diff --git a/clang/lib/Basic/Targets/X86.cpp b/clang/lib/Basic/Targets/X86.cpp
@@ -17,6 +17,7 @@
 #include "clang/Basic/TargetBuiltins.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringSwitch.h"
+#include "llvm/Support/TargetParser.h"
 
 namespace clang {
 namespace targets {
@@ -1338,6 +1339,63 @@ bool X86TargetInfo::validateCpuSupports(StringRef FeatureStr) const {
       .Default(false);
 }
 
+static llvm::X86::ProcessorFeatures getFeature(StringRef Name) {
+  return llvm::StringSwitch<llvm::X86::ProcessorFeatures>(Name)
+#define X86_FEATURE_COMPAT(VAL, ENUM, STR) .Case(STR, llvm::X86::ENUM)
+#include "llvm/Support/X86TargetParser.def"
+      ;
+  // Note, this function should only be used after ensuring the value is
+  // correct, so it asserts if the value is out of range.
+}
+
+static unsigned getFeaturePriority(llvm::X86::ProcessorFeatures Feat) {
+  enum class FeatPriority {
+#define FEATURE(FEAT) FEAT,
+#include "clang/Basic/X86Target.def"
+  };
+  switch (Feat) {
+#define FEATURE(FEAT)                                                          \
+  case llvm::X86::FEAT:                                                        \
+    return static_cast<unsigned>(FeatPriority::FEAT);
+#include "clang/Basic/X86Target.def"
+  default:
+    llvm_unreachable("No Feature Priority for non-CPUSupports Features");
+  }
+}
+
+unsigned X86TargetInfo::multiVersionSortPriority(StringRef Name) const {
+  // Valid CPUs have a 'key feature' that compares just better than its key
+  // feature.
+  CPUKind Kind = getCPUKind(Name);
+  if (Kind != CK_Generic) {
+    switch (Kind) {
+    default:
+      llvm_unreachable(
+          "CPU Type without a key feature used in 'target' attribute");
+#define PROC_WITH_FEAT(ENUM, STR, IS64, KEY_FEAT)                              \
+  case CK_##ENUM:                                                              \
+    return (getFeaturePriority(llvm::X86::KEY_FEAT) << 1) + 1;
+#include "clang/Basic/X86Target.def"
+    }
+  }
+
+  // Now we know we have a feature, so get its priority and shift it a few so
+  // that we have sufficient room for the CPUs (above).
+  return getFeaturePriority(getFeature(Name)) << 1;
+}
+
+std::string X86TargetInfo::getCPUKindCanonicalName(CPUKind Kind) const {
+  switch (Kind) {
+  case CK_Generic:
+    return "";
+#define PROC(ENUM, STRING, IS64BIT)                                            \
+  case CK_##ENUM:                                                              \
+    return STRING;
+#include "clang/Basic/X86Target.def"
+  }
+  llvm_unreachable("Invalid CPUKind");
+}
+
 // We can't use a generic validation scheme for the cpus accepted here
 // versus subtarget cpus accepted in the target attribute because the
 // variables intitialized by the runtime only support the below currently

diff --git a/clang/lib/Basic/Targets/X86.h b/clang/lib/Basic/Targets/X86.h
@@ -111,6 +111,8 @@ class LLVM_LIBRARY_VISIBILITY X86TargetInfo : public TargetInfo {
 
   CPUKind getCPUKind(StringRef CPU) const;
 
+  std::string getCPUKindCanonicalName(CPUKind Kind) const;
+
   enum FPMathKind { FP_Default, FP_SSE, FP_387 } FPMath = FP_Default;
 
 public:
@@ -256,6 +258,11 @@ class LLVM_LIBRARY_VISIBILITY X86TargetInfo : public TargetInfo {
     return checkCPUKind(CPU = getCPUKind(Name));
   }
 
+  bool supportsMultiVersioning() const override {
+    return getTriple().isOSBinFormatELF();
+  }
+  unsigned multiVersionSortPriority(StringRef Name) const override;
+
   bool setFPMath(StringRef Name) override;
 
   CallingConvCheckResult checkCallingConvention(CallingConv CC) const override {

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -2305,6 +2305,60 @@ void CodeGenFunction::EmitSanitizerStatReport(llvm::SanitizerStatKind SSK) {
   CGM.getSanStats().create(IRB, SSK);
 }
 
+llvm::Value *
+CodeGenFunction::FormResolverCondition(const MultiVersionResolverOption &RO) {
+  llvm::Value *TrueCondition = nullptr;
+  if (!RO.ParsedAttribute.Architecture.empty())
+    TrueCondition = EmitX86CpuIs(RO.ParsedAttribute.Architecture);
+
+  if (!RO.ParsedAttribute.Features.empty()) {
+    SmallVector<StringRef, 8> FeatureList;
+    llvm::for_each(RO.ParsedAttribute.Features,
+                   [&FeatureList](const std::string &Feature) {
+                     FeatureList.push_back(StringRef{Feature}.substr(1));
+                   });
+    llvm::Value *FeatureCmp = EmitX86CpuSupports(FeatureList);
+    TrueCondition = TrueCondition ? Builder.CreateAnd(TrueCondition, FeatureCmp)
+                                  : FeatureCmp;
+  }
+  return TrueCondition;
+}
+
+void CodeGenFunction::EmitMultiVersionResolver(
+    llvm::Function *Resolver, ArrayRef<MultiVersionResolverOption> Options) {
+  assert((getContext().getTargetInfo().getTriple().getArch() ==
+              llvm::Triple::x86 ||
+          getContext().getTargetInfo().getTriple().getArch() ==
+              llvm::Triple::x86_64) &&
+         "Only implemented for x86 targets");
+
+  // Main function's basic block.
+  llvm::BasicBlock *CurBlock = createBasicBlock("entry", Resolver);
+  Builder.SetInsertPoint(CurBlock);
+  EmitX86CpuInit();
+
+  llvm::Function *DefaultFunc = nullptr;
+  for (const MultiVersionResolverOption &RO : Options) {
+    Builder.SetInsertPoint(CurBlock);
+    llvm::Value *TrueCondition = FormResolverCondition(RO);
+
+    if (!TrueCondition) {
+      DefaultFunc = RO.Function;
+    } else {
+      llvm::BasicBlock *RetBlock = createBasicBlock("ro_ret", Resolver);
+      llvm::IRBuilder<> RetBuilder(RetBlock);
+      RetBuilder.CreateRet(RO.Function);
+      CurBlock = createBasicBlock("ro_else", Resolver);
+      Builder.CreateCondBr(TrueCondition, RetBlock, CurBlock);
+    }
+  }
+
+  assert(DefaultFunc && "No default version?");
+  // Emit return from the 'else-ist' block.
+  Builder.SetInsertPoint(CurBlock);
+  Builder.CreateRet(DefaultFunc);
+}
+
 llvm::DebugLoc CodeGenFunction::SourceLocToDebugLoc(SourceLocation Location) {
   if (CGDebugInfo *DI = getDebugInfo())
     return DI->SourceLocToDebugLoc(Location);

diff --git a/clang/lib/CodeGen/CodeGenFunction.h b/clang/lib/CodeGen/CodeGenFunction.h
@@ -3988,6 +3988,29 @@ class CodeGenFunction : public CodeGenTypeCache {
 
   void EmitSanitizerStatReport(llvm::SanitizerStatKind SSK);
 
+  struct MultiVersionResolverOption {
+    llvm::Function *Function;
+    TargetAttr::ParsedTargetAttr ParsedAttribute;
+    unsigned Priority;
+    MultiVersionResolverOption(const TargetInfo &TargInfo, llvm::Function *F,
+                               const clang::TargetAttr::ParsedTargetAttr &PT)
+        : Function(F), ParsedAttribute(PT), Priority(0u) {
+      for (StringRef Feat : PT.Features)
+        Priority = std::max(Priority,
+                            TargInfo.multiVersionSortPriority(Feat.substr(1)));
+
+      if (!PT.Architecture.empty())
+        Priority = std::max(Priority,
+                            TargInfo.multiVersionSortPriority(PT.Architecture));
+    }
+
+    bool operator>(const MultiVersionResolverOption &Other) const {
+      return Priority > Other.Priority;
+    }
+  };
+  void EmitMultiVersionResolver(llvm::Function *Resolver,
+                                ArrayRef<MultiVersionResolverOption> Options);
+
 private:
   QualType getVarArgType(const Expr *Arg);
 
@@ -4004,6 +4027,7 @@ class CodeGenFunction : public CodeGenTypeCache {
   llvm::Value *EmitX86CpuSupports(const CallExpr *E);
   llvm::Value *EmitX86CpuSupports(ArrayRef<StringRef> FeatureStrs);
   llvm::Value *EmitX86CpuInit();
+  llvm::Value *FormResolverCondition(const MultiVersionResolverOption &RO);
 };
 
 /// Helper class with most of the code for saving a value for a

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -395,6 +395,7 @@ void CodeGenModule::Release() {
   applyGlobalValReplacements();
   applyReplacements();
   checkAliases();
+  emitMultiVersionFunctions();
   EmitCXXGlobalInitFunc();
   EmitCXXGlobalDtorFunc();
   EmitCXXThreadLocalInitFunc();
@@ -725,36 +726,48 @@ void CodeGenModule::setTLSMode(llvm::GlobalValue *GV, const VarDecl &D) const {
   GV->setThreadLocalMode(TLM);
 }
 
-StringRef CodeGenModule::getMangledName(GlobalDecl GD) {
-  GlobalDecl CanonicalGD = GD.getCanonicalDecl();
+static void AppendTargetMangling(const CodeGenModule &CGM,
+                                 const TargetAttr *Attr, raw_ostream &Out) {
+  if (Attr->isDefaultVersion())
+    return;
 
-  // Some ABIs don't have constructor variants.  Make sure that base and
-  // complete constructors get mangled the same.
-  if (const auto *CD = dyn_cast<CXXConstructorDecl>(CanonicalGD.getDecl())) {
-    if (!getTarget().getCXXABI().hasConstructorVariants()) {
-      CXXCtorType OrigCtorType = GD.getCtorType();
-      assert(OrigCtorType == Ctor_Base || OrigCtorType == Ctor_Complete);
-      if (OrigCtorType == Ctor_Base)
-        CanonicalGD = GlobalDecl(CD, Ctor_Complete);
-    }
+  Out << '.';
+  const auto &Target = CGM.getTarget();
+  TargetAttr::ParsedTargetAttr Info =
+      Attr->parse([&Target](StringRef LHS, StringRef RHS) {
+                    return Target.multiVersionSortPriority(LHS) >
+                           Target.multiVersionSortPriority(RHS);
+                  });
+
+  bool IsFirst = true;
+
+  if (!Info.Architecture.empty()) {
+    IsFirst = false;
+    Out << "arch_" << Info.Architecture;
   }
 
