Index: include/clang/AST/ASTContext.h
===================================================================
--- include/clang/AST/ASTContext.h
+++ include/clang/AST/ASTContext.h
@@ -70,6 +70,7 @@
   class VTableContextBase;
 
   namespace Builtin { class Context; }
+  enum BuiltinTemplateKind : int;
 
   namespace comments {
     class FullComment;
@@ -246,6 +247,9 @@
   /// The identifier 'NSCopying'.
   IdentifierInfo *NSCopyingName = nullptr;
 
+  /// The identifier '__make_integer_seq'.
+  mutable IdentifierInfo *MakeIntegerSeqName = nullptr;
+
   QualType ObjCConstantStringType;
   mutable RecordDecl *CFConstantStringTypeDecl;
   
@@ -399,6 +403,7 @@
   
   TranslationUnitDecl *TUDecl;
   mutable ExternCContextDecl *ExternCContext;
+  mutable BuiltinTemplateDecl *MakeIntegerSeqDecl;
 
   /// \brief The associated SourceManager object.a
   SourceManager &SourceMgr;
@@ -821,6 +826,7 @@
   TranslationUnitDecl *getTranslationUnitDecl() const { return TUDecl; }
 
   ExternCContextDecl *getExternCContextDecl() const;
+  BuiltinTemplateDecl *getMakeIntegerSeqDecl() const;
 
   // Builtin Types.
   CanQualType VoidTy;
@@ -894,6 +900,9 @@
   void PrintStats() const;
   const SmallVectorImpl<Type *>& getTypes() const { return Types; }
 
+  BuiltinTemplateDecl *buildBuiltinTemplateDecl(BuiltinTemplateKind BTK,
+                                                const IdentifierInfo *II) const;
+
   /// \brief Create a new implicit TU-level CXXRecordDecl or RecordDecl
   /// declaration.
   RecordDecl *buildImplicitRecord(StringRef Name,
@@ -1397,6 +1406,12 @@
     return NSCopyingName;
   }
 
+  IdentifierInfo *getMakeIntegerSeqName() const {
+    if (!MakeIntegerSeqName)
+      MakeIntegerSeqName = &Idents.get("__make_integer_seq");
+    return MakeIntegerSeqName;
+  }
+
   /// \brief Retrieve the Objective-C "instancetype" type, if already known;
   /// otherwise, returns a NULL type;
   QualType getObjCInstanceType() {
Index: include/clang/AST/DataRecursiveASTVisitor.h
===================================================================
--- include/clang/AST/DataRecursiveASTVisitor.h
+++ include/clang/AST/DataRecursiveASTVisitor.h
@@ -1551,6 +1551,10 @@
     TRY_TO(TraverseFunctionInstantiations(D));
 })
 
+DEF_TRAVERSE_DECL(BuiltinTemplateDecl, {
+  TRY_TO(TraverseTemplateParameterListHelper(D->getTemplateParameters()));
+})
+
 DEF_TRAVERSE_DECL(TemplateTemplateParmDecl, {
   // D is the "T" in something like
   //   template <template <typename> class T> class container { };
Index: include/clang/AST/DeclTemplate.h
===================================================================
--- include/clang/AST/DeclTemplate.h
+++ include/clang/AST/DeclTemplate.h
@@ -25,6 +25,7 @@
 
 namespace clang {
 
+enum BuiltinTemplateKind : int;
 class TemplateParameterList;
 class TemplateDecl;
 class RedeclarableTemplateDecl;
@@ -1490,6 +1491,35 @@
   friend TrailingObjects;
 };
 
