diff --git a/clang/lib/AST/DeclTemplate.cpp b/clang/lib/AST/DeclTemplate.cpp
@@ -65,32 +65,29 @@ TemplateParameterList *TemplateParameterList::Create(
 
 unsigned TemplateParameterList::getMinRequiredArguments() const {
   unsigned NumRequiredArgs = 0;
-  for (iterator P = const_cast<TemplateParameterList *>(this)->begin(), 
-             PEnd = const_cast<TemplateParameterList *>(this)->end(); 
-       P != PEnd; ++P) {
-    if ((*P)->isTemplateParameterPack()) {
-      if (NonTypeTemplateParmDecl *NTTP = dyn_cast<NonTypeTemplateParmDecl>(*P))
+  for (const NamedDecl *P : asArray()) {
+    if (P->isTemplateParameterPack()) {
+      if (const auto *NTTP = dyn_cast<NonTypeTemplateParmDecl>(P))
         if (NTTP->isExpandedParameterPack()) {
           NumRequiredArgs += NTTP->getNumExpansionTypes();
           continue;
         }
-      
+
       break;
     }
-  
-    if (TemplateTypeParmDecl *TTP = dyn_cast<TemplateTypeParmDecl>(*P)) {
+
+    if (const auto *TTP = dyn_cast<TemplateTypeParmDecl>(P)) {
       if (TTP->hasDefaultArgument())
         break;
-    } else if (NonTypeTemplateParmDecl *NTTP 
-                                    = dyn_cast<NonTypeTemplateParmDecl>(*P)) {
+    } else if (const auto *NTTP = dyn_cast<NonTypeTemplateParmDecl>(P)) {
       if (NTTP->hasDefaultArgument())
         break;
-    } else if (cast<TemplateTemplateParmDecl>(*P)->hasDefaultArgument())
+    } else if (cast<TemplateTemplateParmDecl>(P)->hasDefaultArgument())
       break;
-    
+
     ++NumRequiredArgs;
   }
-  
+
   return NumRequiredArgs;
 }
 
@@ -111,12 +108,10 @@ unsigned TemplateParameterList::getDepth() const {
 
 static void AdoptTemplateParameterList(TemplateParameterList *Params,
                                        DeclContext *Owner) {
-  for (TemplateParameterList::iterator P = Params->begin(), 
-                                    PEnd = Params->end();
-       P != PEnd; ++P) {
-    (*P)->setDeclContext(Owner);
-
-    if (TemplateTemplateParmDecl *TTP = dyn_cast<TemplateTemplateParmDecl>(*P))
+  for (NamedDecl *P : *Params) {
+    P->setDeclContext(Owner);
+
+    if (auto *TTP = dyn_cast<TemplateTemplateParmDecl>(P))
       AdoptTemplateParameterList(TTP->getTemplateParameters(), Owner);
   }
 }
@@ -157,8 +152,8 @@ RedeclarableTemplateDecl::CommonBase *RedeclarableTemplateDecl::getCommonPtr() c
   }
 
   // Update any previous declarations we saw with the common pointer.
-  for (unsigned I = 0, N = PrevDecls.size(); I != N; ++I)
-    PrevDecls[I]->Common = Common;
+  for (const RedeclarableTemplateDecl *Prev : PrevDecls)
+    Prev->Common = Common;
 
   return Common;
 }
@@ -205,44 +200,41 @@ void RedeclarableTemplateDecl::addSpecializationImpl(
 /// \brief Generate the injected template arguments for the given template
 /// parameter list, e.g., for the injected-class-name of a class template.
 static void GenerateInjectedTemplateArgs(ASTContext &Context,
-                                        TemplateParameterList *Params,
+                                         TemplateParameterList *Params,
                                          TemplateArgument *Args) {
-  for (TemplateParameterList::iterator Param = Params->begin(),
-                                    ParamEnd = Params->end();
-       Param != ParamEnd; ++Param) {
+  for (NamedDecl *Param : *Params) {
     TemplateArgument Arg;
-    if (TemplateTypeParmDecl *TTP = dyn_cast<TemplateTypeParmDecl>(*Param)) {
+    if (auto *TTP = dyn_cast<TemplateTypeParmDecl>(Param)) {
       QualType ArgType = Context.getTypeDeclType(TTP);
       if (TTP->isParameterPack())
         ArgType = Context.getPackExpansionType(ArgType, None);
 
