When a value has been optimized away by the compiler, set its value to

runtime/vm/symbols.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_SYMBOLS_H_
 #define VM_SYMBOLS_H_
 
 #include "vm/object.h"
 #include "vm/snapshot_ids.h"
 
@@ skipping 270 matching lines @@
   V(_LocalLibraryMirrorImpl, "_LocalLibraryMirrorImpl")                        \
   V(_LocalMethodMirrorImpl, "_LocalMethodMirrorImpl")                          \
   V(_LocalVariableMirrorImpl, "_LocalVariableMirrorImpl")                      \
   V(_LocalParameterMirrorImpl, "_LocalParameterMirrorImpl")                    \
   V(_LocalIsolateMirrorImpl, "_LocalIsolateMirrorImpl")                        \
   V(_LocalMirrorSystemImpl, "_LocalMirrorSystemImpl")                          \
   V(_LocalTypedefMirrorImpl, "_LocalTypedefMirrorImpl")                        \
   V(_LocalTypeVariableMirrorImpl, "_LocalTypeVariableMirrorImpl")              \
   V(hashCode, "get:hashCode")                                                  \
   V(_leftShiftWithMask32, "_leftShiftWithMask32")                              \
+  V(OptimizedOut, "<optimized out>")                                           \
 
 
 // Contains a list of frequently used strings in a canonicalized form. This
 // list is kept in the vm_isolate in order to share the copy across isolates
 // without having to maintain copies in each isolate.
 class Symbols : public AllStatic {
  public:
   enum { kMaxOneCharCodeSymbol = 0xFF };
 
   // List of strings that are pre created in the vm isolate.
@@ skipping 188 matching lines @@
   friend class SnapshotReader;
   friend class SnapshotWriter;
   friend class ApiMessageReader;
 
   DISALLOW_COPY_AND_ASSIGN(Symbols);
 };
 
 }  // namespace dart
 
 #endif  // VM_SYMBOLS_H_