Revert rC330794 and some dependent tiny bug fixes

See Richard's humbling feedback here: 
http://lists.llvm.org/pipermail/cfe-commits/Week-of-Mon-20180423/226482.html
http://lists.llvm.org/pipermail/cfe-commits/Week-of-Mon-20180423/226486.html

Wish I'd had the patience to solicit the feedback prior to committing :)

Sorry for the noise guys.

Thank you Richard for being the steward that clang deserves!





git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@330888 91177308-0d34-0410-b5e6-96231b3b80d8

33 files changed, 69 insertions, 629 deletions

diff --git a/include/clang/AST/DeclTemplate.h b/include/clang/AST/DeclTemplate.h
index 1fe95f4a59..9c68352e76 100644
--- a/include/clang/AST/DeclTemplate.h
+++ b/include/clang/AST/DeclTemplate.h
@@ -3015,46 +3015,6 @@ public:
   static bool classofKind(Kind K) { return K == VarTemplate; }
 };
 
-/// \brief Represents a C++2a ([temp] p1) concept-definition.
-class ConceptDecl : public TemplateDecl {
-protected:
-  Expr *ConstraintExpr;
-
-  ConceptDecl(DeclContext *DC,
-              SourceLocation NameLoc, DeclarationName Name,
-              TemplateParameterList *Params,
-              Expr *ConstraintExpr)
-      : TemplateDecl(nullptr, Concept, DC, NameLoc, Name, Params),
-        ConstraintExpr(ConstraintExpr) {};
-public:
-  static ConceptDecl *Create(ASTContext &C, DeclContext *DC,
-                             SourceLocation NameLoc, DeclarationName Name,
-                             TemplateParameterList *Params,
-                             Expr *ConstraintExpr);
-  static ConceptDecl *CreateDeserialized(ASTContext &C, unsigned ID);
-
-  Expr *getConstraintExpr() const {
-    return ConstraintExpr;
-  }
-
-  void setConstraintExpr(Expr *CE) {
-    ConstraintExpr = CE;
-  }
-
-  SourceRange getSourceRange() const override LLVM_READONLY {
-    return SourceRange(getTemplateParameters()->getTemplateLoc(),
-                       getConstraintExpr()->getLocEnd());
-  }
-
-  // Implement isa/cast/dyncast/etc.
-  static bool classof(const Decl *D) { return classofKind(D->getKind()); }
-  static bool classofKind(Kind K) { return K == Concept; }
-
-  friend class ASTReader;
-  friend class ASTDeclReader;
-  friend class ASTDeclWriter;
-};
-
 inline NamedDecl *getAsNamedDecl(TemplateParameter P) {
   if (auto *PD = P.dyn_cast<TemplateTypeParmDecl *>())
     return PD;
diff --git a/include/clang/AST/RecursiveASTVisitor.h b/include/clang/AST/RecursiveASTVisitor.h
index d9cc89b126..57641793f8 100644
--- a/include/clang/AST/RecursiveASTVisitor.h
+++ b/include/clang/AST/RecursiveASTVisitor.h
@@ -1722,13 +1722,6 @@ DEF_TRAVERSE_TMPL_DECL(Class)
 DEF_TRAVERSE_TMPL_DECL(Var)
 DEF_TRAVERSE_TMPL_DECL(Function)
 
-DEF_TRAVERSE_DECL(ConceptDecl, {
-  TRY_TO(TraverseTemplateParameterListHelper(D->getTemplateParameters()));
-  TRY_TO(TraverseStmt(D->getConstraintExpr()));
-  // FIXME: Traverse all the concept specializations (once we implement forming
-  // template-ids with them).
-})
-
 DEF_TRAVERSE_DECL(TemplateTemplateParmDecl, {
   // D is the "T" in something like
   //   template <template <typename> class T> class container { };
diff --git a/include/clang/Basic/DeclNodes.td b/include/clang/Basic/DeclNodes.td
index 0ab6e32e4d..67ca9e5c6c 100644
--- a/include/clang/Basic/DeclNodes.td
+++ b/include/clang/Basic/DeclNodes.td
@@ -69,7 +69,6 @@ def Named : Decl<"named declarations", 1>;
       def TypeAliasTemplate : DDecl<RedeclarableTemplate>;
     def TemplateTemplateParm : DDecl<Template>;
     def BuiltinTemplate : DDecl<Template>;
-    def Concept : DDecl<Template>;
   def Using : DDecl<Named>;
   def UsingPack : DDecl<Named>;
   def UsingShadow : DDecl<Named>;
diff --git a/include/clang/Basic/DiagnosticParseKinds.td b/include/clang/Basic/DiagnosticParseKinds.td
index 4b6c9fcb1a..7c7c0fb24d 100644
--- a/include/clang/Basic/DiagnosticParseKinds.td
+++ b/include/clang/Basic/DiagnosticParseKinds.td
@@ -1150,24 +1150,6 @@ def err_pragma_cannot_end_force_cuda_host_device : Error<
   "force_cuda_host_device begin">;
 } // end of Parse Issue category.
 
-let CategoryName = "Concepts Issue" in {
-def err_concept_at_non_namespace_scope : Error<
-  "'concept' can only appear in namespace scope">;
-
-def err_concept_extra_headers : Error<
-  "extraneous template parameter list in concept definition">;
-def err_concept_unexpected_scope_spec : Error<
-  "invalid nested name specifier; concepts must be defined in their own namespace">;
-def err_concept_nontemplate : Error<"concept definition must be a template; "
-                                    "missing template parameter list">;
-def err_concept_specialized : Error<
-  "'concept' cannot be "
-  "%select{explicitly specialized|partially specialized}0">;
-def note_concept_specialized : Note<
-  "'concept' cannot be "
-  "%select{explicitly specialized|partially specialized}0">;
-}
-
 let CategoryName = "Modules Issue" in {
 def err_unexpected_module_decl : Error<
   "module declaration can only appear at the top level">;
diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index 59b78b6fe6..c1ee929e23 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -2387,16 +2387,33 @@ def warn_private_extern : Warning<
 def note_private_extern : Note<
   "use __attribute__((visibility(\"hidden\"))) attribute instead">;
 
-// C++ Concepts
+// C++ Concepts TS
+def err_concept_wrong_decl_kind : Error<
+  "'concept' can only appear on the definition of a function template or variable template">;
+def err_concept_decls_may_only_appear_in_namespace_scope : Error<
+  "concept declarations may only appear in namespace scope">;
+def err_function_concept_not_defined : Error<
+  "function concept declaration must be a definition">;
+def err_var_concept_not_initialized : Error<
+  "variable concept declaration must be initialized">;
+def err_function_concept_exception_spec : Error<
+  "function concept cannot have exception specification">;
+def err_concept_decl_invalid_specifiers : Error<
+  "%select{variable|function}0 concept cannot be declared "
+  "'%select{thread_local|inline|friend|constexpr}1'">;
+def err_function_concept_with_params : Error<
+  "function concept cannot have any parameters">;
+def err_function_concept_bool_ret : Error<
+  "declared return type of function concept must be 'bool'">;
+def err_variable_concept_bool_decl : Error<
+  "declared type of variable concept must be 'bool'">;
+def err_concept_specified_specialization : Error<
+  "'concept' cannot be applied on an "
+  "%select{explicit instantiation|explicit specialization|partial specialization}0">;
+def err_concept_specialized : Error<
+  "%select{function|variable}0 concept cannot be "
+  "%select{explicitly instantiated|explicitly specialized|partially specialized}1">;
 
