[turbofan] New GraphReducer based LoadElimination.

src/compiler/load-elimination.h

 // 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_LOAD_ELIMINATION_H_
 #define V8_COMPILER_LOAD_ELIMINATION_H_
 
+#include "src/compiler/graph-reducer.h"
+
 namespace v8 {
 namespace internal {
-
-// Forward declarations.
-class Zone;
-
 namespace compiler {
 
-// Forward declarations.
-class Graph;
+// Foward declarations.
+struct FieldAccess;
 
-// Eliminates redundant loads via scalar replacement of aggregates.
-class LoadElimination final {
+class LoadElimination final : public AdvancedReducer {
  public:
-  LoadElimination(Graph* graph, Zone* zone) : graph_(graph), zone_(zone) {}
+  LoadElimination(Editor* editor, Zone* zone)
+      : AdvancedReducer(editor), node_states_(zone) {}
+  ~LoadElimination() final {}
 
-  void Run();
+  Reduction Reduce(Node* node) final;
 
  private:
-  Graph* graph() const { return graph_; }
-  Zone* zone() const { return zone_; }
+  static const size_t kMaxTrackedElements = 8;
 
-  Graph* const graph_;
-  Zone* const zone_;
+  // Abstract state to approximate the current state of an element along the
+  // effect paths through the graph.
+  class AbstractElements final : public ZoneObject {
+   public:
+    explicit AbstractElements(Zone* zone) {
+      for (size_t i = 0; i < arraysize(elements_); ++i) {
+        elements_[i] = Element();
+      }
+    }
+    AbstractElements(Node* object, Node* index, Node* value, Zone* zone)
+        : AbstractElements(zone) {
+      elements_[next_index_++] = Element(object, index, value);
+    }
+
+    AbstractElements const* Extend(Node* object, Node* index, Node* value,
+                                   Zone* zone) const {
+      AbstractElements* that = new (zone) AbstractElements(*this);
+      that->elements_[that->next_index_] = Element(object, index, value);
+      that->next_index_ = (that->next_index_ + 1) % arraysize(elements_);
+      return that;
+    }
+    Node* Lookup(Node* object, Node* index) const;
+    AbstractElements const* Kill(Node* object, Node* index, Zone* zone) const;
+    bool Equals(AbstractElements const* that) const;
+    AbstractElements const* Merge(AbstractElements const* that,
+                                  Zone* zone) const;
+
+   private:
+    struct Element {
+      Element() {}
+      Element(Node* object, Node* index, Node* value)
+          : object(object), index(index), value(value) {}
+
+      Node* object = nullptr;
+      Node* index = nullptr;
+      Node* value = nullptr;
+    };
+
+    Element elements_[kMaxTrackedElements];
+    size_t next_index_ = 0;
+  };
+
+  // Abstract state to approximate the current state of a certain field along
+  // the effect paths through the graph.
+  class AbstractField final : public ZoneObject {
+   public:
+    explicit AbstractField(Zone* zone) : info_for_node_(zone) {}
+    AbstractField(Node* object, Node* value, Zone* zone)
+        : info_for_node_(zone) {
+      info_for_node_.insert(std::make_pair(object, value));
+    }
+
+    AbstractField const* Extend(Node* object, Node* value, Zone* zone) const {
+      AbstractField* that = new (zone) AbstractField(zone);
+      that->info_for_node_ = this->info_for_node_;
+      that->info_for_node_.insert(std::make_pair(object, value));
+      return that;
+    }
+    Node* Lookup(Node* object) const;
+    AbstractField const* Kill(Node* object, Zone* zone) const;
+    bool Equals(AbstractField const* that) const {
+      return this == that || this->info_for_node_ == that->info_for_node_;
+    }
+    AbstractField const* Merge(AbstractField const* that, Zone* zone) const {
+      if (this->Equals(that)) return this;
+      AbstractField* copy = new (zone) AbstractField(zone);
+      for (auto this_it : this->info_for_node_) {
+        Node* this_object = this_it.first;
+        Node* this_value = this_it.second;
+        auto that_it = that->info_for_node_.find(this_object);
+        if (that_it != that->info_for_node_.end() &&
+            that_it->second == this_value) {
+          copy->info_for_node_.insert(this_it);
+        }
+      }
+      return copy;
+    }
+
+   private:
+    ZoneMap<Node*, Node*> info_for_node_;
+  };
+
+  static size_t const kMaxTrackedFields = 16;
+
+  class AbstractState final : public ZoneObject {
+   public:
+    AbstractState() {
+      for (size_t i = 0; i < arraysize(fields_); ++i) {
+        fields_[i] = nullptr;
+      }
+    }
+
+    bool Equals(AbstractState const* that) const;
+    void Merge(AbstractState const* that, Zone* zone);
+
+    AbstractState const* AddField(Node* object, size_t index, Node* value,
+                                  Zone* zone) const;
+    AbstractState const* KillField(Node* object, size_t index,
+                                   Zone* zone) const;
+    Node* LookupField(Node* object, size_t index) const;
+
+    AbstractState const* AddElement(Node* object, Node* index, Node* value,
+                                    Zone* zone) const;
+    AbstractState const* KillElement(Node* object, Node* index,
+                                     Zone* zone) const;
+    Node* LookupElement(Node* object, Node* index) const;
+
+   private:
+    AbstractElements const* elements_ = nullptr;
+    AbstractField const* fields_[kMaxTrackedFields];
+  };
+
+  class AbstractStateForEffectNodes final : public ZoneObject {
+   public:
+    explicit AbstractStateForEffectNodes(Zone* zone) : info_for_node_(zone) {}
+    AbstractState const* Get(Node* node) const;
+    void Set(Node* node, AbstractState const* state);
+
+    Zone* zone() const { return info_for_node_.get_allocator().zone(); }
+
+   private:
+    ZoneVector<AbstractState const*> info_for_node_;
+  };
+
+  Reduction ReduceLoadField(Node* node);
+  Reduction ReduceStoreField(Node* node);
+  Reduction ReduceLoadElement(Node* node);
+  Reduction ReduceStoreElement(Node* node);
+  Reduction ReduceEffectPhi(Node* node);
+  Reduction ReduceStart(Node* node);
+  Reduction ReduceOtherNode(Node* node);
+
+  Reduction UpdateState(Node* node, AbstractState const* state);
+
+  AbstractState const* ComputeLoopState(Node* node,
+                                        AbstractState const* state) const;
+
+  static int FieldIndexOf(FieldAccess const& access);
+
+  AbstractState const* empty_state() const { return &empty_state_; }
+  Zone* zone() const { return node_states_.zone(); }
+
+  AbstractState const empty_state_;
+  AbstractStateForEffectNodes node_states_;
+
+  DISALLOW_COPY_AND_ASSIGN(LoadElimination);
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_LOAD_ELIMINATION_H_