Index: llvm/trunk/include/llvm/ADT/STLExtras.h
===================================================================
--- llvm/trunk/include/llvm/ADT/STLExtras.h
+++ llvm/trunk/include/llvm/ADT/STLExtras.h
@@ -26,10 +26,18 @@
 #include <memory>
 #include <utility> // for std::pair
 
+#include "llvm/ADT/Optional.h"
+#include "llvm/ADT/iterator.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/Support/Compiler.h"
 
 namespace llvm {
+namespace detail {
+
+template <typename RangeT>
+using IterOfRange = decltype(std::begin(std::declval<RangeT>()));
+
+} // End detail namespace
 
 //===----------------------------------------------------------------------===//
 //     Extra additions to <functional>
@@ -235,6 +243,90 @@
                     llvm::make_reverse_iterator(std::begin(C)));
 }
 
+/// An iterator adaptor that filters the elements of given inner iterators.
+///
+/// The predicate parameter should be a callable object that accepts the wrapped
+/// iterator's reference type and returns a bool. When incrementing or
+/// decrementing the iterator, it will call the predicate on each element and
+/// skip any where it returns false.
+///
+/// \code
+///   int A[] = { 1, 2, 3, 4 };
+///   auto R = make_filter_range(A, [](int N) { return N % 2 == 1; });
+///   // R contains { 1, 3 }.
+/// \endcode
+template <typename WrappedIteratorT, typename PredicateT>
+class filter_iterator
+    : public iterator_adaptor_base<
+          filter_iterator<WrappedIteratorT, PredicateT>, WrappedIteratorT,
+          typename std::common_type<
+              std::forward_iterator_tag,
+              typename std::iterator_traits<
+                  WrappedIteratorT>::iterator_category>::type> {
+  using BaseT = iterator_adaptor_base<
+      filter_iterator<WrappedIteratorT, PredicateT>, WrappedIteratorT,
+      typename std::common_type<
+          std::forward_iterator_tag,
+          typename std::iterator_traits<WrappedIteratorT>::iterator_category>::
+          type>;
+
+  struct PayloadType {
+    WrappedIteratorT End;
+    PredicateT Pred;
+  };
+
+  Optional<PayloadType> Payload;
+
+  void findNextValid() {
+    assert(Payload && "Payload should be engaged when findNextValid is called");
+    while (this->I != Payload->End && !Payload->Pred(*this->I))
+      BaseT::operator++();
+  }
+
+  // Construct the begin iterator. The begin iterator requires to know where end
+  // is, so that it can properly stop when it hits end.
+  filter_iterator(WrappedIteratorT Begin, WrappedIteratorT End, PredicateT Pred)
+      : BaseT(std::move(Begin)),
+        Payload(PayloadType{std::move(End), std::move(Pred)}) {
+    findNextValid();
+  }
+
+  // Construct the end iterator. It's not incrementable, so Payload doesn't
+  // have to be engaged.
+  filter_iterator(WrappedIteratorT End) : BaseT(End) {}
+
+public:
+  using BaseT::operator++;
+
+  filter_iterator &operator++() {
+    BaseT::operator++();
+    findNextValid();
+    return *this;
+  }
+
+  template <typename RT, typename PT>
+  friend iterator_range<filter_iterator<detail::IterOfRange<RT>, PT>>
+  make_filter_range(RT &&, PT);
+};
+
+/// Convenience function that takes a range of elements and a predicate,
+/// and return a new filter_iterator range.
+///
+/// FIXME: Currently if RangeT && is a rvalue reference to a temporary, the
+/// lifetime of that temporary is not kept by the returned range object, and the
+/// temporary is going to be dropped on the floor after the make_iterator_range
+/// full expression that contains this function call.
+template <typename RangeT, typename PredicateT>
+iterator_range<filter_iterator<detail::IterOfRange<RangeT>, PredicateT>>
+make_filter_range(RangeT &&Range, PredicateT Pred) {
+  using FilterIteratorT =
+      filter_iterator<detail::IterOfRange<RangeT>, PredicateT>;
+  return make_range(FilterIteratorT(std::begin(std::forward<RangeT>(Range)),
+                                    std::end(std::forward<RangeT>(Range)),
+                                    std::move(Pred)),
+                    FilterIteratorT(std::end(std::forward<RangeT>(Range))));
+}
+
 //===----------------------------------------------------------------------===//
 //     Extra additions to <utility>
 //===----------------------------------------------------------------------===//
Index: llvm/trunk/include/llvm/ADT/iterator.h
===================================================================
--- llvm/trunk/include/llvm/ADT/iterator.h
+++ llvm/trunk/include/llvm/ADT/iterator.h
@@ -175,15 +175,7 @@
 
   iterator_adaptor_base() = default;
 
