diff --git a/tools/CMakeLists.txt b/tools/CMakeLists.txt
index 1b5252e..1bca496 100644
--- a/tools/CMakeLists.txt
+++ b/tools/CMakeLists.txt
@@ -1,5 +1,6 @@
 add_subdirectory(arcmt-test)
 add_subdirectory(c-arcmt-test)
 add_subdirectory(c-index-test)
+add_subdirectory(diagtool)
 add_subdirectory(driver)
 add_subdirectory(libclang)
diff --git a/tools/Makefile b/tools/Makefile
index bfd2a64..4ea2cdd 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -8,7 +8,7 @@
 ##===----------------------------------------------------------------------===##
 
 CLANG_LEVEL := ..
-DIRS := driver libclang c-index-test arcmt-test c-arcmt-test
+DIRS := driver libclang c-index-test arcmt-test c-arcmt-test diagtool
 
 include $(CLANG_LEVEL)/../../Makefile.config
 
diff --git a/tools/diagtool/CMakeLists.txt b/tools/diagtool/CMakeLists.txt
new file mode 100644
index 0000000..e69c8e9
--- /dev/null
+++ b/tools/diagtool/CMakeLists.txt
@@ -0,0 +1,20 @@
+set( LLVM_USED_LIBS
+  clangBasic
+  clangLex
+  clangSema
+  )
+
+add_clang_executable(diagtool
+  diagtool_main.cpp
+  DiagTool.cpp
+  ListWarnings.cpp
+)
+
+if(UNIX)
+  set(CLANGXX_LINK_OR_COPY create_symlink)
+else()
+  set(CLANGXX_LINK_OR_COPY copy)
+endif()
+
+install(TARGETS diagtool 
+  RUNTIME DESTINATION bin)
diff --git a/tools/diagtool/DiagTool.cpp b/tools/diagtool/DiagTool.cpp
new file mode 100644
index 0000000..1e3f4ef
--- /dev/null
+++ b/tools/diagtool/DiagTool.cpp
@@ -0,0 +1,68 @@
+//===- DiagTool.cpp - Classes for defining diagtool tools -------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the boilerplate for defining diagtool tools.
+//
+//===----------------------------------------------------------------------===//
+
+#include "DiagTool.h"
+#include "llvm/ADT/StringMap.h"
+#include "llvm/ADT/SmallString.h"
+#include <vector>
+
+using namespace diagtool;
+
+DiagTool::DiagTool(llvm::StringRef toolCmd,
+                   llvm::StringRef toolDesc)
+  : cmd(toolCmd), description(toolDesc) {}
+
+DiagTool::~DiagTool() {}
+
+typedef llvm::StringMap<DiagTool *> ToolMap;
+static inline ToolMap *getTools(void *v) { return static_cast<ToolMap*>(v); }
+
+DiagTools::DiagTools() : tools(new ToolMap()) {}
+DiagTools::~DiagTools() { delete getTools(tools); }
+
+DiagTool *DiagTools::getTool(llvm::StringRef toolCmd) {
+  ToolMap::iterator it = getTools(tools)->find(toolCmd);
+  return (it == getTools(tools)->end()) ? 0 : it->getValue();
+}
+
+void DiagTools::registerTool(DiagTool *tool) {
+  getTools(tools)->GetOrCreateValue(tool->getName(), tool);  
+}
+
+void DiagTools::printCommands(llvm::raw_ostream &out) {
+  std::vector<llvm::StringRef> toolNames;
+  unsigned maxName = 0;
+  for (ToolMap::iterator it = getTools(tools)->begin(),
+       ei = getTools(tools)->end(); it != ei; ++it) {
+    toolNames.push_back(it->getKey());
+    unsigned len = it->getKey().size();
+    if (len > maxName)
+      maxName = len;    
+  }
+  std::sort(toolNames.begin(), toolNames.end());
+
+  for (std::vector<llvm::StringRef>::iterator it = toolNames.begin(),
+       ei = toolNames.end(); it != ei; ++it) {
+
+    out << "  " << (*it);
+    unsigned spaces = (maxName + 3) - (it->size());
+    for (unsigned i = 0; i < spaces; ++i)
+      out << ' ';
+    
+    out << getTool(*it)->getDescription() << '\n';    