-
-
-def err_concept_initialized_with_non_bool_type : Error<
-  "type of constraint expression must be 'bool' - not '%0'">;
-def err_concept_no_associated_constraints : Error<
-  "concept may not have associated constraints">;
-def err_concept_feature_unimplemented : Error<
-  "unimplemented concept feature: %0 (coming soon)">;
 def err_template_different_associated_constraints : Error<
   "associated constraints differ in template redeclaration">;
 
diff --git a/include/clang/Basic/TemplateKinds.h b/include/clang/Basic/TemplateKinds.h
index 85658af007..ac99ad185f 100644
--- a/include/clang/Basic/TemplateKinds.h
+++ b/include/clang/Basic/TemplateKinds.h
@@ -43,10 +43,10 @@ enum TemplateNameKind {
   /// whether the template name is assumed to refer to a type template or a
   /// function template depends on the context in which the template
   /// name occurs.
-  TNK_Dependent_template_name,
-  /// The name refers to a concept definition.
-  TNK_Concept_template
+  TNK_Dependent_template_name
 };
 
 }
 #endif
+
+
diff --git a/include/clang/Parse/Parser.h b/include/clang/Parse/Parser.h
index 514656ffb9..619b56363f 100644
--- a/include/clang/Parse/Parser.h
+++ b/include/clang/Parse/Parser.h
@@ -1959,16 +1959,7 @@ private:
                         ParsedAttributesWithRange &Attrs);
   DeclSpecContext
   getDeclSpecContextFromDeclaratorContext(DeclaratorContext Context);
-
-  /// \brief Parses declaration-specifiers upto a declarator or ';' emitting
-  /// diagnostics as necessary and storing parsed information within DS.
-  ///
-  /// Note: Asides from parsing the routine C/C++ decl-specifiers (which could
-  /// include entire class or enum definitions), this also parses a concept
-  /// definition and stores the appropriate AST representations (for
-  /// class/enum/concept declarations/definitions, decltype
-  /// expression-operands or types, where appropriate) within DS.
-  void ParseDeclarationSpecifiersOrConceptDefinition(
+  void ParseDeclarationSpecifiers(
       DeclSpec &DS,
       const ParsedTemplateInfo &TemplateInfo = ParsedTemplateInfo(),
       AccessSpecifier AS = AS_none,
@@ -2820,11 +2811,6 @@ private:
                                    SourceLocation &DeclEnd,
                                    AccessSpecifier AS = AS_none);
 
-  /// \brief Parse a single template declaration that declares a concept [c++2a]
-  /// and store the AST node within DS.
-  void ParseConceptDefinition(SourceLocation ConceptLoc, DeclSpec &DS,
-                              const ParsedTemplateInfo &TemplateInfo,
-                              AccessSpecifier AS, DeclSpecContext DSC);
   //===--------------------------------------------------------------------===//
   // Modules
   DeclGroupPtrTy ParseModuleDecl();
diff --git a/include/clang/Sema/DeclSpec.h b/include/clang/Sema/DeclSpec.h
index fc8f57c98c..e9b116fb71 100644
--- a/include/clang/Sema/DeclSpec.h
+++ b/include/clang/Sema/DeclSpec.h
@@ -38,7 +38,6 @@
 namespace clang {
   class ASTContext;
   class CXXRecordDecl;
-  class ConceptDecl;
   class TypeLoc;
   class LangOptions;
   class IdentifierInfo;
@@ -222,13 +221,10 @@ public:
   unsigned location_size() const { return Builder.getBuffer().second; }
 };
 
-/// \brief Captures information about "decl-specifiers" and also concept
-/// definitions.
+/// \brief Captures information about "declaration specifiers".
 ///
 /// "Declaration specifiers" encompasses storage-class-specifiers,
-/// type-specifiers, type-qualifiers, and function-specifiers. This includes
-/// class and enum definitions whose AST representations must be stored - same
-/// with the expression-operands of decltype.
+/// type-specifiers, type-qualifiers, and function-specifiers.
 class DeclSpec {
 public:
   /// \brief storage-class-specifier
@@ -367,14 +363,8 @@ private:
   unsigned Constexpr_specified : 1;
 
   union {
-	// Valid if isTypeRep is true.
     UnionParsedType TypeRep;
-    // If we parsed a concept, class, enum (etc.) defintion or elaborated type
-    // specifier, this stores the AST representation.  This is valid if either
-    // isDeclRep or isConceptSpecified returns true.
     Decl *DeclRep;
-    // If we parsed a typeof(e) or decltype(e) operator, this stores the
-    // expression 'e'.  Valid if isExprRep is true.
     Expr *ExprRep;
   };
 
@@ -403,11 +393,6 @@ private:
   SourceLocation FS_forceinlineLoc;
   SourceLocation FriendLoc, ModulePrivateLoc, ConstexprLoc;
   SourceLocation TQ_pipeLoc;
-  
-  // Even though 'concept' is not a specifier, we handle it here. This allows us
-  // to reuse infrastructure for diagnosing attributes and invalid
-  // decl-specifiers.
-  SourceLocation ConceptLoc;
 
   WrittenBuiltinSpecs writtenBS;
   void SaveWrittenBuiltinSpecs();
@@ -497,10 +482,7 @@ public:
   bool isTypeSpecOwned() const { return TypeSpecOwned; }
   bool isTypeRep() const { return isTypeRep((TST) TypeSpecType); }
   bool isTypeSpecPipe() const { return TypeSpecPipe; }
-  bool isDeclRep() const {
-    return isDeclRep((TST)TypeSpecType);
-  }
-  
+
   ParsedType getRepAsType() const {
     assert(isTypeRep((TST) TypeSpecType) && "DeclSpec does not store a type");
     return TypeRep;
@@ -509,19 +491,6 @@ public:
     assert(isDeclRep((TST) TypeSpecType) && "DeclSpec does not store a decl");
     return DeclRep;
   }
-  // This is a template that should only be instantiated with the type
-  // ConceptDecl.  By making it a template we only require ConceptDecl to be a
-  // complete type where this function is called.
-  template<class ConceptDeclTy = ConceptDecl>
-  ConceptDeclTy *getRepAsConcept() const {
-    static_assert(std::is_same<ConceptDeclTy, ConceptDecl>::value,
-                  "Must only be instantiated with ConceptDecl");
-    assert(isConceptSpecified() && "DeclSpec does not store a concept");
-
-    return cast_or_null<ConceptDeclTy>(DeclRep);
-  }
-
-
   Expr *getRepAsExpr() const {
     assert(isExprRep((TST) TypeSpecType) && "DeclSpec does not store an expr");
     return ExprRep;
@@ -696,20 +665,6 @@ public:
     assert(isDeclRep((TST) TypeSpecType));
     DeclRep = Rep;
   }
-  // This function can only be instantiated with ConceptDecl.  We made it a
-  // template so that ConceptDecl only has to be defined where this is called.
-  template <class ConceptDeclTy = ConceptDecl>
-  void
-  setConceptRep(typename llvm::identity<ConceptDeclTy>::argument_type *Rep) {
-    static_assert(std::is_same<ConceptDeclTy, ConceptDecl>::value,
-                  "Must only be instantiated with ConceptDecl");
-    assert(isConceptSpecified() && "DeclSpec does not store a concept");
-    assert(!DeclRep &&
-           "why is this not null? We expect this function to be called only "
-           "once, and usually right after DeclRep was set to null");
-    DeclRep = Rep;
-  }
-
   void UpdateTypeRep(ParsedType Rep) {
     assert(isTypeRep((TST) TypeSpecType));
     TypeRep = Rep;
@@ -739,8 +694,6 @@ public:
                             unsigned &DiagID);
   bool SetConstexprSpec(SourceLocation Loc, const char *&PrevSpec,
                         unsigned &DiagID);
-  bool setConceptSpec(SourceLocation Loc, const char *&PrevSpec,
-                      unsigned &DiagID, const PrintingPolicy &P);
 
   bool isFriendSpecified() const { return Friend_specified; }
   SourceLocation getFriendSpecLoc() const { return FriendLoc; }
@@ -751,8 +704,6 @@ public:
   bool isConstexprSpecified() const { return Constexpr_specified; }
   SourceLocation getConstexprSpecLoc() const { return ConstexprLoc; }
 
