diff --git a/clang/lib/Driver/Multilib.cpp b/clang/lib/Driver/Multilib.cpp
new file mode 100644
index 0000000..6d68517
--- /dev/null
+++ b/clang/lib/Driver/Multilib.cpp
@@ -0,0 +1,347 @@
+//===--- Multilib.cpp - Multilib Implementation ---------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/Driver/Multilib.h"
+#include "Tools.h"
+#include "clang/Driver/Options.h"
+#include "llvm/ADT/StringMap.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/StringSet.h"
+#include "llvm/ADT/Triple.h"
+#include "llvm/Option/Arg.h"
+#include "llvm/Option/ArgList.h"
+#include "llvm/Option/OptTable.h"
+#include "llvm/Option/Option.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/Path.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Support/Regex.h"
+#include "llvm/Support/YAMLParser.h"
+#include "llvm/Support/YAMLTraits.h"
+#include <algorithm>
+
+using namespace clang::driver;
+using namespace clang;
+using namespace llvm::opt;
+
+static void normalizePathSegment(std::string &Segment) {
+  StringRef SRS(Segment);
+  if (SRS.empty() || SRS == "/." || SRS == "/" || SRS == ".") {
+    SRS = "";
+  } else {
+    if (SRS.back() == '/')
+      SRS = SRS.drop_back();
+    if (SRS.front() != '/')
+      SRS = ("/" + SRS).str();
+  }
+  Segment = SRS;
+}
+
+Multilib::Multilib(StringRef GCCSuffix, StringRef OSSuffix,
+                   StringRef IncludeSuffix)
+    : GCCSuffix(GCCSuffix), OSSuffix(OSSuffix), IncludeSuffix(IncludeSuffix) {
+  normalizePathSegment(this->GCCSuffix);
+  normalizePathSegment(this->OSSuffix);
+  normalizePathSegment(this->IncludeSuffix);
+}
+
+Multilib &Multilib::gccSuffix(StringRef S) {
+  GCCSuffix = S;
+  normalizePathSegment(GCCSuffix);
+  return *this;
+}
+
+Multilib &Multilib::osSuffix(StringRef S) {
+  OSSuffix = S;
+  normalizePathSegment(OSSuffix);
+  return *this;
+}
+
+Multilib &Multilib::includeSuffix(StringRef S) {
+  IncludeSuffix = S;
+  normalizePathSegment(IncludeSuffix);
+  return *this;
+}
+
+void Multilib::print(raw_ostream &OS) const {
+  assert(GCCSuffix.empty() || (StringRef(GCCSuffix).front() == '/'));
+  if (GCCSuffix.empty())
+    OS << ".";
+  else {
+    OS << StringRef(GCCSuffix).drop_front();
+  }
+  OS << ";";
+  for (flags_list::const_iterator I = Flags.begin(), E = Flags.end(); I != E;
+       ++I) {
+    if (StringRef(*I).front() == '+')
+      OS << "@" << I->substr(1);
+  }
+}
+
+bool Multilib::isValid() const {
+  llvm::StringMap<int> FlagSet;
+  for (unsigned I = 0, N = Flags.size(); I != N; ++I) {
+    StringRef Flag(Flags[I]);
+    llvm::StringMap<int>::iterator SI = FlagSet.find(Flag.substr(1));
+
+    assert(StringRef(Flag).front() == '+' || StringRef(Flag).front() == '-');
+
+    if (SI == FlagSet.end())
+      FlagSet[Flag.substr(1)] = I;
+    else if (Flags[I] != Flags[SI->getValue()])
+      return false;
+  }
+  return true;
+}
+
+bool Multilib::operator==(const Multilib &Other) const {
+  // Check whether the flags sets match
+  // allowing for the match to be order invariant
+  llvm::StringSet<> MyFlags;
+  for (flags_list::const_iterator I = Flags.begin(), E = Flags.end(); I != E;
+       ++I) {
+    MyFlags.insert(*I);
+  }
+  for (flags_list::const_iterator I = Other.Flags.begin(),
+                                  E = Other.Flags.end();
+       I != E; ++I) {
+    if (MyFlags.find(*I) == MyFlags.end())
+      return false;
+  }
+
+  if (osSuffix() != Other.osSuffix())
+    return false;
+
