Improve and simplify removal of unreachable code

src/x64/lithium-x64.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2501 matching lines @@
         next_block_(NULL),
         argument_count_(0),
         allocator_(allocator),
         position_(RelocInfo::kNoPosition),
         instruction_pending_deoptimization_environment_(NULL),
         pending_deoptimization_ast_id_(BailoutId::None()) { }
 
   // Build the sequence for the graph.
   LPlatformChunk* Build();
 
+  LInstruction* ElideControlInstruction(HControlInstruction* instr,
+                                        bool condition);
+
+  void PropagateUnreachableBlockMarks();
+
   // Declare methods that deal with the individual node types.
 #define DECLARE_DO(type) LInstruction* Do##type(H##type* node);
   HYDROGEN_CONCRETE_INSTRUCTION_LIST(DECLARE_DO)
 #undef DECLARE_DO
 
   static HValue* SimplifiedDivisorForMathFloorOfDiv(HValue* val);
 
   LInstruction* DoMathFloor(HUnaryMathOperation* instr);
   LInstruction* DoMathRound(HUnaryMathOperation* instr);
   LInstruction* DoMathAbs(HUnaryMathOperation* instr);
@@ skipping 137 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(LChunkBuilder);
 };
 
 #undef DECLARE_HYDROGEN_ACCESSOR
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::int
 
 #endif  // V8_X64_LITHIUM_X64_H_