-  bool isConceptSpecified() const { return ConceptLoc.isValid(); }
-  SourceLocation getConceptLoc() const { return ConceptLoc; }
   void ClearConstexprSpec() {
     Constexpr_specified = false;
     ConstexprLoc = SourceLocation();
diff --git a/include/clang/Sema/Sema.h b/include/clang/Sema/Sema.h
index 7897cf2a27..485c537949 100644
--- a/include/clang/Sema/Sema.h
+++ b/include/clang/Sema/Sema.h
@@ -2126,7 +2126,6 @@ public:
 
   Decl *ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS, DeclSpec &DS,
                                    RecordDecl *&AnonRecord);
-
   Decl *ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS, DeclSpec &DS,
                                    MultiTemplateParamsArg TemplateParams,
                                    bool IsExplicitInstantiation,
@@ -6230,13 +6229,6 @@ public:
                                 SourceLocation TemplateLoc,
                                 const TemplateArgumentListInfo *TemplateArgs);
 
-  ExprResult
-  CheckConceptTemplateId(const CXXScopeSpec &SS,
-                         const DeclarationNameInfo &NameInfo,
-                         ConceptDecl *Template,
-                         SourceLocation TemplateLoc,
-                         const TemplateArgumentListInfo *TemplateArgs);
-
   ExprResult BuildTemplateIdExpr(const CXXScopeSpec &SS,
                                  SourceLocation TemplateKWLoc,
                                  LookupResult &R,
@@ -6515,13 +6507,6 @@ public:
                                   const TemplateArgument *Args,
                                   unsigned NumArgs);
 
-  // Concepts
-  ConceptDecl *ActOnConceptDefinition(
-      Scope *S,
-      MultiTemplateParamsArg TemplateParameterLists,
-      IdentifierInfo *Name, SourceLocation NameLoc,
-      Expr *ConstraintExpr);
-
   //===--------------------------------------------------------------------===//
   // C++ Variadic Templates (C++0x [temp.variadic])
   //===--------------------------------------------------------------------===//
diff --git a/include/clang/Serialization/ASTBitCodes.h b/include/clang/Serialization/ASTBitCodes.h
index 169075983c..1f4e0347bc 100644
--- a/include/clang/Serialization/ASTBitCodes.h
+++ b/include/clang/Serialization/ASTBitCodes.h
@@ -1408,9 +1408,6 @@ namespace serialization {
       /// \brief A TypeAliasTemplateDecl record.
       DECL_TYPE_ALIAS_TEMPLATE,
 
-      /// \brief A ConceptDecl record.
-      DECL_CONCEPT,
-
       /// \brief A StaticAssertDecl record.
       DECL_STATIC_ASSERT,
 
diff --git a/lib/AST/ASTDumper.cpp b/lib/AST/ASTDumper.cpp
index b0f0c5d0f5..cf512b9bd3 100644
--- a/lib/AST/ASTDumper.cpp
+++ b/lib/AST/ASTDumper.cpp
@@ -466,7 +466,6 @@ namespace  {
                                          bool DumpRefOnly);
     template<typename TemplateDecl>
     void VisitTemplateDecl(const TemplateDecl *D, bool DumpExplicitInst);
-    void VisitConceptDecl(const ConceptDecl *D);
     void VisitFunctionTemplateDecl(const FunctionTemplateDecl *D);
     void VisitClassTemplateDecl(const ClassTemplateDecl *D);
     void VisitClassTemplateSpecializationDecl(
@@ -1578,12 +1577,6 @@ void ASTDumper::VisitTemplateDecl(const TemplateDecl *D,
                                     !D->isCanonicalDecl());
 }
 
-void ASTDumper::VisitConceptDecl(const ConceptDecl *D) {
-  dumpName(D);
-  dumpTemplateParameters(D->getTemplateParameters());
-  dumpStmt(D->getConstraintExpr());
-}
-
 void ASTDumper::VisitFunctionTemplateDecl(const FunctionTemplateDecl *D) {
   // FIXME: We don't add a declaration of a function template specialization
   // to its context when it's explicitly instantiated, so dump explicit
diff --git a/lib/AST/DeclBase.cpp b/lib/AST/DeclBase.cpp
index ba02903683..baf83a393c 100644
--- a/lib/AST/DeclBase.cpp
+++ b/lib/AST/DeclBase.cpp
@@ -724,7 +724,6 @@ unsigned Decl::getIdentifierNamespaceForKind(Kind DeclKind) {
     case Binding:
     case NonTypeTemplateParm:
     case VarTemplate:
-    case Concept:
       // These (C++-only) declarations are found by redeclaration lookup for
       // tag types, so we include them in the tag namespace.
       return IDNS_Ordinary | IDNS_Tag;
diff --git a/lib/AST/DeclTemplate.cpp b/lib/AST/DeclTemplate.cpp
index 19778af79f..8854f7879a 100644
--- a/lib/AST/DeclTemplate.cpp
+++ b/lib/AST/DeclTemplate.cpp
@@ -789,27 +789,6 @@ ClassTemplateSpecializationDecl::getSourceRange() const {
 }
 
 //===----------------------------------------------------------------------===//
-// ConceptDecl Implementation
-//===----------------------------------------------------------------------===//
-ConceptDecl *ConceptDecl::Create(ASTContext &C, DeclContext *DC,
-                                 SourceLocation NameLoc, DeclarationName Name,
-                                 TemplateParameterList *Params,
-                                 Expr *ConstraintExpr) {
-  // TODO: Do we need this?
-  //  AdoptTemplateParameterList(Params, cast<DeclContext>(Decl));
-  return new (C, DC) ConceptDecl(DC, NameLoc, Name, Params, ConstraintExpr);
-}
-
-ConceptDecl *ConceptDecl::CreateDeserialized(ASTContext &C,
-                                             unsigned ID) {
-  ConceptDecl *Result = new (C, ID) ConceptDecl(nullptr, SourceLocation(),
-                                                DeclarationName(),
-                                                nullptr, nullptr);
-
-  return Result;
-}
-
-//===----------------------------------------------------------------------===//
 // ClassTemplatePartialSpecializationDecl Implementation
 //===----------------------------------------------------------------------===//
 void ClassTemplatePartialSpecializationDecl::anchor() {}
diff --git a/lib/CodeGen/CGDecl.cpp b/lib/CodeGen/CGDecl.cpp
index 38eb0c8fe7..c9b80e38d4 100644
--- a/lib/CodeGen/CGDecl.cpp
+++ b/lib/CodeGen/CGDecl.cpp
@@ -105,7 +105,6 @@ void CodeGenFunction::EmitDecl(const Decl &D) {
   case Decl::OMPThreadPrivate:
   case Decl::OMPCapturedExpr:
   case Decl::Empty:
-  case Decl::Concept:
     // None of these decls require codegen support.
     return;
 
diff --git a/lib/CodeGen/CodeGenModule.cpp b/lib/CodeGen/CodeGenModule.cpp
index b8bed33b02..063b9be4cd 100644
--- a/lib/CodeGen/CodeGenModule.cpp
+++ b/lib/CodeGen/CodeGenModule.cpp
@@ -4423,7 +4423,6 @@ void CodeGenModule::EmitTopLevelDecl(Decl *D) {
   case Decl::TypeAliasTemplate:
   case Decl::Block:
   case Decl::Empty:
-  case Decl::Concept:
     break;
   case Decl::Using:          // using X; [C++]
     if (CGDebugInfo *DI = getModuleDebugInfo())
diff --git a/lib/Parse/ParseDecl.cpp b/lib/Parse/ParseDecl.cpp
index 9b0828a6d5..3d3abe32ab 100644
--- a/lib/Parse/ParseDecl.cpp
+++ b/lib/Parse/ParseDecl.cpp
@@ -1739,8 +1739,7 @@ Parser::ParseSimpleDeclaration(DeclaratorContext Context,
   ParsingDeclSpec DS(*this);
 