+/// \brief Represents the builtin template declaration which is used to
+/// implement __make_integer_seq.  It serves no real purpose beyond existing as
+/// a place to hold template parameters.
+class BuiltinTemplateDecl : public TemplateDecl {
+  void anchor() override;
+
+  BuiltinTemplateDecl(const ASTContext &C, DeclContext *DC,
+                      DeclarationName Name, BuiltinTemplateKind BTK);
+
+  BuiltinTemplateKind BTK;
+
+public:
+  // Implement isa/cast/dyncast support
+  static bool classof(const Decl *D) { return classofKind(D->getKind()); }
+  static bool classofKind(Kind K) { return K == BuiltinTemplate; }
+
+  static BuiltinTemplateDecl *Create(const ASTContext &C, DeclContext *DC,
+                                     DeclarationName Name,
+                                     BuiltinTemplateKind BTK) {
+    return new (C, DC) BuiltinTemplateDecl(C, DC, Name, BTK);
+  }
+
+  SourceRange getSourceRange() const override LLVM_READONLY {
+    return SourceRange();
+  }
+
+  BuiltinTemplateKind getBuiltinTemplateKind() const { return BTK; }
+};
+
 /// \brief Represents a class template specialization, which refers to
 /// a class template with a given set of template arguments.
 ///
Index: include/clang/AST/RecursiveASTVisitor.h
===================================================================
--- include/clang/AST/RecursiveASTVisitor.h
+++ include/clang/AST/RecursiveASTVisitor.h
@@ -1603,6 +1603,10 @@
   TRY_TO(TraverseTemplateParameterListHelper(D->getTemplateParameters()));
 })
 
+DEF_TRAVERSE_DECL(BuiltinTemplateDecl, {
+  TRY_TO(TraverseTemplateParameterListHelper(D->getTemplateParameters()));
+})
+
 DEF_TRAVERSE_DECL(TemplateTypeParmDecl, {
   // D is the "T" in something like "template<typename T> class vector;"
   if (D->getTypeForDecl())
Index: include/clang/Basic/Builtins.h
===================================================================
--- include/clang/Basic/Builtins.h
+++ include/clang/Basic/Builtins.h
@@ -206,5 +206,12 @@
 };
 
 }
+
+/// \brief Kinds of BuiltinTemplateDecl.
+enum BuiltinTemplateKind : int {
+  /// \brief This names the __make_integer_seq BuiltinTemplateDecl.
+  BTK__make_integer_seq
+};
+
 } // end namespace clang
 #endif
Index: include/clang/Basic/DeclNodes.td
===================================================================
--- include/clang/Basic/DeclNodes.td
+++ include/clang/Basic/DeclNodes.td
@@ -59,6 +59,7 @@
       def VarTemplate : DDecl<RedeclarableTemplate>;
       def TypeAliasTemplate : DDecl<RedeclarableTemplate>;
     def TemplateTemplateParm : DDecl<Template>;
+    def BuiltinTemplate : DDecl<Template>;
   def Using : DDecl<Named>;
   def UsingShadow : DDecl<Named>;
   def ObjCMethod : DDecl<Named>, DeclContext;
Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td
+++ include/clang/Basic/DiagnosticSemaKinds.td
@@ -1993,7 +1993,13 @@
 def warn_cxx98_compat_unicode_type : Warning<
   "'%0' type specifier is incompatible with C++98">,
   InGroup<CXX98Compat>, DefaultIgnore;
- 
+
+// __make_integer_seq
+def err_integer_sequence_negative_length : Error<
+  "integer sequences must have non-negative sequence length">;
+def err_integer_sequence_integral_element_type : Error<
+  "integer sequences must have integral element type">;
+
 // Objective-C++
 def err_objc_decls_may_only_appear_in_global_scope : Error<
   "Objective-C declarations may only appear in global scope">;
Index: include/clang/Sema/Sema.h
===================================================================
--- include/clang/Sema/Sema.h
+++ include/clang/Sema/Sema.h
@@ -9043,6 +9043,7 @@
 
   mutable IdentifierInfo *Ident_super;
   mutable IdentifierInfo *Ident___float128;
+  mutable IdentifierInfo *Ident___make_integer_seq;
 
   /// Nullability type specifiers.
   IdentifierInfo *Ident__Nonnull = nullptr;
@@ -9084,6 +9085,7 @@
 
   IdentifierInfo *getSuperIdentifier() const;
   IdentifierInfo *getFloat128Identifier() const;
+  IdentifierInfo *getMakeIntegerSeqIdentifier() const;
 
   Decl *getObjCDeclContext() const;
 
