Vendor import of llvm-project master 2e10b7a39b9, the last commit beforevendor/llvm-project/llvmorg-11-init-20887-g2e10b7a39b9vendor/llvm-project/master

the llvmorg-12-init tag, from which release/11.x was branched.

1 files changed, 562 insertions, 326 deletions

diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 1184446796eb..c05ed0b14e3e 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -46,6 +46,47 @@ clang::getTemplateParamsRange(TemplateParameterList const * const *Ps,
   return SourceRange(Ps[0]->getTemplateLoc(), Ps[N-1]->getRAngleLoc());
 }
 
+unsigned Sema::getTemplateDepth(Scope *S) const {
+  unsigned Depth = 0;
+
+  // Each template parameter scope represents one level of template parameter
+  // depth.
+  for (Scope *TempParamScope = S->getTemplateParamParent(); TempParamScope;
+       TempParamScope = TempParamScope->getParent()->getTemplateParamParent()) {
+    ++Depth;
+  }
+
+  // Note that there are template parameters with the given depth.
+  auto ParamsAtDepth = [&](unsigned D) { Depth = std::max(Depth, D + 1); };
+
+  // Look for parameters of an enclosing generic lambda. We don't create a
+  // template parameter scope for these.
+  for (FunctionScopeInfo *FSI : getFunctionScopes()) {
+    if (auto *LSI = dyn_cast<LambdaScopeInfo>(FSI)) {
+      if (!LSI->TemplateParams.empty()) {
+        ParamsAtDepth(LSI->AutoTemplateParameterDepth);
+        break;
+      }
+      if (LSI->GLTemplateParameterList) {
+        ParamsAtDepth(LSI->GLTemplateParameterList->getDepth());
+        break;
+      }
+    }
+  }
+
+  // Look for parameters of an enclosing terse function template. We don't
+  // create a template parameter scope for these either.
+  for (const InventedTemplateParameterInfo &Info :
+       getInventedParameterInfos()) {
+    if (!Info.TemplateParams.empty()) {
+      ParamsAtDepth(Info.AutoTemplateParameterDepth);
+      break;
+    }
+  }
+
+  return Depth;
+}
+
 /// \brief Determine whether the declaration found is acceptable as the name
 /// of a template and, if so, return that template declaration. Otherwise,
 /// returns null.
@@ -132,7 +173,8 @@ TemplateNameKind Sema::isTemplateName(Scope *S,
                                       ParsedType ObjectTypePtr,
                                       bool EnteringContext,
                                       TemplateTy &TemplateResult,
-                                      bool &MemberOfUnknownSpecialization) {
+                                      bool &MemberOfUnknownSpecialization,
+                                      bool Disambiguation) {
   assert(getLangOpts().CPlusPlus && "No template names in C!");
 
   DeclarationName TName;
@@ -162,7 +204,8 @@ TemplateNameKind Sema::isTemplateName(Scope *S,
   LookupResult R(*this, TName, Name.getBeginLoc(), LookupOrdinaryName);
   if (LookupTemplateName(R, S, SS, ObjectType, EnteringContext,
                          MemberOfUnknownSpecialization, SourceLocation(),
-                         &AssumedTemplate))
+                         &AssumedTemplate,
+                         /*AllowTypoCorrection=*/!Disambiguation))
     return TNK_Non_template;
 
   if (AssumedTemplate != AssumedTemplateKind::None) {
@@ -328,11 +371,15 @@ bool Sema::LookupTemplateName(LookupResult &Found,
                               QualType ObjectType,
                               bool EnteringContext,
                               bool &MemberOfUnknownSpecialization,
-                              SourceLocation TemplateKWLoc,
-                              AssumedTemplateKind *ATK) {
+                              RequiredTemplateKind RequiredTemplate,
+                              AssumedTemplateKind *ATK,
+                              bool AllowTypoCorrection) {
   if (ATK)
     *ATK = AssumedTemplateKind::None;
 
+  if (SS.isInvalid())
+    return true;
+
   Found.setTemplateNameLookup(true);
 
   // Determine where to perform name lookup
@@ -342,7 +389,7 @@ bool Sema::LookupTemplateName(LookupResult &Found,
   if (!ObjectType.isNull()) {
     // This nested-name-specifier occurs in a member access expression, e.g.,
     // x->B::f, and we are looking into the type of the object.
-    assert(!SS.isSet() && "ObjectType and scope specifier cannot coexist");
+    assert(SS.isEmpty() && "ObjectType and scope specifier cannot coexist");
     LookupCtx = computeDeclContext(ObjectType);
     IsDependent = !LookupCtx && ObjectType->isDependentType();
     assert((IsDependent || !ObjectType->isIncompleteType() ||
@@ -368,11 +415,11 @@ bool Sema::LookupTemplateName(LookupResult &Found,
       Found.clear();
       return false;
     }
-  } else if (SS.isSet()) {
+  } else if (SS.isNotEmpty()) {
     // This nested-name-specifier occurs after another nested-name-specifier,
     // so long into the context associated with the prior nested-name-specifier.
     LookupCtx = computeDeclContext(SS, EnteringContext);
-    IsDependent = !LookupCtx;
+    IsDependent = !LookupCtx && isDependentScopeSpecifier(SS);
 
     // The declaration context must be complete.
     if (LookupCtx && RequireCompleteDeclContext(SS, LookupCtx))
@@ -399,7 +446,7 @@ bool Sema::LookupTemplateName(LookupResult &Found,
     IsDependent |= Found.wasNotFoundInCurrentInstantiation();
   }
 
-  if (!SS.isSet() && (ObjectType.isNull() || Found.empty())) {
+  if (SS.isEmpty() && (ObjectType.isNull() || Found.empty())) {
     // C++ [basic.lookup.classref]p1:
     //   In a class member access expression (5.2.5), if the . or -> token is
     //   immediately followed by an identifier followed by a <, the
@@ -426,7 +473,8 @@ bool Sema::LookupTemplateName(LookupResult &Found,
   if (Found.isAmbiguous())
     return false;
 
-  if (ATK && !SS.isSet() && ObjectType.isNull() && TemplateKWLoc.isInvalid()) {
+  if (ATK && SS.isEmpty() && ObjectType.isNull() &&
+      !RequiredTemplate.hasTemplateKeyword()) {
     // C++2a [temp.names]p2:
     //   A name is also considered to refer to a template if it is an
     //   unqualified-id followed by a < and name lookup finds either one or more
@@ -436,7 +484,7 @@ bool Sema::LookupTemplateName(LookupResult &Found,
     // all language modes, and diagnose the empty lookup in ActOnCallExpr if we
     // successfully form a call to an undeclared template-id.
     bool AllFunctions =
-        getLangOpts().CPlusPlus2a &&
+        getLangOpts().CPlusPlus20 &&
         std::all_of(Found.begin(), Found.end(), [](NamedDecl *ND) {
           return isa<FunctionDecl>(ND->getUnderlyingDecl());
         });
@@ -452,8 +500,9 @@ bool Sema::LookupTemplateName(LookupResult &Found,
     }
   }
 
-  if (Found.empty() && !IsDependent) {
-    // If we did not find any names, attempt to correct any typos.
+  if (Found.empty() && !IsDependent && AllowTypoCorrection) {
+    // If we did not find any names, and this is not a disambiguation, attempt
+    // to correct any typos.
     DeclarationName Name = Found.getLookupName();
     Found.clear();
     // Simple filter callback that, for keywords, only accepts the C++ *_cast
@@ -497,9 +546,11 @@ bool Sema::LookupTemplateName(LookupResult &Found,
 
     // If a 'template' keyword was used, a lookup that finds only non-template
     // names is an error.
-    if (ExampleLookupResult && TemplateKWLoc.isValid()) {
+    if (ExampleLookupResult && RequiredTemplate) {
       Diag(Found.getNameLoc(), diag::err_template_kw_refers_to_non_template)
-        << Found.getLookupName() << SS.getRange();
+          << Found.getLookupName() << SS.getRange()
+          << RequiredTemplate.hasTemplateKeyword()
+          << RequiredTemplate.getTemplateKeywordLoc();
       Diag(ExampleLookupResult->getUnderlyingDecl()->getLocation(),
            diag::note_template_kw_refers_to_non_template)
           << Found.getLookupName();
@@ -1050,7 +1101,8 @@ makeTemplateArgumentListInfo(Sema &S, TemplateIdAnnotation &TemplateId) {
   return TemplateArgs;
 }
 
-bool Sema::ActOnTypeConstraint(TemplateIdAnnotation *TypeConstr,
+bool Sema::ActOnTypeConstraint(const CXXScopeSpec &SS,
+                               TemplateIdAnnotation *TypeConstr,
                                TemplateTypeParmDecl *ConstrainedParameter,
                                SourceLocation EllipsisLoc) {
   ConceptDecl *CD =
@@ -1080,14 +1132,57 @@ bool Sema::ActOnTypeConstraint(TemplateIdAnnotation *TypeConstr,
         makeTemplateArgumentListInfo(*this, *TypeConstr);
   }
   return AttachTypeConstraint(
-      TypeConstr->SS.isSet() ? TypeConstr->SS.getWithLocInContext(Context) :
-      NestedNameSpecifierLoc(),
+      SS.isSet() ? SS.getWithLocInContext(Context) : NestedNameSpecifierLoc(),
       DeclarationNameInfo(DeclarationName(TypeConstr->Name),
                           TypeConstr->TemplateNameLoc), CD,
       TypeConstr->LAngleLoc.isValid() ? &TemplateArgs : nullptr,
       ConstrainedParameter, EllipsisLoc);
 }
 