   DeclSpecContext DSContext = getDeclSpecContextFromDeclaratorContext(Context);
-  ParseDeclarationSpecifiersOrConceptDefinition(DS, ParsedTemplateInfo(),
-                                                       AS_none, DSContext);
+  ParseDeclarationSpecifiers(DS, ParsedTemplateInfo(), AS_none, DSContext);
 
   // If we had a free-standing type definition with a missing semicolon, we
   // may get this far before the problem becomes obvious.
@@ -2387,8 +2386,7 @@ void Parser::ParseSpecifierQualifierList(DeclSpec &DS, AccessSpecifier AS,
   /// specifier-qualifier-list is a subset of declaration-specifiers.  Just
   /// parse declaration-specifiers and complain about extra stuff.
   /// TODO: diagnose attribute-specifiers and alignment-specifiers.
-  ParseDeclarationSpecifiersOrConceptDefinition(DS, ParsedTemplateInfo(), AS,
-                                                DSC);
+  ParseDeclarationSpecifiers(DS, ParsedTemplateInfo(), AS, DSC);
 
   // Validate declspec for type-name.
   unsigned Specs = DS.getParsedSpecifiers();
@@ -2873,12 +2871,11 @@ Parser::DiagnoseMissingSemiAfterTagDefinition(DeclSpec &DS, AccessSpecifier AS,
   // and call ParsedFreeStandingDeclSpec as appropriate.
   DS.ClearTypeSpecType();
   ParsedTemplateInfo NotATemplate;
-  ParseDeclarationSpecifiersOrConceptDefinition(DS, NotATemplate, AS, DSContext,
-                                      LateAttrs);
+  ParseDeclarationSpecifiers(DS, NotATemplate, AS, DSContext, LateAttrs);
   return false;
 }
 
-/// ParseDeclarationSpecifiersOrConceptDefinition
+/// ParseDeclarationSpecifiers
 ///       declaration-specifiers: [C99 6.7]
 ///         storage-class-specifier declaration-specifiers[opt]
 ///         type-specifier declaration-specifiers[opt]
@@ -2905,8 +2902,7 @@ Parser::DiagnoseMissingSemiAfterTagDefinition(DeclSpec &DS, AccessSpecifier AS,
 /// [OpenCL] '__kernel'
 ///       'friend': [C++ dcl.friend]
 ///       'constexpr': [C++0x dcl.constexpr]
-/// [C++2a] 'concept'
-void Parser::ParseDeclarationSpecifiersOrConceptDefinition(DeclSpec &DS,
+void Parser::ParseDeclarationSpecifiers(DeclSpec &DS,
                                         const ParsedTemplateInfo &TemplateInfo,
                                         AccessSpecifier AS,
                                         DeclSpecContext DSContext,
@@ -3684,11 +3680,7 @@ void Parser::ParseDeclarationSpecifiersOrConceptDefinition(DeclSpec &DS,
       ConsumeToken();
       ParseEnumSpecifier(Loc, DS, TemplateInfo, AS, DSContext);
       continue;
-    
-    case tok::kw_concept:
-      ConsumeToken();
-      ParseConceptDefinition(Loc, DS, TemplateInfo, AS, DSContext);
-      continue;
+
     // cv-qualifier:
     case tok::kw_const:
       isInvalid = DS.SetTypeQual(DeclSpec::TQ_const, Loc, PrevSpec, DiagID,
@@ -6374,7 +6366,7 @@ void Parser::ParseParameterDeclarationClause(
     // too much hassle.
     DS.takeAttributesFrom(FirstArgAttrs);
 
-    ParseDeclarationSpecifiersOrConceptDefinition(DS);
+    ParseDeclarationSpecifiers(DS);
 
 
     // Parse the declarator.  This is "PrototypeContext" or 
diff --git a/lib/Parse/ParseDeclCXX.cpp b/lib/Parse/ParseDeclCXX.cpp
index e0db75ced5..0c789c9b1c 100644
--- a/lib/Parse/ParseDeclCXX.cpp
+++ b/lib/Parse/ParseDeclCXX.cpp
@@ -2561,8 +2561,8 @@ Parser::ParseCXXClassMemberDeclaration(AccessSpecifier AS,
   if (MalformedTypeSpec)
     DS.SetTypeSpecError();
 
-  ParseDeclarationSpecifiersOrConceptDefinition(
-      DS, TemplateInfo, AS, DeclSpecContext::DSC_class, &CommonLateParsedAttrs);
+  ParseDeclarationSpecifiers(DS, TemplateInfo, AS, DeclSpecContext::DSC_class,
+                             &CommonLateParsedAttrs);
 
   // Turn off colon protection that was set for declspec.
   X.restore();
diff --git a/lib/Parse/ParseObjc.cpp b/lib/Parse/ParseObjc.cpp
index 203d5e6d0d..0ac418ad70 100644
--- a/lib/Parse/ParseObjc.cpp
+++ b/lib/Parse/ParseObjc.cpp
@@ -1490,7 +1490,7 @@ Decl *Parser::ParseObjCMethodDecl(SourceLocation mLoc,
       cStyleParamWarned = true;
     }
     DeclSpec DS(AttrFactory);
-    ParseDeclarationSpecifiersOrConceptDefinition(DS);
+    ParseDeclarationSpecifiers(DS);
     // Parse the declarator.
     Declarator ParmDecl(DS, DeclaratorContext::PrototypeContext);
     ParseDeclarator(ParmDecl);
@@ -2541,7 +2541,7 @@ StmtResult Parser::ParseObjCTryStmt(SourceLocation atLoc) {
                                         Scope::AtCatchScope);
         if (Tok.isNot(tok::ellipsis)) {
           DeclSpec DS(AttrFactory);
-          ParseDeclarationSpecifiersOrConceptDefinition(DS);
+          ParseDeclarationSpecifiers(DS);
           Declarator ParmDecl(DS, DeclaratorContext::ObjCCatchContext);
           ParseDeclarator(ParmDecl);
 
diff --git a/lib/Parse/ParseTemplate.cpp b/lib/Parse/ParseTemplate.cpp
index 13fb6da3c3..88a5745350 100644
--- a/lib/Parse/ParseTemplate.cpp
+++ b/lib/Parse/ParseTemplate.cpp
@@ -54,15 +54,6 @@ Parser::ParseDeclarationStartingWithTemplate(DeclaratorContext Context,
 ///       template-declaration: [C++ temp]
 ///         'export'[opt] 'template' '<' template-parameter-list '>' declaration
 ///
-///       template-declaration: [C++2a]
-///         template-head declaration
-///         template-head concept-definition
-///
-///       TODO: requires-clause
-///       template-head: [C++2a]
-///         'export'[opt] 'template' '<' template-parameter-list '>'
-///             requires-clause[opt]
-///
 ///       explicit-specialization: [ C++ temp.expl.spec]
 ///         'template' '<' '>' declaration
 Decl *
@@ -157,10 +148,13 @@ Parser::ParseTemplateDeclarationOrSpecialization(DeclaratorContext Context,
   unsigned NewFlags = getCurScope()->getFlags() & ~Scope::TemplateParamScope;
   ParseScopeFlags TemplateScopeFlags(this, NewFlags, isSpecialization);
 
-  return ParseSingleDeclarationAfterTemplate(
-      Context,
-      ParsedTemplateInfo(&ParamLists, isSpecialization, LastParamListWasEmpty),
-      ParsingTemplateParams, DeclEnd, AS, AccessAttrs);
+  // Parse the actual template declaration.
+  return ParseSingleDeclarationAfterTemplate(Context,
+                                             ParsedTemplateInfo(&ParamLists,
+                                                             isSpecialization,
+                                                         LastParamListWasEmpty),
+                                             ParsingTemplateParams,
+                                             DeclEnd, AS, AccessAttrs);
 }
 
