ADT: Split out simple_ilist, a simple intrusive list

Split out a new, low-level intrusive list type with clear semantics.
Unlike iplist (and ilist), all operations on simple_ilist are intrusive,
and simple_ilist never takes ownership of its nodes.  This enables an
intuitive API that has the right defaults for intrusive lists.
- insert() takes references (not pointers!) to nodes (in iplist/ilist,
  passing a reference will cause the node to be copied).
- erase() takes only iterators (like std::list), and does not destroy
  the nodes.
- remove() takes only references and has the same behaviour as erase().
- clear() does not destroy the nodes.
- The destructor does not destroy the nodes.
- New API {erase,remove,clear}AndDispose() take an extra Disposer
  functor for callsites that want to call some disposal routine (e.g.,
  std::default_delete).

This list is not currently configurable, and has no callbacks.

The initial motivation was to fix iplist<>::sort to work correctly (even
with callbacks in ilist_traits<>).  iplist<> uses simple_ilist<>::sort
directly.  The new test in unittests/IR/ModuleTest.cpp crashes without
this commit.

Fixing sort() via a low-level layer provided a good opportunity to:
- Unit test the low-level functionality thoroughly.
- Modernize the API, largely inspired by other intrusive list
  implementations.

Here's a sketch of a longer-term plan:
- Create BumpPtrList<>, a non-intrusive list implemented using
  simple_ilist<>, and use it for the Token list in
  lib/Support/YAMLParser.cpp.  This will factor out the only real use of
  createNode().
- Evolve the iplist<> and ilist<> APIs in the direction of
  simple_ilist<>, making allocation/deallocation explicit at call sites
  (similar to simple_ilist<>::eraseAndDispose()).
- Factor out remaining calls to createNode() and deleteNode() and remove
  the customization from ilist_traits<>.
- Transition uses of iplist<>/ilist<> that don't need callbacks over to
  simple_ilist<>.

llvm-svn: 280107

9 files changed, 1018 insertions, 142 deletions

diff --git a/llvm/include/llvm/ADT/ilist.h b/llvm/include/llvm/ADT/ilist.h
index 5c031a832f7..137d4ec4146 100644
--- a/llvm/include/llvm/ADT/ilist.h
+++ b/llvm/include/llvm/ADT/ilist.h
@@ -24,11 +24,8 @@
 #ifndef LLVM_ADT_ILIST_H
 #define LLVM_ADT_ILIST_H
 
-#include "llvm/ADT/ilist_base.h"
-#include "llvm/ADT/ilist_iterator.h"
-#include "llvm/ADT/ilist_node.h"
+#include "llvm/ADT/simple_ilist.h"
 #include "llvm/Support/Compiler.h"
-#include <algorithm>
 #include <cassert>
 #include <cstddef>
 #include <iterator>
@@ -119,17 +116,14 @@ struct ilist_traits<const Ty> : public ilist_traits<Ty> {};
 /// ilist_sentinel, which holds pointers to the first and last nodes in the
 /// list.
 template <typename NodeTy, typename Traits = ilist_traits<NodeTy>>
-class iplist : public Traits, ilist_base, ilist_node_access {
+class iplist : public Traits, simple_ilist<NodeTy> {
   // TODO: Drop this assertion and the transitive type traits anytime after
   // v4.0 is branched (i.e,. keep them for one release to help out-of-tree code
   // update).
   static_assert(!ilist_detail::HasObsoleteCustomization<Traits, NodeTy>::value,
                 "ilist customization points have changed!");
 
-  ilist_sentinel<NodeTy> Sentinel;
-
-  typedef ilist_node<NodeTy> node_type;
-  typedef const ilist_node<NodeTy> const_node_type;
+  typedef simple_ilist<NodeTy> base_list_type;
 
   static bool op_less(NodeTy &L, NodeTy &R) { return L < R; }
   static bool op_equal(NodeTy &L, NodeTy &R) { return L == R; }
@@ -139,65 +133,42 @@ class iplist : public Traits, ilist_base, ilist_node_access {
   void operator=(const iplist &) = delete;
 
 public:
-  typedef NodeTy *pointer;
-  typedef const NodeTy *const_pointer;
-  typedef NodeTy &reference;
-  typedef const NodeTy &const_reference;
-  typedef NodeTy value_type;
-  typedef ilist_iterator<NodeTy> iterator;
-  typedef ilist_iterator<const NodeTy> const_iterator;
-  typedef size_t size_type;
-  typedef ptrdiff_t difference_type;
-  typedef ilist_iterator<const NodeTy, true> const_reverse_iterator;
-  typedef ilist_iterator<NodeTy, true> reverse_iterator;
+  typedef typename base_list_type::pointer pointer;
+  typedef typename base_list_type::const_pointer const_pointer;
+  typedef typename base_list_type::reference reference;
+  typedef typename base_list_type::const_reference const_reference;
+  typedef typename base_list_type::value_type value_type;
+  typedef typename base_list_type::size_type size_type;
+  typedef typename base_list_type::difference_type difference_type;
+  typedef typename base_list_type::iterator iterator;
+  typedef typename base_list_type::const_iterator const_iterator;
+  typedef typename base_list_type::reverse_iterator reverse_iterator;
+  typedef
+      typename base_list_type::const_reverse_iterator const_reverse_iterator;
 
   iplist() = default;
   ~iplist() { clear(); }
 
-  // Iterator creation methods.
-  iterator begin() { return ++iterator(Sentinel); }
-  const_iterator begin() const { return ++const_iterator(Sentinel); }
-  iterator end() { return iterator(Sentinel); }
-  const_iterator end() const { return const_iterator(Sentinel); }
-
-  // reverse iterator creation methods.
-  reverse_iterator rbegin()            { return ++reverse_iterator(Sentinel); }
-  const_reverse_iterator rbegin() const{ return ++const_reverse_iterator(Sentinel); }
-  reverse_iterator rend()              { return reverse_iterator(Sentinel); }
-  const_reverse_iterator rend() const { return const_reverse_iterator(Sentinel); }
-
   // Miscellaneous inspection routines.
   size_type max_size() const { return size_type(-1); }
-  bool LLVM_ATTRIBUTE_UNUSED_RESULT empty() const { return Sentinel.empty(); }
 
-  // Front and back accessor functions...
-  reference front() {
-    assert(!empty() && "Called front() on empty list!");
-    return *begin();
-  }
-  const_reference front() const {
-    assert(!empty() && "Called front() on empty list!");
-    return *begin();
-  }
-  reference back() {
-    assert(!empty() && "Called back() on empty list!");
-    return *--end();
-  }
-  const_reference back() const {
-    assert(!empty() && "Called back() on empty list!");
-    return *--end();
-  }
+  using base_list_type::begin;
+  using base_list_type::end;
+  using base_list_type::rbegin;
+  using base_list_type::rend;
+  using base_list_type::empty;
+  using base_list_type::front;
+  using base_list_type::back;
 
   void swap(iplist &RHS) {
     assert(0 && "Swap does not use list traits callback correctly yet!");
-    std::swap(Sentinel, RHS.Sentinel);
+    base_list_type::swap(RHS);
   }
 
   iterator insert(iterator where, NodeTy *New) {
-    ilist_base::insertBefore(*where.getNodePtr(), *this->getNodePtr(New));
-
+    auto I = base_list_type::insert(where, *New);
     this->addNodeToList(New);  // Notify traits that we added a node...
-    return iterator(New);
+    return I;
   }
 
   iterator insert(iterator where, const NodeTy &New) {
@@ -212,9 +183,8 @@ public:
   }
 
