[turbofan] Nodes are killed by resetting all their inputs to zero.

src/compiler/node.h

 // Copyright 2013 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_NODE_H_
 #define V8_COMPILER_NODE_H_
 
 #include <deque>
 #include <set>
 #include <vector>
@@ skipping 35 matching lines @@
 // inherited from Vector, Nodes only contain a mutable Operator that may change
 // during compilation, e.g. during lowering passes.  Other information that
 // needs to be associated with Nodes during compilation must be stored
 // out-of-line indexed by the Node's id.
 class Node FINAL : public GenericNode<NodeData, Node> {
  public:
   Node(GenericGraphBase* graph, int input_count)
       : GenericNode<NodeData, Node>(graph, input_count) {}
 
   void Initialize(const Operator* op) { set_op(op); }
+
+  bool IsDead() const { return InputCount() > 0 && InputAt(0) == NULL; }
   void Kill();
 
   void CollectProjections(ZoneVector<Node*>* projections);
   Node* FindProjection(int32_t projection_index);
 };
 
 OStream& operator<<(OStream& os, const Node& n);
 
 typedef GenericGraphVisit::NullNodeVisitor<NodeData, Node> NullNodeVisitor;
 
@@ skipping 16 matching lines @@
 template <typename T>
 static inline T OpParameter(const Node* node) {
   return OpParameter<T>(node->op());
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_NODE_H_