+template<typename ArgumentLocAppender>
+static ExprResult formImmediatelyDeclaredConstraint(
+    Sema &S, NestedNameSpecifierLoc NS, DeclarationNameInfo NameInfo,
+    ConceptDecl *NamedConcept, SourceLocation LAngleLoc,
+    SourceLocation RAngleLoc, QualType ConstrainedType,
+    SourceLocation ParamNameLoc, ArgumentLocAppender Appender,
+    SourceLocation EllipsisLoc) {
+
+  TemplateArgumentListInfo ConstraintArgs;
+  ConstraintArgs.addArgument(
+    S.getTrivialTemplateArgumentLoc(TemplateArgument(ConstrainedType),
+                                    /*NTTPType=*/QualType(), ParamNameLoc));
+
+  ConstraintArgs.setRAngleLoc(RAngleLoc);
+  ConstraintArgs.setLAngleLoc(LAngleLoc);
+  Appender(ConstraintArgs);
+
+  // C++2a [temp.param]p4:
+  //     [...] This constraint-expression E is called the immediately-declared
+  //     constraint of T. [...]
+  CXXScopeSpec SS;
+  SS.Adopt(NS);
+  ExprResult ImmediatelyDeclaredConstraint = S.CheckConceptTemplateId(
+      SS, /*TemplateKWLoc=*/SourceLocation(), NameInfo,
+      /*FoundDecl=*/NamedConcept, NamedConcept, &ConstraintArgs);
+  if (ImmediatelyDeclaredConstraint.isInvalid() || !EllipsisLoc.isValid())
+    return ImmediatelyDeclaredConstraint;
+
+  // C++2a [temp.param]p4:
+  //     [...] If T is not a pack, then E is E', otherwise E is (E' && ...).
+  //
+  // We have the following case:
+  //
+  // template<typename T> concept C1 = true;
+  // template<C1... T> struct s1;
+  //
+  // The constraint: (C1<T> && ...)
+  return S.BuildCXXFoldExpr(/*LParenLoc=*/SourceLocation(),
+                            ImmediatelyDeclaredConstraint.get(), BO_LAnd,
+                            EllipsisLoc, /*RHS=*/nullptr,
+                            /*RParenLoc=*/SourceLocation(),
+                            /*NumExpansions=*/None);
+}
+
 /// Attach a type-constraint to a template parameter.
 /// \returns true if an error occured. This can happen if the
 /// immediately-declared constraint could not be formed (e.g. incorrect number
@@ -1106,51 +1201,21 @@ bool Sema::AttachTypeConstraint(NestedNameSpecifierLoc NS,
                                                        *TemplateArgs) : nullptr;
 
   QualType ParamAsArgument(ConstrainedParameter->getTypeForDecl(), 0);
-  TemplateArgumentListInfo ConstraintArgs;
-  ConstraintArgs.addArgument(
-    TemplateArgumentLoc(
-        TemplateArgument(ParamAsArgument),
-        TemplateArgumentLocInfo(
-            Context.getTrivialTypeSourceInfo(ParamAsArgument,
-                ConstrainedParameter->getLocation()))));
-  if (TemplateArgs) {
-    ConstraintArgs.setRAngleLoc(TemplateArgs->getRAngleLoc());
-    ConstraintArgs.setLAngleLoc(TemplateArgs->getLAngleLoc());
-    for (const TemplateArgumentLoc &ArgLoc : TemplateArgs->arguments())
-      ConstraintArgs.addArgument(ArgLoc);
-  }
 
-  // C++2a [temp.param]p4:
-  //     [...] This constraint-expression E is called the immediately-declared
-  //     constraint of T. [...]
-  CXXScopeSpec SS;
-  SS.Adopt(NS);
-  ExprResult ImmediatelyDeclaredConstraint = CheckConceptTemplateId(SS,
-      /*TemplateKWLoc=*/SourceLocation(), NameInfo, /*FoundDecl=*/NamedConcept,
-      NamedConcept, &ConstraintArgs);
+  ExprResult ImmediatelyDeclaredConstraint =
+      formImmediatelyDeclaredConstraint(
+          *this, NS, NameInfo, NamedConcept,
+          TemplateArgs ? TemplateArgs->getLAngleLoc() : SourceLocation(),
+          TemplateArgs ? TemplateArgs->getRAngleLoc() : SourceLocation(),
+          ParamAsArgument, ConstrainedParameter->getLocation(),
+          [&] (TemplateArgumentListInfo &ConstraintArgs) {
+            if (TemplateArgs)
+              for (const auto &ArgLoc : TemplateArgs->arguments())
+                ConstraintArgs.addArgument(ArgLoc);
+          }, EllipsisLoc);
   if (ImmediatelyDeclaredConstraint.isInvalid())
     return true;
 
-  if (ConstrainedParameter->isParameterPack()) {
-    // C++2a [temp.param]p4:
-    //     [...] If T is not a pack, then E is E', otherwise E is (E' && ...).
-    //
-    // We have the following case:
-    //
-    // template<typename T> concept C1 = true;
-    // template<C1... T> struct s1;
-    //
-    // The constraint: (C1<T> && ...)
-    ImmediatelyDeclaredConstraint =
-        BuildCXXFoldExpr(/*LParenLoc=*/SourceLocation(),
-                         ImmediatelyDeclaredConstraint.get(), BO_LAnd,
-                         EllipsisLoc, /*RHS=*/nullptr,
-                         /*RParenLoc=*/SourceLocation(),
-                         /*NumExpansions=*/None).get();
-    if (ImmediatelyDeclaredConstraint.isInvalid())
-      return true;
-  }
-
   ConstrainedParameter->setTypeConstraint(NS, NameInfo,
                                           /*FoundDecl=*/NamedConcept,
                                           NamedConcept, ArgsAsWritten,
@@ -1158,6 +1223,38 @@ bool Sema::AttachTypeConstraint(NestedNameSpecifierLoc NS,
   return false;
 }
 
+bool Sema::AttachTypeConstraint(AutoTypeLoc TL, NonTypeTemplateParmDecl *NTTP,
+                                SourceLocation EllipsisLoc) {
+  if (NTTP->getType() != TL.getType() ||
+      TL.getAutoKeyword() != AutoTypeKeyword::Auto) {
+    Diag(NTTP->getTypeSourceInfo()->getTypeLoc().getBeginLoc(),
+         diag::err_unsupported_placeholder_constraint)
+       << NTTP->getTypeSourceInfo()->getTypeLoc().getSourceRange();
+    return true;
+  }
+  // FIXME: Concepts: This should be the type of the placeholder, but this is
+  // unclear in the wording right now.
+  DeclRefExpr *Ref = BuildDeclRefExpr(NTTP, NTTP->getType(), VK_RValue,
+                                      NTTP->getLocation());
+  if (!Ref)
+    return true;
+  ExprResult ImmediatelyDeclaredConstraint =
+      formImmediatelyDeclaredConstraint(
+          *this, TL.getNestedNameSpecifierLoc(), TL.getConceptNameInfo(),
+          TL.getNamedConcept(), TL.getLAngleLoc(), TL.getRAngleLoc(),
+          BuildDecltypeType(Ref, NTTP->getLocation()), NTTP->getLocation(),
+          [&] (TemplateArgumentListInfo &ConstraintArgs) {
+            for (unsigned I = 0, C = TL.getNumArgs(); I != C; ++I)
+              ConstraintArgs.addArgument(TL.getArgLoc(I));
+          }, EllipsisLoc);
+  if (ImmediatelyDeclaredConstraint.isInvalid() ||
+     !ImmediatelyDeclaredConstraint.isUsable())
+    return true;
+
+  NTTP->setPlaceholderTypeConstraint(ImmediatelyDeclaredConstraint.get());
+  return false;
+}
+
 /// Check that the type of a non-type template parameter is
 /// well-formed.
 ///
@@ -1242,11 +1339,11 @@ NamedDecl *Sema::ActOnNonTypeTemplateParameter(Scope *S, Declarator &D,
   // Check that we have valid decl-specifiers specified.
   auto CheckValidDeclSpecifiers = [this, &D] {
     // C++ [temp.param]
-    // p1 
+    // p1
     //   template-parameter:
     //     ...
     //     parameter-declaration
-    // p2 
+    // p2
     //   ... A storage class shall not be specified in a template-parameter
     //   declaration.
     // [dcl.typedef]p1:
@@ -1319,6 +1416,11 @@ NamedDecl *Sema::ActOnNonTypeTemplateParameter(Scope *S, Declarator &D,
       TInfo);
   Param->setAccess(AS_public);
 
+  if (AutoTypeLoc TL = TInfo->getTypeLoc().getContainedAutoTypeLoc())
+    if (TL.isConstrained())
+      if (AttachTypeConstraint(TL, Param, D.getEllipsisLoc()))
+        Invalid = true;
+
   if (Invalid)
     Param->setInvalidDecl();
 
