Introduce "optimized_out" oddball marker for compilers.

src/compiler/js-graph.h

 // Copyright 2014 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_COMPILER_JS_GRAPH_H_
 #define V8_COMPILER_JS_GRAPH_H_
 
 #include "src/compiler/common-node-cache.h"
 #include "src/compiler/common-operator.h"
 #include "src/compiler/graph.h"
@@ skipping 23 matching lines @@
         javascript_(javascript),
         simplified_(simplified),
         machine_(machine),
         cache_(zone()) {
     for (int i = 0; i < kNumCachedNodes; i++) cached_nodes_[i] = nullptr;
   }
 
   // Canonicalized global constants.
   Node* CEntryStubConstant(int result_size);
   Node* EmptyFixedArrayConstant();
+  Node* OptimizedOutConstant();
   Node* UndefinedConstant();
   Node* TheHoleConstant();
   Node* TrueConstant();
   Node* FalseConstant();
   Node* NullConstant();
   Node* ZeroConstant();
   Node* OneConstant();
   Node* NaNConstant();
 
   // Creates a HeapConstant node, possibly canonicalized, and may access the
@@ skipping 75 matching lines @@
   Zone* zone() const { return graph()->zone(); }
   Isolate* isolate() const { return isolate_; }
   Factory* factory() const { return isolate()->factory(); }
 
   void GetCachedNodes(NodeVector* nodes);
 
  private:
   enum CachedNode {
     kCEntryStubConstant,
     kEmptyFixedArrayConstant,
+    kOptimizedOutConstant,
     kUndefinedConstant,
     kTheHoleConstant,
     kTrueConstant,
     kFalseConstant,
     kNullConstant,
     kZeroConstant,
     kOneConstant,
     kNaNConstant,
     kEmptyFrameState,
     kDead,
@@ skipping 12 matching lines @@
   Node* NumberConstant(double value);
 
   DISALLOW_COPY_AND_ASSIGN(JSGraph);
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif