[interpreter] Add support for scalable operands.

src/interpreter/register-translator.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_REGISTER_TRANSLATOR_H_
-#define V8_INTERPRETER_REGISTER_TRANSLATOR_H_
-
-#include "src/interpreter/bytecodes.h"
-
-namespace v8 {
-namespace internal {
-namespace interpreter {
-
-class RegisterMover;
-
-// A class that enables bytecodes having only byte sized register operands
-// to access all registers in the two byte space. Most bytecode uses few
-// registers so space can be saved if most bytecodes with register operands
-// just take byte operands.
-//
-// To reach the wider register space, a translation window is reserved in
-// the byte addressable space specifically for copying registers into and
-// out of before a bytecode is emitted. The translation window occupies
-// the last register slots at the top of the byte addressable range.
-//
-// Because of the translation window any registers which naturally lie
-// at above the translation window have to have their register index
-// incremented by the window width before they are emitted.
-//
-// This class does not support moving ranges of registers to and from
-// the translation window. It would be straightforward to add support
-// for constrained ranges, e.g. kRegPair8, kRegTriple8 operands, but
-// these would have two negative effects. The translation window would
-// need to be wider, further limiting the space for byte operands. And
-// every register in a range would need to be moved consuming more
-// space in the bytecode array.
-class RegisterTranslator final {
- public:
-  explicit RegisterTranslator(RegisterMover* mover);
-
-  // Translate and re-write the register operands that are inputs
-  // to |bytecode| when it is about to be emitted.
-  void TranslateInputRegisters(Bytecode bytecode, uint32_t* raw_operands,
-                               int raw_operand_count);
-
-  // Translate and re-write the register operands that are outputs
-  // from |bytecode| when it has just been output.
-  void TranslateOutputRegisters();
-
-  // Returns true if |reg| is in the translation window.
-  static bool InTranslationWindow(Register reg);
-
-  // Return register value as if it had been translated.
-  static Register UntranslateRegister(Register reg);
-
-  // Returns the distance in registers between the translation window
-  // start and |reg|. The result is negative when |reg| is above the
-  // start of the translation window.
-  static int DistanceToTranslationWindow(Register reg);
-
-  // Returns true if |reg| can be represented as an 8-bit operand
-  // after translation.
-  static bool FitsInReg8Operand(Register reg);
-
-  // Returns true if |reg| can be represented as an 16-bit operand
-  // after translation.
-  static bool FitsInReg16Operand(Register reg);
-
-  // Returns the increment to the register count necessary if the
-  // value indicates the translation window is required.
-  static int RegisterCountAdjustment(int register_count, int parameter_count);
-
- private:
-  static const int kTranslationWindowLength = 4;
-  static const int kTranslationWindowLimit = -kMinInt8;
-  static const int kTranslationWindowStart =
-      kTranslationWindowLimit - kTranslationWindowLength + 1;
-
-  Register TranslateAndMove(Bytecode bytecode, int operand_index, Register reg);
-  static bool RegisterIsMovableToWindow(Bytecode bytecode, int operand_index);
-
-  static Register Translate(Register reg);
-
-  RegisterMover* mover() const { return mover_; }
-
-  // Entity to perform register moves necessary to translate registers
-  // and ensure reachability.
-  RegisterMover* mover_;
-
-  // Flag to avoid re-entrancy when emitting move bytecodes for
-  // translation.
-  bool emitting_moves_;
-
-  // Number of window registers in use.
-  int window_registers_count_;
-
-  // State for restoring register moves emitted by TranslateOutputRegisters.
-  std::pair<Register, Register> output_moves_[kTranslationWindowLength];
-  int output_moves_count_;
-};
-
-// Interface for RegisterTranslator helper class that will emit
-// register move bytecodes at the translator's behest.
-class RegisterMover {
- public:
-  virtual ~RegisterMover() {}
-
-  // Move register |from| to register |to| with no translation.
-  // returns false if either register operand is invalid. Implementations
-  // of this method must be aware that register moves with bad
-  // register values are a security hole.
-  virtual void MoveRegisterUntranslated(Register from, Register to) = 0;
-};
-
-}  // namespace interpreter
-}  // namespace internal
-}  // namespace v8
-
-#endif  // V8_INTERPRETER_REGISTER_TRANSLATOR_H_