Index: llvm/trunk/lib/ObjectYAML/CMakeLists.txt
===================================================================
--- llvm/trunk/lib/ObjectYAML/CMakeLists.txt
+++ llvm/trunk/lib/ObjectYAML/CMakeLists.txt
@@ -1,6 +1,7 @@
 add_llvm_library(LLVMObjectYAML
   COFFYAML.cpp
   DWARFEmitter.cpp
+  DWARFVisitor.cpp
   DWARFYAML.cpp
   ELFYAML.cpp
   MachOYAML.cpp
Index: llvm/trunk/lib/ObjectYAML/DWARFEmitter.cpp
===================================================================
--- llvm/trunk/lib/ObjectYAML/DWARFEmitter.cpp
+++ llvm/trunk/lib/ObjectYAML/DWARFEmitter.cpp
@@ -19,6 +19,8 @@
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Support/SwapByteOrder.h"
 
+#include "DWARFVisitor.h"
+
 #include <algorithm>
 
 using namespace llvm;
@@ -117,130 +119,65 @@
   }
 }
 
-void DWARFYAML::EmitDebugInfo(raw_ostream &OS, const DWARFYAML::Data &DI) {
+/// \brief An extension of the DWARFYAML::ConstVisitor which writes compile
+/// units and DIEs to a stream.
+class DumpVisitor : public DWARFYAML::ConstVisitor {
+  raw_ostream &OS;
+
+protected:
+  virtual void onStartCompileUnit(const DWARFYAML::Unit &CU) {
+    writeInitialLength(CU.Length, OS, DebugInfo.IsLittleEndian);
+    writeInteger((uint16_t)CU.Version, OS, DebugInfo.IsLittleEndian);
+    writeInteger((uint32_t)CU.AbbrOffset, OS, DebugInfo.IsLittleEndian);
+    writeInteger((uint8_t)CU.AddrSize, OS, DebugInfo.IsLittleEndian);
+  }
 
-  for (auto CU : DI.CompileUnits) {
-    writeInitialLength(CU.Length, OS, DI.IsLittleEndian);
-    writeInteger((uint16_t)CU.Version, OS, DI.IsLittleEndian);
-    writeInteger((uint32_t)CU.AbbrOffset, OS, DI.IsLittleEndian);
-    writeInteger((uint8_t)CU.AddrSize, OS, DI.IsLittleEndian);
-
-    auto FirstAbbrevCode = CU.Entries[0].AbbrCode;
-
-    for (auto Entry : CU.Entries) {
-      encodeULEB128(Entry.AbbrCode, OS);
-      if (Entry.AbbrCode == 0u)
-        continue;
-      bool Indirect = false;
-      assert(Entry.AbbrCode - FirstAbbrevCode < DI.AbbrevDecls.size() &&
-             "Out of range AbbCode");
-      auto &Abbrev = DI.AbbrevDecls[Entry.AbbrCode - FirstAbbrevCode];
-
-      auto FormVal = Entry.Values.begin();
-      auto AbbrForm = Abbrev.Attributes.begin();
-      for (;
-           FormVal != Entry.Values.end() && AbbrForm != Abbrev.Attributes.end();
-           ++FormVal, ++AbbrForm) {
-        dwarf::Form Form = AbbrForm->Form;
-        do {
-          Indirect = false;
-          switch (Form) {
-          case dwarf::DW_FORM_addr:
-            writeVariableSizedInteger(FormVal->Value, CU.AddrSize, OS,
-                                      DI.IsLittleEndian);
-            break;
-          case dwarf::DW_FORM_ref_addr: {
-            // TODO: Handle DWARF32/DWARF64 after Line Table data is done
-            auto writeSize = CU.Version == 2 ? CU.AddrSize : 4;
-            writeVariableSizedInteger(FormVal->Value, writeSize, OS,
-                                      DI.IsLittleEndian);
-            break;
-          }
-          case dwarf::DW_FORM_exprloc:
-          case dwarf::DW_FORM_block:
-            encodeULEB128(FormVal->BlockData.size(), OS);
-            OS.write(reinterpret_cast<char *>(&FormVal->BlockData[0]),
-                     FormVal->BlockData.size());
-            break;
-          case dwarf::DW_FORM_block1: {
-            auto writeSize = FormVal->BlockData.size();
-            writeInteger((uint8_t)writeSize, OS, DI.IsLittleEndian);
