[ADT] Add a generic breadth-first-search graph iterator.

This will be used in LCSSA to speed up the canonicalization.

Differential Revision:  https://reviews.llvm.org/D31694

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@299660 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/BreadthFirstIterator.h

@@ -0,0 +1,165 @@
+//===- llvm/ADT/BreadthFirstIterator.h - Breadth First iterator -*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file builds on the ADT/GraphTraits.h file to build a generic breadth
+// first graph iterator.  This file exposes the following functions/types:
+//
+// bf_begin/bf_end/bf_iterator
+//   * Normal breadth-first iteration - visit a graph level-by-level.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_BREADTHFIRSTITERATOR_H
+#define LLVM_ADT_BREADTHFIRSTITERATOR_H
+
+#include "llvm/ADT/GraphTraits.h"
+#include "llvm/ADT/None.h"
+#include "llvm/ADT/Optional.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/iterator_range.h"
+#include <iterator>
+#include <queue>
+#include <set>
+#include <utility>
+
+namespace llvm {
+
+// bf_iterator_storage - A private class which is used to figure out where to
+// store the visited set. We only provide a non-external variant for now.
+template <class SetType> class bf_iterator_storage {
+public:
+  SetType Visited;
+};
+
+// The visited state for the iteration is a simple set.
+template <typename NodeRef, unsigned SmallSize = 8>
+using bf_iterator_default_set = SmallPtrSet<NodeRef, SmallSize>;
+
+// Generic Breadth first search iterator.
+template <class GraphT,
+          class SetType =
+              bf_iterator_default_set<typename GraphTraits<GraphT>::NodeRef>,
+          class GT = GraphTraits<GraphT>>
+class bf_iterator
+    : public std::iterator<std::forward_iterator_tag, typename GT::NodeRef>,
+      public bf_iterator_storage<SetType> {
+  typedef std::iterator<std::forward_iterator_tag, typename GT::NodeRef> super;
+
+  typedef typename GT::NodeRef NodeRef;
+  typedef typename GT::ChildIteratorType ChildItTy;
+
+  // First element is the node reference, second is the next child to visit.
+  typedef std::pair<NodeRef, Optional<ChildItTy>> QueueElement;
+
+  // Visit queue - used to maintain BFS ordering.
+  // Optional<> because we need markers for levels.
+  std::queue<Optional<QueueElement>> VisitQueue;
+
+  // Current level.
+  unsigned Level;
+
+private:
+  inline bf_iterator(NodeRef Node) {
+    this->Visited.insert(Node);
+    Level = 0;
+
+    // Also, insert a dummy node as marker.
+    VisitQueue.push(QueueElement(Node, None));
+    VisitQueue.push(None);
+  }
+
+  inline bf_iterator() = default;
+
+  inline void toNext() {
+    Optional<QueueElement> Head = VisitQueue.front();
+    QueueElement H = Head.getValue();
+    NodeRef Node = H.first;
+    Optional<ChildItTy> &ChildIt = H.second;
+
+    if (!ChildIt)
+      ChildIt.emplace(GT::child_begin(Node));
+    while (*ChildIt != GT::child_end(Node)) {
+      NodeRef Next = *(*ChildIt)++;
+
+      // Already visited?
+      if (this->Visited.insert(Next).second)
+        VisitQueue.push(QueueElement(Next, None));
+    }
+    VisitQueue.pop();
+
+    // Go to the next element skipping markers if needed.
+    if (!VisitQueue.empty()) {
+      Head = VisitQueue.front();
+      if (Head != None)
+        return;
+      Level += 1;
+      VisitQueue.pop();
+
+      // Don't push another marker if this is the last
+      // element.
+      if (!VisitQueue.empty())
+        VisitQueue.push(None);
+    }
+  }
+
+public:
+  typedef typename super::pointer pointer;
+
+  // Provide static begin and end methods as our public "constructors"
+  static bf_iterator begin(const GraphT &G) {
+    return bf_iterator(GT::getEntryNode(G));
+  }
+
+  static bf_iterator end(const GraphT &G) { return bf_iterator(); }
+
+  bool operator==(const bf_iterator &RHS) const {
+    assert(VisitQueue.size() == 0);
+    return VisitQueue == RHS.VisitQueue;
+  }
+
+  bool operator!=(const bf_iterator &RHS) const { return !(*this == RHS); }
+
+  const NodeRef &operator*() const { return VisitQueue.front()->first; }
+
+  // This is a nonstandard operator-> that dereferenfces the pointer an extra
+  // time so that you can actually call methods on the node, because the
+  // contained type is a pointer.
+  NodeRef operator->() const { return **this; }
+
+  bf_iterator &operator++() { // Pre-increment
+    toNext();
+    return *this;
+  }
+
+  bf_iterator operator++(int) { // Post-increment
+    bf_iterator ItCopy = *this;
+    ++*this;
+    return ItCopy;
+  }
+
+  unsigned getLevel() const { return Level; }
+};
+
+// Provide global constructors that automatically figure out correct types.
+template <class T> bf_iterator<T> bf_begin(const T &G) {
+  return bf_iterator<T>::begin(G);
+}
+
+template <class T> bf_iterator<T> bf_end(const T &G) {
+  return bf_iterator<T>::end(G);
+}
+
+// Provide an accessor method to use them in range-based patterns.
+template <class T> iterator_range<bf_iterator<T>> breadth_first(const T &G) {
+  return make_range(bf_begin(G), bf_end(G));
+}
+
+} // end namespace llvm
+
+#endif // LLVM_ADT_BREADTHFIRSTITERATOR_H