@@ -1844,16 +1946,46 @@ namespace {
 /// constructor to a deduction guide.
 class ExtractTypeForDeductionGuide
   : public TreeTransform<ExtractTypeForDeductionGuide> {
+  llvm::SmallVectorImpl<TypedefNameDecl *> &MaterializedTypedefs;
+
 public:
   typedef TreeTransform<ExtractTypeForDeductionGuide> Base;
-  ExtractTypeForDeductionGuide(Sema &SemaRef) : Base(SemaRef) {}
+  ExtractTypeForDeductionGuide(
+      Sema &SemaRef,
+      llvm::SmallVectorImpl<TypedefNameDecl *> &MaterializedTypedefs)
+      : Base(SemaRef), MaterializedTypedefs(MaterializedTypedefs) {}
 
   TypeSourceInfo *transform(TypeSourceInfo *TSI) { return TransformType(TSI); }
 
   QualType TransformTypedefType(TypeLocBuilder &TLB, TypedefTypeLoc TL) {
-    return TransformType(
-        TLB,
-        TL.getTypedefNameDecl()->getTypeSourceInfo()->getTypeLoc());
+    ASTContext &Context = SemaRef.getASTContext();
+    TypedefNameDecl *OrigDecl = TL.getTypedefNameDecl();
+    TypeLocBuilder InnerTLB;
+    QualType Transformed =
+        TransformType(InnerTLB, OrigDecl->getTypeSourceInfo()->getTypeLoc());
+    TypeSourceInfo *TSI =
+        TransformType(InnerTLB.getTypeSourceInfo(Context, Transformed));
+
+    TypedefNameDecl *Decl = nullptr;
+
+    if (isa<TypeAliasDecl>(OrigDecl))
+      Decl = TypeAliasDecl::Create(
+          Context, Context.getTranslationUnitDecl(), OrigDecl->getBeginLoc(),
+          OrigDecl->getLocation(), OrigDecl->getIdentifier(), TSI);
+    else {
+      assert(isa<TypedefDecl>(OrigDecl) && "Not a Type alias or typedef");
+      Decl = TypedefDecl::Create(
+          Context, Context.getTranslationUnitDecl(), OrigDecl->getBeginLoc(),
+          OrigDecl->getLocation(), OrigDecl->getIdentifier(), TSI);
+    }
+
+    MaterializedTypedefs.push_back(Decl);
+
+    QualType TDTy = Context.getTypedefType(Decl);
+    TypedefTypeLoc TypedefTL = TLB.push<TypedefTypeLoc>(TDTy);
+    TypedefTL.setNameLoc(TL.getNameLoc());
+
+    return TDTy;
   }
 };
 
@@ -1905,6 +2037,7 @@ struct ConvertConstructorToDeductionGuideTransform {
       // a list of substituted template arguments as we go.
       for (NamedDecl *Param : *InnerParams) {
         MultiLevelTemplateArgumentList Args;
+        Args.setKind(TemplateSubstitutionKind::Rewrite);
         Args.addOuterTemplateArguments(SubstArgs);
         Args.addOuterRetainedLevel();
         NamedDecl *NewParam = transformTemplateParameter(Param, Args);
@@ -1924,6 +2057,7 @@ struct ConvertConstructorToDeductionGuideTransform {
     // substitute references to the old parameters into references to the
     // new ones.
     MultiLevelTemplateArgumentList Args;
+    Args.setKind(TemplateSubstitutionKind::Rewrite);
     if (FTD) {
       Args.addOuterTemplateArguments(SubstArgs);
       Args.addOuterRetainedLevel();
@@ -1938,14 +2072,16 @@ struct ConvertConstructorToDeductionGuideTransform {
     // new ones.
     TypeLocBuilder TLB;
     SmallVector<ParmVarDecl*, 8> Params;
-    QualType NewType = transformFunctionProtoType(TLB, FPTL, Params, Args);
+    SmallVector<TypedefNameDecl *, 4> MaterializedTypedefs;
+    QualType NewType = transformFunctionProtoType(TLB, FPTL, Params, Args,
+                                                  MaterializedTypedefs);
     if (NewType.isNull())
       return nullptr;
     TypeSourceInfo *NewTInfo = TLB.getTypeSourceInfo(SemaRef.Context, NewType);
 
     return buildDeductionGuide(TemplateParams, CD->getExplicitSpecifier(),
                                NewTInfo, CD->getBeginLoc(), CD->getLocation(),
-                               CD->getEndLoc());
+                               CD->getEndLoc(), MaterializedTypedefs);
   }
 
   /// Build a deduction guide with the specified parameter types.
@@ -1996,12 +2132,14 @@ private:
       if (const auto *TC = TTP->getTypeConstraint()) {
         TemplateArgumentListInfo TransformedArgs;
         const auto *ArgsAsWritten = TC->getTemplateArgsAsWritten();
-        if (SemaRef.Subst(ArgsAsWritten->getTemplateArgs(),
+        if (!ArgsAsWritten ||
+            SemaRef.Subst(ArgsAsWritten->getTemplateArgs(),
                           ArgsAsWritten->NumTemplateArgs, TransformedArgs,
                           Args))
           SemaRef.AttachTypeConstraint(
               TC->getNestedNameSpecifierLoc(), TC->getConceptNameInfo(),
-              TC->getNamedConcept(), &TransformedArgs, NewTTP,
+              TC->getNamedConcept(), ArgsAsWritten ? &TransformedArgs : nullptr,
+              NewTTP,
               NewTTP->isParameterPack()
                  ? cast<CXXFoldExpr>(TC->getImmediatelyDeclaredConstraint())
                      ->getEllipsisLoc()
@@ -2038,16 +2176,18 @@ private:
     return NewParam;
   }
 
-  QualType transformFunctionProtoType(TypeLocBuilder &TLB,
-                                      FunctionProtoTypeLoc TL,
-                                      SmallVectorImpl<ParmVarDecl*> &Params,
-                                      MultiLevelTemplateArgumentList &Args) {
+  QualType transformFunctionProtoType(
+      TypeLocBuilder &TLB, FunctionProtoTypeLoc TL,
+      SmallVectorImpl<ParmVarDecl *> &Params,
+      MultiLevelTemplateArgumentList &Args,
+      SmallVectorImpl<TypedefNameDecl *> &MaterializedTypedefs) {
     SmallVector<QualType, 4> ParamTypes;
     const FunctionProtoType *T = TL.getTypePtr();
 
     //    -- The types of the function parameters are those of the constructor.
     for (auto *OldParam : TL.getParams()) {
-      ParmVarDecl *NewParam = transformFunctionTypeParam(OldParam, Args);
+      ParmVarDecl *NewParam =
+          transformFunctionTypeParam(OldParam, Args, MaterializedTypedefs);
       if (!NewParam)
         return QualType();
       ParamTypes.push_back(NewParam->getType());
@@ -2089,9 +2229,9 @@ private:
     return Result;
   }
 
-  ParmVarDecl *
-  transformFunctionTypeParam(ParmVarDecl *OldParam,
-                             MultiLevelTemplateArgumentList &Args) {
+  ParmVarDecl *transformFunctionTypeParam(
+      ParmVarDecl *OldParam, MultiLevelTemplateArgumentList &Args,
+      llvm::SmallVectorImpl<TypedefNameDecl *> &MaterializedTypedefs) {
     TypeSourceInfo *OldDI = OldParam->getTypeSourceInfo();
     TypeSourceInfo *NewDI;
     if (auto PackTL = OldDI->getTypeLoc().getAs<PackExpansionTypeLoc>()) {
@@ -2114,15 +2254,22 @@ private:
     // members of the current instantiations with the definitions of those
     // typedefs, avoiding triggering instantiation of the deduced type during
     // deduction.
-    NewDI = ExtractTypeForDeductionGuide(SemaRef).transform(NewDI);
+    NewDI = ExtractTypeForDeductionGuide(SemaRef, MaterializedTypedefs)
+                .transform(NewDI);
 
     // Resolving a wording defect, we also inherit default arguments from the
     // constructor.
     ExprResult NewDefArg;
     if (OldParam->hasDefaultArg()) {
-      NewDefArg = SemaRef.SubstExpr(OldParam->getDefaultArg(), Args);
-      if (NewDefArg.isInvalid())
-        return nullptr;
+      // We don't care what the value is (we won't use it); just create a
+      // placeholder to indicate there is a default argument.
+      QualType ParamTy = NewDI->getType();
+      NewDefArg = new (SemaRef.Context)
+          OpaqueValueExpr(OldParam->getDefaultArg()->getBeginLoc(),
+                          ParamTy.getNonLValueExprType(SemaRef.Context),
+                          ParamTy->isLValueReferenceType() ? VK_LValue :
+                          ParamTy->isRValueReferenceType() ? VK_XValue :
+                          VK_RValue);
     }
 
     ParmVarDecl *NewParam = ParmVarDecl::Create(SemaRef.Context, DC,
@@ -2139,10 +2286,11 @@ private:
     return NewParam;
   }
 
