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-// 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_