Index: lib/AST/ASTContext.cpp
===================================================================
--- lib/AST/ASTContext.cpp
+++ lib/AST/ASTContext.cpp
@@ -741,7 +741,7 @@
       ucontext_tDecl(nullptr), BlockDescriptorType(nullptr),
       BlockDescriptorExtendedType(nullptr), cudaConfigureCallDecl(nullptr),
       FirstLocalImport(), LastLocalImport(), ExternCContext(nullptr),
-      SourceMgr(SM), LangOpts(LOpts),
+      MakeIntegerSeqDecl(nullptr), SourceMgr(SM), LangOpts(LOpts),
       SanitizerBL(new SanitizerBlacklist(LangOpts.SanitizerBlacklistFiles, SM)),
       AddrSpaceMap(nullptr), Target(nullptr), AuxTarget(nullptr),
       PrintingPolicy(LOpts), Idents(idents), Selectors(sels),
@@ -904,6 +904,24 @@
   return ExternCContext;
 }
 
+BuiltinTemplateDecl *
+ASTContext::buildBuiltinTemplateDecl(BuiltinTemplateKind BTK,
+                                     const IdentifierInfo *II) const {
+  auto *BuiltinTemplate = BuiltinTemplateDecl::Create(*this, TUDecl, II, BTK);
+  BuiltinTemplate->setImplicit();
+  TUDecl->addDecl(BuiltinTemplate);
+
+  return BuiltinTemplate;
+}
+
+BuiltinTemplateDecl *
+ASTContext::getMakeIntegerSeqDecl() const {
+  if (!MakeIntegerSeqDecl)
+    MakeIntegerSeqDecl = buildBuiltinTemplateDecl(BTK__make_integer_seq,
+                                                  getMakeIntegerSeqName());
+  return MakeIntegerSeqDecl;
+}
+
 RecordDecl *ASTContext::buildImplicitRecord(StringRef Name,
                                             RecordDecl::TagKind TK) const {
   SourceLocation Loc;
Index: lib/AST/ASTDumper.cpp
===================================================================
--- lib/AST/ASTDumper.cpp
+++ lib/AST/ASTDumper.cpp
@@ -21,6 +21,7 @@
 #include "clang/AST/DeclVisitor.h"
 #include "clang/AST/StmtVisitor.h"
 #include "clang/AST/TypeVisitor.h"
+#include "clang/Basic/Builtins.h"
 #include "clang/Basic/Module.h"
 #include "clang/Basic/SourceManager.h"
 #include "llvm/Support/raw_ostream.h"
@@ -447,6 +448,7 @@
         const ClassTemplatePartialSpecializationDecl *D);
     void VisitClassScopeFunctionSpecializationDecl(
         const ClassScopeFunctionSpecializationDecl *D);
+    void VisitBuiltinTemplateDecl(const BuiltinTemplateDecl *D);
     void VisitVarTemplateDecl(const VarTemplateDecl *D);
     void VisitVarTemplateSpecializationDecl(
         const VarTemplateSpecializationDecl *D);
@@ -1333,6 +1335,16 @@
   VisitTemplateDecl(D, false);
 }
 
+void ASTDumper::VisitBuiltinTemplateDecl(const BuiltinTemplateDecl *D) {
+  dumpName(D);
+  switch (D->getBuiltinTemplateKind()) {
+  case BTK__make_integer_seq:
+    OS << " __make_integer_seq";
+    break;
+  }
+  dumpTemplateParameters(D->getTemplateParameters());
+}
+
 void ASTDumper::VisitVarTemplateSpecializationDecl(
     const VarTemplateSpecializationDecl *D) {
   dumpTemplateArgumentList(D->getTemplateArgs());
Index: lib/AST/DeclBase.cpp
===================================================================
--- lib/AST/DeclBase.cpp
+++ lib/AST/DeclBase.cpp
@@ -639,6 +639,7 @@
     case ExternCContext:
 