-  NamedDecl *buildDeductionGuide(TemplateParameterList *TemplateParams,
-                                 ExplicitSpecifier ES, TypeSourceInfo *TInfo,
-                                 SourceLocation LocStart, SourceLocation Loc,
-                                 SourceLocation LocEnd) {
+  FunctionTemplateDecl *buildDeductionGuide(
+      TemplateParameterList *TemplateParams, ExplicitSpecifier ES,
+      TypeSourceInfo *TInfo, SourceLocation LocStart, SourceLocation Loc,
+      SourceLocation LocEnd,
+      llvm::ArrayRef<TypedefNameDecl *> MaterializedTypedefs = {}) {
     DeclarationNameInfo Name(DeductionGuideName, Loc);
     ArrayRef<ParmVarDecl *> Params =
         TInfo->getTypeLoc().castAs<FunctionProtoTypeLoc>().getParams();
@@ -2156,6 +2304,8 @@ private:
 
     for (auto *Param : Params)
       Param->setDeclContext(Guide);
+    for (auto *TD : MaterializedTypedefs)
+      TD->setDeclContext(Guide);
 
     auto *GuideTemplate = FunctionTemplateDecl::Create(
         SemaRef.Context, DC, Loc, DeductionGuideName, TemplateParams, Guide);
@@ -2762,7 +2912,7 @@ TemplateParameterList *Sema::MatchTemplateParametersToScopeSpecifier(
     SourceLocation DeclStartLoc, SourceLocation DeclLoc, const CXXScopeSpec &SS,
     TemplateIdAnnotation *TemplateId,
     ArrayRef<TemplateParameterList *> ParamLists, bool IsFriend,
-    bool &IsMemberSpecialization, bool &Invalid) {
+    bool &IsMemberSpecialization, bool &Invalid, bool SuppressDiagnostic) {
   IsMemberSpecialization = false;
   Invalid = false;
 
@@ -2870,8 +3020,9 @@ TemplateParameterList *Sema::MatchTemplateParametersToScopeSpecifier(
 
   auto CheckExplicitSpecialization = [&](SourceRange Range, bool Recovery) {
     if (SawNonEmptyTemplateParameterList) {
-      Diag(DeclLoc, diag::err_specialize_member_of_template)
-        << !Recovery << Range;
+      if (!SuppressDiagnostic)
+        Diag(DeclLoc, diag::err_specialize_member_of_template)
+          << !Recovery << Range;
       Invalid = true;
       IsMemberSpecialization = false;
       return true;
@@ -2892,9 +3043,10 @@ TemplateParameterList *Sema::MatchTemplateParametersToScopeSpecifier(
     else
       ExpectedTemplateLoc = DeclStartLoc;
 
-    Diag(DeclLoc, diag::err_template_spec_needs_header)
-      << Range
-      << FixItHint::CreateInsertion(ExpectedTemplateLoc, "template<> ");
+    if (!SuppressDiagnostic)
+      Diag(DeclLoc, diag::err_template_spec_needs_header)
+        << Range
+        << FixItHint::CreateInsertion(ExpectedTemplateLoc, "template<> ");
     return false;
   };
 
@@ -2984,12 +3136,13 @@ TemplateParameterList *Sema::MatchTemplateParametersToScopeSpecifier(
       if (ParamIdx < ParamLists.size()) {
         if (ParamLists[ParamIdx]->size() > 0) {
           // The header has template parameters when it shouldn't. Complain.
-          Diag(ParamLists[ParamIdx]->getTemplateLoc(),
-               diag::err_template_param_list_matches_nontemplate)
-            << T
-            << SourceRange(ParamLists[ParamIdx]->getLAngleLoc(),
-                           ParamLists[ParamIdx]->getRAngleLoc())
-            << getRangeOfTypeInNestedNameSpecifier(Context, T, SS);
+          if (!SuppressDiagnostic)
+            Diag(ParamLists[ParamIdx]->getTemplateLoc(),
+                 diag::err_template_param_list_matches_nontemplate)
+              << T
+              << SourceRange(ParamLists[ParamIdx]->getLAngleLoc(),
+                             ParamLists[ParamIdx]->getRAngleLoc())
+              << getRangeOfTypeInNestedNameSpecifier(Context, T, SS);
           Invalid = true;
           return nullptr;
         }
@@ -3025,7 +3178,7 @@ TemplateParameterList *Sema::MatchTemplateParametersToScopeSpecifier(
         if (ExpectedTemplateParams &&
             !TemplateParameterListsAreEqual(ParamLists[ParamIdx],
                                             ExpectedTemplateParams,
-                                            true, TPL_TemplateMatch))
+                                            !SuppressDiagnostic, TPL_TemplateMatch))
           Invalid = true;
 
         if (!Invalid &&
@@ -3037,9 +3190,10 @@ TemplateParameterList *Sema::MatchTemplateParametersToScopeSpecifier(
         continue;
       }
 
-      Diag(DeclLoc, diag::err_template_spec_needs_template_parameters)
-        << T
-        << getRangeOfTypeInNestedNameSpecifier(Context, T, SS);
+      if (!SuppressDiagnostic)
+        Diag(DeclLoc, diag::err_template_spec_needs_template_parameters)
+          << T
+          << getRangeOfTypeInNestedNameSpecifier(Context, T, SS);
       Invalid = true;
       continue;
     }
@@ -3075,16 +3229,18 @@ TemplateParameterList *Sema::MatchTemplateParametersToScopeSpecifier(
         AllExplicitSpecHeaders = false;
     }
 
-    Diag(ParamLists[ParamIdx]->getTemplateLoc(),
-         AllExplicitSpecHeaders ? diag::warn_template_spec_extra_headers
-                                : diag::err_template_spec_extra_headers)
-        << SourceRange(ParamLists[ParamIdx]->getTemplateLoc(),
-                       ParamLists[ParamLists.size() - 2]->getRAngleLoc());
+    if (!SuppressDiagnostic)
+      Diag(ParamLists[ParamIdx]->getTemplateLoc(),
+           AllExplicitSpecHeaders ? diag::warn_template_spec_extra_headers
+                                  : diag::err_template_spec_extra_headers)
+          << SourceRange(ParamLists[ParamIdx]->getTemplateLoc(),
+                         ParamLists[ParamLists.size() - 2]->getRAngleLoc());
 
     // If there was a specialization somewhere, such that 'template<>' is
     // not required, and there were any 'template<>' headers, note where the
     // specialization occurred.
-    if (ExplicitSpecLoc.isValid() && HasAnyExplicitSpecHeader)
+    if (ExplicitSpecLoc.isValid() && HasAnyExplicitSpecHeader &&
+        !SuppressDiagnostic)
       Diag(ExplicitSpecLoc,
            diag::note_explicit_template_spec_does_not_need_header)
         << NestedTypes.back();
@@ -3360,6 +3516,10 @@ QualType Sema::CheckTemplateIdType(TemplateName Name,
                                                           DTN->getIdentifier(),
                                                           TemplateArgs);
 
+  if (Name.getAsAssumedTemplateName() &&
+      resolveAssumedTemplateNameAsType(/*Scope*/nullptr, Name, TemplateLoc))
+    return QualType();
+
   TemplateDecl *Template = Name.getAsTemplateDecl();
   if (!Template || isa<FunctionTemplateDecl>(Template) ||
       isa<VarTemplateDecl>(Template) || isa<ConceptDecl>(Template)) {
@@ -3399,9 +3559,8 @@ QualType Sema::CheckTemplateIdType(TemplateName Name,
     // Only substitute for the innermost template argument list.
     MultiLevelTemplateArgumentList TemplateArgLists;
     TemplateArgLists.addOuterTemplateArguments(&StackTemplateArgs);
-    unsigned Depth = AliasTemplate->getTemplateParameters()->getDepth();
-    for (unsigned I = 0; I < Depth; ++I)
-      TemplateArgLists.addOuterTemplateArguments(None);
+    TemplateArgLists.addOuterRetainedLevels(
+        AliasTemplate->getTemplateParameters()->getDepth());
 
     LocalInstantiationScope Scope(*this);
     InstantiatingTemplate Inst(*this, TemplateLoc, Template);
@@ -3707,6 +3866,9 @@ TypeResult Sema::ActOnTagTemplateIdType(TagUseKind TUK,
                                         SourceLocation LAngleLoc,
                                         ASTTemplateArgsPtr TemplateArgsIn,
                                         SourceLocation RAngleLoc) {
+  if (SS.isInvalid())
+    return TypeResult(true);
+
   TemplateName Template = TemplateD.get();
 
   // Translate the parser's template argument list in our AST format.
@@ -4044,7 +4206,7 @@ DeclResult Sema::ActOnVarTemplateSpecialization(
 
     if (isSameAsPrimaryTemplate(VarTemplate->getTemplateParameters(),
                                 Converted) &&
-        (!Context.getLangOpts().ConceptsTS ||
+        (!Context.getLangOpts().CPlusPlus20 ||
          !TemplateParams->hasAssociatedConstraints())) {
       // C++ [temp.class.spec]p9b3:
       //
@@ -4510,21 +4672,28 @@ Sema::BuildQualifiedTemplateIdExpr(CXXScopeSpec &SS,
   return BuildTemplateIdExpr(SS, TemplateKWLoc, R, /*ADL*/ false, TemplateArgs);
 }
 