+  }
+}
+
+namespace diagtool {
+  DiagTools diagTools;
+}
diff --git a/tools/diagtool/DiagTool.h b/tools/diagtool/DiagTool.h
new file mode 100644
index 0000000..5e5e11f
--- /dev/null
+++ b/tools/diagtool/DiagTool.h
@@ -0,0 +1,69 @@
+//===- DiagTool.h - Classes for defining diagtool tools -------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the boilerplate for defining diagtool tools.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef DIAGTOOL_DIAGTOOL_H
+#define DIAGTOOL_DIAGTOOL_H
+
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/raw_ostream.h"
+#include <string>
+
+
+namespace diagtool {
+
+class DiagTool {
+  const std::string cmd;
+  const std::string description;
+public:
+  DiagTool(llvm::StringRef toolCmd, llvm::StringRef toolDesc);
+  virtual ~DiagTool();
+  
+  llvm::StringRef getName() const { return cmd; }  
+  llvm::StringRef getDescription() const { return description; }  
+
+  virtual int run(unsigned argc, char *argv[], llvm::raw_ostream &out) = 0;
+};
+  
+class DiagTools {
+  void *tools;
+public:
+  DiagTools();
+  ~DiagTools();
+  
+  DiagTool *getTool(llvm::StringRef toolCmd);
+  void registerTool(DiagTool *tool);  
+  void printCommands(llvm::raw_ostream &out);  
+};
+
+extern DiagTools diagTools;
+  
+template <typename DIAGTOOL>
+class RegisterDiagTool {
+public:
+  RegisterDiagTool() { diagTools.registerTool(new DIAGTOOL()); }
+};
+
+} // end diagtool namespace
+
+#define DEF_DIAGTOOL(NAME, DESC, CLSNAME)\
+namespace {\
+class CLSNAME : public diagtool::DiagTool {\
+public:\
+  CLSNAME() : DiagTool(NAME, DESC) {}\
+  virtual ~CLSNAME() {}\
+  virtual int run(unsigned argc, char *argv[], llvm::raw_ostream &out);\
+};\
+diagtool::RegisterDiagTool<CLSNAME> Register##CLSNAME;\
+}
+
+#endif
diff --git a/tools/diagtool/ListWarnings.cpp b/tools/diagtool/ListWarnings.cpp
new file mode 100644
index 0000000..70be1c4
--- /dev/null
+++ b/tools/diagtool/ListWarnings.cpp
@@ -0,0 +1,106 @@
+//===- ListWarnings.h - diagtool tool for printing warning flags ----------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file provides a diagtool tool that displays warning flags for
+// diagnostics.
+//
+//===----------------------------------------------------------------------===//
+
+#include "DiagTool.h"
+#include "clang/Basic/Diagnostic.h"
+#include "llvm/Support/Format.h"
+#include "llvm/ADT/StringMap.h"
+
+DEF_DIAGTOOL("list-warnings",
+             "List warnings and their corresponding flags",
+             ListWarnings)
+  
+using namespace clang;
+
+
+namespace {
+struct Entry {
+  llvm::StringRef DiagName;
+  llvm::StringRef Flag;
+  
+  Entry(llvm::StringRef diagN, llvm::StringRef flag)
+    : DiagName(diagN), Flag(flag) {}
+  
+  bool operator<(const Entry &x) const { return DiagName < x.DiagName; }
+};
+}
+
+static void printEntries(std::vector<Entry> &entries, llvm::raw_ostream &out) {
+  for (std::vector<Entry>::iterator it = entries.begin(), ei = entries.end();
+       it != ei; ++it) {
+    out << "  " << it->DiagName;
+    if (!it->Flag.empty())
+      out << " [-W" << it->Flag << "]";
+    out << '\n';
+  }
+}
+
+int ListWarnings::run(unsigned int argc, char **argv, llvm::raw_ostream &out) {
+  llvm::IntrusiveRefCntPtr<DiagnosticIDs> Diags(new DiagnosticIDs);