     case UsingDirective:
+    case BuiltinTemplate:
     case ClassTemplateSpecialization:
     case ClassTemplatePartialSpecialization:
     case ClassScopeFunctionSpecialization:
Index: lib/AST/DeclTemplate.cpp
===================================================================
--- lib/AST/DeclTemplate.cpp
+++ lib/AST/DeclTemplate.cpp
@@ -18,6 +18,7 @@
 #include "clang/AST/Expr.h"
 #include "clang/AST/ExprCXX.h"
 #include "clang/AST/TypeLoc.h"
+#include "clang/Basic/Builtins.h"
 #include "clang/Basic/IdentifierTable.h"
 #include "llvm/ADT/STLExtras.h"
 #include <memory>
@@ -1191,3 +1192,65 @@
                                                          unsigned ID) {
   return new (C, ID) VarTemplatePartialSpecializationDecl(C);
 }
+
+static TemplateParameterList *
+createMakeIntegerSeqParameterList(const ASTContext &C, DeclContext *DC) {
+  // typename T
+  auto *T = TemplateTypeParmDecl::Create(
+      C, DC, SourceLocation(), SourceLocation(), /*Depth=*/1, /*Position=*/0,
+      /*Id=*/nullptr, /*Typename=*/true, /*ParameterPack=*/false);
+
+  // Ints...
+  TypeSourceInfo *TI =
+      C.getTrivialTypeSourceInfo(QualType(T->getTypeForDecl(), 0));
+  auto *N = NonTypeTemplateParmDecl::Create(
+      C, DC, SourceLocation(), SourceLocation(), /*Depth=*/0, /*Position=*/1,
+      /*Id=*/nullptr, TI->getType(), /*ParameterPack=*/true, TI);
+
+  // <typename T, Ints...>
+  NamedDecl *P[2] = {T, N};
+  auto *TPL = TemplateParameterList::Create(
+      C, SourceLocation(), SourceLocation(), P, 2, SourceLocation());
+
+  // template <typename T, Ints...> class IntSeq
+  auto *TemplateTemplateParm = TemplateTemplateParmDecl::Create(
+      C, DC, SourceLocation(), /*Depth=*/0, /*Position=*/0,
+      /*ParameterPack=*/false, /*Id=*/nullptr, TPL);
+
+  // typename T
+  auto *TemplateTypeParm = TemplateTypeParmDecl::Create(
+      C, DC, SourceLocation(), SourceLocation(), /*Depth=*/0, /*Position=*/1,
+      /*Id=*/nullptr, /*Typename=*/true, /*ParameterPack=*/false);
+
+  // Ints...
+  TypeSourceInfo *TInfo = C.getTrivialTypeSourceInfo(
+      QualType(TemplateTypeParm->getTypeForDecl(), 0));
+  auto *NonTypeTemplateParm = NonTypeTemplateParmDecl::Create(
+      C, DC, SourceLocation(), SourceLocation(), /*Depth=*/0, /*Position=*/2,
+      /*Id=*/nullptr, TInfo->getType(), /*ParameterPack=*/false, TInfo);
+  NamedDecl *Params[] = {TemplateTemplateParm, TemplateTypeParm,
+                         NonTypeTemplateParm};
+
+  // template <template <typename T, Ints...> class IntSeq, typename T, Ints...>
+  return TemplateParameterList::Create(C, SourceLocation(), SourceLocation(),
+                                       Params, 3, SourceLocation());
+}
+
+static TemplateParameterList *createBuiltinTemplateParameterList(
+    const ASTContext &C, DeclContext *DC, BuiltinTemplateKind BTK) {
+  switch (BTK) {
+  case BTK__make_integer_seq:
+    return createMakeIntegerSeqParameterList(C, DC);
+  }
+
+  llvm_unreachable("unhandled BuiltinTemplateKind!");
+}
+
+void BuiltinTemplateDecl::anchor() {}
+
+BuiltinTemplateDecl::BuiltinTemplateDecl(const ASTContext &C, DeclContext *DC,
+                                         DeclarationName Name,
+                                         BuiltinTemplateKind BTK)
+    : TemplateDecl(BuiltinTemplate, DC, SourceLocation(), Name,
+                   createBuiltinTemplateParameterList(C, DC, BTK)),
+      BTK(BTK) {}
Index: lib/CodeGen/CGDecl.cpp
===================================================================
--- lib/CodeGen/CGDecl.cpp
+++ lib/CodeGen/CGDecl.cpp
@@ -35,6 +35,7 @@
 
