diff --git a/tools/driver/CMakeLists.txt b/tools/driver/CMakeLists.txt
index ca2f408..706f050 100644
--- a/tools/driver/CMakeLists.txt
+++ b/tools/driver/CMakeLists.txt
@@ -26,6 +26,7 @@
 add_clang_executable(clang
   driver.cpp
   cc1_main.cpp
+  cc1as_main.cpp
   )
 
 if(UNIX)
diff --git a/tools/driver/cc1_main.cpp b/tools/driver/cc1_main.cpp
index 67dc7c6..6dc3a7f 100644
--- a/tools/driver/cc1_main.cpp
+++ b/tools/driver/cc1_main.cpp
@@ -1,4 +1,4 @@
-//===-- cc1_main.cpp - Clang CC1 Driver -----------------------------------===//
+//===-- cc1_main.cpp - Clang CC1 Compiler Frontend ------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
@@ -43,7 +43,7 @@
 // Main driver
 //===----------------------------------------------------------------------===//
 
-void LLVMErrorHandler(void *UserData, const std::string &Message) {
+static void LLVMErrorHandler(void *UserData, const std::string &Message) {
   Diagnostic &Diags = *static_cast<Diagnostic*>(UserData);
 
   Diags.Report(diag::err_fe_error_backend) << Message;
diff --git a/tools/driver/cc1as_main.cpp b/tools/driver/cc1as_main.cpp
new file mode 100644
index 0000000..742a484
--- /dev/null
+++ b/tools/driver/cc1as_main.cpp
@@ -0,0 +1,335 @@
+//===-- cc1as_main.cpp - Clang Assembler  ---------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This is the entry point to the clang -cc1as functionality, which implements
+// the direct interface to the LLVM MC based assembler.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/Basic/Diagnostic.h"
+#include "clang/Driver/Arg.h"
+#include "clang/Driver/ArgList.h"
+#include "clang/Driver/DriverDiagnostic.h"
+#include "clang/Driver/CC1AsOptions.h"
+#include "clang/Driver/OptTable.h"
+#include "clang/Driver/Options.h"
+#include "clang/Frontend/DiagnosticOptions.h"
+#include "clang/Frontend/FrontendDiagnostic.h"
+#include "clang/Frontend/TextDiagnosticPrinter.h"
+#include "llvm/ADT/OwningPtr.h"
+#include "llvm/ADT/StringSwitch.h"
+#include "llvm/MC/MCParser/AsmParser.h"
+#include "llvm/MC/MCCodeEmitter.h"
+#include "llvm/MC/MCContext.h"
+#include "llvm/MC/MCStreamer.h"
+#include "llvm/Support/FormattedStream.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/ManagedStatic.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/PrettyStackTrace.h"
+#include "llvm/Support/SourceMgr.h"
+#include "llvm/Support/Timer.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/System/Host.h"
+#include "llvm/System/Path.h"
+#include "llvm/System/Signals.h"
+#include "llvm/Target/TargetAsmBackend.h"
+#include "llvm/Target/TargetAsmParser.h"
+#include "llvm/Target/TargetData.h"
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/Target/TargetRegistry.h"
+#include "llvm/Target/TargetSelect.h"
+using namespace clang;
+using namespace clang::driver;
+using namespace llvm;
+
+namespace {
+
+/// \brief Helper class for representing a single invocation of the assembler.
+struct AssemblerInvocation {
+  /// @name Target Options
+  /// @{
+
+  std::string Triple;
+
+  /// @}
+  /// @name Language Options
+  /// @{
+
+  std::vector<std::string> IncludePaths;
+  unsigned NoInitialTextSection : 1;
+
+  /// @}
+  /// @name Frontend Options
+  /// @{
+
+  std::string InputFile;
+  std::string OutputPath;
+  enum FileType {
+    FT_Asm,  ///< Assembly (.s) output, transliterate mode.
+    FT_Null, ///< No output, for timing purposes.
+    FT_Obj   ///< Object file output.
+  };
+  FileType OutputType;
+
+  /// @}
+  /// @name Transliterate Options
+  /// @{
+
+  unsigned OutputAsmVariant;
+  unsigned ShowEncoding : 1;
+  unsigned ShowInst : 1;
+
+  /// @}
+  /// @name Assembler Options
+  /// @{
+
+  unsigned RelaxAll : 1;
+
+  /// @}
+
+public:
+  AssemblerInvocation() {
+    Triple = "";
+    NoInitialTextSection = 0;
+    InputFile = "-";
+    OutputPath = "a.out";
+    OutputType = FT_Asm;
+    OutputAsmVariant = 0;
+    ShowInst = 0;
+    ShowEncoding = 0;
+    RelaxAll = 0;
+  }
+
+  static void CreateFromArgs(AssemblerInvocation &Res, const char **ArgBegin,
