return execution_context_; }
   inline void set_execution_context(ContextScope* context) {
     execution_context_ = context;
   }
 
+  void set_result_scope(ExpressionResultScope* result_scope);
+  ExpressionResultScope* result_scope() const;
+  ExpressionResultScope* parent_result_scope() const;
+  TopLevelResultScope* top_level_result_scope() const;
+  void set_top_level_result_scope(TopLevelResultScope* result_scope);
+
   ZoneVector<Handle<Object>>* globals() { return &globals_; }
   inline LanguageMode language_mode() const;
   Strength language_mode_strength() const;
   int feedback_index(FeedbackVectorSlot slot) const;
 
   Isolate* isolate_;
   Zone* zone_;
   BytecodeArrayBuilder builder_;
   CompilationInfo* info_;
   Scope* scope_;
   ZoneVector<Handle<Object>> globals_;
   ControlScope* execution_control_;
   ContextScope* execution_context_;
+  ExpressionResultScope* result_scope_;
+  TopLevelResultScope* top_level_result_scope_;

[rmcilroy, 2015/10/19 12:56:23]

This doesn't seem to be used? Can we remove it for now (or make use of it
instead of having PrepareForBinaryExpression / CompleteBinaryExpression? 

As an aside for when it is later needed, personally I would prefer the top level
result scope not to be separate from the result_scope chain (i.e., it is just
stored at the top of the result_scope_ chain, and possibly has a 'short cut'
method in ExpressionResultScope which points to the top-level so we don't need
to walk the whole chain to get it.

[oth, 2015/10/20 15:28:53]

Removed for now. Having a central reference saves (chain_length - 1) words of
stack.

+
+  int binary_expression_depth_;
+  ZoneSet<int> binary_expression_hazard_set_;
 };
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_INTERPRETER_BYTECODE_GENERATOR_H_