-            OS.write(reinterpret_cast<char *>(&FormVal->BlockData[0]),
-                     FormVal->BlockData.size());
-            break;
-          }
-          case dwarf::DW_FORM_block2: {
-            auto writeSize = FormVal->BlockData.size();
-            writeInteger((uint16_t)writeSize, OS, DI.IsLittleEndian);
-            OS.write(reinterpret_cast<char *>(&FormVal->BlockData[0]),
-                     FormVal->BlockData.size());
-            break;
-          }
-          case dwarf::DW_FORM_block4: {
-            auto writeSize = FormVal->BlockData.size();
-            writeInteger((uint32_t)writeSize, OS, DI.IsLittleEndian);
-            OS.write(reinterpret_cast<char *>(&FormVal->BlockData[0]),
-                     FormVal->BlockData.size());
-            break;
-          }
-          case dwarf::DW_FORM_data1:
-          case dwarf::DW_FORM_ref1:
-          case dwarf::DW_FORM_flag:
-            writeInteger((uint8_t)FormVal->Value, OS, DI.IsLittleEndian);
-            break;
-          case dwarf::DW_FORM_data2:
-          case dwarf::DW_FORM_ref2:
-            writeInteger((uint16_t)FormVal->Value, OS, DI.IsLittleEndian);
-            break;
-          case dwarf::DW_FORM_data4:
-          case dwarf::DW_FORM_ref4:
-            writeInteger((uint32_t)FormVal->Value, OS, DI.IsLittleEndian);
-            break;
-          case dwarf::DW_FORM_data8:
-          case dwarf::DW_FORM_ref8:
-            writeInteger((uint64_t)FormVal->Value, OS, DI.IsLittleEndian);
-            break;
-          case dwarf::DW_FORM_sdata:
-            encodeSLEB128(FormVal->Value, OS);
-            break;
-          case dwarf::DW_FORM_udata:
-          case dwarf::DW_FORM_ref_udata:
-            encodeULEB128(FormVal->Value, OS);
-            break;
-          case dwarf::DW_FORM_string:
-            OS.write(FormVal->CStr.data(), FormVal->CStr.size());
-            OS.write('\0');
-            break;
-          case dwarf::DW_FORM_indirect:
-            encodeULEB128(FormVal->Value, OS);
-            Indirect = true;
-            Form = static_cast<dwarf::Form>((uint64_t)FormVal->Value);
-            ++FormVal;
-            break;
-          case dwarf::DW_FORM_strp:
-          case dwarf::DW_FORM_sec_offset:
-          case dwarf::DW_FORM_GNU_ref_alt:
-          case dwarf::DW_FORM_GNU_strp_alt:
-          case dwarf::DW_FORM_line_strp:
-          case dwarf::DW_FORM_strp_sup:
-          case dwarf::DW_FORM_ref_sup:
-            // TODO: Handle DWARF32/64
-            writeInteger((uint32_t)FormVal->Value, OS, DI.IsLittleEndian);
-            break;
-          case dwarf::DW_FORM_ref_sig8:
-            writeInteger((uint64_t)FormVal->Value, OS, DI.IsLittleEndian);
-            break;
-          case dwarf::DW_FORM_GNU_addr_index:
-          case dwarf::DW_FORM_GNU_str_index:
-            encodeULEB128(FormVal->Value, OS);
-            break;
-          default:
-            break;
-          }
-        } while (Indirect);
-      }
-    }
+  virtual void onStartDIE(const DWARFYAML::Unit &CU,
+                          const DWARFYAML::Entry &DIE) {
+    encodeULEB128(DIE.AbbrCode, OS);
+  }
+
+  virtual void onValue(const uint8_t U) {
+    writeInteger(U, OS, DebugInfo.IsLittleEndian);
+  }
+
+  virtual void onValue(const uint16_t U) {
+    writeInteger(U, OS, DebugInfo.IsLittleEndian);
+  }
+  virtual void onValue(const uint32_t U) {