 void CodeGenFunction::EmitDecl(const Decl &D) {
   switch (D.getKind()) {
+  case Decl::BuiltinTemplate:
   case Decl::TranslationUnit:
   case Decl::ExternCContext:
   case Decl::Namespace:
Index: lib/Sema/Sema.cpp
===================================================================
--- lib/Sema/Sema.cpp
+++ lib/Sema/Sema.cpp
@@ -105,7 +105,8 @@
     CurrentInstantiationScope(nullptr), DisableTypoCorrection(false),
     TyposCorrected(0), AnalysisWarnings(*this), ThreadSafetyDeclCache(nullptr),
     VarDataSharingAttributesStack(nullptr), CurScope(nullptr),
-    Ident_super(nullptr), Ident___float128(nullptr)
+    Ident_super(nullptr), Ident___float128(nullptr),
+    Ident___make_integer_seq(nullptr)
 {
   TUScope = nullptr;
 
Index: lib/Sema/SemaLookup.cpp
===================================================================
--- lib/Sema/SemaLookup.cpp
+++ lib/Sema/SemaLookup.cpp
@@ -627,6 +627,11 @@
         R.addDecl(S.getASTContext().getFloat128StubType());
         return true;
       }
+      if (S.getLangOpts().CPlusPlus && NameKind == Sema::LookupOrdinaryName &&
+          II == S.getASTContext().getMakeIntegerSeqName()) {
+        R.addDecl(S.getASTContext().getMakeIntegerSeqDecl());
+        return true;
+      }
 
       // If this is a builtin on this (or all) targets, create the decl.
       if (unsigned BuiltinID = II->getBuiltinID()) {
Index: lib/Sema/SemaTemplate.cpp
===================================================================
--- lib/Sema/SemaTemplate.cpp
+++ lib/Sema/SemaTemplate.cpp
@@ -18,6 +18,7 @@
 #include "clang/AST/ExprCXX.h"
 #include "clang/AST/RecursiveASTVisitor.h"
 #include "clang/AST/TypeVisitor.h"
+#include "clang/Basic/Builtins.h"
 #include "clang/Basic/LangOptions.h"
 #include "clang/Basic/PartialDiagnostic.h"
 #include "clang/Basic/TargetInfo.h"
@@ -208,7 +209,8 @@
       R.suppressDiagnostics();
     } else {
       assert(isa<ClassTemplateDecl>(TD) || isa<TemplateTemplateParmDecl>(TD) ||
-             isa<TypeAliasTemplateDecl>(TD) || isa<VarTemplateDecl>(TD));
+             isa<TypeAliasTemplateDecl>(TD) || isa<VarTemplateDecl>(TD) ||
+             isa<BuiltinTemplateDecl>(TD));
       TemplateKind =
           isa<VarTemplateDecl>(TD) ? TNK_Var_template : TNK_Type_template;
     }
@@ -2033,6 +2035,7 @@
                                                           TemplateArgs);
 
   TemplateDecl *Template = Name.getAsTemplateDecl();
+
   if (!Template || isa<FunctionTemplateDecl>(Template) ||
       isa<VarTemplateDecl>(Template)) {
     // We might have a substituted template template parameter pack. If so,
@@ -2171,6 +2174,51 @@
     CanonType = Context.getTypeDeclType(Decl);
     assert(isa<RecordType>(CanonType) &&
            "type of non-dependent specialization is not a RecordType");
+  } else if (auto *BTD = dyn_cast<BuiltinTemplateDecl>(Template)) {
+    switch (BTD->getBuiltinTemplateKind()) {
+    case BTK__make_integer_seq:
+      // Specializations of __make_integer_seq<S, T, N> are treated like
+      // S<T, 0, ..., N-1>.
+
+      // C++14 [inteseq.intseq]p1:
+      //   T shall be an integer type.
+      if (!Converted[1].getAsType()->isIntegralType(Context)) {
+        Diag(TemplateArgs[1].getLocation(),
+             diag::err_integer_sequence_integral_element_type);
+        return QualType();
+      }
+
+      // C++14 [inteseq.make]p1:
+      //   If N is negative the program is ill-formed.
+      TemplateArgument NumArgsArg = Converted[2];
+      llvm::APSInt NumArgs = NumArgsArg.getAsIntegral();
+      if (NumArgs < 0) {
+        Diag(TemplateArgs[2].getLocation(),
+             diag::err_integer_sequence_negative_length);
+        return QualType();
+      }
+
+      QualType ArgTy = NumArgsArg.getIntegralType();
+      TemplateArgumentListInfo SyntheticTemplateArgs;
+      // The type argument gets reused as the first template argument in the
+      // synthetic template argument list.
+      SyntheticTemplateArgs.addArgument(TemplateArgs[1]);
+      // Expand N into 0 ... N-1.
+      for (llvm::APSInt I(NumArgs.getBitWidth(), NumArgs.isUnsigned());
+           I < NumArgs; ++I) {
+        TemplateArgument TA(Context, I, ArgTy);
+        Expr *E =
+            BuildExpressionFromIntegralTemplateArgument(TA, SourceLocation())
+                .getAs<Expr>();
+        SyntheticTemplateArgs.addArgument(
+            TemplateArgumentLoc(TemplateArgument(E), E));
+      }
+      // The first template argument will be reused as the template decl that
+      // our synthetic template arguments will be applied to.
+      CanonType = CheckTemplateIdType(Converted[0].getAsTemplate(), TemplateLoc,
+                                      SyntheticTemplateArgs);
+      break;
+    }
   }
 