   NodeTy *remove(iterator &IT) {
-    assert(IT != end() && "Cannot remove end of list!");
-    NodeTy *Node = &*IT++;
-    ilist_base::remove(*this->getNodePtr(Node));
+    NodeTy *Node = &*IT;
+    base_list_type::erase(IT++);
     this->removeNodeFromList(Node);  // Notify traits that we removed a node...
     return Node;
   }
@@ -241,7 +211,7 @@ public:
   ///
   /// This should only be used immediately before freeing nodes in bulk to
   /// avoid traversing the list and bringing all the nodes into cache.
-  void clearAndLeakNodesUnsafely() { Sentinel.reset(); }
+  void clearAndLeakNodesUnsafely() { base_list_type::clear(); }
 
 private:
   // transfer - The heart of the splice function.  Move linked list nodes from
@@ -251,8 +221,7 @@ private:
     if (position == last)
       return;
 
-    ilist_base::transferBefore(*position.getNodePtr(), *first.getNodePtr(),
-                               *last.getNodePtr());
+    base_list_type::splice(position, L2, first, last);
 
     // Callback.  Note that the nodes have moved from before-last to
     // before-position.
@@ -265,9 +234,7 @@ public:
   // Functionality derived from other functions defined above...
   //
 
-  size_type LLVM_ATTRIBUTE_UNUSED_RESULT size() const {
-    return std::distance(begin(), end());
-  }
+  using base_list_type::size;
 
   iterator erase(iterator first, iterator last) {
     while (first != last)
@@ -318,48 +285,12 @@ public:
   void merge(iplist &Right, Compare comp) {
     if (this == &Right)
       return;
-    iterator First1 = begin(), Last1 = end();
-    iterator First2 = Right.begin(), Last2 = Right.end();
-    while (First1 != Last1 && First2 != Last2) {
-      if (comp(*First2, *First1)) {
-        iterator Next = First2;
-        transfer(First1, Right, First2, ++Next);
-        First2 = Next;
-      } else {
-        ++First1;
-      }
-    }
-    if (First2 != Last2)
-      transfer(Last1, Right, First2, Last2);
+    this->transferNodesFromList(Right, Right.begin(), Right.end());
+    base_list_type::merge(Right, comp);
   }
   void merge(iplist &Right) { return merge(Right, op_less); }
 
-  template <class Compare>
-  void sort(Compare comp) {
-    // The list is empty, vacuously sorted.
-    if (empty())
-      return;
-    // The list has a single element, vacuously sorted.
-    if (std::next(begin()) == end())
-      return;
-    // Find the split point for the list.
-    iterator Center = begin(), End = begin();
-    while (End != end() && std::next(End) != end()) {
-      Center = std::next(Center);
-      End = std::next(std::next(End));
-    }
-    // Split the list into two.
-    iplist RightHalf;
-    RightHalf.splice(RightHalf.begin(), *this, Center, end());
-
-    // Sort the two sublists.
-    sort(comp);
-    RightHalf.sort(comp);
-
-    // Merge the two sublists back together.
-    merge(RightHalf, comp);
-  }
-  void sort() { sort(op_less); }
+  using base_list_type::sort;
 
   /// \brief Get the previous node, or \c nullptr for the list head.
   NodeTy *getPrevNode(NodeTy &N) const {
diff --git a/llvm/include/llvm/ADT/ilist_base.h b/llvm/include/llvm/ADT/ilist_base.h
index 27a39bedef0..a41696d1f71 100644
--- a/llvm/include/llvm/ADT/ilist_base.h
+++ b/llvm/include/llvm/ADT/ilist_base.h
@@ -39,10 +39,22 @@ public:
     N.setNext(nullptr);
   }
 
+  static void removeRangeImpl(ilist_node_base &First, ilist_node_base &Last) {
+    ilist_node_base *Prev = First.getPrev();
+    ilist_node_base *Final = Last.getPrev();
+    Last.setPrev(Prev);
+    Prev->setNext(&Last);
+
+    // Not strictly necessary, but helps catch a class of bugs.
+    First.setPrev(nullptr);
+    Final->setNext(nullptr);
+  }
+
   static void transferBeforeImpl(ilist_node_base &Next, ilist_node_base &First,
                                  ilist_node_base &Last) {
-    assert(&Next != &Last && "Should be checked by callers");
-    assert(&First != &Last && "Should be checked by callers");
+    if (&Next == &Last || &First == &Last)
+      return;
+
     // Position cannot be contained in the range to be transferred.
     assert(&Next != &First &&
            // Check for the most common mistake.
@@ -67,6 +79,9 @@ public:
   }
 
   template <class T> static void remove(T &N) { removeImpl(N); }
+  template <class T> static void removeRange(T &First, T &Last) {
+    removeRangeImpl(First, Last);
+  }
 