+  if (gccSuffix() != Other.gccSuffix())
+    return false;
+
+  if (includeSuffix() != Other.includeSuffix())
+    return false;
+
+  return true;
+}
+
+raw_ostream &clang::driver::operator<<(raw_ostream &OS, const Multilib &M) {
+  M.print(OS);
+  return OS;
+}
+
+MultilibSet &MultilibSet::Maybe(const Multilib &M) {
+  Multilib Opposite;
+  // Negate any '+' flags
+  for (Multilib::flags_list::const_iterator I = M.flags().begin(),
+                                            E = M.flags().end();
+       I != E; ++I) {
+    StringRef Flag(*I);
+    if (Flag.front() == '+')
+      Opposite.flags().push_back(("-" + Flag.substr(1)).str());
+  }
+  return Either(M, Opposite);
+}
+
+MultilibSet &MultilibSet::Either(const Multilib &M1, const Multilib &M2) {
+  std::vector<Multilib> Ms;
+  Ms.push_back(M1);
+  Ms.push_back(M2);
+  return Either(Ms);
+}
+
+MultilibSet &MultilibSet::Either(const Multilib &M1, const Multilib &M2,
+                                 const Multilib &M3) {
+  std::vector<Multilib> Ms;
+  Ms.push_back(M1);
+  Ms.push_back(M2);
+  Ms.push_back(M3);
+  return Either(Ms);
+}
+
+MultilibSet &MultilibSet::Either(const Multilib &M1, const Multilib &M2,
+                                 const Multilib &M3, const Multilib &M4) {
+  std::vector<Multilib> Ms;
+  Ms.push_back(M1);
+  Ms.push_back(M2);
+  Ms.push_back(M3);
+  Ms.push_back(M4);
+  return Either(Ms);
+}
+
+MultilibSet &MultilibSet::Either(const Multilib &M1, const Multilib &M2,
+                                 const Multilib &M3, const Multilib &M4,
+                                 const Multilib &M5) {
+  std::vector<Multilib> Ms;
+  Ms.push_back(M1);
+  Ms.push_back(M2);
+  Ms.push_back(M3);
+  Ms.push_back(M4);
+  Ms.push_back(M5);
+  return Either(Ms);
+}
+
+static Multilib compose(const Multilib &Base, const Multilib &New) {
+  SmallString<128> GCCSuffix;
+  llvm::sys::path::append(GCCSuffix, "/", Base.gccSuffix(), New.gccSuffix());
+  SmallString<128> OSSuffix;
+  llvm::sys::path::append(OSSuffix, "/", Base.osSuffix(), New.osSuffix());
+  SmallString<128> IncludeSuffix;
+  llvm::sys::path::append(IncludeSuffix, "/", Base.includeSuffix(),
+                          New.includeSuffix());
+
+  Multilib Composed(GCCSuffix.str(), OSSuffix.str(), IncludeSuffix.str());
+
+  Multilib::flags_list &Flags = Composed.flags();
+
+  Flags.insert(Flags.end(), Base.flags().begin(), Base.flags().end());
+  Flags.insert(Flags.end(), New.flags().begin(), New.flags().end());
+
+  return Composed;
+}
+
+MultilibSet &
+MultilibSet::Either(const std::vector<Multilib> &MultilibSegments) {
+  multilib_list Composed;
+
+  if (Multilibs.empty())
+    Multilibs.insert(Multilibs.end(), MultilibSegments.begin(),
+                     MultilibSegments.end());
+  else {
+    for (std::vector<Multilib>::const_iterator NewI = MultilibSegments.begin(),
+                                               NewE = MultilibSegments.end();
+         NewI != NewE; ++NewI) {
+      for (const_iterator BaseI = begin(), BaseE = end(); BaseI != BaseE;
+           ++BaseI) {
+        Multilib MO = compose(*BaseI, *NewI);
+        if (MO.isValid())
+          Composed.push_back(MO);
+      }
+    }
+
+    Multilibs = Composed;
+  }
+
+  return *this;
+}
+
+MultilibSet &MultilibSet::FilterOut(const MultilibSet::FilterCallback &F) {
+  filterInPlace(F, Multilibs);
+  return *this;
+}
+
+MultilibSet &MultilibSet::FilterOut(std::string Regex) {