 /// \brief Parse a single declaration that declares a template,
@@ -214,7 +208,7 @@ Parser::ParseSingleDeclarationAfterTemplate(
   // the template parameters.
   ParsingDeclSpec DS(*this, &DiagsFromTParams);
 
-  ParseDeclarationSpecifiersOrConceptDefinition(DS, TemplateInfo, AS,
+  ParseDeclarationSpecifiers(DS, TemplateInfo, AS,
                              getDeclSpecContextFromDeclaratorContext(Context));
 
   if (Tok.is(tok::semi)) {
@@ -328,150 +322,6 @@ Parser::ParseSingleDeclarationAfterTemplate(
   return ThisDecl;
 }
 
-
-void
-Parser::ParseConceptDefinition(SourceLocation ConceptLoc,

-                           DeclSpec &DS, const ParsedTemplateInfo &TemplateInfo,

-                           AccessSpecifier AS, 

-                           DeclSpecContext DSC) {
-

-  

-  auto DiagnoseAttributes = [this] {

-    ParsedAttributesWithRange attrs(this->AttrFactory);

-    this->MaybeParseGNUAttributes(attrs);

-    this->MaybeParseCXX11Attributes(attrs);

-    this->MaybeParseMicrosoftDeclSpecs(attrs);
-    this->ProhibitAttributes(attrs);
-  };
-
-
-  // If attributes exist after 'concept' kw but before the concept name,
-  // prohibit them for now (if CWG approves attributes on concepts, this is
-  // likely where they will go...).
-  DiagnoseAttributes();
-
-  // Set the concept specifier at ConceptLoc within 'DS' along with emitting any
-  // incompatible decl-specifier diagnostics.
-  {
-    const char *PrevSpec = 0;
-    unsigned int DiagId = 0;
-    if (DS.setConceptSpec(ConceptLoc, PrevSpec, DiagId,
-                          Actions.getASTContext().getPrintingPolicy())) {
-      Diag(ConceptLoc, DiagId) << PrevSpec;
-    }
-    Actions.DiagnoseFunctionSpecifiers(DS);
-  }
-
-  if (DSC != DeclSpecContext::DSC_top_level) {
-    Diag(ConceptLoc, diag::err_concept_at_non_namespace_scope);
-    // If we are not in a template parameter context, skip to a '}' or ';'. The
-    // error messages are better if we just ignore this within template
-    // parameter lists.
-    if (DSC != DeclSpecContext::DSC_template_param) {
-      SkipUntil(tok::r_brace, StopAtSemi | StopBeforeMatch);
-    } else {
-      tok::TokenKind Tokens[] = { tok::comma, tok::greater };
-      SkipUntil(llvm::makeArrayRef(Tokens),
-                StopAtSemi | StopBeforeMatch);
-    }
-    return;
-  }
-
-  // A scope-guard that (if an error occurs while parsing a concept) skips to
-  // the next semi or closing brace.
-  class SkipUntilSemiOrClosingBraceOnScopeExit {
-    Parser &P;
-    bool Disabled = false;
-
-  public:
-    SkipUntilSemiOrClosingBraceOnScopeExit(Parser &P)
-        : P(P) {}
-    void disable() { Disabled = true; }
-    ~SkipUntilSemiOrClosingBraceOnScopeExit() {
-      if (!Disabled) {
-        // Skip until the semi-colon or a '}'.
-        P.SkipUntil(tok::r_brace, StopAtSemi | StopBeforeMatch);
-      }
-    }
-  } SkipUntilSemiOrClosingBraceOnScopeExit(*this);
-
-  if (TemplateInfo.Kind == ParsedTemplateInfo::NonTemplate) {
-    Diag(ConceptLoc, diag::err_concept_nontemplate);
-    return;
-  }
-  
-  const TemplateParameterLists &ParamLists = *TemplateInfo.TemplateParams;
-
-  
-  // More than one TPL wouldn't make sense here.
-  if (ParamLists.size() != 1) {
-    Diag(Tok.getLocation(), diag::err_concept_extra_headers);
-    return;
-  }
-  const TemplateParameterList *const TPL = ParamLists[0];
-
-  // Explicit specializations of concepts are not allowed.
-  if (TPL->getLAngleLoc().getLocWithOffset(1) == TPL->getRAngleLoc()) {
-    assert(!TPL->size() &&
-           "can not have template parameters within empty angle brackets!");
-    Diag(ConceptLoc, diag::err_concept_specialized) << 0;
-    return;
-  }
-  // Concepts can not be defined with nested name specifiers.
-  CXXScopeSpec SS;
-  if (ParseOptionalCXXScopeSpecifier(SS, nullptr,
-                                     /*EnteringContext=*/false) ||
-      SS.isNotEmpty()) {
-
-    if (SS.isNotEmpty())
-      Diag(Tok.getLocation(), diag::err_concept_unexpected_scope_spec);
-    return;
-  }
-  // An identifier (i.e. the concept-name) should follow 'concept'.
-  if (!Tok.is(tok::identifier)) {
-    Diag(Tok.getLocation(), diag::err_expected) << "concept name";
-    return;
-  }
-
-  IdentifierInfo *Id = Tok.getIdentifierInfo();
-  SourceLocation IdLoc = ConsumeToken();
-  
-  // If attributes exist after the identifier, parse them and diagnose
-  DiagnoseAttributes();
-
-  if (!TryConsumeToken(tok::equal)) {
-    Diag(Tok.getLocation(), diag::err_expected) << "equal";
-    return;
-  }
-
-  ExprResult ConstraintExprResult = ParseConstraintExpression();
-  if (ConstraintExprResult.isInvalid()) {
-    Diag(Tok.getLocation(), diag::err_expected_expression)
-      << "constraint-expression";
-    return;
-  }
-
-  // We can try to create a valid concept decl node now, so disable the
-  // scope-guard.
-  SkipUntilSemiOrClosingBraceOnScopeExit.disable();
-
-  Expr *ConstraintExpr = ConstraintExprResult.get();
-  ConceptDecl *const ConDecl = Actions.ActOnConceptDefinition(
-      getCurScope(), *TemplateInfo.TemplateParams, Id, IdLoc, ConstraintExpr);
-  DS.setConceptRep(ConDecl);
-
-  if (Tok.isNot(tok::semi)) {
-    
-    ExpectAndConsume(tok::semi, diag::err_expected_after, "concept");
-    // Push this token back into the preprocessor and change our current token
-    // to ';' so that the rest of the code recovers as though there were an
-    // ';' after the definition.
-    PP.EnterToken(Tok);
-    Tok.setKind(tok::semi);
-  }
-  return;
-}
-
 /// ParseTemplateParameters - Parses a template-parameter-list enclosed in
 /// angle brackets. Depth is the depth of this template-parameter-list, which
 /// is the number of template headers directly enclosing this template header.
@@ -840,8 +690,8 @@ Parser::ParseNonTypeTemplateParameter(unsigned Depth, unsigned Position) {
   // FIXME: The type should probably be restricted in some way... Not all
   // declarators (parts of declarators?) are accepted for parameters.
   DeclSpec DS(AttrFactory);
-  ParseDeclarationSpecifiersOrConceptDefinition(
-      DS, ParsedTemplateInfo(), AS_none, DeclSpecContext::DSC_template_param);
+  ParseDeclarationSpecifiers(DS, ParsedTemplateInfo(), AS_none,
+                             DeclSpecContext::DSC_template_param);
 