-  auto FoundName = MangledDeclNames.find(CanonicalGD);
-  if (FoundName != MangledDeclNames.end())
-    return FoundName->second;
+  for (StringRef Feat : Info.Features) {
+    if (!IsFirst)
+      Out << '_';
+    IsFirst = false;
+    Out << Feat.substr(1);
+  }
+}
 
-  const auto *ND = cast<NamedDecl>(GD.getDecl());
+static std::string getMangledNameImpl(const CodeGenModule &CGM, GlobalDecl GD,
+                                      const NamedDecl *ND,
+                                      bool OmitTargetMangling = false) {
   SmallString<256> Buffer;
-  StringRef Str;
-  if (getCXXABI().getMangleContext().shouldMangleDeclName(ND)) {
+  llvm::raw_svector_ostream Out(Buffer);
+  MangleContext &MC = CGM.getCXXABI().getMangleContext();
+  if (MC.shouldMangleDeclName(ND)) {
     llvm::raw_svector_ostream Out(Buffer);
     if (const auto *D = dyn_cast<CXXConstructorDecl>(ND))
-      getCXXABI().getMangleContext().mangleCXXCtor(D, GD.getCtorType(), Out);
+      MC.mangleCXXCtor(D, GD.getCtorType(), Out);
     else if (const auto *D = dyn_cast<CXXDestructorDecl>(ND))
-      getCXXABI().getMangleContext().mangleCXXDtor(D, GD.getDtorType(), Out);
+      MC.mangleCXXDtor(D, GD.getDtorType(), Out);
     else
-      getCXXABI().getMangleContext().mangleName(ND, Out);
-    Str = Out.str();
+      MC.mangleName(ND, Out);
   } else {
     IdentifierInfo *II = ND->getIdentifier();
     assert(II && "Attempt to mangle unnamed decl.");
@@ -764,14 +777,74 @@ StringRef CodeGenModule::getMangledName(GlobalDecl GD) {
         FD->getType()->castAs<FunctionType>()->getCallConv() == CC_X86RegCall) {
       llvm::raw_svector_ostream Out(Buffer);
       Out << "__regcall3__" << II->getName();
-      Str = Out.str();
     } else {
-      Str = II->getName();
+      Out << II->getName();
+    }
+  }
+
+  if (const auto *FD = dyn_cast<FunctionDecl>(ND))
+    if (FD->isMultiVersion() && !OmitTargetMangling)
+      AppendTargetMangling(CGM, FD->getAttr<TargetAttr>(), Out);
+  return Out.str();
+}
+
+void CodeGenModule::UpdateMultiVersionNames(GlobalDecl GD,
+                                            const FunctionDecl *FD) {
+  if (!FD->isMultiVersion())
+    return;
+
+  // Get the name of what this would be without the 'target' attribute.  This
+  // allows us to lookup the version that was emitted when this wasn't a
+  // multiversion function.
+  std::string NonTargetName =
+      getMangledNameImpl(*this, GD, FD, /*OmitTargetMangling=*/true);
+  GlobalDecl OtherGD;
+  if (lookupRepresentativeDecl(NonTargetName, OtherGD)) {
+    assert(OtherGD.getCanonicalDecl()
+               .getDecl()
+               ->getAsFunction()
+               ->isMultiVersion() &&
+           "Other GD should now be a multiversioned function");
+    // OtherFD is the version of this function that was mangled BEFORE
+    // becoming a MultiVersion function.  It potentially needs to be updated.
+    const FunctionDecl *OtherFD =
+        OtherGD.getCanonicalDecl().getDecl()->getAsFunction();
+    std::string OtherName = getMangledNameImpl(*this, OtherGD, OtherFD);
+    // This is so that if the initial version was already the 'default'
+    // version, we don't try to update it.
+    if (OtherName != NonTargetName) {
+      Manglings.erase(NonTargetName);
+      auto Result = Manglings.insert(std::make_pair(OtherName, OtherGD));
+      MangledDeclNames[OtherGD.getCanonicalDecl()] = Result.first->first();
+      if (llvm::GlobalValue *Entry = GetGlobalValue(NonTargetName))
+        Entry->setName(OtherName);
     }
   }
+}
+
+StringRef CodeGenModule::getMangledName(GlobalDecl GD) {
+  GlobalDecl CanonicalGD = GD.getCanonicalDecl();
+
+  // Some ABIs don't have constructor variants.  Make sure that base and
+  // complete constructors get mangled the same.
+  if (const auto *CD = dyn_cast<CXXConstructorDecl>(CanonicalGD.getDecl())) {
+    if (!getTarget().getCXXABI().hasConstructorVariants()) {
+      CXXCtorType OrigCtorType = GD.getCtorType();
+      assert(OrigCtorType == Ctor_Base || OrigCtorType == Ctor_Complete);
+      if (OrigCtorType == Ctor_Base)
+        CanonicalGD = GlobalDecl(CD, Ctor_Complete);
+    }
+  }
+
+  auto FoundName = MangledDeclNames.find(CanonicalGD);
+  if (FoundName != MangledDeclNames.end())
+    return FoundName->second;
+
 
   // Keep the first result in the case of a mangling collision.
-  auto Result = Manglings.insert(std::make_pair(Str, GD));
+  const auto *ND = cast<NamedDecl>(GD.getDecl());
+  auto Result =
+      Manglings.insert(std::make_pair(getMangledNameImpl(*this, GD, ND), GD));
   return MangledDeclNames[CanonicalGD] = Result.first->first();
 }
 
@@ -2061,6 +2134,74 @@ void CodeGenModule::EmitGlobalDefinition(GlobalDecl GD, llvm::GlobalValue *GV) {
 static void ReplaceUsesOfNonProtoTypeWithRealFunction(llvm::GlobalValue *Old,
                                                       llvm::Function *NewFn);
 
+void CodeGenModule::emitMultiVersionFunctions() {
+  for (GlobalDecl GD : MultiVersionFuncs) {
+    SmallVector<CodeGenFunction::MultiVersionResolverOption, 10> Options;
+    const FunctionDecl *FD = cast<FunctionDecl>(GD.getDecl());
+    getContext().forEachMultiversionedFunctionVersion(
+        FD, [this, &GD, &Options](const FunctionDecl *CurFD) {
+          GlobalDecl CurGD{
+              (CurFD->isDefined() ? CurFD->getDefinition() : CurFD)};
+          StringRef MangledName = getMangledName(CurGD);
+          llvm::Constant *Func = GetGlobalValue(MangledName);
+          if (!Func) {
+            if (CurFD->isDefined()) {
+              EmitGlobalFunctionDefinition(CurGD, nullptr);
+              Func = GetGlobalValue(MangledName);
+            } else {
+              const CGFunctionInfo &FI =
+                  getTypes().arrangeGlobalDeclaration(GD);
+              llvm::FunctionType *Ty = getTypes().GetFunctionType(FI);
+              Func = GetAddrOfFunction(CurGD, Ty, /*ForVTable=*/false,
+                                       /*DontDefer=*/false, ForDefinition);
+            }
+            assert(Func && "This should have just been created");
+          }
+          Options.emplace_back(getTarget(), cast<llvm::Function>(Func),
+                               CurFD->getAttr<TargetAttr>()->parse());
+        });
+
+    llvm::Function *ResolverFunc = cast<llvm::Function>(
+        GetGlobalValue((getMangledName(GD) + ".resolver").str()));
+    std::stable_sort(
+        Options.begin(), Options.end(),
+        std::greater<CodeGenFunction::MultiVersionResolverOption>());
+    CodeGenFunction CGF(*this);
+    CGF.EmitMultiVersionResolver(ResolverFunc, Options);
+  }
+}
+
+/// If an ifunc for the specified mangled name is not in the module, create and
+/// return an llvm IFunc Function with the specified type.
+llvm::Constant *
+CodeGenModule::GetOrCreateMultiVersionIFunc(GlobalDecl GD, llvm::Type *DeclTy,
+                                            StringRef MangledName,
+                                            const FunctionDecl *FD) {
+  std::string IFuncName = (MangledName + ".ifunc").str();
+  if (llvm::GlobalValue *IFuncGV = GetGlobalValue(IFuncName))
+    return IFuncGV;
+
+  // Since this is the first time we've created this IFunc, make sure
+  // that we put this multiversioned function into the list to be
+  // replaced later.
+  MultiVersionFuncs.push_back(GD);
+
+  std::string ResolverName = (MangledName + ".resolver").str();
+  llvm::Type *ResolverType = llvm::FunctionType::get(
+      llvm::PointerType::get(DeclTy,
+                             Context.getTargetAddressSpace(FD->getType())),
+      false);
+  llvm::Constant *Resolver =
+      GetOrCreateLLVMFunction(ResolverName, ResolverType, GlobalDecl{},
+                              /*ForVTable=*/false);
+  llvm::GlobalIFunc *GIF = llvm::GlobalIFunc::create(
+      DeclTy, 0, llvm::Function::ExternalLinkage, "", Resolver, &getModule());
+  GIF->setName(IFuncName);
+  SetCommonAttributes(FD, GIF);
+
+  return GIF;
+}
+
 /// GetOrCreateLLVMFunction - If the specified mangled name is not in the
 /// module, create and return an llvm Function with the specified type. If there
 /// is something in the module with the specified name, return it potentially
@@ -2074,6 +2215,16 @@ llvm::Constant *CodeGenModule::GetOrCreateLLVMFunction(
     ForDefinition_t IsForDefinition) {
   const Decl *D = GD.getDecl();
 
+  // Any attempts to use a MultiVersion function should result in retrieving
+  // the iFunc instead. Name Mangling will handle the rest of the changes.
+  if (const FunctionDecl *FD = cast_or_null<FunctionDecl>(D)) {
+    if (FD->isMultiVersion() && FD->getAttr<TargetAttr>()->isDefaultVersion()) {
+      UpdateMultiVersionNames(GD, FD);
+      if (!IsForDefinition)
+        return GetOrCreateMultiVersionIFunc(GD, Ty, MangledName, FD);
+    }
+  }
+
   // Lookup the entry, lazily creating it if necessary.
   llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
   if (Entry) {

diff --git a/clang/lib/CodeGen/CodeGenModule.h b/clang/lib/CodeGen/CodeGenModule.h
@@ -324,6 +324,10 @@ class CodeGenModule : public CodeGenTypeCache {
   /// is defined once we get to the end of the of the translation unit.
   std::vector<GlobalDecl> Aliases;
 
+  /// List of multiversion functions that have to be emitted.  Used to make sure
+  /// we properly emit the iFunc.
+  std::vector<GlobalDecl> MultiVersionFuncs;
+
   typedef llvm::StringMap<llvm::TrackingVH<llvm::Constant> > ReplacementsTy;
   ReplacementsTy Replacements;
 
@@ -1247,6 +1251,12 @@ class CodeGenModule : public CodeGenTypeCache {
       llvm::AttributeList ExtraAttrs = llvm::AttributeList(),
       ForDefinition_t IsForDefinition = NotForDefinition);
 