       Arg = TemplateArgument(ArgType);
-    } else if (NonTypeTemplateParmDecl *NTTP =
-               dyn_cast<NonTypeTemplateParmDecl>(*Param)) {
+    } else if (auto *NTTP = dyn_cast<NonTypeTemplateParmDecl>(Param)) {
       Expr *E = new (Context) DeclRefExpr(NTTP, /*enclosing*/ false,
                                   NTTP->getType().getNonLValueExprType(Context),
                                   Expr::getValueKindForType(NTTP->getType()),
                                           NTTP->getLocation());
-      
+
       if (NTTP->isParameterPack())
         E = new (Context) PackExpansionExpr(Context.DependentTy, E,
                                             NTTP->getLocation(), None);
       Arg = TemplateArgument(E);
     } else {
-      TemplateTemplateParmDecl *TTP = cast<TemplateTemplateParmDecl>(*Param);
+      auto *TTP = cast<TemplateTemplateParmDecl>(Param);
       if (TTP->isParameterPack())
         Arg = TemplateArgument(TemplateName(TTP), Optional<unsigned>());
       else
         Arg = TemplateArgument(TemplateName(TTP));
     }
-    
-    if ((*Param)->isTemplateParameterPack())
+
+    if (Param->isTemplateParameterPack())
       Arg = TemplateArgument::CreatePackCopy(Context, Arg);
 
     *Args++ = Arg;
   }
 }
-                                      
+
 //===----------------------------------------------------------------------===//
 // FunctionTemplateDecl Implementation
 //===----------------------------------------------------------------------===//
@@ -421,23 +413,17 @@ void ClassTemplateDecl::getPartialSpecializations(
     = getPartialSpecializations();
   PS.clear();
   PS.reserve(PartialSpecs.size());
-  for (llvm::FoldingSetVector<ClassTemplatePartialSpecializationDecl>::iterator
-       P = PartialSpecs.begin(), PEnd = PartialSpecs.end();
-       P != PEnd; ++P)
-    PS.push_back(P->getMostRecentDecl());
+  for (ClassTemplatePartialSpecializationDecl &P : PartialSpecs)
+    PS.push_back(P.getMostRecentDecl());
 }
 
 ClassTemplatePartialSpecializationDecl *
 ClassTemplateDecl::findPartialSpecialization(QualType T) {
   ASTContext &Context = getASTContext();
-  using llvm::FoldingSetVector;
-  typedef FoldingSetVector<ClassTemplatePartialSpecializationDecl>::iterator
-    partial_spec_iterator;
-  for (partial_spec_iterator P = getPartialSpecializations().begin(),
-                          PEnd = getPartialSpecializations().end();
-       P != PEnd; ++P) {
-    if (Context.hasSameType(P->getInjectedSpecializationType(), T))
-      return P->getMostRecentDecl();
+  for (ClassTemplatePartialSpecializationDecl &P :
+       getPartialSpecializations()) {
+    if (Context.hasSameType(P.getInjectedSpecializationType(), T))
+      return P.getMostRecentDecl();
   }
 
   return nullptr;
@@ -447,12 +433,9 @@ ClassTemplatePartialSpecializationDecl *
 ClassTemplateDecl::findPartialSpecInstantiatedFromMember(
                                     ClassTemplatePartialSpecializationDecl *D) {
   Decl *DCanon = D->getCanonicalDecl();
-  for (llvm::FoldingSetVector<ClassTemplatePartialSpecializationDecl>::iterator
-            P = getPartialSpecializations().begin(),
-         PEnd = getPartialSpecializations().end();
-       P != PEnd; ++P) {
-    if (P->getInstantiatedFromMember()->getCanonicalDecl() == DCanon)
-      return P->getMostRecentDecl();
+  for (ClassTemplatePartialSpecializationDecl &P : getPartialSpecializations()) {
+    if (P.getInstantiatedFromMember()->getCanonicalDecl() == DCanon)
+      return P.getMostRecentDecl();
   }
 
   return nullptr;
@@ -535,20 +518,14 @@ bool TemplateTypeParmDecl::isParameterPack() const {
 // NonTypeTemplateParmDecl Method Implementations
 //===----------------------------------------------------------------------===//
 
