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>
@@ -73,6 +74,48 @@
     }
   };
 
+  /// ForwardIterator for the bits that are set.
+  /// Iterators get invalidated when resize / reserve is called.
+  template <typename BitVectorT>
+  class const_set_iterator_impl {
+    const BitVectorT *Parent = nullptr;
+    int Current = 0;
+
+  public:
+    const_set_iterator_impl(const BitVectorT *Parent, int Current)
+        : Parent(Parent), Current(Current) {}
+    const_set_iterator_impl(const BitVectorT *Parent)
+        : const_set_iterator_impl(Parent, Parent->find_first()) {}
+    const_set_iterator_impl(const const_set_iterator_impl&) = default;
+
+    void advance() {
+      assert(Current != -1 && "Trying to advance past end.");
+      Current = Parent->find_next(Current);
+    }
+
+    const_set_iterator_impl operator++(int) {
+      auto Prev = *this;
+      advance();
+      return Prev;
+    }
+
+    const_set_iterator_impl &operator++() {
+      advance();
+      return *this;
+    }
+
+    int operator*() const { return Current; }
+    const BitVectorT *getParent() const { return Parent; }
+  };
+
+  typedef const_set_iterator_impl<BitVector> const_set_iterator;
+  typedef const_set_iterator set_iterator;
+
+  const_set_iterator set_begin() const { return {this}; }
+  const_set_iterator set_end() const { return {this, -1}; }
+  iterator_range<const_set_iterator> bits_set() const {
+    return make_range(set_begin(), set_end());
+  }
 
   /// BitVector default ctor - Creates an empty bitvector.
   BitVector() : Size(0), Capacity(0) {
@@ -619,6 +662,22 @@
   return X.getMemorySize();
 }
 
+template <typename BitVectorT>
+bool operator==(const BitVector::const_set_iterator_impl<BitVectorT> &This,
+                const BitVector::const_set_iterator_impl<BitVectorT> &Other) {
+  assert(This.getParent() == Other.getParent() &&
+         "Comparing iterators from different BitVectors");
+  return *This == *Other;
+}
+
+template <typename BitVectorT>
+bool operator!=(const BitVector::const_set_iterator_impl<BitVectorT> &This,
+                const BitVector::const_set_iterator_impl<BitVectorT> &Other) {
+  assert(This.getParent() == Other.getParent() &&
+         "Comparing iterators from different BitVectors");
+  return *This != *Other;
+}
+
 } // end namespace llvm
 
 namespace std {
Index: include/llvm/ADT/SmallBitVector.h
===================================================================
--- include/llvm/ADT/SmallBitVector.h
+++ include/llvm/ADT/SmallBitVector.h
@@ -136,6 +136,16 @@
   }
 
 public:
+
+  typedef BitVector::const_set_iterator_impl<SmallBitVector> const_set_iterator;
+  typedef const_set_iterator set_iterator;
+
+  const_set_iterator set_begin() const { return {this}; }
+  const_set_iterator set_end() const { return {this, -1}; }
+  iterator_range<const_set_iterator> bits_set() const {
+    return make_range(set_begin(), set_end());
+  }
+
   /// Creates an empty bitvector.
   SmallBitVector() : X(1) {}
 
Index: unittests/ADT/BitVectorTest.cpp
===================================================================
--- unittests/ADT/BitVectorTest.cpp
+++ unittests/ADT/BitVectorTest.cpp
@@ -501,5 +501,37 @@
   testEmpty(E);
 }
 
+TYPED_TEST(BitVectorTest, Iterators) {
+  TypeParam Filled(10, true);
+  EXPECT_NE(Filled.set_begin(), Filled.set_end());
+  int Counter = 0;
+  for (int Bit : Filled.bits_set())
+    EXPECT_EQ(Bit, Counter++);
+
+  TypeParam Empty;
+  EXPECT_EQ(Empty.set_begin(), Empty.set_end());
+  for (int Bit : Empty.bits_set())
+    EXPECT_FALSE(Bit != 9999);
+
+  TypeParam ToFill(100, false);
+  ToFill.set(0);
+  EXPECT_NE(ToFill.set_begin(), ToFill.set_end());
+  EXPECT_EQ(++ToFill.set_begin(), ToFill.set_end());
+  EXPECT_EQ(*ToFill.set_begin(), 0);
+
+  ToFill.set(1);
+  ToFill.set(10);
+  ToFill.set(99);
+  ToFill.set(25);
+  size_t Count = ToFill.count();
+  EXPECT_EQ((int)Count, 5);
+  size_t ItCount = 0;
+  for (int Bit : ToFill.bits_set()) {
+    (void)Bit;
+    ++ItCount;
+  }
+  EXPECT_EQ(Count, ItCount);
+}
+
 }
 #endif