[interpreter] Wide register support.

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 register operands in bytecode to be
+  // emitted.
+  void TranslateRegisters(Bytecode bytecode, uint32_t* raw_operands,
+                          int raw_operand_count);
+
+  // Undo translations after bytecode has been emitted.
+  void UntranslateRegisters();
+
+  // Returns true if |reg| is in the translation window.
+  static bool InTranslationWindow(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);
+  Register MakeAddressable(Register reg, OperandType reg_type);
+  static Register Translate(Register reg);
+
+  static bool NonRegisterOperandIsValid(Bytecode bytecode, int operand_index);
+  static bool OperandIsMoveable(Bytecode bytecode, int operand_index);
+
+  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_;
+
+  // State for restoring registers after bytecode.
+  Register window_registers_[kTranslationWindowLength];
+  int window_registers_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_