[turbofan] Initial version of RedundancyElimination.

src/compiler/redundancy-elimination.h

Index: src/compiler/redundancy-elimination.h
diff --git a/src/compiler/redundancy-elimination.h b/src/compiler/redundancy-elimination.h
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+++ b/src/compiler/redundancy-elimination.h
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+// Copyright 2016 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_REDUNDANCY_ELIMINATION_H_
+#define V8_COMPILER_REDUNDANCY_ELIMINATION_H_
+
+#include "src/compiler/graph-reducer.h"
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+class RedundancyElimination final : public AdvancedReducer {
+ public:
+  RedundancyElimination(Editor* editor, Zone* zone);
+  ~RedundancyElimination() final;
+
+  Reduction Reduce(Node* node) final;
+
+ private:
+  struct Check {
+    Check(Node* node, Check* next) : node(node), next(next) {}
+    Node* node;
+    Check* next;
+  };
+
+  class EffectPathChecks final {
+   public:
+    static EffectPathChecks* Copy(Zone* zone, EffectPathChecks const* checks);
+    static EffectPathChecks const* Empty(Zone* zone);
+    void Merge(EffectPathChecks const* that);
+
+    EffectPathChecks const* AddCheck(Zone* zone, Node* node) const;
+    Node* LookupCheck(Node* node) const;
+
+   private:
+    EffectPathChecks(Check* head, size_t size) : head_(head), size_(size) {}
+
+    // We keep track of the list length so that we can find the longest
+    // common tail easily.
+    Check* head_;
+    size_t size_;
+  };
+
+  class PathChecksForEffectNodes final {
+   public:
+    explicit PathChecksForEffectNodes(Zone* zone) : info_for_node_(zone) {}
+    EffectPathChecks const* Get(Node* node) const;
+    void Set(Node* node, EffectPathChecks const* checks);
+
+   private:
+    ZoneVector<EffectPathChecks const*> info_for_node_;
+  };
+
+  Reduction ReduceCheckNode(Node* node);
+  Reduction ReduceEffectPhi(Node* node);
+  Reduction ReduceStart(Node* node);
+  Reduction ReduceOtherNode(Node* node);
+
+  Reduction TakeChecksFromFirstEffect(Node* node);
+  Reduction UpdateChecks(Node* node, EffectPathChecks const* checks);
+
+  Zone* zone() const { return zone_; }
+
+  PathChecksForEffectNodes node_checks_;
+  Zone* const zone_;
+
+  DISALLOW_COPY_AND_ASSIGN(RedundancyElimination);
+};
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_COMPILER_REDUNDANCY_ELIMINATION_H_