   template <class T> static void transferBefore(T &Next, T &First, T &Last) {
     transferBeforeImpl(Next, First, Last);
diff --git a/llvm/include/llvm/ADT/simple_ilist.h b/llvm/include/llvm/ADT/simple_ilist.h
new file mode 100644
index 00000000000..f9983d8ed4f
--- /dev/null
+++ b/llvm/include/llvm/ADT/simple_ilist.h
@@ -0,0 +1,269 @@
+//===- llvm/ADT/simple_ilist.h - Simple Intrusive List ----------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_SIMPLE_ILIST_H
+#define LLVM_ADT_SIMPLE_ILIST_H
+
+#include "llvm/ADT/ilist_base.h"
+#include "llvm/ADT/ilist_iterator.h"
+#include "llvm/ADT/ilist_node.h"
+#include <algorithm>
+#include <cassert>
+#include <cstddef>
+
+namespace llvm {
+
+/// A simple intrusive list implementation.
+///
+/// This is a simple intrusive list for a \c T that inherits from \c
+/// ilist_node<T>.  The list never takes ownership of anything inserted in it.
+///
+/// Unlike \a iplist<T> and \a ilist<T>, \a simple_ilist<T> never allocates or
+/// deletes values, and has no callback traits.
+///
+/// The API for adding nodes include \a push_front(), \a push_back(), and \a
+/// insert().  These all take values by reference (not by pointer), except for
+/// the range version of \a insert().
+///
+/// There are three sets of API for discarding nodes from the list: \a
+/// remove(), which takes a reference to the node to remove, \a erase(), which
+/// takes an iterator or iterator range and returns the next one, and \a
+/// clear(), which empties out the container.  All three are constant time
+/// operations.  None of these deletes any nodes; in particular, if there is a
+/// single node in the list, then these have identical semantics:
+/// \li \c L.remove(L.front());
+/// \li \c L.erase(L.begin());
+/// \li \c L.clear();
+///
+/// As a convenience for callers, there are parallel APIs that take a \c
+/// Disposer (such as \c std::default_delete<T>): \a removeAndDispose(), \a
+/// eraseAndDispose(), and \a clearAndDispose().  These have different names
+/// because the extra semantic is otherwise non-obvious.  They are equivalent
+/// to calling \a std::for_each() on the range to be discarded.
+template <typename T> class simple_ilist : ilist_base, ilist_node_access {
+  ilist_sentinel<T> Sentinel;
+
+public:
+  typedef T value_type;
+  typedef T *pointer;
+  typedef T &reference;
+  typedef const T *const_pointer;
+  typedef const T &const_reference;
+  typedef ilist_iterator<T> iterator;
+  typedef ilist_iterator<const T> const_iterator;
+  typedef size_t size_type;
+  typedef ptrdiff_t difference_type;
+  typedef ilist_iterator<const T, true> const_reverse_iterator;
+  typedef ilist_iterator<T, true> reverse_iterator;
+
+  simple_ilist() = default;
+  ~simple_ilist() = default;
+
+  // No copy constructors.
+  simple_ilist(const simple_ilist &) = delete;
+  simple_ilist &operator=(const simple_ilist &) = delete;
+
+  // Move constructors.
+  simple_ilist(simple_ilist &&X) { splice(end(), X); }
+  simple_ilist &operator=(simple_ilist &&X) {
+    clear();
+    splice(end(), X);
+    return *this;
+  }
+
+  iterator begin() { return ++iterator(Sentinel); }
+  const_iterator begin() const { return ++const_iterator(Sentinel); }
+  iterator end() { return iterator(Sentinel); }
+  const_iterator end() const { return const_iterator(Sentinel); }
+  reverse_iterator rbegin() { return ++reverse_iterator(Sentinel); }
+  const_reverse_iterator rbegin() const {
+    return ++const_reverse_iterator(Sentinel);
+  }
+  reverse_iterator rend() { return reverse_iterator(Sentinel); }
+  const_reverse_iterator rend() const {
+    return const_reverse_iterator(Sentinel);
+  }
+
+  /// Check if the list is empty in constant time.
+  bool LLVM_ATTRIBUTE_UNUSED_RESULT empty() const { return Sentinel.empty(); }
+
+  /// Calculate the size of the list in linear time.
+  size_type LLVM_ATTRIBUTE_UNUSED_RESULT size() const {
+    return std::distance(begin(), end());
+  }
+
+  reference front() { return *begin(); }
+  const_reference front() const { return *begin(); }
+  reference back() { return *rbegin(); }
+  const_reference back() const { return *rbegin(); }
+
+  /// Insert a node at the front; never copies.
+  void push_front(reference Node) { insert(begin(), Node); }
+
+  /// Insert a node at the back; never copies.
+  void push_back(reference Node) { insert(end(), Node); }
+
+  /// Remove the node at the front; never deletes.
+  void pop_front() { erase(begin()); }
+
+  /// Remove the node at the back; never deletes.
+  void pop_back() { erase(--end()); }
+
+  /// Swap with another list in place using std::swap.
+  void swap(simple_ilist &X) { std::swap(*this, X); }
+
+  /// Insert a node by reference; never copies.
+  iterator insert(iterator I, reference Node) {
+    ilist_base::insertBefore(*I.getNodePtr(), *this->getNodePtr(&Node));
+    return iterator(&Node);
+  }
+
+  /// Insert a range of nodes; never copies.
+  template <class Iterator>
+  void insert(iterator I, Iterator First, Iterator Last) {
+    for (; First != Last; ++First)
+      insert(I, *First);
+  }
+
+  /// Remove a node by reference; never deletes.
+  ///
+  /// \see \a erase() for removing by iterator.
+  /// \see \a removeAndDispose() if the node should be deleted.
+  void remove(reference N) { ilist_base::remove(*this->getNodePtr(&N)); }
+
+  /// Remove a node by reference and dispose of it.
+  template <class Disposer>
+  void removeAndDispose(reference N, Disposer dispose) {
+    remove(N);
+    dispose(&N);
+  }
+
+  /// Remove a node by iterator; never deletes.
+  ///
+  /// \see \a remove() for removing by reference.
+  /// \see \a eraseAndDispose() it the node should be deleted.
+  iterator erase(iterator I) {
+    assert(I != end() && "Cannot remove end of list!");
+    remove(*I++);
+    return I;
+  }
+
+  /// Remove a range of nodes; never deletes.
+  ///
+  /// \see \a eraseAndDispose() if the nodes should be deleted.
+  iterator erase(iterator First, iterator Last) {
+    ilist_base::removeRange(*First.getNodePtr(), *Last.getNodePtr());
+    return Last;
+  }
+
+  /// Remove a node by iterator and dispose of it.
+  template <class Disposer>
+  iterator eraseAndDispose(iterator I, Disposer dispose) {
+    auto Next = std::next(I);
+    erase(I);
+    dispose(&*I);
+    return Next;
+  }
+
+  /// Remove a range of nodes and dispose of them.
+  template <class Disposer>
+  iterator eraseAndDispose(iterator First, iterator Last, Disposer dispose) {
+    while (First != Last)
+      First = eraseAndDispose(First, dispose);
+    return Last;
+  }
+
+  /// Clear the list; never deletes.
+  ///
+  /// \see \a clearAndDispose() if the nodes should be deleted.
+  void clear() { Sentinel.reset(); }
+
+  /// Clear the list and dispose of the nodes.
+  template <class Disposer> void clearAndDispose(Disposer dispose) {
+    eraseAndDispose(begin(), end(), dispose);
+  }
+
+  /// Splice in another list.
+  void splice(iterator I, simple_ilist &L2) {
+    splice(I, L2, L2.begin(), L2.end());
+  }
+
+  /// Splice in a node from another list.
+  void splice(iterator I, simple_ilist &L2, iterator Node) {
+    splice(I, L2, Node, std::next(Node));
+  }
+
+  /// Splice in a range of nodes from another list.
+  void splice(iterator I, simple_ilist &, iterator First, iterator Last) {
+    ilist_base::transferBefore(*I.getNodePtr(), *First.getNodePtr(),
+                               *Last.getNodePtr());
+  }
+
+  /// Merge in another list.
+  ///
+  /// \pre \c this and \p RHS are sorted.
+  ///@{
+  void merge(simple_ilist &RHS) { merge(RHS, std::less<T>()); }
+  template <class Compare> void merge(simple_ilist &RHS, Compare comp);
+  ///@}
+
+  /// Sort the list.
+  ///@{
+  void sort() { sort(std::less<T>()); }
+  template <class Compare> void sort(Compare comp);
+  ///@}
+};
+
+template <class T>
+template <class Compare>
+void simple_ilist<T>::merge(simple_ilist<T> &RHS, Compare comp) {
+  if (this == &RHS || RHS.empty())
+    return;
+  iterator LI = begin(), LE = end();
+  iterator RI = RHS.begin(), RE = RHS.end();
+  while (LI != LE) {
+    if (comp(*RI, *LI)) {
+      // Transfer a run of at least size 1 from RHS to LHS.
+      iterator RunStart = RI++;
+      RI = std::find_if(RI, RE, [&](reference RV) { return !comp(RV, *LI); });
+      splice(LI, RHS, RunStart, RI);
+      if (RI == RE)
+        return;
+    }
+    ++LI;
+  }
+  // Transfer the remaining RHS nodes once LHS is finished.
+  splice(LE, RHS, RI, RE);
+}
+
+template <class T>
+template <class Compare>
+void simple_ilist<T>::sort(Compare comp) {
+  // Vacuously sorted.
+  if (empty() || std::next(begin()) == end())
+    return;
+
+  // Split the list in the middle.
+  iterator Center = begin(), End = begin();
+  while (End != end() && ++End != end()) {
+    ++Center;
+    ++End;
+  }
+  simple_ilist<T> RHS;
+  RHS.splice(RHS.end(), *this, Center, end());
+
+  // Sort the sublists and merge back together.
+  sort(comp);
+  RHS.sort(comp);
+  merge(RHS, comp);
+}
+
+} // end namespace llvm
+
+#endif // LLVM_ADT_SIMPLE_ILIST_H
diff --git a/llvm/unittests/ADT/CMakeLists.txt b/llvm/unittests/ADT/CMakeLists.txt
index 82df2c97bd5..a041896b6bd 100644
--- a/llvm/unittests/ADT/CMakeLists.txt
+++ b/llvm/unittests/ADT/CMakeLists.txt
@@ -44,6 +44,7 @@ set(ADTSources
   ScopeExitTest.cpp
   SequenceTest.cpp
   SetVectorTest.cpp
+  SimpleIListTest.cpp
   SmallPtrSetTest.cpp
   SmallStringTest.cpp
   SmallVectorTest.cpp
diff --git a/llvm/unittests/ADT/IListBaseTest.cpp b/llvm/unittests/ADT/IListBaseTest.cpp
index 19223327785..34a8e926345 100644
--- a/llvm/unittests/ADT/IListBaseTest.cpp
+++ b/llvm/unittests/ADT/IListBaseTest.cpp
@@ -63,6 +63,46 @@ TEST(IListBaseTest, removeImpl) {
   EXPECT_EQ(nullptr, B.getNext());
 }
 
