[turbofan] Avoid unnecessary copying of nodes during inlining.

src/compiler/graph.h

Index: src/compiler/graph.h
diff --git a/src/compiler/graph.h b/src/compiler/graph.h
index 958a15d282c01b03ad7402b97e89e937541800a0..a694a0b414a578b24b9e0f4f2cc6edb29c8472c6 100644
--- a/src/compiler/graph.h
+++ b/src/compiler/graph.h
@@ -28,11 +28,30 @@ typedef uint32_t Mark;
 // out-of-line data associated with each node.
 typedef uint32_t NodeId;
 
-
-class Graph : public ZoneObject {
+class Graph final : public ZoneObject {
  public:
   explicit Graph(Zone* zone);
 
+  // Scope used when creating a subgraph for inlining. Automatically preserves
+  // the original start and end nodes of the graph, and resets them when you
+  // leave the scope.
+  class SubgraphScope final {
+   public:
+    explicit SubgraphScope(Graph* graph)
+        : graph_(graph), start_(graph->start()), end_(graph->end()) {}
+    ~SubgraphScope() {
+      graph_->SetStart(start_);
+      graph_->SetEnd(end_);
+    }
+
+   private:
+    Graph* const graph_;
+    Node* const start_;
+    Node* const end_;
+
+    DISALLOW_COPY_AND_ASSIGN(SubgraphScope);
+  };
+
   // Base implementation used by all factory methods.
   Node* NewNodeUnchecked(const Operator* op, int input_count,
                          Node* const* inputs, bool incomplete = false);