diff --git a/utils/TableGen/ClangDiagnosticsEmitter.cpp b/utils/TableGen/ClangDiagnosticsEmitter.cpp
index fa139e7729e..f9501fb494d 100644
--- a/utils/TableGen/ClangDiagnosticsEmitter.cpp
+++ b/utils/TableGen/ClangDiagnosticsEmitter.cpp
@@ -22,8 +22,8 @@ typedef std::vector<Record*> RecordVector;
 typedef std::vector<Record*> SuperClassVector;
 typedef std::vector<RecordVal> RecordValVector;
 
-static const RecordVal* findRecordVal(const RecordValVector& Vals,
-                                      const std::string &key) {
+static const RecordVal* findRecordVal(const Record& R, const std::string &key) {  
+  const RecordValVector &Vals = R.getValues();
   for (RecordValVector::const_iterator I=Vals.begin(), E=Vals.end(); I!=E; ++I)
     if ((*I).getName() == key)
       return &*I;
@@ -49,6 +49,11 @@ static void EmitEscaped(std::ostream& OS, const std::string &s) {
     }
 }
 
+static void EmitAllCaps(std::ostream& OS, const std::string &s) {
+  for (std::string::const_iterator I=s.begin(), E=s.end(); I!=E; ++I)
+    OS << char(toupper(*I));  
+}
+
 static void ProcessDiag(std::ostream& OS, const Record* DiagClass,
                         const Record& R) {
 
@@ -57,12 +62,9 @@ static void ProcessDiag(std::ostream& OS, const Record* DiagClass,
     return;
 
   OS << "DIAG(" << R.getName() << ", ";
+  EmitAllCaps(OS, DiagKind->getName());
   
-  const std::string &s = DiagKind->getName();
-  for (std::string::const_iterator I=s.begin(), E=s.end(); I!=E; ++I)
-    OS << char(toupper(*I));
-  
-  const RecordVal* Text = findRecordVal(R.getValues(), "Text");
+  const RecordVal* Text = findRecordVal(R, "Text");
   assert(Text && "No 'Text' entry in Diagnostic.");
   const StringInit* TextVal = dynamic_cast<const StringInit*>(Text->getValue());
   assert(TextVal && "Value 'Text' must be a string.");
@@ -77,8 +79,30 @@ void ClangDiagsDefsEmitter::run(std::ostream &OS) {
   const Record* DiagClass = Records.getClass("Diagnostic");
   assert(DiagClass && "No Diagnostic class defined.");  
   
+  // Write the #if guard
+  if (!Component.empty()) {
+    OS << "#ifdef ";
+    EmitAllCaps(OS, Component);
+    OS << "START\n__";
+    EmitAllCaps(OS, Component);
+    OS << "START = DIAG_START_";
+    EmitAllCaps(OS, Component);
+    OS << ",\n#undef ";
+    EmitAllCaps(OS, Component);
+    OS << "START\n#endif\n";
+  }
+  
   for (RecordVector::const_iterator I=Diags.begin(), E=Diags.end(); I!=E; ++I) {
-    // FIXME: Compare the component.
+    if (!Component.empty()) {
+      const RecordVal* V = findRecordVal(**I, "Component");
+      if (!V)
+        continue;
+
+      const StringInit* SV = dynamic_cast<const StringInit*>(V->getValue());
+      if (SV->getValue() != Component)
+        continue;
+    }
+    
     ProcessDiag(OS, DiagClass, **I);
   }
-}
\ No newline at end of file
+}
diff --git a/utils/TableGen/ClangDiagnosticsEmitter.h b/utils/TableGen/ClangDiagnosticsEmitter.h
index 93979708b07..bedfe5af8f8 100644
--- a/utils/TableGen/ClangDiagnosticsEmitter.h
+++ b/utils/TableGen/ClangDiagnosticsEmitter.h
@@ -23,8 +23,10 @@ namespace llvm {
 ///
 class ClangDiagsDefsEmitter : public TableGenBackend {
   RecordKeeper &Records;
+  const std::string& Component;
 public:
-  explicit ClangDiagsDefsEmitter(RecordKeeper &R) : Records(R) {}
+  explicit ClangDiagsDefsEmitter(RecordKeeper &R, const std::string& component)
+    : Records(R), Component(component) {}
 
   // run - Output the .def file contents
   void run(std::ostream &OS);
diff --git a/utils/TableGen/TableGen.cpp b/utils/TableGen/TableGen.cpp
index e6ed092b62f..22c5d504155 100644
--- a/utils/TableGen/TableGen.cpp
+++ b/utils/TableGen/TableGen.cpp
@@ -110,6 +110,11 @@ namespace {
   cl::list<std::string>
   IncludeDirs("I", cl::desc("Directory of include files"),
               cl::value_desc("directory"), cl::Prefix);
+  
+  cl::opt<std::string>
+  ClangComponent("clang-component",
+                 cl::desc("Only use warnings from specified component"),
+                 cl::value_desc("component"), cl::Hidden);
 }
 
 
@@ -202,7 +207,7 @@ int main(int argc, char **argv) {
       AsmWriterEmitter(Records).run(*Out);
       break;
     case GenClangDiagsDefs:
-      ClangDiagsDefsEmitter(Records).run(*Out);
+      ClangDiagsDefsEmitter(Records, ClangComponent).run(*Out);
       break;
     case GenDAGISel:
       DAGISelEmitter(Records).run(*Out);