+                             const char **ArgEnd, Diagnostic &Diags);
+};
+
+}
+
+void AssemblerInvocation::CreateFromArgs(AssemblerInvocation &Opts,
+                                         const char **ArgBegin,
+                                         const char **ArgEnd,
+                                         Diagnostic &Diags) {
+  using namespace clang::driver::cc1asoptions;
+  // Parse the arguments.
+  OwningPtr<OptTable> OptTbl(createCC1AsOptTable());
+  unsigned MissingArgIndex, MissingArgCount;
+  OwningPtr<InputArgList> Args(
+    OptTbl->ParseArgs(ArgBegin, ArgEnd,MissingArgIndex, MissingArgCount));
+
+  // Check for missing argument error.
+  if (MissingArgCount)
+    Diags.Report(diag::err_drv_missing_argument)
+      << Args->getArgString(MissingArgIndex) << MissingArgCount;
+
+  // Issue errors on unknown arguments.
+  for (arg_iterator it = Args->filtered_begin(cc1asoptions::OPT_UNKNOWN),
+         ie = Args->filtered_end(); it != ie; ++it)
+    Diags.Report(diag::err_drv_unknown_argument) << it->getAsString(*Args);
+
+  // Construct the invocation.
+
+  // Target Options
+  Opts.Triple = Args->getLastArgValue(OPT_triple);
+  if (Opts.Triple.empty()) // Use the host triple if unspecified.
+    Opts.Triple = sys::getHostTriple();
+
+  // Language Options
+  Opts.IncludePaths = Args->getAllArgValues(OPT_I);
+  Opts.NoInitialTextSection = Args->hasArg(OPT_n);
+
+  // Frontend Options
+  if (Args->hasArg(OPT_INPUT)) {
+    bool First = true;
+    for (arg_iterator it = Args->filtered_begin(OPT_INPUT),
+           ie = Args->filtered_end(); it != ie; ++it, First=false) {
+      if (First)
+        Opts.InputFile = it->getValue(*Args);
+      else
+        Diags.Report(diag::err_drv_unknown_argument) << it->getAsString(*Args);
+    }
+  }
+  Opts.OutputPath = Args->getLastArgValue(OPT_o);
+  if (Arg *A = Args->getLastArg(OPT_filetype)) {
+    StringRef Name = A->getValue(*Args);
+    unsigned OutputType = StringSwitch<unsigned>(Name)
+      .Case("asm", FT_Asm)
+      .Case("null", FT_Null)
+      .Case("obj", FT_Obj)
+      .Default(~0U);
+    if (OutputType == ~0U)
+      Diags.Report(diag::err_drv_invalid_value)
+        << A->getAsString(*Args) << Name;
+    else
+      Opts.OutputType = FileType(OutputType);
+  }
+
+  // Transliterate Options
+  Opts.OutputAsmVariant = Args->getLastArgIntValue(OPT_output_asm_variant,
+                                                   0, Diags);
+  Opts.ShowEncoding = Args->hasArg(OPT_show_encoding);
+  Opts.ShowInst = Args->hasArg(OPT_show_inst);
+
+  // Assemble Options
+  Opts.RelaxAll = Args->hasArg(OPT_relax_all);
+}
+
+static formatted_raw_ostream *GetOutputStream(AssemblerInvocation &Opts,
+                                              Diagnostic &Diags,
+                                              bool Binary) {
+  // Make sure that the Out file gets unlinked from the disk if we get a
+  // SIGINT.
+  if (Opts.OutputPath != "-")
+    sys::RemoveFileOnSignal(sys::Path(Opts.OutputPath));
+
+  std::string Error;
+  raw_fd_ostream *Out =
+    new raw_fd_ostream(Opts.OutputPath.c_str(), Error,
+                       (Binary ? raw_fd_ostream::F_Binary : 0));
+  if (!Error.empty()) {
+    Diags.Report(diag::err_fe_unable_to_open_output)
+      << Opts.OutputPath << Error;
+    return 0;
+  }
+
+  return new formatted_raw_ostream(*Out, formatted_raw_ostream::DELETE_STREAM);
+}
+
+static bool ExecuteAssembler(AssemblerInvocation &Opts, Diagnostic &Diags) {
+  // Get the target specific parser.
+  std::string Error;
+  const Target *TheTarget(TargetRegistry::lookupTarget(Opts.Triple, Error));
+  if (!TheTarget) {
+    Diags.Report(diag::err_target_unknown_triple) << Opts.Triple;
+    return false;
+  }
+
+  MemoryBuffer *Buffer = MemoryBuffer::getFileOrSTDIN(Opts.InputFile, &Error);
+  if (Buffer == 0) {
+    Diags.Report(diag::err_fe_error_reading) << Opts.InputFile;
+    return false;
+  }
+
+  SourceMgr SrcMgr;
+
+  // Tell SrcMgr about this buffer, which is what the parser will pick up.
+  SrcMgr.AddNewSourceBuffer(Buffer, SMLoc());
