Index: llvm/include/llvm/DebugInfo/DWARF/DWARFDie.h
===================================================================
--- llvm/include/llvm/DebugInfo/DWARF/DWARFDie.h
+++ llvm/include/llvm/DebugInfo/DWARF/DWARFDie.h
@@ -104,12 +104,24 @@
   /// invalid DWARFDie instance if it doesn't.
   DWARFDie getSibling() const;
 
+  /// Get the previous sibling of this DIE object.
+  ///
+  /// \returns a valid DWARFDie instance if this object has a sibling or an
+  /// invalid DWARFDie instance if it doesn't.
+  DWARFDie getPreviousSibling() const;
+
   /// Get the first child of this DIE object.
   ///
   /// \returns a valid DWARFDie instance if this object has children or an
   /// invalid DWARFDie instance if it doesn't.
   DWARFDie getFirstChild() const;
 
+  /// Get the last child of this DIE object.
+  ///
+  /// \returns a valid null DWARFDie instance if this object has children or an
+  /// invalid DWARFDie instance if it doesn't.
+  DWARFDie getLastChild() const;
+
   /// Dump the DIE and all of its attributes to the supplied stream.
   ///
   /// \param OS the stream to use for output.
@@ -288,6 +300,7 @@
   explicit attribute_iterator(DWARFDie D, bool End);
 
   attribute_iterator &operator++();
+  attribute_iterator &operator--();
   explicit operator bool() const { return AttrValue.isValid(); }
   const DWARFAttribute &operator*() const { return AttrValue; }
   bool operator==(const attribute_iterator &X) const { return Index == X.Index; }
@@ -306,26 +319,23 @@
   return LHS.getOffset() < RHS.getOffset();
 }
 
-class DWARFDie::iterator : public iterator_facade_base<iterator,
-                                                      std::forward_iterator_tag,
-                                                      const DWARFDie> {
+class DWARFDie::iterator
+    : public iterator_facade_base<iterator, std::bidirectional_iterator_tag,
+                                  const DWARFDie> {
   DWARFDie Die;
-  void skipNull() {
-    if (Die && Die.isNULL())
-      Die = DWARFDie();
-  }
 public:
   iterator() = default;
 
   explicit iterator(DWARFDie D) : Die(D) {
-    // If we start out with only a Null DIE then invalidate.
-    skipNull();
   }
 
   iterator &operator++() {
     Die = Die.getSibling();
-    // Don't include the NULL die when iterating.
-    skipNull();
+    return *this;
+  }
+
+  iterator &operator--() {
+    Die = Die.getPreviousSibling();
     return *this;
   }
 
@@ -341,7 +351,7 @@
 }
 
 inline DWARFDie::iterator DWARFDie::end() const {
-  return iterator();
+  return iterator(getLastChild());
 }
 
 inline iterator_range<DWARFDie::iterator> DWARFDie::children() const {
Index: llvm/include/llvm/DebugInfo/DWARF/DWARFUnit.h
===================================================================
--- llvm/include/llvm/DebugInfo/DWARF/DWARFUnit.h
+++ llvm/include/llvm/DebugInfo/DWARF/DWARFUnit.h
@@ -508,7 +508,9 @@
 
   DWARFDie getParent(const DWARFDebugInfoEntry *Die);
   DWARFDie getSibling(const DWARFDebugInfoEntry *Die);
+  DWARFDie getPreviousSibling(const DWARFDebugInfoEntry *Die);
   DWARFDie getFirstChild(const DWARFDebugInfoEntry *Die);
+  DWARFDie getLastChild(const DWARFDebugInfoEntry *Die);
 
   /// Return the DIE object for a given offset inside the
   /// unit's DIE vector.
Index: llvm/lib/DebugInfo/DWARF/DWARFDie.cpp
===================================================================
--- llvm/lib/DebugInfo/DWARF/DWARFDie.cpp
+++ llvm/lib/DebugInfo/DWARF/DWARFDie.cpp
@@ -555,12 +555,24 @@
   return DWARFDie();
 }
 
+DWARFDie DWARFDie::getPreviousSibling() const {
+  if (isValid())
+    return U->getPreviousSibling(Die);
+  return DWARFDie();
+}
+
 DWARFDie DWARFDie::getFirstChild() const {
   if (isValid())
     return U->getFirstChild(Die);
   return DWARFDie();
 }
 
