[interpreter]: Update BytecodeArrayBuilder register handling.

src/interpreter/bytecode-array-builder.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_ARRAY_BUILDER_H_
 #define V8_INTERPRETER_BYTECODE_ARRAY_BUILDER_H_
 
 #include <vector>
 
 #include "src/ast.h"
 #include "src/interpreter/bytecodes.h"
 
 namespace v8 {
 namespace internal {
 
 class Isolate;
 
 namespace interpreter {
 
+class Register;
+
 class BytecodeArrayBuilder {
  public:
   explicit BytecodeArrayBuilder(Isolate* isolate);
   Handle<BytecodeArray> ToBytecodeArray();
 
   // Set number of locals required for bytecode array.
   void set_locals_count(int number_of_locals);
   int locals_count() const;
 
-  // Constant loads to accumulator
+  // Constant loads to accumulator.
   BytecodeArrayBuilder& LoadLiteral(v8::internal::Smi* value);
   BytecodeArrayBuilder& LoadUndefined();
   BytecodeArrayBuilder& LoadNull();
   BytecodeArrayBuilder& LoadTheHole();
   BytecodeArrayBuilder& LoadTrue();
   BytecodeArrayBuilder& LoadFalse();
 
-  // Register-accumulator transfers
-  BytecodeArrayBuilder& LoadAccumulatorWithRegister(int reg);
-  BytecodeArrayBuilder& StoreAccumulatorInRegister(int reg);
+  // Register-accumulator transfers.
+  BytecodeArrayBuilder& LoadAccumulatorWithRegister(Register reg);
+  BytecodeArrayBuilder& StoreAccumulatorInRegister(Register reg);
 
-  // Operators
-  BytecodeArrayBuilder& BinaryOperation(Token::Value binop, int reg);
+  // Operators.
+  BytecodeArrayBuilder& BinaryOperation(Token::Value binop, Register reg);
 
-  // Flow Control
+  // Flow Control.
   BytecodeArrayBuilder& Return();
 
  private:
   static Bytecode BytecodeForBinaryOperation(Token::Value op);
 
   void Output(Bytecode bytecode, uint8_t r0, uint8_t r1, uint8_t r2);
   void Output(Bytecode bytecode, uint8_t r0, uint8_t r1);
   void Output(Bytecode bytecode, uint8_t r0);
   void Output(Bytecode bytecode);
 
   bool OperandIsValid(Bytecode bytecode, int operand_index,
                       uint8_t operand_value) const;
 
   int BorrowTemporaryRegister();
-  void ReturnTemporaryRegister(int reg);
+  void ReturnTemporaryRegister(int reg_index);
 
   Isolate* isolate_;
   std::vector<uint8_t> bytecodes_;
   bool bytecode_generated_;
 
   int local_register_count_;
   int temporary_register_count_;
   int temporary_register_next_;
 
   friend class TemporaryRegisterScope;
   DISALLOW_IMPLICIT_CONSTRUCTORS(BytecodeArrayBuilder);
 };
 
+// An interpreter register which is located in the function's regsiter file
+// in its stack-frame.
+class Register {
+ public:
+  static const int kMaxRegisterIndex = 128;
+
+  explicit Register(int index) : index_(index) {
+    DCHECK_LE(index_, kMaxRegisterIndex);

[oth, 2015/08/13 10:29:55]

Probably worth having a lower bounds DCHECK too.

[rmcilroy, 2015/08/13 10:44:22]

Done.

+  }
+
+  int index() { return index_; }
+  uint8_t ToOperand() { return static_cast<uint8_t>(-index_); }
+  static Register FromOperand(uint8_t operand) { return Register(-operand); }
+
+ private:
+  void* operator new(size_t size);
+  void operator delete(void* p);
+
+  int index_;
+};
+
 // A stack-allocated class than allows the instantiator to allocate
 // temporary registers that are cleaned up when scope is closed.
 class TemporaryRegisterScope {
  public:
   explicit TemporaryRegisterScope(BytecodeArrayBuilder* builder);
   ~TemporaryRegisterScope();
-  int NewRegister();
+  Register NewRegister();
 
  private:
   void* operator new(size_t size);
   void operator delete(void* p);
 
   BytecodeArrayBuilder* builder_;
   int count_;
-  int register_;
+  int last_register_index_;
 
   DISALLOW_COPY_AND_ASSIGN(TemporaryRegisterScope);
 };
 
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_INTERPRETER_BYTECODE_ARRAY_BUILDER_H_