+TEST(IListBaseTest, removeRangeImpl) {
+  ilist_node_base S, A, B, C, D;
+
+  // [S] <-> A <-> B <-> C <-> D <-> [S]
+  S.setPrev(&S);
+  S.setNext(&S);
+  ilist_base::insertBeforeImpl(S, A);
+  ilist_base::insertBeforeImpl(S, B);
+  ilist_base::insertBeforeImpl(S, C);
+  ilist_base::insertBeforeImpl(S, D);
+
+  // [S] <-> A <-> D <-> [S]
+  ilist_base::removeRangeImpl(B, D);
+  EXPECT_EQ(&D, S.getPrev());
+  EXPECT_EQ(&A, D.getPrev());
+  EXPECT_EQ(&S, A.getPrev());
+  EXPECT_EQ(&A, S.getNext());
+  EXPECT_EQ(&D, A.getNext());
+  EXPECT_EQ(&S, D.getNext());
+  EXPECT_EQ(nullptr, B.getPrev());
+  EXPECT_EQ(nullptr, C.getNext());
+}
+
+TEST(IListBaseTest, removeRangeImplAllButSentinel) {
+  ilist_node_base S, A, B;
+
+  // [S] <-> A <-> B <-> [S]
+  S.setPrev(&S);
+  S.setNext(&S);
+  ilist_base::insertBeforeImpl(S, A);
+  ilist_base::insertBeforeImpl(S, B);
+
+  // [S] <-> [S]
+  ilist_base::removeRangeImpl(A, S);
+  EXPECT_EQ(&S, S.getPrev());
+  EXPECT_EQ(&S, S.getNext());
+  EXPECT_EQ(nullptr, A.getPrev());
+  EXPECT_EQ(nullptr, B.getNext());
+}
+
 TEST(IListBaseTest, transferBeforeImpl) {
   ilist_node_base S1, S2, A, B, C, D, E;
 
diff --git a/llvm/unittests/ADT/IListIteratorTest.cpp b/llvm/unittests/ADT/IListIteratorTest.cpp
index 1a87a270a67..ddcab781b9b 100644
--- a/llvm/unittests/ADT/IListIteratorTest.cpp
+++ b/llvm/unittests/ADT/IListIteratorTest.cpp
@@ -7,7 +7,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "llvm/ADT/ilist.h"
+#include "llvm/ADT/simple_ilist.h"
 #include "gtest/gtest.h"
 
 using namespace llvm;
@@ -17,10 +17,10 @@ namespace {
 struct Node : ilist_node<Node> {};
 
 TEST(IListIteratorTest, DefaultConstructor) {
-  iplist<Node>::iterator I;
-  iplist<Node>::reverse_iterator RI;
-  iplist<Node>::const_iterator CI;
-  iplist<Node>::const_reverse_iterator CRI;
+  simple_ilist<Node>::iterator I;
+  simple_ilist<Node>::reverse_iterator RI;
+  simple_ilist<Node>::const_iterator CI;
+  simple_ilist<Node>::const_reverse_iterator CRI;
   EXPECT_EQ(nullptr, I.getNodePtr());
   EXPECT_EQ(nullptr, CI.getNodePtr());
   EXPECT_EQ(nullptr, RI.getNodePtr());
@@ -38,7 +38,7 @@ TEST(IListIteratorTest, DefaultConstructor) {
 }
 
 TEST(IListIteratorTest, Empty) {
-  iplist<Node> L;
+  simple_ilist<Node> L;
 
   // Check iterators of L.
   EXPECT_EQ(L.begin(), L.end());
@@ -49,21 +49,18 @@ TEST(IListIteratorTest, Empty) {
   EXPECT_EQ(L.rend(), L.end().getReverse());
 
   // Iterators shouldn't match default constructors.
-  iplist<Node>::iterator I;
-  iplist<Node>::reverse_iterator RI;
+  simple_ilist<Node>::iterator I;
+  simple_ilist<Node>::reverse_iterator RI;
   EXPECT_NE(I, L.begin());
   EXPECT_NE(I, L.end());
   EXPECT_NE(RI, L.rbegin());
   EXPECT_NE(RI, L.rend());
-
-  // Don't delete nodes.
-  L.clearAndLeakNodesUnsafely();
 }
 
