[Interpreter] Preserve source positions in peephole optimizer.

src/interpreter/bytecode-peephole-optimizer.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_BYTECODE_PEEPHOLE_OPTIMIZER_H_
 #define V8_INTERPRETER_BYTECODE_PEEPHOLE_OPTIMIZER_H_
 
 #include "src/interpreter/bytecode-pipeline.h"
 
 namespace v8 {
@@ skipping 11 matching lines @@
   BytecodePeepholeOptimizer(ConstantArrayBuilder* constant_array_builder,
                             BytecodePipelineStage* next_stage);
 
   void Write(BytecodeNode* node) override;
   size_t FlushForOffset() override;
   void FlushBasicBlock() override;
 
  private:
   BytecodeNode* Optimize(BytecodeNode* current);
 
-  void UpdateCurrentBytecode(BytecodeNode* const current);
+  void UpdateLastAndCurrentBytecodes(BytecodeNode* const current);
   bool CanElideCurrent(const BytecodeNode* const current) const;
   bool CanElideLast(const BytecodeNode* const current) const;
+  bool CanElideLastBasedOnSourcePosition(
+      const BytecodeNode* const current) const;
 
   void InvalidateLast();
   bool LastIsValid() const;
   void SetLast(const BytecodeNode* const node);
 
   bool LastBytecodePutsNameInAccumulator() const;
 
   Handle<Object> GetConstantForIndexOperand(const BytecodeNode* const node,
                                             int index) const;
 
   ConstantArrayBuilder* constant_array_builder_;
   BytecodePipelineStage* next_stage_;
   BytecodeNode last_;
   bool last_is_discardable_;
 
   DISALLOW_COPY_AND_ASSIGN(BytecodePeepholeOptimizer);
 };
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_INTERPRETER_BYTECODE_PEEPHOLE_OPTIMIZER_H_