+DWARFDie DWARFDie::getLastChild() const {
+  if (isValid())
+    return U->getLastChild(Die);
+  return DWARFDie();
+}
+
 iterator_range<DWARFDie::attribute_iterator> DWARFDie::attributes() const {
   return make_range(attribute_iterator(*this, false),
                     attribute_iterator(*this, true));
Index: llvm/lib/DebugInfo/DWARF/DWARFUnit.cpp
===================================================================
--- llvm/lib/DebugInfo/DWARF/DWARFUnit.cpp
+++ llvm/lib/DebugInfo/DWARF/DWARFUnit.cpp
@@ -584,6 +584,24 @@
   return DWARFDie();
 }
 
+DWARFDie DWARFUnit::getPreviousSibling(const DWARFDebugInfoEntry *Die) {
+  if (!Die)
+    return DWARFDie();
+  uint32_t Depth = Die->getDepth();
+  // Unit DIEs always have a depth of zero and never have siblings.
+  if (Depth == 0)
+    return DWARFDie();
+
+  // Find the previous DIE whose depth is the same as the Die's depth.
+  for (size_t I = getDIEIndex(Die) - 1; I >= 0; --I) {
+    if (DieArray[I].getDepth() == Depth - 1)
+      return DWARFDie();
+    if (DieArray[I].getDepth() == Depth)
+      return DWARFDie(this, &DieArray[I]);
+  }
+  return DWARFDie();
+}
+
 DWARFDie DWARFUnit::getFirstChild(const DWARFDebugInfoEntry *Die) {
   if (!Die->hasChildren())
     return DWARFDie();
@@ -595,6 +613,20 @@
   return DWARFDie(this, &DieArray[I]);
 }
 
+DWARFDie DWARFUnit::getLastChild(const DWARFDebugInfoEntry *Die) {
+  if (!Die->hasChildren())
+    return DWARFDie();
+
+  uint32_t Depth = Die->getDepth();
+  for (size_t I = getDIEIndex(Die) + 1, EndIdx = DieArray.size(); I < EndIdx;
+       ++I) {
+    if (DieArray[I].getDepth() == Depth + 1 &&
+        DieArray[I].getTag() == dwarf::DW_TAG_null)
+      return DWARFDie(this, &DieArray[I]);
+  }
+  return DWARFDie();
+}
+
 const DWARFAbbreviationDeclarationSet *DWARFUnit::getAbbreviations() const {
   if (!Abbrevs)
     Abbrevs = Abbrev->getAbbreviationDeclarationSet(Header.getAbbrOffset());
Index: llvm/unittests/DebugInfo/DWARF/DWARFDebugInfoTest.cpp
===================================================================
--- llvm/unittests/DebugInfo/DWARF/DWARFDebugInfoTest.cpp
+++ llvm/unittests/DebugInfo/DWARF/DWARFDebugInfoTest.cpp
@@ -490,6 +490,11 @@
     EXPECT_TRUE(!NullDieDG.getSibling().isValid());
     EXPECT_TRUE(!NullDieDG.getFirstChild().isValid());
   }
+
+  // Verify the previous sibling of our subprogram is our integer base type.
+  IntDieDG = NullDieDG.getPreviousSibling();
+  EXPECT_TRUE(IntDieDG.isValid());
+  EXPECT_EQ(IntDieDG.getTag(), DW_TAG_base_type);
 }
 
 TEST(DWARFDebugInfo, TestDWARF32Version2Addr4Children) {
@@ -1072,6 +1077,27 @@
   // Make sure the parent of all the children of the B are the B.
   EXPECT_EQ(C1.getParent(), C);
   EXPECT_EQ(C2.getParent(), C);
+
+  // Make sure bidirectional iterator works as expected.
+  auto Begin = A.begin();
+  auto End = A.end();
+  auto It = A.begin();
+
+  EXPECT_EQ(It, Begin);
+  EXPECT_EQ(*It, B);
+  ++It;
+  EXPECT_EQ(*It, C);
+  ++It;
+  EXPECT_EQ(*It, D);
+  ++It;
+  EXPECT_EQ(It, End);
+  --It;
+  EXPECT_EQ(*It, D);
+  --It;
+  EXPECT_EQ(*It, C);
+  --It;
+  EXPECT_EQ(*It, B);
+  EXPECT_EQ(It, Begin);
 }
 
 TEST(DWARFDebugInfo, TestDWARFDie) {