+  llvm::Constant *GetOrCreateMultiVersionIFunc(GlobalDecl GD,
+                                               llvm::Type *DeclTy,
+                                               StringRef MangledName,
+                                               const FunctionDecl *FD);
+  void UpdateMultiVersionNames(GlobalDecl GD, const FunctionDecl *FD);
+
   llvm::Constant *GetOrCreateLLVMGlobal(StringRef MangledName,
                                         llvm::PointerType *PTy,
                                         const VarDecl *D,
@@ -1319,6 +1329,8 @@ class CodeGenModule : public CodeGenTypeCache {
 
   void checkAliases();
 
+  void emitMultiVersionFunctions();
+
   /// Emit any vtables which we deferred and still have a use for.
   void EmitDeferredVTables();
 

diff --git a/clang/lib/Sema/Sema.cpp b/clang/lib/Sema/Sema.cpp
@@ -1647,6 +1647,12 @@ static void noteOverloads(Sema &S, const UnresolvedSetImpl &Overloads,
     }
 
     NamedDecl *Fn = (*It)->getUnderlyingDecl();
+    // Don't print overloads for non-default multiversioned functions.
+    if (const auto *FD = Fn->getAsFunction()) {
+      if (FD->isMultiVersion() &&
+          !FD->getAttr<TargetAttr>()->isDefaultVersion())
+        continue;
+    }
     S.Diag(Fn->getLocation(), diag::note_possible_target_of_call);
     ++ShownOverloads;
   }

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
@@ -9157,6 +9157,359 @@ bool Sema::shouldLinkDependentDeclWithPrevious(Decl *D, Decl *PrevDecl) {
            D->getFriendObjectKind() != Decl::FOK_None);
 }
 
+/// \brief Check the target attribute of the function for MultiVersion
+/// validity.
+///
+/// Returns true if there was an error, false otherwise.
+static bool CheckMultiVersionValue(Sema &S, const FunctionDecl *FD) {
+  const auto *TA = FD->getAttr<TargetAttr>();
+  assert(TA && "MultiVersion Candidate requires a target attribute");
+  TargetAttr::ParsedTargetAttr ParseInfo = TA->parse();
+  const TargetInfo &TargetInfo = S.Context.getTargetInfo();
+  enum ErrType { Feature = 0, Architecture = 1 };
+
+  if (!ParseInfo.Architecture.empty() &&
+      !TargetInfo.validateCpuIs(ParseInfo.Architecture)) {
+    S.Diag(FD->getLocation(), diag::err_bad_multiversion_option)
+        << Architecture << ParseInfo.Architecture;
+    return true;
+  }
+
+  for (const auto &Feature : ParseInfo.Features) {
+    auto BareFeat = StringRef{Feature}.substr(1);
+    if (Feature[0] == '-') {
+      S.Diag(FD->getLocation(), diag::err_bad_multiversion_option)
+          << Feature << ("no-" + BareFeat).str();
+      return true;
+    }
+
+    if (!TargetInfo.validateCpuSupports(BareFeat) ||
+        !TargetInfo.isValidFeatureName(BareFeat)) {
+      S.Diag(FD->getLocation(), diag::err_bad_multiversion_option)
+          << Feature << BareFeat;
+      return true;
+    }
+  }
+  return false;
+}
+
+static bool CheckMultiVersionAdditionalRules(Sema &S, const FunctionDecl *OldFD,
+                                             const FunctionDecl *NewFD,
+                                             bool CausesMV) {
+  enum DoesntSupport {
+    FuncTemplates = 0,
+    VirtFuncs = 1,
+    DeducedReturn = 2,
+    Constructors = 3,
+    Destructors = 4,
+    DeletedFuncs = 5,
+    DefaultedFuncs = 6
+  };
+  enum Different {
+    CallingConv = 0,
+    ReturnType = 1,
+    ConstexprSpec = 2,
+    InlineSpec = 3,
+    StorageClass = 4,
+    Linkage = 5
+  };
+
+  // For now, disallow all other attributes.  These should be opt-in, but
+  // an analysis of all of them is a future FIXME.
+  if (CausesMV && OldFD &&
+      std::distance(OldFD->attr_begin(), OldFD->attr_end()) != 1) {
+    S.Diag(OldFD->getLocation(), diag::err_multiversion_no_other_attrs);
+    S.Diag(NewFD->getLocation(), diag::note_multiversioning_caused_here);
+    return true;
+  }
+
+  if (std::distance(NewFD->attr_begin(), NewFD->attr_end()) != 1) {
+    S.Diag(NewFD->getLocation(), diag::err_multiversion_no_other_attrs);
+    return true;
+  }
+
+  if (NewFD->getTemplatedKind() == FunctionDecl::TK_FunctionTemplate) {
+    S.Diag(NewFD->getLocation(), diag::err_multiversion_doesnt_support)
+        << FuncTemplates;
+    return true;
+  }
+
+
+  if (const auto *NewCXXFD = dyn_cast<CXXMethodDecl>(NewFD)) {
+    if (NewCXXFD->isVirtual()) {
+      S.Diag(NewCXXFD->getLocation(), diag::err_multiversion_doesnt_support)
+          << VirtFuncs;
+      return true;
+    }
+
+    if (const auto *NewCXXCtor = dyn_cast<CXXConstructorDecl>(NewFD)) {
+      S.Diag(NewCXXCtor->getLocation(), diag::err_multiversion_doesnt_support)
+          << Constructors;
+      return true;
+    }
+
+    if (const auto *NewCXXDtor = dyn_cast<CXXDestructorDecl>(NewFD)) {
+      S.Diag(NewCXXDtor->getLocation(), diag::err_multiversion_doesnt_support)
+          << Destructors;
+      return true;
+    }
+  }
+
+  if (NewFD->isDeleted()) {
+    S.Diag(NewFD->getLocation(), diag::err_multiversion_doesnt_support)
+      << DeletedFuncs;
+  }
+  if (NewFD->isDefaulted()) {
+    S.Diag(NewFD->getLocation(), diag::err_multiversion_doesnt_support)
+      << DefaultedFuncs;
+  }
+
+  QualType NewQType = S.getASTContext().getCanonicalType(NewFD->getType());
+  const auto *NewType = cast<FunctionType>(NewQType);
+  QualType NewReturnType = NewType->getReturnType();
+
+  if (NewReturnType->isUndeducedType()) {
+    S.Diag(NewFD->getLocation(), diag::err_multiversion_doesnt_support)
+        << DeducedReturn;
+    return true;
+  }
+
+  // Only allow transition to MultiVersion if it hasn't been used.
+  if (OldFD && CausesMV && OldFD->isUsed(false)) {
+    S.Diag(NewFD->getLocation(), diag::err_multiversion_after_used);
+    return true;
+  }
+
+  // Ensure the return type is identical.
+  if (OldFD) {
+    QualType OldQType = S.getASTContext().getCanonicalType(OldFD->getType());
+    const auto *OldType = cast<FunctionType>(OldQType);
+    FunctionType::ExtInfo OldTypeInfo = OldType->getExtInfo();
+    FunctionType::ExtInfo NewTypeInfo = NewType->getExtInfo();
+
+    if (OldTypeInfo.getCC() != NewTypeInfo.getCC()) {
+      S.Diag(NewFD->getLocation(), diag::err_multiversion_diff) << CallingConv;
+      return true;
+    }
+
+    QualType OldReturnType = OldType->getReturnType();
+
+    if (OldReturnType != NewReturnType) {
+      S.Diag(NewFD->getLocation(), diag::err_multiversion_diff) << ReturnType;
+      return true;
+    }
+
+    if (OldFD->isConstexpr() != NewFD->isConstexpr()) {
+      S.Diag(NewFD->getLocation(), diag::err_multiversion_diff)
+          << ConstexprSpec;
+      return true;
+    }
+
+    if (OldFD->isInlineSpecified() != NewFD->isInlineSpecified()) {
+      S.Diag(NewFD->getLocation(), diag::err_multiversion_diff) << InlineSpec;
+      return true;
+    }
+
+    if (OldFD->getStorageClass() != NewFD->getStorageClass()) {
+      S.Diag(NewFD->getLocation(), diag::err_multiversion_diff) << StorageClass;
+      return true;
+    }
+
+    if (OldFD->isExternC() != NewFD->isExternC()) {
+      S.Diag(NewFD->getLocation(), diag::err_multiversion_diff) << Linkage;
+      return true;
+    }
+
+    if (S.CheckEquivalentExceptionSpec(
+            OldFD->getType()->getAs<FunctionProtoType>(), OldFD->getLocation(),
+            NewFD->getType()->getAs<FunctionProtoType>(), NewFD->getLocation()))
+      return true;
+  }
+  return false;
+}
+
+/// \brief Check the validity of a mulitversion function declaration.
+/// Also sets the multiversion'ness' of the function itself.
+///
+/// This sets NewFD->isInvalidDecl() to true if there was an error.
+///
+/// Returns true if there was an error, false otherwise.
+static bool CheckMultiVersionFunction(Sema &S, FunctionDecl *NewFD,
+                                      bool &Redeclaration, NamedDecl *&OldDecl,
+                                      bool &MergeTypeWithPrevious,
+                                      LookupResult &Previous) {
+  const auto *NewTA = NewFD->getAttr<TargetAttr>();
+  if (NewFD->isMain()) {
+    if (NewTA && NewTA->isDefaultVersion()) {
+      S.Diag(NewFD->getLocation(), diag::err_multiversion_not_allowed_on_main);
+      NewFD->isInvalidDecl();
+      return true;
+    }
+    return false;
+  }
+
+  // If there is no matching previous decl, only 'default' can
+  // cause MultiVersioning.
+  if (!OldDecl) {
+    if (NewTA && NewTA->isDefaultVersion()) {
+      if (!NewFD->getType()->getAs<FunctionProtoType>()) {
+        S.Diag(NewFD->getLocation(), diag::err_multiversion_noproto);
+        NewFD->setInvalidDecl();
+        return true;
+      }
+      if (CheckMultiVersionAdditionalRules(S, nullptr, NewFD, true)) {
+        NewFD->setInvalidDecl();
+        return true;
+      }
+      if (!S.getASTContext().getTargetInfo().supportsMultiVersioning()) {
+        S.Diag(NewFD->getLocation(), diag::err_multiversion_not_supported);
+        return true;
+      }
+
+      NewFD->setIsMultiVersion();
+    }
+    return false;
+  }
+
+  if (OldDecl->getDeclContext()->getRedeclContext() !=
+      NewFD->getDeclContext()->getRedeclContext())
+    return false;
+
+  FunctionDecl *OldFD = OldDecl->getAsFunction();
+  // Unresolved 'using' statements (the other way OldDecl can be not a function)
+  // likely cannot cause a problem here.
+  if (!OldFD)
+    return false;
+
+  if (!OldFD->isMultiVersion() && !NewTA)
+    return false;
+
+  if (OldFD->isMultiVersion() && !NewTA) {
+    S.Diag(NewFD->getLocation(), diag::err_target_required_in_redecl);
+    NewFD->setInvalidDecl();
+    return true;
+  }
+
+  TargetAttr::ParsedTargetAttr NewParsed = NewTA->parse();
+  // Sort order doesn't matter, it just needs to be consistent.
+  std::sort(NewParsed.Features.begin(), NewParsed.Features.end());
+
+  const auto *OldTA = OldFD->getAttr<TargetAttr>();
+  if (!OldFD->isMultiVersion()) {
+    // If the old decl is NOT MultiVersioned yet, and we don't cause that
+    // to change, this is a simple redeclaration.
+    if (!OldTA || OldTA->getFeaturesStr() == NewTA->getFeaturesStr())
+      return false;
+
+    // Otherwise, this decl causes MultiVersioning.
+    if (!S.getASTContext().getTargetInfo().supportsMultiVersioning()) {
+      S.Diag(NewFD->getLocation(), diag::err_multiversion_not_supported);
+      S.Diag(OldFD->getLocation(), diag::note_previous_declaration);
+      return true;
+    }
+
+    if (!OldFD->getType()->getAs<FunctionProtoType>()) {
+      S.Diag(OldFD->getLocation(), diag::err_multiversion_noproto);
+      S.Diag(NewFD->getLocation(), diag::note_multiversioning_caused_here);
+      NewFD->setInvalidDecl();
+      return true;
+    }
+
+    if (CheckMultiVersionValue(S, NewFD)) {
+      NewFD->setInvalidDecl();
+      return true;
+    }
+
+    if (CheckMultiVersionValue(S, OldFD)) {
+      S.Diag(NewFD->getLocation(), diag::note_multiversioning_caused_here);
+      NewFD->setInvalidDecl();
+      return true;
+    }
+
+    TargetAttr::ParsedTargetAttr OldParsed =
+        OldTA->parse(std::less<std::string>());
+
+    if (OldParsed == NewParsed) {
+      S.Diag(NewFD->getLocation(), diag::err_multiversion_duplicate);
+      S.Diag(OldFD->getLocation(), diag::note_previous_declaration);
+      NewFD->setInvalidDecl();
+      return true;
+    }
+
+    for (const auto *FD : OldFD->redecls()) {
+      const auto *CurTA = FD->getAttr<TargetAttr>();
+      if (!CurTA || CurTA->isInherited()) {
+        S.Diag(FD->getLocation(), diag::err_target_required_in_redecl);
+        S.Diag(NewFD->getLocation(), diag::note_multiversioning_caused_here);
+        NewFD->setInvalidDecl();
+        return true;
+      }
+    }
+
+    if (CheckMultiVersionAdditionalRules(S, OldFD, NewFD, true)) {
+      NewFD->setInvalidDecl();
+      return true;
+    }
+
+    OldFD->setIsMultiVersion();
+    NewFD->setIsMultiVersion();
+    Redeclaration = false;
+    MergeTypeWithPrevious = false;
+    OldDecl = nullptr;
+    Previous.clear();
+    return false;
+  }
+
+  bool UseMemberUsingDeclRules =
+      S.CurContext->isRecord() && !NewFD->getFriendObjectKind();
+
+  // Next, check ALL non-overloads to see if this is a redeclaration of a
+  // previous member of the MultiVersion set.
+  for (NamedDecl *ND : Previous) {
+    FunctionDecl *CurFD = ND->getAsFunction();
+    if (!CurFD)
+      continue;
+    if (S.IsOverload(NewFD, CurFD, UseMemberUsingDeclRules))
+      continue;
+
+    const auto *CurTA = CurFD->getAttr<TargetAttr>();
+    if (CurTA->getFeaturesStr() == NewTA->getFeaturesStr()) {
+      NewFD->setIsMultiVersion();
+      Redeclaration = true;
+      OldDecl = ND;
+      return false;
+    }
+
+    TargetAttr::ParsedTargetAttr CurParsed =
+        CurTA->parse(std::less<std::string>());
+
+    if (CurParsed == NewParsed) {
+      S.Diag(NewFD->getLocation(), diag::err_multiversion_duplicate);
+      S.Diag(CurFD->getLocation(), diag::note_previous_declaration);
+      NewFD->setInvalidDecl();
+      return true;
+    }
+  }
+
+  // Else, this is simply a non-redecl case.
+  if (CheckMultiVersionValue(S, NewFD)) {
+    NewFD->setInvalidDecl();
+    return true;
+  }
+
+  if (CheckMultiVersionAdditionalRules(S, OldFD, NewFD, false)) {
+    NewFD->setInvalidDecl();
+    return true;
+  }
+
+  NewFD->setIsMultiVersion();
+  Redeclaration = false;
+  MergeTypeWithPrevious = false;
+  OldDecl = nullptr;
+  Previous.clear();
+  return false;
+}
+
 /// \brief Perform semantic checking of a new function declaration.
 ///
 /// Performs semantic analysis of the new function declaration
@@ -9244,6 +9597,10 @@ bool Sema::CheckFunctionDeclaration(Scope *S, FunctionDecl *NewFD,
     }
   }
 