-/// Form a dependent template name.
+/// Form a template name from a name that is syntactically required to name a
+/// template, either due to use of the 'template' keyword or because a name in
+/// this syntactic context is assumed to name a template (C++ [temp.names]p2-4).
+///
+/// This action forms a template name given the name of the template and its
+/// optional scope specifier. This is used when the 'template' keyword is used
+/// or when the parsing context unambiguously treats a following '<' as
+/// introducing a template argument list. Note that this may produce a
+/// non-dependent template name if we can perform the lookup now and identify
+/// the named template.
 ///
-/// This action forms a dependent template name given the template
-/// name and its (presumably dependent) scope specifier. For
-/// example, given "MetaFun::template apply", the scope specifier \p
-/// SS will be "MetaFun::", \p TemplateKWLoc contains the location
+/// For example, given "x.MetaFun::template apply", the scope specifier
+/// \p SS will be "MetaFun::", \p TemplateKWLoc contains the location
 /// of the "template" keyword, and "apply" is the \p Name.
-TemplateNameKind Sema::ActOnDependentTemplateName(Scope *S,
-                                                  CXXScopeSpec &SS,
-                                                  SourceLocation TemplateKWLoc,
-                                                  const UnqualifiedId &Name,
-                                                  ParsedType ObjectType,
-                                                  bool EnteringContext,
-                                                  TemplateTy &Result,
-                                                  bool AllowInjectedClassName) {
+TemplateNameKind Sema::ActOnTemplateName(Scope *S,
+                                         CXXScopeSpec &SS,
+                                         SourceLocation TemplateKWLoc,
+                                         const UnqualifiedId &Name,
+                                         ParsedType ObjectType,
+                                         bool EnteringContext,
+                                         TemplateTy &Result,
+                                         bool AllowInjectedClassName) {
   if (TemplateKWLoc.isValid() && S && !S->getTemplateParamParent())
     Diag(TemplateKWLoc,
          getLangOpts().CPlusPlus11 ?
@@ -4532,95 +4701,115 @@ TemplateNameKind Sema::ActOnDependentTemplateName(Scope *S,
            diag::ext_template_outside_of_template)
       << FixItHint::CreateRemoval(TemplateKWLoc);
 
+  if (SS.isInvalid())
+    return TNK_Non_template;
+
+  // Figure out where isTemplateName is going to look.
   DeclContext *LookupCtx = nullptr;
-  if (SS.isSet())
+  if (SS.isNotEmpty())
     LookupCtx = computeDeclContext(SS, EnteringContext);
-  if (!LookupCtx && ObjectType)
-    LookupCtx = computeDeclContext(ObjectType.get());
-  if (LookupCtx) {
-    // C++0x [temp.names]p5:
-    //   If a name prefixed by the keyword template is not the name of
-    //   a template, the program is ill-formed. [Note: the keyword
-    //   template may not be applied to non-template members of class
-    //   templates. -end note ] [ Note: as is the case with the
-    //   typename prefix, the template prefix is allowed in cases
-    //   where it is not strictly necessary; i.e., when the
-    //   nested-name-specifier or the expression on the left of the ->
-    //   or . is not dependent on a template-parameter, or the use
-    //   does not appear in the scope of a template. -end note]
-    //
-    // Note: C++03 was more strict here, because it banned the use of
-    // the "template" keyword prior to a template-name that was not a
-    // dependent name. C++ DR468 relaxed this requirement (the
-    // "template" keyword is now permitted). We follow the C++0x
-    // rules, even in C++03 mode with a warning, retroactively applying the DR.
-    bool MemberOfUnknownSpecialization;
-    TemplateNameKind TNK = isTemplateName(S, SS, TemplateKWLoc.isValid(), Name,
-                                          ObjectType, EnteringContext, Result,
-                                          MemberOfUnknownSpecialization);
-    if (TNK == TNK_Non_template && MemberOfUnknownSpecialization) {
-      // This is a dependent template. Handle it below.
-    } else if (TNK == TNK_Non_template) {
-      // Do the lookup again to determine if this is a "nothing found" case or
-      // a "not a template" case. FIXME: Refactor isTemplateName so we don't
-      // need to do this.
-      DeclarationNameInfo DNI = GetNameFromUnqualifiedId(Name);
-      LookupResult R(*this, DNI.getName(), Name.getBeginLoc(),
-                     LookupOrdinaryName);
-      bool MOUS;
-      if (!LookupTemplateName(R, S, SS, ObjectType.get(), EnteringContext,
-                              MOUS, TemplateKWLoc) && !R.isAmbiguous())
+  else if (ObjectType)
+    LookupCtx = computeDeclContext(GetTypeFromParser(ObjectType));
+
+  // C++0x [temp.names]p5:
+  //   If a name prefixed by the keyword template is not the name of
+  //   a template, the program is ill-formed. [Note: the keyword
+  //   template may not be applied to non-template members of class
+  //   templates. -end note ] [ Note: as is the case with the
+  //   typename prefix, the template prefix is allowed in cases
+  //   where it is not strictly necessary; i.e., when the
+  //   nested-name-specifier or the expression on the left of the ->
+  //   or . is not dependent on a template-parameter, or the use
+  //   does not appear in the scope of a template. -end note]
+  //
+  // Note: C++03 was more strict here, because it banned the use of
+  // the "template" keyword prior to a template-name that was not a
+  // dependent name. C++ DR468 relaxed this requirement (the
+  // "template" keyword is now permitted). We follow the C++0x
+  // rules, even in C++03 mode with a warning, retroactively applying the DR.
+  bool MemberOfUnknownSpecialization;
+  TemplateNameKind TNK = isTemplateName(S, SS, TemplateKWLoc.isValid(), Name,
+                                        ObjectType, EnteringContext, Result,
+                                        MemberOfUnknownSpecialization);
+  if (TNK != TNK_Non_template) {
+    // We resolved this to a (non-dependent) template name. Return it.
+    auto *LookupRD = dyn_cast_or_null<CXXRecordDecl>(LookupCtx);
+    if (!AllowInjectedClassName && SS.isNotEmpty() && LookupRD &&
+        Name.getKind() == UnqualifiedIdKind::IK_Identifier &&
+        Name.Identifier && LookupRD->getIdentifier() == Name.Identifier) {
+      // C++14 [class.qual]p2:
+      //   In a lookup in which function names are not ignored and the
+      //   nested-name-specifier nominates a class C, if the name specified
+      //   [...] is the injected-class-name of C, [...] the name is instead
+      //   considered to name the constructor
+      //
+      // We don't get here if naming the constructor would be valid, so we
+      // just reject immediately and recover by treating the
+      // injected-class-name as naming the template.
+      Diag(Name.getBeginLoc(),
+           diag::ext_out_of_line_qualified_id_type_names_constructor)
+          << Name.Identifier
+          << 0 /*injected-class-name used as template name*/
+          << TemplateKWLoc.isValid();
+    }
+    return TNK;
+  }
+
+  if (!MemberOfUnknownSpecialization) {
+    // Didn't find a template name, and the lookup wasn't dependent.
+    // Do the lookup again to determine if this is a "nothing found" case or
+    // a "not a template" case. FIXME: Refactor isTemplateName so we don't
+    // need to do this.
+    DeclarationNameInfo DNI = GetNameFromUnqualifiedId(Name);
+    LookupResult R(*this, DNI.getName(), Name.getBeginLoc(),
+                   LookupOrdinaryName);
+    bool MOUS;
+    // Tell LookupTemplateName that we require a template so that it diagnoses
+    // cases where it finds a non-template.
+    RequiredTemplateKind RTK = TemplateKWLoc.isValid()
+                                   ? RequiredTemplateKind(TemplateKWLoc)
+                                   : TemplateNameIsRequired;
+    if (!LookupTemplateName(R, S, SS, ObjectType.get(), EnteringContext, MOUS,
+                            RTK, nullptr, /*AllowTypoCorrection=*/false) &&
+        !R.isAmbiguous()) {
+      if (LookupCtx)
         Diag(Name.getBeginLoc(), diag::err_no_member)
             << DNI.getName() << LookupCtx << SS.getRange();
-      return TNK_Non_template;
-    } else {
-      // We found something; return it.
-      auto *LookupRD = dyn_cast<CXXRecordDecl>(LookupCtx);
-      if (!AllowInjectedClassName && SS.isSet() && LookupRD &&
-          Name.getKind() == UnqualifiedIdKind::IK_Identifier &&
-          Name.Identifier && LookupRD->getIdentifier() == Name.Identifier) {
-        // C++14 [class.qual]p2:
-        //   In a lookup in which function names are not ignored and the
-        //   nested-name-specifier nominates a class C, if the name specified
-        //   [...] is the injected-class-name of C, [...] the name is instead
-        //   considered to name the constructor
-        //
-        // We don't get here if naming the constructor would be valid, so we
-        // just reject immediately and recover by treating the
-        // injected-class-name as naming the template.
-        Diag(Name.getBeginLoc(),
-             diag::ext_out_of_line_qualified_id_type_names_constructor)
-            << Name.Identifier
-            << 0 /*injected-class-name used as template name*/
-            << 1 /*'template' keyword was used*/;
-      }
-      return TNK;
+      else
+        Diag(Name.getBeginLoc(), diag::err_undeclared_use)
+            << DNI.getName() << SS.getRange();
     }
+    return TNK_Non_template;
   }
 
   NestedNameSpecifier *Qualifier = SS.getScopeRep();
 
   switch (Name.getKind()) {
   case UnqualifiedIdKind::IK_Identifier:
-    Result = TemplateTy::make(Context.getDependentTemplateName(Qualifier,
-                                                              Name.Identifier));
+    Result = TemplateTy::make(
+        Context.getDependentTemplateName(Qualifier, Name.Identifier));
     return TNK_Dependent_template_name;
 
   case UnqualifiedIdKind::IK_OperatorFunctionId:
-    Result = TemplateTy::make(Context.getDependentTemplateName(Qualifier,
-                                             Name.OperatorFunctionId.Operator));
+    Result = TemplateTy::make(Context.getDependentTemplateName(
+        Qualifier, Name.OperatorFunctionId.Operator));
     return TNK_Function_template;
 
   case UnqualifiedIdKind::IK_LiteralOperatorId:
-    llvm_unreachable("literal operator id cannot have a dependent scope");
+    // This is a kind of template name, but can never occur in a dependent
+    // scope (literal operators can only be declared at namespace scope).
+    break;
 
   default:
     break;
   }
 
-  Diag(Name.getBeginLoc(), diag::err_template_kw_refers_to_non_template)
+  // This name cannot possibly name a dependent template. Diagnose this now
+  // rather than building a dependent template name that can never be valid.
+  Diag(Name.getBeginLoc(),
+       diag::err_template_kw_refers_to_dependent_non_template)
       << GetNameFromUnqualifiedId(Name).getName() << Name.getSourceRange()
-      << TemplateKWLoc;
+      << TemplateKWLoc.isValid() << TemplateKWLoc;
   return TNK_Non_template;
 }
 
