Index: include/llvm/ADT/BitVector.h
===================================================================
--- include/llvm/ADT/BitVector.h
+++ include/llvm/ADT/BitVector.h
@@ -14,6 +14,7 @@
 #ifndef LLVM_ADT_BITVECTOR_H
 #define LLVM_ADT_BITVECTOR_H
 
+#include "llvm/ADT/iterator_range.h"
 #include "llvm/Support/MathExtras.h"
 #include <algorithm>
 #include <cassert>
@@ -25,6 +26,50 @@
 
 namespace llvm {
 
+/// ForwardIterator for the bits that are set.
+/// Iterators get invalidated when resize / reserve is called.
+template <typename BitVectorT> class const_bits_set_iterator_impl {
+  const BitVectorT &Parent;
+  int Current = 0;
+
+  void advance() {
+    assert(Current != -1 && "Trying to advance past end.");
+    Current = Parent.find_next(Current);
+  }
+
+public:
+  const_bits_set_iterator_impl(const BitVectorT &Parent, int Current)
+      : Parent(Parent), Current(Current) {}
+  explicit const_bits_set_iterator_impl(const BitVectorT &Parent)
+      : const_bits_set_iterator_impl(Parent, Parent.find_first()) {}
+  const_bits_set_iterator_impl(const const_bits_set_iterator_impl &) = default;
+
+  const_bits_set_iterator_impl operator++(int) {
+    auto Prev = *this;
+    advance();
+    return Prev;
+  }
+
+  const_bits_set_iterator_impl &operator++() {
+    advance();
+    return *this;
+  }
+
+  unsigned operator*() const { return Current; }
+
+  bool operator==(const const_bits_set_iterator_impl &Other) const {
+    assert(&Parent == &Other.Parent &&
+           "Comparing iterators from different BitVectors");
+    return Current == Other.Current;
+  }
+
+  bool operator!=(const const_bits_set_iterator_impl &Other) const {
+    assert(&Parent == &Other.Parent &&
+           "Comparing iterators from different BitVectors");
+    return Current != Other.Current;
+  }
+};
+
 class BitVector {
   typedef unsigned long BitWord;
 
@@ -73,6 +118,18 @@
     }
   };
 
+  typedef const_bits_set_iterator_impl<BitVector> const_bits_set_iterator;
+  typedef const_bits_set_iterator set_iterator;
+
+  const_bits_set_iterator bit_set_begin() const {
+    return const_bits_set_iterator(*this);
+  }
+  const_bits_set_iterator bit_set_end() const {
+    return const_bits_set_iterator(*this, -1);
+  }
+  iterator_range<const_bits_set_iterator> bit_set() const {
+    return make_range(bit_set_begin(), bit_set_end());
+  }
 
   /// BitVector default ctor - Creates an empty bitvector.
   BitVector() : Size(0), Capacity(0) {
Index: include/llvm/ADT/SmallBitVector.h
===================================================================
--- include/llvm/ADT/SmallBitVector.h
+++ include/llvm/ADT/SmallBitVector.h
@@ -136,6 +136,19 @@
   }
 
 public:
+  typedef const_bits_set_iterator_impl<SmallBitVector> const_bits_set_iterator;
+  typedef const_bits_set_iterator set_iterator;
+
+  const_bits_set_iterator bit_set_begin() const {
+    return const_bits_set_iterator(*this);
+  }
+  const_bits_set_iterator bit_set_end() const {
+    return const_bits_set_iterator(*this, -1);
+  }
+  iterator_range<const_bits_set_iterator> bit_set() const {
+    return make_range(bit_set_begin(), bit_set_end());
+  }
+
   /// Creates an empty bitvector.
   SmallBitVector() : X(1) {}
 
Index: unittests/ADT/BitVectorTest.cpp
===================================================================
--- unittests/ADT/BitVectorTest.cpp
+++ unittests/ADT/BitVectorTest.cpp
@@ -501,5 +501,34 @@
   testEmpty(E);
 }
 
+TYPED_TEST(BitVectorTest, Iterators) {
+  TypeParam Filled(10, true);
+  EXPECT_NE(Filled.bit_set_begin(), Filled.bit_set_end());
+  int Counter = 0;
+  for (int Bit : Filled.bit_set())
+    EXPECT_EQ(Bit, Counter++);
+
+  TypeParam Empty;
+  EXPECT_EQ(Empty.bit_set_begin(), Empty.bit_set_end());
+  for (int Bit : Empty.bit_set()) {
+    (void)Bit;
+    EXPECT_TRUE(false);
+  }
+
+  TypeParam ToFill(100, false);
+  ToFill.set(0);
+  EXPECT_NE(ToFill.bit_set_begin(), ToFill.bit_set_end());
+  EXPECT_EQ(++ToFill.bit_set_begin(), ToFill.bit_set_end());
+  EXPECT_EQ(*ToFill.bit_set_begin(), 0U);
+  ToFill.reset(0);
+  EXPECT_EQ(ToFill.bit_set_begin(), ToFill.bit_set_end());
+
+  const int List[] = {1, 10, 25, 99};
+  for (int Num : List)
+    ToFill.set(Num);
+  int i = 0;
+  for (int Bit : ToFill.bit_set())
+    EXPECT_EQ(List[i++], Bit);
+}
 }
 #endif