+  if (CheckMultiVersionFunction(*this, NewFD, Redeclaration, OldDecl,
+                                MergeTypeWithPrevious, Previous))
+    return Redeclaration;
+
   // C++11 [dcl.constexpr]p8:
   //   A constexpr specifier for a non-static member function that is not
   //   a constructor declares that member function to be const.

diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
@@ -5957,6 +5957,13 @@ Sema::AddOverloadCandidate(FunctionDecl *Function,
   Candidate.IgnoreObjectArgument = false;
   Candidate.ExplicitCallArguments = Args.size();
 
+  if (Function->isMultiVersion() &&
+      !Function->getAttr<TargetAttr>()->isDefaultVersion()) {
+    Candidate.Viable = false;
+    Candidate.FailureKind = ovl_non_default_multiversion_function;
+    return;
+  }
+
   if (Constructor) {
     // C++ [class.copy]p3:
     //   A member function template is never instantiated to perform the copy
@@ -6581,6 +6588,12 @@ Sema::AddMethodCandidate(CXXMethodDecl *Method, DeclAccessPair FoundDecl,
     Candidate.DeductionFailure.Data = FailedAttr;
     return;
   }
+
+  if (Method->isMultiVersion() &&
+      !Method->getAttr<TargetAttr>()->isDefaultVersion()) {
+    Candidate.Viable = false;
+    Candidate.FailureKind = ovl_non_default_multiversion_function;
+  }
 }
 
 /// \brief Add a C++ member function template as a candidate to the candidate
@@ -6984,6 +6997,12 @@ Sema::AddConversionCandidate(CXXConversionDecl *Conversion,
     Candidate.DeductionFailure.Data = FailedAttr;
     return;
   }
+
+  if (Conversion->isMultiVersion() &&
+      !Conversion->getAttr<TargetAttr>()->isDefaultVersion()) {
+    Candidate.Viable = false;
+    Candidate.FailureKind = ovl_non_default_multiversion_function;
+  }
 }
 
 /// \brief Adds a conversion function template specialization
@@ -9392,6 +9411,8 @@ void Sema::NoteOverloadCandidate(NamedDecl *Found, FunctionDecl *Fn,
                                  QualType DestType, bool TakingAddress) {
   if (TakingAddress && !checkAddressOfCandidateIsAvailable(*this, Fn))
     return;
+  if (Fn->isMultiVersion() && !Fn->getAttr<TargetAttr>()->isDefaultVersion())
+    return;
 
   std::string FnDesc;
   OverloadCandidateKind K = ClassifyOverloadCandidate(*this, Found, Fn, FnDesc);
@@ -10193,6 +10214,9 @@ static void NoteFunctionCandidate(Sema &S, OverloadCandidate *Cand,
     assert(!Available);
     break;
   }
+  case ovl_non_default_multiversion_function:
+    // Do nothing, these should simply be ignored.
+    break;
   }
 }
 
@@ -10929,6 +10953,12 @@ class AddressOfFunctionResolver {
         if (FunctionDecl *Caller = dyn_cast<FunctionDecl>(S.CurContext))
           if (!Caller->isImplicit() && !S.IsAllowedCUDACall(Caller, FunDecl))
             return false;
+      if (FunDecl->isMultiVersion()) {
+        const auto *TA = FunDecl->getAttr<TargetAttr>();
+        assert(TA && "Multiversioned functions require a target attribute");
+        if (!TA->isDefaultVersion())
+          return false;
+      }
 
       // If any candidate has a placeholder return type, trigger its deduction
       // now.

diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -792,6 +792,7 @@ void ASTDeclReader::VisitFunctionDecl(FunctionDecl *FD) {
   FD->IsConstexpr = Record.readInt();
   FD->UsesSEHTry = Record.readInt();
   FD->HasSkippedBody = Record.readInt();
+  FD->IsMultiVersion = Record.readInt();
   FD->IsLateTemplateParsed = Record.readInt();
   FD->setCachedLinkage(Linkage(Record.readInt()));
   FD->EndRangeLoc = ReadSourceLocation();
@@ -2818,6 +2819,21 @@ static bool isSameEntity(NamedDecl *X, NamedDecl *Y) {
                         CtorY->getInheritedConstructor().getConstructor()))
         return false;
     }
+
+    if (FuncX->isMultiVersion() != FuncY->isMultiVersion())
+      return false;
+
+    // Multiversioned functions with different feature strings are represented
+    // as separate declarations.
+    if (FuncX->isMultiVersion()) {
+      const auto *TAX = FuncX->getAttr<TargetAttr>();
+      const auto *TAY = FuncY->getAttr<TargetAttr>();
+      assert(TAX && TAY && "Multiversion Function without target attribute");
+
+      if (TAX->getFeaturesStr() != TAY->getFeaturesStr())
+        return false;
+    }
+
     ASTContext &C = FuncX->getASTContext();
     if (!C.hasSameType(FuncX->getType(), FuncY->getType())) {
       // We can get functions with different types on the redecl chain in C++17

diff --git a/clang/lib/Serialization/ASTWriterDecl.cpp b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -534,6 +534,7 @@ void ASTDeclWriter::VisitFunctionDecl(FunctionDecl *D) {
   Record.push_back(D->IsConstexpr);
   Record.push_back(D->UsesSEHTry);
   Record.push_back(D->HasSkippedBody);
+  Record.push_back(D->IsMultiVersion);
   Record.push_back(D->IsLateTemplateParsed);
   Record.push_back(D->getLinkageInternal());
   Record.AddSourceLocation(D->getLocEnd());
@@ -2072,6 +2073,7 @@ void ASTWriter::WriteDeclAbbrevs() {
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // Constexpr
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // UsesSEHTry
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // SkippedBody
+  Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // MultiVersion
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // LateParsed
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 3)); // Linkage
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));   // LocEnd