+  Diagnostic D(Diags);
+  
+  std::vector<Entry> Flagged, Unflagged;;
+  llvm::StringMap<std::vector<unsigned> > flagHistogram;
+  
+  for (DiagnosticIDs::diag_iterator di = DiagnosticIDs::diags_begin(),
+       de = DiagnosticIDs::diags_end(); di != de; ++di) {
+    
+    unsigned diagID = di.getDiagID();
+    
+    if (DiagnosticIDs::isBuiltinNote(diagID))
+      continue;
+        
+    if (!DiagnosticIDs::isBuiltinWarningOrExtension(diagID))
+      continue;
+  
+    Entry entry(di.getDiagName(),
+                DiagnosticIDs::getWarningOptionForDiag(diagID));
+    
+    if (entry.Flag.empty())
+      Unflagged.push_back(entry);
+    else {
+      Flagged.push_back(entry);
+      flagHistogram.GetOrCreateValue(entry.Flag).getValue().push_back(diagID);
+    }
+  }
+  
+  std::sort(Flagged.begin(), Flagged.end());
+  std::sort(Unflagged.begin(), Unflagged.end());
+
+  out << "Warnings with flags (" << Flagged.size() << "):\n";
+  printEntries(Flagged, out);
+  
+  out << "Warnings without flags (" << Unflagged.size() << "):\n";
+  printEntries(Unflagged, out);
+
+  out << "\nSTATISTICS:\n\n";
+
+  double percentFlagged = ((double) Flagged.size()) 
+    / (Flagged.size() + Unflagged.size()) * 100.0;
+  
+  out << "  Percentage of warnings with flags: " 
+      << llvm::format("%.4g",percentFlagged) << "%\n";
+  
+  out << "  Number of unique flags: "
+      << flagHistogram.size() << '\n';
+  
+  double avgDiagsPerFlag = (double) Flagged.size() / flagHistogram.size();
+  out << "  Average number of diagnostics per flag: "
+      << llvm::format("%.4g", avgDiagsPerFlag) << '\n';
+    
+  out << '\n';
+  
+  return 0;
+}
+
diff --git a/tools/diagtool/Makefile b/tools/diagtool/Makefile
new file mode 100644
index 0000000..22d7411
--- /dev/null
+++ b/tools/diagtool/Makefile
@@ -0,0 +1,25 @@
+##===- tools/driver/Makefile -------------------------------*- Makefile -*-===##
+#
+#                     The LLVM Compiler Infrastructure
+#
+# This file is distributed under the University of Illinois Open Source
+# License. See LICENSE.TXT for details.
+#
+##===----------------------------------------------------------------------===##
+CLANG_LEVEL := ../..
+
+TOOLNAME = diagtool 
+
+# No plugins, optimize startup time.
+TOOL_NO_EXPORTS := 1
+
+# Don't install this.
+NO_INSTALL = 1
+
+LINK_COMPONENTS := support
+ 
+USEDLIBS = clangCodeGen.a clangParse.a clangSema.a \
+           clangAST.a clangLex.a clangBasic.a
+
+include $(CLANG_LEVEL)/Makefile
+
diff --git a/tools/diagtool/diagtool_main.cpp b/tools/diagtool/diagtool_main.cpp
new file mode 100644
index 0000000..66a73e9
--- /dev/null
+++ b/tools/diagtool/diagtool_main.cpp
@@ -0,0 +1,26 @@
+//===- diagtool_main.h - Entry point for invoking all diagnostic tools ----===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the main function for diagtool.
+//
+//===----------------------------------------------------------------------===//
+
+#include "DiagTool.h"
+
+using namespace diagtool;
+
+int main(int argc, char *argv[]) {
+  if (argc > 1)
+    if (DiagTool *tool = diagTools.getTool(argv[1]))
+      return tool->run(argc - 1, &argv[2], llvm::errs());
+
+  llvm::errs() << "usage: diagtool <command> [<args>]\n\n";
+  diagTools.printCommands(llvm::errs());
+  return 1;    
+}