-NonTypeTemplateParmDecl::NonTypeTemplateParmDecl(DeclContext *DC, 
-                                                 SourceLocation StartLoc,
-                                                 SourceLocation IdLoc,
-                                                 unsigned D, unsigned P,
-                                                 IdentifierInfo *Id, 
-                                                 QualType T, 
-                                                 TypeSourceInfo *TInfo,
-                                                 const QualType *ExpandedTypes,
-                                                 unsigned NumExpandedTypes,
-                                                TypeSourceInfo **ExpandedTInfos)
-  : DeclaratorDecl(NonTypeTemplateParm, DC, IdLoc, Id, T, TInfo, StartLoc),
-    TemplateParmPosition(D, P), ParameterPack(true),
-    ExpandedParameterPack(true), NumExpandedTypes(NumExpandedTypes) {
-  if (ExpandedTypes && ExpandedTInfos) {
+NonTypeTemplateParmDecl::NonTypeTemplateParmDecl(
+    DeclContext *DC, SourceLocation StartLoc, SourceLocation IdLoc, unsigned D,
+    unsigned P, IdentifierInfo *Id, QualType T, TypeSourceInfo *TInfo,
+    ArrayRef<QualType> ExpandedTypes, ArrayRef<TypeSourceInfo *> ExpandedTInfos)
+    : DeclaratorDecl(NonTypeTemplateParm, DC, IdLoc, Id, T, TInfo, StartLoc),
+      TemplateParmPosition(D, P), ParameterPack(true),
+      ExpandedParameterPack(true), NumExpandedTypes(ExpandedTypes.size()) {
+  if (!ExpandedTypes.empty() && !ExpandedTInfos.empty()) {
     auto TypesAndInfos =
         getTrailingObjects<std::pair<QualType, TypeSourceInfo *>>();
     for (unsigned I = 0; I != NumExpandedTypes; ++I) {
@@ -568,20 +545,16 @@ NonTypeTemplateParmDecl::Create(const ASTContext &C, DeclContext *DC,
                                              T, ParameterPack, TInfo);
 }
 
-NonTypeTemplateParmDecl *
-NonTypeTemplateParmDecl::Create(const ASTContext &C, DeclContext *DC, 
-                                SourceLocation StartLoc, SourceLocation IdLoc,
-                                unsigned D, unsigned P, 
-                                IdentifierInfo *Id, QualType T, 
-                                TypeSourceInfo *TInfo,
-                                const QualType *ExpandedTypes, 
-                                unsigned NumExpandedTypes,
-                                TypeSourceInfo **ExpandedTInfos) {
+NonTypeTemplateParmDecl *NonTypeTemplateParmDecl::Create(
+    const ASTContext &C, DeclContext *DC, SourceLocation StartLoc,
+    SourceLocation IdLoc, unsigned D, unsigned P, IdentifierInfo *Id,
+    QualType T, TypeSourceInfo *TInfo, ArrayRef<QualType> ExpandedTypes,
+    ArrayRef<TypeSourceInfo *> ExpandedTInfos) {
   return new (C, DC,
               additionalSizeToAlloc<std::pair<QualType, TypeSourceInfo *>>(
-                  NumExpandedTypes))
+                  ExpandedTypes.size()))
       NonTypeTemplateParmDecl(DC, StartLoc, IdLoc, D, P, Id, T, TInfo,
-                              ExpandedTypes, NumExpandedTypes, ExpandedTInfos);
+                              ExpandedTypes, ExpandedTInfos);
 }
 
 NonTypeTemplateParmDecl *
@@ -594,12 +567,14 @@ NonTypeTemplateParmDecl::CreateDeserialized(ASTContext &C, unsigned ID) {
 NonTypeTemplateParmDecl *
 NonTypeTemplateParmDecl::CreateDeserialized(ASTContext &C, unsigned ID,
                                             unsigned NumExpandedTypes) {
-  return new (C, ID,
-              additionalSizeToAlloc<std::pair<QualType, TypeSourceInfo *>>(
-                  NumExpandedTypes))
-      NonTypeTemplateParmDecl(nullptr, SourceLocation(), SourceLocation(), 0, 0,
-                              nullptr, QualType(), nullptr, nullptr,
-                              NumExpandedTypes, nullptr);
+  auto *NTTP =
+      new (C, ID, additionalSizeToAlloc<std::pair<QualType, TypeSourceInfo *>>(
+                      NumExpandedTypes))
+          NonTypeTemplateParmDecl(nullptr, SourceLocation(), SourceLocation(),
+                                  0, 0, nullptr, QualType(), nullptr, None,
+                                  None);
+  NTTP->NumExpandedTypes = NumExpandedTypes;
+  return NTTP;
 }
 