+    writeInteger(U, OS, DebugInfo.IsLittleEndian);
   }
+  virtual void onValue(const uint64_t U, const bool LEB = false) {
+    if (LEB)
+      encodeULEB128(U, OS);
+    else
+      writeInteger(U, OS, DebugInfo.IsLittleEndian);
+  }
+
+  virtual void onValue(const int64_t S, const bool LEB = false) {
+    if (LEB)
+      encodeSLEB128(S, OS);
+    else
+      writeInteger(S, OS, DebugInfo.IsLittleEndian);
+  }
+
+  virtual void onValue(const StringRef String) {
+    OS.write(String.data(), String.size());
+    OS.write('\0');
+  }
+
+  virtual void onValue(const MemoryBufferRef MBR) {
+    OS.write(MBR.getBufferStart(), MBR.getBufferSize());
+  }
+
+public:
+  DumpVisitor(const DWARFYAML::Data &DI, raw_ostream &Out)
+      : DWARFYAML::ConstVisitor(DI), OS(Out) {}
+};
+
+void DWARFYAML::EmitDebugInfo(raw_ostream &OS, const DWARFYAML::Data &DI) {
+  DumpVisitor Visitor(DI, OS);
+  Visitor.traverseDebugInfo();
 }
 
 static void EmitFileEntry(raw_ostream &OS, const DWARFYAML::File &File) {
Index: llvm/trunk/lib/ObjectYAML/DWARFVisitor.h
===================================================================
--- llvm/trunk/lib/ObjectYAML/DWARFVisitor.h
+++ llvm/trunk/lib/ObjectYAML/DWARFVisitor.h
@@ -0,0 +1,97 @@
+//===--- DWARFVisitor.h -----------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_OBJECTYAML_DWARFVISITOR_H
+#define LLVM_OBJECTYAML_DWARFVISITOR_H
+
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/Dwarf.h"
+#include "llvm/Support/MemoryBuffer.h"
+
+namespace llvm {
+
+namespace DWARFYAML {
+
+struct Data;
+struct Unit;
+struct Entry;
+struct FormValue;
+struct AttributeAbbrev;
+
+/// \brief A class to visits DWARFYAML Compile Units and DIEs in preorder.
+///
+/// Extensions of this class can either maintain const or non-const references
+/// to the DWARFYAML::Data object.
+template <typename T> class VisitorImpl {
+protected:
+  T &DebugInfo;
+
+  /// Visitor Functions
+  /// @{
+  virtual void onStartCompileUnit(Unit &CU) {}
+  virtual void onEndCompileUnit(Unit &CU) {}
+  virtual void onStartDIE(Unit &CU, Entry &DIE) {}
+  virtual void onEndDIE(Unit &CU, Entry &DIE) {}
+  virtual void onForm(AttributeAbbrev &AttAbbrev, FormValue &Value) {}
+  /// @}
+
+  /// Const Visitor Functions
+  /// @{
+  virtual void onStartCompileUnit(const Unit &CU) {}
+  virtual void onEndCompileUnit(const Unit &CU) {}
+  virtual void onStartDIE(const Unit &CU, const Entry &DIE) {}
+  virtual void onEndDIE(const Unit &CU, const Entry &DIE) {}
+  virtual void onForm(const AttributeAbbrev &AttAbbrev,
+                      const FormValue &Value) {}
+  /// @}
+
+  /// Value visitors
+  /// @{
+  virtual void onValue(const uint8_t U) {}
+  virtual void onValue(const uint16_t U) {}
+  virtual void onValue(const uint32_t U) {}
+  virtual void onValue(const uint64_t U, const bool LEB = false) {}
+  virtual void onValue(const int64_t S, const bool LEB = false) {}
+  virtual void onValue(const StringRef String) {}
+  virtual void onValue(const MemoryBufferRef MBR) {}
+  /// @}
+
+public:
+  VisitorImpl(T &DI) : DebugInfo(DI) {}
+
+  virtual ~VisitorImpl() {}
+
+  void traverseDebugInfo();
+
+private:
+  void onVariableSizeValue(uint64_t U, unsigned Size);
+};
+
+// Making the visior instantiations extern and explicit in the cpp file. This
+// prevents them from being instantiated in every compile unit that uses the
+// visitors.