 TEST(IListIteratorTest, OneNodeList) {
-  iplist<Node> L;
+  simple_ilist<Node> L;
   Node A;
-  L.insert(L.end(), &A);
+  L.insert(L.end(), A);
 
   // Check address of reference.
   EXPECT_EQ(&A, &*L.begin());
@@ -81,16 +78,13 @@ TEST(IListIteratorTest, OneNodeList) {
   // Check conversions.
   EXPECT_EQ(L.rbegin(), L.begin().getReverse());
   EXPECT_EQ(L.begin(), L.rbegin().getReverse());
-
-  // Don't delete nodes.
-  L.clearAndLeakNodesUnsafely();
 }
 
 TEST(IListIteratorTest, TwoNodeList) {
-  iplist<Node> L;
+  simple_ilist<Node> L;
   Node A, B;
-  L.insert(L.end(), &A);
-  L.insert(L.end(), &B);
+  L.insert(L.end(), A);
+  L.insert(L.end(), B);
 
   // Check order.
   EXPECT_EQ(&A, &*L.begin());
@@ -105,45 +99,36 @@ TEST(IListIteratorTest, TwoNodeList) {
   EXPECT_EQ(L.rbegin(), (++L.begin()).getReverse());
   EXPECT_EQ(++L.begin(), L.rbegin().getReverse());
   EXPECT_EQ(L.begin(), (++L.rbegin()).getReverse());
-
-  // Don't delete nodes.
-  L.clearAndLeakNodesUnsafely();
 }
 
 TEST(IListIteratorTest, CheckEraseForward) {
-  iplist<Node> L;
+  simple_ilist<Node> L;
   Node A, B;
-  L.insert(L.end(), &A);
-  L.insert(L.end(), &B);
+  L.insert(L.end(), A);
+  L.insert(L.end(), B);
 
   // Erase nodes.
   auto I = L.begin();
   EXPECT_EQ(&A, &*I);
-  EXPECT_EQ(&A, L.remove(I++));
+  L.remove(*I++);
   EXPECT_EQ(&B, &*I);
-  EXPECT_EQ(&B, L.remove(I++));
+  L.remove(*I++);
   EXPECT_EQ(L.end(), I);
-
-  // Don't delete nodes.
-  L.clearAndLeakNodesUnsafely();
 }
 
 TEST(IListIteratorTest, CheckEraseReverse) {
-  iplist<Node> L;
+  simple_ilist<Node> L;
   Node A, B;
-  L.insert(L.end(), &A);
-  L.insert(L.end(), &B);
+  L.insert(L.end(), A);
+  L.insert(L.end(), B);
 
   // Erase nodes.
   auto RI = L.rbegin();
   EXPECT_EQ(&B, &*RI);
-  EXPECT_EQ(&B, L.remove(&*RI++));
+  L.remove(*RI++);
   EXPECT_EQ(&A, &*RI);
-  EXPECT_EQ(&A, L.remove(&*RI++));
+  L.remove(*RI++);
   EXPECT_EQ(L.rend(), RI);
-
-  // Don't delete nodes.
-  L.clearAndLeakNodesUnsafely();
 }
 
