[interpreter] Bytecode register optimizer.

src/interpreter/bytecode-register-optimizer.h

+// Copyright 2016 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_REGISTER_OPTIMIZER_H_
+#define V8_INTERPRETER_BYTECODE_REGISTER_OPTIMIZER_H_
+
+#include "src/interpreter/bytecode-pipeline.h"
+
+namespace v8 {
+namespace internal {
+namespace interpreter {
+
+// An optimization stage for eliminating unnecessary transfers between
+// registers. The bytecode generator uses temporary registers
+// liberally for correctness and convenience and this stage removes
+// transfers that are not required and preserves correctness.
+class BytecodeRegisterOptimizer final : public BytecodePipelineStage,
+                                        public TemporaryRegisterObserver,
+                                        public ZoneObject {
+ public:
+  BytecodeRegisterOptimizer(Zone* zone,
+                            TemporaryRegisterAllocator* register_allocator,
+                            int parameter_count,
+                            BytecodePipelineStage* next_stage);
+  virtual ~BytecodeRegisterOptimizer() {}
+
+  // BytecodePipelineStage interface.
+  size_t FlushForOffset() override;
+  void FlushBasicBlock() override;
+  void Write(BytecodeNode* node) override;
+
+ private:
+  const uint32_t kInvalidEquivalenceId = kMaxUInt32;
+
+  class RegisterInfo;
+
+  // TemporaryRegisterObserver interface.
+  void TemporaryRegisterFreeEvent(Register reg) override;
+
+  // Helpers for BytecodePipelineStage interface.
+  void FlushState();
+  void WriteToNextStage(BytecodeNode* node) const;
+  void WriteToNextStage(BytecodeNode* node,
+                        const BytecodeSourceInfo& output_info) const;
+
+  // Update internal state for register transfer from |input| to
+  // |output| using |source_info| as source position information if
+  // any bytecodes are emitted due to transfer.
+  void RegisterTransfer(RegisterInfo* input, RegisterInfo* output,
+                        const BytecodeSourceInfo& source_info);
+
+  // Emit a register transfer bytecode from |input| to |output|.
+  void OutputRegisterTransfer(
+      RegisterInfo* input, RegisterInfo* output,
+      const BytecodeSourceInfo& source_info = BytecodeSourceInfo());
+
+  // Emits a Nop to preserve source position information in the
+  // bytecode pipeline.
+  void EmitNopForSourceInfo(const BytecodeSourceInfo& source_info) const;
+
+  // Handlers for bytecode nodes for register to register transfers.
+  void DoLdar(const BytecodeNode* const node);
+  void DoMov(const BytecodeNode* const node);
+  void DoStar(const BytecodeNode* const node);
+
+  // Operand processing methods for bytecodes other than those
+  // performing register to register transfers.
+  void PrepareOperands(BytecodeNode* const node);
+  void PrepareAccumulator(BytecodeNode* const node);
+  void PrepareRegisterOperands(BytecodeNode* const node);
+
+  void PrepareRegisterOutputOperand(RegisterInfo* reg_info);
+  void PrepareRegisterRangeOutputOperand(Register start, int count);
+  void PrepareRegisterInputOperand(BytecodeNode* const node, Register reg,
+                                   int operand_index);
+  void PrepareRegisterRangeInputOperand(Register start, int count);
+
+  Register GetEquivalentRegisterForInputOperand(Register reg);
+
+  static Register GetRegisterInputOperand(int index, Bytecode bytecode,
+                                          const uint32_t* operands,
+                                          int operand_count);
+  static Register GetRegisterOutputOperand(int index, Bytecode bytecode,
+                                           const uint32_t* operands,
+                                           int operand_count);
+
+  void CreateMaterializedEquivalentIfRequired(RegisterInfo* info);
+  RegisterInfo* GetMaterializedEquivalent(RegisterInfo* info);
+  RegisterInfo* GetMaterializedEquivalentNotAccumulator(RegisterInfo* info);
+  void Materialize(RegisterInfo* info);
+
+  // Methods for finding and creating metadata for each register.
+  RegisterInfo* GetOrCreateRegisterInfo(Register reg);
+  RegisterInfo* GetRegisterInfo(Register reg);
+  RegisterInfo* NewRegisterInfo(Register reg);
+  void GrowRegisterMap(Register reg);
+
+  bool RegisterIsTemporary(Register reg) const {
+    return reg >= temporary_base_;
+  }
+
+  bool RegisterIsObservable(Register reg) const {
+    return reg != accumulator_ && !RegisterIsTemporary(reg);
+  }
+
+  static Register OperandToRegister(uint32_t operand) {
+    return Register::FromOperand(static_cast<int32_t>(operand));
+  }
+
+  size_t GetRegisterInfoTableIndex(Register reg) const {
+    return static_cast<size_t>(reg.index() + register_info_table_offset_);
+  }
+
+  Register RegisterFromRegisterInfoTableIndex(size_t index) const {

[rmcilroy, 2016/05/27 09:18:58]

nit - RegisterFromTableIndex ?

+    return Register(static_cast<int>(index) - register_info_table_offset_);
+  }
+
+  uint32_t NextEquivalenceId() {
+    equivalence_id_++;
+    CHECK_NE(equivalence_id_, kInvalidEquivalenceId);
+    return equivalence_id_;
+  }
+
+  Zone* zone() { return zone_; }
+
+  const Register accumulator_;
+  RegisterInfo* accumulator_info_;
+  const Register temporary_base_;
+
+  // Direct mapping to register info.
+  ZoneVector<RegisterInfo*> register_info_table_;
+  int register_info_table_offset_;
+
+  // Counter for equivalence sets identifiers.
+  int equivalence_id_;

[rmcilroy, 2016/05/27 09:18:58]

uint32_t (given kInvalidEquivalenceId is uint32_t).

+
+  BytecodePipelineStage* next_stage_;
+  bool flushed_;
+  Zone* zone_;
+
+  DISALLOW_COPY_AND_ASSIGN(BytecodeRegisterOptimizer);
+};
+
+}  // namespace interpreter
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_INTERPRETER_BYTECODE_REGISTER_OPTIMIZER_H_