TypeGraph: Introduce NodeTracker for efficient cycle detection

Added to Flattener and TypeIdentifier passes for now as a
proof-of-concept. Other passes can come later.

oi/type_graph/Flattener.cpp

@@ -22,26 +22,19 @@ namespace type_graph {
 
 Pass Flattener::createPass() {
   auto fn = [](TypeGraph& typeGraph) {
-    Flattener flattener;
-    flattener.flatten(typeGraph.rootTypes());
-    // TODO should flatten just operate on a single type and we do the looping
-    // here?
+    Flattener flattener{typeGraph.resetTracker()};
+    for (auto& type : typeGraph.rootTypes()) {
+      flattener.accept(type);
+    }
   };
 
   return Pass("Flattener", fn);
 }
 
-void Flattener::flatten(std::vector<std::reference_wrapper<Type>>& types) {
-  for (auto& type : types) {
-    accept(type);
-  }
-}
-
 void Flattener::accept(Type& type) {
-  if (visited_.count(&type) != 0)
+  if (tracker_.visit(type))
     return;
 
-  visited_.insert(&type);
   type.accept(*this);
 }
 

oi/type_graph/Flattener.h

@@ -16,9 +16,9 @@
 #pragma once
 
 #include <string>
-#include <unordered_set>
 #include <vector>
 
+#include "NodeTracker.h"
 #include "PassManager.h"
 #include "Types.h"
 #include "Visitor.h"
@@ -28,14 +28,15 @@ namespace type_graph {
 /*
  * Flattener
  *
- * Flattens classes by removing parents and adding their members directly into
- * derived classes.
+ * Flattens classes by removing parents and adding their attributes directly
+ * into derived classes.
  */
 class Flattener : public RecursiveVisitor {
  public:
   static Pass createPass();
 
-  void flatten(std::vector<std::reference_wrapper<Type>>& types);
+  Flattener(NodeTracker& tracker) : tracker_(tracker) {
+  }
 
   using RecursiveVisitor::accept;
 
@@ -46,7 +47,7 @@ class Flattener : public RecursiveVisitor {
   static const inline std::string ParentPrefix = "__oi_parent";
 
  private:
-  std::unordered_set<Type*> visited_;
+  NodeTracker& tracker_;
   std::vector<Member> flattened_members_;
   std::vector<uint64_t> offset_stack_;
 };

oi/type_graph/NodeTracker.h

@@ -0,0 +1,70 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#pragma once
+
+#include <vector>
+
+#include "Types.h"
+
+namespace type_graph {
+
+/*
+ * NodeTracker
+ *
+ * Helper class for visitors. Efficiently tracks whether or not a graph node has
+ * been seen before, to avoid infinite looping on cycles.
+ */
+class NodeTracker {
+ public:
+  NodeTracker() = default;
+  NodeTracker(size_t size) : visited_(size) {
+  }
+
+  /*
+   * visit
+   *
+   * Marks a given node as visited.
+   * Returns true if this node has already been visited, false otherwise.
+   */
+  bool visit(const Type& type) {
+    auto id = type.id();
+    if (id < 0)
+      return false;
+    if (visited_.size() <= static_cast<size_t>(id))
+      visited_.resize(id + 1);
+    bool result = visited_[id];
+    visited_[id] = true;
+    return result;
+  }
+
+  /*
+   * reset
+   *
+   * Clears the contents of this NodeTracker and marks every node as unvisited.
+   */
+  void reset() {
+    std::fill(visited_.begin(), visited_.end(), false);
+  }
+
+  void resize(size_t size) {
+    visited_.resize(size);
+  }
+
+ private:
+  std::vector<bool> visited_;
+};
+
+}  // namespace type_graph

oi/type_graph/TypeGraph.cpp

@@ -17,6 +17,12 @@
 
 namespace type_graph {
 
+NodeTracker& TypeGraph::resetTracker() noexcept {
+  tracker_.reset();
+  tracker_.resize(size());
+  return tracker_;
+}
+
 template <>
 Primitive& TypeGraph::makeType<Primitive>(Primitive::Kind kind) {
   switch (kind) {

oi/type_graph/TypeGraph.h

@@ -19,6 +19,7 @@
 #include <memory>
 #include <vector>
 
+#include "NodeTracker.h"
 #include "Types.h"
 
 namespace type_graph {
@@ -47,6 +48,8 @@ class TypeGraph {
     rootTypes_.push_back(type);
   }
 
+  NodeTracker& resetTracker() noexcept;
+
   // Override of the generic makeType function that returns singleton Primitive
   // objects
   template <typename T>
@@ -83,6 +86,7 @@ class TypeGraph {
   std::vector<std::reference_wrapper<Type>> rootTypes_;
   // Store all type objects in vectors for ownership. Order is not significant.
   std::vector<std::unique_ptr<Type>> types_;
+  NodeTracker tracker_;
   NodeId next_id_ = 0;
 };
 

oi/type_graph/TypeIdentifier.cpp

@@ -23,7 +23,8 @@ namespace type_graph {
 Pass TypeIdentifier::createPass(
     const std::vector<ContainerInfo>& passThroughTypes) {
   auto fn = [&passThroughTypes](TypeGraph& typeGraph) {
-    TypeIdentifier typeId{typeGraph, passThroughTypes};
+    TypeIdentifier typeId{typeGraph.resetTracker(), typeGraph,
+                          passThroughTypes};
     for (auto& type : typeGraph.rootTypes()) {
       typeId.accept(type);
     }
@@ -48,10 +49,9 @@ bool TypeIdentifier::isAllocator(Type& t) {
 }
 
 void TypeIdentifier::accept(Type& type) {
-  if (visited_.count(&type) != 0)
+  if (tracker_.visit(type))
     return;
 
-  visited_.insert(&type);
   type.accept(*this);
 }
 

oi/type_graph/TypeIdentifier.h

@@ -15,10 +15,9 @@
  */
 #pragma once
 
-#include <array>
-#include <unordered_set>
 #include <vector>
 
+#include "NodeTracker.h"
 #include "PassManager.h"
 #include "Types.h"
 #include "Visitor.h"
@@ -38,9 +37,12 @@ class TypeIdentifier : public RecursiveVisitor {
   static Pass createPass(const std::vector<ContainerInfo>& passThroughTypes);
   static bool isAllocator(Type& t);
 
-  TypeIdentifier(TypeGraph& typeGraph,
+  TypeIdentifier(NodeTracker& tracker,
+                 TypeGraph& typeGraph,
                  const std::vector<ContainerInfo>& passThroughTypes)
-      : typeGraph_(typeGraph), passThroughTypes_(passThroughTypes) {
+      : tracker_(tracker),
+        typeGraph_(typeGraph),
+        passThroughTypes_(passThroughTypes) {
   }
 
   using RecursiveVisitor::accept;
@@ -49,7 +51,7 @@ class TypeIdentifier : public RecursiveVisitor {
   void visit(Container& c) override;
 
  private:
-  std::unordered_set<Type*> visited_;
+  NodeTracker& tracker_;
   TypeGraph& typeGraph_;
   const std::vector<ContainerInfo>& passThroughTypes_;
 };