Introduce "optimized_out" oddball marker for compilers.

src/crankshaft/hydrogen.h

 // Copyright 2012 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_CRANKSHAFT_HYDROGEN_H_
 #define V8_CRANKSHAFT_HYDROGEN_H_
 
 #include "src/accessors.h"
 #include "src/allocation.h"
 #include "src/ast/ast.h"
@@ skipping 316 matching lines @@
 
   HConstant* GetConstantUndefined();
   HConstant* GetConstant0();
   HConstant* GetConstant1();
   HConstant* GetConstantMinus1();
   HConstant* GetConstantTrue();
   HConstant* GetConstantFalse();
   HConstant* GetConstantBool(bool value);
   HConstant* GetConstantHole();
   HConstant* GetConstantNull();
+  HConstant* GetConstantOptimizedOut();
   HConstant* GetInvalidContext();
 
   bool IsConstantUndefined(HConstant* constant);
   bool IsConstant0(HConstant* constant);
   bool IsConstant1(HConstant* constant);
   bool IsConstantMinus1(HConstant* constant);
   bool IsConstantTrue(HConstant* constant);
   bool IsConstantFalse(HConstant* constant);
   bool IsConstantHole(HConstant* constant);
   bool IsConstantNull(HConstant* constant);
@@ skipping 118 matching lines @@
   ZoneList<HPhi*>* phi_list_;
   ZoneList<HInstruction*>* uint32_instructions_;
   SetOncePointer<HConstant> constant_undefined_;
   SetOncePointer<HConstant> constant_0_;
   SetOncePointer<HConstant> constant_1_;
   SetOncePointer<HConstant> constant_minus1_;
   SetOncePointer<HConstant> constant_true_;
   SetOncePointer<HConstant> constant_false_;
   SetOncePointer<HConstant> constant_the_hole_;
   SetOncePointer<HConstant> constant_null_;
+  SetOncePointer<HConstant> constant_optimized_out_;
   SetOncePointer<HConstant> constant_invalid_context_;
 
   HOsrBuilder* osr_;
 
   CompilationInfo* info_;
   CallInterfaceDescriptor descriptor_;
   Zone* zone_;
 
   bool use_optimistic_licm_;
   bool depends_on_empty_array_proto_elements_;
@@ skipping 2570 matching lines @@
   }
 
  private:
   HOptimizedGraphBuilder* builder_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_CRANKSHAFT_HYDROGEN_H_