[turbofan] Move graph trimming functionality to dedicated GraphTrimmer.

src/compiler/graph-trimmer.h

+// Copyright 2015 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_GRAPH_TRIMMER_H_
+#define V8_COMPILER_GRAPH_TRIMMER_H_
+
+#include "src/compiler/node-marker.h"
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+// Forward declarations.
+class Graph;
+
+
+// Trims dead nodes from the node graph.
+class GraphTrimmer final {
+ public:
+  GraphTrimmer(Zone* zone, Graph* graph);
+  ~GraphTrimmer();
+
+  // Trim nodes in the {graph} that are not reachable from {graph->end()}.
+  void TrimGraph();
+
+  // Trim nodes in the {graph} that are not reachable from either {graph->end()}
+  // or any of the roots in the sequence [{begin},{end}[.
+  template <typename ForwardIterator>
+  void TrimGraph(ForwardIterator begin, ForwardIterator end) {
+    while (begin != end) MarkAsLive(*begin++);
+    TrimGraph();
+  }
+
+ private:
+  V8_INLINE bool IsLive(Node* const node) { return is_live_.Get(node); }
+  V8_INLINE void MarkAsLive(Node* const node) {
+    if (!node->IsDead() && !IsLive(node)) {
+      is_live_.Set(node, true);
+      live_.push_back(node);
+    }
+  }
+
+  Graph* graph() const { return graph_; }
+
+  Graph* const graph_;
+  NodeMarker<bool> is_live_;
+  NodeVector live_;
+
+  DISALLOW_COPY_AND_ASSIGN(GraphTrimmer);
+};
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_COMPILER_GRAPH_TRIMMER_H_