Index: tools/diagtool/CMakeLists.txt
===================================================================
--- tools/diagtool/CMakeLists.txt
+++ tools/diagtool/CMakeLists.txt
@@ -8,6 +8,7 @@
   DiagnosticNames.cpp
   FindDiagnosticID.cpp
   ListWarnings.cpp
+  ListWarningFlags.cpp
   ShowEnabledWarnings.cpp
   TreeView.cpp
 )
Index: tools/diagtool/ListWarningFlags.cpp
===================================================================
--- /dev/null
+++ tools/diagtool/ListWarningFlags.cpp
@@ -0,0 +1,55 @@
+//===- ListWarningFlags.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 only warnings that have a
+// corresponding flags for diagnostics.
+//
+//===----------------------------------------------------------------------===//
+
+#include "DiagTool.h"
+#include "DiagnosticNames.h"
+#include "clang/AST/ASTDiagnostic.h"
+#include "clang/Basic/AllDiagnostics.h"
+#include "clang/Basic/Diagnostic.h"
+#include "llvm/Support/Format.h"
+#include <algorithm>
+#include <vector>
+
+DEF_DIAGTOOL("list-warning-flags", "List only warnings with flags",
+             ListWarningFlags)
+
+using namespace clang;
+using namespace diagtool;
+
+int ListWarningFlags::run(unsigned int argc, char **argv,
+                          llvm::raw_ostream &out) {
+  std::vector<llvm::StringRef> flags;
+
+  ArrayRef<DiagnosticRecord> AllDiagnostics = getBuiltinDiagnosticsByName();
+  for (ArrayRef<DiagnosticRecord>::iterator di = AllDiagnostics.begin(),
+                                            de = AllDiagnostics.end();
+       di != de; ++di) {
+    unsigned diagID = di->DiagID;
+    llvm::StringRef flag = DiagnosticIDs::getWarningOptionForDiag(diagID);
+
+    if (flag.empty())
+      continue;
+
+    flags.push_back(flag);
+  }
+
+  std::sort(flags.begin(), flags.end());
+  flags.erase(std::unique(flags.begin(), flags.end()), flags.end());
+
+  for (auto &flag : flags) {
+    out << "-W" << flag << '\n';
+  }
+
+  return 0;
+}
Index: tools/diagtool/ListWarnings.cpp
===================================================================
--- tools/diagtool/ListWarnings.cpp
+++ tools/diagtool/ListWarnings.cpp
@@ -1,4 +1,4 @@
-//===- ListWarnings.h - diagtool tool for printing warning flags ----------===//
+//===- ListWarnings.h - diagtool tool for printing warnings ---------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
@@ -7,7 +7,7 @@
 //
 //===----------------------------------------------------------------------===//
 //
-// This file provides a diagtool tool that displays warning flags for
+// This file provides a diagtool tool that displays all warning for
 // diagnostics.
 //
 //===----------------------------------------------------------------------===//
@@ -21,9 +21,9 @@
 #include "llvm/Support/Format.h"
 
 DEF_DIAGTOOL("list-warnings",
-             "List warnings and their corresponding flags",
+             "List all (internal) warnings",
              ListWarnings)
-  
+
 using namespace clang;
 using namespace diagtool;
 
@@ -31,10 +31,10 @@
 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; }
 };
 }
@@ -52,23 +52,23 @@
 int ListWarnings::run(unsigned int argc, char **argv, llvm::raw_ostream &out) {
   std::vector<Entry> Flagged, Unflagged;
   llvm::StringMap<std::vector<unsigned> > flagHistogram;
-  
+
   ArrayRef<DiagnosticRecord> AllDiagnostics = getBuiltinDiagnosticsByName();
 
   for (ArrayRef<DiagnosticRecord>::iterator di = AllDiagnostics.begin(),
                                             de = AllDiagnostics.end();
        di != de; ++di) {
     unsigned diagID = di->DiagID;
-    
+
     if (DiagnosticIDs::isBuiltinNote(diagID))
       continue;
-        
+
     if (!DiagnosticIDs::isBuiltinWarningOrExtension(diagID))
       continue;
-  
+
     Entry entry(di->getName(),
                 DiagnosticIDs::getWarningOptionForDiag(diagID));
-    
+
     if (entry.Flag.empty())
       Unflagged.push_back(entry);
     else {
@@ -76,24 +76,24 @@
       flagHistogram[entry.Flag].push_back(diagID);
     }
   }
-  
+
   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()) 
+  double percentFlagged = ((double) Flagged.size())
     / (Flagged.size() + Unflagged.size()) * 100.0;
-  
-  out << "  Percentage of warnings with flags: " 
+
+  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';
@@ -102,7 +102,7 @@
       << flagHistogram["pedantic"].size() << '\n';
 
   out << '\n';
-  
+
   return 0;
 }