 } // end namespace
diff --git a/llvm/unittests/ADT/SimpleIListTest.cpp b/llvm/unittests/ADT/SimpleIListTest.cpp
new file mode 100644
index 00000000000..f252080c782
--- /dev/null
+++ b/llvm/unittests/ADT/SimpleIListTest.cpp
@@ -0,0 +1,586 @@
+//===- unittests/ADT/SimpleIListTest.cpp - simple_ilist unit 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/simple_ilist.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace {
+
+struct Node : ilist_node<Node> {};
+bool operator<(const Node &L, const Node &R) { return &L < &R; }
+bool makeFalse(const Node &, const Node &) { return false; }
+
+struct deleteNode : std::default_delete<Node> {};
+void doNothing(Node *) {}
+
+TEST(SimpleIListTest, DefaultConstructor) {
+  simple_ilist<Node> L;
+  EXPECT_EQ(L.begin(), L.end());
+  EXPECT_TRUE(L.empty());
+  EXPECT_EQ(0u, L.size());
+}
+
+TEST(SimpleIListTest, pushPopFront) {
+  simple_ilist<Node> L;
+  Node A, B;
+  L.push_front(B);
+  L.push_front(A);
+  EXPECT_EQ(&A, &L.front());
+  EXPECT_EQ(&B, &L.back());
+  EXPECT_FALSE(L.empty());
+  EXPECT_EQ(2u, L.size());
+
+  // Pop front and check the new front.
+  L.pop_front();
+  EXPECT_EQ(&B, &L.front());
+
+  // Pop to empty.
+  L.pop_front();
+  EXPECT_TRUE(L.empty());
+}
+
+TEST(SimpleIListTest, pushPopBack) {
+  simple_ilist<Node> L;
+  Node A, B;
+  L.push_back(A);
+  L.push_back(B);
+  EXPECT_EQ(&A, &L.front());
+  EXPECT_EQ(&B, &L.back());
+  EXPECT_FALSE(L.empty());
+  EXPECT_EQ(2u, L.size());
+
+  // Pop back and check the new front.
+  L.pop_back();
+  EXPECT_EQ(&A, &L.back());
+
+  // Pop to empty.
+  L.pop_back();
+  EXPECT_TRUE(L.empty());
+}
+
+TEST(SimpleIListTest, swap) {
+  simple_ilist<Node> L1, L2;
+  Node A, B;
+  L1.push_back(A);
+  L1.push_back(B);
+  L1.swap(L2);
+  EXPECT_TRUE(L1.empty());
+  EXPECT_EQ(0u, L1.size());
+  EXPECT_EQ(&A, &L2.front());
+  EXPECT_EQ(&B, &L2.back());
+  EXPECT_FALSE(L2.empty());
+  EXPECT_EQ(2u, L2.size());
+}
+
+TEST(SimpleIListTest, insertEraseAtEnd) {
+  simple_ilist<Node> L;
+  Node A, B;
+  L.insert(L.end(), A);
+  L.insert(L.end(), B);
+  EXPECT_EQ(&A, &L.front());
+  EXPECT_EQ(&B, &L.back());
+  EXPECT_FALSE(L.empty());
+  EXPECT_EQ(2u, L.size());
+}
+
+TEST(SimpleIListTest, insertAtBegin) {
+  simple_ilist<Node> L;
+  Node A, B;
+  L.insert(L.begin(), B);
+  L.insert(L.begin(), A);
+  EXPECT_EQ(&A, &L.front());
+  EXPECT_EQ(&B, &L.back());
+  EXPECT_FALSE(L.empty());
+  EXPECT_EQ(2u, L.size());
+}
+
+TEST(SimpleIListTest, remove) {
+  simple_ilist<Node> L;
+  Node A, B, C;
+  L.push_back(A);
+  L.push_back(B);
+  L.push_back(C);
+  EXPECT_EQ(&A, &L.front());
+  EXPECT_EQ(&B, &*++L.begin());
+  EXPECT_EQ(&C, &L.back());
+  EXPECT_EQ(3u, L.size());
+
+  L.remove(B);
+  EXPECT_EQ(&A, &L.front());
+  EXPECT_EQ(&C, &L.back());
+  EXPECT_EQ(2u, L.size());
+
+  L.remove(A);
+  EXPECT_EQ(&C, &L.front());
+  EXPECT_EQ(1u, L.size());
+
+  L.remove(C);
+  EXPECT_TRUE(L.empty());
+}
+
+TEST(SimpleIListTest, removeAndDispose) {
+  simple_ilist<Node> L;
+  Node A, C;
+  Node *B = new Node;
+  L.push_back(A);
+  L.push_back(*B);
+  L.push_back(C);
+  EXPECT_EQ(&A, &L.front());
+  EXPECT_EQ(B, &*++L.begin());
+  EXPECT_EQ(&C, &L.back());
+  EXPECT_EQ(3u, L.size());
+
+  L.removeAndDispose(*B, deleteNode());
+  EXPECT_EQ(&A, &L.front());
+  EXPECT_EQ(&C, &L.back());
+  EXPECT_EQ(2u, L.size());
+}
+
+TEST(SimpleIListTest, removeAndDisposeNullDeleter) {
+  simple_ilist<Node> L;
+  Node A, B, C;
+  L.push_back(A);
+  L.push_back(B);
+  L.push_back(C);
+  EXPECT_EQ(&A, &L.front());
+  EXPECT_EQ(&B, &*++L.begin());
+  EXPECT_EQ(&C, &L.back());
+  EXPECT_EQ(3u, L.size());
+
+  L.removeAndDispose(B, doNothing);
+  EXPECT_EQ(&A, &L.front());
+  EXPECT_EQ(&C, &L.back());
+  EXPECT_EQ(2u, L.size());
+}
+
+TEST(SimpleIListTest, erase) {
+  simple_ilist<Node> L;
+  Node A, B, C;
+  L.push_back(A);
+  L.push_back(B);
+  L.push_back(C);
+  EXPECT_EQ(&A, &L.front());
+  EXPECT_EQ(&B, &*++L.begin());
+  EXPECT_EQ(&C, &L.back());
+  EXPECT_EQ(3u, L.size());
+
+  EXPECT_EQ(C.getIterator(), L.erase(B.getIterator()));
+  EXPECT_EQ(&A, &L.front());
+  EXPECT_EQ(&C, &L.back());
+  EXPECT_EQ(2u, L.size());
+}
+
+TEST(SimpleIListTest, eraseAndDispose) {
+  simple_ilist<Node> L;
+  Node A, C;
+  Node *B = new Node;
+  L.push_back(A);
+  L.push_back(*B);
+  L.push_back(C);
+  EXPECT_EQ(&A, &L.front());
+  EXPECT_EQ(B, &*++L.begin());
+  EXPECT_EQ(&C, &L.back());
+  EXPECT_EQ(3u, L.size());
+
+  L.eraseAndDispose(B->getIterator(), deleteNode());
+  EXPECT_EQ(&A, &L.front());
+  EXPECT_EQ(&C, &L.back());
+  EXPECT_EQ(2u, L.size());
+}
+
+TEST(SimpleIListTest, eraseAndDisposeNullDeleter) {
+  simple_ilist<Node> L;
+  Node A, B, C;
+  L.push_back(A);
+  L.push_back(B);
+  L.push_back(C);
+  EXPECT_EQ(&A, &L.front());
+  EXPECT_EQ(&B, &*++L.begin());
+  EXPECT_EQ(&C, &L.back());
+  EXPECT_EQ(3u, L.size());
+
+  L.eraseAndDispose(B.getIterator(), doNothing);
+  EXPECT_EQ(&A, &L.front());
+  EXPECT_EQ(&C, &L.back());
+  EXPECT_EQ(2u, L.size());
+}
+
+TEST(SimpleIListTest, eraseRange) {
+  simple_ilist<Node> L;
+  Node A, B, C, D, E;
+  L.push_back(A);
+  L.push_back(B);
+  L.push_back(C);
+  L.push_back(D);
+  L.push_back(E);
+  auto I = L.begin();
+  EXPECT_EQ(&A, &*I++);
+  EXPECT_EQ(&B, &*I++);
