Introduce "optimized_out" oddball marker for compilers.

src/runtime/runtime-debug.cc

 // 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.
 
 #include "src/runtime/runtime-utils.h"
 
 #include "src/arguments.h"
 #include "src/debug/debug.h"
 #include "src/debug/debug-evaluate.h"
 #include "src/debug/debug-frames.h"
@@ skipping 536 matching lines @@
   Handle<FixedArray> locals =
       isolate->factory()->NewFixedArray(local_count * 2);
 
   // Fill in the values of the locals.
   int local = 0;
   int i = 0;
   for (; i < scope_info->StackLocalCount(); ++i) {
     // Use the value from the stack.
     if (scope_info->LocalIsSynthetic(i)) continue;
     locals->set(local * 2, scope_info->LocalName(i));
-    locals->set(local * 2 + 1, *(frame_inspector.GetExpression(i)));
+    Handle<Object> value = frame_inspector.GetExpression(i);
+    // TODO(yangguo): We convert optimized out values to {undefined} when they
+    // are passed to the debugger. Eventually we should handle them somehow.
+    if (value->IsOptimizedOut()) value = isolate->factory()->undefined_value();
+    locals->set(local * 2 + 1, *value);
     local++;
   }
   if (local < local_count) {
     // Get the context containing declarations.
     Handle<Context> context(
         Handle<Context>::cast(frame_inspector.GetContext())->closure_context());
     for (; i < scope_info->LocalCount(); ++i) {
       if (scope_info->LocalIsSynthetic(i)) continue;
       Handle<String> name(scope_info->LocalName(i));
       VariableMode mode;
@@ skipping 1080 matching lines @@
   return Smi::FromInt(isolate->debug()->is_active());
 }
 
 
 RUNTIME_FUNCTION(Runtime_DebugBreakInOptimizedCode) {
   UNIMPLEMENTED();
   return NULL;
 }
 }  // namespace internal
 }  // namespace v8