@@ -4655,10 +4844,7 @@ bool Sema::CheckTemplateTypeArgument(TemplateTypeParmDecl *Param,
     CXXScopeSpec SS;
     DeclarationNameInfo NameInfo;
 
-    if (DeclRefExpr *ArgExpr = dyn_cast<DeclRefExpr>(Arg.getAsExpr())) {
-      SS.Adopt(ArgExpr->getQualifierLoc());
-      NameInfo = ArgExpr->getNameInfo();
-    } else if (DependentScopeDeclRefExpr *ArgExpr =
+   if (DependentScopeDeclRefExpr *ArgExpr =
                dyn_cast<DependentScopeDeclRefExpr>(Arg.getAsExpr())) {
       SS.Adopt(ArgExpr->getQualifierLoc());
       NameInfo = ArgExpr->getNameInfo();
@@ -4677,6 +4863,7 @@ bool Sema::CheckTemplateTypeArgument(TemplateTypeParmDecl *Param,
       if (Result.getAsSingle<TypeDecl>() ||
           Result.getResultKind() ==
               LookupResult::NotFoundInCurrentInstantiation) {
+        assert(SS.getScopeRep() && "dependent scope expr must has a scope!");
         // Suggest that the user add 'typename' before the NNS.
         SourceLocation Loc = AL.getSourceRange().getBegin();
         Diag(Loc, getLangOpts().MSVCCompat
@@ -5716,6 +5903,11 @@ bool UnnamedLocalNoLinkageFinder::VisitDependentSizedExtVectorType(
   return Visit(T->getElementType());
 }
 
+bool UnnamedLocalNoLinkageFinder::VisitDependentSizedMatrixType(
+    const DependentSizedMatrixType *T) {
+  return Visit(T->getElementType());
+}
+
 bool UnnamedLocalNoLinkageFinder::VisitDependentAddressSpaceType(
     const DependentAddressSpaceType *T) {
   return Visit(T->getPointeeType());
@@ -5734,6 +5926,11 @@ bool UnnamedLocalNoLinkageFinder::VisitExtVectorType(const ExtVectorType* T) {
   return Visit(T->getElementType());
 }
 
+bool UnnamedLocalNoLinkageFinder::VisitConstantMatrixType(
+    const ConstantMatrixType *T) {
+  return Visit(T->getElementType());
+}
+
 bool UnnamedLocalNoLinkageFinder::VisitFunctionProtoType(
                                                   const FunctionProtoType* T) {
   for (const auto &A : T->param_types()) {
@@ -5815,7 +6012,9 @@ bool UnnamedLocalNoLinkageFinder::VisitDependentNameType(
 
 bool UnnamedLocalNoLinkageFinder::VisitDependentTemplateSpecializationType(
                                  const DependentTemplateSpecializationType* T) {
-  return VisitNestedNameSpecifier(T->getQualifier());
+  if (auto *Q = T->getQualifier())
+    return VisitNestedNameSpecifier(Q);
+  return false;
 }
 
 bool UnnamedLocalNoLinkageFinder::VisitPackExpansionType(
@@ -5845,6 +6044,15 @@ bool UnnamedLocalNoLinkageFinder::VisitPipeType(const PipeType* T) {
   return false;
 }
 
+bool UnnamedLocalNoLinkageFinder::VisitExtIntType(const ExtIntType *T) {
+  return false;
+}
+
+bool UnnamedLocalNoLinkageFinder::VisitDependentExtIntType(
+    const DependentExtIntType *T) {
+  return false;
+}
+
 bool UnnamedLocalNoLinkageFinder::VisitTagDecl(const TagDecl *Tag) {
   if (Tag->getDeclContext()->isFunctionOrMethod()) {
     S.Diag(SR.getBegin(),
@@ -5869,6 +6077,7 @@ bool UnnamedLocalNoLinkageFinder::VisitTagDecl(const TagDecl *Tag) {
 
 bool UnnamedLocalNoLinkageFinder::VisitNestedNameSpecifier(
                                                     NestedNameSpecifier *NNS) {
+  assert(NNS);
   if (NNS->getPrefix() && VisitNestedNameSpecifier(NNS->getPrefix()))
     return true;
 
@@ -6177,8 +6386,11 @@ CheckTemplateArgumentAddressOfObjectOrFunction(Sema &S,
       Arg = subst->getReplacement()->IgnoreImpCasts();
   }
 
-  DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(Arg);
-  ValueDecl *Entity = DRE ? DRE->getDecl() : nullptr;
+  ValueDecl *Entity = nullptr;
+  if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(Arg))
+    Entity = DRE->getDecl();
+  else if (CXXUuidofExpr *CUE = dyn_cast<CXXUuidofExpr>(Arg))
+    Entity = CUE->getGuidDecl();
 
   // If our parameter has pointer type, check for a null template value.
   if (ParamType->isPointerType() || ParamType->isNullPtrType()) {
@@ -6205,16 +6417,7 @@ CheckTemplateArgumentAddressOfObjectOrFunction(Sema &S,
     return false;
   }
 
-  if (isa<CXXUuidofExpr>(Arg)) {
-    if (CheckTemplateArgumentIsCompatibleWithParameter(S, Param, ParamType,
-                                                       ArgIn, Arg, ArgType))
-      return true;
-
-    Converted = TemplateArgument(ArgIn);
-    return false;
-  }
-
-  if (!DRE) {
+  if (!Entity) {
     S.Diag(Arg->getBeginLoc(), diag::err_template_arg_not_decl_ref)
         << Arg->getSourceRange();
     S.Diag(Param->getLocation(), diag::note_template_param_here);
@@ -6241,13 +6444,14 @@ CheckTemplateArgumentAddressOfObjectOrFunction(Sema &S,
 
   FunctionDecl *Func = dyn_cast<FunctionDecl>(Entity);
   VarDecl *Var = dyn_cast<VarDecl>(Entity);
+  MSGuidDecl *Guid = dyn_cast<MSGuidDecl>(Entity);
 
   // A non-type template argument must refer to an object or function.
-  if (!Func && !Var) {
+  if (!Func && !Var && !Guid) {
     // We found something, but we don't know specifically what it is.
     S.Diag(Arg->getBeginLoc(), diag::err_template_arg_not_object_or_func)
         << Arg->getSourceRange();
-    S.Diag(DRE->getDecl()->getLocation(), diag::note_template_arg_refers_here);
+    S.Diag(Entity->getLocation(), diag::note_template_arg_refers_here);
     return true;
   }
 
@@ -6268,30 +6472,7 @@ CheckTemplateArgumentAddressOfObjectOrFunction(Sema &S,
     return true;
   }
 
-  if (Func) {
-    // If the template parameter has pointer type, the function decays.
-    if (ParamType->isPointerType() && !AddressTaken)
-      ArgType = S.Context.getPointerType(Func->getType());
-    else if (AddressTaken && ParamType->isReferenceType()) {
-      // If we originally had an address-of operator, but the
-      // parameter has reference type, complain and (if things look
-      // like they will work) drop the address-of operator.
-      if (!S.Context.hasSameUnqualifiedType(Func->getType(),
-                                            ParamType.getNonReferenceType())) {
-        S.Diag(AddrOpLoc, diag::err_template_arg_address_of_non_pointer)
-          << ParamType;
-        S.Diag(Param->getLocation(), diag::note_template_param_here);
-        return true;
-      }
-
-      S.Diag(AddrOpLoc, diag::err_template_arg_address_of_non_pointer)
-        << ParamType
-        << FixItHint::CreateRemoval(AddrOpLoc);
-      S.Diag(Param->getLocation(), diag::note_template_param_here);
-
-      ArgType = Func->getType();
-    }
-  } else {
+  if (Var) {
     // A value of reference type is not an object.
     if (Var->getType()->isReferenceType()) {
       S.Diag(Arg->getBeginLoc(), diag::err_template_arg_reference_var)
@@ -6307,50 +6488,53 @@ CheckTemplateArgumentAddressOfObjectOrFunction(Sema &S,
       S.Diag(Var->getLocation(), diag::note_template_arg_refers_here);
       return true;
     }
+  }
 
-    // If the template parameter has pointer type, we must have taken
-    // the address of this object.
-    if (ParamType->isReferenceType()) {
-      if (AddressTaken) {
-        // If we originally had an address-of operator, but the
-        // parameter has reference type, complain and (if things look
-        // like they will work) drop the address-of operator.
-        if (!S.Context.hasSameUnqualifiedType(Var->getType(),
-                                            ParamType.getNonReferenceType())) {
-          S.Diag(AddrOpLoc, diag::err_template_arg_address_of_non_pointer)
-            << ParamType;
-          S.Diag(Param->getLocation(), diag::note_template_param_here);
-          return true;
-        }
+  if (AddressTaken && ParamType->isReferenceType()) {
+    // If we originally had an address-of operator, but the
+    // parameter has reference type, complain and (if things look
+    // like they will work) drop the address-of operator.
+    if (!S.Context.hasSameUnqualifiedType(Entity->getType(),
+                                          ParamType.getNonReferenceType())) {
+      S.Diag(AddrOpLoc, diag::err_template_arg_address_of_non_pointer)
+        << ParamType;
+      S.Diag(Param->getLocation(), diag::note_template_param_here);
+      return true;
+    }
 