   // Build the fully-sugared type for this class template
Index: lib/Sema/SemaTemplateInstantiateDecl.cpp
===================================================================
--- lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -922,6 +922,11 @@
   llvm_unreachable("EnumConstantDecls can only occur within EnumDecls.");
 }
 
+Decl *
+TemplateDeclInstantiator::VisitBuiltinTemplateDecl(BuiltinTemplateDecl *D) {
+  llvm_unreachable("BuiltinTemplateDecls cannot be instantiated.");
+}
+
 Decl *TemplateDeclInstantiator::VisitClassTemplateDecl(ClassTemplateDecl *D) {
   bool isFriend = (D->getFriendObjectKind() != Decl::FOK_None);
 
Index: lib/Serialization/ASTCommon.cpp
===================================================================
--- lib/Serialization/ASTCommon.cpp
+++ lib/Serialization/ASTCommon.cpp
@@ -329,6 +329,7 @@
   case Decl::ClassScopeFunctionSpecialization:
   case Decl::Import:
   case Decl::OMPThreadPrivate:
+  case Decl::BuiltinTemplate:
     return false;
 
   // These indirectly derive from Redeclarable<T> but are not actually
Index: lib/Serialization/ASTReaderDecl.cpp
===================================================================
--- lib/Serialization/ASTReaderDecl.cpp
+++ lib/Serialization/ASTReaderDecl.cpp
@@ -293,6 +293,7 @@
     DeclID VisitTemplateDecl(TemplateDecl *D);
     RedeclarableResult VisitRedeclarableTemplateDecl(RedeclarableTemplateDecl *D);
     void VisitClassTemplateDecl(ClassTemplateDecl *D);
+    void VisitBuiltinTemplateDecl(BuiltinTemplateDecl *D);
     void VisitVarTemplateDecl(VarTemplateDecl *D);
     void VisitFunctionTemplateDecl(FunctionTemplateDecl *D);
     void VisitTemplateTemplateParmDecl(TemplateTemplateParmDecl *D);
@@ -1856,6 +1857,10 @@
   }
 }
 
+void ASTDeclReader::VisitBuiltinTemplateDecl(BuiltinTemplateDecl *D) {
+  llvm_unreachable("BuiltinTemplates are not serialized");
+}
+
 /// TODO: Unify with ClassTemplateDecl version?
 ///       May require unifying ClassTemplateDecl and
 ///        VarTemplateDecl beyond TemplateDecl...
Index: tools/libclang/CIndex.cpp
===================================================================
--- tools/libclang/CIndex.cpp
+++ tools/libclang/CIndex.cpp
@@ -5110,6 +5110,7 @@
   case Decl::Import:
   case Decl::OMPThreadPrivate:
   case Decl::ObjCTypeParam:
+  case Decl::BuiltinTemplate:
     return C;
 
   // Declaration kinds that don't make any sense here, but are