[Interpreter] Add a simple dead-code elimination bytecode optimizer.

src/interpreter/bytecode-dead-code-optimizer.h

Index: src/interpreter/bytecode-dead-code-optimizer.h
diff --git a/src/interpreter/bytecode-dead-code-optimizer.h b/src/interpreter/bytecode-dead-code-optimizer.h
new file mode 100644
index 0000000000000000000000000000000000000000..8d68e54b0ea1ca13ed058f90a1aff93a55ffd12e
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+++ b/src/interpreter/bytecode-dead-code-optimizer.h
@@ -0,0 +1,41 @@
+// 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_DEAD_CODE_OPTIMIZER_H_
+#define V8_INTERPRETER_BYTECODE_DEAD_CODE_OPTIMIZER_H_
+
+#include "src/interpreter/bytecode-pipeline.h"
+
+namespace v8 {
+namespace internal {
+namespace interpreter {
+
+// An optimization stage for eliminating obviously dead code in bytecode
+// generation.
+class BytecodeDeadCodeOptimizer final : public BytecodePipelineStage,
+                                        public ZoneObject {
+ public:
+  explicit BytecodeDeadCodeOptimizer(BytecodePipelineStage* next_stage);
+
+  // BytecodePipelineStage interface.
+  void Write(BytecodeNode* node) override;
+  void WriteJump(BytecodeNode* node, BytecodeLabel* label) override;
+  void BindLabel(BytecodeLabel* label) override;
+  void BindLabel(const BytecodeLabel& target, BytecodeLabel* label) override;
+  Handle<BytecodeArray> ToBytecodeArray(
+      int fixed_register_count, int parameter_count,
+      Handle<FixedArray> handler_table) override;
+
+ private:
+  BytecodePipelineStage* next_stage_;
+  bool exit_seen_in_block_;
+
+  DISALLOW_COPY_AND_ASSIGN(BytecodeDeadCodeOptimizer);
+};
+
+}  // namespace interpreter
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_INTERPRETER_BYTECODE_DEAD_CODE_OPTIMIZER_H_