 SourceRange NonTypeTemplateParmDecl::getSourceRange() const {
@@ -624,12 +599,12 @@ void TemplateTemplateParmDecl::anchor() { }
 TemplateTemplateParmDecl::TemplateTemplateParmDecl(
     DeclContext *DC, SourceLocation L, unsigned D, unsigned P,
     IdentifierInfo *Id, TemplateParameterList *Params,
-    unsigned NumExpansions, TemplateParameterList * const *Expansions)
-  : TemplateDecl(TemplateTemplateParm, DC, L, Id, Params),
-    TemplateParmPosition(D, P), ParameterPack(true),
-    ExpandedParameterPack(true), NumExpandedParams(NumExpansions) {
-  if (Expansions)
-    std::uninitialized_copy(Expansions, Expansions + NumExpandedParams,
+    ArrayRef<TemplateParameterList *> Expansions)
+    : TemplateDecl(TemplateTemplateParm, DC, L, Id, Params),
+      TemplateParmPosition(D, P), ParameterPack(true),
+      ExpandedParameterPack(true), NumExpandedParams(Expansions.size()) {
+  if (!Expansions.empty())
+    std::uninitialized_copy(Expansions.begin(), Expansions.end(),
                             getTrailingObjects<TemplateParameterList *>());
 }
 
@@ -650,8 +625,7 @@ TemplateTemplateParmDecl::Create(const ASTContext &C, DeclContext *DC,
                                  ArrayRef<TemplateParameterList *> Expansions) {
   return new (C, DC,
               additionalSizeToAlloc<TemplateParameterList *>(Expansions.size()))
-      TemplateTemplateParmDecl(DC, L, D, P, Id, Params, Expansions.size(),
-                               Expansions.data());
+      TemplateTemplateParmDecl(DC, L, D, P, Id, Params, Expansions);
 }
 
 TemplateTemplateParmDecl *
@@ -663,10 +637,12 @@ TemplateTemplateParmDecl::CreateDeserialized(ASTContext &C, unsigned ID) {
 TemplateTemplateParmDecl *
 TemplateTemplateParmDecl::CreateDeserialized(ASTContext &C, unsigned ID,
                                              unsigned NumExpansions) {
-  return new (C, ID,
-              additionalSizeToAlloc<TemplateParameterList *>(NumExpansions))
-      TemplateTemplateParmDecl(nullptr, SourceLocation(), 0, 0, nullptr,
-                               nullptr, NumExpansions, nullptr);
+  auto *TTP =
+      new (C, ID, additionalSizeToAlloc<TemplateParameterList *>(NumExpansions))
+          TemplateTemplateParmDecl(nullptr, SourceLocation(), 0, 0, nullptr,
+                                   nullptr, None);
+  TTP->NumExpandedParams = NumExpansions;
+  return TTP;
 }
 
 SourceLocation TemplateTemplateParmDecl::getDefaultArgumentLoc() const {
@@ -896,15 +872,12 @@ ClassTemplatePartialSpecializationDecl::CreateDeserialized(ASTContext &C,
 
 void FriendTemplateDecl::anchor() { }
 
-FriendTemplateDecl *FriendTemplateDecl::Create(ASTContext &Context,
-                                               DeclContext *DC,
-                                               SourceLocation L,
-                                               unsigned NParams,
-                                               TemplateParameterList **Params,
-                                               FriendUnion Friend,
-                                               SourceLocation FLoc) {
-  return new (Context, DC) FriendTemplateDecl(DC, L, NParams, Params,
-                                              Friend, FLoc);
+FriendTemplateDecl *
+FriendTemplateDecl::Create(ASTContext &Context, DeclContext *DC,
+                           SourceLocation L,
+                           MutableArrayRef<TemplateParameterList *> Params,
+                           FriendUnion Friend, SourceLocation FLoc) {
+  return new (Context, DC) FriendTemplateDecl(DC, L, Params, Friend, FLoc);
 }
 