+
+  // Record the location of the include directories so that the lexer can find
+  // it later.
+  SrcMgr.setIncludeDirs(Opts.IncludePaths);
+
+  OwningPtr<MCAsmInfo> MAI(TheTarget->createAsmInfo(Opts.Triple));
+  assert(MAI && "Unable to create target asm info!");
+
+  MCContext Ctx(*MAI);
+  bool IsBinary = Opts.OutputType == AssemblerInvocation::FT_Obj;
+  formatted_raw_ostream *Out = GetOutputStream(Opts, Diags, IsBinary);
+  if (!Out)
+    return false;
+
+  // FIXME: We shouldn't need to do this (and link in codegen).
+  OwningPtr<TargetMachine> TM(TheTarget->createTargetMachine(Opts.Triple, ""));
+  if (!TM) {
+    Diags.Report(diag::err_target_unknown_triple) << Opts.Triple;
+    return false;
+  }
+
+  OwningPtr<MCCodeEmitter> CE;
+  OwningPtr<MCStreamer> Str;
+  OwningPtr<TargetAsmBackend> TAB;
+
+  if (Opts.OutputType == AssemblerInvocation::FT_Asm) {
+    MCInstPrinter *IP =
+      TheTarget->createMCInstPrinter(Opts.OutputAsmVariant, *MAI);
+    if (Opts.ShowEncoding)
+      CE.reset(TheTarget->createCodeEmitter(*TM, Ctx));
+    Str.reset(createAsmStreamer(Ctx, *Out,TM->getTargetData()->isLittleEndian(),
+                                /*asmverbose*/true, IP, CE.get(),
+                                Opts.ShowInst));
+  } else if (Opts.OutputType == AssemblerInvocation::FT_Null) {
+    Str.reset(createNullStreamer(Ctx));
+  } else {
+    assert(Opts.OutputType == AssemblerInvocation::FT_Obj &&
+           "Invalid file type!");
+    CE.reset(TheTarget->createCodeEmitter(*TM, Ctx));
+    TAB.reset(TheTarget->createAsmBackend(Opts.Triple));
+    Str.reset(createMachOStreamer(Ctx, *TAB, *Out, CE.get(), Opts.RelaxAll));
+  }
+
+  AsmParser Parser(SrcMgr, Ctx, *Str.get(), *MAI);
+  OwningPtr<TargetAsmParser> TAP(TheTarget->createAsmParser(Parser));
+  if (!TAP) {
+    Diags.Report(diag::err_target_unknown_triple) << Opts.Triple;
+    return false;
+  }
+
+  Parser.setTargetParser(*TAP.get());
+
+  bool Success = !Parser.Run(Opts.NoInitialTextSection);
+
+  // Close the output.
+  delete Out;
+
+  // Delete output on errors.
+  if (!Success && Opts.OutputPath != "-")
+    sys::Path(Opts.OutputPath).eraseFromDisk();
+
+  return Success;
+}
+
+static void LLVMErrorHandler(void *UserData, const std::string &Message) {
+  Diagnostic &Diags = *static_cast<Diagnostic*>(UserData);
+
+  Diags.Report(diag::err_fe_error_backend) << Message;
+
+  // We cannot recover from llvm errors.
+  exit(1);
+}
+
+int cc1as_main(const char **ArgBegin, const char **ArgEnd,
+               const char *Argv0, void *MainAddr) {
+  // Print a stack trace if we signal out.
+  sys::PrintStackTraceOnErrorSignal();
+  PrettyStackTraceProgram X(ArgEnd - ArgBegin, ArgBegin);
+  llvm_shutdown_obj Y;  // Call llvm_shutdown() on exit.
+
+  // Initialize targets and assembly printers/parsers.
+  InitializeAllTargetInfos();
+  // FIXME: We shouldn't need to initialize the Target(Machine)s.
+  InitializeAllTargets();
+  InitializeAllAsmPrinters();
+  InitializeAllAsmParsers();
+
+  // Construct our diagnostic client.
+  TextDiagnosticPrinter DiagClient(errs(), DiagnosticOptions());
+  DiagClient.setPrefix("clang -cc1as");
+  Diagnostic Diags(&DiagClient);
+
+  // Set an error handler, so that any LLVM backend diagnostics go through our
+  // error handler.
+  install_fatal_error_handler(LLVMErrorHandler,
+                                    static_cast<void*>(&Diags));
+
+  // Parse the arguments.
+  AssemblerInvocation Asm;
+  AssemblerInvocation::CreateFromArgs(Asm, ArgBegin, ArgEnd, Diags);
+
+  // Execute the invocation, unless there were parsing errors.
+  bool Success = false;
+  if (!Diags.getNumErrors())
+    Success = ExecuteAssembler(Asm, Diags);
+
+  // If any timers were active but haven't been destroyed yet, print their
+  // results now.
+  TimerGroup::printAll(errs());
+
+  return !Success;
+}
diff --git a/tools/driver/driver.cpp b/tools/driver/driver.cpp
index 3f1cca1..c4b12cb 100644
--- a/tools/driver/driver.cpp
+++ b/tools/driver/driver.cpp
@@ -170,15 +170,28 @@
 