+  EXPECT_EQ(&C, &*I++);
+  EXPECT_EQ(&D, &*I++);
+  EXPECT_EQ(&E, &*I++);
+  EXPECT_EQ(L.end(), I);
+  EXPECT_EQ(5u, L.size());
+
+  // Erase a range.
+  EXPECT_EQ(E.getIterator(), L.erase(B.getIterator(), E.getIterator()));
+  EXPECT_EQ(&A, &L.front());
+  EXPECT_EQ(&E, &L.back());
+  EXPECT_EQ(2u, L.size());
+}
+
+TEST(SimpleIListTest, eraseAndDisposeRange) {
+  simple_ilist<Node> L;
+  Node A, *B = new Node, *C = new Node, *D = new Node, E;
+  L.push_back(A);
+  L.push_back(*B);
+  L.push_back(*C);
+  L.push_back(*D);
+  L.push_back(E);
+  auto I = L.begin();
+  EXPECT_EQ(&A, &*I++);
+  EXPECT_EQ(B, &*I++);
+  EXPECT_EQ(C, &*I++);
+  EXPECT_EQ(D, &*I++);
+  EXPECT_EQ(&E, &*I++);
+  EXPECT_EQ(L.end(), I);
+  EXPECT_EQ(5u, L.size());
+
+  // Erase a range.
+  EXPECT_EQ(E.getIterator(),
+            L.eraseAndDispose(B->getIterator(), E.getIterator(), deleteNode()));
+  EXPECT_EQ(&A, &L.front());
+  EXPECT_EQ(&E, &L.back());
+  EXPECT_EQ(2u, L.size());
+}
+
+TEST(SimpleIListTest, eraseAndDisposeRangeNullDeleter) {
+  simple_ilist<Node> L;
+  Node A, B, C, D, E;
+  L.push_back(A);
+  L.push_back(B);
+  L.push_back(C);
+  L.push_back(D);
+  L.push_back(E);
+  auto I = L.begin();
+  EXPECT_EQ(&A, &*I++);
+  EXPECT_EQ(&B, &*I++);
+  EXPECT_EQ(&C, &*I++);
+  EXPECT_EQ(&D, &*I++);
+  EXPECT_EQ(&E, &*I++);
+  EXPECT_EQ(L.end(), I);
+  EXPECT_EQ(5u, L.size());
+
+  // Erase a range.
+  EXPECT_EQ(E.getIterator(),
+            L.eraseAndDispose(B.getIterator(), E.getIterator(), doNothing));
+  EXPECT_EQ(&A, &L.front());
+  EXPECT_EQ(&E, &L.back());
+  EXPECT_EQ(2u, L.size());
+}
+
+TEST(SimpleIListTest, clear) {
+  simple_ilist<Node> L;
+  Node A, B;
+  L.push_back(A);
+  L.push_back(B);
+  L.clear();
+  EXPECT_TRUE(L.empty());
+  EXPECT_EQ(0u, L.size());
+}
+
+TEST(SimpleIListTest, clearAndDispose) {
+  simple_ilist<Node> L;
+  Node *A = new Node;
+  Node *B = new Node;
+  L.push_back(*A);
+  L.push_back(*B);
+  L.clearAndDispose(deleteNode());
+  EXPECT_TRUE(L.empty());
+  EXPECT_EQ(0u, L.size());
+}
+
+TEST(SimpleIListTest, clearAndDisposeNullDeleter) {
+  simple_ilist<Node> L;
+  Node A, B;
+  L.push_back(A);
+  L.push_back(B);
+  L.clearAndDispose(doNothing);
+  EXPECT_TRUE(L.empty());
+  EXPECT_EQ(0u, L.size());
+}
+
+TEST(SimpleIListTest, spliceList) {
+  simple_ilist<Node> L1, L2;
+  Node A, B, C, D;
+
+  // [A, D].
+  L1.push_back(A);
+  L1.push_back(D);
+
+  // [B, C].
+  L2.push_back(B);
+  L2.push_back(C);
+
+  // Splice in L2, giving [A, B, C, D].
+  L1.splice(--L1.end(), L2);
+  EXPECT_TRUE(L2.empty());
+  EXPECT_EQ(4u, L1.size());
+  auto I = L1.begin();
+  EXPECT_EQ(&A, &*I++);
+  EXPECT_EQ(&B, &*I++);
+  EXPECT_EQ(&C, &*I++);
+  EXPECT_EQ(&D, &*I++);
+  EXPECT_EQ(L1.end(), I);
+}
+
+TEST(SimpleIListTest, spliceSingle) {
+  simple_ilist<Node> L1, L2;
+  Node A, B, C, D, E;
+
+  // [A, C].
+  L1.push_back(A);
+  L1.push_back(C);
+
+  // [D, B, E].
+  L2.push_back(D);
+  L2.push_back(B);
+  L2.push_back(E);
+
+  // Splice B from L2 to L1, giving [A, B, C] and [D, E].
+  L1.splice(--L1.end(), L2, ++L2.begin());
+  auto I = L1.begin();
+  EXPECT_EQ(&A, &*I++);
+  EXPECT_EQ(&B, &*I++);
+  EXPECT_EQ(&C, &*I++);
+  EXPECT_EQ(L1.end(), I);
+
+  I = L2.begin();
+  EXPECT_EQ(&D, &*I++);
+  EXPECT_EQ(&E, &*I++);
+  EXPECT_EQ(L2.end(), I);
+}
+
+TEST(SimpleIListTest, spliceRange) {
+  simple_ilist<Node> L1, L2;
+  Node A, B, C, D, E, F;
+
+  // [A, D].
+  L1.push_back(A);
+  L1.push_back(D);
+
+  // [E, B, C, F].
+  L2.push_back(E);
+  L2.push_back(B);
+  L2.push_back(C);
+  L2.push_back(F);
+
+  // Splice B from L2 to L1, giving [A, B, C, D] and [E, F].
+  L1.splice(--L1.end(), L2, ++L2.begin(), --L2.end());
+  auto I = L1.begin();
+  EXPECT_EQ(&A, &*I++);
+  EXPECT_EQ(&B, &*I++);
+  EXPECT_EQ(&C, &*I++);
+  EXPECT_EQ(&D, &*I++);
+  EXPECT_EQ(L1.end(), I);
+
+  I = L2.begin();
+  EXPECT_EQ(&E, &*I++);
+  EXPECT_EQ(&F, &*I++);
+  EXPECT_EQ(L2.end(), I);
+}
+
+TEST(SimpleIListTest, merge) {
+  for (bool IsL1LHS : {false, true}) {
+    simple_ilist<Node> L1, L2;
+    Node Ns[10];
+
+    // Fill L1.
+    L1.push_back(Ns[0]);
+    L1.push_back(Ns[3]);
+    L1.push_back(Ns[4]);
+    L1.push_back(Ns[8]);
+
+    // Fill L2.
+    L2.push_back(Ns[1]);
+    L2.push_back(Ns[2]);
+    L2.push_back(Ns[5]);
+    L2.push_back(Ns[6]);
+    L2.push_back(Ns[7]);
+    L2.push_back(Ns[9]);
+
+    // Check setup.
+    EXPECT_EQ(4u, L1.size());
+    EXPECT_EQ(6u, L2.size());
+    EXPECT_TRUE(std::is_sorted(L1.begin(), L1.end()));
+    EXPECT_TRUE(std::is_sorted(L2.begin(), L2.end()));
+
+    // Merge.
+    auto &LHS = IsL1LHS ? L1 : L2;
+    auto &RHS = IsL1LHS ? L2 : L1;
+    LHS.merge(RHS);
+    EXPECT_TRUE(RHS.empty());
+    EXPECT_FALSE(LHS.empty());
+    EXPECT_TRUE(std::is_sorted(LHS.begin(), LHS.end()));
+    auto I = LHS.begin();
+    for (Node &N : Ns)
+      EXPECT_EQ(&N, &*I++);
+    EXPECT_EQ(LHS.end(), I);
+  }
+}
+
+TEST(SimpleIListTest, mergeIsStable) {
+  simple_ilist<Node> L1, L2;
+  Node Ns[5];
+
+  auto setup = [&]() {
+    EXPECT_TRUE(L1.empty());
+    EXPECT_TRUE(L2.empty());
+
+    // Fill L1.
+    L1.push_back(Ns[0]);
+    L1.push_back(Ns[3]);
+    L1.push_back(Ns[4]);
+
+    // Fill L2.
+    L2.push_back(Ns[1]);
+    L2.push_back(Ns[2]);
+
+    // Check setup.
+    EXPECT_EQ(3u, L1.size());