 FriendTemplateDecl *FriendTemplateDecl::CreateDeserialized(ASTContext &C,
@@ -1060,23 +1033,17 @@ void VarTemplateDecl::getPartialSpecializations(
       getPartialSpecializations();
   PS.clear();
   PS.reserve(PartialSpecs.size());
-  for (llvm::FoldingSetVector<VarTemplatePartialSpecializationDecl>::iterator
-           P = PartialSpecs.begin(),
-           PEnd = PartialSpecs.end();
-       P != PEnd; ++P)
-    PS.push_back(P->getMostRecentDecl());
+  for (VarTemplatePartialSpecializationDecl &P : PartialSpecs)
+    PS.push_back(P.getMostRecentDecl());
 }
 
 VarTemplatePartialSpecializationDecl *
 VarTemplateDecl::findPartialSpecInstantiatedFromMember(
     VarTemplatePartialSpecializationDecl *D) {
   Decl *DCanon = D->getCanonicalDecl();
-  for (llvm::FoldingSetVector<VarTemplatePartialSpecializationDecl>::iterator
-           P = getPartialSpecializations().begin(),
-           PEnd = getPartialSpecializations().end();
-       P != PEnd; ++P) {
-    if (P->getInstantiatedFromMember()->getCanonicalDecl() == DCanon)
-      return P->getMostRecentDecl();
+  for (VarTemplatePartialSpecializationDecl &P : getPartialSpecializations()) {
+    if (P.getInstantiatedFromMember()->getCanonicalDecl() == DCanon)
+      return P.getMostRecentDecl();
   }
 
   return nullptr;
@@ -1134,11 +1101,10 @@ VarTemplateDecl *VarTemplateSpecializationDecl::getSpecializedTemplate() const {
 
 void VarTemplateSpecializationDecl::setTemplateArgsInfo(
     const TemplateArgumentListInfo &ArgsInfo) {
-  unsigned N = ArgsInfo.size();
   TemplateArgsInfo.setLAngleLoc(ArgsInfo.getLAngleLoc());
   TemplateArgsInfo.setRAngleLoc(ArgsInfo.getRAngleLoc());
-  for (unsigned I = 0; I != N; ++I)
-    TemplateArgsInfo.addArgument(ArgsInfo[I]);
+  for (const TemplateArgumentLoc &Loc : ArgsInfo.arguments())
+    TemplateArgsInfo.addArgument(Loc);
 }
 
 //===----------------------------------------------------------------------===//

diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -12676,10 +12676,9 @@ Decl *Sema::ActOnFriendTypeDecl(Scope *S, const DeclSpec &DS,
   // friend a member of an arbitrary specialization of your template).
 
   Decl *D;
-  if (unsigned NumTempParamLists = TempParams.size())
+  if (!TempParams.empty())
     D = FriendTemplateDecl::Create(Context, CurContext, Loc,
-                                   NumTempParamLists,
-                                   TempParams.data(),
+                                   TempParams,
                                    TSI,
                                    DS.getFriendSpecLoc());
   else

diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -2155,16 +2155,11 @@ Decl *TemplateDeclInstantiator::VisitNonTypeTemplateParmDecl(
 
   NonTypeTemplateParmDecl *Param;
   if (IsExpandedParameterPack)
-    Param = NonTypeTemplateParmDecl::Create(SemaRef.Context, Owner,
-                                            D->getInnerLocStart(),
-                                            D->getLocation(),
-                                    D->getDepth() - TemplateArgs.getNumLevels(),
-                                            D->getPosition(),
-                                            D->getIdentifier(), T,
-                                            DI,
-                                            ExpandedParameterPackTypes.data(),
-                                            ExpandedParameterPackTypes.size(),
-                                    ExpandedParameterPackTypesAsWritten.data());
+    Param = NonTypeTemplateParmDecl::Create(
+        SemaRef.Context, Owner, D->getInnerLocStart(), D->getLocation(),
+        D->getDepth() - TemplateArgs.getNumLevels(), D->getPosition(),
+        D->getIdentifier(), T, DI, ExpandedParameterPackTypes,
+        ExpandedParameterPackTypesAsWritten);
   else
     Param = NonTypeTemplateParmDecl::Create(SemaRef.Context, Owner,
                                             D->getInnerLocStart(),