diff --git a/clang/test/CodeGen/attr-target-mv-func-ptrs.c b/clang/test/CodeGen/attr-target-mv-func-ptrs.c
@@ -0,0 +1,32 @@
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm %s -o - | FileCheck %s
+int __attribute__((target("sse4.2"))) foo(int i) { return 0; }
+int __attribute__((target("arch=sandybridge"))) foo(int);
+int __attribute__((target("arch=ivybridge"))) foo(int i) {return 1;}
+int __attribute__((target("default"))) foo(int i) { return 2; }
+
+typedef int (*FuncPtr)(int);
+void func(FuncPtr);
+
+int bar() {
+  func(foo);
+  FuncPtr Free = &foo;
+  FuncPtr Free2 = foo;
+
+  return 0;
+  return Free(1) + Free(2);
+}
+
+// CHECK: @foo.ifunc = ifunc i32 (i32), i32 (i32)* ()* @foo.resolver
+// CHECK: define i32 @foo.sse4.2(
+// CHECK: ret i32 0
+// CHECK: define i32 @foo.arch_ivybridge(
+// CHECK: ret i32 1
+// CHECK: define i32 @foo(
+// CHECK: ret i32 2
+
+// CHECK: define i32 @bar()
+// CHECK: call void @func(i32 (i32)* @foo.ifunc)
+// CHECK: store i32 (i32)* @foo.ifunc
+// CHECK: store i32 (i32)* @foo.ifunc
+
+// CHECK: declare i32 @foo.arch_sandybridge(
diff --git a/clang/test/CodeGen/attr-target-mv-va-args.c b/clang/test/CodeGen/attr-target-mv-va-args.c
@@ -0,0 +1,26 @@
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm %s -o - | FileCheck %s
+int __attribute__((target("sse4.2"))) foo(int i, ...) { return 0; }
+int __attribute__((target("arch=sandybridge"))) foo(int i, ...);
+int __attribute__((target("arch=ivybridge"))) foo(int i, ...) {return 1;}
+int __attribute__((target("default"))) foo(int i, ...) { return 2; }
+
+int bar() {
+  return foo(1, 'a', 1.1) + foo(2, 2.2, "asdf");
+}
+
+// CHECK: @foo.ifunc = ifunc i32 (i32, ...), i32 (i32, ...)* ()* @foo.resolver
+// CHECK: define i32 @foo.sse4.2(i32 %i, ...)
+// CHECK: ret i32 0
+// CHECK: define i32 @foo.arch_ivybridge(i32 %i, ...)
+// CHECK: ret i32 1
+// CHECK: define i32 @foo(i32 %i, ...)
+// CHECK: ret i32 2
+// CHECK: define i32 @bar()
+// CHECK: call i32 (i32, ...) @foo.ifunc(i32 1, i32 97, double
+// CHECK: call i32 (i32, ...) @foo.ifunc(i32 2, double 2.2{{[0-9Ee+]+}}, i8* getelementptr inbounds 
+// CHECK: define i32 (i32, ...)* @foo.resolver()
+// CHECK: ret i32 (i32, ...)* @foo.arch_sandybridge
+// CHECK: ret i32 (i32, ...)* @foo.arch_ivybridge
+// CHECK: ret i32 (i32, ...)* @foo.sse4.2
+// CHECK: ret i32 (i32, ...)* @foo
+// CHECK: declare i32 @foo.arch_sandybridge(i32, ...)
diff --git a/clang/test/CodeGen/attr-target-mv.c b/clang/test/CodeGen/attr-target-mv.c
@@ -0,0 +1,79 @@
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm %s -o - | FileCheck %s
+int __attribute__((target("sse4.2"))) foo(void) { return 0; }
+int __attribute__((target("arch=sandybridge"))) foo(void);
+int __attribute__((target("arch=ivybridge"))) foo(void) {return 1;}
+int __attribute__((target("default"))) foo(void) { return 2; }
+
+int bar() {
+  return foo();
+}
+
+inline int __attribute__((target("sse4.2"))) foo_inline(void) { return 0; }
+inline int __attribute__((target("arch=sandybridge"))) foo_inline(void);
+inline int __attribute__((target("arch=ivybridge"))) foo_inline(void) {return 1;}
+inline int __attribute__((target("default"))) foo_inline(void) { return 2; }
+
+int bar2() {
+  return foo_inline();
+}
+
+inline __attribute__((target("default"))) void foo_decls(void);
+inline __attribute__((target("sse4.2"))) void foo_decls(void);
+void bar3() {
+  foo_decls();
+}
+inline __attribute__((target("default"))) void foo_decls(void) {}
+inline __attribute__((target("sse4.2"))) void foo_decls(void) {}
+
+// CHECK: @foo.ifunc = ifunc i32 (), i32 ()* ()* @foo.resolver
+// CHECK: @foo_inline.ifunc = ifunc i32 (), i32 ()* ()* @foo_inline.resolver
+// CHECK: @foo_decls.ifunc = ifunc void (), void ()* ()* @foo_decls.resolver
+
+// CHECK: define i32 @foo.sse4.2()
+// CHECK: ret i32 0
+// CHECK: define i32 @foo.arch_ivybridge()
+// CHECK: ret i32 1
+// CHECK: define i32 @foo()
+// CHECK: ret i32 2
+// CHECK: define i32 @bar()
+// CHECK: call i32 @foo.ifunc()
+
+// CHECK: define i32 ()* @foo.resolver()
+// CHECK: call void @__cpu_indicator_init()
+// CHECK: ret i32 ()* @foo.arch_sandybridge
+// CHECK: ret i32 ()* @foo.arch_ivybridge
+// CHECK: ret i32 ()* @foo.sse4.2
+// CHECK: ret i32 ()* @foo
+
+// CHECK: define i32 @bar2()
+// CHECK: call i32 @foo_inline.ifunc()
+
+// CHECK: define i32 ()* @foo_inline.resolver()
+// CHECK: call void @__cpu_indicator_init()
+// CHECK: ret i32 ()* @foo_inline.arch_sandybridge
+// CHECK: ret i32 ()* @foo_inline.arch_ivybridge
+// CHECK: ret i32 ()* @foo_inline.sse4.2
+// CHECK: ret i32 ()* @foo_inline
+
+// CHECK: define void @bar3()
+// CHECK: call void @foo_decls.ifunc()
+
+// CHECK: define void ()* @foo_decls.resolver()
+// CHECK: ret void ()* @foo_decls.sse4.2
+// CHECK: ret void ()* @foo_decls
+
+// CHECK: declare i32 @foo.arch_sandybridge()
+
+// CHECK: define available_externally i32 @foo_inline.sse4.2()
+// CHECK: ret i32 0
+
+// CHECK: declare i32 @foo_inline.arch_sandybridge()
+//
+// CHECK: define available_externally i32 @foo_inline.arch_ivybridge()
+// CHECK: ret i32 1
+// CHECK: define available_externally i32 @foo_inline()
+// CHECK: ret i32 2
+
+// CHECK: define available_externally void @foo_decls()
+// CHECK: define available_externally void @foo_decls.sse4.2()
+
diff --git a/clang/test/CodeGenCXX/attr-target-mv-diff-ns.cpp b/clang/test/CodeGenCXX/attr-target-mv-diff-ns.cpp
@@ -0,0 +1,54 @@
+// RUN: %clang_cc1 -std=c++11 -triple x86_64-linux-gnu -emit-llvm %s -o - | FileCheck %s
+// Test ensures that this properly differentiates between types in different 
+// namespaces.
+int __attribute__((target("sse4.2"))) foo(int) { return 0; }
+int __attribute__((target("arch=sandybridge"))) foo(int);
+int __attribute__((target("arch=ivybridge"))) foo(int) {return 1;}
+int __attribute__((target("default"))) foo(int) { return 2; }
+
+namespace ns {
+int __attribute__((target("sse4.2"))) foo(int) { return 0; }
+int __attribute__((target("arch=sandybridge"))) foo(int);
+int __attribute__((target("arch=ivybridge"))) foo(int) {return 1;}
+int __attribute__((target("default"))) foo(int) { return 2; }
+}
+
+int bar() {
+  return foo(1) + ns::foo(2);
+}
+
+// CHECK: @_Z3fooi.ifunc = ifunc i32 (i32), i32 (i32)* ()* @_Z3fooi.resolver
+// CHECK: @_ZN2ns3fooEi.ifunc = ifunc i32 (i32), i32 (i32)* ()* @_ZN2ns3fooEi.resolver
+
+// CHECK: define i32 @_Z3fooi.sse4.2(i32)
+// CHECK: ret i32 0
+// CHECK: define i32 @_Z3fooi.arch_ivybridge(i32)
+// CHECK: ret i32 1
+// CHECK: define i32 @_Z3fooi(i32)
+// CHECK: ret i32 2
+
+// CHECK: define i32 @_ZN2ns3fooEi.sse4.2(i32)
+// CHECK: ret i32 0
+// CHECK: define i32 @_ZN2ns3fooEi.arch_ivybridge(i32)
+// CHECK: ret i32 1
+// CHECK: define i32 @_ZN2ns3fooEi(i32)
+// CHECK: ret i32 2
+
+// CHECK: define i32 @_Z3barv()
+// CHECK: call i32 @_Z3fooi.ifunc(i32 1)
+// CHECK: call i32 @_ZN2ns3fooEi.ifunc(i32 2)
+
+// CHECK: define i32 (i32)* @_Z3fooi.resolver()
+// CHECK: ret i32 (i32)* @_Z3fooi.arch_sandybridge
+// CHECK: ret i32 (i32)* @_Z3fooi.arch_ivybridge
+// CHECK: ret i32 (i32)* @_Z3fooi.sse4.2
+// CHECK: ret i32 (i32)* @_Z3fooi
+//
+// CHECK: define i32 (i32)* @_ZN2ns3fooEi.resolver()
+// CHECK: ret i32 (i32)* @_ZN2ns3fooEi.arch_sandybridge
+// CHECK: ret i32 (i32)* @_ZN2ns3fooEi.arch_ivybridge
+// CHECK: ret i32 (i32)* @_ZN2ns3fooEi.sse4.2
+// CHECK: ret i32 (i32)* @_ZN2ns3fooEi
+
+// CHECK: declare i32 @_Z3fooi.arch_sandybridge(i32)
+// CHECK: declare i32 @_ZN2ns3fooEi.arch_sandybridge(i32)
diff --git a/clang/test/CodeGenCXX/attr-target-mv-func-ptrs.cpp b/clang/test/CodeGenCXX/attr-target-mv-func-ptrs.cpp
@@ -0,0 +1,45 @@
+// RUN: %clang_cc1 -std=c++11 -triple x86_64-linux-gnu -emit-llvm %s -o - | FileCheck %s
+void temp();
+void temp(int);
+using FP = void(*)(int);
+void b() {
+  FP f = temp; 
+}
+
+int __attribute__((target("sse4.2"))) foo(int) { return 0; }
+int __attribute__((target("arch=sandybridge"))) foo(int);
+int __attribute__((target("arch=ivybridge"))) foo(int) {return 1;}
+int __attribute__((target("default"))) foo(int) { return 2; }
+
+struct S {
+int __attribute__((target("sse4.2"))) foo(int) { return 0; }
+int __attribute__((target("arch=sandybridge"))) foo(int);
+int __attribute__((target("arch=ivybridge"))) foo(int) {return 1;}
+int __attribute__((target("default"))) foo(int) { return 2; }
+};
+
+using FuncPtr = int (*)(int);
+using MemFuncPtr = int (S::*)(int);
+
+void f(FuncPtr, MemFuncPtr);
+
+int bar() {
+  FuncPtr Free = &foo;
+  MemFuncPtr Member = &S::foo;
+  S s;
+  f(foo, &S::foo);
+  return Free(1) + (s.*Member)(2);
+}
+
+
+// CHECK: @_Z3fooi.ifunc 
+// CHECK: @_ZN1S3fooEi.ifunc