   // Parse this as a typename.
   Declarator ParamDecl(DS, DeclaratorContext::TemplateParamContext);
diff --git a/lib/Parse/ParseTentative.cpp b/lib/Parse/ParseTentative.cpp
index 5648d994fc..ebd6f0f5b8 100644
--- a/lib/Parse/ParseTentative.cpp
+++ b/lib/Parse/ParseTentative.cpp
@@ -1351,7 +1351,6 @@ Parser::isCXXDeclarationSpecifier(Parser::TPResult BracedCastResult,
   case tok::kw_struct:
   case tok::kw_union:
   case tok::kw___interface:
-  case tok::kw_concept:
     // enum-specifier
   case tok::kw_enum:
     // cv-qualifier
diff --git a/lib/Parse/Parser.cpp b/lib/Parse/Parser.cpp
index 17d046958d..d8f9f7a390 100644
--- a/lib/Parse/Parser.cpp
+++ b/lib/Parse/Parser.cpp
@@ -919,7 +919,7 @@ Parser::ParseDeclOrFunctionDefInternal(ParsedAttributesWithRange &attrs,
                                        AccessSpecifier AS) {
   MaybeParseMicrosoftAttributes(DS.getAttributes());
   // Parse the common declaration-specifiers piece.
-  ParseDeclarationSpecifiersOrConceptDefinition(DS, ParsedTemplateInfo(), AS,
+  ParseDeclarationSpecifiers(DS, ParsedTemplateInfo(), AS,
                              DeclSpecContext::DSC_top_level);
 
   // If we had a free-standing type definition with a missing semicolon, we
@@ -1287,7 +1287,7 @@ void Parser::ParseKNRParamDeclarations(Declarator &D) {
 
     // Parse the common declaration-specifiers piece.
     DeclSpec DS(AttrFactory);
-    ParseDeclarationSpecifiersOrConceptDefinition(DS);
+    ParseDeclarationSpecifiers(DS);
 
     // C99 6.9.1p6: 'each declaration in the declaration list shall have at
     // least one declarator'.
@@ -1647,7 +1647,7 @@ bool Parser::TryKeywordIdentFallback(bool DisableKeyword) {
 /// Actions.getTypeName will not be needed to be called again (e.g. getTypeName
 /// will not be called twice, once to check whether we have a declaration
 /// specifier, and another one to get the actual type inside
-/// ParseDeclarationSpecifiersOrConceptDefinition).
+/// ParseDeclarationSpecifiers).
 ///
 /// This returns true if an error occurred.
 ///
diff --git a/lib/Sema/DeclSpec.cpp b/lib/Sema/DeclSpec.cpp
index 5f5d94eee3..2fad5a18ba 100644
--- a/lib/Sema/DeclSpec.cpp
+++ b/lib/Sema/DeclSpec.cpp
@@ -426,7 +426,6 @@ unsigned DeclSpec::getParsedSpecifiers() const {
   return Res;
 }
 
-
 template <class T> static bool BadSpecifier(T TNew, T TPrev,
                                             const char *&PrevSpec,
                                             unsigned &DiagID,
@@ -492,6 +491,7 @@ const char *DeclSpec::getSpecifierName(TSS S) {
   }
   llvm_unreachable("Unknown typespec!");
 }
+
 const char *DeclSpec::getSpecifierName(DeclSpec::TST T,
                                        const PrintingPolicy &Policy) {
   switch (T) {
@@ -969,69 +969,6 @@ bool DeclSpec::SetConstexprSpec(SourceLocation Loc, const char *&PrevSpec,
   return false;
 }
 
-bool DeclSpec::setConceptSpec(const SourceLocation Loc, const char *&PrevSpec,
-                              unsigned &DiagID, const PrintingPolicy &PP) {
-  assert(Loc.isValid() && "Loc must be valid, since it is used to identify "
-                          "that this function was called before");
-  assert(!ConceptLoc.isValid() &&
-         "how is this called if concept was already encountered and triggered "
-         "ParseConceptDefinition which parses upto the semi-colon");
-
-  PrevSpec = nullptr;
-  if (TypeSpecType != TST_unspecified) {
-    PrevSpec = DeclSpec::getSpecifierName(static_cast<TST>(TypeSpecType), PP);
-	  ClearTypeSpecType();
-  }
-  if (TypeSpecSign != TSS_unspecified) {
-    PrevSpec = DeclSpec::getSpecifierName(static_cast<TSS>(TypeSpecSign));
-	  TypeSpecSign = TSS_unspecified;
-  }
-  if (TypeSpecWidth != TSW_unspecified) {
-    PrevSpec = DeclSpec::getSpecifierName(static_cast<TSW>(TypeSpecWidth));
-	  TypeSpecWidth = TSW_unspecified;
-  }
-  if (StorageClassSpec != SCS_unspecified) {
-    PrevSpec = DeclSpec::getSpecifierName(static_cast<SCS>(StorageClassSpec));
-	  ClearStorageClassSpecs();
-  }
-  if (ThreadStorageClassSpec != TSCS_unspecified) {
-    PrevSpec =
-        DeclSpec::getSpecifierName(static_cast<TSCS>(ThreadStorageClassSpec));
-    ClearStorageClassSpecs();
-  }
-  if (TypeSpecComplex != TSC_unspecified) {
-    PrevSpec = DeclSpec::getSpecifierName(static_cast<TSC>(TypeSpecComplex));
-    TypeSpecComplex = TSC_unspecified;
-  }
-  if (getTypeQualifiers()) {
-	  PrevSpec = DeclSpec::getSpecifierName(static_cast<TQ>(TypeQualifiers));
-    ClearTypeQualifiers();
-  }
-  if (isFriendSpecified()) {
-    PrevSpec = "friend";
-    Friend_specified = false;
-    FriendLoc = SourceLocation();
-  }
-  if (isConstexprSpecified()) {
-    PrevSpec = "constexpr";
-    Constexpr_specified = false;
-    ConstexprLoc = SourceLocation();
-  }
-  if (isInlineSpecified()) {
-    PrevSpec = "inline";
-    FS_inlineLoc = SourceLocation();
-    FS_inline_specified = false;
-  }
-
-  if (PrevSpec) {
-    DiagID = diag::err_invalid_decl_spec_combination;
-  }
-  // We set the concept location regardless of whether an error occurred.
-  DeclRep = nullptr;
-  ConceptLoc = Loc;
-  return PrevSpec; // If this is non-null, an error occurred.
-}
-
 void DeclSpec::SaveWrittenBuiltinSpecs() {
   writtenBS.Sign = getTypeSpecSign();
   writtenBS.Width = getTypeSpecWidth();
@@ -1333,7 +1270,6 @@ void DeclSpec::Finish(Sema &S, const PrintingPolicy &Policy) {
   // TODO: return "auto function" and other bad things based on the real type.
 
   // 'data definition has no type or storage class'?
-
 }
 
 bool DeclSpec::isMissingDeclaratorOk() {
diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index acbec1aca9..1bcc9329e4 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -4212,12 +4212,6 @@ Sema::ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS, DeclSpec &DS,
                                  MultiTemplateParamsArg TemplateParams,
                                  bool IsExplicitInstantiation,
                                  RecordDecl *&AnonRecord) {
-
-  // We don't need to do any additional declspecifier checking on concept
-  // definitions since that should already have been done when the concept kw
-  // location was set within DS.
-  if (DS.isConceptSpecified()) return DS.getRepAsConcept();
-  
   Decl *TagD = nullptr;
   TagDecl *Tag = nullptr;
   if (DS.getTypeSpecType() == DeclSpec::TST_class ||
diff --git a/lib/Sema/SemaDeclCXX.cpp b/lib/Sema/SemaDeclCXX.cpp
index 0fc399a375..678f6af068 100644
--- a/lib/Sema/SemaDeclCXX.cpp
+++ b/lib/Sema/SemaDeclCXX.cpp
@@ -9467,7 +9467,7 @@ UsingShadowDecl *Sema::BuildUsingShadowDecl(Scope *S,
     NonTemplateTarget = TargetTD->getTemplatedDecl();
 