+extern template class VisitorImpl<DWARFYAML::Data>;
+extern template class VisitorImpl<const DWARFYAML::Data>;
+
+class Visitor : public VisitorImpl<Data> {
+public:
+  Visitor(Data &DI) : VisitorImpl<Data>(DI) {}
+};
+
+class ConstVisitor : public VisitorImpl<const Data> {
+public:
+  ConstVisitor(const Data &DI) : VisitorImpl<const Data>(DI) {}
+};
+
+} // namespace DWARFYAML
+} // namespace llvm
+
+#endif
Index: llvm/trunk/lib/ObjectYAML/DWARFVisitor.cpp
===================================================================
--- llvm/trunk/lib/ObjectYAML/DWARFVisitor.cpp
+++ llvm/trunk/lib/ObjectYAML/DWARFVisitor.cpp
@@ -0,0 +1,167 @@
+//===--- DWARFVisitor.cpp ---------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+//===----------------------------------------------------------------------===//
+
+#include "DWARFVisitor.h"
+#include "llvm/ObjectYAML/DWARFYAML.h"
+
+using namespace llvm;
+
+template <typename T>
+void DWARFYAML::VisitorImpl<T>::onVariableSizeValue(uint64_t U, unsigned Size) {
+  switch (Size) {
+  case 8:
+    onValue((uint64_t)U);
+    break;
+  case 4:
+    onValue((uint32_t)U);
+    break;
+  case 2:
+    onValue((uint16_t)U);
+    break;
+  case 1:
+    onValue((uint8_t)U);
+    break;
+  default:
+    llvm_unreachable("Invalid integer write size.");
+  }
+}
+
+unsigned getRefSize(const DWARFYAML::Unit &Unit) {
+  if (Unit.Version == 2)
+    return Unit.AddrSize;
+  return Unit.Length.isDWARF64() ? 8 : 4;
+}
+
+template <typename T> void DWARFYAML::VisitorImpl<T>::traverseDebugInfo() {
+  for (auto &Unit : DebugInfo.CompileUnits) {
+    onStartCompileUnit(Unit);
+    auto FirstAbbrevCode = Unit.Entries[0].AbbrCode;
+
+    for (auto &Entry : Unit.Entries) {
+      onStartDIE(Unit, Entry);
+      if (Entry.AbbrCode == 0u)
+        continue;
+      auto &Abbrev = DebugInfo.AbbrevDecls[Entry.AbbrCode - FirstAbbrevCode];
+      auto FormVal = Entry.Values.begin();
+      auto AbbrForm = Abbrev.Attributes.begin();
+      for (;
+           FormVal != Entry.Values.end() && AbbrForm != Abbrev.Attributes.end();
+           ++FormVal, ++AbbrForm) {
+        onForm(*AbbrForm, *FormVal);
+        dwarf::Form Form = AbbrForm->Form;
+        bool Indirect;
+        do {
+          Indirect = false;
+          switch (Form) {
+          case dwarf::DW_FORM_addr:
+            onVariableSizeValue(FormVal->Value, Unit.AddrSize);
+            break;
+          case dwarf::DW_FORM_ref_addr:
+            onVariableSizeValue(FormVal->Value, getRefSize(Unit));
+            break;
+          case dwarf::DW_FORM_exprloc:
+          case dwarf::DW_FORM_block:
+            onValue((uint64_t)FormVal->BlockData.size(), true);
+            onValue(
+                MemoryBufferRef(StringRef((const char *)&FormVal->BlockData[0],
+                                          FormVal->BlockData.size()),
+                                ""));
+            break;
+          case dwarf::DW_FORM_block1: {
+            auto writeSize = FormVal->BlockData.size();
+            onValue((uint8_t)writeSize);
+            onValue(
+                MemoryBufferRef(StringRef((const char *)&FormVal->BlockData[0],
