[turbofan] Introduce DeadValue and DeadEffect operators.

src/compiler/js-graph.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/code-stubs.h"
 #include "src/compiler/js-graph.h"
 #include "src/compiler/node-properties.h"
 #include "src/compiler/typer.h"
 
 namespace v8 {
@@ skipping 185 matching lines @@
         common()->FrameState(JS_FRAME, BailoutId::None(),
                              OutputFrameStateCombine::Ignore()),
         state_values, state_values, state_values, NoContextConstant(),
         UndefinedConstant(), graph()->start());
     cached_nodes_[kEmptyFrameState] = empty_frame_state;
   }
   return empty_frame_state;
 }
 
 
+Node* JSGraph::DeadValue() {
+  return CACHED(kDeadValue, graph()->NewNode(common()->DeadValue()));
+}
+
+
 Node* JSGraph::DeadControl() {
   return CACHED(kDeadControl, graph()->NewNode(common()->Dead()));
 }
 
 
 void JSGraph::GetCachedNodes(NodeVector* nodes) {
   cache_.GetCachedNodes(nodes);
   for (size_t i = 0; i < arraysize(cached_nodes_); i++) {
     if (Node* node = cached_nodes_[i]) {
       if (!node->IsDead()) nodes->push_back(node);
     }
   }
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8