+
+// CHECK: define i32 @_Z3barv()
+// Store to Free of ifunc
+// CHECK: store i32 (i32)* @_Z3fooi.ifunc
+// Store to Member of ifunc
+// CHECK: store { i64, i64 } { i64 ptrtoint (i32 (%struct.S*, i32)* @_ZN1S3fooEi.ifunc to i64), i64 0 }, { i64, i64 }* [[MEMBER:%[a-z]+]]
+
+// Call to 'f' with the ifunc
+// CHECK: call void @_Z1fPFiiEM1SFiiE(i32 (i32)* @_Z3fooi.ifunc
diff --git a/clang/test/CodeGenCXX/attr-target-mv-member-funcs.cpp b/clang/test/CodeGenCXX/attr-target-mv-member-funcs.cpp
@@ -0,0 +1,137 @@
+// RUN: %clang_cc1 -std=c++11 -triple x86_64-linux-gnu -emit-llvm %s -o - | FileCheck %s
+
+struct S {
+  int __attribute__((target("sse4.2"))) foo(int) { return 0; }
+  int __attribute__((target("arch=sandybridge"))) foo(int);
+  int __attribute__((target("arch=ivybridge"))) foo(int) { return 1; }
+  int __attribute__((target("default"))) foo(int) { return 2; }
+
+  S &__attribute__((target("arch=ivybridge"))) operator=(const S &) {
+    return *this;
+  }
+  S &__attribute__((target("default"))) operator=(const S &) {
+    return *this;
+  }
+};
+
+struct ConvertTo {
+  __attribute__((target("arch=ivybridge"))) operator S() const {
+    return S{};
+  }
+  __attribute__((target("default"))) operator S() const {
+    return S{};
+  }
+};
+
+int bar() {
+  S s;
+  S s2;
+  s2 = s;
+
+  ConvertTo C;
+  s2 = static_cast<S>(C);
+
+  return s.foo(0);
+}
+
+struct S2 {
+  int __attribute__((target("sse4.2"))) foo(int);
+  int __attribute__((target("arch=sandybridge"))) foo(int);
+  int __attribute__((target("arch=ivybridge"))) foo(int);
+  int __attribute__((target("default"))) foo(int);
+};
+
+int bar2() {
+  S2 s;
+  return s.foo(0);
+}
+
+int __attribute__((target("sse4.2"))) S2::foo(int) { return 0; }
+int __attribute__((target("arch=ivybridge"))) S2::foo(int) { return 1; }
+int __attribute__((target("default"))) S2::foo(int) { return 2; }
+
+template<typename T>
+struct templ {
+  int __attribute__((target("sse4.2"))) foo(int) { return 0; }
+  int __attribute__((target("arch=sandybridge"))) foo(int);
+  int __attribute__((target("arch=ivybridge"))) foo(int) { return 1; }
+  int __attribute__((target("default"))) foo(int) { return 2; }
+};
+
+int templ_use() {
+  templ<int> a;
+  templ<double> b;
+  return a.foo(1) + b.foo(2);
+}
+
+// CHECK: @_ZN1SaSERKS_.ifunc = ifunc %struct.S* (%struct.S*, %struct.S*), %struct.S* (%struct.S*, %struct.S*)* ()* @_ZN1SaSERKS_.resolver
+// CHECK: @_ZNK9ConvertTocv1SEv.ifunc = ifunc void (%struct.ConvertTo*), void (%struct.ConvertTo*)* ()* @_ZNK9ConvertTocv1SEv.resolver
+// CHECK: @_ZN1S3fooEi.ifunc = ifunc i32 (%struct.S*, i32), i32 (%struct.S*, i32)* ()* @_ZN1S3fooEi.resolver
+// CHECK: @_ZN2S23fooEi.ifunc = ifunc i32 (%struct.S2*, i32), i32 (%struct.S2*, i32)* ()* @_ZN2S23fooEi.resolver
+// Templates:
+// CHECK: @_ZN5templIiE3fooEi.ifunc = ifunc i32 (%struct.templ*, i32), i32 (%struct.templ*, i32)* ()* @_ZN5templIiE3fooEi.resolver
+// CHECK: @_ZN5templIdE3fooEi.ifunc = ifunc i32 (%struct.templ.0*, i32), i32 (%struct.templ.0*, i32)* ()* @_ZN5templIdE3fooEi.resolver
+
+// CHECK: define i32 @_Z3barv()
+// CHECK: %s = alloca %struct.S, align 1
+// CHECK: %s2 = alloca %struct.S, align 1
+// CHECK: %C = alloca %struct.ConvertTo, align 1
+// CHECK: call dereferenceable(1) %struct.S* @_ZN1SaSERKS_.ifunc(%struct.S* %s2
+// CHECK: call void @_ZNK9ConvertTocv1SEv.ifunc(%struct.ConvertTo* %C)
+// CHECK: call dereferenceable(1) %struct.S* @_ZN1SaSERKS_.ifunc(%struct.S* %s2
+// CHECK: call i32 @_ZN1S3fooEi.ifunc(%struct.S* %s, i32 0)
+
+// CHECK: define %struct.S* (%struct.S*, %struct.S*)* @_ZN1SaSERKS_.resolver()
+// CHECK: ret %struct.S* (%struct.S*, %struct.S*)* @_ZN1SaSERKS_.arch_ivybridge
+// CHECK: ret %struct.S* (%struct.S*, %struct.S*)* @_ZN1SaSERKS_
+
+// CHECK: define void (%struct.ConvertTo*)* @_ZNK9ConvertTocv1SEv.resolver()
+// CHECK: ret void (%struct.ConvertTo*)* @_ZNK9ConvertTocv1SEv.arch_ivybridge
+// CHECK: ret void (%struct.ConvertTo*)* @_ZNK9ConvertTocv1SEv
+
+// CHECK: define i32 (%struct.S*, i32)* @_ZN1S3fooEi.resolver()
+// CHECK: ret i32 (%struct.S*, i32)* @_ZN1S3fooEi.arch_sandybridge
+// CHECK: ret i32 (%struct.S*, i32)* @_ZN1S3fooEi.arch_ivybridge
+// CHECK: ret i32 (%struct.S*, i32)* @_ZN1S3fooEi.sse4.2
+// CHECK: ret i32 (%struct.S*, i32)* @_ZN1S3fooEi
+
+// CHECK: define i32 @_Z4bar2v()
+// CHECK:call i32 @_ZN2S23fooEi.ifunc
+// define i32 (%struct.S2*, i32)* @_ZN2S23fooEi.resolver()
+// CHECK: ret i32 (%struct.S2*, i32)* @_ZN2S23fooEi.arch_sandybridge
+// CHECK: ret i32 (%struct.S2*, i32)* @_ZN2S23fooEi.arch_ivybridge
+// CHECK: ret i32 (%struct.S2*, i32)* @_ZN2S23fooEi.sse4.2
+// CHECK: ret i32 (%struct.S2*, i32)* @_ZN2S23fooEi
+
+// CHECK: define i32 @_ZN2S23fooEi.sse4.2(%struct.S2* %this, i32)
+// CHECK: define i32 @_ZN2S23fooEi.arch_ivybridge(%struct.S2* %this, i32)
+// CHECK: define i32 @_ZN2S23fooEi(%struct.S2* %this, i32)
+
+// CHECK: define i32 @_Z9templ_usev()
+// CHECK:  call i32 @_ZN5templIiE3fooEi.ifunc
+// CHECK:  call i32 @_ZN5templIdE3fooEi.ifunc
+
+
+// CHECK: define i32 (%struct.templ*, i32)* @_ZN5templIiE3fooEi.resolver()
+// CHECK: ret i32 (%struct.templ*, i32)* @_ZN5templIiE3fooEi.arch_sandybridge
+// CHECK: ret i32 (%struct.templ*, i32)* @_ZN5templIiE3fooEi.arch_ivybridge
+// CHECK: ret i32 (%struct.templ*, i32)* @_ZN5templIiE3fooEi.sse4.2
+// CHECK: ret i32 (%struct.templ*, i32)* @_ZN5templIiE3fooEi
+//
+// CHECK: define i32 (%struct.templ.0*, i32)* @_ZN5templIdE3fooEi.resolver()
+// CHECK: ret i32 (%struct.templ.0*, i32)* @_ZN5templIdE3fooEi.arch_sandybridge
+// CHECK: ret i32 (%struct.templ.0*, i32)* @_ZN5templIdE3fooEi.arch_ivybridge
+// CHECK: ret i32 (%struct.templ.0*, i32)* @_ZN5templIdE3fooEi.sse4.2
+// CHECK: ret i32 (%struct.templ.0*, i32)* @_ZN5templIdE3fooEi
+
+// CHECK: define linkonce_odr i32 @_ZN1S3fooEi.sse4.2(%struct.S* %this, i32)
+// CHECK: ret i32 0
+
+// CHECK: declare i32 @_ZN1S3fooEi.arch_sandybridge(%struct.S*, i32)
+
+// CHECK: define linkonce_odr i32 @_ZN1S3fooEi.arch_ivybridge(%struct.S* %this, i32)
+// CHECK: ret i32 1
+
+// CHECK: define linkonce_odr i32 @_ZN1S3fooEi(%struct.S* %this, i32)
+// CHECK: ret i32 2
+
diff --git a/clang/test/CodeGenCXX/attr-target-mv-modules.cpp b/clang/test/CodeGenCXX/attr-target-mv-modules.cpp
@@ -0,0 +1,29 @@
+// RUN: %clang_cc1 -std=c++11 -triple x86_64-linux-gnu -fmodules -emit-llvm %s -o - | FileCheck %s
+#pragma clang module build A
+module A {}
+#pragma clang module contents
+#pragma clang module begin A
+__attribute__((target("default"))) void f();
+__attribute__((target("sse4.2"))) void f();
+#pragma clang module end
+#pragma clang module endbuild
+
+#pragma clang module build B
+module B {}
+#pragma clang module contents
+#pragma clang module begin B
+__attribute__((target("default"))) void f();
+__attribute__((target("sse4.2"))) void f();
+#pragma clang module end
+#pragma clang module endbuild
+
+#pragma clang module import A
+#pragma clang module import B
+void g() { f(); }
+
+// Negative tests to validate that the resolver only calls each 1x.
+// CHECK: define void ()* @_Z1fv.resolver
+// CHECK: ret void ()* @_Z1fv.sse4.2
+// CHECK-NOT: ret void ()* @_Z1fv.sse4.2
+// CHECK: ret void ()* @_Z1fv
+// CHECK-NOT: ret void ()* @_Z1fv
diff --git a/clang/test/CodeGenCXX/attr-target-mv-out-of-line-defs.cpp b/clang/test/CodeGenCXX/attr-target-mv-out-of-line-defs.cpp
@@ -0,0 +1,39 @@
+// RUN: %clang_cc1 -std=c++11 -triple x86_64-linux-gnu -emit-llvm %s -o - | FileCheck %s
+struct S {
+  int __attribute__((target("sse4.2"))) foo(int);
+  int __attribute__((target("arch=sandybridge"))) foo(int);
+  int __attribute__((target("arch=ivybridge"))) foo(int);
+  int __attribute__((target("default"))) foo(int);
+};
+
+int __attribute__((target("default"))) S::foo(int) { return 2; }
+int __attribute__((target("sse4.2"))) S::foo(int) { return 0; }
+int __attribute__((target("arch=ivybridge"))) S::foo(int) { return 1; }
+
+int bar() {
+  S s;
+  return s.foo(0);
+}
+
+// CHECK: @_ZN1S3fooEi.ifunc = ifunc i32 (%struct.S*, i32), i32 (%struct.S*, i32)* ()* @_ZN1S3fooEi.resolver
+
+// CHECK: define i32 @_ZN1S3fooEi(%struct.S* %this, i32)
+// CHECK: ret i32 2
+
+// CHECK: define i32 @_ZN1S3fooEi.sse4.2(%struct.S* %this, i32)
+// CHECK: ret i32 0
+
+// CHECK: define i32 @_ZN1S3fooEi.arch_ivybridge(%struct.S* %this, i32)
+// CHECK: ret i32 1
+
+// CHECK: define i32 @_Z3barv()
+// CHECK: %s = alloca %struct.S, align 1
+// CHECK: %call = call i32 @_ZN1S3fooEi.ifunc(%struct.S* %s, i32 0)
+
+// CHECK: define i32 (%struct.S*, i32)* @_ZN1S3fooEi.resolver()
+// CHECK: ret i32 (%struct.S*, i32)* @_ZN1S3fooEi.arch_sandybridge