+                                          FormVal->BlockData.size()),
+                                ""));
+            break;
+          }
+          case dwarf::DW_FORM_block2: {
+            auto writeSize = FormVal->BlockData.size();
+            onValue((uint16_t)writeSize);
+            onValue(
+                MemoryBufferRef(StringRef((const char *)&FormVal->BlockData[0],
+                                          FormVal->BlockData.size()),
+                                ""));
+            break;
+          }
+          case dwarf::DW_FORM_block4: {
+            auto writeSize = FormVal->BlockData.size();
+            onValue((uint32_t)writeSize);
+            onValue(
+                MemoryBufferRef(StringRef((const char *)&FormVal->BlockData[0],
+                                          FormVal->BlockData.size()),
+                                ""));
+            break;
+          }
+          case dwarf::DW_FORM_data1:
+          case dwarf::DW_FORM_ref1:
+          case dwarf::DW_FORM_flag:
+            onValue((uint8_t)FormVal->Value);
+            break;
+          case dwarf::DW_FORM_data2:
+          case dwarf::DW_FORM_ref2:
+            onValue((uint16_t)FormVal->Value);
+            break;
+          case dwarf::DW_FORM_data4:
+          case dwarf::DW_FORM_ref4:
+            onValue((uint32_t)FormVal->Value);
+            break;
+          case dwarf::DW_FORM_data8:
+          case dwarf::DW_FORM_ref8:
+            onValue((uint64_t)FormVal->Value);
+            break;
+          case dwarf::DW_FORM_sdata:
+            onValue((int64_t)FormVal->Value, true);
+            break;
+          case dwarf::DW_FORM_udata:
+          case dwarf::DW_FORM_ref_udata:
+            onValue((uint64_t)FormVal->Value, true);
+            break;
+          case dwarf::DW_FORM_string:
+            onValue(FormVal->CStr);
+            break;
+          case dwarf::DW_FORM_indirect:
+            onValue((uint64_t)FormVal->Value, true);
+            Indirect = true;
+            Form = static_cast<dwarf::Form>((uint64_t)FormVal->Value);
+            ++FormVal;
+            break;
+          case dwarf::DW_FORM_strp:
+          case dwarf::DW_FORM_sec_offset:
+          case dwarf::DW_FORM_GNU_ref_alt:
+          case dwarf::DW_FORM_GNU_strp_alt:
+          case dwarf::DW_FORM_line_strp:
+          case dwarf::DW_FORM_strp_sup:
+          case dwarf::DW_FORM_ref_sup:
+            onVariableSizeValue(FormVal->Value, getRefSize(Unit));
+            break;
+          case dwarf::DW_FORM_ref_sig8:
+            onValue((uint64_t)FormVal->Value);
+            break;
+          case dwarf::DW_FORM_GNU_addr_index:
+          case dwarf::DW_FORM_GNU_str_index:
+            onValue((uint64_t)FormVal->Value, true);
+            break;
+          default:
+            break;
+          }
+        } while (Indirect);
+      }
+      onEndDIE(Unit, Entry);
+    }
+    onEndCompileUnit(Unit);
+  }
+}
+
+// Explicitly instantiate the two template expansions.
+template class DWARFYAML::VisitorImpl<DWARFYAML::Data>;
+template class DWARFYAML::VisitorImpl<const DWARFYAML::Data>;