-        S.Diag(AddrOpLoc, diag::err_template_arg_address_of_non_pointer)
-          << ParamType
-          << FixItHint::CreateRemoval(AddrOpLoc);
-        S.Diag(Param->getLocation(), diag::note_template_param_here);
+    S.Diag(AddrOpLoc, diag::err_template_arg_address_of_non_pointer)
+      << ParamType
+      << FixItHint::CreateRemoval(AddrOpLoc);
+    S.Diag(Param->getLocation(), diag::note_template_param_here);
 
-        ArgType = Var->getType();
-      }
-    } else if (!AddressTaken && ParamType->isPointerType()) {
-      if (Var->getType()->isArrayType()) {
-        // Array-to-pointer decay.
-        ArgType = S.Context.getArrayDecayedType(Var->getType());
-      } else {
-        // If the template parameter has pointer type but the address of
-        // this object was not taken, complain and (possibly) recover by
-        // taking the address of the entity.
-        ArgType = S.Context.getPointerType(Var->getType());
-        if (!S.Context.hasSameUnqualifiedType(ArgType, ParamType)) {
-          S.Diag(Arg->getBeginLoc(), diag::err_template_arg_not_address_of)
-              << ParamType;
-          S.Diag(Param->getLocation(), diag::note_template_param_here);
-          return true;
-        }
+    ArgType = Entity->getType();
+  }
 
+  // If the template parameter has pointer type, either we must have taken the
+  // address or the argument must decay to a pointer.
+  if (!AddressTaken && ParamType->isPointerType()) {
+    if (Func) {
+      // Function-to-pointer decay.
+      ArgType = S.Context.getPointerType(Func->getType());
+    } else if (Entity->getType()->isArrayType()) {
+      // Array-to-pointer decay.
+      ArgType = S.Context.getArrayDecayedType(Entity->getType());
+    } else {
+      // If the template parameter has pointer type but the address of
+      // this object was not taken, complain and (possibly) recover by
+      // taking the address of the entity.
+      ArgType = S.Context.getPointerType(Entity->getType());
+      if (!S.Context.hasSameUnqualifiedType(ArgType, ParamType)) {
         S.Diag(Arg->getBeginLoc(), diag::err_template_arg_not_address_of)
-            << ParamType << FixItHint::CreateInsertion(Arg->getBeginLoc(), "&");
-
+          << ParamType;
         S.Diag(Param->getLocation(), diag::note_template_param_here);
+        return true;
       }
+
+      S.Diag(Arg->getBeginLoc(), diag::err_template_arg_not_address_of)
+        << ParamType << FixItHint::CreateInsertion(Arg->getBeginLoc(), "&");
+
+      S.Diag(Param->getLocation(), diag::note_template_param_here);
     }
   }
 
@@ -6530,7 +6714,12 @@ ExprResult Sema::CheckTemplateArgument(NonTypeTemplateParmDecl *Param,
       DeductionArg = PE->getPattern();
     if (DeduceAutoType(
             Context.getTrivialTypeSourceInfo(ParamType, Param->getLocation()),
-            DeductionArg, ParamType, Depth) == DAR_Failed) {
+            DeductionArg, ParamType, Depth,
+            // We do not check constraints right now because the
+            // immediately-declared constraint of the auto type is also an
+            // associated constraint, and will be checked along with the other
+            // associated constraints after checking the template argument list.
+            /*IgnoreConstraints=*/true) == DAR_Failed) {
       Diag(Arg->getExprLoc(),
            diag::err_non_type_template_parm_type_deduction_failure)
         << Param->getDeclName() << Param->getType() << Arg->getType()
@@ -6670,12 +6859,7 @@ ExprResult Sema::CheckTemplateArgument(NonTypeTemplateParmDecl *Param,
       // -- a predefined __func__ variable
       APValue::LValueBase Base = Value.getLValueBase();
       auto *VD = const_cast<ValueDecl *>(Base.dyn_cast<const ValueDecl *>());
-      if (Base && !VD) {
-        auto *E = Base.dyn_cast<const Expr *>();
-        if (E && isa<CXXUuidofExpr>(E)) {
-          Converted = TemplateArgument(ArgResult.get()->IgnoreImpCasts());
-          break;
-        }
+      if (Base && (!VD || isa<LifetimeExtendedTemporaryDecl>(VD))) {
         Diag(Arg->getBeginLoc(), diag::err_template_arg_not_decl_ref)
             << Arg->getSourceRange();
         return ExprError();
@@ -6762,7 +6946,9 @@ ExprResult Sema::CheckTemplateArgument(NonTypeTemplateParmDecl *Param,
       QualType IntegerType = ParamType;
       if (const EnumType *Enum = IntegerType->getAs<EnumType>())
         IntegerType = Enum->getDecl()->getIntegerType();
-      Value = Value.extOrTrunc(Context.getTypeSize(IntegerType));
+      Value = Value.extOrTrunc(IntegerType->isExtIntType()
+                                   ? Context.getIntWidth(IntegerType)
+                                   : Context.getTypeSize(IntegerType));
 
       Converted = TemplateArgument(Context, Value,
                                    Context.getCanonicalType(ParamType));
@@ -6856,7 +7042,9 @@ ExprResult Sema::CheckTemplateArgument(NonTypeTemplateParmDecl *Param,
 
       // Coerce the template argument's value to the value it will have
       // based on the template parameter's type.
-      unsigned AllowedBits = Context.getTypeSize(IntegerType);
+      unsigned AllowedBits = IntegerType->isExtIntType()
+                                 ? Context.getIntWidth(IntegerType)
+                                 : Context.getTypeSize(IntegerType);
       if (Value.getBitWidth() != AllowedBits)
         Value = Value.extOrTrunc(AllowedBits);
       Value.setIsSigned(IntegerType->isSignedIntegerOrEnumerationType());
@@ -7102,6 +7290,11 @@ bool Sema::CheckTemplateTemplateArgument(TemplateTemplateParmDecl *Param,
       //   [temp.constr.order].
       SmallVector<const Expr *, 3> ParamsAC, TemplateAC;
       Params->getAssociatedConstraints(ParamsAC);
+      // C++2a[temp.arg.template]p3
+      //   [...] In this comparison, if P is unconstrained, the constraints on A
+      //   are not considered.
+      if (ParamsAC.empty())
+        return false;
       Template->getAssociatedConstraints(TemplateAC);
       bool IsParamAtLeastAsConstrained;
       if (IsAtLeastAsConstrained(Param, ParamsAC, Template, TemplateAC,
@@ -7872,13 +8065,11 @@ bool Sema::CheckTemplatePartialSpecializationArgs(
 
 DeclResult Sema::ActOnClassTemplateSpecialization(
     Scope *S, unsigned TagSpec, TagUseKind TUK, SourceLocation KWLoc,
-    SourceLocation ModulePrivateLoc, TemplateIdAnnotation &TemplateId,
-    const ParsedAttributesView &Attr,
+    SourceLocation ModulePrivateLoc, CXXScopeSpec &SS,
+    TemplateIdAnnotation &TemplateId, const ParsedAttributesView &Attr,
     MultiTemplateParamsArg TemplateParameterLists, SkipBodyInfo *SkipBody) {
   assert(TUK != TUK_Reference && "References are not specializations");
 
-  CXXScopeSpec &SS = TemplateId.SS;
-
   // NOTE: KWLoc is the location of the tag keyword. This will instead
   // store the location of the outermost template keyword in the declaration.
   SourceLocation TemplateKWLoc = TemplateParameterLists.size() > 0
@@ -8048,7 +8239,7 @@ DeclResult Sema::ActOnClassTemplateSpecialization(
 
     if (Context.hasSameType(CanonType,
                         ClassTemplate->getInjectedClassNameSpecialization()) &&
-        (!Context.getLangOpts().ConceptsTS ||
+        (!Context.getLangOpts().CPlusPlus20 ||
          !TemplateParams->hasAssociatedConstraints())) {
       // C++ [temp.class.spec]p9b3:
       //
@@ -8274,7 +8465,7 @@ Decl *Sema::ActOnConceptDefinition(Scope *S,
   ConceptDecl *NewDecl = ConceptDecl::Create(Context, DC, NameLoc, Name,
                                              TemplateParameterLists.front(),
                                              ConstraintExpr);
-                                             
+
   if (NewDecl->hasAssociatedConstraints()) {
     // C++2a [temp.concept]p4:
     // A concept shall not have associated constraints.
@@ -10012,24 +10203,12 @@ Sema::ActOnTypenameType(Scope *S, SourceLocation TypenameLoc,
       << FixItHint::CreateRemoval(TypenameLoc);
 