+// CHECK: ret i32 (%struct.S*, i32)* @_ZN1S3fooEi.arch_ivybridge
+// CHECK: ret i32 (%struct.S*, i32)* @_ZN1S3fooEi.sse4.2
+// CHECK: ret i32 (%struct.S*, i32)* @_ZN1S3fooEi
+
+// CHECK: declare i32 @_ZN1S3fooEi.arch_sandybridge(%struct.S*, i32)
diff --git a/clang/test/CodeGenCXX/attr-target-mv-overloads.cpp b/clang/test/CodeGenCXX/attr-target-mv-overloads.cpp
@@ -0,0 +1,50 @@
+// RUN: %clang_cc1 -std=c++11 -triple x86_64-linux-gnu -emit-llvm %s -o - | FileCheck %s
+
+int __attribute__((target("sse4.2"))) foo_overload(int) { return 0; }
+int __attribute__((target("arch=sandybridge"))) foo_overload(int);
+int __attribute__((target("arch=ivybridge"))) foo_overload(int) {return 1;}
+int __attribute__((target("default"))) foo_overload(int) { return 2; }
+int __attribute__((target("sse4.2"))) foo_overload(void) { return 0; }
+int __attribute__((target("arch=sandybridge"))) foo_overload(void);
+int __attribute__((target("arch=ivybridge"))) foo_overload(void) {return 1;}
+int __attribute__((target("default"))) foo_overload(void) { return 2; }
+
+int bar2() {
+  return foo_overload() + foo_overload(1);
+}
+
+// CHECK: @_Z12foo_overloadv.ifunc = ifunc i32 (), i32 ()* ()* @_Z12foo_overloadv.resolver
+// CHECK: @_Z12foo_overloadi.ifunc = ifunc i32 (i32), i32 (i32)* ()* @_Z12foo_overloadi.resolver
+
+
+// CHECK: define i32 @_Z12foo_overloadi.sse4.2(i32)
+// CHECK: ret i32 0
+// CHECK: define i32 @_Z12foo_overloadi.arch_ivybridge(i32)
+// CHECK: ret i32 1
+// CHECK: define i32 @_Z12foo_overloadi(i32)
+// CHECK: ret i32 2
+// CHECK: define i32 @_Z12foo_overloadv.sse4.2()
+// CHECK: ret i32 0
+// CHECK: define i32 @_Z12foo_overloadv.arch_ivybridge()
+// CHECK: ret i32 1
+// CHECK: define i32 @_Z12foo_overloadv()
+// CHECK: ret i32 2
+
+// CHECK: define i32 @_Z4bar2v()
+// CHECK: call i32 @_Z12foo_overloadv.ifunc()
+// CHECK: call i32 @_Z12foo_overloadi.ifunc(i32 1)
+
+// CHECK: define i32 ()* @_Z12foo_overloadv.resolver()
+// CHECK: ret i32 ()* @_Z12foo_overloadv.arch_sandybridge
+// CHECK: ret i32 ()* @_Z12foo_overloadv.arch_ivybridge
+// CHECK: ret i32 ()* @_Z12foo_overloadv.sse4.2
+// CHECK: ret i32 ()* @_Z12foo_overloadv
+
+// CHECK: define i32 (i32)* @_Z12foo_overloadi.resolver()
+// CHECK: ret i32 (i32)* @_Z12foo_overloadi.arch_sandybridge
+// CHECK: ret i32 (i32)* @_Z12foo_overloadi.arch_ivybridge
+// CHECK: ret i32 (i32)* @_Z12foo_overloadi.sse4.2
+// CHECK: ret i32 (i32)* @_Z12foo_overloadi
+
+// CHECK: declare i32 @_Z12foo_overloadv.arch_sandybridge()
+// CHECK: declare i32 @_Z12foo_overloadi.arch_sandybridge(i32)
diff --git a/clang/test/Sema/attr-target-mv-bad-target.c b/clang/test/Sema/attr-target-mv-bad-target.c
@@ -0,0 +1,10 @@
+// RUN: %clang_cc1 -triple x86_64-windows-pc  -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple arm-none-eabi  -fsyntax-only -verify %s
+
+int __attribute__((target("sse4.2"))) redecl1(void) { return 1; }
+//expected-error@+2 {{function multiversioning is not supported on the current target}}
+//expected-note@-2 {{previous declaration is here}}
+int __attribute__((target("avx")))  redecl1(void) { return 2; }
+
+//expected-error@+1 {{function multiversioning is not supported on the current target}}
+int __attribute__((target("default"))) with_def(void) { return 1;}
diff --git a/clang/test/Sema/attr-target-mv.c b/clang/test/Sema/attr-target-mv.c
@@ -0,0 +1,103 @@
+// RUN: %clang_cc1 -triple x86_64-linux-gnu  -fsyntax-only -verify %s
+
+void __attribute__((target("sse4.2"))) no_default(void);
+void __attribute__((target("arch=sandybridge")))  no_default(void);
+
+void use1(void){
+  // expected-error@+1 {{no matching function for call to 'no_default'}}
+  no_default();
+}
+
+void __attribute__((target("sse4.2"))) has_def(void);
+void __attribute__((target("default")))  has_def(void);
+
+void use2(void){
+  // expected-error@+2 {{reference to overloaded function could not be resolved; did you mean to call it?}}
+  // expected-note@-4 {{possible target for call}}
+  +has_def;
+}
+
+int __attribute__((target("sse4.2"))) no_proto();
+// expected-error@-1 {{multiversioned function must have a prototype}}
+// expected-note@+1 {{function multiversioning caused by this declaration}}
+int __attribute__((target("arch=sandybridge"))) no_proto();
+
+// The following should all be legal, since they are just redeclarations.
+int __attribute__((target("sse4.2"))) redecl1(void);
+int __attribute__((target("sse4.2"))) redecl1(void) { return 1; }
+int __attribute__((target("arch=sandybridge")))  redecl1(void) { return 2; }
+
+int __attribute__((target("sse4.2"))) redecl2(void) { return 1; }
+int __attribute__((target("sse4.2"))) redecl2(void);
+int __attribute__((target("arch=sandybridge")))  redecl2(void) { return 2; }
+
+int __attribute__((target("sse4.2"))) redecl3(void) { return 0; }
+int __attribute__((target("arch=ivybridge"))) redecl3(void) { return 1; }
+int __attribute__((target("arch=sandybridge")))  redecl3(void);
+int __attribute__((target("arch=sandybridge")))  redecl3(void) { return 2; }
+
+int __attribute__((target("sse4.2"))) redecl4(void) { return 1; }
+int __attribute__((target("arch=sandybridge")))  redecl4(void) { return 2; }
+int __attribute__((target("arch=sandybridge")))  redecl4(void);
+
+int __attribute__((target("sse4.2"))) redef(void) { return 1; }
+int __attribute__((target("arch=ivybridge"))) redef(void) { return 1; }
+int __attribute__((target("arch=sandybridge")))  redef(void) { return 2; }
+// expected-error@+2 {{redefinition of 'redef'}}
+// expected-note@-2 {{previous definition is here}}
+int __attribute__((target("arch=sandybridge")))  redef(void) { return 2; }
+
+int __attribute__((target("default"))) redef2(void) { return 1;}
+// expected-error@+2 {{redefinition of 'redef2'}}
+// expected-note@-2 {{previous definition is here}}
+int __attribute__((target("default"))) redef2(void) { return 1;}
+
+int __attribute__((target("sse4.2"))) mv_after_use(void) { return 1; }
+int use3(void) {
+  return mv_after_use();
+}
+
+// expected-error@+1 {{function declaration cannot become a multiversioned function after first usage}}
+int __attribute__((target("arch=sandybridge")))  mv_after_use(void) { return 2; }
+
+int __attribute__((target("sse4.2,arch=sandybridge"))) mangle(void) { return 1; }
+//expected-error@+2 {{multiversioned function redeclarations require identical target attributes}}
+//expected-note@-2 {{previous declaration is here}}
+int __attribute__((target("arch=sandybridge,sse4.2")))  mangle(void) { return 2; }
+
+int prev_no_target(void);
+int __attribute__((target("arch=sandybridge")))  prev_no_target(void) { return 2; }
+// expected-error@-2 {{function declaration is missing 'target' attribute in a multiversioned function}}
+// expected-note@+1 {{function multiversioning caused by this declaration}}
+int __attribute__((target("arch=ivybridge")))  prev_no_target(void) { return 2; }
+
+int __attribute__((target("arch=sandybridge")))  prev_no_target2(void);
+int prev_no_target2(void);
+// expected-error@-1 {{function declaration is missing 'target' attribute in a multiversioned function}}
+// expected-note@+1 {{function multiversioning caused by this declaration}}
+int __attribute__((target("arch=ivybridge")))  prev_no_target2(void);
+
+void __attribute__((target("sse4.2"))) addtl_attrs(void);
+//expected-error@+1 {{attribute 'target' multiversioning cannot be combined}}
+void __attribute__((used,target("arch=sandybridge")))  addtl_attrs(void);
+
+//expected-error@+1 {{attribute 'target' multiversioning cannot be combined}}
+void __attribute__((target("default"), used)) addtl_attrs2(void);
+
+//expected-error@+2 {{attribute 'target' multiversioning cannot be combined}}
+//expected-note@+2 {{function multiversioning caused by this declaration}}
+void __attribute__((used,target("sse4.2"))) addtl_attrs3(void);
+void __attribute__((target("arch=sandybridge")))  addtl_attrs3(void);
+
+void __attribute__((target("sse4.2"))) addtl_attrs4(void);
+void __attribute__((target("arch=sandybridge")))  addtl_attrs4(void);
+//expected-error@+1 {{attribute 'target' multiversioning cannot be combined}}
+void __attribute__((used,target("arch=ivybridge")))  addtl_attrs4(void);
+
+int __attribute__((target("sse4.2"))) diff_cc(void);
+// expected-error@+1 {{multiversioned function declaration has a different calling convention}}
+__vectorcall int __attribute__((target("arch=sandybridge")))  diff_cc(void);
+
+int __attribute__((target("sse4.2"))) diff_ret(void);
+// expected-error@+1 {{multiversioned function declaration has a different return type}}
+short __attribute__((target("arch=sandybridge")))  diff_ret(void);