unittests/ADT/BreadthFirstIteratorTest.cpp

@@ -0,0 +1,74 @@
+//=== llvm/unittest/ADT/BreadthFirstIteratorTest.cpp - BFS iterator tests -===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/BreadthFirstIterator.h"
+#include "TestGraph.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace llvm {
+
+TEST(BreadthFristIteratorTest, Basic) {
+  typedef bf_iterator<Graph<4>> BFIter;
+
+  Graph<4> G;
+  G.AddEdge(0, 1);
+  G.AddEdge(0, 2);
+  G.AddEdge(1, 3);
+
+  auto It = BFIter::begin(G);
+  auto End = BFIter::end(G);
+  EXPECT_EQ(It.getLevel(), 0U);
+  EXPECT_EQ(*It, G.AccessNode(0));
+  ++It;
+  EXPECT_EQ(It.getLevel(), 1U);
+  EXPECT_EQ(*It, G.AccessNode(1));
+  ++It;
+  EXPECT_EQ(It.getLevel(), 1U);
+  EXPECT_EQ(*It, G.AccessNode(2));
+  ++It;
+  EXPECT_EQ(It.getLevel(), 2U);
+  EXPECT_EQ(*It, G.AccessNode(3));
+  ++It;
+  EXPECT_EQ(It, End);
+}
+
+TEST(BreadthFristIteratorTest, Cycle) {
+  typedef bf_iterator<Graph<4>> BFIter;
+
+  Graph<4> G;
+  G.AddEdge(0, 1);
+  G.AddEdge(1, 0);
+  G.AddEdge(1, 2);
+  G.AddEdge(2, 1);
+  G.AddEdge(2, 1);
+  G.AddEdge(2, 3);
+  G.AddEdge(3, 2);
+  G.AddEdge(3, 1);
+  G.AddEdge(3, 0);
+
+  auto It = BFIter::begin(G);
+  auto End = BFIter::end(G);
+  EXPECT_EQ(It.getLevel(), 0U);
+  EXPECT_EQ(*It, G.AccessNode(0));
+  ++It;
+  EXPECT_EQ(It.getLevel(), 1U);
+  EXPECT_EQ(*It, G.AccessNode(1));
+  ++It;
+  EXPECT_EQ(It.getLevel(), 2U);
+  EXPECT_EQ(*It, G.AccessNode(2));
+  ++It;
+  EXPECT_EQ(It.getLevel(), 3U);
+  EXPECT_EQ(*It, G.AccessNode(3));
+  ++It;
+  EXPECT_EQ(It, End);
+}
+
+} // end namespace llvm

unittests/ADT/CMakeLists.txt

@@ -9,6 +9,7 @@ set(ADTSources
   ArrayRefTest.cpp
   BitmaskEnumTest.cpp
   BitVectorTest.cpp
+  BreadthFirstIteratorTest.cpp
   BumpPtrListTest.cpp
   DAGDeltaAlgorithmTest.cpp
   DeltaAlgorithmTest.cpp