   NestedNameSpecifierLoc QualifierLoc = SS.getWithLocInContext(Context);
+  TypeSourceInfo *TSI = nullptr;
   QualType T = CheckTypenameType(TypenameLoc.isValid()? ETK_Typename : ETK_None,
-                                 TypenameLoc, QualifierLoc, II, IdLoc);
+                                 TypenameLoc, QualifierLoc, II, IdLoc, &TSI,
+                                 /*DeducedTSTContext=*/true);
   if (T.isNull())
     return true;
-
-  TypeSourceInfo *TSI = Context.CreateTypeSourceInfo(T);
-  if (isa<DependentNameType>(T)) {
-    DependentNameTypeLoc TL = TSI->getTypeLoc().castAs<DependentNameTypeLoc>();
-    TL.setElaboratedKeywordLoc(TypenameLoc);
-    TL.setQualifierLoc(QualifierLoc);
-    TL.setNameLoc(IdLoc);
-  } else {
-    ElaboratedTypeLoc TL = TSI->getTypeLoc().castAs<ElaboratedTypeLoc>();
-    TL.setElaboratedKeywordLoc(TypenameLoc);
-    TL.setQualifierLoc(QualifierLoc);
-    TL.getNamedTypeLoc().castAs<TypeSpecTypeLoc>().setNameLoc(IdLoc);
-  }
-
   return CreateParsedType(T, TSI);
 }
 
@@ -10166,6 +10345,35 @@ static bool isEnableIf(NestedNameSpecifierLoc NNS, const IdentifierInfo &II,
   return true;
 }
 
+QualType
+Sema::CheckTypenameType(ElaboratedTypeKeyword Keyword,
+                        SourceLocation KeywordLoc,
+                        NestedNameSpecifierLoc QualifierLoc,
+                        const IdentifierInfo &II,
+                        SourceLocation IILoc,
+                        TypeSourceInfo **TSI,
+                        bool DeducedTSTContext) {
+  QualType T = CheckTypenameType(Keyword, KeywordLoc, QualifierLoc, II, IILoc,
+                                 DeducedTSTContext);
+  if (T.isNull())
+    return QualType();
+
+  *TSI = Context.CreateTypeSourceInfo(T);
+  if (isa<DependentNameType>(T)) {
+    DependentNameTypeLoc TL =
+        (*TSI)->getTypeLoc().castAs<DependentNameTypeLoc>();
+    TL.setElaboratedKeywordLoc(KeywordLoc);
+    TL.setQualifierLoc(QualifierLoc);
+    TL.setNameLoc(IILoc);
+  } else {
+    ElaboratedTypeLoc TL = (*TSI)->getTypeLoc().castAs<ElaboratedTypeLoc>();
+    TL.setElaboratedKeywordLoc(KeywordLoc);
+    TL.setQualifierLoc(QualifierLoc);
+    TL.getNamedTypeLoc().castAs<TypeSpecTypeLoc>().setNameLoc(IILoc);
+  }
+  return T;
+}
+
 /// Build the type that describes a C++ typename specifier,
 /// e.g., "typename T::type".
 QualType
@@ -10173,32 +10381,38 @@ Sema::CheckTypenameType(ElaboratedTypeKeyword Keyword,
                         SourceLocation KeywordLoc,
                         NestedNameSpecifierLoc QualifierLoc,
                         const IdentifierInfo &II,
-                        SourceLocation IILoc) {
+                        SourceLocation IILoc, bool DeducedTSTContext) {
   CXXScopeSpec SS;
   SS.Adopt(QualifierLoc);
 
-  DeclContext *Ctx = computeDeclContext(SS);
-  if (!Ctx) {
-    // If the nested-name-specifier is dependent and couldn't be
-    // resolved to a type, build a typename type.
-    assert(QualifierLoc.getNestedNameSpecifier()->isDependent());
-    return Context.getDependentNameType(Keyword,
-                                        QualifierLoc.getNestedNameSpecifier(),
-                                        &II);
+  DeclContext *Ctx = nullptr;
+  if (QualifierLoc) {
+    Ctx = computeDeclContext(SS);
+    if (!Ctx) {
+      // If the nested-name-specifier is dependent and couldn't be
+      // resolved to a type, build a typename type.
+      assert(QualifierLoc.getNestedNameSpecifier()->isDependent());
+      return Context.getDependentNameType(Keyword,
+                                          QualifierLoc.getNestedNameSpecifier(),
+                                          &II);
+    }
+
+    // If the nested-name-specifier refers to the current instantiation,
+    // the "typename" keyword itself is superfluous. In C++03, the
+    // program is actually ill-formed. However, DR 382 (in C++0x CD1)
+    // allows such extraneous "typename" keywords, and we retroactively
+    // apply this DR to C++03 code with only a warning. In any case we continue.
+
+    if (RequireCompleteDeclContext(SS, Ctx))
+      return QualType();
   }
 
-  // If the nested-name-specifier refers to the current instantiation,
-  // the "typename" keyword itself is superfluous. In C++03, the
-  // program is actually ill-formed. However, DR 382 (in C++0x CD1)
-  // allows such extraneous "typename" keywords, and we retroactively
-  // apply this DR to C++03 code with only a warning. In any case we continue.
-
-  if (RequireCompleteDeclContext(SS, Ctx))
-    return QualType();
-
   DeclarationName Name(&II);
   LookupResult Result(*this, Name, IILoc, LookupOrdinaryName);
-  LookupQualifiedName(Result, Ctx, SS);
+  if (Ctx)
+    LookupQualifiedName(Result, Ctx, SS);
+  else
+    LookupName(Result, CurScope);
   unsigned DiagID = 0;
   Decl *Referenced = nullptr;
   switch (Result.getResultKind()) {
@@ -10207,7 +10421,7 @@ Sema::CheckTypenameType(ElaboratedTypeKeyword Keyword,
     // a more specific diagnostic.
     SourceRange CondRange;
     Expr *Cond = nullptr;
-    if (isEnableIf(QualifierLoc, II, CondRange, Cond)) {
+    if (Ctx && isEnableIf(QualifierLoc, II, CondRange, Cond)) {
       // If we have a condition, narrow it down to the specific failed
       // condition.
       if (Cond) {
@@ -10223,12 +10437,14 @@ Sema::CheckTypenameType(ElaboratedTypeKeyword Keyword,
         return QualType();
       }
 
-      Diag(CondRange.getBegin(), diag::err_typename_nested_not_found_enable_if)
+      Diag(CondRange.getBegin(),
+           diag::err_typename_nested_not_found_enable_if)
           << Ctx << CondRange;
       return QualType();
     }
 
-    DiagID = diag::err_typename_nested_not_found;
+    DiagID = Ctx ? diag::err_typename_nested_not_found
+                 : diag::err_unknown_typename;
     break;
   }
 
@@ -10294,6 +10510,19 @@ Sema::CheckTypenameType(ElaboratedTypeKeyword Keyword,
     //   is a placeholder for a deduced class type [...].
     if (getLangOpts().CPlusPlus17) {
       if (auto *TD = getAsTypeTemplateDecl(Result.getFoundDecl())) {
+        if (!DeducedTSTContext) {
+          QualType T(QualifierLoc
+                         ? QualifierLoc.getNestedNameSpecifier()->getAsType()
+                         : nullptr, 0);
+          if (!T.isNull())
+            Diag(IILoc, diag::err_dependent_deduced_tst)
+              << (int)getTemplateNameKindForDiagnostics(TemplateName(TD)) << T;
+          else
+            Diag(IILoc, diag::err_deduced_tst)
+              << (int)getTemplateNameKindForDiagnostics(TemplateName(TD));
+          Diag(TD->getLocation(), diag::note_template_decl_here);
+          return QualType();
+        }
         return Context.getElaboratedType(
             Keyword, QualifierLoc.getNestedNameSpecifier(),
             Context.getDeducedTemplateSpecializationType(TemplateName(TD),
@@ -10301,12 +10530,14 @@ Sema::CheckTypenameType(ElaboratedTypeKeyword Keyword,
       }
     }
 
-    DiagID = diag::err_typename_nested_not_type;
+    DiagID = Ctx ? diag::err_typename_nested_not_type
+                 : diag::err_typename_not_type;
     Referenced = Result.getFoundDecl();
     break;
 
   case LookupResult::FoundOverloaded:
-    DiagID = diag::err_typename_nested_not_type;
+    DiagID = Ctx ? diag::err_typename_nested_not_type
+                 : diag::err_typename_not_type;
     Referenced = *Result.begin();
     break;
 
@@ -10318,9 +10549,14 @@ Sema::CheckTypenameType(ElaboratedTypeKeyword Keyword,
   // type. Emit an appropriate diagnostic and return an error.
   SourceRange FullRange(KeywordLoc.isValid() ? KeywordLoc : SS.getBeginLoc(),
                         IILoc);
-  Diag(IILoc, DiagID) << FullRange << Name << Ctx;
+  if (Ctx)
+    Diag(IILoc, DiagID) << FullRange << Name << Ctx;
+  else
+    Diag(IILoc, DiagID) << FullRange << Name;
   if (Referenced)
-    Diag(Referenced->getLocation(), diag::note_typename_refers_here)
+    Diag(Referenced->getLocation(),
+         Ctx ? diag::note_typename_member_refers_here
+             : diag::note_typename_refers_here)
       << Name;
   return QualType();
 }
@@ -10515,7 +10751,7 @@ Sema::getTemplateArgumentBindingsText(const TemplateParameterList *Params,
   }
 
   Out << ']';
-  return Out.str();
+  return std::string(Out.str());
 }
 
 void Sema::MarkAsLateParsedTemplate(FunctionDecl *FD, Decl *FnD,