 extern int cc1_main(const char **ArgBegin, const char **ArgEnd,
                     const char *Argv0, void *MainAddr);
+extern int cc1as_main(const char **ArgBegin, const char **ArgEnd,
+                      const char *Argv0, void *MainAddr);
 
 int main(int argc, const char **argv) {
   llvm::sys::PrintStackTraceOnErrorSignal();
   llvm::PrettyStackTraceProgram X(argc, argv);
 
-  // Dispatch to cc1_main if appropriate.
-  if (argc > 1 && llvm::StringRef(argv[1]) == "-cc1")
-    return cc1_main(argv+2, argv+argc, argv[0],
-                    (void*) (intptr_t) GetExecutablePath);
+  // Handle -cc1 integrated tools.
+  if (argc > 1 && llvm::StringRef(argv[1]).startswith("-cc1")) {
+    llvm::StringRef Tool = argv[1] + 4;
+
+    if (Tool == "")
+      return cc1_main(argv+2, argv+argc, argv[0],
+                      (void*) (intptr_t) GetExecutablePath);
+    if (Tool == "as")
+      return cc1as_main(argv+2, argv+argc, argv[0],
+                      (void*) (intptr_t) GetExecutablePath);
+
+    // Reject unknown tools.
+    llvm::errs() << "error: unknown integrated tool '" << Tool << "'\n";
+    return 1;
+  }
 
   bool CanonicalPrefixes = true;
   for (int i = 1; i < argc; ++i) {