diff --git a/clang/test/SemaCXX/attr-target-mv.cpp b/clang/test/SemaCXX/attr-target-mv.cpp
@@ -0,0 +1,178 @@
+// RUN: %clang_cc1 -triple x86_64-linux-gnu  -fsyntax-only -verify -fexceptions -fcxx-exceptions %s -std=c++14
+void __attribute__((target("sse4.2"))) no_default(void);
+void __attribute__((target("arch=sandybridge")))  no_default(void);
+
+void use1(void){
+  // expected-error@+1 {{no matching function for call to 'no_default'}}
+  no_default();
+}
+constexpr int __attribute__((target("sse4.2"))) foo(void) { return 0; }
+constexpr int __attribute__((target("arch=sandybridge"))) foo(void);
+//expected-error@+1 {{multiversioned function declaration has a different constexpr specification}}
+int __attribute__((target("arch=ivybridge"))) foo(void) {return 1;}
+constexpr int __attribute__((target("default"))) foo(void) { return 2; }
+
+int __attribute__((target("sse4.2"))) foo2(void) { return 0; }
+//expected-error@+1 {{multiversioned function declaration has a different constexpr specification}}
+constexpr int __attribute__((target("arch=sandybridge"))) foo2(void);
+int __attribute__((target("arch=ivybridge"))) foo2(void) {return 1;}
+int __attribute__((target("default"))) foo2(void) { return 2; }
+
+static int __attribute__((target("sse4.2"))) bar(void) { return 0; }
+static int __attribute__((target("arch=sandybridge"))) bar(void);
+//expected-error@+1 {{multiversioned function declaration has a different storage class}}
+int __attribute__((target("arch=ivybridge"))) bar(void) {return 1;}
+static int __attribute__((target("default"))) bar(void) { return 2; }
+
+int __attribute__((target("sse4.2"))) bar2(void) { return 0; }
+//expected-error@+1 {{multiversioned function declaration has a different storage class}}
+static int __attribute__((target("arch=sandybridge"))) bar2(void);
+int __attribute__((target("arch=ivybridge"))) bar2(void) {return 1;}
+int __attribute__((target("default"))) bar2(void) { return 2; }
+
+
+inline int __attribute__((target("sse4.2"))) baz(void) { return 0; }
+inline int __attribute__((target("arch=sandybridge"))) baz(void);
+//expected-error@+1 {{multiversioned function declaration has a different inline specification}}
+int __attribute__((target("arch=ivybridge"))) baz(void) {return 1;}
+inline int __attribute__((target("default"))) baz(void) { return 2; }
+
+int __attribute__((target("sse4.2"))) baz2(void) { return 0; }
+//expected-error@+1 {{multiversioned function declaration has a different inline specification}}
+inline int __attribute__((target("arch=sandybridge"))) baz2(void);
+int __attribute__((target("arch=ivybridge"))) baz2(void) {return 1;}
+int __attribute__((target("default"))) baz2(void) { return 2; }
+
+float __attribute__((target("sse4.2"))) bock(void) { return 0; }
+//expected-error@+1 {{multiversioned function declaration has a different return type}}
+int __attribute__((target("arch=sandybridge"))) bock(void);
+//expected-error@+1 {{multiversioned function declaration has a different return type}}
+int __attribute__((target("arch=ivybridge"))) bock(void) {return 1;}
+//expected-error@+1 {{multiversioned function declaration has a different return type}}
+int __attribute__((target("default"))) bock(void) { return 2; }
+
+int __attribute__((target("sse4.2"))) bock2(void) { return 0; }
+//expected-error@+1 {{multiversioned function declaration has a different return type}}
+float __attribute__((target("arch=sandybridge"))) bock2(void);
+int __attribute__((target("arch=ivybridge"))) bock2(void) {return 1;}
+int __attribute__((target("default"))) bock2(void) { return 2; }
+
+auto __attribute__((target("sse4.2"))) bock3(void) -> int { return 0; }
+//expected-error@+1 {{multiversioned function declaration has a different return type}}
+auto __attribute__((target("arch=sandybridge"))) bock3(void) -> short { return (short)0;}
+
+int __attribute__((target("sse4.2"))) bock4(void) noexcept(false) { return 0; }
+//expected-error@+2 {{exception specification in declaration does not match previous declaration}}
+//expected-note@-2 {{previous declaration is here}}
+int __attribute__((target("arch=sandybridge"))) bock4(void) noexcept(true) { return 1;}
+
+// FIXME: Add support for templates and virtual functions!
+template<typename T>
+int __attribute__((target("sse4.2"))) foo(T) { return 0; }
+// expected-error@+2 {{multiversioned functions do not yet support function templates}}
+template<typename T>
+int __attribute__((target("arch=sandybridge"))) foo(T);
+
+// expected-error@+2 {{multiversioned functions do not yet support function templates}}
+template<typename T>
+int __attribute__((target("default"))) foo(T) { return 2; }
+
+struct S {
+  template<typename T>
+  int __attribute__((target("sse4.2"))) foo(T) { return 0; }
+  // expected-error@+2 {{multiversioned functions do not yet support function templates}}
+  template<typename T>
+  int __attribute__((target("arch=sandybridge"))) foo(T);
+
+  // expected-error@+2 {{multiversioned functions do not yet support function templates}}
+  template<typename T>
+  int __attribute__((target("default"))) foo(T) { return 2; }
+
+  // expected-error@+1 {{multiversioned functions do not yet support virtual functions}}
+  virtual void __attribute__((target("default"))) virt();
+};
+
+extern "C" {
+int __attribute__((target("sse4.2"))) diff_mangle(void) { return 0; }
+}
+//expected-error@+1 {{multiversioned function declaration has a different linkage}}
+int __attribute__((target("arch=sandybridge"))) diff_mangle(void) { return 0; }
+
+// expected-error@+1 {{multiversioned functions do not yet support deduced return types}}
+auto __attribute__((target("default"))) deduced_return(void) { return 0; }
+// expected-error@-1 {{cannot initialize return object of type 'auto' with an rvalue of type 'int'}}
+
+auto __attribute__((target("default"))) trailing_return(void)-> int { return 0; }
+
+__attribute__((target("default"))) void DiffDecl();
+namespace N {
+using ::DiffDecl;
+// expected-error@+3 {{declaration conflicts with target of using declaration already in scope}}
+// expected-note@-4 {{target of using declaration}}
+// expected-note@-3 {{using declaration}}
+__attribute__((target("arch=sandybridge"))) void DiffDecl();
+} // namespace N
+
+struct SpecialFuncs {
+  // expected-error@+1 {{multiversioned functions do not yet support constructors}}
+  __attribute__((target("default"))) SpecialFuncs();
+  // expected-error@+1 {{multiversioned functions do not yet support destructors}}
+  __attribute__((target("default"))) ~SpecialFuncs();
+
+  // expected-error@+1 {{multiversioned functions do not yet support defaulted functions}}
+  SpecialFuncs& __attribute__((target("default"))) operator=(const SpecialFuncs&) = default;
+  // expected-error@+1 {{multiversioned functions do not yet support deleted functions}}
+  SpecialFuncs& __attribute__((target("default"))) operator=(SpecialFuncs&&) = delete;
+};
+
+class Secret {
+  int i = 0;
+  __attribute__((target("default")))
+  friend int SecretAccessor(Secret &s);
+  __attribute__((target("arch=sandybridge")))
+  friend int SecretAccessor(Secret &s);
+};
+
+__attribute__((target("default")))
+int SecretAccessor(Secret &s) {
+  return s.i;
+}
+
+__attribute__((target("arch=sandybridge")))
+int SecretAccessor(Secret &s) {
+  return s.i + 2;
+}
+
+__attribute__((target("arch=ivybridge")))
+int SecretAccessor(Secret &s) {
+  //expected-error@+2{{'i' is a private member of 'Secret'}}
+  //expected-note@-20{{implicitly declared private here}}
+  return s.i + 3;
+}
+
+constexpr int __attribute__((target("sse4.2"))) constexpr_foo(void) {
+  return 0;
+}
+constexpr int __attribute__((target("arch=sandybridge"))) constexpr_foo(void);
+constexpr int __attribute__((target("arch=ivybridge"))) constexpr_foo(void) {
+  return 1;
+}
+constexpr int __attribute__((target("default"))) constexpr_foo(void) {
+  return 2;
+}
+
+void constexpr_test() {
+  static_assert(foo() == 2, "Should call 'default' in a constexpr context");
+}
+
+struct BadOutOfLine {
+  int __attribute__((target("sse4.2"))) foo(int);
+  int __attribute__((target("default"))) foo(int);
+};
+
+int __attribute__((target("sse4.2"))) BadOutOfLine::foo(int) { return 0; }
+int __attribute__((target("default"))) BadOutOfLine::foo(int) { return 1; }
+// expected-error@+3 {{out-of-line definition of 'foo' does not match any declaration in 'BadOutOfLine'}}
+// expected-note@-3 {{member declaration nearly matches}}
+// expected-note@-3 {{member declaration nearly matches}}
+int __attribute__((target("arch=atom"))) BadOutOfLine::foo(int) { return 1; }