-  template <typename U>
-  explicit iterator_adaptor_base(
-      U &&u,
-      typename std::enable_if<
-          !std::is_base_of<typename std::remove_cv<
-                               typename std::remove_reference<U>::type>::type,
-                           DerivedT>::value,
-          int>::type = 0)
-      : I(std::forward<U &&>(u)) {}
+  explicit iterator_adaptor_base(WrappedIteratorT u) : I(std::move(u)) {}
 
   const WrappedIteratorT &wrapped() const { return I; }
 
Index: llvm/trunk/unittests/Support/IteratorTest.cpp
===================================================================
--- llvm/trunk/unittests/Support/IteratorTest.cpp
+++ llvm/trunk/unittests/Support/IteratorTest.cpp
@@ -116,4 +116,73 @@
   EXPECT_EQ(End, I);
 }
 
+TEST(FilterIteratorTest, Lambda) {
+  auto IsOdd = [](int N) { return N % 2 == 1; };
+  int A[] = {0, 1, 2, 3, 4, 5, 6};
+  auto Range = make_filter_range(A, IsOdd);
+  SmallVector<int, 3> Actual(Range.begin(), Range.end());
+  EXPECT_EQ((SmallVector<int, 3>{1, 3, 5}), Actual);
+}
+
+TEST(FilterIteratorTest, CallableObject) {
+  int Counter = 0;
+  struct Callable {
+    int &Counter;
+
+    Callable(int &Counter) : Counter(Counter) {}
+
+    bool operator()(int N) {
+      Counter++;
+      return N % 2 == 1;
+    }
+  };
+  Callable IsOdd(Counter);
+  int A[] = {0, 1, 2, 3, 4, 5, 6};
+  auto Range = make_filter_range(A, IsOdd);
+  EXPECT_EQ(2, Counter);
+  SmallVector<int, 3> Actual(Range.begin(), Range.end());
+  EXPECT_GE(Counter, 7);
+  EXPECT_EQ((SmallVector<int, 3>{1, 3, 5}), Actual);
+}
+
+TEST(FilterIteratorTest, FunctionPointer) {
+  bool (*IsOdd)(int) = [](int N) { return N % 2 == 1; };
+  int A[] = {0, 1, 2, 3, 4, 5, 6};
+  auto Range = make_filter_range(A, IsOdd);
+  SmallVector<int, 3> Actual(Range.begin(), Range.end());
+  EXPECT_EQ((SmallVector<int, 3>{1, 3, 5}), Actual);
+}
+
+TEST(FilterIteratorTest, Composition) {
+  auto IsOdd = [](int N) { return N % 2 == 1; };
+  std::unique_ptr<int> A[] = {make_unique<int>(0), make_unique<int>(1),
+                              make_unique<int>(2), make_unique<int>(3),
+                              make_unique<int>(4), make_unique<int>(5),
+                              make_unique<int>(6)};
+  using PointeeIterator = pointee_iterator<std::unique_ptr<int> *>;
+  auto Range = make_filter_range(
+      make_range(PointeeIterator(std::begin(A)), PointeeIterator(std::end(A))),
+      IsOdd);
+  SmallVector<int, 3> Actual(Range.begin(), Range.end());
+  EXPECT_EQ((SmallVector<int, 3>{1, 3, 5}), Actual);
+}
+
+TEST(FilterIteratorTest, InputIterator) {
+  struct InputIterator
+      : iterator_adaptor_base<InputIterator, int *, std::input_iterator_tag> {
+    using BaseT =
+        iterator_adaptor_base<InputIterator, int *, std::input_iterator_tag>;
+
+    InputIterator(int *It) : BaseT(It) {}
+  };
+
+  auto IsOdd = [](int N) { return N % 2 == 1; };
+  int A[] = {0, 1, 2, 3, 4, 5, 6};
+  auto Range = make_filter_range(
+      make_range(InputIterator(std::begin(A)), InputIterator(std::end(A))),
+      IsOdd);
+  SmallVector<int, 3> Actual(Range.begin(), Range.end());
+  EXPECT_EQ((SmallVector<int, 3>{1, 3, 5}), Actual);
+}
+
 } // anonymous namespace