+    EXPECT_EQ(2u, L2.size());
+    EXPECT_TRUE(std::is_sorted(L1.begin(), L1.end(), makeFalse));
+    EXPECT_TRUE(std::is_sorted(L2.begin(), L2.end(), makeFalse));
+  };
+
+  // Merge.  Should be stable.
+  setup();
+  L1.merge(L2, makeFalse);
+  EXPECT_TRUE(L2.empty());
+  EXPECT_FALSE(L1.empty());
+  EXPECT_TRUE(std::is_sorted(L1.begin(), L1.end(), makeFalse));
+  auto I = L1.begin();
+  EXPECT_EQ(&Ns[0], &*I++);
+  EXPECT_EQ(&Ns[3], &*I++);
+  EXPECT_EQ(&Ns[4], &*I++);
+  EXPECT_EQ(&Ns[1], &*I++);
+  EXPECT_EQ(&Ns[2], &*I++);
+  EXPECT_EQ(L1.end(), I);
+
+  // Merge the other way.  Should be stable.
+  L1.clear();
+  setup();
+  L2.merge(L1, makeFalse);
+  EXPECT_TRUE(L1.empty());
+  EXPECT_FALSE(L2.empty());
+  EXPECT_TRUE(std::is_sorted(L2.begin(), L2.end(), makeFalse));
+  I = L2.begin();
+  EXPECT_EQ(&Ns[1], &*I++);
+  EXPECT_EQ(&Ns[2], &*I++);
+  EXPECT_EQ(&Ns[0], &*I++);
+  EXPECT_EQ(&Ns[3], &*I++);
+  EXPECT_EQ(&Ns[4], &*I++);
+  EXPECT_EQ(L2.end(), I);
+}
+
+TEST(SimpleIListTest, mergeEmpty) {
+  for (bool IsL1LHS : {false, true}) {
+    simple_ilist<Node> L1, L2;
+    Node Ns[4];
+
+    // Fill L1.
+    L1.push_back(Ns[0]);
+    L1.push_back(Ns[1]);
+    L1.push_back(Ns[2]);
+    L1.push_back(Ns[3]);
+
+    // Check setup.
+    EXPECT_EQ(4u, L1.size());
+    EXPECT_TRUE(L2.empty());
+    EXPECT_TRUE(std::is_sorted(L1.begin(), L1.end()));
+
+    // Merge.
+    auto &LHS = IsL1LHS ? L1 : L2;
+    auto &RHS = IsL1LHS ? L2 : L1;
+    LHS.merge(RHS);
+    EXPECT_TRUE(RHS.empty());
+    EXPECT_FALSE(LHS.empty());
+    EXPECT_TRUE(std::is_sorted(LHS.begin(), LHS.end()));
+    auto I = LHS.begin();
+    for (Node &N : Ns)
+      EXPECT_EQ(&N, &*I++);
+    EXPECT_EQ(LHS.end(), I);
+  }
+}
+
+TEST(SimpleIListTest, mergeBothEmpty) {
+  simple_ilist<Node> L1, L2;
+  L1.merge(L2);
+  EXPECT_TRUE(L1.empty());
+  EXPECT_TRUE(L2.empty());
+}
+
+TEST(SimpleIListTest, sort) {
+  simple_ilist<Node> L;
+  Node Ns[10];
+
+  // Fill L.
+  for (int I : {3, 4, 0, 8, 1, 2, 6, 7, 9, 5})
+    L.push_back(Ns[I]);
+
+  // Check setup.
+  EXPECT_EQ(10u, L.size());
+  EXPECT_FALSE(std::is_sorted(L.begin(), L.end()));
+
+  // Sort.
+  L.sort();
+  EXPECT_TRUE(std::is_sorted(L.begin(), L.end()));
+  auto I = L.begin();
+  for (Node &N : Ns)
+    EXPECT_EQ(&N, &*I++);
+  EXPECT_EQ(L.end(), I);
+}
+
+TEST(SimpleIListTest, sortIsStable) {
+  simple_ilist<Node> L;
+  Node Ns[10];
+
+  // Compare such that nodes are partitioned but not fully sorted.
+  auto partition = [&](const Node &N) { return &N >= &Ns[5]; };
+  auto compare = [&](const Node &L, const Node &R) {
+    return partition(L) < partition(R);
+  };
+
+  // Fill L.
+  for (int I : {3, 4, 7, 8, 1, 2, 6, 0, 9, 5})
+    L.push_back(Ns[I]);
+
+  // Check setup.
+  EXPECT_EQ(10u, L.size());
+  EXPECT_FALSE(std::is_sorted(L.begin(), L.end(), compare));
+
+  // Sort.
+  L.sort(compare);
+  EXPECT_TRUE(std::is_sorted(L.begin(), L.end(), compare));
+  auto I = L.begin();
+  for (int O : {3, 4, 1, 2, 0})
+    EXPECT_EQ(&Ns[O], &*I++);
+  for (int O : {7, 8, 6, 9, 5})
+    EXPECT_EQ(&Ns[O], &*I++);
+  EXPECT_EQ(L.end(), I);
+}
+
+TEST(SimpleIListTest, sortEmpty) {
+  simple_ilist<Node> L;
+  L.sort();
+}
+
+} // end namespace
diff --git a/llvm/unittests/IR/CMakeLists.txt b/llvm/unittests/IR/CMakeLists.txt
index 2baa4370c70..750f638c7a4 100644
--- a/llvm/unittests/IR/CMakeLists.txt
+++ b/llvm/unittests/IR/CMakeLists.txt
@@ -20,6 +20,7 @@ set(IRSources
   LegacyPassManagerTest.cpp
   MDBuilderTest.cpp
   MetadataTest.cpp
+  ModuleTest.cpp
   PassManagerTest.cpp
   PatternMatch.cpp
   TypeBuilderTest.cpp
diff --git a/llvm/unittests/IR/ModuleTest.cpp b/llvm/unittests/IR/ModuleTest.cpp
new file mode 100644
index 00000000000..ef1652b3eb2
--- /dev/null
+++ b/llvm/unittests/IR/ModuleTest.cpp
@@ -0,0 +1,48 @@
+//===- unittests/IR/ModuleTest.cpp - Module unit tests --------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/IR/GlobalVariable.h"
+#include "llvm/IR/Module.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace {
+
+bool sortByName(const GlobalVariable &L, const GlobalVariable &R) {
+  return L.getName() < R.getName();
+}
+
+bool sortByNameReverse(const GlobalVariable &L, const GlobalVariable &R) {
+  return sortByName(R, L);
+}
+
+TEST(ModuleTest, sortGlobalsByName) {
+  LLVMContext Context;
+  for (auto compare : {sortByName, sortByNameReverse}) {
+    Module M("M", Context);
+    Type *T = Type::getInt8Ty(Context);
+    GlobalValue::LinkageTypes L = GlobalValue::ExternalLinkage;
+    (void)new GlobalVariable(M, T, false, L, nullptr, "A");
+    (void)new GlobalVariable(M, T, false, L, nullptr, "F");
+    (void)new GlobalVariable(M, T, false, L, nullptr, "G");
+    (void)new GlobalVariable(M, T, false, L, nullptr, "E");
+    (void)new GlobalVariable(M, T, false, L, nullptr, "B");
+    (void)new GlobalVariable(M, T, false, L, nullptr, "H");
+    (void)new GlobalVariable(M, T, false, L, nullptr, "C");
+    (void)new GlobalVariable(M, T, false, L, nullptr, "D");
+
+    // Sort the globals by name.
+    EXPECT_FALSE(std::is_sorted(M.global_begin(), M.global_end(), compare));
+    M.getGlobalList().sort(compare);
+    EXPECT_TRUE(std::is_sorted(M.global_begin(), M.global_end(), compare));
+  }
+}
+
+} // end namespace