   UsingShadowDecl *Shadow;
-  if (!isa<ConceptDecl>(Target) && isa<CXXConstructorDecl>(NonTemplateTarget)) {
+  if (isa<CXXConstructorDecl>(NonTemplateTarget)) {
     bool IsVirtualBase =
         isVirtualDirectBase(cast<CXXRecordDecl>(CurContext),
                             UD->getQualifier()->getAsRecordDecl());
diff --git a/lib/Sema/SemaTemplate.cpp b/lib/Sema/SemaTemplate.cpp
index f3cb04ac6a..190dd0721f 100644
--- a/lib/Sema/SemaTemplate.cpp
+++ b/lib/Sema/SemaTemplate.cpp
@@ -232,11 +232,9 @@ TemplateNameKind Sema::isTemplateName(Scope *S,
     } else {
       assert(isa<ClassTemplateDecl>(TD) || isa<TemplateTemplateParmDecl>(TD) ||
              isa<TypeAliasTemplateDecl>(TD) || isa<VarTemplateDecl>(TD) ||
-             isa<BuiltinTemplateDecl>(TD) || isa<ConceptDecl>(TD));
+             isa<BuiltinTemplateDecl>(TD));
       TemplateKind =
-          isa<VarTemplateDecl>(TD) ? TNK_Var_template :
-          isa<ConceptDecl>(TD) ? TNK_Concept_template :
-          TNK_Type_template;
+          isa<VarTemplateDecl>(TD) ? TNK_Var_template : TNK_Type_template;
     }
   }
 
@@ -3036,8 +3034,7 @@ QualType Sema::CheckTemplateIdType(TemplateName Name,
 
   TemplateDecl *Template = Name.getAsTemplateDecl();
   if (!Template || isa<FunctionTemplateDecl>(Template) ||
-      isa<VarTemplateDecl>(Template) ||
-      isa<ConceptDecl>(Template)) {
+      isa<VarTemplateDecl>(Template)) {
     // We might have a substituted template template parameter pack. If so,
     // build a template specialization type for it.
     if (Name.getAsSubstTemplateTemplateParmPack())
@@ -3991,18 +3988,6 @@ Sema::CheckVarTemplateId(const CXXScopeSpec &SS,
                                   /*FoundD=*/nullptr, TemplateArgs);
 }
 
-ExprResult
-Sema::CheckConceptTemplateId(const CXXScopeSpec &SS,
-                             const DeclarationNameInfo &NameInfo,
-                             ConceptDecl *Template,
-                             SourceLocation TemplateLoc,
-                             const TemplateArgumentListInfo *TemplateArgs) {
-  // TODO: Do concept specialization here.
-  Diag(Template->getLocation(), diag::err_concept_feature_unimplemented)
-      << "can not form concept template-id";
-  return ExprError();
-}
-
 ExprResult Sema::BuildTemplateIdExpr(const CXXScopeSpec &SS,
                                      SourceLocation TemplateKWLoc,
                                      LookupResult &R,
@@ -7713,61 +7698,6 @@ Decl *Sema::ActOnTemplateDeclarator(Scope *S,
   return NewDecl;
 }
 
-ConceptDecl *Sema::ActOnConceptDefinition(Scope *S,
-    MultiTemplateParamsArg TemplateParameterLists, IdentifierInfo *Name,
-    SourceLocation NameLoc, Expr *ConstraintExpr) {
-  // C++2a [temp.concept]p3:
-  // A concept-definition shall appear in the global scope or in a namespace
-  // scope.
-  assert(
-      CurContext->isFileContext() &&
-      "We check during parsing that 'concept's only occur at namespace scope");
-
-  // Forbid any prior declaration of this name within the current namespace.
-  LookupResult Previous(*this,
-                        DeclarationNameInfo(DeclarationName(Name), NameLoc),
-                        LookupOrdinaryName);
-  LookupName(Previous, S);
-  if (!Previous.empty()) {
-    const NamedDecl *PrevDecl = Previous.getRepresentativeDecl();
-    if (PrevDecl->getDeclContext()->Equals(CurContext)) {
-      if (Previous.isSingleResult() &&
-          isa<ConceptDecl>(Previous.getFoundDecl())) {
-        Diag(NameLoc, diag::err_redefinition) << Name;
-      } else {
-        Diag(NameLoc, diag::err_redefinition_different_kind) << Name;
-      }
-      Diag(PrevDecl->getLocation(), diag::note_previous_decl) << PrevDecl;
-      return nullptr;
-    }
-  }
-
-  ConceptDecl *NewDecl = ConceptDecl::Create(Context, CurContext, NameLoc,
-                                             Name, TemplateParameterLists[0],
-                                             ConstraintExpr);
-
-  if (!NewDecl)
-    return nullptr;
-
-  if (NewDecl->getAssociatedConstraints()) {
-    // C++2a [temp.concept]p4:
-    // A concept shall not have associated constraints.
-    // TODO: Make a test once we have actual associated constraints.
-    Diag(NameLoc, diag::err_concept_no_associated_constraints);
-    NewDecl->setInvalidDecl();
-  }
-
-  assert((S->isTemplateParamScope() || !TemplateParameterLists[0]->size()) &&
-         "Not in template param scope?");
-  assert(S->getParent() && !S->getParent()->isTemplateParamScope() &&
-         "Parent scope should exist and not be template parameter.");
-
-  ActOnDocumentableDecl(NewDecl);
-  PushOnScopeChains(NewDecl, S->getParent(), /*AddToContext=*/true);
-
-  return NewDecl;
-}
-
 /// \brief Strips various properties off an implicit instantiation
 /// that has just been explicitly specialized.
 static void StripImplicitInstantiation(NamedDecl *D) {
diff --git a/lib/Sema/SemaTemplateInstantiateDecl.cpp b/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 0ebcb03ca3..a7883c67b8 100644
--- a/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -3073,11 +3073,6 @@ Decl *TemplateDeclInstantiator::VisitFriendTemplateDecl(FriendTemplateDecl *D) {
   return nullptr;
 }
 
-Decl *TemplateDeclInstantiator::VisitConceptDecl(ConceptDecl *D) {
-  llvm_unreachable("Concept definitions cannot reside inside a template");
-  return nullptr;
-}
-
 Decl *TemplateDeclInstantiator::VisitDecl(Decl *D) {
   llvm_unreachable("Unexpected decl");
 }
diff --git a/lib/Serialization/ASTCommon.cpp b/lib/Serialization/ASTCommon.cpp
index 82809cb465..535aacb8c4 100644
--- a/lib/Serialization/ASTCommon.cpp
+++ b/lib/Serialization/ASTCommon.cpp
@@ -313,7 +313,6 @@ bool serialization::isRedeclarableDeclKind(unsigned Kind) {
   case Decl::BuiltinTemplate:
   case Decl::Decomposition:
   case Decl::Binding:
-  case Decl::Concept:
     return false;
 
   // These indirectly derive from Redeclarable<T> but are not actually
diff --git a/lib/Serialization/ASTReaderDecl.cpp b/lib/Serialization/ASTReaderDecl.cpp
index 1b0e1bbbf7..7a5d22c00f 100644
--- a/lib/Serialization/ASTReaderDecl.cpp
+++ b/lib/Serialization/ASTReaderDecl.cpp
@@ -381,7 +381,6 @@ namespace clang {
     void VisitBindingDecl(BindingDecl *BD);
     void VisitNonTypeTemplateParmDecl(NonTypeTemplateParmDecl *D);
     DeclID VisitTemplateDecl(TemplateDecl *D);
-    void VisitConceptDecl(ConceptDecl *D);
     RedeclarableResult VisitRedeclarableTemplateDecl(RedeclarableTemplateDecl *D);
     void VisitClassTemplateDecl(ClassTemplateDecl *D);
     void VisitBuiltinTemplateDecl(BuiltinTemplateDecl *D);
@@ -2032,11 +2031,6 @@ DeclID ASTDeclReader::VisitTemplateDecl(TemplateDecl *D) {
   return PatternID;
 }
 