+  class REFilter : public MultilibSet::FilterCallback {
+    mutable llvm::Regex R;
+
+  public:
+    REFilter(std::string Regex) : R(Regex) {}
+    bool operator()(const Multilib &M) const LLVM_OVERRIDE {
+      std::string Error;
+      if (!R.isValid(Error)) {
+        llvm::errs() << Error;
+        assert(false);
+        return false;
+      }
+      return R.match(M.gccSuffix());
+    }
+  };
+
+  REFilter REF(Regex);
+  filterInPlace(REF, Multilibs);
+  return *this;
+}
+
+void MultilibSet::push_back(const Multilib &M) { Multilibs.push_back(M); }
+
+void MultilibSet::combineWith(const MultilibSet &Other) {
+  Multilibs.insert(Multilibs.end(), Other.begin(), Other.end());
+}
+
+bool MultilibSet::select(const Multilib::flags_list &Flags, Multilib &M) const {
+  class FilterFlagsMismatch : public MultilibSet::FilterCallback {
+    llvm::StringMap<bool> FlagSet;
+
+  public:
+    FilterFlagsMismatch(const std::vector<std::string> &Flags) {
+      // Stuff all of the flags into the FlagSet such that a true mappend
+      // indicates the flag was enabled, and a false mappend indicates the
+      // flag was disabled
+      for (Multilib::flags_list::const_iterator I = Flags.begin(),
+                                                E = Flags.end();
+           I != E; ++I) {
+        FlagSet[StringRef(*I).substr(1)] = isFlagEnabled(*I);
+      }
+    }
+    bool operator()(const Multilib &M) const LLVM_OVERRIDE {
+      for (Multilib::flags_list::const_iterator I = M.flags().begin(),
+                                                E = M.flags().end();
+           I != E; ++I) {
+        StringRef Flag(*I);
+        llvm::StringMap<bool>::const_iterator SI = FlagSet.find(Flag.substr(1));
+        if (SI != FlagSet.end())
+          if ((*SI).getValue() != isFlagEnabled(Flag))
+            return true;
+      }
+      return false;
+    }
+  private:
+    bool isFlagEnabled(StringRef Flag) const {
+      char Indicator = Flag.front();
+      assert(Indicator == '+' || Indicator == '-');
+      return Indicator == '+';
+    }
+  };
+
+  FilterFlagsMismatch FlagsMismatch(Flags);
+
+  multilib_list Filtered = filterCopy(FlagsMismatch, Multilibs);
+
+  if (Filtered.size() == 0) {
+    return false;
+  } else if (Filtered.size() == 1) {
+    M = Filtered[0];
+    return true;
+  }
+
+  // TODO: pick the "best" multlib when more than one is suitable
+  assert(false);
+
+  return false;
+}
+
+void MultilibSet::print(raw_ostream &OS) const {
+  for (const_iterator I = begin(), E = end(); I != E; ++I)
+    OS << *I << "\n";
+}
+
+MultilibSet::multilib_list
+MultilibSet::filterCopy(const MultilibSet::FilterCallback &F,
+                        const multilib_list &Ms) {
+  multilib_list Copy(Ms);
+  filterInPlace(F, Copy);
+  return Copy;
+}
+
+namespace {
+// Wrapper for FilterCallback to make operator() nonvirtual so it
+// can be passed by value to std::remove_if
+class FilterWrapper {
+  const MultilibSet::FilterCallback &F;
+public:
+  FilterWrapper(const MultilibSet::FilterCallback &F) : F(F) {}
+  bool operator()(const Multilib &M) const { return F(M); }
+};
+} // end anonymous namespace
+
+void MultilibSet::filterInPlace(const MultilibSet::FilterCallback &F,
+                                multilib_list &Ms) {
+  Ms.erase(std::remove_if(Ms.begin(), Ms.end(), FilterWrapper(F)), Ms.end());
+}
+
+raw_ostream &clang::driver::operator<<(raw_ostream &OS, const MultilibSet &MS) {
+  MS.print(OS);
+  return OS;
+}