-void ASTDeclReader::VisitConceptDecl(ConceptDecl *D) {
-  VisitTemplateDecl(D);
-  D->setConstraintExpr(Record.readExpr());
-}
-
 ASTDeclReader::RedeclarableResult
 ASTDeclReader::VisitRedeclarableTemplateDecl(RedeclarableTemplateDecl *D) {
   RedeclarableResult Redecl = VisitRedeclarable(D);
@@ -3601,9 +3595,6 @@ Decl *ASTReader::ReadDeclRecord(DeclID ID) {
   case DECL_TYPE_ALIAS_TEMPLATE:
     D = TypeAliasTemplateDecl::CreateDeserialized(Context, ID);
     break;
-  case DECL_CONCEPT:
-    D = ConceptDecl::CreateDeserialized(Context, ID);
-    break;
   case DECL_STATIC_ASSERT:
     D = StaticAssertDecl::CreateDeserialized(Context, ID);
     break;
diff --git a/lib/Serialization/ASTWriter.cpp b/lib/Serialization/ASTWriter.cpp
index a055899009..7f2b1861d1 100644
--- a/lib/Serialization/ASTWriter.cpp
+++ b/lib/Serialization/ASTWriter.cpp
@@ -1280,7 +1280,6 @@ void ASTWriter::WriteBlockInfoBlock() {
   RECORD(DECL_TEMPLATE_TYPE_PARM);
   RECORD(DECL_NON_TYPE_TEMPLATE_PARM);
   RECORD(DECL_TEMPLATE_TEMPLATE_PARM);
-  RECORD(DECL_CONCEPT);
   RECORD(DECL_TYPE_ALIAS_TEMPLATE);
   RECORD(DECL_STATIC_ASSERT);
   RECORD(DECL_CXX_BASE_SPECIFIERS);
diff --git a/lib/Serialization/ASTWriterDecl.cpp b/lib/Serialization/ASTWriterDecl.cpp
index 432c2559e4..189de14cff 100644
--- a/lib/Serialization/ASTWriterDecl.cpp
+++ b/lib/Serialization/ASTWriterDecl.cpp
@@ -102,7 +102,6 @@ namespace clang {
     void VisitBindingDecl(BindingDecl *D);
     void VisitNonTypeTemplateParmDecl(NonTypeTemplateParmDecl *D);
     void VisitTemplateDecl(TemplateDecl *D);
-    void VisitConceptDecl(ConceptDecl *D);
     void VisitRedeclarableTemplateDecl(RedeclarableTemplateDecl *D);
     void VisitClassTemplateDecl(ClassTemplateDecl *D);
     void VisitVarTemplateDecl(VarTemplateDecl *D);
@@ -1396,12 +1395,6 @@ void ASTDeclWriter::VisitTemplateDecl(TemplateDecl *D) {
   Record.AddTemplateParameterList(D->getTemplateParameters());
 }
 
-void ASTDeclWriter::VisitConceptDecl(ConceptDecl *D) {
-  VisitTemplateDecl(D);
-  Record.AddStmt(D->getConstraintExpr());
-  Code = serialization::DECL_CONCEPT;
-}
-
 void ASTDeclWriter::VisitRedeclarableTemplateDecl(RedeclarableTemplateDecl *D) {
   VisitRedeclarable(D);
 
diff --git a/test/Parser/cxx-concept-declaration.cpp b/test/Parser/cxx-concept-declaration.cpp
new file mode 100644
index 0000000000..2e9d1ac2fc
--- /dev/null
+++ b/test/Parser/cxx-concept-declaration.cpp
@@ -0,0 +1,7 @@
+
+// Support parsing of concepts
+// Disabled for now.
+// expected-no-diagnostics
+
+// RUN:  %clang_cc1 -std=c++14 -fconcepts-ts -x c++ -verify %s
+// template<typename T> concept C1 = true;
diff --git a/test/Parser/cxx2a-concept-declaration.cpp b/test/Parser/cxx2a-concept-declaration.cpp
deleted file mode 100644
index 7c0923cfe7..0000000000
--- a/test/Parser/cxx2a-concept-declaration.cpp
+++ /dev/null
@@ -1,83 +0,0 @@
-// RUN:  %clang_cc1 -std=c++2a -fconcepts-ts -verify %s
-// Support parsing of concepts
-
-concept X;  //expected-error {{must be a template}}
-
-template<typename T> concept C1 = true; //expected-note{{declared here}}  <-- previous declaration
-
-template<typename T> concept C1 = true; // expected-error {{redefinition of 'C1'}}
-
-template<concept T> concept D1 = true; // expected-error {{'concept' can only appear in namespace scope}} \
-                                          expected-error {{expected template parameter}}
-
-template<> concept X = true; // expected-error {{cannot be explicitly specialized}}
-
-namespace ns1 {
-template<> concept D1 = true;  // expected-error {{cannot be explicitly specialized}}
-template<typename T> const concept C1 = true; //expected-error{{cannot combine with}}
-namespace ns12 {
-template<typename T> decltype(T{}) concept C2 = true; //expected-error{{cannot combine with}}
-template<typename T> bool concept C3 = true; //expected-error{{cannot combine with}}
-template<typename T> unsigned concept C4 = true; //expected-error{{cannot combine with}}
-template<typename T> short concept C5 = true; //expected-error{{cannot combine with}}
-template<typename T> typedef concept C6 = true; //expected-error{{cannot combine with}}
-}
-template<class> concept 
-                        const  //expected-error{{expected concept name}}
-						      C2 = true; 
-							  
-void f() {
-	concept X; //expected-error{{'concept' can only appear in namespace scope}}
-}
-template<concept X,  //expected-error{{'concept' can only appear in namespace scope}} \
-                                          expected-error {{expected template parameter}}
-				  int J> void f();
-}
-
-template<class T>
-concept [[test]] X2 [[test2]] = T::value; //expected-error2{{attribute list cannot appear here}}
-
-namespace ns2 {
-template<class T>
-concept [[test]] X2 [[test2]] = T::value; //expected-error2{{attribute list cannot appear here}}
-	
-}
-
-namespace ns3 {
-   template<typename T> concept C1 = true; 
-
-  namespace ns1 {
-	using ns3::C1; //expected-note{{declared here}}
-	template<typename T> concept C1 = true; // expected-error {{redefinition of 'C1'}}
-  }
-
-}
-
-// TODO:
-// template<typename T> concept C2 = 0.f; // expected error {{constraint expression must be 'bool'}}
-
-struct S1 {
-  template<typename T> concept C1 = true; // expected-error {{can only appear in namespace scope}}
-};
-
-template<typename A>
-template<typename B>
-concept C4 = true; // expected-error {{extraneous template parameter list in concept definition}}
-
-template<typename T> concept C5 = true; // expected-note {{previous}} expected-note {{previous}}
-int C5; // expected-error {{redefinition}}
-struct C5 {}; // expected-error {{redefinition}}
-
-struct C6 {}; //expected-note{{declared here}}  <-- previous declaration
-template<typename T> concept C6 = true; // expected-error {{redefinition of 'C6' as different kind of symbol}}
-
-namespace thing {};
-
-template<typename T> concept thing::C7 = true;  // expected-error {{concepts must be defined in their own namespace}}
-
-
-namespace ns5 {
-}
-
-// TODO: Add test to prevent explicit specialization, partial specialization
-// and explicit instantiation of concepts.
diff --git a/tools/libclang/CIndex.cpp b/tools/libclang/CIndex.cpp
index 17548f3379..497a3ca8f5 100644
--- a/tools/libclang/CIndex.cpp
+++ b/tools/libclang/CIndex.cpp
@@ -6173,7 +6173,6 @@ CXCursor clang_getCursorDefinition(CXCursor C) {
   case Decl::PragmaComment:
   case Decl::PragmaDetectMismatch:
   case Decl::UsingPack:
-  case Decl::Concept:
     return C;
 
   // Declaration kinds that don't make any sense here, but are